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Sample records for magmatic sources setting

  1. Pyroxene megacrysts in Proterozoic anorthosites: Implications for tectonic setting, magma source and magmatic processes at the Moho

    NASA Astrophysics Data System (ADS)

    Bybee, G. M.; Ashwal, L. D.; Shirey, S. B.; Horan, M.; Mock, T.; Andersen, T. B.

    2014-03-01

    from which the anorthosites are derived. Modeling of these anorthositic magmas with MELTS indicates that their ultramafic cumulates would have sunk in the magma and been sequestered at the Moho, where they may have sunk deeper into the mantle resulting in large-scale compositional differentiation. The HAOMs thus represent a rare example of part of a cumulate assemblage that was carried to the upper crust during anorthosite emplacement and, together with the anorthosites, illustrate the dramatic influence that magma ponding and differentiation at the Moho has on residual magmas traveling towards the surface. The new geochronologic and isotopic data indicate that the magmas were derived by melting of the mantle, forming magmatic systems that could have been long-lived (e.g. 80-100 m.y.). A geologic setting that would fit these temporal constraints is a long-lived Andean-type margin.

  2. Copahue volcano and its regional magmatic setting

    USGS Publications Warehouse

    Varekamp, J C; Zareski, J E; Camfield, L M; Todd, Erin

    2016-01-01

    Copahue volcano (Province of Neuquen, Argentina) has produced lavas and strombolian deposits over several 100,000s of years, building a rounded volcano with a 3 km elevation. The products are mainly basaltic andesites, with the 2000–2012 eruptive products the most mafic. The geochemistry of Copahue products is compared with those of the main Andes arc (Llaima, Callaqui, Tolhuaca), the older Caviahue volcano directly east of Copahue, and the back arc volcanics of the Loncopue graben. The Caviahue rocks resemble the main Andes arc suite, whereas the Copahue rocks are characterized by lower Fe and Ti contents and higher incompatible element concentrations. The rocks have negative Nb-Ta anomalies, modest enrichments in radiogenic Sr and Pb isotope ratios and slightly depleted Nd isotope ratios. The combined trace element and isotopic data indicate that Copahue magmas formed in a relatively dry mantle environment, with melting of a subducted sediment residue. The back arc basalts show a wide variation in isotopic composition, have similar water contents as the Copahue magmas and show evidence for a subducted sedimentary component in their source regions. The low 206Pb/204Pb of some backarc lava flows suggests the presence of a second endmember with an EM1 flavor in its source. The overall magma genesis is explained within the context of a subducted slab with sediment that gradually looses water, water-mobile elements, and then switches to sediment melt extracts deeper down in the subduction zone. With the change in element extraction mechanism with depth comes a depletion and fractionation of the subducted complex that is reflected in the isotope and trace element signatures of the products from the main arc to Copahue to the back arc basalts.

  3. Isotopic evidence of magmatism and a sedimentary carbon source at the Endeavour hydrothermal system

    SciTech Connect

    Brown, T A; Proskurowski, G; Lilley, M D

    2004-01-07

    Stable and radiocarbon isotope measurements made on CO{sub 2} from high temperature hydrothermal vents on the Endeavour Segment of the Juan de Fuca Ridge indicate both magmatic and sedimentary sources of carbon to the hydrothermal system. The Endeavour segment is devoid of overlying sediments and has shown no observable signs of surficial magmatic activity during the {approx}20 years of ongoing studies. The appearance of isotopically heavy, radiocarbon dead CO{sub 2} after a 1999 earthquake swarm requires that this earthquake event was magmatic in origin. Evidence for a sedimentary organic carbon source suggests the presence of buried sediments at the ridge axis. These findings, which represent the first temporally coherent set of radiocarbon measurements from hydrothermal vent fluids, demonstrate the utility of radiocarbon analysis in hydrothermal studies. The existence of a sediment source at Endeavour and the occurrence of magmatic episodes illustrate the extremely complex and evolving nature of the Endeavour hydrothermal system.

  4. Geochemical evolution of Cenozoic-Cretaceous magmatism and its relation to tectonic setting, southwestern Idaho, U.S.A

    NASA Technical Reports Server (NTRS)

    Norman, Marc D.; Leeman, William P.

    1989-01-01

    The relationships between Cretaceous to Neogene magmatism and the tectonic setting of southwestern and central Idaho are evaluated. An overview of the tectonics and geology of the northwestern U.S. is presented. Major element, trace element, and Sr, Pb, and Nd isotopic data for the region are used to place constraints on magma source characteristics, the manner in which the magmatic sources evolved through time, and the nature of interactions among mantle and crustal domains in response to changing tectonic environment.

  5. Australia and Indonesia in collision: geochemical sources of magmatism

    NASA Astrophysics Data System (ADS)

    Elburg, M. A.; Foden, J. D.; van Bergen, M. J.; Zulkarnain, I.

    2005-01-01

    The islands of Alor, Lirang, Wetar and Romang are located in the extinct section of the Sunda-Banda arc, where the collision with the Australian continent has brought subduction to a halt. Intrusive and extrusive igneous samples show a wide range of Sr, Nd and Pb isotopic characteristics. Samples from the northeast coast of Alor extend the trend of increasing 206Pb/ 204Pb ratios along the arc in an easterly direction, with values as high as 19.6. Samples from Alor's south coast, Lirang, Wetar and Romang have appreciably lower 206Pb/ 204Pb ratios (≤19.1), and 143Nd/ 144Nd ratios down to 0.5119. The Pb isotope data are interpreted as reflecting mixing between two internally variable end members within the subducting Australian continent, either the upper and lower crust, or two upper crustal end members of different ages. These melts may come up virtually unmodified, giving rise to the felsic, low 143Nd/ 144Nd samples, or may interact with the mantle, of which the partial melts and the fractionation products thereof give rise to basalts to rhyodacites with more intermediate Nd isotopic characteristics. Mixing modelling of the latter samples' isotopic ratios constrains the amount of crustal material that has been added to the mantle wedge to reach up to 9%. The isotopic and trace element heterogeneity in the samples studied is likely to reflect inhomogeneity of the crustal sources contributing to magmatism.

  6. Magma sources during Gondwana breakup: chemistry and chronology of Cretaceous magmatism in Westland, New Zealand

    NASA Astrophysics Data System (ADS)

    van der Meer, Quinten H. A.; Waight, Tod E.; Scott, James M.

    2013-04-01

    Cretaceous-Paleogene rifting of the Eastern Gondwana margin thinned the continental crust of Zealandia and culminated in the opening of the Tasman Sea between Australia and New Zealand and the Southern Ocean, separating both from Antarctica. The Western Province of New Zealand consists of a succession of metasedimentary rocks intruded by Palaeozoic and Mesozoic granitoids that formed in an active margin setting through the Phanerozoic. Upon cessation of subduction, the earliest stages of extension (~110-100 Ma) were expressed in the formation of metamorphic core complexes, followed by emplacement of granitoid plutons, the deposition of terrestrial Pororari Group sediments in extensional half-grabens across on- and offshore Westland, and the intrusion of mafic dikes from ~90 Ma. These dikes are concentrated in the swarms of the Paparoa and Hohonu Ranges and were intruded prior to and simultaneous with volumetrically minor A-type plutonism at 82 Ma. The emplacement of mafic dikes and A-type plutonism at ~82 Ma is significant as it coincides with the age of the oldest seafloor in the Tasman Sea, therefore it represents magmatism coincident with the initiation of seafloor spreading which continued until ~53 Ma. New 40Ar-39Ar ages indicate that the intrusion of mafic dikes in basement lithologies both preceded and continued after the initial opening of the Tasman Sea, including an additional population of ages at ~70 Ma. This indicates either a prolonged period of extension-related magmatism that continued >10 Ma after initial breakup, or two discrete episodes of magmatism during Tasman Sea spreading. Volumetrically minor Cenozoic within-plate magmatism continued sporadically throughout the South Island and bears a characteristic HIMU (high time integrated U/Pb) signature. A detailed geochemistry and chronological study of Cretaceous mafic and felsic magmatism is currently in progress and aims to better understand the transition of magma sources from a long lived active

  7. Hydrogen Isotope Composition of Magmatic Water: Review of Variations due to Source, Igneous Environment, and Degassing Processes

    NASA Astrophysics Data System (ADS)

    Taylor, B. E.

    2001-05-01

    The familiar "magmatic water box" frequently shown on plots of δ D vs. δ 18O both represents and misrepresents the hydrogen isotope composition of magmatic water because of the influences of different source compositions and degassing processes. On the one hand, the hydrogen isotope composition of magma source materials in arcs versus continental tectonic settings contributes to differences in the primary δ D values of magmas. On the other hand, water remaining in magmatic rocks and glass is residual, and may express large variations in δ D due either to active degassing, during depressurization associated with emplacement and/or eruption, or to passive degassing during crystallization. The magnitudes of these variations are governed by hydrogen isotope fractionations involving melts, minerals, and dissolved hydrogen (H2O + OH), by water solubility, and whether the process is dominantly a closed- or open-system one. Estimating the primary δ D value of magmatic water requires extrapolation of isotopic and water content data for a suite of co-magmatic samples to a probable undegassed composition (e.g., 5 wt.% H2O). Island arcs and continental settings comprise two principal tectonic settings in which crustal source materials can differ in their hydrogen isotope composition (and dominate over mantle sources). For example, magmas formed in island arcs derive water from subducted marine clays, metamorphosed, hydrothermally altered, and weathered oceanic crust, from pore waters, and possibly, variably metasomatized mantle. Arc magmatic water, sometimes referred to as "andesitic water", tends to have an average δ D value of ca. -30 +/- 5 ‰ , whereas the average δ D value of water from magmas in continental crust regimes can be slightly lighter (e.g. δ D of ca. -45 +/- 10 ‰ ). This difference may be ascribed largely to the fact that continental crust contains water primarily as metamorphic and igneous minerals, whose average values of δ D reflect, among others

  8. Synchronous alkaline and subalkaline magmatism during the late Neoproterozoic-early Paleozoic Ross orogeny, Antarctica: Insights into magmatic sources and processes within a continental arc

    NASA Astrophysics Data System (ADS)

    Hagen-Peter, Graham; Cottle, John M.

    2016-10-01

    Extensive exposure of intrusive igneous rocks along the Ross orogen of Antarctica-an ancient accretionary orogen on the margin of East Gondwana-provides an exceptional opportunity to study continental arc magmatism. There is significant petrologic and geochemical variability in igneous rocks within a ~ 500-km-long segment of the arc in southern Victoria Land. The conspicuous occurrence of carbonatite and alkaline silicate rocks (nepheline syenite, A-type granite, and alkaline mafic rocks) adjacent to large complexes of subalkaline granitoids is not adequately explained by traditional models for continental arc magmatism. Extensive geochemical analysis (> 100 samples) and zircon U-Pb geochronology (n = 70) confirms that alkaline and carbonatitic magmatism was partially contemporaneous with the emplacement of large subduction-related igneous complexes in adjacent areas. Major pulses of subalkaline magmatism were compositionally distinct and occurred at different times along the arc. Large bodies of subalkaline orthogneiss and granite (sensu lato) were emplaced over similar time intervals (ca. 25 Myr) to the north (ca. 515-492 Ma) and south (ca. 550-525 Ma) of the alkaline magmatic province, although the initiation of these major pulses of magmatism was offset by ca. 35 Myr. Alkaline and carbonatitic magmatism spanned at least ca. 550-509 Ma, overlapping with voluminous subalkaline magmatism in adjacent areas. The most primitive rocks from each area have similarly enriched trace element compositions, indicating some common characteristics of the magma sources along the arc. The samples from the older subalkaline complex have invariably low Sr/Y ratios (< 40), consistent with relatively shallow magma generation and differentiation. The younger subalkaline complex and subalkaline rocks within the area of the alkaline province extend to higher Sr/Y ratios (up to ~ 300), indicative of generation and differentiation at deeper levels. The significant spatial and temporal

  9. Mode of rifting in magmatic-rich setting: Tectono-magmatic evolution of the Central Afar rift system

    NASA Astrophysics Data System (ADS)

    Stab, Martin; Bellahsen, Nicolas; Pik, Raphaël; Leroy, Sylvie; Ayalew, Dereje

    2014-05-01

    Observation of deep structures related to break-up processes at volcanic passive margins (VPM) is often a troublesome exercise: thick pre- to syn-breakup seaward-dipping reflectors (SDR) usually mask the continent-ocean boundary and hide the syn-rift tectonic structures that accommodate crustal stretching and thinning. Some of the current challenges are about clarifying 1) if tectonic stretching fits the observed thinning and 2) what is the effect of continuous magma supply and re-thickening of the crust during extension from a rheological point of view? The Afar region in Ethiopia is an ideal natural laboratory to address those questions, as it is a highly magmatic rift that is probably close enough to breakup to present some characteristics of VPM. Moreover, the structures related to rifting since Oligocene are out-cropping, onshore and well preserved. In this contribution, we present new structural field data and lavas (U-Th/He) datings along a cross-section from the Ethiopian Plateau, through the marginal graben down to the Manda-Hararo active rift axis. We mapped continent-ward normal fault array affecting highly tilted trapp series unconformably overlain by tilted Miocene (25-7 Ma) acid series. The main extensional and necking/thinning event took place during the end of this Miocene magmatic episode. It is itself overlain by flat lying Pliocene series, including the Stratoid. Balanced cross-sections of those areas allow us to constrain a surface stretching factor of about 2.1-2.9. Those findings have the following implications: - High beta factor constrained from field observations is at odd with thinning factor of ~1.3 predicted by seismic and gravimetric studies. We propose that the continental crust in Central Afar has been re-thickened by the emplacement of underplated magma and SDR. - The deformation in Central Afar appears to be largely distributed through space and time. It has been accommodated in a 200-300 km wide strip being a diffuse incipient

  10. Boninitic magmatism in a continental margin setting, Yukon- Tanana terrane, southeastern Yukon, Canada

    NASA Astrophysics Data System (ADS)

    Piercey, Stephen J.; Murphy, Donald C.; Mortensen, James K.; Paradis, Suzanne

    2001-08-01

    Mid-Paleozoic mafic rocks in the Finlayson Lake region of the Yukon-Tanana terrane, southeastern Yukon, Canada, have the diagnostic geochemical signatures of boninites: high MgO, Cr, Ni, and Co contents, intermediate SiO2 contents, high Mg#'s (MgO/ (MgO+FeO*), Al2O3/TiO2, and Zr(Hf)/middle rare earth element (REE) ratios; low TiO2, REE, and high-field-strength element contents; and U-shaped primitive mantle normalized trace element patterns. However, unlike most modern and ancient boninitic rocks that are typically associated with intraoceanic realms, those from the Finlayson Lake region are part of a mid-Paleozoic continental margin arc-backarc magmatic system. We propose a model in which the boninitic rocks from the Finlayson Lake region formed as a result of spreading ridge propagation into an arc built on composite basement of oceanic and continental crust. In the oceanic segment, upwelling asthenosphere induced melting of a subducted-slab metasomatized refractory mantle source to form boninitic magmatism. In the continental sector, upwelling asthenospheric mantle, and/or the melts derived thereof, induced crustal melting, which explains the large volume of temporally equivalent felsic volcanic and intrusive rocks.

  11. Towards a magmatic quartz database: tracing melt sources

    NASA Astrophysics Data System (ADS)

    Tailby, N. D.; Ackerson, M. R.; Watson, E. B.; Thomas, J. B.

    2014-12-01

    Quartz composition has seen increasing interest among the scientific community over the last decade due to new calibrations (e.g., Ti-in-quartz) and the proliferation of trace element analytical facilities. What is presently lacking in the field of quartz research is a quartz composition database. Such a single body of information can be used to evaluate whether variation seen in different crystallization environments is equally manifest in quartz composition. In this study we present >2000 new quartz analyses from >70 different granitoids and volcanic settings from around the globe (Lachlan Fold Belt, High Himalaya, French Massif, Cordilleran, Caledonian, White Mountains, Bishop, Toba, Snake River, Oman ophiolite and a number of other select locations). This dataset also combines data from a number of previous studies and together the data may collectively be used to determine which geochemical characteristics can be used to distinguish quartz from different magma types. A number of trace element concentrations or ratios (e.g., Al/Ti, Ge, Li, P and B) are notably useful when distinguishing peraluminous (e.g., cordierite-bearing granitoid) systems from more metaluminous systems (e.g., hornblende granodiorite) or plagiogranites.

  12. Imaging the magmatic system of Newberry Volcano using Joint active source and teleseismic tomography

    NASA Astrophysics Data System (ADS)

    Heath, Benjamin A.; Hooft, Emilie E. E.; Toomey, Douglas R.; Bezada, Maximiliano J.

    2015-12-01

    In this paper, we combine active and passive source P wave seismic data to tomographically image the magmatic system beneath Newberry Volcano, located east of the Cascade arc. By using both travel times from local active sources and delay times from teleseismic earthquakes recorded on closely spaced seismometers (300-800 m), we significantly improve recovery of upper crustal velocity structure (<10 km depth). The tomographic model reveals a low-velocity feature between 3 and 5 km depth that lies beneath the caldera, consistent with a magma body. In contrast to earlier tomographic studies, where elevated temperatures were sufficient to explain the recovered low velocities, the larger amplitude low-velocity anomalies in our joint tomography model require low degrees of partial melt (˜10%), and a minimum melt volume of ˜2.5 km3. Furthermore, synthetic tests suggest that even greater magnitude low-velocity anomalies, and by inference larger volumes of magma (up to 8 km3), are needed to explain the observed waveform variability. The lateral extent and shape of the inferred magma body indicates that the extensional tectonic regime at Newberry influences the emplacement of magmatic intrusions. Our study shows that jointly inverting active source and passive source seismic data improves tomographic imaging of the shallow crustal seismic structure of volcanic systems and that active source experiments would benefit from longer deployment times to also record teleseismic sources.

  13. Numerical study of conductive heat losses from a magmatic source at Phlegraean Fields

    NASA Astrophysics Data System (ADS)

    Di Maio, Rosa; Piegari, Ester; Mancini, Cecilia; Scandone, R.

    2015-01-01

    The thermal evolution of the Phlegraean magmatic system (southern Italy) is studied by analyzing the influence of the thermal property variations on the solution of the heat conduction equation. The aim of this paper is to verify if appropriate choices of thermal parameters can reproduce, at least to greater depths, the high temperatures measured in the geothermal wells, drilled inside the caldera, under the assumption of heat loss from a magma chamber by conduction. Since the main purpose is to verify the plausibility of such an assumption, rather simple models of the magmatic system are adopted and only major volcanic events (i.e., the Campanian Ignimbrite and the Neapolitan Yellow Tuff eruptions) are considered. The results of the simulated two-dimensional model scenarios show that by assuming an extended source region, whose emplacement time is longer than 40 ka, heat conduction mechanisms can provide temperatures as high as those measured at depths deeper than about 2000 m. On the other hand, the 1D simulations show that appropriate choices for the thermal conductivity depth profiles can reproduce the observed temperatures at depths deeper than about 1000 m. These findings question the apparent consensus that convection is the only dominant form of heat transfer at Phlegraean Fields and might motivate new research for reconstructing the thermal evolution of the Phlegraean magmatic system.

  14. Wave Propagation in Axi-Symmetrical Magmatic Conduits Due to an Internal Source

    NASA Astrophysics Data System (ADS)

    De Negri, R. S.; Sanchez-Sesma, F. J.; Arciniega-Ceballos, A.

    2014-12-01

    The classical Trefftz's method is implemented to simulate wave propagation in and around axi-symmetrical magmatic conduits. In this fluid-solid system the fluid (magma) is confined by an elastic unbounded medium that represents the surrounding rock. Our aim is to associate wave behavior with mechanical and geometrical conduit characteristics. The source is assumed to be at a point along the conduit centered axis medium are constructed in both cases as linear combinations of particular solutions.Within the fluid such solutions are spherical standing waves that are smooth at the origins. In the elastic solid region the field is constructed with monopoles and dipoles for the P waves and spheroidal dipoles for SV waves. The particular solutions satisfy the elastodynamic equations that govern the wave motion at those media and are associated to origins (selected points) distributed along the conduit axis. For the surrounding rock the solutions are sources that satisfy Sommerfeld's radiation condition. These sets of solutions are assumed to be complete. This conjecture is exact in 2D acoustic problems. The conduit can be closed or open at the ends and the surrounding elastic domain is unbounded. In order to find the coefficients of Trefftz's wave expansions, boundary conditions at the fluid-solid interface (null shear and continuity of pressures and normal velocities) are satisfied in the least squares sense. The solution is obtained in the frequency domain and the source time function can be introduced using Fourier analysis.Regardless the low order of the formulation our results display a rich variety of behaviors. For a uniform infinite cylinder we reproduced the exact analytical solution. In addition, this approach allows identifying some important effects of the conduit geometry, including changes of sections. Lateral and longitudinal resonances of irregular axi-symmetric conduits are well resolved. The stiffness of the solid domain with respect to the fluid

  15. Tectonic setting of the North Gondwana margin during the Early Ordovician: A comparison of the Ollo de Sapo and Famatina magmatic events

    NASA Astrophysics Data System (ADS)

    Del Greco, Kassandra; Johnston, Stephen T.; Shaw, Jessica

    2016-06-01

    This paper presents a comparison of compiled geochronological and geochemical data from the Ollo de Sapo and Famatina magmatic events. The Ollo de Sapo magmatic sequence is located in northwest Iberia and was emplaced during the early-Ordovician from 495 to 474 Ma. The Famatina Complex is a magmatic sequence located in Northern Argentina that was emplaced during the early- to mid-Ordovician from 483 to 463 Ma. These magmatic events are currently interpreted to have been emplaced in different tectonic settings despite both having occurred along the North Gondwana margin. Geochronological data indicates that these magmatic events occurred contemporaneously over at least 9 m.y. and therefore can provide a snapshot of the northern Gondwana margin during the mid-Ordovician. Major element data indicates that both magmatic suites are calc-alkaline to alkali-calcic and trace element and REE data show magmatic signatures that are indistinguishable. This study highlights the similarity between the Ollo de Sapo and the Famatina magmatic suites and discusses alternative models for their emplacement based on paleomagnetic and paleobiogeographical data. These data indicate that the Ollo de Sapo was likely emplaced in a subduction zone setting, while the Famatina magmatic suite may be of parautochthonous origin to Gondwana, implying that the Pampeanan margin may not have been active during the early- to mid-Ordovician.

  16. Martian Magmatic-Driven Hydrothermal Sites: Potential Sources of Energy, Water, and Life

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Dohm, J. M.; Baker, V. R.; Ferris, J. C.; Hare, T. M.; Tanaka, K. L.; Klemaszewski, J. E.; Skinner, J. A.; Scott, D. H.

    2000-01-01

    Magmatic-driven processes and impact events dominate the geologic record of Mars. Such recorded geologic activity coupled with significant evidence of past and present-day water/ice, above and below the martian surface, indicate that hydrothermal environments certainly existed in the past and may exist today. The identification of such environments, especially long-lived magmatic-driven hydrothermal environments, provides NASA with significant target sites for future sample return missions, since they (1) could favor the development and sustenance of life, (2) may comprise a large variety of exotic mineral assemblages, and (3) could potentially contain water/ice reservoirs for future Mars-related human activities. If life developed on Mars, the fossil record would presumably be at its greatest concentration and diversity in environments where long-term energy sources and water coexisted such as at sites where long-lived, magmatic-driven hydrothermal activity occurred. These assertions are supported by terrestrial analogs. Small, single-celled creatures (prokaryotes) are vitally important in the evolution of the Earth; these prokaryotes are environmentally tough and tolerant of environmental extremes of pH, temperature, salinity, and anoxic conditions found around hydrothermal vents. In addition, there is a great ability for bacteria to survive long periods of geologic time in extreme conditions, including high temperature hydrogen sulfide and sulfur erupted from Mount St. Helens volcano. Our team of investigators is conducting a geological investigation using multiple mission-derived datasets (e.g., existing geologic map data, MOC imagery, MOLA, TES image data, geophysical data, etc.) to identify prime target sites of hydrothermal activity for future hydrological, mineralogical, and biological investigations. The identification of these sites will enhance the probability of success for future missions to Mars.

  17. Magmatic vapor source for sulfur dioxide released during volcanic eruptions: Evidence from Mount Pinatubo

    USGS Publications Warehouse

    Wallace, P.J.; Gerlach, T.M.

    1994-01-01

    Sulfur dioxide (SO2) released by the explosive eruption of Mount Pinatubo on 15 June 1991 had an impact on climate and stratospheric ozone. The total mass of SO2 released was much greater than the amount dissolved in the magma before the eruption, and thus an additional source for the excess SO2 is required. Infrared spectroscopic analyses of dissolved water and carbon dioxide in glass inclusions from quartz phenocrysts demonstrate that before eruption the magma contained a separate, SO2-bearing vapor phase. Data for gas emissions from other volcanoes in subduction-related arcs suggest that preeruptive magmatic vapor is a major source of the SO2 that is released during many volcanic eruptions.

  18. Early Mesozoic granitoid and rhyolite magmatism of the Bureya Terrane of the Central Asian Orogenic Belt: Age and geodynamic setting

    NASA Astrophysics Data System (ADS)

    Sorokin, A. A.; Kotov, A. B.; Kudryashov, N. M.; Kovach, V. P.

    2016-09-01

    Early Mesozoic granitoids and volcanic rocks are widespread throughout the structures of all of the continental massifs in the eastern part of the Central Asian Orogenic Belt, although its tectonic setting is not yet clear. Generally, they are associated with subduction and plume processes or rifting. Such uncertainty is mostly explained by the unequal investigation of Early Mesozoic magmatism. This paper presents the results of geochemical, Sm-Nd isotope, and U-Pb geochronologic (ID-TIMS) studies of "key-type" Early Mesozoic magmatic rock complexes of the Bureya Terrane. This is one of the largest continental massifs in the eastern Central Asian Orogenic Belt and knowledge of its geological structure is of fundamental importance in understanding the history of its formation. It has been established that the leucogranites of the Altakhtinsky Complex and the trachyrhyolites of the Talovsky Complex are practically coeval (~ 209-208 Ma). The subalkaline leucogranites of the Kharinsky Complex have a slightly younger age of ~ 199 Ma. These data correspond to the general stage of Early Mesozoic magmatic and metamorphic events (236-180 Ma) in most continental massifs in the eastern Central Asian Orogenic Belt. We believe that large-scale Early Mesozoic events were related to the amalgamation of the continental massifs of the eastern Central Asian Orogenic Belt into a single continental structure (the Amur superterrane or microcontinent Amuria) and collision with the North Asian Craton. It should be noted that the collision processes were followed by crustal thickening, thus creating the conditions for metamorphism and formation of magmatic rock complexes of various geochemical types.

  19. Modes of rifting in magma-rich settings: Tectono-magmatic evolution of Central Afar

    NASA Astrophysics Data System (ADS)

    Stab, Martin; Bellahsen, Nicolas; Pik, Raphaël.; Quidelleur, Xavier; Ayalew, Dereje; Leroy, Sylvie

    2016-01-01

    Recent research in Afar (northern Ethiopia) has largely focused on the formation of the present-day ocean-continent transition at active segments (e.g., Manda Hararo). However, the Oligo-Miocene history of extension, from the onset of rifting at ~25 Ma to the eruption of the massive Stratoïd flood basalts at ~4 Ma, remains poorly constrained. Here we present new structural data and radiometric dating from Central Afar, obtained along a zone stretching from the undeformed Oligocene Ethiopian plateau to the Manda Hararo and Tat'Ale active volcanic segments. Basaltic and rhyolitic formations were mapped in two key areas corresponding to the proximal and distal parts of a half-rift. We present a balanced composite cross section of Central Afar, reconstructed using our new data and previously published geophysical data on the crustal structure. Our main findings are as follows: (1) Extension during the Mio-Pliocene corresponds to a "wide rift" style of rifting. (2) The lower crust has been underplated/intruded and rethickened during rifting by magmatic injection. (3) Our restoration points to the existence of midcrustal shear zones that have helped to distribute extension in the upper crust and to localize extension at depth in a necking zone. Moreover, we suggest that there is a close relationship between the location of a shear zone and the underplated/intruded material. In magma-rich environments such as Central Afar, breakup should be achieved once the initial continental crust has been completely replaced by the newly, magmatically accreted crust. Consequently, and particularly in Afar, crustal thickness is not necessarily indicative of breakup but instead reflects differences in tectono-magmatic regimes.

  20. Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

    USGS Publications Warehouse

    Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

    2016-01-01

    The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion–collision processes in NW China, and hosts Paleozoic Cu–Pb–Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U–Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U–Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9–213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67–1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and

  1. Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

    NASA Astrophysics Data System (ADS)

    Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

    2016-05-01

    The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion-collision processes in NW China, and hosts Paleozoic Cu-Pb-Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U-Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U-Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9-213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67-1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere. In contrast, the

  2. Source and tectonic implications of tonalite-trondhjemite magmatism in the Klamath Mountains

    USGS Publications Warehouse

    Barnes, C.G.; Petersen, S.W.; Kistler, R.W.; Murray, R.; Kays, M.A.

    1996-01-01

    In the Klamath Mountains, voluminous tonalite-trondhjemite magmatism was characteristic of a short period of time from about 144 to 136 Ma (Early Cretaceous). It occurred about 5 to l0 m.y. after the ??? 165 to 159 Ma Josephine ophiolite was thrust beneath older parts of the province during the Nevadan orogeny (thrusting from ??? 155 to 148 Ma). The magmatism also corresponds to a period of slow or no subduction. Most of the plutons crop out in the south-central Klamath Mountains in California, but one occurs in Oregon at the northern end of the province. Compositionally extended members of the suite consist of precursor gabbroic to dioritic rocks followed by later, more voluminous tonalitic and trondhjemitic intrusions. Most plutons consist almost entirely of tonalite and trondhjemite. Poorlydefined concentric zoning is common. Tonalitic rocks are typically of the Iow-Al type but trondhjemites are generally of the high-Al type, even those that occur in the same pluton as low-Al tonalite??. The suite is characterized by low abundances of K2O, Rb, Zr, and heavy rare earth elements. Sr contents are generally moderate ( ???450 ppm) by comparison with Sr-rich arc lavas interpreted to be slab melts (up to 2000 ppm). Initial 87Sr/ 86Sr, ??18O, and ??Nd are typical of mantle-derived magmas or of crustally-derived magmas with a metabasic source. Compositional variation within plutons can be modeled by variable degrees of partial melting of a heterogeneous metabasaltic source (transitional mid-ocean ridge to island arc basalt), but not by fractional crystallyzation of a basaltic parent. Melting models require a residual assemblage of clinopyroxene+garnet??plagioclase??amphibole; residual plagioclase suggests a deep crustal origin rather than melting of a subducted slab. Such models are consistent with the metabasic part of the Josephine ophiolite as the source. Because the Josephine ophiolite was at low T during Nevadan thrusting, an external heat source was probably

  3. Compositions of biotite from granitoids of the Sierra Nevada batholith: constraints on magmatic source rocks

    SciTech Connect

    Ague, J.J.; Brimhall, G.H.

    1985-01-01

    Two compositional types of biotite from the Cretaceous Sierra Nevada batholith occur in a systematic regional pattern which reflects magmatic source material and correlates with tungsten mineralization. Biotite from each group may be characterized in terms of F/OH and Mg/Fe as follows. Type I biotites generally coexist with hornblende and magnetite + sphene. Type II biotites coexist with ilmenite +/- magnetite, but hornblende only occurs at contacts with Type I intrusives. Intrusives with Type IA biotite occur as a continuous belt along the entire western margin of the exposed batholith. Type IB biotite is found to the east of this belt, and Type IC biotite is confined to the eastern side of the Sierra. Type II biotite is present in the eastern and south-western portions of the Sierra, and sporadically in the metamorphic foothills belt. The two intrusive groups, here characterized by biotite compositions, correspond to two of the source rock and porphyry mineralization models of Burnham (1981). Type I rocks (Cu deposits) are derived from mafic amphiobolites whereas Type II (Sn-W deposits) form from relatively reduced muscovite-rich metasediments. The biotite compositions indicate that the majority of the batholith formed from amphibolite sources. Type II intrusives and W deposits occur in areas underlain by Precambrian crust as defined by radiogenic isotope studies.

  4. Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil): Neoproterozoic crust recycling constrained by elemental and isotope (Sr-Nd-Pb) geochemistry

    NASA Astrophysics Data System (ADS)

    Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa

    2016-07-01

    Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The

  5. Tracking magmatic intrusions in real-time by means of free-shaped volcanic source modelling

    NASA Astrophysics Data System (ADS)

    Cannavo', Flavio; Camacho, Antonio G.; Scandura, Danila; González, Pablo J.; Mattia, Mario; Fernández, José

    2014-05-01

    Nowadays continuous measurements of geophysical parameters provide a general real-time view of current state of the volcano. Nonetheless, a current challenge is to localize and track in real-time the evolution of the magma source beneath the volcano. Here we present a new methodology to rapidly estimate magmatic sources from surface geodetic data and track their evolution in time without any a priori assumption about source geometry. Indeed, the proposed approach takes the advantages of fast calculation from the analytical models and adds the capability to model free-shape distributed sources. Assuming homogenous elastic conditions, the approach can determine general geometrical configurations of pressured and/or density source and/or sliding structures corresponding to prescribed values of anomalous density, pressure and slip. These source bodies are described as aggregation of elemental point sources for pressure, density and slip, and they fit the whole data (keeping some 3D regularity conditions). In this work we show an application of the methodology to model the real-time evolution of the volcanic source for 2008 eruption of Mount Etna (Italy). To this aim the High-Rate GPS data, coming from the Continuous GPS network, are processed in real-time to obtain sub-daily solutions for tracking the fast dynamics of the magma migration. In our test case we reproduced the real-time scenario of the eruption. Though the data of the test were processed after data collection, real-time operation was emulated. From the results, it is possible to extrapolate the dynamic of a deep and a shallow magma source and the dyke intrusion. In particular, results show at 5 am UTC a magma batch likely migrating towards the surface leaving behind a deflating volume at about 2 km bsl and a deep elongated body from 2 km bsl to 10 km bsl which runs along the High Vp Body and likely represents the deep conduit from where the magma rises up. We demonstrate that the proposed methodology is

  6. Isotopic Constraints on Magmatic Sources at Nyiragongo and Nyamulagira Volcanoes, Virunga Volcanic Province, DR Congo

    NASA Astrophysics Data System (ADS)

    Phillips, E. H. W.; Sims, K. W. W.; Tedesco, D.; Blichert-Toft, J.; Scott, S. R.; Reagan, M. K.

    2015-12-01

    The active volcanoes Nyiragongo and Nyamulagira in the DR Congo have very different physical and geochemical characteristics, despite being situated a mere 15 km apart. Nyiragongo's foiditic lavas are some of the most silica-undersaturated on earth, whereas the highly effusive Nyamulagira erupts primarily basanites and tephrites. To determine the extent and scale of mantle heterogeneities and gain insight into the magmatic sources beneath this portion of the East African Rift, we have measured Hf and Pb isotope compositions for 43 samples from Nyiragongo and Nyamulagira. The Nd and Sr isotope data for the same sample dissolutions are forthcoming. Nyiragongo lavas are clearly distinct from Nyamulagira lavas in terms of their Hf and Pb isotope compositions, suggesting that a long-lived and small-scale heterogeneous mantle source exists beneath these two volcanoes. Nyiragongo lavas have ɛHf ranging from +1.8 to +5.5 with an average of +2.9 (n=29) and 206Pb/204Pb ranging from 19.4049 to 19.7252 with an average of 19.6329 (n=29). Nyamulagira lavas have ɛHf ranging from -0.5 to +1.5 with an average of +0.5 (n=14) and 206Pb/204Pb ranging from 19.2518 to 19.2828 with an average of 19.2663 (n=13). Nyiragongo lavas erupted in 2002 or later have amongst the highest 206Pb/204Pb within this suite of samples. We note that Chakrabarti et al. (2009, Chem Geol 259) measured bulk silicate earth-like Nd and Sr isotope compositions for Nyiragongo lavas and proposed a primitive mantle/bulk-earth plume source for this volcano. Our new Hf isotope compositions for Nyiragongo, however, are higher than bulk silicate earth, suggesting a more depleted source for these highly alkaline lavas. We also note that the He isotope compositions of olivine and clinopyroxene from Nyiragongo lavas (R/Ra = 6.7-8.5; Pik et al., 2006, Chem Geol 226; Tedesco et al., 2010, J Geophys Res 115) are inconsistent with a long-term bulk silicate earth-like source.

  7. Rapid Rejuvenation of the Source of a Backarc Sheeted Magmatic Complex (Torres del Paine, Patagonia): Evidence From Hf isotopes in Zircon

    NASA Astrophysics Data System (ADS)

    Ewing, T. A.; Muntener, O.; Leuthold, J.; Chiaradia, M.; Baumgartner, L. P.; Putlitz, B.

    2014-12-01

    The Miocene Torres del Paine intrusive complex (TPIC) in Patagonia is a spectacularly exposed example of a bimodal shallow crustal laccolith, made up of a sill complex and a subvertical feeder system. The TPIC was emplaced in a back-arc setting, but slightly older arc-related intrusive units in this area testify to an earlier shift from an arc to a backarc setting. The entire ~88 km3 main complex was emplaced over short time scales of 162 ± 11 ka between ~12.4 and 12.6 Ma, with mafic units from the feeder zone found to be older than mafic units from the sill complex1,2. We aim to assess whether successive pulses of mafic magmatism can tap different geochemical reservoirs in sheeted magmatic complexes emplaced on such short timescales. Hf isotope compositions of individual zircons from mafic units from both the feeder zone and the sill complex were determined by solution MC-ICPMS. Zircons from all units have Hf isotope compositions that indicate a slightly enriched mantle source. Zircons from the mafic sill complex units have higher (more juvenile) initial ɛHf than zircons from feeder zone mafic units. The shift towards more depleted Hf isotope compositions in the sill complex units, which are younger, demonstrates the rapid input of new juvenile material into the source region between ~12.6 Ma and ~12.5 Ma. A similar shift is also seen in bulk rock Nd and Sr isotope data for related samples3. The Hf isotope data demonstrate that significant variability in source geochemistry is possible for sheeted magmatic complexes built up on very short timescales. Analysis of zircons from a range of dikes and intrusive bodies external to the main Torres del Paine complex, with ages that span ~12-29 Ma, will provide a more complete picture in time and space of the geochemical evolution of this magmatic system as it switches between an arc and backarc setting. 1Leuthold et al., 2012, EPSL, 325: 85-92 2Michel et al., 2008, Geology, 36: 459-462 3Leuthold et al., 2013, JPET, 54

  8. The magmatic source of the Tristan da Cunha hotspot: Implication from electrical conductivity

    NASA Astrophysics Data System (ADS)

    Chen, Jin; Baba, Kiyoshi; Jegen, Marion; Utada, Hisashi; Geissler, Wolfram; Jokat, Wilfried

    2016-04-01

    Tristan da Cunha Island is one of the classical hot spots in the Atlantic Ocean, situated at the western end of the aseismic Walvis Ridge which forms a connection to the Cretaceous Etendeka flood basalt province in northwestern Namibia. The discussion about its source (in shallow asthenosphere or deeper mantle) have not reached consensus yet because of lack of the geophysical observations in the area. A marine magnetotelluric (MT) experiment was conducted together with seismological observations in the area in 2012-2013 through a German-Japanese collaboration with the goal to constrain the physical state of the mantle beneath the area. A total of 26 MT seafloor stations were deployed around the Tristan da Cunha Islands and available data were retrieved and processed from 24 stations. We applied iterative topographic effect correction and one-dimensional (1-D) conductivity structure inversion to the data. Then, three-dimensional (3-D) inversion analysis incorporating the topographic effect was carried out, using the 1-D model as the initial model. The local small-scale topography and the far continental coast effects are incorporated as the distortion term in the 3-D inversion. The preliminary result of our analysis shows no evidence of a significant conductive anomaly arising from the mantle transition zone, suggesting that the current magmatic source (major place of melting) of the hotspot activity is in the shallow upper mantle. This is in contrast to results from geochemical analysis, in which samples along the Tristan track exhibit an ocean-island-basalt-type incompatible element pattern pointing to a deep mantle source of the melt. Our findings therefore might indicate that the deep mantle up-welling underneath Tristan da Cunha Islands may be almost dead. A conductive anomaly at approx. 100 km depth in our derived conductivity model to the southwest of Tristan da Cunha Islands suggests an interaction between the mid-ocean ridge and/or up-welling further south

  9. The setting, style, and role of magmatism in the formation of volcanogenic massive sulfide deposits

    NASA Astrophysics Data System (ADS)

    Piercey, Stephen J.

    2011-07-01

    Throughout Earth's history, all volcanogenic massive sulfide (VMS)-hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry (petrochemical assemblages) indicative of formation at anomalously high temperatures within extensional geodynamic environments. In mafic-dominated (juvenile/ophiolitic) VMS environments, there is a preferential association with mafic rocks with boninite and low-Ti tholeiite, mid-ocean ridge basalt (MORB), and/or back-arc basin basalt affinities representing forearc rifting or back-arc initiation, mid-ocean ridges or back-arc basin spreading, or back-arc basins, respectively. Felsic rocks in juvenile oceanic arc environments in Archean terrains are high field strength element (HFSE) and rare earth element (REE) enriched. In post-Archean juvenile oceanic arc terrains, felsic rocks are commonly HFSE and REE depleted and have boninite like to tholeiitic signatures. In VMS environments that are associated with continental crust (i.e., continental arc and back-arc) and dominated by felsic volcanic and/or sedimentary rocks (evolved environments), felsic rocks are the dominant hosts to mineralization and are generally HFSE and REE enriched with calc-alkalic, A-type, and/or peralkalic affinities, representing continental arc rifts, continental back-arcs, and continental back-arcs to continental rifts, respectively. Coeval mafic rocks in evolved environments have alkalic (within-plate/ocean island basalt like) and MORB signatures that represent arc to back-arc rift versus back-arc spreading, respectively. The high-temperature magmatic activity in VMS environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments (e.g., mid-ocean ridges, back-arc basins, and intra-arc rifts). Underplated basaltic magma provides the heat required to drive hydrothermal circulation. Extensional geodynamic activity also provides accommodation space at the base

  10. Discovery of a Triassic magmatic arc source for the Permo-Triassic Karakaya subduction complex, NW Turkey

    NASA Astrophysics Data System (ADS)

    Ayda Ustaömer, Petek; Ustaömer, Timur; Gerdes, Axel; Robertson, Alastair H. F.; Zulauf, Gernold

    2014-05-01

    The Permo-Triassic Karakaya Complex is well explained by northward subduction of Palaeotethys but until now no corresponding magmatic arc has been identified in the region. With the aim of determining the compositions and ages of the source units, ten sandstone samples were collected from the mappably distinct Ortaoba, Hodul, Kendirli and Orhanlar Units. Zircon grains were extracted from these sandstones and >1300 were dated by the U-Pb method and subsequently analysed for the Lu-Hf isotopic compositions by LA-MC-ICPMS at Goethe University, Frankfurt. The U-Pb-Hf isotope systematics are indicative of two different sediment provenances. The first, represented by the Ortaoba, Hodul and Kendirli Units, is dominated by igneous rocks of Triassic (250-220 Ma), Early Carboniferous-Early Permian (290-340 Ma) and Early to Mid-Devonian (385-400 Ma) ages. The second provenance, represented by the Orhanlar Unit, is indicative of derivation from a peri-Gondwanan terrane. In case of the first provenance, the Devonian and Carboniferous source rocks exibit intermediate eHf(t) values (-11 to -3), consistent with the formation at a continental margin where juvenile mantle-derived magmas mixed with (recycled) old crust having Palaeoproterozoic Hf model ages. In contrast, the Triassic arc magma exhibits higher eHf(t) values (-6 to +6), consistent with the mixing of juvenile mantle-derived melts with (recycled) old crust perhaps somewhat rejuvanated during the Cadomian period. We have therefore identified a Triassic magmatic arc as predicted by the interpretation of the Karakaya Complex as an accretionary complex related to northward subduction (Carboniferous and Devonian granites are already well documented in NW Turkey). Possible explanations for the lack of any outcrop of the source magmatic arc are that it was later subducted or the Karakaya Complex was displaced laterally from its source arc (both post 220 Ma). Strike-slip displacement (driven by oblique subduction?) can also

  11. Paraná Magmatic Province Tristan da Cunha plume system: fixed versus mobile plume, petrogenetic considerations and alternative heat sources

    NASA Astrophysics Data System (ADS)

    Ernesto, M.; Marques, L. S.; Piccirillo, E. M.; Molina, E. C.; Ussami, N.; Comin-Chiaramonti, P.; Bellieni, G.

    2002-11-01

    Paleomagnetic reconstructions demonstrate that the Tristan da Cunha (TC) plume, which is usually related to the genesis of the high- and low-Ti flood tholeiites of the Paraná Magmatic Province (PMP), was located ˜1000 km south of the Paraná Province at the time of the magma eruptions. Assuming plume mobility, and considering the low-velocity zone identified in the northern portion of the PMP as the TC 'fossil' plume (˜20° from the present TC position), the plume migrated southward from 133-132 (main volcanic phase) to 80 Ma at a rate of about 40 mm/yr. From 80 Ma to Present the plume remained virtually fixed, leaving a track (Walvis Ridge) compatible with the African plate movement. However, geochemical and Sr-Nd-Pb isotopic data do not support that the tholeiites from Walvis Ridge, Rio Grande Rise and Paraná can result from mixing dominated by the TC plume and mid-ocean ridge basalt components. The similarity among the high-Ti basalts from Rio Grande Rise, part of Walvis Ridge (525A) and the Paraná Province suggests that delaminated subcontinental lithospheric mantle must be considered in their genesis. Regional thermal anomalies in deep mantle mapped by geoid and seismic tomography data offer an alternative non-plume-related heat source for the generation of intracontinental magmatic provinces.

  12. The southern margin of the Caribbean Plate in Venezuela: tectono-magmatic setting of the ophiolitic units and kinematic evolution

    NASA Astrophysics Data System (ADS)

    Giunta, Giuseppe; Beccaluva, Luigi; Coltorti, Massimo; Siena, Franca; Vaccaro, Carmela

    2002-07-01

    The southern Caribbean Plate margin in Venezuela consists of a W-E elongated deformed belt, composed of several tectonic units dismembered along the northern part of the South America continental Plate since the Late Cretaceous. The present review, based on petrology and tectono-magmatic significance of each unit, makes it possible to define the main geotectonic elements and to reconstruct the paleogeographic domains from Late Jurassic to Tertiary: (a) Mid-Ocean Ridge Basalt (MORB) proto-Caribbean oceanic basin (Loma de Hierro Unit); (b) oceanic plateau (Dutch and Venezuelan Islands basement); (c) rifted continental margin (Cordillera de La Costa and Caucagua-El Tinaco Units) with Within Plate Tholeiitic (WPTh) magmatism; (d) an intra-oceanic subduction zone represented by Island Arc Tholeiitic (IAT) magmatism (Villa de Cura and Dos Hermanas Units) of Early Cretaceous age; (e) an Early Cretaceous ocean-continent subduction trench filled by melange (Franja Costera); (f) a new intra-oceanic subduction zone, represented by the tonalitic arc magmatism of Late Cretaceous age (Dutch and Venezuelan Islands). Regional tectonic constraints and coherent kinematic reconstruction suggest an original "near-Mid America" location of the Jurassic-Cretaceous "proto-Caribbean" oceanic realm. From Early to Late Cretaceous one sub-continental subduction with melanges (Franja Costera Unit) and two main stages of intra-oceanic arc magmatism are recorded in the so-called "eo-Caribbean" phases. The first consists of generally metamorphosed and deformed volcano-plutonic sequences with IAT affinity (Villa de Cura and Dos Hermanas Units), probably in relation to a southeastward-dipping subduction. The second is mainly represented by generally unmetamorphosed tonalitic intrusives cutting the oceanic plateau in the Dutch and Venezuelan Islands, and related to the new intra-oceanic subduction with reverse lithospheric sinking. The latter probably marked the onset of the Aves/Lesser Antilles arc

  13. The Ezhimala Igneous Complex, southern India: Possible imprint of Late Cretaceous magmatism within rift setting associated with India-Madagascar separation

    NASA Astrophysics Data System (ADS)

    Mohan, M. Ram; Shaji, E.; Satyanarayanan, M.; Santosh, M.; Tsunogae, T.; Yang, Qiong-Yan; Dhanil Dev, S. G.

    2016-05-01

    The gabbro-granophyre-granite complex of Ezhimala emplaced along the western rifted continental margin of India preserves evidence for bimodal magmatism, with related magma mixing and mingling processes. Here we report petrological, geochemical, zircon U-Pb geochronological and Lu-Hf isotopic data from the Ezhimala Igneous Complex (EIC) that provide insights into the Late Cretaceous magmatic activity. Field investigations and petrographic observations in Zircon U-Pb data from the granophyres show emplacement ages of 93.21 ± 0.6 Ma and 94.26 ± 0.92 Ma. The evolved Lu-Hf isotopic systematics for these rocks are indicative of the involvement of older crustal material during magma genesis. The geochemical systematics together with isotopic data suggest magma generation in a rift-related setting, and interaction with or melting of Neoproterozoic basement rocks. The timing of magmatism broadly correlates with the Late Cretaceous Marion hotspot activity which is considered to be responsible for the break-up of India and Madagascar. We thus interpret the EIC to be one of the rare signatures in southern India for the final phase of rifting of Gondwana.

  14. New constraints on the magmatic system beneath Newberry Volcano from the analysis of active and passive source seismic data, and ambient noise

    NASA Astrophysics Data System (ADS)

    Heath, B.; Toomey, D. R.; Hooft, E. E. E.

    2014-12-01

    Magmatic systems beneath arc-volcanoes are often poorly resolved by seismic imaging due to the small spatial scale and large magnitude of crustal heterogeneity in combination with field experiments that sparsely sample the wavefield. Here we report on our continued analysis of seismic data from a line of densely-spaced (~300 m), three-component seismometers installed on Newberry Volcano in central Oregon for ~3 weeks; the array recorded an explosive shot, ~20 teleseismic events, and ambient noise. By jointly inverting both active and passive-source travel time data, the resulting tomographic image reveals a more detailed view of the presumed rhyolitic magma chamber at ~3-5 km depth, previously imaged by Achauer et al. (1988) and Beachly et al. (2012). The magma chamber is elongated perpendicular to the trend of extensional faulting and encircled by hypocenters of small (M < 2) earthquakes located by PNSN. We also model teleseismic waveforms using a 2-D synthetic seismogram code to recreate anomalous amplitudes observed in the P-wave coda for sites within the caldera. Autocorrelation of ambient noise data also reveals large amplitude waveforms for a small but spatially grouped set of stations, also located within the caldera. On the basis of these noise observations and 2-D synthetic models, which both require slow seismic speeds at depth, we conclude that our tomographic model underestimates low-velocity anomalies associated with the inferred crustal magma chamber; this is due in large part to wavefront healing, which reduces observed travel time anomalies, and regularization constraints, which minimize model perturbations. Only by using various methods that interrogate different aspects of the seismic data are we able to more realistically constrain the complicated, heterogeneous volcanic system. In particular, modeling of waveform characteristics provides a better measure of the spatial scale and magnitude of crustal velocities near magmatic systems.

  15. Late orogenic mafic magmatism in the North Cascades, Washington: Petrology and tectonic setting of the Skymo layered intrusion

    USGS Publications Warehouse

    Whitney, D.L.; Tepper, J.H.; Hirschmann, M.M.; Hurlow, H.A.

    2008-01-01

    The Skymo Complex in the North Cascades, Washington, is a layered mafic intrusion within the Ross Lake fault zone, a major orogen-parallel structure at the eastern margin of the Cascades crystalline core. The complex is composed dominantly of troctolite and gabbro, both with inclusions of primitive olivine gabbro. Low-pressure minerals in the metasedimentary contact aureole and early crystallization of olivine + plagioclase in the mafic rocks indicate the intrusion was emplaced at shallow depths (<12 km). The Skymo rocks have trace-element characteristics of arc magmas, but the association of Mg-rich olivine (Fo88-80) with relatively sodic plagioclase (An75-60) and the Al/Ti ratios of clinopyroxene are atypical of arc gabbros and more characteristic of rift-related gabbros. A Sm-Nd isochron indicates crystallization in the early Tertiary (ca. 50 Ma), coeval with the nearby Golden Horn alkaline granite. Mantle melting to produce Skymo magma likely occurred in a mantle wedge with a long history of arc magmatism. The Skymo mafic complex and the Golden Horn granite were emplaced during regional extension and collapse of the North Cascades orogen and represent the end of large-scale magmatism in the North Cascades continental arc. ?? 2008 Geological Society of America.

  16. An assessment of the record in compositional variations from mantle source to magmatism at East Island, Crozet archipelago

    NASA Astrophysics Data System (ADS)

    Meyzen, C. M.; Marzoli, A.; Bellieni, G.

    2013-12-01

    The Crozet archipelago, located midway between Madagascar and Antarctica, constitutes the emerged part of the easternmost bank of the Crozet plateau, which lies upon upper Cretaceous oceanic seafloor derived from the Southeast Indian Ridge. It forms an elongated chain of five islands and islets, divided into two groups: an older eastern island group (< 9 Ma) composed by large-scale volcanic landmasses (i.e. East and Possession islands) and a younger western one (< 5.5 Ma) with pint-sized islands. The whole region exhibits some of the most typical gravimetric, seismic and bathymetric characteristics associated with upwelling hotter than average mantle including: a geoid high, a topographic swell, a deep low-velocity zone (up to 2350 km), an anomalous heat flow and a thickened crust (10-16.5 km). Most of these features are exacerbated by the near stationary absolute motion of the Antarctic plate. However, since thirty years, the chemical composition of Crozet archipelago magmas has beneficiated from little interest compared to that of other Earth's hotspots. Because of the occurrence of both a thick and old lithosphere and of a near stagnant absolute plate motion, new data from the Crozet archipelago magmatic record will provide new critical perspective on oceanic island building processes. The data presented here are based on a basaltic suite of ~ 25 samples collected by a 'Terres Australes et Antarctiques Francaises' expedition in 1969 from the northern part of East Island. Our alkali basalts from the Crozet archipelago are distinct from other oceanic within-plate magmatic rocks in showing ubiquitous large depletions in LILE with respect to other incompatible elements, although these rocks constitute one of the most incompatible-element-enriched suites among Earth's oceanic island basalts (OIB). The similarity of their trace element ratios and parallelism of their rare earth element patterns indicate: (1) a mantle source homogeneity over at least 1 Ma; (2) an

  17. Dating intrusion and cooling of Cenozoic granitoids in the Dinarides of Southern Serbia and discussion of the geodynamic setting of Paleocene-Miocene magmatism in the Balkan Peninsula

    NASA Astrophysics Data System (ADS)

    Senecio, Schefer; Cvetković, Vladica; Fügenschuh, Bernhard; Kounov, Alexandre; Ovtcharova, Maria; Schaltegger, Urs; Schmid, Stefan

    2010-05-01

    This paper presents the results of high precision single grain U-Pb dating and Hf isotope analyses of thermally annealed and chemically abraded zircons from the Kopaonik, Drenje, Željin, Golija and Polumir intrusions in the inner Dinarides of southern Serbia. In addition, new zircon and apatite fission-track data together with local structural observations, allow for constraining the subsequent exhumation history of these intrusions. Two age groups were determined for the granitoid intrusions: (i) Oligocene intrusive bodies (Kopaonik, Drenje, Željin) ranging in age from 31.7 to 30.6 Ma and (ii) Miocene Golija and Polumir intrusions which emplaced at 20.58-20.17 and 18.06-17.74 Ma, respectively. The apatite fission-track modelling combined with zircon central ages show rapid cooling from above 300 to ca. 80 °C between 16 and 10 Ma for granitoids of both age groups, followed by rather slow cooling to surface temperatures for the last 10 Ma. Fast Middle Miocene cooling between 16 and 10 Ma is caused by extensional exhumation of the plutons that are located in the footwall of core-complexes. This documents that Miocene magmatism and core-complex formation leading to formation of the Pannonian basin also affected a part of the mountainous areas of the internal Dinarides. The discussion of an extensive set of age data from the literature and the geodynamic setting of the Balkan Peninsula reveals that there is no direct connection of the Dinaridic Late Eocene to earliest Miocene magmatic belt with contemporaneous Periadriatic intrusions in the Alps and along the Mid-Hungarian fault zone as proposed in the literature. We insist on the fact that the subduction polarity in the Alps, including that within the Western Carpathians north of the Mid-Hungarian fault zone, is opposite to that of the Dinarides during the given time span. Instead, we propose that Late Eocene to Oligocene magmatism, which affects the Adria-derived lower plate units of the internal Dinarides, may be

  18. EXCITATION OF A BURIED MAGMATIC PIPE: A SEISMIC SOURCE MODEL FOR VOLCANIC TREMOR.

    USGS Publications Warehouse

    Chouet, Bernard

    1985-01-01

    A model of volcanic tremor is presented in which the modes of vibration of a volcanic pipe are excited by the motion of the fluid within the pipe in response to a short-term perturbation in pressure. The model shows the relative importance of the various parts constituting this composite source in the radiated elastic field at near and intermediate distances. The paper starts with the presentation of the elastic field radiated by the source, and proceeds with an analysis of the energy balance between hydraulic and elastic motions. Next, the hydraulic excitation of the source is addressed and, finally, the ground response to this excitation is analyzed in the simple case of a pipe buried in a homogeneous half space.

  19. Petrogenesis of postcollisional magmatism at Scheelite Dome, Yukon, Canada: Evidence for a lithospheric mantle source for magmas associated with intrusion-related gold systems

    USGS Publications Warehouse

    Mair, John L.; Farmer, G. Lang; Groves, David I.; Hart, Craig J.R.; Goldfarb, Richard J.

    2011-01-01

    are attributes of the ancient North American cratonic margin that appear to be essential prerequisites to this style of postcollisional magmatism and associated gold-rich fluid exsolution. This type of magmatic hydrothermal activity occurs in a very specific tectonic setting that typically sets intrusion-related gold deposits apart from orogenic gold deposits, which are synorogenic in timing and have no consistent direct relationship to such diverse and contemporaneous lithospheric mantle-derived magmas, although they too are commonly sited adjacent to lithospheric boundaries.

  20. The giant Pan-African Hook Batholith, Central Zambia: A-type magmatism in a syn-collisional setting

    NASA Astrophysics Data System (ADS)

    Milani, Lorenzo; Lehmann, Jérémie; Naydenov, Kalin V.; Saalmann, Kerstin; Kinnaird, Judith A.; Daly, J. Stephen; Frei, Dirk; Lobo-Guerrero Sanz, Alberto

    2015-04-01

    The Pan-African Hook Batholith formed during the assembly of the Gondwana supercontinent between 570 and 520 Ma (U-Pb on zircon) as a result of syn-collisional stage interaction between the Congo and Kalahari Cratons1. The extension of the batholith, exposed and undercover, is estimated to be between 25,000 and 30,000 km2. The bimodal magmatism (mafic to predominantly felsic) is characterized by both an alkali-calcic and an alkalic suite, with the felsic rocks featuring a typical A-type, metaluminous, high Fe/Mg and K/Na geochemical signature. The scattered outcrops of gabbroic rocks, both tholeiitic and alkaline, suggest periodic input of mantle material, which, in some cases, interacted with metasomatizing fluids. Fractional crystallization is invoked for the most differentiated products, while Sr-Nd isotopes rule out any significant contribution from crustal assimilation. Exceptionally highly radiogenic Pb isotopes have been measured on both unaltered and hydrothermally altered rocks, and attest to the radiogenic character of the batholith. The Pb isotopes indicate that the anomalous signature was acquired during, or soon after, magma emplacement, and was likely enhanced by metasomatizing fluids. An enrichment in Th and U, affecting large portions of the crust along the southern margin of the Congo Craton, is suggested by comparable anomalous Pb isotopes measured in basement gneisses in the Domes Region, Zambian Copperbelt. Geochemical and isotopic evidence support interaction between mantle components and portions of the deep crust at pressures of < 10 kbar, while decompression melting of rising asthenospheric mantle ponding at the base of the crust heated, and ultimately melted, crustal material. Low-pressure mineral phases in metasedimentary wall rocks along the eastern margin of the pluton indicate that the magma was subsequently emplaced at shallow crustal depths. A crucial contribution to the crustal melting was likely provided by internal radiogenic heat

  1. Timing of magmatism following initial convergence at a passive margin, southwestern U.S. Cordillera, and ages of lower crustal magma sources

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.

    2006-01-01

    Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali-calcic Fe- and Sr-enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal-miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo-Triassic intrusion ages, and a prolonged postemplacement thermal history within the long-lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc. ?? 2006 by The University of Chicago. All rights reserved.

  2. Cenozoic magmatism in the South China Basin: Decompression melting and implications of an enriched mantle source

    SciTech Connect

    Flower, M.F.J.; Kan Tu; Ming Zhang ); Guanghong Xie )

    1990-06-01

    A widespread eposide of interplate volcanism followed the cessation of seafloor spreading in the South China Basin (SCB), affecting the South China Sea, and fringing areas of southern China and Indochina. Geochemical data for basalts from South China Sea islands and seamounts, Hainan Island, and Taiwan define an enriched (Dupal-like) mantle domain yielding oceanic island basalt (OIB) suites with {Delta}7/4Pb = 2-13, {Delta}8/4Pb = 45-73, {sup 87}Sr/{sup 86}Sr > {approximately}0.70325, Th/Ta > 2, and Th/Ba > 0.02. Opening of the SCB resulted from disaggregation of the South China block in response to the Indo-Eurasian collision, a process involving at least one seafloor spreading episode, terminated by collision of microcontinents with the Philippines and Borneo. The lack of precursive flood basalt suggests that active mantle upwelling was not involved and that melting was a passive effect of lithosphere stretching. However, while mantle decompression at ambient stretching factors ({approximately}1.7-2.5) appears to permit melting on the observed scale, the enriched source may preclude such a simple mantle dynamic. Three alternatives are considered: (1) passive melting of a mature metasomatised boundary layer, (2) active melting of thermally eroded subcontinental lithosphere (deep enrichment) or metasomatised boundary layer (shallow enrichment), and (3) relict diapirs of pre-SCB and/or Java trench subduction slabs (intermediate/deep enrichment). These models are evaluated in terms of chemical and isotopic mass balances associated with the generation and movement of small melt fractions in depleted, nondepleted, and enriched mantle.

  3. Mid-Tertiary magmatism in western Big Bend National Park, Texas, U.S.A.: Evolution of basaltic source regions and generation of peralkaline rhyolite

    NASA Astrophysics Data System (ADS)

    Parker, Don F.; Ren, Minghua; Adams, David T.; Tsai, Heng; Long, Leon E.

    2012-07-01

    Tertiary magmatism in the Big Bend region of southwestern Texas spanned 47 to 17 Ma and included representatives of all three phases (Early, Main and Late) of the Trans-Pecos magmatic province. Early phase magmatism was manifested in the Alamo Creek Basalt, an alkalic lava series ranging from basalt to benmoreite, and silicic alkalic intrusions of the Christmas Mountains. Main phase magmatism in the late Eocene/early Oligocene produced Bee Mountain Basalt, a lava series ranging from hawaiite and potassic trachybasalt to latite, widespread trachytic lavas of Tule Mountain Trachyte and silicic rocks associated with the Pine Mountain Caldera in the Chisos Mountains. Late main phase magmatism produced trachyte lava and numerous dome complexes of peralkaline Burro Mesa Rhyolite (~ 29 Ma) in western Big Bend National Park. Late stage basaltic magmatism is sparsely represented by a few lavas in the Big Bend Park area, the adjacent Black Gap area and, most notably, in the nearby Bofecillos Mountains, where alkalic basaltic rocks were emplaced as lava and dikes concurrent with active normal faulting. Trace element modeling, Nd isotope ratios and calculated depths of segregation for estimated ancestral basaltic magmas suggest that Alamo Creek basalts (ɛNdt ~ 6.15 to 2.33) were derived from depths (~ 120 to 90 km) near the lithosphere/asthenosphere boundary at temperatures of ~ 1600 to1560 °C, whereas primitive Bee Mountain basalts (ɛNdt ~ 0.285 to - 1.20) may have been segregated at shallower depths (~ 80 to 50 km) and lower temperatures (~ 1520 to 1430 °C) within the continental lithosphere. Nb/La versus Ba/La plots suggest that all were derived from OIB-modified continental lithosphere. Late stage basaltic rocks from the Bofecillos Mountains may indicate a return to source depths and temperatures similar to those calculated for Alamo Creek Basalt primitive magmas. We suggest that a zone of melting ascended into the continental lithosphere during main-phase activity and

  4. Magmatism in the Tsagaandelger, Eastern Mongolian volcanic belt: Petrological, geochemical and isotopic constraints on Mesozoic geodynamic setting

    NASA Astrophysics Data System (ADS)

    Oidov, M.; Fujimaki, H.

    2008-12-01

    The vast territory of Mongolia lies in the heart of the Central Asian Orogenic Belt, one of largest provinces of the Phanerozoic continental growth on Earth (Jahn et al., 2004). We present new petrographic, geochemical and Sr-Nd isotopic analyses on Mesozoic igneous rocks emplaced in Central Mongolia. The Mesozoic igneous suites, those exposed in the Tsagaandelger area, pass upwards from alkaline series trachytic rocks and overlain by tuffaceous sediments. Those are intruded by calc alkaline leucocratic granites and covered by Late Mesozoic calc alkaline bimodal volcanic rocks consisting of basalts and rhyolite. Alkaline series volcanic sequences were erupted in Early-Middle Triassic (241 Ma) and characterized by LILE, LREE enrichment and significant Nb-Ta depletion. Rocks have weakly enriched initial 87Sr86Sr ratios of 0.705 to 0.706 and positive ɛNd(t) values (0.7 to 4). The crystallization age of intrusive rocks is 231 Ma. The majority of samples is slightly peraluminous and can be classified as granite, including monzogranite, granodiorite and aplite. Granites are characterized by near- zero ɛNd(t) values (0.7 to 2) and tetrad effect in their REE distribution patterns. Further Cretaceous volcanic sequences have lower contents of LILE and higher contents of HFS and REE, comparing with Triassic volcanic sequences. The Cretaceous volcanic rocks have the initial 87Sr86Sr ratios between 0.705 and 0.719 and near-zero ɛNd(t) values (-0.7 to 1.6). Trace element geochemistry indicates that Mesozoic volcanic rocks from the studied area are arc related. The Triassic volcanic and plutonic rocks could be emplaced in active continental margin settings. Post collisional extensional regime could be started with Early Cretaceous volcanism. The mass balance calculation suggests that the all Mesozoic volcanic and plutonic rocks were derived from sources composed of more than 80% juvenile mantle-derived component. Our data confirm the earlier observations of similar isotopic

  5. Magmatic tritium

    SciTech Connect

    Goff, F.; Aams, A.I.; McMurtry, G.M.; Shevenell, L.; Pettit, D.R.; Stimac, J.A.; Werner, C.

    1997-07-01

    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 have wide application to a host of other volcanological topics.

  6. A two-component mantle source feeding Mt. Etna magmatism: Insights from the geochemistry of primitive magmas

    NASA Astrophysics Data System (ADS)

    Correale, Alessandra; Paonita, Antonio; Martelli, Mauro; Rizzo, Andrea; Rotolo, Silvio G.; Corsaro, Rosa Anna; Di Renzo, Valeria

    2014-01-01

    The major elements, trace elements and Sr and Nd isotopes of selected Etnean primitive rocks (< 15 ky BP) were studied in order to characterize their mantle source. The noble-gas geochemistry of fluid inclusions in minerals from the same lavas was also investigated. The major element compositions of whole rocks and minerals showed that these products are among the most primitive at Mt. Etna, comprising 6.3-17.5 wt.% MgO. The variable LREE (Light Rare Earth Elements) enrichment relative to MORB (Mid-Ocean Ridge Basalt) (Lan/Ybn = 11-26), together with the patterns of certain trace-element ratios (i.e., Ce/Yb versus Zr/Nb and Th/Y versus La/Yb), can be attributed to varying degrees of melting of a common mantle source. Numerical simulations performed with the MELTS program allowed the melting percentages associated with each product to be estimated. This led us to recalculate the hypothetical parental trace-element content of the Etnean mantle source, which was common to all of the investigated rocks. The characteristics of the Sr, Nd and He isotopes confirmed the primitive nature of the rocks, with the most-depleted and primitive lava being that of Mt. Spagnolo (SPA; 143Nd/144Nd = 0.512908 87Sr/86Sr = 0.703317-0.703325 and 3He/4He = 7.6 Ra), and highlighted the similarity of the mantle sources feeding the volcanic activity of Mt. Etna and the Hyblean Plateau (a region to the south of Mt. Etna and characterized by older magmatism than Mt. Etna). The coupling of noble gases and trace elements suggests an origin for the investigated Etnean lavas from melting of a Hyblean-like mantle, consisting of a two-component source where a peridotitic matrix is veined by 10% pyroxenite. A variable degree of mantle contamination by crustal-like fluids, probably related to subduction, is proposed to explain the higher Sr-isotope and lower Nd-isotope values in some rocks (143Nd/144Nd up to 0.512865 and 87Sr/86Sr up to 0.703707). This process probably occurred in the source prior to

  7. Neoproterozoic-Early Devonian magmatism in the Antigonish Highlands, Avalon terrane, Nova Scotia: Tracking the evolution of the mantle and crustal sources during the evolution of the Rheic Ocean

    NASA Astrophysics Data System (ADS)

    Murphy, J. Brendan; Dostal, Jaroslav; Keppie, J. Duncan

    2008-12-01

    The Antigonish Highlands lies in the Avalon terrane (Avalonia) in the Canadian Appalachians and records four episodes of continental rift-related bimodal magmatism ranging in age from Late Neoproterozoic to Middle Devonian. The oldest episode (ca. 615 Ma Clydesdale Formation) was emplaced in a local rift setting in an Andean-style arc when Avalonia resided along the northern Gondwanan margin. Early Cambrian magmatism (Arbuckle Brook Formation) occurred in a local transtensional setting after arc magmatism had given way to a San Andreas-type transform environment. Middle Ordovician (Dunn Point and Bears Brook formations) magmatism occurred in a local rift in an ensialic island arc setting, analogous to the modern Taupo Volcanic Zone in northern New Zealand, after Avalonia had separated from Gondwana. Middle Devonian (McArras Brook Formation and correlatives) occurred after Avalonia had collided with Laurentia. In each episode, mafic rocks are characterized by high FeO t, FeO t/MgO, TiO 2, Zr/Y and Ti/Y typical of differentiated within-plate mafic magmas. Multi-element spider-diagrams indicate that all four episodes were generated in an enriched sub-continental lithospheric mantle. LIL, HFS and REE patterns indicate that the Clydesdale, Dunn Point/Bears Brook and McArras Brook formations were sourced in the shallow (spinel lherzolite) mantle, and that the Arbuckle Brook Formation was generated in the deeper (garnet lherzolite) mantle. In each episode, coeval felsic rocks were generated by crustal anatexis. Taken together, the Sm-Nd isotopic data for the mafic rocks form an envelope that defines the evolution of the mantle source beneath the Antigonish Highlands that was enriched between 0.8 and 1.1 Ga and has an average Sm/Nd ratio of ca. 0.24 (a value that is typical of an enriched mantle source). Sm-Nd isotopic data for the felsic rocks are characterized by a recurrence of TDM ages between 0.95 and 1.0 Ga, interpreted to reflect repeated melting of the lower crust

  8. Magmatic Enclaves

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.

    2011-12-01

    Over the past three decades, the term "magmatic enclave" has become widely accepted for small (typically <1 m) spheroidal bodies of igneous rock that are compositionally distinct from their coeval lava or intrusive hosts (e.g., Didier and Barbarin, 1991). Certain magmatic enclaves are crystal cumulates but most are globs of magma more mafic and hotter than their host. Understanding the origins and scientific utility of enclaves is aided by their common occurrence in both plutonic and volcanic rocks. Enclaves were noticed and described by geologists and petrographers for decades (e.g., Lacroix, 1890; Pabst, 1928; Williams, 1931) before it was demonstrated that many enclaves were introduced into their hosts while both were in a magmatic state: For example, in plutons by Wager and Bailey (1953), Walker and co-workers (1960's), Didier (1973), Wiebe (1980), and Vernon (1984), and in volcanic rocks by Wilcox (1944), Eichelberger (1980), and Bacon (1986). Spheroidal forms, crenulated or fine-grained margins, and crystal textures of enclaves are evidence of magmatic behavior. On entrapment, an enclave rapidly loses heat to its host and grows groundmass crystals whose size and morphology reflect the degree of enclave undercooling that is closely related to compositional contrast. At depth, some of the water dissolved in enclave magma may enter hydrous silicates but much can exsolve, including during partial crystallization. Vapor exsolution creates spherical vesicles and irregular gas pockets between crystals that give most volcanic enclaves porous textures. A vapor pressure gradient between an incompletely crystallized rigid enclave interior and host magma can drive residual melt into segregation vesicles and even out of the enclave by gas-driven filter pressing. Such enclaves have cores with cumulate-like compositions. Felsic droplets in mafic inclusions in plutonic rocks are interpreted as crystallized segregation vesicles. Enclaves are samples of magma that may not

  9. Transition from adakitic to bimodal magmatism induced by the paleo-Pacific plate subduction and slab rollback beneath SE China: Evidence from petrogenesis and tectonic setting of the dike swarms

    NASA Astrophysics Data System (ADS)

    Xia, Yan; Xu, Xisheng; Liu, Lei

    2016-02-01

    The late Mesozoic magmatic record of SE China is dominated by felsic volcanics and intrusions. However, this magmatism mainly occurred in coastal areas at 110-80 Ma, in contrast to poorly researched dike swarms that were emplaced inland at 165-120 Ma. Here, we focus on Early Cretaceous mafic and felsic dike swarms that provide new insights into the tectono-magmatic evolution of SE China. The swarms were intruded into Neoproterozoic plutons and include granodioritic porphyry, granitic porphyry, and diabase dikes. The granodioritic porphyry (128 ± 2 Ma) dikes are geochemically similar to adakitic rocks, suggesting that inland adakitic magmatism occurred between ca. 175 and ca. 130 Ma. The majority of these adakitic rocks are calc-alkaline and have Sr-Nd-Hf-O isotopic compositions that are indicative of derivation from a Neoproterozoic magmatic arc source within the lower crust. The granitic porphyry and diabase dikes were emplaced coevally at ca. 130 Ma, and the former contain high alkali and high field strength element (HFSE; e.g., Zr, Nb, Ce, and Y) concentrations that together with their high Ga/Al and FeOT/(FeOT + MgO) ratios imply an A-type affinity. The widespread ca. 130 Ma magmatism that formed the A-type granites and coeval diabase dikes defines a NE-SW trending inland belt of bimodal magmatism in SE China. The presence of mafic enclaves in some of the A-type granites, and the Sr-Nd-Hf isotopic compositions of the latter are indicative of inadequate mixing between the basement sediment-derived and coeval mantle-derived basaltic melts that define the bimodal magmatism. The transition from adakitic rocks to bimodal magmatism in the inland region of SE China indicates a change in the prevailing tectonic regime. This change was associated with an increase in the dip angle of the northwestward-subducting paleo-Pacific Plate beneath SE China between the Middle Jurassic and the Early Cretaceous. This resulted in a transition from a local intra-plate extensional

  10. Timing and sources of granite magmatism in the Ribeira Belt, SE Brazil: Insights from zircon in situ U-Pb dating and Hf isotope geochemistry in granites from the São Roque Domain

    NASA Astrophysics Data System (ADS)

    Janasi, Valdecir de Assis; Andrade, Sandra; Vasconcellos, Antonio Carlos B. C.; Henrique-Pinto, Renato; Ulbrich, Horstpeter H. G. J.

    2016-07-01

    Eight new in situ U-Pb zircon age determinations by SHRIMP and LA-MC-ICPMS reveal that the main granitic magmatism in the São Roque Domain, which is largely dominated by metaluminous high-K calc-alkaline monzogranites with subordinate peraluminous leucogranites, occurred between 604 ± 3 and 590 ± 4 Ma. This small temporal range is ca. 20-30 Ma younger than previously admitted based on U-Pb TIMS dates from literature, some of which obtained in the same occurrences now dated. The observed discrepancy seems related to the presence of small Paleoproterozoic inherited cores in part of the zircon populations used for TIMS multigrain dating, which could also respond for the unusually high (up to 10 Ma) uncertainty associated with most of these dates. The younger age range now identified for the São Roque granite magmatism has important implications for the evolution of the Ribeira Fold Belt. Whilst previously admitted ages ca. 620-630 Ma substantiated correlations with the widespread and intensely foliated high-K calc-alkaline granitoid rocks of the neighbor Socorro-Guaxupé Nappe (potentially associated with an accretionary continental margin), the ˜600-590 Ma interval seems more consistent with a late deformation tectonic setting. Strongly negative ɛHf(t) characterize the magmatic zircons from the São Roque Domain granites. An eastward increase from -22 in the São Roque Granite to -11 in the Cantareira Granite and neighboring stocks suggests an across-domain shift in granite sources. Such eastward younging of sources, also indicated by Sm-Nd isotope data from granites and supracrustal sequences in neighboring domains, is suggestive that some of the first-order limits and discontinuities in this belt are not defined by the strike-slip fault systems traditionally taken to separate distinct domains. Although the negative ɛHf(t) and ɛNd(t) indicate sources with long crustal residence for all studied granite plutons, the observed range is more radiogenic than the

  11. Timing and sources of granite magmatism in the Ribeira Belt, SE Brazil: Insights from zircon in situ U–Pb dating and Hf isotope geochemistry in granites from the São Roque Domain

    NASA Astrophysics Data System (ADS)

    Janasi, Valdecir de Assis; Andrade, Sandra; Vasconcellos, Antonio Carlos B. C.; Henrique-Pinto, Renato; Ulbrich, Horstpeter H. G. J.

