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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. Oxygen isotope geochemistry of mafic magmas at Mt. Vesuvius

    NASA Astrophysics Data System (ADS)

    Dallai, Luigi; Raffaello, Cioni; Chiara, Boschi; Claudia, D'oriano

    2010-05-01

    Pumice and scoria from different eruptive layers of Mt. Vesuvius volcanic products contain mafic minerals consisting of High-Fo olivine and Diopsidic Pyroxene. These phases were crystallized in unerupted trachibasaltic to tephritic magmas, and were brought to surface by large phonolitic/tephri-phonolitic (e.g. Avellino and Pompei) and/or of tephritic and phono-tephritic (Pollena) eruptions. A large set of these mm-sized crystals was accurately separated from selected juvenile material and measured for their chemical compositions (EPMA, Laser Ablation ICP-MS) and 18O/16O ratios (conventional laser fluorination) to constrain the nature and evolution of the primary magmas at Mt. Vesuvius. Uncontaminated mantle δ18O values are hardly recovered in Italian Quaternary magmas, mostly due to the widespread occurrence of crustal contamination of the primary melts during their ascent to the surface (e.g. Alban Hills, Ernici Mts., and Aeolian Islands). At Mt. Vesuvius, measured olivine and clinopyroxene share quite homogeneous chemical compositions (Olivine Fo 85-90 ; Diopside En 45-48, respectively), and represent phases crystallized in near primary mafic magmas. Trace element composition constrains the near primary nature of the phases. Published data on volatile content of melt inclusions hosted in these crystals reveal the coexistence of dissolved water and carbon dioxide, and a minimum trapping pressure around 200-300 MPa, suggesting that crystal growth occurred in a reservoir at about 8-10 km depth. Recently, experimental data have suggested massive carbonate assimilation (up to about 20%) to derive potassic alkali magmas from trachybasaltic melts. Accordingly, the δ18O variability and the trace element content of the studied minerals suggest possible contamination of primary melts by an O-isotope enriched, REE-poor contaminant like the limestone of Vesuvius basement. Low, nearly primitive δ18O values are observed for olivine from Pompeii eruption, although still

  3. 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

  4. Temporal changes in arc magma geochemistry, northern Sulawesi, Indonesia

    NASA Astrophysics Data System (ADS)

    Elburg, Marlina; Foden, John

    1998-11-01

    Late Miocene to recent subduction-related volcanics from the Sangihe Arc in northern Sulawesi show a pattern of geochemical change through time. The oldest of these suites have compositions that indicate that the mantle source underlying the arc has experienced a previous event of melt extraction, causing a relative depletion in incompatible elements. The geochemical signature of the subduction zone component in these volcanics implies early domination by a fluid, which was mainly derived from altered MORB. The geochemical and isotopic signature of the modern lavas, especially those from volcanic centres located furthest away from the trench, are different from those of the older lavas and indicate that the subduction zone component is now dominated by a melt of sedimentary origin. The change from a fluid-dominated to a melt-dominated subduction zone component may be related to the collision between the Halmahera and Sangihe arcs. These systematic changes appear to be superimposed upon quite variable parent magma compositions reflecting variation in mantle source composition.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  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. 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)

  16. Geochemistry and volatile content of magmas feeding explosive eruptions at Telica volcano (Nicaragua)

    NASA Astrophysics Data System (ADS)

    Robidoux, P.; Rotolo, S. G.; Aiuppa, A.; Lanzo, G.; Hauri, E. H.

    2017-07-01

    Telica volcano, in north-west Nicaragua, is a young stratovolcano of intermediate magma composition producing frequent Vulcanian to phreatic explosive eruptions. The Telica stratigraphic record also includes examples of (pre)historic sub-Plinian activity. To refine our knowledge of this very active volcano, we analyzed major element composition and volatile content of melt inclusions from some stratigraphically significant Telica tephra deposits. These include: (1) the Scoria Telica Superior (STS) deposit (2000 to 200 years Before Present; Volcanic Explosive Index, VEI, of 2-3) and (2) pyroclasts from the post-1970s eruptive cycle (1982; 2011). Based on measurements with nanoscale secondary ion mass spectrometry, olivine-hosted (forsterite [Fo] > 80) glass inclusions fall into 2 distinct clusters: a group of H2O-rich (1.8-5.2 wt%) inclusions, similar to those of nearby Cerro Negro volcano, and a second group of CO2-rich (360-1700 μg/g CO2) inclusions (Nejapa, Granada). Model calculations show that CO2 dominates the equilibrium magmatic vapor phase in the majority of the primitive inclusions (XCO2 > 0.62-0.95). CO2, sulfur (generally < 2000 μg/g) and H2O are lost to the vapor phase during deep decompression (P > 400 MPa) and early crystallization of magmas. Chlorine exhibits a wide concentration range (400-2300 μg/g) in primitive olivine-entrapped melts (likely suggesting variable source heterogeneity) and is typically enriched in the most differentiated melts (1000-3000 μg/g). Primitive, volatile-rich olivine-hosted melt inclusions (entrapment pressures, 5-15 km depth) are exclusively found in the largest-scale Telica eruptions (exemplified by STS in our study). These eruptions are thus tentatively explained as due to injection of deep CO2-rich mafic magma into the shallow crustal plumbing system. More recent (post-1970), milder (VEI 1-2) eruptions, instead, do only exhibit evidence for low-pressure (P < 50-60 MPa), volatile-poor (H2O < 0.3-1.7 wt%; CO2 < 23

  17. 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

  18. A Tale of Two Magma Series: Geochronology and Geochemistry of Volcanism on Grenada, Lesser Antilles

    NASA Astrophysics Data System (ADS)

    White, W. M.; Devine *Deceased, J. D.; Copeland, P.

    2015-12-01

    Volcanic rocks from Grenada have long been recognized to belong to two distinct magma series: the olivine microphyric M-series and the ankaramitic, calcium-rich C-series. Mafic members of both series are readily distinguished on the basis of both major and trace element compositions and radiogenic isotope ratios, with the M-series having more radiogenic Sr and Pb and less radiogenic Nd than the C-series. The two series evolve along distinct paths to compositionally and isotopically similar silica-rich hornblende andesites and dacites. We report 29 new 40Ar/39Ar dates ranging from 0.06 to 6.06 Ma, which are notably younger than previous K-Ar ages ranging up to 21 Ma, perhaps reflecting non-atmospheric inherited Ar. The two series have erupted contemporaneously and ages of both series tend to cluster in two periods: 0 to 1.7 Ma and 4.8 to 6 Ma. The oldest lavas are located in the northeastern and southwestern ends of the island. There is little or no systematic variation in chemistry with age. A dike intruding Tufton Hall Formation (THF) sediments in the south of the island is much older at 37.8 Ma; C-series isotope ratios correlate with MgO, which has previously been interpreted as a consequence of fractional crystallization and assimilation (AFC) of marine sediments. Isotope ratios of M-series lavas, in contrast, show no systematic variation with MgO. We agree that the C-series magmas have experienced AFC, but argue that the assimilant is simply the M-series products that makes up two-thirds of the mass of the island. A variety of evidence supports this interpretation. First, K2O/Na2O ratios decrease with decreasing MgO in the C-series. Second, the THF is volcanogenic likely derived from ancestral volcanoes and also are not a suitable isotopic end-member. Third, O isotope ratios in clinopyroxenes correlate with radiogenic isotope ratios, but not with MgO. Finally, the most differentiated C-series lavas are indistinguishable, isotopically and otherwise, from M

  19. Petrology and Geochemistry of the Trachyte Mesa Magma Sheets, Henry Mountains, Utah.

    NASA Astrophysics Data System (ADS)

    Matty, D. J.; Student, J. J.; Morgan, S. S.

    2006-12-01

    Trachyte Mesa (TM) is a satellite laccolithic intrusion peripheral to the Mount Hillers intrusive center in the Henry Mountains of south-central Utah. The TM outcrops are characteristically composed of plagioclase- hornblende porphyry which contain rare mafic crustal xenoliths. On the basis of geophysical evidence, Morgan and others (GSA Annual Meeting Field Guide, 2005) have suggested that the Mount Hillers center fed TM via several "magma fingers" as opposed to dikes. Moreover, on the basis of outcrop relationships, they proposed that the TM developed its laccolithic shape through inflation related to successive emplacement of several magma "sheets." Given the well-exposed nature of the TM sheets, numerous samples were collected and analyzed to evaluate geochemical characteristics and potential compositional variations within and among the sheets. Our preliminary results indicate that the analyzed sheets are compositionally classified as dacite, and fall within the range of values published by other authors for laccolithic rocks of the Henry Mountains (e.g. Nelson and Davidson, 1997). The TM samples are characterized by the following compositional ranges: SiO2=62.5-65.5%; TiO2=.44-.53%; Al2O3 =17.5-19%; Fe2O3=3.4-4.7%; MnO=.05-.15%; MgO=0.4-1.5%; CaO=4.8-7%; Na2O=3.5-4.3%; K2O=2-2.6%; P2O5=.19-.23%; Nb=4-9ppm; Zr=120-160ppm; Y=14-18ppm; Sr=650-950ppm; Rb=25-40ppm; Pb=12-25ppm; V=53-77ppm; and Ba=950-1100ppm. Within individual sheets, the observed compositional variation of major and trace elements is relatively small, with no obvious evidence of systematic geochemical change. Similarly, among various sheets, the compositional variation of most major and trace elements also appears to be small, however, our existing data do not preclude the possibility of real but subtle geochemical variations between individual sheets. At present, however, our data and observations suggest that the TM laccolith was formed from a rather homogeneous magma characterized by a lack of

  20. 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.

  1. 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.

  2. Age and geochemistry of the Newania dolomite carbonatites, India: implications for the source of primary carbonatite magma

    NASA Astrophysics Data System (ADS)

    Ray, Jyotiranjan S.; Pande, Kanchan; Bhutani, Rajneesh; Shukla, Anil D.; Rai, Vinai K.; Kumar, Alok; Awasthi, Neeraj; Smitha, R. S.; Panda, Dipak K.

    2013-12-01

    The Newania carbonatite complex of India is one of the few dolomite-dominated carbonatites of the world. Intruding into Archean basement gneisses, the rocks of the complex have undergone limited diversification and are not associated with any alkaline silicate rock. Although the magmatic nature of the complex was generally accepted, its age of emplacement had remained equivocal because of the disturbed nature of radioisotope systems. Many questions about the nature of its mantle source and mode of origin had remained unanswered because of lack of geochemical and isotopic data. Here, we present results of our effort to date the complex using 147Sm-143Nd, 207Pb-206Pb and 40Ar-39Ar dating techniques. We also present mineral chemistry, major and trace element geochemistry and Sr-Nd isotopic ratio data for these carbonatites. Our age data reveal that the complex was emplaced at ~1,473 Ma and parts of it were affected by a thermal event at ~904 Ma. The older 207Pb-206Pb ages reported here (~2.4 Ga) and by one earlier study (~2.3 Ga; Schleicher et al. Chem Geol 140:261-273, 1997) are deemed to be a result of heterogeneous incorporation of crustal Pb during the post-emplacement thermal event. The thermal event had little effect on many magmatic signatures of these rocks, such as its dolomite-magnesite-ankerite-Cr-rich magnetite-magnesio-arfvedsonite-pyrochlore assemblage, mantle like δ13C and δ18O and typical carbonatitic trace element patterns. Newania carbonatites show fractional crystallization trend from high-Mg to high-Fe through high-Ca compositions. The least fractionated dolomite carbonatites of the complex possess very high Mg# (≥80) and have similar major element oxide contents as that of primary carbonatite melts experimentally produced from peridotitic sources. In addition, lower rare earth element (and higher Sr) contents than a typical calcio-carbonatite and mantle like Nb/Ta ratios indicate that the primary magma for the complex was a magnesio

  3. Geochemistry and degassing systematics of silicate magma at Ol Doinyo Lengai, Tanzania

    NASA Astrophysics Data System (ADS)

    de Moor, J.; Fischer, T. P.; King, P. L.; Hilton, D. R.; Sharp, Z. D.; Barry, P. H.; Ramirez, C.; Mangasini, F.

    2009-12-01

    Ol Doinyo Lengai (OL) volcano is unique in that it produces natro-carbonatite lavas. However, every ~25 years the volcano explosively erupts nephelinitic ash. OL entered an explosive phase in September 2007, which lasted until November 2008, and carbonatite activity resumed early in 2009. This study assesses the composition of the 2007-2009 eruptive products and volatiles to characterize degassing and magmatic processes during the explosive eruption. Ash samples collected in 2008 and 2009 are extremely crystal-rich with scarce scoria. Bulk compositions show that the ash is dominated by alkali- and volatile-rich silicate ash with a secondary carbonatite component (SiO2 37.3%, CO3 4.3%, MgO 1.8%, CaO 15.4%, Na2O 11.2%, K2O 3.5%, S 0.14%, Cl 0.20%). Electron microprobe analyses of vesicular scoria show that the matrix glass (SiO2 41.0%, Na22 but enriched in incompatible elements compared to nepheline-hosted glass inclusions (SiO2 43.2%, Na2O 15.8%). S correlates positively with Cl and F in nepheline-hosted glass inclusions (S 0.2-0.4%, Cl 0.3-0.5%, F 0.3-0.8%) showing that these species behaved incompatibly and were not saturated in the parental melt. Matrix glass extends to higher S concentrations (up to 0.7%) at relatively constant Cl and F (Cl ~0.5%, F ~0.7%) resulting in increasing S/Cl and S/F in the residual melt. This is interpreted to reflect Cl and F saturation in the melt due to further crystallization and partitioning of these species into the gas phase while S was undersaturated. Reflectance FTIR shows that the matrix glass has no detectible H2O and ~3% CO2. Glass inclusions have <1.8% H2O based on a calibration for basaltic glasses [1] and up to 7.5% CO2. The OL magma was therefore initially H2O-poor and CO2-rich and degassed <1.8% H2O and <4.5% CO2 between glass inclusion entrapment and eruption. The average S isotope composition of juvenile rock products is -0.7‰ (vs. CDT), which is MORB-like [2]. The ratio of H2S/SO2 in fumarolic gases is ~26, with

  4. Evolution of the Youngest Toba Tuff magma reservoir as recorded by Zircon Geochemistry and Crystallization Temperatures

    NASA Astrophysics Data System (ADS)

    Gaither, T.; Reid, M. R.

    2010-12-01

    The ~74 ka eruption of the Youngest Toba Tuff (YTT) in Sumatra, Indonesia, was one of the largest single volcanic eruptions in geologic history. We are exploring the compositional and thermal evolution of the magma reservoir prior to eruption through spatially-sensitive analyses of the trace element characteristics of zircon. Stepwise serial sectioning of rims and interior domains (ID=5 µm below the rim) was performed on forty-four zircons from pumices with a compositional range of 70-76 wt% SiO2. These rims and IDs were analyzed on the UCLA Cameca ims 1270 ion microprobe. Both rims and IDs from individual pumices exhibit a range in Zr/Hf ratios indicative of growth from melts variously affected by zircon fractionation; zircons from the high silica rhyolite did, however, crystallize from more evolved melts. Eu/Eu*, Nd/Yb, and Th/U decrease with decreasing Zr, showing that the variation in zircon compositions may be related by co-precipitation of feldspar and allanite along with zircon, throughout the growth history represented by the interior to rim chemistry. Titanium contents also decrease with decreasing Zr/Hf, suggesting that crystallization was driven by magma cooling. There is no apparent trend from compositionally homogeneous interiors to more rim diverse compositions prior to eruption, contrary to what is observed for Toba allanite (Vazquez and Reid, 2004): compositional variability for the IDs is similar to that for the rims. It is possible that not all Toba allanite and zircon populations co-crystallized, given zircon crystallizion in compositionally diverse domains throughout a significant part of their growth. Rim-ID pairs provide evidence of both normal and reverse zoning within individual crystals, with more than half of the zircons from each pumice sample being normally zoned. Temperatures of crystallization calculated using the Ti-in-zircon geothermometer (Watson et al., 1996), assuming a melt aTiO2 of 0.5, yield median temperatures for zircon rims

  5. Geochemistry of the Kalkarindji Magmas: Insights into the Source of the Oldest Phanerozoic Large Igneous Province

    NASA Astrophysics Data System (ADS)

    Ware, B. D.; Jourdan, F.; Hodges, K.; Tessalina, S.; Chiaradia, M.; Evins, L.; Gole, M.

    2014-12-01

    The Kalkarindji continental flood basalt province (CFBP) of northern Australia is the oldest Phanerozoic large igneous province (LIP) in the world. The extent of this Middle Cambrian LIP has been estimated to at least 2.1 x 106 km2 with exposures in Western Australia, Northern Territory, Queensland, and South Australia. The research into Kalkarindji is still in its infancy with only a handful of studies published. The rocks of the Kalkarindji province occur as lava flows, sills, dykes, and volcanic tuffs. Kalkarindji has been linked to an extinction event at the Early-Middle Cambrian boundary. The Kalkarindji province displays Low-Ti values and high SiO2 values compared to other large igneous provinces, enriched 87Sr/86Sr values, and low 187Os/188Os. This project presents a large data set of new geochemical analyses of the various constituents of the Kalkarindji CFBP. Source mixing calculations, assimilation and fractionation models, coupled with Monte Carlo simulations were carried out to understand the petrogenesis of the province. The trace element and 87Sr/86Sr values indicate a contribution of enriched crustal-like material into the source region; however, the Os values fall into typical mantle ranges. These geochemical patterns suggest that the mantle source(s) of the Kalkarindji CFBP has been directly enriched at some stage of history, before the emplacement of the province. This study will provide further insights into the magma source and origin processes needed to create one of the world's largest and oldest Phanerozoic large igneous provinces.

  6. The 1669 eruption at Mount Etna: chronology, petrology and geochemistry, with inferences on the magma sources and ascent mechanisms

    NASA Astrophysics Data System (ADS)

    Corsaro, Rosa Anna; Cristofolini, Renato; Patanè, Loredana

    1996-12-01

    Analysis of the petrochemical characters of the 1669 Etnean lavas shows that they can be grouped into two sets: SET1 lavas were erupted from 11 to 20 March and are more primitive in composition than SET2, erupted later until the end of activity. Both sets may be interpreted as the result of crystallization under different conditions of two primary magmas which are compositionally slightly distinct and which fractionate different volumetric proportions of minerals. To explain why more mafic lavas (SET1) were erupted earlier than more acid ones (SET2), we argue that new deeper magma rose up into a reservoir where residing magma was fractionating. Density calculations demonstrate that new magma is less dense and may originate a plume, rapidly rising through the residing magma which is cooler and more volatile-depleted than the new magma. Calculations of uprise velocity assuming laminar flow are consistent with this hypothesis.

  7. 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

  8. On the magma chamber characteristics as inferred from surface geology and geochemistry: examples from Mexican geothermal areas

    NASA Astrophysics Data System (ADS)

    Verma, Surendra P.

    1985-12-01

    A procedure is described which enables us to obtain estimates of some physical and chemical characteristics of sub-surface magma chambers. This is applied to three geothermal areas of the Mexican Volcanic Belt (MVB) in central Mexico. The approximate volumes estimated for the underlying chemically and thermally zoned magma chambers are: 1500 km 3 for Los Humeros, 600 km 3 for La Primavera, and 400 km 3 for Los Azufres. These estimates will have to be modified as more geological-geochemical data become available.

  9. 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

  10. 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.

  11. 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

  12. 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, Thomas W.; Nakano, Natsuko; Coombs, Michelle L.; Lipman, Peter 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

  13. Geochemistry and Temperatures Recorded by Zircon During the Final Stages of the Youngest Toba Tuff Magma Chamber, Sumatra, Indonesia

    NASA Astrophysics Data System (ADS)

    Gaither, T.; Reid, M. R.; Vazquez, J. A.

    2009-12-01

    The ~74 ka eruption of the Youngest Toba Tuff (YTT) in Sumatra, Indonesia, was one of the largest single volcanic eruptions in geologic history, on par with other voluminous silicic eruptions such as the Huckleberry Ridge Tuff of Yellowstone and the Bishop Tuff of Long Valley, California. We are exploring how zircon and other accessory mineral phases record compositional and thermal changes that occurred in the YTT magma, and the important clues these crystal scale records hold for magma chamber dynamics and processes that lead up to supervolcano eruptions. In this study, we report trace element (REE, U, Th, Ti, and Hf) characteristics, Ti-in-zircon crystallization temperatures, and apparent REE partition coefficients obtained for YTT zircon rims. Twenty-nine zircons from pumices with a compositional range of 70-76 wt% SiO2 were analyzed on the UCLA Cameca ims 1270 ion microprobe. The grains were mounted so that only the outermost ~1.5 microns of the crystals were analyzed. Median Zr/Hf ratios of 34 to 38 characterize zircons from the pumices; the high silica rhyolite grains have lower Zr/Hf. Chondrite-normalized REE patterns are strongly LREE-depleted. Positive Ce anomalies are large (Ce/Ce* ranges up to 88) and Eu/Eu* varies by a factor of four (0.05 to 0.21). Eu/Eu*, Nd/Yb, and Th/U decrease with decreasing Zr/Hf, showing that the variation in zircon rim compositions may be related by co-precipitation of feldspar and allanite along with zircon. Titanium contents also decrease with decreasing Zr/Hf, suggesting that the chemical differences could be related to temperature changes. REE partition coefficients calculated from zircon rim compositions and pumice glass compositions give a good fit to a lattice strain model. They are also quite similar to the partition coefficients of Sano et al. (2002) which have been shown to be successful at reproducing melt compositions in other settings. Temperatures of crystallization calculated using the Ti

  14. 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

  15. 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.

  16. 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.

  17. Geochemistry of hypabyssal kimberlites from Lac de Gras, Canada: Comparisons to a global database and applications to the parent magma problem

    NASA Astrophysics Data System (ADS)

    Kjarsgaard, B. A.; Pearson, D. G.; Tappe, S.; Nowell, G. M.; Dowall, D. P.

    2009-11-01

    We present 104 whole-rock geochemical analyses of hypabyssal kimberlite from the Lac de Gras field. Screens using Yb versus Al 2O 3 and ln Si/Al versus ln Mg/Yb effectively discriminate crustally contaminated samples. The remaining "non-contaminated" kimberlites samples have variable (5 to 50%) entrainment of cratonic peridotite. It is problematic to effectively screen for small amounts (< 5%) of digested crust in samples with higher (> 20%) contents of peridotite contamination. We utilize the Lac de Gras data suite to calculate, by two different methods, parent magma compositions and identify two (and potentially three) geochemically distinct parent magma types. The Lac de Gras parent magma compositions are compared to those calculated from other localities in Canada, Greenland, South Africa and Russia. Together, these calculated parent magmas define a range, albeit limited, of viable, yet distinct, kimberlite parent magma compositions. Geochemically, kimberlite parent magmas have high volatile contents (H 2O and CO 2), high MgO, and low SiO 2, Al 2O 3 and alkalis, with K > Na and Na + K/Al < 1. It is difficult to reconcile differences between various calculated kimberlite parent magma compositions from different cratonic areas as merely due to the effects of craton specific lithospheric mantle contamination, indicating the intra- and inter-cratonic variation of parent magma compositions reflect differing source region characteristics and/or partial melting regimes.

  18. Tephra sequences as indicators of magma evolution: 40Ar/ 39Ar ages and geochemistry of tephra sequences in the southwest Nevada volcanic field

    NASA Astrophysics Data System (ADS)

    Huysken, K. T.; Vogel, T. A.; Layer, P. W.

    2001-04-01

    Changes in rock chemistry with 40Ar/ 39Ar ages in tephra layers record the temporal and magmatic history of two volcanic systems in southwestern Nevada. Tephra layers from the Post-Grouse Canyon tephra sequence record three distinct groups. These groups are chemically distinct and have 40Ar/ 39Ar ages of 13.52±0.06, 13.31±0.18, and 12.95±0.10 Ma. The age groups correspond to three distinct chemical groups based on trace element distributions. These chemical groups cannot be related by any reasonable fractional crystallization or magma mixing model and are interpreted as distinct magma batches. The Pre-Rainier Mesa tephra sequence records two 40Ar/ 39Ar ages (12.79±0.10 and 11.84±0.18 Ma). The upper portion of this sequence is equivalent in age and chemistry to part of the overlying Rainier Mesa ash-flow sheet. The lower portion of the sequence is equivalent in age to the underlying Tiva Canyon ash-flow sheet but is chemically distinct from this sheet. The formation of this chemical group is consistent with mixing of low silica Tiva Canyon and high silica, low Th, Rainier Mesa magma. Post-Grouse Canyon magmas were most likely emplaced as a series of small, unrelated magma bodies, which allowed them to evolve independently. The mixed Pre-Rainier Mesa magma was produced by infilling of the Tiva Canyon magma chamber with Rainier Mesa-like magma after eruption of the Tiva Canyon ash-flow sheet at approximately 12.8 Ma. The upper portion of the Pre-Rainier Mesa tephra sequence represents eruption of Rainier Mesa magma less than 0.3 My. before that of the voluminous (1200 km 3) Rainier Mesa ash-flow sheet at approximately 11.71 Ma.

  19. The Complex Geochemistry of Magma Bodies Undergoing Open-System Processes: Energy-Constrained Recharge, Assimilation and Fractional Crystallization (EC-RAFC)

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

    A new version of the energy-constrained simulator tracks the thermal and geochemical evolution of a magma body undergoing the processes of magma recharge, assimilation, and fractional crystallization (EC-RAFC). The conceptual framework is presented in a companion abstract (Spera and Bohrson, this issue). The EC-RAFC model tracks trace element and isotopic trends of a magma body (melt + solids) undergoing fractional crystallization and continuous or episodic magma recharge; assimilation may or may not occur. EC-RAFC yields complex, distinctly non-monotonic element-element and element-isotope trends that are a consequence of the nonlinear, coupled nature of the processes that influence the system. Among the plethora of petrologic problems that can be investigated with this simulator are the geochemical distinctions that arise when a magma body undergoes continuous vs. episodic recharge, the connection between erupted magmas and associated cumulate bodies, the geochemical fingerprints of mafic enclaves that form as a consequence of mafic recharge into a more silicic magma body, and the conditions under which magmatic systems reach chemical "steady-state." All of these have important, well-documented analogues in nature and thus, the ability to predict associated geochemical signatures affords the opportunity to begin to discriminate among the many physiochemical and tectonomagmatic models involving complex magmatic systems. Investigation of the effects of continuous vs. episodic recharge for an initially mafic magma undergoing assimilation and recharge in the lower crust indicates that the resulting geochemical trends for melt and solids are highly sensitive to the style of recharge. Geochemical differences in systems experiencing episodic vs. continuous recharge can be well outside analytical uncertainty, suggesting that EC-RAFC represents a tool that can directly link volcanological and geochemical models of magmatic systems. EC-RAFC also predicts complex

  20. Petrology and geochemistry of ca. 2100-1000 a.B.P. magmas of Augustine volcano, Alaska, based on analysis of prehistoric pumiceous tephra

    NASA Astrophysics Data System (ADS)

    Tappen, Christine M.; Webster, James D.; Mandeville, Charles W.; Roderick, David

    2009-05-01

    Geochemical and textural features of whole-rock samples, phenocrysts, matrix glasses, and silicate melt inclusions from five prehistoric pumiceous tephra units of Augustine volcano, Alaska, were investigated to interpret processes of magma storage and evolution. The bulk-rock compositions of the tephra (designated G, erupted ca. 2100 a.B.P.; I ca. 1700 a.B.P.; H ca. 1400 a.B.P.; and C1 and C2 ca. 1000 a.B.P.) are silicic andesite; they contain rhyolitic matrix glasses and silicate melt inclusions with 74-79 wt.% SiO 2. The rocks are comprised of microlite-bearing matrix glass and phenocrysts of plagioclase, orthopyroxene, clinopyroxene, magnesio-hornblende, titanomagnetite, and ilmenite ± Al-rich amphibole with minor to trace apatite and rare sulfides and quartz. The felsic melt inclusions in plagioclase, pyroxenes, and amphibole are variably enriched in volatile components and contain 1.6-8.0 wt.% H 2O, 2100-5400 ppm Cl, < 40-1330 ppm CO 2, and 30-390 ppm S. Constraints from Fe-Ti oxides imply that magma evolution occurred at 796 ± 6 °C to 896 ± 8 °C and log ƒ O2 of NNO + 2.2 to + 2.6. This is consistent with conditions recorded for 1976, 1986, and 2006 eruptive materials and implies that magmatic and eruptive processes have varied little during the past 2100 years. Prehistoric Augustine magmas represented by these silicic andesites evolved via fractional crystallization, magma mingling and mixing, and/or chemical contamination due to magma-volcanic rock interaction. The occurrence of fractional crystallization is supported by the abundance of normally zoned phenocrysts, the presence of felsic matrix glass and melt inclusions within andesitic rock samples, trace-element data, and by geochemical modeling. The modeling constrains the influence of crystal fractionation on melt differentiation and is consistent with the evolution of the melt phase from felsic andesite to rhyodacite compositions. Magma mixing, mingling, and/or contamination by magma-volcanic rock

  1. Volatile Abundances and Magma Geochemistry of Recent (2006) Through Ancient Eruptions (Less Than 2100 aBP) of Augustine Volcano, Alaska

    NASA Astrophysics Data System (ADS)

    Webster, J. D.; Mandeville, C. W.; Gerard, T.; Goldoff, B.; Coombs, M. L.

    2006-12-01

    Augustine Volcano, Cook Inlet, Alaska, is a subduction-related Aleutian arc volcano located approximately 275 km southwest of Anchorage. During the past 200 years, Augustine volcano has shown explosive eruptive behavior seven times, with the most recent activity occurring in January through March 2006. Its ash and pumice eruptions pose a threat to commercial air traffic, the local fishing industry, and the inhabitants of the region. Following prior investigations on volatile abundances and processes of evolution for magmas associated with the 1976 (Johnston, 1978) and 1986 (Roman et al., 2005) eruptions of Augustine, we have analyzed phenocrysts, matrix glasses, and silicate melt inclusions in andesites formed during 5 pre-historic eruptions (ranging from 2100 to 1000 years in age) as well as the 1986 and recent 2006 eruptions. Outcrops of basaltic units on Augustine are rare, and basaltic melt inclusions are as well, so most melt inclusions studied range from andesitic to rhyolitic compositions. Comparison of the volatile abundances in felsic melt inclusion glasses shows few differences in H2O, CO2, S, and Cl, respectively, between eruptive materials of the pre- historic, 1976 (Johnston, 1978), and 1986 (Roman et al., 2005; our data) events. The magmas associated with these eruptions contained 1.6 to 8.0 wt.% H2O with 0.21 to 0.84 wt.% Cl, 100 to 1800 ppm CO2, and 100 to 400 ppm S. In contrast, preliminary research on rhyodacitic to rhyolitic melt inclusions in a single 2006 andesite sample collected from a lahar deposit indicates they contain somewhat lower H2O contents and higher Cl and S abundances than felsic melt inclusions from prior eruptions, and they exhibit geochemical trends consonant with magma mixing. Relationships involving H2O, CO2, S, and Cl in prehistoric through 1986 melt inclusions are consistent with fluid-saturated magma evolution of andesitic to rhyolitic melt compositions during closed-system ascent. The various batches of magma rose through

  2. 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

  3. Kimberlites: Magmas or mixtures?

    NASA Astrophysics Data System (ADS)

    Patterson, Michael; Francis, Don; McCandless, Tom

    2009-11-01

    Although the presence of xenocrystic olivine is widely recognized in kimberlite, there is little consensus about its contribution to the existing estimates for the composition of kimberlite magma. Whole rock geochemistry is critical to the debate regarding the composition of kimberlite magma, however, it has received little attention as an indicator of diamond grade due to conventional thought that diamonds are xenocrysts unrelated to their host kimberlite. The Foxtrot kimberlite Field in Northern Québec is comprised of at least three distinct kimberlite intrusions exhibiting variation in both diamond grade and geochemistry making it an ideal suite with which to test a possible correlation between diamond grade and whole rock composition. Olivine is ubiquitous (30 to 70%) in the Foxtrot kimberlites and exhibits a restricted composition that overlaps that of olivine in harzburgite xenoliths suggesting that the majority of olivine is xenocrystic. Carbonate is also abundant (8 to 35%) in the Foxtrot kimberlites and exhibits magmatic textures requiring that carbon be considered in any petrogenetic model for the Foxtrot kimberlites. Pearce element ratio analysis assuming P as a conserved element indicates that much of the major element variation in the Foxtrot kimberlites can be explained by variable amounts of olivine and orthopyroxene in proportions (~ 80/20), similar to that of cratonic mantle xenoliths. The xenocrystic nature of olivine requires that the contribution of mantle harzburgite must be removed to constrain the composition of the magma. The calculated magma composition that results from the mathematical removal of olivine and orthopyroxene (80/20) from the whole rock compositions is significantly poorer in MgO (15 wt.%) and silica (~ 24 wt.%), but CO 2 rich (~ 17 wt.%) compared to previous estimates for kimberlite magma. The Foxtrot kimberlites are best modelled as mixtures of harzburgite mantle and a relatively carbonate-rich magma. According to this

  4. Unraveling the complex magma dynamics during the Eyjafjallajökull 2010 eruption by high-resolution geochemistry of volcanic ash

    NASA Astrophysics Data System (ADS)

    Laeger, K.; Petrelli, M.; Andronico, D.; Misiti, V.; Scarlato, P.; Cimarelli, C.; Taddeucci, J.; Perugini, D.

    2016-12-01

    The April-May 2010 eruption of Eyjafjallajökull (Iceland) volcano was characterized by a change in eruptive style and a large compositional variability of erupted products. Lava deposits of the initial phase consist of evolved Fe-Ti-basalt ( 47 wt% SiO2), whereas fallout deposits of the explosive phases are characterized by a wider compositional spread. We present new EMPA and LA-ICP-MS analyses on groundmass glasses of ash particles erupted between May 18th and 22nd in 2010, i.e. the last days of the eruption. The glasses define two well-separated groups; a basalt composition ranging from 49.98 to 51.76wt% SiO2 and a second group of trachyandesitic and rhyolitic compositions between 57.13 and 70.38 wt% SiO2. Introduction of basalt to a resident silicic melt increased that compositional diversity in the chamber. The ash particles contain plagioclase (An81-10), clinopyroxene (Mg#=0.44-0.71), olivine (Fo83-42) and magnetite. Several plagioclase and clinopyroxene crystals exhibit resorbed cores and rims suggesting disequilibrium caused by recharge of a hotter magma. Additionally, certain clinopyroxene reveals reverse zoning (core: Mg# = 0.53-0.60, rim: Mg# = 0.59-0.71) what can be taken as evidence for mixing between a younger, less evolved magma, and one with a more evolved composition. Here, we unravel the genesis of the compositional variance using petrological, mineralogical and geochemical implications. Magma mixing modeling and element concentration frequency diagrams indicate that incomplete magma mixing between a trachyandesite magma and a trachyte-rhyolite component is the probable main process forming the great compositional variability observed in the erupted products. The rhyolite composition probably represents the residual melt of the AD 1821-23 eruption of Eyjafjallajökull. We suggest that different magmas generated and emplaced separately prior to the eruption have been mobilized by a new intrusion in 2010, and have mingled and mixed with each other

  5. 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

  6. Geochemistry and petrogenesis of extension-related magmas close to the volcanic front of the central part of the Trans-Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Verma, Surendra P.; Torres-Sánchez, Darío; Velasco-Tapia, Fernando; Subramanyam, K. S. V.; Manikyamba, C.; Bhutani, Rajneesh

    2016-12-01

    New geochemical data for 23 samples from the Sierra de Chichinautzin (SCN) and Sierra Santa Catarina (SSC) located at the volcanic front of the central part of the Trans-Mexican Volcanic Belt were combined with the published data on 580 samples from the SCN to explore the origin and evolution of the Quaternary trachybasalt and basalt to andesite and dacite. The rare-earth element concentrations for the evolved intermediate and acid rocks are lower than those for the more basic varieties, implying that the evolved magmas cannot be generated by a simple fractional crystallisation process without crustal assimilation. The size of the Nb and Ta negative anomalies increases from basic to acid, which is similar to the behaviour of most continental rifts and extension-related areas, but contrasts from all island and continental arcs. The multidimensional tectonomagmatic diagrams indicate a continental rift setting from basic and alkaline intermediate magmas. The SSC represents a new site of within-plate alkaline magmas discovered in this work, which complements the earlier interpretation of the adjacent SCN as a manifestation of continental rift or extension-related magmatism.

  7. 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

  8. 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

  9. Periodic input of primitive magmas in a complex plumbing system revealed by noble gas geochemistry: the case of Mt Etna (Italy)

    NASA Astrophysics Data System (ADS)

    Paonita, Antonio; Caracausi, Antonio; Martelli, Mauro; Rizzo, Andrea

    2015-04-01

    A long-term series of noble gas compositions (He and Ar isotope abundances plus elemental Ne) coming from geochemical monitoring of five peripheral gas emissions at the base of Mt Etna, integrated by some fumaroles located in the rim of the summit crater, have allowed to put constraints on the magmatic system feeding the volcano. The peripheral gas emissions seem to be released by magmatic degassing occurring at depths of 200-400 MPa, while the crater fumaroles receive contributes coming from magmas residing at shallower levels (up to 130 MPa), which mix to the fluids from the deep levels. These estimations are in good agreement with the depth of the two main magma ponding zones (i.e., 5-12 km and 2-3 km b.s.l.) inferred by petrological and geophysical studies. The long-term monitoring of 3He/4He ratios from both peripheral and crater gases has allowed us to recognize phases of increase of the isotope ratios, occurred at all the sampled emissions some months before the onset of eruptive activities. This behaviour has been systematic for all the main eruptive phases occurred at Mt Etna since 2001 (i.e., 2001, 2002-2003, 2006, 2008-2009, 2011-2012, 2013, and 2014, except for the 2004-2005 eruption), making this parameter a very powerful tool in evaluating the activity level of the volcano and in eruption forecast. A detailed investigation of the 3He/4He time series displays that there is no defined time gap between the isotope ratio increase and the onset of the eruptive activity, this interval ranging from one to several months. After examination of shape and duration of the isotope increases versus main features of the eruptive events (e.g. duration, amount of erupted material, eruption rate), no systematic relationships emerge. It seems only that the rate of 3He/4He increase was anomalously high (by almost 10 times) during the only two eccentric eruptions since 2001 (i.e., 2001 and 2002-2003). The differences among He isotopic composition between the peripheral

  10. 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

  11. Chalcophile element geochemistry and petrogenesis of high-Ti and low-Ti magmas in the Permian Emeishan large igneous province, SW China

    NASA Astrophysics Data System (ADS)

    Wang, Christina Yan; Zhou, Mei-Fu; Qi, Liang

    2011-02-01

    Sulfide-poor mafic layered intrusions, sills/dykes and lava flows in the Funing region, SW China, are part of the ~260 Ma Emeishan large igneous province. They belong to either a high-Ti group (TiO2 = 1.6-4.4 wt%) with elevated Ti/Y ratios (351-1,018), or a low-Ti group (TiO2 < 1.2 wt%) with low Ti/Y ratios (133-223). This study investigates the role of fractionation of olivine, chromite and sulfide on the distributions of chalcophile elements, Ni, Cu and PGE, of the high-Ti and low-Ti group rocks at Funing. The high-Ti group rocks contain 1.6-5.3 ppb Pt + Pd, 0.06-0.43 ppb Ir and 0.01-0.13 ppb Ru, and show relative constant (Cu/Pd)PM ratios (4.0-9.7) and a negative correlation between Ni/Pd and Cu/Ir ratios. Fractionated IPGE/PPGE patterns and very negative Ru anomalies of the high-Ti group rocks, together with low Fo values (59-62 mol%) of olivine, indicate that the high-Ti magmas may have experienced fractionation of olivine and chromite under S-undersaturated condition. Based on the PGE concentrations, the low-Ti group rocks can be further divided into two subgroups; a high-PGE low-Ti subgroup and a low-PGE low-Ti subgroup. The high-PGE low-Ti group rocks are rich in MgO (10-20 wt%), but Fo values of olivine from the rocks are low (74-76 mol%). The rocks contain highly variable PGE (Pt + Pd = 1.7-88 ppb, Ir = 0.05-1.3 ppb), Ni (179 -1,380 ppm) and Cu (59-568 ppm). They have Cu/Zr ratios >1, low (Y/Pd)PM ratios (0.2-7.1) and nearly constant (Cu/Pd)PM ratios (1.5-3.8). The even and parallel chalcophile element patterns of the high-PGE low-Ti subgroup rocks are likely a result of olivine-dominated fractionation under S-undersaturated condition. The low-PGE low-Ti group rocks have low MgO (4.5-8.9 wt%) and very poor PGE (Pt + Pd 0.5-1.6 ppb, Ir 0.004-0.02 ppb) with low Cu/Zr ratios (0.1-0.5), high (Y/Pd)PM (26-70) and variable (Cu/Pd)PM ratios (2.8-14). The trough-like chalcophile element patterns of the low-PGE low-Ti subgroup rocks indicate that the magmas were

  12. 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.

