Sample records for deep magmatic processes

  1. History of the Magmatic Feeding System of the Campi Flegrei Caldera

    NASA Astrophysics Data System (ADS)

    Orsi, G.; Civetta, L.; Arienzo, I.; D'Antonio, M.; di Renzo, V.; di Vito, M. A.

    2007-12-01

    The definition of the magmatic feeding system of active volcanoes, in terms of composition, time-scale of crystallization, relation between composition of the erupted magma and structural position of vents, magma chamber processes and architecture, is of extreme importance for the hazard evaluation. The studies that are carried out for the definition of the magmatic systems include detailed mineralogical, geochemical and isotopic analyses (Sr, Nd, Pb). The Campi Flegrei caldera magmatic structure is characterized by deep and shallow magma chambers. In the deep reservoir (20-10 km depth) mantle derived magmas differentiate and are contaminated with continental crust. In the shallow reservoirs isotopically distinct magmas further differentiate, mix and mingle before the eruptions. These processes generated isotopically distinct components that were variably involved along different structures of the Campi Flegrei caldera during time. At Campi Flegrei caldera the relation between the structural position of the eruptive vent, for the last 14 ka of activity, and the isotopic composition of the emitted magma allow us to reconstruct the architecture of the magmatic feeding system and to infer the chemical and isotopic composition, and the magma chamber location and processes, of the future eruption, according to the position of the vent

  2. History of the magmatic feeding system of the Campi Flegrei caldera (Italy)

    NASA Astrophysics Data System (ADS)

    Civetta, L.; Arienzo, I.; D'Antonio, M.; di Renzo, V.; di Vito, M. A.; Orsi, G.

    2007-05-01

    The definition of the magmatic feeding system of active volcanoes in terms of architecture, composition, crystallization time-scale, relationships between composition of the erupted magmas and structural position of the vents, and magma processes, is of paramount importance for volcanic hazards evaluation. Investigations aimed at defining the Campi Flegeri magmatic system, include detailed mineralogical, geochemical and isotopic analyses (Sr, Nd, Pb, Th,U). The magmatic feeding system of the Campi Flegrei caldera is characterized by deep and shallow magma reservoirs. In the deep reservoirs (20-10 km depth) mantle- derived magmas differentiated and were contaminated by continental crust. In the shallow reservoirs isotopically distinct magmas, further differentiated, contaminated, and mixed and mingled before eruptions. These processes generated isotopically distinct components, variably interacting with the different structural elements of the Campi Flegrei caldera through time. The relationships between the structural position of the eruption vents, during the last 15 ka of activity, and the isotopic composition of the magmas erupted at the Campi Flegrei caldera allow us to reconstruct the architecture of the magmatic feeding system and to infer the chemical and isotopic composition of the magma feeding a future eruption, according to vent position.

  3. Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring.

    PubMed

    de Moor, J Maarten; Aiuppa, A; Avard, G; Wehrmann, H; Dunbar, N; Muller, C; Tamburello, G; Giudice, G; Liuzzo, M; Moretti, R; Conde, V; Galle, B

    2016-08-01

    Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high-frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO 2 -rich gas (CO 2 /S total  > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur-rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8-10 km deep, whereas the shallow magmatic gas source is at ~3-5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H 2 S/SO 2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO 2 and H 2 S/SO 2  > 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H 2 S/SO 2  < 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high-temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.

  4. Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high‐frequency gas monitoring

    PubMed Central

    Aiuppa, A.; Avard, G.; Wehrmann, H.; Dunbar, N.; Muller, C.; Tamburello, G.; Giudice, G.; Liuzzo, M.; Moretti, R.; Conde, V.; Galle, B.

    2016-01-01

    Abstract Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high‐frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2‐rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur‐rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is ~8–10 km deep, whereas the shallow magmatic gas source is at ~3–5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H2S/SO2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO2 and H2S/SO2 > 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H2S/SO2 < 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high‐temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity. PMID:27774371

  5. Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring

    NASA Astrophysics Data System (ADS)

    de Moor, J. Maarten; Aiuppa, A.; Avard, G.; Wehrmann, H.; Dunbar, N.; Muller, C.; Tamburello, G.; Giudice, G.; Liuzzo, M.; Moretti, R.; Conde, V.; Galle, B.

    2016-08-01

    Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San José. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high-frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2-rich gas (CO2/Stotal > 4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2 weeks before eruptions, which are accompanied by shallowly derived sulfur-rich magmatic gas emissions. Degassing modeling suggests that the deep magmatic reservoir is 8-10 km deep, whereas the shallow magmatic gas source is at 3-5 km. Two cycles of degassing and eruption are observed, each attributed to pulses of magma ascending through the deep reservoir to shallow crustal levels. The magmatic degassing signals were overprinted by a fluid contribution from the shallow hydrothermal system, modifying the gas compositions, contributing volatiles to the emissions, and reflecting complex processes of scrubbing, displacement, and volatilization. H2S/SO2 varies over 2 orders of magnitude through the monitoring period and demonstrates that the first eruptive episode involved hydrothermal gases, whereas the second did not. Massive degassing (>3000 T/d SO2 and H2S/SO2 > 1) followed, suggesting boiling off of the hydrothermal system. The gas emissions show a remarkable shift to purely magmatic composition (H2S/SO2 < 0.05) during the second eruptive period, reflecting the depletion of the hydrothermal system or the establishment of high-temperature conduits bypassing remnant hydrothermal reservoirs, and the transition from phreatic to phreatomagmatic eruptive activity.

  6. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Eichelberger, J.C.

    Magmatic activity, and particularly silicic magmatic activity, is the fundamental process by which continental crust forms and evolves. The transport of magma from deep crustal reservoirs to the surface is a neglected but important aspect of magmatic phenomena. It encompasses problems of eruptive behavior, hydrothermal circulation, and ore deposition, and must be understood in order to properly interpret deeper processes. Drilling provides a means for determining the relationship of shallow intrusive processes to eruption processes at young volcanoes where eruptions are best understood. Drilling also provides a means for directly observing the processes of heat and mass transfer by whichmore » recently emplaced intrusions approach equilibrium with their new environment. Drilling in the Inyo Chain, a 600-year-old chain of volcanic vents in California, has shown the close relationship of silicic eruption to shallow dike emplacement, the control of eruptive style by shallow porous-flow degassing, the origin of obsidian by welding, the development of igneous zonation by viscosity segregation, and the character and size of conduits in relation to well-understood magmatic and phreatic eruptions. 36 refs., 9 figs.« less

  7. DOE Office of Scientific and Technical Information (OSTI.GOV)

    Goff, F.; Aams, A.I.; McMurtry, G.M.

    This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory. Detailed geochemical sampling of high-temperature fumaroles, background water, and fresh magmatic products from 14 active volcanoes reveal that they do not produce measurable amounts of tritium ({sup 3}H) of deep origin (<0.1 T.U. or <0.32 pCi/kg H{sub 2}O). On the other hand, all volcanoes produce mixtures of meteoric and magmatic fluids that contain measurable {sup 3}H from the meteoric end-member. The results show that cold fusion is probably not a significant deep earth process but the samples and data havemore » wide application to a host of other volcanological topics.« less

  8. The Magmatic Structure of Mt. Vesuvius: Isotopic and Thermal Constraints

    NASA Astrophysics Data System (ADS)

    Civetta, L.; D'Antonio, M.; de Lorenzo, S.; Gasparini, P.

    2002-12-01

    Mt. Vesuvius is an active volcano famous for the AD 79 eruption that destroyed Pompeii, Herculaneum and Stabiae. Because of the intense urbanization around and on the volcano, the risk today is very high. Therefore, the knowledge of the structure and behavior of the magmatic system is fundamental both for the interpretation of any change in the dynamics of the volcano and for prediction of eruptions. A review of available and new isotopic data on rocks from Mt. Vesuvius, together with mineralogical and geochemical data and recent geophysical results, allow us to constrain a thermal modeling that describes history and present state of Mt. Vesuvius magmatic system. This system is formed by a "deep", complex magmatic reservoir where mantle-derived magmas arrive, stagnate and differentiate. The reservoir extends discontinuously between 10 and 20 km of depth, is hosted in densely fractured crustal rocks, where magmas and crust can interact, and has been fed more than once since 400 ka. The hypothesis of crustal contamination is favored by the high temperatures reached by crustal rocks as a consequence of repetitive intrusions of magma. From the "deep" reservoir magmas of K-basaltic to K-tephritic to K-phonotephritic composition rise to shallow depths where they stagnate at 3-5 km of depth before plinian eruptions, and through crystallization and mixing processes with the residual portion of the feeding systems, generate isotopically and geochemically layered reservoirs. Alternatively, during "open conduit" conditions deep, volatile-rich magma batches rise from the "deep" reservoir to less than 1 km of depth and mix with the crystal-rich, volatile-poor resident magma, triggering eruptions.

  9. The Magmatic Budget of Rifted Margins: is it Related to Inheritance?

    NASA Astrophysics Data System (ADS)

    Manatschal, G.; Tugend, J.; Gillard, M.; Sauter, D.

    2017-12-01

    High quality reflection and refraction seismic surveys show a divergent style of margin architecture often referred to as magma-poor or magma-rich. More detailed studies show, however, that the evolution of these margins can be similar, despite the variable quantity and distribution of magmatism. These observations suggest that simple relations between magmatic and extensional systems are inappropriate to describe the magmatic history of rifted margins. Moreover, the study of magmatic additions indicates that they may occur, prior to, during or after lithospheric breakup. Furthermore, the observation that the magmatic budget may change very abruptly along strike and across the margin is difficult to reconcile with the occurrence of plumes or other deep-seated large-scale mantle phenomena only. These overall observations result in questions on how magmatic and tectonic processes are interacting during rifting and lithospheric breakup and on how far the inherited composition and temperature of the decompressing mantle may control the magmatic budget during rifting. In our presentation we will review examples from present-day and fossil rifted margins to discuss their structural and magmatic evolution and whether they are considered as magma-rich or magma-poor. The key questions that we aim to address are: 1) whether decompression melting is the driving force, or rather the consequence of extension, 2) how far the magmatic budget is controlled by inherited mantle composition and temperature, and 3) how important magma storage is during initial stages of rifting. Eventually, we will discuss to what extent the evolution of margins may reflect the interplay between inheritance (innate/"genetic code") and the actual physical processes (acquired/external factors).

  10. Petrology and geochemistry of primitive lower oceanic crust from Pito Deep: Implications for the accretion of the lower crust at the Southern East Pacific Rise

    USGS Publications Warehouse

    Perk, N.W.; Coogan, L.A.; Karson, J.A.; Klein, E.M.; Hanna, H.D.

    2007-01-01

    A suite of samples collected from the uppermost part of the plutonic section of the oceanic crust formed at the southern East Pacific Rise and exposed at the Pito Deep has been examined. These rocks were sampled in situ by ROV and lie beneath a complete upper crustal section providing geological context. This is only the second area (after the Hess Deep) in which a substantial depth into the plutonic complex formed at the East Pacific Rise has been sampled in situ and reveals significant spatial heterogeneity in the plutonic complex. In contrast to the uppermost plutonic rocks at Hess Deep, the rocks studied here are generally primitive with olivine forsterite contents mainly between 85 and 88 and including many troctolites. The melt that the majority of the samples crystallized from was aggregated normal mid-ocean ridge basalt (MORB). Despite this high Mg# clinopyroxene is common despite model predictions that clinopyroxene should not reach the liquidus early during low-pressure crystallization of MORB. Stochastic modeling of melt crystallisation at various levels in the crust suggests that it is unlikely that a significant melt mass crystallized in the deeper crust (for example in sills) because this would lead to more evolved shallow level plutonic rocks. Similar to the upper plutonic section at Hess Deep, and in the Oman ophiolite, many samples show a steeply dipping, axis-parallel, magmatic fabric. This suggests that vertical magmatic flow is an important process in the upper part of the seismic low velocity zone beneath fast-spreading ridges. We suggest that both temporal and spatial (along-axis) variability in the magmatic and hydrothermal systems can explain the differences observed between the Hess Deep and Pito Deep plutonics. ?? Springer-Verlag 2007.

  11. Re-appraisal of the Magma-rich versus Magma-poor Paradigm at Rifted Margins: consequences for breakup processes

    NASA Astrophysics Data System (ADS)

    Tugend, J.; Gillard, M.; Manatschal, G.; Nirrengarten, M.; Harkin, C. J.; Epin, M. E.; Sauter, D.; Autin, J.; Kusznir, N. J.; McDermott, K.

    2017-12-01

    Rifted margins are often classified based on their magmatic budget only. Magma-rich margins are commonly considered to have excess decompression melting at lithospheric breakup compared with steady state seafloor spreading while magma-poor margins have suppressed melting. New observations derived from high quality geophysical data sets and drill-hole data have revealed the diversity of rifted margin architecture and variable distribution of magmatism. Recent studies suggest, however, that rifted margins have more complex and polyphase tectono-magmatic evolutions than previously assumed and cannot be characterized based on the observed volume of magma alone. We compare the magmatic budget related to lithospheric breakup along two high-resolution long-offset deep reflection seismic profiles across the SE-Indian (magma-poor) and Uruguayan (magma-rich) rifted margins. Resolving the volume of magmatic additions is difficult. Interpretations are non-unique and several of them appear plausible for each case involving variable magmatic volumes and mechanisms to achieve lithospheric breakup. A supposedly 'magma-poor' rifted margin (SE-India) may show a 'magma-rich' lithospheric breakup whereas a 'magma-rich' rifted margin (Uruguay) does not necessarily show excess magmatism at lithospheric breakup compared with steady-state seafloor spreading. This questions the paradigm that rifted margins can be subdivided in either magma-poor or magma-rich margins. The Uruguayan and other magma-rich rifted margins appear characterized by an early onset of decompression melting relative to crustal breakup. For the converse, where the onset of decompression melting is late compared with the timing of crustal breakup, mantle exhumation can occur (e.g. SE-India). Our work highlights the difficulty in determining a magmatic budget at rifted margins based on seismic reflection data alone, showing the limitations of margin classification based solely on magmatic volumes. The timing of decompression melting onset and melting rates (magmatic processes) relative to crustal thinning (tectonic processes) appear equally, if not more important, than the magmatic budget for unravelling the evolution of rifted margins.

  12. The Magmatic Plumbing System of the Campi Flegrei Caldera.

    NASA Astrophysics Data System (ADS)

    Lucia, C.; Ilenia, A.; Massimo, D.; Valeria, D.; Mauro, D.; Giovanni, O.

    2006-12-01

    The Campi Flegrei caldera is a nested and resurgent structure generated by at least two major collapses. Large sectors of the structural boundary of both calderas resulted from partial reactivation of pre-existing faults generated by regional tectonism. Its magmatic system is still active with the last eruption occurring in 1538 A.D. (Monte Nuovo), widespread fumaroles and hot springs activity, and the unrest episodes in the last 35 years, with a maximum net uplift of about 3.5 m in the Pozzuoli area. The definition of the history of the magmatic feeding system of this caldera, in terms of composition, time- scale and depth of crystallization, relation between composition of the erupted magma and structural position of the vent, and magma chamber processes, is of extreme importance for a better understanding of the dynamic conditions of the present day magma chamber and for evaluating of the extent to which the behavior of the magmatic system can be predicted. The Campi Flegrei caldera magmatic plumbing system is characterized by deep and shallow reservoirs. Campi Flegrei magmas originated in a subduction modified mantle source, stagnate at mid crustal level (20- 10 km depth), where they differentiated and are contaminated with the continental crust. From the "deep reservoir" shoshonitic to latitic magmas rise towards the surface along the NE aligned regional fault reactivated during the caldera collapse, whereas trachytic magmas rise mostly along faults and fractures bordering the resurgent block and the southern part of the Campi Flegrei caldera. Repeated arrival of trachytic to phonolitic magmas form shallow reservoirs at 4-3 km depth, in which differentiation and mixing processes occur before and during the eruption.

  13. Disclosing Multiple Magma Degassing Sources Offers Unique Insights of What's Behind the Campi Flegrei Caldera Unrest

    NASA Astrophysics Data System (ADS)

    Moretti, R.; Civetta, L.; Orsi, G.; Arienzo, I.; D'Antonio, M.; Di Renzo, V.

    2013-12-01

    The definition of the structure and evolution of the magmatic system of Campi Flegrei caldera (CFc), Southern Italy, has been a fundamental tool for the assessment of the short-term volcanic hazard. The ensemble of geophysical and petrologic data show that the CFc magmatic system has been -and still is- characterized by two major reservoirs at different depths. From the deep one (around 8 km), less evolved magmas crystallize and degas, supplying fluids and magmas to the shallow (3-4 km) reservoirs. A thorough reconstruction of processes occurring in magma chamber/s prior and/or during the CFc eruptions has shown that magmas entering shallow reservoirs mixed with resident and crystallized batches. Also the 1982-85 unrest episode has been related to a magma intrusion of 2.1 x 10^7 m^3 at 3-4 km depth, on the basis of geophysical data (ground deformation, gravimetry, seismic imaging) and their interpretation. Thermodynamic evaluation of magma properties, at the time of emplacement, suggests for such an intrusion a bulk density of 2.000 kg/m^3 . Such a value testifies the high amount of exsolved volatiles within the system. The available record of geochemical and isotopic data on surface fumaroles, coupled with melt inclusion data, has already shown that dual (deep and shallow) magma degassing from such two reservoirs, as well as their interaction with the hydrothermal system, allows explaining the relevant fluctuations observed at crater fumaroles after the 1982-85 magma intrusion. An important role was played by the rapid crystallization (around 30 years) of the shallow magma, such that in the recent years gas discharges should be fuelled mostly by the deep magma. Such a process is well recorded in the fumarolic gas composition of the last ~10 years, but has to be reconciled with the unrest dynamics which took place after year 2000, characterized by a slow but continuous ground uplift. All geochemical indicators (major species and noble gases) point to three possible scenarios: 1) only deep gases enter the hydrothermal system, because the shallow magmatic body is now fully crystallized and degassed. 2) The shallow magmatic body, invested by the arrival of deep gases, starts remelting and releasing gases into the hydrothermal system. 3) Magma from the deep reservoir slowly rises to shallow depths, well below the ductile-fragile transition for this area. These three scenarios carry contrasting implications for the volcanic hazard assessment, and demand a comprehensive treatment of geochemical and geophysical data in a way coherent with the knowledge that we have of the 1982-85 unrest

  14. A comprehensive approach to monitoring volcano deformation as a window on the eruption cycle

    USGS Publications Warehouse

    Dzurisin, D.

    2003-01-01

    Since the 1980 eruption of Mount St. Helens, volcanologists have made considerable progress toward predicting eruptions on the basis of precursors that typically start a few days to several months in advance. Although accurate eruption prediction is by no means routine, it may now be possible in some cases to extend the effective warning period by anticipating the onset of short-term precursors. Three promising indicators of deep magmatic processes are (1) deep, long-period earthquakes and tremor that indicate the ascent of magma through the crust, (2) magmatic CO2 emission rate as a proxy for magma supply rate, and (3) relatively broad, generally aseismic surface uplift caused by magmatic intrusions. In the latter case it is essential to sample the deformation field thoroughly in both time and space to adequately constrain source models. Until recently, this has been nearly impossible because high-precision sensors could not be deployed in sufficient numbers, nor could extensive geodetic surveys be conducted often enough. Advances in instrumentation, interferometric synthetic aperture radar (InSAR), and telecommunications are helping to overcome these limitations. As a result, comprehensive geodetic monitoring of selected volcanoes is now feasible. A combination of InSAR, large-aperture GPS surveys, microgravity surveys, and dense arrays of continuous GPS stations, strain meters, and tiltmeters can reveal both spatial and temporal patterns of ground deformation throughout the eruption cycle. Improved geodetic monitoring of many of the world's volcanoes would be a major stride toward better understanding of magmatic processes and longer-term eruption forecasts.

  15. Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment.

    PubMed

    Chiaradia, Massimo; Caricchi, Luca

    2017-03-15

    Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i.e., Sr/Y) to the formation of porphyry Cu deposits of different sizes. Our analysis shows that economic deposits (particularly the largest ones) may only form in association with magma accumulated in the lower-middle crust (P > ~0.5 GPa) during ≥2-3 Ma, and subsequently transferred to and degassed in the upper crust over periods of up to ~2.0 Ma. Magma accumulation and evolution at shallower depths (<~0.4 GPa) dramatically reduces the potential of magmatic systems to produce economic deposits. Our modelling also predicts the association of the largest porphyry deposits with a specific Sr/Y interval (~100 ± 50) of the associated magmatic rocks, which is virtually identical to the range measured in giant porphyry copper deposits.

  16. Stochastic modelling of deep magmatic controls on porphyry copper deposit endowment

    PubMed Central

    Chiaradia, Massimo; Caricchi, Luca

    2017-01-01

    Porphyry deposits, our main source of copper and of significant amounts of Mo, Re and Au, form at convergent margins in association with intermediate-felsic magmas. Although it is accepted that copper is transported and precipitated by fluids released by these magmas, the magmatic processes leading to the formation of economic deposits remain elusive. Here we perform Monte Carlo petrological and geochemical modelling to quantitatively link crustal magmatic processes and the geochemical signatures of magmas (i.e., Sr/Y) to the formation of porphyry Cu deposits of different sizes. Our analysis shows that economic deposits (particularly the largest ones) may only form in association with magma accumulated in the lower-middle crust (P > ~0.5 GPa) during ≥2–3 Ma, and subsequently transferred to and degassed in the upper crust over periods of up to ~2.0 Ma. Magma accumulation and evolution at shallower depths (<~0.4 GPa) dramatically reduces the potential of magmatic systems to produce economic deposits. Our modelling also predicts the association of the largest porphyry deposits with a specific Sr/Y interval (~100 ± 50) of the associated magmatic rocks, which is virtually identical to the range measured in giant porphyry copper deposits. PMID:28295045

  17. The effects of magmatic redistribution of heat producing elements on the lunar mantle evolution inferred from numerical models that start from various initial states

    NASA Astrophysics Data System (ADS)

    Ogawa, Masaki

    2018-02-01

    To discuss how redistribution of heat producing elements (HPEs) by magmatism affects the lunar mantle evolution depending on the initial condition, I present two-dimensional numerical models of magmatism in convecting mantle internally heated by incompatible HPEs. Mantle convection occurs beneath a stagnant lithosphere that inhibits recycling of the HPE-enriched crustal materials to the mantle. Magmatism is modeled by a permeable flow of magma generated by decompression melting through matrix. Migrating magma transports heat, mass, and HPEs. When the deep mantle is initially hot with the temperature TD around 1800 K at its base, magmatism starts from the beginning of the calculated history to extract HPEs from the mantle. The mantle is monotonously cooled, and magmatism ceases within 2 Gyr, accordingly. When the deep mantle is initially colder with TD around 1100 K, HPEs stay in the deep mantle for a longer time to let the planet be first heated up and then cooled only slightly. If, in addition, there is an HPE-enriched domain in the shallow mantle at the beginning of the calculation, magma continues ascending to the surface through the domain for more than 3 Gyr. The low TD models fit in with the thermal and magmatic history of the Moon inferred from spacecraft observations, although it is not clear if the models are consistent with the current understanding of the origin of the Moon and its magnetic field. Redistribution of HPEs by magmatism is a crucial factor that must be taken into account in future studies of the evolution of the Moon.

  18. Evidence of a modern deep water magmatic hydrothermal system in the Canary Basin (eastern central Atlantic Ocean)

    NASA Astrophysics Data System (ADS)

    Medialdea, T.; Somoza, L.; González, F. J.; Vázquez, J. T.; de Ignacio, C.; Sumino, H.; Sánchez-Guillamón, O.; Orihashi, Y.; León, R.; Palomino, D.