    2016-07-01

    Eight new in situ U-Pb zircon age determinations by SHRIMP and LA-MC-ICPMS reveal that the main granitic magmatism in the São Roque Domain, which is largely dominated by metaluminous high-K calc-alkaline monzogranites with subordinate peraluminous leucogranites, occurred between 604 ± 3 and 590 ± 4 Ma. This small temporal range is ca. 20-30 Ma younger than previously admitted based on U-Pb TIMS dates from literature, some of which obtained in the same occurrences now dated. The observed discrepancy seems related to the presence of small Paleoproterozoic inherited cores in part of the zircon populations used for TIMS multigrain dating, which could also respond for the unusually high (up to 10 Ma) uncertainty associated with most of these dates. The younger age range now identified for the São Roque granite magmatism has important implications for the evolution of the Ribeira Fold Belt. Whilst previously admitted ages ca. 620-630 Ma substantiated correlations with the widespread and intensely foliated high-K calc-alkaline granitoid rocks of the neighbor Socorro-Guaxupé Nappe (potentially associated with an accretionary continental margin), the ∼600-590 Ma interval seems more consistent with a late deformation tectonic setting. Strongly negative εHf(t) characterize the magmatic zircons from the São Roque Domain granites. An eastward increase from -22 in the São Roque Granite to -11 in the Cantareira Granite and neighboring stocks suggests an across-domain shift in granite sources. Such eastward younging of sources, also indicated by Sm-Nd isotope data from granites and supracrustal sequences in neighboring domains, is suggestive that some of the first-order limits and discontinuities in this belt are not defined by the strike-slip fault systems traditionally taken to separate distinct domains. Although the negative εHf(t) and εNd(t) indicate sources with long crustal residence for all studied granite plutons, the observed range is more radiogenic than the

  12. Petrologic observations and multiphase dynamics in highly-crystalline magmatic mushes sourcing Galápagos Island volcanoes

    NASA Astrophysics Data System (ADS)

    Schleicher, J.; Bergantz, G. W.; Geist, D.

    2013-12-01

    The inability to directly observe magma chambers makes it difficult to understand their dynamics. Yet conditions within the chamber determines whether an eruption will occur, or if the magma is allowed to cool to complete crystallization. Eruption styles are also conditioned by these dynamics, as the amount of overpressure within the chamber regulates effusive or explosive eruptions. Plutons and volcanoes appear to share similar states: magma reservoirs that are temporally and spatially dominated by crystal-rich states, known as magmatic mushes. To explore the dynamics of mushes, we turn to the relatively simple ocean island end-member of magmatic systems. Ocean island porphyritic basalt flows provide a snapshot of the mush conditions prior to eruption. The Galápagos Islands are a system of ocean islands displaying spatial and temporal variation in their eruption styles and deposits. We have collected porphyritic basalt samples from Rábida Island of the Galápagos Archipelago which contains deposits ranging in ages from 0.7-1.0 Ma. Chemical zoning within phenocrysts indicates intermittent efficient mixing occurs within the mush, despite high viscosities and corresponding low-Reynolds number conditions. To further explore the dynamics of mixing, we present preliminary Eulerian-Lagrangian multiphase models using the fluids modeling software MFIX (Multiphase Flow with Interphase eXchanges). This computational fluid dynamics-discrete element method (CFD-DEM) allows for individual crystal tracking within the system and monitors interactions between the fluid and solid phases. Of special interest is the open-system dynamical response of a mush to a reintrusion event. Unlike high-Reynolds number flows, such as air or water systems, magmatic mushes have high viscosities, indicating that turbulent motion is not the primary mixing mechanism. Instead, mixing appears to be caused by mechanical unlocking from an increase in pore pressure as additional magma is injected. The

  13. An experimental and petrologic investigation of the source regions of lunar magmatism in the context of the primordial differentiation of the moon

    NASA Astrophysics Data System (ADS)

    Elardo, Stephen M.

    The primordial differentiation of the Moon via a global magma ocean has become the paradigm under which all lunar data are interpreted. The success of this model in explaining multiple geochemical, petrologic, and isotopic characteristics lunar geology has led to magma oceans becoming the preferred model for the differentiation of Earth, Mars, Mercury, Vesta, and other large terrestrial bodies. The goal of this work is to combine petrologic analyses of lunar samples with high pressure, high temperature petrologic experiments to place new and detailed constraints the petrogenetic processes that operated during different stages of lunar magmatism, the processes that have acted upon these magmas to obscure their relationship to their mantle source regions, and how those source regions fit into the context of the lunar magma ocean model. This work focuses on two important phases of lunar magmatism: the ancient crust-building plutonic lithologies of the Mg-suite dating to ~4.3 Ga, and the most recent known mare basaltic magmas dating to ~3 Ga. These samples provide insight into the petrogenesis of magmas and interior thermal state when the Moon was a hot, juvenile planet, and also during the last gasps of magmatism from a cooling planet. Chapter 1, focusing on Mg-suite troctolite 76535, presents data on chromite symplectites, olivine-hosted melt inclusions, intercumulus mineral assemblages, and cumulus mineral chemistry to argue that the 76535 was altered by metasomatism by a migrating basaltic melt. This process could effectively raise radioisotope systems above their mineral-specific blocking temperatures and help explain some of the Mg-suite-FAN age overlap. Chapter 2 focuses on lunar meteorites NWA 4734, 032, and LAP 02205, which are 3 of the 5 youngest igneous samples from the Moon. Using geochemical and isotopic data combined with partial melting models, it is shown that these basalts do not have a link to the KREEP reservoir, and a model is presented for low

  14. Examining Student Factors in Sources of Setting Accommodation DIF

    ERIC Educational Resources Information Center

    Lin, Pei-Ying; Lin, Yu-Cheng

    2014-01-01

    This exploratory study investigated potential sources of setting accommodation resulting in differential item functioning (DIF) on math and reading assessments for examinees with varied learning characteristics. The examinees were those who participated in large-scale assessments and were tested in either standardized or accommodated testing…

  15. The Mount Kozak magmatic complex, Western Anatolia

    NASA Astrophysics Data System (ADS)

    Altunkaynak, Ş.; Yılmaz, Y.

    1998-10-01

    The Mount Kozak igneous complex is located close to the towns of Ayvalık, Bergama and Burhaniye in the Western Anatolia, Turkey. Magmatic activity occurred during the Late Oligocene-Early Miocene, beginning with the emplacement of the Kozak pluton. Sheet intrusive rocks formed around it coevally. They are surrounded by the volcanic rocks, partly contemporaneously with the emplacement of the granitic rocks during the Early Miocene. The Upper Oligocene-Lower Miocene magmatic rocks of the Kozak region are represented by a high-K, calc-alkaline suite of predominantly intermediate and acidic composition. Their geochemical characteristics suggest that the magmas are hybrid, and were formed from a similar source, representing mantle-derived magmas, contaminated by crustal materials. The cogenetic plutonic rocks, the hypabyssal rocks and the overlying volcanic associations are related to one another in space and time, and appear to have been connected to a shallow level granitic intrusion in a caldera collapse setting. The calc-alkaline magmatic activity waned during the Middle Miocene. When the volcanism was rejuvenated during the Late Miocene-Pliocene, alkaline basalt lavas were formed as fissure eruptions.

  16. Secular Changes in Lava/Magma Channelization and the Volcanic/Subvolcanic/Plutonic Settings of Magmatic Ni-Cu-PGE and Chromite Mineralization on Earth

    NASA Astrophysics Data System (ADS)

    Lesher, C. M.

    2015-12-01

    The degree of channelization in magmatic systems is controlled by magma density, viscosity, and flux; environment of emplacement (subaerial/submarine) and substrate topography if volcanic; and country rock density/rheology/structure and degree/orientation of differential stress if subvolcanic/plutonic. Lower viscosity Archean komatiites ascended rapidly, producing lava channels (e.g., Kambalda) and subvolcanic feeder sills (e.g., Mt. Keith). Higher viscosity Proterozoic komatiitic basalts/ferropicrites/picrites had more difficulty ascending through the crust and produced subvolcanic feeder dikes (e.g., Eagle-Tamarack, Voisey's Bay) and sills (e.g., Thompson, Pechenga) and fewer lava channels (e.g., Raglan). Phanerozoic picrites/basalts produced mainly dikes (e.g., Kalatongke) and feeder sills (e.g., Noril'sk, Jinchuan). All were capable of eroding S-rich substrates/wall rocks and generating magmatic Ni-Cu-PGE deposits. Some chromite deposits appear to have formed in channelized magmatic systems, and although typically finer-grained chromite is much easier to transport than typically larger sulfide melt droplets, almost all known volcanic Ni-Cu-PGE deposits formed during lava emplacement and no volcanic chromite deposits have yet been identified. This suggests that Fe-Ni-Cu-(PGE) sulfides and chromite are more easily transported horizontally within sills and lava channels, but less easily transported vertically. If magmatic Fe-Ni-Cu-(PGE) deposits can form by partial melting of Fe sulfide-rich sediments underneath lava/magma channels and dynamic upgrading of sulfide xenomelts by reaction with the magma (the prevailing model), then magmatic chromite deposits can form by partial melting of Fe oxide-rich sediments underneath lava/magma channels and dynamic upgrading of oxide xenocrysts by reaction with the magma. The anomalously thick (up to 100m) Black Thor-Blackbird, Inyala, Ipueira-Medrado, Kemi, Nkomati, and Sukinda chromite deposits may be examples of this process.

  17. New constraints on the magmatic system beneath Newberry Volcano from the analysis of active and passive source seismic data and ambient noise

    NASA Astrophysics Data System (ADS)

    Heath, Benjamin Allen

    Using joint P-wave seismic tomography, receiver functions, and ambient noise we image the magmatic structure beneath Newberry Volcano, located near Bend, Oregon. Use of active source and teleseismic events in a joint tomographic inversion provides the ray crossings necessary to resolve a low velocity body around 4 km depth. Receiver functions show large lateral heterogeneity and are consistent with the location of a low velocity body derived from the tomography but require a larger low velocity anomaly. Ambient noise autocorrelations are used to image a low velocity reflector, located at ~3 km depth, shallower than the imaged low velocity body recovered using tomography and receiver functions. Ultimately, our results reveal a magma chamber at 3-4 km depth beneath Newberry caldera, with an overlying partially molten sill at ~3 km depth. These results show the usefulness of dense seismometer deployments over volcanoes.

  18. Source-inherited compositional diversity in granite batholiths: The geochemical message of Late Paleozoic intrusive magmatism in central Calabria (southern Italy)

    NASA Astrophysics Data System (ADS)

    Fiannacca, Patrizia; Cirrincione, Rosolino; Bonanno, Fiorenza; Carciotto, Manuele Mario

    2015-11-01

    magma source. Mantle-derived magmas do not appear to have played a role in the geochemical diversity of the Serre Batholith granitoids; their inherited arc signature resulted from partial melting of crustal material of magmatic arc derivation, such as magnesian igneous rocks and sediments derived from their rapid erosion. This study suggests that post-collisional granitoid magmatism is likely not to be associated with the direct generation of new continental crust; all the granitoid rock types appear to represent recycled and reworked crustal material.

  19. Magmatic gas source for the stratospheric SO[sub 2] cloud from the June 15, 1991, eruption of Mount Pinatubo

    SciTech Connect

    Westrich, H.R. ); Gerlach, T.M. )

    1992-10-01

    A water-rich magmatic gas phase escaped explosively from Mount Pinatubo on June 15, 1991, taking with it a load of crystalline and molten material sufficient to form pumice and tephra deposits with an estimated total dense-rock-equivalent volume of 3-5 km[sup 3], and carrying in it enough sulfur to form a 20 Mt SO[sub 2] cloud in the stratosphere. Application of the petrologic method for estimating sulfur degassing during the climatic event from the sulfur content of trapped glass inclusions and matrix glasses in the pumice deposits requires an unacceptably large volume of erupted magma to account for SO[sub 2] in the stratospheric cloud. The ubiquitous presence of primary vapor bubbles in glass inclusions and unaltered anhydrite phenocrysts in the pumice suggest that sulfur was present in a separate H[sub 2]O-rich gas phase of the Pinatubo magma before eruption. Thus, for this eruption, and perhaps others, the petrologic method for estimating sulfur degassing is prone to substantial underestimation of sulfur release and the potential climatic impact of past explosive eruptions.

  20. The lower Paleozoic granitoids from the central part of the Qilian block, NW China: An example of granitoid magmatism in a continental backarc setting

    NASA Astrophysics Data System (ADS)

    Tung, kuo-an; Yang, Houng-yi; Yang, Huai-jen; Liu, Dunyi; Zhang, Jianxin; Wu, Cailai; Shau, Yen-hong; Tseng, Chien-yuan

    2016-04-01

    The petrology, geochemistry, geochronology, and Sr-Nd-Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402-447 Ma for the S-type and 419-451 Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu* = 0.18-0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu* = 0.71-1.16). The initial (87Sr/86Sr) values are 0.708848-0.713651 for the S-type and 0.704230-0.718108 for the I-type granitoids. The ɛNd(450 Ma) values are -8.9-~-4.1 and -9.7~+1.9 for the S-type and I-type granitoids, respectively. The TDM values are 1.5-2.4 Ga for the S-type and 1.0-2.3 Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50 million years. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0 Ga for the Qilian block.

  1. Evolution of Northeast Atlantic magmatic continental margins

    NASA Astrophysics Data System (ADS)

    England, Richard; Cornwell, David; Ramsden, Alice

    2014-05-01

    One of the major problems interpreting the evolution of magmatic continental margins such as those which dominate the Irish, UK and Norwegian margins of the NE Atlantic 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 contraints we have examined the Ethiopian ñ Afar rift system to try to understand the rifting process. This magmatic rift system provides, along its length, a series of ësnapshotsí into the possible tectonic evolution of a magmatic continental margin which are associated with different amounts of extension. The Main Ethiopian rift contains an embryonic magmatic passive margin dominated by faulting at the margins of the rift and en-echlon magmatic zones at the centre. Further north toward Afar the rift becomes infilled with extensive lava flows fed from fissure systems in the widening rift zone. Deep seismic profiles crossing the NE Atlantic margins reveal ocean dipping reflector sequences (ODRS) of basaltic lavas overlying extended crust and lower crustal sill complexes of intruded igneous rock, often referred to as underplate, which extend back beneath the continental margin. The ODRS show a variety of morphologies and settings but 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

  2. Crustal rifting and magmatic underplating in the Izu-Ogasawara (Bonin) intra-oceanic arc detected by active source seismic studies

    NASA Astrophysics Data System (ADS)

    Takahashi, N.; Kodaira, S.; Yamashita, M.; Miura, S.; Sato, T.; No, T.; Tatsumi, Y.; Kaneda, Y.

    2009-12-01

    Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has carried out seismic experiments using a multichannel reflection system and ocean bottom seismographs (OBSs) in the Izu-Ogasawara (Bonin)-Mariana (IBM) arc region since 2002 to understand growth process of continental crust. The source was an airgun array with a total capacity of 12,000 cubic inches and the OBSs as the receiver were deployed with an interval of 5 km for all seismic refraction experiments. As the results, we obtained crustal structures across the whole IBM arc with an interval of 50 km and detected the structural characteristics showing the crustal growth process. The IBM arc is one of typical oceanic island arc, which crustal growth started from subduction of an oceanic crust beneath the other oceanic crust. The arc crust has developed through repeatedly magmatic accretion from subduction slab and backarc opening. The volcanism has activated in Eocene, Oligocene, Miocene and Quaternary (e.g., Taylor, 1992), however, these detailed locations of past volcanic arc has been remained as one of unknown issues. In addition, a role of crustal rifting for the crustal growth has also been still unknown issue yet. Our seismic structures show three rows of past volcanic arc crusts except current arc. A rear arc and a forearc side have one and two, respectively. The first one, which was already reported by Kodaira et al. (2008), distributes in northern side from 27 N of the rear arc region. The second one, which develops in the forearc region next to the recent volcanic front, distributes in whole of the Izu-Ogasawara arc having crustal variation along arc direction. Ones of them sometimes have thicker crust than that beneath current volcanic front and no clear topographic high. Last one in the forearc connects to the Ogasawara Ridge. However, thickest crust is not always located beneath these volcanic arcs. The initial rifting region like the northern end of the Mariana Trough and the Sumisu

  3. Evidence for prolonged mid-Paleozoic plutonism and ages of crustal sources in east-central Alaska from SHRIMP U-Pb dating of syn-magmatic, inherited, and detrital zircon

    USGS Publications Warehouse

    Dusel-Bacon, C.; Williams, I.S.

    2009-01-01

    Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses of igneous zircons from the Lake George assemblage in the eastern Yukon-Tanana Upland (Tanacross quadrangle) indicate both Late Devonian (???370 Ma) and Early Mississippian (???350 Ma) magmatic pulses. The zircons occur in four textural variants of granitic orthogneiss from a large area of muscovite-biotite augen gneiss. Granitic orthogneiss from the nearby Fiftymile batholith, which straddles the Alaska-Yukon border, yielded a similar range in zircon U-Pb ages, suggesting that both the Fiftymile batholith and the Tanacross orthogneiss body consist of multiple intrusions. We interpret the overall tectonic setting for the Late Devonian and Early Mississippian magmatism as an extending continental margin (broad back-arc region) inboard of a northeast-dipping (present coordinates) subduction zone. New SHRIMP U-Pb ages of inherited zircon cores in the Tanacross orthogneisses and of detrital zircons from quartzite from the Jarvis belt in the Alaska Range (Mount Hayes quadrangle) include major 2.0-1.7 Ga clusters and lesser 2.7-2.3 Ga clusters, with subordinate 3.2, 1.4, and 1.1 Ga clusters in some orthogneiss samples. For the most part, these inherited and core U-Pb ages match those of basement provinces of the western Canadian Shield and indicate widespread potential sources within western Laurentia for most grain populations; these ages also match the detrital zircon reference for the northern North American miogeocline and support a correlation between the two areas.

  4. Source rock potential of shallow-water evaporitic settings

    SciTech Connect

    Warren, J.K.

    1986-05-01

    In the major evaporitic environments on the world's surface today, most organic matter accumulates in shallow subaqueous to seasonally subaerially exposed, algal-mat sediments. Given the present depositional setting, this organic matter probably could not be preserved to form source rocks. However, if the authors place such evaporite deposition into a geologic context, source rocks could have formed in shallow-water settings in the past. Such settings were characterized by hydrologic conditions that allowed the retention of hypersaline, anoxic pore water to depths where the organic material was buried deep enough to generate hydrocarbons. When deep-basin, shallow-water, evaporite successions were laid down in basins such as the Mediterranean during the late Miocene, the Michigan basin during the Silurian, and in other large saline giants, conditions were right for source rocks to form within shallow-water and salt-flat evaporitic environments. The evaporites in these saline giants were deposited under conditions of relatively shallow water (< 50 m); the basin never appears to have dried out, but water levels changed quickly (approx. 10,000 years) from shallow to deep. Continual water saturation coupled with saline pore fluids prevented the inflow of fresh, oxidizing ground water into the basin center of shallow-water organic-rich evaporites. Immature hydrocarbons derived from such rocks today drip from the 5.5-m.y. old evaporites of Sicily in active salt and sulfur mines. Organic-rich sediments could also be preserved to generate hydrocarbons in rapidly subsiding rift basins. In such basins, rapid burial has prevented the entrance of fresher oxygenated waters and the associated degradation and destruction of the organic matter. The early continental rift stage generates the source rocks; the ephemeral streams, wadis, and dune fields become the reservoirs, and the subsequent evaporite stage seals the reservoir.

  5. Comprehensive, Multi-Source Cyber-Security Data Set

    DOE Data Explorer

    Kent, Alexander D. [Los Alamos National Laboratory

    2015-05-21

    This data set represents 58 consecutive days of de-identified event data collected from five sources within Los Alamos National Laboratory’s corporate, internal computer network. The data sources include Windows-based authentication events from both individual computers and centralized Active Directory domain controller servers; process start and stop events from individual Windows computers; Domain Name Service (DNS) lookups as collected on internal DNS servers; network flow data as collected on at several key router locations; and a set of well-defined red teaming events that present bad behavior within the 58 days. In total, the data set is approximately 12 gigabytes compressed across the five data elements and presents 1,648,275,307 events in total for 12,425 users, 17,684 computers, and 62,974 processes. Specific users that are well known system related (SYSTEM, Local Service) were not de-identified though any well-known administrators account were still de-identified. In the network flow data, well-known ports (e.g. 80, 443, etc) were not de-identified. All other users, computers, process, ports, times, and other details were de-identified as a unified set across all the data elements (e.g. U1 is the same U1 in all of the data). The specific timeframe used is not disclosed for security purposes. In addition, no data that allows association outside of LANL’s network is included. All data starts with a time epoch of 1 using a time resolution of 1 second. In the authentication data, failed authentication events are only included for users that had a successful authentication event somewhere within the data set.

  6. Unsupervised Source Separation for Large Planetary Data Sets

    NASA Astrophysics Data System (ADS)

    Schmidt, A.; Moussaoui, S.; Legendre, M.; Schmidt, F.

    2012-12-01

    Implementations of non-negative matrix approximation (NNMA) algorithms have reached a level of maturity that makes them suitable for application on large planetary datasets. Our results imply that they can effectively factor large collections of hyperspectral measurements into sources and abundances under linearity and non-negativity constraints with reasonable resources. This work presents our first steps towards automated large-scale analysis of hyperspectral data sets with the focus on spectral and geographical summarization using NNMA. The method we implement consists of various steps: after initial calibration, randomized NNMA is used to extract source spectra; these are then distributed on a virtual sphere and classified according to similarity and proximity; for each class of source, an abundance map is generated and presented to the user for interpretation. We use the method on both imaging and point spectrometer data but require a selection of appropriate imagery (for example, a consistent set of nadir pointing images with compatible illumination conditions). Results can be obtained with reasonable resources in minutes to hours, depending on the size of the dataset and the accuracy required. For the datasets we studied, results have been mostly in line with related work and community opinion. Future work includes treatment of overlapping image regions, incorporation of more robust features and inclusion of more datasets.

  7. Dynamic model of intrusion of magma and/or magmatic fluids in the large-scale deformation source of the Campi Flegrei caldera (Italy).

    NASA Astrophysics Data System (ADS)

    Crescentini, Luca; Amoruso, Antonella; Luongo, Annamaria

    2015-04-01

    The Campi Flegrei (CF) caldera is located in a densely populated area close to Naples (Southern Italy). It is renowned as a site of continual slow vertical movements. After the last eruption in 1538, the caldera generally subsided until 1969 when minor uplift occurred. In the early 1970s this uplift became significant (~1.5 m max). A further large uplift episode occurred from 1982 to 1984 (~1.8 m max), and subsequently smaller uplift episodes have occurred since then. Amoruso et al. (2014a,b) have recently shown that the CF surface deformation field from 1980 to 2013 can be decomposed into two stationary parts. Large-scale deformation can be explained by a quasi-horizontal source, oriented NW to SE and mathematically represented by a pressurized finite triaxial ellipsoid (PTE) ~4 km deep, possibly related to the injection of magma and/or magmatic fluids from a deeper magma chamber into a sill, or pressurization of interconnected (micro)cavities. Residual deformation not accounted for by PTE is confined to the Solfatara fumarolic area and can be mathematically explained by a small (point) pressurized oblate spheroid (PS) ~2 km below the Solfatara fumarolic field, that has been equated with a poroelastic response of the substratum to pore pressure increases near the injection point of hot magmatic fluids into the hydrothermal system. A satisfying feature of this double source model is that the geometric source parameters of each are constant over the period 1980-2013 with the exception of volume changes (potencies). Several papers have ascribed CF deformation to the injection of magmatic fluids at the base of the hydrothermal system. All models predict complex spatial and temporal evolution of the deformation pattern and consequently contrast with the observed deformation pattern stationarity. Also recently proposed dynamic models of sill intrusion in a shallow volcanic environment do not satisfy the observed CF deformation pattern stationarity. We have developed an

  8. The Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion, northeast of Beijing (North China): Implications for the mantle source of the giant Late Mesozoic magmatic event in the North China Craton

    NASA Astrophysics Data System (ADS)

    Liu, Ping-Ping; Zhou, Mei-Fu; Yan, Dan-Ping; Zhao, Guo-Chun; Su, Shang-Guo; Wang, Xiao-Lin

    2015-08-01

    The Early Cretaceous Shangzhuang Fe-Ti oxide-bearing layered mafic intrusion in the Yanshan Belt northeast of Beijing is coeval with the giant Late Mesozoic igneous province in the eastern part of the North China Craton (NCC). This magmatic event was associated with lithospheric thinning and thus the igneous rocks have been used to characterize the nature of the Mesozoic mantle beneath the NCC. The Shangzhuang mafic pluton intruded a large granodioritic complex and crystallized at ~ 850-872°C at a depth of 13-14 km. It is composed, from the base upward, of troctolite, Fe-Ti oxide-bearing gabbronorite and gabbro. Rocks from this intrusion have low initial 87Sr/86Sr ratios (0.7053-0.7058), negative initial εNd values (- 9.4 to - 10.7), highly differentiated LREE and nearly flat HREE patterns indicative of an EMI-like mantle source unaffected by upper crustal contamination. The occurrence of Fe-Ti oxide ore layers, magnetite-ilmenite exsolution lamellae in hornblende and high TiO2 contents of the silicate rocks indicate that they formed from Fe- and Ti-rich ferrobasaltic magmas, which may have been generated by addition of magmas from a deeper mantle source. The presence of orthopyroxene, high-Mg ilmenite (up to 8.5 wt %), hornblende, biotite and high oxygen fugacities calculated from coexisting titanomagnetite-ilmenite pairs can be explained by derivation from an enriched EMI-type mantle modified by fluids from a subducted slab and mixed with asthenospheric or deeper-mantle materials in an extensional setting. Exposure of the complex occurred during large-scale uplift (at least 13 km) and exhumation of the Yanshan orogenic belt in the Early Cretaceous. Chemical metasomatism triggered by water and enhanced by heat from a deep magma source may have played an important role in removing the ancient cratonic root, generating partial melting of the lithospheric mantle and producing coeval magmatic activity in the Mesozoic eastern NCC.

  9. Joint analysis of geodetic and earthquake fault-plane solution data to constrain magmatic sources: A case study from Kīlauea Volcano

    USGS Publications Warehouse

    Wauthier, Christelle; Roman, Diana C.; Poland, Michael

    2016-01-01

    A joint analysis of geodetic and seismic datasets from Kīlauea Volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex, multi-source system. At the end of 2003, Kīlauea's summit began a four-year-long period of inflation due to a surge in magma supply to the volcano. In 2006, for the first time since 1982, Kīlauea's Southwest Rift Zone (SWRZ) also experienced inflation. To investigate the characteristics of active magma sources and the nature of their interactions with faults in the SWRZ during 2006, we integrate, through Coulomb stress modeling, contemporary geodetic data from InSAR and GPS with a new catalogue of double-couple fault-plane solutions for volcano-tectonic earthquakes. We define two periods of inflation during 2006 based on the rate of deformation measured in daily GPS data, spanning February to 15 March 2006 (Period 1) and 16 March to 30 September 2006 (Period 2). InSAR data for these two periods are inverted to determine the position, change in size, and shape of inflation sources in each period. Our new models are consistent with microseismic activity from each period. They suggest that, during Period 1, deformation in the SWRZ can be explained by pressurization of magma in a spherical reservoir beneath the south caldera, and that, during Period 2, magma was also aseismically intruded farther to the southwest into the SWRZ along a sub-horizontal plane. Our Coulomb stress analysis shows that the microseismicity recorded in the SWRZ is induced by overpressurization of the south caldera reservoir, and not by magma intrusion into the SWRZ. This study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation.

  10. A-type magmatism in a syn-collisional setting: The case of the Pan-African Hook Batholith in Central Zambia

    NASA Astrophysics Data System (ADS)

    Milani, Lorenzo; Lehmann, Jérémie; Naydenov, Kalin V.; Saalmann, Kerstin; Kinnaird, Judith A.; Daly, J. Stephen; Frei, Dirk; Lobo-Guerrero Sanz, Alberto

    2015-02-01

    The Pan-African Hook Batholith formed during the assembly of the Gondwana supercontinent as a result of syn-collisional stage interaction between the Congo and Kalahari Cratons. The bimodal magmatism (mafic to predominantly felsic) is characterized by both an alkali-calcic and an alkalic suite, with typical A-type, metaluminous, high Fe/Mg and K/Na geochemical signature. Occasionally, sodic granitoids have been documented. Compositions were driven to more differentiated products by fractional crystallization, while Sr-Nd isotopes exclude crustal assimilation during crystallization. Recent new U-Pb age data constrain most of the felsic magmatism between 550 and 540 Ma. Scattered outcrops of gabbroic rocks, both tholeiitic and alkaline, testify to periodic input of mantle material, and, in some cases, to interaction with metasomatizing fluids. Crystallization ages on mafic rocks span from 570 to 520 Ma, thus indicating that they were contemporaneous with the major granitic intrusion, which was the result of a number of successive felsic batches, eventually forming a coalescing batholith. Highly radiogenic Pb isotopic values attest to the radiogenic character of the rocks. Such an anomalous signature was acquired during, or soon after, magma emplacement, perhaps as result of metasomatizing fluids. Enrichment in Th-U of large portions of the crust along this part of the margin of the Congo Craton is suggested. Geochemical and isotopic evidence support the interaction between mantle components and portions of the deep crust at pressure of < 10 kbar, while decompression melting of rising asthenospheric mantle ponding at the base of the crust heated, and ultimately melted, crustal material. An additional and crucial contribution to the crustal melting was likely provided by internal radiogenic heat production of the thickened crust, and is in agreement with the high radioactivity of the pluton. A tectono-thermal model, implying crustal accretion accompanied by slab

  11. Hydrothermal-flow regime and magmatic heat source of the Cerro Prieto geothermal system, Baja California, Mexico

    SciTech Connect

    Elders, W.A.; Bird, D.K.; Williams, A.E.; Schiffman, P.

    1982-01-01

    This detailed three-dimensional model of the natural flow regime of the Cerro Prieto geothermal field, before steam production began, is based on patterns of hydrothermal mineral zones and light stable isotopic ratios observed in rock samples from more than fifty deep wells, together with temperature gradients, wireline logs and other data. At the level so far penetrated by drilling, this hydrothermal system was heated by a thermal plume of water close to boiling, inclined at 45/sup 0/, rising from the northeast and discharging to the west. To the east a zone of cold water recharge overlies the inclined thermal plume. Fission track annealing studies shows that the reservoir reached 170/sup 0/C only 10/sup 4/ years ago. Oxygen isotope exchange data indicate that a 12 km/sup 3/ volume of rock subsequently reacted with three times its volume of water hotter than 200/sup 0/C. Averaged over the duration of the heating event this would require a flow velocity of about 6 m/year through the pores of a typical cross section of the reservoir having an average porosity of 10%. Although this is an extensional tectonic environment of leaky transform faulting in which repeated intrusions of basalt magma are likely, for simplicity of computation possible heat sources were modelled as simple two dimensional basalt intrusions of various sizes, shapes and locations. We have calculated a series of two-dimensional convective heat transfer models, with different heat sources and permeability distributions. The models which produce the best fit for the temperature distributions observed in the field today have in common a heat source which is a funnel-shaped basalt intrusion, 4 km wide at the top, emplaced at a depth of 5 km to 6 km about 40,000 to 50,000 years ago.

  12. The gravimetric picture of magmatic and hydrothermal sources driving hybrid unrest on Tenerife in 2004/5

    NASA Astrophysics Data System (ADS)

    Prutkin, Ilya; Vajda, Peter; Gottsmann, Jo

    2014-08-01

    We present results from the inversion of gravity changes observed at the central volcanic complex (CVC) of Tenerife, Canary Islands, between May 2004 and July 2005. Marking a period of elevated activity and a reawakening of the volcanic system, the data depict spatial and temporal variations in the sub-surface processes that defined this period of unrest at the Pico Viejo (PV)-Pico Teide (PT) complex, after the last volcanic eruption on Tenerife in 1909. An initial non-linear inversion, based on 3D line segments approximation, yielded three line segments at depths between 1 km a.s.l. and 2 km b.s.l. Our interpretation of the initial inversion results is that the line segments represent apparent composite sources, a superposition of deep and shallow seated sources. We therefore decomposed the gravity changes into shallow and deep parts (fields) using a procedure based on triple harmonic continuation. The shallow and deep fields could then be inverted separately, using the same inversion methodology. The deep field constrains two connected line segments at the depth of about 6 km b.s.l., in the center of the NW seismogenic zone of VT event swarm of the seismic unrest, that we interpret as magma input. The inversion of the shallow field images three weak line segments that are all situated at very shallow, near-surface depths. We interpret the weak segments as hydrothermal sources potentially excited by the deeper magma injection. Our results indicate no significant input into the shallow phonolitic plumbing system of the PV-PT complex, but rather a deeper-seated rejuvenation of the mafic feeder reservoir. The emerging picture from our analysis is that the 2004/5 unrest on Tenerife was of a hybrid nature due to the combination of a deep magma injection (failed eruption?) coupled with fluid migration to shallow depths. The identified causative link between deep and shallow unrest sources indicates the presence of permeable pathways for shallow fluid migration at the

  13. Transition of Mount Etna lavas from a mantle-plume to an island-arc magmatic source.

    PubMed

    Schiano, P; Clocchiatti, R; Ottolini, L; Busà, T

    2001-08-30

    Mount Etna lies near the boundary between two regions that exhibit significantly different types of volcanism. To the north, volcanism in the Aeolian island arc is thought to be related to subduction of the Ionian lithosphere. On Sicily itself, however, no chemical or seismological evidence of subduction-related volcanism exists, and so it is thought that the volcanism-including that on Mount Etna itself-stems from the upwelling of mantle material, associated with various surface tectonic processes. But the paucity of geological evidence regarding the primary composition of magma from Mount Etna means that its source characteristics remain controversial. Here we characterize the trace-element composition of a series of lavas emitted by Mount Etna over the past 500 kyr and preserved as melt inclusions inside olivine phenocrysts. We show that the compositional change in primary magmas from Mount Etna reflects a progressive transition from a predominantly mantle-plume source to one with a greater contribution from island-arc (subduction-related) basalts. We suggest that this is associated with southward migration of the Ionian slab, which is becoming juxtaposed with a mantle plume beneath Sicily. This implies that the volcanism of Mount Etna has become more calc-alkaline, and hence more explosive, during its evolution.

  14. Magmatic systems of large continental igneous province

    NASA Astrophysics Data System (ADS)

    Sharkov, Evgenii

    2014-05-01

    major series: (1) "green" - spinel peridotite (maily lherzolite) and minor spinel pyroxenite (websterites), and (2) "black" - wehrlite, Al-Ti-augite and hornblende clinopyroxenite, hornblendite, etc., and megacrysts of Al-Ti-augite, kaersutite, ilmenite, sanidine, etc. They often contain vesicles which evidence that their crystallization occurred from fluid-saturated melts. The rocks of this series form veins in peridotite matrix. So, two types of material participated in melting process: moderate-depleted peridotites and geochemical-enriched phase - fluid-saturated melts or high-density fluid. Because the both types of xenoliths are fragments of upper cooled rim of mantle plume head above magma-generation zone, we suggest that they together represent material, which composed plume head and accordingly - the melting substratum. At that the fluid phase exactly provided specific composition of basaltic melts at the initial stages of LIPs development, typical for intraplate settings. The middle level of magmatic systems is represented by transitional magmatic chambers (now large layered mafic-ultramafic intrusions), where newly-formed magmas were accumulated, undergone by crystallizing differentiation, mixing and crustal contamination. Such transformed in a variable degree magmas continued their way to surface led to general diversity of magmatic rocks, erupted on the surface; contribution of subvolcanic magmatic chambers was, probably, small. So, systematic study of processes in LIPs' magmatic systems as a whole can help to reveal processes of primary magmas transformation and thereby to determine their initial composition and source material.

  15. Diffuse CO2 Emanations from a Deep Magmatic Source-Multiphase Dynamics, Soil Impacts, and Lessons for Sequestration Monitoring

    NASA Astrophysics Data System (ADS)

    Stonestrom, D. A.; Werner, C. A.; Schulz, M. S.; Howle, J. F.; Farrar, C. D.; Smith, T. R.; Rogie, J. D.

    2011-12-01

    Naturally occurring emissions of nearly pure CO2 at Mammoth Mountain, California, have been suggested as an analog of possible leakage from large-scale carbon capture and sequestration operations. Impacts of sustained elevated levels (>20%) of soil CO2 are greater than the observable forest dieback. Repeated soil-transect studies six and 22 years after onset of CO2 emissions demonstrate substantial degradation of base-cation status in the area of active emission. Detailed time series of soil-gas pressures, CO2 concentrations and fluxes, water contents, and snow-cover dynamics show large short-term (minutes-to-days) variability and switching between quasi-stable states, suggesting countercurrent gas and liquid movement within a shared fracture-pore network. Single fluid phase (Darcian-Fickian) approaches are inadequate to explain the gross features of the measured time series; engineering equations developed for two-fluid-phase flow reactors are more likely to apply. Micrometeorological data show that atmospheric forcing affects total CO2 fluxes. Data presented here show that interactions among the atmospheric boundary layer, water in all its forms (snowpack, percolating soil moisture, groundwater), and upward moving CO2 must be taken into account so that changes in surface CO2 concentrations and fluxes due to hydrologic perturbations can be differentiated from those due to changes in sources at depth.

  16. Potential Fields Illuminate Earthquake Sources in Subduction-Margin Settings

    NASA Astrophysics Data System (ADS)

    Blakely, R. J.; Wells, R. E.

    2008-05-01

    Potential-field anomalies can be used to map the geologic structure of earthquake source regions in subduction zones and thus provide promise for assessing future earthquake hazards. Satellite free-air gravity anomalies over subduction zones consist of an offshore trench-parallel gravity low and a subparallel coastal gravity high that reflect the topography and structure of the inner trench slope and coast ranges, respectively. Large coseismic slip in shallow megathrust earthquakes correlates with gravity lows centered on large forearc sedimentary basins along the deep sea terrace offshore. The trench-parallel gravity low, the basins, and the earthquakes are all thought to be related to the resistance to slip along the plate boundary, and basin-centered gravity lows in similar settings may be the likely source of asperities in future earthquakes. Landward of the shallow megathrust, magnetic anomalies provide clues to processes occurring within the subducting slab and overlying mantle wedge. In some subduction zones, water released from the transformation of basalt to eclogite hydrates overlying sub-continental mantle, producing serpentinite, and embrittles the downgoing slab, promoting intraslab earthquakes. The 1970 central Peru earthquake (MW 7.5 to 8.0) and the 1949 Olympia, Washington, earthquake (MW 7.1) are recent examples. Thermal models indicate that the hydrated mantle wedge in most subduction zones is below the Curie temperature of magnetite. If serpentinite is sufficiently abundant, hydrated mantle wedges will produce long-wavelength magnetic anomalies observable at the earth's surface. A crust-mantle model of the Cascadia subduction margin based on magnetic, gravity, and seismic data, is consistent with the presence of significant volumes of hydrated mantle. The advent of new global magnetic databases may allow us to map hydrated mantle worldwide. The World Digital Magnetic Anomaly Map and the CHAMP satellite magnetic field, processed to emphasize

  17. Two mantle sources, two plumbing systems: Tholeiitic and alkaline magmatism of the Maymecha River basin, Siberian flood volcanic province

    USGS Publications Warehouse

    Arndt, N.; Chauvel, C.; Czamanske, G.; Fedorenko, V.

    1998-01-01

    Rocks of two distinctly different magma series are found in a ???4000-m-thick sequence of lavas and tuffs in the Maymecha River basin which is part of the Siberian flood-volcanic province. The tholeiites are typical low-Ti continental flood basalts with remarkably restricted, petrologically evolved compositions. They have basaltic MgO contents, moderate concentrations of incompatible trace elements, moderate fractionation of incompatible from compatible elements, distinct negative Ta(Nb) anomalies, and ??Nd values of 0 to + 2. The primary magmas were derived from a relatively shallow mantle source, and evolved in large crustal magma chambers where they acquired their relatively uniform compositions and became contaminated with continental crust. An alkaline series, in contrast, contains a wide range of rock types, from meymechite and picrite to trachytes, with a wide range of compositions (MgO from 0.7 to 38 wt%, SiO2 from 40 to 69 wt%, Ce from 14 to 320 ppm), high concentrations of incompatible elements and extreme fractionation of incompatible from compatible elements (Al2O3/TiO2 ??? 1; Sm/Yb up to 11). These rocks lack Ta(Nb) anomalies and have a broad range of ??Nd values, from -2 to +5. The parental magmas are believed to have formed by low-degree melting at extreme mantle depths (>200 km). They bypassed the large crustal magma chambers and ascended rapidly to the surface, a consequence, perhaps, of high volatile contents in the primary magmas. The tholeiitic series dominates the lower part of the sequence and the alkaline series the upper part; at the interface, the two types are interlayered. The succession thus provides evidence of a radical change in the site of mantle melting, and the simultaneous operation of two very different crustal plumbing systems, during the evolution of this flood-volcanic province. ?? Springer-Verlag 1998.

  18. Permian to Triassic I to S-type magmatic switch in the northeast Sierra Nevada de Santa Marta and adjacent regions, Colombian Caribbean: Tectonic setting and implications within Pangea paleogeography

    NASA Astrophysics Data System (ADS)

    Cardona, A.; Valencia, V.; Garzón, A.; Montes, C.; Ojeda, G.; Ruiz, J.; Weber, M.

    2010-10-01

    The Late Paleozoic to Triassic tectonics of northwestern South America have major implications for the understanding of Laurentia-Gondwana interactions that formed Pangea, and the origin of several tectonostratigraphic terranes dispersed by the break-up of this supercontinent during the formation of the Caribbean. Two mylonitic and orthogneissic granitoid suites have been recognized in the northeastern segment of the Sierra Nevada de Santa Marta, the lower Magdalena basin and the Guajira Serranias, within the Caribbean region of Colombia. For the Santa Marta region U/Pb LAM-ICP-MS analysis yielded zircon crystallization ages of 288.1 ± 4.5 Ma, 276.5 ± 5,1 Ma and 264.9 ± 4.0 Ma, related to the magmatic intrusion. Geochemical and modal variations show a compositional spectrum between diorite and granite, whereas LREE enrichment, Ti and Nb anomalies and geochemical discrimination suggest that this granitoid suite was formed within a magmatic arc setting. Inherited zircons suggest that this Early Permian plutonism was formed with the participation of Neoproterozoic and Grenvillian basement proximal to the South American continent. Evidence of a superimposed Early Triassic (ca. 250 Ma) deformational event in Santa Marta, together with a well defined S-type magmatism in the basement rocks from the adjacent lower Magdalena Valley and Guajira Peninsula regions are related to a major shift in the regional tectonic evolution. It's envisioned that this event records either terrane accretion or strong plate coupling during the final stages of Pangea agglutination. Connections with the main Alleghanian-Ouachitan Pangean orogen are precluded due to their timing differences. The plutons temporally and compositionally correlate with an arc found in the northern Andes and Mexican Gondwana terranes, and represent a broader magmatic event formed at the proto-Pacific margin, outside the nucleus of the Laurentia-Gondwana Alleghanian-Oachitan orogens. Evidence of lower temperature

  19. Tectonic Setting and Bimodal Magmatic Evolution of Eocene Volcanic Rocks of the Bijgerd-Kuh-e Kharchin area, Uromieh-Dokhtar Zone, Iran

    NASA Astrophysics Data System (ADS)

    Davarpanah, A.; Khalatbari-Jafari, M.; Babaie, H. A.; Krogstad, E. J.; Mobasher, K.; La Tour, T. E.; Deocampo, D. M.

    2008-12-01

    Geochemical composition and texture of the Middle and Late Eocene volcanic, volcaniclastic, and volcanic- sedimentary rocks in the Bijgerd-Kuh-e Kharchin area, northwest of Saveh, provide significant geochemical and geological clues for the tectonic and magmatic evolution of the Uromieh-Dokhtar volcanic-plutonic zone of Iran. The Middle Eocene volcanic rocks have an intermediate composition and include green tuff and tuffaceous sandstone with intercalated sandstone, sandy tuff, and shale. The shale has lenses of nummulite- bearing limestone with a Middle Eocene detrital age. The time between the Middle and Late Eocene volcanic activities in this area is marked by the presence of andesite and rhyolitic tuff. The Late Eocene succession is distinguished by the presence of four alternating levels (horizons) of intermediate lava and ignimbrite which we designate as Eig. The ignimbrites of the Eig sequence have a rhyolitic composition and include ignimbrite- breccia, ignimbrite-tuff, and ignimbrite-lava pairs. The volume of the felsic volcanic rocks in this sequence far exceeds that of the intermediate rocks, which makes it unlikely that they evolved through the magmatic differentiation of a basaltic magma. The presence of the nummulite-bearing limestone lenses, and sandstone and conglomerate interbeds between the ignimbrites, suggests a shallow marine environment for the pyroclastic deposition and probably the eruptions. The tuff and siltstone of the Est unit that sits above the first ignimbrite may represent deep water, Late Eocene deposit. Oligo-Miocene limestone of the Qom Formation unconformably overlies the uppermost Late Eocene ignimbrite. Washings from red marls give microfossils with Late Eocene age for the Eig sequence, which is synchronous with other paleontological evidence that puts the peak volcanic activity as Late Eocene in the Bijgerd-Kuh-e Kharchin area. Field and petrographic evidence for magma mixing/mingling is given by the presence of mafic

  20. Cenozoic magmatism of north Victoria Land, Antarctica: an experimental study on the mantle source of a primary basanite from the McMurdo Volcanic Group

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Freda, C.; Misiti, V.; Perinelli, C.

    2009-04-01

    Volcanoes of the McMurdo Vocanic Group (MMVG) (Antarctica) dot the eastern shoulder of Ross Sea Rift System giving rise to alkaline transitional volcanic suites which in north Victoria Land are emplaced since Early Cenozoic. Geochemical geological, geophysical and geochronological data on Cenozoic volcanic activity in NVL suggest that the region is a site of passive astenospheric rise, rather than affected by a thermally active mantle plume. Furthermore the comparison of geochemical and isotopical data of basic lavas with those provided by mantle xenoliths they carry to the surface, document the compositional heterogeneity of sublithospheric mantle caused by the coupled action of partial melting and metasomatism. In particular the metasomatic episode is probably linked to the amagmatic extensional event that affected the West Antarctic Rift System in the Late Cretaceous. The astenospheric melts generated during this event, moving through the upper mantle, can have crystallized as veins or may have led to the formation of metasomatic minerals such as amphibole or phlogopite. In this scenario the mineralogical and chemical composition of sources responsible for Cenozoic magmatism, amphibole-bearing spinel-peridotite versus pyroxenite in the garnet stability field, it is still a matter of debate. To shed light on this argument a previous experimental study on a basanite of MMVG, representative of primary magma (Orlando et al., 2000) has been integrated with new experimental investigation on the same basanitic composition. The preliminary experiments were conducted to pressures of 1.0 - 2.0GPa in the presence of 0-1% of added water and indicate olivine on the liquidus at 1.0 GPa that is substitute by clinopyroxene at 2.0GPa. The addition of 1% of water induces a decrease of liquidus temperature of about 40°C shifting its value in the T range (1280-1310°C) the same that was inferred by melt inclusions hosted in the olivine phenocrysts of the studied basanite.

  1. The Timing of Early Magmatism and Extension in the Southern East African Rift: Tracking Geochemical Source Variability with 40Ar/39Ar Geochronology at the Rungwe Volcanic Province, SW Tanzania

    NASA Astrophysics Data System (ADS)

    Mesko, G. T.; Class, C.; Maqway, M. D.; Boniface, N.; Manya, S.; Hemming, S. R.

    2014-12-01

    The Rungwe Volcanic Province is the southernmost expression of volcanism in the East African Rift System. Rungwe magmatism is focused in a transfer zone between two weakly extended rift segments, unlike more developed rifts where magmatism occurs along segment axes (e.g. mid-ocean ridges). Rungwe was selected as the site of the multinational SEGMeNT project, an integrated geophysical, geochronological and geochemical study to determine the role of magmatism during early stage continental rifting. Argon geochronology is underway for an extensive collection of Rungwe volcanic rocks to date the eruptive sequence with emphasis on the oldest events. The age and location of the earliest events remains contested, but is critical to evaluating the relationship between magmatism and extension. Dated samples are further analyzed to model the geochemistry and isotopic signature of each melt's source and define it as lithospheric, asthenospheric, or plume. Given the goals, the geochronology focuses on mafic lavas most likely to preserve the geochemical signature of the mantle source. Groundmass was prepared and analyzed at the LDEO AGES lab. Twelve preliminary dates yield ages from 8.5 to 5.7Ma, consistent with prior results, supporting an eruptive episode concurrent with tectonic activity on the Malawi and Rukwa border faults (Ebinger et al., JGR 1989; 1993). Three additional samples yield ages from 18.51 to 17.6 Ma, consistent with the 18.6 ±1.0 Ma age obtained by Rasskazov et al. (Russ. Geology & Geophys. 2003). This eruptive episode is spatially limited to phonolite domes in the Usangu Basin and a mafic lava flow on the uplifted Mbeya Block. These eruptions predate the current tectonic extensional structure, suggesting magmatism predates extension, or that the two are not highly interdependent. No Rungwe samples dated yet can be the source of the of 26Ma carbonatitic tuffs in the nearby Songwe River Basin sequence (Roberts et al., Nature Geoscience 2012). Isochron ages

  2. The Interplay Between Saline Fluid Flow and Dynamic Permeability in Magmatic-Hydrothermal Systems

    NASA Astrophysics Data System (ADS)

    Weis, P.

    2014-12-01

    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.

  3. Setting priorities: the key to nonpoint source control. Final report

    SciTech Connect

    Maas, R.P.; Smolen, M.D.; Jamieson, C.A.; Weinberg, A.C.

    1987-07-01

    Guidance for states in setting up water-quality programs is given. Recommendations and procedures are presented to focus resources to limited areas to achieve visible water quality improvements in a reasonable timeframe. The document reviews priority setting for water resources, planning, and organization of watershed projects; includes watershed-level targeting.

  4. Discrete ordinates with new quadrature sets and modified source conditions

    SciTech Connect

    Ganguly, K.; Allen, E.J., Victory, H.D. Jr. )

    1989-01-01

    A major shortcoming of the discrete ordinates method with the Gauss-Legendre quadrature set is that when the number of secondaries per primary c and the order of approximation N are not too large, all the (N + 1)v (the flux being of the form exp({minus}x/v)) lie in ({minus}1,1). It is known, however, that the largest v{sub j} corresponding to the asymptotic flux is greater than unity. The Legendre polynomial used for obtaining the quadrature set is orthogonal with respect to weight unity in the range ({minus}1,1). However, the Case and Zweifel eigenfunctions derived from the exact solution of one-speed transport theory are orthogonal with respect to a complicated weight function w({mu}) and {mu} in the half-range and full-range cases, respectively. In this paper, the authors have used a set of orthogonal polynomials with respect to w ({mu}) to develop quadrature sets to be used in the discrete ordinates calculation.

  5. An overview of the volatile systematics of the Lau Basin - Resolving the effects of source variation, magmatic degassing and crustal contamination

    NASA Astrophysics Data System (ADS)

    Hahm, Doshik; Hilton, David R.; Castillo, Paterno R.; Hawkins, James W.; Hanan, Barry B.; Hauri, Erik H.

    2012-05-01

    The Lau Basin erupts lavas with a range of geochemical features reflecting a complex history of interaction involving different mantle sources. The Valu Fa Ridge (VFR) and Mangatolu Triple Junction (MTJ) region have lavas with arc-like characteristics, Niuafo'ou Island (NV), Peggy Ridge and Central and Eastern Lau Spreading Centers (PR, CLSC and ELSC) erupt mid-ocean ridge basalt (MORB)-like volcanics, whereas the Rochambeau Bank (RB) has features akin to ocean island basalt (OIB). To characterize the volatile systematics of these various regions, we report a comprehensive study of 39 submarine lavas from these various eruptive centers encompassing analyses of the noble gases (He, Ne, and Ar) and carbon (CO2) - both isotopes and abundances - together with other major volatile phases (H2O, S, Cl, and F). Helium isotope ratios of the NV, MTJ, CLSC, and ELSC are MORB-like for the most part except for differentiated lavas that tend to have lower, more radiogenic 3He/4He values. The RB has considerably higher 3He/4He ratios (up to 23 RA in this work) which extend as far south as the PR. The influence of 'plume-like' sources in the RB is also apparent in Ne isotopes: RB samples follow a trend similar to Hawaiian basalts in 3-isotope neon space. However, RB lavas have lower 40Ar/36Ar (300-730) and higher [36Ar] than CLSC and ELSC, suggesting greater air contamination. Elemental He/Ne ratios (3He/22NeS and 4He/21Ne∗ where S = solar and * = nucleogenic) are high throughout the Lau Basin and identify the Lau mantle as one of only two high 3He/4He provinces worldwide with such an enrichment of He relative to Ne. Magmatic CO2 and δ13C fall in the range 7-350 ppm and -28‰ to -6‰, respectively. RB lavas have less [CO2] and slightly lower δ13C than CLSC and ELSC. The lowest values are found among MTJ lavas. These lavas also have the highest [H2O], [F], [Cl], and [S] whereas the PR, ELSC and CLSC have the lowest. RB has intermediate [H2O]. We estimate primary [CO2] in

  6. Magmatism in the Carolina terrane: Isotopic evidence for a Grenville-age source for Late Proterozoic volcanics and a mantle source for Silurian Concord syenite

    SciTech Connect

    Kozuch, M.; Heatherington, A.L.; Mueller, P.A. . Dept. of Geology); Offield, T.W.; Koeppen, R.P.; Klein, T.L. )

    1992-01-01

    Rhyolitic to andesitic volcanic rocks from the central portion of the Carolina slate belt in North Carolina were analyzed for Sr and Nd isotopic composition and dated by U-Pb zircon geochronology. Samples were from the greenschist-facies Late Proterozoic Albemarle Group, Uwharrie Formation, and the informal Virginia sequence. A rhyolite from the Cid Formation of the Albemarle Group dated by U-Pb zircon geochronology yielded a Pb-207/Pb-206 age of 575 [+-] 7.6 Ma, consistent with its position below strata containing the Late Proterozoic trace fossil Pteridinium and above rocks previously dated at 586 [+-] 10 Ma. Rb-Sr isotopic analyses of late Proterozoic rocks showed average initial Sr-87/Sr-86 ratios of approximately 0.704, indicating a moderately depleted source for these samples. E[sub ND] values at 600 Ma are moderately positive (+0.7 [minus] +2.3) and T(DM) values range from 1.19--1.04 Ga. These isotopic data, along with major and trace element data, suggest that andesites and rhyolites of the Carolina slate belt may have formed by partial melting of attenuated, Grenville-aged continental lithosphere during a 600 Ma episode of arc volcanism. In contrast, Sr and Nd data for the younger ([approximately]400 Ma) Concord pluton indicate it was derived from a depleted mantle source (Sr-87/Sr-86 = 0.7021 and E[sub ND] = +0.4 at 400 Ma) without significant involvement of older lithosphere (T(DM) = 370 Ma).

  7. Physics Mining of Multi-Source Data Sets

    NASA Technical Reports Server (NTRS)

    Helly, John; Karimabadi, Homa; Sipes, Tamara

    2012-01-01

    Powerful new parallel data mining algorithms can produce diagnostic and prognostic numerical models and analyses from observational data. These techniques yield higher-resolution measures than ever before of environmental parameters by fusing synoptic imagery and time-series measurements. These techniques are general and relevant to observational data, including raster, vector, and scalar, and can be applied in all Earth- and environmental science domains. Because they can be highly automated and are parallel, they scale to large spatial domains and are well suited to change and gap detection. This makes it possible to analyze spatial and temporal gaps in information, and facilitates within-mission replanning to optimize the allocation of observational resources. The basis of the innovation is the extension of a recently developed set of algorithms packaged into MineTool to multi-variate time-series data. MineTool is unique in that it automates the various steps of the data mining process, thus making it amenable to autonomous analysis of large data sets. Unlike techniques such as Artificial Neural Nets, which yield a blackbox solution, MineTool's outcome is always an analytical model in parametric form that expresses the output in terms of the input variables. This has the advantage that the derived equation can then be used to gain insight into the physical relevance and relative importance of the parameters and coefficients in the model. This is referred to as physics-mining of data. The capabilities of MineTool are extended to include both supervised and unsupervised algorithms, handle multi-type data sets, and parallelize it.

  8. Source and mode of the Permian Panjal Trap magmatism: Evidence from zircon U-Pb and Hf isotopes and trace element data from the Himalayan ultrahigh-pressure rocks

    NASA Astrophysics Data System (ADS)

    Rehman, Hafiz Ur; Lee, Hao-Yang; Chung, Sun-Lin; Khan, Tahseenullah; O'Brien, Patrick J.; Yamamoto, Hiroshi

    2016-09-01

    We present an integrated study of LA-ICP-MS U-Pb age, Hf isotopes, and trace element geochemistry of zircons from the Himalayan eclogites (mafic rocks) and their host gneisses (felsic rocks) from the Kaghan Valley in Pakistan in order to understand the source and mode of their magmatic protoliths and the effect of metamorphism. Zircons from the so-called Group I (high-pressure) eclogites yielded U-Pb mean ages of 259 ± 10 Ma (MSWD = 0.74), whereas those of Group II (ultrahigh-pressure) eclogites yielded 48 ± 3 Ma (MSWD = 0.71). In felsic gneisses the central or core domains of zircons yielded ages similar to those from Group I eclogites but zircon overgrowth domains yielded 47 ± 1 Ma (MSWD = 1.9). Trace element data suggest a magmatic origin for Group I-derived (having Th/U ratios: > 0.5) and metamorphic origin for Group II-derived (Th/U < 0.07) zircons, respectively. Zircon Hf isotope data, obtained from the same dated spots, show positive initial 176Hf/177Hf isotopic ratios referred to as "ƐHf(t)" of around + 10 in Group I eclogites; + 7 in Group II eclogites; and + 8 in felsic gneisses zircons, respectively, thus indicate a juvenile mantle source for the protolith rocks (Panjal Traps) with almost no contribution from the ancient crustal material. The similar ƐHf(t) values, identical protolith ages and trace element compositions of zircons in felsic (granites or rhyolites) and mafic (basalt and dolerite) rocks attest to a bimodal magmatism accounting for the Panjal Traps during the Permian. Later, during India-Asia collision in Eocene times, both the felsic and mafic lithologies were subducted to mantle-depths (> 90 km: coesite-stable) and experienced ultrahigh-pressure metamorphism before their final exhumation.

  9. Sources of Artefacts in Synthetic Aperture Radar Interferometry Data Sets

    NASA Astrophysics Data System (ADS)

    Becek, K.; Borkowski, A.

    2012-07-01

    In recent years, much attention has been devoted to digital elevation models (DEMs) produced using Synthetic Aperture Radar Interferometry (InSAR). This has been triggered by the relative novelty of the InSAR method and its world-famous product—the Shuttle Radar Topography Mission (SRTM) DEM. However, much less attention, if at all, has been paid to sources of artefacts in SRTM. In this work, we focus not on the missing pixels (null pixels) due to shadows or the layover effect, but rather on outliers that were undetected by the SRTM validation process. The aim of this study is to identify some of the causes of the elevation outliers in SRTM. Such knowledge may be helpful to mitigate similar problems in future InSAR DEMs, notably the ones currently being developed from data acquired by the TanDEM-X mission. We analysed many cross-sections derived from SRTM. These cross-sections were extracted over the elevation test areas, which are available from the Global Elevation Data Testing Facility (GEDTF) whose database contains about 8,500 runways with known vertical profiles. Whenever a significant discrepancy between the known runway profile and the SRTM cross-section was detected, a visual interpretation of the high-resolution satellite image was carried out to identify the objects causing the irregularities. A distance and a bearing from the outlier to the object were recorded. Moreover, we considered the SRTM look direction parameter. A comprehensive analysis of the acquired data allows us to establish that large metallic structures, such as hangars or car parking lots, are causing the outliers. Water areas or plain wet terrains may also cause an InSAR outlier. The look direction and the depression angle of the InSAR system in relation to the suspected objects influence the magnitude of the outliers. We hope that these findings will be helpful in designing the error detection routines of future InSAR or, in fact, any microwave aerial- or space-based survey. The

  10. A multi-phase level set framework for source reconstruction in bioluminescence tomography

    SciTech Connect

    Huang Heyu; Qu Xiaochao; Liang Jimin; He Xiaowei; Chen Xueli; Yang Da'an; Tian Jie

    2010-07-01

    We propose a novel multi-phase level set algorithm for solving the inverse problem of bioluminescence tomography. The distribution of unknown interior source is considered as piecewise constant and represented by using multiple level set functions. The localization of interior bioluminescence source is implemented by tracing the evolution of level set function. An alternate search scheme is incorporated to ensure the global optimal of reconstruction. Both numerical and physical experiments are performed to evaluate the developed level set reconstruction method. Reconstruction results show that the proposed method can stably resolve the interior source of bioluminescence tomography.

  11. Three-dimensional seismic velocity models, high-precision earthquake locations and their implications for seismic, tectonic and magmatic settings in the Coso Geothermal Field, California

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Lin, G.

    2012-12-01

    The Coso Geothermal Field (CGF) lies at the east of Sierra Nevada and is situated in tectonically active area with the presence of hot spring, rhyolite domes at the surface, strike-slip and normal faulting and frequent seismic activity. In this study, we present our comprehensive analysis of three-dimensional velocity structure, high-precision earthquake relocation and in situ Vp/Vs estimates. We select 1,893 master events among 177,000 events between 1981 and 2011 recorded by the Southern California Seismic Network stations. High-resolution three-dimensional (3-D) Vp and Vp/Vs models in Coso are inverted from the master events with 52,160 P- and 23,688 S-wave first arrivals by using the SIMUL2000 algorithm. The tomographic model reveals slightly high Vp and Vp/Vs in most regions of Coso near the surface compared to the layers at depth of 6 and 12 km, which is consistent with the fact that the Coso area is filled with diorite and minor basalt. The feature of low Vp, low Vs and low Vp/Vs between 6 and 12 km depths underneath the CGF can be related to the porous, gas-filled rock or volatile-rich magma. The low Vp, low Vs and low Vp/Vs structure from the surface to 3 km depth beneath the Indian Wells Valley is consistent with the existence of the 2 km deep sediment strata revealed by the borehole data. The resulting new 3-D velocity model is used to improve the absolute event location accuracy. We then apply waveform cross-correlation, similar event cluster analysis and differential time relocation methods to improve relative event location accuracy with the horizontal and vertical location uncertainties in tens of meters. The relocated seismicity indicates that the brittle-ductile transition depth is as shallow as 5 km underneath the CGF. We also estimate in situ near-source Vp/Vs ratio within each event cluster using differential times from cross-correlation to complement the Vp/Vs model from tomographic inversions, which will help to estimate the volume fraction of

  12. "Fingerprinting" tectono-magmatic provenance using trace elements in igneous zircon

    NASA Astrophysics Data System (ADS)

    Grimes, C. B.; Wooden, J. L.; Cheadle, M. J.; John, B. E.

    2015-12-01

    Over 5300 recent SHRIMP-RG analyses of trace elements (TE) in igneous zircon have been compiled and classified based on their original tectono-magmatic setting to empirically evaluate "geochemical fingerprints" unique to those settings. Immobile element geochemical fingerprints used for lavas are applied with the same rational to zircon, including consideration of mineral competition on zircon TE ratios, and new criteria for distinguishing mid-ocean ridge (MOR), magmatic arc, and ocean island (and other plume-influenced) settings are proposed. The elemental ratios in zircon effective for fingerprinting tectono-magmatic provenance are systematically related to lava composition from equivalent settings. Existing discrimination diagrams using zircon U/Yb versus Hf or Y do not distinguish TE-enriched ocean island settings (i.e., Iceland, Hawaii) from magmatic arc settings. However, bivariate diagrams with combined cation ratios involving U-Nb-Sc-Yb-Gd-Ce provide a more complete distinction of zircon from these settings. On diagrams of U/Yb versus Nb/Yb, most MOR, ocean island, and kimberlite zircon define a broad "mantle-zircon array"; arc zircon defines a parallel array offset to higher U/Yb. Distinctly low U/Yb ratios of MOR zircon (typically <0.1) mirror their parental magmas and long-term incompatible element depletion of the MORB mantle. Plume-influenced sources are distinguished from MOR by higher U/Yb, U/Nb, Nb/Yb, and Nb/Sc. For zircon with U/Yb > 0.1, high Sc/Yb separates arc settings from low-Sc/Yb plume-influenced sources. The slope of scandium enrichment trends in zircon differ between MOR and continental arc settings, likely reflecting the involvement of amphibole during melt differentiation. Scandium is thus also critical for discriminating provenance, but its behavior in zircon probably reflects contrasting melt fractionation trends between tholeiitic and calc-alkaline systems more than compositional differences in primitive magmas sourced at each

  13. Chromites from the Gogoł;ów-Jordanów Serpentinite Massif (SW Poland) - evidence of the arc setting magmatism

    NASA Astrophysics Data System (ADS)

    Wojtulek, Piotr; Puziewicz, Jacek; Ntaflos, Theodoros; Bukała, Michał

    2014-05-01

    The Gogołów-Jordanów Serpentinite Massif (GJSM) is a peridotitic member of the Variscan Ślęża Ophiolite (SW Poland). Chromitite veinlets and pockets occur in the central part of the massif in the Czernica Hill area within completely serpentinized rocks. Chromitites consist of rounded chromite grains up to 4 cm and chlorite filling the interstices. The veins are embedded in serpentine-olivine-chlorite aggregates. Chemical composition of chromite occurring in chromitites defines two varieties. Chromite I (Cr# = 0.49 - 0.58) contains 23.32 - 28.36 wt.% Al2O3, 40.29 - 48.10 wt.% Cr2O3, 15.10 - 15.50 wt.% FeO, 14.50 - 15.50 wt.% MgO and ~0.1 wt.% TiO2. Chromite II (Cr# = 0.71 - 0.73) contains 13.83 - 15.24 wt.% Al2O3, 54.85 - 56.65 wt.% Cr2O3, 16.71 - 18.04 wt.% FeO, 10.62 - 11.59 wt.% MgO and 0.1 wt.% TiO2. Chromite grains are composed mostly of chromite I. Chromite II forms irregular spongy domains up to 150 µm, located at fissures or forming grain rims. The bulk chromitite composition of the massive ores reveals Rb, Ba, Pb and Sb enrichment relative to primitive mantle; Pt and Pd (up to 36 ppb) are also enriched relative to primitive mantle. Other phases coexisting with chromite are chlorite and olivine. Chlorite (Fe# = 0.02) contains 17.5 - 23.0 wt.% Al2O3, 0.6 - 1.8 wt.% Cr2O3 and 31.8 - 34.2 wt.% MgO. Olivine (Fo93.5-96.2) contains 0.44- 0.51 wt.% NiO. Olivine grains are zoned - the low-forsteritic cores are surrounded by high-forsteritic domain. Chromite II and chlorite are secondary phases and were probably formed due to greenschist facies metamorphism. Chromitites are cumuletes of melt blocked during its flow through peridotitic host. Low TiO2 content and moderate chromian number of the GJSM chromitites is typical for chromian spinels originated from melt derived from back arc depleted source (cf. Python et al., 2008, Gonzalez-Jimenez, 2011). The GJSM chromitites are rich in Al and poor in Pt and Pd what is typical for chromitites occurring in the

  14. Syn- and post-orogenic alkaline magmatism in a continental arc: Along-strike variations in the composition, source, and timing of igneous activity in the Ross Orogen, Antarctica

    NASA Astrophysics Data System (ADS)

    Hagen-Peter, G.; Cottle, J. M.

    2013-12-01

    Neoproterozoic-Paleozoic convergence and subduction along the margin of East Gondwana (Australia, New Zealand, Antarctica) resulted in a belt of deformed and metamorphosed sedimentary rocks and batholith-scale igneous intrusions comparable in size to the present day Andes. Mid-crustal levels of this belt, known as the Ross Orogen in Antarctica, are exposed in the basement of the Cenozoic Transantarctic Mountains, providing snapshots of the intrusive magma system of a major continental arc. Whole rock major- and trace-element geochemistry, Hf isotopes in zircon, and U-Pb geochronology have identified along-strike variations in the composition, source, and timing of magmatism along ~200 km of the southern Victoria Land segment of the orogen. There is an apparent younging of the igneous activity from south to north. New U-Pb ages for intrusive rocks from the Koettlitz Glacier Alkaline Province (KGAP) reveal that igneous activity spanned ca. 565-500 Ma (~30 m.y. longer than previously recognized), while immediately to the north in the Dry Valleys area most igneous activity was confined to a relatively short period (ca. 515-495 Ma). Alkaline and subalkaline igneous rocks occur in both the Dry Valleys area and the KGAP, but alkaline rocks in the Dry Valleys are restricted to the latest phase of magmatism. Na-alkaline rocks in the KGAP, including nepheline syenites, carbonatites, and A-type granites, range in age from ca. 545-500 Ma and overlap in age with more typical subduction/collision-related I- and S-type granites elsewhere in southern Victoria Land. Strong enrichments in the LILE and LREE and high LILE/HFSE and LREE/HREE of samples from the KGAP reveal a source enriched in aqueous-mobile elements, potentially a strongly metasomatized mantle wedge beneath the arc. In the Dry Valleys area, rocks with alkali-calcic composition constitute only the youngest intrusions (505-495 Ma), apparently reflecting a shift to post-orogenic magmatism. Zircons from Dry Valleys

  15. Modelling the role of magmatic intrusions in the post-breakup thermal evolution of Volcanic Passive Margins

    NASA Astrophysics Data System (ADS)

    Peace, Alexander; McCaffrey, Ken; Imber, Jonny; van Hunen, Jeroen; Hobbs, Richard; Gerdes, Keith

    2013-04-01

    Passive margins are produced by continental breakup and subsequent seafloor spreading, leaving a transition from continental to oceanic crust. Magmatism is associated with many passive margins and produces diagnostic criteria that include 1) abundant breakup related magmatism resulting in a thick igneous crust, 2) a high velocity zone in the lower crust and 3) seaward dipping reflectors (SDRs) in seismic studies. These Volcanic Passive Margins (VPMs) represent around 75% of the Atlantic passive margins, but beyond this high level description, these magma-rich settings remain poorly understood and present numerous challenges to petroleum exploration. In VPMs the extent to which the volume, timing, location and emplacement history of magma has played a role in controlling heat flow and thermal evolution during margin development remains poorly constrained. Reasons for this include; 1) paucity of direct heat flow and thermal gradient measurements at adequate depth ranges across the margins, 2) poor onshore exposure 3) highly eroded flood basalts and 4) poor seismic imaging beneath thick offshore basalt sequences. As a result, accurately modelling the thermal history of the basins located on VPMs is challenging, despite the obvious importance for determining the maturation history of potential source rocks in these settings. Magmatism appears to have affected the thermal history of the Vøring Basin on the Norwegian VPM, in contrast the effects on the Faeroe-Shetland Basin was minimal. The more localised effects in the Faeroe-Shetland Basin compared to Vøring Basin may be explained by the fact that the main reservoir sandstones appear to be synchronous with thermal uplift along the basin margin and pulsed volcanism, indicating that the bulk of the magmatism occurred at the basin extremities in the Faeroe-Shetland Basin, where its effect on source maturation was lessened. Our hypothesis is that source maturation occurs as a result of regional temperature and pressure

  16. Mars: Fluvial Erosion Driven by Magmatism

    NASA Astrophysics Data System (ADS)

    Tanaka, K. L.; Skinner, J. A.; Chapman, M. G.

    2002-12-01

    Mars at present has a thin, dry, and cold atmosphere relative to Earth's. The cold temperatures suggest that any subsurface water (perhaps combined with carbon dioxide as clathrate) would likely be frozen within a couple kilometers or more of the surface. This condition may have been prevalent following widespread fluvial dissection that formed numerous valley networks in highland rocks during the Noachian. The sources of some ancient and of most relatively young valley systems, particularly the large outflow channels, occur within or near volcanic rocks or display morphologic evidence for volcanic and/or tectonic associations. Such geologic relations have led many investigators to propose that magmatic activity has been a significant (if not dominant) driver of younger fluvial erosion on the surface of Mars. Magmatism may have provided the heat to raise local subsurface temperatures to near or above the freezing point of water; furthermore, intrusive activity may have fractured aquifers that provided conduits for release of substantial volumes of ground volatiles. Evidence of such interactions includes lengthy outflow channels sourced from fissures or depressions in volcanic rocks of the Tharsis/Valles Marineris, Elysium, and eastern Hellas regions. Depressions filled with chaotic terrain at the heads of the circum-Chryse outflow channels may be sites where large volumes of magmatic material may have interacted with water and perhaps carbon dioxide in rocks beneath the cryosphere, leading to catastrophic expulsion of the volatiles and collapse of country rock. Other evidence for magmatically driven erosion may include the low Hellas rim areas, where Malea and Hesperia Plana reside, and the channeled flanks of possible Noachian volcanoes in Thaumasia (south Tharsis region). Mars Global Surveyor's MOLA topography data and MOC images and Mars Odyssey's THEMIS images are providing new insights into the possible interactions between magmatism and fluvial erosion on

  17. Dissolution of an emplaced source of DNAPL in a natural aquifer setting.

    PubMed

    Rivett, Michael O; Feenstra, Stanley

    2005-01-15

    Field-scale dissolution of a multicomponent DNAPL (dense nonaqueous-phase liquid) source intentionally emplaced below the water table is evaluated in a well-characterized natural aquifer setting. The block-shaped source contained 23 kg of a trichloromethane, trichloroethene, and perchloroethene mixture homogeneously distributed at 5% saturation of pore space. Dissolution was monitored for 3 yr via down-gradient samplers (1-m fence) and occasional intra-source sampling. Although intra-source equilibrium dissolution was shown and endorsed by supporting modeling and literature lab data, less than equilibrium concentrations were predominantly monitored in the 1-m fence. This was ascribed to significant by-passing of the source by groundwater flow due to its low permeability relative to the aquifer and associated dilution of concentrations emitted from the source. Heterogeneous source dissolution occurred despite the relative homogeneity of the source and aquifer and was ascribed to dissolution fingering, which has not been previously field-demonstrated. Bulk bypass of groundwater flow around the source zone caused slow dissolution rates, with 77% of the source remaining after 3 yr and a projected longevity of approximately 25 yr. Observed dissolution fingering would have significantly increased longevity as it increasingly caused intra-source bypass of remaining DNAPL. Our dissolution interpretations were endorsed by additional data collected after 6 yr during source remediation via permanganate oxidation.

  18. The role of granites in volcanic-hosted massive sulphide ore-forming systems: an assessment of magmatic-hydrothermal contributions

    NASA Astrophysics Data System (ADS)

    Huston, David L.; Relvas, Jorge M. R. S.; Gemmell, J. Bruce; Drieberg, Susan

    2011-07-01

    Assessment of geological, geochemical and isotopic data indicates that a significant subgroup of volcanic-hosted massive sulphide (VHMS) deposits has a major or dominant magmatic-hydrothermal source of ore fluids and metals. This group, which is typically characterised by high Cu and Au grades, includes deposits such as those in the Neoarchean Doyon-Bousquet-LaRonde and Cambrian Mount Lyell districts. These deposits are distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents intimately associated with ore zones. In many of these deposits, δ34Ssulphide is low, with a major population below -3‰; δ34Ssulphate differs from coexisting seawater and Δ34Ssulphate-sulphide ˜ 20-30‰. These characteristics are interpreted as the consequence of disproportionation of magmatic SO2 as magmatic-hydrothermal fluids ascended and cooled and as a definitive evidence for a significant magmatic-hydrothermal contribution. Other characteristics that we consider diagnostic of significant magmatic-hydrothermal input into VHMS ore fluids include uniformly high (>3 times modern seawater values) salinities or very 18O-enriched (δ18O > 5‰) ore fluids. We do not consider other criteria [e.g. variable salinity, moderately high δ18Ofluid (2-5‰), δ34Ssulphide near 0‰, metal assemblages or a spatial association with porphyry Cu or other clearly magmatic-hydrothermal deposits] that have been used previously to advocate significant magmatic-hydrothermal contributions to be diagnostic as they can be produced by non-magmatic processes known to occur in VHMS mineral systems. However, in general, a small magmatic-hydrothermal contribution cannot be excluded in most VHMS systems considered. Conclusive data that imply minimal magmatic-hydrothermal contributions are only available in the Paleoarchean Panorama district where coeval seawater-dominated and magmatic-hydrothermal systems appear to have been physically separated. This district, which is

  19. Loop Heat Pipe Operation Using Heat Source Temperature for Set Point Control

    NASA Technical Reports Server (NTRS)

    Ku, Jentung; Paiva, Kleber; Mantelli, Marcia

    2011-01-01

    The LHP operating temperature is governed by the saturation temperature of its reservoir. Controlling the reservoir saturation temperature is commonly accomplished by cold biasing the reservoir and using electrical heaters to provide the required control power. Using this method, the loop operating temperature can be controlled within +/- 0.5K. However, because of the thermal resistance that exists between the heat source and the LHP evaporator, the heat source temperature will vary with its heat output even if LHP operating temperature is kept constant. Since maintaining a constant heat source temperature is of most interest, a question often raised is whether the heat source temperature can be used for LHP set point temperature control. A test program with a miniature LHP has been carried out to investigate the effects on the LHP operation when the control temperature sensor is placed on the heat source instead of the reservoir. In these tests, the LHP reservoir is cold-biased and is heated by a control heater. Tests results show that it is feasible to use the heat source temperature for feedback control of the LHP operation. Using this method, the heat source temperature can be maintained within a tight range for moderate and high powers. At low powers, however, temperature oscillations may occur due to interactions among the reservoir control heater power, the heat source mass, and the heat output from the heat source. In addition, the heat source temperature could temporarily deviate from its set point during fast thermal transients. The implication is that more sophisticated feedback control algorithms need to be implemented for LHP transient operation when the heat source temperature is used for feedback control.