  13. Late Archaean crust-mantle interactions: geochemistry of LREE-enriched mantle derived magmas. Example of the Closepet batholith, southern India

    NASA Astrophysics Data System (ADS)

    Jayananda, M.; Martin, H.; Peucat, J.-J.; Mahabaleswar, B.

    1995-03-01

    The Closepet batholith in South India is generally considered as a typical crustal granite emplaced 2.5 Ga ago and derived through partial melting of the surrounding Peninsular Gneisses (3.3 to 3.0 Ga). In the field, it appears as a composite batholith made up of at least two groups of intrusions. (a) An early SiO2-poor group (clinopyroxene quartz-monzonite and porphyritic phyritic monzogranite) is located in the central part of the batholith. These rocks display a narrow range in both initial 87Sr/86Sr (0.7017 0.7035) and ɛNd(-0.9to -4.1). (b) A later SiO2-rich group (equigranular grey and pink granites) is located along the interface between the SiO2-poor group and the Peninsular Gneisses. They progressively grade into migmatised Peninsular Gneisses, thus indicating their anatectic derivation. Their isotopic characteristics vary over a wide range (87Sr/86Sr ratios=0.7028 0.7336 and ɛNd values from-2.7 to-8.3, at 2.52 Ga). Field and geochronological evidence shows that the two groups are broadly contemporaneous (2.518 2.513 Ga) and mechanically mixed. This observation is supported by the chemical data that display well defined mixing trends in the ɛSr vs ɛNd and elemental variation diagrams. The continuous chemical variation of the two magmatic bodies is interpreted in terms of interaction and mixing of two unrelated end-members derived from different source regions (enriched peridotitic mantle and Peninsular Gneisses). It is proposed that the intrusion of mantle-derived magmas into mid-crustal levels occurred along a transcurrent shear zone; these magmas supplied additional heat and fluids that initiated anatexis of the surrounding crust. During this event, large-scale mixing occurred between mantle and crustal melts, thus generating the composite Closepet batholith. The mantle-derived magmatism is clearly associated with granulite facies metamorphism 2.51±0.01 Ga ago. Both are interpreted as resulting from a major crustal accretion event, possibly related

  14. 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

  15. 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.

  16. Lithosphere Response to Intracratonic Rifting: Examples from Europe and Siberia

    NASA Astrophysics Data System (ADS)

    Artemieva, I. M.; Thybo, H.; Herceg, M.; Cherepanova, Y. V.; Chemia, Z.; Cammarano, F.

    2012-12-01

    Several cratons have experienced a significant modification of their crustal and mantle lithosphere structure during Phanerozoic large-scale lithosphere-mantle interactions. In Eurasia, the most prominent examples include the Dniepre-Donets rift in the East European craton, the Oslo graben in the Baltic shield, the Viluy rift and the Baikal rift in Siberia. Despite some similarities, mostly in the crustal structure, there are also significant differences in the lithospheric structure of these rifts. Besides, a large lithosphere-scale Riphean suture/rift runs across the East European craton. While this suture can be recognized in the crustal structure, it is not clearly seen in the structure of the lithospheric mantle. In contrast, Phanerozoic processes associated with emplacement of large magma volumes had a strong effect on modification of the lithosphere structure, primarily by infiltration of basaltic magmas and consequently in a change in mantle density and seismic velocities. Although kimberlite magmatism is commonly not considered as a rifting events, its deep causes may be similar to the mantle-driven rifting and, as a consequence, modification of mantle density and velocity structure may also be expected. We present a new model for the structure of the crust in an area that encompasses the East European craton, the West Siberian basin, and the Siberian cratons. The region includes a nearly continuous age record for lithosphere evolution over ca. 3.6-3.8 billion years. The crustal model is based on critically assessed results from various seismic studies, including reflection and refraction profiles and receiver function studies. We also use global shear-wave tomography models, gravity constraints based on GOCE data, and thermal models for the lithosphere to speculate on thermo-chemical heterogeneity of the mantle. An analysis of the lithosphere structural heterogeneity is presented in relation to geotectonic setting and mantle geodynamics based on

  17. 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

  18. Warm storage for arc magmas.

    PubMed

    Barboni, Mélanie; Boehnke, Patrick; Schmitt, Axel K; Harrison, T Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2016-12-06

    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the "cold storage" model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

  19. Warm storage for arc magmas

    PubMed Central

    Barboni, Mélanie; Schmitt, Axel K.; Harrison, T. Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2016-01-01

    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the “cold storage” model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes. PMID:27799558

  20. Warm storage for arc magmas

    NASA Astrophysics Data System (ADS)

    Barboni, Mélanie; Boehnke, Patrick; Schmitt, Axel K.; Harrison, T. Mark; Shane, Phil; Bouvier, Anne-Sophie; Baumgartner, Lukas

    2016-12-01

    Felsic magmatic systems represent the vast majority of volcanic activity that poses a threat to human life. The tempo and magnitude of these eruptions depends on the physical conditions under which magmas are retained within the crust. Recently the case has been made that volcanic reservoirs are rarely molten and only capable of eruption for durations as brief as 1,000 years following magma recharge. If the “cold storage” model is generally applicable, then geophysical detection of melt beneath volcanoes is likely a sign of imminent eruption. However, some arc volcanic centers have been active for tens of thousands of years and show evidence for the continual presence of melt. To address this seeming paradox, zircon geochronology and geochemistry from both the frozen lava and the cogenetic enclaves they host from the Soufrière Volcanic Center (SVC), a long-lived volcanic complex in the Lesser Antilles arc, were integrated to track the preeruptive thermal and chemical history of the magma reservoir. Our results show that the SVC reservoir was likely eruptible for periods of several tens of thousands of years or more with punctuated eruptions during these periods. These conclusions are consistent with results from other arc volcanic reservoirs and suggest that arc magmas are generally stored warm. Thus, the presence of intracrustal melt alone is insufficient as an indicator of imminent eruption, but instead represents the normal state of magma storage underneath dormant volcanoes.

  1. 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.

  2. Magma-magma interaction in the mantle beneath eastern China

    NASA Astrophysics Data System (ADS)

    Zeng, Gang; Chen, Li-Hui; Yu, Xun; Liu, Jian-Qiang; Xu, Xi-Sheng; Erdmann, Saskia

    2017-04-01

    In addition to magma-rock and rock-rock reaction, magma-magma interaction at mantle depth has recently been proposed as an alternative mechanism to produce the compositional diversity of intraplate basalts. However, up to now no compelling geochemical evidence supports this novel hypothesis. Here we present geochemistry for the Longhai basalts from Fujian Province, southeastern China, which demonstrates the interaction between two types of magma at mantle depth. At Longhai, the basalts form two groups, low-Ti basalts (TiO2/MgO < 0.25) and high-Ti basalts (TiO2/MgO > 0.25). Calculated primary compositions of the low-Ti basalts have compositions close to L + Opx + Cpx + Grt cotectic, and they also have low CaO contents (7.1-8.1 wt %), suggesting a mainly pyroxenite source. Correlations of Ti/Gd and Zr/Hf with the Sm/Yb ratios, however, record binary mixing between the pyroxenite-derived melt and a second, subordinate source-derived melt. Melts from this second source component have low Ti/Gd and high Zr/Hf and Ca/Al ratios, thus likely representing a carbonated component. The Sr, Nd, Hf, and Pb isotopic compositions of the high-Ti basalts are close to the low-Ti basalts. The Sm/Yb ratio of the high-Ti basalts, however, is markedly elevated and characterized by crossing rare earth element patterns at Ho, suggesting that they have source components comparable to the low-Ti basalts, but that they have experienced garnet and clinopyroxene fractionation. We posit that mingling of SiO2-saturated tholeiitic magma with SiO2-undersaturated alkaline magma might trigger such fractionation. Therefore, the model of magma-magma interaction and associated deep evolution of magma in the mantle is proposed to explain the formation of Longhai basalts. It may, moreover, serve as a conceptual model for the formation of tholeiitic to alkaline intraplate basalts worldwide.

  3. Architecture of a Neoproterozoic intracratonic carbonate ramp succession: Wynniatt Formation, Amundsen Basin, Arctic Canada

    NASA Astrophysics Data System (ADS)

    Thomson, Danielle; Rainbird, Robert H.; Dix, George

    2014-01-01

    The Neoproterozoic Wynniatt Formation, part of the upper Shaler Supergroup, is exposed in the Minto Inlier of Victoria Island, Canada, and was deposited in the intracratonic Amundsen Basin. The unit consists of a southwest-thickening (480 to 1000 m over ~ 300 km) shallowing-upward succession of three carbonate ramp sequences separated by regional unconformities. In ascending order: 1) inner to outer ramp carbonate facies, gradationally overlain by siliciclastic rocks of a pro-delta slope setting; 2) inner to mid-ramp subtidal carbonate facies, including a regional stromatolitic barrier system; and 3) outer ramp carbonate (gravity flow) facies overlain by shallowing-upward subtidal to intertidal, mixed siliciclastic-carbonate inner ramp facies. Spatial arrangements of nineteen lithofacies illustrates that each carbonate ramp sequence represents part of a distally steepened, storm-dominated carbonate ramp, with an interval of deep-water carbonate rocks coincident with oceanic restriction that elevated salinity. Migration of depocentre loci for successive ramp stages reflects changing patterns of subsidence. This may identify far-field extensional effects in this intracratonic basin because ages of the lower (~ 850 Ma) and middle (~ 761 Ma) formation bracket initiation of supercontinent (Rodinia) break-up. Our work offers an improved sedimentary framework for interbasinal correlation with coeval Neoproterozoic basins. It highlights temporal changes in carbonate facies compared to older carbonate successions in the Shaler Supergroup, and it defines depositional context for the Tawuia-Chuaria assemblage zone, providing important interbasinal biostratigraphic correlation.

  4. Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma: Insights from integrated zircon U-Pb ages, petrography, geochemistry and Nd-Sr-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Liu, Xiu-Jin; Liu, Li-Juan

    2013-10-01

    Whole rock major and trace element, Nd-Sr and zircon Hf isotopic compositions and secondary-ion mass spectrometry zircon U-Pb ages of eleven granitoid intrusions and dioritic rocks from the East Junggar (NW China) were analyzed in this study. The East Junggar granitoids were emplaced during terminal Early to Late Carboniferous (325-301 Ma) following volcanic eruption of the Batamayi Formation. Zircons from the East Junggar granitoids yielded 210 concordant 206Pb/238U ages which are all younger than 334 Ma and exhibit ɛHf(t) values distinctly higher than Devonian arc volcanic-rocks. Seismic P-wave velocities of deep crust of the East Junggar proper resemble those of oceanic crust (OC). These characteristics suggest absence of volcanic rock and volcano-sedimentary rock of Devonian and Early Carboniferous from the source region. The East Junggar granitoids show ɛNd(t) and initial 87Sr/86Sr values substantially overlapping those of the Armantai ophiolite in the area. The Early Paleozoic OC with seamount-like composition as the Zhaheba-Armantai ophiolites remained in the lower crust and formed main source rock of the East Junggar granitoids. Based on petrography and geochemistry, the East Junggar granitoids are classified into peralkaline A-type in the northern subarea, I-type (I1 and I2 subgroups) mainly in the north and A-type in the south of the southern subarea. The perthitic or argillated core and oligoclasic rim with an argillated boundary of feldspar phenocrysts and inclusion of perthites or its overgrowth by matrix plagioclase, in the monzogranites (northern subarea), suggest mixing of peralkaline granitic magma with mafic magma. In the north of the southern subarea, the presence of magmatic microdioritic enclaves (MMEs) in the I1 subgroup granitoids, transfer of plagioclase phenocrysts and hornblendes between host granodiorite and the MME across the boundary and a prominent resorption surface in the plagioclase phenocrysts indicate mixing of crustal magma (I2

  5. Magma dynamics

    NASA Astrophysics Data System (ADS)

    Bergantz, George

    What are the processes that drive magmatic diversity? How is it that volcanic centers can exist for millions of years erupting a variety of chemical types? What are the means by which large batholithic complexes become assembled? Magmas (silicate melts)differ from other geophysical fluids, such as oceans and atmospheres, in that their physiochemical history is largely governed by the processes of solidification and melting. This yields a system with strongly varying physical properties where bouyancy can be generated in complex ways. Much of the recent progress has come from numerical and experimental work specifically directed at the complex interactions of multicomponent systems undergoing phase changes and transport. Geochemical studies also indicate that magmatism is the result of thermal and chemical perturbations on a crustal scale.

  6. 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…

  7. 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

  8. Sr, Nd, Pb and Li isotope geochemistry and Ar-Ar dating of alkaline lavas from northern James Ross Island (Antarctic Peninsula) - implications for back-arc magma formation

    NASA Astrophysics Data System (ADS)

    Kosler, J.; Magna, T.; Mlcoch, B.; Mixa, P.; Hendriks, B. W. H.; Holub, F. V.; Nyvlt, D.

    2009-04-01

    The elemental and isotopic (Sr, Nd, Pb and Li) composition of Cenozoic back-arc alkaline basalts emplaced east of the Antarctic Peninsula in James Ross Island Volcanic Group (JRIVG) is different from the compositions of the fore-arc alkaline volcanic rocks in Southern Shetlands and nearby Bransfield Strait. The variability in elemental and isotopic composition is not consistent with the JRIVG derivation from a single mantle source but rather it suggests that the magma was mainly derived from a depleted mantle with subordinate OIB-like enriched mantle component (EM II). The isotopic data are consistent with mantle melting during extension and possible roll-back of the subducted lithosphere of the Antarctic plate in Miocene to Pliocene times, as indicated by the existing geochronological data and the new Ar-Ar age determinations. Magma contamination by Triassic - Early Tertiary clastic sediments deposited in the back-arc basin was only localized and affected Li isotopic composition in two of the samples, while most of the basalts show very little variation in delta 7Li values, as anticipated for "mantle-driven" Li isotopic composition. These variations are difficult to resolve with radiogenic isotope systematics but Li isotopes may prove sensitive in tracking complex geochemical processes acting through the oceanic crust pile, including hydrothermal leaching and seawater equilibration.

  9. 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.

  10. 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.

  11. 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.

  12. Magma Mingling of Multiple Mush Magmas

    NASA Astrophysics Data System (ADS)

    Graham, B.; Leitch, A.; Dunning, G.

    2016-12-01

    This field, petrographic, and geochemical study catalogues complicated magma mingling at the field to thin section scale, and models the emplacement of multiple crystal-rich pulses into a growing magma chamber. Modern theories present magma chambers as short-lived reservoirs that are continuously fed by intermittent magma pulses and suggest processes that occur within them can be highly dynamic. Differences in the rheology of two mingling magmas, largely affected by crystallinity, can result in varied textural features that can be preserved in igneous rocks. Field evidence of complex magma mingling is observed at Wild Cove, located along the northeast shoreline of Fogo Island, Newfoundland, an area interpreted to represent the roof/wall region of the Devonian Fogo Batholith. Fine-grained intermediate enclaves are contained in host rocks of similar composition and occur in round to amoeboid shapes. Dykes of similar composition are also observed near enclaves suggesting they were broken up into globules in localized areas. These provide evidence for a possible mechanism by which enclaves were formed as dykes passed through a more liquid-rich region of the magma chamber. The irregular but sharp nature of the boundaries between units suggest that all co-existed as "mushy" magmas with variable crystallinities reflecting a wide range in temperature between their respective liquidus and solidus. Textural evidence of complex mingling between mush units includes the intrusion of tonalite dykes into quartz diorite and granite mushes. The dykes were later pulled apart and subsequently back-intruded by liquid from the host mush (Figure). Observed magmatic tubes of intermediate magma cross-cutting through magma of near identical composition likely reflect compaction of the underlying mush after intrusion of new pulses of magma into the system. Petrographic examination of contacts between units reveals that few are chilled and medium to coarse grained boundaries are the norm.

  13. 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)

  14. Unstable flow, magma mixing and magma-rock deformation in a deep-seated conduit: the Gil-Márquez Complex, south-west Spain

    NASA Astrophysics Data System (ADS)

    Castro, A.; la Rosa, J. D. De; Fernández, C.; Moreno-Ventas, I.

    The Gil-Márquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of magma transport through the continental crust. This conduit allowed the intrusion of magmas of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic magma generated by partial melting of a depleted-mantle source. Both magmas rose through a common channel in which favorable conditions for unstable flow and magma mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid magmas.

  15. Unstable flow, magma mixing and magma-rock deformation in a deep-seated conduit: the Gil-Márquez Complex, south-west Spain

    NASA Astrophysics Data System (ADS)

    Castro, A.; de La Rosa, J. D.; Fernández, C.; Moreno-Ventas, I.

    1995-06-01

    The Gil-Marquez Complex is an exceptional outcrop of plutonic rocks ranging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian basement of Iberia. A combined study of this complex, including field geology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of magma transport through the continental crust. This conduit allowed the intrusion of magmas of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic magma generated by partial melting of a depletedmantle source. Both magmas rose through a common channel in which favorable conditions for unstable flow and magma mixing occurred. The observed relations in the Gil-Márquez Complex show that mixing in conduits may be an important mechanism for producing homogeneous hybrid magmas.

  16. 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.

  17. 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

  18. 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.

  19. Geochemistry of Los Humeros Caldera, Puebla, Mexico

    NASA Astrophysics Data System (ADS)

    Verma, S. P.; Lopez, M.

    1982-03-01

    Geochemistry of Pliocene to recent volcanic rocks from Los Humeros caldera (19°30' N - 19°50' N and 97°15° W - 97°35' W) in East-Central mexico is described. The volcanic rocks from this area seem to represent both alkali and high-alumina basalt series, or both calcalkaline and high-K calc-alkaline sequences. The available bulk-chemical analyses (23 this study and 18 from unpublished literature) show that the entire sequence of rocks from basalts to rhyolites are present in this area. Different degrees of partial melting of the source region followed by extensive shallow-level crystal differentiation seem to have taken place before most volcanic eruptions. These processes are perhaps the most important mechanisms for magma genesis in Los Humeros caldera. Geophysical studies in this area are not sufficient and more detailed geophysical surveys and a better geological interpretation are needed in order to delimit the underlying magma chamber.

  20. The Meaning of "Magma"

    NASA Astrophysics Data System (ADS)

    Bartley, J. M.; Glazner, A. F.; Coleman, D. S.

    2016-12-01

    Magma is a fundamental constituent of the Earth, and its properties, origin, evolution, and significance bear on issues ranging from volcanic hazards to planetary evolution. Unfortunately, published usages indicate that the term "magma" means distinctly different things to different people and this can lead to miscommunication among Earth scientists and between scientists and the public. Erupting lava clearly is magma; the question is whether partially molten rock imaged at depth and too crystal-rich to flow should also be called magma. At crystal fractions > 50%, flow can only occur via crystal deformation and solution-reprecipitation. As the solid fraction increases to 90% or more, the material becomes a welded crystal framework with melt in dispersed pores and/or along grain boundaries. Seismic images commonly describe such volumes of a few % melt as magma, yet the rheological differences between melt-rich and melt-poor materials make it vital not to confuse a large rock volume that contains a small melt fraction with melt-rich material. To ensure this, we suggest that "magma" be reserved for melt-rich materials that undergo bulk fluid flow on timescales consonant with volcanic eruptions. Other terms should be used for more crystal-rich and largely immobile partially molten rock (e.g., "crystal mush," "rigid sponge"). The distinction is imprecise but useful. For the press, the public, and even earth scientists who do not study magmatic systems, "magma" conjures up flowing lava; reports of a large "magma" body that contains a few percent melt can engender the mistaken perception of a vast amount of eruptible magma. For researchers, physical processes like crystal settling are commonly invoked to account for features in plutonic rocks, but many such processes are only possible in melt-rich materials.

  1. Meteoric water in magmas

    USGS Publications Warehouse

    Friedman, I.; Lipman, P.W.; Obradovich, J.D.; Gleason, J.D.; Christiansen, R.L.

    1974-01-01

    Oxygen isotope analyses of sanidine phenocrysts from rhyolitic sequences in Nevada, Colorado, and the Yellowstone Plateau volcanic field show that ??18O decreased in these magmas as a function of time. This decrease in ??18O may have been caused by isotopic exchange between the magma and groundwater low in 18O. For the Yellowstone Plateau rhyolites, 7000 cubic kilometers of magma could decrease in ??18O by 2 per mil in 600,000 years by reacting with water equivalent to 3 millimeters of precipitation per year, which is only 0.3 percent of the present annual precipitation in this region. The possibility of reaction between large magmatic bodies and meteoric water at liquidus temperatures has major implications in the possible differentiation history of the magma and in the generation of ore deposits.

  2. Meteoric water in magmas.

    PubMed

    Friedman, I; Lipman, P W; Obradovich, J D; Gleason, J D; Christiansen, R L

    1974-06-07

    Oxygen isotope analyses of sanidine phenocrysts from rhyolitic sequences in Nevada, Colorado, and the Yellowstone Plateau volcanic field show that delta(18)O decreased in these magmas as a function of time. This decrease in delta(18)O may have been caused by isotopic exchange between the magma and groundwater low in (18)O. For the Yellowstone Plateau rhyolites, 7000 cubic kilometers of magma could decrease in delta(18)O by 2 per mil in 600,000 years by reacting with water equivalent to 3 millimeters of precipitation per year, which is only 0.3 percent of the present annual precipitation in this region. The possibility of reaction between large magmatic bodies and meteoric water at liquidus temperatures has major implications in the possible differentiation history of the magma and in the generation of ore deposits.

  3. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine V.; Giordano, Guido

    2014-11-01

    Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; petrologists have used the eruptive products to probe conditions of magma storage (and thus processes that drive magma evolution), while volcanologists have used them to study the conditions under which large volumes of magma are transported to, and emplaced on, the Earth's surface. Traditionally, both groups have worked on the assumption that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. Here we explore the implications of complex magma reservoir configurations for eruption dynamics and caldera formation. We first examine mafic systems, where stacked-sill models have long been invoked but which rarely produce explosive eruptions. An exception is the 2010 eruption of Eyjafjallajökull volcano, Iceland, where seismic and petrologic data show that multiple sills at different depths fed a multi-phase (explosive and effusive) eruption. Extension of this concept to larger mafic caldera-forming systems suggests a mechanism to explain many of their unusual features, including their protracted explosivity, spatially variable compositions and pronounced intra-eruptive pauses. We then review studies of more common intermediate and silicic caldera-forming systems to examine inferred conditions of magma storage, time scales of melt accumulation, eruption triggers, eruption dynamics and caldera collapse. By compiling data from large and small, and crystal-rich and crystal-poor, events, we compare eruptions that are well explained by simple evacuation of a zoned

  4. 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.

  5. 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.

  6. Petrology and geochemistry Toro Ankole kamafugite magmas: isotopic constraints.

    NASA Astrophysics Data System (ADS)

    Muravyeva, N. S.; Belyatsky, B. V.

    2009-04-01

    Kamafugites are represented a group silica-undersaturated perpotassium volcanic rocks originally named after three petrographically-defined rock types - katungite, mafurite and ugandite from the Toro-Ankole province in the Western branch of the East African rift zone. These ultra-potassium high-magnesian rocks are the deepest on the Earth together with the kimberlites and lamproites. In Toro-Ankole there are three volcanic fields: Fort Portal, Katwe-Kikorongo and Bunyaruguru. This study is focused on the Bunyaruguru volcanic field which stretches southwards from the south shore of Lake George, partly over the floor of the western Rift depression and partly over the adjacent plateau to the south and east of the Rift. The common minerals of phenocrysts are olivine, leucite, clinopyroxene, Cr-spinelides and phlogopite. There are perovskite and melilite phenocrysts in the katungites. Spinelides are frequently occured as inclusions in the olivines which contain also fluid inclusions and sometimes carbonate, sulfate and sulfide inclusions. The composition of phenocrysts, megacrysts and groundmass minerals were analyzed. The conditions of mineral equilibria were calculated using these data. Unlike lavas from volcanic fields further south in the western branch, the effects of crystal fractionation on the kamafugitic lavas are minor. Primitive features, such as high Mg# - up to 79, and high Ni - up to 780 ppm, Cr - up to 1170 ppm, are in strong contrast to their extreme enrichment in incompatible trace elements. The composition of kamafugite olivines phenocrysts close to the olivines of the mantle xenoliths: forsterite content up to Fo92, NiO - up to 0.48 wt.%, CaO (min) - 0.07 wt.%. Spinelides are the high-chromium varieties: Cr2O3 - up to 58.4 wt.%, Al2O3 - up to 10.65 wt.%, the minimum of TiO2 - 2.36 wt.%. The Ti-content increases in the outer zone of Cr-spinelide phenocrysts and sometimes titanomagnetite forms individual grains. The spinel composition trend of studied samples resembles the kimberlite trend. The temperature and oxygen fugacity of olivine-spinel equilibrium were calculated (Ballhaus et al., 1991) use data on mineral compositions. The pressure of phenocrysts crystallization was estimated with the Cpx-geobarometer. The obtained results show that the kamafugites crystallization passed over the wide temperature interval - 1300-716оC and fO2 exceeding buffer QFM (0.8<ΔQFM<3.6), that is considerably higher the same of most basalts and unchanged upper mantle material. The presence of the sulfate microinclusions in the mafurite olivine confirms the correct results, obtained by olivine-spinel method. High oxygen fugacity values for the primitive melts may be mainly explained by the special features of the upper mantle composition where metasomatism processes were intensively developed and usually accompanied by oxidation of the source. Sr and Nd isotope signatures for kamafugites form a slightly enriched relative to BSE cluster (87Sr/86Sr = 0.704629 - 0.705356; 143Nd/144Nd = 0.512488 - 0.512550). Some inverse correlation with major element contents is observed: 87Sr/86Sr - CaO, 143Nd/144Nd - Mg#, 87Sr/86Sr - Mg#. Sr-Nd isotope data of Bunyaruguru kamafugites suggest that its mantle source composition is nearly EM1. But the range of Pb composition for investigated is 206Pb/204Pb: 18.998 - 19.566; 207Pb/204Pb: 15.686 - 15.737; 208Pb/204Pb: 39.303 - 40.264. On these data the mantle source composition for studied kamafugites is close to EM2 or Dupal characteristics. Reference: Ballhaus C., Berry R.F., Green D.H. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle 1991. Contrib. Mineral. Petrol. vol.107, p.27 - 40.

  7. Watching magma from space

    USGS Publications Warehouse

    Lu, Zhong; Wicks, Charles W.; 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. 

  8. Structural styles of Paleozoic intracratonic fault reactivation: A case study of the Grays Point fault zone in southeastern Missouri, USA

    USGS Publications Warehouse

    Clendenin, C.W.; Diehl, S.F.

    1999-01-01

    A pronounced, subparallel set of northeast-striking faults occurs in southeastern Missouri, but little is known about these faults because of poor exposure. The Commerce fault system is the southernmost exposed fault system in this set and has an ancestry related to Reelfoot rift extension. Recent published work indicates that this fault system has a long history of reactivation. The northeast-striking Grays Point fault zone is a segment of the Commerce fault system and is well exposed along the southeast rim of an inactive quarry. Our mapping shows that the Grays Point fault zone also has a complex history of polyphase reactivation, involving three periods of Paleozoic reactivation that occurred in Late Ordovician, Devonian, and post-Mississippian. Each period is characterized by divergent, right-lateral oblique-slip faulting. Petrographic examination of sidwall rip-out clasts in calcite-filled faults associated with the Grays Point fault zone supports a minimum of three periods of right-lateral oblique-slip. The reported observations imply that a genetic link exists between intracratonic fault reactivation and strain produced by Paleozoic orogenies affecting the eastern margin of Laurentia (North America). Interpretation of this link indicate that right-lateral oblique-slip has occurred on all of the northeast-striking faults in southeastern Missouri as a result of strain influenced by the convergence directions of the different Paleozoic orogenies.

  9. 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.

  10. 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.

  11. 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.

  12. Crystals in magma chambers

    NASA Astrophysics Data System (ADS)

    Higgins, M.

    2011-12-01

    Differentiation processes in igneous systems are one way in which the diversity of igneous rocks is produced. Traditionally, magmatic diversity is considered as variations in the overall chemical composition, such as basalt and rhyolite, but I want to extend this definition to include textural diversity. Such textural variations can be manifested as differences in the amount of crystalline (and immiscible liquid) phases and in the origin and identity of such phases. One important differentiation process is crystal-liquid separation by floatation or decantation, which clearly necessitates crystals in the magma. Hence, it is important to determine if magmas in chambers (sensu lato) have crystals. The following discussion is framed in generalities - many exceptions occur. Diabase (dolerite) dykes are a common, widespread result of regional mafic magmatism. The rims of most diabase dykes have few or no phenocrysts and crystals in the cores are commonly thought to have crystallized in place. Hence, this major mafic magmatic source did not have crystals, although compositional diversity of these dykes is commonly explained by crystal-liquid separation. This can be resolved if crystallisation was on the walls on the magma chamber. Similarly, most flood basalts are low in crystals and separation of those that are present cannot always explain the observed compositional diversity. Crystal-rich flows do occur, for example the 'Giant Plagioclase Basalts' of the Deccan series, but the crystals are thought to form or accumulate in a crystal-rich zone beneath the roof of the chamber - the rest of the chamber probably has few crystals. Some magmas from Hawaii contain significant amounts of olivine crystals, but most of these are deformed and cannot have crystallised in the chamber. In this case the crystals are thought to grow as the magma passes through a decollement zone. They may have grown on the walls or been trapped by filters. Basaltic andesite ignimbrites generally have

  13. 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.

  14. 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.

  15. 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

  16. Origins of organic geochemistry

    USGS Publications Warehouse

    Kvenvolden, K.A.

    2008-01-01

    When organic geochemistry actually began as a recognized geoscience is a matter of definition and perspective. Constraints on its beginning are placed by the historical development of its parent disciplines, geology and organic chemistry. These disciplines originated independently and developed in parallel, starting in the latter half of the 18th century and flourishing thereafter into the 21st century. Organic geochemistry began sometime between 1860 and 1983; I argue that 1930 is the best year to mark its origin.

  17. Tectonism and an Upper Silurian ramp-prodelta-rimmed shelf succession from Arctic Canada: an intracratonic product of Caledonian Compression

    SciTech Connect

    Packard, J.J.; Dixon, O.A.

    1987-05-01

    Late Silurian and Early Devonian shelf architecture in the vicinity of Cornwallis Island in the central Arctic Archipelago was largely determined by a series of diastrophic events that are collectively termed the Cornwallis disturbance. The disturbance affected a fault-bounded, basement-cored, intracratonic crustal segment, the Boothia Uplift, which forms a northerly trending feature some 1000 km long and 80 to 150 km wide oriented normal to the tectonodepositional strike of both the Franklinian and younger Sverdrup basins. Marine deposition within the vicinity of the uplift can be divided into five phases corresponding to changes in the relative intensity of penecontemporaneous regional tectonism. Phase 1 (late Ludlovian) is a quiescent stage, typified by carbonate ramp sedimentation. The Douro Ramp was a homoclinal ramp that bordered a low-energy, turbid, meromict sea. Phase 2 represents the termination of the stable carbonate ramp and the onset of syntectonic sedimentation. Phase 2 (late Ludlovian) is represented in the rock record by the precipitous and near-simultaneous occurrence of stacked hardgrounds, slope failure phenomena, ox-redox banding, tempestites with significant siliciclastic content, and abrupt shallowing of biofacies. Phase 3 (latest Ludlovian) corresponds to a period of continental wasting and deltaic sedimentation as the newly emergent terrane of the Boothia Uplift shed its detritus northward to form the Hotham clinoform. Phase 4 (latest Ludlovian to earliest Lochkovian) is represented by the Barlow Inlet Platform, an attached rimmed shelf with an accretionary shelf margin. The platform sequence is punctuated by a number (7 minimum) of major forestepping and backstepping events that are attributed to episodic movement of the Boothia Uplift. Phase 5 is the denouement of carbonate sedimentation in the study area.

  18. 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.

  19. Modelling the petrogenesis of high Rb/Sr silicic magmas

    USGS Publications Warehouse

    Halliday, A.N.; Davidson, J.P.; Hildreth, W.; Holden, P.

    1991-01-01

    Rhyolites can be highly evolved with Sr contents as low as 0.1 ppm and Rb Sr > 2,000. In contrast, granite batholiths are commonly comprised of rocks with Rb Sr 100. Mass-balance modelling of source compositions, differentiation and contamination using the trace-element geochemistry of granites are therefore commonly in error because of the failure to account for evolved differentiates that may have been erupted from the system. Rhyolitic magmas with very low Sr concentrations (???1 ppm) cannot be explained by any partial melting models involving typical crustal source compositions. The only plausible mechanism for the production of such rhyolites is Rayleigh fractional crystallization involving substantial volumes of cumulates. A variety of methods for modelling the differentiation of magmas with extremely high Rb/Sr is discussed. In each case it is concluded that the bulk partition coefficients for Sr have to be large. In the simplest models, the bulk DSr of the most evolved types is modelled as > 50. Evidence from phenocryst/glass/whole-rock concentrations supports high Sr partition coefficients in feldspars from high silica rhyolites. However, the low modal abundance of plagioclase commonly observed in such rocks is difficult to reconcile with such simple fractionation models of the observed trace-element trends. In certain cases, this may be because the apparent trace-element trend defined by the suite of cognetic rhyolites is the product of different batches of magma with separate differentiation histories accumulating in the magma chamber roof zone. ?? 1991.

  20. 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.

  1. Calderas and magma reservoirs

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine; Giordano, Guido

    2015-04-01

    Large caldera-forming eruptions have long been a focus of both petrological and volcanological studies; traditionally, both have assumed that eruptible magma is stored within a single long-lived melt body. Over the past decade, however, advances in analytical techniques have provided new views of magma storage regions, many of which provide evidence of multiple melt lenses feeding a single eruption, and/or rapid pre-eruptive assembly of large volumes of melt. These new petrological views of magmatic systems have not yet been fully integrated into volcanological perspectives of caldera-forming eruptions. We discuss the implications of syn-eruptive melt extraction from complex, rather than simple, reservoirs and its potential control over eruption size and style, and caldera collapse timing and style. Implications extend to monitoring of volcanic unrest and eruption progress under conditions where successive melt lenses may be tapped. We conclude that emerging views of complex magma reservoir configurations provide exciting opportunities for re-examining volcanological concepts of caldera-forming systems

  2. 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.

  3. Experimental Constraints on the Bishop Tuff Magma Body

    NASA Astrophysics Data System (ADS)

    Gardner, J. E.; Befus, K. S.; Gualda, G. A.; Ghiorso, M. S.

    2013-12-01

    Hundreds to thousands of cubic kilometers of magma must accumulate just before immense "super volcano" eruptions. The petrology and geochemistry of the giant magma body that erupted to form the Bishop Tuff has served for decades as a cornerstone for petrologic models of such large accumulations of magma. A benchmark for those models has been the thermal gradient of over 100° C thought to be preserved by the compositional variations of magnetite and ilmenite throughout the Bishop Tuff. Yet, despite the importance of the Bishop Tuff in our community's thinking about large magma bodies, little experimental work has been carried out on its products to help constrain its pre-eruptive storage conditions. We have thus carried hydrothermal experiments using representative samples of the Bishop Tuff, all of which were run at conditions near the Ni-NiO oxygen buffer, equivalent to those recorded by magnetite-ilmenite equilibrium. Our results agree well with those predicted by the Rhyolite-MELTS thermodynamic model, including finding a narrow temperature range separating the crystallization of the first felsic mineral and the onset of the ternary minimum (quartz plus two feldspars), and extensive crystallization over a narrow temperature range once that minimum is reached. The hottest parts of the Bishop Tuff magma, the so-called Late Bishop Tuff (LBT), crystallized two feldspars and quartz at water pressures of 100-120 MPa, based on water contents dissolved in quartz glass inclusions. Given those constraints, our results indicate that the LBT magma was colder than about 740° C. Such low temperatures conflict with the much hotter ones purportedly preserved by magnetite-ilmenite compositions in the LBT (785° C for the sample used in the experiments). Experimentally, however, ilmenite and magnetite coexist only at temperatures below 750° C. The composition of clinopyroxene in LBT is homogeneous, and matches that of experimental clinopyroxene grown only at high temperature

  4. 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

  5. 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.

  6. 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.

  7. Crystallization of the magma ocean

    NASA Astrophysics Data System (ADS)

    Caracas, R.; Nomura, R.; Hirose, K.; Ballmer, M. D.

    2015-12-01

    We model the crystallization of the magma ocean using pyrolite as a proxy for its composition. We employ first-principles molecular-dynamics calculations to determine the density of the magmas. We use diamond-anvil cell experiments to trace the chemical evolution of the magmas during cooling and crystallization. We build a grid of pressure and temperature points, following the chemical evolution of the magma during the entire fractional crystallization of perovskite. Then we construct a geodynamical model of the evolving magma fully taking into account the density and chemistry of the melts and crystals. We show that the dynamics of the crystallization of the magma ocean is highly dependent (i) on extrinsic parameters, like pressure at the core-mantle boundary and temperature profile through the magma ocean, and (ii) on intrinsic parameters, like relative density relations between the melt and the crystals and vigor of the stirring. Formation of a solid layer in the middle of the magma ocean is possible, which can lead to the eventual formation of a basal magma ocean.

  8. 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

  9. Summary - Magma Energy R&D Strategies and Applications

    SciTech Connect

    Tennyson, George P. Jr.

    1989-03-21

    In this session, this vast resource of thermal energy was described by Dr. James C. Dunn (SNLA) as an estimated 500,000 quads in U.S. crustal magma bodies with temperatures in excess of 600 degrees Celsius and at depths of less than 10 km. The aim is to develop technology which can experimentally extract energy from a silicic magma body to demonstrate the feasibility of utilizing this resource. Energy extraction from molten rock has been demonstrated in Hawaii at the Kilauea Iki lava lake. The program is showing significant progress in Geophysics and Site Selection, Energy Extraction Processes, and Geochemistry/Materials. The next major step is to drill and evaluate a deep exploratory well at the Long Valley caldera in California. Extensive analyses by the program and from previous work indicate that active magma may be expected. John T. Finger (SNLA) then summarized the proposed four-phase drilling plan. The four phases will be approximately one year apart, and are expected to result in a large diameter well to a total depth of about 20,000 feet. The well design (by Livesay, Inc.) was described in considerable detail, together with predictions of the expected drilling problems. The well design and schedule includes accommodation of not only a substantial time for both program and outside experiments, but also the restrictions imposed by regulatory agencies including noise, disposal of wastes, and consideration of wildlife migratory patterns. Last, but hardly least, was a relation of the well and its drilling to the benefits to be accrued to the magma energy technology. The deep borehole measurements which can, and will be taken at the Long Valley well present a unique opportunity to test and validate geophysical techniques for locating magma, analyzing the geophysical parameters of the site and testing the theory that magma is still present at drillable depths within the central portion of the caldera. Assuming the drilling indicates that there is magma present

  10. 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).

  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. 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…

  13. 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…

  14. 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.

  15. Mercury's Magma Ocean

    NASA Astrophysics Data System (ADS)

    Parman, S. W.; Parmentier, E. M.; Wang, S.

    2016-12-01

    The crystallization of Mercury's magma ocean (MMO) would follow a significantly different path than the terrestrial or lunar magma ocean. Evidence from the MESSENGER mission [1] indicates that Mercury's interior has an oxygen fugacity (fO2) orders of magnitude lower any other terrestrial planet (3-8 log units below the iron-wustite buffer = IW-3 to IW-8; [2]). At these conditions, silicate melts and minerals have negligible Fe contents. All Fe is present in sulfides or metal. Thus, the build up of Fe in the last dregs of the lunar magma ocean, that is so important to its evolution, would not happen in the MMO. There would be no overturn or plagioclase flotation crust. Sulfur solubility in silicate melts increases dramatically at low fO2, from 1 wt% at IW-3 to 8wt% at IW-8 [3]. Thus it is possible, perhaps probable, that km-thick layers of sulfide formed during MMO crystallization. Some of the sulfides (e.g. CaS) have high partition coefficients for trace elements and so could control the spatial distribution of radioactive heat producing elements such as U, Th and K. This in turn would have first order effects on the thermal and chemical evolution of the planet. The distribution of the sulfide layers depend upon the density of the sulfides that form in the MMO. At such low fO2, S forms compounds with a range of elements not typical for other planets: Ca, Mg, Na, K. The densities of these sulfides vary widely, with Mg and Ca-rich sulfides being more dense than estimated MMO densities, and Na and K-rich sulfides being less dense than the MMO. Thus sulfide sinking and floating may produce substantial chemical layering on Mercury, potentially including an Mg-Ca rich deep layer and a Na-K rich shallow layer or possibly floatation crust. The total amount of S in the MMO depends on the fO2 and the bulk S content of Mercury, both of which are poorly constrained. In the most extreme case, if the MMO had an fO2of IW-8 and was sulfide saturated from the start, a total

  16. 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.

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

    NASA Technical Reports Server (NTRS)

    Shervais, J. W.; Taylor, L. A.; Laul, J. C.; Smith, M. R.

    1984-01-01

    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.

