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Sample records for intracratonic magmas geochemistry

  1. Comparative assessment of five potential sites for hydrothermal magma systems: geochemistry

    SciTech Connect

    White, A.F.

    1980-08-01

    A brief discussion is given of the geochemical objectives and questions that must be addressed in such an evaluation. A summary of the currently published literature that is pertinent in answering these questions is presented for each of the five areas: The Geysers-Clear Lake region, Long Valley, Rio Grand Rift, Roosevelt Hot Springs, and the Salton Trough. The major geochemical processes associated with proposed hydrothermal sites are categorized into three groups for presentation: geochemistry of magma and associated volcanic rocks, geochemistry of hydrothermal solutions, and geochemistry of hydrothermal alteration. (MHR)

  2. Petrography and major element geochemistry of the Permo-Triassic sandstones, central India: Implications for provenance in an intracratonic pull-apart basin

    NASA Astrophysics Data System (ADS)

    Ghosh, Sampa; Sarkar, Soumen; Ghosh, Parthasarathi

    2012-01-01

    Detrital mode, composition of feldspars and heavy minerals, and major element chemistry of sandstones from the Permo-Triassic succession in the intracratonic Satpura Gondwana basin, central India have been used to investigate provenance. The Talchir Formation, the lowermost unit of the succession, comprises glacio-marine and glacio-fluvial deposits. The rest of the succession (base to top) comprising the Barakar, Motur, Bijori, Pachmarhi and Denwa formations, largely represent variety of fluvial depositional systems with minor fluvio-deltaic and fluvio-lacustrine sedimentation under a variety of climatic conditions including cold, warm, arid, sub-humid and semi-arid. QFL compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault-bounded basement uplift tectonic setting. Compositional maturity of sandstones gradually increases upwards from the Early Permian Talchir to the Middle Triassic Denwa but is punctuated by a sharp peak of increased maturity in the Barakar sandstones. This temporal change in maturity was primarily controlled by temporal variation in fault-induced basement uplift in the craton and was also influenced by climatic factors. Plots of different quartz types suggest plutonic source rocks for the Talchir sandstones and medium-to high-rank metamorphic plus plutonic source rocks for the younger sandstones. Composition of alkali feldspars in the Permo-Triassic sandstones and in different Precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks. Compositions of plagioclase in the Talchir and Bijori sandstones are comparable with those of granite, acid volcanic and metasedimentary rocks of the Precambrian basement suggesting the latter as possible source. Rare presence of high-K plagioclase in the Talchir sandstones, however, indicates minor contribution from volcanic source rock. Exclusively plagioclase-bearing metasedimentary rock, tonalite gneiss and mafic rocks

  3. FY 1984 and FY 1985 geochemistry and materials studies in support of the Magma Energy Extraction Program

    SciTech Connect

    Westrich, H.R.; Weirick, L.J.; Cygan, R.T.; Reece, M.; Hlava, P.F.; Stockman, H.W.; Gerlach, T.M.

    1986-04-01

    Geochemistry and materials studies are being performed in support of the Magma Energy Extraction Program. The work is largely restricted to: (1) characterizing magmatic environments at sites of interest, (2) testing engineering materials in laboratory simulated magmatic environments, (3) investigating chemical mass transport effects inherent in designs for direct contact heat exchangers, and (4) evaluating degassing hazards associated with drilling into and extracting energy from shallow magma. Magma characterization studies have been completed for shallow magma at Long Valley, Coso volcanic field, and Kilauea volcano. The behavior of 17 commercially available materials has been examined in rhyolite magma at 850/sup 0/C and 200 MPa for periods up to seven days. Analysis of reaction products from materials tests to date indicate that oxidation is the main corrosion problem for most alloys in rhyolitic magma. Considerations of corrosion resistance, high-temperature strength, and cost indicate nickel-base superalloys offer the most promise as candidates for use in rhyolitic magma.

  4. Palaeoweathering, composition and tectonics of provenance of the Proterozoic intracratonic Kaladgi-Badami basin, Karnataka, southern India: Evidence from sandstone petrography and geochemistry

    NASA Astrophysics Data System (ADS)

    Dey, Sukanta; Rai, A. K.; Chaki, Anjan

    2009-05-01

    Petrographic and geochemical data on the sandstones of the Proterozoic intracratonic Kaladgi-Badami basin, southern India are presented to elucidate the palaeoweathering pattern, and composition and tectonics of their provenance. The Kaladgi-Badami basin, hosting the Kaladgi Supergroup, occupies an E-W trending area. The Supergroup unconformably overlies Archaean basement TTG gneisses, granites and greenstones, comprises a cyclic arenite-pelite-carbonate association and is divided into the Bagalkot and Badami Groups. The immature arkosic character of the basal Saundatti Quartzite Member (Bagalkot Group) containing fresh and angular feldspars, along the northern margin of the basin, suggests that during the initial stage of deposition, this part of the basin received sediments from a restricted, uplifted and less weathered source dominated by K-rich granites occurring to the north. In contrast, the Saundatti Quartzite along the southern margin displays a mostly mature, quartz-rich character with less abundant but severely weathered feldspars, and higher SiO 2 and CIA but lower Al 2O 3, TiO 2, Rb, Sr, Ba, K 2O, K 2O/Na 2O, Zr/Ni and Zr/Cr. This is interpreted in terms of a tectonically stable, considerably weathered mixed source (Archaean gneisses, granites and greenstones) along the southern fringe of the basin. The highly mature (quartz arenite) Muchkundi Quartzite Member (also of the Bagalkot Group), occurring higher up in the succession, exhibits minor but severely altered feldspars, and higher SiO 2, Na 2O, CIA, Cr and Ni with lower K 2O, Al 2O 3, TiO 2 and K 2O/Na 2O. This reflects that with the passage of time the source evolved to a uniform, extensively weathered, tectonically stable peneplained provenance which consisted of less evolved TTG gneisses and greenstones. This was followed by closure, deformation and upliftment of the basin hosting the Bagalkot Group and subsequent deposition of the Badami Group. Sandstone Members of this younger Group (Cave

  5. Geochemistry and materials studies in support of the Magma Energy Extraction Program

    SciTech Connect

    Westrich, H.R.; Weirick, L.J.

    1986-01-01

    Geochemistry and materials studies are being performed in support of the Magma Energy Extraction Program. The scope of the studies is dictated by the sites under consideration and the designs of the drilling and energy extraction systems. The work has been largely restricted to characterizing magmatic environments at sites of interest and testing engineering materials in laboratory simulated rhyolite magmatic environments. The behavior of 17 commercially available materials has been examined at magmatic conditions. Analysis of reaction products reveal that oxidation, and not sulfidation, is the main corrosion problem for most alloys in rhyolite, and that reaction with other magmatic components is limited. Considerations of corrosion resistance, high-temperature strength, and cost indicate nickel-base superalloys offer the most promise as candidates for use in rhyolitic magma.

  6. Sr, Nd, Pb Isotope geochemistry and magma evolution of the potassic volcanic rocks, Wudalianchi, Northeast China

    USGS Publications Warehouse

    Junwen, W.; Guanghong, X.; Tatsumoto, M.; Basu, A.R.

    1989-01-01

    Wudalianchi volcanic rocks are the most typical Cenozoic potassic volcanic rocks in eastern China. Compositional comparisons between whole rocks and glasses of various occurrences indicate that the magma tends to become rich in silica and alkalis as a result of crystal differentiation in the course of evolution. They are unique in isotopic composition with more radiogenic Sr but less radiogenic Pb.87Sr /86 Sr is higher and143Nd/144Nd is lower than the undifferentiated global values. In comparison to continental potash volcanic rocks, Pb isotopes are apparently lower. These various threads of evidence indicate that the rocks were derived from a primary enriched mantle which had not been subjected to reworking and shows no sign of incorporation of crustal material. The correlation between Pb and Sr suggests the regional heterogeneity in the upper mantle in terms of chemical composition. ?? 1989 Institute of Geochemistry, Chinese Academy of Sciences.

  7. Geochemistry of the mantle source and magma feeding system beneath Turrialba volcano, Costa Rica

    NASA Astrophysics Data System (ADS)

    Di Piazza, A.; Rizzo, A. L.; Barberi, F.; Carapezza, M. L.; De Astis, G.; Romano, C.; Sortino, F.

    2015-09-01

    Turrialba volcano lies in the southern sector of the Central American Volcanic Front (CAVF) in Costa Rica. The geochemistry of major and trace elements, and Sr and Nd isotopes of a selected suite of volcanic rocks ranging in composition from basaltic andesite to dacite and belonging to the last 10 ka of activity of Turrialba volcano is described, together with the He-, Ne-, and Ar-isotope compositions of fluid inclusions hosted in olivine and pyroxene crystals. Most of the variability in the rock chemistry is consistent with typical trends of fractional crystallization, but there is an outlying group of andesites that displays an adakite-like composition (with a consistent depletion in high-field-strength elements and a marked enrichment in Sr) and low 3He/4He ratios (7.0-7.2 Ra). The trace-element composition of these rocks is typical of subduction-related magmas influenced by an OIB-like component at the source associated with the subduction of the Galapagos seamounts. The 87Sr/86Sr (0.703612-0.703678) and 143Nd/144Nd (0.512960-0.512984) ratios of the bulk rocks vary within narrow ranges, and are among the least-radiogenic isotope signatures of the CAVF volcanoes. The 3He/4He ratios measured in fluid inclusions hosted in olivine crystals (up to 8.1 Ra) are among the highest for the CAVF, and indicate that radiogenic 4He from fluids derived from the subducting slab contribute negligibly to the mantle wedge. The difference in He isotopes between most of studied rocks and those showing adakite-like features reasonably reflects two distinct components in the local mantle: (1) a MORB-like component, characterized by the highest He-isotope ratios (7.8-8.1 Ra), and (2) an OIB-like component, characterized by lower He-isotope ratios (7.0-7.2 Ra), coming from the subduction of the Galapagos seamounts. An overview at the regional scale indicates that high He-isotope ratios are peculiar to the two extreme sectors of the CAVF (Costa Rica to the south and Guatemala to the

  8. Magma Reservoir Processes Revealed by Geochemistry of the Ongoing East Rift Zone Eruption, Kilauea Volcano, Hawaii

    NASA Astrophysics Data System (ADS)

    Thornber, C. R.

    2002-12-01

    Geochemical data were examined for a suite of 1,000 near-vent lava samples from the Pu`u `O`o-Kupaianaha eruption of Kilauea, collected from January 1983 through October 2001. Bulk lava and glass compositions reveal short- and long-term changes in pre-eruptive magma conditions that can be correlated with changes in edifice deformation, shallow magma transfer and eruptive behavior. Two decades of eruption on Kilauea's east rift zone has yielded ~2 km3 of lava, 97% of which is sparsely olivine-phyric with an MgO range of 6.8 to 9.6 wt%. During separate brief intervals of low-volume, fissure eruption (episodes 1 to 3 and 54), isolated rift-zone reservoirs with lower-MgO and olv-cpx-plg-phryic magma were incorporated by more mafic magma immediately prior to eruption. During prolonged, near-continuous eruption(e.g.,episodes 48-53 and most of 55), steady-state effusion is marked by cyclic variations in olivine-saturated magma chemistry. Bulk lava MgO and eruption temperature vary in cycles of monthly to bi-annual frequency, while olivine-incompatible elements vary inversely to these cycles. However, MgO-normalized values and ratios of highly to moderately incompatible elements (HINCE/MINCE), which nullify olivine fractionation effects, reveal cycles in magma chemistry that occur prior to olivine crystallization over the magmatic temperature range that is tapped by this eruption (1205-1155°C). These short-term cycles are superimposed on a long-term decrease of HINCE/MINCE, which is widely thought to reflect a 20-year change in mantle-source conditions. While HINCE/MINCE variation in primitive recharge magma cannot be ruled out, the short-term fluctuations of this signature may require unreasonably complex mantle variations. Alternatively, the correspondence of HINCE/MINCE cycles with edifice deformation and eruptive behavior suggests that the long-term evolving magmatic condition is a result of prolonged succession of short-term shallow magmatic events. The consistent

  9. Geochemistry of basalts from small eruptive centers near Villarrica stratovolcano, Chile: Evidence for lithospheric mantle components in continental arc magmas

    NASA Astrophysics Data System (ADS)

    Hickey-Vargas, R.; Sun, M.; Holbik, S.

    2016-07-01

    In the Central Southern Volcanic Zone (CSVZ) of the Andes, the location of stratovolcanoes and monogenetic small eruptive centers (SEC) is controlled by the Liquiñe-Ofqui Fault Zone (LOFZ), a trench-parallel strike-slip feature of over 1000 km length. The geochemistry of basalts from SEC is different from those of stratovolcanoes, and are termed Type 2 and Type 1 basalts, respectively. In the region of Villarrica stratovolcano, contemporaneous SEC are more MgO-rich, and have greater light rare earth element (LREE) enrichment, lower 87Sr/86Sr and 143Nd/144Nd, and lower ratios of large ion lithophile elements (LILE) to LREE and high field strength elements (HFSE). A unique finding in this region is that basalts from one SEC, San Jorge, has Type 1 character, similar to basalts from Villarrica stratovolcano. Type 1 basalts from Villarrica and San Jorge SEC have strong signals from time-sensitive tracers of subduction input, such as high 10Be/9Be and high (238U/230Th), while Type 2 SEC have low 10Be/9Be and (238U/230Th) near secular equilibrium. Based on new trace element, radiogenic isotope and mineral analyses, we propose that Type 1 basaltic magma erupted at San Jorge SEC and Villarrica stratovolcano forms by melting of the ambient actively subduction-modified asthenosphere, while Type 2 SEC incorporate melts of pyroxenite residing in the supra-subduction zone mantle lithosphere. This scenario is consistent with the close proximity of the volcanic features and their inferred depths of magma separation. The pyroxenite forms from arc magma produced during earlier episodes of subduction modification and magmatism, which extend back >300 Ma along this segment of the western South American margin. Type 2 basaltic magmas may reach the surface during LOFZ-related decompression events, and they may also be a normal but episodic part of the magma supply to large stratovolcanoes, resulting in cryptic geochemical variations over time. The presence and mobilization of stored

  10. Magma genesis, storage and eruption processes at Aluto volcano, Ethiopia: lessons from remote sensing, gas emissions and geochemistry

    NASA Astrophysics Data System (ADS)

    Hutchison, William; Biggs, Juliet; Mather, Tamsin; Pyle, David; Gleeson, Matthew; Lewi, Elias; Yirgu, Gezahgen; Caliro, Stefano; Chiodini, Giovanni; Fischer, Tobias

    2016-04-01

    One of the most intriguing aspects of magmatism during the transition from continental rifting to sea-floor spreading is that large silicic magmatic systems develop within the rift zone. In the Main Ethiopian Rift (MER) these silicic volcanoes not only pose a significant hazard to local populations but they also sustain major geothermal resources. Understanding the journey magma takes from source to surface beneath these volcanoes is vital for determining its eruption style and for better evaluating the geothermal resources that these complexes host. We investigate Aluto, a restless silicic volcano in the MER, and combine a wide range of geochemical and geophysical techniques to constrain magma genesis, storage and eruption processes and shed light on magmatic-hydrothermal-tectonic interactions. Magma genesis and storage processes at Aluto were evaluated using new whole-rock geochemical data from recent eruptive products. Geochemical modelling confirms that Aluto's peralkaline rhyolites, that constitute the bulk of recent erupted products, are generated from protracted fractionation (>80 %) of basalt that is compositionally similar to rift-related basalts found on the margins of the complex. Crustal melting did not play a significant role in rhyolite genesis and melt storage depths of ~5 km can reproduce almost all aspects of their geochemistry. InSAR methods were then used to investigate magma storage and fluid movement at Aluto during an episode of ground deformation that took place between 2008 and 2010. Combining new SAR imagery from different viewing geometries we identified an accelerating uplift pulse and found that source models support depths of magmatic and/or fluid intrusion at ~5 km for the uplift and shallower depths of ~4 km for the subsidence. Finally, gas samples collected on Aluto in 2014 were used to evaluate magma and fluid transport processes. Our results show that gases are predominantly emanating from major fault zones on Aluto and that they

  11. Geochemistry.

    ERIC Educational Resources Information Center

    Fyfe, William S.

    1979-01-01

    Techniques in geochemistry continue to improve in sensitivity and scope. The exciting areas of geochemistry still include the classical fields of the origin of the elements and objects in space, but environmental crisis problems are important as well. (Author/BB)

  12. Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry

    NASA Astrophysics Data System (ADS)

    Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.

    2015-12-01

    Porphyry Cu (Mo-Au) and epithermal Au-Ag ores are globally associated with shallow hydrous, strongly oxidized, and sulfur-rich arc intrusions. In many localities, long-lived magmatism includes evolution from early andesitic volcanic (v) and plutonic (p) rocks to later dacitic or rhyolitic compositions dominated by plutons. We compare zircon compositions from three igneous suites with different time spans: Yerington, USA (1 m.y., p>v), El Salvador, Chile (4 m.y., p>v), and Yanacocha, Peru (6 m.y., v>p). At Yerington granite dikes and ores formed in one event, at ES in 2 to 3 events spanning 3 m.y., and at Yanacocha in 6 events spanning 5 m.y. At both ES and Yanacocha, high-Al amphiboles likely crystallized at high temperature in the mid-crust and attest to deep magmas that periodically recharged the shallow chambers. At Yanacocha, these amphiboles contain anhydrite inclusions that require magmas were sulfur-rich and strongly oxidized (~NNO+2). The Ti-in-zircon geothermometer provides estimates of 920º to 620º C for zircon crystallization, and records both core to rim cooling and locally high temperature rim overgrowths. Ore-related silicic porphyries yield near-solidus crystallization temperatures of 750-650°C consistent with low zircon saturation temperatures. The latter zircons have large positive Ce/Ce* and small negative Eu/Eu*≥0.4 anomalies attesting to strongly oxidized conditions (Ballard et al., 2001), which we propose result from crystallization and SO2 loss to the magmatic-hydrothermal ore fluid (Dilles et al., 2015). The Hf, REE, Y, U, and Th contents of zircons are diverse in the magma suites, and Th/U vs Yb/Gd plots suggest a dominant role of crystal fractionation with lesser roles for both crustal contamination and mixing with high temperature deep-sourced mafic magma. Ce/Sm vs Yb/Gd plots suggest that magma REE contents at <900°C are dominated by early crystallization of hornblende and apatite, and late crystallization (~<780°C) of titanite

  13. Change in Magma Dynamics at Okataina Rhyolite Caldera revealed by Plagioclase Textures and Geochemistry

    NASA Astrophysics Data System (ADS)

    Shane, P. A. R.

    2015-12-01

    A fundamental reorganization of magma dynamics at Okataina volcano, New Zealand, occurred at 26 ka involving a change from smaller volume, high-temperature rhyodacite magmas to a lower eruptive tempo of larger volume, low-temperature, rhyolite magmas. Zircon studies demonstrate the presence of a periodically active, long-lived (100,000 yr) magmatic reservoir. However, there is little correlation between periods of zircon crystallization and eruption events. In contrast, the changing magmatic dynamics is revealed in plagioclase growth histories. Crystals from the ~0.7 ka Kaharoa eruption are characterized by resorbed cores displaying a cellular-texture of high-An (>40) zones partially replaced by low-An (<30) zones, surrounded by a resorption surface and a prominent normal-zoned rim (An50-20). Elevated An, Fe, Mg, Sr and Ti follow the resorption surface and display rimward depletion trends, accompanied by Ba and REE enrichment. The zonation is consistent with fractional crystallization and cooling. The cores display wide trace element diversity, pointing to crystallization in a variety of melts, before transport and mixing into a common magma where the rims grew. Plagioclase from the ~36 ka Hauparu eruption display several regrowth zones separated by resorption surfaces, which surround small resorbed cores with a spongy cellular texture of variable An content (An 40-50). The crystals display step-wise re-growth of successively higher An, Fe, Mg and Ti content, consistent with progressive mafic recharge. Two crystal groups are distinguished by trace element chemistry indicating growth in separate melts and co-occurrence via magma-mingling. The contrasting zoning patterns in plagioclase correspond to the evolutionary history of magmatism at Okataina. Emptying of the magma reservoir following caldera eruption at 46 ka reduced barriers to mafic magma ascent. This is recorded by the frequent resorption and recharge episodes in Hauparu crystals. Subsequent re

  14. Geochemistry

    ERIC Educational Resources Information Center

    Ailin-Pyzik, Iris B.; Sommer, Sheldon E.

    1977-01-01

    Enumerates some of the research findings in geochemistry during the last year, including X-ray analysis of the Mars surface, trace analysis of fresh and esterarine waters, and analysis of marine sedements. (MLH)

  15. Magma Plumbing and Transport at Yellowstone--Implications from Geodesy and Geochemistry (Invited)

    NASA Astrophysics Data System (ADS)

    Dzurisin, D.; Wicks, C. W.; Lowenstern, J. B.

    2013-12-01

    Surface deformation, thermal activity, and outgassing at the Yellowstone caldera are manifestations of a vigorous magmatic system that has been active for more than 2 million years. Viable models for Yellowstone's magma plumbing and transport system must account for: (1) high contemporary fluxes of heat and CO2; (2) ground deformation sources beneath each of two resurgent domes, and a third near the intersection of the north caldera rim and Norris-Mammoth corridor; (3) interplay among these sources, as suggested by the timing of major changes in deformation mode; (4) repeated cycles of uplift and subsidence and sudden changes from uplift to subsidence or vice versa; (5) spatial and temporal relationships between changes in deformation mode and earthquake swarms; and (6) lateral dimensions of all three deforming areas that indicate source depths in the range 5-15 km. Seismic tomography studies have imaged a partly molten silicic magma body in the upper crust beneath the caldera and a mantle feeder zone for mafic magma. A model in which surface displacements are caused primarily by variations in the flux of mafic magma into the crust satisfies known thermal, geochemical, and geodetic constraints. In the model, a conduit system centered beneath the northeast part of the caldera supplies basalt from a mantle source to an accumulation zone 5-10 km deep, perhaps at a rheological boundary beneath a crystal-rich rhyolite body remnant from past eruptions. Increases in magma flux favor surface uplift and decreases favor subsidence. A delicate equilibrium exists among the mass and heat flux from basaltic intrusions, heat and volatile loss from the rhyolite, and the overlying hydrothermal system. In the absence of basalt input, steady subsidence should occur as a result of fluid loss from the rhyolite, but if a self-sealing zone in the deep hydrothermal system prevents fluid escape the resulting pressure increase contributes to surface uplift. Such episodes end when the seal

  16. Geochemistry

    SciTech Connect

    Foster, N.H.; Beaumont, E.A.

    1988-01-01

    Papers in this text are part of a reprint series designed to be useful to those involved in petroleum exploration and development. The authors divide the topic of geochemistry into four sections: (1) petroleum formation,(2) source rock evaluation, (3) migration, and (4) surface geochemistry. Petroleum formation contains papers that discuss accumulation and preservation of organic matter, conversion to kerogen, conversion to petroleum, and effects that different types of kerogen have on the types of petroleum generated. The section on source rocks contain papers that review methods for estimating total organic content of source rocks, potential amount of petroleum they can expel, and quantity of petroleum expelled from these source rocks.Migration deals with mechanisms for expulsion and migration of petroleum from source rocks and in carrier beds. The section on surface geochemistry discusses the problems associated with using geochemical methods in exploration.

  17. Magma feeding 2011 unrest at Turrialba volcano: insights from noble gas geochemistry

    NASA Astrophysics Data System (ADS)

    Di Piazza, A.; Barberi, F.; Carapezza, M.; Rizzo, A.; Romano, C.; De Astis, G.

    2013-12-01

    After almost 150 years of quiescence accompanied by weak fumarolic activity, Turrialba volcano (Costa Rica Central Cordillera) is showing signals of potential reawakening. Since 1996, the degassing has become more intense with the extension of the fumarolic field, the opening of new fractures and the occurrence of phreatic explosions (2010-2013). Here, we present a noble gas isotope investigation of crater fumaroles and of fluid inclusions hosted in olivines and pyroxenes from lavas and scoria erupted in the last 10 ka. The 3He/4He ratio of fluid inclusions from the most mafic eruptive products (SiO2=52.5wt% and MgO=6wt%) varies from 7.86 to 8.07 Ra, while that from andesite lavas varies from 7.03 to 7.18 Ra. The most evolved products (SiO2=63wt% and MgO=3wt%) display the lowest 3He/4He ratio (Rc/Ra=6.5). The He isotope values of the most mafic products are in the range of typical arc volcanoes (7-8 Ra), suggesting that contamination of the mantle wedge below the volcano by crustal He is negligible. On the other hand, the lowest values of 3He/4He ratio measured in the most silicic rocks of the series (dacitic) could be representative of a crustal contamination undergone by magma in the plumbing system of Turrialba. The fumaroles collected in 2007-2011 show an helium isotope composition of 7.50-7.96 Ra, which is well in the range of that measured in fluid inclusions from more mafic and recently erupted rocks. This implies that magma involved in the ongoing unrest phase and feeding the crater fumarolic field has petrological and geochemical features comparable to the basaltic-andesitic rocks analyzed in this study. In addition, long-term monitoring of He isotope composition carried out in the last years at Turrialba displays a progressive increase of 3He/4He ratios, which could be related to the simultaneous unrest testified by the increased seismic activity. We infer that this variation could be related to a refill of the plumbing system by 3He-rich magmas, which

  18. Magma evolution as seen through zircon geochemistry: an example from the Southern Adamello Batholith, N. Italy

    NASA Astrophysics Data System (ADS)

    Broderick, C.; Schaltegger, U.; Gerdes, A.; Frick, D.; Guenther, D.; Brack, P.

    2012-04-01

    Zircon is an ubiquitous accessory mineral often used for U-Pb geochronology but is also an important recorder of geochemical information. The trace element and isotopic characteristics of zircon yield potential for tracking changes in an evolving magma through time. With recent advances in U-Pb zircon geochronology, 10-100 ka to Ma timescales are observed for incremental pluton construction (Michel et al., 2008, Schaltegger et al., 2009). In observed 100 ka timescales of zircon crystallization, can zircon record the processes that produce trace element variations in a magma? This study focuses on the Val Fredda Complex (VFC) in the southern tip of the 43 to 33 Ma Adamello batholith, N. Italy. The VFC displays complex relationships among mafic melts that were injected into solidifying felsic magmas. Single zircon crystals were dated using CA-ID-TIMS. With permil uncertainties on 206Pb/238U zircon dates, zircons reveal complexities within single populations. The mafic units crystallized potential autocrystic zircons over a duration of 100 - 150ka, whereas the felsic units record up to 200ka of zircon crystallization. In order to understand these complex zircon populations, we analyzed Hf isotopes and trace elements, on the same volume of zircon used for U-Pb dating, following the TIMS-TEA method (Schoene et al., 2010). This detailed zircon study will allow us to look at how magmas are evolving with time. Hf isotopes of VFC mafic zircons reveal distinct ɛHf values between the three mafic units and their ɛHf values remain consistent through time, whereas the VFC felsic units record more complexity in their ɛHf values. We observe changes such as increasing and slight decreases in ɛHf with time which suggest different processes are occurring to produce the different felsic units. Trace element ratios in zircon reveal differences which allow us to make distinctions between felsic and mafic units (e.g. Th/U, (Lu/Gd)N, REEs). The VFC records 200 ka of zircon

  19. Geochemistry and argon thermochronology of the Variscan Sila Batholith, southern Italy: source rocks and magma evolution

    USGS Publications Warehouse

    Ayuso, R.A.; Messina, A.; de Vivo, B.; Russo, S.; Woodruff, L.G.; Sutter, J.F.; Belkin, H.E.

    1994-01-01

    . Although the granitic groups cannot be uniquely distinguished on the basis of their Pb isotope compositions most of the post-tectonic tonalites to granodiorites as well as two-mica granites are somewhat less radiogenic than the syn-tetonic tonalites and granodiorites. Only a few of the mafic enclaves overlap the Pb isotope field of the granitic rocks and are consistent with a cogenetic origin. The Sila batholith was generated by mixing of material derived from at least two sources, mantle-derived and crustal, during the closing stages of plate collision and post-collision. The batholith ultimately owes its origin to the evolution of earlier, more mafic parental magmas, and to complex intractions of the fractionating mafic magmas with the crust. Hybrid rocks produced by mixing evolved primarily by crystal fractionation although a simple fractionation model cannot link all the granitic rocks, or explain the entire spectrum of compositions within each group of granites. Petrographic and geochemical features characterizing the Sila batholith have direct counterparts in all other granitic massifs in the Calabrian-Peloritan Arc. This implies that magmatic events in the Calabrian-Peloritan Arc produced a similar spectrum of granitic compositions and resulted in a distinctive type of granite magmatism consisting of coeval, mixed, strongly peraluminous and metaluminous granitic magmas. ?? 1994 Springer-Verlag.

  20. Unraveling the geochemistry of melts in exhumed mantle domains in present-day and fossil magma-poor rifted margins

    NASA Astrophysics Data System (ADS)

    Amann, Méderic; Ulrich, Marc; Autin, Julia; Manatschal, Gianreto; Epin, Marie-Eva; Müntener, Othmar; Boiron, Marie-Christine; Sauter, Daniel

    2016-04-01

    899B are less LREE depleted compared to clinopyroxenes from other sites in the Iberia margin, showing a lower partial melting rate and thus a differential magmatic activity within this margin transect trough time and space. Moreover, new analysis on clinopyroxenites from ODP leg 173 site 1070, will help to constrain the PT conditions during formation of the OCT. Future work in the Platta nappe will be useful to test whether or not the geochemistry of melts and its establishment are defined by the same characteristics in fossil magma-poor margins.

  1. Magma energy

    SciTech Connect

    Dunn, J.C.

    1987-01-01

    The thermal energy contained in magmatic systems represents a huge potential resource. In the US, useful energy contained in molten and partially-molten magma within the upper 10 km of the crust has been estimated at 5 to 50 x 10/sup 22/ J (50,000 to 500,000 Quads). The objective of the Magma Energy Extraction Program is to determine the engineering feasibility of locating, accessing, and utilizing magma as a viable energy resource. This program follows the DOE/OBES-funded Magma Energy Research Project that concluded scientific feasibility of the magma energy concept. A primary long-range goal of this program is to conduct an energy extraction experiment directly in a molten, crustal magma body. Critical to determining engineering feasibility are several key technology tasks: (1) Geophysics - to obtain detailed definition of potential magma targets, (2) Geochemistry/Materials - to characterize the magma environment and select compatible engineering materials, (3) Drilling - to develop drilling and completion techniques for entry into a magma body, and (4) Energy Extraction - to develop heat extraction technology.

  2. Interaction between felsic and mafic magmas in the Salmas intrusive complex, Northwestern Iran: Constraints from petrography and geochemistry

    NASA Astrophysics Data System (ADS)

    Ghaffari, Mitra; Rashidnejad-Omran, Nematollah; Dabiri, Rahim; Santos, José Francisco; Mata, João; Buchs, David; McDonald, Iain; Appel, Peter; Garbe-Schönberg, Dieter

    2015-11-01

    The Salmas plutonic complex, in the northernmost part of Sanandaj-Sirjan Zone of Iran, provides evidence for magma interaction processes. The complex contains mafic-intermediate, hybrid and felsic rocks which intruded into the Paleozoic metamorphic complex. They show typical relationships described in many mafic-felsic mingling and mixing zones worldwide, such as mafic microgranular enclaves (in felsic and hybrid rocks), mafic sheets, and hybrid rocks. The mafic microgranular enclaves (MMEs) are characterized by fine-grained, equigranular and hypidiomorphic texture and some special types of microscopic textures, e.g., quartz xenocrysts, oscillatory-zoned plagioclase, small lath-shaped plagioclase in large plagioclase, spike zones in plagioclase and spongy-cellular plagioclase textures, rounded plagioclase megacrysts blade-shaped biotite, acicular apatite. The mafic sheets and MMEs in granites (MME-Gr), which indicated magma mingling structures, show ISr values and εNd(i) similar to diorites. The hybrid rocks and their mafic enclaves (MME-H) show isotope signatures similar to each other. Granites have isotope signatures [higher 87Sr/86Sr(i) (0.70788-0.71075) and lower εNd(i) (-2.4 to -4.2)] distinct to those of the all rock types and MMEs. Major, trace and REE modeling show that hybrid rocks are generated via 40-60% mixing of mafic (dioritic) and felsic (granitic) end-members. All the geochemical data suggest that underplating of dioritic magma, which has been produced by fractional crystallization of gabbros, under the lower crust caused its melting to make felsic (granitic) magma. Injection of dioritic magma into the base of the felsic magma chamber and a limited mixing of two end-members, the lower crust-derived magma and mantle-derived melts, formed hybrid magma and their enclaves. Injections of new mafic magma pulses into hybrid magma generated mafic enclaves into them. The injections of denser dioritic magma pulses into a felsic magma chamber and spreading

  3. Magma mingling and chemical diffusion in the Taojiang granitoids in the Hunan Province, China: evidences from petrography, geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Wang, Kai-Xing; Chen, Pei-Rong; Chen, Wei-Feng; Ling, Hong-Fei; Zhao, Kui-Dong; Yu, Zhi-Qiang

    2012-11-01

    Petrographic study and zircon LA-ICP-MS U-Pb dating reveal that the Taojiang pluton is mainly composed of Late Indosinian biotite granodiorites (216 ± 2 Ma, 217 ± 1 Ma and 217 ± 1 Ma) with contemporaneous microgranular enclaves (219 ± 3 Ma). The host rocks belong to metaluminous to peraluminous and high-K calc-alkaline granodiorite with mean K2O/Na2O ratio less than 1, while the microgranular enclaves belong to metaluminous and shoshonitic monzodiorite and quartz monzonite, with average K2O/Na2O greater than 1. The enclaves contain back-veins and xenocrysts of quartz, biotite and plagioclase, and have contents of K, Rb and total REE higher than their host rocks, indicating mingling of two different magmas and elemental diffusion from the felsic magma to the mafic magma due to temperature gradient between them. The host granodiorites have initial 87Sr/86Sr of 0.71411 0.71508, ɛ Nd(t) values of -6.05 -7.39 and Nd isotope two stage model ages ( {T_{NdDM}^2} ) of 1.49 Ga to 1.60 Ga, while the enclaves have initial 87Sr/86Sr of 0.71438, ɛ Nd(t) values of -6.92 and T_{NdDM}^2 of 1.56 Ga, showing similar features. The zircon ɛ Hf(t) values of the enclaves (-4.21 0.54) are slightly higher than those of the host rocks (-6.77 -2.18), and the zircon Hf isotopic two stage model ages ( {T_{NfDM}^2} ) of the enclaves (mainly 1.21 Ga 1.45 Ga) are accordingly slightly younger compared with those of the host rocks (1.39 Ga to 1.75 Ga). These data suggest that the host rock magma was derived mainly from partial melting of Mesoproterozoic - Paleoproterozoic crustal rocks, while the enclave magma was originated from partial melting of basic/ultrabasic rocks intruding in the crust during Mesoproterozoic period. Three inherited zircon cores from the granodiorites are dated 1512 Ma, 2325 Ma and 2458 Ma, also giving evidence for involvement of Mesoproterozoic- Paleoproterozoic crust rocks in the magma formation. The more evident negative Eu anomaly of the enclaves than their host

  4. Mechanisms and timescales of generating eruptible rhyolitic magmas at Yellowstone caldera from zircon and sanidine geochronology and geochemistry

    USGS Publications Warehouse

    Stelten, Mark; Cooper, Kari M.; Vazquez, Jorge A.; Calvert, Andrew T.; Glessner, Justin G

    2015-01-01

    We constrain the physical nature of the magma reservoir and the mechanisms of rhyolite generation at Yellowstone caldera via detailed characterization of zircon and sanidine crystals hosted in three rhyolites erupted during the (ca. 170 – 70 ka) Central Plateau Member eruptive episode – the most recent post-caldera magmatism at Yellowstone. We present 238U-230Th crystallization ages and trace-element compositions of the interiors and surfaces (i.e., unpolished rims) of individual zircon crystals from each rhyolite. We compare these zircon data to 238U- 230Th crystallization ages of bulk sanidine separates coupled with chemical and isotopic data from single sanidine crystals. Zircon age and trace-element data demonstrate that the magma reservoir that sourced the Central Plateau Member rhyolites was long-lived (150 – 250 kyr) and genetically related to the preceding episode of magmatism, which occurred ca. 256 ka. The interiors of most zircons in each rhyolite were inherited from unerupted material related to older stages of Central Plateau Member magmatism or the preceding late Upper Basin Member magmatism (i.e., are antecrysts). Conversely, most zircon surfaces crystallized near the time of eruption from their host liquids (i.e., are autocrystic). The repeated recycling of zircon interiors from older stages of magmatism demonstrates that sequentially erupted Central Plateau Member rhyolites are genetically related. Sanidine separates from each rhyolite yield 238U-230Th crystallization ages at or near the eruption age of their host magmas, coeval with the coexisting zircon surfaces, but are younger than the coexisting zircon interiors. Chemical and isotopic data from single sanidine crystals demonstrate that the sanidines in each rhyolite are in equilibrium with their host melts, which considered along with their near-eruption crystallization ages suggests that nearly all CPM sanidines are autocrystic. The paucity of antecrystic sanidine crystals relative to

  5. Petrology and geochemistry of Late Holocene felsic magmas from Rungwe volcano (Tanzania), with implications for trachytic Rungwe Pumice eruption dynamics

    NASA Astrophysics Data System (ADS)

    Fontijn, Karen; Elburg, Marlina A.; Nikogosian, Igor K.; van Bergen, Manfred J.; Ernst, Gerald G. J.

    2013-09-01

    Rungwe in southern Tanzania is an active volcanic centre in the East African Rift System, characterised by Plinian-style explosive eruptions of metaluminous to slightly peralkaline trachytic silica-undersaturated magmas during its late Holocene history. Variations in whole-rock major and trace element compositions of erupted products have been investigated, in combination with electron microprobe data for melt inclusions and phenocrysts comprising sanidine, biotite, clinopyroxene, titanomagnetite, ilmenite, haüyne, titanite, apatite and traces of plagioclase and amphibole. Compositional variations largely reflect fractional crystallisation, with a limited influence of magma mixing. Subtle variations in whole-rock composition and mineralogical characteristics between and within deposits, suggest the existence of a chemically zoned trachytic magma chamber beneath Rungwe. For the two most important studied deposits, the Isongole and Rungwe Pumice, co-existing Fe-Ti oxides constrain pre-eruptive temperature to 915-950 °C and oxygen fugacity to NNO + 0.25-NNO + 0.45. For the Rungwe Pumice, melt inclusions suggest that the melt was water-undersaturated (maximum inferred H2O concentration 5.5 wt.%). In the range of the defined pre-eruptive temperatures, this corresponds to melt viscosities as low as 103.3 Pa · s, i.e. significantly lower than magmas that typically generate highly explosive eruptions. Because no microlites formed in the conduit during ascent, which would have strongly increased the effective magma viscosity, the highly explosive nature of the eruptions may be attributable to a crucial role of exsolved CO2 and S phases, and very high ascent rates.

  6. Trace element geochemistry of nyerereite and gregoryite phenocrysts from natrocarbonatite lava, Oldoinyo Lengai, Tanzania: Implications for magma mixing

    NASA Astrophysics Data System (ADS)

    Mitchell, Roger H.; Kamenetsky, Vadim S.

    2012-11-01

    The abundances of Li, P, Cl, V, Mn, Rb, Sr, Y, Cs, Ba, Pb, Th, U and REE, within and between, phenocrysts of nyerereite and gregoryite occurring in natrocarbonatite lavas erupted from the active volcano Oldoinyo Lengai (Tanzania) have been determined by electron microprobe, LA-ICP-MS and SIMS. These data show that, in general, nyerereite is enriched in Rb (71-137 ppm), Sr (14,485-23,240 ppm), Y (2.0-8.9 ppm), Cs (1.6-5.3 ppm), Ba (4000-11,510 ppm), but poorer in Li (21-91 ppm), P (820-1900 ppm) and V (5.1-47 ppm) relative to gregoryite (Rb = 43-106; Sr = 4255-7275; Y = 0.3-4.0; Cs = 0.6-5.1; Ba = 1125-7052; Li 84-489; P = 6790-15,860; V = 33-155 ppm). Nyerereite is highly enriched in REE (La = 236-973; Ce = 395-1044 ppm) relative to gregoryite (La = 59-309; Ce = 59-301 ppm). Chondrite normalized REE distribution patterns for nyerereite and gregoryite are parallel and linear with no Eu anomalies. They show extreme enrichment in light REE and depletion in heavy REE (nyerereite La/YbCN = 1759-7079; gregoryite La/YbCN = 1051-10,247). Significant differences exist in the abundances of trace elements within and between coexisting crystals occurring in diverse natrocarbonatite flows, although there do not appear to be any significant secular variations in phenocryst compositions in lavas erupted from a given vent. It is concluded that both major, minor and trace element compositional data for nyerereite and gregoryite phenocrysts occurring in natrocarbonatite lavas are derived by the crystallization of several different batches of magma in a continuously replenished fractionating magma chamber. Natrocarbonatite lavas are considered to be hybrids formed by the mixing of both crystals and melts formed from several batches of natrocarbonatite magma; thus bulk rock compositions cannot represent the compositions of the primary magma composition before the onset of fractionation. Differentiation of natrocarbonatite melts leads to enrichment of residua in Ba and Mg.

  7. Geochemistry of lavas from Taal volcano, southwestern Luzon, Philippines: evidence for multiple magma supply systems and mantle source heterogeneity

    USGS Publications Warehouse

    Miklius, Asta; Flower, M.F.J.; Huijsmans, J.P.P.; Mukasa, S.B.; Castillo, P.

    1991-01-01

    Taal lava series can be distinguished from each other by differences in major and trace element trends and trace element ratios, indicating multiple magmatic systems associated with discrete centers in time and space. On Volcano Island, contemporaneous lava series range from typically calc-alkaline to iron-enriched. Major and trace element variation in these series can be modelled by fractionation of similar assemblages, with early fractionation of titano-magnetite in less iron-enriched series. However, phase compositional and petrographic evidence of mineral-liquid disequilibrium suggests that magma mixing played an important role in the evolution of these series. -from Authors

  8. Isotope geochemistry of early Kilauea magmas from the submarine Hilina bench: The nature of the Hilina mantle component

    NASA Astrophysics Data System (ADS)

    Kimura, Jun-Ichi; Sisson, Thomas W.; Nakano, Natsuko; Coombs, Michelle L.; Lipman, Peter W.

    2006-03-01

    Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr-Nd-Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of early Kilauea magmas ( Sisson et al., 2002). These samples are among the highest 206Pb/ 204Pb known from Hawaii and may represent melts from a distinct geochemical and isotopic end-member involved in the generation of most Hawaiian tholeiites. This end-member is similar to the postulated literature Kea component, but we propose that it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina end-member but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both "Koolau" (high 87Sr/ 86Sr, low 206Pb/ 204Pb) and depleted (low 87Sr/ 86Sr, intermediate 206Pb/ 204Pb) source materials. This shift in isotopic character from nearly uniform, end-member, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea's magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling mantle source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the Koolau

  9. Isotope geochemistry of early Kilauea magmas from the submarine Hilina bench: The nature of the Hilina mantle component

    USGS Publications Warehouse

    Kimura, Jun-Ichi; Sisson, T.W.; Nakano, N.; Coombs, M.L.; Lipman, P.W.

    2006-01-01

    Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr-Nd-Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of early Kilauea magmas (Sisson et al., 2002). These samples are among the highest 206Pb/204Pb known from Hawaii and may represent melts from a distinct geochemical and isotopic end-member involved in the generation of most Hawaiian tholeiites. This end-member is similar to the postulated literature Kea component, but we propose that it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina end-member but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both "Koolau" (high 87Sr/86Sr, low 206Pb/204Pb) and depleted (low 87Sr/86Sr, intermediate 206Pb/204Pb) source materials. This shift in isotopic character from nearly uniform, end-member, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea's magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling mantle source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the Koolau component

  10. Zircon trace element geochemistry and growth of the Pleistocene to Holocene Mono Craters rhyolite magma system, California (USA)

    NASA Astrophysics Data System (ADS)

    Baker, N.; Miller, J. S.; Vazquez, J. A.; Marcaida, M.; Lidzbarski, M. I.

    2015-12-01

    The Mono Craters, part of the Mono-Inyo volcanic chain in eastern California, comprise at least 27 high-silica Pleistocene to Holocene rhyolite domes, lava flows and tephra cones. The Holocene chronology of the Mono Craters is well constrained but only recently has 238U-230Th zircon and 40Ar/39Ar dating elucidated the Pleistocene eruptive history. We performed trace element analysis on dated zircon crystal rims and sectioned interiors (using SHRIMP-RG) from 3 rhyolite domes (21, 12.5, and 7 ka) with additional rim data on 5 ashes separated from juvenile pumice clasts in the correlative Wilson Creek Formation (spanning from 62 to 21 ka). Ti-in-zircon (TTi,zrc) thermometry (titania activity from coexisting Fe-Ti oxides) gives temperatures predominantly between 650°C and 750°C, similar to average zircon saturation temperatures (Tzrc,sat). The observation that Tzrc,sat ≈ TTi,zrc indicates that Mono Craters rhyolite magmas were zircon-saturated and erupted at these temperatures (near water-saturated granite eutectic). Variations in key trace elements are relatively limited overall and zircons display similar REE patterns with generally curved MREE to HREE patterns and prominent negative Eu anomalies. Most of the variation is observed in zircons from older eruptions (62-41 ka). Zircon rims from Ash 17 of the Wilson Creek Formation (59 ka) have elevated Th/U, Eu/Eu*, and Ti and lower Hf compared to Ash 19 (62 ka), which suggests a thermal rejuvenation event between these two eruptions. Zircon rims from Ash 15 (41 ka) are characterized by a trend toward high Hf, at relatively low and relatively constant Ti, and low Eu/Eu*, consistent with rhyolite magma undergoing eutectic-like crystallization just prior to eruption. Zircon surfaces and interiors for the 21, 12.5, and 7 ka dome eruptions have very similar Hf, low Eu/Eu*, low Ti, and low Th/U. This requires zircon crystallization in a very uniform thermal and chemical environment from the latest Pleistocene to Holocene

  11. Geochemistry and Magmagenesis of the Early May 2008 Rhyolitic Magma Erupted by Chaiten Volcano, Southern Andes Volcanic Zone

    NASA Astrophysics Data System (ADS)

    Munoz, J. O.; Basualto, D.; Moreno, H.; Peña, P.; Mella, M.

    2008-12-01

    , located 15 km to the east and to the Upper Pleistocene rhyolite from Yate volcano, approximately 100 km to the north. Geochemical data suggest that Chaiten rhyolites (both old and current eruption) were not produced by fractional crystallization of a basaltic magma derived from an astenospheric or lithospheric mantle source, as could be the case of the nearby Michinmahuida volcano. Also, Chaiten rhyolites appears to be derived from a less mafic source than the rhyolite from Yate volcano (Mella, 2008). Preliminary non-modal dynamic melting models for mafic and intermediate source suggests that 5-10 percent of partial melting of an intermediate source (modal composition including 10 Cpx, 30 Hb, 45 Pl, 4 Bt, 1 Mt) is the best fit model. As indicate by precursory and early eruption volcanotectonic seismicity, this intermediate source could be an amphibolite (facies either acquired during accretion or within the crust) located at 10-15 km depth, in a 30 km thickness crust with relatively high geothermal gradient, as it was previously proposed by Lopez et al. (1993). Crystals may be relict from the magma plumbing system. Lopez, L., Kilian, R., Kempton, P. D.., Tagiti, M. 1993. Rev. Geol.. Chile 22(1):33-55. Mella, M., 2008. Tese de Doutoramento, Universidade de Sao Paulo, 180 p. Brasil. Naranjo, J.A., Stern C., 2004. Rev. Geol. Chile 31(2): 225-240. Stern, C., Navarro, X. and Munoz, J. 2002. Anal. Inst. Patagonia 30: 167-174.

  12. Major, trace element and isotope geochemistry (Sr-Nd-Pb) of interplinian magmas from Mt. Somma-Vesuvius (Southern Italy)

    USGS Publications Warehouse

    Somma, R.; Ayuso, R.A.; de Vivo, B.; Rolandi, G.

    2001-01-01

    compositions in the interplinian rocks show a tendency to become slightly more radiogenic with age, from the Protohistoric (143Nd/144Nd=0.51240-0.51247) to Ancient Historic (143Nd/144Nd=0.51245-0.51251). Medieval interplinian activity (143Nd/144Nd: 0.51250-0.51241) lacks meaningful internal trends. All the interplinian rocks have virtually homogeneous compositions of 207Pb/204Pb and 208Pb/204Pb in acid-leached residues (207Pb/204Pb ???15.633 to 15.687, 208Pb/204Pb ???38.947 to 39.181). Values of 206Pb/204Pb are very distinctive, however, and discriminate among the three interplinian cycles of activity (Protohistoric: 18.929-18.971, Ancient Historic: 19.018-19.088, Medieval: 18.964-19.053). Compositional trends of major, trace element and isotopic compositions clearly demonstrate strong temporal variations of the magma types feeding the Somma-Vesuvius activity. These different trends are unlikely to be related only to low pressure evolutionary processes, and reveal variations of parental melt composition. Geochemical data suggest a three component mixing scheme for the interplinian activity. These involve HIMU-type and DMM-type mantle and Calabrian-type lower crust. Interaction between these components has taken place in the source; however, additional quantitative constraints must be acquired in order to better discriminate between magma characteristics inherited from the sources and those acquired during shallow level evolution.

  13. Sedimentation in Magma Chambers: Evidence From the Geochemistry, Microstructure and Crystallography of Troctolite and Gabbro Cumulates, Rum Layered Intrusion, Scotland.

    NASA Astrophysics Data System (ADS)

    Lo Ré, F. C.; Cheadle, M. J.; Swapp, S. M.; Coogan, L. A.

    2003-12-01

    The formation of igneous cumulates remains poorly understood. In particular, petrologists disagree about the relative importance of crystal accumulation by sedimentation or in-situ growth, partly because post-cumulus processes often overprint evidence for the primary mechanism. We address this problem with a detailed geochemical, microstructural and crystallographic study of gabbros and troctolites from the Eastern Layered Series of the Rum Layered Intrusion, NW Scotland. We collected samples, approximately every 50cm, through the complete 11m sequence of foliated gabbros and troctolites from Unit 9. The samples were quantitatively analyzed for crystal shape and size, shape preferred orientation (SPO), crystallographic preferred orientation (CPO), modal mineralogy, and whole rock and mineral chemistry. We present the following results: Within cumulate layers just cm's apart, olivine crystal shape can vary from sub-equant to tabular, and crystal diameter can vary from 1-8mm. This suggests at least one olivine population was derived elsewhere in the magma chamber. Complex anorthite zoning is also consistent with an extended history of plagioclase crystal transport. A one-crystal thick olivine layer between feldspathic layers of differing grain size is interpreted to be a lag deposit. Two possible examples of cross bedding also exist. Taken together, these observations suggest sedimentation was the primary method of crystal accumulation. The data also provide constraints on post-cumulus processes. Complex plagioclase zoning suggests that processes of viscous compaction and/or recrystallization were not extensive. The preservation of magmatic and deformation twins and absence of a polygonal fabric support this conclusion. In addition, the CPO and SPO are the same. Lacking evidence for compaction and recrystallization lead us to believe similar CPO and SPO are the preserved artifact of a sedimentary foliation. Therefore, we conclude the gabbros and troctolites of Unit 9

  14. The magma plumbing system of Bezymianny Volcano: Insights from a 54 year time series of trace element whole-rock geochemistry and amphibole compositions

    NASA Astrophysics Data System (ADS)

    Turner, Stephen J.; Izbekov, Pavel; Langmuir, Charles

    2013-08-01

    Samples from 33 individual eruptions of Bezymianny volcano between 1956 and 2010 provide an opportunity to study in detail the temporal evolution of an arc volcano. Major element and ICP-MS trace element analyses show that the eruptive products shifted progressively from relatively silicic magma in 1956 (~ 60.4% SiO2) to more mafic compositions (e.g. 56.8% SiO2 in 2010). Amphibole compositions changed concurrently from low-Al2O3 to high-Al2O3. Whole rock element-element variation diagrams show tight compositional arrays, some with a distinct kink in the late 1970s, which cannot be reproduced by fractionation of a single magma along a liquid line of descent. Amphibole thermobarometry indicates amphibole crystallization in two separate reservoirs, one between 200 and 300 MPa, and another between 500 and 750 MPa. Liquid compositions calculated from the amphibole analyses show that liquids stored in each reservoir become increasingly mafic from 1956 to 2010, suggesting that each reservoir received magma inputs from more mafic sources throughout the eruptive cycle. End member mixing analysis of the dataset allows calculation of three end member compositions that can be combined in varying proportions to reproduce major and trace element whole rock compositions. The end-member mixing proportions vary systematically between 1956 and 2010, with maxima for end-members A, B and C during 1956, 1977, and 2010, respectively. Major element compositions of phenocrysts, combined with published trace element partition coefficients, show that each end member may have evolved from a common parental magma by fractionation of three different mineral assemblages, possibly due to different pressures of crystallization and volatile contents. The petrologic data are consistent with three magma reservoirs at different depths. Magmas from the shallowest reservoir erupted first, with increasing proportions of deeper reservoirs over time. Past studies have demonstrated similarities in eruptive

  15. Late Triassic intrusive complex in the Jidong region, Jiamusi-Khanka Block, NE China: Geochemistry, zircon U-Pb ages, Lu-Hf isotopes, and implications for magma mingling and mixing

    NASA Astrophysics Data System (ADS)

    Yang, Hao; Ge, Wen-chun; Zhao, Guo-chun; Dong, Yu; Xu, Wen-liang; Ji, Zheng; Yu, Jie-jiang

    2015-05-01

    Whole-rock major and trace element geochemistry together with zircon U-Pb ages and Lu-Hf isotope compositions are reported for a Late Triassic intrusive complex in the Jidong region, Jiamusi-Khanka Block, NE China. Zircon U-Pb dating yields ages between 211 and 208 Ma for enclaves of microgranular diorite and quartz diorite, and between 211 and 209 Ma for the host granitoids. These ages correlate with a previously established intensive Late Triassic magmatic event along the eastern Asian margin. Field observations, together with petrographic features, geochemistry, and zircon Hf isotope data, preclude simple crystal fractionation or restite unmixing as a genetic link for the various rock types within the intrusive complex. The syenogranite suite has high SiO2 (75.5-76.3 wt.%) and low MgO (0.15-0.19 wt.%), and yields enriched LILE and LREE patterns. Most of the zircons in the syenogranites have two-stage model ages of 766 and 1461 Ma, together with positive εHf(t) values of + 0.6 to + 9.1. These results indicate that the granitoid magmas were generated by partial melting of Meso- to Neoproterozoic lower crust. The gabbro suite has a restricted range of SiO2 (46.1-51.9 wt.%) together with high Mg# values (49-70) and high concentrations of Ni, Co, and Cr. Zircons from two diorite samples have single-stage Hf model ages of 557-787 Ma and εHf(t) values of + 1.9 to + 8.3 that are consistent with the coeval gabbros previously studied in the Jidong region. These features, together with the observation that all the gabbros are enriched in LREE and LILE, suggest that the mafic magmas were derived from melting of depleted Neoproterozoic lithospheric mantle that had been metasomatized by slab-derived fluids. It is concluded that the dominant igneous suites within the Late Triassic intrusive complex formed by mingling/mixing of felsic and mafic magmas. The geochemical data, combined with regional geological investigations, indicate that the Late Triassic intrusive complex

  16. From a long-lived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)

    NASA Astrophysics Data System (ADS)

    Buret, Yannick; von Quadt, Albrecht; Heinrich, Christoph; Selby, David; Wälle, Markus; Peytcheva, Irena

    2016-09-01

    The formation of world class porphyry copper deposits reflect magmatic processes that take place in a deeper and much larger underlying magmatic system, which provides the source of porphyry magmas, as well as metal and sulphur-charged mineralising fluids. Reading the geochemical record of this large magmatic source region, as well as constraining the time-scales for creating a much smaller porphyry copper deposit, are critical in order to fully understand and quantify the processes that lead to metal concentration within these valuable mineral deposits. This study focuses on the Bajo de la Alumbrera porphyry copper deposit in Northwest Argentina. The deposit is centred on a dacitic porphyry intrusive stock that was mineralised by several pulses of porphyry magma emplacement and hydrothermal fluid injections. To constrain the duration of ore formation, we dated zircons from four porphyry intrusions, including pre-, syn- and post-mineralisation porphyries based on intersection relations between successive intrusion and vein generations, using high precision CA-ID-TIMS. Based on the youngest assemblages of zircon grains, which overlap within analytical error, all four intrusions were emplaced within 29 ka, which places an upper limit on the total duration of hydrothermal mineralisation. Re/Os dating of hydrothermal molybdenite fully overlaps with this high-precision age bracket. However, all four porphyries contain zircon antecrysts which record protracted zircon crystallisation during the ∼200 ka preceding the emplacement of the porphyries. Zircon trace element variations, Ti-in-zircon temperatures, and Hf isotopic compositions indicate that the four porphyry magmas record a common geochemical and thermal history, and that the four intrusions were derived from the same upper-crustal magma chamber. Trace element zoning within single zircon crystals confirms a fractional crystallisation trend dominated by titanite and apatite crystallisation. However, zircon

  17. How mantle heterogeneity can affect geochemistry of magmas and their styles of emplacement: a fascinating tale revealed by Etna alkaline lavas

    NASA Astrophysics Data System (ADS)

    Viccaro, Marco; Zuccarello, Francesco

    2016-04-01

    Geochemical investigations of Mt. Etna magmas have led to notable findings on the nature of compositional heterogeneity of the mantle source beneath the volcano. Some of the observed features explain the short-term geochemical variability of volcanic rocks erupted at Mt. Etna in recent times, which are characterized by increase of LILE, 87Sr/86Sr and decrease of 143Nd/144Nd, 206Pb/204Pb,176Hf/177Hf. This compositional behavior has not attributed exclusively to differentiation processes such as fractional crystallization, crustal assimilation and effects of volatile flushing. In this study, based on some geochemical similarities of the Etnean and Hyblean alkaline magmas, we have modeled partial melting of a composite source constituted by two rock types, inferred by various observations performed on some Hyblean xenoliths, namely: a spinel lherzolite bearing phlogopite-amphibole and a garnet pyroxenite in form of veins intruded into lherzolite that is interpreted as metasomatic high-temperature fluids (silicate melts) crystallized at mantle conditions. Partial melting modeling has been applied to each rock type and the resulting primary liquids have been then mixed in various proportions. The concentrations of major and trace elements along with the water obtained from the modeling are remarkably comparable with those of Etnean melts re-equilibrated at primary conditions. Different proportions of spinel lherzolite bearing metasomatic phases and garnet pyroxenite can account for the signature of a large spectrum of Etnean alkaline magmas and for their geochemical variability through time. Our study implies that magmas characterized by variable compositions and volatile contents directly inherited from the source can undergo distinct histories of ascent and evolution in the plumbing system at crustal levels, potentially leading to a wide range of eruptive styles. A rather shallow source inferred from the model also excludes the presence of deep mantle structures

  18. Formation and emplacement of two contrasting late-Mesoproterozoic magma types in the central Namaqua Metamorphic Complex (South Africa, Namibia): Evidence from geochemistry and geochronology

    NASA Astrophysics Data System (ADS)

    Bial, Julia; Büttner, Steffen H.; Frei, Dirk

    2015-05-01

    The Namaqua Metamorphic Complex is a Mesoproterozoic low-pressure, granulite facies belt along the southern and western margin of the Kaapvaal Craton. The NMC has formed between ~ 1.3 and 1.0 Ga and its central part consists essentially of different types of granitoids intercalated with metapelites and calc-silicate rocks. The granitoids can be subdivided into three major groups: (i) mesocratic granitoids, (ii) leucocratic granitoids and (iii) leucogranites. The high-K, ferroan mesocratic granitoids (54-75 wt% SiO2) have a variable composition ranging from granitic to tonalitic, and contain biotite and/or hornblende or orthopyroxene. They are strongly enriched in REE and LILE, indicating A-type chemical characteristics, and are depleted in Ba, Sr, Eu, Nb, Ta and Ti. The leucocratic granitoids and leucogranites (68-76 wt% SiO2) differ from the other group in having a granitic or slightly syenitic composition containing biotite and/or garnet/sillimanite. They have lower REE and MgO, FeOt, CaO, TiO2, MnO concentrations, but higher Na2O and K2O contents. Compositional variations in mesocratic granitoids indicate their formation by fractional crystallization of a mafic parental magma. Leucocratic granitoids and leucogranites lack such trends, which suggests melting of a felsic crustal source without subsequent further evolution of the generated magmas. The mineralogical and geochemical characteristics of the mesocratic granitoids are consistent magmatic differentiation of a mantle derived, hot (> 900 °C) parental magma. The leucocratic granitoids and leucogranites granites were formed from low-temperature magmas (< 730 °C), generated during fluid-present melting from metasedimentary sources. New U-Pb zircon ages reveal that both magma types were emplaced into the lower crust within a 30-40 million years interval between 1220-1180 Ma. In this time period the crust reached its thermal peak, which led to the formation of the leucocratic granitoids and leucogranites. A

  19. A review of the geochronology and geochemistry of Late Yanshanian (Cretaceous) plutons along the Fujian coastal area of southeastern China: Implications for magma evolution related to slab break-off and rollback in the Cretaceous

    NASA Astrophysics Data System (ADS)

    Li, Zhen; Qiu, Jian-Sheng; Yang, Xue-Mei

    2014-01-01

    The Cretaceous plutonic suites in the Fujian coastal area include abundant I-type and A-type granitoids and lesser gabbroids. They are important components of the Late Yanshanian magmatic belt along the southeastern coast of China, and define a linear NNE-SSW-trending belt of magmatism. Geochronological, geochemical and geological data from thirty intrusions are summarised in this paper, and the data provide distinct magmatic, geochemical and tectonic patterns in the area. A compilation of geochronological data for these intrusive rocks indicates emplacement mainly from around 125 to 90 Ma, with a major peak from 115 to 90 Ma, and a subordinate peak from 125 to 115 Ma. Besides their temporal and spatial coexistence, all these intrusive rocks have similar geochemical patterns which point to involvement of components from a depleted asthenospheric mantle source for the parental magmas, most probably by magma mixing. The first appearance of sparse I-type granitoids with post-collisional extensional granite affinities, and the emplacement of the Baijuhuajian and Suzhou A-type granites, mark the beginning of extension during the Early Cretaceous at ca. 125 to 119 Ma. The subsequent development of bimodal magmatism at 115 to 90 Ma, with numerous arc-related mafic gabbros and I-type granites, together with some A-type granites, suggests that this major igneous event took place as a response to back-arc extension. On the basis of petrology, geochronology, tectonics, and elemental and isotopic geochemistry, we speculate that break-off and rollback of the subducting Palaeo-Pacific Plate during the Cretaceous were responsible for the Late Yanshanian regional tectono-magmatic evolution in the area. We suggest that this process facilitated a strong and rapid linear upwelling of the asthenospheric mantle beneath the coastal area of southeastern China, with consequential extension of the overlying continental lithosphere, and ultimately the large-scale Late Yanshanian magmatism

  20. Geochemistry and tectonic significance of amphibolites of the Ducktown mining district, Tennessee

    SciTech Connect

    Lawson, J.S.; Misra, K.C.

    1985-01-01

    The Ducktown massive sulfide deposits have several characteristics of volcanogenic-exhalative deposits but occur in an overwhelmingly sedimentary environment. Recent isotopic studies have suggested a magmatic component to ore formation. This study is an evaluation of the geochemistry and tectonic significance of late Proterozoic amphibolite units spatially associated with the ore bodies. The amphibolites are interpreted to be igneous in origin based on Niggli trends, relict igneous textures, and bulk chemistry. The protolith was an olivine tholeiite, as judged from normative composition, the AFM diagram, and Y/Nb ratios. Discrimminant diagrams using immobile trace elements (Ti-Y-Zr, TiO/sub 2/-Zr, Zr/Y-Zr, Ti-Cr, Ti-V) indicate an affinity with mid-ocean ridge basalts, an interpretation in agreement with that suggested for amphibolites associated with the very similar Gossan Lead deposits (Virginia) in Ocoee-equivalent metasediments (Gair and Slack, 1984), but apparently inconsistent with the ensialic setting of the Ducktown deposits. However, tholeiitic magmas associated with continental breakup may show chemical affinities with MORB, despite their intrusion into continental crust. The Ducktown amphibolites are interpreted to be diabasic sills emplaced during deposition of Ocoee sediments and related to intracratonic rifting along the eastern margin of Laurentia during the incipient development of the Iapetus Ocean.

  1. Effect of Mantle Wedge Hybridization by Sediment Melt on Geochemistry of Arc Magma and Arc Mantle Source - Insights from Laboratory Experiments at High Pressures and Temperatures

    NASA Astrophysics Data System (ADS)

    Mallik, A.; Dasgupta, R.; Tsuno, K.; Nelson, J. M.

    2015-12-01

    Generation of arc magmas involves metasomatism of the mantle wedge by slab-derived H2O-rich fluids and/or melts and subsequent melting of the modified source. The chemistry of arc magmas and the residual mantle wedge are not only regulated by the chemistry of the slab input, but also by the phase relations of metasomatism or hybridization process in the wedge. The sediment-derived silica-rich fluids and hydrous partial melts create orthopyroxene-rich zones in the mantle wedge, due to reaction of mantle olivine with silica in the fluid/melt [1,2]. Geochemical evidence for such a reaction comes from pyroxenitic lithologies coexisting with peridotite in supra-subduction zones. In this study, we have simulated the partial melting of a parcel of mantle wedge modified by bulk addition of sediment-derived melt with variable H2O contents to investigate the major and trace element chemistry of the magmas and the residues formed by this process. Experiments at 2-3 GPa and 1150-1300 °C were conducted on mixtures of 25% sediment-derived melt and 75% lherzolite, with bulk H2O contents varying from 2 to 6 wt.%. Partial reactive crystallization of the rhyolitic slab-derived melt and partial melting of the mixed source produced a range of melt compositions from ultra-K basanites to basaltic andesites, in equilibrium with an orthopyroxene ± phlogopite ± clinopyroxene ± garnet bearing residue, depending on P and bulk H2O content. Model calculations using partition coefficients (from literature) of trace elements between experimental minerals and silicate melt suggest that the geochemical signatures of the slab-derived melt, such as low Ce/Pb and depletion in Nb and Ta (characteristic slab signatures) are not erased from the resulting melt owing to reactive crystallization. The residual mineral assemblage is also found to be similar to the supra-subduction zone lithologies, such as those found in Dabie Shan (China) and Sanbagawa Belt (Japan). In this presentation, we will also

  2. Adiabat_1ph 3.0 and the MAGMA website: educational and research tools for studying the petrology and geochemistry of plate margins

    NASA Astrophysics Data System (ADS)

    Antoshechkina, P. M.; Asimow, P. D.

    2010-12-01

    features to be incorporated into adiabat_1ph after its release was the ability to simulate flux melting, in which a metasomatic fluid or melt, of fixed composition, was added to the system before each equilibration step. This idea was further developed in the coupled dynamic and petrological subduction zone model GyPSM, so that fluid flux into the wedge was controlled by the location of dehydration reactions in the slab. The adiabat_1ph release candidate includes a similar option so that the user may specify assimilated compositions, which evolve as the calculation proceeds. This added flexibility opens up a number of possibilities, such as more realistic simulations of melt-rock reactions at mid-ocean ridges. Adiabat_1ph files may be downloaded from the MAGMA website at http://magmasource.caltech.edu/ and feedback is welcomed at a dedicated forum, especially ideas for new software features. MAGMA is an online resource for the study of mantle melting and magma evolution, hosted by Caltech. As well as MELTS-related resources, there are tools for visualization of binary and ternary phase diagrams. Flash movies of phase diagrams for adiabatic decompression melting of peridotite and pyroxenite sources can be played in a web browser or downloaded from a server.

  3. Evaluation of the ongoing rifting and subduction processes in the geochemistry of magmas from the western part of the Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Verma, Surendra P.; Pandarinath, Kailasa; Rivera-Gómez, M. Abdelaly

    2016-03-01

    A compilation of new and published geochemical data for 1512 samples of volcanic rocks from the western part of the Mexican Volcanic Belt was first subdivided according to the age group (136 samples of Miocene and 1376 samples of Pliocene-Holocene). Rocks of the younger group were then subdivided as Rift (1014 samples from the triple-rift system) and No Rift (362 samples outside of the triple-rift system) or Near Trench (937 samples) and Far Trench (439 samples) magmas. These subdivisions were considered separately as basic, intermediate, and acid magmatic rocks. The application of the conventional and multidimensional techniques confirmed the great tectonic and geochemical complexity of this region. The presence of oceanic-type basalts suggested to result from a mantle plume was not confirmed from the tectonomagmatic multidimensional diagrams. The Miocene rocks, which are present at the surface far from the Middle-America Trench, showed a likely continental rift setting in most diagrams for basic rocks and a continental arc setting for intermediate rocks. These differences can be explained in terms of the petrogenetic origin of the magmas. Unlike the current thinking, the triple-rift system seems to have influenced the chemistry of Pliocene-Holocene basic rocks, which indicated a continental rift setting. The Pliocene-Holocene intermediate and acid rocks, however, did not show such an influence. The Pliocene-Holocene basic rocks indicated a continental rift setting, irrespective of the Near Trench and Far Trench subdivision because numerous Near Trench rocks also lie in the triple-rift and graben systems. However, the intermediate rocks having a crustal component in their genesis indicated a continental arc (Near Trench) or a transitional arc to within-plate setting (Far Trench). The acid rocks having a crustal component also suggested a continental arc (Near Trench) or a transitional setting (Far Trench). The application of the tectonomagmatic multidimensional

  4. Trace- and rare-earth-element geochemistry of the June 1993 natrocarbonatite lavas, Oldoinyo Lengai (Tanzania): Implications for the origin of carbonatite magmas

    NASA Astrophysics Data System (ADS)

    Simonetti, Antonio; Bell, Keith; Shrady, Catherine

    1997-01-01

    Major-, trace- and rare-earth-element data from ten natrocarbonatite lavas collected during the June 1993 extrusive activity define two distinct groups. Although both groups are characterized by low Nb and Zr contents, and low Th/U (~1.0); Ba/Sr>1.0; (La/Sm) N>40; high Ba, Mo, Sr, W contents; and LREE contents ~1000 to 2000×chondrite, one group has much higher Al 2O 3, Fe 2O 3, Nb, Pb, SiO 2, Zr and total REEs contents. These differences are attributed to the presence of silicate spheroids in natrocarbonatites that form within the latter group. Similarity in trace- and rare-earth-element-normalized patterns for both groups of natrocarbonatite lavas suggest either a common source or generation from a common parental melt. Models proposed for the origin of natrocarbonatites include immiscible separation from a peralkaline, silicate magma, or late-stage fractionation from a parent olivine sövite magma. Although natrocarbonatite melt formation may be controlled by either of these differentiation processes, certain trace-element ratios for the 1993 lavas, such as Ce/Pb (~9), and Th/Nb (~0.1) are similar to those estimated for primitive mantle, and their Sm/Nd ratios (~0.07) are quite different to the average value of 0.15 for most carbonatites world-wide. The similarity in element ratios in many of the older silicate lavas at Oldoinyo Lengai (e.g., Zr/Nb, La/Nb, Ba/Nb, Rb/Nb, and Ba/La) to those estimated for HIMU and EM I suggest that source characteristics can be reflected in such melts. Even if the natrocarbonatites are formed by liquid immiscibility, recent experiments have shown that partition coefficients for trace elements (e.g., Ba, Ce, Mo, Nb, Pb, Th, U) between conjugate carbonate and silicate melts approach unity with increasing temperature. Alternatively, the similarity in trace-element ratios between those for the silicate lavas from Oldoinyo Lengai and mantle components are simply fortuitous.

  5. Magma Fragmentation

    NASA Astrophysics Data System (ADS)

    Gonnermann, Helge M.

    2015-05-01

    Magma fragmentation is the breakup of a continuous volume of molten rock into discrete pieces, called pyroclasts. Because magma contains bubbles of compressible magmatic volatiles, decompression of low-viscosity magma leads to rapid expansion. The magma is torn into fragments, as it is stretched into hydrodynamically unstable sheets and filaments. If the magma is highly viscous, resistance to bubble growth will instead lead to excess gas pressure and the magma will deform viscoelastically by fracturing like a glassy solid, resulting in the formation of a violently expanding gas-pyroclast mixture. In either case, fragmentation represents the conversion of potential energy into the surface energy of the newly created fragments and the kinetic energy of the expanding gas-pyroclast mixture. If magma comes into contact with external water, the conversion of thermal energy will vaporize water and quench magma at the melt-water interface, thus creating dynamic stresses that cause fragmentation and the release of kinetic energy. Lastly, shear deformation of highly viscous magma may cause brittle fractures and release seismic energy.

  6. Imaging three-dimensional crustal conductivity structures reflecting continental flood basalt effects hidden beneath thick intracratonic sedimentary basin

    NASA Astrophysics Data System (ADS)

    Padilha, Antonio L.; Vitorello, Ícaro; Antunes, Cassio E.; Pádua, Marcelo B.

    2015-07-01

    A large-scale array of long-period magnetic data and a deep-probing magnetotelluric profile were recorded in the intracratonic Paraná sedimentary basin in central eastern South America, which presents a thick and extensive sedimentary-magmatic sequence that allows its basement to be investigated only by indirect methods. Integration of the results from both methods showed that the crust beneath the basin presents several quasi-linear highly conductive channeled zones with limited lateral extent, in coincidence with some of the main tectonic structures recognized at the surface, and a moderate but pervasive lithosphere conductivity enhancement beneath its central part. Upward movement of CO2-bearing volatiles and magmas precipitating highly conducting mineral phases along discrete subvertical fault zones that served as feeder conduits for Early Cretaceous voluminous continental flood basalts was a likely process responsible for the localized conductivity enhancements. Correlation between some of the linear conductive zones and elongated magnetic anomalies and between the maximum depth occurrence of most of these conductive anomalies and the Curie depth at which crustal rocks lose their magnetism gives strong support to interconnected iron oxides (especially magnetite) and iron sulfides (such as pyrrhotite) as the main conductive sources. The moderate bulk conductivity increase in the crust and upper mantle beneath the central part of the basin is unexpected for a postulated cratonic basement and is tentatively associated with impregnation of the lithosphere by conducting minerals related either to widespread tectonic events in the Ordovician or Late Precambrian or to dispersed magmatic residues of an Early Cretaceous magma differentiation contaminating the entire lithosphere.

  7. Magma energy

    SciTech Connect

    Hardee, H.C.

    1985-01-01

    The paper briefly describes the potential magma resources in the US and worldwide, and possible ways of exploiting this resource. Two target sites for field experiments to characterize magma targets are identified: Long Valley Caldera and Coso Hot Springs. 11 refs. (ACR)

  8. The Surtsey Magma Series

    PubMed Central

    Ian Schipper, C.; Jakobsson, Sveinn P.; White, James D.L.; Michael Palin, J.; Bush-Marcinowski, Tim

    2015-01-01

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50th anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption’s four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland’s Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume. PMID:26112644

  9. The Surtsey Magma Series.

    PubMed

    Schipper, C Ian; Jakobsson, Sveinn P; White, James D L; Michael Palin, J; Bush-Marcinowski, Tim

    2015-01-01

    The volcanic island of Surtsey (Vestmannaeyjar, Iceland) is the product of a 3.5-year-long eruption that began in November 1963. Observations of magma-water interaction during pyroclastic episodes made Surtsey the type example of shallow-to-emergent phreatomagmatic eruptions. Here, in part to mark the 50(th) anniversary of this canonical eruption, we present previously unpublished major-element whole-rock compositions, and new major and trace-element compositions of sideromelane glasses in tephra collected by observers and retrieved from the 1979 drill core. Compositions became progressively more primitive as the eruption progressed, with abrupt changes corresponding to shifts between the eruption's four edifices. Trace-element ratios indicate that the chemical variation is best explained by mixing of different proportions of depleted ridge-like basalt, with ponded, enriched alkalic basalt similar to that of Iceland's Eastern Volcanic Zone; however, the systematic offset of Surtsey compositions to lower Nb/Zr than other Vestmannaeyjar lavas indicates that these mixing end members are as-yet poorly contained by compositions in the literature. As the southwestern-most volcano in the Vestmannaeyjar, the geochemistry of the Surtsey Magma Series exemplifies processes occurring within ephemeral magma bodies on the extreme leading edge of a propagating off-axis rift in the vicinity of the Iceland plume. PMID:26112644

  10. The structure and sedimentary sequence of intracratonic rift from Late Sinian to Early Cambrian in the Sichuan Basin, South China

    NASA Astrophysics Data System (ADS)

    Gu, Zhidong; Zhang, Baomin; Lu, Weihu; Zhai, Xiufen; Jiang, Hua

    2016-04-01

    Sichuan Basin is located in the northwest of Upper Yangtze craton of South China, and there is developed an intracratonic rift from Late Sinian to Early Cambrian in the middle of Sichuan Basin, and the paper systematically discusses the structure and sedimentary sequence of the intracratonic rift based on the fields, drilling and seismic data, and so on. Detailed structural interpretation of 2D and 3D seismic profiles displays the development of two stages of intracratonic rift due to regional extension with the depth of 2000m, and plane distribution of intracratonic rift presents the V-pattern from the northwest to the southeast in the middle of Sichuan Basin with the width from 100km to 20km. The drilling data from the intracratonic rift shows the obvious thinning of Upper Sinian and thickening of Lower Cambrian. And field outcrops situated in the intracratonic rift reveal that the Upper Sinian is mainly composed of siliceous rock, shale and carbonate, with the thickness of less than 100m, but the thickness of Upper Sinian on the platform reaches 1000m by contrast; They also reveals that Lower Cambrian is mainly composed of shale, mudstone, and siltstone with the development of gravity current, and the thickness of Lower Cambrian reaches 2000m. The formation of intracratonic rift may be initiated by pre-existing basement weakness zone and deep mantle dynamics.