  20. Loop Heat Pipe Operation Using Heat Source Temperature for Set Point Control

    NASA Technical Reports Server (NTRS)

    Ku, Jentung; Paiva, Kleber; Mantelli, Marcia

    2011-01-01

    Loop heat pipes (LHPs) have been used for thermal control of several NASA and commercial orbiting spacecraft. The LHP operating temperature is governed by the saturation temperature of its compensation chamber (CC). Most LHPs use the CC temperature for feedback control of its operating temperature. There exists a thermal resistance between the heat source to be cooled by the LHP and the LHP's CC. Even if the CC set point temperature is controlled precisely, the heat source temperature will still vary with its heat output. For most applications, controlling the heat source temperature is of most interest. A logical question to ask is: "Can the heat source temperature be used for feedback control of the LHP operation?" A test program has been implemented to answer the above question. Objective is to investigate the LHP performance using the CC temperature and the heat source temperature for feedback control

  1. Public Data Set: Impedance of an Intense Plasma-Cathode Electron Source for Tokamak Plasma Startup

    DOE Data Explorer

    Hinson, Edward T. [University of Wisconsin-Madison] (ORCID:000000019713140X); Barr, Jayson L. [University of Wisconsin-Madison] (ORCID:0000000177685931); Bongard, Michael W. [University of Wisconsin-Madison] (ORCID:0000000231609746); Burke, Marcus G. [University of Wisconsin-Madison] (ORCID:0000000176193724); Fonck, Raymond J. [University of Wisconsin-Madison] (ORCID:0000000294386762); Perry, Justin M. [University of Wisconsin-Madison] (ORCID:0000000171228609)

    2016-05-31

    This data set contains openly-documented, machine readable digital research data corresponding to figures published in E.T. Hinson et al., 'Impedance of an Intense Plasma-Cathode Electron Source for Tokamak Plasma Startup,' Physics of Plasmas 23, 052515 (2016).

  2. Was Late Cretaceous Magmatism in the Northern Rocky Mountains Really Arc-Related?

    NASA Astrophysics Data System (ADS)

    Farmer, G.

    2011-12-01

    Calc-alkaline, Cretaceous magmatism affected much of the northern Rocky Mountain region in the western U.S. and is generally interpreted as continental arc magmatism despite the fact that it occurred as far east into the continental interior as the Late Cretaceous (75 Ma to 78 Ma) Sliderock Mountain volcanoplutonic complex in south-central Montana. Magmatism may have migrated so far inboard as a response to shallowing of the dip angle of underthrust oceanic lithosphere, but the exact sources, tectonic setting and trigger mechanisms for the Late Cretaceous igneous activity remain unclear. In this study, new trace element and Nd and Sr isotopic data, combined with existing age and major element data (duBray et al., 1998, USGS Prof. Paper 1602), from the most mafic lavas present at the Sliderock Mountain Volcano were used to further define the source regions of the Late Cretaceous magmatism. The most mafic lava flows are high K (~2-3 wt. % K2O), low Ti (< 1 wt. % TiO2), low Ni (< 20 ppm) basaltic andesites. Major element oxide contents for these rocks are only weakly correlated with increasing wt. % SiO2 on conventional Harker diagrams. All of the rocks are characterized by high LILE/HFSE ratios and high Pb contents (17-20 ppm), as expected for arc-related magmatism. The rocks also have high (La/Yb)N (7-20) but show decreasing (Dy/Yb)N with increasing wt.% SiO2, suggesting a cryptic role for amphibole fractionation during evolution of their parental magmas. Initial ɛNd values range from -19 to -29 but do not covary with rock bulk composition and as a result are unlikely to represent the result of interaction with local Archean continental crust. Initial 87Sr/86Sr, in contrast, vary over a restricted range from 0.7045 to 0.7065. The lowest 87Sr/86Sr correspond to samples with the highest Sr/Y (120-190). The low ɛNd values for the basaltic andesites suggest that if these volcanic rocks were ultimately derived from ultramafic mantle sources, melting must have occurred

  3. Venus magmatic and tectonic evolution

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Hansen, V. L.

    1993-01-01

    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.

  4. The geochemistry of primitive volcanic rocks of the Ankaratra volcanic complex, and source enrichment processes in the genesis of the Cenozoic magmatism in Madagascar

    NASA Astrophysics Data System (ADS)

    Melluso, L.; Cucciniello, C.; le Roex, A. P.; Morra, V.

    2016-07-01

    The Ankaratra volcanic complex in central Madagascar consists of lava flows, domes, scoria cones, tuff rings and maars of Cenozoic age that are scattered over 3800 km2. The mafic rocks include olivine-leucite-nephelinites, basanites, alkali basalts and hawaiites, and tholeiitic basalts. Primitive samples have high Mg# (>60), high Cr and Ni concentrations; their mantle-normalized patterns peak at Nb and Ba, have troughs at K, and smoothly decrease towards the least incompatible elements. The Ankaratra mafic rocks show small variation in Sr-Nd-Pb isotopic compositions (e.g., 87Sr/86Sr = 0.70377-0.70446, 143Nd/144Nd = 0.51273-0.51280, 206Pb/204Pb = 18.25-18.87). These isotopic values differ markedly from those of Cenozoic mafic lavas of northern Madagascar and the Comoro archipelago, typical Indian Ocean MORB and oceanic basalt end-members. The patterns of olivine nephelinitic magmas can be obtained through 3-10% partial melting of a mantle source that was enriched by a Ca-rich alkaline melt, and that contained garnet, carbonates and phlogopite. The patterns of tholeiitic basalts can be obtained after 10-12% partial melting of a source enriched with lower amounts of the same alkaline melt, in the spinel- (and possibly amphibole-) facies mantle, hence in volumes where carbonate is not a factor. The significant isotopic change from the northernmost volcanic rocks of Madagascar and those in the central part of the island implicates a distinct source heterogeneity, and ultimately assess the role of the continental lithospheric mantle as source region. The source of at least some volcanic rocks of the still active Comoro archipelago may have suffered the same time-integrated geochemical and isotopic evolution as that of the northern Madagascar volcanic rocks.

  5. Changes in magmatic oxidation state induced by degassing

    NASA Astrophysics Data System (ADS)

    Brounce, M. N.; Stolper, E. M.; Eiler, J. M.

    2015-12-01

    Temporal variations in the oxygen fugacity (fO2) of the mantle may have been transmitted to Earth's atmosphere and oceans by volcanic degassing. However, it is unclear how redox states of volatiles relate to their source magmas because degassing and assimilation can impact fO2 before or during eruption. To explore this, we present µ-XANES measurements of the oxidation states of Fe and S and laser fluorination measurements of 18O/16O ratios in submarine glasses from two settings where degassing is recorded: 1) submarine glasses from the Reykjanes Ridge as it shoals to Iceland, including subglacial glasses from the Reykjanes Peninsula; and 2) submarine glasses from Mauna Kea recovered by the Hawaii Shield Drilling Program (HSDP). Glasses from both settings are basalts with 5.5-9.9 wt% MgO and 350-1790 ppm S. Submarine Reykjanes glasses are sulfide saturated. Subglacial Reykjanes and HSDP glasses are not sulfide saturated, and S and H2O contents are consistent with S+H2O degassing. Submarine Reykjanes glasses have 18O/16O indistinguishable from MORB and become progressively 18O-depleted as MgO decreases. Subglacial glasses have lower 18O/16O than submarine glasses at a given MgO, but both sample types project to a common 18O/16O near 10 wt% MgO, suggesting that 18O-depletion in these lavas is generated by fractional crystallization and assimilation of an 18O-depleted crustal component. The oxidation state of Fe increases only slightly as 18O/16O decrease, suggesting that the assimilant is not oxidized enough to change magmatic fO2. Fe and S do not oxidize or reduce with decreasing S or H2O, suggesting that relatively reduced magmas at depth degassed S+H2O without changing magmatic fO2, and that the fO2 of these lavas reflect the fO2of their mantle source. The oxidation states of Fe and S in HSDP glasses are broadly correlated and samples with the highest S concentrations are the most oxidized. Both Fe and S reduce with decreasing S and H2O contents. This suggests

  6. Magmatic intrusions and hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Gulick, Virginia Claire

    1993-01-01

    This dissertation investigates the possible role of hydrothermally driven ground-water outflow in the formation of fluvial valleys on Mars. Although these landforms have often been cited as evidence for a past warmer climate and denser atmosphere, recent theoretical modeling precludes such climatic conditions on early Mars when most fluvial valleys formed. Because fluvial valleys continued to form throughout Mars' geological history and the most Earth-like stream valleys on Mars formed well after the decline of the early putative Earth-like climate, it may be unnecessary to invoke drastically different climatic conditions for the formation of the earliest stream valleys. The morphology of most Martian fluvial valleys indicates formation by ground-water sapping which is consistent with a subsurface origin. Additionally, many Martian fluvial valleys formed on volcanoes, impact craters, near fractures, or adjacent to terrains interpreted as igneous intrusions; all are possible locales of vigorous, geologically long-lived hydrothermal circulation. Comparison of Martian valley morphology to similar features on Earth constrains valley genesis scenarios. Volumes of measured Martian fluvial valleys range from 1010 to 1013 m3. Based on terrestrial analogs, total water volumes required to erode these valleys range from approximately 1010 to 1015 m3. The clustered distribution of Martian valleys within a given terrain type, the sapping dominated morphology, and the general lack of associated runoff valleys all indicate the importance of localized ground-water outflow in the formation of these fluvial systems. An analytic model of a conductively cooling cylindrical intrusion is coupled with the U.S. Geological Survey's numerical ground-water computer code SUTRA to evaluate the magnitude of ground-water outflow expected from magmatically-driven hydrothermal systems on Mars. Results indicate that magmatic intrusions of several 102 km3 or larger can provide sufficient ground

  7. Petrography and geochemistry of lower carboniferous greywacke and mudstones in Northeast Junggar, China: Implications for provenance, source weathering, and tectonic setting

    NASA Astrophysics Data System (ADS)

    Tao, Huifei; Sun, Shu; Wang, Qingchen; Yang, Xiaofa; Jiang, Lin

    2014-06-01

    Northeast Junggar occupies an important position that links East Junggar and Chinese Altai. Numerous magmatic and sedimentary rocks of the Paleozoic in this area recorded the final amalgamation processes of East Junggar and Chinese Altai. This study analyzes the petrological and geochemical characteristics of sandstones and mudstones from the Early Carboniferous Nanmingshui formation in Northeast Junggar. The provenance and tectonic setting of these clastic rocks are discussed. Petrography indicates that the composition and texture maturity of the sandstones are low. The components of the sandstones are mainly volcanic fragments (61-87%), feldspars (9-30%), and monocrystalline quartz (2-18%), with a few polycrystalline quartz and other minerals. Slice observation indicates that the majority of the volcanic fragments of sandstones are basic-intermediate volcanic rocks with a few dacite and felsic plutonic fragments. The detrital modes of the sandstones reflect that these sandstones are derived from undissected arcs. A low to moderate chemical index of alteration and the Al2O3-CaO* + Na2O-K2O diagram reflect a low to moderate weathering degree in the source area. Trace and rare earth element (e.g., La, Th, Hf, Sc, Cr, Co, and Eu) contents and their ratios suggest that the source rocks of the clastic rocks are intermediate-basic rocks with some felsic rocks. Compared with sandstones, the source rocks for mudstones are more felsic. The petrography and geochemistry characteristics of the clastic rocks suggest that the proximal Dulate arc should be the primary source area. Mixing calculations based on REE data suggest that approximately two-thirds of the sandstone fragments are intermediate-basic volcanic rocks. The contents of the major and trace elements, as well as the stratum features, of the clastic rocks manifest that these clastic rocks resemble sedimentary rocks in a back-arc basin. The formation of this back-arc basin is caused by the southward subduction of the

  8. East Asia: Seismotectonics, magmatism and mantle dynamics

    NASA Astrophysics Data System (ADS)

    Zhao, Dapeng; Yu, Sheng; Ohtani, Eiji

    2011-02-01

    In this article, we review the significant recent results of geophysical studies and discuss their implications on seismotectonics, magmatism, and mantle dynamics in East Asia. High-resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes, which may reflect magma and fluids that affected the rupture nucleation of large earthquakes. In subduction zone regions, the crustal fluids originate from the dehydration of the subducting slab. Magmatism in arc and back-arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab. The intraplate magmatism has different origins. The continental volcanoes in Northeast Asia (such as Changbai and Wudalianchi) seem to be caused by the corner flow in the big mantle wedge (BMW) above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well. The Tengchong volcano in Southwest China is possibly caused by a similar process in BMW above the subducting Burma microplate (or Indian plate). The Hainan volcano in southernmost China seems to be a hotspot fed by a lower-mantle plume associated with the Pacific and Philippine Sea slabs' deep subduction in the east and the Indian slab's deep subduction in the west down to the lower mantle. 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 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 beneath the subducting slabs and cause the slab-plume interactions. Some of these issues, such as the origin of intraplate magmatism, are still controversial, and so further detailed studies are needed from now.

  9. Activities and source mechanisms of volcanic deep low-frequency earthquakes and its implication for deep crustal process in magmatic arc (Invited)

    NASA Astrophysics Data System (ADS)

    Nakamichi, H.

    2013-12-01

    Rocks under upper mantle and lower crustal temperatures and pressures typically deform in a ductile manner, therefore it is difficult to accumulate enough deviatoric stress in rocks to generate brittle failure under this condition. However earthquakes occur at upper mantle and lower crust beneath active volcanoes, and are recognized as volcanic deep low-frequency earthquakes (VDLFs). VDLFs are characterized by mostly low-frequency energy (<5 Hz), emergent arrivals and long-duration codas. VDLF activity observed at depths of 10-50 km in Japan, the Philippines, Alaska and the Western US (Power et al., 2004; Ukawa, 2005; Nichols et al. 20011), has generally been attributed to magma transport in the mid-to-lower crustal and uppermost mantle regions. However because VDLF seismicity is infrequent, with relatively weak and emergent signals, the relationship between deep magma transport and seismic radiation remains poorly understood. Borehole dense seismic observation systems, such as the high-sensitivity seismograph network 'Hi-net' in Japan (Obara et al. 2005), are effective for detecting not only non-VDLFs (Obara, 2002) but also VDLFs. Since 1997 the Japan Meteorological Agency has routinely detected and located DLFs using the Hi-net dataset, and have identified DLFs in and around most quaternary volcanoes in Japan (Takahashi and Miyamura, 2009). Several studies have attempted to estimate source mechanisms of VDLFs in Japan. The first attempt by Ukawa and Ohtake (1987), obtained a single force as the source mechanism of a VDLF beneath Izu-Ohshima by using particle motions of S-waves. Following that work strike-slip type and non-double-couple source mechanisms were obtained using waveform inversions for VDLFs in Northeast Japan (Nishidomi and Takeo 1996; Okada and Hasegawa, 2000). Nakamichi et al. (2003; 2004) estimated the source mechanisms of Mts. Iwate and Fuji through the moment tensor inversion of spectral ratios of body waves from using data from a dense seismic

  10. Paired MEG data set source localization using recursively applied and projected (RAP) MUSIC.

    PubMed

    Ermer, J J; Mosher, J C; Huang, M; Leahy, R M

    2000-09-01

    An important class of experiments in functional brain mapping involves collecting pairs of data corresponding to separate "Task" and "Control" conditions. The data are then analyzed to determine what activity occurs during the Task experiment but not in the Control. Here we describe a new method for processing paired magnetoencephalographic (MEG) data sets using our recursively applied and projected multiple signal classification (RAP-MUSIC) algorithm. In this method the signal subspace of the Task data is projected against the orthogonal complement of the Control data signal subspace to obtain a subspace which describes spatial activity unique to the Task. A RAP-MUSIC localization search is then performed on this projected data to localize the sources which are active in the Task but not in the Control data. In addition to dipolar sources, effective blocking of more complex sources, e.g., multiple synchronously activated dipoles or synchronously activated distributed source activity, is possible since these topographies are well-described by the Control data signal subspace. Unlike previously published methods, the proposed method is shown to be effective in situations where the time series associated with Control and Task activity possess significant cross correlation. The method also allows for straightforward determination of the estimated time series of the localized target sources. A multiepoch MEG simulation and a phantom experiment are presented to demonstrate the ability of this method to successfully identify sources and their time series in the Task data.

  11. Source components and magmatic processes in the genesis of Miocene to Quaternary lavas in western Turkey: constraints from HSE distribution and Hf-Pb-Os isotopes

    NASA Astrophysics Data System (ADS)

    Aldanmaz, Ercan; Pickard, Megan; Meisel, Thomas; Altunkaynak, Şafak; Sayıt, Kaan; Şen, Pınar; Hanan, Barry B.; Furman, Tanya

    2015-08-01

    Hf-Pb-Os isotope compositions and highly siderophile element (HSE) abundance variations are used to evaluate the mantle source characteristics and possible effects of differentiation processes in lavas from western Turkey, where the eruption of Late Miocene to Quaternary OIB-type intraplate mafic alkaline lavas followed pre-Middle Miocene convergent margin-type volcanism. Concentrations of Os, Ir, and Ru (IPGE) in the OIB-type intraplate lavas decrease with fractionation for primitive melts (MgO > 10 wt%), suggesting that these elements reside predominantly in olivine and associated HSE retaining trace phases and behave compatibly during olivine-dominated fractionation. Fractional crystallization trends indicate distinctly lower bulk partition coefficients for IPGE in more evolved lavas, possibly reflecting a change in the fractionating assemblages. Pd and Re in the primitive melts display negative correlations with MgO, demonstrating moderately incompatible behavior of these elements during fractionation, while the significantly scattered variation in Pt against MgO may indicate the effects of micronuggets of a Pt-rich alloy. Os-rich alkaline primary lavas (>50 ppt Os) exhibit a limited range of 187Os/188Os (0.1361-0.1404), with some xenolith-bearing lavas displaying depletions in 187Os/188Os (0.1131-0.1232), suggesting slight compositional modification of primitive melts through contamination with highly depleted, Os-rich mantle lithosphere. More radiogenic Os isotope ratios (187Os/188Os > 0.1954) in the evolved lavas reflect contamination of the magmas by high187Os/188Os crustal material during shallow differentiation. The OIB-type lavas show limited variations in Hf and Pb isotopes with 176Hf/177Hf = 0.282941-0.283051, 206Pb/204Pb = 18.683-19.091, 207Pb/204Pb = 15.579-15.646, 208Pb/204Pb = 38.550-38.993; 176Hf/177Hf ratios correlate negatively with 208Pb*/206Pb*, suggesting the effects of similar mantle processes on the evolution of time-integrated Th/U and Lu

  12. He, Ar, N and C isotope compositions in Tatun Volcanic Group (TVG), Taiwan: Evidence for an important contribution of pelagic carbonates in the magmatic source

    NASA Astrophysics Data System (ADS)

    Roulleau, Emilie; Sano, Yuji; Takahata, Naoto; Yang, Frank T.; Takahashi, Hiroshi A.

    2015-09-01

    The Tatun Volcanic Group (TVG), Northeastern Taiwan, is considered to be the extension of the Ryukyu arc, and belongs to the post-collisional collapse Okinawa Trough. Strong hydrothermal activity is concentrated along the Chinshan fault, and Da-you-keng (DYK) represents the main fumarolic area where the most primitive isotopic and chemical composition is observed. In this study, we present chemical and He, Ar, C and N isotopic compositions of fumaroles, bubbling gas and water from hot springs sampled in 2012 and 2013. High 3He/4He ratios from DYK fumaroles (≈ 6.5 Ra) show a typical arc-like setting, whereas other sampling areas show a strong dependence of 3He/4He and CH4/3He ratios with the distance from the main active hydrothermal area (DYK). This could mean strong crustal contamination and thermal decomposition of organic matter from local sediments. Carbon isotope compositions of DYK range from - 6.67‰ to - 5.85‰, and indicate that carbon contribution comes mainly from pelagic carbonates from the slab (limestone, mantle and sediment contributions are 63%, 19% and 18%, respectively). This is consistent with the negative δ15N values (- 1.4 ± 0.5‰) observed for DYK, implying a strong nitrogen-mantle contribution, and an absence of contribution from nitrogen-pelagic carbonates. These results have important consequences related to the Ryukyu subducted slab. In fact, the Ryukyu margin presents little in off scraping the sedimentary cover to the subducting plate that does not permit any nitrogen contribution in magma from TVG.

  13. Magmatism on the Moon

    NASA Astrophysics Data System (ADS)

    Michaut, Chloé; Thorey, Clément; Pinel, Virginie

    2016-04-01

    Volcanism on the Moon is dominated by large fissure eruptions of mare basalt and seems to lack large, central vent, shield volcanoes as observed on all the other terrestrial planets. Large shield volcanoes are constructed over millions to several hundreds of millions of years. On the Moon, magmas might not have been buoyant enough to allow for a prolonged activity at the same place over such lengths of time. The lunar crust was indeed formed by flotation of light plagioclase minerals on top of the lunar magma ocean, resulting in a particularly light and relatively thick crust. This low-density crust acted as a barrier for the denser primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basins where at least part of the crust was removed by the impact process. Thus, the ascent of lunar magmas might have been limited by their reduced buoyancy, leading to storage zone formation deep in the lunar crust. Further magma ascent to shallower depths might have required local or regional tensional stresses. Here, we first review evidences of shallow magmatic intrusions within the lunar crust of the Moon that consist in surface deformations presenting morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. We then study the preferential zones of magma storage in the lunar crust as a function of the local and regional state of stress. Evidences of shallow intrusions are often contained within complex impact craters suggesting that the local depression caused by the impact exerted a strong control on magma ascent. The depression is felt over a depth equivalent to the crater radius. Because many of these craters have a radius less than 30km, the minimum crust thickness, this suggests that the magma was already stored in deeper intrusions before ascending at shallower depth. All the evidences for intrusions are also preferentially located in the internal

  14. Dynamic multi-source X-ray tomography using a spacetime level set method

    NASA Astrophysics Data System (ADS)

    Niemi, Esa; Lassas, Matti; Kallonen, Aki; Harhanen, Lauri; Hämäläinen, Keijo; Siltanen, Samuli

    2015-06-01

    A novel variant of the level set method is introduced for dynamic X-ray tomography. The target is allowed to change in time while being imaged by one or several source-detector pairs at a relatively high frame-rate. The algorithmic approach is motivated by the results in [22], showing that the modified level set method can tolerate highly incomplete projection data in stationary tomography. Furthermore, defining the level set function in spacetime enforces temporal continuity in the dynamic tomography context considered here. The tomographic reconstruction is found as a minimizer of a nonlinear functional. The functional contains a regularization term penalizing the L2 norms of up to n derivatives of the reconstruction. The case n = 1 is shown to be equivalent to a convex Tikhonov problem that has a unique minimizer. For n ≥ 2 the existence of a minimizer is proved under certain assumptions on the signal-to-noise ratio and the size of the regularization parameter. Numerical examples with both simulated and measured dynamic X-ray data are included, and the proposed method is found to yield reconstructions superior to standard methods such as FBP or non-negativity constrained Tikhonov regularization and favorably comparable to those of total variation regularization. Furthermore, the methodology can be adapted to a wide range of measurement arrangements with one or more X-ray sources.

  15. Evolution of the late Paleozoic accretionary complex and overlying forearc-magmatic arc, south central Chile (38°-41°S): Constraints for the tectonic setting along the southwestern margin of Gondwana

    NASA Astrophysics Data System (ADS)

    Martin, Mark W.; Kato, Terence T.; Rodriguez, Carolina; Godoy, Estanislao; Duhart, Paul; McDonough, Michael; Campos, Alberto

    1999-08-01

    Stratigraphic, structural, metamorphic, and geochronologic studies of basement rocks in the Andean foothills and Coast Ranges of south central Chile (39°-41°S) suggest a protracted late Paleozoic to middle Mesozoic deformational and metamorphic history that imposes important constraints on the tectonic development of the southwestern Gondwana margin. In the study area the late Paleozoic paired metamorphic belt, coeval magmatic arc, and overlying Triassic sedimentary units preserve a record of Late Carboniferous to Early Permian subduction and arc magmatism, subsequent deep exhumation of the Western Series subduction complex, and diminished uplift and erosion of the Eastern Series arc-forearc region by the Late Triassic. Late Paleozoic structural elements and metamorphic assemblages formed during early subduction and arc magmatism, collectively referred to as Dl, are largely erased in the Western Series by the dominant D2 schistosity and lower greenschist grade metamorphism. D1 structural features, as well as original sedimentary textures, are relatively well preserved in the less penetratively deformed Eastern Series. The regional distribution of late Paleozoic arc magmatism suggests that the late Paleozoic convergent margin deviated from a N-S trend north of this area to a NW-SE trend near this latitude and faced an open marine environment to the southwest. A transition from F2 isoclinal folding to more open, larger-scale F3 folds, interpreted as change in ductility during differential uplift of the Western Series, is not apparent in the Eastern Series. Despite a lesser degree of uplift during the main exhumational D2 event, delineation of unconformities and U-Pb dating of detrital zircons and intrusions into the Eastern Series allow tighter constraints to be placed on timing of uplift and denudation of the Eastern Series than on that in the Western Series. A regional unconformity exposed in the Lake District that separates more highly deformed Eastern Series

  16. Geochemistry of the Ediacaran-Early Cambrian transition in Central Iberia: Tectonic setting and isotopic sources

    NASA Astrophysics Data System (ADS)

    Fuenlabrada, José Manuel; Pieren, Agustín P.; Díez Fernández, Rubén; Sánchez Martínez, Sonia; Arenas, Ricardo

    2016-06-01

    A complete Ediacaran-Early Cambrian stratigraphic transition can be observed in the southern part of the Central Iberian Zone (Iberian Massif). Two different stratigraphic units, underlying Ordovician series, display geochemical and Sm-Nd isotopic features in agreement with an evolving geodynamic setting. Pusa Shales (Early Cambrian) rest unconformably on greywackes of the Lower Alcudian Formation (Late Ediacaran). Both sequences present minor compositional variations for major and trace element contents and similar REE patterns, close to those of PAAS (Post Archean Australian Shale). Trace element contents and element ratios suggest mixed sources, with intermediate to felsic igneous contributions for both units. Tectonic setting discrimination diagrams for the Ediacaran greywackes indicate that these turbiditic series were deposited in a sedimentary basin associated with a mature active margin (volcanic arc). However, the compositions of the Cambrian shales fit better with a more stable context, a back-arc or retro-arc setting. εNd(T) and TDM ages are compatible with dominance of a similar cratonic source for both sequences, probably the West Africa Craton. εNd565 values for the Ediacaran greywackes (- 3.0 to - 1.4) along with TDM ages (1256-1334 Ma) imply a significant contribution of juvenile material, probably derived from the erosion of the volcanic arc. However, εNd530 values in the Cambrian shales (- 5.2 to - 4.0) together with older TDM ages (1444-1657 Ma), suggest a higher contribution of cratonic isotopic sources, probably derived from erosion of the adjacent mainland. Coeval with the progressive cessation of arc volcanism along the peri-Gondwanan realm during the Cambrian, there was a period of more tectonic stability and increasing arrival of sediments from cratonic areas. The geochemistry of the Ediacaran-Cambrian transition in Central Iberia documents a tectonic switch in the periphery of Gondwana, from an active margin to a more stable context

  17. An integrated, open-source set of tools for urban vulnerability monitoring from Earth observation data

    NASA Astrophysics Data System (ADS)

    De Vecchi, Daniele; Harb, Mostapha; Dell'Acqua, Fabio; Aurelio Galeazzo, Daniel

    2015-04-01

    Aim: The paper introduces an integrated set of open-source tools designed to process medium and high-resolution imagery with the aim to extract vulnerability indicators [1]. Problem: In the context of risk monitoring [2], a series of vulnerability proxies can be defined, such as the extension of a built-up area or buildings regularity [3]. Different open-source C and Python libraries are already available for image processing and geospatial information (e.g. OrfeoToolbox, OpenCV and GDAL). They include basic processing tools but not vulnerability-oriented workflows. Therefore, it is of significant importance to provide end-users with a set of tools capable to return information at a higher level. Solution: The proposed set of python algorithms is a combination of low-level image processing and geospatial information handling tools along with high-level workflows. In particular, two main products are released under the GPL license: source code, developers-oriented, and a QGIS plugin. These tools were produced within the SENSUM project framework (ended December 2014) where the main focus was on earthquake and landslide risk. Further development and maintenance is guaranteed by the decision to include them in the platform designed within the FP 7 RASOR project . Conclusion: With the lack of a unified software suite for vulnerability indicators extraction, the proposed solution can provide inputs for already available models like the Global Earthquake Model. The inclusion of the proposed set of algorithms within the RASOR platforms can guarantee support and enlarge the community of end-users. Keywords: Vulnerability monitoring, remote sensing, optical imagery, open-source software tools References [1] M. Harb, D. De Vecchi, F. Dell'Acqua, "Remote sensing-based vulnerability proxies in the EU FP7 project SENSUM", Symposium on earthquake and landslide risk in Central Asia and Caucasus: exploiting remote sensing and geo-spatial information management, 29-30th January 2014

  18. The 40-year OMNI 2 Data Set: Challenges in Building Virtual Multi-source Data Products

    NASA Astrophysics Data System (ADS)

    King, J. H.; Papitashvili, N. E.

    2003-12-01

    "Virtual observatories" aspire to enable the finding, retrieval and possibly display of data from distributed sites. To our awareness, none (at least in space physics) yet strives to support the on-the-fly creation of multi-source data products where the data have been cleaned and normalized to a fiducial data set. We address some challenges of such an activity by describing the building of the OMNI 2 data set using data gathered at NSSDC from multiple sites. OMNI 2 is a 40-year, hourly resolution, multi-spacecraft compilation of near-Earth solar wind magnetic field and plasma data, energetic proton fluxes, geomagnetic activity indices and sunspot numbers. The primary sources for recent years are the IMP 8, Wind and ACE spacecraft. Data cleaning procedures are described, especially for IMP 8 using a recently created database of IMP 8 bow shock crossings. A new approach to the time-shifting of high-resolution ISEE 3, Wind and ACE data is discussed. Extensive comparisons between pairs and triads of data from concurrently operating missions are described, with an emphasis on IMP 8, Wind and ACE. Normalizations of 1971-2003 plasma densities and temperatures to those from Wind/SWE are discussed. OMNI 2 may be considered a multi-decadal data set from a "virtual spacecraft" located in front of the Earth's magnetosphere. The OMNI 2 data set is accessible from the reference below, which also links to detailed OMNI 2 documentation and to the hourly and higher resolution data contributing to OMNI 2.

  19. Magmatism of the Lunar Highlands and the Early Paleoproterozoic Magmatism of the Earth: Similarities and Distinctions

    NASA Astrophysics Data System (ADS)

    Sharkov, E. V.; Bogatilkov, O. A.

    1999-01-01

    Important feature of tectonic-magmatic activity on the Moon is it closeness to the Earth's early Paleoproterozoic stage of evolution. The most ancient magmatism of the Moon was begun at highlands from low-Ti melts of the magnesian suite, which were rather close in composition of rocks, their mineralogy and geochemistry to the early Palaeoproterozoic terrestrial magmatism of the siliceous high-Mg (boninite-like) series (SHMS). Around 3.8 Ga, it was changed by basaltic magmatism of maria, where high-Ti varieties were common. This type of magmatism is resembled the oceanic-type magmatism of the Earth (including Fe-Ti basalts of oceanic islands), which firstly appeared in the late Palaeoproterozoic: ca. 2 Ga. On the Moon are lacking both analogs of the Archean type of activity of the Earth, when formation of granite-greenstone terranes occurred, and the Phanerozoic subduction-related magmatism. On Earth, the SHMS rocks of 2.5-2.1 Ga formed large igneous provinces within the Archean granite-greenstone cratons. For example, on the Baltic Shield such province evolved on territory measuring about 1 million square-km and represented by different volcanics (low-Ti picrites, Mg basalts, high-Al basalts, andesites, dacites, and rhyolites, where basalts predominated) in riftlike structures, gabbronorite dyke swarms, and large layered intrusions. The latter consist of dunites, harzburgites, pyroxenites, norites and gabbronorites, including pigeonite varieties, gabbro-anorthosites, Mgt gabbronorites, and diorites. The SHMS rocks on their major, rare, and rare earth elements contents were rather close to the Phanerozoic calc-alkaline series related to subduction zones, but on its geological position they had within-plate tectonic settings and look like the continental flood basalt province. The Epsilon-Nd(T) value of -1 to -2 is characteristic for the studied SHMS-rocks, indicating that the origin of such melts was linked with large-scale assimilation of crustal rocks by high

  20. Why are plutons dry? Outgassing mechanisms of crustal magmatic bodies

    NASA Astrophysics Data System (ADS)

    parmigiani, andrea; Huber, Christian; Bachmann, Olivier; Leclaire, Sébastien

    2016-04-01

    Magma bodies crystallizing to completion within the crust (i.e., forming plutons) typically undergo significant amounts of second boiling (i.e. cooling and crystallization of dominantly anhydrous minerals lead to volatile saturation and bubble nucleation/growth). The low water content (< 1 wt % H2O) and vanishing residual porosity of most plutons, despite the high volatile concentrations of their magma sources (commonly > 6 wt % H2O for evolved compositions in subduction zones), testify that outgassing from crystalline mushy reservoirs must be an efficient and widespread process. Understanding this outgassing mechanism is key to understand how volatiles are transferred from mantle depths to the surface. From the hydrodynamics point of view, the mass balance of exsolved volatiles in these plutonic bodies is controlled by the difference between the rate of degassing (formation of bubbles by 2nd boiling) and outgassing (transport of gas out of the magma body). In this study, we use pore-scale multiphase modeling to constrain these rates as function of the crystal and volatile contents in the magma. Because second boiling is a slow process, one can consider equilibrium degassing as a valid assumption. Outgassing, on the other end, is controlled by the competition between buoyancy, capillary and viscous forces. Our numerical simulations are used to determine the most efficient setting for gas to escape its magmatic trap. The high viscosity of interstitial melts and capillary forces (due to the non-wetting nature of the gas phase with most of the mineral phases in magmatic systems) strongly limits gas transport until vertically extensive gas channels are generated. We show that channels can readily form in volatile-rich coarse-grained mush zones in the upper crust, and allow efficient outgassing at crystallinities around 50-75 vol%, when millimetric bubbles can still win capillary resistive forces.

  1. Sediment composition of big Chinese and Indochinese rivers reflects geology of their source, not tectonic setting of their sink.

    NASA Astrophysics Data System (ADS)

    Garzanti, Eduardo; Andò, Sergio; Limonta, Mara; Nie, Junsheng; Resentini, Alberto; Vezzoli, Giovanni; Wang, Jiangang; Yang, Shouye

    2016-04-01

    There are several reasons why the tectonic setting of a sedimentary basin cannot be inferred from the composition of its sedimentary fill. One is that sediments can, and quite often are transported for thousands of kilometers from sources uplifted by certain tectonic processes to subsident basins created by totally different tectonic processes. A classical case is the Amazon River, carrying detritus from the Andean Cordillera to the Atlantic passive margin on the opposite side of South America (Franzinelli and Potter, 1983; Dickinson, 1988). Similar is the case of major rivers in China and Indochina, sourced in Tibetan orogenic highlands and reaching the Chinese passive margin or the back-arc/pull-apart Andaman Sea. The Huang He (Yellow River), the most sediment-laden river in the world, delivers annually to the Bohai Sea 1 billion tons of litho-feldspatho-quartzose sedimentaclastic/metamorphiclastic sediments with moderately rich, amphibole-epidote-garnet suites including apatite and zircon (Nie et al., 2015). The Changjiang (Yangtze) River, the fourth longest on Earth and the largest in Eurasia, carries to the East China Sea litho-feldspatho-quartzose sedimentaclastic/metamorphiclastic sand with moderately poor, amphibole-epidote suites including clinopyroxene and garnet (Vezzoli et al., 2016). The Ayeyarwadi (Irrawaddy) River, ranking among the five major rivers in the world for its annual load of 0.4 billion tons, carries to the Andaman Sea litho-feldspatho-quartzose metamorphiclastic/sedimentaclastic sand with moderately rich, amphibole-epidote suites including garnet and clinopyroxene (Garzanti et al., 2013). Detrital modes in these three very big river basins are thus similar, and would plot in the "Recycled Orogen" field of Dickinson (1985) rather than in the "Continental Block" or "Magmatic Arc" fields. The orogenic signature acquired in mountainous headwaters is carried all the way to the mouth, and even after long-distance transport across wide

  2. Linking magmatism with collision in an accretionary orogen

    NASA Astrophysics Data System (ADS)

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-05-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen.

  3. Linking magmatism with collision in an accretionary orogen.

    PubMed

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-01-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251-245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen. PMID:27167207

  4. Linking magmatism with collision in an accretionary orogen

    PubMed Central

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

    2016-01-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen. PMID:27167207

  5. Injections given in healthcare settings as a major source of acute hepatitis B in Moldova.

    PubMed

    Hutin, Y J; Harpaz, R; Drobeniuc, J; Melnic, A; Ray, C; Favorov, M; Iarovoi, P; Shapiro, C N; Woodruff, B A

    1999-08-01

    Two case-control studies were conducted between January 1994 and August 1995 to determine the relative importance of injections and other exposures as a source of acute hepatitis B in Moldova among adults (aged 15 years) and children (aged 2-15 years). Results showed that injections in various health care settings were associated with acute hepatitis B and showed a higher proportion among adults compared with children. Contact with an HBsAg-positive person was also associated with illnesses; however, there was no statistically significant association between acute hepatitis B and other exposures. The risk of HBV transmission following percutaneous exposure is high (at least 30%). Calculation of the population attributable to risk suggests that injections associated with acute hepatitis B cases occurred in adults (52%) and children (21%). Adverse effects of injections may not be apparent in causing chronic infections. Transmission of blood-borne pathogens through unsafe injection practices is a problem increasingly identified worldwide.

  6. Examination of frit vent from Sixty-Watt Heat Source simulant fueled clad vent set

    SciTech Connect

    Ulrich, G.B.

    1995-11-01

    The flow rate and the metallurgical condition of a frit vent from a simulant-fueled clad vent set (CVS) that had been hot isostatically pressed (HIP) for the Sixty-Watt Heat Source program were evaluated. The flow rate form the defueled vent cup subassembly was reduced approximately 25% from the original flow rate. No obstructions were found to account for the reduced flow rate. Measurements indicate that the frit vent powder thickness was reduced about 30%. Most likely, the powder was compressed during the HIP operation, which increased the density of the powder layer and thus reduced the flow rate of the assembly. All other observed manufacturing attributes appeared to be normal, but the vent hole activation technique needs further refinement before it is used in applications requiring maximum CVS integrity.

  7. Magmatic unrest beneath Mammoth Mountain, California

    USGS Publications Warehouse

    Hill, D.P.; Prejean, S.

    2005-01-01

    Mammoth Mountain, which stands on the southwest rim of Long Valley caldera in eastern California, last erupted ???57,000 years BP. Episodic volcanic unrest detected beneath the mountain since late 1979, however, emphasizes that the underlying volcanic system is still active and capable of producing future volcanic eruptions. The unrest symptoms include swarms of small (M ??? 3) earthquakes, spasmodic bursts (rapid-fire sequences of brittle-failure earthquakes with overlapping coda), long-period (LP) and very-long-period (VLP) volcanic earthquakes, ground deformation, diffuse emission of magmatic CO2, and fumarole gases with elevated 3He/4He ratios. Spatial-temporal relations defined by the multi-parameter monitoring data together with earthquake source mechanisms suggest that this Mammoth Mountain unrest is driven by the episodic release of a volume of CO2-rich hydrous magmatic fluid derived from the upper reaches of a plexus of basaltic dikes and sills at mid-crustal depths (10-20 km). As the mobilized fluid ascends through the brittle-plastic transition zone and into overlying brittle crust, it triggers earthquake swarm activity and, in the case of the prolonged, 11-month-long earthquake swarm of 1989, crustal deformation and the onset of diffuse CO2 emissions. Future volcanic activity from this system would most likely involve steam explosions or small-volume, basaltic, strombolian or Hawaiaan style eruptions. The impact of such an event would depend critically on vent location and season.

  8. Tonian granitic magmatism of the Borborema Province, NE Brazil: A review

    NASA Astrophysics Data System (ADS)

    Guimarães, Ignez P.; de Fatima L. de Brito, Maria; de A. Lages, Geysson; da Silva Filho, Adejardo F.; Santos, Lucilene; Brasilino, Roberta G.

    2016-07-01

    involvement of distinct proportions of mantle and crustal components in the source of their protoliths. There is no consensus in the literature about the tectonic setting of the CVG ie they have been related to either continental margin magmatic arc, with possible back-arc association, or extention-related setting, with generation of A-type granites. However, all the available geochemical data suggest that the CVG represent extension related magmatism. The geochemical signature associated to bimodal volcanism, including pyroclastic rocks, with similar ages, and absence, up to now, of evidence for metamorphism of Tonian age, support the hypothesis of extension - related magmatism.

  9. Measuring Data Quality Through a Source Data Verification Audit in a Clinical Research Setting.

    PubMed

    Houston, Lauren; Probst, Yasmine; Humphries, Allison

    2015-01-01

    Health data has long been scrutinised in relation to data quality and integrity problems. Currently, no internationally accepted or "gold standard" method exists measuring data quality and error rates within datasets. We conducted a source data verification (SDV) audit on a prospective clinical trial dataset. An audit plan was applied to conduct 100% manual verification checks on a 10% random sample of participant files. A quality assurance rule was developed, whereby if >5% of data variables were incorrect a second 10% random sample would be extracted from the trial data set. Error was coded: correct, incorrect (valid or invalid), not recorded or not entered. Audit-1 had a total error of 33% and audit-2 36%. The physiological section was the only audit section to have <5% error. Data not recorded to case report forms had the greatest impact on error calculations. A significant association (p=0.00) was found between audit-1 and audit-2 and whether or not data was deemed correct or incorrect. Our study developed a straightforward method to perform a SDV audit. An audit rule was identified and error coding was implemented. Findings demonstrate that monitoring data quality by a SDV audit can identify data quality and integrity issues within clinical research settings allowing quality improvement to be made. The authors suggest this approach be implemented for future research.

  10. Sources of Cognitive Inflexibility in Set-Shifting Tasks: Insights Into Developmental Theories From Adult Data.

    PubMed

    Dick, Anthony Steven

    2012-01-01

    Two experiments examined processes underlying cognitive inflexibility in set-shifting tasks typically used to assess the development of executive function in children. Adult participants performed a Flexible Item Selection Task (FIST) that requires shifting from categorizing by one dimension (e.g., color) to categorizing by a second orthogonal dimension (e.g., shape). The experiments showed performance of the FIST involves suppression of the representation of the ignored dimension; response times for selecting a target object in an immediately-following oddity task were slower when the oddity target was the previously-ignored stimulus of the FIST. However, proactive interference from the previously relevant stimulus dimension also impaired responding. The results are discussed with respect to two prominent theories of the source of difficulty for children and adults on dimensional shifting tasks: attentional inertia and negative priming. In contrast to prior work emphasizing one over the other process, the findings indicate that difficulty in the FIST, and by extension other set-shifting tasks, can be attributed to both the need to shift away from the previously attended representation (attentional inertia), and the need to shift to the previously ignored representation (negative priming). Results are discussed in relation to theoretical explanations for cognitive inflexibility in adults and children.

  11. InP MMIC Chip Set for Power Sources Covering 80-170 GHz

    NASA Technical Reports Server (NTRS)

    Ngo, Catherine

    2001-01-01

    We will present a Monolithic Millimeter-wave Integrated Circuit (MMIC) chip set which provides high output-power sources for driving diode frequency multipliers into the terahertz range. The chip set was fabricated at HRL Laboratories using a 0.1-micrometer gate-length InAlAs/InGaAs/InP high electron mobility transistor (HEMT) process, and features transistors with an f(sub max) above 600 GHz. The HRL InP HEMT process has already demonstrated amplifiers in the 60-200 GHz range. In this paper, these high frequency HEMTs form the basis for power sources up to 170 GHz. A number of state-of-the-art InP HEMT MMICs will be presented. These include voltage-controlled and fixed-tuned oscillators, power amplifiers, and an active doubler. We will first discuss an 80 GHz voltage-controlled oscillator with 5 GHz of tunability and at least 17 mW of output power, as well as a 120 GHz oscillator providing 7 mW of output power. In addition, we will present results of a power amplifier which covers the full WRIO waveguide band (75-110 GHz), and provides 40-50 mW of output power. Furthermore, we will present an active doubler at 164 GHz providing 8% bandwidth, 3 mW of output power, and an unprecedented 2 dB of conversion loss for an InP HEMT MMIC at this frequency. Finally, we will demonstrate a power amplifier to cover 140-170 GHz with 15-25 mW of output power and 8 dB gain. These components can form a power source in the 155-165 GHz range by cascading the 80 GHz oscillator, W-band power amplifier, 164 GHz active doubler and final 140-170 GHz power amplifier for a stable, compact local oscillator subsystem, which could be used for atmospheric science or astrophysics radiometers.

  12. Sediment and weathering control on the distribution of Paleozoic magmatic tin-tungsten mineralization

    NASA Astrophysics Data System (ADS)

    Romer, Rolf L.; Kroner, Uwe

    2015-03-01

    The formation of major granite-hosted Sn and/or W deposits and lithium-cesium-tantalum (LCT) type pegmatites in the Acadian, Variscan, and Alleghanian orogenic belts of Europe and Atlantic Northern America involves weathering-related Sn and W enrichment in the sedimentary debris of the Cadomian magmatic arc and melting of these sedimentary source rocks during later tectonic events, followed by magmatic Sn and W enrichment. We suggest that within this, more than 3,000-km long late Paleozoic belt, large Sn and/or W deposits are only found in regions where later redeposition of the Sn-W-enriched weathered sediments, followed by tectonic accumulation, created large volumes of Sn-W-enriched sedimentary rocks. Melting of these packages occurred both during the formation of Pangea, when continental collision subjected these source rocks to high-grade metamorphism and anatexis, and during post-orogenic crustal extension and mantle upwelling. The uncoupling of source enrichment and source melting explains (i) the diachronous occurrence of tin granites and LCT pegmatites in this late Paleozoic orogenic belt, (ii) the occurrence of Sn and/or W mineralizations and LCT pegmatites on both sides of the Rheic suture, and (iii) the contrasting tectonic setting of Sn and/or W mineralizations within this belt. Source enrichment, sedimentary and tectonic accumulation of the source rocks, and heat input to mobilize metals from the source rocks are three unrelated requirements for the formation of Sn and/or W granites. They are the controlling features on the large scale. Whether a particular granite eventually generates a Sn and/or W deposit depends on local conditions related to source melting, melt extraction, and fractionation processes.

  13. Mesoarchean Gabbroanorthosite Magmatism of the Kola Region

    NASA Astrophysics Data System (ADS)

    Kudryashov, N.; Mokrushin, A.

    2012-04-01

    The Kola peninsula is the region marked with development of anorthosite magmatism in the NE Baltic Shield. The Archaean gabbroanorthosites intrusions - Tsaginsky, Achinsky and Medvezhe-Schucheozersky - have the age of 2.7-2.6 Ga (Bayanova, 2004). The Patchemvarek and Severny gabbroanorthosites intrusions are located in the junction zone of the Kolmozero-Voronja greenstone belt and the Murmansk domain. Age data for sedimentaryvolcanogenic rocks of the Kolmozero-Voronja belt and Murmansk domain granitoids are 2.8-2.7 Ga. The gabbroanorthosites intrusions have more calcic composition (70-85% An) of normative plagioclase, and low contents of TiO2, FeO, and Fe2O3. In terms of chemical composition, the gabbroanorthosites of the studied massifs are close to the rocks of the Fiskenesset Complex (Greenland) and to the anorthosites of the Vermillion Lake Complex (Canada). U-Pb zircon dating established Mesoarchean ages of 29257 and 29358 Ma for the gabbroanorthosites of the Patchemvarek and Severny massifs, respectively. It was shown that the gabbroanorthosites of the studied massifs have fairly low REE contents (Cen = 2.2-4.2, Ybn = 1.6-2.6) and distinct positive Eu anomaly. Comagmatic ultrabasic differentiates have practically unfractionated REE pattern, low total REE contents (Cen = 1.2, Ybn = 1.1, La/Ybn = 1.32), and no Eu anomaly. The studied samples of the Archean gabbroanorthosites are characterized by positive "Nd= + 2.68 for the gabbroanorthosites of the Severny Massif and from + 2.77 to + 1.66 for the Patchemvarek Massif. The rocks of the Severny and Patchemvarek massifs has 87Sr/86Sri = 0.702048 and 87Sr/86Sri = 0.70258_8, respectively. The oldest U-Pb zircon ages for the gabbroanorthosites of the Patchemvarek and Severny massifs marking the Mesoarchean stage in the evolution of region. The differences in the initial 143Nd/144Nd ratios between the Neoarchean and the Mesoarchean gabbroanorthosites suggest the existence of two mantle sources. One of them produced

  14. On the scaling of multicrystal data sets collected at high-intensity X-ray and electron sources

    PubMed Central

    Coppens, Philip; Fournier, Bertrand

    2015-01-01

    The need for data-scaling has become increasingly evident as time-resolved pump-probe photocrystallography is rapidly developing at high intensity X-ray sources. Several aspects of the scaling of data sets collected at synchrotrons, XFELs (X-ray Free Electron Lasers) and high-intensity pulsed electron sources are discussed. They include laser-ON/laser-OFF data scaling, inter- and intra-data set scaling. PMID:26798829

  15. Geochemical characterization of fluids along the Dead Sea Rift: implications for fluids sources and regional geodynamic setting

    NASA Astrophysics Data System (ADS)

    Inguaggiato, Claudio; Censi, Paolo; D'Alessandro, Walter; Zuddas, Pierpaolo

    2016-04-01

    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

  16. Petrogenesis of Sveconorwegian magmatism in southwest Norway; constraints from zircon U-Pb-Hf-O and whole-rock geochemistry

    NASA Astrophysics Data System (ADS)

    Roberts, Nick M. W.; Slagstad, Trond; Parrish, Randall R.; Norry, Michael J.; Marker, Mogens; Horstwood, Matthew S. A.; Røhr, Torkil

    2013-04-01

    The Sveconorwegian orogen is traditionally interpreted as a Himalayan-scale continental collision, and the eastward continuation of the Grenville Province of Laurentia; however, it has recently been proposed that it represents an accretionary orogen without full-scale continental collision (Slagstad et al., in press). We suggest that magmatism is one of the key constraints to differentiate between different types of orogens; thus, detailed investigation of the timing and petrogenesis of the magmatic record is a requirement for better understanding of the Sveconorwegian orogen as a whole. Here, we present new U-Pb geochronology, zircon Hf-O isotope, and whole-rock geochemical data to constrain the petrogenesis of the early -Sveconorwegian Sirdal Magmatic Belt (SMB). The SMB is a batholithic-scale complex of intrusions that intrudes into most of the Rogaland-Hardangervidda Block in southwest Norway. Current age constraints put emplacement between ~1050 to 1020 Ma. New ages from the Suldal region indicate that the onset of SMB magmatism can be put back to 1070 Ma, which is some 30-50 Myrs prior to high-grade metamorphism. Average initial ɛHf signatures range from ~0 to 4; these overlap with later post-Sveconorwegian granites and with early-/pre-Sveconorwegian ferroan (A-type) granites. Average δ18O signatures range from ~5.7 to 8.7, except for one anomalous granite at ~11.6. The Hf-O signatures are compatible with a mixed mantle-crustal source. Crustal sources may include ~1500 Ma Telemarkian or ~1200 Ma juvenile crust. Hf-O bulk-mixing modelling using a 1500 Ma crustal source indicates >50 % mantle input. Although much further mapping and geochronological work is required, granitic magmatism appears to have persisted throughout much of the ~1100 to 900 Ma period that spans the Sveconorwegian orogen. This magmatism is consistently ferroan (i.e. dry); however, the SMB marks a clear transition to magnesian (i.e. wet) magmatism, with a return to ferroan magmatism at

  17. Global combustion sources of organic aerosols: model comparison with 84 AMS factor-analysis data sets

    NASA Astrophysics Data System (ADS)

    Tsimpidi, Alexandra P.; Karydis, Vlassis A.; Pandis, Spyros N.; Lelieveld, Jos

    2016-07-01

    Emissions of organic compounds from biomass, biofuel, and fossil fuel combustion strongly influence the global atmospheric aerosol load. Some of the organics are directly released as primary organic aerosol (POA). Most are emitted in the gas phase and undergo chemical transformations (i.e., oxidation by hydroxyl radical) and form secondary organic aerosol (SOA). In this work we use the global chemistry climate model ECHAM/MESSy Atmospheric Chemistry (EMAC) with a computationally efficient module for the description of organic aerosol (OA) composition and evolution in the atmosphere (ORACLE). The tropospheric burden of open biomass and anthropogenic (fossil and biofuel) combustion particles is estimated to be 0.59 and 0.63 Tg, respectively, accounting for about 30 and 32 % of the total tropospheric OA load. About 30 % of the open biomass burning and 10 % of the anthropogenic combustion aerosols originate from direct particle emissions, whereas the rest is formed in the atmosphere. A comprehensive data set of aerosol mass spectrometer (AMS) measurements along with factor-analysis results from 84 field campaigns across the Northern Hemisphere are used to evaluate the model results. Both the AMS observations and the model results suggest that over urban areas both POA (25-40 %) and SOA (60-75 %) contribute substantially to the overall OA mass, whereas further downwind and in rural areas the POA concentrations decrease substantially and SOA dominates (80-85 %). EMAC does a reasonable job in reproducing POA and SOA levels during most of the year. However, it tends to underpredict POA and SOA concentrations during winter indicating that the model misses wintertime sources of OA (e.g., residential biofuel use) and SOA formation pathways (e.g., multiphase oxidation).

  18. Tectonic significance of Neoproterozoic magmatism of Nakora area, Malani igneous suite, Western Rajasthan, India

    NASA Astrophysics Data System (ADS)

    Kumar, Naresh; Vallinayagam, G.

    2014-05-01

    Three magmatic phases are distinguished in the Neoproterozoic Nakora Ring Complex (NRC) of Malani Igneous Suite (MIS), namely (a) Extrusive (b) Intrusive and (c) Dyke phase. Magmatism at NRC initiated with minor amount of (basic) basalt flows and followed by the extensive/voluminous acid (rhyolites-trachytes) flows. The ripple marks are observed at the Dadawari area of NRC in tuffaceous rhyolite flow which suggests the aqueous condition of flows deposition. The emplacement of the magma appears to have been controlled by a well defined NE-SW tectonic lineament and cut by radial pattern of dykes. These NE-SW tectonic lineaments are the linear zones of crustal weakness and high heat flow. The spheroidal and rapakivi structures in the Nakora acid volcanics indicate the relationship between genetic link and magma mixing. Basalt-trachyte-rhyolite association suggests that the large amount of heat is supplied to the crust from the magma chamber before the eruption. The field (elliptical/ring structures), mineralogical and geochemical characteristics of Nakora granites attest an alkaline character in their evolution and consistent with within plate tectonic setting. The emplacement of these granites and associated volcanics is controlled by ring structures, a manifestation of plume activity and cauldron subsidence, an evidence of extensional tectonic environment. NRC granites are the product of partial melting of rocks similar to banded gneiss from Kolar Schist Belt of India. The present investigations suggest that the magmatic suites of NRC rocks are derived from a crustal source and the required heat supplied from a mantle plume.

  19. Porphyry Cu-Au mineralization in the Mirkuh Ali Mirza magmatic complex, NW Iran

    NASA Astrophysics Data System (ADS)

    Maghsoudi, A.; Yazdi, M.; Mehrpartou, M.; Vosoughi, M.; Younesi, S.

    2014-01-01

    The Mirkuh Ali Mirza Cu-Au porphyry system in East Azerbaijan Province is located on the western part of the Cenozoic Alborz-Azerbaijan volcanic belt. The belt is also an important Cu-Mo-Au metallogenic province in northwestern Iran. The exposed rocks in the study area consist of a volcaniclastic sequence, subvolcanic rocks and intermediate to mafic lava flows of Neogene age. The volcanic rocks show a typical subduction-related magmatic arc geological and geochemical signature, with low concentration of Nb, Ta, and Ti. Mineralization is hosted by Neogene dacitic tuff and porphyritic dacite situated at the intersections of northeast and northwest faults. Field observations, alteration zonation, geochemical haloes and isotopic data of the Mirkuh Ali Mirza magmatic complex show similarities with typical convergent margin Cu-Au porphyry type deposits. The following features confirm the classic model for Cu-Au porphyry systems: (a) close spatial association with high-K calcalkaline to shoshonitic rock related to post-collision extensional setting (b) low grade Cu (0.57%) (c) stockworks as well as disseminated sulfides (c) zonality of the alteration patterns from intense phyllic at the center to outward weak-phyllic, argillic, and propylitic (d) the presence of a pyritic halo (e) accompanied by sheeted veins and low-sulfidation epithermal gold (f) mineralization spatially associated with intersection of structures, (g) genetically related to diorite porphyry stocks at depth (h) geochemical zonation of (Cu ± Au ± Ag ± Bi) → (Cu + Mo ± Bi ± Au ± Pb ± Zn ± As) → (Au + Mo ± Pb ± Zn) → (As + Ag + Sb + Mn + Ba + Pb + Zn + Hg) → Hg from center to outwards (i) The range of sulfur isotopic values is approximately zero (interpreted to have magmatic source) and similar to other subduction-related porphyry Cu deposits.

  20. Comparison of Proterozoic and Phanerozoic rift-related basaltic-granitic magmatism

    NASA Astrophysics Data System (ADS)

    Haapala, Ilmari; Rämö, O. Tapani; Frindt, Stephen

    2005-03-01

    This paper compares the 1.67-1.47 Ga rapakivi granites of Finland and vicinity to the 1.70-1.68 Ga rapakivi granites of the Beijing area in China, the anorogenic ˜130 Ma granites of western Namibia, and the 20-15 Ma granites of the Colorado River extensional corridor in the Basin and Range Province of southern Nevada. In Finland and China, the tectonic setting was incipient, aborted rifting of Paleoproterozoic or Archean continental crust, in Namibia it was continental rifting and mantle plume activity that led to the opening of southern Atlantic at ˜130 Ma. The 20-15 Ma granites of southern Nevada were related to rifting that followed the Triassic-Paleogene subduction of the Farallon plate beneath the southwestern United States. In all cases, extension-related magmatism was bimodal and accompanied by swarms of diabase and rhyolite-quartz latite dikes. Rapakivi texture with plagioclase-mantled alkali feldspar megacrysts occurs in varying amounts in the granites, and the latest intrusive phases are commonly topaz-bearing granites or rhyolites that may host tin, tungsten, and beryllium mineralization. The granites are typically ferroan alkali-calcic metaluminous to slightly peraluminous rocks with A-type and within-plate geochemical and mineralogical characteristics. Isotope studies (Nd, Sr) suggest dominant crustal sources for the granites. The preferred genetic model is magmatic underplating involving dehydration melting of intermediate-felsic deep crust. Juvenile mafic magma was incorporated either via magma mingling and mixing, or by remelting of newly hybridized lower crust. In Namibia, partial melting of subcontinental lithospheric mantle was caused by the Tristan mantle plume, in the other cases the origin of the mantle magmatism is controversial. For the Fennoscandian suites, extensive long-time mantle upwelling associated with periodic, migrating melting of the subcontinental lithospheric mantle, governed by heat flow and deep crustal structures, is

  1. Mesozoic magmatism and metallogeny in the Chizhou area, Middle-Lower Yangtze Valley, SE China: Constrained by petrochemistry, geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Song, Guoxue; Qin, Kezhang; Li, Guangming; Evans, Noreen J.; Li, Xianhua

    2014-09-01

    The Chizhou area, southeast China, hosts extensive W-Mo-Pb-Zn and Cu-Au deposits but remains relatively unstudied. A wide range of Mesozoic magmatic intrusives were analyzed (whole-rock geochemistry, Sr-Nd isotopes, zircon U-Pb dating, and zircon Lu-Hf isotopes) in order to elucidate their genesis, relationship to W-Mo-Pb-Zn-Cu-Au mineralization, and the tectonic setting of emplacement. Zircon U-Pb geochronology yielded a range of ages (147-110 Ma) encompassing three magmatic episodes; 147-135 Ma, 130-120 Ma, and 115-110 Ma. This work marks the first time the youngest episode has been identified. The oldest episode resulted in the formation of small granite porphyries, always associated with skarn-porphyry type W-Mo-Pb-Zn-Cu-Au deposits under an extensional setting. The 130-120 Ma and 115-110 Ma intrusives were the products of enhanced N-S extension with no associated mineralization. A comparative study reveals two types of magmatism-mineralization systems: acid magmatic rocks in the Chizhou area related to skarn-porphyry type W-Mo-Pb-Zn-Cu-Au deposits and intermediate-acid magmatic rocks in the Tongling area related to skarn-porphyry type Cu-Au-Fe-S deposits. Whole-rock Sr-Nd isotopes, zircon Lu-Hf isotopes, and inherited zircon U-Pb ages suggest that the lower crust and meso-neoproterozoic Shangxi group rocks were the main sources of magmatic rocks and related W-Mo-Pb-Zn-Cu-Au deposits. A genetic model for Mesozoic magmatism-skarn-porphyry type W-Mo-Pb-Zn-Cu-Au mineralization involves partial melting of the lower crust, mixing with the re-melted products of Meso-neoproterozoic Shangxi group rocks, and assimilation/fractional crystallization process. Results from this study suggest that there is great potential for the discovery of more and larger skarn-porphyry type W-Mo deposits in the transitional W-Mo-Pb-Zn metallogenic belt.

  2. On the scaling of multicrystal data sets collected at high-intensity X-ray and electron sources

    DOE PAGES

    Coppens, Philip; Fournier, Bertrand

    2015-11-11

    Here, the need for data-scaling has become increasingly evident as time-resolved pump-probe photocrystallography is rapidly developing at high intensity X-ray sources. Several aspects of the scaling of data sets collected at synchrotrons, XFELs (X-ray Free Electron Lasers) and high-intensity pulsed electron sources are discussed. They include laser-ON/laser-OFF data scaling, inter- and intra-data set scaling. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

  3. Quaternary Magmatism in the Cascades - Geologic Perspectives

    USGS Publications Warehouse

    Hildreth, Wes

    2007-01-01

    Foreward The Cascade magmatic arc is a belt of Quaternary volcanoes that extends 1,250 km from Lassen Peak in northern California to Meager Mountain in Canada, above the subduction zone where the Juan de Fuca Plate plunges beneath the North American Plate. This Professional Paper presents a synthesis of the entire volcanic arc, addressing all 2,300 known Quaternary volcanoes, not just the 30 or so visually prominent peaks that comprise the volcanic skyline. Study of Cascade volcanoes goes back to the geological explorers of the late 19th century and the seminal investigations of Howel Williams in the 1920s and 1930s. However, major progress and application of modern scientific methods and instrumentation began only in the 1970s with the advent of systematic geological, geophysical, and geochemical studies of the entire arc. Initial stimulus from the USGS Geothermal Research Program was enhanced by the USGS Volcano Hazards Program following the 1980 eruption of Mount St. Helens. Together, these two USGS Programs have provided more than three decades of stable funding, staffing, and analytical support. This Professional Paper summarizes the resultant USGS data sets and integrates them with the parallel contributions of other investigators. The product is based upon an all-encompassing and definitive geological database, including chemical and isotopic analyses to characterize the rocks and geochronology to provide the critical time constraints. Until now, this massive amount of data has not been summarized, and a systematic and uniform interpretation firmly grounded in geological fact has been lacking. Herein lies the primary utility of this Cascade volume. It not only will be the mandatory starting point for new workers, but also will provide essential geological context to broaden the perspectives of current investigators of specific Cascade volcanoes. Wes Hildreth's insightful understanding of volcanic processes and his uncompromising scientific integrity make him

  4. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins.

    PubMed

    Sommer, Carlos A; Lima, Evandro F; Nardi, Lauro V S; Liz, Joaquim D; Waichel, Breno L

    2006-09-01

    The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.

  5. Rural Parentage and Labor Market Disadvantage in a Sub-Saharan Setting: Sources and Trends

    ERIC Educational Resources Information Center

    Giroux, Sarah C.

    2008-01-01

    High unemployment in many developing countries is intensifying job competition and raising concern for the employment prospects of vulnerable groups, including children of rural parents. This paper examines the trends and sources in employment disadvantage associated with rural parentage in Cameroon. In documenting the sources of inequality, the…

  6. Quantification of Methane Source Locations and Emissions in AN Urban Setting

    NASA Astrophysics Data System (ADS)

    Crosson, E.; Richardson, S.; Tan, S. M.; Whetstone, J.; Bova, T.; Prasad, K. R.; Davis, K. J.; Phillips, N. G.; Turnbull, J. C.; Shepson, P. B.; Cambaliza, M. L.

    2011-12-01

    The regulation of methane emissions from urban sources such as landfills and waste-water treatment facilities is currently a highly debated topic in the US and in Europe. This interest is fueled, in part, by recent measurements indicating that urban emissions are a significant source of Methane (CH4) and in fact may be substantially higher than current inventory estimates(1). As a result, developing methods for locating and quantifying emissions from urban methane sources is of great interest to industries such as landfill and wastewater treatment facility owners, watchdog groups, and the governmental agencies seeking to evaluate or enforce regulations. In an attempt to identify major methane source locations and emissions in Boston, Indianapolis, and the Bay Area, systematic measurements of CH4 concentrations and meteorology data were made at street level using a vehicle mounted cavity ringdown analyzer. A number of discrete sources were detected at concentration levels in excess of 15 times background levels. Using Gaussian plume models as well as tomographic techniques, methane source locations and emission rates will be presented. In addition, flux chamber measurements of discrete sources such as those found in natural gas leaks will also be presented. (1) Wunch, D., P.O. Wennberg, G.C. Toon, G. Keppel-Aleks, and Y.G. Yavin, Emissions of Greenhouse Gases from a North American Megacity, Geophysical Research Letters, Vol. 36, L15810, doi:10.1029/2009GL)39825, 2009.

  7. Platinum metals magmatic sulfide ores.

    PubMed

    Naldrett, A J; Duke, J M

    1980-06-27

    Platinum-group elements (PGE) are mined predominantly from deposits that have formed by the segregation of molten iron-nickel-copper sulfides from silicate magmas. The absolute concentrations of PGE in sulfides from different deposits vary over a range of five orders of magnitude, whereas those of other chalcophile elements vary by factors of only 2 to 100. However, the relative proportions of the different PGE in a given deposit are systematically related to the nature of the parent magma. The absolute and relative concentrations of PGE in magmatic sulfides are explained in terms of the degree of partial melting of mantle peridotite required to produce the parent magma and the processes of batch equilibration and fractional segregation of sulfides. The Republic of South Africa and the U.S.S.R. together possess more than 97 percent of the world PGE reserves, but significant undeveloped resources occur in North America. The Stillwater complex in Montana is perhaps the most important example.

  8. Using Narrative as a Data Source and Analytic Method to Investigate Learning Outside of Traditional School Settings with Diverse Youth

    ERIC Educational Resources Information Center

    Martell, Sandra Toro; Antrop-Gonzalez, Rene

    2008-01-01

    Narrative is used to describe and understand how people construct meaning of their lives and experiences and how they think about their own and others' identities. We examined narrative as both data source and method of analysis for investigating learning in non-traditional school settings with students from diverse socio-economic status and…

  9. Nominally hydrous magmatism on the Moon.

    PubMed

    McCubbin, Francis M; Steele, Andrew; Hauri, Erik H; Nekvasil, Hanna; Yamashita, Shigeru; Hemley, Russell J

    2010-06-22

    For the past 40 years, the Moon has been described as nearly devoid of indigenous water; however, evidence for water both on the lunar surface and within the lunar interior have recently emerged, calling into question this long-standing lunar dogma. In the present study, hydroxyl (as well as fluoride and chloride) was analyzed by secondary ion mass spectrometry in apatite [Ca(5)(PO(4))(3)(F,Cl,OH)] from three different lunar samples in order to obtain quantitative constraints on the abundance of water in the lunar interior. This work confirms that hundreds to thousands of ppm water (of the structural form hydroxyl) is present in apatite from the Moon. Moreover, two of the studied samples likely had water preserved from magmatic processes, which would qualify the water as being indigenous to the Moon. The presence of hydroxyl in apatite from a number of different types of lunar rocks indicates that water may be ubiquitous within the lunar interior, potentially as early as the time of lunar formation. The water contents analyzed for the lunar apatite indicate minimum water contents of their lunar source region to range from 64 ppb to 5 ppm H(2)O. This lower limit range of water contents is at least two orders of magnitude greater than the previously reported value for the bulk Moon, and the actual source region water contents could be significantly higher.

  10. Nominally hydrous magmatism on the Moon

    PubMed Central

    McCubbin, Francis M.; Steele, Andrew; Hauri, Erik H.; Nekvasil, Hanna; Yamashita, Shigeru; Hemley, Russell J.

    2010-01-01

    For the past 40 years, the Moon has been described as nearly devoid of indigenous water; however, evidence for water both on the lunar surface and within the lunar interior have recently emerged, calling into question this long-standing lunar dogma. In the present study, hydroxyl (as well as fluoride and chloride) was analyzed by secondary ion mass spectrometry in apatite [Ca5(PO4)3(F,Cl,OH)] from three different lunar samples in order to obtain quantitative constraints on the abundance of water in the lunar interior. This work confirms that hundreds to thousands of ppm water (of the structural form hydroxyl) is present in apatite from the Moon. Moreover, two of the studied samples likely had water preserved from magmatic processes, which would qualify the water as being indigenous to the Moon. The presence of hydroxyl in apatite from a number of different types of lunar rocks indicates that water may be ubiquitous within the lunar interior, potentially as early as the time of lunar formation. The water contents analyzed for the lunar apatite indicate minimum water contents of their lunar source region to range from 64 ppb to 5 ppm H2O. This lower limit range of water contents is at least two orders of magnitude greater than the previously reported value for the bulk Moon, and the actual source region water contents could be significantly higher. PMID:20547878

  11. Magmatic occurrences in the Central Arava (southern Israel) based on Geology and Magnetometry

    NASA Astrophysics Data System (ADS)

    Hanan, Ginat; Michael, Rybakov; Boris, Shirman; Michael, Lazar

    2014-05-01

    The Eshet Ridge is located in the Central Arava near Wadi Paran. Geological data were collected using ground magnetic surveys and petrophysical measurements (magnetic susceptibility and density). The goal was to reveal the structure and nature of a concealed magmatic body under the ridge. Integrated gravity and magnetic interpretation together with seismic reflection data (including 2¾ modeling) indicated the presence of a deep-seated basic magmatic intrusion. Occurrence of Fe-mineralized rocks along the ridge supports subsurface data. The magmatic body was intruded in the hard Turonian rocks of the Eshet Ridge. Basic magmatic exposures dating from the Early Miocene were evident along Wadi Ashosh (in the eastern Negev) and its margins 18 km. to the north of the ridge. A new outcrop of basic magmatic intrusion was found southwest of the Tzukim settlement. Magnetic measurements indicated a similarity between their magnetic pattern and the Ashosh basic magmatics, which were dated to 20.4 ± 0.7 Ma. Volcanoclastic tuff pebbles (magnetic susceptibility of around 2-7 * 10-3 SI) surrounded by conglomerate were discovered at two sites in Wadi Demma and Wadi Menuha (streams that drain near the Eshet Ridge and 2 km south of it, respectively). The conglomerates contained mostly limestone, chalk and chert fragments; not more than 5% of which were volcanic pebbles. Two pebbles were dated to 24.4 ± 0.7and 21.5 ± 0.5 Ma. The magmatic outcrops in Wadi Ashosh, the magmatic dyke near Tzukim and the volcanic purple and black pebbles near Wadi Menuha were all dated to the very Late Oligocene-Early Miocene. The magmatic body identified in this study under the Eshet Ridge was termed the Eshet Intrusion and is connected to, and even the source of, all these phenomena.

  12. Estimation of distance error by fuzzy set theory required for strength determination of HDR (192)Ir brachytherapy sources.

    PubMed

    Kumar, Sudhir; Datta, D; Sharma, S D; Chourasiya, G; Babu, D A R; Sharma, D N

    2014-04-01

    Verification of the strength of high dose rate (HDR) (192)Ir brachytherapy sources on receipt from the vendor is an important component of institutional quality assurance program. Either reference air-kerma rate (RAKR) or air-kerma strength (AKS) is the recommended quantity to specify the strength of gamma-emitting brachytherapy sources. The use of Farmer-type cylindrical ionization chamber of sensitive volume 0.6 cm(3) is one of the recommended methods for measuring RAKR of HDR (192)Ir brachytherapy sources. While using the cylindrical chamber method, it is required to determine the positioning error of the ionization chamber with respect to the source which is called the distance error. An attempt has been made to apply the fuzzy set theory to estimate the subjective uncertainty associated with the distance error. A simplified approach of applying this fuzzy set theory has been proposed in the quantification of uncertainty associated with the distance error. In order to express the uncertainty in the framework of fuzzy sets, the uncertainty index was estimated and was found to be within 2.5%, which further indicates that the possibility of error in measuring such distance may be of this order. It is observed that the relative distance li estimated by analytical method and fuzzy set theoretic approach are consistent with each other. The crisp values of li estimated using analytical method lie within the bounds computed using fuzzy set theory. This indicates that li values estimated using analytical methods are within 2.5% uncertainty. This value of uncertainty in distance measurement should be incorporated in the uncertainty budget, while estimating the expanded uncertainty in HDR (192)Ir source strength measurement.

  13. CO2-fluxing collapses metal mobility in magmatic vapour

    DOE PAGES

    van Hinsberg, V. J.; Berlo, K.; Migdisov, A. A.; Williams-Jones, A. E.

    2016-05-18

    Magmatic systems host many types of ore deposits, including world-class deposits of copper and gold. Magmas are commonly an important source of metals and ore-forming fluids in these systems. In many magmatic-hydrothermal systems, low-density aqueous fluids, or vapours, are significant metal carriers. Such vapours are water-dominated shallowly, but fluxing of CO2-rich vapour exsolved from deeper magma is now recognised as ubiquitous during open-system magma degassing. Furthermore, we show that such CO2-fluxing leads to a sharp drop in element solubility, up to a factor of 10,000 for Cu, and thereby provides a highly efficient, but as yet unrecognised mechanism for metalmore » deposition.« less

  14. Remains of early Ordovician mantle-derived magmatism in the Santander Massif (Colombian Eastern Cordillera)

    NASA Astrophysics Data System (ADS)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Cottle, John M.; Hart, Craig J. R.

    2012-10-01

    An Early Ordovician magmatic event has been documented in the Santander Massif (north-Eastern Cordillera, Colombia). Three U/Pb laser ablation ages of 477 ± 2 Ma (Arenig), were obtained from metamorphosed and foliated calc-alkaline diorites. The 176Hf/177Hf values in zircons from these meta-diorites, yielded epsilon Hf values (ɛHft) > 0 (Mean = 2 ± 1, at 477 Ma). These data allow interpretation of the origin of these zircons from a radiogenic initial Hf isotope source, which is characteristic of the Earth's mantle. This, together with the fact that the rocks have been affected subsequently by tectonometamorphic processes, suggests that the early Ordovician diorites have been emplaced in a supra-subduction tectonic setting, related to onset of the Iapetus Ocean closure.

  15. Magmatic volatiles and the weathering of Mars

    NASA Technical Reports Server (NTRS)

    Clark, B. C.

    1993-01-01

    The sources for volatiles on Mars have been the subject of many hypotheses for exogenous influences including late accretion of volatile-enriched material, impact devolatilization to create massive early atmospheres, and even major bombardment by comets. However, the inventory of chemically active volatiles observable at the contemporary surface of Mars is consistent with domination by endogenous, subsequent planetary processes, viz., persistent magmatic outgassing. Volcanism on Mars has been widespread in both space and time. Notwithstanding important specific differences between the mantles of Earth and Mars, the geochemical similarities are such that the suite of gases emitted from Martian volcanic activity should include H2O, CO2, S-containing gases (e.g. H2S and/or SO2), and Cl-containing gases (e.g., Cl2 and/or HCl). H2O and CO2 exist in the atmosphere of Mars. Both are also present as surface condensates. However, spectroscopic observations of the Martian atmosphere clearly show that the S- and Cl-containing gases are severely depleted, with upper limits of less than or equal to 10(exp -7) the abundance of CO2. Likewise, there is no evidence of polar condensates of compounds of these elements as there is for CO2 and H2O. Within the soil, on the other hand, there has been direct measurement of incorporated H2O and abundant compounds containing S and Cl. Barring some as yet implausible geochemical sequestering process, the S/Cl ratio of about 6:1 in Martian soils implies a limit of 5% on the contribution of matter of solarlike composition (e.g., carbonaceous chondrite or cometary material) to these volatiles. Hence, exogenous sources are minor or not yet observed. From analysis of elemental trends in Martian soils, it has been recently shown that a simple two-component model can satisfy the Viking in situ measurements. Component A includes Si and most or all the Al, Ca, Ti, and Fe. Component B, taken as 16 +/- 3% by weight of the total, contains S and most or

  16. Time-Dependent Selection of an Optimal Set of Sources to Define a Stable Celestial Reference Frame

    NASA Technical Reports Server (NTRS)

    Le Bail, Karine; Gordon, David

    2010-01-01

    Temporal statistical position stability is required for VLBI sources to define a stable Celestial Reference Frame (CRF) and has been studied in many recent papers. This study analyzes the sources from the latest realization of the International Celestial Reference Frame (ICRF2) with the Allan variance, in addition to taking into account the apparent linear motions of the sources. Focusing on the 295 defining sources shows how they are a good compromise of different criteria, such as statistical stability and sky distribution, as well as having a sufficient number of sources, despite the fact that the most stable sources of the entire ICRF2 are mostly in the Northern Hemisphere. Nevertheless, the selection of a stable set is not unique: studying different solutions (GSF005a and AUG24 from GSFC and OPA from the Paris Observatory) over different time periods (1989.5 to 2009.5 and 1999.5 to 2009.5) leads to selections that can differ in up to 20% of the sources. Observing, recording, and network improvement are some of the causes, showing better stability for the CRF over the last decade than the last twenty years. But this may also be explained by the assumption of stationarity that is not necessarily right for some sources.

  17. Magmatic epidote and its petrologic significance

    SciTech Connect

    Zen, A.; Hammarstrom, J.M.