  18. Using Intensive Variables to Constrain Magma Source Regions

    NASA Astrophysics Data System (ADS)

    Edwards, B. R.; Russell, J. K.

    2006-05-01

    In the modern world of petrology, magma source region characterization is commonly the realm of trace element and isotopic geochemistry. However, major element analyses of rocks representing magmatic compositions can also be used to constrain source region charactertistics, which enhance the results of isotopic and trace element studies. We show examples from the northern Cordilleran volcanic province (NCVP), in the Canadian Cordillera, where estimations of thermodynamic intensive variables are used to resolve different source regions for mafic alkaline magmas. We have taken a non-traditional approach to using the compositions of three groups of mafic, alkaline rocks to characterize the source regions of magmas erupted in the NCVP. Based on measured Fe2O3 and FeO in rocks from different locations, the Atlin volcanic district (AVD), the Fort Selkirk volcanic complex (FSVC), the West Tuya volcanic field, (WTVF), we have estimated oxygen fugacities (fO2) for the source regions of magmas based on the model of Kress and Carmichael (1991) and the computational package MELTS/pMelts (Ghiorso and Sack, 1995; Ghiorso et al., 2002). We also have used Melts/pMelts to estimate liquidus conditions for the compositions represented by the samples as well as activities of major element components. The results of our calculations are useful for distinguishing between three presumably different magma series: alkaline basalts, basanites, and nephelinites (Francis and Ludden, 1990; 1995). Calculated intensive variables (fO2, activities SiO2, KAlSiO4, Na2SiO3) show clear separation of the samples into two groups: i) nephelinites and ii) basanites/alkaline basalts. The separation is especially evident on plots of log fO2 versus activity SiO2. The source region for nephelinitic magmas in the AVD is up to 2 log units more oxidized than that for the basanites/basalts as well as having a distinctly lower range of activities of SiO2. Accepting that our assumptions about the magmas

  19. 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.

  20. Volatile Changes in Magma Related to Magma Evolution: Influences From Magma Mixing, Crustal Assimilation, and Crystallization

    NASA Astrophysics Data System (ADS)

    Sosa-Ceballos, G.; Gardner, J.

    2008-12-01

    The volatile budget of magma is the cumulative product of magma mixing, crustal assimilation, and crystallization, with the concentration of each volatile resulting from how much is added by each process and whether the magma is gas saturate. In order to clarify how volatile budgets fluctuate during magma evolution, we are measuring volatile concentrations in melt inclusions trapped within individual zones of plagioclase crystals from different dacitic Plinian eruptions and a recent small-scale explosion of Popocatépetl Volcano. The plagioclase zones were analyzed for their anorthite (An) composition and their Sr isotopic (87Sr/86Sr) composition in order to investigate the evolutionary processes responsible for crystal growth and their relation to volatile concentrations measured in the melt inclusions. In general, plagioclase from all eruptions display three different correlations between An content and Sr isotopes, with each recording different conditions under which crystals grew. Some crystals have nearly constant 87Sr/86Sr compositions from core to rim with either variable An compositions or a continuous decrease in An, suggesting these crystals were affected only by crystallization and, in some cases, thermal fluctuations. Other crystals display anti-correlations between An and Sr isotopes, which record mass inputs into the system from either magma mixing or crustal assimilation. Single crystals record a variety of processes during their growth, and single pumices contain an extremely heterogeneous population of such crystals, suggesting that the magma system is highly dynamic. Our preliminary results show that water can vary by several weight percent and carbon dioxide by hundreds of ppm between different zones of individual crystals. Interestingly, we find that inclusions related to recharge events by hotter, more primitive magma are more hydrous than those related to assimilation of more radiogenic wall rock. This suggests that the volatile budget of

  1. Geochemistry and mineralogy of mafic Icelandic hyaloclastites

    NASA Astrophysics Data System (ADS)

    Hudak, M. R.; Feineman, M. D.; Eyer, C.; Bindeman, I. N.; Sigmarsson, O.

    2016-12-01

    Hyaloclastite in the crust may be a cryptic contaminant contributing to some volatile-rich Icelandic basalts and in some places reach 2.5 km1. Hyaloclastites are highly fragmented composites of lithics, glass, and crystals in a palagonite matrix that form as a result of magma-ice or magma-water interactions. These rocks have high water content and porosity and a high initial glass content, which makes them susceptible to rapid alteration by ambient or hydrothermal waters and potentially fast digestion by magmas. Due to low density and ductility, they have the potential to stall ascending mantle-derived magmas to form sills, and in the process may contribute exotic volatile or fluid-mobile components. We have characterized the geochemistry and mineralogy of 18 hyaloclastite samples from the Reykjanes Peninsula (RP), Vestmannajyar, and the southern coast of Iceland. Major and trace elements were obtained using ICP-AES and ICP-MS, respectively, and mineralogy was determined by XRD. Loss on ignition is highly variable (0.44 - 15.7 wt.%) and positively correlated with alkali loss reflected in the Chemical Index of Alteration [34.8 - 51.3; CIA = Al2O3/(Al2O3+CaO+Na2O+K2O)]. Primitive mantle normalized multi-element plots for RP hyaloclastites are broadly similar to those for unaltered RP Holocene basalts. Two samples have trace element profiles resembling those of picrites in the region. The samples from the south coast and Vestmannaeyjar have OIB-like enrichments similar to local Holocene basalts. Five well-sorted hyaloclastite samples have broad humps in their XRD patterns from 20-50° 2q. These samples contain only primary magmatic mineral phases (plagioclase, olivine, and pyroxene), if any, while other hyaloclastites contain both primary phases and secondary alteration phases including halite, calcite, clays, chlorite, and zeolites. Preliminary O and H isotope investigation demonstrates large ranges in both parameters. Future work will include oxygen isotope analyses

  2. 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

  3. Seismic evidence for a magma chamber beneath the slow-spreading Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Calvert, A. J.

    1995-10-01

    SEISMIC reflections from magma chambers have been observed along the fast-spreading East Pacific Rise1,2 and the intermediate-spreading Valu Fa Ridge3,4; sub-axial reflections also exist beneath the intermediate-spreading Juan de Fuca Ridge5. But no magma chambers have been identified beneath the slow-spreading Mid-Atlantic Ridge, suggesting that here magma chambers lie unusually deep or are transient features6-11. Seismic reflection profiles acquired in 1989 over the Snake Pit hydrothermal area, in the rift valley of the Mid-Atlantic Ridge ˜25 km south of the Kane fracture zone, showed no evidence of magmatic activity12, although geochemical analyses of hydrothermal vent fluids suggest the existence of magma at depths as shallow as 1-2 km13,14. By suppressing in these data high-amplitude coherent noise generated at the sea floor, I have obtained images, in an otherwise non-reflective crust, of seismic reflections beneath, and just south of, the Snake Pit hydrothermal area. These reflections define a small, 4-km-wide dome whose apex is ˜ 1,200 m beneath the sea floor. As bright reflections from the upper flanks of this dome occur in the depth range suggested by the vent-fluid geochemistry, I interpret the dome to be the seismic expression of a small magma chamber.

  4. Magma surge from the mantle: the Father's Day Eruption, Kīlauea Volcano, Hawai'i

    NASA Astrophysics Data System (ADS)

    Salem, L. C.; Edmonds, M.; Maclennan, J.; Houghton, B. F.; Poland, M. P.

    2015-12-01

    The geometry of the shallow plumbing system of Kīlauea Volcano, Hawai'i, is constrained by both geophysical and petrologic studies, yet the loci of lower crustal magma storage and timescales of magma ascent are almost entirely unknown. The petrography and texture of erupted magmas are largely overprinted by processes in the shallow reservoir and conduit. Direct petrological evidence for lower crustal storage and transport is enigmatic but exists in the form of fine-scale crystal zoning in the cores of olivine phenocrysts, in the geochemical heterogeneity of melt inclusions and in fluid inclusion density. The 2007 Father's Day intrusion and eruption occurred at the culmination of a surge in magma supply to the summit reservoir and during a period of heightened CO2 outgassing flux. The erupted lavas provide an opportunity to analyze atypically primitive melts, with > 8.5 wt% MgO in the whole rock, which have undergone relatively little shallow crustal processing. We characterise melt inclusions and their host olivine crystals through a detailed study of olivine morphology, diffusion modelling, and melt and fluid inclusion geochemistry. We show that the melt inclusions preserve primitive geochemical heterogeneity, which we use to reconstruct fractionation, mixing and degassing processes through the crust. We infer timescales and pressures of magma ascent, storage, and CO2 degassing through the crustal plumbing system. These observations are interpreted in the context of the exceptionally detailed set of volcano monitoring data at Kīlauea Volcano.

  5. Assessing in situ crystal-liquid separation in a fossil, large-volume, silicic, magma reservoir

    NASA Astrophysics Data System (ADS)

    Eddy, M. P.

    2016-12-01

    The origin of high-SiO2 rhyolites is controversial. Geochemical gradients in large ignimbrites and regional-scale variations in pluton geochemistry suggest that some of these magmas are generated through differentiation of silicic (>65 wt% SiO2) parent melts in upper crustal magma `mush' zones. This process predicts that large volumes of vertically stratified silicic cumulate should be present within the upper crustal plutonic record. Nevertheless, the number of individual plutons with this type of stratification is limited and geochronologic data has demonstrated that many large, upper crustal plutonic complexes were emplaced at rates too slow (< 0.003 km3/a) and durations too long (>> 1 Ma) to construct a large mush. These observations have led to an alternative hypothesis whereby high-SiO2rhyolites form within the middle or lower crust with little to no differentiation in the upper crust. The Eocene Golden Horn batholith, WA offers a unique opportunity to test the efficiency of crystal-liquid separation. This composite batholith was emplaced at 7-8 km depth and is composed of several distinct magmatic sheets. U-Pb zircon geochronology from the largest sheet, a >424 km3 body of granodiorite and granite with a distinctive rapakivi texture, suggests that it was built at magma emplacement rates compatible with building a large silicic mush. Initial field and geochemical evidence, including lenticular bodies of leucogranite at high elevations and systematic vertical variations in whole rock geochemistry in a short vertical section, suggest that this fossil magma reservoir may have undergone some degree of crystal-liquid separation. I expand on these initial results and present new detailed geologic mapping of textural and compositional variation within a 1 km vertical section coupled with new whole rock geochemical measurements and zircon trace element data to assess the degree to which in situ differentiation may have occurred within this fossil magma reservoir.

  6. The data of geochemistry

    USGS Publications Warehouse

    Clarke, Frank Wigglesworth

    1924-01-01

    Upon the subject of geochemistry a vast literature exists, but it is widely scattered and portions of it are difficult of access. The general treatises, like the classical works of Bischof and of Koth, are not recent, and great masses of modern data are as yet uncorrelated. The American material alone is singularly rich, but most of it has been accumulated since Roth's treatise was published. The science of chemistry, moreover, has undergone great changes during the last 25 years, and many subjects now appear under new and generally unfamiliar aspects. The methods and principles of physical chemistry are being more and more applied to the solution of geochemical problems,1 as is shown by the well-known researches of Van't Hoff upon the Stassfurt salts and the magmatic studies of Vogt, Doelter, and others. The great work in progress at the geophysical laboratory of the Carnegie Institution is another illustration of the change now taking place in geochemical investigation. To bring some of the data together, to formulate a few of the problems and to present certain general conclusions in their modern form are the purposes of this memoir. It is not an exhaustive monograph upon geochemistry, but rather a critical summary of what is now known, and a guide to the more important literature of the subject. If it does no more than to make existing data available to the reader, its preparation will be justified.

  7. Geochemistry of Peralkaline Melts at Kone Volcanic Complex, Main Ethiopian Rift

    NASA Astrophysics Data System (ADS)

    Iddon, F. E.; Edmonds, M.; Jackson, C.; Hutchison, W.; Mather, T. A.; Fontijn, K.; Pyle, D. M.

    2016-12-01

    The East Africa rift system (EARS) is the archetypal example of continental rifting, with the Main Ethiopian rift (MER) segment offering a unique opportunity to examine the dynamics of peralkaline magmas; the development of central volcanoes; melt distribution and transport in the crust; the volatile budgets of rift magmas and their implications for the formation of ore deposits. The alkali- and halogen-rich magmas of the MER differ from their calc-alkaline counterparts in other settings due to their lower viscosities and higher volatile contents, which have important implications for magma transport, reservoir dynamics and eruptive hazards. The high halogen contents of the magmas give rise to halogen-rich vapor which has the capacity to transport and concentrate metals and REE. The Kone Volcanic complex is one of the lesser studied Quaternary peralkaline centres, located on the axial portion of the MER. It comprises two superimposed calderas, surrounded by ignimbrite deposits and unwelded felsic pyroclastic material, small basaltic vents and rhyolitic domes. Unusually for the central volcanoes of the MER, the caldera has refilled with basaltic lava, not pyroclastic material. We use whole rock and micro-analysis to characterize a range of Kone tephras, glasses, crystal phases and melt inclusions in terms of major, trace and volatile element abundances, alongside detailed textural analysis using QEMSCAN and SEM. The whole rock geochemistry reflects the clear peralkaline nature of the suite, with a distinct compositional gap between 50 wt% and 65 wt% SiO2, controlled largely by fractional crystallization. Trace element systematics illustrate that trachytes entrain alkali feldspars, with the crystal cargo of the entire suite reflecting the structure of the magma reservoir at depth, with liquid-rich lenses and regions of syenitic mush. Melt inclusion geochemistry allows reconstruction of complex, multiphase differentiation processes and the exsolution of both a vapor

  8. Multiphase Dynamics of Magma Oceans

    NASA Astrophysics Data System (ADS)

    Boukaré, Charles-Edouard; Ricard, Yanick; Parmentier, Edgar M.

    2017-04-01

    Since the earliest study of the Apollo lunar samples, the magma ocean hypothesis has received increasing consideration for explaining the early evolution of terrestrial planets. Giant impacts seem to be able to melt significantly large planets at the end of their accretion. The evolution of the resulting magma ocean would set the initial conditions (thermal and compositionnal structure) for subsequent long-term solid-state planet dynamics. However, magma ocean dynamics remains poorly understood. The major challenge relies on understanding interactions between the physical properties of materials (e.g., viscosity (at liquid or solid state), buoyancy) and the complex dynamics of an extremely vigorously convecting system. Such complexities might be neglected in cases where liquidus/adiabat interactions and density stratification leads to stable situations. However, interesting possibilities arise when exploring magma ocean dynamics in other regime. In the case of the Earth, recent studies have shown that the liquidus might intersect the adiabat at mid-mantle depth and/or that solids might be buoyant at deep mantle conditions. These results require the consideration of more sophisticated scenarios. For instance, how does bottom-up crystallization look with buoyant crystals? To understand this complex dynamics, we develop a multiphase phase numerical code that can handle simultaneously phase change, the convection in each phase and in the slurry, as well as the compaction or decompaction of the two phases. Although our code can only run in a limited parameter range (Rayleigh number, viscosity contrast between phases, Prandlt number), it provides a rich dynamics that illustrates what could have happened. For a given liquidus/adiabat configuration and density contrast between melt and solid, we explore magma ocean scenarios by varying the relative timescales of three first order processes: solid-liquid separation, thermo-chemical convective motions and magma ocean cooling.

  9. Shallow-level magma-sediment interaction and explosive behaviour at Anak Krakatau (Invited)

    NASA Astrophysics Data System (ADS)

    Troll, V. R.; Jolis, E. M.; Dahren, B.; Deegan, F. M.; Blythe, L. S.; Harris, C.; Berg, S. E.; Hilton, D. R.; Freda, C.

    2013-12-01

    Crustal contamination of ascending arc magmas is generally thought to be a significant process which occurs at lower- to mid-crustal magma storage levels where magmas inherit their chemical and isotopic character by blending, assimilation and differentiation [1]. Anak Krakatau, like many other volcanoes, erupts shallow-level crustal xenoliths [2], indicating a potential role for upper crustal modification and hence late-stage changes to magma rheology and thus potential eruptive behaviour. Distinguishing deep vs. shallow crustal contamination processes at Krakatau, and elsewhere, is therefore crucial to understand and assess pre-eruptive magmatic conditions and their associated hazard potential. Here we report on a multi-disciplinary approach to unravel the crustal plumbing system of the persistently-active and dominantly explosive Anak Krakatau volcano [2, 3], employing rock-, mineral- and gas-isotope geochemistry and link these results with seismic tomography [4]. We show that pyroxene crystals formed at mid- and lower-crustal levels (9-11 km) and carry almost mantle-like isotope signatures (O, Sr, Nd, He), while feldspar crystals formed dominantly at shallow levels (< 5km) and display unequivocal isotopic evidence for late stage contamination (O, Sr, Nd). This obeservation places a significant element of magma-crust interaction into the uppermost, sediment-rich crust beneath the volcano. Magma storage in the uppermost crust can thus offer a possible explanation for the compositional modifications of primitive Krakatau magmas, and likely provides extra impetus to increased explosivity at Anak Krakatau. [1] Annen, et al., 2006. J. Petrol. 47, 505-539. [2] Gardner, et al., 2013. J. Petrol. 54, 149-182. [3] Dahren, et al., 2012. Contrib. Mineral. Petrol. 163, 631-651. [4] Jaxybulatov, et al., 2011. J. Volcanol. Geoth. Res. 206, 96-105.

  10. 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.

  11. 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

  12. Numerical Simulation of Magma Effects on Hydrothermal Venting at Ultra-Slow Spreading Southwest Indian Ridge

    NASA Astrophysics Data System (ADS)

    Zang, Hong; Niu, Xiongwei; Ruan, Aiguo; Li, Jiabiao; Meng, Lin

    2017-04-01

    Finite element method is used to numerically simulate oceanic crust thermal dynamics in order to understand the hydrothermal venting mechanism at ultra-slow spreading ridge, whether is the ancient magma chamber still living and supplying hot magma for vents or have surrounding hotspots been affecting on the ridge continually with melting and hot magma. Two models are simulated, one is a horizontal layered oceanic crust model and the other is a model derived from wide angle seismic experiment of OBS at the ultra-slow spreading Southwest Indian Ridge (50°E, Zhao et al., 2013; Li et al., 2015; Niu et al., 2015). For the former two cases are simulated: without magma from upper mantel or with continuous magma supply, and for the latter supposing magma supply occurs only once in short period. The main conclusions are as follows: (1) Without melt magma supply at the oceanic crust bottom, a magma chamber can live only thousands ten thousand years. According to the simulated results in this case, the magma chamber revealed by seismic data at the mid-east shallow section of the Southwest Indian Ridge could only last 0.8Ma, the present hydrothermal venting is impossible to be the caused by the magma activity occurred during 8-11Ma (Sauter et al., 2009). (2) The magma chamber can live long time with continuous hot magma supply beneath the oceanic crust due to the melting effects of surrounding ridge hotspots, and would result hydrothermal venting with some tectonic structures condition such as detachment faults. We suggest that the present hydrothermal activities at the mid-east shallow section of the Southwest Indian Ridge are the results of melting effects or magma supply from surrounding hotspots. This research was granted by the National Basic Research program of China (grant 2012CB417301) and the National Natural Science Foundation of China (grants 41176046, 91228205). References Zhao, M., Qiu, X., Li, J., et al., 2013. Three-dimensional seismic structure of the Dragon

  13. 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

  14. 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.

  15. Proceedings of the MEVTV workshop on the evolution of magma bodies on mars

    SciTech Connect

    Mouginis-Mark, P.; Holloway, J.

    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.

  16. 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.

  17. Petrography and geochemistry of lower Paleozoic sandstones, East Sinai, Egypt: Implications for provenance and tectonic setting

    NASA Astrophysics Data System (ADS)

    Akarish, Adel I. M.; El-Gohary, Amr M.

    2008-09-01

    Petrography, mineralogy and chemical analyses were combined to investigate the lower Paleozoic sandstones at Wadi El-Quseiyeb area, East Sinai. They are mainly classified texturally as silty sandstones, sandstones and clayey siltstone. Their average modal composition (QFL, 87:11:2), classifies them as quartz arenite and arkosic arenite, with high proportions of quartz, monocrystalline quartz grains, more potash feldspar than plagioclase and a low plagioclase/total feldspar ratio ( P/ F < 0.2). High SiO 2, K 2O > Na 2O, and low Fe 2O 3 + MgO values revealed by chemical analyses are consistent with the modal data. Other criteria include elevated Ba and Sr contents and depletion in the ferromagnesian elements. The petrography and geochemistry suggest a stable continental (passive) margin or intracratonic basin, analogous to that of an Atlantic-type continental shelf. Also, they reflect a stable craton interior source, devoid, to a large extent, of basic debris and ultimately derived from a low-lying granite-rich Precambrian craton. Chemical index of alteration (CIA) and the Plagioclase index of Alteration (PIA) values range from 57.2 to 93.0 and from 79.7 to 94.6, respectively. However, most samples have values more than 60, suggesting a moderate to relatively high degree of alteration (weathering) in the source area.

  18. Detecting magma bodies in the Icelandic crust: Constraints from Volcano Geodesy and Joint Interpretation with Other Data

    NASA Astrophysics Data System (ADS)

    Sigmundsson, F.; Parks, M.; Hooper, A. J.; Gudmundsson, M. T.; Halldorsson, S. A.; Einarsson, P.; Dumont, S.; Jonsdottir, K.; Sigmarsson, O.; Drouin, V.; Hreinsdottir, S.; Geirsson, H.; Brandsdóttir, B.; Vogfjord, K. S.; Heimisson, E. R.; Sturkell, E.; Eichelberger, J. C.; Markusson, S.

    2016-12-01

    Detailed geodetic observations have been carried on a number of volcanoes in Iceland, including both GPS-measurements and interferometric analysis of synthetic aperture radar images acquired by satellites (InSAR), with observed surface deformation interpreted in terms of magmatic processes. Volcanoes where data has been interpreted in terms of persistent magma reservoirs (magma storage areas) include Krafla, Askja, Bárdarbunga, Grímsvötn, Hekla, Katla and Eyjafjallajökull volcanoes. Magma storage is inferred beneath the centers of these volcanoes, at depth ranging from 2-25 km, when deformation data is interpreted in terms of point sources of pressure (Mogi models), or alternatively as sills or spheroids. The lateral dimensions and volume of the sources are difficult to constrain from geodesy alone, but the geodetic data suggests though in all cases localized reservoirs under the center of the volcanoes (beneath calderas or maxima in volcanic production). In some cases, external constraints applied on geodetic models are crucial, such as for the study of 2014-2015 caldera collapse (>60 m), dyking and major eruption within the Bárðarbunga volcanic system 2014-2015. Geobarometry from petrology and geochemistry provides independent constraints on depth of a magma reservoir, and together all data suggest a depth range of 10-12 km. Volume extracted from the reservoir was about 2 cubickilometers. For the case of caldera collapse, incorporation of slip on caldera into geodetic models is required to properly address the data. Geodetic data relating to a magma reservoir under Bárðarbunga and other volcanoes in Iceland will be reviewed and compared to other constraints from petrology, geochemistry and seismology, with joint models of interpretation presented, considering possibilities and resolution of each type of data. At one volcano (Krafla) inferred models of subsurface magma plumbing can be compared to results from drilling into a rhyolitic magma body at 2.1 km

  19. 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.

  20. Assimilation of preexisting Pleistocene intrusions at Long Valley by periodic magma recharge accelerates rhyolite generation: rethinking the remelting model

    NASA Astrophysics Data System (ADS)

    Simon, Justin I.; Weis, Dominique; DePaolo, Donald J.; Renne, Paul R.; Mundil, Roland; Schmitt, Axel K.

    2014-01-01

    Rhyolite flows and tuffs from the Long Valley area of California, which were erupted over a two-million-year time period, exhibit systematic trends in Nd, Hf, and Pb isotopes, trace element composition, erupted volume, and inferred magma residence time that provide evidence for a new model for the production of large volumes of silica-rich magma. Key constraints come from geochronology of zircon crystal populations combined with a refined eruption chronology from Ar-Ar geochronology; together these data give better estimates of magma residence time that can be evaluated in the context of changing magma compositions. Here, we report Hf, Nd, and Sr isotopes, major and trace element compositions, 40Ar/39Ar ages, and U-Pb zircon ages that combined with existing data suggest that the chronology and geochemistry of Long Valley rhyolites can be explained by a dynamic interaction of crustal and mantle-derived magma. The large volume Bishop Tuff represents the culmination of a period of increased mantle-derived magma input to the Long Valley volcanic system; the effect of this input continued into earliest postcaldera time. As the postcaldera evolution of the system continued, new and less primitive crustal-derived magmas dominated the system. A mixture of varying amounts of more mafic mantle-derived and felsic crustal-derived magmas with recently crystallized granitic plutonic materials offers the best explanation for the observed chronology, secular shifts in Hf and Nd isotopes, and the apparently low zircon crystallization and saturation temperatures as compared to Fe-Ti oxide eruption temperatures. This scenario in which transient crustal magma bodies remained molten for varying time periods, fed eruptions before solidification, and were then remelted by fresh recharge provides a realistic conceptual framework that can explain the isotopic and geochemical evidence. General relationships between crustal residence times and magma sources are that: (1) precaldera rhyolites

  1. Volatile budget of Eyjafjallajokull magmas

    NASA Astrophysics Data System (ADS)

    Sigurdsson, H.; Mandeville, C. W.

    2010-12-01

    Volatile elments played a critical role in the style of activity during the 2010 eruptions of the glacier-covered Eyjafjallajokull volcano in Iceland. The alkali basalt flank eruption at Fimmvorduhals was dominated by vigorous fire fountaining that produced dominantly spatter-fed aa lava flows. Production of fine ash during the subsequent summit eruption has been variously attributed to magma fragmentation, either due to water-ice-magma interaction related to the 250 m thick glacier cover over the crater, or juvenile volatile content of the magma. Considering the great impact of the ash dispersal on trans-North Atlantic aviation, knowledge of the fragmentation mechanism and the relative roles of juvenile magmatic gases versus phreatomagmatic fragmentation is of prime significance. To evaluate the potential importance of juvenile components, the concentrations of volatiles in magmas erupted in 2010 from Eyjafjallajokull volcano in Iceland have been measured. Analysis of glass inclusions in olivine Fo 77-85 and plagioclase phenocrysts in the alkali basalt magma erupted at Fimmvorduhals flank eruption contain high total volatiles in the range 0.96 - 2.12 wt.%, and sulfur 0.10 - 0.16 wt.%. These glass inclusions are comparable to major element bulk composition of Fimmvörduháls alkali basalt lavas. In contrast, tephra from the explosive summit crater eruption are trachy-andesitic. This magma contains a rather wide range of olivine and plagioclase phenocrysts of Fo48-79 and An 69-81, with both basaltic and andesitic glass inclusions. This diversity is also reflected in a much wider range of total volatile content from 0.1 - 2.88 wt.% and sulfur 0.1 - 0.24 wt.%. At the basic end, the glass inclusions are comparable to the Fimmvorduhals alkali basalt lava, but some have andesitic composition. The highest volatile content is observed in the andesitic glass inclusions in plagioclase An78. Further analysis of glass inclusions and matrix glass by FTIR and ion probe is in

  2. Magma, Magma, Quite Contaminated, How Does Your Garnet Grow?

    NASA Astrophysics Data System (ADS)

    Lackey, J.; Romero, G. A.; Valley, J. W.

    2010-12-01

    Garnet in granitoid rocks has drawn considerable attention and discussion because of uncertainty surrounding its origins. For example, enrichment of Al, resulting in peraluminous magmas capable of crystallizing garnets, may be controlled by contamination or extreme differentiation; Mn enrichment in aplitic and pegmatitic phases suggests garnet may appear only at relatively low, near solidus temperatures. Peritectic garnet, grown by magma-wallrock reaction, may be confused with magmatic garnet, and xenocrysts of metamorphic garnet, entrained from wallrocks, further complicate interpretation. We address these uncertainties with the SIMS analysis of oxygen isotope variations in single garnet crystals and crystal populations in granitic rocks. Values of δ18O were measured on a CAMECA IMS 1280 using a 10 µm spot size and typical precision of ± 0.3 at 2 standard deviations. Analyses were corrected for instrumental mass fractionation according to the newly solved bias correction protocol for garnet (Page et al. 2010). Samples were collected from the Devonian Togus and Hallowell plutons in the south central Maine. These plutons are an ideal site for this study because they are peraluminous and contain pervasive garnet, they locally intrude pelitic, garnet-bearing wallrocks, and they have field evidence of xenolith entrainment and peritectic reaction of xenoliths and the host magmas. Garnet δ18O values of 7.5-10.5‰ show a large range of crustal input to host magmas. Crystal-to-crystal variation of δ18O in hand-samples varies up to 2‰, confirming that garnet populations have complex origins. Traverses (20-50 spots) of single crystals show that δ18O varies up to 1‰, with rims of crystals (outer 50-100µm) being up to 1‰ higher or lower than interiors. Increases of δ18O are interpreted as late-stage contamination, whereas lower δ18O rims, with correspondence to decreasing Fe/Mg ratio, suggest growth during falling magma temperature (50-100°C). Some garnet

  3. 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.

  4. The Magma Reservoir Under Bárdarbunga, Constraints from 2014-2015 Caldera Collapse

    NASA Astrophysics Data System (ADS)

    Gudmundsson, M. T.; Hooper, A. J.; Sigmundsson, F.; Sigmarsson, O.; Halldorsson, S. A.; Jonsdottir, K.; Vogfjord, K. S.; Holohan, E. P.; Ofeigsson, B.; Hensch, M.; Guðmundsson, G.; Einarsson, P.; Parks, M.; Hognadottir, T.; Jarosch, A. H.; Jonasson, K.; Magnússon, E.; Hreinsdottir, S.; Bagnardi, M.; Pálsson, F.; Cesca, S.; Walter, T. R.; Dahm, T.; Barsotti, S.; Hjorleifsdottir, V.; Pfeffer, M. A.; Dürig, T.

    2016-12-01

    The slow caldera collapse of Bárdarbunga, central Iceland, in August 2014-February 2015 was monitored in more detail than possible in earlier caldera collapses. It occurred during a major rifting event when 2 km3 of basaltic magma were withdrawn from underneath the volcano, partly intruded in the crust as a dike while the majority was erupted, forming the Holuhraun lava field, 40-50 km to the northeast of the volcano. Time series obtained include rate of collapse, shape of subsidence bowl, seismicity, fault movements, magma reservoir withdrawal rate, and various geochemical parameters. A down-sag caldera with a diameter/maximum subsidence ratio of 150 was formed, mostly within the 500-700 m deep pre-existing caldera. The magma reservoir was constrained with geobarometry and geodesy to be at approximately 12 km depth. Distinct element modeling indicates that the ring faults extend from the magma reservoir up to about 1-3 km below the surface. The collapsing piston inside the ring-faults is approximately 6-7 km wide and 10 km long, maximum subsidence was 65 m and the volume of the subsidence bowl 1.8 km3. These values suggest a that the magma reservoir extends over 30-55 km2, has a minimum thickness of 0.1 km but may be much thicker. The geochemistry of the erupted magma is consistent with a compositionally homogeneous and thus reasonably well mixed reservoir. At least when viewed on a time scale of hours or longer, outflow was regular and followed a near exponential decline, controlled by reduction in driving pressure. These observations are consistent with a single, liquid and convecting magma body. Events at Bárdarbunga in 2014-15 highlight the role of crustal magma reservoirs under central volcanoes as sources of major effusive eruptions on the associated fissure swarms. Given the magnitude of past eruptions, e.g. Laki in 1783, caldera collapses and thus minimum thicknesses of extensive magma reservoirs may have been several hundred meters.

  5. Regional and temporal variability of melts during a Cordilleran magma pulse: Age and chemical evolution of the jurassic arc, eastern mojave desert, California

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.; Miller, David; Howard, Keith A.; Fox, Lydia; Schermer, Elizabeth R.; Jacobson, C.E.

    2017-01-01

    Intrusive rock sequences in the central and eastern Mojave Desert segment of the Jurassic Cordilleran arc of the western United States record regional and temporal variations in magmas generated during the second prominent pulse of Mesozoic continental arc magmatism. U/Pb zircon ages provide temporal control for describing variations in rock and zircon geochemistry that reflect differences in magma source components. These source signatures are discernible through mixing and fractionation processes associated with magma ascent and emplacement. The oldest well-dated Jurassic rocks defining initiation of the Jurassic pulse are a 183 Ma monzodiorite and a 181 Ma ignimbrite. Early to Middle Jurassic intrusive rocks comprising the main stage of magmatism include two high-K calc-alkalic groups: to the north, the deformed 183–172 Ma Fort Irwin sequence and contemporaneous rocks in the Granite and Clipper Mountains, and to the south, the 167–164 Ma Bullion sequence. A Late Jurassic suite of shoshonitic, alkali-calcic intrusive rocks, the Bristol Mountains sequence, ranges in age from 164 to 161 Ma and was emplaced as the pulse began to wane. Whole-rock and zircon trace-element geochemistry defines a compositionally coherent Jurassic arc with regional and secular variations in melt compositions. The arc evolved through the magma pulse by progressively greater input of old cratonic crust and lithospheric mantle into the arc magma system, synchronous with progressive regional crustal thickening.

  6. 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.

  7. 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.

  8. 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

  9. The genetics of geochemistry.

    PubMed

    Croal, Laura R; Gralnick, Jeffrey A; Malasarn, Davin; Newman, Dianne K

    2004-01-01

    Bacteria are remarkable in their metabolic diversity due to their ability to harvest energy from myriad oxidation and reduction reactions. In some cases, their metabolisms involve redox transformations of metal(loid)s, which lead to the precipitation, transformation, or dissolution of minerals. Microorganism/mineral interactions not only affect the geochemistry of modern environments, but may also have contributed to shaping the near-surface environment of the early Earth. For example, bacterial anaerobic respiration of ferric iron or the toxic metalloid arsenic is well known to affect water quality in many parts of the world today, whereas the utilization of ferrous iron as an electron donor in anoxygenic photosynthesis may help explain the origin of Banded Iron Formations, a class of ancient sedimentary deposits. Bacterial genetics holds the key to understanding how these metabolisms work. Once the genes and gene products that catalyze geochemically relevant reactions are understood, as well as the conditions that trigger their expression, we may begin to predict when and to what extent these metabolisms influence modern geochemical cycles, as well as develop a basis for deciphering their origins and how organisms that utilized them may have altered the chemical and physical features of our planet.

  10. Mathematical and numerical modelling of fractional crystallization coupled with chemical exchanges and differential magma-solid transport in magma chambers

    NASA Astrophysics Data System (ADS)

    Lakhssassi, Morad; Guy, Bernard; Cottin, Jean-Yves; Touboul, Eric

    2010-05-01

    The knowledge of the chemical evolution of magmas is a major concern in geochemistry and petrology. The jumps (or discontinuities) of chemical composition observed in volcanic series from the same province are also the subject of many studies. In particular the phenomenon of "Daly gap" (Daly 1910, 1925), the name given to the jump in chemical composition between the mafic rocks (basalt) and felsic rocks (trachyte, rhyolite, phonolite), corresponding to the absence or scarcity of rocks of intermediate composition (andesite), in both ocean and continental series. Some authors explain these compositional jumps thanks to the intervention of various geological phenomena which follow in time. For example, when a magma chamber turns from a closed to an open system, the lava of a specific composition is ejected to the surface, favoring the rise of the lightest, the most volatile-rich and the less sticky magmas to the surface of the earth (Geist et al., 1995, Thompson et al., 2001). The various explanations offered, although they agree satisfactorily with the natural data, most often lead us away from basic phenomena of melting / solidification, relative migration and chemical equilibrium between solid and liquid and involve various additional phenomena. In our study, we propose a numerical modelling of the crystallization of a closed magma chamber. The physical and mathematical model distinguishes three main classes of processes occurring simultaneously: - heat transfer and solidification, - relative migration between the solid and the liquid magma, - chemical reactions between the two (solid and liquid) phases. Writing the partial differential equations with dimensionless numbers makes two parameters appear, they express the respective ratios of the solidification velocity on the transport velocity, and the kinetics of chemical exchange on the transport velocity. The speed of relative movement between the solid and the liquid, the solidification velocity and the chemical

  11. The lherzolitic shergottite Grove Mountains 99027: Rare earth element geochemistry

    NASA Astrophysics Data System (ADS)

    Hsu, Weibiao; Guan, Yunbin; Wang, Henian; Leshin, Laurie A.; Wang, Rucheng; Zhang, Wenlan; Chen, Xiaoming; Zhang, Fusheng; Lin, Chengyi

    2004-05-01

    We report here on an ion probe study of rare earth element (REE) geochemistry in the lherzolitic shergottite Grove Mountains (GRV) 99027. This meteorite shows almost identical mineralogy, petrology, and REE geochemistry to those of the lherzolitic shergottites Allan Hills (ALH) A77005, Lewis Cliff (LEW) 88516, and Yamato (Y-) 793605. REE concentrations in olivine, pyroxenes, maskelynite, merrillite, and melt glass are basically comparable to previous data obtained from ALH A77005, LEW 88516, and Y-793605. Olivine is the dominant phase in this meteorite. It is commonly enclosed by large (up to several mm) pigeonite oikocrysts. Non-poikilitic areas consist of larger olivine grains (~mm), pigeonite, augite, and maskelynite. Minor merrillite (up to 150 mm in size) is widespread in non-poikilitic regions, occurring interstitially between olivine and pyroxene grains. It is the main REE carrier in GRV 99027 and has relatively higher REEs (200-1000 Å CI) than that of other lherzolitic shergottites. A REE budget calculation for GRV 99027 yields a whole rock REE pattern very similar to that of other lherzolites. It is characterized by the distinctive light REE depletion and a smooth increase from light REEs to heavy REEs. REE microdistributions in GRV 99027 strongly support the idea that all lherzolitic shergottites formed by identical igneous processes, probably from the same magma chamber on Mars. Despite many similarities in mineralogy, petrography, and trace element geochemistry, subtle differences exist between GRV 99027 and other lherzolitic shergottites. GRV 99027 has relatively uniform mineral compositions (both major elements and REEs), implying that it suffered a higher degree of sub-solidus equilibration than the other three lherzolites. It is notable that GRV 99027 has experienced terrestrial weathering in the Antarctic environment, as its olivine and pyroxenes commonly display a light REE enrichment and a negative Ce anomaly. Caution needs to be taken in future

  12. Geochemistry and chronology of the Bunburra Rockhole ungrouped achondrite

    NASA Astrophysics Data System (ADS)

    Spivak-Birndorf, Lev J.; Bouvier, Audrey; Benedix, Gretchen K.; Hammond, Samantha; Brennecka, Gregory A.; Howard, Kieren; Rogers, Nick; Wadhwa, Meenakshi; Bland, Philip A.; Spurný, Pavel; Towner, Martin C.

    2015-05-01

    Bunburra Rockhole is a unique basaltic achondrite that has many mineralogical and petrographic characteristics in common with the noncumulate eucrites, but differs in its oxygen isotope composition. Here, we report a study of the mineralogy, petrology, geochemistry, and chronology of Bunburra Rockhole to better understand the petrogenesis of this meteorite and compare it to the eucrites. The geochemistry of bulk samples and of pyroxene, plagioclase, and Ca-phosphate in Bunburra Rockhole is similar to that of typical noncumulate eucrites. Chronological data for Bunburra Rockhole indicate early formation, followed by slow cooling and perhaps multiple subsequent heating events, which is also similar to some noncumulate eucrites. The 26Al-26Mg extinct radionuclide chronometer was reset in Bunburra Rockhole after the complete decay of 26Al, but a slight excess in the radiogenic 26Mg in a bulk sample allows the determination of a model 26Al-26Mg age that suggests formation of the parent melt for this meteorite from its source magma within the first ~3 Ma of the beginning of the solar system. The 207Pb-206Pb absolute chronometer is also disturbed in Bunburra Rockhole minerals, but a whole-rock isochron provides a re-equilibration age of ~4.1 Ga, most likely caused by impact heating. The mineralogy, geochemistry, and chronology of Bunburra Rockhole demonstrate the similarities of this achondrite to the eucrites, and suggest that it formed from a parent melt with a composition similar to that for noncumulate eucrites and subsequently experienced a thermal history and evolution comparable to that of eucritic basalts. This implies the formation of multiple differentiated parent bodies in the early solar system that had nearly identical bulk elemental compositions and petrogenetic histories, but different oxygen isotope compositions inherited from the solar nebula.

  13. Petrogenesis of the Doros Gabbroic Complex, Namibia: Multiple mingling magma mushes?

    NASA Astrophysics Data System (ADS)

    Owen-Smith, T. M.; Ashwal, L. D.; Torsvik, T. H.; Harris, C.