  11. Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia

    NASA Astrophysics Data System (ADS)

    Johansson, Åke; Waight, Tod; Andersen, Tom; Simonsen, Siri L.

    2016-02-01

    Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U-Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous with ongoing deformation. The strong similarity in geochemical signatures indicate that they all belong to a single igneous suite composed of alkali-calcic biotite-hornblende quartz monzonites to more evolved biotite granites, albeit with an apparent gap in SiO2 content at around 70 wt%, dividing the suite into an intermediate and a felsic part. These dominantly metaluminous rocks are strongly ferroan and potassic, and with highly elevated concentrations of many trace elements, traits that are typical for A-type granitoids. The presence of magnetite and titanite indicates relatively oxidized compositions, and Nb/Y ratios designate them to the A2 subtype. Initial whole rock εNd values range between + 1 and - 2 (with one outlier at + 4), and initial zircon εHf values between + 3 and - 4. These values may be explained by melting of relatively juvenile crust similar to that forming the Transscandinavian Igneous Belt alone, but the spread in Hf and Nd isotope compositions to values overlapping with the Svecofennian mantle at 1.45 Ga suggests involvement of a mantle-derived component. This indicates the magmatism was associated with juvenile crustal growth. There are no systematic differences in isotope or trace element characteristics between the orthogneisses and the less deformed granitoids, suggesting similar origins for both rock types, and no systematic changes in isotopic composition with SiO2 concentration. Trace element compositions indicate a within-plate setting, similar to other 1.45 Ga granites in southwest Fennoscandia, in spite of the close relation between magmatism and deformation on Bornholm. We therefore suggest intracratonic A-type magmatism within an active

  12. Magma Energy Overview and Status Report

    SciTech Connect

    Dunn, James C.

    1989-03-21

    Up to 500,000 Quads of thermal energy are believed to be contained in crustal magma bodies within the U.S. at temperatures in excess of 600 C and at depths less than 10 km. Scientific feasibility of utilizing this energy resource was concluded after a seven-year study that culminated in successful energy extraction experiments in molten rock at Kilauea Iki lava lake. The current DOE program is developing technology to experimentally extract energy from a silicic magma body so that engineering feasibility of the magma energy concept can be evaluated. At this point, significant progress has been achieved in three areas: Geophysics and site selection. Energy Extraction Processes, and Geochemistry/Materials. Future activities will be focused by drilling and evaluating a deep exploratory well in Long Valley caldera where active magma is expected.

  13. Magma chambers

    NASA Technical Reports Server (NTRS)

    Marsh, Bruce D.

    1989-01-01

    Recent observational and theoretical investigations of terrestrial magma chambers (MCs) are reviewed. Consideration is given to the evidence for MCs with active convection and crystal sorting, problems of direct MC detection, theoretical models of MC cooling, the rheology and dynamics of solidification fronts, crystal capture and differentiation, convection with solidification, MC wall flows, and MC roof melting. Diagrams, graphs, and a list of problems requiring further research are provided.

  14. Magma mixing origin for the post-collisional adakitic monzogranite of the Triassic Yangba pluton, Northwestern margin of the South China block: geochemistry, Sr-Nd isotopic, zircon U-Pb dating and Hf isotopic evidences

    NASA Astrophysics Data System (ADS)

    Qin, Jiang-Feng; Lai, Shao-Cong; Diwu, Chun-Rong; Ju, Yin-Juan; Li, Yong-Fei

    2010-03-01

    Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major and trace element, whole-rock Sr-Nd isotope, zircon U-Pb and Hf isotope data for a suite of adakitic monzogranite and its mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental setting. The host monzogranite and MMEs from the Yangba pluton have zircon U-Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively. The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element and evolved Sr-Nd isotopic compositions [(87Sr/86Sr)i = 0.707069-0.707138, and ɛNd( t) = -6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive ɛHf( t) values of 2.3-8.2 with single-stage Hf model ages of 531-764 Ma. Thus, the MMEs would be derived from partial melts of the Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5-14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81-0.90), suggesting that garnet was stable in their source during partial melting. Its evolved Sr-Nd isotopic compositions [(87Sr/86Sr)i = 0.7041-0.7061, and ɛNd( t) = -3.1 to -4.3] and high contents of K2O (3.22-3.84%) and Th (13.7-19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51-55), Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the

  15. Tectonic and climate history influence the geochemistry of large-volume silicic magmas: New δ18O data from the Central Andes with comparison to N America and Kamchatka

    NASA Astrophysics Data System (ADS)

    Folkes, Chris B.; de Silva, Shanaka L.; Bindeman, Ilya N.; Cas, Raymond A. F.

    2013-07-01

    New δ18O data from magmatic quartz, plagioclase and zircon crystals in Neogene large-volume, rhyodacitic ignimbrites from the Central Andean Ignimbrite Province reveal uniformly high-δ18O values (δ18O(Qtz) from + 8.1 to + 9.6‰ - 43 analyses from 15 ignimbrites; δ18O(Plag) from + 7.4 to + 8.3‰ - 10 analyses from 6 ignimbrites; δ18O(Zrc) from + 6.7 to + 7.8‰ - 5 analyses from 4 ignimbrites). These data, combined with crustal radiogenic isotopic signatures of Sr, Nd and Pb, imply progressive contamination of basaltic magmas with up to 50 vol.% upper crust in these large volume silicic systems. The narrow range of δ18O values also demonstrate that surprising homogeneity was achieved through space (100's km) and time (~ 10 Ma to recent) in these large-volume magmas, via residence in their parental middle to upper crustal bodies. Low-δ18O values of many large volume (> 10 km3) silicic magmas in North America and Kamchatka, discussed here for comparison, reflect the influence of meteoric-hydrothermal events and glaciations in lowering these δ18O values via the assimilation of hydrothermally-altered crustal material. Conversely, there is a scarcity of a low-δ18O signature in the Central Andes and subduction-related or influenced systems in North America, such as the Oligocene Great Basin of Nevada and Utah, the Southern Rocky Mountain Volcanic Field of Colorado, and the SW Nevada volcanic field system. In these regions, the generally heavy-δ18O magmatic signature is interpreted as a reflection of how a broadly compressional regime, high elevation, aridity and evaporation rates limit availability and infiltration of large amounts of surface meteoric water and hydrothermal alteration of the shallow crust. This leads us to speculate that the δ18O values of large volume silicic magmas in these areas record a paleoelevation and paleoclimate signal. If this is the case, δ18O values of ignimbrites can potentially be used to track the effects of a meteoric

  16. Exploration Geochemistry.

    ERIC Educational Resources Information Center

    Closs, L. Graham

    1983-01-01

    Contributions in mineral-deposit model formulation, geochemical exploration in glaciated and arid environments, analytical and sampling problems, and bibliographic research were made in symposia held and proceedings volumes published during 1982. Highlights of these symposia and proceedings and comments on trends in exploration geochemistry are…

  17. Geochemistry of anorthositic differentiated sills in the Archean (~ 2970 Ma) Fiskenæsset Complex, SW Greenland: Implications for parental magma compositions, geodynamic setting, and secular heat flow in arcs

    NASA Astrophysics Data System (ADS)

    Polat, Ali; Fryer, Brian J.; Appel, Peter W. U.; Kalvig, Per; Kerrich, Robert; Dilek, Yildirim; Yang, Zhaoping

    2011-04-01

    The Fiskenæsset Complex, SW Greenland, is one of the best preserved layered Archean intrusions in the world, consisting of an association of ca. 550-meter-thick anorthosite, leucogabbro, gabbro, and ultramafic rocks (dunite, peridotite, pyroxenite, and hornblendite). Despite poly-phase deformation and amphibolite to granulite facies metamorphism, primary cumulate textures and igneous layering are well-preserved in the complex. This study reports new major and trace element data for three variably thick (1 to 5 m) differentiated (dunite, through peridotite, pyroxenite, gabbro leucogabbro, to anorthosite) sequences (Sequences 1, 2 and 3) in the Sinarssuk area of the Fiskenæsset region. On several variation diagrams, samples from these sequences plot along a well-defined liquid line of descent, consistent with in situ fractional crystallization. The average chemical compositions of these sequences are used to constrain their approximate parental magma compositions. Petrographic observations and geochemical data suggest that Sequences 2 and 3 solidified from evolved magmas that underwent olivine fractionation prior to their intrusion. In contrast, Sequence 1 appears to have been derived from a near-primary parental magma (SiO 2 = 43 wt.%, MgO = 20 wt.%, Al 2O 3 = 16 wt.%, CaO = 9.3 wt.%, Ni = 840 ppm, Mg-number = 80). The trace element patterns of this parental magma are comparable to those of Phanerozoic boninites, consistent with a supra-subduction zone geodynamic setting. If the relative thickness of ultramafic layers, the sum of dunite, peridotite and pyroxenite layers, in differentiated sequences is taken as an analog for the original complex emplaced into Archean oceanic crust, the Fiskenæsset Complex might have had a minimum thickness of 1000 m, with a 500 m thick ultramafic unit at the bottom. The thickness of the ultramafic unit in the preserved complex is less than 50 m, suggesting that more than 90% of the original ultramafic unit was either delaminated

  18. 40Ar/39Ar geochronology and geochemistry of the Central Saurashtra mafic dyke swarm: insights into magmatic evolution, magma transport, and dyke-flow relationships in the northwestern Deccan Traps

    NASA Astrophysics Data System (ADS)

    Cucciniello, Ciro; Demonterova, Elena I.; Sheth, Hetu; Pande, Kanchan; Vijayan, Anjali

    2015-05-01

    The Central Saurashtra mafic dyke swarm in the northwestern Deccan Traps contains a few picrites, several subalkalic basalts and basaltic andesites, and an andesite. We have obtained precise 40Ar/39Ar ages of 65.6 ± 0.2 Ma, 66.6 ± 0.3, and 62.4 ± 0.3 Ma (2σ errors) for three of the dykes, indicating the emplacement of the swarm over several million years. Mineral chemical and whole-rock major and trace element and Sr-Nd isotopic data show that fractional crystallization and crystal accumulation were important processes. Except for two dykes (with ɛNd t values of -8.2 and -12.3), the magmas were only moderately contaminated by continental crust. The late-emplaced (62.4 Ma) basalt dyke has compositional characteristics (low La/Sm and Th/Nb, high ɛNd t of +4.3) suggesting little or no crustal contamination. Most dykes are low-Ti and a few high-Ti, and these contrasting Ti types cannot be produced by fractional crystallization processes but require distinct parental magmas. Some dykes are compositionally homogeneous over tens of kilometers, whereas others are heterogeneous, partly because they were formed by multiple magma injections. The combined field and geochemical data establish the Sardhar dyke as ≥62 km long and the longest in Saurashtra, but this and the other Central Saurasthra dykes cannot have fed any of the hitherto studied lava-flow sequences in Saurashtra, given their very distinct Sr-Nd isotopic compositions. As observed previously, high-Ti lavas and dykes only outcrop east-northeast of a line joining Rajkot and Palitana, probably because of underlying enriched mantle at ~65 Ma.

  19. High precision Pb, Sr, and Nd isotope geochemistry of alkalic early Kilauea magmas from the submarine Hilina bench region, and the nature of the Hilina/Kea mantle component

    NASA Astrophysics Data System (ADS)

    Kimura, J.; Sisson, T. W.; Nakano, N.; Coombs, M. L.; Lipman, P. W.

    2004-12-01

    Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr-Nd-Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of early Kilauea magmas (Sisson et al., 2002). These samples are among the highest 206Pb/204Pb known from the Hawaii islands and may represent melts from a distinct geochemical and isotopic endmember involved in the generation of most Hawaiian tholeiites. This endmember is similar to the postulated literature Kea component, but we propose it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina endmember but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both _gKoolau_h (high 87Sr/86Sr, low 206Pb/204Pb) and depleted (low 87Sr/86Sr, intermediate 206Pb/204Pb) source materials. This shift in isotopic character from nearly uniform, endmember, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea_fs magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling mantle source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the Koolau

  20. Zircon geochronology and geochemistry to constrain the youngest eruption events and magma evolution of the Mid-Miocene ignimbrite flare-up in the Pannonian Basin, eastern central Europe

    NASA Astrophysics Data System (ADS)

    Lukács, Réka; Harangi, Szabolcs; Bachmann, Olivier; Guillong, Marcel; Danišík, Martin; Buret, Yannick; von Quadt, Albrecht; Dunkl, István; Fodor, László; Sliwinski, Jakub; Soós, Ildikó; Szepesi, János

    2015-12-01

    A silicic ignimbrite flare-up episode occurred in the Pannonian Basin during the Miocene, coeval with the syn-extensional period in the region. It produced important correlation horizons in the regional stratigraphy; however, they lacked precise and accurate geochronology. Here, we used U-Pb (LA-ICP-MS and ID-TIMS) and (U-Th)/He dating of zircons to determine the eruption ages of the youngest stage of this volcanic activity and constrain the longevity of the magma storage in crustal reservoirs. Reliability of the U-Pb data is supported by (U-Th)/He zircon dating and magnetostratigraphic constraints. We distinguish four eruptive phases from 15.9 ± 0.3 to 14.1 ± 0.3 Ma, each of which possibly includes multiple eruptive events. Among these, at least two large volume eruptions (>10 km3) occurred at 14.8 ± 0.3 Ma (Demjén ignimbrite) and 14.1 ± 0.3 Ma (Harsány ignimbrite). The in situ U-Pb zircon dating shows wide age ranges (up to 700 kyr) in most of the crystal-poor pyroclastic units, containing few to no xenocrysts, which implies efficient recycling of antecrysts. We propose that long-lived silicic magma reservoirs, mostly kept as high-crystallinity mushes, have existed in the Pannonian Basin during the 16-14 Ma period. Small but significant differences in zircon, bulk rock and glass shard composition among units suggest the presence of spatially separated reservoirs, sometimes existing contemporaneously. Our results also better constrain the time frame of the main tectonic events that occurred in the Northern Pannonian Basin: We refined the upper temporal boundary (15 Ma) of the youngest counterclockwise block rotation and the beginning of a new deformation phase, which structurally characterized the onset of the youngest volcanic and sedimentary phase.

  1. Geochemistry for Chemists.

    ERIC Educational Resources Information Center

    Hostettler, John D.

    1985-01-01

    A geochemistry course for chemists is described. Includes: (1) general course information; (2) subject matter covered; and (3) a consideration of the uses of geochemistry in a chemistry curriculum, including geochemical "real world" examples, geochemistry in general chemistry, and geochemistry as an elective. (JN)

  2. Dynamics and evolution of a magma ocean

    NASA Technical Reports Server (NTRS)

    Stevenson, D. J.

    1992-01-01

    The prevailing view of very large impacts during earth accretion suggests an initial state for earth evolution that was totally molten or nearly so. The problem confronted is to understand the evolution from this state to an almost completely solidified mantle. Two crucial questions are asked by the author: (1) is the resulting endstate of magma ocean freezing compatible with geological record, inferred mantle structure and evidence from geochemistry; and (2) does the freezing event leave a signature that can be discerned in the present earth. The emphasis on this keynote introduction will be to set the stage for the more detailed analyses to follow and to clarify the crucial questions and uncertainties.

  3. Magma volumes and storage in the middle crust

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Barnes, C. G.; Paterson, S. R.

    2015-12-01

    Quantifying magma volumes in magma plumbing systems is mostly done through geophysical means or based on volcanic eruptions. Detailed studies of plutons, however, are useful in revealing depths and evolving volumes of stored magmas over variable lifetimes of magma systems. Knowledge of the location, volume, and longevity of stored magma is critical for understanding where in the crust magmas attain their chemical signature, how these systems physically behave and how source, storage levels, and volcanoes are connected. Detailed field mapping, combined with single mineral geochemistry and geochronology of plutons, allow estimates of size and longevity of melt-interconnected magma batches that existed during the construction of magma storage sites. The Tuolumne intrusive complex (TIC) recorded a 10 myr magmatic history. Detailed maps of the major units in different parts of the TIC indicate overall smaller scale (cm- to <1 km) compositional variation in the oldest, outer Kuna Crest unit and mainly larger scale (>10 km) changes in the younger Half Dome and Cathedral Peak units. Mineral-scale trace element data from hornblende of granodiorites to gabbros from the Kuna Crest lobe show distinct hornblende compositions and zoning patterns. Mixed hornblende populations occur only at the transition to the main TIC. This compositional heterogeneity in the first 1-2 myr points to low volume magmatism resulting in smaller, discrete and not chemically interacting magma bodies. Trace element and Sr- and Pb-isotope data from growth zones of K-feldspar phenocrysts from the two younger granodiorites indicate complex mineral zoning, but general isotopic overlap, suggesting in-situ, inter-unit mixing and fractionation. This is supported by hybrid zones between units, mixing of zircon, hornblende, and K-feldspar populations and late leucogranites. Thus, magma body sizes increased later resulting in overall more homogeneous, but complexly mixing magma mushes that fractionated locally.

  4. Seismic reflection structure of intracratonic palmyride fold-thrust belt and surrounding Arabian platform, Syria

    SciTech Connect

    McBride, J.H.; Barazangi, M.; Best, J. ); Al-Saad, D.; Sawaf, T.; Al-Otri, M.; Gebran, A. )

    1990-03-01

    Seismic reflection and drill-hole data from central Syria provide a detailed view of the subsurface structure (10-15 km depth) of the relatively little-studied intracratonic Palmyride fold and thrust belt. The data set, together with surface geologic mapping, constrains a structural/stratigraphic section spanning the northeast sector of the belt and the surrounding subprovinces of the Arabian platform. The seismic reflection and drill-hole data show Mesozoic stratigraphic sequences thickening abruptly into the Palmyrides from the adjacent, arched Paleozoic platforms Neogene (alpine) folding and thrusting of the Mesozoic basin, as documented on the seismic data, are sharply restricted to the narrow width of the belt ({approximately}100 km), in contrast to the relatively undeformed Phanerozoic strata of the platforms to the north and south. The seismic and drill-hole data support the hypothesis that the palmyrides began as a Permian-Triassic failed rift connected to the Levantine passive continental margin, which was inverted and complexly deformed by the interfering effects of Cenozoic movements along the Dead Sea transform fault system and the Turkish Bitlis convergent zone. The seismic data provide a first view into the extent and depth of the early basin formation and subsequent compressional deformation, and as such represent a necessary element for constraining reconstructions of northern Middle East plate motions. 20 figs.

  5. Architecture and subsidence history of the intracratonic Hudson Bay Basin, northern Canada

    NASA Astrophysics Data System (ADS)

    Pinet, Nicolas; Lavoie, Denis; Dietrich, Jim; Hu, Kezhen; Keating, Pierre

    2013-10-01

    The Phanerozoic Hudson Bay Basin is a large intracratonic basin that is almost completely encircled by Precambrian rocks of the Canadian Shield. The preserved sedimentary succession is up to 2500 m thick and consists mainly of Upper Ordovician to Upper Devonian limestones, dolostones, evaporites and minor siliciclastics that were deposited in shallow marine conditions. Backstripping, based on new paleontological data and well correlations, reveals an irregular subsidence history marked by several periods of exhumation. In seismic data, the Hudson Bay Basin appears to have a relatively simple geometry, characterized by a lower sedimentary package cut by high-angle faults, overlain by a saucer-shape, essentially underformed upper sedimentary package. Normal (or transtensional) faults imaged on seismic reflection profiles provide clear evidence for crustal extension during deposition of the older sedimentary packages or slightly later, indicating that the basin is, at least partly, extensional in nature. However, significant changes in the depocenter location during the Paleozoic and variable exhumation values required by new maturation data indicate that other mechanisms influenced the subsidence/exhumation history of the basin. In particular, the influence of far-field events and dynamic topography transmitted by large-scale mantle flow in the continental interior (creating long-wavelength tilting and unconformities) is suspected but not yet proven.

  6. Anatomy of an intracratonic fold belt: Examples from the southwestern Palmyride fold belt in central Syria

    SciTech Connect

    Chaimov, T.A.; Barazangi, M.; Best, J.A. ); Al-Saad, D.; Sawaf, T.; Gebran, A. )

    1991-03-01

    The Palmyride fold belt, a 400 {times} 100 km, NE-trending, transpressive belt in central Syria, represents the late Mesozoic and Cenozoic inversion of a linear intracratonic basin. The southwestern Palmyrides are characterized by short wavelength (2-5 km) folds separated by small intermontane basins. To elucidate the subsurface structure, a three-dimensional model, based mainly on about 450 km of two-dimensional seismic reflection data, was generated using a LandMark{reg sign} graphics workstation. The new model includes many features not identified in outcrop. Short, NW-trending transcurrent, or transfer, faults link the short, en echelon NE-trending thrust faults and blind thrusts of the Palmyrides. Varying structural styles are observed within the southwestern part of the belt. In one instance the structure of Mesozoic and Cenozoic rocks mimics that in deeper Paleozoic rocks; elsewhere, a strong discordance between Paleozoic and Mesozoic rocks appears to be related to the development of a regional detachment in Triassic rocks at about 4 km depth. Shortening the southwestern palmyrides totals about 20-25 km, based on palinspastic restoration of a balanced cross section across the belt. Seismic stratigraphy constrains the timing of at least three distinct episodes of Palmyride shortening: Late Cretaceous, middle Eocene, and Miocene to present. All three episodes were penecontemporaneous with specific tectonic events along the northern Arabian plate boundaries.

  7. Twenty-five million years of silicic volcanism in the southern central volcanic zone of the Andes: Geochemistry and magma genesis of ignimbrites from 25 to 27 °S, 67 to 72 °W

    NASA Astrophysics Data System (ADS)

    Schnurr, W. B. W.; Trumbull, R. B.; Clavero, J.; Hahne, K.; Siebel, W.; Gardeweg, M.

    2007-09-01

    Silicic volcanism in the Andean Central Volcanic Zone (CVZ) produced one of the world's largest Neogene ignimbrite provinces. The largest and best-known CVZ ignimbrites are located on the Altiplano-Puna plateau north of 24 °S. Their compositions and huge erupted volumes suggest an origin by large-scale crustal melting, and present-day geophysical anomalies in this region suggest still active zones of partial melting in the middle crust. Farther south in the CVZ, the Cerro Galán complex erupted ignimbrites in the late Miocene and Pliocene that are quite similar in volume and composition to those from north of 24 °S and they have a similar origin. However, there are a great many other, smaller ignimbrites in the southern CVZ whose compositions and geodynamic significance are poorly known. These are the subject of this paper. We present a geochemical study of 28 ignimbrite units from the southern CVZ at 25 °S to 27 °S, whose ages cover the full span of arc activity in this area, from about 25 Ma to 1 Ma. The small to medium volume ignimbrites (< 10 km 3) form valley-fill or sheet-like deposits, many of which are chemically zoned. Notwithstanding individual differences, there are several common characteristic features within the group of southern CVZ ignimbrites. By far the dominant composition is metaluminous, crystal-poor rhyolite (mean values from 236 samples: SiO 2 = 73.5 wt.%, A/CNK = 1.02, K 2O/Na 2O = 1.4). Regular major and trace element differentiation trends suggest fractionation from intermediate arc magmas and this is supported by radiogenic isotopic ratios of Sr, Nd and Pb, which show complete overlap between the silicic ignimbrites and andesite-dacites from contemporary stratovolcanoes. There are no major changes in composition of the silicic ignimbrites over the 25 Ma span of activity. We attribute minor but significant differences in isotopic composition and Nb-Ta concentration according to location in the West Cordillera (Chile) or the southern

  8. Eocene Granitic Magmatism in NW Anatolia (Turkey) revisited: New implications from comparative zircon SHRIMP U-Pb and 40Ar-39Ar geochronology and isotope geochemistry on magma genesis and emplacement

    NASA Astrophysics Data System (ADS)

    Altunkaynak, Şafak; Sunal, Gürsel; Aldanmaz, Ercan; Genç, Can Ş.; Dilek, Yıldırım; Furnes, Harald; Foland, Kenneth A.; Yang, Jingsui; Yıldız, Merve

    2012-12-01

    During the Eocene, the northern Neo-Tethys suture zone and immediately adjacent areas in NW Turkey were loci of emplacement of a number of granitoid plutons with age relations and geochemical signatures indicative of magma generation in association with plate convergence. Discrete granitoid plutons of Eocene age in this region are exposed mainly in two distinct belts within and north of the northern Neo-Tethys suture zone. We report new SHRIMP U-Pb zircon and 40Ar/39Ar geochronology along with Sr-Nd isotope data from the granitoids in order to constrain their melt source(s), cooling history, and tectono-magmatic evolution with respect to the Early Cenozoic collisional tectonics of the region. Ranging in composition from diorite to granite, the plutons are largely represented by medium- to high-K calc-alkaline, I-type granites accompanied by minor amounts of shoshonitic rocks with syenite compositions and mafic microgranular enclaves in some of the plutons. In terms of trace element systematics the granitoids and the associated enclaves from the entire Eocene suite display close similarities to magmas from subduction-related or active continental margin settings, characterized by significant enrichment in LILE/HFSE relative to MORB. The rocks display significantly heterogeneous distributions of radiogenic isotopes with 87Sr/86Sr and 143Nd/144Nd ranging from 0.705824 to 0.708363 and from 0.512384 to 0.512718 respectively, suggesting multi-component melt interaction in their genesis. The granitoids from the southern and northern belts yielded zircon SHRIMP U-Pb ages of 52.8 ± 1.8 to 45.41 ± 0.34 Ma and 47.02 ± 0.82 to 36.79 ± 0.67 Ma, respectively, indicating overlapping emplacement ages, with some relatively younger ages from the northern belt. 40Ar/39Ar dating of biotite and hornblende also yielded similarly overlapping cooling ages (51.8 ± 0.1 to 44.9 ± 0.2 Ma and 45.3 ± 0.1 to 36.0 ± 0.1 Ma, respectively). Our combined geochronological data from the co

  9. Magma energy extraction

    SciTech Connect

    Dunn, J.C.; Ortega, A.; Hickox, C.E.; Chu, T.Y.; Wemple, R.P.; Boehm, R.F.

    1987-01-01

    The rate at which energy can be extracted from crustal magma bodies has an important influence on the economic viability of the magma energy concept. Open heat exchanger systems where fluid is circulated through solidified magma offer the promise of high energy extraction rates. This concept was successfully demonstrated during experiments in the molten zone of Kilauea Iki lava lake. Ongoing research is directed at developing a fundamental understanding of the establishment and long term operation of open systems in a crustal magma body. These studies show that magma solidifying around a cooled borehole will be extensively fractured and form a permeable medium through which fluid can be circulated. Numerical modeling of the complete magma energy extraction process predicts that high quality thermal energy can be delivered to the wellhead at rates that will produce from 25 to 30 MW electric.

  10. Magma Energy Extraction

    SciTech Connect

    Dunn, J.C.; Ortega, A.; Hickox, C.E.; Chu, T.Y.; Wemple, R.P.; Boehm, R.F.

    1987-01-20

    The rate at which energy can be extracted from crustal magma bodies has an important influence on the economic viability of the magma energy concept. Open heat exchanger systems where fluid is circulated through solidified magma offer the promise of high energy extraction rates. This concept was successfully demonstrated during experiments in the molten zone of Kilauea Iki lava lake. Ongoing research is directed at developing a fundamental understanding of the establishment and long term operation of open systems in a crustal magma body. These studies show that magma solidifying around a cooled borehole will be extensively fractured and form a permeable medium through which fluid can be circulated. Numerical modeling of the complete magma energy extraction process predicts that high quality thermal energy can be delivered to the wellhead at rates that will produce from 25 to 30 MW electric. 10 figs., 10 refs.

  11. Evidence for crustal recycling during the Archean: The parental magmas of the stillwater complex

    NASA Technical Reports Server (NTRS)

    Mccallum, I. S.

    1988-01-01

    The petrology and geochemistry of the Stillwater Complex, an Archean (2.7 Ga) layered mafic intrusion in the Beartooth Mountains of Montana is discussed. Efforts to reconstruct the compositions of possible parental magmas and thereby place some constraints on the composition and history of their mantle source regions was studied. A high-Mg andesite or boninite magma best matches the crystallization sequences and mineral compositions of Stillwater cumulates, and represents either a primary magma composition or a secondary magma formed, for example, by assimilation of crustal material by a very Mg-rich melt such as komatiite. Isotopic data do not support the extensive amounts of assimilation required by the komatiite parent hypothesis, and it is argued that the Stillwater magma was generated from a mantle source that had been enriched by recycling and homogenization of older crustal material over a large area.

  12. Watching magma from space

    USGS Publications Warehouse

    Lu, Zhong; Wicks, Charles W., Jr.; Dzurisin, Daniel; Thatcher, Wayne R.; Freymueller, Jeffrey T.; McNutt, Stephen R.; Mann, Dorte

    2000-01-01

    Westdahl is a broad shield volcano at the western end of Unimak Island in the Aleutian chain. It has apparently been dormant since a 1991-92 eruption and seismicity levels have been low. However, satellite radar imaging shows that in the years following 1992 the upper flanks of Westdahl have risen several centimeters, probably from the influx of new magma deep below its summit. Until now, deep magma reservoirs have been difficult to detect beneath most volcanoes. But using space geodetic technologies, specifically interferometric synthetic aperture radar (InSAR), we have discovered a deep magmatic source beneath Westdahl. 

  13. Magma energy for power generation

    SciTech Connect

    Dunn, J.C.

    1987-01-01

    Thermal energy contained in crustal magma bodies represents a large potential resource for the US and magma generated power could become a viable alternative in the future. Engineering feasibility of the magma energy concept is being investigated as part of the Department of Energy's Geothermal Program. This current project follows a seven-year Magma Energy Research Project where scientific feasibility of the concept was concluded.

  14. Self Sealing Magmas

    NASA Astrophysics Data System (ADS)

    von Aulock, Felix W.; Wadsworth, Fabian B.; Kennedy, Ben M.; Lavallee, Yan

    2015-04-01

    During ascent of magma, pressure decreases and bubbles form. If the volume increases more rapidly than the relaxation timescale, the magma fragments catastrophically. If a permeable network forms, the magma degasses non-violently. This process is generally assumed to be unidirectional, however, recent studies have shown how shear and compaction can drive self sealing. Here, we additionally constrain skin formation during degassing and sintering. We heated natural samples of obsidian in a dry atmosphere and monitored foaming and impermeable skin formation. We suggest a model for skin formation that is controlled by diffusional loss of water and bubble collapse at free surfaces. We heated synthetic glass beads in a hydrous atmosphere to measure the timescale of viscous sintering. The beads sinter at drastically shorter timescales as water vapour rehydrates an otherwise degassed melt, reducing viscosity and glass transition temperatures. Both processes can produce dense inhomogeneities within the timescales of magma ascent and effectively disturb permeabilities and form barriers, particularly at the margins of the conduit, where strain localisation takes place. Localised ash in failure zones (i.e. Tuffisite) then becomes associated with water vapour fluxes and alow rapid rehydration and sintering. When measuring permeabilities in laboratory and field, and when discussing shallow degassing in volcanoes, local barriers for degassing should be taken into account. Highlighting the processes that lead to the formation of such dense skins and sintered infills of cavities can help understanding the bulk permeabilities of volcanic systems.

  15. Magma energy: a feasible alternative

    SciTech Connect

    Colp, J.L.

    1980-03-01

    A short review of the work performed by Sandia Laboratories in connection with its Magma Energy Research Project is provided. Results to date suggest that boreholes will remain stable down to magma depths and engineering materials can survive the downhole environments. Energy extraction rates are encouraging. Geophysical sensing systems and interpretation methods require improvement, however, to clearly define a buried magma source.

  16. Zircon reveals protracted magma storage and recycling beneath Mount St. Helens

    USGS Publications Warehouse

    Claiborne, L.L.; Miller, C.F.; Flanagan, D.M.; Clynne, M.A.; Wooden, J.L.

    2010-01-01

    Current data and models for Mount St. Helens volcano (Washington, United States) suggest relatively rapid transport from magma genesis to eruption, with no evidence for protracted storage or recycling of magmas. However, we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust, cool and crystallize beneath the volcano, and are then rejuvenated and incorporated by hotter, young magmas on their way to the surface. Estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century. Zircon elemental compositions reflect the increasing influence of mafic input into the system through time, recording growth from hotter, less evolved magmas tens of thousands of years prior to the appearance of mafic magmas at the surface, or changes in whole-rock geochemistry and petrology, and providing a new, time-correlated record of this evolution independent of the eruption history. Zircon data thus reveal the history of the hidden, long-lived intrusive portion of the Mount St. Helens system, where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh influxes of magmas that traverse the intrusive reservoir before erupting. ?? 2010 Geological Society of America.

  17. Mush Column Magma Chambers

    NASA Astrophysics Data System (ADS)

    Marsh, B. D.

    2002-12-01

    Magma chambers are a necessary concept in understanding the chemical and physical evolution of magma. The concept may well be similar to a transfer function in circuit or time series analysis. It does what needs to be done to transform source magma into eruptible magma. In gravity and geodetic interpretations the causative body is (usually of necessity) geometrically simple and of limited vertical extent; it is clearly difficult to `see' through the uppermost manifestation of the concentrated magma. The presence of plutons in the upper crust has reinforced the view that magma chambers are large pots of magma, but as in the physical representation of a transfer function, actual magma chambers are clearly distinct from virtual magma chambers. Two key features to understanding magmatic systems are that they are vertically integrated over large distances (e.g., 30-100 km), and that all local magmatic processes are controlled by solidification fronts. Heat transfer considerations show that any viable volcanic system must be supported by a vertically extensive plumbing system. Field and geophysical studies point to a common theme of an interconnected stack of sill-like structures extending to great depth. This is a magmatic Mush Column. The large-scale (10s of km) structure resembles the vertical structure inferred at large volcanic centers like Hawaii (e.g., Ryan et al.), and the fine scale (10s to 100s of m) structure is exemplified by ophiolites and deeply eroded sill complexes like the Ferrar dolerites of the McMurdo Dry Valleys, Antarctica. The local length scales of the sill reservoirs and interconnecting conduits produce a rich spectrum of crystallization environments with distinct solidification time scales. Extensive horizontal and vertical mushy walls provide conditions conducive to specific processes of differentiation from solidification front instability to sidewall porous flow and wall rock slumping. The size, strength, and time series of eruptive behavior

  18. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, John H.

    1999-01-01

    The question of whether the Earth ever passed through a magma ocean stop is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of mar (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of An contrast strongly to those of the Earth: (1) the extremely ancient ages of the martian core, mantle, and crust (approx. 4.55 b.y.); (2) the highly depleted nature of the martian mantle; and (3) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle.

  19. Lunar magma transport phenomena

    NASA Technical Reports Server (NTRS)

    Spera, Frank J.

    1992-01-01

    An outline of magma transport theory relevant to the evolution of a possible Lunar Magma Ocean and the origin and transport history of the later phase of mare basaltic volcanism is presented. A simple model is proposed to evaluate the extent of fractionation as magma traverses the cold lunar lithosphere. If Apollo green glasses are primitive and have not undergone significant fractionation en route to the surface, then mean ascent rates of 10 m/s and cracks of widths greater than 40 m are indicated. Lunar tephra and vesiculated basalts suggest that a volatile component plays a role in eruption dynamics. The predominant vapor species appear to be CO CO2, and COS. Near the lunar surface, the vapor fraction expands enormously and vapor internal energy is converted to mixture kinetic energy with the concomitant high-speed ejection of vapor and pyroclasts to form lunary fire fountain deposits such as the Apollo 17 orange and black glasses and Apollo 15 green glass.

  20. Comparative Magma Oceanography

    NASA Technical Reports Server (NTRS)

    Jones, J. H.

    1999-01-01

    The question of whether the Earth ever passed through a magma ocean stage is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of martian (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of Mars contrast strongly to those of the Earth: (i) the extremely ancient ages of the martian core, mantle, and crust (about 4.55 b.y.); (ii) the highly depleted nature of the martian mantle; and (iii) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle. The easiest way to explain the ages and diverse isotopic compositions of martian basalts is to postulate that Mars had an early magma ocean. Cumulates of this magma ocean were later remelted to form the SNC meteorite suite and some of these melts assimilated crustal materials enriched in incompatible elements. The REE pattern of the crust assimilated by these SNC magmas was LREE enriched. If this pattern is typical of the crust as a whole, the martian crust is probably similar in composition to melts generated by small degrees of partial melting (about 5%) of a primitive source. Higher degrees of partial melting would cause the crustal LREE pattern to be essentially flat. In the context of a magma ocean model, where large degrees of partial melting presumably prevailed, the crust would have to be dominated by late-stage, LREE-enriched residual liquids. Regardless of the exact physical setting, Nd and W isotopic evidence indicates that martian geochemical reservoirs must have formed early and that they have not been efficiently remixed since. The important point is that in both the Moon and Mars we see evidence of a magma ocean phase and that we recognize it as such. Several lines of theoretical inference point to an early Earth that was also hot

  1. Intracratonic basins : subtle records of long wavelength deformations and eustasy - the case example of the Paris Basin

    NASA Astrophysics Data System (ADS)

    Robin, Cecile; Guillocheau, Francois

    2014-05-01

    Subtle vertical movements, major constraints for lithospheric and mantle dynamics models, are difficult to quantify and to date. In sedimentary basins, this quantification is based on subsidence measurements by backstripping. The error bars on this technique can be high, mainly in the low subsiding domains were dates, water depths and eustasy are important data. We developed a 3D high-resolution method of accommodation space measurement at the scale of intracratonic basins, with a precise quantification of the water depth. Based on this 3D quantification of the accommodation, it was possible to discriminate the deformation and the eustatic controls based on the principle that the basin-scale signal contain the eustasy and the local control is of tectonic origin. (1) The application of this technique to the Paris Basin questioned the importance of the long term subsidence signal versus major deformation events of at least European-scale (Mid and Neo-Cimmerian, Austrian, Senonian deformations..) that control, in the Paris Basin, major subsidence centers reorganization. (2) The stratigraphic record of the Paris Basin, with those excellent datings (inheritance of 2 centuries of biostratigraphy), is also a unique place for constraining eustasy, its timing (with now a good knowledge of the sea water temperatures since the Jurassic) and the order of magnitude of the sea level variations. Back, those sea level amplitude constraints can be inputs for a better quantification of the vertical movements.

  2. Progressive mixed-magma recharging of Izu-Oshima volcano, Japan: A guide to magma chamber volume

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Taylor, Rex N.; Geshi, Nobuo; Oikawa, Teruki; Kawanabe, Yoshihisa; Ogitsu, Itaru

    2015-11-01

    To discover how magmas move and interact beneath an arc we have examined the temporal and spatial evolution of the largest Izu-Bonin frontal arc volcano Izu-Oshima and the adjacent Izu-Tobu field of backarc volcanoes. Extensive 14C ages and geochemical analysis of subaerial satellite cones as well as other effusives has enabled us to construct a well-constrained ∼ 14 ka record of Izu-Oshima volcanism. The geochemistry of Izu-Oshima is found to change systematically through the last 14 000 yr. Ba/La, Pb/Ce, 87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb all decrease between 10 ka and 5 ka before increasing between 5 ka and the present, while La/Yb and Nb/Zr show the reverse. These changes in composition match the addition of Izu-Tobu (backarc) magma to the Izu-Oshima plumbing system with a maximum of a 40% Izu-Tobu at around 5 ka. Progressive but asymptotically declining changes in composition through the 10-5 ka period are found to fit a model where pre-mixed magma is episodically added to, and mixed with, a chamber beneath Izu-Oshima. The 5-0 ka period reverses this trend, but is again progressive and declining, suggesting a switch to a progressive influx of pure Izu-Oshima frontal arc magma. Combining flux and eruption volume estimates with the observed geochemical mixing rates indicates that the accessible melt volume of the Izu-Oshima magma system is ∼ 16 km3. Interaction and pre-mixing between the fluid-dominated frontal arc melt and the sediment-bearing backarc magmas must occur at deeper levels within the arc crust. This deep reservoir receives a continuous feed from the frontal arc mantle, but may periodically intercept rising magmas from the backarc source to produce episodes of magma mixing on timescales of ∼ 5000 yr. This study demonstrates that interaction between frontal arc and backarc magma needs to be considered to achieve better understanding of material transfers and elemental budgets at subduction zones.

  3. Magma energy: engineering feasibility of energy extraction from magma bodies

    SciTech Connect

    Traeger, R.K.

    1983-12-01

    A research program was carried out from 1975 to 1982 to evaluate the scientific feasibility of extracting energy from magma, i.e., to determine if there were any fundamental scientific roadblocks to tapping molten magma bodies at depth. The next stage of the program is to evaluate the engineering feasibility of extracting energy from magma bodies and to provide insight into system economics. This report summarizes the plans, schedules and estimated costs for the engineering feasibility study. Tentative tasks and schedules are presented for discussion and critique. A bibliography of past publications on magma energy is appended for further reference. 69 references.

  4. 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.

  5. Stability of rift axis magma reservoirs: Spatial and temporal evolution of magma supply in the Dabbahu rift segment (Afar, Ethiopia) over the past 30 kyr

    NASA Astrophysics Data System (ADS)

    Medynski, S.; Pik, R.; Burnard, P.; Vye-Brown, C.; France, L.; Schimmelpfennig, I.; Whaler, K.; Johnson, N.; Benedetti, L.; Ayelew, D.; Yirgu, G.

    2015-01-01

    Unravelling the volcanic history of the Dabbahu/Manda Hararo rift segment in the Afar depression (Ethiopia) using a combination of cosmogenic (36Cl and 3He) surface exposure dating of basaltic lava-flows, field observations, geological mapping and geochemistry, we show in this paper that magmatic activity in this rift segment alternates between two distinct magma chambers. Recent activity in the Dabbahu rift (notably the 2005-2010 dyking crises) has been fed by a seismically well-identified magma reservoir within the rift axis, and we show here that this magma body has been active over the last 30 kyr. However, in addition to this axial magma reservoir, we highlight in this paper the importance of a second, distinct magma reservoir, located 15 km west of the current axis, which has been the principal focus of magma accumulation from 15 ka to the subrecent. Magma supply to the axial reservoir substantially decreased between 20 ka and the present day, while the flank reservoir appears to have been regularly supplied with magma since 15 ka ago, resulting in less variably differentiated lavas. The trace element characteristics of magmas from both reservoirs were generated by variable degrees of partial melting of a single homogeneous mantle source, but their respective magmas evolved separately in distinct crustal plumbing systems. Magmatism in the Dabbahu/Manda Hararo rift segment is not focussed within the current axial depression but instead is spread out over at least 15 km on the western flank. This is consistent with magneto-telluric observations which show that two magma bodies are present below the segment, with the main accumulation of magma currently located below the western flank, precisely where the most voluminous recent (<15 ka) flank volcanism is observed at the surface. Applying these observations to slow spreading mid-ocean ridges indicates that magma bodies likely have a lifetime of a least 20 ka, and that the continuity of magmatic activity is

  6. Determining the Magma Genesis of Mo Porphyry Deposits

    NASA Astrophysics Data System (ADS)

    Gaynor, S.; Coleman, D. S.; Rosera, J.

    2015-12-01

    The high flux of magma associated with super eruptions is hypothesized to rebuild the deep crust, altering the source(s) of subsequent magmatism. Climax-type Mo deposits are commonly generated immediately after eruption of large ignimbrites within a volcanic field, and provide an opportunity to understand the evolution of magma sources following high flux events. The Questa caldera of the Latir volcanic field, NM exposes a 10 Ma long record of pre-, syn- and post-ignimbrite intrusive and extrusive rocks, and hosts the Questa Climax-type Mo deposit. New detailed geochronology and geochemistry from Questa (including extensive sampling of subsurface rocks in the mine) permit detailed reconstruction of the temporal evolution of magma sources through the waxing and waning stages of super eruption magmatism. Comparison of chemical and isotopic data waxing, ignimbrite, Mo-mineralizing and waning stage magmas reveals several patterns. Waxing and waning magmas (waxing: 29-25.7 Ma; waning: 24.5-19 Ma) have intermediate trace elements and radiogenic isotopes relative to other magmatism (87Sr/86Sri=0.7050 to 0.7070, ɛNd=-5.2 to -7.2). Ignimbrite magmatism (25.5 Ma) is depleted in incompatible elements, enriched in MREE and HREE's and has more evolved radiogenic isotopes (87Sr/86Sri=0.7095, ɛNd=-8.0). Molybdenum mineralizing magmas (24.9-24.5 Ma), are enriched in incompatible elements, depleted in MREE and HREE's and have distinct radiogenic isotopes (87Sr/86Sri=0.7055 to 0.7075, ɛNd=-4.2 to -5.7). We suggest the lower crustal source of magmas changed during ignimbrite generation, and as a result, subsequent mineralizing magmas incorporated more juvenile, mafic components. This mantle influence is the metallogenesis for Climax-type deposits and indicates that deep crustal hybridization, rather than upper crustal differentiation, is pivotal in their generation. These results indicate that a lower crustal source of magmatism for a volcanic field is altered due to super

  7. Magmas and reservoirs beneath the Rabaul caldera (Papua New Guinea)

    NASA Astrophysics Data System (ADS)

    Bouvet de Maisonneuve, C.; Costa Rodriguez, F.; Huber, C.

    2013-12-01

    trace element geochemistry, volatile contents, and the comparison of successive eruptions since 1400 y BP to address the question of whether another potentially caldera-forming magma is presently brewing beneath Rabaul. In addition, we apply kinetic modeling of olivine and plagioclase zoning to the recently erupted products to address the prolonged period of seismic and deformational precursory activity. We estimate that at least 20-35 wt% basalt has mixed with the resident silicic magma at time scales that coincide with the main period of unrest (1971 to 1985).

  8. The cretaceous source rocks in the Zagros Foothills of Iran: An example of a large size intracratonic basin

    SciTech Connect

    Bordenave, M.L. ); Huc, A.Y. )

    1993-02-01

    The Zagros orogenic belt of Iran is one of the world most prolific petroleum producing area. However, most of the oil production is originated from a relatively small area, the 60,000 km[sup 2] wide Dezful Embayment which contains approximately 12% of the proven oil global reserves. The distribution of the oil and gas fields results from the area extent of six identified source rock layers, their thermal history and reservoir, cap rock and trap availability. In this paper, the emphasis is three of the layers of Cretaceous sources rocks. The Garau facies was deposited during the Neocomian to Albian interval over Lurestan, Northeast Khuzestan and extends over the extreme northeast part of Fars, the Kazhdumi source rock which deposited over the Dezful Embayment, and eventually the Senonian Gurpi Formation which has marginal source rock characteristics in limited areas of Khuzestan and Northern Fars. The deposition environment of these source rock layers corresponds to semipermanent depressions, included in an overall shallow water intracratonic basin communicating with the South Tethys Ocean. These depressions became anoxic when climatic oceanographical and geological conditions were adequate, i.e., humid climate, high stand water, influxes of fine grained clastics and the existence of sills separating the depression from the open sea. Distribution maps of these source rock layers resulting from extensive field work and well control are also given. The maturation history of source rocks is reconstructed from a set of isopachs. It was found that the main contributor to the oil reserves is the Kazhdumi source rock which is associated with excellent calcareous reservoirs.

  9. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles can be…

  10. Superheat in magma oceans

    NASA Technical Reports Server (NTRS)

    Jakes, Petr

    1992-01-01

    The existence of 'totally molten' planets implies the existence of a superheat (excess of heat) in the magma reservoirs since the heat buffer (i.e., presence of crystals having high latent heat of fusion) does not exist in a large, completely molten reservoir. Any addition of impacting material results in increase of the temperature of the melt and under favorable circumstances heat is stored. The behavior of superheat melts is little understood; therefore, we experimentally examined properties and behavior of excess heat melts at atmospheric pressures and inert gas atmosphere. Highly siliceous melts (70 percent SiO2) were chosen for the experiments because of the possibility of quenching such melts into glasses, the slow rate of reaction in highly siliceous composition, and the fact that such melts are present in terrestrial impact craters and impact-generated glasses. Results from the investigation are presented.

  11. Infrared Spectroscopy and Stable Isotope Geochemistry of Hydrous Silicate Glasses

    SciTech Connect

    Stolper, Edward

    2007-03-05

    The focus of this DOE-funded project has been the study of volatile components in magmas and the atmosphere. Over the twenty-one year period of this project, we have used experimental petrology and stable isotope geochemistry to study the behavior and properties of volatile components dissolved in silicate minerals and melts and glasses. More recently, we have also studied the concentration and isotopic composition of CO2 in the atmosphere, especially in relation to air quality issues in the Los Angeles basin.

  12. Appendix G: Geochemistry

    SciTech Connect

    Cantrell, Kirk J.; Serne, R. Jeffrey; Zachara, John M.; Krupka, Kenneth M.; Dresel, P. Evan; Brown, Christopher F.; Freshley, Mark D.

    2008-01-17

    This appendix discusses the geology of the Hanford Site and singe-shell tank (SST) waste management areas (WMAs). The purpose is to provide the most recent geochemical information available for the SST WMAs and the Integrated Disposal Facility. This appendix summarizes the information in the geochemistry data package for the SST WMAs.

  13. Pristine highland clasts in consortium breccia 14305 Petrology and geochemistry

    SciTech Connect

    Shervais, J.W.; Taylor, L.A.

    1984-11-15

    Data are presented on the petrography and mineral chemistry of six pristine highland clasts chipped from the polymict lunar breccia 14305. Major and trace elements in the clasts were determined by instrumental neutron activation analysis, and mineral analyses were performed by electron microprobe. Mg-suite clasts have eastern geochemical affinities, reaffirming the importance of local variations in geochemistry. These local variations are superimposed on the moon-wide, longitudinal variations noted by Warren and Wasson (1980). Alkali anorthosites and Mg-suite troctolites and anorthosites are not comagmatic, and cannot be related to a single parent magma by either fractional crystallization or variable assimilation of KREEP. Both magma suites may have assimilated varied amounts of KREEP into distinct parent magmas. Alternatively, alkali anorthosites may have crystallized directly from a KREEP-basalt parent magma. A thick crust of ferroan anorthosite probably never existed on the western lunar nearside, or was removed by basin-forming impacts prior to intrusion of later plutonic suites.

  14. Multiple Use of Magma Pathways: Mechanism for Hybridization

    NASA Astrophysics Data System (ADS)

    Hasalova, P.; Weinberg, R. F.; Reichardt, H.

    2010-12-01

    magma-filled cracks cutting across a pre-existing magmatic rock; (ii) compositional zoning of early-crystallized plagioclase and K-feldspar; (iii) quartz overgrows documented by CL imaging; (iv) corrosion of early-formed grains; and (v) different CPO of early-formed quartz and its overgrowths. In summary, the early formed dykes provided a pathway exploited by new magma batches. Once formed, the magma channels remained open either intermittently or continuously and the new melt batches migrated through following predominantly grain boundaries along an S-C fabric related to syn-magmatic shearing. Accordingly, hybrid signature results from the microscopic interaction between previously crystallized magmatic rock and new magma batch, through local equilibration, not from magma mixing. We conclude that leucosomes and magmatic bodies formed by the magma that flushed through them have a complex origin and composition that is reflected in the geochemistry and isotope chemistry. Final composition is a result of the accumulation of magma residue. This in turn depends on compositional changes of magma influx, P-T conditions, and the interaction of new magma with early crystallized magmatic products.

  15. Heat transfer in magma in situ

    SciTech Connect

    Dunn, J.C.; Carrigan, C.R.; Wemple, R.P.

    1983-12-16

    Heat transfer rates in a basaltic magma were measured under typical magma chamber conditions and a numerical model of the experiment was used to estimate magma viscosity. The results are of value for assessing methods of thermal energy extraction from magma bodies in the upper crust as well as for modeling the evolutionary track of these systems. 13 references, 3 figures.

  16. The Mineralogy, Geochemistry, and Redox State of Multivalent Cations During the Crystallization of Primitive Shergottitic Liquids at Various (f)O2. Insights into the (f)O2 Fugacity of the Martian Mantle and Crustal Influences on Redox Conditions of Martian Magmas.

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Bell, A. S.; Burger, P. V.; Papike, J. J.; Jones, J.; Le, L.; Muttik, N.

    2016-01-01

    The (f)O2 [oxygen fugacity] of crystallization for martian basalts has been estimated in various studies to range from IW-1 to QFM+4 [1-3]. A striking geochemical feature of the shergottites is the large range in initial Sr isotopic ratios and initial epsilon(sup Nd) values. Studies by observed that within the shergottite group the (f)O2 [oxygen fugacity] of crystallization is highly correlated with these chemical and isotopic characteristics with depleted shergottites generally crystallizing at reduced conditions and enriched shergottites crystallizing under more oxidizing conditions. More recent work has shown that (f)O2 [oxygen fugacity] changed during the crystallization of these magmas from one order of magnitude in Y980459 (Y98) to several orders of magnitude in Larkman Nunatak 06319. These real or apparent variations within single shergottitic magmas have been attributed to mixing of a xenocrystic olivine component, volatile loss-water disassociation, auto-oxidation during crystallization of mafic phases, and assimilation of an oxidizing crustal component (e.g. sulfate). In contrast to the shergottites, augite basalts such as NWA 8159 are highly depleted yet appear to be highly oxidized (e.g. QFM+4). As a first step in attempting to unravel petrologic complexities that influence (f)O2 [oxygen fugacity] in martian magmas, this study explores the effect of (f)O2 [oxygen fugacity] on the liquid line of descent (LLD) for a primitive shergottite liquid composition (Y98). The results of this study will provide a fundamental basis for reconstructing the record of (f)O2 [oxygen fugacity] in shergottites and other martian basalts, its effect on both mineral chemistries and valence state partitioning, and a means for examining the role of crystallization (and other more complex processes) on the petrologic linkages between olivine-phyric and pyroxene-plagioclase shergottites.

  17. Terrestrial magma ocean and core segregation in the earth

    NASA Technical Reports Server (NTRS)

    Ohtani, Eiji; Yurimoto, Naoyoshi

    1992-01-01

    According to the recent theories of formation of the earth, the outer layer of the proto-earth was molten and the terrestrial magma ocean was formed when its radius exceeded 3000 km. Core formation should have started in this magma ocean stage, since segregation of metallic iron occurs effectively by melting of the proto-earth. Therefore, interactions between magma, mantle minerals, and metallic iron in the magma ocean stage controlled the geochemistry of the mantle and core. We have studied the partitioning behaviors of elements into the silicate melt, high pressure minerals, and metallic iron under the deep upper mantle and lower mantle conditions. We employed the multi-anvil apparatus for preparing the equilibrating samples in the ranges from 16 to 27 GPa and 1700-2400 C. Both the electron probe microanalyzer (EPMA) and the Secondary Ion Mass spectrometer (SIMS) were used for analyzing the run products. We obtained the partition coefficients of various trace elements between majorite, Mg-perovskite, and liquid, and magnesiowustite, Mg-perovskite, and metallic iron. The examples of the partition coefficients of some key elements are summarized in figures, together with the previous data. We may be able to assess the origin of the mantle abundances of the elements such as transition metals by using the partitioning data obtained above. The mantle abundances of some transition metals expected by the core-mantle equilibrium under the lower mantle conditions cannot explain the observed abundance of some elements such as Mn and Ge in the mantle. Estimations of the densities of the ultrabasic magma Mg-perovskite at high pressure suggest existence of a density crossover in the deep lower mantle; flotation of Mg-perovskite occurs in the deep magma ocean under the lower mantle conditions. The observed depletion of some transition metals such as V, Cr, Mn, Fe, Co, and Ni in the mantle may be explained by the two stage process, the core-mantle equilibrium under the lower

  18. Mare basalt magma source region and mare basalt magma genesis

    SciTech Connect

    Binder, A.B.

    1982-11-15

    Given the available data, we find that the wide range of mare basaltic material characteristics can be explained by a model in which: (1) The mare basalt magma source region lies between the crust-mantle boundary and a maximum depth of 200 km and consists of a relatively uniform peridotite containing 73--80% olivine, 11--14% pyroxene, 4--8% plagioclase, 0.2--9% ilmenite and 1--1.5% chromite. (2) The source region consists of two or more density-graded rhythmic bands, whose compositions grade from that of the very low TiO/sub 2/ magma source regions (0.2% ilmenite) to that of the very high TiO/sub 2/ magma source regions (9% ilmenite). These density-graded bands are proposed to have formed as co-crystallizing olivine, pyroxene, plagioclase, ilmenite, and chromite settled out of a convecting magma (which was also parental to the crust) in which these crystals were suspended. Since the settling rates of the different minerals were governed by Stoke's law, the heavier minerals settled out more rapidly and therefore earlier than the lighter minerals. Thus the crystal assemblages deposited nearest the descending side of each convection cell were enriched in heavy ilmenite and chromite with respect to lighter olivine and pyroxene and very much lighter plagioclase. The reverse being the case for those units deposited near the ascending sides of the convection cells.

  19. Fractionation and Assimilation Processes Dominate in the Generation of Silicic Magmas from Four Kermadec Arc Volcanoes

    NASA Astrophysics Data System (ADS)

    Barker, S. J.; Wilson, C. J.; Baker, J.; Wysoczanski, R. J.; Rotella, M. D.; Millet, M.; Wright, I. C.

    2010-12-01

    Recent work has shown that silicic volcanism can be abundant in intra-oceanic subduction settings, and is often associated with large explosive caldera forming eruptions. Several major petrogenic questions arise from the generation and eruption of large silicic magma bodies in such a simple subduction setting, where continental crust is absent. We have investigated the geochemistry of pyroclasts collected from four volcanoes along the Kermadec arc; a relatively young (<2 Ma) oceanic subduction zone. Raoul, Macauley and a newly discovered volcano in the northern Kermadec arc, and Healy volcano in the southern Kermadec arc have all erupted dacite-rhyolite pumice within the last 10 kyr. Examination of whole-rock, mineral and glass major and trace element chemical data shows patterns which indicate that evolved magmas are primarily generated through crystal fractionation and not by partial melting of lower crustal lithologies, particularly amphibolite. Silicic magmas and co-eruptive mafic enclaves show sub-parallel REE patterns, and crystal zonation suggests that mafic and silicic magmas are closely related, spatially and temporally. However, distinctive crystal populations in both pumice samples and plutonic xenoliths suggest that many of the crystals did not grow in the evolved magmas, but were mixed in from other sources including gabbros and tonalites. Such open system mixing is ubiquitous in magmas from the four Kermadec volcanoes. Although crystallization is the dominant process driving melt evolution in the Kermadec volcanoes, the magmatic systems are open to contributions from both newly arriving melts and previously crystallized plutonic bodies. Such contributions occur in variable proportions between magma batches, reflected by the chemical variations observed between eruption units in subaerial sequences on Raoul Island and between clustered pumice chemical compositions in dredged samples from the submarine volcanoes.

  20. Parsing Aleutian Arc Magma Compositions

    NASA Astrophysics Data System (ADS)

    Nye, C. J.

    2011-12-01

    The first-order subdivision of Aleutian arc magma compositions is based on SiO2, and the second-order subdivision is usually based on the change of FeOt/MgO as a function of SiO2, resulting in the additional twofold subdivision into (TH) and calcalkaline (CA) magmas. However, additional robust compositional variations exist. The two most important of these are (1) variation of the calcium number [Ca#; Ca/(Na+Ca)] as a function of SiO2, and (2) the Rate of Incompatible Trace-element Enrichment (RITE) at individual volcanic centers. Additionally, the data show that the low FeOt/MgO of CA andesite and dacite is more controlled by MgO excess than FeOt depletion. The Ca# of andesites and dacites is strongly bimodal. The low-Ca# group is "calc-alkalic", while the high-Ca# group is "calcic", using Peacock (1931) criteria. A continuum of Ca#s exists, but lavas intermediate between high-Ca# and low-Ca# are much less abundant. Ca#s merge below about 55% SiO2, and have a simple normal distribution. RITE, with rare but important exceptions, is generally constant at the temporal and spatial scale of a single volcano. Among high-RITE magmas LILE, LREE, HFSE, and Th increase ~3.5-fold, and HREE increase ~2.5-fold from basalt or basaltic-andesite through andesite to dacite. There is no strong indication that RITE is silica-dependant. High-RITE magmas develop a strong negative Eu anomaly, and are qualitatively compatible with an origin primarily involving fractionation of plagioclase-dominated mineral assemblages. Low-RITE magmas, in contrast, have nearly invariant REE and HFSE, and LILE and Th increase merely 1.5-fold over the same silica range. Low-RITE magmas are not compatible with fractionation of a plagioclase-dominant mineral assemblage. Alternative qualitatively plausible explanations (needing rigorous evaluation) include fractionation of an ultramafic mineral assemblage (Alaskan-type mafic-ultramafic bodies may be a model; see USGS Prof Paper 1564); that low-RITE basaltic

  1. Geochemical evidences of magma dynamics at Campi Flegrei (Italy)

    NASA Astrophysics Data System (ADS)

    Caliro, S.; Chiodini, G.; Paonita, A.

    2014-05-01

    Campi Flegrei caldera, within the Neapolitan area of Italy, is potentially one of the most dangerous volcanoes in the world, and during the last decade it has shown clear signs of reactivation, marked by the onset of uplift and changes in the geochemistry of gas emissions. We describe a 30-year-long data set of the CO2-He-Ar-N2 compositions of fumarolic emissions from La Solfatara crater, which is located in the center of the caldera. The data display continuous decreases in both the N2/He and N2/CO2 ratios since 1985, paralleled by an increase in He/CO2. These variations cannot be explained by either processes of boiling/condensation in the local hydrothermal system or with changes in the mixing proportions between a magmatic vapor and hydrothermal fluids. We applied the magma degassing model of Nuccio and Paonita (2001, Earth Planet. Sci. Lett. 193, 467-481) using the most recent inert-gas solubilities in order to interpret these peculiar features in accordance with petrologic constraints derived from the ranges of the melt compositions and reservoir pressures at Campi Flegrei. The model simulations for mafic melts (trachybasalt and shoshonite) show a remarkably good agreement with the measured data. Both decompressive degassing of an ascending magma and mixing between magmatic fluids exsolved at various levels along the ascent path can explain the long-term geochemical changes. Recalling that (i) a sill-like reservoir of gases at a depth of 3-4 km seems to be the main source of ground inflation and (ii) there is petrologic and geophysical evidence for a reservoir of magma at about 8 km below Campi Flegrei, we suggest that the most-intense episodes of inflation occur when the gas supply to the sill-like reservoir comes from the 8 km-deep magma, although fluids exsolved by magma bodies at shallower depths also contribute to the gas budget. Our work highlights that, in caldera systems where the presence of hydrothermal aquifers commonly masks the magmatic signature

  2. Electrical Properties of Hydrous Magmas

    NASA Astrophysics Data System (ADS)

    Laumonier, M.; Sifre, D.; Gaillard, F.

    2013-12-01

    Volatiles strongly affect physical and chemical properties of magmas which are major vectors of mass and heat transfer in the Earth's. In subduction zones, hydrated melts prevail during the entire course of differentiation from basalts, andesites, dacites to rhyolites. Several electrical surveys obtained by magneto telluric investigations are currently deployed at subduction zones. The electrical conductivity of hydrous melts is however poorly constrained: so far only three studies have experimentally addressed this topic. Here, we show in situ electrical impedance of natural dacites, andesites (from Uturuncu Volcano, Bolivia) and basaltic magmas obtained with a 4-wire set up in a piston cylinder and internally heated pressure vessel. The range of temperature (500 to 1300°C), pressure (0.3 to 2 Gpa), and the various water contents and crystal fractions covers the respective ranges occurring at natural conditions. First results show that the conductivity increases with the temperature, the melt fraction, and a slightly decreases with the pressure and the crystal fraction. The compilation of these results with previous studies (rhyolitic, phonolitic and basaltic compositions) will lead to a general model of the electrical properties of magmas. Such a model will help in (i) interpreting the electrical signature of natural magmas and (ii) constraining their conditions (chemical composition, temperature, pressure, water content, melt fraction) from the source to the storage location.

  3. Carbonate assimilation during magma evolution at Nisyros (Greece), South Aegean Arc: Evidence from clinopyroxenite xenoliths

    NASA Astrophysics Data System (ADS)

    Spandler, Carl; Martin, Lukas H. J.; Pettke, Thomas

    2012-08-01

    To contribute to the understanding of magma evolution in arc settings we investigate the oldest volcanic unit (Kanafià Synthem) of Nisyros volcano, located in the eastern Aegean Sea (Greece). The unit consists of porphyritic pillow lavas of basaltic andesite composition with trace element signatures that are characteristic of island-arc magmas. Two lava types are distinguished on the basis of geochemistry and the presence or absence of xenoliths, with the xenolith-bearing lavas having distinctly elevated Sr, MREE/HREE and MgO/Fe2O3 compared to the xenolith-free lavas. Xenoliths include relatively rare quartzo-feldspathic fragments that represent continental-type material, and coarse clinopyroxenite xenoliths that consist largely of aluminous and calcic clinopyroxene, and accessory aluminous spinel. Anorthite-diopside reaction selvages preserved around the clinopyroxenite xenoliths demonstrate disequilibrium between the xenoliths and the host magma. The xenolith clinopyroxene is distinctly enriched in most lithophile trace elements compared to clinopyroxene phenocrysts in the host magmas. A notable exception is the Sr concentration, which is similar in both clinopyroxene types. The high Al and low Na contents of the clinopyroxenites preclude a cumulate, deep metamorphic, or mantle origin for these xenoliths. Instead, their composition and mineralogy are diagnostic of skarn rocks formed by magma-carbonate interaction in the mid/upper crust. The Kanafià lavas are interpreted to have undergone crystal fractionation, magma mixing/mingling and crustal assimilation while resident in the upper crust. We show that magma-carbonate reaction and associated skarn formation does not necessarily result in easily recognised modification of the melt composition, with the exception of increasing Sr contents. Carbonate assimilation also releases significant CO2, which will likely form a free vapour phase due to the low CO2 solubility of arc magmas. In the broader context, we stress

  4. Proceedings of the MEVTV Workshop on The Evolution of Magma Bodies on Mars

    NASA Technical Reports Server (NTRS)

    Mouginis-Mark, P. (Editor); Holloway, J. (Editor)

    1990-01-01

    The workshop focused on many of the diverse approaches related to the evolution of magma bodies on Mars that have been pursued during the course of the Mars Evolution of Volcanism, Tectonism, and Volatiles (MEVTV) Program. Approximately 35 scientists from the Mars volcanology, petrology, geochemistry, and modeling communities attended. Segments of the meeting concentrated of laboratory analyses and investigations of SNC meteorites, the interpretation of Viking Orbiter and Lander datasets, and the interpretation of computer codes that model volcanic and tectonic processes on Mars. Abstracts of these reports are presented.

  5. Comparative assessment of five potential sites for hydrothermal-magma systems: summary

    SciTech Connect

    Luth, W.C.; Hardee, H.C.

    1980-11-01

    A comparative assessment of five potential hydrothermal-magma sites for this facet of the Thermal Regimes part of the CSDP has been prepared for the DOE Office of Basic Energy Sciences. The five sites are: The Geysers-Clear Lake, CA, Long Valley, CA, Rio Grande Rift, NM, Roosevelt Hot Springs, UT, and Salton Trough, CA. This site assessment study has drawn together background information (geology, geochemistry, geophysics, and energy transport) on the five sites as a preliminary stage to site selection. Criteria for site selection are that potential sites have identifiable, or likely, hydrothermal systems and associated magma sources, and the important scientific questions can be identified and answered by deep scientific holes. Recommendations were made.

  6. Sulfide Mineralogy and Geochemistry

    NASA Astrophysics Data System (ADS)

    Dilles, John

    2007-02-01

    Reviews in Mineralogy and Geochemistry Series, Volume 61 David J. Vaughan, Editor Geochemical Society and Mineralogical Society of America; ISBN 0-939950-73-1 xiii + 714 pp.; 2006; $40. Sulfide minerals as a class represent important minor rock-forming minerals, but they are generally known as the chief sources of many economic metallic ores. In the past two decades, sulfide research has been extended to include important roles in environmental geology of sulfide weathering and resultant acid mine drainage, as well as in geomicrobiology in which bacteria make use of sulfides for metabolic energy sources. In the latter respect, sulfides played an important role in early evolution of life on Earth and in geochemical cycling of elements in the Earth's crust and hydrosphere.

  7. Variations in magma supply and magma partitioning: the role of tectonic settings

    NASA Astrophysics Data System (ADS)

    Takada, Akira

    1999-11-01

    Magma supply rates for 200 years at Krafla and Lakagigar, Iceland, and those for 150 years at Kilauea and Mauna Loa, Hawaii, are estimated roughly, based on their geophysical and geological observations. A diagram that relates erupted volumes to eruption intervals at volcanoes under various tectonic settings is represented. These results lead to a new model that a large volume (1-10 km 3) of magma is supplied intermittently at a long interval (10 2-10 4 years) beneath volcanoes in rift zones, while magma is supplied continuously with oscillations or fluctuations beneath intraplate volcanoes. Chemical data such as the MgO wt.% of lava may be one indicator in evaluating the magma supply rates of Hawaiian volcanoes. Systematic variation with time in magma partitioning within a volcano or to the surface is obtained in comparisons between among migration patterns of eruption sites, cumulative supplied volumes, and the volume ratios of erupted to supplied magma at Krafla and Kilauea. The variations suggest that a magma plumbing system may act under self-control (regulating) system through stress as one system. In response to a change in magma supply rate, the system partitions magma horizontally into dikes or vertically toward the surface. A large magma supply rate promotes the vertical extent of a crack to result in an eruption with a large volume ratio of erupted to supplied magma. This tendency is supported by field observations of flood basalts. The partitioned magma as dike intrusions suppresses magma supply partially in the shallow crust. Using analog experiments on liquid-filled cracks in gelatin, this paper demonstrates fundamental processes for magma partitioning on the effect of magma supply and stress change by the partitioned magma. A dynamical system of two differential equations on magma supply rate and stress around a magma plumbing system is proposed, to understand the qualitative variations in magma supply rate imposed by tectonic settings.

  8. Mushy magma processes in the Tuolumne intrusive complex, Sierra Nevada, California

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Paterson, S. R.

    2012-12-01

    whole rock data. 4) Single mineral geochemistry suggests that this increased heterogeneity in the interior of the complex is likely caused by the presence of mixed mineral populations that acquired their compositional zoning in magmas different than the one they most recently crystallized in. 5) Mixed mineral populations have also been found in places of local magma mixing (e.g., tubes and troughs), and 6) oscillatory trace element zoning in K-feldspar phenocrysts most likely represents magma replenishment. All of these phenomena suggest a fairly dynamic environment of magma replenishment, magmatic erosion and extensive mixing at the locus of chamber growth. Magma replenishment subsided after episodic flare-ups and the magma mush dominantly underwent fractional crystallization and magmatic fabric formation during waning stages, when it was capable of preserving the evidence at map to crystal scale, lacking any later overprint by mixing. Fractionation related evidence is apparent in the presence of 1) map to outcrop scale leucogranite lenses and dikes in all major Tuolumne units (including the Johnson Peak granite itself), 2) the concentric compositional zonation of magmatic lobes (e.g., southern Half Dome lobe), 3) local crystal accumulations and widespread schlieren, and 4) fractionation related single mineral element zoning.

  9. Impermeable high-porosity magmas

    NASA Astrophysics Data System (ADS)

    Heap, Michael; Vona, Alessandro; Kolzenburg, Stephan; Ryan, Amy; Russell, Kelly

    2016-04-01

    Magma vesiculation (i.e., porosity increase) is the consequence of decompression-driven volatile release during ascent and/or heating. The ease at which these exsolved volatiles can escape is thought to strongly impact volcanic explosivity. Permeability is usually considered to increase as a function of porosity. High and low porosity are typically associated with high and low permeability, respectively. Here we present permeability experiments on foamed natural rhyolitic melts containing total porosities from 0.12 to 0.65; we compliment these data with measurements on synthetic foamed glasses (prepared by FOAMGLAS®) that contain a total porosity of 0.9. The rhyolitic melts (from Krafla, Iceland: Tg = 690 °C) were kept at atmospheric pressure and 1000 °C for 0.5, 1, 2, and 4 hours, followed by quenching. The four experiments yielded total porosities of 0.12, 0.44, 0.51, and 0.65, respectively. The permeability of these samples was then measured using a steady-state, benchtop permeameter under a confining pressure of 1 MPa. The permeability of the foamed samples containing a porosity of 0.12 and 0.44 were not measurable in our system, meaning their permeabilities are lower than ~10-18 m2. The permeability of the samples containing a porosity of 0.51 and 0.65 were 8.7 × 10-15 and 1.0 × 10-15 m2, respectively. Both types of FOAMGLAS® - containing a porosity of 0.9 - also have permeabilities lower than ~10-18 m2. Our study highlights that highly porous magmas are not necessarily permeable due to the absence of a connected network of pores. These data suggest that (1) the percolation threshold for magma requires further thought and, (2) that the liberation of exsolved volatiles will require the fracturing of bubble walls to connect the network of pores within the magma.

  10. Partially molten magma ocean model

    SciTech Connect

    Shirley, D.N.

    1983-02-15

    The properties of the lunar crust and upper mantle can be explained if the outer 300-400 km of the moon was initially only partially molten rather than fully molten. The top of the partially molten region contained about 20% melt and decreased to 0% at 300-400 km depth. Nuclei of anorthositic crust formed over localized bodies of magma segregated from the partial melt, then grew peripherally until they coverd the moon. Throughout most of its growth period the anorthosite crust floated on a layer of magma a few km thick. The thickness of this layer is regulated by the opposing forces of loss of material by fractional crystallization and addition of magma from the partial melt below. Concentrations of Sr, Eu, and Sm in pristine ferroan anorthosites are found to be consistent with this model, as are trends for the ferroan anorthosites and Mg-rich suites on a diagram of An in plagioclase vs. mg in mafics. Clustering of Eu, Sr, and mg values found among pristine ferroan anorthosites are predicted by this model.

  11. Petrologic Insights into Magma System Response to Edifice Collapse

    NASA Astrophysics Data System (ADS)

    Shipman, J. S.; Izbekov, P. E.; Gavrilenko, M.

    2011-12-01

    In order to understand eruptive behavior at volcanic centers and to improve models for monitoring and prediction of volcanic eruptions, it is important to constrain magma storage conditions and transport in the system. Here the post-collapse eruptive behavior at Bezymianny and Shiveluch volcanoes, (Kamchatka Peninsula, Russia) are each compared to the well-known sequence at Mount St. Helens, Washington, USA (from 1956, 1964, and 1980, respectively). The magma system responds to rapid unloading of overburden pressure, due to edifice collapse, with a violent large-scale paroxysmal eruption. This reflects the amplitude of the triggering decompression event with later dome-building and explosive activity due to the reduction of vent elevation. The massive unloading events and post-collapse eruptive chronologies, provides a unique opportunity for comparison of the sources driving the catastrophic eruptions and eruptive style transitions. Analytical techniques employed included X-ray fluorescence spectroscopy, electron probe micro-analyses, Fe-Ti oxide and two-pyroxene geothermometry, X-ray elemental mapping, and a novel image processing technique. Presented here are results from petrological investigations into the temporal variations of whole-rock geochemistry, geothermometry, mineral modal abundances and textures. Bezymianny is becoming more mafic over time from 61.0 to 57.3 wt.% SiO2 (1956 and 2010). Pre-eruptive magma temperatures increased from 950oC to 1050oC from 1956 to 2006. Plagioclase and amphibole disequilibrium textures are observed throughout the time series and rare mafic enclaves exist. The whole-rock chemical trend at Shiveluch shows a subtle, yet reversed trend from 60.6 to 64.2 wt.% SiO2 (1964 and 2007). Two-pyroxene geothermometry yields ~950oC+30oC (2001-2007) and is consistent with data from the 2001 -2004 eruption, of 834-978oC+60oC. Mafic enclaves occurred throughout the entire period of eruptive activity at Shiveluch. In contrast to both

  12. Magma rheology variation in sheet intrusions (Invited)

    NASA Astrophysics Data System (ADS)

    Magee, C.; O'Driscoll, B.; Petronis, M. S.; Stevenson, C.