    1984-09-01

    Epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the Mesozoic accreted terranes between northern California and southeastern Alaska. Textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase. The observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure. Plutonic rocks bearing magmatic epidote must have formed under moderately high pressures, corresponding to lower crustal depths, under fairly oxidizing conditions. 23 references, 3 figures, 1 table.

  18. Sources of Cognitive Inflexibility in Set-Shifting Tasks: Insights into Developmental Theories from Adult Data

    ERIC Educational Resources Information Center

    Dick, Anthony Steven

    2012-01-01

    Two experiments examined processes underlying cognitive inflexibility in set-shifting tasks typically used to assess the development of executive function in children. Adult participants performed a Flexible Item Selection Task (FIST) that requires shifting from categorizing by one dimension (e.g., color) to categorizing by a second orthogonal…

  19. Limits On Rms Radio Source Contributions To The Microwave Sky Set By WMAP

    NASA Astrophysics Data System (ADS)

    Partridge, R. Bruce; Boughn, S.

    2007-12-01

    Cross correlations between the WMAP full sky K, Ka, Q, V, and W-band maps with the 1.4 GHz NVSS source count map and the HEAO I A2 2-10 keV full sky X-ray flux map are used to constrain rms fluctuations due to unresolved & undetected microwave sources in the WMAP frequency range. In the Q band (40.7 GHz), a lower limit, taking account only of those fluctuations correlated with the 1.4 GHz radio counts and the X-ray flux, corresponds to an rms Rayleigh-Jeans temperature of 2μK for a solid angle of one square degree. The correlated fluctuations at the other bands are consistent with a α = -0.1 ± 0.4 frequency spectrum. Using the rms fluctuations of X-ray flux and radio source flux, and the cross correlation of these two quantities as a guide, the above lower limit leads to a plausible estimate of 5μK for Q-band rms fluctuations in one square degree. This value is similar to that implied by the excess, small angular scale, Q-band fluctuations observed by WMAP, and is consistent with estimates made by extrapolating low-frequency source counts.

  20. Magmatic versus sedimentary volcanism: similarities of two different geological phenomena

    NASA Astrophysics Data System (ADS)

    Mazzini, Adriano

    2015-04-01

    Sedimentary volcanoes (or more commonly called mud volcanoes) are geological phenomena that are present in sedimentary basins of passive and active margins. At these localities gas and water related to hydrocarbon diagenetic and catagenetic production generate overpressure facilitating the rise of mobile and ductily deformable materials that breach through the denser overlying rocks. The results are surface powerful manifestations of mud eruptions that strikingly resemble to those of magmatic volcanoes. Magmatic and sedimentary volcanoes share many other similarities. Initially both systems are essentially gas driven and the subsurface plumbing systems are characterized by intrusions and a complex system of fractures and conduits that bifurcate from a central feeder channel that manifest in the surface as numerous satellite seeps and vents. In both cases are inferred secondary shallower chambers where reactions take place. Comparable structural morphologies (e.g. conical, elongated, pie-shaped, multicrater, swap-like, caldera collapse, subsiding flanks, plateau-like) and/or alteration of the original shape are in both cases related to e.g. density and viscosity of the erupted solids, to the gas content, to the frequency of the eruptions, and to the action of meteoric factors (e.g. strong erosion by rain, wind, temperature changes etc. etc.). Like for magmatic volcanoes, the periodicity of the eruptive activity is related to the time required to charge the system and create new overpressure, as well as how the structure seals during periods of dormancy. Earthquakes are documented to be a powerful trigger capable to activate faults (often hosting magmatic and sedimentary volcanoes) and/or facilitating the breaching of the upper layers, and allowing the rise of deeper charged fluids. Finally, both systems significantly contribute as active source for CH4 (sedimentary) and CO2 (magmatic) resulting of great importance for global budget estimates of sensitive gasses. The

  1. Characterization of gas chemistry and noble-gas isotope ratios of inclusion fluids in magmatic-hydrothermal and magmatic-steam alunite

    USGS Publications Warehouse

    Landis, G.P.; Rye, R.O.

    2005-01-01

    -hydrothermal or magmatic-steam fluids. Thus, the oxidation of SO2 to aqueous sulfate in the magmatic-steam fluids did not result from mixing with atmospheric oxygen. Both of the fluid types are characterized by high H2 contents that range from 0.2 mol% to the extraordinarily large amounts (66 mol%) observed in some magmatic-steam fluids. Modeling of gas speciation using SOLVGAS requires most of the gas species to have been in disequilibrium at the time of their trapping in the fluid inclusions. The origin of such extreme H2 concentrations, although problematic, is thought to be largely related to accumulation of H2 from the reaction of water with ferrous iron during the rise of magma and probably even after exsolution of fluid from a magma. The large contents of reduced gases in the inclusion fluids are far in excess of those observed in volcanic emanations, and are thought to reflect the close "sampling position" of the host alunite relative to the location of the magma. Isotope ratios of He and Ne indicate largely crustal sources for these gases in the alunite parental fluids derived from Tertiary magmas, but a greater mantle component for the gases in alunite parental fluids derived from Proterozoic magmas.

  2. The synoptic setting and possible energy sources for mesoscale wave disturbances

    NASA Technical Reports Server (NTRS)

    Uccellini, Louis W.; Koch, Steven E.

    1987-01-01

    Published data on 13 cases of mesoscale wave disturbances and their environment were examined to isolate common features for these cases and to determine possible energy sources for the waves. These events are characterized by either a singular wave of depression or wave packets with periods of 1-4 h, horizontal wavelengths of 50-500 km, and surface-pressure perturbation amplitudes of 0.2-7.0 mb. These wave events are shown to be associated with a distinct synoptic pattern (including the existence of a strong inversion in the lower troposphere and the propagation of a jet streak toward a ridge axis in the upper troposphere) while displaying little correlation with the presence of convective storm cells. The observed development of the waves is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.

  3. Using an alternate light source to detect electrically singed feathers and hair in a forensic setting.

    PubMed

    Viner, Tabitha C; Kagan, Rebecca A; Johnson, Jennifer L

    2014-01-01

    Mortality due to electrical injury in wildlife may occur in the form of lightning strike or power line contact. Evidence of electrical contact may be grossly obvious, with extensive singeing, curling, and blackening of feathers, fur, or skin. Occasionally, changes may be subtle, owing to lower current or reduced conductivity, making a definitive diagnosis of electrocution more difficult. We describe the use of an alternate light source in the examination of cases of lightning strike and power line contact in wildlife, and the enhanced detection of changes due to electrical currents in the hair and feathers of affected animals. Subtle changes in the wing feathers of 12 snow geese and 1 wolf that were struck by separate lightning events were made obvious by the use of an alternate light source. Similarly, this technique can be used to strengthen the evidence for power line exposure in birds. PMID:24290056

  4. FDTD verification of deep-set brain tumor hyperthermia using a spherical microwave source distribution

    SciTech Connect

    Dunn, D.; Rappaport, C.M.; Terzuoli, A.J. Jr.

    1996-10-01

    Although use of noninvasive microwave hyperthermia to treat cancer is problematic in many human body structures, careful selection of the source electric field distribution around the entire surface of the head can generate a tightly focused global power density maximum at the deepest point within the brain. An analytic prediction of the optimum volume field distribution in a layered concentric head model based on summing spherical harmonic modes is derived and presented. This ideal distribution is then verified using a three-dimensional finite difference time domain (TDTD) simulation with a discretized, MRI-based head model excited by the spherical source. The numerical computation gives a very similar dissipated power pattern as the analytic prediction. This study demonstrates that microwave hyperthermia can theoretically be a feasible cancer treatment modality for tumors in the head, providing a well-resolved hot-spot at depth without overheating any other healthy tissue.

  5. Nutrient Patterns and Their Food Sources in an International Study Setting: Report from the EPIC Study

    PubMed Central

    Moskal, Aurelie; Pisa, Pedro T.; Ferrari, Pietro; Byrnes, Graham; Freisling, Heinz; Boutron-Ruault, Marie-Christine; Cadeau, Claire; Nailler, Laura; Wendt, Andrea; Kühn, Tilman; Boeing, Heiner; Buijsse, Brian; Tjønneland, Anne; Halkjær, Jytte; Dahm, Christina C.; Chiuve, Stephanie E.; Quirós, Jose R.; Buckland, Genevieve; Molina-Montes, Esther; Amiano, Pilar; Huerta Castaño, José M.; Gurrea, Aurelio Barricarte; Khaw, Kay-Tee; Lentjes, Marleen A.; Key, Timothy J.; Romaguera, Dora; Vergnaud, Anne-Claire; Trichopoulou, Antonia; Bamia, Christina; Orfanos, Philippos; Palli, Domenico; Pala, Valeria; Tumino, Rosario; Sacerdote, Carlotta; de Magistris, Maria Santucci; Bueno-de-Mesquita, H. Bas; Ocké, Marga C.; Beulens, Joline W. J.; Ericson, Ulrika; Drake, Isabel; Nilsson, Lena M.; Winkvist, Anna; Weiderpass, Elisabete; Hjartåker, Anette; Riboli, Elio; Slimani, Nadia

    2014-01-01

    Background Compared to food patterns, nutrient patterns have been rarely used particularly at international level. We studied, in the context of a multi-center study with heterogeneous data, the methodological challenges regarding pattern analyses. Methodology/Principal Findings We identified nutrient patterns from food frequency questionnaires (FFQ) in the European Prospective Investigation into Cancer and Nutrition (EPIC) Study and used 24-hour dietary recall (24-HDR) data to validate and describe the nutrient patterns and their related food sources. Associations between lifestyle factors and the nutrient patterns were also examined. Principal component analysis (PCA) was applied on 23 nutrients derived from country-specific FFQ combining data from all EPIC centers (N = 477,312). Harmonized 24-HDRs available for a representative sample of the EPIC populations (N = 34,436) provided accurate mean group estimates of nutrients and foods by quintiles of pattern scores, presented graphically. An overall PCA combining all data captured a good proportion of the variance explained in each EPIC center. Four nutrient patterns were identified explaining 67% of the total variance: Principle component (PC) 1 was characterized by a high contribution of nutrients from plant food sources and a low contribution of nutrients from animal food sources; PC2 by a high contribution of micro-nutrients and proteins; PC3 was characterized by polyunsaturated fatty acids and vitamin D; PC4 was characterized by calcium, proteins, riboflavin, and phosphorus. The nutrients with high loadings on a particular pattern as derived from country-specific FFQ also showed high deviations in their mean EPIC intakes by quintiles of pattern scores when estimated from 24-HDR. Center and energy intake explained most of the variability in pattern scores. Conclusion/Significance The use of 24-HDR enabled internal validation and facilitated the interpretation of the nutrient patterns derived from FFQs

  6. Introduction to Special Section: Magmatism and Extension

    NASA Astrophysics Data System (ADS)

    Metcalf, Rodney V.; Smith, Eugene I.

    1995-06-01

    The relationship between magmatism and the formation of continental rift zones is the subject of much controversy. In particular, the cause and effect relationships between magmatism and extension and the mode of generation of magma during the process of extension are still hotly debated. This controversy served as the theme of a symposium on "Cenozoic Magmatism in the Colorado River Extensional Corridor and Adjacent Areas" and a field trip held as part of the Geological Society of America Cordilleran/Rocky Mountain Section meeting in Reno, Nevada [Metcalf et al., 1993]. It was clear from data presented at the symposium that a considerable amount of new information has become available regarding magmatism and extension since the last special section on this topic published by the Journal of Geophysical Research (June 1989).

  7. Platinum metals magmatic sulfide ores.

    PubMed

    Naldrett, A J; Duke, J M

    1980-06-27

    Platinum-group elements (PGE) are mined predominantly from deposits that have formed by the segregation of molten iron-nickel-copper sulfides from silicate magmas. The absolute concentrations of PGE in sulfides from different deposits vary over a range of five orders of magnitude, whereas those of other chalcophile elements vary by factors of only 2 to 100. However, the relative proportions of the different PGE in a given deposit are systematically related to the nature of the parent magma. The absolute and relative concentrations of PGE in magmatic sulfides are explained in terms of the degree of partial melting of mantle peridotite required to produce the parent magma and the processes of batch equilibration and fractional segregation of sulfides. The Republic of South Africa and the U.S.S.R. together possess more than 97 percent of the world PGE reserves, but significant undeveloped resources occur in North America. The Stillwater complex in Montana is perhaps the most important example. PMID:17796685

  8. Collision zone magmatism aids continental crustal growth

    NASA Astrophysics Data System (ADS)

    Savov, Ivan; Meliksetian, Khachatur; Ralf, Halama; Gevorg, Navasardian; Chuck, Connor; Massimo, D'Antonio; Samuele, Agostini; Osamu, Ishizuka; Sergei, Karapetian; Arkadi, Karakhanian

    2014-05-01

    .51282, respectively). These isotopic signatures are much more similar to those typical of intra-oceanic subduction zones than those typical of continental crust, likely due to the very young age of the rocks. In contrast, trace element abundances reveal many similarities to average CC, such as Nb-Ta and Ti troughs and Pb peaks. The range of d11B isotope ratios (-8.7 to +2.1 per mil) signifies magmas originating from moderately metasomatised (arc preconditioned) mantle sources. Our combined results reveal that the collision-related mantle melting is capable of generating large volumes of plutons and volcanic rocks that resemble (although not perfectly) the composition of the average CC. We will attempt to use the new combined datasets in order to quantify the importance of the collision zone magmatism for continental crustal growth. [1] Lee et al. (2007) EPSL 263, 370-387; [2] Niu et al. (2013) Earth-Science Reviews 127, 96-110; [3] Connor et al., (2012) J.Applied Volcanology, 1:3, 1-19.

  9. Impulsive Wave Propagation within Magmatic Conduits with Axial Symmetry

    NASA Astrophysics Data System (ADS)

    De Negri Leiva, R. S.; Arciniega-Ceballos, A.; Scheu, B.; Dingwell, D. B.; Sanchez-Sesma, F. J.

    2013-12-01

    We implemented Trefftz's method to simulate wave propagation in a fluid-solid system aimed to represent a magmatic conduit. Assuming axial symmetry, a set of multipoles is used to build a complete system of wave functions for both the solid and the fluid. These functions are solutions of the elastodynamic equations that govern the motions in the fluid and the solid, respectively. The conduit can be closed or open and the exterior elastic domain may be unlimited or with an exterior boundary. In order to find the functions coefficients, boundary conditions (null shear and continuity of pressures and normal velocities) are satisfied in the least squares sense. The impulsive nature of the source is considered using Fourier analysis. Despite the simplicity of the formulation our results display a rich variety of behaviors. In fact, for a uniform infinite cylinder we reproduced the analytical solution. Moreover, this approach allows establishing some important effects of conduit geometry, including changes of sections. Lateral effects and bump resonances are well resolved. We compared our numerical calculations with results obtained from experimental simulations of volcanic explosions in which rapid depressurization induces fragmentation of volcanic rocks. These experiments are performed within a shock-tube apparatus at room temperature and various pressures using Argon (Ar) gas, particles and pumice samples of different porosities, from Popocatepetl volcano. The mechanical system is well characterized and the dynamics of the explosive process is monitored with high precision piezoelectric sensors located at the pipe surface. The combination of analytical and experimental approaches is very useful to understand the seismic wave field of volcanic conduit dynamics.

  10. Depositional setting and hydrocarbon source potential of the Miocene Gulf of Suez syn-rift evaporites

    SciTech Connect

    Richardson, M.; Arthur, M.A.; Quinn, J.S.; Whelan, J.K.; Katz, B.J. )

    1988-08-01

    The Red Sea rift basin and its northern continuation, the Gulf of Suez, has experienced continuous deposition of marine evaporites throughout much of its development from the early Miocene to the Pliocene resulting in the accumulation of up to 5 km of evaporite strata in the rift. In this paper, the geologic history of these evaporites are discussed, along with their petroleum source rock potential. The authors hypothesize that rapid deposition of organic matter occurred during episodic storms and freshening events in which a less saline surface layer developed.

  11. Numerical model for the evaluation of Earthquake effects on a magmatic system.

    NASA Astrophysics Data System (ADS)

    Garg, Deepak; Longo, Antonella; Papale, Paolo

    2016-04-01

    A finite element numerical model is presented to compute the effect of an Earthquake on the dynamics of magma in reservoirs with deformable walls. The magmatic system is hit by a Mw 7.2 Earthquake (Petrolia/Capo Mendocina 1992) with hypocenter at 15 km diagonal distance. At subsequent times the seismic wave reaches the nearest side of the magmatic system boundary, travels through the magmatic fluid and arrives to the other side of the boundary. The modelled physical system consists in the magmatic reservoir with a thin surrounding layer of rocks. Magma is considered as an homogeneous multicomponent multiphase Newtonian mixture with exsolution and dissolution of volatiles (H2O+CO2). The magmatic reservoir is made of a small shallow magma chamber filled with degassed phonolite, connected by a vertical dike to a larger deeper chamber filled with gas-rich shoshonite, in condition of gravitational instability. The coupling between the Earthquake and the magmatic system is computed by solving the elastostatic equation for the deformation of the magmatic reservoir walls, along with the conservation equations of mass of components and momentum of the magmatic mixture. The characteristic elastic parameters of rocks are assigned to the computational domain at the boundary of magmatic system. Physically consistent Dirichlet and Neumann boundary conditions are assigned according to the evolution of the seismic signal. Seismic forced displacements and velocities are set on the part of the boundary which is hit by wave. On the other part of boundary motion is governed by the action of fluid pressure and deviatoric stress forces due to fluid dynamics. The constitutive equations for the magma are solved in a monolithic way by space-time discontinuous-in-time finite element method. To attain additional stability least square and discontinuity capturing operators are included in the formulation. A partitioned algorithm is used to couple the magma and thin layer of rocks. The

  12. Terminal magmatic activities along the Solonker suture zone in the southern Central Asian Orogenic Belt: New insights from the end-Permian magmatic record

    NASA Astrophysics Data System (ADS)

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Xiao, Wen-Jiao; Wang, Tao; Guo, Qian-Qian

    2016-04-01

    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geologic evidence, suggest that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred at 255 to 251 Ma along the Solonker-Xar Moron suture zone. The linear end-Permian magmatism is interpreted as in a setting of continental contraction and crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the earliest phases of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251-245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, probably caused by regional lithospheric extension and orogenic collapse. The proposed collision-related magmatism from the southern CAOB is thus a prime example of minor, yet tell-tale linking magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen.

  13. Vapor intrusion in urban settings: effect of foundation features and source location

    PubMed Central

    Yao, Yijun; Pennell, Kelly G.; Suuberg, Eric

    2013-01-01

    In many urban settings, groundwater contains volatile organic compounds, such as tricholoroethene, tetrachloroethene, benzene, etc., at concentrations that are at or slightly below non-potable groundwater standards. Some non-potable groundwater standards do not protect against human health risks that might result from vapor intrusion. Vapor intrusion is a process by which vapor phase contaminants present in the subsurface migrate through the soil and ultimately enter a building through foundation cracks. The end result is a decrease in air quality within the building. Predicting whether or not vapor intrusion will occur at rates sufficient to cause health risks is extremely difficult and depends on many factors. In many cities, a wide-range of property uses take place over a relatively small area. For instance, schools, commercial buildings and residential buildings may all reside within a few city blocks. Most conceptual site models assume the ground surface is open to the atmosphere (i.e. green space); however the effect that an impervious surface (e.g. paving) may have on vapor transport rates is not routinely considered. Using a 3-D computational fluid dynamics model, we are investigating how the presence of impervious surfaces affects vapor intrusion rates. To complement our modeling efforts, we are in the initial stages of conducting a field study in a neighborhood where vapor intrusion is occurring. PMID:24619471

  14. Vapor intrusion in urban settings: effect of foundation features and source location.

    PubMed

    Yao, Yijun; Pennell, Kelly G; Suuberg, Eric

    2011-01-01

    In many urban settings, groundwater contains volatile organic compounds, such as tricholoroethene, tetrachloroethene, benzene, etc., at concentrations that are at or slightly below non-potable groundwater standards. Some non-potable groundwater standards do not protect against human health risks that might result from vapor intrusion. Vapor intrusion is a process by which vapor phase contaminants present in the subsurface migrate through the soil and ultimately enter a building through foundation cracks. The end result is a decrease in air quality within the building. Predicting whether or not vapor intrusion will occur at rates sufficient to cause health risks is extremely difficult and depends on many factors. In many cities, a wide-range of property uses take place over a relatively small area. For instance, schools, commercial buildings and residential buildings may all reside within a few city blocks. Most conceptual site models assume the ground surface is open to the atmosphere (i.e. green space); however the effect that an impervious surface (e.g. paving) may have on vapor transport rates is not routinely considered. Using a 3-D computational fluid dynamics model, we are investigating how the presence of impervious surfaces affects vapor intrusion rates. To complement our modeling efforts, we are in the initial stages of conducting a field study in a neighborhood where vapor intrusion is occurring.

  15. Vapor intrusion in urban settings: effect of foundation features and source location.

    PubMed

    Yao, Yijun; Pennell, Kelly G; Suuberg, Eric

    2011-01-01

    In many urban settings, groundwater contains volatile organic compounds, such as tricholoroethene, tetrachloroethene, benzene, etc., at concentrations that are at or slightly below non-potable groundwater standards. Some non-potable groundwater standards do not protect against human health risks that might result from vapor intrusion. Vapor intrusion is a process by which vapor phase contaminants present in the subsurface migrate through the soil and ultimately enter a building through foundation cracks. The end result is a decrease in air quality within the building. Predicting whether or not vapor intrusion will occur at rates sufficient to cause health risks is extremely difficult and depends on many factors. In many cities, a wide-range of property uses take place over a relatively small area. For instance, schools, commercial buildings and residential buildings may all reside within a few city blocks. Most conceptual site models assume the ground surface is open to the atmosphere (i.e. green space); however the effect that an impervious surface (e.g. paving) may have on vapor transport rates is not routinely considered. Using a 3-D computational fluid dynamics model, we are investigating how the presence of impervious surfaces affects vapor intrusion rates. To complement our modeling efforts, we are in the initial stages of conducting a field study in a neighborhood where vapor intrusion is occurring. PMID:24619471

  16. Limitations of electron cyclotron resonance ion source performances set by kinetic plasma instabilities.

    PubMed

    Tarvainen, O; Laulainen, J; Komppula, J; Kronholm, R; Kalvas, T; Koivisto, H; Izotov, I; Mansfeld, D; Skalyga, V

    2015-02-01

    Electron cyclotron resonance ion source (ECRIS) plasmas are prone to kinetic instabilities due to anisotropy of the electron energy distribution function stemming from the resonant nature of the electron heating process. Electron cyclotron plasma instabilities are related to non-linear interaction between plasma waves and energetic electrons resulting to strong microwave emission and a burst of energetic electrons escaping the plasma, and explain the periodic oscillations of the extracted beam currents observed in several laboratories. It is demonstrated with a minimum-B 14 GHz ECRIS operating on helium, oxygen, and argon plasmas that kinetic instabilities restrict the parameter space available for the optimization of high charge state ion currents. The most critical parameter in terms of plasma stability is the strength of the solenoid magnetic field. It is demonstrated that due to the instabilities the optimum Bmin-field in single frequency heating mode is often ≤0.8BECR, which is the value suggested by the semiempirical scaling laws guiding the design of modern ECRISs. It is argued that the effect can be attributed not only to the absolute magnitude of the magnetic field but also to the variation of the average magnetic field gradient on the resonance surface. PMID:25725830

  17. Limitations of electron cyclotron resonance ion source performances set by kinetic plasma instabilities

    SciTech Connect

    Tarvainen, O. Laulainen, J.; Komppula, J.; Kronholm, R.; Kalvas, T.; Koivisto, H.; Izotov, I.; Mansfeld, D.; Skalyga, V.

    2015-02-15

    Electron cyclotron resonance ion source (ECRIS) plasmas are prone to kinetic instabilities due to anisotropy of the electron energy distribution function stemming from the resonant nature of the electron heating process. Electron cyclotron plasma instabilities are related to non-linear interaction between plasma waves and energetic electrons resulting to strong microwave emission and a burst of energetic electrons escaping the plasma, and explain the periodic oscillations of the extracted beam currents observed in several laboratories. It is demonstrated with a minimum-B 14 GHz ECRIS operating on helium, oxygen, and argon plasmas that kinetic instabilities restrict the parameter space available for the optimization of high charge state ion currents. The most critical parameter in terms of plasma stability is the strength of the solenoid magnetic field. It is demonstrated that due to the instabilities the optimum B{sub min}-field in single frequency heating mode is often ≤0.8B{sub ECR}, which is the value suggested by the semiempirical scaling laws guiding the design of modern ECRISs. It is argued that the effect can be attributed not only to the absolute magnitude of the magnetic field but also to the variation of the average magnetic field gradient on the resonance surface.

  18. Limitations of electron cyclotron resonance ion source performances set by kinetic plasma instabilities

    NASA Astrophysics Data System (ADS)

    Tarvainen, O.; Laulainen, J.; Komppula, J.; Kronholm, R.; Kalvas, T.; Koivisto, H.; Izotov, I.; Mansfeld, D.; Skalyga, V.

    2015-02-01

    Electron cyclotron resonance ion source (ECRIS) plasmas are prone to kinetic instabilities due to anisotropy of the electron energy distribution function stemming from the resonant nature of the electron heating process. Electron cyclotron plasma instabilities are related to non-linear interaction between plasma waves and energetic electrons resulting to strong microwave emission and a burst of energetic electrons escaping the plasma, and explain the periodic oscillations of the extracted beam currents observed in several laboratories. It is demonstrated with a minimum-B 14 GHz ECRIS operating on helium, oxygen, and argon plasmas that kinetic instabilities restrict the parameter space available for the optimization of high charge state ion currents. The most critical parameter in terms of plasma stability is the strength of the solenoid magnetic field. It is demonstrated that due to the instabilities the optimum Bmin-field in single frequency heating mode is often ≤0.8BECR, which is the value suggested by the semiempirical scaling laws guiding the design of modern ECRISs. It is argued that the effect can be attributed not only to the absolute magnitude of the magnetic field but also to the variation of the average magnetic field gradient on the resonance surface.

  19. Loop Heat Pipe Transient Behavior Using Heat Source Temperature for Set Point Control with Thermoelectric Converter on Reservoir

    NASA Technical Reports Server (NTRS)

    Ku, Jentung; Paiva, Kleber; Mantelli, Marcia

    2011-01-01

    The LHP operating temperature is governed by the saturation temperature of its reservoir. Controlling the reservoir saturation temperature is commonly done by cold biasing the reservoir and using electrical heaters to provide the required control power. With this method, the loop operating temperature can be controlled within 0.5K or better. However, because the thermal resistance that exists between the heat source and the LHP evaporator, the heat source temperature will vary with its heat output even if the LHP operating temperature is kept constant. Since maintaining a constant heat source temperature is of most interest, a question often raised is whether the heat source temperature can be used for LHP set point temperature control. A test program with a miniature LHP was carried out to investigate the effects on the LHP operation when the control temperature sensor was placed on the heat source instead of the reservoir. In these tests, the LHP reservoir was cold-biased and was heated by a control heater. Test results show that it was feasible to use the heat source temperature for feedback control of the LHP operation. In particular, when a thermoelectric converter was used as the reservoir control heater, the heat source temperature could be maintained within a tight range using a proportional-integral-derivative or on/off control algorithm. Moreover, because the TEC could provide both heating and cooling to the reservoir, temperature oscillations during fast transients such as loop startup could be eliminated or substantially reduced when compared to using an electrical heater as the control heater.

  20. Magmatism in rifting and basin formation

    NASA Astrophysics Data System (ADS)

    Thybo, H.

    2008-12-01

    Whether heating and magmatism cause rifting or rifting processes cause magmatic activity is highly debated. The stretching factor in rift zones can be estimated as the relation between the initial and the final crustal thickness provided that the magmatic addition to the crust is insignificant. Recent research demonstrates substantial magmatic intrusion into the crust in the form of sill like structures in the lowest crust in the presently active Kenya and Baikal rift zones and the DonBas palaeo-rift zone in Ukraine. This result may be surprising as the Kenya Rift is associated with large amounts of volcanic products, whereas the Baikal Rift shows very little volcanism. Identification of large amounts of magmatic intrusion into the crust has strong implications for estimation of stretching factor, which in the case of Baikal Rift Zone is around 1.7 but direct estimation gives a value of 1.3-1.4 if the magmatic addition is not taken into account. This may indicate that much more stretching has taken place on rift systems than hitherto believed. Wide sedimentary basins may form around aborted rifts due to loading of the lithosphere by sedimentary and volcanic in-fill of the rift. This type of subsidence will create wide basins without faulting. The Norwegian- Danish basin in the North Sea area also has subsided gradually during the Triassic without faulting, but only few rift structures have been identified below the Triassic sequences. We have identified several mafic intrusions in the form of large batholiths, typically more than 100 km long, 20-40 km wide and 20 km thick. The associated heating would have lifted the surface by about 2 km, which may have been eroded before cooling. The subsequent contraction due to solidification and cooling would create subsidence in a geometry similar to basins that developed by loading. These new aspects of magmatism will be discussed with regard to rifting and basin formation.

  1. Developing open source, self-contained disease surveillance software applications for use in resource-limited settings

    PubMed Central

    2012-01-01

    Background Emerging public health threats often originate in resource-limited countries. In recognition of this fact, the World Health Organization issued revised International Health Regulations in 2005, which call for significantly increased reporting and response capabilities for all signatory nations. Electronic biosurveillance systems can improve the timeliness of public health data collection, aid in the early detection of and response to disease outbreaks, and enhance situational awareness. Methods As components of its Suite for Automated Global bioSurveillance (SAGES) program, The Johns Hopkins University Applied Physics Laboratory developed two open-source, electronic biosurveillance systems for use in resource-limited settings. OpenESSENCE provides web-based data entry, analysis, and reporting. ESSENCE Desktop Edition provides similar capabilities for settings without internet access. Both systems may be configured to collect data using locally available cell phone technologies. Results ESSENCE Desktop Edition has been deployed for two years in the Republic of the Philippines. Local health clinics have rapidly adopted the new technology to provide daily reporting, thus eliminating the two-to-three week data lag of the previous paper-based system. Conclusions OpenESSENCE and ESSENCE Desktop Edition are two open-source software products with the capability of significantly improving disease surveillance in a wide range of resource-limited settings. These products, and other emerging surveillance technologies, can assist resource-limited countries compliance with the revised International Health Regulations. PMID:22950686

  2. Barbecue Fumes: An Overlooked Source of Health Hazards in Outdoor Settings?

    PubMed

    Wu, Chen-Chou; Bao, Lian-Jun; Guo, Ying; Li, Shao-Meng; Zeng, Eddy Y

    2015-09-01

    Barbecuing or charcoal-grilling has become part of popular outdoor recreational activities nowadays; however, potential human health hazards through outdoor exposure to barbecue fumes have yet to be adequately quantified. To fill this knowledge gap, atmospheric size-fractioned particle and gaseous samples were collected near an outdoor barbecuing vendor stall (along with charcoal-grilled food items) in Xinjiang of Northwest China with a 10-stage micro-orifice uniform deposit impactor and a polyurethane foam (PUF) sampler and were analyzed for particulate matter and polycyclic aromatic hydrocarbons (PAHs). Exposure to PAHs through inhalation and dermal contact by adult consumers who spent 1 h per day near a charcoal-grilling vendor for a normal meal (lunch or dinner) amounted to a BaP equivalent (BaPeq) dosage of 3.0-77 ng day(-1) (inhalation: 2.8-27 ng day(-1) of BaPeq; dermal contact: 0.2-50 ng day(-1) of BaPeq), comparable to those (22-220 ng day(-1) of BaPeq) from consumer exposure through the consumption of charcoal-grilled meat, assumed to be at the upper limit of 50-150 g. In addition, the potential health risk was in the range of 3.1 × 10(-10) to 1.4 × 10(-4) for people of different age groups with inhalation and dermal contact exposure to PAHs once a day, with a 95% confidence interval (7.2 × 10(-9) to 1.2 × 10(-5)) comparable to the lower limit of the potential cancer risk range (1 × 10(-6) to 1 × 10(-4)). Sensitivity analyses indicated that the area of dermal contact with gaseous contaminants is a critical parameter for risk assessment. These results indicated that outdoor exposure to barbecue fumes (particularly dermal contact) may have become a significant but largely neglected source of health hazards to the general population and should be well-recognized. PMID:26259039

  3. Magmatic gas scrubbing: Implications for volcano monitoring

    USGS Publications Warehouse

    Symonds, R.B.; Gerlach, T.M.; Reed, M.H.

    2001-01-01

    Despite the abundance of SO2(g) in magmatic gases, precursory increases in magmatic SO2(g) are not always observed prior to volcanic eruption, probably because many terrestrial volcanoes contain abundant groundwater or surface water that scrubs magmatic gases until a dry pathway to the atmosphere is established. To better understand scrubbing and its implications for volcano monitoring, we model thermochemically the reaction of magmatic gases with water. First, we inject a 915??C magmatic gas from Merapi volcano into 25??C air-saturated water (ASW) over a wide range of gas/water mass ratios from 0.0002 to 100 and at a total pressure of 0.1 MPa. Then we model closed-system cooling of the magmatic gas, magmatic gas-ASW mixing at 5.0 MPa, runs with varied temperature and composition of the ASW, a case with a wide range of magmatic-gas compositions, and a reaction of a magmatic gas-ASW mixture with rock. The modeling predicts gas and water compositions, and, in one case, alteration assemblages for a wide range of scrubbing conditions; these results can be compared directly with samples from degassing volcanoes. The modeling suggests that CO2(g) is the main species to monitor when scrubbing exists; another candidate is H2S(g), but it can be affected by reactions with aqueous ferrous iron. In contrast, scrubbing by water will prevent significant SO2(g) and most HCl(g) emissions until dry pathways are established, except for moderate HCl(g) degassing from pH 100 t/d (tons per day) of SO2(g) in addition to CO2(g) and H2S(g) should be taken as a criterion of magma intrusion. Finally, the modeling suggests that the interpretation of gas-ratio data requires a case-by-case evaluation since ratio changes can often be produced by several mechanisms; nevertheless, several gas ratios may provide useful indices for monitoring the drying out of gas pathways. Published by Elsevier Science B.V.

  4. Cretaceous crust-mantle interaction and tectonic evolution of Cathaysia Block in South China: Evidence from pulsed mafic rocks and related magmatism

    NASA Astrophysics Data System (ADS)

    Li, Bin; Jiang, Shao-Yong; Zhang, Qian; Zhao, Hai-Xiang; Zhao, Kui-Dong

    2015-10-01

    Cretaceous tectono-magmatic evolution of the Cathaysia Block in South China is important but their mechanism and geodynamics remain highly disputed. In this study we carried out a detailed geochemical study on the recently found Kuokeng mafic dikes in the western Fujian Province (the Interior Cathaysia Block) to reveal the petrogenesis and geodynamics of the Cretaceous magmatism. Kuokeng mafic dikes were emplaced in three principal episodes: ~ 129 Ma (monzogabbro), ~ 107 Ma (monzodiorite), and ~ 97 Ma (gabbro). Geochemical characteristics indicate that the monzogabbros were derived from the unmodified mantle source, while gabbros were likely derived from metasomatized mantle by subducted slab (fluids and sediments). Sr-Nd isotope compositions indicate that the parental magmas of the monzodiorites were generated by mixing of enriched, mantle-derived, mafic magmas and felsic melts produced by partial melting of crustal materials. Until the Early Cretaceous (~ 123 Ma), the dominant ancient Interior Cathaysia lithospheric mantle exhibited insignificant subduction signature, indicating the melting of asthenospheric mantle and the consequent back-arc extension, producing large-scale partial melting of the crustal materials under the forward subduction regime of the paleo-Pacific plate. The monzodiorites and gabbros appear to be associated with northwestward subduction of Pacific plate under an enhanced lithospheric extensional setting, accompanying with mantle modification, which triggered shallower subduction-related metasomatically enriched lithospheric mantle to melt partially. After ca. 110 Ma, the coastal magmatic belts formed due to a retreat and rollback of the subducting Pacific Plate underneath SE China in the continental margin arc system.

  5. Time scales of Magmatic Processes

    NASA Astrophysics Data System (ADS)

    Hawkesworth, C. J.

    2002-05-01

    Knowledge of the rates of natural processes is critical to the development of physically realistic models. For magmatic processes, rates are increasingly well determined from short lived isotopes, and from diffusion modified element profiles, on time scales that vary from 10s of 1000s of years to a few years. Our understanding of the melting processes beneath MOR have been revolutionised by the application of U-series isotopes, because they include isotopes with half lives similar to the time scales of melt generation and extraction. For island arcs there is much discussion of how to incorporate suggestions that Ra and Ba are transferred from the slab in a few 1000 years, and yet significantly more time is required to generate the excess Pa isotopes. Once in the crust, crystallisation and differentiation may be driven by cooling, degassing and decompression, and these should be characterised by different time scales. Crystals preserve rich high-resolution records of changing magma compositions, but the time scales of those changes are difficult to establish. Isotope studies have shown that more evolved rock types tend to contain more old crystals that may be 10s of 1000s of years old at the time of eruption. Whether these are xenocrysts, or evidence for long term crystallisation histories remains controversial. Moreover, diffusion modified element profiles, and crystal size distributions, suggest that crystals are often less than a 100 years old. An alternative approach is to consider U-series isotope ratios in the magma, and how these may change with degree of magma evolution. These suggest that differentiation time scales may be up to 200 ky for magmas at the base of the crust, but for magmas that crystallise at shallower levels the time scales are much shorter. In some cases these are in weeks and months, and crystallisation is likely to be due to decompression and degassing. One consequence of the short crystallisation times, is that there may be insufficient

  6. Evaporatic-source model for igneous-related Fe oxide (REE-Cu-Au-U) mineralization

    SciTech Connect

    Barton, M.D.; Johnson, D.A.

    1996-03-01

    We propose that many igneous-related Fe oxide-rich (REE-Cu-Au-U-bearing) deposits form by hydrothermal processes involving evaporitic ligand sources, either coeval salars or older evaporites. These deposits are abundant in both Phanerozoic and Proterozoic extensional continental and continent-margin settings. They commonly form in global arid zones, but they also occur where magmatism is superimposed upon older evaporites. Magmatic compositions exert only second-order control, mainly on alteration mineralogy and on element abundances. Hot S-poor brines generated by interaction with evaporitic materials are consistent with geologic settings and help rationalize the distinctive element enrichments (siderophile, lithophile) and hydrothermal alteration (sodic, locally alkaline) found in these systems. This model contrasts with immiscible oxide melt and magmatic-hydrothermal origins commonly proposed for these deposits, although all three mechanisms can occur. 31 refs., 3 figs., 1 tab.

  7. How tectonics controlled post-collisional magmatism within the Dinarides: Inferences based on study of tectono-magmatic events in the Kopaonik Mts. (Southern Serbia)

    NASA Astrophysics Data System (ADS)

    Mladenović, Ana; Trivić, Branislav; Cvetković, Vladica

    2015-04-01

    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

  8. Detecting Aseismic Fault Slip and Magmatic Intrusion From Seismicity Data

    NASA Astrophysics Data System (ADS)

    Llenos, A. L.; McGuire, J. J.

    2007-12-01

    Seismicity triggered by aseismic deformation, such as magmatic intrusions or afterslip, can be used to detect the occurrence of these otherwise difficult to observe processes. Recent studies suggest that aseismic deformation can trigger large amounts of seismicity in a variety of plate tectonic settings. We have developed a new technique that takes advantage of this triggered seismicity to estimate the time-history of aseismic stressing rate on a fault- zone by combining the rate and state dependent friction and the Epidemic Type Aftershock Sequence (ETAS) models of seismicity-rate [ Dieterich, 1994; Ogata, 1988]. In the rate-state model, the integration of an observed seismicity rate results in an estimate of the stress rate acting in a given space-time window. However, the seismicity rate observed in any catalog comes from 3 primary sources: coseismically-triggered seismicity (aftershocks), tectonically-triggered seismicity (i.e., from long-term tectonic loading), and aseismically-triggered seismicity (e.g., from dike intrusion, aseismic slip transients, or fluid migration). In catalogs dominated by directly triggered aftershocks (i.e., ETAS branching ratios >~0.7), the coseismically-triggered seismicity rate will be much larger than the aseismically-triggered rate and will dominate the estimate of stressing-rate, obscuring the aseismic transient of interest if the rate-state method is applied directly. The challenge therefore lies in isolating the aseismically-triggered seismicity rate from the coseismically-triggered seismicity rate. The ETAS model [ Ogata, 1988] provides a natural way to separate the aseismic and coseismic seismicity rates, as the ETAS parameter μ essentially reflects the aseismically-triggered rate (as well as the background tectonically-triggered rate). To develop a method that can resolve the magnitude and time history of aseismic stress transients even in high branching ratio regions, we combine the rate-state and ETAS models into a

  9. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    NASA Astrophysics Data System (ADS)

    Ruch, J.; Vezzoli, L.; De Rosa, R.; Di Lorenzo, R.; Acocella, V.

    2016-02-01

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic, and structural field data along the strike-slip central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures, and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activities steadily migrated eastward and currently focus on a 10 km long × 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  10. The magmatic history of the Vetas-California mining district, Santander Massif, Eastern Cordillera, Colombia

    NASA Astrophysics Data System (ADS)

    Mantilla Figueroa, Luis C.; Bissig, Thomas; Valencia, Víctor; Hart, Craig J. R.

    2013-08-01

    The Vetas-California Mining District (VCMD), located in the central part of the Santander Massif (Colombian Eastern Cordillera), based on U-Pb dating of zircons, records the following principal tectono-magmatic events: (1) the Grenville Orogenic event and high grade metamorphism and migmatitization between ˜1240 and 957 Ma; (2) early Ordovician calc-alkalic magmatism, which was synchronous with the Caparonensis-Famatinian Orogeny (˜477 Ma); (3) middle to late Ordovician post-collisional calc-alkalic magmatism (˜466-436 Ma); (4) late Triassic to early Jurassic magmatism between ˜204 and 196 Ma, characterized by both S- and I-type calc-alkalic intrusions and; (5) a late Miocene shallowly emplaced intermediate calc-alkaline intrusions (10.9 ± 0.2 and 8.4 ± 0.2 Ma). The presence of even younger igneous rocks is possible, given the widespread magmatic-hydrothermal alteration affecting all rock units in the area. The igneous rocks from the late Triassic-early Jurassic magmatic episodes are the volumetrically most important igneous rocks in the study area and in the Colombian Eastern Cordillera. They can be divided into three groups based on their field relationships, whole rock geochemistry and geochronology. These are early leucogranites herein termed Alaskites-I (204-199 Ma), Intermediate rocks (199-198 Ma), and late leucogranites, herein referred to as Alaskites-II (198-196 Ma). This Mesozoic magmatism is reflecting subtle changes in the crustal stress in a setting above an oblique subduction of the Panthalassa plate beneath Pangea. The lower Cretaceous siliciclastic Tambor Formation has detrital zircons of the same age populations as the metamorphic and igneous rocks present in the study area, suggesting that the provenance is related to the erosion of these local rocks during the late Jurassic or early Cretaceous, implying a local supply of sediments to the local depositional basins.

  11. North Atlantic magmatism controlled by temperature, mantle composition and buoyancy

    NASA Astrophysics Data System (ADS)

    Brown, Eric L.; Lesher, Charles E.

    2014-11-01

    Large igneous provinces are characterized by anomalously high rates of magma production. Such voluminous magmatism is commonly attributed to partial melting of hot, buoyantly upwelling mantle plume material. However, compositional heterogeneity in the mantle, caused by the subduction of oceanic crust, can also enhance magma production, diminishing the need for elevated temperatures associated with upwelling plumes. A plume origin for the North Atlantic large igneous province has been questioned because lava compositions correlate with crustal thickness, implying a link between magma productivity and mantle source composition. Here we use a numerical model that simulates upwelling and melting of compositionally heterogeneous mantle material to constrain the conditions that gave rise to magmatism in the North Atlantic. Using observations of lava compositions and volumes from the North Atlantic, we show that subducted crustal material represented less than 10% of the mantle source. We further show that mantle temperatures have remained elevated by 85-210 °C and increased mantle upwelling up to 14 times the rate of plate separation has occurred over the past 56 Myr. The enhanced temperatures and upwelling rates extended along more than 1,000 km of the Palaeogene rift, but are substantially more restricted along the modern Mid-Atlantic Ridge. These findings reflect the long-term manifestation of a mantle plume.

  12. Mid-ocean ridge jumps associated with hotspot magmatism

    NASA Astrophysics Data System (ADS)

    Mittelstaedt, Eric; Ito, Garrett; Behn, Mark D.

    2008-02-01

    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

  13. Magmatic evolution of the Andean Eastern Cordillera of Colombia during the Cretaceous: Influence of previous tectonic processes

    NASA Astrophysics Data System (ADS)

    Vásquez, Mónica; Altenberger, Uwe; Romer, Rolf L.; Sudo, Masafumi; Moreno-Murillo, Juan Manuel

    2010-03-01

    The Eastern Cordillera of the Colombian Andes represents an inverted Cretaceous basin where Cretaceous magmatism is characterized by rare mafic dykes and sills. We use 40Ar/ 39Ar, Sr-Nd-Pb isotopes, as well as major and trace elements analyses of Cretaceous intrusions from both flanks of the Eastern Cordillera in combination with structural data to document the complex evolution of the basin. Magmatism, which is diachronous and geochemically diverse, seems to be related to mantle melting beneath the most subsiding segments of each sub-basin during enhanced extensional tectonics. The mafic intrusions display two different compositional series: an alkaline one with OIB-like pattern and a tholeiitic one with MORB-like features. This indicates at least two diverse mantle sources. Trace-element patterns suggest that the intrusions were emplaced in an extensional setting. 40Ar/ 39Ar dating on primary plagioclase and hornblende provides plateau ages between ˜136 and ˜74 Ma. The geochemical and temporal diversities show that the emplacement of the magmas was tectonically controlled, each sub-basin reflecting an individual subsidence event.

  14. Model of the magmatic thermolysis of coal matter deep in the earth (short communication)

    SciTech Connect

    Yu.M. Korolev; S.G. Gagarin

    2008-06-15

    A model of contact thermolysis was constructed based on a combined set of equations for heat transfer from a magmatic intrusion to a coal bed and the kinetics of thermal coal conversion. This model was illustrated by the generation of petroleum hydrocarbons deep in the earth by the thermolysis of the sapropelic matter of boghead.

  15. Late-Variscan rare metal ore deposition and plume-related magmatism in the eastern European Variscides (D, CZ)

    NASA Astrophysics Data System (ADS)

    Seifert, Thomas

    2014-05-01

    includes a range of mafic calc-alkaline and shoshonitic rock types, and lamprophyres (spessartites and camptonites) with age data between 300-270 Ma. The Mid-European Variscides show a large number of Permo-Carboniferous magmatic complexes with similar ages (Halle Volcanic Complex, Saar-Nahe Basin, Thuringian Forest, Harz Mts., Northwest-Saxonian Volcanic Complexes, bimodal volcanic rocks of the Sub-Erzgebirge basin and the Rhyolite Complex of Tharandt as well as Li-F-Sn small intrusion granites and lamprophyric intrusions in the Erzgebirge. It is important to note that the late-Variscan W-Mo, Sn-W-Mo, Ag-bearing Sn-In-base metal, Ag-Sb-base metal, and U mineralizations in the Erzgebirge-Krušné hory are spatially and temporal associated with intrusion centers of Permo-Carboniferous post-collisional mafic and rhyolitic (sub)volcanic bimodal magmatism (315-290 Ma) along deep-rooted NW-SE fault zones, especially at the intersections with NE-SW, E-W, and N-S major regional structural zones. The bimodal lamprophyre-rhyolite assemblage in the Erzgebirge / Sub-Erzgebirge basin area was formed during intracontinental rifting in a 'Fast Extension' setting by melting of a metasomatic enriched mantle source. The emplacement of fluid-enriched lamprophyres and F-rich rhyolitic intrusions at the same time is probably associated with decompression melting of updoming asthenosphere which is possibly associated with the above mentioned mantle plume.

  16. Spatial and temporal variations of loads and sources of total and dissolved Phosphorus in a set of rivers (Western France).

    NASA Astrophysics Data System (ADS)

    Legeay, Pierre-Louis; Moatar, Florentina; Gascuel-Odoux, Chantal; Gruau, Gérard

    2015-04-01

    In intensive agricultural regions with important livestock farming, long-term land application of Phosphorus (P) both as chemical fertilizer and animal wastes, have resulted in elevated P contents in soils. Since we know that high P concentrations in rivers is of major concern, few studies have been done at to assess the spatiotemporal variability of P loads in rivers and apportionment of point and nonpoint source in total loads. Here we focus on Brittany (Western France) where even though P is a great issue in terms of human and drinking water safety (cyano-toxins), environmental protection and economic costs for Brittany with regards to the periodic proliferations of cyanobacteria that occur every year in this region, no regional-scale systematic study has been carried out so far. We selected a set of small rivers (stream order 3-5) with homogeneous agriculture and granitic catchment. By gathering data from three water quality monitoring networks, covering more than 100 measurements stations, we provide a regional-scale quantification of the spatiotemporal variability of dissolved P (DP) and total P (TP) interannual loads from 1992 to 2012. Build on mean P load in low flows and statistical significance tests, we developed a new indicator, called 'low flow P load' (LFP-load), which allows us to determine the importance of domestic and industrial P sources in total P load and to assess their spatiotemporal variability compared to agricultural sources. The calculation and the map representation of DP and TP interannual load variations allow identification of the greatest and lowest P contributory catchments over the study period and the way P loads of Brittany rivers have evolved through time. Both mean DP and TP loads have been divided by more than two over the last 20 years. Mean LFDP-load decreased by more than 60% and mean LFTP-load by more than 45% on average over the same period showing that this marked temporal decrease in total load is largely due to the

  17. Magmatic record of India-Asia collision.

    PubMed

    Zhu, Di-Cheng; Wang, Qing; Zhao, Zhi-Dan; Chung, Sun-Lin; Cawood, Peter A; Niu, Yaoling; Liu, Sheng-Ao; Wu, Fu-Yuan; Mo, Xuan-Xue

    2015-01-01

    New geochronological and geochemical data on magmatic activity from the India-Asia collision zone enables recognition of a distinct magmatic flare-up event that we ascribe to slab breakoff. This tie-point in the collisional record can be used to back-date to the time of initial impingement of the Indian continent with the Asian margin. Continental arc magmatism in southern Tibet during 80-40 Ma migrated from south to north and then back to south with significant mantle input at 70-43 Ma. A pronounced flare up in magmatic intensity (including ignimbrite and mafic rock) at ca. 52-51 Ma corresponds to a sudden decrease in the India-Asia convergence rate. Geological and geochemical data are consistent with mantle input controlled by slab rollback from ca. 70 Ma and slab breakoff at ca. 53 Ma. We propose that the slowdown of the Indian plate at ca. 51 Ma is largely the consequence of slab breakoff of the subducting Neo-Tethyan oceanic lithosphere, rather than the onset of the India-Asia collision as traditionally interpreted, implying that the initial India-Asia collision commenced earlier, likely at ca. 55 Ma. PMID:26395973

  18. Magmatic record of India-Asia collision

    PubMed Central

    Zhu, Di-Cheng; Wang, Qing; Zhao, Zhi-Dan; Chung, Sun-Lin; Cawood, Peter A.; Niu, Yaoling; Liu, Sheng-Ao; Wu, Fu-Yuan; Mo, Xuan-Xue

    2015-01-01

    New geochronological and geochemical data on magmatic activity from the India-Asia collision zone enables recognition of a distinct magmatic flare-up event that we ascribe to slab breakoff. This tie-point in the collisional record can be used to back-date to the time of initial impingement of the Indian continent with the Asian margin. Continental arc magmatism in southern Tibet during 80–40 Ma migrated from south to north and then back to south with significant mantle input at 70–43 Ma. A pronounced flare up in magmatic intensity (including ignimbrite and mafic rock) at ca. 52–51 Ma corresponds to a sudden decrease in the India-Asia convergence rate. Geological and geochemical data are consistent with mantle input controlled by slab rollback from ca. 70 Ma and slab breakoff at ca. 53 Ma. We propose that the slowdown of the Indian plate at ca. 51 Ma is largely the consequence of slab breakoff of the subducting Neo-Tethyan oceanic lithosphere, rather than the onset of the India-Asia collision as traditionally interpreted, implying that the initial India-Asia collision commenced earlier, likely at ca. 55 Ma. PMID:26395973

  19. Magmatic record of India-Asia collision.

    PubMed

    Zhu, Di-Cheng; Wang, Qing; Zhao, Zhi-Dan; Chung, Sun-Lin; Cawood, Peter A; Niu, Yaoling; Liu, Sheng-Ao; Wu, Fu-Yuan; Mo, Xuan-Xue

    2015-09-23

    New geochronological and geochemical data on magmatic activity from the India-Asia collision zone enables recognition of a distinct magmatic flare-up event that we ascribe to slab breakoff. This tie-point in the collisional record can be used to back-date to the time of initial impingement of the Indian continent with the Asian margin. Continental arc magmatism in southern Tibet during 80-40 Ma migrated from south to north and then back to south with significant mantle input at 70-43 Ma. A pronounced flare up in magmatic intensity (including ignimbrite and mafic rock) at ca. 52-51 Ma corresponds to a sudden decrease in the India-Asia convergence rate. Geological and geochemical data are consistent with mantle input controlled by slab rollback from ca. 70 Ma and slab breakoff at ca. 53 Ma. We propose that the slowdown of the Indian plate at ca. 51 Ma is largely the consequence of slab breakoff of the subducting Neo-Tethyan oceanic lithosphere, rather than the onset of the India-Asia collision as traditionally interpreted, implying that the initial India-Asia collision commenced earlier, likely at ca. 55 Ma.

  20. Multiple rifting and alkaline magmatism in southern India during Paleoproterozoic and Neoproterozoic

    NASA Astrophysics Data System (ADS)

    Renjith, M. L.; Santosh, M.; Satyanarayanan, M.; Rao, D. V. Subba; Tang, Li

    2016-06-01

    The Southern Granulite Terrane (SGT) in India preserves the history of tectonothermal events ranging from Paleoarchean to latest Neoproterozoic-Cambrian. Here we investigate alkaline magmatism possibly associated with rifting events in Paleoproterozoic and Neoproterozoic based on petrological, geochemical and zircon U-Pb and Lu-Hf isotopic studies on the alkaline complexes of Korangani (KGAC) and Kambamettu (KAC) in the Madurai Block of SGT. The mica pyroxenite which represents the first intrusive phase at KGAC crystallized from a mildly alkaline hydrous magma derived from a metasomatized mantle. The younger shoshonitic syenite was emplaced at 2533 ± 16 Ma, carries mafic microgranular enclaves, and shows trace-elements ratios consistent with magma mixing trend, and zircon εHf(t) values display mixed positive and negative values - 2.6 to 3.6 suggesting the mixing of adakite-like felsic crustal melt and non-adakitic mantle derived melt. In KAC, four distinct magmatic intrusions are identified: i) quartz-monzonite (emplaced at 2498 ± 16 Ma), an ultrapotassic adakitic rock derived from a carbonated alkali-rich lower crustal source with negative zircons εHf(t) values in zircon (- 8.0 to - 0.8); Y/Nb (> 1.2) and Th/Ce (0.03-0.8) ratios; lower Ni (< 30 ppm) and Cr (< 14 ppm) contents; ii) phlogopite-rich pyroxenite, crystallized from an alkali-rich basaltic parental magma derived from carbonate metasomatized mantle; iii) mantle derived high Ba-Sr carbonatite (emplaced at 2470 ± 15 Ma); and iv) shoshonitic peralkaline syenite rock (emplaced at 608 ± 6 Ma) with strong adakitic signature, low MgO (< 1 wt.%), Ni (12-5 ppm) and Cr (49-35 ppm) contents and negative zircon εHf(t) values (- 30.3 to - 27.3) and trough of Zr-Hf in spidergrams suggesting a carbonated alkali-rich garnet-bearing crustal source. The geochemical features and petrogenetic considerations of the felsic shoshonitic-ultrapotassic adakite-like rocks (syenite, quartz monzonite), mica-pyroxenites and

  1. Magmatism on rift flanks: Insights from ambient noise phase velocity in Afar region

    NASA Astrophysics Data System (ADS)

    Korostelev, Félicie; Weemstra, Cornelis; Leroy, Sylvie; Boschi, Lapo; Keir, Derek; Ren, Yong; Molinari, Irene; Ahmed, Abdulhakim; Stuart, Graham W.; Rolandone, Frédérique; Khanbari, Khaled; Hammond, James O. S.; Kendall, J. M.; Doubre, Cécile; Ganad, Ismail Al; Goitom, Berhe; Ayele, Atalay

    2015-04-01

    During the breakup of continents in magmatic settings, the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis. Magmatic processes near the rift flanks are commonly ignored. We present phase velocity maps of the crust and uppermost mantle of the conjugate margins of the southern Red Sea (Afar and Yemen) using ambient noise tomography to constrain crustal modification during breakup. Our images show that the low seismic velocities characterize not only the upper crust beneath the axial volcanic systems but also both upper and lower crust beneath the rift flanks where ongoing volcanism and hydrothermal activity occur at the surface. Magmatic modification of the crust beneath rift flanks likely occurs for a protracted period of time during the breakup process and may persist through to early seafloor spreading.

  2. Decreasing Magmatic Footprints of Individual Volcanos in a Waning Basaltic Field

    SciTech Connect

    G.A> Valentine; F.V. Perry

    2006-06-06

    The distribution and characteristics of individual basaltic volcanoes in the waning Southwestern Nevada Volcanic Field provide insight into the changing physical nature of magmatism and the controls on volcano location. During Pliocene-Pleistocene times the volumes of individual volcanoes have decreased by more than one order of magnitude, as have fissure lengths and inferred lava effusion rates. Eruptions evolved from Hawaiian-style eruptions with extensive lavas to eruptions characterized by small pulses of lava and Strombolian to violent Strombolian mechanisms. These trends indicate progressively decreasing partial melting and length scales, or magmatic footprints, of mantle source zones for individual volcanoes. The location of each volcano is determined by the location of its magmatic footprint at depth, and only by shallow structural and topographic features that are within that footprint. The locations of future volcanoes in a waning system are less likely to be determined by large-scale topography or structures than were older, larger volume volcanoes.

  3. Integrating GRACE and multi-source data sets to quantify the seasonal groundwater depletion in mega agricultural regions

    NASA Astrophysics Data System (ADS)

    Tang, Y.; Wang, D.; Zhu, T.; Ringler, C.; Sun, A. Y.

    2015-12-01

    It is challenging to quantify the groundwater depletion in the mega basins owing to the huge spatial scale and the intensive anthrophonic activities (e.g. dams and reservoirs). Recently, the satellite Gravity Recovery and Climate Experiment (GRACE) data provides an opportunity to monitor large-scale groundwater depletion. However, the data is only available after 2002, limiting the understanding of inter-annual variability of seasonal groundwater depletion. In this study, a simple model with two parameters is developed, based on the seasonal Budyko framework for quantifying the seasonal groundwater depletion. The model is applied to the Indus and Ganges River basin in South Asia and the High Plain/Ogallala aquifer in United States. The parameters of the model are estimated by integrating GRACE and other multi-source data sets. Total water storage changes before 2003 are reconstructed based on the developed model with available data of evaporation, precipitation, and potential evaporation.

  4. The aeromagnetic method as a tool to identify Cenozoic magmatism in the West Antarctic Rift System beneath the West Antarctic Ice Sheet: a review; Thiel subglacial volcano as possible source of the ash layer in the WAISCOR

    USGS Publications Warehouse

    Behrendt, John C.

    2013-01-01

    The West Antarctic Ice Sheet (WAIS) flows through the volcanically active West Antarctic Rift System (WARS). The aeromagnetic method has been the most useful geophysical tool for identification of subglacial volcanic rocks, since 1959–64 surveys, particularly combined with 1978 radar ice-sounding. The unique 1991–97 Central West Antarctica (CWA) aerogeophysical survey covering 354,000 km2 over the WAIS, (5-km line-spaced, orthogonal lines of aeromagnetic, radar ice-sounding, and aerogravity measurements), still provides invaluable information on subglacial volcanic rocks, particularly combined with the older aeromagnetic profiles. These data indicate numerous 100–>1000 nT, 5–50-km width, shallow-source, magnetic anomalies over an area greater than 1.2 × 106 km2, mostly from subglacial volcanic sources. I interpreted the CWA anomalies as defining about 1000 “volcanic centers” requiring high remanent normal magnetizations in the present field direction. About 400 anomaly sources correlate with bed topography. At least 80% of these sources have less than 200 m relief at the WAIS bed. They appear modified by moving ice, requiring a younger age than the WAIS (about 25 Ma). Exposed volcanoes in the WARS are The present rapid changes resulting from global warming, could be accelerated by subglacial volcanism.

  5. The aeromagnetic method as a tool to identify Cenozoic magmatism in the West Antarctic Rift System beneath the West Antarctic Ice Sheet — A review; Thiel subglacial volcano as possible source of the ash layer in the WAISCORE

    NASA Astrophysics Data System (ADS)

    Behrendt, John C.

    2013-02-01

    The West Antarctic Ice Sheet (WAIS) flows through the volcanically active West Antarctic Rift System (WARS). The aeromagnetic method has been the most useful geophysical tool for identification of subglacial volcanic rocks, since 1959-64 surveys, particularly combined with 1978 radar ice-sounding. The unique 1991-97 Central West Antarctica (CWA) aerogeophysical survey covering 354,000 km2 over the WAIS, (5-km line-spaced, orthogonal lines of aeromagnetic, radar ice-sounding, and aerogravity measurements), still provides invaluable information on subglacial volcanic rocks, particularly combined with the older aeromagnetic profiles. These data indicate numerous 100->1000 nT, 5-50-km width, shallow-source, magnetic anomalies over an area greater than 1.2 × 106 km2, mostly from subglacial volcanic sources. I interpreted the CWA anomalies as defining about 1000 "volcanic centers" requiring high remanent normal magnetizations in the present field direction. About 400 anomaly sources correlate with bed topography. At least 80% of these sources have less than 200 m relief at the WAIS bed. They appear modified by moving ice, requiring a younger age than the WAIS (about 25 Ma). Exposed volcanoes in the WARS are < 34 Ma, but at least four are active. If a few buried volcanic centers are active, subglacial volcanism may well affect the WAIS regime. Aerogeophysical data (Blankenship et al., 1993, Mt. Casertz; Corr and Vaughan, 2008, near Hudson Mts.) indicated active subglacial volcanism. Magnetic data indicate a caldera and a surrounding "low" in the WAISCORE vicinity possibly the result of a shallow Curie isotherm. High heat flow reported from temperature logging in the WAISCORE (Conway et al., 2011; Clow, personal commun.) and a volcanic ash layer (Dunbar, 2012) are consistent with this interpretation. A subaerially erupted subglacial volcano, (Mt Thiel), about 100 km distant, may be the ash source. The present rapid changes resulting from global warming, could be

  6. New boron isotopic evidence for sedimentary and magmatic fluid influence in the shallow hydrothermal vent system of Milos Island (Aegean Sea, Greece)

    NASA Astrophysics Data System (ADS)

    Wu, Shein-Fu; You, Chen-Feng; Lin, Yen-Po; Valsami-Jones, Eugenia; Baltatzis, Emmanuel

    2016-01-01

    Magmatic sources may contribute a significant amount of volatiles in geothermal springs; however, their role is poorly understood in submarine hydrothermal systems worldwide. In this study, new results of B and δ11B in 41 hydrothermal vent waters collected from the shallow hydrothermal system of Milos island in the Aegean Sea were combined with previously published data from other tectonic settings and laboratory experiments to quantify the effects of phase separation, fluid/sediment interaction and magmatic contribution. Two Cl-extreme solutions were identified, high-Cl waters (Cl as high as 2000 mM) and low-Cl waters (Cl < 80 mM). Both sets of waters were characterized by high B/Cl (~ 1.2-5.3 × 10- 3 mol/mol) and extremely low δ11B (1.4-6.3‰), except for the waters with Mg content of near the seawater value and δ11B = 10.3-17.4‰. These high-Cl waters with high B/Cl and low δ11B plot close to the vent waters in sediment-hosted hydrothermal system (i.e., Okinawa Trough) or fumarole condensates from on-land volcanoes, implying B addition from sediment or magmatic fluids plays an important role. This is in agreement with fluid/sediment interactions resulting in the observed B and δ11B, as well as previously reported Br/I/Cl ratios, supporting a scenario of slab-derived fluid addition with elevated B, 11B-rich, and low Br/Cl and I/Cl, which is derived from the dehydration of subducted-sediments. The slab fluid becomes subsequently mixed with the parent magma of Milos. The deep brine reservoir is partially affected by injections of magmatic fluid/gases during degassing. The results presented here are crucial for deciphering the evolution of the brine reservoirs involved in phase separation, fluid/sediment interaction and magmatic contribution in the deep reaction zone of the Milos hydrothermal system; they also have implications in the understanding of the formation of metallic vein mineralization.

  7. The potential role of magmatic gases in the genesis of Illinois- Kentucky fluorspar deposits: implications from chemical reaction path modeling

    USGS Publications Warehouse

    Plumlee, G.S.; Goldhaber, M.B.; Rowan, E.L.

    1995-01-01

    Presents results of reaction path calculations using the chemical speciation and reaction path program SOLVEQ and CHILLER to model possible fluorite deposition mechanisms in the Illinois-Kentucky fluorspar district. The results indicate that the fluids responsible for Illinois-Kentucky fluorspar mineralization were most likely quite acidic (pH < 4) and rich in fluorine in order to produce the fluorite-rich, dolomite-poor mineral assemblages and extensive dissolution of host limestones. A possible source for the acid and fluorine may have been HF-rich gases which were expelled from alkalic magmas and then incorporated by migrating basinal brines. An analysis of the geologic setting of other fluorite deposits and districts worldwide suggests that involvement of magmatic gases is probable for many of these districts as well. -from Authors

  8. Web-MCQ: a set of methods and freely available open source code for administering online multiple choice question assessments.

    PubMed

    Hewson, Claire

    2007-08-01

    E-learning approaches have received increasing attention in recent years. Accordingly, a number of tools have become available to assist the nonexpert computer user in constructing and managing virtual learning environments, and implementing computer-based and/or online procedures to support pedagogy. Both commercial and free packages are now available, with new developments emerging periodically. Commercial products have the advantage of being comprehensive and reliable, but tend to require substantial financial investment and are not always transparent to use. They may also restrict pedagogical choices due to their predetermined ranges of functionality. With these issues in mind, several authors have argued for the pedagogical benefits of developing freely available, open source e-learning resources, which can be shared and further developed within a community of educational practitioners. The present paper supports this objective by presenting a set of methods, along with supporting freely available, downloadable, open source programming code, to allow administration of online multiple choice question assessments to students.

  9. Does subduction zone magmatism produce average continental crust

    NASA Technical Reports Server (NTRS)

    Ellam, R. M.; Hawkesworth, C. J.

    1988-01-01

    The question of whether present day subduction zone magmatism produces material of average continental crust composition, which perhaps most would agree is andesitic, is addressed. It was argued that modern andesitic to dacitic rocks in Andean-type settings are produced by plagioclase fractionation of mantle derived basalts, leaving a complementary residue with low Rb/Sr and a positive Eu anomaly. This residue must be removed, for example by delamination, if the average crust produced in these settings is andesitic. The author argued against this, pointing out the absence of evidence for such a signature in the mantle. Either the average crust is not andesitic, a conclusion the author was not entirely comfortable with, or other crust forming processes must be sought. One possibility is that during the Archean, direct slab melting of basaltic or eclogitic oceanic crust produced felsic melts, which together with about 65 percent mafic material, yielded an average crust of andesitic composition.

  10. Breakup Style and Magmatic Underplating West of the Lofoten Islands, Norway, Based on OBS Data.

    NASA Astrophysics Data System (ADS)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.; Murai, Y.; Flueh, E. R.

    2014-12-01

    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

  11. Simulating the Thermochemical Magmatic and Tectonic Evolution of Venus's Mantle and Lithosphere: Intrusive vs. Extrusive Magmatism

    NASA Astrophysics Data System (ADS)

    Tackley, Paul; Armann, Marina

    2013-04-01

    Here we extend the models of [1]. Numerical convection models of the thermochemical evolution of Venus are compared to present-day topography and geoid, recent resurfacing history and surface deformation. The models include melting, magmatism, decaying heat-producing elements, core cooling, realistic temperature-dependent viscosity and either stagnant lid or episodic lithospheric overturn. In [1] it was found that in stagnant lid convection the dominant mode of heat loss is magmatic heat pipe, which requires massive magmatism and produces very thick crust, inconsistent with observations. Partitioning of heat-producing elements into the crust helps but does not help enough. Episodic lid overturn interspersed by periods of quiescence effectively loses Venus's heat while giving lower rates of volcanism and a thinner crust. Calculations predict 5-8 overturn events over Venus's history, each lasting ~150 Myr, initiating in one place and then spreading globally. During quiescent periods convection keeps the lithosphere thin. Magmatism keeps the mantle temperature constant over Venus's history. Crustal recycling occurs by entrainment in stagnant lid convection, and by lid overturn in episodic mode. Venus-like amplitudes of topography and geoid can be produced in either stagnant or episodic modes, with a viscosity profile that is Earth-like but shifted to higher values. The basalt density inversion below the olivine-perovskite transition causes compositional stratification around 730 km; breakdown of this layering increases episodicity but far less than episodic lid overturn. The classical stagnant lid mode with interior temperature rheological temperature scale lower than TCMB is not reached because mantle temperature is controlled by magmatism while the core cools slowly from a superheated start. Core heat flow decreases with time, possibly shutting off the dynamo, particularly in episodic cases. Here we extend [1] by considering intrusive magmatism as an alternative to

  12. Paired Magmatic-Metallogenic Belts in Myanmar - an Andean Analogue?

    NASA Astrophysics Data System (ADS)

    Gardiner, Nicholas; Robb, Laurence; Searle, Michael; Morley, Christopher

    2015-04-01

    Myanmar (Burma) is richly endowed in precious and base metals, having one of the most diverse collections of natural resources in SE Asia. Its geological history is dominated by the staged closing of Tethys and the suturing of Gondwana-derived continental fragments onto the South China craton during the Mesozoic-Cenozoic. The country is located at a crucial geologic juncture where the main convergent Tethyan collision zone swings south around the Namche Barwa Eastern Himalayan syntaxis. However, despite recent work, the geological and geodynamic history of Myanmar remains enigmatic. Plate margin processes, magmatism, metasomatism and the genesis of mineral deposits are intricately linked, and there has long been recognized a relationship between the distribution of certain mineral deposit types, and the tectonic settings which favour their genesis. A better knowledge of the regional tectonic evolution of a potential exploration jurisdiction is therefore crucial to understanding its minerals prospectivity. This strong association between tectonics and mineralization can equally be applied in reverse. By mapping out the spatial, and temporal, distribution of presumed co-genetic mineral deposits, coupled with an understanding of their collective metallogenetic origin, a better appreciation of the tectonic evolution of a terrane may be elucidated. Identification and categorization of metallotects within a geodynamically-evolving terrane thus provides a complimentary tool to other methodologies (e.g. geochemical, geochronological, structural, geophysical, stratigraphical), for determining the tectonic history and inferred geodynamic setting of that terrane through time. Myanmar is one such study area where this approach can be undertaken. Here are found two near-parallel magmatic belts, which together contain a significant proportion of that country's mineral wealth of tin, tungsten, copper, gold and silver. Although only a few 100 km's apart, these belts exhibit a

  13. Silurian magmatism in eastern Senegal and its significance for the Paleozoic evolution of NW-Gondwana

    NASA Astrophysics Data System (ADS)

    Fullgraf, Thomas; Ndiaye, Papa Moussa; Blein, Olivier; Buscail, François; Lahondère, Didier; Le Métour, Joël; Sergeev, Sergey; Tegyey, Monique

    2013-02-01

    Submarine basalt and trachyte of the Nandoumba group occur in eastern Senegal within the Bassarides branch of the Mauritanides orogen. The unit forms part of the parautochthonous domain which is stacked between underlying Neoproterozoic to Paleozoic foreland and overlying Variscan nappes. The crystallisation age of the volcanic to subvolcanic rocks has been determined by U-Pb single zircon SHRIMP method at 428 ± 5.2 Ma whereas zircon xenocryst ages vary from 500 to 2200 Ma. The shape of the xenocryst grains document proximal Neo- and Paleoproterozoic and distal Mesoproterozoic provenance areas for assimilated sediments. This is compatible with the Paleoproterozoic Birimian basement and Neoproterozoic cover rocks nearby whereas an origin from the Amazonian craton could be assumed for distal Mesoproterozoic zircons. Geochemical and Sm-Nd isotope whole rock analysis show that basalts of the Nandoumba group are similar to modern transitional to alkaline volcanic lavas in intraplate settings. Those basalts have a deep mantle source with a great contribution of a recycled mantle component such as EM1 and/or EM2. The basalts resemble in their composition those from the Meguma terrane of Nova Scotia which are of similar age suggesting a common source and therefore connection of Meguma with Gondwana during this period. Review of circum-Atlantic Silurian magmatism indicates ongoing fragmentation of NW-Gondwana that started in Cambro/Ordovician times.

  14. Bidirectional feedback observed between a magmatic intrusion and shallow earthquake

    NASA Astrophysics Data System (ADS)

    Ebmeier, Susanna; Elliott, John; Nocquet, Jean-Mathieu; Biggs, Juliet; Mothes, Patricia; Jarrín, Paúl; Yépez, Marco; Aguaiza, Santiago; Lundgren, Paul; Samsonov, Sergey

    2016-04-01

    Moderate volcano-tectonic earthquakes (M 5-6) during volcanic unrest are unusual, and tend to be associated with major stress perturbations to the crust, occurring during episodes of rifting or the onset of volcanic eruptions. The feedback from such events may be positive, easing magma ascent and eruption, or, as we demonstrate here, negative, hindering any further magma movement. We present measurements of deformation at Chiles-Cerro Negro volcanoes on the Ecuador-Colombian border. There was previously no record of historical activity at either volcano, but between 2013 and early 2015 there were three episodes of unrest characterised by swarms of volcano-tectonic earthquakes of increasing energy and duration and thought to be associated with the hydrothermal system. In October 2014, magmatic processes not only caused many thousands of small earthquakes per day, but culminated in a Mw 5.6 earthquake located on a system of active tectonic faults that last ruptured in 1868. We find that inflation of a mid-crustal magmatic source ~10 km south of the volcanoes ceased abruptly at the time of the earthquake, after which time the rate of seismicity also began a gradual decline. The Chiles-Cerro Negro unrest is therefore an interesting example of magma ascent triggering a moderate earthquake on a tectonic fault and subsequently being inhibited by co-seismic stress changes. This is an important observation for the interpretation of moderate earthquakes during volcanic unrest in terms of evolving hazard.

  15. Magmatic gas emissions at Holocene volcanic features near Mono Lake, California, and their relation to regional magmatism

    USGS Publications Warehouse

    Bergfeld, D.; Evans, William C.; Howle, James F.; Hunt, Andrew G.

    2015-01-01

    Silicic lavas have erupted repeatedly in the Mono Basin over the past few thousand years, forming the massive domes and coulees of the Mono Craters chain and the smaller island vents in Mono Lake. We report here on the first systematic study of magmatic CO2 emissions from these features, conducted during 2007–2010. Most notably, a known locus of weak steam venting on the summit of North Coulee is actually enclosed in a large area (~ 0.25 km2) of diffuse gas discharge that emits 10–14 t/d of CO2, mostly at ambient temperature. Subsurface gases sampled here are heavily air-contaminated, but after standard corrections are applied, show average δ13C-CO2 of − 4.72‰, 3He/4He of 5.89RA, and CO2/3He of 0.77 × 1010, very similar to the values in fumarolic gas from Mammoth Mountain and the Long Valley Caldera immediately to the south of the basin. If these values also characterize the magmatic gas source at Mono Lake, where CO2 is captured by the alkaline lake water, a magmatic CO2 upflow beneath the lake of ~ 4 t/d can be inferred. Groundwater discharge from the Mono Craters area transports ~ 13 t/d of 14C-dead CO2 as free gas and dissolved carbonate species, and adding in this component brings the estimated total magmatic CO2 output to 29 t/d for the two silicic systems in the Mono Basin. If these emissions reflect intrusion and degassing of underlying basalt with 0.5 wt.% CO2, a modest intrusion rate of 0.00075 km3/yr is indicated. Much higher intrusion rates are required to account for CO2 emissions from Mammoth Mountain and the West Moat of the Long Valley Caldera.