    2012-04-01

    The 132 Ma Paraná-Etendeka Large Igneous Province has been attributed to the impingement of the Tristan mantle plume and the associated opening of the South Atlantic Ocean, during the Early Cretaceous breakup of West Gondwana (Miller, 2008). On the Namibian side of the rift, this is preserved as the extensive Etendeka flood volcanics, and the Damaraland Intrusive Suite, a series of subvolcanic intrusions within the Damara Orogenic Belt (Miller, 2008). The Doros Complex is a relatively small mafic layered intrusion that forms part of the Damaraland Suite. Doros consists of a gently inward-dipping series of stacked layers of massive or foliated olivine gabbro with varying compositions and mineral proportions, cut by gabbro pegmatite, monzodiorite and dolerite dykes. This study investigates the petrogenesis of the Doros magmas, using major element, trace element and Sr-, Nd- and Pb-isotopic data. Trace element and isotope geochemistry confirm that all the Doros rock types, except the dolerite, are derived from the same magma source. The dolerite is interpreted to belong to the Horingbaai dyke suite of the Etendeka. The mineralogy and rock compositions indicate negligible crustal contamination, apart from a glassy chill margin that shows evidence of assimilation of local Damaran metasediments. Depleted 143Nd/144Nd, moderate 87Sr/86Sr and particular trends in incompatible trace element ratios indicate that the Doros magma was derived primarily from enriched Tristan plume melts with a significant component of entrained depleted upper mantle and minor lower crustal or lithospheric mantle contamination. It is argued that the Doros intrusion cannot be explained by the emplacement and subsequent differentiation of a single body of magma. We present evidence, including intrusive interlayer contacts, grain-size layering, flow foliation patterns, cumulus crystal enclaves, and a lack of simple progressive fractionation trends in whole-rock and mineral chemistry, that favours

  14. 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.

  15. Differentiation of Historical Hekla Magmas

    NASA Astrophysics Data System (ADS)

    Oswald, P.; Geist, D.; Harpp, K.; Christensen, B.; Wallace, P.

    2007-12-01

    straightforward way to the rock compositions, lack significant zoning, and have little variation in each sample. Some lavas show thin reaction rims of pyroxene mantling olivine crystals. Our interpretation is that the phenocrysts grew from the host liquids after the SiO2 gradient was established in the magma reservoir. The data collected thus far are consistent with a persistent basaltic andesite magma chamber beneath Hekla volcano in which the top of the magma column evolves through fractional crystallization proportional to the length of time between eruption events. Melt inclusions in olivine from the 2000 basaltic andesite tephra and 1104 rhyolite tephra have H2O contents ranging from 2.5-2.7 wt.% and 4.6-6.0 wt.%, respectively, but CO2 contents for all melt inclusions are below detection. Calculated vapor saturation pressures at magmatic temperatures range from ~0.6 kbars for the basaltic andesite to 1.4-2.2 kbars for the rhyolite. These values are significantly less than the >3 kbar estimate for the present-day Hekla magma chamber indicating either: 1) crystallization under vapor-undersaturated conditions in the magma reservoir; or 2) formation of at least some crystals within the conduit system above the reservoir. The ubiquitous zoning in Hekla magmas suggests a stable thermal state and recharge rate through time extending at least since the last large rhyolite eruption.

  16. Strontium Isotopes and Magma Dynamics

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ellis, B. S.; Ramos, F. C.

    2010-12-01

    Over the past decade, it has become clear that volcanic rocks commonly exhibit internal heterogeneity in radiogenic isotopes. In particular, strontium isotopic disequilibrium between co-exisitng phenocrysts, between phenocrysts and matrix, and isotopic zoning within single crystals has been demonstrated in basalts, andesites, dacites, rhyolites and alkaline magmas; in some cases, the range in 87Sr/86Sr among different components in the same rock may equal or exceed the bulk-rock range seen in the entire formation, volcanic center, or province. High-temperature “Snake River type” rhyolites appear to be an exception. Despite the occurrence of Snake River Plain rhyolites in a region of isotopically highly variable crust and mantle, and significant differences from rhyolite unit to rhyolite unit, internally they are near-homogeneous in 87Sr/86Sr. Little or no zoning is found within feldspar phenocrysts, and feldspars within a single unit are tightly grouped. Some units show minor contrasts between phenocrysts and matrix. High temperature rhyolitic magmas possess a unique combination of temperature and melt viscosity. Although they are typically 200°C hotter than common rhyolites, the effect on visocity is offset by lower water contents (~2 wt%), hence their melt viscosities are in the same range as common, water-rich, cool rhyolites (105 - 106 Pa s). Yet magmatic temperatures are in the same range as basaltic andesites and andesites, consequently cation diffusion rates in feldspar are 2 - 3 orders of magnitude greater than in common rhyolites. We hypothesize that this combination of characteristics promotes Sr isotopic homogeneity: high melt viscosities tend to inhibit crystal transfer and mixing of isotopically distinct components on timescales shorter than those required for diffusive homogenization of Sr between phenocrysts and matrix (100 - 1000 years). This is not the case for most magmas, in which either crystal transfer is rapid (<< 100 years) due to low

  17. 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.

  18. 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.

  19. 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.

  20. Geochemistry of sedimentary ore deposits

    SciTech Connect

    Maynard, J. B.

    1983-01-01

    A text providing a sedimentological treatment of a study on ore deposits, and especially as related to geochemistry. Excellently documented (about 5000 citations). Well indexed with the index of deposits and localities separated. Contents, Iron. Copper and silver. Aluminum and nickel. Manganese. Uranium. Lead and zinc. Volcanic-sedimentary ores. Appendix. Indexes.

  1. 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.

  2. Advancing Geomicrobiology and Microbial Geochemistry

    NASA Astrophysics Data System (ADS)

    Druschel, Gregory K.; Dick, Gregory J.

    2014-03-01

    By examining microbial and geochemical processes together, scientists have been able to gain a vastly clearer picture of how microorganisms shape their surrounding environment and vice versa. This was the central theme of a 2-day workshop held in October 2013 in Chicago, Ill., that brought together 30 leading scientists from the rapidly growing field of geomicrobiology and microbial geochemistry (GMG).

  3. 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

  4. Electromagnetic imaging of crustal magma bodies

    NASA Astrophysics Data System (ADS)

    Unsworth, M. J.

    2016-12-01

    Magma bodies are the location of a number of important processes that have formed the crust. In a magma chamber, a parent magma differentiates to produce magmas with a range of compositions that may either be erupted, or crystallize to form intrusions. Geological studies of erupted lavas and crystallized magma bodies exposed at the surface have given valuable information about processes occurring in magma bodies. Numerical modelling has given important insights into the complex processes occurring in these bodies. Geophysical studies complement geological observations and give real time images of magma bodies. Seismic studies have delineated a number of magma bodies and can constrain the melt fraction through studies of velocity and attenuation, while geodetic data have detected time variations in size through the associated surface deformation. Electromagnetic (EM) methods offer an alternative view of crustal magmatism. Both magma bodies and associated hydrothermal systems are characterized by electrical resistivity values that are much lower than the surrounding crystalline rock. Magnetotellurics (MT) is one of the most widely used EM methods and can image the subsurface resistivity structure in 3-D using natural EM signals. The resistivity of the magma body depends on the amount, geometry and composition of the melt. Interpretation of the electrical resistivity of partially molten zones was previously quite non-unique. However, when resistivity models are combined with (1) other geophysical data, (2) petrological constrains of melt composition and (3) laboratory measurements of the resistivity of partial melts, the non-uniqueness can be greatly reduced. This presentation will review what can be determined about crustal magma bodies using EM methods. The MT method will be reviewed with an emphasis on which resistivity model features of magmatic and hydrothermal are well resolved by EM surveys. The approach outlined above to reduce the uncertainty in resistivity

  5. Exploring fractionation models for Martian magmas

    NASA Astrophysics Data System (ADS)

    Udry, Arya; Balta, J. Brian; McSween, Harry Y.

    2014-01-01

    primary compositions, i.e., magmas that did not experience fractionation and/or contamination after extraction from the mantle, occur as a subset of Martian meteorites and a few lavas analyzed on the planet's surface by rovers. Eruptions of primary magmas are rare on Earth and presumably on Mars. Previous studies of fractional crystallization of Martian primary magmas have been conducted under isobaric conditions, simulating idealized crystallization in magma chambers. Polybaric fractionation, which occurs during magma ascent, has not been investigated in detail for Martian magmas. Using the MELTS algorithm and the pMELTS revision, we present comprehensive isobaric and polybaric thermodynamic calculations of the fractional crystallization of four primary or parental Martian magmas (Humphrey, Fastball, Y-980459 shergottite, and nakhlite parental melts) using various pressure-temperature paths, oxygen fugacities, and water contents to constrain how these magmas might evolve. We then examine whether known Martian alkaline rock compositions could have formed through fractional crystallization of these magmas under the simulated conditions. We find that isobaric and polybaric crystallization paths produce similar residual melt compositions, but given sufficient details, we may be able to distinguish between them. We calculate that Backstay (Gusev Crater) likely formed by fractionation of a primary magma under polybaric conditions, while Jake_M (Gale Crater) may have formed through melting of a metasomatized mantle, crustal assimilation, or fractional crystallization of an unknown primary magma. The best fits for the Backstay composition indicate that consideration of polybaric crystallization paths can help improve the quality of fit when simulating liquid lines of descent.

  6. 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

  7. Molecular environmental geochemistry

    NASA Astrophysics Data System (ADS)

    O'Day, Peggy A.

    1999-05-01

    The chemistry, mobility, and bioavailability of contaminant species in the natural environment are controlled by reactions that occur in and among solid, aqueous, and gas phases. These reactions are varied and complex, involving changes in chemical form and mass transfer among inorganic, organic, and biochemical species. The field of molecular environmental geochemistry seeks to apply spectroscopic and microscopic probes to the mechanistic understanding of environmentally relevant chemical processes, particularly those involving contaminants and Earth materials. In general, empirical geochemical models have been shown to lack uniqueness and adequate predictive capability, even in relatively simple systems. Molecular geochemical tools, when coupled with macroscopic measurements, can provide the level of chemical detail required for the credible extrapolation of contaminant reactivity and bioavailability over ranges of temperature, pressure, and composition. This review focuses on recent advances in the understanding of molecular chemistry and reaction mechanisms at mineral surfaces and mineral-fluid interfaces spurred by the application of new spectroscopies and microscopies. These methods, such as synchrotron X-ray absorption and scattering techniques, vibrational and resonance spectroscopies, and scanning probe microscopies, provide direct chemical information that can elucidate molecular mechanisms, including element speciation, ligand coordination and oxidation state, structural arrangement and crystallinity on different scales, and physical morphology and topography of surfaces. Nonvacuum techniques that allow examination of reactions in situ (i.e., with water or fluids present) and in real time provide direct links between molecular structure and reactivity and measurements of kinetic rates or thermodynamic properties. Applications of these diverse probes to laboratory model systems have provided fundamental insight into inorganic and organic reactions at

  8. 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

  9. 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.

    2014-12-01

    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.

  10. 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.

  11. 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.

  12. 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.

  13. Convection and mixing in magma chambers

    NASA Astrophysics Data System (ADS)

    Turner, J. S.; Campbell, I. H.

    1986-08-01

    This paper reviews advances made during the last seven years in the application of fluid dynamics to problems of igneous petrology, with emphasis on the laboratory work with which the authors have been particularly involved. Attention is focused on processes in magma chambers which produce diversity in igneous rocks, such as fractional crystallization, assimilation and magma mixing. Chamber geometry, and variations in the density and viscosity of the magma within it, are shown to play a major role in determining the dynamical behaviour and the composition of the erupted or solidified products. Various convective processes are first reviewed, and in particular the phenomenon of double-diffusive convection. Two types of double-diffusive interfaces between layers of different composition and temperature are likely to occur in magma chambers. A diffusive interface forms when a layer of hot dense magma is overlain by cooler less dense magma. Heat is transported between the layers faster than composition, driving convection in both layers and maintaining a sharp interface between them. If a layer of hot slightly less dense magma overlies a layer of cooler, denser but compositionally lighter magma, a finger interface forms between them, and compositional differences are transported downwards faster than heat (when each is expressed in terms of the corresponding density changes). Processes leading to the establishment of density, compositional and thermal gradients or steps during the filling of a magma chamber are considered next. The stratification produced, and the extent of mixing between the inflowing and resident magmas, are shown to depend on the flow rate and on the relation between the densities and viscosities of the two components. Slow dense inputs of magma may mix very little with resident magma of comparable viscosity as they spread across the floor of the chamber. A similar pulse injected with high upward momentum forms a turbulent "fountain", which is a

  14. 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

  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. 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.

  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. Taxonomy of Magma Mixing II: Thermochemistry of Mixed Crystal-Bearing Magmas Using the Magma Chamber Simulator

    NASA Astrophysics Data System (ADS)

    Bohrson, W. A.; Spera, F. J.; Neilson, R.; Ghiorso, M. S.

    2013-12-01

    Magma recharge and magma mixing contribute to the diversity of melt and crystal populations, the abundance and phase state of volatiles, and thermal and mass characteristics of crustal magma systems. The literature is replete with studies documenting mixing end-members and associated products, from mingled to hybridized, and a catalytic link between recharge/mixing and eruption is likely. Given its importance and the investment represented by thousands of detailed magma mixing studies, a multicomponent, multiphase magma mixing taxonomy is necessary to systematize the array of governing parameters (e.g., pressure (P), temperature (T), composition (X)) and attendant outcomes. While documenting the blending of two melts to form a third melt is straightforward, quantification of the mixing of two magmas and the subsequent evolution of hybrid magma requires application of an open-system thermodynamic model. The Magma Chamber Simulator (MCS) is a thermodynamic, energy, and mass constrained code that defines thermal, mass and compositional (major, trace element and isotope) characteristics of melt×minerals×fluid phase in a composite magma body-recharge magma-crustal wallrock system undergoing recharge (magma mixing), assimilation, and crystallization. In order to explore fully hybridized products, in MCS, energy and mass of recharge magma (R) are instantaneously delivered to resident magma (M), and M and R are chemically homogenized and thermally equilibrated. The hybrid product achieves a new equilibrium state, which may include crystal resorption or precipitation and/or evolution of a fluid phase. Hundreds of simulations systematize the roles that PTX (and hence mineral identity and abundance) and the mixing ratio (mass of M/mass of R) have in producing mixed products. Combinations of these parameters define regime diagrams that illustrate possible outcomes, including: (1) Mixed melt composition is not necessarily a mass weighted mixture of M and R magmas because

  19. 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.

  20. Depth of origin of magma in eruptions.

    PubMed

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

    2013-09-26

    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.

  1. 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

  2. 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.

  3. 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.

  4. Magma chamber dynamics and Vesuvius eruption forecasting

    NASA Astrophysics Data System (ADS)

    Dobran, F.

    2003-04-01

    Magma is continuously or periodically refilling an active volcano and its eruption depends on the mechanical, fluid, thermal, and chemical aspects of the magma storage region and its surroundings. A cyclically loaded and unloaded system can fail from a weakness in the system or its surroundings, and the fluctuating stresses can produce system failures at stress levels that are considerably below the yield strength of the material. Magma in a fractured rock system within a volcano is unstable and propagates toward the surface with the rate depending on the state of the system defined by the inertia, gravity, friction, and permeability parameters of magma and its source region. Cyclic loading and unloading of magma from a reservoir caused by small- or medium-scale eruptions of Vesuvius can produce catastrophic plinian eruptions because of the structural failure of the system and the quiescent periods between these eruptions increase with time until the next eruption cycle which will be plinian or subplinian and will occur with a very high probability this century. Such a system behavior is predicted by a Global Volcanic Simulator of Vesuvius developed for simulating different eruption scenarios for the purpose of urban planning the territory, reducing the number of people residing too close to the cone of the volcano, and providing safety to those beyond about 5 km radius of the crater. The magma chamber model of the simulator employs a thermomechanical model that includes magma inflow and outflow from the chamber, heat and mass transfer between the chamber and its surroundings, and thermoelastoplastic deformation of the shell surrounding the magma source region. These magma chamber, magma ascent, and pyroclastic dispersion models and Vesuvius eruption forecasting are described in Dobran, F., VOLCANIC PROCESSES, Kluwer Academic/Plenum Publishers, 2001, 590 pp.

  5. 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).

  6. Sources and formation conditions of sulfide-silicate magmas in the Noril'sk district

    NASA Astrophysics Data System (ADS)

    Gorbachev, N. S.

    2012-05-01

    Geology, tectonomagmatic reactivation of the Noril'sk district, as well as stratigraphy and geochemistry of the volcanic sequence are considered. Sources and formation mechanism of ore-bearing magma and the scope of ore formation are discussed. The Permian-Triassic flood-basalt magmatism of the Noril'sk district developed in part of the Siberian Platform with Archean-Paleoproterozoic basement broken into blocks and overlapped by a sedimentary cover up to 13 km thick and a volcanic sequence reaching 3.7 km in thickness. The geophysical data show that remnants of the subducted ancient oceanic crust exist in the mantle and fragments of transitional magma chambers and conduits are retained at different levels of the Earth's crust. The cyclic tectonomagmatic evolution of the territory was characterized by alternation of extension with intense volcanic activity and compression accompanied by waning of volcanic eruptions. The early rifting, transitional stage, and late dispersed spreading are distinguished. The associations of volcanic (lavas and tuffs) and intrusive rocks were formed during each stage. The volcanic sequence is subdivided into 11 formations. The intrusions of the Talnakh and Noril'sk ore fields are distinguished by two-level structure with the Upper Noril'sk ore-bearing intrusions above and the Lower Noril'sk barren intrusions below. Two types of primary magmas differ in geochemistry of lavas and intrusions: (1) OIB-type high-Ti magma (iv, sv, gd formations of the first stage from bottom to top) and (2) low-Ti magma (hk, tk, nd formations of the second stage and mr-mk formations of the third stage). The nd formation depleted in ore elements and the ore-bearing cumulus composed of silicate and sulfide melts in combination with early silicate minerals and chromite are products of the fractionation of the primary low-Ti magma. As follows from geochemical parameters, intrusions of the Lower Noril'sk type are comagmatic to the evolved lavas of the nd3

  7. 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.

  8. Timing magma ascent at Popocatepetl Volcano, Mexico, 2000-2001

    NASA Astrophysics Data System (ADS)

    Martin-Del Pozzo, A. L.; Cifuentes, G.; Cabral-Cano, E.; Bonifaz, R.; Correa, F.; Mendiola, I. F.

    2003-07-01

    Magnetic anomalies may be used to constrain magma ascent and are useful as precursors to eruptions especially when correlated with other geophysical and geochemical data. In this paper we present multiparameter data on the magnetics, dome morphology, geochemistry and seismicity associated with the December 2000-January 2001 eruptions, the largest of the recent eruptions at Popocatepetl Volcano. A 6-month data period was studied in order to evaluate the precursors and post-eruption processes. Several cycles of dome construction and destruction occurred from September 2000 through February 2001. In December, large amplitude tremor associated with a higher effusion rate resulted in the formation of a large dome which filled the crater to within about 50 m of the lowest part of the crater rim. Seismic activity in December was marked by many volcanotectonic earthquakes and both high frequency and harmonic tremor. On December 12 and 13, an increase in the tremor amplitude was followed by ash eruptions with 1.7-5-km-high columns. Tremor amplitude increased again on December 15 and oscillated for the next four days. Activity remained high until the end of the month. On January 22, an 18-km-high plume produced ash and pumice fall to the east as well as pyroclastic flows and mudflows which reached 6 km from the crater. The eruption left three concentric explosion pits, partially destroying the December dome. Mixing of a mafic olivine-bearing melt with a more evolved magma triggered the larger eruption on January 22 as can be seen from the higher MgO concentrations in some of the ejecta and the presence of a dark andesitic scoria with lower silica content and a white andesitic pumice with higher silica content. Precursory negative magnetic anomalies up to 5 nT (-3.2 nT, -5 nT, -2.9 nT) were associated with the ascent of the larger batches of magma which preceded the increases in seismicity, before the December 2000-January 22 VEI 3-4 eruptions. No significant increases in

  9. 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

  10. Rethinking early Earth phosphorus geochemistry.

    PubMed

    Pasek, Matthew A

    2008-01-22

    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 (HPO(3)(2-)), 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.

  11. 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.

  12. Time to Solidify an Ocean of Magma

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2009-03-01

    Cosmochemists are reasonably sure that a global ocean of magma surrounded the Moon when it formed. This was a monumentally important event in lunar history, forming the primary feldspar-rich crust of the lunar highlands and setting the stage for subsequent melting inside the Moon to make additional crustal rocks. Numerous questions remain about the complex array of processes that could have operated in such a huge amount of magma, and about how long it took to solidify the magma ocean. Alex Nemchin and colleagues at Curtin University of Technology (Australia), Westfailische Wilhelms-Universitat (Munster, Germany), and the Johnson Space Center (Houston, Texas, USA) dated a half-millimeter grain of the mineral zircon (ZrSiO4) in an impact melt breccia from the Apollo 17 landing site. They used an ion microprobe to measure the concentrations of lead and uranium isotopes in the crystal, finding that one portion of the grain recorded an age of 4.417 ± 0.006 billion years. Because zircon does not crystallize until more than 95% of the magma ocean has crystallized, this age effectively marks the end of magma ocean crystallization. Magma ocean cooling and crystallization began soon after the Moon-forming giant impact. Other isotopic studies show that this monumental event occurred 4.517 billion years ago. Thus, the difference between the two ages means that the magma ocean took 100 million years to solidify.

  13. 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.

  14. Million-year melt-presence in monotonous intermediate magma for a volcanic-plutonic assemblage in the Central Andes: Contrasting histories of crystal-rich and crystal-poor super-sized silicic magmas

    NASA Astrophysics Data System (ADS)

    Kaiser, Jason F.; de Silva, Shanaka; Schmitt, Axel K.; Economos, Rita; Sunagua, Mayel

    2017-01-01

    The melt-present lifetime of super-sized monotonous intermediate magmas that feed supereruptions and end life as granodioritic plutons is investigated using zircon chronochemistry. These data add to the ongoing discussion on magma assembly rates and have implications for how continental batholiths are built. Herein, we estimate ∼1.1 Ma of continuous melt presence before and after the climactic caldera-forming 2.89 ± 0.01 Ma (2σ error) Pastos Grandes Ignimbrite (PGI) supereruption (∼1500 km3 of magma) in the Andes of southwest Bolivia. Zircon crystallization in PGI pumice and lava from the faulted Southern Postcaldera Dome span ∼0.7 Ma prior to the climactic eruption and formation of the eponymous caldera, whereas younger, unfaulted Postcaldera Dome lavas (termed Northern and Middle) and a granodioritic plutonic clast within the products of a Pleistocene eruption indicate a further ∼0.4 Ma of post-climactic zircon crystallization. Bulk-rock compositions as well as zircon thermometry and geochemistry indicate the presence of homogeneous dacitic magma before and after the climactic eruption, but a trend to zircon crystallization at higher temperatures and from less evolved melts is seen for post-climactic zircon. We propose a model in which a large volume of crystal-rich dacite magma was maintained above solidus temperatures by periodic andesitic recharge that is chemically invisible in the erupted components. The climactic caldera-forming eruption vented the upper portions of the magma system zircon was saturated. Zircon in postcaldera lavas indicate that residual magma from this system remained locally viable for eruption at least for some time after the caldera-forming event. Subsequently, deeper "remnant" dacite magma previously outside the zone of zircon saturation rose to shallower levels to re-establish hydraulic and isostatic equilibrium where zircon crystallization commenced anew, and drove more resurgent volcanism and uplift. The same magma

  15. 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

  16. Magma beneath Yellowstone National Park

    USGS Publications Warehouse

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

    1975-01-01

    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

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Energy extraction from crustal magma bodies

    SciTech Connect

    Dunn, J.C.

    1982-01-01

    An open heat exchanger system for extracting thermal energy directly from shallow crustal magma bodies is described. The concept relies on natural properties of magma to create a permeable, solidified region surrounding a borehole drilled into the magma chamber. The region is fractured, possessing large surface area, and is sealed from the overburden. Energy is extracted by circulating a fluid through the system. Thermal stress analysis shows that such a fractured region can be developed at depths up to 10 km. An open heat exchanger experiment conducted in the partial melt zone of Kilauea Iki lava lake demonstrated the validity of this concept. Effective heat transfer surface area an order of magnitude greater than the borehole area was established during a two-day test period. The open heat exchanger concept greatly extends the number of magma systems that can be economically developed to produce energy.

  2. 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

  3. 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.

  4. 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

  5. Linking enclave formation to magma rheology

    NASA Astrophysics Data System (ADS)

    Hodge, K. F.; Jellinek, A. M.

    2012-10-01

    Magmatic enclaves record the history of deformation and disaggregation (i.e., fragmentation) of relatively hot, compositionally more mafic magmas injected into actively convecting silicic magma chambers through dikes. Enclave size distributions may provide crucial clues for understanding the nature of this mechanical mixing process. Accordingly, we conduct a comprehensive field study to measure enclave size distributions in six Cascade lava flows. Using results from recent fluid dynamics experiments along with thermodynamic and modeling constraints on key physical properties of the injected and host magmas (i.e., temperature, density and effective viscosity), we use the size distributions of enclaves to characterize the magmatic flow regime governing enclave formation. Scaling arguments suggest that the viscous stresses related to magma chamber flow acting against the yield strength of a crystallizing injected magma control the breakup of 1 m-wide mafic dikes into millimeter- to centimeter-scale enclaves. Our data analysis identifies a characteristic length scale of breakup that constrains the yield strength of the injected magmas in a more restrictive way than existing empirical models for yield strength based on crystal content. In all six lava flows, we show that the progressive fragmentation of the injected magma is self-similar and characterized by a fractal dimensionDf ˜ 2, which is comparable to previous studies on enclaves. We also find a small but statistically significant dependence of Df on the effective viscosity ratio between host and enclave magmas, such that large variations in effective viscosity enhance breakup. This work demonstrates that field observations of enclave size distributions can reliably constrain the rheological and flow conditions in which enclaves form.

  6. Chemical consequences of perovskite fractionation from an ultramafic liquid with application to the evolving composition of a basal magma ocean

    NASA Astrophysics Data System (ADS)

    Jackson, Colin; Ziegler, Leah; Zhang, Hongluo; Jackson, Matt; Stegman, Dave

    2013-04-01

    Heterogeneity in the present day mantle is evidenced by seismology and geochemistry, with significant heterogeneity apparent in the lowermost mantle, just above the core-mantle boundary. Origins of this structure are hypothesized to be related to the initial solidification of a deep magma ocean. In particular, in a scenario where solidification begins mid-mantle, a resulting basal magma ocean could be long-lived and geochemically isolated, with the final crystallization products accumulating at the core mantle boundary. The geochemical makeup of the basal magma ocean products depends on fractionation of elements (major, minor, trace) by Mg-perovskite (MgPv), the dominant lower mantle mineral. Here we compile a comprehensive database of elemental partitioning by MgPv from published experimental studies and use it to generate a set of parameterized partition coefficients (f[melt composition]). Partition coefficients are then applied to a crystallization model. Uncertainty bounds are calculated from monte carlo methods. Partitioning of minor and trace elements (i.e. Fe, REE, HFSE, U+Th) depend significantly on melt composition, particularly Al and Ca content, due to charge coupled substitution and site size effects. After accounting for these effects through our parameterized partition coefficients, we present the resulting evolution of the melt and solid (MgPv) phases during magma ocean crystallization. Using a simple model of fractional crystallization, the chemical evolution is calculated until the liquid becomes saturated in a second solid phase (likely ferropericlase). The co-saturation point is uncertain but is estimated to be at ~50% crystallization of the magma ocean. During crystallization of MgPv, the melt phase becomes enriched in Fe, leading to compositionally denser products in the later stages of crystallization. The enrichment in Fe, however, is less extreme than predicted by recent experimental work (e.g. Nomura et al., 2011), bringing into question

  7. Origin of reverse compositional and textural zoning in granite plutons by localized thermal overturn of stratified magma chambers

    NASA Astrophysics Data System (ADS)

    Trubač, Jakub; Janoušek, Vojtěch; Žák, Jiří; Somr, Michael; Kabele, Petr; Švancara, Jan; Gerdes, Axel; Žáčková, Eliška

    2017-04-01

    This study integrates gravimetry and thermal modelling with petrology, U-Th-Pb monazite and zircon geochronology and whole-rock geochemistry of the early Carboniferous Říčany Pluton, Bohemian Massif, in order to discuss the origin of compositional and textural zoning in granitic plutons and complex histories of horizontally stratified, multiply replenished magma chambers. The pluton consists of two coeval, nested biotite (-muscovite) granite facies: outer one, strongly porphyritic (SPm) and inner one, weakly porphyritic (WPc). Their contact is concealed but is likely gradational over several hundreds of meters. The two facies have nearly identical modal composition, are subaluminous to slightly peraluminous and geochemically evolved. Mafic microgranular enclaves, commonly associated with K-feldspar phenocryst patches, are abundant in the pluton center and indicate a repeated basic magma injection and its multistage interactions with the granitic magma and nearly solidified cumulates. Furthermore, the gravimetric data show that the nested pluton is only a small outcrop of a large anvil-like body reaching the depth of at least 14 km, where the pluton root is expected. Trace-element compositions reveal that the pluton is doubly reversely zoned. On the pluton scale, the outer SRG is geochemically more evolved than the inner WPc. On the scale of individual units, outward whole-rock geochemical variations within each facies (SPm, WPc) are compatible with fractional crystallization dominated by feldspars. The proposed genetic model invokes vertical overturn of a deeper, horizontally stratified anvil-shaped magma chamber. The overturn was driven by reactivation of resident felsic magma from the K-feldspar-rich crystal mush. The energy for the melt remobilization, extraction and subsequent ascent is thought to be provided by a long-lived thermal anomaly above the pluton feeding zone, enhanced by the multiple injections of hot basic magmas. In general, it is concluded

  8. 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

  9. 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].

  10. 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.

  11. Hydrothermal systems and volcano geochemistry

    USGS Publications Warehouse

    Fournier, R.O.

    2007-01-01

    The upward intrusion of magma from deeper to shallower levels beneath volcanoes obviously plays an important role in their surface deformation. This chapter will examine less obvious roles that hydrothermal processes might play in volcanic deformation. Emphasis will be placed on the effect that the transition from brittle to plastic behavior of rocks is likely to have on magma degassing and hydrothermal processes, and on the likely chemical variations in brine and gas compositions that occur as a result of movement of aqueous-rich fluids from plastic into brittle rock at different depths. To a great extent, the model of hydrothermal processes in sub-volcanic systems that is presented here is inferential, based in part on information obtained from deep drilling for geothermal resources, and in part on the study of ore deposits that are thought to have formed in volcanic and shallow plutonic environments.

  12. Evolution of high-K arc magma, Egmont volcano, Taranaki, New Zealand: evidence from mineral chemistry

    NASA Astrophysics Data System (ADS)

    Stewart, R. B.; Price, R. C.; Smith, I. E. M.

    1996-12-01

    Magmas from Egmont volcano contain xenocrysts and glomerocrysts entrained from melt zones at or near the base of the crust. Lava whole- rock geochemistry therefore reflects mixing between these crystals and melt and no longer represents melt compositions. As an alternative to using whole-rock analyses, mineral chemistry is used to determine processes occurring during early stages of magma evolution. Primitive magmas at Egmont volcano were hydrous high-magnesian basalts with original ƒ O 2 2.5-3 log units above FMQ. By the time of eruption this had fallen to 0.8-1.0 log units above FMQ. Early fractionation of olivine (Fo 87) and chromite (Cr# 0.7-0.8 and Fe 3+ # 0.24-0.31), and later olivine + clinopyroxene + titanomagnetite drove the evolution of the magma to a high-alumina basalt composition. At the base of the crust these evolved magmas entered the amphibole stability field and reaction between both anhydrous mafic cumulates and wall rocks crystallised amphibole, buffering the melt composition to basaltic andesite. Tapping of these melts to higher levels took them out of the amphibole stability field, resulting in decompressive melting of amphibole phenocrysts and incongruent melting of amphibole in lower to mid-crustal wall rocks in contact with the melt. K 2O-rich liquids from incongruent melting were a major source of potassium in the Egmont high-K andesites. Some plagioclase fractionation occurred in higher-level magma chambers but melt segregation was also an important process. H 2O-saturated melts fractionated amphibole as the amphibole stability field was again intersected and these melts evolved along a calc-alkaline trend to dacite. In contrast drier melts did not fractionate amphibole and evolved only to andesites. As most of the K 2O present is in the groundmass of the lavas, that is, in the liquid phase, the melts formed by the highest degree of melt extraction are the most potassic and these are the melts which tend to evolve to dacite.

  13. 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

  14. 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.

  15. Dynamical model for temporal variation in magma type and eruption interval at Kohala volcano, Hawaii

    NASA Astrophysics Data System (ADS)

    Feigenson, Mark D.; Spera, Frank J.

    1981-11-01

    At Kohala volcano, Hawaii, the amount of source partial melting decreases rapidly toward the end of magmatic activity. The decreasing amounts of partial fusion lead to progressively higher concentrations of incompatible trace elements in lavas erupted during the waning stages of volcanism. In addition to the geochemical variations that characterize the transition from tholeiitic to alkalic basalt production, there is a pronounced decrease in the eruption frequency observed for the younger lavas. A model of magma generation by viscous dissipation can duplicate the relationships between geochemistry and age of the lavas. A reduction in the shear stress that produces deformation causes both a decrease in the amount of mantle partial melting and an increase in the eruption interval. *Present address: Department of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903

  16. Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

    NASA Astrophysics Data System (ADS)

    Dahren, Börje; Troll, Valentin R.; Andersson, Ulf B.; Chadwick, Jane P.; Gardner, Màiri F.; Jaxybulatov, Kairly; Koulakov, Ivan

    2012-04-01

    Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2-8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7-12 km, while plagioclase records both shallow crustal (3-7 km) and sub-Moho (23-28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.

  17. 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

  18. 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

  19. 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

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

    PubMed

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

    2014-03-10

    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.

  1. 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.

  2. Pressure of Partial Crystallization of Katla Magmas: Implications for Magma Chamber Depth and for the Magma Plumbing System

    NASA Astrophysics Data System (ADS)

    Tenison, A.; Kelley, D. F.; Barton, M.

    2012-12-01

    Iceland is home to some of the most active volcanoes in the world, and recent eruptions emphasize the need for additional studies to better understand the volcanism and tectonics in this region. Historical patterns of eruptive activity and an increase in seismic activity suggest that Katla is showing signs of an impending eruption. The last major eruption in 1918 caused massive flooding and deposited enough sediment to extend part of Iceland's southern shoreline by 5 km. It also generated sufficient ash over many weeks to cause a brief drop in global temperature. A future eruption similar to the 1918 event could have serious global consequences, including severe disruptions in air travel, short-term global cooling, and shortened growing seasons. Relatively few studies have focused on establishing the depth of the main magma chamber beneath Katla, although knowledge of magma chamber depth is essential for constraining models for magma evolution and for understanding the eruption dynamics of this volcano. The results of seismic and geodetic studies suggest the presence of a shallow magma body at a depth of 2-4 km, but do not provide firm evidence for the presence of deeper chambers in contrast to results obtained for other volcanoes in Iceland. Studies of volcanic ash layers reveal a history of alternating cycles of basaltic and silicic eruptions. We suggest that the shallow magma chamber is primarily the source of silica-rich magma, and postulate that there must be one or more additional chambers in the middle or deep crust that serve as the storage site of the basaltic magma erupted as lava and ash. We have tested this proposal by calculating the pressures of partial crystallization for basalts erupted at Katla using petrological methods. These pressures can be converted to depths and the results provide insight into the likely configuration of the magma plumbing system. Published analyses of volcanic glasses (lava, ash and hyaloclastite) were used as input data

  3. 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

  4. Vesiculation of basaltic magma during eruption

    USGS Publications Warehouse

    Mangan, Margaret T.; Cashman, Katharine V.; Newman, Sally

    1993-01-01

    Vesicle size distributions in vent lavas from the Pu'u'O'o-Kupaianaha eruption of Kilauea volcano are used to estimate nucleation and growth rates of H2O-rich gas bubbles in basaltic magma nearing the earth's surface (≤120 m depth). By using well-constrained estimates for the depth of volatile exsolution and magma ascent rate, nucleation rates of 35.9 events ⋅ cm-3 ⋅ s-1 and growth rates of 3.2 x 10-4cm/s are determined directly from size-distribution data. The results are consistent with diffusion-controlled growth as predicted by a parabolic growth law. This empirical approach is not subject to the limitations inherent in classical nucleation and growth theory and provides the first direct measurement of vesiculation kinetics in natural settings. In addition, perturbations in the measured size distributions are used to examine bubble escape, accumulation, and coalescence prior to the eruption of magma.

  5. Isotope Geochemistry for Comparative Planetology of Exoplanets

    NASA Astrophysics Data System (ADS)

    Mandt, K. E.; Atreya, S. A.; Luspay-Kuti, A.; Mousis, O.; Simon, A.; Hofstadter, M. D.

    2017-02-01

    Isotope geochemistry has played a critical role in understanding the origins of solar system bodies. Application of these techniques to exoplanets would be revolutionary and would allow comparative planetology with origins of exoplanet systems.

  6. A tale of two magmas, Fuego, Guatemala

    NASA Astrophysics Data System (ADS)

    Berlo, Kim; Stix, John; Roggensack, Kurt; Ghaleb, Bassam

    2012-03-01

    Fuego volcano in Guatemala erupted in 1974 in a basaltic sub-Plinian event, which has been well documented and studied. In 1999, after a period of quiescence lasting 20 years, Fuego erupted again, this time less violently, but with persistent low-level activity. This study investigates the link between these episodes. Previous melt inclusion studies have shown magma erupted in 1974 to have been a volatile-rich hybrid tapped from a vertically extensive system. By contrast, magma erupted in 1999 and 2003 is similar in composition to that erupted in 1974, but melt inclusions are more evolved. Although melt inclusions from the later period are CO2 rich (up to ˜1,500 ppm), they have low H2O concentration (max 1.5 wt.%, compared to ˜6 wt.% in 1974). These melt inclusions have a modified H2O concentration due to diffusive re-equilibration at shallow pressures. Despite this diffusive exchange, both eruptions show evidence of recent mingling of the same low and higher K melts, one of which was slightly cooler than the other and as a result traversed the amphibole stability field. (210Pb/226Ra) data on selected bulk rock samples from 1974 suggest that whereas the cooler, more evolved end-member may have been degassing since the last major eruption in the 1930s, the warmer end-member intruded at most a decade prior to the 1974 eruption. The two end-members are thus batches of the same magma emplaced shallowly ˜30 years apart during which time the older batch was cooled and differentiated before mixing with the younger influx. The presence of the same two melts in the later eruptions suggests that magma in 1999 and 2003 is partly residual from 1974. The current eruptive activity is clearing the system of this residual magma prior to an expected new magma batch.

  7. Volatile transport in subvolcanic magma reservoirs

    NASA Astrophysics Data System (ADS)

    Huber, C.; Parmigiani, A.; Degruyter, W.; Bachmann, O.; Lecleaire, S.

    2016-12-01

    Volatiles exsolving from magma reservoirs within magmatic columns play a significant role in their thermo-mechanical state, impacting forthcoming eruptions. The transport of these volatiles across reservoirs and up to the surface is an essential component of volatile cycling between the earth's mantle and atmosphere, and also plays an important role for the formation of ore deposits. We focus here on three fundamental questions (1) how does magmatic vapor migrate in heterogeneous shallow magma reservoirs, (2) how does it influence the evolution of the reservoir itself and (3) what are the physical processes and optimal conditions that allow crystal-rich magma to outgas efficiently and become ultimately dry (< 1 wt% water) as they solidify to form plutons? We approach these questions by investigating the pore-scale fluid dynamics that controls the transport of the vapor in crystal-rich and crystal-poor magmas. We show how the interplay between capillary stresses and the viscosity contrast between the vapor phase and the host melt results in counterintuitive dynamics, whereby the vapor tends to migrate efficiently in crystal-rich parts of a magma reservoir and accumulate in crystal-poor regions. We find that outgassing by permeable buoyant migration is most efficient between 50 and 70 vol. % of crystals for typical magmatic conditions, and that subsequent outgassing is promoted by capillary fracturing to overcome the large capillary stresses. We implement these results in a magma chamber model to test several outgassing scenarios and to assess how macro-scale processes might control the efficiency of gas loss.

  8. 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.

  9. Large-volume lateral magma transport from the Mull volcano: An insight to magma chamber processes

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Taylor, Rex N.; Geshi, Nobuo; Mochizuki, Nobutatsu

    2017-04-01

    Long-distance lateral magma transport within the crust has been inferred for various magmatic systems including oceanic island volcanoes, mid-oceanic ridges, and large igneous provinces. However, studying the physical and chemical properties of active fissure systems is difficult. Hence, this study investigates the movement of magma away from the Mull volcano in the North Atlantic Igneous Province, where erosion has exposed its upper crustal dike networks. Magmatic lineations within dikes indicate that the magma flow in the Mull dike suite changed from near vertical to horizontal within 30 km of the volcanic center. This implies that distal dikes were fed by lateral magma transport from Mull. Geochemical characteristics indicate that many <50 km long dikes have deep crustal signatures, reflecting storage and assimilation in Lewisian basement. Following crystallization and assimilation in the lower crust, magma fed an upper crustal reservoir, where further fractionation and incorporation of Moinian rocks generated felsic compositions. Distal dikes are andesitic and reflect events in which large volumes of mafic and felsic magma were combined by mixing between lower and upper crustal reservoirs to generate the 30-80 km3 required to supply the long-distance dikes. Once propagated, compositions along dikes were not significantly affected by assimilation and crystallization. Supplying the distal dikes with magma would have required a large-scale evacuation of the crustal reservoirs that acted as a potential trigger for explosive volcanism and the caldera formation recorded in Mull central complex.