    2017-08-01

    New seismic profiles, bathymetric data, and sediment-rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800-5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the Canary Basin (Eastern Atlantic Ocean, 500 km west of the Canary Islands). A complex of sill intrusions is imaged on seismic profiles showing saucer-shaped, parallel, or inclined geometries. Three main types of structures are related to these intrusions. Type I consists of cone-shaped depressions developed above inclined sills interpreted as hydrothermal vents. Type II is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer-shaped sills. Domes are interpreted as seabed expressions of reservoirs of CH4 and CO2-rich fluids formed by degassing and contact metamorphism of organic-rich sediments around sill intrusions. Type III are hydrothermal-volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice. Parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones. Core and dredges revealed that these volcanoes, which must be among the deepest in the world, are constituted by OIB-type, basanites with an outer ring of blue-green hydrothermal Al-rich smectite muds. Magmatic activity is dated, based on lava samples, at 0.78 ± 0.05 and 1.61 ± 0.09 Ma (K/Ar methods) and on tephra layers within cores at 25-237 ky. The Subvent hydrothermal-volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity.Plain Language SummarySubmarine volcanism and associated hydrothermal systems are relevant processes for the evolution of the ocean basins, due their impact on the geochemistry of the oceans, their potential to form significant ore deposits, and their implications for global climate change, considering the heat transport, maturation of organic matter and the release of carbon-rich fluids associated to these systems. Hydrothermal vent complexes have been found all over the world in the fossil record related to large igneous provinces as those found in the North Atlantic margins. Nevertheless, studies focused on modern deep water magmatic hydrothermal systems are generally confined to ocean spreading centers, while scarce works address their study in deep oceanic intraplate basins. This study reports and documents for the first time the discovery of a recent deep water system of magmatic-induced hydrothermal vents at 4800-5200 m depth in an unexplored area of the Canary Basin (eastern central Atlantic), located about 500 km west of the Canary Islands. The analysis and interpretation of the newly acquired data set has shown that the study area is characterized by the presence of a huge magmatic complex of sills that intrudes the sedimentary sequence and exceptionally deep volcanoes so far unknown.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.478..203F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.478..203F"><span>Numerical models of the magmatic processes induced by slab breakoff</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Freeburn, Rebecca; Bouilhol, Pierre; Maunder, Ben; Magni, Valentina; van Hunen, Jeroen</p> <p>2017-11-01</p> <p>After the onset of continental collision, magmatism often persists for tens of millions of years, albeit with a different composition, in reduced volumes, and with a more episodic nature and more widespread spatial distribution, compared to normal arc magmatism. Kinematic modelling studies have suggested that slab breakoff can account for this post-collisional magmatism through the formation of a slab window and subsequent heating of the overriding plate and decompression melting of upwelling asthenosphere, particularly if breakoff occurs at depths shallower than the overriding plate. To constrain the nature of any melting and the geodynamic conditions required, we numerically model the collision of two continental plates following a period of oceanic subduction. A thermodynamic database is used to determine the (de)hydration reactions and occurrence of melt throughout this process. We investigate melting conditions within a parameter space designed to generate a wide range of breakoff depths, timings and collisional styles. Under most circumstances, slab breakoff occurs deeper than the depth extent of the overriding plate; too deep to generate any decompressional melting of dry upwelling asthenosphere or thermal perturbation within the overriding plate. Even if slab breakoff is very shallow, the hot mantle inflow into the slab window is not sustained long enough to sufficiently heat the hydrated overriding plate to cause significant magmatism. Instead, for relatively fast, shallow breakoff we observe melting of asthenosphere above the detached slab through the release of water from the tip of the heating detached slab. Melting of the subducted continental crust during necking and breakoff is a more common feature and may be a more reliable indicator of the occurrence of breakoff. We suggest that magmatism from slab breakoff alone is unable to explain several of the characteristics of post-collisional magmatism, and that additional geodynamical processes need to be considered when interpreting magmatic observations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T22C..01B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T22C..01B"><span>The influence of inherited structures on magmatic and amagmatic processes in the East African Rift.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Biggs, J.; Lloyd, R.; Hodge, M.; Robertson, E.; Wilks, M.; Fagereng, A.; Kendall, J. M.; Mdala, H. S.; Lewi, E.; Ayele, A.</p> <p>2017-12-01</p> <p>The idea that crustal heterogeneities, particularly inherited structures, influence the initiation and evolution of continental rifts is not new, but now modern techniques allow us to explore these controls from a fresh perspective, over a range of lengthscales, timescales and depths. In amagmatic rifts, I will demonstrate that deep fault structure is controlled by the stress orientation during the earliest phase of rifting, while the surface expression exploits near-surface weaknesses. I will show that pre-existing structures control the storage and orientation of deeper magma reservoirs in magmatic rifts, while the tectonic stress regime controls intra-rift faulting and shallow magmatism and stresses related to surface loading and cycles of inflation and deflation dominate at volcanic edifices. Finally, I will show how cross-rift structures influence short-term processes such as deformation and seismicity. I will illustrate the talk throughout using examples from along the East African Rift, including Malawi, Tanzania, Kenya and Ethiopia.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li class="active"><span>1</span></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_1 --> <div id="page_2" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li class="active"><span>2</span></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="21"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T52C..04E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T52C..04E"><span>Evolution of Northeast Atlantic Magmatic Continental Margins from an Ethiopian-Afar Perspective</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>England, R. W.; Cornwell, D. G.; Ramsden, A. M.</p> <p>2014-12-01</p> <p>One of the major problems interpreting the evolution of magmatic continental margins is that the structure which should record the pre-magmatic evolution of the rift and which potentially influences the character of the rifting process is partially or completely obscured by thick basalt lava flows and sills. A limited number of deep reflection seismic profiles acquired with tuned seismic sources have penetrated the basalts and provide an image of the pre-magmatic structure, otherwise the principle data are lower resolution wide-angle/refraction profiles and potential field models which have greater uncertainties associated with them. In order to sidestep the imaging constraints we have examined the Ethiopian - Afar rift system to try to understand the rifting process. The Main Ethiopian rift contains an embryonic magmatic passive margin dominated by faulting at the margins of the rift and en-echelon magmatic zones at the centre. Further north toward Afar the rift becomes in-filled with extensive lava flows fed from fissure systems in the widening rift zone. This rift system provides, along its length, a series of 'snapshots' into the possible tectonic evolution of a magmatic continental margin. Deep seismic profiles crossing the NE Atlantic margins reveal ocean dipping reflector sequences (ODRS) overlying extended crust and lower crustal sill complexes of intruded igneous rock, which extend back beneath the continental margin. The ODRS frequently occur in fault bounded rift structures along the margins. We suggest, by analogy to the observations that can be made in the Ethiopia-Afar rift that these fault bounded basins largely form at the embryonic rift stage and are then partially or completely filled with lavas fed from fissures which are now observed as the ODRS. Also in the seismic profiles we identify volcanic constructs on the ODRS which we interpret as the equivalent of the present day fissure eruptions seen in Afar. The ocean ward dip on the ODRS is predominantly the result of post-eruption differential subsidence, as opposed to syn-eruption extension. The timing of intrusion of the lower crustal sill complexes remains unclear but they are most likely to have been emplaced as the supply of magma increased, which implies they are a late stage addition.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912474V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912474V"><span>Geothermal surveys in the oceanic volcanic island of Mauritius</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Verdoya, Massimo; Chiozzi, Paolo; Pasqua, Claudio</p> <p>2017-04-01</p> <p>Oceanic island chains are generally characterised by young volcanic systems that are predominately composed of basaltic lavas and related magmatic products. Although hot springs are occasionally present, the pervasive, massive, recent outpourings of basaltic lavas are the primary manifestation of the existence of geothermal resources. These islands may have, in principle, significant potential for the exploitation of geothermal energy. In this paper, we present results of recent investigations aimed at the evaluation of geothermal resources of the island of Mauritius, that is the emerging portion of a huge submarine, aseismic, volcanic plateau extending in the SW part of the Indian Ocean. The plateau is related to a long-lived hotspot track, whose present-day expression is the active volcano of La Réunion Island, located about 200 km SW of Mauritius. The island does not show at present any volcanic activity, but magmatism is quite recent as it dates from 7.8 to 0.03 Myr. Geochemical data from water samples collected from boreholes do not indicate the presence of mature water, i.e. circulating in high-temperature geothermal reservoirs, and argue for short-term water-rock interaction in shallow hydrogeological circuits. However, this cannot rule out that a deep magmatic heat source, hydraulically insulated from shallow aquifers, may occur. To evaluate the geothermal gradient, a 270-m-deep hole was thus drilled in the island central portion, in which the most recent volcanic activity (0.03 Myr) took place. Temperature-depth profiles, recorded after complete thermal equilibration, revealed a thermal gradient of 40 mK/m. Attempts of extracting additional thermal information were also made by measuring the temperature in a 170-m-deep deep water hole, no longer used. The results were consistent with the gradient hole, i.e. pointing to a weak or null deep-seated thermal anomaly beneath Mauritius and low geothermal potential. The deep thermal process (mantle plume) invoked to occur in the hotspot area thus seems to yield no particular thermal signature.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V31D..06B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V31D..06B"><span>The Deep Crust Magmatic Refinery, Part 2 : The Magmatic Output of Numerical Models.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bouilhol, P.; Riel, N., Jr.; Van Hunen, J.</p> <p>2016-12-01</p> <p>Metamorphic and magmatic processes occurring in the deep crust ultimately control the chemical and physical characteristic of the continental crust. A complex interplay between magma intrusion, crystallization, and reaction with the pre-existing crust provide a wide range of differentiated magma and cumulates (and / or restites) that will feed the upper crustal levels with evolved melt while constructing the lower crust. With growing evidence from field and experimental studies, it becomes clearer that crystallization and melting processes are non-exclusive but should be considered together. Incoming H2O bearing mantle melts will start to fractionate to a certain extent, forming cumulates but also releasing heat and H2O to the intruded host-rock allowing it to melt in saturated conditions. The end-result of such dynamic system is a function of the amount and composition of melt input, and extent of reaction with the host which is itself dependent on the migration mode of the melts. To better constrain lower crust processes, we have built up a numerical model [see Riel et al. associated abstract for methods] to explore different parameters, unravelling the complex interplay between melt percolation / crystallization and degassing / re-melting in a so called "hot zone" model. We simulated the intrusion of water bearing mantle melts at the base of an amphibolitized lower crust during a magmatic event that lasts 5 Ma. We varied several parameters such as Moho depth and melt rock ratio to better constrain what controls the final melt / lower crust composition.. We show the evolution of the chemical characteristics of the melt that escape the system during this magmatic event, as well as the resulting lower crust characteristics. We illustrate how the evolution of melt major elements composition reflects the progressive replacement of the crust towards compositions that are dominated by the mantle melt input. The resulting magmas cover a wide range of composition from tonalite to granite, and the modelled lower crust shows all the petrological characteristic of observed lower arc-crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035465','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035465"><span>Petrology and geochronology of crustal xenoliths from the Bering Strait region: Linking deep and shallow processes in extending continental crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Akinin, V.V.; Miller, E.L.; Wooden, J.L.</p> <p>2009-01-01</p> <p>Petrologic, geochemical, and metamorphic data on gneissic xenoliths derived from the middle and lower crust in the Neogene Bering Sea basalt province, coupled with U-Pb geochronology of their zircons using sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG), yield a detailed comparison between the P-T-t and magmatic history of the lower crust and magmatic, metamorphic, and deformational history of the upper crust. Our results provide unique insights into the nature of lithospheric processes that accompany the extension of continental crust. The gneissic, mostly maficxenoliths (constituting less than two percent of the total xenolith population) from lavas in the Enmelen, RU, St. Lawrence, Nunivak, and Seward Peninsula fields most likely originated through magmatic fractionation processes with continued residence at granulite-facies conditions. Zircon single-grain ages (n ??? 125) are interpreted as both magmatic and metamorphic and are entirely Cretaceous to Paleocene in age (ca. 138-60 Ma). Their age distributions correspond to the main ages of magmatism in two belts of supracrustal volcanic and plutonic rocks in the Bering Sea region. Oscillatory-zoned igneous zircons, Late Cretaceous to Paleocene metamorphic zircons and overgrowths, and lack of any older inheritance in zircons from the xenoliths provide strong evidence for juvenile addition of material to the crust at this time. Surface exposures of Precambrian and Paleozoic rocks locally reached upper amphibolite-facies (sillimanite grade) to granulite-facies conditions within a series of extension-related metamorphic culminations or gneiss domes, which developed within the Cretaceous magmatic belt. Metamorphic gradients and inferred geotherms (??30-50 ??C/km) from both the gneiss domes and xenoliths aretoo high to be explained by crustal thickening alone. Magmatic heat input from the mantle is necessary to explain both the petrology of the magmas and elevated metamorphic temperatures. Deep-crustal seismic-reflection and refraction data reveal a 30-35-km-thick crust, a sharp Moho and refl ective lower and middle crust. Velocities do not support a largely mafic (underplated) lower crust, but together with xenolith data suggest that Late Cretaceous to early Paleocene maficintrusions are likely increasingly important with depth in the crust and that the elevated temperatures during granulite-facies metamorphism led to large-scale flow of crustal rocks to produce gneiss domes and the observed subhorizontal refl ectivity of the crust. This unique combined data set for the Bering Shelf region provides compelling evidence for the complete reconstitution/re-equilibration of continental crust from the bottom up during mantle-driven magmatic events associated with crustal extension. Thus, despite Precambrian and Paleozoic rocks at the surface and Alaska's accretionary tectonic history, it is likely that a significant portion of the Bering Sea region lower crust is much younger and related to post-accretionary tectonic and magmatic events. ?? 2009 The Geological Society of America.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V33B3125R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V33B3125R"><span>The Deep Crust Magmatic Refinery, Part 1: A Coupled Thermodynamic and Two-phase Flow Model</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Riel, N., Jr.; Bouilhol, P.; Van Hunen, J.; Velic, M.; Magni, V.</p> <p>2016-12-01</p> <p>Metamorphic and magmatic processes occurring in the deep crust ultimately control the chemical and physical characteristic of the continental crust. A complex interplay between magma intrusion, crystallization, and reaction with the pre-existing crust provide a wide range of differentiated magma and cumulates (and / or restites) that will feed the upper crustal levels with evolved melt while constructing the lower crust. With growing evidence from field and experimental studies, it becomes clearer that crystallization and melting processes are non-exclusive but should be considered together. Incoming H2O bearing mantle melts will start to fractionate to a certain extent, forming cumulates but also releasing heat and H2O to the intruded host-rock allowing it to melt in saturated conditions. The end-result of such dynamic system is a function of the amount and composition of melt input, and extent of reaction with the host which is itself dependent on the migration mode of the melts. To assess the dynamics of this deep magmatic system we developed a new 2-D two-phase flow code using finite volume method. Our formulation takes into account: (i) melt flow through a viscous porous matrix with temperature- and melt-content dependent host-rock viscosity, (ii) heat transfer, assuming local thermal equilibrium between solid and liquid, (iii) thermodynamic modelling of stable phases, (iv) injection of fractionated melt from crystallizing basalt at the Moho and (v) chemical advection of both the solid and liquid compositions. Here we present the core of our modelling approach, especially the petrological implementation. We show in details that our thermodynamic model can reproduce well both the sub- and supra solidus phase relationship and composition of the host-rock. We apply our method to an idealized amphibolite lower crust that is affected by a magmatic event represented by the intrusion of a wet mantle melt into the crust at Moho depth. The models [see Bouilhol et al. associated abstract for results] allow calculating the different proportion of phases present in the system through time.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007ESF....14..165L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007ESF....14..165L"><span>Metallogeny by Trans-magmatic Fluids—Theoretical Analysis and Field Evidence</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Luo, Zhaohua; Mo, Xuanxue; Lu, Xinxiang; Chen, Bihe; Ke, Shan; Hou, Zengqian; Jiang, Wan</p> <p></p> <p>This paper is aimed at introducing and developing the principle of Metallogenic Theory through Trans-magmatic Fluids (MTTF) proposed by the Russian Kozhinskii's school. Some fundamental problems of metallogeny are discussed on geodynamic bases. In this theory, the trans-magmatic fluid is interpreted as a moving fluid passing through magma which is not yet consolidated. The intensive wallrock alteration of most of hydrothermal ore systems suggests that large scale fluid flow accompanies metallogenesis. However, geological observations and experiments imply a very limited solubility of fluids in magmas. In addition, the close relationship between small igneous bodies and large ore systems together with the difficulty of fluids that from the wallrocks might enter a magmatic body, which is under high pressure and temperature, need also to be considered. Those ore-bearing fluids that originate from a deep fluid system, are independent of magmas. Experiments show rapid increases of the solubility of ore-forming elements or their compounds in hydrothermal fluids. Therefore, the essential prerequisites for mineralization are (1) large volumes of deep ore-bearing fluids with high concentration of metals, and (2) the large amounts of metal accumulation depend on the rapid ascent of the deep ore-bearing fluid. Magmas are the favorable medium for the ascending fluids, because these magmas provide conditions that prevent re-equilibrium between the fluid and the wallrocks at different deep levels. The fluids in turn, may provide the driving force for the rapid ascent of magmas. Therefore, the two systems act together to account for the close relationship between magmatism and metallogeny. According to this theory, the scale and location of an ore-forming process are decided by (1) the volumetric ratio of the magma and the fluid systems, (2) the ascending rate of the ore-bearing fluid, (3) the boundary conditions for metal accumulation and (4) the segregation of the fluid from the magma. The field investigations of copper-bearing Melanocratic Macrogranular Enclaves (MME) in the Qushui massif, Gangdise belt are very helpful for understanding of source, transport and precipitation of ore-forming materials. In this example, it can be seen that fluid-rich MMEs is the source of the ore-forming element copper. Copper is transported out from MMEs by the fluid, following dispersal in the granitic magma. The copper-bearing fluid is then transferred through the magma and induced to deposit mineralization elsewhere. These processes have been noted when comparing the metallogenic features in both MME in the Qushui massif and the porphyry copper deposits in Yulong, eastern Tibet. It is obvious that MTTF is a very important theory for metallogeny of endogenic deposits. Using this theory, many paradoxes in metallogenesis can be interpreted in easier manner.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70193725','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70193725"><span>Shallow and deep controls on lava lake surface motion at Kīlauea Volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Patrick, Matthew R.; Orr, Tim R.; Swanson, Don; Lev, Einat</p> <p>2016-01-01</p> <p>Lava lakes provide a rare window into magmatic behavior, and lake surface motion has been used to infer deeper properties of the magmatic system. At Halema'uma'u Crater, at the summit of Kīlauea Volcano, multidisciplinary observations for the past several years indicate that lava lake surface motion can be broadly divided into two regimes: 1) stable and 2) unstable. Stable behavior is driven by lava upwelling from deeper in the lake (presumably directly from the conduit) and is an intrinsic process that drives lava lake surface motion most of the time. This stable behavior can be interrupted by periods of unstable flow (often reversals) driven by spattering – a shallowly-rooted process often extrinsically triggered by small rockfalls from the crater wall. The bursting bubbles at spatter sources create void spaces and a localized surface depression which draws and consumes surrounding surface crust. Spattering is therefore a location of lava downwelling, not upwelling. Stable (i.e. deep, upwelling-driven) and unstable (i.e. shallow, spattering-driven) behavior often alternate through time, have characteristic surface velocities, flow directions and surface temperature regimes, and also correspond to changes in spattering intensity, outgassing rates, lava level and seismic tremor. These results highlight that several processes, originating at different depths, can control the motion of the lava lake surface, and long-term interdisciplinary monitoring is required to separate these influences. These observations indicate that lake surface motion is not always a reliable proxy for deeper lake or magmatic processes. From these observations, we suggest that shallow outgassing (spattering), not lake convection, drives the variations in lake motion reported at Erta 'Ale lava lake.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..328..247P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..328..247P"><span>Shallow and deep controls on lava lake surface motion at Kīlauea Volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Patrick, M. R.; Orr, T.; Swanson, D. A.; Lev, E.</p> <p>2016-12-01</p> <p>Lava lakes provide a rare window into magmatic behavior, and lake surface motion has been used to infer deeper properties of the magmatic system. At Halema'uma'u Crater, at the summit of Kīlauea Volcano, multidisciplinary observations for the past several years indicate that lava lake surface motion can be broadly divided into two regimes: 1) stable and 2) unstable. Stable behavior is driven by lava upwelling from deeper in the lake (presumably directly from the conduit) and is an intrinsic process that drives lava lake surface motion most of the time. This stable behavior can be interrupted by periods of unstable flow (often reversals) driven by spattering - a shallowly-rooted process often extrinsically triggered by small rockfalls from the crater wall. The bursting bubbles at spatter sources create void spaces and a localized surface depression which draws and consumes surrounding surface crust. Spattering is therefore a location of lava downwelling, not upwelling. Stable (i.e. deep, upwelling-driven) and unstable (i.e. shallow, spattering-driven) behavior often alternate through time, have characteristic surface velocities, flow directions and surface temperature regimes, and also correspond to changes in spattering intensity, outgassing rates, lava level and seismic tremor. These results highlight that several processes, originating at different depths, can control the motion of the lava lake surface, and long-term interdisciplinary monitoring is required to separate these influences. These observations indicate that lake surface motion is not always a reliable proxy for deeper lake or magmatic processes. From these observations, we suggest that shallow outgassing (spattering), not lake convection, drives the variations in lake motion reported at Erta 'Ale lava lake.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.268...76J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.268...76J"><span>An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.; Cliff, John B.; Belousova, Elena A.; Sheppard, Stephen</p> <p>2017-01-01</p> <p>The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as 'cratonization', is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons from several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons. The majority of magmatic zircons from the main magmatic cycles have Hf isotopic compositions that are generally more evolved than CHUR, forming vertical arrays that extend to moderately radiogenic compositions. Complimentary O isotope data, also show a significant variation in composition. However, combined, these data define not only the source components from which the magmas were derived, but also a range of physio-chemical processes that operated during magma transport and emplacement. These data also identify a previously unknown crustal reservoir in the Capricorn Orogen.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024302','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024302"><span>Upper-mantle origin of the Yellowstone hotspot</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Christiansen, R.L.; Foulger, G.R.; Evans, J.R.</p> <p>2002-01-01</p> <p>Fundamental features of the geology and tectonic setting of the northeast-propagating Yellowstone hotspot are not explained by a simple deep-mantle plume hypothesis and, within that framework, must be attributed to coincidence or be explained by auxiliary hypotheses. These features include the persistence of basaltic magmatism along the hotspot track, the origin of the hotspot during a regional middle Miocene tectonic reorganization, a similar and coeval zone of northwestward magmatic propagation, the occurrence of both zones of magmatic propagation along a first-order tectonic boundary, and control of the hotspot track by preexisting structures. Seismic imaging provides no evidence for, and several contraindications of, a vertically extensive plume-like structure beneath Yellowstone or a broad trailing plume head beneath the eastern Snake River Plain. The high helium isotope ratios observed at Yellowstone and other hotspots are commonly assumed to arise from the lower mantle, but upper-mantle processes can explain the observations. The available evidence thus renders an upper-mantle origin for the Yellowstone system the preferred model; there is no evidence that the system extends deeper than ???200 km, and some evidence that it does not. A model whereby the Yellowstone system reflects feedback between upper-mantle convection and regional lithospheric tectonics is able to explain the observations better than a deep-mantle plume hypothesis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/6879160-geophysical-data-deep-seated-magmatic-activity-below-kamchatka-estimate-forces-cause-rise-magmas-volcanoes','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/6879160-geophysical-data-deep-seated-magmatic-activity-below-kamchatka-estimate-forces-cause-rise-magmas-volcanoes"><span></span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Fedotov, S.A.</p> <p></p> <p>Using geophysical data, the mechanism of deep-seated magmatic and volcanic activity was studied in the region of the island arcs and associated structures. Data on magmatic activity below the volcanic belt of East Kamchatka, obtained during geophysical investigations, mainly during detailed seismological investigations and deep seismic sounding, provide evidence for an association between the volcanoes and the processes in the Pacific Ocean focal layer of earthquakes, and for the accumulation of magmas below the volcanic belt at depths less than 60 km. Anomalous columnar bodies more than 5 to 7 km across were found linking the volcanoes with the focalmore » layer. There was also a very large concentration of convective heat flow and volatiles in the magma columns feeding the volcanoes. As to the role of different forces in the uprise of magmas into the volcanoes, hydrostatic forces probably predominate in the asthenosphere, supplemented by tectonic pressure in the lithosphere and forces associated with boiling of magmas during release of volatiles in the crust, especially in its upper layers.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/1339796-isotopic-perspective-growth-differentiation-proterozoic-orogenic-crust-from-subduction-magmatism-cratonization','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1339796-isotopic-perspective-growth-differentiation-proterozoic-orogenic-crust-from-subduction-magmatism-cratonization"><span>An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.</p> <p></p> <p>The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as ‘cratonization’, is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons frommore » several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NatGe..11..280N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NatGe..11..280N"><span>Lower-mantle plume beneath the Yellowstone hotspot revealed by core waves</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nelson, Peter L.; Grand, Stephen P.</p> <p>2018-04-01</p> <p>The Yellowstone hotspot, located in North America, is an intraplate source of magmatism the cause of which is hotly debated. Some argue that a deep mantle plume sourced at the base of the mantle supplies the heat beneath Yellowstone, whereas others claim shallower subduction or lithospheric-related processes can explain the anomalous magmatism. Here we present a shear wave tomography model for the deep mantle beneath the western United States that was made using the travel times of core waves recorded by the dense USArray seismic network. The model reveals a single narrow, cylindrically shaped slow anomaly, approximately 350 km in diameter that we interpret as a whole-mantle plume. The anomaly is tilted to the northeast and extends from the core-mantle boundary to the surficial position of the Yellowstone hotspot. The structure gradually decreases in strength from the deepest mantle towards the surface and if it is purely a thermal anomaly this implies an initial excess temperature of 650 to 850 °C. Our results strongly support a deep origin for the Yellowstone hotspot, and also provide evidence for the existence of thin thermal mantle plumes that are currently beyond the resolution of global tomography models.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011Tectp.500...20D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011Tectp.500...20D"><span>Multiscale magmatic cyclicity, duration of pluton construction, and the paradoxical relationship between tectonism and plutonism in continental arcs</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>de Saint Blanquat, Michel; Horsman, Eric; Habert, Guillaume; Morgan, Sven; Vanderhaeghe, Olivier; Law, Richard; Tikoff, Basil</p> <p>2011-03-01</p> <p>The close relationship between crustal magmatism, an expression of heat dissipation, and tectonics, an expression of stress dissipation, leads to the question of their mutual relationships. Indeed, the low viscosity of magmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization in magmas, and then possible "magmatic" initiation of structures at a wide range of scales. However, new data about 3-d pluton shape and duration of pluton construction perturb this simple geological image, and indicate some independence between magmatism and tectonics. In some cases we observe a direct genetic link and strong arguments for physical interactions between magmas and tectonics. In other cases, we observe an absence of these interactions and it is unclear how magma transfer and emplacement are related to lithospheric-plate dynamics. A simple explanation of this complexity follows directly from the pulsed, incremental assembly of plutons and its spatial and temporal characteristics. The size of each pluton is related to a magmatic pulsation at a particular time scale, and each of these coupled time/space scales is related to a specific process: in small plutons, we can observe the incremental process, the building block of plutons; in larger plutons, the incremental process is lost, and the pulsation, which consists of a cycle of injections at different timescales, must be related to the composition and thermal regime of the source region, itself driving magmatic processes (melting, segregation, and transfer) that interact with tectonic boundary conditions. The dynamics of pulsed magmatism observed in plutonic systems is then a proxy for deep lithospheric and magmatic processes. From our data and a review of published work, we find a positive corelation between volume and duration of pluton construction. The larger a pluton, the longer its construction time. Large/fast or small/slow plutons have not been identified to date. One consequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamic setting to another and also over various geologic time spans. A second consequence of this correlation is that small plutons, which are constructed in a geologically short length of time, commonly record little about tectonic conditions, and result only from the interference between magma dynamics and the local geologic setting. The fast rate of magma transfer in the crust (on the order of cm/s) relative to tectonic rates (on the order of cm/yr) explain why the incremental process of pluton construction is independent of - but not insensitive to - the tectonic setting. However, in large plutonic bodies, which correspond to longer duration magmatic events, regional deformation has time to interact with the growing pluton and can be recorded within the pluton-wall rock structure. Magma transfer operates at a very short timescale (comparable to volcanic timescales), which can be sustained over variable periods, depending on the fertility of the magma source region and its ability to feed the system. The fast operation of magmatic processes relative to crustal tectonic processes ensures that the former control the system from below.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JVGR..344..197W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JVGR..344..197W"><span>Surface deformation induced by magmatic processes at Pacaya Volcano, Guatemala revealed by InSAR</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wnuk, K.; Wauthier, C.</p> <p>2017-09-01</p> <p>Pacaya Volcano, Guatemala is a continuously active, basaltic volcano with an unstable western flank. Despite continuous activity since 1961, a lack of high temporal resolution geodetic surveying has prevented detailed modeling of Pacaya's underlying magmatic plumbing system. A new, temporally dense dataset of Interferometric Synthetic Aperture Radar (InSAR) RADARSAT-2 images, spanning December 2012 to March 2014, show magmatic deformation before and during major eruptions in January and March 2014. Inversion of InSAR surface displacements using simple analytical forward models suggest that three magma bodies are responsible for the observed deformation: (1) a 4 km deep spherical reservoir located northwest of the summit, (2) a 0.4 km deep spherical source located directly west of the summit, and (3) a shallow dike below the summit. Periods of heightened volcanic activity are instigated by magma pulses at depth, resulting in rapid inflation of the edifice. We observe an intrusion cycle at Pacaya that consists of deflation of one or both magma reservoirs followed by dike intrusion. Intrusion volumes are proportional to reservoir volume loss and do not always result in an eruption. Periods of increased activity culminate with larger dike-fed eruptions. Large eruptions are followed by inter-eruptive periods marked by a decrease in crater explosions and a lack of detected deformation. Co-eruptive flank motion appears to have initiated a new stage of volcanic rifting at Pacaya defined by repeated NW-SE oriented dike intrusions. This creates a positive feedback relationship whereby magmatic forcing from eruptive dike intrusions induce flank motion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V33A2201M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V33A2201M"><span>Plutonism at Different Crustal Levels of an Arc: Insights From the 5 to 40 km (Paleodepth) North Cascades Crustal Section, Washington</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, R. B.; Paterson, S. R.; Matzel, J. P.</p> <p>2008-12-01</p> <p>The crystalline core of the North Cascades preserves a Cretaceous crustal section that facilitates evaluation of pluton construction, emplacement, geometry, composition, and deformation at widely variable crustal levels (~5 to 40 km paleodepth) in a thick (> 55 km) continental magmatic arc. The oldest and largest pulse of plutonism was focused between 96-89 Ma when fluxes were a minimum of 3.9x10-6km3/yr/km of arc length, but the coincidence with regional crustal thickening and underthrusting of a cool outboard terrane resulted in relatively low mid- to deep-crustal temperatures for an arc. A second, smaller peak of magmatism at 78-71 Ma (minimum of 8.2x10-7km3/yr/km of arc length) occurred during regional transpression. Tonalite dominates at all levels of the section. Intrusions range from large plutons to thin (< 50 m) dispersed sheets encased in metamorphic rocks that record less focused magmatism. The percentage of igneous rocks increases systematically from shallow to middle to deep levels; from approximately 37% to 55% to 65% of the total rock volume. Unfocused magmas comprise much higher percentages (approximately 19%) of the total plutonic rock at deep- and mid-crustal depths, but only 1% at shallower levels, whereas the largest intrusions were emplaced into shallow crust. Plutons have a range of shapes, including: asymmetric wedges to funnels; subhorizontal tabular sheets; steep-sided, blade-shaped bodies with high aspect ratios in map view; and steep-sided, vertically extensive (> 8 km) bodies shaped like thick disks and/or hockey pucks. Sheeted intrusions and gently dipping tabular bodies are more common with depth. Some of these plutons fit the model that most intrusions are subhorizontal and tabular, but many do not, reflecting the complex changes in lithology and rheology in arc crust undergoing regional shortening. The steep sheeted plutons partly represent magma transfer zones that fed the large shallow plutons, which were sites of intermittent magma accumulation for up to 5.5 m.y. Downward movement of host rocks by multiple processes occurred at all crustal levels during pluton emplacement. Ductile flow and accompanying rigid rotation were the dominant processes; stoping played an important secondary role, and magma wedging and regional deformation also aided emplacement. Overall, there are some striking changes with increasing depth, but many features and processes in the arc are similar throughout the crustal section, probably reflecting the relatively small differences in peak temperatures between the mid- and deep crust. Such patterns may be representative of thick continental magmatic arcs constructed during regional shortening.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012MEEP....1....1Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012MEEP....1....1Z"><span>Tomography and Dynamics of Western-Pacific Subduction Zones</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhao, D.</p> <p>2012-01-01</p> <p>We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V/low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle. Suggestions are also made for future directions of the seismological research of subduction zones.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010PEPI..181...60N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010PEPI..181...60N"><span>Deep crustal electromagnetic structure of central India tectonic zone and its implications</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Naganjaneyulu, K.; Naidu, G. Dhanunjaya; Rao, M. Someswara; Shankar, K. Ravi; Kishore, S. R. K.; Murthy, D. N.; Veeraswamy, K.; Harinarayana, T.</p> <p>2010-07-01</p> <p>Magnetotelluric data at 45 locations along the Mahan-Khajuria Kalan profile in the central India tectonic zone are analysed. This 290 km long profile yields data in the period range 0.001-1000 s across the tectonic elements of the study region bounded by Purna fault, Gavligarh fault, Tapti fault, Narmada South fault and Narmada North fault. Multi-site, multi-frequency analysis suggests N70°E as the geo-electric strike direction. Data rotated into the N70°E strike direction are modelled using a non-linear conjugate gradient scheme with error floors of 10% for both apparent resistivity and phase components. Two-dimensional magnetotelluric model yields conductors that correlate with known faults in the study region and regional seismicity. Presence of a -30 mgal gravity high together with the observed conductive bodies (less than 20 ohm m) in the deep crust beneath the Purna graben and Tapti valley is explained by the process of magmatic underplating. The conductive bodies beneath the Mahakoshal rift belt and Vindhyans accompanied by regional gravity lows of the order -70 mgal are attributed to the presence of deep crustal fluids. Following the re-activation model proposed for the entire region, the conductors (20 ohm m) at various depth levels correspond to mafic magmatic and/or fluid intrusions controlled by deep-seated faults that seem to tap reservoirs beyond the crust-mantle boundary. The shallow depth localized faults also seem to have facilitated further upward movement of these underplated material and fluids release during this process.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016278','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016278"><span>GLIMPCE Seismic reflection evidence of deep-crustal and upper-mantle intrusions and magmatic underplating associated with the Midcontinent Rift system of North America</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behrendt, John C.; Hutchinson, D.R.; Lee, M.; Thornber, C.R.; Tréhu, A.; Cannon, W.; Green, A.</p> <p>1990-01-01</p> <p>Deep-crustal and Moho reflections, recorded on vertical incidence and wide angle ocean bottom Seismometer (OBS) data in the 1986 GLIMPCE (Great Lakes International Multidisciplinary Program on Crustal Evolution) experiment, provide evidence for magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension in the Midcontinent Rift system at 1100 Ma. The rift fill consists of 20-30 km (7-10 s) of basalt flows, secondary syn-rift volcaniclastic and post-basalt sedimentary rock. Moho reflections recorded in Lake Superior over the Midcontinent Rift system have times from 14-18 s (about 46 km to as great as 58 km) in contrast to times of about 11-13 s (about 36-42 km crustal thickness) beneath the surrounding Great Lakes. The Seismically complex deep-crust to mantle transition zone (30-60 km) in north-central Lake Superior, which is 100 km wider than the rift half-graben, reflects the complicated products of tectonic and magmatic interaction of lower-crustal and mantle components during evolution or shutdown of the aborted Midcontinent Rift. In effect, mantle was changed into crust by lowering Seismic velocity (through intrusion of lower density magmatic rocks) and increasing Moho (about 8.1 km s-1 depth. </p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3428M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3428M"><span>The volcanism of the Comores archipelago: mantle plume or lithosperic deformation?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michon, Laurent</p> <p>2015-04-01</p> <p>The development of the Comores archipelago in the Mozambique channel has been diversely interpreted since the 1970's. The two end-members causes are, on the one hand, a deep mantle plume that developed a hotspot track from the Seychelles Plateau to the Grande Comore, and, on the other hand, a lithospheric deformation that reactivated transform faults and controlled the magma path. The present work first surveys the sparse geological, geophysical and geochronological data available for this archipelago, re-evaluates the age of the magmatic activity and integrates this evolution at a regional scale. Combining realistic magma production rates, the volume of each edifice and the geochronological, it is showed that the magmatic activity started first in Mayotte about 20 Ma and second, almost simultaneously, in Anjouan, Mohéli and Grande Comore about 10 Ma ago. This magmatism, coeval with magmatic periods in areas surrounding the Mozambic channel, the southern East African rift and Madagascar, is organised in three periods since Late Oligocene. Magmatic provinces are now superimposed with seismic zones and graben structures. In consequence, the Comores archipelago is tentatively interpret as part of the East African rift rather than related to a distinct deep mantle plume.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li class="active"><span>2</span></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_2 --> <div id="page_3" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="41"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70074274','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70074274"><span>Geochemical evidence for a magmatic CO2 degassing event at Mammoth Mountain, California, September-December 1997</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>McGee, K.A.; Gerlach, T.M.; Kessler, R.; Doukas, M.P.</p> <p>2000-01-01</p> <p>Recent time series soil CO2 concentration data from monitoring stations in the vicinity of Mammoth Mountain, California, reveal strong evidence for a magmatic degassing event during the fall of 1997 lasting more than 2 months. Two sensors at Horseshoe Lake first recorded the episode on September 23, 1997, followed 10 days later by a sensor on the north flank of Mammoth Mountain. Direct degassing from shallow intruding magma seems an implausible cause of the degassing event, since the gas released at Horseshoe Lake continued to be cold and barren of other magmatic gases, except for He. We suggest that an increase in compressional strain on the area south of Mammoth Mountain driven by movement of major fault blocks in Long Valley caldera may have triggered an episode of increased degassing by squeezing additional accumulated CO2 from a shallow gas reservoir to the surface along faults and other structures where it could be detected by the CO2 monitoring network. Recharge of the gas reservoir by CO2 emanating from the deep intrusions that probably triggered deep long-period earthquakes may also have contributed to the degassing event. The nature of CO2 discharge at the soil-air interface is influenced by the porous character of High Sierra soils and by meteorological processes. Solar insolation is the primary source of energy for the Earth atmosphere and plays a significant role in most diurnal processes at the Earth surface. Data from this study suggest that external forcing due largely to local orographic winds influences the fine structure of the recorded CO2 signals.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P54A..06O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P54A..06O"><span>Evolution of the earliest mantle caused by the magmatism-mantle upwelling feedback: Implications for the Moon and the Earth</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ogawa, M.</p> <p>2017-12-01</p> <p>The two most important agents that cause mantle evolution are magmatism and mantle convection. My earlier 2D numerical models of a coupled magmatism-mantle convection system show that these two agents strongly couple each other, when the Rayleigh number Ra is sufficiently high: magmatism induced by a mantle upwelling flow boosts the upwelling flow itself. The mantle convection enhanced by this positive feedback (the magmatism-mantle upwelling, or MMU, feedback) causes vigorous magmatism and, at the same time, strongly stirs the mantle. I explored how the MMU feedback influences the evolution of the earliest mantle that contains the magma ocean, based on a numerical model where the mantle is hot and its topmost 1/3 is partially molten at the beginning of the calculation: The evolution drastically changes its style, as Ra exceeds the threshold for onset of the MMU feedback, around 107. At Ra < 107, basaltic materials generated by the initial widespread magmatism accumulate in the deep mantle to form a layer; the basaltic layer is colder than the overlying shallow mantle. At Ra > 107, however, the mantle remains compositionally more homogeneous in spite of the widespread magmatism, and the deep mantle remains hotter than the shallow mantle, because of the strong convective stirring caused by the feedback. The threshold value suggests that the mantle of a planet larger than Mars evolves in a way substantially different from that in the Moon does. Indeed, in my earlier models, magmatism makes the early mantle compositionally stratified in the Moon, but the effects of strong convective stirring overwhelms that of magmatism to keep the mantle compositionally rather homogeneous in Venus and the Earth. The MMU feedback is likely to be a key to understanding why vestiges of the magma ocean are so scarce in the Earth.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.U23B..10R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.U23B..10R"><span>The Run-up to Volcanic Eruption Unveiled by Forensic Petrology and Geophysical Observations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rasmussen, D. J.; Plank, T. A.; Roman, D. C.</p> <p>2017-12-01</p> <p>Volcanoes often warn of impending eruptions. However, one of the greatest challenges in volcano research is translating precursory geophysical signals into physical magmatic processes. Petrology offers powerful tools to study eruption run-up that benefit from direct response to magmatic forcings. Developing these tools, and tying them to geophysical observations, will help us identify eruption triggers (e.g., magmatic recharge, gas build-up, tectonic events) and understand the significance of monitored signals of unrest. We present an overview of petrologic tools used for studying eruption run-up, highlighting results from our study of the 1999 eruption of Shishaldin volcano. Olivine crystals contain chemical gradients, the consequence of diffusion following magma mixing events, which is modeled to determine mixing timescales. Modeled timescales provide strong evidence for at least three mixing events, which were triggered by magmatic recharge. Petrologic barometers indicate these events occurred at very shallow depths (within the volcanic edifice). The first mixing event occurred nine months before eruption, which was signaled by a swarm of deep-long period earthquake. Minor recharge events followed over two months, which are indicated by a second deep-long period earthquake swarm and a change in the local stress orientation measured by shear-wave splitting. Following these events, the system was relatively quiet until a large mixing event occurred 45 days prior to eruption, which was heralded by a large earthquake (M5.2). Following this event, geophysical signals of unrest intensified and became continuous. The final mixing event, beginning roughly a week before eruption, represents the final perturbation to the system before eruption. Our findings point to a relatively long run-up, which was subtle at first and intensified several weeks before eruption. This study highlights the strong link between geophysical signals of volcanic unrest and magmatic events, and helps open the door for the application of forensic petrology to unmonitored eruptions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53C3116W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53C3116W"><span>Temporal Evolution of Surface Deformation and Magma Sources at Pacaya Volcano, Guatemala Revealed by InSAR</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wnuk, K.; Wauthier, C.</p> <p>2016-12-01</p> <p>Pacaya Volcano, Guatemala is a persistently active volcano whose western flank is unstable. Despite continuous activity since 1961, a lack of high temporal resolution geodetic surveying has prevented detailed modeling of Pacaya's underlying magmatic plumbing system. A new, temporally dense dataset of Interferometric Synthetic Aperture Radar (InSAR) RADARSAT-2 images, spanning December 2012 to March 2014, shows magmatic deformation before and during major eruptions in January and March 2014. Inverse modeling of InSAR surface displacements suggest that three magma bodies are responsible for observed deformation: (1) a 3.7 km deep spherical reservoir located northwest of the summit, (2) a 0.4 km deep spherical source located directly west of the summit, and (3) a shallow dike below the summit that provides the primary transport pathway for erupted materials. Periods of heightened activity are brought on by magma pulses at depth, which result in rapid inflation of the edifice. We observe an intrusion cycle at Pacaya that consists of deflation of one or both magma reservoirs followed by dike intrusion. Intrusion volumes are proportional to reservoir volume loss, and do not always result in an eruption. Periods of increased activity culminate with larger dike fed eruptions. Large eruptions are followed by inter eruptive periods marked by a decrease in crater explosions and a lack of deformation. A full understanding of magmatic processes at Pacaya is required to assess potential impacts on other aspects of the volcano such as the unstable western flank. Co-eruptive flank motion appears to have initiated a new stage of volcanic rifting at Pacaya defined by repeated NW-SE dike intrusions. This creates a positive feedback relationship whereby magmatic forcing from eruptive dike intrusions induces flank motion</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.302..126L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.302..126L"><span>Role of deep-Earth water cycling in the growth and evolution of continental crust: Constraints from Cretaceous magmatism in southeast China</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Zhen; Wang, Xuan-Ce; Wilde, Simon A.; Liu, Liang; Li, Wu-Xian; Yang, Xuemei</p> <p>2018-03-01</p> <p>The late Mesozoic igneous province in southeast China provides an excellent opportunity to understand the processes that controlled the growth and evolution of Phanerozoic continental crust. Here we report petrological, whole-rock geochemical and isotopic data, and in situ zircon U-Pb-Lu-Hf isotopic data from granitoids and associated gabbros in the Pingtan and Tong'an complexes, southeast China. Through combining the new results with published datasets in southeast China, we show that the Early Cretaceous magmatic rocks are dominated by juvenile Nd-Hf isotopic compositions, whereas the Late Cretaceous ones display less radiogenic Nd-Hf isotope signatures. Furthermore, Nd-Hf isotope systematics are coupled with decreasing abundance of hydrous minerals and an increase of zircon saturation temperatures. Compiled zircon Hf-O data indicates that the 117-116 Ma granites have zircon δ18O values ranging from mantle values (close to 5.3‰) to as low as 3.9‰, but with dominantly positive initial epsilon Hf (εHf(t)) values. Zircon grains from 105 to 98 Ma rocks have δ18O values plotting within the mantle-like range (6.5‰ - 4.5‰), but mainly with negative εHf(t) values. Zircon grains from ca. 87 Ma rocks have positive εHf(t) values (+ 9.8 to + 0.7) and a large range of δ18O values (6.3‰ - 3.5‰). The variations in Hf-Nd-O isotopic compositions are correlated with decreasing abundance of magma water contents, presenting a case that water-fluxed melting generated large-scale granitic magmatism. Deep-Earth water cycling provides an alternative or additional mechanism to supply volatiles (e.g., H2O) for hydrous basaltic underplating, continental crustal melting, and magmatic differentiation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V43I..04H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V43I..04H"><span>Evidence of Tectonic Rotations and Magmatic Flow Within the Sheeted Dike Complex of Super-Fast Spread Crust Exposed at the Pito Deep Rift</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Horst, A. J.; Varga, R. J.; Gee, J. S.; Karson, J. A.</p> <p>2008-12-01</p> <p>Escarpments bounding the Pito Deep Rift expose cross-sections into ~3 Ma oceanic crust accreted at a super-fast spreading (>140 mm/yr) segment of the East Pacific Rise (EPR). Dikes within the sheeted dike complex persistently strike NE, parallel to local abyssal hill lineaments and magnetic anomaly stripes, and dip SE, outward and away from the EPR. During the Pito Deep 2005 Cruise, both ALVIN and JASON II used the Geocompass to fully orient a total of 69 samples [63 basaltic dikes, 6 massive gabbros] collected in situ. Paleomagnetic analyses of these oriented samples provide a quantitative constraint of kinematics of structural rotations of dikes. Magnetic remanence of dike samples indicates a dominant normal polarity with almost all directions rotated clockwise from the expected direction. The most geologically plausible model to account for these dispersions using these data coupled with the general orientation of the dikes incorporates two different structural rotations: 1) A horizontal-axis rotation that occurred near the EPR axis, related to sub-axial subsidence, and 2) A clockwise vertical-axis rotation, associated with the rotation of the Easter microplate consistent with current models. Additionally, the anisotropy of magnetic susceptibility (AMS) of dike samples indicates rock fabric and magmatic flow direction within dikes. In most samples, two of three AMS eigenvectors lie near the dike plane orientations. Generally, Kmin lies perpendicular to dike planes, while Kmax is often shallow within the dike planes, indicating dominantly subhorizontal magma flow. Steep Kmax in a few samples indicates vertical flow directions that suggest either primary flow or gravitational back-flow during waning stages of dike intrusion. These results provide the first direct evidence for primarily horizontal magma flow in sheeted dikes of super-fast spread oceanic crust. Results for Pito Deep Rift and previous results for Hess Deep Rift reveal outward dipping dikes that are interpreted as a result of subaxial spreading processes that are not evident from surface studies of spreading centers. Both areas show evidence of subaxial subsidence during accretion and lateral magmatic flow in the sheeted dike complex.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1919034M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1919034M"><span>Data integration and conceptual modelling of the Larderello geothermal area, Italy</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Manzella, Adele; Gola, Gianluca; Bertini, Giovanni; Bonini, Marco; Botteghi, Serena; Brogi, Andrea; De Franco, Roberto; Dini, Andrea; Donato, Assunta; Gianelli, Giovanni; Liotta, Domenico; Montanari, Domenico; Montegrossi, Giordano; Petracchini, Lorenzo; Ruggieri, Giovanni; Santilano, Alessandro; Scrocca, Davide; Trumpy, Eugenio</p> <p>2017-04-01</p> <p>The Larderello geothermal field, located in southern Tuscany (Italy), is one of the most important long-living hydrothermal system in the world. The inner zone of the Northern Apennines is characterized by high heat flow, well constrained by several hundred measurements deriving from both shallow boreholes and deep exploration wells. It is widely accepted that the interplay among extensional tectonics, thinning of the previously overthickened crust and lithosphere, and magmatism related to crustal melting and hybridism, controlled the NW-SE trending geothermal anomaly occurring in southern Tuscany. At Larderello, the geothermal exploitation started at the beginning of the last century from the shallow evaporite-carbonate reservoir (about 700 - 1000 m b.g.l. on average) hosting a super-heated steam with temperature ranging from 150°C to 260°C. A deep exploration program was carried out in the early 1980s. Deep boreholes found a super-heated steam-dominated system hosted in the metamorphic basement (about 2500 - 4000 m b.g.l), characterized by temperatures ranging from 300°C to 350°C. In the SW part of the Larderello area (Lago locality), a temperature exceeding 400°C was measured down to 3000 m b.s.l. The 2D and 3D seismic exploration activities provided evidences of a seismic marker, locally showing bright spot features, defining the top of a deeper reflective crustal interval, named as "K-horizon". The K-horizon has not yet been drilled, but some boreholes approached it. This seismic reflector exhibits interesting positive correlation with the maximum peak of the hypocentre distribution of low-magnitude earthquakes and, at the same time, its shape coincides with the thermal anomaly distribution, in plain view. The review and updating of the velocity and resistivity models suggest the existence of over-pressurized fluids, likely of magmatic and/or thermo-metamorphic origin, which originate the seismic velocity anomalies. The upward migration and storage of the fluids can be controlled by: i) structural conduits crossing a multi-layered crust affected by magmatic intrusions; ii) mechanisms controlling the fluid migration in different rheological settings; and iii) self-sealing processes of magmatic hypersaline fluids arising from the brittle/ductile transition. Our study is addressed to the better understanding of the structure of the deepest part of the Larderello geothermal field, by integrating structural, geological, geochemical and geophysical data. Based on downward temperature extrapolation, fluid inclusions and geothermometers analyses, the possible occurrence of super-hot fluids, in supercritical conditions, nearby the K-horizon is envisaged. The final goal is to achieve a comprehensive understanding of the geological structure and the physical conditions (pressure and temperature) of the deep reservoir including also the zone corresponding to the K-horizon, to characterize the supercritical geothermal system as well as the deep crustal processes that work in synergy leading to the regional anomaly.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V54A..03E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V54A..03E"><span>Intraplate mafic magmatism: New insights from Africa and N. America</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, C. J.; van der Lee, S.; Tepp, G.; Pierre, S.</p> <p>2017-12-01</p> <p>Plate tectonic concepts consider that continental interiors are stable, with magmatism and strain localized to plate boundaries. We re-evaluate the role of pre-existing and evolving lithospheric heterogeneities in light of perspectives afforded by surface to mantle results from active and ancient rift zones in Africa and N. America. Our process-oriented approach addresses the localization of strain and magmatism and stability of continental plate interiors. In both Africa and N. America, geophysical imaging and xenolith studies reveal that thick, buoyant, and chemically distinct Archaean cratons with deep roots may deflect mantle flow, and localize magmatism and strain over many tectonic cycles. Studies of the Colorado Plateau and East African rift reveal widespread mantle metasomatism, and high levels of magma degassing along faults and at active volcanoes. The volcanoes and magmatic systems show a strong dependence on pre-existing heterogeneities in plate structure. Syntheses of the EarthScope program ishow that lateral density contrasts and migration of volatiles that accumulated during subduction can refertilize mantle lithosphere, and enable volatile-rich magmatism beneath relatively thick continental lithosphere. For example, the passive margin of eastern N. America shows uplift and magmatism long after the onset of seafloor spreading, demonstrating the dynamic nature of coupling between the lithosphere, asthenosphere, and deeper mantle. As demonstrated by the East African Rift, the Mid-Continent Rift, and other active and ancient rift zones, the interiors of continents, including thick, cold Archaean cratons are not immune to mafic magmatism and tectonism. Recent studies in N. America and Africa reveal ca. 1000 km-wide zones of dynamic uplift, low upper mantle velocities, and broadly distributed strain. The distribution of magmatism and volatile release, in combination with geophysical signals, indicates a potentially convective origin for widespread intraplate earthquakes and magmatism, across areas broader than the surface expression of rifting. Integrated geophysical, geological and geochemical studies reveal large volumes and rates of magmatism at rift zones, provoking re-evaluation of crustal accretion and carbon and water cycles, as well as earthquake and volcanic hazards.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70193254','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70193254"><span>Deep magmatic degassing versus scrubbing: Elevated CO2 emissions and C/S in the lead-up to the 2009 eruption of Redoubt Volcano, Alaska</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Werner, Cynthia A.; Evans, William C.; Kelly, Peter; McGimsey, Robert G.; Pfeffer, Melissa; Doukas, Michael P.; Neal, Christina</p> <p>2012-01-01</p> <p>We report CO2, SO2, and H2S emission rates and C/S ratios during the five months leading up to the 2009 eruption of Redoubt Volcano, Alaska. CO2emission rates up to 9018 t/d and C/S ratios ≥30 measured in the months prior to the eruption were critical for fully informed forecasting efforts. Observations of ice-melt rates, meltwater discharge, and water chemistry suggest that surface waters represented drainage from surficial, perched reservoirs of condensed magmatic steam and glacial meltwater. These fluids scrubbed only a few hundred tonnes/day of SO2, not the >2100 t/d SO2expected from degassing of magma in the mid- to upper crust (3–6.5 km), where petrologic analysis shows the final magmatic equilibration occurred. All data are consistent with upflow of a CO2-rich magmatic gas for at least 5 months prior to eruption, and minimal scrubbing of SO2by near-surface groundwater. The high C/S ratios observed could reflect bulk degassing of mid-crustal magma followed by nearly complete loss of SO2in a deep magmatic-hydrothermal system. Alternatively, high C/S ratios could be attributed to decompressional degassing of low silica andesitic magma that intruded into the mid-crust in the 5 months prior to eruption, thereby mobilizing the pre-existing high silica andesite magma or mush in this region. The latter scenario is supported by several lines of evidence, including deep long-period earthquakes (−28 to −32 km) prior to and during the eruption, and far-field deformation following the onset of eruptive activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4869H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4869H"><span>Magma genesis, storage and eruption processes at Aluto volcano, Ethiopia: lessons from remote sensing, gas emissions and geochemistry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hutchison, William; Biggs, Juliet; Mather, Tamsin; Pyle, David; Gleeson, Matthew; Lewi, Elias; Yirgu, Gezahgen; Caliro, Stefano; Chiodini, Giovanni; Fischer, Tobias</p> <p>2016-04-01</p> <p>One of the most intriguing aspects of magmatism during the transition from continental rifting to sea-floor spreading is that large silicic magmatic systems develop within the rift zone. In the Main Ethiopian Rift (MER) these silicic volcanoes not only pose a significant hazard to local populations but they also sustain major geothermal resources. Understanding the journey magma takes from source to surface beneath these volcanoes is vital for determining its eruption style and for better evaluating the geothermal resources that these complexes host. We investigate Aluto, a restless silicic volcano in the MER, and combine a wide range of geochemical and geophysical techniques to constrain magma genesis, storage and eruption processes and shed light on magmatic-hydrothermal-tectonic interactions. Magma genesis and storage processes at Aluto were evaluated using new whole-rock geochemical data from recent eruptive products. Geochemical modelling confirms that Aluto's peralkaline rhyolites, that constitute the bulk of recent erupted products, are generated from protracted fractionation (>80 %) of basalt that is compositionally similar to rift-related basalts found on the margins of the complex. Crustal melting did not play a significant role in rhyolite genesis and melt storage depths of ~5 km can reproduce almost all aspects of their geochemistry. InSAR methods were then used to investigate magma storage and fluid movement at Aluto during an episode of ground deformation that took place between 2008 and 2010. Combining new SAR imagery from different viewing geometries we identified an accelerating uplift pulse and found that source models support depths of magmatic and/or fluid intrusion at ~5 km for the uplift and shallower depths of ~4 km for the subsidence. Finally, gas samples collected on Aluto in 2014 were used to evaluate magma and fluid transport processes. Our results show that gases are predominantly emanating from major fault zones on Aluto and that they display a clear magmatic carbon signature of -4.2 to -4.5 ‰. This provides compelling evidence that the magmatic and hydrothermal reservoirs of Aluto are physically connected. Bringing the new data sets together provides an integrated picture of the plumbing system of this restless rift volcano. Aluto's silicic magmas are generated and stored at depths of ~5 km. Magmatic intrusion and/or fluid injection in the cap of this magmatic reservoir drives edifice wide inflation while subsequent deflation is related to magmatic degassing and/or cooling of the geothermal reservoir at shallower depths. Tectonic faults that dissect the complex are a key component of this plumbing system and by connecting the deep reservoirs to the surface they not only provide important degassing pathways but will almost certainly be exploited during future eruptive events.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V13B2616S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V13B2616S"><span>Deep-crustal seismicity in volcanic regions by fluid-enhanced wallrock embrittlement</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sisson, T. W.; Power, J. A.</p> <p>2013-12-01</p> <p>Spatial association of deep long-period (DLP) seismicity with volcanoes [1,2], spectral frequencies resembling shallow events attributed to fluid motions, and temporal associations with some eruptions, prompt the interpretation that DLPs mark the locations of magma, or magma with percolating exsolved vapor, in the mid and lower crust. However, various factors are more consistent with the events taking place in the walls surrounding the hot aseismic cores of deep magmatic systems, due to expelled magmatic fluids elevating pore pressures and reducing wall rock brittle strengths, or possibly in largely solidified peripheral intrusions embrittled by interstitial residual melt. First, although exceptions are known, deep seismic events are typically displaced to one or more sides of the locus of volcanism. Compilation of >1000 mid to deep crustal DLP and volcano tectonic events from the Aleutian arc, plotted as radial distance from the respective volcanic locus vs. depth, shows a minimum of events beneath the volcanic loci, encased in a downward broadening halo of events, typically displaced about 6 km to the sides of the volcanic locus. Lateral offsets of deep events are also well established for volcanoes of the Washington Cascades [3], averaging 7.5×4.5(1σ) km, and for some centers in California [1]. Second, while mafic parental magmas can have high concentrations of H2O (CO2 concentrations are comparatively negligible), H2O is highly soluble at mid to lower crustal pressures and will not exsolve appreciably until advanced crystallization and second boiling. Deep vapor exsolution will proceed gradually, delayed well after replenishment events, due to slow cooling and crystallization in the hot deep crust. Exsolution dominantly at high crystallinities argues against bubbles moving through largely liquid replenishing magmas as a major cause of DLPs. Third, isotherms around the mid to deep crustal portions of magmatic systems will propagate outward with time1/2 due to dominantly conductive heat transfer at those depths. Over the ca. 1-5×105 yr durations of convergent margin volcanoes, characteristic isotherms propagate <10 km (k: 2.25 W/mK); temperature dependent thermal conductivity [4] would reduce these distances. Deep magmatic systems are therefore encased in relatively thin thermal sheaths, outboard of which temperatures drop sharply to near-ambient values, and rock strengths increase accordingly. Collectively, these factors support a scenario wherein magmas crystallize in the roots of volcanic systems, gradually exsolving and releasing vapor, some of which percolates into surrounding wallrocks. Beyond some critical isotherm, plastic rock strength increases sufficiently for fluid enhanced brittle failure when the walls are stressed by magma replenishments or by ordinary tectonic forces. If so, the statistical spatial distribution of DLPs indicates that the hot, active portions of the deep magmatic systems are relatively narrow, commonly <6 km in semi-minor radius. 1. Pitt et al., 2002, Seis Res Lett 73:144-152 2. Power et al., 2004, Jour Volc Geotherm Res 138:243-266 3. Nichols et al., 2011, Jour Volc Geotherm Res 200:116-128 4. Whittington et al., 2009, Nature 458, 319-321</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S54B..05L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S54B..05L"><span>Geology is the Key to Explain Igneous Activity in the Mediterranean Area</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lustrino, M.</p> <p>2014-12-01</p> <p>Igneous activity in tectonically complex areas can be interpreted in many different ways, producing completely different petrogenetic models. Processes such as oceanic and continental subduction, lithospheric delamination, changes in subduction polarity, slab break-off and mantle plumes have all been advocated as causes for changes in plate boundaries and magma production, including rate and temporal distribution, in the circum-Mediterranean area. This region thus provides a natural laboratory to investigate a range of geodynamic and magmatic processes. Although many petrologic and tectonic models have been proposed, a number of highly controversial questions still remain. No consensus has yet been reached about the capacity of plate-tectonic processes to explain the origin and style of the magmatism. Similarly, there is still not consensus on the ability of geochemical and petrological arguments to reveal the geodynamic evolution of the area. The wide range of chemical and mineralogical magma compositions produced within and around the Mediterranean, from carbonatites to strongly silica-undersaturated silico-carbonatites and melilitites to strongly silica-oversaturated rhyolites, complicate models and usually require a large number of unconstrained assumptions. Can the calcalkaline-sodic alkaline transition be related to any common petrogenetic point? Is igneous activity plate-tectonic- (top-down) or deep-mantle-controlled (bottom-up)? Do the rare carbonatites and carbonate-rich igneous rocks derive from the deep mantle or a normal, CO2-bearing upper mantle? Do ultrapotassic compositions require continental subduction? Understanding chemically complex magmas emplaced in tectonically complex areas require open minds, and avoiding dogma and assumptions. Studying the geology and shallow dynamics, not speculating about the deep lower mantle, is the key to understanding the igneous activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.431..140K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.431..140K"><span>Deep intrusions, lateral magma transport and related uplift at ocean island volcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Klügel, Andreas; Longpré, Marc-Antoine; García-Cañada, Laura; Stix, John</p> <p>2015-12-01</p> <p>Oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions. Dykes and other intrusive bodies within volcanic edifices are comparatively well studied, but intrusive processes deep beneath the volcanoes remain elusive. Although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift, this has rarely been demonstrated by real-time monitoring. Here we use geophysical and petrological data from El Hierro, Canary Islands, to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth. Seismicity and ground deformation associated with a submarine eruption in 2011-2012 reveal deep subhorizontal intrusive sheets (sills), which have caused island-scale uplift of tens of centimetres. The pre-eruptive intrusions migrated 15-20 km laterally within the lower oceanic crust, opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface. During six post-eruptive episodes between 2012 and 2014, further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally, resulting in magma accumulation exceeding that of the pre-eruptive phase. A comparison of geobarometric data for the 2011-2012 El Hierro eruption with data for other Atlantic intraplate volcanoes shows similar bimodal pressure distributions, suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport. These processes add significant material to the oceanic crust, cause uplift, and are thus fundamentally important for the growth and evolution of volcanic islands. We suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution, and is a consequence of increasing size and complexity of the mantle reservoir system, and potentially the lithospheric stresses imposed by increasing edifice load.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI51A0286G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI51A0286G"><span>Magma emplacement in 3D</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gorczyk, W.; Vogt, K.</p> <p>2017-12-01</p> <p>Magma intrusion is a major material transfer process in Earth's continental crust. Yet, the mechanical behavior of the intruding magma and its host are a matter of debate. In this study, we present a series of numerical thermo-mechanical experiments on mafic magma emplacement in 3D.In our model, we place the magmatic source region (40 km diameter) at the base of the mantle lithosphere and connect it to the crust by a 3 km wide channel, which may have evolved at early stages of magmatism during rapid ascent of hot magmatic fluids/melts. Our results demonstrate continental crustal response due to magma intrusion. We observe change in intrusion geometries between dikes, cone-sheets, sills, plutons, ponds, funnels, finger-shaped and stock-like intrusions as well as injection time. The rheology and temperature of the host-rock are the main controlling factors in the transition between these different modes of intrusion. Viscous deformation in the warm and deep crust favours host rock displacement and magma pools along the crust-mantle boundary forming deep-seated plutons or magma ponds in the lower to middle-crust. Brittle deformation in the cool and shallow crust induces cone-shaped fractures in the host rock and enables emplacement of finger- or stock-like intrusions at shallow or intermediate depth. A combination of viscous and brittle deformation forms funnel-shaped intrusions in the middle-crust. Low-density source magma results in T-shaped intrusions in cross-section with magma sheets at the surface.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.1747L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.1747L"><span>Temperature estimation for the most upper part of magmatic chamber of the Elbrus volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Likhodeev, Dmitry</p> <p>2013-04-01</p> <p>The results of theoretical and experimental studies on thermal processes in the Elbrus volcanic center and adjacent territories are presented. Distributed temperature measurements on the Elbrus volcano and near the Maloye Azau glacier by means of temperature data loggers («High Capacity Temperature Loggers iButton» and «Rejim-avtomat-termo-10-100») have been performed. The comparative time series analysis is provided. On the basis of the Geophysical Observatory in Northern Caucasus, in the laboratory located some 20 km from the Elbrus volcano in the tunnel at a depth of 4 km the array of temperature sensors has been deployed. Results of continuous observations over variations of underground temperatures, including pin-point measurements in the vicinity of sources of carbonaceous mineral waters are presented and discussed. Temperature estimations for the most upper part of the shallow magmatic chamber of the of the Elbrus volcano were obtained on the basis of experimental measurements in the 180-meter deep borehole drilled through the glacier on the western plateau of Mount Elbrus. The estimations of deep temperatures have confirmed the possibility of existence of the magmatic chamber at depths of 0-1 km below sea level. At the same time the magnitudes of local heat flux were identified with enhanced precision. Thus, the original scientific results provide significant extension to our knowledge on possible resumption of volcanic activity in the vicinity of Mount Elbrus.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T22D..08H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T22D..08H"><span>Imaging the Magmatic System of Erebus Volcano, Antarctica using the Magnetotelluric Method</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hill, G.; Wannamaker, P. E.; Stodt, J. A.; Unsworth, M. J.; Maris, V.; Bedrosian, P.; Wallin, E.; Kordy, M. A.; Ogawa, Y.; Kyle, P. R.; Uhlmann, D. F.</p> <p>2017-12-01</p> <p>Erebus volcano, on Ross Island, Antarctica, in the south west Ross Sea, offers a unique opportunity to understand the magmatic system of an active alkaline volcano, and rifting within the West Antarctica Rift System. Erebus has the world's only persistent phonolite lava lake in its summit crater, and thus provides a window into the heart of a degassing volcano's magmatic system. Phonolite magmas like those at Erebus have been responsible for devastating eruptions (e.g. Pompeii 79 AD; Tambora 1815). Petrologic models suggest that Erebus is undergoing fractional crystallisation of deep mantle-derived parental basanite magma in one or more crustal magma chambers. We are using magnetotelluric (MT) methods and instrumentation, especially developed for use in Antarctica, to image the resistivity structure (magmatic system) of Erebus and the older volcanoes forming Ross Island. In addition, we mapping the rifted crustal structure and examining the mantle source of the magma and the role that the Terror Rift system plays in the active volcanism. Data collection occurred over three field seasons from 2014-2017. Measurements were made at 129 locations on Ross Island and vicinity. A pool of 11 Phoenix Geophysics V5 systems coupled with Numeric Resources high impedance preamplifiers were used. A primary goal of this work is to constrain the distribution of melt within and beneath the volcanic edifice. In addition, we are imaging the interpreted mantle source region for Erebus magmas and investigating the role that the Terror Rift system plays in generating and focusing magmatism. Preliminary modelling suggests that we are able to resolve the crustal residence zones and the path taken by the magma as it ascends from the mantle to the surface. Our work provides new insight into the formation of phonolite magma and has implications for understanding the magmatic process occurring in rift systems globally. It further provides an opportunity to compare volcanic processes in both compressional and extensional tectonics settings.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70031280','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70031280"><span>Using SHRIMP zircon dating to unravel tectonothermal events in arc environments. The early Palaeozoic arc of NW Iberia revisited</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Abati, J.; Castineiras, P.G.; Arenas, R.; Fernandez-Suarez, J.; Barreiro, J.G.; Wooden, J.L.</p> <p>2007-01-01</p> <p>Dating of zircon cores and rims from granulites developed in a shear zone provides insights into the complex relationship between magmatism and metamorphism in the deep roots of arc environments. The granulites belong to the uppermost allochthonous terrane of the NW Iberian Massif, which forms part of a Cambro-Ordovician magmatic arc developed in the peri-Gondwanan realm. The obtained zircon ages confirm that voluminous calc-alkaline magmatism peaked around 500Ma and was shortly followed by granulite facies metamorphism accompanied by deformation at c. 480Ma, giving a time framework for crustal heating, regional metamorphism, deformation and partial melting, the main processes that control the tectonothermal evolution of arc systems. Traces of this arc can be discontinuously followed in different massifs throughout the European Variscan Belt, and we propose that the uppermost allochthonous units of the NW Iberian Massif, together with the related terranes in Europe, constitute an independent and coherent terrane that drifted away from northern Gondwana prior to the Variscan collisional orogenesis. ?? 2007 Blackwell Publishing Ltd.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA....11323A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA....11323A"><span>Magmatic history of mt. Vesuvius on the basis of new geochemical and isotopic data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arienzo, I.; Civetta, L.; D'Antonio, M.; di Renzo, V.; di Vito, M. A.; Giordano, F.; Orsi, G.</p> <p>2003-04-01</p> <p>Mt. Vesuvius is an active volcano famous for the AD 79 eruption that destroyed Pompeii, Herculaneum and Stabiae. Because of the intense urbanization around and on the volcano itself, volcanic risk is very high. Therefore, the knowledge of the structure and behaviour of the magmatic system is fundamental for both interpretation of any change in the dynamics of the volcano and eruption forecasting. We have produced new geochemical and isotopic data on rocks from a 240-m deep core drilled along the southern slope of the volcano. The investigated portion of the core includes lava flows aged between 39 and 20 ka. The obtained results, together with those already available for the younger than 20 ka activity, have allowed us to reconstruct the complex history of the magmatic system. Mt. Vesuvius magmas, originated in a mantle source variably contaminated by slab derived components, stagnate in a deep complex reservoir, located between 10 and 20 km of depth, where they differentiate and contaminate with continental crust. From the deep reservoir magmas discontinuously rise up to shallow reservoirs, where they differentiate, mingle and mix, feeding the volcanic activity. The shallow reservoirs are located at depth of about 3-5 km before Plinian eruptions, and of less than 1 km before strombolian activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V31B0513X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V31B0513X"><span>Deep Ore-controlling Role Beneath the Collision-related Deposit Zone in South Tibetan Plateau, Preliminary Results Revealed by Magnetotelluric Data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xie, C.; Jin, S.; Wei, W.; Ye, G.; Fang, Y.; Zhang, L.; Dong, H.; Yin, Y.</p> <p>2017-12-01</p> <p>The Tibetan plateau is the largest and most recent plateau orogenic belt in the world, and the south part is expected as the ongoing India-Eurasia continental collision zone. The collision-related deposit zones which are distributed in south plateau could be roughly divided into three parts: the porphyry deposit in the Gangdese magmatic belt, the chromite deposit along the Yarlung-Zangbo suture (YZS) and the prospective deposit along the gneiss domes in the Tethys Himalayan. The deep ore-controlling role of those deposit zones is still remain controversial. Previous magnetotelluric (MT) data deployed from Himalayan to Gangdese terrane were inverted using a three dimensional (3D) MT inversion algorithm ModEM. The results show that the resistivity cover layers above -10 km are distributed along the whole profiles, whereas small and sporadic conductors could be also imaged. The middle to lower crust beneath -25 km is imaged as large scale but discontinuous conductive zones which have a central resistivity less than 10 ohm·m. We suggest the middle to lower crustal conductors could be interpreted as partial melting. This hypothesis is supported by some previous geological and geochemical studies. The Metallogenesis and partial melting play an important role in promoting each other. For the metallogenesis, the high water content is one of the prominent factors, and could be released on breakdown of amphibole in eclogite and garnet amphibolite during melting. On the other hand, the increasing of the water content would probably advance partial melting. The results indicate that the deep process and magmatism beneath different deposit zones are probably varying. We studied the rheological characteristics from the perspective of subsurface electrical structures. We hope by comparative analysis, the process of `origins - migration -formation' for the system of deep `magma - rheology - deposition' would be better understood.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170001339','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170001339"><span>The Role of KREEP in the Production of Mg-Suite Magmas and Its Influence on the Extent of Mg-Suite Magmatism in the Lunar Crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Elardo, S. M.; Shearer, C. K.; McCubbin, F. M.</p> <p>2017-01-01</p> <p>The lunar magnesian-suite, or Mg-suite, is a series of ancient plutonic rocks from the lunar crust. They have received a considerable amount of attention from lunar scientists since their discovery for three primary reasons: 1) their ages and geochemistry indicate they represent pristine magmatic samples that crystallized very soon after the formation of the Moon; 2) their ages often overlap with ages of the ferroan anorthosite (FAN) crust; and 3) planetary-scale processes are needed in formation models to account for their unique geochemical features. Taken as a whole, the Mg-suite samples, as magmatic cumulate rocks, approximate a fractional crystallization sequence in the low-pressure forsterite-anorthite-silica system, and thus these samples are generally thought to be derived from layered mafic intrusions which crystallized very slowly from magmas that intruded the anorthositic crust. However, no direct linkages have been established between different Mg-suite samples based either on field relationships or geochemistry.The model for the origin of the Mg-suite, which best fits the limited available data, is one where Mg-suite magmas form from melting of a hybrid cumulate package consisting of deep mantle dunite, crustal anorthosite, and KREEP (potassium-rare earth elements-phosphorus) at the base of the crust under the Procellarum KREEP Terrane (PKT). In this model, these three LMO (Lunar Magma Ocean) cumulate components are brought into close proximity by the cumulate overturn process. Deep mantle dunitic cumulates with an Mg number of approximately 90 rise to the base of the anorthositic crust due to their buoyancy relative to colder, more dense Fe- and Ti-rich cumulates. This hybridized source rock melts to form Mg-suite magmas, saturated in Mg-rich olivine and anorthitic plagioclase, that have a substantial KREEP component.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_1");'>1</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li class="active"><span>3</span></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_3 --> <div id="page_4" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="61"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T53A2491C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T53A2491C"><span>Underthrusting of passive margin strata into deep crustal hot zones associated with Cretaceous arc magmatism in North America: links and timescales of magmatic vs. tectonic thickening</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chin, E. J.; Lee, C.; Tollstrup, D. L.; Xie, L.; Wimpenny, J.; Yin, Q.</p> <p>2011-12-01</p> <p>The North American Cordillera experienced lithospheric thickening during the Cretaceous as a result of subduction-induced magmatism and tectonic shortening. Several studies suggest correlations between increased plate convergence rates and crustal underthrusting with apparent magmatic flux and evolved isotopic excursions, yet questions still remain regarding causality between tectonic and magmatic thickening. Here, we use lower crustal garnet-bearing metaquartzite (80% SiO2) xenoliths hosted in late Miocene basalts in the central Sierra Nevada Batholith, California to constrain the P-T-t (pressure-temperature-time) history of crustal thickening. The xenoliths are equigranular in texture and are comprised of >50% quartz, ~10% metamorphic garnet, <40% plagioclase, and trace rutile, kyanite, and biotite. High quartz mode, abundant well-rounded detrital zircons, and oriented graphite laths demonstrating sedimentary or metamorphic layering point to a supracrustal sedimentary protolith. However, final equilibration temperatures using titanium-in-quartz thermometry are 700 - 800 °C, and final equilibration pressures using the GASP barometer yield 0.9 - 1.3 GPa, indicating the metaquartzites equilibrated within a hot lower crust (18 - 45 km). Low whole-rock REE totals, lack of whole-rock HREE enrichment relative to LREE and MREE, and absence of positive Eu anomalies suggest that significant melting in the garnet or plagioclase fields did not occur. The whole-rock trace element geochemistry is also consistent with an initially garnet-free protolith. Simultaneous LA-ICP-MS measurements of U-Pb and Hf isotopes in detrital zircons show that all zircons have discordant U-Pb with variable upper intercept ages (1.7, 2.7, 3.3 Ga; consistent with Hf model ages), but common lower intercept ages (100 Ma). The above indicate that protoliths of the metaquartzites were North American Proterozoic to Paleozoic passive margin sediments which were simultaneously emplaced into the lower crust at ~100 Ma, during the peak of Cretaceous arc magmatism. We envision underthrusting of N. American lithosphere beneath the active Sierran arc as the mechanism for transporting these sediments to high P, T conditions, but underthrusting cold continental lithosphere alone cannot explain the xenoliths' high final temperatures. An additional heat source, derived from deep crustal magmatic "hot zones", seems required. We are currently exploring diffusion modeling in garnet porphyroblasts as a way to estimate rates of thickening. Because the protoliths were initially garnet-free, growth of metamorphic garnet can potentially record the length of time it took the metaquartzites to achieve their high P, T conditions. We will also use Ti zonation in detrital zircons as an added constraint on timescales involved in thickening. So far, our results indicate firsthand that tectonic underthrusting of continental supracrustal rocks extends all the way into deep magmatic zones beneath arcs, implying that magmatic differentiation alone is not the only mechanism by which continental crust achieves its felsic composition.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.490..170L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.490..170L"><span>An Andean-type retro-arc foreland system beneath northwest South China revealed by SINOPROBE profiling</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Jianhua; Dong, Shuwen; Cawood, Peter A.; Zhao, Guochun; Johnston, Stephen T.; Zhang, Yueqiao; Xin, Yujia</p> <p>2018-05-01</p> <p>In the Mesozoic, South China was situated along the convergent margin between the Asian and Pacific plates, providing an excellent laboratory to understand the interactions between deformation, sedimentation and magmatism in a retroarc environment. The crustal architecture of northwest South China is displayed along the ∼600-km-long SINOPROBE deep seismic reflection profiles and reveals from east to west: (1) highly folded and truncated reflectors in the upper crust of the Yangtze Fold Zone, which correspond to thin- and thick-skinned thrust systems, and document large-scale intraplate structural imbrication and shortening; (2) a crustal-scale flat-ramp-flat structure, termed the Main Yangtze decollement, which forms a weak, viscous layer to accommodate strain decoupling and material transport in the thin- and thick-skinned systems; and (3) nearly flat-lying reflectors in the Sichuan Basin, which support interpretation of the basin as a weakly deformed depocentre. The Yangtze Fold Zone and the Sichuan Basin represent a retro-arc foreland basin system that is >800 km away from the continental-margin magmatic arc. We suggest that tectonic processes across the arc and retro-arc systems, including arc magma flare-up, basin sedimentation, retroarc thrust propagation, lithosphere underthrusting, root foundering, and extension-related magmatism were interrelated and governed mass transfer. Age data and geological relations link the tectonic processes to evolving geodynamics of the subducting Paleo-Pacific plate.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997JGR...102.2645G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997JGR...102.2645G"><span>Vertical movements following intracontinental magmatism: An example from southern Israel</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gvirtzman, Zohar; Garfunkel, Zvi</p> <p>1997-02-01</p> <p>We present a quantitative thermal model for vertical movements following continental magmatism, focusing on how the associated elevation changes depend on the depth of intrusion. When an intrusion is emplaced within the lithosphere, its buoyancy causes a quick initial movement which is followed by long-term movements caused by thermal relaxation. Intrusions emplaced within the gabbro stability field produce initial uplifting which is about 12% of their thickness. Subsequent thermal relaxation reduces the uplift to a residual value of 9-10% of the intrusion thickness. In contrast, intrusions emplaced within the eclogite stability field produce a small subsidence from the very beginning which is slowly increased by thermal relaxation and may reach a residual value of some 4% of the intrusion thickness. In both cases the rates of the thermal subsidence depend on the depth of intrusion: it is relatively fast when the intrusions are shallow but considerably slower when the intrusions are deep. The model enables us to infer volumes and depths of intrusions from amplitudes and rates of vertical movements. As an example we apply the model to analyze the geodynamic evolution of the central Negev, southern Israel, during the Early Cretaceous. Two distinct magmatic pulses that were recognized there represent the two basic situations envisaged by the model, i.e., shallow magma emplacement in the gabbro field associated with uplifting, and deep intrusion in the eclogite field associated with subsidence. In a wider context we think that this model may help in understanding intracratonic basins in nonextensional settings. In particular, deep and thick eclogite intrusions can explain subsidence of regions which were not extended nor uplifted and in regions where crustal magmatism and heating were not observed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70176492','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70176492"><span>Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo</p> <p>2016-01-01</p> <p>Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4997606','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4997606"><span>Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Di Vito, Mauro A.; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P.; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo</p> <p>2016-01-01</p> <p>Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common. PMID:27558276</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27558276','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27558276"><span>Magma transfer at Campi Flegrei caldera (Italy) before the 1538 AD eruption.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Di Vito, Mauro A; Acocella, Valerio; Aiello, Giuseppe; Barra, Diana; Battaglia, Maurizio; Carandente, Antonio; Del Gaudio, Carlo; de Vita, Sandro; Ricciardi, Giovanni P; Ricco, Ciro; Scandone, Roberto; Terrasi, Filippo</p> <p>2016-08-25</p> <p>Calderas are collapse structures related to the emptying of magmatic reservoirs, often associated with large eruptions from long-lived magmatic systems. Understanding how magma is transferred from a magma reservoir to the surface before eruptions is a major challenge. Here we exploit the historical, archaeological and geological record of Campi Flegrei caldera to estimate the surface deformation preceding the Monte Nuovo eruption and investigate the shallow magma transfer. Our data suggest a progressive magma accumulation from ~1251 to 1536 in a 4.6 ± 0.9 km deep source below the caldera centre, and its transfer, between 1536 and 1538, to a 3.8 ± 0.6 km deep magmatic source ~4 km NW of the caldera centre, below Monte Nuovo; this peripheral source fed the eruption through a shallower source, 0.4 ± 0.3 km deep. This is the first reconstruction of pre-eruptive magma transfer at Campi Flegrei and corroborates the existence of a stationary oblate source, below the caldera centre, that has been feeding lateral eruptions for the last ~5 ka. Our results suggest: 1) repeated emplacement of magma through intrusions below the caldera centre; 2) occasional lateral transfer of magma feeding non-central eruptions within the caldera. Comparison with historical unrest at calderas worldwide suggests that this behavior is common.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V43J..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V43J..01M"><span>Crystals and Crystals: On the Mythology of Magmatic Processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marsh, B.</p> <p>2008-12-01</p> <p>The intimate records of the deep functioning of magmatic systems reside in the temporal and spatial records of magma flux, composition and crystal load. The records for a single system are piecemeal: Plutons show good spatial records, but poor temporal records. Volcanoes give through lava sequences good temporal records, but no spatial context. Because of this dichotomy, two, almost mutually exclusive, branches of magmatology have developed, whereas in Nature there is only a single process. The processes envisioned in these schools necessary to deliver the end rock record are distinct. It is our tools and historic perspectives that have steered the science, not the subject itself. Due to this approach an almost mythical conception of how magmas function has become commonplace. The circumvention of this dilemma rests in carefully evaluating the records on hand in the light of a broad understanding of the fundamental mechanics of how magma lives and dies. It is these basic principles that promise to unify plutonic and volcanic evidence to reveal the full nature of magmatism on all scales. The two most basic features of all magmatic processes are the universal presence of solidification fronts and the presence or absence of a crystal cargo. Almost without exception (e.g., shallow pressure quenching) all first generation crystals grow in marginal solidification fronts (SFs) bordering all magmas. The package of isotherms bounded by the liquidus and solidus define SFs, which propagate in response to the rate of cooling. All physical and chemical processes occurring within SFs compete with the advancement or retreat of solidification. SFs are governed by crystallinity regimes: Suspension Zone (<25 % xtals), Capture Front (~25 %), Mush Zone (25-55%), Rigidity Front (~55%; Critical Crystallinity), and Rigid Crust Zone (>55% xtals). Magmas are laced with nuclei that multiply and grow when overtaken. Crystal growth rates are bounded; tiny crystals reside at the front of SFs and big crystals at the rear. It is unlikely that crystals can ever escape SFs once beyond the Capture Front, and crystals that do fall (singly or in plumes) from the leading edge of SFs may suffer resorbtion upon transit through deeper, hotter magma. Above all, differentiation is severely limited as there is no crystallization in the central, hottest part of the body, and the crystals that are available for separation are tiny and have little effect on melt composition. Recall, ~50% loss of olivine enhances silica by 5%, but this places this magma at Critical Crystallinity. Phenocrysts come from disrupted SFs and are essential to read as such; they may come from a wide range of P's and T's. Ragged old crystals rolling about for untold numbers of flushing times record specious process times; telling more about transport and crystal-chemical noise in the system than the life of typical, first generation crystallization processes. Yet, noise is a system characteristic as is exemplified by the disharmonious isotope heritage of neighbor phenocrysts. Differentiation mainly comes from the sudden loss of a dynamically entrained load of crystals of diverse heritage equilibrating with the 'carrier' magma. Big crystals carrying fluid inclusions, for example, come from deep within SFs where residual melt is low and enriched and not from the central, early, primitive magma. All systems show these characteristics. They are exceedingly important to recognize and to put in the context of the power, longevity, and geometry of the system. Not recognizing them for what they are and what they are not recording only builds mythological magmatic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5654511','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5654511"><span>Magmatic pulse driven by sea-level changes associated with the Messinian salinity crisis</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Sternai, Pietro; Caricchi, Luca; Garcia-Castellanos, Daniel; Jolivet, Laurent; Sheldrake, Tom E.; Castelltort, Sébastien</p> <p>2017-01-01</p> <p>Between 5 and 6 million years ago, during the so-called Messinian salinity crisis, the Mediterranean basin became a giant salt repository. The possibility of abrupt and kilometre-scale sea-level changes during this extreme event is debated. Messinian evaporites could signify either deep- or shallow-marine deposits, and ubiquitous erosional surfaces could indicate either subaerial or submarine features. Significant and fast reductions in sea level unload the lithosphere, which can increase the production and eruption of magma. Here we calculate variations in surface load associated with the Messinian salinity crisis and compile the available time constraints for pan-Mediterranean magmatism. We show that scenarios involving a kilometre-scale drawdown of sea level imply a phase of net overall lithospheric unloading at a time that appears synchronous with a magmatic pulse from the pan-Mediterranean igneous provinces. We verify the viability of a mechanistic link between unloading and magmatism using numerical modelling of decompression partial mantle melting and dike formation in response to surface load variations. We conclude that the Mediterranean magmatic record provides an independent validation of the controversial kilometre-scale evaporative drawdown and sheds new light on the sensitivity of magmatic systems to the surface forcing. PMID:29081834</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T41E..02P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T41E..02P"><span>Lithospheric drip magmatism and magma-assisted rifting: a case study in the Western Rift, East Africa</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pitcavage, E.; Furman, T.; Nelson, W. R.</p> <p>2017-12-01</p> <p>The East African Rift System (EARS) is earth's largest continental divergent boundary and an unparalleled natural laboratory for understanding magmatism related to successful continental rifting. Classic views of continental rifting suggest that faulting and extension are facilitated by ascending magmas that weaken the lithosphere thermally and structurally within basin-bounding accommodation zones. In the EARS Western Rift (WR), many volcanic fields are not aligned along rift-bounding faults, and magma compositions lack evidence for asthenospheric inputs expected along lithosphere-penetrating fault systems. We note that compositional input from the Cenozoic Afar mantle plume is not recognized convincingly in WR mafic alkaline lavas1. Rather, magma compositions demonstrate significant input from anciently metasomatized sub-continental lithospheric mantle (SCLM). Destabilization and foundering of metasomatized SCLM has an increasingly recognized role in continental magmatism worldwide, producing volatile-rich, alkaline volcanics when drips of foundered SCLM devolatilize and melt on descent. This magmatism can lead to faulting: the lithospheric thinning that results from this process may play a role in physical aspects of rifting, contrasting with faulting facilitated by asthenospheric melts. Geochemical and geophysical evidence indicates that drip magmatism has occurred in several EARS provinces, including Turkana, Chyulu Hills, and in Afar2 where it is geographically coincident with successful rifting. We present bulk geochemical data that suggest drip melting of metasomatized SCLM is occurring in several WR volcanic fields. We focus on Bufumbira (Uganda), where mafic lavas are derived from garnet+phlogopite+amphibole+zircon-bearing pyroxenite, indicating a deep metasomatized SCLM source. Isotopic and trace element data suggest that extent of melting increased with depth of melting, a signature of lithospheric drip. We propose that drip magmatism is an important driver of volcanism in the early history of these igneous provinces and may be fundamentally related to the onset of successful rifting. 1. Graham, D. et al. Goldschmidt Conference Abstracts (2011). 2. Furman, T., et al. Geochim. Cosmochim. Acta 185, 418-434 (2016).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.6798M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.6798M"><span>Geodynamic Implications of Himu Mantle In The Source of Tertiary Volcanics From The Veneto Region (south Eastern Alps)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Macera, P.; Gasperini, D.; Blichert-Toft; Bosch, D.; del Moro, A.; Dini, G.; Martin, S.; Piromallo, C.</p> <p></p> <p>DuringTertiary times extensive mafic volcanism took place in the South-Eastern Alps, along a half-graben structure bounded by the Schio-Vicenza main fault. This mag- matism gave rise to four main volcanic centers: Lessini, Berici, Euganei, and Maros- tica. The dominating rock types are alkali basalts, basanites and transitional basalts, with hawaiites, trachybasalts, tephrites, basaltic andesites, and differentiated rocks be- ing less common. Major and trace element and Sr-Nd-Hf-Pb isotopic data for the most primitive lavas from each volcanic center show the typical features of HIMU hotspot volcanism, variably diluted by a depleted asthenospheric mantle component (87Sr/86Sr48Ma = 0.70314-0.70321; eNd48Ma = +6.4 to +6.5; eHf48Ma = +6.4 to +8.1, 206Pb/204Pb48Ma = 18.786-19.574). Since the HIMU component is consid- ered to be of deep mantle origin, its presence in a tectonic environment dominated by subduction (the Alpine subduction of the European plate below the Adria plate) has significant geodynamic implications. Slab detachment and ensuing rise of deep man- tle material into the lithospheric gap is proposed to be a viable mechanism of hotspot magmatism in a subduction zone setting. Interaction between deep-seated plume ma- terial and shallow depleted asthenospheric mantle may account for the geochemical features of the Veneto volcanics, as well as those of the so-called enriched astheno- spheric reservoir (EAR) component. Ascending counterflow of deep mantle material through the lithospheric gap to the top of the subducting slab further may induce heat- ing of the overriding plate and trigger it to partially melt. Upwelling of the resulting mafic magmas and their subsequent underplating at the mantle-lower crust bound- ary would favor partial melting of the lower crust, thereby giving rise to the bimodal mafic-felsic magmatism that characterizes the whole Periadriatic province. According to this model, the HIMU-like magmatism of the Alpine foreland is therefore closely related to the calc-alkaline magmatism of the Periadriatic Lineament, and caused by the same mechanism of Tertiary Alpine convergence tectonics.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFMED41C1179W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFMED41C1179W"><span>Improving Student Understanding of Magmatic Differentiation Using an M&M Magma Chamber</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wirth, K. R.</p> <p>2003-12-01</p> <p>Many students, especially those in introductory geology courses, have difficulty developing a deep understanding of the processes of magmatic differentiation. In particular, students often struggle to understand Bowen's reaction series and fractional crystallization. The process of fractional crystallization by gravity settling can be illustrated using a model magma chamber consisting of M&M's. In this model, each major cation (e.g., Si, Ti, Al, Fe, Mg, Ca, Na, K) is represented by a different color M&M; other kinds of differently colored or shaped pieces could also be used. Appropriate numbers of each color M&M are combined to approximate the cation proportions of a basaltic magma. Students then fractionate the magma by moving M&M's to the bottom of the magma chamber forming a series of cumulus layers; the M&M's are removed in the stoichiometric proportions of cations in the crystallizing minerals (e.g., olivine, pyroxene, feldspars, quartz, magnetite, ilmenite). Students observe the changing cation composition (proportions of colors of M&M's) in the cumulus layers and in the magma chamber and graph the results using spreadsheet software. More advanced students (e.g., petrology course) can classify the cumulates and resulting liquid after each crystallization step, and they can compare the model system with natural magmatic systems (e.g., absence of important fractionating phases, volatiles). Students who have completed this exercise generally indicate a positive experience and demonstrate increased understanding of Bowen's reaction series and fractionation processes. They also exhibit greater familiarity with mineral stoichiometry, classification, solid-solution in minerals, element behavior (e.g., incompatibility), and chemical variation diagrams. Other models (e.g., paths of equilibrium and fractional crystallization on phase diagrams) can also be used to illustrate differentiation processes in upper level courses (e.g., mineralogy and petrology).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T41E2992R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T41E2992R"><span>Stratal stacking patterns and tectono-sedimentary evolution of hyperextended magma-poor rifted margins</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ribes, C.; Gillard, M.; Epin, M. E.; Ghienne, J. F.; Manatschal, G.; Karner, G. D.; Johnson, C. A.</p> <p>2016-12-01</p> <p>Research on the formation and evolution of deep-water rifted margins has undergone a major paradigm shift in recent years. An increasing number of studies of present-day and fossil rifted margins allow us to identify and characterize the structural architecture of the most distal parts of rifted margins, the so-called hyperextended, magma-poor rifted margins. However, at present, little is known about the depositional environments, sedimentary facies, stacking patterns, subsidence and thermal history within these domains. In this context, characterizing the stratal stacking patterns and understanding their spatial and temporal evolution is a new challenge. The major difficulty comes from the fact that the observed stratigraphic geometries and facies relationships are a result of the complex interplay between sediment supply and available accommodation, which is controlled by not only the regional generation of accommodation, but also by local tectono-magmatic processes. These parameters are poorly constrained or even sufficiently known in these tectonic settings. Indeed, the complex structural evolution of hyperextended magma-poor rifted margins, including the development of poly-phase in-sequence and out of sequence extensional detachment faults and associated mantle exhumation and magmatic activity, can generate complex accommodation patterns over a highly structured top basement. The presentation summarizes early results concerning the controlling parameters on ultra-deep water stratigraphic stacking patterns and to provide a conceptual framework. This observation-driven approach combines fieldwork from fossil Alpine Tethys margins exposed in the Alps and the analysis of seismic reflection data from present-day deep water rifted margins such as the Australian-Antarctic, East India and Iberia-Newfoundland margins.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035988','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035988"><span>Magma at depth: A retrospective analysis of the 1975 unrest at Mount Baker, Washington, USA</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Crider, Juliet G.; Frank, David; Malone, Stephen D.; Poland, Michael P.; Werner, Cynthia; Caplan-Auerbach, Jacqueline</p> <p>2011-01-01</p> <p>Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements suggest slight deflation of the edifice between 1981-83 and 2006-07. The volcano remains seismically quiet with regard to impulsive volcano-tectonic events, but experiences shallow (10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential to this assessment of magmatic activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611234C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611234C"><span>OCT structure, COB location and magmatic type of the S Angolan & SE Brazilian margins from integrated quantitative analysis of deep seismic reflection and gravity anomaly data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cowie, Leanne; Kusznir, Nick; Horn, Brian</p> <p>2014-05-01</p> <p>Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been applied to the S Angolan and SE Brazilian margins to determine OCT structure, COB location and magmatic type. Knowledge of these margin parameters are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the S Angolan and SE Brazilian rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Gravity anomaly inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated for profiles Lusigal 12 and ISE-01 on the Iberian margin. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola deep seismic reflection lines. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along the seismic profiles. Gravity inversion, RDA and subsidence analysis along the ION-GXT BS1-575 profile, which crosses the Sao Paulo Plateau and Florianopolis Ridge of the SE Brazilian margin, predict the COB to be located SE of the Florianopolis Ridge. Integrated quantitative analysis shows no evidence for exhumed mantle on this margin profile. The joint inversion technique predicts oceanic crustal thicknesses of between 7 and 8 km thickness with normal oceanic basement seismic velocities and densities. Beneath the Sao Paulo Plateau and Florianopolis Ridge, joint inversion predicts crustal basement thicknesses between 10-15km with high values of basement density and seismic velocities under the Sao Paulo Plateau which are interpreted as indicating a significant magmatic component within the crustal basement. The Sao Paulo Plateau and Florianopolis Ridge are separated by a thin region of crustal basement beneath the salt interpreted as a regional transtensional structure. Sediment corrected RDAs and gravity derived "synthetic" RDAs are of a similar magnitude on oceanic crust, implying negligible mantle dynamic topography. Gravity inversion, RDA and subsidence analysis along the S Angolan ION-GXT CS1-2400 profile suggests that exhumed mantle, corresponding to a magma poor margin, is absent..The thickness of earliest oceanic crust, derived from gravity and deep seismic reflection data, is approximately 7km consistent with the global average oceanic crustal thicknesses. The joint inversion predicts a small difference between oceanic and continental crustal basement density and seismic velocity, with the change in basement density and velocity corresponding to the COB independently determined from RDA and subsidence analysis. The difference between the sediment corrected RDA and that predicted from gravity inversion crustal thickness variation implies that this margin is experiencing approximately 500m of anomalous uplift attributed to mantle dynamic uplift.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IJEaS.107...71Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IJEaS.107...71Z"><span>Geothermal constraints on Emeishan mantle plume magmatism: paleotemperature reconstruction of the Sichuan Basin, SW China</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhu, Chuanqing; Hu, Shengbiao; Qiu, Nansheng; Jiang, Qiang; Rao, Song; Liu, Shuai</p> <p>2018-01-01</p> <p>The Middle-Late Permian Emeishan Large Igneous Province (ELIP) in southwestern China represents a classic example of a mantle plume origin. To constrain the thermal regime of the ELIP and contemporaneous magmatic activity in the northeastern Sichuan Basin, maximum paleotemperature profiles of deep boreholes were reconstructed using vitrinite reflectance (Ro) and apatite fission track data. Two heating patterns were identified: (1) heating of the overlying lithosphere by magma storage regions and/or magmatic activity related to the mantle plume, which resulted in a relatively strong geothermal field and (2) direct heating of country rock by stock or basalt. Borehole Ro data and reconstructed maximum paleotemperature profiles near the ELIP exhibit abrupt tectonothermal unconformities between the Middle and Late Permian. The profiles in the lower subsections (i.e., pre-Middle Permian) exhibited significantly higher gradients than those in the upper subsections. Distal to the basalt province, high paleo-geotemperatures (hereafter, paleotemperatures) were inferred, despite deformation of the paleogeothermal curve due to deep faults and igneous rocks within the boreholes. In contrast, Ro profiles from boreholes without igneous rocks (i.e., Late Permian) contained no break at the unconformity. Paleotemperature gradients of the upper and the lower subsections and erosion at the Middle/Late Permian unconformity revealed variations in the thermal regime. The inferred spatial distribution of the paleothermal regime and the erosion magnitudes record the magmatic and tectonic-thermal response to the Emeishan mantle plume.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.430..140H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.430..140H"><span>Seismic imaging of deep crustal melt sills beneath Costa Rica suggests a method for the formation of the Archean continental crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harmon, Nicholas; Rychert, Catherine A.</p> <p>2015-11-01</p> <p>Continental crust formed billions of years ago but cannot be explained by a simple evolution of primary mantle magmas. A multi-step process is required that likely includes re-melting of wet metamorphosed basalt at high pressures. Such a process could occur at depth in oceanic crust that has been thickened by a large magmatic event. In Central America, variations in geologically inferred, pre-existing oceanic crustal thickness beneath the arc provides an excellent opportunity to study its effect on magma storage, re-melting of meta-basalts, and the potential for creating continental crust. We use surface waves derived from ambient noise tomography to image 6% radially anisotropic structures in the thickened oceanic plateau crust of Costa Rica that likely represent deep crustal melt sills. In Nicaragua, where the arc is forming on thinner oceanic crust, we do not image these deep crustal melt sills. The presence of these deep sills correlates with more felsic arc outputs from the Costa Rican Arc suggesting pre-existing thickened crust accelerates processing of primary basalts to continental compositions. In the Archean, reprocessing thickened oceanic crust by subsequent hydrated hotspot volcanism or subduction zone volcanism may have similarly enhanced formation of early continental crust. This mechanism may have been particularly important if subduction did not initiate until 3 Ga.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T21A2520C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T21A2520C"><span>OCT structure, COB location and magmatic type of the SE Brazilian & S Angolan margins from integrated quantitative analysis of deep seismic reflection and gravity anomaly data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cowie, L.; Kusznir, N. J.; Horn, B.</p> <p>2013-12-01</p> <p>Knowledge of ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and magmatic type are of critical importance for understanding rifted continental margin formation processes and in evaluating petroleum systems in deep-water frontier oil and gas exploration. The OCT structure, COB location and magmatic type of the SE Brazilian and S Angolan rifted continental margins are much debated; exhumed and serpentinised mantle have been reported at these margins. Integrated quantitative analysis using deep seismic reflection data and gravity inversion have been used to determine OCT structure, COB location and magmatic type for the SE Brazilian and S Angolan margins. Gravity inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning. Residual Depth Anomaly (RDA) analysis has been used to investigate OCT bathymetric anomalies with respect to expected oceanic bathymetries and subsidence analysis has been used to determine the distribution of continental lithosphere thinning. These techniques have been validated on the Iberian margin for profiles IAM9 and ISE-01. In addition a joint inversion technique using deep seismic reflection and gravity anomaly data has been applied to the ION-GXT BS1-575 SE Brazil and ION-GXT CS1-2400 S Angola. The joint inversion method solves for coincident seismic and gravity Moho in the time domain and calculates the lateral variations in crustal basement densities and velocities along profile. Gravity inversion, RDA and subsidence analysis along the S Angolan ION-GXT CS1-2400 profile has been used to determine OCT structure and COB location. Analysis suggests that exhumed mantle, corresponding to a magma poor margin, is absent beneath the allochthonous salt. The thickness of earliest oceanic crust, derived from gravity and deep seismic reflection data is approximately 7km. The joint inversion predicts crustal basement densities and seismic velocities which are slightly less than expected for 'normal' oceanic crust. The difference between the sediment corrected RDA and that predicted from gravity inversion crustal thickness variation implies that this margin is experiencing ~300m of anomalous uplift attributed to mantle dynamic uplift. Gravity inversion, RDA and subsidence analysis have also been used to determine OCT structure and COB location along the ION-GXT BS1-575 profile, crossing the Sao Paulo Plateau and Florianopolis Ridge of the SE Brazilian margin. Gravity inversion, RDA and subsidence analysis predict the COB to be located SE of the Florianopolis Ridge. Analysis shows no evidence for exhumed mantle on this margin profile. The joint inversion technique predicts normal oceanic basement seismic velocities and densities and beneath the Sao Paulo Plateau and Florianopolis Ridge predicts crustal basement thicknesses between 10-15km. The Sao Paulo Plateau and Florianopolis Ridge are separated by a thin region of crustal basement beneath the salt interpreted as a regional transtensional structure. Sediment corrected RDAs and gravity derived 'synthetic' RDAs are of a similar magnitude on oceanic crust, implying negligible mantle dynamic topography.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035612','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035612"><span>Middle Jurassic Topawa group, Baboquivari Mountains, south-central Arizona: Volcanic and sedimentary record of deep basins within the Jurassic magmatic arc</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Haxel, G.B.; Wright, J.E.; Riggs, N.R.; Tosdal, R.M.; May, D.J.</p> <p>2005-01-01</p> <p>Among supracrustal sequences of the Jurassic magmatic arc of the southwestern Cordillera, the Middle Jurassic Topawa Group, Baboquivari Mountains, south-central Arizona, is remarkable for its lithologic diversity and substantial stratigraphic thickness, ???8 km. The Topawa Group comprises four units (in order of decreasing age): (1) Ali Molina Formation-largely pyroclastic rhyolite with interlayered eolian and fluvial arenite, and overlying conglomerate and sandstone; (2) Pitoikam Formation-conglomerate, sedimentary breccia, and sandstone overlain by interbedded silt- stone and sandstone; (3) Mulberry Wash Formation-rhyolite lava flows, flow breccias, and mass-flow breccias, with intercalated intraformational conglomerate, sedimentary breccia, and sandstone, plus sparse within-plate alkali basalt and comendite in the upper part; and (4) Tinaja Spring Porphyry-intrusive rhyolite. The Mulberry Wash alkali basalt and comendite are genetically unrelated to the dominant calcalkaline rhyolite. U-Pb isotopic analyses of zircon from volcanic and intrusive rocks indicate the Topawa Group, despite its considerable thickness, represents only several million years of Middle Jurassic time, between approximately 170 and 165 Ma. Sedimentary rocks of the Topawa Group record mixing of detritus from a minimum of three sources: a dominant local source of porphyritic silicic volcanic and subvolcanic rocks, identical or similar to those of the Topawa Group itself; Meso- proterozoic or Cambrian conglomerates in central or southeast Arizona, which contributed well-rounded, highly durable, polycyclic quartzite pebbles; and eolian sand fields, related to Middle Jurassic ergs that lay to the north of the magmatic arc and are now preserved on the Colorado Plateau. As the Topawa Group evidently represents only a relatively short interval of time, it does not record long-term evolution of the Jurassic magmatic arc, but rather represents a Middle Jurassic "stratigraphic snapshot" of the arc. This particular view of the arc has been preserved primarily because the Topawa Group accumulated in deep intra-arc basins. These nonmarine basins were fundamentally tectonic and extensional, rather than volcano-tectonic, in origin. Evidence from the Topawa Group supports two previous paleogeographic inferences: the Middle Jurassic magmatic arc in southern Arizona was relatively low standing, and externally derived sediment was introduced into the arc from the continent (northeast) side, without appreciable travel along the arc. We speculate that because the Topawa Group intra-arc basins were deep and rapidly subsiding, they became the locus of a major (though probably intermittent) fluvial system, which flowed into the low-standing magmatic arc from its northeast flank. ?? 2005 Geological Society of America.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29062023','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29062023"><span>The effect of giant lateral collapses on magma pathways and the location of volcanism.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maccaferri, Francesco; Richter, Nicole; Walter, Thomas R</p> <p>2017-10-23</p> <p>Flank instability and lateral collapse are recurrent processes during the structural evolution of volcanic edifices, and they affect and are affected by magmatic activity. It is known that dyke intrusions have the potential to destabilise the flanks of a volcano, and that lateral collapses may change the style of volcanism and the arrangement of shallow dykes. However, the effect of a large lateral collapse on the location of a new eruptive centre remains unclear. Here, we use a numerical approach to simulate the pathways of magmatic intrusions underneath the volcanic edifice, after the stress redistribution resulting from a large lateral collapse. Our simulations are quantitatively validated against the observations at Fogo volcano, Cabo Verde. The results reveal that a lateral collapse can trigger a significant deflection of deep magma pathways in the crust, favouring the formation of a new eruptive centre within the collapse embayment. Our results have implications for the long-term evolution of intraplate volcanic ocean islands.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70027272','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70027272"><span>Massive collapse of volcano edifices triggered by hydrothermal pressurization</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Reid, M.E.</p> <p>2004-01-01</p> <p>Catastrophic collapse of steep volcano flanks threatens lives at stratovolcanoes around the world. Although destabilizing shallow intrusion of magma into the edifice accompanies some collapses (e.g., Mount St. Helens), others have occurred without eruption of juvenile magmatic materials (e.g., Bandai). These latter collapses can be difficult to anticipate. Historic collapses without magmatic eruption are associated with shallow hydrothermal groundwater systems at the time of collapse. Through the use of numerical models of heat and groundwater flow, I evaluate the efficacy of hydrothermally driven collapse. Heating from remote magma intrusion at depth can generate temporarily elevated pore-fluid pressures that propagate upward into an edifice. Effective-stress deformation modeling shows that these pressures are capable of destabilizing the core of an edifice, resulting in massive, deep-seated collapse. Far-field pressurization only occurs with specific rock hydraulic properties; however, data from numerous hydrothermal systems illustrate that this process can transpire in realistic settings. ?? 2004 Geological Society of America.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_2");'>2</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li class="active"><span>4</span></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_4 --> <div id="page_5" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="81"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015BVol...77...37E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015BVol...77...37E"><span>Basaltic maar-diatreme volcanism in the Lower Carboniferous of the Limerick Basin (SW Ireland)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elliott, H. A. L.; Gernon, T. M.; Roberts, S.; Hewson, C.</p> <p>2015-05-01</p> <p>Lead-zinc exploration drilling within the Limerick Basin (SW Ireland) has revealed the deep internal architecture and extra-crater deposits of five alkali-basaltic maar-diatremes. These were emplaced as part of a regional north-east south-west tectonomagmatic trend during the Lower Carboniferous Period. Field relationships and textural observations suggest that the diatremes erupted into a shallow submarine environment. Limerick trace element data indicates a genetic relationship between the diatremes and extra-crater successions of the Knockroe Formation, which records multiple diatreme filling and emptying cycles. Deposition was controlled largely by bathymetry defined by the surrounding Waulsortian carbonate mounds. An initial non-diatreme forming eruption stage occurred at the water-sediment interface, with magma-water interaction prevented by high magma ascent rates. This was followed by seawater incursion and the onset of phreatomagmatic activity. Magma-water interaction generated poorly vesicular blocky clasts, although the co-occurrence of plastically deformed and highly vesicular clasts indicate that phreatomagmatic and magmatic processes were not mutually exclusive. At a later stage, the diatreme filled with a slurry of juvenile lapilli and country rock lithic clasts, homogenised by the action of debris jets. The resulting extra-crater deposits eventually emerged above sea level, so that water ingress significantly declined, and late-stage magmatic processes became dominant. These deposits, largely confined to the deep vents, incorporate high concentrations of partially sintered globular and large `raggy' lapilli showing evidence for heat retention. Our study provides new insights into the dynamics and evolution of basaltic diatremes erupting into a shallow water (20-120 m) submarine environment.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V41A3105M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V41A3105M"><span>Magma ascent and magmatism controlled by cratering on the Moon</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michaut, C.; Pinel, V.</p> <p>2016-12-01</p> <p>The lunar primary crust was formed by flotation of light plagioclase minerals on top of the lunar magma ocean, resulting in a relatively light and thick crust. This crust acted as a barrier for the denser primary mantle melts: mare basalts erupted primarily within large impact basins where at least part of this crust was removed. Thus, lunar magmas likely stored at the base of or deep in the lunar crust and the ascent of magma to shallow depths probably required local or regional tensional stresses. On the Moon, evidences of shallow sites of magmatism are mostly concentrated within old and degraded simple and complex craters that surround the Mare basalts. Impacts, that were numerous in the early times of the Moon, created depressions at the lunar surface that induced specific states of stress. Below a crater, magma ascent is helped by the tensional stresses caused by the depression up to a depth that is close to the crater radius. However, many craters that are the sites of shallow magmatism are less than 10 to 20 km in radius and are equally situated in regions of thin (i.e. 20 km) or thick (i.e. 60km) crust suggesting that the depression, although significant enough to control magma emplacement, was not large enough to induce it. Since the sites of magmatism surround the mare basalts, we explore the common idea that the weight of the Mare induced a tensile state of stress in the surrounding regions. We constrain the regional state of stress that was necessary to help magma ascent to shallow depths but was low enough for the local depression due to a crater to control magma emplacement. This state of stress is consistent with a relatively thin but extended mare load. We also show that the depression due to the crater probably caused the horizontalization and hence the storage of the magmatic intrusion at shallow depth below the crater. In the end, because of the neutral buoyancy of magmas in the crust and the lack of tectonic processes, impact processes largely controlled magma transport and secondary crust formation on the Moon.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Tectp.726..121Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Tectp.726..121Z"><span>Continentward-dipping detachment fault system and asymmetric rift structure of the Baiyun Sag, northern South China Sea</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhou, Zhichao; Mei, Lianfu; Liu, Jun; Zheng, Jinyun; Chen, Liang; Hao, Shihao</p> <p>2018-02-01</p> <p>The rift architecture and deep crustal structure of the distal margin at the mid-northern margin of the South China Sea have been previously investigated by using deep seismic reflection profiles. However, one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins (Baiyun Sag and Liwan Sag) within the distal margin because of the limited amount of seismic data. Based on new 3D seismic survey data and 2D seismic reflection profiles, we observe an array of fault blocks in the Baiyun Sag, which were tilted towards the ocean by extensional faulting. The extensional faults consistently dip towards the continent. Beneath the tilted fault blocks and extensional faults, a low-angle, high-amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process. During rifting, the continentward-dipping normal faults evolved in a sequence from south to north, generating the asymmetric rift structure of the Baiyun Sag. The Baiyun Sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 Ma and a ridge jump to the south at 26-24 Ma. Therefore, we propose that magmatism played a significant role in the continental extension and final breakup in the South China Sea.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Tecto..37..705G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Tecto..37..705G"><span>Intrusion of Magmatic Bodies Into the Continental Crust: 3-D Numerical Models</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gorczyk, Weronika; Vogt, Katharina</p> <p>2018-03-01</p> <p>Magma intrusion is a major material transfer process in the Earth's continental crust. Yet the mechanical behavior of the intruding magma and its host are a matter of debate. In this study we present a series of numerical thermomechanical simulations on magma emplacement in 3-D. Our results demonstrate the response of the continental crust to magma intrusion. We observe change in intrusion geometries between dikes, cone sheets, sills, plutons, ponds, funnels, finger-shaped and stock-like intrusions, and injection time. The rheology and temperature of the host are the main controlling factors in the transition between these different modes of intrusion. Viscous deformation in the warm and deep crust favors host rock displacement and plutons at the crust-mantle boundary forming deep-seated plutons or magma ponds in the lower to middle crust. Brittle deformation in the cool and shallow crust induces cone-shaped fractures in the host rock and enables emplacement of finger- or stock-like intrusions at shallow or intermediate depth. Here the passage of magmatic and hydrothermal fluids from the intrusion through the fracture pattern may result in the formation of ore deposits. A combination of viscous and brittle deformation forms funnel-shaped intrusions in the middle crust. Intrusion of low-density magma may more over result in T-shaped intrusions in cross section with magma sheets at the surface.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.304...38W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.304...38W"><span>Early Miocene rapid exhumation in southern Tibet: Insights from P-T-t-D-magmatism path of Yardoi dome</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Kai; Zhang, Jin-Jiang; Liu, Xiao-Chi</p> <p>2018-04-01</p> <p>Reconstructing the evolution of Gneiss domes within orogenic belts poses challenges because domes can form in a variety of geodynamic settings and by multiple doming mechanisms. For the North Himalayan gneiss domes (NHGD), it is debated whether they formed during shortening, extension or collapse of the plateau, and what is the spatial and temporal relationship of magmatism, metamorphism and deformation. This study investigates the Yardoi dome in southern Tibet using field mapping, petrography, phase equilibria modelling and new monazite ages. The resulting P-T-time-deformation-magmatism path for the first time reveals the spatial and temporal relationship of metamorphism, deformation and magmatism in the Yardoi dome: a) the dome mantle recorded prograde loading to kyanite-grade Barrovian metamorphic conditions of 650 ± 30 °C and 9 ± 1 kbar (M2) in the Early Miocene (18-17 Ma); b) the main top-to-the-north deformation fabric (D2) formed syn- to post-peak-metamorphism; c) the emplacement of leucorgranites related to doming is syn-metamorphism at 19-17 Ma. The link between the detachment shear zone in the Yardoi dome and the South Tibetan detachment system (STDS) is confirmed. By comparing with orogen-scale tectonic processes in the Himalaya, we suggest that north-south extension in a convergent geodynamic setting during Early Miocene accounts for formation of the Yardoi dome. In a wider tectonic context, the Early Miocene rapid exhumation of deep crustal rocks was contemporaneous with the rapid uplift of southern Tibet and the Himalayan orogen.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T43B2012T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T43B2012T"><span>Segmentation and Accretionary Processes Near the Andrew Bain Mega-Transform Fault: The Southwest Indian Ridge 25°-35°E</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takeuchi, C. S.; Sclater, J. G.; Grindlay, N. R.; Madsen, J. A.; Rommevaux-Jestin, C.</p> <p>2008-12-01</p> <p>The ultra-slow spreading Southwest Indian Ridge (SWIR) separates the Antarctic and African plates. We present results from two surveys covering the SWIR between 26° and 27°30'E and between 32° and 35°E, lying on either side of the long-offset Andrew Bain transform fault. The objectives of the surveys were to characterize the segmentation of an ultra-slow spreading ridge on either side of a long-offset transform fault and to examine the structure of the individual segments. Four transform faults, the Du Toit, Andrew Bain, Marion, and Prince Edward, and one non-transform discontinuity bound four accretionary segments in the survey areas. Two segments lie northeast of the Andrew Bain (32°-35°E). Large central axial volcanoes, deep, broad mantle Bouguer anomaly (MBA) lows, and high magnetization intensities centered on the spreading axis result from high magmatic activity. Increased magmatism on the ridge axis is likely caused by high mantle temperatures produced by the close proximity of the Marion Plume, which abuts the northern end of the Andrew Bain. Two segments lie southwest of the Andrew Bain (26°-27°30'E). Discrepancies in the locations of the axial rift valley, central magnetization high, and an irregularly-shaped MBA low suggest complex accretionary processes at the western segment (~26°-27° E). The eastern segment (~27°-27°30'E), which abuts the southwest end of the Andrew Bain, shows a deep axial valley, MBA values which increase to the east, and nearly nonexistent magnetization intensity. These features are probably the result of amagmatic accretion caused by the transform edge effect of the Andrew Bain. A transition in the character of topography at 26°45'E suggests that the current segment configuration may not be temporally stable. High-relief (~1 km) ridge-trough structures south of the spreading axis may be the result of an episodic interplay between accretion, both magmatic and amagmatic, and tectonic extension.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1215379C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1215379C"><span>The role of amphibole in Merapi arc magma petrogenesis: insights from petrology and geochemistry of lava hosted xenoliths and xenocrysts</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chadwick, J. P.; Troll, V. R.; Schulz, B.; Dallai, L.; Freda, C.; Schwarzkopf, L. M.; Annersten, H.; Skogby, H.</p> <p>2010-05-01</p> <p>Recently, increasing attention has been paid to the role of amphibole in the differentiation of arc magmas. The geochemical composition of these magmas suggests that deep to mid crustal fractionation of amphibole has occurred. However, this phase is typically an infrequent modal phenocryst phase in subduction zone eruptive deposits(1). Nevertheless, erupted material only represents a portion of the magmatism produced in subduction zone settings, with many opportunities for melts to stall on route to the surface. This discrepancy between whole rock geochemistry and petrological interpretation of arc magmas has lead many scientists to postulate that, at mid to deep crustal levels, there may be significant volumes of amphibole bearing lithologies. Amphibole instability at shallow levels can also contribute to its scarcity in eruptive deposits. This argument is strengthened by field and petrological evidence, including the widespread occurrence of amphibole-rich intrusive rocks in exhumed orogenicbelts formed during subduction zone activity, e.g. the Adamello batholith (2),as well as the presence of amphibole-rich xenoliths and xenocrysts preserved in arc lavas worldwide, e.g. in Indonesia, Antilles, and Central America. Thus, amphibole appears to play an integral role in subduction zone magmatism and identifying and constraining this role is central to understanding arc magma petrogenisis. Amphibole-rich melts or bodies in the deep to mid crust could be a significant hydrous reservoir for intra-crustal melts and fluids (1). In this preliminary study, we have carried out petrological and geochemical analyses of recent basaltic andesite and amphibole bearing crystalline igneous inclusions and xenocrysts from Merapi volcano in Java, Indonesia. The basaltic andesite geochemistry is consistent with amphibole fractionation and the crystalline inclusions are cogenetic to the Merapi magmatic system. These inclusions are likely to represent fractionation residues reflecting deep- to mid-crustal processes given the stability field of amphibole. The individual amphibole xenocrysts are also co-genetic to the Merapi magma system and indicative of high-pressure crystallisation. Hydrogen isotope analyses of these large amphibole megacrysts, record a broad range of dD ratios (permil deviation of D/H isotope ratio from Standard Mean Ocean Water). The dD values of some of these crystals appear to be modified significantly from expected primary compositions, particularly towards the rims of amphiboles showing breakdown textures. The measured dD values possibly result from H-isotope re-equilibration with surrounding volatile vapour during eruption or via dehydration reactions. Mossbauer analysis of a selected pristine amphibole megacryst from this suite records 67 % of iron as Fe3+ in the M-sites. Complementary IR spectroscopy of this amphibole indicates no serious loss of OH groups. High H2O pressures at formation depth for this crystal have stabilized full hydrous compositions at ~ 2% H2O concentration in the amphibole. Such fully hydrated amphiboles could release their H2O on depressurisation on ascent prior to eruption, a process that consistent with the dD data. Analysis of these samples is ongoing, however this initial data indicates that amphibole is a key phase in Merapi magmatic evolution and is a likely source of volatiles through dehydration on ascent. This is of particular significance given the fact that water content of magma has a considerable impact on the explosive potential of subduction zone volcanism. (1) Davidson et al., 2007. Geology, 35: 787-790. (2) Tiepolo et al., 2002 Contrib. Min. Pet., 144:1-15.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1214516V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1214516V"><span>Geophysical Observations Supporting Research of Magmatic Processes at Icelandic Volcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vogfjörd, Kristín. S.; Hjaltadóttir, Sigurlaug; Roberts, Matthew J.</p> <p>2010-05-01</p> <p>Magmatic processes at volcanoes on the boundary between the European and North American plates in Iceland are observed with in-situ multidisciplinary geophysical networks owned by different national, European or American universities and research institutions, but through collaboration mostly operated by the Icelandic Meteorological Office. The terrestrial observations are augmented by space-based interferometric synthetic aperture radar (InSAR) images of the volcanoes and their surrounding surface. Together this infrastructure can monitor magma movements in several volcanoes from the base of the crust up to the surface. The national seismic network is sensitive enough to detect small scale seismicity deep in the crust under some of the voclanoes. High resolution mapping of this seismicity and its temporal progression has been used to delineate the track of the magma as it migrates upwards in the crust, either to form an intrusion at shallow levels or to reach the surface in an eruption. Broadband recording has also enabled capturing low frequency signals emanating from magmatic movements. In two volcanoes, Eyjafjallajökull and Katla, just east of the South Iceland Seismic Zone (SISZ), seismicity just above the crust-mantle boundary has revealed magma intruding into the crust from the mantle below. As the magma moves to shallower levels, the deformation of the Earth‘s surface is captured by geodetic systems, such as continuous GPS networks, (InSAR) images of the surface and -- even more sensitive to the deformation -- strain meters placed in boreholes around 200 m below the Earth‘s surface. Analysis of these signals can reveal the size and shape of the magma as well as the temporal evolution. At near-by Hekla volcano flanking the SISZ to the north, where only 50% of events are of M>1 compared to 86% of earthquakes in Eyjafjallajökull, the sensitivity of the seismic network is insufficient to detect the smallest seismicity and so the volcano appears less active and deep seismicity has not been detected. Improved seismic station density may improve the resolution of deep processes. Due do Hekla‘s continued expansion, the concentration of the continuous GPS network has been increased around Hekla and a strain meter will be installed by the volcano in 2010. The increased density of geodetic observations is expected to increase the resolution of the depth, volume and geometry of the magma chamber. Before the volcano's latest eruption in 2000, the increased seismicity and deformation signal recorded by the nearest seismic station and strain meter (at 15 km distance) enabled a public warning to be issued of the impending eruption 30 minutes prior to eruption. The additional instrumentation around Hekla is expected to extend the previous advance warning time.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.H51C1222M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.H51C1222M"><span>Exploring for geothermal resource in a dormant volcanic system: The Haleakala Southwest Rift Zone, Maui, Hawai'i</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martini, B. A.; Lewicki, J. L.; Kennedy, B. M.; Lide, C.; Oppliger, G.; Drakos, P. S.</p> <p>2011-12-01</p> <p>Suites of new geophysical and geochemical surveys provide compelling evidence for geothermal resource at the Haleakala Southwest Rift Zone (HSWRZ) on Maui Island, Hawai'i. Ground-based gravity (~400 stations) coupled with heli-borne magnetics (~1500 line kilometers) define both deep and shallow fractures/faults while also delineating potentially widespread subsurface hydrothermal alteration on the lower flanks (below approximately 1800 feet a.s.l.). Multi-level, upward continuation calculations and 2-D gravity and magnetic modeling provide information on source depths, but lack of lithologic information leaves ambiguity in the estimates. Lithology and physical property data from future drilling will improve these interpretations. Additionally, several well-defined gravity lows (possibly vent zones) lie coincident with magnetic highs suggesting the presence of dike intrusions at depth; a potentially young source of heat for a modern geothermal system. Soil CO2 fluxes were measured along transects across geophysically-defined faults and fractures as well as young cinder cones along the HSWRZ; a weak anomalous flux signal was observed at one young cinder cone location. Dissolved inorganic carbon concentrations and δ13C compositions and 3He/4He values measured in several shallow groundwater samples indicate addition of magmatic CO2 and He to the groundwater system. The general lack of observed magmatic surface CO2 signals on the HSWRZ is therefore likely due to a combination of groundwater 'scrubbing' of CO2 and relatively high biogenic surface CO2 fluxes that mask magmatic CO2. Similar surveys at the Puna geothermal field on the Kilauea Lower East Rift Zone (KLERZ) also showed a lack of surface CO2 flux signals attributed to a magmatic source, while aqueous geochemistry indicated contribution of magmatic CO2 and He to shallow groundwaters at both Maui and Puna. As magma has been intercepted in geothermal drilling at the Puna field, the lack of measured surface CO2 flux associated with upflow of magmatic fluids here is likely due to the aforementioned 'scrubbing' from extensive groundwater flow, as well as high background biogenic CO2 flux. Deep, temperature gradient core holes have been sited based on these geophysical and geochemical datasets.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://www.geotimes.org/nov00/geophenomena.html','USGSPUBS'); return false;" href="http://www.geotimes.org/nov00/geophenomena.html"><span>Watching magma from space</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lu, Zhong; Wicks, Charles W.; Dzurisin, Daniel; Thatcher, Wayne R.; Freymueller, Jeffrey T.; McNutt, Stephen R.; Mann, Dorte</p> <p>2000-01-01</p> <p>Westdahl is a broad shield volcano at the western end of Unimak Island in the Aleutian chain. It has apparently been dormant since a 1991-92 eruption and seismicity levels have been low. However, satellite radar imaging shows that in the years following 1992 the upper flanks of Westdahl have risen several centimeters, probably from the influx of new magma deep below its summit. Until now, deep magma reservoirs have been difficult to detect beneath most volcanoes. But using space geodetic technologies, specifically interferometric synthetic aperture radar (InSAR), we have discovered a deep magmatic source beneath Westdahl. </p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAESc.149..124L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAESc.149..124L"><span>Magmatic-like fluid source of the Chingshui geothermal field, NE Taiwan evidenced by carbonate clumped-isotope paleothermometry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lu, Yi-Chia; Song, Sheng-Rong; Wang, Pei-Ling; Wu, Chung-Che; Mii, Horng-Sheng; MacDonald, John; Shen, Chuan-Chou; John, Cédric M.</p> <p>2017-11-01</p> <p>The Chingshui geothermal field, a moderate-temperature and water-dominated hydrothermal system, was the site of the first geothermal power plant in Taiwan. Many geological, geophysical and geochemical studies using more than 21 drilled wells have been performed since the 1960s. However, there are still controversies regarding the heat and fluid sources due to the tectonically complicated geological setting. To clarify the heat and fluid sources, we analyzed clumped isotopes with carbon and oxygen isotopic compositions of calcite scaling in geothermal wells and veins on outcrops and calculated the δ18O values of the source fluids. Two populations of δ18O values were calculated: -5.8 ± 0.8‰ VSMOW from scaling in the well and -1.0 ± 1.6‰ to 10.0 ± 1.3‰ VSMOW from outcropping calcite veins, indicative of meteoric and magmatic fluid sources, respectively. Meanwhile, two hydrothermal reservoirs at different depths have been identified by magnetotelluric (MT) imaging with micro-seismicity underneath this area. As a result, we propose a two-reservoir model: the shallow reservoir provides fluids from meteoric water for the scaling sampled from wells, whereas the deep reservoir provides magmatic fluids from deep marble decarbonization recorded in outcropping calcite veins.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.477..156C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.477..156C"><span>Seismic anisotropy from compositional banding in granulites from the deep magmatic arc of Fiordland, New Zealand</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cyprych, Daria; Piazolo, Sandra; Almqvist, Bjarne S. G.</p> <p>2017-11-01</p> <p>We present calculated seismic velocities and anisotropies of mafic granulites and eclogites from the Cretaceous deep lower crust (∼40-65 km) of Fiordland, New Zealand. Both rock types show a distinct foliation defined by cm-scale compositional banding. Seismic properties are estimated using the Asymptotic Expansion Homogenisation - Finite Element (AEH-FE) method that, unlike the commonly used Voigt-Reuss-Hill homogenisation, incorporates the phase boundary network into calculations. The predicted mean P- and S-wave velocities are consistent with previously published data for similar lithologies from other locations (e.g., Kohistan Arc), although we find higher than expected anisotropies (AVP ∼ 5.0-8.0%, AVS ∼ 3.0-6.5%) and substantial S-wave splitting along foliation planes in granulites. This seismic signature of granulites results from a density and elasticity contrast between cm-scale pyroxene ± garnet stringers and plagioclase matrix rather than from crystallographic orientations alone. Banded eclogites do not show elevated anisotropies as the contrast in density and elastic constants of garnet and pyroxene is too small. The origin of compositional banding in Fiordland granulites is primarily magmatic and structures described here are expected to be typical for the base of present day magmatic arcs. Hence, we identify a new potential source of anisotropy within this geotectonic setting.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.6241L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.6241L"><span>The lithosphere architecture and geodynamic of the Middle and Lower Yangtze metallogenic belt in eastern China: constraints from integrated geophysical data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lü, Qingtian; Shi, Danian; Jiang, Guoming; Dong, Shuwen</p> <p>2014-05-01</p> <p>The lithosphere structure and deep processes are keys to understanding mineral system and ore-forming processes. Lithosphere-scale process could create big footprints or signatures which can be observed by geophysics methods. SinoProbe has conducted an integrated deep exploration across middle and lower reaches of Yangtze Metallogenic Belt (YMB) in Eastern China, these included broadband seismic, reflection seismic, wide-angle reflection and magnetotellurics survey. Seismic reflection profiles and MT survey were also performed in Luzong, Tongling and Ningwu ore districts to construct 3D geological model. The resulting geophysical data provides new information which help to better understanding the lithosphere structure, geodynamic, deformation and heat and mass transportation that lead to the formation of the Metallogenic Belt. The major results are: (1) Lower velocity body at the top of upper mantle and a SE dipping high velocity body were imaged by teleseismic tomography beneath YMB; (2) Shear wave splitting results show NE parallel fast-wave polarization direction which parallel with tectonic lineament; (3) The reflection seismic data support the crustal-detachment model, the lower and upper crust was detached during contraction deformation near Tanlu fault and Ningwu volcanic basin; (4) Broadband and reflection seismic confirm the shallow Moho beneath YMB; (5) Strong correlation of lower crust reflectivity with magmatism; (6) The lower crust below Luzong Volcanics shows obvious reflective anisotropy both at the crust-mantle transition and the brittle-ductile transition in the crust. All these features suggest that introcontinental subduction, lithosphere delamination, mantle sources magmatic underplating, and MASH process are responsible for the formation of this Mesozoic metallogenic belt. Acknowledgment: We acknowledge the financial support of SinoProbe by the Ministry of Finance and Ministry of Land and Resources, P. R. China, under Grant sinoprobe-03, and financial support by National Natural Science Foundation of China under Grant 40930418</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3420A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3420A"><span>Crustal processes cause adakitic chemical signatures in syn-collision magmatism from SE Iran</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Allen, Mark; Kheirkhah, Monireh; Neill, Iain</p> <p>2015-04-01</p> <p>We report new elemental and Nd-Sr isotopic analyses for Late Cenozoic intrusive and extrusive rocks emplaced in SE Iran as part of the wider syn-collision magmatic province within the Turkish-Iranian Plateau. The sample sites are near the town of Dehaj in Kerman Province. Most of the rocks are from stocks and batholiths, interpreted as the roots of central volcanoes. Age controls are not precise, but the rocks are likely to be Late Miocene-Quaternary in age. Basaltic to andesitic lavas crop out nearby; their relationships to the intrusive rocks are uncertain. Geochemically, the entire range of rocks from basalt lavas through to rhyolitic intrusives ranges from 51-71 wt.% silica and isotopic signatures are similar to Bulk Earth, without any clear evidence for large-scale crustal contamination. The basaltic to andesitic lavas appear to have variable and often high La/Yb and Sr/Y such that they range from calc-alkaline arc-like rocks to adakitic compositions depending on the degree of fractionation. The intrusive rocks seem to form a separate suite, with clear indications of increasing Sr/Y and Dy/Yb with fractionation. Previous interpretations relate adakitic magmatism to Tethyan oceanic slab break-off and slab melting beneath the collision zone. However, as the 'adakitic signature' is increasingly apparent in more evolved magmas, at least in the intrusives, adakite generation is more likely to have occurred during melt evolution from an initial low Sr/Y and low La/Yb parent. This parental melt may have been similar in starting composition to proposed non-adakitic basaltic melts from elsewhere in the collision zone. The high Sr/Yb and La/Yb signatures are best explained by the suppression of plagioclase fractionation by high magmatic water contents, promoting incompatible behaviour of Sr. Conversely, Y and Yb are compatible during amphibole and garnet fractionation at crustal or uppermost mantle levels. Rather than a localised slab break-off or melting effect, the Dehaj magmatism may have developed its geochemical signature during deep fractionation as the ascent of the magmas was impeded by thick orogenic crust. The rocks may be seen as just another part of the widespread syn-collision magmatism that has affected widespread areas of Turkey, Iran, Armenia and neighbouring countries in the last ~10-15 Ma, and need not be used as markers for debateable geodynamic events such as break-off. Adakites are also present in NE Iran without any obvious association with subduction processes. We argue that magmatism across much of the plateau is linked at least in part to mantle upwelling following Miocene slab break-off, but also to small-scale convection beneath the collision zone, as predicted by numerical modelling. Particular compositions such as those at Dehaj are influenced by local sources and differentiation processes, but there is no need for independent triggers for initial melting across disparate locations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53B4673B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53B4673B"><span>Breakup Style and Magmatic Underplating West of the Lofoten Islands, Norway, Based on OBS Data.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breivik, A. J.; Faleide, J. I.; Mjelde, R.; Murai, Y.; Flueh, E. R.</p> <p>2014-12-01</p> <p>The breakup of the Northeast Atlantic in the Early Eocene was magma-rich, forming the major part of the North Atlantic Igneous Province (NAIP). This is seen as extrusive and intrusive magmatism in the continental domain, and as a thicker than normal oceanic crust produced the first few million years after continental breakup. The maximum magma productivity and the duration of excess magmatism varies along the margins of Northwest Europe and East Greenland, to some extent as a function of the distance from the Iceland hotspot. The Vøring Plateau off mid-Norway is the northernmost of the margin segments in northwestern Europe with extensive magmatism. North of the plateau, magmatism dies off towards the Lofoten Margin, marking the northern boundary of the NAIP here. In 2003, as part of the Euromargins Program we collected an Ocean Bottom Seismometer (OBS) profile from mainland Norway, across the Lofoten Islands, and out into the deep ocean. Forward velocity modeling using raytracing reveals a continental margin that shows transitional features between magma-rich and magma-poor rifting. On one hand, we detect an up to 2 km thick and 40-50 km wide magmatic underplate of the outer continent, on the other hand, continental thinning is greater and intrusive magmatism less than farther south. Continental breakup also appears to be somewhat delayed compared to breakup on the Vøring Plateau, consistent with increased extension. This indicates that magmatic diking, believed to quickly lead to continental breakup of volcanic margins and thus to reduce continental thinning, played a much lesser role here than at the plateau. Early post-breakup oceanic crust is up to 8 km thick, less than half of that observed farther south. The most likely interpretation of these observations, is that the source for the excess magmatism of the NAIP was not present at the Lofoten Margin during rifting, and that the excess magmatism actually observed was the result of lateral transport from the south around breakup time.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T51B0448D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T51B0448D"><span>Cratonic roots and lower crustal seismicity: Investigating the role of deep intrusion in the Western rift, Africa</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Drooff, C.; Ebinger, C. J.; Lavayssiere, A.; Keir, D.; Oliva, S. J.; Tepp, G.; Gallacher, R. J.</p> <p>2017-12-01</p> <p>Improved seismic imaging beneath the African continent reveals lateral variations in lithospheric thickness, and crustal structure, complementing a growing crust and mantle xenolith data base. Border fault systems in the active cratonic rifts of East Africa are characterized by lower crustal seismicity, both in magmatic sectors and weakly magmatic sectors, providing constraints on crustal rheology and, in some areas, magmatic fluid migration. We report new seismicity data from magmatic and weakly magmatic sectors of the East African rift zone, and place the work in the context of independent geophysical and geochemical studies to models for strain localization during early rifting stages. Specifically, multidisciplinary studies in the Magadi Natron rift sectors reveal volumetrically large magmatic CO2 degassing along border faults with seismicity along projections of surface dips to the lower crust. The magmatic CO2 degassing and high Vp/Vs ratios and reflectivity of the lower crust implies that the border fault serves a conduit between the lower crustal underplating and the atmospheric. Crustal xenoliths in the Eastern rift sector indicate a granulitic lower crust, which is relatively weak in the presence of fluids, arguing against a strong lower crust. Within magmatic sectors, seismic, structural, and geochemistry results indicate that frequent lower crustal earthquakes are promoted by elevated pore pressures from volatile degassing along border faults, and hydraulic fracture around the margins of magma bodies. Within some weakly magmatic sectors, lower crustal earthquakes also occur along projections of border faults to the lower crust (>30 km), and they are prevalent in areas with high Vp/Vs in the lower crust. Within the southern Tanganyika rift, focal mechanisms are predominantly normal with steep nodal planes. Our comparative studies suggest that pervasive metasomatism above a mantle plume, and melt extraction in thin zones between cratonic roots, lead to high pore pressures that promote brittle failure in the lower crust, even in areas with no surface expression of magmatism.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16..637R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16..637R"><span>Magmatic versus tectonic influence in the Eolian arc: the case of Vulcano and Lipari islands revisited</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruch, Joel; Di Lorenzo, Riccardo; Vezzoli, Luigina Maria; De Rosa, Rosanna; Acocella, Valerio; Catalano, Stefano; Romagnoli, Gino</p> <p>2014-05-01</p> <p>The prevalent influence of magma versus tectonics for the edification and the evolution of volcanic zones is matter of debate. Here we focus on Vulcano and Lipari, two active volcanic islands located in the central sector of the Eolian arc (North of Sicily). Both systems are influenced by regional tectonics and affected by historical magmatic events taking place along a NS oriented structure, connecting both islands. We revisit and implement previous structural studies performed during the 1980's considering several new geophysical, geochemical and geodynamical findings. Four extensive structural campaigns have been performed on both islands and along the shorelines in 2012-2013 covering about 80% of the possible accessible outcrops. We collected ~500 measurements (e.g. faults, fractures and dikes) at 40 sites. Overall, most of the observed structures are oriented N-S and NNW-SSE, confirming previous studies, however, almost all features are strikingly dominated by an EW-oriented extensive regime, which is a novelty. These findings are supported by kinematic indicators and suggest a predominant dip-slip component (pitch from 80 and 130°) with alternating left and right kinematics. Marginal faulting in most recent formations have been observed, suggesting that the deformation may occur preferentially during transient deformation related to periods of magmatic activity, instead of resulting from continuous regional tectonic processes. Overall, fault and dike planes are characterized by a dominant eastward immersion, suggesting an asymmetric graben-like structure of the entire area. This may be explained by the presence of a topographic gradient connecting both islands to the deep Gioia basin to the East, leading to a preferential ample gravitational collapse. Finally, we propose a model in which the stress field rotates northward. It transits from a pure right lateral strike-slip regime along the Tindari fault zone (tectonic-dominant) to an extensive regime explained by the presence of magma at depth inducing a local magmatic stress field affecting structures on Vulcano and Lipari islands (magmatic dominant).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V51C2680S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V51C2680S"><span>Raton-Clayton Volcanic Field magmatism in the context of the Jemez Lineament</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schrader, C. M.; Pontbriand, A.</p> <p>2013-12-01</p> <p>The Raton-Clayton Volcanic Field (RCVF) was active from 9 Ma to approximately 50 Ka and stretches from Raton, New Mexico in the west to Clayton, New Mexico in the east. The field occurs in the Great Plains at the northeastern end of the Jemez Lineament, a major crustal feature and focus of volcanism that extends southwest to the Colorado Plateau in Arizona and encompasses five other major volcanic fields. Jemez Lineament magmatism is temporally related to Rio Grande Rift magmatism, though it extends NE and SW from the rift itself, and it has been suggested that it represents an ancient crustal suture that serves as a conduit for magmatism occurring beneath the larger region of north and central New Mexico (Magnani et al., 2004, GEOL SOC AM BULL, 116:7/8, pp. 1-6). This study extends our work into the RCVF from prior and ongoing work in the Mount Taylor Volcanic Field, where we identified different mantle sources with varying degrees of subduction alteration and we determined some of the crustal processes that contribute to the diversity of magma chemistry and eruptive styles there (e.g., AGU Fall Meeting, abst. #V43D-2884 and #V43D-2883). In the RCVF, we are analyzing multiple phases by electron microprobe and plagioclase phenocrysts and glomerocrysts by LA-ICPMS for Sr isotopes and trace elements. We are undertaking this investigation with the following goals: (1) to evaluate previous magma mixing and crustal assimilation models for Sierra Grande andesites (Zhu, 1995, unpublished Ph.D. dissertation, Rice University; Hesse, 1999, unpublished M.S. thesis, Northern Arizona University); (2) to evaluate subduction-modified mantle as the source for RCVF basanites (specifically those at Little Grande); and (3) to assess the possible role of deep crustal cumulates in buffering transitional basalts. In the larger context, these data will be used to evaluate the varying degree of subduction-modification and the effect of crustal thickness on magmatism along the Jemez Lineament.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T32A..04B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T32A..04B"><span>The dynamics of continental breakup-related magmatism on the Norwegian volcanic margin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breivik, A. J.; Faleide, J. I.; Mjelde, R.</p> <p>2007-12-01</p> <p>The Vøring margin off mid-Norway was initiated during the earliest Eocene (~54 Ma), and large volumes of magmatic rocks were emplaced during and after continental breakup. In 2003, an ocean bottom seismometer survey was acquired on the Norwegian margin to constrain continental breakup and early seafloor spreading processes. The profile P-wave model described here crosses the northern part of the Vøring Plateau. Maximum igneous crustal thickness was found to be 18 km, decreasing to ~6.5 km over ~6 M.y. after continental breakup. Both the volume and the duration of excess magmatism after breakup is about twice of what is observed off the Møre Margin south of the Jan Mayen Fracture Zone, which offsets the margin segments by ~170 km. A similar reduction in magmatism occurs to the north over an along-margin distance of ~100 km to the Lofoten margin, but without a margin offset. There is a strong correlation between magma productivity and early plate spreading rate, which are highest just after breakup, falling with time. This is seen both at the Møre and the Vøring margin segments, suggesting a common cause. A model for the breakup- related magmatism should be able to (1) explain this correlation, (2) the magma production peak at breakup, and (3) the magmatic segmentation. Proposed end-member hypotheses are elevated upper-mantle temperatures caused by a hot mantle plume, or edge-driven small-scale convection fluxing mantle rocks through the melt zone. Both the average P-wave velocity and the major-element data at the Vøring margin indicate a low degree of melting consistent with convection. However, small scale convection does not easily explain the issues listed above. An elaboration of the mantle plume model by N. Sleep, in which buoyant plume material fills the rift-topography at the base of the lithosphere, can explain these: When the continents break apart, the buoyant plume-material flows up into the rift zone, causing excess magmatism by both elevated temperature and excess flux, and magmatism dies off as this rift-restricted material is spent. The buoyancy of the plume-material also elevates the plate boundaries and enhances plate spreading forces initially. The rapid drop in magma productivity to the north correlates with the northern boundary of the wide and deep Cretaceous Vøring Basin, thus less plume material was accommodated off Lofoten. This model predicts that the magma segmentation will show little variation in the geochemical signature.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Geote..51...40M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Geote..51...40M"><span>Development of continental margins of the Atlantic Ocean and successive breakup of the Pangaea-3 supercontinent</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Melankholina, E. N.; Sushchevskaya, N. M.</p> <p>2017-01-01</p> <p>Comparative tectonic analysis of passive margins of the Atlantic Ocean has been performed. Tectonotypes of both volcanic and nonvolcanic margins are described, and their comparison with other passive Atlantic margins is given. The structural features of margins, peculiarities of magmatism, its sources and reasons for geochemical enrichment of melts are discussed. The important role of melting of the continental lithosphere in the development of magmatism is demonstrated. Enriched EM I and EM II sources are determined for the lower parts of the volcanic section, and a depleted or poorly enriched source is determined for the upper parts of the volcanic section based on isotope data. The conclusions of the paper relate to tectonic settings of the initial occurrence of magmatism and rifting and breakup during the period of opening of the Mesozoic Ocean. It was found out that breakup and magmatism at proximal margins led only to insignificant structural transformations and reduction of the thickness of the ancient continental crust, while very important magmatic events happened later in the distal zone. New growth of magmatic crust at the stage of continental breakup is determined as a typical feature of distal zones of the margins under study. The relationship of development of margins with the impact of deep plumes as the source of magmatic material or a heat source only is discussed. Progradation of the zone of extension and breakup into the areas of cold lithosphere of the Atlantic and the formation of a single tectonomagmatic system of the ocean are under consideration.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_3");'>3</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li class="active"><span>5</span></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_5 --> <div id="page_6" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="101"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.8701X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.8701X"><span>Magmatic plumbing system from lower mantle of Hainan plume</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xia, Shaohong; Sun, Jinlong; Xu, Huilong; Huang, Haibo; Cao, Jinghe</p> <p>2017-04-01</p> <p>Intraplate volcanism during Late Cenozoic in the Leiqiong area of southernmost South China, with basaltic lava flows covering a total of more than 7000 km2, has been attributed to an underlying Hainan plume. However, detailed features of Hainan plume, such as morphology of magmatic conduits, depth of magmatic pool in the upper mantle and pattern of mantle upwelling, are still enigmatic. Here we present seismic tomographic images of the upper 1100 km of the mantle beneath the southern South China. Our results show a mushroom-like continuous low-velocity anomaly characterized by a columnar tail with diameter of about 200-300 km that tilts downward to lower mantle beneath north of Hainan hotspot and a head that spreads laterally near the mantle transition zone, indicating a magmatic pool in the upper mantle. Further upward, this head is decomposed into small patches, but when encountering the base of the lithosphere, a pancake-like anomaly is shaped again to feed the Hainan volcanism. Our results challenge the classical model of a fixed thermal plume that rises vertically to the surface, and propose the new layering-style pattern of magmatic upwelling of Hainan plume. This work indicates the spatial complexities and differences of global mantle plumes probably due to heterogeneous compositions and changefully thermochemical structures of deep mantle.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28963475','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28963475"><span>Magmatic tempo of Earth's youngest exposed plutons as revealed by detrital zircon U-Pb geochronology.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ito, Hisatoshi; Spencer, Christopher J; Danišík, Martin; Hoiland, Carl W</p> <p>2017-09-29</p> <p>Plutons are formed by protracted crystallization of magma bodies several kilometers deep within the crust. The temporal frequency (i.e. episodicity or 'tempo') of pluton formation is often poorly constrained as timescales of pluton formation are largely variable and may be difficult to resolve by traditional dating methods. The Hida Mountain Range of central Japan hosts the youngest exposed plutons on Earth and provides a unique opportunity to assess the temporal and spatial characteristics of pluton emplacement at high temporal resolution. Here we apply U-Pb geochronology to zircon from the Quaternary Kurobegawa Granite and Takidani Granodiorite in the Hida Mountain Range, and from modern river sediments whose fluvial catchments include these plutons in order to reconstruct their formation. The U-Pb data demonstrate that the Kurobegawa pluton experienced two magmatic pulses at ~2.3 Ma and ~0.9 Ma; whereas, to the south, the Takidani pluton experienced only one magmatic pulse at ~1.6 Ma. These data imply that each of these magmatic systems were both spatially and temporally distinct. The apparent ~0.7 Myr age gap between each of the three magmatic pulses potentially constrains the recharge duration of a single pluton within a larger arc plutonic complex.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V31D..01W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V31D..01W"><span>Deep Crustal Melting and the Survival of Continental Crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Whitney, D.; Teyssier, C. P.; Rey, P. F.; Korchinski, M.</p> <p>2017-12-01</p> <p>Plate convergence involving continental lithosphere leads to crustal melting, which ultimately stabilizes the crust because it drives rapid upward flow of hot deep crust, followed by rapid cooling at shallow levels. Collision drives partial melting during crustal thickening (at 40-75 km) and/or continental subduction (at 75-100 km). These depths are not typically exceeded by crustal rocks that are exhumed in each setting because partial melting significantly decreases viscosity, facilitating upward flow of deep crust. Results from numerical models and nature indicate that deep crust moves laterally and then vertically, crystallizing at depths as shallow as 2 km. Deep crust flows en masse, without significant segregation of melt into magmatic bodies, over 10s of kms of vertical transport. This is a major mechanism by which deep crust is exhumed and is therefore a significant process of heat and mass transfer in continental evolution. The result of vertical flow of deep, partially molten crust is a migmatite dome. When lithosphere is under extension or transtension, the deep crust is solicited by faulting of the brittle upper crust, and the flow of deep crust in migmatite domes traverses nearly the entire thickness of orogenic crust in <10 million years. This cycle of burial, partial melting, rapid ascent, and crystallization/cooling preserves the continents from being recycled into the mantle by convergent tectonic processes over geologic time. Migmatite domes commonly preserve a record of high-T - low-P metamorphism. Domes may also contain rocks or minerals that record high-T - high-P conditions, including high-P metamorphism broadly coeval with host migmatite, evidence for the deep crustal origin of migmatite. There exists a spectrum of domes, from entirely deep-sourced to mixtures of deep and shallow sources. Controlling factors in deep vs. shallow sources are relative densities of crustal layers and rate of extension: fast extension (cm/yr) promotes efficient ascent of deep crust, whereas slow extension (mm/yr) produces significantly less exhumation. Recognition of the importance of migmatite (gneiss) domes as archives of orogenic deep crust is applicable to determining the chemical and physical properties of continental crust, as well as mechanisms and timescales of crustal differentiation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70023793','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70023793"><span>Apatite fission-track evidence of widespread Eocene heating and exhumation in the Yukon-Tanana Upland, interior Alaska</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Dusel-Bacon, C.; Murphy, J.M.</p> <p>2001-01-01</p> <p>We present an apatite fission-track (AFT) study of five plutonic rocks and seven metamorphic rocks across 310 km of the Yukon-Tanana Upland in east-central Alaska. Samples yielding ???40 Ma AFT ages and mean confined track lengths > 14 ??m with low standard deviations cooled rapidly from >120??C to 40 Ma suggest partial annealing and, therefore, lower maximum temperatures (???90-105??C). A few samples with single-grain ages of ???20 Ma apparently remained above ???50??C after initial cooling. Although the present geothermal gradient in the western Yukon-Tanana Upland is ???32??C/km, it could have been as high as 45??C/km during a widespread Eocene intraplate magmatic episode. Prior to rapid exhumation, samples with ???40 Ma AFT ages were >3.8-2.7 km deep and samples with >50 Ma AFT ages were >3.3-2.0 km deep. We calculate a 440-320 m/Ma minimum rate for exhumation of all samples during rapid cooling. Our AFT data, and data from rocks north of Fairbanks and from the Eielson deep test hole, indicate up to 3 km of post-40 Ma vertical displacement along known and inferred northeast-trending high-angle faults. The predominance of 40-50 Ma AFT ages throughout the Yukon-Tanana Upland indicates that, prior to the post-40 Ma relative uplift along some northeast-trending faults, rapid regional cooling and exhumation closely followed the Eocene extensional magmatism. We propose that Eocene magmatism and exhumation were somehow related to plate movements that produced regional-scale oroclinal rotation, northward translation of outboard terranes, major dextral strike-slip faulting, and subduction of an oceanic spreading ridge along the southern margin of Alaska.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024478','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024478"><span>Gas geochemistry of the Valles caldera region, New Mexico and comparisons with gases at Yellowstone, Long Valley and other geothermal systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Goff, F.; Janik, C.J.</p> <p>2002-01-01</p> <p>Noncondensible gases from hot springs, fumaroles, and deep wells within the Valles caldera geothermal system (210-300??C) consist of roughly 98.5 mo1% CO2, 0.5 mol% H2S, and 1 mol% other components. 3He/4He ratios indicate a deep magmatic source (R/Ra up to 6) whereas ??13C-CO2 values (-3 to -5???) do not discriminate between a mantle/magmatic source and a source from subjacent, hydrothermally altered Paleozoic carbonate rocks. Regional gases from sites within a 50-km radius beyond Valles caldera are relatively enriched in CO2 and He, but depleted in H2S compared to Valles gases. Regional gases have R/Ra values ???1.2 due to more interaction with the crust and/or less contribution from the mantle. Carbon sources for regional CO2 are varied. During 1982-1998, repeat analyses of gases from intracaldera sites at Sulphur Springs showed relatively constant CH4, H2, and H2S contents. The only exception was gas from Footbath Spring (1987-1993), which experienced increases in these three components during drilling and testing of scientific wells VC-2a and VC-2b. Present-day Valles gases contain substantially less N2 than fluid inclusion gases trapped in deep, early-stage, post-caldera vein minerals. This suggests that the long-lived Valles hydrothermal system (ca. 1 Myr) has depleted subsurface Paleozoic sedimentary rocks of nitrogen. When compared with gases from many other geothermal systems, Valles caldera gases are relatively enriched in He but depleted in CH4, N2 and Ar. In this respect, Valles gases resemble end-member hydrothermal and magmatic gases discharged at hot spots (Galapagos, Kilauea, and Yellowstone). Published by Elsevier Science B.V.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUSM.V51A..07J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUSM.V51A..07J"><span>Assessing Magmatic Processes and Hazards at two Basaltic Monogenetic Centers: Volcan Jorullo, Mexico, and Blue Lake Maar, Oregon</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, E. R.; Cashman, K.; Wallace, P.; Delgado Granados, H.</p> <p>2007-05-01</p> <p>Although monogenetic basaltic volcanoes exhibit a wide variety of eruption styles, the origin of this diversity is poorly understood and often ignored when assessing volcanic hazards. To better understand magmatic processes and hazards associated with these eruptions, we have studied two monogenetic centers with differing behavior: Volcan Jorullo, a cinder cone in Mexico, and Blue Lake, a maar in the Oregon High Cascades. Although compositionally similar (medium-K basalt to basaltic andesite), their eruptive styles and products are quite different. Jorullo had violent strombolian eruptions that deposited alternating beds of ash and tephra, as well as lava flows. In contrast, Blue Lake exhibited initial phreatomagmatism that formed a 100m deep crater and produced surge deposits. This activity was followed by magmatic eruptions that produced deposits of tephra and bombs, but no lava flows. The diversity in eruptive style at these two centers reflects different magma ascent and crystallization processes, deduced using olivine-hosted melt inclusions. Jorullo melt inclusions trap variably degassed melts (0.5-5 wt% H2O; 0-1000 ppm CO2), with associated crystallization pressures that decrease from early (<4 kbars) to late (<100 bars) in the eruption. These data support the formation of a shallow storage region beneath the volcano that facilitated both crystallization and magma degassing, which is consistent with effusion of degassed lavas from the base of the cone throughout the eruption. In contrast, Blue Lake inclusions trap melts with a restricted range of volatiles (2.6-4 wt% H2O; 677-870 ppm CO2) corresponding to crystallization pressures of 2.2-3.2 kbars. This suggests that the magma feeding Blue Lake stalled in the upper crust and crystallized before ascending rapidly to the surface, without further crystallization of olivine or shallow storage. This is consistent with both the observed unstratified tephra deposits (indicating single rather than pulsatory eruptions) and the absence of lava flows. Our data suggest that in spite of similar compositions and volatile contents, these two volcanoes produced distinctive eruption styles. Although external water clearly played an important role in the eruption at Blue Lake, both volcanoes had explosive, magmatic volatile-driven eruptions. These eruptions clearly show that monogenetic centers are capable of a wide variety of eruptive styles and hazards, which may depend in large part on processes of magma ascent, degassing, and crystallization.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009ESRv...96....1C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009ESRv...96....1C"><span>Continental rift evolution: From rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Corti, Giacomo</p> <p>2009-09-01</p> <p>The Main Ethiopian Rift is a key sector of the East African Rift System that connects the Afar depression, at Red Sea-Gulf of Aden junction, with the Turkana depression and Kenya Rift to the South. It is a magmatic rift that records all the different stages of rift evolution from rift initiation to break-up and incipient oceanic spreading: it is thus an ideal place to analyse the evolution of continental extension, the rupture of lithospheric plates and the dynamics by which distributed continental deformation is progressively focused at oceanic spreading centres. The first tectono-magmatic event related to the Tertiary rifting was the eruption of voluminous flood basalts that apparently occurred in a rather short time interval at around 30 Ma; strong plateau uplift, which resulted in the development of the Ethiopian and Somalian plateaus now surrounding the rift valley, has been suggested to have initiated contemporaneously or shortly after the extensive flood-basalt volcanism, although its exact timing remains controversial. Voluminous volcanism and uplift started prior to the main rifting phases, suggesting a mantle plume influence on the Tertiary deformation in East Africa. Different plume hypothesis have been suggested, with recent models indicating the existence of deep superplume originating at the core-mantle boundary beneath southern Africa, rising in a north-northeastward direction toward eastern Africa, and feeding multiple plume stems in the upper mantle. However, the existence of this whole-mantle feature and its possible connection with Tertiary rifting are highly debated. The main rifting phases started diachronously along the MER in the Mio-Pliocene; rift propagation was not a smooth process but rather a process with punctuated episodes of extension and relative quiescence. Rift location was most probably controlled by the reactivation of a lithospheric-scale pre-Cambrian weakness; the orientation of this weakness (roughly NE-SW) and the Late Pliocene (post 3.2 Ma)-recent extensional stress field generated by relative motion between Nubia and Somalia plates (roughly ESE-WNW) suggest that oblique rifting conditions have controlled rift evolution. However, it is still unclear if these kinematical boundary conditions have remained steady since the initial stages of rifting or the kinematics has changed during the Late Pliocene or at the Pliocene-Pleistocene boundary. Analysis of geological-geophysical data suggests that continental rifting in the MER evolved in two different phases. An early (Mio-Pliocene) continental rifting stage was characterised by displacement along large boundary faults, subsidence of rift depression with local development of deep (up to 5 km) asymmetric basins and diffuse magmatic activity. In this initial phase, magmatism encompassed the whole rift, with volcanic activity affecting the rift depression, the major boundary faults and limited portions of the rift shoulders (off-axis volcanism). Progressive extension led to the second (Pleistocene) rifting stage, characterised by a riftward narrowing of the volcano-tectonic activity. In this phase, the main boundary faults were deactivated and extensional deformation was accommodated by dense swarms of faults (Wonji segments) in the thinned rift depression. The progressive thinning of the continental lithosphere under constant, prolonged oblique rifting conditions controlled this migration of deformation, possibly in tandem with the weakening related to magmatic processes and/or a change in rift kinematics. Owing to the oblique rifting conditions, the fault swarms obliquely cut the rift floor and were characterised by a typical right-stepping arrangement. Ascending magmas were focused by the Wonji segments, with eruption of magmas at surface preferentially occurring along the oblique faults. As soon as the volcano-tectonic activity was localised within Wonji segments, a strong feedback between deformation and magmatism developed: the thinned lithosphere was strongly modified by the extensive magma intrusion and extension was facilitated and accommodated by a combination of magmatic intrusion, dyking and faulting. In these conditions, focused melt intrusion allows the rupture of the thick continental lithosphere and the magmatic segments act as incipient slow-spreading mid-ocean spreading centres sandwiched by continental lithosphere. Overall the above-described evolution of the MER (at least in its northernmost sector) documents a transition from fault-dominated rift morphology in the early stages of extension toward magma-assisted rifting during the final stages of continental break-up. A strong increase in coupling between deformation and magmatism with extension is documented, with magma intrusion and dyking playing a larger role than faulting in strain accommodation as rifting progresses to seafloor spreading.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Litho.136....1Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Litho.136....1Z"><span>Processes in continental collision zones: Preface</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zheng, Yong-Fei; Zhang, Lifei; McClelland, William C.; Cuthbert, Simon</p> <p>2012-04-01</p> <p>Formation and exhumation of high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in continental subduction zones are the two fundamental geodynamic aspects of collisional orogensis. This volume is based on the Session 08c titled "Geochemical processes in continental collision zones" at Goldschmidt 2010 in Knoxville, USA. It focuses on micro- to macro-scale processes that are temporally and spatially linked to different depths of crustal subduction/exhumation and associated mineralogical changes. They are a key to understanding a wide spectrum of phenomena, involving HP/UHP metamorphism and syn-/post-collisional magmatism. Papers in this volume report progresses in petrological, geochronological and geochemical studies of UHP metamorphic rocks and their derivatives in China, with tectonic settings varying from arc-continent collision to continent-continent collision. Microbeam in-situ analyses of metamorphic and magmatic minerals are successfully utilized to solve various problems in the study of continental deep subduction and UHP metamorphism. In addition to their geochronological applications to dating of HP to UHP metamorphic events during continental collision, microbeam techniques have also served as an efficient means to recognize different generations of mineral growth during continental subduction-zone metamorphism. Furthermore, metamorphic dehydration and partial melting of UHP metamorphic rocks during subduction and exhumation are highlighted with respect to their effects on fluid action and element mobilization. These have provided new insights into chemical geodynamics in continental subduction zones.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T51B0466B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T51B0466B"><span>The Transition from Volcanic to Rift Dominated Crustal Breakup - From the Vøring Plateau to the Lofoten Margin, Norway</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breivik, A. J.; Faleide, J. I.; Mjelde, R.; Flueh, E.; Murai, Y.</p> <p>2017-12-01</p> <p>The Vøring Plateau was part of the Northeast Atlantic igneous province (NAIP) during early Cenozoic crustal breakup. Crustal breakup at the Vøring Plateau occurred marginal to the deep Cretaceous basins on the shelf, with less extension of the crust. Intrusive magmatism and oceanic crust up to three times normal thickness caused a period of sub-aerial magmatism around breakup time. The transition to the Lofoten Margin is rapid to a deep-water plain. Still, there is some excess magmatism north of this transition, where early oceanic crustal thickness is reduced to half of that of the Vøring Plateau 150 km away. Our estimates of the earliest seafloor spreading rates using new ship-track magnetic profiles on different margin segments offer a clue to what caused this rapid transition. While crustal breakup occurred within the magnetic polarity C24r in other parts of the NAIP, there is a delayed breakup for the Lofoten/Vesterålen margin. Modeling of the earliest seafloor spreading with geomagnetic reversals, indicate a breakup within C24n.3n (anomaly 24b), approximately 1 m.y. later. Both old wide-angle seismic models (from Ocean Bottom Seismometers) off southern Lofoten and a newly published profile farther north show a strongly extended outer margin. Applying early seafloor half-spreading rates ( 30 mm/y) from other NAIP margin segments for 1 m.y. can account for 30 km extra extension, giving a factor of three crustal thinning, and gives a high strain rate of 3.2 ·10-14. Crustal breakup at the magma-poor Iberian Margin occurred at a low strain rate of 4.4·10-15, allowing the ascending mantle to cool, favoring tectonic extension over magmatism. Similar strain rates are found within the main Ethiopian Rift, but there is much magmatism and crustal separation is dominated by dike injection. Mantle tomography models show an exceptionally low seismic velocity below the area interpreted as an unusually hot upper mantle, which will favor magmatism. The transition from the Vøring Plateau to the Lofoten Margin can therefore be explained by the presence/absence of hot mantle plume material under the different segments during rifting. Only after significant extension and close to crustal breakup time did a minor amount of plume material reach the Lofoten/Vesterålen margin to cause some elevated but short-lived excess magmatism there.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V53D3135V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V53D3135V"><span>Monogenetic Arc Volcanism in the Central Andes: The "Hidden" Mafic Component in the Land of Andesite and Ignimbrite</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Alderwerelt, B. M.; Ukstins Peate, I.; Ramos, F. C.</p> <p>2016-12-01</p> <p>Faulting in the upper crust of the Central Andes has provided passage for small volumes of mafic magma to reach the surface, providing a window into petrogenetic processes in the region's deep crust and upper mantle. Mafic lavas are rare in the Central Andean region dominated by intermediate-composition arc volcanism and massive sheets of silicic ignimbrite, and provide key data on magmatic origin, evolution, and transport. This work characterizes fault-controlled, within-arc monogenetic eruptive centers representative of the most mafic volcanism in the Altiplano-Puna region of the Andes since (at least) the Mesozoic. Olivine-phyric basaltic andesite (54 wt% SiO2, 7.3 wt% MgO) at Cerro Overo maar and associated dome, La Albóndiga Grande, and an olivine-clinopyroxene flow (53 wt% SiO2, 6.7 wt% MgO) from Cordón de Puntas Negras have been erupted at the intersection of regional structural features and the modern volcanic arc. Bulk magma chemistry, radiogenic isotopes, and microanalyses of mineral and melt inclusion composition provide insight on the composition(s) of mafic magmas being delivered to the lowermost crust and the deep crustal processes which shape central Andean magma. Bulk major and trace elements follow regional arc differentiation trends and are clearly modified by crustal magmatic processes. In contrast, microanalyses reveal a much richer history with olivine-hosted melt inclusions recording multiple distinct magmas, including potential primary melts. Single crystal olivine 87Sr/86Sr from Cerro Overo (0.7041-0.7071) define a broader range than whole rock (0.7062-0.7065), indicating preservation of juvenile melt in olivine-hosted inclusions lost at the whole rock scale. Mineral chemistry (via EMPA) P-T calculations define a petrogenetic history for these endmember lavas. Field mapping, bulk chemistry, and microanalyses outline the generation, storage, transportation, and eventual eruption of the "hidden" mafic component of the Andean arc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V13E2656S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V13E2656S"><span>Magmatism at different crustal levels in the ancient North Cascades magmatic arc</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shea, E. K.; Bowring, S. A.; Miller, R. B.; Miller, J. S.</p> <p>2013-12-01</p> <p>The mechanisms of magma ascent and emplacement inferred from study of intrusive complexes have long been the subject of intense debate. Current models favor incremental construction based on integration of field, geochemical, geochronologic, and modeling studies. Much of this work has been focused on a single crustal level. However, study of magmatism throughout the crust is critical for understanding how magma ascends through and intrudes surrounding crustal material. Here, we present new geochronologic and geochemical work from intrusive complexes emplaced at a range of crustal depths in the Cretaceous North Cascades magmatic arc. These complexes were intruded between 92 and 87 Ma at depths of at ≤5 -10 km, ~20 km, and ~25 km during this time. U-Pb CA-TIMS geochronology in zircon can resolve <0.1% differences in zircon dates and when combined with detailed field relationships allow new insights into how magmatic systems are assembled. We can demonstrate highly variable rates of intrusion at different crustal levels: the shallow-crustal (5-10 km) Black Peak intrusive complex was assembled semi-continuously over ~5 My, while the deep-crustal (25-30 km) Tenpeak intrusive complex was assembled in brief, high-flux events over ~2.6 My. Between these bodies is the Seven-Fingered Jack-Entiat intrusive complex, a highly elongate amalgamation of intrusions recording two episodes of magmatism between~92-88 Ma and ~80-77 Ma. Each of these complexes provides a window into crustal processes that occur at different depths. Our data suggest assembly of the Black Peak intrusive complex occurred via a series of small (0.5-2 km2) magmatic increments from ~92 Ma to ~87 Ma. Field relations and zircon trace element geochemistry indicate each of these increments were emplaced and crystallized as closed systems-we find no evidence for mixing between magmas in the complex. However, zircon inheritance becomes more common in younger intrusions, indicating assimilation of older plutonic material, possibly during magma production or transport. The Seven-Fingered Jack intrusive complex, emplaced around 15-20 km, preserves a much more discontinuous record of intrusion than the Black Peak. Our data indicate major magmatism in the complex occurred between ~92.1-91.1 Ma. Inheritance in the Seven-Fingered Jack is common, particularly along contacts between intrusions. The Tenpeak intrusive complex, assembled between ~92 Ma and 89 Ma, represents one of the deepest exhumed complexes in the North Cascades. Our geochronology indicates that plutons comprising the complex were intruded rapidly (<200 ka) and followed by periods of magmatic quiescence. Contact relations between contemporaneous intrusions are often mixed, further supporting rapid assembly. Zircon systematics in the Tenpeak are relatively simple, showing no evidence for inheritance from the surrounding host rock or from earlier intrusions. However, zircon oxygen isotope data indicates many magmas contain significant crustal input. The Black Peak, Seven-Fingered Jack, and Tenpeak intrusions illustrate the complicated nature of magmatism at different crustal levels in the 92-87 Ma North Cascades magmatic arc. Our data support incremental assembly of these complexes, but show that many features, such as style of emplacement, zircon chemical and temporal systematics, and magma composition vary between these intrusions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V31C0516S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V31C0516S"><span>The Acoculco caldera magmas: genesis, evolution and relation with the Acoculco geothermal system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sosa-Ceballos, G.; Macías, J. L.; Avellán, D.</p> <p>2017-12-01</p> <p>The Acoculco Caldera Complex (ACC) is located at the eastern part of the Trans Mexican Volcanic Belt; México. This caldera complex have been active since 2.7 Ma through reactivations of the system or associated magmatism. Therefore the ACC is an excellent case scenario to investigate the relation between the magmatic heat supply and the evolution processes that modified magmatic reservoirs in a potential geothermal field. We investigated the origin and the magmatic processes (magma mixing, assimilation and crystallization) that modified the ACC rocks by petrography, major oxides-trace element geochemistry, and isotopic analysis. Magma mixing is considered as the heat supply that maintain active the magmatic system, whereas assimilation yielded insights about the depth at which processes occurred. In addition, we performed a series of hydrothermal experiments in order to constrain the storage depth for the magma tapped during the caldera collapse. Rocks from the ACC were catalogued as pre, syn and post caldera. The post caldera rocks are peralkaline rhyolites, in contrast to all other rocks that are subalkaline. Our investigation is focus to investigate if the collapse modified the plumbing system and the depth at which magmas stagnate and recorded the magmatic processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.9167R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.9167R"><span>Origin of maar volcanoes: external water, internal volatiles, or both?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rausch, J.; Schmincke, H.-U.</p> <p>2012-04-01</p> <p>The origin of maar volcanoes has been interpreted as due to explosive magma-water interaction for more than 40 years (Fisher and Waters 1970; Lorenz 1973 and Fisher and Schmincke 1984). Earlier suspicions that CO2-degassing plays a role in maar formation (Schmincke 1977) are now followed up by re-examining maar deposits of four different compositions in the maar-type locality (Eifel, Germany). These four compositions comprise: (1) melilite-nephelinites (West Eifel), (2) leucitites/nephelinites (West Eifel), (3) Na-rich basanites (West Eifel), and (4) K-rich basanites (East Eifel). At present, we focus on high-resolution stratigraphy, sedimentology, grain-size distribution, component analysis (accidental vs. juvenile clasts), and morphological and textural particle studies, accompanied by standard glass and bulk chemical and mineralogical analyses. Interestingly, maar deposits of highly silica-undersaturated and - by inference - CO2-rich composition (melilite-nephelinites and leucitites/nephelinites) show features contrasting with the classical catalogue of criteria for hydroclastic fragmentation (Fisher and Schmincke 1984). Their deposits are medium- to coarse-grained (MdØ mainly: 2 - 8 mm), mostly moderate- to well-sorted (σØ mainly: 1 - 2.5) and in some cases juvenile-rich (up to 50-70 wt. %). Transport and depositional mechanisms comprise a mixture of surge and fallout differing from the general assumption that maar deposits are dominated by surges. Additionally, features of juvenile clasts of highly silica-undersaturated composition largely differ from the features of "classic" hydroclastic particles (e.g.: dense, blocky, glassy shards). Juvenile clasts of highly silica-undersaturated composition show: (a) round- to semiround morphologies, (b) slight- to moderate vesicularities, (c) near absence of glassy material, (d) abundance of deep-seated xenoliths (mantle and lower crust), (e) agglutinated lava rinds enveloping the mantle- and crust-xenoliths, and (f) carbonate fragments, most probably of magmatic origin, within the groundmass. In contrast, basanitic maar deposits - by inference with low CO2 concentrations - and particularly their juvenile clasts show more conventional features of hydroclastic fragmentation processes. They are finer-grained, moderate- to poorly-sorted, extremely lithoclast-rich, and the juvenile clasts are generally angular, slightly- to non-vesicular and glassy. Moreover, deep-seated xenoliths and carbonate fragments are lacking. At this stage in our study we postulate that the high CO2 concentrations of highly silica-undersaturated maar volcanoes in the West Eifel could have played a significant role in maar-forming processes. These magmas may have undergone magmatic fragmentation due to rapid CO2-exsolution prior to shallow magma-water interaction resulting in explosive eruptions governed by both, magmatic and phreatomagmatic fragmentation and eruptive processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T32C..08D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T32C..08D"><span>The Atlantis Bank Gabbro Massif, SW Indian Ridge: the Largest Know Exposure of the Lower Crust in the Oceans</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dick, H. J.; Kvassnes, A. J.; Kinoshita, H.; MacLeod, C. J.; Robinson, P. T.</p> <p>2017-12-01</p> <p>Until the discovery of oceanic core complexes little was known and much inferred about the lower ocean crust at slow-spreading ridges. Their study shows the ocean crust isn't simply a uniform layer-cake of pillow lavas, sheeted dikes and gabbros, but is highly variable in thickness, composition and architecture, and even absent over large regions. The 660 km2 Atlantis Bank Gabbro Massif in the rift-mountains of the SW Indian Ridge flanking the Atlantis II Transform is the magmatic end member for ocean core complexes, and best approximates `average' slow-spread crust. Thus it has been a focus for drilling since its discovery in 1986, leading to the current attempt to drill to Moho there (Project SloMo). There are 3 ODP and IODP drill holes on its crest: 1508-m deep Hole 735B, 158-m deep Hole 1105A, and 809.4-m deep Hole U1473. These provide a 200 Kyr view of lower crustal accretion at a slow-spread ocean ridge. Here we extend this view to 2.7 Myr. Mapping and sampling shows the gabbro massif extends nearly the length of a single 2nd order magmatic ridge segment. With numerous inliers of the dike-gabbro transition at numerous locations, and a crust-mantle boundary, traced for 30-km along the transform wall, it would appear to represent a full section of the lower crust. As Moho is at 5.5 ± 1 km mbsf near Hole 735B, and 4.5 km beneath the transform, it is likely a serpentinization front. The crust-mantle boundary was crossed by dives at 4 locations. In each case gabbros at the base of the crust crystallized from melt that had previously fractionated 50% or more from a likely parent. Thus the gabbro massif must be laterally zoned, and the parental mantle melts had to have been emplaced at the center of the paleo-ridge segment, before intruding laterally to the distal end of the complex. Gabbros on a lithospheric flow line down the center of the massif closely resemble those from the drill holes. This shows that while lateral variations in crustal composition and thickness exist at Atlantis Bank, we can extend the conclusions derived from drilling at Hole U1473 that there is a continuum of accretionary magmatic and tectonic processes for 2.7 Myr, and a centrally located deep hole through the lower crust and mantle there will likely be representative of the 660-km2 Atlantis Bank gabbro massif as a whole.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T41A0596G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T41A0596G"><span>Mediterranean Magmatism: Bimodal Melting Patterns Inferred By Numerical Models</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gogus, O.; Ueda, K.; Gerya, T.</p> <p>2017-12-01</p> <p>Melt production by the decompression melting of the asthenospheric mantle occurs in the course of the lithospheric foundering process. The magmatic imprints of such foundering process are often described as anorogenic magmatism and this is usually followed by the orogenic magmatism, related to the subduction events in the Mediterranean region. Here, by using numerical geodynamic experiments we explore various styles of magmatism, their interaction with each other and the amount of magma production in the ocean subduction to slab peel away/delamination configuration. Model results show that the early stage of the ocean subduction under the continental lithosphere is associated with the short pulse of wet melting-orogenic magmatism and then the melting process is mostly dominated by dry melting-anorogenic magmatism, until the slab break-off occurs. While the melt types mixes/alternates during the evolution of the model, the wet melting facilitates the production of dry melting because of its uprising and emplacement under the crust where dry melting is present. The melt production pattern and the amount does not change significantly with different depths of the slab break-off (160-200 km). Model results can explain the transition from the calc-alkaline to alkaline volcanism in the western Mediterranean (Alboran domain) where ocean subduction to delamination has been interpreted.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V43D0552C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V43D0552C"><span>Brine/Rock Interaction in Deep Oceanic Layered Gabbros: Petrological Evidence from Cl-Rich Amphibole, High-Temperature Hydrothermal Veins, and Experiments</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Currin Sala, A. M.; Koepke, J.; Almeev, R. R.; Teagle, D. A. H.; Zihlmann, B.; Wolff, P. E.</p> <p>2017-12-01</p> <p>Evidence of high temperature brine/rock interaction is found in hydrothermal veins and dykelets that cross-cut layered olivine gabbros in the deep palaeocrust of the Sumail Ophiolite, Sultanate of Oman. Here we present petrological and geochemical data from these samples, and an experimental attempt to simulate brine/gabbro interaction using externally heated cold seal pressure vessels. The studied natural veins and dykelets contain pargasite, hornblende, actinolite, and Cl-rich pargasite with up to 5 wt% Cl, showing a range of formation conditions from magmatic to metamorphic (hydrothermal) and thus a complex history of brine/rock interaction. In addition, the isotopic study of the radiogenic 87/86Sr and stable 18O in different amphibole types provide an estimate for the extent of seawater influence as alteration agent in the veins of the studied samples. Experiments performed at 750 °C and 200 MPa with different starting materials (chlorine-free amphibole, olivine gabbro powder) and 20 wt% NaCl aqueous brine, illustrate the process by which gabbro-hosted amphibole-rich veins evolve at subsolidus temperatures in the presence of a seawater-derived fluid. Our results demonstrate a decrease in olivine, plagioclase and magnetite content in favour of hastingsite, pargasite and magnesiohornblende, a decrease of IVAl and Ti in the starting amphibole, and an increase in Cl in amphibole, up to 0.2 Cl wt%. Our experiments show the change of magmatic pargasite towards more magnesium and silica-rich end members with results comparable to mildly chlorine-rich pargasites and hornblendes found in the natural samples studied. However, the experimental setup also presents limitations in the attainment of very high-chlorine amphibole (up to 5 wt%). Our analytical and experimental results provide further evidence for the existence of a hydrothermal cooling system in the deep oceanic crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.8715L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.8715L"><span>The 2007 and 2014 eruptions of Stromboli at match: monitoring the potential occurrence of effusion-driven basaltic paroxysmal explosions from a volcanic CO2 flux perspective</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liuzzo, Marco; Aiuppa, Alessandro; Salerno, Giuseppe; Burton, Mike; Federico, Cinzia; Caltabiano, Tommaso; Giudice, Gaetano; Giuffrida, Giovanni</p> <p>2015-04-01</p> <p>The recent effusive unrests of Stromboli occurred in 2002 and 2007 were both punctuated by short-lived, violent paroxysmal explosions generated from the volcano's summit craters. When effusive activity recently resumed on Stromboli, on 6 August 2014, much concern was raised therefore on whether or not a paroxysm would have occurred again. The occurrence of these potentially hazardous events has stimulated research toward understanding the mechanisms through which effusive eruptions can perturb the volcano's plumbing system, to eventually trigger a paroxysm. The anomalously large CO2 gas emissions measured prior to the 15 March 2007 paroxysmal explosion of Stromboli [1] have first demonstrated the chance to predict days in advance the effusive-to-explosive transition. Here 2007 and 2014 volcanic CO2 flux records have been compared for exploring causes/conditions that had not triggered any paroxysm event in the 2014 case. We show that the 2007 and 2014 datasets shared both similarities and remarkable differences. The pre-eruptive trends of CO2 and SO2 flux emissions were strikingly similar in both 2007 and 2014, indicating similar conditions within the plumbing system prior to onset of both effusive crises. In both events, the CO2 flux substantially accelerated (relative to the pre-eruptive mean flux) after onset of the effusion. However, this CO2 flux acceleration was a factor 3 lower in 2014 than in 2007, and the excess CO2 flux (the fraction of CO2 not associated with the shallowly emplaced/erupted magma, and therefore contributed by the deep magmatic system) never returned to the very high levels observed prior to the 15 March 2007 paroxysm. We conclude therefore that, although similar quantities of magma were effusively erupted in 2007 and 2014, the deep magmatic system was far less perturbed in the most recent case. We speculate that the rate at which the deep magmatic system is decompressed, rather than the level of de-compression itself, determine if the deep Stromboli's plumbing system is prone to erupt in a paroxysm, or not. [1] A. Aiuppa et al., Geophys Res Lett, 2010.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.S13B0667M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.S13B0667M"><span>Analysis of Deep Long-Period Subglacial Seismicity in Marie Byrd Land, Antarctica</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McMahon, N. D.; Aster, R. C.; Myers, E. K.; Lough, A. C.</p> <p>2017-12-01</p> <p>We utilize subspace detection methodology to extend the detection and analysis of deep, long-period seismic activity associated with the subglacial and lower crust magmatic complex beneath the Executive Committee Range volcanoes of Marie Byrd Land (Lough et al., 2013). The Marie Byrd Land (MBL) volcanic province is a remote continental region that is almost completely covered by the West Antarctic Ice Sheet (WAIS). The southern extent of Marie Byrd Land lies within the West Antarctic Rift System (WARS), which includes the volcanic Executive Committee Range. Lough et al. noted that seismic stations in the POLENET/ANET seismic network detected two swarms of seismic activity during 2010 and 2011. These events have been interpreted as deep, long-period (DLP) earthquakes based on their depth (25-40 km), tectonic context, and low frequency spectra. The DLP events in MBL lie beneath an inferred volcanic edifice that is visible in ice penetrating radar images via subglacial topography and intraglacial ash deposits, and have been interpreted as a present location of Moho-proximal magmatic activity. The magmatic swarm activity in MBL provides a promising target for advanced subspace detection, and for the temporal, spatial, and event size analysis of an extensive deep long period earthquake swarm using a remote and sparse seismographic network. We utilized a catalog of 1370 traditionally identified DLP events to construct subspace detectors for the nine nearest stations using two years of data spanning 2010-2011. Via subspace detection we increase the number of observable detections more than 70 times at the highest signal to noise station while decreasing the overall minimum magnitude of completeness. In addition to the two previously identified swarms during early 2010 and early 2011, we find sustained activity throughout the two years of study that includes several previously unidentified periods of heightened activity. These events have a very high Gutenberg-Richter b-value (>2.0). We also note evidence of continuing seismicity through 2015 examining data from the small number of longer-running POLENET stations in the region.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.S43F..07A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.S43F..07A"><span>Deep Long-period Seismicity Beneath the Executive Committee Range, Marie Byrd Land, Antarctica, Studied Using Subspace Detection</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aster, R. C.; McMahon, N. D.; Myers, E. K.; Lough, A. C.</p> <p>2015-12-01</p> <p>Lough et al. (2014) first detected deep sub-icecap magmatic events beneath the Executive Committee Range volcanoes of Marie Byrd Land. Here, we extend the identification and analysis of these events in space and time utilizing subspace detection. Subspace detectors provide a highly effective methodology for studying events within seismic swarms that have similar moment tensor and Green's function characteristics and are particularly effective for identifying low signal-to-noise events. Marie Byrd Land (MBL) is an extremely remote continental region that is nearly completely covered by the West Antarctic Ice Sheet (WAIS). The southern extent of Marie Byrd Land lies within the West Antarctic Rift System (WARS), which includes the volcanic Executive Committee Range (ECR). The ECR shows north-to-south progression of volcanism across the WARS during the Holocene. In 2013, the POLENET/ANET seismic data identified two swarms of seismic activity in 2010 and 2011. These events have been interpreted as deep, long-period (DLP) earthquakes based on depth (25-40 km) and low frequency content. The DLP events in MBL lie beneath an inferred sub-WAIS volcanic edifice imaged with ice penetrating radar and have been interpreted as a present location of magmatic intrusion. The magmatic swarm activity in MBL provides a promising target for advanced subspace detection and temporal, spatial, and event size analysis of an extensive deep long period earthquake swarm using a remote seismographic network. We utilized a catalog of 1,370 traditionally identified DLP events to construct subspace detectors for the six nearest stations and analyzed two years of data spanning 2010-2011. Association of these detections into events resulted in an approximate ten-fold increase in number of locatable earthquakes. In addition to the two previously identified swarms during early 2010 and early 2011, we find sustained activity throughout the two years of study that includes several previously unidentified periods of heightened activity. Correlation with large global earthquakes suggests that the DLP activity is not sensitive to remote teleseismic triggering.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.493...47F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.493...47F"><span>Progressive reactivation of the volcanic plumbing system beneath Tolbachik volcano (Kamchatka, Russia) revealed by long-period seismicity</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Frank, William B.; Shapiro, Nikolaï M.; Gusev, Alexander A.</p> <p>2018-07-01</p> <p>After lying dormant for 36 yr, the Tolbachik volcano of the Klyuchevskoy group started to erupt on 27 November 2012. We investigate the preparatory phase of this eruption via a statistical analysis of the temporal behavior of long-period (LP) earthquakes that occurred beneath this volcanic system. The LP seismicity occurs close to the surface beneath the main volcanic edifices and at 30 km depth in the vicinity of a deep magmatic reservoir. The deep LP earthquakes and those beneath the Klyuchevskoy volcano occur quasi-periodically, while the LP earthquakes beneath Tolbachik are clustered in time. As the seismicity rate increased beneath Tolbachik days before the eruption, the level of the time clustering decreased. We interpret this as a manifestation of the evolution of the volcano plumbing system. We suggest that when a plumbing system awakes after quiescence, multiple cracks and channels are reactivated simultaneously and their interaction results in the strong time clustering of LP earthquakes. With time, this network of channels and cracks evolves into a more stable state with an overall increased permeability, where fluids flow uninhibited throughout the plumbing system except for a few remaining impediments that continue to generate seismic radiation. The inter-seismic source interaction and the level of earthquake time clustering in this latter state is weak. This scenario suggests that the observed evolution of the statistical behavior of the shallow LP seismicity beneath Tolbachik is an indicator of the reactivation and consolidation of the near-surface plumbing system prior to the Tolbachik eruption. The parts of the plumbing system above the deep magmatic reservoir and beneath the Klyuchevskoy volcano remain in nearly permanent activity, as demonstrated by the continuous occurrence of the deep LP earthquakes and very frequent Klyuchevskoy eruptions. This implies that these parts of the plumbing system remain in a stable permeable state and contain a few weakly interacting seismogenic sources. Our results provide new constraints on future mechanical models of the magmatic plumbing systems and demonstrate that the level of time clustering of LP earthquakes can be a useful parameter to infer information about the state of the plumbing system.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.248..272M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.248..272M"><span>Revealing magma degassing below closed-conduit active volcanoes: Geochemical features of volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.</p> <p>2016-04-01</p> <p>The elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions have been measured for rocks at various degrees of evolution and belonging to high-K calcalkaline-shoshonitic and shoshonitic-potassic series in order to cover the entire volcanological history of Vulcano Island (Italy). The major- and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the theoretical value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic history of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-erupted Vulcanello latites (Punta del Roveto), which have anomalously high He isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs, since an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He-isotope ratios between fluid inclusions and fumarolic gases shows that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that the most probable magma which actually feeds the fumarolic emissions is a latitic body that ponded at about 3-3.5 km of depth and is flushed by fluids coming from a deeper and basic magma.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8144M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8144M"><span>Revealing the magmas degassing below closed-conduit active volcanoes: noble gases in volcanic rocks versus fumarolic fluids at Vulcano (Aeolian Islands, Italy)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mandarano, Michela; Paonita, Antonio; Martelli, Mauro; Viccaro, Marco; Nicotra, Eugenio; Millar, Ian L.</p> <p>2016-04-01</p> <p>With the aim to constrain the nature of magma currently feeding the fumarolic field of Vulcano, we measured the elemental and isotopic compositions of noble gases (He, Ne, and Ar) in olivine- and clinopyroxene-hosted fluid inclusions in high-K calcalcaline-shoshonitic and shoshonitic-potassic series so as to cover the entire volcanological history of Vulcano Island (Italy). The major and trace-element concentrations and the Sr- and Pb-isotope compositions for whole rocks were integrated with data obtained from the fluid inclusions. 3He/4He in fluid inclusions is within the range of 3.30 and 5.94 R/Ra, being lower than the value for the deep magmatic source expected for Vulcano Island (6.0-6.2 R/Ra). 3He/4He of the magmatic source is almost constant throughout the volcanic record of Vulcano. Integration of the He- and Sr-isotope systematics leads to the conclusion that a decrease in the He-isotope ratio of the rocks is mainly due to the assimilation of 10-25% of a crustal component similar to the Calabrian basement. 3He/4He shows a negative correlation with Sr isotopes except for the last-emitted Vulcanello latites (Punta del Roveto), which have high He- and Sr-isotope ratios. This anomaly has been attributed to a flushing process by fluids coming from the deepest reservoirs. Indeed, an input of deep magmatic volatiles with high 3He/4He values increases the He-isotope ratio without changing 87Sr/86Sr. A comparison of the He isotope ratios between fluid inclusions and fumarolic gases showed that only the basalts of La Sommata and the latites of Vulcanello have comparable values. Taking into account that the latites of Vulcanello relate to one of the most-recent eruptions at Vulcano (in the 17th century), we infer that that the most probable magma which actually feeds the fumarolic emissions is a latitic body ponding at about 3-3.5 km of depth and flushed by fluids coming from a deeper and basic magma.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.3583S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.3583S"><span>Latest Cambrian-Early Ordovician rift-related magmatic activity in the Kouřim Unit, Bohemian Massif</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Soejono, Igor; Machek, Matej; Sláma, Jiří; Janoušek, Vojtěch</p> <p>2017-04-01</p> <p>Pre-collisional history of high-grade Variscan complexes is mostly difficult to reveal, due to intense reworking during the development of the orogenic belt. An ancient magmatism could provide a unique possibility to study it. The Kouřim Unit represents an extensive pre-Variscan plutonic body involved into the tectonic collage of the Kutná Hora Crystalline Complex, at the northern margin of the Moldanubian Domain in the Bohemian Massif. The LA-ICP-MS zircon ages and geochemical characteristics of (meta-)igneous rocks from the Kouřim Unit allow us to determine the timing and nature of magmatic activity within this part of the Bohemian Massif and thus to decipher its pre-Variscan evolution. The Kouřim Unit is composed of strongly metamorphosed and deformed sequence of magmatic rocks, dominated mainly by various types of migmatites, coarse-grained orthogneisses and minor metadiorites. The newly obtained LA-ICP-MS U-Pb zircon ages of four orthogneisses ranging between 486 ± 2 Ma and 484 ± 2 Ma are interpreted as timing the magma crystallization. The single metadiorite gave concordia age of 337 ± 2 Ma interpreted as the age of migmatitization. Few discordant older ages from metadiorite are considered as older xenocrysts more or less reset during the Variscan metamorphism. The orthogneisses are acid (SiO2 = 68.6-76.4 wt. %), exclusively subaluminous and seem to form a single calc-alkaline trend, whereas the metadiorite is intermediate (SiO2 = 54.3 wt. %; mg# = 61), distinctly metaluminous and displays tholeiitic character. The chondrite-normalized REE patterns for the orthogneisses show LREE enrichment (LaN/YbN = 1.5-8.9) and deep negative Eu anomalies (Eu/Eu* = 0.42-0.32); the NMORB-normalized spiderplots feature LILE/HFSE enrichment with deep negative Nb- Ta-Ti anomalies. In contrast, both patterns of metadiorite resemble those of NMORB (LaN/YbN = 0.5, Eu/Eu* = 0.96). The apparent magmatic arc-like geochemical signature of the orthogneisses is interpreted as inherited from the source, represented most likely by recycled immature arc-related material (?metagraywackes). The real tectonic setting of this Late Cambrian magmatic activity seems rather indicated by the within-plate geochemistry of the metadiorite. These results bring further evidence for the presence of the Late Cambrian-Early Ordovician extensional event documented throughout the basement of the European Variscan Belt. Together with other occurrences of bimodal magmatism, as well as metamorphic and sedimentary record, indicate an important period of lithospheric thinning. This overall Early Palaeozoic rift-related architecture is often considered as a consequence of the Rheic Ocean opening.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3449286','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3449286"><span>Why large porphyry Cu deposits like high Sr/Y magmas?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Chiaradia, Massimo; Ulianov, Alexey; Kouzmanov, Kalin; Beate, Bernardo</p> <p>2012-01-01</p> <p>Porphyry systems supply most copper and significant gold to our economy. Recent studies indicate that they are frequently associated with high Sr/Y magmatic rocks, but the meaning of this association remains elusive. Understanding the association between high Sr/Y magmatic rocks and porphyry-type deposits is essential to develop genetic models that can be used for exploration purposes. Here we present results on a Pleistocene volcano of Ecuador that highlight the behaviour of copper in magmas with variable (but generally high) Sr/Y values. We provide indirect evidence for Cu partitioning into a fluid phase exsolved at depths of ~15 km from high Sr/Y (>70) andesitic magmas before sulphide saturation. This lends support to the hypothesis that large amounts of Cu- and S-bearing fluids can be accumulated into and released from a long-lived high Sr/Y deep andesitic reservoir to a shallower magmatic-hydrothermal system with the potential of generating large porphyry-type deposits. PMID:23008750</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23008750','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23008750"><span>Why large porphyry Cu deposits like high Sr/Y magmas?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chiaradia, Massimo; Ulianov, Alexey; Kouzmanov, Kalin; Beate, Bernardo</p> <p>2012-01-01</p> <p>Porphyry systems supply most copper and significant gold to our economy. Recent studies indicate that they are frequently associated with high Sr/Y magmatic rocks, but the meaning of this association remains elusive. Understanding the association between high Sr/Y magmatic rocks and porphyry-type deposits is essential to develop genetic models that can be used for exploration purposes. Here we present results on a Pleistocene volcano of Ecuador that highlight the behaviour of copper in magmas with variable (but generally high) Sr/Y values. We provide indirect evidence for Cu partitioning into a fluid phase exsolved at depths of ~15 km from high Sr/Y (>70) andesitic magmas before sulphide saturation. This lends support to the hypothesis that large amounts of Cu- and S-bearing fluids can be accumulated into and released from a long-lived high Sr/Y deep andesitic reservoir to a shallower magmatic-hydrothermal system with the potential of generating large porphyry-type deposits.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://geosphere.geoscienceworld.org/cgi/content/abstract/7/5/1102','USGSPUBS'); return false;" href="http://geosphere.geoscienceworld.org/cgi/content/abstract/7/5/1102"><span>Petrologic, tectonic, and metallogenic evolution of the Ancestral Cascades magmatic arc, Washington, Oregon, and northern California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>du Bray, Edward A.; John, David A.</p> <p>2011-01-01</p> <p>Present-day High Cascades arc magmatism was preceded by ~40 m.y. of nearly cospatial magmatism represented by the ancestral Cascades arc in Washington, Oregon, and northernmost California (United States). Time-space-composition relations for the ancestral Cascades arc have been synthesized from a recent compilation of more than 4000 geochemical analyses and associated age data. Neither the composition nor distribution of ancestral Cascades magmatism was uniform along the length of the ancestral arc through time. Initial (>40 to 36 Ma) ancestral Cascades magmatism (mostly basalt and basaltic andesite) was focused at the north end of the arc between the present-day locations of Mount Rainier and the Columbia River. From 35 to 18 Ma, initial basaltic andesite and andesite magmatism evolved to include dacite and rhyolite; magmatic activity became more voluminous and extended along most of the arc. Between 17 and 8 Ma, magmatism was focused along the part of the arc coincident with the northern two-thirds of Oregon and returned to more mafic compositions. Subsequent ancestral Cascades magmatism was dominated by basaltic andesite to basalt prior to the post–4 Ma onset of High Cascades magmatism. Transitional tholeiitic to calc-alkaline compositions dominated early (before 40 to ca. 25 Ma) ancestral Cascades eruptive products, whereas the majority of the younger arc rocks have a calc-alkaline affinity. Tholeiitic compositions characteristic of the oldest ancestral arc magmas suggest development associated with thin, immature crust and slab window processes, whereas the younger, calc-alkaline magmas suggest interaction with thicker, more evolved crust and more conventional subduction-related magmatic processes. Presumed changes in subducted slab dip through time also correlate with fundamental magma composition variation. The predominance of mafic compositions during latest ancestral arc magmatism and throughout the history of modern High Cascades magmatism probably reflects extensional tectonics that dominated during these periods of arc magmatism. Mineral deposits associated with ancestral Cascades arc rocks are uncommon; most are small and low grade relative to those found in other continental magmatic arcs. The small size, low grade, and dearth of deposits, especially in the southern two-thirds of the ancestral arc, probably reflect many factors, the most important of which may be the prevalence of extensional tectonics within this arc domain during this magmatic episode. Progressive clockwise rotation of the forearc block west of the evolving Oregon part of the ancestral Cascades magmatism produced an extensional regime that did not foster significant mineral deposit formation. In contrast, the Washington arc domain developed in a transpressional to mildly compressive regime that was more conducive to magmatic processes and hydrothermal fluid channeling critical to deposit formation. Small, low-grade porphyry copper deposits in the northern third of the ancestral Cascades arc segment also may be a consequence of more mature continental crust, including a Mesozoic component, beneath Washington north of Mount St. Helens.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016303','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016303"><span>Recent crustal subsidence at Yellowstone Caldera, Wyoming</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Dzurisin, D.; Savage, J.C.; Fournier, R.O.</p> <p>1990-01-01</p> <p>Following a period of net uplift at an average rate of 15??1 mm/year from 1923 to 1984, the east-central floor of Yellowstone Caldera stopped rising during 1984-1985 and then subsided 25??7 mm during 1985-1986 and an additional 35??7 mm during 1986-1987. The average horizontal strain rates in the northeast part of the caldera for the period from 1984 to 1987 were: {Mathematical expression}1 = 0.10 ?? 0.09 ??strain/year oriented N33?? E??9?? and {Mathematical expression}2 = 0.20 ?? 0.09 ??strain/year oriented N57?? W??9?? (extension reckoned positive). A best-fit elastic model of the 1985-1987 vertical and horizontal displacements in the eastern part of the caldera suggests deflation of a horizontal tabular body located 10??5 km beneath Le Hardys Rapids, i.e., within a deep hydrothermal system or within an underlying body of partly molten rhyolite. Two end-member models each explain most aspects of historical unrest at Yellowstone, including the recent reversal from uplift to subsidence. Both involve crystallization of an amount of rhyolitic magma that is compatible with the thermal energy requirements of Yellowstone's vigorous hydrothermal system. In the first model, injection of basalt near the base of the rhyolitic system is the primary cause of uplift. Higher in the magmatic system, rhyolite crystallizes and releases all of its magmatic volatiles into the shallow hydrothermal system. Uplift stops and subsidence starts whenever the supply rate of basalt is less than the subsidence rate produced by crystallization of rhyolite and associated fluid loss. In the second model, uplift is caused primarily by pressurization of the deep hydrothermal system by magmatic gas and brine that are released during crystallization of rhyolite and them trapped at lithostatic pressure beneath an impermeable self-sealed zone. Subsidence occurs during episodic hydrofracturing and injection of pore fluid from the deep lithostatic-pressure zone into a shallow hydrostatic-pressure zone. Heat input from basaltic intrusions is required to maintain Yellowstone's silicic magmatic system and shallow hydrothermal system over time scales longer than about 105 years, but for the historical time period crystallization of rhyolite can account for most aspects of unrest at Yellowstone, including seismicity, uplift, subsidence, and hydrothermal activity. ?? 1990 Springer-Verlag.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JVGR..192...57A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JVGR..192...57A"><span>Water-rock interaction in the magmatic-hydrothermal system of Nisyros Island (Greece)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ambrosio, Michele; Doveri, Marco; Fagioli, Maria Teresa; Marini, Luigi; Principe, Claudia; Raco, Brunella</p> <p>2010-04-01</p> <p>In this work, we investigated the water-rock interaction processes taking place in the hydrothermal reservoir of Nisyros through both: (1) a review of the hydrothermal mineralogy encountered in the deep geothermal borehole Nisyros-2; and (2) a comparison of the analytically-derived redox potentials and acidities of fumarolic-related liquids, with those controlled by redox buffers and pH buffers, involving hydrothermal mineral phases. The propylitic zone met in the deep geothermal borehole Nisyros-2, from 950 to 1547 m (total depth), is characterised by abundant, well crystallised epidote, adularia, albite, quartz, pyrite, chlorite, and sericite-muscovite, accompanied by less abundant anhydrite, stilpnomelane, wairakite, garnet, tremolite and pyroxene. These hydrothermal minerals were produced in a comparatively wide temperature range, from 230 to 300 °C, approximately. Hydrothermal assemblages are well developed from 950 to 1360 m, whereas they are less developed below this depth, probably due to low permeability. Based on the RH values calculated for fumarolic gases and for the deep geothermal fluids of Nisyros-1 and Nisyros-2 wells, redox equilibrium with the (FeO)/(FeO 1.5) rock buffer appears to be closely attained throughout the hydrothermal reservoir of Nisyros. This conclusion may be easily reconciled with the nearly ubiquitous occurrence of anhydrite and pyrite, since RH values controlled by coexistence of anhydrite and pyrite can be achieved by gas separation. The pH of the liquids feeding the fumarolic vents of Stephanos and Polybote Micros craters was computed, by means of the EQ3 code, based on the Cl- δD relationship which is constrained by the seawater-magmatic water mixing occurring at depth in the hydrothermal-magmatic system of Nisyros. The temperature dependence of analytically-derived pH values for the reservoir liquids feeding the fumarolic vents of Stephanos and Polybote Micros craters suggests that some unspecified pH buffer fixes the acidity of these reservoir liquids at values of 4.72-4.85 and 4.88-5.23, respectively. Many of these pH values are lower than those expected for the full-equilibrium condition, although they are close to those of the reservoir liquids of Nisyros-1, 5.16, and Nisyros-2, 4.87. It is likely that this excess of acidity-producing species, chiefly CO 2, promotes release of Fe(II) and Fe(III) to the reservoir liquids through rock dissolution, permitting the attainment of redox equilibrium with the (FeO)/(FeO 1.5) rock buffer, as already suggested by the late Werner Giggenbach.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI11A2335G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI11A2335G"><span>Record of Cyclical Massive Upwellings from the Pacific Large Low Shear Velocity Province in the Mesozoic</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gazel, E.; Madrigal, P.; Flores, K. E.; Bizimis, M.; Jicha, B. R.</p> <p>2016-12-01</p> <p>Global tomography and numerical models suggest that mantle plume occurrences are closely linked to the margins of the large low shear velocity provinces (LLSVPs). In these locations the ascent of material from the core-mantle boundary connects the deep Earth with surface processes through mantle plume activity, forming large igneous provinces (LIPs) and some of the modern hotspot volcanoes. Petrological and geodynamic evidence suggest a link between the formation of oceanic plateaus and the interactions of mantle plumes and mid-ocean ridges (MOR). Therefore, it is possible to trace the potential interactions between MORs and deep mantle plume upwellings by referencing the tectonic and magmatic evolution of the Pacific Plate in time to the current location of the LLSVP, considering the long-lived ( 500 Ma) existence of these thermochemical anomalies. We identified episodic upwellings of the Pacific LLSVP during the Mesozoic separated by 10 to 20 Ma, by reconstructing the kinematic evolution of the Pacific Plate in the last 170 Ma. The fact that the bulk emplacement of LIPs ( 120-80 Ma) in the Pacific coincides with the timing of the Cretaceous Normal Superchron, that can be related to fluctuations of mantle-core heat fluxes further supports the hypothesis of deep mantle origin for LIPs. The potential cyclicity of LIP emplacement could be tied to core heat fluctuations interacting with the lower mantle, the rheology contrast of material crossing the transition zone (either upwelling hot material or downgoing dense slabs as mantle avalanches), the rate of entrainment of recycled materials, or a combination of the processes mentioned. Recognizing patterns and possible cycles is crucial to the link between deep processes and life as these pulses impacted the marine biota resulting in episodes of anoxia and mass extinctions shortly after their eruption.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.491..160C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.491..160C"><span>Modulation of magmatic processes by CO2 flushing</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caricchi, Luca; Sheldrake, Tom E.; Blundy, Jon</p> <p>2018-06-01</p> <p>Magmatic systems are the engines driving volcanic eruptions and the source of fluids responsible for the formation of porphyry-type ore deposits. Sudden variations of pressure, temperature and volume in magmatic systems can produce unrest, which may culminate in a volcanic eruption and/or the abrupt release of ore-forming fluids. Such variations of the conditions within magmatic systems are commonly ascribed to the injection of new magma from depth. However, as magmas fractionating at depth or rising to the upper crust release CO2-rich fluids, the interaction between carbonic fluids and H2O-rich magmas stored in the upper crust (CO2 flushing), must also be a common process affecting the evolution of subvolcanic magma reservoirs. Here, we investigate the effect of gas injection on the stability and chemical evolution of magmatic systems. We calculate the chemical and physical evolution of magmas subjected to CO2-flushing using rhyolite-MELTS. We compare the calculations with a set of melt inclusion data for Mt. St. Helens, Merapi, Etna, and Stromboli volcanoes. We provide an approach that can be used to distinguish between melt inclusions trapped during CO2 flushing, magma ascent and decompression, or those affected by post-entrapment H2O-loss. Our results show that CO2 flushing is a widespread process in both felsic and mafic magmatic systems. Depending upon initial magma crystallinity and duration of CO2 input, flushing can either lead to volcanic eruption or fluid release. We suggest that CO2 flushing is a fundamental process modulating the behaviour and chemical evolution of crustal magmatic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.246..110G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.246..110G"><span>Long-lived interaction between hydrothermal and magmatic fluids in the Soultz-sous-Forêts granitic system (Rhine Graben, France)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gardien, Véronique; Rabinowicz, Michel; Vigneresse, Jean-Louis; Dubois, Michel; Boulvais, Philippe; Martini, Rossana</p> <p>2016-03-01</p> <p>The 5 km deep drilling at Soultz-sous-Forêts samples a granitic intrusion under its sedimentary cover. Core samples at different depths allow study of the evolving conditions of fluid-rock interaction, from the syn-tectonic emplacement of Hercynian granites at depth until post-cooling history and alteration close to the surface. Hydrogen, carbon and oxygen isotope compositions of CO2 and H2O have been measured in fluid inclusions trapped in magmatic quartz within samples collected along the drill core. Early Fluid Inclusions Assemblage (FIA) contains aqueous carbonic fluids whereas the latest FIA are H2O-rich. In the early FIA, the amount of CO2 and the δ13C value both decrease with depth, revealing two distinct sources of carbon, one likely derived from sedimentary carbonates (δ13C = - 2‰ V-PDB) and another from the continental crust (δ13C = - 9‰ V-PDB). The carbon isotope composition of bulk granites indicates a third carbon source of organic derivation (δ13C = - 20‰ V-PDB). Using a δD - δ18O plot, we argue that the water trapped in quartz grains is mainly of meteoric origin somewhat mixed with magmatic water. The emplacement of the Soultz-sous-Forêts granite pluton occurred in a North 030-040° wrench zone. After consolidation of the granite mush at 600 °C, sinistral shear (γ 1) concentrated the final leucocratic melt in vertical planes oriented along (σ1, σ2). Crystallization of this residual leucocratic melt occurred while shearing was still active. At a temperature of 550 °C, crystallization ended with the formation of vertical quartz veins spaced about 5 mm, and exhibiting a width of several cm. The quartz veins form a connected network of a few kilometers in height, generated during hydrothermal contraction of the intrusion. Quartz crystallization led to the exsolution of 30% by volume of the aqueous fluid. As quartz grains were the latest solid phase still plastic, shearing localized inside the connected quartz network. Aqueous fluid was thus concentrated in these vertical channels. Eventually, when the channels intersected the top of the crack network, water boiling caused the formation of primary inclusions. At the same temperature, the saline magmatic waters, which were denser than the meteoric waters, initiated thermohaline convection with the buoyant "cold" hydrothermal water layer. This mechanism can explain the mixing of surface and deep-seated fluids in the same primary inclusions trapped during the crystallization of magmatic minerals. This study, which separately considers fluid-rock interactions at the level of successive mineral facies, brings new insights into how fluids may be different, their origin and composition, and depending on tectono-thermal conditions, bears implications for eventual ore forming processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70029368','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70029368"><span>Origin of secondary sulfate minerals on active andesitic stratovolcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Zimbelman, D.R.; Rye, R.O.; Breit, G.N.</p> <p>2005-01-01</p> <p>Sulfate minerals in altered rocks on the upper flanks and summits of active andesitic stratovolcanoes result from multiple processes. The origin of these sulfates at five active volcanoes, Citlalte??petl (Mexico), and Mount Adams, Hood, Rainier, and Shasta (Cascade Range, USA), was investigated using field observations, petrography, mineralogy, chemical modeling, and stable-isotope data. The four general groups of sulfate minerals identified are: (1) alunite group, (2) jarosite group, (3) readily soluble Fe- and Al-hydroxysulfates, and (4) simple alkaline-earth sulfates such as anhydrite, gypsum, and barite. Generalized assemblages of spatially associated secondary minerals were recognized: (1) alunite+silica??pyrite??kaolinite?? gypsum??sulfur, (2) jarosite+alunite+silica; (3) jarosite+smectite+silica??pyrite, (4) Fe- and Al-hydroxysulfates+silica, and (5) simple sulfates+silica??Al-hydroxysulfates??alunite. Isotopic data verify that all sulfate and sulfide minerals and their associated alteration assemblages result largely from the introduction of sulfur-bearing magmatic gases into meteoric water in the upper levels of the volcanoes. The sulfur and oxygen isotopic data for all minerals indicate the general mixing of aqueous sulfate derived from deep (largely disproportionation of SO2 in magmatic vapor) and shallow (oxidation of pyrite or H2S) sources. The hydrogen and oxygen isotopic data of alunite indicate the mixing of magmatic and meteoric fluids. Some alunite-group minerals, along with kaolinite, formed from sulfuric acid created by the disproportionation of SO2 in a condensing magmatic vapor. Such alunite, observed only in those volcanoes whose interiors are exposed by erosion or edifice collapse, may have ??34S values that reflect equilibrium (350??50 ??C) between aqueous sulfate and H2S. Alunite with ??34S values indicating disequilibrium between parent aqueous sulfate and H2S may form from aqueous sulfate created in higher level low-temperature environments in which SO2 is scrubbed out by groundwater or where H2S is oxidized. Jarosite-group minerals associated with smectite in only slightly altered volcanic rock are formed largely from aqueous sulfate derived from supergene oxidation of hydrothermal pyrite above the water table. Soluble Al- and Fehydroxysulfates form in low-pH surface environments, especially around fumaroles, and from the oxidation of hydrothermal pyrite. Anhydrite/gypsum, often associated with native sulfur and occasionally with small amounts of barite, also commonly form around fumaroles. Some occurrences of anhydrite/gypsum may be secondary, derived from the dissolution and reprecipitation of soluble sulfate. Edifice collapse may also reveal deep veins of anhydrite/gypsum??barite that formed from the mixing of saline fluids with magmatic sulfate and dilute meteoric water. Alteration along structures associated with both hydrothermal and supergene sulfates, as well as the position of paleo-water tables, may be important factors in edifice collapse and resulting debris flows at some volcanoes. ?? 2004 Elsevier B.V. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70019296','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70019296"><span>The grand tour of the Ruby-East Humboldt metamorphic core complex, northeastern Nevada: Part 1 - Introduction & road log</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Snoke, A.W.; Howard, K.A.; McGrew, A.J.; Burton, B.R.; Barnes, C.G.; Peters, M.T.; Wright, J.E.</p> <p>1997-01-01</p> <p>The purpose of this geological excursion is to provide an overview of the multiphase developmental history of the Ruby Mountains and East Humboldt Range, northeastern Nevada. Although these mountain ranges are commonly cited as a classic example of a Cordilleran metamorphic core complex developed through large-magnitude, mid-Tertiary crustal extension, a preceding polyphase Mesozoic contractional history is also well preserved in the ranges. An early phase of this history involved Late Jurassic two-mica granitic magmatism, high-temperature but relatively low-pressure metamorphism, and polyphase deformation in the central Ruby Mountains. In the northern Ruby Mountains and East Humboldt Range, a Late Cretaceous history of crustal shortening, metamorphism, and magmatism is manifested by fold-nappes (involving Archean basement rocks in the northern East Humboldt Range), widespread migmatization, injection of monzogranitic and leucogranitic magmas, all coupled with sillimanite-grade metamorphism. Following Late Cretaceous contraction, a protracted extensional deformation partially overprinted these areas during the Cenozoic. This extensional history may have begun as early as the Late Cretaceous or as late as the mid-Eocene. Late Eocene and Oligocene magmatism occurred at various levels in the crust yielding mafic to felsic orthogneisses in the deep crust, a composite granitic pluton in the upper crust, and volcanic rocks at the surface. Movement along a west-rooted, extensional shear zone in the Oligocene and early Miocene led to core-complex exhumation. The shear zone produced mylonitic rocks about 1 km thick at deep crustal levels, and an overprint of brittle detachment faulting at shallower levels as unroofing proceeded. Megabreccias and other synextensional sedimentary deposits are locally preserved in a tilted, upper Eocene through Miocene stratigraphic sequence. Neogene magmatism included the emplacement of basalt dikes and eruption of rhyolitic rocks. Subsequent Basin and Range normal faulting, as young as Holocene, records continued tectonic extension.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T32A..01H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T32A..01H"><span>Model for the Evolution of an Oceanic Core Complex and its Hydrothermal Vent on the Ultraslow-Spreading Mid Cayman Spreading Center</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harding, J.; Van Avendonk, H. J.; Hayman, N. W.; Grevemeyer, I.; Peirce, C.</p> <p>2016-12-01</p> <p>The Mid Cayman Spreading Center (MCSC) is an ultraslow-spreading center (15 mm yr-1 full rate) along the Caribbean-North American plate boundary. Despite the paradigm that ultraslow-spreading centers are amagmatic and cold, two hydrothermal vent fields have recently been discovered along the MCSC. The Beebe Vent Field is a black smoker in the northern axial deep, and the Von Damm Vent Field (VDVF) is a moderate-temperature, talc precipitating vent found atop an oceanic core complex (OCC). This OCC, "Mt. Dent", is a large (3 km high) massif that formed beneath a detachment fault, which exhumed lower crustal and upper mantle material. The CaySeis Experiment was conducted in April, 2015 in order to collect wide-angle refraction data of the MCSC crust and upper mantle. We modeled the across-axis crustal structure of Mt. Dent as well as the surrounding lithosphere using 2.5D P-wave tomography. Using this tomographic model, along with geochemistry, we propose a model for the formation and evolution of the OCC Mt. Dent and the VDVF. A detachment fault formed in a magma-poor environment due to a pulse of magmatism, producing a large gabbro body that was then exhumed and rotated into the OCC footwall. Once magmatism waned and the gabbroic body cooled, the OCC was faulted and fractured due to plate flexure and increased tectonic extensional stress in the naturally cold and thick lithosphere. These faults provide a permeable and deep network of hydrothermal pathways that mine deep lithospheric heat and expose gabbro and fresh mantle peridotite. This model is consistent with the basalt geochemistry, hydrothermal fluid geochemistry, and the distribution of brittle vs. ductile structures along the detachment shear zone. The VDVF is therefore a product of a pulse of magmatism in an overall melt-poor environment, conditions that may be found at other ultraslow-spreading ridges.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JAESc.153..238W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JAESc.153..238W"><span>Carboniferous - Early Permian magmatic evolution of the Bogda Range (Xinjiang, NW China): Implications for the Late Paleozoic accretionary tectonics of the SW Central Asian Orogenic Belt</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wali, Guzalnur; Wang, Bo; Cluzel, Dominique; Zhong, Linglin</p> <p>2018-03-01</p> <p>The Late Paleozoic magmatic evolution of the Bogda Range (Chinese North Tianshan) is important for understanding the accretionary history of the Central Asian Orogenic Belt. We investigated the Carboniferous and Lower Permian volcanic and sedimentary sequences of the Daheyan section, southern Bogda Range, and present new zircon U-Pb ages and whole-rock geochemical data for the volcanic rocks. One Carboniferous rhyolite is dated at 298 ± 8 Ma; a Permian basalt yielded many Proterozoic zircon xenocrysts, and its maximum age (∼297 Ma) is constrained by the detrital zircon ages of the sandstone that stratigraphically underlies it. These volcanic rocks belong to calc-alkaline series. We further synthesize previous geochronological, geochemical and isotopic data of magmatic and sedimentary rocks in the Bogda Range. The available data indicate that the magmatism occurred continuously from 350 Ma to 280 Ma. A comprehensive analysis allows us to propose that: (1) the Carboniferous to Early Permian magmatic rocks of the Bogda Range generally show consistent arc-type features; (2) increasing mantle input through time suggests intra-arc extension in a supra-subduction zone; (3) the localized occurrence of Early Permian alkaline pillow basalts and deep water sediments close to the major shear zone advocate a transtensional crustal thinning during the transition from Carboniferous convergence to Early Permian transcurrent tectonics; (4) occurrence of a large number of Proterozoic zircon xenocrysts in the Late Paleozoic magmatic rocks, and Proterozoic detrital zircons in the coeval clastic sediments suggest a continental or transitional basement of the Bogda Arc; (5) subduction in the Bogda area terminated prior to the deposition of Middle Permian terrestrial sediments.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NatGe..11...97S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NatGe..11...97S"><span>A Palaeoproterozoic tectono-magmatic lull as a potential trigger for the supercontinent cycle</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spencer, Christopher J.; Murphy, J. Brendan; Kirkland, Christopher L.; Liu, Yebo; Mitchell, Ross N.</p> <p>2018-02-01</p> <p>The geologic record exhibits periods of active and quiescent geologic processes, including magmatism, metamorphism and mineralization. This apparent episodicity has been ascribed either to bias in the geologic record or fundamental changes in geodynamic processes. An appraisal of the global geologic record from about 2.3 to 2.2 billion years ago demonstrates a Palaeoproterozoic tectono-magmatic lull. During this lull, global-scale continental magmatism (plume and arc magmatism) and orogenic activity decreased. There was also a lack of passive margin sedimentation and relative plate motions were subdued. A global compilation of mafic igneous rocks demonstrates that this episode of magmatic quiescence was terminated about 2.2 billion years ago by a flare-up of juvenile magmatism. This post-lull magmatic flare-up is distinct from earlier such events, in that the material extracted from the mantle during the flare-up yielded significant amounts of continental material that amalgamated to form Nuna — Earth's first hemispheric supercontinent. We posit that the juvenile magmatic flare-up was caused by the release of significant thermal energy that had accumulated over some time. This flux of mantle-derived energy could have provided a mechanism for dramatic growth of continental crust, as well as the increase in relative plate motions required to complete the transition to modern plate tectonics and the supercontinent cycle. These events may also be linked to Palaeoproterozoic atmospheric oxygenation and equilibration of the carbon cycle.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990JGeo...12...65Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990JGeo...12...65Z"><span>A simple 2-D model for the evolution of an island-arc system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zharinov, S. E.; Demin, S. S.</p> <p>1990-07-01</p> <p>Slow seismotectonic movements along inclined deep fault planes under compressive horizontal stresses are supposed to be the principal mechanism controlling the structure and processes in island-arc systems. In order to treat the stress variations caused by this mechanism, a simple geomechanical model is investigated. We consider a shearing surface crack embedded in a homogeneous elastic half-space. The key element of the model is viscous interaction between the sides of the crack, the viscosity varying with depth. The model differs from the classical steady-state mode of subduction by nonstationary creep processes on deep faults and possibly by cyclical evolution of island-arc systems. The results of our numerical analysis are in good agreement with geological, geophysical and seismological data. (i) Vertical displacements of the free surface in the model fit well with the typical topography of a trench—arc-basement rise—back-arc basin system. (ii) The Benioff seismic zone is supposed to be formed due to the concentration of shear stresses near the fault plane. The characteristic patterns of seismicity, the fine geometry of Benioff zones, and their double-planed structure can be explained in terms of our model. (iii) A zone of considerable heat generation caused by viscous dissipation along the fault plane is found within a narrow area in the depth range 100-200 km. Moreover, the island-arc basement rise is characterized in the model by a relative tension of a few tens or even hundreds of bars, while at depths of 100-150 km below the surface, additional compression of the same order of magnitude acts. The magmatic plumbing system may be visualised as a "toothpaste tube" or a sponge filled with magma which is squeezed from the depths to the surface due to the redistribution of the tectonic stresses only. This can explain the physical origin of island-arc magmatism and the typical position of volcanic belts.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27703141','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27703141"><span>Pre-eruptive magmatic processes re-timed using a non-isothermal approach to magma chamber dynamics.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Petrone, Chiara Maria; Bugatti, Giuseppe; Braschi, Eleonora; Tommasini, Simone</p> <p>2016-10-05</p> <p>Constraining the timescales of pre-eruptive magmatic processes in active volcanic systems is paramount to understand magma chamber dynamics and the triggers for volcanic eruptions. Temporal information of magmatic processes is locked within the chemical zoning profiles of crystals but can be accessed by means of elemental diffusion chronometry. Mineral compositional zoning testifies to the occurrence of substantial temperature differences within magma chambers, which often bias the estimated timescales in the case of multi-stage zoned minerals. Here we propose a new Non-Isothermal Diffusion Incremental Step model to take into account the non-isothermal nature of pre-eruptive processes, deconstructing the main core-rim diffusion profiles of multi-zoned crystals into different isothermal steps. The Non-Isothermal Diffusion Incremental Step model represents a significant improvement in the reconstruction of crystal lifetime histories. Unravelling stepwise timescales at contrasting temperatures provides a novel approach to constraining pre-eruptive magmatic processes and greatly increases our understanding of magma chamber dynamics.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5476789','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5476789"><span>Pre-eruptive magmatic processes re-timed using a non-isothermal approach to magma chamber dynamics</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Petrone, Chiara Maria; Bugatti, Giuseppe; Braschi, Eleonora; Tommasini, Simone</p> <p>2016-01-01</p> <p>Constraining the timescales of pre-eruptive magmatic processes in active volcanic systems is paramount to understand magma chamber dynamics and the triggers for volcanic eruptions. Temporal information of magmatic processes is locked within the chemical zoning profiles of crystals but can be accessed by means of elemental diffusion chronometry. Mineral compositional zoning testifies to the occurrence of substantial temperature differences within magma chambers, which often bias the estimated timescales in the case of multi-stage zoned minerals. Here we propose a new Non-Isothermal Diffusion Incremental Step model to take into account the non-isothermal nature of pre-eruptive processes, deconstructing the main core-rim diffusion profiles of multi-zoned crystals into different isothermal steps. The Non-Isothermal Diffusion Incremental Step model represents a significant improvement in the reconstruction of crystal lifetime histories. Unravelling stepwise timescales at contrasting temperatures provides a novel approach to constraining pre-eruptive magmatic processes and greatly increases our understanding of magma chamber dynamics. PMID:27703141</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28336610','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28336610"><span>Vertically extensive and unstable magmatic systems: A unified view of igneous processes.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cashman, Katharine V; Sparks, R Stephen J; Blundy, Jonathan D</p> <p>2017-03-24</p> <p>Volcanoes are an expression of their underlying magmatic systems. Over the past three decades, the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust. A transcrustal perspective must balance slow (plate tectonic) rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions. Reconciling these observations is engendering active debate about the physical state, spatial distribution, and longevity of melt in the crust. Here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt-rich layers, focusing particularly on conditions that cause them to destabilize, ascend, and accumulate in voluminous but ephemeral shallow magma chambers. Copyright © 2017, American Association for the Advancement of Science.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.292....1S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.292....1S"><span>Geochronology and geochemistry of deep-seated crustal xenoliths in the northern North China Craton: Implications for the evolution and structure of the lower crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Su, Yuping; Zheng, Jianping; Griffin, William L.; Huang, Yan; Wei, Ying; Ping, Xianquan</p> <p>2017-11-01</p> <p>The age and composition of the lower crust are critical in understanding the processes of continental formation and evolution, and deep-seated granulite xenoliths can offer direct information on the lower crust. Here, we report mineral chemistry, whole-rock major and trace elements, Sr-Nd isotopes and zircon U-Pb-Hf results for a suite of deep-seated crustal xenoliths, recently discovered in the Cenozoic basalts of the Nangaoya area in the northern part of the North China Craton (NCC). Based on the P-T estimates, these xenoliths including mafic, intermediate and felsic granulites and hornblendites were sampled from different levels of the lower crust. While a hornblendite has a flat REE pattern, all other xenoliths display LREE enrichment and depletion of Nb, Ta, Th and Ti. The mafic granulite xenolith has relatively high whole-rock εNd(t) value of - 13.37, and yields Mesozoic (188-59 Ma) zircons ages with high εHf(t) values from - 15.3 to - 9.2. The garnet-bearing intermediate granulite-facies rocks show low εNd(t) values from - 16.92 to - 17.48, and reveal both Paleoproterozoic (1948 Ma) and Mesozoic (222-63 Ma) zircon U-Pb ages. Their Mesozoic zircons have lower εHf(t) values (from - 18.4 to - 13.8) than those from the mafic xenolith. The remaining intermediate to felsic xenoliths show Paleoproterozoic zircon ages, and the lowest εNd(t) values (from - 20.78 to - 24.03). The mafic-intermediate granulites with Mesozoic zircons originated from the interaction of lower crust-derived magmas with mantle melts, with higher proportions of mantle magmas involved in the generation of mafic granulite, whereas intermediate to felsic xenoliths without Mesozoic zircons represent ancient Paleoproterozoic to Neoarchean deep crust. These deep-seated xenoliths reveal complicated crustal evolution processes, including crustal growth during Neoarchean (2.5-2.7 Ga), middle Paleoproterozoic (2.2-2.1 Ga) and Mesozoic, and reworking during early Paleoproterozoic, late Paleoproterozoic and Mesozoic related to magmatic underplating. The integrated analyses of lithological, geochemical and age data for a suite of deep-seated xenoliths show that the lower crust in the Nangaoya area is temporally and compositionally zoned. The upper part of the lower crust mainly comprises Neoarchean to Paleoproterozoic intermediate-felsic rocks with intercalated hornblendites, the majority of which record 1950 and 1850 Ma metamorphism; the middle part is dominated by a Paleoproterozoic and Mesozoic intermediate garnet-bearing granulite-facies hybrid layer; and the lowermost crust is represented by a Mesozoic mafic granulite layer, which was significantly modified by episodic magmatic underplating. Such a modification induced by crust-mantle interaction can result in Mesozoic ages and more mafic components for xenolith granulites, and thus is an effective mechanism to explain the differences between exposed and xenolithic granulites.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IJEaS.tmp...40E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IJEaS.tmp...40E"><span>Contributions of gravity and field data on the structural scheme updating of the Tellian domain and its foreland (Nefza-Bizerte region, northern Tunisia)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Essid, El Mabrouk; Kadri, Ali; Balti, Hadhemi; Gasmi, Mohamed; Zargouni, Fouad</p> <p>2018-03-01</p> <p>The Nefza-Bizerte region, eastern part of the Tunisian Alpine chain, covers the thrust sheets domain called the Tell and its Atlassic foreland. The deep structures under the Tellian thrust sheets are not enough explored. The structural interpretation of magmatic rocks, Triassic outcrops and the depressions are still a subject of discussion. In this work, we intend to investigate deep faults and their eventual role in magmatism and Triassic salt setting up and to explain the depression genesis. Analysis of the Bouguer anomaly map and its derivatives reveals the main gravity lineaments, organized in major NE- and NW-trending systems. The NE-trending system, dipping towards the NW, is the main component of the structural scheme and has controlled the tectonic evolution of this area. After the immobilization of the Tellian thrust sheets during the uppermost Langhian, the Tell and its Atlassic foreland were affected by the Tortonian compressive event with a NW-trending maximum horizontal stress. The reverse kinematics of the NE-trending deep-seated faults created at their front continental environments filled later by post-nappes Neogene deposits. After the early Pleistocene, a NNW-directed compressional stress regime deformed the post-nappes Neogene series and generated NW-trending grabens. This coexistence of compression-extension continues until present day.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983E%26PSL..65..322V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983E%26PSL..65..322V"><span>Thermal anomalies and magmatism due to lithospheric doubling and shifting</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vlaar, N. J.</p> <p>1983-11-01</p> <p>We present some thermal and magmatic consequences of the processes of lithospheric doubling and lithospheric shifting. Lithospheric doubling concerns the obduction of a cold continental or old oceanic lithospheric plate over a young and hot oceanic lithosphere/upper mantle system, including an oceanic ridge. Lithospheric shifting concerns the translation and rotation of a lithospheric plate relative to the upper mantle. In both cases the resulting thermal state of the upper mantle below the obducting or shifting lithosphere may be perturbed relative to a "normal" continental or oceanic geothermal situation. The perturbed geothermal state gives rise to a density inversion at depth and thus induces a vertical gravitational instability which favours magmatism. We speculate about the magmatic consequences of this situation and infer that in the case of lithospheric doubling our model may account for the petrology and geochemistry of the resulting magma. The original layering and composition of the overridden young oceanic lithosphere may strongly influence magmatic processes. We dwell shortly on the genesis of kimberlites within the framework of our lithospheric doubling model and on magmatism in general. Lithospheric recycling is inherent to the mechanism of lithospheric doubling.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JVGR..164..254Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JVGR..164..254Z"><span>Magmatic structures in the Krkonoše Jizera Plutonic Complex, Bohemian Massif: evidence for localized multiphase flow and small-scale thermal mechanical instabilities in a granitic magma chamber</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Žák, Jiří; Klomínský, Josef</p> <p>2007-08-01</p> <p>The present paper examines magmatic structures in the Jizera and Liberec granites of the Krkonoše-Jizera Plutonic Complex, Bohemian Massif. The magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal-rich mushes, and to capture the evolution of physical processes in an ancient granitic magma chamber. We propose that after chamber-wide mixing and hybridization, as suggested by recent petrological studies, laminar magma flow became highly localized to weaker channel-like domains within the higher-strength crystal framework. Mafic schlieren formed at flow rims, and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape. Local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure. After the cessation or deceleration of channel flow, gravity-driven processes (settling of crystals and enclaves, gravitational differentiation, development of downward dripping instabilities), accompanied by compaction, filter pressing and melt segregation, dominated in the crystal mush within the flow channels. Subsequently, magmatic folds developed in schlieren layers and the magma chamber recorded complex, late magmatic strains at high magma crystallinities. Late-stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization. We emphasize that the most favorable environments for the formation and preservation of magmatic structures, such as those hosted in the Jizera and Liberec granites, are slowly cooling crystal-rich mushes. Therefore, where preserved in plutons, these structures may lend strong support for a "mush model" of magmatic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.7643G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.7643G"><span>Is the Gop rift oceanic? A reevaluation of the Seychelles-India conjugate margins</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guan, Huixin; Werner, Philippe; Geoffroy, Laurent</p> <p>2016-04-01</p> <p>Recent studies reevaluated the timing and evolution of the breakup process between the Seychelles continental ridge and India, and the relationship between this evolution and mantle melting associated with the Deccan Igneous Province1,2,3. Those studies, mainly based on gravity and seismic refraction surveys, point that the oceanic domain located between the Seychelles and the Laxmi Ridge (here designed as the Carlsberg Basin) is the youngest oceanic domain between India and the Seychelles. To the East of the Laxmi Ridge, the aborted Gop Rift is considered as an older highly magmatic extensional continental system with magmatism, breakup and oceanic spreading being coeval with or even predating the emplacement of the major pulse of the Deccan trapps. This interpretation on the oceanic nature of the Gop Rift conflicts with other extensive surveys based on magnetic and seismic reflection data4 which suggest that the Gop Rift is an extended syn-magmatic continental domain. In our work based (a) on the existing data, (b) on new deep-seismic reflection surveys (already published by Misra5) down to the Moho and underlying mantle and (c) on new concepts on the geometry of volcanic passive margins, we propose a distinct interpretation of the Seychelles-India system. As proposed by former authors6,7, the Indian margin suffered some continental stretching and thinning before the onset of the Deccan traps during the Mesozoic. Thus continental crust thickness cannot be used easily as a proxy of syn-magmatic stretching-thinning processes or even to infer the presence or not of oceanic-type crust based, solely, on crustal thickness. However, some remarkable features appear on some of the deep penetration seismic lines we studied. We illustrate that the whole Seychelles/India system, before the opening of the present-day "Carlsberg Basin" may simply be regarded as a pair of sub-symmetric conjugate volcanic passive margins (VPMs) with inner and outer SDR wedges dipping towards the Gop Rift axis. We propose that the conspicuous buoyant central part of the Gop Rift is likely associated with a continental C-Block as described in a recent paper on conjugated VPMs8, at least in the southern part of the Gop Rift. The crust below the Laxmi basin is probably transitional continental i.e. strongly intruded. West of India and west of the Laxmi Ridge, the transition to the Carlsberg Basin occurs along a clearly-expressed transform fault, not through an extended and thinned continental margin. We reinterpret the whole system based on those observations and propositions, giving some explanations on controversial magnetic anomalies based on similar observations from the southern Atlantic Ocean. 1: Collier et al., 2008. Age of the Seychelles-India break-up. Earth and Planetary Science Letters. 2: Minshull et al., 2008. The relationship between riftingand magmatism in the northeastern Arabian Sea. Nature Geoscience. 3 : Armitage et al., 2010. The importance of rift history for volcanic margin. Nature. 4 : Krishna et al., 2006. Nature of the crust in the Laxmi Basin (14 degrees-20 degrees N), western continental margin of India. Tectonics. 5 : Misra et al., 2015. Repeat ridge jumps and microcontinent separation: insights from NE Arabian Sea. Marine and Petroleum Geology. 6 : Biswas, 1982. Rift basins in the western margin of India and their hydrocarbon prospects. Bull. Am. Assoc. Pet. Geol. 7 : Chatterjee et al., 2013. The longest voyage: Tectonic, magmatic, and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia. Gondwana Research. 8 : Geoffroy et al., 2015. Volcanic passive margins: anotherway to break up continents. Scientific Reports.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1610232M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1610232M"><span>Petrology of exhumed mantle rocks at passive margins: ancient lithosphere and rejuvenation processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Müntener, Othmar; McCarthy, Anders; Picazo, Suzanne</p> <p>2014-05-01</p> <p>Mantle peridotites from ocean-continent transition zones (OCT's) and ultraslow spreading ridges question the commonly held assumption of a simple link between mantle melting and MORB. 'Ancient' and partly refertilized mantle in rifts and ridges illustrates the distribution of the scale of chemical and isotopic upper mantle heterogeneity even on a local scale. Field data and petrology demonstrates that ancient, thermally undisturbed, pyroxenite-veined subcontinental mantle blobs formed parts of the ocean floor next to thinned continental crust. These heterogeneities might comprise an (ancient?) subduction component. Upwelling of partial melts that enter the conductive lithospheric mantle inevitably leads to freezing of the melt and refertilization of the lithosphere and this process might well be at the origin of the difference between magma-poor and volcanic margins. Similar heterogeneity might be created in the oceanic lithosphere, in particular at slow to ultra-slow spreading ridges where the thermal boundary layer (TBM) is thick and may be veined with metasomatic assemblages that might be recycled in subduction zones. In this presentation, we provide a summary of mantle compositions from the European realm to show that inherited mantle signatures from previous orogenies play a key role on the evolution of rift systems and on the chemical diversity of peridotites exposed along passive margins and ultra-slow spreading ridges. Particularly striking is the abundance of plagioclase peridotites in the Alpine ophiolites that are interpreted as recorders of refertilization processes related to thinning and exhumation of mantle lithosphere. Another important result over the last 20 years was the discovery of extremely refractory Nd-isotopic compositions with highly radiogenic 147Sm/144Nd which indicates that partial melting processes and Jurassic magmatism in the Western Thetys are decoupled. Although the isotopic variability might be explained by mantle heterogeneities, an alternative is that these depleted domains represent snapshots of melting processes that are related to Permian and/or even older crust forming processes. The findings of the these refractory mantle rocks over the entire Western Alpine arc and the similarity in model ages of depletion suggests a connection to the Early Permian magmatic activity. Shallow and deep crustal magmatism in the Permian is widespread over Western Europe and the distribution of these mafic rocks are likely to pre-determine the future areas of crustal thinning and exhumation during formation of the Thethyan passive margins.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.9241B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.9241B"><span>Crustal architecture and deep structure of the Namibian passive continental margin around Walvis Ridge from wide-angle seismic data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Behrmann, Jan H.; Planert, Lars; Jokat, Wilfried; Ryberg, Trond; Bialas, Jörg; Jegen, Marion</p> <p>2013-04-01</p> <p>The opening of the South Atlantic ocean basin was accompanied by voluminous magmatism on the conjugate continental margins of Africa and South America, including the formation of the Parana and Entendeka large igneous provinces (LIP), the build-up of up to 100 km wide volcanic wedges characterized by seaward dipping reflector sequences (SDR), as well as the formation of paired hotspot tracks on the rifted African and South American plates, the Walvis Ridge and the Rio Grande Rise. The area is considered as type example for hotspot or plume-related continental break-up. However, SDR, and LIP-related features on land are concentrated south of the hotspot tracks. The segmentation of the margins offers a prime opportunity to study the magmatic signal in space and time, and investigate the interrelation with rift-related deformation. A globally significant question we address here is whether magmatism drives continental break-up, or whether even rifting accompanied by abundant magmatism is in response to crustal and lithospheric stretching governed by large-scale plate kinematics. In 2010/11, an amphibious set of wide-angle seismic data was acquired around the landfall of Walvis Ridge at the Namibian passive continental margin. The experiments were designed to provide crustal velocity information and to investigate the structure of the upper mantle. In particular, we aimed at identifying deep fault zones and variations in Moho depth, constrain the velocity signature of SDR sequences, as well as the extent of magmatic addition to the lower crust near the continent-ocean transition. Sediment cover down to the igneous basement was additionally constrained by reflection seismic data. Here, we present tomographic analysis of the seismic data of one long NNW oriented profile parallel to the continental margin across Walvis Ridge, and a second amphibious profile from the Angola Basin across Walvis Ridge and into the continental interior, crossing the area of the Etendeka Plateau basalts. The most striking feature is the sharp transition in crustal structure and thickness across the northern boundary of Walvis Ridge. Thin oceanic crust (6.5 km) of the Angola Basin lies next to the up to 35 km thick igneous crustal root founding the highest elevated northern portions of Walvis Ridge. Both structures are separated by a very large transform fault zone. The velocity structure of Walvis Ridge lower crust is indicative of gabbro, and, in the lowest parts, of cumulate sequences. On the southern side of Walvis Ridge there is a smooth gradation into the adjacent 25-30 km thick crust underlying the ocean-continent boundary, with a velocity structure resembling that of Walvis Ridge The second profile shows a sharp transition from oceanic to rifted continental crust. The transition zone may be underlain by hydrated uppermost mantle. Below the Etendeka Plateau, an extensive high-velocity body, likely representing gabbros and their cumulates at the base of the crust, indicates magmatic underplating. We summarize by stating that rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magmatic-dominated segment to the south, and an amagmatic segment north of Walvis Ridge.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JVGR..349....1A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JVGR..349....1A"><span>Origin, evolution and geothermometry of the thermal waters in the Gölemezli Geothermal Field, Denizli Basin (SW Anatolia, Turkey)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alçiçek, Hülya; Bülbül, Ali; Brogi, Andrea; Liotta, Domenico; Ruggieri, Giovanni; Capezzuoli, Enrico; Meccheri, Marco; Yavuzer, İbrahim; Alçiçek, Mehmet Cihat</p> <p>2018-01-01</p> <p>The Gölemezli Geothermal Field (GGF) is one of the best known geothermal fields in western Anatolia (Turkey). The exploited fluids are of meteoric origin, mixed with deep magmatic fluids, which interacted with the metamorphic rocks of the Menderes Massif. The geothermal fluids are channeled along Quaternary faults belonging to the main normal faults system delimiting the northern side of the Denizli Basin and their associated transfer zones. In this study, hydrochemical and isotopic analyses of the thermal and cold waters allow us to determine water-rock interactions, fluid paths and mixing processes. Two groups of thermal waters have been distinguished: (i) Group 1A, comprising Na-SO4 type and Ca-SO4 type and (ii) Group 1B, only consisting Ca-HCO3 type waters. Differently, two groups were recognized in the cold waters: (i) Group 2A, corresponding to Ca-HCO3 type and (ii) Group 2B, including Mg-HCO3 type. Their geochemical characteristics indicate interactions with the Paleozoic metamorphic rocks of the Menderes Massif and with the Neogene lacustrine sedimentary rocks. Dissolution of host rock and ion-exchange reactions modify thermal water composition in the reservoir of the GGF. High correlation in some ionic ratios and high concentrations of some minor elements suggest an enhanced water-rock interaction. None of the thermal waters has been reached a complete chemical re-equilibrium, possibly as a result of mixing with cold water during their pathways. Geothermal reservoir temperatures are calculated in the range of 130-210°C for the Gölemezli field. Very negative δ18O and δ2H isotopic ratios are respectively between -8.37 and -8.13‰ and -61.09 and -59.34‰ for the SO4-rich thermal waters, and ca. - 8.40 and -8.32‰ and - 57.80 and -57.41‰ for the HCO3-rich thermal waters. Low tritium (< 1 TU) and low oxygen isotope values reflect a deep circuit and fluids of meteoric origin. Positive δ13CDIC ratios (+ 5.11 to + 7.54‰) of all thermal waters imply a contribution of metamorphic origin. Heating is guaranteed by a deep circuit within an overheated continental crust, mainly affected by damaged rock volumes. Volatile ascent from deep magmatic sources through crustal structures can explain the occurrence of mantle volatiles at shallow depth in the Denizli Basin. The NW- and NE-trending fault systems, associated with their related fractures, played as hydraulic conduits underlining the strict link existing between fractures and fluid convection in the extensional settings. In this view, the GGF is a very good example of geothermal field associated to active tectonic setting and magmatism, as it is the case of the other geothermal fields occurring in the Denizli Basin.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Natur.533...82C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Natur.533...82C"><span>Chondritic xenon in the Earth’s mantle</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caracausi, Antonio; Avice, Guillaume; Burnard, Peter G.; Füri, Evelyn; Marty, Bernard</p> <p>2016-05-01</p> <p>Noble gas isotopes are powerful tracers of the origins of planetary volatiles, and the accretion and evolution of the Earth. The compositions of magmatic gases provide insights into the evolution of the Earth’s mantle and atmosphere. Despite recent analytical progress in the study of planetary materials and mantle-derived gases, the possible dual origin of the planetary gases in the mantle and the atmosphere remains unconstrained. Evidence relating to the relationship between the volatiles within our planet and the potential cosmochemical end-members is scarce. Here we show, using high-precision analysis of magmatic gas from the Eifel volcanic area (in Germany), that the light xenon isotopes identify a chondritic primordial component that differs from the precursor of atmospheric xenon. This is consistent with an asteroidal origin for the volatiles in the Earth’s mantle, and indicates that the volatiles in the atmosphere and mantle originated from distinct cosmochemical sources. Furthermore, our data are consistent with the origin of Eifel magmatism being a deep mantle plume. The corresponding mantle source has been isolated from the convective mantle since about 4.45 billion years ago, in agreement with models that predict the early isolation of mantle domains. Xenon isotope systematics support a clear distinction between mid-ocean-ridge and continental or oceanic plume sources, with chemical heterogeneities dating back to the Earth’s accretion. The deep reservoir now sampled by the Eifel gas had a lower volatile/refractory (iodine/plutonium) composition than the shallower mantle sampled by mid-ocean-ridge volcanism, highlighting the increasing contribution of volatile-rich material during the first tens of millions of years of terrestrial accretion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27111512','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27111512"><span>Chondritic xenon in the Earth's mantle.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Caracausi, Antonio; Avice, Guillaume; Burnard, Peter G; Füri, Evelyn; Marty, Bernard</p> <p>2016-05-05</p> <p>Noble gas isotopes are powerful tracers of the origins of planetary volatiles, and the accretion and evolution of the Earth. The compositions of magmatic gases provide insights into the evolution of the Earth's mantle and atmosphere. Despite recent analytical progress in the study of planetary materials and mantle-derived gases, the possible dual origin of the planetary gases in the mantle and the atmosphere remains unconstrained. Evidence relating to the relationship between the volatiles within our planet and the potential cosmochemical end-members is scarce. Here we show, using high-precision analysis of magmatic gas from the Eifel volcanic area (in Germany), that the light xenon isotopes identify a chondritic primordial component that differs from the precursor of atmospheric xenon. This is consistent with an asteroidal origin for the volatiles in the Earth's mantle, and indicates that the volatiles in the atmosphere and mantle originated from distinct cosmochemical sources. Furthermore, our data are consistent with the origin of Eifel magmatism being a deep mantle plume. The corresponding mantle source has been isolated from the convective mantle since about 4.45 billion years ago, in agreement with models that predict the early isolation of mantle domains. Xenon isotope systematics support a clear distinction between mid-ocean-ridge and continental or oceanic plume sources, with chemical heterogeneities dating back to the Earth's accretion. The deep reservoir now sampled by the Eifel gas had a lower volatile/refractory (iodine/plutonium) composition than the shallower mantle sampled by mid-ocean-ridge volcanism, highlighting the increasing contribution of volatile-rich material during the first tens of millions of years of terrestrial accretion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.461...73B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.461...73B"><span>The arc arises: The links between volcanic output, arc evolution and melt composition</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brandl, Philipp A.; Hamada, Morihisa; Arculus, Richard J.; Johnson, Kyle; Marsaglia, Kathleen M.; Savov, Ivan P.; Ishizuka, Osamu; Li, He</p> <p>2017-03-01</p> <p>Subduction initiation is a key process for global plate tectonics. Individual lithologies developed during subduction initiation and arc inception have been identified in the trench wall of the Izu-Bonin-Mariana (IBM) island arc but a continuous record of this process has not previously been described. Here, we present results from International Ocean Discovery Program Expedition 351 that drilled a single site west of the Kyushu-Palau Ridge (KPR), a chain of extinct stratovolcanoes that represents the proto-IBM island arc, active for ∼25 Ma following subduction initiation. Site U1438 recovered 150 m of oceanic igneous basement and ∼1450 m of overlying sediments. The lower 1300 m of these sediments comprise volcaniclastic gravity-flow deposits shed from the evolving KPR arc front. We separated fresh magmatic minerals from Site U1438 sediments, and analyzed 304 glass (formerly melt) inclusions, hosted by clinopyroxene and plagioclase. Compositions of glass inclusions preserve a temporal magmatic record of the juvenile island arc, complementary to the predominant mid-Miocene to recent activity determined from tephra layers recovered by drilling in the IBM forearc. The glass inclusions record the progressive transition of melt compositions dominated by an early 'calc-alkalic', high-Mg andesitic stage to a younger tholeiitic stage over a time period of 11 Ma. High-precision trace element analytical data record a simultaneously increasing influence of a deep subduction component (e.g., increase in Th vs. Nb, light rare earth element enrichment) and a more fertile mantle source (reflected in increased high field strength element abundances). This compositional change is accompanied by increased deposition rates of volcaniclastic sediments reflecting magmatic output and maturity of the arc. We conclude the 'calc-alkalic' stage of arc evolution may endure as long as mantle wedge sources are not mostly advected away from the zones of arc magma generation, or the rate of wedge replenishment by corner flow does not overwhelm the rate of magma extraction.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V43D..08W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V43D..08W"><span>Detecting deep crustal magma movement: Exploring linkages between increased gas emission, deep seismicity, and deformation (Invited)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Werner, C. A.; Poland, M. P.; Power, J. A.; Sutton, A. J.; Elias, T.; Grapenthin, R.; Thelen, W. A.</p> <p>2013-12-01</p> <p>Typically in the weeks to days before a volcanic eruption there are indisputable signals of unrest that can be identified in geophysical and geochemical data. Detection of signals of volcanic unrest months to years prior to an eruption, however, relies on our ability to recognize and link more subtle changes. Deep long-period earthquakes, typically 10-45 km beneath volcanoes, are thought to represent magma movement and may indicate near future unrest. Carbon dioxide (CO2 ) exsolves from most magmas at similar depths and increases in CO2 discharge may also provide a months-to-years precursor as it emits at the surface in advance of the magma from which it exsolved. Without the use of sensitive monitoring equipment and routine measurements, changes in CO2 can easily go undetected. Finally, inflation of the surface, through use of InSAR or GPS stations (especially at sites tens of km from the volcano) can also indicate accumulation of magma in the deep crust. Here we present three recent examples, from Redoubt, Kilauea, and Mammoth Mountain volcanoes, where increases in CO2 emission, deep long-period earthquakes, and surface deformation data indicate either the intrusion of magma into the deep crust in the months to years preceding volcanic eruptions or a change in ongoing volcanic unrest. At Redoubt volcano, Alaska, elevated CO2 emission (~ 1200 t/d, or roughly 20 times the background emission) was measured in October, 2008, over 5 months prior to the first magmatic eruption in March, 2009. In addition to CO2 release, deep long-period earthquakes were first recorded in December, 2008, and a deep deformation signal was detected starting in May 2008, albeit retrospectively. At Kilauea, Hawaii, increases in CO2 emissions from the summit (up to nearly 25 kt/d, over three times the background emission) were measured mid-2004, roughly coincident with a change in deformation behavior from deflation to inflation. Nearly 3 years later, a change in eruptive activity occurred as a result of a burgeoning supply of magma to the volcano, which overwhelmed the ability of the ongoing east rift zone eruption to accommodate the increased flux of magma into the edifice. At Mammoth Mountain, California, diffuse CO2 degassing doubled between 2007 and 2012 following three swarms of deep earthquakes that began in 2006. In contrast to Redoubt and Kilauea, the CO2 emission rate at Mammoth is on the order of hundreds of t/d as opposed to thousands. This reasonably indicates a smaller volume of magma at depth, and changes do not suggest volcanic activity is imminent. In these examples there was no visual indication of increased CO2 emission, and geophysical signals of unrest were often subtle. Routine measurement of all volcanic gases, most importantly CO2 , coupled with a geophysical monitoring, therefore, has better potential to recognize changes in deep (10s of km) magmatic processes. Such indicators are key to better eruption forecasts, especially on the months-to years timescales that often elude volcanologists.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1211439J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1211439J"><span>The iron source in phreatomagmatic pipes in the Tunguska Basin (eastern Siberia): insights into hydrothermal-metasomatic leaching processes from Fe isotopes, microstructures, and mass balances.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>John, Timm; Svensen, Henrik; Weyer, Stefan; Polozov, Alexander; Planke, Sverre</p> <p>2010-05-01</p> <p>The Siberian iron-bearing phreatomagmatic pipes represent world class Fe-ore deposit, and 5-6 are currently mined in eastern Siberia. The pipes formed within the vast Tunguska Basin, cutting thick accumulations of carbonates (dolostones) and evaporites (anhydrite, halite, dolostone). These sediments were intruded by the sub-volcanic part of the Siberian Traps at 252 Ma, and sills and dykes are abundant throughout the basin. The pipes formed during sediment-magma interactions in the deep parts of the basin, and the degassing is believed to have triggered the end-Permian environmental crisis. A major problem with understanding the pipe formation is related to the source of iron. Available hypotheses state that the iron was leached from a Fe-enriched magmatic melt that incorporated dolostones. It is currently unclear how the magmatic, hydrothermal, and sedimentary processes interacted to form the deposits, as there are no actual constraints to pin down the iron source. We hypothesize two end-member scenarios to account for the magnetite enrichment and deposition, which is testable by analyzing Fe-isotopes of magnetite: 1) Iron sourced from dolerite magma through leaching and metasomatism by chloride brines. 2) Leaching of iron from sedimentary rocks (shale, dolostone) during magma-sediment interactions. We focus on understanding the Fe-isotopic architecture of the pipes in order constrain the source of the Fe and the mechanism that caused this significant Fe redistribution. We further evaluate possible fractionation during fast metasomatic ore-forming process that took place soon after pipe formation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1511867L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1511867L"><span>Seismicity and magmatic processes in the Rwenzori region of the Albertine Rift.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lindenfeld, Michael; Rümpker, Georg; Kasereka, Celestin M.; Batte, Arthur; Schumann, Andreas</p> <p>2013-04-01</p> <p>In this presentation we summarize results from two extensive seismic field studies with temporary station networks in the Rwenzori region of the Albertine rift, located at the border between Uganda and the Democratic Republic of Congo. The first network was running from February 2006 to September 2007. It consisted of 27 seismic stations which were deployed in the Ugandan part of the area. A second network of 33 stations was operated between October 2009 and October 2011. It traversed the whole rift segment from the eastern rift shoulder in Uganda to the western shoulder in the D.R. Congo, covering the whole Rwenzori region. The data analysis revealed a pronounced local earthquake activity in this area with an average rate of more than 800 events per month and proves that this segment of the Albertine Rift belongs to the seismically most active regions of the whole East African Rift System. The earthquake distribution is highly heterogeneous. The highest activity is observed in the northeastern part of the Rwenzori area. Here, the mountains are connected to the eastern rift shoulder whereas they are surrounded by rift segments elsewhere. We were able to locate seismicity bursts with more than 300 events per day. The depth extent of seismicity ranges from 20 to 39 km and correlates well with Moho depths that were derived from teleseismic receiver functions. The majority of the derived fault plane solutions exhibit normal faulting with WNW-ESE oriented T-axes, which is perpendicular to the rift axis and in good agreement with kinematic rift models. The area of highest seismic activity is also characterized by the existence of several vertical elongated earthquake clusters in the crust. From petrological considerations we presume that these events are triggered by fluids and gases which originate from a magmatic source below the crust. The existence of a magmatic source within the lithosphere is supported by the detection of mantle earthquakes at about 40 - 60 km depth below the cluster area. We interpret these observations as an indication of deep magmatic infiltration processes that play a significant role in rift formation and that may eventually lead to the complete detachment of the Rwenzori block from the surrounding rift flanks.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MS%26E..269a2063Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MS%26E..269a2063Y"><span>Geological and Geochemical Characteristics of Skarn Type Lead-Zinc Deposit in Baoshan Block, Yunnan Province</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Xue; Wang, Peng</p> <p>2017-11-01</p> <p>Baoshan block is an important Pb-Zn-Fe-Cu polymetallic ore-concentration area which is located in southern of the Sanjiang metallogenic belt in western Yunnan. The article is studying about the geological and geochemical characteristics of the skarn type lead-zinc deposit in Baoshan block. The skarn-type lead-zinc deposit Baoshan block is characterized by skarn and skarn marble, and the orebodies are layered, or bedded along the interlayer fault, which are significantly controlled by structure. The research about Stable isotope S, H and O indicates that the ore-forming fluids are mainly derived from magmatic water, partly mixed with parts of metamorphic water and atmospheric precipitation. The initial Sr isotopic Sr87/Sr86 ratio suggests that the ore-forming materials derived from deep concealed magmatic rock, age of Rb-Sr mineralization is similar to that of Yanshanian granite. In conclusion, the Yanshanian tectonic-magmatic-fluid coupling mineralization of Yanshan formation is the main reason for the skarn-type lead-zinc deposit in the Baoshan block.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.9720G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.9720G"><span>Toward self-consistent tectono-magmatic numerical model of rift-to-ridge transition</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gerya, Taras; Bercovici, David; Liao, Jie</p> <p>2017-04-01</p> <p>Natural data from modern and ancient lithospheric extension systems suggest three-dimensional (3D) character of deformation and complex relationship between magmatism and tectonics during the entire rift-to-ridge transition. Therefore, self-consistent high-resolution 3D magmatic-thermomechanical numerical approaches stand as a minimum complexity requirement for modeling and understanding of this transition. Here we present results from our new high-resolution 3D finite-difference marker-in-cell rift-to-ridge models, which account for magmatic accretion of the crust and use non-linear strain-weakened visco-plastic rheology of rocks that couples brittle/plastic failure and ductile damage caused by grain size reduction. Numerical experiments suggest that nucleation of rifting and ridge-transform patterns are decoupled in both space and time. At intermediate stages, two patterns can coexist and interact, which triggers development of detachment faults, failed rift arms, hyper-extended margins and oblique proto-transforms. En echelon rift patterns typically develop in the brittle upper-middle crust whereas proto-ridge and proto-transform structures nucleate in the lithospheric mantle. These deep proto-structures propagate upward, inter-connect and rotate toward a mature orthogonal ridge-transform patterns on the timescale of millions years during incipient thermal-magmatic accretion of the new oceanic-like lithosphere. Ductile damage of the extending lithospheric mantle caused by grain size reduction assisted by Zenner pinning plays critical role in rift-to-ridge transition by stabilizing detachment faults and transform structures. Numerical results compare well with observations from incipient spreading regions and passive continental margins.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70036578','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70036578"><span>Failed magmatic eruptions: Late-stage cessation of magma ascent</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Moran, S.C.; Newhall, C.; Roman, D.C.</p> <p>2011-01-01</p> <p>When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: "deep intrusion", "shallow intrusion", "sluggish/viscous magmatic eruption", and "rapid, often explosive magmatic eruption". We define "failed eruptions" as instances in which magma reaches but does not pass the "shallow intrusion" stage, i. e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T22A..03H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T22A..03H"><span>The Generation of Continents through Subduction Zone Processing of Large Igneous Provinces: A Case Study from the Central American Subduction Zone</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harmon, N.; Rychert, C.</p> <p>2013-12-01</p> <p>Billions of years ago primary mantle magmas evolved to form the continental crust, although no simple magmatic differentiation process explains the progression to average andesitic crustal compositions observed today. A multiple stage process is often invoked, involving subduction and or oceanic plumes, to explain the strong depletion observed in Archean xenoliths and as well as pervasive tonalite-trondhjemite-granodiorite and komatiite protoliths in the greenstone belts in the crust in the cratons. Studying modern day analogues of oceanic plateaus that are currently interacting with subductions zones can provide insights into continental crust formation. Here we use surface waves to image crustal isotropic and radially anisotropic shear velocity structure above the central American subduction system in Nicaragua and Costa Rica, which juxtaposes thickened ocean island plateau crust in Costa Rica with continental/normal oceanic crust in Nicaragua. We find low velocities beneath the active arc regions (3-6% slower than the surrounding region) and up to 6% radially anisotropic structures within the oceanic crust of the Caribbean Large Igneous Province beneath Costa Rica. The low velocities and radial anisotropy suggest the anomalies are due to pervasive deep crustal magma sills. The inferred sill structures correlate spatially with increased silicic outputs in northern Costa Rica, indicating that deep differentiation of primary magmas is more efficient beneath Costa Rica relative to Nicaragua. Subduction zone alteration of large igneous provinces promotes efficient, deep processing of primary basalts to continental crust. This scenario can explain the formation of continental lithosphere and crust, by both providing strongly depleted mantle lithosphere and a means for rapidly generating a silicic crustal composition.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V23A0467L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V23A0467L"><span>Ring-fault activity at subsiding calderas studied from analogue experiments and numerical modeling</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Y. K.; Ruch, J.; Vasyura-Bathke, H.; Jonsson, S.</p> <p>2017-12-01</p> <p>Several subsiding calderas, such as the ones in the Galápagos archipelago and the Axial seamount in the Pacific Ocean have shown a complex but similar ground deformation pattern, composed of a broad deflation signal affecting the entire volcanic edifice and of a localized subsidence signal focused within the caldera. However, it is still debated how deep processes at subsiding calderas, including magmatic pressure changes, source locations and ring-faulting, relate to this observed surface deformation pattern. We combine analogue sandbox experiments with numerical modeling to study processes involved from initial subsidence to later collapse of calderas. The sandbox apparatus is composed of a motor driven subsiding half-piston connected to the bottom of a glass box. During the experiments the observation is done by five digital cameras photographing from various perspectives. We use Photoscan, a photogrammetry software and PIVLab, a time-resolved digital image correlation tool, to retrieve time-series of digital elevation models and velocity fields from acquired photographs. This setup allows tracking the processes acting both at depth and at the surface, and to assess their relative importance as the subsidence evolves to a collapse. We also use the Boundary Element Method to build a numerical model of the experiment setup, which comprises contracting sill-like source in interaction with a ring-fault in elastic half-space. We then compare our results from these two approaches with the examples observed in nature. Our preliminary experimental and numerical results show that at the initial stage of magmatic withdrawal, when the ring-fault is not yet well formed, broad and smooth deflation dominates at the surface. As the withdrawal increases, narrower subsidence bowl develops accompanied by the upward propagation of the ring-faulting. This indicates that the broad deflation, affecting the entire volcano edifice, is primarily driven by the contraction of the magmatic source, whereas the ring-faulting tends to concentrate deformation within the caldera. This interaction between ring-faulting and pressure decrease in a magma reservoir therefore provides a possible explanation for the deformation pattern observed at several subsiding calderas.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.484....1T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.484....1T"><span>Geodynamics of kimberlites on a cooling Earth: Clues to plate tectonic evolution and deep volatile cycles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tappe, Sebastian; Smart, Katie; Torsvik, Trond; Massuyeau, Malcolm; de Wit, Mike</p> <p>2018-02-01</p> <p>Kimberlite magmatism has occurred in cratonic regions on every continent. The global age distribution suggests that this form of mantle melting has been more prominent after 1.2 Ga, and notably between 250-50 Ma, than during early Earth history before 2 Ga (i.e., the Paleoproterozoic and Archean). Although preservation bias has been discussed as a possible reason for the skewed kimberlite age distribution, new treatment of an updated global database suggests that the apparent secular evolution of kimberlite and related CO2-rich ultramafic magmatism is genuine and probably coupled to lowering temperatures of Earth's upper mantle through time. Incipient melting near the CO2- and H2O-bearing peridotite solidus at >200 km depth (1100-1400 °C) is the petrologically most feasible process that can produce high-MgO carbonated silicate melts with enriched trace element concentrations akin to kimberlites. These conditions occur within the convecting asthenospheric mantle directly beneath thick continental lithosphere. In this transient upper mantle source region, variable CHO volatile mixtures control melting of peridotite in the absence of heat anomalies so that low-degree carbonated silicate melts may be permanently present at ambient mantle temperatures below 1400 °C. However, extraction of low-volume melts to Earth's surface requires tectonic triggers. Abrupt changes in the speed and direction of plate motions, such as typified by the dynamics of supercontinent cycles, can be effective in the creation of lithospheric pathways aiding kimberlite magma ascent. Provided that CO2- and H2O-fluxed deep cratonic keels, which formed parts of larger drifting tectonic plates, existed by 3 Ga or even before, kimberlite volcanism could have been frequent during the Archean. However, we argue that frequent kimberlite magmatism had to await establishment of an incipient melting regime beneath the maturing continents, which only became significant after secular mantle cooling to below 1400 °C during post-Archean times, probably sometime shortly after 2 Ga. At around this time kimberlites replace komatiites as the hallmark mantle-derived magmatic feature of continental shields worldwide. The remarkable Mesozoic-Cenozoic 'kimberlite bloom' between 250-50 Ma may represent the ideal circumstance under which the relatively cool and volatile-fluxed cratonic roots of the Pangea supercontinent underwent significant tectonic disturbance. This created more than 60% of world's known kimberlites in a combination of redox- and decompression-related low-degree partial melting. Less than 2% of world's known kimberlites formed after 50 Ma, and the tectonic settings of rare 'young' kimberlites from eastern Africa and western North America demonstrate that far-field stresses on cratonic lithosphere enforced by either continental rifting or cold subduction play a crucial role in enabling kimberlite magma transfer to Earth's surface.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMOS54B..08Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMOS54B..08Y"><span>Lithospheric structure beneath the extinct ridge of South China Sea: Constraints from Rayleigh wave phase velocity tomography using OBS data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, T.; Le, B. M.; passive-Source Seismic Team, S.</p> <p>2016-12-01</p> <p>What would happen when a mid-ocean-ridge stops spreading? Global occurrences of such ridges appear to indicate that magmatic activities had continued for million years after ridges were abandoned and often formed seamount chains over ridges. The extinct ridge and the seamount chain at the South China Sea represent one classic example of such ridges. To understand this unique process and the lithospheric and deep mantle structure, we carry out a Rayleigh wave phase velocity tomography using data from a passive-source OBS array experiment in South China Sea from 2012 to 2013. We correct OBS clock errors by using Scholte waves retrieved through cross-correlating hydrophone records of each OBS pair. 60 regional and teleseismic events with high quality Rayleigh waves are selected and their dispersion curves at the OBS array are used to inverse the phase velocities of periods from 15 s to 100 s. The shear wave velocity model derived from phase velocities of all periods shows a strong low-velocity zone situated beneath the seamounts starting at about 30 km depth. The lithosphere thickness of the extinct ridge inferred from this model provide insights on the cooling process and magmatism at this unique oceanic setting. In addition, our model images the tear of the subducting South China Sea plate beneath the Manila trench and Luzon island, which is clearly generated by the subduction of the extinct ridge and overriding seamounts.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA......586C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA......586C"><span>Time and Geochemical Distribution of Central Italy Magmatism : Paleosubduction processes or Crustal Stretching?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cadoux, A.; Aznar, C.; Pinti, D. L.; Chiesa, S.; Lefèvre, J. C.; Gillot, P. Y.</p> <p>2003-04-01</p> <p>Italian Plio-Quaternary magmatism is related to episodes of metasomatism produced by the subduction, rollback of the Adria Plate beneath Italy, and the opening of the Tyrrhenian back-arc basin. Authors interpret the space and time progression of the Cenozoic Italian volcanism as an indicator of the evolutionary history of the subduction processes or alternatively as local episodes of crustal stretching. Earlier magmatism (e.g.; Tuscan Magmatic Province; Pontine Islands) does not show a clear relationship between paleosubduction processes and its spatial and temporal distribution. At this regard, we started a study of the first magmatic manifestations in the northwestern Pontine Archipelago (located at the border of the continental shelf between Rome and Naples). In order to establish their relation with the known Italian magmatic provinces and better understand the magmatic processes at the source, we carried out a geochronological and geochemical combined study of the acidic lavas of the Ponza and Palmarola islands. Twenty-two new K/Ar ages show that the construction of these two islands has been relatively short. The island of Ponza has been built in less than 300 Ka, between 4.0 and 3.7 Ma, with the emplacement of rhyolitic domes, followed by ignimbrite-like flows, between 3.2 and 3.0 Ma. The volcanic activity has successively migrated westwards, forming the island of Palmarola in ca. 100 Ka, between 1.6 to 1.5 Ma. Previous hypothesis suggested Pliocene ages for these products. Final volcanic activity has been the trachytic dome south of Ponza, at 1Ma. Although separated by only few kilometers, Ponza and Palmarola have different geochemical signatures. Ponza rhyolites show an orogenic affinity whereas those of Palmarola and the Ponza trachyte, have a signature close to alkaline intraplate lavas. In terms of ages and trace elements distribution, the Ponza rhyolites could be related to some of the acidic manifestations of the Tuscan Magmatic Province, while Palmarola has some differences in the trace elements distribution. Although, Ponza and Palmarola show a predominant “orogenic“ character, it is attenuated with time, as shown by a decrease of the Th/Ta ratio, from 21 at 4.0 Ma to 11 at 1 Ma. This change seems to reflect an evolution of the geodynamical context: syn-collisional in the older products of Ponza to post-collisional, evoluting toward an intraplate magmatism, for the Palmarola products and the trachytic dome of Ponza. We are testing the hypothesis of a genetic link between earlier volcanic manifestations of the Tuscan Magmatic Province and the Pontine magmatism through a detailed geochronological and geochemical study of its products (Roccastrada, Amiata among others) and for which we will present preliminary data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMNH11A0096B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMNH11A0096B"><span>The Newberry Deep Drilling Project (NDDP)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bonneville, A.; Cladouhos, T. T.; Petty, S.; Schultz, A.; Sorle, C.; Asanuma, H.; Friðleifsson, G. Ó.; Jaupart, C. P.; Moran, S. C.; de Natale, G.</p> <p>2017-12-01</p> <p>We present the arguments to drill a deep well to the ductile/brittle transition zone (T>400°C) at Newberry Volcano, central Oregon state, U.S.A. The main research goals are related to heat and mass transfer in the crust from the point of view of natural hazards and geothermal energy: enhanced geothermal system (EGS supercritical and beyond-brittle), volcanic hazards, mechanisms of magmatic intrusions, geomechanics close to a magmatic system, calibration of geophysical imaging techniques and drilling in a high temperature environment. Drilling at Newberry will bring additional information to a very promising field of research initiated by ICDP in the Deep Drilling project in Iceland with IDDP-1 on Krafla in 2009, followed by IDDP-2 on the Reykjanes ridge in 2016, and the future Japan Beyond-Brittle project and Krafla Magma Testbed. Newberry Volcano contains one of the largest geothermal heat reservoirs in the western United States, extensively studied for the last 40 years. All the knowledge and experience collected make this an excellent choice for drilling a well that will reach high temperatures at relatively shallow depths (< 5000 m). The large conductive thermal anomaly (320°C at 3000 m depth), has already been well-characterized by extensive drilling and geophysical surveys. This will extend current knowledge from the existing 3000 m deep boreholes at the sites into and through the brittle-ductile transition approaching regions of partial melt like lateral dykes. The important scientific questions that will form the basis of a full drilling proposal, have been addressed during an International Continental Drilling Program (ICDP) workshop held in Bend, Oregon in September 2017. They will be presented and discussed as well as the strategic plan to address them.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/5572756-bermuda-appalachian-labrador-rises-common-non-hotspot-processes','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/5572756-bermuda-appalachian-labrador-rises-common-non-hotspot-processes"><span>Bermuda and Appalachian-Labrador rises: Common non-hotspot processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Vogt, P.R.</p> <p>1991-01-01</p> <p>Other than the Corner Rise-New England seamounts and associated White Mountains, most postbreakup intraplate igneous activity and topographic uplift in the western North Atlantic and eastern North America do not readily conform to simple hotspot models. For examples, the Bermuda Rise trends normal to its predicted hotspot trace. On continental crust, Cretaceous-Eocene igneous activity is scattered along a northeast-trending belt {approximately}500-1,000 km west of and paralleling the continent-ocean boundary. Corresponding activity in the western Atlantic generated seamounts preferentially clustered in a belt {approximately}1,000 km east of the boundary. The Eocene volcanism on Bermuda is paired with coeval magmatism of themore » Shenandoah igneous province, and both magmatic belts are associated with northeast-trending topographic bulges - the Appalachian-Labrador Rise to the west and the Bermuda Rise (Eocene ) to the east. The above observations suggest the existence of paired asthenosphere upwelling, paralleling and controlled by the deep thermal contrast across the northeast-trending continental margin. Such convection geometry, apparently fixed to the North American plate rather than to hotspots, is consistent with recent convection models by B. Hager. The additional importance of plate-kinematic reorganizations (causing midplate stress enhancement) is suggested by episodic igneous activity ca. 90-100 Ma and 40-45 Ma.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.7667E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.7667E"><span>Polyphase tectono-magmatic and fluid history related to mantle exhumation in an ultra-distal rift domain: example of the fossil Platta domain, SE Switzerland</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Epin, Marie-Eva; Manatschal, Gianreto; Amann, Méderic; Lescanne, Marc</p> <p>2017-04-01</p> <p>Despite the fact that many studies have investigated mantle exhumation at magma-poor rifted margins, there are still numerous questions concerning the 3D architecture, magmatic, fluid and thermal evolution of these ultra-distal domains that remain unexplained. Indeed, it has been observed in seismic data from ultra-distal magma-poor rifted margins that top basement is heavily structured and complex, however, the processes controlling the morpho-tectonic and magmatic evolution of these domains remain unknown. The aim of this study is to describe the 3D top basement morphology of an exhumed mantle domain, exposed over 200 km2 in the fossil Platta domain in SE Switzerland, and to define the timing and processes controlling its evolution. The examined Platta nappe corresponds to a remnant of the former ultra-distal Adriatic margin of the Alpine Tethys. The rift-structures are relatively well preserved due to the weak Alpine tectonic and metamorphic overprint during the emplacement in the Alpine nappe stack. Detailed mapping of parts of the Platta nappe enabled us to document the top basement architecture of an exhumed mantle domain and to investigate its link to later, rift/oceanic structures, magmatic additions and fluids. Our observations show a polyphase and/or complex: 1) deformation history associated with mantle exhumation along low-angle exhumation faults overprinted by later high-angle normal faults, 2) top basement morphology capped by magmato-sedimentary rocks, 3) tectono-magmatic evolution that includes gabbros, emplaced at deeper levels and subsequently exhumed and overlain by younger extrusive magmatic additions, and 4) fluid history including serpentinization, calcification, hydrothermal vent, rodingitization and spilitization affecting exhumed mantle and associated magmatic rocks. The overall observations provide important information on the temporal and spatial evolution of the tectonic, magmatic and fluid systems controlling the formation of ultra-distal magma-poor rifted margins as well as the processes controlling lithospheric breakup. In this context, our field observations can help to better understand the tectono-magmatic processes associated to these, not yet drilled domains that may form in young, narrow rifted margins (e.g. Red Sea, Gulf of Aden) or may represent the Ocean-Continent Transition in more mature, magma-poor Atlantic type systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.9671H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.9671H"><span>Insights into the crustal structure and magmatic evolution of the High and Western Plateau of the Manihiki Plateau, Central Pacific</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hochmuth, Katharina; Gohl, Karsten; Uenzelmann-Neben, Gabriele</p> <p>2014-05-01</p> <p>The Manihiki Plateau is a Large Igneous Province (LIP) located in the Central Pacific. It is assumed, that the formation of the Manihiki Plateau took place during the early Cretaceous in multiple volcanic stages as part of the "Super-LIP" Ontong-Java-Nui. The plateau consists of several sub-plateaus of which the Western Plateau und High Plateau are the largest. In addressing the plateau's magmatic evolutionary history, one of the key questions is whether all sub-plateaus experienced the same magmatic history or if distinct phases of igneous or tectonic processes led to its fragmentation. During the RV Sonne cruise SO-224 in 2012; we collected two deep crustal seismic refraction/wide-angle reflection lines, crossing the two main sub-plateaus. Modeling of P- and S-wave phases reveals the different crustal nature of both sub-plateaus. On the High Plateau, the 20 km thick crust is divided into four seismic units, interpreted to range from basaltic composition in the uppermost crust to peridotitic composition in the middle and lower crust. The Western Plateau on the other hand shows multiple rift structures and no indications of basalt flows. With a maximum of 17 km crustal thickness, the Western Plateau is also thinner than the High Plateau. The upper basement layers show relatively low P-wave velocities (3.0 - 5.0 km/s), which infers that on the Western Plateau these layers consist of volcanoclastic and carbonatic rocks rather than basaltic flow units. Later volcanic stages may be restricted to the High Plateau with a possible eastward trend in the center of volcanic activity. Extensive secondary volcanism does not seem to have occurred on the Western Plateau, and its later deformation is mainly caused by tectonic extension and rifting.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16..178O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16..178O"><span>Magmatic arc structure around Mount Rainier, WA, from the joint inversion of receiver functions and surface wave dispersion</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Obrebski, Mathias; Abers, Geoffrey A.; Foster, Anna</p> <p>2015-01-01</p> <p>The deep magmatic processes in volcanic arcs are often poorly understood. We analyze the shear wave velocity (VS) distribution in the crust and uppermost mantle below Mount Rainier, in the Cascades arc, resolving the main velocity contrasts based on converted phases within P coda via source normalization or receiver function (RF) analysis. To alleviate the trade-off between depth and velocity, we use long period phase velocities (25-100 s) obtained from earthquake surface waves, and at shorter period (7-21 s) we use seismic noise cross correlograms. We use a transdimensional Bayesian scheme to explore the model space (VS in each layer, number of interfaces and their respective depths, level of noise on data). We apply this tool to 15 broadband stations from permanent and Earthscope temporary stations. Most results fall into two groups with distinctive properties. Stations east of the arc (Group I) have comparatively slower middle-to-lower crust (VS = 3.4-3.8 km/s at 25 km depth), a sharp Moho and faster uppermost mantle (VS = 4.2-4.4 km/s). Stations in the arc (Group II) have a faster lower crust (VS = 3.7-4 km/s) overlying a slower uppermost mantle (VS = 4.0-4.3 km/s), yielding a weak Moho. Lower crustal velocities east of the arc (Group I) most likely represent ancient subduction mélanges mapped nearby. The lower crust for Group II ranges from intermediate to felsic. We propose that intermediate-felsic to felsic rocks represent the prearc basement, while intermediate composition indicates the mushy andesitic crustal magmatic system plus solidified intrusion along the volcanic conduits. We interpret the slow upper mantle as partial melt.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70037335','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70037335"><span>The Mackenzie River magnetic anomaly, Yukon and Northwest Territories, Canada-Evidence for Early Proterozoic magmatic arc crust at the edge of the North American craton</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pilkington, M.; Saltus, R.W.</p> <p>2009-01-01</p> <p>We characterize the nature of the source of the high-amplitude, long-wavelength, Mackenzie River magnetic anomaly (MRA), Yukon and Northwest Territories, Canada, based on magnetic field data collected at three different altitudes: 300??m, 3.5??km and 400??km. The MRA is the largest amplitude (13??nT) satellite magnetic anomaly over Canada. Within the extent of the MRA, source depth estimates (8-12??km) from Euler deconvolution of low-altitude aeromagnetic data show coincidence with basement depths interpreted from reflection seismic data. Inversion of high-altitude (3.5??km) aeromagnetic data produces an average magnetization of 2.5??A/m within a 15- to 35-km deep layer, a value typical of magmatic arc complexes. Early Proterozoic magmatic arc rocks have been sampled to the southeast of the MRA, within the Fort Simpson magnetic anomaly. The MRA is one of several broad-scale magnetic highs that occur along the inboard margin of the Cordillera in Canada and Alaska, which are coincident with geometric changes in the thrust front transition from the mobile belt to stable cratonic North America. The inferred early Proterozoic magmatic arc complex along the western edge of the North American craton likely influenced later tectonic evolution, by acting as a buttress along the inboard margin of the Cordilleran fold-and-thrust belt. Crown Copyright ?? 2008.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V11C0357H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V11C0357H"><span>Investigating Magmatic Processes in the Lower Levels of Mantle-derived Magmatic Systems: The Age & Emplacement of the Kunene Anorthosite Complex (SW Angola)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hayes, B.; Bybee, G. M.; Owen-Smith, T.; Lehmann, J.; Brower, A. M.; Ashwal, L. D.; Hill, C. M.</p> <p>2017-12-01</p> <p>Our understanding of mantle-derived magmatic systems has shifted from a notion of upper crustal, melt-dominated magma chambers that feed short-lived volcanic eruptions, to a view of more long-lived trans-crustal, mush-dominated systems. Proterozoic massif-type anorthosite systems are voluminous, plagioclase-dominated plutonic suites with ubiquitous intermediate compositions (An 50 ± 10) that represent mantle-derived magmas initially ponded at Moho depths and crystallized polybarically until emplacement at mid-crustal levels. Thus, these systems provide unique insight into magma storage and processing in the lower reaches of the magma mush column, where such interpretation has previously relied on cumulate xenoliths in lavas, geophysical data and experimental/numerical modeling. We present new CA-ID-TIMS ages and a series of detailed field observations from the largest Proterozoic anorthosite massif on Earth, the Kunene Anorthosite Complex (KAC) of SW Angola. Field structures indicate that (i) the bulk of the material was emplaced in the form of crystal mushes, as both plutons and sheet-like intrusions; (ii) prolonged magmatism led to cumulate disaggregation (block structure development) and remobilization, producing considerable textural heterogeneity; (iii) crystal-rich magmatic flow induced localized recrystallization and the development of protoclastic (mortar) textures; and (iv) late residual melts were able to migrate locally prior to complete solidification. Dating of pegmatitic pods entrained from cumulate zones at the base of the crust (1500 ± 13 Ma) and their host anorthosites (1375-1438 Ma) reveals time periods in the range of 60-120 Myr between the earliest products of the system and the final mushes emplaced at higher crustal levels. Therefore, the KAC represents a complex, mushy magmatic system that developed over a long period of time. Not only do these observations help in refining our understanding of Proterozoic anorthosite petrogenesis, they also allow us to place constraints on the types of magmatic processes that operate in the lower levels of other trans-crustal magmatic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAESc.144..184P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAESc.144..184P"><span>Hydrous parental magmas of Early to Middle Permian gabbroic intrusions in western Inner Mongolia, North China: New constraints on deep-Earth fluid cycling in the Central Asian Orogenic Belt</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pang, Chong-Jin; Wang, Xuan-Ce; Xu, Bei; Luo, Zhi-Wen; Liu, Yi-Zhi</p> <p>2017-08-01</p> <p>The role of fluids in the formation of the Permian-aged Xigedan and Mandula gabbroic intrusions in western Inner Mongolia was significant to the evolution of the Xing'an Mongolia Orogenic Belt (XMOB), and the active northern margin of the North China Craton (NCC). Secondary Ion Mass Spectroscopy (SIMS) U-Pb zircon geochronology establishes that the Xigedan gabbroic intrusion in the northern NCC was emplaced at 266 Ma, and is therefore slightly younger than the ca 280 Ma Mandula gabbroic intrusion in the XMOB. Along with their felsic counterparts, the mafic igneous intrusions record extensive bimodal magmatism along the northern NCC and in the XMOB during the Early to Middle Permian. The Mandula gabbroic rocks have low initial 87Sr/86Sr ratios (0.7040-0.7043) and positive εNd(t) (+6.2 to +7.3) and εHf(t) values (+13.4 to +14.5), resembling to those of contemporaneous Mandula basalts. These features, together with the presence of amphibole and the enrichment of large ion lithophile elements (LILE, e.g., Rb, Ba, U and Sr) and depletion of Nb-Ta suggest that the parental magmas of the Mandula mafic igneous rocks were derived from a depleted mantle source metasomatized by water-rich fluids. In contrast, the Xigedan gabbroic rocks are characterised by high 87Sr/86Sr ratios (0.7078-0.7080) and zircon δ18O values (5.84-6.61‰), but low εNd(t) (-9.3 to -10.2) and εHf(t) values (-8.76 to -8.54), indicative of a long-term enriched subcontinental lithosphere mantle source that was metasomatized by recycled, high δ18O crustal materials prior to partial melting. The high water contents (4.6-6.9 wt%) and arc-like geochemical signature (enrichment of fluid-mobile elements and depletion of Nb-Ta) of the parental magmas of the Xigedan gabbroic rocks further establish the existence of a mantle hydration event caused by fluid/melts released from hydrated recycled oceanic crust. Incompatible element modelling shows that 5-10% partial melting of an enriched mantle source by adding respectively 0.5% and 2% sediment melts and fluids, could have produced the parental magmas of the Xigedan gabbroic rocks. A range of geological evidence establishes an intracontinental origin for Late Paleozoic mafic igneous rocks along the northern NCC and in the XMOB, rather than a subduction-related setting. We therefore propose a deep-Earth water cycling process to account for mantle hydration and subsequent Late Paleozoic magmatism, supporting a geodynamic link between deep-Earth water cycling, and intracontinental magmatism and lithospheric extension.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFM.V21E..02H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFM.V21E..02H"><span>Understanding the dynamics of magmatic systems - evidence from Long Valley Caldera and Kilauea Volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hill, D. P.; Swanson, D. A.</p> <p>2001-12-01</p> <p>Active magmatic processes produce a wide range of signals that are capable of detection at the Earth's surface by modern geophysical and geochemical instrumentation. The most robust of these signals include spatial-temporal patterns of (1) ground deformation spanning a broad spectrum from gradual secular and quasi-static changes to the high-frequency vibrations associated with seismic waves generated by local, brittle-failure earthquakes and (2) magmatic gas emissions of, most notably, SO2 and CO2. The long records of deformation (in this broad sense) and geochemical data accumulated for Kilauea Volcano on the Island of Hawai`i and in Long Valley Caldera in eastern California exemplify the value of spatially and temporally dense monitoring as a basis for understanding the dynamics of magmatic systems. Kilauea's magma conduit, defined by brittle failure and LP earthquakes, has the form of a narrow, straw-like structure extending from within the lithosphere at a depth of >40 km to a magma chamber centered roughly 5 km beneath the summit crater (Halemaumau). This shallow magma chamber, which consists of a plexus of dikes and sills, is capable of feeding eruptions both within the summit caldera and along the east and southwest rift zones. The current eruption from vents along the east rift zone, which began 18 years ago, appears to be gradually draining this summit magma chamber, as Kilauea's summit has been subsiding about 10 cm/yr since the eruption began. This is equivalent to a volume of about 0.01 km3/yr, 10 percent of the eruption rate of 0.1 km3/yr. Most of the gas released by the magma column escapes through the summit caldera as it ascends from the magma chamber toward the summit and thence through conduits to the active vents on the east rift zone. Indeed, the CO2 flux (about 10,000 tones/yr) from the caldera serves as a proxy for magma flux through the conduit system. Dynamic interaction of the active magma conduit with the hydrothermal system beneath the summit crater produces sequences of shallow LP and VLP earthquakes. Two magmatic systems contribute to the 20 years of unrest in Long Valley Caldera: one beneath the resurgent dome in the center of the caldera and the other beneath Mammoth Mountain on the southwest rim of the caldera. Cumulative uplift of the resurgent dome by 80 cm reflects a volume increase of roughly 0.3 km3 in magma to chamber centered at a depth of 7 to 10 km beneath the surface. Recurring swarms of brittle-failure earthquakes in the south moat follow increased inflation rates with the more energetic episodes associated with intrusions of magma or magmatic brine into the brittle crust. The absence of seismicity at depths greater than 10 km beneath the caldera, however, leaves a question mark for the nature of this magmatic system at mid- to lower-crustal depths. The absence of magmatic gas emissions in the vicinity of the resurgent dome and south moat suggests that the volatile components of this magmatic system remain trapped below an impermeable seal. In contrast, a dike-like distribution of deep LP earthquakes overlain by a volume of brittle-failure earthquakes, including several shallow VLP earthquakes, delineate the magmatic system beneath Mammoth Mountain from mid-crustal depths of 30 km to within 3 or 4 km of the surface. This system, which became activated with a six-month-long earthquake swarm and intrusion beneath Mammoth Mountain in 1989, has continued to produce a diffuse efflux of magmatic CO2 at a rate of 200 to 300 tones/day apparently fed by basaltic magma distributed in a plexus of dikes and sills at mid-crustal depths.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V11C2057M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V11C2057M"><span>Subaqueous non-vesicular to poorly-vesicular shards: hydroclastic fragmentation on seamounts and summit calderas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mueller, W. U.; Dingwell, D. B.; Downey, W. S.; Mastin, L. G.</p> <p>2008-12-01</p> <p>Recognizing pyroclastic deposits that originate directly from magmatic and phreatomagmatic explosions in a subaqueous setting is based upon sedimentary structures, such as massive, stratified, and graded beds as well as (pyro)clast size. Ideally such deposits form ordered fining-and thinning-upward sequences. Pumice, scoria, glass shards, euhedral and broken crystals, and lithic fragments are constituents that support an explosive heritage. Recent deep-sea ROV and submersible dives have retrieved non-vesicular to vesicle- poor, mm-scale, mafic shards in 5-15 cm-thick massive and/or graded (stratified) deposits, for which a subaqueous explosive origin has been inferred. These sheet hyaloclastites with variable shard shapes were first documented on Seamount 6 as deep-sea Limu O Pele at water depths > 1000 m. We identified in Seamount 6 samples equant to blocky shards with angular to subrounded terminations, but also subordinate hair-like and contorted glassy filaments, warped shards and irregular shards. Shards display internal laminations (flow-banding?) and have local perlitic fractures. Bubble wall shards derived from scoria burst were rare. In combination with all the above and a poor shard vesicularity (< 2%), a magmatic explosive origin seems improbable. Such small-volume deposits have been reported from seamounts and summit calderas associated with subaqueous drainage tubes and ponded magma in depths > 1000 m. We envision that hydrostatic pressure commensurate with water depth played a significant role. The deposits can be readily explained by a hydroclastic process whereby fragmentation occurred at the milli-second (Limu) to second scale (hyaloclastite). Hence, hyperquenched glass shards or thread-like glass filaments need not require magmatic explosivity. Constant surface interaction between aphyric, low-viscosity, high temperature, magma-lava at depth with seawater causes fragmentation (granulation) that can generate such delicate shards. The transfer of heat to the ambient medium, seawater, favours turbulent convection causing strong water movement that strips glassy rinds and lofts the fine-grained shards and Limu O Pele into the water column. Once entrained, shards are deposited after water turbulence abates. Congestion of the water column causes deposition from low-density turbidity currents and subaqueous fallout. In this manner delicate textures would remain intact even if removed from the site of hydroclastic fragmentation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912321G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912321G"><span>Magmatism in Lithosphere Delamination process inferred from numerical models</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Göǧüş, Oǧuz H.; Ueda, Kosuke; Gerya, Taras</p> <p>2017-04-01</p> <p>The peel away of the oceanic/continental slab from the overlying orogenic crust has been suggested as a ubiquitous process in the Alpine-Mediterranean orogenic region (e.g. Carpathians, Apennines, Betics and Anatolia). The process is defined as lithospheric delamination where a slab removal/peel back may allow for the gradual uprising of sub-lithospheric mantle, resulting in high heat flow, transient surface uplift/subsidence and varying types of magma production. Geodynamical modeling studies have adressed the surface response to the delamination in the context of regional tectonic processes and explored wide range of controlling parameters in pre-syn and post collisional stages. However, the amount and styles of melt production in the mantle (e.g. decompression melting, wet melting in the wedge) and the resulting magmatism due to the lithosphere delamination remains uncertain. In this work, by using thermomechanical numerical experiments, designed in the configuration of subduction to collision, we investigated how melting in the mantle develops in the course of delamination. Furthermore, model results are used to decipher the distribution of volumetric melt production, melt extraction and the source of melt and the style of magmatism (e.g. igneous vs. volcanic). The model results suggest that a broad region of decompression melting occurs under the crust, mixing with the melting of the hydrated mantle derived by the delaminating/subducting slab. Depending on the age of the ocean slab, plate convergence velocity and the mantle temperature, the melt production and crust magmatism may concentrate under the mantle wedge or in the far side of the delamination front (where the subduction begins). The slab break-off usually occurs in the terminal stages of the delamination process and it may effectively control the location of the magmatism in the crust. The model results are reconciled with the temporal and spatial distribution of orogenic vs. anorogenic magmatism in the Mediterranean region in which the latter may have developed due to the delamination process.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tectp.718...25B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tectp.718...25B"><span>A new tectono-magmatic model for the Lofoten/Vesterålen Margin at the outer limit of the Iceland Plume influence</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breivik, Asbjørn Johan; Faleide, Jan Inge; Mjelde, Rolf; Flueh, Ernst R.; Murai, Yoshio</p> <p>2017-10-01</p> <p>The Early Eocene continental breakup was magma-rich and formed part of the North Atlantic Igneous Province. Extrusive and intrusive magmatism was abundant on the continental side, and a thick oceanic crust was produced up to a few m.y. after breakup. However, the extensive magmatism at the Vøring Plateau off mid-Norway died down rapidly northeastwards towards the Lofoten/Vesterålen Margin. In 2003 an Ocean Bottom Seismometer profile was collected from mainland Norway, across Lofoten, and into the deep ocean. Forward/inverse velocity modeling by raytracing reveals a continental margin transitional between magma-rich and magma-poor rifting. For the first time a distinct lower-crustal body typical for volcanic margins has been identified at this outer margin segment, up to 3.5 km thick and ∼50 km wide. On the other hand, expected extrusive magmatism could not be clearly identified here. Strong reflections earlier interpreted as the top of extensive lavas may at least partly represent high-velocity sediments derived from the shelf, and/or fault surfaces. Early post-breakup oceanic crust is moderately thickened (∼8 km), but is reduced to 6 km after 1 m.y. The adjacent continental crystalline crust is extended down to a minimum of 4.5 km thickness. Early plate spreading rates derived from the Norway Basin and the northern Vøring Plateau were used to calculate synthetic magnetic seafloor anomalies, and compared to our ship magnetic profile. It appears that continental breakup took place at ∼53.1 Ma, ∼1 m.y. later than on the Vøring Plateau, consistent with late strong crustal extension. The low interaction between extension and magmatism indicates that mantle plume material was not present at the Lofoten Margin during initial rifting, and that the observed excess magmatism was created by late lateral transport from a nearby pool of plume material into the lithospheric rift zone at breakup time.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70010544','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70010544"><span>Petrology of eucrites, howardites and mesosiderites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Duke, M.B.; Silver, L.T.</p> <p>1967-01-01</p> <p>The eucrite and howardite calcium-rich achondrites and many mesosiderites are considered as a coherent meteorite assemblage, their silicates consisting essentially of calciumpoor monoclinic and orthorhombic pyroxenes and calcium-rich plagioclase feldspar. The achondrites can be grouped according to their brecciated structure as follows: eucrites-unbrecciated and monomict brecciated achondrites; howardites-polymict brecciated achondrites. Many mesosiderites contain brecciated structures; they are distinguished from the achondrites by their large metallic fraction. The structure and composition of rock fragments in the breccias indicate a complicated sequence of events including magmatic differentiation, brecciation, recrystallization and refragmentation, and ejection from the parent body. Detailed mineralogical and chemical data suggest that the magmatic differentiation proceeded primarily by the separation of pyroxene from an ultrabasic parent material that had a much lower alkali content than ordinary chondrites. Magmatic crystallization took place in environments ranging from extrusive to deep-seated intrusive. Polymict breccias contain fragments with a wide variety of magmatic and recrystallization textures, which suggests that the breccias were formed either in very large or repeated fragmentation events. Monomict breccias contain fragments with a small range of similar magmatic textures, which suggests that these breccias were formed by small or single events. Petrographic evidence suggests that many of the breccias are impact breccias. Either in their original magmatic crystallization sites or in the sites of breccia accumulation, most of these meteorites apparently had a near-surface location prior to ejection from the parent body. Evidence obtained from eucrites, howardites and mesosiderites forms an important part of our understanding of the early evolution of the surface regions of their parent body. Chemical and oxidation conditions were different from those presently found in the Earth's crust and upper mantle, but the necessary conditions may have been present in the early history of the Earth. A lunar origin for eucrites, howardites and mesosiderites is proposed, but an asteroidal origin can not be presently excluded. ?? 1967.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70161997','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70161997"><span>Imaging the magmatic system of Mono Basin, California with magnetotellurics in three--dimensions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peacock, Jared R.; Mangan, Margaret T.; McPhee, Darcy K.; Ponce, David A.</p> <p>2015-01-01</p> <p>A three–dimensional (3D) electrical resistivity model of Mono Basin in eastern California unveils a complex subsurface filled with zones of partial melt, fluid–filled fracture networks, cold plutons, and regional faults. In 2013, 62 broadband magnetotelluric (MT) stations were collected in an array around southeastern Mono Basin from which a 3D electrical resistivity model was created with a resolvable depth of 35 km. Multiple robust electrical resistivity features were found that correlate with existing geophysical observations. The most robust features are two 300 ± 50 km3 near-vertical conductive bodies (3–10 Ω·m) that underlie the southeast and north-eastern margin of Mono Craters below 10 km depth. These features are interpreted as magmatic crystal–melt mush zones of 15 ± 5% interstitial melt surrounded by hydrothermal fluids and are likely sources for Holocene eruptions. Two conductive east–dipping structures appear to connect each magma source region to the surface. A conductive arc–like structure (< 0.9 Ω·m) links the northernmost mush column at 10 km depth to just below vents near Panum Crater, where the high conductivity suggests the presence of hydrothermal fluids. The connection from the southernmost mush column at 10 km depth to below South Coulée is less obvious with higher resistivity (200 Ω·m) suggestive of a cooled connection. A third, less constrained conductive feature (4–10 Ω·m) 15 km deep extending to 35 km is located west of Mono Craters near the eastern front of the Sierra Nevada escarpment, and is coincident with a zone of sporadic, long–period earthquakes that are characteristic of a fluid-filled (magmatic or metamorphic) fracture network. A resistive feature (103–105 Ω·m) located under Aeolian Buttes contains a deep root down to 25 km. The eastern edge of this resistor appears to structurally control the arcuate shape of Mono Craters. These observations have been combined to form a new conceptual model of the magmatic system beneath Mono Craters to a depth of 30 km.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CoMP..173....9B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CoMP..173....9B"><span>Melt inclusion constraints on volatile systematics and degassing history of the 2014-2015 Holuhraun eruption, Iceland</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bali, E.; Hartley, M. E.; Halldórsson, S. A.; Gudfinnsson, G. H.; Jakobsson, S.</p> <p>2018-02-01</p> <p>The mass of volatiles emitted during volcanic eruptions is often estimated by comparing the volatile contents of undegassed melt inclusions, trapped in crystals at an early stage of magmatic evolution, with that of the degassed matrix glass. Here we present detailed characterisation of magmatic volatiles (H2O, CO2, S, Fl and Cl) of crystal-hosted melt and fluid inclusions from the 2014-2015 Holuhraun eruption of the Bárðarbunga volcanic system, Iceland. Based on the ratios of magmatic volatiles to similarly incompatible trace elements, the undegassed primary volatile contents of the Holuhraun parental melt are estimated at 1500-1700 ppm CO2, 0.13-0.16 wt% H2O, 60-80 ppm Cl, 130-240 ppm F and 500-800 ppm S. High-density fluid inclusions indicate onset of crystallisation at pressures ≥ 0.4 GPa ( 12 km depth) promoting deep degassing of CO2. Prior to the onset of degassing, the melt CO2 content may have reached 3000-4000 ppm, with the total magmatic CO2 budget estimated at 23-55 Mt. SO2 release commenced at 0.12 GPa ( 3.6 km depth), eventually leading to entrapment of SO2 vapour in low-density fluid inclusions. We calculate the syn-eruptive volatile release as 22.2 Mt of magmatic H2O, 5.9-7.7 Mt CO2, and 11.3 Mt of SO2 over the course of the eruption; F and Cl release were insignificant. Melt inclusion constraints on syn-eruptive volatile release are similar to estimates made during in situ field monitoring, with the exception of H2O, where field measurements may be heavily biased by the incorporation of meteoric water.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V53A..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V53A..01M"><span>Resolving the potential mantle reservoirs that influence volcanism in the West Antarctic Rift System</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maletic, E. L.; Darrah, T.</p> <p>2017-12-01</p> <p>Lithospheric extension and magmatism are key characteristics of active continental rift zones and are often associated with long-lasting alkaline magmatic provinces. In these settings, a relationship between lithospheric extension and mantle plumes is often assumed for the forces leading to rift evolution and the existence of a plume is commonly inferred, but typically only extension is supported by geological evidence. A prime example of long-lasting magmatism associated with an extensive area of continental rifting is the West Antarctic Rift System (WARS), a 2000 km long zone of ongoing extension within the Antarctic plate. The WARS consists of high alkaline silica-undersaturated igneous rocks with enrichments in light rare earth elements (LREEs). The majority of previous geochemical work on WARS volcanism has focused on bulk classification, modal mineralogy, major element composition, trace element chemistry, and radiogenic isotopes (e.g., Sr, Nd, and Pb isotopes), but very few studies have evaluated volatile composition of volcanics from this region. Previous explanations for WARS volcanism have hypothesized a plume beneath Marie Byrd Land, decompression melting of a fossilized plume head, decompression melting of a stratified mantle source, and mixing of recycled oceanic crust with one or more enriched mantle sources from the deep mantle, though researchers are yet to reach a consensus. Unlike trace elements and radiogenic isotopes which can be recycled between the crust and mantle and which are commonly controlled by degrees of partial melting and prior melt differentiation, noble gases are present in low concentrations and chemically inert, allowing them to serve as reliable tracers of volatile sources and subsurface processes. Here, we present preliminary noble gas isotope (e.g., 3He/4He, CO2/3He, CH4/3He, 40Ar/36Ar, 40Ar*/4He) data for a suite of lava samples from across the WARS. By coupling major and trace element chemistry with noble gas elemental and isotopic composition and other volatiles from a suite of volcanic rocks in the WARS, we can better constrain a magmatic source and provide geological evidence that could support or oppose the existence of a mantle plume, HIMU plume, or deconvolve mantle-lithosphere interactions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JAESc..72..129W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JAESc..72..129W"><span>Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Xiaoxia; Wang, Tao; Zhang, Chengli</p> <p>2013-08-01</p> <p>The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction of the Mianlue Ocean between the South Qinling Belt and the South China Block. Voluminous late-stage (225-185 Ma) magmatism evolved from early I-type to later I-A-type granitoids associated with contemporaneous lamprophyres, representative of a transition from syn- to post-collisional setting in response to the collision between the North China and the South China blocks. Late Mesozoic (158-100 Ma) granitoids, located in the southern margin of the North China Block and the eastern part of the North Qinling Belt, are characterized by I-type, I- to A-type, and A-type granitoids that were emplaced in a post-orogenic or intraplate setting. The first three of the four periods of magmatism were associated with three important orogenic processes and the last one with intracontinental process. These suggest that the tectonic evolution of the Qinling Orogen is very complicated.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JVGR..166..255G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JVGR..166..255G"><span>Major hydrogeochemical processes in the two reservoirs of the Yangbajing geothermal field, Tibet, China</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guo, Qinghai; Wang, Yanxin; Liu, Wei</p> <p>2007-10-01</p> <p>The Yangbajing geothermal field with the highest reservoir temperature in China is located about 90 km northwest to Lhasa City, capital of Tibet, where high temperature geothermal fluids occur both in shallow and deep reservoirs. The geophysical survey by the INDEPTH (International Deep Profiling of Tibet and the Himalayas) project group proved the existence of magmatic heat source at Yangbajing. In the study area, the hydrochemistry of cold surface waters and groundwaters and that of thermal groundwaters from both reservoirs are distinctively different. However, analysis of the relationship between enthalpy values and Cl concentrations of cold groundwaters and geothermal fluids indicates that the geothermal fluids from the shallow reservoir were formed as a result of mixing of cold groundwaters with geothermal fluids from the deep reservoir. In other words, the geothermal fluids from the deep reservoir flowed upwards into the shallow reservoir where it was diluted by the shallow cold groundwaters to form the shallow geothermal fluids with much lower temperature. A binary mixing model with two endmembers (the cold groundwaters and the deep geothermal fluids) was proposed and the mixing ratios for the geothermal fluid from each shallow well were estimated. Using the mixing ratios, the concentrations of some constituents in shallow geothermal fluids, such as As, B, SiO 2, SO 42- and F, were calculated and their differences with the actual concentrations were estimated. The results show that the differences between estimated and actual concentrations of As and B are small (the average absolute values being only 1.9% and 7.9%, respectively), whereas those of SiO 2, SO 42- and F are much bigger, indicating that other hydrogeochemical processes are responsible for the concentrations of these constituents. It is postulated that SiO 2 precipitation due to water temperature decrease, H 2S oxidation and ion exchange between OH - in geothermal waters and exchangeable F - in fluoride bearing silicate minerals during the geothermal fluid upflow might be the causes for the observed concentration differences.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009DokES.429.1439V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009DokES.429.1439V"><span>Early Archean sialic crust of the Siberian craton: Its composition and origin of magmatic protoliths</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vovna, G. M.; Mishkin, M. A.; Sakhno, V. G.; Zarubina, N. V.</p> <p>2009-12-01</p> <p>This study demonstrates that the base of the Archean deep-seated granulite complexes within the Siberian craton consists of a metabasite-enderbite association. The major and trace element distribution patterns revealed that the protoliths of this association are represented by calc-alkaline andesites and dacites, containing several minor sequences of komatiitic-tholeiitic volcanic rocks. The origin of the primary volcanic rocks of the metabasite-enderbite association is inferred on the basis of a model of mantle plume magmatism, which postulates that both andesitic and dacitic melts were derived from the primary basitic crust at the expense of heat generated by ascending mantle plumes. The formation of the protoliths of the Archen metabasite-enderbite association of the Siberian craton began at 3.4 Ga and continued until the late Archean.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V33E3157S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V33E3157S"><span>The Colima volcano magmatic system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spica, Z.; Perton, M.; Legrand, D.</p> <p>2016-12-01</p> <p>We show how and where magmas are produced and stored at Colima volcano, Mexico, by performing an ambient noise tomography inverting jointly the Rayleigh and Love wave dispersion curves for both phase and group velocities. We obtain shear wave velocity and radial anisotropy models. The shear wave velocity model shows a deep, large and well-delineated elliptic-shape magmatic reservoir below the Colima volcano complex at a depth of about 15 km. The radial anisotropy model shows an important negative feature rooting up to ≥35 km depth until the roof of the magma reservoir, suggesting the presence of vertical fractures where fluids migrate upward and accumulate in the magma reservoir. The convergence of both a low velocity zone and a negative anisotropy suggests that the magma is mainly stored in conduits or inter-fingered dykes as opposed to horizontally stratified magma reservoir.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8171P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8171P"><span>Quantitative assessment of magmatic refill and overpressure in crustal reservoirs by monitoring He isotope composition from volcanic gases: the case of Mt Etna (Italy)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paonita, Antonio; Caracausi, Antonio; Martelli, Mauro; Rizzo, Andrea</p> <p>2016-04-01</p> <p>There is agreement in recognizing episodes of magma injection into crustal chambers as main triggers of eruptive activity of volcanoes (Caricchi et al., 2014). These events cause in fact a buildup of the internal pressure in magma chamber, which in turn controls outpouring magma amount, possible failure of wall-rocks, dike opening, up to a potential eruption. Assessment of the time-dependent pressurization while occurring in chamber is therefore challenging aim of current volcanological research. Recent advancements in estimating the time-dependent pressurization as long as occurring in chamber come from inverse modeling of ground deformation data, which does not however calculate internal evolution of the magma reservoir (Gregg et al., 2013; Cannavò et al., 2015). On the other hand, the geochemistry of volcanic gases has basically addressed to the pressure(depth) of gas exsolution so far (Caracausi et al., 2003; Aiuppa et al., 2007; Paonita et al., 2012). We developed an pioneering tool that computes the changes of 3He/4He isotope ratio of volcanic gases with respect to a background, as a function of the time-dependent outflow of volatiles from a chamber subjected to evolution of internal pressure through an injection event. Our approach postulates a low-3He/4He gas endmember coming from resident magmas stored in crust, that mixes with a high-3He/4He gas endmember from deep parental magmas refilling the deep chamber. We couple a mass balance between the two gas endmembers to a physical model of the magma chamber. When a deep input pressurizes the chamber, the latter releases large amounts of the high-3He/4He gas endmember, so as to change 3He/4He of discharged volcanic gases. We applied the model to the long-term series of He isotope ratios from geochemical monitoring of some peripheral gas emissions at the base of Mt Etna, fed by magmatic degassing occurring at 200-400 MPa (Paonita et al., 2012). The isotope ratios have in fact displayed phases of increase occurred at all the sampled emissions some months before the onset of eruptions, due to deep magma recharges. This behaviour has been systematic for all the main eruptive phases occurred at Mt Etna since 2001. For most of the events, we quantitatively estimated the rate of magmatic refill during the pre-eruptive recharges of the system, as well as the growth of the overpressure in the deep chamber. Failure of the wall rocks and dike opening is also explained in the case of 2001 eruption, because chamber overpressure overcame the yield strength of rocks. The results suggest that key parameters as the rate of magma inflow and the volume change in deep chamber can be estimated prior to impending eruptions and directly compared to inferences from geodetic signals.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JGRB..108.2028H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JGRB..108.2028H"><span>Mixing of magmatic volatiles with groundwater and interaction with basalt on the summit of Kilauea Volcano, Hawaii</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hurwitz, Shaul; Goff, Fraser; Janik, Cathy J.; Evans, William C.; Counce, Dale A.; Sorey, Michael L.; Ingebritsen, Steven E.</p> <p>2003-01-01</p> <p>We interpret new chemical and isotopic data from samples collected between October 1998 and March 2002 from the NSF well (also called the Keller well), the only deep well on the summit of Kilauea Volcano, Hawaii. Sample collection followed cleaning of the well, which renewed access to the hydrothermal system very close to the loci of magmatic and fumarolic activity. The chemical and isotopic compositions of the new samples differ remarkably from data published previously. On the basis of the S/Cl ratio and carbon and helium isotopes we conclude that the thermal fluids formed by condensation of magmatic gas into shallow meteoric groundwater. Gas condensation was followed by a complex pattern of basalt dissolution accompanied by an increase of fluid pH and precipitation of secondary minerals. Geochemical modeling and geothermometry imply that the fluids equilibrated with an assemblage of secondary minerals at temperatures between 90 and 140°C. The significantly different chemical composition of the NSF well fluids from that of springs along the southern coast of the island indicates that mass transport from the summit region toward the lower flanks of the volcano is limited.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P53G..01R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P53G..01R"><span>Divergent Geophysical Evolution of Vesta and Ceres</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Raymond, C. A.; Ermakov, A.; Castillo, J. C.; Fu, R. R.; McSween, H. Y., Jr.; McCord, T. B.; Park, R. S.; Russell, C. T.; De Sanctis, M. C.; Jaumann, R.; Konopliv, A. S.</p> <p>2017-12-01</p> <p>The Dawn mission explored two massive protoplanets in the main asteroid belt, Vesta and Ceres, that are fossils from the earliest epoch of solar system formation. Dawn's data provide evidence that these bodies formed very early, within the first few million years after CAIs, yet they followed divergent evolutionary paths. Vesta formed <1.5 Myr after CAIs of volatile-depleted chondritic material. Dawn confirmed the HED-based prediction that Vesta melted, forming at least a partial magma ocean, that yielded a large iron core. Gravity and spectral data support a complex magmatic evolution, resulting in a compositionally stratified mantle, with olivine sequestered in the deep mantle, and eruption of evolved melts. Such complexity can explain the apparent distinct magmatic reservoirs implied by trace elements in the HED clan. Discovery of hydrated material on Vesta's surface implies that volatile delivery to the inner solar system was an important process. Thus, while the basic HED paradigm was confirmed, we learned that differentiation on a small planet is more complex than envisioned. Dwarf planet Ceres was known to be water-rich before Dawn arrived. However, contrary to the expected ice-rich, viscously-relaxed smooth surface resulting from physical differentiation and freezing of an ancient subsurface ocean, its surface has many craters, implying a mechanically strong thick crust. The lack of large craters and Ceres' gravitationally-relaxed shape at long wavelengths implies that a strong crust overlies a weaker deep interior. The globally homogeneous distribution of minerals across the surface indicates that Ceres' interior experienced pervasive alteration. Topography and morphology of the surface reveals smoother, apparently resurfaced areas, generally at lower elevation, and rougher areas with greater relief. Local morphology such as crater floor deposits, isolated mountains, and enigmatic bright areas indicate recently active processes on Ceres, likely driven by brine cryovolcanism. Causes of the divergent evolution of these bodies include their accretionary environment, timing of accretion and size. Acknowledgements: Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to the National Aeronautics and Space Administration.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020074676&hterms=geological&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dgeological','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020074676&hterms=geological&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dgeological"><span>The Moon: Keystone to Understanding Planetary Geological Processes and History</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2002-01-01</p> <p>Extensive and intensive exploration of the Earth's Moon by astronauts and an international array of automated spacecraft has provided an unequaled data set that has provided deep insight into geology, geochemistry, mineralogy, petrology, chronology, geophysics and internal structure. This level of insight is unequaled except for Earth. Analysis of these data sets over the last 35 years has proven fundamental to understanding planetary surface processes and evolution, and is essential to linking surface processes with internal and thermal evolution. Much of the understanding that we presently have of other terrestrial planets and outer planet satellites derives from the foundation of these data. On the basis of these data, the Moon is a laboratory for understanding of planetary processes and a keystone for providing evolutionary perspective. Important comparative planetology issues being addressed by lunar studies include impact cratering, magmatic activity and tectonism. Future planetary exploration plans should keep in mind the importance of further lunar exploration in continuing to build solid underpinnings in this keystone to planetary evolution. Examples of these insights and applications to other planets are cited.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940016210&hterms=plate+tectonics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dplate%2Btectonics','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940016210&hterms=plate+tectonics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dplate%2Btectonics"><span>Venus magmatic and tectonic evolution</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Phillips, R. J.; Hansen, V. L.</p> <p>1993-01-01</p> <p>Two years beyond the initial mapping by the Magellan spacecraft, hypotheses for the magmatic and tectonic evolution of Venus have become refined and focused. We present our view of these processes, attempting to synthesize aspects of a model for the tectonic and magmatic behavior of the planet. The ideas presented should be taken collectively as an hypothesis subject to further testing. The quintessence of our model is that shear and buoyancy forces in the upper boundary layer of mantle convection give rise to a spatially and temporally complex pattern of strain in a one-plate Venusian lithosphere and modulate the timing and occurrence of magmatism on a global basis.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JVGR..344...79B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JVGR..344...79B"><span>Repeated magmatic intrusions at El Hierro Island following the 2011-2012 submarine eruption</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Benito-Saz, Maria A.; Parks, Michelle M.; Sigmundsson, Freysteinn; Hooper, Andrew; García-Cañada, Laura</p> <p>2017-09-01</p> <p>After more than 200 years of quiescence, in July 2011 an intense seismic swarm was detected beneath the center of El Hierro Island (Canary Islands), culminating on 10 October 2011 in a submarine eruption, 2 km off the southern coast. Although the eruption officially ended on 5 March 2012, magmatic activity continued in the area. From June 2012 to March 2014, six earthquake swarms, indicative of magmatic intrusions, were detected underneath the island. We have studied these post-eruption intrusive events using GPS and InSAR techniques to characterize the ground surface deformation produced by each of these intrusions, and to determine the optimal source parameters (geometry, location, depth, volume change). Source inversions provide insight into the depth of the intrusions ( 11-16 km) and the volume change associated with each of them (between 0.02 and 0.13 km3). During this period, > 20 cm of uplift was detected in the central-western part of the island, corresponding to approximately 0.32-0.38 km3 of magma intruded beneath the volcano. We suggest that these intrusions result from deep magma migrating from the mantle, trapped at the mantle/lower crust discontinuity in the form of sill-like bodies. This study, using joint inversion of GPS and InSAR data in a post-eruption period, provides important insight into the characteristics of the magmatic plumbing system of El Hierro, an oceanic intraplate volcanic island.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ESASP.728E..15B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ESASP.728E..15B"><span>Geological Implications From Complete Gondwana GOCE- Products Reconstructions and Link to Lithospheric Roots</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Braitenberg, Carla; Mariani, Patrizia</p> <p>2015-03-01</p> <p>The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to analyze tectonic structures at continental scale. Geologic correlation studies propose to continue the tectonic lineaments across continents to the pre-breakup position. Tectonic events that induce density changes, as metamorphic events and magmatic events, should then show up in the gravity field. Applying geodynamic plate reconstructions to the GOCE gravity field places today’s observed field at the pre-breakup position. The same reconstruction can be applied to the seismic velocity models, to allow a joint gravity-velocity analysis. The geophysical fields allow to control the likeliness of the hypothesized continuation of lineations based on sparse surface outcrops. Total absence of a signal, makes the cross-continental continuation of the lineament improbable, as continental-wide lineaments are controlled by rheologic and compositional differences of lithospheric mantle. It is found that the deep lithospheric roots as those found below cratons control the position of the positive gravity values. The explanation is that the deep lithospheric roots focus asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. The study is carried out over the African and South American continents.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFM.T52A0906E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFM.T52A0906E"><span>Along-axis steps in Ethiopian rift Bouguer gravity anomalies: Implications for crustal thinning and melt emplacement prior to breakup</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, C. J.; Tiberi, C.; Fowler, M. R.; Hunegnaw, A.</p> <p>2001-12-01</p> <p>The southern Afar depression, Africa, is virtually the only area worldwide where the transition from continental rifting to seafloor spreading is exposed onshore. During mid-Miocene to Pleistocene time the rift valley was segmented along its length by long normal faults; since Pleistocene time, faulting and magmatism have jumped to a narrow ca. 60 km-long volcanic mound marked by small faults. These magmatic segments are structurally similar to slow-spreading mid-ocean ridges, yet the rift is floored by continental crust. As part of the Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE), we examine new and existing Bouguer gravity anomaly data from the rift to study the modification of the lithosphere by extensional and magmatic processes. New and existing Bouguer gravity anomaly data also show an along-axis segmentation of elongate relative positive anomalies that coincide with the magmatic segments. These anomalies are superposed on a regionally eastward increasing field as one approaches true seafloor spreading in the Gulf of Aden, and crustal thickness decreases. Quite remarkably, the magmatic segment boundaries, where data coverage is good, are marked by 15-25 mGal steps. The amplitude of the along-axis steps, as well as their across-axis characteristics, indicate that magmatic intrusion and ca. 2 km relief at the crust-mantle interface contribute to the steps. We use inverse and forward models of gravity data constrained by existing seismic and petrological data to evaluate models for the along-axis steps. EAGLE seismic data will be acquired across and along the magmatic segments to improve our understanding of breakup processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611748F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611748F"><span>Structure and degree of magmatism of North and South Atlantic rifted margins</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Faleide, Jan Inge; Breivik, Asbjørn J.; Blaich, Olav A.; Tsikalas, Filippos; Planke, Sverre; Mansour Abdelmalak, Mohamed; Mjelde, Rolf; Myklebust, Reidun</p> <p>2014-05-01</p> <p>The structure and evolution of conjugate rifted margins in the South and North Atlantic have been studied mainly based on seismic reflection and refraction profiles, complemented by potential field data and plate reconstructions. All margins exhibit distinct along-margin structural and magmatic changes reflecting both structural inheritance extending back to a complex pre-breakup geological history and the final breakup processes. The sedimentary basins at the conjugate margins developed as a result of multiple phases of rifting, associated with complex time-dependent thermal structure of the lithosphere. A series of conjugate crustal transects reveal tectonomagmatic asymmetry, both along-strike and across the conjugate margin systems. The continent-ocean transitional domain along the magma-dominated margin segments is characterized by a large volume of flood basalts and high-velocity/high-density lower crust emplaced during and after continental breakup. Both the volume and duration of excess magmatism varies. The extrusive and intrusive complexes make it difficult to pin down a COB to be used in plate reconstructions. The continent-ocean transition is usually well defined as a rapid increase of P-wave velocities at mid- to lower crustal levels. The transition is further constrained by comparing the mean P-wave velocity to the thickness of the crystalline crust. By this comparison we can also address the magmatic processes associated with breakup, whether they are convection dominated or temperature dominated. In the NE Atlantic there is a strong correlation between magma productivity and early plate spreading rate, suggesting a common cause. A model for the breakup-related magmatism should be able to explain this correlation, but also the magma production peak at breakup, the along-margin magmatic segmentation, and the active mantle upwelling. It is likely that mantle plumes (Iceland in the NE Atlantic, Tristan da Cunha in the South Atlantic) may have influenced the volume of magmatism but they did not necessarily alter the process of rifted margin formation, implying that parts of the margins may have much in common with more magma-poor margins. Conjugate margin segments from the North and South Atlantic will be compared and discussed with particular focus on the tectonomagmatic processes associated with continental breakup.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018NatGe..11..322L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018NatGe..11..322L"><span>Efficient cooling of rocky planets by intrusive magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lourenço, Diogo L.; Rozel, Antoine B.; Gerya, Taras; Tackley, Paul J.</p> <p>2018-05-01</p> <p>The Earth is in a plate tectonics regime with high surface heat flow concentrated at constructive plate boundaries. Other terrestrial bodies that lack plate tectonics are thought to lose their internal heat by conduction through their lids and volcanism: hotter planets (Io and Venus) show widespread volcanism whereas colder ones (modern Mars and Mercury) are less volcanically active. However, studies of terrestrial magmatic processes show that less than 20% of melt volcanically erupts, with most melt intruding into the crust. Signatures of large magmatic intrusions are also found on other planets. Yet, the influence of intrusive magmatism on planetary cooling remains unclear. Here we use numerical magmatic-thermo-mechanical models to simulate global mantle convection in a planetary interior. In our simulations, warm intrusive magmatism acts to thin the lithosphere, leading to sustained recycling of overlying crustal material and cooling of the mantle. In contrast, volcanic eruptions lead to a thick lithosphere that insulates the upper mantle and prevents efficient cooling. We find that heat loss due to intrusive magmatism can be particularly efficient compared to volcanic eruptions if the partitioning of heat-producing radioactive elements into the melt phase is weak. We conclude that the mode of magmatism experienced by rocky bodies determines the thermal and compositional evolution of their interior.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.296..600L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.296..600L"><span>Portrait of a giant deep-seated magmatic conduit system: The Seiland Igneous Province</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Larsen, Rune B.; Grant, Thomas; Sørensen, Bjørn E.; Tegner, Christian; McEnroe, Suzanne; Pastore, Zeudia; Fichler, Christine; Nikolaisen, Even; Grannes, Kim R.; Church, Nathan; ter Maat, Geertje W.; Michels, Alexander</p> <p>2018-01-01</p> <p>The Seiland Igneous Province (SIP), Northern Norway, contains > 5000 km2 of mafic and ultramafic intrusions with minor alkaline, carbonatite and felsic rocks that were intruded into the lower continental crust at a depth of 25 to as much as 35 km. The SIP can be geochemically and temporally correlated to numerous dyke swarms throughout Scandinavia at 560-610 Ma, and is linked to magmatic provinces in W-Greenland and NE-America that are collectively known as the Central Iapetus Magmatic Province (CIMP). Revised mapping show that the SIP exposes 85-90% layered tholeiitic- alkaline- and syeno-gabbros, 8-10% peridotitic complexes, 2-5% carbonatite, syenite and diorite that formed within a narrow (< 10 Ma) time frame in the Ediacaran (560-570 Ma). Large peridotite complexes were emplaced into the still hot and unconsolidated gabbro (no dating available) and are regarded as the main-conduit systems. Gravimetric data implies an average thickness of igneous rocks of 4-5 km and also features six deep lithospheric roots of ultramafic rocks extending min 9 km into the crust. Together, the root structures represent the main volcanic conduits conveying thousands of km3 of mafic-ultramafic melts from the asthenosphere to the lithosphere. The ultramafic complexes were predominantly emplaced into the layered gabbros at four major igneous centres, respectively, Nordre Brumandsfjord, Melkvann, Kvalfjord and Reinfjord. All complexes are situated in a right-way-up position and are steep sided forming large plugs. A marginal hybrid zone forms at the contact with country-rock and transitions gradually from olivine-mela-gabbro over pyroxenites that grades in to an olivine-clinopyroxenite zone, which is followed by a wehrlite zone and, finally, the centre of the complexes comprises pure dunite. From pyroxenite to dunite, olivine changes from Fo72 to Fo85 and clinopyroxene from Di80 to Di92 i.e. the complexes observe a reverse fractional crystallisation sequence with time. Parental melt compositions modelled from early dykes indicate komatiitic to picritic melts with 16-22 wt% MgO, Cr of 1594 ppm and Ni of 611 ppm, which were emplaced at 1450-1500 °C. Melt compositions calculated from clinopyroxene compositions from Reinfjord are OIB-like with LREE enriched over HREE. The high abundance of carbonatites and lamproites demonstrates the volatile-rich nature of the mantle source region and is further corroborated by the unusually high abundance of magmatic sulphides (0.5-1%) and carbonated and hydrous assemblages (c. 1%) throughout the region. In Reinfjord, they are also closely associated with PGE-Cu-Ni reef deposits. Essentially, the ultramafic complexes in the SIP comprises deep-seated transient magma chambers that facilitated mixing and homogenisation of a rich diversity of fertile asthenospheric melts en route to the upper parts of the continental crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.5456S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.5456S"><span>Aquifers as indicators of volcanic unrest - models of hydrological responses to magmatic activity and their geophysical signals</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Strehlow, Karen; Gottsmann, Jo</p> <p>2014-05-01</p> <p>Aquifers respond to and modify the surface expressions of magmatic activity, and they can also become agents of unrest themselves. Therefore, monitoring the hydrology can provide a valuable window into subsurface processes in volcanic areas. Interpretations of unrest signals as groundwater responses to changes in the magmatic system can be found for many volcanoes. Changes in temperature and strain conditions, seismic excitation or the injection of magmatic fluids into hydrothermal systems are just a few of the proposed processes induced by magmatic activity that affect the local hydrology. Aquifer responses are described to include changes in water table levels, changes in temperature or composition of hydrothermal waters and pore pressure-induced ground deformation. We can observe these effects at the surface via geophysical and geochemical signals. To fully to utilise these indicators as monitoring and forecasting tools, however, it is necessary to improve our still poor understanding of the ongoing mechanisms in the interactions of hydrological and magmatic systems. An extensive literature research provided an overview on reported effects, which we investigate in detail using numerical modelling. The hydrogeophysical study uses finite element analysis to quantitatively test proposed mechanisms of aquifer excitation and the resultant geophysical signals. We present a set of generic models for two typical volcanic landforms - a stratovolcano and a caldera - that simulate the interaction between deeper magmatic systems with shallow-seated aquifers, focusing on strain and temperature effects. They predict pore pressure induced hydraulic head changes in the aquifer as well as changing groundwater temperatures and strain induced fluid migration. Volcano observatories can track these hydrological effects for example with potential field investigations or the monitoring of wells. The models allow us to explore the parameter space, contributing to a better understanding of the coupling of these two highly complex systems. Our results provide further insight into the subsurface processes at volcanic systems and will aid the evaluation of unrest signals with potential for improved eruption forecasting.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17..976M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17..976M"><span>The 2012-2014 eruptive cycle of Copahue Volcano, Southern Andes. Magmatic-Hydrothermal system interaction and manifestations.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morales, Sergio; Alarcón, Alex; Basualto, Daniel; Bengoa, Cintia; Bertín, Daniel; Cardona, Carlos; Córdova, Maria; Franco, Luis; Gil, Fernando; Hernandez, Erasmo; Lara, Luis; Lazo, Jonathan; Mardones, Cristian; Medina, Roxana; Peña, Paola; Quijada, Jonathan; San Martín, Juan; Valderrama, Oscar</p> <p>2015-04-01</p> <p>Copahue Volcano (COPV), in Southern Andes of Chile, is an andesitic-basaltic stratovolcano, which is located on the western margin of Caviahue Caldera. The COPV have a NE-trending fissure with 9 aligned vents, being El Agrio the main currently active vent, with ca. 400 m in diameter. The COPV is placed into an extensive hydrothermal system which has modulated its recent 2012-2014 eruptive activity, with small phreatic to phreatomagmatic eruptions and isolated weak strombolian episodes and formation of crater lakes inside the main crater. Since 2012, the Southern Andes Volcano Observatory (OVDAS) carried out the real-time monitoring with seismic broadband stations, GPS, infrasound sensors and webcams. In this work, we report pre, sin, and post-eruptive seismic activity of the last two main eruptions (Dec, 2012 and Oct, 2014) both with different seismic precursors and superficial activity, showing the second one a particularly appearance of seismic quiescence episodes preceding explosive activity, as an indicator of interaction between magmatic-hydrothermal systems. The first episode, in late 2012, was characterized by a low frequency (0.3-0.4 Hz and 1.0-1.5 Hz) continuous tremor which increased gradually from background noise level amplitude to values of reduced displacement (DR), close to 50 cm2 at the peak of the eruption, reaching an eruptive column of ~1.5 km height. After few months of recording low energy seismicity, a sequence of low frequency, repetitive and low energy seismic events arose, with a frequency of occurrence up to 300 events/hour. Also, the VLP earthquakes were added to the record probably associated with magma intrusion into a deep magmatic chamber during all stages of eruptive process, joined to the record of VT seismicity during the same period, which is located throughout the Caviahue Caldera area. Both kind of seismic patterns were again recorded in October 2014, being the precursor of the new eruptive cycle at this time as well as the deformation of the volcanic edifice detected by GPS network. In this new eruptive process, the record of tremor was followed by particular seismic quiescence, as precursors of explosive activity which evolved from low acoustic energy signals toward more energetic signals with impulsive first arrivals and strong attenuation, joined to night incandescence in the main vent without evident juvenile material ejected, which could be associated to the temporal depression of the hydrothermal system located in the volcano system. The recent eruptive episode at Copahue Volcano is a good example of the complex temporal evolution of the interaction between magmatic and hydrothermal systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.484..318P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.484..318P"><span>Unraveling the dynamics of magmatic CO2 degassing at Mammoth Mountain, California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peiffer, Loïc; Wanner, Christoph; Lewicki, Jennifer L.</p> <p>2018-02-01</p> <p>The accumulation of magmatic CO2 beneath low-permeability barriers may lead to the formation of CO2-rich gas reservoirs within volcanic systems. Such accumulation is often evidenced by high surface CO2 emissions that fluctuate over time. The temporal variability in surface degassing is believed in part to reflect a complex interplay between deep magmatic degassing and the permeability of degassing pathways. A better understanding of the dynamics of CO2 degassing is required to improve monitoring and hazards mitigation in these systems. Owing to the availability of long-term records of CO2 emissions rates and seismicity, Mammoth Mountain in California constitutes an ideal site towards such predictive understanding. Mammoth Mountain is characterized by intense soil CO2 degassing (up to ∼1000 t d-1) and tree kill areas that resulted from leakage of CO2 from a CO2-rich gas reservoir located in the upper ∼4 km. The release of CO2-rich fluids from deeper basaltic intrusions towards the reservoir induces seismicity and potentially reactivates faults connecting the reservoir to the surface. While this conceptual model is well-accepted, there is still a debate whether temporally variable surface CO2 fluxes directly reflect degassing of intrusions or variations in fault permeability. Here, we report the first large-scale numerical model of fluid and heat transport for Mammoth Mountain. We discuss processes (i) leading to the initial formation of the CO2-rich gas reservoir prior to the occurrence of high surface CO2 degassing rates and (ii) controlling current CO2 degassing at the surface. Although the modeling settings are site-specific, the key mechanisms discussed in this study are likely at play at other volcanic systems hosting CO2-rich gas reservoirs. In particular, our model results illustrate the role of convection in stripping a CO2-rich gas phase from a rising hydrothermal fluid and leading to an accumulation of a large mass of CO2 (∼107-108 t) in a shallow gas reservoir. Moreover, we show that both, short-lived (months to years) and long-lived (hundreds of years) events of magmatic fluid injection can lead to critical pressures within the reservoir and potentially trigger fault reactivation. Our sensitivity analysis suggests that observed temporal fluctuations in surface degassing are only indirectly controlled by variations in magmatic degassing and are mainly the result of temporally variable fault permeability. Finally, we suggest that long-term CO2 emission monitoring, seismic tomography and coupled thermal-hydraulic-mechanical modeling are important for CO2-related hazard mitigation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAsGe...6...90S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAsGe...6...90S"><span>Study of Conrad and Shaban deep brines, Red Sea, using bathymetric, parasound and seismic surveys</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salem, Mohamed</p> <p>2017-06-01</p> <p>Red Sea was formed where African and Arabian plates are moving apart. Each year the plates drift about 2.5 cm farther apart, so that the Red Sea is slowly but steadily growing hence known as the next coming ocean simply an embryonic ocean. It is characterized by the presence of many deep fractures, located almost exactly along the middle of the Sea from northwest to southeast. Theses fractures have steep sides, rough bottom and brines coming up form on the bottom. Brine deposits are the result of subsurface magmatic activity. They are formed in graben structure as shown by the bathymetric, parasound and seismic studies in the investigated area.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009Litho.112..465M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009Litho.112..465M"><span>The importance of the transport system in shaping the growth and form of kimberlite volcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McClintock, Murray; Ross, Pierre-Simon; White, James D. L.</p> <p>2009-11-01</p> <p>Understanding the range of transport styles recorded by kimberlite deposits is key to describing the type and style of eruptions. Building a clear picture of the processes that shape deposits is essential for selecting exploration targets and evaluating the grade and value of diamond-bearing kimberlites. Variations in grade reflect differences in the diamond content of different magma parcels erupted during the lifetime of the kimberlite volcano, sorting during transport of eruption products, or reworking of diamonds during crater growth, cone collapse and erosion. The form of the kimberlite volcano is largely determined when the magma arrives near the surface. If magma comes into contact with external water, transport will be driven by a combination of magmatic gases + steam. From a diamond exploration perspective, the resulting deep diatremes make the most attractive targets because they survive erosion and tend to form large geophysical anomalies. If water is too abundant, a tuff cone or tuff ring with no diatreme or a shallow one will form. On the other hand, if external water is very limited or if the conduit is rapidly sealed by chilled melt, the transport system will be driven by magmatic gases alone. The result will then be a spatter cone or cinder cone underlain by a dike, possibly with a related lava flow, but with no diatreme.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUSM.V41A..01M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUSM.V41A..01M"><span>Characteristic Time Scales of Characteristic Magmatic Processes and Systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marsh, B. D.</p> <p>2004-05-01</p> <p>Every specific magmatic process, regardless of spatial scale, has an associated characteristic time scale. Time scales associated with crystals alone are rates of growth, dissolution, settling, aggregation, annealing, and nucleation, among others. At the other extreme are the time scales associated with the dynamics of the entire magmatic system. These can be separated into two groups: those associated with system genetics (e.g., the production and transport of magma, establishment of the magmatic system) and those due to physical characteristics of the established system (e.g., wall rock failure, solidification front propagation and instability, porous flow). The detailed geometry of a specific magmatic system is particularly important to appreciate; although generic systems are useful, care must be taken to make model systems as absolutely realistic as possible. Fuzzy models produce fuzzy science. Knowledge of specific time scales is not necessarily useful or meaningful unless the hierarchical context of the time scales for a realistic magmatic system is appreciated. The age of a specific phenocryst or ensemble of phenocrysts, as determined from isotopic or CSD studies, is not meaningful unless something can be ascertained of the provenance of the crystals. For example, crystal size multiplied by growth rate gives a meaningful crystal age only if it is from a part of the system that has experienced semi-monotonic cooling prior to chilling; crystals entrained from a long-standing cumulate bed that were mechanically sorted in ascending magma may not reveal this history. Ragged old crystals rolling about in the system for untold numbers of flushing times record specious process times, telling more about the noise in the system than the life of typical, first generation crystallization processes. The most helpful process-related time scales are those that are known well and that bound or define the temporal style of the system. Perhaps the most valuable of these times comes from the observed durations and rates of volcanism. There can be little doubt that the temporal styles of volcanism are the same as those of magmatism in general. Volcano repose times, periodicity, eruptive fluxes, acoustic emission structures, lava volumes, longevity, etc. must also be characteristic of pluton-dominated systems. We must therefore give up some classical concepts (e.g., instantaneous injection of crystal-free magma as an initial condition) for any plutonic/chambered system and move towards an integrated concept of magmatism. Among the host of process-related time scales, probably the three most fundamental of any magmatic system are (1) the time scale associated with crystal nucleation (J) and growth (G) (tx}=C{1(G3 J)-{1}/4; Zieg & Marsh, J. Pet. 02') along with the associated scales for mean crystal size (L) and population (N), (2) the time scale associated with conductive cooling controlled by a local length scale (d) (tc}=C{2 d2/K; K is thermal diffusivity), and (3) the time scale associated with intra-crystal diffusion (td}=C{3 L2/D; D is chemical diffusivity). It is the subtle, clever, and insightful application of time scales, dovetailed with realistic system geometry and attention paid to the analogous time scales of volcanism, that promises to reveal the true dynamic integration of magmatic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.5120M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.5120M"><span>Various-scale controls of complex subduction dynamics on magmatic-hydrothermal processes in eastern Mediterranean</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Menant, Armel; Jolivet, Laurent; Sternai, Pietro; Ducoux, Maxime; Augier, Romain; Rabillard, Aurélien; Gerya, Taras; Guillou-Frottier, Laurent</p> <p>2014-05-01</p> <p>In subduction environment, magmatic-hydrothermal processes, responsible for the emplacement of magmatic bodies and related mineralization, are strongly controlled by slab dynamics. This 3D dynamics is often complex, resulting notably in spatial evolution through time of mineralization and magmatism types and in fast kinematic changes at the surface. Study at different scales of the distribution of these magmatic and hydrothermal products is useful to better constrain subduction dynamics. This work is focused on the eastern Mediterranean, where the complex dynamics of the Tethyan active margin since the upper Cretaceous is still largely debated. We propose new kinematic reconstructions of the region also showing the distribution of magmatic products and mineralization in space and time. Three main periods have thus been identified with a general southward migration of magmatic and ore bodies. (1) From late Cretaceous to lower Paleocene, calc-alkaline magmatism and porphyry Cu deposits emplaced notably in the Balkans, along a long linear cordillera. (2) From late Paleocene to Eocene, a barren period occurred while the Pelagonian microcontinent was buried within the subduction zone. (3) Since the Oligocene, Au-rich deposits and related K-rich magmatism emplaced in the Rhodopes, the Aegean and western Anatolian extensional domains in response to fast slab retreat and related mantle flow inducing the partial melting of the lithospheric mantle or the base of the upper crust where Au was previously stored. The emplacement at shallow level of this mineralization was largely controlled by large-scale structures that drained the magmatic-hydrothermal fluids. In the Cyclades for instance, field studies show that Au-rich but also base metal-rich ore deposits are syn-extensional and spatially related to large-scale detachment systems (e.g. on Tinos, Mykonos, Serifos islands), which are recognized as subduction-related structures. These results highlight the importance at different scales of subduction dynamics and related mantle flow on the emplacement of mineralization and magmatic bodies. Indeed, besides a general southward migration of the magmatic-hydrothermal activity since the upper Cretaceous from the Balkans to the present-day Aegean volcanic arc, a secondary westward migration is observed during the Miocene from the Menderes massif to the Cyclades. This feature is a possible consequence of a slab tearing event and related mantle flow, as suggested notably by tomographic models below western Anatolia. To further test the effects of slab retreat and tearing on the flow and temperature field within the mantle, we performed 3D thermo-mechanical numerical modeling. Models suggest that the asthenospheric flow induced by the development of a slab tear controls the migration of magmatic products stored at the base of the crust, influencing the distribution of potentially fertile magmas within the upper crust.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V31E4799P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V31E4799P"><span>Investigating the long-term geodetic response to magmatic intrusions at volcanoes in northern California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Parker, A. L.; Biggs, J.; Annen, C.; Houseman, G. A.; Yamasaki, T.; Wright, T. J.; Walters, R. J.; Lu, Z.</p> <p>2014-12-01</p> <p>Ratios of intrusive to extrusive activity at volcanic arcs are thought to be high, with estimates ranging between 5:1 and 30:1. Understanding the geodetic response to magmatic intrusion is therefore fundamental to large-scale studies of volcano deformation, providing insight into the dynamics of the inter-eruptive period of the volcano cycle and the building of continental crust. In northern California, we identify two volcanoes - Medicine Lake Volcano (MLV) and Lassen Volcanic Center (LaVC) - that exhibit long-term (multi-decadal) subsidence. We test the hypothesis that deformation at these volcanoes results from processes associated with magmatic intrusions. We first constrain the spatial and temporal characteristics of the deformation fields, establishing the first time-series of deformation at LaVC using InSAR data, multi-temporal analysis techniques and global weather models. Although the rates of deformation at the two volcanoes are similar (~1 cm/yr), our results show that the ratio of vertical to horizontal displacements is significantly different, suggesting contrasting source geometries. To test the origin of deformation, we develop modeling strategies to investigate thermal and viscoelastic processes associated with magmatic intrusions. The first model we develop couples analytical geodetic models to a numerical model of volume loss due to cooling and crystallization based upon temperature-melt fraction relationships from petrological experiments. This model provides evidence that magmatic intrusion at MLV has occurred more recently than the last eruption ~1 ka. The second model we test uses a finite element approach to simulate the time-dependent viscoelastic response of the crust to magmatic intrusion. We assess the magnitude and timescales of ground deformation that may result from these processes, exploring the model parameter space before applying the models to our InSAR observations of subsidence in northern California.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70019247','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70019247"><span>Magmatic processes that generated the rhyolite of Glass Mountain, Medicine Lake volcano, N. California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Grove, T.L.; Donnelly-Nolan, J. M.; Housh, T.</p> <p>1997-01-01</p> <p>Glass Mountain consists of a 1 km3, compositionally zoned rhyolite to dacite glass flow containing magmatic inclusions and xenoliths of underlying shallow crust. Mixing of magmas produced by fractional crystallization of andesite and crustal melting generated the rhyolite of Glass Mountain. Melting experiments were carried out on basaltic andesite and andesite magmatic inclusions at 100, 150 and 200 MPa, H2O-saturated with oxygen fugacity controlled at the nickel-nickel oxide buffer to provide evidence of the role of fractional crystallization in the origin of the rhyolite of Glass Mountain. Isotopic evidence indicates that the crustal component assimilated at Glass Mountain constitutes at least 55 to 60% of the mass of erupted rhyolite. A large volume of mafic andesite (2 to 2.5 km3) periodically replenished the magma reservoir(s) beneath Glass Mountain, underwent extensive fractional crystallization and provided the heat necessary to melt the crust. The crystalline residues of fractionation as well as residual liquids expelled from the cumulate residues are preserved as magmatic inclusions and indicate that this fractionation process occurred at two distinct depths. The presence and composition of amphibole in magmatic inclusions preserve evidence for crystallization of the andesite at pressures of at least 200 MPa (6 km depth) under near H2O-saturated conditions. Mineralogical evidence preserved in olivine-plagioclase and olivine-plagioclase-high-Ca clinopyroxene-bearing magmatic inclusions indicates that crystallization under near H2O-saturated conditions also occurred at pressures of 100 MPa (3 km depth) or less. Petrologic, isotopic and geochemical evidence indicate that the andesite underwent fractional crystallization to form the differentiated melts but had no chemical interaction with the melted crustal component. Heat released by the fractionation process was responsible for heating and melting the crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/4074','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/4074"><span></span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Davisson, M.L.; Rose, T.P.</p> <p></p> <p>Quaternary-age volcanic peaks of Mt. Lassen, Mt. Shasta, and Medicine Lake Volcano preferentially recharge and transport large volumes of annual precipitation into mega- scale channels hosted in underlying volcanic layers. At the terminus of laterally extensive lava flows, or in deep incisions of these layers, groundwater emerges as large volume cold springs. The combined discharge of these springs contributes half the annual storage capacity of Shasta Reservoir, and is utilized to generate 2000 gigawatts of hydroelectric power each year. Moreover, the springs provide a natural habitat for many rare and endangered species. In the Hat Creek Valley, located north ofmore » Mt. Lassen, Rose et al. (1996) showed that the low d 18 O discharge of large volume springs at Rising River and Crystal Lake originates from snow melt in the high elevation, high precipitation region surrounding Lassen Peak. Groundwater transport in this basin is enhanced by the occurrence of the Quaternary Hat Creek basalt flow, which extends nearly the entire length of Hat Creek Valley. In contrast, the d 18 O values of large- volume springs that discharge in the Mt. Shasta region indicate a larger percentage of local recharge at lower elevations since the high elevation snow melt on the volcano is depleted by >1 per mil relative to the largest springs. The d 18 O value of the Fall River Springs (FRS) system is similar to small springs that occur at high elevations on Medicine Lake Volcano. The large volume of the FRS discharge coupled with a lack of surficial drainages in this area indicates that a large percentage of the annual precipitation over an ~750 mi 2 area of the Medicine Lake volcanic plateau goes to recharge the FRS aquifer system. Groundwater transport to the FRS is enhanced by the occurrence of the 10 kyr Giant Crater lava flow, a single geologic unit that extends from the base of Medicine Lake Volcano to the FRS. many of the large volume springs in the southern Cascade Range. For example, the radiocarbon concentration in Rising River Springs is 80 pmc, which indicates at least 20% of its dissolved inorganic carbon is derived from a magmatic source in the Lassen region. The radiocarbon activity in the FRS is as low as 73 pmc, indicating a minimum contribution of 27% magmatic CO2 from Medicine Lake volcano. Magmatic CO2 fluxes in the Shasta region are highest around the base of the volcano, where low- volume, CO2 -rich, 14 C- absent soda springs occur. Relatively large quantities of magmatic CO2 are observed in the Big Springs of the McCloud River, which have a d 18 O signature consistent with low elevation recharge in the Shasta region. relative to Mt. Lassen and Medicine Lake Volcano reflect significant differences in the geomorphology of the volcanoes. In particular, the composite nature of the Shasta stratocone tends to limit the depth of groundwater recharge, confining the majority of groundwater flow to the shallowest layers, which tend to be of more local extent. The lower permeability of the composite cone also acts as a trap for magmatic CO2 emissions, generally limiting the gas discharge to localized fracture zones at lower elevations. At Mt. Lassen and Medicine Lake Volcano, groundwater recharge occurs primarily at high elevations, along vertical fracture systems with high permeabilities. These features, combined with laterally extensive basalt flows, act to focus groundwater transport deeper and over longer lateral distances. The magmatic CO2 dissolution process probably occurs in close proximity to the geothermal systems at Lassen and Medicine Lake, where CO2 gas escaping along deep fractures encounters downward percolating groundwater.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.1132K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.1132K"><span>Numerical experiments of volcanic dominated rifts and passive margins</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Korchinski, Megan; Teyssier, Christian; Rey, Patrice; Whitney, Donna; Mondy, Luke</p> <p>2017-04-01</p> <p>Continental rifting is driven by plate tectonic forces (passive rifting), thermal thinning of the lithosphere over a hotspot (active rifting), or a combination of the two. Successful rifts develop into passive margins where pre-drift stretching is accompanied by normal faulting, clastic sedimentation, and various degrees of magmatism. The structure of volcanic passive margins (VPM) differs substantially from margins that are dominated by sedimentation. VPMs are typically narrow, with a lower continental crust that is intruded by magma and can flow as a low-viscosity layer. To investigate the role of the deep crust in the early development of VPMs, we have developed a suite of 2D thermomechanical numerical experiments (Underworld code) in which the density and viscosity of the deep crust and the density of the rift basin fill are systematically varied. Our experiments show that, for a given rifting velocity, the viscosity of the deep crust and the density of the rift basin fill exert primary controls on early VPM development. The viscosity of the deep crust controls the degree to which the shallow crust undergoes localised faulting or distributed thinning. A weak deep crust localises rifting and is efficiently exhumed to the near-surface, whereas a strong deep crust distributes shallow crust extension and remains buried. A high density rift basin fill results in gravitational loading and increased subsidence rate in cases in which the viscosity of the deep crust is sufficiently low to allow that layer to be displaced by the sinking basin fill. At the limit, a low viscosity deep crust overlain by a thick basalt-dominated fill generates a gravitational instability, with a drip of cool basalt that sinks and ponds at the Moho. Experiment results indicate that the deep crust plays a critical role in the dynamic development of volcanic dominated rifts and passive margins. During rifting, the deep continental crust is heated and readily responds to solicitations of the shallow crust (rooting of normal faults, exhumation of the deep crust in normal fault footwalls). Gravitational instabilities caused by high density rift infill similar to those observed in our numerical experiments may be present in the Mesoproterozoic ( 1100 Ma) North American Midcontinent Rift System (MRS). The MRS is a failed rift that is filled with >20 km of dominantly basaltic volcanic deposits, and therefore represents an end member VPM (high density basin fill) where the initial structure of a pre-drift VPM is preserved. Magmatism occurred in two pulses over <15 Ma involving deep mantle melting first (>150 km), then shallow melting (40-70 km). Post-rift subsidence accumulated up to 10 km of clastic sediments in the center of the basin. Evidence of cool, dense rocks sinking into a low-viscosity deep crust as predicted in our numerical experiments may be present in the western arm of the MRS, where crustal density analyses suggest the presence of dense bodies (eclogite) at the base of the crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3812654','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3812654"><span>Capturing the fingerprint of Etna volcano activity in gravity and satellite radar data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Negro, Ciro Del; Currenti, Gilda; Solaro, Giuseppe; Greco, Filippo; Pepe, Antonio; Napoli, Rosalba; Pepe, Susi; Casu, Francesco; Sansosti, Eugenio</p> <p>2013-01-01</p> <p>Long-term and high temporal resolution gravity and deformation data move us toward a better understanding of the behavior of Mt Etna during the June 1995 – December 2011 period in which the volcano exhibited magma charging phases, flank eruptions and summit crater activity. Monthly repeated gravity measurements were coupled with deformation time series using the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique on two sequences of interferograms from ERS/ENVISAT and COSMO-SkyMed satellites. Combining spatiotemporal gravity and DInSAR observations provides the signature of three underlying processes at Etna: (i) magma accumulation in intermediate storage zones, (ii) magmatic intrusions at shallow depth in the South Rift area, and (iii) the seaward sliding of the volcano's eastern flank. Here we demonstrate the strength of the complementary gravity and DInSAR analysis in discerning among different processes and, thus, in detecting deep magma uprising in months to years before the onset of a new Etna eruption. PMID:24169569</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001Tectp.342..351M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001Tectp.342..351M"><span>Influence of lithological heterogeneity, mechanical anisotropy, and magmatism on the rheology of an arc, North Cascades, Washington</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miller, Robert B.; Paterson, Scott R.</p> <p>2001-12-01</p> <p>Many aspects of crustal dynamics are dependent on changes in rheology and strength with depth in the lithosphere. Several of the controlling factors for rheology are difficult to study experimentally, particularly lithological heterogeneity, mechanical anisotropy, and magmatism, and we focus on these in a study of the deformation patterns in a thick crustal section (˜5- to 40-km paleodepth) through the Cretaceous Cascades core of the NW Cordillera. This magmatic arc consists of metamorphosed oceanic and arc terranes intruded by magmatic bodies ranging from <10-cm-thick sheets to large plutons. Heterogeneous brittle deformation marked by serpentinite melange characterizes the shallowest part of the crustal section, and the remainder of the section is characterized by heterogeneous, fold-dominated ductile deformation. Early tight to isoclinal recumbent folds and associated axial-planar fabrics are refolded by one or more cycles of nearly coaxial, open to isoclinal, upright to overturned folds. Layering played a mechanically active role during folding at all levels, as indicated by cleavage refraction, boudinaged layers, and kinematic indicators that record fold-related shear. Ductile deformation intensifies in the narrow structural aureoles of plutons, and SW-directed, reverse shear was partitioned into some of the aureoles. The poor strain memory of these magmatic bodies makes it difficult to determine if deformation was focused in the pluton magma chambers before they reached the solidus, as commonly predicted. All of the plutons have magmatic foliations that at least in part reflect regional strains, and these foliations are strong in the deeper plutons. The thinner sheets acted as competent bodies during folding and boudinage, after they reached the solidus, but generally did not cause marked strain gradients in their hosts. A relative strength profile constructed for the Cascades crustal section shows an overall decrease in strength with depth for the ductile part of the arc that fits idealized strength profiles. However, in more detail relative strengths are markedly variable. Units were able to accumulate large ductile strains, but even small variations in the physical properties of interlayered rock types exerted a strong influence on deformation patterns throughout the mid- to deep-crustal part of the profile. This profile thus emphasizes the complex vertical rheological stratification of arcs at the crustal to thin section scale, and should be applicable to many other magmatic arcs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tectp.646...36M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tectp.646...36M"><span>How tectonics controlled post-collisional magmatism within the Dinarides: Inferences based on study of tectono-magmatic events in the Kopaonik Mts. (Southern Serbia)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mladenović, Ana; Trivić, Branislav; Cvetković, Vladica</p> <p>2015-04-01</p> <p>In this study, we report evidence about coupling between tectonic and magmatic processes in a complex orogenic system. The study focuses on the Kopaonik Mts. situated between the Dinarides and the Carpatho-Balkanides (Southern Serbia), and a perfect area for investigating tectono-magmatic evolution. We combine a new data set on tectonic paleostress tensors with the existing information on Cenozoic magmatic rocks in the wider Kopaonik Mts. area. The paleostress study revealed the presence of four brittle deformational phases. The established link between fault mechanism and igneous processes suggests that two large tectono-magmatic events occurred in this area. The Late Eocene-Early Miocene tectono-magmatic event was generally characterized by transpressional tectonics that provided conditions for formation of basaltic underplating and subsequent lower crustal melting and generation of I-type magmas. Due to predominant compression in the first half of this event, these magmas could not reach the upper crustal levels. Later on, limited extensional pulses that occurred before the end of this event opened pathways for newly formed mantle melts to reach shallower crustal levels and mix with the evolving I-type magmas. The second event is Middle-Late Miocene in age. It was first associated with clear extensional conditions that caused advancing of basaltic melts to mid-crustal levels. This, in turn, induced the elevation of geotherms, melting of shallow crust and S-type granite formation. This event terminated with transpression that produced small volumes of basaltic melts and finally closed the igneous scene in this part of the Balkan Peninsula. Although we agree that the growth of igneous bodies is usually internally controlled and can be independent from the ambient structural pattern, we have strong reasons to believe that the integration of regional scale observations of fault kinematics with crucial petrogenetic information can be used for establishing spatial-temporal relationships between brittle tectonics and magmatism.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V24D..03K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V24D..03K"><span>Understanding the Yellowstone magmatic system using 3D geodynamic inverse models</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaus, B. J. P.; Reuber, G. S.; Popov, A.; Baumann, T.</p> <p>2017-12-01</p> <p>The Yellowstone magmatic system is one of the largest magmatic systems on Earth. Recent seismic tomography suggest that two distinct magma chambers exist: a shallow, presumably felsic chamber and a deeper much larger, partially molten, chamber above the Moho. Why melt stalls at different depth levels above the Yellowstone plume, whereas dikes cross-cut the whole lithosphere in the nearby Snake River Plane is unclear. Partly this is caused by our incomplete understanding of lithospheric scale melt ascent processes from the upper mantle to the shallow crust, which requires better constraints on the mechanics and material properties of the lithosphere.Here, we employ lithospheric-scale 2D and 3D geodynamic models adapted to Yellowstone to better understand magmatic processes in active arcs. The models have a number of (uncertain) input parameters such as the temperature and viscosity structure of the lithosphere, geometry and melt fraction of the magmatic system, while the melt content and rock densities are obtained by consistent thermodynamic modelling of whole rock data of the Yellowstone stratigraphy. As all of these parameters affect the dynamics of the lithosphere, we use the simulations to derive testable model predictions such as gravity anomalies, surface deformation rates and lithospheric stresses and compare them with observations. We incorporated it within an inversion method and perform 3D geodynamic inverse models of the Yellowstone magmatic system. An adjoint based method is used to derive the key model parameters and the factors that affect the stress field around the Yellowstone plume, locations of enhanced diking and melt accumulations. Results suggest that the plume and the magma chambers are connected with each other and that magma chamber overpressure is required to explain the surface displacement in phases of high activity above the Yellowstone magmatic system.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.S52G..06E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.S52G..06E"><span>Initiation and Along-Axis Segmentation of Seaward-Dipping Volcanic Sequences Captured in Afar</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, C.; Wolfenden, E.; Yirgu, G.; Keir, D.</p> <p>2003-12-01</p> <p>The Afar triple junction zone provides a unique opportunity to examine the early development of magmatic margins, as respective limbs of the triple junction capture different stages of the breakup process. Initial rifting in the southernmost Red Sea occurred concurrent with, or soon after flood basaltic magmatism at ~31 Ma in the Ethiopia-Yemen plume province, whereas the northern part of the Main Ethiopian rift initiated after 12 Ma. Both rift systems initiated with the development of high-angle border fault systems bounding broad basins, but 8-10 My after rifting we see riftward migration of strain from the western border fault to narrow zones of increasingly more basaltic magmatism. These localised zones of faulting and volcanism (magmatic segments) show a segmentation independent of the border fault segmentation. The much older, more evolved magmatic segments in the southern Red Sea, where not onlapped by Pliocene-Recent sedimentary strata, dip steeply riftward and define a regional eastward flexure into transitional oceanic crust, as indicated by gravity models constrained by seismic refraction and receiver function data. The southern Red Sea magmatic segments have been abandoned in Pliocene-Recent triple junction reorganisations, whereas the process of seaward-dipping volcanic sequence emplacement is ongoing in the seismically and volcanically active Main Ethiopian rift. Field, remote sensing, gravity, and seismicity data from the Main Ethiopian and southern Red Sea rifts indicate that seaward-dipping volcanic sequences initiate in moderately stretched continental crust above a narrow zone of dike-intrusion. Our comparison of active and ancient magmatic segments show that they are the precursors to seaward-dipping volcanic sequences analogous to those seen on passive continental margins, and provides insights into the initiation of along-axis segmentation of seafloor-spreading centers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMGP34A..07P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMGP34A..07P"><span>Large scale magmatic event, magnetic anomalies and ore exploration in northern Norway</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pastore, Z.; Church, N. S.; ter Maat, G. W.; Michels, A.; McEnroe, S. A.; Fichler, C.; Larsen, R. B.</p> <p>2016-12-01</p> <p>More than 17000 km3of igneous melts intruded into the deep crust at ca. 560-580 Ma and formed the Seiland Igneous Province (SIP), the largest complex of mafic and ultramafic intrusions in northern Fennoscandia. The original emplacement of the SIP is matter of current discussion. The SIP is now located within the Kalak Nappe Complex (KNC), a part of the Middle Allochthon of the North Norwegian Caledonides. The province is believed to represent a cross section of the deep plumbing system of a large igneous province and it is known for its layered intrusions sharing geological features with large ore-forming exploration provinces. In this study we investigate one of the four major ultramafic complexes of the province, the Reinfjord Complex. This was emplaced during three magmatic events in a time span of 4 Ma, and consists in a cylindrically zoned complex with a slightly younger dunite core (Central Series) surrounded by wehrlite and lherzolite dominated series (Upper and Lower Layered Series). Sulphides are present throughout the complex, and an electromagnetic survey identified a Ni-Cu-and a PGE reef deposit within the dunite, 100 meters below the surface. This discovery increased the ore potential of the complex and subsequently 4 deep drill cores were made. High-resolution magnetic helicopter survey was later followed up with ground magnetic and gravity surveys. Extensive sampling of surface rocks and drill cores were made to measure the rock-magnetic and physical properties of the samples and to explore the subsurface structure of the complex. Here, we developed a magnetic model for the Reinfjord complex integrating petrophysical data from both oriented surface samples and from the deep drill cores, with the new ground magnetic, and helicopter data (SkyTEM survey). A 3D model of the geometry of the ultramafic intrusion is presented and a refinement of the geological interpretation of the Reinfjord ultramafic intrusion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoRL..40.5632C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoRL..40.5632C"><span>Sudden deep gas eruption nearby Rome's airport of Fiumicino</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ciotoli, Giancarlo; Etiope, Giuseppe; Florindo, Fabio; Marra, Fabrizio; Ruggiero, Livio; Sauer, Peter E.</p> <p>2013-11-01</p> <p>24 August 2013 a sudden gas eruption from the ground occurred in the Tiber river delta, nearby Rome's international airport of Fiumicino. We assessed that this gas, analogous to other minor vents in the area, is dominantly composed of deep, partially mantle-derived CO2, as in the geothermal gas of the surrounding Roman Comagmatic Province. Increased amounts of thermogenic CH4 are likely sourced from Meso-Cenozoic petroleum systems, overlying the deep magmatic fluids. We hypothesize that the intersection of NE-SW and N-S fault systems, which at regional scale controls the location of the Roman volcanic edifices, favors gas uprising through the impermeable Pliocene and deltaic Holocene covers. Pressurized gas may temporarily be stored below these covers or within shallower sandy, permeable layers. The eruption, regardless the triggering cause—natural or man-made, reveals the potential hazard of gas-charged sediments in the delta, even at distances far from the volcanic edifices.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.6868S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.6868S"><span>Towards an integrated magmatic, structural and metamorphic model for the 1.1-0.9 Ga Sveconorwegian orogeny</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Slagstad, Trond; Roberts, Nick M. W.; Røhr, Torkil S.; Marker, Mogens K.</p> <p>2013-04-01</p> <p>Orogeny involves magmatic, metamorphic, deformational and erosional processes that are caused by or lead to crustal thickening and the development of high topography. In general, these processes operate along the margins of continental plates, either as a result of subduction of oceanic crust (accretionary) or collision between two or more continental plates (collisional). Many of these processes are common to accretionary and collisional orogeny, and do not uniquely discriminate between the two. With only a fragmented geological record, unravelling the style of orogenesis in ancient orogens may, therefore, be far from straightforward. Adding to the complexity, modern continental margins, e.g., the southern Asian margin, display significant variation in orogenic style along strike, rendering along-strike comparisons and correlations unreliable. The late Mesoproterozoic Sveconorwegian province in SW Baltica is traditionally interpreted as the eastward continuation of the Grenville province in Canada, resulting from collision with Amazonia and forming a central part in the assembly of the Rodinia supercontinent. We recently proposed that the Sveconorwegian segment of this orogen formed as a result of accretionary processes rather than collision. This hypothesis was based mainly on considerations of the Sveconorwegian magmatic evolution. Here, we show how the metamorphic/structural record supports (or at least may be integrated in) our model as well. The key elements in our accretionary model are: 1) formation of the Sirdal Magmatic Belt (SMB) between 1070 and 1020 Ma, most likely representing a continental arc batholith. Coeval deformation and high-grade metamorphism farther east in the orogen could represent deformation in the retroarc. 2) cessation of SMB magmatism at 1020 Ma followed by UHT conditions at 1010-1005 Ma, with temperatures in excess of 1000°C at 7.5 kbar. Subduction of a spreading ridge at ca. 1020 Ma would result in an end to arc magmatism and juxtaposition of hot asthenosphere and lower crust. This is a plausible explanation for the UTH event, in contrast to simple crustal thickening and radiogenic self-heating that are generally considered unable to produce such PT conditions. 3) long-lived (990-920 Ma) ferroan magmatism, temporally associated with high-grade metamorphism and large-scale deformation, probably reflecting formation inboard of an alternating compressional/extensional continental margin. We have no known record of events after ca. 920 Ma, but it is conceivable that the active margin persisted well into the Neoproterozoic, possibly indicated by metamorphic and magmatic activity recorded in Grenville/Sveconorwegian orogen-derived sedimentary rocks.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUSMMA72A..04C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUSMMA72A..04C"><span>Are diamond-bearing Cretaceous kimberlites related to shallow-angle subduction beneath western North America?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Currie, C. A.; Beaumont, C.</p> <p>2009-05-01</p> <p>The origin of deep-seated magmatism (in particular, kimberlites and lamproites) within continental plate interiors remains enigmatic in the context of plate tectonic theory. One hypothesis proposes a relationship between kimberlite occurrence and lithospheric subduction, such that a subducting plate releases fluids below a continental craton, triggering melting of the deep lithosphere and magmatism (Sharp, 1974; McCandless, 1999). This study provides a quantitative evaluation of this hypothesis, focusing on the Late Cretaceous- Eocene (105-50 Ma) kimberlites and lamproites of western North America. These magmas were emplaced along a corridor of Archean and Proterozoic lithosphere, 1000-1500 km inboard of the plate margin separating the subducting Farallon Plate and continental North America Plate. Kimberlite-lamproite magmatism coincides with tectonic events, including the Laramide orogeny, shut-down of the Sierra Nevada arc, and eastward migration of volcanism, that are commonly attributed to a change in Farallon Plate geometry to a shallow-angle trajectory (<25° dip). Thermal-mechanical numerical models demonstrate that rapid Cretaceous plate convergence rates and enhanced westward velocity of North America result in shallow-angle subduction that places the Farallon Plate beneath the western edge of the cratonic interior of North America. This geometry is consistent with the observed continental dynamic subsidence that lead to the development of the Western Interior Seaway. The models also show that the subducting plate has a cool thermal structure, and subducted hydrous minerals (serpentine, phengite and phlogopite) remain stable to more than 1200 km from the trench, where they may break down and release fluids that infiltrate the overlying craton lithosphere. This is supported by geochemical studies that indicate metasomatism of the Colorado Plateau and Wyoming craton mantle lithosphere by an aqueous fluid and/or silicate melt with a subduction signature. Through Cretaceous shallow-angle subduction, the Farallon Plate was in a position to mechanically and chemically interact with North American craton lithosphere at the time of kimberlite-lamproite magmatism, making the subduction hypothesis a viable mechanism for the genesis of these magmas. REFERENCES: McCandless, T.E., Proceedings of the 7th International Kimberlite Conference, v.2, pp.545-549, 1999; Sharp, W.E., Earth Planet. Sci. Lett., v.21, pp.351-354, 1974.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.geoscienceworld.org/books/book/680/chapter/3808156/Composite-Sunrise-Butte-pluton-Insights-into','USGSPUBS'); return false;" href="https://pubs.geoscienceworld.org/books/book/680/chapter/3808156/Composite-Sunrise-Butte-pluton-Insights-into"><span>Composite Sunrise Butte pluton: Insights into Jurassic–Cretaceous collisional tectonics and magmatism in the Blue Mountains Province, northeastern Oregon</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Johnson, Kenneth H.; Schwartz, J.J.; Žák, Jiří; Verner, Krystof; Barnes, Calvin G.; Walton, Clay; Wooden, Joseph L.; Wright, James E.; Kistler, Ronald W.</p> <p>2015-01-01</p> <p>The composite Sunrise Butte pluton, in the central part of the Blue Mountains Province, northeastern Oregon, preserves a record of subduction-related magmatism, arc-arc collision, crustal thickening, and deep-crustal anatexis. The earliest phase of the pluton (Desolation Creek unit) was generated in a subduction zone environment, as the oceanic lithosphere between the Wallowa and Olds Ferry island arcs was consumed. Zircons from this unit yielded a 206Pb/238U age of 160.2 ± 2.1 Ma. A magmatic lull ensued during arc-arc collision, after which partial melting at the base of the thickened Wallowa arc crust produced siliceous magma that was emplaced into metasedimentary rocks and serpentinite of the overthrust forearc complex. This magma crystallized to form the bulk of the Sunrise Butte composite pluton (the Sunrise Butte unit; 145.8 ± 2.2 Ma). The heat necessary for crustal anatexis was supplied by coeval mantle-derived magma (the Onion Gulch unit; 147.9 ± 1.8 Ma).The lull in magmatic activity between 160 and 148 Ma encompasses the timing of arc-arc collision (159–154 Ma), and it is similar to those lulls observed in adjacent areas of the Blue Mountains Province related to the same shortening event. Previous researchers have proposed a tectonic link between the Blue Mountains Province and the Klamath Mountains and northern Sierra Nevada Provinces farther to the south; however, timing of Late Jurassic deformation in the Blue Mountains Province predates the timing of the so-called Nevadan orogeny in the Klamath Mountains. In both the Blue Mountains Province and Klamath Mountains, the onset of deep-crustal partial melting initiated at ca. 148 Ma, suggesting a possible geodynamic link. One possibility is that the Late Jurassic shortening event recorded in the Blue Mountains Province may be a northerly extension of the Nevadan orogeny. Differences in the timing of these events in the Blue Mountains Province and the Klamath–Sierra Nevada Provinces suggest that shortening and deformation were diachronous, progressing from north to south. We envision that Late Jurassic deformation may have collapsed a Gulf of California–style oceanic extensional basin that extended from the Klamath Mountains (e.g., Josephine ophiolite) to the central Blue Mountains Province, and possibly as far north as the North Cascades (i.e., the coeval Ingalls ophiolite).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912391W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912391W"><span>Preliminary results of layered modelling of seismic refraction data at the East Limpopo Margin, Mozambique (PAMELA project, MOZ3/5 cruise)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Watremez, Louise; Evain, Mikael; Leprêtre, Angélique; Verrier, Fanny; Aslanian, Daniel; Leroy, Sylvie; Dias, Nuno; Afilhado, Alexandra; Schnurle, Philippe; d'Acremont, Elia; de Clarens, Philippe; Castilla, Raymi; Moulin, Maryline</p> <p>2017-04-01</p> <p>The East Limpopo Margin is a continental margin located offshore southern Mozambique, in the Mozambique Channel. The southern Mozambique margin has not been studied much until now, but its formation is assumed to be the result of the separation of the African plate from the Antarctica plate. A new geophysical survey MOZ3/5 (February-April 2016; PAMELA project*) allowed the acquisition of seven wide-angle reflection and refraction seismic profiles across the southernmost Mozambique margin. In this work, we show the first results obtained from the layered modelling of an approximately 400 km long transect crossing the East Limpopo Margin and including information from 22 ocean-bottom seismometers and 18 land seismometers. The velocity model, compared to coincident seismic reflection data, allows to observe (1) the variations of seismic velocities together with the variations of reflectivity characteristics in the sediments, including the occurrence of some magmatism, (2) some deep features located below the acoustic basement and that can be related to the pre-to-syn-rift history of the margin, (3) the velocities and Moho depths in the different areas of the crust, from the thick continental crust to the clear oceanic crust (magnetic anomalies), helping to define the nature of the crust and the presence of magmatic features along the whole profile, and (4) some velocity information in the uppermost mantle. These results will allow us to (1) understand the deep structures of the East Limpopo Margin and to have better constraints on the formation of the margin, helping kinematic reconstructions, improving the quantification of the magmatism along this margin, and (2) improve the knowledge of both the thermal evolution of the sediments and the potential magmatic sources in the study area. *The PAMELA project (PAssive Margin Exploration Laboratories) is a scientific project led by Ifremer and TOTAL in collaboration with Université de Bretagne Occidentale, Université Rennes 1, Université Pierre and Marie Curie, CNRS and IFPEN. Moulin, M., Aslanian, D., et al 2016. PAMELA-MOZ03 cruise, RV Pourquoi pas ?, http://dx.doi.org/10.17600/16001600 Moulin, M., Evain, M., et al. 2016. PAMELA-MOZ05 cruise, RV Pourquoi pas ?, http://dx.doi.org/10.17600/16009500</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70028877','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70028877"><span>Grenvillian magmatism in the northern Virginia Blue Ridge: Petrologic implications of episodic granitic magma production and the significance of postorogenic A-type charnockite</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Tollo, R.P.; Aleinikoff, J.N.; Borduas, E.A.; Dickin, A.P.; McNutt, R.H.; Fanning, C.M.</p> <p>2006-01-01</p> <p>Grenvillian (1.2 to 1.0 Ga) plutonic rocks in northern Virginia preserve evidence of episodic, mostly granitic magmatism that spanned more than 150 million years (m.y.) of crustal reworking. Crystallization ages determined by sensitive high resolution ion microprobe (SHRIMP) U-Pb isotopic analyses of zircon and monazite, combined with results from previous studies, define three periods of magmatic activity at 1183-1144 Ma (Magmatic Interval I), 1120-1111 Ma (Magmatic Interval II), and 1078-1028 Ma (Magmatic Interval III). Magmatic activity produced dominantly tholeiitic plutons composed of (1) low-silica charnockite, (2) leucogranite, (3) non-leucocratic granitoid (with or without orthopyroxene (opx)), and (4) intermediate biotite-rich granitoid. Field, petrologic, geochemical, and geochronologic data indicate that charnockite and non-charnockitic granitoids were closely associated in both space and time, indicating that presence of opx is related to magmatic conditions, not metamorphic grade. Geochemical and Nd isotopic data, combined with results from experimental studies, indicate that leucogranites (Magmatic Intervals I and III) and non-leucocratic granitoids (Magmatic Intervals I and II) were derived from parental magmas produced by either a high degree of partial melting of isotopically evolved tonalitic sources or less advanced partial melting of dominantly tonalitic sources that also included a more mafic component. Post-orogenic, circa 1050 Ma low-silica charnockite is characterized by A-type compositional affinity including high FeOt/(FeOt + MgO), Ga/Al, Zr, Nb, Y, and Zn, and was derived from parental magmas produced by partial melting of potassic mafic sources in the lower crust. Linear geochemical trends defined by leucogranites, low-silica charnockite, and biotite-rich monzogranite emplaced during Magmatic Interval III reflect differences in source-related characteristics; these features do not represent an igneous fractionation sequence. A compositional gap between circa 1160 Ma magnesian low-silica charnockite and penecontemporaneous higher silica lithologies likewise precludes a fractionation relationship among plutons intruded during Magmatic Interval I. Correspondence in timing of magmatic activity between the Blue Ridge and neighboring Mesoproterozoic terranes underscores the widespread nature of Grenvillian processes in the region.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1512782S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1512782S"><span>Geochemical characteristics of Antarctic magmatism connected with Karoo-Maud and Kerguelen mantle plumes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sushchevskaya, Nadezhda; Krymsky, Robert; Belyatsky, Boris; Antonov, Anton; Migdisova, Natalya</p> <p>2013-04-01</p> <p>Emplacement (130-115 m.y. ago) of dikes and sills of alkaline-ultrabasic composition within Jetty oasis (East Antarctica) is suggested as a later appearance of plume magmatism within the East-Antarctic Shield [Andronikov et al., 1993, 2001; Laiba et al., 1987]. This region is located opposite Kerguelen Islands and possibly could be properly connected with activity of the Kerguelen-plume [Foley et al., 2001, 2006]. Jurassic-Cretaceous dykes, stocks and sills of alkaline-ultrabasic rocks, relatively close to kimberlite-type, are exposed within Jetty oasis and on the southern shore of the Raddock Lake. This alkaline-ultrabasic magmatism has appeared to be connected with the main Mesozoic stage of the evolution of the Lambert and Amery glaciers riftogenic structure [Kurinin et al., 1980, 1988]. The alkaline-ultrabasic dikes and sills within Jetty oasis cut the rocks of the Beaver complex, Permo-Triassic terrigeneous successions of the Amery complex, and late Paleozoic low-alkaline basic dikes as well. Dashed chain of 6 stock bodies spread out on 15 km along the eastern shore of the Beaver Lake, marked their allocation with submeridianal zone of the deep cracks, boarded of the eastern side of the Beaver Lake trough. At the same time, new data upon Quaternary magmatism of the mountain Gaussberg has confirmed the unique features of ultra-potassium alkaline magmatism (up to 14-17% K2O) formed under exclusively continental conditions [Murphy et al., 2002]. Volcanic cone is located at the continuation of Gaussberg rift zone which is possibly a part of Lambert fracture zone. Its formation is connected with the early stages of Gondwana development, perhaps, reactivated in different Precambrian events and according to numerous data is a single rift zone which is traced Indian inland (Indrani graben, [Golynsky, 2011]). The time of lamproitic magmas eruption is estimated at 56000±5000 yeas ago [Tingey et al., 1983]. Earlier it had been shown the Mesozoic (about 170 Ma) basaltic dykes of the Schirmacher Oasis and basalts and dolerites of the Queen Maud Land (180 Ma) are identical in petrology and geochemistry terms and supposedly could be interpreted as the manifestation of the Karoo-Maud plume activity in Antarctica [Sushchevskaya et al., 2012]. The spatial distribution of the dikes indicates the eastward spreading of the plume material from DML to the Schirmacher Oasis within at least 10 Ma (up to ~35 Ma, taking into account the uncertainty of age determination). On the other hand, the considerable duration and multistage character of plume magmatism related to the activity of the Karoo-Maud plume in Antarctica and Africa [Leat et al., 2007; Luttinen et al., 2002] may indicate that the Mesozoic dikes of the oasis correspond to a single stage of plume magmatism. On the basis of obtained isotopic data it has been determined two magmatic melt evolution trends for basalts from: Queen Maud Land - Kerguelen Archipelago - Afanasy Nikitin Rise (Indian Ocean) and Jetty - Schirmacher oasises which mantle sources are quite different. Thus the Jetty - Schirmacher oasises magmatic melt sources are characterized by prevalence of the matter of moderately enriched or primitive chondritic mantle source and lithospheric mantle of Proterozoic ages but the substances of depleted mantle source similar to MORB-type and ancient mantle are absent. New data obtained on Nd, Sr, Pb isotopic and lithophile elements compositions of the alkaline-ultrabasic rocks from the Jetty oasis and Gaussberg volcano completed imagine of the Kerguelen-plume evolution. It has been confirmed unique character of the alkaline lamproiites of the Gaussberg volcano enrichments. Highly radiogenic Sr and Pb isotope ratios of these lamproiites reflect melting of the ancient sublithospheric depleted mantle which was stored from the Archean till nowadays unaffected by metasomatic-enrichment processes. During modern melting of this mantle part there is input of additional substances (crustal fluid of sediment origins, subducted sediments etc.) with high Rb/Sr ratio.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V11A0339F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V11A0339F"><span>An Overview of Thermal Measurements (IR) at the Summit of Piton de la Fournaise Active Volcano and Inferences on the Structure and Dynamics of its Hydrothermal System</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fontaine, F.; Peltier, A.; Kowalski, P.; Di Muro, A.; Villeneuve, N.; Ferrazzini, V.; Staudacher, T.</p> <p>2017-12-01</p> <p>Piton de la Fournaise, located on La Réunion Island in the South East Indian Ocean, is one of the most active basaltic volcanoes (hotspot) of the world with a mean eruption frequency <6 months over the last 20 years. The central dome of the shield is thought to host an active hydrothermal system evidenced by self-potential techniques early in the 90's and mining heat from a magmatic source located about 2-2.5 km below the summit. Surface manifestations of this activity such as fumeroles or hot grounds have however never been observed before 2007 when deep magma withdrawal from the magmatic horizon during the "eruption of the century" (>100×106 m3) on the island, led to the formation of a 400-m-deep, 1000-m-large, funnel-shaped summit caldera. Since then, the floor and inner flanks of this summit depression hosting hot grounds and active fumaroles, are monitored using an infra-red camera device permanently installed on the caldera rim.This thermal dataset constitutes the first opportunity to understand the structure and dynamics of the hydrothermal system and its ability to relay deep-seated heat and mass perturbations. We present in this communication an overview of this thermal datasets focusing on ground/fumaroles temperature evolution during volcanic crisis and rest periods and analyzing correlations with the other permanently acquired data such as the temporal evolution of gas geochemistry (CO2, SO2, H2S), ground deformation and micro-seismic activity. We finally propose a conceptual model of fluid flow architecture within the edifice which paves the way for future quantitative models of hydrothermal heat and mass transfers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IzPSE..54..444K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IzPSE..54..444K"><span>Deep Structure of the Zone of Tolbachik Fissure Eruptions (Kamchatka, Klyuchevskoy Volcano Group): Evidence from a Complex of Geological and Geophysical Data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kugaenko, Yu. A.; Saltykov, V. A.; Gorvatikov, A. V.; Stepanova, M. Yu.</p> <p>2018-05-01</p> <p>With the use of the method of low-frequency microseismic sounding, the configuration of the magmatic feeding system of the Tolbachinsky Dol—a regional zone of areal basaltic volcanism in the southern part of the Klyuchevskoy volcano group in Kamchatka—is studied. The initial data are obtained by a stepby-step recording of the background microseismic noise in 2010-2015 within a thoroughly marked-out survey area covering the zones of fissure eruptions in 1975-1976 and 2012-2013 and, partly, the edifice of the Ploskii (flat) Tolbachik volcano. The depth sections reflecting the distributions of the relative velocities of seismic waves in the Earth's crust are constructed. For a more reliable interpretation of the revealed deep anomalies, the results of independent geological and geophysical studies are used. The ascertained low-velocity structures are closely correlated to the manifestations of present-day volcanism. It is shown that the feeding structure of the Tolbachinsky Dol is spatially heterogeneous, incorporating subvertical and lateral pipeshaped magma conduits, closely spaced magma feeding channels, and shallow magma reservoirs. A longlived local transcrustal magma conducting zone is revealed, and regularities in the deep structure of the feeding systems of fissure eruptions are identified. The configuration of the established subvertical magma conduits permits basalts moving to rise to the surface by different paths, which, inter alia, explains the contrasting magma compositions observed during a single eruption. Thus, based on the instrumental data, it is shown that the magmatic feeding structure of the Tolbachinsky Dol has a number of specific peculiarities and is significantly more complicated than has been previously thought about the areal volcanic fields.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..320...50I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..320...50I"><span>Geochemical characterisation of gases along the dead sea rift: Evidences of mantle-co2 degassing</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Inguaggiato, C.; Censi, P.; D'Alessandro, W.; Zuddas, P.</p> <p>2016-06-01</p> <p>The Dead Sea Transform (DST) fault system, where a lateral displacement between the African and Arabian plates occurs, is characterised by anomalous heat flux in the Israeli area close to the border with Syria and Jordan. The concentration of He and CO2, and isotopic composition of He and total dissolved inorganic carbon were studied in cold and thermal waters collected along the DST, in order to investigate the source of volatiles and their relationship with the tectonic framework of the DST. The waters with higher temperature (up to 57.2 °C) are characterised by higher amounts of CO2 and helium (up to 55.72 and 1.91 ∗ 10- 2 cc l- 1, respectively). Helium isotopic data (R/Ra from 0.11 to 2.14) and 4He/20Ne ratios (0.41-106.86) show the presence of deep-deriving fluids consisting of a variable mixture of mantle and crust end-members, with the former reaching up to 35%. Carbon isotope signature of total dissolved carbon from hot waters falls within the range of magmatic values, suggesting the delivery of deep-seated CO2. The geographical distribution of helium isotopic data and isotopic carbon (CO2) values coupled with (CO2/3He ratios) indicate a larger contribution of mantle-derived fluids affecting the northern part of the investigated area, where the waters reach the highest temperature. These evidences suggest the occurrence of a favourable tectonic framework, including a Moho discontinuity up-rise and/or the presence of a deep fault system coupled with the recent magmatic activity recognised in the northern part of Israel.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V51F0422A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V51F0422A"><span>The Root of the Butte Porphyry Cu Deposit: A Zone of Fluid Accumulation, Discharge and Collapse</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Acosta, M. D.; Reed, M. H.; Watkins, J. M.</p> <p>2017-12-01</p> <p>The deep zones of porphyry Cu deposits are the focus of the hydrothermal-magmatic transition, where hydrothermal fluid emerges from crystallizing magma. In the Butte, MT porphyry Cu deposit at a paleodepth of 8 km, we observe a zone of intense silicification and brecciation. This deep in the system, where the distinction between hydrothermal and magmatic processes is ambiguous, we obtain a rare look into how a magma and its coeval fluid phase feed into porphyry Cu deposits. We characterize this zone through a suite of analyses. We used rock pulps from 15m lengths of drill core to estimate the volume percentage of quartz veins. Estimates based upon Si, Ti, and Zr are 2-12%, 14-41%, and 15-48%, respectively. In thin section, three texturally distinct populations of quartz are present: quartz that permeates altered granite such that the sample consists of 40-50% quartz of variable grain size, quartz in veins with diffuse and non-planar boundaries, and quartz in quartz-pyrite veins with sharp walls that merge with quartz-pyrite veins with irregular and diffuse boundaries. The concentrations of Ti in of each of the quartz populations do not exceed 50 ppm, and the lowest is below the detection limit of 4 ppm. Temperature estimates based on the TitaniQ thermobarometer for 50 ppm Ti range from 583 °C at hydrostatic pressure (0.7 kb), to 665 °C at lithostatic pressure (2.5 kb). Cathodoluminescence (CL) images of each population are also remarkably similar, being almost entirely homogeneous/mottled cut by CL-dark later quartz veinlets. Only the quartz-pyrite veinlet with planar walls contained euhedral CL oscillations. The large abundance of quartz in these deep samples, combined with the lack of sharp, planar boundaries, and the temperature estimates suggest that the rock was at least locally ductile as the quartz veins formed, and afterwards. The large quartz abundance further indicates that the base of the porphyry Cu deposit underwent intermittent fluid accumulation and expulsion. Together, these observations suggest that this region of intense silicification is the volume where fluid exsolving from a magma repeatedly collected and discharged to the upward, brittle portion of the deposit.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014FrEaS...2...21C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014FrEaS...2...21C"><span>Trace element and Sr-Nd-Pb isotope geochemistry of Rungwe Volcanic Province, Tanzania: Implications for a superplume source for East Africa Rift magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Castillo, Paterno; Hilton, David; Halldórsson, Sæmundur</p> <p>2014-09-01</p> <p>The recently discovered high, plume-like 3He/4He ratios at Rungwe Volcanic Province (RVP) in southern Tanzania, similar to those at the Main Ethiopian Rift in Ethiopia, strongly suggest that magmatism associated with continental rifting along the entire East African Rift System (EARS) has a deep mantle contribution (Hilton et al., 2011). New trace element and Sr-Nd-Pb isotopic data for high 3He/4He lavas and tephras from RVP can be explained by binary mixing relationships involving Early Proterozoic (+/- Archaean) lithospheric mantle, present beneath the southern EARS, and a volatile-rich carbonatitic plume with a limited range of compositions and best represented by recent Nyiragongo lavas from the Virunga Volcanic Province also in the Western Rift. Other lavas from the Western Rift and from the southern Kenya Rift can also be explained through mixing between the same endmember components. In contrast, lavas from the northern Kenya and Main Ethiopian rifts can be explained through variable mixing between the same mantle plume material and the Middle to Late Proterozoic lithospheric mantle, present beneath the northern EARS. Thus, we propose that the bulk of EARS magmatism is sourced from mixing among three endmember sources: Early Proterozoic (+/- Archaean) lithospheric mantle, Middle to Late Proterozoic lithospheric mantle and a volatile-rich carbonatitic plume with a limited range of compositions. We propose further that the African Superplume, a large, seismically anomalous feature originating in the lower mantle beneath southern Africa, influences magmatism throughout eastern Africa with magmatism at RVP and Main Ethiopian Rift representing two different heads of a single mantle plume source. This is consistent with a single mantle plume origin of the coupled He-Ne isotopic signatures of mantle-derived xenoliths and/or lavas from all segments of the EARS (Halldorsson et al., 2014).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JAfES.139..354H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JAfES.139..354H"><span>Geochemical, Sr-Nd isotopic investigations and U-Pb zircon chronology of the Takht granodiorite, west Iran: Evidence for post-collisional magmatism in the northern part of the Urumieh-Dokhtar magmatic assemblage</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Haghighi Bardineh, Seyyed Nematollah; Zarei Sahamieh, Reza; Zamanian, Hassan; Ahmadi Khalaji, Ahmad</p> <p>2018-03-01</p> <p>Subduction of Neo-Tethys lithosphere beneath the Iranian plateau during Neogene led to the formation of a NW-SE trending volcano-plutonic zone called Urumieh-Dokhtar magmatic assemblage (UDMA). The Takht granodiorite (NE of Hamedan Province, western Iran) belongs to the UDMA and has geochemical properties of post-collisional granitoids that was formed after the collision of Arabian and Iranian plateaus. This body contains rounded mafic micro-granular enclaves with relatively gradational rims indicating the effect of magma mixing/mingling in formation of the granodiorite body. The determination of U-Pb zircon age proved the Takht granodiorite was formed at Miocene (16.8 ± 0.24 Ma). The Nd-Sr isotope ratios and Sr/Nd, Nb/La and Th/U ratios of the granodiorite confirmed the magma was formed mainly by melting of continental crust, and its enclaves originated from a mantle derived mafic magma. Samples show negative anomalies in Nb, Sr, Ti, P and Eu, whereas positive anomalies in Th, K, Zr, Yb and Rb that reveals contribution of mantle and crustal materials in their generation. The Takht granodiorite has geochemical features of A2-type granites and also shows properties of both the volcanic arc and within plate magmatism association granitoids (high levels of LILEs and HFSEs). Regarding this interpretation and also post-collisional tectonic regime, it can be concluded that post-collision extensions caused deep faults in the UDMA that let mantle derived magmas rise up to the thicken crust. Such magma triggered melting in the middle crustal levels and was contaminated with crustal materials to generate granodiorite and enclave magmas respectively. The results of the current study decipher collision between the Arabian and the Iranian plateaus occurred before Miocene and the magmatism in the UDMA continued after closure of Neo-Tethys.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V42A..04R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V42A..04R"><span>Tracking Volatile Movement and Fluxing in Magmatic Systems with Mineral Geochemistry: A Comparison Between two Mount St. Helens Eruptions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rowe, M. C.; Kent, A. J.; Cashman, K.; Thornber, C. R.</p> <p>2008-12-01</p> <p>Lithium abundances in amphibole and feldspar have recently been applied to studies of volatile migration and fluxing in shallow magmatic systems. Lithium is advantageous because it 1) partitions into Cl- and H2O- rich volatile components at shallow pressures and 2) has a high diffusion coefficient in many minerals, recording relative short timescales of crystallization, enrichment, and depletion in magmatic systems. Prior studies at Mount St. Helens have identified high Li concentrations in feldspar phenocrysts, interpreted to record volatile fluxing to shallow magma in both the 1980 and 2004 eruptions. This interpretation is based largely on rapid diffusion and re-equilibration of Li in feldspar but is also supported by fluctuations in Li concentrations in melt inclusions. We have extended previous results by measuring the concentration of Li in amphibole phenocrysts, in addition to associated plagioclase. Amphibole is stable only at pressures > ~100 MPa and therefore is expected to retain information about degassing deep in the magmatic systems. In 1980 eruptive material, the temporal variability in amphibole Li abundance parallels that of feldspar and Li partitioning between both phases is in accord with measured equilibrium values. In contrast, amphibole grains in the 2004 eruptive products have Li abundances that are antithetical to those in feldspar, recording an initial depletion, followed by significant enrichment by Jan 2005 (from ~10 to ~1000 ug/g). One interpretation of the 2004- 08 trend is that Li abundances simply reflect melt composition and concentrations are dictated by amphibole/melt partitioning. Alternatively, because Li rapid diffuses, low-Li amphibole in 2004 could also result from extensive diffusion between a high-Li amphibole and low-Li melt. The vastly different temporal trends in amphibole Li concentrations between the 1980s and the 2004-08 eruptions raise significant questions about partitioning and diffusion of Li in shallow magmatic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035386','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035386"><span>The geophysical character of southern Alaska - Implications for crustal evolution</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Saltus, R.W.; Hudson, T.L.; Wilson, Frederic H.</p> <p>2007-01-01</p> <p>The southern Alaska continental margin has undergone a long and complicated history of plate convergence, subduction, accretion, and margin-parallel displacements. The crustal character of this continental margin is discernible through combined analysis of aeromagnetic and gravity data with key constraints from previous seismic interpretation. Regional magnetic data are particularly useful in defining broad geophysical domains. One of these domains, the south Alaska magnetic high, is the focus of this study. It is an intense and continuous magnetic high up to 200 km wide and ∼1500 km long extending from the Canadian border in the Wrangell Mountains west and southwest through Cook Inlet to the Bering Sea shelf. Crustal thickness beneath the south Alaska magnetic high is commonly 40–50 km. Gravity analysis indicates that the south Alaska magnetic high crust is dense. The south Alaska magnetic high spatially coincides with the Peninsular and Wrangellia terranes. The thick, dense, and magnetic character of this domain requires significant amounts of mafic rocks at intermediate to deep crustal levels. In Wrangellia these mafic rocks are likely to have been emplaced during Middle and (or) Late Triassic Nikolai Greenstone volcanism. In the Peninsular terrane, the most extensive period of mafic magmatism now known was associated with the Early Jurassic Talkeetna Formation volcanic arc. Thus the thick, dense, and magnetic character of the south Alaska magnetic high crust apparently developed as the response to mafic magmatism in both extensional (Wrangellia) and subduction-related arc (Peninsular terrane) settings. The south Alaska magnetic high is therefore a composite crustal feature. At least in Wrangellia, the crust was probably of average thickness (30 km) or greater prior to Triassic mafic magmatism. Up to 20 km (40%) of its present thickness may be due to the addition of Triassic mafic magmas. Throughout the south Alaska magnetic high, significant crustal growth was caused by the addition of mafic magmas at intermediate to deep crustal levels.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012MarGR..33...33L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012MarGR..33...33L"><span>Magnetic signature of the Sicily Channel volcanism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lodolo, E.; Civile, D.; Zanolla, C.; Geletti, R.</p> <p>2012-03-01</p> <p>Widespread Late Miocene to Quaternary volcanic activity is know to have occurred in the Sicily Channel continuing up to historical time. New magnetic anomaly data acquired in the Pantelleria Graben, one of the three main tectonic depressions forming the WNW-trending Sicily Channel rift system, integrated with available profiles, are used to identify and map volcanic bodies in this sector of the northern African margin. Some of these manifestations, both outcropping at the sea-floor or buried beneath a variable thickness of Plio-Quaternary sedimentary cover, have been imaged by seismic reflection profiles. Three main positive magnetic anomalies have been found: to the S-E of the Pantelleria Island, the largest emerged caldera of the Sicily Channel, along the eastern margin of the Nameless Bank, and at the north-western termination of the Linosa Graben. Only the anomaly located off the south-eastern coast of the Pantelleria Island, associated with a large outcropping body gradually buried beneath a substantially undisturbed Upper Pliocene-Quaternary sediments, aligns with the trend of the tectonic depression. 2-D geophysical models produced along seismic transects perpendicularly crossing the Pantelleria Graben have allowed to derive its deep crustal structure, and detect the presence of buried magmatic bodies which generate the anomalies. Marginal faults seem to have played a major role in focussing magma emplacement in this sector of the Sicily Channel. The other anomalies represent off-axis volcanic episodes and generally do not show evident magmatic manifestations at the sea-floor. These magnetic maxima seem to follow a NNE-SSW-trending belt extending from Linosa Island to the Nameless Bank, where pre-existing crustal anisotropies may have conditioned magma emplacement both at deep and shallow crustal levels. In general, data analysis has shown that there is a structural control on magma emplacement, with the major magmatic features located in specific locations like boundary faults and transfer zones, in a manner similar to that found along several segments of the East African Rift system.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016414','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016414"><span>Tectonic development of passive continental margins of the southern and central Red Sea with a comparison to Wilkes Land, Antarctica</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bohannon, R.G.; Eittreim, S.L.</p> <p>1991-01-01</p> <p>The continental margins of the southern and central Red Sea and most of Wilkes Land, Antarctica have bulk crustal configurations and detailed structures that are best explained by a prolonged history of magmatic expansion that followed a brief, but intense period of mechanical extension. Extension on the Red Sea margins was spatially confined to a rift that was 20-30 km in width. The rifting phase along the Arabian margin of the central and southern Red Sea occurred 25-32 Ma ago, primarily by detachment faulting at upper crustal levels and ductile uniform stretching at depth. Rifting was followed by an early magmatic phase during which the margin was invaded by dikes and plutons, primarily of gabbro and diorite, at 20-24 Ma, after the crust was mechanically thinned from 40 km to ??? 20 km. We infer continued spreading after that in which broad shelves were formed by a process of magmatic expansion, because the offshore crust is only 8-15 km thick, including sediment, and seismic reflection data do not depict horst and graben or half graben structures from which mechanical extension might be inferred. The Wilkes Land margin is similar to the Arabian example. The margin is about 150 km in width, the amount of upper crustal extension is too low to explain the change in sub-sediment crustal thickness from ??? 35 km on the mainland to < 10 km beneath the margin and reflectors in the deepest seismic sequence are nearly flat lying. Our model requires large volumes of melt in the early stages of continental rifting. The voluminous melt might be partly a product of nearby hot spots, such as Afar and partly the result of an initial period of partial fusion in the deep continental lithosphere under lower temperatures than ordinarily required by dry solidus conditions. ?? 1991.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T51B0460S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T51B0460S"><span>Central Atlantic Break-up: A competition between CAMP Hotspot and thinning rate.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sapin, F.; Maurin, T.</p> <p>2017-12-01</p> <p>The break-up of the Central Atlantic is known to have ended at about 190Myrs while the CAMP (Central Atlantic Magmatic Province) was still active. Several seismic lines, acquired recently in the deep offshore Senegal and Mauritanian domain, provide detailed images of continent-ocean transition and the oceanic crust architecture. Their interpretation is the opportunity to describe the progressive interaction between the hot spot activity, the architecture and timing of break up and the oceanic crust production. In the North, seismic data and gravity/magnetic inversions suggest an extremely thinned continental crust with possible mantle exhumation. In the South, the continental crust is thick and the transition to oceanic crust is sharp. In addition, three oceanic crust facies were described along the margin in an extremely slow spreading ridge setting ( 0.8cm/yr during the first 20Myrs): facies (1) with a poorly imaged Moho and a strongly faulted thin oceanic crust or exhumed mantle; facies (2) with an extensively faulted 6km thick oceanic crust; facies (3) with abnormally thick (9km) oceanic crust marked by SDR-type reflections. They are diachronous from North to South and the two first one disappear southwards and (facies 3) being younger toward the North. Only a single very thick oceanic crust (12-14km) remains in front of the Guinea Plateau. We concluded that, in the South, the break-up had been forced through a thick or thickened continental crust due to the remnant activity of the CAMP Hotspot. In the North, the magmatic pulse arrived far after the break-up during the spreading and the thinning of the continental crust could lead to hyper extension. This evolution emphasizes that the architecture, and thus processes leading to the break-up can vary a lot considering the influence of thermal vertical forces (mantle dynamics/hotspot/magmatism) and mechanical horizontal forces (plate movement/faulting/spreading), both of them being necessary for a rift to succeed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013CoMP..166..351N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013CoMP..166..351N"><span>The Axum-Adwa basalt-trachyte complex: a late magmatic activity at the periphery of the Afar plume</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Natali, C.; Beccaluva, L.; Bianchini, G.; Siena, F.</p> <p>2013-08-01</p> <p>The Axum-Adwa igneous complex consists of a basalt-trachyte (syenite) suite emplaced at the northern periphery of the Ethiopian plateau, after the paroxysmal eruption of the Oligocene (ca 30 Ma) continental flood basalts (CFB), which is related to the Afar plume activity. 40Ar/39Ar and K-Ar ages, carried out for the first time on felsic and basaltic rocks, constrain the magmatic age of the greater part of the complex around Axum to 19-15 Ma, whereas trachytic lavas from volcanic centres NE of Adwa are dated ca 27 Ma. The felsic compositions straddle the critical SiO2-saturation boundary, ranging from normative quartz trachyte lavas east of Adwa to normative (and modal) nepheline syenite subvolcanic domes (the obelisks stones of ancient axumites) around Axum. Petrogenetic modelling based on rock chemical data and phase equilibria calculations by PELE (Boudreau 1999) shows that low-pressure fractional crystallization processes, starting from mildly alkaline- and alkaline basalts comparable to those present in the complex, could generate SiO2-saturated trachytes and SiO2-undersaturated syenites, respectively, which correspond to residual liquid fractions of 17 and 10 %. The observed differentiation processes are consistent with the development of rifting events and formation of shallow magma chambers plausibly located between displaced (tilted) crustal blocks that favoured trapping of basaltic parental magmas and their fractionation to felsic differentiates. In syenitic domes, late- to post-magmatic processes are sometimes evidenced by secondary mineral associations (e.g. Bete Giorgis dome) which overprint the magmatic parageneses, and mainly induce additional nepheline and sodic pyroxene neo-crystallization. These metasomatic reactions were promoted by the circulation of Na-Cl-rich deuteric fluids (600-400 °C), as indicated by mineral and bulk rock chemical budgets as well as by δ18O analyses on mineral separates. The occurrence of this magmatism post-dating the CFB event, characterized by comparatively lower volume of more alkaline products, conforms to the progressive vanishing of the Afar plume thermal effects and the parallel decrease of the partial melting degrees of the related mantle sources. This evolution is also concomitant with the variation of the tectono-magmatic regime from regional lithospheric extension (CFB eruption) to localized rifting processes that favoured magmatic differentiation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Icar..248..424J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Icar..248..424J"><span>Lunar floor-fractured craters as magmatic intrusions: Geometry, modes of emplacement, associated tectonic and volcanic features, and implications for gravity anomalies</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jozwiak, Lauren M.; Head, James W.; Wilson, Lionel</p> <p>2015-03-01</p> <p>Lunar floor-fractured craters are a class of 170 lunar craters with anomalously shallow, fractured floors. Two end-member processes have been proposed for the floor formation: viscous relaxation, and subcrater magmatic intrusion and sill formation. Recent morphometric analysis with new Lunar Reconnaissance Orbiter Laser Altimeter (LOLA) and image (LROC) data supports an origin related to shallow magmatic intrusion and uplift. We find that the distribution and characteristics of the FFC population correlates strongly with crustal thickness and the predicted frequency distribution of overpressurization values of magmatic dikes. For a typical nearside lunar crustal thickness, dikes with high overpressurization values favor surface effusive eruptions, medium values favor intrusion and sill formation, and low values favor formation of solidified dikes concentrated lower in the crust. We develop a model for this process, make predictions for the morphologic, morphometric, volcanic, and geophysical consequences of the process and then compare these predictions with the population of observed floor-fractured craters. In our model, the process of magmatic intrusion and sill formation begins when a dike propagates vertically towards the surface; as the dike encounters the underdense brecciated region beneath the crater, the magmatic driving pressure is insufficient to continue vertical propagation, but pressure in the stalled dike exceeds the local lithostatic pressure. The dike then begins to propagate laterally forming a sill which does not propagate past the crater floor region because increased overburden pressure from the crater wall and rim crest pinch off the dike at this boundary; the sill then continues to inflate, further raising and fracturing the brittle crater floor. When the intrusion diameter to intrusion depth ratio is smaller than a critical value, the intrusion assumes a laccolith shape with a domed central region. When the ratio exceeds a critical value, the intrusion concentrates bending primarily at the periphery, resulting in a flat, tabular intrusion. We predict that this process will result in concentric fractures over the region of greatest bending. This location is close to the crater wall in large, flat-floored craters, as observed in the crater Humboldt, and interior to the crater over the domed floor in smaller craters, as observed in the crater Vitello. A variety of volcanic features are predicted to be associated with the solidification and degassing of the intrusion; these include: (1) surface lava flows associated with concentric fractures (e.g., in the crater Humboldt); (2) vents with no associated pyroclastic material, from the deflation of under-pressurized magmatic foam (e.g., the crater Damoiseau); and (3) vents with associated pyroclastic deposits from vulcanian eruptions of highly pressurized magmatic foam (e.g., the crater Alphonsus). The intrusion of basaltic magma beneath the crater is predicted to contribute a positive component to the Bouguer gravity anomaly; we assess the predicted Bouguer anomalies associated with FFCs and outline a process for their future interpretation. We conclude that our proposed mechanism serves as a viable formation process for FFCs and accurately predicts numerous morphologic, morphometric, and geophysical features associated with FFCs. These predictions can be further tested using GRAIL (Gravity Recovery and Interior Laboratory) data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T31D0645V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T31D0645V"><span>Inferring the thermal structure of the Panama Basin by seismic attenuation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vargas-Jimenez, C. A.; Pulido, J. E.; Hobbs, R. W.</p> <p>2017-12-01</p> <p>Using recordings of earthquakes on Oceanic Bottom Seismographs and onshore stations on the coastal margins of Colombia, Panama, and Ecuador, we discriminate intrinsic and scattering attenuation processes in the upper lithosphere of the Panama Basin. The tomographic images of the derived coda-Q values are correlated with estimates of Curie Point Depth and measured and theoretical heat flow. Our study reveals three tectonic domains where magmatic/hydrothermal activity or lateral variations of the lithologic composition in the upper lithosphere can account for the modelled thermal structure and the anelasticity. We find that the Costa Rica Ridge and the Panama Fracture Zone are significant tectonic features in the study area. We interpret a large and deep intrinsic attenuation anomaly as related to the heat source at this ocean spreading center and show how interactions with regional fault systems cause contrasting attenuation anomalies.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18.1244M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18.1244M"><span>A geochemical and geophysical reappraisal to the significance of the recent unrest at Campi Flegrei caldera (Southern Italy)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moretti, Roberto; De Natale, Giuseppe; Troise, Claudia</p> <p>2017-03-01</p> <p>Volcanic unrest at calderas involves complex interaction between magma, hydrothermal fluids, and crustal stress and strain. Campi Flegrei caldera (CFc), located in the Naples (Italy) area and characterized by the highest volcanic risk on Earth for the extreme urbanization, undergoes unrest phenomena involving several meters of uplift and intense shallow microseismicity since several decades. Despite unrest episodes display in the last decade only moderate ground deformation and seismicity, current interpretations of geochemical data point to a highly pressurized hydrothermal system. We show that at CFc, the usual assumption of vapor-liquid coexistence in the fumarole plumes leads to largely overestimated hydrothermal pressures and, accordingly, interpretations of elevated unrest. By relaxing unconstrained geochemical assumptions, we infer an alternative model yielding better agreement between geophysical and geochemical observations. The model reconciles discrepancies between what observed (1) for two decades since the 1982-1984 large unrest, when shallow magma was supplying heat and fluids to the hydrothermal system, and (2) in the last decade. Compared to the 1980's unrest, the post-2005 phenomena are characterized by much lower aquifers overpressure and magmatic involvement, as indicated by geophysical data and despite large changes in geochemical indicators. Our interpretation points out a model in which shallow sills, intruded during 1969-1984, have completely cooled, so that fumarole emissions are affected now by deeper, CO2-richer, magmatic gases producing the modest heating and overpressure of the hydrothermal system. Our results have important implications on the short-term eruption hazard assessment and on the best strategies for monitoring and interpreting geochemical data.<abstract type="synopsis"><title type="main">Plain Language SummaryCampi Flegrei is one of the most dangerous volcanoes on Earth. Last eruption occurred in 1538 but since decades it undergoes unrest phenomena involving ground uplift and seismicity. Geochemical evidences show that current unrest (about 40 cm of uplift since 2005) has different causes to that of 1982-1984, when ground uplift totaled 1.8 m. For many geochemists, the 1982-1984 movement was caused by hydrothermal activity, the degassing magma being deep, and the current activity is caused by shallow magma, but we show that it goes on the contrary. We have checked more than 30 years of geochemical records, and our ongoing interpretation of released gases and physical signals is consistent with current activity being hydrothermal, with the support of very deep magmatic gases, rather than due to the activity of a shallow (3-4 km deep) magma chamber, which instead characterized the 1982-1984 episode. This is only apparently better news, at least for now: activity in which magma is shallow tends to be associated with an increased chance of an eruption, but the change from hydrothermal to magmatic activity can take place at any time. Therefore, a conservative and precautionary attitude and a high level of attention are absolutely necessary.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V43C2589V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V43C2589V"><span>Geochemical and Isotopic Evidences of the Magmatic Sources in the Eastern Sector of the Trans-Mexican Volcanic Belt: Xihuingo-Chichicuautla Volcanic Field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Valadez, S.; Martinez-serrano, R.; Juarez-Lopez, K.; Solis-Pichardo, G.; Perez-Arvizu, O.</p> <p>2011-12-01</p> <p>The study of magmatism in the Trans-Mexican Volcanic Belt (TMVB) has great importance due to several features such as its obliquity with respect to the Middle American Trench and its petrological and geochemical variability, which are not common in most typical volcanic arcs. Although several papers have contributed significantly to the understanding of most important magmatic processes in this province, there are still several questions such as the characterization of magmatic sources. In the present work, we provide new stratigraphic, petrographic, geochemical and Sr, Nd and Pb isotopic data as well as some K-Ar age determinations from the Xihuingo-Chichicuautla volcanic field (XCVF), located at the eastern part of the TMVB, with the aim to identify the magmatic sources that produced the main volcanic rocks. The volcanic structures in the XCVF are divided in two main groups according to the petrographic and geochemical compositions: 1) dacitic domes, andesitic lava flows and some dacitic-rhyolitic ignimbrites and 2) scoria cones, shield volcanoes and associated lava flows of basalt to basaltic-andesite composition. Distribution of most volcanic structures is probably controlled by NE-SW fault and fractures system. This fault system was studied by other authors who established that volcanic activity started ca. 13.5 Ma ago, followed by a volcanic hiatus of ca. 10 Ma, and the late volcanic activity began ca. 3 to 1 Ma. In this work we dated 2 rock samples by K-Ar method, which yielded ages of 402 and 871 Ka, which correspond to the most recent volcanic activity in this study area. The volcanic rocks of the XCVF display compositions from basalts to rhyolites but in general all rocks show trace element patterns typical of magmatic arcs. However, we can identify two main magmatic sources: a depleted magmatic source represented by dacitic-andesitic rocks which present a LILE enrichment with respect to HFSE indicating that a magmatic source was modified by fluids derived from the subduction processes. These magmas probably suffered fractional crystallization and minor assimilation in the continental crust. Sr, Nd isotopic compositions for this first group display the most radiogenic values (87Sr/86Sr from 0.7046 to 0.7047 and ɛNd from 2.2 to 2.8). The second source for the basaltic-andesite and basalt could be associated with an enriched mantle. These rocks present a minor LILE enrichment with respect to HSFE, and Sr and Nd isotopic values less radiogenic than the felsic rocks of the first group (87Sr/86Sr from 0.7040 to 0.7045 and ɛNd from 3.1 to 4.8). According to these evidences we can establish that the magmas emplaced in the study area were produced from a heterogeneous mantle source with complex magmatic processes combined with different interaction degrees between the magmas and continental crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28831089','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28831089"><span>Magmatic evolution of a Cordilleran flare-up and its role in the creation of silicic crust.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ward, Kevin M; Delph, Jonathan R; Zandt, George; Beck, Susan L; Ducea, Mihai N</p> <p>2017-08-22</p> <p>The role of magmatic processes as a significant mechanism for the generation of voluminous silicic crust and the development of Cordilleran plateaus remains a lingering question in part because of the inherent difficulty in quantifying plutonic volumes. Despite this difficulty, a growing body of independently measured plutonic-to-volcanic ratios suggests the volume of plutonic material in the crust related to Cordilleran magmatic systems is much larger than is previously expected. To better examine the role of crustal magmatic processes and its relationship to erupted material in Cordilleran systems, we present a continuous high-resolution crustal seismic velocity model for an ~800 km section of the active South American Cordillera (Puna Plateau). Although the plutonic-to-volcanic ratios we estimate vary along the length of the Puna Plateau, all ratios are larger than those previously reported (~30:1 compared to 5:1) implying that a significant volume of intermediate to silicic plutonic material is generated in the crust of the central South American Cordillera. Furthermore, as Cordilleran-type margins have been common since the onset of modern plate tectonics, our findings suggest that similar processes may have played a significant role in generating and/or modifying large volumes of continental crust, as observed in the continents today.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19..575P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19..575P"><span>Asymmetric rifting, breakup and magmatism across conjugate margin pairs: insights from Newfoundland to Ireland</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peace, Alexander L.; Welford, J. Kim; Foulger, Gillian R.; McCaffrey, Ken J. W.</p> <p>2017-04-01</p> <p>Continental extension, subsequent rifting and eventual breakup result in the development of passive margins with transitional crust between extended continental crust and newly created oceanic crust. Globally, passive margins are typically classified as either magma-rich or magma-poor. Despite this simple classification, magma-poor margins like the West Orphan Basin, offshore Newfoundland, do exhibit some evidence of localized magmatism, as magmatism to some extent invariably accompanies all continental breakup. For example, on the Newfoundland margin, a small volcanic province has been interpreted near the termination of the Charlie Gibbs Fracture Zone, whereas on the conjugate Irish margin within the Rockall Basin, magmatism appears to be more widespread and has been documented both in the north and in the south. The broader region over which volcanism has been identified on the Irish margin is suggestive of magmatic asymmetry across this conjugate margin pair and this may have direct implications for the mechanisms governing the nature of rifting and breakup. Possible causes of the magmatic asymmetry include asymmetric rifting (simple shear), post-breakup thermal anomalies in the mantle, or pre-existing compositional zones in the crust that predispose one of the margins to more melting than its conjugate. A greater understanding of the mechanisms leading to conjugate margin asymmetry will enhance our fundamental understanding of rifting processes and will also reduce hydrocarbon exploration risk by better characterizing the structural and thermal evolution of hydrocarbon bearing basins on magma-poor margins where evidence of localized magmatism exists. Here, the latest results of a conjugate margin study of the Newfoundland-Ireland pair utilizing seismic interpretation integrated with other geological and geophysical datasets are presented. Our analysis has begun to reveal the nature and timing of rift-related magmatism and the degree to which magmatic asymmetry exists between these conjugate margins. The main implications from this work are that different processes may have operated during and after rifting on these conjugate margins. This concept should be carried forward when conducting conjugate margin studies elsewhere, particularly when exploring for hydrocarbons as prospectivity on one margin may not be predictive for its conjugate as different thermal and structural regimes may have been in operation during conjugate basin evolution.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1911204L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1911204L"><span>Parallel Extension Tectonics (PET): Early Cretaceous tectonic extension of the Eastern Eurasian continent</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Junlai; Ji, Mo; Ni, Jinlong; Guan, Huimei; Shen, Liang</p> <p>2017-04-01</p> <p>The present study reports progress of our recent studies on the extensional structures in eastern North China craton and contiguous areas. We focus on characterizing and timing the formation/exhumation of the extensional structures, the Liaonan metamorphic core complex (mcc) and the Dayingzi basin from the Liaodong peninsula, the Queshan mcc, the Wulian mcc and the Zhucheng basin from the Jiaodong peninsula, and the Dashan magmatic dome within the Sulu orogenic belt. Magmatic rocks (either volcanic or plutonic) are ubiquitous in association with the tectonic extension (both syn- and post-kinematic). Evidence for crustal-mantle magma mixing are popular in many syn-kinematic intrusions. Geochemical analysis reveals that basaltic, andesitic to rhyolitic magmas were generated during the tectonic extension. Sr-Nd isotopes of the syn-kinematic magmatic rocks suggest that they were dominantly originated from ancient or juvenile crust partly with mantle signatures. Post-kinematic mafic intrusions with ages from ca. 121 Ma to Cenozoic, however, are of characteristic oceanic island basalts (OIB)-like trace element distribution patterns and relatively depleted radiogenic Sr-Nd isotope compositions. Integrated studies on the extensional structures, geochemical signatures of syn-kinematic magmatic rocks (mostly of granitic) and the tectono-magmatic relationships suggest that extension of the crust and the mantle lithosphere triggered the magmatisms from both the crust and the mantle. The Early Cretaceous tectono-magmatic evolution of the eastern Eurasian continent is governed by the PET in which the tectonic processes is subdivided into two stages, i.e. an early stage of tectonic extension, and a late stage of collapse of the extended lithosphere and transformation of lithospheric mantle. During the early stage, tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle, resulted in the loss of some of the subcontinental roots, gave rise to the exhumation of the mccs, and triggered plutonic emplacement and volcanic eruptions of hybrid magmas. During the late stage, the nature of mantle lithosphere in North China was changed from the ancient SCLM to the juvenile SCLM. Extensional structures in eastern Eurasian continent provide a general architecture of the extensional tectonics of a rifted continent. Progressive extension resulted a sudden collaps of the crust (lithosphere) at ca. 130 to 120 Ma, associated with exhumation of mcc's and giant syn-kinematic magmatism, and post-kinematic magmatism. Parallel extension of both the crust and the mantle resulted in detachment faulting and magmatism, and also contributed to inhomogeneous thinning of the NCC lithosphere. Paleo-Pacific plate subduction and roll-back of the subducting oceanic plate contributed to the PET tectonic processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008GGG.....9.8008V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008GGG.....9.8008V"><span>Direct evidence from anisotropy of magnetic susceptibility for lateral melt migration at superfast spreading centers</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Varga, Robert J.; Horst, Andrew J.; Gee, Jeffrey S.; Karson, Jeffrey A.</p> <p>2008-08-01</p> <p>Rare, fault-bounded escarpments expose natural cross sections of ocean crust in several areas and provide an unparalleled opportunity to study the end products of tectonic and magmatic processes that operated at depth beneath oceanic spreading centers. We mapped the geologic structure of ocean crust produced at the East Pacific Rise (EPR) and now exposed along steep cliffs of the Pito Deep Rift near the northern edge of the Easter microplate. The upper oceanic crust in this area is typified by basaltic lavas underlain by a sheeted dike complex comprising northeast striking, moderately to steeply southeast dipping dikes. Paleomagnetic remanence of oriented blocks of dikes collected with both Alvin and Jason II indicate clockwise rotation of ˜61° related to rotation of the microplate indicating structural coupling between the microplate and crust of the Nazca Plate to the north. The consistent southeast dip of dikes formed as the result of tilting at the EPR shortly after their injection. Anisotropy of magnetic susceptibility of dikes provides well-defined magmatic flow directions that are dominantly dike-parallel and shallowly plunging. Corrected to their original EPR orientation, magma flow is interpreted as near-horizontal and parallel to the ridge axis. These data provide the first direct evidence from sheeted dikes in ocean crust for along-axis magma transport. These results also suggest that lateral transport in dikes is important even at fast spreading ridges where a laterally continuous subaxial magma chamber is present.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V33C4895C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V33C4895C"><span>Whole Rock and Mineral Chemistry from the Central Atlantic Magmatic Province (CAMP)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chau, K. X.; Draper, G.; Sen, G.</p> <p>2014-12-01</p> <p>The Central Atlantic Magmatic Province (CAMP) was a large igneous province (LIP) emplaced approximately 200 million years ago during the rifting of Pangaea, shortly before the opening of the Atlantic Ocean. Although a comparatively small amount of the original province remains today, the locations of the existing outcrops on four continents (North America, South America, Africa, and Europe) show the extensive reach of igneous activity and indicate that the CAMP was likely one of the biggest LIPs known. Because of the geologic and global significance of this episode, a knowledge of the conditions that generated and emplaced such a large volume of magma would help better understand mantle and tectonic processes. In this study, we compare whole rock and mineral chemistry data from three of the North American outcrops: the Palisades Sill of the Newark Basin in eastern New York and New Jersey, the Centreville Sheet of the Culpeper Basin in northern Virginia, and the York Haven pluton of the Gettysburg Basin in southeastern Pennsylvania. The diabases are quartz-normative theoleiites; their chemistries are indicate high degrees of internal differentiation and thermal disequilbirum, consistent with magma bodies cooling as a closed or near-closed system. The trace element data shows that, although there is evidence to support a deep mantle source for CAMP melts, there is also a shallower component influencing the chemistries of the samples. We interpret this as the signal of an ancient subducted slab through which CAMP melts passed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.185..182H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.185..182H"><span>Compositional variation within thick (>10 m) flow units of Mauna Kea Volcano cored by the Hawaii Scientific Drilling Project</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huang, Shichun; Vollinger, Michael J.; Frey, Frederick A.; Rhodes, J. Michael; Zhang, Qun</p> <p>2016-07-01</p> <p>Geochemical analyses of stratigraphic sequences of lava flows are necessary to understand how a volcano works. Typically one sample from each lava flow is collected and studied with the assumption that this sample is representative of the flow composition. This assumption may not be valid. The thickness of flows ranges from <1 to >100 m. Geochemical heterogeneity in thin flows may be created by interaction with the surficial environment whereas magmatic processes occurring during emplacement may create geochemical heterogeneities in thick flows. The Hawaii Scientific Drilling Project (HSDP) cored ∼3.3 km of basalt erupted at Mauna Kea Volcano. In order to determine geochemical heterogeneities in a flow, multiple samples from four thick (9.3-98.4 m) HSDP flow units were analyzed for major and trace elements. We found that major element abundances in three submarine flow units are controlled by the varying proportion of olivine, the primary phenocryst phase in these samples. Post-magmatic alteration of a subaerial flow led to loss of SiO2, CaO, Na2O, K2O and P2O5, and as a consequence, contents of immobile elements, such as Fe2O3 and Al2O3, increase. The mobility of SiO2 is important because Mauma Kea shield lavas divide into two groups that differ in SiO2 content. Post-magmatic mobility of SiO2 adds complexity to determining if these groups reflect differences in source or process. The most mobile elements during post-magmatic subaerial and submarine alteration are K and Rb, and Ba, Sr and U were also mobile, but their abundances are not highly correlated with K and Rb. The Ba/Th ratio has been used to document an important role for a plagioclase-rich source component for basalt from the Galapagos, Iceland and Hawaii. Although Ba/Th is anomalously high in Hawaiian basalt, variation in Ba abundance within a single flow shows that it is not a reliable indicator of a deep source component. In contrast, ratios involving elements that are typically immobile, such as La/Nb, La/Th, Nb/Th, Ce/Pb, Sr/Nd, La/Sm, Sm/Yb, Nb/Zr, Nb/Y and La/Yb, are uniform within the units, and they can be used to constrain petrogenetic processes. Nevertheless all elements are mobile under some conditions. For example, a surprising result is that relative to other samples, the uppermost sample collected from subaerial flow Unit 70, less than 1 m below the flow surface, is depleted in P, HREE and Y relative to all other samples from this flow unit. This result is complementary to the P, REE and Y enrichment found in subaerial lava flows from several Hawaiian shields, e.g., Kahoolawe and Koolau Volcanoes. These enrichments require mobilization of REE and followed by deposition a P-rich mineral.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1918682G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1918682G"><span>Lithospheric convective removal related post-collisional middle Eocene magmatism along the Izmir-Ankara-Erzincan suture zone (NE Turkey).</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Göçmengil, Gönenç; Karacık, Zekiye; Genç, Ş. Can</p> <p>2017-04-01</p> <p>Obliteration of the Mesozoic Neo-Tethyan Ocean and succeeding collision of the micro plates along the northern part of Turkey lead the development of the İzmir-Ankara-Erzincan suture zone (IAESZ). The suturing and collision stages terminate with the amalgamation of the three different crustal blocks (Pontides, Central Anatolian Crystalline Complex and Anatolide-Tauride Block) in the Paleocene-Early Eocene period. After the collisional stage; a new phase of extension and magmatism concomitantly developed at the both sides and as well as along the IAESZ during the Middle Eocene period. However, the origin, mechanism and driving force of the post-collisional magmatism is still enigmatic. To understand and better constrain the syn-to post collisional evolutionary stages, we have carried out volcano-stratigraphy and geochemistry based study on the middle Eocene magmatic associations along a transect ( 100 km) from Pontides to the Central Anatolian Crystalline Complex (CACC) at the NE part of the Turkey. Middle Eocene magmatic activity in the region has been represented by calc-alkaline, alkaline, shoshonitic volcanic and granitic rocks together with scarce gabbroic intrusions. We particularly focused on middle Eocene volcano-sedimentary successions (MEVSS) to constrain the tectono-magmatic evolution of the abovementioned transect. The volcano-sedimentary succsessions are coevally developed and cover the crustal blocks (Pontides and CACC) and the IAESZ with a region wide unconformity. We have differentiated three lava series (V1-V2-V3) and their sub-groups (V1a-V1b; V2a-V2b) in MEVSS. Generally, all lava series have middle-K to shoshonitic composition with distinct subduction characteristics. V1 series is marked by presence of hydrous phenocrysts such as amphibole+biotite. V1a sub-group constitute the first volcanic product and characterized by the high Mg# (42-69); alkaline basaltic andesite, and hawaiites. V1b sub-group is represented by calc-alkaline, low Mg# (24-57) andesite and dacites. V2 series made up of the olivine+pyroxene rich anhydrous lavas. V2a sub-group displays calc-alkaline/mildly alkaline character, moderate Mg# (33-54) and represented by basaltic andesites. Furthermore, V2b sub-group has mildly alkaline/alkaline in character and represented by more Mg# rich (40-62) basalt and trachy-basalt lavas. Final products, V3 series, cut the older units and made up of high-K - shoshonitic trachyte and trachy-andesites. The V1a sub-group, showing the alkali nature and high Mg#, is probably derived from the partial melting of a hydrous spinel lherzolitic source with minor garnet and amphibole while the V1b sub-group is a fractionated (FC) derivative of them. The V2 series are mixed products of varying amounts of magma sources similar to V1b type with a high Mg#, deep-seated magma source and their fractionated assemblages. The V3 series developed independently from the other series in shallow magma chambers, displaying the large amounts of crustal assimilation and constitutes the final product of the Middle Eocene volcanism. The data presented above shown that volcanic units; (i) are rich in potassium, (ii) have subduction-related signatures, (iii) display fluctuant alkalinity and Mg# during the course of volcanism, (iv) coevally developed on both amalgamated continental blocks after the cessation of subduction. These characteristics imply that, lithospheric convective removal related processes can be the most plausible driving mechanism of the middle Eocene magmatism.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JGR....8911195S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JGR....8911195S"><span>The Pliocene seamount series of La Palma/Canary Islands</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Staudigel, Hubert; Schmincke, Hans-Ulrich</p> <p>1984-12-01</p> <p>A Pliocene submarine series of alkali basaltic pillow lavas, hyaloclastites, and breccias (A), a sheeted dike swarm (B), and a basal suite of gabbro and ultramafic rocks (C) from La Palma (Canary Islands) is interpreted as a cross section through an uplifted seamount. This series has been tilted to its present orientation of 50°/230° (plunge and azimuth), probably by upwarping due to intrusions in the central portion of the island. The basal plutonic complex (C) also includes intrusives coeval with up to 2000 m of younger subaerial alkali basaltic lavas unconformably overlying the submarine series. The plutonic suite (C) is overlain abruptly by more than 1800 m of sills (B), 0.4-1 m thick on average, with minor screens of lavas and breccias. Extrusives (A) form a 1750 m thick sequence of pillow lavas, breccias, and hyaloclastites. The clastic rocks increase in abundance upward and are of four main types: (1) breccias, consisting of partly broken pillows, formed nearly in situ, (2) heterolithologic pillow fragment breccias, (3) hyaloclastites composed dominantly of highly vesicular lapilli and ash sized shards, the latter thought to have formed by near surface explosive eruptions and been subsequently transported downslope by mass flows, (2) and (3) being interpreted to have been resedimented, and (4) pillow scoria breccias from the upper 700 m of the extrusive section consisting of amoeboidal, highly vesicular "pillows" and lava stringers and local bombs, probably formed by cracking and "bleeding" of gas-rich expanding pillow lava and some shallow submarine/subaerial lava fountaining. The extrusive series is chemically and mineralogically crudely zoned, with the most differentiated rocks (metatrachytes and mugearites) at the base and most picritic lavas occurring near the top of the series. Subsequent to emplacement, the entire extrusive and intrusive series has been hydrothermally altered, the lower part to greenschist and the upper part to smectite—zeolite facies mineral assemblages. The La Palma succession, combined with evidence from surface studies of seamounts, suggests that seamounts are formed by intrusive and extrusive processes in approximately equal portions. The nature of eruptive clastic and depositional mechanisms changes drastically during growth of a seamount if the critical depth for major magmatic degassing is surpassed and especially if magmatic explosive processes can occur at very shallow water depth, the critical depth depending on magma and thus volatile composition. Changes in slopes of a seamount influence depositional processes. Based on these factors, at least three major depositional sites develop as a seamount grows: summit, flank, and apron facies. Nonexplosive, extrusive processes prevail in the Deep Water Stage, dominantly producing pillow lavas (75%). These consist of individual pillow volcanoes up to 200 m high, with large pillows near the base and decreasing pillow size toward the top of a volcano. Pillow breccias, and pillow fragment breccias comprise approximately 20% of this facies. The deep water flank and apron facies are characterized by debris flow deposits with possibjy rather dense matrix material. The Shallow Water (shoaling) Stage is reached when the seamount top reaches the critical depth for drastic increase in exsolution of magmatic volatiles, about 800 m for the alkali basaltic seamount of La Palma, resulting in formation of mainly clastic rocks (70%): in situ pillow rind breccias and scoriaceous amoeboidal breccias and pillows are formed in the summit regions of the seamount, by repeated expansion and leaking of frothy pillow lava possibly by lava fountaining. Resedimented, heterolithologic pillow fragment breccias, lapilli breccias, and hyaloclastites are deposited on the flanks and aprons of the seamount. Pillow lavas comprise < 30% of these deposits.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.171...15K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.171...15K"><span>Trace elements in magnetite from massive iron oxide-apatite deposits indicate a combined formation by igneous and magmatic-hydrothermal processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Knipping, Jaayke L.; Bilenker, Laura D.; Simon, Adam C.; Reich, Martin; Barra, Fernando; Deditius, Artur P.; Wälle, Markus; Heinrich, Christoph A.; Holtz, François; Munizaga, Rodrigo</p> <p>2015-12-01</p> <p>Iron oxide-apatite (IOA) deposits are an important source of iron and other elements (e.g., REE, P, U, Ag and Co) vital to modern society. However, their formation, including the namesake Kiruna-type IOA deposit (Sweden), remains controversial. Working hypotheses include a purely magmatic origin involving separation of an Fe-, P-rich, volatile-rich oxide melt from a Si-rich silicate melt, and precipitation of magnetite from an aqueous ore fluid, which is either of magmatic-hydrothermal or non-magmatic surface or metamorphic origin. In this study, we focus on the geochemistry of magnetite from the Cretaceous Kiruna-type Los Colorados IOA deposit (∼350 Mt Fe) located in the northern Chilean Iron Belt. Los Colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in IOA deposits. Laser ablation-inductively coupled plasma-mass spectroscopy (LA-ICP-MS) transects and electron probe micro-analyzer (EPMA) wavelength-dispersive X-ray (WDX) spectrometry mapping demonstrate distinct chemical zoning in magnetite grains, wherein cores are enriched in Ti, Al, Mn and Mg. The concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt, whereas magnetite rims show a pronounced depletion in these elements, consistent with magnetite grown from an Fe-rich magmatic-hydrothermal aqueous fluid. Further, magnetite grains contain polycrystalline inclusions that re-homogenize at magmatic temperatures (>850 °C). Smaller inclusions (<5 μm) contain halite crystals indicating a saline environment during magnetite growth. The combination of these observations are consistent with a formation model for IOA deposits in northern Chile that involves crystallization of magnetite microlites from a silicate melt, nucleation of aqueous fluid bubbles on magnetite surfaces, and formation and ascent of buoyant fluid bubble-magnetite aggregates. Decompression of the fluid-magnetite aggregate during ascent along regional-scale transcurrent faults promotes continued growth of the magmatic magnetite microlites from the Fe-rich magmatic-hydrothermal fluid, which manifests in magnetite rims that have trace element abundances consistent with growth from a magmatic-hydrothermal fluid. Mass balance calculations indicate that this process can leach and transport sufficient Fe from a magmatic source to form large IOA deposits such as Los Colorados. Furthermore, published experimental data demonstrate that a saline magmatic-hydrothermal ore fluid will scavenge significant quantities of metals such as Cu and Au from a silicate melt, and when combined with solubility data for Fe, Cu and Au, it is plausible that the magmatic-hydrothermal ore fluid that continues to ascend from the IOA depositional environment can retain sufficient concentrations of these metals to form iron oxide copper-gold (IOCG) deposits at lateral and/or stratigraphically higher levels in the crust. Notably, this study provides a new discrimination diagram to identify magnetite from Kiruna-type deposits and to distinguish them from IOCG, porphyry and Fe-Ti-V/P deposits, based on low Cr (<100 ppm) and high V (>500 ppm) concentrations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12702874','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12702874"><span>Mantle fault zone beneath Kilauea Volcano, Hawaii.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wolfe, Cecily J; Okubo, Paul G; Shearer, Peter M</p> <p>2003-04-18</p> <p>Relocations and focal mechanism analyses of deep earthquakes (>/=13 kilometers) at Kilauea volcano demonstrate that seismicity is focused on an active fault zone at 30-kilometer depth, with seaward slip on a low-angle plane, and other smaller, distinct fault zones. The earthquakes we have analyzed predominantly reflect tectonic faulting in the brittle lithosphere rather than magma movement associated with volcanic activity. The tectonic earthquakes may be induced on preexisting faults by stresses of magmatic origin, although background stresses from volcano loading and lithospheric flexure may also contribute.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70025641','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025641"><span>Mantle fault zone beneath Kilauea Volcano, Hawaii</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Wolfe, C.J.; Okubo, P.G.; Shearer, P.M.</p> <p>2003-01-01</p> <p>Relocations and focal mechanism analyses of deep earthquakes (???13 kilometers) at Kilauea volcano demonstrate that seismicity is focused on an active fault zone at 30-kilometer depth, with seaward slip on a low-angle plane, and other smaller, distinct fault zones. The earthquakes we have analyzed predominantly reflect tectonic faulting in the brittle lithosphere rather than magma movement associated with volcanic activity. The tectonic earthquakes may be induced on preexisting faults by stresses of magmatic origin, although background stresses from volcano loading and lithospheric flexure may also contribute.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70195108','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70195108"><span>Unraveling the dynamics of magmatic CO2 degassing at Mammoth Mountain, California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pfeiffer, Loic; Wanner, Christoph; Lewicki, Jennifer L.</p> <p>2018-01-01</p> <p>The accumulation of magmatic CO2 beneath low-permeability barriers may lead to the formation of CO2-rich gas reservoirs within volcanic systems. Such accumulation is often evidenced by high surface CO2 emissions that fluctuate over time. The temporal variability in surface degassing is believed in part to reflect a complex interplay between deep magmatic degassing and the permeability of degassing pathways. A better understanding of the dynamics of CO2 degassing is required to improve monitoring and hazards mitigation in these systems. Owing to the availability of long-term records of CO2 emissions rates and seismicity, Mammoth Mountain in California constitutes an ideal site towards such predictive understanding. Mammoth Mountain is characterized by intense soil CO2 degassing (up to ∼1000 t d−1) and tree kill areas that resulted from leakage of CO2 from a CO2-rich gas reservoir located in the upper ∼4 km. The release of CO2-rich fluids from deeper basaltic intrusions towards the reservoir induces seismicity and potentially reactivates faults connecting the reservoir to the surface. While this conceptual model is well-accepted, there is still a debate whether temporally variable surface CO2 fluxes directly reflect degassing of intrusions or variations in fault permeability. Here, we report the first large-scale numerical model of fluid and heat transport for Mammoth Mountain. We discuss processes (i) leading to the initial formation of the CO2-rich gas reservoir prior to the occurrence of high surface CO2 degassing rates and (ii) controlling current CO2 degassing at the surface. Although the modeling settings are site-specific, the key mechanisms discussed in this study are likely at play at other volcanic systems hosting CO2-rich gas reservoirs. In particular, our model results illustrate the role of convection in stripping a CO2-rich gas phase from a rising hydrothermal fluid and leading to an accumulation of a large mass of CO2 (∼107–108 t) in a shallow gas reservoir. Moreover, we show that both, short-lived (months to years) and long-lived (hundreds of years) events of magmatic fluid injection can lead to critical pressures within the reservoir and potentially trigger fault reactivation. Our sensitivity analysis suggests that observed temporal fluctuations in surface degassing are only indirectly controlled by variations in magmatic degassing and are mainly the result of temporally variable fault permeability. Finally, we suggest that long-term CO2 emission monitoring, seismic tomography and coupled thermal–hydraulic–mechanical modeling are important for CO2-related hazard mitigation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1986GeCoA..50.2847P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1986GeCoA..50.2847P"><span>Mantle helium in Sacramento basin natural gas wells</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Poreda, R. J.; Jenden, P. D.; Kaplan, I. R.; Craig, H.</p> <p>1986-12-01</p> <p>Helium isotope ratios in Sacramento basin natural gas wells show a strong mantle signal. The3He/4He ratios range from 0.11 times the atmospheric ratio (0.11 RA) in the Rio Vista field to 2.75 RA in the Moon Bend field, indicating that 1% to 34% of the helium is mantle-derived. 3He/4He versus CH4/4He ratios provide evidence of two-component mixing between crustal and magmatic end-members. Extrapolation of the linear regression line to CH4/4He = 0 gives a hypothetical magmatic end-member 3He/4He ratio of 3.84 RA, half the typical mantle ratio. This indicates that the magmatic end-member may actually represent a mixture of mantle and crustal helium. Gases which deviate from the simple two-component mixture can be explained by addition of pure methane, radiogenic 4He, or a high N2-He component with 3He/4He = 0.6 Ra to 1.0 RA. The CH4/3He ratio of the magmatic end-member remains poorly constrained (0 to 3 × 109) and one cannot rule out the possibility that a significant proportion of the methane in some fields may be of deep-earth origin. However, fields with the highest 3He/4He ratios are associated with buried Plio-Pleistocene intrusives which have up-arched sediments to form hydrocarbon traps. The methane in these fields may have been produced by rapid thermal alteration of the intruded sediment. Elsewhere, the methane appears either to have migrated from deeply-buried sediments in the western basin or to have been produced by local microbial activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70074413','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70074413"><span>Crustal migration of CO2-rich magmatic fluids recorded by tree-ring radiocarbon and seismicity at Mammoth Mountain, CA, USA</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lewicki, Jennifer L.; Hilley, George E.; Shelly, David R.; King, John C.; McGeehin, John P.; Mangan, Margaret T.; Evans, William C.</p> <p>2014-01-01</p> <p>Unrest at Mammoth Mountain over the past several decades, manifest by seismicity, ground deformation, diffuse CO2 emissions, and elevated 3He/4He ratios in fumarolic gases has been driven by the release of CO2-rich fluids from basaltic intrusions in the middle to lower crust. Recent unrest included the occurrence of three lower-crustal (32–19 km depth) seismic swarms beneath Mammoth Mountain in 2006, 2008 and 2009 that were consistently followed by peaks in the occurrence rate of shallow (≤10 km depth) earthquakes. We measured 14C in the growth rings (1998–2012) of a tree growing in the largest (∼0.3 km2) area of diffuse CO2 emissions on Mammoth Mountain (the Horseshoe Lake tree kill; HLTK) and applied atmospheric CO2 concentration source area modeling to confirm that the tree was a reliable integrator of magmatic CO2 emissions over most of this area. The tree-ring 14C record implied that magmatic CO2 emissions from the HLTK were relatively stable from 1998 to 2009, nearly doubled from 2009 to 2011, and then declined by the 2012 growing season. The initial increase in CO2 emissions was detected during the growing season that immediately followed the largest (February 2010) peak in the occurrence rate of shallow earthquakes. Migration of CO2-rich magmatic fluids may have driven observed patterns of elevated deep, then shallow seismicity, while the relationship between pore fluid pressures within a shallow (upper 3 km of crust) fluid reservoir and permeability structure of the reservoir cap rock may have controlled the temporal pattern of surface CO2 emissions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1374327','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1374327"><span>The thermal regime of the Campi Flegrei magmatic system reconstructed through 3D numerical simulations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Di Renzo, Valeria; Wohletz, Kenneth; Civetta, Lucia</p> <p></p> <p>In this paper, we illustrate a quantitative conductive/convective thermal model incorporating a wide range of geophysical, petrological, geological, geochemical and isotopical observations that constrain the thermal evolution and present state of the Campi Flegrei caldera (CFc) magmatic system. The proposed model has been computed on the basis of the current knowledge of: (1) the volcanic and magmatic history of the volcano over the last 44 ka, (2) its underlying crustal structure, and (3) the physical properties of the erupted magmas. 3D numerical simulations of heat conduction and convection within heterogeneous rock/magma materials with evolving heat sources and boundary conditions thatmore » simulate magma rise from a deep (≥ 8 km depth) to shallow (2–6 km) reservoirs, magma chamber formation, magma extrusion, caldera collapse, and intra-caldera hydrothermal convection, have been carried out. The evolution of the CFc magmatic system through time has been simulated through different steps related to its changes in terms of depth, location and size of magma reservoirs and their replenishment. The thermal modeling results show that both heat conduction and convection have played an important role in the CFc thermal evolution, although with different timing. Finally, the simulated present heat distribution is in agreement with the measured geothermal profiles (Agip, 1987), reproduces the thermal gradient peaks at the CFc margins in correspondence to the anomalies in surface gradients (Corrado et al., 1998), and suggests temperatures of 700 °C at depth of 4 km in the central portion of the caldera, in agreement with the estimated temperature for the brittle-ductile transition (Hill, 1992).« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1374327-thermal-regime-campi-flegrei-magmatic-system-reconstructed-through-numerical-simulations','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1374327-thermal-regime-campi-flegrei-magmatic-system-reconstructed-through-numerical-simulations"><span>The thermal regime of the Campi Flegrei magmatic system reconstructed through 3D numerical simulations</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Di Renzo, Valeria; Wohletz, Kenneth; Civetta, Lucia; ...</p> <p>2016-11-11</p> <p>In this paper, we illustrate a quantitative conductive/convective thermal model incorporating a wide range of geophysical, petrological, geological, geochemical and isotopical observations that constrain the thermal evolution and present state of the Campi Flegrei caldera (CFc) magmatic system. The proposed model has been computed on the basis of the current knowledge of: (1) the volcanic and magmatic history of the volcano over the last 44 ka, (2) its underlying crustal structure, and (3) the physical properties of the erupted magmas. 3D numerical simulations of heat conduction and convection within heterogeneous rock/magma materials with evolving heat sources and boundary conditions thatmore » simulate magma rise from a deep (≥ 8 km depth) to shallow (2–6 km) reservoirs, magma chamber formation, magma extrusion, caldera collapse, and intra-caldera hydrothermal convection, have been carried out. The evolution of the CFc magmatic system through time has been simulated through different steps related to its changes in terms of depth, location and size of magma reservoirs and their replenishment. The thermal modeling results show that both heat conduction and convection have played an important role in the CFc thermal evolution, although with different timing. Finally, the simulated present heat distribution is in agreement with the measured geothermal profiles (Agip, 1987), reproduces the thermal gradient peaks at the CFc margins in correspondence to the anomalies in surface gradients (Corrado et al., 1998), and suggests temperatures of 700 °C at depth of 4 km in the central portion of the caldera, in agreement with the estimated temperature for the brittle-ductile transition (Hill, 1992).« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009MinPe..96..177U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009MinPe..96..177U"><span>Lutetian arc-type magmatism along the southern Eurasian margin: New U-Pb LA-ICPMS and whole-rock geochemical data from Marmara Island, NW Turkey</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ustaömer, P. Ayda; Ustaömer, Timur; Collins, Alan S.; Reischpeitsch, Jörg</p> <p>2009-07-01</p> <p>The rocks of Turkey, Greece and Syria preserve evidence for the destruction of Tethys, the construction of much of the continental crust of the region and the formation of the Tauride orogenic belt. These events occurred between the Late Cretaceous and Miocene, but the detailed evolution of the southern Eurasian margin during this period of progressive continental accretion is largely unknown. Marmara Island is a basement high lying at a key location in the Cenozoic Turkish tectonic collage, with a Palaeogene suture zone to the south and a deep Eocene sedimentary basin to the north. North-dipping metamorphic thrust sheets make up the island and are interlayered with a major metagranitoid intrusion. We have dated the intrusion by Laser Ablation ICP-MS analysis of U and Pb isotopes on zircon separates to 47.6 ± 2 Ma. We also performed major- and trace-elemental geochemical analysis of 16 samples of the intrusion that revealed that the intrusion is a calc-alkaline, metaluminous granitoid, marked by Nb depletion relative to LREE and LIL-element enrichment when compared to ocean ridge granite (ORG). We interpret the metagranitoid sill as a member of a mid-Eocene magmatic arc, forming a 30 km wide and more than 200 km long arcuate belt in NW Turkey that post-dates suturing along the İzmir-Ankara-Erzincan Suture zone. The arc magmatism was emplaced at the early stages of mountain building, related to collision of Eurasia with the Menderes-Taurus Platform in early Eocene times. Orogenesis and magmatism loaded the crust to the north creating coeval upward-deepening marine basins partially filled by volcanoclastic sediments.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T23C2289B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T23C2289B"><span>Crustal structure of Tolfa domes complex (northern Latium - Italy) inferred from receiver functions analysis: an interplay between tectonics and magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buttinelli, M.; Bianchi, I.; Anselmi, M.; Chiarabba, C.; de Rita, D.; Quattrocchi, F.</p> <p>2010-12-01</p> <p>The Tolfa-Cerite volcanic district developed along the Tyrrhenian passive margin of central Italy, as part of magmatic processes started during the middle Pliocene. In this area the uncertainties on the deep crustal structures and the definition of the intrusive bodies geometry are focal issues that still need to be addressed. After the onset of the spreading of the Tyrrhenian sea during the Late Miocene, the emplacement of the intrusive bodies of the Tolfa complex (TDC), in a general back-arc geodynamical regime, generally occurred in a low stretching rate, in correspondence of the junctions between major lithospheric discontinuities. Normal faults, located at the edge of Mio-Pliocene basins, were used as preferential pathways for the rising of magmatic masses from the mantle to the surface. We used teleseismic recordings at the TOLF and MAON broad band station of the INGV seismic network (located between the Argentario promontory and Tolfa-Ceriti dome complexes -TDC-) to image the principal seismic velocity discontinuities by receiver function analysis (RF's). Together with RF’s velocity models of the area computed using the teleseismic events recorded by a temporary network of eight stations deployed around the TDC, we achieve a general crustal model of this area. The geometry of the seismic network has been defined to focus on the crustal structure beneath the TDC, trying to define the main velocity changes attributable to the intrusive bodies, the calcareous basal complex, the deep metamorphic basement, the lower crust and the Moho. The analysis of these data show the Moho at a depth of 23 km in the TDC area and 20 km in the Argentario area. Crustal models also show an unexpected velocity decrease between 12 and 18 km, consistent with a slight dropdown of the Vp/Vs ratio, imputable to a regional mid-crustal shear zone inherited from the previous alpine orogenesis, re-activated in extensional tectonic by the early opening phases of the Tyrrhenian sea. Above this low Vs layer, we find some interesting features corresponding to: - a low Vs shallow and 2 km thick layer of Liguride and Plio-Pleistocene units (z = 0-2 km of depth) - a high Vs 4-5 km thick anisotropic layer of limestones (z = 2-7 km of depth) - a very high Vs (3.8 km/s) 4 km thick layer probably corresponding to the metamorphic basement. The analysis of the geometry of the velocity changes between these layers (from the surface to the bottom of metamorphic basement), also yield evidence of crustal block tilting, due to the development of the eastern continental passive margin of the Tyrrhenian sea. The general crustal setting observed between the TDC and the Argentario areas is also consistent with the simple shear models suggested for back-arc basins opening. Comparison of RF’s TDC models with MAON station data also led to important considerations confirming the initial evolutive phase of the Tyrrhenian sea opening, in association with the first occurrences of intrusive magmatism in these areas.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhDT.......280M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhDT.......280M"><span>USArray Imaging of North American Continental Crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Xiaofei</p> <p></p> <p>The layered structure and bulk composition of continental crust contains important clues about its history of mountain-building, about its magmatic evolution, and about dynamical processes that continue to happen now. Geophysical and geological features such as gravity anomalies, surface topography, lithospheric strength and the deformation that drives the earthquake cycle are all directly related to deep crustal chemistry and the movement of materials through the crust that alter that chemistry. The North American continental crust records billions of years of history of tectonic and dynamical changes. The western U.S. is currently experiencing a diverse array of dynamical processes including modification by the Yellowstone hotspot, shortening and extension related to Pacific coast subduction and transform boundary shear, and plate interior seismicity driven by flow of the lower crust and upper mantle. The midcontinent and eastern U.S. is mostly stable but records a history of ancient continental collision and rifting. EarthScope's USArray seismic deployment has collected massive amounts of data across the entire United States that illuminates the deep continental crust, lithosphere and deeper mantle. This study uses EarthScope data to investigate the thickness and composition of the continental crust, including properties of its upper and lower layers. One-layer and two-layer models of crustal properties exhibit interesting relationships to the history of North American continental formation and recent tectonic activities that promise to significantly improve our understanding of the deep processes that shape the Earth's surface. Model results show that seismic velocity ratios are unusually low in the lower crust under the western U.S. Cordillera. Further modeling of how chemistry affects the seismic velocity ratio at temperatures and pressures found in the lower crust suggests that low seismic velocity ratios occur when water is mixed into the mineral matrix, and the combination of high temperature and water may point to small amounts of melt in the lower crust of Cordillera.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhDT........74S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhDT........74S"><span>Structure and kinematics of segment-scale crustal accretion processes in Iceland and implications for analogous mid-ocean ridge systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Siler, Drew Lorenz</p> <p>2011-12-01</p> <p>The sub-surface geologic structure of the crust is controlled by the magmatic and tectonic processes that construct the crust during plate spreading. As a result, geologic structure provides constraints on the processes that occur during plate spreading. The crust of the Skagi region of northern Iceland, where this study was focused, was accreted by magmatic construction to Iceland ˜7-10 Ma and subsequently glacially eroded, exhuming ˜1-3 km of structural relief. Continuous spreading-parallel and spreading-orthogonal mountain ranges expose the crust accreted at discrete spreading segments, the fundamental intervals upon which plate spreading and crustal accretion occur. As a result, Skagi is an ideal location to employ geologic structure analysis to study magmatic rifting processes. Within spreading segments structural patterns vary significantly between segment centers and distal fissure swarms. While segment centers are characterized by focused magmatic construction and km-scale sub-volcanic subsidence, fissure swarms are characterized by limited magmatic construction, minor sub-axial subsidence and lateral dike injection. Such along-strike variation indicates that both magma in the upper crust and gabbroic material in the lower crust must be redistributed along-strike within spreading segments during plate spreading. Material flow is directed from beneath segment centers towards distal fissure swarms. At the regional scale, each spreading segment is a structurally discrete interval of Iceland's Neovolcanic Zone. As a result of west-northwestward movement of Iceland relative to the Iceland hotspot, the rift zone axis has progressively relocated to the east-southeast with time, leaving a series of abandoned rift zones throughout western Iceland. A compilation of published K/Ar and 40Ar/39Ar age data and geologic data from across northern Iceland shows that rift relocation occurs via frequent (2-3 Ma), small-scale (˜20 km) rift propagations rather than rare, 100s of km 'rift jumps' as is conventional models suggest. The structure relationships we define in the Icelandic crust are similar to that of other magmatic rift systems including Mid-Ocean Ridges, continental rifts and ancient volcanic rift margins. As such, we suggest that many of the crustal accretion processes we have inferred from Icelandic data may be important in these analogous environments as well.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.H32F..01W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.H32F..01W"><span>The Interplay Between Saline Fluid Flow and Dynamic Permeability in Magmatic-Hydrothermal Systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weis, P.</p> <p>2014-12-01</p> <p>Magmatic-hydrothermal ore deposits document the interplay between saline fluid flow and rock permeability. Numerical simulations of multi-phase flow of variably miscible, compressible H20-NaCl fluids in concert with a dynamic permeability model can reproduce characteristics of porphyry copper and epithermal gold systems. This dynamic permeability model incorporates depth-dependent permeability profiles characteristic for tectonically active crust as well as pressure- and temperature-dependent relationships describing hydraulic fracturing and the transition from brittle to ductile rock behavior. In response to focused expulsion of magmatic fluids from a crystallizing upper crustal magma chamber, the hydrothermal system self-organizes into a hydrological divide, separating an inner part dominated by ascending magmatic fluids under near-lithostatic pressures from a surrounding outer part dominated by convection of colder meteoric fluids under near-hydrostatic pressures. This hydrological divide also provides a mechanism to transport magmatic salt through the crust, and prevents the hydrothermal system to become "clogged" by precipitation of solid halite due to depressurization of saline, high-temperature magmatic fluids. The same physical processes at similar permeability ranges, crustal depths and flow rates are relevant for a number of active systems, including geothermal resources and excess degassing at volcanos. The simulations further suggest that the described mechanism can separate the base of free convection in high-enthalpy geothermal systems from the magma chamber as a driving heat source by several kilometers in the vertical direction in tectonic settings with hydrous magmatism. This hydrology would be in contrast to settings with anhydrous magmatism, where the base of the geothermal systems may be closer to the magma chamber.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.usgs.gov/pp/1750/chapters/pp2008-1750_chapter30.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/pp/1750/chapters/pp2008-1750_chapter30.pdf"><span>Petrology of the 2004-2006 Mount St. Helens lava dome -- implications for magmatic plumbing and eruption triggering: Chapter 30 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pallister, John S.; Thornber, Carl R.; Cashman, Katharine V.; Clynne, Michael A.; Lowers, Heather; Mandeville, Charles W.; Brownfield, Isabelle K.; Meeker, Gregory P.; Sherrod, David R.; Scott, William E.; Stauffer, Peter H.</p> <p>2008-01-01</p> <p>The question of new versus residual magma has implications for the long-term eruptive behavior of Mount St. Helens, because arrival of a new batch of dacitic magma from the deep crust could herald the beginning of a new long-term cycle of eruptive activity. It is also important to our understanding of what triggered the eruption and its future course. Two hypotheses for triggering are considered: (1) top-down fracturing related to the shallow groundwater system and (2) an increase in reservoir pressure brought about by recent magmatic replenishment. With respect to the future course of the eruption, similarities between textures and character of eruption of the 2004-6 dome and the long-duration (greater than 100 years) pre-1980 summit dome, along with the low eruptive rate of the current eruption, suggest that the eruption could continue sluggishly or intermittently for years to come.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V24B..08L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V24B..08L"><span>Synchronous partial melting, deformation, and magmatism: evidence from in an exhumed Proterozoic orogen</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Levine, J. S. F.; Mosher, S.</p> <p>2017-12-01</p> <p>Older orogenic belts that now expose the middle and lower crust record interaction between partial melting, magmatism, and deformation. A field- and microstructural-based case study from the Wet Mountains of central Colorado, an exhumed section of Proterozoic rock, shows structures associated with anatexis and magmatism, from the grain- to the kilometer-scale, that indicate the interconnection between deformation, partial melting, and magmatism, and allow reconstructions of the processes occurring in hot active orogens. Metamorphic grade, along with the degree of deformation, partial melting, and magmatism increase from northwest to southeast. Deformation synchronous with this high-grade metamorphic event is localized into areas with greater quantities of former melt, and preferential melting occurs within high-strain locations. In the less deformed northwest, partial melting occurs dominantly via muscovite-dehydration melting, with a low abundance of partial melting, and an absence of granitic magmatism. The central Wet Mountains are characterized by biotite dehydration melting, abundant former melt and foliation-parallel inferred melt channels along grain boundaries, and the presence of a nearby granitic pluton. Rocks in the southern portion of the Wet Mountains are characterized by partial melting via both biotite dehydration and granitic wet melting, with widespread partial melting as evidenced by well-preserved former melt microstructures and evidence for back reaction between melt and the host rocks. The southern Wet Mountains has more intense deformation and widespread plutonism than other locations and two generations of dikes and sills. Recognition of textures and fabrics associated with partial melting in older orogens is paramount for interpreting the complex interplay of processes occurring in the cores of orogenic systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70014830','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70014830"><span>Liquid carbon dioxide of magmatic origin and its role in volcanic eruptions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Chivas, A.R.; Barnes, I.; Evans, William C.; Lupton, J.E.; Stone, J.O.</p> <p>1987-01-01</p> <p>Natural liquid carbon dioxide is produced commercially from a 2.5-km-deep well near the 4,500-yr-old maar volcano, Mount Gambier, South Australia. The carbon dioxide has accumulated in a dome that is located on the extension of a linear chain of volcanic activity. A magmatic origin for the fluid is suggested by the geological setting, ??13CPDB of -4.0???, for the CO2 (where PDB represents the carbon-isotope standard), and a relatively high 3He component of the contained helium and high 3He/C ratio (6.4 x 10-10). The 3He/ 4He and He/Ne ratios are 3.0 and > 1,370 times those of air, respectively. The CO2, as collected at the Earth's surface at 29.5 ??C and 75 bar, expands more than 300-fold to form a gas at 1 atm and 22 ??C. We suggest that liquid CO2 or high-density CO2 fluid (the critical point is 31.1 ??C, 73.9 bar) of volcanic origin that expands explosively from shallow levels in the Earth's crust may be a major contributor to 'phreatic' volcanic eruptions and maar formation. Less violent release of magmatic CO2 into crater lakes may cause gas bursts with equally disastrous consequences such as occurred at Lake Nyos, Cameroon, in August 1986. ?? 1987 Nature Publishing Group.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001JGeo...32..519P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001JGeo...32..519P"><span>Stable isotope geochemistry of fumaroles: an insight into volcanic surveillance</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Panichi, C.; La Ruffa, G.</p> <p>2001-12-01</p> <p>In active volcanic environments magmatic water may accumulate in the volcanic-hosted geothermal systems, or, more rarely may reach the surface along deep fractures inside the volcano crater. Knowledge of magmatic contribution to emerging fluids in volcanic active areas is critical to understanding the chemical evolution of the magma, the conditions in which it exists in the crust, and the mechanisms by which it erupts in the crust. The source of volatiles (especially water) is also of interest when eruptions are driven by the expansion of hydrothermal fluids against atmospheric pressure, without the involvement of fresh magma ('hydrothermal' or 'phreatomagmatic' eruptions). In both cases the occurrence of volcanic and/or phreatic activities is likely to be preceded by substantial isotopic and chemical changes in the crater fumarolic systems. H and O isotopic composition of condensed water from crater fumaroles appear to be able to give strong evidence for the existence of magmatic waters in the high-temperature manifestations of the volcanic systems. Isotopic data and specific hydrological models from seven different volcanic systems (Galeras Volcano, Colombia, Kilauea Volcano, Hawaii, Kudryvy Volcano, Kuril volcanic arc, Mt St Helens, USA; Guagua Pichincha, Ecuador; Vulcano island, Italy; the Aegean Volcanic Arc, Greece) are discussed in order to highlight the possibility to use those isotopic parameters in the assessment of the environmental risks of an active volcanic area.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JVGR..261...38T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JVGR..261...38T"><span>Magmatic differentiation processes at Merapi Volcano: inclusion petrology and oxygen isotopes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Troll, Valentin R.; Deegan, Frances M.; Jolis, Ester M.; Harris, Chris; Chadwick, Jane P.; Gertisser, Ralf; Schwarzkopf, Lothar M.; Borisova, Anastassia Y.; Bindeman, Ilya N.; Sumarti, Sri; Preece, Katie</p> <p>2013-07-01</p> <p>Indonesian volcano Merapi is one of the most hazardous volcanoes on the planet and is characterised by periods of active dome growth and intermittent explosive events. Merapi currently degasses continuously through high temperature fumaroles and erupts basaltic-andesite dome lavas and associated block-and-ash-flows that carry a large range of magmatic, coarsely crystalline plutonic, and meta-sedimentary inclusions. These inclusions are useful in order to evaluate magmatic processes that act within Merapi's plumbing system, and to help an assessment of which phenomena could trigger explosive eruptions. With the aid of petrological, textural, and oxygen isotope analysis we record a range of processes during crustal magma storage and transport, including mafic recharge, magma mixing, crystal fractionation, and country rock assimilation. Notably, abundant calc-silicate inclusions (true xenoliths) and elevated δ18O values in feldspar phenocrysts from 1994, 1998, 2006, and 2010 Merapi lavas suggest addition of limestone and calc-silicate materials to the Merapi magmas. Together with high δ13C values in fumarole gas, crustal additions to mantle and slab-derived magma and volatile sources are likely a steady state process at Merapi. This late crustal input could well represent an eruption trigger due to sudden over-pressurisation of the shallowest parts of the magma storage system independently of magmatic recharge and crystal fractionation. Limited seismic precursors may be associated with this type of eruption trigger, offering a potential explanation for the sometimes erratic behaviour of Merapi during volcanic crises.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1812178G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1812178G"><span>From magma-poor Ocean Continent Transitions to steady state oceanic spreading: the balance between tectonic and magmatic processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gillard, Morgane; Manatschal, Gianreto; Autin, Julia; Decarlis, Alessandro; Sauter, Daniel</p> <p>2016-04-01</p> <p>The evolution of magma-poor rifted margins is linked to the development of a transition zone whose basement is neither clearly continental nor oceanic. The development of this Ocean-Continent Transition (OCT) is generally associated to the exhumation of serpentinized mantle along one or several detachment faults. That model is supported by numerous observations (IODP wells, dredges, fossil margins) and by numerical modelling. However, if the initiation of detachment faults in a magma-poor setting tends to be better understood by numerous studies in various area, the transition with the first steady state oceanic crust and the associated processes remain enigmatic and poorly studied. Indeed, this latest stage of evolution appears to be extremely gradual and involves strong interactions between tectonic processes and magmatism. Contrary to the proximal part of the exhumed domain where we can observe magmatic activity linked to the exhumation process (exhumation of gabbros, small amount of basalts above the exhumed mantle), in the most distal part the magmatic system appears to be independent and more active. In particular, we can observe large amounts of extrusive material above a previously exhumed and faulted basement (e.g. Alps, Australia-Antarctica margins). It seems that some faults can play the role of feeder systems for the magma in this area. Magmatic underplating is also important, as suggested by basement uplift and anomalously thick crust (e.g. East Indian margin). It results that the transition with the first steady state oceanic crust is marked by the presence of a hybrid basement, composed by exhumed mantle and magmatic material, whose formation is linked to several tectonic and magmatic events. One could argue that this basement is not clearly different from an oceanic basement. However, we consider that true, steady state oceanic crust only exists, if the entire rock association forming the crust is created during a single event, at a localized spreading center. The interest of that definition is that it does not restrain the term oceanic crust to a basement composition and consequently does not exclude the creation of magma-poor oceanic crust, as observed at slow spreading ridges for example. Indeed, the initiation of steady state oceanic spreading is not necessarily magmatic (e.g. some segments of the Australian-Antarctic margins). In this case, drifting is accommodated by mantle exhumation. However, in this magma-poor transition, and without clear markers of a gradual increase of magmatism, it thus appears difficult to clearly differentiate an exhumed OCT basement and an exhumed oceanic basement. Some theoretical differences can be nevertheless considered: exhumed OCT basement should display a chemical evolution toward the ocean from a subcontinental to an oceanic signature. Moreover, extensional detachment faults are probably long-lived due to the poor influence of the asthenosphere at this stage. On the contrary, exhumed oceanic basement should only display an oceanic signature. In this case, extensional detachment faults are certainly short-lived, due to the strong influence of the asthenosphere, which tends to quickly re-localize the deformation above the spreading center.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.288..311Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.288..311Z"><span>Late Early-Cretaceous quartz diorite-granodiorite-monzogranite association from the Gaoligong belt, southeastern Tibet Plateau: Chemical variations and geodynamic implications</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhu, Ren-Zhi; Lai, Shao-Cong; Qin, Jiang-Feng; Zhao, Shao-Wei; Wang, Jiang-Bo</p> <p>2017-09-01</p> <p>Geochemical variations in granitic rocks may be controlled by their source rocks, melting reactions and subsequent magmatic processes, which resulted from various geodynamic processes related to subduction, collision, or slab break-off. Here we report new LA-ICP-MS zircon U-Pb ages and Hf isotopes, whole-rock chemistry and Sr-Nd isotopes for the late Early Cretaceous quartz diorite, granodiorite and monzogranite in the Gaoligong belt, southeastern Tibet Plateau. The zircon U-Pb dating yield ages of 113.9 ± 1.6, 111.7 ± 0.8, and 112.8 ± 1.7 Ma for the quartz diorite, granodiorite, and monzogranite, respectively, which are coeval with bimodal magmatism in the central and northern Lhasa sub-terrane. There are the distinct sources regions for the quartz diorite and granodiorite-monzogranite association. The quartz diorites are sodic, calc-alkaline and have high Mg# (52-54) values. They also have elevated initial 87Sr/86Sr (0.707019 to 0.709176) and low εNd(t) (- 5.16 to - 7.63), with variable zircon εHf(t) values (+ 5.65 to - 9.02). Zircon chemical data indicate a typical crustal-derived character with high Th (142-1260 ppm) and U (106-1082 ppm) and moderate U/Yb ratios (0.30 to 2.32) and Y content (705-1888 ppm). Those data suggest that the quartz diorites were derived from partial melting of ancient basaltic lower crust by a mantle-derived magma in source region. The granodiorite-monzogranite association has high-K calc-alkaline, weakly peraluminous characters. They show lower Nb/Ta (5.57 to 13.8), CaO/Na2O (0.62 to 1.21), higher Al2O3/TiO2 (24.4 to 44.4) ratios, more evolved whole-rock Sr-Nd and zircon Hf isotopic signatures, all of which suggest derivation from mixed basaltic and metasedimentary source rocks in a deep crustal zone. We propose that the granitic magmatisms at ca. 113-110 Ma in the Gaologong belt was triggered by the slab break-off of Bangong-Nujiang Tethyan oceanic lithosphere. Supplementary Dataset Table 2. Single-grain zircon Hf isotopic data for granitic rocks in the Gaoligong belt, SW China.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T33D0752Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T33D0752Y"><span>Hydrothermal plume anomalies over the southwest Indian ridge: magmatic control</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yue, X.; Li, H.; Tao, C.; Ren, J.; Zhou, J.; Chen, J.; Chen, S.; Wang, Y.</p> <p>2017-12-01</p> <p>Here we firstly reported the extensive survey results of the hydrothermal activity along the ultra-slow spreading southwest Indian ridge (SWIR). The study area is located at segment 27, between the Indomed and Gallieni transform faults, SWIR. The seismic crustal thickness reaches 9.5km in this segment (Li et al., 2015), which is much thicker than normal crustal. The anomaly thickened crust could be affected by the Crozet hotspot or highly focused melt delivery from the mantle. The Duanqiao hydrothermal field was reported at the ridge valley of the segment by Tao et al (2009). The Deep-towed Hydrothermal Detection System (DHDS) was used to collect information related with hydrothermal activity, like temperature, turbidity, oxidation-reduction potential (ORP) and seabed types. There are 15 survey lines at the interval of 2 to 3 km which are occupied about 1300 km2 in segment 27. After processing the raw data, including wiping out random noise points, 5-points moving average processing and subtracting the ambient, we got anomalous Nephelometric Turbidity Units values (ΔNTU). And dE/dt was used to identify the ORP anomalous as the raw data is easily influenced by electrode potentials drifting (Baker et al., 2016). According to the results of water column turbidity and ORP distributions, we confirmed three hydrothermal anomaly fields named A1, A2 and A3. The three fields are all located in the western part of the segment. The A1 field lies on the ridge valley, west side of Duanqiao field. The A2 and A3 field lie on the northern and southern of the ridge valley, respectively. We propose that recent magmatic activity probably focus on the western part of segment 27.And the extensive distribution of hydrothermal plume in the segment is the result of the discrete magma intrusion. References Baker E T, et al. How many vent fields? New estimates of vent field populations on ocean ridges from precise mapping of hydrothermal discharge locations. EPSL, 2016, 449:186-196. Li J, et al. Seismic observation of an extremely magmatic accretion at the ultraslow spreading Southwest Indian Ridge. GRL, 2015, 42:2656-2663. Tao C, Wu G, Ni J, et al. New hydrothermal fields found along the SWIR during the Legs 5-7 of the Chinese DY115-20 Expedition. AGU 2009.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41F..06H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41F..06H"><span>The effects of thick sediment upon continental breakup: seismic imaging and thermal modeling of the Salton Trough, southern California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Han, L.; Hole, J. A.; Lowell, R. P.; Stock, J. M.; Fuis, G. S.; Driscoll, N. W.; Kell, A. M.; Kent, G. M.; Harding, A. J.; Gonzalez-Fernandez, A.; Lázaro-Mancilla, O.</p> <p>2015-12-01</p> <p>Continental rifting ultimately creates a deep accommodation space for sediment. When a major river flows into a late-stage rift, thick deltaic sediment can change the thermal regime and alter the mechanisms of extension and continental breakup. The Salton Trough, the northernmost rift segment of the Gulf of California plate boundary, has experienced the same extension as the rest of the Gulf, but is filled to sea level by sediment from the Colorado River. Unlike the southern Gulf, seafloor spreading has not initiated. Instead, seismicity, high heat flow, and minor volcanoes attest to ongoing rifting of thin, transitional crust. Recently acquired controlled-source seismic refraction and wide-angle reflection data in the Salton Trough provide constraints upon crustal architecture and active rift processes. The crust in the central Salton Trough is only 17-18 km thick, with a strongly layered but relatively one-dimensional structure for ~100 km in the direction of plate motion. The upper crust includes 2-4 km of Colorado River sediment. Crystalline rock below the sediment is interpreted to be similar sediment metamorphosed by the high heat flow and geothermal activity. Meta-sediment extends to at least 9 km depth. A 4-5 km thick layer in the middle crust is either additional meta-sediment or stretched pre-existing continental crust. The lowermost 4-5 km of the crust is rift-related mafic magmatic intrusion or underplating from partial melting in the hot upper mantle. North American lithosphere in the Salton Trough has been almost or completely rifted apart. The gap has been filled by ~100 km of new transitional crust created by magmatism from below and sedimentation from above. These processes create strong lithologic, thermal, and rheologic layering. While heat flow in the rift is very high, rapid sedimentation cools the upper crust as compared to a linear geotherm. Brittle extension occurs within new meta-sedimentary rock. The lower crust, in comparison, is maintained hot and weak by the overlying sedimentary thermal blanket. The lower crust stretches by ductile flow and magmatism is not localized. In this passive rift driven by distant plate motions, rapid sedimentation and its thermal effects delay final breakup of the crust and the onset of seafloor spreading.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29326978','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29326978"><span>Seismic signature of active intrusions in mountain chains.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Di Luccio, Francesca; Chiodini, Giovanni; Caliro, Stefano; Cardellini, Carlo; Convertito, Vincenzo; Pino, Nicola Alessandro; Tolomei, Cristiano; Ventura, Guido</p> <p>2018-01-01</p> <p>Intrusions are a ubiquitous component of mountain chains and testify to the emplacement of magma at depth. Understanding the emplacement and growth mechanisms of intrusions, such as diapiric or dike-like ascent, is critical to constrain the evolution and structure of the crust. Petrological and geological data allow us to reconstruct magma pathways and long-term magma differentiation and assembly processes. However, our ability to detect and reconstruct the short-term dynamics related to active intrusive episodes in mountain chains is embryonic, lacking recognized geophysical signals. We analyze an anomalously deep seismic sequence (maximum magnitude 5) characterized by low-frequency bursts of earthquakes that occurred in 2013 in the Apennine chain in Italy. We provide seismic evidences of fluid involvement in the earthquake nucleation process and identify a thermal anomaly in aquifers where CO 2 of magmatic origin dissolves. We show that the intrusion of dike-like bodies in mountain chains may trigger earthquakes with magnitudes that may be relevant to seismic hazard assessment. These findings provide a new perspective on the emplacement mechanisms of intrusive bodies and the interpretation of the seismicity in mountain chains.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5756663','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5756663"><span>Seismic signature of active intrusions in mountain chains</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Di Luccio, Francesca; Chiodini, Giovanni; Caliro, Stefano; Cardellini, Carlo; Convertito, Vincenzo; Pino, Nicola Alessandro; Tolomei, Cristiano; Ventura, Guido</p> <p>2018-01-01</p> <p>Intrusions are a ubiquitous component of mountain chains and testify to the emplacement of magma at depth. Understanding the emplacement and growth mechanisms of intrusions, such as diapiric or dike-like ascent, is critical to constrain the evolution and structure of the crust. Petrological and geological data allow us to reconstruct magma pathways and long-term magma differentiation and assembly processes. However, our ability to detect and reconstruct the short-term dynamics related to active intrusive episodes in mountain chains is embryonic, lacking recognized geophysical signals. We analyze an anomalously deep seismic sequence (maximum magnitude 5) characterized by low-frequency bursts of earthquakes that occurred in 2013 in the Apennine chain in Italy. We provide seismic evidences of fluid involvement in the earthquake nucleation process and identify a thermal anomaly in aquifers where CO2 of magmatic origin dissolves. We show that the intrusion of dike-like bodies in mountain chains may trigger earthquakes with magnitudes that may be relevant to seismic hazard assessment. These findings provide a new perspective on the emplacement mechanisms of intrusive bodies and the interpretation of the seismicity in mountain chains. PMID:29326978</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70017108','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70017108"><span>Metallogeny of the midcontinent rift system of North America</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Nicholson, S.W.; Cannon, W.F.; Schulz, K.J.</p> <p>1992-01-01</p> <p>The 1.1 Ga Midcontinent rift system of North America is one of the world's major continental rifts and hosts a variety of mineral deposits. The rocks and mineral deposits of this 2000 km long rift are exposed only in the Lake Superior region. In the Lake Superior region, the rift cuts across Precambrian basement terranes ranging in age from ??? 1850 Ma to more than 3500 Ma. Where exposed, the rift consists of widespread tholeiitic basalt flows with local interlayered rhyolite and clastic sedimentary rocks. Beneath the center of Lake Superior the volcanic and sedimentary rocks are more than 30 km deep as shown by recent seismic reflection profiles. This region hosts two major classes of mineral deposits, magmatic and hydrothermal. All important mineral production in this region has come from hydrothermal deposits. Rift-related hydrothermal deposits include four main types: (1) native copper deposits in basalts and interflow sediments; (2) sediment-hosted copper sulfide and native copper; (3) copper sulfide veins and lodes hosted by rift-related volcanic and sedimentary rocks; and (4) polymetallic (five-element) veins in the surrounding Archean country rocks. The scarcity of sulfur within the rift rocks resulted in the formation of very large deposits of native metals. Where hydrothermal sulfides occur (i.e., shale-hosted copper sulfides), the source of sulfur was local sedimentary rocks. Magmatic deposits have locally supported exploration and minor production, but most are subeconomic presently. These deposits occur in intrusions exposed near the margins of the rift and include CuNiPGE and TiFe (V) in the Duluth Complex, U-REE-Nb in small carbonatites, and breccia pipes resulting from local hydrothermal activity around small felsic intrusions. Mineralization associated with some magmatic bodies resulted from the concentration of incompatible elements during fractional crystallization. Most of the sulfide deposits in intrusions, however, contain sulfur derived from country rocks; the interaction between magma and country rocks was important in generation of the magmatic CuNi sulfide deposits. A mantle plume origin has been proposed for the formation of the Midcontinent rift. More than 1 million km3 of mafic magma was erupted in the rift and a comparable volume of mafic intrusions are inferred beneath the rift, providing a ready and structurally confined supply of mafic source rocks that were available for leaching of metals by basinal brines. These brines were heated by a steep geothermal gradient that resulted from the melting and underplating of magma derived from the plume. Hydrothermal deposits were emplaced for at least 30-40 m.y. after rift magmatism and extension ceased. This time lag may reflect either the time required to heat deeply buried rocks and fluids within the rift, or may be due to the timing of post-rift compression that may have provided the driving mechanism for expulsion of hydrothermal fluids from deep portions of the rift. ?? 1992.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70018631','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70018631"><span>U-Pb and K-Ar geochronology in Paleozoic and Mesozoic intrusive rocks of the Coastal Cordillera, Valparaiso, Chile</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Gana, Paulina; Tosdal, Richard M.</p> <p>1996-01-01</p> <p>The U-Pb and K-Ar geochronology applied to intrusive rocks from the Coastal Batholith of Central Chile, demonstrates the existence of a basement block of the Mirasol Unit, with a crystallization age of 299??10 Ma, exposed in the northern block of the Melipilla Fault. The age of 214??1 Ma obtained in the 'Dioritas Gne??isicas de Cartagena Unit', indicates that a Late Triassic magmatism took place in this region; it coincides with the end of an extensive crustal melting period, proposed for northern Chile. The ages of the Jurassic plutonic units (Laguna Verde, Sauce, Pen??uelas and Limache) are restricted to the 156-161 Ma interval, showing in certain cases, inherited zircons from an unknown source. The difference between ages obtained using both chronological methods is a few million years, indicating that a short time passed between the crystallization and the cooling of the plutonic bodies, as well as a fast magmatic differentiation process. The Laguna Verde and Sauce Units, experienced a fast uplift, probably as a result of an extensional tectonic process in the magmatic arc, or induced by the magmatic pressure through fracture zones during Middle Jurassic.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.278..445F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.278..445F"><span>The Cotoncello Shear Zone (Elba Island, Italy): The deep root of a fossil oceanic detachment fault in the Ligurian ophiolites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Frassi, Chiara; Musumeci, Giovanni; Zucali, Michele; Mazzarini, Francesco; Rebay, Gisella; Langone, Antonio</p> <p>2017-05-01</p> <p>The ophiolite sequences in the western Elba Island are classically interpreted as a well-exposed ocean-floor section emplaced during the Apennines orogeny at the top of the tectonic nappe-stack. Stratigraphic, petrological and geochemical features indicate that these ophiolite sequences are remnants of slow-ultraslow spreading oceanic lithosphere analogous to the present-day Mid-Atlantic Ridge and Southwest Indian Ridge. Within the oceanward section of Tethyan lithosphere exposed in the Elba Island, we investigated for the first time a ​10s of meters-thick structure, the Cotoncello Shear Zone (CSZ), that records high-temperature ductile deformation. We used a multidisciplinary approach to document the tectono-metamorphic evolution of the shear zone and its role during spreading of the western Tethys. In addition, we used zircon U-Pb ages to date formation of the gabbroic lower crust in this sector of the Apennines. Our results indicate that the CSZ rooted below the brittle-ductile transition at temperature above 800 °C. A high-temperature ductile fabric was overprinted by fabrics recorded during progressive exhumation up to shallower levers under temperature < 500 °C. We suggest that the CSZ may represent the deep root of a detachment fault that accomplished exhumation of an ancient oceanic core complex (OCC) in between two stages of magmatic accretion. We suggest that the CSZ represents an excellent on-land example enabling to assess relationships between magmatism and deformation when extensional oceanic detachments are at work.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T51C2925P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T51C2925P"><span>Geochemical Insights Into Lithospheric Melting and Instability in the Bufumbira Volcanic Field of the Western Rift, Uganda</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pitcavage, E.; Furman, T.; Nelson, W. R.</p> <p>2016-12-01</p> <p>The East African Rift System (EARS) is the earth's largest continental divergent boundary and is an unparalleled natural laboratory for understanding magmatic processes related to continental rifting. A fundamental unresolved question in EARS magmatism is the degree to which volcanism and rifting are influenced by Cenozoic plume-related melting rather than older, tectonically-driven metasomatism. In the latter scenario, metasomatism by carbonatite or silicate magmas and/or fluids that accompanies tectonic events such as the Proterozoic Pan-African Orogeny will create geochemical heterogeneities and rheological weaknesses in the sub-continental lithospheric mantle (SCLM). In the Western Rift, abundant alkaline mafic lavas record significant contributions from metasomatized SCLM. Modification, destabilization and foundering of metasomatized SCLM has an increasingly recognized role in continental magmatism worldwide. Lithospheric drip magmatism occurs when foundered lithosphere devolatilizes and melts on descent. Lithospheric thinning is one consequence of this process, and may play a role in physical aspects of rifting. Geochemical and geophysical evidence that drip magmatism has occurred in several areas of the EARS, including Turkana, Chyulu Hills, and Oligocene HT2 flood basalts in Afar, suggests that this process is fundamentally related to the onset of successful rifting. We use geochemical characteristics of primitive lavas from the Bufumbira volcanic field in the Western Rift's Virunga Province to demonstrate that ancient, tectonically-driven metasomatism modified the SCLM and contributes to recent volcanism. Further, we identify geochemical signatures which indicate that lithospheric drip melting is the primary petrogenetic process generating these lavas. Sr-Nd-Pb-Hf isotopic data show that the northern portion of the Western Rift, including Bufumbira, requires magma sources distinct from the rest of the EARS. Trace element data show that Bufumbira lavas are derived from depths within the garnet stability field and that source mineralogy includes phlogopite with potential amphibole and zircon; and that extent of melting increased with depth of melting, a signature of lithospheric drip.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16943836','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16943836"><span>Discovery of a magma chamber and faults beneath a Mid-Atlantic Ridge hydrothermal field.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Singh, Satish C; Crawford, Wayne C; Carton, Hélène; Seher, Tim; Combier, Violaine; Cannat, Mathilde; Pablo Canales, Juan; Düsünür, Doga; Escartin, Javier; Miranda, J Miguel</p> <p>2006-08-31</p> <p>Crust at slow-spreading ridges is formed by a combination of magmatic and tectonic processes, with magmatic accretion possibly involving short-lived crustal magma chambers. The reflections of seismic waves from crustal magma chambers have been observed beneath intermediate and fast-spreading centres, but it has been difficult to image such magma chambers beneath slow-spreading centres, owing to rough seafloor topography and associated seafloor scattering. In the absence of any images of magma chambers or of subsurface near-axis faults, it has been difficult to characterize the interplay of magmatic and tectonic processes in crustal accretion and hydrothermal circulation at slow-spreading ridges. Here we report the presence of a crustal magma chamber beneath the slow-spreading Lucky Strike segment of the Mid-Atlantic Ridge. The reflection from the top of the magma chamber, centred beneath the Lucky Strike volcano and hydrothermal field, is approximately 3 km beneath the sea floor, 3-4 km wide and extends up to 7 km along-axis. We suggest that this magma chamber provides the heat for the active hydrothermal vent field above it. We also observe axial valley bounding faults that seem to penetrate down to the magma chamber depth as well as a set of inward-dipping faults cutting through the volcanic edifice, suggesting continuous interactions between tectonic and magmatic processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMOS23B..05O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMOS23B..05O"><span>Geological characteristics of the Shinkai Seep Field, a serpentinite-hosted ecosystem in the Southern Mariana Forearc</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ohara, Y.; Stern, R. J.; Martinez, F.; Michibayashi, K.; Reagan, M. K.; Fujikura, K.; Watanabe, H.; Ishii, T.; Kelley, K. A.</p> <p>2012-12-01</p> <p>Most hydrothermal vents along mid-ocean spreading ridges are high-temperature, sulfide-rich, and low pH (acidic environments). For this reason, the discovery of the Lost City hydrothermal field on the Mid-Atlantic Ridge has stimulated interest in the role of serpentinization of peridotite in generating H2- and CH4-rich fluids and associated carbonate chimneys, as well as in the biological communities adapted to highly reduced, alkaline environments. A new serpentinite-hosted ecosystem, the Shinkai Seep Field (SSF), was discovered by a Shinkai 6500 dive in the inner trench slope of the southern Mariana Trench, near the Challenger Deep, during YK10-12 cruise of R/V Yokosuka in September 2010. Abundant chemosynthetic biological communities, principally consisting of vesicomyid clams are associated with serpentinized peridotite in the SSF. Serpentinization beneath several hydrothermal sites on the Mid-Atlantic Ridge is controlled by interacting seawater and peridotite, variably influenced by magmatic heat. In contrast, the SSF is located in a deep inner trench slope where magmatic heat contribution is unlikely. Instead, serpentinization reactions feeding the SSF may be controlled by persistent fluid flow from the subducting slab. Slab-derived fluid flow is probably controlled by flow through fractures because no serpentinite mud volcano can be discerned along the southern Mariana forearc. Deep-towed IMI-30 sonar backscatter imaging during TN273 cruise of R/V Thomas G. Thompson in January 2012 indicates that the SSF is associated with a small, low backscatter feature that may be a small mound. There are 20 or more of these features in the imaged area, the size of which is ~200 m width and ~200 m to ~700 m long. Since the southern Mariana forearc is heavily faulted, with a deep geology that is dominated by peridotite, more SSF-type seeps are likely to exist along the forearc above the Challenger Deep. The discovery of the SSF suggests that serpentinite-hosted vents may be more widespread on the ocean floor than presently known. The discovery further indicates that such serpentinite-hosted low-temperature fluid vents can sustain high-biomass communities and has implications for the chemical budget of the oceans and the distribution of abyssal chemosynthetic life. Since we know nothing about the chemistry and microbiology of the SSF, we hope to return for further studies with Shinkai 6500 in 2013.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.308...53C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.308...53C"><span>Syn-collisional felsic magmatism and continental crust growth: A case study from the North Qilian Orogenic Belt at the northern margin of the Tibetan Plateau</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Shuo; Niu, Yaoling; Xue, Qiqi</p> <p>2018-05-01</p> <p>The abundant syn-collisional granitoids produced and preserved at the northern Tibetan Plateau margin provide a prime case for studying the felsic magmatism as well as continental crust growth in response to continental collision. Here we present the results from a systematic study of the syn-collisional granitoids and their mafic magmatic enclaves (MMEs) in the Laohushan (LHS) and Machangshan (MCS) plutons from the North Qilian Orogenic Belt (NQOB). Two types of MMEs from the LHS pluton exhibit identical crystallization age ( 430 Ma) and bulk-rock isotopic compositions to their host granitoids, indicating their genetic link. The phase equilibrium constraints and pressure estimates for amphiboles from the LHS pluton together with the whole rock data suggest that the two types of MMEs represent two evolution products of the same hydrous andesitic magmas. In combination with the data on NQOB syn-collisional granitoids elsewhere, we suggest that the syn-collisional granitoids in the NQOB are material evidence of melting of ocean crust and sediment. The remarkable compositional similarity between the LHS granitoids and the model bulk continental crust in terms of major elements, trace elements, and some key element ratios indicates that the syn-collisional magmatism in the NQOB contributes to net continental crust growth, and that the way of continental crust growth in the Phanerozoic through syn-collisional felsic magmatism (production and preservation) is a straightforward process without the need of petrologically and physically complex processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14.9425B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14.9425B"><span>Deep-tow geophysical survey above large exhumed mantle domains of the eastern Southwest Indian ridge</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bronner, A.; Munschy, M.; Sauter, D.; Carlut, J.; Searle, R.; Cannat, M.</p> <p>2012-04-01</p> <p>The recent discovery of a new type of seafloor, the "smooth seafloor", formed with no or very little volcanic activity along the easternmost part of the ultra-slow spreading Southwest Indian ridge (SWIR) shows an unexpected complexity in processes of generation of the oceanic lithosphere. There, detachment faulting is thought to be a mechanism for efficient exhumation of deep-seated mantle rocks. We present here a deep-tow geological-geophysical survey over smooth seafloor at the eastern SWIR (62-64°N) combining multibeam bathymetric data, magnetic data, geology mapping from sidescan sonar (TOBI) images and results from dredge sampling. We introduce a new type of calibration approach for deep-tow fluxgate magnetometer. We show that magnetic data can be corrected from the magnetic effect of the vehicle with no recourse to its attitude (pitch, roll and heading) but only using the 3 components recorded by the magnetometer and an approximation of the scalar intensity of the Earth magnetic field. The collected dredge samples as well as the sidescan sonar images confirm the presence of large areas of exhumed mantle-derived peridodites surrounded by a few volcanic constructions. We investigate the possibility that magnetic anomalies are either caused by serpentinized peridotites and/or magmatic intrusions. We show that the magnetic signature of the smooth seafloor is clearly weaker than the surrounding volcanic areas. Moreover, the calculated magnetization of a source layer as well as the comparison between deep-tow and sea-surface magnetic data argue for strong East-West variability in the distribution of the magnetized sources. This variability may result from fluid-rock interactions along the detachment faults as well as from the occurrence of small sized and thin volcanic patches and thus questions the seafloor spreading origin of the corresponding magnetic anomalies. Finally, we provide magnetic arguments, as calculation of block rotation or spreading asymmetry in order to better constrain tectonic mechanisms that occur during the formation of this peculiar seafloor.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T23A2370B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T23A2370B"><span>Deep-tow magnetic survey above large exhumed mantle domains of the eastern Southwest Indian ridge</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bronner, A.; Munschy, M.; Carlut, J. H.; Searle, R. C.; Sauter, D.; Cannat, M.</p> <p>2011-12-01</p> <p>The recent discovery of a new type of seafloor, the "smooth seafloor", formed with no or very little volcanic activity along the ultra-slow spreading Southwest Indian ridge (SWIR) shows an unexpected complexity in processes of generation of the oceanic lithosphere. There, detachment faulting is thought to be a mechanism for efficient exhumation of deep-seated mantle rocks. We present here a deep-tow geological-geophysical survey over smooth seafloor at the eastern SWIR (62-64°N) combining magnetic data, geology mapping from side-scan sonar images and results from dredge sampling. We introduce a new type of calibration approach for deep-tow fluxgate magnetometer. We show that magnetic data can be corrected from the magnetic effect of the vehicle with no recourse to its attitude (pitch, roll and heading) but only using the 3 components recorded by the magnetometer and an approximation of the scalar intensity of the Earth magnetic field. The collected dredge samples as well as the side-scan images confirm the presence of large areas of exhumed mantle-derived peridodites surrounded by a few volcanic constructions. This allows us to hypothesis that magnetic anomalies are caused by serpentinized peridotites or magmatic intrusions. We show that the magnetic signature of the smooth seafloor is clearly weaker than the surrounding volcanic areas. Moreover, the calculated magnetization of a source layer as well as the comparison between deep-tow and sea-surface magnetic data argue for strong East-West variability in the distribution of the magnetized sources. This variability may results from fluid-rocks interaction along the detachment faults as well as from the repartition of the volcanic material and thus questions the seafloor spreading origin of the corresponding magnetic anomalies. Finally, we provide magnetic arguments, as calculation of block rotation or spreading asymmetry in order to better constrain tectonic mechanisms that occur during the formation of this peculiar seafloor.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.451..263F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.451..263F"><span>Contrasting hydrological processes of meteoric water incursion during magmatic-hydrothermal ore deposition: An oxygen isotope study by ion microprobe</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fekete, Szandra; Weis, Philipp; Driesner, Thomas; Bouvier, Anne-Sophie; Baumgartner, Lukas; Heinrich, Christoph A.</p> <p>2016-10-01</p> <p>Meteoric water convection has long been recognized as an efficient means to cool magmatic intrusions in the Earth's upper crust. This interplay between magmatic and hydrothermal activity thus exerts a primary control on the structure and evolution of volcanic, geothermal and ore-forming systems. Incursion of meteoric water into magmatic-hydrothermal systems has been linked to tin ore deposition in granitic plutons. In contrast, evidence from porphyry copper ore deposits suggests that crystallizing subvolcanic magma bodies are only affected by meteoric water incursion in peripheral zones and during late post-ore stages. We apply high-resolution secondary ion mass spectrometry (SIMS) to analyze oxygen isotope ratios of individual growth zones in vein quartz crystals, imaged by cathodo-luminescence microscopy (SEM-CL). Existing microthermometric information from fluid inclusions enables calculation of the oxygen isotope composition of the fluid from which the quartz precipitated, constraining the relative timing of meteoric water input into these two different settings. Our results confirm that incursion of meteoric water directly contributes to cooling of shallow granitic plutons and plays a key role in concurrent tin mineralization. By contrast, data from two porphyry copper deposits suggest that downward circulating meteoric water is counteracted by up-flowing hot magmatic fluids. Our data show that porphyry copper ore deposition occurs close to a magmatic-meteoric water interface, rather than in a purely magmatic fluid plume, confirming recent hydrological modeling. On a larger scale, the expulsion of magmatic fluids against the meteoric water interface can shield plutons from rapid convective cooling, which may aid the build-up of large magma chambers required for porphyry copper ore formation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.294..263C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.294..263C"><span>The post-collisional late Variscan ferroan granites of southern Sardinia (Italy): Inferences for inhomogeneity of lower crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Conte, Aida Maria; Cuccuru, Stefano; D'Antonio, Massimo; Naitza, Stefano; Oggiano, Giacomo; Secchi, Francesco; Casini, Leonardo; Cifelli, Francesca</p> <p>2017-12-01</p> <p>The post-collisional late Variscan magmatism of Sardinia-Corsica batholith attained a peak at about 290 Ma. In southern Sardinia, in the frontal part of the Variscan orogenic wedge, this magmatism is represented by three suites of granitoids, here defined as GS1, GS2 and GS3. GS1, GS2 and GS3 are slightly peraluminous and F-bearing granitoids; GS1 and GS3 granites show in addition a ferroan character, whereas GS2 rocks range from magnesian to ferroan, from granodiorites to leucogranites. From magnetic susceptibility data, GS1 and GS2 belong to the ilmenite series, whereas GS3 is a slightly oxidized rock-suite plotting on the ilmenite/magnetite series boundary. Each rock-suite shows distinctive characters, in terms of petrography, petrochemistry, rock associations, as well as metallogenic signature of the related fluids. The distinction among rock-suite types is made on the basis of both mafic and characteristic accessory minerals. Siderophyllitic dark mica as the only mafic phase, and accessory xenotime (Y) characterize the GS1 rocks; GS2 mineral associations include biotite ± hornblende + allanite + magnetite; GS3 rocks show an association of hastingsite + annite + allanite + magnetite. Chemical variations in the studied samples suggest different magmatic evolution of independent magmas. Pb, Sr and Nd isotopic data constrain the origin of magmas to lower crustal sources. Chemical composition of rocks and dark micas meet those of liquids experimentally obtained by low degrees of partial melting of different meta-igneous deep crustal sources, felsic for GS1 rock-types and more mafic for GS3 rock-types. GS1 intrusions show granophile-type (Sn-W-Mo) metallogenic signatures, very low magnetic susceptibility, and Nd model ages (referred to the Depleted Mantle - TDM) of 2.3 Ga, coherent with a possible derivation from an old (early Proterozoic-Neoarchean), reduced and weathered basement, tectonically buried under Variscan covers. A definite deep crustal inhomogeneity is mirrored by GS3 granites, whose compositional and isotopic features indicate a younger (Nd model age: 1.6 Ga) tonalitic amphibolite source. Overall, the peculiarities of the studied granitoids suggest further compositional differences in the deep crust between southern and northern portion of the Sardinia-Corsica Variscan transect. Late Variscan lithospheric delamination appears as the most reliable mechanism that may have determined the high thermal regime that triggered partial melting of the crust. The close field association, at 290 Ma, of tholeiitic dike swarms and ferroan granitoids, supports this inference.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IJEaS.tmp...55D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IJEaS.tmp...55D"><span>Petrological, geochemical, isotopic, and geochronological constraints for the Late Devonian-Early Carboniferous magmatism in SW Gondwana (27-32°LS): an example of geodynamic switching</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dahlquist, Juan A.; Alasino, Pablo H.; Basei, Miguel A. S.; Morales Cámera, Matías M.; Macchioli Grande, Marcos; da Costa Campos Neto, Mario</p> <p>2018-04-01</p> <p>We report a study integrating 13 new U-Pb LA-MC-ICP-MS zircon ages and Hf-isotope data from dated magmatic zircons together with complete petrological and whole-rock geochemistry data for the dated granitic rocks. Sample selection was strongly based on knowledge reported in previous investigations. Latest Devonian-Early Carboniferous granite samples were collected along a transect of 900 km, from the inner continental region (present-day Eastern Sierras Pampeanas) to the magmatic arc (now Western Sierras Pampeanas and Frontal Cordillera). Based on these data together with ca. 100 published whole-rock geochemical analyses we conclude that Late Devonian-Early Carboniferous magmatism at this latitude represents continuous activity (ranging from 322 to 379 Ma) on the pre-Andean margin of SW Gondwana, although important whole-rock and isotopic compositional variations occurred through time and space. Combined whole-rock chemistry and isotope data reveal that peraluminous A-type magmatism started in the intracontinental region during the Late Devonian, with subsequent development of synchronous Carboniferous peraluminous and metaluminous A-type magmatism in the retro-arc region and calc-alkaline magmatism in the western paleomargin. We envisage that magmatic evolution was mainly controlled by episodic fluctuations in the angle of subduction of the oceanic plate (between flat-slab and normal subduction), supporting a geodynamic switching model. Subduction fluctuations were relatively fast (ca. 7 Ma) during the Late Devonian and Early Carboniferous, and the complete magmatic switch-off and switch-on process lasted for 57 Ma. Hf T DM values of zircon (igneous and inherited) from some Carboniferous peraluminous A-type granites in the retro-arc suggest that Gondwana continental lithosphere formed during previous orogenies was partly the source of the Devonian-Carboniferous granitic magmas, thus precluding the generation of the parental magmas from exotic terranes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70022809','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70022809"><span>Dilational processes accompanying earthquakes in the Long Valley Caldera</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Dreger, Douglas S.; Tkalcic, Hrvoje; Johnston, M.</p> <p>2000-01-01</p> <p>Regional distance seismic moment tensor determinations and broadband waveforms of moment magnitude 4.6 to 4.9 earthquakes from a November 1997 Long Valley Caldera swarm, during an inflation episode, display evidence of anomalous seismic radiation characterized by non-double couple (NDC) moment tensors with significant volumetric components. Observed coseismic dilation suggests that hydrothermal or magmatic processes are directly triggering some of the seismicity in the region. Similarity in the NDC solutions implies a common source process, and the anomalous events may have been triggered by net fault-normal stress reduction due to high-pressure fluid injection or pressurization of fluid-saturated faults due to magmatic heating.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V31D4777W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V31D4777W"><span>Lawsonite Blueschists in Recycled Mélange Involved in K-Rich Orogenic Magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Y.; Prelevic, D.; Foley, S. F.; Buhre, S.; Galer, S. J. G.</p> <p>2014-12-01</p> <p>The origin of K-rich orogenic magmatism in the Alpine-Himalayan belt and its relationship to the large-scale elevations in several massifs of the orogen is controversial, particularly the significance of the widespread presence of a geochemical signal typical for recycled continental crust. Two competing scenarios invoke direct melting of continental crust during deep intercontinental subduction and removal of heavily metasomatised mantle lithosphere by delamination into the convecting mantle. Here we investigate the coupling of high Th/La ratio with crustal isotopic signatures in K-rich orogenic lavas that does not occur in volcanic rocks from other collisional environments to distinguish between these two models. High-pressure experimental results on a phyllite representing upper crustal composition and a detailed mineral and geochemical study of blueschists from Tavşanlı mélange, Turkey, indicate that this geochemical fingerprint originates by melting of subducted mélange. Melting of crust at the top of the subducted continental lithosphere cannot produce observed fingerprint, whereas lawsonites, especially those with terrigenous sediment origin from blueschists with high Th/La can. Lawsonites that grow in various components of a subduction mélange inherit the geochemical characteristics of either oceanic or continental protoliths. It is currently uncertain whether those carrying the high Th/La signature originate by direct melting of continental blocks in the mélange or by the introduction of supercritical fluids from lawsonite blueschist of continental origin that infiltrate oceanic sediment blocks. Either way, the high Th/La is later released into subsequently formed melts. This confirms the supposition that lawsonite is the main progenitor of the high Th/La and Sm/La ratio. However, lawsonite must break down completely to impart this unique feature to subsequent magmas. The source regions of the potassic volcanic rocks consist of blueschist facies mélanges imbricated together with extremely depleted fore-arc peridotites in a mantle lithosphere that was newly formed during the convergence of small continental blocks and oceans. This process takes place entirely at shallow depths (<60-80km) and does not require any deep subduction of continental materials.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V13F..02M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V13F..02M"><span>On the Principles of Building a Layered Intrusion</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marsh, B. D.</p> <p>2009-12-01</p> <p>An accurate and realistic understanding of all magmatic processes involves knowing the combined physical and chemical fundamentals governing the overall process. Magmatic processes involve such a vast array of sub-processes (e.g., heat and mass transfer, crystal growth, slurry transport and sorting, annealing, resorbtion, etc.) that rarely is there any single feature or measurement that can be safely inverted to solve the problem. And each event as in the formation of an intrusion must at some level for heuristic purposes be defined as an isolated event. This is commonly done without much forethought, as is the absolutely critical assumption of the initial conditions defining the beginning of the event. Almost without exception, it is the initial conditions that determine the outcome of the entire process in all physical and biological systems. Automobile factories produce motorized vehicles not water melons or chimpanzees. Nucleosynthesis of H and He always gives the same set of elements. The initial conditions of the magma giving rise to the end product for mafic layered systems are especially difficult to discern and must be bounded by observing simpler, real time magmatic and volcanic processes. Initial conditions come from posing a series of questions: What was the style and duration of filling? What was the rate of influx and final volume of each delivery of magma? What was the compositional variation and phenocryst content of the individual magmatic deliveries? If phenocrysts are present, were they sorted prior to injection during ascension? What was the original and ongoing shape of the magmatic reservoir? A failure to appreciate or answer such basic questions leads to vastly untenable evolutionary scenarios. Unrealistic initial conditions necessarily lead to unrealistic magmatic scenarios. There are certain safe starting points. Eruptive and emplacement fluxes are limited. The larger an intrusion is the longer it took to build and the longer to build the more varied are the deliveries in time, volume, and constitution. Instantaneous emplacement of crystal free magma are unlikely initial conditions for a large intrusion. The most realistic initial conditions are that intrusions are made of a combination of crystal poor and crystal-rich inputs. Examples abound of the outcomes of systems with clearly known initial conditions. The huge Sudbury magma was produced in 5 minutes at a temperature of 1700C. Clearly crystal free, it produced no layering whatsoever. Sills worldwide, regardless of size, approaching these initial conditions are similarly featureless. At the other extreme are the lava outputs of large volcanic systems like Kilauea. The ensuing lava lakes produced over months are filled with magma containing varied amounts of phenocrysts/xenocrysts and ultramafic layers are produced. Intrusions abound of all sizes that show the same characteristics. Ponding in crystal-laden sills forms layered systems with many of the features of large bodies. Rapid cooling preserves diagnostic textural relations lost to annealing in large bodies. Slow cooling promotes annealing to sharpen and accentuate the initial modal and cryptic layering. Initial conditions are fundamental to understanding the final product. Physical processes buttressed by chemistry mainly dominate magmatic systems.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22622575','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22622575"><span>Statistical geochemistry reveals disruption in secular lithospheric evolution about 2.5 Gyr ago.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Keller, C Brenhin; Schoene, Blair</p> <p>2012-05-23</p> <p>The Earth has cooled over the past 4.5 billion years (Gyr) as a result of surface heat loss and declining radiogenic heat production. Igneous geochemistry has been used to understand how changing heat flux influenced Archaean geodynamics, but records of systematic geochemical evolution are complicated by heterogeneity of the rock record and uncertainties regarding selection and preservation bias. Here we apply statistical sampling techniques to a geochemical database of about 70,000 samples from the continental igneous rock record to produce a comprehensive record of secular geochemical evolution throughout Earth history. Consistent with secular mantle cooling, compatible and incompatible elements in basalts record gradually decreasing mantle melt fraction through time. Superimposed on this gradual evolution is a pervasive geochemical discontinuity occurring about 2.5 Gyr ago, involving substantial decreases in mantle melt fraction in basalts, and in indicators of deep crustal melting and fractionation, such as Na/K, Eu/Eu* (europium anomaly) and La/Yb ratios in felsic rocks. Along with an increase in preserved crustal thickness across the Archaean/Proterozoic boundary, these data are consistent with a model in which high-degree Archaean mantle melting produced a thick, mafic lower crust and consequent deep crustal delamination and melting--leading to abundant tonalite-trondhjemite-granodiorite magmatism and a thin preserved Archaean crust. The coincidence of the observed changes in geochemistry and crustal thickness with stepwise atmospheric oxidation at the end of the Archaean eon provides a significant temporal link between deep Earth geochemical processes and the rise of atmospheric oxygen on the Earth.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018IJEaS.107.1097Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018IJEaS.107.1097Z"><span>Spatial coincidence and similar geochemistry of Late Triassic and Eocene-Oligocene magmatism in the Andes of northern Chile: evidence from the MMH porphyry type Cu-Mo deposit, Chuquicamata District</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zentilli, Marcos; Maksaev, Victor; Boric, Ricardo; Wilson, Jessica</p> <p>2018-04-01</p> <p>The MMH porphyry type copper-molybdenum deposit in northern Chile is the newest mine in the Chuquicamata District, one of largest copper concentrations on Earth. Mineralized Eocene-Oligocene porphyry intrusions are hosted by essentially barren Triassic granodiorites. Despite a century of exploitation, geologists still have problems in the mine distinguishing the Triassic granodiorite from the most important ore-carrying Eocene porphyries in the district. To resolve the problem, internally consistent high-quality geochemical analyses of the Triassic and Tertiary intrusives were carried out: explaining the confusion, they show that the rock units in question are nearly identical in composition and thus respond equally to hydrothermal alteration. In detail, the only difference in terms of chemical composition is that the main Eocene-Oligocene porphyries carry relatively less Fe and Ni. Unexpectedly, the mineralized Eocene-Oligocene porphyries have consistently less U and Th than other Tertiary intrusions in the district, a characteristic that may be valuable in exploration. The supergiant copper-molybdenum deposits in the Central Andes were formed within a narrow interval between 45 and 31 Ma, close to 7% of the 200 My duration of "Andean" magmatism, which resulted from subduction of oceanic lithosphere under South America since the Jurassic. Although recent work has shown that subduction was active on the margin since Paleozoic times, pre-Andean (pre-Jurassic) "Gondwanan" magmatism is often described as being very different, having involved crustal melting and the generation of massive peraluminous rhyolites and granites. This study shows that the indistinguishable Late Triassic and Eocene-Oligocene intrusions occupy the same narrow NS geographic belt in northern Chile. If it is accepted that magma character may determine the potential to generate economic Cu-Mo deposits, then Late Triassic volcano-plutonic centres in the same location in the South American margin could have contained valuable ore deposits, although their preservation will depend on the level attained by pre-mid Jurassic erosion. Both Late Triassic and Eocene-Oligocene magmatic events occurred during the waning stages of vigorous volcano-plutonic cycles, and both preceded apparent gaps in igneous activity (Rhaetian and post-Oligocene), abrupt lateral shifts of the volcanic front and radical changes in the character of the magmas generated. Both Late Triassic and Eocene-Oligocene intrusions were emplaced along the same narrow strip of crust; it is probable that they both exploited the same deep crustal structures. The Eocene-Oligocene magmatic front was controlled by an orogen-parallel shear system caused by oblique subduction; it is possible that Late Triassic magmatism along the same belt had a similar setting. The identified Rhaetian gap in subduction and magmatism may have widespread implications.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940016363&hterms=magma&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dmagma','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940016363&hterms=magma&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dmagma"><span>The parent magma of the Nakhla (SNC) meteorite: Reconciliation of composition estimates from magmatic inclusions and element partitioning</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Treiman, A. H.</p> <p>1993-01-01</p> <p>The composition of the parent magma of the Nakhla meteorite was difficult to determine, because it is accumulate rock, enriched in olivine and augite relative to a basalt magma. A parent magma composition is estimated from electron microprobe area analyses of magmatic inclusions in olivine. This composition is consistent with an independent estimate based on the same inclusions, and with chemical equilibria with the cores of Nakhla's augites. This composition reconciles most of the previous estimates of Nakhla's magma composition, and obviates the need for complex magmatic processes. Inconsistency between this composition and those calculated previously suggests that magma flowed through and crystallized into Nakhla as it cooled.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035494','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035494"><span>Isotopic evolution of the idaho batholith and Challis intrusive province, Northern US Cordillera</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Gaschnig, Richard M.; Vervoort, J.D.; Lewis, R.S.; Tikoff, B.</p> <p>2011-01-01</p> <p>The Idaho batholith and spatially overlapping Challis intrusive province in the North American Cordillera have a history of magmatism spanning some 55 Myr. New isotopic data from the ???98 Ma to 54 Ma Idaho batholith and ???51 Ma to 43 Ma Challis intrusions, coupled with recent geochronological work, provide insights into the evolution of magmatism in the Idaho segment of the Cordillera. Nd and Hf isotopes show clear shifts towards more evolved compositions through the batholith's history and Pb isotopes define distinct fields correlative with the different age and compositionally defined suites of the batholith, whereas the Sr isotopic compositions of the various suites largely overlap. The subsequent Challis magmatism shows the full range of isotopic compositions seen in the batholith. These data suggest that the early suites of metaluminous magmatism (98-87 Ma) represent crust-mantle hybrids. Subsequent voluminous Atlanta peraluminous suite magmatism (83-67 Ma) results primarily from melting of different crustal components. This can be attributed to crustal thickening, resulting from either subduction processes or an outboard terrane collision. A later, smaller crustal melting episode, in the northern Idaho batholith, resulted in the Bitterroot peraluminous suite (66-54 Ma) and tapped different crustal sources. Subsequent Challis magmatism was derived from both crust and mantle sources and corresponds to extensional collapse of the over-thickened crust. ?? The Author 2011. Published by Oxford University Press. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70047248','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70047248"><span>Seismic observations of Redoubt Volcano, Alaska - 1989-2010 and a conceptual model of the Redoubt magmatic system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Power, John A.; Stihler, Scott D.; Chouet, Bernard A.; Haney, Matthew M.; Ketner, D.M.</p> <p>2013-01-01</p> <p>Seismic activity at Redoubt Volcano, Alaska, has been closely monitored since 1989 by a network of five to ten seismometers within 22 km of the volcano's summit. Major eruptions occurred in 1989-1990 and 2009 and were characterized by large volcanic explosions, episodes of lava dome growth and failure, pyroclastic flows, and lahars. Seismic features of the 1989-1990 eruption were 1) weak precursory tremor and a short, 23-hour-long, intense swarm of repetitive shallow long-period (LP) events centered 1.4 km below the crater floor, 2) shallow volcano-tectonic (VT) and hybrid earthquakes that separated early episodes of dome growth, 3) 13 additional swarms of LP events at shallow depths precursory to many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity, and 4) a persistent cluster of VT earthquakes at 6 to 9 km depth. In contrast the 2009 eruption was preceded by a pronounced increase in deep-LP (DLP) events at lower crustal depths (25 to 38 km) that began in mid-December 2008, two months of discontinuous shallow volcanic tremor that started on January 23, 2009, a strong phreatic explosion on March 15, and a 58-hour-long swarm of repetitive shallow LP events. The 2009 eruption consisted of at least 23 major explosions between March 23 and April 5, again accompanied by shallow VT earthquakes, several episodes of shallow repetitive LP events and dome growth continuing until mid July. Increased VT earthquakes at 4 to 9 km depth began slowly in early April, possibly defining a mid-crustal magma source zone. Magmatic processes associated with the 2009 eruption seismically activated the same portions of the Redoubt magmatic system as the 1989-1990 eruption, although the time scales and intensity vary considerably among the two eruptions. The occurrence of precursory DLP events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths. Based on the evolution of seismicity during the 1989-1990 and 2009 eruptions the Redoubt magmatic system is envisioned to consist of a shallow system of cracks extending 1 to 2 km below the crater floor, a magma storage or source region at roughly 3 to 9 km depth, and a diffuse magma source region at 25 to 38 km depth. Close tracking of seismic activity allowed the Alaska Volcano Observatory to successfully issue warnings prior to many of the hazardous explosive events that occurred in 2009.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMDI51A0284D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMDI51A0284D"><span>Electrical structure of the lithosphere across the Western Paraná suture zone: the role of a Neoproterozoic-Cambrian subduction in generating the Paraná Magmatic Province</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dragone, G. N.; Bologna, M.; Gimenez, M. E.; Alvarez, O.; Lince Klinger, F. G.; Correa-Otto, S.; Ussami, N.</p> <p>2017-12-01</p> <p>The Paraná Magmatic Province (PMP) together with the Etendeka Province (EP) in Africa is one of the Earth's largest igneous provinces originated prior to the Western Gondwanaland break-up and the inception of the South Atlantic Ocean in the Lower Cretaceous. Geochemical data of PMP-EP basalts collected since late 1980's indicate the origin of PMP-EP by melting of a heterogeneous and enriched subcontinental lithospheric mantle with fast rate of eruption (< 3 My). The geodynamical cause of this magmatism is still a matter of debate (deep mantle plume x plate model). New isotopic geochemical data from Re-Os systematics (Rocha-Jr et al., 2012, EPSL) of PMP basalts indicate metasomatized asthenospheric mantle component probably generated at the mantle wedge between the PMP-EP lithosphere and the subducting oceanic plate. A combined seismic velocity and density model of PMP by Chaves et al. (2016, G3) indicates high velocity and a density increase of PMP ancient lithosphere interpreted as due to a long-term mantle refertilization process. To investigate the role of the subduction zones in the development of both the Paraná basin subsidence and the magmatic province we present the results of regional scale broad-band MT-magnetotelluric soundings across the western and southern borders of the PMP, the Western Paraná suture zone (WPS in Fig. 1). We discuss the electrical properties of the lithosphere along three MT profiles across the WPS. MT-A profile (Padilha et al., 2015, JGR) extends from Rio Apa craton towards the center of PMP (high-TiO2 basalts). Profile MT-B extends from Tebicuary craton towards the center of PMP (low-TiO2) and profile MT-C extends from Rio de la Plata craton towards the southern PMP (low- and high-TiO2). All profiles show a resistive ( 104 ohm m) and thick (> 150 km) lithosphere in the cratonic areas whereas the electrical lithosphere is thinner (<100 km) with alternating high and low resistivities within PMP. Vertically elongated and high electrical conductivity anomalies ( 10 ohm m) centered at 40 km depth occur along the -30 mGal contour line in the three profiles, and are interpreted as the location of the suture and former subduction zone. We will discuss the correlation between geochemical and petrological characteristics of basalts and the electrical properties of the lithospheric mantle underneath.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1411779A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1411779A"><span>Earthquake and Volcanic Hazard Mitigation and Capacity Building in Sub-Saharan Africa</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ayele, A.</p> <p>2012-04-01</p> <p>The East African Rift System (EARS) is a classic example of active continental rifting, and a natural laboratory setting to study initiation and early stage evolution of continental rifts. The EARS is at different stages of development that varies from relatively matured rift (16 mm/yr) in the Afar to a weakly extended Okavango Delta in the south with predicted opening velocity < 3 mm/yr. Recent studies in the region helped researchers to highlight the length and timescales of magmatism and faulting, the partitioning of strain between faulting and magmatism, and their implications for the development of along-axis segmentation. Although the human resource and instrument coverage is sparse in the continent, our understanding of rift processes and deep structure has improved in the last decade after the advent of space geodesy and broadband seismology. The recent major earthquakes, volcanic eruptions and mega dike intrusions that occurred along the EARS attracted several earth scientist teams across the globe. However, most African countries traversed by the rift do not have the full capacity to monitor and mitigate earthquake and volcanic hazards. Few monitoring facilities exist in some countries, and the data acquisition is rarely available in real-time for mitigation purpose. Many sub-Saharan Africa governments are currently focused on achieving the millennium development goals with massive infrastructure development scheme and urbanization while impending natural hazards of such nature are severely overlooked. Collaborations with overseas researchers and other joint efforts by the international community are opportunities to be used by African institutions to best utilize limited resources and to mitigate earthquake and volcano hazards.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.215...92H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.215...92H"><span>U-series disequilibria of trachyandesites from minor volcanic centers in the Central Andes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huang, Fang; Sørensen, Erik V.; Holm, Paul M.; Zhang, Zhao-Feng; Lundstrom, Craig C.</p> <p>2017-10-01</p> <p>Young trachyandesite lavas from minor volcanic centers in the Central Andes record the magma differentiation processes at the base of the lower continental crust. Here we report U-series disequilibrium data for the historical lavas from the Andagua Valley in Southern Peru to define the time-scale and processes of magmatism from melting in the mantle wedge to differentiation in the crust. The Andagua lavas show (230Th)/(238U), (231Pa)/(235U), and (226Ra)/(230Th) above unity except for one more evolved lava with 230Th depletion likely owing to fractional crystallization of accessory minerals. The 226Ra excess indicates that the time elapsed since magma emplacement and differentiation in the deep crust is within 8000 years. Based on the correlations of U-series disequilibria with SiO2 content and ratios of incompatible elements, we argue that the Andagua lavas were produced by mixing of fresh mantle-derived magma with felsic melt of earlier emplaced basalts in the deep crust. Because of the lack of sediment in the Chile-Peru trench, there is no direct link of recycled slabs with 230Th and 231Pa excesses in the Andagua lavas. Instead, 230Th and 231Pa excesses are better explained by in-growth melting in the upper mantle followed by magma differentiation in the crust. Such processes also produced the 226Ra excess and the positive correlations among (226Ra)/(230Th), Sr/Th, and Ba/Th in the Andagua lavas. The time-scale of mantle wedge melting should be close to the half-life of 231Pa (ca. 33 ka), while it takes less than a few thousand years for magma differentiation to form intermediate volcanic rocks at a convergent margin.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035304','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035304"><span>Late Cretaceous to Paleocene metamorphism and magmatism in the Funeral Mountains metamorphic core complex, Death Valley, California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Mattinson, C.G.; Colgan, J.P.; Metcalf, J.R.; Miller, E.L.; Wooden, J.L.</p> <p>2007-01-01</p> <p>Amphibolite-facies Proterozoic metasedimentary rocks below the low-angle Ceno-zoic Boundary Canyon Detachment record deep crustal processes related to Meso-zoic crustal thickening and subsequent extension. A 91.5 ?? 1.4 Ma Th-Pb SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) monazite age from garnet-kyanite-staurolite schist constrains the age of prograde metamorphism in the lower plate. Between the Boundary Canyon Detachment and the structurally deeper, subparallel Monarch Spring fault, prograde metamorphic fabrics are overprinted by a pervasive greenschist-facies retrogression, high-strain subhorizontal mylonitic foliation, and a prominent WNW-ESE stretching lineation parallel to corrugations on the Boundary Canyon Detachment. Granitic pegmatite dikes are deformed, rotated into parallelism, and boudinaged within the mylonitic foliation. High-U zircons from one muscovite granite dike yield an 85.8 ?? 1.4 Ma age. Below the Monarch Spring fault, retrogression is minor, and amphibolite-facies mineral elongation lineations plunge gently north to northeast. Multiple generations of variably deformed dikes, sills, and leucosomal segregations indicate a more complex history of partial melting and intrusion compared to that above the Monarch Spring fault, but thermobarometry on garnet amphibolites above and below the Monarch Spring fault record similar peak conditions of 620-680 ??C and 7-9 kbar, indicating minor (<3-5 km) structural omission across the Monarch Spring fault. Discordant SHRIMP-RG U-Pb zircon ages and 75-88 Ma Th-Pb monazite ages from leucosomal segregations in paragneisses suggest that partial melting of Proterozoic sedimentary protoliths was a source for the structurally higher 86 Ma pegmatites. Two weakly deformed two-mica leucogranite dikes that cut the high-grademetamorphic fabrics below the Monarch Spring fault yield 62.3 ?? 2.6 and 61.7 ?? 4.7 Ma U-Pb zircon ages, and contain 1.5-1.7 Ga cores. The similarity of metamorphic, leuco-some, and pegmatite ages to the period of Sevier belt thrusting and the period of most voluminous Sierran arc magmatism suggests that both burial by thrusting and regional magmatic heating contributed to metamorphism and subsequent partial melting. ??2007 Geological Society of America. All rights reserved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.132....1C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.132....1C"><span>Geochemical evidences of magma dynamics at Campi Flegrei (Italy)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caliro, S.; Chiodini, G.; Paonita, A.</p> <p>2014-05-01</p> <p>Campi Flegrei caldera, within the Neapolitan area of Italy, is potentially one of the most dangerous volcanoes in the world, and during the last decade it has shown clear signs of reactivation, marked by the onset of uplift and changes in the geochemistry of gas emissions. We describe a 30-year-long data set of the CO2-He-Ar-N2 compositions of fumarolic emissions from La Solfatara crater, which is located in the center of the caldera. The data display continuous decreases in both the N2/He and N2/CO2 ratios since 1985, paralleled by an increase in He/CO2. These variations cannot be explained by either processes of boiling/condensation in the local hydrothermal system or with changes in the mixing proportions between a magmatic vapor and hydrothermal fluids. We applied the magma degassing model of Nuccio and Paonita (2001, Earth Planet. Sci. Lett. 193, 467-481) using the most recent inert-gas solubilities in order to interpret these peculiar features in accordance with petrologic constraints derived from the ranges of the melt compositions and reservoir pressures at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a remarkably good agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-term geochemical changes. Recalling that (i) a sill-like reservoir of gases at a depth of 3-4 km seems to be the main source of ground inflation and (ii) there is petrologic and geophysical evidence for a reservoir of magma at about 8 km below Campi Flegrei, we suggest that the most-intense episodes of inflation occur when the gas supply to the sill-like reservoir comes from the 8 km-deep magma, although fluids exsolved by magma bodies at shallower depths also contribute to the gas budget. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature of reactive volatiles, inert gases are the preferred species to use when seeking information on the melt composition, dynamics, and structure of the plumbing systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.V13E2076E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.V13E2076E"><span>Geochemistry of 24 Ma Basalts from Northeast Egypt: Implications for Small-Scale Convection Beneath the East African Rift System</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Endress, C. A.; Furman, T.; Ali Abu El-Rus, M.</p> <p>2009-12-01</p> <p>Basalts ~24 Ma in the Cairo-Suez and Fayyum districts of NE Egypt represent the youngest and northernmost lavas potentially associated with the initiation of rifting of the Red Sea. The age of these basalts corresponds to a time period of significant regional magmatism that occurred subsequent to emplacement of 30 Ma flood basalts attributed to the Afar Plume in Ethiopia and Yemen. Beginning ~28 Ma, widespread magmatism occurred across supra-equatorial Africa in Hoggar (Algeria), Tibesti (Chad), Darfur (Sudan), Turkana (Kenya) and Samalat, Bahariya, Quesir and the Sinai Peninsula (Egypt) (e.g. Allegre et al., 1981; Meneisy, 1990; Baldridge et al., 1991; Wilson and Guiraud, 1992; Furman et al., 2006; Lucassen et al., 2008). Available geochemical and isotopic data indicate that Hoggar and Darfur basalts are similar to Turkana lavas, although no direct link between the N African lavas and the Kenya Plume has been made. New geochemical data on the NE Egyptian basalts provide insight into the thermochemical, isotopic, and mineralogical characteristics of the mantle beneath the region in which they were emplaced. The basalts are subalkaline with OIB-like incompatible trace element abundances and homogeneous major element, trace element and isotopic geochemistry. They display relatively flat ITE patterns, with notable positive Pb and negative P anomalies. Isotopic (143Nd/144Nd = 0.51274-0.51285, 87Sr/86Sr = 0.7049-0.7050) and trace element signatures (Ce/Pb = 16-22, Ba/Nb = 9-14, and La/Nb = 0.9-1.0) are consistent with melting of a sub-lithospheric source that has been slightly contaminated by continental crust during ascent and emplacement. The Pb isotopic ratios (206Pb/204Pb = 18.53-18.62, 207Pb/204Pb = 15.59-15.64, and 208Pb/204Pb = 38.80-39.00) in the Egyptian basalts are close to the range of those found in the 30 Ma Ethiopian flood basalts, which are distinct from the more highly radiogenic, high-μ type signature seen in basalts from Turkana, Darfur, and Hoggar. However, measured 207Pb/204Pb and 87Sr/86Sr values are higher than those observed in the Ethiopian flood basalts (Pik et al., 1999) and suites from the Red Sea and Gulf of Aden (Schilling et al., 1992; Volker and McCulloch, 1993; Volker et al., 1997), consistent with trace element evidence of crustal contamination. We aim to develop a broad framework for understanding tectono-magmatic activity throughout northern Africa since the Miocene. The NE Egyptian basalts show evidence of both lithospheric and sublithospheric contributions and represent a time period that is critical to ongoing debate surrounding the relationship between shallow magmatism, crustal extension, and deep mantle processes exemplified by the features within and beneath the African Plate. A plausible model for the widespread volcanism during the early Miocene is that each local magmatic event was related to small scale convection rising above a plume or plumes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T54B..06C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T54B..06C"><span>Thinning Mechanism of the South China Sea Crust: New Insight from the Deep Crustal Images</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chang, S. P.; Pubellier, M. F.; Delescluse, M.; Qiu, Y.; Liang, Y.; Chamot-Rooke, N. R. A.; Nie, X.; Wang, J.</p> <p>2017-12-01</p> <p>The passive margin in the South China Sea (SCS) has experienced a long-lived extension period from Paleocene to late Miocene, as well as an extreme stretching which implies an unusual fault system to accommodate the whole amount of extension. Previous interpretations of the fault system need to be revised to explain the amount of strain. We study a long multichannel seismic profile crossing the whole rifted margin in the southwest of SCS, using 6 km- and 8 km-long streamers. After de-multiple processing by SRME, Radon and F-K filtering, an enhanced image of the crustal geometry, especially on the deep crust, allows us to illustrate two levels of detachment at depth. The deeper detachment is around 7-8 sec TWT in the profile. The faults rooting at this detachment are characterized by large offset and are responsible for thicker synrift sediment. A few of these faults appear to reach the Moho. The geometry of the acoustic basement between these boundary faults suggests gentle tilting with a long wavelength ( 200km), and implies some internal deformation. The shallower detachment is located around 4-5 sec TWT. The faults rooting at this detachment represent smaller offset, a shorter wavelength of the basement and thinner packages of synrift sediment. Two detachments separate the crust into upper, middle and lower crust. If the lower crust shows ductile behavior, the upper and middle crust is mostly brittle and form large wavelength boudinage structure, and the internal deformation of the boudins might imply low friction detachments at shallower levels. The faults rooting to deep detachment have activated during the whole rifting period until the breakup. Within the upper and middle crust, the faults resulted in important tilting of the basement at shallow depth, and connect to the deep detachment at some places. The crustal geometry illustrates how the two detachments are important for the thinning process, and also constitute a pathway for the following magmatic activity from the mantle to the surface.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tecto..36.3254S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tecto..36.3254S"><span>Transfer of Metasupracrustal Rocks to Midcrustal Depths in the North Cascades Continental Magmatic Arc, Skagit Gneiss Complex, Washington</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sauer, K. B.; Gordon, S. M.; Miller, R. B.; Vervoort, J. D.; Fisher, C. M.</p> <p>2017-12-01</p> <p>The metasupracrustal units within the north central Chelan block of the North Cascades Range, Washington, are investigated to determine mechanisms and timescales of supracrustal rock incorporation into the deep crust of continental magmatic arcs. Zircon U-Pb and Hf-isotope analyses were used to characterize the protoliths of metasedimentary and metaigneous rocks from the Skagit Gneiss Complex, metasupracrustal rocks from the Cascade River Schist, and metavolcanic rocks from the Napeequa Schist. Skagit Gneiss Complex metasedimentary rocks have (1) a wide range of zircon U-Pb dates from Proterozoic to latest Cretaceous and (2) a more limited range of dates, from Late Triassic to latest Cretaceous, and a lack of Proterozoic dates. Two samples from the Cascade River Schist are characterized by Late Cretaceous protoliths. Amphibolites from the Napeequa Schist have Late Triassic protoliths. Similarities between the Skagit Gneiss metasediments and accretionary wedge and forearc sediments in northwestern Washington and Southern California indicate that the protolith for these units was likely deposited in a forearc basin and/or accretionary wedge in the Early to Late Cretaceous (circa 134-79 Ma). Sediment was likely underthrust into the active arc by circa 74-65 Ma, as soon as 7 Ma after deposition, and intruded by voluminous magmas. The incorporation of metasupracrustal units aligns with the timing of major arc magmatism in the North Cascades (circa 79-60 Ma) and may indicate a link between the burial of sediments and pluton emplacement.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JVGR..341..193B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JVGR..341..193B"><span>Investigating the deepest part of a volcano plumbing system: Evidence for an active magma path below the western flank of Piton de la Fournaise (La Réunion Island)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boudoire, G.; Liuzzo, M.; Di Muro, A.; Ferrazzini, V.; Michon, L.; Grassa, F.; Derrien, A.; Villeneuve, N.; Bourdeu, A.; Brunet, C.; Giudice, G.; Gurrieri, S.</p> <p>2017-07-01</p> <p>Peripheral diffuse degassing of CO2 from the soil occurs across the western flank of Piton de la Fournaise volcano (La Réunion Island, Indian Ocean) along a narrow zone. In this area, carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end-members. The zones with the strongest magmatic signature (highest δ13C) overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a N135° degassing lineament, with a minimum length of 11 km and 140 ± 20 m-width. Such orientation is in accordance with that of an old dyke network along the rift zone and with N120-130° and N140-155° lineaments related to the inheritance of oceanic lithosphere structures. Our findings show that this N135° lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank. Moreover, spatial distributions of recent eccentric cones indicate a well-founded possibility that future eruptions may by-pass the shallow plumbing system of the central area of the volcano, taking a lateral pathway along this structure. Our results also confirm that Piton de la Fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high-risk area on the densely populated western flank of the volcano.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70047395','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70047395"><span>Sulfur, carbon, hydrogen, and oxygen isotope geochemistry of the Idaho cobalt belt</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Johnson, Craig A.; Bookstrom, Arthur A.; Slack, John F.</p> <p>2012-01-01</p> <p>Cobalt-copper ± gold deposits of the Idaho cobalt belt, including the deposits of the Blackbird district, have been analyzed for their sulfur, carbon, hydrogen, and oxygen isotope compositions to improve the understanding of ore formation. Previous genetic hypotheses have ranged widely, linking the ores to the sedimentary or diagenetic history of the host Mesoproterozoic sedimentary rocks, to Mesoproterozoic or Cretaceous magmatism, or to metamorphic shearing. The δ34S values are nearly uniform throughout the Blackbird dis- trict, with a mean value for cobaltite (CoAsS, the main cobalt mineral) of 8.0 ± 0.4‰ (n = 19). The data suggest that (1) sulfur was derived at least partly from sedimentary sources, (2) redox reactions involving sulfur were probably unimportant for ore deposition, and (3) the sulfur was probably transported to sites of ore for- mation as H2S. Hydrogen and oxygen isotope compositions of the ore-forming fluid, which are calculated from analyses of biotite-rich wall rocks and tourmaline, do not uniquely identify the source of the fluid; plausible sources include formation waters, metamorphic waters, and mixtures of magmatic and isotopically heavy meteoric waters. The calculated compositions are a poor match for the modified seawaters that form vol- canogenic massive sulfide (VMS) deposits. Carbon and oxygen isotope compositions of siderite, a mineral that is widespread, although sparse, at Blackbird, suggest formation from mixtures of sedimentary organic carbon and magmatic-metamorphic carbon. The isotopic compositions of calcite in alkaline dike rocks of uncertain age are consistent with a magmatic origin. Several lines of evidence suggest that siderite postdated the emplacement of cobalt and copper, so its significance for the ore-forming event is uncertain. From the stable isotope perspective, the mineral deposits of the Idaho cobalt belt contrast with typical VMS and sedimentary exhalative deposits. They show characteristics of deposit types that form in deeper environments and could be related to metamorphic processes or magmatic processes, although the isotopic evidence for magmatic components is relatively weak.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.6730H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.6730H"><span>Lunar Geoscience: Key Questions for Future Lunar Exploration</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Head, James</p> <p>2014-05-01</p> <p>Lunar Geoscience: Key Questions for Future Lunar Exploration James W. Head, Department of Geological Sciences, Brown University, Providence, RI 02912 USA. (Invited paper/solicited talk for EGU 2014 PS2.3 Lunar session, Bernard H. Foing, Convener EGU PS2.3) The last several decades of intensive robotic exploration of the Moon has built on early Apollo and Luna exploration to provide fundamental knowledge of Earth's satellite and an excellent perspective on the most well-documented planetary body other than Earth. This new planetological perspective has raised substantial new questions about the nature of the origin of the Moon, its early differentiation and bombardment history, its internal thermal evolution, the production of its secondary crust as exemplified by the lunar maria, and tertiary crust as potentially seen in steep-sided domes and impact melt differentiates, the abundance of interior volatiles and their role in volcanic eruptions, and the abundance of surface volatiles and their concentration in polar regions. On the basis of this new information, a series of specific outstanding geoscience questions can be identified that can serve as guides for future human and robotic exploration. These include: 1) What is the nature and abundance of impact melt seas and what rock types do they produce upon differentiation and solidification? 2) Where are lunar mantle samples located on the lunar surface and what processes are responsible for placing them there? 3) What processes are responsible for producing the silica-rich viscous domes, such as those seen at Gruithuisen? 4) What are the volatile species involved in the emplacement of lunar pyroclastic deposits and what clues do they provide about deep magmatic volatiles and shallow volatile formation processes? 5) How do we account for the differing characteristics of regional dark mantling pyroclastic deposits? 6) When did mare basalt volcanism begin (earliest cryptmaria) and how and where is it manifested? 7) Was there extensive volcanism and resurfacing prior to mare basalt volcanism; if so, what is its origin and how is it manifested? 8) Are there other shallow magmatic intrusions besides floor-fractured craters, and if so, what is their origin? 9) What clues can we derive from the geology and gravity structure of floor-fractured craters concerning the modes of emplacement and magmatic evolution of shallow intrusions; does differentiation and volatile build-up take place? 10) What are the factors that explain the formation of complex craters, peak-ring basins and multi-ring basins? 11) What are the ages of key multi-ring basin impact melt sheets and how do they help to determine lunar impact chronology and flux? 12) How can lunar crustal density and thickness structure revealed by GRAIL be related to geological impact, magmatic and tectonic processes? 13) What is the origin, distribution and mode of emplacement of polar and circum-polar volatile deposits? 14) What is the origin of central peaks and their often unusual mineralogy and how do we account for the evidence for heterogeneous melt composition and structure? These and other major geoscience questions form the basis for robust and exciting future international robotic and human exploration and sample return missions. A series of candidate sites of interest are identified that can address these questions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.V23D0662M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.V23D0662M"><span>Tracking Down Batholith Construction Through Time Using Lobes From The Tuolumne Batholith, Sierra Nevada, CA.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Memeti, V.; Paterson, S. R.</p> <p>2006-12-01</p> <p>Data gained using various geologic tools from large, composite batholiths, such as the 95-85 Ma old Tuolumne Batholith (TB), Sierra Nevada, CA, indicate complex batholithic processes at the chamber construction site, in part since they record different increments of batholith construction through time. Large structural and compositional complexity generally occurs throughout the main batholith such as (1) geochemistry, (2) internal contacts between different units (Bateman, 1992; Zak &Paterson, 2005), (3) batholith/host rock contacts, (4) geochronology (Coleman et al., 2004; Matzel et al., 2005, 2006), and (5) internal structures such as schlieren layering and fabrics (Bateman, 1992; Zak et al., 2006) leading to controversies regarding batholith construction models. By using magmatic lobes tongues of individual batholithic units that extend into the host rock away from the main batholith we avoid some of the complexity that evolved over longer times within the main batholith. Magmatic lobes are "simpler" systems, because they are spatially separated from other units of the batholith and thus ideally represent processes in just one unit at the time of emplacement. Furthermore, they are shorter lived than the main batholith since they are surrounded by relatively cold host rock and "freeze in" (1) "snapshots" of batholith construction, and (2) relatively short-lived internal processes and resulting structures and composition in each individual unit. Thus, data from lobes of all batholith units representing different stages of a batholith's lifetime, help us to understand internal magmatic and external host rock processes during batholith construction. Based on field and analytic data from magmatic lobes of the Kuna Crest, Half Dome, and the Cathedral Peak granodiorites, we conclude that (1) the significance of internal processes in the lobes (fractionation versus mixing versus source heterogeneity) is unique for each individual TB unit; (2) emplacement mechanisms such as stoping, downward flow or ductile deformation of host rock act in a very short period of time (only a few 100,000 yrs); and (3) a variety of different magmatic fabrics, formed by strain caused by magma flow, marginal effects, or regional stress, can be found in each lobe. These data lead to the conclusion that the size of the studied lobes indicate the minimum pulse size for TB construction and that fractionation crystallization, even though slightly varying in its magnitude, is an important internal process in each individual TB unit.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4284643','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4284643"><span>Partial melting of deeply subducted eclogite from the Sulu orogen in China</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wang, Lu; Kusky, Timothy M.; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin</p> <p>2014-01-01</p> <p>We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. PMID:25517619</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70028108','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70028108"><span>Headward growth of chasmata by volatile outbursts, collapse, and drainage: Evidence from ganges chaos, Mars</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Rodriguez, J.A.P.; Kargel, J.; Crown, D.A.; Bleamaster, L. F.; Tanaka, K.L.; Baker, V.; Miyamoto, H.; Dohm, J.M.; Sasaki, S.; Komatsu, G.</p> <p>2006-01-01</p> <p>The nature and significance of collapse processes in Capri, Eos, and Ganges Chasmata remain poorly understood. Using Ganges Chasma as a type locality, these chasmata are interpreted to be the result of clustering and assimilation of multiple chaotic terrains, which primarily formed by localized depressurization-induced or thermally-triggered dissociation of buried gas clathrate hydrates and explosive eruption of gas-saturated ground water. Such crustal destabilization could have been triggered by (1) deep fracture propagation from the Martian surface, (2) magmatic intrusions and associated heating and inflation-induced terrain fracturing, and/or (3) climatic thaw and thinning/weakening of the permafrost over the clathrate and gas-rich groundwater zones. Volume increases associated with release of gases contributed to the xpulsion of groundwater and fluidized sediments at the surface, thereby carving the higher outflow channels peripheral to the chasmata and the lower outflow channel floors of the chasmata and outflow channels. Copyright 2006 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70012947','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70012947"><span>YELLOWSTONE MAGMATIC-HYDROTHERMAL SYSTEM, U. S. A.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Fournier, R.O.; Pitt, A.M.; ,</p> <p>1985-01-01</p> <p>At Yellowstone National Park, the deep permeability and fluid circulation are probably controlled and maintained by repeated brittle fracture of rocks in response to local and regional stress. Focal depths of earthquakes beneath the Yellowstone caldera suggest that the transition from brittle fracture to quasi-plastic flow takes place at about 3 to 4 km. The maximum temperature likely to be attained by the hydrothermal system is 350 to 450 degree C, the convective thermal output is about 5. 5 multiplied by 10**9 watts, and the minimum average thermal flux is about 1800 mW/m**2 throughout 2,500 km**2. The average thermal gradient between the heat source and the convecting hydrothermal system must be at least 700 to 1000 degree C/km. Crystallization and partial cooling of about 0. 082 km**3 of basalt or 0. 10 km**3 of rhyolite annually could furnish the heat discharged in the hot-spring system. The Yellowstone magmatic-hydrothermal system as a whole appears to be cooling down, in spite of a relatively large rate of inflation of the Yellowstone caldera.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PApGe.175.1889M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PApGe.175.1889M"><span>Contemporary State of the Elbrus Volcanic Center (The Northern Caucasus)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Milyukov, Vadim; Rogozhin, Eugeny; Gorbatikov, Andrey; Mironov, Alexey; Myasnikov, Andrey; Stepanova, Marina</p> <p>2018-05-01</p> <p>The Elbrus volcanic center is located in southern Russia on the northern slope of the main ridge of the Greater Caucasus. Current classifications define Elbrus as a dormant volcano that could become active even after millennia of quiescence. In this study, we use two new geophysical methods to assess the contemporary state of the Elbrus volcano. The first method is based on an evaluation of parameters of resonant modes "reemitted" by the resonant structure (i.e., volcanic chamber) in response to the excitation of a seismic impact and recorded by a precise laser interferometer-strainmeter. The second method is based on low-frequency microseismic sounding and allows determination of the deep structure of complicated geological objects. Our study locates the magma chamber at depths of 1-8 km and extended magma source at depths of 15-40 km beneath the Elbrus eastern summit. An unknown magmatic structure, comparable to the Elbrus magmatic structure but currently much colder, was also identified 50 km from Mt. Elbrus. Based on our analysis, we assess the Elbrus volcano to be currently in a quasi-stable state of thermodynamic equilibrium.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.S21C0727R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.S21C0727R"><span>Evolution of deep crustal magma structures beneath Mount Baekdu volcano (MBV) intraplate volcano in northeast Asia</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rhie, J.; Kim, S.; Tkalcic, H.; Baag, S. Y.</p> <p>2017-12-01</p> <p>Heterogeneous features of magmatic structures beneath intraplate volcanoes are attributed to interactions between the ascending magma and lithospheric structures. Here, we investigate the evolution of crustal magmatic stuructures beneath Mount Baekdu volcano (MBV), which is one of the largest continental intraplate volcanoes in northeast Asia. The result of our seismic imaging shows that the deeper Moho depth ( 40 km) and relatively higher shear wave velocities (>3.8 km/s) at middle-to-lower crustal depths beneath the volcano. In addition, the pattern at the bottom of our model shows that the lithosphere beneath the MBV is shallower (< 100 km) compared to surrounding regions. Togather with previous P-wave velocity models, we interpret the observations as a compositional double layering of mafic underplating and a overlying cooled felsic structure due to fractional crystallization of asthenosphere origin magma. To achieve enhanced vertical and horizontal model coverage, we apply two approaches in this work, including (1) a grid-search based phase velocity measurement using real-coherency of ambient noise data and (2) a transdimensional Bayesian joint inversion using multiple ambient noise dispersion data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GGG....19..471C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GGG....19..471C"><span>Space-Time Evolution of Magma Storage and Transfer at Mt. Etna Volcano (Italy): The 2015-2016 Reawakening of Voragine Crater</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cannata, Andrea; Di Grazia, Giuseppe; Giuffrida, Marisa; Gresta, Stefano; Palano, Mimmo; Sciotto, Mariangela; Viccaro, Marco; Zuccarello, Francesco</p> <p>2018-02-01</p> <p>The eruptions of December 2015 and May 2016 at Voragine crater were among the most explosive recorded during the last two decades at Mt. Etna volcano. Here we present data coming from geophysics (infrasound, LP, VLP, volcanic tremor, VT earthquakes, and ground deformations) and petrology (textural and microanalytical data on plagioclase and olivine crystals) to investigate the preeruptive magma storage and transfer dynamics leading to these exceptional explosive eruptions. Integration of all the available data has led us to constrain chemically, physically, and kinetically the environments where magmas were stored before the eruption, and how they have interacted during the transfer en-route to the surface. Although the evolution and behavior of volcanic phenomena at the surface was rather similar, some differences in storage and transfer dynamics were observed for 2015 and 2016 eruptions. Specifically, the 2015 eruptions have been fed by magmas stored at shallow levels that were pushed upward as a response of magma injections from deeper environments, whereas evidence of chemical interaction between shallow and deep magmatic environments becomes more prominent during the 2016 eruptions. Main findings evidence the activation of magmatic environments deeper than those generally observed for other recent Etnean eruptions, with involvement of deep basic magmas that were brought to shallow crustal levels in very short time scales (˜1 month). The fast transfer from the deepest levels of the plumbing system of basic, undegassed magmas might be viewed as the crucial triggering factor leading to development of exceptionally violent volcanic phenomena even with only basic magma involved.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004EOSTr..85..317M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004EOSTr..85..317M"><span>Prototype PBO Instrumentation of CALIPSO Project Captures World-Record Lava Dome Collapse on Montserrat Volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mattioli, Glen S.; Young, Simon R.; Voight, Barry; Sparks, R. Steven J.; Shalev, Eylon; Selwyn, Sacks; Malin, Peter; Linde, Alan; Johnston, William; Hadayat, Dannie; Elsworth, Derek; Dunkley, Peter; Herd, Richard; Neuberg, Jurgen; Norton, Gillian; Widiwijayanti, Christina</p> <p>2004-08-01</p> <p>This article is an update on the status of an innovative new project designed to enhance generally our understanding of andesitic volcano eruption dynamics and, specifically, the monitoring and scientific infrastructure at the active Soufriàre Hills Volcano (SHV), Montserrat. The project has been designated as the Caribbean Andesite Lava Island Precision Seismo-geodetic Observatory, known as CALIPSO. Its purpose is to investigate the dynamics of the entire SHV magmatic system using an integrated array of specialized instruments in four strategically located ~200-m-deep boreholes in concert with several shallower holes and surface sites. The project is unique, as it represents the first, and only, such borehole volcano-monitoring array deployed at an andesitic stratovolcano. CALIPSO may be considered as a prototype for planned Plate Boundary Observatory (PBO) installations at several volcanic targets in the western United States. Scientific objectives of the EarthScope Integrated Science Plan (ES-ISP) relevant to magmatic systems are to investigate (1) melt generation in the mantle; (2) melt migration from the mantle to and through the crust to the surface; (3) melt residence times at various deep reservoirs; and (4) delineation of characteristic patterns of surface deformation and seismicity, which may prove useful in eruption forecasting. The CALIPSO project shares most of the same scientific goals and has, moreover, the benefit of a rich existing geophysical context in its deployment at SHV. Our experience during instrument design, planning, drilling and installation, systems integration, and early operation of CALIPSO, moreover, may prove valuable to EarthScope and PBO managers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29765056','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29765056"><span>Anatomy of a fumarolic system inferred from a multiphysics approach.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gresse, Marceau; Vandemeulebrouck, Jean; Byrdina, Svetlana; Chiodini, Giovanni; Roux, Philippe; Rinaldi, Antonio Pio; Wathelet, Marc; Ricci, Tullio; Letort, Jean; Petrillo, Zaccaria; Tuccimei, Paola; Lucchetti, Carlo; Sciarra, Alessandra</p> <p>2018-05-15</p> <p>Fumaroles are a common manifestation of volcanic activity that are associated with large emissions of gases into the atmosphere. These gases originate from the magma, and they can provide indirect and unique insights into magmatic processes. Therefore, they are extensively used to monitor and forecast eruptive activity. During their ascent, the magmatic gases interact with the rock and hydrothermal fluids, which modify their geochemical compositions. These interactions can complicate our understanding of the real volcanic dynamics and remain poorly considered. Here, we present the first complete imagery of a fumarolic plumbing system using three-dimensional electrical resistivity tomography and new acoustic noise localization. We delineate a gas reservoir that feeds the fumaroles through distinct channels. Based on this geometry, a thermodynamic model reveals that near-surface mixing between gas and condensed steam explains the distinct geochemical compositions of fumaroles that originate from the same source. Such modeling of fluid interactions will allow for the simulation of dynamic processes of magmatic degassing, which is crucial to the monitoring of volcanic unrest.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.266...64A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.266...64A"><span>Archean crustal evolution in the Southern São Francisco craton, Brazil: Constraints from U-Pb, Lu-Hf and O isotope analyses</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Albert, Capucine; Farina, Federico; Lana, Cristiano; Stevens, Gary; Storey, Craig; Gerdes, Axel; Dopico, Carmen Martínez</p> <p>2016-12-01</p> <p>In this study we present U-Pb and Hf isotope data combined with O isotopes in zircon from Neoarchean granitoids and gneisses of the southern São Francisco craton in Brazil. The basement rocks record three distinct magmatic events: Rio das Velhas I (2920-2850 Ma), Rio das Velhas II (2800-2760 Ma) and Mamona (2750-2680 Ma). The three sampled metamorphic complexes (Bação, Bonfim and Belo Horizonte) have distinct εHf vs. time arrays, indicating that they grew as separate terranes. Paleoarchean crust is identified as a source which has been incorporated into younger magmatic rocks via melting and mixing with younger juvenile material, assimilation and/or source contamination processes. The continental crust in the southern São Francisco craton underwent a change in magmatic composition from medium- to high-K granitoids in the latest stages, indicating a progressive HFSE enrichment of the sources that underwent anatexis in the different stages and possibly shallowing of the melting depth. Oxygen isotope data shows a secular trend towards high δ18O (up to 7.79‰) indicating the involvement of metasediments in the petrogenesis of the high potassium granitoids during the Mamona event. In addition, low δ18O values (down to 2.50‰) throughout the Meso- and Neoarchean emphasize the importance of meteoritic fluids in intra-crustal magmatism. We used hafnium isotope modelling from a compilation of detrital zircon compositions to constrain crustal growth rates and geodynamics from 3.50 to 2.65 Ga. The modelling points to a change in geodynamic process in the southern São Francisco craton at 2.9 Ga, from a regime dominated by net crustal growth in the Paleoarchean to a Neoarchean regime marked by crustal reworking. The reworking processes account for the wide variety of granitoid magmatism and are attributed to the onset of continental collision.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70025117','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025117"><span>Groundwater flow, heat transport, and water table position within volcanic edifices: Implications for volcanic processes in the Cascade Range</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hurwitz, S.; Kipp, K.L.; Ingebritsen, S.E.; Reid, M.E.</p> <p>2003-01-01</p> <p>The position of the water table within a volcanic edifice has significant implications for volcano hazards, geothermal energy, and epithermal mineralization. We have modified the HYDROTHERM numerical simulator to allow for a free-surface (water table) upper boundary condition and a wide range of recharge rates, heat input rates, and thermodynamic conditions representative of continental volcano-hydrothermal systems. An extensive set of simulations was performed on a hypothetical stratovolcano system with unconfined groundwater flow. Simulation results suggest that the permeability structure of the volcanic edifice and underlying material is the dominant control on water table elevation and the distribution of pressures, temperatures, and fluid phases at depth. When permeabilities are isotropic, water table elevation decreases with increasing heat flux and increases with increasing recharge, but when permeabilities are anisotropic, these effects can be much less pronounced. Several conditions facilitate the ascent of a hydrothermal plume into a volcanic edifice: a sufficient source of heat and magmatic volatiles at depth, strong buoyancy forces, and a relatively weak topography-driven flow system. Further, the plume must be connected to a deep heat source through a pathway with a time-averaged effective permeability ???1 ?? 10-16 m2, which may be maintained by frequent seismicity. Topography-driven flow may be retarded by low permeability in the edifice and/or the lack of precipitation recharge; in the latter case, the water table may be relatively deep. Simulation results were compared with observations from the Quaternary stratovolcanoes along the Cascade Range of the western United States to infer hydrothermal processes within the edifices. Extensive ice caps on many Cascade Range stratovolcanoes may restrict recharge on the summits and uppermost flanks. Both the simulation results and limited observational data allow for the possibility that the water table beneath the stratovolcanoes is relatively deep.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAESc.135..212Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAESc.135..212Z"><span>Late Jurassic-Early Cretaceous episodic development of the Bangong Meso-Tethyan subduction: Evidence from elemental and Sr-Nd isotopic geochemistry of arc magmatic rocks, Gaize region, central Tibet, China</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Yu-Xiu; Li, Zhi-Wu; Yang, Wen-Guang; Zhu, Li-Dong; Jin, Xin; Zhou, Xiao-Yao; Tao, Gang; Zhang, Kai-Jun</p> <p>2017-03-01</p> <p>The Bangong Meso-Tethys plays a critical role in the development of the Tethyan realm and the initial elevation of the Tibetan Plateau. However, its precise subduction polarity, and history still remain unclear. In this study, we synthesize a report for the Late Jurassic-Early Cretaceous two-phase magmatic rocks in the Gaize region at the southern margin of the Qiangtang block located in central Tibet. These rocks formed during the Late Jurassic-earliest Cretaceous (161-142 Ma) and Early Cretaceous (128-106 Ma), peaking at 146 Ma and 118 Ma, respectively. The presence of inherited zircons indicates that an Archean component exists in sediments in the shallow Qiangtang crust, and has a complex tectonomagmatic history. Geochemical and Sr-Nd isotopic data show that the two-phase magmatic rocks exhibit characteristics of arc magmatism, which are rich in large-ion incompatible elements (LIIEs), but are strongly depleted in high field strength elements (HFSEs). The Late Jurassic-earliest Cretaceous magmatic rocks mixed and mingled among mantle-derived mafic magmas, subduction-related sediments, or crustally-derived felsic melts and fluids, formed by a northward and steep subduction of the Bangong Meso-Tethys ocean crust. The magmatic gap at 142-128 Ma marks a flat subduction of the Meso-Tethys. The Early Cretaceous magmatism experienced a magma MASH (melting, assimilation, storage, and homogenization) process among mantle-derived mafic magmas, or crustally-derived felsic melts and fluids, as a result of the Meso-Tethys oceanic slab roll-back, which triggered simultaneous back-arc rifting along the southern Qiangtang block margin.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.260..457M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.260..457M"><span>The Grizzly Lake complex (Yellowstone Volcano, USA): Mixing between basalt and rhyolite unraveled by microanalysis and X-ray microtomography</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morgavi, Daniele; Arzilli, Fabio; Pritchard, Chad; Perugini, Diego; Mancini, Lucia; Larson, Peter; Dingwell, Donald B.</p> <p>2016-09-01</p> <p>Magma mixing is a widespread petrogenetic process. It has long been suspected to operate in concert with fractional crystallization and assimilation to produce chemical and temperature gradients in magmas. In particular, the injection of mafic magmas into felsic magma chambers is widely regarded as a key driver in the sudden triggering of what often become highly explosive volcanic eruptions. Understanding the mechanistic event chain leading to such hazardous events is a scientific goal of high priority. Here we investigate a mingling event via the evidence preserved in mingled lavas using a combination of X-ray computed microtomographic and electron microprobe analyses, to unravel the complex textures and attendant chemical heterogeneities of the mixed basaltic and rhyolitic eruption of Grizzly Lake in the Norris-Mammoth corridor of the Yellowstone Plateau volcanic field (YVF). We observe evidence that both magmatic viscous inter-fingering of magmas and disequilibrium crystallization/dissolution processes occur. Furthermore, these processes constrain the timescale of interaction between the two magmatic components prior to their eruption. X-ray microtomography images show variegated textural features, involving vesicle and crystal distributions, filament morphology, the distribution of enclaves, and further textural features otherwise obscured in conventional 2D observations and analyses. Although our central effort was applied to the determination of mixing end members, analysis of the hybrid portion has led to the discovery that mixing in the Grizzly Lake system was also characterized by the disintegration and dissolution of mafic crystals in the rhyolitic magma. The presence of mineral phases in both end member, for example, forsteritic olivine, sanidine, and quartz and their transport throughout the magmatic mass, by a combination of both mixing dynamics and flow imposed by ascent of the magmatic mass and its eruption, might have acted as a "geometric perturbation" of flow fields further fuelling mass exchange between magmas in terms of both chemical diffusion and crystal transfer. These results illuminate the complexity of mixing in natural magmatic systems, identifying several reaction-related textural factors that must be understood more deeply in order to advance our understanding of this igneous process.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..324..156L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..324..156L"><span>Evidence of recent deep magmatic activity at Cerro Bravo-Cerro Machín volcanic complex, central Colombia. Implications for future volcanic activity at Nevado del Ruiz, Cerro Machín and other volcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Londono, John Makario</p> <p>2016-09-01</p> <p>In the last nine years (2007-2015), the Cerro Bravo-Cerro Machín volcanic complex (CBCMVC), located in central Colombia, has experienced many changes in volcanic activity. In particular at Nevado del Ruiz volcano (NRV), Cerro Machin volcano (CMV) and Cerro Bravo (CBV) volcano. The recent activity of NRV, as well as increasing seismic activity at other volcanic centers of the CBCMVC, were preceded by notable changes in various geophysical and geochemical parameters, that suggests renewed magmatic activity is occurring at the volcanic complex. The onset of this activity started with seismicity located west of the volcanic complex, followed by seismicity at CBV and CMV. Later in 2010, strong seismicity was observed at NRV, with two small eruptions in 2012. After that, seismicity has been observed intermittently at other volcanic centers such as Santa Isabel, Cerro España, Paramillo de Santa Rosa, Quindío and Tolima volcanoes, which persists until today. Local deformation was observed from 2007 at NRV, followed by possible regional deformation at various volcanic centers between 2011 and 2013. In 2008, an increase in CO2 and Radon in soil was observed at CBV, followed by a change in helium isotopes at CMV between 2009 and 2011. Moreover, SO2 showed an increase from 2010 at NRV, with values remaining high until the present. These observations suggest that renewed magmatic activity is currently occurring at CBCMVC. NRV shows changes in its activity that may be related to this new magmatic activity. NRV is currently exhibiting the most activity of any volcano in the CBCMVC, which may be due to it being the only open volcanic system at this time. This suggests that over the coming years, there is a high probability of new unrest or an increase in volcanic activity of other volcanoes of the CBCMVC.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70036597','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70036597"><span>Processes active in mafic magma chambers: The example of Kilauea Iki Lava Lake, Hawaii</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Helz, R.T.</p> <p>2009-01-01</p> <p>Kilauea Iki lava lake formed in 1959 as a closed chamber of 40??million m3 of picritic magma. Repeated drilling and sampling of the lake allows recognition of processes of magmatic differentiation, and places time restrictions on the periods when they operated. This paper focuses on evidence for the occurrence of lateral convection in the olivine-depleted layer, and constraints on the timing of this process, as documented by chemical, petrographic and thermal data on drill core from the lake. Lateral convection appears to have occurred in two distinct layers within the most olivine-poor part of the lake, created a slightly olivine-enriched septum in the center of the olivine-depleted section. A critical marker for this process is the occurrence of loose clusters of augite microphenocrysts, which are confined to the upper half of the olivine-poor zone. This process, which took place between late 1962 and mid-1964, is inferred to be double-diffusive convection. Both this convection and a process of buoyant upwelling of minimum-density liquid from deep within the lake (Helz, R.T., Kirschenbaum H. and Marinenko, J.W., 1989. Diapiric melt transfer: a quick, efficient process of igneous differentiation: Geological Society of America Bulletin, v. 101, 578-594) result from the fact that melt density in Kilauea Iki compositions decreases as olivine and augite crystallize, above the incoming of plagioclase. The resulting density vs. depth profile creates (1) a region of gravitationally stable melt at the top of the chamber (the locus of double-diffusive convection) and (2) a region of gravitationally unstable melt at the base of the melt column (the source of upwelling minimum-density melt, Helz, R.T., Kirschenbaum H. and Marinenko, J.W., 1989. Diapiric melt transfer: a quick, efficient process of igneous differentiation: Geological Society of America Bulletin, v. 101, 578-594). By contrast the variation of melt density with temperature for the 1965 Makaopuhi lava lake does not show a decrease in density as temperature decreases, so neither process should have occurred in that lava lake. Because many mafic magmas crystallize significant olivine and/or pyroxene before they begin to crystallize plagioclase, the density relations observed for Kilauea Iki, and the processes that result from them, may be relevant to crystallization in other mafic magma chambers. The results for the 1965 Makaopuhi lava lake emphasize the role of bulk composition as a critical control on magmatic processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004Litho..72..147A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004Litho..72..147A"><span>Magmatic anhydrite and calcite in the ore-forming quartz-monzodiorite magma at Santa Rita, New Mexico (USA): genetic constraints on porphyry-Cu mineralization</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Audétat, A.; Pettke, T.; Dolejš, D.</p> <p>2004-02-01</p> <p>A quartz-monzodioritic dike associated with the porphyry-Cu mineralized stock at Santa Rita, NM, has been studied to constrain physico-chemical factors ( P, T, fO 2, and volatile content) responsible for mineralization. The dike contains a low-variance mineral assemblage of amphibole, plagioclase (An 30-50), quartz, biotite, sphene, magnetite, and apatite, plus anhydrite and calcite preserved as primary inclusions within the major phenocryst phases. Petrographic relationships demonstrate that anhydrite originally was abundant in the form of phenocrysts (1-2 vol.%), but later was replaced by either quartz or calcite. Hornblende-plagioclase thermobarometry suggests that several magmas were involved in the formation of the quartz-monzodiorite, with one magma having ascended directly from ≥14 km depth. Rapid magma ascent is supported by the presence of intact calcite inclusions within quartz phenocrysts. The assemblage quartz+sphene+magnetite+Mg-rich amphibole in the quartz-monzodiorite constrains magmatic oxygen fugacity at log fO 2>NNO+1, in agreement with the presence of magmatic anhydrite and a lack of magmatic sulfides. The same reasoning generally applies for rocks hosting porphyry-Cu deposits, seemingly speaking against a major role of magmatic sulfides in the formation of such mineralizations. There is increasing evidence, however, that magmatic sulfides play an important role in earlier stages of porphyry-Cu evolution, the record of which is often obliterated by later processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T23D2432G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T23D2432G"><span>Oceanic-type accretion may begin before complete continental break-up</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Geoffroy, L.; Zalan, P. V.; Viana, A. R.</p> <p>2011-12-01</p> <p>Oceanic accretion is thought to be the process of oceanic crust (and lithosphere) edification through adiabatic melting of shallow convecting mantle at oceanic spreading ridges. It is usually considered as a post-breakup diagnostic process following continents rupturing. However, this is not always correct. The structure of volcanic passive margins (representing more than 50% of passive continental margins) outlines that the continental lithosphere is progressively changed into oceanic-type lithosphere during the stage of continental extension. This is clear at least, at crustal level. The continental crust is 'changed' from the earliest stages of extension into a typical -however thicker- oceanic crust with the typical oceanic magmatic layers (from top to bottom: lava flows/tuffs, sheeted dyke complexes, dominantly (sill-like) mafic intrusions in the lower crust). The Q-rich continental crust is highly extended and increases in volume (due to the magma) during the extensional process. At the continent-ocean transition there is, finally, no seismic difference between this highly transformed continental crust and the oceanic crust. Using a large range of data (including deep seismic reflection profiles), we discuss the mantle mechanisms that governs the process of mantle-assisted continental extension. We outline the large similarity between those mantle processes and those acting at purely-oceanic spreading axis and discuss the effects of the inherited continental lithosphere in the pattern of new mafic crust edification.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70015635','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70015635"><span>Fluid inclusion gas chemistry as a potential minerals exploration tool: Case studies from Creede, CO, Jerritt Canyon, NV, Coeur d'Alene district, ID and MT, southern Alaska mesothermal veins, and mid-continent MVT's</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Landis, G.P.; Hofstra, A.H.</p> <p>1991-01-01</p> <p>Recent advances in instrumentation now permit quantitative analysis of gas species from individual fluid inclusions. Fluid inclusion gas data can be applied to minerals exploration empirically to establish chemical (gas composition) signatures of the ore fluids, and conceptually through the development of genetic models of ore formation from a framework of integrated geologic, geochemical, and isotopic investigations. Case studies of fluid inclusion gas chemistry from ore deposits representing a spectrum of ore-forming processes and environments are presented to illustrate both the empirical and conceptual approaches. We consider epithermal silver-gold deposits of Creede, Colorado, Carlin-type sediment-hosted disseminated gold deposits of Jerritt Canyon, Nevada, metamorphic silver-base-metal veins of the Coeur d'Alene district, Idaho and Montana, gold-quartz veins in accreted terranes of southern Alaska, and the mid-continent base-metal sulfide deposits of Mississippi Valley-Type (MVT's). Variations in gas chemistry determine the redox state of the ore fluids, provide compositional input for gas geothermometers, characterize ore fluid chemistry (e.g., CH4CO2, H2SSO2, CO2/H2S, organic-rich fluids, gas-rich and gas-poor fluids), identify magmatic, meteoric, metamorphic, shallow and deep basin fluids in ore systems, locate upwelling plumes of magmatic-derived volatiles, zones of boiling and volatile separation, interfaces between contrasting fluids, and important zones of fluid mixing. Present techniques are immediately applicable to exploration programsas empirical studies that monitor fluid inclusion gas threshold concentration levels, presence or absence of certain gases, or changes in gas ratios. We suggest that the greater contribution of fluid inclusion gas analysis is in the integrated and comprehensive chemical dimension that gas data impart to genetic models, and in the exploration concepts based on processes and environments of ore formation derived from these genetic models. ?? 1991.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..44.8785H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.8785H"><span>Deep crustal melt plumbing of Bárðarbunga volcano, Iceland</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hudson, T. S.; White, R. S.; Greenfield, T.; Ágústsdóttir, T.; Brisbourne, A.; Green, R. G.</p> <p>2017-09-01</p> <p>Understanding magmatic plumbing within the Earth's crust is important for understanding volcanic systems and improving eruption forecasting. We discuss magma plumbing under Bárðarbunga volcano, Iceland, over a 4 year period encompassing the largest Icelandic eruption in 230 years. Microseismicity extends through the usually ductile region of the Earth's crust, from 7 to 22 km depth in a subvertical column. Moment tensor solutions for an example earthquake exhibits opening tensile crack behavior. This is consistent with the deep (>7 km) seismicity being caused by the movement of melt in the normally aseismic crust. The seismically inferred melt path from the mantle source is offset laterally from the center of the Bárðarbunga caldera by 12 km, rather than lying directly beneath it. It is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/14508480','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/14508480"><span>Bending-related faulting and mantle serpentinization at the Middle America trench.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ranero, C R; Morgan, J Phipps; McIntosh, K; Reichert, C</p> <p>2003-09-25</p> <p>The dehydration of subducting oceanic crust and upper mantle has been inferred both to promote the partial melting leading to arc magmatism and to induce intraslab intermediate-depth earthquakes, at depths of 50-300 km. Yet there is still no consensus about how slab hydration occurs or where and how much chemically bound water is stored within the crust and mantle of the incoming plate. Here we document that bending-related faulting of the incoming plate at the Middle America trench creates a pervasive tectonic fabric that cuts across the crust, penetrating deep into the mantle. Faulting is active across the entire ocean trench slope, promoting hydration of the cold crust and upper mantle surrounding these deep active faults. The along-strike length and depth of penetration of these faults are also similar to the dimensions of the rupture area of intermediate-depth earthquakes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1611479M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1611479M"><span>Breakup magmatism style on the North Atlantic Igneous Province: insight from Mid-Norwegian volcanic margin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mansour Abdelmalak, Mohamed; Faleide, Jan Inge; Planke, Sverre; Theissen-Krah, Sonja; Zastrozhnov, Dmitrii; Breivik, Asbjørn Johan; Gernigon, Laurent; Myklebust, Reidun</p> <p>2014-05-01</p> <p>The distribution of breakup-related igneous rocks on rifted margins provide important constraints on the magmatic processes during continental extension and lithosphere separation which lead to a better understanding of the melt supply from the upper mantle and the relationship between tectonic setting and volcanism. The results can lead to a better understanding of the processes forming volcanic margins and thermal evolution of associated prospective basins. We present a revised mapping of the breakup-related igneous rocks in the NE Atlantic area, which are mainly based on the Mid-Norwegian (case example) margin. We divided the breakup related igneous rocks into (1) extrusive complexes, (2) shallow intrusive complexes (sills/dykes) and (3) deep intrusive complexes (Lower Crustal Body: LCB). The extrusive complex has been mapped using the seismic volcanostratigraphic method. Several distinct volcanic seismic facies units have been identified. The top basalt reflection is easily identified because of the high impedance contrast between the sedimentary and volcanic rocks resulting in a major reflector. The basal sequence boundary is frequently difficult to identify but it lies usually over the intruded sedimentary basin. Then the base is usually picked above the shallow sill intrusions identified on seismic profile. The mapping of the top and the base of the basaltic sequences allows us to determine the basalt thickness and estimate the volume of the magma production on the Mid- Norwegian margin. The thicker part of the basalt corresponds to the seaward dipping reflector (SDR). The magma feeder system, mainly formed by dyke and sill intrusions, represents the shallow intrusive complex. Deeper interconnected high-velocity sills are also mappable in the margin. Interconnected sill complexes can define continuous magma network >10 km in vertical ascent. The large-scale sill complexes, in addition to dyke swarm intrusions, represent a mode of vertical long-range magma transport through the upper crust. The deep intrusive complex represents the Lower Crustal Body (LCB) which is observed along the margin and characterized by high P-wave velocity bodies (Vp> 7km/s). On the Vøring margin a strong amplitude dome-shaped reflection (the so-called T-Reflection) has been identified and interpreted as the top LCB. In the sedimentary part of the margin, sill intrusions are the major feeder system and seem to be connected with LCB. In the volcanic part of the margin, dykes represent the main feeder system and lie above the thicker part of the LCB.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V31D3059W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V31D3059W"><span>Along-Strike Geochemical Variations in the Late Triassic Nikolai Magmatic System, Wrangellia, Central Alaska</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wypych, A.; Twelker, E.; Lande, L. L.; Newberry, R.</p> <p>2015-12-01</p> <p>The Nikolai Basalt and related mafic to ultramafic intrusions are one of the world's most complete and best exposed sections of a large igneous province (Amphitheater Mountains, Alaska), and have been explored for magmatic Ni-Cu-Co-PGE mineralization (Wellgreen deposit in the Kluane Ranges, Yukon Territory, and Eureka zone in the Eastern Alaska Range). The full extent of the basalts and the intrusions, as well as along-strike variations in the geochemical and petrological composition and the causes for those variations has yet to be fully established. To better understand the extent and magmatic architecture of this system, the Alaska Division of Geological & Geophysical Surveys conducted mapping and geochemical investigations of the province from 2013 through 2015 field seasons. We present major and trace element data from whole rock, olivine, and chromite from samples of Triassic basalts and intrusives collected over a 250 km along-strike transect. This data is used to answer questions about variations in magma generation, temperature of crystallization, and degree of fractional crystallization required to produce the Nikolai Basalts. Using chalcophile elements, we examine the history of sulfide solubility, further adding to our understanding of the processes of magma evolution and its influence on the formation of economic mineral deposits. Our initial findings corroborate the presence of two phases of magma generation and eruption, as well as along-strike variation in composition of these phases. We propose that the major along-strike variations are due to differences in amount of cumulate olivine and other late-stage processes. This magmatic architecture has important implications for exploration for magmatic sulfide deposits of nickel-copper and strategic and critical platinum group elements (PGEs) as it can help to better understand the occurrences and point to future possible deposits within the system.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tecto..36.1861W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tecto..36.1861W"><span>Birth, life, and demise of the Andean-syn-collisional Gissar arc: Late Paleozoic tectono-magmatic-metamorphic evolution of the southwestern Tian Shan, Tajikistan</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Worthington, James R.; Kapp, Paul; Minaev, Vladislav; Chapman, James B.; Mazdab, Frank K.; Ducea, Mihai N.; Oimahmadov, Ilhomjon; Gadoev, Mustafo</p> <p>2017-10-01</p> <p>The amalgamation of the Central Asian Orogenic Belt in the southwestern Tian Shan in Tajikistan is represented by tectono-magmatic-metamorphic processes that accompanied late Paleozoic ocean closure and collision between the Karakum-Tarim and Kazakh-Kyrgyz terranes. Integrated U-Pb geochronology, thermobarometry, pseudosection modeling, and Hf geochemistry constrain the timing and petro-tectonic nature of these processes. The Gissar batholith and the Garm massif represent an eastward, along-strike increase in paleodepth from upper-batholith ( 21-7 km) to arc-root ( 36-19 km) levels of the Andean-syn-collisional Gissar arc, which developed from 323-288 Ma in two stages: (i) Andean, I-type granitoid magmatism from 323-306 Ma due to northward subduction of the Gissar back-arc ocean basin under the Gissar microcontinent, which was immediately followed by (ii) syn-collisional, I-S-type granitoid magmatism in the Gissar batholith and the Garm massif from 304-288 Ma due to northward subduction/underthrusting of Karakum marginal-continental crust under the Gissar microcontinent. A rapid isotopic pull-up from 288-286 Ma signals the onset of juvenile, alkaline-syenitic, post-collisional magmatism by 280 Ma, which was driven by delamination of the Gissar arclogite root and consequent convective asthenospheric upwelling. Whereas M-HT/LP prograde metamorphism in the Garm massif (650-750°C/6-7 kbar) from 310-288 Ma was associated with subduction-magma inundation and crustal thickening, HT/LP heating and decompression to peak-metamorphic temperatures ( 800-820°C/6-4 kbar) at 288 ± 6 Ma was driven by the transmission of a post-collisional, mantle-derived heat wave through the Garm-massif crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP13E..06G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP13E..06G"><span>Sink- or Source-driven Phanerozoic carbon cycle?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Godderis, Y.; Donnadieu, Y.; Maffre, P.; Carretier, S.</p> <p>2017-12-01</p> <p>The Phanerozoic evolution of the atmospheric CO2 level is controlled by the fluxes entering or leaving the exospheric system. Those fluxes (including continental weathering, magmatic degassing, organic carbon burial, oxidation of sedimentary organic carbon) are intertwined, and their relative importance in driving the global carbon cycle evolution may have fluctuated through time. Deciphering the causes of the Phanerozoic climate evolution thus requires a holistic and quantitative approach. Here we focus on the role played by the paleogeographic configuration on the efficiency of the CO2 sink by continental silicate weathering, and on the impact of the magmatic degassing of CO2. We use the spatially resolved numerical model GEOCLIM (geoclimmodel.worpress.com) to compute the response of the silicate weathering and atmospheric CO2 to continental drift for 22 time slices of the Phanerozoic. Regarding the CO2 released by the magmatic activity, we reconstruct several Phanerozoic histories of this flux, based on published indexes. We calculate the CO2 evolution for each degassing scenario, and accounting for the paleogeographic setting. We show that the paleogeographic setting is a main driver of the climate from 540 Ma to about the beginning of the Jurassic. Regarding the role of the magmatic degassing, the various reconstructions do not converge towards a single signal, and thus introduce large uncertainties in the calculated CO2 level over time. Nevertheless, the continental dispersion, which prevails since the Jurassic, promotes the CO2 consumption by weathering and forces atmospheric CO2 to stay low. Warm climates of the "middle" Cretaceous and early Cenozoic require enhanced CO2 degassing by magmatic activity. In summary, the Phanerozoic climate evolution can be hardly assigned to a single process, but is the result of complex and intertwined processes.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V13C0395W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V13C0395W"><span>Magmatic and Volcanic Processes Interpreted from Recent Ash Emissions from Nevado del Ruiz, Colombia</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wall, K. T.; Harpel, C. J.; Martinez, L. M.; Ceballos, J. A.; Cortés, G. P.</p> <p>2017-12-01</p> <p>Nevado del Ruiz is a composite volcano located in the Colombian Central Cordillera. It is the modern edifice of the Nevado del Ruiz Volcanic Complex that has been active since 1.8 Ma. Through historic times, Ruiz has exhibited decades-long eruptive stages that include minor explosions and fumarolic activity bracketing one major magmatic event. Modern eruptive activity began with seismic unrest in 1984, a small explosive eruption on September 11, 1985, and the catastrophic lahar-generating eruption of November 13, 1985. Since then, Ruiz has periodically erupted plumes up to a few kilometers above the crater, including a phreatomagmatic eruption on September 1, 1989, eruptions on May 29 (1 km plume) and June 30 (8 km plume) 2012, and frequent minor ash emissions from 2015 through the present. We have examined a suite of samples from the 1985, 1989, 2012, and 2015 eruptions to assess the origin of erupted materials (juvenile vs. non-juvenile) and nature of eruptive and subvolcanic processes (e.g. fresh intrusion, phreatic explosion). The November 1985 ash is dominated by beige to light gray pumice and free crystals, while samples from September 1985 and the 1989 through 2015 eruptions contain other fresh looking angular to subangular particles, including dense glassy to microcrystalline chips and vesicular glass shards. If juvenile, as we suspect, these components indicate phreatomagmatic to magmatic eruptive processes. Vesicular glass ranges from colorless to brown, often within the same sample, suggesting that bimodal magmatic sources, as recorded by mingled pumices of November 1985, have continued to play a role in eruptions at Ruiz. In particular, ash from 1989 contains vesicular glass that is 65% colorless to beige and 35% brown. Sparse, very dark brown vesicular glass appears in ash from June 2012—a larger eruption than that of May 2012—and is also observed in some 2015 samples, suggesting a more prominent mafic component. In addition to our observations from binocular microscopy, we will present results from SEM and electron microprobe analyses that further clarify the magmatic conditions that produced these dense and vesicular glassy components, and that test our hypothesis that these particles represent juvenile material from continued phreatomagmatic to magmatic eruptions at Ruiz.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19970025445','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19970025445"><span>Studies of Magmatic Inclusions in the Basaltic Martian Meteorites Shergotty, Zagami, EETA 79001 and QUE 94201</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Harvey, Ralph P.; McKay, Gordon A.</p> <p>1997-01-01</p> <p>Currently there are 12 meteorites thought by planetary scientists to be martian samples, delivered to the Earth after violent impacts on that planet's surface. Of these 12 specimens, 4 are basaltic: Shergotty, Zagami, EETA 79001 and QUE 94201. Basalts are particularly important rocks to planetary geologists- they are the most common rocks found on the surfaces of the terrestrial planets, representing volcanic activity of their parent worlds. In addition, because they are generated by partial melting of the mantle and/or lower crust, they can serve as guide posts to the composition and internal processes of a planet. Consequently these four meteorites can serve as 'ground-truth' representatives of the predominant volcanic surface rocks of Mars, and offer researchers a glimpse of the magmatic history of that planet. Unfortunately, unraveling the parentage of a basaltic rock is not always straightforward. While many basalts are simple, unaltered partial melts of the mantle, others have undergone secondary processes which change the original parental chemistry, such as assimilation of other crustal rocks, mixing with other magmas, accumulation, re-equilibration between mineral species after crystallization, loss of late-stage magmatic fluids and alteration by metamorphic or metasomatic processes. Fortunately, magmatic inclusions can trap the evolving magmatic liquid, isolating it from many of these secondary processes and offering a direct look at the magma during different stages of development. These inclusions form when major or minor phases grow skeletally, surrounding small amounts of the parental magma within pockets in the growing crystal. The inclusion as a whole (usually consisting of glass with enclosed crystals) continues to represent the composition of the parental magma at the time the melt pocket closed, even when the rock as a whole evolves under changing conditions. The four basaltic martian meteorites contain several distinct generations of melt inclusions; those found within early-forming pigeonite, intermediate and late-forming Ti, Fe-oxides and sulfides, and intermediate to late-forming phosphates. In this summer' s study we have made a detailed study of all of the various forms of inclusions found within the 4 basaltic martian meteorites listed above. Glasses and minerals within the inclusions were analyzed using the Camera SX-100 Electron Microprobe in Building 31. The mineralogy and textural context of the inclusions will then be used to explore the crystallization history of these specimens, and to investigate any differences in crystallization history or parental magma compositions between these rocks. In this manner, the magmatic inclusions provide a road map backwards toward the 'parental' compositions for the basaltic martian meteorites and provide significant insight into the igneous processes found within the crust of Mars.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70000255','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70000255"><span>Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>John, D.A.; Sisson, T.W.; Breit, G.N.; Rye, R.O.; Vallance, J.W.</p> <p>2008-01-01</p> <p>Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8??km3 Osceola Mudflow (5600??y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz-alunite, quartz-topaz, quartz-pyrophyllite, quartz-dickite/kaolinite, and quartz-illite (all with pyrite). Clasts of smectite-pyrite and steam-heated opal-alunite-kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite-pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite-pyrite assemblages, whereas the proximal Electron Mudflow and a < 100??y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures. The pre-Osceola Mudflow alteration geometry is inferred to have consisted of a narrow feeder zone of intense magmatic-hydrothermal alteration limited to near the conduit of the volcano, which graded outward to more widely distributed, but weak, smectite-pyrite alteration within 1??km of the edifice axis, developed chiefly in porous breccias. The edifice was capped by a steam-heated alteration zone, most of which resulted from condensation of fumarolic vapor and oxidation of H2S in the unsaturated zone above the water table. Weakly developed smectite-pyrite alteration extended into the west and east flanks of the edifice, spatially associated with dikes that are localized in those sectors; other edifice flanks lack dikes and associated alteration. The Osceola collapse removed most of the altered core and upper east flank of the volcano, but intensely altered rocks remain on the uppermost west flank. Major conclusions of this study are that: (1) Hydrothermal-mineral assemblages and distributions at Mount Rainier can be understood in the framework of hydrothermal processes and environments developed from studies of ore deposits formed in analogous settings. (2) Frequent eruptions supplied sufficient hot magmatic fluid to alter the upper interior of the volcano hydrothermally, despite the consistently deep (??? 8??km) magma reservoir which may have precluded formation of economic mineral deposits within or at shallow depths beneath Mount Rainier. The absence of indicator equilibrium alteration-mineral assemblages in the debris flows that effectively expose the volcano to a depth of 1-1.5??km also suggests a low potential for significant high-sulfidation epithermal or porphyry-type mineral deposits at depth. (3) Despite the long and complex history of the volcano, intensely altered collapse-prone rocks were spatially restricted to near the volcano's conduit system and summit, and short distances onto the upper east and west flanks, due to the necessary supply of reactive components carried by ascending magmatic fluids. (4) Intensely altered rocks were removed from the summit, east flank, and edifice interior by the Osceola collapse, but remain on the upper west flank in the Sunset Amphitheater area and present a continuing collapse hazard. (5) Visually conspicuous rocks on the lower east and mid-to-lower</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V41B4809S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V41B4809S"><span>Laboratory and numerical decompression experiments: an insight into the nucleation and growth of bubbles</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spina, L.; Colucci, S.; De'Michieli Vitturi, M.; Scheu, B.; Dingwell, D. B.</p> <p>2014-12-01</p> <p>Numerical modeling, joined with experimental investigations, is fundamental for studying the dynamics of magmatic fluid into the conduit, where direct observations are unattainable. Furthermore, laboratory experiments can provide invaluable data to vunalidate complex multiphase codes. With the aim on unveil the essence of nucleation process, as well as the behavior of the multiphase magmatic fluid, we performed slow decompression experiments in a shock tube system. We choose silicon oil as analogue for the magmatic melt, and saturated it with Argon at 10 MPa for 72h. The slow decompression to atmospheric conditions was monitored through a high speed camera and pressure sensors, located into the experimental conduit. The experimental conditions of the decompression process have then been reproduced numerically with a compressible multiphase solver based on OpenFOAM. Numerical simulations have been performed by the OpenFOAM compressibleInterFoam solver for 2 compressible, non-isothermal immiscible fluids, using a VOF (volume of fluid) phase-fraction based interface capturing approach. The data extracted from 2D images obtained from laboratory analyses were compared to the outcome of numerical investigation, showing the capability of the model to capture the main processes studied.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V51C2685K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V51C2685K"><span>The differentiation process of the I-type granitoids in southwest Japan and New South Wares in Australia</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kawakatsu, K.; Iwamoto, Y.; Ebisu, S.; Hasegawa, M.; Hiraiwa, N.; Kawakatsu, T.; Kitano, A.; Masuta, T.; Ootsubo, H.; Wakazono, R.</p> <p>2013-12-01</p> <p>Cretaceous-Paleogene Granitoids in the inner zone of southwest Japan have been divided into two series: the magnetite series that is distributed mainly in the San-in belt and the ilmenite series that is distributed mainly in San-yo belt. For 8 years, we have been investigating the two series to clear their processes of magmatic differentiation. Recently, we discovered oscillatory zoned structure, exsolution lamellae of amphibole, and relics of pyroxene left in the core of amphibole from Harima granodiorite, Nunobiki granodiorite (San-yo belt) and Daito-Yokota quartz diorite (San-in belt). The amphibole that has microstructure coexists with magnetite, ilmenite and pyrrhotite. We compared the two series for crystallization and re-equilibrium by ion substitution using the microstructure of the amphibole as 'time measure' during the differentitation process of acidic magma. While magnetites and ilmenites coexist with the core of the amphiboles, the oxygen fugacity of the San-yo belt magma was low until the later stage of magmatic differentiation where H2S from the Earth's crust mixed with it. In the subsolidus process, hydrothermal solutions circulated. On the other hand, the oxygen fugacity of the San-in belt magma began to rise in the early stage of magmatic differentiation. In the later stage, mafic magma was contaminated with SO2. The rims of amphiboles coexist with pyrrhotites in both of belts. Furthermore, the re-equilibrium of minerals underwent progressive oxidation and hydrothermal fluid circulated actively in the subsolidus process. Bingie Bingie Point at New South Wares (Eurobodalla National Park) is a peninsula about a meter around. The plutonic rocks were formed in the Devonian period and belong to the magnetite series. They are classified I-type granitoids such as those found in the inner zone of southwest Japan. They have only trace amounts of oxide minerals and pyrrhotite. The amphiboles of the granitoids have oscillatory zoned structures at pale green rims. The structures are formed by the fluid circulations of intruded granodiorite magma. The relic pyroxene is left in the core of amphibole. These minerals were crystallized under stable conditions and the microstructures were developed in the amphiboles under the subsolidus conditions. These researches contribute to clarifying magmatic differentiation and are the foundation of understanding the exchange of substances in magmatic activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016328','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016328"><span>Continental extension, magmatism and elevation; formal relations and rules of thumb</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lachenbruch, A.H.; Morgan, P.</p> <p>1990-01-01</p> <p>To investigate simplified relations between elevation and the extensional, magmatic and thermal processes that influence lithosphere buoyancy, we assume that the lithosphere floats on an asthenosphere of uniform density and has no flexural strength. A simple graph relating elevation to lithosphere density and thickness provides an overview of expectable conditions around the earth and a simple test for consistancy of continental and oceanic lithosphere models. The mass-balance relations yield simple general rules for estimating elevation changes caused by various tectonic, magmatic and thermal processes without referring to detailed models. The rules are general because they depend principally on buoyancy, which under our assumptions is specified by elevation, a known quantity; they do not generally require a knowledge of lithosphere thickness and density. The elevation of an extended terrain contains important information on its tectonic and magmatic history. In the Great Basin where Cenozoic extension is estimated to be 100%, the present high mean elevation ( ~ 1.75 km) probably requires substantial low-density magmatic contributions to the extending lithosphere. The elevation cannot be reasonably explained solely as the buoyant residue of a very high initial terrane, or of a lithosphere that was initially very thick and subsequently delaminated and heated. Even models with a high initial elevation typically call for 10 km or so of accumulated magmatic material of near-crustal density. To understand the evolution of the Great Basin, it is important to determine whether such intruded material is present; some could replenish the stretching crust by underplating and crustal intrusion and some might reside in the upper mantle. The elevation maintained or approached by an intruded extending lithosphere depends on the ratio B of how fast magma is supplied from the asthenosphere ( b km/Ma) to how fast the lithosphere spreads the magma out by extension (?? Ma-1). For a surface maintained 2 1 2km below sea level (e.g., an ocean ridge) B is about 5 km; for continental extension the ratio may be much greater. The frequent association of volcanism with continental extension, the high elevation (and buoyancy) of some appreciably extended terrains, and the oceanic spreading analog all suggest that magmatism may play an important role in continental extension. Better estimates of total extension and elevation change in extended regions can help to identify that role. ?? 1990.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2003/0435/pdf/of03-435.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2003/0435/pdf/of03-435.pdf"><span>Scrubbing masks magmatic degassing during repose at Cascade-Range and Aleutian-Arc volcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Symonds, Robert B.; Janik, C.J.; Evans, William C.; Ritchie, B.E.; Counce, Dale; Poreda, R.J.; Iven, Mark</p> <p>2003-01-01</p> <p>Between 1992 and 1998, we sampled gas discharges from ≤173°C fumaroles and springs at 12 quiescent but potentially restless volcanoes in the Cascade Range and Aleutian Arc (CRAA) including Mount Shasta, Mount Hood, Mount St. Helens, Mount Rainier, Mount Baker, Augustine Volcano, Mount Griggs, Trident, Mount Mageik, Aniakchak Crater, Akutan, and Makushin. For each site, we collected and analyzed samples to characterize the chemical (H2O, CO2, H2S, N2, CH4, H2, HCl, HF, NH3, Ar, O2, He) and isotopic (δ13C of CO2, 3He/4He, 40Ar/36Ar, δ34S, δ13C of CH4, δ15N, and δD and δ18O of water) compositions of the gas discharges, and to create baseline data for comparison during future unrest. The chemical and isotopic data show that these gases contain a magmatic component that is heavily modified from scrubbing by deep hydrothermal (150° - 350°C) water (primary scrubbing) and shallow meteoric water (secondary scrubbing). The impact of scrubbing is most pronounced in gas discharges from bubbling springs; gases from boiling-point fumaroles and superheated vents show progressively less impact from scrubbing. The most effective strategies for detecting gas precursors to future CRAA eruptions are to measure periodically the emission rates of CO2 and SO2, which have low and high respective solubilities in water, and to monitor continuously CO2 concentrations in soils around volcanic vents. Timely resampling of fumaroles can augment the geochemical surveillance program by watching for chemical changes associated with drying of fumarolic pathways (all CRAA sites), increases in gas geothermometry temperatures (Mount Mageik, Trident, Mount Baker, Mount Shasta), changes in δ13C of CO2 affiliated with magma movement (all CRAA site), and increases in 3He/4He coupled with intrusion of new magma (Mount Rainier, Augustine Volcano, Makushin, Mount Shasta). Repose magmatic degassing may discharge substantial amounts of S and Cl into the edifices of Mount Baker and several other CRAA volcanoes that is trapped by primary and secondary scrubbing. The consequent acidic fluids produce ongoing alteration in the 0.2- to 3-km-deep hydrothermal systems and in fields of boiling-point fumaroles near the surface. Such alteration may influence edifice stability and contribute to the formation of more-hazardous cohesive debris flows. In particular, we recommend further investigation of the volume, extent, and hazards of hydrothermal alteration at Mount Baker. Other potential hazards associated with the CRAA volcano hydrothermal systems include hydrothermal eruptions and, for deeper systems intruded by magma, deep-seated edifice collapse.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.usgs.gov/sir/2017/5022/j1/sir2017-5022J1.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/sir/2017/5022/j1/sir2017-5022J1.pdf"><span>Geologic field trip guide to Mount Mazama and Crater Lake Caldera, Oregon</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bacon, Charles R.; Wright, Heather M.</p> <p>2017-08-08</p> <p>Crater Lake partly fills one of the most spectacular calderas of the world—an 8 by 10 kilometer (km) basin more than 1 km deep formed by collapse of the Mount Mazama volcano during a rapid series of explosive eruptions ~7,700 years ago. Having a maximum depth of 594 meters (m), Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 square kilometers (km2) of pristine forested and alpine terrain, including the lake itself, and virtually all of Mount Mazama. The geology of the area was first described in detail by Diller and Patton (1902) and later by Williams (1942), whose vivid account led to international recognition of Crater Lake as the classic collapse caldera. Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes. For example, the climactic ejecta are renowned among volcanologists as evidence for systematic compositional zonation within a subterranean magma chamber. Mount Mazama’s climactic eruption also is important as the source of the widespread Mazama ash, a useful Holocene stratigraphic marker throughout the Pacific Northwest United States, adjacent Canada, and offshore. A detailed bathymetric survey of the floor of Crater Lake in 2000 (Bacon and others, 2002) provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve. In addition, many smaller volcanoes of the High Cascades beyond the limits of Mount Mazama provide information on the flux of mantle-derived magma through the region. General principles of magmatic and eruptive processes revealed by geologic research at Crater Lake have been incorporated not only in scientific investigations elsewhere, but also in the practical evaluation of local hazards (Bacon and others, 1997b) and geothermal resources (Bacon and Nathenson, 1996). The 1:24,000-scale geologic map of Mount Mazama and Crater Lake caldera (Bacon, 2008) is unusual because it portrays bedrock (outcrop), surficial, and lake floor geology. Caldera wall geology is depicted in detail on the accompanying geologic panoramas, and bedrock geology is shown in a 1:50,000-scale geologic map. This field guide supersedes earlier geology guides of Crater Lake (Bacon, 1987, 1989).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://ngmdb.usgs.gov/Prodesc/proddesc_85260.htm','USGSPUBS'); return false;" href="http://ngmdb.usgs.gov/Prodesc/proddesc_85260.htm"><span>Geologic Map of Mount Mazama and Crater Lake Caldera, Oregon</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bacon, Charles R.</p> <p>2008-01-01</p> <p>Crater Lake partly fills one of the most spectacular calderas of the world, an 8-by-10-km basin more than 1 km deep formed by collapse of the volcano known as Mount Mazama (fig. 1) during a rapid series of explosive eruptions about 7,700 years ago. Having a maximum depth of 594 m, Crater Lake is the deepest lake in the United States. Crater Lake National Park, dedicated in 1902, encompasses 645 km2 of pristine forested and alpine terrain, including the lake itself, virtually all of Mount Mazama, and most of the area of the geologic map. The geology of the area was first described in detail by Diller and Patton (1902) and later by Williams (1942), whose vivid account led to international recognition of Crater Lake as the classic collapse caldera. Because of excellent preservation and access, Mount Mazama, Crater Lake caldera, and the deposits formed by the climactic eruption constitute a natural laboratory for study of volcanic and magmatic processes. For example, the climactic ejecta are renowned among volcanologists as evidence for systematic compositional zonation within a subterranean magma chamber. Mount Mazama's climactic eruption also is important as the source of the widespread Mazama ash, a useful Holocene stratigraphic marker throughout the Pacific Northwest, adjacent Canada, and offshore. A detailed bathymetric survey of the floor of Crater Lake in 2000 (Bacon and others, 2002) provides a unique record of postcaldera eruptions, the interplay between volcanism and filling of the lake, and sediment transport within this closed basin. Knowledge of the geology and eruptive history of the Mount Mazama edifice, greatly enhanced by the caldera wall exposures, gives exceptional insight into how large volcanoes of magmatic arcs grow and evolve. Lastly, the many smaller volcanoes of the High Cascades beyond the limits of Mount Mazama are a source of information on the flux of mantle-derived magma through the region. General principles of magmatic and eruptive processes revealed by the present study have been incorporated not only in scientific investigations elsewhere, but in the practical evaluation of hazards (Bacon and others, 1997b) and geothermal resources (Bacon and Nathenson, 1996) in the Crater Lake region. In addition to papers in scientific journals, field trip guides, and the hazard and geothermal reports, the major product of this long-term study of Mount Mazama is the geologic map. The map is unusual because it portrays bedrock (outcrop), surficial, and lake floor geology. Caldera wall geology is depicted in detail on the accompanying geologic panoramas.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009MinDe..44..415L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009MinDe..44..415L"><span>A geochemical study of the Sweet Home Mine, Colorado Mineral Belt, USA: hydrothermal fluid evolution above a hypothesized granite cupola</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lüders, Volker; Romer, Rolf L.; Gilg, H. Albert; Bodnar, Robert J.; Pettke, Thomas; Misantoni, Dean</p> <p>2009-05-01</p> <p>Deposition of quartz-molybdenite-pyrite-topaz-muscovite-fluorite and subsequent hübnerite and sulfide-fluorite-rhodochrosite mineralization at the Sweet Home Mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby world-class Climax molybdenum deposit about 26 to 25 m.y. ago. The mineralization occurred at depths of about 3,000 m and is related to at least two major fluid systems: (1) one dominated by magmatic fluids, and (2) another dominated by meteoric water. The sulfur isotopic composition of pyrite, strontium isotopes and REY distribution in fluorite suggest that the early-stage quartz-molybdenite-pyrite-topaz-muscovite-fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating pressure regime at temperatures of about 400°C as indicated by CO2-bearing, moderately saline (7.5-12.5 wt.% NaCl equiv.) fluid inclusions. LA-ICPMS analyses of fluid inclusions in quartz demonstrate that fluids from the Sweet Home Mine are enriched in incompatible elements but have considerably lower metal contents than those reported from porphyry-Cu-Au-Mo or Climax-type deposits. The ore-forming fluid exsolved from a highly differentiated magma possibly related to the deep-seated Alma Batholith or distal porphyry stock(s). Sulfide mineralization, marking the periphery of Climax-type porphyry systems, with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic pressure regime from low-salinity ± CO2-bearing fluids with low metal content at temperatures below 400°C. The sulfide mineralization is characterized by mostly negative δ34S values for sphalerite, galena, chalcopyrite, and tetrahedrite, highly variable δ18O values for rhodochrosite, and low REE contents in fluorite. The Pb isotopic composition of galena as well as the highly variable 87Sr/86Sr ratios of fluorite, rhodochrosite, and apatite indicates that at least part of the Pb and Sr originated from a much more radiogenic source than Climax-type granites. It is suggested that the sulfide mineralization at the Sweet Home Mine formed from magmatic fluids that mixed with variable amounts of externally derived fluids. The migration of the latter fluids, that were major components during late-stage mineralization at the Sweet Home Mine, was probably driven by a buried magmatic intrusion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/1242411','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/1242411"><span>Blind Geothermal System Exploration in Active Volcanic Environments; Multi-phase Geophysical and Geochemical Surveys in Overt and Subtle Volcanic Systems, Hawai’i and Maui</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Fercho, Steven; Owens, Lara; Walsh, Patrick</p> <p>2015-08-01</p> <p>Suites of new geophysical and geochemical exploration surveys were conducted to provide evidence for geothermal resource at the Haleakala Southwest Rift Zone (HSWRZ) on Maui Island, Hawai’i. Ground-based gravity (~400 stations) coupled with heli-bourne magnetics (~1500 line kilometers) define both deep and shallow fractures/faults, while also delineating potentially widespread subsurface hydrothermal alteration on the lower flanks (below approximately 1800 feet a.s.l.). Multi-level, upward continuation calculations and 2-D gravity and magnetic modeling provide information on source depths, but lack of lithologic information leaves ambiguity in the estimates. Additionally, several well-defined gravity lows (possibly vent zones) lie coincident with magnetic highs suggestingmore » the presence of dike intrusions at depth which may represent a potentially young source of heat. Soil CO2 fluxes were measured along transects across geophysically-defined faults and fractures as well as young cinder cones along the HSWRZ. This survey generally did not detect CO2 levels above background, with the exception of a weak anomalous flux signal over one young cinder cone. The general lack of observed CO2 flux signals on the HSWRZ is likely due to a combination of lower magmatic CO2 fluxes and relatively high biogenic surface CO2 fluxes which mix with the magmatic signal. Similar surveys at the Puna geothermal field on the Kilauea Lower East Rift Zone (KLERZ) also showed a lack of surface CO2 flux signals, however aqueous geochemistry indicated contribution of magmatic CO2 and He to shallow groundwater here. As magma has been intercepted in geothermal drilling at the Puna field, the lack of measured surface CO2 flux indicative of upflow of magmatic fluids here is likely due to effective “scrubbing” by high groundwater and a mature hydrothermal system. Dissolved inorganic carbon (DIC) concentrations, δ13C compositions and 3He/4He values were sampled at Maui from several shallow groundwater samples indicating only minor additions of magmatic CO2 and He to the groundwater system, although much less than observed near Puna. The much reduced DIC and He abundances at Maui, along with a lack of hotsprings and hydrothermal alteration, as observed near Puna, does not strongly support a deeper hydrothermal system within the HSWRZ.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140012598','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140012598"><span>Vesicles in Apollo 15 Green Glasses: The Nature of Ancient Lunar Gases</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thomas-Keprta, K. L.; Clemett, S. J.; Berger, E. L.; Rahman, Z.; McKay, D. S.; Gibson, E. K.; Wentworth, S. J.</p> <p>2014-01-01</p> <p>Detailed studies of Apollo 15 green glass and related beads have shown they were formed in gas-rich fire fountains.. As the magmatic fluid became super-saturated in volatile gas, bubbles or vesicles formed within the magma. These exsolved gases became trapped within vesicles as the glasses were ejected from the fire-fountain and subsequently quenched. One of the keys to understanding formation processes on the ancient moon includes determining the composition of volatile species and elements, including metals, dissolved in magmatic gases. Here we report the nature of mineral phases spatially associated with vesicles in a green glass bead from Apollo sample 15411,42. The phases reflect the composition of the cooling/degassing magmatic vapors and fluids present at the time of bead formation approx, 3 Ga ago</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70025019','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70025019"><span>Location of long-period events below Kilauea Volcano using seismic amplitudes and accurate relative relocation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Battaglia, J.; Got, J.-L.; Okubo, P.</p> <p>2003-01-01</p> <p>We present methods for improving the location of long-period (LP) events, deep and shallow, recorded below Kilauea Volcano by the permanent seismic network. LP events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport. However, it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals. At Kilauea, similar LP waveform signatures suggest the existence of LP multiplets. The waveform similarity suggests spatially close sources, while catalog solutions using arrival time estimates are widely scattered beneath Kilauea's summit caldera. In order to improve estimates of absolute LP location, we use the distribution of seismic amplitudes corrected for station site effects. The decay of the amplitude as a function of hypocentral distance is used for inferring LP location. In a second stage, we use the similarity of the events to calculate their relative positions. The analysis of the entire LP seismicity recorded between January 1997 and December 1999 suggests that a very large part of the LP event population, both deep and shallow, is generated by a small number of compact sources. Deep events are systematically composed of a weak high-frequency onset followed by a low-frequency wave train. Aligning the low-frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated. This observation favors an interpretation in terms of triggering and resonance of a magmatic conduit. Instead of defining fault planes, the precise relocation of similar LP events, based on the alignment of the high-energy low-frequency wave trains, defines limited size volumes. Copyright 2003 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1710130B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1710130B"><span>High precision time calibration of the Permian-Triassic boundary mass extinction event in a deep marine context</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baresel, Björn; Bucher, Hugo; Brosse, Morgane; Bagherpour, Borhan; Schaltegger, Urs</p> <p>2015-04-01</p> <p>To construct a revised and high resolution calibrated time scale for the Permian-Triassic boundary (PTB) we use (1) high-precision U-Pb zircon age determinations of a unique succession of volcanic ash layers interbedded with deep water fossiliferous sediments in the Nanpanjiang Basin (South China) combined with (2) accurate quantitative biochronology based on ammonoids, conodonts, radiolarians, and foraminifera and (3) tracers of marine bioproductivity (carbon isotopes) across the PTB. The unprecedented precision of the single grain chemical abrasion isotope-dilution thermal ionization mass spectrometry (CA-ID-TIMS) dating technique at sub-per mil level (radio-isotopic calibration of the PTB at the <100 ka level) now allows calibrating magmatic and biological timescales at resolution adequate for both groups of processes. Using these alignments allows (1) positioning the PTB in different depositional setting and (2) solving the age contradictions generated by the misleading use of the first occurrence (FO) of the conodont Hindeodus parvus, whose diachronous first occurrences are arbitrarily used for placing the base of the Triassic. This new age framework provides the basis for a combined calibration of chemostratigraphic records with high-resolution biochronozones of the Late Permian and Early Triassic. Here, we present new single grain U-Pb zircon data of volcanic ash layers from two deep marine sections (Dongpan and Penglaitan) revealing stratigraphic consistent dates over several volcanic ash layers bracketing the PTB. These analyses define weighted mean 206Pb/238U ages of 251.956±0.033 Ma (Dongpan) and 252.062±0.043 Ma (Penglaitan) for the last Permian ash bed. By calibration with detailed litho- and biostratigraphy new U-Pb ages of 251.953±0.038 Ma (Dongpan) and 251.907±0.033 Ma (Penglaitan) are established for the onset of the Triassic.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1712272B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1712272B"><span>Control of deep lithospheric roots on crustal scale GOCE gravity and gradient fields evident in Gondwana reconstructions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Braitenberg, Carla; Mariani, Patrizia</p> <p>2015-04-01</p> <p>The GOCE gravity field is globally homogeneous at the resolution of about 80km or better allowing for the first time to analyze tectonic structures at continental scale. Geologic correlation studies based on age determination and mineral composition of rock samples propose to continue the tectonic lineaments across continents to the pre-breakup position. Tectonic events which induce density changes, as metamorphic events and magmatic events, should then show up in the gravity field. Therefore gravity can be used as a globally available supportive tool for interpolation of isolated samples. Applying geodynamic plate reconstructions to the GOCE gravity field places today's observed field at the pre-breakup position. In order to test the possible deep control of the crustal features, the same reconstruction is applied to the seismic velocity models, and a joint gravity-velocity analysis is performed. The geophysical fields allow to control the likeliness of the hypothesized continuation of lineations based on sparse surface outcrops. Total absence of a signal, makes the cross-continental continuation of the lineament improbable, as continental-wide lineaments are controlled by rheologic and compositional differences of lithospheric mantle. It is found that the deep lithospheric roots as those found below cratons control the position of the positive gravity values. The explanation is that the deep lithospheric roots focus asthenospheric upwelling outboard of the root protecting the overlying craton from magmatic intrusions. The study is carried out over the African and South American continents. The background for the study can be found in the following publications where the techniques which have been used are described: Braitenberg, C., Mariani, P. and De Min, A. (2013). The European Alps and nearby orogenic belts sensed by GOCE, Boll. Bollettino di Geofisica Teorica ed Applicata, 54(4), 321-334. doi:10.4430/bgta0105 Braitenberg, C. and Mariani, P. (2015). Geological implications from complete Gondwana GOCE-products reconstructions and link to lithospheric roots. Proceedings of 5th International GOCE User Workshop, 25 - 28 November 2014. Braitenberg, C. (2015). Exploration of tectonic structures with GOCE in Africa and across-continents. Int. J.Appl. Earth Observ. Geoinf. 35, 88-95. http://dx.doi.org/10.1016/j.jag.2014.01.013 Braitenberg, C. (2015). A grip on geological units with GOCE, IAG Symp. 141, in press.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T51B0459A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T51B0459A"><span>Breakup magmatism on the Vøring Margin, mid-Norway: New insight from interpretation of high-quality 2D and 3D seismic reflection data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abdelmalak, M. M.; Planke, S.; Millett, J.; Jerram, D. A.; Maharjan, D.; Zastrozhnov, D.; Schmid, D. W.; Faleide, J. I.; Svensen, H.; Myklebust, R.</p> <p>2017-12-01</p> <p>The Vøring Margin offshore mid-Norway is a classic volcanic rifted margin, characterized by voluminous Paleogene igneous rocks present on both sides of the continent-ocean boundary. The margin displays (1) thickened transitional crust with a well-defined lower crustal high-velocity body and prominent deep crustal reflections, the so-called T-Reflection, (2) seaward dipping reflector (SDR) wedges and a prominent northeast-trending escarpment on the Vøring Marginal High, and (3) extensive sill complexes in the adjacent Cretaceous Vøring Basin. During the last decade, new 2D and 3D industry seismic data along with improved processing techniques, such as broadband processing and noise reduction processing sequences, have made it possible to image and map the breakup igneous complex in much greater detail than previously possible. Our interpretation includes a combination of (1) seismic horizon picking, (2) integrated seismic-gravity-magnetic (SGM) interpretation, (3) seismic volcanostratigraphy, and (4) igneous seismic geomorphology. The results are integrated with published wide-angle seismic data, re-analyzed borehole data including new geochronology, and new geodynamic modeling of the effects of magmatism on the thermal history and subsidence of the margin. The extensive sill complexes and associated hydrothermal vent complexes in the Vøring Basin have a Paleocene-Eocene boundary age based on high-precision U/Pb dating combined with seismic mapping constraints. On the marginal high, our results show a highly variable crustal structure, with a pre-breakup configuration consisting of large-scale structural highs and sedimentary basins. These structures were in-filled and covered by basalt flows and volcanogenic sediments during the early stages of continental breakup in the earliest Eocene. Subsequently, rift basins developed along the continent-ocean boundary and where infilled by up to ca. 6 km thick basalt sequences, currently imaged as SDRs fed by a dike swarm imaged on seismic data. The addition of magma within the crust had a prominent effect on the thermal history and hydrocarbon maturation of the sedimentary basin, causing uplift, delayed subsidence, and possibly contributing to the triggering of global warming during the Paleocene-Eocene Thermal Maximum (PETM).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V43B3129B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V43B3129B"><span>Magnetotelluric Investigation of Melt Storage Beneath Okmok Caldera, Alaska</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bennington, N. L.; Bedrosian, P.; Key, K.; Zelenak, G.</p> <p>2015-12-01</p> <p>Alaska accounts for nearly 99% of the seismic moment release within the US. Much of this is associated with the Aleutian volcanic arc, the most tectonically active region in North America, and an ideal location for studying arc magmatism. Okmok is an active volcano located in the central Aleutian arc, defined by a pair of nested, 10 km diameter calderas. The subdued topography of Okmok, relative to other Aleutian volcanoes, improves access and permits dense sampling within the caldera closer to the underlying magmatic system. Okmok volcano was selected as the site of study for this project due to frequent volcanic activity and the presence of a crustal magma reservoir as inferred from previous coarse resolution seismic studies. In June-July 2015, we carried out an amphibious geophysical field deployment at Okmok. Onshore work in and around the volcano included collection of an array of magnetotelluric (MT) stations and installation of a temporary, year-long seismic array. A ring of 3D offshore MT deployments made around the island augments the onshore array. An additional 2D tectonic-scale profile spans the trench, volcanic arc, and backarc. This new geophysical data will be used to gain a greater understanding of Aleutian arc melt generation, migration, and storage beneath an active caldera. We present results from the analysis of the newly collected amphibious 3D MT data. This data will be used to model the distribution and migration of melt within Okmok's crustal magma reservoir. Initial processing of the data shows strong MT signal levels, in particular from a geomagnetic storm that occurred from June 21-23, 2015. A companion abstract discussing the 2D tectonic scale MT profile, which constrains the mantle and deep crust beneath Okmok volcano, is discussed by Zelenak et al.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.473..227Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.473..227Y"><span>Duration of and decoupling between carbon isotope excursions during the end-Triassic mass extinction and Central Atlantic Magmatic Province emplacement</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yager, Joyce A.; West, A. Joshua; Corsetti, Frank A.; Berelson, William M.; Rollins, Nick E.; Rosas, Silvia; Bottjer, David J.</p> <p>2017-09-01</p> <p>Changes in δ13Ccarb and δ13Corg from marine strata occur globally in association with the end-Triassic mass extinction and the emplacement of the Central Atlantic Magmatic Province (CAMP) during the break up of Pangea. As is typical in deep time, the timing and duration of these isotopic excursions has remained elusive, hampering attempts to link carbon cycle perturbations to specific processes. Here, we report δ13Ccarb and δ13Corg from Late Triassic and Early Jurassic strata near Levanto, Peru, where intercalated dated ash beds permit temporal calibration of the carbon isotope record. Both δ13Ccarb and δ13Corg exhibit a broad positive excursion through the latest Triassic into the earliest Jurassic. The first order positive excursion in δ13Corg is interrupted by a negative shift noted in many sections around the world coincident with the extinction horizon. Our data indicate that the negative excursion lasts 85 ± 25 kyrs, longer than inferred by previous studies based on cyclostratigraphy. A 260 ± 80 kyr positive δ13Corg shift follows, during which the first Jurassic ammonites appear. The overall excursion culminates in a return to pre-perturbation carbon isotopic values over the next 1090 ± 70 kyrs. Via chronologic, isotopic, and biostratigraphic correlation to other successions, we find that δ13Ccarb and δ13Corg return to pre-perturbation values as CAMP volcanism ceases and in association with the recovery of pelagic and benthic biota. However, the initiation of the carbon isotope excursion at Levanto predates the well-dated CAMP sills from North America, indicating that CAMP may have started earlier than thought based on these exposures, or that the onset of carbon cycle perturbations was not related to CAMP.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/1378022-dual-stable-isotopes-ch-from-yellowstone-hot-springs-suggest-hydrothermal-processes-involving-magmatic-co','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/1378022-dual-stable-isotopes-ch-from-yellowstone-hot-springs-suggest-hydrothermal-processes-involving-magmatic-co"><span>Dual stable isotopes of CH 4 from Yellowstone hot-springs suggest hydrothermal processes involving magmatic CO 2</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Moran, James J.; Whitmore, Laura M.; Jay, Zackary J.</p> <p></p> <p>Volcanism and post-magmatism contribute both significant annual CH 4 fluxes to the atmosphere (on par with other natural sources such as forest fire and wild animal emissions) and have been implicated in past climate-change events. The Yellowstone hot spot is one of the largest volcanic systems on Earth and is known to emit methane in addition to other greenhouse gases (e.g. carbon dioxide) but the ultimate source of this methane flux has not been elucidated. Here we use dual stable isotope analysis (δ 2H and δ 13C) of CH 4(g) sampled from ten high-temperature geothermal pools in Yellowstone National Parkmore » to show that the predominant flux of CH4(g) is abiotic. The average δ 13C and δ 2H values of CH 4(g) emitted from hot springs (-26.7 (±2.4) and -236.9 (±12.0) ‰, respectively) are not consistent with biotic (microbial or thermogenic) methane sources, but are within previously reported ranges for abiotic methane production. Correlation between δ 13C CH4 and δ 13C-dissolved inorganic C (DIC) also suggests that CO 2 is a parent C source for the observed CH 4(g). Moreover, CH 4-CO 2 isotopic geothermometry was used to estimate CH 4(g) formation temperatures ranging from ~ 250 - 350°C, which is just below the temperature estimated for the hydrothermal reservoir and consistent with the hypothesis that subsurface, rock-water interactions are responsible for large methane fluxes from this volcanic system. An understanding of conditions leading to the abiotic production of methane and associated isotopic signatures are central to understanding the evolutionary history of deep carbon sources on Earth.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T33B4665K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T33B4665K"><span>3D Numerical Model of Continental Breakup via Plume Lithosphere Interaction Near Cratonic Blocks: Implications for the Tanzanian Craton</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koptev, A.; Calais, E.; Burov, E. B.; Leroy, S. D.; Gerya, T.</p> <p>2014-12-01</p> <p>Although many continental rift basins and their successfully rifted counterparts at passive continental margins are magmatic, some are not. This dichotomy prompted end-member views of the mechanism driving continental rifting, deep-seated and mantle plume-driven for some, owing to shallow lithospheric stretching for others. In that regard, the East African Rift (EAR), the 3000 km-long divergent boundary between the Nubian and Somalian plates, provides a unique setting with the juxtaposition of the eastern, magma-rich, and western, magma-poor, branches on either sides of the 250-km thick Tanzanian craton. Here we implement high-resolution rheologically realistic 3D numerical model of plume-lithosphere interactions in extensional far-field settings to explain this contrasted behaviour in a unified framework starting from simple, symmetrical initial conditions with an isolated mantle plume rising beneath a craton in an east-west tensional far field stress. The upwelling mantle plume is deflected by the cratonic keel and preferentially channelled along one of its sides. This leads to the coeval development of a magma-rich branch above the plume head and a magma-poor one along the opposite side of the craton, the formation of a rotating microplate between the two rift branches, and the feeding of melt to both branches form a single mantle source. The model bears strong similarities with the evolution of the eastern and western branches of the central EAR and the geodetically observed rotation of the Victoria microplate. This result reconciles the passive (plume-activated) versus active (far-field tectonic stresses) rift models as our experiments shows both processes in action and demonstrate the possibility of developing both magmatic and amagmatic rifts in identical geotectonic environments.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CoMP..173...48H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CoMP..173...48H"><span>Melt segregation from silicic crystal mushes: a critical appraisal of possible mechanisms and their microstructural record</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holness, Marian B.</p> <p>2018-06-01</p> <p>One of the outstanding problems in understanding the behavior of intermediate-to-silicic magmatic systems is the mechanism(s) by which large volumes of crystal-poor rhyolite can be extracted from crystal-rich mushy storage zones in the mid-deep crust. The mechanisms commonly invoked are hindered settling, micro-settling, and compaction. The concept of micro-settling involves extraction of grains from a crystal framework during Ostwald ripening and has been shown to be non-viable in the metallic systems for which it was originally proposed. Micro-settling is also likely to be insignificant in silicic mushes, because ripening rates are slow for quartz and plagioclase, contact areas between grains in a crystal mush are likely to be large, and abundant low-angle grain boundaries promote grain coalescence rather than ripening. Published calculations of melt segregation rates by hindered settling (Stokes settling in a crystal-rich system) neglect all but fluid dynamical interactions between particles. Because tabular silicate minerals are likely to form open, mechanically coherent, frameworks at porosities as high as 75%, settling of single crystals is only likely in very melt-rich systems. Gravitationally-driven viscous compaction requires deformation of crystals by either dissolution-reprecipitation or dislocation creep. There is, as yet, no reported microstructural evidence of extensive, syn-magmatic, internally-generated, viscous deformation in fully solidified silicic plutonic rocks. If subsequent directed searches do not reveal clear evidence for internally-generated buoyancy-driven melt segregation processes, it is likely that other factors, such as rejuvenation by magma replenishment, gas filter-pressing, or externally-imposed stress during regional deformation, are required to segregate large volumes of crystal-poor rhyolitic liquids from crustal mushy zones.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1810679L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1810679L"><span>Analysis of Marine Gravity Anomalies in the Ulleung Basin (East Sea/Sea of Japan) and Its Implications for the Architecture of Rift-Dominated Backarc Basin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Sang-Mook; Kim, Yoon-Mi</p> <p>2016-04-01</p> <p>Marginal basins locate between the continent and arc islands often exhibit diverse style of opening, from regions that appear to have formed by well-defined and localized spreading center (manifested by the presence of distinct seafloor magnetic anomaly patterns) to those with less obvious zones of extension and a broad magmatic emplacement most likely in the lower crust. Such difference in the style of back-arc basin formation may lead to marked difference in crustal structure in terms of its overall thickness and spatial variations. The Ulleung Basin, one of three major basins in the East Sea/Sea of Japan, is considered to represent a continental rifting end-member of back-arc opening. Although a great deal of work has been conducted on the sedimentary sections in the last several decades, the deep crustal sections have not been systematically investigated for long time, and thus the structure and characteristics of the crust remain poorly understood. This study examines the marine gravity anomalies of the Ulleung Basin in order to understand the crustal structure using crucial sediment-thickness information. Our analysis shows that the Moho depth in general varies from 16 km at the basin center to 22 km at the margins. However, within the basin center, the inferred thickness of the crust is more or less the same (10-12 km), thus by varying only about 10-20% of the total thickness, contrary to the previous impression. The almost-uniformly-thick crust that is thicker than a normal oceanic crust (~ 7 km) is consistent with previous observations using ocean bottom seismometers and recent deep seismic results from the nearby Yamato Basin. Another important finding is that small residual mantle gravity anomaly highs exist in the northern part of the basin. These highs are aligned in the NNE-SSW direction which correspond to the orientation of the major tectonic structures on the Korean Peninsula, raising the possibility that, though by a small degree, they are a consequence of localized extension and extra crustal thinning at the time of basin formation. Alternative explanation is that they are the result of a small post-rift underplating at the base of the crust. Two important processes appear to have shaped the Ulleung Basin following its formation: post-rifting magmatism which occurred in the north, especially in the northeast sections of the Ulleung Basin, and the deflection of crust in response to preferential sediment loading towards the south. The median high in the basin may be a consequence of the flexural bending. Based on our evidence for almost-uniformly-thick crust, we argue that, unlike many other rift-dominated basins which exhibit large variations in crustal thickness, decompressional melting that took place during basin extension resulted in a widespread magmatic emplacement that not only smoothed but also enhanced the crustal thickness.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2047.6102H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2047.6102H"><span>Magmatic Ascent and Eruption Processes on Mercury</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Head, J. W.; Wilson, L.</p> <p>2018-05-01</p> <p>MESSENGER volcanic landform data and information on crustal composition allow us to model the generation, ascent, and eruption of magma; Mercury explosive and effusive eruption processes differ significantly from other terrestrial planetary bodies.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....1264M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....1264M"><span>EAGLE The controlled source experiment</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maguire, P. K. H.; Eagle Controlled Source Group</p> <p>2003-04-01</p> <p>In January 2003, a wide-angle reflection / refraction seismic project was carried out over the north-eastern section of the Main Ethiopian Rift as part of the international EAGLE (Ethiopia Afar Geoscientific Lithospheric Experiment) programme. EAGLE comprises a combination of passive and controlled source seismic experiments to determine the geometry and kinematics of a continental rift immediately prior to break-up, enabling the development of magmatic margin break-up models. A total of ˜900 seismic instruments were deployed along two 450km profiles, one along the axis of the Ethiopian Rift into the south-west corner of Afar; and a second across the rift, extending north and south across the uplifted, flood basalt covered, Ethiopian plateau. The two profiles intersect over the Nazret volcanic segment in the rift. This may be indicative of the transition from continental style rifting in which strain is accommodated on the rift bounding border faults, to a state where strain and magmatism have migrated to a narrow zone within the rift, a necessary pre-cursor to break-up. A further ˜300 instruments were deployed in a 100x100km^2 array around the intersection of the two profiles. A total of 16 borehole and 2 lake shots were fired into the network over a period of four days. The principal objectives of the controlled source project were to examine crustal strain, the distribution of crustal magmatic intrusions, the influence of pre-rift crustal property variations on rift development and also to provide a crustal seismic velocity distribution to improve images of the deep mantle, as well as earthquake locations derived from the EAGLE passive arrays.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70028673','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70028673"><span>A note on the correlation between geophysical observations and seismicity in the Arava/(Araba) Valley at the southern part of the Dead Sea fault</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Rybakov, M.; Shapira, A.; Al-Zoubi, A.; ten Brink, Uri S.; Hofstetter, R.; Kraeva, N.; Feldman, L.</p> <p>2006-01-01</p> <p>The spatial distribution of the earthquakes in the Arava Valley, a 150-km section of the Dead Sea Transform, is compared for the first time with the local subsurface geological features derived from geophysical and geological data. Gravity data suggested that the Gharandal, Timna, and Elat basins were filled by low-density young sediments. These features were confirmed by seismic reflection profiles and high-resolution aeromagnetic (HRAM) survey. The HRAM survey delineated the trace of the Dead Sea Transform (DST), which separates magnetic anomalies in the eastern and western parts of the valley, and revealed the occurrence of the unknown deep magmatics. Overall, the earthquake activity appears to be strongly related to the Dead Sea Transform. However, on a local scale, there is no apparent correlation between the seismicity and the mapped fault segments comprising the DST fault system. Absence of the correlation may be a result of insufficient accuracy of the earthquake localization and/or the inclined fault plane. However, in spite of such inaccuracy, it is clearly observed that the large clusters of the low-magnitude earthquakes coincide well with the sedimentary basins. Two pronounced clusters appear to coincide with the subsurface magmatics. We assume that the subsurface geology predetermines areas of stress accumulation and earthquakes. These areas can be the end of faults, or fault jogs, which sometimes create basins. Magmatism can also be affected by the stress field and predetermine the stress and earthquakes' allocation. ?? 2007 Science From Israel/LPPLtd.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002GMS...128..193S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002GMS...128..193S"><span>Submarine alkalic through tholeiitic shield-stage development of Kīlauea volcano, Hawai'i</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sisson, Thomas W.; Lipman, Peter W.; Naka, Jiro</p> <p></p> <p>The submarine Hilina region exposes a succession of magma compositions spanning the juvenile "Lō'ihi" through tholeiitic shield stages of Kīlauea volcano. Early products, preserved as glass grains and clasts in volcaniclastic rocks of the 3000 m deep Hilina bench, include nephelinite, basanite, phonotephrite, hawaiite, alkali basalt, transitional basalt, and rare alkali-poor Mauna Loa-like tholeiite. Transitional basalt pillow lavas overlie the volcaniclastic section and record an early phase of subsequent subalkaline magmatism. Rare degassed tholeiitic pillow lava and talus above the volcaniclastic section are products of subaerial shield volcanism. Major and trace element variations of clasts and pillow lavas point to a factor of 2-2.5 increase in degree of melting from juvenile alkalic to modern tholeiitic Kīlauea. Progressive changes in element ratios that distinguish Hawaiian shield volcanoes, without commensurate changes in elements fractionated by partial melting, also signal increased contributions from Mauna Loa-type source regions as Kīlauea matured from its juvenile alkalic to its tholeiitic shield stage. Ancestral Kīlauea basanites and nephelinites were not primitive magmas but might have evolved from plume-derived alkali picritic parents by lithospheric-level crystallization differentiation, or solidification and remelting, involving pyroxene and garnet, similar to the subcrustal differentiation origin of hawaiites [Frey et al., 1990]. Low magmatic productivity early in Kīlauea's history sustained a poorly integrated trans-lithospheric conduit system in which magmas stalled and differentiated, producing evolved hawaiites, nephelinites, and basanites. This contrasts with shield-stage Kīlauea where high magmatic productivity flushes the conduit system and delivers primitive magmas to shallow levels.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CoMP..173...23P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CoMP..173...23P"><span>A cross correlation method for chemical profiles in minerals, with an application to zircons of the Kilgore Tuff (USA)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Probst, L. C.; Sheldrake, T. E.; Gander, M. J.; Wallace, G.; Simpson, G.; Caricchi, L.</p> <p>2018-03-01</p> <p>Magmatic crystals are characterised by chemical zonation patterns that reflect the thermal and chemical conditions within magma reservoirs in which they grew. Crystals that exhibit similar patterns of zonation are often interpreted to have experienced similar conditions of growth. These patterns of zonation may represent continuous processes such as cooling, or more instantaneous events such as magma injection, and provide an insight into the structure and evolution of a magmatic system, both temporally and spatially. We have developed an algorithm that is objectively able to quantify the similarity within and between suites of magmatic crystals from different samples. Significantly, the algorithm is able to identify correlation that occurs between the interiors of two crystals, but does not extend to the rim, which provides an opportunity to understand the long-term evolution of magmatic systems. We develop and explain the mathematical basis for our algorithm and introduce its application using cathodoluminescence images of zircons from the Kilgore Tuff (USA). The results allow us to correlate samples from two different outcrops that are found over 80 km apart.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI41B4344J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI41B4344J"><span>Investigating Transition Zone Thickness Variation under the Arabian Plate: Evidence Lacking for Deep Mantle Upwellings</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Juliá, J.; Tang, Z.; Mai, P. M.; Zahran, H.</p> <p>2014-12-01</p> <p>Cenozoic volcanic outcrops in Arabia - locally known as harrats - span more than 2000 km along the western half of the Arabian plate, from eastern Yemen to southern Syria. The magmatism is bimodal in character, with older volcanics (30 to 20 My) being tholeiitic-to-transitional and paralleling the Red Sea margin, and younger volcanics (12 Ma to Recent) being transitional-to-strongly-alkalic and aligning in a more north-south direction. The bimodal character has been attributed to a two-stage rifting process along the Red Sea, where the old volcanics would have produced from shallow sources related to an initial passive rifting stage, and young volcanics would have originated from one or more deep-seated mantle plumes driving present active rifting. Early models suggested the harrats would have resulted from either lateral flow from the Afar plume in Ethiopia, or more locally from a separate mantle plume directly located under the shield. Most recently, tomographic images of the Arabian mantle have suggested the northern harrats could be resulting from flow originating at a deep plume under Jordan. In this work, we investigate the location of deep mantle plumes under the Arabian plate by mapping transition zone thickness with teleseismic receiver functions. The transition zone is bounded by seismic discontinuities, nominally at 410 and 660 km depth, originating from phase transitions in the olivine-normative component of the mantle. The precise depth of the discontinuities is strongly dependent on temperature and, due to the opposing signs of the corresponding Clapeyron slopes, positive temperature anomalies are expected to result in thinning of the transition zone. Our dataset consists of ~5000 low-frequency (fc < 0.25 Hz) receiver function waveforms obtained at ~110 broadband stations belonging to a number of permanent and temporary seismic networks in the region. The receiver functions were migrated to depth and stacked along a ~2000 km long record section displaying P-to-S conversions at seismic discontinuities under Western Arabia. Our results display a normal to thicker-than-average transition zone under the study area, suggesting thermal perturbations of the transition zone due to deep mantle upwellings under the western shield and/or Jordan are unlikely.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940011735','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940011735"><span>Petrologic constraints on the surface processes on asteroid 4 Vesta and on excavation depths of diogenite fragments</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grove, T. L.</p> <p>1993-01-01</p> <p>The eucrite-howardite-diogenite meteorite groups are though to be related by magmatic processes. Asteroid 4 Vesta has been proposed as the parent body for these basaltic achondrite meteorites. The similarity of the planetesimal's surface composition to eucrite and diogenite meteorites and the large size of the asteroid (r = 250 km) make it an attractive source, but its position in the asteroid belt far from the known resonances from which meteorites originate make a relation between Vesta and eucrite-howardite-giogenite group problematic. It has been proposed that diogenites are low-Ca pyroxene-rich cumulates that crystallized from a magnesian parent (identified in howardite breccias), and this crystallization process led to evolved eucrite derivative magmas. This eucrite-diogenite genetic relationship places constraints on the physical conditions under which crystallization occurred. Elevated pressure melting experiments on magnesian eucrite parent compositions show that the minimum pressure at which pyroxene crystallization could lead to the observed compositions of main series eucrites is 500 bars, equivalent to a depth of 135 km in a 4 Vesta-sized eucrite parent body. Therefore, the observation of diogenite on the surface of 4 Vesta requires a post-crystallization process that excavates diogenite cumulate from depth. The discovery of diogenite asteroidal fragments is consistent with an impact event on 4 Vesta that penetrated the deep interior of this planetesimal.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015CoMP..170...53H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015CoMP..170...53H"><span>Extreme enrichment of Se, Te, PGE and Au in Cu sulfide microdroplets: evidence from LA-ICP-MS analysis of sulfides in the Skaergaard Intrusion, east Greenland</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Holwell, David A.; Keays, Reid R.; McDonald, Iain; Williams, Megan R.</p> <p>2015-12-01</p> <p>The Platinova Reef, in the Skaergaard Intrusion, east Greenland, is an example of a magmatic Cu-PGE-Au sulfide deposit formed in the latter stages of magmatic differentiation. As is characteristic with such deposits, it contains a low volume of sulfide, displays peak metal offsets and is Cu rich but Ni poor. However, even for such deposits, the Platinova Reef contains extremely low volumes of sulfide and the highest Pd and Au tenor sulfides of any magmatic ore deposit. Here, we present the first LA-ICP-MS analyses of sulfide microdroplets from the Platinova Reef, which show that they have the highest Se concentrations (up to 1200 ppm) and lowest S/Se ratios (190-700) of any known magmatic sulfide deposit and have significant Te enrichment. In addition, where sulfide volume increases, there is a change from high Pd-tenor microdroplets trapped in situ to larger, low tenor sulfides. The transition between these two sulfide regimes is marked by sharp peaks in Au, and then Te concentration, followed by a wider peak in Se, which gradually decreases with height. Mineralogical evidence implies that there is no significant post-magmatic hydrothermal S loss and that the metal profiles are essentially a function of magmatic processes. We propose that to generate these extreme precious and semimetal contents, the sulfides must have formed from an anomalously metal-rich package of magma, possibly formed via the dissolution of a previously PGE-enriched sulfide. Other processes such as kinetic diffusion may have also occurred alongside this to produce the ultra-high tenors. The characteristic metal offset pattern observed is largely controlled by partitioning effects, producing offset peaks in the order Pt+Pd>Au>Te>Se>Cu that are entirely consistent with published D values. This study confirms that extreme enrichment in sulfide droplets can occur in closed-system layered intrusions in situ, but this will characteristically form ore deposits that are so low in sulfide that they do not conform to conventional deposit models for Cu-Ni-PGE sulfides which require very high R factors, and settling of sulfide liquids.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP21A1243J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP21A1243J"><span>Continental Arcs as Both Carbon Source and Sink in Regulating Long Term Climate</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jiang, H.; Lee, C. T.</p> <p>2017-12-01</p> <p>The long-term variability of atmospheric pCO2 is determined by the balance between the rate of geologic inputs of CO­­2 (e.g., magmatic/metamorphic degassing, carbonate weathering) and the rate of carbonate precipitation driven by silicate weathering. The Late Cretaceous-Early Cenozoic was characterized by elevated atmospheric pCO2 and greenhouse climate, likely due to increased magmatic flux from mid-ocean ridges and, in particular, continental arcs. However, it has been suggested that continental arc magmatism is accompanied by rapid uplift and erosion due to magmatic/tectonic thickening of the crust, thus continental arcs likely enhance the chemical weathering flux, in turn increasing the carbon sink. To assess the contribution of continental arcs to global carbon inputs and sinks, we conducted a case study in the Cretaceous Peninsular Ranges batholith (PRB) and associated forearc basin in southern California, USA, representing one segment of the Cretaceous Cordillera arc-forearc system. Arc magmatism occurred between 170-85 Ma, peaking at 100 Ma, but erosion of the arc continues into the early Eocene, with forearc sediments representing this protracted arc unroofing. During magmatism, we estimate the CO2 degassing flux from the PRB was at least 5-25*105 mol·km-2·yr-1. By calculating the depletion of Ca and Mg in the forearc sediments relative to their arc protoliths, we estimate the silicate weathering/carbonate precipitation flux to be 106 mol·km-2·yr-1 during Late Cretaceous magmatism, decreasing to 105 mol·km-2·yr-1 by the Early Eocene. We show that during active continental arc magmatism, the CO2 degassing flux is comparable to CO2 consumption driven by silicate weathering in the arc. However, after magmatism ends, a regional imbalance arises in which the arc no longer contributes to CO2 inputs but continued silicate weathering of the arc drives carbonate precipitation such that the arc indirectly becomes CO2 sink. We propose that the development of continental arcs increases weatherability through mountain building processes, and therefore may affect the strength of the global negative feedback between silicate weathering and climate. Future studies are needed to quantify the variability in weathering feedback strength associated with global continental arc development.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995Metic..30Q.593W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995Metic..30Q.593W"><span>Angrites: A Volatile-rich Variety of Asteroidal Basalt (Except for Alkalis and Gallium!)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Warren, P. H.; Kallemeyn, G. W.</p> <p>1995-09-01</p> <p>Angrites are commonly viewed as extremely volatile-depleted, and a related notion is that they formed by differentiation of a very CAI-rich material [e.g., 1]. Partial melting experiments reportedly reproduce the bulk compositions (although not fassaite-rich mineralogy) of angrites with Allende as starting material [2], but highly CAI-rich parent materials are difficult to reconcile with isotopic and REE data [3,4]. Mittlefehldt and Lindstrom [5] inferred from the low Na/Al ratios of angrites that outgassing, and thus primordial magmatism, was more intense on their parent body than on the eucrite parent asteroid. Of seven elements that (a) have been adequately determined in angrites, and (b) are far more volatile (solar-nebula 50% condensation T [6] = 690-430 K) than the alkalis (1000-910 K), four are enriched, and none is significantly depleted, in average angrite compared to average eucrite or low-Ti mare basalt (Figure). Gallium, which is of intermediate volatility (830 K), is depleted to roughly the same extent as Na and K. Results for A881371 [3] are incomplete (Zn, 6 micrograms/g, is near INAA detection limit), but even based only on AdoR and the two LEW angrites, this pattern seems firmly established. Apparent gas cavities in A881371 [7] also suggest that volatiles are far from uniformly depleted. The only elements known to be depleted, as volatiles, by clearly significant factors in angrites versus eucrites or lunar basalts, are alkalis plus gallium. Besides being moderately volatile, a noteworthy characteristic shared among Ga and alkalis (and not shared with elements such as Br, Se, and Zn) is that these elements probably tend to partition into crustal feldspar during gross differentiation of small (low-pressure) bodies. If gallium + alkalis were depleted by a single process starting from "normal" chondritic material, that process would seem to require selective exposure of a feldspar-enriched region (i.e., crust) to extremely high temperature. Igneous crystallization of the angrites occurred when the solar system was still extremely young, and apparently <=2 Ma after the volatile-depletion process [4]. The data of [4] eliminate 26Al as a potential heat source for magmatism. The angrite volatile pattern may be the product of heating by an intense, short-lived heat source that melted and partially vaporized the crust of an asteroid(s) (not necessarily the final angrite asteroid), without much affecting the deep interior(s), which later (through mixing and/or magmatism) replenished the angritic materials in most volatiles, but not alkalis and Ga. Exogenic heating, as in the often-conjectured (but hard to test) hypothesis that a major early heat source was enhanced solar luminosity (as in FU-Orionis cycles), would seem to be required. LEW 87051 and A881371 are rich in compositionally diverse olivine xenocrysts, and A881371 contains a possible FeS xenocryst [7]. These, and the angrites' great siderophile diversity [3], tend to suggest that magmatism and intensely disruptive cratering (with mixing of precursor materials) were contemporaneous. This scenario is admittedly speculative, but the volatile-depletion pattern is difficult to rationalize with any other model. References: [1] Prinz M. and Weisberg M. (1995) Antarct. Meteorites, XX, 207-210. [2] Jurewicz A. et al. (1993) GCA, 57, 2123-2139. [3] Warren P. et al. (1995) Antarct. Meteorites, XX, 261-264. [4] Lugmair G. and Galer S. 1992) GCA, 56, 1673-1694. [5] Mittlefehldt D. and Lindstrom M. (1990) GCA, 54, 3209-3218. [6] Wasson J. (1985) Meteorites. [7] Warren P. and Davis A. (1995) Antarct. Meteorites, XX, 257-260.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1914551G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1914551G"><span>Petrological study of the products of 2011-2012 paroxysmal eruptions: new insight of the intensive variables of the Mt. Etna magmatic system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giacomoni, Pier Paolo; Coltorti, Massimo; Mollo, Silvio; Ferlito, Carmelo; Braiato, Mirko; Scarlato, Piergiorgio</p> <p>2017-04-01</p> <p>Mt. Etna activity from January 2011 to April 2012 was characterized by 24 paroxysmal short-lasting (few to several hours) eruptions from the New South East summit crater. Despite the violence of the activity, no appreciable geophysical signals were recorded during this period, except for an increase in the seismic tremors just minutes/hours before the occurrence of the paroxysm. This type of activity represents a significant shift from the mainly effusive eruptions of 2004; 2006; 2008/2009 and from the lateral rift-related event of 2001 and 2002/2003. The 2011-2012 paroxysmal activity thus represent a unique opportunity to investigate the effects of magmatic chemical-physical intensive variables (P-T-fO2) on the crystallization and fractionation processes occurring in the Mt. Etna open conduit feeding system. We investigated the petrographic and geochemical features of lava and scoria clasts from 10 paroxysmal events. Whole rock compositions plot inside the trachy-basalt field with the typical etnean intraplate chondrite normalized trace element distribution characterized by positive U, Th and La and negative Rb, K, Nb anomalies. MELTs and mass balance fractional crystallization modelling suggest that most of the eruptive events were fed by magma differentiating along the conduit and by a deep basic magma recharge during the 4/3/2012 event. Olivine (Ol), clinopyroxene (Cpx) and plagioclase (Plg) crystal-melt equilibrium conditions were checked before applying thermo-barometric, oxy-fugacity and hygrometer equations by comparing the composition of phenocrysts with those of whole rock, glass and reconstructed primitive magma. Results show that the erupted products are made up of a mixture of phenocrysts in equilibrium with the whole rock or disequilibrated toward more basic or more evolved compositions. Thermobarometric calculations indicate that ol is the first phase on the liquidus (1270 °C, up to 1200 MPa). Cpx crystallizes from 1200 °C, at 700 Mpa in most basic melt (4/3/2012), to 1100 °C at 100 Mpa. Plg nucleation is constrained by the dissolved amount of H2O in the melt and mostly occur above 250 Mpa. Hygrometer determinations indicate that basic magma contains up to 3.7 wt% of dissolved H2O. The overall dataset suggests that the magmatic feeding system of 2011-2012 eruptive events was vertically extended without any significant ponding zone. The conduit is periodically filled with a H2O-rich basic magma at +2 FMQ average oxidation condition. The H2O degassing in the shallower portion of the magmatic column (<200 Mpa) induce a vertical differentiation. The deeper portion of the magmatic column at a pressure >300 Mpa) and low undercooling degree present a more femic geochemical features. The intermediate portion (300-200 Mpa) is repeatedly pushed above the H2O exsolution depth which promotes the plagioclase saturation and nucleation. In the shallower portion (>200 Mpa) the efficient H2O exsolution result in a strong undercooling and promote the massive plg nucleation and differentiation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V34B..04R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V34B..04R"><span>Cenozoic East African Magmatism and the African LLSVP</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rooney, T. O.</p> <p>2017-12-01</p> <p>The Ethiopian-Arabian Large Igneous Province preserves a 45 Ma record of mantle-lithosphere interaction, manifesting as flood basalts, shield volcanoes, silicic eruptions, and monogenetic magmatic events. During the Cenozoic, magmatism in in this region has resulted from the interplay between lithospheric extension and material upwelling from the African large low-velocity shear velocity province (LLSVP). Consequently, the study of magmatism in East Africa provides a complement to investigations of the Pacific LLSVP. The volumetrically significant flood basalt events of the Eocene to Early Miocene suggest a role for material upwelling from the African LLSVP, however the modern focusing of East African magmatism into oceanic spreading centers and continental rifts also highlights the control of lithospheric thinning in magma generation processes. The study of the mantle reservoirs derived from the African LLSVP is complicated by the slow relative motion of the African plate during the Cenozoic, resulting in significant spatial overlap in lavas derived from different magmatic events. This complexity is being resolved with enhanced geochronological precision and a focus on the geochemical characteristics of the volcanic products. It is now apparent that there are three distinct pulses of basaltic volcanism, followed by either by bimodal or silicic volcanism, totaling ca. 720,000 km3 of magmatism: (A) Eocene Initial Phase from 45-34 Ma, which is dominated by basaltic volcanism and focused on Southern Ethiopia and Northern Kenya (Turkana). (B) Oligocene Traps phase from 33.9-27 Ma, which coincides with a significant increase in the aerial extent of volcanism. Broadly age equivalent 1 to 2 km thick sequences of dominantly basalt are centered on the NW Ethiopian Plateau and Yemen, but also Turkana during this period. (C) Early Miocene resurgence phase from 26.9-22 Ma, where basaltic volcanism is seen throughout the region but is less volumetrically significant than the prior two basaltic pulses. With our developing understanding of the persistence of LLSVP anomalies within the mantle, I propose that the three basaltic pulses are ostensibly manifestations of the same plume-lithosphere interaction, requiring revision to the duration, magmatic extent, and magma volume of this Large Igneous Province.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T51B0461E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T51B0461E"><span>How does continental lithosphere break-apart? A 3D seismic view on the transition from magma-poor rifted margin to magmatic oceanic lithosphere</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Emmanuel, M.; Lescanne, M.; Picazo, S.; Tomasi, S.</p> <p>2017-12-01</p> <p>In the last decade, high-quality seismic data and drilling results drastically challenged our ideas about how continents break apart. New models address their observed variability and are presently redefining basics of rifting as well as exploration potential along deepwater rifted margins. Seafloor spreading is even more constrained by decades of scientific exploration along Mid Oceanic Ridges. By contrast, the transition between rifting and drifting remains a debated subject. This lithospheric breakup "event" is geologically recorded along Ocean-Continent Transitions (OCT) at the most distal part of margins before indubitable oceanic crust. Often lying along ultra-deepwater margin domains and buried beneath a thick sedimentary pile, high-quality images of these domains are rare but mandatory to get strong insights on the processes responsible for lithospheric break up and what are the consequences for the overlying basins. We intend to answer these questions by studying a world-class 3D seismic survey in a segment of a rifted margin exposed in the Atlantic. Through these data, we can show in details the OCT architecture between a magma-poor hyper-extended margin (with exhumed mantle) and a classical layered oceanic crust. It is characterized by 1- the development of out-of-sequence detachment systems with a landward-dipping geometry and 2- the increasing magmatic additions oceanwards (intrusives and extrusives). Geometry of these faults suggests that they may be decoupled at a mantle brittle-ductile interface what may be an indicator on thermicity. Furthermore, magmatism increases as deformation migrates to the future first indubitable oceanic crust what controls a progressive magmatic crustal thickening below, above and across a tapering rest of margin. As the magmatic budget increases oceanwards, full-rate divergence is less and less accommodated by faulting. Magmatic-sedimentary architectures of OCT is therefore changing from supra-detachment to magmatic oceanic half-grabens (low-crustal extension, high magma additions) and to ultimate layered oceanic crust (quasi-none crustal extension, full magmatic accretion). All of these elements suggest that lithospheric breakup can be addressed as a tectonic-magma competition as the brittle-ductile mantle interface is shallowing along OCT.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T11D..04M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T11D..04M"><span>Beating the Heat: Magmatism in the Low-Temperature Thermochronologic Record</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Murray, K. E.; Reiners, P. W.; Braun, J.; Karlstrom, L.; Morriss, M. C.</p> <p>2017-12-01</p> <p>The low-temperature thermochronology community was quick to recognize upper-crustal complexities in the geotherm that reflect landscape evolution, but the complex effects of crustal magmatism on thermochronometers can be difficult to independently document and remain underexplored. Because magmatism is common in many regions central to our understanding of tectonics, this is a significant gap in our ability to robustly interpret rock cooling. Here, we use several different numerical approaches to examine how local and regional crustal magmatism affects cooling age patterns and present examples from the western US that demonstrate the importance—and utility—of considering these effects. We modified the finite-element code Pecube to calculate how thermochronometers document the emplacement of simple hot bodies at different crustal levels. Results demonstrate the potential for mid-crustal plutons, emplaced at 10-15 km depth, to reset cooling ages in the overlying rocks at partial-retention depths at the time of magmatism. Permo-Triassic sandstones from the Colorado Plateau's Canyonlands region have apatite cooling ages that exemplify the resulting ambiguity: Oligocene rock cooling can be attributed to either 1 km of erosion or relaxation of a geothermal gradient transiently doubled by mid-crustal magmatism. Despite these complexities, there are compelling reasons to target rocks with magmatic histories. Shallowly emplaced plutons can usefully reset cooling ages in country rocks with protracted near-surface histories, as we have demonstrated in the Colorado Plateau's Henry Mountains. Cooling age patterns are also useful for quantifying magmatic processes themselves. In an ongoing project, we use the pattern of thermochronometer resetting around individual dikes that fed the Columbia River flood basalts, which are exposed in the Wallowa Mountains, to identify long-lived feeder dikes and model their thermal aureoles to further constrain eruptive dynamics. The pattern of resetting around dikes compliments higher-temperature constraints on the longevity of magma flow from phase equilibria in partially melted wall rocks. In principal, this technique should also resolve along-strike variability in flow localization, providing novel constraints on eruptive flux in large igneous provinces.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1213267G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1213267G"><span>Geochemical Specific Characters of the Oil and the Origin of the Oil and Gas Fields</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gottikh, Rimma; Pisotskiy, Bogdan; Plotnikova, Irina</p> <p>2010-05-01</p> <p>It is generally assumed that the fluid regime of the basement of ancient platforms is not associated with that of the sedimentary cover. This assumption is mainly due to the substantial time gap between the formation of the crystalline and sedimentary rocks as well as the evolutionary differences between the thermal regime of the interior and the redox potentials of fluid systems. The presence of loosely aggregated zones filled with salt-water solutions, oil or gas in the upper basement is explained by downward fluid flows from sedimentary rocks through tectonic faults into the disintegrated crystalline rocks. The formation of such zones is believed to be due to the crustal stratification due to Earth's pulsation, periodic variations of its rotational rate, hydrogenic deconsolidation, burial of the post-Early Proterozoic disintegration zones, etc. This pattern suggests that the matter and energy exchange between the Earth's spheres in the late stages of the platform development could only take place with the help of magmatic melts and the associated fluids during the tectonomagmatic cycles of the Earth's crust transformation. Gas and liquid hydrocarbon components mainly occur in crystalline basement rocks of ancient platforms penetrated to a depth of more than 3000 m due to deep degassing processes. The traces of the upward migration of fluids are sealed in the geological sequence, including the sedimentary cover, within secondary inclusions of rocks and minerals. The fluids are complex, reduced, multicomponent systems that transport lithophilous, chalcophilous and siderophilous elements. The presence of microelements in the bituminous phase of inclusions indicates that metals mainly occur in the complexes containing organic ligands. During the evolution of the fluid systems under new pressure and temperature conditions, low-solubility substances were separated out of the fluid to form hard bitumen, and the lighter components migrated into the overlying fractured and porous rocks. The high metal content of carbonaceous substances and their compositional variations governed by homogenisation temperatures of the inclusions suggest that they are not the products of the decomposition of oil fields. The constant presence of uranium in the fluid and its differentiation products allows the tracing of the systems' migration ways from the crystalline basement to oil-saturated reservoir zones of the sedimentary cover The known geochemical properties of bitumen and oil - high platinum content, specific distributions of rare earth elements, that are not characteristic of the upper crust formations, as well as 143Nd/144Nd and 87Sr/86Sr isotopic compounds, which are out of balance with the organic matter of sedimentary rocks - suggest that hydrocarbons are accumulated in the presence of cooling high-alkalinity mafite-ultramafite intrusions. This logically corresponds to the distribution of seismic anomalies and magnetic and gravity fields in the consolidated crust below the various petroleum fields (for example, South Tatarstan and Nepsky arches of the Romashkino and Verkhne-Chonskoye oil fields). The acquired geochemical and thermodynamic characteristics of the reduced fluids and their differentiation products from the crystalline basement and the sedimentary cover of the southern Siberian and eastern East European platforms indicate that these were formed outside of the sedimentary cover and that the migration was directed upwards. The analysis of the magmatic evolution on platforms reveals its alkaline trend due to the impeded degassing of magmatic sources at depth and the inflow of new doses of alkaline fluids or melts into them. Further evolution of the zones of partial melting of the substratum led, in the authors' view, to the generation of oil-forming fluids and their transportation into the Earth's upper crust. Their interaction with the surrounding rocks in turn led to the formation of oil accumulations. Thus, oil is the product of the interaction of deep, reduced fluids. Oil, graphite of the Archaean crystalline complexes and hard bitumens are interrelated elements of the evolution of deep, high-enthalpy systems. These large-scale reduced palaeofluid phenomena are obviously related to geodynamic and tectonomagmatic processes. The source of these fluid systems, their impact on the geological environment and its consequences can be determined through additional integrated geochemical studies using the isotopes of heavy elements and through the correlation of the observed potential fields with the structure of the consolidated crust and the sedimentary cover for the identification of geodynamic processes in geophysically inhomogeneous zones of the geological medium.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/biblio/5416312-updating-geological-geothermal-research-milos-island','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/5416312-updating-geological-geothermal-research-milos-island"><span>Updating of the geological and geothermal research on Milos island</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Fytikas, M.</p> <p>1989-01-01</p> <p>The oldest geologic formations outcropping in Milos are an Alpine age crystalline basement and a transgressive marine Neogene sequence. The island is mainly volcanic. It belongs to the Aegean Active Arc, within which the Milos archipelago shows the most important volcanism in terms of quantity, variety of products and duration of activity (3.5-0.8 M.a.). There are no large central volcanic edifices but different, frequently coeval eruption centres. The initial and intermediate phases of activity were mainly pyroclastic and submarine, whereas the last one (0.1 M.a.) was subaerial and formed tuff rings, surge deposits and lava flows, all of homogenous rhyoliticmore » composition. Recent detailed studies have addressed the mechanism of feeding and the type of magmatic chambers beneath Milos. Distention tectonics have two main phases: an earlier one (Pliocene) with NE-SW direction and a much more intense recent (Quaternary) one, trending NW-SE. The geological, tectonic and magmatic activity favoured the formation of a high enthalpy geothermal field. Many fossil and active thermal manifestations exist: hot springs, fumaroles, hot grounds, phreatic explosion craters. The hydrothermal alteration of the volcanites produced, by self sealing, a perfect cover for the geothermal fluids. Geothermometry of the surface fluids indicated high values for the source temperatures and very high geothermal gradients in central and eastern Milos. Geothermally anomalous zones, defined by two different methods, together with superficial geological and tectonic information, permitted the location of sites for deep drilling. Five exploratory wells 1000-1400m deep gave satisfactory results of flow rate (40-120 t/h), temperature (300-320{sup 0}C) and enthalpy.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1910582D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1910582D"><span>On the relation between crustal deformation and seismicity during the 2012-2014 magmatic intrusions in El Hierro island.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Domínguez Cerdeña, Itahiza; García-Cañada, Laura; Ángeles Benito Saz, María; Del Fresno, Carmen</p> <p>2017-04-01</p> <p>The last volcanic eruption in the Canary Islands took place in 2011 less than 2 km offshore El Hierro island, after 3 months of measuring surface deformation (up to 5 cm) and locating more than 10 000 earthquakes. In the two years following the end of the submarine eruption on 5 March 2012, six deep magmatic intrusions were recorded beneath the island. Despite the short time duration of these intrusions, these events have been more energetic that the 2011 pre-eruptive intrusive event but none of them ended in a new eruption. These post-eruptive reactivations are some of the few examples in the world of well monitored magmatic intrusions related with monogenetic volcanism. In order to understand these processes we have analyzed the geodetic and seismic data with different techniques. First, we did a joint hypocentral relocation of the six seismic swarms, including more than 6 300 events, to analyze the relative distribution of the earthquakes from different intrusions. The uncertainties of the earthquakes relocations was reduced to an average value of 300 m. New earthquakes' distribution shows the alignments of the different intrusions and a temporal migration of the events to larger depths. Moreover, we show the results of the ground deformation using GPS data from the network installed on the island (for each of the six intrusive events) and their inversion considering spherical models. In most of the intrusions the optimal source model was shallower and southern than the corresponding seismicity hypocenters. The intruded magma volume ranges from 0.02 to 0.13 km3. Finally, we also computed the b value from the Gutenberg Richter equation by means of a bootstrap method. The spatial and temporal evolution of the b value for the seismicity show a clear correlation with the temporal evolution of the crustal deformation. The six magma intrusions can be grouped, depending on their location, in three pairs each one associated with each of the three active rifts of El Hierro island. Although all intrusions show similar magma supply rate (60-90 m3/s) we found particular characteristic for each the three groups of intrusions, including the relation between seismic energy and deformation or the ratio between seismic and geodetic moment. We discuss the compatibility or not of these results with the possible triaxial nature of the origin of El Hierro island. As a conclusion, we have reviewed the historical seismic catalog and compared these post-eruptive intrusions with other possible magmatic intrusions in the Canary Islands. We found that a maximum of 50% of the volcanic unrests occurred in the Canary Islands in the last century ended in eruptions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V11B4720K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V11B4720K"><span>Alberca De Guadalupe Maar Crater, Zacapu Basin : A Rare Type of Volcano within the Michoacán-Guanajuato Volcanic Field, México</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kshirsagar, P. V.; Siebe, C.; Guilbaud, M. N.; Salinas, S.</p> <p>2014-12-01</p> <p>Phreato-magmatic vents (esp. maar craters) are rare in the ~40,000 Km2 Plio-Quaternary monogenetic Michoacán-Guanajuato Volcanic Field (MGVF) located in the central part of the Mexican Volcanic Belt. In contrast to >1000 scoria cones, only 2 dozen phreato-magmatic monogenetic vents (e.g. tuff cones, tuff rings, and maars) have been identified. About half of these form a cluster near Valle de Santiago in the Lerma river valley at the northern margin of the MGVF, while the others occur in a rather scattered fashion. Here we discuss the origin of Alberca de Guadalupe maar crater, one of the three phreato-magmatic vents (in addition to El Caracol and Alberca de Los Espinos) that occur within the boundaries of the inter-montane lacustrine Zacapu basin, a tectonic graben bound by an ENE-WSW normal fault system. The maar crater came into existence between 20,000 and 23,000 y BP, forming a 140 m deep hole in the otherwise planar surrounding ground of theearly Pleistocene lava flows of Cerro Pelón.The maar crater has a diameter of ~1 Km and bears a 9 m deep lake. Eruptive products include typical surge deposits that are best exposed around the rim and inner crater walls. They are poorly sorted (Mdø= -1.56 to -3.75, ø= 1.43 to 3.23), rich in accidental lithics (angular andesitic lava and ignimbrite clasts) constituting 51-88% of the deposit with few juveniles (basaltic andesite with phenocrysts of plagioclase, olivine, and pyroxene in a quenched glassy matrix; SiO2=54-58 wt. %). Dry surge units are friable and clast-supported, in contrast the wet surge units are fairly indurated and bear accretionary lapilli. Bedding is frequently distorted by ballistic impact-sag structures. The entire construct is disrupted by an E-W trending regional fault, downthrowing the northern part by ~30 m.The unusual formation of this maar crater in the semi-arid highlands of Zacapu was favored by the local hydrological and topographical conditions. Such conditions still prevail in several parts of the MGVF, making it possible for such an event to occur again, considering the active nature of this region, which is famous for its historic 1943-1952 eruption of Paricutin.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JSG....92...46P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JSG....92...46P"><span>Contrasting magmatic structures between small plutons and batholiths emplaced at shallow crustal level (Sierras de Córdoba, Argentina)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pinotti, Lucio P.; D'Eramo, Fernando J.; Weinberg, Roberto F.; Demartis, Manuel; Tubía, José María; Coniglio, Jorge E.; Radice, Stefania; Maffini, M. Natalia; Aragón, Eugenio</p> <p>2016-11-01</p> <p>Processes like injection, magma flow and differentiation and influence of the regional strain field are here described and contrasted to shed light on their role in the formation of small plutons and large batholiths their magmatic structures. The final geometric and compositional arrangement of magma bodies are a complex record of their construction and internal flow history. Magma injection, flow and differentiation, as well as regional stresses, all control the internal nature of magma bodies. Large magma bodies emplaced at shallow crustal levels result from the intrusion of multiple magma batches that interact in a variety of ways, depending on internal and external dynamics, and where the early magmatic, growth-related structures are commonly overprinted by subsequent history. In contrast, small plutons emplaced in the brittle-ductile transition more likely preserve growth-related structures, having a relatively simple cooling history and limited internal magma flow. Outcrop-scale magmatic structures in both cases record a rich set of complementary information that can help elucidate their evolution. Large and small granitic bodies of the Sierra Pampeanas preserve excellent exposures of magmatic structures that formed as magmas stepped through different rheological states during pluton growth and solidification. These structures reveal not only the flow pattern inside magma chambers, but also the rheological evolution of magmas in response to temperature evolution.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V52A..08C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V52A..08C"><span>Modulation of magmatic processes by carbon dioxide</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Caricchi, L.; Sheldrake, T. E.; Blundy, J. D.</p> <p>2017-12-01</p> <p>Volatile solubility in magmas increases with pressure, although the solubility of CO2 is much lower than that of H2O. Consequently, magmas rising from depth release CO2-rich fluids, which inevitably interact with H2O-poor magmas in the upper crust (CO2-flushing). CO2-flushing triggers the exsolution of H2O-rich fluids, leading to an increase of volume and magma crystallisation. While the analyses of eruptive products demonstrates that this process operates in virtually all magmatic system, its impact on magmatic and volcanic processes has not been quantified. Here we show that depending on the initial magma crystallinity, and the depth of magma storage, CO2-flushing can lead to volcanic eruptions or promote conditions that favour the impulsive release of mineralising fluids. Our calculations show that the interaction between a few hundred ppm of carbonic fluids, and crystal-poor magmas stored at shallow depths, produces rapid pressurisation that can potentially lead to an eruption. Further addition of CO2 increases magma compressibility and crystallinity, reducing the potential for volcanic activity, promoting the formation of ore deposits. Increasing the depth of fluid-magma interaction dampens the impact of CO2-flushing on the pressurisation of a magma reservoir. CO2-flushing may result in surface inflation and increases in surface CO2 fluxes, which are commonly considered signs of an impending eruption, but may not necessarily result in eruption depending on the initial crystallnity and depth of the magmatic reservoir. We propose that CO2-flushing is a powerful agent modulating the pressurisation of magma reservoirs and the release of mineralising fluids from upper crustal magma reservoirs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70021758','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70021758"><span>Mesoproterozoic rapakivi granites of the Rondonia Tin Province, southwestern border of the Amazonian craton, Brazil-I. Reconnaissance U-Pb geochronology and regional implications</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bettencourt, Jorge S.; Tosdal, R.M.; Leite, W.B.; Payolla, B.L.</p> <p>1999-01-01</p> <p>Rapakivi granites and associated mafic and ultramafic rocks in the Rondonia Tin Province, southwestern Amazonian craton, Brazil were emplaced during six discrete episodes of magmatism between ca 1600 and 970 Ma. The seven rapakivi granite suites emplaced at this time were the Serra da Providencia Intrusive Suite (U-Pb ages between 1606 and 1532 Ma); Santo Antonio Intrusive Suite (U-Pb age 1406 Ma); Teotonio Intrusive Suite (U-Pb age 1387 Ma); Alto Candeias Intrusive Suite (U-Pb ages between 1346 and 1338 Ma); Sao Lourenco-Caripunas Intrusive Suite (U-Pb ages between 1314 and 1309 Ma); Santa Clara Intrusive Suite (U-Pb ages between 1082 and 1074 Ma); and Younger Granites of Rondonia (U-Pb ages between 998 and 974 Ma). The Serra da Providencia Intrusive Suite intruded the Paleoproterozoic (1.80 to 1.70 Ga) Rio Negro-Juruena crust whereas the other suites were emplaced into the 1.50 to 1.30 Ga Rondonia-San Ignacio crust. Their intrusion was contemporaneous with orogenic activity in other parts of the southwestern Amazonian craton, except for the oldest, Serra da Providencia Intrusive Suite. Orogenic events coeval with emplacement of the Serra da Providencia Intrusive Suite are not clearly recognized in the region. The Santo Antonio, Teotonio, Alto Candeias and Sao Lourenco-Caripunas Intrusive Suites are interpreted to represent extensional anorogenic magmatism associated with the terminal stages of the Rondonian-San Ignacio orogeny. At least the Sao Lourenco-Caripunas rapakivi granites and coeval intra-continental rift sedimentary rocks may, in contrast, represent the products of extensional tectonics and rifting preceding the Sunsas/Aguapei orogeny (1.25 to 1.0 Ga). The two youngest rapakivi suites, the Santa Clara Intrusive Suite and Younger Granites of Rondonia, seemingly represent inboard magmatism in the Rondonian-San Ignacio Province during a younger episode of reworking in the Rio Negro-Juruena Province during the waning stages of the collisional 1.1 to 1.0 Ga Sunsas/Aguapei orogeny. The six intra-plate rapakivi granite episodes in the southwestern part of the Amazonian craton form three broad periods of anorogenic magmatism that have age-correlative events composed of similar rocks and geologic environments in eastern Laurentia and Baltica, although the exact timing of magmatism appears slightly different. Recognition of lithologic and chronological correlations between various cratons provide important constraints to models explaining the interplay between rapakivi granite magmatism and deep crustal evolution of an early Mesoproterozoic supercontinent. They are, furthermore, important to plate tectonic models for the assembly, dispersal and reassembly of Amazonia, Laurentia and Baltica in the Mesoproterozoic and Neoproterozoic.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70030945','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70030945"><span>Bald Mountain gold mining district, Nevada: A Jurassic reduced intrusion-related gold system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Nutt, C.J.; Hofstra, A.H.</p> <p>2007-01-01</p> <p>The Bald Mountain mining district has produced about 2 million ounces (Moz) of An. Geologic mapping, field relationships, geochemical data, petrographic observations, fluid inclusion characteristics, and Pb, S, O, and H isotope data indicate that An mineralization was associated with a reduced Jurassic intrusion. Gold deposits are localized within and surrounding a Jurassic (159 Ma) quartz monzonite porphyry pluton and dike complex that intrudes Cambrian to Mississippian carbonate and clastic rocks. The pluton, associated dikes, and An mineralization were controlled by a crustal-scale northwest-trending structure named the Bida trend. Gold deposits are localized by fracture networks in the pluton and the contact metamorphic aureole, dike margins, high-angle faults, and certain strata or shale-limestone contacts in sedimentary rocks. Gold mineralization was accompanied by silicification and phyllic alteration, ??argillic alteration at shallow levels. Although An is typically present throughout, the system exhibits a classic concentric geochemical zonation pattern with Mo, W, Bi, and Cu near the center, Ag, Pb, and Zn at intermediate distances, and As and Sb peripheral to the intrusion. Near the center of the system, micron-sized native An occurs with base metal sulfides and sulfosalts. In peripheral deposits and in later stages of mineralization, Au is typically submicron in size and resides in pyrite or arsenopyrite. Electron microprobe and laser ablation ICP-MS analyses show that arsenopyrite, pyrite, and Bi sulfide minerals contain 10s to 1,000s of ppm Au. Ore-forming fluids were aqueous and carbonic at deep levels and episodically hypersaline at shallow levels due to boiling. The isotopic compositions of H and O in quartz and sericite and S and Pb in sulfides are indicative of magmatic ore fluids with sedimentary sulfur. Together, the evidence suggests that Au was introduced by reduced S-bearing magmatic fluids derived from a reduced intrusion. The reduced character of the intrusion was caused by assimilation of carbonaceous sedimentary rocks. Tertiary faults dismember the area and drop down the upper part of the mineralizing system to the west. The abundant and widespread kaolinite in oxide ores is relatively disordered (1A polytype) and has ??D and ??18O values suggestive of a supergene origin. The deep weathering and oxidation of the ores associated with exhumation made them amenable to open-pit mining and processing using cyanide heap leach methods. ?? 2007 Society of Economic Geologists, Inc.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAESc.131...12W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAESc.131...12W"><span>Petrogenesis and tectonic implications of the Neoarchean North Liaoning tonalitic-trondhjemitic gneisses of the North China Craton, North China</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Maojiang; Liu, Shuwen; Wang, Wei; Wang, Kang; Yan, Ming; Guo, Boran; Bai, Xiang; Guo, Rongrong</p> <p>2016-12-01</p> <p>Tonalitic-trondhjemitic-granodioritic (TTG) gneisses are dominant lithological assemblages in Archean high grade metamorphic terranes in the world. These TTG gneisses preserve important information in formation and evolution of Archean continental crust. Tangtu-Majuanzi microblock in North Liaoning Province (NLP) is one of the major Neoarchean metamorphic basement terranes in the northeastern margin of the North China Craton (NCC). The Tangtu-Majuanzi microblock is composed mainly of Neoarchean tonalitic-trondhjemitic (TT) gneisses, subordinate granodioritic to monzogranitic association (GMA) and minor supracrustal rocks. The tonalitic-trondhjemitic gneisses are divided into high MgO Group (HMG) and low MgO Group (LMG) based on their chemical compositions. Detailed petrogenetic investigations suggest that the magmatic precursors of the HMG samples were derived from partial melting of subducted slabs and contaminated by the overlying mantle wedge during its ascent; whereas, magmatic precursors of the LMG samples were derived from the juvenile lower crust. LA-ICPMS zircon U-Pb isotopic dating analyses reveal that the magmatic precursors of the HMG samples were formed at 2553-2531 Ma. An older HMG tonalitic gneiss sample was discovered at Sandaoguan in the southmost of the studied area, with its magmatic precursor emplaced at 2680 Ma. The magmatic precursors of the LMG samples emplaced at 2595-2583 Ma. Combined with previous credible chronological data, our newly obtained zircon U-Pb dating and Lu-Hf isotopic data indicate that three episodes of magmatism at ∼2700-2680 Ma, ∼2600-2570 Ma and ∼2550-2510 Ma occurred in the Tangtu-Majuanzi microblock, and the TT gneisses in this microblock were subjected to generally amphibolite-facies metamorphism at ∼2520-2470 Ma. Based on the above Neoarchean crust-mantle thermal-dynamic processes, we propose that the Neoarchean magmatism and metamorphism in the Tangtu-Majuanzi microblock of North Liaoning Province occurred in an active continental margin.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70019704','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70019704"><span>Igneous evolution of a complex laccolith-caldera, the Solitario, Trans-Pecos Texas: Implications for calderas and subjacent plutons</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Henry, C.D.; Kunk, Michael J.; Muehlberger, W.R.; McIntosh, W.C.</p> <p>1997-01-01</p> <p>The Solitario is a large, combination laccolith and caldera (herein termed "laccocaldera"), with a 16-km-diameter dome over which developed a 6 x 2 km caldera. This laccocaldera underwent a complex sequence of predoming sill, laccolith, and dike intrusion and concurrent volcanism; doming with emplacement of a main laccolith; ash-flow eruption and caldera collapse; intracaldera sedimentation and volcanism; and late intrusion. Detailed geologic mapping and 40Ar/39Ar dating reveal that the Solitario evolved over an interval of approximately 1 m.y. in three distinct pulses at 36.0, 35.4, and 35.0 Ma. The size, duration, and episodicity of Solitario magmatism are more typical of large ash-flow calderas than of most previously described laccoliths. Small volumes of magma intruded as abundant rhyolitic to trachytic sills and small laccoliths and extruded as lavas and tuffs during the first pulse at 36.0 Ma. Emplacement of the main laccolith, doming, ash-flow eruption, and caldera collapse occurred at 35.4 Ma during the most voluminous pulse. A complex sequence of debris-flow and debris-avalanche deposits, megabreccia, trachyte lava, and minor ash-flow tuff subsequently filled the caldera. The final magmatic pulse at 35.0 Ma consisted of several small laccoliths or stocks and numerous dikes in caldera fill and along the ring fracture. Solitario rocks appear to be part of a broadly cogenetic, metaluminous suite. Peralkaline rhyolite lava domes were emplaced north and west of the Solitario at approximately 35.4 Ma, contemporaneous with laccolith emplacement and the main pulse in the Solitario. The spatial and temporal relation along with sparse geochemical data suggest that the peralkaline rhyolites are crustal melts related to the magmatic-thermal flux represented by the main pulse of Solitario magmatism. Current models of laccolith emplacement and evolution suggest a continuum from initial sill emplacement through growth of the main laccolith. Although the Solitario laccocaldera followed this sequence of events, our field and 40Ar/39Ar data demonstrate that it developed through repeated, episodic magma injections, separated by 0.4 to 0.6 m.y. intervals of little or no activity. This evolution requires a deep, long-lived magma source, well below the main laccolith. Laccoliths are commonly thought to be small, shallow features that are not representative of major, silicic magmatic systems such as calderas and batholiths. In contrast, we suggest that magma chambers beneath many ashflow calderas are tabular, floored intrusions, including laccoliths. Evidence for this conclusion includes the following: (1) many large plutons are recognized to be laccoliths or at least tabular, (2) the Solitario and several larger calderas are known to have developed over laccoliths, and (3) magma chambers beneath calderas, which are as much as 80 km in diameter, cannot be as deep as they are wide or some would extend into the upper mantle. The Solitario formed during a tectonically neutral period following Laramide deformation and preceding Basin and Range extension. Therefore, space for the main laccolith was made by uplift of its roof and possibly subsidence of the floor, not by concurrent faulting. Laccolith-type injection is probably a common way that space is made for magma bodies of appreciable areal extent in the upper crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70098931','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70098931"><span>Aeromagnetic search for Cenozoic magmatism over the Admiralty Mountains Block (East Antarctica)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>,; ,; Ferraccioli, F.; Zunino, A.; Bozzo, E.; Rocchi, S.; Armienti, P.</p> <p>2007-01-01</p> <p>Cenozoic magmatic rocks of the Transantarctic Mountains provide an important window on the tectonic and magmatic processes of the West Antarctic Rift System. Previous aeromagnetic investigations in northern Victoria Land have delineated Cenozoic volcanic and intrusive complexes assigned to the McMurdo Volcanic Group and Meander Intrusives over the Transantarctic Mountains. We present a new aeromagnetic anomaly map for the region north of the Mariner Glacier to study the extent and spatial distribution of these Cenozoic rocks over the previously unexplored Admiralty Mountains. The new map shows that the Meander Intrusives are restricted to the coastal region between the Malta Plateau and the Daniell Peninsula. However, the McMurdo Volcanic Group rocks extend further inland, and may delineate a hitherto unrecognised volcano-tectonic rift zone, extending as far north as the Trafalgar Glacier.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JAESc.160...78M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JAESc.160...78M"><span>Devonian volcanic rocks of the southern Chinese Altai, NW China: Petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Xiaomei; Cai, Keda; Zhao, Taiping; Bao, Zihe; Wang, Xiangsong; Chen, Ming; Buslov, M. M.</p> <p>2018-07-01</p> <p>Ridge-trench interaction is a common tectonic process of the present-day Pacific Rim accretionary orogenic belts, and this process may facilitate "slab-window" magmatism that can produce significant thermal anomalies and geochemically unusual magmatic events. However, ridge-trench interaction has rarely been well-documented in the ancient geologic record, leading to grossly underestimation of this process in tectonic syntheses of plate margins. The Chinese Altai was inferred to have undergone ridge subduction in the Devonian and a slab-window model is proposed to interpret its high-temperature metamorphism and geochemically unique magmatic rocks, which can serve as an excellent and unique place to refine the tectonic evolution associated with ridge subduction in an ancient accretionary orogeny. For this purpose, we carried out geochemical and geochronological studies on Devonian basaltic rocks in this region. Secondary ion mass spectrometry (SIMS) zircon U-Pb dating results yield an age of 376.2 ± 2.4 Ma, suggesting an eruption at the time of Late Devonian. Geochemically, the samples in this study have variable SiO2 (43.3-58.3 wt%), low K2O (0.02-0.07 wt%) and total alkaline contents (2.16-5.41 wt%), as well as Fe2O3T/MgO ratios, showing typical tholeiitic affinity. On the other hand, the basaltic rocks display MORB-like REE patterns ((La/Yb)N = 0.90-2.57) and (Ga/Yb)N = 0.97-1.28), and have moderate positive εNd(t) values (+4.4 to +5.4), which collectively suggest a derivation from a mixing source comprising MORB-like mantle of a mature back-arc basin and subordinate arc mantle wedge. These basaltic rocks are characterized by Low La/Yb (1.26-3.69), Dy/Yb (1.51-1.77) and Sm/Yb (0.83-1.32) ratios, consistent with magmas derived from low degree (∼10%) partial melting of the spinel lherzolite source at a quite shallow mantle depth. Considering the distinctive petrogenesis of the basaltic rocks in this region, the Late Devonian basalts in the southern Chinese Altai is suggested to have witnessed the propagating process of slab-window magmatism that was induced by ridge subduction in a nascent rifting stage of a back-arc basin.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMOS23E..03Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMOS23E..03Y"><span>Preliminary results of the Source China Sea passive source OBS array experiment</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, T.; Liu, C.; Pei, Y.; Xia, S.</p> <p>2013-12-01</p> <p>The Scarborough, or Huangyan, Seamount chain in South China Sea (SCS) represents an extreme case of the global mid-ocean ridge system where the magmatism continues for many million years after the cessation of spreading. To understand this unique process, the South China Sea Deep (SCSD) program funded an experiment deploying a passive source OBS array to image the lithospheric structure beneath the extinct ridge. In April 2012, 18 passive source OBSs, including 15 Guralp CMG-40T OBS and 3 I-4C OBS, were deployed around the Huangyan Island for one year. 11 OBSs were successfully recovered this April, and their data are being processed. Here we present some preliminary results from analyses of this dataset, including the general quality of three-component seismograms, characteristics of seafloor ambient noise spectra, determining the OBS orientation from the Rayleigh wave polarization, and the dispersion analysis of Rayleigh waves. We found that, for most stations, seismograms from teleseismic, regional and local events are generally good with the horizontal records being comparable with vertical component. The noise levels in these seafloor stations are much higher than land-based stations, especially in shorter periods, likely suggesting the direct and stronger impact from the tempestuous SCS. Applications of more sophisticated seismic techniques such as surface wave tomography, seismic anisotropy, receiver function and ambient noise cross-correlation are underway. In addition to the low recovery rate, there are other lessons learned from this experiment. For example, at least two stations have detectable timing problems; Airgun shots should have been used to constrain the timings and orientations in both deployment and recovery. It is still challenging and costly to carry out long-term passive source seismic observations in deep sea.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017NatGe..10..930P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017NatGe..10..930P"><span>Evidence for a spike in mantle carbon outgassing during the Ediacaran period</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Paulsen, Timothy; Deering, Chad; Sliwinski, Jakub; Bachmann, Olivier; Guillong, Marcel</p> <p>2017-12-01</p> <p>Long-term cycles in Earth's climate are thought to be primarily controlled by changes in atmospheric CO2 concentrations. Changes in carbon emissions from volcanic activity can create an imbalance in the carbon cycle. Large-scale changes in volcanic activity have been inferred from proxies such as the age abundance of detrital zircons, but the magnitude of carbon emissions depends on the style of volcanism as well as the amount. Here we analyse U-Pb age and trace element data of detrital zircons from Antarctica and compare the results with the global rock record. We identify a spike in CO2-rich carbonatite and alkaline magmatism during the Ediacaran period. Before the Ediacaran, secular cooling of the mantle and the advent of cooler subduction regimes promoted the sequestration of carbon derived from decarbonation of subducting oceanic slabs in the mantle. We infer that subsequent magmatism led to the extensive release of carbon that may at least in part be recorded in the Shuram-Wonoka carbon isotope excursion. We therefore suggest that this pulse of alkaline volcanism reflects a profound reorganization of the Neoproterozoic deep and surface carbon cycles and promoted planetary warming before the Cambrian radiation.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JVGR..289..193S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JVGR..289..193S"><span>Crustal imaging of western Michoacán and the Jalisco Block, Mexico, from Ambient Seismic Noise</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Spica, Zack; Cruz-Atienza, Víctor M.; Reyes-Alfaro, Gabriel; Legrand, Denis; Iglesias-Mendoza, Arturo</p> <p>2014-12-01</p> <p>Detailed crustal imaging of western Michoacán and the Jalisco Block is obtained from ambient noise tomography. Results show a deep and well-delineated volcanic system below the Colima volcano complex, rooting up to ~ 22 km depth, with a shallow magmatic chamber constrained to the first ~ 7 km. A shallow low-velocity system to the south of the Chapala rift and west of the Michoacán-Guanajuato volcanic field merges, underneath the Colima rift, with the Colima volcano system at about 20 km depth, honoring the geometry of the Trans-Mexican Volcanic Belt. For depths greater than ~30 km, low-velocity features become parallel to the slab strike, right beneath the Mascota, Ayutla and Tapalpa volcanic fields, suggesting the presence of the mantle wedge above the Rivera plate. All mentioned low-velocity bodies are spatially correlated with the superficial volcanic activity suggesting their magmatic origin so that, the shallower these bodies, the younger are the associated volcanic deposits. Along the coast, different depths of the uppermost layer of the Rivera and the Cocos plates suggest that the latter plate subducts with an angle ~ 9° steeper than the former.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017CoMP..172...49A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017CoMP..172...49A"><span>A cascade of magmatic events during the assembly and eruption of a super-sized magma body</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Allan, Aidan. S. R.; Barker, Simon J.; Millet, Marc-Alban; Morgan, Daniel J.; Rooyakkers, Shane M.; Schipper, C. Ian; Wilson, Colin J. N.</p> <p>2017-07-01</p> <p>We use comprehensive geochemical and petrological records from whole-rock samples, crystals, matrix glasses and melt inclusions to derive an integrated picture of the generation, accumulation and evacuation of 530 km3 of crystal-poor rhyolite in the 25.4 ka Oruanui supereruption (New Zealand). New data from plagioclase, orthopyroxene, amphibole, quartz, Fe-Ti oxides, matrix glasses, and plagioclase- and quartz-hosted melt inclusions, in samples spanning different phases of the eruption, are integrated with existing data to build a history of the magma system prior to and during eruption. A thermally and compositionally zoned, parental crystal-rich (mush) body was developed during two periods of intensive crystallisation, 70 and 10-15 kyr before the eruption. The mush top was quartz-bearing and as shallow as 3.5 km deep, and the roots quartz-free and extending to >10 km depth. Less than 600 year prior to the eruption, extraction of large volumes of 840 °C low-silica rhyolite melt with some crystal cargo (between 1 and 10%), began from this mush to form a melt-dominant (eruptible) body that eventually extended from 3.5 to 6 km depth. Crystals from all levels of the mush were entrained into the eruptible magma, as seen in mineral zonation and amphibole model pressures. Rapid translation of crystals from the mush to the eruptible magma is reflected in textural and compositional diversity in crystal cores and melt inclusion compositions, versus uniformity in the outermost rims. Prior to eruption the assembled eruptible magma body was not thermally or compositionally zoned and at temperatures of 790 °C, reflecting rapid cooling from the 840 °C low-silica rhyolite feedstock magma. A subordinate but significant volume (3-5 km3) of contrasting tholeiitic and calc-alkaline mafic material was co-erupted with the dominant rhyolite. These mafic clasts host crystals with compositions which demonstrate that there was some limited pre-eruptive physical interaction of mafic magmas with the mush and melt-dominant body. However, the mafic magmas do not appear to have triggered the eruption or controlled magmatic temperatures in the erupted rhyolite. Integration of textural and compositional data from all available crystal types, across all dominant and subordinate magmatic components, allow the history of the Oruanui magma body to be reconstructed over a wide range of temporal scales using multiple techniques. This history spans the tens of millennia required to grow the parental magma system (U-Th disequilibrium dating in zircon), through the centuries and decades required to assemble the eruptible magma body (textural and diffusion modelling in orthopyroxene), to the months, days, hours and minutes over which individual phases of the eruption occurred, identified through field observations tied to diffusion modelling in magnetite, olivine, quartz and feldspar. Tectonic processes, rather than any inherent characteristics of the magmatic system, were a principal factor acting to drive the rapid accumulation of magma and control its release episodically during the eruption. This work highlights the richness of information that can be gained by integrating multiple lines of petrologic evidence into a holistic timeline of field-verifiable processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.5104I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.5104I"><span>Geochemical characterization of fluids along the Dead Sea Rift: implications for fluids sources and regional geodynamic setting</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Inguaggiato, Claudio; Censi, Paolo; D'Alessandro, Walter; Zuddas, Pierpaolo</p> <p>2016-04-01</p> <p>The Dead Sea Fault where a lateral displacement between the African and Arabian plates occurs is characterized by anomalous heat flux in the northern Israel area close to the border with Syria and Jordan (Shalev et al., 2012). The concentrations of He and CO2, and isotopic composition of He and total dissolved inorganic carbon were studied in cold and thermal waters collected along the Dead Sea Fault, in order to investigate the source of volatiles and their relationship with the tectonic framework of the Dead Sea Fault. The waters with higher temperature (up to 57.2 ° C) are characterized by higher amounts of CO2and helium (up to 55.72 and 1.91*10-2 cc l-1, respectively). Helium isotopic data (R/Ra from 0.11 to 2.14) and 4He/20Ne ratios (0.41 - 106.86) show the presence of deep-deriving fluids consisting of a variable mixture of mantle and crust end-members, with the former reaching up to 35%. Carbon isotope signature of total dissolved carbon from hot waters falls within the range of magmatic values, suggesting the delivery of deep-seated CO2. The geographical distribution of helium isotopic data and isotopic carbon (CO2) values coupled with (CO2/3He ratios) indicate a larger contribution of mantle-derived fluids affecting the northern part of the investigated area, where the waters reach the highest temperature and anomalous heat flux was recognized by Shalev et al. (2012). Such occurrence is probably favoured by the peculiar tectonic framework recognized in the northern part of Israel (Segev et al., 2006), including a Moho discontinuity up-rise and/or the presence of a deep fault system coupled with the recent magmatic activity. References: Segev, A., Rybakov, M., Lyakhovsky, V, Hofstetter, A, Tibor, G., Goldshmidt, V., 2006. The structure, isostasy and gravity field of the Levant continental margin and the southeast Mediterranean area. Tectonophysics 425, 137-157. Shalev, E., Lyakhosky, V., Weinstein, Y., Ben-Avraham, Z., 2013. The thermal structure of Israel and Dead Sea Fault. Tectonophysics 602, 69-77.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014E%26PSL.388..123P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014E%26PSL.388..123P"><span>Filling in the juvenile magmatic gap: Evidence for uninterrupted Paleoproterozoic plate tectonics</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Partin, C. A.; Bekker, A.; Sylvester, P. J.; Wodicka, N.; Stern, R. A.; Chacko, T.; Heaman, L. M.</p> <p>2014-02-01</p> <p>Despite several decades of research on growth of the continental crust, it remains unclear whether the production of juvenile continental crust has been continuous or episodic throughout the Precambrian. Models for episodic crustal growth have gained traction recently through compilations of global U-Pb zircon age frequency distributions interpreted to delineate peaks and lulls in crustal growth through geologic time. One such apparent trough in zircon age frequency distributions between ∼2.45 and 2.22 Ga is thought to represent a pause in crustal addition, resulting from a global shutdown of magmatic and tectonic processes. The ∼2.45-2.22 Ga magmatic shutdown model envisions a causal relationship between the cessation of plate tectonics and accumulation of atmospheric oxygen over the same period. Here, we present new coupled U-Pb, Hf, and O isotope data for detrital and magmatic zircon from the western Churchill Province and Trans-Hudson orogen of Canada, covering an area of approximately 1.3 million km2, that demonstrate significant juvenile crustal production during the ∼2.45-2.22 Ga time interval, and thereby argue against the magmatic shutdown hypothesis. Our data is corroborated by literature data showing an extensive 2.22-2.45 Ga record in both detrital and magmatic rocks on every continent, and suggests that the operation of plate tectonics continued throughout the early Paleoproterozoic, while atmospheric oxygen rose over the same time interval. We argue that uninterrupted plate tectonics between ∼2.45 and 2.22 Ga would have contributed to efficient burial of organic matter and sedimentary pyrite, and the consequent rise in atmospheric oxygen documented for this time interval.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tecto..36.2846H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tecto..36.2846H"><span>Active Magmatic Underplating in Western Eger Rift, Central Europe</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hrubcová, Pavla; Geissler, Wolfram H.; Bräuer, Karin; Vavryčuk, Václav; Tomek, Čestmír.; Kämpf, Horst</p> <p>2017-12-01</p> <p>The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high-velocity lower crust and relate them to the distribution and chemical status of mantle-derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local-scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high-velocity lower crust with pronounced reflectivity and a high-velocity reflection-free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection-free lower crust together with a strong reflector at its top at depths of 28-30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Litho.286..264R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Litho.286..264R"><span>The Cenozoic magmatism of East-Africa: Part I - Flood basalts and pulsed magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rooney, Tyrone O.</p> <p>2017-08-01</p> <p>Cenozoic magmatism in East Africa results from the interplay between lithospheric extension and material upwelling from the African Large Low Shear Velocity Province (LLSVP). The modern focusing of East African magmatism into oceanic spreading centers and continental rifts highlights the modern control of lithospheric thinning in magma generation processes, however the widespread, and volumetrically significant flood basalt events of the Eocene to Early Miocene suggest a significant role for material upwelling from the African LLSVP. The slow relative motion of the African plate during the Cenozoic has resulted in significant spatial overlap in lavas derived from different magmatic events. This complexity is being resolved with enhanced geochronological precision and a focus on the geochemical characteristics of the volcanic products. It is now apparent that there are three distinct pulses of basaltic volcanism, followed by either bimodal lavas or silicic volcanic products during this period: (A) Eocene Initial Phase from 45 to 34 Ma. This is a period of dominantly basaltic volcanism focused in Southern Ethiopia and Northern Kenya (Turkana). (B) Oligocene Traps phase from 33.9 to 27 Ma. This period coincides with a significant increase in the aerial extent of volcanism with broadly age equivalent 1 to 2 km thick sequences of dominantly basalt centered on the NW Ethiopian Plateau and Yemen, (C) Early Miocene resurgence phase from 26.9 to 22 Ma. This resurgence in basaltic volcanism is seen throughout the region at ca. 24-23 Ma, but is less volumetrically significant than the prior two basaltic pulses. With our developing understanding of the persistence of LLSVP anomalies within the mantle, I propose that the three basaltic pulses are ostensibly manifestations of the same plume-lithosphere interaction, requiring revision to the duration, magmatic extent, and magma volume of the African-Arabian Large Igneous Province.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1616771S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1616771S"><span>Magma emplacement mechanisms and syn-magmatic deformation - a new approach to the Knaben area in Vest Agder, Norway</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stormoen, Martin Austin; Slagstad, Trond; Henderson, Iain</p> <p>2014-05-01</p> <p>The Knaben area, known for its molybdenite mining, defines a N-S striking (~30 degrees dip towards the east) belt, consisting of porphyry granite with a varying density of amphibolite and varieties of deformed granite, lying within the Sirdal Magmatic Belt, is important for understanding the emplacement- and deformation mechanisms of the batholith. Detailed geological mapping combined with geochronology, geochemistry, and structural geology will be the focus areas. Last autumn's fieldwork indicated that several of the formerly mapped enclaves of amphibolite and deformed granite are more coherent then previously indicated, and some have been followed for a few kilometres. Several varieties of granite make up the area, mainly a dominating red porphyry granite, and a grey molybdenite-bearing finer grained granite. Structural investigations revealed consistent "top to the west" compressional kinematics on mappable shear zone networks often displaying west-directed duplex geometries. The Knaben area could possibly comprise a boundary between two individual plutons in the Sirdal Magmatic Belt, or a zone with remaining host rock. Geochronology of the eastern and western plutons will be done. Currently, largely different paleomagnetic vectors of the eastern and western porphyry granites indicate that they are separate plutons. Exploring how the emplacement- and deformation mechanisms have acted and are related, will be one of the main objectives. If the deformed granite is host rock, or syn- to post-magmatic deformed porphyry granite has been one of the major questions. A better understanding of the formation of the Knaben area, also regarding the emplacement of molybdenite, will prove useful for understanding the regional batholith, and possibly the possibility for molybdenite to occur elsewhere. The Sirdal Magmatic Belt, and also Knaben, seem to be of great value for studying magmatic processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Litho.198..129C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Litho.198..129C"><span>Zircon petrochronology reveals the temporal link between porphyry systems and the magmatic evolution of their hidden plutonic roots (the Eocene Coroccohuayco deposit, Peru)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chelle-Michou, Cyril; Chiaradia, Massimo; Ovtcharova, Maria; Ulianov, Alexey; Wotzlaw, Jörn-Frederik</p> <p>2014-06-01</p> <p>We present zircon geochronologic (LA-ICPMS and ID-TIMS), trace element and Hf isotopic evidence for a complex evolution of the plutonic roots of the Eocene Coroccohuayco porphyry system, southern Peru. LA-ICPMS U-Pb dating has initially been carried out to optimize grain selection for subsequent high-precision ID-TIMS dating and to characterize crustal assimilation (xenocrystic cores). This combined in-situ and whole-grain U-Pb dating of the same grains has been further exploited to derive a robust temporal interpretation of the complex magmatic system associated with the Coroccohuayco porphyry-skarn deposit. Our data reveal that a heterogeneous gabbrodioritic complex was emplaced at ca. 40.4 Ma and was followed by a nearly 5 Ma-long magmatic lull until the emplacement of dacitic porphyry stocks and dykes associated with the mineralizing event at ca. 35.6 Ma. However, at the sample scale, zircons from the porphyries provide insight into a 2 Ma-long lived “hidden” magmatism (probably at 4-9 km paleodepth) prior to porphyry intrusion and mineralization for which no other evidence can be found on the surface today. These dates together with zircon trace element analysis and Hf isotopes argue for the development of a long-lived magmatic system dominated by amphibole fractionation with an increasing amount of crustal assimilation and the development of a large and sustained thermal anomaly. The system was probably rejuvenated at an increasing rate from 37.5 to 35.6 Ma with injection of fresh and oxidized magma from the lower crust, which caused cannibalism and remelting of proto-plutons. The porphyry intrusions at Coroccohuayco were emplaced at the peak thermal conditions of this upper crustal magma chamber, which subsequently cooled and expelled ore fluids. Zircon xenocrysts and Hf isotopes in the porphyritic rocks suggest that this large upper crustal system evolved at stratigraphic levels corresponding to Triassic sediments similar to the Mitu group that may be present below the district. Using the zircon Ce anomaly as a proxy for oxidation state of the magma through time, we show that the high oxidation state of the porphyries is not the result of upper-crustal processes but is rather controlled by magmatic processes occurring at deeper levels. A comparison of our data with available high-precision geochronologic data at other porphyry systems suggests that such deposits may form when injection rate, volume and heat of their long-lived upper crustal magmatic system reach their peaks. These features might be diagnostic of a productive deposit.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T11D..06M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T11D..06M"><span>Seismic and Petrological Constraints on Deep Crustal Evolution in North America: Where and What are 7.x Layers?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mahan, K. H.; Schulte-Pelkum, V.; Shen, W.; Ritzwoller, M. H.</p> <p>2012-12-01</p> <p>Continental crust worldwide has been found to have areas with a lowermost layer characterized by unusually high seismic P velocities of over 7 km/s, often called 7.x layers. Such layers are commonly ascribed to underplating - in some cases by underthrusting, but in most cases by magmatic processes. In North America, high-velocity lower crust underlies upper crust of Archean, Proterozoic, and younger ages. Its presence reflects the tectonic and magmatic processes associated with continental rifting, collision, subduction, and other evolutionary (e.g. thermal) trends, and its occurrence also provides clues on the nature of the underlying mantle. Detection of a lower crustal high-velocity layer stems mostly from seismic refraction and wide-angle reflection experiments, and information on its geographical extent is very spotty. Similarly sparse are age determinations and knowledge of the tectonic processes responsible for construction of these layers. Despite glimpses of 7.x layers on many profiles across the continental U.S. and Canada, there is no systematic geographical and age information on this fundamental process of crustal growth, and many of the existing observations contradict current hypotheses on underplating. We compare compositional and physical property data of lower crustal and uppermost mantle xenoliths from Montana, Wyoming, and other localities with maps of lower crustal and uppermost mantle seismic velocities obtained from joint inversions of receiver functions with surface waves, and to mapped distinct high-velocity lower crustal layers in receiver functions in areas covered by the EarthScope Transportable Array. Xenolith observations from Montana indicate that portions of metasomatized uppermost mantle exist in that area that may be difficult to distinguish from mafic lower crust based on seismic velocities alone, raising the interesting question of whether a 7.x layer may be below rather than above the seismic Moho in some cases. The persistence of high-velocity, presumably strong lower crust under the Laramide-affected Wyoming craton and the Colorado Plateau suggest that crustal strength may influence surface deformation. The Rocky Mountain Front and Rio Grande rift largely separate fast lower crust to the East from slower lower crust to the West, cutting across NE-SW trends inherited from continental assembly and suggesting that the velocity distribution may be dominated by thermal effects; however, recent volcanics do not correlate well geographically with lower crustal velocity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005GMS...160..165A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005GMS...160..165A"><span>Self-gravity, self-consistency, and self-organization in geodynamics and geochemistry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Anderson, Don L.</p> <p></p> <p>The results of seismology and geochemistry for mantle structure are widely believed to be discordant, the former favoring whole-mantle convection and the latter favoring layered convection with a boundary near 650 km. However, a different view arises from recognizing effects usually ignored in the construction of these models, including physical plausibility and dimensionality. Self-compression and expansion affect material properties that are important in all aspects of mantle geochemistry and dynamics, including the interpretation of tomographic images. Pressure compresses a solid and changes physical properties that depend on volume and does so in a highly nonlinear way. Intrinsic, anelastic, compositional, and crystal structure effects control seismic velocities; temperature is not the only parameter, even though tomographic images are often treated as temperature maps. Shear velocity is not a good proxy for density, temperature, and composition or for other elastic constants. Scaling concepts are important in mantle dynamics, equations of state, and wherever it is necessary to extend laboratory experiments to the parameter range of the Earth's mantle. Simple volume-scaling relations that permit extrapolation of laboratory experiments, in a thermodynamically self-consistent way, to deep mantle conditions include the quasiharmonic approximation but not the Boussinesq formalisms. Whereas slabs, plates, and the upper thermal boundary layer of the mantle have characteristic thicknesses of hundreds of kilometers and lifetimes on the order of 100 million years, volume-scaling predicts values an order of magnitude higher for deep-mantle thermal boundary layers. This implies that deep-mantle features are sluggish and ancient. Irreversible chemical stratification is consistent with these results; plausible temperature variations in the deep mantle cause density variations that are smaller than the probable density contrasts across chemical interfaces created by accretional differentiation and magmatic processes. Deep-mantle features may be convectively isolated from upper-mantle processes. Plate tectonics and surface geochemical cycles appear to be entirely restricted to the upper ˜1,000 km. The 650-km discontinuity is mainly an isochemical phase change but major-element chemical boundaries may occur at other depths. Recycling laminates the upper mantle and also makes it statistically heterogeneous, in agreement with high-frequency scattering studies. In contrast to standard geochemical models and recent modifications, the deeper layers need not be accessible to surface volcanoes. There is no conflict between geophysical and geochemical data, but a physical basis for standard geochemical and geodynamic mantle models, including the two-layer and whole-mantle versions, and qualitative tomographic interpretations has been lacking.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.470...96F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.470...96F"><span>Effects of crustal thickness on magmatic differentiation in subduction zone volcanism: A global study</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Farner, Michael J.; Lee, Cin-Ty A.</p> <p>2017-07-01</p> <p>The majority of arc magmas are highly evolved due to differentiation within the lithosphere or crust. Some studies have suggested a relationship between crustal thickness and magmatic differentiation, but the exact nature of this relationship is unclear. Here, we examine the interplay of crustal thickness and magmatic differentiation using a global geochemical dataset compiled from active volcanic arcs and elevation as a proxy for crustal thickness. With increasing crustal thickness, average arc magma compositions become more silicic (andesitic) and enriched in incompatible elements, indicating that on average, arc magmas in thick crust are more evolved, which can be easily explained by the longer transit and cooling times of magmas traversing thick arc lithosphere and crust. As crustal thickness increases, arc magmas show higher degrees of iron depletion at a given MgO content, indicating that arc magmas saturate earlier in magnetite when traversing thick crust. This suggests that differentiation within thick crust occurs under more oxidizing conditions and that the origin of oxidation is due to intracrustal processes (contamination or recharge) or the role of thick crust in modulating melting degree in the mantle wedge. We also show that although arc magmas are on average more silicic in thick crust, the most silicic magmas (>70 wt.% SiO2) are paradoxically found in thin crust settings, where average compositions are low in silica (basaltic). We suggest that extreme residual magmas, such as those exceeding 70 wt.% SiO2, are preferentially extracted from shallow crustal magma bodies than from deep-seated magma bodies, the latter more commonly found in regions of thick crust. We suggest that this may be because the convective lifespan of crustal magma bodies is limited by conductive cooling through the overlying crustal lid and that magma bodies in thick crust cool more slowly than in thin crust. When the crust is thin, cooling is rapid, preventing residual magmas from being extracted; in the rare case that residual magmas can be extracted, they represent the very last melt fractions, which are highly silicic. When the crust is thick, cooling is slow, so intermediate melt fractions can readily segregate and erupt to the surface, where they cool and crystallize before highly silicic residual melts can be generated.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007MinDe..42..665C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007MinDe..42..665C"><span>Petrology, geochemistry and U-Pb geochronology of magmatic rocks from the high-sulfidation epithermal Au-Cu Chelopech deposit, Srednogorie zone, Bulgaria</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chambefort, Isabelle; Moritz, Robert; von Quadt, Albrecht</p> <p>2007-10-01</p> <p>The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern part of the Panagyurishte mineral district. It lies within the Banat-Srednegorie metallogenic belt, which extends from Romania through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech deposit have been affected by propylitic, quartz-sericite, and advanced argillic alteration, but the igneous textures have been preserved. Alteration processes have resulted in leaching of Na2O, CaO, P2O5, and Sr and enrichment in K2O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the Chelopech magmatism, were dated by high-precision U-Pb geochronology. Zircons of an altered andesitic body, which has been thrust over the deposit, yield a concordant 206Pb/238U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech. Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean 206Pb/238U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted by hydrothermal alteration give a concordant 206Pb/238U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech epithermal high-sulfidation deposit. 176Hf/177Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the Chelopech area and the about 92-Ma-old Elatsite porphyry-Cu deposit, suggest two different magma sources in the Chelopech-Elatsite magmatic area. Magmatic rocks associated with the Elatsite porphyry-Cu deposit and the dacitic dome-like body north of Chelopech are characterized by zircons with ɛHfT90 values of ˜5, which suggest an important input of mantle-derived magma. Some zircons display lower ɛHfT90 values, as low as -6, and correlate with increasing 206Pb/238U ages up to about 350 Ma, suggesting assimilation of basement rocks during magmatism. In contrast, zircon grains in andesitic rocks from Chelopech are characterized by homogeneous 176Hf/177Hf isotope ratios with ɛHfT90 values of ˜1 and suggest a homogeneous mixed crust-mantle magma source. We conclude that the Elatsite porphyry-Cu and the Chelopech high-sulfidation epithermal deposits were formed within a very short time span and could be partly contemporaneous. However, they are related to two distinct upper crustal magmatic reservoirs, and they cannot be considered as a genetically paired porphyry-Cu and high-sulfidation epithermal related to a single magmatic-hydrothermal system centered on the same intrusion.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EOSTr..90..362L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EOSTr..90..362L"><span>Probing the Hawaiian Hot Spot With New Broadband Ocean Bottom Instruments</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Laske, Gabi; Collins, John A.; Wolfe, Cecily J.; Solomon, Sean C.; Detrick, Robert S.; Orcutt, John A.; Bercovici, David; Hauri, Erik H.</p> <p>2009-10-01</p> <p>The Hawaiian hot spot is regarded as the textbook example of the product of a deep-rooted mantle plume [Wilson, 1963; Morgan, 1971]. Its isolated location, far from any plate boundary, should provide an opportunity to test most basic hypotheses on the nature of plume-plate interaction and related magmatism [e.g., Ribe and Christensen, 1999]. Yet the lack of crucial geophysical data has sustained a debate about whether Hawaii's volcanism is plume-related or is instead the consequence of more shallow processes, such as the progressive fracturing of the plate in response to extensional stresses [Turcotte and Oxburgh, 1973]. In the plume model for Hawaii's volcanism, hot material is expected to ascend near vertically within the more viscous surrounding mantle before ponding and spreading laterally beneath the rigid lithosphere. Mantle convection in general, and the fast moving Pacific plate in particular, shear and tilt the rising plume. The plume top is dragged downstream by the plate, and this dragged material may give rise to an elongated bathymetric swell [Davies, 1988; Olson, 1990; Sleep, 1990; Phipps Morgan et al., 1995]. However, identifying the dominant cause of the swell remains elusive, and proposed mechanisms include thermal rejuvenation, dynamic support, compositional buoyancy, and mechanical erosion (see Li et al. [2004] for a summary). There is also considerable debate about the continuity of the plume within the mantle, how discrete islands are formed, and how a deep-rooted plume interacts with the mantle transition zone [e.g., van Keken and Gable, 1995].</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70036519','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70036519"><span>Mantle to surface degassing of alkalic magmas at Erebus volcano, Antarctica</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Oppenheimer, C.; Moretti, R.; Kyle, P.R.; Eschenbacher, A.; Lowenstern, J. B.; Hervig, R.L.; Dunbar, N.W.</p> <p>2011-01-01</p> <p>Continental intraplate volcanoes, such as Erebus volcano, Antarctica, are associated with extensional tectonics, mantle upwelling and high heat flow. Typically, erupted magmas are alkaline and rich in volatiles (especially CO2), inherited from low degrees of partial melting of mantle sources. We examine the degassing of the magmatic system at Erebus volcano using melt inclusion data and high temporal resolution open-path Fourier transform infrared (FTIR) spectroscopic measurements of gas emissions from the active lava lake. Remarkably different gas signatures are associated with passive and explosive gas emissions, representative of volatile contents and redox conditions that reveal contrasting shallow and deep degassing sources. We show that this unexpected degassing signature provides a unique probe for magma differentiation and transfer of CO2-rich oxidised fluids from the mantle to the surface, and evaluate how these processes operate in time and space. Extensive crystallisation driven by CO2 fluxing is responsible for isobaric fractionation of parental basanite magmas close to their source depth. Magma deeper than 4kbar equilibrates under vapour-buffered conditions. At shallower depths, CO2-rich fluids accumulate and are then released either via convection-driven, open-system gas loss or as closed-system slugs that ascend and result in Strombolian eruptions in the lava lake. The open-system gases have a reduced state (below the QFM buffer) whereas the closed-system gases preserve their deep oxidised signatures (close to the NNO buffer). ?? 2011 Elsevier B.V.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70026278','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70026278"><span>Evidence for a Battle Mountain-Eureka crustal fault zone, north-central Nevada, and its relation to Neoproterozoic-Early Paleozoic continental breakup</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Grauch, V.J.S.; Rodriguez, B.D.; Bankey, V.; Wooden, J.L.</p> <p>2003-01-01</p> <p>Combined evidence from gravity, radiogenic isotope, and magnetotelluric (MT) data indicates a crustal fault zone that coincides with the northwest-trending Battle Mountain-Eureka (BME) mineral trend in north-central Nevada, USA. The BME crustal fault zone likely originated during Neoproterozoic-Early Paleozoic rifting of the continent and had a large influence on subsequent tectonic events, such as emplacement of allochthons and episodic deformation, magmatism, and mineralization throughout the Phanerozoic. MT models show the fault zone is about 10 km wide, 130-km long, and extends from 1 to 5 km below the surface to deep crustal levels. Isotope data and gravity models imply the fault zone separates crust of fundamentally different character. Geophysical evidence for such a long-lived structure, likely inherited from continental breakup, defies conventional wisdom that structures this old have been destroyed by Cenozoic extensional processes. Moreover, the coincidence with the alignment of mineral deposits supports the assertion by many economic geologists that these alignments are indicators of buried regional structures.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V23A0465W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V23A0465W"><span>Numerical modeling of magma-tectonic interactions at Pacaya Volcano, Guatemala</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wauthier, C.</p> <p>2017-12-01</p> <p>Pacaya Volcano is composed of several volcanic cones located along the southern rim of the Amatitlan caldera, approximately 25 km south of Guatemala City. It is a basaltic volcano located in the Central American Volcanic Arc. The shallow magma plumbing system at Pacaya likely includes at least three magma reservoirs: a very shallow ( 0.2-0.4 km depth) reservoir located below and possibly within the MacKenney cone, a 4 km deep reservoir located northwest of the summit, and a shallow dike-like conduit below the summit which fed the recent flank eruptions. Pacaya's western flank is slipping in a stick-slip fashion, and the instability seems associated with larger volume eruptions. Flank instability phases indeed occurred in 2010 and 2014 in coincidence with major intrusive and eruptive phases, suggesting a positive feedback between the flank motion and major intrusions. Simple analytical models are insufficient to fit the geodetic observations and model the flank processes and their mechanical interactions with the magmatic system. Here, numerical modeling approaches are used to characterize the 2014 flank deformation episode and magma-tectonic interactions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JGRB..116.1102M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JGRB..116.1102M"><span>Repeat ridge jumps associated with plume-ridge interaction, melt transport, and ridge migration</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mittelstaedt, Eric; Ito, Garrett; van Hunen, Jeroen</p> <p>2011-01-01</p> <p>Repeated shifts, or jumps, of mid-ocean ridge segments toward nearby hot spots can produce large, long-term changes to the geometry and location of the tectonic plate boundaries. Ridge jumps associated with hot spot-ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off-axis volcanism. To study how these processes influence ridge jumps, we use numerical models to simulate 2-D (in cross section) viscous flow of the mantle, viscoplastic deformation of the lithosphere, and melt migration upward from the asthenospheric melting zone, laterally along the base of the lithosphere, and vertically through the lithosphere. The locations and rates that magma penetrates and heats the lithosphere are controlled by the time-varying accumulation of melt beneath the plate and the depth-averaged lithospheric porosity. We examine the effect of four key parameters: magmatic heating rate of the lithosphere, plate spreading rate, age of the seafloor overlying the plume, and the plume-ridge migration rate. Results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate. The time required to complete a ridge jump decreases with larger values of magmatic heating rate, younger plate age, and faster spreading rate. For cases with migrating ridges, models predict a range of behaviors including repeating ridge jumps, much like those exhibited on Earth. Repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere. The tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the Mid-Atlantic Ridge. Model results also suggest that magmatic heating may significantly thin the lithosphere, as has been suggested at Hawaii and other hot spots.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatGe...9..237W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatGe...9..237W"><span>Porphyry copper enrichment linked to excess aluminium in plagioclase</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Williamson, B. J.; Herrington, R. J.; Morris, A.</p> <p>2016-03-01</p> <p>Porphyry copper deposits provide around 75%, 50% and 20% of world copper, molybdenum and gold, respectively. The deposits are mainly centred on calc-alkaline porphyry magmatic systems in subduction zone settings. Although calc-alkaline magmas are relatively common, large porphyry copper deposits are extremely rare and increasingly difficult to discover. Here, we compile existing geochemical data for magmatic plagioclase, a dominant mineral in calc-alkaline rocks, from fertile (porphyry-associated) and barren magmatic systems worldwide, barren examples having no associated porphyry deposit. We show that plagioclase from fertile systems is distinct in containing `excess’ aluminium. This signature is clearly demonstrated in a case study carried out on plagioclase from the fertile La Paloma and Los Sulfatos copper porphyry systems in Chile. Further, the presence of concentric zones of high excess aluminium suggests its incorporation as a result of magmatic processes. As excess aluminium has been linked to high melt water contents, the concentric zones may record injections of hydrous fluid or fluid-rich melts into the sub-porphyry magma chamber. We propose that excess aluminium may exclude copper from plagioclase, so enriching the remaining melts. Furthermore, this chemical signature can be used as an exploration indicator for copper porphyry deposits.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3709P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3709P"><span>Cooling of a magmatic system under thermal chaotic mixing</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petrelli, Maurizio; El Omari, Kamal; Le Guer, Yves; Perugini, Diego</p> <p>2015-04-01</p> <p>The cooling of a melt undergoing chaotic advection is studied numerically for a magma with a temperature-dependent viscosity in a 2D cavity with moving boundary. Different statistical mixing and energy indicators are used to characterize the efficiency of cooling by thermal chaotic mixing. We show that different cooling rates can be obtained during the thermal mixing even of a single basaltic magmatic batch undergoing chaotic advection. This process can induce complex temperature patterns inside the magma chamber. The emergence of chaotic dynamics strongly affects the temperature field during time and greatly increases the cooling rates. This mechanism has implications for the lifetime of a magmatic body and may favor the appearance of chemical heterogeneities in igneous systems as a result of different crystallization rates. Results from this study also highlight that even a single magma batch can develop, under chaotic thermal advection, complex thermal and therefore compositional patterns resulting from different cooling rates, which can account for some natural features that, to date, have received unsatisfactory explanations. Among them, the production of magmatic enclaves showing completely different cooling histories compared with the host magma, compositional zoning in mineral phases, and the generation of large-scale compositionally zoning observed in many plutons worldwide.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.296..580G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.296..580G"><span>Magmatic sulphides in Quaternary Ecuadorian arc magmas</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Georgatou, Ariadni; Chiaradia, Massimo; Rezeau, Hervé; Wälle, Markus</p> <p>2018-01-01</p> <p>New petrographic and geochemical data on magmatic sulphide inclusions (MSIs) are presented and discussed for 15 Quaternary volcanic centers of the Ecuadorian frontal, main and back volcanic arc. MSIs occur mostly in Fe-Ti oxides (magnetite and/or magnetite-ilmenite pair) and to a lesser extent in silicate minerals (amphibole, plagioclase, and pyroxene). MSIs are present in all volcanic centers ranging in composition from basalt to dacite (SiO2 = 50-67 wt.%), indicating that sulphide saturation occurs at various stages of magmatic evolution and independently from the volcano location along the volcanic arc. MSIs also occur in dioritic, gabbroic and hornblenditic magmatic enclaves of the volcanic rocks. MSIs display variable sizes (1-30 μm) and shapes (globular, ellipsoidal, angular, irregular) and occur mostly as polymineralic inclusions composed of Fe-rich and Cu-poor (pyrrhotite) and Cu-rich (mostly chalcopyrite) phases. Aerial sulphide relative abundances range from 0.3 to 7 ppm in volcanic host rocks and from 13 to 24 ppm in magmatic enclaves. Electron microprobe analyses of MSIs indicate maximum metal contents of Cu = 65.7 wt.%, Fe = 65.2 wt.%, Ni = 10.1 wt.% for those hosted in the volcanic rocks and of Cu = 57.7 wt.%, Fe = 60.9 wt.%, Ni = 5.1 wt.%, for those hosted in magmatic enclaves. Relationships of the sulphide chemistry to the host whole rock chemistry show that with magmatic differentiation (e.g., increasing SiO2) the Cu and Ni content of sulphides decrease whereas the Fe and S contents increase. The opposite behavior is observed with the increase of Cu in the whole rock, because the latter is anti-correlated with the SiO2 whole rock content. Laser ablation ICP-MS analyses of MSIs returned maximum values of PGEs and noble metals of Pd = 30 ppm, Rh = 8.1 ppm, Ag = 92.8 ppm and Au = 0.6 ppm and Pd = 43 ppm, Rh = 22.6 ppm, Ag = 89 ppm and Au = 1 ppm for those hosted in volcanic rocks and magmatic enclaves, respectively. These PGE contents display a different range of values with respect to those in previously investigated magmatic sulphides. MSIs that are Cu- and PGE/Cu-rich are found in less evolved rocks (i.e., lower SiO2 contents) that also display a lower amount of sulphide inclusions. Cu-rich sulphide phases (chalcopyrite ± bornite) are mostly hosted by magnetite, whereas PGE-rich ones consist of a Cu-poor phase (pyrrhotite) hosted by plagioclase. However, no systematic changes in the chemistry of the host silicate mineral are observed in coincidence with the occurrence of MSIs. We use the results of our study to draw some implications on Cu (and other chalcophile elements) behavior during arc magmatic processes potentially associated with the formation of porphyry-type deposits.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14...57R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14...57R"><span>Geodynamic models of the deep structure of the natural disaster regions of the Earth</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rodnikov, A. G.; Sergeyeva, N. A.; Zabarinskaya, L. P.</p> <p>2012-04-01</p> <p>Investigation of the deep structure and creation of geodynamic models of natural disaster regions are important for understanding of the nature of such phenomena as earthquakes, eruptions of volcanoes, tsunami and others. Carrying out of such researches is necessary for definition of areas of potential risk, forecasting and the prevention of negative consequences of acts of nature. Research region is active continental margins of the Sea of Okhotsk, and especially the area of Neftegorsk earthquake which has occurred on May, 28th 1995 in the North Sakhalin and caused many victims and destructions. The geodynamic model of the lithosphere in the region of Neftegorsk earthquake has been constructed along the profile crossing the North Sakhalin Basin, Deryugin Basin and ophiolite complex between them. The Deryugin Basin was formed at the site of an ancient deep trench after the subduction of the Okhotsk Sea Plate under Sakhalin. The basin is located above a hot plume in the mantle at a depth of 25 km. The ophiolite belt of ultramafic magmatic rocks is an ancient (K2-Pg) paleosubduction zone separating the Deryugin basin from the North Sakhalin Basin. The thickness of the ancient seismic focal zone is 80 km. It is probably that the structures of the North Sakhalin have been formed in the following way. In the Late Cretaceous the oceanic Okhotsk Sea Plate subducted under Sakhalin, the eastern part of which was an andesite island arc. Approximately in Miocene the subduction of the plate apparently ceased. In that time the Tatar Rift Strait was formed. Ophiolite rocks of the subduction zones as a result of compression have been squeezed out on a surface. The ophiolite complex combined by the ultrabasic rocks, fixes position of ancient subduction zone. It is probable that the manifestation of the Neftegorsk earthquake was a result of activization of this ancient subduction zone. On a surface the subduction zone manifests itself as deep faults running along Sakhalin. The center of the Neftegorsk earthquake was directly formed by burst of activity of this ancient subduction zone. From a position of the ancient subduction zone under Sakhalin, which is a cause of strong earthquakes here, it follows that the region is one of seismic dangerous in Russia. Constructed on the basis of complex interpretation of the geologic-geophysical data the geodynamic models of natural disaster regions give the chance: to study a deep structure under seismic dangerous zones; to investigate a role of deep processes in the upper mantle in formation of structures of earth crust; to relate the geological features, tectonomagmatic, hydrothermal activity with the processes in the upper mantle; to plot maps in detail with zones of increasing risks to prevent active building or other economic activities in such dangerous regions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMEP11C..08M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMEP11C..08M"><span>Detrital zircons and Earth system evolution</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McKenzie, R.</p> <p>2016-12-01</p> <p>Zircon is a mineral commonly produced in silicic magmatism. Therefore, due to its resilience and exceedingly long residence times in the continental crust, detrital zircon records can be used to track processes associated with silicic magmatism throughout Earth history. In this contribution I will address the potential role of preservational biases in zircon record, and further discuss how zircon datasets can be used to help better understand the relationship between lithospheric and Earth system evolution. I will use large compilations of zircon data to trace the composition and weatherability of the continental crust, to evaluate temporal rates of crustal recycling, and finally to track spatiotemporal variation in continental arc magmatism and volcanic CO2 outgassing throughout Earth history. These records demonstrate that secular changes in plate tectonic regimes played a prominent role in modulating conditions of the ocean+atmosphere system and long-term climate state for the last 3 billion years.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T54B..01K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T54B..01K"><span>Opening of the Central Atlantic Ocean: Implications for Geometric Rifting and Asymmetric Initial Seafloor Spreading after Continental Breakup</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Klingelhoefer, F.; Biari, Y.; Sahabi, M.; Funck, T.; Benabdellouahed, M.; Schnabel, M.; Reichert, C. J.; Gutscher, M. A.; Bronner, A.; Austin, J. A., Jr.</p> <p>2017-12-01</p> <p>The structure of conjugate passive margins provides information about rifting styles, the initial phases of the opening of an ocean and the formation of its associated sedimentary basins. The study of the deep structure of conjugate passive continental margins combined with precise plate kinematic reconstructions can provide constraints on the mechanisms of rifting and formation of initial oceanic crust. In this study the Central Atlantic conjugate margins are compared, based on compilation of wide-angle seismic profiles from the NW-Africa Nova Scotian and US passive margins. Plate cinematic reconstructions were used to place the profiles in the position at opening and at the M25 magnetic anomaly. The patterns of volcanism, crustal thickness, geometry, and seismic velocities in the transition zone. suggest symmetric rifting followed by asymmetric oceanic crustal accretion. Conjugate profiles in the southern Central Atlantic image differences in the continental crustal thickness. While profiles on the eastern US margin are characterized by thick layers of magmatic underplating, no such underplate was imaged along the NW-African continental margin. It has been proposed that these volcanic products form part of the CAMP (Central Atlantic Magmatic Province). In the north, two wide-angle seismic profiles acquired in exactly conjugate positions show that the crustal geometry of the unthinned continental crust and the necking zone are nearly symmetric. A region including seismic velocities too high to be explained by either continental or oceanic crust is imaged along the Nova Scotia margin off Eastern Canada, corresponding on the African side to an oceanic crust with slightly elevated velocities. These might result from asymmetric spreading creating seafloor by faulting the existing lithosphere on the Canadian side and the emplacement of magmatic oceanic crust including pockets of serpentinite on the Moroccan margin. A slightly elevated crustal thickness along the African margin can be explained by the influence of the Canary hotspot between 60 and 30 Ma in the study region. After isochron M25, a large-scale plate reorganization may then have led to an increase in spreading velocity and the production of a more typical but thin magmatic crust on both sides.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017MarGR..38...61S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017MarGR..38...61S"><span>The potential hydrothermal systems unexplored in the Southwest Indian Ocean</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Suo, Yanhui; Li, Sanzhong; Li, Xiyao; Zhang, Zhen; Ding, Dong</p> <p>2017-06-01</p> <p>Deep-sea hydrothermal vents possess complex ecosystems and abundant metallic mineral deposits valuable to human being. On-axial vents along tectonic plate boundaries have achieved prominent results and obtained huge resources, while nearly 90% of the global mid-ocean ridge and the majority of the off-axial vents buried by thick oceanic sediments within plates remain as relatively undiscovered domains. Based on previous detailed investigations, hydrothermal vents have been mapped along five sections along the Southwest Indian Ridge (SWIR) with different bathymetry, spreading rates, and gravity features, two at the western end (10°-16°E Section B and 16°-25°E Section C) and three at the eastern end (49°-52°E Section D, 52°-61°E Section E and 61°-70°E Section F). Hydrothermal vents along the Sections B, C, E and F with thin oceanic crust are hosted by ultramafic rocks under tectonic-controlled magmatic-starved settings, and hydrothermal vents along the Section D are associated with exceed magmatism. Limited coverage of investigations is provided along the 35°-47°E SWIR (between Marion and Indomed fracture zones) and a lot of research has been done around the Bouvet Island, while no hydrothermal vents has been reported. Analyzing bathymetry, gravity and geochemical data, magmatism settings are favourable for the occurrence of hydrothermal systems along these two sections. An off-axial hydrothermal system in the southern flank of the SWIR that exhibits ultra-thin oceanic crust associated with an oceanic continental transition is postulated to exist along the 100-Ma slow-spreading isochron in the Enderby Basin. A discrete, denser enriched or less depleted mantle beneath the Antarctic Plate is an alternative explanation for the large scale thin oceanic crust concentrated on the southern flank of the SWIR.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70193633','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70193633"><span>Soil CO2 emissions as a proxy for heat and mass flow assessment, Taupō Volcanic Zone, New Zealand</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bloomberg, S.; Werner, Cynthia A.; Rissmann, C.F.; Mazot, A.; Horton, Travis B.; Gravley, D; Kennedy, B.; Oze, C</p> <p>2014-01-01</p> <p>The quantification of heat and mass flow between deep reservoirs and the surface is important for understanding magmatic and hydrothermal systems. Here, we use high-resolution measurement of carbon dioxide flux (φCO2) and heat flow at the surface to characterize the mass (CO2 and steam) and heat released to the atmosphere from two magma-hydrothermal systems. Our soil gas and heat flow surveys at Rotokawa and White Island in the Taupō Volcanic Zone, New Zealand, include over 3000 direct measurements of φCO2 and soil temperature and 60 carbon isotopic values on soil gases. Carbon dioxide flux was separated into background and magmatic/hydrothermal populations based on the measured values and isotopic characterization. Total CO2 emission rates (ΣCO2) of 441 ± 84 t d−1 and 124 ± 18 t d−1were calculated for Rotokawa (2.9 km2) and for the crater floor at White Island (0.3 km2), respectively. The total CO2 emissions differ from previously published values by +386 t d−1 at Rotokawa and +25 t d−1 at White Island, demonstrating that earlier research underestimated emissions by 700% (Rotokawa) and 25% (White Island). These differences suggest that soil CO2 emissions facilitate more robust estimates of the thermal energy and mass flux in geothermal systems than traditional approaches. Combining the magmatic/hydrothermal-sourced CO2 emission (constrained using stable isotopes) with reservoir H2O:CO2mass ratios and the enthalpy of evaporation, the surface expression of thermal energy release for the Rotokawa hydrothermal system (226 MWt) is 10 times greater than the White Island crater floor (22.5 MWt).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAESc.127..100S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAESc.127..100S"><span>Late Paleozoic tectonics of the Solonker Zone in the Wuliji area, Inner Mongolia, China: Insights from stratigraphic sequence, chronology, and sandstone geochemistry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shi, Guanzhong; Song, Guangzeng; Wang, Hua; Huang, Chuanyan; Zhang, Lidong; Tang, Jianrong</p> <p>2016-09-01</p> <p>The geology in the Wuliji area (including the Enger Us and Quagan Qulu areas) is important for understanding the Late Paleozoic tectonics of the Solonker Zone. Ultramafic/mafic rocks in the Enger Us area, previously interpreted as an ophiolitic suture, are actually lava flows and sills in a Permian turbiditic sequence and a small body of fault breccia containing serpentinite. Subduction zone features, such as accretionary complexes, magmatic arc volcanics or LP/HP metamorphism are absent. Early Permian N-MORB mafic rocks and Late Permian radiolarian cherts accompanied by turbidites and tuffeous rocks indicate a deep water setting. In the Quagan Qulu area, outcrops of the Late Carboniferous to Permian Amushan Formation are composed of volcano-sedimenary rocks and guyot-like reef limestone along with a Late Permian volcano-sedimentary unit. A dacite lava in the Late Permian volcano-sedimentary unit yields a zircon U-Pb age of 254 Ma. The gabbros in the Quagan Qulu area are intruded into the Amushan Formation and caused contact metamorphism of country rocks. Sandstones in the Upper Member of the Amushan Formation contain detrital clasts of volcanic fragments and mineral clasts of crystalline basement rocks (i.e. biotite, muscovite and garnet). Geochemical analysis of volcaniclastic sandstones shows a magmatic affinity to both continental island arc (CIA) and active continental margin (ACM) tectonic settings. A Late Permian incipient rift setting is suggested by analyzing the lithostratigraphic sequence and related magmatism in the Wuliji area. The volcano-sedimentary rocks in the Wuliji area experienced a nearly N-S shortening that was probably related to the Early Mesozoic nearly N-S compression well developed in other areas close to the Wuliji area.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018MarGR.tmp...17D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018MarGR.tmp...17D"><span>Episodic normal faulting and magmatism during the syn-spreading stage of the Baiyun sag in Pearl River Mouth Basin: response to the multi-phase seafloor spreading of the South China Sea</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Deng, Peng; Mei, Lianfu; Liu, Jun; Zheng, Jinyun; Liu, Minghui; Cheng, Zijie; Guo, Fengtai</p> <p>2018-03-01</p> <p>Considerable post-breakup extensional deformation is recorded in the continental margins of the South China Sea (SCS). To recognize the nature and origin of the significant deformation during the syn-spreading stage (32-15.5 Ma) in the SCS, we comprehensively analyzed the geometry and kinematics of the faults and contemporaneous magmas in the Baiyun sag, northern margin of the SCS, using high-resolution regional three-dimensional seismic data. The kinematic analyses indicate that the faults in the Baiyun sag are recently formed following the onset of seafloor spreading in the SCS. The faults exhibit multiple episodes of growth history, with three active episodes, 32-29, 23.8-21 and 18.5-16.5 Ma, separated by periods of inactivity. Four volcanic groups comprising 98 volcanic mounds have been identified and described, located separately in the northwestern, the central, the southeastern and the northern slope areas. The occurrence of multiple palaeo-seafloors, complemented by the biostratigraphic and K-Ar dating data, reveals multiple extrusive events of the syn-spreading magmas in the Baiyun sag, with three active periods of 23.8-21, 18.5-17.5 and 17.5-16.5 Ma. This study confirms that the normal faulting has a shared genetic origin with the contemporaneous magmatism during the syn-spreading stage in the deep-offshore Baiyun sag, northern margin of the SCS. The episodic fault growth and magmatic extrusive events reveal that the Baiyun sag has undergone at least three episodic tectonic events during the syn-spreading stage, which evolved in response to the multi-stage seafloor spreading of the SCS.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Geote..49..379P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Geote..49..379P"><span>The role of mantle plumes in the evolution of the African segment of Pangea and the formation of the Atlantic Ocean</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peyve, A. A.</p> <p>2015-09-01</p> <p>In this paper, we discuss a broad range of issues related to the formation of large igneous provinces in the African segment of Pangea on the basis of modern seismic tomography data. The formation of older igneous provinces (Central American and Karoo) is attributed to a prolonged phase of upwelling of hot mantle material or fluids in separate jets within a much larger area than the supposed plume head. Owing to its huge size and the thick, dense continental crust, Pangea acted as a shield promoting the accumulation and lateral channeling of heat energy beneath the lithosphere. The changes in global Earth dynamics and the generation of extensional stresses alone may have led to the breakup of Pangea, triggering the eruption of large volumes of magma over short period of time. The same factors led to the opening of the Atlantic Ocean. We provide arguments that the African superplume represents a Cenozoic structure not associated with the emplacement of the Karoo province. At the same time, the hot material brought under the lithosphere by this superplume synchronously with the start of magmatism in east Africa then spread out to the northwest to form local melting areas in Central and Northwestern Africa. We suggest that magmatic activity within the same region may have lasted, with interruptions, over tens of millions of years. Because of plate motion, these lowvelocity zones acting as heat sources appear to have lost their deep-seated roots, so that mantle reservoirs surviving at the base of the lithosphere may have fed magmatism and drifted together with the lithosphere.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17843792','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17843792"><span>Deep magma body beneath the summit and rift zones of kilauea volcano, hawaii.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Delaney, P T; Fiske, R S; Miklius, A; Okamura, A T; Sako, M K</p> <p>1990-03-16</p> <p>A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016871','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016871"><span>Deep magma body beneath the summit and rift zones of Kilauea Volcano, Hawaii</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Delaney, P.T.; Fiske, R.S.; Miklius, Asta; Okamura, A.T.; Sako, M.K.</p> <p>1990-01-01</p> <p>A magnitude 7.2 earthquake in 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward in response to slippage along a deep fault. Since then, a large part of the volcano's edifice has been adjusting to this perturbation. The summit of Kilauea extended at a rate of 0.26 meter per year until 1983, the south flank uplifted more than 0.5 meter, and the axes of both the volcano's rift zones extended and subsided; the summit continues to subside. These ground-surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones. Kilauea's magmatic system is, therefore, probably deeper and more extensive than previously thought; the summit and both rift zones may be underlain by a thick, near vertical dike-like magma system at a depth of 3 to 9 kilometers.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010MinPe..98...55E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010MinPe..98...55E"><span>Large igneous provinces (LIPs) and carbonatites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ernst, Richard E.; Bell, Keith</p> <p>2010-03-01</p> <p>There is increasing evidence that many carbonatites are linked both spatially and temporally with large igneous provinces (LIPs), i.e. high volume, short duration, intraplate-type, magmatic events consisting mainly of flood basalts and their plumbing systems (of dykes, sills and layered intrusions). Examples of LIP-carbonatite associations include: i. the 66 Ma Deccan flood basalt province associated with the Amba Dongar, Sarnu-Dandali (Barmer), and Mundwara carbonatites and associated alkali rocks, ii. the 130 Ma Paraná-Etendeka (e.g. Jacupiranga, Messum); iii. the 250 Ma Siberian LIP that includes a major alkaline province, Maimecha-Kotui with numerous carbonatites, iv. the ca. 370 Ma Kola Alkaline Province coeval with basaltic magmatism widespread in parts of the East European craton, and v. the 615-555 Ma CIMP (Central Iapetus Magmatic Province) of eastern Laurentia and western Baltica. In the Superior craton, Canada, a number of carbonatites are associated with the 1114-1085 Ma Keweenawan LIP and some are coeval with the pan-Superior 1880 Ma mafic-ultramafic magmatism. In addition, the Phalaborwa and Shiel carbonatites are associated with the 2055 Ma Bushveld event of the Kaapvaal craton. The frequency of this LIP-carbonatite association suggests that LIPs and carbonatites might be considered as different evolutionary ‘pathways’ in a single magmatic process/system. The isotopic mantle components FOZO, HIMU, EM1 but not DMM, along with primitive noble gas signatures in some carbonatites, suggest a sub-lithospheric mantle source for carbonatites, consistent with a plume/asthenospheric upwelling origin proposed for many LIPs.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70188498','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70188498"><span>Volcanoes of the passive margin: The youngest magmatic event in eastern North America</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Mazza, Sarah E; Gazel, Esteban; Johnson, Elizabeth A; Kunk, Michael J.; McAleer, Ryan J.; Spotila, James A; Bizimis, Michael; Coleman, Drew S</p> <p>2014-01-01</p> <p>The rifted eastern North American margin (ENAM) provides important clues to the long-term evolution of continental margins. An Eocene volcanic swarm exposed in the Appalachian Valley and Ridge Province of Virginia and West Virginia (USA) contains the youngest known igneous rocks in the ENAM. These magmas provide the only window into the most recent deep processes contributing to the postrift evolution of this margin. Here we present new 40Ar/39Ar ages, geochemical data, and radiogenic isotopes that constrain the melting conditions and the timing of emplacement. Modeling of the melting conditions on primitive basalts yielded an average temperature and pressure of 1412 ± 25 °C and 2.32 ± 0.31 GPa, corresponding to a mantle potential temperature of ∼1410 °C, suggesting melting conditions slightly higher than average mantle temperatures beneath mid-ocean ridges. When compared with magmas from Atlantic hotspots, the Eocene ENAM samples share isotopic signatures with the Azores and Cape Verde. This similarity suggests the possibility of a large-scale dissemination of similar sources in the upper mantle left over from the opening of the Atlantic Ocean. Asthenosphere upwelling related to localized lithospheric delamination is a possible process that can explain the intraplate signature of these magmas that lack evidence of a thermal anomaly. This process can also explain the Cenozoic dynamic topography and evidence of rejuvenation of the central Appalachians.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T33C2438P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T33C2438P"><span>Numerical modeling of continental lithospheric weak zone over plume</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perepechko, Y. V.; Sorokin, K. E.</p> <p>2011-12-01</p> <p>The work is devoted to the development of magmatic systems in the continental lithosphere over diffluent mantle plumes. The areas of tension originating over them are accompanied by appearance of fault zones, and the formation of permeable channels, which are distributed magmatic melts. The numerical simulation of the dynamics of deformation fields in the lithosphere due to convection currents in the upper mantle, and the formation of weakened zones that extend up to the upper crust and create the necessary conditions for the formation of intermediate magma chambers has been carried out. Thermodynamically consistent non-isothermal model simulates the processes of heat and mass transfer of a wide class of magmatic systems, as well as the process of strain localization in the lithosphere and their influence on the formation of high permeability zones in the lower crust. The substance of the lithosphere is a rheologic heterophase medium, which is described by a two-velocity hydrodynamics. This makes it possible to take into account the process of penetration of the melt from the asthenosphere into the weakened zone. The energy dissipation occurs mainly due to interfacial friction and inelastic relaxation of shear stresses. The results of calculation reveal a nonlinear process of the formation of porous channels and demonstrate the diversity of emerging dissipative structures which are determined by properties of both heterogeneous lithosphere and overlying crust. Mutual effect of a permeable channel and the corresponding filtration process of the melt on the mantle convection and the dynamics of the asthenosphere have been studied. The formation of dissipative structures in heterogeneous lithosphere above mantle plumes occurs in accordance with the following scenario: initially, the elastic behavior of heterophase lithosphere leads to the formation of the narrow weakened zone, though sufficiently extensive, with higher porosity. Further, the increase in the width of the weakened area with a small decrease in porosity occurs due to the increase of inelastic stresses. The longitudinal scale of the structure remain unchanged. The evolution of intraplate magmatic systems associated with weakened zones is accompanied by the formation of intermediate intracrustal magma chambers. This work was financially supported by the project #24.1.2, the program of RAS #24.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4677E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4677E"><span>Numerical modelling of volatiles in the deep mantle</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eichheimer, Philipp; Thielmann, Marcel; Golabek, Gregor J.</p> <p>2017-04-01</p> <p>The transport and storage of water in the mantle significantly affects several material properties of mantle rocks and thus water plays a key role in a variety of geodynamical processes (tectonics, magmatism etc.). The processes driving transport and circulation of H2O in subduction zones remain a debated topic. Geological and seismological observations suggest different inflow mechanisms of water e.g. slab bending, thermal cracking and serpentinization (Faccenda et al., 2009; Korenaga, 2017), followed by dehydration of the slab. On Earth both shallow and steep subduction can be observed (Li et al., 2011). However most previous models (van Keken et al., 2008; Wilson et al., 2014) did not take different dip angles and subduction velocities of slabs into account. To which extent these parameters and processes influence the inflow of water still remains unclear. We present 2D numerical models simulating the influence of the various water inflow mechanisms on the mantle with changing dip angle and subduction velocity of the slab over time. The results are used to make predictions regarding the rheological behavior of the mantle wedge, dehydration regimes and volcanism at the surface. References: van Keken, P. E., et al. A community benchmark for subduction zone modeling. Phys. Earth Planet. Int. 171, 187-197 (2008). Faccenda, M., T.V. Gerya, and L. Burlini. Deep slab hydration induced by bending-related variations in tectonic pressure. Nat. Geosci. 2, 790-793 (2009). Korenaga, J. On the extent of mantle hydration caused by plate bending. Earth Planet. Sci. Lett. 457, 1-9 (2017). Wilson, C. R., et al. Fluid flow in subduction zones: The role of solid rheology and compaction pressure. Earth Planet. Sci. Lett. 401, 261-274 (2014). Li, Z. H., Z. Q. Xu, and T. V. Gerya. Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision zones. Earth Planet. Sci. Lett. 301, 65-77 (2011).</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T13B3006S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T13B3006S"><span>Processes accompanying of mantle plume emplacement into continental lithosphere: Evidence from NW Arabian plate, Western Syria</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sharkov, E. V.</p> <p>2015-12-01</p> <p>Lower crustal xenoliths occurred in the Middle Cretaceous lamprophyre diatremes in Jabel Ansaria (Western Syria) (Sharkov et al., 1992). They are represented mainly garnet granulites and eclogite-like rocks, which underwent by deformations and retrograde metamorphism, and younger fresh pegmatoid garnet-kaersutite-clinopyroxene (Al-Ti augite) rocks; mantle peridotites are absent in these populations. According to mineralogical geothermobarometers, forming of garnet-granulite suite rocks occurred under pressure 13.5-15.4 kbar (depths 45-54 kn) and temperature 965-1115oC. At the same time, among populations of mantle xenoliths in the Late Cenozoic platobasalts of the region, quite the contrary, lower crustal xenoliths are absent, however, predominated spinel lherzolites (fragments of upper cooled rim of a plume head), derived from the close depths (30-40 km: Sharkov, Bogatikov, 2015). From this follows that ancient continental crust was existed here even in the Middle Cretaceous, but in the Late Cenozoic was removed by extended mantle plume head; at that upper sialic crust was not involved in geomechanic processes, because Precambrian metamorphic rocks survived as a basement for Cambrian to Cenozoic sedimentary cover of Arabian platform. In other words, though cardinal rebuilding of deep-seated structure of the region occurred in the Late Cenozoic but it did not affect on the upper shell of the ancient lithosphere. Because composition of mantle xenolithis in basalts is practically similar worldwide, we suggest that deep-seated processes are analogous also. As emplacement of the mantle plume heads accompanied by powerful basaltic magmatism, very likely that range of lower (mafic) continental crust existence is very convenient for extension of plume heads and their adiabatic melting. If such level, because of whatever reasons, was not reached, melting was limited but appeared excess of volatile matters which led to forming of lamprophyre or even kimberlite.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Litho.248...40B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Litho.248...40B"><span>Age and geochemistry of host rocks of the Cobre Panama porphyry Cu-Au deposit, central Panama: Implications for the Paleogene evolution of the Panamanian magmatic arc</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baker, Michael J.; Hollings, Peter; Thompson, Jennifer A.; Thompson, Jay M.; Burge, Colin</p> <p>2016-04-01</p> <p>The Cobre Panama porphyry Cu-Au deposit, located in the Petaquilla district of central Panama, is hosted by a sequence of medium- to high-K calc-alkaline volcanic and sub-volcanic rocks. New crystallisation ages obtained from a granodiorite Petaquilla batholith and associated mineralised diorite to granodiorite porphyry stocks and dikes at Cobre Panama indicate that the batholith was emplaced as a multi-phase intrusion, over a period of 4 million years from 32.20 ± 0.76 Ma to 28.26 ± 0.61 Ma, while the porphyritic rocks were emplaced over a 2 million year period from 28.96 ± 0.62 Ma to 27.48 ± 0.68 Ma. Both the volcanic to sub-volcanic host rocks and intrusive rocks of the Cobre Panama deposit evolved via fractional crystallisation processes, as demonstrated by the major elements (e.g. Al2O3, Fe2O3, TiO2 and MgO) displaying negative trends with increasing SiO2. The Petaquilla intrusive rocks, including the diorite-granodiorite porphyries and granodiorite batholith, are geochemically evolved and appear to have formed from more hydrous magmas than the preceding host volcanic rocks, as evidenced by the presence of hornblende phenocrysts, higher degrees of large-ion lithophile element (LILE) and light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion, and higher Sr/Y and La/Yb values. However, the degree of LREE enrichment, HREE depletion and La/Yb values are insufficient for the intrusive rocks to be considered as adakites. Collectively, the volcanic and intrusive rocks have LILE, REE and mobile trace element concentrations similar to enriched Miocene-age Cordilleran arc magmatism found throughout central and western Panama. Both the Petaquilla and Cordilleran arc magmatic suites are geochemically more evolved than the late Cretaceous to Eocene Chagres-Bayano arc magmas from northeastern Panama, as they display higher degrees of LILE and LREE enrichment. The geochemical similarities between the Petaquilla and Cordilleran arc magmas suggest that evolved calc-alkaline arc magmatism may extend to the late Eocene, at least 10 million years earlier than previously estimated. The crystallisation ages for intrusive rocks associated with mineralisation at Cobre Panama imply that the deposit formed in the early Oligocene, between a period of late Cretaceous to Eocene magmatism (ca. 66-42 Ma; Chagres-Bayano arc) and Cordilleran arc magmatism (22-7 Ma). Similarities in the timing of intrusive suite emplacement and the fingerprinting of magmatic fractionation processes between the Cobre Panama porphyry deposit and the Cerro Colorado porphyry deposit in western Panama (ca. 5.3 Ma) suggest that these features provide favourable geodynamic and geochemical prerequisites for the formation of porphyry deposits along the Panamanian magmatic arc during the Cenozoic.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tectp.691..185P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tectp.691..185P"><span>Devonian magmatism in the Timan Range, Arctic Russia - subduction, post-orogenic extension, or rifting?</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pease, V.; Scarrow, J. H.; Silva, I. G. Nobre; Cambeses, A.</p> <p>2016-11-01</p> <p>Devonian mafic magmatism of the northern East European Craton (EEC) has been variously linked to Uralian subduction, post-orogenic extension associated with Caledonian collision, and rifting. New elemental and isotopic analyses of Devonian basalts from the Timan Range and Kanin Peninsula, Russia, in the northern EEC constrain magma genesis, mantle source(s) and the tectonic process(es) associated with this Devonian volcanism to a rift-related context. Two compositional groups of low-K2O tholeiitic basalts are recognized. On the basis of Th concentrations, LREE concentrations, and (LREE/HREE)N, the data suggest two distinct magma batches. Incompatible trace elements ratios (e.g., Th/Yb, Nb/Th, Nb/La) together with Nd and Pb isotopes indicate involvement of an NMORB to EMORB 'transitional' mantle component mixed with variable amounts of a continental component. The magmas were derived from a source that developed high (U,Th)/Pb, U/Th and Sm/Nd over time. The geochemistry of Timan-Kanin basalts supports the hypothesis that the genesis of Devonian basaltic magmatism in the region resulted from local melting of transitional mantle and lower crust during rifting of a mainly non-volcanic continental rifted margin.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.4805B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.4805B"><span>Magmatic development of the outer Vøring Margin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breivik, Asbjorn; Faleide, Jan Inge; Mjelde, Rolf; Flueh, Ernst; Murai, Yoshio</p> <p>2013-04-01</p> <p>The Vøring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired on the Vøring and Lofoten margins. One profile crosses from the Vøring Plateau to the Vøring Spur, an oceanic plateau north of the EJMFZ. The P-wave data were modeled by ray-tracing in a 2D velocity model of the crust. The process behind the excess magmatism can be estimated by comparing seismic velocity (VP) with igneous thickness (H). This profile and two other profiles farther north show a positive H-VP correlation, consistent with a hot mantle reservoir of finite extent under the margin at breakup. However, during the first two million years, magma production appears to be augmented by a secondary process. By 51-51.5 Ma melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows at least two inversion events, with the main episode tentatively in the Upper Miocene, apparently through igneous growth to create the up to 15 km crustal thickness. The H-VP correlation of the spur is low, indicating constant and moderate-degree mantle melting not tied to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, discounting that compressional flexure at the EJMFZ shaped the high. We also find no evidence for the proposed Early Eocene triple junction in the area.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRB..119.6733B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRB..119.6733B"><span>Magmatic development of the outer Vøring margin from seismic data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breivik, Asbjørn; Faleide, Jan Inge; Mjelde, Rolf; Flueh, Ernst; Murai, Yoshio</p> <p>2014-09-01</p> <p>The Vøring Plateau off mid-Norway is a volcanic passive margin, located north of the East Jan Mayen Fracture Zone (EJMFZ). Large volumes of magmatic rocks were emplaced during Early Eocene margin formation. In 2003, an ocean bottom seismometer survey was acquired over the margin. One profile crosses from the Vøring Plateau to the Vøring Spur, a bathymetric high north of the EJMFZ. The P wave data were ray traced into a 2-D crustal velocity model. The velocity structure of the Vøring Spur indicates up to 15 km igneous crustal thickness. Magmatic processes can be estimated by comparing seismic velocity (VP) with igneous thickness (H). This and two other profiles show a positive H-VP correlation at the Vøring Plateau, consistent with elevated mantle temperature at breakup. However, during the first 2 Ma magma production was augmented by a secondary process, possibly small-scale convection. From ˜51.5 Ma excess melting may be caused by elevated mantle temperature alone. Seismic stratigraphy around the Vøring Spur shows that it was created by at least two uplift events, with the main episode close to the Miocene/Pliocene boundary. Low H-VP correlation of the spur is consistent with renewed igneous growth by constant, moderate-degree mantle melting, not related to the breakup magmatism. The admittance function between bathymetry and free-air gravity shows that the high is near local isostatic equilibrium, precluding that compressional flexure at the EJMFZ uplifted the high. We find a proposed Eocene triple junction model for the margin to be inconsistent with observations.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4517C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4517C"><span>Tibet and Beyond: Magmatic Records from CIA (Caucasus-Iran-Anatolia) and Southern Tibet with Implications for Asian Orogeny and Continental Growth</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chung, Sun-Lin</p> <p>2016-04-01</p> <p>This study, based on an ongoing joint research project "Tibet and Beyond", presents a synthesis of principal magmatic records from the CIA (Caucasus-Iran-Anatolia) and Tibet-Himalaya orogens resulting from the continental collisions of Arabia and India, respectively, with Eurasia. In both orogens, through this and other recent studies, the temporal and spatial variations in magmatism pre-, syn- and post-dating the collisions can now be much better defined, thus improving our understanding of collision zone magmatism that appears to have evolved with changes in the lithospheric structures over time and space by collisional processes. The two "collisional" Tethyan orogens were preceded by accretionary orogenic processes, which not only had produced a substantial amount of juvenile continental crust but also fulfill the "orogenic cycle" that evolved from an accretionary into a collisional system. Geochemical data reveal that in contrast to generating vast portions of juvenile crust in the early, accretionary stages of orogenic development, crustal recycling plays a more important role in the later, collisional stages. The latter, as exemplified in SE Turkey and southern Tibet, involves addition of older continental crust material back into the mantle, which subsequently melted and caused compositional transformation of the juvenile crust produced in the accretionary stages. Similar features are observed in young volcanic rocks from eastern Taiwan, the northern Luzon arc complex and part of the active subduction/accretion/collision system in Southeast Asia that may evolve one day to resemble the eastern Tethyan and central Asian orogenic belts by collision with the advancing Australian continent.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70193082','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70193082"><span>Pb-Sr-Nd-O isotopic characterization of Mesozoic rocks throughout the northern end of the Peninsular Ranges batholith: Isotopic evidence for the magmatic evolution of oceanic arc–continental margin accretion during the Late Cretaceous of southern California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kistler, Ronald W.; Wooden, Joseph L.; Premo, Wayne R.; Morton, Douglas M.</p> <p>2014-01-01</p> <p>Within the duration of the U.S. Geological Survey (USGS)–based Southern California Areal Mapping Project (SCAMP), many samples from the northern Peninsular Ranges batholith were studied for their whole-rock radioisotopic systematics (rubidium-strontium [Rb-Sr], uranium-thorium-lead [U-Th-Pb], and samarium-neodymium [Sm-Nd]), as well as oxygen (O), a stable isotope. The results of three main studies are presented separately, but here we combine them (>400 analyses) to produce a very complete Pb-Sr-Nd-O isotopic profile of an arc-continent collisional zone—perhaps the most complete in the world. In addition, because many of these samples have U-Pb zircon as well as argon mineral age determinations, we have good control of the timing for Pb-Sr-Nd-O isotopic variations.The ages and isotopic variations help to delineate at least four zones across the batholith from west to east—an older western zone (126–108 Ma), a transitional zone (111–93 Ma), an eastern zone (94–91 Ma), and a much younger allochthonous thrust sheet (ca. 84 Ma), which is the upper plate of the Eastern Peninsular Ranges mylonite zone. Average initial 87Sr/86 Sr (Sri), initial 206Pb/204Pb (206 Pbi), initial 208Pb/204Pb (average 208Pbi), initial epsilon Nd (average εNdi), and δ18O signatures range from 0.704, 18.787, 38.445, +3.1, and 4.0‰–9.0‰, respectively, in the westernmost zone, to 0.7071, 19.199, 38.777, −5, and 9‰–12‰, respectively, in the easternmost zone. The older western zone is therefore the more chemically and isotopically juvenile, characterized mostly by values that are slightly displaced from a mantle array at ca. 115 Ma, and similar to some modern island-arc signatures. In contrast, the isotopic signatures in the eastern zones indicate significant amounts of crustal involvement in the magmatic plumbing of those plutons. These isotopic signatures confirm previously published results that interpreted the Peninsular Ranges batholith as a progressively contaminated magmatic arc. The Peninsular Ranges batholith magmatic arc was initially an oceanic arc built on Panthalassan lithosphere that eventually evolved into a continental margin magmatic arc collision zone, eventually overriding North American cratonic lithosphere. Our Pb-Sr-Nd data further suggest that the western arc rocks represent a nearshore or inboard oceanic arc, as they exhibit isotopic signatures that are more enriched than typical mid-ocean-ridge basalt (MORB). Isotopic signatures from the central zone are transitional and indicate that enriched crustal magma sources were becoming involved in the northern Peninsular Ranges batholith magmatic plumbing. As the oceanic arc–continental margin collision progressed, a mixture of oceanic mantle and continental magmatic sources transpired. Magmatic production in the northern Peninsular Ranges batholith moved eastward and continued to tap enriched crustal magmatic sources. Similar modeling has been previously proposed for two other western margin magmatic arcs, the Sierra Nevada batholith of central California and the Idaho batholith.Calculated initial Nd signatures at ca. 100 Ma for Permian–Jurassic and Proterozoic basement rocks from the nearby San Gabriel Mountains and possible source areas along the southwestern Laurentian margin of southern California, southwestern Arizona, and northern Sonora strongly suggest their involvement with deep crustal magma mixing beneath the eastern zones of the Peninsular Ranges batholith, as well as farther east in continental lithospheric zones.Last, several samples from the allochthonous, easternmost upper-plate zone, which are considerably younger (ca. 84 Ma) than any of the rocks from the northern Peninsular Ranges batholith proper, have even more enriched average Sri, 206Pbi, 208Pbi, and εNdisignatures of 0.7079, 19.344, 38.881, and −6.6, respectively, indicative of the most-evolved magma sources in the northern Peninsular Ranges batholith and similar to radioisotopic values for rocks from the nearby Transverse Ranges, suggesting a genetic connection between the two.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUOSIS52A..03M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUOSIS52A..03M"><span>Advancing an In situ Laser Spectrometer for Carbon Isotope Analyses in the Deep Ocean</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michel, A.; Wankel, S. D.; Kapit, J.; Girguis, P. R.</p> <p>2016-02-01</p> <p>Development of in situ chemical sensors is critical for improving our understanding of deep-ocean biogeochemistry and recent advances in chemical sensors are already expanding the breadth and depth of deep sea/seafloor exploration and research. Although initially developed for high sensitivity measurements of atmospheric gases, laser-based spectroscopic sensors are now being developed for research in the deep sea by incorporating the use of semi-permeable membranes. Here we present on recent deep-sea deployments of an in situ laser-based analyzer of carbon isotopes of methane (δ13CH4), highlighting several advances including a new capability for also measuring δ13C of DIC or CO2 by incorporating a second laser and an in line acidification module. A bubble trapping approach was designed and implemented for the collection and analysis of both CH4 and CO2 from deep-sea bubbles. The newly advanced laser spectrometer was deployed at both Kick `Em Jenny volcano off of the island of Grenada and in a brine pool in the western Gulf of Mexico ("The Jacuzzi of Despair") using the E/V Nautilus and the ROV Hercules. At Kick `Em Jenny, seafloor measurements were made of both emanating fluids and bubbles from within and around the crater - revealing high levels of magmatic CO2 with minor amounts of CH4 and hydrogen sulfide. At the brine pool, spot measurements and depth profile measurements into the brine pool were made for chemical mapping, revealing fluids that were saturated with respect to methane. New technologies such as the laser spectrometer will enable us to obtain high resolution and near real-time, in situ chemical and isotopic data and to make geochemical maps over a range of spatial and temporal scales.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008GeoRL..35.9302D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008GeoRL..35.9302D"><span>Mechanical erosion of xenoliths by magmatic shear flow</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Del Gaudio, Piero; Ventura, Guido</p> <p>2008-05-01</p> <p>We focus on the role of mechanical erosion by magmatic shear flow in the formation of xenoliths occurring in lava flows. The process is analyzed by combining the physics of fragmentation and erosion to the concept of rock mass. The conditions for the country rock fragmentation are analyzed as a function of the magma viscosity, strain rate and tensile strength of the rock mass. In reservoirs, mechanical processes play a subordinate role and thermal erosion processes prevail. In conduits, intermediate and silicic magmas may erode and, eventually, fragment good to poor quality country rock masses. Basalts may erode poor quality country rocks. A crystal-rich magma has more chance to break up the conduit walls with respect to a vesiculated melt. The variety of xenoliths of a lava reflects a set of wall-rocks with similar mechanical properties and may not mirror the stratigraphy of the substratum of a volcanic area.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V43E..05P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V43E..05P"><span>Shallow outgassing changes disrupt steady lava lake activity, Kilauea Volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Patrick, M. R.; Orr, T. R.; Swanson, D. A.; Lev, E.</p> <p>2015-12-01</p> <p>Persistent lava lakes are a testament to sustained magma supply and outgassing in basaltic systems, and the surface activity of lava lakes has been used to infer processes in the underlying magmatic system. At Kilauea Volcano, Hawai`i, the lava lake in Halema`uma`u Crater has been closely studied for several years with webcam imagery, geophysical, petrological and gas emission techniques. The lava lake in Halema`uma`u is now the second largest on Earth, and provides an unprecedented opportunity for detailed observations of lava lake outgassing processes. We observe that steady activity is characterized by continuous southward motion of the lake's surface and slow changes in lava level, seismic tremor and gas emissions. This normal, steady activity can be abruptly interrupted by the appearance of spattering - sometimes triggered by rockfalls - on the lake surface, which abruptly shifts the lake surface motion, lava level and gas emissions to a more variable, unstable regime. The lake commonly alternates between this a) normal, steady activity and b) unstable behavior several times per day. The spattering represents outgassing of shallowly accumulated gas in the lake. Therefore, although steady lava lake behavior at Halema`uma`u may be deeply driven by upwelling of magma, we argue that the sporadic interruptions to this behavior are the result of shallow processes occurring near the lake surface. These observations provide a cautionary note that some lava lake behavior is not representative of deep-seated processes. This behavior also highlights the complex and dynamic nature of lava lake activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T53A4661I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T53A4661I"><span>Crustal Accretion at Subduction Initiation Along Izu-Bonin-Mariana Arc and the Link to SSZ Ophiolites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ishizuka, O.; Tani, K.; Reagan, M. K.; Kanayama, K.; Umino, S.; Harigane, Y.; Sakamoto, I.</p> <p>2014-12-01</p> <p>The Izu-Bonin-Mariana (IBM) forearc preserves the earliest arc magmatic history from subduction initiation to the establishment of the arc. Recent investigations have established a bottom to top igneous stratigraphy of: 1) mantle peridotite, 2) gabbroic rocks, 3) a sheeted dyke complex, 4) basaltic pillow lavas (forearc basalts: FAB), 5) boninites and magnesian andesites, 6) tholeiites and calcalkaline arc lavas. This stratigraphy has many similarities to supra-subduction zone (SSZ) ophiolites. One of the most important common characteristics between the SSZ ophiolites and the forearc crust is the occurrence of MORB-like basaltic lavas underlying or accompanying boninites and early arc volcanic suites. A key observation from the IBM forearc is that FAB differs from nearby back-arc lavas in chemical characteristics, including a depletion in moderately incompatible elements. This indicates that FAB is not a pre-existing oceanic basement of the arc, but the first magmatic product after subduction initiation. Sheeted dikes of FAB composition imply that this magmatism was associated with seafloor spreading, possibly triggered by onset of slab sinking. Recognition of lavas with transitional geochemical characteristics between the FAB and the boninites strongly implies genetic linkage between these two magma types. The close similarity of the igneous stratigraphy of SSZ ophiolites to the IBM forearc section strongly implies a common magmatic evolutionary path, i.e., decompressional melting of a depleted MORB-type mantle is followed by melting of an even more depleted mantle with the addition of slab-derived fluid/melt to produce boninite magma. Similarity of magmatic process between IBM forearc and Tethyan ophiolites appears to be reflected on common characteristics of upper mantle section. Peridotite from both sections show more depleted characteristics compared to upper mantle rocks from mid-ocean ridges. Age determinations reveal that first magmatism at the IBM arc occurred at c. 52 Ma, and transition from forearc basalt to normal arc magmatism took 7-8 million years. Combined with the age information from SSZ-ophiolites, significant constraints on time scale of subduction initiation and associated crustal accretion might be obtained.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005E%26PSL.235..663C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005E%26PSL.235..663C"><span>Magmatic @d^1^8O in 4400-3900 Ma detrital zircons: A record of the alteration and recycling of crust in the Early Archean [rapid communication</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cavosie, A. J.; Valley, J. W.; Wilde, S. A.</p> <p>2005-07-01</p> <p>Ion microprobe analyses of δ 18O in 4400-3900 Ma igneous zircons from the Jack Hills, Western Australia, provide a record of the oxygen isotope composition of magmas in the earliest Archean. We have employed a detailed analysis protocol aimed at correlating spatially related micro-volumes of zircon concordant in U/Pb age with δ 18O and internal zoning. Simultaneous analysis of 18O and 16O with dual Faraday cup detectors, combined with frequent standardization, has yielded data with improved accuracy and precision over prior studies, and resulted in a narrower range of what is interpreted as magmatic δ 18O in > 3900 Ma zircons. Preserved magmatic δ 18O values from individual zircons (Zrc) range from 5.3‰ to 7.3‰ (VSMOW), and increasingly deviate from the mantle range of 5.3 ± 0.3‰ as zircons decrease in age from 4400 to 4200 Ma. Elevated δ 18O (Zrc) values up to 6.5‰ occur as early as 4325 Ma, which suggests that evolved rocks were incorporated into magmas within ˜230 Ma of Earth's accretion. Values of magmatic δ 18O (Zrc) as high as 7.3‰ are recorded in zircons by 4200 Ma, and are common thereafter. The protoliths of the magmas these zircons crystallized in were altered by low temperature interaction with liquid water near Earth's surface. These results provide the strongest evidence yet for the existence of liquid water oceans and supracrustal rocks by approximately 4200 Ma, and possibly as early as 4325 Ma. The range of magmatic δ 18O values in the 4400-3900 Ma zircons is indistinguishable from Archean igneous zircons, suggesting similar magmatic processes occurred over the first two billion years of recorded Earth history. Zircons with sub-solidus alteration histories, identified by the presence of disturbed internal zoning patterns, record δ 18O values both below (4.6‰) and above (10.3‰) the observed range for primary magmatic zircon, and are unreliable indicators of Early Archean magma chemistry.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JAESc.157..141E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JAESc.157..141E"><span>The final pulse of the Early Cenozoic adakitic activity in the Eastern Pontides Orogenic Belt (NE Turkey): An integrated study on the nature of transition from adakitic to non-adakitic magmatism in a slab window setting</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eyuboglu, Yener; Dudas, Francis O.; Santosh, M.; Eroğlu-Gümrük, Tuğba; Akbulut, Kübra; Yi, Keewook; Chatterjee, Nilanjan</p> <p>2018-05-01</p> <p>The Eastern Pontides Orogenic Belt, one of the best examples of a fossil continental arc in the Alpine-Himalayan system, is characterized by adakitic magmatism during the Early Cenozoic. Popular models correlate the adakitic magmatism to syn- or post-collisional processes occurring after the collision between the Eastern Pontides Orogenic Belt and the Tauride Platform at the end of Late Mesozoic and/or beginning of the Cenozoic. We present new geological, petrological and chronological data from andesites and felsic tuffs exposed in the Bayburt area, in the southern part of the Eastern Pontides Orogenic Belt, and discuss the nature of the transition from adakitic to non-adakitic activities in a continental arc. Major, trace and rare earth element concentrations of both andesites and felsic tuffs clearly suggest that they are related to arc magmatism in a continental arc with adakitic composition. The isotopic compositions are permissive of mixing between a component similar to depleted mantle and a second component that is either mafic lower crust or subducted oceanic crust. 39Ar/40Ar hornblende and U/Pb zircon dating indicate that this adakitic magmatism in the Bayburt area ended by about 47 Ma, and transformed into non-adakitic, granitoid arc magmatism in the area immediately north of Bayburt in the Lutetian (∼46 Ma). Based on our new results in conjunction with available data, we propose that the beginning of northward rollback of a south-directed subducting slab, and simultaneous opening of a slab window related to ridge subduction, triggered both adakitic magmatism for approximately a 10 Myr period between 57.6 and 47 Ma and arc-parallel extension that caused the opening of the Early Cenozoic sedimentary basins. We also suggest that the shallow marine environment, in which Nummulite-bearing sandy limestones accumulated in the Early Cenozoic, was transformed into a saline-lake environment during the pyroclastic activity that produced the studied felsic tuffs at ∼47 Ma.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JAfES.140..199E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JAfES.140..199E"><span>Intrusion-Related Gold Deposits: New insights from gravity and hydrothermal integrated 3D modeling applied to the Tighza gold mineralization (Central Morocco)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Eldursi, Khalifa; Branquet, Yannick; Guillou-Frottier, Laurent; Martelet, Guillaume; Calcagno, Philippe</p> <p>2018-04-01</p> <p>The Tighza (or Jebel Aouam) district is one of the most important polymetallic districts in Morocco. It belongs to the Variscan Belt of Central Meseta, and includes W-Au, Pb-Zn-Ag, and Sb-Ba mineralization types that are spatially related to late-Carboniferous granitic stocks. One of the proposed hypotheses suggests that these granitic stocks are connected to a large intrusive body lying beneath them and that W-Au mineralization is directly related to this magmatism during a 287-285 Ma time span. A more recent model argues for a disconnection between the older barren outcropping magmatic stocks and a younger hidden magmatic complex responsible for the W-Au mineralization. Independently of the magmatic scenario, the W-Au mineralization is consensually recognized as of intrusion-related gold deposit (IRGD) type, W-rich. In addition to discrepancies between magmatic sceneries, the IRGD model does not account for published older age corresponding to a high-temperature hydrothermal event at ca. 291 Ma. Our study is based on gravity data inversion and hydro-thermal modeling, and aims to test this model of IRGD and its related magmatic geometries, with respect to subsurface geometries, favorable physical conditions for deposition and time record of hydrothermal processes. Combined inversion of geology and gravity data suggests that an intrusive body is rooted mainly at the Tighza fault in the north and that it spreads horizontally toward the south during a trans-tensional event (D2). Based on the numerical results, two types of mineralization can be distinguished: 1) the "Pre-Main" type appears during the emplacement of the magmatic body, and 2) the "Main" type appears during magma crystallization and the cooling phase. The time-lag between the two mineralization types depends on the cooling rate of magma. Although our numerical model of thermally-driven fluid flow around the Tighza pluton is simplified, as it does not take into account the chemical and deformation contributions, it provides evidence for abandoning the time-lag as an argument for invalidating the existence of a genetic link between older mineralizations and/or hydrothermal events spatially related to younger parent plutons.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T42D..02M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T42D..02M"><span>Constraints on crustal structure in the Southeastern United States from the SUGAR 2 refraction seismic refraction experiment</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Marzen, R. E.; Shillington, D. J.; Lizarralde, D.; Harder, S. H.</p> <p>2016-12-01</p> <p>The Southeastern United States is an ideal location to study the interactions between continental collision, extensive but short-lived magmatism, and continental rifting. Continental collision during the Alleghenian Orogeny ( 290 Ma) formed the supercontinent Pangea. Extension leading to the breakup of Pangea began 230 Ma, forming the South Georgia Basin and other rift basins. The extensive Central Atlantic Magmatic Province (CAMP) magmatism was emplaced at 200 Ma, and continental separation occurred afterwards. During these processes, part of the African continent was added to North America. Prior work has raised questions including (1) the location and geometry of the suture zone and implications for the style of collision (thin-skinned versus thick-skinned), (2) the role of pre-existing structures on later rifting, and (3) the distribution of magmatism, and possible relationships between magmatism and rifting. To address these questions, we present preliminary velocity models for the 400-km-long refraction seismic line from the SUwanee Suture and GA Rift basin experiment (SUGAR) Line 2. This line is central to CAMP magmatism, and crosses the South Georgia rift basin and two hypothesized locations for the ancient suture zone. The data were collected in August 2015 by a team of over 40 students and scientists. Fifteen shots spaced at 20-40 km were recorded by 1981 Texans spaced at 250 m. We observe refractions from the basin, crust, and upper mantle, and wide-angle reflections from the base of the sediments, within the crust, and from the Moho. Prominent mid crustal reflections may arise from the top of elevated lower crustal velocities and possible lower crustal layering. The starting velocity model and constraints on the upper sedimentary basin velocity structure are obtained through forward modeling, which show basin sediment thickness increasing to the South. We then invert for smooth 2D velocity structure using first arrivals (FAST) and a layered velocity model using refractions and reflections (RAYINVR) to evaluate the crust and upper mantle velocity structure. Model results will be compared to other geological and geophysical data, including the roughly parallel SUGAR Line 1, to examine along-strike changes in rift structure, suture structure, and evidence of magmatism.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V54B..01S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V54B..01S"><span>The evolution of Yellowstone's magmatic system over the past 630 kyr: Insights from the crystal record</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stelten, M. E.</p> <p>2017-12-01</p> <p>The Yellowstone Plateau volcanic field in northwestern Wyoming is one of the world's largest, active silicic volcanic centers, and has produced three caldera-forming "super eruptions" over the past 2.1 Myr. As a result, the petrologic evolution of Yellowstone's magmatic system has been the focus of numerous studies over the past 60 years. Early studies at Yellowstone focused on characterizing whole-rock chemical and isotopic variations observed in magmas erupted over Yellowstone's lifetime. While these have provided important insights into the source of Yellowstone magmas and the processes controlling their compositional evolution though time, whole-rock studies are limited in their ability to identify the mechanisms and timescales of rhyolite generation. In contrast, much of the recent work at Yellowstone has focused on applying micro-analytical techniques to characterize the age and composition of phenocrysts hosted in Yellowstone rhyolites. These studies have greatly advanced our understanding of the magmatic system at Yellowstone and have provided crucial new insights into the mechanisms and timescales of rhyolite generation. In particular, recent work has focused on applying micro-analytical techniques to study the age and origin of the [1] three caldera-forming eruptions that produced the Huckleberry Ridge, Mesa Falls, Lava Creek tuffs and [2] post-Lava Creek tuff intracaldera rhyolites that compose the Plateau Rhyolite. As a result, a wealth of crystal-chemical data now exists for rhyolites erupted throughout Yellowstone's 2.1 Myr history. These data provide a unique opportunity to create a detailed reconstruction of Yellowstone's magmatic system through time. In this contribution, I integrate available age, chemical, and isotopic data for phenocrysts hosted in Yellowstone rhyolites to construct a model for the evolution of Yellowstone's magmatic system from the caldera-forming eruption of the Lava Creek tuff at ca. 0.63 Ma to the present day. In particular, I highlight new insights into [1] the physical nature of Yellowstone's magmatic system, [2] the ways in which the mechanisms and timescales of rhyolite generation have changed though time, and [3] implications for the current state of the Yellowstone's magmatic system.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1113106L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1113106L"><span>Temporal evolution of the Western and Central volcanism of the Aeolian Island Arc (Italy, southern Tyrhhenian Sea)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leocat, E.; Gillot, P.-Y.; Peccerillo, A.</p> <p>2009-04-01</p> <p>The Aeolian Archipelago is a volcanic arc in the Southern Tyrrhenian Sea located on the continental margin of the Calabro-Peloritan basement. The Aeolian volcanism occurs in a very complex geodynamic setting linked to the convergence of the European and African plates. For that reason, it is strongly related to regional tectonic lineaments, such as the NW-SE trending Tindari-Letojani (TL) fault. The archipelago consists of seven main islands and several seamounts, which extend around the Marsili Basin, forming a ring-like shape, typical for an island arc. While the seamounts began their activities around 1 Ma , the emerged part is active since about 400 ka. The magmatic products of the whole arc range from typical island arc calc-alkaline (CA) and shoshonitic series, to slightly silica undersaturated potassic alkaline series that are typical of post-collisional settings. Furthermore, the TL fault, along which the Lipari and Vulcano islands are developed, separates a calc-alkaline western sector (Alicudi, Filicudi and Salina islands) from the calc-alkaline to potassic eastern system (Panarea and Stromboli islands) (Peccerillo,1999). This makes of the Aeolian Islands a complex volcanism, with a still controversial origin. In this context, the aim of this work is to constrain the sources and spatio-temporal evolution of this magmatism. We present here new K-Ar ages based on the accurate Cassignol-Gillot technique devoted to the dating of very young rocks (Gillot et Cornette, 1986). These geochronological data were used together with new geochemical data on the same samples. In this study, we attempt to understand the origin of those magmatic events and the relationship between the deep processes and the shallow structures. Our results allow us to define specific periods of very quick geomechemical changes. In the case of Filicudi island, the first rocks range in composition from CA basalts to andesites. This period ended with the edification of the Mte Guardia at 189±4 ka. Then the activity was followed by the construction of the Mte Terrione at 168±4 ka (Gillot 1987), which is matched by High K-Ca andesites emplaced in the Chiumento crater. Therefore, two different magmatic series took place in only 15 ka. The last eruption of Filicudi built the High K-CA dacite lava dome of Mte Montagnola. For Lipari island, the same event is observed around 120-100 ka. In fact, the emitted products evolved from CA andesitic basalts, that emplaced from 256±8 ka (Monte Chirica) to 119±7 ka (Monterosa), to High K-CA andesite after 100 ka. The rocks becam more and more differentiated to achieve High K-CA rhyolite composition during the last 40 ka. At the same time, the Monte Fossa delle Felci of Salina island shows a geochemical "excursion" around 100 ka, characterised by High K-CA dacite. The lower limit of Pollara explosive eruption, that emitted High K-CA rhyolite products, is constrain by a Monte dei Porri lava flow affected by Pollara crater and dated at 13±2 ka. Thus, all these magmatic changes correlate with morphological and volcanic variations. Finally, our first results confirm that the Aeolian arc volcanism is generated in a complex source, with important roles of both arc-type and anorogenic-type compositions. Datings on key samples show that role of different mantle sources change within a very short time span, especially in the central portion of the arc, along the TL lithosheric fault system. This work also gives new geochronological constrains on the duration of magmatic evolution and eruptive phases.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70036630','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70036630"><span>Implications of estimated magmatic additions and recycling losses at the subduction zones of accretionary (non-collisional) and collisional (suturing) orogens</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scholl, D. W.; von Huene, Roland E.</p> <p>2009-01-01</p> <p>Arc magmatism at subduction zones (SZs) most voluminously supplies juvenile igneous material to build rafts of continental and intra-oceanic or island arc (CIA) crust. Return or recycling of accumulated CIA material to the mantle is also most vigorous at SZs. Recycling is effected by the processes of sediment subduction, subduction erosion, and detachment and sinking of deeply underthrust sectors of CIA crust. Long-term (>10-20 Ma) rates of additions and losses can be estimated from observational data gathered where oceanic crust underruns modern, long-running (Cenozoic to mid-Mesozoic) ocean-margin subduction zones (OMSZs, e.g. Aleutian and South America SZs). Long-term rates can also be observationally assessed at Mesozoic and older crust-suturing subduction zone (CSSZs) where thick bodies of CIA crust collided in tectonic contact (e.g. Wopmay and Appalachian orogens, India and SE Asia). At modern OMSZs arc magmatic additions at intra-oceanic arcs and at continental margins are globally estimated at c. 1.5 AU and c. 1.0 AU, respectively (1 AU, or Armstrong Unit,= 1 km3 a-1 of solid material). During collisional suturing at fossil CSSZs, global arc magmatic addition is estimated at 0.2 AU. This assessment presumes that in the past the global length of crustal collision zones averaged c. 6000 km, which is one-half that under way since the early Tertiary. The average long-term rate of arc magmatic additions extracted from modern OMSZs and older CSSZs is thus evaluated at 2.7 AU. Crustal recycling at Mesozoic and younger OMSZs is assessed at c. 60 km3 Ma-1 km-1 (c. 60% by subduction erosion). The corresponding global recycling rate is c. 2.5 AU. At CSSZs of Mesozoic, Palaeozoic and Proterozoic age, the combined upper and lower plate losses of CIA crust via subduction erosion, sediment subduction, and lower plate crustal detachment and sinking are assessed far less securely at c. 115 km3 Ma-1 km-1. At a global length of 6000 km, recycling at CSSZs is accordingly c. 0.7 AU. The collective loss of CIA crust estimated for modern OMSZs and for older CSSZs is thus estimated at c. 3.2 AU. SZ additions (2.7 AU) and subtractions (23.2 AU) are similar. Because many uncertainties and assumptions are involved in assessing and applying them to the deep past, the net growth of CIA crust during at least Phanerozoic time is viewed as effectively nil. With increasing uncertainty, the long-term balance can be applied to the Proterozoic, but not before the initiation of the present style of subduction at c. 3 Ga. Allowing that since this time a rounded-down rate of recycling of 3 AU is applicable, a startlingly high volume of CIA crust equal to that existing now has been recycled to the mantle. Although the recycled volume (c. 9 ?? 109 km3) is small (c. 1%) compared with that of the mantle, it is large enough to impart to the mantle the signature of recycled CIA crust. Because subduction zones are not spatially fixed, and their average global lengths have episodically been less or greater than at present, recycling must have contributed significantly to creating recognized heterogeneities in mantle geochemistry. ?? The Geological Society of London 2009.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018CoMP..173...28B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018CoMP..173...28B"><span>Response of zircon to melting and metamorphism in deep arc crust, Fiordland (New Zealand): implications for zircon inheritance in cordilleran granites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bhattacharya, Shrema; Kemp, A. I. S.; Collins, W. J.</p> <p>2018-04-01</p> <p>The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths. Thus, our integrative approach provides the opportunity to discriminate between igneous and metamorphic zircon within deep-crustal complexes. Also, without the tight field relations at Mt Daniel, the scatter beyond a statistically coherent group might be ascribed to the presence of "antecrysts", but it is clear that the WFO solidified before the MDC was emplaced, and these older "igneous" grains are inherited. The bimodal age range of inherited igneous grains, dominated by 125 Ma and 350-320 Ma age clusters, indicate that the adjacent WFO and a Carboniferous metaigneous basement were the main sources of the MDC magmas. Mafic lenses, stretched and highly attenuated into wisps within the MDC and dominated by 124 Ma inherited zircons, are considered to be entrained restitic material from the WFO. A comparison with lower- and upper-crustal, high Sr/Y metaluminous granites elsewhere in Fiordland shows that zircon inheritance is common in the deep crust, near the source region, but generally much less so in coeval, shallow magma chambers (plutons). This is consistent with previous modelling on rapid zircon dissolution rates and high Zr saturation concentrations in metaluminous magmas. Accordingly, unless unusual circumstances exist, such as MDC preservation in the deep crust, low temperatures of magma generation, or rapid emplacement and crystallization at higher structural levels, information on zircon inheritance in upper crustal, Cordilleran plutons is lost during zircon dissolution, along with information on the age, nature and variety of the source material. The observation that dioritic magmas can form at these low temperatures (< 750 °C) also suggests that the petrogenesis of mafic rocks in the arc root might need to be re-assessed.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.210..465P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.210..465P"><span>Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Plasman, M.; Tiberi, C.; Ebinger, C.; Gautier, S.; Albaric, J.; Peyrat, S.; Déverchère, J.; Le Gall, B.; Tarits, P.; Roecker, S.; Wambura, F.; Muzuka, A.; Mulibo, G.; Mtelela, K.; Msabi, M.; Kianji, G.; Hautot, S.; Perrot, J.; Gama, R.</p> <p>2017-07-01</p> <p>Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 × 200 km2 area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15-18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a mid-lithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho but with a more slanting direction (NE-SW) compared to the NS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8-9 per cent. We relate this interface to melt ponding, possibly favouring here deformation process such as grain-boundary sliding (EAGBS) due to lithospheric strain. Its geometry might have been controlled by inherited lithospheric fabrics and heterogeneous upper mantle structure. We evidence that crustal and mantle magmatic processes represent first order mechanisms to ease and locate the deformation during the first stage of a cratonic lithospheric breakup.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V11C0364C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V11C0364C"><span>Determining the physical and chemical processes behind four caldera-forming eruptions in rapid succession in the San Juan caldera cluster, Colorado, USA</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Curry, A. C.; Caricchi, L.; Lipman, P. W.</p> <p>2017-12-01</p> <p>A primary goal of volcanology is to understand the frequency and magnitude of large, explosive volcanic eruptions to mitigate their impact on society. Recent studies show that the average magma flux and the time between magma injections into a given magmatic-volcanic system fundamentally control the frequency and magnitude of volcanic eruptions, yet these parameters are unknown for many volcanic regions on Earth. We focus on major and trace element chemistry of individual phases and whole-rock samples, initial zircon ID-TIMS analyses, and zircon SIMS oxygen isotope analyses of four caldera-forming ignimbrites from the San Juan caldera cluster in the Southern Rocky Mountain volcanic field, Colorado, to determine the physical and chemical processes leading to large eruptions. We collected outflow samples along stratigraphy of the three caldera-forming ignimbrites of the San Luis caldera complex: the Rat Creek Tuff ( 150 km3), Cebolla Creek Tuff ( 250 km3), and Nelson Mountain Tuff (>500 km3); and we collected samples of both outflow and intracaldera facies of the Snowshoe Mountain Tuff (>500 km3), which formed the Creede caldera. Single-crystal sanidine 40Ar/39Ar ages show that these large eruptions occurred in rapid succession between 26.91 ± 0.02 Ma (Rat Creek Tuff) and 26.87 ± 0.02 Ma (Snowshoe Mountain Tuff), providing an opportunity to investigate the temporal evolution of magmatic systems feeding large, explosive volcanic eruptions. Major and trace element analyses show that the first and last eruption of the San Luis caldera complex (Rat Creek Tuff and Nelson Mountain Tuff) are rhyolitic to dacitic ignimbrites, whereas the Cebolla Creek Tuff and Snowshoe Mountain Tuff are crystal-rich, dacitic ignimbrites. Trace elements show enrichment in light rare-earth elements (LREEs) over heavy rare-earth elements (HREEs), and whereas the trace element patterns are similar for each caldera cycle, trace element values for each ignimbrite show variability in HREE concentrations. This variability indicates that these large eruptions sampled a magmatic system with some degree of internal heterogeneity. These results have implications for the chemical and physical processes, such as magmatic flux and injection periodicity, leading to the formation of large magmatic systems prior to large, explosive eruptions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70017603','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70017603"><span>Anatexis, hybridization and the modification of ancient crust: Mesozoic plutonism in the Old Woman Mountains area, California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Miller, C.F.; Wooden, J.L.</p> <p>1994-01-01</p> <p>A compositionally expanded array of granitic (s.l.) magmas intruded the > 2 Ga crust of the Old Woman Mountains area between 160 and 70 Ma. These magmas were emplaced near the eastern (inland) edge of the Jurassic/Cretaceous arcs of western North America, in an area where magma flux, especially during the Jurassic, was considerably lower than to the west. The Jurassic intrusives and over half of the Cretaceous intrusives are predominantly metaluminous and variable in composition; a major Cretaceous suite comprises only peraluminous monzogranite. Only the Jurassic intrusions show clear evidence for the presence of mafic liquids. All units, including the most mafic rocks, reveal isotopic evidence for a significant crustal component. However, none of the Mesozoic intrusives matches in isotopic composition either average pre-intrusion crust or any major unit of the exposed crust. Elemental inconsistencies also preclude closed system derivation from exposed crust. Emplacement of these magmas, which doubled the volume of the mid- to upper crust, did not dramatically change its elemental composition. It did, however, affect its Nd and especially Sr isotopic composition and modify some of the distinctive aspects of the elemental chemistry. We propose that Jurassic magmatism was open-system, with a major influx of mantle-derived mafic magma interacting strongly with the ancient crust. Mesozoic crustal thickening may have led to closed-system crustal melting by the Late Cretaceous, but the deep crust had been profoundly modified by earlier Mesozoic hybridization so that crustal melts did not simply reflect the original crustal composition. The clear evidence for a crustal component in magmas of the Old Woman Mountains area may not indicate any fundamental differences from the processes at work elsewhere in this or other magmatic arcs where the role of pre-existing crust is less certain. Rather, a compositionally distinctive, very old crust may simply have yielded a more readily identifiable crustal fingerprint. The same processes that were involved here-mafic magma influx, hybridization, and remelting of hybridized crust-are likely to be typical of arc settings. ?? 1994.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780063755&hterms=onion&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Donion','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780063755&hterms=onion&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Donion"><span>Rare-earth abundances in chondritic meteorites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Evensen, N. M.; Hamilton, P. J.; Onions, R. K.</p> <p>1978-01-01</p> <p>Fifteen chondrites, including eight carbonaceous chondrites, were analyzed for rare earth element abundances by isotope dilution. Examination of REE for a large number of individual chondrites shows that only a small proportion of the analyses have flat unfractionated REE patterns within experimental error. While some of the remaining analyses are consistent with magmatic fractionation, many patterns, in particular those with positive Ce anomalies, can not be explained by known magmatic processes. Elemental abundance anomalies are found in all major chondrite classes. The persistence of anomalies in chondritic materials relatively removed from direct condensational processes implies that anomalous components are resistant to equilibrium or were introduced at a late stage of chondrite formation. Large-scale segregation of gas and condensate is implied, and bulk variations in REE abundances between planetary bodies is possible.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008JVGR..175..289J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008JVGR..175..289J"><span>Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>John, David A.; Sisson, Thomas W.; Breit, George N.; Rye, Robert O.; Vallance, James W.</p> <p>2008-08-01</p> <p>Hydrothermal alteration at Mount Rainier waxed and waned over the 500,000-year episodic growth of the edifice. Hydrothermal minerals and their stable-isotope compositions in samples collected from outcrop and as clasts from Holocene debris-flow deposits identify three distinct hypogene argillic/advanced argillic hydrothermal environments: magmatic-hydrothermal, steam-heated, and magmatic steam (fumarolic), with minor superimposed supergene alteration. The 3.8 km 3 Osceola Mudflow (5600 y BP) and coeval phreatomagmatic F tephra contain the highest temperature and most deeply formed hydrothermal minerals. Relatively deeply formed magmatic-hydrothermal alteration minerals and associations in clasts include quartz (residual silica), quartz-alunite, quartz-topaz, quartz-pyrophyllite, quartz-dickite/kaolinite, and quartz-illite (all with pyrite). Clasts of smectite-pyrite and steam-heated opal-alunite-kaolinite are also common in the Osceola Mudflow. In contrast, the Paradise lahar, formed by collapse of the summit or near-summit of the edifice at about the same time, contains only smectite-pyrite and near-surface steam-heated and fumarolic alteration minerals. Younger debris-flow deposits on the west side of the volcano (Round Pass and distal Electron Mudflows) contain only low-temperature smectite-pyrite assemblages, whereas the proximal Electron Mudflow and a < 100 y BP rock avalanche on Tahoma Glacier also contain magmatic-hydrothermal alteration minerals that are exposed in the avalanche headwall of Sunset Amphitheater, reflecting progressive incision into deeper near-conduit alteration products that formed at higher temperatures. The pre-Osceola Mudflow alteration geometry is inferred to have consisted of a narrow feeder zone of intense magmatic-hydrothermal alteration limited to near the conduit of the volcano, which graded outward to more widely distributed, but weak, smectite-pyrite alteration within 1 km of the edifice axis, developed chiefly in porous breccias. The edifice was capped by a steam-heated alteration zone, most of which resulted from condensation of fumarolic vapor and oxidation of H 2S in the unsaturated zone above the water table. Weakly developed smectite-pyrite alteration extended into the west and east flanks of the edifice, spatially associated with dikes that are localized in those sectors; other edifice flanks lack dikes and associated alteration. The Osceola collapse removed most of the altered core and upper east flank of the volcano, but intensely altered rocks remain on the uppermost west flank. Major conclusions of this study are that: (1) Hydrothermal-mineral assemblages and distributions at Mount Rainier can be understood in the framework of hydrothermal processes and environments developed from studies of ore deposits formed in analogous settings. (2) Frequent eruptions supplied sufficient hot magmatic fluid to alter the upper interior of the volcano hydrothermally, despite the consistently deep (≥ 8 km) magma reservoir which may have precluded formation of economic mineral deposits within or at shallow depths beneath Mount Rainier. The absence of indicator equilibrium alteration-mineral assemblages in the debris flows that effectively expose the volcano to a depth of 1-1.5 km also suggests a low potential for significant high-sulfidation epithermal or porphyry-type mineral deposits at depth. (3) Despite the long and complex history of the volcano, intensely altered collapse-prone rocks were spatially restricted to near the volcano's conduit system and summit, and short distances onto the upper east and west flanks, due to the necessary supply of reactive components carried by ascending magmatic fluids. (4) Intensely altered rocks were removed from the summit, east flank, and edifice interior by the Osceola collapse, but remain on the upper west flank in the Sunset Amphitheater area and present a continuing collapse hazard. (5) Visually conspicuous rocks on the lower east and mid-to-lower west flanks are not intensely altered and probably have not significantly weakened the rock, and thus do not present significant collapse hazards. (6) Alteration developed most intensely within breccia units, because of their high permeability and porosity. Volcanoes with abundant near-conduit upper-edifice breccias are prone to alteration increasing the possibility of collapse, whereas those that are breccia-poor (e.g., massive domes) are less prone to alteration.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19910039652&hterms=rare+earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Drare%2Bearth','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19910039652&hterms=rare+earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Drare%2Bearth"><span>Rare earth elements in Angra dos Reis and Lewis Cliff 86010, two meteorites with similar but distinct magma evolutions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Crozaz, Ghislaine; Mckay, Gordon</p> <p>1990-01-01</p> <p>Data are presented on ion microprobe measurements of REE and selected trace element abundances in individual grains of merrillite, fassaite, olivine, kirschsteinite, and plagioclase of Lewis Cliff 86010 (LEW 86010) meteorite and in merrillite and fassaite grains of Angra dos Reis (ADOR). Results show a close relationship between the two meteorites and support a magmatic origin for LEW 86010. However, the measurements indicate that, despite numerous common characteristics, the two meteorites must have been produced in separate magmatic events involving similar but distinct processes and parent melts.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/14684818','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/14684818"><span>Melt inclusions in veins: linking magmas and porphyry Cu deposits.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Harris, Anthony C; Kamenetsky, Vadim S; White, Noel C; van Achterbergh, Esmé; Ryan, Chris G</p> <p>2003-12-19</p> <p>At a porphyry copper-gold deposit in Bajo de la Alumbrera, Argentina, silicate-melt inclusions coexist with hypersaline liquid- and vapor-rich inclusions in the earliest magmatic-hydrothermal quartz veins. Copper concentrations of the hypersaline liquid and vapor inclusions reached maxima of 10.0 weight % (wt %) and 4.5 wt %, respectively. These unusually copper-rich inclusions are considered to be the most primitive ore fluid found thus far. Their preservation with coexisting melt allows for the direct quantification of important oreforming processes, including determination of bulk partition coefficients of metals from magma into ore-forming magmatic volatile phases.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70186663','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70186663"><span>The role of magmas in the formation of hydrothermal ore deposits</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hedenquist, Jeffrey W.; Lowenstern, Jacob B.</p> <p>1994-01-01</p> <p>Magmatic fluids, both vapour and hypersaline liquid, are a primary source of many components in hydrothermal ore deposits formed in volcanic arcs. These components, including metals and their ligands, become concentrated in magmas in various ways from various sources, including subducted oceanic crust. Leaching of rocks also contributes components to the hydrothermal fluid—a process enhanced where acid magmatic vapours are absorbed by deeply circulating meteoric waters. Advances in understanding the hydrothermal systems that formed these ore deposits have come from the study of their active equivalents, represented at the surface by hot springs and volcanic fumaroles.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018GeCoA.226..192S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018GeCoA.226..192S"><span>Mg isotope systematics during magmatic processes: Inter-mineral fractionation in mafic to ultramafic Hawaiian xenoliths</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stracke, A.; Tipper, E. T.; Klemme, S.; Bizimis, M.</p> <p>2018-04-01</p> <p>Observed differences in Mg isotope ratios between bulk magmatic rocks are small, often on a sub per mill level. Inter-mineral differences in the 26Mg/24Mg ratio (expressed as δ26Mg) in plutonic rocks are on a similar scale, and have mostly been attributed to equilibrium isotope fractionation at magmatic temperatures. Here we report Mg isotope data on minerals in spinel peridotite and garnet pyroxenite xenoliths from the rejuvenated stage of volcanism on Oahu and Kauai, Hawaii. The new data are compared to literature data and to theoretical predictions to investigate the processes responsible for inter-mineral Mg isotope fractionation at magmatic temperatures. Theory predicts up to per mill level differences in δ26Mg between olivine and spinel at magmatic temperatures and a general decrease in Δ26Mgolivine-spinel (=δ26Mgolivine - δ26Mgspinel) with increasing temperature, but also with increasing Cr# in spinel. For peridotites with a simple petrogenetic history by melt depletion, where increasing depletion relates to increasing melting temperatures, Δ26Mgolivine-spinel should thus systematically decrease with increasing Cr# in spinel. However, most natural peridotites, including the Hawaiian spinel peridotites investigated in this study, are overprinted by variable extents of melt-rock reaction, which disturb the systematic primary temperature and compositionally related olivine-spinel Mg isotope systematics. Diffusion, subsolidus re-equilibration, or surface alteration may further affect the observed olivine-spinel Mg isotope fractionation in peridotites, making Δ26Mgolivine-spinel in peridotites a difficult-to-apply geothermometer. The available Mg isotope data on clinopyroxene and garnet suggest that this mineral pair is a more promising geothermometer, but its application is restricted to garnet-bearing igneous (garnet pyroxenites) and metamorphic rocks (eclogites). Although the observed δ26Mg variation is on a sub per mill range in bulk magmatic rocks, the clearly resolvable inter-mineral Mg isotope differences imply that crystallization or preferential melting of isotopically distinct minerals such garnet, spinel, and clinopyroxene should cause Mg isotope fractionation between bulk melt and residue. Calculated Mg isotope variations during partial mantle melting indeed predict differences between melt and residue, but these are analytically resolvable only for melting of mafic lithologies, that is, garnet pyroxenites. Contributions from garnet pyroxenite melts may thus account for some of the isotopically light δ26Mg observed in ocean island basalts and trace lithological mantle heterogeneity. Consequently, applications for high-temperature Mg isotope fractionations are promising and diverse, and recent advances in analytical precision may allow the full petrogenetic potential inherent in the sub per mill variations in δ26Mg in magmatic rocks to be exploited.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAfES.127....3I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAfES.127....3I"><span>A historical overview of Moroccan magmatic events along northwest edge of the West African Craton</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ikenne, Moha; Souhassou, Mustapha; Arai, Shoji; Soulaimani, Abderrahmane</p> <p>2017-03-01</p> <p>Located along the northwestern edge of the West African Craton, Morocco exhibits a wide variety of magmatic events from Archean to Quaternary. The oldest magmatic rocks belong to the Archean Reguibat Shield outcrops in the Moroccan Sahara. Paleoproterozoic magmatism, known as the Anti-Atlas granitoids, is related to the Eburnean orogeny and initial cratonization of the WAC. Mesoproterozoic magmatism is represented by a small number of mafic dykes known henceforth as the Taghdout mafic volcanism. Massive Neoproterozoic magmatic activity, related to the Pan-African cycle, consists of rift-related Tonian magmatism associated with the Rodinia breakup, an Early Cryogenian convergent margin event (760-700 Ma), syn-collisional Bou-Azzer magmatism (680-640 Ma), followed by widespread Ediacaran magmatism (620-555 Ma). Each magmatic episode corresponded to a different geodynamic environment and produced different types of magma. Phanerozoic magmatism began with Early Cambrian basaltic (rift?) volcanism, which persisted during the Middle Cambrian, and into the Early Ordovician. This was succeeded by massive Late Devonian and Carboniferous, pre-Variscan tholeiitic and calc-alkaline (Central Morocco) volcanic flows in basins of the Moroccan Meseta. North of the Atlas Paleozoic Transform Zone, the Late Carboniferous Variscan event was accompanied by the emplacement of 330-300 Ma calc-alkaline granitoids in upper crustal shear zones. Post-Variscan alkaline magmatism was associated with the opening of the Permian basins. Mesozoic magmatism began with the huge volumes of magma emplaced around 200 Ma in the Central Atlantic Magmatic Province (CAMP) which was associated with the fragmentation of Pangea and the subsequent rifting of Central Atlantic. CAMP volcanism occurs in all structural domains of Morocco, from the Anti-Atlas to the External Rif domain with a peak activity around 199 Ma. A second Mesozoic magmatic event is represented by mafic lava flows and gabbroic intrusions in the Internal Maghrebian flysch nappes as well as in the external Mesorif. This event consists of Middle-Upper Jurassic MORB tholeiites emplaced during opening of the Alpine Tethys ocean. The Central High Atlas also records Early Cretaceous alpine Tethys magmatism associated with the aborted Atlas rift, or perhaps linked to plume activity on the edge of the WAC. Cenozoic magmatism is associated with Tertiary and Quaternary circum-Mediterranean alkaline provinces, and is characterized by an intermittent activity over 50 Ma from the Anti-Atlas to the Rif Mountain along a SW-NE volcanic lineament which underlines a thinned continental lithosphere.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.7193T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.7193T"><span>Some aspects of the role of rift inheritance on Alpine-type orogens</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tugend, Julie; Manatschal, Gianreto; Mohn, Geoffroy; Chevrot, Sébastien</p> <p>2017-04-01</p> <p>Processes commonly recognized as fundamental for the formation of collisional orogens include oceanic subduction, arc-continent and continent-continent collision. As collisional belts result from the closure of oceanic basins and subsequent inversion of former rifted margins, their formation and evolution may also in theory be closely interlinked with the initial architecture of the former rifted margins. This assumption is indeed more likely to be applicable in the case of Alpine-type orogens, mainly controlled by mechanical processes and mostly devoid of arc-related magmatism. More and more studies from present-day magma-poor rifted margins illustrate the complex evolution of hyperextended domains (i.e. severely thinned continental crust (<10 km) and/or exhumed serpentinized mantle with relatively minor magmatic additions) between unequivocal continental and oceanic domains. In this contribution, we compare the deep structure of the Pyrenean and Alpine belts to discuss some aspects of the relative role of rift-inherited hyperextension and collisional processes in building Alpine-type orogens. The Pyrenees and Western to Central Alps respectively result from the inversion of a Late Jurassic to Mid Cretaceous and an Early to Middle Jurassic rift system eventually floored by hyperextended crust, exhumed mantle and/or proto-oceanic crust. In spite of uncertainties on the initial width of the hyperextended and proto-oceanic domains, the rift-related pre-collisional architecture of the Alps shows many similarities with that proposed for the Pyrenees. Remnants of these domains occur in the internal parts of both orogens, but they are largely affected by orogeny-related deformation and show a HP-LT to HT-MP metamorphic overprint in the Alps as a result of a polyphase deformation history. Yet, recent high-resolution tomographic images across the Pyrenees (PYROPE) and the Alps (CIFALPS) reveal a surprisingly comparable present-day overall crustal and lithospheric structure. Based on the comparison between the two orogens we discuss: (1) the nature and depth of decoupling levels inherited from hyperextension; (2) the implications for restorations and interpretations of orogenic roots (former hyperextended domains vs. lower crust only); and (3) the nature and major role of buttresses in controlling the final stage of collisional processes. Eventually, we discuss the variability of the role of rift-inheritance in building Alpine-type orogens. The Pyrenees seem to represent one extreme, where rift-inheritance is important at different stages of collisional processes. In contrast, in the Alps the role of rift-inheritance is subtler, likely because of its more complex and polyphase compressional deformation history.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGeo..110...12M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGeo..110...12M"><span>Syn-convergence extension in the southern Lhasa terrane: Evidence from late Cretaceous adakitic granodiorite and coeval gabbroic-dioritic dykes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ma, Xuxuan; Xu, Zhiqin; Meert, Joseph G.</p> <p>2017-10-01</p> <p>Late Cretaceous (∼100-80 Ma) magmatism in the Gangdese magmatic belt plays a pivotal role in understanding the evolutionary history and tectonic regime of the southern Lhasa terrane. The geodynamic process for the formation of the early Late Cretaceous magmatism has long been an issue of hot debates. Here, petrology, geochronology and geochemistry of early Late Cretaceous granodiorite and coeval gabbroic-dioritic dykes in the Caina region, southern Lhasa, were investigated in an effort to ascertain their petrogenesis, age of intrusion, magma mixing and tectonic setting. Zircon U-Pb dating of granodiorite yields 206Pb/238U ages of 85.8 ± 1.7 and 86.4 ± 1.1 Ma, whilst that of the E-W trending dykes yields ages of 82.7 ± 2.6 and 83.5 ± 3.5 Ma. Within error, the crystallization ages of the dykes and the granodiorite are indistinguishable. Field observations and mineralogical microstructures are suggestive of a magma mixing process during the formation of the dykes and the granodiorite. The granodiorite exhibits geochemical features that are in agreement with those of subduction-related high-SiO2 adakites. The granodiorite and dykes have relatively constant εNd(t) values of +2.2 to +4.9 and initial 87Sr/86Sr ratios (0.7045-0.7047). These similar characteristics are herein interpreted as an evolutionary series from the dykes to granodiorite, consistent with magma mixing process. Ti-in-zircon thermometer and Al-in-hornblende barometer indicate that the granodiorite and the dioritic dyke crystallized at temperatures of ca. 750 and 800 °C, depths of ca. 6-10 and 5-9 km, respectively. Taking into account the synchronous magmatic rocks in the Gangdese Belt and the coeval rifted basin within the Lhasa terrane, the granodiorite and dykes reveal an early Late Cretaceous syn-convergence extensional regime in the southern Lhasa terrane, triggered by slab rollback of the Neotethyan oceanic lithosphere.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Geote..52..194P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Geote..52..194P"><span>Similarity and Differences of Cretaceous Magmatism in the Arctic Region</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peyve, A. A.</p> <p>2018-03-01</p> <p>The paper considers Cretaceous magmatism at the continental margin of the Arctic Region. It is shown that Cretaceous igneous rocks of this region are rather heterogeneous in age, composition, and geodynamic formation setting. This differentiates them from rocks of typical large igneous provinces (LIPs). Local areas of magmatic activity, their substantial remoteness them from one another, and significant distinctions in age, composition of rocks, and formation conditions prevent us from unreservedly combining all occurrences of Cretaceous magmatism at the continental margin of the Arctic Region into a common igneous province. The stage of tholeiitic magmatism in the Svalbard Archipelago, Franz Josef Land, Arctic Canada, and the Alpha-Mendeleev Rise, which can be considered an LIP, began in the Early Cretaceous and continued for a long time, at least until the Campanian. The magmatism apparently had a plume source and was caused by extension during opening of the Canada Basin. Tholeiitic magmatism gave way to the alkaline magmatism stage from the Campanian to the onset of the Paleocene, related to continental rifting at the initial stage of formation of Eurasian Basin in the Arctic Region. No convincing evidence for a genetic link between Early Cretaceous tholeiitic and Late Cretaceous alkaline magmatism is known at present, nor for the alkaline magmatism belonging to a plume source.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18.3646S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18.3646S"><span>Hydrothermal Venting at Hinepuia Submarine Volcano, Kermadec Arc: Understanding Magmatic-Hydrothermal Fluid Chemistry</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stucker, Valerie K.; Walker, Sharon L.; de Ronde, Cornel E. J.; Caratori Tontini, Fabio; Tsuchida, Shinji</p> <p>2017-10-01</p> <p>The Hinepuia volcanic center is made up of two distinct edifices aligned northwest to southeast, with an active cone complex in the SE. Hinepuia is one of several active volcanoes in the northern segment of the Kermadec arc. Regional magnetic data show no evidence for large-scale hydrothermal alteration at Hinepuia, yet plume data confirm present-day hydrothermal discharge, suggesting that the hydrothermal system may be too young to have altered the host rocks with respect to measurable changes in magnetic signal. Gravity data are consistent with crustal thinning and shallow mantle under the volcanic center. Following the discovery of hydrothermal plumes over Hinepuia, the submersible Shinkai 6500 was used to explore the SE cone and sample hydrothermal fluids. The chemistry of hydrothermal fluids from submarine arc and backarc volcanoes is typically dominated by water-rock interactions and/or magmatic degassing. Chemical analyses of vent fluids show that Hinepuia does not quite fit either traditional model. Moreover, the Hinepuia samples fall between those typically ascribed to both end-member fluid types when plotted on a K-Mg-SO4 ternary diagram. Due to evidence of strong degassing, abundant native sulfur deposition, and H2S presence, the vent sampled at Hinepuia is ultimately classified as a magmatic-hydrothermal system with a water-rock influence. This vent is releasing water vapor and magmatic volatiles with a notable lack of salinity due to subcritical boiling and phase separation. Magmatic-hydrothermal fluid chemistry appears to be controlled by a combination of gas flux, phase separation processes, and volcano evolution and/or distance from the magma source.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Tecto..36.3298E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Tecto..36.3298E"><span>Crustal Structure of Active Deformation Zones in Africa: Implications for Global Crustal Processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinger, C. J.; Keir, D.; Bastow, I. D.; Whaler, K.; Hammond, J. O. S.; Ayele, A.; Miller, M. S.; Tiberi, C.; Hautot, S.</p> <p>2017-12-01</p> <p>The Cenozoic East African rift (EAR), Cameroon Volcanic Line (CVL), and Atlas Mountains formed on the slow-moving African continent, which last experienced orogeny during the Pan-African. We synthesize primarily geophysical data to evaluate the role of magmatism in shaping Africa's crust. In young magmatic rift zones, melt and volatiles migrate from the asthenosphere to gas-rich magma reservoirs at the Moho, altering crustal composition and reducing strength. Within the southernmost Eastern rift, the crust comprises 20% new magmatic material ponded in the lower crust and intruded as sills and dikes at shallower depths. In the Main Ethiopian Rift, intrusions comprise 30% of the crust below axial zones of dike-dominated extension. In the incipient rupture zones of the Afar rift, magma intrusions fed from crustal magma chambers beneath segment centers create new columns of mafic crust, as along slow-spreading ridges. Our comparisons suggest that transitional crust, including seaward dipping sequences, is created as progressively smaller screens of continental crust are heated and weakened by magma intrusion into 15-20 km thick crust. In the 30 Ma Recent CVL, which lacks a hot spot age progression, extensional forces are small, inhibiting the creation and rise of magma into the crust. In the Atlas orogen, localized magmatism follows the strike of the Atlas Mountains from the Canary Islands hot spot toward the Alboran Sea. CVL and Atlas magmatism has had minimal impact on crustal structure. Our syntheses show that magma and volatiles are migrating from the asthenosphere through the plates, modifying rheology, and contributing significantly to global carbon and water fluxes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JGeo..113...13F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGeo..113...13F"><span>Late Eocene volcanism in North Patagonia (42°30‧-43°S): Arc resumption after a stage of within-plate magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fernández Paz, Lucía; Litvak, Vanesa D.; Echaurren, Andrés; Iannelli, Sofía B.; Encinas, Alfonso; Folguera, Andrés; Valencia, Víctor</p> <p>2018-01-01</p> <p>Mid-Cenozoic widespread arc magmatism in North Patagonia extends from the forearc to the retroarc zones, representing an anomalous large volume when compared to the present-day arc zone and even other past arc configurations. It represents a crucial stage in Andean arc evolution as was developed after a period of arc waning and within plate magmatism. Controversies exist regarding the origin of these volcanic sequences, with scarce integrated field, geochemical and geochronological analyses. We focused our study on the El Maitén Belt, located in the present-day retroarc zone, particularly on a poorly studied section corresponding to the southern outcrops of this volcanic belt. This volcanism consists of basaltic and andesitic lava flows and interbedded pyroclastic deposits, whose emplacement was controlled by extensional tectonics as indicated by the occurrence of wedge-like strata associated with normal faults. A U-Pb age on the basal part of this section shows that magmatic activity started by 37 Ma, earlier than previous studies that considered this volcanism as Oligocene. Geochemically, these rocks are part of the subalkaline and particularly tholeiitic series. All samples show trace element enrichments, depletions and ratios characteristic of arc magmas, though fluids and sediment imprint seem limited. On these bases, we propose decompression melting as the main process associated with the genesis of this volcanism. Therefore, this magmatic association constrained to the late Eocene represents the earliest evidence of arc volcanism in the Patagonian Andes, under an extensional regime, after a Paleogene waning of arc activity.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PApGe.172.1835E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PApGe.172.1835E"><span>Cooling of a Magmatic System Under Thermal Chaotic Mixing</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>El Omari, Kamal; Le Guer, Yves; Perugini, Diego; Petrelli, Maurizio</p> <p>2015-07-01</p> <p>The cooling of a basaltic melt undergoing chaotic advection is studied numerically for a magma with a temperature-dependent viscosity in a two-dimensional (2D) cavity with moving boundary. Different statistical mixing and energy indicators are used to characterize the efficiency of cooling by thermal chaotic mixing. We show that different cooling rates can be obtained during the thermal mixing of a single basaltic magmatic batch undergoing chaotic advection. This process can induce complex temperature patterns inside the magma chamber. The emergence of chaotic dynamics strongly modulates the temperature fields over time and greatly increases the cooling rates. This mechanism has implications for the thermal lifetime of the magmatic body and may favor the appearance of chemical heterogeneities in the igneous system as a result of different crystallization rates. Results from this study also highlight that even a single magma batch can develop, under chaotic thermal advection, complex thermal and therefore compositional patterns resulting from different cooling rates, which can account for some natural features that, to date, have received unsatisfactory explanations, including the production of magmatic enclaves showing completely different cooling histories compared with the host magma, compositional zoning in mineral phases, and the generation of large-scale compositional zoning observed in many plutons worldwide.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011NatGe...4...50L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011NatGe...4...50L"><span>Carbon release by off-axis magmatism in a young sedimented spreading centre</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lizarralde, Daniel; Soule, S. Adam; Seewald, Jeff S.; Proskurowski, Giora</p> <p>2011-01-01</p> <p>Continental rifting creates narrow ocean basins, where coastal ocean upwelling results in high biological productivity and organic-rich sedimentation. In addition, topographic gradients promote silicate weathering, which consumes atmospheric CO2 (ref. 1). The carbon flux associated with these processes has led to the suggestion that rifting may cool the atmosphere, leading in some cases to glaciation and even a snowball Earth scenario. Guaymas basin, within the Gulf of California, is a young spreading system where new igneous crust is formed beneath a layer of organic-rich sediment that is 1-2kmthick. Here we present seismic data from Guaymas basin that image recent, basin-wide magmatic intrusions into sediments; sonar backscatter and seafloor photographs that indicate numerous, broadly distributed chemosynthetic seafloor biological communities, and geochemical analyses of water samples suggesting that the methane that supports these communities is derived from magma-driven thermogenic alteration of sediments. Our results suggest that active shallow magmatism releases carbon from sediments up to 50km away from the plate boundary. This is a much larger area than the less than 5km found at unsedimented mid-ocean ridges, and than previously recognized. We conclude that thick sediments may promote broad magmatism, reducing the efficiency of natural carbon sequestration within young sedimented rifts.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.2090A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.2090A"><span>Granitoids of different geodynamic settings of Baikal region (Russia) their geochemical evolution and origin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Antipin, Viktor; Sheptyakova, Natalia</p> <p>2016-04-01</p> <p>In the southern folded framing of the Siberian craton the granitoid magmatism of different ages involves batholiths, small low-depth intrusions and intrusion-dyke belts with diverse mineral and geochemical characteristics of rocks. Granitoid formation could be related to the Early Paleozoic collision stage and intra-plate magmatism of the Late Paleozoic age of the geologic development of Baikal area. The Early Paleozoic granitoids of Khamar-Daban Ridge and Olkhon region revealed their closeness in age and composition. They were referred to syncollision S-type formations derived from gneiss-schistose substratum of metamorphic sequences. The magmatic rocks were classified into various geochemical types comprising formations of normal Na-alkalinity (migmatites and plagiogranites), calc-alkaline and subalkaline (K-Na granitoids, granosyenites and quartz syenites) series. It is significant, that plagiomigmatites and plagiogranites in all elements repeat the shape of the chart of normalized contents marked for trend of K-Na granitoids, but at considerably lower level of concentrations of all elements. This general pattern of element distribution might indicate similar anatectic origin of both granitoid types, but from crustal substrata distinguished by composition and geochemical features. Comparative geochemical analysis pointed out that the source of melts of the Early Paleozoic granitoids of the Olkhon (505-477 Ma) and Khamar-Daban (516-490 Ma) complexes of the Baikal region could be the crustal substratum, which is obviously the criterion for their formation in the collisional geodynamic setting. Using the Late Paleozoic subalkaline magmatism proceeding at the Khamar-Daban Range (Khonzurtay pluton, 331 Ma) as an example, it was found that the formation of monzodiorite-syenite-leucogranite series was considerably contributed by the processes of hybridism and assimilation through mixing of the upper mantle basaltoid magma derived melts of granitic composition. The involvement of the deep source is indicated by low Rb/Sr ratios and 87Sr/86Sr ratio (0.70592±0.00021) in rocks (Kazimirovskiy, 2006). The intra-plate biotite granites and leucogranites are represented by rare-metal geochemical type of rocks (311-321 Ma). Geochemical evolution promoted an increase of F, Li, Rb, Cs, Sn, Be, Ta, and Pb and a decrease of Ba, Sr, Zn, Zr, Th, and U contents in rare-metal granites, that reflects their formation from deeply differentiated residual magma. The substance of the lower crust could have the composition of biotite-bearing granulites rich in lithophyle rare elements. It is noteworthy, that the composition and isotope-geochemical features of the supposed magma-forming substratum correspond to the characteristics of the ancient Precambrian continental crust of the Southern Baikal region. These conclusions agree with the results of preceding studies of rare-metal granites in the other regions of Central Asia (Kovalenko et al, 1999). Research has been supported by RNF grant № 15-17-10010.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26PSL.482..213S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26PSL.482..213S"><span>Methane clumped isotopes in the Songliao Basin (China): New insights into abiotic vs. biotic hydrocarbon formation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shuai, Yanhua; Etiope, Giuseppe; Zhang, Shuichang; Douglas, Peter M. J.; Huang, Ling; Eiler, John M.</p> <p>2018-01-01</p> <p>Abiotic hydrocarbon gas, typically generated in serpentinized ultramafic rocks and crystalline shields, has important implications for the deep biosphere, petroleum systems, the carbon cycle and astrobiology. Distinguishing abiotic gas (produced by chemical reactions like Sabatier synthesis) from biotic gas (produced from degradation of organic matter or microbial activity) is sometimes challenging because their isotopic and molecular composition may overlap. Abiotic gas has been recognized in numerous locations on the Earth, although there are no confirmed instances where it is the dominant source of commercially valuable quantities in reservoir rocks. The deep hydrocarbon reservoirs of the Xujiaweizi Depression in the Songliao Basin (China) have been considered to host significant amounts of abiotic methane. Here we report methane clumped-isotope values (Δ18) and the isotopic composition of C1-C3 alkanes, CO2 and helium of five gas samples collected from those Xujiaweizi deep reservoirs. Some geochemical features of these samples resemble previously suggested identifiers of abiotic gas (13C-enriched CH4; decrease in 13C/12C ratio with increasing carbon number for the C1-C4 alkanes; abundant, apparently non-biogenic CO2; and mantle-derived helium). However, combining these constraints with new measurements of the clumped-isotope composition of methane and careful consideration of the geological context, suggests that the Xujiaweizi depression gas is dominantly, if not exclusively, thermogenic and derived from over-mature source rocks, i.e., from catagenesis of buried organic matter at high temperatures. Methane formation temperatures suggested by clumped-isotopes (167-213 °C) are lower than magmatic gas generation processes and consistent with the maturity of local source rocks. Also, there are no geological conditions (e.g., serpentinized ultramafic rocks) that may lead to high production of H2 and thus abiotic production of CH4 via CO2 reduction. We propose that the Songliao gas is representative of an atypical type of thermogenic gas that can be mistaken for abiotic gas. Such gases may be encountered more frequently in future exploration of deep or over-mature petroleum systems.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMNH23A0232U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMNH23A0232U"><span>The complex emplacement dynamics and tsunami genesis of the 1888 Ritter Island sector collapse from 3D seismic data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Urlaub, M.; Karstens, J.; Berndt, C.; Watt, S. F.; Micallef, A.; Klaucke, I.; Klaeschen, D.; Brune, S.; Kühn, M.</p> <p>2017-12-01</p> <p>On March 13 1888, a large sector of the subaerial and submarine edifice of Ritter Island (Papua New Guinea) collapsed and slid into the Bismarck Sea, triggering a tsunami with run-up heights of more than 25 m on the neighboring islands. The tsunami traveled for more than 600 km and caused destruction in several settlements. German colonists described in detail the timing of the arriving waves. During research cruise SO252 onboard RV Sonne, we collected a comprehensive set of multibeam and sediment echosounder data, seafloor video footage, rock samples, 2D seismic profiles, and a 60 km2 high-resolution Pcable 3D seismic cube. This dataset, combined with the historic eyewitness accounts, allows detailed reconstruction of the large-scale volcanic sector collapse and the associated tsunami genesis. The 3D seismic cube reveals a change of emplacement dynamics during the collapse of the volcanic edifice. The initial failure occurred along a deep slide plane extending from the volcanic cone up to 300 m deep into the seafloor sediments adjacent to the volcanic edifice. Movement of large, intact sediment blocks and shortening characterize this deep-rooted mass-movement. In contrast to the well-preserved mobilization structures in the deep part of the volcanic edifice related to the initial phase of mass movement, there are hardly any deposits of the upper part of the volcanic cone comprising of well-stratified volcaniclastic layers. The 2 km3 cone was mobilized in the final stage of the sector collapse and its highly energetic slide mass eroded deeply into the previously emplaced slide deposits. The fast moving mass was channelized between two volcanic ridges, transported into the basin west of Sakar Island, and then deposited more than 30 km away from its source. We interpret the separation into two phases as the result of decoupling of the sliding mass of the cone from the deeper volcanic edifice. This process may be explained by gravitational acceleration of the sliding mass or a phreatomagmatic explosion due to the contact of the magmatic conduit with seawater.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70016797','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70016797"><span>On the formation of granulites</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bohlen, S.R.</p> <p>1991-01-01</p> <p>The tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure-temperature-time (P-T-time) paths and constrained by petrological and geophysical considerations. P-T conditions deduced for regional granulites require transient, average geothermal gradients of greater than 35??C km-1, implying minimum heat flow in excess of 100 mW m-2. Such high heat flow is probably caused by magmatic heating. Tectonic settings wherein such conditions are found include convergent plate margins, continental rifts, hot spots and at the margins of large, deep-seated batholiths. Cooling paths can be constrained by solid-solid and devolatilization equilibria and geophysical modelling. -from Author</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4595843','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4595843"><span>Volcanic passive margins: another way to break up continents</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Geoffroy, L.; Burov, E. B.; Werner, P.</p> <p>2015-01-01</p> <p>Two major types of passive margins are recognized, i.e. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere. In contrast with non-volcanic margins, continentward-dipping detachment faults accommodate crustal necking at both conjugate volcanic margins. These faults root on a two-layer deformed ductile crust that appears to be partly of igneous nature. This lower crust is exhumed up to the bottom of the syn-extension extrusives at the outer parts of the margin. Our numerical modelling suggests that strengthening of deep continental crust during early magmatic stages provokes a divergent flow of the ductile lithosphere away from a central continental block, which becomes thinner with time due to the flow-induced mechanical erosion acting at its base. Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain. Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle. PMID:26442807</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26442807','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26442807"><span>Volcanic passive margins: another way to break up continents.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Geoffroy, L; Burov, E B; Werner, P</p> <p>2015-10-07</p> <p>Two major types of passive margins are recognized, i.e. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere. In contrast with non-volcanic margins, continentward-dipping detachment faults accommodate crustal necking at both conjugate volcanic margins. These faults root on a two-layer deformed ductile crust that appears to be partly of igneous nature. This lower crust is exhumed up to the bottom of the syn-extension extrusives at the outer parts of the margin. Our numerical modelling suggests that strengthening of deep continental crust during early magmatic stages provokes a divergent flow of the ductile lithosphere away from a central continental block, which becomes thinner with time due to the flow-induced mechanical erosion acting at its base. Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain. Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.V34B..05C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.V34B..05C"><span>The Role of Magmatic Volatile Input, Near-surface Seawater Entrainment and Sulfide Deposition in Regulating Metal Concentrations Within Manus Basin Hydrothermal Systems</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Craddock, P. R.; Tivey, M. K.; Seewald, J. S.; Rouxel, O.; Bach, W.</p> <p>2007-12-01</p> <p>Analyses of Fe, Mn, Cu, Zn, Pb, Ag, Cd, Co and Sb in vent fluid samples from four hydrothermal systems in the Manus back-arc basin, Papua New Guinea, were carried out by ICP-MS. Vienna Woods is located on the well- defined, basalt-dominated Manus Spreading Center, while the other systems are hosted in felsic volcanics on the Pual Ridge (PACMANUS), within a caldera (DESMOS), and on volcanic cones (SuSu Knolls). Metal concentrations were coupled with other fluid data (pH, SO4, Ca, H2S) to discriminate effects of deep- seated water-rock reaction and magmatic volatile input from near surface seawater entrainment, mixing, and consequent mineral precipitation and metal remobilization. Both magmatic volatile input (e.g. SO2, HCl, HF) and sulfide precipitation can increase fluid acidity and thus affect the aqueous mobility of metals. At Vienna Woods, 280°C end-member (Mg = 0) fluids have high pH (>4.2) and low metal contents (Fe <160 uM, Cu <10 uM, Zn <40 uM) relative to most mid-ocean ridge (MOR) vent fluids. The high pH and lack of evidence for magmatic volatile input are consistent with fluid compositions regulated by subsurface seawater- basalt/andesite reactions. Despite low aqueous Zn concentrations, Zn-rich (wurtzite-lined) chimneys are common at Vienna Woods active vents, reflecting deposition from fluids characterized by low Fe and Cu and high pH. At PACMANUS, black smoker fluids (T >300°C, pH ~ 2.7) are enriched in sulfide-forming metals by an order of magnitude relative to Vienna Woods fluids. Enrichments at PACMANUS reflect efficient leaching of metals at low pH, with the lower pH likely a result of input of magmatic volatiles. In addition, some vents fluids show clear evidence for seawater entrainment, subsurface precipitation of Cu-Fe-sulfides and preferential remobilization of Zn-sulfides (lower T, non-zero Mg, lower Fe, Cu, H2S and pH (2.3-2.4), but higher Zn, Pb, Cd and Ag, compared to black smokers). The higher metal concentrations and lower pH of fluids from PACMANUS versus Vienna Woods are reflected in chimney deposit compositions with Zn-poor sulfide linings composed of Cu-Fe-sulfides and As-Sb-sulfosalts in high T and lower T vents, respectively. At DESMOS caldera, fluid data suggest extensive magmatic volatile input (e.g. pH <1.5, elevated F and SO4) but lesser reaction with the basement felsic rocks (low Li, Rb, Mn). Sampled "acid-sulfate" fluids are low temperature (T ~180°C) with Mg >46 mM, and very high concentrations of some metals for these Mg concentrations (Fe >5 mM, Zn >50 - 400 uM). At SuSu Knolls, vent fluid compositions similar to those at both PACMANUS and DESMOS are observed. Smoker fluids have high but variable metal concentrations of similar magnitude to PACMANUS. Acid-sulfate fluids from North Su have low pH (<2), non-zero Mg (>40 mM), and high Fe and Zn concentrations, similar to DESMOS fluids. At SuSu Knolls, fluid compositions reflect either high temperature water-rock reaction (smoker fluids) or magmatic volatile input (acid-sulfate fluids). As at PACMANUS, chimney deposits that correspond to venting fluids are Cu-Fe-As-Sb-rich and Zn-poor, likely reflecting deposition from low pH, high Cu and Fe fluids.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMGP31A..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMGP31A..02S"><span>Controls on Magmatic and Hydrothermal Processes at Yellowstone Supervolcano: The Wideband Magnetotelluric Component of an Integrated MT/Seismic Investigation</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schultz, A.; Bennington, N. L.; Bowles-martinez, E.; Imamura, N.; Cronin, R. A.; Miller, D. J.; Hart, L.; Gurrola, R. M.; Neal, B. A.; Scholz, K.; Fry, B.; Carbonari, R.</p> <p>2017-12-01</p> <p>Previous seismic and magnetotelluric (MT) studies beneath Yellowstone (YS) have provided insight into the origin and migration of magmatic fluids within the volcanic system. However, important questions remain concerning the generation of magmatism at YS, the migration and storage of these magmatic fluids, as well as their relationships to hydrothermal expressions. Analysis of regional-scale EarthScope MT data collected previously suggests a relative absence of continuity in crustal partial melt accumulations directly beneath YS. This is in contrast to some seismic interpretations, although such long-period MT data have limited resolving power in the upper-to-mid crustal section. A wideband MT experiment was designed as a component of an integrated MT/seismic project to examine: the origin and location of magmatic fluids at upper mantle/lower crustal depths, the preferred path of migration for these magmatic fluids into the mid- to upper-crust, the resulting distribution of the magma reservoir, the composition of the magma reservoir, and implications for future volcanism at YS. A high-resolution wideband MT survey was carried out in the YS region in the summer of 2017, with more than forty-five wideband stations installed within and immediately surrounding the YS National Park boundary. These data provided nearly six decades of bandwidth ( 10-3 Hz -to- 103 Hz). Extraordinary permitting restrictions prevented us from using conventional installation methods at many of our sites, and an innovative "no-dig" subaerial method of wideband MT was developed and used successfully. Using these new data along with existing MT datasets, we are inverting for the 3D resistivity structure at upper crustal through upper mantle scales at YS. Complementary to this MT work, a joint inversion for the 3D crustal velocity structure is being carried out using both ambient noise and earthquake travel time data. Taken together, these data should better constrain the crustal velocity structure of this volcanic system and produce enhanced images of magma storage.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815633S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815633S"><span>A temporal record of pre-eruptive magmatic volatile contents at Campi Flegrei: Insights from texturally-constrained apatite analyses</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stock, Michael J.; Isaia, Roberto; Humphreys, Madeleine C. S.; Smith, Victoria C.; Pyle, David M.</p> <p>2016-04-01</p> <p>Apatite is capable of incorporating all major magmatic volatile species (H2O, CO2, S, Cl and F) into its crystal structure. Analysis of apatite volatile contents can be related to parental magma compositions through the application of pressure and temperature-dependent exchange reactions (Piccoli and Candela, 1994). Once included within phenocrysts, apatite inclusions are isolated from the melt and preserve a temporal record of magmatic volatile contents in the build-up to eruption. In this work, we measured the volatile compositions of apatite inclusions, apatite microphenocrysts and pyroxene-hosted melt inclusions from the Astroni 1 eruption of Campi Flegrei, Italy (Stock et al. 2016). These data are coupled with magmatic differentiation models (Gualda et al., 2012), experimental volatile solubility data (Webster et al., 2014) and thermodynamic models of apatite compositional variations (Piccoli and Candela, 1994) to decipher pre-eruptive magmatic processes. We find that apatite halogen/OH ratios decreased through magmatic differentiation, while melt inclusion F and Cl concentrations increased. Melt inclusion H2O contents are constant at ~2.5 wt%. These data are best explained by volatile-undersaturated differentiation over most of the crystallisation history of the Astroni 1 melt, with melt inclusion H2O contents reset at shallow levels during ascent. Given the high diffusivity of volatiles in apatite (Brenan, 1993), the preservation of volatile-undersaturated melt compositions in microphenocrysts suggests that saturation was only achieved 10 - 103 days before eruption. We suggest that late-stage transition into a volatile-saturated state caused an increase in magma chamber overpressure, which ultimately triggered the Astroni 1 eruption. This has major implications for monitoring of Campi Flegrei and other similar volcanic systems. Piccoli and Candela, 1994. Am. J. of Sc., 294, 92-135. Stock et al., 2016, Nat. Geosci. Gualda et al., 2012. J. Pet., 53, 875-890. Webster et al., 2014. J. Pet., 55, 2217-2248. Brenan, 1993. Chem. Geol., 110, 195-210.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T43C2693M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T43C2693M"><span>Nature of the Mantle Sources and Bearing on Tectonic Evolution in the West Antarctic Rift System</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukasa, S. B.; Rilling-Hall, S.; Marcano, M. C.; Wilson, T. J.; Lawver, L. A.; LeMasurier, W. E.</p> <p>2012-12-01</p> <p>We collected samples from subaerial lava flows and dredged some Neogene basanitic lavas from seven volcanic edifices in the Ross Sea, Antarctica - a part of the West Antarctic Rift System (WARS) and one of the world's largest alkaline magmatic provinces - for a study aimed at two principal objectives: (1) Geochemical interrogation of the most primitive magmatic rocks to try and understand the nature of the seismically abnormal mantle domain recently identified beneath the shoulder of the Transantarctic Mountains (TAM), the Ross Sea Embayment and Marie Byrd Land; and (2) Using 40Ar/39Ar geochronology to establish a temporal link between magmatism and tectonism, particularly in the Terror Rift. We have attempted to answer the questions of whether magmatism is due to a hot mantle or wet mantle, and whether rifting in the area triggered magmatic activity or vice versa. Results show that the area does not have an age-progressive hotspot track, and the magmatism post-dates the main phase of extension along the Terror Rift within the WARS, which supports a decompression-melting model without the benefit of a significant thermal anomaly. In fact, preliminary volatile measurements on olivine-hosted melt inclusions have yielded water concentrations in excess of 2 wt%, indicating that flux melting was an important complementary process to decompression melting. The major oxide compositions of lavas in the WARS are best matched to experimental melts of carbonated peridotite, though garnet pyroxenite can also be a minor source. The Pb and Nd isotopic systems are decoupled from each other, suggesting removal of fluid-mobile elements from the mantle source possibly during the long history of subduction along the Paleo-Pacific margin of Gondwana. Extremely unradiogenic 187Os/188Os ranging to as low as 0.1081 ± 0.0001 hints at the involvement of lithospheric components in generation of magmas in the WARS.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tectp.664..256J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tectp.664..256J"><span>Mantle dynamics and Cretaceous magmatism in east-central China: Insight from teleseismic tomograms</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jiang, Guoming; Zhang, Guibin; Zhao, Dapeng; Lü, Qingtian; Li, Hongyi; Li, Xinfu</p> <p>2015-11-01</p> <p>Both the rich mineralization in the Lower Yangtze Block (LYB) and the post-collisional mafic rocks in the Dabie Orogen (DBO) are closely related to the Cretaceous magmatism in east-central China. Various geodynamic models have been proposed for explaining the mechanism of the Cretaceous magmatism, but these models are controversial and even contradictory with each other, especially on the mechanism of adakites. A unified geodynamic model is required for explaining the magmatism in east-central China, in particular, the spatial and temporal correlations of magmatic activity in the DBO and that in the LYB. For this purpose, we apply teleseismic tomography to study P-wave velocity structure down to 800 km depth beneath east-central China. A modified multiple-channel cross-correlation method is used to collect 28,805 high-quality P-wave arrival-time data from seismograms of distant earthquakes recorded by permanent seismic stations and our temporary stations in the study region. To remove the influence of crustal heterogeneity on the mantle tomography, we used the CRUST1.0 model to correct the teleseismic relative residuals. Our tomography revealed distinct high-velocity (high-V) anomalies beneath the DBO and two flanks of the LYB, and low-velocity (low-V) anomalies above the high-V zones. Combining our tomographic images with previous geological, geochemical and geophysical results, we infer that these high-V and low-V anomalies reflect the detached lithosphere and upwelling asthenospheric materials, respectively, which are associated with the Late Mesozoic dynamic process and the Cretaceous magmatism. We propose a double-slab subduction model that a ridge subduction yielded the adakitic rocks in the LYB during 150-135 Ma and the subsequent Pacific Plate subduction played a crucial role in not only the formation of igneous rocks in the LYB but also remelting of the subducted South China Block beneath the DBO during 135-101 Ma.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GGG....18..531L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GGG....18..531L"><span>Rapid variations in fluid chemistry constrain hydrothermal phase separation at the Main Endeavour Field</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Love, Brooke; Lilley, Marvin; Butterfield, David; Olson, Eric; Larson, Benjamin</p> <p>2017-02-01</p> <p>Previous work at the Main Endeavour Field (MEF) has shown that chloride concentration in high-temperature vent fluids has not exceeded 510 mmol/kg (94% of seawater), which is consistent with brine condensation and loss at depth, followed by upward flow of a vapor phase toward the seafloor. Magmatic and seismic events have been shown to affect fluid temperature and composition and these effects help narrow the possibilities for sub-surface processes. However, chloride-temperature data alone are insufficient to determine details of phase separation in the upflow zone. Here we use variation in chloride and gas content in a set of fluid samples collected over several days from one sulfide chimney structure in the MEF to constrain processes of mixing and phase separation. The combination of gas (primarily magmatic CO2 and seawater-derived Ar) and chloride data, indicate that neither variation in the amount of brine lost, nor mixing of the vapor phase produced at depth with variable quantities of (i) brine or (ii) altered gas rich seawater that has not undergone phase separation, can explain the co-variation of gas and chloride content. The gas-chloride data require additional phase separation of the ascending vapor-like fluid. Mixing and gas partitioning calculations show that near-critical temperature and pressure conditions can produce the fluid compositions observed at Sully vent as a vapor-liquid conjugate pair or as vapor-liquid pair with some remixing, and that the gas partition coefficients implied agree with theoretically predicted values.<abstract type="synopsis"><title type="main">Plain Language SummaryWhen the chemistry of fluids from deep sea hot springs changes over a short time span, it allows us to narrow down the conditions and processes that created those fluids. This gives us a better idea what is happening under the seafloor where the water is interacting with hot rocks and minerals, boiling, and taking on the character it will have when it emerges at the seafloor. Gasses like argon can be especially helpful here. We found that the fluids we sampled must have been formed by multiple boiling (phase separation) events, and that one of these would have to be close to the critical point of these fluids.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T53B1317M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T53B1317M"><span>The Generation of Oceanic Lithosphere in an Embryonic Oceanic Crust : the Example of the Chenaillet Ophiolite in the Western Alps</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masini, E.; Manatschal, G.; Muntener, O.</p> <p>2007-12-01</p> <p>The Chenaillet Ophiolite exposed in the Franco-Italian Alps represents a well-preserved ocean-floor sequence that was only weakly affected by later Alpine convergence. Based on the similarity between rock types and structures reported from ultraslow spreading ridges and those observed in the Chenaillet Ophiolite, it may represent a field analogue for slow to ultraslow spreading ridges such as the Gakkel Ridge or the Southwest Indian Ridge. Mapping of the Chenaillet Ophiolite enabled to identify an oceanic detachment fault that extends over a surface of about 16 km2 capping exhumed mantle and gabbros onto which clastic sediments have been deposited. The footwall of the detachment is formed by mafic and ultramafic rocks. The mantle rocks are strongly serpentinized lherzolites and subordinate harzburgites and dunites. Microstructures reminiscent of impregnation, and cpx major and trace element chemistry indicate that spinel peridotite is (locally) replaced by plagioclase-bearing assemblages. Pyroxene thermometry on primary minerals indicates high temperatures of equilibration ( max 1200°C) for the mantle rocks. Gabbros range from troctolite and olivine-gabbros to Fe-Ti gabbros and show clear evidence of syn-magmatic deformation, partially obliterated by retrograde amphibolite and low-grade metamorphic conditions. In sections perpendicular to the detachment within the footwall, syn-tectonic gabbros and serpentinized peridotites grade over some tens of meters into cataclasites that are capped by fault gouges. Petro-structural investigations of the fault rocks reveal a syn-tectonic retrograde metamorphic evolution. Clasts of dolerite within the fault zone suggest that detachment faulting was accompanied by magmatic activity. Hydrothermal alteration is indicated by strong mineralogical and chemical modifications. Gabbro and serpentinized peridotite, together with serpentinite cataclasites occur as clasts in tectono-sedimentary breccias overlying directly the detachment fault. Across the whole Chenaillet Ophiolite, volcanic rocks directly overlie either the detachment fault or the sediments. In several places, N-S trending high-angle normal faults have been mapped. These faults truncate and displace the detachment fault leading to small domino-like structures. The basins, limited by these high-angle faults, are some hundreds to a few kilometres wide and few tens to some hundreds of meters deep. Because these high- angle faults are sealed locally by basalts and obliterated by volcanic structures, we interpret them as oceanic structures being active during the emplacement of the basalts. The alignment of porphyritic basaltic dykes parallel to, and their increasing abundance towards the high-angle faults suggest that they may have served as feeder channels for the overlying volcanic rocks. The complex poly-phase tectonic and magmatic processes observed in the Chenaillet Ophiolite are reminiscent of those reported from slow to ultraslow spreading ridges. The key result from our study is that mantle exhumation along detachment faults is followed by syn-magmatic normal faulting resulting in the emplacement of laterally variable, up to 300 meters thick massive lavas and pillow basalts covering the exhumed detachment fault. This implies that off-axis processes are more important as previously assumed and that large-scale detachment faults may be buried under massive volcanic sequences suggesting that detachment faulting is presumably more common than suggested by dredging or morpho-structural investigations of ultra- to slow- spreading oceanic crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T11C0726G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T11C0726G"><span>Introducing tectonically and thermo-mechanically realistic lithosphere in the models of plume head -lithosphere interactions (PLI) including intra-continental plate boundaries.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guillou-Frottier, L.; Burov, E.; Cloetingh, S.</p> <p>2007-12-01</p> <p>Plume-Lithosphere Interactions (PLI) in continets have complex topographic and magmatic signatures and are often identified near boundaries between younger plates (e.g., orogenic) and older stable plates (e.g., cratons), which represent important geometrical, thermal and rheological barriers that interact with the emplacement of the plume head (e.g., Archean West Africa, East Africa, Pannonian - Carpathian system). The observable PLI signatures are conditioned by plume dynamics but also by complex rheology and structure of continental lithosphere. We address this problem by considering a new free-surface thermo-mechanical numerical model of PLI with two stratified elasto-viscous-plastic (EVP) continental plates of contrasting age, thickness and structure. The results show that: (1) surface deformation is poly-harmonic and contains smaller wavelengths (50-500 km) than that associated with the plume head (>1000 km). (2) below intra-plate boundaries, plume head flattening is asymmetric, it is blocked from one side by the cold vertical boundary of the older plate, which leads to mechanical decoupling of crust from mantle lithosphere, and to localized faulting at the cratonic margin; (2) the return flow from the plume head results in sub-vertical down-thrusting (delamination) of the lithosphere at the margin, producing sharp vertical cold boundary down to the 400 km depth; (3) plume head flattening and migration towards the younger plate results in concurrent surface extension above the centre of the plume and in compression (pushing), down-thrusting and magmatic events at the cratonic margin (down-thrusting is also produced at the opposite border of the younger plate); these processes may result in continental growth at the "craton side"; (4) topographic signatures of PLI show basin-scale uplifts and subsidences preferentially located at cratonic margins. Negative Rayleigh-Taylor instabilities in the lithosphere above the plume head provide a mechanism for crustal delamination. In case of several cratonic blocks, the combined effect of subsidence and lithospheric thinning at cratons edges, while plume head material is being stocked in between the cratons, favours major magmatic events at cratonic margins. Numerous field evidence (West Africa, Western Australia) underline the trapping effect of cratonic margins for formation of (e.g.) orogenic gold deposits, which require particular extreme P-T conditions. Location of gemstones deposits is also associated with cratonic margins, as demonstrated by the Tanzanian Ruby belt. Their formation depend on particularly fast isothermal deepening processes, which can be reproduced by slab-like instabilities induced by plume head-cratonic margin interaction. On the other hand, absence of magmatic events should not be interpreted as evidence for the absence of plume: at surface, these events may not necessary have unambiguous deep geochemical signatures, as the hot source plume material stalls below Moho and forms a long-lasting (10 to 100 Myr) sub-Moho reservoir. This should induce strong crustal melting that may overprint deeper signatures since crustal melts are generated at much lower temperatures than mantle, and produce light low-viscous rapidly ascending magmas. Drip-like down- sagging of the lithospheric mantle and metamorphic lower crustal material inside the plume head may contaminate the latter and also alter the geochemical signature of related magmas.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.T33D0748S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.T33D0748S"><span>Controls on mid-ocean ridge segmentation and transform fault formation from laboratory experiments using fluids of complex rheology.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sibrant, A.; Mittelstaedt, E. L.; Davaille, A.</p> <p>2017-12-01</p> <p>Mid-ocean ridges are tectonically segmented at scales of 10s to 100s of kilometers by several types of offsets including transform faults (TF), overlapping spreading centers (OSC), and slow-spreading non-transform offsets (NTO). Differences in segmentation along axis have been attributed to changes in numerous processes including magma supply from the upwelling mantle, viscous flow in the asthenosphere, ridge migration, and plate spreading direction. The wide variety of proposed mechanisms demonstrate that the origin of tectonic offsets and their relationship to segment-scale magmatic processes remain actively debated; each of the above processes, however, invoke combinations of tectonic and magmatic processes to explain changes in segmentation. To address the role of tectonic deformation and magmatic accretion on the development of ridge offsets, we present a series of analogue experiments using colloidal silica dispersions as an Earth analogue. Saline water solutions placed in contact with these fluids, cause formation of a skin through salt diffusion, whose rheology evolves from purely viscous to elastic and brittle with increasing salinity. Experiments are performed in a Plexiglas tank with two Plexiglas plates suspended above the base of the tank. The tank is filled with the colloidal fluid to just above the suspended plates, a thin layer of saline water is spread across the surface, and spreading initiated by moving the suspended Plexiglas plates apart at a fixed rate. Results show formation of OSCs, NTOs, and TFs. For parameters corresponding to the Earth, TF offsets are < 5 mm and form at all spreading velocities, corresponding to transform offsets of < 100 km on Earth. Measured TF offset size and ridge segment lengths exhibit a Poisson-type distribution with no apparent dependence on spreading rate. Observations of TF offset size on Earth show a similar distribution for TFs <100 km long and supports the hypothesis that TFform spontaneously through a mechanical instability of the axis. Here, we present an analysis of the magmatic and tectonic controls on axis instability leading to the formation of TFs, OSCs, and NTOs, and their implications for the evolution of mid-ocean ridges.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1399720-origin-lunar-highlands-mg-suite-integrated-petrology-geochemistry-chronology-remote-sensing-perspective','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1399720-origin-lunar-highlands-mg-suite-integrated-petrology-geochemistry-chronology-remote-sensing-perspective"><span>Origin of the lunar highlands Mg-suite: An integrated petrology, geochemistry, chronology, and remote sensing perspective</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Shearer, C. K.; Elardo, S. M.; Petro, N. E.; ...</p> <p>2014-12-23</p> <p>The Mg-suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation. This review examines the mineralogy, geochemistry, petrology, chronology, and the planetary-scale distribution of this suite of highlands plutonic rocks, presents models for their origin, examines petrogenetic relationships to other highlands rocks, and explores the link between this style of magmatism and early stages of lunar differentiation. Of the models considered for the origin of the parent magmas for the Mg-suite, the data best fit a process in which hot (solidus temperature at ≥2 GPa = 1600 to 1800more » °C) and less dense (r ~3100 kg/m3) early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn. Some decompressional melting would occur, but placing a hot cumulate horizon adjacent to the plagioclase-rich primordial crust and KREEP-rich lithologies (at temperatures of <1300 °C) would result in the hybridization of these divergent primordial lithologies, producing Mg-suite parent magmas. As urKREEP (primeval KREEP) is not the “petrologic driver” of this style of magmatism, outside of the Procellarum KREEP Terrane (PKT), Mg-suite magmas are not required to have a KREEP signature. Evaluation of the chronology of this episode of highlands evolution indicates that Mg-suite magmatism was initiated soon after primordial differentiation (<10 m.y.). Alternatively, the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust. Petrogenetic relationships between the Mg-suite and other highlands suites (e.g., alkali-suite and magnesian anorthositic granulites) are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.osti.gov/servlets/purl/10145993','SCIGOV-STC'); return false;" href="https://www.osti.gov/servlets/purl/10145993"><span>Vent processes during the 1912 eruption at Novarupta, Katmai National Park, Alaska. Progress report, [November 15, 1991--November 14, 1992</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Bates, T.; Eichelberger, J.; Swanson, S.</p> <p></p> <p>Blocks of welded fragmental material ejected at Novarupta during the great eruption of 1912 provide evidence of the contents and development of the vent. Because they appear to represent material held at magmatic temperature for hours to days and then quenched at depth and ejected, they provide unusual information on the timing of processes of degassing, welding, and magma mixing. Two breccia types are distinguished by proportions of the three magmatic components. Type 1 breccia (Hildreth`s ``vitrophyre``) is rhyolite- and andesite-rich (``volcanic inclusions`` in the glassy matrix were found to be 1912 andesite), contains abundant lithics, and is found throughoutmore » deposits of the eruption`s second and third days. It corresponds to magmatic proportions being erupted toward the end of the first day, or Episode I. Type 2 is dacite-rich and poor in lithics, and occurs only at the surface. It corresponds to magmatic proportions erupted during Episodes II and III. A pyroclastic dike exposed in a bomb of Type 2 vent breccia is petrologically related to Novarupta lava. Water is strongly but not completely degassed from vent breccias (Type I breccia at 0.30 wt % H{sub 2}O and Type 2 breccia at 0.15 wt % H{sub 2}O even when bread crusted) and more thoroughly degassed from dome lava (rhyolite and andesite at < 0.10 wt % H{sub 2}O), but the pyroclastic dike retains significant water (averages 0.90 wt. % H{sub 2}O) and its host breccia likewise contains elevated water concentrations (0.30--0.40 wt % H{sub 2}O). The mafic component in Novarupta dome is derived from andesitic, rather than dacitic magma, and has crystallized substantially in response to mixing with its cooler host.« less</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JVGR..353..114M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JVGR..353..114M"><span>The hydrothermal evolution of the Kawerau geothermal system, New Zealand</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Milicich, S. D.; Chambefort, I.; Wilson, C. J. N.; Charlier, B. L. A.; Tepley, F. J.</p> <p>2018-03-01</p> <p>Hydrothermal alteration zoning and processes provide insights into the evolution of heat source(s) and fluid compositions associated with geothermal systems. Traditional petrological techniques, combined with hydrothermal alteration studies, stable isotope analyses and geochronology can resolve the nature of the fluids involved in hydrothermal processes and their changes through time. We report here new findings along with previous unpublished works on alteration patterns, fluid inclusion measurements and stable isotope data to provide insights into the thermal and chemical evolution of the Kawerau geothermal system, New Zealand. These data indicate the presence of two hydrothermal events that can be coupled with chronological data. The earlier period of hydrothermal activity was initiated at 400 ka, with the heat driving the hydrothermal system inferred to be from the magmatic system that gave rise to rhyolite lavas and sills of the Caxton Formation. Isotopic data fingerprint fluids attributed to this event as meteoric, indicating that the magma primarily served as a heat source driving fluid circulation, and was not releasing magmatic fluids in sufficient quantity to affect the rock mineralogy and thus inferred fluid compositions. The modern Kawerau system was initiated at 16 ka with hydrothermal eruptions linked to shallow intrusion of magma at the onset of activity that gave rise to the Putauaki andesite cone. Likely associated with this later event was a pulse of magmatic CO2, resulting in large-scale deposition of hydrothermal calcite enriched in 18O. Meteoric water-dominated fluids subsequently overwhelmed the magmatic fluids associated with this 18O-rich signature, and both the fluid inclusion microthermometry and stable isotope data reflect a change to the present-day fluid chemistry of low salinity, meteoric-dominated waters.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Tectp.638..112W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Tectp.638..112W"><span>Crustal magmatism and lithospheric geothermal state of western North America and their implications for a magnetic mantle</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Jian; Li, Chun-Feng</p> <p>2015-01-01</p> <p>The western North American lithosphere experienced extensive magmatism and large-scale crustal deformation due to the interactions between the Farallon and North American plates. To further understand such subduction-related dynamic processes, we characterize crustal structure, magmatism and lithospheric thermal state of western North America based on various data processing and interpretation of gravimetric, magnetic and surface heat flow data. A fractal exponent of 2.5 for the 3D magnetization model is used in the Curie-point depth inversion. Curie depths are mostly small to the north of the Yellowstone-Snake River Plain hotspot track, including the Steens Mountain and McDermitt caldera that are the incipient eruption locations of the Columbia River Basalts and Yellowstone hotspot track. To the south of the Yellowstone hotspot track, larger Curie depths are found in the Great Basin. The distinct Curie depths across the Yellowstone-Snake River Plain hotspot track can be attributed to subduction-related magmatism induced by edge flow around fractured slabs. Curie depths confirm that the Great Valley ophiolite is underlain by the Sierra Nevada batholith, which can extend further west to the California Coast Range. The Curie depths, thermal lithospheric thickness and surface heat flow together define the western edge of the North American craton near the Roberts Mountains Thrust (RMT). To the east of the RMT, large Curie depths, large thermal lithospheric thickness, and low thermal gradient are found. From the differences between Curie-point and Moho depth, we argue that the uppermost mantle in the oceanic region is serpentinized. The low temperature gradients beneath the eastern Great Basin, Montana and Wyoming permit magnetic uppermost mantle, either by serpentinization/metasomatism or in-situ magnetization, which can contribute to long-wavelength and low-amplitude magnetic anomalies and thereby large Curie-point depths.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70034531','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70034531"><span>Diffusion-driven magnesium and iron isotope fractionation in Hawaiian olivine</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Teng, F.-Z.; Dauphas, N.; Helz, R.T.; Gao, S.; Huang, S.</p> <p>2011-01-01</p> <p>Diffusion plays an important role in Earth sciences to estimate the timescales of geological processes such as erosion, sediment burial, and magma cooling. In igneous systems, these diffusive processes are recorded in the form of crystal zoning. However, meaningful interpretation of these signatures is often hampered by the fact that they cannot be unambiguously ascribed to a single process (e.g., magmatic fractionation, diffusion limited transport in the crystal or in the liquid). Here we show that Mg and Fe isotope fractionations in olivine crystals can be used to trace diffusive processes in magmatic systems. Over sixty olivine fragments from Hawaiian basalts show isotopically fractionated Mg and Fe relative to basalts worldwide, with up to 0.4??? variation in 26Mg/24Mg ratios and 1.6??? variation in 56Fe/54Fe ratios. The linearly and negatively correlated Mg and Fe isotopic compositions [i.e., ??56Fe=(??3.3??0.3)????26Mg], co-variations of Mg and Fe isotopic compositions with Fe/Mg ratios of olivine fragments, and modeling results based on Mg and Fe elemental profiles demonstrate the coupled Mg and Fe isotope fractionation to be a manifestation of Mg-Fe inter-diffusion in zoned olivines during magmatic differentiation. This characteristic can be used to constrain the nature of mineral zoning in igneous and metamorphic rocks, and hence determine the residence times of crystals in magmas, the composition of primary melts, and the duration of metamorphic events. With improvements in methodology, in situ isotope mapping will become an essential tool of petrology to identify diffusion in crystals. ?? 2011 Elsevier B.V.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAfES.132...47H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAfES.132...47H"><span>Mineralogical and geochemical features of the alteration processes of magmatic ores in the Beni Bousera ultramafic massif (north Morocco)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hajjar, Zaineb; Gervilla, Fernando; Essaifi, Abderrahim; Wafik, Amina</p> <p>2017-08-01</p> <p>The Beni Bousera ultramafic massif (Internal Rif, Morocco) is characterized by the presence of two types of small-scale magmatic mineralizations (i) a mineralization consisting mainly of chromite and Ni arsenides associated to orthopyroxene and cordierite (Cr-Ni ores), and (ii) a mineralization mainly composed of magmatic Fe-Ni-Cu sulfides containing variable amounts of graphite and chromite associated to phlogopite, clinopyroxène and plagioclase (S-G ores). Theses ores underwent High-T (450-550 °C) and Low-T (150-300 °C) alteration processes. The High-T alteration processes are tentatively related to intrusion of leucogranite dykes. They are preserved in the Galaros Cr-Ni ore deposit where nickeline is partly dissolved and transformed to maucherite, and orthopyroxene alters to phlogopite. Ni and Co were mobilized to the fluid phase, rising up their availability and promoting their diffusion into chromite and phlogopite, which have significantly higher contents in Ni and Co in phlogopite-rich ores than in orthopyroxene- and nickeline-rich ones. The Low-T alteration processes are related to serpentinization/weathering spatially associated with a regional shear zone. They affected both the Cr-Ni and S-G ores. In the Cr-Ni ores, Ni-arsenides were completely leached out while chromite is fractured within a matrix of chlorite, vermiculite and Ni-rich serpentine. In S-G ores, the silicates were altered into amphibole, Fe-rich chlorite and pectolite in clinopyroxene- and plagioclase-bearing ores while sulfides were completely leached out in phlogopite-bearing ores where iron oxides and hydroxides, and Fe-rich vermiculite were deposited. Chromite composition is not affected by the Low-T alteration processes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000JAfES..31..597V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000JAfES..31..597V"><span>Palæo- and Neoproterozoic granitoids and rhyolites from the West Congolian Belt (Gabon, Congo, Cabinda, north Angola): chemical composition and geotectonic implications</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vicat, J.-P.; Pouclet, A.</p> <p>2000-11-01</p> <p>Various Palæo- and Neoproterozoic granitoid bodies and related rhyolites are located in the West Congolian Belt. The Palæoproterozoic granitoids, dated around 2 Ga, exhibit an Archæan-type tonalite-trondhjemite-granodiorite suite chemical signature and are related to the Eburnean tectnno-magmatic event. In contrast, Neoproterozoic granitoids and rhyolites, dated around 1 Ga, have chemical geotectonic signatures that range from orogenic to intraplate (Nb-negative anomaly, large ion lithophile element enrichment and high field strength element depletion). However, a late Kibaran orogenic event (1.35-1.00 Ga) is unknown in this area. The Neoproterozoic magmatism is interpreted as a consequence of the initiation of pre-Pan-African rifting, which implies the formation or the reactivation of major crustal strike-slip faults with asthenospheric upwelling and the generation of a thermal anomaly. This thermal anomaly could have been responsible for magmatic processes involving the lower crust, as encountered in post-orogenic environments.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12219992','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12219992"><span>Thermal-field propagation in an exocontact zone of a magmatic body and its impact on radiogenic isotope concentrations in minerals.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Brandt, I S; Rasskazov, S V; Brandt, S B; Ivanov, A V</p> <p>2002-03-01</p> <p>In application of radioactive isotope systems (K-Ar, Rb-Sr etc.) during the last decades, experience was gained not only on their geochronometrical uses, but also on estimations of some important parameters of geological processes, especially temperatures and durations of superimposed thermal events. In this paper, the formation of an exocontact thermal field of a magmatic intrusion is considered as a spreading of a thermal source delta-function. Appropriate solutions of the heat-transfer equation are deduced and correlated with diffusion parameters of the radiogenic argon, coupling radioactive, thermal and kinetic parameters in an exocontant zone of a magmatic body. These solutions were used for quantitative reinterpretations of data taken from Hart's classical paper [The petrology and isotopic mineral age relations of a contact zone in the Front Range, Colorado. J. Geol., 1964, v. 72, pp. 493-525]. Theoretic and measured radiogenic argon and strontium concentrations within exocontact aureoles are found to be in good concordance.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70033749','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70033749"><span>The evolution of volcano-hosted geothermal systems based on deep wells from Karaha-Telaga Bodas, Indonesia</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Moore, J.N.; Allis, R.G.; Nemcok, M.; Powell, T.S.; Bruton, C.J.; Wannamaker, P.E.; Raharjo, I.B.; Norman, D.I.</p> <p>2008-01-01</p> <p>Temperature and pressure surveys, fluid samples, and petrologic analyses of rock samples from deep drill holes at the Karaha - Telaga Bodas geothermal field on the volcanic ridge extending northward from Galunggung Volcano, West Java, have provided a unique opportunity to characterize the evolution of an active volcano-hosted geothermal system. Wells up to 3 km in depth have encountered temperatures as high as 353??C and a weakly altered granodiorite that intruded to within 2 to 3 km of the surface. The intrusion is shallowest beneath the southern end of the field where an acid lake overlies a nearly vertical low resistivity structure (<10 ohm-m) defined by magnetotelluric measurements. This structure is interpreted to represent a vapor-dominated chimney that provides a pathway to the surface for magmatic gases. Four distinct hydrothermal mineral assemblages document the evolution of the geothermal system and the transition from liquid- to vapor-dominated conditions. The earliest assemblage represents the initial liquid-dominated system generated during emplacement of the granodiorite between 5910 ?? 76 and 4200 ?? 150 y BP. Tourmaline, biotite, actinolite, epidote and clay minerals were deposited contemporaneously at progressively greater distances from the intrusive contact (assemblage 1). At 4200 ?? 150 y BP, flank collapse and the formation of the volcano's crater, Kawah Galunggung, resulted in catastrophic decompression and boiling of the hydrothermal fluids. This event initiated development of the modern vapor-dominated regime. Chalcedony and then quartz were deposited as the early low salinity liquids boiled (assemblage 2). Both vapor- and liquid-rich fluid inclusions were trapped in the quartz crystals. Liquid-rich fluid inclusions from the southern part of the field record salinities ranging from 0 to 26 weight percent NaCl- CaCl2 equivalent and locally contain fluorite daughter crystals. We suggest, based on temperature-salinity relationships and evidence of boiling, that these fluids were progressively concentrated as steam was lost from the system. However, mixing with fluids derived from the underlying intrusion or generated during the formation of acid SO4 water on the vapor-dominated chimney margins could have contributed to the observed salinities. As pressures declined, CO2- and SO4-rich steam-heated water drained downward, depositing anhydrite and calcite (assemblage 3) in the fractures, limiting further recharge. Fluid inclusions with salinities up to 31 weight percent NaCl equivalent were trapped in these minerals as the descending water vaporized. The final assemblage is represented by precipitates of NaCl, KCl and FeClx deposited on rock surfaces in portions of the vapor-dominated zone that boiled dry. Vapor-dominated conditions extend over a distance of at least 10 km and to depths below sea level. Deep wells drilled into the underlying liquid-dominated reservoir in the northern and central part of the volcanic ridge produce low salinity fluids representing recent recharge of meteoric and steam-heated water. The evolution of volcanic-hosted vapor-dominated geothermal systems can be described by a five stage model. Stage 1 involves the formation of an over-pressured liquid-dominated geothermal system soon after magmatic intrusion. In Stages 2 and 3, pressures progressively decrease, and a curtain of steam-heated water surrounding a magmatic vapor-dominated chimney at 350??C and 14 ?? 2 MPa develops. The relatively low pressure near the base of the chimney causes liquid inflow adjacent to the intrusion and the development of a secondary marginal vapor-dominated zone. In Stage 4, the magmatic vapor discharge from the intrusion becomes small, vapor pressure declines, and the secondary vapor-dominated zone expands above the intrusion. In Stage 5, the vapor-dominated zone floods because heat from the intrusion is insufficient to boil all liquid inflow. A more common, liquid-dominated volcanic-hosted system the</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996GMS....96..179B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996GMS....96..179B"><span>Volatile transfer and recycling at convergent margins: Mass-balance and insights from high-P/T metamorphic rocks</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bebout, Gray E.</p> <p></p> <p>The efficiency with which volatiles are deeply subducted is governed by devolatilization histories and the geometries and mechanisms of fluid transport deep in subduction zones. Metamorphism along the forearc slab-mantle interface may prevent the deep subduction of many volatile components (e.g., H2O, Cs, B, N, perhaps As, Sb, and U) and result in their transport in fluids toward shallower reservoirs. The release, by devolatilization, and transport of such components toward the seafloor or into the forearc mantle wedge, could in part explain the imbalances between the estimated amounts of subducted volatiles and the amounts returned to Earth's surface. The proportion of the initially subducted volatile component that is retained in rocks subducted to depths greater than those beneath magmatic arcs (>100 km) is largely unknown, complicating assessments of deep mantle volatile budgets. Isotopic and trace element data and volatile contents for the Catalina Schist, the Franciscan Complex, and eclogite-facies complexes in the Alps (and elsewhere) provide insight into the nature and magnitude of fluid production and transport deep in subduction zones and into the possible effects of metamorphism on the compositions of subducting rocks. Compatibilities of the compositions of the subduction-related rocks and fluids with the isotopic and trace element compositions of various mantle-derived materials (igneous rocks, xenoliths, serpentinite seamounts) indicate the potential to trace the recycling of rock and fluid reservoirs chemically and isotopically fractionated during subduction-zone metamorphism.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008E%26PSL.266..256M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008E%26PSL.266..256M"><span>Mid-ocean ridge jumps associated with hotspot magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mittelstaedt, Eric; Ito, Garrett; Behn, Mark D.</p> <p>2008-02-01</p> <p>Hotspot-ridge interaction produces a wide range of phenomena including excess crustal thickness, geochemical anomalies, off-axis volcanic ridges and ridge relocations or jumps. Ridges are recorded to have jumped toward many hotspots including, Iceland, Discovery, Galápagos, Kerguelen and Tristan de Cuhna. The causes of ridge jumps likely involve a number of interacting processes related to hotspots. One such process is reheating of the lithosphere as magma penetrates it to feed near-axis volcanism. We study this effect by using the hybrid, finite-element code, FLAC, to simulate two-dimensional (2-D, cross-section) viscous mantle flow, elasto-plastic deformation of the lithosphere and heat transport in a ridge setting near an off-axis hotspot. Heating due to magma transport through the lithosphere is implemented within a hotspot region of fixed width. To determine the conditions necessary to initiate a ridge jump, we vary four parameters: hotspot magmatic heating rate, spreading rate, seafloor age at the location of the hotspot and ridge migration rate. Our results indicate that the hotspot magmatic heating rate required to initiate a ridge jump increases non-linearly with increasing spreading rate and seafloor age. Models predict that magmatic heating, itself, is most likely to cause jumps at slow spreading rates such as at the Mid-Atlantic Ridge on Iceland. In contrast, despite the higher magma flux at the Galápagos hotspot, magmatic heating alone is probably insufficient to induce a ridge jump at the present-day due to the intermediate ridge spreading rate of the Galápagos Spreading Center. The time required to achieve a ridge jump, for fixed or migrating ridges, is found to be on the order of 10 5-10 6 years. Simulations that incorporate ridge migration predict that after a ridge jump occurs the hotspot and ridge migrate together for time periods that increase with magma flux. Model results also suggest a mechanism for ridge reorganizations not related to hotspots such as ridge jumps in back-arc settings and ridge segment propagation along the Mid-Atlantic Ridge.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.V44A..06A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.V44A..06A"><span>Tomographic imaging of the transition from asthenospheric to lithospheric melt migration processes: 3-D structure of the topmost mantle and crust at the Endeavour Segment, Juan de Fuca Ridge</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arnoux, G. M.; Toomey, D. R.; Hooft, E. E. E.; Wilcock, W. S. D.</p> <p>2017-12-01</p> <p>We present tomographic images of the intermediate-spreading Endeavour Segment that constrain the nature of an axial magmatic system as it transitions from asthenospheric- to lithospheric-dominated rheologies. We use seismic energy from 5500 air gun shots refracted through the crust (Pg), reflected off the Moho (PmP), and refracted below the Moho (Pn)—as recorded by 64 OBSs from the Endeavour tomography experiment—to image the isotropic and anisotropic P-wave velocity structure of the topmost mantle and crust, as well as crustal thickness. At crustal depths, results reveal a low-velocity zone (LVZ)—inferred to be the axial magmatic system—that: (i) is continuous along the entire Endeavour Segment at depths of 2-3 km below seafloor and closely follows the axis of spreading, (ii) broadens and becomes more discontinuous at lower crustal depths, and (iii) has its largest amplitude from the mid- to lower-crust at the segment center. The ridge-tracking trend of the mid-crustal LVZ is in contrast to the crustal thickness pattern; in particular, a swath of thin crust is skewed with respect to both the ridge axis and the mid-crustal magmatic system and connects two overlapping spreading centers bounding the segment. The trend of thinner crust, however, is aligned with the mantle LVZ, which constrains the thermal structure and distribution of melt within the topmost mantle. The systematic depth variation of the map-view orientation and structure of the magmatic system indicates a distinct transition from a broad, cross-axis regime in the topmost asthenosphere governed by a regional, north-south trending thermal structure, to a narrow, cross-axis regime in the mid- to upper-crust governed by lithospheric rifting, magma injection, and hydrothermal processes. The lower-crustal magmatic system connects these two regimes. We also postulate that accumulation and differentiation of magma immediately beneath the crust-mantle boundary increases temperatures and suppresses plagioclase crystallization, thereby reducing the depth of lower crustal accretion and resulting in the observed north-south trending swath of thinner crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V21A3016F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V21A3016F"><span>Extent and impact of Cretaceous magmatism on the formation and evolution of Jurassic oceanic crust in the western Pacific</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Feng, H.; Lizarralde, D.; Tominaga, M.; Hart, L.; Tivey, M.; Swift, S. A.</p> <p>2015-12-01</p> <p>Multi-channel seismic (MCS) images and wide-angle sonobuoy data acquired during a 2011 cruise on the R/V Thomas G. Thompson (TN272) show widespread emplacement of igneous sills and broadly thickened oceanic Layer 2 through hundreds of kilometers of oceanic crust in one of the oldest ocean basins in the western Pacific, a region known as the Jurassic Quiet Zone (JQZ). Oceanic crust from the JQZ has grown through at least two main magmatic phases: It was formed by mid-ocean ridge processes in the Jurassic (at ~170 Ma), and then it was added to by a substantial Cretaceous magmatic event (at ~75-125 Ma). The scale of Cretaceous magmatism is exemplified by massive seafloor features such as the Ontong Java Plateau, Mid-Pacific Mountains, Marshall-Gilbert Islands, Marcus-Wake Seamount Chain, and numerous guyots, seamounts, and volcaniclastic flows observed throughout the region. We use seismic data to image heavily intruded and modified oceanic crust along an 800-km-long transect through the JQZ in order to examine how processes of secondary crustal growth - including magmatic emplacement, transport, and distribution - are expressed in the structure of modified oceanic crust. We also model gravity anomalies to constrain crustal thickness and depth to the Moho. Our observations suggest that western Pacific crust was modified via the following modes of emplacement: (a) extrusive seafloor flows that may or may not have grown into seamounts, (b) seamounts formed through intrusive diking that pushed older sediments aside during their formation, and (c) igneous sills that intruded sediments at varying depths. Emplacement modes (a) and (b) tend to imply a focused, pipe-like mechanism for melt transport through the lithosphere. Such a mechanism does not explain the observed broadly distributed intrusive emplacement of mode (c) however, which may entail successive sill emplacement between igneous basement and sediments thickening oceanic Layer 2 along ~400 km of our seismic line. This mode of crustal growth seems to require broad zones of melt transport through the lithosphere and across the Moho.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018MinDe.tmp....1R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018MinDe.tmp....1R"><span>Mineralized breccia clasts: a window into hidden porphyry-type mineralization underlying the epithermal polymetallic deposit of Cerro de Pasco (Peru)</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rottier, Bertrand; Kouzmanov, Kalin; Casanova, Vincent; Bouvier, Anne-Sophie; Baumgartner, Lukas P.; Wälle, Markus; Fontboté, Lluís</p> <p>2018-01-01</p> <p>Cerro de Pasco (Peru) is known for its large epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) mineralization emplaced at shallow level, a few hundred meters below the paleo-surface, at the border of a large diatreme-dome complex. Porphyry-style veins crosscutting hornfels and magmatic rock clasts are found in the diatreme breccia and in quartz-monzonite porphyry dikes. Such mineralized veins in clasts allow investigation of high-temperature porphyry-style mineralization developed in the deep portions of magmatic-hydrothermal systems. Quartz in porphyry-style veins contains silicate melt inclusions as well as fluid and solid mineral inclusions. Two types of high-temperature (> 600 °C) quartz-molybdenite-(chalcopyrite)-(pyrite) veins are found in the clasts. Early, thin (1-2 mm), and sinuous HT1 veins are crosscut by slightly thicker (up to 2 cm) and more regular HT2 veins. The HT1 vein quartz hosts CO2- and sulfur-rich high-density vapor inclusions. Two subtypes of the HT1 veins have been defined, based on the nature of mineral inclusions hosted in quartz: (i) HT1bt veins with inclusions of K-feldspar, biotite, rutile, and minor titanite and (ii) HT1px veins with inclusions of actinolite, augite, titanite, apatite, and minor rutile. Using an emplacement depth of the veins of between 2 and 3 km (500 to 800 bar), derived from the diatreme breccia architecture and the supposed erosion preceding the diatreme formation, multiple mineral thermobarometers are applied. The data indicate that HT1 veins were formed at temperatures > 700 °C. HT2 veins host assemblages of polyphase brine inclusions, generally coexisting with low-density vapor-rich inclusions, trapped at temperatures around 600 °C. Rhyolitic silicate melt inclusions found in both HT1 and HT2 veins represent melt droplets transported by the ascending hydrothermal fluids. LA-ICP-MS analyses reveal a chemical evolution coherent with the crystallization of an evolved rhyolitic melt. Quartz from both HT1 and HT2 veins also contains secondary, low-temperature ( 300 °C) brine and aqueous fluid inclusions that record the cooling of the system. Both vein types are locally crosscut and/or reopened by a pre-diatreme polymetallic event consisting of pyrite, sphalerite with "chalcopyrite disease," galena, chalcopyrite, tetrahedrite-tennantite, and minor quartz. LA-ICP-MS analyses of mineral and high-temperature fluid inclusions hosted in HT1 and HT2 veins and in situ secondary-ion mass spectrometry oxygen isotope analyses of vein quartz indicate a magmatic signature for the mineralizing fluids with no major meteoric water input and allow reconstruction of the source and chemical evolution of fluids that formed these porphyry-style veins as snapshots of the early and deep mineralizations at Cerro de Pasco. This detailed study of the porphyry-type mineralization hosted in clasts offers a unique opportunity to reconstruct the late magmatic and early hydrothermal evolutions of porphyry mineralization underlying the world-class Cerro de Pasco epithermal polymetallic (Zn-Pb-Ag-Cu-Bi) deposit.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.V31B4730B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.V31B4730B"><span>Towards Solving the Conundrum of Fast-Spread Ocean Crust Formation: Insights from Textural Analysis of Gabbroic Rocks from Pito Deep and Hess Deep, East Pacific Rise</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brown, T. C.; Cheadle, M. J.; John, B. E.; Coogan, L. A.; Gee, J. S.; Karson, J. A.; Meyer, R.; Ceuleneer, G.; Swapp, S.</p> <p>2014-12-01</p> <p>Few examples of in situ fast-spread lower ocean crust exist for sampling. Here we present detailed textural analyses of two sample sets that formed at the East Pacific Rise, collected from tectonic windows at Pito (PD) and Hess (HD) deeps. PD samples (collected by ROV) span the upper ~900 m of lower crust. HD samples (collected by seafloor drilling during IODP Exp. 345) come from >1500 m below the sheeted dike gabbro transition (mbsd). PD gabbroic rock textures are consistent with a gabbro glacier flow model generating the uppermost plutonic crust. Shallow samples (41-72 mbsd) likely formed at the distal edge of the magma lens, analogous to similar rocks from Oman. These gabbros are relatively evolved (cpx Mg#75-77, An53-61 and 1-4% Fe-Ti oxides), and have elongate plagioclase grains (aspect ratios up to 1:2:10) exhibiting a strong shape preferred orientation (SPO) with <40% of grains showing dislocation creep textures. Deeper samples (177-876 mbsd) likely began crystallizing in the magma lens then subsided and 'flowed' through the underlying mush zone. These gabbros are more primitive below 386 mbsd (Fo83-88, cpx Mg# 85-89 and An70-82), and plagioclase grains have more equilibrated morphologies (aspect ratios < 1:2:6) that define ~vertical SPOs which increase in strength with depth. Plagioclase exhibits magmatic crystal-lattice preferred orientations (CPOs) which are also vertical. Significantly, the proportion of grains showing dislocation creep textures increases with depth, and plagioclase grain size distributions show a smaller range of sizes at depth; observations that perhaps reflect the effect of increasing strain with depth. IODP Hole U1415I at HD recovered gabbros and troctolitic gabbros from the mid lower crust that show distinctive cm-dm scale modal layering. Strong plagioclase SPOs parallel layering and magmatic CPOs vary dramatically in strength over just 4.5 m of core. Plagioclase grains are relatively equant (aspect ratios < 1:2:4), wrap around large cpx oikocrysts, and exhibit fewer dislocation creep textures than the PD gabbros. These observations perhaps suggest primary crystal accumulation rather than bulk strain/flow. The similar mineralogy and textures of these samples to those from the Rum layered intrusion suggest HD U1415I gabbros may have formed by mid-crust sill injection.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.V51D2069N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.V51D2069N"><span>Deep low-frequency earthquake activities during the failed magmatic eruptions of Mts. Iwate and Fuji, Japan</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakamichi, H.; Hamaguchi, H.; Ukawa, M.; Tanaka, S.; Ueki, S.; Nishimura, T.</p> <p>2008-12-01</p> <p>I review deep low-frequency earthquake (DLF) activities during the failed magmatic eruptions of Mts. Iwate and Fuji, Japan. Volcanic unrests at Mts. Iwate and Fuji were observed in 1998-1999 and 2000-2001, respectively. Several hundred DLFs occurred during the unrest at Mt. Iwate; the number of DLFs in a normal year is less than or equal to 10. The DLF activity at Mt. Fuji increased sharply during the period from September 2000 to May 2001. The frequency of DLFs at Mt. Fuji during the DLF swarm was 20 times higher than that during normal activity. The DLFs of Mts. Iwate and Fuji show non-DC source mechanisms and suggest fluid motion at the focal regions. The DLF hypocenters of Mt. Fuji defined an ellipsoid with a diameter of 5 km; their focal depths are 11-16 km. The ellipsoid was centered 3 km northeast of the summit, and its major axis was directed in the northwest-southeast direction. The center of the ellipsoid gradually migrated upward, and 2-3 km in the northwest direction during 1998-2001. The migration of the DLFs reflects the volcanic fluid migration associated with a northwest-southeast-oriented dike beneath Mt. Fuji. The DLFs of Mt. Iwate were located at intermediate depths (5-12 km) beneath the summit and at deep depths (31-37 km) in the regions located 10 km south and 10 km northeast of the summit. In April 1998, the frequency of DLFs increased five days before an increase in the occurrence of shallow volcanic earthquakes at Mt. Iwate. Hypocenter migration of the DLFs at intermediate depths was observed from April 1998 to September 1998. New fumarole activity in the western region of Mt. Iwate commenced in 1999. These observations indicate that DLFs at Mts. Fuji and Iwate have common features in their activities and source mechanisms. But, shallow volcanic activities at these two volcanoes were much different: strong shallow seismic activity and volcano inflations as well as a new formation of fumarolic area were observed at Mt. Iwate, while such shallow activities were not detected at Mt. Fuji. Although it is still unknown what mechanisms control their magma supply systems, we may say that activation of DLF beneath active volcanoes does not always accompany magma intrusions in the shallow volcano edifice.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.9535P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.9535P"><span>The 2001 Mt. Etna eruption: new constraints on the intrusive mechanism from ground deformation data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palano, Mimmo; González, Pablo J.</p> <p>2013-04-01</p> <p>The occurrence of seismic swarms beneath the SW flank of Mt. Etna, often observed just a few months before an eruption, has been considered as the fragile response to a magma intrusion (Bonanno et al., 2011 and reference therein). These intrusions and/or pressurization of deep magmatic bodies, have been able to significantly affect the seismic pattern within the volcano edifice, leading to a changes in the local stress field. For example, during the months preceding the 1991-1993 Mt. Etna eruption, shallow intense seismic swarms (4-6 km deep) occurring in the SW flank (e.g. Cocina et al., 1998), related to the magma intrusion before the eruption onset, were observed contemporaneously with a rotation of stress field of about 90°. A similar scenario was observed during January 1998, when a magma recharging phases induced a local rotation of stress tensor, forcing a buried fault zone located beneath the SW flank of Mt. Etna to slip as a right-lateral strike-slip fault (Bonanno et al., 2011). This fault system was forced to slip again, during late April 2001 (more than 200 events in less than 5 days; maximum Magnitude = 3.6) by the pressurization of the magmatic bodies feeding the July-August 2001 Mt. Etna eruption. Here we analyzed in detail the July-August 2001 Mt. Etna eruption as well as the dynamics preceding this event, by using a large dataset of geodetic data (GPS and synthetic aperture radar interferometry) collected between July 2000 and August 2001. References Cocina, O., Neri, G., Privitera, E. and Spampinato S., 1998. Seismogenic stress field beneath Mt. Etna South Italy and possible relationships with volcano-tectonic features. J. Volcanol. Geotherm. Res., 83, 335-348. Bonanno A., Palano M., Privitera E., Gresta S., Puglisi G., 2011. Magma intrusion mechanisms and redistribution of seismogenic stress at Mt. Etna volcano (1997-1998). Terra Nova, 23, 339-348, doi: 10.1111/j.1365-3121.2011.01019.x, 2011.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAESc.121..139H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAESc.121..139H"><span>Crustal structure across the post-spreading magmatic ridge of the East Sub-basin in the South China Sea: Tectonic significance</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>He, Enyuan; Zhao, Minghui; Qiu, Xuelin; Sibuet, Jean-Claude; Wang, Jian; Zhang, Jiazheng</p> <p>2016-05-01</p> <p>The 140-km wide last phase of opening of the South China Sea (SCS) corresponds to a N145° direction of spreading with rift features identified on swath bathymetric data trending N055° (Sibuet et al., 2016). These N055° seafloor spreading features of the East Sub-basin are cut across by a post-spreading volcanic ridge oriented approximately E-W in its western part (Zhenbei-Huangyan seamounts chain). The knowledge of the deep crustal structure beneath this volcanic ridge is essential to elucidate not only the formation and tectonic evolution of the SCS, but also the mechanism of emplacement of the post-spreading magmatism. We use air-gun shots recorded by ocean bottom seismometers to image the deep crustal structure along the N-S oriented G8G0 seismic profile, which is perpendicular to the Zhenbei-Huangyan seamounts chain but located in between the Zhenbei and Huangyan seamounts, where topographic changes are minimum. The velocity structure presents obvious lateral variations. The crust north and south of the Zhenbei-Huangyan seamounts chain is ca. 4-6 km in thickness and velocities are largely comparable with those of normal oceanic crust of Atlantic type. To the south, the Jixiang seamount with a 7.2-km thick crust, seems to be a tiny post-spreading volcanic seamount intruded along the former extinct spreading ridge axis. In the central part, a 1.5-km thick low velocity zone (3.3-3.7 km/s) in the uppermost crust is explained by the presence of extrusive rocks intercalated with thin sedimentary layers as those drilled at IODP Site U1431. Both the Jixiang seamount and the Zhenbei-Huangyan seamounts chain started to form by the intrusion of decompressive melt resulting from the N-S post-spreading phase of extension and intruded through the already formed oceanic crust. The Jixiang seamount probably formed before the emplacement of the E-W post-spreading seamounts chain.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tectp.621..132S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tectp.621..132S"><span>Petrology and geochemistry of mafic magmatic rocks from the Sarve-Abad ophiolites (Kurdistan region, Iran): Evidence for interaction between MORB-type asthenosphere and OIB-type components in the southern Neo-Tethys Ocean</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Saccani, Emilio; Allahyari, Khalil; Rahimzadeh, Bahman</p> <p>2014-05-01</p> <p>The Sarve-Abad (Sawlava) ophiolites crop out in the Main Zagros Thrust Zone and represent remnants of the Mesozoic southern Neo-Tethys Ocean that was located between the Arabian shield and Sanandaj-Sirjan continental block. They consist of several incomplete ophiolitic sequences including gabbroic bodies, a dyke complex, and pillow lava sequences. These rocks generally range from sub-alkaline to transitional character. Mineral chemistry and whole-rock geochemistry indicate that they have compositions akin to enriched-type mid-ocean ridge basalts (E-MORB) and plume-type MORB (P-MORB). Nonetheless, the different depletion degrees in heavy rare earth elements (HREE), which can be observed in both E-MORB like and P-MORB like rocks enable two main basic chemical types of rocks to be distinguished as Type-I and Type-II. Type-I rocks are strongly depleted in HREE (YbN < ~ 6), whereas Type-II rocks are moderately depleted in HREE (YbN > 9.0). Petrogenetic modeling shows that Type-I rocks originated from 7 to 16% polybaric partial melting of a MORB-type mantle source, which was significantly enriched by plume-type components. These rocks resulted from the mixing of variable fractions of melts generated in garnet-facies and the spinel-facies mantle. In contrast, Type-II rocks originated from 5 to 8% partial melting in the spinel-facies of a MORB-type source, which was moderately enriched by plume-type components. A possible tectono-magmatic model for the generation of the southern Neo-Tethys oceanic crust implies that the continental rift and subsequent oceanic spreading were associated with uprising of MORB-type asthenospheric mantle featuring plume-type component influences decreasing from deep to shallow mantle levels. These deep plume-type components were most likely inherited from Carboniferous mantle plume activity that was associated with the opening of Paleo-Tethys in the same area.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T33B4655L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T33B4655L"><span>Supercontinent break-up: Causes and consequences</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Z. X.</p> <p>2014-12-01</p> <p>Supercontinent break-up has most commonly been linked to plume or superplume events, and/or supercontinent thermal insulation, but precise mechanisms are yet to be worked out. Even less know is if and what roles other factors may play. Key factors likely include gravitational force due to the continental superswell driven by both the lower-mantle superplume and continental thermal insulation, mental convention driven by the superplume and individual plumes atop the superplume, assisted by thermal/magmatic weakening of the supercontinent interior (both plume heat and thermal insulation heat). In addition, circum-supercontinent slab downwelling may not only drive the formation of the antipodal superplumes (thus the break-up of the supercontinent), the likely roll-back of the subduction system would also create extension within the supercontinent, facilitating supercontinent break-up. Consequences of supercontinent break-up include long-term sea-level rise, climatic changes due to changes in ocean circulation pattern and carbon cycle, and biodiversification. It has long been demonstrated that the existence of the supercontinent Pangea corresponds to a long-term sea-level drop, whereas the break-up of the supercontinent corresponds to a long-term sea-level rise (170 m higher than it is today). A recent analysis of Neoproterozoic sedimentary facies illustrates that the time of Neoproterozoic supercontinent Rodinia corresponds to a low in the percentage of deep marine facies occurrence, whereas the time of Rodinia break-up corresponds to a significantly higher percentage of deep marine facies occurrence. The long-tern sea-level drop during supercontinent times were likely caused by both plume/superplume dynamic topography and an older mean age of the oceanic crust, whereas long-tern sea-level rise during supercontinent break-up (720-580 Ma for Rodinia and Late Jurassic-Cretaceous for Pangea) likely corresponds to an younger mean age of the oceanic crust, massive plume-induced magmatism in the oceans, and perhaps the effect of continents drifting away from a weakening sub-supercontinent superplume.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.457..173L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.457..173L"><span>Giant magmatic water reservoirs at mid-crustal depth inferred from electrical conductivity and the growth of the continental crust</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Laumonier, Mickael; Gaillard, Fabrice; Muir, Duncan; Blundy, Jon; Unsworth, Martyn</p> <p>2017-01-01</p> <p>The formation of the continental crust at subduction zones involves the differentiation of hydrous mantle-derived magmas through a combination of crystallization and crustal melting. However, understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs. Here we report new high-pressure electrical conductivity and petrological experiments on hydrated andesitic melt from Uturuncu volcano on the Bolivian Altiplano. By applying our results to regional magnetotelluric data, we show that giant conductive anomalies at mid-crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents (≥8 wt.% H2O). Below Uturuncu, the Altiplano-Puna Magma Body (APMB) displays an electrical conductivity that requires high water content (up to 10 wt.%) dissolved in the melt based on crystal-liquid equilibria and melt H2O solubility experiments. Such a super-hydrous andesitic melt must constitute about 10% of the APMB, the remaining 90% being a combination of magmatic cumulates and older crustal rocks. The crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid-crust, resulting in decompression-induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation. Similar high conductivity features are observed beneath the Cascades volcanic arc and Taupo Volcanic Zone. This suggests that large amounts of water in super-hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust. One Sentence Summary: Geophysical, laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the Central Andes, Cascades and Taupo Volcanic Zone image the ponding of super-hydrous andesitic melts which contributes to the growth of continental crust.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.1381P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.1381P"><span>Discussion on final rifting evolution and breakup : insights from the Mid Norwegian - North East Greenland rifted system</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peron-Pinvidic, Gwenn; Terje Osmundsen, Per</p> <p>2016-04-01</p> <p>In terms of rifted margin studies, the characteristics of the distal and outer domains are among the today's most debated questions. The architecture and composition of deep margins are rarely well constrained and hence little understood. Except from in a handful number of cases (eg. Iberia-Newfoundland, Southern Australia, Red Sea), basement samples are not available to decipher between the various interpretations allowed by geophysical models. No consensus has been reached on the basement composition, tectonic structures, sedimentary geometries or magmatic content. The result is that non-unique end-member interpretations and models are still proposed in the literature. So, although these domains mark the connection between continents and oceans, and thus correspond to unique stages in the Earth's lithospheric life cycle, their spatial and temporal evolution are still unresolved. The Norwegian-Greenland Sea rift system represents an exceptional laboratory to work on questions related to rifting, rifted margin formation and sedimentary basin evolution. It has been extensively studied for decades by both the academic and the industry communities. The proven and expected oil and gas potentials led to the methodical acquisition of world-class geophysical datasets, which permit the detailed research and thorough testing of concepts at local and regional scales. This contribution is issued from a three years project funded by ExxonMobil aiming at better understanding the crustal-scale nature and evolution of the Norwegian-Greenland Sea. The idea was to take advantage of the data availability on this specific rift system to investigate further the full crustal conjugate scale history of rifting, confronting the various available datasets. In this contribution, we will review the possible structural and sedimentary geometries of the distal margin, and their connection to the oceanic domain. We will discuss the definition of 'breakup' and introduce a first order conceptual model that proposes a combined influence of tectonic and magmatic processes on the outbuilding of the distal, outer and oceanic domains.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMDI23B2619H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMDI23B2619H"><span>The PROTEUS Experiment: Active Source Seismic Imaging of the Crustal Magma Plumbing Structure of the Santorini Arc Volcano</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hooft, E. E. E.; Morgan, J. V.; Nomikou, P.; Toomey, D. R.; Papazachos, C. V.; Warner, M.; Heath, B.; Christopoulou, M. E.; Lampridou, D.; Kementzetzidou, D.</p> <p>2016-12-01</p> <p>The goal of the PROTEUS seismic experiment (Plumbing Reservoirs Of The Earth Under Santorini) is to examine the entire crustal magma plumbing system beneath a continental arc volcano and determine the magma geometry and connections throughout the crust. These physical parameters control magma migration, storage, and eruption and inform the question of how physical and chemical processing of magma at arc volcanoes forms the andesitic rock compositions that dominate the lower continental crust. These physical parameters are also important to understand volcanic-tectonic interactions and geohazards. Santorini is ideal for these goals because the continental crust has been thinned by extension and so the deep magmatic system is more accessible, also it is geologically well studied. Since the volcano is a semi-submerged, it was possible to collect a unique 3D marine-land active source seismic dataset. During the PROTEUS experiment in November-December of 2015, we recorded 14,300 marine sound sources from the US R/V Langseth on 89 OBSIP short period ocean bottom seismometers and 60 German and 5 Greek land seismometers. The experiment was designed for high-density spatial sampling of the seismic wavefield to allow us to apply two state-of-the-art 3D inversion methods: travel time tomography and full waveform inversion. A preliminary travel time tomography model of the upper crustal seismic velocity structure of the volcano and surrounding region is presented in an accompanying poster. We also made marine geophysical maps of the seafloor using multi-beam bathymetry and of the gravity and magnetic fields. The new seafloor map reveals the detailed structure of the major fault system between Santorini and Amorgos, of associated landslides, and of newly discovered volcanic features. The PROTEUS project will provide new insights into the structure of the whole crustal magmatic system of a continental arc volcano and its evolution within the surrounding tectonic setting.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P43C2115B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P43C2115B"><span>Floor-Fractured Craters on Ceres and Implications for Internal Composition and Processes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buczkowski, D.; Schenk, P.; Scully, J. E. C.; Park, R. S.; Preusker, F.; Raymond, C. A.; Russell, C. T.</p> <p>2016-12-01</p> <p>Several of the impact craters on Ceres have patterns of fractures on their floors. These fractures appear similar to those found within a class of lunar craters referred to as Floor-Fractured Craters (FFCs) [1]. Lunar FFCs are characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures, and have been classified into crater classes, Types 1 through 6, based on their morphometric properties [1,2]. Models for their formation have included both floor uplift due to magmatic intrusion below the crater or floor shallowing due to viscous relaxation. However, the observation that the depth versus diameter (d/D) relationship of the FFCs is distinctly shallower than the same association for other lunar craters supports the hypotheses that the floor fractures form due to shallow magmatic intrusion under the crater [2]. We have cataloged the Ceres FFCs according to the classification scheme designed for the Moon. Large (>50 km) Ceres FFCs are most consistent with Type 1 lunar FFCs, having deep floors, central peaks, wall terraces, and radial and/or concentric fractures. Smaller craters on Ceres are more consistent with Type 4 lunar FFCs, having less-pronounced floor fractures and v-shaped moats separating the wall scarp from the crater interior. An analysis of the d/D ratio for Ceres craters shows that, like lunar FFCs, the Ceres FFCs are anomalously shallow. This suggests that the fractures on the floor of Ceres FFCs may be due the intrusion of a low-density material below the craters that is uplifting their floors. While on the Moon the intrusive material is hypothesized to be silicate magma, this is unlikely for Ceres. However, a cryovolcanic extrusive edifice has been identified on Ceres [3], suggesting that cryomagmatic intrusions could be responsible for the formation of the Ceres FFCs. References: [1] Schultz P. (1976) Moon, 15, 241-273 [2] Jozwiak L.M. et al (2015) JGR 117, doi: 10.1029/2012JE004134 [3] Ruesch O. et al (2016) Science</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhDT.......103L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhDT.......103L"><span>Compositional Zoning in Kilauea Olivine: A Geochemical Tool for Investigating Magmatic Processes at Hawaiian Volcanoes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lynn, Kendra J.</p> <p></p> <p>Olivine compositions and zoning patterns have been widely used to investigate the evolution of magmas from their source to the Earthfs surface. Modeling the formation of compositional zoning in olivine crystals has been used to retrieve timescales of magma residence, mixing, and transit. This dissertation is composed of three projects that apply diffusion chronometry principles to investigate how zoned olivine phenocrysts record magmatic processes at Hawaiian volcanoes. Olivine phenocrysts from K.lauea, the most active and thoroughly studied volcano in Hawaiei, are used to develop a better understanding of how Hawaiian olivine crystals record magmatic histories. This work begins by examining how crustal processes such as magma mixing and diffusive reequilibration can modify olivine compositions inherited from growth in parental magmas (Chapter 2). Diffusive re-equilibration of Fe-Mg, Mn, and Ni in olivine crystals overprints the chemical relationships inherited during growth, which strongly impacts interpretations about mantle processes and source components. These issues are further complicated by sectioning effects, where small (400 ƒEm along the c-axis) olivine crystals are more susceptible to overprinting compared to large (800 ƒEm) crystals. Olivine compositions and zoning patterns are then used to show that magmas during K.laueafs explosive Keanak.koei Tephra period (1500-1823 C.E.) were mixed and stored in crustal reservoirs for weeks to months prior to eruption (Chapter 3). Fe-Mg disequilibrium between olivine rims and their surrounding glasses show that a late-stage mixing event likely occurred hours to days prior to eruption, but the exact timescale is difficult to quantify using Fe-Mg and Ni diffusion. Lithium, a rapidly diffusing trace element in olivine, is modeled for the first time in a natural volcanic system to quantify this late-stage, short-duration mixing event (Chapter 4). Lithium zoning in olivine records both growth and diffusion processes that are affected by charge balancing requirements with growth zoning of P. Timescales from modeling diffuse Li zoning range from a few hours to three weeks, but most record short storage durations of four days or less. These timescales correspond to short storage periods after mixing. Thus, Li probably records the final perturbation of a magmatic system prior to eruption.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70189738','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70189738"><span>New insights into the Kawah Ijen hydrothermal system from geophysical data</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Caudron, Corentin; Mauri, G.; Williams-Jones, Glyn; Lecocq, Thomas; Syahbana, Devy Kamil; de Plaen, Raphael; Peiffer, Loic; Bernard, Alain; Saracco, Ginette</p> <p>2017-01-01</p> <p>Volcanoes with crater lakes and/or extensive hydrothermal systems pose significant challenges with respect to monitoring and forecasting eruptions, but they also provide new opportunities to enhance our understanding of magmatic–hydrothermal processes. Their lakes and hydrothermal systems serve as reservoirs for magmatic heat and fluid emissions, filtering and delaying the surface expressions of magmatic unrest and eruption, yet they also enable sampling and monitoring of geochemical tracers. Here, we describe the outcomes of a highly focused international experimental campaign and workshop carried out at Kawah Ijen volcano, Indonesia, in September 2014, designed to answer fundamental questions about how to improve monitoring and eruption forecasting at wet volcanoes.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001JAfES..32..655E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001JAfES..32..655E"><span>Les granitoïdes néoprotérozoïques de Khzama, Anti-Atlas central, Maroc: marqueurs de l'évolution d'un magmatisme d'arc à un magmatisme alcalineNeoproterozoic granitoids from Khzama, central Anti-Atlas, Morocco: evolution markers from arc magmatism to alkaline magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>El-Khanchaoui, T.; Lahmam, M.; El-Boukhari, A.; El-Beraaouz, H.</p> <p>2001-05-01</p> <p>Petrological study and zircon typology provide important information that is related to the classification and genesis of Neoproterozoic granitoids in the Khzama area (northeast Siroua). The Pan-African granitoids show a transition from island-arc magmatism to alkaline magmatism. A space and time zonation of magmatism from the north to the south is evident. Early Pan-African granitoids were generated from various magma sources through different petrogenetic mechanisms. The first association corresponds to the low-K calc-alkaline plutons of Ait Nebdas, the second one correponds to high-K calc-alkaline post-collisional granites (Tamassirte-Tiferatine and Ifouachguel). Finally, shoshonitic magmatism (Irhiri) ends the magmatic evolution of the region. Thus, the late Pan-African granitic plutonism began with calc-alkaline associations and ended with K-alkaline magmatism in a transtensional setting, heralding the onset of the Moroccan Palæozoic cycle.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024613','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024613"><span>Gunbarrel mafic magmatic event: A key 780 Ma time marker for Rodinia plate reconstructions</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Harlan, S.S.; Heaman, L.; LeCheminant, A.N.; Premo, W.R.</p> <p>2003-01-01</p> <p>Precise U-Pb baddeleyite dating of mafic igneous rocks provides evidence for a widespread and synchronous magmatic event that extended for >2400 km along the western margin of the Neoproterozoic Laurentian craton. U-Pb baddeleyite analyses for eight intrusions from seven localities ranging from the northern Canadian Shield to northwestern Wyoming-southwestern Montana are statistically indistinguishable and yield a composite U-Pb concordia age for this event of 780.3 ?? 1.4 Ma (95% confidence level). This 780 Ma event is herein termed the Gunbarrel magmatic event. The mafic magmatism of the Gunbarrel event represents the largest mafic dike swarm yet identified along the Neoproterozoic margin of Laurentia. The origin of the mafic magmatism is not clear, but may be related to mantle-plume activity or upwelling asthenosphere leading to crustal extension accompanying initial breakup of the supercontinent Rodinia and development of the proto-Pacific Ocean. The mafic magmatism of the Gunbarrel magmatic event at 780 Ma predates the voluminous magmatism of the 723 Ma Franklin igneous event of the northwestern Canadian Shield by ???60 m.y. The precise dating of the extensive Neoproterozoic Gunbarrel and Franklin magmatic events provides unique time markers that can ultimately be used for robust testing of Neoproterozoic continental reconstructions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Natur.545..332R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Natur.545..332R"><span>Continental crust formation on early Earth controlled by intrusive magmatism</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rozel, A. B.; Golabek, G. J.; Jain, C.; Tackley, P. J.; Gerya, T.</p> <p>2017-05-01</p> <p>The global geodynamic regime of early Earth, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean mantle temperature and more intense juvenile magmatism than in the present-day Earth, two crust-mantle interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism and the “Plutonic squishy lid” tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce Earth-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean Earth operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JGRB..123..941D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JGRB..123..941D"><span>Enhanced Mantle Upwelling/Melting Caused Segment Propagation, Oceanic Core Complex Die Off, and the Death of a Transform Fault: The Mid-Atlantic Ridge at 21.5°N</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dannowski, A.; Morgan, J. P.; Grevemeyer, I.; Ranero, C. R.</p> <p>2018-02-01</p> <p>Crustal structure provides the key to understand the interplay of magmatism and tectonism, while oceanic crust is constructed at Mid-Ocean Ridges (MORs). At slow spreading rates, magmatic processes dominate central areas of MOR segments, whereas segment ends are highly tectonized. The TAMMAR segment at the Mid-Atlantic Ridge (MAR) between 21°25'N and 22°N is a magmatically active segment. At 4.5 Ma this segment started to propagate south, causing the termination of the transform fault at 21°40'N. This stopped long-lived detachment faulting and caused the migration of the ridge offset to the south. Here a segment center with a high magmatic budget has replaced a transform fault region with limited magma supply. We present results from seismic refraction profiles that mapped the crustal structure across the ridge crest of the TAMMAR segment. Seismic data yield crustal structure changes at the segment center as a function of melt supply. Seismic Layer 3 underwent profound changes in thickness and became rapidly thicker 5 Ma. This correlates with the observed "Bull's Eye" gravimetric anomaly in that region. Our observations support a temporal change from thick lithosphere with oceanic core complex formation and transform faulting to thin lithosphere with focused mantle upwelling and segment growth. Temporal changes in crustal construction are connected to variations in the underlying mantle. We propose that there is a link between the neighboring segments at a larger scale within the asthenosphere, to form a long, highly magmatically active macrosegment, here called the TAMMAR-Kane Macrosegment.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70137844','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70137844"><span>Yellowstone plume trigger for Basin and Range extension and emplacement of the Nevada-Columbia Basin magmatic belt</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Camp, Victor E; Pierce, Kenneth L.; Morgan Morzel, Lisa Ann</p> <p>2015-01-01</p> <p>Widespread extension began across the northern and central Basin and Range Province at 17–16 Ma, contemporaneous with magmatism along the Nevada–Columbia Basin magmatic belt, a linear zone of dikes and volcanic centers that extends for >1000 km, from southern Nevada to the Columbia Basin of eastern Washington. This belt was generated above an elongated sublithospheric melt zone associated with arrival of the Yellowstone mantle plume, with a north-south tabular shape attributed to plume ascent through a propagating fracture in the Juan de Fuca slab. Dike orientation along the magmatic belt suggests an extension direction of 245°–250°, but this trend lies oblique to the regional extension direction of 280°–300° during coeval and younger Basin and Range faulting, an ∼45° difference. Field relationships suggest that this magmatic trend was not controlled by regional stress in the upper crust, but rather by magma overpressure from below and forceful dike injection with an orientation inherited from a deeper process in the sublithospheric mantle. The southern half of the elongated zone of mantle upwelling was emplaced beneath a cratonic lithosphere with an elevated surface derived from Late Cretaceous to mid-Tertiary crustal thickening. This high Nevadaplano was primed for collapse with high gravitational potential energy under the influence of regional stress, partly derived from boundary forces due to Pacific–North American plate interaction. Plume arrival at 17–16 Ma resulted in advective thermal weakening of the lithosphere, mantle traction, delamination, and added buoyancy to the northern and central Basin and Range. It was not the sole cause of Basin and Range extension, but rather the catalyst for extension of the Nevadaplano, which was already on the verge of regional collapse.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70073370','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70073370"><span>Late Cenozoic crustal extension and magmatism, southern Death Valley region, California</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Calzia, J.P.; Rämö, O.T.</p> <p>2000-01-01</p> <p>The late Cenozoic geologic history of the southern Death Valley region is characterized by coeval crustal extension and magamatism. Crustal extension is accommodated by numerous listric and planar normal faults as well as right- and left-lateral strike slip faults. The normal faults sip 30°-50° near the surface and flatten and merge leozoic miogeoclinal rocks; the strike-slip faults act as tear faults between crustal blocks that have extended at different times and at different rates. Crustal extension began 13.4-13.1 Ma and migrated northwestward with time; undeformed basalt flows and lacustrine deposits suggest that extension stopped in this region (but continued north of the Death Valley graben) between 5 and 7 Ma. Estimates of crustal extension in this region vary from 30-50 percent to more than 100 percent. Magmatic rocks syntectonic with crustal extension in the southern Death Valley region include 12.4-6.4 Ma granitic rocks as well as bimodal 14.0-4.0 Ma volcanic rocks. Geochemical and isotopic evidence suggest that the granitic rocks get younger and less alkalic from south to north; the volcanic rocks become more mafic with less evidence of crustal interaction as they get younger. The close spatial and temporal relation between crustal extension and magmatism suggest a genetic and probably a dynamic relation between these geologic processes. We propose a rectonic-magmatic model that requires heat to be transported into the crust by mantle-derived mafic magmas. These magmas pond at lithologic or rheologic boundaries, begin the crystallize, and partially melt the surrounding crustal rocks. With time, the thermally weakened crust is extended (given a regional extensional stress field) concurrent with granitic magmatism and bimodal volcanism.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.6720K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.6720K"><span>Magmatism and deformation during continental breakup</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keir, Derek</p> <p>2013-04-01</p> <p>The rifting of continents and the transition to seafloor spreading is characterised by extensional faulting and thinning of the lithosphere, and is sometimes accompanied by voluminous intrusive and extrusive magmatism. In order to understand how these processes develop over time to break continents apart, we have traditionally relied on interpreting the geological record at the numerous fully developed, ancient rifted margins around the world. In these settings, however, it is difficult to discriminate between different mechanisms of extension and magmatism because the continent-ocean transition is typically buried beneath thick layers of volcanic and sedimentary rocks, and the tectonic and volcanic activity that characterised breakup has long-since ceased. Ongoing continental breakup in the African and Arabian rift systems offers a unique opportunity to address these problems because it exposes several sectors of tectonically active rift sector development spanning the transition from embryonic continental rifting in the south to incipient seafloor spreading in the north. Here I synthesise exciting, multidisciplinary observational and modelling studies using geophysical, geodetic, petrological and numerical techniques that uniquely constrain the distribution, time-scales, and interactions between extension and magmatism during the progressive breakup of the African Plate. This new research has identified the previously unrecognised role of rapid and episodic dike emplacement in accommodating a large proportion of extension during continental rifting. We are now beginning to realise that changes in the dominant mechanism for strain over time (faulting, stretching and magma intrusion) impact dramatically on magmatism and rift morphology. The challenge now is to take what we're learned from East Africa and apply it to the rifted margins whose geological record documents breakup during entire Wilson Cycles.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70033591','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70033591"><span>Textural, mineralogical and stable isotope studies of hydrothermal alteration in the main sulfide zone of the Great Dyke, Zimbabwe and the precious metals zone of the Sonju Lake Intrusion, Minnesota, USA</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Li, C.; Ripley, E.M.; Oberthur, T.; Miller, J.D.; Joslin, G.D.</p> <p>2008-01-01</p> <p>Stratigraphic offsets in the peak concentrations of platinum-group elements (PGE) and base-metal sulfides in the main sulfide zone of the Great Dyke and the precious metals zone of the Sonju Lake Intrusion have, in part, been attributed to the interaction between magmatic PGE-bearing base-metal sulfide assemblages and hydrothermal fluids. In this paper, we provide mineralogical and textural evidence that indicates alteration of base-metal sulfides and mobilization of metals and S during hydrothermal alteration in both mineralized intrusions. Stable isotopic data suggest that the fluids involved in the alteration were of magmatic origin in the Great Dyke but that a meteoric water component was involved in the alteration of the Sonju Lake Intrusion. The strong spatial association of platinum-group minerals, principally Pt and Pd sulfides, arsenides, and tellurides, with base-metal sulfide assemblages in the main sulfide zone of the Great Dyke is consistent with residual enrichment of Pt and Pd during hydrothermal alteration. However, such an interpretation is more tenuous for the precious metals zone of the Sonju Lake Intrusion where important Pt and Pd arsenides and antimonides occur as inclusions within individual plagioclase crystals and within alteration assemblages that are free of base-metal sulfides. Our observations suggest that Pt and Pd tellurides, antimonides, and arsenides may form during both magmatic crystallization and subsolidus hydrothermal alteration. Experimental studies of magmatic crystallization and hydrothermal transport/deposition in systems involving arsenides, tellurides, antimonides, and base metal sulfides are needed to better understand the relative importance of magmatic and hydrothermal processes in controlling the distribution of PGE in mineralized layered intrusions of this type. ?? Springer-Verlag 2007.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28482358','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28482358"><span>Continental crust formation on early Earth controlled by intrusive magmatism.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rozel, A B; Golabek, G J; Jain, C; Tackley, P J; Gerya, T</p> <p>2017-05-18</p> <p>The global geodynamic regime of early Earth, which operated before the onset of plate tectonics, remains contentious. As geological and geochemical data suggest hotter Archean mantle temperature and more intense juvenile magmatism than in the present-day Earth, two crust-mantle interaction modes differing in melt eruption efficiency have been proposed: the Io-like heat-pipe tectonics regime dominated by volcanism and the "Plutonic squishy lid" tectonics regime governed by intrusive magmatism, which is thought to apply to the dynamics of Venus. Both tectonics regimes are capable of producing primordial tonalite-trondhjemite-granodiorite (TTG) continental crust but lithospheric geotherms and crust production rates as well as proportions of various TTG compositions differ greatly, which implies that the heat-pipe and Plutonic squishy lid hypotheses can be tested using natural data. Here we investigate the creation of primordial TTG-like continental crust using self-consistent numerical models of global thermochemical convection associated with magmatic processes. We show that the volcanism-dominated heat-pipe tectonics model results in cold crustal geotherms and is not able to produce Earth-like primordial continental crust. In contrast, the Plutonic squishy lid tectonics regime dominated by intrusive magmatism results in hotter crustal geotherms and is capable of reproducing the observed proportions of various TTG rocks. Using a systematic parameter study, we show that the typical modern eruption efficiency of less than 40 per cent leads to the production of the expected amounts of the three main primordial crustal compositions previously reported from field data (low-, medium- and high-pressure TTG). Our study thus suggests that the pre-plate-tectonics Archean Earth operated globally in the Plutonic squishy lid regime rather than in an Io-like heat-pipe regime.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70011685','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70011685"><span>Pleistocene high-silica rhyolites of the Coso volcanic field, Inyo County, California.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bacon, C.R.; Macdonald, R.; Smith, R.L.; Baedecker, P.A.</p> <p>1981-01-01</p> <p>The high-silica rhyolite domes and lava flows of the bimodal Pleistocene part of the Coso volcanic field provide an example of the early stages of evolution of a silicic magmatic system of substantial size and longevity. Major and trace element compositions are consistent with derivation from somewhat less silicic parental material by liquid state differentiation processes in compositionally and thermally zoned magmatic systems. Seven chemically homogeneous eruptive groups can be distinguished on the basis of trace element and K/Ar data. The oldest two groups are volumetrically minor and geochemically distinct from the younger groups, all five of which appear to have evolved from the same magmatic system. Erupted volume-time relations suggest that small amounts of magma were bled from the top of a silicic reservoir at a nearly constant long-term rate over the last 0.24Ma. The interval of repose between eruptions appears to be proportional to the volume of the preceding eruptive group. This relationship suggests that eruptions take place when some parameter which increases at a constant rate reaches a critical value; this parameter may be extensional strain accumulated in roof rocks. Extension of the lithosphere favors intrusion of basalt into the crust, attendant partial melting, and maintenance of a long-lived silicic magmatic system. The Coso silicic system may contain a few hundred cubic kilometers of magma. The Coso magmatic system may eventually have the potential for producing voluminous pyroclastic eruptions if the safety valve provided by rapid crustal extension becomes inadequate to 1) defuse the system through episodic removal of volatile-rich magma from its top and 2) prohibit migration of the reservoir to a shallow crustal level.-from Authors</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSAES..80..174D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSAES..80..174D"><span>Geochronology and thermochronology of the gneisses of the Brasiliano/Pan-African Araguaia Belt: Records of exhumation of West Gondwana and Pangea break up</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dias, A. N. C.; Moura, C. A. V.; Milhomem Neto, J. M.; Chemale, F., Jr.; Girelli, T. J.; Masuyama, K. M.</p> <p>2017-12-01</p> <p>The 1200 km long Araguaia Belt, central-north Brazil, was formed as a result of the Neoproterozoic (Ediacaran) to Early Cambrian collage of West Gondwana and has several dome structures in whose nuclei crop out basement inliers of Archean and Paleoproterozoic orthogneisses. Thus, the orthogneisses from Lontra, Cocalândia, Colméia and Cantão dome structures were selected for fission-track thermochronology and U-Pb double dating. Three Archean magmatic episodes ranging from 2830.9 ± 6.9 Ma (Colméia dome) to 2905 ± 5.1 Ma (Lontra dome) and one Paleoproterozoic magmatic event at 1835 ± 31 Ma (Cantão dome) are recognized by U-Pb LA-MC-ICP-MS zircon dating. Fission-track thermochronology in zircon permitted to identify three well-defined age populations, which correspond to major regional geological events. The older population (489 ± 15 Ma to 498±8Ma) records the exhumation process and the orogenetic collapse of the Araguaia Belt. The intermediate population (331 ± 8 Ma to 345 ± 13 Ma) is related to the Gondwanides orogeny which affected the western margin of Gondwana and therefore the interior of South American. Finally, the younger fission track ages (197 ± 3 Ma, 197 ± 4 Ma, 198 ± 2 Ma and 208 ± 10 Ma) reflect crustal heating around 200 Ma, which is associated with the Lower Jurassic Mosquito tholeiitic magmatism and extended the influence of the Central Atlantic Magmatic Province to the Araguaia Belt. This mafic magmatism has been recognized in different regions of the South American and was an important source of heat for hydrocarbon generation in some Paleozoic intracratonic basins.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSAES..80..316O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSAES..80..316O"><span>Zircon U-Pb ages and Hf isotopes for the Diablillos Intrusive Complex, Southern Puna, Argentina: Crustal evolution of the Lower Paleozoic Orogen, Southwestern Gondwana margin</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ortiz, Agustín; Hauser, Natalia; Becchio, Raúl; Suzaño, Néstor; Nieves, Alexis; Sola, Alfonso; Pimentel, Marcio; Reimold, Wolf</p> <p>2017-12-01</p> <p>The evolution of the rocks of the Lower Paleozoic Orogen in Puna, at the Southwestern Gondwana margin, has been widely debated. In particular, the scarce amount of geological and geochemical data available for the Diablillos Intrusive Complex, Eastern Magmatic Belt, Southern Puna, require a further study for new evidence towards the understanding of sources, magmatic processes and emplacement of magmas, in order to better comprehend the crustal evolution in this setting. We present new combined U-Pb and Hf isotope analyses on zircon by LA-MC-ICP-MS from monzogranite, granodiorite and diorite rocks of the Diablillos Intrusive Complex. We obtained 206Pb/238U concordant weighted average ages of 517 ± 3 Ma and 515 ± 6 Ma for the monzogranite and diorite, respectively, and a concordant age of 521 ± 4 Ma for the granodiorite. These ages permit to constrain the climax of magmatic activity in the Diablillos Complex around ∼515-520 Ma, while the emplacement of the complex took place between ∼540 Ma and 490 Ma (representing a ca. 50 Ma magmatic event). Major and trace element data, initial 87Sr/86Sr values varying from 0.70446 to 0.71278, positive and negative ɛNd(t) values between +2.5 and -4, as well as ɛHf(t) for zircon data between + 3 and -3 indicate that the analyzed samples represent contaminated magmas. The ɛHf(t) and the ɛNd(t) values for this complex specify that these rocks are derived from interaction of a dominant Mesoproterozoic crystalline and/or a metasedimentary source and juvenile mantle-derived magmas, with a TDM model age range of ∼1.2-1.5 Ga, with later reworking during lower Paleozoic times. The combined data obtained in this contribution together with previous data, allow us to suggest that the formation of the Eastern Magmatic Belt of the Puna was part of a long-lived magmatic event during Early Paleozoic times. Whereby the granitoids of the Eastern Magmatic Belt formed through intra-crustal recycling at an active continental margin, with minor contributions from juvenile material in the back-arc setting.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.302..405K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.302..405K"><span>Early Permian intrusions of the Alai range: Understanding tectonic settings of Hercynian post-collisional magmatism in the South Tien Shan, Kyrgyzstan</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Konopelko, D.; Wilde, S. A.; Seltmann, R.; Romer, R. L.; Biske, Yu. S.</p> <p>2018-03-01</p> <p>We present geochemical and Sr-Nd-Pb-Hf isotope data as well as the results of single grain U-Pb zircon dating for ten granitoid and alkaline intrusions of the Alai segment of Kyrgyz South Tien Shan (STS). The intrusions comprise four geochemically contrasting series or suites, including (1) I-type and (2) shoshonitic granitoids, (3) peraluminous granitoids including S-type leucogranites and (4) alkaline rocks and carbonatites, closely associated in space. New geochronological data indicate that these diverse magmatic series of the Alai segment formed in a post-collisional setting. Five single grain U-Pb zircon ages in the range 287-281 Ma, in combination with published ages, define the main post-collisional magmatic pulse at 290-280 Ma, which is similar to ages of post-collisional intrusions elsewhere in the STS. An age of 287 ± 4 Ma, obtained for peraluminous graniodiorite of the Liayliak massif, emplaced in amphibolite-facies metamorphic rocks of the Zeravshan-Alai block, is indistinguishable from ca. 290 Ma age of peraluminous granitoids emplaced coevally with Barrovian-type metamorphism in the Garm block, located ca. 40 km south-west of the research area. The Sr-Nd-Pb-Hf isotopic compositions of the studied intrusions are consistent with the reworking of crustal material with 1.6-1.1 Ga average crustal residence times, indicating the formation of the Alai segment on a continental basement with Mesoproterozoic or older crust. The pattern of post-collisional magmatism in the Alai segment, characterized by emplacement of I-type and shoshoninitic granitoids in combination with coeval Barrovian-type metamorphism, is markedly different from the pattern of post-collisional magmatism in the adjacent Kokshaal segment of the STS with predominant A-type granitoids that formed on a former passive margin of the Tarim Craton. We suggest that during the middle-late Carboniferous the Alai segment probably comprised a microcontinent with Precambrian basement located between the Turkestan Ocean to the north and an inferred oceanic basin to the south, where the evidence of supra-subduction magmatism was largely destroyed by subsequent tectonic processes. In this scenario, after collision, the position of the Alai microcontinent between two major sutures enabled delamination of its lithospheric mantle, which resulted in production of diverse post-collisional magmatic series by interaction of ascending asthenospheric material with lithospheric mantle and various crustal protoliths.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024964','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024964"><span>Relationship of epithermal gold deposits to large-scale fractures in northern Nevada</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Ponce, D.A.; Glen, J.M.G.</p> <p>2002-01-01</p> <p>Geophysical maps of northern Nevada reveal at least three and possibly six large-scale arcuate features, one of which corresponds to the northern Nevada rift that possibly extends more than 1,000 km from the Oregon- Idaho border to southern Nevada. These features may reflect deep discontinuities within the earth's crust, possibly related to the impact of the Yellowstone hot spot. Because mid-Miocene epithermal gold deposits have been shown to correlate with the northern Nevada rift, we investigate the association of other epithermal gold deposits to other similar arcuate features in northern Nevada. Mid-Miocene and younger epithermal gold- silver deposits also occur along two prominent aeromagnetic anomalies west of the northern Nevada rift. Here, we speculate that mid-Miocene deposits formed along deep fractures in association with mid-Miocene rift- related magmatism and that younger deposits preferentially followed these preexisting features. Statistical analysis of the proximity of epithermal gold deposits to these features suggests that epithermal gold deposits in northern Nevada are spatially associated with large-scale crustal features interpreted from geophysical data.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2047.6009C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2047.6009C"><span>Perspectives on Magmatic Differentiation of Mercury</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Charlier, B.; Namur, O.; Cartier, C.</p> <p>2018-05-01</p> <p>Silicate/metal liquid immiscibility, crystallization of a magma ocean, partial melting of mantle rocks, and surface crystallization have shaped Mercury as we know it today. We review these processes based on high-T experiments at reducing conditions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70024918','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70024918"><span>Interaction of sea water and lava during submarine eruptions at mid-ocean ridges</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Perfit, M.R.; Cann, J.R.; Fornari, D.J.; Engels, J.; Smith, D.K.; Ridley, W.I.; Edwards, M.H.</p> <p>2003-01-01</p> <p>Lava erupts into cold sea water on the ocean floor at mid-ocean ridges (at depths of 2,500 m and greater), and the resulting flows make up the upper part of the global oceanic crust. Interactions between heated sea water and molten basaltic lava could exert significant control on the dynamics of lava flows and on their chemistry. But it has been thought that heating sea water at pressures of several hundred bars cannot produce significant amounts of vapour and that a thick crust of chilled glass on the exterior of lava flows minimizes the interaction of lava with sea water. Here we present evidence to the contrary, and show that bubbles of vaporized sea water often rise through the base of lava flows and collect beneath the chilled upper crust. These bubbles of steam at magmatic temperatures may interact both chemically and physically with flowing lava, which could influence our understanding of deep-sea volcanic processes and oceanic crustal construction more generally. We infer that vapour formation plays an important role in creating the collapse features that characterize much of the upper oceanic crust and may accordingly contribute to the measured low seismic velocities in this layer.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018Litho.302..359D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018Litho.302..359D"><span>A model for Nb-Zr-REE-Ga enrichment in Lopingian altered alkaline volcanic ashes: Key evidence of H-O isotopes</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dai, Shifeng; Nechaev, Victor P.; Chekryzhov, Igor Yu.; Zhao, Lixin; Vysotskiy, Sergei V.; Graham, Ian; Ward, Colin R.; Ignatiev, Alexander V.; Velivetskaya, Tatyana A.; Zhao, Lei; French, David; Hower, James C.</p> <p>2018-03-01</p> <p>Clay-altered volcanic ash with highly-elevated concentrations of Nb(Ta), Zr(Hf), rare earth elements (REE), and Ga, is a new type of critical metal deposit with high commercial prospects that has been discovered in Yunnan Province, southwest China. Previous studies showed that the volcanic ashes had been subjected to hydrothermal fluids, the nature of which, however, is not clear. Here we show that the volcanic ashes were originated from alkaline magmatism, followed by a continuous hydrothermal-weathering process. Heated meteoric waters, which were sourced from acidic rains and mixed with CO2 from degassing of the Emeishan plume, have caused partial, but widespread, acidic leaching of Nb, Ta, Zr, Hf, REE, and Ga into ground water and residual enrichment of these elements, along with Al and Ti, in the deeply altered rocks. Subsequent alteration occurring under cooler, neutral or alkaline conditions, caused by water-rock interaction, resulted in precipitation of the leached critical metals in the deposit. Polymetallic mineralization of similar origin may be found in other continental regions subjected to explosive alkaline volcanism associated with deep weathering in humid conditions.</p> </li> <li> <p><a target="_blank" rel="noopener noreferrer" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/29581539','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/29581539"><span>Slab narrowing in the Central Mediterranean: the Calabro-Ionian subduction zone as imaged by high resolution seismic tomography.</span></a></p> <p><a target="_blank" rel="noopener noreferrer" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Scarfì, L; Barberi, G; Barreca, G; Cannavò, F; Koulakov, I; Patanè, D</p> <p>2018-03-26</p> <p>A detailed 3D image of the Calabro-Ionian subduction system in the central Mediterranean was obtained by means of a seismic tomography, exploiting a large dataset of local earthquakes and computing algorithms able to build a dense grid of measure nodes. Results show that the slab is continuous below the southern sector of the Calabro-Peloritan Arc, but the deformation processes developing at its edges are leading to its progressive narrowing, influencing tectonics and magmatism at the surface, and with possible stress concentration in the tip zones. In the southwest, the deformation occurring at a free slab edge lead to propagation of a vertical lithospheric tear in the overriding plate, which extends along a NW-SE fault system (Aeolian-Tindari-Letojanni) up to about 30 km into the Ionian Sea; further southeast, the lithosphere appears only flexed and not broken yet. In the northeast, the slab seems to break progressively, parallel to the trench. Finally, northwest of Mt. Etna, the tomography highlights low V P that can be related to an upwelling of deep mantle material likely flowing laterally through a window opened by the complete slab detachment.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <div class="footer-extlink text-muted" style="margin-bottom:1rem; text-align:center;">Some links on this page may take you to non-federal websites. 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