  16. Four flavours of orogenic plateau magmatism: what's melting beneath the Turkish-Iranian Plateau?

    NASA Astrophysics Data System (ADS)

    Neill, Iain; Allen, Mark; Kheirkhah, Monireh; Meliksetian, Khachatur; Kaislaniemi, Lars; van Hunen, Jeroen

    2014-05-01

    Orogenic plateaux are first order topographic features of the continents, occurring in collision zones such as Tibet and Andean-style continental arcs. Plateaux are sites of abundant mantle-derived magmatism, but there is little understanding of its geodynamic cause in spite of widespread assumptions that slab break-off or lithospheric thinning are controlling factors. Late Cenozoic magmatism is distributed 100s of km from the Arabia-Eurasia suture zone across the modern Turkish-Iranian Plateau (TIP) in the countries of Armenia, Iran, Turkey and adjacent areas. There is huge compositional variation. Here we document four varieties of recent TIP magmas and argue their occurrence is controlled by: geographic location, prior fertilisation of the lithospheric mantle, lithospheric thickness, temperature and stability, and asthenospheric convection. (1) Close to the original Arabia-Eurasia suture in Eastern Turkey, slab break-off is likely to have occurred at ~10 Myr, and the lithosphere is presently thin (45-50 km) with little or no mantle lithosphere present. Magmatism is mostly calk-alkaline, sourced from the asthenosphere or any remaining mantle lithosphere, and is affected by crustal contamination. (2) In the Lesser Caucasus up to ~500 km from the suture, magmatism is more alkaline, less contaminated and is derived from subduction-modified lithospheric mantle. (3) Close to the suture in Iran, the lithosphere has thickened to >200 km during collision. Magmatism is volumetrically limited and derived almost exclusively from the lithospheric mantle, with highly enriched alkaline or ultrapotassic compositions. Unlike the Lesser Caucasus, there is little or no magmatism in the Iranian desert up to 500 km from the suture. (4) Beyond ~500 km from the suture zone, magmatism is sparse and varies in composition: dominantly OIB-like in Eastern Iran, alkaline but arc-like in the Alborz, and more felsic above the relatively thick (~55 km) crust of the Greater Caucasus. Magmatism

  17. Mantle source of the 2.44-2.50-Ga mantle plume-related magmatism in the Fennoscandian Shield: evidence from Os, Nd, and Sr isotope compositions of the Monchepluton and Kemi intrusions

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Hong; Hanski, Eero; Li, Chao; Maier, Wolfgang D.; Huhma, Hannu; Mokrushin, Artem V.; Latypov, Rais; Lahaye, Yann; O'Brien, Hugh; Qu, Wen-Jun

    2016-08-01

    Significant PGE and Cr mineralization occurs in a number of 2.44-2.50-Ga mafic layered intrusions located across the Karelian and Kola cratons. The intrusions have been interpreted to be related to mantle plume activity. Most of the intrusions have negative ɛNd values of about -1 to -2 and slightly radiogenic initial Sr isotope compositions of about 0.702 to 0.703. One potential explanation is crustal contamination of a magma derived from a mantle plume, but another possibility is that the magma was derived from metasomatized sub-continental lithospheric mantle. Samples from the upper chromitite layers of the Kemi intrusion and most samples from the previously studied Koitelainen and Akanvaara intrusions have supra-chondritic γOs values indicating some crustal contamination, which may have contributed to the formation of chromitites in these intrusions. Chromite separates from the main ore zone of the Kemi and Monchepluton intrusions show nearly chondritic γOs, similar to the coeval Vetreny belt komatiites. We suggest that the Os isotope composition of the primitive magma was not significantly changed by crustal contamination due to a high Os content of the magma and a low Os content of the contaminant. Modeling suggests that the Os and Nd isotope compositions of the Monchepluton and Kemi intrusions cannot be explained by assuming a magma source in the sub-continental lithospheric mantle with sub-chondritic γOs. A better match for the isotope data would be a plume mantle source with chondritic Re/Os and Os isotope composition, followed by crustal contamination.

  18. Aspects of the magmatic geochemistry of bismuth

    USGS Publications Warehouse

    Greenland, L.P.; Gottfried, D.; Campbell, E.Y.

    1973-01-01

    Bismuth has been determined in 74 rocks from a differentiated tholeiitic dolerite, two calc-alkaline batholith suites and in 66 mineral separates from one of the batholiths. Average bismuth contents, weighted for rock type, of the Great Lake (Tasmania) dolerite, the Southern California batholith and the Idaho batholith are, 32, 50 and 70 ppb respectively. All three bodies demonstrate an enrichment of bismuth in residual magmas with magmatic differentiation. Bismuth is greatly enriched (relative to the host rock) in the calcium-rich accessory minerals, apatite and sphene, but other mineral analyses show that a Bi-Ca association is of little significance to the magmatic geochemistry of bismuth. Most of the bismuth, in the Southern California batholith at least, occurs in a trace mineral phase (possibly sulfides) present as inclusions in the rock-forming minerals. ?? 1973.

  19. Sublithospheric Triggers for Episodic Silicic Magmatism in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Gerya, T.; Vogt, K.; Schubert, M.

    2014-12-01

    The melt source and ascent mechanisms for crustal-scale silicic magmatism in subduction zones remain a matter of debate. Recent petrological-thermo-mechanical numerical experiments suggest that important physical controls of this process can be of sublithospheric origin. Firstly, deep sources of silicic magma can be related to episodic development of positively buoyant diapiric structures in the mantle wedge originated from deeply subducted rock mélanges (Gerya and Yuen, 2003; Castro and Gerya, 2008). Partial melting of these rapidly ascending lithologically mixed structures can produce silicic magmas with a relatively constant major element composition and variable time-dependent isotopic ratios inherited from the mélange (Vogt et al., 2013). Secondly, episodic injections of subduction-related mantle-derived mafic magmas into a partially molten hot zone of the arc lower crust can drive ascents of pre-existing felsic crustal magmas toward upper crustal levels. The injection of mafic magma induces overpressure in the lower crustal magma reservoir, which increases crustal stresses and triggers development of brittle/plastic fracture zones serving as conduits for the rapid episodic ascent of felsic magmas (Shubert et al., 2013). Our numerical results thus imply that subduction-related sublithospheric magma intrusions into the lower arc crust may both be the prime source for the generation of silicic magmas and the major physical driving mechanism for their episodic ascent toward upper crustal levels. References:Castro, A., and Gerya, T.V., 2008. Magmatic implications of mantle wedge plumes: experimental study. Lithos 103, 138-148. Gerya, T.V., and Yuen, D.A., 2003. Rayleigh-Taylor instabilities from hydration and melting propel "cold plumes" at subduction zones. Earth and Planetary Science Letters 212, 47-62.Schubert, M., Driesner, T., Gerya, T.V., Ulmer, P., 2013. Mafic injection as a trigger for felsic magmatism: A numerical study. Geochemistry, Geophysics

  20. Magmatism of the Shuteen Complex and Carboniferous subduction of the Gurvansaikhan terrane, South Mongolia

    NASA Astrophysics Data System (ADS)

    Batkhishig, Bayaraa; Noriyoshi, Tsuchiya; Greg, Bignall

    2010-03-01

    The Carboniferous Shuteen Complex, a volcano-plutonic ring complex associated with Cu-Au porphyry mineralization, is located in the Gurvansaikhan island arc terrane of South Mongolia. This paper presents new data on the petrography, major and trace element chemistry, and Sr-Nd isotopic chemistry of the Shuteen Complex. We discuss the relationship between volcanic and plutonic rocks of the complex, and consider their similarity to high-Al 2O 3 trondhjemite-tonalite-granodiorite and adakites. We also consider the origin, magma source, and dynamic processes of the Shuteen Complex; propose a petrogenetic model; and investigate the composition of the subducting slab and the features of arc volcanism at the time. We assess some of the magmatic processes likely to have occurred within the Shuteen Complex, such as Carboniferous slab subduction and partial melting, and examine their influence on magma composition. The Shuteen Complex is geochemically similar to adakite-type rocks. The complex is silica-saturated (SiO 2 ⩾ 56%), rich in Al 2O 3 (⩾15%), MgO (<6%), Y (⩽18 ppm), and Yb (⩽1.9 ppm), depleted in heavy rare earth elements, rich in Sr (>400 ppm), and depleted in high field strength elements. It also has a high Sr/Y value, and ( 87Sr/ 86Sr) I < 0.7040. The Shuteen Pluton yields a well-defined isochron age of 321 ± 9 Ma, whereas the age of the Shuteen andesites is 336 ± 24 Ma. The Shuteen Complex formed within an island arc setting, and partial melting was the dominant process during petrogenesis. The primary Shuteen magma had an adakitic composition and was probably derived from the partial melting of subducting oceanic crust, possibly with minor local interaction with mantle material. The results of quantitative modelling of mass balance and partial melt equilibrium for the magma source indicate that the subducting slab contained oceanic basalt and a minor component of oceanic sediment, which together with a restite eclogite phase formed the source of the

  1. Magmatic Evolution of the Coso Geothermal Area, California

    NASA Astrophysics Data System (ADS)

    Glazner, A. F.; Miller, J. S.; Leeman, W. P.; Johnson, B. R.; Monastero, F. C.

    2007-12-01

    as the geothermal production area is approached suggests that the magmatic flux is highest there even though erupted volumes are significantly larger outside the geothermal area. One scenario consistent with the above data is as follows. Post-subduction tectonic events triggered magmatism at 3.5 Ma, tapping fertile, subduction-metasomatized lithospheric mantle. Basalts stalled in and partially melted the mid-crust, generating a mixed-magma series and copious volcanism. Depletion of the mantle source by 2 Ma led to a hiatus in magmatism. A change in basalt chemistry to OIB- affinity in the last 1 Ma suggests a profound change in magma source - likely involving decompression melting of ascending asthenospheric mantle, perhaps related to lithosphere delamination. Injection of such magmas into the lower crust, would have generated rhyolites by remelting of earlier emplaced mafic bodies - imparting a juvenile isotopic signature in the late rhyolites. Precursory Pliocene magmatism is a common feature of other western U.S. geothermal areas, including Twin Peaks, The Geysers, and Long Valley.

  2. Rockfall source characterization at high rock walls in complex geological settings by photogrammetry, structural analysis and DFN techniques

    NASA Astrophysics Data System (ADS)

    Agliardi, Federico; Riva, Federico; Galletti, Laura; Zanchi, Andrea; Crosta, Giovanni B.

    2016-04-01

    Rockfall quantitative risk analysis in areas impended by high, subvertical cliffs remains a challenge, due to the difficult definition of potential rockfall sources, event magnitude scenarios and related probabilities. For this reasons, rockfall analyses traditionally focus on modelling the runout component of rockfall processes, whereas rock-fall source identification, mapping and characterization (block size distribution and susceptibility) are over-simplified in most practical applications, especially when structurally complex rock masses are involved. We integrated field and remote survey and rock mass modelling techniques to characterize rock masses and detect rockfall source in complex geo-structural settings. We focused on a test site located at Valmadrera, near Lecco (Southern Alps, Italy), where cliffs up to 600 m high impend on a narrow strip of Lake Como shore. The massive carbonates forming the cliff (Dolomia Principale Fm), normally characterized by brittle structural associations due to their high strength and stiffness, are here involved in an ENE-trending, S-verging kilometre-scale syncline. Brittle mechanisms associated to folding strongly controlled the nature of discontinuities (bedding slip, strike-slip faults, tensile fractures) and their attributes (spacing and size), as well as the spatial variability of bedding attitude and fracture intensity, with individual block sizes up to 15 m3. We carried out a high-resolution terrestrial photogrammetric survey from distances ranging from 1500 m (11 camera stations from the opposite lake shore, 265 pictures) to 150 m (28 camera stations along N-S directed boat routes, 200 pictures), using RTK GNSS measurements for camera station geo-referencing. Data processing by Structure-from-Motion techniques resulted in detailed long-range (1500 m) and medium-range (150 to 800 m) point clouds covering the entire slope with maximum surface point densities exceeding 50 pts/m2. Point clouds allowed a detailed

  3. Zircon U-Pb and Hf Isotopes Provide Insights into Triassic Magmatism in the Chinese Pamir

    NASA Astrophysics Data System (ADS)

    Imrecke, D. B.; Robinson, A. C.

    2015-12-01

    Recent research has improved understanding of Triassic magmatism and sedimentation in the Songpan-Ganzi/Hoh-Xil Terranes of Tibet and the implications for the closure of the Paleotethys ocean (Pullen et al., 2008; Ding et al,. 2013; Zhang et al., 2014). However, our knowledge of the age of magmatism in the laterally equivalent Karakul-Mazar Terrane in the Northern Pamir is limited. While previous investigations indicate Karakul-Mazar igneous bodies have generally documented crystallization ages 225-245 Ma, detrital zircon studies of Late Triassic/Early Jurassic strata within the Northern Pamir and the Tarim Basin record a significant quantity of <220 Ma zircons (Bershaw et al., 2011) sourced from the Pamir. 6 granite samples were analyzed for zircon U-Pb and Hf isotopes, representing plutons distributed across the Chinese Pamir, to determine the distribution of crystallization ages and chemical maturity of the magma source. Analyses yielded 204 Ma and 212-214 Ma zircon U-Pb crystallization ages. The dated samples yield ɛHf(t) values ranging from -6.7 to 9.6. Results show that a large volume of magmatic rocks in the Northern Pamir intruded in the Late Triassic prior to closure of the Paleotethys Ocean at ~200 Ma (Angiolini et al., 2013). Weakly positive and negative ɛHf(t) values indicate a primitive source for the dated magmatic bodies. Additionally, compliation of previously published data with these results suggests two pulses of magmatism, ~210 Ma and 230-245 Ma respectively. Finally, Triassic igneous bodies in the Pamir show similar crystallization ages and chemical signatures compared to plutons in the Songpan-Ganzi/Hoh-Xil Terranes to the east, suggesting lateral continuity of geodynamic processes across the terrane in the Mesozoic.

  4. A model for northern Vermont's Acadian magmatism with insight from Italy's Tuscan magmatic province

    SciTech Connect

    Westerman, D.S. . Dept. of Geology)

    1993-03-01

    S-type Devonian acidic intrusives in northern Vermont occur scattered throughout the turbiditic flysch sequence and pervasive horizon of mafic Standing Pond Volcanics of the Connecticut Valley--Gaspe Trough (CVGT). These granitoids formed in a successor basin that opened over the stalled Taconic subduction zone located between the Bronson Hill--Boundary Mountain Volcanic arc (east) and the ophiolite-bearing accretionary complex of the Green Mountains (west). Contact aureoles surrounding the granitoids are superimposed over low-pressure facies series metamorphic isograds that have concentric pattern correlated with the centers of intrusion. Italy's Tuscan Magmatic Province, also dominated by S-type acidic intrusives, developed between 7 and 2 Ma in a successor basin over an extinct subduction zone. In that case, the basin and its plutons developed when the Corsica-Sardinia plate pulled back to form the Tyrrhenian Sea after having collided with Italy to form the Apennine range approximately 10 m.y. earlier. In this model for northern Vermont, a volcanic arc and accretionary complex developed during Ordovician subduction, perhaps with continuing trench--arc separation due to shallow subduction. When the leading edge of continental North America entered the subduction zone, the process stalled and the subducted Iapetus slab continued to lose heat and increase density, promoting its separation from the overlying plate. Upwelling under the former forearc region rifted the crust to form the CVGT. The mantle-derived mafic melts rose, transferring heat to metamorphose and partially melt the basin fill. The Standing Pond Volcanics represent this melt that reached the surface at one stage and flooded the basin. Northern Vermont's granitoids rose, penetrating the domed strata above their source region, as extensional tectonism was replaced by Acadian compression.

  5. Modelling magmatic gas scrubbing in hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Di Napoli, Rossella; Aiuppa, Alessandro; Valenza, Mariano; Bergsson, Baldur; Ilyinskaya, Evgenia; Pfeffer, Melissa Anne; Rakel Guðjónsdóttir, Sylvía

    2015-04-01

    In volcano-hosted hydrothermal systems, the chemistry of deeply rising magmatic gases is extensively modified by gas-water-rock interactions taking place within the hydrothermal reservoir, and/or at shallow groundwaters conditions. These reactions can scrub reactive, water-soluble species (S, halogens) from the magmatic gas phase, so that their quantitative assessment is central to understanding the chemistry of surface gas manifestations, and brings profound implications to the interpretation of volcanic-hydrothermal unrests. Here, we present the results of numerical simulations of magmatic gas scrubbing, in which the reaction path modelling approach (Helgeson, 1968) is used to reproduce hydrothermal gas-water-rock interactions at both shallow (temperature up to 109°C; low-T model runs) and deep reservoir (temperature range: 150-250 °C; high-T model runs) conditions. The model was built based upon the EQ3/6 software package (Wolery and Daveler, 1992), and consisted into a step by step addition of a high-temperature magmatic gas to an initial meteoric water, in the presence of a dissolving aquifer rock. The model outputted, at each step of gas addition, the chemical composition of a new aqueous solution formed after gas-water-rock interactions; which, upon reaching gas over-pressuring (PgasTOT > Psat(H2O) at run T), is degassed (by single-step degassing) to separate a scrubbed gas phase. As an application of the model results, the model compositions of the separated gases are finally compared with compositions of natural gas emissions from Hekla volcano (T< 100°C) and from Krisuvik geothermal system (T> 100°C), resulting into an excellent agreement. The compositions of the model solutions are also in fair agreement with compositions of natural thermal water samples. We conclude that our EQ3/6-based reaction path simulations offer a realistic representation of gas-water-rock interaction processes occurring underneath active magmatic-hydrothermal systems

  6. Magmatic Volatile Histories From Apatite Phenocrysts

    NASA Astrophysics Data System (ADS)

    Boyce, J. W.; Hervig, R. L.

    2008-12-01

    Apatite phenocrysts contain as part of their structure all the major magmatic volatile elements (H, C, F, S, and Cl). For this reason we have explored the potential for apatite to record magmatic volatile histories [1], and compared the volatile record in apatite with that derived from melt inclusions [2]. Apatite has been observed at many central American volcanoes including Irazu, Arenal, Concepcion, Fuego, and Pacaya, and therefore there is great potential to extend this record, and use it to understand local and regional complexities in magmatic volatile behavior. Our results from Volcan Irazu (Costa Rica) are the first such measurements from the Central American volcanic arc. At Irazu, apatite [2] and melt inclusions [3] from the 1723 eruption have high to moderate H and Cl contents as compared with the 1963 apatite and melt inclusions. Both individual apatite crystals and populations of crystals from each sample are heterogeneous with respect to H, F, and Cl. Such heterogeneities could only be preserved for short periods of time (days to years) in the face of diffusive equilibration. In addition, core to rim volatile variations place relative temporal constraints on the processes affecting volatiles, and allow us to differentiate between monotonic evolution of a single magma batch and processes involving separate components. Using estimated partition coefficients, we can model melt volatile chemistry based on the apatite volatile data. The result of such modeling is that melt inclusions and apatite from the same hand samples yield identical, nonlinear trends in ternary H-F-Cl space, trends that - when combined with the relative timing given by volatile stratigraphy within zoned apatites - are consistent with late stage magma mixing between components with strikingly different volatile chemistry. References 1. Boyce, J.W. and R.L. Hervig, Magmatic degassing histories from apatite volatile stratigraphy. Geology, 2008. 36(1): p. 63. 2. Boyce, J.W. and R

  7. Magmatic Systems in 3-D

    NASA Astrophysics Data System (ADS)

    Kent, G. M.; Harding, A. J.; Babcock, J. M.; Orcutt, J. A.; Bazin, S.; Singh, S.; Detrick, R. S.; Canales, J. P.; Carbotte, S. M.; Diebold, J.

    2002-12-01

    , even if one data object lies behind another. Stereoscopic viewing is another powerful tool to investigate 3-D relationships between objects. This form of immersion is constructed through viewing two separate images that are interleaved--typically 48 frames per second, per eye--and synced through an emitter and a set of specialized polarizing eyeglasses. The polarizing lenses flicker at an equivalent rate, blanking the eye for which a particular image was not drawn, producing the desired stereo effect. Volumetric visualization of the ARAD 3-D seismic dataset will be presented. The effective use of transparency reveals detailed structure of the melt-lens beneath the 9°03'N overlapping spreading center (OSC) along the East Pacific Rise, including melt-filled fractures within the propagating rift-tip. In addition, range-gated images of seismic reflectivity will be co-registered to investigate the physical properties (melt versus mush) of the magma chamber at this locale. Surface visualization of a dense, 2-D grid of MCS seismic data beneath Axial seamount (Juan de Fuca Ridge) will also be highlighted, including relationships between the summit caldera and rift zones, and the underlying (and humongous) magma chamber. A selection of Quicktime movies will be shown. Popcorn will be served, really!

  8. Source to Sink studies in Spain: a catalogue and data set of Mediterranean river basins and deltaic systems

    NASA Astrophysics Data System (ADS)

    Canals, M.; Arnau, P.; Colas, S.

    2003-04-01

    Deltas and their alongshore extensions form most of the low Spanish Mediterranean shorelines. Prodeltas form the offshore, fine-grained continuation of deltaic edifices. Both large river systems, like the Ebro, and tens of small to very small river systems coexist in the Spanish Mediterrranean watershed. A general north (wetter) to south (drier) climatic gradient has an influence on precipitation and natural river discharge. Local precipitation anomalies appear mostly because of altitudinal differences. The Ebro is a especial case since its upper basin is under the influence of the Atlantic climate. This natural scenario has been profoundly disturbed by river management schemes. Damming and water diversion has been almost everywhere particularly intensive during the XXth century and has strongly reduced water and sediment discharge at river mouths. The Ebro River is the most dramatic example, with up to 97% of the basin surface now behind dams, and >90% reduction of the sediment discharge, suspended and bedload, at its mouth. Beach stability has much suffered because of the drastic reduction in the volumes of solid load reaching river mouth and being redistributed by alongshore currents. A similar situation, although perhaps less dramatic, could be depicted for other Mediterranean countries. However, a consistent and comprehensive catalogue and data set of Mediterranean river basins and deltaic systems are still lacking. Although some information can be easilly accessed (i.e., via Internet), lots of valuable information remain to be mined to a great extent from basin authorities in order to achieve a comprehensive compilation and understanding of source to sink river systems in the Spanish Mediterranean. A team from the University of Barcelona has collected a vast quantity of information on the totality of Spanish Mediterranean river systems, with a substantial amount of it kindly provided by river basin authorities. The collection includes DTMs, aerial photographs

  9. Hydrothermal activity at slow-spreading ridges: variability and importance of magmatic controls

    NASA Astrophysics Data System (ADS)

    Escartin, Javier

    2016-04-01

    Hydrothermal activity along mid-ocean ridge axes is ubiquitous, associated with mass, chemical, and heat exchanges between the deep lithosphere and the overlying envelopes, and sustaining chemiosynthetic ecosystems at the seafloor. Compared with hydrothermal fields at fast-spreading ridges, those at slow spreading ones show a large variability as their location and nature is controlled or influenced by several parameters that are inter-related: a) tectonic setting, ranging from 'volcanic systems' (along the rift valley floor, volcanic ridges, seamounts), to 'tectonic' ones (rift-bounding faults, oceanic detachment faults); b) the nature of the host rock, owing to compositional heterogeneity of slow-spreading lithosphere (basalt, gabbro, peridotite); c) the type of heat source (magmatic bodies at depth, hot lithosphere, serpentinization reactions); d) and the associated temperature of outflow fluids (high- vs.- low temperature venting and their relative proportion). A systematic review of the distribution and characteristics of hydrothermal fields along the slow-spreading Mid-Atlantic Ridge suggests that long-lived hydrothermal activity is concentrated either at oceanic detachment faults, or along volcanic segments with evidence of robust magma supply to the axis. A detailed study of the magmatically robust Lucky Strike segment suggests that all present and past hydrothermal activity is found at the center of the segment. The association of these fields to central volcanos, and the absence of indicators of hydrothermal activity along the remaining of the ridge segment, suggests that long-lived hydrothermal activity in these volcanic systems is maintained by the enhanced melt supply and the associated magma chamber(s) required to build these volcanic edifices. In this setting, hydrothermal outflow zones at the seafloor are systematically controlled by faults, indicating that hydrothermal fluids in the shallow crust exploit permeable fault zones to circulate. While

  10. Modeling Heat Transfer, Fluid Circulation and Permeability Alteration in Hydrothermal Systems with Loose Coupling to Magmatic Intrusion Modeling in the Lower Crust

    NASA Astrophysics Data System (ADS)

    Taron, J.; Karakas, O.; Mangan, M.; Dufek, J.; Ingebritsen, S.; Hickman, S. H.; Williams, C. F.

    2014-12-01

    The evolution of large scale hydrothermal systems entails spatially and temporally evolving permeability fields. During hydrothermal circulation, thermo-elastic stress and fluid pressure changes act upon partially open or hydrothermally altered fracture sets to modify permeability within the system, thereby shifting the patterns of circulation. To explore these interactions we are developing a thermo-hydromechanical (THM) simulator capable of coupling the dominant physics of the hydrothermal system and allowing flexibility in the use of monolithic or staggered numerical schemes. Permeability is allowed to evolve under several constitutive models tailored to both porous media and fractures, considering the influence of thermo-hydromechanical stress, creep, and elasto-plastic shear and dilation in a ubiquitously fractured medium. To expand our understanding of the long-term evolution of these systems, simulations incorporate information gleaned from the modeling of magmatic processes in the lower crust, where characteristics of the heat source are crucial in defining hydrothermal evolution. Results of a stochastic dike intrusion model are fed into the hydrothermal simulator to explore sensitivity relative to characteristics of the magmatic source. This is a first step to examining feedback mechanisms between heat transfer within geothermal fields and heat supply from the lower crust in a rigorous manner. We compare several simulations that elucidate the relative importance of magma intrusion rate and spatial distribution on overall heat transfer characteristics.

  11. Constraining earthquake source inversions with GPS data: 2. A two-step approach to combine seismic and geodetic data sets

    USGS Publications Warehouse

    Custodio, S.; Page, M.T.; Archuleta, R.J.

    2009-01-01

    We present a new method to combine static and wavefield data to image earthquake ruptures. Our combined inversion is a two-step procedure, following the work of Hernandez et al. (1999), and takes into account the differences between the resolutions of the two data sets. The first step consists of an inversion of the static field, which yields a map of slip amplitude. This inversion exploits a special irregular grid that takes into account the resolution of the static data. The second step is an inversion of the radiated wavefield; it results in the determination of the time evolution of slip on the fault. In the second step, the slip amplitude is constrained to resemble the static slip amplitude map inferred from the GPS inversion. Using this combined inversion, we study the source process of the 2004 M6 Parkfield, California, earthquake. We conclude that slip occurred in two main regions of the fault, each of which displayed distinct rupture behaviors. Slip initiated at the hypocenter with a very strong bilateral burst of energy. Here, slip was localized in a narrow area approximately 10 km long, the rupture velocity was very fast (???3.5 km/s), and slip only lasted a short period of time (<1 s). Then the rupture proceeded to a wider region 12-20 km northwest of the hypocenter. Here, the earthquake developed in a more moderated way: the rupture velocity slowed to ???3.0 km/s and slip lasted longer (1-2 s). The maximum slip amplitude was 0.45 m. Copyright 2009 by the American Geophysical Union.

  12. Detrital geochronology of unroofing magmatic complexes

    NASA Astrophysics Data System (ADS)

    Malusà, Marco Giovanni; Villa, Igor Maria; Vezzoli, Giovanni; Garzanti, Eduardo

    2010-05-01

    Tectonic reconstructions performed in recent years are increasingly based on petrographic (Dickinson & Suczek, 1979; Garzanti et al., 2007) and geochronological (Brandon et al., 1998; DeCelles et al., 2004) analyses of detrital systems. Detrital age patterns are traditionally interpreted as a result of cooling induced by exhumation (Jäger, 1967; Dodson, 1973). Such an approach can lead to infer extremely high erosion rates (Giger & Hurford 1989) that conflict with compelling geological evidence (Garzanti & Malusà, 2008). This indicates that interpretations solely based on exhumational cooling may not have general validity (Villa, 2006). Here we propose a new detrital geochronology model that takes into account the effects of both crystallization and exhumational cooling on geochronometers, from U-Pb on zircon to fission tracks on apatite. This model, specifically designed for unroofing magmatic complexes, predicts both stationary and moving mineral-age peaks. Because its base is the ordinary interaction between endogenic and exogenic processes, it is applicable to any geological setting. It was tested on the extremely well-studied Bregaglia-Bergell pluton in the Alps, and on the sedimentary succession derived from its erosion. The consistency between predicted and observed age patterns validates the model. Our results demonstrate that volcanoes were active on top of the growing Oligocene Alps, and resolve a long-standing paradox in quantitative erosion-sedimentation modelling, the scarcity of sediment during apparently fast erosion. Dickinson, W. R. & Suczek, C. A. Plate tectonics and sandstone composition. Am. Assoc. Petrol. Geol. Bull. 63, 2164-2172 (1979). Garzanti, E., Doglioni, C., Vezzoli. G. & Andò, S. Orogenic belts and orogenic sediment provenance. J. Geol. 115, 315-334 (2007). Brandon, M. T., Roden-Tice, M. K. & Garver, J. I. Cenozoic exhumation of the Cascadia accretionary wedge in the Olympic Mountains, northwest Washington State. Geol. Soc. Am. Bull

  13. Intrusive LIPs: Deep crustal magmatic processes during the emplacement of Large Igneous Provinces

    NASA Astrophysics Data System (ADS)

    Richards, M. A.; Karlstrom, L.

    2011-12-01

    Large Igneous Provinces (LIPs) are characterized by magmatic activity on two distinct timescales. While these provinces have total active lifetimes of order 10-30 Ma, most of the erupted volume is emplaced within <1 Ma in many cases. The latter timescale is likely controlled by magmatic intrusion/evolution processes within the deep crust. We present seismic evidence for 5-15 km thick Moho-level ultramafic intrusive/cumulate layers underlying Phanerozoic LIPs worldwide [Ridley and Richards, 2010]. These deep crustal bodies are both observed and predicted to have volumes at least as large as the extrusive components of flood volcanism. The evidence for these layers is particularly clear for oceanic LIPs (plateaus). We hypothesize that thermally activated creep of the lower crust due to magma chamber emplacement controls a transition from largely extrusive to largely intrusive magmatism during mantle plume impingement on the lithosphere [Karlstrom and Richards, 2011]. We explore this hypothesis by modeling the thermomechanical evolution of Moho-level magma chambers. Comparing the timescale for viscoelastic relaxation of intrusion-related stresses with the timescale for sill formation and magma differentiation, we find that fracture processes leading to diking from Moho levels may plausibly be shut off on a timescale of ~1 Ma. Continued melt influx therefore results in intrusive magmatism, which may be manifest as plateau growth in oceanic settings. We suggest that maximum intrusion size may be limited by crustal thickness, resulting in smaller volume individual eruptions in oceanic versus continental LIPs.

  14. Ga/Mg ratio as a new geochemical tool to differentiate magmatic from metamorphic blue sapphires

    NASA Astrophysics Data System (ADS)

    Peucat, J. J.; Ruffault, P.; Fritsch, E.; Bouhnik-Le Coz, M.; Simonet, C.; Lasnier, B.

    2007-10-01

    Using ICP-MS-LA analyses, we demonstrate that the use of the Ga/Mg ratio, in conjunction with the Fe concentration, is an efficient tool in discriminating between "metamorphic" and "magmatic" blue sapphires. Magmatic blue sapphires found in alkali basalts (e.g. southeastern Asia, China, Africa) are commonly medium-rich to rich in Fe (with average contents between 2000 and 11000 ppm), high in Ga (> 140 ppm), and low in Mg (generally < 20 ppm) with high Ga/Mg ratios (> 10). Conversely, metamorphic blue sapphires found in basalts (e.g. Pailin pastel) and in metamorphic terrains (e.g. Mogok, Sri Lanka, Ilakaka) are characterized by low average iron contents (< 3000 ppm), low Ga contents (< 75 ppm), and high Mg values (> 60 ppm) with low average Ga/Mg ratios (< 10). Basaltic magmatic sapphires have Fe, Ga and Mg contents similar to those obtained for primary magmatic sapphires found in the Garba Tula syenite. This suggests that these both sets of sapphires have a possible common "syenitic" origin, as previously proposed from other criteria. In addition, plumasite-related sapphires and metamorphic sapphires also exhibit similar composition in trace elements. Based on results from the present study, we suggest that fluid circulations during a metamorphic stage produced metasomatic exchanges between mafic and acidic rocks (plumasite model), thus explaining the high Mg contents and converging Ga/Mg ratios observed in metamorphic sapphires.

  15. A General Model for Shallow Magmatic Intrusions

    NASA Astrophysics Data System (ADS)

    Thorey, C.; Michaut, C.

    2015-12-01

    Shallow magmatic intrusions make room for themselves by upward bending of the elastic overburden. Previous studies have shown that the bending of the overlying layer first controls the dynamics. Then, when the radius reaches a few times the flexural wavelength of the overburden, it transitions to a gravity current regime. This model predicts the appropriate geometry for both terrestrial laccoliths and large mafic sills. However, it underestimates the absolute dimensions of these magmatic intrusions; in particular, it requires abnormally high viscosity to reconcile both observations and predictions. To get some insights into the effective flow viscosity, we develop a model that account for the cooling of such elastic-plated gravity currents. We show that the coupling between the temperature field and the flow itself leads to the formation of a highly viscous region at the tip that slows down the spreading in both regimes. The intrusions are predicted to be thicker and their dimensions, especially in the bending regime, are now consistent with observations. By introducing the potentially complex structure of the overburden, we also show that the topography largely contributes to constrain the final intrusion morphology. For instance, in the case of an intrusion centered below a circular depression, the model predicts that the lithostatic increase at the crater rim prevents the magma from spreading laterally and enhances the thickening of the intrusion. This model has already proven successful in reproducing the deformations observed on potential intrusion centered below lunar impact craters. Caldera complexes often exhibit ground deformations that might be associated to the formation of shallow magmatic intrusions. InSAR imaging and GPS measurements now provide efficient tools to monitor these deformations. We conclude this study by examining the ability of the model to reproduce the deformation observed in several caldera complexes.

  16. Tritium and stable isotopes of magmatic waters

    NASA Astrophysics Data System (ADS)

    Goff, F.; McMurtry, G. M.

    2000-04-01

    To investigate the isotopic composition and age of water in volcanic gases and magmas, we analyzed samples from 11 active volcanoes ranging in composition from tholeiitic basalt to rhyolite: Mount St. Helens (USA), Kilauea (USA), Pacaya (Guatemala), Galeras (Colombia), Satsuma Iwo-Jima (Japan), Sierra Negra and Alcedo (Ecuador), Vulcano (Italy), Parı´cutin (Mexico), Kudryavy (Russia), and White Island (New Zealand). Tritium at relatively low levels (0.1-5 T.U.) is found in most emissions from high-temperature volcanic fumaroles sampled, even at discharge temperatures >700°C. Although magmatic fluids sampled from these emissions usually contain high CO 2, S total, HCl, HF, B, Br, 3He R/ RA, and low contents of air components, stable isotope and tritium relations of nearly all such fluids show mixing of magmatic volatiles with relatively young meteoric water (model ages≤75 y). Linear δD/ δ18O and 3H/ δ18O mixing trends of these two end-members are invariably detected at arc volcanoes. Tritium is also detected in fumarole condensates at hot spot basalt volcanoes, but collecting samples approaching the composition of end-member magmatic fluid is exceedingly difficult. In situ production of 3H, mostly from spontaneous fission of 238U in magmas is calculated to be <0.001 T.U., except for the most evolved compositions (high U, Th, and Li and low H 2O contents). These values are below the detection limit of 3H by conventional analytical techniques (about 0.01 T.U. at best). We found no conclusive evidence that natural fusion in the Earth produces anomalous amounts of detectable 3H (>0.05 T.U.).

  17. Magmatic volatiles in explosive rhyolitic eruptions

    SciTech Connect

    Eichelberger, J.C.; Westrich, H.R.

    1981-07-01

    Obsidian clasts in rhyolitic tephra deposits preserve preeruption magmatic volatile contents, providing a direct means for determining the volatile content of explosively erupted magmas. Small to moderate volume Plinian eruptions (10/sup -3/ to 10/sup -1/ km/sup 3/) appear to be driven by 0.5--1.0 wt.% volatiles, consisting dominantly of H/sub 2/O with minor CO/sub 2/. Analysis of obsidian from eruptive sequences consisting of tephra and flows indicates that this hydrous magma abruptly overlies magma with only 0.1--0.2 wt.% H/sub 2/O.

  18. Real Time Tracking of Magmatic Intrusions by means of Ground Deformation Modeling during Volcanic Crises.

    PubMed

    Cannavò, Flavio; Camacho, Antonio G; González, Pablo J; Mattia, Mario; Puglisi, Giuseppe; Fernández, José

    2015-06-09

    Volcano observatories provide near real-time information and, ultimately, forecasts about volcano activity. For this reason, multiple physical and chemical parameters are continuously monitored. Here, we present a new method to efficiently estimate the location and evolution of magmatic sources based on a stream of real-time surface deformation data, such as High-Rate GPS, and a free-geometry magmatic source model. The tool allows tracking inflation and deflation sources in time, providing estimates of where a volcano might erupt, which is important in understanding an on-going crisis. We show a successful simulated application to the pre-eruptive period of May 2008, at Mount Etna (Italy). The proposed methodology is able to track the fast dynamics of the magma migration by inverting the real-time data within seconds. This general method is suitable for integration in any volcano observatory. The method provides first order unsupervised and realistic estimates of the locations of magmatic sources and of potential eruption sites, information that is especially important for civil protection purposes.

  19. Real Time Tracking of Magmatic Intrusions by means of Ground Deformation Modeling during Volcanic Crises

    PubMed Central

    Cannavò, Flavio; Camacho, Antonio G.; González, Pablo J.; Mattia, Mario; Puglisi, Giuseppe; Fernández, José

    2015-01-01

    Volcano observatories provide near real-time information and, ultimately, forecasts about volcano activity. For this reason, multiple physical and chemical parameters are continuously monitored. Here, we present a new method to efficiently estimate the location and evolution of magmatic sources based on a stream of real-time surface deformation data, such as High-Rate GPS, and a free-geometry magmatic source model. The tool allows tracking inflation and deflation sources in time, providing estimates of where a volcano might erupt, which is important in understanding an on-going crisis. We show a successful simulated application to the pre-eruptive period of May 2008, at Mount Etna (Italy). The proposed methodology is able to track the fast dynamics of the magma migration by inverting the real-time data within seconds. This general method is suitable for integration in any volcano observatory. The method provides first order unsupervised and realistic estimates of the locations of magmatic sources and of potential eruption sites, information that is especially important for civil protection purposes. PMID:26055494

  20. Real Time Tracking of Magmatic Intrusions by means of Ground Deformation Modeling during Volcanic Crises

    NASA Astrophysics Data System (ADS)

    Cannavò, Flavio; Camacho, Antonio G.; González, Pablo J.; Mattia, Mario; Puglisi, Giuseppe; Fernández, José

    2015-06-01

    Volcano observatories provide near real-time information and, ultimately, forecasts about volcano activity. For this reason, multiple physical and chemical parameters are continuously monitored. Here, we present a new method to efficiently estimate the location and evolution of magmatic sources based on a stream of real-time surface deformation data, such as High-Rate GPS, and a free-geometry magmatic source model. The tool allows tracking inflation and deflation sources in time, providing estimates of where a volcano might erupt, which is important in understanding an on-going crisis. We show a successful simulated application to the pre-eruptive period of May 2008, at Mount Etna (Italy). The proposed methodology is able to track the fast dynamics of the magma migration by inverting the real-time data within seconds. This general method is suitable for integration in any volcano observatory. The method provides first order unsupervised and realistic estimates of the locations of magmatic sources and of potential eruption sites, information that is especially important for civil protection purposes.

  1. Real Time Tracking of Magmatic Intrusions by means of Ground Deformation Modeling during Volcanic Crises.

    PubMed

    Cannavò, Flavio; Camacho, Antonio G; González, Pablo J; Mattia, Mario; Puglisi, Giuseppe; Fernández, José

    2015-01-01

    Volcano observatories provide near real-time information and, ultimately, forecasts about volcano activity. For this reason, multiple physical and chemical parameters are continuously monitored. Here, we present a new method to efficiently estimate the location and evolution of magmatic sources based on a stream of real-time surface deformation data, such as High-Rate GPS, and a free-geometry magmatic source model. The tool allows tracking inflation and deflation sources in time, providing estimates of where a volcano might erupt, which is important in understanding an on-going crisis. We show a successful simulated application to the pre-eruptive period of May 2008, at Mount Etna (Italy). The proposed methodology is able to track the fast dynamics of the magma migration by inverting the real-time data within seconds. This general method is suitable for integration in any volcano observatory. The method provides first order unsupervised and realistic estimates of the locations of magmatic sources and of potential eruption sites, information that is especially important for civil protection purposes. PMID:26055494

  2. Rhenium and Iridium Partitioning in Silicate and Magmatic Spinels: Implications for Planetary Magmatism and Mantles

    NASA Technical Reports Server (NTRS)

    Righter, K.

    2001-01-01

    Highly siderophile elements Re, Ru and Ir partition strongly into spinel structures with large octahedral sites. New experimental results for both magmatic and silicate spinels will be presented with a few planetary implications. Additional information is contained in the original extended abstract.

  3. Post-supereruption magmatic recovery at Taupo volcano, New Zealand

    NASA Astrophysics Data System (ADS)

    Barker, S. J.; Wilson, C. J.; Baker, J. A.; Wooden, J. L.; Charlier, B. L.

    2012-12-01

    Large explosive silicic supereruptions have received much attention because of the challenges in explaining how such large volumes of magma are accumulated and stored and over what time intervals. The processes that follow the main eruption are less fully documented and, in particular, how and on what time scales the overall magma system moves into a post-caldera mode of activity. The 530 km3 Oruanui eruption from Taupo volcano, New Zealand, is the world's youngest (25.4 ka) supereruption. Following this event and after only 5 kyr of quiescence, Taupo volcano erupted three dacitic pyroclastic units of modest volume (< 0.1 km3), followed by another 5 kyr year time break, and then eruption of the modern sequence of rhyolitic units starting at 12 ka. Here we present major and trace element bulk rock, glass and mineral chemistry, along with U/Th model-age dating of zircons from pumices erupted from the post-Oruanui dacites and rhyolites to investigate how the magmatic system was reactivated following the Oruanui supereruption. The dacitic units contain strongly zoned plagioclase and orthopyroxene crystals with wide compositional variations, including core compositions consistent with derivation from less evolved mafic magmas. Bulk rock compositions also imply that the dacites are derived from parental magmas of contrasting composition to that of the Oruanui magma. Zircon model ages and crystal compositions in the first erupted rhyolites also indicate that there is minimal inheritance of crystals from either of the two dominant modes (35 and 90 ka) in the Oruanui magma source, and that the magmatic system was effectively reset after the Oruanui supereruption. Zircons in the rhyolites predominantly have post-Oruanui model ages, with model-age spectra centered close to eruption ages and subordinate pre-300 ka plutonic and pre-100 Ma greywacke grains. In addition, there is consistent inheritance of grains between the post-Oruanui eruption groups, allowing the

  4. Magmatic Degassing and the Volatile Depletion of the Moon

    NASA Astrophysics Data System (ADS)

    Rutherford, M. J.; Saal, A. E.; Hauri, E.

    2015-12-01

    The detection of highly volatile elements in lunar volcanic glasses and melt inclusions has provided the first definitive evidence for the accretion and retention of these elements in the Moon's interior1,2. Measurement of H in lunar apatite, at levels similar to terrestrial apatite, has added weight to this discovery3,4. These results are at odds with the longest-standing observations that the abundances of highly- and moderately-volatile elements in lunar basalts are as much as 1000 times more depleted than in terrestrial basalts5. We will show that most of these apparent contradictions have arisen due to the previously unappreciated importance of a single widespread process, magmatic degassing. Degassing occurs in all eruptions of magma, with the consequent release of volatile elements into an exsolved vapor phase. We use ours and previously published results to evaluate lunar magmatic degassing and to show that A) volatile element contents for the bulk silicate Moon (BSM) are only moderately depleted compared with the bulk silicate Earth (range 0.5-0.1, avg. 0.25 x BSE), B) they essentially overlap the composition of the terrestrial depleted MORB source and C) the volatile depletion pattern for the BSM is largely flat, and so does not correlate with condensation temperature at 10-4 bars, nor with bond energy for likely ligands. Published high-precision Sr and Pb isotope ratios on well-dated lunar rocks6-8 reveal 87Rb/86Sr and 238U/204Pb ratios of the lunar mantle a factor of 0.3-0.5 and 0.28-0.85 depleted compared to those of the BSE, respectively; lending support to our estimates for the abundances of Rb (0.245 x BSE) and Pb (0.187 x BSE) in the BSM. Before the Moon's extent of volatile depletion can be confidently attributed to the accretion processes, magmatic degassing must be examined and critically evaluated. References [1] Saal et al., 2008. Nature 454, 192. [2] Hauri et al., 2015. FEPS 409, 252. [3] Boyce et al., 2014. Sc. 344, 400. [4] Anand et al

  5. Grenvillian magmatism in the northern Virginia Blue Ridge: Petrologic implications of episodic granitic magma production and the significance of postorogenic A-type charnockite

    USGS Publications Warehouse

    Tollo, R.P.; Aleinikoff, J.N.; Borduas, E.A.; Dickin, A.P.; McNutt, R.H.; Fanning, C.M.

    2006-01-01

    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

  6. DEVELOPING AND EXPLOITING A UNIQUE SEISMIC DATA SET FROM SOUTH AFRICAN GOLD MINES FOR SOURCE CHARACTERIZATION AND WAVE PROPAGATION

    SciTech Connect

    Julia, J; Nyblade, A A; Gok, R; Walter, W R; Linzer, L; Durrheim, R

    2008-07-08

    In this project, we are developing and exploiting a unique seismic data set to address the characteristics of small seismic events and the associated seismic signals observed at local (< 200 km) and regional (< 2000 km) distances. The dataset is being developed using mining-induced events from 3 deep gold mines in South Africa recorded on inmine networks (< 1 km) comprised of tens of high-frequency sensors, a network of 4 broadband stations installed as part of this project at the surface around the mines (1-10 km), and a network of existing broadband seismic stations at local/regional distances (50-1000 km) from the mines. After 1 year of seismic monitoring of mine activity (2007), over 10,000 events in the range -3.4 < ML < 4.4 have been catalogued and recorded by the in-mine networks. Events with positive magnitudes are generally well recorded by the surface-mine stations, while magnitudes 3.0 and larger are seen at regional distances (up to {approx}600 km) in high-pass filtered recordings. We have analyzed in-mine recordings in detail at one of the South African mines (Savuka) to (i) improve on reported hypocentral locations, (ii) verify sensor orientations, and (iii) determine full moment tensor solutions. Hypocentral relocations on all catalogued events have been obtained from P- and S-wave travel-times reported by the mine network operator through an automated procedure that selects travel-times falling on Wadati lines with slopes in the 0.6-0.7 range; sensor orientations have been verified and, when possible, corrected by correlating P-, SV-, and SH-waveforms obtained from theoretical and empirical (polarization filter) rotation angles; full moment tensor solutions have been obtained by inverting P-, SV-, and SH- spectral amplitudes measured on the theoretically rotated waveforms with visually assigned polarities. The relocation procedure has revealed that origin times often necessitate a negative correction of a few tenths of second and that hypocentral

  7. From birth to death of arc magmatism: The igneous evolution of Komandorsky Islands recorded tectonic changes during 50 Ma of westernmost Aleutian history

    NASA Astrophysics Data System (ADS)

    Höfig, T. W.; Portnyagin, M.; Hoernle, K.; Hauff, F. F.; van den Bogaard, P.; Garbe-Schoenberg, C.

    2013-12-01

    The Komandorsky Islands form the westernmost end of the Aleutian Island Arc. Four igneous complexes, spanning almost 50 Ma of magmatism, have previously been identified (Ivaschenko et al., 1984: Far East Scientific Centre, Vladivostok, 192 pp.). The petrogenesis of this protracted magmatic record and accurate absolute ages of events, however, remain poorly constrained. Our study investigates the relationship between magma composition and tectonic setting. The Komandorsky igneous basement formed in subduction zone setting. It hosts some of the oldest igneous rocks of the entire Aleutian Arc with the onset of magmatism occurring at 47 Ma. This early stage was characterized by classic fluid-dominated arc volcanism, which produced two coeval but likely genetically unrelated magmatic series of tholeiitic mafic and tholeiitic to calc-alkaline felsic rocks. To date, no boninites have been found and therefore arc initiation is different at the Aleutians than at Izu-Bonin-Marianas or the oldest rocks in the Aleutians have yet to be discovered. The prolonged production of the contrasting basalt-rhyolite association on Komandorsky Islands had lasted ~25 Ma and ceased around the Oligocene-Miocene boundary. Concurrently to this long-lasting activity, a gradual transition to a different mode of arc magmatism took place reflected by newly discovered Sr-enriched, HREE-depleted calc-alkaline basaltic andesitic lavas of mid-upper Eocene age spanning a time of at least ~7 Ma. This so-called Transition Series displays a moderate garnet signature marking the increased contribution of a slab-melt component to the magma sources of the Komandorsky Islands. Slab-melt contribution increased with decreasing age leading to strongly adakitic magmatism as early as ~33 Ma (Lower Oligocene), reflected by eruption of high-Sr (up to 2,500 ppm), highly HREE-depleted Adak-type magnesian basaltic andesites and andesites. These remarkable magmas became predominant during the Lower Miocene. They were

  8. The Modulation of Crustal Magmatic Systems by Tectonic Forcing

    NASA Astrophysics Data System (ADS)

    Karakas, O.; Dufek, J.

    2010-12-01

    The amount, location and residence time of melt in the crust significantly impacts crustal structure and influences the composition, frequency, and volume of eruptive products. In this study, we develop a two dimensional model that simulates the response of the crust to prolonged mantle-derived intrusions in arc environments. The domain includes the entire crustal section and upper mantle and focuses on the evolving thermal structure due to intrusions and external tectonic forcing. Magmatic intrusion into the crust can be accommodated by extension or thickening of the crust or some combination of both mechanisms. Additionally, external tectonic forcing can generate thicker crustal sections, while tectonic extension can significantly thin the crust. We monitor the thermal response, melt fraction and surface heat flux for different tectonic conditions and melt flux from the mantle. The amount of crustal melt versus fractionated primary mantle melts present in the crustal column helps determine crustal structure and growth through time. We express the amount of crustal melting in terms of an efficiency; we define the melting efficiency as the ratio of the melted volume of crustal material to the volume of melt expected from a strict enthalpy balance as explained by Dufek and Bergantz (2005). Melting efficiencies are less than 1 in real systems because heat diffuses to sections of the crust that never melt. In general, thick crust and crust experiencing extended compressional regimes results in an increased melting efficiency; and thin crust and crust with high extension rates have lower efficiency. In most settings, maximum efficiencies are less than 0.05-0.10. We also observe that with a geophysically estimated flux, the mantle-derived magma bodies build up isolated magma pods that are distributed in the crust. One of the aspects of this work is to monitor the location and size of these magma chambers in the crustal column. We further investigate the rheological

  9. Magmatic Processes and Systems Deduced from Single Crystals

    NASA Astrophysics Data System (ADS)

    Davidson, J.; Bezard, R. C.; Morgan, D. J.; Ginibre, C.

    2014-12-01

    When crystals grow in liquids the composition of their outermost layer will reflect that of the host with which they are in equilibrium and will therefore record the liquid composition, pressure and temperature.. Following separation from their sources, magmas differentiate. This change in liquid composition is driven largely by crystallisation in response to cooling or decompression. Other open system processes such as mixing and contamination are common. These can lead to abrupt changes in trace element and isotopic composition, accompanied by petrographic features, such as dissolution surfaces or zones of melt inclusions. Where such careful mineral-scale studies have been performed, the prevalence of open system processes is clear. In many cases these are shown by core-rim isotopic variations. Crystal-scale compositional variations in the context of whole rock compositions and petrography have allowed us to show crustal assimilation even from regions of supposedly oceanic crust such as the Lesser Antilles. In tandem with tracking magma evolution, core-rim analyses of appropriate crystals have also provided diffusion profiles which reflect timescales of magmatic processes. A key point, long recognised by Bruce Marsh, is that in situ geochemical data should be considered in a petrographic context in order to gain the most (and most credible) insights on the workings of magma systems from hand specimen to whole volcano/pluton scales: The petrographic microscope is not dead yet Identification of magmatic processes from in situ scrutiny allows us to synthesise the architectures and inner workings of magma systems. The evidence for interaction among magmas in many systems is compelling and suggests that many exist as stacked dike-sill arrangements with wall-rock focussed crystal growth and mush zones. These are consistent with many of the systematics suggested some time ago by Bruce Marsh

  10. Magmatic heat and the El Nino cycle

    USGS Publications Warehouse

    Shaw, H.R.; Moore, J.G.

    1988-01-01

    Large submarine lava flows with apparent volumes exceeding 10 km3 have recently been imaged on the deep ocean floor in various parts of the Pacific by means of GLORIA and SeaMarc side-looking sonar surveys. Such flows may produce thermal anomalies large enough to perturb the cyclic processes of the ocean and could be a factor in the genesis of El Nino phenomena. We find that known volume rates of mid-ocean magma production could generate repetitive thermal anomalies as large as 10% of the average El Nino sea surface anomaly at intervals of about 5 years (the mean interval of El Nino events between 1935 and 1984). Likewise, estimated rates of eruption, cooling of lava on the seafloor, and transfer of heat to the near-surface environment could reasonably produce a thermal anomaly comparable to that associated with El Nino. Larger magmatic events, associated with fluctuations in the total magmatic power and seismicity along the East Pacific Rise, are possible at longer intervals and may explain the extreme size of some El Nino events, such as that of 1982-1983. -Authors

  11. Claritas rise, Mars: Pre-Tharsis magmatism?

    USGS Publications Warehouse

    Dohm, J.M.; Anderson, R.C.; Williams, J.-P.; Ruiz, J.; McGuire, P.C.; Buczkowski, D.L.; Wang, R.; Scharenbroich, L.; Hare, T.M.; Connerney, J.E.P.; Baker, V.R.; Wheelock, S.J.; Ferris, J.C.; Miyamoto, H.

    2009-01-01

    Claritas rise is a prominent ancient (Noachian) center of tectonism identified through investigation of comprehensive paleotectonic information of the western hemisphere of Mars. This center is interpreted to be the result of magmatic-driven activity, including uplift and associated tectonism, as well as possible hydrothermal activity. Coupled with its ancient stratigraphy, high density of impact craters, and complex structure, a possible magnetic signature may indicate that it formed during an ancient period of Mars' evolution, such as when the dynamo was in operation. As Tharsis lacks magnetic signatures, Claritas rise may pre-date the development of Tharsis or mark incipient development, since some of the crustal materials underlying Tharsis and older parts of the magmatic complex, respectively, could have been highly resurfaced, destroying any remanent magnetism. Here, we detail the significant characteristics of the Claritas rise, and present a case for why it should be targeted by the Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Express spacecrafts, as well as be considered as a prime target for future tier-scalable robotic reconnaissance. ?? 2009 Elsevier B.V.

  12. A 17 Ma onset for the post-collisional K-rich calc-alkaline magmatism in the Maghrebides: Evidence from Bougaroun (northeastern Algeria) and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Abbassene, Fatiha; Chazot, Gilles; Bellon, Hervé; Bruguier, Olivier; Ouabadi, Aziouz; Maury, René C.; Déverchére, Jacques; Bosch, Delphine; Monié, Patrick

    2016-04-01

    Bougaroun is the largest pluton (~ 200 km2) in the 1200 km-long Neogene magmatic belt located along the Mediterranean coast of Maghreb. New U-Pb dating on zircons and K-Ar ages on whole rocks and separated minerals document its emplacement at 17 Ma within the Lesser Kabylian basement, a continental block that collided with the African margin during the Neogene. This Upper Burdigalian intrusion is therefore the oldest presently identified K-rich calc-alkaline massif in the whole Maghrebides magmatic lineament and marks the onset of its activity. The Bougaroun peraluminous felsic rocks display a very strong crustal imprint. Associated mafic rocks (LREE-enriched gabbros) have preserved the "orogenic" (subduction-related) geochemical signature of their mantle source. Older depleted gabbros cropping out at Cap Bougaroun are devoid of clear subduction-related imprint and yielded Ar-Ar hornblende ages of 27.0 ± 3.0 Ma and 23.3 ± 3.2 Ma. We suggest that they are related to the Upper Oligocene back-arc rifted margin and Early Miocene oceanic crust formation of the nearby Jijel basin, an extension of the Algerian basin developed during the African (Tethyan) slab rollback. The fact that the Bougaroun pluton intrudes exhumed Kabylian lower crustal units, mantle slices and flysch nappes indicates that the Kabylian margin was already stretched and in a post-collisional setting at 17 Ma. We propose a tectono-magmatic model involving an Early Miocene Tethyan slab breakoff combined with delamination of the edges of the African and Kabylian continental lithospheres. At 17 Ma, the asthenospheric thermal flux upwelling through the slab tear induced the thermal erosion of the Kabylian lithospheric mantle metasomatized during the previous subduction event and triggered its partial melting. We attribute the strong trace element and isotopic crustal signature of Bougaroun felsic rocks to extensive interactions between ascending mafic melts and the African crust underthrust beneath the

  13. Imaging the magmatic and hydrothermal systems of Long Valley Caldera, California with magnetotellurics

    NASA Astrophysics Data System (ADS)

    Peacock, J.; Mangan, M.; McPhee, D.; Ponce, D. A.

    2015-12-01

    Long Valley Caldera (LVC) in Eastern California contains active hydrothermal systems, areas of episodic seismicity, and areas of elevated gas emissions, all of which are related to a deeper magmatic system that is not well characterized. To better image the Long Valley magmatic system, 60 full-tensor broadband magnetotelluric (MT) stations were collected in LVC and modeled in three-dimensions to constrain the subsurface electrical resistivity structure down to 30 km. Three conductive zones are imaged in the preferred resistivity model. The most prominent conductive zone (<7 Ohm-m) is located 5 km beneath the resurgent dome (near the center of Long Valley Caldera), where it elongates in a north-south direction, and has westward connection to the surface close to well 44-16 near Deer Mountan. This conductive zone is interpreted to be an accumulation zone of hydrothermal fluids originating from a deeper magmatic source. The shape of the conductive body suggests that the fluids pool under the resurgent dome and migrate westward, upwelling just south of well 44-16 to feed the near surface geothermal system. A second conductive zone (<10 Ohm-m) is 4 km southeast of the resurgent dome and 5 km deep and coincident with the seismic swarm of 2014. This is another zone of fluid accumulation, where the source could be the fluid accumulation zone to the west or an independent deeper source. The third conductive anomaly (<10 Ohm-m) is a few kilometers south of the resurgent dome below a depth of 15 km, and collocated with a low p- and s-wave velocity zone, and directly beneath a GPS inflation area, all of which advocate for a magma mush zone of as much as 30% interstitial melt. The preferred resistivity model suggests an accumulation of hydrothermal fluids 5 km below the resurgent dome that originates from a deeper magmatic source at 15 km depth.

  14. Identification of the sources of Escherichia coli in a watershed using carbon-utilization patterns and composite data sets.

    PubMed

    Moussa, Samir H; Massengale, Rene D

    2008-06-01

    The field of bacterial source tracking (BST) has been rapidly evolving to meet the demands of water pollution analysis, specifically the contamination of waterways and drinking water reservoirs by point source and nonpoint source pollution. The goal of the current study was to create a BST library based on carbon-utilization patterns (CUP) for predicting sources of E. coli in a watershed, to compare this library to an antibiotic-resistance analysis (ARA) library previously published for the same isolates, and to determine the efficacy of using a composite dataset which combines data from both datasets into a single library for predicting the source of unknown isolates. This was accomplished by generating a CUP dataset and a composite ARA-CUP dataset for the E. coli isolates from known fecal sources within a watershed. These libraries were then used to predict the sources of E. coli isolates collected from 13 water sites in the same watershed and compared in regard to predictive accuracy. The dominant sources of E. coli in the South Bosque watershed were cattle as identified by all three methods. The 6-source composite library had higher average rates of correct classification (96.7%), specificity (99.2%), positive-predictive value (99.1%), and negative-predictive value (96.8%) than either the ARA or CUP 6 source libraries (ARCC 80.1% and 86.7% respectively). The current study is the first field study to compare two phenotypic methods, Antibiotic Resistance Analysis (ARA) and Carbon Utilization Profiling (CUP). This study is also the first to combine both of these methods to create a composite "toolbox" type approach.

  15. Investigating the long-term geodetic response to magmatic intrusions at volcanoes in northern California

    NASA Astrophysics Data System (ADS)

    Parker, A. L.; Biggs, J.; Annen, C.; Houseman, G. A.; Yamasaki, T.; Wright, T. J.; Walters, R. J.; Lu, Z.

    2014-12-01

    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.

  16. The Tertiary dike magmatism in the Southern Alps: geochronological data and geodynamic significance

    NASA Astrophysics Data System (ADS)

    Bergomi, Maria Aldina; Zanchetta, Stefano; Tunesi, Annalisa

    2015-03-01

    The relationships between tectonics and magmatic activity in the Alps are still debated. Despite an active subduction since the Late Cretaceous, no arc-related magmatism is recorded prior of the Middle Eocene. The emplacement of plutons along the Insubric Fault in a short time span (~34-28 Ma) has been generally interpreted in terms of the slab break-off model. The Tertiary magmatism, however, is also characterized by the occurrence of widespread calcalkaline dikes not necessarily intruded along the Insubric Fault. The geochemical features of dikes vary along the Alps belt and are interpreted in terms of mantle source heterogeneity and degree of crustal contamination. U-Pb zircon dating of studied dikes indicates intrusion ages in the 42- to 34-Ma time interval. These data provide evidence for a pre-Oligocene magmatic activity that was not solely limited to the Adamello batholith. Moreover, it appears that dikes rejuvenate from SE to NW, in an opposite direction with respect to the Alpine subduction polarity. Thus, a more complex geodynamic scenario than the slab break-off model must be envisaged. The absence of arc magmatism prior to the Middle Eocene can be explained by the low-angle subduction of the Tethyan slab that confined the mantle partial melting zone away from the orogenic wedge. The onset of the Apennines subduction at 55-50 Ma caused the Alpine slab to retreat. The partial melting zone progressively migrated beneath the orogenic wedge and finally reached the axial belt in the Late Eocene, when the Alpine collision was completed. Only at this stage, slab break-off occurred and promoted the intrusion of the Periadriatic plutons.

  17. Magmatism at different crustal levels in the ancient North Cascades magmatic arc

    NASA Astrophysics Data System (ADS)

    Shea, E. K.; Bowring, S. A.; Miller, R. B.; Miller, J. S.

    2013-12-01

    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

  18. USE OF COMPOSITE DATA SETS FOR SOURCE-TRACKING ENTEROCCOCCI IN THE WATER COLUMN AND SHORELINE INTERSTITIAL WATERS ON PENSACOLA BEACH, FL

    EPA Science Inventory

    Genthner, Fred J., Joseph B. James, Diane F. Yates and Stephanie D. Friedman. Submitted. Use of Composite Data Sets for Source-Tracking Enterococci in the Water Column and Shoreline Interstitial Waters on Pensacola Beach Florida. Mar. Pollut. Bull. 33 p. (ERL,GB 1212).

    So...

  19. Supercontinental inheritance and its influence on supercontinental breakup: The Central Atlantic Magmatic Province and the breakup of Pangea

    NASA Astrophysics Data System (ADS)

    Whalen, Lisa; Gazel, Esteban; Vidito, Christopher; Puffer, John; Bizimis, Michael; Henika, William; Caddick, Mark J.

    2015-10-01

    The Central Atlantic Magmatic Province (CAMP) is the large igneous province (LIP) that coincides with the breakup of the supercontinent Pangea. Major and trace element data, Sr-Nd-Pb radiogenic isotopes, and high-precision olivine chemistry were collected on primitive CAMP dikes from Virginia (VA). These new samples were used in conjunction with a global CAMP data set to elucidate different mechanisms for supercontinent breakup and LIP formation. On the Eastern North American Margin, CAMP flows are found primarily in rift basins that can be divided into northern or southern groups based on differences in tectonic evolution, rifting history, and supercontinental inheritance. Geochemical signatures of CAMP suggest an upper mantle source modified by subduction processes. We propose that the greater number of accretionary events, or metasomatism by sediment melts as opposed to fluids on the northern versus the southern Laurentian margin during the formation of Pangea led to different subduction-related signatures in the mantle source of the northern versus southern CAMP lavas. CAMP samples have elevated Ni and low Ca in olivine phenocrysts indicating a significant pyroxenite component in the source, interpreted here as a result of subduction metasomatism. Different collisional styles during the Alleghanian orogeny in the North and South may have led to the diachroneity of the rifting of Pangea. Furthermore, due to a low angle of subduction, the Rheic Plate may have underplated the lithosphere then delaminated, triggering both the breakup of Pangea and the formation of CAMP.

  20. The thermal evolution of a episodic, convergent-margin, magmatic center: Evidence from the Tatoosh Magmatic Complex, Mount Rainier National Park, southern Washington Cascades

    SciTech Connect

    Murphy, M.T. )

    1992-01-01

    Use of Mount Rainier as an IAVCEI Decade Volcano requires an assessment of long-term, magmatic activity cycles. Recent activity could represent either a waxing or waning step, relative to the main cone. The Tertiary record at Mount Rainier, represented by the Tatoosh complex, suggests evolution into larger and more energetic systems. This sequence included bimodal dikes and sills (Chinook Pass episode), through dacitic dome and pyroclastic eruptions (Sourdough Mountains episode), shallow monzonitic plutons, culminating in large granodiorite plutons (White River episode). Limited geochronology, geochemistry and field relations support this conceptual model. Simple thermal modeling of this hypothesis suggests that for the first two episodes, transport was insufficient to support a magma chamber. This is consistent with field relations. Repeated magmatism could have perturbed the geotherm, allowing a magma chamber during White River time. This suggests a potential 3 million-year-long, volcanic source for dacitic clasts of the Ellensburg Formation. Uplifts from such a thermal load would be consistent with independent estimates of Miocene deformation in the Washington Cascades. A 7 million year cycle for magmatism at Mount Rainier is consistent with the rock record and the cooling of a 0.5-km accumulation zone of melt at the mid crust. This suggests that any current activity at Mount Rainier could relate to the 0.7-Ma stratovolcano or the Lily Creek Formation (3 Ma). These results indicate the detailed petrologic and geochronological work in the Tatoosh complex necessary to Decade Volcano studies at Mount Rainier.

  1. Contrasting hydrological processes of meteoric water incursion during magmatic-hydrothermal ore deposition: An oxygen isotope study by ion microprobe

    NASA Astrophysics Data System (ADS)

    Fekete, Szandra; Weis, Philipp; Driesner, Thomas; Bouvier, Anne-Sophie; Baumgartner, Lukas; Heinrich, Christoph A.

    2016-10-01

    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.

  2. The magmatic and eruptive response of arc volcanoes to deglaciation: insights from southern Chile

    NASA Astrophysics Data System (ADS)

    Rawson, Harriet; Mather, Tamsin A.; Pyle, David M.; Smith, Victoria C.; Fontijn, Karen; Lachowycz, Stefan; Naranjo, José A.; Watt, Sebastian F. L.

    2016-04-01

    Volcanism exerts a major influence on Earth's atmosphere and surface environments. Understanding feedbacks between climate and long-term changes in rates or styles of volcanism is important, but unresolved. For example, it has been proposed that a pulse of activity at once-glaciated volcanoes contributed to increasing atmospheric carbon dioxide accelerating early Holocene climate change. In plate-tectonic settings where magmatism is driven by decompression melting there is convincing evidence that activity is modulated by changes in ice- or water-loading across glacial/interglacial cycles. The response of subduction-related volcanoes, where the crust is typically thicker and mantle melting is dominated by flux melting, remains unclear. Since arc volcanoes account for 90% of subaerial eruptions, they are the most significant sources of volcanic gases and tephra directly to the atmosphere. Testing the response of arc volcanoes to deglaciation requires careful work to piece together eruption archives. Records of effusive eruptions from long-lived, arc stratovolcanoes are challenging to obtain and date; while deposits from the explosive eruptions, which dominate arc records, are prone to erosion and reworking. Our new high-resolution post-glacial (<18 ka) eruption record from a large stratovolcano in southern Chile (Mocho Choshuenco) provides new insight into the magmatic response following the removal of a regional ice load. We observe significant variations in eruptive flux, eruption size and magma composition across three distinct phases of post-glacial volcanic activity. Phase 1, shortly after deglaciation, was dominated by large explosive eruptions of dacite and rhyolite. During Phase 2 (7.3 - 2.9 ka) eruption rates and eruptive fluxes were lower, and activity was dominated by moderate-scale basaltic-andesite eruptions. For the past 2.4 kyr (Phase 3), eruptive fluxes have been elevated, and dominated by explosive eruptions of intermediate magmas. We propose that

  3. Central Atlantic Magmatic Province (CAMP): The Palisade Sill Connection

    NASA Astrophysics Data System (ADS)

    Ghatak, A.; Basu, A. R.

    2012-12-01

    The extensively studied 200Ma Central Atlantic Magmatic Province (CAMP) is considered to be the world's largest continental Large Igneous Province (LIP) covering up to 7 X 106 km2. This igneous province has been linked to the ~200Ma Mesozoic opening of the Central Atlantic Ocean. This opening fragmented the CAMP into several segments that occur on four different tectonic plates today. The CAMP related LIP is different from others in that it constitutes almost entirely of dikes and sills with sparse volcanic outflows. The 200 Ma Palisade Sill, exposed along the Hudson River in northeastern North America is an expression of the CAMP magmatism. On the basis of similar ages of eruption, Palisade Sill tholeiites have been correlated to other CAMP exposures in four continents. We provide an isotopic tracer study of the Palisade Sill basalts and relate them to low-Ti (<2 wt %) CAMP related tholeiites from North and South America, western Europe, and West Africa. We report Nd-Sr-Pb isotopic and multiple trace element data of 19 basalts and gabbros, 3 chilled margin basalts, and 4 sandstones spanning the entire length and thickness of the Palisade Sill in New York and New Jersey. These geochemical data are essential to understand the relationship between mantle geodynamic processes involved in the generation of the CAMP tholeiites prior to the formation of the of the Atlantic Ocean crust. The Palisade Sill basalts of this study yield the typical composition of low-Ti CAMP tholeiites with small LREE enrichments (LaN/SmN = 1.7 to 2.3), radiogenic Sr and negative ɛNd(I) values (87Sr/87Sr(I) = 0.70668 to 0.71037; ɛNd(I) = -0.64 to -3.8), and Pb-isotopic ratios (e.g. 206Pb/204Pb = 18.11 to 18.69) above the NHRL and subparallel to it. These geochemical data indicate the Palisade Sill basalts were derived from a slightly enriched OIB-like mantle source. Further, these rocks were derived by ~15% melting of a slightly depleted spinel peridotite with up to 20% contamination by the

  4. Diffuse degassing through magmatic arc crust (Invited)

    NASA Astrophysics Data System (ADS)

    Manning, C. E.; Ingebritsen, S.

    2013-12-01

    The crust of magmatic arcs plays an important role in the volatile cycle at convergent margins. The fluxes of subduction- and arc-related volatiles such as H2O, C, Cl, S are poorly known. It is commonly believed that gases emitted from volcanoes account nearly quantitatively for the volatiles that cross the Moho beneath the volcanic front. This volcanic degassing may occur during eruption, emission from summit fumaroles and hot springs, or more 'diffuse' delivery to volcano flanks. However, several observations suggest that volatiles also transit arc crust by even more diffuse pathways, which could account for significant volatile loss on long time and length scales. Active metamorphism of arc crust produces crustal-scale permeability that is sufficient to transport a large volume of subducted volatiles (Ingebritsen and Manning, 2002, PNAS, 99, 9113). Arc magmas may reach volatile saturation deeper than the maximum depths recorded by melt inclusions (e.g., Blundy et al., 2010, EPSL, 290, 289), and exhumed sections of magmatic arc crust typically record voluminous plutons reflecting magma crystallization and volatile loss at depths well below the volcanic edifice. At shallower depths, topographically driven meteoric groundwater systems can absorb magmatic volatiles and transport them laterally by tens of km (e.g., James et al., 1999, Geology, 27, 823; Evans et al., 2002, JVGR, 114, 291). Hydrothermal ore deposits formed at subvolcanic depths sequester vast amounts of volatiles, especially sulfur, that are only returned to the surface on the time scale of exhumation and/or erosion. Water-rich metamorphic fluids throughout the crust can readily carry exsolved volcanic gases because the solubilities of volatile bearing minerals such as calcite, anhydrite, and fluorite are quite high at elevated pressure and temperature (e.g., Newton and Manning, 2002, Am Min, 87, 1401; 2005, J Pet, 46, 701; Tropper and Manning, 2007, Chem Geol, 242, 299). Taken together, these

  5. The pulse of large silicic magmatic systems

    NASA Astrophysics Data System (ADS)

    de Silva, S. L.; Schmitt, A. K.

    2008-12-01

    Large silicic volcanic fields (LSVFs) are considered windows into the tops of upper crustal batholiths that are the foundations of the continental crust. The space-time-volume records of volcanism in LSVFs are therefore assumed to mirror the accumulation record of the associated upper crustal batholith. However, key questions about the link between the volcanic and plutonic realms remain to be addressed if this view is to be substantiated. Among these are: 1) What does the surface pattern of volcanism really tell us about the development of the plutonic system below? Do these eruptions represent evacuation from a distinct batch of magma that formed just prior to eruption or do they represent the periodic tapping of a long lived regional magma body? 2) What does the cyclicity of the large caldera systems and the regional concordance of eruptions tell us about the development of the magmatic systems beneath? Does the repose period represent the time scale of development of the next magma batch or does the erupted magma develop in a timescale much shorter than the repose period? 3) What does the self-organization of single batholithic scale magmatic systems, for instance the development of a zoned system, tell us about the dynamics and time scales over which these systems differentiate and evolve? We are addressing some of these questions in the Altiplano-Puna Volcanic Complex of the Central Andes. Here, time scales of assembly and organization of batholith-scale silicic magma systems investigated using 40Ar/39Ar and U-Pb in zircon connote: 1) Supereruptions in the APVC evacuated distinct magma batches that accumulated within a few hundred thousand years prior to eruption 2) The repose period of cyclic supervolcanic systems is considerably longer than the time scale to develop the next eruptible magma batch 3) Batholith scale-silicic magma chambers can develop significant zonations in time scales of a few hundred thousand years. Additionally, our data suggest quasi

  6. Geodynamics of late Paleozoic magmatism in the Tien Shan and its framework

    NASA Astrophysics Data System (ADS)

    Biske, Yu. S.; Konopelko, D. L.; Seltmann, R.

    2013-07-01

    The Devonian-Permian history of magmatic activity in the Tien Shan and its framework has been considered using new isotopic datings. It has been shown that the intensity of magmatism and composition of igneous rocks are controlled by interaction of the local thermal upper mantle state (plumes) and dynamics of the lithosphere on a broader regional scale (plate motion). The Kazakhstan paleocontinent, which partly included the present-day Tien Shan and Kyzylkum, was formed in the Late Ordovician-Early Silurian as a result of amalgamation of ancient continental masses and island arcs. In the Early Devonian, heating of the mantle resulted in the within-plate basaltic volcanism in the southern framework of the Kazakhstan paleocontinent (Turkestan paleoocean) and development of suprasubduction magmatism over an extensive area at its margin. In the Middle-Late Devonian, the margins of the Turkestan paleoocean were passive; the area of within-plate oceanic magmatism shifted eastward, and the active margin was retained at the junction with the Balkhash-Junggar paleoocean. A new period of active magmatism was induced by an overall shortening of the region under the settings of plate convergence. The process started in the Early Carboniferous at the Junggar-Balkhash margin of the Kazakhstan paleocontinent and the southern (Paleotethian) margin of the Karakum-Tajik paleocontinent. In the Late Carboniferous, magmatism developed along the northern boundary of the Turkestan paleoocean, which was closing between them. The disappearance of deepwater oceanic basins by the end of the Carboniferous was accompanied by collisional granitic magmatism, which inherited the paleolocations of subduction zones. Postcollision magmatism fell in the Early Permian with a peak at 280 Ma ago. In contrast to Late Carboniferous granitic rocks, the localization of Early Permian granitoids is more independent of collision sutures. The magmatism of this time comprises: (1) continuation of the

  7. Paleoproterozoic gabbro-diorite-granite magmatism of the Batomga Rise (NE Aldan Shield): Sm-Nd isotope geochemical evidence

    NASA Astrophysics Data System (ADS)

    Kuzmin, V. K.; Bogomolov, E. S.; Glebovitskii, V. A.

    2016-02-01

    The geochemical similarity and almost simultaneous (2055-2060 Ma) formation of Utakachan gabbro-amphibolite, Jagdakin granodiorite-diorite, Khoyunda granitoid, and Tygymyt leucogranite complexes, which inruded metamorphic formations of the Batomga Group are evidence of their formaton from unified magmatic source. All this makes it possibble to combine aforementioned complexes into the unified Early Proterozoic diferentiated gabbro-diorite-granite complex.

  8. Off-axis magmatism along a subaerial back-arc rift: Observations from the Taupo Volcanic Zone, New Zealand.

    PubMed

    Hamling, Ian J; Hreinsdóttir, Sigrun; Bannister, Stephen; Palmer, Neville

    2016-06-01

    Continental rifting and seafloor spreading play a fundamental role in the generation of new crust. However, the distribution of magma and its relationship with tectonics and volcanism remain poorly understood, particularly in back-arc settings. We show evidence for a large, long-lived, off-axis magmatic intrusion located on the margin of the Taupo Volcanic Zone, New Zealand. Geodetic data acquired since the 1950s show evidence for uplift outside of the region of active extension, consistent with the inflation of a magmatic body at a depth of ~9.5 km. Satellite radar interferometry and Global Positioning System data suggest that there was an increase in the inflation rate from 2003 to 2011, which correlates with intense earthquake activity in the region. Our results suggest that the continued growth of a large magmatic body may represent the birth of a new magma chamber on the margins of a back-arc rift system. PMID:27386580

  9. Off-axis magmatism along a subaerial back-arc rift: Observations from the Taupo Volcanic Zone, New Zealand

    PubMed Central

    Hamling, Ian J.; Hreinsdóttir, Sigrun; Bannister, Stephen; Palmer, Neville

    2016-01-01

    Continental rifting and seafloor spreading play a fundamental role in the generation of new crust. However, the distribution of magma and its relationship with tectonics and volcanism remain poorly understood, particularly in back-arc settings. We show evidence for a large, long-lived, off-axis magmatic intrusion located on the margin of the Taupo Volcanic Zone, New Zealand. Geodetic data acquired since the 1950s show evidence for uplift outside of the region of active extension, consistent with the inflation of a magmatic body at a depth of ~9.5 km. Satellite radar interferometry and Global Positioning System data suggest that there was an increase in the inflation rate from 2003 to 2011, which correlates with intense earthquake activity in the region. Our results suggest that the continued growth of a large magmatic body may represent the birth of a new magma chamber on the margins of a back-arc rift system. PMID:27386580

  10. Off-axis magmatism along a subaerial back-arc rift: Observations from the Taupo Volcanic Zone, New Zealand.

    PubMed

    Hamling, Ian J; Hreinsdóttir, Sigrun; Bannister, Stephen; Palmer, Neville

    2016-06-01

    Continental rifting and seafloor spreading play a fundamental role in the generation of new crust. However, the distribution of magma and its relationship with tectonics and volcanism remain poorly understood, particularly in back-arc settings. We show evidence for a large, long-lived, off-axis magmatic intrusion located on the margin of the Taupo Volcanic Zone, New Zealand. Geodetic data acquired since the 1950s show evidence for uplift outside of the region of active extension, consistent with the inflation of a magmatic body at a depth of ~9.5 km. Satellite radar interferometry and Global Positioning System data suggest that there was an increase in the inflation rate from 2003 to 2011, which correlates with intense earthquake activity in the region. Our results suggest that the continued growth of a large magmatic body may represent the birth of a new magma chamber on the margins of a back-arc rift system.