  10. Interdisciplinary Studies of Magma-Tectonic Interactions

    NASA Astrophysics Data System (ADS)

    LaFemina, Peter; Stix, John; Saballos, Armando

    2013-08-01

    The Pan-American Advanced Studies Institute (PASI) Magma-Tectonic Interactions in the Americas brought together researchers, postdoctoral fellows, and graduate students from every country in the Americas with active volcanoes and one participant from Iceland. Lecturers presented the latest geochemical and geophysical approaches to studying magma-tectonic interactions. Participants were introduced to the tectonics and volcanism of Nicaragua through a daylong field trip and given opportunities to collect and analyze their own data, including seismic, geodetic, and geochemical data, at the Cerro Negro volcano.

  11. Isotopic geochemistry of Panama rivers

    USGS Publications Warehouse

    Harmon, Russell S.; Worner, Gerhard; Pribil, Michael; Kern, Zoltan; Forizs, Istvan; Lyons, W. Berry; Gardner, Christopher B.; Goldsmith, Steven T.

    2015-01-01

    River water samples collected from 78 watersheds rivers along a 500-km transect across a Late Cretaceous-Tertiary andesitic volcanic arc terrane in west-central Panama provide a synoptic overview of riverine geochemistry, chemical denudation, and CO2 consumption in the tropics. D/H and 18O/16O relationships indicate that bedrock dissolution of andesitic arc crust in Panama is driven by water-rock interaction with meteoric precipitation as it passes through the critical zone, with no evidence of a geothermal or hydrothermal input. Sr-isotope relationships suggest a geochemical evolution for Panama riverine waters that involves mixing of bedrock pore water with water having 87Sr/86Sr ratios between 0.7037-0.7043 and relatively high Sr-contents with waters of low Sr content that enriched in radiogenic Sr that are diluted by infiltrating rainfall to variable extents.

  12. 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

  13. 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

  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. 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)

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  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. Applied Geochemistry Special Issue on Environmental geochemistry of modern mining

    USGS Publications Warehouse

    Seal, Robert R.; Nordstrom, D. Kirk

    2015-01-01

    Environmental geochemistry is an integral part of the mine-life cycle, particularly for modern mining. The critical importance of environmental geochemistry begins with pre-mining baseline characterization and the assessment of environmental risks related to mining, continues through active mining especially in water and waste management practices, and culminates in mine closure. The enhanced significance of environmental geochemistry to modern mining has arisen from an increased knowledge of the impacts that historical and active mining can have on the environment, and from new regulations meant to guard against these impacts. New regulations are commonly motivated by advances in the scientific understanding of the environmental impacts of past mining. The impacts can be physical, chemical, and biological in nature. The physical challenges typically fall within the purview of engineers, whereas the chemical and biological challenges typically require a multidisciplinary array of expertise including geologists, geochemists, hydrologists, microbiologists, and biologists. The modern mine-permitting process throughout most of the world now requires that potential risks be assessed prior to the start of mining. The strategies for this risk assessment include a thorough characterization of pre-mining baseline conditions and the identification of risks specifically related to the manner in which the ore will be mined and processed, how water and waste products will be managed, and what the final configuration of the post-mining landscape will be.In the Fall 2010, the Society of Economic Geologists held a short course in conjunction with the annual meeting of the Geological Society of America in Denver, Colorado (USA) to examine the environmental geochemistry of modern mining. The intent was to focus on issues that are pertinent to current and future mines, as opposed to abandoned mines, which have been the focus of numerous previous short courses. The geochemical

  5. 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

  6. The mechanics of shallow magma reservoir outgassing

    NASA Astrophysics Data System (ADS)

    Parmigiani, A.; Degruyter, W.; Leclaire, S.; Huber, C.; Bachmann, O.

    2017-08-01

    Magma degassing fundamentally controls the Earth's volatile cycles. The large amount of gas expelled into the atmosphere during volcanic eruptions (i.e., volcanic outgassing) is the most obvious display of magmatic volatile release. However, owing to the large intrusive:extrusive ratio, and considering the paucity of volatiles left in intrusive rocks after final solidification, volcanic outgassing likely constitutes only a small fraction of the overall mass of magmatic volatiles released to the Earth's surface. Therefore, as most magmas stall on their way to the surface, outgassing of uneruptible, crystal-rich magma storage regions will play a dominant role in closing the balance of volatile element cycling between the mantle and the surface. We use a numerical approach to study the migration of a magmatic volatile phase (MVP) in crystal-rich magma bodies ("mush zones") at the pore scale. Our results suggest that buoyancy-driven outgassing is efficient over crystal volume fractions between 0.4 and 0.7 (for mm-sized crystals). We parameterize our pore-scale results for MVP migration in a thermomechanical magma reservoir model to study outgassing under dynamical conditions where cooling controls the evolution of the proportion of crystal, gas, and melt phases and to investigate the role of the reservoir size and the temperature-dependent viscoelastic response of the crust on outgassing efficiency. We find that buoyancy-driven outgassing allows for a maximum of 40-50% volatiles to leave the reservoir over the 0.4-0.7 crystal volume fractions, implying that a significant amount of outgassing must occur at high crystal content (>0.7) through veining and/or capillary fracturing.

  7. 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.

  8. 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.

  9. Minor-element and Sr-isotope geochemistry of tertiary stocks, Colorado mineral belt

    USGS Publications Warehouse

    Simmons, E.C.; Hedge, C.E.

    1978-01-01

    Rocks of the northeast portion of the Colorado mineral belt form two petrographically, chemically and geographically distinct rock suites: (1) a silica oversaturated granodiorite suite; and (2) a silica saturated, high alkali monzonite suite. Rocks of the granodiorite suite generally have Sr contents less than 1000 ppm, subparallel REE patterns and initial 87Sr/ 86Sr ratios greater than 0.707. Rocks of the monzonite suite are restricted to the northeast part of the mineral belt, where few rocks of the granodiorite suite occur, and generally have Sr contents greater than 1000 ppm, highly variable REE patterns and 87Sr/86Sr initial ratios less than 0.706. Despite forming simple, smooth trends on major element variation diagrams, trace element data for rocks of the granodiorite suite indicate that they were not derived from a single magma. These rocks were derived from magmas having similar REE patterns, but variable Rb and Sr contents, and Rb/Sr ratios. The preferred explanation for these rocks is that they were derived by partial melting of a mixed source, which yielded pyroxene granulite or pyroxenite residues. The monzonite suite is chemically and petrographically more complex than the granodiorite suite. It is subdivided here into alkalic and mafic monzonites, and quartz syenites, based on the textural relations of their ferromagnesian phases and quartz. The geochemistry of these three rock types require derivation from separate and chemically distinct magma types. The preferred explanation for the alkalic monzonites is derivation from a heterogeneous mafic source, leaving a residue dominated by garnet and clinopyroxene. Early crystallization of sphene from these magmas was responsible for the severe depletion of the REE observed in the residual magmas. The lower Sr content and higher Rb/Sr ratios of the mafic monzonites requires a plagioclase-bearing source. The Sr-isotope systematics of the majority of these rocks are interpreted to be largely primary, and not

  10. 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

  11. 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

  12. The Role of KREEP in the Production of Mg-Suite Magmas and Its Influence on the Extent of Mg-Suite Magmatism in the Lunar Crust

    NASA Technical Reports Server (NTRS)

    Elardo, S. M.; Shearer, C. K.; McCubbin, F. M.

    2017-01-01

    The lunar magnesian-suite, or Mg-suite, is a series of ancient plutonic rocks from the lunar crust. They have received a considerable amount of attention from lunar scientists since their discovery for three primary reasons: 1) their ages and geochemistry indicate they represent pristine magmatic samples that crystallized very soon after the formation of the Moon; 2) their ages often overlap with ages of the ferroan anorthosite (FAN) crust; and 3) planetary-scale processes are needed in formation models to account for their unique geochemical features. Taken as a whole, the Mg-suite samples, as magmatic cumulate rocks, approximate a fractional crystallization sequence in the low-pressure forsterite-anorthite-silica system, and thus these samples are generally thought to be derived from layered mafic intrusions which crystallized very slowly from magmas that intruded the anorthositic crust. However, no direct linkages have been established between different Mg-suite samples based either on field relationships or geochemistry.The model for the origin of the Mg-suite, which best fits the limited available data, is one where Mg-suite magmas form from melting of a hybrid cumulate package consisting of deep mantle dunite, crustal anorthosite, and KREEP (potassium-rare earth elements-phosphorus) at the base of the crust under the Procellarum KREEP Terrane (PKT). In this model, these three LMO (Lunar Magma Ocean) cumulate components are brought into close proximity by the cumulate overturn process. Deep mantle dunitic cumulates with an Mg number of approximately 90 rise to the base of the anorthositic crust due to their buoyancy relative to colder, more dense Fe- and Ti-rich cumulates. This hybridized source rock melts to form Mg-suite magmas, saturated in Mg-rich olivine and anorthitic plagioclase, that have a substantial KREEP component.

  13. 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

  14. 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

  15. 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

  16. Deformation-induced magma degassing (Invited)

    NASA Astrophysics Data System (ADS)

    Caricchi, L.; Pommier, A.; Pistone, M.; Castro, J. M.; Burgisser, A.

    2009-12-01

    The style and rate of magma degassing during its rise in volcanic conduits controls the eruptive behavior of volcanoes. For example, the transition from extremely explosive to an effusive eruption of lava, as observed recently at Chaitén volcano, Chile, may be the consequence of efficient degassing of highly viscous magmas through a permeable bubble network. Magma experiences extensive shear deformation along conduit walls during its rise to the surface, which could enhance gas bubble coalescence and favor degassing of magma at depth. We performed a series of simple shear deformation experiments using an internally heated Paterson-type apparatus, on bubbly magmas at 100 MPa confining pressure and temperatures between 823 and 873K. Crystal free silicate-melt of tephri-phonolitic composition containing about 15 vol.% H2O-pressurized bubbles was used for the experiments. The experimental products were analyzed both in two and three-dimensions using an optical microscope and a X-ray nanotomographer respectively. The water content of the starting material and the deformed samples was measured by infrared spectroscopy (FTIR). The analyses of the samples after deformation show that simple shear enhances bubble coalescence and degassing, especially at high strain (gamma~10, about 2.5 rotations). The water content of the deformed glasses is equal to the starting material at relatively low gamma (~2) while it decreases dramatically at high strain, to a value (~0.1 wt.%) much lower than the H2O-saturation limit at 100 MPa (~4.2 wt.%). An additional static experiment was performed for the same duration as the high strain experiment to check if the samples were degassing with time. The FTIR analyses confirmed that the bulk water content of the sample remains constant in the absence of shear and over the timescale of the high strain experiments. The observation that the residual water content is lower than 100 MPa-saturation value, indicates that the degassing process is not

  17. Laguna del Maule magma feeding system and construction of a shallow silicic magma reservoir

    NASA Astrophysics Data System (ADS)

    Cáceres, Francisco; Castruccio, Ángelo; Parada, Miguel; Scheu, Bettina

    2017-04-01

    Laguna del Maule Volcanic Field is composed by at least 130 basaltic-to-rhyolitic eruptive vents that erupted more than 350 km3 of lavas and pyroclasts since Pleistocene in the Chilean Andes. It has captivated attention because of its current high accelerated uplift suggested to be formed by a growing shallow rhyolitic magma reservoir beneath the zone of deformation. Studying six Holocene post-glacial andesitic-to-rhyolitic lavas and one dome that partially overlap the ground-inflation zone, we determined the architecture and steps of construction of the magma feeding system that generated its post-glacial effusive volcanism. Further we suggest a possible origin for the rhyolitic magma that generated the ring of rhyolites encircling the lake and remain active causing the uplift. Mineral chemistry and textures suggest the same provenance of magma for the studied units, as well as complex magmatic history before eruptions. Similar temperatures, pressures, H2O and fO2 conditions for amphibole crystallisation in first stages indicate a common ˜17 km deep original reservoir that differentiated via in-situ crystallisation. The chemistry of the amphiboles present in all not-rhyolitic units shows trends that indicate a temperature domain on their crystallisation over other thermodynamic parameters such as pressure, water activity or chemistry of co-crystallising phases. All this supports a mush-like reservoir differentiating interstitial magma while crystallisation occurs. P-T conditions for amphibole crystallisation indicate that only amphiboles from rhyodacites show a non-adiabatic decompression that give rise to a polybaric and polythermal evolution trend from ˜450-200 MPa and ˜1030-900 ˚ C. In addition, unbuffered fO2 conditions were calculated for rhyodacite amphibole crystallisation upon cooling from melts with rather constant H2O contents. We propose that a large part of these rhyodacite amphiboles were formed during a non-adiabatic magma ascent similar to that

  18. 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

  19. 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

  20. Thermomechanics of Triggering the Eruption of Large Magma Reservoirs: The Effects of Buoyancy and Magma Recharge

    NASA Astrophysics Data System (ADS)

    Gregg, P. M.; Grosfils, E. B.; de Silva, S. L.

    2014-12-01

    The evacuation of large silicic magma reservoirs via catastrophic caldera forming eruptions that emplace 100s to 1000s of km3 of material is a devastating and rare natural disaster on Earth. Given the destructive nature of these eruptions, it is critical to better understand the evolution of large silicic systems and what parameters are responsible for either maintaining magma in storage conditions or triggering an eruption. The formation of large, shallow magma bodies requires thermal maturation of the upper crust through elevated magma fluxes over periods of 104-106 years. Once the crust is thermally primed, the viscoelastic response of the host rock buffers the reservoir and stifles the generation of significant overpressure, thus accommodating the accumulation of large magma volumes (103-104 km3). Given that overpressures are difficult to generate in magma reservoirs of this size, increasing attention has been focused on better understanding what mechanisms may trigger their eruption. Recent analytical models suggest that buoyancy may play a critical role in generating the necessary overpressures to trigger eruption of the largest systems. We build upon these findings and utilize numerical models to quantify overpressure generation due to buoyancy and magmatic recharge. Furthermore, the interplay between reservoir growth and fault formation is explored to determine whether eruption triggering is most likely to occur due to fault development within the overlying roof or due to rupture at the reservoir boundary. Specifically, we utilize viscoelastic finite element models with Mohr-Coulomb and von Mises failure criteria to explore foundering in the roof and failure development at the reservoir boundary during buoyant magma recharge. Presented results will compare temperature- and non-temperature dependent viscosities with elastic models to investigate end-member controls on fault formation and reservoir rupture.

  1. Krafla Magma Testbed: An International Project Crossing The Scientific Frontier From Geothermal System Into Magma

    NASA Astrophysics Data System (ADS)

    Eichelberger, J. C.; Dingwell, D. B.; Ludden, J. N.; Mandeville, C. W.; Markusson, S.; Papale, P.; Sigmundsson, F.

    2016-12-01

    Few Earth regimes are subject to as much inference and as little direct knowledge as magma. Among the most important mysteries is the transition from hydrothermal to magmatic, i.e. from aqueous fluid-present to silicate melt-present, regimes. Because solid rock is ductile at near-solidus temperature, fractures should have fleeting existence and therefore heat transfer should be by conduction. Heat and mass transport across this zone influences evolution of magma bodies. The hydrothermal regime influences eruptive behavior when magma intrudes it and propagation of the transition zone toward magma is demonstrated by physical and chemical evidence. Both drilling observations and heat-balance considerations indicate that the melt- and fluid-absent transition zone is thin. Drilling of Iceland Deep Drilling Project's IDDP-1, 2 km into Krafla Caldera, showed that the transition from deep-solidus fine-grained granite to liquidus rhyolite is less than 30 m thick, probably much less. For the first time, we have the opportunity to interrogate an entire system of heat and mass transport, from magmatic source through the hydrothermal zone to surface volcanism, and in so doing unite the disciplines of volcanology and geothermal energy. With support from industry, national geoscience agencies, community stakeholders, and the International Continental Scientific Drilling Program (ICDP), we are developing a broad program to push the limits of knowledge and technology in extremely hot Earth. We use the term "testbed" for two reasons: Surface and borehole observations used in volcano monitoring and geothermal exploration will be tested and reinterpreted in light of the first "ground-truth" about magma. More than "observing", magma and the transition zone will be manipulated through fluid injection and extraction to understand time-dependent behavior. Sensor technology will be pushed to measure magmatic conditions directly. Payoffs are in fundamental planetary science, volcano

  2. 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.

  3. Continuous magma recharge at Mt. Etna during the 2011-2013 period controls the style of volcanic activity and compositions of erupted lavas

    NASA Astrophysics Data System (ADS)

    Viccaro, Marco; Calcagno, Rosario; Garozzo, Ileana; Giuffrida, Marisa; Nicotra, Eugenio

    2015-02-01

    Volcanic rocks erupted during the January 2011 - April 2013 paroxysmal sequence at Mt. Etna volcano have been investigated through in situ microanalysis of mineral phases and whole rock geochemistry. These products have been also considered within the framework of the post-2001 record, evidencing that magmas feeding the 2011-2013 paroxysmal activity inherited deep signature comparable to that of the 2007-2009 volcanic rocks for what concerns their trace element concentration. Analysis performed on plagioclase, clinopyroxene and olivine, which are sensitive to differentiation processes, show respectively fluctuations of the An, Mg# and Fo contents during the considered period. Also major and trace elements measured on the whole rock provide evidence of the evolutionary degree variations through time. Simulations by MELTS at fixed chemical-physical parameters allowed the definition of feeding system dynamics controlling the geochemical variability of magmas during the 2011-2013 period. Specifically, compositional changes have been interpreted as due to superimposition of fractional crystallization and mixing in variable proportions with more basic magma ascending from intermediate to shallower levels of the plumbing system. Composition of the recharging end-member is compatible with that of the most basic magmas emitted during the 2007 and the early paroxysmal eruptions of 2012. Analysis of the erupted volumes of magma combined with its petrologic evolution through time support the idea that large volumes of magma are continuously intruded and stored in the intermediate plumbing system after major recharging phases in the deepest levels of it. Transient recharge from the intermediate to the shallow levels is then responsible for the paroxysmal eruptions.

  4. 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.

  5. Magma vesiculation and pyroclastic volcanism on Venus

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Head, J. W.; Wilson, L.

    1982-01-01

    Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO2 is the primary magmatic volatile. However, the high surface atmospheric pressure (about 90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5-4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

  6. Magma vesiculation and pyroclastic volcanism on Venus

    NASA Astrophysics Data System (ADS)

    Garvin, J. B.; Head, J. W.; Wilson, L.

    1982-11-01

    Theoretical consideration of the magma vesiculation process under observed and inferred venusian surface conditions suggests that vesicles should form in basaltic melts, especially if CO2 is the primary magmatic volatile. However, the high surface atmospheric pressure (about 90 bars) and density on Venus retard bubble coalescence and disruption sufficiently to make explosive volcanism unlikely. The products of explosive volcanism (fire fountains, convecting eruption clouds, pyroclastic flows, and topography-mantling deposits of ash, spatter, and scoria) should be rare on Venus, and effusive eruptions should dominate. The volume fraction of vesicles in basaltic rocks on Venus are predicted to be less than in chemically similar rocks on earth. Detection of pyroclastic landforms or eruption products on Venus would indicate either abnormally high volatile contents of Venus magmas (2.5-4 wt%) or different environmental conditions (e.g., lower atmospheric pressure) in previous geologic history.

  7. Magma in forearcs: implication for ophiolite generation

    NASA Astrophysics Data System (ADS)

    Jakeŝ, Petr; Miyake, Yasuyuki

    1984-07-01

    Forearc areas ("non-volcanic" arcs) of contemporary island arcs at convergent plate boundaries contain magmatic rocks. Geological evidence, seismic profiles, heat flow data, density considerations and petrological and geochemical arguments suggest that a forearc tholeiitic association (FAT) (containing high-Mg calc-alkaline andesites) is present in "non-volcanic" arcs at some stage of island-arc development. The fractionated, as well as primitive magma, is unable to penetrate low-density sediments and underplates thick piles of unconsolidated accreting rocks. The underplating causes upwelling. The occurrence of magma in forearcs provides an alternative interpretation for the tectonic setting of some ophiolitic masses. Rather than "ocean-ridge formation" and later "obduction" it offers an autochthonous (island-arc bound and geologically-substantiated) interpretation for the ophiolite suite.

  8. Magma Oceans on Exoplanets and Early Earth

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, Linda

    2009-09-01

    Late, giant accretionary impacts likely form multiple magma oceans of some depth in young rocky planets. Models of magma ocean solidification that incorporate water, carbon, and other incompatible volatile elements in small amounts predict a range of first-order outcomes important to planetary evolution. First, initial planetary bulk composition and size determine the composition of the earliest degassed atmosphere. This early atmosphere appears in a rapid burst at the end of solidification, determined by the ability of nucleating bubbles to reach the surface. Larger planets will have briefer and more catastrophic atmospheric degassing during solidification of any magma ocean. Second, this early atmosphere is sufficiently insulating to keep the planetary surface hot for millions of years. Depending upon the atmospheric composition and temperature structure these hot young planets may be observable from Earth or from satellites. Third, small but significant quantities of volatiles remain in the planet's solid mantle, encouraging convection, plate tectonics, and later atmospheric degassing through volcanism. A critical outcome of magma ocean solidification is the development of a solid mantle density gradient with den-sity increasing with radius, which will flow to gravitational stability. Shallow, dense, damp material will carry its water content as it sinks into the perovskite stability zone and transforms into perovskite. Even in models with very low initial water contents, a large fraction of the sinking upper mantle material will be forced to dewater as it crosses the boundary into the relatively dry lower mantle, leaving its water behind in a rapid flux as it sinks. This water ad-dition could initiate or speed convection in planets in which perovskite is stable, that is, planets larger than Mars.

  9. 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.

  10. Pressure waves in a supersaturated bubbly magma

    USGS Publications Warehouse

    Kurzon, I.; Lyakhovsky, V.; Navon, O.; Chouet, B.

    2011-01-01

    We study the interaction of acoustic pressure waves with an expanding bubbly magma. The expansion of magma is the result of bubble growth during or following magma decompression and leads to two competing processes that affect pressure waves. On the one hand, growth in vesicularity leads to increased damping and decreased wave amplitudes, and on the other hand, a decrease in the effective bulk modulus of the bubbly mixture reduces wave velocity, which in turn, reduces damping and may lead to wave amplification. The additional acoustic energy originates from the chemical energy released during bubble growth. We examine this phenomenon analytically to identify conditions under which amplification of pressure waves is possible. These conditions are further examined numerically to shed light on the frequency and phase dependencies in relation to the interaction of waves and growing bubbles. Amplification is possible at low frequencies and when the growth rate of bubbles reaches an optimum value for which the wave velocity decreases sufficiently to overcome the increased damping of the vesicular material. We examine two amplification phase-dependent effects: (1) a tensile-phase effect in which the inserted wave adds to the process of bubble growth, utilizing the energy associated with the gas overpressure in the bubble and therefore converting a large proportion of this energy into additional acoustic energy, and (2) a compressive-phase effect in which the pressure wave works against the growing bubbles and a large amount of its acoustic energy is dissipated during the first cycle, but later enough energy is gained to amplify the second cycle. These two effects provide additional new possible mechanisms for the amplification phase seen in Long-Period (LP) and Very-Long-Period (VLP) seismic signals originating in magma-filled cracks.

  11. Large-scale lateral magma transport: what processes occur on a 200km journey?

    NASA Astrophysics Data System (ADS)

    Ishizuka, Osamu; Geshi, Nobuo; Mochizuki, Nobutatsu; Taylor, Rex N.

    2013-04-01

    -100 km away are predominantly aligned with an assimilation (mixing) vector. Dykes recognized as having a negligible or minor assimilation component show an additional geochemical variation reflecting a contribution from an enriched mantle component (low 143Nd/144Nd, Sm/Yb>2, Th/Ce<0.03). Some dykes within 60 km of Mull have higher Nb/Zr and Nb/Ta than other dykes at a similar distance, implying a variable contribution from the enriched component. Equivalent variation in incompatible element enrichment has been reported from the Mull lava sequence (e.g., Kerr et al., 1999). Accordingly, isolating geochemical signatures constrained by high-precision 40Ar/39Ar dating of dyke rocks enable us to isolate individual magma transport stages (dyke formation) and their correlation with known effusive events. Based on the correlation between geochemistry and distance from the magmatic centre, the effects of magmatic differentiation/crustal assimilation during long-distance magma transport will be evaluated in this presentation.

  12. 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.

  13. Native gold in Hawaiian alkalic magma

    USGS Publications Warehouse

    Sisson, T.W.

    2003-01-01

    Native gold found in fresh basanite glass from the early submarine phase of Kilauea volcano, Hawaii, may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle-derived magma. The gold-bearing glass is a grain in bedded volcanic glass sandstone (Japan Marine Science and Technology Center (JAMSTEC) sample S508-R3) collected by the submersible Shinkai 6500 at 3879 m depth off Kilauea's south flank. Extensive outcrops there expose debris-flow breccias and sandstones containing submarine-erupted alkalic rock fragments and glasses from early Kilauea. Precipitation of an immiscible gold liquid resulted from resorption of magmatic sulfides during crystallization-differentiation, with consequent liberation of sulfide-hosted gold. Elevated whole-rock gold concentrations (to 36 ppb) for fresh lavas and clasts from early Kilauea further show that some magmas erupted at the beginning stages of Hawaiian shield volcanoes were distinctly gold rich, most likely owing to limited residual sulfide in their mantle source. Alkalic magmas at other ocean islands may also be gold rich, and oceanic hot-spot provinces may contain underappreciated gold resources.

  14. Voluminous granitic magmas from common basaltic sources

    USGS Publications Warehouse

    Sisson, T.W.; Ratajeski, K.; Hankins, W.B.; Glazner, A.F.

    2005-01-01

    Granitic-rhyolitic liquids were produced experimentally from moderately hydrous (1.7-2.3 wt% H2O) medium-to-high K basaltic compositions at 700 MPa and f O2 controlled from Ni-NiO -1.3 to +4. Amount and composition of evolved liquids and coexisting mineral assemblages vary with fO2 and temperature, with melt being more evolved at higher fO2s, where coexisting mineral assemblages are more plagioclase- and Fe-Ti oxide-rich and amphibole-poor. At fO2 of Ni-NiO +1, typical for many silicic magmas, the samples produce 12-25 wt% granitic-rhyolitic liquid, amounts varying with bulk composition. Medium-to-high K basalts are common in subduction-related magmatic arcs, and near-solidus true granite or rhyolite liquids can form widely, and in geologically significant quantities, by advanced crystallization-differentiation or by low-degree partial remelting of mantle-derived basaltic sources. Previously differentiated or weathered materials may be involved in generating specific felsic magmas, but are not required for such magmas to be voluminous or to have the K-rich granitic compositions typical of the upper continental crust. ?? Springer-Verlag 2005.

  15. Viscosity of mafic magmas at high pressures

    NASA Astrophysics Data System (ADS)

    Cochain, B.; Sanloup, C.; Leroy, C.; Kono, Y.

    2017-01-01

    While it is accepted that silica-rich melts behave anomalously with a decrease of their viscosity at increased pressures (P), the viscosity of silica-poor melts is much less constrained. However, modeling of mantle melts dynamics throughout Earth's history, including the magma ocean era, requires precise knowledge of the viscous properties of silica-poor magmas. We extend here our previous measurements on fayalite melt to natural end-members pyroxenite melts (MgSiO3 and CaSiO3) using in situ X-ray radiography up to 8 GPa. For all compositions, viscosity decreases with P, rapidly below 5 GPa and slowly above. The magnitude of the viscosity decrease is larger for pyroxene melts than for fayalite melt and larger for the Ca end-member within pyroxene melts. The anomalous viscosity decrease appears to be a universal behavior for magmas up to 13 GPa, while the P dependence of viscosity beyond this remains to be measured. These results imply that mantle melts are very pervasive at depth.

  16. Organic geochemistry - A retrospective of its first 70 years

    USGS Publications Warehouse

    Kvenvolden, K.A.

    2006-01-01

    Organic geochemistry had its origin in the early part of the 20th century when organic chemists and geologists realized that detailed information on the organic materials in sediments and rocks was scientifically interesting and of practical importance. The generally acknowledged "father" of organic geochemistry is Alfred E. Treibs (1899-1983), who discovered and described, in 1936, porphyrin pigments in shale, coal, and crude oil, and traced the source of these molecules to their biological precursors. Thus, the year 1936 marks the beginning of organic geochemistry. However, formal organization of organic geochemistry dates from 1959 when the Organic Geochemistry Division (OGD) of The Geochemical Society was founded in the United States, followed 22 years later (1981) by the establishment of the European Association of Organic Geochemists (EAOG). Organic geochemistry (1) has its own journal, Organic Geochemistry (beginning in 1979) which, since 1988, is the official journal of the EAOG, (2) convenes two major conferences [International Meeting on Organic Geochemistry (IMOG), since 1962, and Gordon Research Conferences on Organic Geochemistry (GRC), since 1968] in alternate years, and (3) is the subject matter of several textbooks. Organic geochemistry is now a widely recognized geoscience in which organic chemistry has contributed significantly not only to geology (i.e., petroleum geochemistry, molecular stratigraphy) and biology (i.e., biogeochemistry), but also to other disciplines, such as chemical oceanography, environmental science, hydrology, biochemical ecology, archaeology, and cosmochemistry.

  17. Along-arc Variations in Subduction Inputs and Mantle Source in Cascadia: Insights from Basaltic Arc Magmas

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.; Walowski, K. J.; Wallace, P. J.; DeBari, S. M.; Bindeman, I. N.

    2015-12-01

    The Cascade arc spans ~1300 km from northern California into southern British Columbia, and basaltic magmas have erupted throughout the arc. The compositions of arc basalts are particularly useful in discerning mantle origins and inputs to the magmatic system, as basalts have undergone less differentiation en route to the surface. This presentation will draw on both existing datasets and new research to summarize our knowledge of Cascades arc basalt geochemistry and explore along-arc variability in mantle compositions and subduction recycling (oceanic crust and sediment). Cascades basalts are highly variable in composition; at least five types of primitive basalts erupt in the arc, with calc-alkaline basalts (CAB) and low-K tholeiites (LKT, also called high-alumina olivine tholeiites) being the most common. Such variability has been suggested to correlate with mantle heterogeneities and/or mantle melting processes, with CAB originating from fluid-fluxing of the mantle and LKT representing decompression melts (e.g., Leeman et al., 1990; Schmidt et al., 2008). However, recent work has suggested that, at least in some localities, CAB and LKT magmas could originate from a common mantle source (Mullen et al., 2014). A compilation of published primitive (>7 wt% MgO) basaltic magma compositions illustrates potential mantle heterogeneity along the arc, as well as variations in subduction recycling. Increases in melt H2O contents, radiogenic isotopes, oxygen isotopes, and LILE from north to south along the arc commonly suggest an increase in the amount of subduction component added to the mantle beneath the southern Cascades. The origin of the subduction component (crust vs. sediment) appears variable as well. With recent work on the seafloor sediments offshore of the north Cascades (Carpentier et al., 2010, 2013, 2014), researchers have been able to model the contributions of subducted sediment and crust to the north Cascades arc magmas and have suggested that sediment

  18. 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

  19. 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

  20. 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

  1. The Magma Chamber Simulator: Modeling Compositional, Temperature and Mass Variations in a Composite Magma-Wallrock System

    NASA Astrophysics Data System (ADS)

    Bohrson, W. A.; Spera, F. J.; Creamer, J. B.; Ghiorso, M. S.

    2012-12-01

    Elucidation of the spectrum of compositional and mineralogical characteristics that can be generated by assimilation-fractional crystallization (AFC) contributes to the goal of defining the thermal and mass characteristics required to develop and maintain magma storage and transport systems in a range of tectonic settings. The Magma Chamber Simulator (MCS) utilizes the thermodynamic functionality of MELTS (Ghiorso & Sack 1995) to assess thermal, compositional and mass variations that develop in a composite magma-wallrock (M-WR) system undergoing AFC. Wallrock of defined initial conditions (e.g., PTX) heats up and potentially melts as magma cools and crystallizes. Energy balance is maintained between magma and wallrock and informs the thermal condition of wallrock, which dictates the amount and composition of anatectic melt that is incorporated into magma. As magma cools through a defined T path, output includes thermal, mass, compositional, and physical parameters for melt and solids in magma and wallrock. The simulation is complete when thermal equilibrium between magma and wallrock is achieved. Key parameters that impact the bulk composition and mineralogy of magma undergoing AFC include the initial wallrock to magma mass ratio, wallrock initial T, and initial compositions of magma and wallrock. While other system parameters are held constant, assimilation of lherzolite vs. granite by high-alumina basalt (HAB) yields differences in the total mass of anatectic melt at thermal equilibrium (e.g., 4 vs. 12% of starting magma mass, respectively) but magma SiO2 range is similar (51-53 wt. %). Thus, basaltic samples with similar Si contents can have different assimilation histories and thus manifest different trace element/isotopic characteristics; caution is therefore required when interpreting the origin of compositional heterogeneity of basalts. Initial mass of wallrock impacts magma chemical evolution as illustrated by two cases in a HAB-granite M-WR system in which

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. Mesozoic dykes and sills from Uruguay: Sr - Nd isotope and trace element geochemistry

    NASA Astrophysics Data System (ADS)

    Muzio, Rossana; Peel, Elena; Porta, Natalia; Scaglia, Fernando

    2017-08-01

    The Mesozoic mafic intrusions in Uruguay comprise dykes and sills grouped as the Cuaró Formation. They are mainly distributed along the southern portion of the Paraná basin, and they are considered part of the Paraná Magmatic Province. They crop out as typically grey moderately altered dykes and sills, characterized by glomero-porphyritic textures, with clusters of plagioclase and occasional clinopyroxene, set in a fine-grained groundmass composed by labradorite, augite and titaniferous magnetite. We present new lithogeochemical results particularly regarding Sr - Nd isotopes to discuss petrogenetic processes. All samples have high 87Sr/86Sr (0.71160-0.70781) and low 143Nd/144Nd ratios (0.512274-0.512585), with epsilon Nd(0) between -4.37 and -7.1. TDM model ages, calculated for 130 Ma, are composed of approximately 1.41-1.61 Ga, except for one dyke with 1.29 Ga. The isotopic data allow their classification as derived from the Gramado magma-type. Trace element geochemistry and isotopic data indicate that the primary magma would be a product of an enriched mantle source with a strong crustal signature, probably due to inherited subduction components and/or assimilation processes.

  7. Geochemistry and petrogenesis of a peralkaline granite complex from the Midian Mountains, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Harris, N. B. W.; Marriner, G. F.

    1980-10-01

    A zoned intrusion with a biotite granodiorite core and arfvedsonite granite rim represents the source magma for an albitised granite plug near its eastern margin and radioactive siliceous veins along its western margin. A study of selected REE and trace elements of samples from this complex reveals that the albitised granite plug has at least a tenfold enrichment in Zr, Hf, Nb, Ta, Y, Th, U and Sr, and a greatly enhanced heavy/light REE ratio compared with the peralkaline granite. The siliceous veins have even stronger enrichment of these trace elements, but a heavy/light REE ratio and negative eu anomaly similar to the peralkaline granite. It is suggested that the veins were formed from acidic volatile activity and the plug from a combination of highly fractionated magma and co-existing alkaline volatile phase. The granodiorite core intrudes the peralkaline granite and has similar trace element geochemistry. The peralkaline granite is probably derived from the partial melting of the lower crust in the presence of halide-rich volatiles, and the granodiorite from further partial melting under volatile-free conditions.

  8. Primary melt from Sannome-gata volcano, NE Japan arc: constraints on generation conditions of rear-arc magmas

    NASA Astrophysics Data System (ADS)

    Kuritani, T.; Yoshida, T.; Kimura, J.; Takahashi, T.; Hirahara, Y.; Miyazaki, T.; Senda, R.; Chang, Q.; Ito, Y.

    2013-12-01

    Material and energy transport in subduction zones has played an important role in Earth's evolution, and has been investigated extensively in petrological, geochemical, experimental, numerical, and geophysical studies. In these approaches, petrological and geochemical studies on arc basalts have remarkably contributed to the quantitative understanding of subduction-zone processes. However, a more rigorous understanding is limited by the fact that primary magmas generated in the mantle erupt only very occasionally without significant thermal and mechanical interaction with the crust. In this study, the conditions under which arc magma is generated are estimated using primary basalts from the Sannome-gata volcano, located in the rear of the NE Japan arc. The NE Japan arc has been investigated extensively, and is one of the best-documented volcanic arcs on Earth. Therefore, the reliable estimates of the magma generation conditions are expected to contribute to gaining a better understanding of subduction-zone processes. The Sannome-gata maar is located in the Oga Peninsula, NE Japan. The age of the volcanic activity is 20-24 ka (Kitamura 1990). We have examined the petrology and geochemistry of basaltic scoria samples that were collected from scoria fall deposits, outcropping around 500 m southwest of the Sannome-gata maar (Yoshinaga and Nakagawa 1999). The scoriae occur with abundant mantle and crustal xenoliths, suggesting that the magma ascended rapidly from the upper mantle. They show significant variations in their whole-rock compositions (7.9-11.1 wt.% in MgO). High-MgO scoriae (MgO > ~9.5 wt.%) have mostly homogeneous 87Sr/86Sr ratios (~0.70318), whereas low-MgO scoriae (MgO <~9 wt.%) have higher 87Sr/86Sr ratios (>0.70327); ratios tend to increase with decreasing MgO content. The high-MgO scoriae are aphyric, containing ~5 vol.% olivine microphenocrysts with Mg# of up to 90. In contrast, the low-MgO scoriae have crustal xenocrysts of plagioclase, alkali

  9. Evaluating the mush extraction + multiple magma batch model for the Lake City magmatic system (Colorado, USA) using zircon U/Pb TIMS-TEA

    NASA Astrophysics Data System (ADS)

    Pamukcu, A. S.; Schoene, B.; Deering, C. D.

    2016-12-01

    Volcanic eruptions that involve a wide range of magma types highlight questions on genetic and geometric relationships between magmas in the crust prior to eruption. The Lake City magmatic system (Colorado, USA) is one such example: exposed in the caldera are ignimbrites from the 23 Ma Sunshine Peak Tuff, which range in composition and crystallinity with time (crystal-poor rhyolite to crystal-rich trachyte), and resurgent intrusions of porphyritic syenite, monzonite, and dacite (Hon 1987). Field relations and bulk rock geochemistry suggest the Lake City magmatic system was complex, with magmas of these various types existing concurrently as multiple magma batches, though not necessarily always in contact (Kennedy et al. 2015). Geochemical modeling further suggests that the crystal-poor rhyolites were liquids extracted from a syenitic mush and that the crystal-rich trachytes are remobilized portions of this cumulate. To address the genetic and geometric links between these magmas in more detail, we utilize TIMS-TEA to assess U/Pb zircon geochronology and trace element geochemistry in concert. For each eruptive unit/magma type, zircons were roughly separated into size groupings (small, medium, large), imaged by cathodoluminescence (CL), and analyzed individually by CA-ID-TIMS. Preliminary results indicate that zircons crystallized over a period of 177±31 ky, which is within the range suggested by Ar/Ar geochronology (80-300 ky, Bove et al. 2001). Consistent with the current model for the Lake City system, zircons from the rhyolites and trachytes overlap in age, while those of the dacites are younger. There is no clear relationship between age and CL zoning pattern or crystal size (e.g., small crystals are not always the youngest). We can further address relationships between the rhyolite, trachyte, and syenite using TEA to assess trace elements of the dated zircons. Rhyolite-MELTS models suggest that zircons crystallized in a rhyolitic melt derived from the trachyte

  10. Stress modelling of magma storage zones and its implications for rapid kimberlitic magma ascent

    NASA Astrophysics Data System (ADS)

    Baruah, A.; Mandal, N.

    2012-12-01

    Rapid ascent of low viscous kimberlitic magmas is reflected from the presence of meta-stable diamond phenocrysts. Existing models suggest that high velocity magma ascent takes place as a mechanical coupling interaction between the CO2-rich volatile phase originating from the magma and the hydraulic fracture (Type-I). However, for such fracturing to occur at a depth of ~200 km, the system need to have a huge tensile stress to overcome the lithostatic pressure (~60 Kb) and the tensile strength of the rocks (0.4 - 0.5 Kb). The objective of the present work is to present a mechanical model and show the specific conditions in which the magma storage zone (MSZ) can build up such large tensile stresses to cause fracturing for magma ascent. Finite Element (FE) method was employed to map the stress field in the mantle rock around a magma chamber. MSZ was modeled as a semi-elliptical zone at bottom of the model of 150 km depth and 300 km width. Two types of FE modelling was performed considering two factors: (1) density contrast (Δρ) between magma and ambient mantle, and (2) shape (Ar: ratio of vertical and horizontal dimensions) of the MSZ. Figure 1 show the Δρ contrasts required for tensile fracturing to occur at the MSZ tip for different values of their Ar. Results reveal a distinct zone of maximum tensile stresses in the neighborhood of the MSZ, suggesting the potential locations of tensile fracturing. It shows that the tensile stress magnitude decreases exponentially away from the MSZ top vertically. The results illustrate a nonlinear relation of stress with increasing Δρ (Figure 1). We show that for models with Ar >1 there is a localization of tensile stress at the MSZ tip, and for the models with Ar << 1 it diffuse along the boundary (Figure 2). We also show that for a particular Δρ, tensile stress increases for increasing Ar. The results indicate that MSZ with large Ar are more potential for tensile fracturing to occur at their vertices. Considering the

  11. Pre-eruptive magmatic conditions at Augustine Volcano, Alaska, 2006: Evidence from amphibole geochemistry and textures

    USGS Publications Warehouse

    De Angelis, Sarah; Larsen, Jessica D; Coombs, Michelle L.