    2013-12-01

    The rheology of magma fundamentally controls igneous intrusion style as well as the explosivity and type of volcanic eruptions. Importantly, the dynamic interplay between the viscosity of magma and other processes active during intrusion (e.g., crystallisation, magma mixing, assimilation of crystal mushes and/or xenolith entrainment) will likely bear an influence on the temporal variation of magma rheology. Constraining the timing of rheological changes during magma transit therefore plays an important role in understanding the nuances of volcanic systems. However, the rheological evolution of actively emplacing igneous intrusions cannot be directly studied. While significant advances have been made via experimental modelling and analysis of lava flows, how these findings relate to intruding magma remains unclear. This has led to an increasing number of studies that analyse various characteristics of fully crystallised intrusions in an attempt to ';back-out' the rheological conditions governing emplacement. For example, it has long been known that crystallinity affects the rheology and, consequently, the velocity of intruding magma. This means that quantitative textural analysis of crystal populations (e.g., crystal size distribution; CSD) used to elucidate crystallinity at different stages of emplacement can provide insights into magma rheology. Similarly, methods that measure flow-related fabrics (e.g., anisotropy of magnetic susceptibility; AMS) can be used to discern velocity profiles, a potential proxy for the magma rheology. To illustrate these ideas, we present an integrated AMS and petrological study of several sheet intrusions located within the Ardnamurchan Central Complex, NW Scotland. We focus on the entrainment and transport dynamics of gabbroic inclusions that were infiltrated by the host magma upon entrainment. Importantly, groundmass magnetic fabrics within and external to these inclusions are coaxial. This implies that a deviatoric stress was

  13. Diverse magma flow directions during construction of sheeted dike complexes at fast- to superfast-spreading centers

    NASA Astrophysics Data System (ADS)

    Horst, A. J.; Varga, R. J.; Gee, J. S.; Karson, J. A.

    2014-12-01

    Dike intrusion is a fundamental process during upper oceanic crustal accretion at fast- to superfast-spreading ridges. Based on the distribution of magma along fast-spreading centers inferred from marine geophysical data, models predict systematic steep flow at magmatically robust segment centers and shallow magma flow toward distal segment ends. Anisotropy of magnetic susceptibility (AMS) fabrics from 48 fully-oriented block samples of dikes from upper oceanic crust exposed at Hess Deep Rift and Pito Deep Rift reveal a wide range of magma flow directions that are not consistent with such simple magma supply models. The AMS is interpreted to arise from distribution anisotropy of titanomagnetite crystals based on weak shape-preferred orientation of opaque oxide and plagioclase crystals generally parallel to AMS maximum eigenvectors. Most dike samples show normal AMS fabrics with maximum eigenvector directions ranging from subvertical to subhorizontal. The distributions of inferred magma flow lineations from maximum eigenvectors show no preferred flow pattern, even after structural correction. We use a Kolmogorov-Smirnov test (KS-test) to show that the distribution of bootstrapped flow lineation rakes from Pito Deep are not statistically distinct from Hess Deep, and neither are distinguishable from Oman and Troodos Ophiolite AMS data. Magma flow directions in sheeted dikes from these two seafloor escarpments also do not correlate with available geochemistry in any systematic way as previously predicted. These results indicate distinct compositional sources feed melt that is injected into dikes at fast- to superfast-spreading ridges with no preference for subhorizontal or subvertical magma flow. Collectively, results imply ephemeral melt lenses at different along-axis locations within the continuous axial magma chamber and either direct injection or intermingling of melt from other deeper ridge-centered or off-axis sources.

  14. Magma chamber paradox: decompression upon replenishment

    NASA Astrophysics Data System (ADS)

    Papale, Paolo; Longo, Antonella; Montagna, Chiara Paola

    2013-04-01

    The invasion of active magma chambers by fresh magma of deeper provenance is invariably assumed to cause chamber pressurization. Pressure increase thus stands as an intuitive consequence of magma chamber replenishment. However, new numerical simulations demonstrate that pressure evolution is highly non-linear, and that decompression dominates when large density contrasts exist between injected and resident magmas. This apparent paradox originates from the compressible nature of volatile-rich magma and the dynamics of convection associated with injections of buoyant magma. While decompression can dominate in a shallow chamber, pressure increase develops in the connected deep regions of magma provenance. These results contradict classical views adopted to interpret observations at active as well as fossil magma chambers, and demonstrate that a simple reliance on intuition is insufficient: what may be perceived as a paradox - magma chamber decompression upon replenishment - is instead likely, and rooted in the complex physics that governs the multiphase, multi-component dynamics of magma transport in geometrically composite, spatially extended magmatic systems.

  15. Response of a low-subsiding intracratonic basin to long wavelength deformations: the Palaeocene-early Eocene period in the Paris Basin

    NASA Astrophysics Data System (ADS)

    Briais, J.; Guillocheau, F.; Lasseur, E.; Robin, C.; Châteauneuf, J. J.; Serrano, O.

    2016-02-01

    The uppermost Cretaceous to early Palaeogene is a period of major deformations of the western part of the Eurasian plate with prominent basin inversions starting from the Coniacian onwards. These deformations occur in a complex geodynamic setting within both the context of the Africa-Eurasia convergence and the North Atlantic opening. While Mesozoic graben inversions have been extensively studied, particularly in Eastern Europe and the North Sea, more gentle deformations that affect thicker crust areas (intracratonic basins and emerged lands) are not as well documented. The objective of this study is to constrain the exact timing, type, and magnitude of the early Palaeogene deformations affecting the intracratonic Paris Basin and to integrate them at the western European scale. Low-amplitude deformations are attempted through a high-resolution reconstitution of its stratigraphic record based on well-dated outcrops and well-dated wells, and a high number of well-logs that are correlated using the "stacking pattern" sequence stratigraphic technique. Two orders of sequences are identified (third and fourth order) and correlated throughout the basin. Basin geometric and palaeogeographic reconstitutions are based on sediment thickness and facies analysis. Two-dimensional accommodation space measurements were taken in order to quantify the magnitude of the deformations. Three phases of deformation were recognized. 1. An intra-Maastrichtian-pre-Thanetian (59 Ma) deformation, with major uplift and erosion of the Cretaceous strata with two sub-periods of deformation: Maastrichtian-pre-middle-Danian and Upper Danian-pre-Thanetian long-wavelength deformations. This period of major deformation is coeval with Upper Cretaceous/pre-Danian compressive deformations linked to the Africa-Eurasia convergence in southern France and with volcanic activity from the North Atlantic to Massif Central and the Rhenish Shield during the Palaeocene. 2. An early Ypresian (55.1-54.3 Ma) medium

  16. Response of a low subsiding intracratonic basin to long wavelength deformations: the Palaeocene-early Eocene period in the Paris basin

    NASA Astrophysics Data System (ADS)

    Briais, J.; Guillocheau, F.; Lasseur, E.; Robin, C.; Châteauneuf, J. J.; Serrano, O.

    2015-12-01

    The uppermost Cretaceous to early Palaeogene is a period of major deformations of the western part of the Eurasian plate with prominent basin inversions starting from the Coniacian onwards. These deformations occur in a complex geodynamic setting within both the context of the Africa-Eurasia convergence and the North Atlantic opening. While Mesozoic graben inversions have been extensively studied, particularly in Eastern Europe and the North Sea, more gentle deformations that affect thicker crust areas (intracratonic basins and emerged lands) are not as well documented. The objective of this study is to constrain the exact timing, type and magnitude of the early Palaeogene deformations affecting the intracratonic Paris basin and to integrate them at the Western European scale. Relatively gentle deformations are attempted through a high-resolution reconstitution of its stratigraphic record based on outcrops and well-dated wells, and a high number of well-logs that are correlated using the "stacking pattern" sequence stratigraphic technique. Two orders of sequences are identified (third- and fourth-order) and correlated throughout the basin. Basin geometric and palaeogeographic reconstitutions are based on sediment thickness and facies analysis. Two-dimensional accommodation space measurements were taken in order to quantify the magnitude of the deformations. Three phases of deformation were recognized. 1. An intra-Maastrichtian-pre-Thanetian (59 Ma) deformation, with major uplift and erosion of the Cretaceous strata with two sub-periods of deformation: Maastrichtian-pre-middle-Danian and Upper Danian-pre-Thanetian long wavelength deformations. This period of major deformation is coeval with Upper Cretaceous-pre-Danian compressive deformations linked to the Africa-Eurasia convergence in southern France and with volcanic activity from the North Atlantic to Massif Central and the Rhenish Shield during the Palaeocene; 2. an early Ypresian (55.1-54.3 Ma) medium

  17. Numerical simulation of magma chamber dynamics.

    NASA Astrophysics Data System (ADS)

    Longo, Antonella; Papale, Paolo; Montagna, Chiara Paola; Vassalli, Melissa; Giudice, Salvatore; Cassioli, Andrea

    2010-05-01

    Magma chambers are characterized by periodic arrivals of deep magma batches that give origin to complex patterns of magma convection and mixing, and modify the distribution of physical quantities inside the chamber. We simulate the transient, 2D, multi-component homogeneous dynamics in geometrically complex dyke+chamber systems, by means of GALES, a finite element parallel C++ code solving mass, momentum and energy equations for multi-component homogeneous gas-liquid (± crystals) mixtures in compressible-to-incompressible flow conditions. Code validation analysis includes several cases from the classical engineering literature, corresponding to a variety of subsonic to supersonic gas-liquid flow regimes (see http://www.pi.ingv.it/~longo/gales/gales.html). The model allows specification of the composition of the different magmas in the domain, in terms of ten major oxides plus the two volatile species H2O and CO2. Gas-liquid thermodynamics are modeled by using the compositional dependent, non-ideal model in Papale et al. (Chem.. Geol., 2006). Magma properties are defined in terms of local pressure, temperature, and composition including volatiles. Several applications are performed within domains characterized by the presence of one or more magma chambers and one or more dykes, with different geometries and characteristic size from hundreds of m to several km. In most simulations an initial compositional interface is placed at the top of a feeding dyke, or at larger depth, with the deeper magma having a lower density as a consequence of larger volatile content. The numerical results show complex patterns of magma refilling in the chamber, with alternating phases of magma ingression and magma sinking from the chamber into the feeding dyke. Intense mixing takes place in feeding dykes, so that the new magma entering the chamber is always a mixture of the deep and the initially resident magma. Buoyant plume rise occurs through the formation of complex convective

  18. Coal Formation and Geochemistry

    NASA Astrophysics Data System (ADS)

    Orem, W. H.; Finkelman, R. B.

    2003-12-01

    Coal is one of the most complex and challenging natural materials to analyze and to understand. Unlike most rocks, which consist predominantly of crystalline mineral grains, coal is largely an assemblage of amorphous, degraded plant remains metamorphosed to various degrees and intermixed with a generous sprinkling of minute syngenetic, diagenetic, epigenetic, and detrital mineral grains, and containing within its structure various amounts of water, oils, and gases. Each coal is unique, having been derived from different plant sources over geologic time, having experienty -45ced different thermal histories, and having been exposed to varying geologic processes. This diversity presents a challenge to constructing a coherent picture of coal geochemistry and the processes that influence the chemical composition of coal.Despite the challenge coal presents to geochemists, a thorough understanding of the chemistry and geology of this complex natural substance is essential because of its importance to our society. Coal is, and will remain for sometime, a crucial source of energy for the US and for many other countries (Figure 1). In the USA, more than half of the electricity is generated by coal-fired power plants, and almost 90% of the coal mined in the USA is sold for electricity generation (Pierce et al., 1996). It is also an important source of coke for steel production, chemicals, pharmaceuticals, and even perfumes ( Schobert, 1987). It may also, in some cases, be an economic source of various mineral commodities. The utilization of coal through mining, transport, storage, combustion, and the disposal of the combustion by-products, also presents a challenge to geochemists because of the wide range of environmental and human health problems arising from these activities. The sound and effective use of coal as a natural resource requires a better understanding of the geochemistry of coal, i.e., the chemical and mineralogical characteristics of the coal that control its

  19. Recurrent patterns in fluid geochemistry data prior to phreatic eruptions

    NASA Astrophysics Data System (ADS)

    Rouwet, Dmitri; Sandri, Laura; Todesco, Micol; Tonini, Roberto; Pecoraino, Giovannella; Diliberto, Iole Serena

    2016-04-01

    Not all volcanic eruptions are magma-driven: the sudden evaporation and expansion of heated groundwater may cause phreatic eruptions, where the magma involvement is absent or negligible. Active crater lakes top some of the volcanoes prone to phreatic activity. This kind of eruption may occur suddenly, and without clear warning: on September 27, 2014 a phreatic eruption of Ontake, Japan, occurred without timely precursors, killing 57 tourists near the volcano summit. Phreatic eruptions can thus be as fatal as higher VEI events, due to the lack of recognised precursory signals, and because of their explosive and violent nature. In this study, we tackle the challenge of recognising precursors to phreatic eruptions, by analysing the records of two "phreatically" active volcanoes in Costa Rica, i.e. Poás and Turrialba, respectively with and without a crater lake. These volcanoes cover a wide range of time scales in eruptive behaviour, possibly culminating into magmatic activity, and have a long-term multi-parameter dataset mostly describing fluid geochemistry. Such dataset is suitable for being analysed by objective pattern recognition techniques, in search for recurrent schemes. The aim is to verify the existence and nature of potential precursory patterns, which will improve our understanding of phreatic events, and allow the assessment of the associated hazard at other volcanoes, such as Campi Flegrei or Vulcano, in Italy. Quantitative forecast of phreatic activity will be performed with BET_UNREST, a Bayesian Event Tree tool recently developed within the framework of FP7 EU VUELCO project. The study will combine the analysis of fluid geochemistry data with pattern recognition and phreatic eruption forecast on medium and short-term. The study will also provide interesting hints on the features that promote or hinder phreatic activity in volcanoes that host well-developed hydrothermal circulation.

  20. Formation of crustal magma chambers in Iceland

    SciTech Connect

    Gudmundsson, A.

    1986-02-01

    Formation of crustal magma chambers in Iceland may be facilitated by the occurrence of stress barriers that lead to formation of thick sills. Such sills absorb the magma of all dikes that enter them and may evolve into magma chambers. Ideal sites for stress barriers, and hence for magma chambers, are rock formations where individual layers have different elastic properties. The rocks formed during the Pleistocene have notably different elastic properties, and when buried in the volcanic zones, they form more promising sites for magma chambers than the Tertiary rocks. This may explain why the number of magma chambers, indicated by the number of corresponding central volcanoes, during the late Pleistocene (i.e., during the past 0.7 m.y.) appears to be proportionally greater than the number of chambers (i.e., central volcanoes) active during Tertiary time.

  1. Shallow magma targets in the western US

    SciTech Connect

    Hardee, H.C.

    1984-10-01

    Within the next few years a hole will be drilled into a shallow magma body in the western US for the purpose of evaluating the engineering feasibility of magma energy. This paper examines potential drilling sites for these engineering feasibility experiments. Target sites high on the list are ones that currently exhibit good geophysical and geological data for shallow magma and also have reasonable operational requirements. Top ranked sites for the first magma energy well are Long Valley, CA, and Coso/Indian Wells, CA. Kilauea, HI, also in the top group, is an attractive site for some limited field experiments. A number of additional sites offer promise as eventual magma energy sites, but sparsity of geophysical data presently prevents these sites from being considered for the first magma energy well.

  2. Isotopic geochemistry and cosmochemistry

    NASA Astrophysics Data System (ADS)

    Shchukoliukov, Iu. A.

    The book includes recent information on isotope geology, geochemistry, and cosmochemistry, discussed at a recent Soviet-Japanese symposium (at Irkutsk, USSR). Attention is given to numerical modeling of geochronometric systems, a classification of noble-gas components in the earth's interior, the feasibility of using ion microprobe for local isotope analysis of zircons for the purpose of deriving the early history of the earth (on the example of the Novopavlovsk complex from the Ukranian shield), a geological and geochronological study of the Ganalski complex of Kamchatka, and strontium isotopes as a criterion of the nature of acid melts (i.e., mantle- or crust-related). Other papers are on the geochronology and geology of Siberian kimberlites, the nature of sulfur from effusive rocks of the Kamchatka-Kuril-Japan island arc, mass-spectrometric studies of volatile components in exocontact rocks of alkaline-basic intrusions, and an analytical method for stable-isotope analysis in ultrasmall amounts of CO2 and its application to studies of the microscale isotopic zoning in calcite and graphite crystals in marble.

  3. Geochemistry of Groundwater

    NASA Astrophysics Data System (ADS)

    Chapelle, F. H.

    2003-12-01

    Differentiation of terrestrial planets includes separation of a metallic core and possible later fractionation of mineral phases within either a solid or molten mantle (Figure 1). Lithophile and siderophile elements can be used to understand these two different physical processes, and ascertain whether they operated in the early Earth. The distribution of elements in planets can be understood by measuring the partition coefficient, D (ratio of concentrations of an element in different phases (minerals, metals, or melts)). (14K)Figure 1. Schematic cross-section through the Earth, showing: (a) an early magma ocean stage and (b) a later cool and differentiated stage. The siderophile elements (iron-loving) encompass over 30 elements and are defined as those elements for which D(metal/silicate)>1, and are useful for deciphering the details of core formation. This group of elements is commonly broken up into several subclasses, including the slightly siderophile elements (1104). Because these three groups encompass a wide range of partition coefficient values, they can be very useful in trying to determine the conditions under which metal may have equilibrated with the mantle (or a magma ocean). Because metal and silicate may equilibrate by several different mechanisms, such as at the base of a deep magma ocean, or as metal droplets descend through a molten mantle, partition coefficients can potentially shed light on which mechanism may be most important, thus linking the physics and chemistry of core formation. In this chapter, we summarize metal/silicate partitioning of siderophile elements and show how they may be used to understand planetary core formation.Once a planet is differentiated into core and mantle, a mantle will cool during convection, and can start in either a molten or solid state, depending upon the initial thermal conditions. If hot enough, minerals will

  4. Recent progress in magma energy extraction

    SciTech Connect

    Ortega, A.; Dunn, J.C.; Chu, T.Y.; Wemple, R.P.; Hickox, C.E.

    1987-01-01

    Ongoing research in the area of Magma Energy Extraction is directed at developing a fundamental understanding of the establishment and long term operation of an open, direct-contact heat exchanger in a crustal magma body. The energy extraction rate has a direct influence on the economic viability of the concept. An open heat exchanger, in which fluid is circulated through the interconnecting fissures and fractures in the solidified region around drilling tubing, offers the promise of very high rates of heat transfer. This paper discusses recent research in five areas: (1) fundamental mechanisms of solidifying and thermally fracturing magma; (2) convective heat transfer in the internally fractured solidified magma; (3) convective flow in the molten magma and heat transfer from the magma to the cooled heat exchanger protruding into it; (4) numerical simulation of the overall energy extraction process; and (5) the thermodynamics of energy conversion in a magma power plant at the surface. The studies show that an open heat exchanger can be formed by solidifying magma around a cooled borehole and that the resulting mass will be extensively fractured by thermally-induced stresses. Numerical models indicate that high quality thermal energy can be delivered at the wellhead at nominal rates from 25 to 30 MW electric. It is shown that optimum well circulation rates can be found that depend on the heat transfer characteristics of the magma heat exchanger and the thermodynamic power conversion efficiencies of the surface plant.

  5. Replenishment of magma chambers by light inputs

    NASA Astrophysics Data System (ADS)

    Huppert, Herbert E.; Sparks, R. Stephen J.; Whitehead, John A.; Hallworth, Mark A.

    1986-05-01

    Magma chambers, particularly those of basaltic composition, are often replenished by an influx of magma whose density is less than that of the resident magma. This paper describes the fundamental fluid mechanics involved in the replenishment by light inputs. If ρ denotes the uniform density of the resident magma and ρ — Δρ that of the input, the situation is described by the reduced gravity g' = gΔρ/ρ, the volume flux Q, and the viscosities of the resident and input magmas νe and νi, respectively. The (nondimensional) Reynolds numbers, Ree = (g'Q3)1/5/νe and Rei = (g'Q3)1/5/νi and chamber geometry then completely specify the system. For sufficiently low values of the two Reynolds numbers (each less than approximately 10), the input rises as a laminar conduit. For larger values of the Reynolds numbers, the conduit may break down and exhibit either a varicose or a meander instability and entrain some resident magma. At still larger Reynolds numbers, the flow will become quite unsteady and finally turbulent. The values of the Reynolds numbers at which these transitions occur have been documented by a series of experiments with water, glycerine, and corn syrup. If the input rises as a turbulent plume, significant entrainment of the resident magma can take place. The final spatial distribution of the mixed magma depends on the geometry of the chamber. If the chamber is much wider than it is high, the mixed magma forms a compositionally stratified region between the roof and a sharp front above uncontaminated magma. In the other geometrical extreme, the input magma is mixed with almost all of the resident magma. If the density of the resident magma is already stratified, the input plume may penetrate only part way into the chamber, even though its initial density is less than that of the lowest density resident magma. The plume will then intrude horizontally and form a hybrid layer at an intermediate depth. This provides a mechanism for preventing even

  6. Magma mixing in a zoned alkalic intrusion

    SciTech Connect

    Price, J.G.; Henry, C.D.; Barker, D.S.; Rubin, J.N.

    1985-01-01

    The Marble Canyon stock is unique among the alkalic intrusions of the Trans-Pecos magmatic province in being zoned from a critically silica-undersaturated rim of alkali gabbro (AG) to a silica-oversaturated core of quartz syenite (QS). Hybrid rocks of intermediate chemical and mineralogical compositions occur between the rim and core. Nepheline-syenite dikes occur only within the AG. Silica-rich dikes of quartz trachyte, pegmatite, and aplite cut the AG, QS, and hybrid rocks. Thermodynamic calculations of silica activity in the magmas illustrate the presence of two trends with decreasing temperature: a silica-poor trend from AG to nepheline syenite and a silica-rich trend from hybrid rocks to QS. Least-square modeling of rock and mineral compositions suggests 1) the nepheline syenites were derived by crystal-liquid fractionation from nearly solidified AG at the rim of the stock, 2) AG magma farther from the rim mixed with a small proportion of granitic magma, and 3) the mixture then differentiated to produce the hybrid rocks and QS. Zirconium dioxide inclusions in plagioclase crystals of the hybrid rocks and QS indicate that the AG magma contained some crystals before it mixed with the granitic magma. Two origins for the granitic magma are possible: 1) a late-stage differentiate of a mantle-derived hypersthene-normative magma and 2) melting of crustal material by the AG magma. Recognition of magma mixing might not have been possible if the AG had been hypersthene-normative.

  7. Evaluating volumes for magma chambers and magma withdrawn for caldera collapse

    NASA Astrophysics Data System (ADS)

    Geshi, Nobuo; Ruch, Joel; Acocella, Valerio

    2014-06-01

    We develop an analytical model to infer the total volume of a magma chamber associated with caldera collapse and the critical volume of magma that must be withdrawn to induce caldera collapse. The diameter of caldera border fault, depth to the magma chamber, and volumes of magma erupted before the onset of collapse and of entire eruption are compiled for 14 representative calderas. The volume of erupted magma at the onset of collapse aligns between the total erupted volume of the other representative caldera-forming eruptions and the volume of eruptions without collapse during the post-caldera stage, correlating with the structural diameter of the calderas. The total volume of magma chamber is evaluated using a piston-cylinder collapse model, in which the competition between the decompression inside magma chamber and friction along the caldera fault controls the collapse. Estimated volumes of the magma chambers associated with caldera collapse are 3-10 km3 for Vesuvius 79 A.D. to 3000-10 500 km3 for Long Valley, correlating with the cube of caldera diameters. The estimated volumes of magma chamber are always larger than the total volume of erupted magma for caldera formation, suggesting that the magma chambers are never completely emptied by the caldera-forming eruptions. The minimum volumes of erupted magma to trigger collapse are calculated from the correlation between the caldera diameters and the evaluated volume of magma chambers. The minimum eruptive volume for the collapse correlates with the square of the caldera radius r and the square of the depth to the magma chamber h, and inversely correlates with the bulk modulus of magma, which is mainly controlled by the bubble fraction in the magma. A bubble fraction between 5 and 10% at the onset of collapse may explain the distribution of the erupted volumes at the onset of collapse of the calderas in nature.

  8. Geochemical heterogeneities and dynamics of magmas inside the plumbing system of a persistently active volcano: evidences from Stromboli

    NASA Astrophysics Data System (ADS)

    Pompilio, Massimo; Bertagnini, Antonella; Métrich, Nicole; Belhadj, Oulfa

    2010-05-01

    significant modifications in eruptive style and/or volcano structure can only be identified by interpreting the geochemistry of pumice since they represent pristine magmas transferred directly from deep portions of the plumbing system.

  9. Formation of redox gradients during magma-magma mixing

    NASA Astrophysics Data System (ADS)

    Ruprecht, P.; Fiege, A.; Simon, A. C.

    2015-12-01

    Magma-mixing is a key process that controls mass transfer in magmatic systems. The variations in melt compositions near the magma-magma interface potentially change the Fe oxidation state [1] and, thus, affect the solubility and transport of metals. To test this hypothesis, diffusion-couple experiments were performed at 1000 °C, 150 MPa and QFM+4. Synthesized crystal-bearing cylinders of hydrous dacite and hydrous basaltic andesite were equilibrated for up to 80 h. The run products show that mafic components (Fe, Mg, etc.) were transported from the andesite into the dacite, while Si, Na and K diffused from the dacite into the andesite. A crystal dissolution sequence in the order of cpx, opx, plag, and spl/il was observed for the andesite. We combined μ-XANES spectroscopy at Fe K-edge [2] with two-oxide oxybarometry [3] to measure redox profiles within our experiments. Here, fO2 decreased towards the interface within the dacite and increased towards the interface within the andesite. This discontinuous fO2 evolution, with a sharp redox gradient of ~1.8 log fO2 units at the interface was maintained throughout the time-series despite the externally imposed fO2 of the vessel. We propose a combination of two mechanisms that create and sustain this redox gradient: 1) The dissolution of cpx and opx in the andesite mainly introduced Fe2+ into the melt, which diffused towards the dacite, lowering Fe3+/SFe near the interface. 2) Charge balance calculations in the melt during diffusive exchange suggest net positive charge excess in the andesite near the interface (i.e., oxidation) and net negative charge excess in the dacite near the interface (i.e., reduction). We suggest that this (metastable) redox layer can help to explain the contrasting Au/Cu ratios observed for arc-related porphyry-type ore deposits. [1] Moretti (2005), Ann. Geophys. 48, 583-608. [2] Cottrell et al. (2009), Chem. Geol. 268, 167-179. [3] Ghiorso and Evans (2008), Am. J. Sci. 308, 957-1039.

  10. Why do Martian Magmas erupt?

    NASA Astrophysics Data System (ADS)

    Balta, J. B.; McSween, H. Y.

    2011-12-01

    Eruption of silicate lava, whether on Earth or another planet, requires that at some depth the melt has lower density than the surrounding rocks. As the densities of silicate liquids change during crystallization, whether a particular silicate liquid will erupt or be trapped at a level of neutral buoyancy is a complex yet fundamental issue for planetary dynamics. In general, 3 factors drive surface eruptions: inherent buoyancy relative to mantle phases, compositional evolution, and volatile contents. These factors manifest on Earth as terrestrial basalts commonly have compositions close to a density minimum [1]. Recent work has produced estimates of Martian parental magma compositions [2-5] based on shergottite meteorites and from Gusev crater. Using the MELTS algorithm [6] and other density calibrations, we simulated evolution of these liquids, focusing on density changes. For much of the crystallization path, density is controlled by FeO. All of the liquids begin with ρ ~ 2.8 g/cc at 1 bar, and the evolution of liquid density is controlled by the liquidus phases. At low pressures, olivine is the liquidus phase for each melt, and as FeO is not incompatible in olivine, olivine crystallization decreases liquid density, increasing buoyancy with crystallization. However, FeO is incompatible in pyroxene, and thus liquids crystallizing pyroxene become denser and less buoyant with crystallization, producing liquids with densities up to and above 3.0 g/cc. As the olivine-pyroxene saturation relationship is affected by pressure and chemistry, the identity of the liquidus phase and density evolution will vary between magmas. Without spreading centers, Mars has no location where the mantle approaches the surface, and it is likely that any magma which is denser than the crust will stall below or within that crust. The crystallization path of a liquid is a function of pressure, with pyroxene crystallizing first at P > 10 kbar (~80 km depth), close to the base of the Martian

  11. Taxonomy Of Magma Mixing I: Magma Mixing Metrics And The Thermochemistry Of Magma Hybridization Illuminated With A Toy Model

    NASA Astrophysics Data System (ADS)

    Spera, F. J.; Bohrson, W. A.; Schmidt, J.

    2013-12-01

    The rock record preserves abundant evidence of magma mixing in the form of mafic enclaves and mixed pumice in volcanic eruptions, syn-plutonic mafic or silicic dikes and intrusive complexes, replenishment events recorded in cumulates from layered intrusions, and crystal scale heterogeneity in phenocrysts and cumulate minerals. These evidently show that magma mixing in conjunction with crystallization (perfect fractional or incremental batch) is a first-order petrogenetic process. Magma mixing (sensu lato) occurs across a spectrum of mixed states from magma mingling to complete blending. The degree of mixing is quantified (Oldenburg et al, 1989) using two measures: the statistics of the segregation length scales (scale of segregation, L*) and the spatial contrast in composition (C) relative to the mean C (intensity of segregation, I). Mingling of dissimilar magmas produces a heterogeneous mixture containing discrete regions of end member melts and populations of crystals with L* = finite and I > 0. When L*→∞ and I→0 , the mixing magmas become hybridized and can be studied thermodynamically. Such hybrid magma is a multiphase equilibrium mixture of homogeneous melt, unzoned crystals and possible bubbles of a supercritical fluid. Here, we use a toy model to elucidate the principles of magma hybridization in a binary system (components A and B with pure crystals of α or β phase) with simple thermodynamics to build an outcome taxonomy. This binary system is not unlike the system Anorthite-Diopside, the classic low-pressure model basalt system. In the toy model, there are seven parameters describing the phase equilibria (eutectic T and X, specific heat, melting T and fusion enthalpies of α and β crystals) and five variables describing the magma mixing conditions: end member bulk compositions, temperatures and fraction of resident magma (M) that blends with recharge (R) magma to form a single equilibrium hybrid magma. There are 24 possible initial states when M

  12. Magma energy research project, FY80 annual progress report

    NASA Astrophysics Data System (ADS)

    Colp, J. L.

    1982-04-01

    The technical feasibility of extracting energy from magma bodies is explored. Five aspects of the project are studied: resource location and definition, source tapping, magma characterization, magma/material compatibility, and energy extraction.

  13. Magma Energy Research Project, FY80 annual progress report

    SciTech Connect

    Colp, J.L.

    1982-04-01

    The technical feasibility of extracting energy from magma bodies is explored. Five aspects of the project are studied: resource location and definition, source tapping, magma characterization, magma/material compatibility, and energy extraction.

  14. Geochemistry of alkali syenites from the Budun massif and their petrogenetic properties (Ol'khon Island)

    NASA Astrophysics Data System (ADS)

    Makrygina, V. A.; Suvorova, L. F.; Zarubina, O. V.; Bryanskii, N. V.

    2016-07-01

    The first data on the geochemistry of the alkali syenite massif in Cape Budun of Ol'khon Island, where it makes contact in the south with the Khuzir gabbroid massif, are presented. Syenites occur among granite gneisses of the Sharanur dome and, like its granites, are enriched with Zr and REEs, but depleted in other trace elements. They contain anorthoclase, corundum, rare nepheline, zircon, and hercynite and are accompanied by desilicified pegmatites. Their unusual geochemical properties allow the assumption that alkaline magmas resulted from the interaction between basic and granitoid melts.

  15. Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust

    NASA Astrophysics Data System (ADS)

    Sarkar, Saheli; Saha, Lopamudra; Satyanarayan, Manavalan; Pati, Jayanta

    2015-04-01

    Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust Sarkar, S.1, Saha, L.1, Satyanarayan, M2. and Pati, J.K.3 1. Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667, Haridwar, India, 2. HR-ICPMS Lab, Geochemistry Group, CSIR-National Geophysical Research Institute, Hyderabad-50007, India. 3. Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad-211002, India. Tonalite-Trondhjemite-Granodiorite (TTGs) group of rocks, that mostly constitute the Archaean continental crusts, evolved through a time period of ~3.8 Ga-2.7 Ga with major episodes of juvenile magma generations at ~3.6 Ga and ~2.7 Ga. Geochemical signatures, especially HREE depletions of most TTGs conform to formation of this type of magma by partial melting of amphibolites or eclogites at 15-20 kbar pressure. While TTGs (mostly sodic in compositions) dominates the Eoarchaean (~3.8-3.6 Ga) to Mesoarchaean (~3.2-3.0 Ga) domains, granitic rocks (with significantly high potassium contents) became more dominant in the Neoarchaean period. The most commonly accepted model proposed for the formation of the potassic granite in the Neoarchaean time is by partial melting of TTGs along subduction zones. However Archaean granite intrusive into the gabbro-ultramafic complex from Scourie, NW Scotland has been interpreted to have formed by fractional crystallization of hornblende and plagioclase from co-existing trondhjemitic gneiss. In this study we have studied fractional crystallization paths from a Mesoarchaean trondhjemite from the central Bundelkhand craton, India using MELTS algorithm. Fractional crystallization modeling has been performed at pressure ranges of 20 kbar to 7 kbar. Calculations have shown crystallization of garnet-clinopyroxene bearing assemblages with progressive cooling of the magma at 20 kbar. At pressure ranges 19-16 kbar, solid phases

  16. Lithospheric Controls on Magma Composition along Earth's Longest Continental Hotspot-Track

    NASA Astrophysics Data System (ADS)

    Rawlinson, N.; Davies, R.; Iaffaldano, G.; Campbell, I. H.

    2015-12-01

    Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic examples include the Hawaiian-Emperor chain and the Yellowstone-Snake River Plain province. The majority are believed to form as Earth's tectonic plates move over long-lived mantle plumes: buoyant upwellings that bring hot material from Earth's deep-mantle to its surface. It has long been recognised that lithospheric thickness limits the rise height of plumes and, thereby, their minimum melting pressure. It should, therefore, have a controlling influence on the geochemistry of plume-related magmas, although unambiguous evidence of this has, thus far, been lacking. Here we integrate observational constraints from surface geology, geochronology, plate-motion reconstructions, geochemistry and seismology to ascertain plume melting depths beneath Earth's longest continental hotspot-track, a ~2000 km long track in eastern Australia that displays a record of volcanic activity between ~33 and ~9 Ma, which we call the Cosgrove track. Our analyses highlight a strong correlation between lithospheric thickness and magma composition along this track, with: (i) standard basaltic compositions in regions where lithospheric thickness is less than ~110 km; (ii) volcanic gaps in regions where lithospheric thickness exceeds ~150 km; and (iii) low-volume, leucitite-bearing volcanism in regions of intermediate lithospheric thickness. Trace-element concentrations from samples along this track support the notion that these compositional variations result from different degrees of partial-melting, which is controlled by the thickness of overlying lithosphere. Our results place the first observational constraints on the subcontinental melting depth of mantle plumes and provide direct evidence that lithospheric thickness has a dominant influence on the volume and chemical composition of plume-derived magmas.

  17. Lithospheric controls on magma composition along Earth's longest continental hotspot track

    NASA Astrophysics Data System (ADS)

    Davies, D. R.; Rawlinson, N.; Iaffaldano, G.; Campbell, I. H.

    2015-09-01

    Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic examples include the Hawaiian-Emperor chain and the Yellowstone-Snake River Plain province. The majority are believed to form as Earth's tectonic plates move over long-lived mantle plumes: buoyant upwellings that bring hot material from Earth's deep mantle to its surface. It has long been recognized that lithospheric thickness limits the rise height of plumes and, thereby, their minimum melting pressure. It should, therefore, have a controlling influence on the geochemistry of plume-related magmas, although unambiguous evidence of this has, so far, been lacking. Here we integrate observational constraints from surface geology, geochronology, plate-motion reconstructions, geochemistry and seismology to ascertain plume melting depths beneath Earth's longest continental hotspot track, a 2,000-kilometre-long track in eastern Australia that displays a record of volcanic activity between 33 and 9 million years ago, which we call the Cosgrove track. Our analyses highlight a strong correlation between lithospheric thickness and magma composition along this track, with: (1) standard basaltic compositions in regions where lithospheric thickness is less than 110 kilometres; (2) volcanic gaps in regions where lithospheric thickness exceeds 150 kilometres; and (3) low-volume, leucitite-bearing volcanism in regions of intermediate lithospheric thickness. Trace-element concentrations from samples along this track support the notion that these compositional variations result from different degrees of partial melting, which is controlled by the thickness of overlying lithosphere. Our results place the first observational constraints on the sub-continental melting depth of mantle plumes and provide direct evidence that lithospheric thickness has a dominant influence on the volume and chemical composition of plume-derived magmas.

  18. Lithospheric controls on magma composition along Earth's longest continental hotspot track.

    PubMed

    Davies, D R; Rawlinson, N; Iaffaldano, G; Campbell, I H

    2015-09-24

    Hotspots are anomalous regions of volcanism at Earth's surface that show no obvious association with tectonic plate boundaries. Classic examples include the Hawaiian-Emperor chain and the Yellowstone-Snake River Plain province. The majority are believed to form as Earth's tectonic plates move over long-lived mantle plumes: buoyant upwellings that bring hot material from Earth's deep mantle to its surface. It has long been recognized that lithospheric thickness limits the rise height of plumes and, thereby, their minimum melting pressure. It should, therefore, have a controlling influence on the geochemistry of plume-related magmas, although unambiguous evidence of this has, so far, been lacking. Here we integrate observational constraints from surface geology, geochronology, plate-motion reconstructions, geochemistry and seismology to ascertain plume melting depths beneath Earth's longest continental hotspot track, a 2,000-kilometre-long track in eastern Australia that displays a record of volcanic activity between 33 and 9 million years ago, which we call the Cosgrove track. Our analyses highlight a strong correlation between lithospheric thickness and magma composition along this track, with: (1) standard basaltic compositions in regions where lithospheric thickness is less than 110 kilometres; (2) volcanic gaps in regions where lithospheric thickness exceeds 150 kilometres; and (3) low-volume, leucitite-bearing volcanism in regions of intermediate lithospheric thickness. Trace-element concentrations from samples along this track support the notion that these compositional variations result from different degrees of partial melting, which is controlled by the thickness of overlying lithosphere. Our results place the first observational constraints on the sub-continental melting depth of mantle plumes and provide direct evidence that lithospheric thickness has a dominant influence on the volume and chemical composition of plume-derived magmas. PMID:26367795

  19. Tomography & Geochemistry: Precision, Repeatability, Accuracy and Joint Interpretations

    NASA Astrophysics Data System (ADS)

    Foulger, G. R.; Panza, G. F.; Artemieva, I. M.; Bastow, I. D.; Cammarano, F.; Doglioni, C.; Evans, J. R.; Hamilton, W. B.; Julian, B. R.; Lustrino, M.; Thybo, H.; Yanovskaya, T. B.

    2015-12-01

    Seismic tomography can reveal the spatial seismic structure of the mantle, but has little ability to constrain composition, phase or temperature. In contrast, petrology and geochemistry can give insights into mantle composition, but have severely limited spatial control on magma sources. For these reasons, results from these three disciplines are often interpreted jointly. Nevertheless, the limitations of each method are often underestimated, and underlying assumptions de-emphasized. Examples of the limitations of seismic tomography include its ability to image in detail the three-dimensional structure of the mantle or to determine with certainty the strengths of anomalies. Despite this, published seismic anomaly strengths are often unjustifiably translated directly into physical parameters. Tomography yields seismological parameters such as wave speed and attenuation, not geological or thermal parameters. Much of the mantle is poorly sampled by seismic waves, and resolution- and error-assessment methods do not express the true uncertainties. These and other problems have become highlighted in recent years as a result of multiple tomography experiments performed by different research groups, in areas of particular interest e.g., Yellowstone. The repeatability of the results is often poorer than the calculated resolutions. The ability of geochemistry and petrology to identify magma sources and locations is typically overestimated. These methods have little ability to determine source depths. Models that assign geochemical signatures to specific layers in the mantle, including the transition zone, the lower mantle, and the core-mantle boundary, are based on speculative models that cannot be verified and for which viable, less-astonishing alternatives are available. Our knowledge is poor of the size, distribution and location of protoliths, and of metasomatism of magma sources, the nature of the partial-melting and melt-extraction process, the mixing of disparate

  20. Magma ocean: Mechanisms of formation

    NASA Technical Reports Server (NTRS)

    Kaula, W. M.

    1992-01-01

    The thermal state of the Earth at the time relevant to formation of a magma ocean was dominated by the great impact that created the Moon. As shown in computer experiments, the iron in the impacting bodies quickly sank to the core of the proto-Earth, while a significant fraction of silicates was pushed far enough out beyond the geosynchronous limit to constitute the main material of the Moon. Most of any atmosphere would have been pushed aside, rather than being expelled in the impact. However, the energy remaining in the material not going to the core or expelled was still sufficient to raise its temperature some 1000's of degrees, enough to vaporize silicates and to generate a strong 'planetary wind': a hydrodynamic expansion carrying with it virtually all volatiles plus appreciable silicates. This expansion was violent and uneven in its most energetic stage, but probably the resulting magma ocean was global. The duration, until cooling, was sufficient for silicates to condense to melt and the duration was probably short. Comparison of the Earth and Venus indicates that the great impact was extraordinarily effective in removing volatiles from the proto-Earth; in particular, the enormous differences in primordial inert gases between the planets demand a catastrophic difference in origin circumstances. On the other hand, the comparison limits the amount of silicates lost by the Earth to a rather minor fraction; most of that expelled in the wind must have condensed soon enough for the silicate to fall back to Earth or be swept up by the proto-Moon. So the Earth was left with a magma ocean. The question is whether sufficient water was retained to constitute a steam atmosphere. Probably not, but unknowns affecting this question are the efficiencies of outgassing in great impacts and in subsequent convective churnings deep in the mantle. During the stage when mantle convection is turbulent, an appreciable fraction of volatiles were also retained at depth, perhaps in

  1. Depth of origin of magma in eruptions.

    PubMed

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-01-01

    Many volcanic hazard factors--such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses--relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11-15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011-2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide. PMID:24067336

  2. Depth of origin of magma in eruptions

    PubMed Central

    Becerril, Laura; Galindo, Ines; Gudmundsson, Agust; Morales, Jose Maria

    2013-01-01

    Many volcanic hazard factors - such as the likelihood and duration of an eruption, the eruption style, and the probability of its triggering large landslides or caldera collapses - relate to the depth of the magma source. Yet, the magma source depths are commonly poorly known, even in frequently erupting volcanoes such as Hekla in Iceland and Etna in Italy. Here we show how the length-thickness ratios of feeder dykes can be used to estimate the depth to the source magma chamber. Using this method, accurately measured volcanic fissures/feeder-dykes in El Hierro (Canary Islands) indicate a source depth of 11–15 km, which coincides with the main cloud of earthquake foci surrounding the magma chamber associated with the 2011–2012 eruption of El Hierro. The method can be used on widely available GPS and InSAR data to calculate the depths to the source magma chambers of active volcanoes worldwide. PMID:24067336

  3. Gas-driven filter pressing in magmas

    USGS Publications Warehouse

    Sisson, T.W.; Bacon, C.R.

    1999-01-01

    Most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less. The buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization, and this process of gas-driven filter pressing assists the crystallization differentiation of magmas. For gas-driven filter pressing to be effective, the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt These conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs. Gas-driven filter pressing thereby adds fractionated melt to magma bodies. Gas-driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons; this process could also account for the production of voluminous, crystal-poor rhyolites.

  4. More Evidence for Multiple Meteorite Magmas

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-02-01

    Cosmochemists have identified six main compositional types of magma that formed inside asteroids during the first 100 million years of Solar System history. These magmas vary in their chemical and mineralogical make up, but all have in common low concentrations of sodium and other volatile elements. Our low-sodium-magma diet has now changed. Two groups of researchers have identified a new type of asteroidal magma that is rich in sodium and appears to have formed by partial melting of previously unmelted, volatile-rich chondritic rock. The teams, one led by James Day (University of Maryland) and the other by Chip Shearer (University of New Mexico), studied two meteorites found in Antarctica, named Graves Nunatak 06128 and 06129, using a battery of cosmochemical techniques. These studies show that an even wider variety of magmas was produced inside asteroids than we had thought, shedding light on the melting histories and formation of asteroids.

  5. Medical geochemistry of tropical environments

    NASA Astrophysics Data System (ADS)

    Dissanayake, C. B.; Chandrajith, Rohana

    1999-10-01

    Geochemically, tropical environments are unique. This uniqueness stems from the fact that these terrains are continuously subjected to extreme rainfall and drought with resulting strong geochemical fractionation of elements. This characteristic geochemical partitioning results in either severe depletion of elements or accumulation to toxic levels. In both these situations, the effect on plant, animal and human health is marked. Medical geochemistry involves the study of the relationships between the geochemistry of the environment in which we live and the health of the population living in this particular domain. Interestingly, the relationships between geochemistry and health are most marked in the tropical countries, which coincidentally are among the poorest in the world. The very heavy dependence on the immediate environment for sustainable living in these lands enables the medical geochemist to observe correlations between particular geochemical provinces and the incidence of certain diseases unique to these terrains. The aetiology of diseases such as dental and skeletal fluorosis, iodine deficiency disorders, diseases of humans and animals caused by mineral imbalances among others, lie clearly in the geochemical environment. The study of the chemistry of the soils, water and stream sediments in relation to the incidence of geographically distributed diseases in the tropics has not only opened up new frontiers in multidisciplinary research, but has offered new challenges to the medical profession to seriously focus attention on the emerging field of medical geochemistry with the collaboration of geochemists and epidemiologists.

  6. Source component mixing in the regions of arc magma generation

    NASA Astrophysics Data System (ADS)

    Arculus, Richard J.; Powell, Roger

    1986-05-01

    Most recent workers attribute the main features of island arc basalt geochemistry to variable contributions of at least two source components. The major source appears to be the peridotitic wedge of upper mantle overlying the subducted slab, but the nature of the second component and the processes by which the sources become mixed during genesis of arc magmas are in dispute. A metasomatic addition to the wedge resulting from devolatilization in the slab is the simplest explanation of the marked enrichment of the alkali and alkaline earth elements with respect to the rare earths in island arc basalts, together with the variably developed trends in Pb, Sr, and Nd isotopic data toward sedimentary contaminants. However, lack of the correlations between relative degrees of trace element fractionation and radiogenic isotopic ratios expected of such processes requires a more complex explanation. Alternative models that suggest that all of the characteristics of island arc basalts can be accounted for by melting of an intraoceanic, hot spot type of mantle source also face specific difficulties, particularly with regard to the strong depletions of trace high-field-strength elements in arc compared with hot spot magmas. A possible resolution of these specific geochemical difficulties may lie in dynamic transport processes within the wedge linked with the slab through coupled drag, and the marked depression of mantle isotherms in subduction zones. Inefficient escape of melts and subsequent repeated freezing within the overturning wedge can lead to local mineralogic and geochemical heterogeneity of the peridotite overlying the slab. Fluids released from the slab may infiltrate the heterogeneous wedge and preferentially scavenge the alkalis and alkaline earths with respect to the rare earths and high field strength elements from locally enriched portions of the wedge. Incorporation of such metasomatic fluids in renewed melting at shallower but hotter levels within the wedge can

  7. Forecasting the failure of heterogeneous magmas

    NASA Astrophysics Data System (ADS)

    Vasseur, J.; Wadsworth, F. B.; Lavallée, Y.; Bell, A. F.; Main, I. G.; Dingwell, D. B.

    2015-12-01

    Eruption prediction is a long-sought-after goal of volcanology. Yet applying existing techniques retrospectively (hindcasting), we fail to predict events more often than we success. As much of the seismicity associated with intermediate to silicic volcanic eruptions comes from the brittle response of the ascending magma itself, we clearly require a good understanding of the parameters that control the ability to forecast magma failure itself. Here, we present suites of controlled experiments at magmatic temperatures using a range of synthetic magmas to investigate the control of microstructures on the efficacy of forecast models for material failure. We find that the failure of magmas with very little microstructural heterogeneity - such as melts - is very challenging to predict; whereas, the failure of very heterogeneous magmas is always well-predicted. To shed further light on this issue, we provide a scaling law based on the relationship between the microstructural heterogeneity in a magma and the error in the prediction of its failure time. We propose this method be used to elucidate the variable success rate of predicting volcanic predictions. We discuss this scaling in the context of the birth, life and death of structural heterogeneity during magma ascent with specific emphasis on obsidian-forming eruptions such as Chaitèn, 2008. During such eruptions, the repetitive creation and destruction of fractures filled with granular magma, which are thought to be the in situ remnants of seismogenic fracturing itself, are expressions of the life-cycle of heterogeneity in an otherwise coherent, melt-rich magma. We conclude that the next generation of failure forecast tools available to monitoring teams should incorporate some acknowledgment of the magma microstructure and not be solely based on the geophysical signals prior to eruption.

  8. The Effects of Preeruptive Magma Viscosity on Eruption Styles and Magma Eruption Rates

    NASA Astrophysics Data System (ADS)

    Tomiya, A.; Koyaguchi, T.; Kozono, T.; Takeuchi, S.

    2014-12-01

    We have collected data on magma eruption rate, which is one of the most fundamental parameters for a volcanic eruption. There are several compilations on eruption rates, for example, for Plinian eruptions (Carey and Sigurdsson, 1989), basaltic eruptions (Wadge, 1981), lava dome eruptions (Newhall and Melson, 1983), and all combined (Tomiya and Koyaguchi, 1998; Pyle, 2000). However, they did not quantitatively discuss the effects of magma viscosity, which must control eruption rates. Here, we discuss the effects of magma viscosity on eruption rates, by using 'preeruptive magma viscosities', which are important measures of magma eruptibility (Takeuchi, 2011). Preeruptive magma viscosity is the viscosity of magma (melt, dissolved water, and crystals) in the magma chamber at the preeruptive conditions, and can be approximately obtained only by the bulk rock SiO2 and phenocryst content, using an empirical formula (Takeuchi, 2010). We have found some interesting relationships, such as (1) eruption styles and rates are correlated to preeruptive magma viscosity but not correlated to bulk rock composition, and (2) the gap (ratio) in eruption rates between explosive and effusive phases in a series of eruptions is proportional to preeruptive magma viscosity. We also propose, by combining (1) and (2), that (3) the radius (or width) of volcanic conduit is positively correlated with preeruptive magma viscosity. Our data also show that the eruptive magmas are divided into two types. One is the low-viscosity type (basalt ~ phenocryst-poor andesite), characterized by lava flow and sub-Plinian eruptions. The other is the high-viscosity type (phenocryst-rich andesite ~ rhyolite), characterized by lava dome and Plinian eruptions. The boundary is at about 104 Pa s. These two types may be closely linked to the magma generation processes (fractional/batch crystallization vs. extraction from a mushy magma chamber).

  9. Age, geochemistry and melt flux variations for the Hawaiian Ridge

    NASA Astrophysics Data System (ADS)

    Garcia, M. O.; Weis, D. A.; Greene, A. R.; Wessel, P.; Harrison, L.; Tree, J.

    2012-12-01

    The Hawaiian Ridge portion of the Hawaiian-Emperor Chain, the classic example of a mantle plume produced linear island chain, is 6000 km in length, active for 80+ Myr, and tectonically simple. Despite its importance to our understanding of mantle plumes and Cenozoic plate motion, there are large data gaps for the age and geochemistry of lavas from volcanoes along the Hawaiian Ridge (HR) portion of the Chain. Ages: Only volcanoes near the Hawaiian-Emperor bend and in the Hawaiian Islands have modern Ar-Ar ages, leaving a gap of 2000 km where existing K-Ar ages suggest synchronous volcanism over a 1000 km section. Geochemistry: There is a 2900 km gap in high precision geochemical data for the HR. The Emperor Seamounts (>45 Ma) have better regional coverage of recent isotopic data and show a correlation of Sr isotope composition with age of the underlying oceanic lithosphere (Regelous et al. 2003). The HR has an unexplained, exponential increase in magma flux over the last 30 Myr (Vidal & Bonneville 2004). Potential explanations for the increase in magma flux include: changes in melting conditions (temperature and/or pressure), change in source fertility related to rock type (pyroxenite vs. peridotite) or previous melting history, and/or changes in plate stresses resulting from reconfigurations of plate motion. Our new multi-disciplinary project will: 1) Determine 40Ar/39Ar ages, and whole-rock major, trace element, and Pb, Sr, Nd and Hf isotopic geochemistry for lavas from 20 volcanoes spanning ~2150 km of the HR (NW of the Hawaiian Islands). 2) Use the geochemical data to determine the long-term evolution of the Hawaiian mantle plume source components and to evaluate whether there have been systematic variations in mantle potential temperature, melting pressure, and/or source lithology during the creation of the HR. If so, are they responsible for the 300% variation in melt production along the Ridge? Also, we will assess when the more fertile Loa source component

  10. Sequence stratigraphy of Middle Triassic carbonates and terrigenous deposits (Muschelkalk and Lower Keuper) in the SW Germanic Basin: maximum flooding versus maximum depth in intracratonic basins

    NASA Astrophysics Data System (ADS)

    Vecsei, A.; Duringer, P.

    2003-08-01

    We analyze the sequence stratigraphy of the Middle Muschelkalk to the Lower Keuper strata (Middle Triassic) in the SW Germanic Basin. The sequences are interpreted on the basis of a synthesis of facies in the neritic carbonates, terrigenous sediments and evaporites along a basin margin to center transect. Continental sediments (CS, lower Middle Muschelkalk) occur at the base of the Middle-Upper Muschelkalk sequence. Thick retrogradational marginal-marine sediments overlain by open-marine deposits (middle Middle Muschelkalk to lower Upper Muschelkalk) form the transgressive systems tract. In the basin center, only bathymetric criteria are available for recognition of this systems tract. The maximum flooding surface (mfs) at the basin margin differs in age from the maximum depth interval in the basin center. Maximum depth surfaces or intervals (mdi, new term) should be recognized in many deep basins where flooding is not recorded. The highstand systems tract (upper Upper Muschelkalk) is strongly progradational. The upper sequence boundary (Muschelkalk/Keuper boundary) is characterized by subaerial exposure at the basin margin and submarine erosion in most other sections. Along this boundary, the low paleo-relief resulted in a lack of coarse-grained clastic deposits. In the basin center, a strongly regressive succession (lower Lower Keuper) allows, possibly for the first time in an intracratonic basin, the distinction of an early or late lowstand systems tract (ELST or LLST). High-frequency, low-amplitude sea-level fluctuations resulted in parasequences in the open-marine Upper Muschelkalk, but in high-frequency sequences in the coastal plain sediments of the overlying parts of the Lower Keuper.

  11. Hyperextension, micro-continents, magma-poor and magma-rich segments in the pre-Caledonian margin of Baltica: research in progress

    NASA Astrophysics Data System (ADS)

    Andersen, Torgeir B.; Jakob, Johannes; Jørgen Kjøll, Hans; Corfu, Fernando; Tegner, Christian; Alsaif, Manar; Enger, Ander S.; Kjeldberg, Øystein

    2016-04-01

    The more than 2400 km long pre-Caledonian passive margin of Baltica evolved into a highly complex geological province, formed by magma-poor and magma-rich rifting and extreme crustal attenuation in the late Neoproterozoic (Ediacaran) and the Cambrian. Transition from continental rifting and extension to oceanic spreading was probably related to emplacement of a ~610-590 Ma Large Igneous Province (LIP) dominated by basalt magmatism. The LIP geochemistry and aspects of the dyke-swarm emplacement and geometries will be discussed further in other presentations at this meeting (see abstracts by Chr. Tegner et al. and HJ. Kjøll et al.). The magma-rich domain presently constitutes a more than 800km long segment in central Scandinavia. This segment shows transitions into a magma-poor domain in south-central Norway and possibly also in the north (see abstracts by J.Jakob et al.1 & 2 and F. Corfu & TB. Andersen). The magma-poor southern segment is dominated by large crystalline nappe complexes (NC) of Proterozoic continental crust with Baltican affinity, comprising both lower- to upper crustal units in the Jotun, Lindås and Bergsdalen NCs, respectively. These NCs are underlain and partly inter-finger with the melange matrix dominated by deep marine metasediments. The melange also contains numerous exhumed solitary mantle-peridotite, ophicarbonates and smaller slivers of Proterozoic gneisses of Baltican age affinity, as well as local coarser-grained meta-sediments including conglomerates and monomict detrital serpentinites. Some of these large crystalline nappes probably constituted structural highs of continental slivers or even micro-continents separated by hyperextended to immature oceanic (?) basins along the ancient margin of Baltica. The youngest basin sediments in the melange(s) are of Lower-Middle Ordovician age, as demonstrated by fossils and minimum ages of clastic zircons. Further details, including age and metamorphism as well as stable isotope signature of

  12. Eruption Depths, Magma Storage and Magma Degassing at Sumisu Caldera, Izu-Bonin Arc: Evidence from Glasses and Melt Inclusions

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.

    2015-12-01

    Island arc volcanoes can become submarine during cataclysmal caldera collapse. The passage of a volcanic vent from atmospheric to under water environment involves complex modifications of the eruption style and subsequent transport of the pyroclasts. Here, we use FTIR measurements of the volatile contents of glass and melt inclusions in the juvenile pumice clasts in the Sumisu basin and its surroundings (Izu-Bonin arc) to investigate changes in eruption depths, magma storage and degassing over time. This study is based on legacy cores from ODP 126, where numerous unconsolidated (<65 ka), extremely thick (few m to >250 m), massive to normally graded pumice lapilli-tuffs were recovered over four cores (788C, 790A, 790B and 791A). Glass and clast geochemistry indicate the submarine Sumisu caldera as the source of several of these pumice lapilli-tuffs. Glass chips and melt inclusions from these samples were analyzed using FTIR for H2O and CO2 contents. Glass chips record variable H2O contents; most chips contain 0.6-1.6 wt% H2O, corresponding to eruption depths of 320-2100 mbsl. Variations in glass H2O and pressure estimates suggest that edifice collapse occurred prior-to or during eruption of the oldest of these samples, and that the edifice may have subsequently grown over time. Sanidine-hosted melt inclusions from two units record variably degassed but H2O-rich melts (1.1-5.6 wt% H2O). The lowest H2O contents overlap with glass chips, consistent with degassing and crystallization of melts until eruption, and the highest H2O contents suggest that large amounts of degassing accompanied likely explosive eruptions. Most inclusions, from both units, contain 2-4 wt% H2O, which further indicates that the magmas crystallized at pressures of ~50-100 MPa, or depths ~400-2800 m below the seafloor. Further glass and melt inclusion analyses, including major element compositions, will elucidate changes in magma storage, degassing and evolution over time.

  13. Zircon chemistry and magma mixing, SE China: In-situ analysis of Hf isotopes, Tonglu and Pingtan igneous complexes

    NASA Astrophysics Data System (ADS)

    Griffin, W. L.; Wang, Xiang; Jackson, S. E.; Pearson, N. J.; O'Reilly, Suzanne Y.; Xu, Xisheng; Zhou, Xinmin

    2002-04-01

    Field relations and whole-rock geochemistry indicate that magma mixing has been important in the genesis of the late Mesozoic I-type igneous complexes at Pingtan and Tonglu in SE China. Morphological and trace-element studies of zircon populations in rocks from each of these complexes have defined several distinct growth stages [Mineral. Mag. (2001)]. In-situ LAM-MC-ICPMS microanalysis shows large variations in 176Hf/ 177Hf (up to 15 ɛHf units) between zircons of different growth stages within a single rock, and between zones within single zircon grains (up to 9 ɛHf units). These variations suggest that each of the observed magmas in both complexes developed through hybridisation of ≥2 magmas with different sources. Although this mixing has produced similar Sr and Nd isotopic compositions in the different rock types of each complex, the zircons have functioned as "tape recorders" and have preserved details of the assembly of the different magmas. In the Tonglu complex the most primitive magma is a mafic monzonite (preserved as enclaves), whose isotopic composition suggests derivation from the lower crust; rhyodacites, rhyolites and quartz diorites reflect the mixing of the monzonite with ≥2 more felsic magmas, derived from older crustal materials. In the Pingtan complex, zircons in a quartz diorite enclave suggest mixing between a crustal magma and a more primitive mantle-derived component. Zircons from granites and granodiorite enclaves indicate mixing between the quartz diorite and more felsic melts with lower 176Hf/ 177Hf. Major changes in 176Hf/ 177Hf correlate with discontinuous changes in the trace-element composition and morphology of the zircons, in particular the development of sector zoning that suggests rapid disequilibrium crystallisation. We suggest that the magma mixing recorded by the changes in 176Hf/ 177Hf occurred during transport in magma conduits. The in-situ analysis of Hf-isotopic stratigraphy in zircons is a new and powerful tool for

  14. Reconstructing magma reservoir dynamics from field evidence

    NASA Astrophysics Data System (ADS)

    Verberne, R.; Muntener, O.; Ulmer, P.

    2013-12-01

    Reconstructing the dynamics within magma reservoirs during and after emplacement greatly enhance our understanding of their formation and evolution. By determining the length and timescales over which magma remains mobile within magma reservoirs, fluxes of magma that is possibly extractable can be quantified, providing a link between plutonic and volcanic systems, and constraints on the likelihood of a pluton feeding volcanic eruptions. However, the general absence of marker beds and uncertainties regarding at which crystal fractions super-solidus foliation patterns are recorded make it difficult to reconstruct and quantify deformation inside plutons, especially the deformation that occurred at low crystal fractions. Here we present a case study of the Listino Ring Structure (LRS) of the Adamello Batholith in N-Italy, a 300-500 m-wide semi-circular zone of intensely foliated tonalite containing abundant evidence for magmatic deformation and magma mingling (Brack, 1984). The differences in the interaction between felsic and mafic magmas recorded in the form of mafic dikes, sheets and enclaves can be used to determine spatial and/or temporal differences of magma rheology during evolution of the reservoir. Detailed field mapping shows a clear difference in intrusion style between the southern and eastern sides of the LRS, as mafic magma intrudes into different felsic host magmas. An attempt is made to quantify these differences in terms of the physical state of the host magmas, using a variety of analyses pertaining to the breakup of mafic dikes into enclaves, the assimilation of phenocrysts from the host magma by the mafic magma, and the back-veining of mafic dikes and enclaves. The common component of these analyses is a parametrization of the phase petrology of the magmas as a function of temperature, which allows for the determination of melt fraction and composition at super-solidus conditions, from which physical properties such as density and viscosity can be

  15. Evidence for seismogenic fracture of silicic magma.

    PubMed

    Tuffen, Hugh; Smith, Rosanna; Sammonds, Peter R

    2008-05-22

    It has long been assumed that seismogenic faulting is confined to cool, brittle rocks, with a temperature upper limit of approximately 600 degrees C (ref. 1). This thinking underpins our understanding of volcanic earthquakes, which are assumed to occur in cold rocks surrounding moving magma. However, the recent discovery of abundant brittle-ductile fault textures in silicic lavas has led to the counter-intuitive hypothesis that seismic events may be triggered by fracture and faulting within the erupting magma itself. This hypothesis is supported by recent observations of growing lava domes, where microearthquake swarms have coincided with the emplacement of gouge-covered lava spines, leading to models of seismogenic stick-slip along shallow shear zones in the magma. But can fracturing or faulting in high-temperature, eruptible magma really generate measurable seismic events? Here we deform high-temperature silica-rich magmas under simulated volcanic conditions in order to test the hypothesis that high-temperature magma fracture is seismogenic. The acoustic emissions recorded during experiments show that seismogenic rupture may occur in both crystal-rich and crystal-free silicic magmas at eruptive temperatures, extending the range of known conditions for seismogenic faulting. PMID:18497823

  16. Numerical modeling of bubble dynamics in magmas

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Su, Yanqing; Parmigiani, Andrea

    2014-05-01

    Understanding the complex non-linear physics that governs volcanic eruptions is contingent on our ability to characterize the dynamics of bubbles and its effect on the ascending magma. The exsolution and migration of bubbles has also a great impact on the heat and mass transport in and out of magma bodies stored at shallow depths in the crust. Multiphase systems like magmas are by definition heterogeneous at small scales. Although mixture theory or homogenization methods are convenient to represent multiphase systems as a homogeneous equivalent media, these approaches do not inform us on possible feedbacks at the pore-scale and can be significantly misleading. In this presentation, we discuss the development and application of bubble-scale multiphase flow modeling to address the following questions : How do bubbles impact heat and mass transport in magma chambers ? How efficient are chemical exchanges between the melt and bubbles during magma decompression? What is the role of hydrodynamic interactions on the deformation of bubbles while the magma is sheared? Addressing these questions requires powerful numerical methods that accurately model the balance between viscous, capillary and pressure stresses. We discuss how these bubble-scale models can provide important constraints on the dynamics of magmas stored at shallow depth or ascending to the surface during an eruption.

  17. History of the recognition of organic geochemistry in geoscience

    USGS Publications Warehouse

    Kvenvolden, K.A.

    2002-01-01

    The discipline of organic geochemistry is an outgrowth of the application of the principles and methods of organic chemistry to sedimentary geology. Its origin goes back to the last part of the nineteenth century and the first part of the twentieth century concurrent with the evolution of the applied discipline of petroleum geochemistry. In fact, organic geochemistry was strongly influenced by developments in petroleum geochemistry. Now, however, organic geochemistry is considered an umbrella geoscience discipline of which petroleum geochemistry is an important component.

  18. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2004-01-01

    The research described in this progress report involved the study of petrological, geochemical, and volcanic processes that occur on the Moon and the SNC meteorite parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the types of magmas (magma compositions) present, the role of volatiles in magmatic processes, and on processes of magma evolution on these planets. We are also interested in how these processes and magma types varied over time.In earlier work on the A15 green and A17 orange lunar glasses, we discovered a variety of metal blebs. Some of these Fe-Ni metal blebs occur in the glass; others (in A17) were found in olivine phenocrysts that we find make up about 2 vol 96 of the orange glass magma. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption . They also yield important information about the composition of the gas phase present, the gas that drove the lunar fire-fountaining. During the tenure of this grant, we have continued to work on the remaining questions regarding the origin and evolution of the gas phase in lunar basaltic magmas, what they indicate about the lunar interior, and how the gas affects volcanic eruptions. Work on Martian magmas petrogenesis questions during the tenure of this grant has resulted in advances in our methods of evaluating magmatic oxidation state variations in Mars and some new insights into the compositional variations that existed in the SNC magmas over time . Additionally, Minitti has continued to work on the problem of possible shock effects on the abundance and distribution of water in Mars minerals.

  19. Magma Beneath Yellowstone National park.

    PubMed

    Eaton, G P; Christiansen, R L; Iyer, H M; Pitt, A D; Mabey, D R; Blank, H R; Zietz, I; Gettings, M E

    1975-05-23

    The Yellowstone plateau volcanic field is less than 2 million years old, lies in a region of intense tectonic and hydrothermal activity, and probably has the potential for further volcanic activity. The youngest of three volcanic cycles in the field climaxed 600,000 years ago with a voluminous ashflow eruption and the collapse of two contiguous cauldron blocks. Doming 150,000 years ago, followed by voluminous rhyolitic extrusions as recently as 70,000 years ago, and high convective heat flow at present indicate that the latest phase of volcanism may represent a new magmatic insurgence. These observations, coupled with (i) localized postglacial arcuate faulting beyond the northeast margin of the Yellowstone caldera, (ii) a major gravity low with steep bounding gradients and an amplitude regionally atypical for the elevation of the plateau, (iii) an aeromagnetic low reflecting extensive hydrothermal alteration and possibly indicating the presence of shallow material above its Curie temperature, (iv) only minor shallow seismicity within the caldera (in contrast to a high level of activity in some areas immediately outside), (v) attenuation and change of character of seismic waves crossing the caldera area, and (vi) a strong azimuthal pattern of teleseismic P-wave delays, strongly suggest that a body composed at least partly of magma underlies the region of the rhyolite plateau, including the Tertiary volcanics immediately to its northeast. The Yellowstone field represents the active end of a system of similar volcanic foci that has migrated progressively northeastward for 15 million years along the trace of the eastern Snake River Plain (8). Regional aeromagnetic patterns suggest that this course was guided by the structure of the Precambrian basement. If, as suggested by several investigators (24), the Yellowstone magma body marks a contemporary deep mantle plume, this plume, in its motion relative to the North American plate, would appear to be "navigating" along a

  20. Volatiles Which Increase Magma Viscosity

    NASA Astrophysics Data System (ADS)

    Webb, S.

    2015-12-01

    The standard model of an erupting volcano is one in which the viscosity of a decompressing magma increases as the volatiles leave the melt structure to form bubbles. It has now been observed that the addition of the "volatiles" P, Cl and F result in an increase in silicate melt viscosity. This observation would mean that the viscosity of selected degassing magmas would decrease rather than increase. Here we look at P, Cl and F as three volatiles which increase viscosity through different structural mechanisms. In all three cases the volatiles increase the viscosity of peralkaline composition melts, but appear to always decrease the viscosity of peraluminous melts. Phosphorus causes the melt to unmix into a Na-P rich phase and a Na-poor silicate phase. Thus as the network modifying Na (or Ca) are removed to the phosphorus-rich melt, the matrix melt viscosity increases. With increasing amounts of added phosphorus (at network modifying Na ~ P) the addition of further phosphorus causes a decrease in viscosity. The addition of chlorine to Fe-free aluminosilicate melts results in an increase in viscosity. NMR data on these glass indicates that the chlorine sits in salt-like structures surrounded by Na and/or Ca. Such structures would remove network-modifying atoms from the melt structure and thus result in an increase in viscosity. The NMR spectra of fluorine-bearing glasses shows that F takes up at least 5 different structural positions in peralkaline composition melts. Three of these positions should result in a decrease in viscosity due to the removal of bridging oxygens. Two of the structural positons of F, however, should result in an increase in viscosity as they require the removal of network-modifying atoms from the melt structure (with one of the structures being that observed for Cl). This would imply that increasing amounts of F might result in an increase in viscosity. This proposed increase in viscosity with increasing F has now been experimentally confirmed.

  1. Volcanology and Geochemistry of the Taney Seamounts northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Coumans, J. P.; Clague, D. A.; Stix, J.

    2011-12-01

    The Taney seamounts are a NW-SE trending, linear, near-ridge chain consisting of five submarine volcanoes located on the Pacific plate 300 km west of San Francisco, California. Morphologically, the seamounts are characterized as truncated cones with nested calderas decreasing in age towards the ridge axis. This study examines the volcanology and geochemistry of the largest and oldest seamount, (Taney A, ~26 Ma), which is comprised of four well-exposed nested calderas. Each successive collapse event exposes previously infilled lavas, defining a relative chronology. The caldera walls and intracaldera pillow mounds were carefully sampled by the remotely operated vehicle (ROV) Doc Ricketts to obtain stratigraphically-controlled samples. Whole rock samples were analyzed for major and trace elements, volcanic glasses were analyzed for major and volatile elements(S, Cl), and plagioclase phenocrysts were separated for mineral and glass inclusion microprobe analysis. Overall, the erupted lavas are mostly subalkalic mid-ocean ridge basalts (MORB) varying from differentiated to more primitive (6.0 - 8.2 wt. % MgO) with decreasing age. Incompatible elements and REE profiles normalized to primitive mantle suggest that the lavas are transitional to slightly enriched (0.1 - 0.3 wt. % K2O; 1.1 - 2.2 wt. % TiO2), which is unusual for near-ridge seamounts. Sc, which is compatible in clinopyroxene, increases linearly with TiO2 at primitive compositions (>7.0 wt. % MgO). In more evolved seamount basalts (<7.0 wt. % MgO), the low CaO and Sc contents and decreasing CaO/Al2O3 suggest that there is either extensive clinopyroxene fractionation, or mixing with magmas that have undergone extensive clinopyroxene fractionation. MELTS modeling suggests that clinopyroxene fractionation occurs at <6.0 wt. % MgO, inconsistent with the observed clinopyroxene imprint at <7.0 wt. % MgO. The discrepancy could indicate magma mixing. Although whole rock ICP-MS data have some scatter, especially for

  2. Rethinking early Earth phosphorus geochemistry

    PubMed Central

    Pasek, Matthew A.

    2008-01-01

    Phosphorus is a key biologic element, and a prebiotic pathway leading to its incorporation into biomolecules has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochemistry of phosphorus on the early Earth was instead controlled by reduced oxidation state phosphorus compounds such as phosphite (HPO32−), which are more soluble and reactive than orthophosphates. This reduced oxidation state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atmosphere. This alternate view of early Earth phosphorus geochemistry provides an unexplored route to the formation of pertinent prebiotic phosphorus compounds, suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochemical usage of reduced oxidation state phosphorus compounds in life today. Possible studies are suggested that may detect reduced oxidation state phosphorus compounds in ancient Archean rocks. PMID:18195373

  3. Petrogenesis of the Late Triassic volcanic rocks in the Southern Yidun arc, SW China: Constraints from the geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Leng, Cheng-Biao; Huang, Qiu-Yue; Zhang, Xing-Chun; Wang, Shou-Xu; Zhong, Hong; Hu, Rui-Zhong; Bi, Xian-Wu; Zhu, Jing-Jing; Wang, Xin-Song

    2014-03-01

    Studies on zircon ages, petrology, major and trace element geochemistry, and Sr-Nd-Hf-Pb isotopic geochemistry of intermediate volcanic rocks from the Southern Yidun arc, Sanjiang-Tethyan Orogenic Belt, SW China have been undertaken in this paper. They are used to discuss the petrogenesis of these rocks and to constrain the tectonic setting and evolution of the Yidun arc. These intermediate volcanic rocks were erupted at ca. 220 Ma (U-Pb zircon ages). Trachyandesite is the dominant lithology among these volcanic rocks, and is mainly composed of hornblende and plagioclase, with minor clinopyroxene and biotite. A hornblende geobarometer suggests that the stagnation of magma in the lower crust, where plagioclase crystallization was suppressed while hornblende crystallized, giving rise to high Sr/Y ratios that are one of the distinguishing features of adakites, after the primary magma originated from the lithospheric mantle wedge. Steeply right-inclined Rare Earth Element (REE) pattern combined with high La/Yb ratios suggests adakitic affinity of these volcanic rocks, implying that slab-melt from the subducting oceanic crust is a necessary component in the primary magma. Besides, trace element geochemistry and isotopic geochemistry also indicate that partial melting of pelagic sediments in the subduction zone and noticeable contamination with the lower crust were involved in the evolution of parental magma of these volcanic rocks. Based on previous work on the Northern Yidun arc and this study, we propose that the subduction was initiated in the Northern Yidun arc and extended to the southern part and that the Northern Yidun arc is an island arc while the Southern Yidun arc represents a continental arc, probably caused by the existence of the Zhongza Massif, that was invoked to be derived from Yangtze Block, as a possible basement of the Southern Yidun arc.

  4. Process for forming hydrogen and other fuels utilizing magma

    DOEpatents

    Galt, John K.; Gerlach, Terrence M.; Modreski, Peter J.; Northrup, Jr., Clyde J. M.

    1978-01-01

    The disclosure relates to a method for extracting hydrogen from magma and water by injecting water from above the earth's surface into a pocket of magma and extracting hydrogen produced by the water-magma reaction from the vicinity of the magma.

  5. Thermal stress fracturing of magma simulant materials

    SciTech Connect

    Wemple, R.P.; Longcope, D.B.

    1986-10-01

    Direct contact heat exchanger concepts for the extraction of energy from magma chambers are being studied as part of the DOE-funded Magma Energy Research Program at Sandia National Laboratories. These concepts require the solidification of molten material by a coolant circulated through a borehole drilled into the magma and subsequent fracture of the solid either as a natural consequence of thermal stress or by deliberate design (intentional flaws, high pressure, etc.). This report summarizes the results of several thermal stress fracturing experiments performed in the laboratory and compares the results with an analysis developed for use as a predictive tool. Information gained from this test series has been the basis for additional work now under way to simulate magma melt solidification processes.

  6. Rheology of Halogen-Rich Magmas

    NASA Astrophysics Data System (ADS)

    Webb, S. L.