  11. SOURCE APPORTIONMENT OF SEATTLE PM 2.5: A COMPARISON OF IMPROVE AND ENHANCED STN DATA SETS

    EPA Science Inventory

    Seattle, WA, STN and IMPROVE data sets with STN temperature resolved carbon peaks were analyzed with both the PMF and Unmix receptor models. In addition, the IMPROVE trace element data was combined with the major STN species to examine the role of IMPROVE metals. To compare the ...

  12. Environmental Illumination and Human Behavior: The Effects of Spectrum of Light Source on Human Performance in a University Setting.

    ERIC Educational Resources Information Center

    Kleiber, Douglas A.; And Others

    Two experiments tested the general question of whether a more "natural" artificial light (Vita-Lite) would have any different effects on classroom behavior and the ability to study than would a traditional (cool-white) light source. Fifty-nine undergraduates took part in the first experiment that utilized an 8-week counterbalanced design.…

  13. Shear-tensile/implosion source model vs. moment tensor: benefit in single-azimuth monitoring. Cotton Valley set-up.

    NASA Astrophysics Data System (ADS)

    Sileny, J.

    2012-12-01

    Moment tensor (MT) has become a standard for description of seismic sources, both in earthquake seismology and for various types of induced seismicity. It is a general dipole source, but for practice it may be too general, its generality causing troubles during its reconstruction from noisy data in the inverse process, which may be additionally ill-conditioned due to inexact hypocenter location or availability of a rough velocity/attenuation model only. Then, the retrieved source may be biased. It seems reasonable to assume a simpler and intuitivelly more physical source model directly describing the physical phenomena anticipated in the particular focus. A simple combination of a shear slip with tensile crack or 1D implosion (STI) may be a good model both for natural earthquakes and induced events. The model simplification introduced is crucial in cases of depleted sensor configuration when the moment tensor fails, in single-azimuth monitoring in particular. This is just the case of application in oil and gas industry, where the monitoring of seismicity induced by hydrofracturing is typically performed from single monitoring borehole. Then, MT is able to provide constrained solutions only (e.g. deviatoric), but STI detects also non-shear component correctly, providing important information on increase of permeability of the reservoir.

  14. Remote detection of magmatic water in Bullialdus crater on the Moon

    USGS Publications Warehouse

    Klima, Rachel L.; Cahill, John; Hagerty, Justin J.; Lawrence, David

    2013-01-01

    Once considered dry compared with Earth, laboratory analyses of igneous components of lunar samples have suggested that the Moon’s interior is not entirely anhydrous. Water and hydroxyl have also been detected from orbit on the lunar surface, but these have been attributed to nonindigenous sources, such as interactions with the solar wind. Magmatic lunar volatiles—evidence for water indigenous to the lunar interior—have not previously been detected remotely. Here we analyse spectroscopic data from the Moon Mineralogy Mapper (M3) and report that the central peak of Bullialdus Crater is significantly enhanced in hydroxyl relative to its surroundings. We suggest that the strong and localized hydroxyl absorption features are inconsistent with a surficial origin. Instead, they are consistent with hydroxyl bound to magmatic minerals that were excavated from depth by the impact that formed Bullialdus Crater. Furthermore, estimates of thorium concentration in the central peak using data from the Lunar Prospector orbiter indicate an enhancement in incompatible elements, in contrast to the compositions of water-bearing lunar samples. We suggest that the hydroxyl-bearing material was excavated from a magmatic source that is distinct from that of samples analysed thus far.

  15. A Late Proterozoic Early Paleozoic magmatic cycle in Sierra de la Ventana, Argentina

    NASA Astrophysics Data System (ADS)

    Gregori, D. A.; López, V. L.; Grecco, L. E.

    2005-06-01

    Late Proterozoic-Early Paleozoic intrusive and volcanic rocks of Sierra de la Ventana can be grouped into two magmatic assemblages: the Meyer and Cochenleufú suites. The older (700-570 Ma) is composed of S-type quartz-monzodiorites, synogranites, and monzogranites associated with andesites and rhyolites and related to volcanic-arc and postcollisional settings. The younger (540-470 Ma) corresponds to highly fractionated homogeneous A-type monzogranites, linked to final plutonic events during postorogenic extension in collisional belts. Strong similarities between Sierra de la Ventana magmatic rocks and the S- and A-type granites of the Cape granite suite in South Africa allow positive correlation. In both areas, primitive volcanic arcs or collisional orogens are recognized. Continuous transpressional shearing between the Swartland and Tygerberg terranes in the Saldania belt may have triggered the generation and emplacement of both suites.

  16. The Dynamics of the Post-Caldera Magmatic System at Yellowstone: Insights from Age, Trace Element, and Isotopic Data of Zircon and Sanidine

    NASA Astrophysics Data System (ADS)

    Stelten, M. E.; Cooper, K. M.; Vazquez, J. A.; Calvert, A. T.; Glessner, J. J.; Wimpenny, J.; Yin, Q. Z.

    2014-12-01

    Yellowstone hosts a voluminous magmatic system that produced three silicic caldera-forming eruptions over the past 2.1 My. Following the most recent of these (the Lava Creek Tuff at 639 ka), the magma system at Yellowstone underwent two episodes of intracaldera eruptions, the latest of which produced the Central Plateau Member (CPM) rhyolites. The CPM rhyolites erupted intermittently from ca. 170 ka to ca. 70 ka and can be viewed as snapshots of the magma system through time, which provides a unique opportunity to study the dynamics of an evolving caldera system. To constrain the nature and timescales of magmatic processes at Yellowstone we examine four CPM rhyolites that erupted from ca. 116 ka to ca. 74 ka and present a comprehensive data set that integrates (1) 238U-230Th ages, trace-elements, and Hf isotope compositions of the surfaces and interiors of single zircons, (2) bulk 238U-230Th ages and in situ Ba and Pb isotope compositions of sanidines, (3) sanidine 40Ar-39Ar ages, and (4) trace-element and isotopic compositions of the CPM glasses. Zircon 238U-230Th ages and Hf isotope data demonstrate that isotopically juvenile magmas, derived from Yellowstone basalts, were added to the Yellowstone magma reservoir over time and were fundamental to its post-caldera isotopic evolution. We use zircon Hf isotope data along with new Hf isotope data (and existing O isotope data) for the Yellowstone basalts (whole-rocks), older Yellowstone rhyolites (glasses), and local crustal sources to quantify the role of isotopically juvenile magma in the evolution of the magmatic system. Additionally, linking age, trace-element, and isotopic data from zircon and sanidine demonstrates that eruptible CPM rhyolites were generated by extracting melt and antecrystic zircon from a long-lived (>200 ky) crystal mush, while sanidine remained trapped in the crystal network. The extracted melts amalgamated and then crystallized new sanidines and rims on the antecrystic zircons that were in

  17. Relationships between deformation and magmatism in the Pan-African Kandi Shear Zone: Microstructural and AMS studies of Ediacaran granitoid intrusions in central Bénin (West Africa)

    NASA Astrophysics Data System (ADS)

    Adissin Glodji, L.; Bascou, J.; Yessoufou, S.; Ménot, R.-P.; Villaros, A.

    2014-09-01

    Relationships between the metamorphic basement, granitic intrusions and the Kandi Shear Zone (KSZ) in central Bénin have been investigated using petrological and structural approaches, in order to better understand the space and time parameters of the Pan-African shear deformation and the Ediacaran magmatism. In central Bénin, metamorphic rocks from the KSZ display a steep to vertical N-S trending foliation, a sub-horizontal mineral lineation together with kinematic indicators in agreement with a dextral transcurrent mega-shear zone. Four granitic intrusions (Dassa, Tré, Gobada and Tchetti) show many petrological similarities. They are biotite ± amphibole - ilmenite ± magnetite monzogranites with ferrous and metaluminous I-type features derived from high-K calk-alkaline magma. A fifth intrusion (Fita) is an alkali-feldspar, biotite, magnetite and ilmenite bearing granite crystallized from an alkaline magma. Moreover, high K2O, Zr, Y, Nb and low CaO, MgO and Al2O3 contents together with high (FeOt/MgO) and low LIL/HFS elements ratios suggesting an A-type granite affinity. Microstructural and AMS investigations presented in this paper show (i) solid-state deformation evidence for Dassa pluton and (ii) a magmatic deformation for the Tré, Tchetti, Gobada and Fita granitoids. Foliation in Dassa is parallel to the mesoscopic planar mylonitic foliation of the metamorphic basement. In the Tré, Tchetti, Gobada and Fita granitoids, magmatic textures and magnetic fabrics are coherent with the KSZ activity. These data suggest (i) a syn-kinematic nature for most of the intrusions (Tré, Gobada, Tchetti and Fita), except Dassa which correspond to an earlier event (ii) the succession of high-K calk-alkaline (Dassa, Tré, Gobada, Tchetti) evolves toward alkaline magmas (Fita) during the KSZ strike-slip tectonics. These observations highlight the changing nature of magma composition, magmatic processes and the different sources during KSZ activity in the Bénin Nigerian

  18. Magmatic differentiation in a chaotic background: A comparison of multiphase simulations and magmatic chronometers

    NASA Astrophysics Data System (ADS)

    Dufek, J.

    2015-12-01

    The location and timescales of silicic magma production has received much recent attention and these questions are at the forefront of understanding incubation times for eruptive episodes and ultimately, the production of continental crust. While idealizations of differentiation in simplified magma reservoir geometries have been useful to frame end-member behavior, most magmatic systems, and particular large magma reservoirs, are open systems with time varying geometries. Evidence of open systems and assembly of magmatic systems incrementally are present in a range of plutonic and volcanic rocks. To evaluate the timescales of silicic magma production, a 3D multiphase dynamics model was implemented that includes heat transfer, phase change and magma dynamics. The size of the magmatic systems under consideration are not prescribed, but rather grow or shrink in response to the flux of heat and intrusions. To compare simulations to a range of data, major element chemistry, phase assemblage, and tracking of representative crystals are made through time. A particular focus of this presentation is a comparison of dynamic processes to proxies used as chronometers. This includes recording the timescale of appearance of different phases that can be compared to timescales inferred from diffusion profiles and monitoring zircon saturation and dispersal. Both the differentiation timescale and timescales of the major growth of zircons are a relatively small fraction of the melt-present lifetime of magma reservoirs, and in particular, typically represent relatively smaller fractions for larger magmatic systems. Melt can exist at low melt fraction (<0.2) for timescales of 100s kyr for the largest systems, while spending only a small amount of time at high melt fraction. Nevertheless, these reservoirs can be assembled incrementally with magma fluxes in the ranges estimated for arcs. A mid-upper crust location is important to have phase assemblages with sufficient leverage to produce

  19. Permian-Triassic Magmatism Along the Southern Gondwana Margin: Correlating Proximal and Distal Volcanic Deposits

    NASA Astrophysics Data System (ADS)

    McKay, M. P.; Weislogel, A. L.; Fildani, A.

    2014-12-01

    Active margins are dominated by erosion, structural deformation, tectonic dissection, and igneous intrusions. These destructive processes lead to an incomplete record of past magmatism in active margins. Volcanic airfall tuffs that are transported and deposited in distal sedimentary basins may be more likely to be preserved in the rock record. Tuffs, however, may be affected by atmospheric fractionation during transport, postdepositional weathering, and diagenesis during burial, potentially altering ash texture, mineralogy, and geochemistry. We use outcrop observations, stratigraphic relationships, whole rock geochemistry, U-Pb zircon geochronology, and zircon rare-earth element geochemistry from Permian-Triassic strata of South Africa and South America to correlate distal volcanic ashes to proximal volcanic deposits and plutonic suites within southern Gondwana. U-Pb zircon signals of the tuffs are treated as "detrital"; the distinct zircon signals were then used to correlate distal airfall ashes to potential magmatic sources. This suggests that airfall fractionation of zircon populations is not a significant concern in tuff geochronology. Additionally, zircon inheritance may be a useful tool in matching far-traveled ashes with parental magmatic suites. Although previous studies have shown that the geochemistry of volcanic tuff deposits varies with distance from the volcanic vent, we employ whole rock and zircon REE compositions to differentiate distinct magmatic periods using distal ashes that were deposited >750 km from the volcanic source. The results of this study support a geochronologic interpretation that the Karoo strata of S. Africa are >10 Ma younger than previously thought based on biostratigraphy. Since the Karoo basin is heavily studied as a record of the end-Permian extinction and paleoclimate change, our results have major implication for this key time in Earth History.

  20. Petrological variability in recent magmatism at Axial Seamount

    NASA Astrophysics Data System (ADS)

    Dreyer, B. M.; Clague, D. A.; Gill, J. B.

    2011-12-01

    Axial Seamount is known for its compositional homogeneity. We report on petrological variability in lavas from the summit caldera and rims of Axial Seamount during the last ~1.2ka and its implications for shallow crustal magma dynamics. AUVs have mapped the summit at ~1 m resolution, and ROVs have collected numerous lavas and volcaniclastic cores. Geospatial, superpositional, compositional, and age constraint data were used to outline flow units and construct geologic maps. Nearly 200 glasses from summit lavas were analyzed for major elements. A subset of ~20 samples were analyzed for selected trace elements, Pb-, U-, and Th- isotope ratios, and 226Ra and 210Pb. The results a) confirm a high degree compositional homogeneity, b) demonstrate a more restricted range in Pb-isotope ratios than previous data, c) indicate uniform compositional source component(s) genetically linked to that of the Cobb-Eickelberg seamount chain, and d) expand the dataset of distinctly-low 230Th/232Th lavas and subdivide them into geospatial groups. Hundreds of volcaniclastic grains collected from subsurface depths of up to several tens of cm analyzed for major elements extend the record of summit magmatism beyond what is exposed. Summit lava glasses are compositionally N-MORB. Summit volcaniclastics range to higher MgO (+1%); thus, magmatism likely included more mafic episodes than is recorded in the flows as yet sampled or that volcaniclastics preferentially sample higher temperature lavas. Negative correlation of CaO/Al2O3 with MgO in all glasses suggests fractionation from parental melt(s) of plag ± ol but not cpx. K2O/TiO2 ranges are typical for much of the JdFR. Summit lavas range from aphyric to ~35% plag phyric ± a few % ol. Plag-phyric summit lavas tend to have greater MgO (>7.5%), lower CaO/Al2O3 (<0.80), and lower K2O/TiO2 (<0.10) compared to aphyric lavas. For ~18 caldera flows with absolute or relative age control, plag-phyric lavas are older than aphyric lavas, the oldest of

  1. Community-based Services that Facilitate Interoperability and Inter-comparison Between Precipitation Data Sets from Multiple Sources

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Kempler, S. J.; Teng, W. L.; Leptoukh, G. G.; Ostrenga, D.

    2010-12-01

    Over the past 12 years, large volumes of precipitation data have been generated from space-based observatories (e.g., TRMM), merging of data products (e.g., gridded 3B42), models (e.g., GMAO), climatologies (e.g., Chang SSM/I derived rain indices), field campaigns, and ground-based measuring stations. The science research, applications, and education communities have greatly benefited from the unrestricted availability of these data from the Goddard Earth Sciences Data and Information Services Center (GES DISC) and, in particular, the services tailored toward precipitation data access and usability. In addition, tools and services that are responsive to the expressed evolving needs of the precipitation data user communities have been developed at the Precipitation Data and Information Services Center (PDISC) (http://disc.gsfc.nasa.gov/precipitation or google NASA PDISC), located at the GES DISC, to provide users with quick data exploration and access capabilities. In recent years, data management and access services have become increasingly sophisticated, such that they now afford researchers, particularly those interested in multi-data set science analysis and/or data validation, the ability to homogenize data sets, in order to apply multi-variant, comparison, and evaluation functions. Included in these services is the ability to capture data quality and data provenance. These interoperability services can be directly applied to future data sets, such as those from the Global Precipitation Measurement (GPM) mission. This presentation describes the data sets and services at the PDISC that are currently used by precipitation science and applications researchers, and which will be enhanced in preparation for GPM and associated multi-sensor data research. Specifically, the GES-DISC Interactive Online Visualization ANd aNalysis Infrastructure (Giovanni) will be illustrated. Giovanni enables scientific exploration of Earth science data without researchers having to

  2. Zircon geochronology and Hf isotopic composition of Mesozoic magmatic rocks from Chizhou, the Lower Yangtze Region: Constraints on their relationship with Cu-Au mineralization

    NASA Astrophysics Data System (ADS)

    Yang, Wei; Zhang, Hong-Fu

    2012-10-01

    Zircon U-Pb ages and Hf isotopic compositions of Mesozoic magmatic rocks from the Chizhou Area are systematically investigated to reveal the tectonic setting of magmatism and their relationship with Cu-Au mineralization in the Lower Yangtze River Belt, southeastern China. The samples cover nearly all types of magmatic rocks in a 30 × 50 km2 region, including 6 granite porphyries, 6 dacites and 4 granites. The zircon U-Pb geochronology yields a range of 151-124 Ma, with granite porphyries ranging from 151 to 146 Ma, dacites from 132 to 127 Ma and granites from 127 to 124 Ma, indicating two magmatic episodes of the late Jurassic and the early Cretaceous. The earlier episode mainly formed small granite porphyries (generally < 5 km) and is always associated with porphyry Cu-Au deposits. The later episode began with dacites and was then dominated by large granite intrusions (generally > 10 km), which are barren in mineralization. The ore-barren dacites and the granites (131-124 Ma) are poor in inherited zircons. Zircons in these rocks yield a very large ɛHf(t) variation of - 20.8-0.4, suggesting a mixing between mantle-derived and crustal-derived magmas. By contrast, the ore-bearing porphyries (151-146 Ma) are rich in inherited zircons. The magmatic zircons have ɛHf(t) values of - 8.8-0.9, and the inherited ones yield U-Pb ages of 1156-811 Ma with ɛHf(t) values of 2.5-11.5. The existence of quantitative inherited zircons indicates that the crustal rocks of 1156-811 Ma significantly contribute to the formation of the ore-bearing porphyries, either being source or contamination. Since these inherited zircons are igneous as indicated by their oscillatory zonings, they may derive from components of the Grenvillian oceanic crust (ca. 1100-1000 Ma), i.e. the Neoproterozoic magmatic rocks related to arc (970-890 Ma) and Nanhua rift (ca. 825 Ma). Recent studies reveal that the ore-baring porphyries of the Lower Yangtze River Belt have slab melt features and conclude that

  3. Evolution of Northeast Atlantic Magmatic Continental Margins from an Ethiopian-Afar Perspective

    NASA Astrophysics Data System (ADS)

    England, R. W.; Cornwell, D. G.; Ramsden, A. M.

    2014-12-01

    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

  4. Simulating the behavior of volatiles belonging to the C-O-H-S system in silicate melts under magmatic conditions with the software D-Compress

    NASA Astrophysics Data System (ADS)

    Burgisser, Alain; Alletti, Marina; Scaillet, Bruno

    2015-06-01

    Modeling magmatic degassing, or how the volatile distribution between gas and melt changes at pressure varies, is a complex task that involves a large number of thermodynamical relationships and that requires dedicated software. This article presents the software D-Compress, which computes the gas and melt volatile composition of five element sets in magmatic systems (O-H, S-O-H, C-S-O-H, C-S-O-H-Fe, and C-O-H). It has been calibrated so as to simulate the volatiles coexisting with three common types of silicate melts (basalt, phonolite, and rhyolite). Operational temperatures depend on melt composition and range from 790 to 1400 °C. A specificity of D-Compress is the calculation of volatile composition as pressure varies along a (de)compression path between atmospheric and 3000 bars. This software was prepared so as to maximize versatility by proposing different sets of input parameters. In particular, whenever new solubility laws on specific melt compositions are available, the model parameters can be easily tuned to run the code on that composition. Parameter gaps were minimized by including sets of chemical species for which calibration data were available over a wide range of pressure, temperature, and melt composition. A brief description of the model rationale is followed by the presentation of the software capabilities. Examples of use are then presented with outputs comparisons between D-Compress and other currently available thermodynamical models. The compiled software and the source code are available as electronic supplementary materials.

  5. Magmatic intrusions in the lunar crust

    NASA Astrophysics Data System (ADS)

    Michaut, C.; Thorey, C.

    2015-10-01

    The lunar highlands are very old, with ages covering a timespan between 4.5 to 4.2 Gyr, and probably formed by flotation of light plagioclase minerals on top of the lunar magma ocean. The lunar crust provides thus an invaluable evidence of the geological and magmatic processes occurring in the first times of the terrestrial planets history. According to the last estimates from the GRAIL mission, the lunar primary crust is particularly light and relatively thick [1] This low-density crust acted as a barrier for the dense primary mantle melts. This is particularly evident in the fact that subsequent mare basalts erupted primarily within large impact basin: at least part of the crust must have been removed for the magma to reach the surface. However, the trajectory of the magma from the mantle to the surface is unknown. Using a model of magma emplacement below an elastic overlying layer with a flexural wavelength Λ, we characterize the surface deformations induced by the presence of shallow magmatic intrusions. We demonstrate that, depending on its size, the intrusion can show two different shapes: a bell shape when its radius is smaller than 4 times Λ or a flat top with small bended edges if its radius is larger than 4 times Λ[2]. These characteristic shapes for the intrusion result in characteristic deformations at the surface that also depend on the topography of the layer overlying the intrusion [3].Using this model we provide evidence of the presence of intrusions within the crust of the Moon as surface deformations in the form of low-slope lunar domes and floor-fractured craters. All these geological features have morphologies consistent with models of magma spreading at depth and deforming an overlying elastic layer. Further more,at floor-fractured craters, the deformation is contained within the crater interior, suggesting that the overpressure at the origin of magma ascent and intrusion was less than the pressure due to the weight of the crust removed by

  6. Volatile Exsolution Experiments: Sampling Exsolved Magmatic Fluids

    NASA Astrophysics Data System (ADS)

    Tattitch, B.; Blundy, J. D.

    2015-12-01

    In magmatic arcs the conditions of volatile exsolution exert a direct control on the composition of exsolved magmatic volatiles phases (MVPs), as well as on their parental magmas. The ability to accurately assess the exchange of major and trace elements between MVPs and magmas is key to understanding the evolution of arc magmas. The trace element signatures measured in arc volcanoes, fumaroles, and hydrothermal ore deposits are greatly influenced by the role of MVPs. In order to investigate the interplay and evolution of melts and MVPs we need experimental methods to simulate MVP exsolution that impose minimal external constraints on their equilibration. Previous experiments have focused on evaluating the exchange of elements between aqueous fluids and silicate melts under equilibrium conditions[1,2]. However, the large mass proportion of fluid to melt in these experiment designs is unrealistic. As a result, the idealized compositions of the aqueous fluids may exert a strong control on melt compositions for which they are out of equilibrium, especially at low melt fractions. In contrast, other experiments have focused on the melt during crystallization but must calculate MVP compositions by mass balance[3]. In order to investigate MVPs and magmas during this critical period of MVP exsolution, we present a new two-stage fluid-melt experimental design. Stage one experiments generate super-liquidus hydrous melts using Laguna del Maule rhyolites and dactites, as analogues for ascending arc magmas. Stage two experiments allow aliquots of stage one melt/glass to crystallize and exsolve MVPs. The design then uses pressure cycling to promote infiltration of in-situ fractured quartz[4] and traps the MVPs as synthetic fluid inclusions. We present results from trial stage 2 experiments, which produced synthetic fluid inclusions consistent with literature values of fluid-melt Cl partitioning[5] and of sufficient size for LA-ICPMS analysis. Trace element partitioning for Li, Na

  7. Assessment of deterioration in water quality from source to household storage in semi-urban settings of developing countries.

    PubMed

    John, Viji; Jain, Priyanka; Rahate, Manish; Labhasetwar, Pawan

    2014-02-01

    This study has investigated the common risks associated with the water quality changes from the source to the consumer households and the associated disease burden in the piped water supplies. Samples from the source to the household storage from Nagpur City were collected and analysed for heavy metals, nutrient and microbial parameters. Sanitary risks were identified at the households during the socio-economic and sanitary survey. The water quality deterioration was the most at household storage around 30.3% indicating that measures need to be taken to safeguard the water quality at the consumer level. Then, 31.2% of the samples collected from public standposts and handpumps were positive for faecal contamination which implies that it is the weaker sections of the society who suffer the consequences of drinking unsafe water the most. On the basis of the laboratory results, risk analysis by surveying the WTPs, point-of-use behaviour at households and sanitary status at different socio-economic strata, the Water Safety Plan for Nagpur City was structured. The aim was to ensure that safe and improved water is reached to the individual household.

  8. Colorado Plateau magmatism and uplift by warming of heterogeneous lithosphere.

    PubMed

    Roy, Mousumi; Jordan, Thomas H; Pederson, Joel

    2009-06-18

    The forces that drove rock uplift of the low-relief, high-elevation, tectonically stable Colorado Plateau are the subject of long-standing debate. While the adjacent Basin and Range province and Rio Grande rift province underwent Cenozoic shortening followed by extension, the plateau experienced approximately 2 km of rock uplift without significant internal deformation. Here we propose that warming of the thicker, more iron-depleted Colorado Plateau lithosphere over 35-40 Myr following mid-Cenozoic removal of the Farallon plate from beneath North America is the primary mechanism driving rock uplift. In our model, conductive re-equilibration not only explains the rock uplift of the plateau, but also provides a robust geodynamic interpretation of observed contrasts between the Colorado Plateau margins and the plateau interior. In particular, the model matches the encroachment of Cenozoic magmatism from the margins towards the plateau interior at rates of 3-6 km Myr(-1) and is consistent with lower seismic velocities and more negative Bouguer gravity at the margins than in the plateau interior. We suggest that warming of heterogeneous lithosphere is a powerful mechanism for driving epeirogenic rock uplift of the Colorado Plateau and may be of general importance in plate-interior settings.

  9. Understanding the hydrologic sources and sinks in the Nile Basin using multisource climate and remote sensing data sets

    NASA Astrophysics Data System (ADS)

    Senay, Gabriel B.; Velpuri, Naga Manohar; Bohms, Stefanie; Demissie, Yonas; Gebremichael, Mekonnen

    2014-11-01

    In this study, we integrated satellite-drived precipitation and modeled evapotranspiration data (2000-2012) to describe spatial variability of hydrologic sources and sinks in the Nile Basin. Over 2000-2012 period, 4 out of 11 countries (Ethiopia, Tanzania, Kenya, and Uganda) in the Nile Basin showed a positive water balance while three downstream countries (South Sudan, Sudan, and Egypt) showed a negative balance. Gravity Recovery and Climate Experiment (GRACE) mass deviation in storage data analysis showed that at annual timescales, the Nile Basin storage change is substantial while over longer time periods, it is minimal (<1% of basin precipitation). We also used long-term gridded runoff and river discharge data (1869-1984) to understand the discrepancy in the observed and expected flow along the Nile River. The top three countries that contribute most to the flow are Ethiopia, Tanzania, and Kenya. The study revealed that ˜85% of the runoff generated in the equatorial region is lost in an interstation basin that includes the Sudd wetlands in South Sudan; this proportion is higher than the literature reported loss of 50% at the Sudd wetlands alone. The loss in runoff and flow volume at different sections of the river tend to be more than what can be explained by evaporation losses, suggesting a potential recharge to deeper aquifers that are not connected to the Nile channel systems. On the other hand, we also found that the expected average annual Nile flow at Aswan is greater (97 km3) than the reported amount (84 km3). Due to the large variations of the reported Nile flow at different locations and time periods, the study results indicate the need for increased hydrometeorological instrumentation of the basin. The study also helped improve our understanding of the spatial dynamics of water sources and sinks in the Nile Basin and identified emerging hydrologic questions that require further attention.

  10. Physical setting and natural sources of exposure to carcinogenic trace elements and radionuclides in Lahontan Valley, Nevada

    USGS Publications Warehouse

    Seiler, Ralph L.

    2012-01-01

    In Lahontan Valley, Nevada, arsenic, cobalt, tungsten, uranium, radon, and polonium-210 are carcinogens that occur naturally in sediments and groundwater. Arsenic and cobalt are principally derived from erosion of volcanic rocks in the local mountains and tungsten and uranium are derived from erosion of granitic rocks in headwater reaches of the Carson River. Radon and 210Po originate from radioactive decay of uranium in the sediments. Arsenic, aluminum, cobalt, iron, and manganese concentrations in household dust suggest it is derived from the local soils. Excess zinc and chromium in the dust are probably derived from the vacuum cleaner used to collect the dust, or household sources such as the furnace. Some samples have more than 5 times more cobalt in the dust than in the local soil, but whether the source of the excess cobalt is anthropogenic or natural cannot be determined with the available data. Cobalt concentrations are low in groundwater, but arsenic, uranium, radon, and 210Po concentrations often exceed human-health standards, and sometime greatly exceed them. Exposure to radon and its decay products in drinking water can vary significantly depending on when during the day that the water is consumed. Although the data suggests there have been no long term changes in groundwater chemistry that corresponds to the Lahontan Valley leukemia cluster, the occurrence of the very unusual leukemia cluster in an area with numerous 210Po and arsenic contaminated wells is striking, particularly in conjunction with the exceptionally high levels of urinary tungsten in Lahontan Valley residents. Additional research is needed on potential exposure pathways involving food or inhalation, and on synergistic effects of mixtures of these natural contaminants on susceptibility to development of leukemia.

  11. Physical setting and natural sources of exposure to carcinogenic trace elements and radionuclides in Lahontan Valley, Nevada.

    PubMed

    Seiler, Ralph

    2012-04-01

    In Lahontan Valley, Nevada, arsenic, cobalt, tungsten, uranium, radon, and polonium-210 are carcinogens that occur naturally in sediments and groundwater. Arsenic and cobalt are principally derived from erosion of volcanic rocks in the local mountains and tungsten and uranium are derived from erosion of granitic rocks in headwater reaches of the Carson River. Radon and 210Po originate from radioactive decay of uranium in the sediments. Arsenic, aluminum, cobalt, iron, and manganese concentrations in household dust suggest it is derived from the local soils. Excess zinc and chromium in the dust are probably derived from the vacuum cleaner used to collect the dust, or household sources such as the furnace. Some samples have more than 5 times more cobalt in the dust than in the local soil, but whether the source of the excess cobalt is anthropogenic or natural cannot be determined with the available data. Cobalt concentrations are low in groundwater, but arsenic, uranium, radon, and 210Po concentrations often exceed human-health standards, and sometime greatly exceed them. Exposure to radon and its decay products in drinking water can vary significantly depending on when during the day that the water is consumed. Although the data suggests there have been no long term changes in groundwater chemistry that corresponds to the Lahontan Valley leukemia cluster, the occurrence of the very unusual leukemia cluster in an area with numerous 210Po and arsenic contaminated wells is striking, particularly in conjunction with the exceptionally high levels of urinary tungsten in Lahontan Valley residents. Additional research is needed on potential exposure pathways involving food or inhalation, and on synergistic effects of mixtures of these natural contaminants on susceptibility to development of leukemia.

  12. Magmatic and fragmentation controls on volcanic ash surface chemistry

    NASA Astrophysics Data System (ADS)

    Ayris, Paul M.; Diplas, Spyros; Damby, David E.; Hornby, Adrian J.; Cimarelli, Corrado; Delmelle, Pierre; Scheu, Bettina; Dingwell, Donald B.

    2016-04-01

    The chemical effects of silicate ash ejected by explosive volcanic eruptions on environmental systems are fundamentally mediated by ash particle surfaces. Ash surfaces are a composite product of magmatic properties and fragmentation mechanisms, as well as in-plume and atmospheric alteration processes acting upon those surfaces during and after the eruption. Recent attention has focused on the capacity of alteration processes to shape ash surfaces; most notably, several studies have utilised X-ray photoelectron spectroscopy (XPS), a technique probing the elemental composition and coordination state of atoms within the top 10 nm of ash surfaces, to identify patterns of elemental depletions and enrichments relative to bulk ash chemical composition. Under the presumption of surface and bulk equivalence, any disparities have been previously attributed to surface alteration processes, but the ubiquity of some depletions (e.g., Ca, Fe) across multiple ash studies, irrespective of eruptive origin, could suggest these to be features of the surface produced at the instant of magma fragmentation. To investigate this possibility further, we conducted rapid decompression experiments at different pressure conditions and at ambient and magmatic temperature on porous andesitic rocks. These experiments produced fragmented ash material untouched by secondary alteration, which were compared to particles produced by crushing of large clasts from the same experiments. We investigated a restricted size fraction (63-90 μm) from both fragmented and crushed materials, determining bulk chemistry and mineralogy via XRF, SEM-BSE and EPMA, and investigated the chemical composition of the ash surface by XPS. Analyses suggest that fragmentation under experimental conditions partitioned a greater fraction of plagioclase-rich particles into the selected size fraction, relative to particles produced by crushing. Trends in surface chemical composition in fragmented and crushed particles mirror that

  13. Does magmatism influence low-angle normal faulting?

    USGS Publications Warehouse

    Parsons, Thomas E.; Thompson, George A.

    1993-01-01

    Synextensional magmatism has long been recognized as a ubiquitous characteristic of highly extended terranes in the western Cordillera of the United States. Intrusive magmatism can have severe effects on the local stress field of the rocks intruded. Because a lower angle fault undergoes increased normal stress from the weight of the upper plate, it becomes more difficult for such a fault to slide. However, if the principal stress orientations are rotated away from vertical and horizontal, then a low-angle fault plane becomes more favored. We suggest that igneous midcrustal inflation occurring at rates faster than regional extension causes increased horizontal stresses in the crust that alter and rotate the principal stresses. Isostatic forces and continued magmatism can work together to create the antiformal or domed detachment surface commonly observed in the metamorphic core complexes of the western Cordillera. Thermal softening caused by magmatism may allow a more mobile mid-crustal isostatic response to normal faulting.

  14. 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

    NASA Astrophysics Data System (ADS)

    Chin, E. J.; Lee, C.; Tollstrup, D. L.; Xie, L.; Wimpenny, J.; Yin, Q.

    2011-12-01

    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.

  15. Spatial and temporal variation of OIB-like magmatism in the Western Pacific: Plume or non-plume related enriched magmatism?

    NASA Astrophysics Data System (ADS)

    Ishizuka, O.; Taylor, R. N.; Ohara, Y.; Tani, K.; Yuasa, M.

    2012-12-01

    We present new 40Ar/39Ar ages as well as geochemical data for samples recovered from bathymetric highs in the West Philippine Basin (WPB) and Daito Ridge group in the Philippine Sea. This data defines the volcanic history of OIB-like magmatism in and around the WPB and enables a tectonic reconstruction of the early history of the Philippine Sea. The prominent bathymetric features in the WPB include broad highs (plateaus) of Benham Rise and Urdaneta Plateau which lie at equal distances from the extinct spreading centre of the WPB. The northern margin of the WPB is marked by Daito Ridge group, including Oki-Daito and Daito Ridges, and Amami Plateau as well as the recently-defined Oki-Daito Rise. New drilling and dredge sampling from these bathymetric features as well as from the WPB, recovered dominantly basaltic lavas with minor but significant quantites of more differentiated volcanic rocks. Basalts with OIB-like geochemical characteristics (an overall enrichment of incompatible elements and associated radiogenic isotopes) were found from these bathymetric highs and some locations on the Daito Ridge group. In addition, basalts from the WPB are found to have variable enrichment relative to N-MORB. The age range obtained from OIB-like basalts from Urdaneta Plateau (34.6 to 38.0Ma) agrees with that reported from the Benham Rise. Meanwhile, older ages of around 40-42 Ma were obtained from basalts from the Oki-Daito Rise, north of Urdaneta Plateau. These ages overlap with those we have determined from the Minami-Daito Basin (Hickey-Vargas, 1998). This implies that Urdaneta Plateau and Oki-Daito Rise represent age-progressive record of OIB-like magmatism in the West Philippine Basin, and the source for the OIB-like magmatism existed near the spreading center of the West Philippine Basin at 34-42 Ma. Significantly, the OIB-like magmatism is not restricted to the plateaus, but is also found on the WPB floor. This might indicate that besides the continuous supply of the

  16. Cenozoic extension and magmatism in Arizona

    NASA Technical Reports Server (NTRS)

    Reynolds, S. J.; Spencer, J. E.

    1985-01-01

    The Basin and Range Province of Arizona was the site of two episodes of Cenozoic extension that can be distinguished on the basis of timing, direction and style of extension, and associated magmatism. The first episode of extension occurred during Oligocene to mid-Miocene time and resulted in the formation of low-angle detachment faults, ductile shear zones (metamorphic core complexes), and regional domains of tilted fault blocks. Evidence for extreme middle Tertiary crustal extension in a NE to SW to SW to ENE to WSW direction has been recognized in various parts of the Basin and Range of Arizona, especially in the Lake Mead area and along the belf of metamorphic core complexes that crosses southern Arizona from Parker to Tucson. New geologic mapping and scrutiny of published geologic maps indicates that significant middle Tertiary extension is more widely distributed than previously thought. The state can be subdivided into regional tilt-block domains in which middle Tertiary rocks dip consistently in one direction. The dip direction in any tilt-block domain is generally toward the breakaway of a low-angle detachment fault that underlies the tilt-block domain; we interpret this an indicating that normal faults in the upper plate of a detechment fault are generally synthetic, rather than antithetic, with respect to the detachment fault.

  17. Numerical simulation of magmatic hydrothermal systems

    USGS Publications Warehouse

    Ingebritsen, S.E.; Geiger, S.; Hurwitz, S.; Driesner, T.

    2010-01-01

    The dynamic behavior of magmatic hydrothermal systems entails coupled and nonlinear multiphase flow, heat and solute transport, and deformation in highly heterogeneous media. Thus, quantitative analysis of these systems depends mainly on numerical solution of coupled partial differential equations and complementary equations of state (EOS). The past 2 decades have seen steady growth of computational power and the development of numerical models that have eliminated or minimized the need for various simplifying assumptions. Considerable heuristic insight has been gained from process-oriented numerical modeling. Recent modeling efforts employing relatively complete EOS and accurate transport calculations have revealed dynamic behavior that was damped by linearized, less accurate models, including fluid property control of hydrothermal plume temperatures and three-dimensional geometries. Other recent modeling results have further elucidated the controlling role of permeability structure and revealed the potential for significant hydrothermally driven deformation. Key areas for future reSearch include incorporation of accurate EOS for the complete H2O-NaCl-CO2 system, more realistic treatment of material heterogeneity in space and time, realistic description of large-scale relative permeability behavior, and intercode benchmarking comparisons. Copyright 2010 by the American Geophysical Union.

  18. Platinum metals in magmatic sulfide ores

    USGS Publications Warehouse

    Naldrett, A.J.; Duke, J.M.

    1980-01-01

    Platinum-group elements (PGE) are mined predominantly from deposits that have formed by the segregation of molten iron-nickel-copper sulfides from silicate magmas. The absolute concentrations of PGE in sulfides from different deposits vary over a range of five orders of magnitude, whereas those of other chalcophile elements vary by factors of only 2 to 100. However, the relative proportions of the different PGE in a given deposit are systematically related to the nature of the parent magma. The absolute and relative concentrations of PGE in magmatic sulfides are explained in terms of the degree of partial melting of mantle peridotite required to produce the parent magma and the processes of batch equilibration and fractional segregation of sulfides. The Republic of South Africa and the U.S.S.R. together possess more than 97 percent of the world PGE reserves, but significant undeveloped resources occur in North America. The Stillwater complex in Montana is perhaps the most important example. Copyright ?? 1980 AAAS.

  19. The Role of Magma Mixing in Creating Magmatic Diversity

    NASA Astrophysics Data System (ADS)

    Davidson, J. P.; Collins, S.; Morgan, D. J.

    2012-12-01

    Most magmas derived from the mantle are fundamentally basaltic. An assessment of actual magmatic rock compositions erupted at the earth's surface, however, shows greater diversity. While still strongly dominated by basalts, magmatic rock compositions extend to far more differentiated (higher SiO2, LREE enriched) compositions. Magmatic diversity is generated by differentiation processes, including crystal fractionation/ accumulation, crustal contamination and magma mixing. Among these, magma mixing is arguably inevitable in magma systems that deliver magmas from source-to-surface, since magmas will tend to multiply re-occupy plumbing systems. A given mantle-derived magma type will mix with any residual magmas (and crystals) in the system, and with any partial melts of the wallrock which are generated as it is repeatedly flushed through the system. Evidence for magma mixing can be read from the petrography (identification of crystals derived from different magmas), a technique which is now well-developed and supplemented by isotopic fingerprinting (1,2) As a means of creating diversity, mixing is inevitably not efficient as its tendency is to blend towards a common composition (i.e. converging on homogeneity rather than diversity). It may be surprising then that many systems do not tend to homogenise with time, meaning that the timescales of mixing episodes and eruption must be similar to external magma contributions of distinct composition (recharge?). Indeed recharge and mixing/ contamination may well be related. As a result, the consequences of magma mixing may well bear on eruption triggering. When two magmas mix, volatile exsolution may be triggered by retrograde boiling, with crystallisation of anhydrous phase(s) in either of the magmas (3) or volatiles may be generated by thermal breakdown of a hydrous phase in one of the magmas (4). The generation of gas pressures in this way probably leads to geophysical signals too (small earthquakes). Recent work pulling

  20. Seismic constraints on Late Mesozoic magmatic plumbing system in the onshore-offshore area of Hong Kong

    NASA Astrophysics Data System (ADS)

    Xia, S.; Qiu, X.; Wan, K.

    2015-12-01

    We used active source wide-angle seismic data to determine a crustal structure beneath the onshore-offshore area of Hong Kong at the southern end of a broad belt dominated by Late Mesozoic intrusive and extrusive rocks in the coastal region of Southeast China. High-resolution tomographic images provide direct seismic evidence for the magmatic plumbing system of Late Mesozoic calderas. A localized high-velocity anomaly is revealed in the lower crust offshore between Hong Kong and Dangan Island, which may reflect basaltic underplating that induced voluminous silicic eruptions and granitoid plutons in the onshore-offshore area of Hong Kong. Tilted high-velocity zones are revealed in the entire crust beneath Dangan Island and the Late Mesozoic calderas of Hong Kong, which may reflect ascending magma chambers. We propose a paleo-Pacific plate subduction model to interpret our tomographic results and the generation of strong granitic magmatism in the Hong Kong area. Combining the tomographic image beneath the Lianhuashan Fault Zone with the distribution of Late Mesozoic calderas, we infer that the Lianhuashan Fault Zone might be the dominant magmatic conduit for mantle-derived magmas ascending to the upper crust. In addition, intersecting faults with different orientations could control the distribution and geometry of the vents, calderas, dykes and plutons and play an important role in forming magma conduits for individual volcanoes. Keywords: Basaltic underplating; Magmatic plumbing; Southeast China; Calderas; Active-source seismic tomography

  1. Magmatic origin of giant ‘Kiruna-type’ apatite-iron-oxide ores in Central Sweden

    PubMed Central

    Jonsson, Erik; Troll, Valentin R.; Högdahl, Karin; Harris, Chris; Weis, Franz; Nilsson, Katarina P.; Skelton, Alasdair

    2013-01-01

    Iron is the most important metal for modern industry and Sweden is by far the largest iron-producer in Europe, yet the genesis of Sweden's main iron-source, the ‘Kiruna-type’ apatite-iron-oxide ores, remains enigmatic. We show that magnetites from the largest central Swedish ‘Kiruna-type’ deposit at Grängesberg have δ18O values between −0.4 and +3.7‰, while the 1.90−1.88 Ga meta-volcanic host rocks have δ18O values between +4.9 and +9‰. Over 90% of the magnetite data are consistent with direct precipitation from intermediate to felsic magmas or magmatic fluids at high-temperature (δ18Omgt > +0.9‰, i.e. ortho-magmatic). A smaller group of magnetites (δ18Omgt ≤ +0.9‰), in turn, equilibrated with high-δ18O, likely meteoric, hydrothermal fluids at low temperatures. The central Swedish ‘Kiruna-type’ ores thus formed dominantly through magmatic iron-oxide precipitation within a larger volcanic superstructure, while local hydrothermal activity resulted from low-temperature fluid circulation in the shallower parts of this system. PMID:23571605

  2. Eruptive history and magmatic stability of Erebus volcano, Antarctica: Insights from englacial tephra

    NASA Astrophysics Data System (ADS)

    Iverson, Nels A.; Kyle, Philip R.; Dunbar, Nelia W.; McIntosh, William C.; Pearce, Nicholas J. G.

    2014-11-01

    tephrostratigraphy of the active Antarctic Erebus volcano was determined from englacial tephra on the ice-covered flanks of Erebus and an adjacent volcano. The tephra are used to reconstruct the eruptive history and magmatic evolution of Erebus. More fine-grained and blocky particles define tephra formed in phreatomagmatic eruptions and larger fluidal shards are characteristic of magmatic eruptions and in some cases both eruptive types are identified in a single mixed tephra. The eruptions forming the mixed tephra likely started as phreatomagmatic eruptions which transitioned into Strombolian eruptions as the nonmagmatic water source was exhausted. We reconstructed the eruptive history of Erebus using the tephra layers stratigraphic position, 40Ar/39Ar ages, shard morphology, and grain size. Major and trace element analyses of individual glass shards were measured by electron probe microanalysis and LA-ICP-MS. Trachybasalt, trachyte, and phonolite tephra were identified. All phonolitic tephra are Erebus-derived with compositions similar to volcanic bombs erupted from Erebus over the past 40 years. The tephra show that Erebus magma has not significantly changed for 40 ka. The uniformity of the glass chemical composition implies that the phonolite magma has crystallized in the same manner without change throughout the late Quaternary, suggesting long-term stability of the Erebus magmatic system. Trachyte and trachybasalt tephra were likely erupted from Marie Byrd Land and the McMurdo Sound area, respectively. The trachytic tephra can be regionally correlated and could provide an important time-stratigraphic marker in Antarctic ice cores.

  3. Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia

    NASA Astrophysics Data System (ADS)

    Vásquez, Mónica; Altenberger, Uwe; Romer, Rolf L.

    2009-07-01

    The Cretaceous oil-bearing source and reservoir sedimentary succession in the Putumayo Basin, SW Colombia, was intruded by gabbroic dykes and sills. The petrological and geochemical character of the magmatic rocks shows calc-alkaline tendency, pointing to a subduction-related magmatic event. K/Ar dating of amphibole indicates a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous episode in the basin. Therefore, we assume the intrusions to be part of the Andean magmatism of the Northern Volcanic Zone (NVZ). The age of the intrusions has significant tectonic and economic implications because it coincides with two regional events: (1) the late Miocene/Pliocene Andean orogenic uplift of most of the sub-Andean regions in Peru, Ecuador and Colombia and (2) a pulse of hydrocarbon generation and expulsion that has reached the gas window. High La/Yb, K/Nb and La/Nb ratios, and the obtained Sr-Nd-Pb isotopic compositions suggest the involvement of subducted sediments and/or the assimilation of oceanic crust of the subducting slab. We discuss the possibility that magma chamber(s) west of the basin, below the Cordillera, did increase the heat flow in the basin causing generation and expulsion of hydrocarbons and CO2.

  4. Jurassic Magmatism and Tectonics of the North American Cordillera

    NASA Astrophysics Data System (ADS)

    Boettcher, Stefan

    The relationship of Jurassic magmatic arc rocks to the tectonic evolution of the North American Cordilleran continental margin is a principle theme of Geological Society of America Special Paper 299. The volume gives readers a comprehensive view of the early stages of magmatic arc evolution on a continental margin and is a tribute to the contributions of Richard Lee Armstrong, whose pioneering studies provide a framework for current geologic investigations of the North American Cordillera.

  5. Sr-Nd-Os-S isotope and PGE geochemistry of the Xiarihamu magmatic sulfide deposit in the Qinghai-Tibet plateau, China

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaowei; Tang, Qingyan; Li, Chusi; Wang, Yalei; Ripley, Edward M.

    2016-03-01

    The newly discovered Xiarihamu Ni-Cu deposit is located in the Eastern Kunlun orogenic belt in the northern part of the Qinghai-Tibet plateau, western China. It is the largest magmatic Ni-Cu sulfide deposit found thus far in an arc setting worldwide and ranks second in China in terms of total Ni resources. Fe-Ni-Cu sulfide mineralization occurs in a small ultramafic body that is part of a larger mafic-ultramafic complex formed by protracted Silurian-Early Devonian basaltic magmatism. The mineralized ultramafic body is composed predominantly of lherzolite and olivine websterite, with minor dunite, websterite and orthopyroxenite. Here we report new PGE (platinum group element) data and the results of a new, integrated Sr-Nd-Os-S isotope study. The initial concentrations of Rh and Pd in the parental magma are estimated to be 0.014 ppb and 0.24 ppb, respectively, which are more than one order of magnitude lower than those in undepleted mantle-derived magmas such as many continental picrites. The observed PGE depletions in the Xiarihamu parental magma are attributed to sulfide retention in the source mantle, because the degree of partial melting required to generate the Xiarihamu primary magma was not high enough for a magma of that composition to dissolve all sulfides in the source. The (87Sr/86Sr) i ratios and ɛNd (t) of the Xiarihamu host rocks range from 0.7062 to 0.7105 and from -1.97 to -5.74, respectively, indicating 5-30 wt% crustal contamination in the Xiarihamu magma. These data also reveal that the source mantle for the Xiarihamu magma is isotopically (Sr-Nd) more enriched than that for the average Cenozoic arc basalt. The γOs(t) and δ34S values of sulfide ores from the Xiarihamu deposit range from 78 to 1393 and from 2 to 6‰, respectively. These values clearly indicate addition of crustal Os and S to the Xiarihamu parental magma. Metal tenors such as Ni and Rh are inversely correlated with γOs(t) and δ34S values. This indicates that mixing between

  6. The Importance of Magmatic Fluids in Continental Rifting in East Africa

    NASA Astrophysics Data System (ADS)

    Muirhead, J.; Kattenhorn, S. A.; Ebinger, C. J.; Lee, H.; Fischer, T. P.; Roecker, S. W.; Kianji, G.

    2015-12-01

    The breakup of strong continental lithosphere requires more than far-field tectonic forces. Growing evidence for early-stage cratonic rift zones points to the importance of heat, magma and volatile transfer in driving lithospheric strength reduction. The relative contributions of these processes are fundamental to our understanding of continental rifting. We present a synthesis of results from geological, geochemical and geophysical studies in one of the most seismically and volcanically active sectors of the East African Rift (Kenya-Tanzania border) to investigate the role of fluids during early-stage rifting (<10 Ma). Xenolith data indicate that rifting initiated in initially thick lithosphere. Diffuse soil CO2 flux maxima occur in the vicinity of faults, with carbon isotope values exhibiting a mantle-derived signature. These faults feed aligned sets of hydrothermal springs, which have N2-He-Ar relative abundances also indicating a mantle-derived source. Geochemical and surface faulting information are integrated with subsurface imaging and fault kinematic data derived from the 38-station CRAFTI broadband seismic array. Teleseismic and abundant local earthquakes enable assessment of the state-of-stress and b-values as a function of depth. High Vp/Vs ratios and tomographic imaging suggest the presence of fluids in the crust, with high pore fluid pressures driving failure at lower tectonic stress. Together, these cross-disciplinary data provide compelling evidence that early-stage rifting in East Africa is assisted by fluids exsolved from deep magma bodies, some of which are imaged in the lower crust. We assert that the flux of deep magmatic fluids during rift initiation plays a key role in weakening lithosphere and localizing strain. High surface gas fluxes, fault-fed hydrothermal springs and persistent seismicity highlight the East African Rift as the ideal natural laboratory for investigating fluid-driven faulting processes in extensional tectonic environments.

  7. Phosphorus as indicator of magmatic olivine residence time, morphology and growth rate

    NASA Astrophysics Data System (ADS)

    Sobolev, Alexander; Batanova, Valentina

    2015-04-01

    Phosphorus is among of slowest elements by diffusion rate in silicate melts and crystals (e.g. Spandler et al, 2007). In the same time it is moderately incompatible to compatible with olivine (Brunet & Chazot, 2001; Grant & Kohn, 2013). This makes phosphorus valuable tracer of olivine crystallization in natural conditions. Indeed, it is shown that natural magmatic olivine crystals commonly posses strong and complicated zoning in phosphorus (Milman-Barris et al, 2008; Welsch et al, 2014). In this paper we intend to review phosphorus behavior in olivine in published experimental and natural olivine studies and present large set of new EPMA data on phosphorus zoning in olivine phenocrysts from MORBs, OIBs, komatiites and kimberlites. We will show that sharp olivine zones enriched in phosphorus by a factor of 10-20 over prediction by equilibrium partition may be due to formation of P-rich boundary layer on the interface of fast growing olivine. This is proved by finding of small-size (normally 10 mkm or less) exceptionally P-rich melt inclusions in olivine, which are otherwise similar in composition to typical melt. These observations could provide potential olivine growth speedometer. We will also demonstrate, that sharp zoning in phosphorus may provide valuable information on the residence time of olivine crystals in different environments: magma chambers and conduits as well as mantle sources. This study has been founded by Russian Science Foundation grant 14-17-00491. References: Spandler, et al, 2007, Nature, v. 447, p. 303-306; Brunet & Chazot, 2001, Chemical Geology, v. 176, p. 51-72; Grant & Kohn, 2013, American Mineralogist, v. 98, p. 1860-1869; Milman-Barris et al, 2008, Contr. Min. Petrol. v. 155, p.739-765; Welsch et al, 2014, Geology, v. 42, p.867-870.

  8. Constraints from Li isotope systematics on subduction recycling, arc magmatism, and continent growth: An overview

    NASA Astrophysics Data System (ADS)

    Leeman, W. P.; Lee, C. A.; Chan, L. H.

    2008-12-01

    Great expectations that Li isotopic systematics can uniquely constrain many fluid-mitigated geologic processes have met with mixed success for a variety of reasons. On a local scale (some volcanic arc segments) Li composition can be highly correlated with other geochemical tracers of subduction fluids whereas, globally, such correlations tend to be disappointingly poor. The utility of Li isotopes as a tracer is limited in part by extensive overlap between mantle and subduction inputs, by limited understanding of equilibrium isotopic fractionation effects, and by apparent departures from equilibrium behavior. On the other hand, Li elemental systematics provide important constraints on global recycling processes because major litho-tectonic reservoirs have distinctive enrichments or depletions with respect to Nb or other HFSEs. Such chemical fractionations can be understood in terms of differential solubility of these elements in aqueous fluids vs. silicate melts, as well as the roles of weathering, dehydration, metamorphic or melting processes. For example, arc lavas are are systematically enriched in Li compared to those from other settings and typically have Li/Nb greater than BSE (consistent with addition of Li-rich fluids to their sources). In contrast, bulk continental crust and orogenic granitoids tend to have lower Li/Nb than BSE or arc lavas. Moreover, mass balance implies that the residual mantle (DM) produced by segregation of crust has higher Li/Nb than BSE. However, if continental crust is ultimately derived by subduction related magmatism, high Li/Nb would be expected for the crust and low Li/Nb for the upper mantle. This interesting conundrum is easiest explained in terms of selective Li removal from crustal protolith rocks via chemical weathering and erosion, which also is consistent with Li isotopic compositions of crust, mantle and seawater reservoirs. Thus, Li elemental and isotopic systematics (and relevant proxies) provide complementary

  9. The role of continental arc magmatism in driving long-term climate change

    NASA Astrophysics Data System (ADS)

    McKenzie, R.; Planavsky, N.; Penman, D. E.; Horton, B. K.; Loomis, S. E.; Stockli, D. F.; Lee, C. T.

    2015-12-01

    Earth's long-term climate states - icehouses and greenhouses - are largely governed by shifts in the concentration of atmospheric CO2. Silicate weathering and the burial of organic matter are primary sinks for CO2 and metamorphic and volcanic degassing are the primary sources. Continental magmatic arcs, in particular, have the ability produce large CO2 fluxes by liberating C preserved in continental bedrock. Assessment of a large compilation of detrital zircon U-Pb age data demonstrates systematic shifts in global zircon production that correspond with major shifts in icehouse-greenhouse climates: zircon generation is highest during greenhouses and lowest during icehouses. As zircon is predominantly produced in felsic melts in continental arc systems, these data demonstrate a first-order relationship between spatiotemporal variation in continental magmatism and major transitions in climate state. Since no clear consistent relationship can be discerned between long-term climate shifts and the paleogeographic location of continents or the global extent of uplift with regard to silicate weathering, it appears that the volcanic CO2 flux exerts a dominant control on shifts in baseline climate. The most prominent lulls in arc magmatism coincide with dramatic glaciations (e.g, Proterozoic Snowball Earth events), whereas extensive global volcanism and magmatic flare-ups correspond with intervals of documented environmental stress and mass extinctions, illustrating the fundamental influence of plate tectonic processes on Earth's surface environment and the evolution of the biosphere. In addition, the carbon cycle model LOSCAR is used to quantify the potential leverage of varying volcanic CO2 flux on equilibrium atmospheric CO2 under varying strengths and formulations of the silicate weathering feedback, which demonstrates the importance of the volcanic flux on baseline atmospheric CO2.

  10. U-Pb geochronology and Lu-Hf isotopes of zircons from newly identified Permian-Early Triassic plutons in western Liaoning province along the northern margin of the North China Craton: constraints on petrogenesis and tectonic setting

    NASA Astrophysics Data System (ADS)

    Bai, Xiang; Liu, Shuwen; Wang, Wei; Yang, Pengtao; Li, Qiugen

    2013-04-01

    Mafic to felsic gneisses along the northern margin of the North China Craton (NMNCC), in western Liaoning province, China, were previously assumed to be part of Archean metamorphic basement but are here identified as younger (Permian-Early Triassic) intrusions. LA-ICP-MS zircon U-Pb isotopic dating reveals that the magmatic precursors of the mafic gneisses were emplaced from 295 ± 3 to 259 ± 2 Ma and that the magmatic precursors of the dioritic and monzogranitic gneisses were emplaced at 267 ± 1 and 251 ± 2 Ma, respectively, thus recording a continuum of Permian to Early Triassic magmatism. The mafic and dioritic rocks exhibit zircon ɛHf( t) values from -20.7 to -3.3, suggesting they were mainly derived from a metasomatized lithospheric mantle source, possibly involving some crustal contamination. The monzogranitic rocks display their zircon ɛHf( t) values of +0.9 to +4.7, indicating the acidic magma was derived from partial melting of juvenile crustal materials from the depleted mantle source. Crustal model ages ( T {DM/C}) obtained from zircon Hf isotopes of these monzogranitic rocks range from 976 to 1,215 Ma, with an average of 1,074 ± 32 Ma, possibly implying an episode of Grenvillian crustal growth in western Liaoning province. These new lines of evidence show that the NMNCC witnessed abundant magmatic activity and interaction of the crust and mantle during the Permian and Early Triassic and that the mafic magmatism was earlier than the monzogranitic activity. These findings indicate that the monzogranitic activity was the result of underplating of mafic magma with an enriched mantle source. In the context of regional Late Paleozoic to Early Mesozoic magmatic activity, the Permian magmatism occurred in an Andean-style continental margin setting when the Paleo-Asian oceanic plate was subducted beneath the NMNCC, and in this context, the Late Permian to Early Triassic magmatism may have been linked to post-collisional extension and asthenospheric

  11. Risk assessment of water pollution sources based on an integrated k-means clustering and set pair analysis method in the region of Shiyan, China.

    PubMed

    Li, Chunhui; Sun, Lian; Jia, Junxiang; Cai, Yanpeng; Wang, Xuan

    2016-07-01

    Source water areas are facing many potential water pollution risks. Risk assessment is an effective method to evaluate such risks. In this paper an integrated model based on k-means clustering analysis and set pair analysis was established aiming at evaluating the risks associated with water pollution in source water areas, in which the weights of indicators were determined through the entropy weight method. Then the proposed model was applied to assess water pollution risks in the region of Shiyan in which China's key source water area Danjiangkou Reservoir for the water source of the middle route of South-to-North Water Diversion Project is located. The results showed that eleven sources with relative high risk value were identified. At the regional scale, Shiyan City and Danjiangkou City would have a high risk value in term of the industrial discharge. Comparatively, Danjiangkou City and Yunxian County would have a high risk value in terms of agricultural pollution. Overall, the risk values of north regions close to the main stream and reservoir of the region of Shiyan were higher than that in the south. The results of risk level indicated that five sources were in lower risk level (i.e., level II), two in moderate risk level (i.e., level III), one in higher risk level (i.e., level IV) and three in highest risk level (i.e., level V). Also risks of industrial discharge are higher than that of the agricultural sector. It is thus essential to manage the pillar industry of the region of Shiyan and certain agricultural companies in the vicinity of the reservoir to reduce water pollution risks of source water areas. PMID:27016678

  12. The calc-alkaline and adakitic volcanism of the Sabzevar structural zone (NE Iran): Implications for the Eocene magmatic flare-up in Central Iran

    NASA Astrophysics Data System (ADS)

    Moghadam, Hadi Shafaii; Rossetti, Federico; Lucci, Federico; Chiaradia, Massimo; Gerdes, Axel; Martinez, Margarita Lopez; Ghorbani, Ghasem; Nasrabady, Mohsen

    2016-04-01

    A major magmatic flare-up is documented along the Bitlis-Zagros suture zone in Eocene-Oligocene times. The Cenozoic magmatism of intraplate Central Iran is an integrant part of this tectono-magmatic scenario. The Cenozoic magmatism of the Sabzevar structural zone consists of mostly intermediate to felsic intrusions and volcanic products. These igneous rocks have calc-alkaline and adakitic geochemical signatures, with nearly coincident zircon U-Pb and mica Ar-Ar ages of ca. 45 Ma. Adakitic rocks have quite low HREE and high Sr/Y ratio, but share most of their geochemical features with the calc-alkaline rocks. The Sabzevar volcanic rocks have similar initial Sr, Nd and Pb isotope ratios, showing their cogenetic nature. Nd model ages cluster tightly around ~ 0.2-0.3 Ga. The geochemistry of the Sabzevar volcanic rocks, along with their isotopic signatures, might strangle that an upper mantle source, metasomatized by slab-derived melts was involved in generating the Sabzevar calc-alkaline rocks. A bulk rock trace element modeling suggests that amphibole-plagioclase-titanite-dominated replenishment-fractional crystallization (RFC) is further responsible for the formation of the middle Eocene Sabzevar adakitic rocks. Extensional tectonics accompanied by lithospheric delamination, possibly assisted by slab break-off and melting at depth was responsible for the Eocene formation of the Sabzevar magmatic rocks and, more in general, for the magmatic "flare-up" in Iran.

  13. Three stages in the Late Paleozoic to Triassic magmatism of southwestern Gondwana, and the relationships with the volcanogenic events in coeval basins

    NASA Astrophysics Data System (ADS)

    Sato, Ana María; Llambías, Eduardo J.; Basei, Miguel A. S.; Castro, Carlos E.

    2015-11-01

    The intermediate to acid Choiyoi Magmatic Province is the most conspicuous feature along the Late Paleozic continental margin of southwestern Gondwana, and is generally regarded as the possible source for the widespread ash fall deposits interlayered with sedimentary sequences in the adjacent Gondwana basins. The Choiyoi magmatism is geologically constrained between the early Permian San Rafael orogenic phase and the Triassic extensional Huarpica phase in the region of Argentine Frontal Cordillera, Precordillera and San Rafael Block. In order to better assess the Choiyoi magmatism in Argentine Frontal Cordillera, we obtained 6 new LA-ICPMS U-Pb ages between 278.8 ± 3.4 Ma and 252.5 ± 1.9 Ma from plutonic rocks of the Colangüil Batholith and an associated volcanic rock. The global analysis of age data compiled from Chilean and Argentine Late Paleozoic to Triassic outcrops allows us to identify three stages of magmatism: (1) pre-Choiyoi orogenic magmatism, (2) Choiyoi magmatism (286-247 Ma), and (3) post-Choiyoi magmatism related to extensional tectonics. In the Choiyoi stage is there an eastward shift and expansion of the magmatism to the southeast, covering an extensive region that defines the Choiyoi magmatic province. On the basis of comparison with the ages from volcanogenic levels identified in the coeval Gondwana basins, we propose: (a) The pre-Choiyoi volcanism from the Paganzo basin (320-296 Ma) probably has a local source in addition to the Frontal Cordillera region. (b) The pre-Choiyoi and Choiyoi events identified in the Paraná basin (304-275 Ma) are likely to have their source in the Chilean Precordillera. (c) The early stage of the Choiyoi magmatism found in the Sauce Grande basin (284-281 Ma) may have come from the adjacent Las Matras to Chadileuvú blocks. (d) The pre-Choiyoi and Choiyoi events in the Karoo basins (302-253 Ma) include the longest Choiyoi interval, and as a whole bear the best resemblance to the age records along the Chilean and

  14. Updated Magmatic Flux Rate Estimates for the Hawaii Plume

    NASA Astrophysics Data System (ADS)

    Wessel, P.

    2013-12-01

    Several studies have estimated the magmatic flux rate along the Hawaiian-Emperor Chain using a variety of methods and arriving at different results. These flux rate estimates have weaknesses because of incomplete data sets and different modeling assumptions, especially for the youngest portion of the chain (<3 Ma). While they generally agree on the 1st order features, there is less agreement on the magnitude and relative size of secondary flux variations. Some of these differences arise from the use of different methodologies, but the significance of this variability is difficult to assess due to a lack of confidence bounds on the estimates obtained with these disparate methods. All methods introduce some error, but to date there has been little or no quantification of error estimates for the inferred melt flux, making an assessment problematic. Here we re-evaluate the melt flux for the Hawaii plume with the latest gridded data sets (SRTM30+ and FAA 21.1) using several methods, including the optimal robust separator (ORS) and directional median filtering techniques (DiM). We also compute realistic confidence limits on the results. In particular, the DiM technique was specifically developed to aid in the estimation of surface loads that are superimposed on wider bathymetric swells and it provides error estimates on the optimal residuals. Confidence bounds are assigned separately for the estimated surface load (obtained from the ORS regional/residual separation techniques) and the inferred subsurface volume (from gravity-constrained isostasy and plate flexure optimizations). These new and robust estimates will allow us to assess which secondary features in the resulting melt flux curve are significant and should be incorporated when correlating melt flux variations with other geophysical and geochemical observations.

  15. Hydrodynamic modeling of magmatic-hydrothermal activity at submarine arc volcanoes, with implications for ore formation

    NASA Astrophysics Data System (ADS)

    Gruen, Gillian; Weis, Philipp; Driesner, Thomas; Heinrich, Christoph A.; de Ronde, Cornel E. J.

    2014-10-01

    Subduction-related magmas have higher volatile contents than mid-ocean ridge basalts, which affects the dynamics of associated submarine hydrothermal systems. Interaction of saline magmatic fluids with convecting seawater may enhance ore metal deposition near the seafloor, making active submarine arcs a preferred modern analogue for understanding ancient massive sulfide deposits. We have constructed a quantitative hydrological model for sub-seafloor fluid flow based on observations at Brothers volcano, southern Kermadec arc, New Zealand. Numerical simulations of multi-phase hydrosaline fluid flow were performed on a two-dimensional cross-section cutting through the NW Caldera and the Upper Cone sites, two regions of active venting at the Brothers volcanic edifice, with the former hosting sulfide mineralization. Our aim is to explore the flow paths of saline magmatic fluids released from a crystallizing magma body at depth and their interaction with seawater circulating through the crust. The model includes a 3×2 km sized magma chamber emplaced at ∼2.5 km beneath the seafloor connected to the permeable cone via a ∼200 m wide feeder dike. During the simulation, a magmatic fluid was temporarily injected from the top of the cooling magma chamber into the overlying convection system, assuming hydrostatic conditions and a static permeability distribution. The simulations predict a succession of hydrologic regimes in the subsurface of Brothers volcano, which can explain some of the present-day hydrothermal observations. We find that sub-seafloor phase separation, inferred from observed vent fluid salinities, and the temperatures of venting at Brothers volcano can only be achieved by input of a saline magmatic fluid at depth, consistent with chemical and isotopic data. In general, our simulations show that the transport of heat, water, and salt from magmatic and seawater sources is partly decoupled. Expulsion of magmatic heat and volatiles occurs within the first few

  16. Small Atomic Orbital Basis Set First-Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources.

    PubMed

    Sure, Rebecca; Brandenburg, Jan Gerit; Grimme, Stefan

    2016-04-01

    In quantum chemical computations the combination of Hartree-Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double-zeta quality is still widely used, for example, in the popular B3LYP/6-31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean-field methods. PMID:27308221

  17. Small Atomic Orbital Basis Set First-Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources.

    PubMed

    Sure, Rebecca; Brandenburg, Jan Gerit; Grimme, Stefan

    2016-04-01

    In quantum chemical computations the combination of Hartree-Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double-zeta quality is still widely used, for example, in the popular B3LYP/6-31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean-field methods.

  18. Small Atomic Orbital Basis Set First‐Principles Quantum Chemical Methods for Large Molecular and Periodic Systems: A Critical Analysis of Error Sources

    PubMed Central

    Sure, Rebecca; Brandenburg, Jan Gerit

    2015-01-01

    Abstract In quantum chemical computations the combination of Hartree–Fock or a density functional theory (DFT) approximation with relatively small atomic orbital basis sets of double‐zeta quality is still widely used, for example, in the popular B3LYP/6‐31G* approach. In this Review, we critically analyze the two main sources of error in such computations, that is, the basis set superposition error on the one hand and the missing London dispersion interactions on the other. We review various strategies to correct those errors and present exemplary calculations on mainly noncovalently bound systems of widely varying size. Energies and geometries of small dimers, large supramolecular complexes, and molecular crystals are covered. We conclude that it is not justified to rely on fortunate error compensation, as the main inconsistencies can be cured by modern correction schemes which clearly outperform the plain mean‐field methods. PMID:27308221

  19. Open-source point-of-care electronic medical records for use in resource-limited settings: systematic review and questionnaire surveys

    PubMed Central

    Bru, Juan; Berger, Christopher A

    2012-01-01

    Background Point-of-care electronic medical records (EMRs) are a key tool to manage chronic illness. Several EMRs have been developed for use in treating HIV and tuberculosis, but their applicability to primary care, technical requirements and clinical functionalities are largely unknown. Objectives This study aimed to address the needs of clinicians from resource-limited settings without reliable internet access who are considering adopting an open-source EMR. Study eligibility criteria Open-source point-of-care EMRs suitable for use in areas without reliable internet access. Study appraisal and synthesis methods The authors conducted a comprehensive search of all open-source EMRs suitable for sites without reliable internet access. The authors surveyed clinician users and technical implementers from a single site and technical developers of each software product. The authors evaluated availability, cost and technical requirements. Results The hardware and software for all six systems is easily available, but they vary considerably in proprietary components, installation requirements and customisability. Limitations This study relied solely on self-report from informants who developed and who actively use the included products. Conclusions and implications of key findings Clinical functionalities vary greatly among the systems, and none of the systems yet meet minimum requirements for effective implementation in a primary care resource-limited setting. The safe prescribing of medications is a particular concern with current tools. The dearth of fully functional EMR systems indicates a need for a greater emphasis by global funding agencies to move beyond disease-specific EMR systems and develop a universal open-source health informatics platform. PMID:22763661

  20. Dissolved inert gases (He, Ne, N2) as marker of groundwater flow-lines and degassing sources in Etnean area

    NASA Astrophysics Data System (ADS)

    Paonita, A.; Longo, M.; Bellomo, S.; Brusca, L.; D'Alessandro, W.

    2015-12-01

    Several studies in the past three decades have demonstrated the role played by monitoring chemical and isotopic composition of dissolved gases in groundwaters hosted in volcanic area, which represents by now a powerful tool to evaluate the state of activity of volcanoes and its evolution. The first step to make it possible, is a comprehensive understanding of fluids circulation inside the volcano edifice, starting from groundwaters characterization up to the identification of the underground pathways and their relationships with tectonic structures, that enhance interactions between waters and magmatic gases. In this work, we focussed on chemical composition of inert dissolved gases (He, Ne, N2) and He isotope abundances coming from groundwaters circulating in Mt Etna, as having great contrast between magmatic and shallow sources and no chemical interaction with rocks. We identified waters which intersect anomalous degassing areas, such as well evident or buried tectonic structures. These waters show both nearly magmatic He isotopic composition and high ratios of dissolved magmatic gases (He, CO2) versus the atmospherics ones (N2). Along the hydrologic flow-lines and faraway from the degassing structures, we found waters with lower He isotopic ratios and consequently richer of atmospheric-derived gases (Ne, N2). On this basis, we set-up a model of unidimensional dispersion-advection, coupled to a two-layer dynamic exchange of volatiles between the aquifer surface and atmosphere. The model is able to quantitatively explain the progressive "dilution" of the magmatic signal through several kilometres-long distances, from the source point of the anomaly towards the final stage of flow-lines at the coast. Typical hydro geological parameters, such as rock permeability, could be constrained by this approach. Moreover, anomalous compositions found along water flow-lines could represent possible new sources of degassing, allowing to detect hidden degassing structures.

  1. Contrasting magmatic structures between small plutons and batholiths emplaced at shallow crustal level (Sierras de Córdoba, Argentina)

    NASA Astrophysics Data System (ADS)

    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

    2016-11-01

    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.

  2. K-T magmatism of western Rajasthan, India: Manifestation of Reunion plume activity or extensional lithospheric tectonics?

    NASA Astrophysics Data System (ADS)

    Sharma, K.

    2004-12-01

    Seychelles microcontinent from India, sedimentary basin development in western Rajasthan and the alkaline magmatism of Mundwara, Sarnu-Dandali and elsewhere are considered to be the products of Reunion plume activity in western India. However, basin development began in western Rajasthan in the Jurassic period and no plume has been suggested for this. The continual extensional tectonic regime caused deep fractures in the continental and oceanic lithosphere. The Cambay-Sanchor-Barmer rift developed in continental lithosphere. The Mundwara, Sarnu-Dandali and Barmer magmatism with nephelinite-carbonatite affinity at the basin margin represents a typical rift-tectonic setting. The tectonic setting and crustal development during the K-T period in western Rajasthan represents an extensional tectonic regime rather than the manifestation of Reunion plume activity.

  3. The Mesozoic Continental Magmatism in Brazil: its Role in the Western Gondwana Evolution from Integrated Paleomagnetic and Geochemical Data

    NASA Astrophysics Data System (ADS)

    Ernesto, M.; Marques, L. S.

    2011-12-01

    Most of the Paleozoic era in the South American platform represents a period of tectonic quiescence during which large sedimentary basins evolved. Subsequently an intense magmatic activity took place preceding the disclosure of the Gondwana from Pangea, and later the disruption of the western Gondwana blocks (South America and Africa separation). In Brazil Early Jurassic (~220-180 Ma) tholeiitic basalts erupted mostly in the northern area (Amazonas and Parnaíba basins), whereas the Early Cretaceous (~140-120 Ma) is best represented by the huge magmatism of the Serra Geral Formation (Paraná basin, southeastern Brazil). An intense associated intrusive activity in the form of dykes and sills of both ages is widespread all over the country but tends to concentrate towards the continental margins. The integration of paleomagnetic and geochemical data on the Brazilian Mesozoic magmatism put some constraints on the timing, duration and the mantle sources involved in the generation of the magma products related to the different magmatic events.

  4. Oceanic magmatic evolution during ocean opening under influence of mantle plume

    NASA Astrophysics Data System (ADS)

    Sushchevskaya, Nadezhda; Melanholina, Elena; Belyatsky, Boris; Krymsky, Robert; Migdisova, Natalya

    2015-04-01

    Petrology, geochemistry and geophysics as well as numerical simulation of spreading processes in plume impact environments on examples of Atlantic Ocean Iceland and the Central Atlantic plumes and Kerguelen plume in the Indian Ocean reveal: - under interaction of large plume and continental landmass the plume can contribute to splitting off individual lithosphere blocks, and their subsequent movement into the emergent ocean. At the same time enriched plume components often have geochemical characteristics of the intact continental lithosphere by early plume exposure. This is typical for trap magmatism in Antarctica, and for magmatism of North and Central Atlantic margins; - in the course of the geodynamic reconstruction under the whole region of the South Atlantic was formed (not in one step) metasomatized enriched sub-oceanic mantle with pyroxenite mantle geochemical characteristics and isotopic composition of enriched HIMU and EM-2 sources. That is typical for most of the islands in the West Antarctic. This mantle through spreading axes jumping involved in different proportions in the melting under the influence of higher-temperature rising asthenospheric lherzolite mantle; - CAP activity was brief enough (200 ± 2 Ma), but Karoo-Maud plume worked for a longer time and continued from 180 to 170 Ma ago in the main phase. Plume impact within Antarctica distributed to the South and to the East, leading to the formation of extended igneous provinces along the Transantarctic Mountains and along the east coast (Queen Maud Land province and Schirmacher Oasis). Moreover, this plume activity may be continued later on, after about 40 million years cessation, as Kerguelen plume within the newly-formed Indian Ocean, significantly affects the nature of the rift magmatism; - a large extended uplift in the eastern part of the Indian Ocean - Southeastern Indian Ridge (SEIR) was formed on the ancient spreading Wharton ridge near active Kerguelen plume. The strongest plume

  5. Factors controlling structural style and magmatism in passive margins

    NASA Astrophysics Data System (ADS)

    Lu, Gang; Huismans, Ritske S.

    2015-04-01

    Comparing volcanic and non-volcanic passive margins, the distinct variability in geometry and subsidence history implies that the thermo-mechanical conditions vary at the time of rifting. Volcanic rifted margins (such as in the North Atlantic) show large magmatic activity and shallow water condition at the rift-drift transition, implying high geothermal gradients. For non-volcanic rifted margins where the initial thermal condition is potentially colder, it may develop in two end-member styles (Type I and Type II). Type-I margin with limited magmatism can be observed at Iberia-Newfoundland conjugate margins where the continental crustal thins across a narrow region and large tracts of continental mantle lithosphere are exposed at the seafloor. Type-II margin as observed in the ultra-wide central South Atlantic margins, in contrast, has normal magmatic activity and has a strongly thinned continental crust that span very wide regions (>250 km) below which the continental mantle lithosphere was removed. Here we perform thermo-mechanical finite element numerical experiments to investigate factors that are potentially important for the formation of volcanic and non-volcanic passive margins. Forward numerical models are used to predict the structural styles and characteristic magmatism associated with each of these end members. A number of parameters including different rheological stratifications and thermal gradients are tested and factors that control the degree of magmatism and structural style during rifting are focused.

  6. Identification of bloodmeal sources and Trypanosoma cruzi infection in triatomine bugs (Hemiptera: Reduviidae) from residential settings in Texas, the United States.

    PubMed

    Kjos, Sonia A; Marcet, Paula L; Yabsley, Michael J; Kitron, Uriel; Snowden, Karen F; Logan, Kathleen S; Barnes, John C; Dotson, Ellen M

    2013-09-01

    The host-vector-parasite interactions in Chagas disease peridomestic transmission cycles in the United States are not yet well understood. Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) infection prevalence and bloodmeal sources were determined for adult and immature triatomine (Hemiptera: Reduviidae) specimens collected from residential settings in central Texas. Sequenced cytochrome b DNA segments obtained from triatomine digestive tract identified nine vertebrate hosts and one invertebrate host in four triatomine species (Triatoma gerstaeckeri, Triatoma indictiva, Triatoma protracta, and Triatoma sanguisuga). The broad range of wild and domestic host species detected in triatomine specimens collected from residential sites indicates high host diversity and potential movement between the sylvatic and peridomestic settings. Domestic dogs appear to be key in the maintenance of the peridomestic transmission cycle as both a blood host for the triatomine vectors and a potential reservoir for the parasite. The high rate of T. cruzi infection among triatomine specimens that were collected from inside houses, outside houses, and dog kennels (69, 81, and 82%, respectively) suggests a current risk for Chagas disease vector-borne transmission for humans and domestic animals in residential settings in Texas because of overlap with the sylvatic cycle.

  7. Identification of Bloodmeal Sources and Trypanosoma cruzi Infection in Triatomine Bugs (Hemiptera: Reduviidae) From Residential Settings in Texas, the United States

    PubMed Central

    KJOS, SONIA A.; MARCET, PAULA L.; YABSLEY, MICHAEL J.; KITRON, URIEL; SNOWDEN, KAREN F.; LOGAN, KATHLEEN S.; BARNES, JOHN C.; DOTSON, ELLEN M.

    2014-01-01

    The host–vector–parasite interactions in Chagas disease peridomestic transmission cycles in the United States are not yet well understood. Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) infection prevalence and bloodmeal sources were determined for adult and immature triatomine (Hemiptera: Reduviidae) specimens collected from residential settings in central Texas. Sequenced cytochrome b DNA segments obtained from triatomine digestive tract identified nine vertebrate hosts and one invertebrate host in four triatomine species (Triatoma gerstaeckeri, Triatoma indictiva, Triatoma protracta, and Triatoma sanguisuga). The broad range of wild and domestic host species detected in triatomine specimens collected from residential sites indicates high host diversity and potential movement between the sylvatic and peridomestic settings. Domestic dogs appear to be key in the maintenance of the peridomestic transmission cycle as both a blood host for the triatomine vectors and a potential reservoir for the parasite. The high rate of T. cruzi infection among triatomine specimens that were collected from inside houses, outside houses, and dog kennels (69, 81, and 82%, respectively) suggests a current risk for Chagas disease vector-borne transmission for humans and domestic animals in residential settings in Texas because of overlap with the sylvatic cycle. PMID:24180119

  8. Application of near real-time radial semblance to locate the shallow magmatic conduit at Kilauea Volcano, Hawaii

    USGS Publications Warehouse

    Dawson, P.; Whilldin, D.; Chouet, B.

    2004-01-01

    Radial Semblance is applied to broadband seismic network data to provide source locations of Very-Long-Period (VLP) seismic energy in near real time. With an efficient algorithm and adequate network coverage, accurate source locations of VLP energy are derived to quickly locate the shallow magmatic conduit system at Kilauea Volcano, Hawaii. During a restart in magma flow following a brief pause in the current eruption, the shallow magmatic conduit is pressurized, resulting in elastic radiation from various parts of the conduit system. A steeply dipping distribution of VLP hypocenters outlines a region extending from sea level to about 550 m elevation below and just east of the Halemaumau Pit Crater. The distinct hypocenters suggest the shallow plumbing system beneath Halemaumau consists of a complex plexus of sills and dikes. An unconstrained location for a section of the conduit is also observed beneath the region between Kilauea Caldera and Kilauea Iki Crater.

  9. Atmospheric PCO₂ perturbations associated with the Central Atlantic Magmatic Province.

    PubMed

    Schaller, Morgan F; Wright, James D; Kent, Dennis V

    2011-03-18

    The effects of a large igneous province on the concentration of atmospheric carbon dioxide (PCO₂) are mostly unknown. In this study, we estimate PCO₂ from stable isotopic values of pedogenic carbonates interbedded with volcanics of the Central Atlantic Magmatic Province (CAMP) in the Newark Basin, eastern North America. We find pre-CAMP PCO₂ values of ~2000 parts per million (ppm), increasing to ~4400 ppm immediately after the first volcanic unit, followed by a steady decrease toward pre-eruptive levels over the subsequent 300 thousand years, a pattern that is repeated after the second and third flow units. We interpret each PCO₂ increase as a direct response to magmatic activity (primary outgassing or contact metamorphism). The systematic decreases in PCO₂ after each magmatic episode probably reflect consumption of atmospheric CO₂ by weathering of silicates, stimulated by fresh CAMP volcanics.

  10. Atmospheric PCO₂ perturbations associated with the Central Atlantic Magmatic Province.

    PubMed

    Schaller, Morgan F; Wright, James D; Kent, Dennis V

    2011-03-18

    The effects of a large igneous province on the concentration of atmospheric carbon dioxide (PCO₂) are mostly unknown. In this study, we estimate PCO₂ from stable isotopic values of pedogenic carbonates interbedded with volcanics of the Central Atlantic Magmatic Province (CAMP) in the Newark Basin, eastern North America. We find pre-CAMP PCO₂ values of ~2000 parts per million (ppm), increasing to ~4400 ppm immediately after the first volcanic unit, followed by a steady decrease toward pre-eruptive levels over the subsequent 300 thousand years, a pattern that is repeated after the second and third flow units. We interpret each PCO₂ increase as a direct response to magmatic activity (primary outgassing or contact metamorphism). The systematic decreases in PCO₂ after each magmatic episode probably reflect consumption of atmospheric CO₂ by weathering of silicates, stimulated by fresh CAMP volcanics. PMID:21330490

  11. Retrowedge-related Carboniferous units and coeval magmatism in the northwestern Neuquén province, Argentina

    NASA Astrophysics Data System (ADS)

    Zappettini, Eduardo O.; Chernicoff, Carlos J.; Santos, Joao O. S.; Dalponte, Marcelo; Belousova, Elena; McNaughton, Neal

    2012-11-01

    The studied Carboniferous units comprise metasedimentary (Guaraco Norte Formation), pyroclastic (Arroyo del Torreón Formation), and sedimentary (Huaraco Formation) rocks that crop out in the northwestern Neuquén province, Argentina. They form part of the basement of the Neuquén Basin and are mostly coeval with the Late Paleozoic accretionary prism complex of the Coastal Cordillera, south-central Chile. U-Pb SHRIMP dating of detrital zircon yielded a maximum depositional age of 374 Ma (Upper Devonian) for the Guaraco Norte Formation and 389 Ma for the Arroyo del Torreón Formation. Detrital magmatic zircon from the Guaraco Norte Formation are grouped into two main populations of Devonian and Ordovician (Famatinian) ages. In the Arroyo del Torreón Formation, zircon populations are also of Devonian and Ordovician (Famatinian), as well as of Late Neoproterozoic and Mesoproterozoic ages. In both units, there is a conspicuous population of Devonian magmatic zircon grains (from 406 ± 4 Ma to 369 ± 5 Ma), indicative of active magmatism at that time range. The ɛHf values of this population range between -2.84 and -0.7, and the TDM-(Hf) are mostly Mesoproterozoic, suggesting that the primary sources of the Devonian magmatism contained small amounts of Mesoproterozoic recycled crustal components. The chemical composition of the Guaraco Norte Formation corresponds to recycled, mature polycyclic sediment of mature continental provenance, pointing to a passive margin with minor inputs from continental margin magmatic rocks. The chemical signature of the Huaraco Formation indicates that a magmatic arc was the main provenance for sediments of this unit, which is consistent with the occurrence of tuff—mostly in the Arroyo del Torreón Formation and very scarcely in the Huaraco Formation—with a volcanic-arc signature, jointly indicating the occurrence of a Carboniferous active arc magmatism during the deposition of the two units. The Guaraco Norte Formation is interpreted

  12. Geochemistry of Jamari complex, central-eastern Rondônia: Andean-type magmatic arc and Paleoproterozoic crustal growth of the southwestern Amazonian Craton, Brazil

    NASA Astrophysics Data System (ADS)

    Scandolara, Jaime E.; Fuck, Reinhardt A.; Dantas, Elton L.; Souza, Valmir S.

    2013-10-01

    metamorphosed under upper amphibolite to granulite facies conditions that only mildly disturbed their igneous characteristics. Zircon U-Pb crystallization ages (ID-TIMS, SHRIMP and LA-ICP-MS) set the acretional phase of the magmatic arc in Rondônia between 1.76 and 1.74 Ga. Metamorphic mineral paragenesis and textural features in these rocks, combined with geochronologic data, indicate that metamorphic conditions in the study area reached the granulite facies (T = ca. 750-800 °C, P = 7 to 8 kbar) in a tectonothermal collisional event that occurred between 1.67 and 1.63 Ga. The Jamari complex in this region was subsequently reworked during the Rondonian-San Ignácio Orogeny (1.50-1.30 Ga), a tectonic episode characterized by crytical metamorphic mineral assemblages and anatexis, suggesting upper-amphibolite-facies metamorphism. The youngest tectonic event recognized in the Jamari complex is associated with tectonic reactivation, deformation, thermal overprint, and magmatism related to the Sunsás Orogeny (1.30-0.95 Ga). Its effects are represented by extensive development of shear zones (Ji-Paraná system), mylonitic belts, rifts and sedimentary deposits, and post-collisional A-type intrusions. Nd isotopic data of the high-grade orthogneisses show a wide range of ɛNd values (-1.5 to +5.6) and a wide spectrum of TDM model-ages, from 1.79 to 2.2 Ga. These values demonstrate that the crustal generation processes involved juvenile mantle sources and variable proportions of older recycled crust.

  13. The timing of kimberlite magmatism in North America: implications for global kimberlite genesis and diamond exploration

    NASA Astrophysics Data System (ADS)

    Heaman, L. M.; Kjarsgaard, B. A.; Creaser, R. A.

    2003-12-01

    -prolific periods of magmatism in the Eocene (50-53 Ma), Jurassic (150-190) and Triassic (˜235 Ma). Several discrete episodes of pre-Mesozoic kimberlite magmatism variably occur in North America, southern Africa and Yakutia at 590-615, 520-540, 435-450, 400-410 and 345-360 Ma. One of the surprises in the timing of kimberlite magmatism worldwide is the common absence of activity between about 250 and 360 Ma; this period is even longer in southern Africa. This >110 my period of quiescence in kimberlite magmatism is likely linked to relative crustal and mantle stability during the lifetime of the supercontinent Gondwanaland. Economic diamond deposits in kimberlite occur throughout the Phanerozoic from the Cambrian (Venetia, South Africa; Snap Lake and Kennady Lake, Canada) to the Tertiary (Mwadui, Tanzania; Ekati and Diavik in Lac de Gras, Canada). There are clearly some discrete periods when economic kimberlite-hosted diamond deposits formed globally. In contrast, the Devonian event, which is such an important source of diamonds in Yakutia, is notably absent in the kimberlite record from both southern Africa and North America.

  14. Arabian Shield magmatic cycles and their relationship with Gondwana assembly: Insights from zircon U-Pb and Hf isotopes

    NASA Astrophysics Data System (ADS)

    Robinson, F. A.; Foden, J. D.; Collins, A. S.; Payne, J. L.

    2014-12-01

    The Arabian Shield preserves a protracted magmatic record of amalgamated juvenile terranes that host a diverse range of early Neoproterozoic to Cambrian granitoids intruding volcanosedimentary basin assemblages that have corollaries in other parts of the East African Orogen. New zircon U-Pb geochronology of 19 granitoids intruding eight Arabian Shield terranes, define four discrete magmatic events: island arc (∼845 Ma), syncollisional (∼710 Ma), post-tectonic (∼620 Ma) and anorogenic (∼525 Ma). Zircon Lu-Hf isotopic analyses indicate that all studied granitoids are juvenile with typical εHf values of >+5 to +10 and Stenian-Tonian (∼1100-900 Ma) model ages, regardless of their precise intrusive ages or spatial relationship. Subtle changes in isotopic signatures between ∼850 and 600 Ma, suggest the result from changes in granite source materials brought about by; basaltic underplating, limited crustal interaction with Palaeoproterozoic basement and a change to lithospheric delamination/subduction roll-back processes driving juvenile ANS crustal growth. The cycle of granite intrusion reflects accretionary cycles initiated during Mozambique Ocean closure and during Gondwana amalgamation and final assembly. Post-tectonic magmatism is divided into a ∼636-600 Ma phase and post 600 Ma event that reflects first subduction and then within-plate related processes. The identification of magmatism at ∼525 Ma is now the youngest granitoid identified so far in the Saudi Arabian Shield and may change the identified age of the regional, basal Palaeozoic unconformity. This late magmatism may be generated by the Najd Fault reactivation correlating with the Malagasy/Kunnga Orogeny that marked the final stages of Gondwana assembly.

  15. Effects of magmatic intrusion on mineralogy and geochemistry of coals from the Fengfeng-Handan Coalfield, Hebei, China

    SciTech Connect

    Shifeng Dai; Deyi Ren

    2007-06-15

    This paper describes the effects of magmatic intrusions on petrology, mineralogy, and geochemistry of the late Palaeozoic coals from the Fengfeng-Handan coalfield, Hebei, China. The narrowly zoned coals of variable ranks, from high-volatile A bituminous (hvAb), through medium-volatile bituminous (mvb), low-volatile bituminous (lvb), semianthracite (sa), and anthracite (an), to meta-anthracite (ma) in the coalfield, were found to be best explained by magmatic inputs. The minerals derived from magmatic thermal alteration consist of pyrite, calcite, and ankerite, which mainly occur as fracture or vesicle fillings in the thermally altered high-rank coals. The variation in element concentrations with coal ranks (enrichment, depletion, and no variation) and mineralogical affinity were used to classify elements in coals into six groups, groups A-F. Elements in group A (B, F, Cl, Br, and Hg), group B (As, Co, Cu, Ni, and Pb), group C (Sr, Mg, Ca, Mn, and Zn), and Group D (U) were enriched in the altered coals, indicating that the magmatic inputs are the source of these elements. Group A elements are volatile elements that probably came from the hydrothermal solutions, then deposited or were driven off from an organic component in coal by magmatic heat, and then redeposited in the coal. Group B elements mainly distribute in the fracture or vesicle fillings of pyrites. The dominant carriers of group C elements are thermally altered calcite and ankerite. Uranium in group D occurs in organic-bonded and silicate associations. Group E elements, including Sb, Sc, and V, have a depletion trend in the altered coals, and the remaining elements in group F do not clearly vary in the unaltered, slightly altered, or altered coals. The element concentrations independent of coal ranks in groups E and F may suggest that these elements are inherent to the coal. 44 refs., 15 figs., 5 tabs.

  16. Magmatic Differentiation Exposed on a Crustal Scale: A Field Example from Sierra Valle Fértil, Argentina

    NASA Astrophysics Data System (ADS)

    Banik, T. J.; Bergantz, G. W.; Bachmann, O.

    2010-12-01

    Two endmember models of magmatic arc assembly have been proposed: (1) a model where an upper-crust silicic magma body is fed by a lower-crust mafic source area with the mid-crust largely uninvolved, serving as a transport zone, and (2), a model of progressive and spatially continuous construction of arc basement that requires a few million years of thermal maturation before voluminous silicic magmas accumulate in the upper crust. One way to assess the generality of these two models is to look at crustal cross-sections. A particularly well-exposed example of such a cross-section is within the Ordovician Famatinian magmatic arc, a 1500 km long suite of magmatic units ranging from deep mafic to shallower intermediate plutonic bodies and silicic eruptive products. The deepest complete section of the arc is exposed in the Sierras Valle Fértil-La Huerta (SVF) with magmatic crystallization pressures ranging from greater than 8 kb to 4 kb. The SVF displays continuous outcrop that preserves the geological record of the magmatic role of igneous input, thermal prograde processes, and assimilation during arc crust assembly, thereby allowing us to construct a time-composition-volume evolution of the SVF arc section. Field observations—such as large, multiply intruded gabbro bodies interspersed with metapelitic septa, the absence of regional vertical structures, a sharp horizontal contact between mafic and felsic units, minor pelite assimilation, and no remelting of precursory mafic forerunners (amphibolites)—constrain possible processes of magmatic differentiation and preserve complex features indicative of emplacement during a common thermal prograde event. CA-ID-TIMS U-Pb geochronology from gabbroic, dioritic, and granodioritic rocks in the SVF yields crystallization ages from 471.47 Ma to 467.14 Ma. This 4.33 Myr time frame for the initial construction and evolution of arc crust is consistent with examples from continental and oceanic arcs that indicate an active

  17. Magmatism and Tectonics in the Meso-Archean Pongola Supergroup, South Africa

    NASA Astrophysics Data System (ADS)

    Wilson, Allan

    2013-04-01

    The Pongola Supergroup is one of the most extensive and well preserved volcano-sedimentary successions emplaced in a continental setting in the Meso-Archean (c. 2.95 Ga). It contrasts with both the older (Barberton type c.3.5 Ga) and younger (Belingwe type c.2.7 Ga) greenstone belts in southern Africa in that the sequence has not undergone the strong horizontal compressional tectonics typically related to greenstone belt-TTG environments. However, it is appropriate to compare this sequence with rocks of the Barberton greenstone belt by which the final phase of deposition preceded that of the juxtaposed Pongola basin with a relatively small time interval. The Pongola succession, which commenced with the first major magmatic event after the Barberton greenstone belt, overlies granitoids and remnants of greenstone belts in SE South Africa and in SW Swaziland. Formation was not in a continental rift environment but most likely in a marginal epicontinental basin with syn-depositional subsidence in a half-graben fault system in the type area. The Pongola rocks occur in two domains related to a NW-trending central basement high in the Kaapvaal Craton and achieving a maximum thickness of 8 km in the northern areas. The lower section (Nsuze group 3.7 km thick) is made up mainly of lavas and pyroclastic rocks and the upper section (Mozaan Group 4.3 km thick) is aranaceous sediments and argillites with a thick volcanic unit observed in the south-eastern facies. Chemical affinities of the lavas include tholeiite and calc-alkaline over the compositional range of basalt to rhyolite. There is a preponderance of andesites in the compositional array. The preservation of these rocks gives insight into the range of volcanic processes that took place at this stage of Earth history and in some areas it is possible to identify eruptions from a single source over several kilometres, as well as feeder-dyke systems to the lava flows. Simultaneous eruption of contrasting magmas from several

  18. The belt of metagabbros of La Pampa: Lower Paleozoic back-arc magmatism in south-central Argentina

    NASA Astrophysics Data System (ADS)

    Chernicoff, Carlos J.; Zappettini, Eduardo O.; Villar, Luisa M.; Chemale, Farid, Jr.; Hernández, Laura

    2009-12-01

    Combined geological, geochronological, geochemical and geophysical studies have led to identification of a large (˜300 km long, ˜5 km wide) N-S trending belt of metagabbros in the province of La Pampa, south-central Argentina. This belt, though only poorly exposed in the localities of Valle Daza and Sierra de Lonco Vaca, stands out in the geophysical data (aeromagnetics and gravity). Modeling of the aeromagnetic data permits estimation of the geometry of the belt of metagabbros and surrounding rocks. The main rock type exposed is metagabbros with relict magmatic nucleii where layering is preserved. A counterclockwise P-T evolution affected these rocks, i.e., during the Middle Ordovician the protolith reached an initial granulite facies of metamorphism (M1), evolving to amphibolite facies (M2). During the Upper Devonian, a retrograde, greenschist facies metamorphism (M3) partially affected the metagabbros. The whole-rock Sm-Nd data suggest a juvenile source from a depleted mantle, with model ages ranging from 552 to 574 Ma, and positive Epsilon values of 6.51-6.82. A crystallization age of 480 Ma is based on geological considerations, i.e. geochronological data of the host rocks as well as comparisons with the Las Aguilas mafic-ultramafic belt of Sierra de San Luis (central Argentina). The geochemical studies indicate an enriched MORB and back-arc signature. The La Pampa metagabbros are interpreted to be originated as a result of the extension that took place in a back-arc setting coevally with the Famatinian magmatic arc (very poorly exposed in the western part of the study area). The extensional event was 'aborted' by the collision of the Cuyania terrane with Pampia-Gondwana in the Middle Ordovician, causing deformation and metamorphism throughout the arc-back-arc region. The similarities between the La Pampa metagabbros and the mafic-ultramafic Las Aguilas belt of the Sierra de San Luis are very conspicuous, for example, the age (Lower Paleozoic), geochemical

  19. Magmatism at the Eurasian–North American modern plate boundary: Constraints from alkaline volcanism in the Chersky Belt (Yakutia)

    PubMed Central

    Tschegg, Cornelius; Bizimis, Michael; Schneider, David; Akinin, Vyacheslav V.; Ntaflos, Theodoros

    2011-01-01

    The Chersky seismic belt (NE-Russia) forms the modern plate boundary of the Eurasian−North American continental plate. The geodynamic evolution of this continent−continent setting is highly complex and remains a matter of debate, as the extent and influence of the Mid-Arctic Ocean spreading center on the North Asian continent since the Eocene remains unclear. The progression from a tensional stress regime to a modern day transpressional one in the Chersky seismic belt, makes the understanding even more complicated. The alkaline volcanism that has erupted along the Chersky range from Eocene through to the Recent can provide constraints on the geodynamic evolution of this continental boundary, however, the source and petrogenetic evolution of these volcanic rocks and their initiating mechanisms are poorly understood. We studied basanites of the central Chersky belt, which are thought to represent the first alkaline volcanic activity in the area, after initial opening of the Arctic Ocean basin. We present mineral and bulk rock geochemical data as well as Sr–Nd–Pb–Hf isotopes of the alkaline suite of rocks combined with new precise K–Ar and 40Ar/39Ar dating, and discuss an integrated tectono-magmatic model for the Chersky belt. Our findings show that the basanites were generated from a homogeneous asthenospheric mantle reservoir with an EM-1 isotopic flavor, under relatively ‘dry’ conditions at segregation depths around 110 km and temperatures of ~ 1500 °C. Trace element and isotope systematics combined with mantle potential temperature estimates offer no confirmation of magmatism related to subduction or plume activity. Mineral geochemical and petrographical observations together with bulk geochemical evidence indicate a rapid ascent of melts and high cooling rates after emplacement in the continental crust. Our preferred model is that volcanism was triggered by extension and thinning of the lithosphere combined with adiabatic upwelling of the

  20. The potential importance of phosphorus for martian magmatism

    NASA Astrophysics Data System (ADS)

    Toplis, Michael

    2015-04-01

    Magmatic rocks from Mars shows many important compositional differences compared to terrestrial counterparts. For example, one of the most striking features of volcanic rocks from Mars is that they are significantly richer in iron and poorer in silica than lavas produced by partial melting of the Earth's mantle. The iron-rich nature of Martian volcanics has been attributed to a higher FeO content of the Martian mantle [1], while the low silica content has no widely accepted explanation. It is also of note that the SNC meteorites generally show superchondritic Ca/Al, an observation which contrasts with most terrestrial basalts, and which places constraints on the composition of the mantle source which produced the SNC's. In addition to these differences in major-element chemistry, the available analyses of Martian rocks suggest that the sampled silicate portion of Mars is significantly richer in phosphorus than the Earth's crust/ upper mantle. On the other hand, no particular importance has been attached to this observation. It is the aim of this contribution to make the case that this difference may be potentially important. One of the most significant influences of the addition of small amounts of phosphorus to a peridotite assemblage concerns the compositions of liquids produced by partial melting. The presence of phosphorus in a silicate melt is known to dramatically affect silica activity, as elegantly demonstrated by the experimental results of [2]. Using the MELTS thermodynamic calculator [3], it is shown that for a bulk Martian mantle containing ~0.17wt% P2O5 [1], low degree partial melts on Mars will be particularly silica-poor, in contrast to the Earth where the relative absence of P and competing effect of alkalis leads to high silica contents. The difference in silica content between liquids produced from a mantle with 0 and 0.2 wt% P2O5 is predicted to be almost 10wt% SiO2 when the degree of partial melting is 3%, a value more or less independent of

  1. The Capilla del Monte pluton, Sierras de Córdoba, Argentina: the easternmost Early Carboniferous magmatism in the pre-Andean SW Gondwana margin

    NASA Astrophysics Data System (ADS)

    Dahlquist, Juan A.; Pankhurst, Robert J.; Rapela, Carlos W.; Basei, Miguel A. S.; Alasino, Pablo H.; Saavedra, Julio; Baldo, Edgardo G.; Murra, Juan A.; da Costa Campos Neto, Mario

    2016-07-01

    New geochronological, geochemical, and isotopic data are reported for the Capilla del Monte two-mica granite pluton in the northeastern Sierras de Córdoba. An Early Carboniferous age is established by a U-Pb zircon concordia (336 ± 3 Ma) and a Rb-Sr whole-rock isochron (337 ± 2 Ma). Zircon saturation geothermometry indicates relatively high temperatures (735-800 °C). The granites have high average SiO2 (74.2 %), Na2O + K2O (7.8 %), and high field-strength elements, high K2O/Na2O (1.7) and FeO/MgO ratios (5.1), with low CaO content (0.71 %). REE patterns with marked negative Eu anomalies (Eu/Eu* 0.14-0.56) indicate crystal fractionation, dominantly of plagioclase and K-feldspar, from a peraluminous magma enriched in F. Isotope data (87Sr/86Srinitial = 0.7086, ɛ Nd336 = -5.5 to -4.4 with T DM = 1.5 Ga, zircon ɛ Hf336 +0.8 to -6.1; mean T DM = 1.5 Ga) suggest a Mesoproterozoic continental source, albeit with some younger or more juvenile material indicated by the Hf data. The pluton is the easternmost member of a Carboniferous A-type magmatic suite which shows an increase in juvenile input toward the west in this part of the pre-Andean margin. The petrological and geochemical data strongly suggest a similar intraplate geodynamic setting to that of the nearby but much larger, Late Devonian, Achala batholith, although Hf isotope signatures of zircon suggest a more uniformly crustal origin for the latter. Further studies are required to understand whether these bodies represent two independent magmatic episodes or more continuous activity.

  2. Magmatism, mantle evolution and geodynamics at the converging plate margins of Italy

    NASA Astrophysics Data System (ADS)

    Frezzotti, M. L.; Peccerillo, A.

    2015-12-01

    The Plio-Quaternary magmatism in the Tyrrhenian Sea area exhibits wide compositional variations, which cover almost entirely those observed for volcanic rocks worldwide. Some volcanoes (Etna, Iblei, Sardinia, etc.) range from tholeiitic to Na-alkaline, and display elemental and isotope signatures typical of FOZO and EM-1 ocean-island basalts (OIB). Other volcanoes (Aeolian Arc, Italian peninsula) range from calc-alkaline-shoshonitic to K-alkaline, exhibit typical 'subduction-related' trace element signatures (low Ta-Nb, high Rb-Cs-REE), and show a large range of radiogenic isotope ratios, from mantle-like in the Aeolian Arc to crustal-like in central Italy. Geochemical data suggest that OIB-type magmatism originated in lithosphere-sthenosphere sources that were unaffected by recent subduction. In contrast, subduction-related magmas come from mantle sources that underwent Eocene to present mixing with various amounts and types of subducted crustal components. Fluxing of the mantle wedge by water-rich fluids from a mid-ocean ridge basalt-type slab ± sediments occurred in the southern Tyrrhenian Sea, whereas interaction between peridotite and various types of sediments occurred in central Italy. These contrasting styles of mantle contaminations relate to the nature (oceanic or continental) of the foreland, slab geometry and pre-metasomatic mantle compositions, which vary greatly along the Apennine arc and are the reason for the formation of the wide variety of orogenic magmas in Italy.

  3. Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

    NASA Astrophysics Data System (ADS)

    Chen, Heng; Savage, Paul S.; Teng, Fang-Zhen; Helz, Rosalind T.; Moynier, Frédéric

    2013-05-01

    The zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation. The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰<δ66Zn<0.36‰; δ66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe-Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰<δ66Zn<0.33‰), however, the degree of fractionation caused by magmatic differentiation is less significant (only 0.07‰) and no correlation between isotope composition and degree of differentiation is seen. We conclude that high temperature magmatic differentiation can cause Zn isotope fractionation that is resolvable at current levels of precision, but only in compositionally-evolved lithologies. With regards to primitive (ultramafic and basaltic) material, this signifies that the terrestrial mantle is essentially homogeneous with respect to Zn isotopes. Utilizing basaltic and ultramafic sample analyses, from different geologic settings, we estimate that the average Zn isotopic composition of Bulk Silicate Earth is δ66Zn=0.28

  4. Igneous geology of the Carlin trend, Nevada: The importance of Eocene magmatism in gold mineralization

    NASA Astrophysics Data System (ADS)

    Ressel, Michael Walter, Jr.

    not to magmatism, metamorphism, and/or large-scale extension. A recently established Eocene age for major gold introduction narrows the possibilities, and two principal models have emerged: one involving Eocene magmatism as the heat source to drive shallow hydrothermal circulation and the other advocating deeply sourced metamorphic fluids released into the upper crust during regional extension. Critical to the latter argument is the temporal association of extension to gold mineralization, which as yet, is not demonstrated. We argue that Eocene magmatism in the form of large underlying plutons, was the major recognized process that affected the Carlin trend during gold mineralization. These plutons supplied the heat that drove discrete hydrothermal systems. (Abstract shortened by UMI.)

  5. Use of diverse geochemical data sets to determine sources and sinks of nitrate and methane in groundwater, Garfield County, Colorado, 2009

    USGS Publications Warehouse

    McMahon, P.B.; Thomas, J.C.; Hunt, A.G.

    2011-01-01

    Previous water-quality assessments reported elevated concentrations of nitrate and methane in water from domestic wells screened in shallow zones of the Wasatch Formation, Garfield County, Colorado. In 2009, the U.S. Geological Survey, in cooperation with the Colorado Department of Public Health and Environment, analyzed samples collected from 26 domestic wells for a diverse set of geochemical tracers for the purpose of determining sources and sinks of nitrate and methane in groundwater from the Wasatch Formation. Nitrate concentrations ranged from less than 0.04 to 6.74 milligrams per liter as nitrogen (mg/L as N) and were significantly lower in water samples with dissolved-oxygen concentrations less than 0.5 mg/L than in samples with dissolved-oxygen concentrations greater than or equal to 0.5 mg/L. Chloride/bromide mass ratios and tracers of groundwater age (tritium, chlorofluorocarbons, and sulfur hexafluoride) indicate that septic-system effluent or animal waste was a source of nitrate in some young groundwater (less than 50 years), although other sources such as fertilizer also may have contributed nitrate to the groundwater. Nitrate and nitrogen gas (N2) concentrations indicate that denitrification was the primary sink for nitrate in anoxic groundwater, removing 99 percent of the original nitrate content in some samples that had nitrate concentrations greater than 10 mg/L as N at the time of recharge. Methane concentrations ranged from less than 0.0005 to 32.5 mg/L and were significantly higher in water samples with dissolved-oxygen concentrations less than 0.5 mg/L than in samples with dissolved-oxygen concentrations greater than or equal to 0.5 mg/L. High methane concentrations (greater than 1 mg/L) in some samples were biogenic in origin and appeared to be derived from a relatively deep source on the basis of helium concentrations and isotopic data. One such sample had water-isotopic and major-ion compositions similar to that of produced water from the

  6. Controls on Calcite Solubility in Metamorphic and Magmatic Fluids

    NASA Astrophysics Data System (ADS)

    Manning, C. E.; Eguchi, J.; Galvez, M.

    2015-12-01

    Calcite is an important hydrothermal alteration product in a wide range of environments. The role of calcite in hydrothermal alteration depends on its solubility in geologic fluids, especially H2O. At ambient T and P, calcite solubility is low and it exhibits well-known declining, or "reverse", solubility with rising T. However, experimental and theoretical studies show that increasing P yields higher solubility and restricts the region of reverse solubility behavior to higher temperature. At 0.2 GPa the reverse solubility region lies at T>600°C; at 0.5 GPa, >800°C. Thus, whereas calcite possesses relatively low solubility in pure H2O in shallow hydrothermal systems (typically <10 ppm C), it is substantially more soluble at conditions of middle and lower crustal metamorphism and magmatism, reaching concentrations ≥1000 ppm. At the higher P of subduction zones, aragonite solubility in H2O is even greater. Thus, neglecting other solubility controls, calcite precipitation is favored as crustal fluids cool and/or decompress. However, the solubility of calcite in H2O also depends strongly on other solutes, pH, and fO2. Sources of alkalinity decrease calcite solubility. In contrast, sources of acidity such as CO2 and Cl increase solubility. Crustal fluids can be enriched in alkali halides such as NaCl. Calcite solubility increases with increasing salt content at a given P and T. From approximately seawater salinity to salt saturation, the fluid behaves as a dilute molten salt and calcite solubility increases as the square of the salt mole fraction regardless of the alkali (Li, Na, K, Cs) or halogen (F, Cl, Br, I) considered. Similar behavior is seen in mixed salt solutions. At lower salinities, solubility behavior is as expected in dilute electrolyte solutions. The transition from dilute electrolyte to molten salt is fundamental to the properties of crustal fluids. Reduction of carbonate species or CO2 in the fluid to CH4, which is common during serpentinization of

  7. Geochemistry of the Neoproterozoic metasediments of Malhaq and Um Zariq formations, Kid metamorphic complex, Sinai, Egypt: Implications for source-area weathering, provenance, recycling, and depositional tectonic setting

    NASA Astrophysics Data System (ADS)

    El-Bialy, Mohammed Zaky

    2013-08-01

    The Um Zariq and Malhaq formations occupy roughly the northern half of the Kid metamorphic complex of SE Sinai, in the NE part of the Arabian-Nubian Shield. The Um Zariq Formation metasediments are relicts of an old sedimentary sequence (Cryogenian; 813 ± 6 Ma), whereas the Malhaq Formation records several phases of Ediacaran sedimentation and volcanic activity (615-607 Ma). The Um Zariq Formation is mainly represented by well-bedded metapelitic schists, while the Malhaq Formation comprises a series of structureless to schistose felsic to intermediate metavolcanics interbedded with mica-rich phyllites and schists. The Um Zariq metasediments are depleted in SiO2, CaO and K2O and enriched in TiO2, Al2O3 and K2O relative to those of the Malhaq Formation. Aside from the relatively low Ni and Cr concentrations, compatible transition elements of these metasediments are comparable to average crustal contents. Except for marked Sr depletion, LILEs are around average continental crust values. Pronounced negative Nb-Ta anomalies and enrichment of Um Zariq samples in Th, U, Zr, Ti and Y relative to Malhaq ones are the main features of HFSEs. The REE patterns of all samples are parallel to sub-parallel LREE-enriched, with distinct negative Eu anomalies and weakly fractionated HREE segments. The source rocks of the Malhaq Formation metasediments underwent mild to moderate chemical weathering, whereas those of the Um Zariq Formation have suffered severe chemical weathering. These metasediments are predominately derived from felsic to intermediate igneous sources, with a particular slight addition from recycled sedimentary source to the Malhaq Formation metasediments. They are collectively geochemically immature and have suffered minor sedimentary recycling, with the experience of the Malhaq Formation metasediments from higher degree of sorting and reworking. The Malhaq and Um Zariq metasediments were originally deposited in a continental arc setting, most probably back

  8. Yellowstone Lake: A Large Volcanic Lake Influenced by the Yellowstone Magmatic System

    NASA Astrophysics Data System (ADS)

    Shanks, W. C.; Morgan, L. A.

    2010-12-01

    controlled by reaction with sub-lacustrine volcanic rocks and sediments. Second, linear relationships between the concentration of Cl and many elements in the lake and in hydrothermal vent fluids indicates that Yellowstone Lake water is a mixture of inflowing surface water, hydrothermal fluid, and magmatic volatiles. Sulfur isotope values of hydrothermal vent H2S (δ34S = -0.5 to 3.6) and SO4 (derived from H2S oxidation) in lake waters (δ34S = 2.8 to 3.9) indicate that magmatic H2S is the dominant sulfur source in the lake. Similarly, carbon isotope values of dissolved HCO3 in lake water and vent fluids (δ13C = -1.5 to -8.8) indicate a strong component of magmatic CO2. Locally both δ13C and δ34S values may be affected by a small amount of C or S addition from sedimentary sources, or by local isotopic exchange between reduced and oxidized species. Hydrothermal flux estimates based on Cl indicate that ~10% of the total hydrothermal fluid flux in Yellowstone National Park occurs in Yellowstone Lake.

  9. The age and petrogenesis of alkaline magmatism in the Ampasindava Peninsula and Nosy Be archipelago, northern Madagascar

    NASA Astrophysics Data System (ADS)

    Cucciniello, C.; Tucker, R. D.; Jourdan, F.; Melluso, L.; Morra, V.

    2016-04-01

    The Ampasindava alkaline province consists of a series of circular and elliptical intrusions, lava flows, dyke swarms and plugs of Cenozoic age emplaced into the Mesozoic-Cenozoic sedimentary rocks of the Antsiranana basin (NW Madagascar) and above the crystalline basement. The magmatism in the Ampasindava region is linked to a NW-SE trending extensional tectonic setting. New 40Ar/39Ar age determinations on feldspar separate of alkali granites and basaltic dykes yielded ages of 18.01 ± 0.36 Ma and 26 ± 7 Ma, respectively. Alkali basalts and basanites, nepheline syenites and phonolites, and silica saturated-to-oversaturated syenites, trachytes, granites and rhyolites are the main outcropping lithologies. These rocks have sodic affinity. The felsic rocks are dominant, and range from peraluminous to peralkaline. The mantle-normalized incompatible element patterns of the mafic lavas match those of Na-alkaline lavas in within-plate rift settings. The patterns are identical in shape and absolute concentrations to those of the Bobaomby (Cap d'Ambre) and Massif d'Ambre primitive volcanic rocks. These geochemical features are broadly compatible with variable degrees of partial melting of incompatible element-enriched mantle sources. The mineralogical and geochemical variations are consistent with fractional crystallization processes involving removal of olivine, feldspar, clinopyroxene, amphibole, Fe-Ti oxides and apatite. Removal of small amount of titanite explains the concave upward lanthanide pattern in the evolved nepheline syenites and phonolites, which are additionally rich in exotic silicates typical of agpaitic magmas (eudialyte, F-disilicates).

  10. Constraints on the depth of generation and emplacement of a magmatic epidote-bearing quartz diorite pluton in the Coast Plutonic Complex, British Columbia

    USGS Publications Warehouse

    Chang, J.M.; Andronicos, C.L.

    2009-01-01

    Petrology and P-T estimates indicate that a magmatic epidote-bearing quartz diorite pluton from Mt. Gamsby, Coast Plutonic Complex, British Columbia, was sourced at pressures below ???1.4 GPa and cooled nearly isobarically at ???0.9 GPa. The P-T path indicates that the magma was within the stability field of magmatic epidote early and remained there upon final crystallization. The pluton formed and crystallized at depths greater than ???30 km. REE data indicate that garnet was absent in the melting region and did not fractionate during crystallization. This suggests that the crust was less than or equal to ???55 km thick at 188 Ma during the early phases of magmatism in the Coast Plutonic Complex. Late Cretaceous contractional deformation and early Tertiary extension exhumed the rocks to upper crustal levels. Textures of magmatic epidote and other magmatic phases, combined with REE data, can be important for constraining the P-T path followed by magmas. ?? 2009 Blackwell Publishing Ltd.

  11. Foreland-forearc collisional granitoid and mafic magmatism caused by lower-plate lithospheric slab breakoff: The Acadian of Maine, and other orogens

    USGS Publications Warehouse

    Schoonmaker, A.; Kidd, W.S.F.; Bradley, D.C.

    2005-01-01

    During collisional convergence, failure in extension of the lithosphere of the lower plate due to slab pull will reduce the thickness or completely remove lower-plate lithosphere and cause decompression melting of the asthenospheric mantle; magmas from this source may subsequently provide enough heat for substantial partial melting of crustal rocks under or beyond the toe of the collisional accretionary system. In central Maine, United States, this type of magmatism is first apparent in the Early Devonian West Branch Volcanics and equivalent mafic volcanics, in the slightly younger voluminous mafic/silicic magmatic event of the Moxie Gabbro-Katahdin batholith and related ignimbrite volcanism, and in other Early Devonian granitic plutons. Similar lower-plate collisional sequences with mafic and related silicic magmatism probably caused by slab breakoff are seen in the Miocene-Holocene Papuan orogen, and the Hercynian-Alleghenian belt. Magmatism of this type is significant because it gives evidence in those examples of whole-lithosphere extension. We infer that normal fault systems in outer trench slopes of collisional orogens in general, and possibly those of oceanic subduction zones, may not be primarily due to flexural bending, but are also driven by whole-lithosphere extension due to slab pull. The Maine Acadian example suggests that slab failure and this type of magmatism may be promoted by pre-existing large margin-parallel faults in the lower plate. ?? 2005 Geological Society of America.

  12. A mass balance and isostasy model: Exploring the interplay between magmatism, deformation and surface erosion in continental arcs using central Sierra Nevada as a case study

    NASA Astrophysics Data System (ADS)

    Cao, Wenrong; Paterson, Scott

    2016-06-01

    A one-dimensional mass balance and isostasy model is used to explore the feedbacks between magmatism, deformation and surface erosion and how they together affect crustal thickness, elevation, and exhumation in a continental arc. The model is applied to central Sierra Nevada in California by parameterizing magma volume and deformational strain. The simulations capture the first-order Mesozoic-Cenozoic histories of crustal thickness, elevation and erosion including moderate Triassic crustal thickening and Jurassic crustal thinning followed by a strong Cretaceous crustal thickening, the latter resulting in a 60-70 km-thick crust plus a 20 km-thick arc eclogitic root, and a ˜5 km elevation in the Late Cretaceous. The contribution of contractional deformation to the crustal thickening is twice that of the magmatism. The contribution to elevation from magmatism is dampened by the formation of an eclogitic root. Erosion rate increases with the magnitude of crustal thickening (by magmatism and deformation) but its peak rate always lags behind the peak rate of thickening. We propose that thickened crust initially promotes magma generation by downward transport of materials to the magma source region, which may eventually jam the mantle wedge affecting the retro-arc underthrusting process and reducing arc magmatism.

  13. Tomographic Imaging of the Magmatic System at Mount St. Helens with the iMUSH Broadband Array

    NASA Astrophysics Data System (ADS)

    Ulberg, C. W.; Creager, K. C.; Levander, A.; Kiser, E.; Moran, S. C.; Abers, G. A.; Schmandt, B.; Vidale, J. E.; Houston, H.; Denlinger, R. P.; Williams, M. C. B.

    2015-12-01

    We deployed 70 broadband seismometers in the summer of 2014 to image the velocity structure beneath Mount St. Helens (MSH), Washington, USA as part of a collaborative project called imaging Magma Under St. Helens (iMUSH). Our goal is to illuminate the MSH magmatic system, using active- and passive-source seismology, magnetotellurics and petrology. Details of the velocity structure, coupled with other geophysical and geologic data, can help constrain the geometry and physical state of any bodies of melt beneath the volcano. The broadband array has a diameter of ~100 km centered on MSH with an average station spacing of 10 km, and will remain deployed through summer 2016. It is augmented by dozens of permanent stations in the area. We determine P-wave arrival times using Antelope software and incorporate permanent network picks for the region. We use the program struct3DP to invert travel times to obtain a 3-D seismic velocity model and relocate hypocenters, computing travel times using a 3-D eikonal-equation solver. There were more than 500 useable local events during the first year of iMUSH broadband recording, which to date have provided 5000 arrival times, with the number growing rapidly. The local events include 23 active shots that were set off in the summer of 2014 as part of the iMUSH experiment, which recorded with good signal-to-noise ratios across the entire array. The absolute P times will be augmented by differential times calculated by cross-correlation between observations at the same station for nearby event pairs. These will be incorporated into our model using double-difference tomography. We anticipate that our 3D velocity model will provide the highest resolution image of volcanic plumbing at MSH thus far. Our model interpretation will incorporate results from active-source and ambient noise tomography, receiver functions, magnetotellurics, and petrology.

  14. Os and U-Th isotope signatures of arc magmatism near Mount Mazama, Crater Lake, Oregon

    NASA Astrophysics Data System (ADS)

    Ankney, Meagan E.; Shirey, Steven B.; Hart, Garret L.; Bacon, Charles R.; Johnson, Clark M.

    2016-03-01

    Interaction of mantle melts with the continental crust can have significant effects on the composition of the resulting melts as well as on the crust itself, and tracing this interaction is key to our understanding of arc magmatism. Lava flows and pyroclastic deposits erupted from ∼50 to 7.7 ka at Mt. Mazama (Crater Lake, Oregon) were analyzed for their Re/Os and U-Th isotopic compositions. Mafic lavas from monogenetic vents around Mt. Mazama that erupted during the buildup to its climactic eruption have lower 187Os/188Os ratios (0.1394 to 0.1956) and high 230Th excess ((230Th/238U)0 of 1.180 to 1.302), whereas dacites and rhyodacites tend to have higher 187Os/188Os ratios (0.2292 to 0.2788) and significant 238U excess ((230Th/238U)0 of 0.975 to 0.989). The less radiogenic Os isotope compositions of the mafic lavas can be modeled by assimilation of young (∼2.5 to 7 Ma), mafic lower crust that was modified during regional extension, whereas the more radiogenic Os isotope compositions of the dacites and rhyodacites can be attributed to assimilation of older (∼10 to 16 Ma), mid to upper crust that acquired its composition during an earlier period of Cascade magmatism. Production of Th excesses in the lower crust requires very young garnet formation accompanying dehydration melting in the lower crust at less than a few 100 ka by heat from recent basaltic magma injection. The results from this study suggest that the combination of Os and Th isotopes may be used to provide insights into the timescales of evolution of the continental crust in arc settings, as well as the influence of the crust on erupted magmas, and suggest a link between the age and composition of the lower and upper crust to regional tectonic extension and/or earlier Cascade magmatism.

  15. Mantle refertilization and magmatism in old orogenic regions: The role of late-orogenic pyroxenites

    NASA Astrophysics Data System (ADS)

    France, Lydéric; Chazot, Gilles; Kornprobst, Jacques; Dallai, Luigi; Vannucci, Riccardo; Grégoire, Michel; Bertrand, Hervé; Boivin, Pierre

    2015-09-01

    Pyroxenites and garnet pyroxenites are mantle heterogeneities characterized by a lower solidus temperature than the enclosing peridotites; it follows that they are preferentially involved during magma genesis. Constraining their origin, composition, and the interactions they underwent during their subsequent evolution is therefore essential to discuss the sources of magmatism in a given area. Pyroxenites could represent either recycling of crustal rocks in mantle domains or mantle originated rocks (formed either by olivine consuming melt-rock reactions or by crystal fractionation). Petrological and geochemical (major and trace elements, Sr-Nd and O isotopes) features of xenoliths from various occurrences (French Massif-Central, Jordan, Morocco and Cameroon) show that these samples represent cumulates crystallized during melt percolation at mantle conditions. They formed in mantle domains at pressures of 1-2 GPa during post-collisional magmatism (possibly Hercynian for the French Massif-Central, and Panafrican for Morocco, Jordan and Cameroon). The thermal re-equilibration of lithospheric domains, typical of the late orogenic exhumation stages, is also recorded by the samples. Most of the samples display a metasomatic overprint that may be either inherited or likely linked to the recent volcanic activity that occurred in the investigated regions. The crystallization of pyroxenites during late orogenic events has implications for the subsequent evolution of the mantle domains. The presence of large amounts of mantle pyroxenites in old orogenic regions indeed imparts peculiar physical and chemical characteristics to these domains. Among others, the global solidus temperature of the whole lithospheric domain will be lowered; in turn, this implies that old orogenic regions are refertilized zones where magmatic activity would be enhanced.

  16. Tectonic, magmatic, and metallogenic evolution of the Late Cretaceous arc in the Carpathian-Balkan orogen

    NASA Astrophysics Data System (ADS)

    Gallhofer, Daniela; Quadt, Albrecht von; Peytcheva, Irena; Schmid, Stefan M.; Heinrich, Christoph A.

    2015-09-01

    The Apuseni-Banat-Timok-Srednogorie Late Cretaceous magmatic arc in the Carpathian-Balkan orogen formed on the European margin during closure of the Neotethys Ocean. It was subsequently deformed into a complex orocline by continental collisions. The Cu-Au mineralized arc consists of geologically distinct segments: the Apuseni, Banat, Timok, Panagyurishte, and Eastern Srednogorie segments. New U-Pb zircon ages and geochemical whole rock data for the Banat and Apuseni segments are combined with previously published data to reconstruct the original arc geometry and better constrain its tectonic evolution. Trace element and isotopic signatures of the arc magmas indicate a subduction-enriched source in all segments and variable contamination by continental crust. The magmatic arc was active for 25 Myr (~92-67 Ma). Across-arc age trends of progressively younger ages toward the inferred paleo-trench indicate gradual steepening of the subducting slab away from the upper plate European margin. This leads to asthenospheric corner flow in the overriding plate, which is recorded by decreasing 87Sr/86Sr (0.70577 to 0.70373) and increasing 143Nd/144Nd (0.51234 to 0.51264) ratios over time in some segments. The close spatial relationship between arc magmatism, large-scale shear zones, and related strike-slip sedimentary basins in the Timok and Pangyurishte segments indicates mild transtension in these central segments of the restored arc. In contrast, the Eastern Srednogorie segment underwent strong orthogonal intraarc extension. Segmental distribution of tectonic stress may account for the concentration of rich porphyry Cu deposits in the transtensional segments, where lower crustal magma storage and fractionation favored the evolution of volatile-rich magmas.

  17. A physical model for metal extraction and transport in shallow magmatic systems

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Bachmann, Olivier; Vigneresse, Jean-Louis; Dufek, Josef; Parmigiani, Andrea

    2012-08-01

    The highest concentrations of metals (e.g., Cu, Au, Ag, Mo) in the Earth's crust are found in porphyry-type deposits. The metals are ultimately sourced from magmas, and appear to be concentrated hundred to thousand-fold from typical magmatic contents (ppm-ppb) in the exsolved volatile phase. To better quantify the purging and transport of metals, we develop a physical model of volatile evolution in an incrementally built upper crustal magma reservoirs that considers (1) partitioning of metals from the melt to an exsolved volatile phase, and (2) advection of the buoyant volatile phase using a single dimensionless parameter, the Péclet number (Pe; ratio of advection rate over diffusion rate). We propose that metal extraction and segregation from magmas can occur in 3 stages with different Pe: (1) during exsolution of the magmatic volatile phase in shallow, crystal-poor magma bodies (slow volatile advection; Pe ≪ 1), (2) during the growth of volatile channels that develop in the reservoir as crystallinity increases (Pe < 1), and (3) during advection in connected channels (rapid volatile advection, high Pe ≥ 1). For each stage, a metal enrichment factor can be calculated, allowing insight into the optimal conditions to maximize metal mass flux into the overlying hydrothermal system. The model predicts that the most efficient purging of metals occurs for magmas with intermediate volatile contents and is enhanced during late-stage magmatic activity, as the reservoirs reach high crystallinity and are not disturbed by volcanic venting, in agreement with natural observations suggesting that ore formation post-dates volcanic activity.

  18. Structure of continental rifts: Role of older features and magmatism

    SciTech Connect

    Keller, G.R.

    1996-12-31

    Recent geological and geophysical studies in several continental rifts have begun to shed light on the details of the processes which govern the structural evolution of these important exploration targets. In Kenya and Tanzania, the classic East African rift has been the object of several investigations which reveal that its location follows the boundary (suture ?) between the Tanzanian craton (Archean) and Mozambiquan belt (Proterozoic), The Baikal rift also follows a similar boundary, and the Mid-continent rift of North America appears to do the same. Rifts themselves often act as zones of weakness which are reactivated by younger tectonic regimes. The classic North American example of this effect is the Eocambrian Southern Oklahoma aulacogen which was deformed to create the Anadarko basin and Wichita uplift in the late Paleozoic. The Central basin platform has a similar history although the original rift formed at {approximately}1,100Ma. Integration of geophysical data with petrologic and geochemical data from several rift zones has also provided a new picture of the nature and extent of magmatic modification of the crust. An interesting contradiction is that Phanerozoic rifts, except the Afar region, show little evidence for major magmatic modification of the crust whereas, at least in North America, many Precambrian rifts are associated with very large mafic bodies in the crust. The Kenya rift displays evidence for modification of the lower crust in a two-phase magmatic history, but upper crustal magmatic features are limited to local intrusions associated with volcanoes. In this rift, complex basement structure plays a much more important role than previously realized, and the geophysical signatures of basement structure and magmatism are easy to confuse. If this is also the case in other rifts, additional rift basins remain to be discovered.

  19. Structure of continental rifts: Role of older features and magmatism

    SciTech Connect

    Keller, G.R. )

    1996-01-01

    Recent geological and geophysical studies in several continental rifts have begun to shed light on the details of the processes which govern the structural evolution of these important exploration targets. In Kenya and Tanzania, the classic East African rift has been the object of several investigations which reveal that its location follows the boundary (suture ) between the Tanzanian craton (Archean) and Mozambiquan belt (Proterozoic), The Baikal rift also follows a similar boundary, and the Mid-continent rift of North America appears to do the same. Rifts themselves often act as zones of weakness which are reactivated by younger tectonic regimes. The classic North American example of this effect is the Eocambrian Southern Oklahoma aulacogen which was deformed to create the Anadarko basin and Wichita uplift in the late Paleozoic. The Central basin platform has a similar history although the original rift formed at [approximately]1,100Ma. Integration of geophysical data with petrologic and geochemical data from several rift zones has also provided a new picture of the nature and extent of magmatic modification of the crust. An interesting contradiction is that Phanerozoic rifts, except the Afar region, show little evidence for major magmatic modification of the crust whereas, at least in North America, many Precambrian rifts are associated with very large mafic bodies in the crust. The Kenya rift displays evidence for modification of the lower crust in a two-phase magmatic history, but upper crustal magmatic features are limited to local intrusions associated with volcanoes. In this rift, complex basement structure plays a much more important role than previously realized, and the geophysical signatures of basement structure and magmatism are easy to confuse. If this is also the case in other rifts, additional rift basins remain to be discovered.

  20. Geochemistry of the Neoproterozoic metasediments of Malhaq and Um Zariq formations, Kid Metamorphic Complex, Sinai, Egypt: implications for source-area weathering, provenance, recycling, and depositional tectonic setting

    NASA Astrophysics Data System (ADS)

    El-Bialy, Mohammed Z.

    2013-04-01

    Formation metasediments. They are collectively geochemically immature and have suffered minor sedimentary recycling, with the bearing of Malhaq Formation metasediments from advanced degree of sorting and reworking. The Malhaq and Um Zariq metasediments had been originally deposited in a continental arc setting, most probably back-arc basin, despite the wide time span between their individual depositions. Various geochemical evidences imply that the main source from which these two chronologically distinct metasediments (Ediacaran vs. Cryogenian) have been derived from the juvenile (arc-type) Arabian-Nubian Shield crust.

  1. Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

    USGS Publications Warehouse

    Chang, W.-L.; Smith, R.B.; Wicks, C.; Farrell, J.M.; Puskas, C.M.

    2007-01-01

    The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of ???1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.

  2. Evolution of the Cretaceous magmatism in the Apuseni-Timok-Srednogorie metallogenic belt and implications for the geodynamic reconstructions: new insight from geochronology, geochemistry and isotope studies

    NASA Astrophysics Data System (ADS)

    von Quadt, A.; Peytcheva, I.; Heinrich, C. A.; Frank, M.; Cvetkovic, V.

    2003-04-01

    Most major Cu-Au (-PGE) deposits in the Carpathian Balkan orogen are related to a 1500 km long belt of Upper Cretaceous magmatism extending from southern Romania through Yugoslavia to Bulgaria, with a likely continuation southeast of the Black Sea into Turkey, known as the Apuseni Banat Timok Srednogorie (ABTS) belt (Popov et al., 2000). In the frame of ABTS belt a new investigation was started to reveal the relation between Cretaceous magmatism and the Cu-Au-PGE deposits across the belt in East Serbia (Yugoslavia) and the Panagyurishte district (Bulgaria). The Late Cretaceous (Palaeogene?) magmatism of East Serbia developed along the Timok Magmatic Complex (TMC) in the east and the Ridanj Krepoljin Zone (RKZ) in the west. High precision U-Pb single zircon dating and a combination of isotope tracing, geochronological data as well as petrological data were used to provide additional data for the geodynamic evolution. A maximum life span of 2.5 Ma could be calculated for the first phase of volcanic activity in TMC, starting with the Amf-andesites of Veliki Kravelj (86.29 ± 0.32 Ma) and finishing with the Timozites (84.66 ± 0.5 Ma). Ore bearing magmatism in a single deposit (Veliki Kravelj) extended a maximum of 0.6 Ma ("pre-ore": 86.29 ± 0.32 Ma, "post-ore": 86.17 ± 0.15 Ma). Preliminary data for the dacites (70.3 ± 3.5 Ma) outcropping near Krepoljin give evidence for a shifting of the volcanic activity from TMC to RKZ together with changing the ore-deposit type from Cu-Au-PGE (TMC) to Pb-Zn-Cu (RKZ). Isotope tracing give evidence for mantle dominated source with increasing of crustal contamination in the same direction: (87Sr/86Sr ratios: 0.70388 to 0.706050, e-Hf-zircon data: +12 in TMC to +4.5 in RKZ). The Panagyurishte district (Bulgaria) show a duration time of the magmatic activity of 14 Ma, starting in the north at 92 Ma and finishing in the south at 78 Ma. Ore-related magmatism becomes younger in the same direction but finishes with 86 Ma. Multiple short

  3. Controls on the Mobilization and Transport of Hfse in Ore-Forming Magmatic-Hydrothermal Systems

    NASA Astrophysics Data System (ADS)

    Sanchez-Valle, C.; Louvel, M.

    2015-12-01

    The genesis of economical rare metals (Zr, Nb, REE) ore deposits in largegranitic complexes (e.g., Strange Lake and Thor Lake Nechalacho deposit, Canada; Galineiro complex, Spain) is related to the intrusion of alkaline halogen-rich magmatic bodies. Although the role of exolved magmatic fluids in the mobilization and transport of HFSE is widely recognized, the physico-chemical conditions and atomic-scale mechanisms that control the formation of the ore deposits remain poorly understood. We present new experimental constraints on behavior of HFSE during the exsolution of aqueous fluids from peralkaline granitic magmas at crustal conditions. In situ partitioning and speciation studies of Zr in the haplogranite-(F)-H2O systems using synchrotron X-ray spectroscopies provide evidence for large controls of fluid chemistry and temperature on the mobilization and transport of HFSE in crustal settings. At shallow crustal pressure conditions (> 800 °C and 0.3 GPa), Zr preferentially partitions into the exolved aqueous fluid in the presence of fluorine (Df/mZr = 1.40 ± 0.10) as previously reported for Nb in F- (and Cl-) bearing metaluminous granitic systems at similar conditions. The reverse partitioning of HFSE (Zr and Nb) into the aqueous phase at temperature above 800 °C contrast with the behavior observed at lower temperatures, where the Df/mZr remain lower than 1 at all pressures. The enrichment of the aqueous phase in HFSE (Zr, Nb) in the earlier stages of the magmatic evolution is likely related to the enhanced peralkalinity of low pressure (< 0.4 GPa), F-bearing aqueous fluid coexisting with granitic melts as temperature increases. This particular fluid chemistry provides the favorable conditions for the mobilization of HFSE via the formation of HFSE-O-Si/Na clusters in the fluid as shown by the in situ Zr speciation data. Our results show that the exsolution of highly alkaline early magmatic fluid at pressures below 0.4 GPa has the potential to extract HFSE from F

  4. Crustal Strain Patterns in Magmatic and Amagmatic Early Stage Rifts: Border Faults, Magma Intrusion, and Volatiles

    NASA Astrophysics Data System (ADS)

    Ebinger, C. J.; Keir, D.; Roecker, S. W.; Tiberi, C.; Aman, M.; Weinstein, A.; Lambert, C.; Drooff, C.; Oliva, S. J. C.; Peterson, K.; Bourke, J. R.; Rodzianko, A.; Gallacher, R. J.; Lavayssiere, A.; Shillington, D. J.; Khalfan, M.; Mulibo, G. D.; Ferdinand-Wambura, R.; Palardy, A.; Albaric, J.; Gautier, S.; Muirhead, J.; Lee, H.

    2015-12-01

    Rift initiation in thick, strong continental lithosphere challenges current models of continental lithospheric deformation, in part owing to gaps in our knowledge of strain patterns in the lower crust. New geophysical, geochemical, and structural data sets from youthful magmatic (Magadi-Natron, Kivu), weakly magmatic (Malawi, Manyara), and amagmatic (Tanganyika) sectors of the cratonic East African rift system provide new insights into the distribution of brittle strain, magma intrusion and storage, and time-averaged deformation. We compare and contrast time-space relations, seismogenic layer thickness variations, and fault kinematics using earthquakes recorded on local arrays and teleseisms in sectors of the Western and Eastern rifts, including the Natron-Manyara basins that developed in Archaean lithosphere. Lower crustal seismicity occurs in both the Western and Eastern rifts, including sectors on and off craton, and those with and without central rift volcanoes. In amagmatic sectors, lower crustal strain is accommodated by slip along relatively steep border faults, with oblique-slip faults linking opposing border faults that penetrate to different crustal levels. In magmatic sectors, seismicity spans surface to lower crust beneath both border faults and eruptive centers, with earthquake swarms around magma bodies. Our focal mechanisms and Global CMTs from a 2007 fault-dike episode show a local rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with time-averaged strain recorded in vent and eruptive chain alignments. These patterns suggest that strain localization via widespread magma intrusion can occur during the first 5 My of rifting in originally thick lithosphere. Lower crustal seismicity in magmatic sectors may be caused by high gas pressures and volatile migration from active metasomatism and magma degassing, consistent with high CO2 flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and

  5. Major and Trace Element Geochemistry of the Mafic Magmatic Rocks from the Betul Mobile Belt, Central Indian Tectonic Zone

    NASA Astrophysics Data System (ADS)

    Choudhury, A.; Ghatak, A.

    2015-12-01

    Peninsular shield of India is composed of several Archaean cratons bordered by Proterozoic mobile belts which amalgamated the Archaean cratons and helped in the growth of the Indian subcontinent. The ENE-WSW trending Central Indian Tectonic Zone (CITZ) is one such important mobile belt which sutures the Bundelkhand and the Aravalli craton in the north and Bastar, Singhbhum and Dharwar cratons in the south. The CITZ is a collection of lithotectonic terranes ranging in age from Archaean to recent and comprises supracrustal belts, granulite belts, shear zones and felsic-mafic magmatic rocks. The Betul belt is characterized by a litho-package of plutonic magmatic rocks, volcano-sedimentary rocks, bimodal volcanics and associated base metal sulphide mineralization. The petrological, geochemical and geochronological evolution of the mafic magmatic rocks has significance in our understanding of Proterozoic crustal evolution in central India. Here we report major and trace element concentrations of 14 mafic samples (basaslts, gabbors, pyroxenites and dolerites) in an attempt to classify, characterise and suggest a spatial and temporal evolution of the mafic magmatic rocks of the Betul mobile belt vis-à-vis CITZ. Traditionally these rocks have been classified as being calc-alkaline rocks, related to arc volcanism and rift tectonics. We have divided these rocks into those have a positive Europium anomaly and those having a negative Europium anomaly to better understand the source and the contaminant for these rocks. We find characterisitic difference specifically in the trace element ratios and concentrations of the rocks with +Eu anomaly [La=10.69ppm; LaN/YbN=3.65] and those with -Eu anomaly [La=27.59; LaN/YbN=8.86]. Based on these data we propose that the Betul mafic rocks may have been derived from an enriched mantle source that experienced contamination from the lower continental crust or sub-continental lithosphere prior to eruption.

  6. Crustal processes cause adakitic chemical signatures in syn-collision magmatism from SE Iran

    NASA Astrophysics Data System (ADS)

    Allen, Mark; Kheirkhah, Monireh; Neill, Iain

    2015-04-01

    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.

  7. Ulkan-Dzhugdzhur ore-bearing anorthosite-rapakivi granite-peralkaline granite association, Siberian Craton: Age, tectonic setting, sources, and metallogeny

    NASA Astrophysics Data System (ADS)

    Larin, A. M.

    2014-07-01

    The paper systematizes and integrates the results of geological, isotopic geochronological, and geochemical studies of the igneous rocks that make up the Ulkan-Dzhugdzhur anorthosite-rapakivi granite-peralkaline granite association and related mineralization. This association is a typical example of anorogenic igneous rocks that formed in the within-plate geodynamic setting most likely under effect of the mantle superplume, which was active in the territory of the Siberian Craton 1.75-1.70 Ga ago. The igneous rock association formed in a discrete regime that reflected the pulsatory evolution of a sublithospheric mantle source. The prerift (1736-1727 Ma) and rift proper (1722-1705 Ma) stages and a number of substages are distinguished. All igneous rocks pertaining to this association have mixed mantle-crustal origin. Basic rocks crystallized from the OIB-type basaltic magma, which underwent crustal contamination at various depths. Felsic rocks are products of mantle and crustal magma mixing. The contribution of mantle component progressively increased in a time-dependent sequence: moderately alkaline subsolvus granite → moderately alkaline and alkaline hypersolvus granites → peralkaline hypersolvus granite. All endogenic deposits in the studied district are related to a single source represented by the mantle plume and its derivatives. The Fe-Ti-apatite deposits hosted in anorthosite formed as a result of intense lower crustal contamination of basaltic magma near the Moho discontinuity and two stages of fractional crystallization at lower and upper crustal depth levels. The rare-metal deposits are genetically related to peralkaline granite. Formation of uranium deposits was most likely caused by Middle Riphean rejuvenation of the region, which also involved rocks of the Ulkan-Dzhugdzhur association.

  8. The influence of magmatic differentiation on the oxidation state of Fe in a basaltic arc magma

    SciTech Connect

    Kelley, Katherine A.; Cottrell, Elizabeth

    2012-05-09

    Subduction zone basalts are more oxidized than basalts from other tectonic settings (e.g., higher Fe{sup 3+}/{Sigma}Fe), and this contrast may play a central role in the unique geochemical processes that generate arc and continental crust. The processes generating oxidized arc magmas, however, are poorly constrained, although they appear inherently linked to subduction. Near-surface differentiation processes unique to arc settings might drive oxidation of magmas that originate in equilibrium with a relatively reduced mantle source. Alternatively, arc magmas could record the oxidation conditions of a relatively oxidized mantle source. Here, we present new measurements of olivine-hosted melt inclusions from a single eruption of Agrigan volcano, Marianas, in order to test the influence of differentiation processes vs. source conditions on the Fe{sup 3+}/{Sigma}Fe ratio, a proxy for system oxygen fugacity (fO{sub 2}). We determined Fe{sup 3+}/{Sigma}Fe ratios in glass inclusions using {mu}-XANES and couple these data with major elements, dissolved volatiles, and trace elements. After correcting for post-entrapment crystallization, Fe{sup 3+}/{Sigma}Fe ratios in the Agrigan melt inclusions (0.219 to 0.282), and their modeled fO{sub 2}s ({Delta}QFM + 1.0 to + 1.8), are uniformly more oxidized than MORB, and preserve a portion of the evolution of this magma from 5.7 to 3.2 wt.% MgO. Fractionation of olivine {+-} clinopyroxene {+-} plagioclase should increase Fe{sup 3+}/{Sigma}Fe as MgO decreases in the melt, but the data show Fe{sup 3+}/{Sigma}Fe ratios decreasing as MgO decreases below 5 wt.% MgO. The major element trajectories, taken in combination with this strong reduction trend, are inconsistent with crystallization of common ferromagnesian phases found in the bulk Agrigan sample, including magnetite. Rather, decreasing Fe{sup 3+}/{Sigma}Fe ratios correlate with decreasing S concentrations, suggesting that electronic exchanges associated with SO{sub 2} degassing may

  9. Characteristic Time Scales of Characteristic Magmatic Processes and Systems

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.

    2004-05-01

    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

  10. Carbon dioxide and helium emissions from a reservoir of magmatic gas beneath Mammoth Mountain, California

    USGS Publications Warehouse

    Sorey, M.L.; Evans, William C.; Kennedy, B.M.; Farrar, C.D.; Hainsworth, L.J.; Hausback, B.

    1998-01-01

    Carbon dioxide and helium with isotopic compositions indicative of a magmatic source (??13C = -4.5 to -5???, 3He/4He = 4.5 to 6.7 RA) are discharging at anomalous rates from Mammoth Mountain, on the southwestern rim of the Long Valley caldera in eastern California. The gas is released mainly as diffuse emissions from normal-temperature soils, but some gas issues from steam vents or leaves the mountain dissolved in cold groundwater. The rate of gas discharge increased significantly in 1989 following a 6-month period of persistent earthquake swarms and associated strain and ground deformation that has been attributed to dike emplacement beneath the mountain. An increase in the magmatic component of helium discharging in a steam vent on the north side of Mammoth Mountain, which also began in 1989, has persisted until the present time. Anomalous CO2 discharge from soils first occurred during the winter of 1990 and was followed by observations of several areas of tree kill and/or heavier than normal needlecast the following summer. Subsequent measurements have confirmed that the tree kills are associated with CO2 concentrations of 30-90% in soil gas and gas flow rates of up to 31,000 g m-2 d-1 at the soil surface. Each of the tree-kill areas and one area of CO2 discharge above tree line occurs in close proximity to one or more normal faults, which may provide conduits for gas flow from depth. We estimate that the total diffuse CO2 flux from the mountain is approximately 520 t/d, and that 30-50 t/d of CO2 are dissolved in cold groundwater flowing off the flanks of the mountain. Isotopic and chemical analyses of soil and fumarolic gas demonstrate a remarkable homogeneity in composition, suggesting that the CO2 and associated helium and excess nitrogen may be derived from a common gas reservoir whose source is associated with some combination of magmatic degassing and thermal metamorphism of metasedimentary rocks. Furthermore, N2/Ar ratios and nitrogen isotopic values

  11. Geochronology and geochemistry of rhyolites from Hormuz Island, southern Iran: A new record of Cadomian arc magmatism in the Hormuz Formation

    NASA Astrophysics Data System (ADS)

    Faramarzi, Narges Sadat; Amini, Sadraddin; Schmitt, Axel Karl; Hassanzadeh, Jamshid; Borg, Gregor; McKeegan, Kevin; Razavi, Seyed Mohammad Hosein; Mortazavi, Seyed Mohsen

    2015-11-01

    Hormuz Island, a salt-gypsum dome in the Persian Gulf in southern Iran, is a complex halotectonic melange comprising evaporites, carbonates, volcanic and volcaniclastic rocks, as well as low-grade metamorphic and sedimentary rocks. Based on trace element (including rare earth elements REE) compositions of whole rocks and zircon, Hormuz rhyolites are inferred to have formed from subduction-related magmas generated in an active continental margin setting. Ion microprobe analyses of zircon crystals yielded concordant U-Pb ages with weighted mean 206Pb/238U age of 558 ± 7 Ma (juvenile zircons in contrast to those from previous magmatic episodes or xenocrysts) along with younger and older discordant ages which likely represent Pb loss and the presence of xenocrystic domains, respectively. Trace element ratios and in particular REE patterns of juvenile zircon from Hormuz rhyolites indicate crystallization from continental crustal source rocks typical for subduction environments. The concordant 206Pb/238U zircon age agrees with ages obtained from most other structural zones of Iran which indicate regional consolidation of igneous basement during the Neoproterozoic to Early Cambrian. Furthermore, Hormuz rhyolite ages and compositions correlate with counterparts that co-evolved along the northern margin of Gondwana, and are now preserved along the southern coast of the Persian Gulf. Hormuz rhyolites erupted synchronously with the deposition of carbonates and evaporites, suggesting that volcanism occupied an extensional backarc or retroarc setting. Such depositional environments predominated in the northern Gondwana continental margin where convergent (Proto-Tethyan) and extensional (Najd) tectonic regimes coexisted.

  12. Sills as Piecemeal Emplacements of a Layered Intrusion: The Ferrar Magmatic System, Dry Valleys, Antarctica

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.

    2007-12-01

    It is especially difficult to discern for mafic layered systems the initial magmatic conditions giving rise to the end product. What was the style and duration of filling? What was the compositional variation and phenocryst content of the individual magmatic pulses? And, if phenocrysts are present, were they sorted prior to injection during ascension? The Ferrar dolerite magmatic system (~180 ma; > 5,000 km3) contains information fundamental to these questions. The central stack of (at least) four massive sills (~300-750 m thick) represents an episodic or serial loading of a magmatic system with compositionally and temporally contiguous aliquots of phenocryst-free tholeiitic and phenocryst-laden ultramafic magma. The same magmatic-volcanic episode gave rise to the overlying extensive Kirkpatrick basalt (e.g., Fleming et al., 1995; CMP,121;217). Whole rock compositions (e.g., CaO vs MgO) for the suite of sills shows a sweeping pattern very similar to that of Hawaii except that the context of each sample in its natural setting, as opposed to a stack of lavas, is well known. Rock composition can be related to the physical setting of the sample and the spatial setting of the contiguous rock mass. The internal structure of the ultramafic Basement Sill, the youngest and most mafic sill, reflects a long succession of filling events. It is stuffed by a vast tongue of large (1-20 mm) orthopyroxene and much smaller (< 1 mm) plagioclase; both were present in the inflowing magma, with plagioclase growing during transport. Bulk composition (7-20 MgO) and opx size and composition (En40-En90) symmetrically vary vertically through the sill, reflecting sorting during ascent. (The marginal quench zones argue against significant post emplacement re-equilibration.) The size and high concentration of opx has generally allowed little relative post- emplacement settling, but this opx matrix has acted as a sieve to the plagioclase, forming anorthosite stringers and layers pervasively and

  13. Zinc isotope fractionation during magmatic differentiation and the isotopic composition of the bulk Earth

    USGS Publications Warehouse

    Chen, Heng; Savage, Paul S.; Teng, Fang-Zehn; Helz, Rosalind T.; Moynier, Frédéric

    2013-01-01

    he zinc stable isotope system has been successfully applied to many and varied fields in geochemistry, but to date it is still not completely clear how this isotope system is affected by igneous processes. In order to evaluate the potential application of Zn isotopes as a proxy for planetary differentiation and volatile history, it is important to constrain the magnitude of Zn isotopic fractionation induced by magmatic differentiation. In this study we present high-precision Zn isotope analyses of two sets of chemically diverse, cogenetic samples from Kilauea Iki lava lake, Hawaii, and Hekla volcano, Iceland, which both show clear evidence of having undergone variable and significant degrees of magmatic differentiation. The Kilauea Iki samples display small but resolvable variations in Zn isotope composition (0.26‰66Zn66Zn defined as the per mille deviation of a sample's 66Zn/64Zn compositional ratio from the JMC-Lyon standard), with the most differentiated lithologies exhibiting more positive δ66Zn values. This fractionation is likely a result of the crystallization of olivine and/or Fe–Ti oxides, which can both host Zn in their crystal structures. Samples from Hekla have a similar range of isotopic variation (0.22‰66Zn66Zn=0.28±0.05‰ (2s.d.).

  14. Age of the Emeishan flood magmatism and relations to Permian-Triassic boundary events

    NASA Astrophysics Data System (ADS)

    Lo, Ching-Hua; Chung, Sun-Lin; Lee, Tung-Yi; Wu, Genyao

    2002-05-01

    The Permian-Triassic (P-T) mass extinction, the greatest biological mortality event in the Earth's history, was probably caused by dramatic and global forcing mechanisms such as the Siberian flood volcanism. Here we present the first set of high-precision 40Ar/ 39Ar dating results of volcanic and intrusive rocks from the Emeishan Traps, South China, which define a main stage of the flood magmatism at ˜251-253 Ma and a subordinate precursory activity at ˜255 Ma. This time span is generally coeval with, or slightly older than, the age of the P-T boundary estimated by the ash beds in the Meishan stratotype section and the main eruption of the Siberian Traps. Our data reinforces the notion that the eruption of the Emeishan Traps, rather than eruption of the Siberian Traps, accounted for the formation of the P-T boundary ash beds in South China. The Emeishan flood magmatism, which occurred in the continental margin comprising thick marine limestone formations, moreover, may have triggered rapid release of large volumes of methane and carbon dioxide that could have been responsible for the global δ 13C excursion and associated environmental crisis leading to the mass extinction at the P-T boundary.

  15. The volcaniclastic series from the Luang Prabang Basin, Laos: A witness of a triassic magmatic arc?

    NASA Astrophysics Data System (ADS)

    Rossignol, Camille; Bourquin, Sylvie; Poujol, Marc; Hallot, Erwan; Dabard, Marie-Pierre; Nalpas, Thierry

    2016-04-01

    The paleogeographic evolution of South East Asia (SEA) during the early Mesozoic is still poorly understood and a number of models have recently been put forward to account for the geodynamic evolution of SEA. The Luang Prabang Basin (north Laos), located in the core of a "paleogeographic jigsaw" in SEA, recorded a long lasting volcanism that spanned for ∼ 35 my from the earliest Triassic up to Late Triassic as evidenced by combined stratigraphic and geochronological (U-Pb/zircon) analyses performed on both volcanic and volcaniclastic series. The volcanic rocks are arc tholeiites and calk-alkaline andesites to dacites. The volcaniclastic rocks contain, in part, volcaniclasts produced contemporaneously with sedimentation. Both the volcanic and volcaniclastic series display geochemical features characteristic of a subduction related volcanism. Therefore, the Luang Prabang Basin documents a magmatic arc in a good agreement with the recent recognition of neighboring ophiolitic rocks in the Luang Prabang area. Following a passive margin setting that prevailed from the late Carboniferous to the late Permian, an active margin then initiated along the western margin of the Indochina Block. This active magmatic arc developed as the result of an east-dipping subduction below the Indochina Block during most of the Triassic, at least from ca. 250 to 215 Ma. Subsequently, this oceanic subduction episode must have been followed by a continental collision of the Indochina Block with the eastern Simao Block, at a period that remains to be defined.

  16. Liquid carbon dioxide of magmatic origin and its role in volcanic eruptions

    USGS Publications Warehouse

    Chivas, A.R.; Barnes, I.; Evans, William C.; Lupton, J.E.; Stone, J.O.

    1987-01-01

    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.

  17. Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest

    USGS Publications Warehouse

    Farrar, C.D.; Sorey, M.L.; Evans, William C.; Howle, J.F.; Kerr, B.D.; Kennedy, B.M.; King, C.-Y.; Southon, J.R.

    1995-01-01

    MAMMOTH Mountain, in the western United States, is a large dacitic volcano with a long history of volcamsm that began 200 kyr ago1 and produced phreatic eruptions as recently as 500 ?? 200 yr BP (ref. 2). Seismicity, ground deformation and changes in fumarole gas composition suggested an episode of shallow dyke intrusion in 1989-90 (refs 3, 4). Areas of dying forest and incidents of near asphyxia in confined spaces, first reported in 1990, prompted us to search for diffuse flank emissions of magmatic CO2, as have been described at Mount Etna5 and Vulcano6. Here we report the results of a soil-gas survey, begun in 1994, that revealed CO2 concentrations of 30-96% in a 30-hectare region of killed trees, from which we estimate a total CO2 flux of ???1,200 tonnes per day. The forest die-off is the most conspicuous surface manifestation of magmatic processes at Mammoth Mountam, which hosts only weak fumarolic vents and no summit activity. Although the onset of tree kill coincided with the episode of shallow dyke intrusion, the magnitude and duration of the CO2 flux indicates that a larger, deeper magma source and/or a large reservoir of high-pressure gas is being tapped.

  18. Tectonic transition associated with Kazakhstan Orocline in the Late Paleozoic: magmatic archives of western Chinese Tianshan

    NASA Astrophysics Data System (ADS)

    Cai, Keda

    2016-04-01

    Kazakhstan accretionary system was a principle component of the Central Asian Orogenic Belt (CAOB) that is one of the largest accretionary orogens on earth. The Kazakhstan composite continent could have been established in the Early Paleozoic by the Kazakhstan accretionary system in the form of progressively amalgamations of diverse tectonic units, such as continental ribbon, accretionary prim, oceanic remnant and arc material. Subsequently, the composite continent was bended to form a spectacular U-shaped architecture that probably occurred in the Late Paleozoic. The western Chinese Tianshan is situated on the south wing of the Kazakhstan Orocline, featured by extensive magmatim, intense deformation and voluminous mineralization. Our new geochronological and geochemical data suggest a noticeable magmatic gap between Late Devonian and Early carboniferous and contrasting magma sources of these magmatic rocks. The significant shifts correspond to the tectonic transition from terrane amalgamation to mountain bending in the Early Paleozoic. This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (2014CB448000), Xinjiang outstanding youth scientific grant (2013711003) and the Talent Awards to KDC from the China Government under the 1000 Talent Plan.

  19. Trace element and isotopic constraints on magmatic evolution at Lassen volcanic center

    SciTech Connect

    Bullen, T.D.; Clynne, M.A. )

    1990-11-10

    Magmatic evolution at the Lassen volcanic center (LVC) is characterized by a transition from predominantly andesitic to predominantly silicic volcanism with time. Magmas of the adesitic, or Brokeoff phase of volcanism range in composition from basaltic andesite to dacite, whereas those of silicic, or Lassen phase range in composition from basaltic andesite to rhyolite. The distinctive mixing-dominated arrays for each volcanic phase manifest the generation and evolution of two physically distinct, but genetically related magma systems. The LVC magmas have Sr, Nd, and Pb isotope characteristics that approximate two-component mixing arrays. One isotopic component is similar in composition to that of NE Pacific Ocean ridge and seamount basalts (MORB component), the other to mafic Mesozoic granitoids sampled from the neighboring Klamath and Sierra Nevada provinces (KSN component). The lack of a correlation between the major element and isotopic compositions of LVC magmas seriously limits any model for magmatic evolution that relies on assimilation of old middle to upper crust by isotopically homogeneous mafic magmas during their ascent through the crust. Alternatively, the isotopic and geochemical uniformity of the most silicic magmas of the Brokeoff and Lassen phases suggests that they are well-homogenized partial melts. The likely source region for these silicic melts is the lower crust, which the authors envision to consist primarily of mafic igneous rocks that are similar in geochemical and isotopic diversity to the regional mafic lavas.

  20. Jurassic magmatism in Dronning Maud Land: synthesis of results of the MAMOG project

    USGS Publications Warehouse

    Leat, P.T.; Curtis, M.L.; Riley, T.R.; Ferraccioli, F.

    2007-01-01

    The Jurassic Karoo large igneous province (LIP) of Antarctica, and its conjugate margin in southern Africa, is critical for investigating important questions about the relationship of basaltic LIPs to mantle plumes. Detailed aerogeophysical, structural, anisotropy of magnetic susceptibility (AMS), geochronological and geochemical investigations completed under the British Antarctic Survey’s MAMOG project have provided some of the answers. Across most of the area, magma volumes were small compared to those in southern Africa. Jurassic dikes intruding the Archean craton are sparse and the Jutulstraumen trough, a Jurassic rift, is interpreted, from aerogeophysical data, as largely amagmatic. The largest volumes of magma were emplaced along the margin of the craton and close to the Africa-Antarctica rift. Although dikes were emplaced by both vertical and horizontal flow, overwhelmingly magmas in Dronning Maud Land were locally derived, and not emplaced laterally from distant sources. Basaltic magmatism was protracted in Dronning Maud Land (several dike emplacement episodes between ~206 and 175 Ma), and the small magma volumes resulted in highly diverse magma compositions, including picrites and ferropicrites interpreted to have been derived from hot mantle in a mantle plume. The protracted magmatism before the locally ~177 Ma flood lava eruptions, and evidence for a radiating dike swarm, favor a model of mantle plume incubation for 20-30 million years before flood lava eruption.

  1. Magmatic consequences of the transition from orthogonal to oblique subduction in Panama

    NASA Astrophysics Data System (ADS)

    Rooney, Tyrone O.; Morell, Kristin D.; Hidalgo, Paulo; Fraceschi, Pastora

    2015-12-01

    The closure of the Central American Seaway is linked with tectonic and magmatic processes that have controlled the evolution of the Isthmus of Panama. We focus on the terminal stages of arc activity in the Central Panama region, and present new geochemical data from ˜9 Ma explosive silicic volcanism preserved in three syngenetic tuff beds from the Gatun. The magmatic evolution of the Gatun Formation is controlled by a series of magma mushes where pyroxene is the dominant early forming mafic mineral, with amphibole appearing only relatively late in the fractionation sequence. Our data show Gatun lavas exhibit a strong subduction signature, consistent with plate reconstruction models showing arc-normal subduction from Costa Rica to Panama pre-8.5 Ma. However, large ion lithophile elements are depleted in the Gatun Formation in comparison to other regional suites, indicative of a lower flux of subduction fluid to the Gatun Formation mantle source, which is explained by a shift toward magma generation by decompression following the collision of the arc with South America. Oblique subduction commencing ˜8.5 Ma resulted in the shutdown of normal arc activity throughout Panama. We interpret subsequent regional Quaternary adakitic volcanism as a response to this oblique subduction. The now more refractory mantle wedge required greater fluid flux in order to melt. The resultant volatile-rich melts were more prone to deep fractionation of amphibole and garnet cumulates forming adakites. Deep fractionation was potentially enhanced by changing stress regimes on the upper plate caused by oblique subduction.

  2. Mt. St. Helens: Influence of Magmatic Activity on the Biogeochemistry of Thermal Springs

    NASA Astrophysics Data System (ADS)

    Montross, S. N.; Skidmore, M.; Abrahamson, I. S.

    2005-12-01

    Mt St. Helens erupted explosively in 1980, and the intense heat of this event effectively sterilized the crater. The crater is filled with significant ash and volcanic debris and the crater environment has limited vegetation despite relatively abundant water, from rainfall and snowmelt. However, microorganisms thrive in the hot springs that have developed in the crater since the 1980 eruption in this otherwise biologically hostile environment. Channelized drainages exiting the crater contain numerous hot spring sources which result from thermal heating of meteoric water and gain solutes from water-rock interactions. These solutes are important inputs for the microbial communities found within the crater thermal systems. Water samples collected in August 2004 and August 2005 from thermal springs in Step Canyon allow the opportunity to assess the effects of recent magmatic activity in the crater since September 2004, on the aqueous chemistry and microbiology of thermal spring water. We have investigated the composition of microbial communities in crater hot spring ecosystems by identifying small subunit ribosomal RNA sequences amplified directly from extracted genomic DNA. Initial screening of cloned DNA (16S rRNA gene sequence) by restriction fragment length polymorphism and sequencing indicates moderate microbial diversity in this environment with representatives from the domains Bacteria and Archaea. The presentation will examine relationships between the aqueous geochemistry and the microbial communities and temporal changes in these related to the recent magmatic activity.

  3. Tectonic evolution of the Notre Dame magmatic arc, Newfoundland Appalachians

    NASA Astrophysics Data System (ADS)

    van Staal, C.

    2003-12-01

    Notre Dame continental arc magmatism in Newfoundland had an overall lifespan of c. 60 Ma (489-429 Ma). Extensive age dating suggests that arc construction took place in 3 distinct stages, separated by gaps of magmatic quiescence (arc shut-off). The first phase of quiescence (c. 480-468 Ma) corresponds to the start of Taconic collision between the initially west-facing Notre Dame arc and Laurentia. The second phase of magmatic quiescence (455-445 Ma) corresponds to collision between the now east-facing Notre Dame arc and the west-facing, peri-Gondwanan Victoria arc built on a piece of Ganderian crust. Resurgence of arc magmatism followed stepping- back of the west-dipping subduction zone into the oceanic marginal basin that separated the Victoria arc from the Gander margin. A gradual transition (431-429 Ma) from arc-like to mainly juvenile, bimodal within plate-like magmatism coincides with suturing of the Notre Dame arc with the Gander margin along the Dog Bay line and probably reflects break off of the west-dipping Ganderian slab. Preservation of an unconformable and unmetamorphosed Silurian cover, consisting of red beds and bimodal volcanic rocks, over large tracts of the Notre Dame arc indicates that the arc was extinct and stabilized by the Late Silurian (c. 425 Ma) and did not experience any significant overprint during the Early Devonian Acadian orogeny, the effects of which were mainly localized further to the east due to accretion of Avalonia to Laurentia. The second, Mid-Ordovician phase of arc magmatism (c. 469-456 Ma) appears most voluminous and was mainly characterized by K-poor, calc-alkaline quartz diorite to tonalite and, to a lesser extent granodiorite, plutons. These calc-alkaline plutons intruded during deformation and significant thickening of the Notre Dame arc, presumably as a result of ongoing shortening following initial collision with Laurentia and an arc-polarity reversal. Such a tectonic scenario is consistent with the high metamorphic

  4. The physical and chemical evolution of low-salinity magmatic fluids at the porphyry to epithermal transition: a thermodynamic study

    NASA Astrophysics Data System (ADS)

    Heinrich, Christoph A.

    2005-03-01

    Fluid-phase relationships and thermodynamic reaction modelling based on published mineral solubility data are used to re-assess the Cu Au-mineralising fluid processes related to calc-alkaline magmatism. Fluid inclusion microanalyses of porphyry ore samples have shown that vapour-like fluids of low to intermediate salinity and density (~2 10 wt% NaCl eq.; ~0.1 0.3 g cm-3) can carry percentage-level concentrations of copper and several ppm gold at high temperature and pressure. In epithermal deposits, aqueous fluids of similar low to intermediate salinity but liquid-like density are ubiquitous and commonly show a magmatic isotope signature. This paper explores the physical evolution of low-salinity to medium-salinity magmatic fluids of variable density, en route from their magmatic source through the porphyry regime to the near-surface epithermal environment, and investigates the chemical conditions required for effective transport of gold and other components from the magmatic to the epithermal domain. Multicomponent reaction modelling guided by observations of alteration zonation and vein overprinting relationships predicts that epithermal gold deposits are formed most efficiently by a specific succession of processes during the evolution of a gradually cooling magmatic hydrothermal system. (1) The low-salinity to medium-salinity fluid, after separating from the magma and possibly condensing out some hypersaline liquid in the high-temperature porphyry environment, must physically separate from the denser and more viscous liquid, and then cool within the single-phase fluid stability field. By cooling under adequate confining pressure, such a vapour will evolve above the critical curve and contract, without any heterogeneous phase change, to an aqueous liquid of the same salinity. (2) High concentrations of gold, transported as stable Au bisulphide complexes supporting >1 ppm Au even at 200°C, can be maintained throughout cooling, provided that the fluid initially

  5. Fault diagnosis and fault-tolerant finite control set-model predictive control of a multiphase voltage-source inverter supplying BLDC motor.

    PubMed

    Salehifar, Mehdi; Moreno-Equilaz, Manuel

    2016-01-01

    Due to its fault tolerance, a multiphase brushless direct current (BLDC) motor can meet high reliability demand for application in electric vehicles. The voltage-source inverter (VSI) supplying the motor is subjected to open circuit faults. Therefore, it is necessary to design a fault-tolerant (FT) control algorithm with an embedded fault diagnosis (FD) block. In this paper, finite control set-model predictive control (FCS-MPC) is developed to implement the fault-tolerant control algorithm of a five-phase BLDC motor. The developed control method is fast, simple, and flexible. A FD method based on available information from the control block is proposed; this method is simple, robust to common transients in motor and able to localize multiple open circuit faults. The proposed FD and FT control algorithm are embedded in a five-phase BLDC motor drive. In order to validate the theory presented, simulation and experimental results are conducted on a five-phase two-level VSI supplying a five-phase BLDC motor. PMID:26549566

  6. Fault diagnosis and fault-tolerant finite control set-model predictive control of a multiphase voltage-source inverter supplying BLDC motor.

    PubMed

    Salehifar, Mehdi; Moreno-Equilaz, Manuel

    2016-01-01

    Due to its fault tolerance, a multiphase brushless direct current (BLDC) motor can meet high reliability demand for application in electric vehicles. The voltage-source inverter (VSI) supplying the motor is subjected to open circuit faults. Therefore, it is necessary to design a fault-tolerant (FT) control algorithm with an embedded fault diagnosis (FD) block. In this paper, finite control set-model predictive control (FCS-MPC) is developed to implement the fault-tolerant control algorithm of a five-phase BLDC motor. The developed control method is fast, simple, and flexible. A FD method based on available information from the control block is proposed; this method is simple, robust to common transients in motor and able to localize multiple open circuit faults. The proposed FD and FT control algorithm are embedded in a five-phase BLDC motor drive. In order to validate the theory presented, simulation and experimental results are conducted on a five-phase two-level VSI supplying a five-phase BLDC motor.

  7. Oceanic Intraplate Magmatism Off The Vøring Volcanic Passive Margin, Norway - Constraints On Origin From Seismic Velocity Structure

    NASA Astrophysics Data System (ADS)

    Breivik, A. J.; Faleide, J. I.; Mjelde, R.

    2009-12-01

    Early Eocene continental breakup in the NE Atlantic was associated with voluminous extrusive and intrusive magmatism, and initial seafloor spreading produced anomalously thick oceanic crust. During 2003, a wide-angle seismic data set was collected on the Norwegian Margin under the Euromargins 2003 program. One target was a bathymetric high of unclear nature on oceanic crust off the Vøring Plateau. Velocity modeling of the data shows a 14-15 km thick crust supporting the high, and both velocity structure and dimension are similar to the thick igneous crust created at the Vøring margin during breakup. By analyzing stratigraphic disturbances of sedimentary strata on multichannel seismic reflection data around the high, we argued in a recent G3 paper that the bathymetric relief of this Mid- to Late Eocene oceanic crust was established much later, probably Late Miocene. We estimated that ~57500 cubic-km of igneous material was added to the crust at that time, forcing up the high by dominantly lower-crustal growth. This explanation has, however, not been universally accepted, and it has been argued that the crustal thickness may be primary, tied to the strong magmatism following crustal breakup, and later uplift caused by movement on East Jan Mayen Fracture Zone bordering the high to the Southwest. We have looked closer at the velocity structure of the igneous crust of the high in an attempt to constrain the melting mode of the mantle. In recent years several groups have compared igneous crustal thickness to mean seismic velocity (H-Vp) at the northeast Atlantic margins, and always found a positive correlation. This correlation indicates that the breakup magmatism was caused by elevated mantle temperature, cooling down as seafloor spreading progressed. We obtain the same result for the margin part of our profile, but the H-Vp diagram for the bathymetric high itself shows a low correlation. We conclude that melting was quite uniform and the melting degree moderate here

  8. The Axum-Adwa basalt-trachyte complex: a late magmatic activity at the periphery of the Afar plume

    NASA Astrophysics Data System (ADS)

    Natali, C.; Beccaluva, L.; Bianchini, G.; Siena, F.

    2013-08-01

    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.

  9. Timing of magmatism and migmatization in the 2.0-1.8 Ga accretionary Svecokarelian orogen, south-central Sweden

    NASA Astrophysics Data System (ADS)

    Johansson, Åke; Stephens, Michael B.

    2016-07-01

    The Palaeoproterozoic (2.0-1.8 Ga) Svecokarelian orogen in central Sweden consists of a low-pressure, predominantly medium-grade metamorphic domain (central part of Bergslagen lithotectonic unit), enclosed to the north and south by low-pressure migmatite belts. Two periods of metamorphism (1.87-1.85 and 1.83-1.79 Ga) are known in the migmatite belts. In this study, new U-Th-Pb ion microprobe data on zircon and monazite from twelve samples of locally migmatized gneisses and felsic intrusive bodies determine both protolith and metamorphic ages in four sample areas north of Stockholm, inside or immediately adjacent to the medium-grade metamorphic domain. Two orthogneiss samples from the Rimbo area yield unusually old protolith ages of 1909 ± 4 and 1908 ± 4 Ma, while three orthogneisses from the Skutskär and Forsmark areas yield more typical protolith ages between 1901 ± 3 and 1888 ± 3 Ma. Migmatized paragneiss samples from this and two earlier studies contain a significant detrital component sourced from this 1.9 Ga magmatic suite. They are interpreted to be deposited contemporaneously with or shortly after this magmatism. Migmatization of the paragneiss at Rimbo was followed by intrusion of leucogranite at 1846 ± 3 Ma. Even in the other sample areas to the north (Hedesunda-Tierp, Skutskär and Forsmark), metamorphism including migmatization is constrained to the 1.87-1.85 Ga interval and penetrative ductile deformation is limited by earlier studies in the Forsmark area to 1.87-1.86 Ga. However, apart from a metamorphic monazite age of 1863 ± 1 Ma, precise ages were not possible to obtain due to the presence of only partially reset recrystallized domains in zircon, or highly discordant U-rich metamict and altered metamorphic rims. Migmatization was contemporaneous with magmatic activity at 1.87-1.84 Ga in the Bergslagen lithotectonic unit involving a mantle-derived component, and there is a spatial connection between migmatization and this magmatic phase in the

  10. Mare Basaltic Magmatism: A View from the Sample Suite With and Without a Remote-Sensing Prospective

    NASA Astrophysics Data System (ADS)

    Shearer, C. K.; Papike, J. J.; Gaddis, L. R.

    1999-01-01

    and will continue to bear fruit are the duration and early history of lunar volcanism and the relationship between mare basalt composition and eruptive history. Although the petrologic record has been obscured by the early catastrophic impact history of the Moon, there is abundant evidence of pre-3.9 Ga nonmare basaltic volcanism [e.g., 7-8]. Most of this record is retained in small clasts from highland soils and breccias or has been identified through remote sensing. The relationship between the samples and units identified through remote sensing is speculative. Further identification and delineation of older episodes of volcanism and their relationship to episodes of crustal plutonism (Mg and alkali suites) is critical to our interpretation of mantle evolution following magma ocean crystallization and prior to the onset of mare volcanism. Combined sample and remote sensing data sets will allow us to better distinguish among the wide range of models that have been proposed for these early periods of lunar magmatism (Mg suite, alkali suite, KREEP basalts). These models include (1) impact origin; (2) magma ocean crystallization; (3) melting and remobilization of late magma ocean cumulates and/or KREEP infiltrated lower crust; (4) melting of the lower portions of the cumulate pile followed by assimilation of KREEP or anorthositic crust; and (5) melting of deep, hybrid mixed cumulate sources. Additional information is contained in the original.

  11. Granitoid magmatism of Alarmaut granite-metamorphic dome, West Chukotka, NE Russia

    NASA Astrophysics Data System (ADS)

    Luchitskaya, M. V.; Sokolov, S. D.; Bondarenko, G. E.; Katkov, S. M.

    2009-04-01

    structural data indicate temporal relation between magmatism, metamorphism and deformations, accompanying formation of dome structure. Structural data also indicate the dome formation between two regional strike-slips. Strike-slip deformations of terminal stage of collision might have resulted in local zones of extensions [6, 8]. Intrusive contacts of studied granitoid plutons with already deformed host deposits indicate their postcollisional origin. Wide petrographical spectrum of granitoids, hornblende and biotite existence in granites, metaluminous high-K and shoshonite character, biotites compositions allow belonging them to high-K granites of I-type. Appearance of I-type granites in postcollisional setting is usually related to crustal anatexis under the influence of hot asthenospheric mantle due to delamination of lower parts of lithosphere. At the same time the processes of mingling of magmas of different composition, assimilation, fractional crystallization take place. Thus, in tectonic scenario of Alarmaut dome formation except dominating submergence of Chukotka microcontinent margin beneath the structures of North-Asian craton active margin we should assume slab-breakoff or delamination of lithospheric mantle which might have facilitated heat transfer, necessary for melting of granite magma. Aptian-Albian volcanism, localized in postcollisional extensional structures, confirms this assumption. Interrelations of major oxides in granitoids show that compositions of Alarmaut intermediate rocks fall in the fields of melts, experimentally obtained during partial melting of amphibolites, and compositions of granodiorites and granites, along the boundary zone of partial melts of greywackes and dacites, tonalites. Heterogeneity of granitoids source composition or different level of magma contamination by ancient crustal material is confirmed by Sr-Nd data. It is expressed in significant dispersal of ɛNd(Т) and 87Sr/86Sr values in granitoids. Work is carried out at the

  12. Petrology, geochemistry and U-Pb geochronology of magmatic rocks from the high-sulfidation epithermal Au-Cu Chelopech deposit, Srednogorie zone, Bulgaria

    NASA Astrophysics Data System (ADS)

    Chambefort, Isabelle; Moritz, Robert; von Quadt, Albrecht

    2007-10-01

    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.

  13. Bimodal magmatism produced by progressively inhibited crustal assimilation.

    PubMed

    Meade, F C; Troll, V R; Ellam, R M; Freda, C; Font, L; Donaldson, C H; Klonowska, I

    2014-01-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism. PMID:24947142

  14. Bimodal magmatism produced by progressively inhibited crustal assimilation.

    PubMed

    Meade, F C; Troll, V R; Ellam, R M; Freda, C; Font, L; Donaldson, C H; Klonowska, I

    2014-01-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose 'progressively inhibited crustal assimilation' (PICA) as a major cause of bimodality in continental volcanism.

  15. Quantifying crustal thickness over time in magmatic arcs

    NASA Astrophysics Data System (ADS)

    Profeta, Lucia; Ducea, Mihai N.; Chapman, James B.; Paterson, Scott R.; Gonzales, Susana Marisol Henriquez; Kirsch, Moritz; Petrescu, Lucian; Decelles, Peter G.

    2015-12-01

    We present global and regional correlations between whole-rock values of Sr/Y and La/Yb and crustal thickness for intermediate rocks from modern subduction-related magmatic arcs formed around the Pacific. These correlations bolster earlier ideas that various geochemical parameters can be used to track changes of crustal thickness through time in ancient subduction systems. Inferred crustal thicknesses using our proposed empirical fits are consistent with independent geologic constraints for the Cenozoic evolution of the central Andes, as well as various Mesozoic magmatic arc segments currently exposed in the Coast Mountains, British Columbia, and the Sierra Nevada and Mojave-Transverse Range regions of California. We propose that these geochemical parameters can be used, when averaged over the typical lifetimes and spatial footprints of composite volcanoes and their intrusive equivalents to infer crustal thickness changes over time in ancient orogens.

  16. Quantifying crustal thickness over time in magmatic arcs

    PubMed Central

    Profeta, Lucia; Ducea, Mihai N.; Chapman, James B.; Paterson, Scott R.; Gonzales, Susana Marisol Henriquez; Kirsch, Moritz; Petrescu, Lucian; DeCelles, Peter G.

    2015-01-01

    We present global and regional correlations between whole-rock values of Sr/Y and La/Yb and crustal thickness for intermediate rocks from modern subduction-related magmatic arcs formed around the Pacific. These correlations bolster earlier ideas that various geochemical parameters can be used to track changes of crustal thickness through time in ancient subduction systems. Inferred crustal thicknesses using our proposed empirical fits are consistent with independent geologic constraints for the Cenozoic evolution of the central Andes, as well as various Mesozoic magmatic arc segments currently exposed in the Coast Mountains, British Columbia, and the Sierra Nevada and Mojave-Transverse Range regions of California. We propose that these geochemical parameters can be used, when averaged over the typical lifetimes and spatial footprints of composite volcanoes and their intrusive equivalents to infer crustal thickness changes over time in ancient orogens. PMID:26633804

  17. Volcanology. A large magmatic sill complex beneath the Toba caldera.

    PubMed

    Jaxybulatov, K; Shapiro, N M; Koulakov, I; Mordret, A; Landès, M; Sens-Schönfelder, C

    2014-10-31

    An understanding of the formation of large magmatic reservoirs is a key issue for the evaluation of possible strong volcanic eruptions in the future. We estimated the size and level of maturity of one of the largest volcanic reservoirs, based on radial seismic anisotropy. We used ambient-noise seismic tomography below the Toba caldera (in northern Sumatra) to observe the anisotropy that we interpret as the expression of a fine-scale layering caused by the presence of many partially molten sills in the crust below 7 kilometers. This result demonstrates that the magmatic reservoirs of present (non-eroded) supervolcanoes can be formed as large sill complexes and supports the concept of the long-term incremental evolution of magma bodies that lead to the largest volcanic eruptions.

  18. Quantifying crustal thickness over time in magmatic arcs.

    PubMed

    Profeta, Lucia; Ducea, Mihai N; Chapman, James B; Paterson, Scott R; Gonzales, Susana Marisol Henriquez; Kirsch, Moritz; Petrescu, Lucian; DeCelles, Peter G

    2015-01-01

    We present global and regional correlations between whole-rock values of Sr/Y and La/Yb and crustal thickness for intermediate rocks from modern subduction-related magmatic arcs formed around the Pacific. These correlations bolster earlier ideas that various geochemical parameters can be used to track changes of crustal thickness through time in ancient subduction systems. Inferred crustal thicknesses using our proposed empirical fits are consistent with independent geologic constraints for the Cenozoic evolution of the central Andes, as well as various Mesozoic magmatic arc segments currently exposed in the Coast Mountains, British Columbia, and the Sierra Nevada and Mojave-Transverse Range regions of California. We propose that these geochemical parameters can be used, when averaged over the typical lifetimes and spatial footprints of composite volcanoes and their intrusive equivalents to infer crustal thickness changes over time in ancient orogens. PMID:26633804

  19. Bimodal magmatism produced by progressively inhibited crustal assimilation

    NASA Astrophysics Data System (ADS)

    Meade, F. C.; Troll, V. R.; Ellam, R. M.; Freda, C.; Font, L.; Donaldson, C. H.; Klonowska, I.

    2014-06-01

    The origin of bimodal (mafic-felsic) rock suites is a fundamental question in volcanology. Here we use major and trace elements, high-resolution Sr, Nd and Pb isotope analyses, experimental petrology and thermodynamic modelling to investigate bimodal magmatism at the iconic Carlingford Igneous Centre, Ireland. We show that early microgranites are the result of extensive assimilation of trace element-enriched partial melts of local metasiltstones into mafic parent magmas. Melting experiments reveal the crust is very fusible, but thermodynamic modelling indicates repeated heating events rapidly lower its melt-production capacity. Granite generation ceased once enriched partial melts could no longer form and subsequent magmatism incorporated less fertile restite compositions only, producing mafic intrusions and a pronounced compositional gap. Considering the frequency of bimodal magma suites in the North Atlantic Igneous Province, and the ubiquity of suitable crustal compositions, we propose ‘progressively inhibited crustal assimilation’ (PICA) as a major cause of bimodality in continental volcanism.

  20. Using multiple continuous fine particle monitors to characterize tobacco, incense, candle, cooking, wood burning, and vehicular sources in indoor, outdoor, and in-transit settings

    NASA Astrophysics Data System (ADS)

    Ott, Wayne R.; Siegmann, Hans C.

    This study employed two continuous particle monitors operating on different measurement principles to measure concentrations simultaneously from common combustion sources in indoor, outdoor, and in-transit settings. The pair of instruments use (a) photo-charging (PC) operating on the principle ionization of fine particles that responds to surface particulate polycyclic aromatic hydrocarbons (PPAHs), and (b) diffusion charging (DC) calibrated to measure the active surface area of fine particles. The sources studied included: (1) secondhand smoke (cigarettes, cigars, and pipes), (2) incense (stick and cone), (3) candles used as food warmers, (4) cooking (toasting bread and frying meat), (5) fireplaces and ambient wood smoke, and (6) in-vehicle exposures traveling on California arterials and interstate highways. The ratio of the PC to the DC readings, or the PC/DC ratio, was found to be different for major categories of sources. Cooking, burning toast, and using a "canned heat" food warmer gave PC/DC ratios close to zero. Controlled experiments with 10 cigarettes averaged 0.15 ng mm -2 (ranging from 0.11 to 0.19 ng mm -2), which was similar to the PC/DC ratio for a cigar, although a pipe was slightly lower (0.09 ng mm -2). Large incense sticks had PC/DC ratios similar to those of cigarettes and cigars. The PC/DC ratios for ambient wood smoke averaged 0.29 ng mm -2 on 6 dates, or about twice those of cigarettes and cigars, reflecting a higher ratio of PAH to active surface area. The smoke from two artificial logs in a residential fireplace had a PC/DC ratio of 0.33-0.35 ng mm -2. The emissions from candles were found to vary, depending on how the candles were burned. If the candle flickered and generated soot, a higher PC/DC ratio resulted than if the candle burned uniformly in still air. Inserting piece of metal into the candle's flame caused high PPAH emissions with a record PC/DC reading of 1.8 ng mm -2. In-vehicle exposures measured on 43- and 50-min drives on a

  1. Two Distinct Sets of Magma Sources in Cretaceous Rocks From Magnet Cove, Prairie Creek, and Other Igneous Centers of the Arkansas Alkaline Province, USA

    NASA Astrophysics Data System (ADS)

    Duke, G. I.; Carlson, R. W.; Eby, G. N.

    2008-12-01

    Two distinct sets of magma sources from the Arkansas alkaline province (~106-89 Ma) are revealed by Sr-Nd-Pb isotopic compositions of olivine lamproites vs. other alkalic rock types, including carbonatite, ijolite, lamprophyres, tephrite, malignite, jacupirangite, phonolite, trachyte, and latite. Isotopic compositions of diamond-bearing olivine lamproites from Prairie Creek and Dare Mine Knob point to Proterozoic lithosphere as an important source, and previous Re-Os isotopic data indicate derivation from subcontinental mantle lithosphere. Both sources were probably involved in lamproite generation. Magnet Cove carbonatites and other alkalic magmas were likely derived from an asthenospheric source. Lamproite samples are isotopically quite different from other rock types in Sr-Nd-Pb isotopic space. Although three lamproite samples from Prairie Creek have a large range of SiO2 contents (40-60 wt %), initial values of ɛNd (-10 to -13), 206Pb/204Pb (16.61-16.81), 207Pb/204Pb (15.34-15.36), and 208Pb/204Pb (36.57-36.76) are low and similar. Only 87Sr/86Sr(i) displays a wide range in the Prairie Creek lamproites (0.70627-0.70829). A fourth lamproite from Dare Mine Knob has the most negative ɛNd(i) of -19. Lamproite isotope values show a significant crustal component and isotopically overlap subalkalic rhyolites from the Black Hills (SD), which assimilated Proterozoic crust. Six samples of carbonatite, ijolite, and jacupirangite from Magnet Cove and Potash Sulphur Springs exhibit the most depleted Sr-Nd isotopic signatures of all samples. For these rock types, 87Sr/86Sr(i) is 0.70352 - 0.70396, and ɛNd(i) is +3.8 - +4.3. Eight other rock types have a narrow range of ɛNd(i) (+1.9 - +3.7), but a wide range of 87Sr/86Sr(i) (0.70424 - 0.70629). These 14 samples comprise a fairly tight cluster of Pb isotopic values: 206Pb/204Pb (18.22-19.23), 207Pb/204Pb (15.54-15.62), and 208Pb/204Pb (38.38-38.94), suggesting very little crustal assimilation. They are most similar to EM-2

  2. Pliocene-Quaternary Post-collisional Magmatism in the Greater Caucasus

    NASA Astrophysics Data System (ADS)

    Bewick, Samuel; Harris, Nigel; Parkinson, Ian; Hammond, Sam; Adamia, Shota

    2014-05-01

    Whole-rock elemental and isotopic analyses are presented for Pliocene-Quaternary volcanism from northern Georgia. Intense magmatic activity erupted through the thickened crust (50-60km) of the Greater Caucasus mountain belt, tens of millions of years following continental collision between the Arabian and Eurasian plates. Compositions range from basaltic-andesite to dacite (56-67 wt% SiO2). Enrichment of large ion lithophile elements (LILEs) and light rare earth elements (LREEs) relative to the high field strength elements (HFSEs) is seen in all samples. Rare earth element patterns have small enrichments in the middle to heavy REE ((Dy/Yb)N ratios (1.22-1.65)). Strontium (87Sr/86Sr of 0.7041-0.7049) and Pb isotope ratios suggest a source that has been enriched relative to DMM with Pb isotopes plotting on an array sub-parallel to, but enriched compared to the northern hemisphere reference line (Δ7/6 = 10.7-11.3). LILE enrichment may be indicative of a source enriched by subduction related fluids. Compositions are also similar to local crustal samples. On Pb isotope plots, samples lie on a trend extending towards radiogenic crustal values. Trace elements and isotopes are used to decipher the importance of these two signatures. Heavy REE data provide evidence melting was relatively shallow ( 10wt%) indicate fractionation occurred deep in the crust. Further investigation will allow the sources for Greater Caucasus magmatism to be better constrained and the petrologic evolution of the magmas to be compared with those from the wider Arabia-Eurasia collision zone and hence integrated into a post-collisional tectonic model for the region.

  3. Failed magmatic eruptions: Late-stage cessation of magma ascent

    USGS Publications Warehouse

    Moran, S.C.; Newhall, C.; Roman, D.C.

    2011-01-01

    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.

  4. Magnetite compositions and oxygen fugacities of the Khibina magmatic system

    NASA Astrophysics Data System (ADS)

    Ryabchikov, Igor D.; Kogarko, L. N.

    2006-10-01

    Most titanomagnetite in the Khibina alkaline igneous complex, sampled through 500 m of a vertical cross-section, is represented by Ti-rich varieties. The ulvöspinel component is most commonly around 55 mol%, rarely reaching up to 80 mol%. We calculated an fO 2- T diagram for magnetite + ilmenite + titanite + clinopyroxene + nepheline + alkali feldspar and magnetite + titanite+ clinopyroxene + nepheline + alkali feldspar phase assemblages at a hedenbergite activity of 0.2. The diagram shows that magnetites with 55 mol% of ulvöspinel crystallized at oxygen fugacities just slightly below the quartz-fayalite-magnetite buffer. More Ti-rich varieties crystallized at higher temperatures and slightly lower ΔQMF values, whereas more Ti-poor magnetites crystallized at or below about 650 °C. Under the redox conditions estimated for the apatite-bearing intrusion of the Khibina complex (close to the QFM buffer), substantial quantities of methane may only form during cooling below 400 °C in equilibrium with magma. However, even at higher orthomagmatic temperatures and redox conditions corresponding to ΔQMF = 0, the hydrogen content in the early magmatic stage is not negligible. This hydrogen present in the gas phase at magmatic temperatures may migrate to colder parts of a solidifying magma chamber and trigger Fischer-Tropsch-type reactions there. We propose therefore, that methane in peralkaline systems may form in three distinct stages: orthomagmatic and late-magmatic in equilibrium with a melt and — due to Fischer-Tropsch-type reactions — post-magmatic in equilibrium with a local mineral assemblage.

  5. Magmas and magmatic rocks: An introduction to igneous petrology

    SciTech Connect

    Middlemost, E.A.K.

    1986-01-01

    This book melds traditional igneous petrology with the emerging science of planetary petrology to provide an account of current ideas on active magmatic and volcanic processes, drawing examples from all igneous provinces of the world as well as from the moon and planets. It reviews the history and development of concepts fundamental to modern igneous petrology and includes indepth sections on magmas, magnetic differentiation and volcanology.

  6. Involvement of magmatic fluids at the Laloki and Federal Flag massive sulfide Cu-Zn-Au-Ag deposits, Astrolabe mineral district, Papua New Guinea: sulfur isotope evidence

    NASA Astrophysics Data System (ADS)

    Noku, Shadrach K.; Espi, Joseph O.; Matsueda, Hiroharu

    2015-01-01

    We present the first sulfur (S) isotope data of sulfides, sulfates, pyrite in host mudstone, and bulk sulfur of gabbroic rocks from the Laloki and Federal Flag massive Cu-Zn-Au-Ag deposits in the Astrolabe mineral district, Papua New Guinea. Early-stage pyrite-marcasite, chalcopyrite, and sphalerite from Laloki display wide range of δ34S values from -4.5 to +7.0 ‰ ( n = 16). Late-stage pyrite, chalcopyrite, and sphalerite have restricted δ34S values of -1.9 to +4.7 ‰ ( n = 16). The mineralizing stage these correspond to had moderately saline (5.9-8.4 NaCl eq. wt%) mineralizing fluids of possible magmatic origin. A single analysis of late-stage barite has a value of δ34S +17.9 ‰, which is likely similar to coexisting seawater sulfate. Pyrite from the foot-wall mudstone at Laloki has very light δ34S values of -36.1 to -33.8 ‰ ( n = 2), which suggest an organic source for S. Pyrite-marcasite and chalcopyrite from Federal Flag show δ34S values of -2.4 to -1.9 ‰ ( n = 2), consistent with a magmatic origin, either leached from intrusive magmatic rocks or derived from magmatic-hydrothermal fluids. The very narrow range and near-zero δ34S values (-1.0 to +0.6 ‰) of bulk gabbroic samples is consistent with mantle-derived magmatic S. Sulfur isotope characteristics of sulfides and sulfates are, however, very similar to base metal sulfide accumulations associated with modern volcanic arcs and sedimented mid-ocean ridges. The most reasonable interpretation is that the range of the sulfide and sulfate δ34S values from both Laloki and Federal Flag massive sulfide deposits is indicative of the complex interaction of magmatic fluids, seawater, gabbroic rocks, and mudstone.

  7. Hf isotope compositions and chronology of magmatic zircons from Tarim continental flood basalts: implications for magmatic evolution of the Early Permian Tarim Large Igneous Province in NW China

    NASA Astrophysics Data System (ADS)

    Li, Y.; Li, Z.; Yu, X.; Langmuir, C. H.; Yang, S.; Chen, H.

    2013-12-01

    The Early Permian Tarim Large Igneous Province (TLIP) in the Tarim cratonic block of northwestern China has been largely regarded to be genetically linked with a mantle plume. Recently, some euhedral zircon crystals with magmatic growth zoning have been obtained from the Tarim continental flood basalts (TCFB) for detailed U-Pb chronological and genetic study. The zircons have the concordant 206Pb/238U ages of 297~283 Ma, coinciding with the previously reported whole-rock 40K/39Ar and 40Ar/39Ar ages (292~283 Ma) of their host basalts. In-situ LA-MC-ICPMS Lu-Hf isotopic analyses of Early Permian zircons from the Keping area of the TCFB reveal that the zircons from two basalt sub-groups (Groups 1a, 1b) have a narrow range of 176Hf/177Hf ratios between 0.282422 and 0.282568. Their corresponding ɛHf(t) (t = 290 Ma) values (-6.8~-1.4) are generally lower than their host basalts (-2.3~2.1), and distinctively different from the intrusive rocks (3.0~7.1) and their zircons (4.9~8.8) from the TLIP and the Precambrian crustal rocks (<-18) in the Tarim block. Combined with their embayed margins produced by magmatic corrosion, these zircons may have crystallized in a concealed pluton shortly prior to the extrusion of basalts and been captured as xenocrysts by the rapidly erupted basaltic lavas. Almost the same ɛHf(t) values between the corroded and uncorroded zircons suggest that the zircons have preserved the initial Hf isotopic compositions from their original source region. Moreover, the very close but relatively higher ɛHf(t) values from the zircons than the inferred sub-continental lithospheric mantle (SCLM) beneath Tarim in the Early Permian [ɛHf(t) = -8.7~-5.2; t = 290 Ma] indicate that the zircons were probably originated from the SCLM with minor addition of depleted mantle magmas during the mantle source partial melting. Both the zircons and their host basalts have almost the same formation ages (~290 Ma) and Hf TDM model ages (ca. 1300~1000 Ma), suggesting that

  8. New U-Pb ages and lithochemical attributes of the Ediacaran Rio Doce magmatic arc, Araçuaí confined orogen, southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Gonçalves, Leonardo; Farina, Federico; Lana, Cristiano; Pedrosa-Soares, Antônio C.; Alkmim, Fernando; Nalini, Hermínio A.

    2014-07-01

    The Araçuaí orogen of southeastern Brazil, together with its counterpart located in Africa, the West Congo belt, formed through closure of a gulf connected to the Adamastor Ocean by the end of the Ediacaran and beginning of the Cambrian. Convergence of the margins of the gulf led to the development of the Rio Doce magmatic arc between 630 Ma and 580 Ma on a continental basement mostly composed of Rhyacian orthogneisses. The Rio Doce arc mainly consists of tonalite-granodiorite batholiths, generally crowded with mafic to dioritic enclaves, and minor gabbronorite-enderbite-charnockite plutons, suggesting mixing processes involving crustal and mantle sources. We investigate the basement, magma sources and emplacement ages of the Rio Doce arc. Our data suggest the arc comprises three main granitic rock groups: i) Opx-bearing rocks mostly of enderbite to charnockite composition; ii) enclave-rich tonalite-granodiorite (ETG); and iii) enclave-poor granite-granodiorite with minor tonalite (GT). The Opx-bearing rocks are magnesian, calc-alkalic to alkali-calcic and metaluminous. Together, the ETG and GT rock groups range in composition from tonalite to granite, are metaluminous to slightly peraluminous, show a predominantly medium- to high-K, expanded calc-alkaline signature, and other geochemical and isotopic attributes typical of a pre-collisional volcanic arc formed on a continental margin setting. Mineralogical, chemical, and geochronological data suggest the involvement of HT-melting of granulitic (H2O-depleted) sources of Rhyacian age for the generation of Opx-bearing granitic rocks, additionally to magma mixing and fractional crystallization processes. In conclusion, the studied rock groups of the Rio Doce arc were likely formed by interactions of mantle and crustal processes, in an active continental margin setting. These processes involved ascent of mantle magmas that induced partial melting on the continental basement represented by the Rhyacian gneisses.

  9. Climate effects on volcanism: influence on magmatic systems of loading and unloading from ice mass variations, with examples from Iceland.

    PubMed

    Sigmundsson, Freysteinn; Pinel, Virginie; Lund, Björn; Albino, Fabien; Pagli, Carolina; Geirsson, Halldór; Sturkell, Erik

    2010-05-28

    Pressure influences both magma production and the failure of magma chambers. Changes in pressure interact with the local tectonic settings and can affect magmatic activity. Present-day reduction in ice load on subglacial volcanoes due to global warming is modifying pressure conditions in magmatic systems. The large pulse in volcanic production at the end of the last glaciation in Iceland suggests a link between unloading and volcanism, and models of that process can help to evaluate future scenarios. A viscoelastic model of glacio-isostatic adjustment that considers melt generation demonstrates how surface unloading may lead to a pulse in magmatic activity. Iceland's ice caps have been thinning since 1890 and glacial rebound at rates exceeding 20 mm yr(-1) is ongoing. Modelling predicts a significant amount of 'additional' magma generation under Iceland due to ice retreat. The unloading also influences stress conditions in shallow magma chambers, modifying their failure conditions in a manner that depends critically on ice retreat, the shape and depth of magma chambers as well as the compressibility of the magma. An annual cycle of land elevation in Iceland, due to seasonal variation of ice mass, indicates an annual modulation of failure conditions in subglacial magma chambers.

  10. The magmatic- and hydrothermal-dominated fumarolic system at the Active Crater of Lascar volcano, northern Chile

    NASA Astrophysics Data System (ADS)

    Tassi, F.; Aguilera, F.; Vaselli, O.; Medina, E.; Tedesco, D.; Delgado Huertas, A.; Poreda, R.; Kojima, S.

    2009-03-01

    Low-to-high temperature fumaroles discharging from the Active Crater of Lascar volcano (northern Chile) have been collected in November 2002, May 2005 and October 2006 for chemical and isotopic analysis to provide the first geochemical survey on the magmatic-hydrothermal system of this active volcano. Chemical and isotopic gas composition shows direct addition of high-temperature fluids from magmatic degassing, mainly testified by the very high contents of SO2, HCl and HF (up to 87,800, 29,500 and 2,900 μmol/mol) and the high R/Ra values (up to 7.29). Contributions from a hydrothermal source, mainly in gas discharges of the Active Crater rim, has also been detected. Significant variations in fluid chemistry, mainly consisting of a general decrease of magmatic-related compounds, i.e. SO2, have affected the fumarolic system during the period of observation, indicating an increase of the influence of the hydrothermal system surrounding the ascending deep fluids. The chemical composition of Active Crater fumaroles has been used to build up a geochemical model describing the main processes that regulate the fluid circulation system of Lascar volcano to be utilized in volcanic surveillance.

  11. Cooling of a Magmatic System Under Thermal Chaotic Mixing

    NASA Astrophysics Data System (ADS)

    El Omari, Kamal; Le Guer, Yves; Perugini, Diego; Petrelli, Maurizio

    2015-07-01

    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.

  12. Cooling of a magmatic system under thermal chaotic mixing

    NASA Astrophysics Data System (ADS)

    Petrelli, Maurizio; El Omari, Kamal; Le Guer, Yves; Perugini, Diego

    2015-04-01

    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.

  13. Lithium isotope traces magmatic fluid in a seafloor hydrothermal system.

    PubMed

    Yang, Dan; Hou, Zengqian; Zhao, Yue; Hou, Kejun; Yang, Zhiming; Tian, Shihong; Fu, Qiang

    2015-01-01

    Lithium isotopic compositions of fluid inclusions and hosted gangue quartz from a giant volcanogenic massive sulfide deposit in China provide robust evidence for inputting of magmatic fluids into a Triassic submarine hydrothermal system. The δ(7)Li results vary from +4.5‰ to +13.8‰ for fluid inclusions and from +6.7‰ to +21.0‰ for the hosted gangue quartz(9 gangue quartz samples containing primary fluid inclusions). These data confirm the temperature-dependent Li isotopic fractionation between hydrothermal quartz and fluid (i.e., Δδ(7)Liquartz-fluid = -8.9382 × (1000/T) + 22.22(R(2) = 0.98; 175 °C-340 °C)), which suggests that the fluid inclusions are in equilibrium with their hosted quartz, thus allowing to determine the composition of the fluids by using δ(7)Liquartz data. Accordingly, we estimate that the ore-forming fluids have a δ(7)Li range from -0.7‰ to +18.4‰ at temperatures of 175-340 °C. This δ(7)Li range, together with Li-O modeling , suggest that magmatic fluid played a significant role in the ore formation. This study demonstrates that Li isotope can be effectively used to trace magmatic fluids in a seafloor hydrothermal system and has the potential to monitor fluid mixing and ore-forming process. PMID:26347051

  14. Lithium isotope traces magmatic fluid in a seafloor hydrothermal system.

    PubMed

    Yang, Dan; Hou, Zengqian; Zhao, Yue; Hou, Kejun; Yang, Zhiming; Tian, Shihong; Fu, Qiang

    2015-09-08

    Lithium isotopic compositions of fluid inclusions and hosted gangue quartz from a giant volcanogenic massive sulfide deposit in China provide robust evidence for inputting of magmatic fluids into a Triassic submarine hydrothermal system. The δ(7)Li results vary from +4.5‰ to +13.8‰ for fluid inclusions and from +6.7‰ to +21.0‰ for the hosted gangue quartz(9 gangue quartz samples containing primary fluid inclusions). These data confirm the temperature-dependent Li isotopic fractionation between hydrothermal quartz and fluid (i.e., Δδ(7)Liquartz-fluid = -8.9382 × (1000/T) + 22.22(R(2) = 0.98; 175 °C-340 °C)), which suggests that the fluid inclusions are in equilibrium with their hosted quartz, thus allowing to determine the composition of the fluids by using δ(7)Liquartz data. Accordingly, we estimate that the ore-forming fluids have a δ(7)Li range from -0.7‰ to +18.4‰ at temperatures of 175-340 °C. This δ(7)Li range, together with Li-O modeling , suggest that magmatic fluid played a significant role in the ore formation. This study demonstrates that Li isotope can be effectively used to trace magmatic fluids in a seafloor hydrothermal system and has the potential to monitor fluid mixing and ore-forming process.

  15. Layered Structures in Magmatic Systems From Double-Diffusive Convection

    NASA Astrophysics Data System (ADS)

    Hansen, U.; Schmalzl, J.

    2004-05-01

    The evolution of magmatic systems is often influenced by the existence of discrete layers. Such layering can not be explained by gravitational settling and other dynamical mechanisms have been proposed. Double-diffusive convection is considered to be such a mechanism. In the diffusive regime, where the slowly diffusing component (e,g composition) acts to stabilize the system and the fast diffusing component /e.g. heat) provides the destabilizing force, the formation of layers has been observed. Most studies. however, concentrated on the properties of layers and not on the actual formation. In a series of two- and three dimensional numerical experiments, we have investigated the evolution of layers from non-layered initial states. Layer formation is found to depend on the ratio of thermal to compositional diffusivities (the Lewis number). The influence of the Lewis number has been systematically investigated by employing a field approach to monitor the evolution of the composition. Magmatic systems have a very high Lewis number which can hardly be realized with such an approach. We have therefore developed a tracer method, allowing to study the system in the limit of an infinite Lewis number. With both methods we obtain qualitative similar layered structures. In order to better understand layer formation in magmatic systems, we have included effects of temperature-and compositionaly dependent viscosity. Our results show that the viscosity has a strong influence on the temporal evolution of the system and on the resulting type of layering

  16. Towards quantifying the arc-scale and global magmatic response to deglaciation

    NASA Astrophysics Data System (ADS)

    Watt, S. F.; Pyle, D. M.; Mather, T. A.

    2012-12-01

    There is a growing body of evidence that the retreat of ice sheets after the last glacial maximum resulted in temporarily enhanced levels of volcanism. This has been postulated on the scale of individual edifices, and on regional scales in intraplate and rift settings. It has been proposed that this pattern was of global significance in contributing to rising atmospheric CO2 concentrations, and thereby formed a feedback process for global warming. However, the impact of deglaciation on volcanic arcs has been incompletely explored. Volcanic arcs account for 90% of present-day subaerial volcanic eruptions, and for volcanically-sourced volatiles they are therefore of first-order significance. Without a proper understanding of fluctuations in arc volcanic output, an assessment of global changes in volcanic activity cannot be made. Here, we present the first systematic assessment of the response of glaciated volcanic arcs to deglaciation. By using comprehensive compilations of eruption records from southern Chile, augmented by records from the Cascade and Kamchatka arcs, we show that the post-glacial increase in volcanism was relatively small in comparison to non-arc volcano-tectonic settings. Where ice unloading was at its greatest, eruption frequency approximately doubled for ~5 kyr, but this pattern is at the limit of statistical significance. The same period coincides with a few notably large explosive eruptions. In less heavily glaciated regions, no pattern can be deduced at the resolution of available data. While eruption patterns are commonly episodic, the timing of increases in activity does not always show a clear link to deglaciation. In light of the above, we critically examine available eruption records in an effort to constrain global-scale changes in volcanic output. We show that great caution must be exercised when attempting to quantify variation in volcanism from such data. Due to extremely sparse sampling (i.e. highly incomplete records), both temporal

  17. Adakitic-like magmatism in western Ossa-Morena Zone (Portugal): Geochemical and isotopic constraints of the Pavia pluton

    NASA Astrophysics Data System (ADS)

    Lima, S. M.; Neiva, A. M. R.; Ramos, J. M. F.

    2013-02-01

    Granitic rocks are a major component of the Earth's continental crust and occur in a wide variety of tectonic settings. Their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation. In this study, we present the first whole rock chemical and isotopic (Sr-Nd-O) data for the Pavia pluton (328-317 Ma), located near the western border of the Ossa-Morena Zone (Évora Massif, Portugal). Major and trace element geochemistry suggests that the different granitic phases composing this intrusive body (enclaves, granites (s.l.) and crosscutting dikes) represent independent magma pulses and the majority is similar to TTGs and adakites. The little Sr-Nd-O isotopic variation, with (87Sr/86Sr)328 = 0.70428-0.70560, ɛNd328 ranging between - 3.4 and + 0.4 and δ18O varying from + 5.6‰ to + 8.4‰ implies an isotopically similar protolith for all phases. The most viable mechanism for the generation of the Pavia pluton adakitic-like magmatism is assimilation-fractional crystallization of a mantle-derived magma. This mechanism was also invoked to explain the genesis of other plutons within the Évora Massif but they have a distinct chemistry (typical arc calc-alkaline rocks). The chemical differences between them and the Pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle-derived magmas by the sinking slab (after subduction blocking and subsequent slab break-off).

  18. Cryogenian alkaline magmatism in the Southern Granulite Terrane, India: Petrology, geochemistry, zircon U-Pb ages and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Santosh, M.; Yang, Qiong-Yan; Ram Mohan, M.; Tsunogae, T.; Shaji, E.; Satyanarayanan, M.

    2014-11-01

    The Southern Granulite Terrane (SGT) in India preserves the records of the formation and recycling of continental crust from Mesoarchean through Paleoproterozoic to Neoproterozoic and Cambrian, involving multiple subduction-accretion-collision associated with major orogenic cycles. A chain of unmetamorphosed and undeformed alkaline magmatic intrusions occurs along the northern margin of the SGT aligned along paleo-suture zones. Here we investigate two representative plutons from this suite, the Angadimogar syenite (AM) and the Peralimala alkali granite (PM) through field, petrological, geochemical, zircon U-Pb and Lu-Hf studies. Magma mixing and mingling textures and mineral assemblages typical of alkaline rocks are displayed by these plutons. The whole-rock major and trace element data characterize their alkaline nature. In trace element discrimination diagrams, the AM rocks straddle between the VAG (volcanic-arc granites) and WPG (within plate granites) fields with most of the samples confined to the VAG field, whereas the PM rocks are essentially confined to the WPG field. The diversity in some of the geochemical features between the two plutons is interpreted to be the reflection of source heterogeneities. Most zircon grains from the AM and PM plutons display oscillatory zoning typical of magmatic crystallization although some grains, particularly those from the PM pluton, show core-rim structures with dark patchy zoned cores surrounded by irregular thin rims resulting from fluid alteration. The weighted mean 206Pb/238U ages of the magmatic zircons from three samples of the AM syenite are in the range of 781.8 ± 3.8 Ma to 798 ± 3.6 Ma and those from two samples of the PM alkali granite yield ages of 797.5 ± 3.7 Ma and 799 ± 6.2 Ma. A mafic magmatic enclave from the AM pluton shows weighted mean 206Pb/238U age of 795 ± 3.3 Ma. The AM and PM plutons also carry rare xeneocrystic zircons which define upper intercept concordia ages of 3293 ± 13 Ma and 2530

  19. Use of gravity potential field methods for defining a shallow magmatic intrusion: the Mt. Amiata case history (Tuscany, Central Italy)

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Rinaldo Barchi, Massimiliano; Pauselli, Cristina; Heyde, Ingo

    2016-04-01

    We analyzed the Bouguer gravity anomaly signal beneath the Mt. Amiata area in order to reconstruct the subsurface setting. The study area is characterized by a pronounced gravity minimum, possibly correlated with the observed anomalous heat flow and hydrothermal activity. Using different approaches, previous authors defined a low density body (generally interpreted as a magmatic intrusion) beneath this area, which could explain the observed gravity anomaly minimum. However the proposed geologic models show different geometries and densities for the batholith. The gravity data used in this study (kindly provided by eni) were acquired from different institutions (eni, OGS, USDMA and Servizio Geologico d'Italia) and collected in a unique dataset, consisting of about 50000 stations, randomly distributed, which cover Central Italy, with a spacing of less than 1 km. For each station the elevation and the Bouguer gravity anomaly data are given. From this dataset, we created two maps of the Bouguer gravity anomaly and the topography, using the Minimum Curvature gridding method considering a grid cell size of 500m x 500m. The Bouguer gravity anomaly has been computed using a density of 2.67 g/cm3. From these maps we extracted a window of about 240 km2 (12x20 km) for the study area, which includes the Mt. Amiata region and the adjacent Radicofani sedimentary basin. The first part of this study was focused on calculating the first order vertical derivative and the power spectra analysis of the Bouguer gravity anomaly to enhance the effect of shallow bodies and estimating the source depth respectively. The second part of this study was focused on constructing a 3D geological density model of the subsurface setting of the studied area, implementing a forward modelling approach. The stratigraphy of the study area's upper crust schematically consists of six litho-mechanical units, whose density was derived from velocity data collected by active seismic surveys. A preliminary

  20. Analysis of sewage sludge using an experimental prompt gamma neutron activation analysis (pgnaa) set-up with an am-be source

    NASA Astrophysics Data System (ADS)

    Idiri, Z.; Redjem, F.; Beloudah, N.

    2016-09-01

    An experimental PGNAA set-up using a 1 Ci Am-Be source has been developed and used for analysis of bulk sewage sludge samples issued from a wastewater treatment plant situated in an industrial area of Algiers. The sample dimensions were optimized using thermal neutron flux calculations carried out with the MCNP5 Monte Carlo Code. A methodology is then proposed to perform quantitative analysis using the absolute method. For this, average thermal neutron flux inside the sludge samples is deduced using average thermal neutron flux in reference water samples and thermal flux measurements with the aid of a 3He neutron detector. The average absolute gamma detection efficiency is determined using the prompt gammas emitted by chlorine dissolved in a water sample. The gamma detection efficiency is normalized for sludge samples using gamma attenuation factors calculated with the MCNP5 code for water and sludge. Wet and dehydrated sludge samples were analyzed. Nutritive elements (Ca, N, P, K) and heavy metals elements like Cr and Mn were determined. For some elements, the PGNAA values were compared to those obtained using Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma (ICP) methods. Good agreement is observed between the different values. Heavy element concentrations are very high compared to normal values; this is related to the fact that the wastewater treatment plant is treating not only domestic but also industrial wastewater that is probably rejected by industries without removal of pollutant elements. The detection limits for almost all elements of interest are sufficiently low for the method to be well suited for such analysis.

  1. Extension and magmatism across the Suwanee Suture and South Georgia Basin from the SUGAR seismic refraction experiment

    NASA Astrophysics Data System (ADS)

    Shillington, D. J.; Lizarralde, D.; Harder, S. H.; Marzen, R.; Kaip, G.; Accardo, N. J.; Gibson, J. C.; Nauer, A.

    2015-12-01

    The South Georgia Basin was at the center of the most recent sequence of continental collision and rifting events to shape eastern North America. It is the largest of the failed Mesozoic rift basins that formed during the breakup of Pangea, and it straddles the Suwannee Suture, the only well-defined remnant of the Alleghenian suture that joined North America and Gondwana. The South Georgia Basin also lies at the center of the Central Atlantic Magmatic Province (CAMP). It is thus an excellent location to examine the importance of magmatism and pre-existing structures on continental extension. Here we present preliminary results from the SUwanee Suture and GA Rift basin (SUGAR) project, an active-source seismic refraction project to image the crustal structure across these features. In March 2014, we acquired data along SUGAR Line 1, a ~325-km-long, NW-SE oriented profile that crossed the Suwanee Suture and western part of South Georgia Basin. The profile was densely instrumented with 1193 single-channel RekTek 125A seismographs ("Texans") spaced at ~250 m. The sources were 100 to 1800 lb shots spaced at ~20-50 km. In August 2015, we will acquire data along SUGAR Lines 2 and 3. SUGAR Line 2 is a ~450-km-long profile spanning the eastern part of the South Georgia Basin and two possible locations for the Suwanee Suture. We will deploy 1983 "Texans" spaced at 250 m and detonate seventeen 400 to 1600 lb shots spaced at ~16-50 km. SUGAR Line 3 targets the Brunswick magnetic anomaly; we plan to instrument a 100-km-long profile with 700 Texans spaced at 150 m and eleven 200 lb shots spaced at ~10 km. Over 68 students participated in field work for SUGAR. Preliminary models of SUGAR Line 1 indicate that the crust thins to ~33 km beneath the South Georgia Basin. Anomalously high lower crustal velocities occur beneath the basin in the area of the greatest crustal thinning and may represent mafic intrusions from CAMP/synrift magmatism. We will present initial velocity models of

  2. Evidence for slab material under Greenland and links to Cretaceous High Arctic magmatism

    NASA Astrophysics Data System (ADS)

    Shephard, G. E.; Trønnes, R. G.; Spakman, W.; Panet, I.; Gaina, C.

    2016-04-01

    Understanding the evolution of extinct ocean basins through time and space demands the integration of surface kinematics and mantle dynamics. We explore the existence, origin, and implications of a proposed oceanic slab burial ground under Greenland through a comparison of seismic tomography, slab sinking rates, regional plate reconstructions, and satellite-derived gravity gradients. Our preferred interpretation stipulates that anomalous, fast seismic velocities at 1000-1600 km depth imaged in independent global tomographic models, coupled with gravity gradient perturbations, represent paleo-Arctic oceanic slabs that subducted in the Mesozoic. We suggest a novel connection between slab-related arc mantle and geochemical signatures in some of the tholeiitic and mildly alkaline magmas of the Cretaceous High Arctic Large Igneous Province in the Sverdrup Basin. However, continental crustal contributions are noted in these evolved basaltic rocks. The integration of independent, yet complementary, data sets provides insight into present-day mantle structure, magmatic events, and relict oceans.

  3. Crustal recycling through intraplate magmatism: Evidence from the Trans-North China Orogen

    NASA Astrophysics Data System (ADS)

    He, Xiao-Fang; Santosh, M.

    2014-12-01

    The North China Craton (NCC) preserves the history of crustal growth and craton formation during the early Precambrian followed by extensive lithospheric thinning and craton destruction in the Mesozoic. Here we present evidence for magma mixing and mingling associated with the Mesozoic tectonic processes from the Central NCC, along the Trans-North China Orogen, a paleo suture along which the Eastern and Western Blocks were amalgamated at end of Paleoproterozoic. Our investigations focus on two granitoids - the Chiwawu and the Mapeng plutons. Typical signatures for the interaction of mafic and felsic magmas are observed in these plutons such as: (1) the presence of diorite enclaves; (2) flow structures; (3) schlierens; (4) varying degrees of hybridization; and (5) macro-, and micro-textures. Porphyritic feldspar crystals show numerous mineral inclusions as well as rapakivi and anti-rapakivi textures. We present bulk chemistry, zircon U-Pb geochronology and REE data, and Lu-Hf isotopes on the granitoids, diorite enclaves, and surrounding basement rocks to constrain the timing of intraplate magmatism and processes of interaction between felsic and mafic magmas. Our LA-ICP-MS zircon U-Pb data show that the pophyritic granodiorite was emplaced at 129.7 ± 1.0 Ma. The diorite enclaves within this granodiorite show identical ages (128.2 ± 1.5 Ma). The basement TTG (tonalite-trondhjemite-granodiorite) gneisses formed at ca. 2.5 Ga coinciding with the major period of crustal accretion in the NCC. The 1.85 Ga age from zircons in the gabbro with positive Hf isotope signature may be related to mantle magmatism during post-collisional extension following the assembly of the Western and Eastern Blocks of the NCC along the Trans-North China Orogen. Our Hf isotope data indicate that the Neoarchean-Paleoproterozoic basement rocks were derived from complex sources of both juvenile magmas and reworked ancient crust, whereas the magma source for the Mesozoic units are dominantly

  4. Imaging the magmatic system of Mono Basin, California with magnetotellurics in three--dimensions

    USGS Publications Warehouse

    Peacock, Jared R.; Mangan, Margaret T.; McPhee, Darcy K.; Ponce, David A.

    2015-01-01

    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

  5. Relation of peralkaline magmatism to heterogeneous extension during the Middle Miocene, southeastern Nevada

    USGS Publications Warehouse

    Scott, R.B.

    1995-01-01

    Volcanism migrated southward in the northern Basin and Range province in the Oligocene and early Miocene to produce voluminous calcalkaline silicic ash flow tuffs. Alkaline volcanism became dominant by middle Miocene (17-14 Ma) as smaller volumes of rhyolite-trachyte-basalt suites were erupted from the relatively small Kane Springs Wash caldera complex in southeastern Nevada. Only minor extension affected the Kane Wash area before the end of calcalkaline activity, but extension expressed by rate of progressive stratal tilt peaked (15-13.5 Ma) with peralkaline magmatism (14.7-14.4 Ma). Variations in distribution, degree, style, and timing of deformation demonstrate heterogeneous extension in the Kane Wash area. Only minor extension and tilting persisted post-middle Miocene (<12 Ma). All major eruptive sources overlap domains of rapid extension. -from Authors

  6. Dynamics of active magmatic and hydrothermal systems at Taal Volcano, Philippines, from continuous GPS measurements

    NASA Astrophysics Data System (ADS)

    Bartel, Beth A.; Hamburger, Michael W.; Meertens, Chuck M.; Lowry, Anthony R.; Corpuz, Ernesto

    2003-10-01

    A dense network of continuous single- and dual-frequency GPS receivers at Taal Volcano, Philippines, reveals four major stages of volcanogenic deformation: deflation, from installation in June 1998 to December 1998; inflation, from January to March 1999; deflation, from April 1999 to February 2000; and inflation, from February to November 2000. The largest displacements occurred during the February-November 2000 period of inflation, which was characterized by ˜120 mm of uplift of the center of Volcano Island relative to the northern caldera rim at average rates up to 216 mm/yr. Deformation sources were modeled using a constrained least squares inversion algorithm. The source of 1999 deflation and inflation in 2000 were modeled as contractional and dilatational Mogi point sources centered at 4.2 and 5.2 km depth, respectively, beneath Volcano Island. The locations of the inflationary and deflationary sources are indistinguishable within the 95% confidence estimates. Modeling using a running 4-month time window from June 1999 to March 2001 reveals little evidence for source migration. We suggest that the two periods of inflation observed at Taal result from episodic intrusions of magma into a shallow reservoir centered beneath Volcano Island. Subsequent deflation may result from exsolution of magmatic fluids and/or gases into an overlying, unconfined hydrothermal system.

  7. From magma-poor Ocean Continent Transitions to steady state oceanic spreading: the balance between tectonic and magmatic processes

    NASA Astrophysics Data System (ADS)

    Gillard, Morgane; Manatschal, Gianreto; Autin, Julia; Decarlis, Alessandro; Sauter, Daniel

    2016-04-01

    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

  8. Permian magmatic sequences of the Bilihe gold deposit in central Inner Mongolia, China: Petrogenesis and tectonic significance

    NASA Astrophysics Data System (ADS)

    Liu, Chunhua; Nie, Fengjun

    2015-08-01

    the formation of norite gabbro; mixing of depleted mantle and lower crust resulted in the formation of granodiorite porphyry; partial melting of lower crust resulted in the formation of granite; and mixing of lower crust and old upper crust resulted in the formation of granodiorite. Magmatic rocks in the ore district with ages of 272-255 Ma were formed during the late stages of closure of the Paleoasian Ocean; i.e., during the transformation from a collisional to extensional setting.

  9. Trace elements in magnetite from massive iron oxide-apatite deposits indicate a combined formation by igneous and magmatic-hydrothermal processes

    NASA Astrophysics Data System (ADS)

    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

    2015-12-01

    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

  10. Evidence of varying magma chambers and magmatic evolutionary histories for the Table Mountain Formation in the Carson-Iceberg Wilderness region, Sonora Pass, California

    NASA Astrophysics Data System (ADS)

    Asami, R.; Putirka, K. D.; Pluhar, C. J.; Farner, M. J.; Torrez, G.; Shrum, B. L.; Jones, S.

    2012-12-01

    The Sonora Pass- Dardanelles region in the Carson- Iceberg Wilderness area is located in the central Sierra Nevada and home to the type section for latites (Slemmons, 1953), a volcanic rock that contains high potassium, clinopyroxene, and plagioclase phenocysts. Latite lavas and tuffs exposed in the Sonora Pass region originated from the sources in the eastern Sierra Nevada (Noble et al., 1974) where lavas flowed toward California's Great Valley, and were emplaced in stream valleys along the way, which are now inverted to form "table mountains", ergo the name "Table Mountain Latite" (TML) (Slemmons, 1966). Similarly high-K volcanic rocks of the same age are exposed at Grouse Meadows, which is just north of the Walker Lane Caldera east of Sonora Pass, and at the type section, between Red Peak and Bald Peak west of Sonora Pass. Latites lavas and tuffs in all three regions were analyzed for major oxides and trace elements with X-ray fluorescence spectrometry at California State University, Fresno. Analysis of three locations of (TML) at the type section show that they (Ransome, 1898), may have a different magmatic evolutionary history compared to other latites, exposed at Sonora Pass and Grouse Meadows, as the latter two show similar major oxide and trace element compositions. Most compelling is the contrast in the behavior of Al2O3 and CaO at the type section. Variation diagrams show that at the type section Al2O3 and CaO enrichment decreases with increasing amounts of MgO as fractional crystallization occurs. Conversely, at Sonora Peak and Grouse Meadows, CaO and Al2O3 concentrations mostly increase as MgO decreases with fractional crystallization. This contrasts shows that plagioclase was a major fractioning phase at the type section, but not at the other two localities. This suggests that the lava flows at the type section were erupted from a distinct set of magma chambers and vents that underwent a very distinct magmatic evolutionary history, perhaps involving

  11. Spatial Distribution of b-value of the Copahue volcano during 2012-2014 eruptive period: Relationship between magmatic and hydrothermal system

    NASA Astrophysics Data System (ADS)

    Lazo, Jonathan; Basualto, Daniel; Bengoa, Cintia; Cardona, Carlos; Franco, Luis; Gil-Cruz, Fernando; Hernández, Erasmo; Lara, Luis; Lundgren, Paul; Medina, Roxana; Morales, Sergio; Peña, Paola; Quijada, Jonathan; Samsonov, Sergey; San Martin, Juan; Valderrama, Oscar

    2015-04-01

    Temporal and spatial variations of b-value have been interpreted as regional stress changes on active tectonic zones or magma ascent and/or hydrothermal fluids mobilization that could affect to active volcanic arc. Increasing of fluids pressure, medium heterogeneities or temperature changes would be the cause of these variations. The Copahue volcano is a shield strato-volcano that has been edified on the western margin of the Caviahue Caldera, located in the international border between Chile and Argentina, which contain an important geothermic field and is located at a horse-tail structure of the Liquiñe-Ofqui Fault Zone. The pre-fracture nature of its basement, as well as an extensive geothermic field, would be producing very complex conditions to fluids movement that could be exploring to use the 'b' value of the recorded seismicity between 2012 and 2014. Based in the database of VT seismic events, we used 2.073 events to calculate the b-value to obtain the 2D and 3D distribution maps. Results showed two anomalous zones: the first one located 9 Km to NE of the active crater, 3-6 Km depth, with high b-values (>1.2) that is associated with a very high production rate of small earthquakes that could suggest a brittle zone, located in the active geothermal field. The second zone, showed a low b-values (~ 0.7), located to east of the volcano edifice at <3 Km depth, associated to a zone where were generated larger magnitude events, suggesting a zone with more stress accumulation that well correlated with the deformation center detected by InSAR measurements. This zone could be interpreted as the magmatic source that interacts with the shallow hydrothermal system. Thus, in a very complex setting as a volcano sitting on top of a geothermal system, the b-value offers a tool to understand the distribution of the seismic sources and hence a physical constrain for the coupled magmatic/hydrothermal system.

  12. Anatomy of an extinct magmatic system along a divergent plate boundary: Alftafjordur, Iceland

    NASA Astrophysics Data System (ADS)

    Urbani, S.; Trippanera, D.; Porreca, M.; Kissel, C.; Acocella, V.

    2015-08-01

    Recent rifting episodes highlight the role of magmatic systems with propagating dikes on crustal spreading. However, our knowledge of magmatic systems is usually limited to surface observations and geophysical data. Eastern Iceland allows direct access to extinct and eroded deeper magmatic systems. Here we collected field structural and AMS (anisotropy of magnetic susceptibility) data on 187 and 19 dikes, respectively, in the 10-12 Ma old Alftafjordur magmatic system. At a paleodepth of ~1.5 km, the extension due to diking is at least 1-2 orders of magnitude larger than that induced by regional tectonics, confirming magmatism as the key mechanism for crustal spreading. This magma-induced extension, inferred from the aspect ratio of the magmatic system, was of ~8 mm/yr, lower than the present one. AMS data suggest that most of dikes have geometrically normal fabric, at least at the margins, consistent with prevalent subvertical magma flow and propagation.

  13. Zircon U-Pb geochronology and geochemistry of two episodes of granitoids from the northwestern Zhejiang Province, SE China: Implication for magmatic evolution and tectonic transition

    NASA Astrophysics Data System (ADS)

    Li, Zilong; Zhou, Jing; Mao, Jianren; Santosh, M.; Yu, Minggang; Li, Yinqi; Hu, Yizhou; Langmuir, Charles H.; Chen, Zhongxing; Cai, Xiongxiang; Hu, Yanhua

    2013-10-01

    Granitoids (175-80 Ma) representing a prominent Yanshanian (Jurassic to Cretaceous) magmatic event in South China widely intrude the Precambrian crystalline basement and Paleozoic strata. Here we report zircon U-Pb age data, geochemical characteristics and Sr-Nd isotopes of the Late Jurassic and Early Cretaceous granitoids from the northwestern Zhejiang Province (ZXB) of southeastern China. Our results reveal two distinct episodes for the Yanshanian magmatism. The Jiemeng and Datongkeng granodiorites formed at 148.6 ± 1.1 Ma, whereas the Huangshitan, Jiuligang and Ruhong aluminous A-type granites were generated between 129.0 ± 0.6 Ma and 126.1 ± 1.1 Ma. The two magmatic phases represent a tectonic transition from an active continental margin to post-orogenic setting during the Late Jurassic (ca. 150 Ma) to Early Cretaceous (ca. 128 Ma). Geochemically, these intrusions are granodioritic to granitic in composition and show an affinity of S-type and A-type granitoids, respectively. The S-type granodiorites of Jiemeng and Datongkeng are characterized by moderate SiO2 (65.0-69.6 wt.%), high K2O + Na2O (5.0-7.6 wt.%), K2O/Na2O (1.2-1.5), Zr (31-109 ppm), Sr (71-190 ppm) and high field strength elements, low to intermediate Mg#, and moderate Nb depletion. The A-type granites of Huangshitan, Jiuligang and Ruhong are characterized by high SiO2 (72.7-77.2 wt.%), K2O + Na2O (6.9-8.8 wt.%), K2O/Na2O (1.3-2.1), FeT/(FeT + Mg), Ga (17-29 ppm, > 20 ppm commonly), Zr (96-197 ppm) and Sr (8-45 ppm) with slight Nb depletion. The S-type granodiorites have higher Mg#, A/NK, Sr, Sr/Ba, Sr/Y, (La/Yb)N, and LREE/HREE, and lower SiO2, K2O + Na2O, Ga and Zr with weak negative Eu anomalies compared to those of the A-type granites with negative Eu anomalies. All these rocks show Y/Nb ratios > 1.2, high initial 87Sr/86Sr (ISr) ratios and low ɛNd(t), and are depleted in Nb, Ti and Sr, indicating crustal origin with subduction zone signatures. We suggested that the ZXB S-type granitic

  14. Eocene slab breakoff of Neotethys as suggested by dioritic dykes in the Gangdese magmatic belt, southern Tibet

    NASA Astrophysics Data System (ADS)

    Ma, Xuxuan; Xu, Zhiqin; Meert, Joseph G.

    2016-04-01

    The Gangdese magmatic belt in southern Tibet demarcates an important boundary between the Indian and Eurasian plates. Due to its location and magmatic evolutionary history, it is key to understanding both the history of Neotethys closure and the Indo-Asian collisional process.