    2013-01-01

    Variations in the geochemistry and texture of amphibole phenocrysts erupted from Augustine Volcano in 2006 provide new insights into pre- and syn-eruptive magma storage and mixing. Amphiboles are rare but present in all magma compositions (low- to high-silica andesites) from the 3 month long eruption. Unzoned magnesiohornblende in the high- and low-silica andesites exhibit limited compositional variability, relatively high SiO2 (up to 49·7 wt %), and relatively low Al2O3 (< 11·1 wt %). Intermediate-silica andesites and quenched mafic enclaves contain amphiboles that vary in composition (e.g. SiO2 40·8–48·9 wt %, Al2O3 6·52–15·2 wt %) and classification (magnesiohornblende–magnesiohastingsite–tschermakite). Compositional variation in amphibole is primarily controlled by temperature-dependent substitutions. Both high- and low-silica andesites represent remnant magmas that were stored in the shallow crust at 4–8 km depth, remaining distinct owing to a complex subsurface plumbing system. Intermediate-silica andesites and quenched mafic inclusions represent pre-eruptive hybrids of resident high- and low-silica andesite magmas and an intruding basalt. Amphiboles in explosive phase high-silica andesites are largely euhedral and unreacted, consistent with the high magma flux rates from depth during this phase (up to 13 800 m3 s–1). Phenocrysts from the other lithologies have reaction rims that range from 1 to >1000 μm in thickness. Reaction rim microlite sizes correlate with reaction rim thicknesses. Reaction rims <50 μm thick contain microlites 1–10 μm in length whereas reaction rims >80 μm thick contain microlites 10–100 μm in length. Differentiating between heating- and decompression-induced amphibole reaction rim formation is problematic because of a lack of experimental constraints. We attempt a new approach to assessing reaction rim formation, based on a kinetic theory of crystal nucleation and growth, in which the differences in reaction

  12. Platinum-group element geochemistry of the Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in western Yangtze Block, SW China: control of platinum-group elements by magnetite

    NASA Astrophysics Data System (ADS)

    Fan, Hong-Peng; Zhu, Wei-Guang; Zhong, Hong; Bai, Zhong-Jie; He, De-Feng; Ye, Xian-Tao; Chen, Cai-Jie; Cao, Chong-Yong

    2014-06-01

    Platinum-group element (PGE) geochemistry combined with elemental geochemistry and magnetite compositions are reported for the Mesoproterozoic Zhuqing Fe-Ti-V oxide ore-bearing mafic intrusions in the western Yangtze Block, SW China. All the Zhuqing gabbros display extremely low concentrations of chalcophile elements and PGEs. The oxide-rich gabbros contain relatively higher contents of Cr, Ni, Ir, Ru, Rh, and lower contents of Pt and Pd than the oxide-poor gabbros. The abundances of whole-rock concentrations of Ni, Ir, Ru, and Rh correlate well with V contents in the Zhuqing gabbros, implying that the distributions of these elements are controlled by magnetite. The fractionation between Ir-Ru-Rh and Pt-Pd in the Zhuqing gabbros is mainly attributed to fractional crystallization of chromite and magnetite, whereas Ru anomalies are mainly due to variable degrees of compatibility of PGE in magnetite. The order of relative incompatibility of PGEs is calculated to be Pd < Pt < Rh < Ir < Ru. The very low PGE contents and Cu/Zr ratios and high Cu/Pd ratios suggest initially S-saturated magma parents that were highly depleted in PGE, which mainly formed due to low degrees of partial melting leaving sulfides concentrating PGEs behind in the mantle. Moreover, the low MgO, Ni, Ir and Ru contents and high Cu/Ni and Pd/Ir ratios for the gabbros suggest a highly evolved parental magma. Fe-Ti oxides fractionally crystallized from the highly evolved magma and subsequently settled in the lower sections of the magma chamber, where they concentrated and formed Fe-Ti-V oxide ore layers at the base of the lower and upper cycles. Multiple episodes of magma replenishment in the magma chamber may have been involved in the formation of the Zhuqing intrusions.

  13. 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)

  14. 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.

  15. 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)

  16. 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

  17. Geochemistry constraints of Mesozoic Cenozoic calc-alkaline magmatism in the South Shetland arc, Antarctica

    NASA Astrophysics Data System (ADS)

    Machado, A.; Lima, E. F.; Chemale, F.; Morata, D.; Oteiza, O.; Almeida, D. P. M.; Figueiredo, A. M. G.; Alexandre, F. M.; Urrutia, J. L.

    2005-03-01

    Geochemical data from basalts, basaltic andesites, and andesites of the Mesozoic-Cenozoic (143-44 Ma) from Livingston, Greenwich, Robert, King George, and Ardley Islands of the South Shetland archipelago, Antarctica, are presented. The rocks have variable SiO 2 of approximately 46-61 wt%, Al 2O 3 of 15-26 wt%, and total alkali (K 2O+Na 2O) of 2-6 wt%. Most samples have low Mg#, Cr, and Ni, which indicates that they have undergone significant fractional crystallization from mantle-derived melts. The presence of olivine cumulatic in the samples from Livingston and Robert Islands explains some high MgO, Ni, and Cr values, whereas low Rb, Zr, and Nb values could be related to undifferentiated magmas. N-MORB-normalized trace element patterns show that South Shetland Islands volcanic rocks have a geochemical pattern similar to that found for other island arcs, with enrichment in LILE relative to HFSE and in LREE relative to HREE. The geochemistry pattern and presence of calcic plagioclase, orthopyroxene, Mg-olivine, and titanomagnetite phenocrysts suggest a source related to the subduction process. The geochemical data also suggest magma evolution from the tholeiitic to the calc-alkaline series; some samples show a transitional pattern. Samples from the South Shetland archipelago show moderate LREE/HREE ratios relative to N-MORB and OIB, depletion in Nb relative to Yb, and high Th/Yb ratios. These patterns probably reflect magma derived from a lithospheric mantle source previously modified by fluids and sediments from a subduction zone.

  18. 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

  19. 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.

  20. Differentiation of an Apollo 12 picrite magma

    NASA Technical Reports Server (NTRS)

    Walker, D.; Hays, J. F.; Longhi, J.; Kirkpatrick, R. J.

    1976-01-01

    The Apollo 12 olivine basalt suite shows a strong positive correlation of grain size with normative olivine content. This correlation is interpreted to mean that the suite of samples represents the basal portion of a cooling unit which differentiated by simple olivine settling. The grain size of plagioclase observed in the coarsest samples indicates the cooling unit may have been as much as 30 m thick. The amount of olivine concentration observed in the suite is quantitatively internally consistent with simple olivine settling in a magma body of this size which has the composition of the chill margin.

  1. 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.

  2. 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

  3. Magma storage under Iceland's Eastern Volcanic Zone

    NASA Astrophysics Data System (ADS)

    Maclennan, J.; Neave, D.; Hartley, M. E.; Edmonds, M.; Thordarson, T.; Morgan, D. J.

    2014-12-01

    The Eastern Volcanic Zone (EVZ) of Iceland is defined by a number of volcanic systems and large basaltic eruptions occur both through central volcanoes (e.g. Grímsvötn) and on associated fissure rows (e.g. Laki, Eldgjá). We have collected a large quantity of micro-analytical data from a number of EVZ eruptions, with the aim of identifying common processes that occur in the premonitory stages of significant volcanic events. Here, we focus on the AD 1783 Laki event, the early postglacial Saksunarvatn tephra and the sub-glacially erupted Skuggafjöll tindar and for each of these eruptions we have >100 olivine-hosted or plagioclase-hosted melt inclusion analyses for major, trace and volatile elements. These large datasets are vital for understanding the history of melt evolution in the plumbing system of basaltic volcanoes. Diverse trace element compositions in melt inclusions hosted in primitive macrocrysts (i.e. Fo>84, An>84) indicate that the mantle melts supplied to the plumbing system of EVZ eruptions are highly variable in composition. Concurrent mixing and crystallisation of these melts occurs in crustal magma bodies. The levels of the deepest of these magma bodies are not well constrained by EVZ petrology, with only a handful of high-CO2 melt inclusions from Laki providing evidence for magma supply from >5 kbar. In contrast, the volatile contents of melt inclusions in evolved macrocrysts, which are close to equilibrium with the carrier liquids, indicate that final depths of inclusion entrapment are 0.5-2 kbar. The major element composition of the matrix glasses shows that the final pressure of equilibration between the melt and its macrocryst phases also occurred at 0.5-2 kbar. The relationship between these pressures and seismic/geodetic estimates of chamber depths needs to be carefully evaluated. The melt inclusion and macrocryst compositional record indicates that injection of porphyritic, gas-rich primitive melt into evolved/enriched and degassed shallow

  4. 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.

  5. 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.

  6. 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

  7. Using magma flow indicators to infer flow dynamics in sills

    NASA Astrophysics Data System (ADS)

    Hoyer, Lauren; Watkeys, Michael K.

    2017-03-01

    Fabrics from Anisotropy of Magnetic Susceptibility (AMS) analyses and Shape Preferred Orientation (SPO) of plagioclase are compared with field structures (such as bridge structures, intrusive steps and magma lobes) formed during magma intrusion in Jurassic sills. This is to constrain magma flow directions in the sills of the Karoo Igneous Province along the KwaZulu-Natal North Coast and to show how accurately certain structures predict a magma flow sense, thus improving the understanding of the Karoo sub-volcanic dynamics. The AMS fabrics are derived from magnetite grains and are well constrained, however the SPO results are commonly steeply inclined, poorly constrained and differ to the AMS fabrics. Both techniques resulted in asymmetrical fabrics. Successful relationships were established between the AMS fabric and the long axes of the magma flow indicators, implying adequate magma flow prediction. However, where numerous sill segments merge, either in the form of magma lobes or bridge structures, the coalescence process creates a new fabric between the segments preserving late-stage magma migration between the merged segments, overprinting the initial magma flow direction.

  8. 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.

  9. 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.

  10. Breaking the paradigm at magma-poor and magma-rich rifted margins

    NASA Astrophysics Data System (ADS)

    Tugend, Julie; Manatschal, Gianreto; Gillard, Morgane; Nirrengarten, Michael; Epin, Marie-Eva; Sauter, Daniel; Autin, Julia; Harkin, Caroline; Kusznir, Nick

    2017-04-01

    Rifted margins used to be classified into volcanic or non-volcanic passive margins. Because magmatism is evidenced even in so-called 'non-volcanic' settings, this terminology was later adjusted to magma-poor and magma-rich rifted margins. This classification represents a simplification into end-member magmatic types depending on the magmatic budget related to rifting and/or breakup processes. New observations derived from higher quality geophysical data sets and drill-hole data revealed the great diversity of rifted margin architecture and highly variable distribution of rift-related and/or breakup related magmatism. Recent studies suggest that rifted margins have a more complex tectono-magmatic evolution than previously assumed and cannot be characterized based on the observed volume of magma alone. In this study, we present seismic observations from 2D high resolution long-offset deep reflection seismic profiles across the East-Indian and South-Atlantic rifted margins. We aim to compare structural similarities between rifted margins with different magmatic budgets. We apply a systematic seismic interpretation approach to describe and characterize the first-order architecture and magmatic budget of our case examples. The identification of magmatic additions based on seismic observations only is indeed not unequivocal, in spite of the high-resolution dataset. Interpretations are related to large uncertainties in particular at ocean-continent transitions (i.e. outer highs) where most of the magmatism seems to be located. For each line, we present three different interpretations based on offshore and/or onshore field analogues. These interpretations illustrate scenarios for the nature of the outer highs that we believe are geologically meaningful and reasonable, and imply different magmatic budgets at breakup. Based on these interpretations we discuss different mechanisms for lithospheric breakup involving either a gradual or more instantaneous process independently

  11. Rapid thermal rejuvenation of high-crystallinity magma linked to porphyry copper deposit formation; evidence from the Koloula Porphyry Prospect, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Tapster, S.; Condon, D. J.; Naden, J.; Noble, S. R.; Petterson, M. G.; Roberts, N. M. W.; Saunders, A. D.; Smith, D. J.

    2016-05-01

    Magmas containing the components needed to form porphyry copper deposits are relatively common within arcs, yet mineralising events are uncommon within the long-lived magmatic systems that host them. Understanding what causes the transition from barren to productive intrusions is critical to the development of conceptual deposit models. We have constrained the tempo of pre- and syn-mineralisation magmatic events in relationship to the thermal evolution of the plutonic body that underlies one of the world's youngest exposed plutonic-porphyry systems, the Inamumu Zoned Pluton, Koloula Porphyry Prospect, Solomon Islands. High precision ID-TIMS U-Pb dates of texturally and chemically characterised zircons indicate pluton emplacement over <150 kyr was superseded after ca. 50 kyr by two discrete episodes of mineralising porphyritic melt emplacement. Their associated hydrothermal systems initiated within ca. 30 kyrs of each other. Zircon populations within evolved intrusions contain resorbed cores that were recycled from the deeper magmatic system, yet their youngest dates are statistically indistinguishable from those yielded by crystals lacking resorption. Comparisons of Ti-in-zircon proxy temperatures, modelled zircon saturation temperatures and temperature-crystallinity relationships suggest that prior to being heated and emplaced within the shallow level pluton, magmas were stored at depth in a high-crystallinity (>50% crystals) state, past the point of rheological lock-up. We estimate that thermal rejuvenation of the deeper high-crystallinity magma and generation of a mobile melt fraction may have occurred ≤10 kyr before its transport and emplacement within the porphyry environment. The underlying pluton likely cooled and returned to high-crystallinity states prior to subsequent remobilisation-emplacement events. Titanium-in-zircon geothermometry and whole-rock geochemistry suggest pre-mineralisation intrusions were remobilised by mixing of a silicic magma with a

  12. 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

  13. Investigating magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions.

    NASA Astrophysics Data System (ADS)

    Dahren, Börje; Troll, Valentin R.; Andersson, Ulf-Bertil; Chadwick, Jane P.; Gardner, Mairi F.

    2010-05-01

    Improving our understanding of magma plumbing and storage remains one of the major challenges for petrologists and volcanologists today. This is especially true for explosive volcanoes, where constraints on magma plumbing are essential for predicting dynamic changes in future activity and thus for hazard mitigation. This study aims to investigate the magma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the 1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rate of ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry [1,2] b.) plagioclase-melt thermo-barometry [3] c.) clinopyroxene composition barometry [2,4] and d.) olivine-melt thermometry [5]. The minerals analysed are from basaltic-andesites erupted between 1990-2002, with an average modal composition of 70% groundmass, 25% plagioclase, 4% clinopyroxene and <1% olivine. Clinopyroxenes are homogenous and display no obvious zoning. Plagioclases are considerably more heterogenous, exhibiting complex zoning and An content between An45-80. In addition, mineral compositions of older clinopyroxenes, erupted between 1883-1981, are used for comparison [6,7]. Previously, both seismic [8] and petrological studies [6,7,9] have addressed the magma plumbing beneath Anak Krakatau. Interestingly, petrological studies indicate shallow magma storage in the region of 2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and 22 km respectively. Our results imply that clinopyroxene presently crystallizes in a mid-crustal storage region (8-12 km), a previously identified depth level for magma storage, using seismic methods [8]. Plagioclases, in turn, form at shallower depths (4-6 km), in concert with previous petrological studies [6,7,9]. Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km), indicating that there may have been an overall shallowing of the plumbing system over the last ~40 years

  14. 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.

  15. Magma evolution inside the 1631 Vesuvius magma chamber and eruption triggering

    NASA Astrophysics Data System (ADS)

    Stoppa, Francesco; Principe, Claudia; Schiazza, Mariangela; Liu, Yu; Giosa, Paola; Crocetti, Sergio

    2017-03-01

    Vesuvius is a high-risk volcano and the 1631 Plinian eruption is a reference event for the next episode of explosive unrest. A complete stratigraphic and petrographic description of 1631 pyroclastics is given in this study. During the 1631 eruption a phonolite was firstly erupted followed by a tephritic phonolite and finally a phonolitic tephrite, indicating a layered magma chamber. We suggest that phonolitic basanite is a good candidate to be the primitive parental-melt of the 1631 eruption. Composition of apatite from the 1631 pyroclastics is different from those of CO2-rich melts indicating negligible CO2 content during magma evolution. Cross checking calculations, using PETROGRAPH and PELE software, accounts for multistage evolution up to phonolite starting from a phonolitic basanite melt similar to the Vesuvius medieval lavas. The model implies crystal settling of clinopyroxene and olivine at 6 kbar and 1220°C, clinopyroxene plus leucite at a pressure ranging from 2.5 to 0.5 kbar and temperature ranging from 1140 to 940°C. Inside the phonolitic magma chamber K-feldspar and leucite would coexist at a temperature ranging from from 940 to 840°C and at a pressure ranging from 2.5 to0.5 kbar. Thus crystal fractionation is certainly a necessary and probably a sufficient condition to evolve the melt from phono tephritic to phonolitic in the 1631 magma chamber. We speculate that phonolitic tephrite magma refilling from deeper levels destabilised the chamber and triggered the eruption, as testified by the seismic precursor phenomena before 1631 unrest.

  16. The 3D Distribution of Magma Bodies that Fed the Paraná Silicic Volcanics, Brazil: A Combination of Field Evidence, Textural Analysis, and Geothermobarometry

    NASA Astrophysics Data System (ADS)

    Harmon, L.; Gualda, G. A. R.; Gravley, D. M.

    2016-12-01

    The Paraná Silicic Volcanics include some of the largest eruptive deposits known in the geological record. However, we know very little about the magma bodies that fed these eruptions. Combining physical volcanology, geochemistry, and geothermobarometry techniques, we aim to find the sources of extinct magma bodies to build a 3D view of the magma structure at the time by discovering storage conditions, eruption styles, and post-eruption alteration. The approach elucidates temporal and spatial eruption styles and sequences of the silicic units that make up the Palmas unit of the Serra Geral formation, Brazil. We use field investigations to determine the history of volcanic deposits, domes, and changes in eruptive style; we map and characterize volcanic deposits based on thickness (thicker is proximal to source) and distribution of effusive (proximal to source) and explosive deposits. We focus on several exposed canyons that exhibit either exclusively explosive or effusive, or a clear progression from explosive to effusive deposits. The progression from explosive to effusive indicates a system change from explosively energetic to effusively waning. Additionally, observation of pervasive flow banding in both effusive and explosive deposits indicates rheomorphic flow through many portions of the field area, an indicator of hot emplacement. Geochemical work focuses on the pre-eruptive magma conditions to determine the depth of magma bodies. We utilize glass bearing samples of both the explosively deposited juvenile blob-like structures and obsidian samples to determine crystallization depth. The glass is variably altered, via silicification and devitrification processes, with the blobs more greatly silicified than the obsidian. We use rhyolite-MELTS geothermobarometry when pristine glass can be found. Initial results indicate shallow ( 80 MPa) storage conditions for the explosively erupted blobs. The combination of techniques builds a 3D understanding of extinct super

  17. Paroxysmal explosions at Stromboli (Aeolian Islands, Italy): Composition of parental magmas, mechanisms of crystallization and degassing as recorded by melt inclusions

    NASA Astrophysics Data System (ADS)

    Bertagnini, A.; Metrich, N.; Landi, P.; Rosi, M.

    2003-04-01

    Paroxysmal eruptions at Stromboli represent the most violent explosive events of the persistent activity and produce K-basaltic nearly aphyric pumices that offer the exceptional opportunity to detail the mixing-crystallization-degassing processes that occur in a steady-state basaltic arc volcano. We present new data on mineralogy, major, volatile and trace element geochemistry of olivine-hosted melt inclusions of pumice produced within the last 1400--1800 years. In addition to previous data [1], they reveal that melt inclusions have recorded parental melts rich in CaO (up to 14.5 wt.%) but low in FeO (6--7 wt.%), whose recognition is exceptional and systematically associated with the most energetic explosive events, only. They demonstrate recurrent variations in the chemistry of these magma batches distinct by their K_2O content (1.6--1.3 wt.%) and S/Cl ratios (1.2--0.8). Their high volatile concentrations (3.4--1.8 wt.% H_2O, 1582 to 1017 ppm CO_2) indicate crystal fractionation and storage, assessed between 3 and 4 kb total fluid pressure, of CaO-rich FeO-poor magma blobs at the origin of the pumice produced at Stromboli. Interactions between parental melts and olivine crystals inherited from pre-existing crystal-mush, and their mixing with the magmas resident at high pressure are recorded only at a scale of the micrometer. Rapid magma ascent combined with restricted temperature gradient and limited crystal nucleation account for the emission of highly vesicular glassy basaltic pumices. In addition, the size and shape of olivines, as well as the high density of irregular melt inclusions and melt/gas ratio in inclusions, attest of crystallization from gas oversaturated magma. Finally, we propose that sulfur degassing is possibly initiated at pressure as high as 3 kb. [1] Métrich, Bertagnini,Landi &Rosi (2001) J. Petrol. 42, 1471--1490.

  18. A felsic MASH zone of crustal magmas - Feedback between granite magma intrusion and in situ crustal anatexis

    NASA Astrophysics Data System (ADS)

    Schwindinger, Martin; Weinberg, Roberto F.

    2017-07-01

    Magma mixing and mingling are described from different tectonic environments and are key mechanisms in the evolution of granitoids. The literature focuses on the interaction between mafic and felsic magmas with only limited research on the interaction between similar magmas. Here, we investigate instead hybridization processes between felsic magmas formed during the 500 Ma Delamerian Orogeny on the south coast of Kangaroo Island. Field relations suggest that a coarse, megacrystic granite intruded and interacted with a fine-grained diatexite that resulted from combined muscovite dehydration and water-fluxed melting of Kanmantoo Group turbidites. The two magmas hybridized during syn-magmatic deformation, explaining the complexity of relationships and variability of granitoids exposed. We suggest that granite intrusion enhanced melting of the turbidites by bringing in heat and H2O. With rising melt fraction, intrusive magmas became increasingly unable to traverse the partially molten terrane, creating a positive feedback between intrusion and anatexis. This feedback loop generated the exposed mid-crustal zone where magmas mixed and homogenized. Thus, the outcrops on Kangaroo Island represent a crustal and felsic melting-assimilation-storage-homogenization (felsic MASH) zone where, instead of having direct mantle magma involvement, as originally proposed, these processes developed in a purely crustal environment formed by felsic magmas.

  19. Open-system dynamics and mixing in magma mushes

    NASA Astrophysics Data System (ADS)

    Bergantz, G. W.; Schleicher, J. M.; Burgisser, A.

    2015-10-01

    Magma dominantly exists in a slowly cooling crystal-rich or mushy state. Yet, observations of complexly zoned crystals, some formed in just one to ten years, as well as time-transgressive crystal fabrics imply that magmas mix and transition rapidly from a locked crystal mush to a mobile and eruptable fluid. Here we use a discrete-element numerical model that resolves crystal-scale granular interactions and fluid flow, to simulate the open-system dynamics of a magma mush. We find that when new magma is injected into a reservoir from below, the existing magma responds as a viscoplastic material: fault-like surfaces form around the edges of the new injection creating a central mixing bowl of magma that can be unlocked and become fluidized, allowing for complex mixing. We identify three distinct dynamic regimes that depend on the rate of magma injection. If the magma injection rate is slow, the intruded magma penetrates and spreads by porous media flow through the crystal mush. With increasing velocity, the intruded magma creates a stable cavity of fluidized magma that is isolated from the rest of the reservoir. At higher velocities still, the entire mixing bowl becomes fluidized. Circulation within the mixing bowl entrains crystals from the walls, bringing together crystals from different parts of the reservoir that may have experienced different physiochemical environments and leaving little melt unmixed. We conclude that both granular and fluid dynamics, when considered simultaneously, can explain observations of complex crystal fabrics and zoning observed in many magmatic systems.

  20. 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.

  1. 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

  2. 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.

  3. 75 FR 28778 - Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, AZ

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-24

    ... Natural Resources Conservation Service Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan... Magma Flood Retarding Structure (FRS) Supplemental Watershed Plan, Pinal County, Arizona. FOR FURTHER... needed for this project. The project proposes to rehabilitate the Magma FRS to provide for...

  4. Dynamics of a Magma Chamber: Insights Into Time and Length Scales of Internal Processes in the Tuolumne Batholith, CA

    NASA Astrophysics Data System (ADS)

    Memeti, V.; Paterson, S. R.; Matzel, J.; Mundil, R.; Ducea, M.; Miller, J. S.

    2007-12-01

    are overprinted by longer term mixing processes (a few myrs) of magmas derived from at least two different sources. While fractionation crystallization pattern dominate in the more quickly crystallized lobes, compositions in the main batholith are hybrids with variable components of different pulses and their differentiates mixing at cm to km scales. Our field observations, geochemistry data and U/Pb geochronology from the TB (Matzel et al., 2007) indicate that sizeable magma chambers form during batholith construction in which pulsing, fractionation and mixing are responsible for compositional variations at the emplacement level.

  5. Small crystals, big implications: glomerocrysts and their connections to large silicic magma reservoirs. Examples from Yellowstone rhyolite lavas.

    NASA Astrophysics Data System (ADS)

    Girard, G.

    2016-12-01

    Characterizing the nature and physical state of the magma reservoirs associated to large silicic volcanoes is critical to assess their potential to erupt. Yellowstone is among the most active of these systems, having produced 3 caldera-forming eruption sequences and >40 rhyolite lava flows over the last 2.15 Ma. The geochemical evolution of the most recently erupted lava flow sequences, the Upper Basin and Central Plateau members, argues for the existence of one large magma reservoir, from which melts are periodically extracted and erupted as lava with <10% phenocrysts. This study focuses on two eruptions closely postdating the second and third caldera collapse events, the 1.28 Ma Osborne Butte lava dome, and the 0.6 Ma East Biscuit Basin lava flow. These more phyric units have complex mineralogy with multiple crystal textures and geochemistry. In particular, they exhibit plagioclase-clinopyroxene-oxides glomerocrysts with grain size < 1mm. These coexist with larger, euhedral, isolated clinopyroxene and plagioclase. In both lavas, glomerocrysts are the components with the most primitive compositions. In the East Biscuit Basin lava, plagioclase from glomerocrysts ranges from An23 to An46 with 560 ± 30 ppm Sr (1σ) while isolated sieved plagioclase has An20-25 with similar Sr. Clinopyroxene in glomerocrysts is En25-31Fs31-43Wo34-38 while isolated crystals are En21-23Fs40-41Wo37-38. Rare earth elements also are more enriched in the isolated clinopyroxene. In the Osborne Butte lava, the glomerocrysts also are the most primitive components with An19-23 and 245 ± 40 ppm Sr in plagioclase, while larger isolated plagioclase has diverse but generally more evolved compositions (An14-24 and 35-280 ppm Sr). The more primitive compositions and plutonic textures of these glomerocrysts, together with their presence being restricted to lavas erupted closely after caldera collapse (when the volcano subsurface is the most disturbed) argue for their origin from the magma body from

  6. Three Dimensional Magma Wagging: Seismic Diagnostics And Forcing Mechanism

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Jellinek, M.; Bercovici, D.

    2016-12-01

    Seismic tremor involving 0.5-7 Hz ground oscillations are common precursors of explosive sillicic volcanism. Here we present recent progress on the development and application of the three dimensional magma-wagging model, which is extended from the magma wagging model for tremor [Jellinek and Bercovici, 2011, Bercovici et al., 2013]. In our model, a stiff magma column rising in a vertical conduit oscillates against a surrounding foamy annulus of bubbly magma, giving rise to tremor. Inside the volcanic conduit, the magma column undergoes swirling motion, in which each horizontal section of the column can trace elliptical trajectories. We propose seismic diagnostics for the characteristics of the swirling motion using the time-lag between seismic stations, and test our model by analyzing pre-eruptive seismic data from the 2009 eruption of Redoubt Volcano. Our analysis demonstrates the existence of elliptical swirling motion more than one week before the eruption, and suggests that the 2009 eruption was accompanied by qualitative changes in the magma wagging behavior including fluctuations in eccentricity and a reversal in the direction of elliptical swirling motion when the eruption was immediately impending. We further explore the coupling between the dynamics of the gas flux in the foamy annulus and the wagging motion of the magma column. We show that the gas flux provides a driving force for the magma column to swirl against viscous damping. The coupling between gas flux and wagging motion also brings the possibility to link observation of out-gassing with seismic measurements.

  7. The role of volatiles in magma chamber dynamics.

    PubMed

    Huppert, Herbert E; Woods, Andrew W

    2002-12-05

    Many andesitic volcanoes exhibit effusive eruption activity, with magma volumes as large as 10(7)-10(9) m(3) erupted at rates of 1-10 m(3) x s(-1) over periods of years or decades. During such eruptions, many complex cycles in eruption rates have been observed, with periods ranging from hours to years. Longer-term trends have also been observed, and are thought to be associated with the continuing recharge of magma from deep in the crust and with waning of overpressure in the magma reservoir. Here we present a model which incorporates effects due to compressibility of gas in magma. We show that the eruption duration and volume of erupted magma may increase by up to two orders of magnitude if the stored internal energy associated with dissolved volatiles can be released into the magma chamber. This mechanism would be favoured in shallow chambers or volatile-rich magmas and the cooling of magma by country rock may enhance this release of energy, leading to substantial increases in eruption rate and duration.

  8. 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.

  9. 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

  10. Isotope Geochemistry for Comparative Planetology of Exoplanets

    NASA Technical Reports Server (NTRS)

    Mandt, K. E.; Atreya, S.; Luspay-Kuti, A.; Mousis, O.; Simon, A.; Hofstadter, M. D.

    2017-01-01

    Isotope geochemistry has played a critical role in understanding processes at work in and the history of solar system bodies. Application of these techniques to exoplanets would be revolutionary and would allow comparative planetology with the formation and evolution of exoplanet systems. The roadmap for comparative planetology of the origins and workings of exoplanets involves isotopic geochemistry efforts in three areas: (1) technology development to expand observations of the isotopic composition of solar system bodies and expand observations to isotopic composition of exoplanet atmospheres; (2) theoretical modeling of how isotopes fractionate and the role they play in evolution of exoplanetary systems, atmospheres, surfaces and interiors; and (3) laboratory studies to constrain isotopic fractionation due to processes at work throughout the solar system.

  11. 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.

  12. An Unlikely Connection: Geochemistry and Nuclear Structure

    NASA Astrophysics Data System (ADS)

    Kragh, Helge

    2000-12-01

    Although geochemistry belongs to the earth sciences, historically it has interacted importantly with the physical sciences, in particular with astrophysics and nuclear physics. These interactions, which in traditional historiography have received little notice from either historians of physics or historians of geology, are the subjects of the present paper, which focuses on the period between 1915 and 1950. During the 1920s, geochemists established empirical regularities in the abundance data of the elements in rocks and meteorites, and from these they suggested that an improved knowledge of the atomic nucleus could be obtained. More significantly, geochemists supplied astrophysicists, cosmologists and nuclear physicists with important data that could not be obtained otherwise. The link between geochemistry and basic, nuclear physics is a historical reality. The paper explores parts of this link.

  13. 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.

  14. 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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    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 (<3 km) low-frequency events likely related to glacier activity, as well as deep (>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.

  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. 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.

  19. Magma mixing induced by particle settling

    NASA Astrophysics Data System (ADS)

    Renggli, Christian J.; Wiesmaier, Sebastian; De Campos, Cristina P.; Hess, Kai-Uwe; Dingwell, Donald B.

    2016-11-01

    A time series of experiments at high temperature have been performed to investigate the influence of particle settling on magma mixing. A natural rhyolite glass was held above a natural basalt glass in a platinum crucible. After melting of the glasses at superliquidus temperatures, a platinum sphere was placed on the upper surface of the rhyolitic melt and sank into the experimental column (rhyolitic melt above basaltic melt). Upon falling through the rhyolitic-basaltic melt interface, the Pt sphere entrained a filament of rhyolitic melt in its further fall. The quenched products of the experiments were imaged using X-ray microCT methods. The images of our time series of experiments document the formation of a rhyolite filament as it is entrained into the underlying basalt by the falling platinum sphere. When the Pt particle reached the bottom of the crucible, the entrained rhyolitic filament started to ascend buoyantly up to the initial rhyolitic-basaltic interface. This generated a significant thickness increase of a comingled "melange" layer at the interface due to "liquid rope coiling" and piling up of the filament. As a consequence, the basalt/rhyolite interface was greatly enlarged and diffusive hybridisation greatly accelerated. Further, bubbles, originating at the interface, are observed to have risen into the overlying rhyolite dragging basalt filaments with them. Upon crossing the basalt/rhyolite interface, the bubbles have non-spherical shapes as they adapt to the differing surface tensions of basaltic and rhyolitic melts. Major element profiles, measured across the rhyolite filaments, exhibit asymmetrical shapes from the rhyolite into the basalt. Na and Ti reveal uphill diffusion from the rhyolite towards the interface in the filament cross sections. These results reveal the potential qualitative complexity of the mingling process between rhyolitic and basaltic magmas in the presence of sinking crystals. They imply that crystal-rich magma mingling may

  20. 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

  1. Electrical conductivity of water-bearing magmas

    NASA Astrophysics Data System (ADS)

    Gaillard, F.

    2003-04-01

    Phase diagrams and chemical analyzes of crystals and glass inclusions of erupted lavas tell us that most explosive volcanic eruptions were caused by extremely water-rich pre-eruptive conditions. Volcanologists estimate volcanic hazards by the pre-eruptive water content of lavas erupted in the past and they hypothesize that future eruptions should show similar features. Alternatively, the development of methods allowing direct estimation of water content of magmas stored in the Earth’s interior would have the advantage of providing direct constraints about upcoming rather than past eruptions. Geoelectrical sounding, being the most sensitive probe to the chemical state of the Earth’s interior, seems a promising tool providing that its interpretation is based on relevant laboratory constraints. However, the current database of electrical conductivity of silicate melt merely constrains anhydrous composition. We have therefore undertaken an experimental program aiming at elucidating the effect of water on the electrical conductivity of natural magmas. Measurements (impedance spectroscopy) are performed using a two electrodes set-up in an internally heated pressure vessel. The explored temperature and pressure range is 25-1350°C and 0.1-400MPa. The material used is a natural rhyolitic obsidian. Hydration of this rhyolite is first performed in Pt capsules with 0.5, 1, 2 and 6wt% of water. In a second step, the conductivity measurements are performed at pressure and temperature in a modified Pt capsule. One end of the capsule is arc-welded whereas the other end is closed with the help of a BN cone and cement through which an inner electrode is introduced in the form a Pt wire. The capsule is used as outer electrode. The electrical cell has therefore a radial geometry. The rhyolite is introduced in the cell in the form of a cylinder drilled in the previously hydrated glass. At dwell condition, the melt is sandwiched between two slices of quartz avoiding any deformation

  2. 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

  3. Flow in an experimental micro-magma chamber

    NASA Astrophysics Data System (ADS)

    Carroll, Michael R.; Wyllie, Peter J.

    The chemical evolution and eruptive behavior of magmas may be controlled largely by convective processes within magma chambers. According to a recent National Research Council Report [Committee on Physics and Chemistry of Earth Materials, 1987], “the style of convection itself, whether it is turbulent, laminar, large-scale, of multiple scales, tiered, or localized and intermittent, is very much at question.” In the U.S. National Report to the International Union of Geodesy and Geophysics, Marsh [1987] reviewed recent theoretical and experimental developments related to the style of convection in magma chambers, noting both significant quantitative advances and also the many remaining uncertainties. With regard to double-diffusive convection, he stated “as ever, the critical question concerns whether or not actual magma chambers convect in this style.” Similarly, Spera et al. [1986] , in discussion of double-diffusive convection, cautioned against “applying results from saltwater tanks to magma chambers.”

  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. 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.

  6. Hydrogen isotopic fractionation during crystallization of the terrestrial magma ocean

    NASA Astrophysics Data System (ADS)

    Pahlevan, K.; Karato, S. I.

    2016-12-01

    Models of the Moon-forming giant impact extensively melt and partially vaporize the silicate Earth and deliver a substantial mass of metal to the Earth's core. The subsequent evolution of the terrestrial magma ocean and overlying vapor atmosphere over the ensuing 105-6 years has been largely constrained by theoretical models with remnant signatures from this epoch proving somewhat elusive. We have calculated equilibrium hydrogen isotopic fractionation between the magma ocean and overlying steam atmosphere to determine the extent to which H isotopes trace the evolution during this epoch. By analogy with the modern silicate Earth, the magma ocean-steam atmosphere system is often assumed to be chemically oxidized (log fO2 QFM) with the dominant atmospheric vapor species taken to be water vapor. However, the terrestrial magma ocean - having held metallic droplets in suspension - may also exhibit a much more reducing character (log fO2 IW) such that equilibration with the overlying atmosphere renders molecular hydrogen the dominant H-bearing vapor species. This variable - the redox state of the magma ocean - has not been explicitly included in prior models of the coupled evolution of the magma ocean-steam atmosphere system. We find that the redox state of the magma ocean influences not only the vapor speciation and liquid-vapor partitioning of hydrogen but also the equilibrium isotopic fractionation during the crystallization epoch. The liquid-vapor isotopic fractionation of H is substantial under reducing conditions and can generate measurable D/H signatures in the crystallization products but is largely muted in an oxidizing magma ocean and steam atmosphere. We couple equilibrium isotopic fractionation with magma ocean crystallization calculations to forward model the behavior of hydrogen isotopes during this epoch and find that the distribution of H isotopes in the silicate Earth immediately following crystallization represents an oxybarometer for the terrestrial

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

    PubMed

    Blundy, Jon; Cashman, Kathy; Humphreys, Madeleine

    2006-09-07

    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.

  8. Transition from magma dominant to magma poor rifting along the Nova Scotia Continental Margin

    NASA Astrophysics Data System (ADS)

    Lau, K. H.; Louden, K. E.; Nedimović, M. R.; Whitehead, M.; Farkas, A.; Watremez, L.; Dehler, S. A.

    2011-12-01

    Passive margins have been characterized as magma-dominant (volcanic) or magma-poor (non-volcanic). However, the conditions under which margins might switch states are not well understood as they typically have been studied as end member examples in isolation to each other. The Nova Scotia (NS) continental margin, however, offers an opportunity to study the nature of such a transition between the magma-dominant US East Coast margin to the south and the magma-poor Newfoundland margin to the north within a single rift segment. This transition is evidenced by a clear along-strike reduction in features characteristic of syn-rift volcanism from south-to-north along the NS margin, such as the weakening of the East Coast Magnetic Anomaly (ECMA) and the coincident disappearance of seaward dipping reflector sequences (SDRS) on multichannel seismic (MCS) reflection profiles. Results from recent industry MCS profiles along and across the margin suggest a potentially narrow magma-dominant to magma-poor along-strike transition between the southern and the central NS margin. Such a transition is broadly consistent with results of several widely-spaced, across-strike ocean bottom seismometer (OBS) wide-angle profiles. In the southern region, the crustal structure exhibits a narrow (~120-km wide) ocean-continent transition (OCT) with a high velocity (7.2 km/s) lower crust, interpreted as a gabbro-rich underplated melt, beneath the SDRS and the ECMA, similar to crustal models across the US East Coast. In contrast, profiles across the central and northern margin contain a much wider OCT (150-200-km wide) underlain by a low velocity mantle layer (7.3-7.9 km/s), interpreted as partially serpentinized olivine, which is similar to the magma-poor Newfoundland margin to the north. However, the central-to-northern OBS profiles also exhibit significant variations within the OCT and the along-strike continuity of these OCT structures is not yet clear. In November 2010, we acquired, in the

  9. 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.

  10. 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.

  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 mixing during caldera forming eruptions

    NASA Astrophysics Data System (ADS)

    Kennedy, B.; Jellinek, M.; Stix, J.