    2010-12-01

    The degassing of magma as it rises through the volcanic conduit to the surface affects the viscosity and rate of movement of the magma. While the production of bubbles in the magma decreases the density of the magma and thus increases its rate of ascent, the loss of volatiles from the magma, in general, results in an increase in the viscosity. This is the ideal scenario for the deformation rate of the magma crossing the relaxation timescale of the increasingly viscous magma which can result in the shattering of the magma in its unrelaxed (glassy) state; which results in an explosive eruption and pyroclastic flow. The effect of the volatiles H2O and F on magma viscosity and relaxation timescale have been extensively studied; with 1 mol% F2O-1 or H2O causing a 4 to 5 order of magnitude decrease in viscosity at ca. 800 C. Early determinations of the effect of chlorine on melt viscosity, however, indicated that chlorine increases the viscosity of Al-bearing melts (but decreases the viscosity of Al-free synthetic melts). Thus the degassing of chlorine would result in a decrease in magma viscosity and a distancing of the physical condition of the magma from the shattering of the magma as it rises to the surface. The viscosity of chlorine-bearing peralkaline Na2O-CaO-Al2O3-SiO2 melts has been investigated using micro-penetration techniques in the 108 - 1013 Pa s viscosity range. The presence of 0.5 mol% (0.6 wt%) Cl2O-1 increases viscosity by 0.5 log10 units. A similar amount of H2O or F2O-1 would decrease viscosity by 2.5 orders of magnitude in this viscosity range. More information about the relative solubility of Cl, F and H2O as a function of composition, temperature and pressure is needed before one can model the relative effects of degassing volatiles on the rheology of magmas. Very little is known about the structural role of chlorine in silicate melts. NMR studies of Na2O-CaO-Al2O3-SiO2 glasses have shown that chlorine does not bond to Al (in contrast to fluorine

  7. Progressive enrichment of arc magmas caused by the subduction of seamounts under Nishinoshima volcano, Izu-Bonin Arc, Japan

    NASA Astrophysics Data System (ADS)

    Sano, Takashi; Shirao, Motomaro; Tani, Kenichiro; Tsutsumi, Yukiyasu; Kiyokawa, Shoichi; Fujii, Toshitsugu

    2016-06-01

    The chemical composition of intraplate seamounts is distinct from normal seafloor material, meaning that the subduction of seamounts at a convergent margin can cause a change in the chemistry of the mantle wedge and associated arc magmas. Nishinoshima, a volcanic island in the Izu-Bonin Arc of Japan, has been erupting continuously over the past 2 years, providing an ideal opportunity to examine the effect of seamount subduction on the chemistry of arc magmas. Our research is based on the whole-rock geochemistry and the chemistry of minerals within lavas and air-fall scoria from Nishinoshima that were erupted before 1702, in 1973-1974, and in 2014. The mineral phases within the analyzed samples crystallized under hydrous conditions (H2O = 3-4 wt.%) at temperatures of 970 °C-990 °C in a shallow (3-6 km depth) magma chamber. Trace element data indicate that the recently erupted Nishinoshima volcanics are much less depleted in the high field strength elements (Nb, Ta, Zr, Hf) than other volcanics within the Izu-Bonin Arc. In addition, the level of enrichment in the Nishinoshima magmas has increased in recent years, probably due to the addition of material from HIMU-enriched (i.e., high Nb/Zr and Ta/Hf) seamounts on the Pacific Plate, which is being subducted westwards beneath the Philippine Sea Plate. This suggests that the chemistry of scoria from Nishinoshima volcano records the progressive addition of components derived from subducted seamounts.

  8. Rates of Magma Transfer in the Crust: Insights into Magma Reservoir Recharge and Pluton Growth

    NASA Astrophysics Data System (ADS)

    Menand, T.; Annen, C.; De Saint Blanquat, M.

    2014-12-01

    Plutons have long been viewed as crystallized remnants of large magma reservoirs, a concept now challenged by high precision geochronological data coupled with thermal models. Similarly, the classical view of silicic eruptions fed by long-lived magma reservoirs that slowly differentiate between mafic recharges is being questioned by petrological and geophysical studies. In both cases, a key and yet unresolved issue is the rate of magma transfer in the crust. Here, we use thermal analysis of magma transport to calculate the minimum rate of magma transfer through dykes. We find that unless the crust is exceptionally hot the recharge of magma reservoirs requires a magma supply rate of at least ~ 0.01 km3/yr, much higher than the long-term growth rate of plutons, which demonstrates unequivocally that igneous bodies must grow incrementally. This analysis argues also for magma reservoirs being short-lived and erupting rapidly after a recharge of already differentiated magma. These findings have strong implications for the monitoring of dormant volcanic systems, and raise questions on our ability to interpret geodetic surface signals related to incipient eruptions.

  9. Magma Chambers, Thermal Energy, and the Unsuccessful Search for a Magma Chamber Thermostat

    NASA Astrophysics Data System (ADS)

    Glazner, A. F.

    2015-12-01

    Although the traditional concept that plutons are the frozen corpses of huge, highly liquid magma chambers ("big red blobs") is losing favor, the related notion that magma bodies can spend long periods of time (~106years) in a mushy, highly crystalline state is widely accepted. However, analysis of the thermal balance of magmatic systems indicates that it is difficult to maintain a significant portion in a simmering, mushy state, whether or not the system is eutectic-like. Magma bodies cool primarily by loss of heat to the Earth's surface. The balance between cooling via energy loss to the surface and heating via magma accretion can be denoted as M = ρLa/q, where ρ is magma density, L is latent heat of crystallization, a is the vertical rate of magma accretion, and q is surface heat flux. If M>1, then magma accretion outpaces cooling and a magma chamber forms. For reasonable values of ρ, L, and q, the rate of accretion amust be > ~15 mm/yr to form a persistent volume above the solidus. This rate is extremely high, an order of magnitude faster than estimated pluton-filling rates, and would produce a body 10 km thick in 700 ka, an order of magnitude faster than geochronology indicates. Regardless of the rate of magma supply, the proportion of crystals in the system must vary dramatically with depth at any given time owing to transfer of heat. Mechanical stirring (e.g., by convection) could serve to homogenize crystal content in a magma body, but this is unachievable in crystal-rich, locked-up magma. Without convection the lower part of the magma body becomes much hotter than the top—a process familiar to anyone who has scorched a pot of oatmeal. Thermal models that succeed in producing persistent, large bodies of magma rely on scenarios that are unrealistic (e.g., omitting heat loss to the planet's surface), self-fulfilling prophecies (e.g., setting unnaturally high temperatures as fixed boundary conditions), or physically unreasonable (e.g., magma is intruded

  10. Silicic magma generation at Askja volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Sigmarsson, O.

    2009-04-01

    Rate of magma differentiation is an important parameter for hazard assessment at active volcanoes. However, estimates of these rates depend on proper understanding of the underlying magmatic processes and magma generation. Differences in isotope ratios of O, Th and B between silicic and in contemporaneous basaltic magmas have been used to emphasize their origin by partial melting of hydrothermally altered metabasaltic crust in the rift-zones favoured by a strong geothermal gradient. An alternative model for the origin of silicic magmas in the Iceland has been proposed based on U-series results. Young mantle-derived mafic protolith is thought to be metasomatized and partially melted to form the silicic end-member. However, this model underestimates the compositional variations of the hydrothermally-altered basaltic crust. New data on U-Th disequilibria and O-isotopes in basalts and dacites from Askja volcano reveal a strong correlation between (230Th/232Th) and delta 18O. The 1875 AD dacite has the lowest Th- and O isotope ratios (0.94 and -0.24 per mille, respectively) whereas tephra of evolved basaltic composition, erupted 2 months earlier, has significantly higher values (1.03 and 2.8 per mille, respectively). Highest values are observed in the most recent basalts (erupted in 1920 and 1961) inside the Askja caldera complex and out on the associated fissure swarm (Sveinagja basalt). This correlation also holds for older magma such as an early Holocene dacites, which eruption may have been provoked by rapid glacier thinning. Silicic magmas at Askja volcano thus bear geochemical signatures that are best explained by partial melting of extensively hydrothermally altered crust and that the silicic magma source has remained constant during the Holocene at least. Once these silicic magmas are formed they appear to erupt rapidly rather than mixing and mingling with the incoming basalt heat-source that explains lack of icelandites and the bi-modal volcanism at Askja

  11. Are the Clast Lithologies Contained in Lunar Breccia 64435 Mixtures of Anorthositic Magmas

    NASA Technical Reports Server (NTRS)

    Simon, J. I.; Mittlefehldt, D. W.; Peng, Z. X.; Nyquist, L. E.; Shih, C.-Y.; Yamaguchi, A.

    2015-01-01

    The anorthositic crust of the Moon is often used as the archtypical example of a primary planetary crust. The abundance and purity of anorthosite in the Apollo sample collection and remote sensing data are generally attributed to an early global magma ocean which produced widespread floating plagioclase cumulates (the ferroan anorthosites; FANs. Recent geochronology studies report evidence of young (less than 4.4 Ga) FAN ages, which suggest that either some may not be directly produced from the magma ocean or that the final solidification age of the magma ocean was younger than previous estimates. A greater diversity of anorthositic rocks have been identified among lunar meteorites as compared to returned lunar samples. Granted that these lithologies are often based on small clasts in lunar breccias and therefore may not represent their actual whole rock composition. Nevertheless, as suggested by the abundance of anorthositic clasts with Mg# [Mg/(Mg+Fe)] less than 0.80 and the difficulty of producing the extremely high plagioclase contents observed in Apollo samples and the remote sensing data, modification of the standard Lunar Magma Ocean (LMO) model may be in order. To ground truth mission science and to further test the LMO and other hypotheses for the formation of the lunar crust, additional coordinated petrology and geochronology studies of lunar anorthosites would be informative. Here we report new mineral chemistry and trace element geochemistry studies of thick sections of a composite of FAN-suite igneous clasts contained in the lunar breccia 64435 in order to assess the significance of this type of sample for petrogenetic studies of the Moon. This work follows recent isotopic studies of the lithologies in 64435 focusing on the same sample materials and expands on previous petrology studies who identified three lithologies in this sample and worked on thin sections.

  12. Describing the chemical character of a magma

    NASA Astrophysics Data System (ADS)

    Duley, Soma; Vigneresse, Jean-Louis; Chattaraj, Pratim K.

    2010-05-01

    We introduce the concepts of hard-soft acid-base (HSAB) and derive parameters to characterize a magma that consists either of a solid rock, a melt or its exsolved gaseous phase. Those parameters are the electronegativity, hardness, electrophilicity, polarisability and optical basicity. They determine the chemical reactivity of each component individually, or its equivalence in the case of a complex system of elements or oxides. This results from equalization methods or from direct computation through density functional theory (DFT). Those global parameters help in characterizing magma, provide insights into the reactivity of the melt or its fluid phase when in contact with another magma, or when considering the affinity of each component for metals. In particular, the description leads to a better understanding on the mechanisms that control metal segregation and transportation during igneous activity. The trends observed during magma evolution, whether they follow a mafic or a felsic trend are also observed using these parameters and can be interpreted as approaching a greater stability. Nevertheless, the trend for felsic magma occurs at constant electrophilicity toward a silica pole of great hardness. Conversely, mafic magmas evolve at a constant hardness and decreasing electrophilicity

  13. Basaltic injections into floored silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Wiebe, R. A.

    Recent studies have provided compelling evidence that many large accumulations of silicic volcanic rocks erupted from long-lasting, floored chambers of silicic magma that were repeatedly injected by basaltic magma. These basaltic infusions are commonly thought to play an important role in the evolution of the silicic systems: they have been proposed as a cause for explosive silicic eruptions [Sparks and Sigurdsson, 1977], compositional variation in ash-flow sheets [Smith, 1979], mafic magmatic inclusions in silicic volcanic rocks [Bacon, 1986], and mixing of mafic and silicic magmas [Anderson, 1976; Eichelberger, 1978]. If, as seems likely, floored silicic magma chambers have frequently been invaded by basalt, then plutonic bodies should provide records of these events. Although plutonic evidence for mixing and commingling of mafic and silicic magmas has been recognized for many years, it has been established only recently that some intrusive complex originated through multiple basaltic injections into floored chambers of silicic magma [e.g., Wiebe, 1974; Michael, 1991; Chapman and Rhodes, 1992].

  14. Final report - Magma Energy Research Project

    SciTech Connect

    Colp, J.L.

    1982-10-01

    Scientific feasibility was demonstrated for the concept of magma energy extraction. The US magma resource is estimated at 50,000 to 500,000 quads of energy - a 700- to 7000-yr supply at the current US total energy use rate of 75 quads per year. Existing geophysical exploration systems are believed capable of locating and defining magma bodies and were demonstrated over a known shallow buried molten-rock body. Drilling rigs that can drill to the depths required to tap magma are currently available and experimental boreholes were drilled well into buried molten rock at temperatures up to 1100/sup 0/C. Engineering materials compatible with the buried magma environment are available and their performances were demonstrated in analog laboratory experiments. Studies show that energy can be extracted at attractive rates from magma resources in all petrologic compositions and physical configurations. Downhole heat extraction equipment was designed, built, and demonstrated successfully in buried molten rock and in the very hot margins surrounding it. Two methods of generating gaseous fuels in the high-temperature magmatic environment - generation of H/sub 2/ by the interaction of water with the ferrous iron and H/sub 2/, CH/sub 4/, and CO generation by the conversion of water-biomass mixtures - have been investigated and show promise.

  15. Magma reservoir systems inferred from tilt patterns

    NASA Astrophysics Data System (ADS)

    Schimozuru, D.

    1981-09-01

    Inflation patterns based on water-tube tiltmeter and levelling observation show different features for Krafla Volcano in Iceland and Kilauea Volcano in Hawaii. Monotonous sawtooth shape inflation is observed at Krafla, while inflation curves at Kileauea are more or less complicated. The difference was attributed to differences in the system of magma reservoir for the two volcanoes. By using the electrical equivalent of a magma reservoir and volcanic conduit as a capacitor and a resistor, an electrical oseillator was considered to be a possible model for a magma reservoir system. In the case of Krafla, the magma reservoir system is replaced with one electric oscillator called «Single system» or «Icelandic type» system. The complicated inflation pattern of Kilauea was interpreted as the assembly of a main magma reservoir and the group of surrounding small reservoirs. The equivalent electric analogue is the composite parallel and serial connection of a single oscillator which generates irregular output voltage during a charging process. The proposed magma reservoir system of Kilauea is called «Multi-coupled system» or «Hawaiian type system» which also help in interpreting the wondering of the uplift center and tidal phenomena of the Halemaumau lava lake.

  16. Rift flank uplift and thermal evolution of an intracratonic rift basin (eastern Canada) determined by combined apatite and zircon (U-Th)/He thermochronology

    NASA Astrophysics Data System (ADS)

    Hardie, Rebecca; Schneider, David; Metcalf, James; Flowers, Rebecca

    2015-04-01

    As a significant portion of the world's oil reserves are retrieved from rift systems, a better understanding of the timing of thermal evolution and burial history of these systems will increase the potential for the discovery of hydrocarbon-bearing rifts. The Ottawa Embayment of the St. Lawrence Platform of eastern Canada is a reactivated intracratonic rift basin related to the opening of the Iapetus Ocean at ca. 620-570 Ma, followed by the formation of the well-developed continental passive margin. Siliciclastic sediments derived from the adjacent uplifted Neoproterozoic Grenville basement provide the basin fill material. Apatite and zircon (U-Th)/He thermochronology allows for low-temperature analysis across the exposed crystalline rift flank into the synrift sedimentary sequence to resolve the unroofing, burial and subsidence history of the region. Samples were collected along a ~250 km NE-SW transect, oblique to the axis of the rift, from Mont-Tremblant, Québec (~900 m) to the central axis of the Paleozoic rift in the Southern Ontario Lowlands (~300 m). Targets included Neoproterozoic metamorphic rocks of the Grenville Province along the rift flank and basinal Cambro-Ordovician Potsdam Group. Samples from the rift flank yield zircon ages from ca. 650 Ma to ca. 560 Ma and apatite ages from ca. 290 Ma to ca. 190 Ma, with a weak positive correlation between age and grain size. Zircon ages demonstrate a strong negative correlation with radiation damage: as eU increases, age decreases. By incorporating (U-Th)/He ages with regional constraints in the thermal modelling program HeFTy, viable temperature time paths for the region can be determined. Through inverse and forward modeling, preliminary rift flank (U-Th)/He ages correspond to post-Grenville cooling with <4 km of post-Carboniferous burial. The data define slow and long episodes of syn- to post-rift cooling with rates between 0.4 and 0.1 °C/Ma. (U-Th)/He dating of samples along the full-length of the transect

  17. Hydroxyl speciation in felsic magmas

    NASA Astrophysics Data System (ADS)

    Malfait, Wim J.; Xue, Xianyu

    2014-09-01

    The hydroxyl speciation of hydrous, metaluminous potassium and calcium aluminosilicate glasses was investigated by 27Al-1H cross polarization and quantitative 1H MAS NMR spectroscopy. Al-OH is present in both the potassium and the calcium aluminosilicate glasses and its 1H NMR partial spectrum was derived from the 27Al-1H cross polarization data. For the calcium aluminosilicate glasses, the abundance of Al-OH could not be determined because of the low spectral resolution. For the potassium aluminosilicate glasses, the fraction of Al-OH was quantified by fitting its partial spectrum to the quantitative 1H NMR spectra. The degree of aluminum avoidance and the relative tendency for Si-O-Si, Si-O-Al and Al-O-Al bonds to hydrolyze were derived from the measured species abundances. Compared to the sodium, lithium and calcium systems, potassium aluminosilicate glasses display a much stronger degree of aluminum avoidance and a stronger tendency for the Al-O-Al linkages to hydrolyze. Combining our results with those for sodium aluminosilicate glasses (Malfait and Xue, 2010a), we predict that the hydroxyl groups in rhyolitic and phonolitic magmas are predominantly present as Si-OH (84-89% and 68-78%, respectively), but with a significant fraction of Al-OH (11-16% and 22-32%, respectively). For both rhyolitic and phonolitic melts, the AlOH/(AlOH + SiOH) ratio is likely smaller than the Al/(Al + Si) ratio for the lower end of the natural temperature range but may approach the Al/(Al + Si) ratio at higher temperatures.

  18. Seismic images of multiple magma sills beneath the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Marjanovic, M.; Carbotte, S. M.; Carton, H. D.; Mutter, J. C.; Nedimovic, M. R.; Canales, J.

    2013-12-01

    Along fast and intermediate spreading centers, thin and narrow axial magma lenses (AMLs) are detected beneath much of the ridge axis, and the notion that the AML is the primary melt reservoir for dike intrusions and volcanic eruptions that build the upper crust is commonly accepted. However the role of the AML in construction of the lower crust is still actively debated. Some models based on geochemistry and structural observations from ophiolites suggest that formation of the lower crustal gabbro section takes place in situ, from multiple small magma sills, with the AML being the shallowest of these. Here, we present new observations from multichannel seismic data collected in 2008 along the East Pacific Rise (EPR) for seismic reflectors below the AML or sub-axial magma lens (SAML). The most prominent SAML events are found between latitudes 9°20' and 9°56'N, where they appear as moderately bright, discontinuous reflectors, at ~ 50 to 300 ms (~ 200-600 m) below the AML. From an analysis of the characteristics of these events, we rule out possible 'artifact' origins for the SAML including, seafloor side scattering, out-of-plane imaging of the AML or other crustal horizons, internal multiples, and the presence of a P-to-S converted phase (PAMLS). We interpret these deep melt lenses to have a low crystalline component (i.e. they are mostly molten). Disruptions in the SAML reflector, represented by relatively abrupt steps in two-way travel time are collocated with small-scale discontinuities in the AML and further support the notion of crustal accretion through small magmatic units. In addition, within the area of documented volcanic eruptions in 1991-1992 and 2005-2006, two prominent gaps centered at 9°46' and 9°50.5' N in the SAML reflectors are identified. We hypothesize that magma from these deeper lenses have also contributed to the eruption, implying hydraulic connectivity between the AML and SAMLs during eruption events. We suggest that the SAMLs play an

  19. Geochemistry and petrogenesis of the 595 Ma shoshonitic Qunai monzogabbro, Jordan

    NASA Astrophysics Data System (ADS)

    Ghanem, Hind; Jarrar, Ghaleb H.

    2013-12-01

    The last stage in the formation of the Arabian Nubian Shield in Jordan was dominated by post-orogenic igneous activity of the ˜610-542 Ma Araba Suite, including a monzogabbroic stock intruding the Saramuj Conglomerate, near the southeastern corner of the Dead Sea. The geological setting, petrography, geochemistry and geothermometry of the monzogabbro and other cogenetic varieties are used to shed light on the petrogenesis of this stock and reveal its magma source. The monzogabbro, megaporphyry dikes, and scattered syenite pockets are co-magmatic and alkaline, potassic and shoshonitic in nature. REE and trace elements patterns indicate that these magmas were produced from a mantle that had been modified by subduction-related metasomatism. The parental mafic magma could have been derived by 10% partial melting of LILE-enriched phlogopite-bearing spinel lherzolite, probably lithospheric mantle, in association with post-collisional extension. Fractional crystallization of this parental magma by olivine and pyroxene gave rise to the monzogabbroic magma. The megaporphyry dikes with their giant labradorite plagioclase megacrysts represent feeders of a voluminous volcanic activity that could have lasted for about 105 years. Thermodynamic modeling applying the MELTS software indicates crystallization of this suite in the temperature range of 1184-760 °C at a pressure of 2 kbars, agreeing with olivine-pyroxene, pyroxene, and two-feldspar thermometry. The modeled mineralogy and sequence of crystallization of constituent minerals using MELTS is in remarkable agreement with the observed modal mineralogy of the monzogabbro. Furthermore, a great degree of congruity exists between the modeled and observed chemistry of the major minerals with only minor discrepancies between modeled composition of biotite and olivine.

  20. Emplacement-related layering in magma slurries

    NASA Astrophysics Data System (ADS)

    Petford, N.

    2009-04-01

    Textures and structures such as layering, grading and foliations preserved in igneous rocks offer a glimpse into the magma emplacement process. However, despite recent advances, a full and proper understanding of the fluid dynamics of congested fluid-particle mixtures during shear remains elusive. This is a shame as without recourse to such fundamental understanding, the interpretation of structural field data in the context of magma flow remains problematic. One way to gain insight into the process is to treat flowing magma as a dynamic material with a rheology similar to sheared, congested slurries. The idea that dense magma equates to a high temperature slurry is an attractive one, and opens up a way to examine the emplacement process that does not rely on equilibrium thermodynamics as a final explanation for commonly observed igneous structures. Using the Basement Sill, Antarctica, as a world class example of a magmatic slurry, shearing at high Peclet (Pe) number where particle diffusion is negligible has the potential to impart a rich diversity of structures including layering, grading and flow segregation. Work to model numerically the flow of the Basement Sill slurry using a range of theoretical and experimentally-derived non-Newtonian magma rheologies will be presented and assessed. A key impilcation is that in addition to more classical explanations such as compaction and gravitational settling, igneous layering can also arise spontaneously during shear associated with the ascent and emplacement of congested magma. A final aspect of the emplacement model considers the irregular geometry of the Basement Sill boundaries. Movement of magma along these boundaries results in the formation of local eddies and fluid swirl/back-flow that add additional complexity to macroscopic flow field.

  1. Radiographic visualization of magma dynamics in an erupting volcano.

    PubMed

    Tanaka, Hiroyuki K M; Kusagaya, Taro; Shinohara, Hiroshi

    2014-01-01

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures. PMID:24614612

  2. Radiographic visualization of magma dynamics in an erupting volcano

    PubMed Central

    Tanaka, Hiroyuki K. M.; Kusagaya, Taro; Shinohara, Hiroshi

    2014-01-01

    Radiographic imaging of magma dynamics in a volcanic conduit provides detailed information about ascent and descent of magma, the magma flow rate, the conduit diameter and inflation and deflation of magma due to volatile expansion and release. Here we report the first radiographic observation of the ascent and descent of magma along a conduit utilizing atmospheric (cosmic ray) muons (muography) with dynamic radiographic imaging. Time sequential radiographic images show that the top of the magma column ascends right beneath the crater floor through which the eruption column was observed. In addition to the visualization of this magma inflation, we report a sequence of images that show magma descending. We further propose that the monitoring of temporal variations in the gas volume fraction of magma as well as its position in a conduit can be used to support existing eruption prediction procedures. PMID:24614612

  3. Rapid Crystallization of the Bishop Magma

    NASA Astrophysics Data System (ADS)

    Gualda, G. A.; Anderson, A. T.; Sutton, S. R.

    2007-12-01

    Substantial effort has been made to understand the longevity of rhyolitic magmas, and particular attention has been paid to the systems in the Long Valley area (California). Recent geochronological data suggest discrete magma bodies that existed for hundreds of thousands of years. Zircon crystallization ages for the Bishop Tuff span 100-200 ka, and were interpreted to reflect slow crystallization of a liquid-rich magma. Here we use the diffusional relaxation of Ti zoning in quartz to investigate the longevity of the Bishop magma. We have used such an approach to show the short timescales of crystallization of Ti-rich rims on quartz from early- erupted Bishop Tuff. We have now recognized Ti-rich cores in quartz that can be used to derive the timescales of their crystallization. We studied four samples of the early-erupted Bishop. Hand-picked crystals were mounted on glass slides and polished. Cathodoluminescence (CL) images were obtained using the electron microprobe at the University of Chicago. Ti zoning was documented using the GeoSoilEnviroCARS x-ray microprobe at the Advanced Photon Source (Argonne National Lab). Quartz crystals in all 4 samples include up to 3 Ti-bearing zones: a central core (50-100 μm in diameter, ca. 50 ppm Ti), a volumetrically predominant interior (~40 ppm Ti), and in some crystals a 50-100 μm thick rim (50 ppm Ti). Maximum estimates of core residence times were calculated using a 1D diffusion model, as the time needed to smooth an infinitely steep profile to fit the observed profile. Surprisingly, even for the largest crystals studied - ca. 2 mm in diameter - core residence times are less than 1 ka. Calculated growth rates imply that even cm-sized crystals crystallized in less than 10 ka. Crystal size distribution data show that crystals larger than 3 mm are exceedingly rare, such that the important inference is that the bulk of the crystallization of the early-erupted Bishop magma occurred in only a few thousand years. This timescale

  4. Magma movements and Iceland's next eruptions (Invited)

    NASA Astrophysics Data System (ADS)

    Sigmundsson, F.; Ofeigsson, B.; Hreinsdottir, S.; Hensch, M.; Gudmundsson, G.; Vogfjord, K. S.; Roberts, M. J.; Geirsson, H.; La Femina, P. C.; Hooper, A. J.; Sturkell, E. C.; Einarsson, P.; Gudmundsson, M. T.; Brandsdottir, B.; Loughlin, S. C.; Team, F.

    2013-12-01

    Iceland, created by hotspot-ridge interaction, is characterized by higher magmatic input and more complicated plate boundary structure than other parts of the Mid-Atlantic rift system. It has 30+ volcanic systems, where 20 confirmed eruptions have occurred in the last 40 years, the most recent at Eyjafjallajökull in 2010 and Grimsvotn in 2011. Likely candidates for the next eruption include the four most active volcanoes in Iceland (Hekla, Katla, Grimsvotn, and Bardarbunga) and other areas of volcanic unrest (Askja region, the Krisuvik area). Present volcano monitoring and research, including the FUTUREVOLC project, aims at providing warnings of impending eruptions and their character. Earthquake monitoring and deformation studies have hereto provided the most relevant information. Hekla continuously accumulates magma at a rate of about 0.003-0.02 km3/yr, according to GPS and InSAR studies, in a magma chamber placed below 14 km depth. A sequence of M0.4-1 earthquakes early this year stands out from otherwise mostly aseismic character of Hekla during repose periods. The Hekla magma chamber does not fail at a constant amount of magma volume, rather a clear pattern is observed with eruption size scaling with the length of the preceding period of dormancy. The ice capped Katla volcano shows unusual annual deformation pattern, seismic activity, and hydrological variations depending on time of year, presumably related to ice load and water pressure variations. It may be in a critical stage and renewed inflow of magma may quickly move the volcano towards failure. Bardarbunga had major earthquake and magma transfer activity in 1996, and has been the site of deep low-frequency earthquakes. Grímsvötn volcano is the only volcano with a shallow magma chamber with ongoing confirmed recharging, and failure criteria closest to 'expected'. A large eruption occurred in 2011 compared to much smaller eruption in 2004. However, the amount of erupted magma did not scale with the

  5. Convective Regimes in Crystallizing Basaltic Magma Chambers

    NASA Astrophysics Data System (ADS)

    Gilbert, A. J.; Neufeld, J. A.; Holness, M. B.

    2015-12-01

    Cooling through the chamber walls drives crystallisation in crustal magma chambers, resulting in a cumulate pile on the floor and mushy regions at the walls and roof. The liquid in many magma chambers, either the bulk magma or the interstitial liquid in the mushy regions, may convect, driven either thermally, due to cooling, or compositionally, due to fractional crystallization. We have constructed a regime diagram of the possible convective modes in a system containing a basal mushy layer. These modes depend on the large-scale buoyancy forcing characterised by a global Rayleigh number and the proportion of the chamber height constituting the basal mushy region. We have tested this regime diagram using an analogue experimental system composed of a fluid layer overlying a pile of almost neutrally buoyant inert particles. Convection in this system is driven thermally, simulating magma convection above and within a porous cumulate pile. We observe a range of possible convective regimes, enabling us to produce a regime diagram. In addition to modes characterised by convection of the bulk and interstitial fluid, we also observe a series of regimes where the crystal pile is mobilised by fluid motions. These regimes feature saltation and scouring of the crystal pile by convection in the bulk fluid at moderate Rayleigh numbers, and large crystal-rich fountains at high Rayleigh numbers. For even larger Rayleigh numbers the entire crystal pile is mobilised in what we call the snowglobe regime. The observed mobilisation regimes may be applicable to basaltic magma chambers. Plagioclase in basal cumulates crystallised from a dense magma may be a result of crystal mobilisation from a plagioclase-rich roof mush. Compositional convection within such a mush could result in disaggregation, enabling the buoyant plagioclase to be entrained in relatively dense descending liquid plumes and brought to the floor. The phenocryst load in porphyritic lavas is often interpreted as a

  6. Magma production and migration within the moon

    NASA Technical Reports Server (NTRS)

    Turcotte, D. L.; Ahern, J. L.

    1978-01-01

    Partial melting is likely to have occurred throughout much of the moon due to heating during accretion and the volumetric heating of radioactive isotopes. Important problems that have received relatively little attention concern the migration of the resulting magmas to form surface or near surface volcanic rock. In the paper the basic mechanism for the migration of the magma through the lunar asthenosphere is considered. A porous flow model is proposed. The magma behaves like a liquid flowing through a porous matrix. The volume fraction of liquid present determines the saturated porosity. The differential buoyancy of the magma drives it upwards. It is shown that the per cent partial melt in the lunar interior will only slightly exceed that required to provide interconnecting porosity. Assuming that the radioactive isotopes are preferentially segregated into the magma, the time dependence of the partial melting of the lunar interior is found. It is shown that the total degree of partial melting of the deep lunar interior is likely to be between five and ten per cent.

  7. Magma fragmentation speed: an experimental determination

    NASA Astrophysics Data System (ADS)

    Spieler, O.; Dingwell, D. B.; Alidibirov, M.

    2004-01-01

    The propagation speed of a fragmentation front, combined with the ascent velocity of magma is, in all likelihood, a controlling factor in the dynamics of explosive volcanic eruptions. Direct measurement of the 'fragmentation speed' in natural systems appears to be impossible at present. Fortunately, laboratory experiments can provide information on the propagation speed of the fragmentation front. Here we present the results of fragmentation speed determinations using a so-called 'fragmentation bomb'. These are, to the best of our knowledge, the first in situ fragmentation speed determinations performed on magma. Natural magma samples (Merapi basaltic andesite, Mount St. Helens dacite and Unzen dacite) have been investigated in the temperature range of 20-950°C and at pressures up to 25 MPa. Two techniques have been employed. Firstly, in experiments at 20°C, dynamic pressure transducers were placed above and below the magma samples and the fragmentation speed of the magma sample was derived from an analysis of the decompression curves. Secondly, at elevated temperatures, an alternative technique was introduced and successfully employed. This involved the severing via fragmentation of conducting wires placed within the samples at various heights. Fragmentation speeds are very low, falling in the range of 2-70 m/s and increasing with an increase in the magnitude of the decompression step responsible for the fragmentation. The first high-temperature determination seems consistent with low-temperature results. Implications for explosive volcanism are discussed briefly.

  8. Crystallization kinetics in magmas during decompression

    NASA Astrophysics Data System (ADS)

    Arzilli, Fabio; Burton, Mike; Carroll, Michael R.

    2016-04-01

    Many variables play a role during magma crystallization at depth or in a volcanic conduit, and through experimentally derived constraints we can better understand pre- and syn-eruptive magma crystallization behavior. The thermodynamic properties of magmas have been extensively investigated as a function of T, P, fO2 and magma composition [1], and this allows estimation of the stability of equilibrium phases and physical parameters (e.g., density, viscosity). However, many natural igneous rocks contain geochemical, mineralogical and textural evidence of disequilibrium, suggesting that magmas frequently follow non-equilibrium, time-dependent pathways that are recorded in the geochemical and petrographic characteristics of the rocks. There are currently no suitable theoretical models capable of calculating nucleation and growth rates in disequilibrium conditions without experimental constraints. The aim of this contribution is provide quantitative data on growth and nucleation rates of feldspar crystals in silicate melts obtained through decompression experiments, in order to determine the magma evolution in pre- and sin-eruptive conditions. Decompression is one of the main processes that induce the crystallization of feldspar during the magma ascent in the volcanic conduit. Decompression experiments have been carried out on trachytic and basaltic melts to investigate crystallization kinetics of feldspar as a function of the effect of the degassing, undercooling and time on nucleation and crystal growth process [2; 3]. Furthermore, feldspar is the main crystals phase present in magmas, and its abundance can strongly vary with small changes in pressure, temperature and water content in the melt, implying appreciable variations in the textures and in the crystallization kinetics. Crystallization kinetics of trachytic melts show that long experiment durations involve more nucleation events of alkali feldspar than short experiment durations [2]. This is an important

  9. Can basal magma oceans generate magnetic fields?

    NASA Astrophysics Data System (ADS)

    Stegman, D. R.; Ziegler, L. B.; Davies, C.

    2015-12-01

    Earth's magnetic field is very old, with recent data now showing the field possibly extended back to 4.1 billion years ago (Tarduno et al., Science, 2015). Yet, based upon our current knowledge there are difficulties in sustained a core dynamo over most of Earth's history. Moreover, recent estimates of thermal and electrical conductivity of liquid iron at core conditions from mineral physics experiments indicate that adiabatic heat flux is approximately 15 TW, nearly 3 times larger than previously thought, exacerbating difficulties for driving a core dynamo by convective core cooling alone throughout Earth history. A long-lived basal magma ocean in the lowermost mantle has been proposed to exist in the early Earth, surviving perhaps into the Archean. While the modern, solid lower mantle is an electromagnetic insulator, electrical conductivities of silicate melts are known to be higher, though as yet they are unconstrained for lowermost mantle conditions. Here we explore the geomagnetic consequences of a basal magma ocean layer for a range of possible electrical conductivities. For the highest electrical conductivities considered, we find a basal magma ocean could be a primary dynamo source region. This would suggest the proposed three magnetic eras observed in paleomagnetic data originate from distinct sources for dynamo generation: from 4.5-2.45 Ga within a basal magma ocean, from 2.25-0.4 Ga within a superadiabatically cooled liquid core, and from 0.4-present within a quasi-adiabatic core that includes a solidifying inner core. We have extended this work by developing a new code, Dynamantle, which is a model with an entropy-based approach, similar to those commonly used in core dynamics models. We present new results using this code to assess the conditions under which basal magma oceans can generate positive ohmic dissipation. This is more generally useful than just considering the early Earth, but also for many silicate exoplanets in which basal magma oceans

  10. Evidence for the mixing of granitic and basaltic magmas in the Pleasant Bay layered intrusion, coastal Maine

    SciTech Connect

    Powers, P.M. . Geology Dept.)

    1993-03-01

    The Pleasant Bay layered intrusion has the shape of a shallow basin about 200 km[sup 2] in area and crops out along the coast of Maine between Bar Harbor and Machias. This intrusion evolved as repeated replenishments of basaltic magma were emplaced into a silicic magma chamber (Wiebe, in press). These replenishments surged into the chamber through fractures, spreading laterally on a floor of silicic cumulates and beneath silicic magma. This produced a sequence of layers (up to 100 m thick) that grade from chilled basalt at the base to gabbroic, dioritic, or granitic emulates at the top. This study focuses on two layers, each of which grades from chilled gabbro at the base to quartz syenite at the top. Petrography and geochemistry suggest that mechanical mixing and other interactions between two stably stratified magmas were responsible for much of this variation. Plagioclase grains typically have corroded calcic cores (An[sub 52--56]) that decrease in size upward and sodic rims (An[sub 32--36]) that thicken upward. Larger plagioclase grains at higher levels often have K-spar cores. Scarce large zircon, apatite, and biotite crystals in the lower parts of the layers are often corroded. The apatites have dark pleochroic halos, suggesting they crystallized from a liquid enriched in U and Th. The silicic melt was likely the source of K and H[sub 2]O needed to crystallize hornblende and biotite. The large corroded zircon, apatite, and biotite crystals, as well as much of the hornblende, probably grew at an interface between separately convecting silicic and basaltic magmas.

  11. Magma mixing enhanced by bubble ascent

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Perugini, D.; De Campos, C. P.; Hess, K.; Lavallee, Y.; Dingwell, D. B.

    2012-12-01

    Understanding the processes that affect the rate of liquid state homogenization provides fundamental clues on the otherwise inaccessible subsurface dynamics of magmatic plumbing systems. Compositional heterogeneities detected in the matrix of magmatic rocks represent the arrested state of a chemical equilibration. Magmatic homogenization has been divided into a) the mechanical interaction of magma batches (mingling) and b) the diffusive equilibration of compositional gradients, where diffusive equilibration is exponentially enhanced by progressive mechanical interaction [1]. The mechanical interaction between two distinct batches of magma has commonly been attributed to shear and folding movements between two liquids of distinct viscosities. A mode of mechanical interaction scarcely invoked is the advection of mafic material into a felsic one through bubble motion. Yet, experiments with analogue materials demonstrated that bubble ascent has the potential to enhance the fluid mechanical component of magma mixing [2]. Here, we present preliminary results from bubble-advection experiments. For the first time, experiments of this kind were performed using natural materials at magmatic temperatures. Cylinders of Snake River Plain (SRP) basalt were drilled with a cavity of defined volume and placed underneath cylinders of SRP rhyolite. Upon melting, the gas pocket, or bubble trapped within the cavity, rose into the rhyolite, so entraining a layer of basalt. Successive iterations of the same experiment at progressive intervals ensured a time series of magmatic interaction caused by bubble segregation. Variations in initial bubble size allowed the tracking of bubble volume to advected material ratio at defined viscosity contrast. The resulting plume-like structures that the advected basalt formed within the rhyolite were characterized by microCT and subsequent high-resolution EMP analyses. The mass of advected material per bubble correlated positively with bubble size. The

  12. Basalt Magma, Whisky and Tequila: finely-crafted mixes of small liquid batches that defy the parent liquid concept but whose complexities teach us much

    NASA Astrophysics Data System (ADS)

    Rubin, K. H.; Sinton, J. M.; Perfit, M. R.

    2015-12-01

    Basalt is the most ubiquitous magma type we know of in the solar system. It comes in various varieties manifested as compositional sub groups, erupts from a wide variety of volcanic systems and tectonic settings, and its eruptions span many order of magnitude in duration and volume. Igneous petrology, thermodynamics, geochemistry, and geodynamical modelling have been used to develop a sophisticated understanding of source lithologies, compositions and formation conditions (e.g., pressure and temperature) for parent melts and their subsequent transport, storage and evolution. These demonstrate some striking systematics as a function of volcano tectonic setting (on Earth). Yet much like Whisky, what makes it into the bottle, or the eruption, is a mixture of different liquids with unique characteristics, sometimes stirred so well that successive batches are indistinguishable, and sometimes stirred more incompletely, preserving small batch characters that are unique. Recently, geochemical and petrological studies in high spatial density within the products of individual eruptions have shown chemical and mineralogical evidence for incompletely mixed heterogeneous magmas in a majority of systems examined, begging the question of when, if ever, is it realistic to speak of a single parent magma composition, and even in cases where it apparently is, if these are instead just more thoroughly stirred multi-parent magmas. For instance, do monogenetic fields really erupt basalts of more varied parent melt compositions than large hot spot and flood basalt eruptions, or are they just more poorly stirred? This presentation will focus on work by ourselves and others constraining spatial and temporal single-eruption basaltic magma histories at different settings, using them to unravel the time and space scales of magma formation and mixing, how these translate to the assembly of an erupted basalt magma, and the implications for deducing things about and from presumed parents.

  13. Evolution and Consequences of Magma Ocean Solidifcation

    NASA Astrophysics Data System (ADS)

    Maurice, Maxime; Tosi, Nicola; Ana-Catalina, Plesa; Breuer, Doris

    2015-04-01

    The various and intense energy sources involved in the early stages of planetary formation, such as kinetic energy of accretion, decay of short-lived radiogenics, release of gravitational potential energy upon core formation, and tidal effects, are thought to have caused partial or possibly entire melting of the mantle of terrestrial planets and moons [Elkins-Tanton2012]. Global or local liquid magma oceans could thus have formed, whose solidification upon planetary cooling could have exerted a significant impact on the differentiation and subsequent evolution of the interior of terrestrial bodies. The solidification of such magma oceans likely proceeds from the bottom upwards because of the steeper slope of the mantle adiabat with respect to the slope of the solidus, and controls the initial compositional stratification of the solid mantle, which, in turn, can play an important role in shaping the earliest forms of mantle convection and surface tectonics. We investigate the thermal evolution of a whole-mantle magma ocean using the finite-volume code Gaia [Huettig2013]. We run two-dimensional simulations of magma ocean cooling and crystallization and investigate in particular the conditions for which the onset of solid-state thermal convection is possible before mantle solidification has completed. We assume an adiabatic temperature profile in the magma ocean and various cooling rates of the surface temperature according to coupled magma ocean-atmosphere models [Lebrun2013]. Upon reaching a critical melt fraction that marks the formation of the so-called rheological front, [Solomatov2007], we self-consistently solve with Gaia the conservation equations of solid-state mantle convection in the partially molten domain assuming a viscosity strongly dependent on temperature and melt content. By varying the reference Rayleigh number and the magma ocean cooling rate, we show that, even for a surface temperature decreasing very rapidly at a rate of 1000 K/Myr, a

  14. Timing of Magma Mixing Prior to the 2011 Eruption of Shinmoedake, Japan: On the Relationship Between Magma Injection, Magma Mixing, and Eruption Triggering

    NASA Astrophysics Data System (ADS)

    Tomiya, A.; Miyagi, I.; Saito, G.; Geshi, N.

    2013-12-01

    Various petrological evidences indicate magma mixing often preceded volcanic eruptions. Magma injection into the associated magma chambers also often occurs prior to eruptions as evidenced by inflation of a volcanic edifice. However, the relationship between magma injection, magma mixing, and eruption triggering is unclear because injection does not necessarily cause instantaneous mixing if the injected magma is sufficiently denser than the pre-existing magma and has formed stable stratified layers. To investigate the relationship, we estimated the timing of magma mixing prior to the 2011 sub-Plinian eruptions of Shinmoedake volcano, Kirishima volcanic group, Japan, on the basis of chemical zoning observed in magnetite phenocrysts and numerical diffusion modeling. We compared the timing with that of volcanic inflation/deflation processes. The eruptive products are comprised mainly of phenocryst-rich (28 vol%) gray pumice (SiO2 = 57 wt%) with minor amount of white pumice (SiO2 = 62 wt%). We recognized two magmatic end members, low-T dacitic magma and high-T mafic magma (basalt or basaltic andesite), and hybrid andesitic magma on the basis of our petrologic studies. Gray pumice is comprised mainly of the hybrid andesitic magma. White pumice is comprised mainly of the low-T dacitic magma with mixing of small volume of the hybrid andesitic magma. Most of the magnetite phenocrysts (type-A1) were crystallized in the hybrid andesitic magma. Their zoning profiles showed considerable increase in Mg and Al contents toward the rims of the phenocrysts, due to mixing with the high-T mafic magma. We calculated the time for diffusion to form these zoning profiles to be only 0.4 to 3 days. The short time scale suggests that the mixing of high-T magma triggered the sub-Plinian eruptions. This mixing process was not accompanied by a significant change in the volume of the magma chamber because no significant crustal deformation was observed several days prior to the eruptions (Japan

  15. MORB differentiation: In situ crystallization in replenished-tapped magma chambers

    NASA Astrophysics Data System (ADS)

    Coogan, L. A.; O'Hara, M. J.

    2015-06-01

    The differentiation of mid-ocean ridge basalt (MORB) is investigated with a focus on intermediate- to fast-spreading ridges and two recently proposed differentiation mechanisms: (i) differentiation in replenished-tapped-crystallizing (RTX) magma chambers, and (ii) chromatographic element separation during melt-rock reaction in the lower crust. There is compelling evidence in the petrology and geochemistry of MORB indicating that magma chambers at mid-ocean ridges behave as open systems, as required on thermal grounds in locations where a steady-state magma chamber exists. It has recently been suggested that the commonly observed over-enrichment of more-to-less incompatible elements during MORB differentiation can be explained by such an RTX model. However, the petrology of samples from the lower oceanic crust suggests an alternative mechanism could produce this over-enrichment. Clinopyroxene crystals in oceanic gabbros are commonly strongly zoned in incompatible elements with crystal rims apparently having grown from melts with very high incompatible element abundances. Elevated Zr/LREE in clinopyroxene rims, which has been interpreted as indicating growth from a melt in which these elements had been fractionated from one another by melt-rock reaction (chromatographic separation), is shown to be more simply explained by post-crystallization diffusive fractionation. However, the high incompatible element abundances in crystal rims demonstrates that the interstitial melt in crystal mush zones becomes highly differentiated. Disaggregation of such mush zones is indicated by the crystal cargo of MORB and must be accompanied by the return of interstitial melt to the eruptible reservoir - a form of in situ crystallization. Both a magma chamber undergoing closed system in situ crystallization, and a RTX magma chamber in which crystallization occurs in situ, are shown to be capable of reproducing the differentiation trends observed in MORB. Simple stochastic models of the

  16. Nature of Beypazari Granitoid: Geology and geochemistry, Northwest Anatolia, Turkey

    NASA Astrophysics Data System (ADS)

    Kadioğlu, Y. K.; Zoroğlu, O.

    2008-07-01

    metamorphic texture with clear metamorphic lineation, sharp contact with host rock and mostly observed at the northwest part of Kirbasi and Tahir region in the form of xenolithic enclaves. They have angular to sub-angular in shape. These types of the enclaves have hornfels in composition at the contact with the host rock as a product of contact metamorphism and amphibolites in composition at the core as a product of high temperature and middle pressure metamorphism. The textural features and mineral composition of the third type of the enclaves may indicate a fragment of metapelitic rocks, which caught by the granitoid magma in the form of xenolithic enclaves. Whole rock geochemistry reveals that Beypazari granitoids are subalkaline and calcalkaline in nature. They are enriched in Light-REE and LIL with respect to High-REE and HFS elements. Tectonic discrimination diagrams of Beypazari granitoid suggest a product of plate convergence and probably belong to Volcanic Arc Granitoid (VAG). The field observations, mineralogy, petrography with the whole geochemical data reveal that the Beypazari Granitoid magmas are derived from a subduction-modified magma and metasomatized mantle source with considerable crustal contribution.

  17. Unusual Iron Redox Systematics of Martian Magmas

    SciTech Connect

    Danielson, L.; Righter, K.; Pando, K.; Morris, R.V.; Graff, T.; Agresti, D.; Martin, A.; Sutton, S.; Newville, M.; Lanzirotti, A.

    2012-03-26

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite. Morris et al. proposed that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks. Magnetite stability in terrestrial magmas is well understood, as are the stabilities of FeO and Fe{sub 2}O{sub 3} in terrestrial magmas. In order to better understand the variation of FeO and Fe{sub 2}O{sub 3}, and the stability of magnetite (and other FeO-bearing phases) in martian magmas, we have undertaken an experimental study with two emphases. First, we determine the FeO and Fe{sub 2}O{sub 3} contents of super- and sub-liquidus glasses from a shergottite bulk composition at 1 bar to 4 GPa, and variable fO{sub 2}. Second, we document the stability of magnetite with temperature and fO{sub 2} in a shergottite bulk composition.

  18. Petrology and Physics of Magma Ocean Crystallization

    NASA Technical Reports Server (NTRS)

    Elkins-Tanton, Linda T.; Parmentier, E. M.; Hess, P. C.

    2003-01-01

    Early Mars is thought to have been melted significantly by the conversion of kinetic energy to heat during accretion of planetesimals. The processes of solidification of a magma ocean determine initial planetary compositional differentiation and the stability of the resulting mantle density profile. The stability and compositional heterogeneity of the mantle have significance for magmatic source regions, convective instability, and magnetic field generation. Significant progress on the dynamical problem of magma ocean crystallization has been made by a number of workers. The work done under the 2003 MFRP grant further explored the implications of early physical processes on compositional heterogeneity in Mars. Our goals were to connect early physical processes in Mars evolution with the present planet's most ancient observable characteristics, including the early, strong magnetic field, the crustal dichotomy, and the compositional characteristics of the SNC meteorite's source regions as well as their formation as isotopically distinct compositions early in Mars's evolution. We had already established a possible relationship between the major element compositions of SNC meteorite sources and processes of Martian magma ocean crystallization and overturn, and under this grant extended the analysis to the crucial trace element and isotopic SNC signatures. This study then demonstrated the ability to create and end the magnetic field through magma ocean cumulate overturn and subsequent cooling, as well as the feasibility of creating a compositionally- and volumetrically-consistent crustal dichotomy through mode-1 overturn and simultaneous adiabatic melting.

  19. Geology of magma systems: background and review

    SciTech Connect

    Peterfreund, A.R.

    1981-03-01

    A review of basic concepts and current models of igneous geology is presented. Emphasis is centered on studies of magma generation, ascent, emplacement, evolution, and surface or near-surface activity. An indexed reference list is also provided to facilitate future investigations.

  20. Isotopic zonations in silicic magma chambers

    SciTech Connect

    Johnson, C.M. )

    1989-12-01

    Many ash-flow tuffs are zoned in radiogenic isotope ratios, indicating that roofward assimilation of crust occurs in ash-flow magma chambers prior to eruption. Cases where relatively well constrained calculations may be made regarding the percentage of assimilation in the roof zone indicate that the percentage of assimilation often exceeds the percentage of phenocrysts in the tuffs. This relation, in addition to the fact that assimilation gradients are opposite to that of the percentage of phenocrysts, suggests that assimilation and crystallization in the silicic roof zones of crustal magma chambers are separated in time and space, and that these processes are best modeled as two-component mixing; true assimilation-fractional crystallization is probably restricted to the lower mafic parts. Most phenocrysts in the silicic upper parts of magma chambers crystallized after assimilation, providing minimum estimates of time between assimilation and eruption (1-100 yr). Preservation of monotonic isotopic gradients suggests that convection is minor in the upper parts of silicic magma chambers during the late stages of evolution.

  1. Frozen magma lenses below the oceanic crust.

    PubMed

    Nedimović, Mladen R; Carbotte, Suzanne M; Harding, Alistair J; Detrick, Robert S; Canales, J Pablo; Diebold, John B; Kent, Graham M; Tischer, Michael; Babcock, Jeffrey M

    2005-08-25

    The Earth's oceanic crust crystallizes from magmatic systems generated at mid-ocean ridges. Whereas a single magma body residing within the mid-crust is thought to be responsible for the generation of the upper oceanic crust, it remains unclear if the lower crust is formed from the same magma body, or if it mainly crystallizes from magma lenses located at the base of the crust. Thermal modelling, tomography, compliance and wide-angle seismic studies, supported by geological evidence, suggest the presence of gabbroic-melt accumulations within the Moho transition zone in the vicinity of fast- to intermediate-spreading centres. Until now, however, no reflection images have been obtained of such a structure within the Moho transition zone. Here we show images of groups of Moho transition zone reflection events that resulted from the analysis of approximately 1,500 km of multichannel seismic data collected across the intermediate-spreading-rate Juan de Fuca ridge. From our observations we suggest that gabbro lenses and melt accumulations embedded within dunite or residual mantle peridotite are the most probable cause for the observed reflectivity, thus providing support for the hypothesis that the crust is generated from multiple magma bodies. PMID:16121179

  2. Loki Patera: A Magma Sea Story

    NASA Technical Reports Server (NTRS)

    Veeder, G. J.; Matson, D. L.; Rathbun, A. G.

    2005-01-01

    We consider Loki Patera on Io as the surface expression of a large uniform body of magma. Our model of the Loki magma sea is some 200 km across; larger than a lake but smaller than an ocean. The depth of the magma sea is unknown, but assumed to be deep enough that bottom effects can be ignored. Edge effects at the shore line can be ignored to first order for most of the interior area. In particular, we take the dark material within Loki Patera as a thin solidified lava crust whose hydrostatic shape follows Io's isostatic surface (approx. 1815 km radius of curvature). The dark surface of Loki appears to be very smooth on both regional and local (subresolution) scales. The thermal contrast between the low and high albedo areas within Loki is consistent with the observed global correlation. The composition of the model magma sea is basaltic and saturated with dissolved SO2 at depth. Its average, almost isothermal, temperature is at the liquidus for basalt. Additional information is included in the original extended abstract.

  3. Volcanology: Look up for magma insights

    USGS Publications Warehouse

    Segall, Paul; Anderson, Kyle

    2014-01-01

    Volcanic plumes can be hazardous to aircraft. A correlation between plume height and ground deformation during an eruption of Grímsvötn Volcano, Iceland, allows us to peer into the properties of the magma chamber and may improve eruption forecasts.

  4. Iron Redox Systematics of Martian Magmas

    NASA Technical Reports Server (NTRS)

    Righter, K.; Danielson, L.; Martin, A.; Pando, K.; Sutton, S.; Newville, M.

    2011-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite [1]. Morris et al. [1] propose that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks [2,3]. Magnetite stability in terrestrial magmas is well understood, as are the stability of FeO and Fe2O3 in terrestrial magmas [4,5]. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas we have undertaken an experimental study with two emphases. First we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition. Second, we determine the FeO and Fe2O3 contents of the same shergottite bulk composition at 1 bar and variable fO2 at 1250 C, and at variable pressure. These two goals will help define not only magnetite stability, but pyroxene-melt equilibria that are also dependent upon fO2.

  5. Unusual Iron Redox Systematics of Martian Magmas

    NASA Technical Reports Server (NTRS)

    Danielson, L.; Righter, K.; Pando, K.; Morris, R. V.; Graff, T.; Agresti, D.; Martin, A.; Sutton, S.; Newville, M.; Lanzirotti, A.

    2012-01-01

    Martian magmas are known to be FeO-rich and the dominant FeO-bearing mineral at many sites visited by the Mars Exploration rovers (MER) is magnetite. Morris et al. proposed that the magnetite appears to be igneous in origin, rather than of secondary origin. However, magnetite is not typically found in experimental studies of martian magmatic rocks. Magnetite stability in terrestrial magmas is well understood, as are the stabilities of FeO and Fe2O3 in terrestrial magmas. In order to better understand the variation of FeO and Fe2O3, and the stability of magnetite (and other FeO-bearing phases) in martian magmas, we have undertaken an experimental study with two emphases. First, we determine the FeO and Fe2O3 contents of super- and sub-liquidus glasses from a shergottite bulk composition at 1 bar to 4 GPa, and variable fO2. Second, we document the stability of magnetite with temperature and fO2 in a shergottite bulk composition.

  6. The rheology of two-phase magmas

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Mader, H. M.; Mueller, S.

    2012-12-01

    Great advances in our understanding of the rheology of two-phase magmatic suspensions (magma with either bubbles or crystals in it) have been made in recent years. These advances are based on laboratory experiments with both magma and analogue materials, and on analytical and numerical modelling. The current state-of-the-art is the culmination of scores of studies undertaken by scores of research groups and presented in scores of publications. Consequently, whilst it is possible to construct a sophisticated rheological description of a two-phase magma based on a few easily-measured properties (melt composition, crystal/vesicle volume fraction, CSD/VSD, etc.) the task of determining how best to do this is daunting to the non-specialist. We present a straightforward, practical, algorithmic approach to determining the rheology of two-phase magma to the degree of sophistication appropriate to most modelling applications. The approach is based on a broad synthesis of the literature, on new experimental data, and on new theoretical analysis.

  7. Magma Processes in Generating Basalts at the Poison Lake Chain, California

    NASA Astrophysics Data System (ADS)

    Wenner, J. M.; Teasdale, R.; Kroeninger, K. L.; Albanese, C.; Duhamel, N.

    2012-12-01

    We present new data for primitive basalts in the Poison Lake chain east of Lassen Volcanic National Park in northern California. The primitive composition and location of Poison Lake chain cinder cones on the western margin of the Basin and Range suggest that extensional tectonics may facilitate efficient magma ascent with little contamination. The Poison Lake chain is an ideal location to study small-scale variations in the mantle beneath the southern Cascades because of the small volumes erupted and the proximity to the Basin and Range. The volcanic field encompasses 39 units that comprise nine chemically distinct groups of primitive calc-alkaline basalts (defined by major element geochemistry and mineralogy). Olivine core compositions range from Fo72 - Fo89; most are in equilibrium with their whole rock compositions. Plagioclase core compositions range from An62-An88. Trace-element and isotope data for the groups confirm distinct chemistries that show little evidence of direct genetic relationships or a common source among these basalts. The small volume and distinct isotopic characteristics of individual groups suggest that they are the product of small mantle source domains. CaO compositions of olivine crystals further support that these basalts represent small independent magma batches. Isotope ratios, major and trace element compositions (whole rock) and crystal compositions reflect pre-eruption processing for some groups, which provide insights into the degree of pre-eruption processing versus the extent of source heterogeneities. Other groups have smaller compositional ranges (whole rock isotopes, trace, and major elements), more homogeneous olivine and plagioclase compositions, and reflect smaller degrees of processing prior to eruption. Compositional ranges within individual groups constrain the degree to which magmas were processed during transport from the mantle source to the surface in the Poison Lake chain.

  8. Magma-poor and magma-rich segments along the hyperextended, pre-Caledonian passive margin of Baltica

    NASA Astrophysics Data System (ADS)

    Andersen, Torgeir B.; Alsaif, Manar; Corfu, Fernando; Jakob, Johannes; Planke, Sverre; Tegner, Christian

    2015-04-01

    The Scandinavian Caledonides constitute a more than 1850 km long 'Himalayan-type' orogen, formed by collision between Baltica-Avalonia and Laurentia. Subduction-related magmatism in the Iapetus ended at ~430 Ma and continental convergence continued for ~30 Myr until ~400 Ma. The collision produced a thick orogenic wedge comprising the stacked remnants of the rifted to hyperextended passive Baltican margin (Andersen et al. 2012), as well as suspect, composite and outboard terranes, which were successively emplaced as large-scale nappe complexes onto Baltica during the Scandian collision (see Corfu et al. 2014 for a recent review). Large parts (~800 km) of the mountain-belt in central Scandinavia, particularly in the Särv and Seve Nappes and their counterparts in Troms, are characterised by spectacular dyke complexes emplaced into continental sediments (e.g. Svenningsen 2001, Hollocher et al. 2007). These constitute a magma-rich segment formed along the margin of Baltica or within hyperextended continental slivers outboard of Baltica. The intensity of the pre-Caledonian magmatism is comparable to that of the present NE-Atlantic and other volcanic passive margins. The volumes and available U-Pb ages of 610-597 Ma (Baird et al. 2014 and refs therein) suggest that the magmatism was short lived, intense and therefore compatible with a large igneous province (LIP). By analogy with present-day margins this LIP may have been associated with continental break-up and onset of sea-floor spreading. The remnants of the passive margin both north and south of the magma-rich segment have different architectures, and are almost devoid of rift/drift related magmatic rocks. Instead, these magma-poor segments are dominated by heterogeneous sediment-filled basins characterised by the abundant presence of solitary bodies of variably altered mantle peridotites, also commonly present as detrital serpentinites. These basins are interpreted to have formed by hyperextension. We suggest that

  9. Direct Observation of Rhyolite Magma by Drilling: The Proposed Krafla Magma Drilling Project

    NASA Astrophysics Data System (ADS)

    Eichelberger, J. C.; Sigmundsson, F.; Papale, P.; Markusson, S.; Loughlin, S.

    2014-12-01

    Remarkably, drilling in Landsvirkjun Co.'s geothermal field in Krafla Caldera, Iceland has encountered rhyolite magma or hypersolidus rhyolite at 2.1-2.5 km depth in 3 wells distributed over 3.5 km2, including Iceland Deep Drilling Program's IDDP-1 (Mortensen, 2012). Krafla's most recent rifting and eruption (basalt) episode was 1975-1984; deformation since that time has been simple decay. Apparently rhyolite magma was either emplaced during that episode without itself erupting or quietly evolved in situ within 2-3 decades. Analysis of drill cuttings containing quenched melt from IDDP-1 yielded unprecedented petrologic data (Zierenberg et al, 2012). But interpreting active processes of heat and mass transfer requires knowing spatial variations in physical and chemical characteristics at the margin of the magma body, and that requires retrieving core - a not-inconceivable task. Core quenched in situ in melt up to 1150oC was recovered from Kilauea Iki lava lake, Hawaii by the Magma Energy Project >30 years ago. The site from which IDDP-1 was drilled, and perhaps IDDP-1 itself, may be available to attempt the first-ever coring of rhyolite magma, now proposed as the Krafla Magma Drilling Project (KMDP). KMDP would also include geophysical and geochemical experiments to measure the response of the magma/hydrothermal system to fluid injection and flow tests. Fundamental results will reveal the behavior of magma in the upper crust and coupling between magma and the hydrothermal system. Extreme, sustained thermal power output during flow tests of IDDP-1 suggests operation of a Kilauea-Iki-like freeze-fracture-flow boundary propagating into the magma and mining its latent heat of crystallization (Carrigan et al, EGU, 2014). Such an ultra-hot Enhanced Geothermal System (EGS) might be developable beneath this and other magma-heated conventional hydrothermal systems. Additionally, intra-caldera intrusions like Krafla's are believed to produce the unrest that is so troubling in

  10. Shallow crystallization of Kilauean olivines: Magma density and picritic eruptions

    SciTech Connect

    Anderson, A.T. Jr.; Brown, G.G. . Dept. of the Geophysical Sciences)

    1992-01-01

    Of 35 analyzed glass inclusions in olivine phenocrysts from the 1959 Kilauea Iki eruption, 23 formed at pressures less than 1 Kbar, 10 between 1 and 2 Kbar and 2 at pressures greater than 2 Kbar. The surprisingly topheavy distribution of formation pressures suggests that the 1959 magma rose rapidly to the upper parts of Kilauea's summit magma storage reservoir where cooling and crystallization dominantly occurred. The implication that the parental magma was buoyant relative to preexisting resident magma is consistent with an expected preeruptive bulk CO[sub 2] content of 0.3wt.% and petrographic evidence for turbulent mixing between parental and preexisting magma. That the 1959 magma was rich not only in crystals but also in gas, as evidenced by its high lava fountains, suggests that the storage time in the summit reservoir was too short for either crystals or gas to be lost. Therefore, the 1959 Kilauean magma probably is a near-parental magma that rose and formed a gas- and crystal-rich cap at the top of Kilauea's summit magma storage reservoir. Whether parental magma rises to the top or ponds at the base of the summit reservoir depends mainly on reservoir pressure and magma gas content. Consequently, it seems likely that the eruptive and degassing behavior of Kilauea is regulated in part by an interplay between the CO[sub 2] content of parental magma and the pressure at the base of the summit storage reservoir.

  11. Numerical simulation of magma energy extraction

    SciTech Connect

    Hickox, C.E.

    1991-01-01

    The Magma Energy Program is a speculative endeavor regarding practical utility of electrical power production from the thermal energy which reside in magma. The systematic investigation has identified an number of research areas which have application to the utilization of magma energy and to the field of geothermal energy. Eight topics were identified which involve thermal processes and which are areas for the application of the techniques of numerical simulation. These areas are: (1) two-phase flow of the working fluid in the wellbore, (2) thermodynamic cycles for the production of electrical power, (3) optimization of the entire system, (4) solidification and fracturing of the magma caused by the energy extraction process, (5) heat transfer and fluid flow within an open, direct-contact, heat-exchanger, (6) thermal convection in the overlying geothermal region, (7) thermal convection within the magma body, and (8) induced natural convection near the thermal energy extraction device. Modeling issues have been identified which will require systematic investigation in order to develop the most appropriate strategies for numerical simulation. It appears that numerical simulations will be of ever increasing importance to the study of geothermal processes as the size and complexity of the systems of interest increase. It is anticipated that, in the future, greater emphasis will be placed on the numerical simulation of large-scale, three-dimensional, transient, mixed convection in viscous flows and porous media. Increased computational capabilities, e.g.; massively parallel computers, will allow for the detailed study of specific processes in fractured media, non-Darcy effects in porous media, and non-Newtonian effects. 23 refs., 13 figs., 1 tab.

  12. Io: Loki Patera as a Magma Sea

    NASA Technical Reports Server (NTRS)

    Matson, Dennis L.; Davies, Ashley Gerard; Veeder, Glenn J.; Rathbun, Julie A.; Johnson, Torrence V.; Castillo, Julie C.

    2006-01-01

    We develop a physical model for Loki Patera as a magma sea. We calculate the total volume of magma moving through the Loki Patera volcanic system every resurfacing cycle (approx.540 days) and the resulting variation in thermal emission. The rate of magma solidification at times reaches 3 x 10(exp 6) kg per second, with a total solidified volume averaging 100 cu km per year. A simulation of gas physical chemistry evolution yields the crust porosity profile and the timescale when it will become dense enough to founder in a manner consistent with observations. The Loki Patera surface temperature distribution shows that different areas are at different life cycle stages. On a regional scale, however, there can be coordinated activity, indicated by the wave of thermal change which progresses from Loki Patera's SW quadrant toward the NE at a rate of approx.1 km per day. Using the observed surface temperature distribution, we test several mechanisms for resurfacing Loki Patera, finding that resurfacing with lava flows is not realistic. Only the crustal foundering process is consistent with observations. These tests also discovered that sinking crust has a 'heat deficit' which promotes the solidification of additional magma onto the sinking plate ("bulking up"). In the limiting case, the mass of sinking material can increase to a mass of approx.3 times that of the foundering plate. With all this solid matter sinking, there is a compensating upward motion in the liquid magma. This can be in excess of 2 m per year. In this manner, solid-liquid convection is occurring in the sea.

  13. Magma Genesis in the Hawaiian Hot Spot: From melting experiments on basalt/peridotite hybrid source

    NASA Astrophysics Data System (ADS)

    Takahashi, E.

    2003-12-01

    Melting mantle peridotite is one of the central themes in experimental petrology. Melting studies in CMAS, NCMAS and natural peridotites have extensively documented the magma genesis process at Mid Oceanic Ridges (e.g., Presnall et al., 1979). Magma genesis in OIBs and LIPs, on the other hand, has been poorly constrained by experiments. Evidences from isotope geochemistry indicate that the source materials for basalt magmas in these provinces are not peridotite alone. Based on a geological and geochemical reconstruction of 3 Ma old Koolau volcano, I proposed that the size of eclogite blocks in the Hawaiian plume would exceed 1000km3 (Takahashi and Nakajima, 2002) and therefore the melting interaction of eclogite blocks and the surrounding peridotite would play essential roles in magma genesis in the Hawaiian hot spot. Melting experiments on basalt/peridotite composite starting materials were carried out at 2.5 to 3.0 GPa at temperatures from the peridotite dry solidus to that of basalt for 20 to 100 hours. Three layered starting materials consisting of 1 basalt to 2 peridotite (in volume) were placed in graphite/Pt double capsules. Peridotite KLB-1 (Fo89.6) and two basalt-starting materials (CLG-46 and CRB72-31) were used as starting materials. In temperatures ca.50-100 degrees below the peridotite solidus, silica-rich partial melts are produced in the basalt zone and the boundaries between the basalt and peridotite are coated with a 10 to 50 micron thick opx reaction band. The chemical reactions between the basalt and peridotite domains are controlled by solid diffusions across the opx reaction band and are very slow. In temperatures within 50 degrees of the peridotite dry solidus, a time dependent reaction process takes place. The basalt/peridotite boundary gradually partial melts as the chemical reaction lowers the peridotite solidus locally. At 2.8 GPa and 1450-1470C after 50-100 hours, resultant melt in the basalt layer becomes saturated with oliv + opx + cpx

  14. Geochemistry

    ERIC Educational Resources Information Center

    Brett, Robin; Hanshaw, Bruce B.

    1978-01-01

    The past year has seen the development of certain fields of geochemical research including Nd-Sm isotope studies of meteorites and ancient terrestrial rocks; the use of the consortium approach of assembling a multidisciplined team to tackle a problem; and the handling and analysis of small quantities of materials. (Author/MA)

  15. Deep magma transport at Kilauea volcano, Hawaii

    USGS Publications Warehouse

    Wright, T.L.; Klein, F.W.

    2006-01-01

    The shallow part of Kilauea's magma system is conceptually well-understood. Long-period and short-period (brittle-failure) earthquake swarms outline a near-vertical magma transport path beneath Kilauea's summit to 20 km depth. A gravity high centered above the magma transport path demonstrates that Kilauea's shallow magma system, established early in the volcano's history, has remained fixed in place. Low seismicity at 4-7 km outlines a storage region from which magma is supplied for eruptions and intrusions. Brittle-failure earthquake swarms shallower than 5 km beneath the rift zones accompany dike emplacement. Sparse earthquakes extend to a decollement at 10-12 km along which the south flank of Kilauea is sliding seaward. This zone below 5 km can sustain aseismic magma transport, consistent with recent tomographic studies. Long-period earthquake clusters deeper than 40 km occur parallel to and offshore of Kilauea's south coast, defining the deepest seismic response to magma transport from the Hawaiian hot spot. A path connecting the shallow and deep long-period earthquakes is defined by mainshock-aftershock locations of brittle-failure earthquakes unique to Kilauea whose hypocenters are deeper than 25 km with magnitudes from 4.4 to 5.2. Separation of deep and shallow long-period clusters occurs as the shallow plumbing moves with the volcanic edifice, while the deep plumbing is centered over the hotspot. Recent GPS data agrees with the volcano-propagation vector from Kauai to Maui, suggesting that Pacific plate motion, azimuth 293.5?? and rate of 7.4 cm/yr, has been constant over Kilauea's lifetime. However, volcano propagation on the island of Hawaii, azimuth 325??, rate 13 cm/yr, requires southwesterly migration of the locus of melting within the broad hotspot. Deep, long-period earthquakes lie west of the extrapolated position of Kilauea backward in time along a plate-motion vector, requiring southwesterly migration of Kilauea's magma source. Assumed ages of 0

  16. Outgassing of silicic magma through bubble and fracture networks (Invited)

    NASA Astrophysics Data System (ADS)

    Okumura, S.; Nakamura, M.; Uesugi, K.

    2013-12-01

    Outgassing of magma is a fundamental process that controls the style and explosivity of volcanic eruptions. Vesiculation during the ascent and decompression of magma results in the formation of bubble networks within the magma. The permeable gas escape through the bubble networks is an efficient way to induce the outgassing of silicic magma (Eichelberger et al., 1986). To understand magma ascent dynamics and predict the style and explosivity of eruptions, it is necessary to constrain the rate of magma outgassing as the magma ascends in a volcanic conduit. However, the gas permeability of natural samples should not be considered, because it reflects complicated processes involving vesiculation, deformation, outgassing, and compaction. Experimental studies have demonstrated that vesiculation and compaction processes show hysteresis behavior (Okumura et al., 2013). Thus, we have performed experiments to simulate magma decompression and the deformation of vesicular magmas (e.g., Okumura et al., 2009, 2012). A series of decompression and deformation experiments indicates that the gas permeability is less than the order of 10-15 m2 for isotropic vesiculation at vesicularity <60-80 vol%. When magma ascent is simulated with shear deformation, the gas permeability is much greater than that observed under isotropic conditions. Akin to bubble networks, permeable networks consisting of shear-induced brittle fractures are thought to be efficient outgassing pathways (Gonnermann and Manga, 2003). Our recent experiments demonstrated that fractured magma has a higher gas permeability than vesicular magma at least at vesicularities <~40 vol%. This indicates that fracture networks in magma become efficient parts for the outgassing. However, as shear fracturing results from high strain rates in highly viscous magma, outgassing via fracture networks can be enhanced in localized shear zones and shallow parts of the conduit. The permeable bubble and fracture networks are preferentially

  17. Magma energy: the ultimate heat source for geothermal fields

    SciTech Connect

    Hardee, H.C.

    1982-07-01

    A scientific feasibility study, funded by DOE/Basic Energy Sciences, of extracting energy directly from buried magma sources is discussed. This study has examined the problems of locating and drilling into the magma and then extracting useful quantities of energy from the magma. Theoretical calculations with supporting laboratory and field measurements have been used to show that there are no theoretical or physical barriers that prevent the direct extraction of energy from magma. As a result of this study it has been concluded that magma energy utilization is scientifically feasible.

  18. Geochemical investigation of a semi-continuous extrusive basaltic section from the Deccan Volcanic Province, India: implications for the mantle and magma chamber processes

    NASA Astrophysics Data System (ADS)

    Vijaya Kumar, Kopparapu; Chavan, Chakradhar; Sawant, Sariput; Naga Raju, K.; Kanakdande, Prachiti; Patode, Sangita; Deshpande, Krishna; Krishnamacharyulu, S. K. G.; Vaideswaran, T.; Balaram, V.

    2010-06-01

    Spatial and temporal variations in the geochemistry of an extrusive basaltic section of Deccan traps record progressive changes in mantle melting and crustal filtration and are relevant to understand continental flood basalt (CFB) magmatism. In the present work we have carried out detailed field, petrographic, density and magnetic susceptibility, and geochemical investigations on a small, semi-continuous extrusive section in the eastern Deccan Volcanic Province (DVP) to understand the role of shallow magma chambers in CFB magmatism. Four formations, Ajanta, Chikhli, Buldhana and Karanja crop out in the Gangakhed-Ambajogai area with increasing elevation. Our studies indicate that: (1) the Karanja Formation represents a major magma addition, as indicated by abrupt change in texture, increases in MgO, CaO, Ni, Cr, and Sr, and drastic decreases in Al2O3, Na2O, K2O, Rb, Ba, REE, bulk-rock density and magnetic susceptibility; (2) assimilation fractional crystallization, crystal-laden magmas, and accessory cumulus phases influence the trace element chemistry of Deccan basalts; (3) the predicted cumulate sequence of olivine gabbro-leucogabbro-oxide-apatite gabbro is supported by the observed layered series in a shallow magma chamber within the DVP; (4) the initial magma was saturated with olivine, plagioclase, and augite, and final the pressure of equilibration for the Gangakhed-Ambajogai section basalts is ~2 kbar (~6 km depth); (5) petrophysical parameters act as proxies for magmatic processes; (6) a small layer of oxide-rich basalts may represent the latest erupted pulse in a given magmatic cycle in the DVP; (7) parental basalts to some of the red boles, considered as formation boundaries, might represent small degree partial melts of the mantle; (8) SW Deccan basaltic-types continue into the eastern DVP; and (9) in addition to the magma chamber processes, dynamic melting of the mantle may have controlled DVP geochemistry. The present study underscores the importance of

  19. Magma Dynamics in Dome-Building Volcanoes

    NASA Astrophysics Data System (ADS)

    Kendrick, J. E.; Lavallée, Y.; Hornby, A. J.; Schaefer, L. N.; Oommen, T.; Di Toro, G.; Hirose, T.

    2014-12-01

    The frequent and, as yet, unpredictable transition from effusive to explosive volcanic behaviour is common to active composite volcanoes, yet our understanding of the processes which control this evolution is poor. The rheology of magma, dictated by its composition, porosity and crystal content, is integral to eruption behaviour and during ascent magma behaves in an increasingly rock-like manner. This behaviour, on short timescales in the upper conduit, provides exceptionally dynamic conditions that favour strain localisation and failure. Seismicity released by this process can be mimicked by damage accumulation that releases acoustic signals on the laboratory scale, showing that the failure of magma is intrinsically strain-rate dependent. This character aids the development of shear zones in the conduit, which commonly fracture seismogenically, producing fault surfaces that control the last hundreds of meters of ascent by frictional slip. High-velocity rotary shear (HVR) experiments demonstrate that at ambient temperatures, gouge behaves according to Byerlee's rule at low slip velocities. At rock-rock interfaces, mechanical work induces comminution of asperities and heating which, if sufficient, may induce melting and formation of pseudotachylyte. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The bulk composition, mineralogy and glass content of the magma all influence frictional behaviour, which supersedes buoyancy as the controlling factor in magma ascent. In the conduit of dome-building volcanoes, the fracture and slip processes are further complicated: slip-rate along the conduit margin fluctuates. The shear-thinning frictional melt yields a tendency for extremely unstable slip thanks to its pivotal position with regard to the glass transition. This thermo-kinetic transition bestows the viscoelastic melt with the ability to either flow or

  20. Fractionation of a Basal Magma Ocean

    NASA Astrophysics Data System (ADS)

    Laneuville, M.; Hernlund, J. W.; Labrosse, S.

    2014-12-01

    Earth's magnetic field is thought to be sustained by dynamo action in a convecting metallic outer core since at least 3.45 Ga (Tarduno et al., 2010). Convection induces an isentropic temperature gradient that drains 13±3 TW of heat from the core by thermal conduction (de Koker et al., 2012; Pozzo et al., 2012; Gomi et al., 2013), and suggests that Earth's core has cooled by ˜1,000 K or more since Earth's formation (Gomi et al., 2013). However, models of Earth's initial thermal evolution following a giant-impact predict rapid cooling to the mantle melting temperature (e.g., Solomatov, 2007). In order to understand how the core could have retained enough heat to explain the age of the geodynamo, we relax a key assumption of the basal magma ocean model of (Labrosse et al., 2007) to allow for the possibility that the magma is stably stratified. Recent giant impact simulations suggest extensive core-mantle mixing (Saitoh and Makino, 2013), which could have produced such a large stratified magma layer at the core-mantle boundary. In the presence of a stable density gradient, heat transfer through the basal magma ocean occurs through conduction and therefore delays heat loss from the core. Partitioning of iron in the liquid phase upon crystallization changes the density profile and triggers convection in the upper part of the basal magma ocean. Our hypothesis suggests that early core cooling is dominated by the diffusion timescale through the basal magma ocean, and predicts a delayed onset of the geodynamo (i.e, during the late Headean/early Archean). This model can therefore be falsified if the existence of a geomagnetic field can be inferred from magnetization of inclusions in Hadean zircons. N. de Koker et al., Proc. Natl. Acad. Sci. 190, 4070-4073 (2012).H. Gomi et al., Phys. Earth Planet. Inter. 224, 88-103 (2013).S. Labrosse et al., Nature 450, 866-869 (2007).M. Pozzo et al., Nature 485, 355-358 (2012).T. Saitoh and J. Makino. Astrophys. J. 768, 44 (2013).V

  1. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    2000-01-01

    The research described in this progress report involved the study of petrological, geochemical and volcanic processes that occur on the Moon and the SNC parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the role of volatiles in magmatic processes and on processes of magma evolution on these planets. The work on the lunar volcanic glasses has resulted in some exciting new discoveries over the years of this grant. During the tenure of the present grant, we discovered a variety of metal blebs in the A17 orange glass. Some of these Fe-Ni metal blebs occur in the glass; others were found in olivine phenocrysts which we find make up about 2 vol % of the orange glass magma. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption. They also yield important information about the composition of the gas phase present, the gas which drove the lunar fire-fountaining. In an Undergraduate senior thesis project, Nora Klein discovered a melt inclusion that remained in a glassy state in one of the olivine phenocrysts. Analyses of this inclusion gave additional information on the CO2, CO and S contents of the orange glass magma prior to its reaching the lunar surface. The composition of lunar volcanic gases has long been one of the puzzles of lunar magmatic processes. One of the more exciting findings in our research over the past year has been the study of magmatic processes linking the SNC meteorite source magma composition with the andesitic composition rocks found at the Pathfinder site. In this project, graduate student Michelle Minitti showed that there was a clear petrologic link between these two magma types via fractional removal of crystals from the SNC parent melt, but the process only worked if there was at least 1 wt

  2. Magma Piracy in the Southern Mariana Backarc

    NASA Astrophysics Data System (ADS)

    Becker, N. C.; Fryer, P.; Martinez, F.; Stern, R. J.; Bloomer, S. H.

    2001-12-01

    Since 1997 the southern Mariana convergent margin system has been mapped with Hydrosweep, MR-1, and SeaBeam swath sonar systems on five cruises resulting in 168,500 km2 of bathymetry data and 186,800 km2 of sidescan data, revealing anomalous processes relative to the rest of the Mariana region. Most of the Mariana Arc is characterized by arc volcanism dominated by large, central volcanoes located at the boundary between a backarc basin with slow-spreading ridge morphology and a nonaccretionary forearc composed of Eocene volcanic arc rocks But southwest of Tracey Seamount, the southernmost large central arc volcano, the character of the arc and backarc changes dramatically. The arc volcanoes become small or nonexistent, but those that do occur lie along relict spreading fabric within the backarc basin. Furthermore, the spreading center appears to have an inflated, fast-spreading morphology, including dueling propagator fabric, and this southern backarc basin forms a shallow plateau overall. The spreading center then becomes less well-defined west of 143oE, and the volcanism appears to cease altogether west of 142oE in an area of amagmatic rifting, an observation supported by earthquake focal mechanisms and magnetics. The inflated morphology of the spreading axis, along with the absence or reduced size of nearby arc volcanoes suggests that arc magmas have been entrained into the backarc-spreading magmatic system. This "magma piracy" would result in arc magma being erupted at the backarc spreading center, therefore the backarc crust would be formed in part from arc magmas. Dredge samples from along the active ridge show compositions consistent with this suggestion. We suggest that this magma piracy has dominated the southern backarc basin for at least the last 3 m.y. since the robust spreading began. We suggest that the apparently higher magma production rate and the hybridized crust could account for the shallowness of the basin, as the more evolved arc-lavas would

  3. Petrology and Geochemistry of the Eocene Volcanic Rocks in the Kahrizak Mountains, Central Iran

    NASA Astrophysics Data System (ADS)

    Yazdani, S.; Castillo, P.; Tutti, F.

    2013-12-01

    The Eocene volcanic rocks in the Kahrizak (KH) Mountains in the northern part of Central Iran were mainly formed by magmatism that accompanied block-faulting tectonism in the region. In the KH area, the volcanic rocks are nonconformably overlain by Oligocene-Pliocene sedimentary deposits, suggesting that the Eocene magmatic activity in the region was followed by a sequence of uplift and shallow marine regression. The volcanic rocks consist of pyroclastics (tuff and ignimbrites) and lava flows (basalt, basaltic trachyandesite, trachyandesite, and rhyolite); superposition indicates an earlier explosive volcanic phase that caused the widespread distribution of rhyolitic ignimbrites and tuffs, and this was followed by a quieter phase of lava eruptions. Petrographic evidence such as mineral zoning, sieve texture and rounded crystals of plagioclase and pyroxene phenocrysts indicate non-equilibrium conditions between melt and crystals during magma cooling. These textures suggest magma mixing, although these may also be due to rapid decompression, where heat loss is minor relative to the ascent rate. The geochemistry of KH samples indicates their subalkaline to alkaline affinity. In terms of trace element contents, most samples exhibit the distinct geochemical trait of arc volcanism, i.e., Nb and Ta depletions relative to LILE (e.g., Ba, Rb) enrichment and positive Sr anomaly; however, Zr and Ti depletions are not prominent. The samples have a light-REE enriched but flat heavy-REE pattern and negative Eu anomaly in the rhyolites and trachyandesites. They have a ~narrow to ~moderate range of Pb isotopic ratios (206Pb/204Pb ~18.6-18.9, 207Pb/204Pb ~15.5-15.6, and 208Pb/204Pb ~38.5-38.8), with basaltic rocks somewhat higher than rhyolitic rocks. Available geochemical and isotopic data suggest a complex origin and evolution of the KH magmas. The magmas originated from an intrinsically ~heterogeneous source and, in addition to fractional crystallization, some of the

  4. Volcanic conduit failure as a trigger to magma fragmentation

    NASA Astrophysics Data System (ADS)

    Lavallée, Y.; Benson, P. M.; Heap, M. J.; Flaws, A.; Hess, K.-U.; Dingwell, D. B.

    2012-01-01

    In the assessment of volcanic risk, it is often assumed that magma ascending at a slow rate will erupt effusively, whereas magma ascending at fast rate will lead to an explosive eruption. Mechanistically viewed, this assessment is supported by the notion that the viscoelastic nature of magma (i.e., the ability of magma to relax at an applied strain rate), linked via the gradient of flow pressure (related to discharge rate), controls the eruption style. In such an analysis, the physical interactions between the magma and the conduit wall are commonly, to a first order, neglected. Yet, during ascent, magma must force its way through the volcanic edifice/structure, whose presence and form may greatly affect the stress field through which the magma is trying to ascend. Here, we demonstrate that fracturing of the conduit wall via flow pressure releases an elastic shock resulting in fracturing of the viscous magma itself. We find that magma fragmentation occurred at strain rates seven orders of magnitude slower than theoretically anticipated from the applied axial strain rate. Our conclusion, that the discharge rate cannot provide a reliable indication of ascending magma rheology without knowledge of conduit wall stability, has important ramifications for volcanic hazard assessment. New numerical simulations are now needed in order to integrate magma/conduit interaction into eruption models.

  5. Magma oceanography. I - Thermal evolution. [of lunar surface

    NASA Technical Reports Server (NTRS)

    Solomon, S. C.; Longhi, J.

    1977-01-01

    Fractional crystallization and flotation of cumulate plagioclase in a cooling 'magma ocean' provides the simplest explanation for early emplacement of a thick feldspar-rich lunar crust. The complementary mafic cumulates resulting from the differentiation of such a magma ocean have been identified as the ultimate source of mare basalt liquids on the basis or rare-earth abundance patterns and experimental petrology studies. A study is conducted concerning the thermal evolution of the early differentiation processes. A range of models of increasing sophistication are considered. The models developed contain the essence of the energetics and the time scale for magma ocean differentiation. Attention is given to constraints on a magma ocean, modeling procedures, single-component magma oceans, fractionating magma oceans, and evolving magma oceans.

  6. Magma transport and storage at Kilauea volcano, HI

    NASA Astrophysics Data System (ADS)

    Wright, T. L.

    2010-12-01

    Thomas L. Wright and Fred W. Klein (USGS, Johns Hopkins University, Baltimore, MD 21218, Menlo Park, CA 94025; 410-516-7040, 650-329-4794) Seismic and deformation data between 1950 and the beginning of the Mauna Ulu eruption of 1969-1974 indicate (1) that summit inflation and deflation cycles are best matched by a magma reservoir beneath Kilauea's summit consisting of concatenated vertical plugs and (2) that magmas erupted at Kilauea's summit are also present beneath the east rift zone where they can cool and fractionate. Three "olivine-controlled" magmas fractionated by removal of olivine only and distinguished from each other by their major-oxide chemistry were erupted at Kilauea's summit within Halemaumau crater in 1952, 1961 and 1967-68. From 1955 to 1969, these three magmas were mixed with fractionated magmas stored beneath Kilauea's east rift zone to form "hybrid" eruptions. Two eruptions important to our interpretation occurred on the lower east rift zone 1n 1955 and 1960. Published mixing calculations show that the 1952 magma mixed with the fractionated 1955 magma in the latter part of the 1955 eruption and that the 1961 magma was intruded in 1955 to become the parent for fractionated magma later erupted in 1977 from the rift zone. The 1960 eruption began with magma hybridized in 1955, then was successively mixed with the remaining 1952 magma, 1961 magma and the 1967-68 magma. The latter two summit magmas were identified in hybrid eruptions from 1961-1965 and also as parents for fractionated magma present in fractionated and hybrid rift eruptions of 1968-69. The mixing in this period demonstrates that the 1952, 1961 and 1967-68 summit magmas appear in that order in hybrid eruptions on the east rift zone before they are erupted at the summit, traveled within the rift without appreciable cooling or mixing with each other, and were identified as eruption components for up to ~ 10 years. Volume calculations indicate that these magmas were stored prior to

  7. The location and timing of magma degassing during Plinian eruptions

    NASA Astrophysics Data System (ADS)

    Giachetti, T.; Gonnermann, H. M.

    2014-12-01

    Water is the most abundant volatile species in explosively erupting silicic magmas and significantly affects magma viscosity, magma fragmentation and the dynamics of the eruption column. The effect that water has on these eruption processes can be modulated by outgassing degassing from a permeable magma. The magnitude, rate and timing of outgassing during magma ascent, in particular in relation to fragmentation, remains a subject of debate. Here we constrain how much, how fast and where the erupting magma lost its water during the 1060 CE Plinian phase of the Glass Mountain eruption of Medicine Lake Volcano, California. Using thermogravimetric analysis coupled with numerical modeling, we show that the magma lost >90% of its initial water upon eruption. Textural analyses of natural pumices, together with numerical modeling of magma ascent and degassing, indicate that 65-90% of the water exsolved before fragmentation, but very little was able to outgas before fragmentation. The magma attained permeability only within about 1 to 10 seconds before fragmenting and during that time interval permeable gas flow resulted in only a modest amount of gas flux from the un-fragmented magma. Instead, most of the water is lost shortly after fragmentation, because gas can escape rapidly from lapilli-size pyroclasts. This results in an efficient rarefaction of the gas-pyroclast mixture above the fragmentation level, indicating that the development of magma permeability and ensuing permeable outgassing are a necessary condition for sustain explosive eruptions of silicic magma. Magma permeability is thus a double-edged sword, it facilitates both, the effusive and the explosive eruption of silicic magma.

  8. Is magma cooling responsible for the periodic activity of Soufrière Hills volcano, Montserrat, West Indies?

    NASA Astrophysics Data System (ADS)

    Caricchi, Luca; Simpson, Guy; Chelle-Michou, Cyril; Neuberg, Jürgen

    2016-04-01

    in the period 2016-2018. Because cooling affects mainly the outer portions of the magmatic reservoir, pressurisation by cooling and crystallisation lead to the release of magma from the inner part of the reservoir with essentially constant composition, as observed at SHV over the last 20 years. REFERENCES Caricchi, L., Biggs, J., Annen, C., & Ebmeier, S. (2014). Earth and Planetary Science Letters, 388, 166-174. doi.org/10.1016/j.epsl.2013.12.002. Christopher, T. E., Blundy, J., Cashman, K., Cole, P., Edmonds, M., Smith, P. J., et al. (2015). Geochemistry Geophysics Geosystems, 16(9), 2797-2811. doi.org/10.1002/2015GC005791. Paulatto, M., Annen, C., Henstock, T. J., Kiddle, E., Minshull, T. A., Sparks, R. S. J., & Voight, B. (2012). Geochemistry Geophysics Geosystems, 13(1), doi.org/10.1029/2011GC003892. Tait, S., Jaupart, C., & Vergniolle, S. (1989). Earth and Planetary Science Letters, 92(1), 107-123. doi.org/10.1016/0012-821X(89)90025-3

  9. Short-lived radioactivity and magma genesis.

    PubMed

    Gill, J; Condomines, M

    1992-09-01

    Short-lived decay products of uranium and thorium have half-lives and chemistries sensitive to the processes and time scales of magma genesis, including partial melting in the mantle and magmatic differentiation in the crust. Radioactive disequilibrium between (238)U, (230)Th, and (226)Ra is widespread in volcanic rocks. These disequilibria and the isotopic composition of thorium depend especially on the extent and rate of melting as well as the presence and composition of vapor during melting. The duration of mantle melting may be several hundred millennia, whereas ascent times are a few decades to thousands of years. Differentiation of most magmas commonly occurs within a few millennia, but felsic ones can be tens of millennia old upon eruption. PMID:17738278

  10. Magma ocean formation due to giant impacts

    NASA Technical Reports Server (NTRS)

    Tonks, W. B.; Melosh, H. J.

    1993-01-01

    The thermal effects of giant impacts are studied by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths. Additionally, the effects of the planet's initial temperature on the generated melt volume are examined. The shock pressure required to completely melt the material is determined using the Hugoniot curve plotted in pressure-entropy space. Once the melting pressure is known, an impact melting model is used to estimate the radial distance melting occurred from the impact site. The melt region's geometry then determines the associated melt volume. The model is also used to estimate the partial melt volume. Magma ocean depths resulting from both excavated and retained melt are calculated, and the melt fraction not excavated during the formation of the crater is estimated. The fraction of a planet melted by the initial shock wave is also estimated using the model.

  11. Magma evolution at mount vulture (Southern Italy)

    NASA Astrophysics Data System (ADS)

    de Fino, M.; La Volpe, L.; Piccarreta, G.

    1982-06-01

    The Vulture complex is made up of foiditic, tephritic, phonolitic-trachytic and phonolitic products. New rock analyses have been performed in order to ascertain whether the various rock types derive from a unique parental magma and, if so, to define its nature. The data presented support that the Vulture suite originated from a foiditic melt which had differentiated at low pressures. The main process determining the foidite → → tephrite → phonolitic trachyte evolution seems to be the crystal fractionation of mainly clinopyroxenes, and opaques, with the contribution of plagioclases and haüyne too in the tephrite → trachyte evolution. Additionary role must have been played by a mixing of melts at different evolution stages occurred in a shallow seated magma chamber.

  12. Yamato 980459: Crystallization of Martian Magnesian Magma

    NASA Technical Reports Server (NTRS)

    Koizumi, E.; Mikouchi, T.; McKay, G.; Monkawa, A.; Chokai, J.; Miyamoto, M.

    2004-01-01

    Recently, several basaltic shergottites have been found that include magnesian olivines as a major minerals. These have been called olivinephyric shergottites. Yamato 980459, which is a new martian meteorite recovered from the Antarctica by the Japanese Antarctic expedition, is one of them. This meteorite is different from other olivine-phyric shergottites in several key features and will give us important clues to understand crystallization of martian meteorites and the evolution of Martian magma.

  13. Magma Suspension As a Complex Fluid

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Kurita, K.

    2012-12-01

    Magma is essentially a multiphase suspension of solid crystals, gaseous bubbles and silicate liquid. As for non-linear properties of magma two aspects have been focused for controlling factors in magma flow instability: the existence of the yield stress and the multiplicity in the relation between driving pressure and flow rate. The emergence of the yield stress in a suspension system has been experimentally investigated by using PNIPAM aqueous suspension as an analogue of magma (Kurokawa et al, EGU 2012-4105-2,2012). In this presentation we focus on the other aspect, the multiplicity in the rheological relationship. We investigate its physical origin of the rheology and its role in generating pressure oscillation associated with tube flow of suspension based on the PNIPAM analogue material. PNIPAM is a polymer gel and undergoes volumetric phase change at the temperature around 35 degree C: below this temperature the gel phase absorbs water and swells while over this temperature, it expels water and shrinks. Due to this property, the volume fraction of gel phase systematically changes with temperature. This makes it possible to observe the change of rheology continuously associated with the change of the fraction of solid phase. By series of rheological measurements PNIPAM aqueous suspension has been revealed to exhibit peculiar ageing effect, which is well known for complex suspension fluid. This ageing effect is responsible for generating the yield stress and the multiplicity. The multiplicity; coexistence of several flow rates at a certain pressure drives jumping between low and high flow rates, which causes oscillatory behavior of flow. We report experimental support of this model by demonstrating pressure oscillation in tube flow of PNIPAM aqueous suspension.

  14. The fundamental role of asthenospherically-derived, OIB-like magmas in volcanism of the North American Cordillera, 50 Ma to present

    SciTech Connect

    Wolff, J.A.; Ellisor, R. . Dept. of Geology); Davidson, J.P. . Dept. of Earth and Space Sciences)

    1993-04-01

    Excluding the small proportion of magmas that bear a clear mantle lithosphere signature, the geochemistry of basalts erupted in the North American Cordillera, over the past 50 Ma, is broadly consistent with a simple model of crustal contamination of magma derived from a mantle source similar to that which produces ocean-island basalts (OIB). Within any one volcanic field or association, the most mafic lavas bear the closest resemblance to OIB; contamination yields basaltic andesites and andesites having characteristics that resemble those of arc magmas. Despite the smaller volumes of andesite produced since the onset of extension compared to the earlier Cenozoic, the same chemical trends are common to both periods. This conclusion can be refined somewhat by using Weaver's trace element characterization of OIB end-member types. Least-contaminated lavas typically lie on mixing lines between depleted MORB mantle (DMM) and enriched mantle (EM). However, a significant role for EM is precluded by high [sup 143]Nd/[sup 144]Nd in the most mafic lavas. Making the conservative assumption that no magma has completely escaped contamination, most suite trends project to a DMM-HIMU mix, typically with a high proportion of DMM. Thus, the mantle component in Cordilleran lavas is essentially identical to common OIB, and it is legitimate to speculate on the possible role of a vigorous mantle plume (or plume family) as the driving force for Cenozoic Cordilleran magmatism.

  15. Magma storage and evolution in the Henties Bay-Outjo dyke swarm, Namibia -feeder systems of the Etendeka lavas

    NASA Astrophysics Data System (ADS)

    Keiding, J. K.; Frei, O.; Renno, A.; Veksler, I. V.; Trumbull, R. B.

    2012-04-01

    At the roots of continental flood basalts in the Paraná-Etendeka province are mafic dyke swarms that cover areas of several hundred kilometers. Studies of these dykes have focused mainly on the age, paleomagnetic properties and geochemistry, but less on pressure (P) and temperature (T) conditions of emplacement. However, the P and T conditions under which dyke magmas are stored are crucial for models of magma plumbing systems in flood basalt provinces. The erupted lavas are typically far from primitive compositions and generally show evidence for strong crustal assimilation in addition to magma fractionation. Unknown is where this magma modification took place in the crust. This is the kind of information that dyke studies can provide. The Henties Bay Outjo dyke swarm (HOD) in NW Namibia is the subject of this study. This is inarguably the best exposed of major dyke swarms associated with South Atlantic rifting and breakup and its geochemical diversity is well documented but aspects relating to the magma dynamics in the dyke swarm have not been studied before. Our approach is to use geochemical data from selected dykes to assess the differentiation and assimilation history of the magmas, and combine that with petrologic constraints on the temperature-pressure conditions of crystallization derived from mineral-melt equilibria. We have determined P-T estimates from olivine-melt and clinopyroxene-melt equilibria using analysis of phenocrysts by electron microprobe and applying the thermodynamic relations from Putirka (2008), who considered the standard error to be 1.7 kbar and 30°C. The calculations reflect only mineral-melt (proxied by whole-rock) compositions that are consistent with equilibrium. Crystallization temperatures range from 1040°C to 1350°C with a mean (n=58) of 1170 °C. These T-variations are not random, the high-temperature results come from a specific region of dyke emplacement but the reason for this is not yet clear. Olivine-melt temperatures

  16. Permeable Gas Flow Influences Magma Fragmentation Speed.

    NASA Astrophysics Data System (ADS)

    Richard, D.; Scheu, B.; Spieler, O.; Dingwell, D.

    2008-12-01

    Highly viscous magmas undergo fragmentation in order to produce the pyroclastic deposits that we observe, but the mechanisms involved remain unclear. The overpressure required to initiate fragmentation depends on a number of physical parameters, such as the magma's vesicularity, permeability, tensile strength and textural properties. It is clear that these same parameters control also the speed at which a fragmentation front travels through magma when fragmentation occurs. Recent mathematical models of fragmentation processes consider most of these factors, but permeable gas flow has not yet been included in these models. However, it has been shown that permeable gas flow through a porous rock during a sudden decompression event increases the fragmentation threshold. Fragmentation experiments on natural samples from Bezymianny (Russia), Colima (Mexico), Krakatau (Indonesia) and Augustine (USA) volcanoes confirm these results and suggest in addition that high permeable flow rates may increase the speed of fragmentation. Permeability from the investigated samples ranges from as low as 5 x 10-14 to higher than 9 x 10- 12 m2 and open porosity ranges from 16 % to 48 %. Experiments were performed for each sample series at applied pressures up to 35 MPa. Our results indicate that the rate of increase of fragmentation speed is higher when the permeability is above 10-12 m2. We confirm that it is necessary to include the influence of permeable flow on fragmentation dynamics.

  17. Magma-assisted rifting in Ethiopia.

    PubMed

    Kendall, J-M; Stuart, G W; Ebinger, C J; Bastow, I D; Keir, D

    2005-01-13

    The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick continental lithosphere. However, Buck has proposed that lithospheric heating by mantle upwelling and related magma production could promote lithospheric rupture at much lower stresses. Such models of mechanical versus magma-assisted extension can be tested, because they predict different temporal and spatial patterns of crustal and upper-mantle structure. Changes in plate deformation produce strain-enhanced crystal alignment and increased melt production within the upper mantle, both of which can cause seismic anisotropy. The Northern Ethiopian Rift is an ideal place to test break-up models because it formed in cratonic lithosphere with minor far-field plate stresses. Here we present evidence of seismic anisotropy in the upper mantle of this rift zone using observations of shear-wave splitting. Our observations, together with recent geological data, indicate a strong component of melt-induced anisotropy with only minor crustal stretching, supporting the magma-assisted rifting model in this area of initially cold, thick continental lithosphere. PMID:15650736

  18. Post-collisional magma systematism after exhumation of UHPM terrane in the North Qaidam UHPM belt, NW China

    NASA Astrophysics Data System (ADS)

    Wang, M.; Song, S.

    2011-12-01

    Various magmatic rocks are identified in North Dulan Belt (NDB), North Qaidam, NW China. They can be divided mainly into six types: two-mica granite, granodiorite (with magic microgranular enclaves), K-feldspar granite, biotite-monzogranite, tonalite and diorite. Most granitic rocks are compositionally homogenous with a typical granitic mineral assemblage of Mica + Pl + Kfs + Q, but granodiorites may result from magma mixing and mingling due to presence of MME and further geochemical evidence. In A/NK-A/CNK diagram samples are all spotted in metaluminous or peraluminous domain. In K2O vs. SiO2 diagram they are calc-alkaline or High-K calc-alkaline. Granite samples are of right-decline REE pattern. Zircon U-Pb LA-ICP-MS ages of magmatic rocks are 396.5±4.8Ma (two-mica granite), (379.9±2.2) -(386±2.4)Ma (granodiorite), 378.7±4.0Ma (K-feldspar granite), 368±2.0Ma (biotite monzogranite) and 360.0±3.1 (diorite) respectively. Combined with evidences from geochronology and geochemistry research, granitic rocks in Dulan UHP belt may generated in post-collisional stage. The original magma of two-mica granites are formed during exhumation of subducted continental crust which also experienced UHP metamorphism. Granodiorite may derived from mixing of crustal and mantle magma, and the magma end member can be represented by crust-formed granites and mantle-origined diorite.

  19. Volatile content of Hawaiian magmas and volcanic vigor

    NASA Astrophysics Data System (ADS)

    Blaser, A. P.; Gonnermann, H. M.; Ferguson, D. J.; Plank, T. A.; Hauri, E. H.; Houghton, B. F.; Swanson, D. A.

    2014-12-01

    We test the hypothesis that magma supply to Kīlauea volcano, Hawai'i may be affected by magma volatile content. We find that volatile content and magma flow from deep source to Kīlauea's summit reservoirs are non-linearly related. For example, a 25-30% change in volatiles leads to a near two-fold increase in magma supply. Hawaiian volcanism provides an opportunity to develop and test hypotheses concerning dynamic and geochemical behavior of hot spot volcanism on different time scales. The Pu'u 'Ō'ō-Kupaianaha eruption (1983-present) is thought to be fed by essentially unfettered magma flow from the asthenosphere into a network of magma reservoirs at approximately 1-4 km below Kīlauea's summit, and from there into Kīlauea's east rift zone, where it erupts. Because Kīlauea's magma becomes saturated in CO2 at about 40 km depth, most CO2 is thought to escape buoyantly from the magma, before entering the east rift zone, and instead is emitted at the summit. Between 2003 and 2006 Kīlauea's summit inflated at unusually high rates and concurrently CO2emissions doubled. This may reflect a change in the balance between magma supply to the summit and outflow to the east rift zone. It remains unknown what caused this surge in magma supply or what controls magma supply to Hawaiian volcanoes in general. We have modeled two-phase magma flow, coupled with H2O-CO2 solubility, to investigate the effect of changes in volatile content on the flow of magma through Kīlauea's magmatic plumbing system. We assume an invariant magma transport capacity from source to vent over the time period of interest. Therefore, changes in magma flow rate are a consequence of changes in magma-static and dynamic pressure throughout Kīlauea's plumbing system. We use measured summit deformation and CO2 emissions as observational constraints, and find from a systematic parameter analysis that even modest increases in volatiles reduce magma-static pressures sufficiently to generate a 'surge' in

  20. Silicic Magma Genesis in Neogene Central Volcanoes in Northeast Iceland

    NASA Astrophysics Data System (ADS)

    Berg, S. E.; Troll, V. R.; Riishuus, M. S.; Burchardt, S.; Krumbholz, M.

    2012-04-01

    We report on a geological expedition to NE Iceland in August 2011. A comprehensive sample suite of intrusive and extrusive rocks, ranging from basaltic to silicic compositions, was collected from the Neogene silicic central volcanic complexes in the region between Borgarfjörður eystri and Loðmundarfjörður. The area contains the second-most voluminous occurrence of silicic rocks in Iceland, including caldera structures, inclined sheet swarms, extensive ignimbrite sheets, sub-volcanic rhyolites and silicic lava flows. Yet it is one of Iceland's geologically least known areas (c.f. Gústafsson, 1992; Martin & Sigmarsson, 2010; Burchardt et al., 2011). The voluminous occurrence of evolved rocks in Iceland (10-12 %) is very unusual for an ocean island or a mid-oceanic ridge, with a typical signal of magmatic bimodality, often called "Bunsen-Daly" compositional gap (e.g. Bunsen, 1851; Daly, 1925; Barth et al., 1939). The Bunsen-Daly Gap is a long-standing fundamental issue in petrology and difficult to reconcile with continuous fractional crystallization as a dominant process in magmatic differentiation (Bowen, 1928), implying that hydrothermal alteration and crustal melting may play a significant role. Our aim is to contribute to a solution of this issue by unravelling the occurrence of voluminous evolved rhyolites in NE Iceland. We will use a combined petrological, textural, experimental and in-situ isotope approach. We plan to perform major, trace element and Sr-Nd-Hf-Pb-He-O isotope geochemistry, as well as U/Pb and Ar/Ar geochronology on rocks and mineral separates. In addition, high pressure-temperature partial melting experiments aim to reproduce and further constrain natural processes. Using the combined data set we intend to produce a comprehensive and quantitative analysis of rhyolite petrogenesis, and of the temporal, structural and geochemical evolution of the silicic volcanism in NE Iceland. The chosen field area serves as a good analogue for active

  1. Emplacement of magma in sedimentary basins

    NASA Astrophysics Data System (ADS)

    Malthe-Sorenssen, A.; Planke, S.

    2002-12-01

    Sheet-like intrusive complexes are commonly present in sedimentary basins on rifted volcanic margins. Such sill complexes have important impact on petroleum maturation, migration and trapping. We are currently completing an integrated seismic, field and theoretical study on the petroleum implications of sill intrusions. One aspect of this study has been to get new understanding of the magma emplacement processes based on integrated numerical modeling and geophysical/geological mapping activities. Extensive sill complexes have been identified and mapped in the NE Atlantic and Karoo basins based on seismic, borehole, remote sensing and field data. Early Tertiary intrusive complexes are present in the Voring and More basins offshore mid-Norway. Similar sill complexes are exposed onshore in Cretaceous to Permian age sedimentary sequences on the conjugate central-east Greenland margin. A voluminous Jurassic age intrusive complex is well exposed in the Permian to Jurassic Karoo basin as the erosionally strong dolerites form an impressive mountainous landscape in large parts of South Africa. The sheet intrusions are found at paleodepths of 0-6 km. Deep intrusions are generally long and smooth, whereas shallow intrusions are rough, transgressive and commonly saucer-shaped. Saucer-shaped intrusions are present in unstructured basin segments. The diameter of the saucers increases with depth. Structured basin segments are characterized by a variety of sill complex geometries. The intrusions generally mimic the basin structure. In nature, magma is emplaced in internally pressurized, planar cracks. The emplacement process is controlled by the local stress field and complex interactions of buoyancy forces, host rock resistance to fracture, elastic deformation of country rock, magma hydrostatic pressure and fluctuating magma pressure, magma viscosity and weight of overburden. We have developed a discrete element model to study the emplacement process. Results from the modeling

  2. Geochemical Evidence for a Terrestrial Magma Ocean

    NASA Technical Reports Server (NTRS)

    Agee, Carl B.

    1999-01-01

    The aftermath of phase separation and crystal-liquid fractionation in a magma ocean should leave a planet geochemically differentiated. Subsequent convective and other mixing processes may operate over time to obscure geochemical evidence of magma ocean differentiation. On the other hand, core formation is probably the most permanent, irreversible part of planetary differentiation. Hence the geochemical traces of core separation should be the most distinct remnants left behind in the mantle and crust, In the case of the Earth, core formation apparently coincided with a magma ocean that extended to a depth of approximately 1000 km. Evidence for this is found in high pressure element partitioning behavior of Ni and Co between liquid silicate and liquid iron alloy, and with the Ni-Co ratio and the abundance of Ni and Co in the Earth's upper mantle. A terrestrial magma ocean with a depth of 1000 km will solidify from the bottom up and first crystallize in the perovskite stability field. The largest effect of perovskite fractionation on major element distribution is to decrease the Si-Mg ratio in the silicate liquid and increase the Si-Mg ratio in the crystalline cumulate. Therefore, if a magma ocean with perovskite fractionation existed, then one could expect to observe an upper mantle with a lower than chondritic Si-Mg ratio. This is indeed observed in modern upper mantle peridotites. Although more experimental work is needed to fully understand the high-pressure behavior of trace element partitioning, it is likely that Hf is more compatible than Lu in perovskite-silicate liquid pairs. Thus, perovskite fractionation produces a molten mantle with a higher than chondritic Lu-Hf ratio. Arndt and Blichert-Toft measured Hf isotope compositions of Barberton komatiites that seem to require a source region with a long-lived, high Lu-Hf ratio. It is plausible that that these Barberton komatiites were generated within the majorite stability field by remelting a perovskite

  3. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C. J.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-08-01

    In order to explore the materials' complexity induced by bubbles rising through mixing magmas, bubble-advection experiments have been performed, employing natural silicate melts at magmatic temperatures. A cylinder of basaltic glass was placed below a cylinder of rhyolitic glass. Upon melting, bubbles formed from interstitial air. During the course of the experimental runs, those bubbles rose via buoyancy forces into the rhyolitic melt, thereby entraining tails of basaltic liquid. In the experimental run products, these plume-like filaments of advected basalt within rhyolite were clearly visible and were characterised by microCT and high-resolution EMP analyses. The entrained filaments of mafic material have been hybridised. Their post-experimental compositions range from the originally basaltic composition through andesitic to rhyolitic composition. Rheological modelling of the compositions of these hybridised filaments yield viscosities up to 2 orders of magnitude lower than that of the host rhyolitic liquid. Importantly, such lowered viscosities inside the filaments implies that rising bubbles can ascend more efficiently through pre-existing filaments that have been generated by earlier ascending bubbles. MicroCT imaging of the run products provides textural confirmation of the phenomenon of bubbles trailing one another through filaments. This phenomenon enhances the relevance of bubble advection in magma mixing scenarios, implying as it does so, an acceleration of bubble ascent due to the decreased viscous resistance facing bubbles inside filaments and yielding enhanced mass flux of mafic melt into felsic melt via entrainment. In magma mixing events involving melts of high volatile content, bubbles may be an essential catalyst for magma mixing. Moreover, the reduced viscosity contrast within filaments implies repeated replenishment of filaments with fresh end-member melt. As a result, complex compositional gradients and therefore diffusion systematics can be

  4. Uranium geochemistry of Orca Basin

    NASA Astrophysics Data System (ADS)

    Weber, F. F., Jr.; Sackett, W. M.

    1981-08-01

    Orca Basin, an anoxic, brine-filled depression at a depth of 2200 m in the Northwestern Gulf of Mexico continental slope, has been studied with respect to its uranium geochemistry. Uranium concentration profiles for four cores from within the basin were determined by delayed-neutron counting. Uranium concentrations ranged from 2.1 to 4.1 ppm on a salt-free and carbonate-corrected basis. The highest uranium concentrations were associated with the lowest percentage and δ 13C organic carbon values. For comparison, cores frm the brine-filled Suakin and Atlantis II Deeps, both in the Red Sea, were also analyzed. Uranium concentrations ranged from 1.2 to 2.6 ppm in the Suakin Deep and from 8.0 to 11.0 ppm in the Atlantis II Deep. No significant correlation was found between uranium concentrations and organic carbon concentrations and δ 13C values for these cores. Although anoxic conditions are necessary for significant uranium uptake by non-carbonate marine sediments, other factors such as dilution by rapidly depositing materials and uranium supply via mixing and diffusion across density gradients may be as important in determining uranium concentrations in hypersaline basin sediments.

  5. Long-term evolution of erupted magma chemistry

    NASA Astrophysics Data System (ADS)

    Caricchi, L.; Simpson, G.

    2014-12-01

    Magmatic reservoirs that feed explosive volcanic activity at the surface are constructed by the periodic injection of magma into the upper crust. The long-term magma flux controls the thermal evolution of these magmatic reservoirs and therefore the possibility of accumulating eruptible magma in the plumbing system of volcanoes. Magma flux, in combination with the periodicity of magma injection, regulates the frequency and magnitude of volcanic eruptions. We combined thermal and mechanical modelling with Monte Carlo simulations to compute the temporal evolution of the chemistry of eruptible magma (<50 vol. % crystals) in systems growing at different characteristic magma fluxes. We simulated the periodic injection of andesitic magma in the upper crust and trace the volume and chemistry of the eruptible magma together with the evolution of the overpressure within the reservoir. Eruptions are prescribed to occur once overpressure reached critical values (1-40 MPa). The calculations show that eruptions of rhyolitic compositions are rare and can only occur after a stage of prolonged thermal maturation of a magmatic reservoir (lasting a few hundredths of thousands of years). Additionally, eruptions of chemically evolved rocks are restricted to a specific range of physical conditions. Interestingly, the probability of eruptions of rhyolitic compositions increases substantially once the injection of magma into the magmatic reservoir ceases, which would imply that rhyolitic eruptions (not produced by partial melting of continental crust) are most likely to occur during the waning (not waxing) stages of magmatic activity.

  6. Modeling of Magma Dynamics Based on Two-Fluid Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Perepechko, Y. V.; Sorokin, K.

    2012-12-01

    Multi-velocity multi-porous models are often used as a hydrodynamic basis to describe dynamics of fluid-magma systems. These models cover such problems as fast acoustic processes or large-scaled dynamics of magma systems having non-compressible magma. Nonlinear dynamics of magma as multiphase compressible medium has not been studied sufficiently. In this work we study nonlinear thermodynamically consistent two-liquid model of magma system dynamics, based on conservation law method. The model is restricted by short times of local heat balance between phases. Pressure balance between phases is absent. Two-fluid magma model have various rheological properties of the composing phases: viscous liquid and viscoelastic Maxwell medium. The dynamics of magna flows have been studied for two types of magma systems: magma channels and intraplate intermediate magma chambers. Numerical problem of the dynamics for such media is solved using the control volume method ensuring physical correctness of the solution. The solutions are successfully verified for benchmark one-velocity models. In this work we give the results of numerical modeling using CVM for a number of non-stationary problems of nonlinear liquid filtering through granulated medium in magma channels and problems two-liquid system convection in intraplate magma chambers for various parameters. In the last case the convection regimes vary depending on non-dimensional Rayleigh and Darcy numbers and the parameter field, where compressibility effects appear, is located. The given model can be used as a hydrodynamic basis to model the evolution of magma, fluid-magma systems to study thermo-acoustic influence on hydrodynamic flows in such systems. This work was financially supported by the Russian Foundation for Basic Research, Grant #12-05-00625.

  7. Oxidized sulfur-rich mafic magma at Mount Pinatubo, Philippines

    USGS Publications Warehouse

    de Hoog, J.C.M.; Hattori, K.H.; Hoblitt, R.P.

    2004-01-01

    Basaltic fragments enclosed in andesitic dome lavas and pyroclastic flows erupted during the early stages of the 1991 eruption of Mount Pinatubo, Philippines, contain amphiboles that crystallized during the injection of mafic magma into a dacitic magma body. The amphiboles contain abundant melt inclusions, which recorded the mixing of andesitic melt in the mafic magma and rhyolitic melt in the dacitic magma. The least evolved melt inclusions have high sulfur contents (up to 1,700 ppm) mostly as SO42, which suggests an oxidized state of the magma (NNO + 1.4). The intrinsically oxidized nature of the mafic magma is confirmed by spinel-olivine oxygen barometry. The value is comparable to that of the dacitic magma (NNO + 1.6). Hence, models invoking mixing as a means of releasing sulfur from the melt are not applicable to Pinatubo. Instead, the oxidized state of the dacitic magma likely reflects that of parental mafic magma and the source region in the sub-arc mantle. Our results fit a model in which long-lived SO2 discharge from underplated mafic magma accumulated in the overlying dacitic magma and immiscible aqueous fluids. The fluids were the most likely source of sulfur that was released into the atmosphere during the cataclysmic eruption. The concurrence of highly oxidized basaltic magma and disproportionate sulfur output during the 1991 Mt. Pinatubo eruption suggests that oxidized mafic melt is an efficient medium for transferring sulfur from the mantle to shallow crustal levels and the atmosphere. As it can carry large amounts of sulfur, effectively scavenge sulfides from the source mantle and discharge SO2 during ascent, oxidized mafic magma forms arc volcanoes with high sulfur fluxes, and potentially contributes to the formation of metallic sulfide deposits. ?? Springer-Verlag 2003.

  8. Magma deformation and emplacement in rhyolitic dykes

    NASA Astrophysics Data System (ADS)

    McGowan, Ellen; Tuffen, Hugh; James, Mike; Wynn, Peter

    2016-04-01

    Silicic eruption mechanisms are determined by the rheological and degassing behaviour of highly-viscous magma ascending within shallow dykes and conduits. However, we have little knowledge of how magmatic behaviour shifts during eruptions as dykes and conduits evolve. To address this we have analysed the micro- to macro-scale textures in shallow, dissected rhyolitic dykes at the Tertiary Húsafell central volcano in west Iceland. Dyke intrusion at ~3 Ma was associated with the emplacement of subaerial rhyolitic pyroclastic deposits following caldera formation[1]. The dykes are dissected to ~500 m depth, 2-3 m wide, and crop out in two stream valleys with 5-30 m-long exposures. Dykes intrude diverse country rock types, including a welded ignimbrite, basaltic lavas, and glacial conglomerate. Each of the six studied dykes is broadly similar, exhibiting obsidian margins and microcrystalline cores. Dykes within pre-fractured lava are surrounded by external tuffisite vein networks, which are absent from dykes within conglomerate, whereas dykes failed to penetrate the ignimbrite. Obsidian at dyke margins comprises layers of discrete colour. These display dramatic thickness variations and collapsed bubble structures, and are locally separated by zones of welded, brecciated and flow-banded obsidian. We use textural associations to present a detailed model of dyke emplacement and evolution. Dykes initially propagated with the passage of fragmented, gas-charged magma and generation of external tuffisite veins, whose distribution was strongly influenced by pre-existing fractures in the country rock. External tuffisites retained permeability throughout dyke emplacement due to their high lithic content. The geochemically homogenous dykes then evolved via incremental magma emplacement, with shear deformation localised along emplacement boundary layers. Shear zones migrated between different boundary layers, and bubble deformation promoted magma mobility. Brittle

  9. Viscosity of Campi Flregrei (Italy) magmas

    NASA Astrophysics Data System (ADS)

    Misiti, Valeria; Vetere, Francesco; Scarlato, Piergiorgio; Behrens, Harald; Mangiacapra, Annarita; Freda, Carmela

    2010-05-01

    Viscosity is an important factor governing both intrusive and volcanic processes. The most important parameters governing silicate melts viscosity are bulk composition of melt and temperature. Pressure has only minor effect at crustal depths, whereas crystals and bubbles have significant influence. Among compositional parameters, the water content is critical above all in terms of rheological behaviour of melts and explosive style of an eruption. Consequently, without an appropriate knowledge of magma viscosity depending on the amount of dissolved volatiles, it is not possible to model the processes (i.e., magma ascent, fragmentation, and dispersion) required to predict realistic volcanic scenarios and thus forecast volcanic hazards. The Campi Flegrei are a large volcanic complex (~150 km2) located west of the city of Naples, Italy, that has been the site of volcanic activity for more than 60 ka and represents a potential volcanic hazard owing to the large local population. In the frame of a INGV-DPC (Department of Civil Protection) project devoted to design a multidisciplinary system for short-term volcano hazard evaluation, we performed viscosity measurements, under dry and hydrous conditions, of primitive melt compositions representative of two Campi Flegrei eruptions (Minopoli-shoshonite and Fondo Riccio-latite). Viscosity of the two melts have been investigated in the high temperature/low viscosity range at atmospheric pressure in dry samples and at 0.5 GPa in runs having water content from nominally anhydrous to about 3 wt%. Data in the low temperature/high viscosity range were obtained near the glass transition temperature at atmospheric pressure on samples whose water contents vary from 0.3 up to 2.43 wt%. The combination of high- and low-viscosity data permits a general description of the viscosity as a function of temperature and water content using a modified Tamman-Vogel-Fulcher equation. logν = a+ --b--+ --d--×exp(g × w-) (T - c) (T - e) T (1) where

  10. Magma-driven subcritical crack growth and implications for dike initiation from a magma chamber

    NASA Astrophysics Data System (ADS)

    Chen, Zuan; Jin, Z.-H.

    2006-10-01

    The purpose of this paper is to explore a viscoelastic energy dissipation theory for subcritical dike growth from a magma chamber. The theoretical relationship between the dike growth velocity and dike length is established using the viscoelastic subcritical crack growth theory proposed by the first author and the solutions of stress intensity factor at the crack tip derived by a perturbation method. Effects of magma chamber over-pressure, buoyancy and viscoelastic properties of the host rock on the subcritical growth rate are included in the model. The numerical results indicate that the viscous energy dissipation of the host rock could allow a short dike to slowly grow on the order of 10-7-10-5 m/s under modest over-pressure and to accelerate when the stress intensity factor increases close to the fracture toughness, followed by the unstable dike propagation. The proposed theory provides a reasonable understanding of dike initiation process from a magma chamber.

  11. The influence of magma viscosity on convection within a magma chamber

    NASA Astrophysics Data System (ADS)

    Schubert, M.; Driesner, T.; Ulmer, P.

    2012-12-01

    Magmatic-hydrothermal ore deposits are the most important sources of metals like Cu, Mo, W and Sn and a major resource for Au. It is well accepted that they are formed by the release of magmatic fluids from a batholith-sized magma body. Traditionally, it has been assumed that crystallization-induced volatile saturation (called "second boiling") is the main mechanism for fluid release, typically operating over thousands to tens of thousands of years (Candela, 1991). From an analysis of alteration halo geometries caused by magmatic fluids, Cathles and Shannon (2007) suggested much shorter timescales in the order of hundreds of years. Such rapid release of fluids cannot be explained by second boiling as the rate of solidification scales with the slow conduction of heat away from the system. However, rapid fluid release is possible if convection is assumed within the magma chamber. The magma would degas in the upper part of the magma chamber and volatile poor magma would sink down again. Such, the rates of degassing can be much higher than due to cooling only. We developed a convection model using Navier-Stokes equations provided by the computational fluid dynamics platform OpenFOAM that gives the possibility to use externally derived meshes with complex (natural) geometries. We implemented a temperature, pressure, composition and crystal fraction dependent viscosity (Ardia et al., 2008; Giordano et al., 2008; Moore et al., 1998) and a temperature, pressure, composition dependent density (Lange1994). We found that the new viscosity and density models strongly affect convection within the magma chamber. The dependence of viscosity on crystal fraction has a particularly strong effect as the steep viscosity increase at the critical crystal fraction leads to steep decrease of convection velocity. As the magma chamber is cooling from outside to inside a purely conductive layer is developing along the edges of the magma chamber. Convection continues in the inner part of the

  12. The Geochemistry of Aplite Dikes at Elliot Lake, Ontario

    NASA Astrophysics Data System (ADS)

    Finlayson, V. A.; Rooney, T.

    2009-05-01

    We present an analysis of the bulk geochemistry of heretofore unstudied aplites associated with the Matinenda Formation at Elliot Lake, Ontario, Canada. We present major and trace element data from six aplites and their quartz pebble conglomerate hosts. Our preliminary data suggests that the aplites are sodic (10-11%) and are only moderately enriched in SiO2 (up to 72%). In contrast the host rock is potassic (3.8%) or sodic (4-6%) but universally enriched in SiO2 (over 85%) in comparison to the aplites. The aplites are characterized by light pink-grey to medium pink coloration, sugary texture, and fairly uniform sub-millimeter quartz and feldspar crystals. Aplites exhibiting darker or pinker coloration contain higher concentrations of sub-millimeter garnet, biotite, muscovite, and pyrite. Pyrite is present in all aplite and quartz pebble conglomerate samples, accumulating preferentially on and around fractures. Quartz pebble conglomerate samples range from light tan-grey to dark pink-grey in color and contain varying amounts of rounded clear to white-yellow quartz grains up to 3 mm in diameter. The quartz pebble conglomerate of the Matinenda Formation, through which the aplite dikes have passed, is known to contain economic concentrations of paleoplacer uraninite. Uraninite is concentrated near the axis of the regional Quirke Lake Syncline structure, possibly as a result of past activity of an underlying metavolcanic-metasedimentary belt (Robertson 1977, OGS). Some aplite and quartz pebble conglomerate drill cores exhibit radioactivity, however we have selected only non-radioactive samples for analysis. This study will examine the petrogenesis of the aplite dikes, and determine if the intrusion of the aplites triggered a hydrothermal circulation system that remobilized the paleoplacer uraninite in the host rock and transported uranyl ions into the aplite magma.

  13. Geochemistry and Minerality of Wine

    NASA Astrophysics Data System (ADS)

    Oze, C.; Horton, T. W.; Beaman, M.

    2010-12-01

    Kaolinite (Al2Si2O5(OH)4) and gibbsite (Al(OH)3) are capable of forming in a variety of environments including anthropogenic solutions such as wine. Here, we evaluate the geochemistry of twelve white wines in order to assess the potential relationship between kaolinite/gibbsite saturation and minerality, a common wine descriptor used to express the rock and/or soil character in the aromas and flavors of wines. Aluminum and Si concentrations ranged from 228-1,281 µg L-1 and 6,583-19,746 µg L-1, respectively, where Si and Al are the only elements to demonstrate positive covariance with minerality scores. Sulfur levels varied from 25,013-167,383 µg L-1 and show the strongest negative covariance with minerality scores. However, like all of the elements studied (Al, Si, Na, Mg, S, K, Ca, and Fe), these trends were not significantly different than random at the 95% confidence level. In contrast, the relative degrees of gibbsite/kaolinite saturation display strong positive covariance with minerality scores and these trends are not random at the greater than 95% confidence level. Overall, our tasters were able to accurately assess the degree of gibbsite/kaolinite saturation amongst the twelve wines based on the objective of assessing minerality. Although the wines were undersaturated with respect to gibbsite/kaolinite, geochemical modeling reveals that increasing the wines’ pHs from ~3.3 to 4.1-4.6 (which is achievable on the palate where saliva has a pH of 7.4) results in gibbsite/kaolinite oversaturation. By considering that minerality is a function of gibbsite/kaolinite saturation and decreasing S, the origin of minerality’s taste and chemical origin in wine with known physical standards becomes increasingly crystalline.

  14. Magma degassing during eruption through water-saturated porous rocks

    NASA Astrophysics Data System (ADS)

    Melnik, O. E.; Afanasyev, A. A.; Zarin, G. A.

    2016-05-01

    In the case of extrusive eruption, we consider the problem on magma degassing which rises in a volcano conduit crossing porous water-saturated rocks. We show that the intensity of outflow of volcanic gases into the rocks is comparable to the intensity of their transport with the rising magma. The magma degassing in the rocks substantially affects the eruption dynamics, in particular, the duration of the periods of eruptive activity.

  15. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Daniele, M.; Renggli, C.; Perugini, D.; De Campos, C.; Hess, K. U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2014-12-01

    Rising bubbles may significantly affect magma mixing paths as has been demonstrated by analogue experiments in the past. Here, bubble-advection experiments are performed for the first time employing natural materials at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears as efficient mechanism to mingle contrasting melt compositions. MicroCT imaging shows bubbles trailing each other and trails of multiple bubbles having converged. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that subsequent bubbles rising are likely to follow the same pathways that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Fundamental implications for the concept of bubble advection in magma mixing are thus a) an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and b) non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a filament. Inside these filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments are likely to have experienced multiple bubbles passing through

  16. Rift initiation with volatiles and magma

    NASA Astrophysics Data System (ADS)

    Ebinger, Cynthia; Muirhead, James; Roecker, Steve; Tiberi, Christel; Muzuka, Alfred; Ferdinand, Rrichard; Mulibo, Gabrile; Kianji, Gladys

    2015-04-01

    Rift initiation in cratonic lithosphere remains an outstanding problem in continental tectonics, but strain and magmatism patterns in youthful sectors of the East African rift provide new insights. Few teleseisms occur in the Eastern rift arm of the East African rift system, except the southernmost sector in northern Tanzania where extension occurs in Archaean lithosphere. The change in seismic energy release occurs over a narrow along-axis zone, and between sectors with and without volcanoes in the central rift valley. Are these differences in strain behavior indicative of along-strike variations in a) rheology; b) strain transfer from border faults to magma intrusion zones; c) dike vs fault slip; and/or d) shallow vs deep magma chambers? We present time-space relations of seismicity recorded on a 38-station array spanning the Kenya-Tanzania border, focal mechanisms for the largest events during those time periods, and compare these to longer-term strain patterns. Lower crustal seismicity occurs along the rift length, including sectors on and off craton, and those with and without central rift valley volcanoes, and we see no clear along-strike variation in seismogenic layer thickness. One explanation for widespread lower crustal seismicity is high gas pressures and volatile migration from active metasomatism of upper mantle and magma degassing, consistent with very high volatile flux along fault zones, and widespread metasomatism of xenoliths. Volatile release and migration may be critical to strength reduction of initially cold, strong cratonic lithosphere. Seismicity patterns indicate strain (and fluid?) transfer from the Manyara border fault to Gelai shield volcano (faulting, diking) via Oldoinyo Lengai volcano. Our focal mechanisms and Global CMTs from an intense fault-dike episode (2007) show a local, temporally stable, rotation from ~E-W extension to NE-SE extension in this linkage zone, consistent with longer term patterns recorded in vent and eruptive

  17. Experimental Study of Lunar and SNC Magmas

    NASA Technical Reports Server (NTRS)

    Rutherford, Malcolm J.

    1998-01-01

    The research described in this progress report involved the study of petrological, geochemical and volcanic processes that occur on the Moon and the SNC parent body, generally accepted to be Mars. The link between these studies is that they focus on two terrestrial-type parent bodies somewhat smaller than earth, and the fact that they focus on the role of volatiles in magmatic processes and on processes of magma evolution on these planets. The work on the lunar volcanic glasses has resulted in some exciting new discoveries over the years of this grant. We discovered small metal blebs initially in the Al5 green glass, and determined the significant importance of this metal in fixing the oxidation state of the parent magma (Fogel and Rutherford, 1995). More recently, we discovered a variety of metal blebs in the Al7 orange glass. Some of these Fe-Ni metal blebs were in the glass; others were in olivine phenocrysts. The importance of these metal spheres is that they fix the oxidation state of the parent magma during the eruption, and also indicate changes during the eruption (Weitz et al., 1997) They also yield important information about the composition of the gas phase present, the gas which drove the lunar fire-fountaining. One of the more exciting and controversial findings in our research over the past year has been the possible fractionation of H from D during shock (experimental) of hornblende bearing samples (Minitti et al., 1997). This research is directed at explaining some of the low H2O and high D/H observed in hydrous phases in the SNC meteorites.

  18. Coupled effect of magma degassing and rheology on silicic volcanism

    NASA Astrophysics Data System (ADS)

    Okumura, Satoshi; Nakamura, Michihiko; Uesugi, Kentaro; Nakano, Tsukasa; Fujioka, Takuma

    2013-01-01

    Explosive volcanism such as the 1991 Mt. Pinatubo, Philippines, and the 2008 Mt. Chaitén, Chile, eruptions is caused by violent vesiculation of hydrous magma. However, gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit. This makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common. Here, we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation X-ray radiography and computed tomography. We observed, for the first time in situ, that the shear localization caused magma fracturing and formed a slip plane, and thus inhibited deformation and outgassing elsewhere. We also observed the compaction of vesicular magma into a dense "lava" as a result of outgassing when shear localization did not occur. In a natural setting, shear localizes along the edges of a volcanic conduit, where the strain rate is high, causing a highly permeable fracturing layer to form at the conduit's edge and leaving less-sheared and less-outgassed magma at its center. The less-outgassed magma in the center may ascend rapidly and cause explosive volcanism. Non-explosive lava effusion may occur only when shear localization does not occur effectively. This new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity (pyroclastic obsidian and highly vesiculated pumice).

  19. Selection of promising sites for magma energy experiments

    SciTech Connect

    Carson, C.C.

    1985-01-01

    The Long Valley and Coso Hot Springs areas of California have been identified as the most promising sites for conducting a magma energy extraction experiment. These two locations were selected from among the potential sites on the basis of several factors that are critical to the success of the proposed long-term energy extraction experiment. These factors include the likelihood of the existence of shallow magma targets as well as several other drilling, energy extraction and programmatic considerations. As the magma energy extraction program continues, these sites will be analyzed in detail so that one can be selected as the site for the planned magma experiment.

  20. Special Relativity Derived from Spacetime Magma

    PubMed Central

    Greensite, Fred

    2014-01-01

    We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid) existing on the union of spacetime frame components and Euclidean which is consistent with an “inversion symmetry” constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of “inverse norms” which play major roles with respect to various unital -algebras more generally. PMID:24959889

  1. Special relativity derived from spacetime magma.

    PubMed

    Greensite, Fred

    2014-01-01

    We present a derivation of relativistic spacetime largely untethered from specific physical considerations, in constrast to the many physically-based derivations that have appeared in the last few decades. The argument proceeds from the inherent magma (groupoid) existing on the union of spacetime frame components [Formula: see text] and Euclidean [Formula: see text] which is consistent with an "inversion symmetry" constraint from which the Minkowski norm results. In this context, the latter is also characterized as one member of a class of "inverse norms" which play major roles with respect to various unital [Formula: see text]-algebras more generally. PMID:24959889

  2. Asteroid differentiation - Pyroclastic volcanism to magma oceans

    NASA Technical Reports Server (NTRS)

    Taylor, G. J.; Keil, Klaus; Mccoy, Timothy; Haack, Henning; Scott, Edward R. D.

    1993-01-01

    A summary is presented of theoretical and speculative research on the physics of igneous processes involved in asteroid differentiation. Partial melting processes, melt migration, and their products are discussed and explosive volcanism is described. Evidence for the existence of asteroidal magma oceans is considered and processes which may have occurred in these oceans are examined. Synthesis and inferences of asteroid heat sources are discussed under the assumption that asteroids are heated mainly by internal processes and that the role of impact heating is small. Inferences of these results for earth-forming planetesimals are suggested.

  3. Role of Yield Stress in Magma Rheology

    NASA Astrophysics Data System (ADS)

    Kurokawa, A.; Di Giuseppe, E.; Davaille, A.; Kurita, K.

    2012-04-01

    Magmas are essentially multiphase material composed of solid crystals, gaseous bubbles and silicate liquids. They exhibit various types of drastic change in rheology with variation of mutual volumetric fractions of the components. The nature of this variable rheology is a key factor in controlling dynamics of flowing magma through a conduit. Particularly the existence of yield stress in flowing magma is expected to control the wall friction and formation of density waves. As the volumetric fraction of solid phase increases yield stress emerges above the critical fraction. Several previous studies have been conducted to clarify this critical value of magmatic fluid both in numerical simulations and laboratory experiments ([Lejeune and Pascal, 1995], [Saar and Manga 2001], [Ishibashi and Sato 2010]). The obtained values range from 13.3 to 40 vol%, which display wide variation and associated change in rheology has not been clarified well. In this presentation we report physical mechanism of emergence of yield stress in suspension as well as the associated change in the rheology based on laboratory experiments using analog material. We utilized thermogel aqueous suspension as an analog material of multiphase magma. Thermogel, which is a commercial name for poly(N-isopropyl acrylamide) (PNIPAM) undergoes volumetric phase change at the temperature around 35C:below this temperature the gel phase absorbs water and swells while below this it expels water and its volume shrinks. Because of this the volumetric fraction of gel phase systematically changes with temperature and the concentration of gel powder. The viscosity measured at lower stress drastically decreases across this phase change with increasing temperature while the viscosity at higher stress does not exhibit large change across the transition. We have performed a series of rheological measurements focusing on the emergence of yield stress on this aqueous suspension. Since the definition of yield stress is not

  4. Magma hybridisation at Soufriere Hills Volcano, Montserrat

    NASA Astrophysics Data System (ADS)

    Humphreys, Madeleine; Edmonds, Marie; Christopher, Thomas; Hards, Vicky

    2010-05-01

    Arc volcanoes commonly show evidence of mingling between mafic and silicic magma. For example, the Soufrière Hills Volcano, Montserrat typically erupts andesitic magma containing basaltic to basaltic-andesite inclusions. However, the andesite also contains a wide variety of phenocryst textures as well as strongly zoned microlites, suggesting that more intimate physical mixing also occurs. Analysis of minor elements in both phenocrysts and microlites allows the discrimination of different crystal populations, and provides insight into their origins. Microlites of plagioclase and orthopyroxene are chemically distinct from the phenocrysts, being enriched in Fe and Mg, and Al and Ca respectively. However, they are indistinguishable from the compositions of these phases in the mafic inclusions. Microlite compositions also give anomalously high temperatures using standard geothermometry techniques, similar to those of the mafic inclusions. Compositions of clinopyroxene from overgrowth rims on quartz and orthopyroxene and coarse-grained breakdown rims on hornblende, are identical to those from the mafic inclusions, indicating that these rims form during interaction with mafic magma. We infer that the inclusions disaggregated under conditions of high shear stress during ascent in the conduit, transferring mafic material into the andesite groundmass. This implies that the mafic component of the system is greater than previously determined from the volume proportion of mafic enclaves. The presence of mafic-derived microlites in the andesite groundmass also means that care must be taken when using this as a starting material for phase equilibrium experiments. Melt inclusions and matrix glasses in the erupted include an anomalously K2O-rich population which overlaps with residual (high-K2O, high-TiO2) mafic inclusion glass. These glasses represent the effects of physical mixing with mafic magma, both during ascent and by diffusive exchange during the formation of mafic

  5. Evidence for magma mixing within the Laacher See magma chamber (East Eifel, Germany)

    USGS Publications Warehouse

    Worner, G.; Wright, T.L.

    1984-01-01

    The final pyroclastic products of the late Quaternary phonolitic Laacher See volcano (East Eifel, W.-Germany) range from feldspar-rich gray phonolite to dark olivine-bearing rocks with variable amounts of feldspar and Al-augite megacrysts. Petrographically and chemically homogeneous clasts occur along with composite lapilli spanning the compositional range from phonolite (MgO 0.9%) to mafic hybrid rock (MgO 7.0%) for all major and trace elements. Both a basanitic and a phonolitic phenocryst paragenesis occur within individual clasts. The phonolite-derived phenocrysts are characterized by glass inclusions of evolved composition, rare inverse zoning and strong resorption indicating disequilibrium with the mafic hybrid matrix. Basanitic (magnesian) clinopyroxene and olivine, in contrast, show skeletal (normally zoned) overgrowths indicative of post-mixing crystallization. In accord with petrographical and other chemical evidence, mass balance calculations suggest mixing of an evolved Laacher See phonolite containing variable amounts of mineral cumulates and a megacryst-bearing basanite magma. Magma mixing occurred just prior to eruption (hours) of the lowermost magma layer of the Laacher See magma chamber but did not trigger the volcanic activity. ?? 1984.

  6. Magma evolution and ascent at the Craters of the Moon and neighboring volcanic fields, southern Idaho, USA: implications for the evolution of polygenetic and monogenetic volcanic fields

    USGS Publications Warehouse

    Putirka, Keith D.; Kuntz, Mel A.; Unruh, Daniel M.; Vaid, Nitin

    2009-01-01

    The evolution of polygenetic and monogenetic volcanic fields must reflect differences in magma processing during ascent. To assess their evolution we use thermobarometry and geochemistry to evaluate ascent paths for neighboring, nearly coeval volcanic fields in the Snake River Plain, in south-central Idaho, derived from (1) dominantly Holocene polygenetic evolved lavas from the Craters of the Moon lava field (COME) and (2) Quaternary non-evolved, olivine tholeiites (NEOT) from nearby monogenetic volcanic fields. These data show that NEOT have high magmatic temperatures (1205 + or - 27 degrees C) and a narrow temperature range (50 degrees C). Prolonged storage of COME magmas allows them to evolve to higher 87Sr/86Sr and SiO2, and lower MgO and 143Nd/144Nd. Most importantly, ascent paths control evolution: NEOT often erupt near the axis of the plain where high-flux (Yellowstone-related), pre-Holocene magmatic activity replaces granitic middle crust with basaltic sills, resulting in a net increase in NEOT magma buoyancy. COME flows erupt off-axis, where felsic crustal lithologies sometimes remain intact, providing a barrier to ascent and a source for crustal contamination. A three-stage ascent process explains the entire range of erupted compositions. Stage 1 (40-20 km): picrites are transported to the middle crust, undergoing partial crystallization of olivine + or - clinopyroxene. COME magmas pass through unarmored conduits and assimilate 1% or less of ancient gabbroic crust having high Sr and 87Sr/86Sr and low SiO2. Stage 2 (20-10 km): magmas are stored within the middle crust, and evolve to moderate MgO (10%). NEOT magmas, reaching 10% MgO, are positively buoyant and migrate through the middle crust. COME magmas remain negatively buoyant and so crystallize further and assimilate middle crust. Stage 3 (15-0 km): final ascent and eruption occurs when volatile contents, increased by differentiation, are sufficient (1-2 wt % H2O) to provide magma buoyancy through the

  7. Geochemistry of coalbed gas - a review

    USGS Publications Warehouse

    Clayton, J.L.

    1998-01-01

    Coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource. Coal mining operations, such as ventilation of coalbed gas from underground mines, release coalbed CH4 into the atmosphere, an important greehouse gas whose concentration in the atmosphere is increasing. Because of these energy and environmental issues, increased research attention has been focused on the geochemistry of coalbed gas in recent years. This paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances.Coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource. Coal mining operations, such as ventilation of coalbed gas from underground mines, release coalbed CH4 into the atmosphere, an important greenhouse gas whose concentration in the atmosphere is increasing. Because of these energy and environmental issues, increased research attention has been focused on the geochemistry of coalbed gas in recent years. This paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances.

  8. U.S. National Committee for Geochemistry

    ERIC Educational Resources Information Center

    Geotimes, 1974

    1974-01-01

    Reports highlights of the April, 1973 meeting of the U.S. National Committee for Geochemistry. Some of the topics reported on were: The Geophysics Research Board, deep drilling, exchange of geochemists with China and the activities of the Subcommittee on Geochemical Environment in Relation to Health and Disease. (BR)

  9. Examining the role of magma mixing with major and minor element distribution patterns in rock-forming minerals in the Tuolumne batholith, Sierra Nevada, CA

    NASA Astrophysics Data System (ADS)

    Krause, J.; Memeti, V.; Paterson, S. R.

    2009-12-01

    Recent geochemical and geochronologic studies emphasize the role of incremental growth of large magma chambers and associated complex magma processes. One of the major results of these studies is that volcanic and plutonic rocks tend to consist of different crystal populations recording complex individual histories. Detailed geochemical observations of individual minerals provide direct access to petrogenetic processes, which are averaged in whole rock analyses. Recent field, U/Pb zircon geochronology and geochemistry data on the 95-85 Ma Tuolumne batholith (TB), Sierra Nevada, CA, have shown ample evidence for extensive mixing between different magmas and internal magma chamber recycling of older marginal units into younger central units within the long lived, main batholith. Its southern lobes are interpreted to represent shorter lived and simpler magma bodies since their composition is attributed to fractionation of magma derived from a single source. In order to test this hypothesis on the mineral scale, X-ray element distribution maps and quantitative analyses have been performed with the electron microprobe on samples from different structural positions both in the lobes and the main chamber of the TB. K-feldspars, ≤ 5 mm large, of the central Kuna Crest lobe, the porphyritic Half Dome lobe, and from the margin of the northern Half Dome lobe often show simple Ba zoning patterns with elevated contents in the center (Ba = 0.8-1.2 wt%) decreasing towards the rim (Ba = 0.4-0.5 wt%). Other K-feldspars ≤ 1.5 mm within the same thin section have reversed zoning with low Ba contents in the core (Ba = 0.1-0.2 wt%) increasing towards the rim (Ba = 0.4-0.6 wt%). A sample from the center of the Cathedral Peak lobe contains idiomorphic K-feldspar phenocrysts ≤ 12 mm with concentric oscillatory Ba-zoning (Ba = 0.6-1.9 wt%) and abundant inclusions of plagioclase. In addition, this sample contains idiomorphic K-feldspars ≤ 1.5 mm with homogeneous cores free of

  10. Magma chamber dynamics constrained by crystal isotope stratigraphy

    NASA Astrophysics Data System (ADS)

    Davidson, J. P.; Tepley, F. J., III; Hora, J. M.

    2003-04-01

    The architecture of subvolcanic magma plumbing systems controls the thermal regime transited by magmas in the lithosphere, and consequently influences the rates and processes by which magmas evolve. The resolution of current geophysical methods is unable to accurately define the shapes, sizes and crystallinity of small magma bodies. Exhumed fossil magma chambers may provide terminal or cumulative plumbing system assemblies but cannot provide snapshots of the system at a given time, and fail to identify ephemeral components such as dikes, which may open and close to transport magma. Petrographically-constrained in situ analysis of the components of volcanic rocks, including crystal isotope stratigraphy, has recently proved an important new approach to constraining the dynamics of magma storage systems. Core-to-rim decreases in 87Sr/86Sr accompanied by increases in Sr concentration for single plagioclase crystals seen at volcanoes such as El Chichon, Mexico, are explained by frequent recharge of a storage reservoir(s). The fact that high 87Sr/86Sr values are restricted to cores suggests that contamination occurs at the initial stages of injection and contact between magma and the crust. This in turn suggests that crystallization occurs at the margins of the magma body where the thermal gradient is strongest, volatiles are concentrated and epitaxial crystallization is promoted. The crystallized boundary zone then isolates the magma and prevents subsequent recharge magma from interacting directly with the crust. In cases such as Ngauruhoe volcano, New Zealand, 87Sr/86Sr increases from core-to-rim of plagioclase crystals suggest that the magma was not completely isolated from a crustal contaminant. In either case, changes in Sr isotope ratio are correlated with punctuated textural evidence for disequilibrium events, underscoring the importance of recharge. Recharge disaggregates and remobilizes much of the material crystallized from earlier events. Petrographic and

  11. Thermal and mechanical constraints on mixing between mafic and silicic magmas

    NASA Astrophysics Data System (ADS)

    Sparks, R. S. J.; Marshall, L. A.

    1986-09-01

    When magmas of different temperature and composition are intimately mingled together, transfer of heat results in substantial changes in the rheological properties of the magmas. Since thermal diffusion rates are orders of magnitude faster than chemical diffusion rates, mixing magmas will come nearly to the same temperature before complete homogenization of the magmas can occur by diffusion and shearing. The ability of magmas to mix thus depends on their physical properties after thermal equilibration. Calculations are presented on how the viscosity and crystal content of mafic and silicic magmas vary as a function of their initial temperatures and the proportion of mafic magma in the mixture. Three physical situations can be identified: (a) where the mafic magma remains less viscous than the silicic magma; (b) where the mafic magma becomes more viscous than the silicic magma due to crystallization; and (c) where the mafic magma is effectively solid due to its high crystal content. In the last situation it is proposed that complete mixing cannot take place, but the mafic magma is dispersed as solid xenoliths or inclusions within the silicic magma. Xenolith or inclusion formation occurs when there is a large temperature difference between the magmas or a large proportion of silicic magma. Complete hybridization can only occur when the magmas both behave as liquids at the same temperature. A diagram is constructed that shows the fields where the mafic magma becomes a solid or remains a fluid on a plot of the proportion of mafic magma against the composition of the mafic magma. Where there is a large proportion of silicic magma, complete hybridization can only occur with evolved mafic magmas (andesitic magmas). An example of this compositional selectivity is described from St. Kilda, Scotland where silicic magmas have only hybridized with highly evolved theoleiitic andesite magmas, although the silicic magma is intimately intermingled with more mafic magmas in net

  12. Magma chambers: Formation, local stresses, excess pressures, and compartments

    NASA Astrophysics Data System (ADS)

    Gudmundsson, Agust

    2012-09-01

    An existing magma chamber is normally a necessary condition for the generation of a large volcanic edifice. Most magma chambers form through repeated magma injections, commonly sills, and gradually expand and change their shapes. Highly irregular magma-chamber shapes are thermo-mechanically unstable; common long-term equilibrium shapes are comparatively smooth and approximate those of ellipsoids of revolution. Some chambers, particularly small and sill-like, may be totally molten. Most chambers, however, are only partially molten, the main part of the chamber being crystal mush, a porous material. During an eruption, magma is drawn from the crystal mush towards a molten zone beneath the lower end of the feeder dyke. Magma transport to the feeder dyke, however, depends on the chamber's internal structure; in particular on whether the chamber contains pressure compartments that are, to a degree, isolated from other compartments. It is only during large drops in the hydraulic potential beneath the feeder dyke that other compartments become likely to supply magma to the erupting compartment, thereby contributing to its excess pressure (the pressure needed to rupture a magma chamber) and the duration of the eruption. Simple analytical models suggest that during a typical eruption, the excess-pressure in the chamber decreases exponentially. This result applies to a magma chamber that (a) is homogeneous and totally fluid (contains no compartments), (b) is not subject to significant replenishment (inflow of new magma into the chamber) during the eruption, and (c) contains magma where exsolution of gas has no significant effect on the excess pressure. For a chamber consisting of pressure compartments, the exponential excess-pressure decline applies primarily to a single erupting compartment. When more than one compartment contributes magma to the eruption, the excess pressure may decline much more slowly and irregularly. Excess pressure is normally similar to the in

  13. Comparison of Magma Residence, Magma Ascent and Magma-Hydrothermal Interaction at EPR 9°N and Endeavour Segment

    NASA Astrophysics Data System (ADS)

    Michael, P. J.; Gill, J. B.; Ramos, F. C.

    2010-12-01

    We compare magmas’ temperatures (Mg#s), their degree of crustal assimilation (“excess” Chlorine) and their residence depth and ascent speed (dissolved CO2 content) at similar scales, using new data for Endeavour and new and published [1] data for EPR 9°N. We relate differences between the two segments to other differences, e.g., depth and width of the AMC reflector. Cl in glasses, and Cl/K or Cl/Nb ratios, are indicators of magma’s interaction with altered crust, probably at the roof of the AMC [1,2]. An excess Cl (in ppm) value for each glass can be calculated by subtracting mantle-derived Cl from measured Cl. At 9°N, excess Cl is negatively correlated with Mg#. Mg# is lower and excess Cl is higher off-axis (up to 4 km). At a given Mg#, Cl is higher off-axis [1]. Endeavour magmas on-axis have lower Mg# than EPR, while their ranges are similar off-axis. At Endeavour, there is no good correlation of excess Cl with Mg#, although glasses with high Mg# are found mostly on-axis. There is no trend of Mg# or excess Cl with distance from the axis. Excess Cl is similar on-axis between the two ridges. At both ridges, assimilation has a stochastic distribution, such that high- and low-Cl glasses are found in most locations. Because CO2 exsolution and bubble formation is slow compared to magma ascent and surface flow, many glasses are oversaturated compared to their eruption depth. Dissolved CO2 contents thus provide information about the duration of a magma’s transit between its last stopping point and final lava emplacement. If magma erupts and cools quickly, its dissolved CO2 should correspond to its last resting point, possibly the AMC. At EPR 9°N, maximum CO2 contents would be in equilibrium at the AMC roof, while minimum CO2 contents are nearly in equilibrium with collection depths. Glasses have high CO2 on-axis and low CO2 off-axis, and there is a negative correlation between CO2 and distance off-axis [1]. This is partly due to post-eruptive flow away from

  14. The Bushveld Complex, South Africa: formation of platinum-palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber

    NASA Astrophysics Data System (ADS)

    Maier, W. D.; Barnes, S.-J.; Groves, D. I.

    2013-01-01

    Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.

  15. Zircons reveal magma fluxes in the Earth's crust.

    PubMed

    Caricchi, Luca; Simpson, Guy; Schaltegger, Urs

    2014-07-24

    Magma fluxes regulate the planetary thermal budget, the growth of continents and the frequency and magnitude of volcanic eruptions, and play a part in the genesis and size of magmatic ore deposits. However, because a large fraction of the magma produced on the Earth does not erupt at the surface, determinations of magma fluxes are rare and this compromises our ability to establish a link between global heat transfer and large-scale geological processes. Here we show that age distributions of zircons, a mineral often present in crustal magmatic rocks, in combination with thermal modelling, provide an accurate means of retrieving magma fluxes. The characteristics of zircon age populations vary significantly and systematically as a function of the flux and total volume of magma accumulated in the Earth's crust. Our approach produces results that are consistent with independent determinations of magma fluxes and volumes of magmatic systems. Analysis of existing age population data sets using our method suggests that porphyry-type deposits, plutons and large eruptions each require magma input over different timescales at different characteristic average fluxes. We anticipate that more extensive and complete magma flux data sets will serve to clarify the control that the global heat flux exerts on the frequency of geological events such as volcanic eruptions, and to determine the main factors controlling the distribution of resources on our planet. PMID:25056063

  16. Oxygen isotope geochemistry of zircon

    NASA Astrophysics Data System (ADS)

    Valley, John W.; Chiarenzelli, Jeffrey R.; McLelland, James M.

    1994-09-01

    ranging from 39 to 75 wt% SiO2. Only olivine metagabbros have lower average values (6.4/mil), consistent with the hypothesis that they represent nearly pristine samples of the anorthosite's parent magma. Whole-rock values of delta (O-18) are also high in the AMCG suite and increase with SiO2 content, as predicted for a process of assimilation and fractional crystallization. Taken together, these data suggest that the elevated values of oxygen isotope ratios result from partial melting and contamination involving metasediments in the deep crust, before the crystallization of zircon. More normal values elsewhere in the Grenville Province record deep-seated, pre-1150 Ma regional differences.

  17. Post-Emplacement Behaviour of Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Roman, A. M.; Jaupart, C. P.

    2015-12-01

    For common crustal structures and melt compositions, basalts are buoyant in the lower crust and negatively buoyant in the upper crust. Intrusion and storage can occur at a depth or an interface where the density of magma becomes larger than that of the overlying rocks. After emplacement, magma density typically increases due to the formation of dense minerals. Fully solidified mafic bodies have bulk densities between 3000-3100 kg m-3 which are much higher than those of the continental rocks they intruded. This negative density contrast is much stronger than the positive one that drove magma ascent. We investigate the dynamical consequences of this marked buoyancy reversal using 3D laboratory experiments on viscous fluids and 2D numerical calculations with complex crustal rheologies. Material is emplaced at a density interface, such that its density is between those of the upper and lower layers. Its bulk density increases as temperature decreases and eventually exceeds that of the lower layer. We observe that the intrusion tends to spread laterally in an initial phase and to sag, and in some cases sink, in a later phase when its density exceeds that of the host. We identified two distinct instability modes. One consists of a single diapiric-like sinker and the other takes the form of spectacular nearly axisymmetric Rayleigh-Taylor-type downwellings. An intermediate mode consists of several long wavelength blobs which disrupt the initial symmetrical arrangement. The transition between the two modes is mainly determined by the aspect ratio of the intrusion at the onset of instability. Sagging can lead to full-fledged sinking to the base of the crust depending mainly on the temperature of country rocks. This proceeds over timescales that are relevant for true magmatic systems (in a range of a few kyr to a few Myr). At shallow crustal depths, cold temperatures and stiff country rocks are able to withstand the load of a large and dense intrusion. Significant post

  18. Experimental Constraints on a Vesta Magma Ocean

    NASA Technical Reports Server (NTRS)

    Hoff, C.; Jones, J. H.; Le, L.

    2014-01-01

    A magma ocean model was devised to relate eucrites (basalts) and diogenites (orthopyroxenites), which are found mixed together as clasts in a suite of polymict breccias known as howardites. The intimate association of eucritic and diogenitic clasts in howardites argues strongly that these three classes of achondritic meteorites all originated from the same planetoid. Reflectance spectral evidence (including that from the DAWN mission) has long suggested that Vesta is indeed the Eucrite Parent Body. Specifically, the magma ocean model was generated as follows: (i) the bulk Vesta composition was taken to be 0.3 CV chondrite + 0.7 L chondrite but using only 10% of the Na2O from this mixture; (ii) this composition is allowed to crystallize at 500 bar until approx. 80% of the system is solid olivine + low-Ca pyroxene; (iii) the remaining 20% liquid crystallizes at one bar from 1250C to 1110C, a temperature slightly above the eucrite solidus. All crystallization calculations were performed using MELTS. In this model, diogenites are produced by cocrystallization of olivine and pyroxene in the >1250C temperature regime, with Main Group eucrite liquids being generated in the 1300-1250C temperature interval. Low-Ca pyroxene reappears at 1210C in the one-bar calculations and fractionates the residual liquid to produce evolved eucrite compositions (Stannern Trend). We have attempted to experimentally reproduce the <1250C portion of the MELTS Vesta magma ocean. In the MELTS calculation, the change from 500 bar to one bar results in a shift of the olivine:low-Ca pyroxene boundary so that the 1250C liquid is now in the olivine field and, consequently, olivine should be the first-crystallizing phase, followed by low-Ca pyroxene at 1210C, and plagioclase at 1170C. Because at one bar the olivine:low-Ca pyroxene boundary is a peritectic, fractional crystallization of the 1210C liquid proceeds with only pyroxene crystallization until plagioclase appears. Thus, the predictions of the

  19. Magma mixing enhanced by bubble segregation

    NASA Astrophysics Data System (ADS)

    Wiesmaier, S.; Morgavi, D.; Renggli, C.; Perugini, D.; De Campos, C. P.; Hess, K.-U.; Ertel-Ingrisch, W.; Lavallée, Y.; Dingwell, D. B.

    2015-04-01

    That rising bubbles may significantly affect magma mixing paths has already been demon strated by analogue experiments. Here, for the first time, bubble-advection experiments are performed employing volcanic melts at magmatic temperatures. Cylinders of basaltic glass were placed below cylinders of rhyolite glass. Upon melting, interstitial air formed bubbles that rose into the rhyolite melt, thereby entraining tails of basaltic liquid. The formation of plume-like filaments of advected basalt within the rhyolite was characterized by microCT and subsequent high-resolution EMP analyses. Melt entrainment by bubble ascent appears to be an efficient mechanism for mingling volcanic melts of highly contrasting compositions and properties. MicroCT imaging reveals bubbles trailing each other and multiple filaments coalescing into bigger ones. Rheological modelling of the filaments yields viscosities of up to 2 orders of magnitude lower than for the surrounding rhyolitic liquid. Such a viscosity contrast implies that bubbles rising successively are likely to follow this pathway of low resistance that previously ascending bubbles have generated. Filaments formed by multiple bubbles would thus experience episodic replenishment with mafic material. Inevitable implications for the concept of bubble advection in magma mixing include thereby both an acceleration of mixing because of decreased viscous resistance for bubbles inside filaments and non-conventional diffusion systematics because of intermittent supply of mafic material (instead of a single pulse) inside a material. Inside the filaments, the mafic material was variably hybridised to andesitic through rhyolitic composition. Compositional profiles alone are ambiguous, however, to determine whether single or multiple bubbles were involved during formation of a filament. Statistical analysis, employing concentration variance as measure of homogenisation, demonstrates that also filaments appearing as single-bubble filaments

  20. Mesoscale pervasive felsic magma migration: alternatives to dyking

    NASA Astrophysics Data System (ADS)

    Weinberg, Roberto F.

    1999-03-01

    This paper reviews the literature on dyking as a mechanism of felsic magma extraction from a source and transport to shallower crustal levels, and review the recent literature suggesting a range of alternative mechanisms of magma migration in hot crustal zones which produce mesoscale pervasive granite sheet intrusions. Recent papers have strongly favoured dyking as the main mechanism controlling magma migration. However, the initiation of dykes from a felsic magma source is fraught with difficulties, even when magma is immediately available for transportation, as in magma chambers. Within a partially molten source, magma may reside in a range of structures with a wide range of shapes, sizes and degrees of connectivity. Whereas the growth of individual dykes within a partially molten zone, and the self-propagation of large dykes into subsolidus crust, have both been studied in some detail, little attention has been given to the crucial intermediate step of the growth of a dyke network capable of producing wide crustal scale dykes. The rarity of granite dyke swarms suggests that, if dyking is the preferred mechanism of magma transport, felsic magma sources produce only few major transporting dykes during their lifetime. Alternatively, dyking is not an important mechanism. The parameters controlling the volume of the catchment drained by one such dyke, as well as other basic geometrical parameters controlling the structure of the dyke network within the source, are unknown. The ability of dyking to drain a partially molten source depends crucially on these variables and particularly on the horizontal permeability of the source. The slow velocity of viscous felsic magmas traveling in rock pores implies that magma drained during dyking is mostly that previously extracted from the pores, and resident in irregular magma bodies or dyke networks. The observation that large volumes of buoyant magma are commonly present in migmatite zones, and that dyking in these zones plays

  1. Magma energy exploratory well Long Valley caldera, Mono County, California

    SciTech Connect

    Bender-Lamb, S.

    1991-04-01

    Intensive study of Long Valley over the past 15 years indicates evidence for magma at depths accessible to drilling. The Department of Energy's Magma Energy Extraction Program is currently drilling a 20,000 foot exploratory well into the Long Valley caldera. The purpose of this program is to determine the feasibility of producing electrical power from magma. If the magma energy experiment is successful, the Long Valley caldera could hypothetically supply the electrical power needs of California for 100 years at present power consumption rates. The paper describes calderas, the potential of geothermal energy, Long Valley geology, the Long Valley magma energy exploratory well, the four phases of the exploratory well drilling program, and Phase 1 results.

  2. Dynamic mixing in magma bodies - Theory, simulations, and implications

    NASA Technical Reports Server (NTRS)

    Oldenburg, Curtis M.; Spera, Frank J.; Yuen, David A.; Sewell, Granville

    1989-01-01

    The magma-mixing process is different from the mantle mixing process in that the mixing components of magma are dynamically active, with the melt density depending strongly on composition. This paper describes simulations of time-dependent variable-viscosity double-diffusive convection which were carried out to investigate quantitatively the mixing dynamics of magma in melt-dominated magma bodies. Results show that the dynamics of double-diffusive convection can impart complex patterns of composition, through time and space. The mixing time depends nonlinearly on many factors, including heat flux driving convection, the rate of diffusion of chemical species, the relative importance of thermal and chemical buoyancy, the viscosities of the mixing components, and the shape of the magma body.

  3. Factors controlling the structures of magma chambers in basaltic volcanoes

    NASA Technical Reports Server (NTRS)

    Wilson, L.; Head, James W.

    1991-01-01

    The depths, vertical extents, and lateral extents of magma chambers and their formation are discussed. The depth to the center of a magma chamber is most probably determined by the density structure of the lithosphere; this process is explained. It is commonly assumed that magma chambers grow until the stress on the roof, floor, and side-wall boundaries exceed the strength of the wall rocks. Attempts to grow further lead to dike propagation events which reduce the stresses below the critical values of rock failure. The tensile or compressive failure of the walls is discussed with respect to magma migration. The later growth of magma chambers is accomplished by lateral dike injection into the country rocks. The factors controlling the patterns of growth and cooling of such dikes are briefly mentioned.

  4. Fate of a perched crystal layer in a magma ocean

    NASA Technical Reports Server (NTRS)

    Morse, S. A.

    1992-01-01

    The pressure gradients and liquid compressibilities of deep magma oceans should sustain the internal flotation of native crystals owing to a density crossover between crystal and liquid. Olivine at upper mantle depths near 250 km is considered. The behavior of a perched crystal layer is part of the general question concerning the fate of any transient crystal carried away from a cooling surface, whether this be a planetary surface or the roof of an intrusive magma body. For magma bodies thicker than a few hundred meters at modest crustal depths, the major cooling surface is the roof even when most solidification occurs at the floor. Importation of cool surroundings must also be invoked for the generation of a perched crystal layer in a magma ocean, but in this case the perched layer is deeply embedded in the hot part of the magma body, and far away from any cooling surface. Other aspects of this study are presented.

  5. Ponding Conditions and Degassing Dynamics of Mafic Magmas Beneath the Azores Islands

    NASA Astrophysics Data System (ADS)

    Metrich, N.; Zanon, V.; D'Oriano, C.

    2014-12-01

    The Azores archipelago is located at the triple junction between the North American, African and Eurasian plates, in an area dominated by transtensive tectonic. The magmatism is concentrated along elongated volcanic ridges, generally orthogonal to the Mid Atlantic Ridge (MAR), where central volcanoes alternate with fissure zones. In order to better understand the relationships between the regional and local tectonics and the magmatism, we carried out a systematic study of basaltic pyroclasts from monogenic Strombolian cones built up on both fissure zones and central volcanoes, on five Azores Islands. We combined the major and trace element geochemistry of bulk rocks, melt inclusions and minerals with microthermometric data of coexisting CO2-rich fluid inclusions. These latter, trapped in Fo88-82 olivines, reveal pressure decrease from west to east for each ridge, but the highest pressures are recorded by fluids trapped in mineral assemblage forming ultramafic cumulates (dunites, harzburgites and wehrlites). All these results fully confirm variable depths of the Moho Transition Zone (MTZ), which marks the upper limit for underplating and correspond to the magma ponding zones where the main processes of magmatic evolution occur. The MTZ is located at 25 km beneath Flores Island, on the North American plate, and 29.5 km beneath the island of São Miguel, 380 km eastward. It reaches a minimum (18.5 km depth) under Faial at ~120 km east of the MAR. In these pressure conditions, the volatile composition is XH2O =0.1 and XCO2=0.9, at 1155-1175 °C, under QFM redox conditions. The maximum dissolved volatile content achieves 1.8-1.9 wt% of H2O and 0.4-0.5 wt% of CO2 in the central archipelago, and 2.3-2.6 wt% of H2O and 0.8-1.0 wt% of CO2 at São Miguel. However, the total pressures (PCO2+PH2O) and the dissolved H2O content recorded by melt inclusions are commonly underestimated. The initial H2O content of the basaltic magmas characteristic of each volcanic system was re

  6. Magma heating by decompression-driven crystallization beneath andesite volcanoes.

    PubMed

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-01

    Explosive volcanic eruptions are driven by exsolution of H2O-rich vapour from silicic magma. Eruption dynamics involve a complex interplay between nucleation and growth of vapour bubbles and crystallization, generating highly nonlinear variation in the physical properties of magma as it ascends beneath a volcano. This makes explosive volcanism difficult to model and, ultimately, to predict. A key unknown is the temperature variation in magma rising through the sub-volcanic system, as it loses gas and crystallizes en route. Thermodynamic modelling of magma that degasses, but does not crystallize, indicates that both cooling and heating are possible. Hitherto it has not been possible to evaluate such alternatives because of the difficulty of tracking temperature variations in moving magma several kilometres below the surface. Here we extend recent work on glassy melt inclusions trapped in plagioclase crystals to develop a method for tracking pressure-temperature-crystallinity paths in magma beneath two active andesite volcanoes. We use dissolved H2O in melt inclusions to constrain the pressure of H2O at the time an inclusion became sealed, incompatible trace element concentrations to calculate the corresponding magma crystallinity and plagioclase-melt geothermometry to determine the temperature. These data are allied to ilmenite-magnetite geothermometry to show that the temperature of ascending magma increases by up to 100 degrees C, owing to the release of latent heat of crystallization. This heating can account for several common textural features of andesitic magmas, which might otherwise be erroneously attributed to pre-eruptive magma mixing. PMID:16957729

  7. Sulfur Concentration of Martian Magmas at Sulfide Saturation at High Pressures and Temperatures - Implications for Martian Magma Ocean and Magmatic Differentiation

    NASA Astrophysics Data System (ADS)

    Ding, S.; Dasgupta, R.

    2012-12-01

    Sulfur is critical for a wide range of processes of terrestrial planets including thermal evolution of core and atmosphere and geochemistry of mantle and crust. For Mars, sulfur is particularly important because it may be abundant in the core [1] while SO 2 and H2 S might have exerted a strong greenhouse climate in the past [2]. A critical parameter that affects sulfur distribution during differentiation is the sulfur carrying capacity of mantle melts. However, most experiments constraining sulfur content at sulfide saturation (SCSS) are conducted on FeO poor (~5-12 wt.%) basalts [3] and recent experiments on high-FeO (~16-22 wt.%, [4]) Martian basalts are restricted to ≤0.8 GPa [5]. To constrain SCSS of Martian magmas at mantle conditions, we simulated basalt-sulfide melt equilibria (S added as 15-30 wt.% FeS) in Gr capsules using a piston cylinder at 1-3 GPa and 1500-1700 °C. Two starting compositions, equivalent to olivine-phyric shergottites Yamato980459 (Y98; ~17.53 wt.% FeO) and NWA 2990 (NWA; ~16.42 wt.% FeO) and thought to be primary magma [6] were used. A composition Y98+1.4 wt.% H2O was also explored to constrain the effect of water on SCSS. All experiments produced quenched sulfide and silicate melts ± opx . FeS species in the NWA glasses was confirmed from peaks at 300-400 cm-1 in Raman spectra [7]. At 1600 °C, SCSS, measured using EPMA, decreases with pressure, 4800 to 3500 ppm from 1 to 2.5 GPa for Y98, ~5440 to 4380 ppm from 1 to 2 GPa for Y98+1.4 wt.% H2O, and 5000 to 3000 ppm from 1 to 3 GPa for NWA. At 2 GPa, SCSS of NWA increases with temperature, 3300 to 4600 ppm from 1500 to 1700 °C. Combining new and previous experiments on Martian basalts [5] (a total of 28 SCSS data with FeO* of 9.3-32.78 wt.%), a preliminary equation of the form LnS (ppm) = a + b.P + c/T +d.XSiO2 + e.XAl2O3 + f.LnXFeO was fitted, where P is in GPa, T in K, and X represents mole fraction of a given oxide. Our study suggests that at conditions of final melt

  8. Fractionation products of basaltic komatiite magmas at lower crustal pressures: implications for genesis of silicic magmas in the Archean

    NASA Astrophysics Data System (ADS)

    Mandler, B. E.; Grove, T. L.

    2015-12-01

    Hypotheses for the origin of crustal silicic magmas include both partial melting of basalts and fractional crystallization of mantle-derived melts[1]. Both are recognized as important processes in modern environments. When it comes to Archean rocks, however, partial melting hypotheses dominate the literature. Tonalite-trondhjemite-granodiorite (TTG)-type silicic magmas, ubiquitous in the Archean, are widely thought to be produced by partial melting of subducted, delaminated or otherwise deeply buried hydrated basalts[2]. The potential for a fractional crystallization origin for TTG-type magmas remains largely unexplored. To rectify this asymmetry in approaches to modern vs. ancient rocks, we have performed experiments at high pressures and temperatures to closely simulate fractional crystallization of a basaltic komatiite magma in the lowermost crust. These represent the first experimental determinations of the fractionation products of komatiite-type magmas at elevated pressures. The aim is to test the possibility of a genetic link between basaltic komatiites and TTGs, which are both magmas found predominantly in Archean terranes and less so in modern environments. We will present the 12-kbar fractionation paths of both Al-depleted and Al-undepleted basaltic komatiite magmas, and discuss their implications for the relative importance of magmatic fractionation vs. partial melting in producing more evolved, silicic magmas in the Archean. [1] Annen et al., J. Petrol., 47, 505-539, 2006. [2] Moyen J-F. & Martin H., Lithos, 148, 312-336, 2012.

  9. Intrusion of granitic magma into the continental crust facilitated by magma pulsing and dike-diapir interactions: Numerical simulations

    NASA Astrophysics Data System (ADS)

    Cao, Wenrong; Kaus, Boris J. P.; Paterson, Scott

    2016-06-01

    We conducted a 2-D thermomechanical modeling study of intrusion of granitic magma into the continental crust to explore the roles of multiple pulsing and dike-diapir interactions in the presence of visco-elasto-plastic rheology. Multiple pulsing is simulated by replenishing source regions with new pulses of magma at a certain temporal frequency. Parameterized "pseudo-dike zones" above magma pulses are included. Simulation results show that both diking and pulsing are crucial factors facilitating the magma ascent and emplacement. Multiple pulses keep the magmatic system from freezing and facilitate the initiation of pseudo-dike zones, which in turn heat the host rock roof, lower its viscosity, and create pathways for later ascending pulses of magma. Without diking, magma cannot penetrate the highly viscous upper crust. Without multiple pulsing, a single magma body solidifies quickly and it cannot ascent over a long distance. Our results shed light on the incremental growth of magma chambers, recycling of continental crust, and evolution of a continental arc such as the Sierra Nevada arc in California.

  10. Session 6: Magma Energy: Engineering Feasibility of Energy Extraction from Magma Bodies

    SciTech Connect

    Traeger, R.K.

    1983-12-01

    Extensive quantities of high-quality energy are estimated to be available from molten magma bodies existing within 10 Km of the US continent's surface. A five-year study sponsored by DOE/BES demonstrated that extraction of energy from these melts was scientifically feasible. The next stage of assessment is to evaluate the engineering feasibility of energy extraction and provide a preliminary economic evaluation. Should the second step demonstrate engineering feasibility, the third step would include detailed economic, market and commercialization endeavors. Evaluation of the engineering feasibility will be initiated in FY 84 in a program supported by DOE/GHTD and managed by Dave Allen. The project will be managed by Sandia Labs in James Kelsey's Geothermal Technology Development Division. The project will continue to draw on expertise throughout the country, especially the scientific base established in the previous BES Magma Energy Program.

  11. Chemical diffusion during isobaric degassing of magma

    NASA Astrophysics Data System (ADS)

    von Aulock, Felix W.; Kennedy, Ben M.; Lavallée, Yan; Henton-de Angelis, Sarah; Oze, Christopher; Morgan, Daniel J.; Clesham, Steve

    2014-05-01

    During ascent of magma, volatiles exsolve and bubbles form. Volatiles can either escape through a permeable network of bubbles in an open system or be trapped in non-connected pores during closed system degassing. Geochemical studies have shown that in most cases both- open system and closed system degassing take place at the same time. During cooling of the melt, diffusion slows down and eventually diffusional gradients get frozen in, preserving a history of degassing and rehydration during bubble growth, bubble collapse and crystal growth. We present data from experiments in which natural obsidian was degassed at atmospheric pressures at 950ºC over timescales of 3-24h. During bubble growth, a skin formed, at the outer edge of the sample, effectively prohibiting any degassing of its interior. Diffusion gradients were measured across the glass surrounding vesicles, and across this impermeable skin. Water contents were analyzed with synchrotron sourced Fourier transform infrared spectroscopy and several major, minor and trace elements were mapped using synchrotron sourced X-ray fluorescence spectroscopy. The samples show a dimpled surface, as well as signs of oxidation and growth of submicroscopic crystals. Water contents around bubbles decrease in simple heating experiments (from ~0.13 wt. % down to ~0.1 wt. %), whereas slight rehydration of the vesicle wall can be observed when a second, cooler step at 850ºC follows the initial 950ºC. Water gradients towards the outside of the sample decrease linearly to a minimum of ~0.045 wt. %, far below the solubility of water in melts at these temperatures. We mapped the distribution of K, Ca, Fe, Ti, Mn, Rb, Sr, Y and Zr. Especially the trace elements show a decrease towards the outside of the sample, whereas K, Fe, Ca and Ti generally do not show significant partitioning between melt and gas/crystal phase. Several effects could attribute to the distribution of these elements, such as the crystal growth and exchange with

  12. The three stages of magma ocean cooling

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1992-01-01

    Models of magma ocean (MO) cooling and crystallization can provide important constraints on MO plausibility for a given planet, on the origin of long term, stable crusts, and even on the origin of the solar system. Assuming the MO is initially extensive enough to have a mostly molten surface, its first stage of cooling is an era of radiative heat loss from the surface, with extremely rapid convection below, and no conductive layer in between. The development of the chill crust starts the second stage of MO cooling. Heat loss is now limited by conduction through the crust. The third stage of cooling starts when the near surface MO evolves compositionally to the point of saturation with feldspar. At this point, the cooling rate again precipitously diminishes, the rate of crustal thickness growth as a function of temperature suddenly increases. More work on incorporating chemical constraints into the evolving physical models of MO solidification would be worthwhile.

  13. Magma ocean formation due to giant impacts

    NASA Technical Reports Server (NTRS)

    Tonks, W. B.; Melosh, H. J.

    1992-01-01

    The effect of giant impacts on the initial chemical and thermal states of the terrestrial planets is just now being explored. A large high speed impact creates an approximately hemispherical melt region with a radius that depends on the projectile's radius and impact speed. It is shown that giant impacts on large planets can create large, intact melt regions containing melt volumes up to a few times the volume of the projectile. These large melt regions are not created on asteroid sized bodies. If extruded to the surface, these regions contain enough melt to create a magma ocean of considerable depth, depending on the impact speed, projectile radius, and gravity of the target planet.

  14. Magma at depth: A retrospective analysis of the 1975 unrest at Mount Baker, Washington, USA

    USGS Publications Warehouse

    Crider, Juliet G.; Frank, David; Malone, Stephen D.; Poland, Michael P.; Werner, Cynthia; Caplan-Auerbach, Jacqueline

    2011-01-01

    Mount Baker volcano displayed a short interval of seismically-quiescent thermal unrest in 1975, with high emissions of magmatic gas that slowly waned during the following three decades. The area of snow-free ground in the active crater has not returned to pre-unrest levels, and fumarole gas geochemistry shows a decreasing magmatic signature over that same interval. A relative microgravity survey revealed a substantial gravity increase in the ~30 years since the unrest, while deformation measurements suggest slight deflation of the edifice between 1981-83 and 2006-07. The volcano remains seismically quiet with regard to impulsive volcano-tectonic events, but experiences shallow (10 km) long-period earthquakes. Reviewing the observations from the 1975 unrest in combination with geophysical and geochemical data collected in the decades that followed, we infer that elevated gas and thermal emissions at Mount Baker in 1975 resulted from magmatic activity beneath the volcano: either the emplacement of magma at mid-crustal levels, or opening of a conduit to a deep existing source of magmatic volatiles. Decadal-timescale, multi-parameter observations were essential to this assessment of magmatic activity.

  15. Insights into Magma Evolution in the Islands of the Four Mountains, Alaska

    NASA Astrophysics Data System (ADS)

    Fulton, A. A.; Izbekov, P. E.; Nicolaysen, K. P.

    2015-12-01

    The Islands of the Four Mountains (IFM) is a group of small volcanoes in the central region of Alaska's Aleutian island arc. There are few studies of this remote group of islands despite their rich archeological history and diverse eruptive histories. This study focuses on silicic deposits from the IFM to shed light on the area's history of large explosive eruptions and the IFM's chemical relationship to the rest of the central Aleutian Islands. This study applies whole rock geochemistry, detailed petrographic analysis, and electron microprobe analysis to samples of volcanic deposits from Tana, Cleveland, Carlisle, and Herbert volcanoes, including the first documented ignimbrite deposit in the IFM, found on northern Tana. The IFM lavas range from basaltic to dacitic and follow typical island arc and calc-alkaline chemical trends, providing evidence of high aqueous fluid input to the mantle wedge, as well as varying levels of influence from subducted sediments. Tana, the largest (~12 km2) and most siliceous of the IFM volcanoes, expresses anomalies in K and Rb concentrations that may aid in the refinement of the continental-oceanic crust boundary location along the Aleutian arc. Plagioclase phenocryst disequilibrium textures and compositions provide evidence of mixing and recharge in the IFM magma chambers. Multiple plagioclase phenocryst populations, euhedral pyroxene crystals in disequilibrium with the melt, and angular xenolithic clasts in the Tana ignimbrite suggest a rapid mixing and heating event that triggered its large explosive eruption during the Pleistocene.

  16. Petrology of some oceanic island basalts: PRIMELT2.XLS software for primary magma calculation

    NASA Astrophysics Data System (ADS)

    Herzberg, C.; Asimow, P. D.

    2008-09-01

    PRIMELT2.XLS software is introduced for calculating primary magma composition and mantle potential temperature (TP) from an observed lava composition. It is an upgrade over a previous version in that it includes garnet peridotite melting and it detects complexities that can lead to overestimates in TP by >100°C. These are variations in source lithology, source volatile content, source oxidation state, and clinopyroxene fractionation. Nevertheless, application of PRIMELT2.XLS to lavas from a wide range of oceanic islands reveals no evidence that volatile-enrichment and source fertility are sufficient to produce them. All are associated with thermal anomalies, and this appears to be a prerequisite for their formation. For the ocean islands considered in this work, TP maxima are typically ˜1450-1500°C in the Atlantic and 1500-1600°C in the Pacific, substantially greater than ˜1350°C for ambient mantle. Lavas from the Galápagos Islands and Hawaii record in their geochemistry high TP maxima and large ranges in both TP and melt fraction over short horizontal distances, a result that is predicted by the mantle plume model.

  17. Roman comagmatic province (central Italy): evidence for subduction-related magma genesis

    SciTech Connect

    Peccerillo, A.

    1985-02-01

    Geochemical data on mafic volcanics show that important affinities exist between the Roman and the calc-alkaline rocks from the Aeolian arc (south Tyrrhenian Sea). These affinities, together with the close association of calc-alkaline and K-rich volcanics in the Aeolian arc and in the Naples area, the continuity in the variation of abundances of incompatible elements from calc-alkaline to potassic suites, and the similarity in terms of major-element geochemistry, support a genetic relationship of the Roman magmatism and the subduction processes that affected the Apennines in Tertiary time and are still active under the Aeolian arc. In the genetic model presented here, both calc-alkaline and K-rich magmas were generated within a mantle heterogenously enriched in LIL elements. Composition of the mantle was modified by addition of material, probably sediments, dragged down by the undergoing slab. The geochemical and petrological differences displayed by the calc-alkaline and K-rich volcanics are accounted for by the different conditions of melting as well as by chemical and isotopic heterogeneities of the source. 26 references, 3 figures, 1 table.

  18. Electromagnetic Imaging of Crustal Magma Chambers

    NASA Astrophysics Data System (ADS)

    Constable, S.; Li, Y.; Key, K.

    2006-12-01

    In February/March 2004 we carried out a combined magnetotelluric (MT) and controlled source electromagnetic (CSEM) study of the mid-ocean ridge in the Pacific Ocean at 9°--10° North latitude. A 40-kilometer line of 22 seafloor electromagnetic recorders at 9°30' collected data from 27 kilometers of deep-towed CSEM transmission at 2~Hz, with a source dipole moment of 22~kAm. In order to obtain a first-order image of the information contained in the CSEM data we computed an apparent resistivity psuedosection based on signal amplitudes. This generates a spectacular image of a 10-kilometer wide, 20~Ømegam magma chamber embedded in a 500~Ømegam crust, along with pockets of melt or brine offset to the east of the ridge. We used the pseudosection to guide trial-and-error forward modeling using a newly developed 2D unstructured finite element code which allows seafloor bathymetry to be accurately meshed. The more rigorous modeling results in a good fit to the data from a much narrower 20~Ømegam `mush' zone only 2.5~km wide, capped by a 600-m thick 5~Ømegam melt lens. Unlike the pseudosection, the forward model requires a conductive (5~Ømegam) tent which extends from the melt lens to within about 100~m of the seafloor, probably corresponding to a zone of hydrothermal circulation. This is in contrast to earlier results from the slow-spreading, deeper magma chamber at the Valu Fa Ridge in the Lau Basin, where a large, asymmetric conductivity anomaly in the upper crust suggests that hydrothermal fluids extend 10~km west of the ridge axis.

  19. Limits to magma mixing based on chemistry and mineralogy of pumice fragments erupted from a chemically zoned magma body

    SciTech Connect

    Vogel, T.A.; Ryerson, F.J.; Noble, D.C.; Younker, L.W.

    1987-09-01

    The chemical variation among pumice fragments from the Pahute Mesa Member of the Thirsty Canyon Tuff (Black Mountain volcanic center, southwestern Nevada) is consistent with magma withdrawal from a chemically zoned magma body. The top of this magma body contained little chemical variations, the lowest concentration of light REEs, and the highest concentrations of SiO/sub 2/, heavy REEs, and Th. The pumice fragments derived from the top of the magma body contain nearly pure ferrohedenbergite and fayalite. The next discrete zone in the magma body contained lower SiO/sub 2/, heavy REEs, and Th concentrations, and very high concentrations of light REEs. The lowest erupted layer contained relatively low concentrations of SiO/sub 2/, Th, and light and heavy REEs. Pumice fragments with polymodal disequilibrium phenocryst populations are a priori evidence of magma mixing. The magma mixing process is constrained by: the systematic vertical distribution of chemically distinct pumice fragments throughout the ash-flow sheet; the presence of disequilibrium phenocrysts within some pumice fragments in all but the lowermost part of the sheet; and the presence of compositionally uniform glass in most pumice fragments, including those with widely varying phenocryst compositions. Negligible mixing occurred at the top of the magma body; limited mixing occurred in the second and third layers. Because mixing did not destroy the original layering, the amount of guest magma must have been small. In order for unzoned disequilibrium phenocrysts to not become zoned, they must have been preserved in the magma body only a short time. And yet, in order to produce the homogeneous liquid that surrounds these phenocrysts, mechanical mixing must have been very efficient. 44 references.

  20. A glassy lava flow from Toconce volcano and its relation with the Altiplano-Puna Magma Body in Central Andes

    NASA Astrophysics Data System (ADS)

    Godoy, B.; Rodriguez, I.; Aguilera, F.

    2012-12-01

    Toconce is a composite stratovolcano located at the San Pedro - Linzor volcanic chain (SPLVC). This volcanic chain distributes within the Altiplano-Puna region (Central Andes) which is characterized by extensive rhyodacitic-to-rhyolitic ignimbritic fields, and voluminous domes of dacitic-to-rhyolitic composition (de Silva, 1989). The felsic melts that gave origin to ignimbrites and domes at this area were generated by mixing of mantle-derived magmas and anatectic melts assimilated during their ascent through the thick crust. Thus, partially molten layers exist in the upper crust below the APVC (de Silva et al., 2006). Evidence of large volumes of such melts has been also proposed by geophysical methods (i.e. the Altiplano-Puna Magma Body; Chmielowsky et al., 1999) In this work, petrography and whole rock, mineralogical and melt inclusions geochemistry of a glassy lava flow of Toconce volcano are presented. Petrographically, this lava flow shows a porphyric texture, with euhdral to subhedral plagioclase, ortho- and clino-pyroxene phenocrysts immersed in a glassy groundmass. Geochemically, the lava flow has 64.7% wt. SiO2. The glassy groundmass (~70% wt. SiO2) is more felsic than all the lavas in the volcanic chain (47-68% wt., Godoy et al., 2011). Analyzed orthopyroxene-hosted melt inclusions show an even higher SiO2 content (72-75% wt.), and a decreasing on Al2O3, Na2O, and CaO content with differentiation. Crystallization pressures of this lava flow, obtained using Putirka's two-pyroxene and clinopyroxene-liquid models (Putirka, 2008), range between 6 and 9 kbar. According to crystallization pressures, and major element composition, a felsic source located at shallow crustal pressures - where plagioclase is a stable mineralogical phase - originated the inclusions. This could be related to the presence of the Altiplano-Puna Magma Body (APMB) located below SPLVC. On the other hand, glassy groundmass, and disequilibrium textures in minerals of this lava flow could

  1. Fifty years of IMOG (International Meetings on Organic Geochemistry)

    USGS Publications Warehouse

    Kvenvolden, Keith A.

    2012-01-01

    IMOG2011 is the 25th of a series of international meetings on organic geochemistry that began in 1962. Thus, this 25th meeting marks the 50th anniversary year of IMOG, which has (a) had a rich history with meetings taking place in 11 different countries, (b) published Proceedings, titled “Advances in Organic Geochemistry,” from each meeting that now number 24 volumes totaling almost 18,000 pages, and (c) documented the content and development of the science of organic geochemistry. IMOG2011 adds a new milestone to the progress of organic geochemistry through time.

  2. Precambrian organic geochemistry - Preservation of the record

    NASA Technical Reports Server (NTRS)

    Hayes, J. M.; Wedeking, K. W.; Kaplan, I. R.

    1983-01-01

    A review of earlier studies is presented, and new results in Precambrian organic geochemistry are discussed. It is pointed out that two lines of evidence can be developed. One is based on structural organic chemistry, while the other is based on isotopic analyses. In the present investigation, the results of both structural and isotopic investigations of Precambrian organic matter are discussed. Processes and products related to organic geochemistry are examined, taking into account the carbon cycle, an approximate view of the principal pathways of carbon cycling associated with organic matter in the present global ecosystem, processes affecting sedimentary organic matter, and distribution and types of organic matter. Attention is given to chemical fossils in Precambrian sediments, kerogen analyses, the determination of the structural characteristics of kerogen, and data concerning the preservation of the Precambrian organic geochemical record.

  3. Mineralogical and geochemical constraints on contribution of magma mixing and fractional crystallization to high-Mg adakite-like diorites in eastern Dabie orogen, East China

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Ma, Changqian; Holtz, Francois; Koepke, Jürgen; Wolff, Paul Eric; Berndt, Jasper

    2013-07-01

    The Liujiawa pluton which is located near the eastern boundary of the Dabie orogen is composed of multiple lithologic units including mainly gabbronorites, diorites, granodiorites and hornblende gabbros. Gabbronorites and hornblende gabbros occur as enclaves in dioritic hosts which show gradual contact with granodiorites. Zircon U-Pb dating indicates that gabbronorites and diorites formed coevally at ~ 128 Ma, but they have distinct zircon Hf isotopes with εHf(t) of - 26 to - 23 (gabbronorite) and of - 32 to - 27 (diorite) respectively. Petrographic observations and rock-forming mineral compositions clearly show mixing between mafic and felsic magma end-members, which might have formed the homogeneous whole-rock Sr-Nd isotopes with εNd(t) of - 17 to - 25 and initial 87Sr/86Sr of 0.707 to 0.709. As revealed by zircon Hf isotopes, F concentrations in amphibole and biotite and thermodynamic modeling of crystallization, the gabbronorites represent enriched lithospheric mantle-derived magmas which evolved by fractional crystallization of orthopyroxene, clinopyroxene, magnetite and/or amphibole, whereas the granodiorites may be derived from the Dabie Archean basement. Mineralogical and geochemical data as well as major and trace element modeling show that the origin of diorites, previously interpreted as high-Mg adakites, can be explained by magma mixing between the crust-derived granodioritic magmas and the differentiation products of mantle-derived gabbronoritic magmas. As a result, the high-Mg adakite-like geochemistry of the diorites is a consequence of magma differentiation at a crustal depth, involving fractional crystallization and magma mixing, rather than an intrinsic feature of primitive melts. The mantle upwelling in the adjacent central Middle-Lower Yangtze River metallogenic (MLYR) belt during Late Jurassic-Early Cretaceous belt might have acted as a precursor and triggered the partial melting of lithospheric mantle beneath the eastern Dabie orogen and the

  4. Long-distance magma transport from arc volcanoes inferred from the submarine eruptive fissures offshore Izu-Oshima volcano, Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Geshi, Nobuo; Kawanabe, Yoshihisa; Ogitsu, Itaru; Taylor, Rex N.; Tuzino, Taqumi; Sakamoto, Izumi; Arai, Kohsaku; Nakano, Shun

    2014-09-01

    Long-distance lateral magma transport away from volcanic centers in island arcs is emerging as a common phenomenon where the regional stress regime is favorable. It should also be recognized as an important factor in the construction and growth of island arcs, and a potential trigger for devastating eruptions. In this contribution, we report on recent investigations into the magma dynamics of Izu-Oshima volcano, an active basaltic volcano with an extensive fissure system. Izu-Oshima is flanked by numerous, subparallel NW-SE trending submarine ridges extending up to 22 km to the NW and the SE from the central vent. During a recent submersible survey we have identified that these ridges are fissures which erupted basaltic spatter and lava flows. Furthermore, lavas are petrographically similar along each ridge, while there are noticeable differences between ridges. The subparallel ridges are observed to transect a series of seamounts - the Izu-Tobu monogenetic volcanoes - which are dispersed across this area of the rear-arc. However, there are consistent petrographic and chemical differences between these seamounts and the ridges, indicating that they have different magma sources, yet, they are essentially bounding each other in dive tracks. The most appropriate scenario for their development is one where the Izu-Tobu Volcanoes are fed by an "in-situ" underlying source, while the NW-SE ridges are fed by lateral magma transport from Izu-Oshima. Magma erupted from each ridge is of a consistent geochemistry along its length, but has experienced crystal fractionation and some plagioclase accumulation. Compositions of the ridges are also very similar to lavas from the subaerial cones that can be traced down the flanks of Izu-Oshima. This implies that pairs of subaerial cones and submarine ridges represent the locus of magma transport events away from the storage system beneath Izu-Oshima. Hence, magma from this crustal reservoir moved upward to feed the on-edifice cones

  5. Timing and mechanisms of mafic magma ascent/emplacement in the continental middle crust: an example from the Permian Sondalo gabbroic complex (Alps, N-Italy)

    NASA Astrophysics Data System (ADS)

    Petri, Benoît; Mohn, Geoffroy; Skrzypek, Etienne; Mateeva, Tsvetomila; Galster, Federico; Robion, Philippe; Schulmann, Karel; Manatschal, Gianreto; Müntener, Othmar

    2015-04-01

    We explore the mechanisms of mafic magma ascent and emplacement in the continental crust by studying the mid-crustal Permian Sondalo gabbroic complex (Campo unit, Eastern Central Alps, N-Italy). We characterized the structure and anisotropy of magnetic susceptibility (AMS) fabric of the concentric gabbroic to dioritic intrusions. We used Laser Ablation ICP-MS U-Pb zircon dating on magmatic and metamorphic rock samples, zircon trace element geochemistry and existing P-T estimates to constrain the timing and depth of magma emplacement. Petrological and geochemical observations provide insights on the crystallization sequence in the magmatic rocks and facilitate the interpretation of the AMS record. The magmatic and magnetic fabrics (foliations and lineations) of the pluton reflect their original orientations and are essentially vertical, indicating vertical magma transfer through the crust. The intrusion was emplaced in two phases. (1) The concordant orientation between the main magmatic foliation and the host-rock xenoliths elongation and foliation in the centre of the pluton suggest that the first magma ascent phase occurred through fracture opening parallel to the vertical fabric of the host metasedimentary rocks. Trace element analyses point to late-magmatic zircon crystallization, which enable to interpret the associated U-Pb results of 289-288 Ma as the age of this initial emplacement stage. (2) The second magma ascent phase is marked by a rheological change in the host-rock. The temperature increase in the contact aureole induced partial melting and decreasing mechanical strength in the metasediments. This resulted in the formation of a vertical foliation in the metamorphic aureole and a weaker but concordant magmatic foliation at the rim of the pluton. This ascent phase occurred at 288-285 Ma and accounts for the contrasted P-T evolution of metasedimentary rocks in the contact aureole. Thermal models of the intrusion indicate that the contact aureole

  6. Forecasting magma-chamber rupture at Santorini volcano, Greece

    NASA Astrophysics Data System (ADS)

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini’s shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano.

  7. Forecasting magma-chamber rupture at Santorini volcano, Greece

    PubMed Central

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-01-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011–2012 unrest period, that the measured 0.02% increase in volume of Santorini’s shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano. PMID:26507183

  8. MAGMA: analysis of two-channel microarrays made easy.

    PubMed

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph

    2007-07-01

    The web application MAGMA provides a simple and intuitive interface to identify differentially expressed genes from two-channel microarray data. While the underlying algorithms are not superior to those of similar web applications, MAGMA is particularly user friendly and can be used without prior training. The user interface guides the novice user through the most typical microarray analysis workflow consisting of data upload, annotation, normalization and statistical analysis. It automatically generates R-scripts that document MAGMA's entire data processing steps, thereby allowing the user to regenerate all results in his local R installation. The implementation of MAGMA follows the model-view-controller design pattern that strictly separates the R-based statistical data processing, the web-representation and the application logic. This modular design makes the application flexible and easily extendible by experts in one of the fields: statistical microarray analysis, web design or software development. State-of-the-art Java Server Faces technology was used to generate the web interface and to perform user input processing. MAGMA's object-oriented modular framework makes it easily extendible and applicable to other fields and demonstrates that modern Java technology is also suitable for rather small and concise academic projects. MAGMA is freely available at www.magma-fgcz.uzh.ch. PMID:17517778

  9. Forecasting magma-chamber rupture at Santorini volcano, Greece.

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-01-01

    How much magma needs to be added to a shallow magma chamber to cause rupture, dyke injection, and a potential eruption? Models that yield reliable answers to this question are needed in order to facilitate eruption forecasting. Development of a long-lived shallow magma chamber requires periodic influx of magmas from a parental body at depth. This redistribution process does not necessarily cause an eruption but produces a net volume change that can be measured geodetically by inversion techniques. Using continuum-mechanics and fracture-mechanics principles, we calculate the amount of magma contained at shallow depth beneath Santorini volcano, Greece. We demonstrate through structural analysis of dykes exposed within the Santorini caldera, previously published data on the volume of recent eruptions, and geodetic measurements of the 2011-2012 unrest period, that the measured 0.02% increase in volume of Santorini's shallow magma chamber was associated with magmatic excess pressure increase of around 1.1 MPa. This excess pressure was high enough to bring the chamber roof close to rupture and dyke injection. For volcanoes with known typical extrusion and intrusion (dyke) volumes, the new methodology presented here makes it possible to forecast the conditions for magma-chamber failure and dyke injection at any geodetically well-monitored volcano. PMID:26507183

  10. Persistent multitiered magma plumbing beneath Katla volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Budd, David A.; Troll, Valentin R.; Dahren, Börje; Burchardt, Steffi

    2016-03-01

    Recent seismic unrest and a persistent Holocene eruption record at Katla volcano, Iceland indicate that a near-future eruption is possible. Previous petrological investigations suggest that Katla is supplied by a simple plumbing system that delivers magma directly from depth, while seismic and geodetic data also point toward the existence of upper-crustal magma storage. To characterize Katla's recent plumbing system, we established mineral-melt equilibrium crystallization pressures from four age-constrained Katla tephras spanning from 8 kyr BP to 1918. The results point to persistent shallow- (≤8 km depth) as well as deep-crustal (ca. 10 - 25 km depth) magma storage beneath Katla throughout the last 8 kyr. The presence of multiple magma storage regions implies that mafic magma from the deeper reservoir system may become gas-rich during ascent and storage in the shallow crust and erupt explosively. Alternatively, it might intersect evolved magma pockets in the shallow-level storage region, and so increase the potential for explosive mixed-magma ash eruptions.

  11. El Ventorrillo, a paleostructure of Popocatépetl volcano: insights from geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.; Macías, J. L.; García-Tenorio, F.; Layer, P.; Schaaf, P.; Solís-Pichardo, G.; Arce, J. L.

    2015-10-01

    Volcán Popocatépetl (México) was constructed over the remains of a volcanic paleostructure. Based on fieldwork, 40Ar/39Ar dating, U-Pb dating, and geochemistry, we have determined the age, chemistry, and location of this paleostructure and named it El Ventorrillo. Most remnants of El Ventorrillo are covered by deposits from subsequent activity of Popocatépetl, except for the El Abanico scarp and the Barranca de Nexpayantla, where the stratigraphy of El Ventorrillo eruptive products can be investigated. Inception of volcanism at El Ventorrillo occurred at 331 ± 10 ka with emission of the Nexpayantla andesitic lavas, and continued with extrusion of the Yoloxochitl (267 ± 31 ka) and microwave (227 ± 6 ka) domes. Intrusion of dikes occurred at 298 ± 94 and 230 ± 3 ka. Activity at El Ventorrillo continued with the emission of lavas that built the El Abanico scarp (193 ± 29 to 96 ± 8 ka) and continued until the Tutti Frutti eruption destroyed the cone 14.1 kyr ago. El Ventorrillo magmas produced rocks divided into two mineralogical groups. The first group contains biotite-amphibole-rich rocks and the second group consists of biotite-amphibole-free lavas. The rocks that contain biotite and amphibole are older than 198 ± 13 ka, whereas the rocks with no hydrous phases are younger than 227 ± 6 ka and contain skarn and granodiorite xenoliths. We interpret the change to an anhydrous mineral assemblage and the occurrence of skarn and granodiorite xenoliths as evidence for the formation of a new, shallower reservoir. A granodiorite xenolith was chosen for 40Ar/39Ar dating and U-Pb zircon analyses. The U-Pb method yielded an age of 540 ± 110 ka and the 40Ar/39Ar an age of 109 ± 24 ka. These ages are interpreted to indicate granodiorite crystallization (540 ± 110 ka), which metamorphosed the calcareous basement beneath Popocatépetl into skarn and an influx of magma (109 ± 24 ka) that reheated the granodiorite. Major and trace elements, Sr, Nd, and Pb isotopic

  12. The Growth of Magma Bodies by Amalgamation of Discrete Sheet Intrusions: Implications for the Formation of Magma Chambers

    NASA Astrophysics Data System (ADS)

    Annen, C.

    2007-12-01

    Until recently, igneous bodies (plutons and magma chambers) were commonly considered to be approximately spherical bodies, rapidly emplaced into the crust. However, field, structural, geophysical, and geochronological studies indicate that many plutons are low aspect-ratio tabular bodies (sills) that are formed by the amalgamation of successive discrete magma pulses. The thermal evolution of an igneous body that grows by accretion of thin magma sheets is fundamentally different from the evolution of a rapidly emplaced magma sphere or of a single thick magma sill. In thin sheet intrusions, the heat loss is through the walls of the sheets and the temperatures within the intrusions do not depend on the volumes injected but on the one-dimension sheets emplacement rate. The first sheets injected in a cold crust rapidly cool down and solidify. The ability of successive intrusions to stay at high temperature and eventually build up a long-lived magma chamber is controlled by the emplacement rate. Heat transfer modeling applied in the context of a volcanic arc shows that average emplacement rates of at least several centimeters per year and an incubation time of tens thousands of years are needed for a persistent magma chamber to form. During the incubation time, the intrusions solidify and when a chamber of high melt fraction magma eventually grows, the volume of eruptible magma only form a small part of the total intruded volume. The emplacement rate of plutons is controversial. Geochronological data suggest that some plutons may be emplaced over millions years. For a pluton that is assembled at a slow rate of a few millimeters per year, millions of years are needed, over which kilometric thicknesses are intruded, before a volume of magma larger than the size of a single intrusion becomes mobile and eruptible. In many cases, volcanic products may come from a deep source without being associated with a long-lived upper crust magma chamber. If volcanism is associated with

  13. Draining mafic magma from conduits during Strombolian eruption

    NASA Astrophysics Data System (ADS)

    Wadsworth, F. B.; Kennedy, B.; Branney, M. J.; Vasseur, J.; von Aulock, F. W.; Lavallée, Y.; Kueppers, U.

    2014-12-01

    During and following eruption, mafic magmas can readily drain downward in conduits, dykes and lakes producing complex and coincident up-flow and down-flow textures. This process can occur at the top of the plumbing system if the magma outgases as slugs or through porous foam, causing the uppermost magma surface to descend and the magma to densify. In this scenario the draining volume is limited by the gas volume outgassed. Additionally, magma can undergo wholesale backflow when the pressure at the base of the conduit or feeder dyke exceeds the driving pressure in the chamber beneath. This second scenario will continue until pressure equilibrium is established. These two scenarios may occur coincidently as local draining of uppermost conduit magma by outgassing can lead to wholesale backflow because the densification of magma is an effective way to modify the vertical pressure profile in a conduit. In the rare case where conduits are preserved in cross section, the textural record of draining is often complex and great care should be taken in interpreting bimodal kinematic trends in detail. Lateral cooling into country rock leads to lateral profiles of physical and flow properties and, ultimately, outgassing potential, and exploration of such profiles elucidates the complexity involved. We present evidence from Red Crater volcano, New Zealand, and La Palma, Canary Islands, where we show that at least one draining phase followed initial ascent and eruption. We provide a rheological model approach to understand gravitational draining velocities and therefore, the timescales of up- and down-flow cycles predicted. These timescales can be compared with observed geophysical signals at monitored mafic volcanoes worldwide. Finally, we discuss the implications of shallow magma draining for edifice stability, eruption longevity and magma-groundwater interaction.

  14. Diatexite Deformation and Magma Extraction on Kangaroo Island, South Australia

    NASA Astrophysics Data System (ADS)

    Hasalova, P.; Weinberg, R. F.; Ward, L.; Fanning, C. M.

    2012-12-01

    Migmatite terranes are structurally complex. We have investigated the relationships between deformation and magma extraction in migmatites formed during the Delamerian orogeny on Kangaroo Island. Several phases of deformation occurred in the presence of melt (D1-D4) and we describe how magma segregation, accumulation and extraction changes with deformation style. During an early upright folding event (D2), magma was channelled towards the hinge of antiforms. Funnel-shaped networks of leucosomes form a root that link towards a central axial planar channel, marking the main magma extraction paths. Extraction was associated with limb collapse, and antiformal hinge disruption. During a later deformation phase (D4), diatexites were sheared so that schollen were disaggregated into smaller blocks and schlieren, and deformed into asymmetric, sigmoidal shapes. Foliations in the magmatic matrix and schollen asymmetry indicate dextral shearing. During flow, magma accumulated in shear planes, indicating a dilational component during shearing (transtension) and on strain shadows of schollen. As deformation waned (post-D4), magma extraction from these diatexites gave rise to steeply dipping, funnel-shaped channels, similar to those developed during folding. The funnel-shape networks are interpreted as magma extraction networks and indicate magma flow direction. Structures developed during this phase are comparable with those developed during dewatering of soft sediments. The magmatic rocks from migmatites formed early, during folding, and formed late after deformation waned were dated. Both have two monazite (U-Pb, SHRIMP) age groups of ~490Ma and ~505-520Ma. The older sample has a well-defined peak at 505-510Ma and trails into the younger ages. The younger sample has the opposite, with few old spots and a well-defined young peak at ~490Ma. The age range indicates the duration of anatexis, and well-defined peaks are interpreted to mark the age of individual magma batch

  15. The Geochemistry of Mass Extinction

    NASA Astrophysics Data System (ADS)

    Kump, L. R.

    2003-12-01

    The course of biological evolution is inextricably linked to that of the environment through an intricate network of feedbacks that span all scales of space and time. Disruptions to the environment have biological consequences, and vice versa. Fossils provide the prima facie evidence for biotic disruptions: catastrophic losses of global biodiversity at various times in the Phanerozoic. However, the forensic evidence for the causes and environmental consequences of these mass extinctions resides primarily in the geochemical composition of sedimentary rocks deposited during the extinction intervals. Thus, advancement in our understanding of mass extinctions requires detailed knowledge obtained from both paleontological and geochemical records.This chapter reviews the state of knowledge concerning the geochemistry of the "big five" extinctions of the Phanerozoic (e.g., Sepkoski, 1993): the Late Ordovician (Hirnantian; 440 Ma), the Late Devonian (an extended or multiple event with its apex at the Frasnian-Famennian (F-F) boundary; 367 Ma), the Permian-Triassic (P-Tr; 251 Ma), the Triassic-Jurassic (Tr-J; 200 Ma), and the Cretaceous-Tertiary (K-T; 65 Ma). The focus on the big five is a matter of convenience, as there is a continuum in extinction rates from "background" to "mass extinction." Although much of the literature on extinctions centers on the causes and extents of biodiversity loss, in recent years paleontologists have begun to focus on recoveries (see, e.g., Hart, 1996; Kirchner and Weil, 2000; Erwin, 2001 and references therein).To the extent that the duration of the recovery interval may reflect a slow relaxation of the environment from perturbation, analysis of the geochemical record of recovery is an integral part of this effort. In interpreting the geochemical and biological records of recovery, we need to maintain a clear distinction among the characteristics of the global biota: their biodiversity (affected by differences in origination and extinction

  16. Evidence for an Early Cretaceous mineralizing event above the basement/sediment unconformity in the intracratonic Paris Basin: paragenetic sequence and Sm-Nd dating of the world-class Pierre-Perthuis stratabound fluorite deposit

    NASA Astrophysics Data System (ADS)

    Gigoux, Morgane; Delpech, Guillaume; Guerrot, Catherine; Pagel, Maurice; Augé, Thierry; Négrel, Philippe; Brigaud, Benjamin

    2015-04-01

    World-class stratabound fluorite deposits are spatially associated with the basement/sediment unconformity of the intracratonic Paris Basin and the Morvan Massif in Burgundy (France). The reserves are estimated to be about 5.5 Mt of fluorite within six fluorite deposits. In this study, we aim to determine the age of the major fluorite mineralization event of the Pierre-Perthuis deposit (1.4 Mt fluorite) by a combined study of the paragenetic mineral sequence and Sm-Nd dating on fluorite crystals. Fluorite occurs as isolated cubes or filling geodes in a Triassic, silicified, dolomitic formation. Three fluorite stages associated with sphalerite, pyrite, galena, barite, and quartz have been distinguished using optical, cathodoluminescence, and scanning electron microscopes. Seven crystals of the geodic fluorite stage were analyzed for their rare earth element (REE) contents and their 147Sm/144Nd and 143Nd/144Nd isotopic compositions. The normalized REE distribution displays homogeneous bell-shaped patterns for all the geodic fluorite samples with a Mid-REE enrichment over the Light-REE and Heavy-REE. The 147Sm/144Nd varies from 0.3108 to 0.5504 and the 143Nd/144Nd from 0.512313 to 0.512518. A six-point Sm-Nd isochron defines an age of 130 ± 15 Ma (initial 143Nd/144Nd = 0.512054, MSWD = 0.21). This Sm-Nd isochron provides the first age for the stratabound fluorite sediment-hosted deposit, related to an unconformity in the Paris Basin, and highlights a major Early Cretaceous fluid circulation event mainly above the basement/sediment unconformity during a flexural deformation of the Paris Basin, which relates to the rifting of the Bay of Biscay and the formation of the Ligurian Sea in the Western Europe domain.

  17. Mechanisms for the generation of compositional heterogeneities in magma chambers

    NASA Technical Reports Server (NTRS)

    Trial, Alain F.; Spera, Frank J.

    1990-01-01

    The two main hypotheses concerning the origin of compositional heterogeneities in magma chambers are discussed: (1) models in which the development of compositional zonation is simultaneous with the birth and growth of the magma body and (2) models in which zonation develops within an initially homogeneous batch of magma. The paper presents an overview of the geological possibilities and evaluates them on the basis of current research. Calculations are presented for boundary-layer flow in isothermal ternary component systems, and it is demonstrated that multicomponent diffusion effects may be very significant, as was earlier suggested by Trial and Spera (1988).

  18. Thermal evolution and chemical differentiation of the terrestrial magma ocean

    NASA Technical Reports Server (NTRS)

    Abe, Y.

    1992-01-01

    The release of gravitational energy resulted in global melting and formation of a magma ocean during accretion of the Earth. Although it is believed that the formation of the magma ocean resulted in gravitational differentiation of melt and solid, the differentiation might be disturbed by the following processes: (1) convective mixing; (2) cooling and solidification; and (3) growth of the earth, which results in secular increase of pressure, and stirring by planetesimal impacts. The purpose of this study is to investigate the differentiation processes of the terrestrial magma ocean by taking into account various disturbing processes.

  19. Magma energy extraction - Annual Report for FY88

    SciTech Connect

    Dunn, J.C.

    1989-08-01

    Thermal energy contained in magmatic systems represents a huge potential resource. In the US, useful energy contained in molten and partially-molten magma within the upper 10 km of the crust has been estimated at 50,000 to 500,000 Quads. The objective of the Magma Energy Extraction Program is to determine engineering feasibility of locating, accessing and utilizing magma as a viable energy resource. Engineering feasibility will depend on size and depth of the resource; extraction rates; and material life times. 11 refs., 29 figs., 1 tab.

  20. How do crystal-rich magmas outgas?

    NASA Astrophysics Data System (ADS)

    Oppenheimer, Julie; Cashman, Katharine V.; Rust, Alison C.; Sandnes, Bjornar

    2014-05-01

    Crystals can occupy ~0 to 100% of the total magma volume, but their role in outgassing remains poorly understood. In particular, the upper half of this spectrum - when the particles touch - involves complex flow behaviours that inevitably affect the geometry and rate of gas migration. We use analogue experiments to examine the role of high particle concentrations on outgassing mechanisms. Mixtures of sugar syrup and glass beads are squeezed between two glass plates to allow observations in 2D. The experiments are performed horizontally, so buoyancy does not intervene, and the suspensions are allowed to expand laterally. Gas flow regimes are mapped out for two sets of experiments: foams generated by chemical reactions, and single air bubbles injected into the particle suspension. Chemically induced bubble nucleation and growth throughout the suspension gradually generated a foam and allowed observations of bubble growth and migration as the foam developed. High particle fractions, close to the random maximum packing, reduced foam expansion (i.e. promoted outgassing). In the early phases of the experiments, they caused a flushing of bubbles from the system which did not occur at low crystal contents. High particle fractions also led to melt segregation and phase re-arrangements, eventually focusing gas escape through connected channels. A more in-depth study of particle-bubble interactions was carried out for single bubbles expanding in a mush. These show a clear change in behaviour close to the limit for loose maximum packing of dry beads, determined experimentally. At concentrations below loose packing, gas expands in a fingering pattern, characterized by a steady advance of widening lobes. This transits to a 'pseudo-fracturing' regime at or near loose packing, whereby gas advances at a point, often in an episodic manner, and outgases with little to no bulk expansion. However, before they can degas, pseudo-fractures typically build up larger internal gas pressures

  1. Boron Isotope Compositions of Selected Fresh MORB Glasses From the Northern EPR (8-10° N): Implications for MORB Magma Contamination

    NASA Astrophysics Data System (ADS)

    Le Roux, P. J.; Shirey, S. B.; Hauri, E. H.; Perfit, M. R.

    2003-12-01

    The petrogenetic role of seawater and seawater-equilibrated altered crust in the magmatic evolution of basalts formed at mid-ocean ridges is not well-constrained. Observed excess Cl in oceanic basaltic magmas led to established models of assimilation of a saline brine component, although the physical form of this component and whether any other components contaminate MORB magmas remain unresolved. Light stable isotopes such as B are valuable in further refining our understanding of these magmatic processes. The light element B has two stable isotopes (mass 11 and 10) and B isotopic ratio ranges significantly in oceanic settings: e.g. depleted upper mantle (δ 11B -10‰ ), fresh MORB magmas (δ 11B -1.2 to -6.5‰ ), altered oceanic crust (δ 11B +2 to +9‰ ), hydrothermal fluids (δ 11B +30 to +36.5‰ ), and seawater (δ 11B +38.5‰ ). We have developed an in situ laser ablation, multiple multiplier ICP-MS at DTM (see le Roux et al., in press) that has reliable uncertainties for B isotope analyses better than 1‰ (2σ ) over concentration ranges from 0.3 ppm to above 30 ppm. This technique makes nearly any size glass sample amenable to B isotope study. B isotopic compositions were obtained on 16 fresh MORB magmas from the northern East Pacific Rise (EPR) from 8 to 10° N. This region of the EPR has an extensive, existing MORB glass collection, with well-constrained general geochemistry and petrology, recovered from sites on-axis, off-axis (including young off-axis eruptions; abyssal hills), and the Siquerios fracture zone. Geophysical data from this region imaged the top of the dike section (layer 2A) and the sub-axial magma chambers (AMC). Data for these MORB glasses indicate the variable addition of H2O, Cl, F, Li and B to these magmas prior to eruption. The excess Cl can be accounted for by variable (<0.5wt%) magma contamination with a saline brine (NaCl 15-50wt%; Kent et al, 1999). Variable magma degassing places the contamination of some of these magmas

  2. The role of magma mixing in the evolution of high-K calc-alkaline granitoid suites: in situ trace element and Sr-Nd-Hf isotope constraints

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Zeh, Armin; Gerdes, Axel; Slaby, Ewa; Villaros, Arnaud

    2015-04-01

    The so-called "I-type", high-K calc-alkaline granitoids are often considered as "hybrid" in origin, i.e. involving both mantle and crustal components in their petrogenesis. The interactions between both components either take place (1) at mantle levels (i.e. enriched mantle source); (2) at emplacement levels (i.e. crustal contamination and/or magma mixing with crustal melts) or (3) both. Magma mixing is, in particular, frequently invoked to explain the compositional range of high-K calc-alkaline granitoid suites, especially phases of intermediate composition (SiO2 = 60-65 wt.%) such as quartz-diorites or granodiorites. We investigated the role of magma mixing in the origin of such rocks using elemental and isotope (Sr-Nd-Hf) chemistry of magmatic minerals (plagioclase, zircon, apatite, titanite, epidote), measured in situ by LA-(MC-)ICPMS, allowing a much greater spatial resolution than classical whole-rock geochemistry. We focused on a suite of late-Archaean (2.69 Ga-old) high-K, calc-alkaline granitoids from the Pietersburg block, northern Kaapvaal Craton (South Africa): the Mashashane, Matlala, Matok and Moletsi plutons. Those plutons range from diorites to monzogranites, emplaced at different crustal levels but all within a relatively short time span and showing evidence for interactions (mingling), both at the outcrop and mineral scale. Hf isotope data on zircon confirm that all rocks are cogenetic (identical ɛHf(t)), but trace element and Sr isotopes in plagioclase point to the involvement of several components in their petrogenesis, at different stages of the magma evolution. The most mafic rocks (diorites) derive from the interaction, at mantle levels, between depleted peridotite and a sedimentary component of quartzofeldspathic nature. The mineral chemistry of more felsic rocks can be explained by (1) differentiation from the diorite magmas through Amp + Plag fractionation; (2) interactions with magmas derived from melting of local crust (tonalites

  3. Granite, gabbro and mafic microgranular enclaves in the Gejiu area, Yunnan Province, China: a case of two-stage mixing of crust- and mantle-derived magmas

    NASA Astrophysics Data System (ADS)

    Cheng, Yanbo; Spandler, Carl; Mao, Jingwen; Rusk, Brian G.

    2012-10-01

    Geochronological, geochemical, whole-rock Sr-Nd, and zircon Hf isotopic analyses were carried out on the Jiasha Gabbro, mafic microgranular enclaves (MME) and host Longchahe Granite samples from the Gejiu area in the southeast Yunnan province, SW China, with the aim of characterizing their petrogenesis. Compositional zoning is evident in the gabbro body as the cumulate textures and mineral proportions in the gabbro interior are distinct from the gabbro margin. The Longchahe Granite largely comprises metaluminous quartz monzonite with distinctive K-feldspar megacrysts, but also contains a minor component of peraluminous leucogranite. The MME have spheroidal to elongated/lenticular shapes with sharp, crenulated and occasionally diffuse contacts with the host granite, which we attribute to the undercooling and disaggregation of mafic magma globules within the cooler host felsic magma. Field observations, geochronology, geochemistry, Sr-Nd and zircon Hf isotopic compositions point to a complex petrogenesis for this granite-MME-gabbro association. Zircon 206Pb/238U ages determined by LA-ICP-MS for a mafic enclave, its host granite and the gabbro body are 83.1 ± 0.9 Ma, 83.1 ± 0.4 Ma and 83.2 ± 0.4 Ma, respectively, indicating coeval crystallization of these igneous rock units. Crystal fractionation processes can explain much of the compositional diversity of the Jiasha Gabbro. The geochemical features of the gabbro, such as high Mg# (up to 70) and Cr (up to 327 ppm), enrichment in LILEs (e.g., Rb, Ba, K2O) and LREEs, and depletion in HFSE (e.g., Nb, Ta, Ti), together with initial 87Sr/86Sr ratios of 0.708-0.709 and negative ɛNd(t) values (-5.23 to -6.45), indicate they were derived from a mantle source that had undergone previous enrichment, possibly by subduction components. The Longchahe Granite has a large range of SiO2 (59.87-74.94 wt%), is distinctly alkaline in composition, and has Sr-Nd-Hf isotopic compositions ((87Sr/86Sr)i > 0.712, ɛNd(t) = -6.93 to -7

  4. Assembly of a zoned volcanic magma chamber from multiple magma batches: The Cerberean Cauldron, Marysville Igneous Complex, Australia

    NASA Astrophysics Data System (ADS)

    Clemens, J. D.; Birch, W. D.

    2012-12-01

    The Late Devonian (374 Ma) Cerberean Cauldron forms the northern part of the Marysville Igneous Complex, in Central Victoria, Australia, filled with around 900 km3 of intra-caldera ignimbrites. The basal volcanic formation is the rhyolitic high-Al Rubicon Ignimbrite, overlain by a larger volume of crystal-rich rhyolitic low-Al Rubicon Ignimbrite, which grades upward into the voluminous, rhyodacitic Lake Mountain Ignimbrite. The rocks are S-type in character, with initial 87Sr/86Sr around 0.709 to 0.710 and ɛNdt varying from - 4.7 to - 6.0, suggesting metagreywacke protoliths. The chemistry of the volcanic rocks is incompatible with formation by a differentiation mechanism. Experimentally determined phase relations of a low-Al Rubicon Ignimbrite and a Lake Mountain Ignimbrite show that early crystallisation of the Lake Mountain magma began at > 450 MPa and at > 875 °C (possibly up to 940 °C), with an initial magma H2O content of 4.1 to 5.3 wt.%. In the pre-eruption magma chamber, the Rubicon Ignimbrite magma had a temperature of ≥ 780 °C and contained ≥ 4 wt.% H2O. Each formation, and indeed smaller volumes of rock, appears to have been produced by partial melting of slightly contrasting greywackes in a protolith with spatial variations in its chemistry and mineralogy, with the magma delivered in batches to a high-level chamber. The Rubicon Ignimbrite magmas underwent some internal differentiation, probably by crystal settling, prior to eruption, and variations in the Lake Mountain Ignimbrite are most probably due to small but variable degrees of peritectic phase entrainment. The limited gradation between the Rubicon Ignimbrite and Lake Mountain Ignimbrite is due to minor, pre-eruption mixing across the magma interface. Such limited mixing between individual magma batches appears typical of anatectic granitic magmas.

  5. H, O, Sr, Nd, and Pb isotope geochemistry of the Latir volcanic field and cogenetic intrusions, New Mexico, and relations between evolution of a continental magmatic center and modifications of the lithosphere

    USGS Publications Warehouse

    Johnson, C.M.; Lipman, P.W.; Czamanske, G.K.

    1990-01-01

    all the postcaldera plutons overlap those of the precaldera rocks and Amalia Tuff, except for those for two late-stage rhyolite dikes associated with the Rio Hondo pluton that have ??18O values of-8.6 and-9.5; these dikes are the only Latir rocks which may be largely crustal melts. Chemical and isotopic data from the Latir field suggest that large fluxes of mantle-derived basaltic magma are necessary for developing and sustaining large-volume volcanic centers. Development of a detailed model suggests that 6-15 km of new crust may have been added beneath the volcanic center; such an addition may result in significant changes in the chemical and Sr and Nd isotopic compositions of the crust, although Pb isotope ratios will remain relatively unchanged. If accompanied by assimilation, crystallization of pooled basaltic magma near the MOHO may produce substantial cumulates beneath the MOHO that generate large changes in the isotopic composition of the upper mantle. The Latir field may be similar to other large-volume, long-lived intracratonal volcanic fields that fundamentally owe their origins to extensive injection of basaltic magma into the lower parts of their magmatic systems. Such fields may overlie areas of significant crustal growth and hybridization. ?? 1990 Springer-Verlag.

  6. Fluid geochemistry monitoring at three California volcanoes (Invited)

    NASA Astrophysics Data System (ADS)

    Evans, W.; Hunt, A. G.; Kennedy, B. M.; Ingebritsen, S.; McGeehin, J. P.

    2013-12-01

    Mammoth Mountain, Lassen, and Shasta are high-threat volcanoes where aqueous and gas geochemistry is studied as part of ongoing monitoring efforts. All three volcanoes host high-elevation gas vents at near-boiling temperatures, and time series of samples from these features can reveal changes in the underlying magma-hydrothermal system. Most notably, a steam vent on Mammoth Mountain has shown significant increases in 3He/4He ratios that correlate with seismic swarms, initially in 1989-1990 and again in 2010-2012. The correlations provide strong evidence that those seismic swarms reflect enhanced upflow of magmatic fluids. Difficult access limits the frequency of sampling at the vents on Lassen and Shasta, but background data do exist, and sampling frequency could be increased in the event of unrest. Geochemical monitoring at the three volcanoes also includes sampling spring waters of diverse types that discharge on the flanks. Lassen supports a large hydrothermal system on its SE flanks consisting of numerous acid-sulfate springs and mudpots and at lower elevations, high-Cl hot springs. Dilute springs on the NE flank contain a few mg/L Cl and are a few °C above normal but are distinctly enriched in magmatic CO2 and represent potentially useful monitoring targets. Similar dilute, slightly thermal springs constitute the only anomalous spring discharges at Shasta (which lacks hot springs), and carbon and helium isotopes demonstrate a magmatic gas component in these features. Mammoth Mountain has one ~50°C hot spring (Reds Meadow tub) at its western base but also hosts a large number of dilute cold springs that are highly enriched in magmatic CO2. These cold springs show no detectable anomalies in Cl or temperature and the CO2 enrichment is best explained as a consequence of direct dissolution of magmatic gas into cold groundwater. Direct gas dissolution into cold groundwater likely occurs at Lassen and Shasta as well, in addition to the small input of geothermal

  7. Implications of magma transfer between multiple reservoirs on eruption cycling.

    PubMed

    Elsworth, Derek; Mattioli, Glen; Taron, Joshua; Voight, Barry; Herd, Richard

    2008-10-10

    Volcanic eruptions are episodic despite being supplied by melt at a nearly constant rate. We used histories of magma efflux and surface deformation to geodetically image magma transfer within the deep crustal plumbing of the Soufrière Hills volcano on Montserrat, West Indies. For three cycles of effusion followed by discrete pauses, supply of the system from the deep crust and mantle was continuous. During periods of reinitiated high surface efflux, magma rose quickly and synchronously from a deflating mid-crustal reservoir (at about 12 kilometers) augmented from depth. During repose, the lower reservoir refilled from the deep supply, with only minor discharge transiting the upper chamber to surface. These observations are consistent with a model involving the continuous supply of magma from the deep crust and mantle into a voluminous and compliant mid-crustal reservoir, episodically valved below a shallow reservoir (at about 6 kilometers). PMID:18845752

  8. Time scales of crystal mixing in magma mushes

    NASA Astrophysics Data System (ADS)

    Schleicher, Jillian M.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain

    2016-02-01

    Magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption. However, the processes and associated time scales that produce the commonly observed expressions of magma mixing are poorly understood, especially under crystal-rich conditions. Here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal-rich magma mush that is subject to open-system reintrusion events. Our approach includes novel numerical simulations that resolve multiphase particle-fluid interactions. It also quantifies the crystal mixing by calculating both the local and system-wide progressive loss of the spatial correlation of individual crystals throughout the mixing region. Both inertial and viscous time scales for bulk mixing are introduced. Estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days.

  9. The Magma Transport System of the Mono Craters, California

    NASA Astrophysics Data System (ADS)

    Johnson, M. R.; Putirka, K. D.

    2013-12-01

    The Mono Craters are a series of 28 volcanic domes, coulees, and craters, just 16 km north of Long Valley. The magmatic products of the Mono Craters include mostly small magmatic bodies, sills, and dikes set in a transtensional tectonic setting. New high-density sampling of the domes reveals a wider range of magma compositions than heretofore recognized, and thus reveals what is likely a more complex magmatic system, involving a greater number of batches of magma and a more complex magma storage/delivery system. Here, we present a model for the magma plumbing system based on space-composition patterns and preliminary estimates of crystallization temperatures and pressures based on olivine-, feldspar- and clinopyroxene-liquid equilibria. Whole rock analyses show three compositionally distinct batches of magma within the Mono Craters proper: a felsic (73-78.4% SiO2), intermediate (64.4-68% SiO2) and mafic (52.7-61% SiO2) group. The Mono Lake Islands (Paoha and Negit) fall into the intermediate group, but contain distinctly lower TiO2 and Fe2O3 at a given SiO2 compared to all other Mono Craters; on this basis, we surmise that the Paoha and Negit eruptions represent a distinct episode of magmatism that is not directly related to the magmatic activity that created the Mono Craters proper. The discontinuous nature of the three groups indicates that magma mixing, while evident to some degree within and between certain domes, did not encompass the entire range of compositions at any given time. The three groups, however, do form a rough linear trend, and some subsets of domes have compositions that fall on distinctly linear (if still discontinuous) trends that cannot be reproduced by fractional crystallization, but rather are indicative of magma mixing. Our high-density sampling also reveals interesting geographical patterns: for example, felsic magmas erupt throughout the entire Mono Craters chain, erupting at a wide range of temperatures, ranging from 650-995°C, but

  10. Preliminary considerations for extraction of thermal energy from magma

    SciTech Connect

    Hickox, C.E.; Dunn, J.C.

    1985-01-01

    Simplified mathematical models are developed to describe the extraction of thermal energy from magma based on the concept of a counterflow heat exchanger inserted into the magma body. Analytical solutions are used to investigate influence of the basic variables on electric power production. Calculations confirm that the proper heat exchanger flow path is down the annulus with hot fluid returning to the surface through the central core. The core must be insulated from the annulus to achieve acceptable wellhead temperatures, but this insulation thickness can be quite small. The insulation is effective in maintaining the colder annular flow below expected formation temperatures so that a net heat gain from the formation above a magma body is predicted. The analyses show that optimum flow rates exist that maximize electric power production. These optimum flow rates are functions of the heat transfer coefficients that describe magma energy extraction. 15 refs., 3 figs.

  11. 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

  12. Magma Dynamics at Yucca Mountain, Nevada

    SciTech Connect

    D. Krier

    2005-08-29

    Small-volume basaltic volcanic activity at Yucca Mountain has been identified as one of the potential events that could lead to release of radioactive material from the U.S. Department of Energy (DOE) designated nuclear waste repository at Yucca Mountain. Release of material could occur indirectly as a result of magmatic dike intrusion into the repository (with no associated surface eruption) by changing groundwater flow paths, or as a result of an eruption (dike intrusion of the repository drifts, followed by surface eruption of contaminated ash) or volcanic ejection of material onto the Earth's surface and the redistribution of contaminated volcanic tephra. Either release method includes interaction between emplacement drifts and a magmatic dike or conduit, and natural (geologic) processes that might interrupt or halt igneous activity. This analysis provides summary information on two approaches to evaluate effects of disruption at the repository by basaltic igneous activity: (1) descriptions of the physical geometry of ascending basaltic dikes and their interaction with silicic host rocks similar in composition to the repository host rocks; and (2) a summary of calculations developed to quantify the response of emplacement drifts that have been flooded with magma and repressurized following blockage of an eruptive conduit. The purpose of these analyses is to explore the potential consequences that could occur during the full duration of an igneous event.

  13. CONDITIONS LEADING TO SUDDEN RELEASE OF MAGMA PRESSURE

    SciTech Connect

    B. Damjanac; E.S. Gaffney

    2005-08-26

    Buildup of magmatic pressures in a volcanic system can arise from a variety of mechanisms. Numerical models of the response of volcanic structures to buildup of pressures in magma in dikes and conduits provide estimates of the pressures needed to reopen blocked volcanic vents. They also can bound the magnitude of sudden pressure drops in a dike or conduit due to such reopening. Three scenarios are considered: a dike that is sheared off by covolcanic normal faulting, a scoria cone over a conduit that is blocked by in-falling scoria and some length of solidified magma, and a lava flow whose feed has partially solidified due to an interruption of magma supply from below. For faulting, it is found that magma would be able to follow the fault to a new surface eruption. A small increase in magma pressure over that needed to maintain flow prior to faulting is required to open the new path, and the magma pressure needed to maintain flow is lower but still greater than for the original dike. The magma pressure needed to overcome the other types of blockages depends on the details of the blockage. For example, for a scoria cone, it depends on the depth of the slumped scoria and on the depth to which the magma has solidified in the conduit. In general, failure of the blockage is expected to occur by radial hydrofracture just below the blocked length of conduit at magma pressures of 10 MPa or less, resulting in radial dikes. However, this conclusion is based on the assumption that the fluid magma has direct access to the rock surrounding the conduit. If, on the other hand, there is a zone of solidified basalt, still hot enough to deform plastically, surrounding the molten magma in the conduit, this could prevent breakout of a hydrofracture and allow higher pressures to build up. In such cases, pressures could build high enough to deform the overlying strata (scoria cone or lava flow). Models of such deformations suggest the possibility of more violent eruptions resulting from

  14. The role of turbulence in explosive magma-water mixing

    NASA Astrophysics Data System (ADS)

    Mastin, L. G.; Walder, J. S.; Stern, L. A.

    2003-12-01

    Juvenile tephra from explosive hydromagmatic eruptions differs from that of dry magmatic eruptions by its fine average grain size and highly variable vesicularity. These characteristics are generally interpreted to indicate that fragmentation, which occurs in dry magmas by bubble growth, is supplemented in hydromagmatic eruptions by quench-fracturing. Quench fragmentation is thought to accelerate heat transfer to water, driving violent steam expansion and increasing eruptive violence. Although some observed hydromagmatic events (e.g. at Surtsey) are indeed violent, others (e.g. quiescent entry of lava into the ocean at Kilauea) are not. We suggest that the violence of magma-water mixing and the grain size and dispersal of hydromagmatic tephras are controlled largely by the turbulence of magma-water mixing. At Surtsey, fine-grained, widely dispersed hydromagmatic tephras were produced primarily during continuous uprush events in which turbulent jets of magma and gas passed through shallow water (Thorarinsson, 1967). During Kilauea's current eruption, videos show generation of fine-grained tephras when turbulent jets of magma, steam, and seawater exited through skylights at the coastline. Turbulence intensity, or the fraction of total jet kinetic energy contained in fine-scale turbulent velocity oscillations, has long been known to control the scale of atomization in spray nozzles and the rate of heat transfer and chemical reaction in fuel injectors. We hypothesize that turbulence intensity also influences grain size and heat transfer rate in magma-water mixing, though such processes are complicated by boiling (in water) and quench fracturing (in magma). We are testing this hypothesis in experiments involving turbulent injection of water (a magma analog) into liquid nitrogen (a water analog). We also suggest that turbulent mixing influences relative proportions of magma and water in hydromagmatic eruptions. Empirical studies indicate that pressure-neutral turbulent

  15. Seismic Tremors and Three-Dimensional Magma Wagging

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Bercovici, D.

    2015-12-01

    Seismic tremor is a feature shared by many silicic volcanoes and is a precursor of volcanic eruption. Many of the characteristics of tremors, including their frequency band from 0.5 Hz to 7 Hz, are common for volcanoes with very different geophysical and geochemical properties. The ubiquitous characteristics of tremor imply that it results from some generation mechanism that is common to all volcanoes, instead of being unique to each volcano. Here we present new analysis on the magma-wagging mechanism that has been proposed to generate tremor. The model is based on the suggestion given by previous work (Jellinek & Bercovici 2011; Bercovici et.al. 2013) that the magma column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the magma inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the magma column is restricted to one vertical plane, the three-dimensional model we employ allows the magma column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the magma column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the magma column can also develop instabilities with higher frequencies than what is found in the original two-dimensional model. Lateral motion can also be out of phase for various depths in the magma column leading to a coiled wagging motion. For the viscous-magma model, we predict a similar damping rate for the uncoiled magma column as in the two-dimensional model, and faster damping for the coiled magma column. The higher damping thus requires the existence of a forcing mechanism to sustain the oscillation, for example the gas-driven Bernoulli effect proposed by Bercovici et al (2013). Finally, using our new 3

  16. Crystallization and saturation front propagation in silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Lake, Ethan T.

    2013-12-01

    The cooling and crystallization style of silicic magma bodies in the upper crust falls on a continuum between whole-chamber processes of convection, crystal settling, and cumulate formation and interface-driven processes of conduction and crystallization front migration. In the end-member case of vigorous convection and crystal settling, volatile saturation advances downward from the roof and upward from the floor throughout the chamber. In the end-member case of stagnant magma bodies, volatile saturation occurs along an inward propagating front from all sides of the chamber. Ambient thermal gradient primarily controls the propagation rate; warm (⩾40 °C/km) geothermal gradients lead to thick (1200+ m) crystal mush zones and slow crystallization front propagation. Cold (<40 °C/km) geothermal gradients lead to rapid crystallization front propagation and thin (<1000 m) mush zones. Magma chamber geometry also exerts a first-order control on propagation rates; bodies with high surface to magma volume ratio and large Earth-surface-parallel faces exhibit more rapid propagation and thinner mush zones. Crystallization front propagation occurs at speeds of greater than 10 cm/yr (rhyolitic magma; 1 km thick sill geometry in a 20 °C/km geotherm), far faster than diffusion of volatiles in magma and faster than bubbles can nucleate, grow, and ascend through the chamber. Numerical simulations indicate saturation front propagation is determined primarily by pressure and magma crystallization rate; above certain initial water contents (4.4 wt.% in a dacite) the mobile magma is volatile-rich enough above 10 km depth to always contains a saturation front. Saturation fronts propagate down from the magma chamber roof at lower water contents (3.3 wt.% in a dacite at 5 km depth), creating an upper saturated interface for most common (4-6 wt.%) magma water contents. This upper interface promotes the production of a fluid pocket underneath the apex of the magma chamber. If the fluid

  17. Diatexite Deformation and Magma Extraction on Kangaroo Island, South Australia

    NASA Astrophysics Data System (ADS)

    Hasalova, Pavlina; Weinberg, Roberto; Ward, Lindsay; Fanning, Mark

    2013-04-01

    Migmatite terranes are structurally complex because of strong rheological contrast between layers with different melt contents and because of magma migration leading to volume changes. Migmatite deformation is intimately linked with magma extraction and the origin of granitoids. We investigate here the relationships between an evolving deformation and magma extraction in migmatites formed during the ca. 500Ma Delamerian orogeny, exposed on Kangaroo Island, South Australia. Here, several phases of deformation occurred in the presence of melt. During an early upright, non-cylindrical folding event, magma was channeled towards the hinge zones of antiforms. Funnel-shaped networks of leucosomes form a root zone that link up towards a central axial planar channel, forming the main magma extraction paths during folding. Extraction was associated with fold limb collapse, and antiformal hinge disruption by magma accumulation and transfer. During a later deformation phase, melt-rich diatexites were deformed, and schollen were disaggregated into smaller blocks and schlieren, and deformed into asymmetric, sigmoidal shapes indicative of dextral shearing flow. During flow, magma accumulated preferentially along shear planes, indicating a dilatational component during shearing (transtension) and in strain shadows of schollen. As deformation waned, magma extraction from these diatexites gave rise to N-trending, steeply dipping, funnel-shaped channels not associated to any deformational feature. The funnel-shape of these structures indicates the direction of magma flow. Structures developed during this phase are comparable with those formed during dewatering of soft sediments. Despite a high degree of complexity, magma migration and extraction features record distinct responses to the evolving deformation which can be used to understand deformation, and nature and direction of melt extraction. The oldest and youngest magmatic rocks from migmatites were dated (U-Pb monazite, SHRIMP

  18. Petrography and geochemistry evidence for supra-subduction ophiolites in Makran, SE Iran

    NASA Astrophysics Data System (ADS)

    Hunziker, Daniela; Burg, Jean-Pierre; Bouilhol, Pierre; Omrani, Jafar

    2010-05-01

    Ophiolites archive tectonic and chemical processes from crystallization of the oceanic lithosphere to accretion during obduction and/or continental collision. The variety of ophiolites has shown that they form in various geotectonic settings and experience complex petrological and geochemical histories during their evolution. We present new results on the structure, petrography, geochemistry and geochronology of the Remeshk/Mokhtaramabad and Fannuj/Maskutan ophiolitic complexes in Makran (Southeast Iran), which have been very scarcely studied before this work. A detailed map and cross sections illustrate temporal and structural relationships between the different lithologies. The extensive ultramafic complexes comprise a lower, harzburgite-dominated unit with few lherzolites overlain by dunites. Pyroxene-bearing peridotites show typical features of tectonized mantle deformed at sub-solidus conditions. The olivine chemistry (xMg = 0.90-0.92, NiO content of 0.4-0.47wt%) indicates that the ultramafic rocks represent an ophiolitic upper mantle. Most dunites are characterized by cumulate textures in olivine and a slightly lower xMg = 0.87-0.89 and NiO content of 0.25-0.35wt%. Dunites are locally impregnated by plagioclase-rich melts with minor amounts of clinopyroxene. They were intruded by gabbroic dykes marking the transition zone between mantle and crust. The gabbroic sequence displays increasingly differentiated rocks originated from the same magma source in the following order: troctolite - olivine gabbro - gabbro - anorthositic dykes - diabase. These rocks were later intruded by plagiogranites and hornblende-gabbros. Petrography and geochemistry show oceanic features of a shallow environment for some lithologies; other lithologies indicate a supra-subduction environment, in particular the late-Cretaceous calc-alkaline pillow lavas that yield a clear arc signal. Advanced trace element analyses and geochronology will constrain the evolution of the Tethys

  19. Low-(18)O Silicic Magmas: Why Are They So Rare?

    SciTech Connect

    Balsley, S.D.; Gregory, R.T.

    1998-10-15

    LOW-180 silicic magmas are reported from only a small number of localities (e.g., Yellowstone and Iceland), yet petrologic evidence points to upper crustal assimilation coupled with fractional crystallization (AFC) during magma genesis for nearly all silicic magmas. The rarity of 10W-l `O magmas in intracontinental caldera settings is remarkable given the evidence of intense 10W-l*O meteoric hydrothermal alteration in the subvolcanic remnants of larger caldera systems. In the Platoro caldera complex, regional ignimbrites (150-1000 km3) have plagioclase 6180 values of 6.8 + 0.1%., whereas the Middle Tuff, a small-volume (est. 50-100 km3) post-caldera collapse pyroclastic sequence, has plagioclase 8]80 values between 5.5 and 6.8%o. On average, the plagioclase phenocrysts from the Middle Tuff are depleted by only 0.3%0 relative to those in the regional tuffs. At Yellowstone, small-volume post-caldera collapse intracaldera rhyolites are up to 5.5%o depleted relative to the regional ignimbrites. Two important differences between the Middle Tuff and the Yellowstone 10W-180 rhyolites elucidate the problem. Middle Tuff magmas reached water saturation and erupted explosively, whereas most of the 10W-l 80 Yellowstone rhyolites erupted effusively as domes or flows, and are nearly devoid of hydrous phenocrysts. Comparing the two eruptive types indicates that assimilation of 10W-180 material, combined with fractional crystallization, drives silicic melts to water oversaturation. Water saturated magmas either erupt explosively or quench as subsurface porphyrins bejiire the magmatic 180 can be dramatically lowered. Partial melting of low- 180 subvolcanic rocks by near-anhydrous magmas at Yellowstone produced small- volume, 10W-180 magmas directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.

  20. Solidification of basaltic magma during flow in a dike.

    USGS Publications Warehouse

    Delaney, P.T.; Pollard, D.D.

    1982-01-01

    A model for time-dependent unsteady heat transfer from magma flowing in a dyke is developed. The ratio of solidification T to magma T is the most important parameter. Observations of volcanic fissure eruptions and study of dykes near Ship Rock, New Mexico, show that the low T at dyke margins and the rapidly advancing solidification front predicted by the model are qualitatively correct.-M.S.

  1. Experimental Fractional Crystallization of the Lunar Magma Ocean

    NASA Technical Reports Server (NTRS)

    Rapp, J. F.; Draper, D. S.

    2012-01-01

    The current paradigm for lunar evolution is of crystallization of a global scale magma ocean, giving rise to the anorthositic crust and mafic cumulate interior. It is thought that all other lunar rocks have arisen from this differentiated interior. However, until recently this paradigm has remained untested experimentally. Presented here are the first experimental results of fractional crystallization of a Lunar Magma Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].

  2. Magma plumbing system of the Aso-3 large pyroclastic eruption cycle at Aso volcano, Southwest Japan: Petrological constraint on the formation of a compositionally stratified magma chamber

    NASA Astrophysics Data System (ADS)

    Kaneko, Katsuya; Inoue, Kazuhisa; Koyaguchi, Takehiro; Yoshikawa, Masako; Shibata, Tomoyuki; Takahashi, Toshiro; Furukawa, Kuniyuki

    2015-09-01

    Aso volcano has the largest caldera (18 × 25 km in diameter) in the southwestern Japan Island Arc, and it formed as the result of four large (VEI = 6-7) pyroclastic-eruption cycles. We study the penultimate large eruption cycle, the Aso-3 cycle, which occurred 123 ka with an ejecta volume of more than 150 km3. The processes in the pre-eruptive magma chamber and the magma genesis of the Aso-3 cycle were inferred from geological data, phenocryst chemistry, and whole-rock chemical and Sr-, Nd-, and Pb isotopic analyses of juvenile clasts. The geological and petrological data indicate that the pre-eruptive magma chamber was stratified compositionally into three layers: from top to bottom, silicic, intermediate, and mafic magma layers. The three magma layers had a uniform isotope composition, suggesting that all the magmas were generated from a single source. The silicic and intermediate magmas were not generated from the mafic magma by fractional crystallization. The silicic magma has higher Ni content (compatible element) than the mafic magma. This suggests that these magmas were produced by partial melting of the same mafic crust but with differing amounts of partial melting: the silicic magma was produced by a low degree of partial melting of the source rock without fractional crystallization, and the mafic magma was produced by a large degree of partial melting followed by fractional crystallization. The intermediate magma compositions plot on the tie line between the silicic magma and the melt of the mafic magma in variation diagrams, and the intermediate magma has phenocrysts whose compositions are identical with those in the silicic magma. This observation indicates that, before the Aso-3 eruption cycle, a two-layer stratified magma chamber of the silicic and mafic magmas was formed as a result of melting of the mafic crust, which was followed by formation of the intermediate layer as a result of interfacial mixing between the silicic magma and the melt of

  3. The Rheology of Three-Phase Basaltic Magma

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Truby, J.; Mueller, S. P.; Mader, H. M.

    2014-12-01

    The transport of magma is controlled by its rheology which, in turn, is a function of its crystal and bubble content. We develop the first empirically-validated model for the rheology of a three-phase magma (i.e. one containing both bubbles and crystals). The model is valid at low bubble capillary number (where bubble deformation is small) which is typical of basaltic magma. We adopt an 'effective-medium' approach in which the bubbly melt is treated as a continuous medium which suspends the crystals. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and crystal suspension rheology, which are taken from the literature. The model is validated against new analogue experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction (0 ≤ Фp ≤0.5) and bubble volume fraction (0 ≤ Фb ≤ 0.3). Consistent with model predictions, experimental results demonstrate that, at low capillarity, bubble growth in a crystal-poor magma increases its viscosity, whilst bubble growth in a crystal-rich magma decreases its viscosity. The validity range of the model makes it particularly applicable to the transport of magma in the sub-volcanic plumbing system. The model is trivially extended to account for variations in crystal shape, and for the high capillarity regime; these extended models await experimental validation.

  4. Crystallization and Cooling of a Deep Silicate Magma Ocean

    NASA Astrophysics Data System (ADS)

    Bower, Dan; Wolf, Aaron

    2016-04-01

    Impact and accretion simulations of terrestrial planet formation suggest that giant impacts are both common and expected to produce extensive melting. The moon-forming impact, for example, likely melted the majority of Earth's mantle to produce a global magma ocean that subsequently cooled and crystallised. Understanding the cooling process is critical to determining magma ocean lifetimes and recognising possible remnant signatures of the magma ocean in present-day mantle heterogeneities. Modelling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (magma ocean) and viscous creep (present-day mantle), in addition to uncertainties in material properties and chemical partitioning. We consider a simplified spherically-symmetric (1-D) magma ocean to investigate both its evolving structure and cooling timescale. Extending the work of Abe (1993), mixing-length theory is employed to determine convective heat transport, producing a high resolution model that parameterises the ultra-thin boundary layer (few cms) at the surface of the magma ocean. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS.

  5. The effects of Venus' thermal structure on buoyant magma ascent

    NASA Technical Reports Server (NTRS)

    Sakimoto, S. E. H.; Zuber, M. T.

    1992-01-01

    The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth.

  6. Dynamically-induced structures formation in congested magma

    NASA Astrophysics Data System (ADS)

    Petford, N.

    2008-12-01

    Crystal fabrics preserved in igneous rocks offer a glimpse into the magma emplacement process. Detailed field mapping, in combination with AMS studies, seem to provide the best available data for unravelling intrusion architecture on the decimetre scale. However, a full and proper understanding of the fluid dynamics of congested fluid-particle mixtures during shear remains elusive. This is a shame as without recourse to such fundamental understanding, the interpretation of structural field data in the context of magma flow remains problematic. One way to gain insight into the process is to treat flowing magma as a dynamic material with a rheology similar to sheared, congested slurries. The fancy that dense magma equates to a high temperature slurry is an attractive one, and opens up a way to examine the emplacement process that does not rely exclusively on equilibrium thermodynamics as a final explanation of commonly observed igneous structures. Instead, using examples from mafic rocks where cooling has been rapid, the idea is put forward that in high Peclet number suspensions (where particle diffusion is negligible), shearing and non- Newtonian behaviour imparts a rich diversity of structures including layering, grading and flow segregation. Key to understanding the rheology, hence flow dynamics of congested magma, is the particle microstructure, a still poorly known essence of suspension flows. Where magma transport is continental in scale and long lived (e.g. Large Igneous Provinces), rotation of the earth may in theory endow a small but potentially measurable imprint on the preserved flow fabric.

  7. Experimental Magma Mixing and Mingling in Volcanic Environments

    NASA Astrophysics Data System (ADS)

    Morgavi, D.; Laumonier, M.; Petrelli, M.; Perugini, D.

    2015-12-01

    Magma mixing and mingling features are commonly observed in both plutonic and volcanic environments. Major occurrences are represented by hybrid products, enclaves and crystals in disequilibrium with the melt. According to present knowledge the complete mixing of magmas in crustal reservoirs (leading to the production of hybrids) requires a low viscosity contrast between the two end-members (0.5 log unit). On another hand, recent experimental and field works have shown that (1) crystal-free magmas with viscosity difference of 3 orders of magnitude produced mingling and mixing features at higher deformation conditions (strain and strain rate) and (2) these features are found in volcanic products out of the above mentioned rheological window. In this study, we performed magma mixing experiments, to test the effects of chaotic deformation of a two component system at volcanic conditions and strain rates comparable to natural magmatic systems (volcanic conduits and lava flows): in the ChaOtic Magma Mixing Apparatus (COMMA) installed at the University of Perugia, a synthetic haplotonalite and a natural basalt from Santorini volcano were juxtaposed and chaotically mixed for several hours at ~1140°C with a moderate strain rate of ~5.10-3. The textural and geochemical (electronic microprobe, laser ablation mass spectrometry) features developed during the experiments show the development of complex patterns with high inter-exchange between both magmas. Our results show how chaotic convection extends the mixing capacities at moderate strain rate.

  8. Geophysical and geochemical evolution of the lunar magma ocean

    NASA Technical Reports Server (NTRS)

    Herbert, F.; Drake, M. J.; Sonett, C. P.

    1978-01-01

    There is increasing evidence that at least the outer few hundred kilometers of the moon were melted immediately following accretion. This paper studies the evolution of this lunar magma ocean. The long time scale for solidification leads to the inference that the plagioclase-rich (ANT) lunar crust began forming, perhaps preceded by local accumulations termed 'rockbergs', at the very beginning of the magma ocean epoch. In this view the cooling and solidification of the magma ocean was primarily controlled by the rate at which heat could be conducted across the floating ANT crust. Thus the thickness of the crust was the factor controlling the lunar solidification time. Heat arising from enthalpy of crystallization was transported in the magma by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The magma ocean is deduced to have been turbulent down to a characteristic length scale of the order of 100 m, and to have overturned on a time scale of the order of 1 yr for most of the magma ocean epoch.

  9. Thermal and mechanical controls on magma supply and volcanic deformation

    NASA Astrophysics Data System (ADS)

    Hickey, James; Gottsmann, Jo; Nakamichi, Haruhisa; Iguchi, Masato

    2016-04-01

    Ground deformation often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rock. Geodetic models aimed at constraining source processes consequently require the implementation of realistic mechanical and thermal rock properties. However, most generic models ignore this requirement and employ oversimplified mechanical assumptions without regard for thermal effects. Here we show how spatio-temporal deformation and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that despite on-going eruptions magma is accumulating faster than it can be ejected, and the current uplift is approaching the level inferred prior to the 1914 Plinian eruption. Our results from inverse and forward numerical models are consistent with petrological constraints and highlight how the location, volume, and rate of magma supply, 0.014 km3/yr, are thermomechanically controlled. Magma storage conditions coincide with estimates for the caldera-forming reservoir ˜29,000 years ago, and the inferred magma supply rate indicates a ˜130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic deformation worldwide.

  10. Composition and origin of basaltic magma of the Hawaiian Islands

    USGS Publications Warehouse

    Powers, H.A.

    1955-01-01

    Silica-saturated basaltic magma is the source of the voluminous lava flows, erupted frequently and rapidly in the primitive shield-building stage of activity, that form the bulk of each Hawaiian volcano. This magma may be available in batches that differ slightly in free silica content from batch to batch both at the same and at different volcanoes; differentiation by fractionation of olivine does not occur within this primitive magma. Silica-deficient basaltic magma, enriched in alkali, is the source of commonly porphyritic lava flows erupted less frequently and in relatively negligible volume during a declining and decadent stage of activity at some Hawaiian volcanoes. Differentiation by fractionation of olivine, plagioclase and augite is evident among these lavas, but does not account for the silica deficiency or the alkali enrichment. Most of the data of Hawaiian volcanism and petrology can be explained by a hypothesis that batches of magma are melted from crystalline paridotite by a recurrent process (distortion of the equatorial bulge by forced and free nutational stresses) that accomplishes the melting only of the plagioclase and pyroxene component but not the excess olivine and more refractory components within a zone of fixed and limited depth. Eruption exhausts the supply of meltable magma under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. ?? 1955.

  11. Dyke Swarms in Southeastern British Columbia: Mineralogical and Geochemical Evidence for Emplacement of Multiple Magma Types During Orogenic Collapse

    NASA Astrophysics Data System (ADS)

    Freeman, M.; Owen, J. P.; Hoskin, P. W.

    2009-05-01

    Eocene dyke swarms in southeastern British Columbia provide an important record of the tectonic and magmatic history of the Cordillera following orogenic collapse. New field mapping, petrographic, and geochemical data is presented for a swarm of more than thirty dykes located near the mining town of Trail, B.C. Detailed field mapping revealed that individual dykes are highly diverse, both in composition and morphology. As a group, the dykes trend northwest (average strike of 338 degrees) and dip steeply to the southwest. Their average thickness is approximately 1.5m, with a range from 4.5m to less than 1cm. Three sub-parallel dykes were mapped for a length of 2km, and exhibit irregularities in their form such as branching and offshoots that follow fractures in the country rock. Thin-section analysis shows a wide variety of rock types within the swarm, including: micro-quartz syenite, micro-syenite, micro-monzonite, latite, basalt, basaltic andesite, and lamprophyre. Texturally, these samples are consistently porphyritic and partially altered to chlorite and sericite. This alteration commonly occurs in concentric rims around phenocrysts. The samples are typically intergranular, although some display trachytic texture. Whole-rock geochemistry shows that the dykes have a wide range in composition, with SiO2 between 76.45 wt.% and 45.15 wt.% and MgO between 0.13 wt.% and 13.16 wt.%. The results also revealed that one dyke has very high values of Ni (430 ppm), Cr (1420 ppm), and Co (50 ppm), giving it a fairly primitive composition. Harker diagrams and trace element plots show three distinct groups: mafic calc-alkaline dykes, felsic calc- alkaline dykes, and minette lamprophyres. The felsic dykes are characterized by negative Eu and Sr anomalies suggesting fractionation of plagioclase feldspar, as well as pronounced negative P and Ti anomalies. The minettes are enriched in LILE and depleted in HSFE relative to the mafic dykes. The three groups do not appear to be

  12. Isotope and trace element geochemistry of lamprophyres and syenites from different areas of South-Chuya complex, SE Altai.

    NASA Astrophysics Data System (ADS)

    Vasyukova, Elena

    2016-04-01

    Major and trace elements and radiogenic isotope data are reported for lamprophyres and syenites of South-Chuya complex associated with ore districts in South East of Gornyi Altai, Russia. Dikes of lamprophyres form big area, elongated from north-west to south-east. Within the area of complex dikes distribute irregularly accompanied the fault zones. Lamprophyres of three largest areas, named Aktash, South Chuya and Yustyd were characterized in terms of geology, petro- and geochemistry, isotopic composition. Some of the lamprophyres judging by the high mg'>60 reveal mantle signatures. They reveal round TRE patterns typical of the primitive low degree partial melts but with the negative Nb- Ta anomalies. The others with the lower mg' suggest their differentiation and contamination in crust material. They reveal slightly lower level of TRE and lower troughs of all HFSE. All dikes had intruded in the period of 250-235 Ma, have similar mineralogical, petro- and geochemistry characteristics which were the reasons for unite all of them in one complex. On the most of geochemistry diagrams dikes from 3 areas form their own, but intersected clusters. But on the isotopic diagrams (Sm/Nd and Rb/Sr systems) they show the principle dissimilarity between dikes from various areas. Yustyd lamprophyres initial isotopic characteristics are close to the BSE. The south-chuya rocks isotopic compositions are more enriched by 87Sr/86Sr and have negative ɛNd (-2.84..-4.05). Contamination by the lower crust material suggested at the early stage during the formation of the lamprophyres. Bu the Yustyd lamprophyres were contaminated also during the ascend by the upper crust. Two competitive hypotheses n the isotopic composition are dicussed: 1) different sources or 2) different proportions between the material from the same sources, which ensemble generate the parental magma for the rocks.

  13. Geochemistry of the Lathrop Wells volcanic center

    SciTech Connect

    Perry, F.V.; Straub, K.T.

    1996-03-01

    Over 100 samples have been gathered from the Lathrop Wells volcanic center to assess different models of basalt petrogenesis and constrain the physical mechanisms of magma ascent in the Yucca Mountain region. Samples have been analyzed for major and trace-element chemistry, Nd, Sr and Ph isotopes, and mineral chemistry. All eruptive units contain olivine phenocrysts, but only the oldest eruptive units contain plagioclase phenocrysts. Compositions of minerals vary little between eruptive units. Geochemical data show that most of the eruptive units at Lathrop Wells defined by field criteria can be distinguished by major and trace-element chemistry. Normative compositions of basalts at Lathrop Wells correlate with stratigraphic position. The oldest basalts are primarily nepheline normative and the youngest basalts are exclusively hypersthene normative, indicating increasing silica saturation with time. Trace-element and major-element variations among eruptive units are statistically significant and support the conclusion that eruptive units at Lathrop Wells represent separate and independent magma batches. This conclusion indicates that magmas in the Yucca Mountain region ascend at preferred eruption sites rather than randomly.

  14. Effects of shallow subvolcanic magma storage regions on magma evolution and eruptions dynamics of small mafic centers

    NASA Astrophysics Data System (ADS)

    Cashman, K. V.; Wallace, P. J.; McKay, D.; Ruscitto, D. M.

    2009-12-01

    The existence of shallow subvolcanic dike and sill complexes has long been recognized in field investigations of mafic cinder cones and shield volcanoes. Evidence that these subvolcanic storage regions develop during (rather than separate from) eruptive activity comes from detailed studies of tephra deposits and lava flows produced during cinder cone eruptions. These deposits show both the variable volatile contents of olivine-hosted melt inclusions and pervasive microphenocryst crystallization, both of which indicate temporary magma storage at shallow levels prior to eruption. The consequences of such shallow magma storage for both eruption dynamics and syn-eruptive magma evolution have not previously been considered. Here we use both physical (density, crystallinity) and compositional (bulk, melt inclusion) data from the 1943-1952 eruption of Parícutin, Mexico to examine the impact of shallow pre-eruptive storage on both the eruption process and on the dramatic evolution in magma composition first described by Wilcox (1954). We supplement these observations with data from recent (1500-2000 ybp) mafic cinder cone eruptions in central Oregon. Our data show that shallow subvolcanic storage of magma permits pre-eruptive degassing and crystallization, which, in turn, are responsible for the (typically) wide density range of basaltic scoria observed in cinder cone activity. As pre-eruptive gas loss will diminish the volatiles available to fuel explosive activity, we further speculate that the ease of syn-eruptive dike and sill formation, which is likely to be controlled by both the rate of magma supply and the specific tectonic setting, may modulate the explosive potential of cinder cone eruptions. Additionally, all of the deposits that we have studied have a range in bulk composition, with the earliest tephra the most mafic and the latest lava the most silicic of the eruptive sequence. This observation suggests that an additional consequence of shallow magma storage

  15. Geochemistry and zircon geochronology of Late Proterozoic leucogranites north of Boston, eastern Massachusetts

    SciTech Connect

    Markus, R.; Hon, R. . Geology and Geophysics); Dunning, G. . Dept. of Earth Sciences)

    1993-03-01

    An igneous sequence that includes Late Precambrian volcanics (Lynn Volcanics) and granites, granodiorites, tonalites, plus diorites of the Dedham North suite, is located in a tectonic block bounded by the Walden Pond and Northern Boundary Faults north of the Boston Basin. Within the block between the rhyolites and granodiorites is a several hundred foot wide zone of leucogranites that contains frequent roof pendants in various stages of partial melting. The migmatitic nature of the pendants suggests that the leucogranites were locally derived by melt extraction from the partially melted pendant xenoliths. U-Pb zircon ages were obtained from samples of the leucogranite, granodiorite and diorite. Their crystallization ages are: leucogranite 609 [+-] 4 Ma, granodiorite 607 [+-] 4 Ma, and diorite 606 [+-] 3 Ma. All three samples yield ages that are identical within their statistical error limits and all three samples contain inherited component with average mid-Proterozoic ages. Major and trace element geochemistry of 43 samples of all representative types show that the predominantly pelitic'' layers underwent extensive partial melting and that the leucogranites represent a minimum granite melt at 0.5 to 2.0 kb of P(H2O). Geochemical modeling also supports the origin by partial melting of the pendant inclusions. Once formed, the leucogranite melts were then mixed with mafic magmas which must have also been the provider of the necessary heat to sustain the partial melting process. The data indicate that the Dedham North plutonic suite was formed at shallow crustal levels and that its compositional range is a result of magma mixing of varying proportions between the leucogranite and mafic melts.

  16. The rheology of crystal-rich magmas (Kuno Award Lecture)

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim

    2016-04-01

    The rheology of magmas controls not only eruption dynamics but also the rate of transport of magmas through the crust and to a large extent the rate of magma differentiation and degassing. Magma bodies stalled in the upper crust are known to spend most of their lifespan above the solidus at a high crystal content (Cooper and Kent, 2014; Huber et al., 2009), where the probability of melt extraction (crystal fractionation) is the greatest (Dufek and Bachmann, 2010). In this study, we explore a new theoretical framework to study the viscosity of crystal bearing magmas. Since the seminal work of A. Einstein and W. Sutherland in the early 20th century, it has been shown theoretically and tested experimentally that a simple self-similar behavior exist between the relative viscosity of dilute (low crystal content) suspensions and the particle volume fraction. The self-similar nature of that relationship is quickly lost as we consider crystal fractions beyond a few volume percent. We propose that the relative viscosity of crystal-bearing magmas can be fully described by two state variables, the intrinsic viscosity and the crowding factor (a measure of the packing threshold in the suspension). These two state variables can be measured experimentally under different conditions, which allows us to develop closure relationships in terms of the applied shear stress and the crystal shape and size distributions. We build these closure equations from the extensive literature on the rheology of synthetic suspensions, where the nature of the particle shape and size distributions is better constrained and apply the newly developed model to published experiments on crystal-bearing magmas. We find that we recover a self-similar behavior (unique rheology curve) up to the packing threshold and show that the commonly reported break in slope between the relative viscosity and crystal volume fraction around the expected packing threshold is most likely caused by a sudden change in the state

  17. Applied geochemistry in the 1980s

    SciTech Connect

    Thorton, I.; Howarth, R.J.

    1986-01-01

    This book explores geochemical achievements in mineral exploration covering both current exploration status and future potential. Early chapters focus on exploration south of the equator, geochemical patterns in the granite terrain of Zimbabwe, and the special problems of exploring for gold. Other topics include detection of concealed mineral and energy resources by vapor chemistry, future use of inductively-coupled plasma atomic emission spectrometry, exploration in the shallow marine environment, deep sea mineral deposits, and geochemistry in relation to animal as well as human health.

  18. Examining the role and relative timing of magma mixing and fractionation in the formation of the Kuna Crest lobe of the Tuolumne batholith, Sierra Nevada, USA

    NASA Astrophysics Data System (ADS)

    Krause, J.; Memeti, V.; Paterson, S. R.

    2010-12-01

    Recent field, U-Pb zircon geochronology and geochemistry data on the 95-85 Ma Tuolumne batholith (TB), Sierra Nevada, CA, have shown ample evidence for extensive mixing between different magmas and internal magma chamber recycling of older marginal units into younger central units within the main batholith. These data also have been examined in four magmatic lobes extending out from the main batholith. The lobes are interpreted to represent shorter lived, simpler magma bodies since their composition is attributed to fractionation and some remixing of magma derived from a single isotopically similar source. In order to test this hypothesis on the mineral scale, X-ray element distribution maps and quantitative analyses for minor and trace elements have been performed on samples from different structural positions in the southern Kuna Crest lobe of the TB. Ophitic, ≤ 5 mm large K-feldspars, of the Kuna Crest lobe show a single cycle of Ba zoning patterns with elevated contents in the center (Ba = 0.8-1.2 wt.%) decreasing towards the rim (Ba = 0.4-0.5 wt.%). Other hypidiomorphic to xenomorphic K-feldspars ≤ 1.5 mm within the same sample have reversed zoning with low Ba contents in the core (Ba = 0.1-0.2 wt.%) increasing towards the rim (Ba = 0.4-0.6 wt.%). The larger, ophitic K-feldspars show decreasing La/Y and Y concentrations from the core (La/Y = 5.0-8.5, Y = 0.15-0.27 ppm) towards the rim (La/Y = 2.8-4.7, Y = 0.09-0.15 ppm). In contrast the smaller K-feldspars within the same thin section have high La/Y at low Y in the core (La/Y = 8-14, Y = 0.04-0.07 ppm), which evolve towards low La/Y at higher Y at the rims (La/Y = 1.5-4.4, Y= 0.09-0.13 ppm) similar to the composition of the rims of the ophitic grains. The occurrence of texturally different K-feldspars with different minor and trace element zoning patterns in the core and similar compositions at the rims is best explained by mixing of different magmas. This contrasts with not only the concentric normal

  19. Geochemistry and age of metamorphosed felsic igneous rocks with A-type affinities in the Willyama Supergroup, Olary Block, South Australia, and implications for mineral exploration

    NASA Astrophysics Data System (ADS)

    Ashley, P. M.; Cook, N. D. J.; Fanning, C. M.

    1996-09-01

    Leucocratic quartzofeldspathic gneisses form a significant proportion of the lower part of the Palaeoproterozoic Willyama Supergroup sequence in the Olary Block, South Australia and have correlatives in the adjacent Broken Hill Block. Field and geochemical data demonstrate that these rocks were originally rhyolitic volcanics and granite, with A-type affinities consistent with magma production during intracratonic rifting, supporting tectonic models proposed for the Willyama Supergroup in the Broken Hill Block. Although the rocks have characteristic high-field-strength element enrichment, many have undergone extensive pervasive pre- or syn-metamorphic sodic alteration and are typically rich in albite. Sensitive high resolution ion microprobe (SHRIMP) U-Pb zircon data tightly constrain the depositional and early intrusive history. Zircons from an interpreted metavolcanic rock containing relict quartz phenocrysts yield an age of 1699 ± 10 Ma, whereas a metagranitoid sample has an age of 1703 ± 6 Ma. These results are compatible with recent geochronological data on felsic metavolcanic rocks from the Broken Hill Block (Page and Laing, 1992) and are indicative of widespread magmatism during deposition of the Willyama Supergroup. Nd signatures for the two Olary Block samples imply the presence of a significant component from a depleted mantle source. The A-type metavolcanic rocks are locally associated with small iron formations, some of which grade into stratiform barite-rich horizons. Although potentially favourable for sediment-hosted exhalative PbZn mineralisation, the Fe- and Ba-rich units, along with transgressive vein and breccia occurrences of Fe oxides ± quartz ± pyrite cutting both the metavolcanic and metagranitoid rocks, may be more prospective for epigenetic Cu-Au mineralisation related to later metamorphic and/or magmatic events. Partial melting of the A-type suite during high grade regional metamorphism at ~ 1600 ± 20 Ma led to the formation of local

  20. When Magma Might but Doesn't Erupt

    NASA Astrophysics Data System (ADS)

    Newhall, C.

    2008-12-01

    If we define failed eruptions as those in which magma seemingly comes close to erupting but doesn't, 3 main variants are seen: (1) where volcanoes exhibit only fumarolic changes (strong steaming, sometimes but not always with high SO2 emission or fumarole temperatures) without notable other unrest (e.g,, Baker 1975; Fourpeaked 2006; Kudriavy, Satsuma-Iwojima, and Momotombo); (2) where seismic swarms, inflation, and other evidence of stress buildup simply stop, abruptly or slowly (e.g., Akutan 1996, Iliamna 1996); and (3) where unrest culminates in phreatic explosions (e.g., Soufrière Guadeloupe 1976, Bulusan-1980'-2000's, Canlaon 1990's-2000's, Iwo-Jima 2001, Huila 2007) A special case of (2) and (3) is when swarms of high-frequency earthquakes under or just off volcano flanks (distal volcano-tectonic earthquakes or DVT's) dominate seismicity (e.g., Tacana 1986, Guagua Pichincha 1998-99 during its phreatic phase); Another category, where deep LP earthquakes and/or deep-focus inflation stop after little or no shallow unrest (e.g., Three Sisters, Fuji), should not be called "failed" because magma isn't (yet) close to erupting. Unrest with or without eruption is especially common at large magma-hydrothermal systems beneath calderas (e.g., Rabaul 1982-84; Campi Flegrei 1969-70, 1982-85, 2004-06; Long Valley 1979-present). These are large, metastable systems that can buffer small incoming intrusions. Unrest is often prolonged. At Rabaul unrest died back but then resurged and magma finally erupted in 1994. At Campi Flegrei and Long Valley, unrest still occurs intermittently as of 2008. Most failed eruptions involve magma intrusion and/or acceleration of magma convection in a conduit; a few may involve late-stage second boiling. The final step to magmatic eruption can be aborted by (a) loss of driving force (gas pressure, magma supply) or (b) a physical barrier (solid; viscous or low-density magma). Degassing diminishes driving force AND increases viscosity - a double

  1. The role of magma mixing in the formation of the Kuna Crest lobe of the Tuolumne batholith, Sierra Nevada, USA: Lessons from minor and trace element distributions in K-feldspar

    NASA Astrophysics Data System (ADS)

    Krause, Joachim; Memeti, Valbone; Paterson, Scott

    2010-05-01

    Geochemical and geochronologic studies emphasize the role of incremental growth of large magma chambers and associated complex magma processes. One of the major results of these studies is that volcanic and plutonic rocks tend to consist of different crystal populations recording complex individual histories. Detailed geochemical observations of individual minerals provide direct access to petrogenetic processes such as magma mixing, assimilation and fractionation and their role for the evolution of the magma chamber. Recent field, U/Pb zircon geochronology and geochemistry data on the 95-85 Ma Tuolumne batholith (TB), Sierra Nevada, CA, have shown ample evidence for extensive mixing between different magmas and internal magma chamber recycling of older marginal units into younger central units within the long lived, main batholith. Field, geochronologic, whole rock geochemical, and isotopic data have been examined in four magmatic lobes extending out from the main batholith. The lobes are interpreted to represent shorter lived and simpler magma bodies since their composition is attributed to fractionation and some remixing of magma derived from a single isotopically similar source. In order to test this hypothesis on the mineral scale, X-ray element distribution maps and quantitative analyses for minor and trace elements have been performed with the electron microprobe and LA-ICPMS on samples from different structural positions in the southern Kuna Crest lobe of the TB. Ophitic, ≤ 5 mm large K-feldspars, of the Kuna Crest lobe show simple Ba zoning patterns with elevated contents in the center (Ba = 0.8-1.2 wt.%) decreasing towards the rim (Ba = 0.4-0.5 wt.%). Other hypidiomorphic to xenomorphic K-feldspars ≤ 1.5 mm within the same thin section have reversed zoning with low Ba contents in the core (Ba = 0.1-0.2 wt.%) increasing towards the rim (Ba = 0.4-0.6 wt.%). The larger, ophitic K-feldspars show decreasing La/Y and Y concentrations from the core (La/Y = 5

  2. Oceanography, bathymetry and syndepositional tectonics of a Precambrian intracratonic basin: integrating sediments, storms, earthquakes and tsunamis in the Belt Supergroup (Helena Formation, ca. 1.45 Ga), western North America

    NASA Astrophysics Data System (ADS)

    Pratt, Brian R.

    2001-06-01

    The carbonate-dominated Helena Formation of the Mesoproterozoic Belt Supergroup of western North America provides an instructive example of how a range of regional depositional and environmental characteristics of an ancient sea can be deduced on the basis of micron- to metre-scale features. Particularly revealing is the window opened by the presence of abundant molar-tooth structure onto the paleoceanography, paleobathymetry, paleoclimate and tectonic regime of this intracratonic Precambrian basin. The facies hosting molar-tooth structure is composed dominantly of lime mud with substantial subangular quartz and feldspar silt and clay derived from the western and southwestern side of the basin. These are low-energy tempestites deposited on a remarkably flat sea bottom at the limit of storm-wave base, at about 50 m. Sporadic domical, stromatolite patch reefs confirm that the sea bottom was normally within the photic zone. The ubiquity of molar-tooth structure suggests frequent, near-field seismic activity during subsidence, which generated ground motion sufficient to liquefy granular lime mud and terrigenous silt. Sporadic tsunamis from major submarine faults far to the west pounded the shallow-water platform to the east. Tsunami off-surge swept ooids and rounded, coarse-grained, feldspathic quartz sand westward into deeper water, and created strongly erosive currents that left gutter casts composed of lags of preferentially cemented molar-tooth structure in otherwise relatively low-energy facies. Mineralogical and geochemical evidence, confirms that the Belt basin was marine. Organic matter was essentially fully oxidized in the water column. Original high-Mg composition and cementation of lime mud in molar-tooth structure indicate that calcite precipitated above the thermocline in supersaturated seawater under tropical conditions. Scattered bimineralic ooids in allochthonous grainstones indicate that shoals on the platform to the east were intermittently above a

  3. Crystallization and Cooling of a Deep Silicate Magma Ocean

    NASA Astrophysics Data System (ADS)

    Wolf, A. S.; Bower, D. J.

    2015-12-01

    Impact and accretion simulations of terrestrial planet formation suggest that giant impacts are both common and expected to produce extensive melting. The moon-forming impact, for example, likely melted the majority of Earth's mantle to produce a global magma ocean that subsequently cooled and crystallized (e.g. Nakajima and Stevenson, 2015). Understanding the cooling process is critical to determining magma ocean lifetimes and recognizing possible remnant signatures of the magma ocean in present-day mantle heterogeneities (i.e. Labrosse et al., 2007). Modeling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (magma ocean) and viscous creep (present-day mantle), in addition to uncertainties in material properties and chemical partitioning. We consider a simplified spherically-symmetric (1-D) magma ocean to investigate both its evolving structure and cooling timescale. Extending the work of Abe (1993), mixing-length theory is employed to determine convective heat transport, producing a high resolution model that captures the ultra-thin boundary layer (few cms) at the surface of the magma ocean. The thermodynamics of mantle melting are represented using a pseudo-one-component model, which retains the simplicity of a standard one-component model while introducing a finite temperature interval for melting (important for multi-component systems). We derive a new high P-T equation of state (EOS) formulation designed to capture the energetics and physical properties of the partially molten system using parameters that are readily interpreted in the context of magma ocean crystallization. This model is used to determine the cooling timescale for a variety of plausible thermodynamic models, with special emphasis on comparing the center-outwards vs bottom-up cooling scenarios that arise from the assumed EOS (e.g., Mosenfelder et al., 2009; Stixrude et al., 2009).

  4. Megacrystals track magma convection between reservoir and surface

    NASA Astrophysics Data System (ADS)

    Moussallam, Yves; Oppenheimer, Clive; Scaillet, Bruno; Buisman, Iris; Kimball, Christine; Dunbar, Nelia; Burgisser, Alain; Ian Schipper, C.; Andújar, Joan; Kyle, Philip

    2015-03-01

    Active volcanoes are typically fed by magmatic reservoirs situated within the upper crust. The development of thermal and/or compositional gradients in such magma chambers may lead to vigorous convection as inferred from theoretical models and evidence for magma mixing recorded in volcanic rocks. Bi-directional flow is also inferred to prevail in the conduits of numerous persistently-active volcanoes based on observed gas and thermal emissions at the surface, as well as experiments with analogue models. However, more direct evidence for such exchange flows has hitherto been lacking. Here, we analyse the remarkable oscillatory zoning of anorthoclase feldspar megacrystals erupted from the lava lake of Erebus volcano, Antarctica. A comprehensive approach, combining phase equilibria, solubility experiments and melt inclusion and textural analyses shows that the chemical profiles are best explained as a result of multiple episodes of magma transport between a deeper reservoir and the lava lake at the surface. Individual crystals have repeatedly travelled up-and-down the plumbing system, over distances of up to several kilometers, presumably as a consequence of entrainment in the bulk magma flow. Our findings thus corroborate the model of bi-directional flow in magmatic conduits. They also imply contrasting flow regimes in reservoir and conduit, with vigorous convection in the former (regular convective cycles of ∼150 days at a speed of ∼0.5 mm s-1) and more complex cycles of exchange flow and re-entrainment in the latter. We estimate that typical, 1-cm-wide crystals should be at least 14 years old, and can record several (from 1 to 3) complete cycles between the reservoir and the lava lake via the conduit. This persistent recycling of phonolitic magma is likely sustained by CO2 fluxing, suggesting that accumulation of mafic magma in the lower crust is volumetrically more significant than that of evolved magma within the edifice.

  5. Experimental constraints on the outgassing dynamics of basaltic magmas

    NASA Astrophysics Data System (ADS)

    Pioli, L.; Bonadonna, C.; Azzopardi, B. J.; Phillips, J. C.; Ripepe, M.

    2012-03-01

    The dynamics of separated two-phase flow of basaltic magmas in cylindrical conduits has been explored combining large-scale experiments and theoretical studies. Experiments consisted of the continuous injection of air into water or glucose syrup in a 0.24 m diameter, 6.5 m long bubble column. The model calculates vesicularity and pressure gradient for a range of gas superficial velocities (volume flow rates/pipe area, 10-2-102 m/s), conduit diameters (100-2 m), and magma viscosities (3-300 Pa s). The model is calibrated with the experimental results to extrapolate key flow parameters such as Co (distribution parameter) and Froude number, which control the maximum vesicularity of the magma in the column, and the gas rise speed of gas slugs. It predicts that magma vesicularity increases with increasing gas volume flow rate and decreases with increasing conduit diameter, until a threshold value (45 vol.%), which characterizes churn and annular flow regimes. Transition to annular flow regimes is expected to occur at minimum gas volume flow rates of 103-104 m3/s. The vertical pressure gradient decreases with increasing gas flow rates and is controlled by magma vesicularity (in bubbly flows) or the length and spacing of gas slugs. This study also shows that until conditions for separated flow are met, increases in magma viscosity favor stability of slug flow over bubbly flow but suggests coexistence between gas slugs and small bubbles, which contribute to a small fraction of the total gas outflux. Gas flow promotes effective convection of the liquid, favoring magma homogeneity and stable conditions.

  6. Modelling of a magma energy geothermal power plant

    SciTech Connect

    Boehm, R.F.; Berg, D.L.; Jr.; Ortega, A.

    1987-01-01

    We are currently investigating the engineering feasibility of drilling into an active magma body at a depth of roughly 5 km from the earth's surface, establishing a downhole heat exchange region, and extracting thermal energy from the magma body by circulating fluid through this heat exchange region. In the present paper, we evaluate the overall thermodynamic performance of various conceptual magma energy systems in which energy is added as heat to the fluid within the magma region and is converted to useful work in a power conversion cycle at the surface. Unusually high return temperatures and pressures may be available at the wellhead of such a circulating well. Cycles investigated here are an open Rankine power system in which steam from the magma well is circulated directly through a power conversion cycle and a closed Rankine cycle where the heated fluid from downhole is circulated through an aboveground heat exchanger to heat the cycle fluid. The downhole heat exchange region is established during the drilling process. As drilling proceeds into the magma, a solidified layer forms about the drilling tube due to heat exchange to the fluid. This solidified layer thermally fractures because of large temperature gradients between the cooled inner region and the heated outer region, thereby opening secondary flow paths. Two models of the downhole behavior have been used. In the simplest approach, denoted as the ''infinite area model,'' the water entering the pipe to return to the surface is assumed to be always at the temperature of the magma, independent of mass flow rate and other parameters. The other model is more detatiled and the fractured heat exchange region is modelled as a cylindrical porous layer through which fluid flows vertically. The net power and the performance aspects for the systems are investigated in terms of various parameters, including the characteristics of the downhole heat transfer.

  7. Linking Plagioclase Zoning Patterns to Active Magma Processes

    NASA Astrophysics Data System (ADS)

    Izbekov, P. E.; Nicolaysen, K. P.; Neill, O. K.; Shcherbakov, V.; Plechov, P.; Eichelberger, J. C.

    2015-12-01

    Plagioclase, one of the most common and abundant mineral phases in volcanic products, will vary in composition in response to changes in temperature, pressure, composition of the ambient silicate melt, and melt H2O concentration. Changes in these parameters may cause dissolution or growth of plagioclase crystals, forming characteristic textural and compositional variations (zoning patterns), the complete core-to-rim sequence of which describes events experienced by an individual crystal from its nucleation to the last moments of its growth. Plagioclase crystals in a typical volcanic rock may look drastically dissimilar despite their spatial proximity and the fact that they have erupted together. Although they shared last moments of their growth during magma ascent and eruption, their prior experiences could be very different, as plagioclase crystals often come from different domains of the same magma system. Distinguishing similar zoning patterns, correlating them across the entire population of plagioclase crystals, and linking these patterns to specific perturbations in the magmatic system may provide additional perspective on the variety, extent, and timing of magma processes at active volcanic systems. Examples of magma processes, which may be distinguished based on plagioclase zoning patterns, include (1) cooling due to heat loss, (2) heating and/or pressure build up due to an input of new magmatic material, (3) pressure drop in response to magma system depressurization, and (4) crystal transfer between different magma domains/bodies. This review will include contrasting examples of zoning patters from recent eruptions of Karymsky, Bezymianny, and Tolbachik Volcanoes in Kamchatka, Augustine and Cleveland Volcanoes in Alaska, as well as from the drilling into an active magma body at Krafla, Iceland.

  8. Magma storage prior to the 1912 eruption at Novarupta, Alaska

    USGS Publications Warehouse

    Hammer, J.E.; Rutherford, M.J.; Hildreth, W.

    2002-01-01

    New analytical and experimental data constrain the storage and equilibration conditions of the magmas erupted in 1912 from Novarupta in the 20th century's largest volcanic event. Phase relations at H2O+CO2 fluid saturation were determined for an andesite (58.7 wt% SiO2) and a dacite (67.7 wt%) from the compositional extremes of intermediate magmas erupted. The phase assemblages, matrix melt composition and modes of natural andesite were reproduced experimentally under H2O-saturated conditions (i.e., PH2O=PTOT) in a negatively sloping region in T-P space from 930 ??C/100 MPa to 960 ??C/75 MPa with fO2???N NO + 1. The H2O-saturated equilibration conditions of the dacite are constrained to a T-P region from 850 ??C/ 50 MPa to 880 ??C/25 MPa. If H2O-saturated, these magmas equilibrated at (and above) the level where coerupted rhyolite equilibrated (???100 MPa), suggesting that the andesite-dacite magma reservoir was displaced laterally rather than vertically from the rhyolite magma body. Natural mineral and melt compositions of intermediate magmas were also reproduced experimentally under saturation conditions with a mixed (H2O + CO2) fluid for the same range in PH2O. Thus, a storage model in which vertically stratified mafic to silicic intermediate magmas underlay H2O-saturated rhyolite is consistent with experimental findings only if the intermediates have XH2Ofl=0.7 and 0.9 for the extreme compositions, respectively. Disequilibrium features in natural pumice and scoria include pristine minerals existing outside their stability fields, and compositional zoning of titanomagnetite in contact with ilmenite. Variable rates of chemical equilibration which would eliminate these features constrain the apparent thermal excursion and re-distribution of minerals to the time scale of days.

  9. Redox systematics of a magma ocean with variable pressure-temperature gradients and composition

    PubMed Central

    Righter, K.; Ghiorso, M. S.

    2012-01-01

    Oxygen fugacity in metal-bearing systems controls some fundamental aspects of the geochemistry of the early Earth, such as the FeO and siderophile trace element content of the mantle, volatile species that influence atmospheric composition, and conditions for organic compounds synthesis. Redox and metal-silicate equilibria in the early Earth are sensitive to oxygen fugacity (fO2), yet are poorly constrained in modeling and experimentation. High pressure and temperature experimentation and modeling in metal-silicate systems usually employs an approximation approach for estimating fO2 that is based on the ratio of Fe and FeO [called “ΔIW (ratio)” hereafter]. We present a new approach that utilizes free energy and activity modeling of the equilibrium: Fe + SiO2 + O2 = Fe2SiO4 to calculate absolute fO2 and relative to the iron-wüstite (IW) buffer at pressure and temperature [ΔIW (P,T)]. This equilibrium is considered across a wide range of pressures and temperatures, including up to the liquidus temperature of peridotite (4,000 K at 50 GPa). Application of ΔIW (ratio) to metal-silicate experiments can be three or four orders of magnitude different from ΔIW (P,T) values calculated using free energy and activity modeling. We will also use this approach to consider the variation in oxygen fugacity in a magma ocean scenario for various thermal structures for the early Earth: hot liquidus gradient, 100 °C below the liquidus, hot and cool adiabatic gradients, and a cool subsolidus adiabat. The results are used to assess the effect of increasing P and T, changing silicate composition during accretion, and related to current models for accretion and core formation in the Earth. The fO2 in a deep magma ocean scenario may become lower relative to the IW buffer at hotter and deeper conditions, which could include metal entrainment scenarios. Therefore, fO2 may evolve from high to low fO2 during Earth (and other differentiated bodies) accretion. Any modeling of

  10. 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

  11. Magma-hydrothermal contact zone of the Stromboli volcano (Italy): evidence from buchite xenoliths

    NASA Astrophysics Data System (ADS)

    Renzulli, A.; Serri, G.; Tribaudino, M.; Santi, P.; Salvioli-Mariani, E.

    2003-04-01

    Large-sized xenoliths (up to 1.5 m) were sampled nearby the summit active craters of Stromboli (Aeolian Islands). The ejecta, erupted during recent eruptions, are spread within an area of ca. 50m2 and consist of fine-grained whitish to light-grey mottled rocks with heterogeneous vesicularity (3--50 vol.%). SEM-EDS and EMP analyses, XRD, TEM investigations and ICP-OES-MS bulk-rock geochemistry were carried out on representative samples. According to petrological and textural data the xenoliths are buchites, i.e. glassy hornfelses produced by high-grade contact metamorphism, up to partial melting. A highly porphyritic shoshonitic basalt generally covers the buchites, both as cm-sized coatings or as thicker spatters. The xenoliths are peraluminous (Al_2O_3 21.4--24.3 wt.%), with SiO_2 62.1--63.6 wt.% and are characterised by fine-grained cordierite (± indialite), plagioclase (An80-95), mullite, orthopyroxene (En74-83), pseudobrookite and rutile. These minerals locally replace, pseudomorphically, mm-sized crystals whose habitus is reminiscent of feldspar and pyroxene phenocrysts. In the xenoliths the glass has a wide range of silica compositions, from 61--66 wt.% (metaluminous) to 69--76 wt.% (peraluminous), going inward from the contact with the basalt coatings. At the xenolith-basalt contact a two mineral xenolith facies often occurs, consisting of a tridymite+clinopyroxene fine-grained glassy hornfels zone up to 5 cm. Cordierites have Mg values 82--91 and contain K_2O up to 1%. TEM and synchrotron powder diffraction examination on cordierites showed the presence of both crystals with fully achieved transformation to the orthorhombic state and euhedra having an hexagonal symmetry (indialites). The presence of different Al-Si ordering state in cordierite, from fully disordered indialite to partially ordered orthorhombic cordierite was observed. This may be due to high K_2O and/or fast cooling of the crystals that inhibited the transformation from hexagonal to

  12. Redox systematics of a magma ocean with variable pressure-temperature gradients and composition.

    PubMed

    Righter, K; Ghiorso, M S

    2012-07-24

    Oxygen fugacity in metal-bearing systems controls some fundamental aspects of the geochemistry of the early Earth, such as the FeO and siderophile trace element content of the mantle, volatile species that influence atmospheric composition, and conditions for organic compounds synthesis. Redox and metal-silicate equilibria in the early Earth are sensitive to oxygen fugacity (fO(2)), yet are poorly constrained in modeling and experimentation. High pressure and temperature experimentation and modeling in metal-silicate systems usually employs an approximation approach for estimating fO(2) that is based on the ratio of Fe and FeO [called "ΔIW (ratio)" hereafter]. We present a new approach that utilizes free energy and activity modeling of the equilibrium: Fe + SiO(2) + O(2) = Fe(2)SiO(4) to calculate absolute fO(2) and relative to the iron-wüstite (IW) buffer at pressure and temperature [ΔIW (P,T)]. This equilibrium is considered across a wide range of pressures and temperatures, including up to the liquidus temperature of peridotite (4,000 K at 50 GPa). Application of ΔIW (ratio) to metal-silicate experiments can be three or four orders of magnitude different from ΔIW (P,T) values calculated using free energy and activity modeling. We will also use this approach to consider the variation in oxygen fugacity in a magma ocean scenario for various thermal structures for the early Earth: hot liquidus gradient, 100 °C below the liquidus, hot and cool adiabatic gradients, and a cool subsolidus adiabat. The results are used to assess the effect of increasing P and T, changing silicate composition during accretion, and related to current models for accretion and core formation in the Earth. The fO(2) in a deep magma ocean scenario may become lower relative to the IW buffer at hotter and deeper conditions, which could include metal entrainment scenarios. Therefore, fO(2) may evolve from high to low fO(2) during Earth (and other differentiated bodies) accretion. Any

  13. Magma Storage Conditions, Eruption Initiation and Magma Evolution Over Time: Investigating the Eruptions of Organ Caldera, Southern NM

    NASA Astrophysics Data System (ADS)

    Lente, J. L.; Johnson, E. R.

    2015-12-01

    The Organ caldera in southern New Mexico formed ~36 Ma from a series of three explosive, voluminous eruptions. The volcanic deposits are now exposed in the Organ Mountains and have a combined thickness of nearly 3 km and an estimated volume between 500 and1000 km3 (Seager & McCurry, 1988). This research uses analyses of quartz-hosted melt inclusions from the first- and last-erupted units to study the storage and differentiation of the magma body prior-to and during the initial eruption, as well as changes in the magma chamber over time as the eruptions progressed and ultimately ceased. Previous work suggests the Organ magma chamber was compositionally stratified (Seager, 1981) erupting top-down and tapping less-evolved magmas over time. However, preliminary results suggest a more complex system; possibly a convecting, homogenized magma chamber or a series of dykes and sills. Results obtained using FTIR analyses of H2O and CO2 in melt inclusions have shown variable volatile contents from the first erupted unit (~2.3 to 6.8 weight percent H2O, 0-118 ppm CO2). Using these values, saturation pressures of 45 to 266 MPa were calculated, indicating a minimum pressure at which the melt inclusion was trapped. These pressures suggest magma storage depths for the first erupted magmas of ~2 to 9 km (with most inclusions trapped between 4 and 8 km) which is inconsistent with the initial eruption coming from the top of a normally stratified chamber. The large variation in volatile contents and storage depths can have many explanations, such as degassing and shallow crystallization during ascent, or perhaps a more complex, elongate magma storage system. These possibilities, and whether or not magma mixing/rejuvenation triggered the initial eruption, will be explored with the acquisition of major and trace element compositions of melt inclusions. Additionally, analyses of melt inclusions from the last erupted ignimbrite, which erupted ~0.5 Ma after the first eruption, will enable

  14. A new method fingerprinting magmatic processes using combined U/Pb ID-TIMS geochronology and accessory mineral geochemistry

    NASA Astrophysics Data System (ADS)

    Schoene, B.; Schaltegger, U.; Latkoczy, C.; Günther, D.

    2009-12-01

    Zircon is commonly used as a recorder of magmatic processes because of its utility in geochronology and ability to retain primary growth information at prolonged magmatic conditions. Recent applications of U-Pb ID-TIMS geochronology have shown that precision on dates of single zircons are often far smaller than the time-scales of magmatic systems. The result is that dates on such grains record various processes occurring over an interval of time during the production, mobilisation, and emplacement of magmas. Combining age information with geochemical data from the same zircons has proved a useful tool, but thus far has been restricted to low-precision in situ dating techniques. Furthermore, these techniques have been unable to combine age data with trace element geochemistry on the same volume of zircon. We have developed a new technique that combines high-precision ID-TIMS dating with geochemical characterization on the exact same material. U and Pb are commonly separated from the other chemical constituents by ion exchange chemistry during sample preparation. We retain this fraction and analyse it using solution nebulization ICP-SFMS with matrix-matched external liquid calibration. We measured elements such as Zr, Hf, Y, Sc, and the REE, which are present in solution at between 10 and >105 ppt; Hf isotopes are subsequently measured on the same solution. Data obtained using this approach allow us to distinguish between models for melt generation, transport, and assembly of the ca. 40 Ma composite mafic to felsic Re di Castello pluton, Adamello batholith, northern Italy. Coupled with age uncertainties on single zircons as low as 10,000 years, zircon geochemistry preserves a rich record of fractional crystallization, crustal assimilation and magma mixing over timescales of <20,000 to >400,000 years. These data can also be used to distinguish between auto-, xeno-, and antecrystic zircon. Combined with field observation and U-Pb sphene thermochronology, we show that

  15. Insights Into Earthquake Nucleation and Fault Evolution Within Magma

    NASA Astrophysics Data System (ADS)

    Tuffen, H.; Sturton, S.; Dingwell, D. B.

    2004-05-01

    Volcanoes erupting highly viscous magma generate an exceptionally large amount of seismic energy per unit volume. Seismicity is unlike that generated on most tectonic faults, being characterised by repeated small events (Mw < 3) with identical waveforms and short inter-event times (from days to less than a second). Events occur in swarms with typical durations of hours to weeks and have anomalously low frequency content (dominant energy in the 1-3 Hz range). They also show no S-wave arrivals and occur within a small volume typically < 2 km from the surface. New field evidence suggests that these earthquakes may occur on small faults that nucleate by shear fracture of magma during conduit flow (Tuffen et al. Geology 31:1089-1092, 2003). Shear fracture occurs due to stress accumulation when strain rates are too high for purely viscous flow. The anastomosing fracture networks generated share many characteristics with "tectonic" pseudotachylites, including injection veins and evidence for fluidisation. Fracture networks evolve with continued slip into near-planar faults up to five metres in length that are rotated parallel to the magma flow direction. Cataclasite on fault planes bears the textural hallmarks of frictional stick-slip behaviour, with localised grain size reduction, slip localisation, and Riedel shear zones. Eventually, cohesive viscous deformation occurs due to frictional heating and strain rate decrease and completely heals the faults. This forms flow banding in obsidian, which is a kind of high-temperature pseudotachylite. This new evidence may help to explain some properties of the low-frequency earthquakes that occur during eruptions of high-viscosity magma: a) The short inter-event time may be due to high strain rates (10-6 to 10-2 s-1 are typical of eruptions of silicic magma). b) Similar events may be generated by multiple slip pulses on fault planes. c) The seismogenic lifetime of faults may be limited by the high temperature of the faulting

  16. Carbon dioxide in magmas and implications for hydrothermal systems

    USGS Publications Warehouse

    Lowenstern, J. B.

    2001-01-01

    This review focuses on the solubility, origin, abundance, and degassing of carbon dioxide (CO2) in magma-hydrothermal systems, with applications for those workers interested in intrusion-related deposits of gold and other metals. The solubility of CO2 increases with pressure and magma alkalinity. Its solubility is low relative to that of H2O, so that fluids exsolved deep in the crust tend to have high CO2/H2O compared with fluids evolved closer to the surface. Similarly, CO2/H2O will typically decrease during progressive decompression- or crystallization-induced degassing. The temperature dependence of solubility is a function of the speciation of CO2, which dissolves in molecular form in rhyolites (retrograde temperature solubility), but exists as dissolved carbonate groups in basalts (prograde). Magnesite and dolomite are stable under a relatively wide range of mantle conditions, but melt just above the solidus, thereby contributing CO2 to mantle magmas. Graphite, diamond, and a free CO2-bearing fluid may be the primary carbon-bearing phases in other mantle source regions. Growing evidence suggests that most CO2 is contributed to arc magmas via recycling of subducted oceanic crust and its overlying sediment blanket. Additional carbon can be added to magmas during magma-wallrock interactions in the crust. Studies of fluid and melt inclusions from intrusive and extrusive igneous rocks yield ample evidence that many magmas are vapor saturated as deep as the mid crust (10-15 km) and that CO2 is an appreciable part of the exsolved vapor. Such is the case in both basaltic and some silicic magmas. Under most conditions, the presence of a CO2-bearing vapor does not hinder, and in fact may promote, the ascent and eruption of the host magma. Carbonic fluids are poorly miscible with aqueous fluids, particularly at high temperature and low pressure, so that the presence of CO2 can induce immiscibility both within the magmatic volatile phase and in hydrothermal systems

  17. Eddy Flow during Magma Emplacement: The Basemelt Sill, Antarctica

    NASA Astrophysics Data System (ADS)

    Petford, N.; Mirhadizadeh, S.

    2014-12-01

    The McMurdo Dry Valleys magmatic system, Antarctica, forms part of the Ferrar dolerite Large Igneous Province. Comprising a vertical stack of interconnected sills, the complex provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle macrostructure of a congested magma slurry1. Image-based numerical modelling where the intrusion geometry defines its own unique finite element mesh allows simulations of the flow regime to be made that incorporate realistic magma particle size and flow geometries obtained directly from field measurements. One testable outcome relates to the origin of rhythmic layering where analytical results imply the sheared suspension intersects the phase space for particle Reynolds and Peclet number flow characteristic of macroscopic structures formation2. Another relates to potentially novel crystal-liquid segregation due to the formation of eddies locally at undulating contacts at the floor and roof of the intrusion. The eddies are transient and mechanical in origin, unrelated to well-known fluid dynamical effects around obstacles where flow is turbulent. Numerical particle tracing reveals that these low Re number eddies can both trap (remove) and eject particles back into the magma at a later time according to their mass density. This trapping mechanism has potential to develop local variations in structure (layering) and magma chemistry that may otherwise not occur where the contact between magma and country rock is linear. Simulations indicate that eddy formation is best developed where magma viscosity is in the range 1-102 Pa s. Higher viscosities (> 103 Pa s) tend to dampen the effect implying eddy development is most likely a transient feature. However, it is nice to think that something as simple as a bumpy contact could impart physical and by implication chemical diversity in igneous rocks. 1Marsh, D.B. (2004), A

  18. Magma Plumbing beneath Askja Volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Greenfield, T. S.; White, R. S.

    2013-12-01

    Through a combination of accurate earthquake locations and tomography we have imaged the melt feeding network beneath Askja, a large central volcano, in the Northern Volcanic Zone, Iceland. We have deployed and operated a dense network of 3-component, broadband seismometers around the volcano since 2006 and have recorded a large number of events (on the order of 150 a day). The majority of these are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes situated in three distinct areas within the volcanic system. These have a lower frequency content to the shallower events which may be the result of highly attenuating lower crust. The deep earthquakes extend from 12-25 km depth, significantly below a well defined brittle-ductile boundary at 8-9 km. These earthquakes indicate the presence of melt moving or degassing at depth as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. To image the structure beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations and velocity structure. Results showed a pronounced low-velocity anomaly beneath the caldera at a depth of ~5 km. The anomaly is ~10% slower than the initial best fitting 1D model and has a Vp/Vs ratio higher than the surrounding crust, suggesting the presence of increased temperature or partial melt. The body is unlikely to be entirely melt as S-waves are still detected at stations directly above the anomaly. This low-velocity body is slightly deeper than the depth range suggested by InSAR and GPS studies of a deflating source beneath

  19. Oxygen Isotope Trajectories of Crystallizing Arc Magmas

    NASA Astrophysics Data System (ADS)

    Bucholz, C. E.; Jagoutz, O. E.; VanTongeren, J. A.; Wang, Z.

    2014-12-01

    Oxygen isotopes are essential to quantify mantle-derived versus 'recycled' crustal contributions to arc magmas. High δ18O values in igneous rocks (i.e., δ18OSMOW > ~5.7) are generally used to identify supra-crustal inputs, but a melt can also become enriched in 18O due to magmatic differentiation [1,2]. To assess magmatic δ18O values of plutonic rocks, δ18Ozircon values, which are resilient to secondary alteration, are often used. Thus, to disentangle the effects of assimilation versus fractionation, both the absolute increase in melt δ18O due to differentiation and ∆18O(WR-zircon) must be determined. However, existing constraints on the effect of magmatic fractionation on melt δ18O are model-based [2] and calculated relationships between WR SiO2, δ18Ozircon, and δ18Omelt do not incorporate complex melt SiO2, H2O, and temperature (T) relationships [3]. To build upon these initial constraints, we combine the first high-precision δ18O data set on natural samples documenting changes in δ18O melt values with increasing extent of differentiation and modeling which incorporates experimentally constrained melt SiO2, H2O, and T relationships. We analyzed 55 mineral separates with infrared laser-fluorination [4] across large fractionation intervals of two well-studied cumulate sequences: (I) a relatively dry (~1 wt.% H2O initial) tholeiitic sequence (analyzed minerals include plag, opx, cpx, & Fe-rich ol) from the Bushveld Complex and (II) a hydrous high-K sequence (analyzed minerals include ol, cpx, bt, fsp, & qtz) from the Dariv paleoarc in Mongolia. Our results indicate that multiple per mil increases in melt δ18O can occur during magmatic fractionation that in detail depend strongly on melt composition and T. Calculated relationships between WR SiO2 and δ18Ozircon for experimental melt compositions show that wet, 'cool' and dry, 'hot' melts are characterized by larger and smaller ∆18O (melt-zircon) fractionations, respectively. Applying our results to

  20. Mineral and whole-rock geochemistry of the Topuk Granitoid (Bursa, Western Anatolia, Turkey)

    NASA Astrophysics Data System (ADS)

    Orhan, Ayşe; Demirbilek, Mehmet; Mutlu, Halim

    2014-05-01

    by the interaction of post-collisional, calc-alkaline, metaluminous and I-type coeval felsic and mafic magmas at shallow depths under similar physicochemical conditions. Keywords: Turkey, Western Anatolia, Topuk Granitoid, geochemistry. Acknowledgement: This study is supported by the Scientific and Technical Research Council of Turkey (TÜBİTAK; YDABAG-111Y289).

  1. Mineralogy and geochemistry of the older (> 40 ka) ignimbrites on the Campanian Plain, southern Italy

    NASA Astrophysics Data System (ADS)

    Belkin, H. E.; Rolandi, G.; Jackson, J. C.; Cannatelli, C.; Doherty, A. L.; Petrosino, P.; De Vivo, B.

    2016-09-01

    The Campanian Plain in southern Italy has been volcanically active for at least the last 300 ka. The Campanian Ignimbrite (CI) erupted at 39.3 ka, has a volume of ≥ 310 km3 and a great areal extent. However, significant, but scattered deposits of older ignimbrites underlie the CI and document a long history of volcanism. We examined the mineralogy and geochemistry of 11 older ignimbrite strata by optical petrography, electron microprobe, scanning electron microscope, X-ray diffraction, and various whole-rock geochemical techniques. We have analyzed strata at Durazzano (116.1 ka), Moschiano (184.7 ka), Seiano Valley (245.9 and 289.6 ka), and Taurano - Acqua Feconia (157.4, 183.8, 205.6, and 210.4 ka) that have been previously dated on unaltered sanidine. The older ignimbrites are highly altered with loss on ignition (LOI) that ranges from 17 to 8 wt%. Whole-rock compositions reflect variable element mobility during weathering; e.g., CaO is enriched and Na2O depleted relative to hydration. X-ray diffraction identified major chabazite, kaolinite, and illite alteration products in some samples. Rhabdophane-(Nd), usually intergrown with chabazite and Mn-carbonate, indicates that some LREE were also mobilized during weathering. The phenocryst mineralogy is typical for Campanian Plain (CP) magmas and consists of plagioclase (An88 Ab11 Or1 to An32 Ab63 Or5), potassium feldspar (Or40 Ab57 An3 to Or79 Ab18 An3), biotite (TiO2 = ~ 4-7 wt%, BaO = up to 2 wt%, F = up to 2 wt%), diopside (Ca47Mg47Fe6 to Ca48Mg29Fe23), and titaniferous magnetite. Relatively immobile trace elements Zr, Hf, Th, Ta, V, and Nb were used to investigate element abundance and ratio compared to the Campanian Ignimbrite and other CP magmas. Zr/Hf of the older ignimbrites is similar to that of the CI, but Ta is depleted relative to Th and V is enriched compared to CI. Th/Ta and Nb/V distributions for most of the older ignimbrites are similar to those in the Neapolitan Yellow Tuff with the exception of

  2. Magmas, Mushes and Mobility: Thermal Histories of Magma Reservoirs from Combined U-Series and Diffusion Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.; Rubin, A. E.; Schrecengost, K.; Kent, A. J.; Huber, C.

    2014-12-01

    The thermal conditions of magma storage control many aspects of the dynamics of a magma reservoir system. For example, the temperature of magma storage directly relates to the crystallinity, and magmas stored at relatively low temperatures in a crystal mush (more than 40-50% crystalline) must be remobilized (e.g., by heating) before they can be erupted. A better understanding of the duration of magma storage at largely-liquid vs. largely-solid conditions is thus critical to understanding crustal magmatic processes such as magma mixing and for quantifying the hazard potential of a given volcano. Although mineral thermometry reflects the conditions of crystal growth or equilibration, these may not correspond to the thermal conditions of crystal storage. The duration of crystal storage at high temperatures can be quantified by comparing U-series crystal ages with the time scales over which disequilibrium trace-element profiles in the same crystals would be erased by diffusion. In the case of Mount Hood, OR, such a comparison for the two most recent eruptions shows that <12% of the total lifetime of plagioclase crystals (minimum 21 kyr) was spent at temperatures high enough that the magma would be easily mobilized. Partial data sets for other systems suggest such behavior is common, although the diffusion and U-series ages in these cases are from different samples and may not be directly comparable. We will present preliminary data combining U-series dating and diffusion timescales on the same samples for other volcanic systems (e.g., Lassen Volcanic Center, Mount St. Helens, Okataina Volcanic Center, New Zealand). Combining these data with numerical models offers additional insights into the controls on the conditions of storage. In addition, extension of this approach to combining U-Th ages with time scales of Li diffusion in zircon offers a promising new method to quantify thermal histories of silicic reservoir systems.

  3. Understanding which parameters control shallow ascent of silicic effusive magma

    NASA Astrophysics Data System (ADS)

    Thomas, Mark E.; Neuberg, Jurgen W.

    2014-11-01

    estimation of the magma ascent rate is key to predicting volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. Linking potential changes of such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models Soufrière that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. We show that variability in the rate of low frequency seismicity, assumed to correlate directly with the rate of magma movement, can be used as an indicator for changes in ascent rate and, therefore, eruptive activity. The results indicate that conduit diameter and excess pressure in the magma chamber are amongst the dominant controlling variables, but the single most important parameter is the volatile content (assumed as only water). Modeling this parameter in the range of reported values causes changes in the calculated ascent velocities of up to 800%.

  4. Implications of magma chamber dynamics for Soret-related fractionation

    NASA Astrophysics Data System (ADS)

    Carrigan, Charles R.; Cygan, Randall T.

    1986-10-01

    Convection of silicate melts in magma chambers is considered as a possible mechanism for producing significant or, at least, detectable chemical fractionation by the Soret effect. Thermal boundary layer analyses show that Soret fractionation would be, at best, an extremely weak process in evolving magmatic systems. For very large amplitude thermally driven convection at horizontal chamber margins, both the magnitude of the temperature gradient and the time scale for residence of magma in the unstable thermal boundary layer are entirely inappropriate for chemical fractionation of the magma at levels comparable to those obtained in laboratory experiments (5-60%). For a typical convecting body a relative concentration enhancement of 0.04% is obtained as an estimate of the upper limit of Soret fractionation. Even if exceedingly large temperature gradients (of the order of 104 °C/m) in a transient thermal regime are attained by compositionally driven convection, the magma residence time in the thermal boundary layer is so brief (100 s) that much less chemical fractionation results (0.002%). For convection near vertical margins a kinematic model of a countercurrent flow regime provides estimates of chemical separation produced by the thermogravitational fractionation mechanism. Incorporating a range of physical and chemical parameters that characterize magma chamber convection, steady state values of concentration enhancement are even smaller than for fractionation near horizontal boundaries.

  5. Petrology, geochemistry, and fluid regime of tectonites

    NASA Astrophysics Data System (ADS)

    Letnikov, Feliks Artem'evich; Savel'Eva, Valentina Borisovna; Balyshev, Sergei Olegovich

    The book discusses the petrology, geochemisry, and fluid regime of the tectonite formation in rocks that differ with respect to the composition of their granulitic, amphylitic, and green-shale metamorphic facies. Tectonites in magma and metamorphic rocks of different composition are described in terms of their petrological, geochemical, and fluid-regime characteristics, and the pressure/temperature conditions of their formation. Using chemical and physical parameters, tectonites are classified according to their type models. The ore-generating capacity of tectonites in various rocks is estimated using a large geochemical database.

  6. Phenomena associated with magma expansion into a drift

    SciTech Connect

    Gaffney, E. S.

    2002-01-01

    One of the significant threats to the proposed Yucca Mountain nuclear waste repository has been identified as the possibility of intersection of the underground structure by a basaltic intrusion. Based on the geology of the region, it is assumed that such an intrusion would consist of an alkali basalt similar to the nearby Lathrop Wells cone, which has been dated at about 78 ka. The threat of radioactive release may be either from eruption through the surface above the repository of basalt that had been contaminated or from migration through ground water of radionucleides released as a result of damage to waste packages that interact with the magma. As part of our study of these threats, we are analyzing the phenomena associated with magma expansion into drifts in tuff. The early phenomena of the encounter of volatile-rich basaltic magma with a drift are discussed here.

  7. Flow patterns of magma in dikes, Makhtesh Ramon, Israel

    SciTech Connect

    Baer, G.; Reches, Z.

    1987-06-01

    Directions of magma flow were measured in a system of radial dikes in Makhtesh Ramon, Israel. The flow directions were determined from field observations of segments, fingers, grooves, and groove molds of the dikes. The study indicates that the mean axis of magma flow is subhorizontal toward the north, in agreement with the direction of divergence of the radial dike system. Two modes of flow were observed: (1) regular, bedding-parallel flow in the well-stratified rock units and (2) irregular, meandering flow in the massive rock units. It is suggested that corrugated dike walls in well-stratified host rocks cause magma channelization, and random or self-generated restrictions in massive host rocks cause the apparent meanders. Furthermore, the major lithologic boundaries in the host units strongly affect segmentation of the dikes.

  8. Origin of silicic magma in Iceland revealed by Th isotopes

    SciTech Connect

    Sigmarsson, O.; Condomines, M. ); Hemond, C. ); Fourcade, S. ); Oskarsson, N. )

    1991-06-01

    Th, Sr, Nd, and O isotopes have been determined in a suite of volcanic rocks from Hekla and in a few samples from Askja and Krafla volcanic centers in Iceland. Although {sup 87}Sr/{sup 86}Sr and {sup 143}Nd/{sup 144}Nd ratios are nearly the same for all compositions at Hekla, the ({sup 230}Th/{sup 232}Th) ratios differ and thus clearly show that the silicic rocks cannot be derived from fractional crystallization of a more primitive magma. Similar results are obtained for the Krafla and Askja volcanic centers, where the {delta}{sup 18}O values are much lower in the silicic magma than in the mafic magma. These data suggest that large volumes of silicic rocks in central volcanoes of the neovolcanic zones in Iceland are produced by partial melting of the underlying crust.

  9. Magma storage in a strike-slip caldera

    PubMed Central

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  10. The magma ocean as an impediment to lunar plate tectonics

    NASA Technical Reports Server (NTRS)

    Warren, Paul H.

    1993-01-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  11. Complexities in Shallow Magma Transport at Kilauea (Invited)

    NASA Astrophysics Data System (ADS)

    Swanson, D. A.

    2013-12-01

    The standard model of Kilauea's shallow plumbing system includes magma storage under the caldera and conduits in the southwest rift zone (SWRZ) and the east rift zone (ERZ). As a field geologist, I find that seemingly aberrant locations and trends of some eruptive vents indicate complexities in shallow magma transport not addressed by the standard model. This model is not wrong but instead incomplete, because it does not account for the development of offshoots from the main plumbing. These offshoots supply magma to the surface at places that tell us much about the complicated stress system within the volcano. Perhaps most readily grasped are fissures peripheral to the north and south sides of the caldera. Somehow magma can apparently be injected into caldera-bounding faults from the summit reservoir complex, but the process and pathways are unclear. Of more importance is the presence of fissures with ENE trends on the east side of the caldera, including Kilauea Iki. Is this a rift zone that forms an acute angle with the ERZ? I think there is another explanation: the main part of the ERZ has migrated ~5 km SSE during the past few tens of thousands of years owing to seaward movement of the south flank, but older parts of the rift zone can be reactivated. The fissures east of the caldera have the ERZ trend and may record such reactivation; this interpretation includes the location of the largest eruption (15th century) known from Kilauea. Whether or not this interpretation has validity, the question remains: what changes in the plumbing system allow magma to erupt east of the caldera? The SWRZ can be divided into two sections, the SWRZ proper and the seismically active part (SASWRZ) southeast of the SWRZ. The total width of both sections is ~4 km. The SWRZ might be migrating SSE, as is the ERZ. Fissures in the SWRZ proper trend SW. Fissures in the SASWRZ, however, have ENE trends like that of the ERZ, although, because of en echelon offsets, the fissure zone itself

  12. The magma ocean as an impediment to lunar plate tectonics

    NASA Astrophysics Data System (ADS)

    Warren, P. H.

    1993-03-01

    The primary impediment to plate tectonics on the moon was probably the great thickness of its crust and particularly its high crust/lithosphere thickness ratio. This in turn can be attributed to the preponderance of low-density feldspar over all other Al-compatible phases in the lunar interior. During the magma ocean epoch, the moon's crust/lithosphere thickness ratio was at the maximum theoretical value, approximately 1, and it remained high for a long time afterwards. A few large regions of thin crust were produced by basin-scale cratering approximately contemporaneous with the demise of the magma ocean. However, these regions probably also tend to have uncommonly thin lithosphere, since they were directly heated and indirectly enriched in K, Th, and U by the same cratering process. Thus, plate tectonics on the moon in the form of systematic lithosphere subduction was impeded by the magma ocean.

  13. Deep-level magma ascent rates at Mt. Etna (Italy)

    NASA Astrophysics Data System (ADS)

    Armienti, P.; Perinelli, C.; Putirka, K. D.

    2012-12-01

    Deep-level ascent rates are related to the triggering mechanisms of volcanic eruptions. Recent models and experimental studies have focused on the very shallow parts of magma plumbing systems, mostly the upper few km, and have thus far emphasized that volatile contents and volatile exsolution, are key to understanding eruption dynamics and its fingerprint in the rock texture. Massive volatile loss induces a dramatic change in the liquidus temperature, thus producing observable effects on the rates of nucleation and growth of minerals . Volatile saturation, however, may well occur at greater depths, which means that initial stages of magma ascent may be triggered by events taking place at much greater depths than those recorded by melt inclusions, likely captured at shallow levels. We present a method to evaluate ascent rates deep in a volcano plumbing system, discussing the implications for magma dehydration and using Mt. Etna as case a study. We investigate the deeper levels of magma transport by presenting detailed P-T paths for Etnean magmas, and combining these with Crystal Size Distribution (CSD)-derived cooling rates. The key to this analysis is the recognition that the slope of a P-T path, as determined from mineral-melt thermobarometry, is a result of magma cooling rate, which is in turn a function of magma ascent via the effect of pressure on volatile solubility. We also rely on a thermodynamic treatment of exsolution of non-ideal H2O-CO2 mixtures, based on the Kerric & Jacobs (1981) model, and the simplified solubility model of CO2 (Spera & Bergman, 1980) and H2O (Nicholls, 1980), recalibrated with experimental and melt inclusions data from Mt. Etna. Our modeling is able to decipher magma ascent velocity, v (dH/dt; H = depth, t = time), from ascent rate (dP/dt), and rate of cooling (dT/dt), where ρ is magma density, P is pressure, T is temperature and g is the acceleration of gravity. This equation for v provides a key to investigating the relationships

  14. Magma storage in a strike-slip caldera

    NASA Astrophysics Data System (ADS)

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-07-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

  15. Iron Redox Systematics of Shergottites and Martian Magmas

    NASA Technical Reports Server (NTRS)

    Righter, Kevin; Danielson, L. R.; Martin, A. M.; Newville, M.; Choi, Y.

    2010-01-01

    Martian meteorites record a range of oxygen fugacities from near the IW buffer to above FMQ buffer [1]. In terrestrial magmas, Fe(3+)/ SigmaFe for this fO2 range are between 0 and 0.25 [2]. Such variation will affect the stability of oxides, pyroxenes, and how the melt equilibrates with volatile species. An understanding of the variation of Fe(3+)/SigmaFe for martian magmas is lacking, and previous work has been on FeO-poor and Al2O3-rich terrestrial basalts. We have initiated a study of the iron redox systematics of martian magmas to better understand FeO and Fe2O3 stability, the stability of magnetite, and the low Ca/high Ca pyroxene [3] ratios observed at the surface.

  16. Magma storage in a strike-slip caldera.

    PubMed

    Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  17. The 280 ka Matahina Eruption, Okataina Volcanic Centre, New Zealand: A Protracted Rhyolite Magma Assembly by Fractional Crystallization, Melt Extraction, Rhyolite-Rhyolite Mixing, and Magmatic Stratification

    NASA Astrophysics Data System (ADS)

    Deering, C. D.; Cole, J. W.

    2007-12-01

    The 280 ka Matahina eruption from the Taupo Volcanic Zone (TVZ), New Zealand, produced voluminous pyroclastic deposits representing >220 km3 of andesitic to rhyolitic magma and the climax of magmatic/volcanic activity from ca. 340 ka to 280 ka within the Okataina Volcanic Centre. The Murupara subgroup of eruptions preceding this large, caldera-forming event is used to document the progressive growth of a large volume magma body in the mid- to upper-crust over 103 or 104 years. The dominant magma composition of the caldera-forming eruption was rhyodacite/rhyolite (70.8 to 78.1 wt % SiO2), with a subordinate volume of andesitic to rhyolitic (58.5 to 77.6 wt % SiO2) juvenile pyroclastics erupted following the caldera collapse. Phenocrysts (plagioclase+quartz+opx±amph+Fe-Ti oxides) from the pumice clasts define two distinct compositional populations that evolved independent of one another following rhyolite melt extraction from a fractionating andesitic parent magma body. We interpret these phenocryst populations to represent two phase assemblages that evolved in a slightly stratified rhyolitic magma chamber overlying a less-evolved basal mush layer. Oxide geothermometry and phase equilibria suggest a 740- 783°C magma storage temperature at 7-10 km depth. Most of the bulk-rock, melt, and phenocryst compositional variations are consistent with fractional crystallization (FC) of an andesitic parent magma body. However, trace element variation in pumice clasts, distinct rhyolitic glass major element compositions, and plagioclase disequilibrium accompanied by complex zoning are not consistent with closed-system FC alone, but are consistent with both FC and mixing in characterizing the magmatic diversity. In addition, the application of Polytopic Vector Analysis (PVA), a multivariate statistical treatment of the bulk-rock geochemistry, provides a mixing solution with a robust platform for accurately defining the timing and nature of the mixing event. Hence, the subtle

  18. Computational Studies in Molecular Geochemistry and Biogeochemistry

    SciTech Connect

    Felmy, Andrew R.; Bylaska, Eric J.; Dixon, David A.; Dupuis, Michel; Halley, James W.; Kawai, R.; Rosso, Kevin M.; Rustad, James R.; Smith, Paul E.; Straatsma, TP; Voth, Gregory A.; Weare, John H.; Yuen, David A.

    2006-04-18

    The ability to predict the transport and transformations of contaminants within the subsurface is critical for decisions on virtually every waste disposal option facing the Department of Energy (DOE), from remediation technologies such as in situ bioremediation to evaluations of the safety of nuclear waste repositories. With this fact in mind, the DOE has recently sponsored a series of workshops on the development of a Strategic Simulation Plan on applications of high perform-ance computing to national problems of significance to the DOE. One of the areas selected for application was in the area of subsurface transport and environmental chemistry. Within the SSP on subsurface transport and environmental chemistry several areas were identified where applications of high performance computing could potentially significantly advance our knowledge of contaminant fate and transport. Within each of these areas molecular level simulations were specifically identified as a key capability necessary for the development of a fundamental mechanistic understanding of complex biogeochemical processes. This effort consists of a series of specific molecular level simulations and program development in four key areas of geochemistry/biogeochemistry (i.e., aqueous hydrolysis, redox chemistry, mineral surface interactions, and microbial surface properties). By addressing these four differ-ent, but computationally related, areas it becomes possible to assemble a team of investigators with the necessary expertise in high performance computing, molecular simulation, and geochemistry/biogeochemistry to make significant progress in each area. The specific targeted geochemical/biogeochemical issues include: Microbial surface mediated processes: the effects of lipopolysacchardies present on gram-negative bacteria. Environmental redox chemistry: Dechlorination pathways of carbon tetrachloride and other polychlorinated compounds in the subsurface. Mineral surface interactions: Describing

  19. The variation of magma discharge during basaltic eruptions

    NASA Astrophysics Data System (ADS)

    Wadge, G.

    1981-12-01

    The rate at which basaltic magma is discharged varies substantially during many eruptions. An individual eruption has an eruption rate ( Qe), the volumetric rate of discharge averaged over the whole or a major part of an eruption, and an effusion rate ( Qf), the volumetric flux rate at any given time. In many examples Qf soon reaches a maximum value after a short period of waxing flow, partly because of magmatic expansion, and then falls more slowly in the later parts of the eruption. The release of elastic strain energy from stored magma and the sub-volcanic reservoir during eruption can produce an exponential form of such waning flow. Comparison of the eruption rates of the historic eruptions of Mauna Loa, Kilauea and Etna shows that for each volcano there is a trend of decreasing Qe with increasing duration of eruption. This relationship is not predicted by a simple elastic model of magma release. Two additional processes are invoked to explain the eruptive histories of these volcanoes: modification of the eruptive conduits, and the continued supply of magma from depth during eruption. Conduits evolving from dikes to plugs by wall-rock erosion or freezing of magma can result in increased early values of Qf and the maintenance of very low values of Qf values for long periods later in the eruption. Discharge variations during three specific eruptions are discussed in detail. Paricutin (1943-1952) had exponentially waning flow, with a time constant of about three years, that is consistent with a deep reservoir. The waning flow of Hekla's 1947-1948 eruption showed some of the characteristics of conduit modification, whilst the 1959 Kilauea Iki eruption is interpreted in terms of a closed system with varying magma rheology.

  20. Cooling magma model for deep volcanic long-period earthquakes

    NASA Astrophysics Data System (ADS)

    Aso, Naofumi; Tsai, Victor C.

    2014-11-01

    Deep long-period events (DLP events) or deep low-frequency earthquakes (deep LFEs) are deep earthquakes that radiate low-frequency seismic waves. While tectonic deep LFEs on plate boundaries are thought to be slip events, there have only been a limited number of studies on the physical mechanism of volcanic DLP events around the Moho (crust-mantle boundary) beneath volcanoes. One reasonable mechanism capable of producing their initial fractures is the effect of thermal stresses. Since ascending magma diapirs tend to stagnate near the Moho, where the vertical gradient of density is high, we suggest that cooling magma may play an important role in volcanic DLP event occurrence. Assuming an initial thermal perturbation of 400°C within a tabular magma of half width 41 m or a cylindrical magma of 74 m radius, thermal strain rates within the intruded magma are higher than tectonic strain rates of ~ 10-14 s-1 and produce a total strain of 2 × 10-4. Shear brittle fractures generated by the thermal strains can produce a compensated linear vector dipole mechanism as observed and potentially also explain the harmonic seismic waveforms from an excited resonance. In our model, we predict correlation between the particular shape of the cluster and the orientation of focal mechanisms, which is partly supported by observations of Aso and Ide (2014). To assess the generality of our cooling magma model as a cause for volcanic DLP events, additional work on relocations and focal mechanisms is essential and would be important to understanding the physical processes causing volcanic DLP events.

  1. 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.

  2. Shallow Magma Ocean on Vesta and Implications for the HEDs

    NASA Astrophysics Data System (ADS)

    Neumann, Wladimir; Breuer, Doris; Spohn, Tilman

    2014-05-01

    The asteroid 4 Vesta is widely held as a differentiated object and as the parent body of the HED meteorites. However, the origin of the HEDs, which is closely linked to the differentiation processes, is still a subject of debate. In particular, various differentiation scenarios have been proposed (e.g. partial melt[1] and residual melt[2,3] scenario) to explain the process of HEDs' formation. Here we present results of numerical calculations of the early thermo-chemical evolution of Vesta, placing constraints on the possible differentiation scenario and on the occurrence and depth of the Vestan mantle magma ocean. We use a numerical heat conduction code[4] that considers accretion, compaction, melting, associated changes of the material properties, partitioning of 26Al, advective heat transport, differentiation by porous flow, and effective cooling of a magma ocean by convection. We show that partitioning of 26Al and its transport with the silicate melt is crucial for the formation of a magma ocean. Previous models that neglect this effect[5,6,7] infer a whole-mantle magma ocean beneath a solid crust. We show that in contrast to these models a deep magma ocean does not form if partitioning of 26Al is considered: Radioactive nuclides are enriched in the melt and relocated towards the surface. Due to the over-production of the radiogenic heat in a shallow layer, the melt fraction increases rapidly above a critical melting threshold (here we assume 50 % of melt) for which the rheology is dominated by the liquid phase, i.e. a magma ocean forms. For formation times of Vesta

  3. Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

    NASA Technical Reports Server (NTRS)

    Rapp, J. F.; Draper, D. S.

    2015-01-01

    The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale magma ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar magma ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep magma ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow magma ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper magma ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after magma ocean crystallization and the nature of KREEP

  4. Gas transport through magma near the percolation threshold (Invited)

    NASA Astrophysics Data System (ADS)

    Llewellin, E. W.; Blower, J.; Leslie, D.

    2009-12-01

    Explosive silicic eruptions may simultaneously produce both tube pumice - containing highly-elongate vesicles - and pumice containing sub-spherical vesicles. This has been cited as evidence for strain localization within the volcanic conduit: in a relatively-undeformed axial ‘plug’ bubbles are spherical (regime 1) whilst near the conduit margin rapidly-shearing magma bears elongate bubbles (regime 2). Published numerical studies support this model and indicate that bubbly-magma rheology or viscous heating may be responsible for strain localization. The difference in bubble morphology in these two regimes has important consequences for magma permeability. We present the results of fluid dynamic simulations which quantify the anisotropy of permeability in regime 2 as a function of gas volume fraction and bubble aspect ratio. In this regime, we find that vertical permeability may be many times greater than radial permeability, and that permeability anisotropy is most pronounced near the percolation threshold. We further use a network model to quantify the development of permeability in regime 1. In the case where the predominantly vertical expansion of the magma is slow compared with bubble relaxation time, we find that permeability is, again, anisotropic, but that radial permeability dominates. This effect is also most pronounced near the percolation threshold, and percolation is expected to occur radially before vertical percolation occurs. Our findings imply that gas transport in regime 1 is predominantly radial, whilst vertical gas transport is favoured in regime 2. Consequently, near the percolation threshold, conditions are appropriate for effective degassing of the central magma plug as gas permeates radially to the conduit margin and then vertically upwards. Repeated cycles of percolation, radial gas loss and densification may degas the central magma plug without the development of large gas volume fractions.

  5. Silicic magma entering a basaltic magma chamber: eruptive dynamics and magma mixing — an example from Salina (Aeolian islands, Southern Tyrrhenian Sea)

    NASA Astrophysics Data System (ADS)

    Calanchi, Natale; de Rosa, Rosanna; Mazzuoli, Roberto; Rossi, Pierluigi; Santacroce, Roberto; Ventura, Guido

    1993-09-01

    The Pollara tuff-ring resulted from two explosive eruptions whose deposits are separated by a paleosol 13 Ka old. The oldest deposits (LPP, about 0.2 km3) consist of three main fall units (A, B, C) deposited from a subplinian column whose height (7 14 km) increased with time from A to C, as a consequence of the increased magma discharge rate during the eruption (1 8x106 kg/s). A highly variable juvenile population characterizes the eruption. Black, dense, highly porphyritic, mafic ejecta (SiO2=50 55%) almost exclusively form A deposits, whereas grey, mildly vesiculated, mildly porphyritic pumice (SiO2=56 67%) and white, highly vesiculated, nearly aphyric pumice (SiO2=66 71%) predominate in B and C respectively. Mafic cumulates are abundant in A, while crystalline lithic ejecta first appear in B and increase upward. The LPP result from the emptying of an unusual and unstable, compositionally zoned, shallow magma chamber in which high density mafic melts capped low density salic ones. Evidence of the existence of a short crystal fractionation series is found in the mafic rocks; the andesitic pumice results from complete blending between rhyolitic and variously fractionated mafic melts (salic component up to 60 wt%), whereas bulk dacitic compositions mainly result from the presence of mafic xenocrysts within rhyolitic glasses. Viscosity and composition-mixing diagrams show that blended liquids formed when the visosities of the two end members had close values. The following model is suggested: 1. A rhyolitic magma rising through the metamorphic basement enterrd a mafic magma chamber whose souter portions were occupied by a highly viscous, mafic crystal mush. 2. Under the pressure of the rhyolitic body the nearly rigid mush was pushed upwards and mafic melts were squeezed against the walls of the chamber, beginning roof fracturing and mingling with silicic melts. 3. When the equilibrium temperature was reached between mafic and silicic melts, blended liquids rapidly

  6. Insights into Igneous Geochemistry from Trace Element Partitioning

    NASA Technical Reports Server (NTRS)

    Jones, J. H.; Hanson, B. Z.

    2001-01-01

    Partitioning of trivalent elements into olivine are used to explore basic issues relevant to igneous geochemistry, such as Henry's law. Additional information is contained in the original extended abstract.

  7. Geochemistry of Intermediate Olivine-Phyric Shergottite Northwest Africa 6234

    NASA Astrophysics Data System (ADS)

    Filiberto, J.; Chin, E.; Day, J. M. D.; Gross, J.; Penniston-Dorland, S. C.; Schwenzer, S. P.; Treiman, A. H.

    2012-03-01

    Here we present major- and trace-element geochemistry, Li-isotope composition and abundance, and Re-Os isotope and highly siderophile element abundance data for the ol-phyric shergottite Northwest Africa 6234.

  8. POLLUTION PREVENTION OPPORTUNITY ASSESSMENT - GEOCHEMISTRY LABORATORY AT SANDIA NATIONAL LABORATORIES

    EPA Science Inventory

    These reports summarize pollution prevention opportunity assessments conducted jointly by EPA and DOE at the Geochemistry Laboratory and the Manufacturing and Fabrication Repair Laboratory at the Department of Energy's Sandia National Laboratories facility in Albuquerque, New Mex...

  9. Magma generation on Mars: Estimated volumes through time

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Schneid, B.

    1991-01-01

    Images of volcanoes and lava flows, chemical analysis by the Viking landers, and studies of meteorites show that volcanism has played an important role in the evolution of Mars. Photogeologic mapping suggests that half of Mars' surface is covered with volcanic materials. Here, researchers present results from new mappings, including estimates of volcanic deposit thicknesses based on partly buried and buried impact craters using the technique of DeHon. The researchers infer the volumes of possible associated plutonic rocks and derive the volumes of magmas on Mars generated in its post-crustal formation history. Also considered is the amount of juvenile water that might have exsolved from the magma through time.

  10. On the cooling of a deep terrestrial magma ocean

    NASA Astrophysics Data System (ADS)

    Monteux, J.; Andrault, D.; Samuel, H.

    2016-08-01

    Several episodes of complete melting have probably occurred during the first stages of the Earth's evolution. We have developed a numerical model to monitor the thermal and melt fraction evolutions of a cooling and crystallizing magma ocean from an initially fully molten mantle. For this purpose, we numerically solve the heat equation in 1D spherical geometry, accounting for turbulent heat transfer, and integrating recent and strong experimental constraints from mineral physics. We have explored different initial magma ocean viscosities, compositions, thermal boundary layer thicknesses and initial core temperatures. We show that the cooling of a thick terrestrial magma ocean is a fast process, with the entire mantle becoming significantly more viscous within 20 kyr. Due to the slope difference between the adiabats and the melting curves, the solidification of the molten mantle occurs from the bottom up. In the meantime, a crust forms due to the high surface radiative heat flow, the last drop of fully molten silicate is restricted to the upper mantle. Among the studied parameters, the magma ocean lifetime is primarily governed by its viscosity. Depending on the thermal boundary layer thickness at the core-mantle boundary, the thermal coupling between the core and magma ocean can either insulate the core during the magma ocean solidification and favor a hot core or drain the heat out of the core simultaneously with the cooling of the magma ocean. Reasonable thickness for the thermal boundary layer, however, suggests rapid core cooling until the core-mantle boundary temperature results in a sluggish lowermost mantle. Once the crystallization of the lowermost mantle becomes significant, the efficiency of the core heat loss decreases. Since a hotter liquidus favors crystallization at hotter temperatures, a hotter deep mantle liquidus favors heat retention within the core. In the context of an initially fully molten mantle, it is difficult to envision the formation of a

  11. Magma dynamics above the Karoo plume, South Africa

    NASA Astrophysics Data System (ADS)

    Ferre, Eric; Geissman, John; Stephanie, Maes; Aneesa, Gillum; Julian, Marsh

    2015-04-01

    Mantle plumes produce voluminous amounts of magma (106 km3) during a short period of time (106 years). The heat input of such plumes into sedimentary basins has been proposed as a significant factor in several global climatic crises. Indeed heat transfer through conductive and advective processes is likely to bake organic matter-rich sediments, which in turn may release greenhouse gases (CO2 and CH4). One of the yet poorly understood aspects of this model is the regional pattern of magma flow. The objective of this study is to constrain magma dynamics in the Karoo Large Igneous Province (LIP) intruded in a continental basin of South Africa. Magnetic fabrics provide an efficient and accurate mean to determine magma flow direction in gabbroic rocks. The anisotropy of magnetic susceptibility (AMS) is particularly suited for this type of study. A previous study had shown that the AMS fabric is a reliable proxy for magma flow as long as samples are collected from the upper chilled margin of a sill. The central part is more complex due to interference caused by thermal convection. Oriented core samples were collected from 30 different sills and yielded 1598 specimens for AMS measurements. The low-field magnetic susceptibility Km ranges widely from about 100 to 20,000 . 10-6 [SI], while the degree of anisotropy P' ranges from 1.01 to 1.10. Thermomagnetic experiments reveal that the main magnetic carrier is titanomagnetite with variable ulvöspinel content. This is confirmed by measurement of hysteresis properties that also indicate that titanomagnetite in general has a pseudo-single domain grain size. The results of this study clearly indicate that magma flow followed a main NW-SE direction in the studied area. The AMS directional data is consistent with the nearly horizontal attitude of the sill in 23 out of 30 cases, with subvertical K3 axes. In 5 out of 30 sills, K3 axes are subhorizontal, characterized by scattered directional data and are considered anomalous AMS

  12. Output rate of magma from active central volcanoes

    NASA Technical Reports Server (NTRS)

    Wadge, G.

    1980-01-01

    For part of their historic records, nine of the most active volcanoes on earth have each erupted magma at a nearly constant rate. These output rates are very similar and range from 0.69 to 0.26 cu m/s. The volcanoes discussed - Kilauea, Mauna Loa, Fuego, Santiaguito, Nyamuragira, Hekla, Piton de la Fournaise, Vesuvius and Etna - represent almost the whole spectrum of plate tectonic settings of volcanism. A common mechanism of buoyantly rising magma-filled cracks in the upper crust may contribute to the observed restricted range of the rates of output.

  13. The Relationship Between Amphibole Cumulates and Adakite Magma

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.

    2009-12-01

    Amphibole, while uncommon as a primary fractioning phase is increasingly recognized as a key constituent in the petrogenesis of arc magmas. Fractional crystallization of water-saturated arc magmas in the lower crust can yield substantial volumes amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production adakite magmas. The origin of adakites, defined by their heavy REE and Y depletion and Sr enrichments, have vigorously debated since their re-discovery in Panama two decades ago. In addition to widespread modern adakitic volcanism, the Panamanian portion of the Central American Arc preserves the magmatic record of arc development in close spatial association with younger magmatism. Late-Oligocene hypabyssal crystal-rich andesites from Cerro Patacon are preserved near the Panama Canal region. These contain nodules of amphibole cumulates, and may be used to examine the amphibole-fractionation model for adakite origin. The cumulate nodules are ~6 cm in diameter and are almost entirely composed of 5-10mm amphibole crystals (dominantly ferri-tschermakite), and are accompanied in the host andesites by amphibole phenocrysts, antecrysts and megacryts. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of the array defined by similarly differentiated (58-60% SiO2) Central American Arc magmas, and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite. Sr/Y which is used as a geochemical tool for discriminating adakites from other arc magams, is transitional in the Cerro Patcon andesites. However La/Yb is within the range for ‘normal’ arc magmas and shows that amphibole fractionation alone is insufficient to generate adakite magmas - some garnet

  14. Magma mingling in the panozero sanukitoid intrusion, baltic shield

    NASA Astrophysics Data System (ADS)

    Rollinson, H.

    2003-04-01

    The 2.7 Ga Panozero pluton is a composite intrusion comprising magmas of sanukitoid affinity, intrusive into the ca. 2.75 Ga Segozero greenstone belt in western Karelia in the Baltic Shield. The intrusion is predominantly a monzonite, is elliptical in form (9 x 6 km) and is undeformed. Along the eastern margin of the intrusion a wide variety of cogenetic magmas have been mapped ranging in composition from biotite-hornblendites, through monzo-gabbro and monzonite to quartz-monzonite. The contact relationships between the different phases of the intrusion are complex and imply magma mingling and incomplete mixing between magma types. The monzogabbros show a gradational relationship with the monzodiorites, but occur as inclusions within, and contain inclusions of, the monzonite implying two coexisting melts. Similar relationships exist between the monzonite and quartz monzonite and in places there is a gneissose banding of the darker phase within the lighter phase. The quartz-syenite is intrusive into all earlier phases, although the latest phase is hornblendite. This is present as net veining in gabbro and as irregular veins, dykes and as irregularly shaped xenoliths in monzonite, quartz monzonite and syenite. The irregular form and deformed state of the hornblendite inclusions within the earlier magmas implies that the hornblendite was emplaced whilst the host magma was hot. Also developed along the eastern margin of the intrusion are breccia pipes. These are found in the monzodiorites, monzonites and in quartz monzonites. They contain elliptical fragments up to 20 cm long of hornblendite, tremolitite, epidotised amphibolite and in the monzodiorite euhedral feldspars with felsic reaction rims. The matrix of the breccias is often very similar to the composition of their host rock. Many of the fragments are thought to be derived from the adjacent greenstone belt. However, metabasaltic rocks are not recorded from this part of the greenstone belt and so may be derived

  15. Do Plinian Eruptions of Mafic Magma Require Fast Ascent Rates?

    NASA Astrophysics Data System (ADS)

    Szramek, L. A.; Gardner, J. E.

    2008-12-01

    Although rare, mafic magma is known to erupt explosively in Plinian fashion. Given that models for such eruptions often invoke high viscosities as pre-requisite, mafic magmas erupting explosively seems to pose a quandary. One possibility is that such magmas can erupt explosively, if they ascend towards the surface very fast, creating conditions that lead to explosive degassing and fragmentation. In order to estimate how fast mafic magma ascends in such eruptions, we are carrying out series of isothermal decompression experiments to examine groundmass textures in natural samples from such eruptions to infer ascent rates. One eruption we are examining is the 122 B.C. Plinian eruption of hawaiite from Mt Etna. Prior work suggests that this magma was stored at 1025°C and 75 MPa before erupting. We find that the groundmass has a total crystallinity of 58 vol.%, consisting of 34 vol.% pyroxene, 20 vol.% plagioclase, and 4 vol.% Fe- Ti oxides. The area number densities are on the order of 3-7 x 10-2μm-2. Thus far, we have been unable to mimic its groundmass textures with either the single-step or multi-step decompression experiments, in which pressure dropped from 75 MPa to 13 MPa at rates ranging from 0.18 to 0.001 MPa s -1. Although the slowest decompression produced the correct groundmass assemblage and total crystallinity it has twice the plagioclase and far too little pyroxene. In addition, area number densities are 1-2 orders of magnitude less. Additionally, hopper shaped plagioclase is observed in all but the slowest experiment, whereas the natural sample contains only tabular to acicular plagioclase. Our results suggest that the textures of the hawaiite scoria cannot be explained by rapid ascent alone. One possibility is that the magma stalled and slowly crystallized prior to eruption. The additional microlites would have increased the viscosity of the melt, allowing the mafic magma to erupt in a Plinian style. In order to further test the rapid ascent model for

  16. Magmatic Water Contents in Mariana and Izu Arc Magmas

    NASA Astrophysics Data System (ADS)

    Parman, S.; Grove, T.; Plank, T.

    2002-05-01

    We estimate the magmatic water content of magmas from the Mariana-Izu arc system using experimental phase equilibria. Our goal is to produce primary H2O estimates for Mariana-Izu magmas to compare with along-arc variations in the trace element and isotopic compositions of the magmas. Such correlations can be used to quantify the chemical inputs into the sub-arc mantle wedge from the subducting Pacific plate. The experiments are performed in externally heated, gas-pressure vessels. H2O-saturatation is maintained throughout the experiment, as well as an fO2 at the Ni-NiO buffer. The experimental melts contain between 5.5 and 6.2 wt.% H2O. The observed LLD for Pagan island in the Mariana arc falls midway between the hydrous 200 MPa LLD and an anhydrous LLD modeled using the MELTS program [Ghiorso and Sack, 1995], suggesting an initial H2O content of ~3 wt.%. This in good agreement with the H2O content (2.7 wt.%, Plank, unpub. data) of an olivine-hosted melt inclusion contained in the Pagan samples. Experiments at lower H2O contents are being conducted to verify this estimate. The LLD for Hachijo-jima in the Izu arc follows the 200 MPa, H2O saturated LLD fairly well, though there is significant scatter in the natural sample compositions, likely due to plagioclase accumulation. Thus our preliminary results indicate higher H2O contents in the Hachijo-jima magmas (5-7 wt.%) relative to the Pagan magmas. The compositions of minerals in the mafic Pagan sample (PAF3b; Woodhead, 1989) indicate a history of mixing. Relative to the hydrous experiments, olivine (ol) phenocrysts in the sample have higher Mg#s (0.867 vs. 0.809), while plag phenocrysts have lower anorthite (An) contents (0.889 vs. 0.946). The lower An contents are consistent with the lower estimated H2O contents in the Pagan magmas relative to the experiments, while the higher ol Mg# indicates that even the most mafic Pagan sample is fractionated or a mixed magma. Glomerocrysts in the sample contain ol with lower

  17. Imaging magma plumbing beneath Askja volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Greenfield, Tim; White, Robert S.

    2015-04-01

    Volcanoes during repose periods are not commonly monitored by dense instrumentation networks and so activity during periods of unrest is difficult to put in context. We have operated a dense seismic network of 3-component, broadband instruments around Askja, a large central volcano in the Northern Volcanic Zone, Iceland, since 2006. Askja last erupted in 1961, with a relatively small basaltic lava flow. Since 1975 the central caldera has been subsiding and there has been no indication of volcanic activity. Despite this, Askja has been one of the more seismically active volcanoes in Iceland. The majority of these events are due to an extensive geothermal area within the caldera and tectonically induced earthquakes to the northeast which are not related to the magma plumbing system. More intriguing are the less numerous deeper earthquakes at 12-24km depth, situated in three distinct areas within the volcanic system. These earthquakes often show a frequency content which is lower than the shallower activity, but they still show strong P and S wave arrivals indicative of brittle failure, despite their location being well below the brittle-ductile boundary, which, in Askja is ~7km bsl. These earthquakes indicate the presence of melt moving or degassing at depth while the volcano is not inflating, as only high strain rates or increased pore fluid pressures would cause brittle fracture in what is normally an aseismic region in the ductile zone. The lower frequency content must be the result of a slower source time function as earthquakes which are both high frequency and low frequency come from the same cluster, thereby discounting a highly attenuating lower crust. To image the plumbing system beneath Askja, local and regional earthquakes have been used as sources to solve for the velocity structure beneath the volcano. Travel-time tables were created using a finite difference technique and the residuals were used to solve simultaneously for both the earthquake locations

  18. Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers

    NASA Astrophysics Data System (ADS)

    Malfait, Wim J.; Seifert, Rita; Petitgirard, Sylvain; Perrillat, Jean-Philippe; Mezouar, Mohamed; Ota, Tsutomu; Nakamura, Eizo; Lerch, Philippe; Sanchez-Valle, Carmen

    2014-02-01

    Super-eruptions that dwarf all historical volcanic episodes in erupted volume and environmental impact are abundant in the geological record. Such eruptions of silica-rich magmas form large calderas. The mechanisms that trigger these super-eruptions are elusive because the processes occurring in conventional volcanic systems cannot simply be scaled up to the much larger magma chambers beneath supervolcanoes. Over-pressurization of the magma reservoir, caused by magma recharge, is a common trigger for smaller eruptions, but is insufficient to generate eruptions from large supervolcano magma chambers. Magma buoyancy can potentially create sufficient overpressure, but the efficiency of this trigger mechanism has not been tested. Here we use synchrotron measurements of X-ray absorption to determine the density of silica-rich magmas at pressures and temperatures of up to 3.6GPa and 1,950K, respectively. We combine our results with existing measurements of silica-rich magma density at ambient pressures to show that magma buoyancy can generate an overpressure on the roof of a large supervolcano magma chamber that exceeds the critical overpressure of 10-40MPa required to induce dyke propagation, even when the magma is undersaturated in volatiles. We conclude that magma buoyancy alone is a viable mechanism to trigger a super-eruption, although magma recharge and mush rejuvenation, volatile saturation or tectonic stress may have been important during specific eruptions.

  19. Geochemistry of carbonatites of the Tomtor massif

    USGS Publications Warehouse

    Kravchenko, S.M.; Czamanske, G.; Fedorenko, V.A.

    2003-01-01

    Carbonatites compose sheet bodies in a 300-m sequence of volcanic lamproites, as well as separate large bodies at depths of >250-300 m. An analysis of new high-precision data on concentrations of major, rare, and rare earth elements in carbonatites shows that these rocks were formed during crystallization differentiation of a carbonatite magma, which resulted in enrichment of the later melt fractions in rare elements and was followed by autometasomatic and allometasomatic hydrothermal processes. Some independent data indicate that the main factor of ore accumulation in the weathered rock zone (also known as the "lower ore horizon" comprising metasomatized volcanics with interbedded carbonatites) was hydrothermal addition of Nb and REEs. The giant size of the Tomtor carbonatite-nepheline syenite massif caused advanced magma differentiation, extensive postmagmatic metasomatism and recrystallization of host rocks, and strong enrichment of carbonatites in incompatible rare and rare earth elements (except for Ta, Zr, Ti, K, and Rb) compared to the rocks of many other carbonatite massifs. We suggest that a wide range of iron contents in carbonatites-2 can be related to extensive magnetite fractionation at the magmatic stage in different parts of the huge massif. Copyright ?? 2003 by MAIK "Nauka/Interperiodica" (Russia).

  20. Investigating urban geochemistry using Geographical Information Systems.

    PubMed

    Thums, C; Farago, M

    2001-01-01

    Geographical Information System (GIS) is an interactive digital extension of the two-dimensional paper map. Customised maps are created by the selection and aggregation of data from independent sources to assist studies in urban geochemistry. The metropolitan area of Wolverhampton, in the West Midlands, UK is used to illustrate the types of output that can be generated. These include: geographic and geological feature; geochemical data and land use. Multi-layered maps can be used to investigate spatial relationships, for example, between elevated concentrations of metals in soils and industrial land use. Such maps can also be used to assist the assessment of potential exposure of groundwater, ecosystems and humans using maps incorporating guideline values for metals in soils. PMID:11732156

  1. Geochemistry and health in the United Kingdom.

    PubMed

    Thornton, I; Webb, J S

    1979-12-11

    Before the 1960s, comparisons between the distribution of trace elements in the environment and health in the United Kingdom were primarily confined to ad hoc studies in areas associated with particular agricultural disorders or with unusual human mortality or morbidity records. More recently, increasing interest in the importance of trace elements in crop and animal production and in the hazards of environmental pollution have created a need for more systematic geochemical data. Geochemical reconnaissance maps for England, Wales, Northern Ireland and parts of Scotland have demonstrated the extent of many known clinical trace element problems in agriculture and have also been valuable in delineating areas within which subclinical disorders may occur. Their application to studies on the composition of soils, food crops and surface waters in relation to public health has proved encouraging. Current knowledge and present investigations into environmental geochemistry and human health in the U.K. are reviewed, together with future research requirements. PMID:43529

  2. Petrology, Geochemistry and Genesis of Ureilites

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, D. W.; Hudon, Pierre; Galindo, Charles, Jr.

    2005-01-01

    Ureilites are enigmatic achondrites that have some characteristics resulting from high temperature igneous processing, yet retain other characteristics inherited from the solar nebula. They are basalt-depleted ultramafic rocks containing 7-66 mg/g elemental C. They are rich in noble gases and display a correlation between mg# and Delta (17)O. This mishmash of properties has engendered various models for ureilite genesis, from those in which nebular processes dominate to those in which parent body igneous processes dominate. Characterization of new ureilites, especially of new subtypes, is an important part of attempts to unravel the history of the ureilite parent body or bodies. Here we report on the petrology and geochemistry of a suite of ureilites, mostly from Antarctica, and use these data to discuss ureilite petrogenesis. Additional information is included in the original extended abstract.

  3. Geochemistry and origin of regional dolomites

    NASA Astrophysics Data System (ADS)

    Hanson, G. N.

    Quantitative, geochemical models for the source, flow paths and chemistry of the diagnetic fluids responsible for the widespread dolomitization of the Mississippi Burlington-Keokuk Fms were developed. Iowa, Illinois and Missouri by integrating geochemistry, fluid inclusion studies, conventional and luminescent petrography, stratigraphy, facies analysis and burial history. The study includes western Illinois and eastern Missouri and southeastern Iowa. This includes most of the area where good sections of facies from near shore to the platform edge. The geochemical studies include: correlation of the major and trace element variations within the various Burlington dolomites developed in southeastern Iowa and adjacent areas of Illinois and Missouri; rare earth element, Nd and Sr isotope analysis of the dolomites and coexisting phases; major and trace element analysis, petrography and X ray mineralogy of selected shaly members in the Burlington-Keokuk formations; and fluid inclusion studies of the calcites and dolomite cements of southeastern Iowa.

  4. Beryllium isotope geochemistry in tropical river basins

    SciTech Connect

    Brown, E.T.; Edmond, J.M. ); Raisbeck, G.M.; Bourles, D.L.; Yiou, F. ); Measures, C.I. )

    1992-04-01

    The distributions of beryllium-9 and beryllium-10 in rivers within the Orinoco and Amazon basins have been examined to extend the understanding of their geochemical cycles and to develop their use both in geochronometry, and in studying erosional processes. Analyses of {sup 9}Be in dissolved and suspended material from rivers with a wide range of chemical compositions indicate that its geochemistry is primarily controlled by two major factors: (1) its abundance in the rocks of the watershed and (2) the extent of its adsorption onto particle surfaces. The relative importance of these parameters in individual rivers is determined by the extent of interaction with flood-plain sediments and the riverine pH. This understanding of {sup 9}Be geochemistry forms a basis for examination of the geochemical cycling of {sup 10}Be. In rivers which are dominated by interaction with sediments, the riverine concentration of dissolved {sup 10}Be is far lower than that in the incoming rainwater, indicating that a substantial proportion of it is retained within the soils of the basin or is adsorbed onto riverine particles. However, in acidic rivers in which the stable dissolved Be concentration is determined by the Be level in the rocks of the drainage basin, dissolved {sup 10}Be has essentially the same concentration as in precipitation. These observations imply that the soil column in such regions must be saturated with respect to {sup 10}Be, and that the ratio of the inventory to the flux does not represent an age, as may be the case in temperate latitudes, but rather a residence time.

  5. Microbial Sulfur Geochemistry in Mine Systems (Invited)

    NASA Astrophysics Data System (ADS)

    Warren, L. A.; Norlund, K. L.; Hitchcock, A.

    2010-12-01

    Acid mine drainage (AMD), metal laden, acidic water, is the most pressing mining environmental issue on a global scale. While it is well recognized that the activity of autotrophic Fe and S bacteria amplify the oxidation of the sulfidic wastes, thereby generating acidity and leaching metals; the underlying microbial geochemistry is not well described. This talk will highlight results revealing the importance of microbial cooperation associated with a novel sulfur-metabolizing consortium enriched from mine waters. Results generated by an integrated approach, combining field characterization, geochemical experimentation, scanning transmission X-ray microscopy (STXM), and fluorescence in situ hybridization (FISH) [1]describing the underlying ecological drivers, the functionally relevant biogeochemical architecture of the consortial macrostructure as well as the identities of this environmental sulphur redox cycling consortium will be presented. The two common mine bacterial strains involved in this consortium, Acidithiobacillus ferroxidans and Acidiphilium sp., are specifically spatially segregated within a macrostructure (pod) of extracellular polymeric substance (EPS) that enables coupled sulphur oxidation and reduction reactions despite bulk, oxygenated conditions. Identical pod formation by type culture strains was induced and linked to ecological conditions. The proposed sulphur geochemistry associated with this bacterial consortium produces 40-90% less acid than expected based on abiotic AMD models, with implications for both AMD mitigation and AMD carbon flux modeling. We are currently investigating the implications of these sulphur-processing pods for metal dynamics in mine systems. These results demonstrate how microbes can orchestrate their geochemical environment to facilitate metabolism, and underscore the need to consider microbial interactions and ecology in constraining their geochemical impacts. [1] Norlund, Southam, Tyliszcczak, Hu, Karunakaran, Obst

  6. Magma supply rates inferred from cinder cone volumes

    NASA Astrophysics Data System (ADS)

    Bemis, K. G.; Borgia, A.; Neri, M.; Kervyn, M.

    2010-12-01

    Revisiting the question of how cinder cones grow suggests the possibility of inferring magma supply rates from cinder cones sizes. We start with a conceptual model of cinder cone growth: (1) Eruption volume flux increases rapidly and then decreases exponentially. (2) Cinder cones get steeper during the initiation of the eruption and then maintain a constant steepness. (3) The initial basal diameter varies with volume flux into the cone. Based on these constraints, we propose a general form for the relationship between cinder cone volume and magma supply rate: V = Q(exp(-t/b)/b - exp(-t/a)/a), where V is volume (in m3), Q is the maximum potential magma flux (in m3/s), t is time (in s), a is a damping factor (in s) controlling the decline in volume flux, and b is a factor controlling the initial increase in volume flux. Then we use the data available on the growth of cinder cones from four modern eruptions to show the relevance of our model and to constrain the supply curves. All four modern cones (Paricutin, Mexico which erupted 1943-1974; Tolbachik, Kamchatka which erupted in 1975-1976; Cono del Laghetto, Mount Etna, Italy which formed in 2001; and a small cone on the summit of Oldoinyo Lengai, Tanzania, which formed during the 2007 eruption) show the basic growth pattern: initial rapid growth followed by declining growth (Figure 1). The regression results yeild the following magma supply rates: The southern Tolbachik cones have the largest predicted magma supply at ~100 m3/s. Paricutin and Laghetto are around 9 m3/s. The Oldoinyo Lengai cone has a magma supply of ~0.5 m3/s. The northern Tolbachik cone has the lowest magma supply of ~0.1 m3/s. In contrast, the damping factor a is generally on the order of 107 (it varies from 8 x 106 at southern Tolbachik to 4 x 107 at northern Tolbachik). The parameter b controlling the initial increase is generally small (<1). The predicted magma supply does not seem to be very sensitive to either parameter. Thus we suggest that

  7. Water-saturated magmas in the Panama Canal region: a precursor to adakite-like magma generation?

    NASA Astrophysics Data System (ADS)

    Rooney, Tyrone O.; Franceschi, Pastora; Hall, Chris M.

    2011-03-01

    Amphibole, while uncommon as a phenocryst in arc lavas, is increasingly recognized as a key constituent in the petrogenesis of arc magmas. Fractional crystallization of water-saturated arc magmas in the lower crust can yield substantial volumes of amphibole cumulates that, depending on the pressure of crystallization, may also contain garnet. Fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature. This study examines newly dated Late-Oligocene (25.37 ± 0.13 Ma) hypabyssal amphibole-rich andesites from Cerro Patacon in the Panama Canal region. These andesites contain nodules of amphibole cumulates that are ~4-6 cm in diameter and are almost entirely composed of 5-10-mm amphibole crystals (dominantly ferri-tschermakite). Geochemical variations, optical and chemical zoning of the Cerro Patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite. Amphiboles hosted within the cumulate nodules differ from those hosted in the Cerro Patacon andesite and contain consistently higher values of Ti. We suggest these nodules represent the early stages of fractionation from a water-saturated magma. Cerro Patacon andesites have REE concentrations that plot at the most depleted end of Central American Arc magmas and exhibit a distinctive depletion in the middle REE. These geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the Cerro Patacon andesite, consistent with the petrographic evidence. Fractionation of water-saturated magmas is a mechanism by which adakitic compositions may be produced, and the Cerro Patacon andesites do exhibit adakite-like geochemical characteristics (e.g., elevated Sr/Y; 28-34). However, the relatively elevated concentrations of Y and HREE indicate garnet was not stable in the fractionating

  8. Progress integrating ID-TIMS U-Pb geochronology with accessory mineral geochemistry: towards better accuracy and higher precision time

    NASA Astrophysics Data System (ADS)

    Schoene, B.; Samperton, K. M.; Crowley, J. L.; Cottle, J. M.

    2012-12-01

    It is increasingly common that hand samples of plutonic and volcanic rocks contain zircon with dates that span between zero and >100 ka. This recognition comes from the increased application of U-series geochronology on young volcanic rocks and the increased precision to better than 0.1% on single zircons by the U-Pb ID-TIMS method. It has thus become more difficult to interpret such complicated datasets in terms of ashbed eruption or magma emplacement, which are critical constraints for geochronologic applications ranging from biotic evolution and the stratigraphic record to magmatic and metamorphic processes in orogenic belts. It is important, therefore, to develop methods that aid in interpreting which minerals, if any, date the targeted process. One promising tactic is to better integrate accessory mineral geochemistry with high-precision ID-TIMS U-Pb geochronology. These dual constraints can 1) identify cogenetic populations of minerals, and 2) record magmatic or metamorphic fluid evolution through time. Goal (1) has been widely sought with in situ geochronology and geochemical analysis but is limited by low-precision dates. Recent work has attempted to bridge this gap by retrieving the typically discarded elution from ion exchange chemistry that precedes ID-TIMS U-Pb geochronology and analyzing it by ICP-MS (U-Pb TIMS-TEA). The result integrates geochemistry and high-precision geochronology from the exact same volume of material. The limitation of this method is the relatively coarse spatial resolution compared to in situ techniques, and thus averages potentially complicated trace element profiles through single minerals or mineral fragments. In continued work, we test the effect of this on zircon by beginning with CL imaging to reveal internal zonation and growth histories. This is followed by in situ LA-ICPMS trace element transects of imaged grains to reveal internal geochemical zonation. The same grains are then removed from grain-mount, fragmented, and

  9. Magma energy research project: state-of-the-project report, October 1, 1978

    SciTech Connect

    Colp, J.L.; Traeger, R.K.

    1980-02-01

    The feasibility of extracting energy from magma bodies is investigated. The work done in FY 76, 77, and 78 in the following tasks are summarized; resource location and definition, source tapping, magma characterization and materials compatibility, and energy extraction. (MHR)

  10. Low-3He/4He sublithospheric mantle source for the most magnesian magmas of the Karoo large igneous province

    NASA Astrophysics Data System (ADS)

    Heinonen, Jussi S.; Kurz, Mark D.

    2015-09-01

    The massive outpourings of Karoo and Ferrar continental flood basalts (CFBs) ∼180 Ma ago mark the initial Jurassic rifting stages of the Gondwana supercontinent. The origin and sources of these eruptions have been debated for decades, largely due to difficulties in defining their parental melt and mantle source characteristics. Recent findings of Fe- and Mg-rich dikes (depleted ferropicrite suite) from Vestfjella, western Dronning Maud Land, Antarctica, have shed light on the composition of the deep sub-Gondwanan mantle: these magmas have been connected to upper mantle sources presently sampled by the Southwest Indian Ocean mid-ocean ridge basalts (SWIR MORBs) or to high 3He/4He plume-entrained non-chondritic primitive mantle sources formed early in Earth's history. In an attempt to determine their He isotopic composition and relative contributions from magmatic, cosmogenic, and radiogenic He sources, we performed in-vacuo stepwise crushing and melting analyses of olivine mineral separates, some of which were abraded to remove the outer layer of the grains. The best estimate for the mantle isotopic composition is given by a sample with the highest amount of He released (>50%) during the first crushing step of an abraded coarse fraction. It has a 3He/4He of 7.03 ± 0.23 (2σ) times the atmospheric ratio (Ra), which is indistinguishable from those measured from SWIR MORBs (6.3-7.3 Ra; source 3He/4He ∼6.4-7.6 Ra at 180 Ma) and notably lower than in the most primitive lavas from the North Atlantic Igneous Province (up to 50 Ra), considered to represent the epitome magmas from non-chondritic primitive mantle sources. Previously published trace element and isotopic (Sr, Nd, and Pb) compositions do not suggest a direct genetic link to any modern hotspot of Indian or southern Atlantic Oceans. Although influence of a mantle plume cannot be ruled out, the high magma temperatures and SWIR MORB-like geochemistry of the suite are best explained by supercontinent insulation

  11. Assimilation of High 18O/16O Crust by Shergottite-Nakhlite-Chassigny (SNC) Magmas on Mars

    NASA Astrophysics Data System (ADS)

    Day, J. M.; Taylor, L. A.; Valley, J. W.; Spicuzza, M. J.

    2005-12-01

    There is significant geochemical evidence for assimilation of crustal material into sub-aerial, mantle-derived, terrestrial basaltic magmas. Some of the most powerful constraints on crustal assimilation come from oxygen isotope studies, because supracrustal rocks often have distinct 18O/16O ratios resulting from interaction with Earth's hydrosphere. From a planetary perspective, studies of carbonate concretions from meteorite ALH84001 have yielded evidence for low-temperature crustal interaction at or near the surface of its putative parent body, Mars. This finding raises the possibility that crustal assimilation processes may be tracked using oxygen isotopes in combination with geochemical data of other reputed martian (SNC) meteorites. The whole-rock oxygen isotope ratios (Laser fluorination δ18O = +4.21 to +5.85‰ VSMOW) of SNC meteorites, correlate with aspects of their incompatible element chemistry. Some of the oxygen isotope variability may be explained by post-magmatic alteration on Mars or Earth; however, it appears, based on petrographic and geochemical observations, that a number of SNC meteorites, especially Shergottites, retain the original whole-rock oxygen isotope values of their magmas prior to crystallisation. Correlations between oxygen isotopes and incompatible element geochemistry are consistent with assimilation of a high-18O/16O, incompatible-element rich, oxidizing crustal component by hot, mantle-derived magmas (δ18O = ~~4.2‰). A crustal component has previously been recognized from Sr-Nd-Os isotope systematics and oxygen fugacity measurements of SNC meteorites. Oxygen isotope evidence from SNC meteorites suggests high-18O/16O crustal contaminants on Mars result from low temperature (< 300°C) interaction with martian hydrosphere. The extent of apparent crustal contamination tracked by oxygen isotopes in SNC meteorites implies that the majority of martian crust may have undergone such interactions. Evidence for assimilation of

  12. Evolution of magma feeding system in Kumanodake agglutinate activity, Zao Volcano, northeastern Japan

    NASA Astrophysics Data System (ADS)

    Takebe, Yoshinori; Ban, Masao

    2015-10-01

    The Kumanodake agglutinate of Zao Volcano in northeastern Japan consists of pyroclastic surge layers accumulated during the early part of the newest stage of activity (ca. 33 ka to present). Our petrologic study of this agglutinate based on systematically collected samples aims to reveal the evolution of magma feeding system. To understand the magma evolution, we have examined samples from the agglutinate by using petrologic data including, petrography, analysis of minerals (plagioclase, pyroxene, and olivine), glass compositions, and whole rock major element and trace element (Ba, Sr, Cr, Ni, V, Rb, Zr, Nb, and Y) compositions. Agglutinate are mixed, medium-K, calc-alkaline olv-cpx-opx basaltic andesite (55.2-56.2% SiO2). Results show that the magma feeding system comprised a shallow felsic chamber injected by mafic magma from depth. The felsic magma (59-62% SiO2, 950-990 °C), which was stored at a shallower depth, had orthopyroxene (Mg# = 60-69), clinopyroxene (Mg# = 65-71), and low-An plagioclase (Anca. 58-70). The mafic magma is further divisible into two types: less-differentiated and more-differentiated, designed respectively as an initial mafic magma-1 and a second mafic magma-2. The original mafic magma-1 was olivine (Fo~ 84) basalt (ca. 48-51% SiO2, 1110-1140 °C). The second mafic magma-2, stored occasionally at 4-6 km depth, was basalt (1070-1110 °C) having Foca. 80 olivine and high-An (Anca. 90) plagioclase phenocrysts. These two magmas mixed (first mixing) to form hybrid mafic magma. The forced injections of the hybrid mafic magmas activated the felsic magma, and these two were mixed (second mixing) shortly before eruptions. The explosivity is inferred to have increased over time because the abundance of large scoria increased. Furthermore, the erupted magma composition became more mafic, which reflects increased percentage of the hybrid mafic magma involved in the second mixing. At the beginning of activity, the mafic magma also acted as a heat

  13. Crystallization of Magma. CEGS Programs Publication Number 14.

    ERIC Educational Resources Information Center

    Berry, R. W.

    Crystallization of Magma is one of a series of single-topic problem modules intended for use in undergraduate geology and earth science courses. Through problems and observations based on two sets of experiments, this module leads to an understanding of how an igneous rock can form from molten material. Environmental factors responsible for…

  14. Degassing of rhyolitic magma during ascent and emplacement

    SciTech Connect

    Westrich, H.R.; Stockman, H.W.; Eichelberger, J.

    1988-06-10

    The degassing history of a rhyolitic igneous system was documented from analyses of drill core samples through the extrusive and intrusive portions of Obsidian Dome and of surface samples of associated tephra. The initial volatile composition of the Inyo magma was estimated to be 4.0 wt % H/sub 2/O, 500 ppm F, 800 ppm Cl, and 80 ppm S. Retained volatile contents of glassy and crystalline samples reflect the effects of decompression and second boiling. Decompression is rapid and involves loss of water-rich fluid until a close approach to lithostatic equilibrium is achieved. Second boiling is a slower process and produces a chlorine-rich fluid, some of which can be trapped during development of extremely fine crystallization textures. Nearly complete dewatering during decompression of surface-extruded magma strongly undercools the system (..delta..Tapprox. =175 /sup 0/C), suppressing crystallization and yielding glassy rhyolitic lava. Partial degassing of shallowly intruded magma permits pervasive crystallization even at high cooling rates. The subvolcanic intrusive regime is the zone of maximum volatile release because second boiling is incomplete in extrusives, and volatile-bearing crystalline phases are stable in magma crystallized at greater depth. copyright Amierican Geophysical Union 1988

  15. Evaluating the Controls on Magma Ascent Rates Through Numerical Modelling

    NASA Astrophysics Data System (ADS)

    Thomas, M. E.; Neuberg, J. W.

    2015-12-01

    The estimation of the magma ascent rate is a key factor in predicting styles of volcanic activity and relies on the understanding of how strongly the ascent rate is controlled by different magmatic parameters. The ability to link potential changes in such parameters to monitoring data is an essential step to be able to use these data as a predictive tool. We present the results of a suite of conduit flow models that assess the influence of individual model parameters such as the magmatic water content, temperature or bulk magma composition on the magma flow in the conduit during an extrusive dome eruption. By systematically varying these parameters we assess their relative importance to changes in ascent rate. The results indicate that potential changes to conduit geometry and excess pressure in the magma chamber are amongst the dominant controlling variables that effect ascent rate, but the single most important parameter is the volatile content (assumed in this case as only water). Modelling this parameter across a range of reported values causes changes in the calculated ascent velocities of up to 800%, triggering fluctuations in ascent rates that span the potential threshold between effusive and explosive eruptions.

  16. Loki Patera as the Surface of a Magma Sea

    NASA Technical Reports Server (NTRS)

    Matson, D. L.; Davies, A. G.; Veeder, G. J.; Rathbun, J. A.; Johnson, T. V.

    2004-01-01

    Inspired by the finding of Schubert et al that Io's figure is consistent with a hydrostatic shape, we explore the consequences of modeling Loki Patera as the surface of a large magma sea. This model is attractive because of its sheer simplicity and its usefulness in interpreting and predicting observations. Here, we report on that work.

  17. On depressurization of volcanic magma reservoirs by passive degassing

    NASA Astrophysics Data System (ADS)

    Girona, Társilo; Costa, Fidel; Newhall, Chris; Taisne, Benoit

    2014-12-01

    Many active volcanoes around the world alternate episodes of unrest and mildly explosive eruptions with quiescent periods dominated by abundant but passive gas emissions. These are the so-called persistently degassing volcanoes, and well-known examples are Mayon (Philippines) and Etna (Italy). Here, we develop a new lumped-parameter model to investigate by how much the gas released during quiescence can decrease the pressure within persistently degassing volcanoes. Our model is driven by the gas fluxes measured with monitoring systems and takes into account the size of the conduit and reservoir, the viscoelastic response of the crust, the magma density change, the bubble exsolution and expansion at depth, and the hydraulic connectivity between reservoirs and deeper magma sources. A key new finding is that, for a vast majority of scenarios, passive degassing reduces the pressure of shallow magma reservoirs by several MPa in only a few months or years, that is, within the intereruptive timescales of persistently degassing volcanoes. Degassing-induced depressurization could be responsible for the subsidence observed at some volcanoes during quiescence (e.g., at Satsuma-Iwojima and Asama, in Japan; Masaya, in Nicaragua; and Llaima, in Chile), and could play a crucial role in the onset and development of the physical processes which may in turn culminate in new unrest episodes and eruptions. For example, degassing-induced depressurization could promote magma replenishment, induce massive and sudden gas exsolution at depth, and trigger the collapse of the crater floor and reservoir roof.

  18. Insights into high temperature tensional fracturing in silicic magma

    NASA Astrophysics Data System (ADS)

    Lamb, Oliver; Lavallée, Yan; De Angelis, Silvio; Hornby, Adrian

    2015-04-01

    During dome-forming eruptions, the rapid transition from effusive to explosive activity is a direct consequence of strain localisation in magma. A deformation mechanism map of magma subjected to strain localisation will help develop accurate numerical models, which, coupled to an understanding of the mechanics driving the monitored geophysical signals precursor to failure, will enhance eruption forecasts. Here we present our work where seismic data is combined with experimental work to give insights into high temperature tensional fracturing in magma. The seismic data is derived from multiple recent dome-forming eruptions including Unzen (Japan), Volcán de Colima (Mexico) and Mt. St. Helens (USA). For the analysis we implemented various methods to study temporal variations in seismicity, such as: automatic event detection, statistical analysis of time-series, waveform correlation, and singular value decomposition. Preliminary results have highlighted various processes during dome formation such as: sub-weekly cycles, clusters during spine extrusion, and variations in precursors to dome extrusion. In our experiments, samples from the above volcanoes were placed under tensional conditions at high temperatures and acoustic emissions were recorded. The data is analysed and compared to the natural seismic data so that constraints may be placed on the conditions of the natural seismogenic sources. Using a combination of field and experimental data promises a greater understanding of the processes affecting the rise of magma during an eruption. This will help with the challenge of forecasting and hazard mitigation during dome-forming eruptions worldwide.

  19. Geologic evidence for a magma chamber beneath Newberry Volcano, Oregon

    SciTech Connect

    Macleod, N.S.; Sherrod, D.R.

    1988-09-10

    At Newberry Volcano, central Oregon, more than 0.5 m.y. of magmatic activity, including caldera collapse and renewed caldera-filling volcanism, has created a structural and thermal chimney that channels magma ascent. Holocene rhyolitic eruptions (1) have been confined mainly within the caldera in an area 5 km in diameter, (2) have been very similar in chemical composition, phenocryst mineralogy, and eruptive style, and (3) have occurred as recently as 1300 years ago, with repose periods of 2000--3000 years between eruptions. Holocene basaltic andesite eruptions are widespread on the flanks but are excluded from the area of rhyolitic volcanism. Basaltic andesite in fissures at the edge of the rhyolite area has silicic inclusions and shows mixed basalt-rhyolite magma relations. These geologic relations and the high geothermal gradient that characterizes the lower part of a drill hole in the caldera (U.S. Geological Survey Newberry 2) indicate that a rhyolitic magma chamber has existed beneath the caldera throughout the Holocene. Its longevity probably is a result of intermittent underplating by basaltic magma.

  20. The crystal's view of upper-crustal magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.; Kent, A. J.; Huber, C.; Stelten, M. E.; Rubin, A. E.; Schrecengost, K.

    2015-12-01

    Upper-crustal magma reservoirs are important sites of magma mixing, crustal refining, and magma storage. Crystals residing in these reservoirs have been shown to represent valuable archives of the chemical and physical evolution of reservoirs, and the time scales of this evolution. This presentation addresses the question of "What do crystals "see" and record about processes within the upper crust? And how is that view similar or different between plutonic and volcanic records?" Three general observations emerge from study of the ages of crystals, combined with crystal-scale geochemical data: 1) Patterns of isotopic and trace-element data over time in zircon crystals from a given magmatic system (e.g., Yellowstone, WY, and Taupo Volcanic Zone, New Zealand) can show systematic changes in the degree of heterogeneity, consistent with extraction of melts from a long-lived (up to 100s of kyr), heterogeneous crystal mush and in some cases continued crystallization and homogenization of the magma during a short period (< a few kyr) preceding eruption. 2) Thermal histories of magma storage derived from crystal records also show that the vast majority of time recorded by major phases was spent in storage as a crystal mush, perhaps at near-solidus conditions. 3) Comparison of ages of accessory phases in both plutonic blocks and host magmas that brought them to the surface do not show a consistent relationship between the two. In some cases, zircons from plutonic blocks have age spectra much older than zircon in the host magma. In other cases, host and plutonic block zircons have similar age spectra and chemical characteristics, suggesting a closer genetic connection between the two. These observations suggest that crystals in plutonic bodies, if examined at similar spatial and temporal scales to those in volcanic rocks, would show records that are highly heterogeneous in chemistry and age on the scale of a pluton or a lobe of a pluton, but that local regions of limited

  1. Magma Plumbing and Emplacement Mechanisms within Sedimentary Basins

    NASA Astrophysics Data System (ADS)

    Schofield, Nick; Magee, Craig; Holford, Simon; Jackson, Christopher

    2013-04-01

    In recent years our understanding of sub-volcanic magmatic plumbing systems has been revolutionised by the study of hydrocarbon industry 3D seismic reflection datasets from offshore sedimentary basins. In particular, 3D seismic reflection data has provided important insights into sheet intrusion geometry and emplacement mechanisms as well as linkages and magma flow between multiple intrusions within sill-complexes. However, even high-quality 3D seismic reflection datasets have a limit to what they can resolve; thus, to allow a better understanding of detailed emplacement mechanisms and to test the validity of subsurface-based interpretations, it is critical to bridge the resolution gap that exists between seismic and outcrop datasets. Magmatic sheet (sill) intrusions contribute significantly to the upper crustal magma transport network. The emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation. Previous observations have highlighted the preponderance of brittle structures (e.g. intrusive steps and broken brides) associated with shallow-level sheet intrusions. However, recent studies have suggested that non-brittle host rock behaviour also occurs, particularly related to the formation of magma fingers during shallow-level sill intrusion. Importantly, these structures can provide insights into emplacement style and magma flow directions. Here, we examine both brittle and non-brittle intrusion mechanisms and structures using both field- and 3D seismic-based observations from a series of widespread and variable magmatic systems. Non-brittle emplacement (i.e. magma finger and lobe development) appears to be primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics. Purely brittle and non-brittle emplacement processes are found to be end members with many intrusions

  2. Extensive, water-rich magma reservoir beneath southern Montserrat

    NASA Astrophysics Data System (ADS)

    Edmonds, M.; Kohn, S. C.; Hauri, E. H.; Humphreys, M. C. S.; Cassidy, M.

    2016-05-01

    South Soufrière Hills and Soufrière Hills volcanoes are 2 km apart at the southern end of the island of Montserrat, West Indies. Their magmas are distinct geochemically, despite these volcanoes having been active contemporaneously at 131-129 ka. We use the water content of pyroxenes and melt inclusion data to reconstruct the bulk water contents of magmas and their depth of storage prior to eruption. Pyroxenes contain up to 281 ppm H2O, with significant variability between crystals and from core to rim in individual crystals. The Al content of the enstatites from Soufrière Hills Volcano (SHV) is used to constrain melt-pyroxene partitioning for H2O. The SHV enstatite cores record melt water contents of 6-9 wt%. Pyroxene and melt inclusion water concentration pairs from South Soufriere Hills basalts independently constrain pyroxene-melt partitioning of water and produces a comparable range in melt water concentrations. Melt inclusions recorded in plagioclase and in pyroxene contain up to 6.3 wt% H2O. When combined with realistic melt CO2 contents, the depth of magma storage for both volcanoes ranges from 5 to 16 km. The data are consistent with a vertically protracted crystal mush in the upper crust beneath the southern part of Montserrat which contains heterogeneous bodies of eruptible magma. The high water contents of the magmas suggest that they contain a high proportion of exsolved fluids, which has implications for the rheology of the mush and timescales for mush reorganisation prior to eruption. A depletion in water in the outer 50-100 μm of a subset of pyroxenes from pumices from a Vulcanian explosion at Soufrière Hills in 2003 is consistent with diffusive loss of hydrogen during magma ascent over 5-13 h. These timescales are similar to the mean time periods between explosions in 1997 and in 2003, raising the possibility that the driving force for this repetitive explosive behaviour lies not in the shallow system, but in the deeper parts of a vertically

  3. New multibeam mapping and geochemistry of the 30° 35° S sector, and overview, of southern Kermadec arc volcanism

    NASA Astrophysics Data System (ADS)

    Wright, I. C.; Worthington, T. J.; Gamble, J. A.

    2006-01-01

    New multibeam mapping and whole-rock geochemistry establish the first order definition of the modern submarine Kermadec arc between 30° and 35° S. Twenty-two volcanoes with basal diameters > 5 km are newly discovered or fully-mapped for the first time; Giggenbach, Macauley, Havre, Haungaroa, Kuiwai, Ngatoroirangi, Sonne, Kibblewhite and Yokosuka. For each large volcano, edifice morphology and structure, surficial deposits, lava fields, distribution of sector collapses, and lava compositions are determined. Macauley and Havre are large silicic intra-oceanic caldera complexes. For both, concentric ridges on the outer flanks are interpreted as recording mega-bedforms associated with pyroclastic density flows and edifice foundering. Other stratovolcanoes reveal complex histories, with repeated cycles of tectonically controlled construction and sector collapse, extensive basaltic flow fields, and the development of summit craters and/or small nested calderas. Combined with existing data for the southernmost arc segment, we provide an overview of the spatial distribution and magmatic heterogeneity along ˜780 km of the Kermadec arc at 30°-36°30' S. Coincident changes in arc elevation and lava composition define three volcano-tectonic segments. A central deeper segment at 32°20'-34°10' S has basement elevations of > 3200 m water-depth, and relatively simple stratovolcanoes dominated by low-K series, basalt-basaltic andesite. In contrast, the adjoining arc segments have higher basement elevations (typically < 2500 m water-depth), multi-vent volcanic centres including caldera complexes, and erupt sub-equal proportions of dacite and basalt-basaltic andesite. The association of silicic magmas with higher basement elevations (and hence thicker crust), coupled with significant inter- and intra-volcano heterogeneity of the silicic lavas, but not the mafic lavas, is interpreted as evidence for dehydration melting of the sub-arc crust. Conversely, the crust beneath the

  4. Seismic tremors and magma wagging during explosive volcanism.

    PubMed

    Jellinek, A Mark; Bercovici, David

    2011-02-24

    Volcanic tremor is a ubiquitous feature of explosive eruptions. This oscillation persists for minutes to weeks and is characterized by a remarkably narrow band of frequencies from about 0.5 Hz to 7 Hz (refs 1-4). Before major eruptions, tremor can occur in concert with increased gas flux and related ground deformation. Volcanic tremor is thus of particular value for eruption forecasting. Most models for volcanic tremor rely on specific properties of the geometry, structure and constitution of volcanic conduits as well as the gas content of the erupting magma. Because neither the initial structure nor the evolution of the magma-conduit syst