    2006-12-01

    During explosive caldera-forming eruptions magma erupts through a ring dyke. Flow is driven, in part, by foundering of a magma chamber roof into underlying buoyant magma. One intriguing and poorly understood characteristic of deposits from calderas is that bulk ignimbrite, pumices, and crystals can show complex stratigraphic zonation. We propose that zonation patterns can be explained by different, and temporally evolving subsidence styles, and that the geometry imposed by subsidence can affect flow and cause mixing in the chamber and ring dyke. We use two series of laboratory experiments to investigate aspects of the mixing properties of flow in the chamber and ring dike during caldera collapse. In the first series, cylindrical blocks of height, h, and diameter, d, are released into circular analog magma chambers of diameter D and height H, containing buoyant fluids with viscosities that we vary. Subsidence occurs as a result of flow through the annular gap (ring dike) between the block and the wall of the surrounding tank of width, w = D-d. Three dimensionless parameters characterize the nature and evolution of the subsidence, and the resulting flow: A Reynolds number, Re, a tilt number, T = w/h and a subsidence number, S = w/H. Whereas Re indicates the importance of inertia for flow and mixing, T and S are geometric parameters that govern the extent of roof tilting, the spatial variation in w during collapse and the wavelength and structure of fluid motions. On the basis of field observations and theoretical arguments we fix T ≍ 0.14 and characterize subsidence and the corresponding flow over a wide range of Re - S parameter space appropriate to silicic caldera systems. Where S < 2 and Re < 103 the roof can rotate or tilt as it sinks and a spectrum of fluid mechanical behavior within the ring dike are observed. The combination of roof rotation and tilting drives unsteady, 3D overturning motions within the ring dike that are inferred to cause extensive mixing

  14. The magma ocean concept and lunar evolution

    NASA Technical Reports Server (NTRS)

    Warren, P. H.

    1985-01-01

    The model of lunar evolution in which the anorthositic plagioclase-rich oldest crust of the moon is formed over a period of 300 Myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies. Consideration is given to the classification of lunar rocks, the evidence for primordial deep global differentiation, constraints on the depth of the molten zone, the effects of pressure on mineral stability relationships, mainly-liquid vs mainly-magmifer ocean models, and the evidence for multiple ancient differentiation episodes. A synthesis of the model of primordial differentiation and its aftereffects is presented, and the generalization of the model to the earth and to Mars, Mercury, Venus, and the asteroids is discussed.

  15. How did the Lunar Magma Ocean crystallize?

    NASA Astrophysics Data System (ADS)

    Davenport, J.; Neal, C. R.

    2012-12-01

    It is generally accepted that the lunar crust and at least the uppermost (500 km) mantle was formed by crystallization of a magma ocean. How the magma ocean cooled and crystallized is still under debate. Parameters such as bulk composition, lunar magma ocean (LMO) crystallization method (fractional vs. equilibrium), depth of the LMO, and time for LMO solidification (effects of tidal heating mechanisms, insulating crustal lid, etc.) are still under debate. Neal (2001, JGR 106, 27865-27885) argues for the presence of garnet in the deep lunar mantle via compositional differences between low- and high-Ti mare basalts and volcanic glasses. Neal (2001) suggests that these compositional differences are due to the presence of garnet in the source regions of certain volcanic glass bead groups. As Neal (2001, JGR 106, 27865-27885) points out, determining if there is garnet in the lunar mantle is important in determining if the LMO was a "whole-Moon" event or if it was limited to certain areas. In the latter case, garnet would have been preserved in the lunar mantle and would have been used in the source material for some of the volcanic glasses. High-pressure experimental work concludes that with the right T-P conditions (2.5-4.5 GPa and 1675-1800° C) there could be a garnet-bearing pyroxene rich protolith at ~500 km depth. This also has significant implications for the bulk Al2O3 composition of the initial bulk Moon. If the LMO was not global, the volcanic glass beads that show evidence of garnet in their sources were formed from the deep, primitive lunar mantle, it begs the questions how was the non-LMO regions of the Moon formed and what was it's bulk composition? To try to answer these questions, it is necessary to thoroughly model the evolution of the LMO and then use that work to model the sources and formation of mare basalts, the volcanic glass beads, and other regions in question. To begin to answer these questions, we developed a scenario we have termed reverse

  16. The Abundance of Sulfur in Venus Magmas

    NASA Astrophysics Data System (ADS)

    Bullock, M. A.; Grinspoon, D. H.

    1999-09-01

    Outgassing of sulfur gases due to volcanism within the past 100 My on Venus is probably responsible for the planet's globally encircling H2SO4 cloud layers. Dramatic changes in volcanic output on Venus would have altered the atmospheric inventory of sulfur gases, and hence the structure of its clouds (Bullock and Grinspoon, Icarus, submitted 1999). Although Magellan radar images provide some constraints on the magnitude of volcanism in the geologically recent past, little is known of the sulfur content of Venus lavas. In order to assess the effects that Venus' volcanic history may have had on cloud and therefore climate change, it is desirable to place some constraints on the abundance of sulfur in Venus magmas. The sulfur content of terrestrial volcanic lavas varies widely, depending upon the local sedimentary environment and the source and history of upwelling magmas. We estimate the average abundance of sulfur in Venus lavas from an analysis of the production and loss of atmospheric SO2. The volumetric rate of resurfacing on Venus in the recent past is approximately 0.1 to 2 km3/yr (Bullock et al., JGR 20, 1993, Basilevsky and Head, GRL 23, 1996). Outgassed SO2 reacts quickly with crustal carbonate -- residence times in the atmosphere with respect to the reaction SO2 + CaCO3 <=> CaSO4 + CO are about 2-30 My (Fegley and Prinn, Nature 337, 1989, Bullock and Grinspoon, Icarus, submitted 1999). Assuming steady state conditions and an abundance of 25-180 ppm of atmospheric SO2 (Oyama et al., JGR 85, 1980, Bertaux et al., JGR 101, 1996), we will discuss constraints on the abundance of this important greenhouse and cloud-precursor gas in Venus lavas.

  17. 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

  18. Crystal Histories and Crustal Magmas: Insights into Magma Storage from U-Series Crystal Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.

    2014-12-01

    The dynamic processes operating within crustal magma reservoirs control many aspects of the chemical composition of erupted magmas, and crystals in volcanic rocks can provide a temporally-constrained archive of these changing environments. A new compilation of 238U-230Th ages of accessory phases and 238U-230Th-226Ra ages of bulk mineral separates of major phases documents that crystals in individual samples often have ages spanning most of the history of a volcanic center. Somewhat surprisingly, this observation holds for surface analyses as well as interior analyses, indicating that the latest stages of growth took place at different times for different grains. Nevertheless, average ages of surfaces are younger than interiors (as expected), and the dominant surface age population is often within error of eruption age. In contrast to accessory phase ages, less than half of the bulk separate 238U-230Th-226Ra ages for major phases are more than 10 kyr older than eruption. This suggests that major phases may in general reflect a later stage of development of an eruptible magma body than do accessory phases, or that the extent of discordance between ages of major and accessory phases reflects the extent to which a crystal mush was remobilized during processes leading to eruption. Crystal ages are most useful for illuminating magmatic processes when combined with crystal-scale trace-element or isotopic data, and I will present several case studies where such combined data sets exist. For example, at Yellowstone and at Okataina Caldera Complex, New Zealand, the combination zircon surface and interior analyses (of age, Hf isotopic, and trace-element data) with bulk dating and in-situ trace-element and isotopic compositions of feldspar allows a comparison of the early history of storage in a crystal mush with the later history of melt extraction and further crystallization prior to eruption, thus tracking development of erupted magma bodies from storage through eruption.

  19. Controls on banded pumice and enclave formation during magma mixing

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.; Manga, M.

    2011-12-01

    The deformation causing magma mixing can occur in a fluid-like manner to produce banded pumice or in a brittle manner to form enclaves. X-ray computed tomography (XRCT) and numerical modeling suggest that mixing style is controlled by whether the or not the host magma begins to convect before the intruding magma solidifies; the same two host and intruding magmas can thus form either enclaves or banded pumice depending on the size of the intruding magma body and the temperatures of the magmas. The critical control on mixing is competition between development of crystal networks in the intruding magma and melting and disruption of networks in the host. Consequently, the size of the intruding dike influences mixing style. XRCT analysis demonstrates that banded pumice from the 1915 Mt. Lassen eruption lack crystal networks and hence experienced mixing dominated by fluid flow. In contrast, rhyodacites with mafic enclaves from Chaos Crags contain well-developed networks of large crystals. Our model relies on three assumptions: 1) when magma crystallinity exceeds a critical value, ~13 vol.%, the magma develops a yield strength; 2) when crystallinity exceeds 40 vol.% (depending on mineral phase) the magma has a crystal network and is effectively solid; and 3) mixing is initiated by the injection of a hot dike into a cooler magma body with a yield strength. We model the mixing process as a 1-dimensional conductive cooling problem, use MELTS to calculate magma density, phase assemblages, and melt composition, and calculate melt viscosity using the method of Giordano et al. (2008), bulk viscosity using the Einstein-Roscoe equation, and yield strength using the method of Hoover et al. (2001). Importantly, because the two magmas are of different compositions, their crystallinities and viscosities do not have the same variations with temperature. Modeling begins with the instantaneous emplacement of a hot, mafic dike with crystallinity below 30 vol.% in a cooler, more silicic

  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. 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

  2. The Perils of Partition: Erroneous Results from Applying D Mineral/Magma to Rocks that Equilibrated Without Magma

    NASA Astrophysics Data System (ADS)

    Treiman, A. H.

    1995-09-01

    Compositions of extraterrestrial magmas are commonly derived from mineral compositions using, using experimentally determined mineral/basalt partition coefficients, Dmineral/basalt [1]. However, Dmineral/basalts cannot be applied to minerals which have experienced post-magmatic (subsolidus or metamorphic) chemical equilibration [2]. A failure to recognize post-magmatic equilibration can lead to wildly erroneous estimates of magma compositions and unrealistic scenarios of magmatic and planetary evolution [3]. To judge the effects of subsolidus chemical equilibration, consider REE distributions in a eucrite basalt, formed from a magma with CREE = 10 x CI. Let this magma crystallize and chemically equilibrate just below its solidus to a rock consisting of 49.5% plagioclase, 49.5% pigeonite, 0.1% whitlockite (a Ca phosphate), and 0.9% minor phases no REE content (silica, Fe metal, troilite); exact proportions are not critical. The total REE content ofthe rock is unchanged at 10 x CI, and distributions of REE among its minerals can be calculated from solidus-temperature Ds, e.g., Dpigeonite/plagioclase = Dpigeonite/basalt / Dplagioclase/basalt (where Dmineral/basalts are chosen to reflect the same magma compositions and temperature). REE abundances in minerals of this equilibrated rock (Figure 1 [5]) are significantly higher than they would be in the presence of magma. For instance, if this eucrite basalt system consisted of 50% magma, 25% pigeonite, and 25% plagioclase, one calculates C(La)Pigeonite = 0 04 x CI and C(La)Plagioclase = 0.8 x CI; with no magma present (Figure 1), C(La)Pigeonite = 0.4 x CI and CLaPIagioclase = 9 x CI! In the absence of magma, the incompatible REE must go somewhere!! If a mineral grain from this rock were used with Dmineral/basalts to derive a magma composition, that "Hparent basalt" would be rich in REE (130-200 x CI), enrichmed in light REE (La/Lu = 1.6 x CI), and strongly depleted in Eu. Compare this to the original eucrite, with REE at

  3. Solidifying the lunar magma ocean: Model results and geochronology (Invited)

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L. T.; Burgess, S. D.; Meyer, J.; Wisdom, J.

    2009-12-01

    The Moon is posited to have formed by reconsolidation of materials produced during a giant impact with the Earth early in solar system evolution. The young Moon appears to have experienced a magma ocean of some depth, which resulted in the formation of an anorthosite flotation crust. There is no simple way to reconcile W-Hf results for the age of Moon formation, U-Pb and Sm-Nd ages of lunar crustal crystallization, and modeling results for magma ocean solidification. At the beginning of magma ocean solidification the dense iron- and magnesium-rich phases crystallizing from the cooling magma are believed to have sunk to the bottom of the magma ocean. When approximately 80% of the lunar magma ocean solidified, anorthite began to crystallize and float upward through the more dense magma ocean liquid; anorthite will continue to be added to this flotation crust until the last dregs of the magma ocean solidify. The crystallization times of the anorthite in the flotation crust, therefore, could span the range from about 80% solidification to what has been interpreted as the lunar magma ocean solidification age. Models including convection in the remaining magma ocean, conduction through the growing anorthosite lid, and radiation into space indicate that the magma ocean may freeze to the point of anorthosite formation in less than 104 years, and perhaps as little as 103 years. After this brief free-surface cooling period the growth of the anorthosite lid radically slows heat loss, and complete solidification of the magma ocean will require additional tens of millions of years. Young anorthosite crustal ages, far younger than models would predict possible, may be explained by further investigations into the evolution of the lunar orbit. Tidal heating of the anorthosite crust as the young Moon experiences a period of high eccentricity may delay closure of minerals with radiogenic phases; these late-closing minerals will then yield young ages, though they originally formed

  4. A new view of the He-Ar-CO 2 degassing at mid-ocean ridges: Homogeneous composition of magmas from the upper mantle

    NASA Astrophysics Data System (ADS)

    Paonita, Antonio; Martelli, Mauro

    2007-04-01

    Deep-sea exploration is rapidly improving our understanding of volatiles geochemistry in mid-ocean-ridge igneous products. It is also placing greater constraints on degassing processes of the Earth's mantle, with the result that degassing models based on vapour-melt equilibrium are no longer able to explain the increasing number of data. In fact, such models force to postulate an upper mantle strongly heterogeneous at any scale, and cannot account for the widespread carbon supersaturation of the recovered igneous products. Here we review the global He-Ar-CO 2 dataset of fluid inclusions in mid-ocean-ridge glasses using the framework of advanced modelling of multicomponent bubble growth in magmas. We display that non-equilibrium fractionations among He, Ar and CO 2, driven by their different diffusivities in silicate melts, are common in most of the natural conditions of magma decompression and their signature strongly depends on pressure of degassing. Due to the comparable Ar and CO 2 diffusivity, magma degassing at low pressure fractionates both the He/Ar and He/CO 2 ratio by a similar extent, while the slower CO 2 diffusion at high pressure causes early kinetic effects on Ar/CO 2 ratio and dramatically changes the degassing path. On this ground, the very different geochemical signatures among suites of data coming from different ridge segments mainly depend on the depth of the magma chamber where the melt was stored. Besides, the variations inside a single suite highlight variable ascent speed and cooling rate of the emplaced lava. The large variations in both the He/CO 2 and Ar/CO 2 ratios at almost constant He/Ar, displayed in glasses coming from the Mid-Atlantic Ridge 24-30°N segment and the Rodriguez Triple Junction, are therefore interpreted as a high-pressure signature. In contrast, the simultaneous increase in both He/CO 2 and He/Ar of the East Pacific Rise, Pito Seamount and South-East Indian Ridge data sets suggests the dominance of low

  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. 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.

  7. 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

  8. 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

  9. Ultra-rapid formation of large volumes of evolved magma

    NASA Astrophysics Data System (ADS)

    Michaut, C.; Jaupart, C.

    2006-10-01

    We discuss evidence for, and evaluate the consequences of, the growth of magma reservoirs by small increments of thin (⋍ 1-2 m) sills. For such thin units, cooling proceeds faster than the nucleation and growth of crystals, which only allows a small amount of crystallization and leads to the formation of large quantities of glass. The heat balance equation for kinetic-controlled crystallization is solved numerically for a range of sill thicknesses, magma injection rates and crustal emplacement depths. Successive injections lead to the accumulation of poorly crystallized chilled magma with the properties of a solid. Temperatures increase gradually with each injection until they become large enough to allow a late phase of crystal nucleation and growth. Crystallization and latent heat release work in a positive feedback loop, leading to catastrophic heating of the magma pile, typically by 200 °C in a few decades. Large volumes of evolved melt are made available in a short time. The time for the catastrophic heating event varies as Q- 2 , where Q is the average magma injection rate, and takes values in a range of 10 5-10 6 yr for typical geological magma production rates. With this mechanism, storage of large quantities of magma beneath an active volcanic center may escape detection by seismic methods.

  10. 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.

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

    PubMed

    Browning, John; Drymoni, Kyriaki; Gudmundsson, Agust

    2015-10-28

    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.

  12. Numerical modeling of shallow magma intrusions with finite element method

    NASA Astrophysics Data System (ADS)

    Chen, Tielin; Cheng, Shaozhen; Fang, Qian; Zhou, Cheng

    2017-03-01

    A numerical approach for simulation of magma intrusion process, considering the couplings of the stress distribution, the viscous fluid flow of magma, and the fracturing of host rock, has been developed to investigate the mechanisms of fracture initiation and propagation in host rock during magma intrusion without pre-placing a set of fractures. The study focused on the dike intrusions filled with injected viscous magma in shallow sediments. A series of numerical modellings were carried out to simulate the process of magma intrusion in host rocks, with particular attention on the magma propagation processes and the formation of intrusion shapes. The model materials were Mohr-Coulomb materials with tension failure and shear failure. The scenarios of both stochastically heterogeneous host rocks and layered host rocks were analyzed. The injected magma formed intrusions shapes of (a) dyke, (b) sill, (c) cup-shaped intrusion, (d) saucer-shaped intrusion. The numerical results were in agreement with the experimental and field observed results, which confirmed the adequacy and the power of the numerical approach.

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

    PubMed Central

    Rehrauer, Hubert; Zoller, Stefan; Schlapbach, Ralph

    2007-01-01

    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

  14. 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.

  15. Insights Into Magma Mixing from Bimodal Volcanic Centers

    NASA Astrophysics Data System (ADS)

    Hudgins, T.

    2016-12-01

    Magma mixing has been described as ubiquitous by some, and unlikely by others. Intermediate magmas in arc environments are oft attributed to magma mixing, however critics of magma mixing point to bimodal volcanic centers as evidence that magma mixing is not a plausible mechanism to generate intermediate magmas, given the large volumes of mafic and felsic lavas and the absence of intermediate lavas. Here we present a model that investigates the physical plausibility of mixing mafic and felsic magmas at bimodal volcanic centers. To do this we utilize the chemical and thermodynamic output of MELTS (Ghiorso and Sack, 1995) to constrain the changes in chemistry, crystallinity, viscosity, and enthalpy for mafic and felsic lavas erupted from the Trans-Mexican Volcanic Belt. The Trans-Mexican Volcanic Belt is an ideal place for this investigation as it erupted abundant mafic and felsic lavas from 7.5 - 3.0 Ma and has been well studied, providing a wealth of well characterized samples to work with. Using the MELTS output of these data we can assess under what conditions the viscosities (η) of the mafic and felsic magmas satisfy the experimentally constrained Δlog η (log(ηmafic/ηfelsic)) < 0.5 threshold for mixing. Variations between magma chamber conditions such as pressure, temperature, and composition in the Trans-Mexican Volcanic Belt and volcanic centers where mixing is proposed and has been modeled (e.g. Mt. Hood, Oregon; Mutnovsky, Kamchatka) are used to provide insight into why intermediate lavas are not present in bimodal volcanic centers.

  16. The Role and Behavior of Exsolved Volatiles in Magma Reservoirs

    NASA Astrophysics Data System (ADS)

    Edmonds, M.; Woods, A.

    2016-12-01

    There is an abundance of evidence for complex, vertically protracted and frequently recharged magma reservoirs in a range of tectonic settings. Geophysical evidence suggests that vertically protracted mushy zones with liquid-rich regions may extend throughout much of the crust and even beyond the Moho. Geochemical evidence suggests that magma mixing, as well as extensive fractional crystallization, dominates the differentiation of crystal-rich magmas. These magmas may reside for long timescales close to their solidus temperatures in the crust before being recharged by mafic magmas, which supply heat and volatiles. The volatile budgets and gas emissions associated with eruptions from these long-lived reservoirs typically show that there is an abundance of magmatic vapor emitted, far above that expected from syn-eruptive degassing of the erupted, crystal-rich intermediate or evolved melts. Eruptions are often associated with muted ground deformation, far less than expected to account for the volumes erupted, suggesting a compressible magma. Breccia pipes in a number of mafic layered intrusion settings, thought to be the expression of diatreme-like volcanism, testify to the importance of gas overpressure in slowly crystallizing magmas. These observations are all consistent with the existence of a substantial fraction of exsolved magmatic vapor throughout much of the upper crustal zones of the magma reservoir, which holds much of the sulfur, as well as carbon dioxide, chlorine and metal species. Reconstruction of the distribution and form of this exsolved vapor phase is a challenge, as there is little geochemical record in the erupted rocks, beyond that which may be established from melt inclusion studies. The most promising approach to understand the distribution and role of exsolved vapor in magma reservoir dynamics is through analogue experiments, which have yielded valuable insights into the role of crystals in modulating gas storage and flow in the plutonic and

  17. 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

  18. 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.

  19. 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).

  20. Geochemistry of Isla Santa Cruz, Galapagos Archipelago, Ecuador

    NASA Astrophysics Data System (ADS)

    Wilson, E. L.; Schwartz, D. M.; Van Kirk, R.; Harpp, K.

    2012-12-01

    The geochemistry of Galapagos volcanoes extends to more depleted signatures than most hotspots, and do not appear to follow a classical tholeiitic to alkalic evolutionary sequence (i.e., Hawaiian Islands). Thus far, no such predictable sequence has been identified for Galapagos volcanoes. Isla Santa Cruz is one of the oldest volcanoes in the archipelago. Bow (1979) identified 3 volcanic stages: the Platform Series, the Shield Series, and the Shield-Modifying stage. The Platform Series defines a liquid line of descent that differs from the one shared by the Shield and Shield-Modifying units, which are genetically related to each other. Within the Shield and Shield-Modifying lavas, K2O/TiO2 ratios reveal three distinct compositional sub-groups: 1) a MORB-like, low-K suite (<0.10); 2) a tholeiitic suite (0.10-0.25); and 3) an alkaline suite (>0.25). These 3 sub-groups are geographically distributed across the island; the low-K suite is only in the north, whereas the alkaline suite constitutes the center highlands and the tholeiitic suite is on the eastern and northern flanks. Variations in La/Sm and Sm/Yb indicate that the magmas supplying the Shield and Shield-Modifying units were generated over a wide range of melting conditions: the alkaline suite melts were generated at the greatest depths and from the smallest melt fraction of the three suites, whereas the low-K suite originates from shallower, greater extents of melting; the tholeiitic lavas were generated at depths intermediate between the other 2 sub-groups. None of the lavas from Santa Cruz resemble material erupted at Fernandina volcano, the presumed center of the plume; radiogenic isotope ratios from previous research indicate that all Santa Cruz lavas are significantly more depleted than western Galapagos lavas. The ~1.2 Ma Platform Series is the most enriched of the Santa Cruz units. The Shield and Shield-Modifying lavas are all shifted towards more depleted signatures, approaching those of MORB, in terms

  1. 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.

  2. 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

  3. Mineral chemistry and geochemistry of ophiolitic ultramafics from central Eastern Desert, Egypt: A case for contaminated mantle-derived magma

    NASA Astrophysics Data System (ADS)

    Abdel-Karim, Abdel-Aal M.; Ali, Shehata; El-Safei, Shymaa A.

    2017-04-01

    The ophiolitic ultramafics are widely distributed in the Eastern Desert of Egypt. The present study is focused on two different localities of ophiolitic ultramafics in the central Eastern Desert (CED); Um Halham and Fawakhir. These ultramafic sections consist of serpentinites, serpentinized peridotites together with talc- and quartz-carbonates. Chromite is the most common original magmatic phase recorded in these rocks then olivine and pyroxene. The chemistry of the Al-chromite indicates a temperature of 500-550 oC consistent with lower amphibolite facies metamorphism. The high Cr# (> 60) of Al-chromites in the studied ultramafics resembles supra-subduction zone (SSZ) peridotites. Moreover, their higher Cr# suggests that they originated from the deeper portion of the mantle section with boninitic affinity. These mantle rocks equilibrated with boninitic melt have been generated by high melting degrees. The estimated melting degrees ( 19-24 %) of these mantle rocks lie within the range of SSZ peridotites. The Serpentinized peridotite and serpentinites have low Al2O3/SiO2 ratios (mostly < 0.03) similar to fore-arc mantle wedge serpentinites and further indicate that their mantle protolith had experienced partial melting before serpentinization process. The LREE-enriched patterns of the ophiolitic ultramafics arose from crustal contamination of their mantle source but not from melt/rock reaction. A higher mantle contamination by crustal materials and/or subduction-related slab fluids of the CED ophiolites relative to that of the SED ophiolites is also proved.

  4. Geochemistry of Cenezoic volcanic rocks, Baja California, Mexico: Implications for the petrogenesis of post-subduction magmas

    NASA Astrophysics Data System (ADS)

    Saunders, A. D.; Rogers, G.; Marriner, G. F.; Terrell, D. J.; Verma, S. P.

    1987-06-01

    Late Cenozoic volcanism in Baja California records the effects of cessation of subduction at a previously convergent, plate margin. Prior to 12.5 m.y., when subduction along the margin of Baja ceased, the predominant volcanic activity had a calc-alkaline signature, ranging in composition from basalt to rhyolite. Acidic pyroclastic activity was common, and possibly represented the westermost, distal edge of the Sierra Madre Occidental province. After 12.5 m.y., however, the style and composition of the magmatic products changed dramatically. The dominant rock type within the Jaraguay and San Borja volcanic fields is a magnesian andesite, with up to 8% MgO at 57% SiO 2, low Fe/Mg ratios, and high Na/K ratios. These rocks have unusual trace-element characteristics, with high abundances of Sr (up to 3000 ppm), low contents of Rb; K/Rb ratios are very high (usually over 1000, and up to 2500), and Rb/Sr ratios are low (less than 0.01). Furthermore, La n/Yb n ratios are high, consistent with derivation from a mantle source with fractionated REE patterns. 87Sr/ 86Sr ratios are less than 0.7048, and usually less than 0.7040, whereas the pre-12.5 m.y. lavas have 87Sr/ 86Sr ratios between 0.7038 and 0.7063. We have previously termed these rocks bajaites, in order to distinguish them from other magnesian andesites. Bajaites also occur in southernmost Chile and the Aleutian Islands, areas which also have histories of attempted or successful ridge subduction. It is proposed that the bajaite series is produced during the unusual physico-chemical conditions operating during the subduction of young oceanic lithosphere, or subduction of a spreading centre. During normal subduction, the oceanic crust dehydrates, releasing volatiles (water, Rb and other large-ion lithophile elements) into the overlying wedge. Subduction of younger crust will result in a progressive decrease, and eventual cessation of the transfer of volatiles when subduction stops. Thermal rebound of the mantle may cause the slab to melt, perhaps under eclogitestable conditions. The resulting melt will be heavy-REE-depleted, perhaps dacitic, but will otherwise inherit MORB-like Rb/Sr and K/Rb ratios. The ascending melt will react with the mantle to form the source of the bajaitic rocks. Furthermore, any amphibole in the mantle, stabilised during the higher PH 2O conditions of earlier subduction, will break down and contribute a high-K/Rb ratio component. The implications of this study are that firstly, the subducted slab does not contribute a highly fractionated REE component in most modern arcs (i.e. the slab does not melt); secondly, Rb has a very short residence time in the mantle, and its abundance in arc rocks is a direct reflection of the input from the dehydrating slab; and thirdly, bajaitelike rocks may provide recognition of attempted or successful ridge subduction in the geologic past.

  5. Primary magmas and mantle temperatures through time

    NASA Astrophysics Data System (ADS)

    Ganne, Jérôme; Feng, Xiaojun

    2017-03-01

    Chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2 = 0.5) or constant redox condition (Fe2+/∑Fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal "horizons" (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (ΔTp) observed between Tp maxima and minima did not change significantly with time (˜170°C). Conversely, a progressive but limited cooling of ˜150°C is proposed since ˜2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al. [2010] (˜150-250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.Plain Language SummaryThe Earth's upper mantle constitutes a major interface between inner and outer envelops of the planet. We explore at high resolution its thermal state evolution (potential temperature of the ambient mantle, Tp) in depth and time using a multi-dimensional database of mafic lavas chemistry (>22</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Litho.155..272C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Litho.155..272C"><span>Assembly of a zoned volcanic <span class="hlt">magma</span> chamber from multiple <span class="hlt">magma</span> batches: The Cerberean Cauldron, Marysville Igneous Complex, Australia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Clemens, J. D.; Birch, W. D.</p> <p>2012-12-01</p> <p>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 <span class="hlt">magma</span> began at > 450 MPa and at > 875 °C (possibly up to 940 °C), with an initial <span class="hlt">magma</span> H2O content of 4.1 to 5.3 wt.%. In the pre-eruption <span class="hlt">magma</span> chamber, the Rubicon Ignimbrite <span class="hlt">magma</span> 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 <span class="hlt">magma</span> delivered in batches to a high-level chamber. The Rubicon Ignimbrite <span class="hlt">magmas</span> 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 <span class="hlt">magma</span> interface. Such limited mixing between individual <span class="hlt">magma</span> batches appears typical of anatectic granitic <span class="hlt">magmas</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005E%26PSL.236..654B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005E%26PSL.236..654B"><span><span class="hlt">Magma</span> differentiation rates from ( 226Ra / 230Th) and the size and power output of <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blake, Stephen; Rogers, Nick</p> <p>2005-08-01</p> <p>We present a mathematical model for the evolution of the ( 226Ra / 230Th) activity ratio during simultaneous fractional crystallization and ageing of <span class="hlt">magma</span>. The model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization. These are tholeiitic basalt from Ardoukoba, Djibouti, MORB from the East Pacific Rise, alkali basalt to mugearite from Vestmannaeyjar, Iceland, and basaltic andesites from Miyakejima, Izu-Bonin arc. In all cases ( 226Ra / 230Th) correlates with indices of fractional crystallization, such as Th, and the data fall close to model curves of constant fractional crystallization rate. The best fit rates vary from 2 to 6 × 10 - 4 yr - 1 . Consequently, the time required to generate moderately evolved <span class="hlt">magmas</span> ( F ≤ 0.7) is of the order of 500 to 1500 yrs and closed <span class="hlt">magma</span> chambers will have lifetimes of 1700 to 5000 yrs. These rates and timescales are argued to depend principally on the specific power output (i.e., power output per unit volume) of the <span class="hlt">magma</span> chambers that are the sites of fractional crystallization. Equating the heat flux at the EPR to the heat flux from the sub-axial <span class="hlt">magma</span> chamber that evolves at a rate of ca. 3 × 10 - 4 yr - 1 implies that the <span class="hlt">magma</span> body is a sill of ca. 100 m thickness, a value which coincides with independent estimates from seismology. The similarity of the four inferred differentiation rates suggests that the specific power output of shallow <span class="hlt">magma</span> chambers in a range of tectonic settings covers a similarly narrow range of ca. 10 to 50 MW km - 3 . Their differentiation rates are some two orders of magnitude slower than that of the basaltic Makaopuhi lava lake, Hawaii, that cooled to the atmosphere. This is consistent with the two orders of magnitude difference in heat flux between Makaopuhi and the East Pacific Rise. ( 226Ra / 230Th) data for <span class="hlt">magma</span> suites related by fractional crystallization allow the <span class="hlt">magma</span> differentiation rate to be estimated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19641894','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19641894"><span>Contaminant <span class="hlt">geochemistry</span>--a new perspective.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Yaron, Bruno; Dror, Ishai; Berkowitz, Brian</p> <p>2010-01-01</p> <p>To date, the field of contaminant <span class="hlt">geochemistry</span>--which deals with the study of chemical interactions in soil and aquifer environments--has focused mainly on pollutant toxicity, retention, persistence, and transport and/or on remediation of contaminated sites. Alteration of subsurface physicochemical properties by anthropogenic chemicals, which reach the land surface as a result of human activity, has been essentially neglected. Contaminant-induced changes in subsurface properties are usually considered as deviations from a normal geological environment, which will disappear under natural attenuation or following remediation procedures. However, contaminants may in many cases cause irreversible changes in both structure and properties of the soil-subsurface geosystem between the land surface and groundwater. The time scales associated with these changes are on a "human time scale", far shorter than geological scales relevant for geochemical processes. In this review, we draw attention to a new perspective of contaminant <span class="hlt">geochemistry</span>, namely, irreversible changes in the subsurface as a result of anthropogenic chemical pollution. We begin by briefly reviewing processes governing contaminant-subsurface interactions. We then survey how chemical contamination causes irreversible changes in subsurface structure and properties. The magnitude of the anthropogenic impact on the soil and subsurface is linked directly to the amounts of chemical contaminants applied and/or disposed of on the land surface. This particular aspect is of major importance when examining the effects of humans on global environmental changes. Consideration of these phenomena opens new perspectives for the field of contaminant <span class="hlt">geochemistry</span> and for research of human impacts on the soil and subsurface regimes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1111985B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1111985B"><span>Halogen behaviours during andesitic <span class="hlt">magma</span> degassing: from <span class="hlt">magma</span> chamber to volcanic plume</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balcone-Boissard, H.; Villemant, B.; Boudon, G.; Michel, A.</p> <p>2009-04-01</p> <p>Halogen (F, Cl, Br and I) behaviours during degassing of H2O-rich silicic <span class="hlt">magmas</span> are investigated using volatile content analysis in glass (matrix glass and melt inclusions) of volcanic clasts (pumice and lava-dome fragments) in a series of plinian, vulcanian and lava dome-forming eruptions. Examples are taken from andesitic systems in subduction zones: Montagne Pelée and Soufrière Hills of Montserrat (Lesser Antilles) and Santa Maria-Santiaguito (Guatemala). Halogens behaviour during shallow degassing primarily depends on their incompatible character in melts and on H2O solubility. But variations in pre-eruptive conditions, degassing kinetics and syn-eruptive melt crystallisation, induce large variations in halogen extraction efficiency during H2O degassing, up to prevent halogen loss. In all studied systems, Cl, Br and I are not fractionated neither by differentiation nor by degassing processes: thus Cl/Br/I ratios remain well preserved in melts from reservoirs to eruption. These ratios measured in erupted clasts are characteristic of pre-eruptive <span class="hlt">magma</span> compositions and may be used to trace deep magmatic processes. Moreover, during plinian eruptions, Cl, Br and I are extracted by H2O degassing but less efficiently than predicted by available experimental fluid-melt partition coefficients, by a factor as high as 5. F behaves as an incompatible element and, contrary to other halogens, is never significantly extracted by degassing. Degassing during lava dome-forming eruptions of andesitic <span class="hlt">magmas</span> occurs mainly at equilibrium and is more efficient at extracting halogens and H2O than explosive degassing. The mobility of H2O and halogens depends on their speciation in both silicate melts and exsolved fluids which strongly varies with pressure. We suggest that the rapid pressure decrease during highly explosive eruptions prevents complete volatile speciation at equilibrium and consequently strongly limits halogen degassing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/859089','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/859089"><span><span class="hlt">Magma</span> Dynamics at Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>D. Krier</p> <p>2005-08-29</p> <p>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 <span class="hlt">magma</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5718994','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5718994"><span>Preliminary considerations for extraction of thermal energy from <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hickox, C.E.; Dunn, J.C.</p> <p>1985-01-01</p> <p>Simplified mathematical models are developed to describe the extraction of thermal energy from <span class="hlt">magma</span> based on the concept of a counterflow heat exchanger inserted into the <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> energy extraction. 15 refs., 3 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016LPICo1921.6148F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016LPICo1921.6148F"><span>Steam Atmosphere — <span class="hlt">Magma</span> Ocean Chemistry on the Early Earth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fegley, B.; Lodders, K.</p> <p>2016-08-01</p> <p>We use experimental data from the literature to calculate chemistry of the steam atmosphere — <span class="hlt">magma</span> ocean system on the early Earth. Our results show partitioning of rocky elements into the steam atmosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T11F..05D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T11F..05D"><span>The Role of <span class="hlt">Magma</span> Mixing in Creating Magmatic Diversity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Davidson, J. P.; Collins, S.; Morgan, D. J.</p> <p>2012-12-01</p> <p>Most <span class="hlt">magmas</span> 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 <span class="hlt">magma</span> mixing. Among these, <span class="hlt">magma</span> mixing is arguably inevitable in <span class="hlt">magma</span> systems that deliver <span class="hlt">magmas</span> from source-to-surface, since <span class="hlt">magmas</span> will tend to multiply re-occupy plumbing systems. A given mantle-derived <span class="hlt">magma</span> type will mix with any residual <span class="hlt">magmas</span> (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 <span class="hlt">magma</span> mixing can be read from the petrography (identification of crystals derived from different <span class="hlt">magmas</span>), 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 <span class="hlt">magma</span> contributions of distinct composition (recharge?). Indeed recharge and mixing/ contamination may well be related. As a result, the consequences of <span class="hlt">magma</span> mixing may well bear on eruption triggering. When two <span class="hlt">magmas</span> mix, volatile exsolution may be triggered by retrograde boiling, with crystallisation of anhydrous phase(s) in either of the <span class="hlt">magmas</span> (3) or volatiles may be generated by thermal breakdown of a hydrous phase in one of the <span class="hlt">magmas</span> (4). The generation of gas pressures in this way probably leads to geophysical signals too (small earthquakes). Recent work pulling</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoRL..43.1543S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoRL..43.1543S"><span>Time scales of crystal mixing in <span class="hlt">magma</span> mushes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schleicher, Jillian M.; Bergantz, George W.; Breidenthal, Robert E.; Burgisser, Alain</p> <p>2016-02-01</p> <p><span class="hlt">Magma</span> mixing is widely recognized as a means of producing compositional diversity and preconditioning <span class="hlt">magmas</span> for eruption. However, the processes and associated time scales that produce the commonly observed expressions of <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.V13G2697J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.V13G2697J"><span>The <span class="hlt">Magma</span> Transport System of the Mono Craters, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, M. R.; Putirka, K. D.</p> <p>2013-12-01</p> <p>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 <span class="hlt">magma</span> compositions than heretofore recognized, and thus reveals what is likely a more complex magmatic system, involving a greater number of batches of <span class="hlt">magma</span> and a more complex <span class="hlt">magma</span> storage/delivery system. Here, we present a model for the <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> mixing. Our high-density sampling also reveals interesting geographical patterns: for example, felsic <span class="hlt">magmas</span> erupt throughout the entire Mono Craters chain, erupting at a wide range of temperatures, ranging from 650-995°C, but</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/211326','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/211326"><span><span class="hlt">Geochemistry</span> of the Lathrop Wells volcanic center</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Perry, F.V.; Straub, K.T.</p> <p>1996-03-01</p> <p>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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> batches. This conclusion indicates that <span class="hlt">magmas</span> in the Yucca Mountain region ascend at preferred eruption sites rather than randomly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5640118','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5640118"><span><span class="hlt">Geochemistry</span> and zircon geochronology of Late Proterozoic leucogranites north of Boston, eastern Massachusetts</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Markus, R.; Hon, R. . Geology and Geophysics); Dunning, G. . Dept. of Earth Sciences)</p> <p>1993-03-01</p> <p>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 <span class="hlt">geochemistry</span> 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 <span class="hlt">magmas</span> 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 <span class="hlt">magma</span> mixing of varying proportions between the leucogranite and mafic melts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T33A3004L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T33A3004L"><span>Relationship between Tectonics and <span class="hlt">Geochemistry</span> at the Mid-Atlantic Ridge from Kane to Atlantis.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Langmuir, C. H.; Fuentes, J.; Escartin, J.; Hamelin, C.; Tucker, J.; Gale, A.</p> <p>2016-12-01</p> <p>Slow-spreading ridges consist of a variety of accretion modes. However, our understanding of the underlying processes leading to these variations is still limited. This study uses <span class="hlt">geochemistry</span> to understand the mantle and magmatic processes that lead to the varying modes of accretion at slows-spreading ridges. We aim to answer the question: Are different accretionary processes related to mantle source, <span class="hlt">magma</span> supply, or <span class="hlt">magma</span> emplacement processes? The 750 km long area of the Mid-Atlantic Ridge between the Kane and Atlantis Fracture Zones is ideal for this study because it is a very normal stretch of ridge far from hotspot influence with a relatively constant obliquity and spreading rate. This eliminates many variables such as large thermal and compositional anomalies. We have defined 13 individual ridge segments with a variety of tectonic characteristics. Some segments are classic slow-spreading ridge segments characterized by a deep rift valley, a clear neovolcanic zone, and accretion dominated by magmatism. Others are dominated by tectonic accretion with either large amounts of normal faults and no clear axial volcanic ridge or a large-scale detachment fault on one side of the ridge axis. Using samples collected from 180 stations during the recent MARPEX cruise in addition to published data, we have compiled a dataset consisting of over 700 samples from 270 stations with major, trace, isotope, and/or noble gas data. For this study, we have measured 375 samples for major elements, 290 samples for trace elements, 71 samples for Sr, Nd, Hf, and Pb isotopes, and 45 samples for He isotopes. All of the data with the exception of one sample is categorized as D-MORB (Gale et al. 2013) with (La/Sm)­n less than 0.8, indicating a homogenous mantle source relative to the rest of the Mid-Atlantic Ridge. Major and trace element data suggest tectonic segments undergo higher pressure fractionation relative to magmatic segments. This implies deeper melt emplacement beneath</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V23A3071L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V23A3071L"><span>Seismic Tremors and Three-Dimensional <span class="hlt">Magma</span> Wagging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liao, Y.; Bercovici, D.</p> <p>2015-12-01</p> <p>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 <span class="hlt">magma</span>-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 <span class="hlt">magma</span> column is surrounded by a compressible, bubble-rich foam annulus while rising inside the volcanic conduit, and that the lateral oscillation of the <span class="hlt">magma</span> inside the annulus causes observable tremor. Unlike the previous two-dimensional wagging model where the displacement of the <span class="hlt">magma</span> column is restricted to one vertical plane, the three-dimensional model we employ allows the <span class="hlt">magma</span> column to bend in different directions and has angular motion as well. Our preliminary results show that, without damping from viscous deformation of the <span class="hlt">magma</span> column, the system retains angular momentum and develops elliptical motion (i.e., the horizontal displacement traces an ellipse). In this ''inviscid'' limit, the <span class="hlt">magma</span> 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 <span class="hlt">magma</span> column leading to a coiled wagging motion. For the viscous-<span class="hlt">magma</span> model, we predict a similar damping rate for the uncoiled <span class="hlt">magma</span> column as in the two-dimensional model, and faster damping for the coiled <span class="hlt">magma</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/884943','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/884943"><span>CONDITIONS LEADING TO SUDDEN RELEASE OF <span class="hlt">MAGMA</span> PRESSURE</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>B. Damjanac; E.S. Gaffney</p> <p>2005-08-26</p> <p>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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span>, and a lava flow whose feed has partially solidified due to an interruption of <span class="hlt">magma</span> supply from below. For faulting, it is found that <span class="hlt">magma</span> would be able to follow the fault to a new surface eruption. A small increase in <span class="hlt">magma</span> pressure over that needed to maintain flow prior to faulting is required to open the new path, and the <span class="hlt">magma</span> pressure needed to maintain flow is lower but still greater than for the original dike. The <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> pressures of 10 MPa or less, resulting in radial dikes. However, this conclusion is based on the assumption that the fluid <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.7236P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.7236P"><span>A cellular automaton model for the rise of <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Piegari, Ester; di Maio, Rosa; Milano, Leopoldo; Scandone, Roberto</p> <p>2010-05-01</p> <p>Eruptions of volcanoes are complex natural events highly variable in size and time. Over the last couple of decades, statistical analyses of erupted volume and repose time catalogues have been performed for a large number of volcanoes. The aim of such analyses is either to predict future eruptive events or to define physical models for improving our understanding of the volcanic processes that cause eruptions. In particular, for this latter purpose we study a statistical model of eruption triggering caused by the fracturing of the crust above a <span class="hlt">magma</span> reservoir residing in the crust. When the fracturing reaches the reservoir, <span class="hlt">magma</span> is allowed to ascend because of its buoyancy. It will be found in batches along the transport region and it will ascend as long as fractures are developed to its tip; when a path is opened to the surface, an eruption occurs involving all batches connected to the opening. We model the vertical section of a volcanic edifice by means of a two-dimensional grid and characterize the state of each cell of the grid by assigning the values of two dynamical variables: a time dependent variable e describing the status of the local stress and a time-dependent variable n describing the presence of <span class="hlt">magma</span>. At first step of approximation, we treat the <span class="hlt">magma</span> presence field n as a diffusing lattice gas, and, therefore, we assume its value to be either zero or one if the corresponding cell is empty or filled by <span class="hlt">magma</span>, respectively. We study the probability distribution, P(V), of eruptions of volume V and the probability distribution, P(t), of inter-event time t and find that the model is able to reproduce, at least in a descriptive way, the essential statistical features of the activity of volcanoes. A key component of <span class="hlt">magma</span> is the quantity of dissolved gas as it gives <span class="hlt">magma</span> its explosive character, because the volume of gas expands as the pressure decreases on raising towards the surface. Then, to more accurately describe the rise of <span class="hlt">magma</span> in a volcanic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.V51B..07M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.V51B..07M"><span>The role of turbulence in explosive <span class="hlt">magma</span>-water mixing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mastin, L. G.; Walder, J. S.; Stern, L. A.</p> <p>2003-12-01</p> <p>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 <span class="hlt">magmas</span> 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 <span class="hlt">magma</span>-water mixing and the grain size and dispersal of hydromagmatic tephras are controlled largely by the turbulence of <span class="hlt">magma</span>-water mixing. At Surtsey, fine-grained, widely dispersed hydromagmatic tephras were produced primarily during continuous uprush events in which turbulent jets of <span class="hlt">magma</span> and gas passed through shallow water (Thorarinsson, 1967). During Kilauea's current eruption, videos show generation of fine-grained tephras when turbulent jets of <span class="hlt">magma</span>, 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 <span class="hlt">magma</span>-water mixing, though such processes are complicated by boiling (in water) and quench fracturing (in <span class="hlt">magma</span>). We are testing this hypothesis in experiments involving turbulent injection of water (a <span class="hlt">magma</span> analog) into liquid nitrogen (a water analog). We also suggest that turbulent mixing influences relative proportions of <span class="hlt">magma</span> and water in hydromagmatic eruptions. Empirical studies indicate that pressure-neutral turbulent</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013E%26PSL.383..182L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013E%26PSL.383..182L"><span>Crystallization and saturation front propagation in silicic <span class="hlt">magma</span> chambers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lake, Ethan T.</p> <p>2013-12-01</p> <p>The cooling and crystallization style of silicic <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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. <span class="hlt">Magma</span> chamber geometry also exerts a first-order control on propagation rates; bodies with high surface to <span class="hlt">magma</span> 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 <span class="hlt">magma</span>; 1 km thick sill geometry in a 20 °C/km geotherm), far faster than diffusion of volatiles in <span class="hlt">magma</span> and faster than bubbles can nucleate, grow, and ascend through the chamber. Numerical simulations indicate saturation front propagation is determined primarily by pressure and <span class="hlt">magma</span> crystallization rate; above certain initial water contents (4.4 wt.% in a dacite) the mobile <span class="hlt">magma</span> is volatile-rich enough above 10 km depth to always contains a saturation front. Saturation fronts propagate down from the <span class="hlt">magma</span> 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.%) <span class="hlt">magma</span> water contents. This upper interface promotes the production of a fluid pocket underneath the apex of the <span class="hlt">magma</span> chamber. If the fluid</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.6524H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.6524H"><span>Diatexite Deformation and <span class="hlt">Magma</span> Extraction on Kangaroo Island, South Australia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hasalova, Pavlina; Weinberg, Roberto; Ward, Lindsay; Fanning, Mark</p> <p>2013-04-01</p> <p>Migmatite terranes are structurally complex because of strong rheological contrast between layers with different melt contents and because of <span class="hlt">magma</span> migration leading to volume changes. Migmatite deformation is intimately linked with <span class="hlt">magma</span> extraction and the origin of granitoids. We investigate here the relationships between an evolving deformation and <span class="hlt">magma</span> 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, <span class="hlt">magma</span> 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 <span class="hlt">magma</span> extraction paths during folding. Extraction was associated with fold limb collapse, and antiformal hinge disruption by <span class="hlt">magma</span> 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, <span class="hlt">magma</span> accumulated preferentially along shear planes, indicating a dilatational component during shearing (transtension) and in strain shadows of schollen. As deformation waned, <span class="hlt">magma</span> 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 <span class="hlt">magma</span> flow. Structures developed during this phase are comparable with those formed during dewatering of soft sediments. Despite a high degree of complexity, <span class="hlt">magma</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.V12B..07G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.V12B..07G"><span>Tracking <span class="hlt">Magma</span> Degassing and Changes in <span class="hlt">Magma</span> Rheology Between Major Dome Collapse Events</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Genareau, K.; Cronin, S. J.; Lube, G.</p> <p>2012-12-01</p> <p>Merapi volcano, Java, Indonesia, produced two particularly large dome collapse events on 26 October and 5 November 2010, during its largest eruption since 1872. These were accompanied by explosive eruptions and highly destructive pyroclastic density currents that killed several hundred people in villages on the southern flanks. Previous work revealed that the tephras from the 26 October surges were dominated by free crystals liberated from a vesicular melt, while the 5 November tephras were dominated by juvenile lava fragments as the result of the development of permeable pathways for gas escape caused by vesicle coalescence and collapse. Scanning electron microscopic (SEM) examination of lava clasts from the 2010 surge-producing events at Merapi revealed differences in the groundmass crystallinities as a result of decompression-induced crystallization during <span class="hlt">magma</span> ascent over a time period of ten days. Lava clasts from the 5 November event contain microlite number densities over an order of magnitude higher than lava clasts from the 26 October collapse, 7.6 x 104 per mm2 versus 5.7 x 103 per mm2, respectively. The number density of plagioclase feldspar microlites is ten times higher in the 5 November event, while the number of pyroxene/Fe-oxide microlites is fifteen times higher compared to the 26 October event. Additionally, textures of the microlites provide information on <span class="hlt">magma</span> ascent rates during the two phases of <span class="hlt">magma</span> extrusion. 26 October lava clasts display euhedral and tabular plagioclase microlites with an average area of 133 μm2(n=100). 5 November lava clasts contain plagioclase microlites with lath-shaped and swallowtail morphologies and pyroxene/Fe-oxide microlites with anhedral, skeletal, and hopper morphologies, with most of the latter on the order of 1 μm in diameter. These variations in groundmass textures indicate that the lava extruded prior to the 5 November collapse event experienced a significant amount of decompression</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMOS43A1886A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMOS43A1886A"><span>A large <span class="hlt">magma</span> chamber and complex <span class="hlt">magma</span> delivery system revealed beneath Axial volcano</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arnulf, A. F.; Harding, A. J.; Kent, G.</p> <p>2013-12-01</p> <p>Axial volcano is located at 46N, 130W at the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg seamount chain. It is the most recent eruptive center of the Cobb hotspot, which last erupted in 2011. The volcano rises ~700 m above the adjacent ridge axis, has two major rift zones extending ~50 km to the north and south and its summit features a 8-km-long, U-shaped caldera with an opening to the southeast where there is an active hydrothermal field and young lava flows. Located at the junction of a mid-ocean ridge and a volcanic hotspot, Axial volcano is part of an atypical segment of the intermediate spreading Juan de Fuca Ridge and its internal structure remains poorly understood. In this study, we have applied an accurate solution for imaging an active volcano combining full waveform inversion (FWI) with reverse time migration (RTM) imaging. Our approach produces images of the magmatic system at Axial volcano with spatial resolutions on the order of ~50 meters, at least an order of magnitude better resolution than traditional tomographic images of active magmatic systems. We show the clearest example to date of an unambiguous basal reflector from a melt lens system beneath a spreading centre. We find that the <span class="hlt">magma</span> reservoir is up to 1 km thick, the thickest <span class="hlt">magma</span> reservoir observed beneath a spreading centre to date. Interestingly, the amplitude of the <span class="hlt">magma</span> reflector is stronger to the southeast of Axial volcano, between 0 and 6 km off axis, which might reflect an offset between the Cobb hotspot at depth and Axial volcano; if this is correct, the narrow ribbon of melt extending away from the caldera may actually funnel melt from a decoupled hotspot toward Axial caldera. In addition, we present a unique image of the magmatic plumbing system underlying an active volcano that appears to be composed of a network of sub-horizontal to shallow dipping features (planes of weakness), which might cyclically be reactivated to transport melt from the <span class="hlt">magma</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8990H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8990H"><span><span class="hlt">Magma</span> Rich Events at <span class="hlt">Magma</span>-Poor Rifted Margins: A South-East Indian Example</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harkin, Caroline; Kusznir, Nick; Tugend, Julie; Manatschal, Gianreto; Horn, Brian</p> <p>2016-04-01</p> <p>The south-east Indian continental rifted margin, as imaged by the INE1-1000 deep long-offset seismic reflection section by ION Geophysical, is a classic example of a <span class="hlt">magma</span>-poor rifted margin, showing highly thinned continental crust, or possibly exhumed mantle, within the ocean-continent transition (OCT). Outboard, the steady-state oceanic crust is between 4 and 5 km thickness, consistent with <span class="hlt">magma</span>-poor continental breakup and sea-floor spreading. It is therefore surprising that between the hyper-extended crust showing thin or absent continental crust (of approximately 75 km width) and the anomalously thin steady-state oceanic crust, there appears to be a region of thicker magmatic crust of approximately 11 km thickness and 100 km width. Magmatic events, at or just after continental breakup, have also been observed at other <span class="hlt">magma</span>-poor rifted margins (e.g. NE Brazil). This interpretation of <span class="hlt">magma</span>-poor OCT structure and thinner than global average oceanic crust separated by thicker magmatic crust on the SE Indian margin is supported by gravity inversion; which uses a 3D spectral technique and includes a lithosphere thermal gravity anomaly correction. Residual depth anomaly (RDA) analysis corrected for sediment loading using flexural backstripping, gives a small negative value (approximately -0.1 km) over the steady-state oceanic crust compared with a positive value (approximately +0.3 km) over the thicker magmatic crust. This RDA difference is consistent with the variation in crustal thickness seen by the seismic reflection interpretation and gravity inversion. We use joint inversion of the time domain seismic reflection and gravity data to investigate the average basement density and seismic velocity of the anomalously thick magmatic crust. An initial comparison of Moho depth from deep long-offset seismic reflection data and gravity inversion suggests that its basement density and seismic velocity are slightly less than that of the outboard steady-state oceanic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUSM.V31B..12F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUSM.V31B..12F"><span>Dyke Swarms in Southeastern British Columbia: Mineralogical and Geochemical Evidence for Emplacement of Multiple <span class="hlt">Magma</span> Types During Orogenic Collapse</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Freeman, M.; Owen, J. P.; Hoskin, P. W.</p> <p>2009-05-01</p> <p>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 <span class="hlt">geochemistry</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1370','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1370"><span>Low-(18)O Silicic <span class="hlt">Magmas</span>: Why Are They So Rare?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Balsley, S.D.; Gregory, R.T.</p> <p>1998-10-15</p> <p>LOW-180 silicic <span class="hlt">magmas</span> 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 <span class="hlt">magma</span> genesis for nearly all silicic <span class="hlt">magmas</span>. The rarity of 10W-l `O <span class="hlt">magmas</span> 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 <span class="hlt">magmas</span> 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 <span class="hlt">magmas</span> 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 <span class="hlt">magmas</span> at Yellowstone produced small- volume, 10W-180 <span class="hlt">magmas</span> directly, thereby circumventing the water saturation barrier encountered through normal AFC processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AREPS..31..399P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AREPS..31..399P"><span>Rheology of Granitic <span class="hlt">Magmas</span> During Ascent and Emplacement</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Petford, Nick</p> <p></p> <p>Considerable progress has been made over the past decade in understanding the static rheological properties of granitic <span class="hlt">magmas</span> in the continental crust. Changes in H2O content, CO2 content, and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid/fluid mixture. Although the strengths of granitic <span class="hlt">magmas</span> over the crystallization interval are still poorly constrained, theoretical investigations suggest that during <span class="hlt">magma</span> ascent, yield strengths of the order of 9 kPa are required to completely retard the upward flow in meter-wide conduits. In low Bagnold number <span class="hlt">magma</span> suspensions with moderate crystal contents (solidosities 0.1 0.3), viscous fluctuations may lead to flow differentiation by shear-enhanced diffusion. AMS and microstructural studies support the idea that granite plutons are intruded as crystal-poor liquids ( 50%), with fabric and foliation development restricted to the final stages of emplacement. If so, then these fabrics contain no information on the ascent (vertical transport) history of the <span class="hlt">magma</span>. Deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt, resulting in a range of local macroscopic flow structures, including layering, crystal alignment, and other mechanical instabilities such as shear zones. As the suspension viscosity varies with stress rate, it is not clear how the timing of proposed rheological transitions formulated from simple equations for static <span class="hlt">magma</span> suspensions applies to mixtures undergoing shear. New theories of <span class="hlt">magmas</span> as multiphase flows are required if the full complexity of granitic <span class="hlt">magma</span> rheology is to be resolved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20120003028','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20120003028"><span>Experimental Fractional Crystallization of the Lunar <span class="hlt">Magma</span> Ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rapp, J. F.; Draper, D. S.</p> <p>2012-01-01</p> <p>The current paradigm for lunar evolution is of crystallization of a global scale <span class="hlt">magma</span> 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 <span class="hlt">Magma</span> Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V33E3164C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V33E3164C"><span>Crystalline heterogeneities and instabilities in thermally convecting <span class="hlt">magma</span> chamber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Culha, C.; Suckale, J.; Qin, Z.</p> <p>2016-12-01</p> <p>A volcanic vent can supply different densities of crystals over an eruption time period. This has been seen in Hawai'i's Kilauea Iki 1959 eruption; however it is not common for all Kilauea or basaltic eruptions. We ask the question: Under what conditions can homogenous <span class="hlt">magma</span> chamber cultivate crystalline heterogeneities? In some laboratory experiments and numerical simulations, a horizontal variation is observed. The region where crystals reside is identified as a retention zone: convection velocity balances settling velocity. Simulations and experiments that observe retention zones assume crystals do not alter the convection in the fluid. However, a comparison of experiments and simulations of convecting <span class="hlt">magma</span> with crystals suggest that large crystal volume densities and crystal sizes alter fluid flow considerably. We introduce a computational method that fully resolves the crystalline phase. To simulate basaltic <span class="hlt">magma</span> chambers in thermal convection, we built a numerical solver of the Navier-Stoke's equation, continuity equation, and energy equation. The modeled <span class="hlt">magma</span> is assumed to be a viscous, incompressible fluid with a liquid and solid phase. Crystals are spherical, rigid bodies. We create Rayleigh-Taylor instability through a cool top layer and hot bottom layer and update <span class="hlt">magma</span> density while keeping crystal temperature and size constant. Our method provides a detailed picture of <span class="hlt">magma</span> chambers, which we compare to other models and experiments to identify when and how crystals alter <span class="hlt">magma</span> chamber convection. Alterations include stratification, differential settling and instabilities. These characteristics are dependent on viscosity, convection vigor, crystal volume density and crystal characteristics. We reveal that a volumetric crystal density variation may occur over an eruption time period, if right conditions are met to form stratifications and instabilities in <span class="hlt">magma</span> chambers. These conditions are realistic for Kilauea Iki's 1959 eruption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70011752','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70011752"><span>Solidification of basaltic <span class="hlt">magma</span> during flow in a dike.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Delaney, P.T.; Pollard, D.D.</p> <p>1982-01-01</p> <p>A model for time-dependent unsteady heat transfer from <span class="hlt">magma</span> flowing in a dyke is developed. The ratio of solidification T to <span class="hlt">magma</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017CoMP..172...80L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017CoMP..172...80L"><span>How do granitoid <span class="hlt">magmas</span> mix with each other? Insights from textures, trace element and Sr-Nd isotopic composition of apatite and titanite from the Matok pluton (South Africa)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Laurent, Oscar; Zeh, Armin; Gerdes, Axel; Villaros, Arnaud; Gros, Katarzyna; Słaby, Ewa</p> <p>2017-09-01</p> <p>In plutonic systems, <span class="hlt">magma</span> mixing is often modelled by mass balance based on whole-rock <span class="hlt">geochemistry</span>. However, <span class="hlt">magma</span> mixing is a chaotic process and chemical equilibration is controlled by non-linear diffusive-advective processes unresolved by the study of bulk samples. Here we present textural observations, LA-(MC-)ICP-MS trace element and Sr-Nd isotopic data of accessory apatites and titanites from a hybrid granodiorite of the Neoarchean Matok pluton (South Africa), collected in a zone of conspicuous mixing between mafic and felsic <span class="hlt">magmas</span>. Apatite grains mostly show a pronounced zoning in CL images, corresponding to abrupt changes in REE and HFSE concentrations recording their transfer through compositionally different melt domains during mixing. These grains crystallized early, at temperatures of 950-1000 °C. Titanite grains crystallized at temperatures of 820-900 °C (Zr-in-sphene thermometry). They show limited intra-grain chemical variations but huge inter-grain compositional scatter in REE and HFSE, pinpointing crystallization within a crystal mush, from isolated melt pockets having different composition from one another owing to incomplete chemical homogenization and variable Rayleigh fractionation. These chemical-textural characteristics, in combination with partitioning models and Polytopic Vector Analysis, point to "self-mixing" between co-genetic dioritic and granodioritic/granitic <span class="hlt">magmas</span>. Both resulted from differentiation of mantle-derived mafic melts, showing that mixing does not necessarily involve <span class="hlt">magmas</span> from contrasted (crust vs. mantle) sources. Systematic variations in ɛNd t (-4.5 to -2.5) and 87Sr/86Sr(i) (0.703-0.707) of titanite and apatite grains/domains crystallized from the two <span class="hlt">magmas</span> point to an isotopically inhomogeneous mantle source, which is not resolved by bulk-rock isotopic data. Interaction between the two <span class="hlt">magmas</span> must have occurred at relatively high temperatures (ca. 900°C) so that their viscosity contrast remained low</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010820','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010820"><span>Composition and origin of basaltic <span class="hlt">magma</span> of the Hawaiian Islands</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Powers, H.A.</p> <p>1955-01-01</p> <p>Silica-saturated basaltic <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span>. Silica-deficient basaltic <span class="hlt">magma</span>, 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> under a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. ?? 1955.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.9373C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.9373C"><span>Non-Newtonian flow of bubbly <span class="hlt">magma</span> in volcanic conduits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Colucci, Simone; Papale, Paolo; Montagna, Chiara Paola</p> <p>2017-04-01</p> <p>The dynamics of <span class="hlt">magma</span> ascent along volcanic conduits towards the Earth's surface affects eruptive styles and contributes to volcanic hazard. The rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent, even determining effusive vs explosive eruptive behaviour. In this work we explore the effects of bubble-induced non-Newtonian rheology on the dynamics of <span class="hlt">magma</span> flow in volcanic conduits. We develop a quasi-2D model of <span class="hlt">magma</span> ascent that incorporates a rheological constitutive equation describing the strain-dependent effect of gas bubbles on the viscosity of the multiphase <span class="hlt">magma</span>. Non-Newtonian <span class="hlt">magma</span> flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges. Our results show that non-Newtonian rheology leads to greater exit velocity, mass flow, and density. The pressure distribution along the conduit remains very similar to the Newtonian case, deviating only at the conduit exit. Plug-like velocity profiles develop approaching the conduit exit, when mixture velocity is high, and are favored by smaller liquid viscosity. Since the mass flow rate, the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics, neglecting the non-Newtonian effect of bubble-bearing <span class="hlt">magmas</span> may result in misinterpretation of the deposit and, consequently, eruptive behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRB..122.1789C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRB..122.1789C"><span>Non-Newtonian flow of bubbly <span class="hlt">magma</span> in volcanic conduits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Colucci, S.; Papale, P.; Montagna, C. P.</p> <p>2017-03-01</p> <p>The dynamics of <span class="hlt">magma</span> ascent along volcanic conduits toward the Earth's surface affects eruptive styles and contributes to volcanic hazard. The rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent, even determining effusive versus explosive eruptive behavior. In this work we explore the effects of bubble-induced non-Newtonian rheology on the dynamics of <span class="hlt">magma</span> flow in volcanic conduits. We develop a quasi 2-D model of <span class="hlt">magma</span> ascent that incorporates a rheological constitutive equation describing the strain-dependent effect of gas bubbles on the viscosity of the multiphase <span class="hlt">magma</span>. Non-Newtonian <span class="hlt">magma</span> flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges. Our results show that non-Newtonian rheology leads to greater exit velocity, mass flow, and density. The pressure distribution along the conduit remains very similar to the Newtonian case, deviating only at the conduit exit. Plug-like velocity profiles develop approaching the conduit exit, when mixture velocity is high, and are favored by smaller liquid viscosity. Since the mass flow rate, the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics, neglecting that the non-Newtonian effect of bubble-bearing <span class="hlt">magmas</span> may result in misinterpretation of the deposit and, consequently, eruptive behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=Evolution+theory+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DEvolution%2Btheory%2Bevidence','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=Evolution+theory+evidence&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DEvolution%2Btheory%2Bevidence"><span>Geophysical and geochemical evolution of the lunar <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Herbert, F.; Drake, M. J.; Sonett, C. P.</p> <p>1978-01-01</p> <p>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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> ocean epoch. In this view the cooling and solidification of the <span class="hlt">magma</span> 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 <span class="hlt">magma</span> by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The <span class="hlt">magma</span> 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 <span class="hlt">magma</span> ocean epoch.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016BVol...78...78V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016BVol...78...78V"><span>Tracking dynamics of <span class="hlt">magma</span> migration in open-conduit systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Valade, Sébastien; Lacanna, Giorgio; Coppola, Diego; Laiolo, Marco; Pistolesi, Marco; Donne, Dario Delle; Genco, Riccardo; Marchetti, Emanuele; Ulivieri, Giacomo; Allocca, Carmine; Cigolini, Corrado; Nishimura, Takeshi; Poggi, Pasquale; Ripepe, Maurizio</p> <p>2016-11-01</p> <p>Open-conduit volcanic systems are typically characterized by unsealed volcanic conduits feeding permanent or quasi-permanent volcanic activity. This persistent activity limits our ability to read changes in the monitored parameters, making the assessment of possible eruptive crises more difficult. We show how an integrated approach to monitoring can solve this problem, opening a new way to data interpretation. The increasing rate of explosive transients, tremor amplitude, thermal emissions of ejected tephra, and rise of the very-long-period (VLP) seismic source towards the surface are interpreted as indicating an upward migration of the <span class="hlt">magma</span> column in response to an increased <span class="hlt">magma</span> input rate. During the 2014 flank eruption of Stromboli, this <span class="hlt">magma</span> input preceded the effusive eruption by several months. When the new lateral effusive vent opened on the Sciara del Fuoco slope, the effusion was accompanied by a large ground deflation, a deepening of the VLP seismic source, and the cessation of summit explosive activity. Such observations suggest the drainage of a superficial <span class="hlt">magma</span> reservoir confined between the crater terrace and the effusive vent. We show how this model successfully reproduces the measured rate of effusion, the observed rate of ground deflation, and the deepening of the VLP seismic source. This study also demonstrates the ability of the geophysical network to detect superficial <span class="hlt">magma</span> recharge within an open-conduit system and to track <span class="hlt">magma</span> drainage during the effusive crisis, with a great impact on hazard assessment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.5543B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.5543B"><span>Crystallization and Cooling of a Deep Silicate <span class="hlt">Magma</span> Ocean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bower, Dan; Wolf, Aaron</p> <p>2016-04-01</p> <p>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 <span class="hlt">magma</span> ocean that subsequently cooled and crystallised. Understanding the cooling process is critical to determining <span class="hlt">magma</span> ocean lifetimes and recognising possible remnant signatures of the <span class="hlt">magma</span> ocean in present-day mantle heterogeneities. Modelling this evolution is challenging, however, due to the vastly different timescales and lengthscales associated with turbulent convection (<span class="hlt">magma</span> 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) <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985RpESc....Q.101K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985RpESc....Q.101K"><span>Thermohydrodynamic model: Hydrothermal system, shallowly seated <span class="hlt">magma</span> chamber</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kiryukhin, A. V.</p> <p>1985-02-01</p> <p>The results of numerical modeling of heat exchange in the Hawaiian geothermal reservoir demonstrate the possibility of appearance of a hydrothermal system over a <span class="hlt">magma</span> chamber. This matter was investigated in hydrothermal system. The equations for the conservation of mass and energy are discussed. Two possible variants of interaction between the <span class="hlt">magma</span> chamber and the hydrothermal system were computated stationary dry <span class="hlt">magma</span> chamber and dry <span class="hlt">magma</span> chamber changing volume in dependence on the discharge of <span class="hlt">magma</span> and taking into account heat exchange with the surrounding rocks. It is shown that the thermal supplying of the hydrothermal system can be ensured by the extraction of heat from a <span class="hlt">magma</span> chamber which lies at a depth of 3 km and is melted out due to receipt of 40 cubic km of basalt melt with a temperature of 1,300 C. The initial data correspond with computations made with the model to the temperature values in the geothermal reservoir and a natural heat transfer comparable with the actually observed values.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=ants&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dants','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790055105&hterms=ants&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Dants"><span>Geophysical and geochemical evolution of the lunar <span class="hlt">magma</span> ocean</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Herbert, F.; Drake, M. J.; Sonett, C. P.</p> <p>1978-01-01</p> <p>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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> ocean epoch. In this view the cooling and solidification of the <span class="hlt">magma</span> 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 <span class="hlt">magma</span> by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The <span class="hlt">magma</span> 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 <span class="hlt">magma</span> ocean epoch.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813444H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813444H"><span>Thermal and mechanical controls on <span class="hlt">magma</span> supply and volcanic deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hickey, James; Gottsmann, Jo; Nakamichi, Haruhisa; Iguchi, Masato</p> <p>2016-04-01</p> <p>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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> supply, 0.014 km3/yr, are thermomechanically controlled. <span class="hlt">Magma</span> storage conditions coincide with estimates for the caldera-forming reservoir ˜29,000 years ago, and the inferred <span class="hlt">magma</span> supply rate indicates a ˜130-year timeframe to amass enough <span class="hlt">magma</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PEPI..229...55X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PEPI..229...55X"><span>Constraints on volatile concentrations of pre-eruptive lunar <span class="hlt">magma</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Yingkui; Zhu, Dan; Wang, Shijie</p> <p>2014-04-01</p> <p>Until recently, the Moon had long been thought to be depleted of volatiles such as H2O, S, COx and Cl2. Researchers have recently measured volatile concentrations in the minerals, glasses and inclusions of lunar samples, and the results show that lunar rocks contain volatiles that are more similar to terrestrial materials than was previously thought. Mare basalts are located on the Earth-facing hemisphere in large impact basins, and they are not representative of the feldspathic highlands. Thus, it is likely that the density of lunar mafic <span class="hlt">magma</span> exceeds that of the highland rocks based on buoyancy alone. According to this observational fact, we calculate the density of mare basalt to give a constraint for the maximum amount of water mare basalt can contain because water can effectively decrease the density of mare <span class="hlt">magma</span>. Our result shows that water contained in the pre-eruptive <span class="hlt">magma</span> could not have been more than 1000 ppm; otherwise, the density of very-low-Ti basaltic <span class="hlt">magma</span> would be less than that of the highland rocks. Additionally, if <span class="hlt">magma</span> contains other species of volatiles such as C-O, S, F, or Cl2, the water in the pre-eruptive <span class="hlt">magma</span> would have to be much less than 1000 ppm because volatiles such as CO2 can effectively decrease the solubility of water in silicate melts. Based on these calculations on densities and a comparison with water in MORB, we conclude that the moon's water is not as great as has been recently suggested.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V33E3176A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V33E3176A"><span>Using Trace Element Mapping to Identify Discrete <span class="hlt">Magma</span> Mixing Events from the Astroni 6 Eruption</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Astbury, R. L.; Petrelli, M.; Arienzo, I.; D'Antonio, M.; Morgavi, D.; Perugini, D.</p> <p>2016-12-01</p> <p>The Astroni volcano, located within the perimeter of the Agnano-Monte Spina volcano-tectonic collapse zone, formed 4.23 cal. ka BP, during the third epoch of activity within the Campi Flegrei caldera (CFc; Southern Italy). The evolution of Astroni deserves further study for two main reasons: (1) Unlike other documented activity within the CFc, the preserved tuff ring of the volcano has been formed from seven eruptions, of varying magnitude, over a relatively short timescale; (2) it has been postulated that the style and magnitude of the eruption which formed the Astroni 6 tephra layer may represent the possible result of a medium-sized event within the CFc, should renewed activity ensue. Previous studies of Astroni have investigated crystals, as well as whole rocks, for Sr, Nd and B isotopic variations with results indicating that mixing/mingling processes occurred within the volcano's plumbing system. However, studies aimed at measuring the composition of discrete growth zones within individual crystals would give a more in-depth comprehension of the dynamic history of Astroni and possibly within the entire CFc. In this study, we focus on the Astroni 6c layer, located at the base of the Unit 6 sequence. Plagioclase, sanidine and diopside crystals, as well as groundmass glass and glassy melt inclusions, were first characterised for major and trace element <span class="hlt">geochemistry</span> through in-situ point analysis. In addition, high resolution trace element mapping was carried out in order to investigate crystal histories, with the aim of detecting discrete zoning events which may otherwise be missed with simple point analysis. Feldspars show a distinct variation in both major and trace elements between core and rim, with around 20% of measured crystals showing an anti-rapakivi texture; plagioclase cores surrounded by K-feldspar rims. In contrast, with respect to major element <span class="hlt">geochemistry</span>, diopside crystals are relatively homogeneous. However, initial multidimensional trace</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.V41F..02Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.V41F..02Z"><span>Why do <span class="hlt">magmas</span> stall? Insights from petrologic and geodetic data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zimmer, M. M.; Plank, T.; Freymueller, J.; Hauri, E. H.; Larsen, J. F.; Nye, C. J.</p> <p>2007-12-01</p> <p><span class="hlt">Magmas</span> stall at various depths in the crust due to their internal properties (<span class="hlt">magma</span> viscosity, buoyancy) and external crustal controls (local stress regime, wallrock strength). Annen et al. (JPet 2006) propose a petrological model in which buoyant <span class="hlt">magma</span> ascends through the crust until the depth of water saturation, after which it crystallizes catastrophically and stalls due to the large increase in <span class="hlt">magma</span> viscosity. <span class="hlt">Magmas</span> may erupt from this storage region, or viscous death may result in pluton formation. In order to test this model, and constrain <span class="hlt">magma</span> storage depths, we combine petrological and geodetic data for several active volcanoes along the Aleutian-Alaska arc. We analyzed glassy, primarily olivine-hosted melt inclusions by SIMS in tephra samples for their pre-eruptive volatile contents, which can be related to the depth of entrapment via pressure-dependent H2O-CO2 solubility models (e.g., VolatileCalc). Melt inclusions are not in equilibrium with pure water vapor (all will contain S and C species), but >50% of the inclusion population are in equilibrium with a vapor containing >85% H2O. Geodetic data (InSAR, GPS) record surface deformation related to volcano inflation/deflation, and can be inverted to solve for the depths of volume change (<span class="hlt">magma</span> storage) in the crust. In the Aleutians, we find that the maximum melt inclusion trapping depths and geodetic depths correlate, suggesting both techniques record crustal <span class="hlt">magma</span> storage and crystallization. Melt inclusions from the 1997 Okmok eruption are trapped at ≤3 km; deformation during the eruption and subsequent inflation occurred at 3±0.5 km (Miyagi et al., EPSL 2004; Lu & Masterlark, JGR 2005). At Akutan, melt inclusions and GPS data indicate <span class="hlt">magma</span> storage at ~5-7 km. Inclusions from flank cones of Makushin yield depths of 7 km, similar to inflation observed beneath the main edifice (6.8 km, Lu et al., JGR 2002). Pleistocene inclusions from Augustine volcano indicate <span class="hlt">magma</span> storage at 10-18 km, in accord</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013CoMP..165..259C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013CoMP..165..259C"><span>Petrology and <span class="hlt">geochemistry</span> of igneous inclusions in recent Merapi deposits: a window into the sub-volcanic plumbing system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chadwick, J. P.; Troll, V. R.; Waight, T. E.; van der Zwan, F. M.; Schwarzkopf, L. M.</p> <p>2013-02-01</p> <p>Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography, <span class="hlt">geochemistry</span> and geobarometric calculations. The inclusions may be classified into four main suites: (1) highly crystalline basaltic-andesite inclusions, (2) co-magmatic enclaves, (3) plutonic crystalline inclusions and (4) amphibole megacrysts. Highly crystalline basaltic-andesite inclusions and co-magmatic enclaves typically display liquid-liquid relationships with their host rocks, indicating mixing and mingling of distinct <span class="hlt">magmas</span>. Co-magmatic enclaves are basaltic in composition and occasionally display chilled margins, whereas highly crystalline basaltic-andesite inclusions usually lack chilling. Plutonic inclusions have variable grain sizes and occasionally possess crystal layering with a spectrum of compositions spanning from gabbro to diorite. Plagioclase, pyroxene and amphibole are the dominant phases present in both the inclusions and the host lavas. Mineral compositions of the inclusions largely overlap with compositions of minerals in recent and historic basaltic-andesites and the enclaves they contain, indicating a cognate or `antelithic' nature for most of the plutonic inclusions. Many of the plutonic inclusions plot together with the host basaltic-andesites along fractional crystallisation trends from parental basalt to andesite compositions. Results for mineral geobarometry on the inclusions suggest a crystallisation history for the plutonic inclusions and the recent and historic Merapi <span class="hlt">magmas</span> that spans the full depth of the crust, indicating a multi-chamber <span class="hlt">magma</span> system with high amounts of semi-molten crystalline mush. There, crystallisation, crystal accumulation, <span class="hlt">magma</span> mixing and mafic recharge take place. Comparison of the barometric results with whole</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.158...79M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.158...79M"><span>Anhydrite solubility in differentiated arc <span class="hlt">magmas</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masotta, M.; Keppler, H.</p> <p>2015-06-01</p> <p>The solubility of anhydrite in differentiated arc <span class="hlt">magmas</span> was experimentally studied at 200 MPa and 800-1000 °C over a range of oxygen fugacities, from 0.5 log units above the Ni-NiO buffer to the hematite-magnetite buffer. Anhydrite is stable only at oxidizing conditions (fO2 ⩾ Re-ReO2), whereas sulfides only form under reducing conditions. The solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption. At oxidizing conditions, the solubility product of anhydrite increases with temperature, nbo/t and melt water content. We provide a new calibration of the anhydrite solubility product (KSP = XCaO * XSO3), which reproduces all available experimental data with greatly improved accuracy: In this equation, the molar fractions XCaO and XSO3 in the melt as well as the number of non-bridging oxygen atoms per tetrahedron (nbo/t) are calculated on an anhydrous basis (H2O refers to the melt water content, T is temperature in Kelvin). We apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 Mt. Pinatubo dacite eruption was unusually large, because only a small fraction of the sulfur was locked up in anhydrite. In general, high sulfur yields are expected when anhydrite solubility in the melt is high, i.e. for somewhat depolymerized melts. For rhyolitic systems, most of the available sulfur will be locked up in anhydrite, so that even very large eruptions may only have a small effect on global surface temperatures. Our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1818532H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1818532H"><span>The rheology of crystal-rich <span class="hlt">magmas</span> (Kuno Award Lecture)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim</p> <p>2016-04-01</p> <p>The rheology of <span class="hlt">magmas</span> controls not only eruption dynamics but also the rate of transport of <span class="hlt">magmas</span> through the crust and to a large extent the rate of <span class="hlt">magma</span> differentiation and degassing. <span class="hlt">Magma</span> 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 <span class="hlt">magmas</span>. 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 <span class="hlt">magmas</span> 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 <span class="hlt">magmas</span>. 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IJEaS.104.1795L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IJEaS.104.1795L"><span><span class="hlt">Geochemistry</span> and eruptive behaviour of the Finca la Nava maar volcano (Campo de Calatrava, south-central Spain)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lierenfeld, Matthias Bernhard; Mattsson, Hannes B.</p> <p>2015-10-01</p> <p>Here we present a detailed investigation into the <span class="hlt">geochemistry</span> and the excavational/depositional processes involved in the maar-diatreme forming Finca la Nava (FlN) eruption in south-central Spain. Bulk rock compositions of hand-picked juvenile fragments indicate derivation of the FIN <span class="hlt">magma</span> from a garnet-bearing mantle source, which has subsequently been overprinted in bulk rock samples by incorporation of a combination of spinel-bearing peridotites and upper-crustal lithics (i.e. quartzites and slates). The dominating phenocryst assemblage with clinopyroxene, olivine, amphibole and phlogopite points to the classification of the juvenile <span class="hlt">magma</span> as being olivine melilititic in composition. Ascent through the lithosphere was rapid as indicated by the calculations of settling rates of mantle peridotites (~0.8 m s-1). The original <span class="hlt">magma</span> fragmentation level in the conduit was probably relatively shallow carrying mainly juvenile pyroclasts (~60 %) intermixed with accidental crustal lithics (~35 %) and mantle xenoliths (<5 %) to the surface. The shapes of individual pyroclasts are sub-rounded to rounded and with highly variable vesicularities (5-45 %). This fact, in combination with abundant fine-grained material in the beginning of the eruption, indicates that both magmatic and phreatomagmatic fragmentation processes may have played important roles in forming the FIN maar. A relatively constant increase in quartzitic fragments from ~35 to <60 % with increasing stratigraphic height in the FIN deposits further indicates that the crater area successively widened during the eruption, which resulted in an increased recycling of quartzitic fragments. This eruption scenario, with the formation of a diatreme at depth, is also consistent with the absence of layers dipping inwards into the crater area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3409746','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3409746"><span>Redox systematics of a <span class="hlt">magma</span> ocean with variable pressure-temperature gradients and composition</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Righter, K.; Ghiorso, M. S.</p> <p>2012-01-01</p> <p>Oxygen fugacity in metal-bearing systems controls some fundamental aspects of the <span class="hlt">geochemistry</span> 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 <span class="hlt">magma</span> 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 <span class="hlt">magma</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22778438','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22778438"><span>Redox systematics of a <span class="hlt">magma</span> ocean with variable pressure-temperature gradients and composition.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi