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Sample records for flood basalt volcanism

  1. The biological consequences of flood basalt volcanism

    NASA Astrophysics Data System (ADS)

    Clapham, M.

    2012-12-01

    Flood basalt eruptions are among the largest environmental perturbations of the Phanerozoic. The rapid release of CO2 from a large igneous province would have triggered a chain of events that can include climate warming, ocean acidification, reduced seawater carbonate saturation, and expanded oceanic anoxia. Those stressors have widely negative impacts on marine organisms, especially on calcified taxa, by affecting their respiratory physiology and reducing energy available for growth and reproduction. Many Phanerozoic extinctions, most notably the end-Permian and end-Triassic mass extinctions, coincided with flood basalt eruptions and shared distinctive patterns of taxonomic and ecological selectivity. In these extinctions, highly active organisms were more likely to survive because they possess physiological adaptations for maintaining internal pH during activity, which also proves useful when buffering pH against ocean acidification. In contrast, species that did not move and had low metabolic rates, such as brachiopods and sponges, suffered considerable losses during these extinctions. Heavily-calcified organisms, especially corals, were particularly vulnerable; as a result, ocean acidification and saturation state changes from flood basalt eruptions often triggered crises in reef ecosystems. This characteristic pattern of selectivity during "physiological" extinctions that closely coincided with flood basalts provides a template for assessing the causes of other extinction events. Because these crises also provide deep time analogues for the ongoing anthropogenic crisis of warming, ocean acidification, and expanded anoxia, the selectivity patterns can also help constrain "winners" and "losers" over upcoming decades.

  2. Flood basalt volcanism during the past 250 million years

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Stothers, Richard B.

    1988-01-01

    A chronology of the initiation dates of major continental flood basalt volcanism is established from published potassium-argon (K-Ar) and argon-argon (Ar-Ar) ages of basaltic rocks and related basic intrusions. The dating is therefore independent of the biostratigraphic and paleomagnetic time scales. Estimated errors of the initiation dates of the volcanic episodes determined from the distributions of the radiometric ages are, approximately, + or - 4 percent. There were 11 distinct episodes during the past 250 million years. Sometimes appearing in pairs, the episodes have occurred quasi-periodically with a mean cycle time of 32 + or - 1 (estimated error of the mean) million years. The initiation dates of the episodes are close to the estimated dates of mass extinctions of marine organisms. Showers of impacting comets may be the cause.

  3. Continental Flood Basalts

    NASA Astrophysics Data System (ADS)

    Continental flood basalts have been receiving considerable scientific attention lately. Recent publications have focused on several particular flood-basalt provinces (Brito-Arctic, Karoo, Parana', Deccan, and Columbia Plateau), and much attention has been given to the proposed connection between flood-basalt volcanism, bolide impacts, and mass extinctions. The editor of Continental Flood Basalts, J. D. Macdougall, conceived the book to assemble in a single volume, from a vast and scattered literature, an overview of each major post-Cambrian flood-basalt province.Continental Flood Basalts has 10 chapters; nine treat individual flood-basalt provinces, and a summary chapter compares and contrasts continental flood-basalts and mid-oceanic ridge basalts. Specifically, the chapters address the Columbia River basalt, the northwest United States including the Columbia River basalt, the Ethiopian Province, the North Atlantic Tertiary Province, the Deccan Traps, the Parana' Basin, the Karoo Province, the Siberian Platform, and Cenozoic basaltic rocks in eastern China. Each chapter is written by one or more individuals with an extensive background in the province.

  4. A minimum U-Pb age for Siberian flood-basalt volcanism

    USGS Publications Warehouse

    Kamo, S.L.; Czamanske, G.K.; Krogh, T.E.

    1996-01-01

    Establishing an accurate and precise age for Siberian flood-basalt volcanism is of great importance in evaluating causes for the unequaled mass extinction of flora and fauna at the Permian-Triassic boundary. We report a new, minimum U-Pb age obtained from zircon and baddeleyite from the mineralized Noril'sk I intrusion that cuts the lower third of this rapidly deposited, 3500-m-thick volcanic sequence near Noril'sk. This 251.2 ?? 0.3 (2??) Ma age is within analytical error of the SHRIMP U-Pb age for zircon from the Permian-Triassic boundary at Meishan, South China [251.1 ?? 3.6 Ma (2??)], and confirms Siberian basaltic volcanism as a possible contributor to the mass extinction.

  5. Earliest Silicic Volcanism Associated with Mid-Miocene Flood Basalts: Tuffs Interbedded with Steens Basalt, Nevada and Oregon

    NASA Astrophysics Data System (ADS)

    Luckett, M.; Mahood, G. A.; Benson, T. R.

    2013-12-01

    During the main phase of Steens and Columbia River flood basalt eruptions between ~16.7 and 15.0 Ma, spatially associated silicic volcanism was widespread, ~4,000 km3 of silicic magma erupting at calderas and smaller centers dispersed across ~25,000 km2 in eastern Oregon and northern Nevada (Coble and Mahood, 2012). The oldest flood basalts erupted from a focus at Steens Mountain in eastern Oregon, where the section of lavas is ~1 km thick. The Steens Basalt thins southward to only a few flows thick in northern Nevada, either because fewer flows were emplaced this far from the focus or because fewer dikes propagated to the surface on encountering thicker continental crust and/or were intercepted by growing bodies of silicic magma that ultimately erupted in McDermitt Caldera Field (Rytuba and McKee, 1984), High Rock Caldera Complex, and the Lone Mountain/Hawks Valley center (Wypych et al., 2011). Rhyolitic tuffs have not been recognized interbedded with the basalt lavas in the type section, but we have identified several silicic tuffs interbedded with Steens Basalt in the southern Pueblo Mountains and in the Trout Creek Mountains. Although noted by previous workers (e.g., Avent, 1965; Minor, 1986; Hart et al., 1989), they have not been studied. We identified six tuffaceous intervals 20 cm to 15 m thick in the escarpment of the southern Pueblo Mountains near the Oregon-Nevada border where the Steens basalt section is ~250 m thick, with the base unexposed. Two intervals are lithic-rich, reworked volcaniclastic sediments, but four are primary or only slightly reworked sequences of fall deposits that range from fine ash to lapilli in grain size. The heat and weight of the overlying basaltic lava flows has fused the tuffs so that the upper parts of thicker tuffaceous intervals and entire thinner ones are converted to vitrophyres, with crystals of alkali feldspar × quartz × biotite typically 1-2 mm in diameter set in a dense, black, variably hydrated, glassy matrix. We

  6. Constructing the volcanic architecture of Kalkarindji, an ancient flood basalt province, using a multidisciplinary approach

    NASA Astrophysics Data System (ADS)

    Marshall, P.; Widdowson, M.; Kelley, S. P.; Mac Niocaill, C.; Murphy, D. T.

    2014-12-01

    The Kalkarindji Continental Flood Basalt Province (CFBP) is the oldest igneous province in the Phanerozoic. Erupted in the mid-Cambrian (505-510 Ma) [1], it is estimated volumes of lava up to 1.5 x 105 km3could have been erupted, making this similar in size to the better known Columbia River Basalts, USA. Relatively little is known about the province, due in part to its remote location, though large swathes remain well preserved (c. 50,000 km2). This study, based on rigorous field investigations, utilises 4 different analytical techniques to construct a volcanic architecture for the Kalkarindji basalts, drawing together these complimentary datasets to generate a series of detailed stratigraphies from around the province. Mineralogy and petrography form the basis while geochemical data aides in defining lava flow stratigraphies and distinguishing individual flow packages in disparate locations around the province. 40Ar/39Ar dating of key stratigraphic marker horizons support stratigraphical correlation across the province whilst the use of palaeomagnetism and magnetostratigraphy has allowed for correlation on a broader scale. Indications from this study point towards an unusual eruption among CFBPs in the Phanerozoic; a lack of tumescence, immediate subsidence of the lava pile following cessation of eruption; and, in the main sub-province, we map a simple volcanic structure thinning to the east from a single source. 1. L. M. Glass, D. Phillips, (2006). Geology. 34, 461-464.

  7. Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism

    NASA Astrophysics Data System (ADS)

    van de Schootbrugge, B.; Quan, T. M.; Lindström, S.; Püttmann, W.; Heunisch, C.; Pross, J.; Fiebig, J.; Petschick, R.; Röhling, H.-G.; Richoz, S.; Rosenthal, Y.; Falkowski, P. G.

    2009-08-01

    One of the five largest mass extinctions of the past 600million years occurred at the boundary of the Triassic and Jurassic periods, 201.6million years ago. The loss of marine biodiversity at the time has been linked to extreme greenhouse warming, triggered by the release of carbon dioxide from flood basalt volcanism in the central Atlantic Ocean. In contrast, the biotic turnover in terrestrial ecosystems is not well understood, and cannot be readily reconciled with the effects of massive volcanism. Here we present pollen, spore and geochemical analyses across the Triassic/Jurassic boundary from three drill cores from Germany and Sweden. We show that gymnosperm forests in northwest Europe were transiently replaced by fern and fern-associated vegetation, a pioneer assemblage commonly found in disturbed ecosystems. The Triassic/Jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons, which, in the absence of charcoal peaks, we interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava. We conclude that the terrestrial vegetation shift is so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone. Instead, we suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction.

  8. The Volcaniclastic Opening Phase of Karoo Flood Basalt Volcanism: Drakensberg Formation, South Africa

    NASA Astrophysics Data System (ADS)

    McClintock, M. K.; Houghton, B. F.; Skilling, I. P.; White, J. D.

    2002-12-01

    New field mapping of a 10 km by 10 km, 150+ m thick volcaniclastic succession in the Sterkspruit Valley, Eastern Cape, South Africa reveals products of a variety of fragmentation, transportation and depositional processes. The succession is the product of (1) quench fragmentation of lava, (2) injection of fluid basalt into unconsolidated volcaniclastic and country rock, (3) phreatomagmatic explosive eruptions, (4) passive effusion of large volumes of lava and (5) reworking and mass transport of the products of (1)-(4). Deposits are divided into (a) structureless to extremely thick-bedded tuff breccia and lapilli tuff, often fining upward into thin bedded tuff and capped by pillow lava, and (b) thinner-bedded lapilli tuff and tuff with minor breccia, capped by subaerial lava. The lapilli-tuff succession rests on a peneplain developed in contemporaneous quartzo-felspathic aeolian-fluvial sediments whereas the structureless to extremely thick-bedded units fill a broad crater-like depression. Minor units in the succession, which provide precise paleo-environmental information, include pillow lava, laminated aeolian and fluvial sandstone, and accretionary-lapilli-fall beds. The Sterkspruit complex contributes to a growing body of evidence that the onset of flood volcanism is often a complex process, with local hydrology and topography playing a significant role in the style of eruption and geometry of resulting deposits. Diversity in these deposits reflects overprinting of these localized controls by the effect of large volumes of magma in the shallow subsurface feeding surface eruptions over a broad area. Under some conditions these early stages of LIP volcanism can generate large, and hitherto under-recognized, volumes of pyroclastic, hyaloclastic, peperitic and reworked deposits, which are typically characterized by mingling and mixing of juvenile basalt with pre-existing and syneruptive sediment.

  9. East Greenland flood basalt volcanism: duration, volatile flux and correlation to the Paleocene-Eocene thermal maximum

    NASA Astrophysics Data System (ADS)

    Tegner, C.; Heilmann-Clausen, C.; Larsen, R. B.; Kent, A. J. R.

    2012-04-01

    Massive flood basalt volcanism in the NE Atlantic 56 million years ago can be related to the initial manifestation of the Iceland plume and ensuing continental rifting, and has been correlated with a short (c. 200,000 years) global warming period, the Paleocene-Eocene thermal maximum (PETM). A hypothesis is that magmatic sills emplaced into organic-rich sediments on the Norwegian margin triggered rapid release of greenhouse gases. However, the largest exposed volcanic succession in the region, the E Greenland flood basalts provide additional details. The alkaline Ash-17 provides regional correlation of continental volcanism and pertubation of the oceanic environment. In E Greenland Ash-17 is interbedded with the uppermost part of the flood basalt succession. In the marine sections of Denmark, Ash-17 postdates PETM, most likely by 3-400,000 years. While radiometric ages bracket the duration of the main flood basalt event to less than a million years, the subsidence history of the Skaergaard intrusion due to flood basalt emplacement indicates it took less than 300,000 years. It is therefore possible that the main flood basalts in E Greenland postdates PETM. This is supported by a scarcity of ash layers within the PETM interval. Continental flood basalt provinces represent some of the highest sustained volcanic outputs preserved within the geologic record. Recent studies have focused on estimating the atmospheric loading of volatile elements and have led to the suggestion that they may be associated with significant global climate changes and mass extinctions. Estimates suggest that c. 400,000 km3 of basaltic lava erupted in E Greenland and the Faeroe islands. Based on measurements of melt inclusions and solubility models, approximately 3000 Gt of SO2 and 220 Gt of HCl were released by these basalts. Calculated yearly fluxes approach 10 Mt/y SO2 and 0.7 Mt/y HCl. Refinements of these estimates, based largely on further melt inclusion measurements, are proceeding. Our

  10. Geology of the Mid-Miocene Rooster Comb Caldera and Lake Owyhee Volcanic Field, eastern Oregon: Silicic volcanism associated with Grande Ronde flood basalt

    NASA Astrophysics Data System (ADS)

    Benson, Thomas R.; Mahood, Gail A.

    2016-01-01

    The Lake Owyhee Volcanic Field (LOVF) of eastern Oregon consists of rhyolitic caldera centers and lava fields contemporaneous with and spatially related to Mid-Miocene Columbia River flood basalt volcanism. Previous studies delineated two calderas in the southeastern part of LOVF near Owyhee Reservoir, the result of eruptions of two ignimbrites, the Tuff of Leslie Gulch and the Tuff of Spring Creek. Our new interpretation is that these two map units are differentially altered parts of a single ignimbrite produced in a major phreatomagmatic eruption at ~ 15.8 Ma. Areas previously mapped as Tuff of Spring Creek are locations where the ignimbrite contains abundant clinoptilolite ± mordenite, which made it susceptible to erosion. The resistant intracaldera Tuff of Leslie Gulch has an alteration assemblage of albite ± quartz, indicative of low-temperature hydrothermal alteration. Our new mapping of caldera lake sediments and pre- and post-caldera rhyolitic lavas and intrusions that are chemically similar to intracaldera Tuff of Leslie Gulch point to a single ~ 20 × 25 km caldera, which we name the Rooster Comb Caldera. Erosion of the resurgently uplifted southern half of the caldera created dramatic exposures of intracaldera Tuff of Leslie Gulch cut by post-caldera rhyolite dikes and intrusions that are the deeper-level equivalents of lava domes and flows that erupted into the caldera lake preserved in exposures to the northeast. The Rooster Comb Caldera has features in common with more southerly Mid-Miocene calderas of the McDermitt Volcanic Field and High Rock Caldera Complex, including formation in a basinal setting shortly after flood basalt eruptions ceased in the region, and forming on eruption of peralkaline ignimbrite. The volcanism at Rooster Comb Caldera postdates the main activity at McDermitt and High Rock, but, like it, begins ~ 300 ky after flood basalt volcanism begins in the area, and while flood basalts don't erupt through the silicic focus, are

  11. Diamondiferous kimberlites in Central India synchronous with Deccan flood basalt volcanism

    NASA Astrophysics Data System (ADS)

    Lehmann, B.; Burgess, R.; Frei, D.; Belyatsky, B. V.; Mainkar, D.; Chalapathi Rao, N. V.

    2009-12-01

    India is known for its historic diamonds from alluvial gravels. The source rocks for these diamonds are thought to be among the so far nearly 100 identified kimberlitic/lamproitic pipes and dikes which occur mostly in the Dharwar craton (Andhra Pradesh) and the Bundelkhand craton (Madhya Pradesh), and which all have Mesoproterozoic ages with a peak at 1.1 Ga. However, diamondiferous kimberlite pipes in the recently discovered Mainpur kimberlite field in central India have surprisingly young 40Ar/39Ar whole-rock ages of 66.5 ±2.0 and 62.4 ±2.9 million years (2σ), confirmed by more precise laser ablation ICP-MS 206Pb/238U perovskite data of 65.1 ±0.8 and 62.3 ±0.8 Ma (2 σ). These ages overlap with the main phase of the Deccan flood basalt magmatism at 65 million years, and suggest a common tectonomagmatic control for both flood basalts (including carbonatite-alkaline rock variants) and kimberlites. The kimberlites were studied in drill core and have textural, bulk and mineral chemical composition typical of orangeite (African kimberlite Group 2), confirmed by Sr and Nd isotope data. The Mainpur kimberlite field is in the Archean Bastar craton with felsic rocks as old as 3.6 Ga. The presence of macrodiamonds in the pipes implies that Central India had a cool and thick lithospheric mantle root at the Cretaceous/Tertiary boundary, significantly different from the modern Indian lithosphere of about 80-100 km thickness only. The loss of India's cratonic roots must have taken place in the Tertiary, i.e. after much of the superfast northward motion of the Indian plate from Gondwana break-up at about 130 million years until the collision with Eurasia at about 50 million years ago. India's unique plate-tectonic behaviour in the Cretaceous cannot be related to a plume-eroded lithosphere. About one third of the Indian lithosphere was lost during or after the Deccan flood basalt event.

  12. Multiple volcanic episodes of flood basalts caused by thermochemical mantle plumes.

    PubMed

    Lin, Shu-Chuan; van Keken, Peter E

    2005-07-14

    The hypothesis that a single mushroom-like mantle plume head can generate a large igneous province within a few million years has been widely accepted. The Siberian Traps at the Permian-Triassic boundary and the Deccan Traps at the Cretaceous-Tertiary boundary were probably erupted within one million years. These large eruptions have been linked to mass extinctions. But recent geochronological data reveal more than one pulse of major eruptions with diverse magma flux within several flood basalts extending over tens of million years. This observation indicates that the processes leading to large igneous provinces are more complicated than the purely thermal, single-stage plume model suggests. Here we present numerical experiments to demonstrate that the entrainment of a dense eclogite-derived material at the base of the mantle by thermal plumes can develop secondary instabilities due to the interaction between thermal and compositional buoyancy forces. The characteristic timescales of the development of the secondary instabilities and the variation of the plume strength are compatible with the observations. Such a process may contribute to multiple episodes of large igneous provinces. PMID:16015328

  13. New Data on mid-Miocene Rhyolite Volcanism in Eastern Oregon Extend Early, co-CRBG Rhyolite Flare up and Constrain Storage Sites of Grande Ronde Flood Basalts

    NASA Astrophysics Data System (ADS)

    Streck, M. J.; Ferns, M. L.; McIntosh, W. C.

    2015-12-01

    The classical view of relating mid-Miocene rhyolites of the tri-state area of Oregon, Nevada, and Idaho to the flood basalts of the Columbia River Basalt was that a mantle plume impinging along the Oregon-Idaho border first causes eruption of the flood basalts but shortly thereafter causes generation of rhyolites at the McDermitt volcanic field from which then hot-spot track rhyolites developed progressively younging towards Yellowstone. More recent work reveals rhyolites as old as found at McDermitt (~16.5 Ma) to occur along a wide E-W tangent along the Oregon-Nevada-Idaho border. And now, our data extend such early rhyolites (>16 Ma) to several locations further north within and in the periphery of the Lake Owyhee Volcanic Field (LOVF) adding to the geographically orphaned old age of 16.7 Ma of the Silver City Rhyolite, Idaho. Hence, the rhyolite flare-up associated with flood basalt magmatism occurred within a circular area of ~400 km centered 100 km NNE of McDermitt. Consequently, no south-to-north progression exists in the onset of rhyolite volcanism; instead, rhyolites started up at the same time over this large area. Province-wide rhyolite volcanism was strongest between ~16.4 and 15.4 Ma coincident with eruptions of the most voluminous member of the CRBG - the Grande Ronde Basalt (GRB). Field evidence for such bimodal volcanism consists of intercalated local GRB units with the Dinner Creek Tuff and Littlefield Rhyolite in the Malheur River Gorge corridor. GRB eruption sites exist and were likely fed from reservoirs residing below or near rhyolitic chambers. Presently, we have petrological evidence for pinning down GRB storages sites to areas from where rhyolites of the Dinner Creek Tuff and lava flows of the Littlefield Rhyolite erupted. In summary, input of GRG and other CRBG magmas were driving co-CRBG rhyolite volcanism which in turn may have influenced whether flood basalt magmas erupted locally or travelled in dikes to more distally located areas.

  14. Flood Basalts and Neoproterozoic Glaciation

    NASA Astrophysics Data System (ADS)

    Halverson, G. P.; Cox, G. M.; Kunzmann, M.; Strauss, J. V.; Macdonald, F. A.

    2014-12-01

    Large igneous provinces (LIPs), which are commonly associated with supercontinental break-up, are the product of the emplacement of >106 km3 of mafic rocks in less than a few million years. LIP magmatism, in particular continental flood basalt (CFB) volcanism, perturbs global climate on shorter time scales through the radiative effects of degassed SO2 and CO2. On longer time scales, CFBs alter climate through the effect of the high weatherabilty of mafic rocks (5-10 times greater than average continental crust) on global silicate weathering. A link between flood basalt weathering, Rodinia break-up, and Neoproterozoic snowball glaciation has been postulated. Here we present a new compilation of Nd isotope data on Neoproterozoic mudstones from Laurentia, Australia, and South China along with a new seawater strontium isotope record from well preserved carbonates that support this hypothesis. These datasets are consistent with an outsized role of basalt weathering on the global silicate weathering budget during the second half of the Tonian period (~850 to 725 Ma). Along with Os isotope data, they also suggest that an additional pulse of basalt weathering at the end of the Tonian may have initiated the Sturtian snowball glaciation. CFBs have relatively high concentrations of phosphorous. Hence, the drawdown in atmospheric CO2 required to trigger the Sturtian snowball Earth was likely accomplished through a combination of increased silicate weathering rates and enhanced biological productivity driven by greater nutrient supply to the oceans. CFBs were also the likely source of the iron in Neoproterozoic iron formation (IF), all significant occurrences of which are restricted to Sturtian-aged glacial successions. Dramatic declines in ɛNd following the Cryogenian snowball glaciations are mirrored by stepwise increases in 87Sr/86Sr, reflecting the scouring of the continents by global ice sheets. This continental resurfacing removed the extensive basalt carapace as well as

  15. Flood basalts and mass extinctions

    NASA Technical Reports Server (NTRS)

    Morgan, W. Jason

    1988-01-01

    There appears to be a correlation between the times of flood basalts and mass-extinction events. There is a correlation of flood basalts and hotspot tracks--flood basalts appear to mark the beginning of a new hotspot. Perhaps there is an initial instability in the mantle that bursts forth as a flood basalt but then becomes a steady trickle that persists for many tens of millions of years. Suppose that flood basalts and not impacts cause the environmental changes that lead to mass-extinctions. This is a very testable hypothesis: it predicts that the ages of the flows should agree exactly with the times of extinctions. The Deccan and K-T ages agree with this hypothesis; An iridium anomaly at extinction boundaries apparently can be explained by a scaled-up eruption of the Hawaiian type; the occurrence of shocked-quartz is more of a problem. However if the flood basalts are all well dated and their ages indeed agree with extinction times, then surely some mechanism to appropriately produce shocked-quartz will be found.

  16. Flood basalt eruptions, comet showers, and mass extinction events

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Stothers, Richard B.

    1988-01-01

    A chronology of initiation dates of the major continental flood basalt episodes has been established from compilation of published K-Ar and Ar-Ar ages of basaltic flows and related basic intrusions. The dating is therefore independent of the biostratigraphic and paleomagnetic time scales, and the estimated errors of the inititation dates are approximately + or - 4 pct. There are 11 distinct episodes of continental flood basalts known during the past 250 Myr. The data show that flood basalt episodes are generally relatively brief geologic events, with intermittent eruptions during peak output periods lasting ony 2 to 3 Myr or less. Statistical analyses suggest that these episodes may have occurred quasi-periodically with a mean cycle time of 32 + or - 1 Myr. The initiation dates of the flood basalts are close to the estimated dates of marine mass extinctions and impact-crater clusters. Although a purely internal forcing might be argued for the flood basalt volcanism, quasi-periodic comet impacts may be the trigger for both the flood basalts and the extinctions. Impact cratering models suggest that large-body impactors lead to deep initial cratering, and therefore may cause mantle disturbances and initiate mantle plume activity. The flood basalt episodes commonly mark the initiation or jump of a mantle hotspot, and are often followed by continental rifting and separation. Evidence from dynamical studies of impacts, occurrences of craters and hotspots, and the geochemistry of boundary layers is synthesized to provide a possible model of impact-generated volcanism. Flood basalt eruptions may themselves have severe effects on climate, and possibly on life. Impacts might, as a result, have led to mass extinctions through direct atmospheric disturbances, and/or indirectly through prolonged flood basalt volcanism.

  17. Post-rift flood-basalt-like volcanism on the Newfoundland Basin nonvolcanic margin: The U event mapped with spectral decomposition

    NASA Astrophysics Data System (ADS)

    Deemer, S.; Hurich, C.; Hall, J.

    2010-10-01

    Diabase sills emplaced at less than .5 km depth (presently ~ 7 km) are imaged throughout the Newfoundland Basin as an extraordinarily high amplitude package of seismic reflections historically referred to as the U event. The sills are extensive, covering roughly 20,000 km 2, and represent a post-rift voluminous magmatic episode along an otherwise nonvolcanic rifted margin. Spectral decomposition is used to estimate a total magmatic volume at roughly 1000-2000 km 3. On an individual basis the major sills are comparable to flows in flood basalt volcanic environments. A proposed mechanism for generating these large volumes of magma which are also very limited in time to perhaps only two major intrusive episodes (2 sills) is the approach of the Canary and Madeira hot spots. Suppressed volcanism while the hot spots traveled under full thickness continental lithosphere of Newfoundland resulted in a local accumulation of magma which was suddenly released when the hot spots approached thinned lithosphere at the eastern edge of the Grand Banks. The emplacement of the sills 'anticipated' the arrival of the hot spots geographically.

  18. Flood basalts and extinction events

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1993-01-01

    The largest known effusive eruptions during the Cenozoic and Mesozoic Eras, the voluminous flood basalts, have long been suspected as being associated with major extinctions of biotic species. Despite the possible errors attached to the dates in both time series of events, the significance level of the suspected correlation is found here to be 1 percent to 4 percent. Statistically, extinctions lag eruptions by a mean time interval that is indistinguishable from zero, being much less than the average residual derived from the correlation analysis. Oceanic flood basalts, however, must have had a different biological impact, which is still uncertain owing to the small number of known examples and differing physical factors. Although not all continental flood basalts can have produced major extinction events, the noncorrelating eruptions may have led to smaller marine extinction events that terminated at least some of the less catastrophically ending geologic stages. Consequently, the 26 Myr quasi-periodicity seen in major marine extinctions may be only a sampling effect, rather than a manifestation of underlying periodicity.

  19. Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP

    NASA Astrophysics Data System (ADS)

    McClintock, Murray; White, James D. L.

    2006-01-01

    The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km2). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris + steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however, probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents. The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water, as well

  20. 40Ar/39Ar dating of the Siberian Traps, USSR: Evaluation of the ages of the two major extinction events relative to episodes of flood-basalt volcanism in the USSR and the Deccan Traps, India

    SciTech Connect

    Baksi, A.K. ); Farrar, E. )

    1991-05-01

    {sup 40}Ar/{sup 39}Ar incremental-heating studies have been carried out on three whole-rock specimens from the Siberian Traps. A basalt lava flow from the lowermost horizon yields and age of 238.4 {plus minus} 1.4 Ma (1{sigma} error). A second basalt lava flow from the top of the section, {approximately}800 m above the first specimen, yields an age of 229.9 {plus minus} 2.3 Ma, indicating that the duration of volcanism was {approximately}5{minus}10 m.y. A doleritic dike intrusive into the lower parts of the Siberian Traps contains excess argon and yields an isochron age of 234 {plus minus} 7 Ma. Critical reexamination of relevant radiometric data relating two separate episodes of flood-basalt volcanism to global faunal extinctions suggests the volcanic event forming the most voluminous sections of the Deccan Traps, India, was coincident to within {plus minus}1 m.y. with the time of the Cretaceous/Tertiary boundary. However, the onset of volcanism in the Siberian Traps apparently occurred at a time postdating that of the Permian/Triassic boundary.

  1. Carbonate Mineralization of Volcanic Province Basalts

    SciTech Connect

    Schaef, Herbert T.; McGrail, B. Peter; Owen, Antionette T.

    2010-03-31

    Flood basalts are receiving increasing attention as possible host formations for geologic sequestration of anthropogenic CO2, with studies underway in the United States, India, Iceland, and Canada. As an extension of our previous experiments with Columbia River basalt, basalts from the eastern United States, India, and South Africa were reacted with aqueous dissolved CO2 and aqueous dissolved CO2-H2S mixtures under supercritical CO2 (scCO2) conditions to study the geochemical reactions resulting from injection of CO2 in such formations. The results of these studies are consistent with cation release behavior measured in our previous experiments (in press) for basalt samples tested in single pass flow through dissolution experiments under dilute solution and mildly acidic conditions. Despite the basalt samples having similar bulk chemistry, mineralogy and apparent dissolution kinetics, long-term static experiments show significant differences in rates of mineralization as well as compositions and morphologies of precipitates that form when the basalts are reacted with CO2-saturated water. For example, basalt from the Newark Basin in the United States was by far the most reactive of any basalt tested to date. Carbonate reaction products for the Newark Basin basalt were globular in form and contained significantly more Fe than the secondary carbonates that precipitated on the other basalt samples. In comparison, the post-reacted samples associated with the Columbia River basalts from the United States contained calcite grains with classic dogtooth spar morphology and trace cation substitution (Mg and Mn). Carbonation of the other basalts produced precipitates with compositions that varied chemically throughout the entire testing period. Examination of polished cross sections of the reacted grains by scanning electron microscopy and energy dispersive x-ray spectroscopy show precipitate overgrowths with varying chemical compositions. Compositional differences in the

  2. An Intense 16.5-16.0 MA Episode of Rhyolitic Volcanism Associated with Flood Basalt Dike Emplacement at Mcdermitt Caldera Field and High Rock Caldera Complex, Nevada and Oregon

    NASA Astrophysics Data System (ADS)

    Benson, T. R.; Mahood, G. A.; Coble, M. A.

    2013-12-01

    Voluminous rhyolites erupted from three major caldera fields and multiple smaller centers contemporaneous with Steens and Columbia River flood basalts at 16.5 to 15.0 Ma (Coble and Mahood, 2012). It has long been known that ignimbrites from McDermitt Caldera Field (MCF) and High Rock Caldera Complex (HRCC) erupted at nearly the same time (e.g., Rytuba and McKee, 1984), but their relative stratigraphic relations have not been previously determined. A west-dipping section on the west flank of the Pueblo Mountains contains four ignimbrites stratigraphically above Steens basalt. A nonwelded metaluminous rhyolitic ignimbrite at the base of the section is chemically distinct from the weakly alkalic to moderately peralkaline rhyolites from MCF and HRCC. This ignimbrite is similar in composition and mineralogy to lavas from the Hawks Valley/Lone Mountain center (HV/LM), north of HRCC, for which Wypych et al. (2011) obtained 40Ar/39Ar ages between ~16.5 and 16.3 Ma. The second ignimbrite in the Pueblo Mountains section is a densely welded, moderately peralkaline, alkali rhyolite that we correlate with the Oregon Canyon Tuff from the MCF based on similar phenocryst abundance and assemblage, whole-rock composition, and an age of 16.51 Ma (FCT=28.02 Ma) from this locality, which is analytically indistinguishable from an age Jarboe et al. (2010) obtained on the tuff in the Trout Creek Mountains. Based on field appearance, mineralogy, and whole-rock composition we correlate the third ignimbrite, a crystal-rich, densely welded, alkali rhyolite, with the Tuff of Trout Creek Mountains, also from MCF. The fourth ignimbrite we identify as the crystal-rich, late-erupted part of the 16.37 Ma Idaho Canyon Tuff. It is the first major ignimbrite known to erupt from HRRC, and in its northernmost outcrops banks in against lavas of HV/LM. At both MCF and HRCC, the interval 16.5-16.0 Ma was a time of intense silicic volcanism, punctuated by the formation of the McDermitt Caldera proper at ~16

  3. The deep water cycle and origin of cratonic flood basalts: two examples from the Siberian craton

    NASA Astrophysics Data System (ADS)

    Ivanov, A. V.

    2014-12-01

    Cratonic flood basalt volcanism is the most puzzling phenomenon compared to all other types of intraplate volcanism. Cratons are thick and cold; the two parameters which suppress melting of either sublithospheric or lithospheric mantle in dry conditions. Fusible eclogites at hot plume geotherm start to melt in sublithospheric depth (~ 230 km), but geochemical arguments require that, in addition to eclogitic component, significant volume of flood basalts are from peridotitic mantle. Dry peridotitic mantle cannot be melted unless the lithospheric thickness reduced to about 60 km. That is why modern plume models incorporate lithospheric delamination and/or initially thinned lithosphere to explain cratonic flood basalts. However, if lithosphere remained thick, which was the case for the Siberian craton by the time of formation of its Devonian (Vilyui) and Permo-Triassic (Siberian) flood basalt provinces, then plume model is unable to explain the flood basalt volcanism. If mantle is wet, the peridotitic solidus lowered such as it can start to melt at sublithospheric depth (for example, 2 wt. % H2O-bearing peridotite starts to melt at ~320 km depth even at a normal mantle geotherm). In this presentation I will show that fluxing of mantle via the deep water cycle process may explain the Siberian craton flood basalts and many other continental flood basalts. According to the deep water cycle model, water is carried to the mantle transition zone by fast subducting slabs (may be in form of solid ice VII), then water is released from the slabs due to warming to the ambient mantle temperature, then localized hydration creates buoyant wet diapirs (or melt-bearing diapirs), the diapirs raise up to the sublithosheric depth were melt accumulates for the following tectonically triggered flood basalt eruptions.

  4. Constraining the onset of flood volcanism in Isle of Skye Lava Field, British Paleogene Volcanic Province

    NASA Astrophysics Data System (ADS)

    Angkasa, Syahreza; Jerram, Dougal. A.; Svensen, Henrik; Millet, John M.; Taylor, Ross; Planke, Sverre

    2016-04-01

    In order to constrain eruption styles at the onset of flood volcanism, field observations were undertaken on basal sections of the Isle of Skye Lava Field, British Paleogene Volcanic Province. This study investigates three specific sections; Camus Ban, Neist Point and Soay Sound which sample a large area about 1500 km2 and can be used to help explain the variability in palaeo-environments at the onset of flood volcanism. Petrological analysis is coupled with petrophysical lab data and photogrammetry data to create detailed facies models for the different styles of initiating flood basalt volcanism. Photogrammetry is used to create Ortho-rectified 3D models which, along with photomontage images, allow detailed geological observations to be mapped spatially. Petrographic analyses are combined with petrophysical lab data to identify key textural variation, mineral compositions and physical properties of the volcanic rocks emplaced during the initial eruptions. Volcanism initiated with effusive eruptions in either subaerial or subaqueous environments resulting in tuff/hyaloclastite materials or lava flow facies lying directly on the older Mesozoic strata. Volcanic facies indicative of lava-water interactions vary significantly in thickness between different sections suggesting a strong accommodation space control on the style of volcanism. Camus Ban shows hyaloclastite deposits with a thickness of 25m, whereas the Soay Sound area has tuffaceous sediments of under 0.1m in thickness. Subaerial lavas overly these variable deposits in all studied areas. The flood basalt eruptions took place in mixed wet and dry environments with some significant locally developed water bodies (e.g. Camus Ban). More explosive eruptions were promoted in some cases by interaction of lavas with these water bodies and possibly by local interaction with water - saturated sediments. We record key examples of how palaeotopography imparts a primary control on the style of volcanism during the

  5. Basaltic volcanic episodes of the Yucca Mountain region

    SciTech Connect

    Crowe, B.M.

    1990-03-01

    The purpose of this paper is to summarize briefly the distribution and geologic characteristics of basaltic volcanism in the Yucca Mountain region during the last 10--12 Ma. This interval largely postdates the major period of silicic volcanism and coincides with and postdates the timing of major extensional faulting in the region. Field and geochronologic data for the basaltic rocks define two distinct episodes. The patterns in the volume and spatial distribution of these basaltic volcanic episodes in the central and southern part of the SNVF are used as a basis for forecasting potential future volcanic activity in vicinity of Yucca Mountain. 33 refs., 2 figs.

  6. Basaltic Volcanism of the Snake River Volcanic Province

    NASA Astrophysics Data System (ADS)

    Shervais, J. W.; Hanan, B. B.; Vetter, S.

    2012-12-01

    The Yellowstone-Snake River Plain (YSRP) volcanic province is the world's best modern example of a time-transgressive hotspot track beneath continental crust. Tomographic images document a thermal anomaly which pierces the Farallon plate at depth and appears to extend to depths of over 1000 km. Many investigators attribute this anomaly to a deep mantle plume, while others recognize the sheet-like aspect of the velocity anomaly and attribute it to lower mantle flow around a fragmented remnant of the Farallon plate. Tholeiitic basalts of the SRP have major element compositions similar to ocean island basalts (OIB), with higher FeO, TiO2, P2O5 and K2O than mid-ocean ridge basalts over a similar range in MgO. Their trace element concentrations also mimic OIB tholeiites, with moderately enriched LREE/HREE ratios, OIB-like HFSE ratios and Nb-Y-Zr systematics. Most SRP basalts show little evidence of crustal assimilation: oxygen isotope compositions are mantle-like, K2O is low and does not increase relative to other incompatible elements during fractionation (e.g., P2O5), and silica contents are consistently low. In contrast, evidence suggests that these basalts evolve primarily through fractional crystallization in relatively shallow magma chambers with episodic magma recharge. Trace element concentration patterns are nearly identical to OIB tholeiites, with somewhat lower slopes on multi-element variations diagrams, consistent with 7-12% partial melting of spinel-facies peridotite (9-18 kb, 40-65 km) with a composition similar to the source of OIB or EMORB. Models show that depleted MORB asthenosphere or primitive mantle peridotite composition sources cannot yield SRP tholeiites, even with residual garnet in the source region to raise LREE/HREE ratios in the melt. There is no indication of residual garnet in the source - which requires that either the lithosphere was relatively thin during formation of the SRP, or that the melts originated within the lithosphere itself

  7. Cambrian intermediate-mafic magmatism along the Laurentian margin: Evidence for flood basalt volcanism from well cuttings in the Southern Oklahoma Aulacogen (U.S.A.)

    NASA Astrophysics Data System (ADS)

    Brueseke, Matthew E.; Hobbs, Jasper M.; Bulen, Casey L.; Mertzman, Stanley A.; Puckett, Robert E.; Walker, J. Douglas; Feldman, Josh

    2016-09-01

    The Southern Oklahoma Aulocogen (SOA) stretches from southern Oklahoma through the Texas panhandle and into Colorado and New Mexico, and contains mafic through silicic magmatism related to the opening of the Iapetus Ocean during the early Cambrian. Cambrian magmatic products are best exposed in the Wichita Mountains (Oklahoma), where they have been extensively studied. However, their ultimate derivation is still somewhat contentious and centers on two very different models: SOA magmatism has been suggested to occur via [1] continental rifting (with or without mantle plume emplacement) or [2] transform-fault related magmatism (e.g., leaky strike-slip faults). Within the SOA, the subsurface in and adjacent to the Arbuckle Mountains in southern Oklahoma contains thick sequences of mafic to intermediate lavas, intrusive bodies, and phreatomagmatic deposits interlayered with thick, extensive rhyolite lavas, thin localized tuffs, and lesser silicic intrusive bodies. These materials were first described in the Arbuckle Mountains region by a 1982 drill test (Hamilton Brothers Turner Falls well) and the best available age constraints from SOA Arbuckle Mountains eruptive products are ~ 535 to 540 Ma. Well cuttings of the mafic through intermediate units were collected from that well and six others and samples from all but the Turner Falls and Morton wells are the focus of this study. Samples analyzed from the wells are dominantly subalkaline, tholeiitic, and range from basalt to andesite. Their overall bulk major and trace element chemistry, normative mineralogy, and Srsbnd Nd isotope ratios are similar to magmas erupted/emplaced in flood basalt provinces. When compared with intrusive mafic rocks that crop out in the Wichita Mountains, the SOA well cuttings are geochemically most similar to the Roosevelt Gabbros. New geochemical and isotope data presented in this study, when coupled with recent geophysical work in the SOA and the coeval relationship with rhyolites, indicates

  8. Extrinsic controls on inter-basaltic plant ecosystems in the Columbia River Flood Basalt Province, Washington State, USA

    NASA Astrophysics Data System (ADS)

    Ebinghaus, Alena; Jolley, David W.; Hartley, Adrian J.

    2015-04-01

    The impact Large Igneous Province (LIP) volcanism may have had on paleoclimate, fauna and flora is still controversy. Inter-lava field plant ecosystems have the potential to record in detail the effects LIPs had on the environment in the immediate vicinity of volcanic activity. The Miocene Columbia River Flood Basalt Province (CRBP), Washington State, USA, provides excellent exposure of an entire LIP stratigraphy and offers a detailed record of inter-basaltic plant ecosystems throughout LIP evolution. The CRBP lava field comprise numerous basaltic lava flows that are intercalated with fluvial and lacustrine sediments which formed during phases of volcanic quiescence. The LIP volcanic evolution is characterised by an initial phase of high eruption volumes and eruptions rates, which is followed by waning volcanism associated with longer interbed intervals. Inter-lava field plant ecosystems are expected to correlate with phases of volcanic evolution: short interbed intervals should be dominated by early seral succession, while longer intervals should record more mature seral successions. The palynological record of the sedimentary interbeds however indicates a decline in successional status within the long interbed intervals of CRBP stratigraphy. An integrated analysis of sedimentary facies and geochemistry suggests intense volcanic ash fall derived from the adjacent Yellowstone hot spot as a major trigger for repetitive successional re-setting. This implies that inter-lava field ecosystem maturity was controlled by extrinsic forcing, and argues against environmental changes solely driven by LIPs of similar scale and magnitude to that of the CRBP.

  9. Stratigraphy and volcanic facies architecture of the Torres Syncline, Southern Brazil, and its role in understanding the Paraná-Etendeka Continental Flood Basalt Province

    NASA Astrophysics Data System (ADS)

    Waichel, Breno L.; de Lima, Evandro F.; Viana, Adriano R.; Scherer, Claiton M.; Bueno, Gilmar V.; Dutra, Gabriel

    2012-02-01

    The Torres Syncline is a large structure that constitutes the eastmost outcrop of the Paraná-Etendeka CFB in South American side, and this work focuses the stratigraphy and facies architecture of the volcanic pile in the syncline. The volcanic sequence along the study area permits the division of three regions: main valley, intermediate zone and south hinge, each of them with distinct stratigraphy, which probably reflects the structural evolution of the syncline. The stratigraphy of the Torres Syncline is composed by: 1 — Botucatu palaeoerg; 2 — Basic volcanic episode I; 3 — Basic volcanic episode II, 4 — Acidic volcanic I, 5 — Basic volcanic episode III and 6 — Acidic volcanic episode II. The five volcanic episodes recognized in study area can be related to five volcanic facies architecture: compound-braided, tabular-classic, tabular/lobate escoriaceous, dome-field (acidic lavas) and tabular flows (acidic lavas). The basic episode I is composed by pahoehoe flows with a compound-braided facies architecture that covered the Botucatu palaeoerg. The basic episode II is a tabular-classic facies architecture predominantly composed by simple flows (10-20 m thick) reaching the total thickness of ~ 500 m in main valley. The acidic episode I is exposed in main valley and south hinge, and is composed by acidic lavas forming lava dome-field facies architecture with a thickness of ~ 150 m. The basic episode III is predominantly constituted by 'a'ā flows with tabular/lobate escoriaceous facies architecture. The acidic episode II is constituted by tabular flow volcanic facies (acidic flows) and outcrops all along the study area. The Torres Syncline constitute the eastmost on-shore exposures of the Paraná-Etendeka CFB in South American side and detailed stratigraphic, volcanological and structural studies in these area, coupled with correlation with Huab Basin (NW Namíbia, Africa) will aim the understanding of the Gondwana breakup process and the early stages of

  10. Pliocene Basaltic Volcanism in The East Anatolia Region (EAR), Turkey

    NASA Astrophysics Data System (ADS)

    Oyan, Vural; Özdemir, Yavuz; Keskin, Mehmet

    2016-04-01

    East Anatolia Region (EAR) is one of the high Plateau which is occurred with north-south compressional regime formed depending on continent-continent collision between Eurasia and Arabia plates (Şengör and Kidd, 1979). Recent studies have revealed that last oceanic lithosphere in the EAR have completely depleted to 20 million years ago based on fission track ages (Okay et al. 2010). Our initial studies suggest that extensively volcanic activity in the EAR peaked in the Pliocene and continued in the same productivity throughout Quaternary. Voluminous basaltic lava plateaus and basaltic lavas from local eruption centers occurred as a result of high production level of volcanism during the Pliocene time interval. In order to better understand the spatial and temporal variations in Pliocene basaltic volcanism and to reveal isotopic composition, age and petrologic evolution of the basaltic volcanism, we have started to study basaltic volcanism in the East Anatolia within the framework of a TUBITAK project (project number:113Y406). Petrologic and geochemical studies carried out on the Pliocene basaltic lavas indicate the presence of subduction component in the mantle source, changing the character of basaltic volcanism from alkaline to subalkaline and increasing the amount of spinel peridotitic melts (contributions of lithospheric mantle?) in the mantle source between 5.5-3.5 Ma. FC, AFC and EC-AFC modelings reveal that the while basaltic lavas were no or slightly influenced by crustal contamination and fractional crystallization, to more evolved lavas such as bazaltictrachyandesite, basalticandesite, trachybasalt might have been important processes. Results of our melting models and isotopic analysis data (Sr, Nd, Pb, Hf, 18O) indicate that the Pliocene basaltic rocks were derived from both shallow and deep mantle sources with different melting degrees ranging between 0.1 - 4 %. The percentage of spinel seems to have increased in the mantle source of the basaltic

  11. Recurrence rates of volcanism in basaltic volcanic fields: An example from the Springerville volcanic field, Arizona

    SciTech Connect

    Condit, C.D.; Connor, C.B.

    1996-10-01

    A spatio-temporal near-neighbor model is used to identify and map variations in the recurrence rate of volcanism in the Springerville volcanic field, Arizona, a large field on the Colorado Plateau boundary. Detailed mapping of individual lava flows and their associated vents, together with radiometric and paleomagnetic dating, demonstrates that 366 volcanic events have formed the Springerville volcanic field. A near-neighbor spatio-temporal recurrence-rate model using seven near-neighbor volcanoes and a 0.5 m.y. time window reveals that (1) areas of waxing and waning magmatism in the Springerville volcanic field are much more localized and (2) volcanic activity within these areas is much more intense than implied by field-wide temporal trends. Because volcanic activity is spatially and temporally clustered, forecasting subsequent activity is more successful if the spatio-temporal recurrence-rate model is used, rather than the average recurrence rates. This success indicates that spatio-temporal recurrence-rate models are useful tools for the quantification of long-term volcanic hazards in basaltic volcanic fields. 61 refs., 13 figs., 2 tabs.

  12. Emplacement of Columbia River flood basalt

    SciTech Connect

    Reidel, Stephen P.)

    1997-11-01

    Evidence is examined for the emplacement of the Umatilla, Wilbur Creek, and the Asotin Members of Columbia River Basalt Group. These flows erupted in the eastern part of the Columbia Plateau during the waning phases of volcanism. The Umatilla Member consists of two flows in the Lewiston basin area and southwestern Columbia Plateau. These flows mixed to form one flow in the central Columbia Plateau. The composition of the younger flow is preserved in the center and the composition of the older flow is at the top and bottom. There is a complete gradation between the two. Flows of the Wilbur Creek and Asotin Members erupted individually in the eastern Columbia Plateau and also mixed together in the central Columbia Plateau. Comparison of the emplacement patterns to intraflow structures and textures of the flows suggests that very little time elapsed between eruptions. In addition, the amount of crust that formed on the earlier flows prior to mixing also suggests rapid emplacement. Calculations of volumetric flow rates through constrictions in channels suggest emplacement times of weeks to months under fast laminar flow for all three members. A new model for the emplacement of Columbia River Basalt Group flows is proposed that suggests rapid eruption and emplacement for the main part of the flow and slower emplacement along the margins as the of the flow margin expands.

  13. Emplacement of Columbia River flood basalt

    SciTech Connect

    Reidel, S.P.

    1998-11-01

    Evidence is examined for the emplacement of the Umatilla, Wilbur Creek, and the Asotin Members of Columbia River Basalt Group. These flows erupted in the eastern part of the Columbia Plateau during the waning phases of volcanism. The Umatilla Member consists of two flows in the Lewiston basin area and southwestern Columbia Plateau. These flows mixed to form one flow in the central Columbia Plateau. The composition of the younger flow is preserved in the center and the composition of the older flow is at the top and bottom. There is a complete gradation between the two. Flows of the Wilbur Creek and Asotin Members erupted individually in the eastern Columbia Plateau and also mixed together in the central Columbia Plateau. Comparison of the emplacement patterns to intraflow structures and textures of the flows suggests that very little time elapsed between eruptions. In addition, the amount of crust that formed on the earlier flows prior to mixing also suggests rapid emplacement. Calculations of volumetric flow rates through constrictions in channels suggest emplacement times of weeks to months under fast laminar flow for all three members. A new model for the emplacement of Columbia River Basalt Group flows is proposed that suggests rapid eruption and emplacement for the main part of the flow and slower emplacement along the margins as the of the flow margin expands.

  14. Selective environmental stress from sulphur emitted by continental flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Schmidt, Anja; Skeffington, Richard; Thordarson, Thorvaldur; Self, Stephen; Forster, Piers; Rap, Alexandru; Ridgwell, Andy; Fowler, David; Wilson, Marjorie; Mann, Graham; Wignall, Paul; Carslaw, Ken

    2016-04-01

    Several biotic crises during the past 300 million years have been linked to episodes of continental flood basalt volcanism, and in particular to the release of massive quantities of magmatic sulphur gas species. Flood basalt provinces were typically formed by numerous individual eruptions, each lasting years to decades. However, the environmental impact of these eruptions may have been limited by the occurrence of quiescent periods that lasted hundreds to thousands of years. Here we use a global aerosol model to quantify the sulphur-induced environmental effects of individual, decade-long flood basalt eruptions representative of the Columbia River Basalt Group, 16.5-14.5 million years ago, and the Deccan Traps, 65 million years ago. For a decade-long eruption of Deccan scale, we calculate a decadal-mean reduction in global surface temperature of 4.5 K, which would recover within 50 years after an eruption ceased unless climate feedbacks were very different in deep-time climates. Acid mists and fogs could have caused immediate damage to vegetation in some regions, but acid-sensitive land and marine ecosystems were well-buffered against volcanic sulphur deposition effects even during century-long eruptions. We conclude that magmatic sulphur from flood basalt eruptions would have caused a biotic crisis only if eruption frequencies and lava discharge rates had been high and sustained for several centuries at a time.

  15. Selective environmental stress from sulphur emitted by continental flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Schmidt, Anja; Skeffington, Richard A.; Thordarson, Thorvaldur; Self, Stephen; Forster, Piers M.; Rap, Alexandru; Ridgwell, Andy; Fowler, David; Wilson, Marjorie; Mann, Graham W.; Wignall, Paul B.; Carslaw, Kenneth S.

    2016-01-01

    Several biotic crises during the past 300 million years have been linked to episodes of continental flood basalt volcanism, and in particular to the release of massive quantities of magmatic sulphur gas species. Flood basalt provinces were typically formed by numerous individual eruptions, each lasting years to decades. However, the environmental impact of these eruptions may have been limited by the occurrence of quiescent periods that lasted hundreds to thousands of years. Here we use a global aerosol model to quantify the sulphur-induced environmental effects of individual, decade-long flood basalt eruptions representative of the Columbia River Basalt Group, 16.5-14.5 million years ago, and the Deccan Traps, 65 million years ago. For a decade-long eruption of Deccan scale, we calculate a decadal-mean reduction in global surface temperature of 4.5 K, which would recover within 50 years after an eruption ceased unless climate feedbacks were very different in deep-time climates. Acid mists and fogs could have caused immediate damage to vegetation in some regions, but acid-sensitive land and marine ecosystems were well-buffered against volcanic sulphur deposition effects even during century-long eruptions. We conclude that magmatic sulphur from flood basalt eruptions would have caused a biotic crisis only if eruption frequencies and lava discharge rates had been high and sustained for several centuries at a time.

  16. Supertoxic Flood Basalts: The CAMP - Siberian Trap Connection

    NASA Astrophysics Data System (ADS)

    Puffer, J. H.

    2007-12-01

    Several diverse magma types are represented throughout the CAMP and Siberian Trap LIPs, however, the main extrusive phase of each province is highly unusual among continental flood basalts. The most widespread extrusions were intermediate titanium (ITi-type) CAMP basalt and the lower portion of the Upper Sequence of Siberian Trap. New and recently published data indicate that the geochemistry and petrology of these basalt suites closely resemble each other and infer similar origins. The basalts are characterized by strong negative Nb- Ta anomalies and unusual island arc-like depletion in high field strength elements, particularly Ti, plotted on spider diagrams. The geochemical data is consistent with significant contributions from subducted slabs into the magma source regions. If contaminated, volatile enriched mantle wedges were trapped beneath thick continental plates during the assembly of Pangea, fertile magma sources would have remained dormant until decompression melting was triggered during failed rift, then early rift stages of continental plate disassembly. The combination of volatile enriched sources and highly extensional tectonism would create rare perfect storms of toxicity. Calculated low viscosities assuming negligible carbon dioxide are consistent with rapid crustal penetration. Resulting aphyric melts extruded at enormous effusive rates as thick sub-parallel flows across wide subareal terrains through fissures extending several hundred km in length. High fountain heights would afford ample opportunity for efficient degassing, perhaps into the stratosphere. When the supply of volatile flux was exhausted magmatism ceased. The mass extinctions that coincide with CAMP and Siberian volcanism contrast with some large plume and superplume events that correlate with expansions of biodiversity. This may be due in part to contrasting magma access to sources of toxic volatiles, particularly sulfur concentrations in anoxic subducted sediments.

  17. Deep degassing and the eruptibility of flood basalt magmas

    NASA Astrophysics Data System (ADS)

    Black, B. A.; Manga, M.

    2015-12-01

    Individual flood basalt lavas often exceed 103 km3 in volume, and many such lavas erupt during emplacement of flood basalt provinces. The large volume of individual flood basalt lavas demands correspondingly large magma reservoirs within or at the base of the crust. To erupt, some fraction of this magma must become buoyant and overpressure must be sufficient to encourage failure and dike propagation. Because the overpressure associated with a new injection of magma is inversely proportional to the total reservoir volume, buoyancy overpressure has been proposed as a trigger for flood basalt eruptions. To test this hypothesis, we develop a new one-dimensional model for buoyancy overpressure-driven eruptions that combines volatile exsolution, bubble growth and rise, assimilation, and permeable fluid escape through the surrounding country rocks. Degassing during emplacement of flood basalt provinces may have major environmental repercussions. We investigate the temporal evolution of permeable degassing through the crust and degassing during eruptive episodes. We find that assimilation of volatile-rich country rocks strongly enhances flood basalt eruptibility, implying that the eruptive dynamics of flood basalts may be intertwined with their climatic consequences.

  18. Growing magma chambers control the distribution of small-scale flood basalts

    PubMed Central

    Yu, Xun; Chen, Li-Hui; Zeng, Gang

    2015-01-01

    Small-scale continental flood basalts are a global phenomenon characterized by regular spatio-temporal distributions. However, no genetic mechanism has been proposed to explain the visible but overlooked distribution patterns of these continental basaltic volcanism. Here we present a case study from eastern China, combining major and trace element analyses with Ar–Ar and K–Ar dating to show that the spatio-temporal distribution of small-scale flood basalts is controlled by the growth of long-lived magma chambers. Evolved basalts (SiO2 > 47.5 wt.%) from Xinchang–Shengzhou, a small-scale Cenozoic flood basalt field in Zhejiang province, eastern China, show a northward younging trend over the period 9.4–3.0 Ma. With northward migration, the magmas evolved only slightly ((Na2O + K2O)/MgO = 0.40–0.66; TiO2/MgO = 0.23–0.35) during about 6 Myr (9.4–3.3 Ma). When the flood basalts reached the northern end of the province, the magmas evolved rapidly (3.3–3.0 Ma) through a broad range of compositions ((Na2O + K2O)/MgO = 0.60–1.28; TiO2/MgO = 0.30–0.57). The distribution and two-stage compositional evolution of the migrating flood basalts record continuous magma replenishment that buffered against magmatic evolution and induced magma chamber growth. Our results demonstrate that the magma replenishment–magma chamber growth model explains the spatio-temporal distribution of small-scale flood basalts. PMID:26581905

  19. Growing magma chambers control the distribution of small-scale flood basalts

    NASA Astrophysics Data System (ADS)

    Yu, Xun; Chen, Li-Hui; Zeng, Gang

    2015-11-01

    Small-scale continental flood basalts are a global phenomenon characterized by regular spatio-temporal distributions. However, no genetic mechanism has been proposed to explain the visible but overlooked distribution patterns of these continental basaltic volcanism. Here we present a case study from eastern China, combining major and trace element analyses with Ar-Ar and K-Ar dating to show that the spatio-temporal distribution of small-scale flood basalts is controlled by the growth of long-lived magma chambers. Evolved basalts (SiO2 > 47.5 wt.%) from Xinchang-Shengzhou, a small-scale Cenozoic flood basalt field in Zhejiang province, eastern China, show a northward younging trend over the period 9.4-3.0 Ma. With northward migration, the magmas evolved only slightly ((Na2O + K2O)/MgO = 0.40-0.66 TiO2/MgO = 0.23-0.35) during about 6 Myr (9.4-3.3 Ma). When the flood basalts reached the northern end of the province, the magmas evolved rapidly (3.3-3.0 Ma) through a broad range of compositions ((Na2O + K2O)/MgO = 0.60-1.28 TiO2/MgO = 0.30-0.57). The distribution and two-stage compositional evolution of the migrating flood basalts record continuous magma replenishment that buffered against magmatic evolution and induced magma chamber growth. Our results demonstrate that the magma replenishment-magma chamber growth model explains the spatio-temporal distribution of small-scale flood basalts.

  20. Growing magma chambers control the distribution of small-scale flood basalts.

    PubMed

    Yu, Xun; Chen, Li-Hui; Zeng, Gang

    2015-01-01

    Small-scale continental flood basalts are a global phenomenon characterized by regular spatio-temporal distributions. However, no genetic mechanism has been proposed to explain the visible but overlooked distribution patterns of these continental basaltic volcanism. Here we present a case study from eastern China, combining major and trace element analyses with Ar-Ar and K-Ar dating to show that the spatio-temporal distribution of small-scale flood basalts is controlled by the growth of long-lived magma chambers. Evolved basalts (SiO2 > 47.5 wt.%) from Xinchang-Shengzhou, a small-scale Cenozoic flood basalt field in Zhejiang province, eastern China, show a northward younging trend over the period 9.4-3.0 Ma. With northward migration, the magmas evolved only slightly ((Na2O + K2O)/MgO = 0.40-0.66; TiO2/MgO = 0.23-0.35) during about 6 Myr (9.4-3.3 Ma). When the flood basalts reached the northern end of the province, the magmas evolved rapidly (3.3-3.0 Ma) through a broad range of compositions ((Na2O + K2O)/MgO = 0.60-1.28; TiO2/MgO = 0.30-0.57). The distribution and two-stage compositional evolution of the migrating flood basalts record continuous magma replenishment that buffered against magmatic evolution and induced magma chamber growth. Our results demonstrate that the magma replenishment-magma chamber growth model explains the spatio-temporal distribution of small-scale flood basalts. PMID:26581905

  1. On the connection between mare basalts and picritic volcanic glasses

    NASA Technical Reports Server (NTRS)

    Longhi, John

    1987-01-01

    The liquid lines of descent were calculated for low-pressure equilibrium and fractional crystallization of mare basaltic liquids in order to examine the postulated link between picritic volcanic glasses and mare basalts. The models of Longhi (1977, 1982) were modified by including expressions for the armalcolite/ilmenite surface boundary and the Cr-spinel liquidus surface, average molar partition coefficients for armalcolite/liquid pairs, and new experimental data of Longhi and Pan (1987). The results indicate that, with two exceptions, mare basalts and picritic volcanic glasses are not related by simple, linear-surface crystallization processes. However, the compositions of Luna 24 ferrobasalt and Apollo 11 high-K basalts could be closely matched with the lines of liquid descent of certain green and orange picritic glasses, respectively. The calculations also show that the picritic magmas would have fractionated to produce basalts with bulk and mineral compositions similar to those of mare basalts, supporting the hypothesis that mare basalts have fractionated compositions and that the small number of observed linkages between basalts and picritic parents is a consequence of limited sampling.

  2. Some volcanologic aspects of Columbia River basalt volcanism relevant to the extinction controversy

    NASA Technical Reports Server (NTRS)

    Swanson, Donald A.

    1988-01-01

    The Columbia River Basalt Group is the youngest and most thoroughly studied flood-basalt province known; information about it should be relevant to questions about the possible relation of flood-basalt volcanism to mass extinctions. The group has a total volume of about 174,000 cu km and covers an area of about 164,000 sq km. It was erupted between 17.5 and 6 Ma, as measured by K-Ar and Ar-40/Ar-39 dates. Early eruptions formed the Imnaha Basalt. More than 85 percent of the group was produced during a 1.5 my period between 17 and 15.5 Ma, forming the Grande Ronde and greatly subordinate Picture Gorge Basalts. Later flows formed the Wanapum Basalt, which includes the well-known Roza Member, and the Saddle Mountains Basalt. Linear vent systems for many of the flows are known and are located only in the eastern third of the Columbia Plateau. No systematic migration of vents occurred throughout the 11.5 my period of activity; this and other considerations make it unlikely that the province is related to a hot spot. Model calculations based on observations that little cooling occurred during flow of hundreds of kilometers suggest eruption and emplacement durations of a few days. Some voluminous flows occur in all formations, but most such flows apparently were erupted during Grande Ronde time. The eruption and emplacement of more than 1,000 cu km of 1100 C basaltic lava on the surface within several days doubtless had at least local meteorologic effects. Whether the effects were broader can at present only be hypothesized. Grande Ronde Basalt and Picture Gorge Basalts contain moderately common but thin sedimentary interbeds between flows, whereas earlier and later formations contain numerous, locally thick sediment accumulations. Volcaniclastic debris derived from extra-plateau sources commonly occurs in the testbeds.

  3. Tracing volatile loss during the eruption of individual flood basalt flows in the Columbia River Flood Basalt Province

    NASA Astrophysics Data System (ADS)

    Burton, K. W.; Vye, C.; Gannoun, A.; Self, S.

    2010-12-01

    Continental flood basalt (CFB) volcanism is characterised by the repeated eruption of huge batches of magma, producing enormous basalt provinces (105-106 km3) over relatively brief intervals of time, and delivering large masses of volcanic gas to the atmosphere. The release of gases and aerosols during CFB volcanism is thought to have had a significant impact on the atmosphere, ocean chemistry and climate [1-3]. The key factors influencing atmospheric chemistry and the environmental impact of CFB eruptions are the timing, mechanism and duration of volatile release during individual eruptions, but for the most part such information remains poorly known. The 187Re-187Os isotope system offers a highly sensitive tracer of the evolution of melt chemistry, and of the timing and mechanism of volatile release. This is partly because the contrasting behaviour of Re and Os during melting results in the extreme fractionation of parent/daughter (Re/Os) isotope ratios, thus magmatic phases can yield precise chronological information, and crustal rocks develop highly radiogenic isotope compositions that can be readily traced if assimilated [4]. Partly also because Re behaves as a highly volatile element during sub-aerial volcanism [5]. This study presents 187Re-187Os isotope data for rocks and minerals from two flows in the Columbia River Flood Basalt Group, one of the youngest flood basalt provinces that formed over a 2 million year interval in the Mid-Miocene. The 2,660 km3 Sand Hollow flow field displays small major and trace element variations, both laterally and vertically across the flow, indicative of fractional crystallisation, but the elemental data cannot be used to distinguish source variations and/or crustal contamination. However, Os isotopes indicate systematic crustal contamination over the timescale of an individual eruption, where the earliest formed lavas show the greatest degree of contamination. Isotope and elemental data for phenocryst phases from the 40

  4. Deep Crustal Structure beneath Large Igneous Provinces and the Petrologic Evolution of Flood Basalts

    NASA Astrophysics Data System (ADS)

    Richards, M. A.; Ridley, V. A.

    2010-12-01

    We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (Vp ~6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ~5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp~7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hotspots such as Hawaii, the Marquesas, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ~6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ~15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as “underplating,” are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better

  5. Deep Crustal Structure beneath Large Igneous Provinces and the Petrologic Evolution of Flood Basalts

    NASA Astrophysics Data System (ADS)

    Richards, Mark; Ridley, Victoria

    2010-05-01

    We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (Vp ~6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ~5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp~7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hotspots such as Hawaii, the Marqueses, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ~6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ~15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as "underplating," are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better

  6. Deep crustal structure beneath large igneous provinces and the petrologic evolution of flood basalts

    NASA Astrophysics Data System (ADS)

    Ridley, Victoria A.; Richards, Mark A.

    2010-09-01

    We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (Vp ˜ 6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ˜5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (Vp ˜ 7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hot spots such as Hawaii, the Marquesas, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ˜6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ˜15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as "underplating," are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby

  7. Continental Flood Basalts of Bennett Island, East Siberian Sea: High Arctic Geodynamics

    NASA Astrophysics Data System (ADS)

    Tegner, Christian; Pease, Victoria

    2014-05-01

    Volcanism provides a means of tracing mantle melting events and crustal evolution. The High Arctic includes a rich portfolio of volcanic rocks outcropping in the Circum-Arctic borderlands and imaged geophysically beneath the Alpha-Mendeleev Ridge that have been lumped together as a High-Arctic Large Igneous Province (HALIP). However, the ages (c. 440-60 Ma) and compositions (tholeiitic-alkaline-calc-alkaline) reported varies considerably and geological correlations remain elusive. One of the possible correlative events is the formation of continental flood basalts and sills in the Canadian Arctic Islands, Svalbard, Franz Josef Land and Bennett Island. These flood basalts have previously been linked to mantle plume melting and may represent a short-lived LIP event at c. 124-122 Ma. We present new data for a 350 m thick continental flood basalt succession at Bennett Island examined during fieldwork in Septemer 2013 on a joint Russian (VSEGEI) - Swedish (SWEDARCTIC) expedition to the De Long Archipelago. This volcanic succession is composed of 20 near-horisontal, undeformed flow units overlying a thin sedimentary succession of Cretaceous age (?) including coal seams and possibly volcaniclastic material that, in turn, unconformably overlies a more steeply dipping succession of Cambrian and Ordovician sediments. The flows are thinnest (c. 2-10 m) and aphyric to very-sparsely olivine-phyric in the lower portion. In contrast, the flows in the upper portion are thicker (>20 m) and aphyric to sparsely plagioclase-phyric. We will discuss new petrographic and compositional data for the Bennett Island flood basalts, possibly including new U-Pb age data. The aim is to evaluate their petrogenesis, to discuss their possible correlation to the flood basalt and sill successions of the Canadian Arctic Islands, Svalbard and Franz Josef Land and evaluate the geodynamic evolution of the High Arctic.

  8. Basaltic Lava Flow vs. Welded Basaltic Ignimbrite: Determining the Depositional Nature of a Volcanic Flow in the Akaroa Volcanic Complex

    NASA Astrophysics Data System (ADS)

    Sexton, E. A.; Hampton, S.

    2014-12-01

    Welded basaltic ignimbrites are one of the rarest forms of ignimbrites found on Earth and can often have characteristics that are indistinguishable from those of basaltic lava flows. This study evaluates a basaltic volcanic flow in a coastal cliff sequence in Raupo Bay, Akaroa Volcanic Complex, Banks Peninsula, New Zealand. The Raupo Bay coastal cliff sequence is comprised of 4 units, termed L1, L2, L3, and A, capped by loess. L1 and L2 are basaltic lavas, L3 proximal scoria deposits, which thin inland, and Unit A, a flow with unusual characteristics, which is the focus of this study. Field mapping, sampling, geochemical analysis and petrology were utilized to characterize units. Further detailed structural analysis of Unit A was completed, to determine the nature of the basal contact, variations in welding throughout the unit and the relationship of the layer to the underlying topography. From these analyses it was found: Unit A is thickest in a paleo-valley and thins and mantles higher topography, welding in the unit increases downwards forming topographic controlled columnar jointing, the top of the unit is brecciated and grades into the lower welded/jointed portion, the basal contact is sharp overlying a regional airfall deposit, the unit has a notably distinct geochemical composition from the underlying stratigraphic units, Unit A contains flattened and sheared scoria clasts, has aligned bubbles, and lava lithics. Further thin section analysis of Unit A identified flattened clast boundaries and microlite rimming around phenocrysts. In comparing these features to previous studies on basaltic lavas and ignimbrites it is hypothesized that Unit A is a welded basaltic ignimbrite that was channelized by paleo-topography on the outer flanks of the Akaroa Volcanic Complex. This study furthers the characterization of basaltic ignimbrites and is the first to recognize basaltic ignimbrites within the Akaroa Volcanic Complex.

  9. Basaltic Volcanism and Ancient Planetary Crusts

    NASA Technical Reports Server (NTRS)

    Shervais, John W.

    1993-01-01

    The purpose of this project is to decipher the origin of rocks which form the ancient lunar crust. Our goal is to better understand how the moon evolved chemically and, more generally, the processes involved in the chemical fractionation of terrestrial planetoids. This research has implications for other planetary bodies besides the Moon, especially smaller planetoids which evolved early in the history of the solar system and are now thermally stable. The three main areas focused on in our work (lunar mare basalts, KREEP basalts, and plutonic rocks of the lunar highlands) provide complementary information on the lunar interior and the processes that formed it.

  10. Thermal models for basaltic volcanism on Io

    USGS Publications Warehouse

    Keszthelyil, L.; McEwen, A.

    1997-01-01

    We present a new model for the thermal emissions from active basaltic eruptions on Io. While our methodology shares many similarities with previous work, it is significantly different in that (1) it uses a field tested cooling model and (2) the model is more applicable to pahoehoe flows and lava lakes than fountain-fed, channelized, 'a'a flows. This model demonstrates the large effect lava porosity has on the surface cooling rate (with denser flows cooling more slowly) and provides a preliminary tool for examining some of the hot spots on Io. The model infrared signature of a basaltic eruption is largely controlled by a single parameter, ??, the average survival time for a lava surface. During an active eruption surfaces are quickly covered or otherwise destroyed and typical values of ?? for a basaltic eruption are expected to be on the order of 10 seconds to 10 minutes. Our model suggests that the Galileo SSI eclipse data are consistent with moderately active to quiescent basaltic lava lakes but are not diagnostic of such activity. Copyright 1997 by the American Geophysical Union.

  11. Bimodal magmatism, basaltic volcanic styles, tectonics, and geomorphic processes of the eastern Snake River Plain, Idaho

    USGS Publications Warehouse

    Hughes, S.S.; Smith, R.P.; Hackett, W.R.; McCurry, M.; Anderson, S.R.; Ferdock, G.C.

    1997-01-01

    Geology presented in this field guide covers a wide spectrum of internal and surficial processes of the eastern Snake River Plain, one of the largest components of the combined late Cenozoic igneous provinces of the western United States. Focus is on widespread Quaternary basaltic plains volcanism that produced coalescent shields and complex eruptive centers that yielded compositionally evolved magmas. The guide is constructed in several parts beginning with discussion sections that provide an overview of the geology followed by road directions, with explanations, for specific locations. The geology overview briefly summarizes the collective knowledge gained, and petrologic implications made, over the past few decades. The field guide covers plains volcanism, lava flow emplacement, basaltic shield growth, phreatomagmatic eruptions, and complex and evolved eruptive centers. Locations and explanations are also provided for the hydrogeology, groundwater contamination, and environmental issues such as range fires and cataclysmic floods associated with the region.

  12. An oceanic flood basalt province within the Caribbean plate

    NASA Astrophysics Data System (ADS)

    Sinton, C. W.; Duncan, R. A.; Storey, M.; Lewis, J.; Estrada, J. J.

    1998-02-01

    The thick oceanic crust of the Caribbean plate appears to be the tectonized remnant of an eastern Pacific oceanic plateau that has been inserted between North and South America. The emplacement of the plateau into its present position has resulted in the obduction and exposure of its margins, providing an opportunity to study the age relations, internal structure and compositional features of the plateau. We present the results of 40Ar- 39Ar radiometric dating, major-, trace-element, and isotopic compositions of basalts from some of the exposed sections as well as drill core basalt samples from Leg 15 of the Deep Sea Drilling Project. Five widely spaced, margin sections yielded ages ranging from 91 to 88 Ma. Less well-constrained radiometric ages from the drill cores, combined with the biostratigraphic age of surrounding sediments indicate a minimum crystallization age of ˜90 Ma in the Venezuelan Basin. The synchroneity of ages across the region is consistent with a flood basalt origin for the bulk of the Caribbean plateau (i.e., large volume, rapidly erupted, regionally extensive volcanism). The ages and compositions are also consistent with plate reconstructions that place the Caribbean plateau in the vicinity of the Galápagos hotspot at its inception. The trace-element and isotopic compositions of the ˜90 Ma rocks indicate a depleted mantle and an enriched, plume-like mantle were involved in melting to varying degrees across the plateau. Within the same region, a volumetrically secondary, but widespread magmatic event occurred at 76 Ma, as is evident in Curaçao, western Colombia, Haiti, and at DSDP Site 152/ODP Site 1001 near the Hess Escarpment. Limited trace-element data indicate that this phase of magmatism was generally more depleted than the first. We speculate that magmatism may have resulted from upwelling of mantle, still hot from the 90 Ma event, during lithospheric extension attending gravitational collapse of the plateau, and/or tectonic

  13. An oceanic flood basalt province within the Caribbean plate

    NASA Astrophysics Data System (ADS)

    Estrada, J. J.; Lewis, J.; Storey, M.; Duncan, R. A.; Sinton, C. W.

    1998-02-01

    The thick oceanic crust of the Caribbean plate appears to be the tectonized remnant of an eastern Pacific oceanic plateau that has been inserted between North and South America. The emplacement of the plateau into its present position has resulted in the obduction and exposure of its margins, providing an opportunity to study the age relations, internal structure and compositional features of the plateau. We present the results of 40Ar-39Ar radiometric dating, major-, trace-element, and isotopic compositions of basalts from some of the exposed sections as well as drill core basalt samples from Leg 15 of the Deep Sea Drilling Project. Five widely spaced, margin sections yielded ages ranging from 91 to 88 Ma. Less well-constrained radiometric ages from the drill cores, combined with the biostratigraphic age of surrounding sediments indicate a minimum crystallization age of ~90 Ma in the Venezuelan Basin. The synchroneity of ages across the region is consistent with a flood basalt origin for the bulk of the Caribbean plateau (i.e., large volume, rapidly erupted, regionally extensive volcanism). The ages and compositions are also consistent with plate reconstructions that place the Caribbean plateau in the vicinity of the Galápagos hotspot at its inception. The trace-element and isotopic compositions of the ~90 Ma rocks indicate a depleted mantle and an enriched, plume-like mantle were involved in melting to varying degrees across the plateau. Within the same region, a volumetrically secondary, but widespread magmatic event occurred at 76 Ma, as is evident in Curaçao, western Colombia, Haiti, and at DSDP Site 152/ODP Site 1001 near the Hess Escarpment. Limited trace-element data indicate that this phase of magmatism was generally more depleted than the first. We speculate that magmatism may have resulted from upwelling of mantle, still hot from the 90 Ma event, during lithospheric extension attending gravitational collapse of the plateau, and/or tectonic emplacement

  14. Mantle and crustal contributions to continental flood volcanism

    USGS Publications Warehouse

    Arndt, N.T.; Czamanske, G.K.; Wooden, J.L.; Fedorenko, V.A.

    1993-01-01

    Arndt, N.T., Czamanske, G.K., Wooden, J.L. and Fedorenko, V.A., 1993. Mantle and crustal contributions to continental flood volcanism. In: M.J.R. Wortel, U. Hansen and R. Sabadini (Editors), Relationships between Mantle Processes and Geological Processes at or near the Earth's Surface. Tectonophysics, 223: 39-52. Most continental flood basalts are enriched in incompatible elements and have high initial 87Sr/86Sr ratios and low ??{lunate}Nd values. Many are depleted in Nb and Ta. The commonly-held view that these characteristics are inherited directly from a source in metasomatized lithospheric mantle is inconsistent with the following arguments: (1) thermomechanical modelling demonstrates that flood basalt magmas come mainly from an asthenospheric or plume source, with minimal direct melting of the continental lithospheric mantle. The low water contents of most flood basalts argue against proposals that hydrous lithosphere was the source. (2) Lithospheric mantle normally has low concentrations of incompatible elements, and chondrite-normalized Nb and Ta contents similar to those of other incompatible elements. Such material cannot be the unmodified source of Nb-Ta-depleted basalts such as those from the Karoo, Ferrar, or Columbia River provinces. We suggest there are two main controls on the compositions of continental flood basalts. The first is lithospheric thickness, which strongly influences the depth and degree of mantle melting of a plume or asthenospheric source, and thus has an important influence on the composition of primary magmas. All liquids formed by partial melting of peridotite at sub-lithosphere depths are highly magnesian (20-25 wt.% MgO) but have variable trace-element contents. Where the lithosphere is thick, the source melts at high pressure, garnet is present, the degree of melting is low, and trace-element concentrations are high. This type of magma evolves to produce the high-Ti type of continental flood basalt. Where the lithosphere is

  15. Mafic volcaniclastic deposits in flood basalt provinces: A review

    NASA Astrophysics Data System (ADS)

    Ross, P.-S.; Ukstins Peate, I.; McClintock, M. K.; Xu, Y. G.; Skilling, I. P.; White, J. D. L.; Houghton, B. F.

    2005-07-01

    Flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks (mostly sills), with any pyroclastic rocks limited to silicic compositions. However, mafic volcaniclastic deposits (MVDs) exist in many provinces, and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions. The province where MVDs are the most voluminous—the Siberian Traps—is also the one temporally associated with the greatest Phanerozoic mass extinction. A lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established, but as a first step, this contribution reviews in some detail the current knowledge on MVDs for the provinces in which they are better known, i.e. the North Atlantic Igneous Province (including Greenland, the Faeroe Islands, the British Isles, and tephra layers in the North Sea basin and vicinity), the Ontong Java plateau, the Ferrar, and the Karoo. We also provide a brief overview of what is known about MVDs in other provinces such as the Columbia River Basalts, the Afro-Arabian province, the Deccan Traps, the Siberian Traps, the Emeishan, and an Archean example from Australia. The thickest accumulations of MVDs occur in flood basalt provinces where they underlie the lava pile (Faeroes: > 1 km, Ferrar province: ≥ 400 m, Siberian Traps: 700 m). In the Faeroes case, the great thickness of MVDs can be attributed to accumulation in a local sedimentary basin, but in the Ferrar and Siberian provinces the deposits are widespread (> 3 × 10 5 km 2 for the latter). On the Ontong Java plateau over 300 m of MVDs occur in one drill hole without any overlying lavas. Where the volcaniclastic deposits are sandwiched between lavas, their thickness is much less. In most of the cases reviewed, primary MVDs are predominantly of phreatomagmatic origin, as indicated by the clast assemblage generally consisting of

  16. Potential for Carbon Dioxide Sequestration in Flood Basalts

    SciTech Connect

    McGrail, B. PETER; Schaef, Herbert T.; Ho, Anita M.; Chien, Yi-Ju; Dooley, James J.; Davidson, Casie L.

    2006-12-01

    Flood basalts are a potentially important host medium for geologic sequestration of anthropogenic CO2. Most lava flows have flow tops that are porous, permeable, and have enormous capacity for storage of CO2. Interbedded sediment layers and dense low-permeability basalt rock overlying sequential flows may act as effective seals allowing time for mineralization reactions to occur. Laboratory experiments confirm relatively rapid chemical reaction of CO2-saturated pore water with basalts to form stable carbonate minerals. Calculations suggest a sufficiently short time frame for onset of carbonate precipitation after CO2 injection that verification of in situ mineralization rates appears feasible in field pilot studies. If proven viable, major flood basalts in the U.S. and India would provide significant additional CO2 storage capacity and additional geologic sequestration options in certain regions where more conventional storage options are limited.

  17. CASERTZ aeromagnetic data reveal late Cenozoic flood basalts (?) in the West Antarctic rift system

    USGS Publications Warehouse

    Behrendt, John C.

    1994-01-01

    The late Cenozoic volcanic and tectonic activity of the enigmatic West Antarctic rift system, the least understood of the great active continental rifts, has been suggested to be plume driven. In 1991-1992, as part of the CASERTZ (Corridor Aerogeophysics of the Southeast Ross Transect Zone) program, an ~25 000 km aeromagnetic survey over the ice-covered Byrd subglacial basin shows magnetic "texture' critical to interpretations of the underlying extended volcanic terrane. The aeromagnetic data reveal numerous semicircular anomalies ~100-1100 nT in amplitude, interpreted as having volcanic sources at the base of the ice sheet; they are concentrated along north-trending magnetic lineations interpreted as rift fabric. The CASERTZ aeromagnetic results, combined with >100 000 km of widely spaced aeromagnetic profiles, indicate at least 106 km3 of probable late Cenozoic volcanic rock (flood basalt?) in the West Antarctic rift beneath the ice sheet and Ross Ice Shelf. -from Authors

  18. Crustal influence in the generation of continental flood basalts

    NASA Technical Reports Server (NTRS)

    Carlson, R. W.; Lugmair, G. W.; Macdougall, J. D.

    1981-01-01

    The suggestion that primordial undifferentiated material may exist in the earth's mantle has recently been revived on the strength of Nd isotope data for two types of young continental rocks - flood basalts and kimberlites. The limited published data show a clustering of Nd isotopic compositions close to those for meteorites with chondritic relative rare-earth (REE) abundance. In contrast, data are presented for samples from the Columbia flood basalt province of the northwestern United States which show large isotopic variability suggestive of mixing processes acting after the separation of the primary magmas from their mantle source.

  19. Intracanyon basalt lavas of the Debed River (northern Armenia), part of a Pliocene-Pleistocene continental flood basalt province in the South Caucasus

    NASA Astrophysics Data System (ADS)

    Sheth, Hetu; Meliksetian, Khachatur; Gevorgyan, Hripsime; Israyelyan, Arsen; Navasardyan, Gevorg

    2015-03-01

    Late Pliocene to Early Pleistocene (~ 3.25-2.05 Ma), 200-400 m thick basalt lavas outcrop in the South Caucasus region, including the Kars-Erzurum Plateau (northeastern Turkey), the Javakheti Plateau (Georgia-Armenia), and the Lori Plateau (northern Armenia). These fissure-fed, rapidly erupted fluid lavas filled pre-existing river valleys over many tens of kilometres. The basalts exposed in the Debed River canyon, northern Armenia, are ~ 200 m thick and of three morphological types: (1) basal pillow basalts and hyaloclastites, overlain by (2) columnar-jointed pahoehoe sheet flows, in turn overlain by (3) slabby pahoehoe and rubbly pahoehoe flows. The lower and middle lavas show evidence for damming of river drainage, like many lavas of the Columbia River flood basalt province, Scotland, Ireland, and Iceland. There is also evidence for syn-volcanic faulting of the early lavas. Related basalts also outcrop in the Gegham Uplands and the Hrazdan River basin in Armenia. This 3.25-2.05 Ma South Caucasus basalt province, covering parts of Turkey, Georgia and Armenia, has an estimated areal extent of ~ 15,000 km2 and volume of ~ 2250 km3. Because its main geological features are remarkably like those of many continental flood basalt (CFB) provinces, we consider it a true, albeit small, CFB province. It is the smallest and youngest CFB in the world. An analogue closely similar in major features is the Late Miocene Altos de Jalisco CFB province in the western Trans-Mexican Volcanic Belt. Both provinces formed during lithospheric pull-apart and transtensional faulting. Their broader significance is in showing flood basalt size distribution to be a continuum without natural breaks, with implications for geodynamic models.

  20. A mantle plume beneath California? The mid-Miocene Lovejoy Flood Basalt, northern California

    USGS Publications Warehouse

    Garrison, N.J.; Busby, C.J.; Gans, P.B.; Putirka, K.; Wagner, D.L.

    2008-01-01

    The Lovejoy basalt represents the largest eruptive unit identified in California, and its age, volume, and chemistry indicate a genetic affinity with the Columbia River Basalt Group and its associated mantle-plume activity. Recent field mapping, geochemical analyses, and radiometric dating suggest that the Lovejoy basalt erupted during the mid-Miocene from a fissure at Thompson Peak, south of Susanville, California. The Lovejoy flowed through a paleovalley across the northern end of the Sierra Nevada to the Sacramento Valley, a distance of 240 km. Approximately 150 km3 of basalt were erupted over a span of only a few centuries. Our age dates for the Lovejoy basalt cluster are near 15.4 Ma and suggest that it is coeval with the 16.1-15.0 Ma Imnaha and Grande Ronde flows of the Columbia River Basalt Group. Our new mapping and age dating support the interpretation that the Lovejoy basalt erupted in a forearc position relative to the ancestral Cascades arc, in contrast with the Columbia River Basalt Group, which erupted in a backarc position. The arc front shifted trenchward into the Sierran block after 15.4 Ma. However, the Lovejoy basalt appears to be unrelated to volcanism of the predominantly calc-alkaline Cascade arc; instead, the Lovejoy is broadly tholeiitic, with trace-element characteristics similar to the Columbia River Basalt Group. Association of the Lovejoy basalt with mid-Miocene flood basalt volcanism has considerable implications for North American plume dynamics and strengthens the thermal "point source" explanation, as provided by the mantle-plume hypothesis. Alternatives to the plume hypothesis usually call upon lithosphere-scale cracks to control magmatic migrations in the Yellowstone-Columbia River basalt region. However, it is difficult to imagine a lithosphere-scale flaw that crosses Precambrian basement and accreted terranes to reach the Sierra microplate, where the Lovejoy is located. Therefore, we propose that the Lovejoy represents a rapid

  1. Origin of Columbia River flood basalt controlled by propagating rupture of the Farallon slab.

    PubMed

    Liu, Lijun; Stegman, Dave R

    2012-02-16

    The origin of the Steens-Columbia River (SCR) flood basalts, which is presumed to be the onset of Yellowstone volcanism, has remained controversial, with the proposed conceptual models involving either a mantle plume or back-arc processes. Recent tomographic inversions based on the USArray data reveal unprecedented detail of upper-mantle structures of the western USA and tightly constrain geodynamic models simulating Farallon subduction, which has been proposed to influence the Yellowstone volcanism. Here we show that the best-fitting geodynamic model depicts an episode of slab tearing about 17 million years ago under eastern Oregon, where an associated sub-slab asthenospheric upwelling thermally erodes the Farallon slab, leading to formation of a slab gap at shallow depth. Driven by a gradient of dynamic pressure, the tear ruptured quickly north and south and within about two million years covering a distance of around 900 kilometres along all of eastern Oregon and northern Nevada. This tear would be consistent with the occurrence of major volcanic dikes during the SCR-Northern Nevada Rift flood basalt event both in space and time. The model predicts a petrogenetic sequence for the flood basalt with sources of melt starting from the base of the slab, at first remelting oceanic lithosphere and then evolving upwards, ending with remelting of oceanic crust. Such a progression helps to reconcile the existing controversies on the interpretation of SCR geochemistry and the involvement of the putative Yellowstone plume. Our study suggests a new mechanism for the formation of large igneous provinces. PMID:22337059

  2. Age distribution of Serra Geral (Paraná) flood basalts, southern Brazil

    USGS Publications Warehouse

    Fodor, R.V.; McKee, E.H.; Roisenberg, A.

    1989-01-01

    We evaluated 193 K-Ar ages (10 newly determined) of basaltic and differentiated rocks of the Serra Geral (Paraná) flood-basalt province for indications of magmatism occurring systematically with progressive rifting and complete separation ( ≈130-105 Ma) of South America from Africa. The K-Ar ages represent basalt emplacement between 35° and 19°S covering about 1,200,000 km2. We note that volcanism appears ubiquitous across the province between about 140 and 115 Ma, and that there are no significant age differences within that relate directly to progressive south-to-north tectonism. On the other hand, the oldest samples, about 140–160 Ma, are among those nearest the Brazil coastline (rift margin), perhaps suggesting migration of activity away from the rift with time. Studies of other flood-basalt provinces now indicate short (<3 m.y.) eruption periods, thereby pointing to the need for re-examination of Serra Geral ages by 40Ar-39Ar incremental heating techniques.

  3. Rapid eruption of the siberian traps flood basalts at the permo-triassic boundary.

    PubMed

    Renne, P R; Basu, A R

    1991-07-12

    The Siberian Traps represent one of the most voluminous flood basalt provinces on Earth. Laser-heating (40)Ar/(39)Ar data indicate that the bulk of these basalts was erupted over an extremely short time interval (900,000 +/- 800,000 years) beginning at about 248 million years ago at mean eruption rates of greater than 1.3 cubic kilometers per year. Such rates are consistent with a mantle plume origin. Magmatism was not associated with significant lithospheric rifting; thus, mantle decompression resulting from rifting was probably not the primary cause of widespread melting. Inception of Siberian Traps volcanism coincided (within uncertainty) with a profound faunal mass extinction at the Permo-Triassic boundary 249 +/- 4 million years ago; these data thus leave open the question of a genetic relation between the two events. PMID:17779134

  4. High-3He plume origin and temporal-spatial evolution of the Siberian flood basalts

    USGS Publications Warehouse

    Basu, A.R.; Poreda, R.J.; Renne, P.R.; Teichmann, F.; Vasiliev, Y.R.; Sobolev, N.V.; Turrin, B.D.

    1995-01-01

    An olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the Siberian flood basalt province (SFBP) yielded a 40ArX39Ar plateau age of 253.3 ?? 2.6 million years, distinctly older than the main tholeiitic pulse of the SFBP at 250.0 million years. Olivine phenocrysts of this rock showed 3He/4He ratios up to 12.7 times the atmospheric ratio; these values suggest a lower mantle plume origin. The neodymium and strontium isotopes, rare earth element concentration patterns, and cerium/lead ratios of the associated rocks were also consistent with their derivation from a near-cnondritic, primitive plume. Geochemical data from the 250-million-year-old volcanic rocks higher up in the sequence indicate interaction of this high-3He SFBP plume with a suboceanic-type upper mantle beneath Siberia.

  5. Twilight of a Volcanic Field: 11 Million Years of Basaltic Volcanism in the Southwestern Nevada Volcanic Field, USA

    NASA Astrophysics Data System (ADS)

    Perry, F. V.; Valintine, G. A.

    2007-12-01

    Following the end of major caldera-forming silicic volcanism in the Southwestern Nevada Volcanic Field (SNVF), at least 10 episodes of alkalic basaltic volcanism have occurred over the last ~11 Ma. An understanding of the past behavior of the volcanic field provides insight for forecasting future eruptive behavior for use in hazard assessment for the high-level radioactive waste repository at Yucca Mountain. A program of geophysics, drilling, Ar-Ar dating and geochemistry conducted since 2004 by Los Alamos National Laboratory and the U.S. Geological Survey, combined with previous and ongoing petrogenetic and physical volcanology studies, sheds more light on the early and middle evolution of the volcanic field, much of which has been buried in alluvial basins. Volumes of erupted basalt have drastically declined over the history of the field, from as much as 50 km3 in the Miocene to about 0.5 km3 in the Pleistocene. The volume decrease is accompanied by a drastic decrease in extension rate, suggesting a close link between magmatism and tectonism. Neodymium and strontium isotopic analyses indicate that enriched lithospheric mantle has been the source of basalt throughout the history of the field. Decreasing eruption volumes are accompanied by an approximate doubling of Ce/Yb ratios, indicating that the volume decrease reflects a decrease in degree of partial melting of the lithospheric source. Eruption style has also changed with time, reflecting an increase in magma volatile content, consistent with decreased amounts of partial melting of a volatile-bearing source. These observations are consistent with a model in which the lithospheric mantle source was hottest during the period of major silicic volcanism and the presence of an active subduction system. After the breakdown of subduction, continued thermal input into the lithosphere ceased, and the lithosphere began to conductively cool. Melt accumulation in non-convecting, static lithosphere is probably related to

  6. Petrophysical and geochemical properties of Columbia River flood basalt: Implications for carbon sequestration

    NASA Astrophysics Data System (ADS)

    Zakharova, Natalia V.; Goldberg, David S.; Sullivan, E. Charlotte; Herron, Michael M.; Grau, James A.

    2012-11-01

    This study presents borehole geophysical data and sidewall core chemistry from the Wallula Pilot Sequestration Project in the Columbia River flood basalt. The wireline logging data were reprocessed, core-calibrated and interpreted in the framework of reservoir and seal characterization for carbon dioxide storage. Particular attention is paid to the capabilities and limitations of borehole spectroscopy for chemical characterization of basalt. Neutron capture spectroscopy logging is shown to provide accurate concentrations for up to 8 major and minor elements but has limited sensitivity to natural alteration in fresh-water basaltic reservoirs. The Wallula borehole intersected 26 flows from 7 members of the Grande Ronde formation. The logging data demonstrate a cyclic pattern of sequential basalt flows with alternating porous flow tops (potential reservoirs) and massive flow interiors (potential caprock). The log-derived apparent porosity is extremely high in the flow tops (20-45%), and considerably overestimates effective porosity obtained from hydraulic testing. The flow interiors are characterized by low apparent porosity (0-8%) but appear pervasively fractured in borehole images. Electrical resistivity images show diverse volcanic textures and provide an excellent tool for fracture analysis, but neither fracture density nor log-derived porosity uniquely correlate with hydraulic properties of the Grande Ronde formation. While porous flow tops in these deep flood basalts may offer reservoirs with high mineralization rates, long leakage migration paths, and thick sections of caprock for CO2 storage, a more extensive multiwell characterization would be necessary to assess lateral variations and establish sequestration capacity in this reservoir.

  7. Petrophysical and Geochemical Properties of Columbia River Flood Basalt: Implications for Carbon Sequestration

    SciTech Connect

    Zakharova, Natalia V.; Goldberg, David S.; Sullivan, E. C.; Herron, Michael M.; Grau, Jim A.

    2012-11-02

    Abstract This study presents borehole geophysical data and sidewall core chemistry from the Wallula Pilot Sequestration Project in the Columbia River flood basalt. The wireline logging data were reprocessed, core-calibrated and interpreted in the framework of reservoir and seal characterization for carbon dioxide storage. Particular attention is paid to the capabilities and limitations of borehole spectroscopy for chemical characterization of basalt. Neutron capture spectroscopy logging is shown to provide accurate concentrations for up to 8 major and minor elements but has limited sensitivity to natural alteration in fresh-water basaltic reservoirs. The Wallula borehole intersected 26 flows from 7 members of the Grande Ronde formation. The logging data demonstrate a cyclic pattern of sequential basalt flows with alternating porous flow tops (potential reservoirs) and massive flow interiors (potential caprock). The log-derived apparent porosity is extremely high in the flow tops (20%-45%), and considerably overestimates effective porosity obtained from hydraulic testing. The flow interiors are characterized by low apparent porosity (0-8%) but appear pervasively fractured in borehole images. Electrical resistivity images show diverse volcanic textures and provide an excellent tool for fracture analysis, but neither fracture density nor log-derived porosity uniquely correlate with hydraulic properties of the Grande Ronde formation. While porous flow tops in these deep flood basalts may offer reservoirs with high mineralization rates, long leakage migration paths, and thick sections of caprock for CO2 storage, a more extensive multi- well characterization would be necessary to assess lateral variations and establish sequestration capacity in this reservoir.

  8. Neodymium isotopes in flood basalts from the Siberian Platform and inferences about their mantle sources

    PubMed Central

    DePaolo, D. J.; Wasserburg, G. J.

    1979-01-01

    The initial isotopic compositions of Nd and Sr in basalts from the Central Siberian Plateau and other major continental flood basalts are reported. The continental flood basalts appear to be the product of partial melting of mantle sources that consist of relatively primitive undifferentiated material and are clearly distinct from midocean ridge basalts, which sample mantle reservoirs that have been modified by extraction of continental crust earlier in earth history. These observations provide fundamental constraints on models of mantle structure and dynamics. Isotopic effects of crustal contamination are clearly recognizable in some continental flood basalts, but these effects can be distinguished from isotopic patterns inherited from the mantle magma sources. PMID:16592671

  9. Volcanic water flows could have flooded Ganymede's planetary rift system

    SciTech Connect

    Allison, M.L.; Clifford, S.M.

    1985-01-01

    Global expansion on Ganymede of only 1 or 2% created a planetary rift system which was resurfaced over a significant period of the planet's history creating bright, grooved terrain. The most reasonable model entails flooding of grabens by water or slush magmas which rose to the surface along normal faults in the rift system. Various models exist for the origin of the water magmas including isostatic rise of freezing ice I or diapirs of unstable ice III. A model considering the heat balance at the surface of an ice-covered water flow is constructed with the simplifying assumption that both laminar flow and a solid ice cover are achieved relatively soon after eruption. The ice cover will thicken until the underlying flowing water is entirely frozen. Energy into the system comes from solar radiation and the latent heat of freezing. Energy lost will be by evaporative and radiative cooling at the ice surface and by conduction into the substratum. Solving the heat balance allows a prediction for the volume of magma that can flood the surface. For example a flow 5 m thick will take tens of days to freeze, so that discharge rates equal to that of average terrestrial basalt flows could flood relatively large areas of the surface before freezing. Volcanic flooding is therefore a physically viable mechanism for the origin of bright terrain. During freezing the water/ice volume increases, lifting and fracturing the ice cover. These fractures may localize continued tectonic forces producing large displacements and creating the present grooved terrain.

  10. Assessing Eruption Column Height in Ancient Flood Basalt Eruptions

    NASA Technical Reports Server (NTRS)

    Glaze, Lori S.; Self, Stephen; Schmidt, Anja; Hunter, Stephen J.

    2015-01-01

    A buoyant plume model is used to explore the ability of flood basalt eruptions to inject climate-relevant gases into the stratosphere. An example from the 1986 Izu-Oshima basaltic fissure eruption validates the model's ability to reproduce the observed maximum plume heights of 12-16 km above sea level, sustained above fire-fountains. The model predicts maximum plume heights of 13-17 km for source widths of between 4-16 m when 32% (by mass) of the erupted magma is fragmented and involved in the buoyant plume (effective volatile content of 6 wt%). Assuming that the Miocene-age Roza eruption (part of the Columbia River Basalt Group) sustained fire-fountains of similar height to Izu-Oshima (1.6 km above the vent), we show that the Roza eruption could have sustained buoyant ash and gas plumes that extended into the stratosphere at approximately 45 deg N. Assuming 5 km long active fissure segments and 9000 Mt of SO2 released during explosive phases over a 10-15 year duration, the approximately 180 km of known Roza fissure length could have supported approximately 36 explosive events/phases, each with a duration of 3-4 days. Each 5 km fissure segment could have emitted 62 Mt of SO2 per day into the stratosphere while actively fountaining, the equivalent of about three 1991 Mount Pinatubo eruptions per day. Each fissure segment could have had one to several vents, which subsequently produced lava without significant fountaining for a longer period within the decades-long eruption. Sensitivity of plume rise height to ancient atmospheric conditions is explored. Although eruptions in the Deccan Traps (approximately 66 Ma) may have generated buoyant plumes that rose to altitudes in excess of 18 km, they may not have reached the stratosphere because the tropopause was substantially higher in the late Cretaceous. Our results indicate that some flood basalt eruptions, such as Roza, were capable of repeatedly injecting large masses of SO2 into the stratosphere. Thus sustained

  11. The mode of emplacement of Neogene flood basalts in eastern Iceland: Facies architecture and structure of simple aphyric basalt groups

    NASA Astrophysics Data System (ADS)

    Óskarsson, Birgir V.; Riishuus, Morten S.

    2014-12-01

    Simple flows (tabular) in the Neogene flood basalt sections of Iceland are described and their mode of emplacement assessed. The flows belong to three aphyric basalt groups: the Kumlafell group, the Hólmatindur group and the Hjálmadalur group. The groups can be traced over 50 km and originate in the Breiðdalur-Thingmuli volcanic zone. The groups have flow fields that display mixed volcanic facies architecture and can be classified after dominating type morphology. The Kumlafell and the Hólmatindur groups have predominantly simple flows of pāhoehoe and rubbly pāhoehoe morphologies with minor compound or lobate pāhoehoe flows. The Hjálmadalur group has simple flows of rubbly pāhoehoe, but also includes minor compound or lobate flows of rubble and 'a'ā. Simple flows are most common in the distal and medial areas from the vents, while more lobate flows in proximal areas. The simple flows are formed by extensive sheet lobes that are several kilometers long with plane-parallel contacts, some reaching thicknesses of ~ 40 m (aspect ratios < 0.01). They have overlapping contacts and are free of tubes and inflation structures. Their internal structure consists generally of a simple upper vesicular crust, a dense core and a thin basal vesicular zone. The brecciated flow-top is formed by clinker and crustal rubble, the clinker often welded or agglutinated. The simple flows erupted from seemingly short-lived fissures and have the characteristics of cooling-limited flows. We estimate the effusion rates to be ~ 105 m3/s for the simple flows of the Kumlafell and Hólmatindur groups and ~ 104 m3/s for the Hjálmadalur group. The longest flows advanced 15-20 km from the fissures, with lava streams of fast propagating flows inducing tearing and brecciation of the chilled crust. Compound or lobate areas appear to reflect areas of low effusion rates or the interaction of the lava with topographic barriers or wetlands, resulting in chaotic flowage. Slowing lobes with

  12. The age of parana flood volcanism, rifting of gondwanaland, and the jurassic-cretaceous boundary.

    PubMed

    Renne, P R; Ernesto, M; Pacca, I G; Coe, R S; Glen, J M; Prévot, M; Perrin, M

    1992-11-01

    The Paraná-Etendeka flood volcanic event produced approximately 1.5 x 10(6) cubic kilometers of volcanic rocks, ranging from basalts to rhyolites, before the separation of South America and Africa during the Cretaceous period. New (40)Ar/(39)Ar data combined with earlier paleomagnetic results indicate that Paraná flood volcanism in southern Brazil began at 133 +/- 1 million years ago and lasted less than 1 million years. The implied mean eruption rate on the order of 1.5 cubic kilometers per year is consistent with a mantle plume origin for the event and is comparable to eruption rates determined for other well-documented continental flood volcanic events. Paraná flood volcanism occurred before the initiation of sea floor spreading in the South Atlantic and was probably precipitated by uplift and weakening of the lithosphere by the Tristan da Cunha plume. The Parana event postdates most current estimates for the age of the faunal mass extinction associated with the Jurassic-Cretaceous boundary. PMID:17794593

  13. A brief Oligocene period of flood volcanism in Yemen: Implications for the duration and rate of continental flood volcanism at the Afro-Arabian triple junction

    USGS Publications Warehouse

    Baker, J.; Snee, L.; Menzies, M.

    1996-01-01

    40Ar39Ar dating of mineral separates and whole-rock (WR) samples has established that basaltic continental flood volcanism (CFV) began between 30.9 and 29.2 Ma in northwestern and southwestern Yemen, respectively. Rhyolitic volcanism commenced at 29.3-29.0 Ma throughout Yemen. Lower basaltic lavas were erupted every 10-100 kyr, whereas upper bimodal volcanic units were erupted every 100-500 kyr, which reflects generation of rhyolitic magmas from basalts that resided for longer periods in lithospheric magma chambers than during the early phase of exclusively mafic magmatism. The youngest dated flood volcanic units were erupted between 26.9 and 26.5 Ma throughout Yemen. The duration of preserved CFV defined by 40Ar/39Ar dating (4.4 myr) contrasts with the wide range of WR K-Ar dates previously obtained in Yemen (> 50 myr). 40Ar/39Ar step-heating studies of WR samples has shown that this discrepancy is due to the disturbed Ar systematics of volcanic samples. Most samples have experienced post-crystallization loss of radiogenic Ar and/or contain excess Ar, with only ca. 25% of the WR K-Ar dates within 1-2 myr of true crystallization ages. WR K-Ar data can be screened for reliability using the radiogenic Ar yield and 40K/36Ar ratio, which reflect the Ar retentivity of the sample, the likelihood that alteration has disturbed a sample's Ar systematics, and the susceptibility of the sample to a finite amount of Ar loss or the presence of a finite amount of excess Ar. Examination of existing WR K-Ar data in the Ethiopian part of this flood volcanic province, using these parameters, suggests that much of these data are also misleading. Two phases of flood volcanism are inferred in Ethiopia and Eritrea at 38-30 Ma and ca. 20 Ma. The older phase is equivalent to that in Yemen, and is consistent with the progression in basal volcanic ages obtained in Yemen moving from north to south. The younger phase is related to the onset of upper crustal extension and incipient Red Sea

  14. High water content in primitive continental flood basalts

    PubMed Central

    Xia, Qun-Ke; Bi, Yao; Li, Pei; Tian, Wei; Wei, Xun; Chen, Han-Lin

    2016-01-01

    As the main constituent of large igneous provinces, the generation of continental flood basalts (CFB) that are characterized by huge eruption volume (>105 km3) within short time span (<1–3 Ma) is in principle caused by an abnormally high temperature, extended decompression, a certain amount of mafic source rocks (e.g., pyroxenite), or an elevated H2O content in the mantle source. These four factors are not mutually exclusive. There are growing evidences for high temperature, decompression and mafic source rocks, albeit with hot debate. However, there is currently no convincing evidence of high water content in the source of CFB. We retrieved the initial H2O content of the primitive CFB in the early Permian Tarim large igneous province (NW China), using the H2O content of ten early-formed clinopyroxene (cpx) crystals that recorded the composition of the primitive Tarim basaltic melts and the partition coefficient of H2O between cpx and basaltic melt. The arc-like H2O content (4.82 ± 1.00 wt.%) provides the first clear evidence that H2O plays an important role in the generation of CFB. PMID:27143196

  15. High water content in primitive continental flood basalts

    NASA Astrophysics Data System (ADS)

    Xia, Qun-Ke; Bi, Yao; Li, Pei; Tian, Wei; Wei, Xun; Chen, Han-Lin

    2016-05-01

    As the main constituent of large igneous provinces, the generation of continental flood basalts (CFB) that are characterized by huge eruption volume (>105 km3) within short time span (<1–3 Ma) is in principle caused by an abnormally high temperature, extended decompression, a certain amount of mafic source rocks (e.g., pyroxenite), or an elevated H2O content in the mantle source. These four factors are not mutually exclusive. There are growing evidences for high temperature, decompression and mafic source rocks, albeit with hot debate. However, there is currently no convincing evidence of high water content in the source of CFB. We retrieved the initial H2O content of the primitive CFB in the early Permian Tarim large igneous province (NW China), using the H2O content of ten early-formed clinopyroxene (cpx) crystals that recorded the composition of the primitive Tarim basaltic melts and the partition coefficient of H2O between cpx and basaltic melt. The arc-like H2O content (4.82 ± 1.00 wt.%) provides the first clear evidence that H2O plays an important role in the generation of CFB.

  16. High water content in primitive continental flood basalts.

    PubMed

    Xia, Qun-Ke; Bi, Yao; Li, Pei; Tian, Wei; Wei, Xun; Chen, Han-Lin

    2016-01-01

    As the main constituent of large igneous provinces, the generation of continental flood basalts (CFB) that are characterized by huge eruption volume (>10(5) km(3)) within short time span (<1-3 Ma) is in principle caused by an abnormally high temperature, extended decompression, a certain amount of mafic source rocks (e.g., pyroxenite), or an elevated H2O content in the mantle source. These four factors are not mutually exclusive. There are growing evidences for high temperature, decompression and mafic source rocks, albeit with hot debate. However, there is currently no convincing evidence of high water content in the source of CFB. We retrieved the initial H2O content of the primitive CFB in the early Permian Tarim large igneous province (NW China), using the H2O content of ten early-formed clinopyroxene (cpx) crystals that recorded the composition of the primitive Tarim basaltic melts and the partition coefficient of H2O between cpx and basaltic melt. The arc-like H2O content (4.82 ± 1.00 wt.%) provides the first clear evidence that H2O plays an important role in the generation of CFB. PMID:27143196

  17. Continental flood basalts derived from the hydrous mantle transition zone.

    PubMed

    Wang, Xuan-Ce; Wilde, Simon A; Li, Qiu-Li; Yang, Ya-Nan

    2015-01-01

    It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can potentially account for the chemical diversity of many continental flood basalts. PMID:26169260

  18. Asteroid/comet impact clusters, flood basalts and mass extinctions: Significance of isotopic age overlaps

    NASA Astrophysics Data System (ADS)

    Glikson, Andrew

    2005-08-01

    Morgan et al. [J. Phipps Morgan, T.J. Reston, C.R. Ranero. Earth Planet. Sci. Lett. 217 (2004) 263-284.], referring to an overlap between the isotopic ages of volcanic events and four epoch/stage extinction boundaries, suggest a dominant role of Continental Flood Basalts (CFB) and of explosive CO 2-rich volcanic pipes ("Verneshots") as mass extinction triggers. Here I point out that Morgan et al. overlook 3 overlaps between the ages of extraterrestrial impacts, volcanic and mass extinction events, and 3 overlaps between the ages of extraterrestrial impact and volcanic events. These overlaps suggest that both extraterrestrial impacts and volcanism served as extinction triggers separately or in combination. A protracted impact cluster overlaps extinctions at the end-Devonian (˜374-359 Ma) and impact-extinction age overlaps occur in the end-Jurassic (˜145-142 Ma), Aptian (˜125-112 Ma); Cenomanian-Turonian (˜95-94 Ma); K-T boundary (˜65.5 Ma) and mid-Miocene (˜16 Ma) ( Table 1). Morgan et al. appear to question the uniqueness of shock metamorphic and geochemical criteria used to identify asteroid/comet impacts. However, shock pressures at 8-35 GPa, indicated by intra-crystalline planar deformation features (PDF), exceed lithospheric and volcanic explosion pressures by an order of magnitude and are not known to be associated with explosive volcanic diatremes, kimberlites or lamproites. These authors make reference to apparent iridium anomalies of volcanic origin. However, platinum group element (PGE) abundance levels, volatile/refractory PGE ratios, and Cr and Os isotopes of meteoritic materials are clearly distinct from those of terrestrial volcanics. Given a Phanerozoic time-integrated oceanic/continent crustal ratio > 2.5 and the difficulty in identifying oceanic impacts, I suggest the effects of large impacts on thin thermally active oceanic crust-capable of triggering regional to global mafic volcanic events and ensuing environmental effects-provide an

  19. Diary of a flood basalt: A stratigraphic tour of two sections within the Oligocene Ethiopian Traps

    NASA Astrophysics Data System (ADS)

    Rooney, T. O.; Bradley, B. L.; Krans, S. R.; Kappelman, J. W.; Yirgu, G.; Ayalew, D.

    2015-12-01

    Flood basalts are the most significant magmatic events on the planet, influencing our environment by modifying the lithosphere and atmosphere. Our understanding of flood basalt processes comes almost entirely from within the rock record - typically a vast pile of basaltic lavas, hiatuses, and sedimentary horizons. Stratigraphic continuity is thus a critical characteristic to constrain the processes associated with the formation of flood basalt provinces. Oceanic flood basalts are difficult to access in situ, leaving continental equivalents our primary target. The Oligocene Ethiopian Traps is among the youngest and most intact flood basalt provinces, making this a premier region to examine flood basalt stratigraphy. Leveraging recent road building, we have constructed a flow by flow stratigraphy for two ~1500m independent sections of the Low-Ti region of the Ethiopian traps, separated by ~70 km. These sections lie towards the edge of the modern exposure of the Ethiopian flood basalts, however the remarkable parallelism of flows and the lack of evidence of pinching suggests that the province was significantly more aerially extensive towards the west. For the most continuous ~1200m section, median flow thickness is about ~15m in the lower ~400m and upper ~400m of the flood basalt sequence, but flows thin significantly to a median of 4m in the central portion of this sequence. The petrography shows distinctive patterns through the pile: largely aphyric and clinopyroxene/olivine phyric flows are more common towards the base of the sequence and transition to largely plagioclase phyric basalts. At the top of the flood basalt pile a further transition from plagioclase phyric to largely aphyric flows is observed. Paleosols become more frequent and are thicker towards the top of the sequence. These observations point to a gradual temporal shift in the differentiation depths and flux of magmas entering the Ethiopian lithosphere.

  20. Geochronology and petrology of Cretaceous basaltic magmatism in the Kwanza basin (western Angola), and relationships with the Paranà-Etendeka continental flood basalt province

    NASA Astrophysics Data System (ADS)

    Marzoli, A.; Melluso, L.; Morra, V.; Renne, P. R.; Sgrosso, I.; D'Antonio, M.; Duarte Morais, L.; Morais, E. A. A.; Ricci, G.

    1999-11-01

    Early Cretaceous tholeiites of the Kwanza basin, western Angola, 300 km South of Luanda, are evolved basalts to basaltic andesites, characterized by low TiO 2 (<2 wt%) and incompatible element contents. Their petrographical, major and trace element and Sr-isotopic (0.70448-0.70752) compositions are similar to those of tholeiites of the Paranà-Etendeka flood basalt province, particularly to those of the southern sector. While inland analogues, i.e. northern Paranà tholeiites are high-TiO 2 basalts, Kwanza tholeiites in western Angola, and flood tholeiites of the Campos marginal basin and Cabo Frio dolerites in southeastern Brazil, define a low-TiO 2 (<2 wt%) basalt 'belt' in the northernmost Paranà-Etendeka. The main pulse of tholeiitic magmatism in the Kwanza basin (131.9±1.6 and 131.6±1.4 Ma, 40Ar/ 39Ar plateau ages), is contemporaneous with flood volcanism in the Paranà-Etendeka (133-131 Ma), which therefore extends by c. 400 km more to the N-E than previously recognized. Slightly younger Kwanza coast-parallel tholeiitic dykes have an age of 126.1±1.4 Ma, similar to those of other coast-parallel dyke swarms in Brazil and Namibia, and are probably associated with the main rifting stages. A younger magmatic episode in central-western Angola is represented by Late Cretaceous sodic alkaline and transitional volcanic rocks. They are intercalated in Late Cretaceous marine sediments, and one alkaline basalt was dated at 91±2 Ma. Alkaline and transitional rocks have similar, OIB-like incompatible element patterns with mantle normalized Nb/K and Nb/La>1.0. Initial 87Sr/ 86Sr ranges from 0.70297 to 0.70302 and from 0.70287 to 0.70495 for alkaline and transitional rocks, respectively. Sodic alkaline and transitional rocks from the Kwanza basin differ in composition from most coeval alkaline rocks of southeastern Brazil, which are of potassic type.

  1. The source and longevity of sulfur in an Icelandic flood basalt eruption plume

    NASA Astrophysics Data System (ADS)

    Ilyinskaya, Evgenia; Edmonds, Marie; Mather, Tamsin; Schmidt, Anja; Hartley, Margaret; Oppenheimer, Clive; Pope, Francis; Donovan, Amy; Sigmarsson, Olgeir; Maclennan, John; Shorttle, Oliver; Francis, Peter; Bergsson, Baldur; Barsotti, Sara; Thordarson, Thorvaldur; Bali, Eniko; Keller, Nicole; Stefansson, Andri

    2015-04-01

    The Holuhraun fissure eruption (Bárðarbunga volcanic system, central Iceland) has been ongoing since 31 August 2014 and is now the largest in Europe since the 1783-84 Laki event. For the first time in the modern age we have the opportunity to study at first hand the environmental impact of a flood basalt fissure eruption (>1 km3 lava). Flood basalt eruptions are one of the most hazardous volcanic scenarios in Iceland and have had enormous societal and economic consequences across the northern hemisphere in the past. The Laki eruption caused the deaths of >20% of the Icelandic population by environmental pollution and famine and potentially also increased European levels of mortality through air pollution by sulphur-bearing gas and aerosol. A flood basalt eruption was included in the UK National Risk Register in 2012 as one of the highest priority risks. The gas emissions from Holuhraun have been sustained since its beginning, repeatedly causing severe air pollution in populated areas in Iceland. During 18-22 September, SO2 fluxes reached 45 kt/day, a rate of outgassing rarely observed during sustained eruptions, suggesting that the sulfur loading per kg of erupted magma exceeds both that of other recent eruptions in Iceland and perhaps also other historic basaltic eruptions globally. This raises key questions regarding the origin of these prodigious quantities of sulphur. A lack of understanding of the source of this sulfur, the conversion rates of SO2 gas into aerosol, the residence times of aerosol in the plume and the dependence of these on meteorological factors is limiting our confidence in the ability of atmospheric models to forecast gas and aerosol concentrations in the near- and far-field from Icelandic flood basalt eruptions. In 2015 our group is undertaking a project funded by UK NERC urgency scheme to investigate several aspects of the sulfur budget at Holuhraun using a novel and powerful approach involving simultaneous tracking of sulfur and

  2. Whole rock major element chemistry of KREEP basalt clasts in lunar breccia 15205: Implications for the petrogenesis of volcanic KREEP basalts

    NASA Technical Reports Server (NTRS)

    Vetter, Scott K.; Shervais, John W.

    1993-01-01

    KREEP basalts are a major component of soils and regolith at the Apollo 15 site. Their origin is controversial: both endogenous (volcanic) and exogenous (impact melt) processes have been proposed, but it is now generally agreed that KREEP basalts are volcanic rocks derived from the nearby Apennine Bench formation. Because most pristine KREEP basalts are found only as small clasts in polymict lunar breccias, reliable chemical data are scarce. The primary aim of this study is to characterize the range in chemical composition of pristine KREEP basalt, and to use these data to decipher the petrogenesis of these unique volcanic rocks.

  3. Age and Duration of the Paraná-Etendeka Flood Basalts and Related Plumbing System

    NASA Astrophysics Data System (ADS)

    Renne, P. R.

    2015-12-01

    The Paraná-Etendeka Igneous Province (PEIP) comprises a large volume sequence of continental flood basalts presently distributed assymetrically between South America (mainly southern Brazil but also parts of Uruguay, Paraguay and Argentina) and southwestern Africa (Namibia, Angola), following opening of the South Atlantic ocean. The PEIP is dominated by tholeiitic basalts to basaltic andesites, with subordinate silicic rocks spanning the dacite-trachyte-rhyolite fields, which occur as lava flows, sills and dike swarms as well as intrusive complexes closely related to the eruptive rocks. The PEIP has long been subject of 40Ar/39Ar geochronologic and paleomagnetic studies which led to conclude its rapid formation near the Hauterivian stage (~133 Ma) with onward progression to Barremian from the intrusive equivalents exposed northwards. Two decades after publication of the first 40Ar/39Ar ages for the Paraná flood basalts (Renne et al., 1992) we report here an updated study of the age and duration of this magmatic event. We calibrated a set of sixty published and new results to the calibration of Renne et al. (2011), which indicates an inception age of the volcanism now estimated at 135 ± 1 Ma, before the initiation of sea floor spreading. Lava extrusion progressed over ~2 Ma from south to north. A protracted duration of ~10 Ma inferred by Stewart et al. (1996) for PEIP volcanism is clearly incorrect, as also concluded by Thiede and Vasconcelos (2010). Low-Ti mafic magmas prevailed during the earlier stages followed over time by enhanced dominance of their silicic equivalents. Eruption of the high-Ti (mafic and silicic) magmas initiated simultaneously ~0.5 m.y. later, continuing up to ~133 Ma with injection of the Ponta Grossa dyke swarm. Despite several paleomagnetic polarity intervals recorded by the lava piles in the southern (> 27°S) and central (latitudes of ~24-27°S) domains of the Brazilian PEIP, the paleomagnetic data show small dispersion in agreement

  4. What happened at the start of the Siberian Traps? Understanding the onset of flood volcanism

    NASA Astrophysics Data System (ADS)

    Jerram, D. A.; Svensen, H.; Planke, S.; Polozov, A. G.; Faleide, J.; Sokalska, E.

    2013-12-01

    The Siberian Traps Large Igneous Province was formed during the end-Permian, about 251 million years ago. Basaltic melt was injected into the organic and salt rich Tunguska sedimentary basin, forming interconnected sill complexes and associated hydrothermal vent complexes. We have conducted field work in Siberia during 2004 to 2010 to study the formation and implications of the SiberianTraps volcanism. Thick deposits of basaltic tuff and tephra have been reported as widespread in the lower succession of the Siberian Traps, commonly taken as direct evidence for the explosive nature of the initial phase of volcanism. The field work in this study revealed that tuffs are virtually absent along a 125 km long transect along the Dyupkun lake, even though tuff is shown on available geological maps. Towards the south and west, the transition between the end-Permian sediments and the flood basalts is either characterized by minor (<2 meters) to no tephra deposits (Khantaika area), hyaloclastites and associated lake-deposited tephra (Kureika area), or massive tephra deposits from local eruptive centers (Severnaya area). Within the intrusive complexes beneath the volcanics, contact metamorphism of the sedimentary rocks around dolerite sills and dikes generated greenhouse gases and halocarbons to such an extent that the process could be responsible for both the end-Permian carbon isotope excursion and the mass extinction. The key processes include 1) metamorphism of oil-saturated rock salt sequences (halocarbon production), 2) methane generation from metamorphism of organic-rich shales (methane production), and 3) decarbonation of dolostones (carbon dioxide production). The new results questions the notion of province-scale explosive volcanism in Siberia during the onset of flood volcanism, with more specific impact coming from vent complexes associated with the intrusions.

  5. Differential Bacterial Colonization of Volcanic Minerals in Deep Thermal Basalts

    NASA Astrophysics Data System (ADS)

    Smith, A. R.; Popa, R.; Fisk, M. R.; Nielsen, M.; Wheat, G.; Jannasch, H.; Fisher, A.; Sievert, S.

    2010-04-01

    There are reports of microbial weathering patterns in volcanic glass and minerals of both terrestrial and Martian origin. Volcanic minerals are colonized differentially in subsurface hydrothermal environments by a variety of physiological types.

  6. Origin of north Queensland Cenozoic volcanism: Relationships to long lava flow basaltic fields, Australia

    NASA Astrophysics Data System (ADS)

    Sutherland, F. L.

    1998-11-01

    A plume model proposed for north Queensland late Cenozoic volcanism and long lava flow distribution combines basalt ages with recent seismic studies of Australia's mantle, regional stress fields, and plate motion. Several basalt fields overlie mantle "thermal" anomalies, and other fields outside these anomalies can be traced to them through past lithospheric motion. Elsewhere, anomalies close to Australia's eastern rift margin show little volcanism, probably due to gravity-enhanced compression. Since final collision of north Queensland with New Guinea, areas of basaltic volcanism have developed over 10 Myr, and episodes appear to migrate southward from 15° to 20°S. Long lava flows increase southward as area/volume of fields increases, but topography, vent distributions, and uplifts play a role. This is attributed to magmatic plume activation within a tensional zone, as lithosphere moves over mantle thermal anomalies. The plume model predicts peak magmatism under the McBride field, coincident with the Undara long lava flow and that long lava flow fields will erupt for another 5-10 Myr. Queensland's movement over a major N-S thermal system imparts a consistent isotopic signature to its northern younger basalts, distinct to basalts from older or more southern thermal systems. Australia's motion toward this northern thermal system will give north Queensland fields continued vigorous volcanism, in contrast to the Victorian field which is leaving its southern thermal system.

  7. Flood volcanism in the northern high latitudes of Mercury revealed by MESSENGER.

    PubMed

    Head, James W; Chapman, Clark R; Strom, Robert G; Fassett, Caleb I; Denevi, Brett W; Blewett, David T; Ernst, Carolyn M; Watters, Thomas R; Solomon, Sean C; Murchie, Scott L; Prockter, Louise M; Chabot, Nancy L; Gillis-Davis, Jeffrey J; Whitten, Jennifer L; Goudge, Timothy A; Baker, David M H; Hurwitz, Debra M; Ostrach, Lillian R; Xiao, Zhiyong; Merline, William J; Kerber, Laura; Dickson, James L; Oberst, Jürgen; Byrne, Paul K; Klimczak, Christian; Nittler, Larry R

    2011-09-30

    MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era. PMID:21960625

  8. New 40Ar/ 39Ar dating of the Grande Ronde lavas, Columbia River Basalts, USA: Implications for duration of flood basalt eruption episodes

    NASA Astrophysics Data System (ADS)

    Barry, T. L.; Self, S.; Kelley, S. P.; Reidel, S.; Hooper, P.; Widdowson, M.

    2010-08-01

    Grande Ronde Basalt (GRB) lavas represent the most voluminous eruptive pulse of the Columbia River-Snake River-Yellowstone hotspot volcanism. With an estimated eruptive volume of 150,000 km 3, GRB lavas form at least 66% of the total volume of the Columbia River Basalt Group. New 40Ar/ 39Ar dates for GRB lavas reveal they were emplaced within a maximum period of 0.42 ± 0.18 My. A well-documented stratigraphy indicates at least 110 GRB flow fields (or individual eruptions), and on this basis suggests an average inter-eruption hiatus of less than 4000 years. Isotopic age-dating cannot resolve time gaps between GRB eruptions, and it is difficult to otherwise form a picture of the durations of eruptions because of non-uniform weathering in the top of flow fields and a general paucity of sediments between GR lavas. Where sediment has formed on top of GRB lavas, it varies in thickness from zero to 20-30 cm of silty to fine-sandy material, with occasional diatomaceous sediment. Individual GRB eruptions varied considerably in volume but many were greater than 1000 km 3 in size. Most probably eruptive events were not equally spaced in time; some eruptions may have followed short periods of volcanic repose (perhaps 10 2 to 10 3 of years), whilst others could have been considerably longer (many 1000 s to > 10 4 years). Recent improvements in age-dating for other continental flood basalt (CFB) lava sequences have yielded estimates of total eruptive durations of less than 1 My for high-volume pulses of lava production. The GRB appears to be a similar example, where the main pulse occupied a brief period. Even allowing for moderate to long-duration pahoehoe flow field production, the amount of time the system spends in active lava-producing mode is small — less than c. 2.6% (based on eruption durations of approximately 10,000 years, compared to the duration of the entire eruptive pulse of c. 420,000 years). A review of available 40Ar/ 39Ar data for the major voluminous phases

  9. Architecture and emplacement of flood basalt flow fields: case studies from the Columbia River Basalt Group, NW USA

    NASA Astrophysics Data System (ADS)

    Vye-Brown, C.; Self, S.; Barry, T. L.

    2013-03-01

    The physical features and morphologies of collections of lava bodies emplaced during single eruptions (known as flow fields) can be used to understand flood basalt emplacement mechanisms. Characteristics and internal features of lava lobes and whole flow field morphologies result from the forward propagation, radial spread, and cooling of individual lobes and are used as a tool to understand the architecture of extensive flood basalt lavas. The features of three flood basalt flow fields from the Columbia River Basalt Group are presented, including the Palouse Falls flow field, a small (8,890 km2, ˜190 km3) unit by common flood basalt proportions, and visualized in three dimensions. The architecture of the Palouse Falls flow field is compared to the complex Ginkgo and more extensive Sand Hollow flow fields to investigate the degree to which simple emplacement models represent the style, as well as the spatial and temporal developments, of flow fields. Evidence from each flow field supports emplacement by inflation as the predominant mechanism producing thick lobes. Inflation enables existing lobes to transmit lava to form new lobes, thus extending the advance and spread of lava flow fields. Minimum emplacement timescales calculated for each flow field are 19.3 years for Palouse Falls, 8.3 years for Ginkgo, and 16.9 years for Sand Hollow. Simple flow fields can be traced from vent to distal areas and an emplacement sequence visualized, but those with multiple-layered lobes present a degree of complexity that make lava pathways and emplacement sequences more difficult to identify.

  10. Lava tubes from the Paraná-Etendeka Continental Flood Basalt Province: Morphology and importance to emplacement models

    NASA Astrophysics Data System (ADS)

    Waichel, Breno L.; Tratz, Eliza B.; Pietrobelli, Gisele; Jerram, Dougal A.; Calixto, Geovane R.; Bacha, Rafael R.; Tomazzolli, Edison R.; da Silva, Wellington B.

    2013-12-01

    Lava tubes are a common feature in active volcanic areas around the world. They are related to pahoehoe and 'a'ā lava flow fields, that are predominantly basaltic, and form as the most efficient mechanism to transport lava in insulated fedder pathways. Continental Flood Basalt Provinces (CFBs) are thick volcanic sequences of predominantly basaltic lava flows and flow fields, which cover huge areas and are often related to continental breakup. The proposed emplacement model for CFB's is synonymous with the inflation processes observed in modern active flows. Although pahoehoe and 'a'ā lava flows are recognized in CFB's provinces, good examples of lava tubes, pipes or tube systems are rarely reported. Lava feeder systems (tube/pipes) are a common feature of modern pahoehoe flow systems so it would be expected to find good examples in CFB's provinces formed by the same emplacement processes. Here we describe the morphology of two lava tube systems discovered in the Paraná CFB Province in Southern Brazil. Comparisons are made with active systems and the importance of CFB lava tube systems, and their recognition in the rock record, are discussed in the context of the current emplacement model.

  11. Evolution of Late Cenozoic basaltic volcanism in the Mojave Desert, California

    SciTech Connect

    Glazner, A.F. . Dept. of Geology); Farmer, G.L. . Dept. of Geological Sciences)

    1993-04-01

    Cenozoic volcanism in the Mojave Desert region of southern California comprises two main groups: early Miocene ([approx]24--18 Ma) synextensional magmatism ranging from basalt to rhyolite, and postkinematic middle Miocene to Quaternary volcanism that is almost exclusively basaltic. Flat-lying basalts of the latter group, herein termed the Mojave Neovolcanic Belt (MNB), are distributed across the central and eastern Mojave Desert, and were erupted in three main pulses: (1) during the middle Miocene ([approx]17--15 Ma), in a belt from near Tiefort Mtn. to the El Paso Mts.; (2) during the late Miocene ([approx]9--4 Ma); and (3) in a Plio-Quaternary pulse ([approx]3--0 Ma) that includes the southern Cima field and all the cones scattered along the axis of the Barstow-Bristol trough. Several temporal and geographic trends are evident in the MNB. In general, younger basalts are higher in [var epsilon][sub Nd], lower in [sup 87]Sr/[sup 86]Sr, more alkalic, less crustally contaminated, and more likely to contain mantle xenoliths than older basalts. Mantle xenoliths are restricted to the eastern and southern Mojave block. Basalts of all three groups become dramatically richer in K[sub 2]O to the east, ranging from subalkaline basalts in the west to alkali basalts and trachybasalts in the east. Isotopic provinciality is apparent, but mantle differences are difficult to distinguish from the effects of crustal contamination. Lavas with mantle xenoliths consistently have [var epsilon][sub Nd] > 5 and [sup 87]Sr/[sup 86]Sr < 0.7042. Eruptive centers of the MNB show no consistent relationship to regional tectonic features. Although alkali basalts are generally associated with rifting, several MNB volcanoes were erupted through active fold and thrust belts.

  12. Heat and Groundwater Flow through Continental Flood Basalt Provinces: Insights Gained from Alternative Models of Permeability/Depth Relationships for the Columbia Plateau, USA

    NASA Astrophysics Data System (ADS)

    Burns, E. R.; Williams, C. F.; Ingebritsen, S.; Voss, C. I.; Spane, F.; DeAngelo, J.

    2014-12-01

    Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (~3.5 orders of magnitude) at 600-900 m depth and ~40oC. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at ~600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Abrupt k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration. Because pore filling hydrothermal minerals are largely controlled by the major mineral assemblages of the volcanic rocks, other continental flood basalt provinces may also have large permeability changes at depths corresponding to ~40oC.

  13. Environmental effects of magmatic sulfur emitted by large-scale flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Schmidt, A.; Skeffington, R.; Thordarson, T.; Self, S.; Forster, P.; Rap, A.; Ridgwell, A.; Fowler, D.; Wilson, M.; Mann, G.; Wignall, P.; Carslaw, K. S.

    2015-12-01

    Continental flood basalt (CFB) volcanism has been temporally, and therefore causally, linked to periods of environmental crisis in the past 260 Ma. The majority of the proposed causal relationships are, however, qualitative, in particular the potential climatic and environmental effects of large amounts of sulfur dioxide (SO2) emitted to the atmosphere. CFB provinces are typically formed by numerous individual eruptions, each lasting years to decades, with highly uncertain periods of quiescence lasting hundreds to thousands of years. I will present results obtained from a global aerosol-climate model set-up to simulate the sulfur-induced climatic and environmental effects of individual decade to century-long CFB eruptions. For sulfur dioxide emissions representative of a single decade-long eruption in the 65 Ma Deccan Trap Volcanic Province, the model predicts a substantial reduction in global surface temperature of 4.5 K, which is in good agreement with multi-proxy palaeo-temperature records. However, the calculated cooling is short-lived and temperatures recover within less than 50 years once volcanic activity ceases. In contrast to previous studies, I show that acid rain from decade-long eruptions cannot cause widespread vegetation stress or loss due to the buffering capacities of soils. The direct exposure of vegetation to acid mists and fogs, however, could cause damage where the exposure is high and sustained, such as at high elevations. Finally, I will use these modeling results to place constraints on the likely environmental effects and habitability by simulating different eruption frequencies and durations as well as hiatus periods and by comparing to the proxy records.

  14. Early and Late Alkali Igneous Pulses and a High-3He Plume Origin for the Deccan Flood Basalts.

    PubMed

    Basu, A R; Renne, P R; Dasgupta, D K; Teichmann, F; Poreda, R J

    1993-08-13

    Several alkalic igneous complexes of nephelinite-carbonatite affinities occur in extensional zones around a region of high heat flow and positive gravity anomaly within the continental flood basalt (CFB) province of Deccan, India. Biotites from two of the complexes yield (40)Ar/(39)Ar dates of 68.53 +/- 0.16 and 68.57 +/- 0.08 million years. Biotite from a third complex, which intrudes the flood basalts, yields an (40)Ar/(39)Ar date of 64.96 +/- 0.1 1 million years. The complexes thus represent early and late magmatism with respect to the main pulse of CFB volcanism 65 million years ago. Rocks from the older complexes show a (3)He/(4)He ratio of 14.0 times the air ratio, an initial (87)Sr/(86)Sr ratio of 0.70483, and other geochemical characteristics similar to ocean island basalts; the later alkalic pulse shows isotopic evidence of crustal contamination. The data document 3.5 million years of incubation of a primitive, high-(3)He mantle plume before the rapid eruption of the Deccan CFB. PMID:17783739

  15. Axial focusing of impact energy in the earth`s interior: A possible link to flood basalts and hotspots

    SciTech Connect

    Boslough, M.B.; Chael, E.P.; Trucano, T.G.; Crawford, D.A.; Campbell, D.L.

    1994-12-01

    We present the results of shock physics and seismological computational simulations that show how energy from a large impact can be coupled to the interior of the Earth. The radially-diverging shock wave generated by the impact decays to linearly elastic seismic waves. These waves reconverge (minus attenuation) along the axis of symmetry between the impact and its antipode. The locations that experience the most strain cycles with the largest amplitudes will dissipate the most energy and have the largest increases in temperature (for a given attenuation efficiency). We have shown that the locus of maximum energy deposition in the mantle lies along the impact axis. Moreover, the most intense focusing is within the asthenosphere at the antipode, within the range of depths where mechanical energy is most readily converted to heat. We propose that if large impacts on the Earth leave geological evidence anywhere other than the impact site itself, it will be at the antipode. We suggest that the most likely result of the focusing for a sufficiently large impact, consistent with features observed in the geological record, would be a flood basalt eruption at the antipode followed by hotspot volcanism. A direct prediction of this model would be the existence of undiscovered impact structures whose reconstructed locations would be antipodal to flood basalt provinces. One such structure would be in the Indian Ocean, associated with the Columbia River Basalts and Yellowstone; another would be a second K/T impact structure in the Pacific Ocean, associated with the Deccan Traps and Reunion.

  16. Basaltic magmatism on the Moon. A perspective from volcanic picritic glasses

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Papike, J. J.

    1993-01-01

    It is widely accepted that basaltic magmas are products of partial fusion of peridotite within planetary mantles. As such they provide valuable insights into the structure and processes of planetary interiors. Those compositions which approach primary melt compositions provide both a clearer vision of planetary interiors and a starting point at which to understand basaltic evolution. Within the collection of lunar samples returned by the Apollo and Luna missions are homogeneous, picritic glass beads of volcanic origin. These glass beads provide a unique perspective concerning the origin of mare basalts, the characteristics of the lunar interior, and processes culminating in the early differentiation of the moon. In this presentation, we report our ion microprobe derived trace element data from all picritic glasses previously identified. We place this trace element data and literature isotopic and experimental data on the picritic glasses with the framework of mare basaltic magmatism.

  17. Rhyolite, dacite, andesite, basaltic andesite, and basalt volcanism on the Alarcon Rise spreading-center, Gulf of California

    NASA Astrophysics Data System (ADS)

    Dreyer, B. M.; Portner, R. A.; Clague, D. A.; Castillo, P. R.; Paduan, J. B.; Martin, J. F.

    2012-12-01

    The Alarcon Rise is a ~50 km long intermediate-rate (~50mm/a) spreading segment at the southern end of the Gulf of California. The Rise is bounded by the Tamayo and Pescadero transforms to the south and north. In Spring 2012, an MBARI-led expedition mapped a ~1.5- 3km wide swath of the ridge axis at 1-m resolution and completed 9 ROV dives (Clague et al., this session). Sampling during the ROV dives was supplemented by use of a wax-tip corer to recover volcanic glass: 194 glassy lava samples were recovered from the Rise. The vast majority of lava flows along the axis are basalt and rare basaltic andesite. More than half the basalts are plagioclase-phyric to ultraphyric (Martin et al., this session), and the rest are aphyric. Rare samples also include olivine or olivine and clinopyroxene phenocrysts. Analyses of half of the recovered glass basalt rinds range in MgO from 4.3 to 8.5 wt.% and those with MgO > 6 wt % have K2O/TiO2 = 0.07-0.11. The basalts are broadly characterized as normal mid-ocean ridge basalts (N-MORB). E-MORB is also present near the center of the ridge segment, but has been found only as pyroclasts in sediment cores. A much greater range in lava composition is associated with an unusual volcanic dome-like edifice that lies ~9 km south of the Pescadero transform. Two dives in the vicinity of the dome collected lava and volcaniclastic samples consisting of moderately to sparsely phyric light brown to colorless volcanic glass. Feldspar is the dominant phase, but magnetite, fayalitic olivine, light tan and light green clinopyroxene, orthopyroxene, zircon, and rare pyrite blebs also occur. Melt-inclusions are common in many phenocrysts, especially of plagioclase. Hydrous mineral phases are not observed. These samples have rhyolitic glass compositions (75.8- 77.4 SiO2 wt %), but their whole-rock compositions will be somewhat less silicic. Pillow flows to the immediate west have dacitic glass compositions (67.4- 68.8 wt % SiO2). Basaltic andesitic

  18. Low titanium magmatism in northwest region of Paraná continental flood basalts (Brazil): volcanological aspects

    NASA Astrophysics Data System (ADS)

    Machado, F. B.; Viana Rocha-Júnior, E. R.; Ranalli Nardy, A. J.; Soares Marques, L.

    2014-08-01

    The early Cretaceous Paraná Continental Flood Basalts (PCFB) is considered as one of the largest volcanic provinces in the world. In Brazil, it completes the last sequence of the sedimentary Paraná Basin (Serra Geral Fm.). The geological unit is contemporary to desert sandstones of Botucatu Fm. and precedes the continental sediments of the Bauru Basin. This Large Igneous Province (LIP) is divided into different types of geochemical magmas which basically are based on TiO2 content (higher - HTi or lower LTi than 2 wt.% in TiO2) and incompatible trace elements ratio. Therefore, we studied the magma LTi (TiO2 < 2.0 wt.%), denominated Ribeira which occurs in the northwestern portion of PCFP which is poorly researched mainly in volcanological and geochemical aspects. This basaltic magma, a short expression in PCFB, occurs in the form of multiple pahoehoe flows with thicknesses ranging from 1.5 to 30 m in compound type flows under low surface slope. Peperites zones are common when associated with the first flows, and sand-filled cracks in the lower and upper edges at all pahoehoe levels when in contact with the sediment. Upward these first sequences of interactions with sediment, on the inside direction basin, simple pahoehoe flows occur being associated with Pitanga magma type (HTi, with TiO2 > 2.0 wt.%). Based on rheology data considering anhydrous environment and the composition of plagioclase (An(42-67)) and clinopyroxene (Wo(30-40)En(34-46)Fs(17-32)) showed that the LTi magma is hotter than HTi, with temperatures that range from 1069 °C to 1248 °C while for the second range from 1020 °C to 1201 °C.

  19. Experimental Parameters for Wax Modeling of the Deccan Traps Flood Basalt Province

    NASA Astrophysics Data System (ADS)

    Rader, E. L.; Vanderkluysen, L.; Clarke, A. B.

    2015-12-01

    The Deccan Traps consist of ~1,000,000 km3 of predominantly tholeiitic basaltic lava flows, which cover the western Indian subcontinent. Their eruption occurred over a ~1-3 million year period overlapping with the Cretaceous-Paleogene (K-Pg) boundary and, hence, has been implicated in one of the most significant extinction events in the history of the planet. The extent of environmental impacts caused by flood basalt eruptions is thought to be related, in part, to the amount, species, and timescales of volcanic gases released. Therefore, constraining the effusion rate of Deccan Traps lava flows is fundamental to understanding the K-Pg extinction event. Previous field and experimental work with polyethylene glycol (PEG) wax has shown that effusion rate is a primary factor controlling flow morphology. While sinuous flows and lava domes have been successfully recreated with PEG wax, the two most common morphologies seen in the Deccan Traps (compound and inflated sheet lobes) have not. We used heated PEG-400 wax injected into a tank of chilled water with a peristaltic pump to form experimental eruptions with high flow rate and low viscosity to replicate inflated flow lobes, and low flow rate with higher viscosity for compound flows. Unlike previous experiments, flow rate was varied during a single experiment to examine the effect on flow morphology. The Psi value is used as a scaling parameter to estimate effusion rates for compound and 'simple' inflated flows in the Deccan Traps. When combined with field work for volume estimates of the two flow types, these experiments will provide the best constraint on eruption rates to date.

  20. Upper mantle seismic structure beneath the Pacific Northwest: A plume-triggered delamination origin for the Columbia River flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Darold, Amberlee; Humphreys, Eugene

    2013-03-01

    We invert teleseismic P and S body waves constrained by an ambient-noise surface wave model and Moho depth inferred from receiver function analysis (Gao et al., 2011) to image mantle structures continuously from the surface to the base of the upper mantle. The major structures coincide with prominent geological features. We focus on a NE-Oregon structure, termed here the Wallowa anomaly, which coincides with the source area for the ˜16 Ma Columbia River flood basalt eruptions and a circular area of topographic relief created during and after these eruptions. Resolution tests indicate that the curtain-like structure previously interpreted as Farallon lithosphere connects with the Wallowa anomaly above 150 km along the northeast margin of the Wallowa anomaly. This connection, along with the pre-flood basalt magmatic and tectonic history of the Pacific Northwest, lead us to conclude that arrival of the Yellowstone plume to south-central Oregon initiated delamination of remnant Farallon lithosphere from the base of NE Oregon, exposing ocean crust to Yellowstone asthenosphere. This hypothesis accounts for the propagation of flood basalt volcanism far north of the Yellowstone hotspot track, and for the high-silica composition of most of the flood basalt magmas.

  1. Siderophile and chalcophile metal variations in Tertiary picrites and basalts from West Greenland with implications for the sulphide saturation history of continental flood basalt magmas

    NASA Astrophysics Data System (ADS)

    Keays, Reid R.; Lightfoot, Peter C.

    2007-04-01

    much more severe than that of the West Greenland contaminated basalts. Moreover, the volumes of the contaminated and metal-depleted volcanic rocks in West Greenland pale is significant when compared to the Nadezhdinsky Formation; local centers rarely contain more than 15 thin flows with a combined thickness of <50 m and more typically 10-20 m, so the volume of the eruptive portions of each system is probably two orders of magnitude smaller than the Nadezhdinsky edifice. The West Greenland centres are juxtaposed along fault zones that appear to be linked to the subsidence of the Tertiary delta, and so emplacement along N-S structures appears to be a principal control on the distribution of lavas and feeder intrusions. This leads us to suggest that the Greenland system is small and segregation of sulphide took place at high levels in the crust, whereas at Noril’sk, the saturation event took place at depth with subsequent emplacement of sulphide-bearing magmas into high levels of the crust. As a consequence, it may be unreasonable to expect that the West Greenland flood basalts experienced mineralizing processes on the scale of the Noril’sk system.

  2. Modeling Cooling Rates of Martian Flood Basalt Columns

    NASA Astrophysics Data System (ADS)

    Weiss, D. K.; Jackson, B.; Milazzo, M. P.; Barnes, J. W.

    2011-12-01

    Columnar jointing in large basalt flows have been extensively studied and can provide important clues about the emplacement conditions and cooling history of a basalt flow. The recent discovery of basalt columns on Mars in crater walls near Marte Vallis provides an opportunity to infer conditions on early Mars when the Martian basalt flows were laid down. Comparison of the Martian columns to Earth analogs allows us to gain further insight into the early Martian climate, and among the best terrestrial analogs are the basalt columns in the Columbia River Basalt Group (CRBG) in eastern Washington. The CRBG is one of the youngest (< 17 Myrs old) and most extensively studied basalt provinces in the world, extending over 163,700 square km with total thickness exceeding 1 km in some places. The morphologies and textures of CRBG basalt columns suggest that in many places flows ~100 m thick cooled at uniform rates, even deep in the flow interior. Such cooling seems to require the presence of water in the column joints since the flow interiors should have cooled much more slowly than the flow margins if conductive cooling dominated. Secondary features, such pillow basalts, likewise suggest the basalt flows were in direct contact with standing water in many places. At the resolution provided by the orbiting HiRISE camera (0.9 m), the Martian basalt columns resemble the CRBG columns in many respects, and so, subject to important caveats, inferences linking the morphologies of the CRBG columns to their thermal histories can be extended in some respects to the Martian columns. In this presentation, we will describe our analysis of the HiRISE images of the Martian columns and what can be reasonably inferred about their thermal histories and the conditions under which they were emplaced. We will also report on a field expedition to the CRBG in eastern Washington State. During that expedition, we surveyed basalt column outcrops on the ground and from the air using Unmanned Aerial

  3. Chemistry and isotope ratios of sulfur in basalts and volcanic gases at Kilauea volcano, Hawaii

    USGS Publications Warehouse

    Sakai, H.; Casadevall, T.J.; Moore, J.G.

    1982-01-01

    Eighteen basalts and some volcanic gases from the submarine and subaerial parts of Kilauea volcano were analyzed for the concentration and isotope ratios of sulfur. By means of a newly developed technique, sulfide and sulfate sulfur in the basalts were separately but simultaneously determined. The submarine basalt has 700 ?? 100 ppm total sulfur with ??34S??s of 0.7 ?? 0.1 ???. The sulfate/sulfide molar ratio ranges from 0.15 to 0.56 and the fractionation factor between sulfate and sulfide is +7.5 ?? 1.5???. On the other hand, the concentration and ??34S??s values of the total sulfur in the subaerial basalt are reduced to 150 ?? 50 ppm and -0.8 ?? 0.2???, respectively. The sulfate to sulfide ratio and the fractionation factor between them are also smaller, 0.01 to 0.25 and +3.0???, respectively. Chemical and isotopic evidence strongly suggests that sulfate and sulfide in the submarine basalt are in chemical and isotopic equilibria with each other at magmatic conditions. Their relative abundance and the isotope fractionation factors may be used to estimate the f{hook}o2 and temperature of these basalts at the time of their extrusion onto the sea floor. The observed change in sulfur chemistry and isotopic ratios from the submarine to subaerial basalts can be interpreted as degassing of the SO2 from basalt thereby depleting sulfate and 34S in basalt. The volcanic sulfur gases, predominantly SO2, from the 1971 and 1974 fissures in Kilauea Crater have ??34S values of 0.8 to 0.9%., slightly heavier than the total sulfur in the submarine basalts and definitely heavier than the subaerial basalts, in accord with the above model. However, the ??34S value of sulfur gases (largely SO2) from Sulfur Bank is 8.0%., implying a secondary origin of the sulfur. The ??34S values of native sulfur deposits at various sites of Kilauea and Mauna Loa volcanos, sulfate ions of four deep wells and hydrogen sulfide from a geothermal well along the east rift zone are also reported. The high

  4. New Insights to the Mid Miocene Calc-alkaline Lavas of the Strawberry Volcanics, NE Oregon Surrounded by the Coeval Tholeiitic Columbia River Basalt Province

    NASA Astrophysics Data System (ADS)

    Steiner, A. R.; Streck, M. J.

    2013-12-01

    The Strawberry Volcanics (SV) of NE Oregon were distributed over 3,400 km2 during the mid-Miocene and comprise a diverse volcanic suite, which span the range of compositions from basalt to rhyolite. The predominant composition of this volcanic suite is calc-alkaline (CA) basaltic andesite and andesite, although tholeiitic (TH) lavas of basalt to andesite occur as well. The coeval flood basalts of the Columbia River province surround the SV. Here we will discuss new ages and geochemical data, and present a new geologic map and stratigraphy of the SV. The SV are emplaced on top of pre-Tertiary accreted terranes of the Blue Mountain Province, Mesozoic plutonic rocks, and older Tertiary volcanic rocks thought to be mostly Oligocene of age. Massive rhyolites (~300 m thick) are exposed mainly along the western flank and underlie the intermediate composition lavas. In the southern portion of this study area, alkali basaltic lavas, thought to be late Miocene to early Pliocene in age, erupted and overlie the SV. In addition, several regional ignimbrites reach into the area. The 9.7 Ma Devine Canyon Tuff and the 7.1 Ma Rattlesnake Tuff also overlie the SV. The 15.9-15.4 Ma Dinner Creek Tuff is mid-Miocene, and clear stratigraphic relationships are found in areas where the tuff is intercalated between thick SV lava flows. All of the basalts of the SV are TH and are dominated by phenocryst-poor (≤2%) lithologies. These basalts have an ophitic texture dominated by plagioclase, clinopyroxene and olivine (often weathered to iddingsite). Basalts and basaltic andesites have olivine Fo #'s ranging from 44 at the rims (where weathered to iddingsite) and as high as 88 at cores. Pyroxene Mg #'s range from 65 to 85. Andesites of the SV are sub-alkaline, and like the basalts, are exceedingly phenocryst-poor (≤3%) with microphenocrysts of plagioclase and lesser pyroxene and olivine, which occasionally occur as crystal clots of ~1-3 mm instead of single crystals. In addition, minimal

  5. Immense vent complex marks flood-basalt eruption in a wet, failed rift: Coombs Hills, Antarctica

    NASA Astrophysics Data System (ADS)

    White, J. D. L.; McClintock, M. K.

    2001-10-01

    Large lava effusions can have impressive explosive antecedents. Although our picture of flood basalt is overwhelmingly effusive, phreatomagmatic eruptions have preceded quiet effusion of some flood basalts and reflect the same influence of vent architecture and hydrology on eruptive style as seen for small-volume eruptions. The scale of phreatomagmatic deposits associated with flood basalts can be huge. At Coombs Hills a vast, but otherwise typical, phreatomagmatic vent complex is exposed over more than 25 km2, and its features are interpreted to reflect processes of tephra-jet eruptions with diatreme development. Similar vent complexes are probably the source of laharic deposits reported elsewhere in the Transantarctic Mountains and in the Karoo province of South Africa.

  6. Basal Adare volcanics, Robertson Bay, North Victoria Land, Antarctica: Late Miocene intraplate basalts of subaqueous origin

    USGS Publications Warehouse

    Mortimer, N.; Dunlap, W.J.; Isaac, M.J.; Sutherland, R.P.; Faure, K.

    2007-01-01

    Late Cenozoic lavas and associated hyaloclastite breccias of the Adare volcanics (Hallett volcanic province) in Robertson Bay, North Victoria Land rest unconformably on Paleozoic greywackes. Abundant hyaloclastite breccias are confined to a paleovalley; their primary geological features, and the stable isotope ratios of secondary minerals, are consistent with eruption in a subaqueous environment with calcite formation probably involving seawater. In contrast, the lavas which stratigraphically overlie the hyaloclastites on Mayr Spur probably were erupted subaerially. K-Ar dating of eight samples from this basal sequence confirms the known older age limit (Late Miocene) of the Hallett volcanic province. Geochemical data reveal an ocean island basalt-like affinity, similar to other Cenozoic igneous rocks of the Hallett volcanic province. If a submarine eruptive paleoenvironment is accepted then there has been net tectonic or isostatic post-Late Miocene uplift of a few hundred metres in the Robertson Bay-Adare Peninsula area

  7. Flood-basalt magmatism of the Vodlozero Block of the Karelian Craton: relations between high- and low-Cr Varieties

    NASA Astrophysics Data System (ADS)

    Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexii

    2016-04-01

    The early Paleoproterozoic (2.5-2.3 Ga) volcanic rocks of the Karelian Craton are ascribed to the large igneous province of the eastern Fennoscandian Shield. They are mainly represented by calc-alkaline low-Ti basalts and basaltic andesites with relatively high SiO2 and clearly pronounced continental trace element signatures. The compositions of the rocks vary in the different domains of the Karelian craton. In particular, basalts developed in the Central Domain are represented by strongly fractionated varieties (Mg # < 50), which cannot be used to decipher the source composition. Basaltic rocks of the Vodlozero Block are clustered in two groups. The first group is usually developed in the lower parts of the early Paleopoterozoic volcanic sequences and includes the low Cr (< 200 ppm), low Mg rocks similar to the fractionated varieties developed in the Central Domain. They are characterized by high contents of Zr, Y, and REE, and LILE, fractionated REE patterns with (La/Yb)n = 5.44-12.34, (La/Sm)n = 4.4-2.03, and (Gd/Yb)n = 1.36-2.71), and demonstrate negative Ti and Nb anomalies. The second group is represented by more primitive high Cr (up to 1000 ppm) high Mg# (up to 68) basalts with high Ni contents. Such composition is close to the primary non-fractionated mantle-derived magmas and may be used to provide insight into parental melts of continental flood basalts and their crustal evolution. In the spidergrams they demonstrate weak positive Ti anomaly at positive or absent Zr anomaly and negative Nb anomaly. The rocks of the second group are also characterized (with rare exception) by LREE enriched but less fractionated patterns than the first group: ((La/Yb)n up to 7.5, (La/Sm)n = up to 2.8, (Gd/Yb)n = up to 2.0). High Cr and low Y contents are indicative of relatively high degree of partial melting of a depleted mantle source. These rocks are simulated by sequential fractionation of uncontaminated continental flood basalts leaving Ol residue and lower crustal

  8. A common parentage for Deccan Continental Flood Basalt and Central Indian Ocean Ridge Basalt? A geochemical and isotopic approach

    NASA Astrophysics Data System (ADS)

    Ray, D.; Misra, S.; Widdowson, M.; Langmuir, C. H.

    2014-04-01

    A comparison of geochemical and Sr-Nd-Pb isotopic compositions for Deccan Continental Flood Basalts (CFBs) and Central Indian Ridge (CIR) Basalts is presented: these data permit assessment of possible parental linkages between the two regions, and comparison of their respective magmatic evolutionary trends in relation to rift-related tectonic events during Gondwana break-up. The present study reveals that Mid-Ocean Ridge Basalt (MORB) from the northern CIR and basalts of Deccan CFB are geochemically dissimilar because of: (1) the Deccan CFB basalts typically show a greater iron-enrichment as compared to the northern CIR MORB, (2) a multi-element spiderdiagram reveals that the Deccan CFBs reveal a more fractionated slope (Ba/YbN > 1), as compared to relatively flat northern CIR MORB (Ba/YbN < 1), (3) there is greater REE fractionation for Deccan CFB than for the northern CIR MORB (i.e., La/YbN ˜ 2.3 and 1 respectively) and (4) substantial variation of compatible-incompatible trace elements and their ratios among the two basalt groups suggests that partial melting is a dominant process for northern CIR MORB, while fractional crystallization was a more important control to the geochemical variation for Deccan CFB. Further, incompatible trace element ratios (Nb/U and Nb/Pb) and radiogenic isotopic data (Sr-Pb-Nd) indicate that the northern CIR MORBs are similar to depleted mantle [and/or normal (N)-MORB], and often lie on a mixing line between depleted mantle and upper continental crust. By contrast, Deccan CFB compositions lie between the lower continental crust and Ocean island basalt. Accordingly, we conclude that the basaltic suites of the northern CIR MORB and Deccan CFB do not share common parentage, and are therefore genetically unrelated to each other. Instead, we infer that the northern CIR MORB were derived from a depleted mantle source contaminated by upper continental crust, probably during the break up of Gondwanaland; the Deccan CFB are more similar to

  9. Eruption and emplacement of flood basalt. An example from the large-volume Teepee Butte Member, Columbia River Basalt Group

    SciTech Connect

    Reidel, S.P. ); Tolan, T.L. )

    1992-12-01

    Flows of the Teepee Butte Member, Grande Ronde Basalt, issued from a vent system in southeastern Washington, northeastern Oregon, and western Idaho. Three distinct basalt flows were erupted: the Limekiln Rapids flow, the Joseph Creek flow, and the Pruitt Draw flow. Together these mappable flows cover more than 52,000 km[sup 2] and have a volume exceeding 5,000 km[sup 3]. A portion of the vent system for the Joseph Creek flow is exposed in cross section in Joseph Canyon, Washington; it is one of the best preserved Columbia River Basalt Group vent complexes known. The vent complex is about 1 km in cross section, 30 m high, and composed of deposits characteristic of Hawaiian-type volcanism. The vent is asymmetrical; the eastern rampart consists of intercalated pyroclastic deposits and thin pahoehoe flows; the western rampart is composed wholly of pahoehoe flows. Flows of the Teepee Butte Member are compositionally homogeneous and were emplaced as sheet flows, each having several local flow units. Our study supports the importance of linear vent systems and the westward Palouse Slope, along with the large-volume lava flows, in controlling the distribution of Columbia River Basalt Group flows. Other factors, including the number of active fissure segments and topography, modified the shape of the flows and the number of flow units. 45 refs., 19 figs., 2 tabs.

  10. Volcanic red-bed copper mineralisation related to submarine basalt alteration, Mont Alexandre, Quebec Appalachians, Canada

    NASA Astrophysics Data System (ADS)

    Cabral, Alexandre Raphael; Beaudoin, Georges

    2007-11-01

    Two types of native copper occur in Upper Silurian basaltic rocks in the Mont Alexandre area, Quebec Appalachians: (1) type 1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin, whereas (2) type 2 occurs as coarse-grained patches rimmed by cuprite in altered porphyritic basalt. Type 1 has higher contents of sulphur (2,000-20,263 ppm) and arsenic (146-6,017 ppm), and a broader range of silver abundances (<65-2,186 ppm Ag) than type 2 (149-1,288 ppm S, <90-146 As, <65-928 ppm Ag). No mineral inclusions of sulphide or arsenide in native copper were observed at the electron-microprobe scale. Primary igneous fabrics are preserved, but the basaltic flows are pervasively oxidised and plagioclase is albitised. Chlorite replaces plagioclase and forms interstitial aggregates in the groundmass and has Fe/(Fe+Mg) ratios ranging from 0.29 to 0.36 with calculated temperatures between 155°C and 182°C. Copper sulphides in vacuoles and veinlets are associated with malachite, fibro-radiating albite and yarrowite (Cu9S8 with up to 0.3 wt% Ag). Bulk-rock concentrations of thallium and lithium range from 70 to 310 ppb and 10 to 22 ppm, respectively, and thallium is positively correlated with Fe2O3. Such concentrations of thallium and lithium are typical of spilitisation during heated seawater-basalt interaction. Spilitisation is consistent with the regional geological setting of deepwater-facies sedimentation, but is different from current models for volcanic red-bed copper, which indicate subaerial oxidation of volcanic flows. The volcanic red-bed copper model should be re-examined to account for native copper mineralisation in basalts altered by warm seawater.

  11. Helium Isotopes in Basalt-Hosted Olivines From the Yellowstone Plateau: Implications on Volcanic Processes

    NASA Astrophysics Data System (ADS)

    Abedini, A. A.; van Soest, M.; Hurwitz, S.; Kennedy, B. M.

    2006-12-01

    The Yellowstone Plateau volcanic field is the youngest part of a magmatic system that began its northeastward propagation along the path of the eastern Snake River Plain in the mid-Miocene. Previous noble gas isotopic studies in Yellowstone have focused on samples from hydrothermal features. Such samples are often subject to shallow crustal contamination that may mask a deeper magmatic component. Most of the reported He-isotope ratios within the Yellowstone caldera perimeter are ~7 ± 1 RA, with peaks occurring around Mud Volcano (~16 RA) and Gibbon Geyser Basin (~13 RA). Outside the caldera, the He-isotope ratios generally drop to <3 RA. The elevated helium isotope data from Mud Volcano and Gibbon Geyser Basin was interpreted as unequivocal evidence for the presence of a deep mantle plume underlying the Yellowstone volcanic field (Craig et al., 1978; Kennedy et al., 1985). However, in an attempt to reconcile the available geochemical and geophysical data some researchers argue solely for a shallow mantle source for the magmatism related to Yellowstone (Christiansen et al., 2002). To gain a better understanding of the helium isotope composition of the mantle source below Yellowstone and its possible changes in time, we have started a study of helium isotopes in basalt-hosted olivines from the Yellowstone volcanic field. A total of 28 samples representing most basalt units from Yellowstone's three eruptive cycles were collected. All of the exposed basalts are located outside the Yellowstone caldera, mainly near Mammoth Hot Springs and Tower Junction to the north and in the Island Park area to the southwest. Most basalts contain 46-52 wt% SIO2, 8-12 wt% FeO, and 0.16-0.23 wt% MgO. Helium was released from aliquots of ~1.5 g olivine by crushing in vacuo, and initial helium isotope results, corrected for 10-15% procedural blank include: 1. The Gerrit basalt from Island Park, with a ratio of 15.7 ± 2.2 RA; 2. Falls River basalt from Island Park, 15.1 ± 0.8 RA; 3. Warm

  12. Basaltic volcanism in the Bering Sea: geochronology and volcanic evolution of St. Paul Island, Pribilof Islands, Alaska

    NASA Astrophysics Data System (ADS)

    Winer, G. S.; Feeley, T. C.; Cosca, M. A.

    2004-07-01

    The evolution of a Pleistocene to Holocene basaltic volcanic field in the back-arc region of the Aleutian subduction system is investigated at St. Paul Island, Alaska, one of the youngest eruptive centers in the Bering Sea basalt province. New 40Ar/ 39Ar and 14C age determinations indicate that subaerial volcanic activity forming the island began as early as 540 ka and has continued nearly to the present; the youngest eruption occurred approximately 3230 years BP. Magmas erupted on St. Paul are basaltic with MgO contents ranging from 14 to 4 wt.% and phenocryst assemblages of olivine+clinopyroxene±plagioclase; all are alkalic. The surface of St. Paul is composed mainly of numerous tephra cones surrounded by coalescing, low-viscosity pahoehoe lava flows. A central highland spans the island from east to west and is constructed of relatively young eruptive centers where rocks show a minimum of weathering and little deformation by faulting. In contrast, older lava flows forming the wave-eroded base of the island are gently to moderately tilted and faulted. Geochronologic, stratigraphic, and geochemical data indicate that eruptive styles on St. Paul evolved from early, mostly effusive eruptions of chemically little evolved lavas that form the base of the island, to more explosive monogenetic scoria cones, to polygenetic centers forming shields by repeated effusive eruptions of evolved low-viscosity lavas. Localization of the monogenetic and polygenetic centers appears to be related to east-west and northeast-southwest trending fault and fissure systems, with polygenetic centers located at intersections of major structures. The combined volcanic and compositional changes on St. Paul Island suggest that the magmatic system as a whole may be trending toward eruption of more evolved magmas related to the progressive development of crustal magma chambers in which crystal fractionation and magmatic differentiation are occurring.

  13. Weak-intensity, basaltic, explosive volcanism: Dynamics of Hawaiian fountains

    NASA Astrophysics Data System (ADS)

    Parcheta, Carolyn

    Hawaiian fountains, typically occurring on basaltic volcanoes, are sustained, weakly-explosive jets of gas and juvenile ejecta. A broad range of Hawaiian fountaining styles occurred during twelve episodes of the Mauna Ulu eruption on Kilauea between May and December 1969. The western episode 1 fissure system is currently well exposed, providing an exclusive opportunity to study processes of low-intensity fissure fountains. Episode 1 fountains occurred along a 5 km long fissure system that exploited the eastern-most kilometer of the Ko'ai fault system. A low, near-continuous, spatter rampart is present on the northern upwind and upslope side of the fissure. Most pyroclastic products, however, fell downwind to the south and little was preserved because of two processes: 1) incorporation of proximal spatter in rheomorphic lava flows 10--20 meters from the vents, and 2) downslope transport of cooler spatter falling on top of these flows >20 meters from vent. There is a clear 'lava-shed' delineation between lava that drained back into the fissure and lava that continued flowing into the flowfield. Vents range in surface geometry from linear--circular, with superimposed irregularity and sinuosity, and range from straight-sided--flaring cross-sectional geometries. Irregularity results from joints in the pre-existing wall rock. Sinuosity results from the local stress field. Geometry of non-flared vents could indicate the true geometry of the dike. Flared vents likely formed through mechanical erosion and thermo-mechanical abrasion. Vent positions along the fissure likely resulted from flow focusing. Uniquely, these vents drained and remain unobstructed (some >100 m depth), despite subsequent nearby eruptive activity. Three vents were imaged .16 m in depth at <4 cm resolution with tripodmounted LiDAR. Textural analyses of pyroclasts from eruptive episodes 2.12 show three distinct degassing and outgassing paths: 1) rapid degassing and quenching with minimal outgassing, 2

  14. Magmatic inclusions in rhyolites, contaminated basalts, and compositional zonation beneath the Coso volcanic field, California

    USGS Publications Warehouse

    Bacon, C.R.; Metz, J.

    1984-01-01

    Basaltic lava flows and high-silica rhyolite domes form the Pleistocene part of the Coso volcanic field in southeastern California. The distribution of vents maps the areal zonation inferred for the upper parts of the Coso magmatic system. Subalkalic basalts (<50% SiO2) were erupted well away from the rhyolite field at any given time. Compositional variation among these basalts can be ascribed to crystal fractionation. Erupted volumes of these basalts decrease with increasing differentiation. Mafic lavas containing up to 58% SiO2, erupted adjacent to the rhyolite field, formed by mixing of basaltic and silicic magma. Basaltic magma interacted with crustal rocks to form other SiO2-rich mafic lavas erupted near the Sierra Nevada fault zone. Several rhyolite domes in the Coso volcanic field contain sparse andesitic inclusions (55-61% SiO2). Pillow-like forms, intricate commingling and local diffusive mixing of andesite and rhyolite at contacts, concentric vesicle distribution, and crystal morphologies indicative of undercooling show that inclusions were incorporated in their rhyolitic hosts as blobs of magma. Inclusions were probably dispersed throughout small volumes of rhyolitic magma by convective (mechanical) mixing. Inclusion magma was formed by mixing (hybridization) at the interface between basaltic and rhyolitic magmas that coexisted in vertically zoned igneous systems. Relict phenocrysts and the bulk compositions of inclusions suggest that silicic endmembers were less differentiated than erupted high-silica rhyolite. Changes in inferred endmembers of magma mixtures with time suggest that the steepness of chemical gradients near the silicic/mafic interface in the zoned reservoir may have decreased as the system matured, although a high-silica rhyolitic cap persisted. The Coso example is an extreme case of large thermal and compositional contrast between inclusion and host magmas; lesser differences between intermediate composition magmas and inclusions lead to

  15. The mantle and basalt-crust interaction below the Mount Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schrader, C. M.; Crumpler, L. S.; Schmidt, M. E.

    2010-12-01

    The Mount Taylor Volcanic Field (MTVF) lies on the Jemez Lineament on the southeastern margin of the Colorado Plateau. The field is centered on the Mt. Taylor composite volcano and includes Mesa Chivato to the NE and Grants Ridge to the WSW. MTVF magmatism spans ~3.8-1.5 Ma (K-Ar, Perry et al., 1990). Magmas are dominantly alkaline with mafic compositions ranging from basanite to hy-basalt and felsic compositions ranging from ne-trachyte to rhyolite. We are investigating the state of the mantle and the spatial and temporal variation in basalt-crustal interaction below the MTVF by examining mantle xenoliths and basalts in the context of new mapping and future Ar-Ar dating. The earliest dated magmatism in the field is a basanite flow south of Mt. Taylor (Perry et al., 1990). Mantle xenolith-bearing alkali basalts and basanites occur on Mesa Chivato (Crumpler, 1980) and in the region of Mt. Taylor, though most basalts are peripheral to the main cone. Xenolith-bearing magmatism persists at least into the early stages of cone-building. Preliminary examination of the mantle xenolith suite suggests it is dominantly lherzolitic but contains likely examples of both melt-depleted (harzburgitic) and melt-enriched (clinopyroxenitic) mantle. There are aphyric and crystal-poor hawaiites, some of which are hy-normative (Perry et al., 1990), on and near Mt. Taylor, but many of the more evolved MTVF basalts show evidence of complex histories. Mt. Taylor basalts higher in the cone-building sequence contain >40% zoned plagioclase pheno- and megacrysts. Other basalts peripheral to Mt. Taylor and at Grants Ridge contain clinopyroxene and plagioclase megacrysts and cumulate-textured xenoliths, suggesting they interacted with lower crustal cumulates. Among the questions we are addressing: What was the chemical and thermal state of the mantle recorded by the basaltic suites and xenoliths and how did it change with time? Are multiple parental basalts (Si-saturated vs. undersaturated

  16. The Mantle and Basalt-Crust Interaction Below the Mount Taylor Volcanic Field, New Mexico

    NASA Technical Reports Server (NTRS)

    Schrader, Christian M.; Crumpler, Larry S.; Schmidt, Marick E.

    2010-01-01

    The Mount Taylor Volcanic Field (MTVF) lies on the Jemez Lineament on the southeastern margin of the Colorado Plateau. The field is centered on the Mt. Taylor composite volcano and includes Mesa Chivato to the NE and Grants Ridge to the WSW. MTVF magmatism spans approximately 3.8-1.5 Ma (K-Ar). Magmas are dominantly alkaline with mafic compositions ranging from basanite to hy-basalt and felsic compositions ranging from ne-trachyte to rhyolite. We are investigating the state of the mantle and the spatial and temporal variation in basalt-crustal interaction below the MTVF by examining mantle xenoliths and basalts in the context of new mapping and future Ar-Ar dating. The earliest dated magmatism in the field is a basanite flow south of Mt. Taylor. Mantle xenolith-bearing alkali basalts and basanites occur on Mesa Chivato and in the region of Mt. Taylor, though most basalts are peripheral to the main cone. Xenolith-bearing magmatism persists at least into the early stages of conebuilding. Preliminary examination of the mantle xenolith suite suggests it is dominantly lherzolitic but contains likely examples of both melt-depleted (harzburgitic) and melt-enriched (clinopyroxenitic) mantle. There are aphyric and crystal-poor hawaiites, some of which are hy-normative, on and near Mt. Taylor, but many of the more evolved MTVF basalts show evidence of complex histories. Mt. Taylor basalts higher in the cone-building sequence contain >40% zoned plagioclase pheno- and megacrysts. Other basalts peripheral to Mt. Taylor and at Grants Ridge contain clinopyroxene and plagioclase megacrysts and cumulate-textured xenoliths, suggesting they interacted with lower crustal cumulates. Among the questions we are addressing: What was the chemical and thermal state of the mantle recorded by the basaltic suites and xenoliths and how did it change with time? Are multiple parental basalts (Si-saturated vs. undersaturated) represented and, if so, what changes in the mantle or in the tectonic

  17. Workshop on Mare Volcanism and Basalt Petrogenesis: Astounding Fundamental Concepts (AFC) Developed Over the Last Fifteen Years

    NASA Technical Reports Server (NTRS)

    Taylor, Lawrence A. (Editor); Longi, John (Editor)

    1991-01-01

    Papers presented at the workshop on mare volcanism and basalt petrogenesis are compiled. The discussion of recent ideas and concepts within the context of this workshop permitted to catch up on the developments over the last 15 years. The following subject areas were covered: (1) geological setting; (2) magma evolution and source regions; (3) magma source and ascent processes; and (4) history of volcanism.

  18. Continental flood basalt weathering as a trigger for Neoproterozoic Snowball Earth

    NASA Astrophysics Data System (ADS)

    Cox, Grant M.; Halverson, Galen P.; Stevenson, Ross K.; Vokaty, Michelle; Poirier, André; Kunzmann, Marcus; Li, Zheng-Xiang; Denyszyn, Steven W.; Strauss, Justin V.; Macdonald, Francis A.

    2016-07-01

    Atmospheric CO2 levels and global climate are regulated on geological timescales by the silicate weathering feedback. However, this thermostat has failed multiple times in Earth's history, most spectacularly during the Cryogenian (c. 720-635 Ma) Snowball Earth episodes. The unique middle Neoproterozoic paleogeography of a rifting, low-latitude, supercontinent likely favored a globally cool climate due to the influence of the silicate weathering feedback and planetary albedo. Under these primed conditions, the emplacement and weathering of extensive continental flood basalt provinces may have provided the final trigger for runaway global glaciation. Weathering of continental flood basalts may have also contributed to the characteristically high carbon isotope ratios (δ13 C) of Neoproterozoic seawater due to their elevated P contents. In order to test these hypotheses, we have compiled new and previously published Neoproterozoic Nd isotope data from mudstones in northern Rodinia (North America, Australia, Svalbard, and South China) and Sr isotope data from carbonate rocks. The Nd isotope data are used to model the mafic detrital input into sedimentary basins in northern Rodinia. The results reveal a dominant contribution from continental flood basalt weathering during the ca. 130 m.y. preceding the onset of Cryogenian glaciation, followed by a precipitous decline afterwards. These data are mirrored by the Sr isotope record, which reflects the importance of chemical weathering of continental flood basalts on solute fluxes to the early-middle Neoproterozoic ocean, including a pulse of unradiogenic Sr input into the oceans just prior to the onset of Cyrogenian glaciation. Hence, our new data support the hypotheses that elevated rates of flood basalt weathering contributed to both the high average δ13 C of seawater in the Neoproterozoic and to the initiation of the first (Sturtian) Snowball Earth.

  19. Stratigraphical framework of basaltic lavas in Torres Syncline main valley, southern Parana-Etendeka Volcanic Province

    NASA Astrophysics Data System (ADS)

    Rossetti, Lucas M.; Lima, Evandro F.; Waichel, Breno L.; Scherer, Claiton M.; Barreto, Carla J.

    2014-12-01

    The Paraná-Etendeka Volcanic Province records the volcanism of the Early Cretaceous that precedes the fragmentation of the South-Gondwana supercontinent. Traditionally, investigations of these rocks prioritized the acquisition of geochemical and isotopic data, considering the volcanic stack as a monotonous succession of tabular flows. Torres Syncline is a tectonic structure located in southern Brazil and where the Parana-Etendeka basalts are well preserved. This work provides a detailed analysis of lithofacies and facies architecture, integrated to petrographic and geochemical data. We identified seven distinct lithofacies grouped into four facies associations related to different flow morphologies. The basaltic lava flows in the area can be divided into two contrasting units: Unit I - pahoehoe flow fields; and Unit II - simple rubbly flows. The first unit is build up by innumerous pahoehoe lava flows that cover the sandstones of Botucatu Formation. These flows occur as sheet pahoehoe, compound pahoehoe, and ponded lavas morphologies. Compound lavas are olivine-phyric basalts with intergranular pyroxenes. In ponded lavas and cores of sheet flows coarse plagioclase-phyric basalts are common. The first pahoehoe lavas are more primitive with higher contents of MgO. The emplacement of compound pahoehoe flows is related to low volume eruptions, while sheet lavas were emplaced during sustained eruptions. In contrast, Unit II is formed by thick simple rubbly lavas, characterized by a massive core and a brecciated/rubbly top. Petrographically these flows are characterized by plagioclase-phyric to aphyric basalts with high density of plagioclase crystals in the matrix. Chemically they are more differentiated lavas, and the emplacement is related to sustained high effusion rate eruptions. Both units are low TiO2 and have geochemical characteristics of Gramado magma type. The Torres Syncline main valley has a similar evolution when compared to other Large Igneous Provinces

  20. Synchronous late Pleistocene extensional faulting and basaltic volcanism in pluvial Fort Rock basin, central Oregon

    NASA Astrophysics Data System (ADS)

    Mackey, B. H.; Castonguay, S. R.; Wallace, P. J.; Weldon, R. J.

    2012-12-01

    Central Oregon, where northern Basin and Range extension intersects the High Lava Plains, exhibits widespread extensional faulting and Quaternary basaltic volcanism, yet the relations between the processes are complex and chronology is poorly constrained. Here we use cosmogenic 3He exposure dating of basalt to quantify the timing of normal faulting and emplacement of a related cinder cone volcanic field on the margins of pluvial Fort Rock Lake. The N15W striking North Christmas Valley fault system offsets High Lava Plains volcanics forming a ~3 km wide graben that transects the eastern Fort Rock Basin. Several young volcanic vents, including the ~740 ka Green Mountain (GM) shield volcano, and younger Four Craters lava field (4C), are aligned parallel with, and bounded by the graben. The western edge of the graben is expressed as an enigmatic monocline with up to10 m vertical throw and a prominent vertical hinge crack due to folding of the overlying GM lava flows. Younger basalt flows of the 4C field abut and flow into this crack, known as the 'Crack in the Ground' fault. Exposure dating of the 4C lava field on the eastern flank of GM indicates an emplacement age of 13 ka, which is largely consistent across multiple flows emerging from the 4 linearly aligned cinder cones. In addition, we dated the GM basalt exposed in the sub-vertical walls of the crack (the fault wall), which are cleanly separated by up to 10 m, but with uneroded (and in places identically matching) crack walls. Samples were taken >3 m below ground surface to avoid pre-faulting inheritance, and required considerable shielding corrections, but return a consistent exposure age of ~13 ka. This suggests substantial crack opening occurred at the same time the 4C lava was emplaced. A small fault offsets the 4C lava where it flows across the Crack, and dating the fault wall of this younger lava also generated an exposure age of 13 ka, indicating it must have ruptured shortly after the 4C lava cooled

  1. A lithospheric instability origin for Columbia River flood basalts and Wallowa Mountains uplift in northeast Oregon.

    PubMed

    Hales, T C; Abt, D L; Humphreys, E D; Roering, J J

    2005-12-01

    Flood basalts appear to form during the initiation of hotspot magmatism. The Columbia River basalts (CRB) represent the largest volume of flood basalts associated with the Yellowstone hotspot, yet their source appears to be in the vicinity of the Wallowa Mountains, about 500 km north of the projected hotspot track. These mountains are composed of a large granitic pluton intruded into a region of oceanic lithosphere affinity. The elevation of the interface between Columbia River basalts and other geological formations indicates that mild pre-eruptive subsidence took place in the Wallowa Mountains, followed by syn-eruptive uplift of several hundred metres and a long-term uplift of about 2 km. The mapped surface uplift mimics regional topography, with the Wallowa Mountains in the centre of a 'bull's eye' pattern of valleys and low-elevation mountains. Here we present the seismic velocity structure of the mantle underlying this region and erosion-corrected elevation maps of lava flows, and show that an area of reduced mantle melt content coincides with the 200-km-wide topographic uplift. We conclude that convective downwelling and detachment of a compositionally dense plutonic root can explain the timing and magnitude of Columbia River basalt magmatism, as well as the surface uplift and existence of the observed melt-depleted mantle. PMID:16341011

  2. Alteration, mass conservation, and magmatic compositions of lavas of the Columbia River flood basalt province: Insights from the Sentinel Bluffs Member, Grande Ronde Basalt

    NASA Astrophysics Data System (ADS)

    Sawlan, M. G.

    2013-12-01

    Understanding magmatic processes involved in flood basalt volcanism, and the ability to correlate flows within the voluminous, widespread lava fields requires accurate characterization of their magmatic geochemistry. Although evidence of alteration is widespread, modifications to lava chemistry by secondary processes are poorly understood. This results in uncertainty in the interpretation of geochemical analyses of Columbia River Basalt Group lava flows, particularly those of the Grande Ronde Basalt (GRB), in which chemical differences between the lavas are subtle. This problem is addressed here using major and trace element analyses (XRF) of samples of the Sentinel Bluffs Member (SB) of the GRB collected from multiple stratigraphic sections within the Columbia Plateau, Columbia River Gorge and Coast Ranges. Sixteen chemical groups, comprising 1-3 flows each, are recognized among multiple SB lava compositions. Flows assigned to three or four successive chemical groups are, in turn, assigned to more broadly defined chemical series based on shared characteristics such as immobile element ratios. Magmatic and alteration trends among SB compositions are clearly distinguished in Al-Ti variations. Magmatic trends are defined by inverse correlation of Al2O3 and TiO2. Alteration trends, extending from the magmatic array to higher abundances, are characterized by constant Al2O3/TiO2. Paired enrichments in Al and Ti, as well as other immobile elements, result from concentration in the residuum of altered rock that has lost mass due to soluble cation removal. Such enrichments are inversely proportional to mass loss. A mass conservation index (MCI), derived from Al-Ti systematics, quantifies mass retention and has multiple applications. MCI normalization eliminates residual concentration accompanying mass loss such that MCI-normalized immobile element abundances in altered rock agree with those in high-MCI rock. Compositions filtered to high-MCI values more closely reflect

  3. Oscillatory Thermochemical Convection as a Cause for the Episodic Mare Basalt Volcanism in the PKT Region of the Moon

    NASA Astrophysics Data System (ADS)

    Qin, C.; Zhong, S.

    2014-12-01

    The Moon possesses a number of hemispheric asymmetries including crustal thickness and mare basalt volcanism. Lunar mare volcanism, which lasted from about 4.0 to 1.5 Ga and occurred mostly on the nearside, is crucial in understanding the evolutionary history of the Moon. Recently, we analyzed the mare basalt age distribution for major mare basins, based on the latest mare basalt dating results from the crater size-frequency distribution measurements. Our analysis shows that most mare basalt eruptions are peaked at ~3.6 Ga and end at ~2.8 Ga, while mares Oceanus Procellarum, Imbrium, and Insularum in the Procelluram KREEP Terrane (PKT) feature episodic volcanism with reducing activities in the late stage. In this study, we propose that the episodic mare basalt volcanism is caused by oscillatory thermochemical convection, and has a strong correlation with the KREEP-enriched PKT. We formulate 3-D spherical thermochemical mantle convection models to investigate the genesis of episodic mare volcanism in one hemisphere, and the role of PKT in inducing and maintaining mare eruptions within its region. A MIC (mixture of ilmenite-rich cumulates and olivine-pyroxene) layer, which is rich in radiogenic elements and has a larger intrinsic density than the ambient mantle, is proposed to be the mare basalt source material. MIC is heated up due to radiogenic heating to become thermally buoyant and rise to the mare basalt source region, causing melting. When the heat is released to the extent that MIC becomes negatively buoyant, MIC sinks back to depth. Such a process may occur repetitively, causing episodic volcanism. On the other hand, the heating from KREEP materials in the PKT may maintain a high temperature anomaly in the nearside mantle that favors very long wavelength (i.e., degree 1) upwellings in the PKT region. This process may control the long-term evolution of the lunar interior and have implication for the present-day lunar mantle structure and dynamics.

  4. Martian volcanism: Festoon-like ridges on terrestrial basalt flows and implications for Mars

    NASA Technical Reports Server (NTRS)

    Theilig, E.; Greeley, Ronald

    1987-01-01

    The Fink and Fletcher, and Fink model was used to assess and compare flow rheology for two terrestrial basalt flows and one Martian flow with previous studies. Based on the morphologic similarities between the Martian flows and the Icelandic flows and knowledge of the emplacement of the terrestrial flows, the flows west of Arsia Mons are considered to have been emplaced as large sheet flows from basaltic flood style eruptions. Festoon ridges represent folding of the surface crust in the last stages of emplacement when viscosities would be high due to cooling. Alternatively, the lava may have had a high crystallinity or was erupted at low temperatures. In addition, increased compressive stress behind halted flow fronts or in ponded areas may have contributed to ridge formation.

  5. Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction.

    PubMed

    Whiteside, Jessica H; Olsen, Paul E; Eglinton, Timothy; Brookfield, Michael E; Sambrotto, Raymond N

    2010-04-13

    A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO(2). The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie's Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO(2) super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date. PMID:20308590

  6. Oxygen Isotopes in Intra-Back Arc Basalts from the Andean Southern Volcanic Zone

    NASA Astrophysics Data System (ADS)

    Parks, B. H.; Wang, Z.; Saal, A. E.; Frey, F. A.; Blusztajn, J.

    2013-12-01

    The chemical compositions of volcanic rocks from the Andean Southern Volcanic Zone (SVZ) reflect complex and dynamic interactions among the subducting oceanic lithosphere, the mantle wedge, and the overlying continental crust. Oxygen isotope ratios of olivine phenocrysts can be a useful means to identifying their relative contributions to the arc magmatism. In this study, we report high-precision oxygen-isotope ratios of olivine phenocrysts in a set of intra-back arc basalts from the SVZ. The samples were collected from monogenetic cinder cones east of the volcanic front (35-39 degrees S), and have been geochemically well-characterized with major and trace element contents, and Sr-Nd-Pb isotope compositions. Compared to lavas from the volcanic front, these intra-back arc lavas have similar radiogenic isotope, and a more alkalic and primitive (higher MgO content) chemical composition. We determined the oxygen-isotope ratios using the CO2-laser-fluorination method set up at the Department of Geology and Geophysics, Yale University following the techniques reported in Wang et al (2011). The samples were analyzed with standards of Gore Mountain Garnet (5.77×0.12‰ 1σ; Valley et al., 1995) and Kilbourne Hole Olivine (5.23×0.07‰ 1σ; Sharp, 1990) in order to account for minor changes in the vacuum line during analyses. The obtained δ18OSMOW values of olivine phenocrysts from the intra-back arc basalts vary from 4.98×0.01 to 5.34×0.01‰. This range, surprisingly, is similar to the δ18O values of olivines from mantle peridotites (5.2×0.2‰). Preliminary results indicate significant correlations of 87Sr/86Sr, 143Nd/144Nd and trace element ratios of the basaltic matrix with the δ18O values of olivine phenocrysts, indicating at least three components involved in the formation of the arc volcanism. By comparing the δ18O with the variations of major and trace element contents (e.g., MgO, TiO2 and Ni), and trace element ratios (e.g. Ba/Nb), we evaluate the effects

  7. Major CO2 source and sink perturbations of the global carbon cycle due to rapid emplacement of Continental Flood Basalts

    NASA Astrophysics Data System (ADS)

    Schaller, M. F.; Wright, J. D.; Kent, D. V.

    2011-12-01

    Recent evidence from the ~201.5 Ma Central Atlantic Magmatic Province (CAMP) in the Newark Rift Basin demonstrates that this Large Igneous Province (LIP) produced a transient doubling of atmospheric pCO2, followed by a ~300 kyr falloff to near pre-eruptive concentrations after each major eruptive episode (Schaller, Wright and Kent; Science, 2011). Here we similarly use pedogenic carbonates to test the million-year effects of the CAMP volcanism on Early Jurassic pCO2 in the corollary Hartford Basin of Eastern North America (ENA). In both basins we find a pre-CAMP pCO2 background of ~2000 ± 700 ppm, increasing to ~4500 ± 1600 ppm immediately above the first flow unit, followed by 300 kyr post-extrusive decrease to near background concentrations. The long post-extrusive section of the Hartford Basin shows the same ~300 kyr pCO2 decrease to pre-eruptive background, which continues to levels below pre-CAMP background over the subsequent 1.5 Myr following the final episode of eruptions. We use a geochemical model to demonstrate that the rapidity of the pCO2 decreases, and the fall to concentrations below background may be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the more highly weatherable CAMP basalts themselves. This indicates that continental flood basalts capable of producing a short-term perturbation of the carbon system may actually have an overall net-cooling effect on global climates due to a long-term net-decrease in pCO2 to below pre-eruptive levels. Analysis of the effusive potential for various submarine and continental LIPs based on reconstructed volumes suggests that those comparable to, or even larger than the CAMP may have had a significant effect on short term pCO2 concentrations, but this effect is highly dependent on effusive timescale. However, we pose the testable hypothesis that only continental flood basalts participate directly on both the CO2 source and sink side of the

  8. Basaltic continental intraplate volcanism as sustained by shear-driven upwelling

    NASA Astrophysics Data System (ADS)

    Ballmer, M. D.; Conrad, C. P.; Smith, E. I.

    2012-04-01

    While most volcanism on Earth occurs at plate boundaries, the study of intraplate basaltic volcanism may provide an opportunity to scrutinize the make-up and dynamics of the mantle. In continental settings, a range of mechanisms were proposed to sustain mantle decompression and hence to support such volcanism. These include mantle plumes, fertile melting anomalies, self-sustaining buoyant decompression melting, lithospheric dripping, and edge-driven small-scale convection. Recently, Conrad et al. showed that basaltic continental volcanism occurs more often where shear across the asthenosphere is greatest, and hence propose shear-driven upwelling (SDU) to support such volcanism¹. SDU does not require density heterogeneity to drive convection, in contrast to other mechanisms. Rather, it develops when rapid shear across the asthenosphere meets lateral viscosity variation2. For example, in a case with a low-viscosity pocket in the mantle, asthenospheric shear is accommodated in a different manner across the pocket than across the ambient mantle. This contrast drives vertical flow close to the margins of the pocket, and may be sufficient to sustain decompression melting, particularly if the viscosity anomaly is supported by higher water contents or temperatures2. Mantle melting is also expected for situations in which asthenospheric shear flow enters a lithospheric cavity, or decompresses across a step in lithospheric thickness3 - and even more so if a low-viscosity pocket is entrained in such a flow. Seismic observations indicate that sublithospheric topography, and heterogeneity in mantle viscosity are indeed common beneath continents (regardless of whether the imaged anomalies are thermal or compositional in origin). We use three-dimensional numerical models to explore shear-driven flow, and investigate a range of cases with pockets of variable viscosity contrast and shape, lithospheric steps of variable offset and spacing, and asthenospheric flow with variable

  9. Rock types of South Pole-Aitken basin and extent of basaltic volcanism

    USGS Publications Warehouse

    Pieters, C.M.; Head, J. W., III; Gaddis, L.; Jolliff, B.; Duke, M.

    2001-01-01

    The enormous pre-Nectarian South Pole-Aitken (SPA) basin represents a geophysically and compositionally unique region on the Moon. We present and analyze the mineralogical diversity across this basin and discuss the implications for basin evolution. Rock types are derived from Clementine multispectral data based on diagnostic characteristics of ferrous absorptions in fresh materials. Individual areas are characterized as noritic (dominated by low-Ca pyroxene), gabbroic/basaltic (dominated by high-Ca pyroxene), feldspathic (<3-6% FeO), and olivine-gabbro (dominated by high-Ca pyroxene and olivine). The anorthositic crust has effectively been removed from the interior of the basin. The style of volcanism within the basin extends over several 100 Myr and includes mare basalt and pyroclastic deposits. Several areas of ancient (pre-Orientale) volcanism, or cryptomaria, have also been identified. The nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically. We interpret this to represent impact melt/breccia deposits derived from the lower crust. A few localized areas are identified within the basin that contain more diverse lithologies (gabbro, olivine-gabbro), some of which may represent material from the deepest part of the lower crust and perhaps uppermost mantle involved in the SPA event. Copyright 2001 by the American Geophysical Union.

  10. Differential control in the formation of river potholes on basalts of the Paraná Volcanic Province

    NASA Astrophysics Data System (ADS)

    Lima, Adalto Gonçalves; Binda, Andrey Luis

    2015-04-01

    Variations in rock properties control geomorphic processes and thus landscape evolution. Potholes developed on basaltic riverbeds are generally associated with vesicular-amygdaloidal zones, although they also occur in massive basalts. Until now, this relationship has not been quantified, nor have the parameters controlling the development of these features in basalts been evaluated. Based on field data collected from 71 sites distributed in three rivers in the Paraná Volcanic Province (PVP), southern Brazil, we investigated the relationship between the occurrence of potholes and features of basalt flows. Reaches were analyzed both in areas with potholes and in areas without these features. The data collected refer to the joint density, the intact rock strength measured with a Schmidt hammer and the typology of basaltic units in terms of vesicularity. It was found that potholes preferentially occur in vesicular-amygdaloidal units (86%). This predominance is not associated with the joint density, which is the same in massive basalts (≈5 m/m2); moreover, potholes occur in basalts with very different joint densities. The intact rock strength is lower in vesicular-amygdaloidal basalts (58) than in massive basalts (61) and does not explain fully the preferential abrasion in vesicular-amygdaloidal units because potholes occur with varying resistances. The basalt strength is a secondary variable. The controlling parameter seems to be vesicularity, which by producing irregularities in the bed and flow triggers the formation of potholes. In the massive basalts, irregularities are produced primarily by joints. In massive basalts there seems to be an upper threshold of stream power beyond which the formation of potholes is restricted (drainage area ≈700 km2; slope ≈0.06). A lower threshold in stream power could also exist to massive basalts of the study area and it is suggested by the inexistence of potholes in sites with drainage area less than 100 km2.

  11. Enriched continental flood basalts from depleted mantle melts: modeling the lithospheric contamination of Karoo lavas from Antarctica

    NASA Astrophysics Data System (ADS)

    Heinonen, Jussi S.; Luttinen, Arto V.; Bohrson, Wendy A.

    2016-01-01

    Continental flood basalts (CFBs) represent large-scale melting events in the Earth's upper mantle and show considerable geochemical heterogeneity that is typically linked to substantial contribution from underlying continental lithosphere. Large-scale partial melting of the cold subcontinental lithospheric mantle and the large amounts of crustal contamination suggested by traditional binary mixing or assimilation-fractional crystallization models are difficult to reconcile with the thermal and compositional characteristics of continental lithosphere, however. The well-exposed CFBs of Vestfjella, western Dronning Maud Land, Antarctica, belong to the Jurassic Karoo large igneous province and provide a prime locality to quantify mass contributions of lithospheric and sublithospheric sources for two reasons: (1) recently discovered CFB dikes show isotopic characteristics akin to mid-ocean ridge basalts, and thus help to constrain asthenospheric parental melt compositions and (2) the well-exposed basaltic lavas have been divided into four different geochemical magma types that exhibit considerable trace element and radiogenic isotope heterogeneity (e.g., initial ɛ Nd from -16 to +2 at 180 Ma). We simulate the geochemical evolution of Vestfjella CFBs using (1) energy-constrained assimilation-fractional crystallization equations that account for heating and partial melting of crustal wall rock and (2) assimilation-fractional crystallization equations for lithospheric mantle contamination by using highly alkaline continental volcanic rocks (i.e., partial melts of mantle lithosphere) as contaminants. Calculations indicate that the different magma types can be produced by just minor (1-15 wt%) contamination of asthenospheric parental magmas by melts from variable lithospheric reservoirs. Our models imply that the role of continental lithosphere as a CFB source component or contaminant may have been overestimated in many cases. Thus, CFBs may represent major juvenile crustal

  12. Late Quaternary geology of small basaltic volcanic centers, SW USA: Disparity among dating methods and implications for volcanic and geomorphic studies

    SciTech Connect

    Wells, S.; McFadden, L.; Perry, F.; Forman, S.; Crowe, B.; Pothis, J.; Olinger, C.

    1992-12-31

    Evaluation of volcanic hazards near the proposed high-level radioactive waste repository at Yucca Mountain provides the impetus for a series of detailed field and geochronologic studies of selected small late Quaternary basaltic scoria cones and lava flows in Nevada and California. Two of the most significant results of these studies are: the presence of chronostratigraphic units which indicate multiple eruptions with significant intervals of no activity between events (polycyclic volcanism); and a marked difference between conventional, numerical ages derived from K-Ar and Ar-40/Ar-39 methods and numerical, calibrated, and relative ages derived from thermoluminescence, cosmogenic He-3, the degree of soil development, and geomorphology of these volcanic landforms. Soil-bounded unconformities and buried stone pavements define the boundaries of chronostratigraphic units within these small volume basaltic centers. Volcanic centers displaying this type of stratigraphy may appear morphological simple but cannot be considered mongenetic. Recent studies by Perry and Crowe demonstrate that geochemical variations within a single basaltic volcanic center in NV are consistent with several magma batches forming a complex polycyclic volcano. The K-Ar and Ar-40/Ar-39 ages are 1--2 orders of magnitude older than either TL or cosmogenic He-3 and appear to have insufficient precision to constrain the ages of chronostratigraphic units within polycyclic volcanoes. In contrast, preliminary data indicate the TL and cosmogenic He-3 dating methods have the ability to resolve the late Quaternary volcanic stratigraphy, and results from these dating methods are consistent with the degree of soil development and geomorphic modification of the volcanic units. K-Ar and Ar-40/Ar-39 dates from these small basaltic volcanic centers have been used to calibrate new Quaternary dating methods, e.g. rock varnish, which in turn have been used to interpret landscape evolution in the SW US.

  13. Lithospheric-folding-based understanding on the origin of the back-arc basaltic magmatism beneath Jeju volcanic island, Korea

    NASA Astrophysics Data System (ADS)

    Yun, S.; Shin, Y.; CHOI, K.; Koh, J.; Nakamura, E.; Na, S.

    2012-12-01

    Jeju Island is an intraplate volcanic island located at the eastern margin on the East Asia behind the Ryukyu Trench, the collisional/subduction boundary between the Eurasian plate and Philippine Sea plate. It is a symmetrical shield volcano, having numerous monogenetic cinder cones, over 365, on the Mt. Halla volcanic edifice. The basement rock mainly consists of Precambrian gneiss, Mesozoic granite and volcanic rocks. Unconsolidated sedimentary rock is found between basement rock and surface lava. The lava plateau is composed of voluminous basaltic lava flows, which extend to the coast region with a gentle slope. Based on the evidence obtained from volcanic stratigraphy, paleontology, and geochronology, the age of the Jeju basalts ranges from the early Pleistocene to Holocene(Historic). The alkaline and tholeiitic basalts exhibits OIB composition from intraplate volcanism which is not associated with plate subduction, while the basement xenolith contained in the volcanic rock indicates that there were volcanic activities associated with the Mesozoic plate subduction. The Geochemical characteristics have been explained with the plume model, lithospheric mantle origin, and melting of shallow asthenosphere by the rapid change of stress regimes between the collision of the India-Eurasia plates and subduction of the Pacific plate, while there has not been any geophysical investigation to disclose it. Compression near collisional plate boundaries causes lithospheric folding which results in the decrease of pressure beneath the ridge of the fold while the pressure increases beneath trough. The decompression beneath lithosphere is likely to accelerate basaltic magmatism along and below the ridge. We investigate the subsurface structure beneath Jeju volcanic island, South Korea and its vicinity and propose an alternative hypothesis that the basaltic magma beneath the island could be caused by episodic lithospheric folding. Unlike the prevailing hypothesis of the

  14. Understanding heat and groundwater flow through continental flood basalt provinces: insights gained from alternative models of permeability/depth relationships for the Columbia Plateau, USA

    USGS Publications Warehouse

    Burns, Erick R.; Williams, Colin F.; Ingebritsen, Steven E.; Voss, Clifford I.; Spane, Frank A.; DeAngelo, Jacob

    2015-01-01

    Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600–900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~ 104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.

  15. Understanding heat and groundwater flow through continental flood basalt provinces: insights gained from alternative models of permeability/depth relationships for the Columbia Plateau, USA

    SciTech Connect

    Burns, Erick R.; Williams, Colin F.; Ingebritsen, Steven E.; Voss, Clifford I.; Spane, Frank A.; DeAngelo, Jacob

    2015-02-01

    Heat-flow mapping of the western USA has identified an apparent low-heat-flow anomaly coincident with the Columbia Plateau Regional Aquifer System, a thick sequence of basalt aquifers within the Columbia River Basalt Group (CRBG). A heat and mass transport model (SUTRA) was used to evaluate the potential impact of groundwater flow on heat flow along two different regional groundwater flow paths. Limited in situ permeability (k) data from the CRBG are compatible with a steep permeability decrease (approximately 3.5 orders of magnitude) at 600–900 m depth and approximately 40°C. Numerical simulations incorporating this permeability decrease demonstrate that regional groundwater flow can explain lower-than-expected heat flow in these highly anisotropic (kx/kz ~ 104) continental flood basalts. Simulation results indicate that the abrupt reduction in permeability at approximately 600 m depth results in an equivalently abrupt transition from a shallow region where heat flow is affected by groundwater flow to a deeper region of conduction-dominated heat flow. Most existing heat-flow measurements within the CRBG are from shallower than 600 m depth or near regional groundwater discharge zones, so that heat-flow maps generated using these data are likely influenced by groundwater flow. Substantial k decreases at similar temperatures have also been observed in the volcanic rocks of the adjacent Cascade Range volcanic arc and at Kilauea Volcano, Hawaii, where they result from low-temperature hydrothermal alteration.

  16. Changing eruptive styles in basaltic explosive volcanism: Examples from Croscat complex scoria cone, Garrotxa Volcanic Field (NE Iberian Peninsula)

    NASA Astrophysics Data System (ADS)

    Di Traglia, F.; Cimarelli, C.; de Rita, D.; Gimeno Torrente, D.

    2009-03-01

    The Croscat pyroclastic succession has been analysed to investigate the transition between different eruptive styles in basaltic monogenetic volcanoes, with particular emphasis on the role of phreatomagmatism in triggering Violent Strombolian eruptions. Croscat volcano, an 11 ka basaltic complex scoria cone in the Quaternary Garrotxa Volcanic Field (GVF) shows pyroclastic deposits related both to magmatic and phreatomagmatic explosions. Lithofacies analysis, grain size distribution, chemical composition, glass shard morphologies, vesicularity, bubble-number density and crystallinity of the Croscat pyroclastic succession have been used to characterize the different eruptive styles. Eruptions at Croscat began with fissural Hawaiian-type fountaining that rapidly changed to eruption types transitional between Hawaiian and Strombolian from a central vent. A first phreatomagmatic phase occurred by the interaction between magma and water from a shallow aquifer system at the waning of the Hawaiian- and Strombolian-types stage. A Violent Strombolian explosion then occurred, producing a widespread (8 km 2), voluminous tephra blanket. The related deposits are characterized by the presence of wood-shaped, highly vesicular scoriae. Glass-bearing xenoliths (buchites) are also present within the deposit. At the waning of the Violent Strombolian phase a second phreatomagmatic phase occurred, producing a second voluminous deposit dispersed over 8.4 km 2. The eruption ended with a lava flow emission and consequent breaching of the western-side of the volcano. Our data suggest that the Croscat Violent Strombolian phase was related to the ascent of deeper, crystal-poor, highly vesicular magma under fast decompression rate. Particles and vesicles elongation and brittle failure observed in the wood-shaped clasts indicate that fragmentation during Violent Strombolian phase was enhanced by high strain-rate of the magma within the conduit.

  17. Osmium and neodymium isotopic constraints on the temporal and spatial evolution of Siberian flood basalt sources

    USGS Publications Warehouse

    Horan, M.F.; Walker, R.J.; Fedorenko, V.A.; Czamanske, G.K.

    1995-01-01

    Picrites from the Gudchikhinsky suite, the oldest rocks examined, have ??Os of +5.3 to +6.1 and ??Nd of +3.7 to +4.0. The osmium and neodymium isotopic compositions of these rocks are similar to some modern ocean-island basalts (OIB), consistent with their derivation from an mantle plume. Picrites from the stratigraphically higher Tuklonsky suite have similar ??Os of +3.4 to +6.5, but ??Nd of -0.9 to -2.6. The similar ??Os, but lower ??Nd , suggest that some magmas from the same OIB-type, mantle source were contaminated by lithospheric components. A differentiated ankaramite flow, associated with the top of the stratigraphically higher Morongovsky suite, has ??Os of +9.8 to +10.2 and ??Nd of +1.3 to +1.4. The higher ??Os may indicate that the plume source was heterogeneous with respect to osmium isotopic composition, consistent with osmium isotopic measurements in rocks from other plume sources. Mg-rich, alkaline rocks (meymechites) from the Guli area that erupted much nearer the end of the flood-basalt event have ??Os of -1.2 to -2.6 and ??Nd of +3.7 to +4.9. These rocks were probably produced by low degrees of partial melting of mantle after the main stages of flood-basalt production. -from Authors

  18. Megacrystic Clinopyroxene Basalts Sample A Deep Crustal Underplate To The Mount Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schmidt, M. E.; Schrader, C. M.; Crumpler, L. S.; Wolff, J. A.

    2012-12-01

    The alkaline and compositionally diverse (basanite to high-Si rhyolite) Mount Taylor Volcanic Field (MTVF), New Mexico comprises 4 regions that cover ~75 x 40 km2: (1) Mount Taylor, a large composite volcano and a surrounding field of basaltic vents; (2) Grants Ridge, constructed of topaz rhyolitic ignimbrite and coulees; (3) Mesa Chivato, a plateau of alkali basalts and mugearitic to trachytic domes; and (4) the Rio Puero basaltic necks. Distributed throughout its history (~3.6 to 1.26 Ma; Crumpler and Goff, 2012) and area (excepting Rio Puerco Necks) is a texturally distinct family of differentiated basalts (Mg# 43.2-53.4). These basalts contain resorbed and moth-eaten megacrysts (up to 2 cm) of plagioclase, clinopyroxene, and olivine ±Ti-magnetite ±ilmenite ±rare orthopyroxene. Some megacrystic lava flows have gabbroic cumulate inclusions with mineral compositions similar to the megacrysts, suggesting a common origin. For instance, gabbroic and megacrystic clinopyroxenes form linear positive arrays in TiO2 (0.2-2.3 wt%) with respect to Al2O3 (0.7-9.3 wt%). The lowest Al clinopyroxenes are found in a gabbroic inclusion and are associated with partially melted intercumulus orthopyroxene. Megacrystic and gabbroic plagioclase (An 41-80) in 4 representative thin sections were analyzed for 87Sr/86Sr by Laser Ablation ICP-MS. 87Sr/86Sr values for the suite range from 0.7036 to 0.7047. The low 87Sr/86Sr plagioclases (0.7036 to 0.7037) are associated with high Ti-Al clinopyroxenes. Likewise, the higher 87Sr/86Sr plagioclases (0.7043 to 0.7047) are associated with the low-Al clinopyroxenes. Taken together, these megacrysts track the differentiation of an intrusive body (or related bodies) from alkaline to Si-saturated conditions by fractional crystallization and crustal assimilation. The intrusive body likely underplates portions of the MTVF that have generated silicic magmas (Mount Taylor, Grants Ridge, Mesa Chivato). Although disequilibrium is implied by resorbed

  19. Petrology and geochemistry of high cascade volcanics in southern Washington: Mount St. Helens volcano and the Indian Heaven basalt field

    SciTech Connect

    Smith, D.R.

    1984-01-01

    Mount St. Helens volcano (Washington, USA) has been characterized by four eruptive periods during the last 2200 years. Eruptive products include a wide spectrum of rock types including basaltic to andesitic lavas, andesitic to dacitic pyroclastic flows and tephra, and dacite domes. The major and trace element compositions of some andesites and dacites are broadly consistent with their derivation from a basaltic andesite parental magma by fractional cyrstallization processes involving the observed phenocryst assemblages. However, the strontium and oxygen isotopic compositions of representative samples of the Mount St. Helens suite indicate that closed system processes cannot explain the isotopic variations. The isotopic rations are positively correlated with one another and the bulk composition (SiO/sub 2/, Mg number, etc.). The vents of the nearby Indian Heaven Quaternary volcanic field erupted several basalt types which can be defined on the basis of major and trace element composition - calcalkaline (low and high TiO/sub 2/ varieties), transitional, and tholeiitic. Several of these basalt types occur at Mount St. Helens as well, but Indian Heaven lavas are generally more primitive as indicated by higher Mg/(Mg + Fe) ratios. The distribution of volcanic rock types in relation to local structures in the Cascade Range of southern Washington and northern Oregon suggests that crustal structure may influence the degree of evolution of specific volcanic fields. Cascade arc suggests that volcanic arc magma evolution does not necessarily produce a continuous sequence from tholeiitic to calcalkaline rocks in time or space.

  20. Basaltic Clasts in Y-86032 Feldspathic Lunar Meteorite: Ancient Volcanism far from the Procellarum Kreep Terrane

    NASA Technical Reports Server (NTRS)

    Yamaguchi, A.; Takeda, H.; Nyquist, L. E.; Bogard, D.; Karouji, Y.; Ebihara, M.

    2008-01-01

    Lunar meteorite, Y-86032 is a fragmental or regolith breccia enriched in Al2O3 (28-31 wt%) and having very low concentrations of REEs and Th, U [e.g., 1]. Nyquist et al. [2] suggested that Y- 86032 contains a variety of lithologies not represented by the Apollo samples. They found clasts with old Ar-Ar ages and an ancient Sm-Nd age, and negative Nd indicating a direct link to the primordial magma ocean. Importantly, the final lithification of the Y-86032 breccia was likely >3.8-4.1 Ga ago. Therefore, any lithic components in the breccia formed prior to 3.8 Ga, and lithic components in breccia clasts in the parent breccia formed even earlier. Here we report textures and mineralogy of basaltic and gabbroic clasts in Y- 86032 to better understand the nature of ancient lunar volcanism far from the Procellarum KREEP Terrain (PKT) [3] and the central nearside.

  1. Neogene to Quaternary basalts of the Jabal Eghei (Nuqay) area (south Libya): Two distinct volcanic events or continuous volcanism with gradual shift in magma composition?

    NASA Astrophysics Data System (ADS)

    Radivojević, Maša; Toljić, Marinko; Turki, Salah M.; Bojić, Zoran; Šarić, Kristina; Cvetković, Vladica

    2015-02-01

    This study reports and discusses a set of new K/Ar age and new petrochemical data on basalts of the Jabal Eghei (Nuqay) area (south Libya). This area is part of a > 1000 km long NNW-SSE Libyan volcanic field that stretches from the Mediterranean coastal near Tripoli to the Tibesti massif in Chad. Whole rock K/Ar ages, stratigraphy, volcanology and rock petrochemistry indicate that the Jabal Eghei developed during two volcanic events. The first occurred from the Middle Miocene to the Pliocene (K/Ar ages from ~ 16 to ~ 5 Ma) when large volumes of low aspect ratio lava flows of transitional basalts formed. The second event happened in Pliocene-mid-Pleistocene time (4-≤ 1 Ma) and it gave rise to basanite spatter to scoria pyroclastic cones and subordinate lava flow facies. The transitional basalts are less primitive and less enriched in incompatible trace elements than the basanites. Petrochemical characteristics reveal that the transitional basalts underwent weak to moderate olivine-dominated fractionation and that crustal assimilation had negligible effects. REE geochemical modeling shows that primary magmas of both transitional basalts and basanites formed by melting of a similar garnet-bearing, primitive mantle-like source with degree of melting of 3-5% and ≤ 1%, respectively. It is also demonstrated that the transitional basalts show systematic compositional changes in time because progressively younger rocks are petrochemically more similar to basanites. We argue that our data definitely prove that the age pattern along the entire Libyan volcanic field is much more complex than it was thought before.

  2. The Cobb-Eickelberg seamount chain: Hotspot volcanism with mid-ocean ridge basalt affinity

    SciTech Connect

    Desonie, D.L.; Duncan, R.A. )

    1990-08-10

    Cobb hotspot, currently located beneath Axial seamount on the Juan de Fuca ridge, has the temporal but not the isotopic characteristics usually attributed to a mantle plume. The earlier volcanic products of the hotspot, form eight volcanoes in the Cobb-Eickelberg seamount (CES) chain, show a westward age progression away from the hotspot and a westward increase in the age difference between the seamounts and the crust on which they formed. These results are consistent with movement of the Pacific plate over a fixed Cobb hotspot and eventual encroachment by the westwardly migrating Juan de Fuca ridge. CES lavas are slightly enriched in alkalies and incompatible elements relative to those of the Juan de Fuca ridge but they have Sr, Nd, and Pb isotopic compositions virtually identical to those found along the ridge. Therefore, Cobb hotspot is a stationary, upper mantle melting anomaly whose volcanic products show strong mid-ocean ridge basalt (MORB) affinity. These observations can be explained by low degrees of partial melting of entrained heterogeneous upper mantle MORB source material within a thermally driven lower mantle diapir or by an intrinsic MORB-like composition of the deeper mantle source region from which northeast Pacific plumes rise.

  3. The geochemistry and petrogenesis of basalts from the Taupo Volcanic Zone and Kermadec Island Arc, S.W. Pacific

    NASA Astrophysics Data System (ADS)

    Gamble, J. A.; Smith, I. E. M.; McCulloch, M. T.; Graham, I. J.; Kokelaar, B. P.

    1993-01-01

    Basalts from the Taupo Volcanic Zone (TVZ), New Zealand, the Kermadec Island Arc (KA) and its back-arc basin, the Havre Trough show systematic variations in trace-element and isotope geochemistry which are attributed to differences in tectonic setting and source heterogeneity along a more or less continuous plate boundary. Basalts from the Kermadec Arc are characterised by low abundances of high field strength elements (HFSE) such as Ti, Zr, Nb, Ta and Hf and have high ratios of Ti/Zr and low ratios of Ti/Sc and Ti/V relative to typical MORB. Basalts from TVZ also show low abundances of the HFS elements relative to MORB but show lower Ti/Zr, higher Ti/V and Ti/Sc ratios and generally higher Zr abundances than KA most basalts. The Havre Trough basalt is mildly alkaline (< 1% normative nepheline) like many back-arc basin basalts from the Pacific rim, contrasting with the hypersthene normative TVZ and KA rocks. It has higher Zr than most TVZ basalts and all KA basalts. Ratios such as Ti/V, Ti/Sc and Ti/Zr are within the range of TVZ and MORB basalts but distinct from KA basalts. The depleted (relative to MORB) HFSE characteristics of the KA and TVZ basalts are complemented by high abundances of large ion lithophile elements (LIL), such as Ba, Rb and K, when compared to MORB, yielding the distinctive LIL-enriched pattern of subduction related rocks on a normalised multi-element plot. In contrast, the Havre Trough basalt is MORB-like. Chondrite-normalised Rare Earth Element (REE) patterns for the TVZ basalts show a field overlapping with that defined by the southern KA (Rumble Sea Mounts), with light REE enriched patterns (Ce/Yb n = ˜ 1.8-3) and flat heavy REE (Tb-Lu). Basalts from the northern KA are typically light REE depleted (Ce/Yb n = 0.5) or slightly enriched (Ce/Yb n = 1.5). The REE pattern of the Havre Trough basalt is distinctive from both the KA and TVZ fields, being richer in the heavy REE, yet similar to many basalts from back-arc basins. Sr and Nd

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

    USGS Publications Warehouse

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

    1998-01-01

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

  5. Oxygen buffering of Kilauea volcanic gases and the oxygen fugacity of Kilauea basalt

    NASA Astrophysics Data System (ADS)

    Gerlach, T. M.

    1993-02-01

    . This conclusion challenges the common assumption that volcanic gases are released from lava in a state of chemical equilibrium and then continue equilibrating homogeneously with falling temperature until reaction rates are unable to keep pace with cooling. No evidence is found, moreover, that certain gas species are kinetically more responsive and able to equilibrate down to lower temperatures than those of the last gas/lava oxygen exchange. Homogeneous reaction rates in the gas phase are apparently slow compared to the time it took for the gases to move from the last site of gas/lava equilibration to the site of collection. An earlier set of data for higher temperature CO 2-rich Type I volcanic gases, which come from sustained summit lava lake eruptions supplied by magma that experienced substantially shorter periods of crustal storage, shows fO2 buffering by oxygen transfer up to 1185°C. Oxygen fugacity measurements in drill holes into ponded lava flows suggest that buffering by oxygen transfer may control the fO2 of residual gases down to several hundred degrees below the solidus in the early stages of cooling. Although the details of the fO2 buffering mechanisms for oxygen transfer are unknown, the fact that fO2 buffering is effective from molten to subsolidus conditions suggests that the reaction mechanisms must change with cooling as the reactants change from predominantly melt, to melt plus crystals, to glass plus crystals. Mass balance calculations suggest that redox reactions between the gas and ferrous/ferric iron in the lava are plausible mechanisms for the oxygen transfer and that the fO2 of the gases is buffered by sliding ferrous/ferric equilibria in the erupting lavas. Contrary to expectations based on models predicting the oxidation of basalt by H 2 and CO escape during crustal storage, CO 2-rich Type I gases and CO 2-poor Type II gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories. Volcanic gas data

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

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

  7. Supercontinental warming of the mantle at the origin of gigantic flood basalts

    NASA Astrophysics Data System (ADS)

    Coltice, N.; Phillips, B. R.; Bertrand, H.; Ricard, Y.; Rey, P.

    2006-12-01

    Continents episodically cluster together into a supercontinent, eventually breaking up with intense magmatic activity supposedly causedby mantle plumes. The break-up of Pangea, the last supercontinent, was accompanied by the emplacement of the largest known continental flood basalt, the Central Atlantic Magmatic Province, causing massive extinctions at the Triassic/Jurassic boundary. However, there is little support for a plume origin for this catastrophic event. On the basis of 2D and 3D spherical convection modelling in a internally heated mantle, we show that continental aggregation leads to large-scale melting without requiring the involvement of plumes. When only internal heat sources in the mantle are considered, the formationof a supercontinent causes the enlargement of the wavelength of the flow and a subcontinental warming as large as 100^{\\mboxo}C. This temperature increase may lead to large- scale melting without the involvment of plumes. Our results suggest the existence of two distinct types of continental flood basalts, caused by plume or by supercontinental warming. We review some potential candidates for our proposed model.

  8. Megacrystic pyroxene basalts sample deep crustal gabbroic cumulates beneath the Mount Taylor volcanic field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schmidt, Mariek E.; Schrader, Christian M.; Crumpler, Larry S.; Rowe, Michael C.; Wolff, John A.; Boroughs, Scott P.

    2016-04-01

    Distributed over the ~ 2.3 m.y. history of the alkaline and compositionally diverse Mount Taylor Volcanic Field (MTVF), New Mexico is a widespread texturally distinct family of differentiated basalts that contain resorbed megacrysts (up to 3 cm) of plagioclase, clinopyroxene, and olivine ± Ti-magnetite ± ilmenite ± orthopyroxene. These lavas have gabbroic cumulate inclusions with mineral compositions similar to the megacrysts, suggesting a common origin. Gabbroic and megacrystic clinopyroxenes form positive linear arrays in TiO2 (0.2-2.3 wt.%) with respect to Al2O3 (0.7-9.3 wt.%). Plagioclase (An41-80) from representative thin sections analyzed for 87Sr/86Sr by laser ablation ICP-MS range from 0.7036 to 0.7048. The low 87Sr/86Sr plagioclases (0.7036 to 0.7037) are associated with high Ti-Al clinopyroxenes. Likewise, the higher 87Sr/86Sr plagioclases (0.7043 to 0.7047) are associated with the low-Al clinopyroxenes. Taken together, the pyroxene and plagioclase megacrysts appear to track the differentiation of a gabbroic pluton (or related plutons) from alkaline to Si-saturated conditions by fractional crystallization and crustal assimilation. Clinopyroxene-liquid geobarometry calculations suggest that crystallization occurred near the crust-mantle transition at an average of ~ 1200 °C and 12-13 kbar. The distribution of the megacrystic pyroxene basalts suggests that a gabbroic intrusive body underlies subregions of the MTVF that have generated silicic magmas. The gabbro is interpreted to be a significant heat and mass input into the lower crust that is capable of driving the petrogenesis of diverse silicic compositions (through fractionation and crustal assimilation), including mugearites, trachytes, trachy-andesites and dacites, high-Si rhyolites, and topaz rhyolites of the MTVF.

  9. Geochemical and petrologic investigation of the Ola Plateau-basalts from the Okhotsk-Chukotka Volcanic Belt (NE Russia)

    NASA Astrophysics Data System (ADS)

    Leitner, Jürgen; Ntaflos, Theodoros; Akinin, Vyacheslav; Tschegg, Cornelius

    2010-05-01

    The Okhotsk-Chukotka volcanic belt to a large degree consists of coeval Cretaceous and Early Tertiary volcanic and plutonic rocks that occur along the continental margin in northeast Russia. These igneous-arc related rocks build up an Andean-style magmatic arc sequence that occurs for about 3.500 km along the entire length of the Eurasian continent, from Chukotka Peninsula in the north down to north-east China. The rocks of the Okhotsk-Chukotka Volcanic Belt (OCVB) comprise Late Cretaceous, andesitic basalts, andesites, dacites, rhyolites, tuffs, rare beds of nonmarine clastic rocks with conglomerates and sandstones in the base and locally Paleocene gently dipping basalts. The duration of the magmatic activity in the Okhotsk-Chukotka volcanic belt is still in debate but generally it has been estimated from middle of Albian to Campanian. The studied area, the Ola Plateau Basalts (OPB) and the Hypotetica Basalts (HB), comprise basaltic andesites, trachy- basalts, basaltic trachy- andesite and rhyolitic dykes, belongs to the Okhotsk-Cukotka volcanic belt and represents the last volcanic activity related to the subduction of the palaeo-Pacific plate in this region. The exposed lavas have a thickness of 0.5 km and the estimated volume is about 222 km³. Fine grained 4 m thick rhyolitic dykes represent the very last event of the studied sequence. According to Ar/Ar and U/Pb dating (Hourigan, Akinin, 2004;), the average age of the OPB/ HB is 78.8 to 74 Ma. The basaltic rocks that build up the Ola Plateau are mainly fine grained calc- alkaline basalts with clinopyroxene, plagioclase and strongly to moderately altered olivine phenocrysts with spinel inclusions. The Mg# of the calc- alkaline basalts vary from 0.35 to 0.57 and the TiO2 from 1.2 to 2.2 wt% whereas CaO correlates positive with MgO contents. The OPB and HB lavas, according to their primitive mantle normalized trace elements, can be divided into three groups: Group (I) is characterized by positive Sr anomaly with

  10. Thermal and mass implications of magmatic evolution in the Lassen volcanic region, California, and minimum constraints on basalt influx to the lower crust

    USGS Publications Warehouse

    Guffanti, M.; Clynne, M.A.; Muffler, L.J.P.

    1996-01-01

    We have analyzed the heat and mass demands of a petrologic model of basaltdriven magmatic evolution in which variously fractionated mafic magmas mix with silicic partial melts of the lower crust. We have formulated steady state heat budgets for two volcanically distinct areas in the Lassen region: the large, late Quaternary, intermediate to silicic Lassen volcanic center and the nearby, coeval, less evolved Caribou volcanic field. At Caribou volcanic field, heat provided by cooling and fractional crystallization of 52 km3 of basalt is more than sufficient to produce 10 km3 of rhyolitic melt by partial melting of lower crust. Net heat added by basalt intrusion at Caribou volcanic field is equivalent to an increase in lower crustal heat flow of ???7 mW m-2, indicating that the field is not a major crustal thermal anomaly. Addition of cumulates from fractionation is offset by removal of erupted partial melts. A minimum basalt influx of 0.3 km3 (km2 Ma)-1 is needed to supply Caribou volcanic field. Our methodology does not fully account for an influx of basalt that remains in the crust as derivative intrusives. On the basis of comparison to deep heat flow, the input of basalt could be ???3 to 7 times the amount we calculate. At Lassen volcanic center, at least 203 km3 of mantle-derived basalt is needed to produce 141 km3 of partial melt and drive the volcanic system. Partial melting mobilizes lower crustal material, augmenting the magmatic volume available for eruption at Lassen volcanic center; thus the erupted volume of 215 km3 exceeds the calculated basalt input of 203 km3. The minimum basalt input of 1.6 km3 (km2 Ma)-1 is >5 times the minimum influx to the Caribou volcanic field. Basalt influx high enough to sustain considerable partial melting, coupled with locally high extension rate, is a crucial factor in development of Lassen volcanic center; in contrast. Caribou volcanic field has failed to develop into a large silicic center primarily because basalt supply

  11. Rare-earth element geochemistry and the origin of andesites and basalts of the Taupo Volcanic Zone, New Zealand

    USGS Publications Warehouse

    Cole, J.W.; Cashman, K.V.; Rankin, P.C.

    1983-01-01

    Two types of basalt (a high-Al basalt associated with the rhyolitic centres north of Taupo and a "low-Al" basalt erupted from Red Crater, Tongariro Volcanic Centre) and five types of andesite (labradorite andesite, labradorite-pyroxene andesite, hornblende andesite, pyroxene low-Si andesite and olivine andesite/low-Si andesite) occur in the Taupo Volcanic Zone (TVZ), North Island, New Zealand. Rare-earth abundances for both basalts and andesites are particularly enriched in light rare-earth elements. High-Al basalts are more enriched than the "low-Al" basalt and have values comparable to the andesites. Labradorite and labradorite-pyroxene andesites all have negative Eu anomalies and hornblende andesites all have negative Ce anomalies. The former is probably due to changing plagioclase composition during fractionation and the latter to late-stage hydration of the magma. Least-squares mixing models indicate that neither high-Al nor "low-Al" basalts are likely sources for labradorite/labradorite-pyroxene andesites. High-Al basalts are considered to result from fractionation of olivine and clinopyroxene from a garnet-free peridotite at the top of the mantle wedge. Labradorite/labradorite-pyroxene andesites are mainly associated with an older NW-trending arc. The source is likely to be garnet-free but it is not certain whether the andesites result from partial melting of the top of the subducting plate or a hydrated lower portion of the mantle wedge. Pyroxene low-Si andesites probably result from cumulation of pyroxene and calcic plagioclase within labradorite-pyroxene andesites, and hornblende andesites by late-stage hydration of labradorite-pyroxene andesite magma. Olivine andesites, low-Si andesites and "low-Al" basalts are related to the NNE-trending Taupo-Hikurangi arc structure. Although the initial source material is different for these lavas they have probably undergone a similar history to the labradorite/labradorite-pyroxene andesites. All lavas show evidence

  12. Catastrophic volcanism

    NASA Technical Reports Server (NTRS)

    Lipman, Peter W.

    1988-01-01

    Since primitive times, catastrophes due to volcanic activity have been vivid in the mind of man, who knew that his activities in many parts of the world were threatened by lava flows, mudflows, and ash falls. Within the present century, increasingly complex interactions between volcanism and the environment, on scales not previously experienced historically, have been detected or suspected from geologic observations. These include enormous hot pyroclastic flows associated with collapse at source calderas and fed by eruption columns that reached the stratosphere, relations between huge flood basalt eruptions at hotspots and the rifting of continents, devastating laterally-directed volcanic blasts and pyroclastic surges, great volcanic-generated tsunamis, climate modification from volcanic release of ash and sulfur aerosols into the upper atmosphere, modification of ocean circulation by volcanic constructs and attendent climatic implications, global pulsations in intensity of volcanic activity, and perhaps triggering of some intense terrestrial volcanism by planetary impacts. Complex feedback between volcanic activity and additional seemingly unrelated terrestrial processes likely remains unrecognized. Only recently has it become possible to begin to evaluate the degree to which such large-scale volcanic processes may have been important in triggering or modulating the tempo of faunal extinctions and other evolutionary events. In this overview, such processes are examined from the viewpoint of a field volcanologist, rather than as a previous participant in controversies concerning the interrelations between extinctions, impacts, and volcanism.

  13. The mode of emplacement of Neogene flood basalts in Eastern Iceland: Facies architecture and structure of the Hólmar and Grjótá olivine basalt groups

    NASA Astrophysics Data System (ADS)

    Óskarsson, Birgir V.; Riishuus, Morten S.

    2013-11-01

    Hólmar and Grjótá are two stratigraphically distinct transitional alkaline olivine basalt lava groups within the westward-dipping Neogene flood basalts of eastern Iceland. The Hólmar olivine basalt group, separated from the overlying Grjótá olivine basalt group by only a few tholeiite flows, can be traced over 80 km north-south, with thicknesses varying from ~ 250 m where thickest to ~ 30 m where thinnest. The Grjótá group can be traced over 50 km also north-south, reaching thicknesses of ~ 250 m and thinning down-dip to ~ 10 m. In contrast to other groups in eastern Iceland that thicken down-dip, the studied olivine basalt groups thicken up-dip. The groups filled topographic confinements and formed aprons around central volcanoes. We have estimated the minimum volumes to be ~ 119 km3 for Hólmar and ~ 86 km3 for Grjótá. Scoria cones are found in the Hólmar group, and two thick olivine dolerite sills cross-cut the Hólmar group and probably belong to the plumbing system that fed the Grjótá group. The architecture of the lava groups are near identical. The architecture is compound, with lobes stacked horizontally and vertically, varying from 1-15 m thick and 2-200 m long, but do also encompass a number of thicker (15-20 m) and more extensive (> 1 km long) lava lobe in the stacks. Filled lava tubes are commonly observed within the lava flows. The constituent lobes of the flows are often directly emplaced or welded together, suggesting rapid buildup, but are also found interbedded with redbeds and thicker tuff deposits, and occasionally preserve tree molds. The internal structure follows the characteristics for lava lobe morphology in general, with an upper vesicular crust forming half to one third of the total thickness, a massive core with abundant vesicle cylinders, and a thin basal vesicular crust. Flow tops are of the pahoehoe type, seldom found with scoria or clinker. Inflation structures such as tumuli and inflation clefts were identified in the

  14. Isotopic and trace element geochemistry of alkalic-mafic-ultramafic-carbonatitic complexes and flood basalts in NE India: Origin in a heterogeneous Kerguelen plume

    NASA Astrophysics Data System (ADS)

    Ghatak, Arundhuti; Basu, Asish R.

    2013-08-01

    The Archean East Indian cratonic margin was affected by the Kerguelen plume (KP) ˜117 Ma, causing flood-basalt eruptions of the Rajmahal-Bengal-Sylhet Traps (RBST). The RBST cover ˜one million km2 in and around the Bengal Basin as alkalic-ultrabasic intrusives in the west and Sikkim in the north, and Sylhet basalts and alkalic-carbonatitic-ultramafic complexes in the Shillong plateau - Mikir hills farther east of the Rajmahal-Bengal Traps. We provide new Nd-Sr-Pb-isotopic and trace element data on 21 unreported discrete lava flows of the Rajmahal Traps, 56 alkalic-carbonatitic-mafic-ultramafic rocks from four alkalic complexes, and three dikes from the Gondwana Bokaro coalfields, all belonging to the RBST. The data allow geochemical correlation of the RBST with some contemporaneous Kerguelen Plateau basalts and KP-related volcanics in the southern Indian Ocean. Specifically, the new data show similarity with previous data of Rajmahal group I-II basalts, Sylhet Traps, Bunbury basalts, and lavas from the southern Kerguelen Plateau, indicating a relatively primitive KP source, estimated as: ɛNd(I) = +2, 87Sr/86Sr(I) = 0.7046, with a nearly flat time-integrated rare earth element (REE) pattern. We model the origin of the uncontaminated RBST basalts by ˜18% batch melting with a 2× chondritic KP source in the spinel-peridotite stability depths of 60-70 km in the mantle. The new geochemical data similar to the Rajmahal group II basalts indicate a light REE enriched average source at ɛNd(I) = -5, 87Sr/86Sr(I) = 0.7069. Our geochemical modeling indicates these lavas assimilated granulites of the Eastern Ghats, reducing the thickness of the continental Indian lithosphere. Lack of an asthenospheric MORB component in the RBST province is indicated by various trace element ratios as well as the Nd-Sr isotopic ratios. Three alkalic complexes, Sung, Samchampi, and Barpung in NE India, and one in Sikkim to the north are of two groups: carbonatites, pyroxenites, lamproites

  15. Conditions of basaltic magma generation at Mount Baker Volcanic Field, North Cascades

    NASA Astrophysics Data System (ADS)

    McCallum, I. S.; Mullen, E. K.

    2011-12-01

    Significant unresolved questions remain on the processes of mantle melting throughout the wide range of thermal conditions encompassed by subduction zones. For example, subducting slabs in "hot" arc settings are thought to dehydrate at relatively shallow depths, yet volcanoes develop in locations indistinguishable from those in "cold" arcs. The northern Cascade arc is considered a classic end-member example of a "hot" subduction zone because the subducting crust is extremely young, 6-10 Ma at the trench [1], with a thick layer of insulating sediment and a relatively low convergence rate [2]. The most magmatically productive volcanic center of the northern Cascades is the Mt. Baker volcanic field (MBVF) [3], and here we glean information from the most primitive MBVF lavas to develop a petrogenetic model for basalt generation in a "hot" arc setting. Whole-rock geochemical data and the compositions of coexisting minerals are used to establish the initial water contents and redox states of the magmas, and the temperatures and pressures of segregation from the mantle. Melt silica activities indicate the MBVF magmas segregated from their residual mantle source assemblages at depths ranging from 60 to 40 km, corresponding to a few km shallower than the hot core of the mantle wedge [4] to the base of the crust. Plagioclase core compositions indicate that the initial water contents of the magmas ranged from 1.7 to 2.3 wt. % H2O, and show a good inverse correlation with segregation depths. Fe-Ti oxide pairs and spinel inclusions in olivine phenocrysts indicate redox states slightly more oxidizing than the quartz-fayalite-magnetite buffer. Segregation depths are also strongly correlated with temperatures calculated from olivine-liquid equilibria, which range from 1286°C to 1350°C. Coupled with the most recent thermal model for the subducting slab in northern Cascadia [4], we use petrologic phase equilibria for the P-T stability of mineral assemblages in the mantle and

  16. Strawberry Rhyolites, Oregon: Northwestern extent of mid-Miocene flood basalt related rhyolites of the Pacific Northwest

    NASA Astrophysics Data System (ADS)

    Steiner, A. R.; Streck, M. J.

    2011-12-01

    Rhyolitic volcanism associated with the Columbia River-Steens flood basalts of the Pacific Northwest has traditionally been viewed to be centered at McDermitt caldera near the Oregon-Nevada border starting at ~16.5 Ma. In recent years, more rhyolitic centers along this latitude with ages between 16.5-15.5 Ma have been identified and associated with the inception of the Yellowstone hotspot. However the footprint of plume-head related rhyolites becomes much larger when silicic centers of mid-Miocene age in eastern Oregon are included extending the distribution of such rhyolites to areas near the towns of Baker City and John Day ~250 km north of McDermitt. This study addresses one of these rhyolitic centers that was virtually unknown and that constitutes the northwestern extent of mid-Miocene rhyolites. Rhyolites are centered ~40 km SSW of John Day and are considered part of the Strawberry Volcanic Field (SVF), which consists of a diverse group of volcanic rocks ranging from basalt to rhyolite with abundant intermediate compositions. One existing age date of 17.3 Ma ± 0.36 (Robyn, 1977) - if confirmed by our ongoing study - places these rhyolites at the very onset of plume-head related rhyolites. Strawberry rhyolitic lavas are most voluminous in the southwestern portion of the SVF covering approximately 500 km2 between Bear and Logan Valley. The rhyolitic lavas tend to be phenocryst-poor (<3%) and range from obsidian to devitrified flow banded rhyolites. The major phenocryst phases include plagioclase, quartz, and occasional biotite. Field evidence suggests that the aphyric high-silica rhyolite lavas (~77 wt. % SiO2) erupted first, followed by rhyolite lava flows with increasing phenocryst proportions and decreasing SiO2 (70 wt. %). Lastly, phenocryst-rich dacite lava erupted on top, capping the rhyolite. There is no evidence of significant time gaps between lavas flows, suggesting eruption in short succession. Rhyolites from the SVF are high-K, calc-alkaline lavas

  17. Flood volcanism on a contracting planet: Insights from Mercury and the Moon

    NASA Astrophysics Data System (ADS)

    Klimczak, C.; Byrne, P. K.; Solomon, S. C.

    2013-12-01

    Tectonic and volcanic processes on one-plate planets are closely tied to the thermal evolution of their interiors. Thermal history models for both the Moon and Mercury predict that after an initial heating phase, the interiors of these bodies began to cool. Such an evolution may have been accompanied by an initial period of planetary expansion, but much of the thermal history was marked by sustained global contraction. A global state of expansion generates a stress state characterized by horizontal extension within the brittle portion of the lithosphere, allowing for upward propagation of magma-filled dikes and widespread volcanic flooding. Global contraction, in contrast, imposes a horizontally compressive stress state on the lithosphere, under which magma ascent through vertical conduits is suppressed and widespread thrust faulting is favored. Both the Moon and Mercury host populations of thrust-fault-related landforms that are interpreted to have accommodated shortening induced by global contraction, but each body also shows evidence for widespread flood volcanism. On the Moon, gravitational signatures suggestive of ancient, buried dikes; large expanses of lunar mare deposits of volcanic origin; and a widely distributed population of extensional graben generally predate the formation of thrust-fault-related landforms that accommodated surface strains due to global contraction. For Mercury, geological evidence suggests that the great number of large thrust faults that accommodated the planet's decrease in planetary radius (~5-7 km) began to form prior to the cessation of the last major episode of volcanic flooding. Such a temporal overlap of flood volcanism and large-scale thrust faulting poses a challenge. Magmatism in a lithosphere dominated by global contraction should be limited to sill intrusions near the depth of the brittle-ductile transition, so widespread volcanism should be precluded. Localized volcanic flooding might nonetheless be triggered by large

  18. Isotopic and chemical evidence concerning the genesis and contamination of basaltic and rhyolitic magma beneath the Yellowstone Plateau Volcanic Field

    USGS Publications Warehouse

    Hildreth, W.; Halliday, A.N.; Christiansen, R.L.

    1991-01-01

    Since 2.2 Ma, the Yellowstone Plateau Volcanic Field has produced ~6000 km3 of rhyolite tuffs and lavas in >60 separate eruptions, as well as ~100 km3 of tholeiitic basalt from >50 vents peripheral to the silicic focus. Intermediate eruptive products are absent. Early postcollapse rhyolites show large shifts in Nd, Sr, Pb, and O isotopic composition caused by assimilation of roof rocks and hydrothermal brines during collapse and resurgence. Younger intracaldera rhyolite lavas record partial isotopic recovery toward precaldera ratios. Thirteen extracaldera rhyolites show none of these effects and have sources independent of the subcaldera magma system. Contributions from the Archaean crust have extreme values and wide ranges of Nd-, Sr, and Pb-isotope ratios, but Yellowstone rhyolites have moderate values and limited ranges. This requires their deep-crustal sources to have been pervasively hybridized by distributed intrusion of Cenozoic basalt, most of which was probably contemporaneous with the Pliocene and Quaternary volcanism. Most Yellowstone basalts had undergone cryptic clinopyroxene fractionation in the lower crust or crust-mantle transition zone and, having also ascended through or adjacent to crustal zones of silicic-magma generation, most underwent some crustal contamination. -from Authors

  19. The geochemical characteristics of basaltic and acidic volcanics around the Myojin depression in the Izu arc, Japan

    NASA Astrophysics Data System (ADS)

    Haraguchi, S.; Tamaki, K.; Kato, Y.; Machida, S.

    2012-12-01

    Around the Myojin Depression, westside of the Myojin-sho caldera in the Izu arc, seamounts are circular distributed and hydrothermal activity with sulfide deposition are found from the Baiyonneise Caldera, one of seamounts at the northern side. Some knoll chains distribute in the eastside of the Myojin Depression, and connect between these knolls. This circulator distribution of seamounts and connected knoll chains considered to the dykes are similar to the geographical features of the Kuroko Depositions in the Hokuroku Region, Northwest Japan (Tanahashi et al., 2008). Hydrothermal activities are also found from the other rifts (Urabe and Kusakabe 1990). Based on these observations, the cruise KT09-12 by R/V Tansei-Maru, Ocean Research Institute (ORI), University of Tokyo, investigated in the Myojin Rift. During the cruise, basaltic to dacitic volcanic rocks and some acidic plutonic rocks were recovered by dredge system. Herein, we present petrographical and chemical analyses of these rock samples with sample dredged by the cruise MW9507 by R/V MOANA WAVE, and consider the association with hydrothermal activities and depositions. Dredges during the cruise KT09-12 were obtained at the Daini-Beiyonneise Knoll at the northern side, Daisan-Beiyonneise Knoll at the southern side, and the Dragonborn Hill, small knoll chains, at the southeastern side of the depression. Many volcanic rocks are basalt, and recovered mainly from the Dragonborn Hill. Andesite and dacite was recovered from the Daini- and the Daini-Bayonneise Knoll. Tonalites were recovered from the Daisan-Bayonneise Knoll. Basalts from the Dragonborn Hill show less than 50% of SiO2 and more than 6 wt% and 0.88 wt% of MgO and TiO2 content. Basalts from the rift zone show depleted in the volcanic front (VF) side and enriched in the reararc (RA) side. The Dragonborn Hill is distributed near the VF, and basalts show depleted geochemical characteristics. However, these characteristics are different from the basalts

  20. Sedimentology, eruptive mechanism and facies architecture of basaltic scoria cones from the Auckland Volcanic Field (New Zealand)

    NASA Astrophysics Data System (ADS)

    Kereszturi, Gábor; Németh, Károly

    2016-09-01

    Scoria cones are a common type of basaltic to andesitic small-volume volcanoes (e.g. 10- 1-10- 5 km3) that results from gas-bubble driven explosive eruptive styles. Although they are small in volume, they can produce complex eruptions, involving multiple eruptive styles. Eight scoria cones from the Quaternary Auckland Volcanic Field in New Zealand were selected to define the eruptive style variability from their volcanic facies architecture. The reconstruction of their eruptive and pyroclastic transport mechanisms was established on the basis of study of their volcanic sedimentology, stratigraphy, and measurement of their pyroclast density, porosity, Scanning Electron Microscopy, 2D particle morphology analysis and Visible and Near Visible Infrared Spectroscopy. Collection of these data allowed defining three end-member types of scoria cones inferred to be constructed from lava-fountaining, transitional fountaining and Strombolian type, and explosive Strombolian type. Using the physical and field-based characteristics of scoriaceous samples a simple generalised facies model of basaltic scoria cones for the AVF is developed that can be extended to other scoria cones elsewhere. The typical AVF scoria cone has an initial phreatomagmatic phases that might reduce the volume of magma available for subsequent scoria cone forming eruptions. This inferred to have the main reason to have decreased cone volumes recognised from Auckland in comparison to other volcanic fields evolved dominantly in dry eruptive condition (e.g. no external water influence). It suggests that such subtle eruptive style variations through a scoria cone evolution need to be integrated into the hazard assessment of a potentially active volcanic field such as that in Auckland.

  1. Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions directly linked to the end-Triassic mass extinction

    PubMed Central

    Whiteside, Jessica H.; Olsen, Paul E.; Eglinton, Timothy; Brookfield, Michael E.; Sambrotto, Raymond N.

    2010-01-01

    A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date. PMID:20308590

  2. Origin of the Mackenzie large igneous province and sourcing of flood basalts from layered intrusions

    NASA Astrophysics Data System (ADS)

    Day, J. M.; Pearson, D.

    2013-12-01

    The 1.27 Ga Coppermine continental flood basalt (CFB) in northern Canada represents the extrusive manifestation of the Mackenzie large igneous province (LIP) that includes the Mackenzie dyke swarm and the Muskox layered intrusion. New Re-Os isotope and highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundance data are reported together with whole-rock major- and trace-element abundances and Nd isotopes to examine the behaviour of the HSE during magmatic differentiation and to place constraints on the extent of crustal interaction with mantle-derived melts. Mineral-chemical data are also reported for an unusual andesite glass flow (4.9 wt.% MgO) found in proximity to newly recognised picrites (>20 wt.% MgO) in the lowermost stratigraphy of the Coppermine CFB. Compositions of mineral phases in the andesite are similar to equivalent phases found in Muskox Intrusion chromitites and the melt composition is identical to Muskox chromite melt inclusions. Elevated HSE contents (e.g., 3.8 ppb Os) and the mantle-like initial Os isotope composition of this andesitic glass contrast strongly with oxygen isotope and lithophile element evidence for extensive crustal contamination. These signatures implicate an origin for the glass as a magma mingling product formed within the Muskox Intrusion during chromitite genesis. The combination of crust and mantle signatures define roles for both these reservoirs in chromitite genesis, but the HSE appear to be dominantly mantle-sourced. Combined with Nd isotope data that places the feeder for lower Coppermine CFB picrites and basalts within the Muskox Intrusion, this provides the strongest evidence yet for direct processing of some CFB within upper-crustal magma chambers. Modeling of absolute and relative HSE abundances in CFB reveal that HSE concentrations decrease with increasing fractionation for melts with <8×1 wt.% MgO in the Coppermine CFB, with picrites (>13.5wt.% MgO) from CFB having higher Os abundances than ocean island

  3. Unique Mineralogy of Triassic Diamondiferous Hypabyssal Kimberlite Postdated Siberian Flood Basalt (sfb) Province

    NASA Astrophysics Data System (ADS)

    Sobolev, N. V.; Sobolev, A. V.; Tomilenko, A. A.; Schertl, H. P.; Neuser, R. D.; Timina, T. Y.; Karmanov, N. S.; Batanova, V. G.; Logvinova, A. M.; Kuzmin, D.

    2014-12-01

    The Siberian flood basalt (SFB) province is the largest terrestrial province with the estimated volume of igneous rocks up to 5 million cubic km. The majority of SFB erupted over less than one million years at 251 Ma. The main epochs of kimberlites emplacement took place in Devonian (344-364 Ma) producing principal diamond mines including Udachnaya mine and in Triassic (about 240 Ma) with only one, Malokuonapskaya kimberlite pipe with near-commercial diamond grade. This indicates the availability of complete lithospheric cross section. It contains flood basalt and peridotite xenoliths. We report here preliminary data on mineralogy of this hypabyssal kimberlite containing fresh olivine. Homogeneous cores of zoned olivine with Fo 78.5-93 are different in compositional range from those of Udachnaya olivines (Fo 85-94). Outer rims composition are also different (Fo 85-86 and 89-90 respectively). Concentration of Ni, Mn, Co, Ca, Cr, Al, Ti, P, Na and Zn were measured by EPMA using an innovative method which has been developed based on earlier publication (Sobolev et al., Science, 2007, 316: 412-417). It made possible to obtain external precision down to 10 ppm (2SD) and detection limit down to 2 ppm. High resolution compositional maps of olivine zoning for all mentioned elements are produced. "Hot cathode" CL microscope was applied for study of luminescent minerals including calcite, apatite and baryte. Twenty percent of representative olivine samples are characterized by low Fo 78.5-85 and NiO from 600 to 2300 ppm. Clear zoning in concentration of some trace elements, P in particular, is detected in the cores of studied olivines. Ba-phlogopite containing BaO from less than 1 up to 14.5 wt.% is another specific feature of Malokuonapskaya kimberlite, which is different from any kimberlites and especially from Udachnaya with highest BaO - 4.85 wt.% of its phlogopite. Chromediopsides contain 1.3 - 5.2 wt.% FeO, 0.6 - 2.0 wt.% Cr2O3 and 0.45 - 2.0 wt.% Na2O. Pyropes

  4. A plume-triggered delamination origin for the Columbia River flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Humphreys, E.; Darold, A. P.

    2015-12-01

    From their initial eruptions in south-central Oregon, Columbia River basalt (CRB) volcanism propagated rapidly north, with the largest eruptions being ~300 km north of the Yellowstone hotspot track. We combine upper mantle seismic tomography, CRB eruption timing constraints, geochemical evolution of magmas, uplift history, and the tectonic context to construct a well-constrained model for the origin of the CRB eruptions. Arrival of the Yellowstone plume below south-central Oregon initiated a north-propagating rollback-style delamination of remnant Farallon lithosphere from the base of northern Oregon, enabled by ocean-lithosphere detachment as sills were emplacement near the (continental or oceanic) Moho. This drew Yellowstone asthenosphere to the north. When delamination propagated beneath the Cretaceous Wallowa pluton, its garnet-rich (dense) root foundered. Root foundering led to: pluton uplift (creating the Wallowa Mts); a mantle return flow that greatly amplified magmatic production; and assimilation of continental crust in the vicinity of a large magma chamber created by the evacuated pluton root. Thus, much of the CRB eruptive volume and history is attributed to lithospheric activity that was triggered by the arrival of mantle that was anomalously magmatically productive.

  5. Pyroclastic Deposits in Floor-Fractured Craters: A Unique Style or Lunar Basaltic Volcanism?

    NASA Technical Reports Server (NTRS)

    Allen, Carlton C.; DonaldsonHanna, Kerri L.; Pieters, Carle M.; Moriarty, Daniel P.; Greenhagen, Benjamin T.; Bennett, Kristen A.; Kramer, Georgiana Y.; Paige, David A.

    2013-01-01

    The lunar maria were formed by effusive fissure flows of low-viscosity basalt. Regional pyroclastic deposits were formed by deep-sourced fire-fountain eruptions dominated by basaltic glass. Basaltic material is also erupted from small vents within floor-fractured impact craters. These craters are characterized by shallow, flat floors cut by radial, concentric and/or polygonal fractures. Schultz [1] identified and classified over 200 examples. Low albedo pyroclastic deposits originate from depressions along the fractures in many of these craters.

  6. Quickly erupted volcanic sections of the Steens Basalt, Columbia River Basalt Group: Secular variation, tectonic rotation, and the Steens Mountain reversal

    USGS Publications Warehouse

    Jarboe, N.A.; Coe, R.S.; Renne, P.R.; Glen, J.M.G.; Mankinen, E.A.

    2008-01-01

    The Steens Basalt, now considered part of the Columbia River Basalt Group (CRBG), contains the earliest eruptions of this magmatic episode. Lava flows of the Steens Basalt cover about 50,000 km2 of the Oregon Plateau in sections up to 1000 m thick. The large number of continuously exposed, quickly erupted lava flows (some sections contain over 200 flows) allows for small loops in the magnetic field direction paths to be detected. For volcanic rocks, this detail and fidelity are rarely found outside of the Holocene and yield estimates of eruption durations at our four sections of ??2.5 ka for 260 m at Pueblo Mountains, 0.5 to 1.5 ka for 190 m at Summit Springs, 1-3 ka for 170 m at North Mickey, and ??3 ka for 160 m at Guano Rim. That only one reversal of the geomagnetic field occurred during the eruption of the Steens Basalt (the Steens reversal at approximately 16.6 Ma) is supported by comparing 40Ar/39Ar ages and magnetic polarities to the geomagnetic polarity timescale. At Summit Springs two 40Ar/39Ar ages from normal polarity flows (16.72 ?? ?? 0.29 Ma (16.61) and 16.92 ?? ?? 0.52 Ma (16.82); ?? ?? equals 2s error) place their eruptions after the Steens reversal, while at Pueblo Mountains an 40Ar/39Ar age of 16.72 ?? ?? 0.21 Ma (16.61) from a reverse polarity flow places its eruption before the Steens reversal. Paleomagnetic field directions yielded 50 nontransitional directional-group poles which, combined with 26 from Steens Mountain, provide a paleomagnetic pole for the Oregon Plateau of 85.7??N, 318.4??E, K = 15.1, A95 = 4.3. Comparison of this new pole with a reference pole derived from CRBG flows from eastern Washington and a synthetic reference pole for North America derived from global data implies relative clockwise rotation of the Oregon Plateau of 7.4 ?? 5.0?? or 14.5 ?? 5.4??, respectively, probably due to northward decreasing extension of the basin and range. ?? 2008 by the American Geophysical Union.

  7. A petrologic study of the Teanaway Basalt: Eocene slab window volcanism in central WA

    NASA Astrophysics Data System (ADS)

    Roepke, E.; Tepper, J. H.; Ivener, D.

    2013-12-01

    The Teanaway Basalt (TB) includes subaerial basalt to andesite flows, mafic to felsic tuffs, and rhyolite domes in the Central Cascades of Washington State. These volcanics overlie the extensive ~47 Ma Teanaway Dike Swarm (TDS) that cuts the underlying Swauk Formation. This study focuses on the tectonic setting of eruption and geochemical variations relating to geography and stratigraphy within the TB. The western-most area of the TB, Easton Ridge (ER), is compared with the eastern-most area of the TB, Liberty Ridge (LR) - 40 km to the east of ER. The bimodal TB consists predominantly of basaltic andesite and andesite (45.3-63.1 wt% SiO2) with subordinate rhyolite (75.9-79.4 wt% SiO2). The mafic rocks classify as primarily medium-K tholeiites (0.1-3.0 wt% K2O), but a few samples classify as alkaline. Enrichment in LILE and depletion in HFSE on spidergrams are indicative of an arc setting. However, compared with the modern Cascade Arc, the TB is distinctly higher in Fe2O3T (8.8-17.1 wt%) and TiO2 (1.1-2.7 wt%), and distinctly lower in Al2O3 (11.2-14.6) and K2O, with a similar range of Mg #s (0.15-0.48). Most tectonic discrimination plots characterize the TB as MORB, but some indicate an arc or within-plate setting. Preliminary Pb isotopic data (206Pb/204Pb = 19.13-19.19, 207Pb/204Pb = 15.62-15.64, and 208Pb/204Pb = 38.78-38.90) indicate the TB and TDS are more enriched than Cascade Arc rocks in 206Pb/204Pb and 208Pb/204Pb. Overall, these geochemical data are consistent with a model in which asthenospheric mantle ascending through a slab window interacts with mantle wedge that has previously acquired arc chemical traits. The existence of a slab window in this region during the mid-Eocene is compatible with plate reconstructions and evidence of extension that have been attributed to subduction of the Resurrection-Kula ridge (Haeussler et al., 2003). Harker plots show lavas at LR are generally more enriched than those at ER in Fe2O3T (11.9-17.1 wt% vs 8.8-15.7 wt%) Mn

  8. Bridging basalts and rhyolites in the Yellowstone-Snake River Plain volcanic province: The elusive intermediate step

    NASA Astrophysics Data System (ADS)

    Szymanowski, Dawid; Ellis, Ben S.; Bachmann, Olivier; Guillong, Marcel; Phillips, William M.

    2015-04-01

    Many magmatic provinces produce strongly bimodal volcanism with abundant mafic and silicic magmas yet a scarcity of intermediate (55-65 wt.% SiO2) compositions. In such bimodal settings, much debate revolves around whether the basaltic magmas act as heat sources to melt pre-existing crust, or whether they are the parents to the silicic magmas (a fractionation-dominated evolution). Until now, this lack of coeval intermediate compositions has commonly been used to support models involving large degrees of crustal melting. Detailed analysis of mineral cargoes of ignimbrites from the 6.6-4 Ma Heise volcanic field in the famously bimodal Yellowstone-Snake River Plain (YSRP) volcanic province has revealed the existence of intermediate liquids associated with main stage rhyolitic volcanism. Two closely spaced rhyolitic ignimbrites, the Wolverine Creek Tuff and the Conant Creek Tuff, contain pyroxene crystals with major and trace elemental compositions in equilibrium with intermediate melts prior to significant plagioclase fractionation. Hosted within these crystals are glassy melt inclusions that have compositions (57-67 wt.% SiO2) directly recording the intermediate liquids. The combined mineral and melt inclusion data provide the first evidence for the occurrence of intermediate melts, typically erased in the high temperature YSRP ignimbrites by crystal resorption or diffusive re-equilibration. The results suggest the existence of mostly unerupted mid-crustal reservoirs that drive magma compositions towards the erupted rhyolites via assimilation-fractional crystallisation (AFC).

  9. Mare Basalt Volcanism: Generation, Ascent, Eruption, and History of Emplacement of Secondary Crust on the Moon

    NASA Astrophysics Data System (ADS)

    Head, J. W.; Wilson, L.

    2016-05-01

    Theoretical analyses of the generation, ascent, intrusion and eruption of basaltic magma provides new insight into magma source depths, supply processes, transport and emplacement mechanisms (dike intrusions, effusive and explosive eruptions).

  10. Geochemistry of Paraná-Etendeka basalts from Misiones, Argentina: Some new insights into the petrogenesis of high-Ti continental flood basalts

    NASA Astrophysics Data System (ADS)

    Rämö, O. Tapani; Heikkilä, Pasi A.; Pulkkinen, Arto H.

    2016-04-01

    The Early Cretaceous (˜135-131 Ma) Paraná-Etendeka continental flood basalts, preserved in bulk in the Paraná basin of southern Brazil and vicinity, have been divided into low-Ti and high-Ti types that govern the southern and northern halves of the basin, respectively. We have examined a new sample set from the southern margin of the northern high-Ti segment of Paraná basalts in Misiones, northeastern Argentina. These basalts are strongly to moderately enriched in TiO2 (2-4 wt.%), have relatively high Ti/Y (300-500), low MgO (3.5-6.5 wt.%), and high Fe (FeO(tot) 12-14 wt.%) and belong to the Pitanga and Paranapanema magma types of Peate et al. (1992). Nd and Sr isotope compositions are quite unvarying with ɛNd (at 133 Ma) values of -4.6 to -3.6 and initial 87Sr/86Sr of 0.7054-0.7059 and show no variation with fractionation. Compared to high-Ti lavas in the central and northern parts of the Paraná high-Ti basalt segment, the lavas from Misiones are similar to those in the northeastern magin of the basin but less radiogenic in initial Nd isotope composition than those in the central part. This variation probably reflects mixed EM1-EM2 source components in the sublithospheric mantle. A polybaric melt model of a sublithospheric mantle source at the garnet lherzolite-spinel lherzolite transition is compatible with the observed Ti budget of the Pitanga and Paranapanema lavas, regardless of the Nd isotope composition of their purported source.

  11. Palaeoweathering characteristics of an intrabasaltic red bole of the Deccan Flood Basalts near Shrivardhan of western coast of India

    NASA Astrophysics Data System (ADS)

    Sayyed, M. R. G.; Pardeshi, R. G.; Islam, R.

    2014-10-01

    An intrabasaltic red bole horizon is studied for its weathering characteristics with respect to the underlying and overlying basalts. The study indicates that all the three units have been considerably weathered; the red bole unit, however shows some distinctive characteristics. The red boles show a higher cation exchange capacity (CEC) and lower sodium adsorption ratio (SAR) and organic carbon (OC) as compared to the weathered basalts. The lower values of Al2O3, TiO2 and Fe2O3(T) in red boles indicate their lesser weathering than the underlying and overlying basalts, which is further corroborated by the weathering intensity measured by the indices like chemical index of alteration (CIA) and statistical empirical index of chemical weathering (W). It is also evident that the red bole samples show more retention of original mafic and felsic components. While K2O exhibits an erratic behaviour, the MgO and CaO do not show much leaching in red boles. Lesser leaching and salinity in the red boles is indicated by the higher values of calcification and lower values of salinization. The SiO2-Al2O3-Fe2O3 plot indicates that red bole samples are close to the basalt field, while the weathered upper basalt is more kaolinized than the weathered lower basalt. These observations reveal that the post-formational weathering processes have least affected the original palaeoweathering characters of the red bole horizon and hence the intrabasaltic palaeosols (weathering horizons) can effectively be used to constrain the palaeoweathering and palaeoclimates during the continental flood basalt episodes in the geologic past.

  12. Cretaceous basaltic phreatomagmatic volcanism in West Texas: Maar complex at Peña Mountain, Big Bend National Park

    NASA Astrophysics Data System (ADS)

    Befus, K. S.; Hanson, R. E.; Lehman, T. M.; Griffin, W. R.

    2008-06-01

    A structurally complex succession of basaltic pyroclastic deposits produced from overlapping phreatomagmatic volcanoes occurs within Upper Cretaceous floodplain deposits in the Aguja Formation in Big Bend National Park, West Texas. Together with similar basaltic deposits recently documented elsewhere in the Aguja Formation, these rocks provide evidence for an episode of phreatomagmatic volcanism that predates onset of arc magmatism in the region in the Paleogene. At Peña Mountain, the pyroclastic deposits are ≥ 70 m thick and consist dominantly of tabular beds of lapillistone and lapilli tuff containing angular to fluidal pyroclasts of altered sideromelane intermixed with abundant accidental terrigenous detritus derived from underlying Aguja sediments. Tephra characteristics indicate derivation from phreatomagmatic explosions involving fine-scale interaction between magma and sediment in the shallow subsurface. Deposition occurred by pyroclastic fall and base-surge processes in near-vent settings; most base-surge deposits lack tractional sedimentary structures and are inferred to have formed by suspension sedimentation from rapidly decelerating surges. Complexly deformed pyroclastic strata beneath a distinct truncation surface within the succession record construction and collapse of an initial volcano, followed by a shift in the location of the conduit and excavation of another maar crater into Aguja strata nearby. Preserved portions of the margin of this second crater are defined by a zone of intense soft-sediment disruption of pyroclastic and nonvolcanic strata. U-Pb isotopic analyses of zircon grains from three basaltic bombs in the succession reveal the presence of abundant xenocrysts, in some cases with ages > 1.0 Ga. The youngest concordant analyses for all three samples yield a weighted mean age of 76.9 ± 1.2 Ma, consistent with the presence of Late Campanian vertebrate fossils in the upper Aguja Formation. We infer that the volcanism is related to the

  13. Geohazards (floods and landslides) in the Ndop plain, Cameroon volcanic line

    NASA Astrophysics Data System (ADS)

    Wotchoko, Pierre; Bardintzeff, Jacques-Marie; Itiga, Zénon; Nkouathio, David Guimolaire; Guedjeo, Christian Suh; Ngnoupeck, Gerald; Dongmo, Armand Kagou; Wandji, Pierre

    2016-07-01

    The Ndop Plain, located along the Cameroon Volcanic Line (CVL), is a volcano-tectonic plain, formed by a series of tectonic movements, volcanic eruptions and sedimentation phases. Floods (annually) and landslides (occasionally) occur with devastating environmental effects. However, this plain attracts a lot of inhabitants owing to its fertile alluvial soils. With demographic explosion in the plain, the inhabitants (143,000 people) tend to farm and inhabit new zones which are prone to these geohazards. In this paper, we use field observations, laboratory analyses, satellite imagery and complementary methods using appropriate software to establish hazard (flood and landslide) maps of the Ndop Plain. Natural factors as well as anthropogenic factors are considered. The hazard maps revealed that 25% of the area is exposed to flood hazard (13% exposed to high flood hazard, 12% to moderate) and 5% of the area is exposed to landslide hazard (2% exposed to high landslide hazard, 3% to moderate). Some mitigation measures for floods (building of artificial levees, raising foundations of buildings and the meticulous regulation of the flood guards at Bamendjing Dam) and landslides (slope terracing, planting of trees, and building retaining walls) are proposed.

  14. Resolving mantle and magmatic processes in basalts from the Cameroon volcanic line using the Re-Os isotope system

    NASA Astrophysics Data System (ADS)

    Gannoun, A.; Burton, K. W.; Barfod, D. N.; Schiano, P.; Vlastélic, I.; Halliday, A. N.

    2015-05-01

    This study presents major-, trace element and Re-Os isotope and elemental data for young alkaline basalts (< 10 Ma) from oceanic (Annobon, S. Tomé, Principe), continental (Manengouba) and continent-oceanic boundary (COB, Mt. Cameroon) sectors of the Cameroon volcanic line (CVL). The CVL is a chain of Tertiary to recent, transitional to strongly alkaline intraplate volcanoes extending from the south Atlantic island of Annobon to the continental interior of West Africa (Biu Plateau). The basalts from the oceanic sector display a range of initial 187Os/188Os ratios between 0.128 and 0.190 and those from the COB and continental sector range between 0.142 and 0.560. The samples with high 206Pb/204Pb (e.g. ratios > 20) possess 187Os/188Os isotope compositions between 0.14 and 0.18 (e.g., basalts from Mt Cameroon and Sao Tomé) which reflect the chemical characteristics that are more likely to be primary features of CVL, and are close to the value of 0.153 attributed to the HIMU end-member (Tubuai-Mangaia). However, most of the lavas from the continental sector show highly radiogenic initial 187Os/188Os ratios (0.36 to 0.56) that are outside the range previously observed for ocean island basalts, with shifts to radiogenic Os isotope compositions accompanied by less radiogenic 206Pb/204Pb and increasing SiO2 contents. The increase in 187Os/188Os is also associated with the decrease of Os, Ni, MgO and phenocryst abundances. These data can be explained by fractional crystallisation and assimilation of continental crust by the ascending magma. The systematic shift to unradiogenic lead isotope compositions from the COB into the oceanic sector is positively correlated with variations in 187Os/188Os isotope composition (from 0.140 to 0.128). At first sight this covariation might be attributed to the mixing of HIMU material with the ambient upper mantle (DMM). However, there is a clear covariation of the Os isotope and elemental composition, best explained with contamination of

  15. Osmium isotope variations accompanying the eruption of a single lava flow field in the Columbia River Flood Basalt Province

    NASA Astrophysics Data System (ADS)

    Vye-Brown, C.; Gannoun, A.; Barry, T. L.; Self, S.; Burton, K. W.

    2013-04-01

    Geochemical interpretations of continental flood basalts usually assume that individual lava flows represent compositionally homogenous and rapidly erupted products of large well-mixed magma reservoirs. However, inflated pāhoehoe lavas may develop over considerable periods of time and preserve chemical variations that can be temporally linked through flow formation to eruption sequence thus providing an understanding of magma evolution over the timescale of a single eruption. This study presents comprehensive major, trace element and Re-Os isotope data for a single eruption that formed the 2660 km3 Sand Hollow flow field in the Columbia River Basalt Province, USA. Major and trace element variations accompanying flow emplacement (e.g. MgO 3.09-4.55 wt%, Ni 17.5-25.6 ppm) are consistent with fractional crystallisation, but other petrogenetic processes or variable sources cannot be distinguished. However, there is a systematic shift in the initial 187Os/188Os isotope composition of the magma (age corrected to 15.27 Ma), from 0.174 (lava core) to 1.444 (lava crust) within a single 35 m thick sheet lobe. Lava crust values are more radiogenic than any known mantle source, consistent with previous data indicating that neither an enriched reservoir nor the sub-continental lithospheric mantle are likely to have sourced these basalts. Rather, these data indicate that lavas emplaced during the earliest stages of eruption have higher degrees of crustal contamination. These results highlight the limitations of applying chemostratigraphic correlation across continental flood basalt provinces, the use of single data points to define melt sources and magmatic processes, and the dangers of using conventional isochron techniques in such basalt sequences for absolute chronology.

  16. U-Pb and 207Pb- 206Pb ages of zircons from basaltic eucrites: Implications for early basaltic volcanism on the eucrite parent body

    NASA Astrophysics Data System (ADS)

    Misawa, Keiji; Yamaguchi, Akira; Kaiden, Hiroshi

    2005-12-01

    We have undertaken petrologic and SHRIMP U-Th-Pb isotopic studies on zircons from basaltic eucrites (Yamato [Y]-75011, Y-792510, Asuka [A]-881388, A-881467 and Padvarninkai) with different thermal and shock histories. Eucritic zircons are associated with ilmenite in most cases and have subhedral shapes in unmetamorphosed and metamorphosed eucrites. Some zircons in highly metamorphosed eucrites with granulitic texture occur alone in pyroxene, and typically have rounded to subrounded shapes due to recrystallization. Superchondritic Zr/Hf ratios of eucritic zircons indicate that they crystallized from incompatible element-rich melts after crystallization of ilmenite. Concentrations of uranium and thorium in zircons in the unmetamorphosed eucrite Y-75011 are higher than those in metamorphosed eucrites. The U-Pb systems of eucritic zircons are almost concordant but some zircon grains show reverse discordance. Radiogenic lead-loss up to 48% from zircons is observed in the shock-melted eucrite Padvarninkai. The 207Pb- 206Pb ages of zircon in Y-75011 (4550 ± 9 Ma, n = 5) are nearly identical, within analytical uncertainty, to the ages of zircons from the metamorphosed eucrite Y-792510 (4545 ± 15 Ma, n = 13), the highly metamorphosed eucrites A-881388 (4555 ± 54 Ma, n = 5) and A-881467 (4558 ± 13 Ma, n = 8), and the shock-melted eucrite Padvarninkai (4555 ± 13 Ma, n = 18). The averaged 207Pb- 206Pb age of zircon from five eucrites analyzed in this study is 4554 ± 7 Ma (95% confidence limits, n = 49), indistinguishable from the averaged U-Pb age (4552 ± 9 Ma) of the same samples. Because of the high closure temperature of lead in zircon ( T closure = ˜1050°C with a cooling rate of 0.2°C/yr), the 207Pb- 206Pb ages of eucritic zircon do not represent metamorphic ages but crystallization ages of extrusive lavas. This fact strongly suggests that volcanism of the eucrite parent body occurred at a very early stage of the Solar System history, 7-20 Ma after CAI formation

  17. Correlating the end-Triassic mass extinction and basalt volcanism of the Central Atlantic Magmatic Province at the 100,000-year level by high-precision U-Pb age determinations

    NASA Astrophysics Data System (ADS)

    Schoene, Blair; Guex, Jean; Bartolini, Annachiara; Schaltegger, Urs; Blackburn, Terrence J.

    2010-05-01

    The end-Triassic mass extinction is one of the five largest extinctions in Earth history, though considerable uncertainty remains in terms of its duration, causes and effects. Many workers suggest that the extinction was related directly or indirectly to adverse climate following the onset of the Central Atlantic Magmatic Province (CAMP), which erupted > 2.5x106 km3 of basalt in less than 1 Ma. However, there remains a need for precise and accurate geochronology to correlate the onset of CAMP volcanism, recorded uniquely in terrestrial sections, with the well-documented marine extinction event. We provide new chemical abrasion ID-TIMS U-Pb age determinations on ash bed and basaltic zircons using the well-calibrated EARTHTIME 202Pb-205Pb-233U-235U tracer solution, yielding data that are up to 70% more precise compared to single-Pb/single-U tracers. We show that the Triassic-Jurassic boundary (TJB) and end-Triassic biological crisis from two independent marine stratigraphic sections in northern Peru and in Nevada (USA) correlate with the onset of terrestrial flood volcanism in the Central Atlantic Magmatic Province (CAMP) to <150 ka. Ash bed samples reveal complicated U-Pb systematics, showing ranges in 206Pb/238U zircon dates of up to 2 Ma, representing a range of growth histories prior to eruption. Therefore, we use the youngest single closed-system zircon to approximate the eruption date. Three volcanic ash beds from the Pucara basin, northern Peru, bracket the TJB to a 206Pb/238U age of 201.31 ± 0.18/0.31/0.43 Ma (internal uncertainties/ with tracer calibration uncertainty/ with decay constant uncertainties). The first discovered ash bed from the New York canyon, Nevada, 1.5 m above TJB requires a boundary age of less than 201.33 ± 0.13 Ma. We also provide data from two laboratories which yield a new 206Pb/238U zircon age of 201.28 ± 0.02/0.22/0.31 Ma for the North Mtn. basalt, the lowest CAMP basalt from the Fundy basin, Nova Scotia. This narrows the

  18. Single Phase 40Ar/39Ar Dating of Rajahmundry Trap Basalts Contemporaneous With Late Stage Deccan Trap Volcanism

    NASA Astrophysics Data System (ADS)

    Knight, K. B.; Knight, K. B.; Renne, P. R.; Renne, P. R.; Halkett, A.; White, N.

    2001-12-01

    The Rajahmundry Traps of eastern peninsular India, often considered to be outliers of the Deccan Traps, occupy ~35 km2 centered on the Krishna-Godavari Basin and extending offshore in the sub-surface. Onshore exposures average 60m in thickness, including a laterally continuous sedimentary interlayer of laterite, limestone and shale ( ~2m thick, total) separating `upper' flows from `lower' flows. 40Ar/39Ar CO2 laser incremental heating analysis of twelve plagioclase separates from Rajahmundry Trap basalts reveal an age of ~64.6 Ma for the entire sequence based on the FCs standard at 28.02 Ma. Flows chosen for dating include 8 sites spanning both the `upper' and `lower' flow sequences. Paleontological studies of sediments adjacent to the basalt at depth in Krishna-Godavari Basin, e.g. Jaiprakash et al. (1993), suggest that the period of time covered by the two flows and intertrappean sediments is up to ca. 6 myr. Dates obtained for this study, however, show that ages for both upper and lower flows are indistinguishable within 2σ error from one another, and span ~2 Ma at most, pointing to a substantial hiatus in the sedimentary record at the top of the upper basalt flows. Extremely high Ca/K ratios (up to ~400) in several samples limits precision due to error propagation attending the large correction necessary for reactor produced 36Ar from Ca. However, plateau ages as precise as 64.8 +/- 0.4 and 65.5 +/- 0.8 from above and below (respectively, 2σ errors) the sedimentary interlayer have been obtained. Samples with both high and low Ca/K ratios confirm rapid eruption of the entire Rajahmundry Trap sequence. A petrogenetic link between these basalts and the Deccan Trap basalts (the remains of which lie over 300 km from the nearest exposure of Rajahmundry Trap) has been suggested but has yet to be substantiated. These new data clearly place the eruption of the Rajahmundry Traps temporally close to the K-T boundary, coincident with late stage Deccan volcanism and

  19. Seawater osmium isotope evidence for a middle Miocene flood basalt event in ferromanganese crust records

    USGS Publications Warehouse

    Klemm, V.; Frank, M.; Levasseur, S.; Halliday, A.N.; Hein, J.R.

    2008-01-01

    Three ferromanganese crusts from the northeast, northwest and central Atlantic were re-dated using osmium (Os) isotope stratigraphy and yield ages from middle Miocene to the present. The three Os isotope records do not show evidence for growth hiatuses. The reconstructed Os isotope-based growth rates for the sections older than 10??Ma are higher than those determined previously by the combined beryllium isotope (10Be/9Be) and cobalt (Co) constant-flux methods, which results in a decrease in the maximum age of each crust. This re-dating does not lead to significant changes to the interpretation of previously determined radiogenic isotope neodymium, lead (Nd, Pb) time series because the variability of these isotopes was very small in the records of the three crusts prior to 10??Ma. The Os isotope record of the central Atlantic crust shows a pronounced minimum during the middle Miocene between 15 and 12??Ma, similar to a minimum previously observed in two ferromanganese crusts from the central Pacific. For the other two Atlantic crusts, the Os isotope records and their calibration to the global seawater curve for the middle Miocene are either more uncertain or too short and thus do not allow for a reliable identification of an isotopic minimum. Similar to pronounced minima reported previously for the Cretaceous/Tertiary and Eocene/Oligocene boundaries, possible interpretations for the newly identified middle Miocene Os isotope minimum include changes in weathering intensity and/or a meteorite impact coinciding with the formation of the No??rdlinger Ries Crater. It is suggested that the eruption and weathering of the Columbia River flood basalts provided a significant amount of the unradiogenic Os required to produce the middle Miocene minimum. ?? 2008 Elsevier B.V.

  20. Origin and Role of Recycled Crust in Flood Basalt Magmatism: Case Study of the Central East Greenland Rifted Margin

    NASA Astrophysics Data System (ADS)

    Brown, E.; Lesher, C. E.

    2015-12-01

    Continental flood basalts (CFB) are extreme manifestations of mantle melting derived from chemically/isotopically heterogeneous mantle. Much of this heterogeneity comes from lithospheric material recycled into the convecting mantle by a range of mechanisms (e.g. subduction, delamination). The abundance and petrogenetic origins of these lithologies thus provide important constraints on the geodynamical origins of CFB magmatism, and the timescales of lithospheric recycling in the mantle. Basalt geochemistry has long been used to constrain the compositions and mean ages of recycled lithologies in the mantle. Typically, this work assumes the isotopic compositions of the basalts are the same as their mantle source(s). However, because basalts are mixtures of melts derived from different sources (having different fusibilities) generated over ranges of P and T, their isotopic compositions only indirectly represent the isotopic compositions of their mantle sources[1]. Thus, relating basalts compositions to mantle source compositions requires information about the melting process itself. To investigate the nature of lithologic source heterogeneity while accounting for the effects of melting during CFB magmatism, we utilize the REEBOX PRO forward melting model[2], which simulates adiabatic decompression melting in lithologically heterogeneous mantle. We apply the model to constrain the origins and abundance of mantle heterogeneity associated with Paleogene flood basalts erupted during the rift-to-drift transition of Pangea breakup along the Central East Greenland rifted margin of the North Atlantic igneous province. We show that these basalts were derived by melting of a hot, lithologically heterogeneous source containing depleted, subduction-modified lithospheric mantle, and <10% recycled oceanic crust. The Paleozoic mean age we calculate for this recycled crust is consistent with an origin in the region's prior subduction history, and with estimates for the mean age of

  1. Alkaline Basalts of The Quaternary Buffalo Valley Volcanic Field, NW Fish Creek Mountains, North-central Nevada, Great Basin

    NASA Astrophysics Data System (ADS)

    Cousens, B.; Henry, C. D.

    2008-12-01

    The Buffalo Valley volcanic field, 5 km southwest of Battle Mountain, consists of approximately 11 cinder cones and associated flows. Youthful volcanoes are rare in the region, and thus this field offers the opportunity to investigate mantle sources currently beneath the central Great Basin. Most of the eruptive centers are distributed along the northwestern margin of the Fish Creek Mountains, a mid-Tertiary caldera complex, along a 13-km-long northeasterly trend that is perpendicular to the regional stress field (or GPS velocity field), suggesting fault control or eruption from a now-buried fissure. The cones are geomorphologically youthful, with well-defined, commonly breached craters. At least one cone, situated slightly east of the main trend, consists of only a thin mantle of scoria and bombs overlying grey Paleozoic limestone. Previous K-Ar and Ar-Ar dating indicate that the cones are between 1.29 and 0.95 Ma in age. Two other nearby Quaternary volcanic centers lie northeast of the Fish Creek Mountains (K-Ar date of 3.3 Ma) and in the center of the Fish Creek caldera (age unknown). Rare Tertiary basalts and more common Tertiary andesites lie around the margin of the caldera. Lavas from the Buffalo Valley cones have vesicular flow tops and more massive interiors. All Quaternary centers are similar petrographically, including 1-2% olivine phenocrysts and megacrysts up to 1 cm in size, and characteristic plagioclase megacrysts that are rarely up to 4 cm long, commonly in a glassy matrix. Two cone samples are alkalic basalt and tephrite with Mg numbers of 0.55, high TiO2 (2.4%), K2O (2.0%), light REE, Nb (60 ppm), but low Cr and Ni (80 ppm), Pb (2 ppm), Ba (450 ppm) and 87Sr/86Sr (0.70375) compared to Late Pliocene/Quaternary volcanic rocks from the western Great Basin near Reno/Carson City/Fallon. The Buffalo Valley cones are similar chemically to lavas from the Pliocene-Quaternary Lunar Craters volcanic field in central Nevada, and are melts of mantle that is

  2. Sulfur release from the Columbia River Basalts and other flood lava eruptions constrained by a model of sulfide saturation

    NASA Astrophysics Data System (ADS)

    Blake, S.; Self, S.; Sharma, K.; Sephton, S.

    2010-11-01

    A very likely cause of widespread environmental impacts of flood basalt eruptions is the emission of sulfur, chlorine, and possibly fluorine from the erupting magma. We present new data on the S contents of rare glass inclusions and matrix glasses preserved in quenched lava selvages from lava fields of the Columbia River Basalt Group (CRBG; Ginkgo, Sand Hollow and Sentinel Gap flows, Wanapum Basalt Formation). We compare these results with published data from Neral and Jawar Formation lavas (Deccan Traps, India) and the Roza flow (CRBG). CRBG glass inclusions have up to 2000 ppm S and 15-16 wt.% FeO total. By contrast, the Deccan examples have about 1400 ppm S and 10 wt.% FeO total. Several of the glass inclusions are partly degassed, indicating entrapment during magma rise, and matrix glasses are typically more evolved than glass inclusions due to small amounts of in situ crystallization. Using only the highest S inclusions and taking account of the effect of in situ crystallization and degassing on the S content of the residual matrix glasses indicates S yields of about 0.07 to 0.1 wt.% from Deccan eruptions and about 0.15 wt.% from Wanapum (CRBG) eruptions. The pre-eruptive S contents of these magmas correlate with weight% FeO total in the same way as undegassed sulfide-saturated mid-ocean ridge basalts. Using oceanic basalts to define a sulfide saturation line, and data on S contents of degassed basalts, we propose an equation to estimate the weight% S yield (ΔS) from initially sulfide-saturated basalt liquid without the need to find well-preserved, rare, undegassed glass inclusions and matrix glasses: ΔS=(0.01418×FeO-0.06381)±0.02635. This compares well with independent estimates derived from the petrologic method by taking the difference in S concentration of glass inclusions and matrix glass. Applying our method to the aphyric Grande Ronde Basalts of the CRBG implies a total yield of about 1000 Gt SO 2 delivered into the Miocene atmosphere in

  3. Quaternary Adakite - Nb-Enriched Basalt Association in the Western - Mexican Volcanic Belt: is There any Slab Melt Evidence?

    NASA Astrophysics Data System (ADS)

    Petrone, C. M.; Ferrari, L.

    2007-05-01

    A spatial and temporal association between adakitic rocks and Nb-enriched basalts (NEB) has been recognised for the first time in the western sector of the Trans-Mexican Volcanic Belt in the San Pedro-Cerro Grande Volcanic Complex (SCVC). The SCVC is composed of subalkalic intermediate to felsic rocks, spanning in composition from high-silica andesites to rhyolites, and by the young transitional hawaiite and mugearite lavas of Amado Nervo shield volcano. Intermediate to felsic rocks of the SCVC show many geochemical characteristics of typical adakites, such as high Sr/Y ratios (up to 180) and low Y (< 18 ppm) and Yb contents. Mafic Amado Nervo rocks have high TiO2 (1.5-2.3 wt), Nb (14-27 ppm), Nb/La (0.5-0.9) and high absolute abundances of HFSE similar to those shown by NEB. However, the Sr and Nd isotopic signature of SCVC rocks is different from that shown by typical adakites and NEB. Although the adakites-NEB association has been traditionally considered as a strong evidence of slab-melting, we suggest that other processes can lead to its generation. Here we show that parental magmas of adakitic rocks of the SCVC derive their adakitic characteristic from high pressure crystal fractionation processes of garnet, amphibole and pyroxene of a normal arc basalt. On the other hand, Amado Nervo Na- alkaline parental magmas have been generated by sediment melting plus MORB-fluid flux melting of a heterogeneous mantle wedge, consisting of a mixture of depleted and an enriched mantle sources (90DM+10EM). We can not exclude a contribution to the subduction component of slab melts, because the component signature is dominated by sediment melt, but we argue that caution is needed in interpreting the adakites-NEB association in a genetic sense

  4. Basaltic volcanism on the eucrite parent body - Petrology and chemistry of the polymict eucrite ALHA80102

    NASA Technical Reports Server (NTRS)

    Treiman, A. H.; Drake, M. J.

    1985-01-01

    The polymict eucrite meteorite ALHA80102 is an unequilibrated breccia of basaltic and gabbroic clasts in a fragmental matrix. Clasts include basalts of many textural types, cumulate gabbro, black 'glass', and ferroan troctolite (plagioclase, silica, Fe-rich olivine, ilmenite, mesostasis). Ferroan troctolite has not been previously reported from eucrites or howardites; it is interpreted as the end-product of fractional crystallization of eucritic magmas. Bulk and trace element compositions (by electron microprobe and INAA) of clasts and matrix from ALHA80102 are similar to those of other eucrites; the meteorite contains clasts similar to Juvinas and to Stannern. A clast of cumulate eucrite gabbro is enriched in the light rare earths (La/Lu = 2XCI). This clast is interpreted as an unrepresentative sample of metamorphically equilibrated gabbro; LREE-enriched magmas need not be invoked. ALHA80102 is similar to other polymict eucrites from the Allan Hills and may be paired with ALHA76005, ALHA77302, and ALHA78040.

  5. Helium isotopic evidence for modification of the cratonic lithosphere during the Permo-Triassic Siberian flood basalt event

    NASA Astrophysics Data System (ADS)

    Barry, Peter H.; Hilton, David R.; Day, James M. D.; Pernet-Fisher, John F.; Howarth, Geoffrey H.; Magna, Tomas; Agashev, Aleksey M.; Pokhilenko, Nikolay P.; Pokhilenko, Lyudmila N.; Taylor, Lawrence A.

    2015-02-01

    Major flood basalt emplacement events can dramatically alter the composition of the sub-continental lithospheric mantle (SCLM). The Siberian craton experienced one of the largest flood basalt events preserved in the geologic record - eruption of the Permo-Triassic Siberian flood basalts (SFB) at ~ 250 Myr in response to upwelling of a deep-rooted mantle plume beneath the Siberian SCLM. Here, we present helium isotope (3He/4He) and concentration data for petrologically-distinct suites of peridotitic xenoliths recovered from two temporally-separated kimberlites: the 360 Ma Udachnaya and 160 Ma Obnazhennaya pipes, which erupted through the Siberian SCLM and bracket the eruption of the SFB. Measured 3He/4He ratios span a range from 0.1 to 9.8 RA (where RA = air 3He/4He) and fall into two distinct groups: 1) predominantly radiogenic pre-plume Udachnaya samples (mean clinopyroxene 3He/4He = 0.41 ± 0.30 RA (1σ); n = 7 excluding 1 outlier), and 2) 'mantle-like' post plume Obnazhennaya samples (mean clinopyroxene 3He/4He = 4.20 ± 0.90 RA (1σ); n = 5 excluding 1 outlier). Olivine separates from both kimberlite pipes tend to have higher 3He/4He than clinopyroxenes (or garnet). Helium contents in Udachnaya samples ([He] = 0.13-1.35 μcm3STP/g; n = 6) overlap with those of Obnazhennaya ([He] = 0.05-1.58 μcm3STP/g; n = 10), but extend to significantly higher values in some instances ([He] = 49-349 μcm3STP/g; n = 4). Uranium and thorium contents are also reported for the crushed material from which He was extracted in order to evaluate the potential for He migration from the mineral matrix to fluid inclusions. The wide range in He content, together with consistently radiogenic He-isotope values in Udachnaya peridotites suggests that crustal-derived fluids have incongruently metasomatized segments of the Siberian SCLM, whereas high 3He/4He values in Obnazhennaya peridotites show that this section of the SCLM has been overprinted by Permo-Triassic (plume-derived) basaltic

  6. Mantle sources of quaternary volcanism on Zhokhov Island (De Long Islands, East Arctic): Isotope-geochemical features of the basalts and spinel lherzolite xenoliths

    NASA Astrophysics Data System (ADS)

    Sakhno, V. G.; Krymsky, R. Sh.; Belyatsky, B. V.; Shevchenko, S. S.; Sergeev, S. A.

    2015-02-01

    This paper reports the results of isotope-geochemical studies and distribution patterns for trace elements and rare earth elements in a collection of specimens of Cenozoic alkaline olivine basalts and spinel lherzolite xenoliths sampled at Zhokhov Island, De Long Archipelago (New Siberian Islands), East Arctic. In spite of various contributions of xenogenic minerals of mantle lherzolite xenoliths (olivine, pyroxene and spinel), the bulk-rock isotope composition of the studied specimens deviates within insignificant limits. This evidences the isotopic and geochemical homogeneity of the mantle source and the absence of a significant effect of processes of contamination by crustal host rocks, which frequently occur within the basalts as xenoliths. On the other hand this reflects the short lifetime of existence and evolution of the mantle melt source. The studied basalts by their isotope and geochemical characteristics resemble volcanics of oceanic islands, intraplate continental volcanics, and those of ocean rises, relate to the activity of mantle plumes. The lack of elevated U/Pb in the studied specimens permits us to correlate the occurrence of the Cenozoic volcanism at De Long Islands of East Arctic with intraplate continental plume volcanism of the rifting stage (analogous to plume magmatism of the East African Rift, Mesozoic alkaline ultramafic volcanism of Eastern India, and others).

  7. The survival of early Earth mantle reservoirs: Evidence from flood basalts

    NASA Astrophysics Data System (ADS)

    Jackson, M. G.

    2011-12-01

    isotopic characteristics to match the predicted composition of a primitive, non-chondritic Earth. Jackson et al. (2010, Nature) reported primitive Nd and Pb isotopic compositions in Baffin Island lavas, which are known to host the highest terrestrial mantle 3He/4He ratios (Kent et al., 2003, Nature; Graham et al., 1998 EPSL). Baffin Island lavas constitute a large igneous province (LIP). Using the wisdom gained from Baffin Island, Jackson and Carlson (2011, Nature) prospected for primitive mantle isotopic characteristics in LIPs globally, and they identified a pervasive signature of non-chondritic primitive mantle 143Nd/144Nd and primitive Pb-isotopic ratios in the largest LIPs: Deccan, Siberia, Ontong Java, Kerguelen and Karoo. The geochemical and petrologic characteristics of a primitive mantle reservoir may explain its ubiquitous presence in LIPs. A primitive reservoir will host higher concentrations of the incompatible radioactive elements than depleted reservoirs, and it will therefore be hotter. Similarly, such a reservoir has never had melt extracted, so it will be more fertile and yield more melt. Therefore, a hotter, more fusible (non-chondritic) primitive mantle source sourcing LIPs may constitute the perfect recipe for flood basalt genesis.

  8. Memories of Earth Formation in the Modern Mantle: W Isotopic Composition of Flood Basalt Lavas

    NASA Astrophysics Data System (ADS)

    Rizo Garza, H. L.; Walker, R. J.; Carlson, R.; Horan, M. F.; Mukhopadhyay, S.; Francis, D.; Jackson, M. G.

    2015-12-01

    Four and a half billion years of geologic activity has overprinted much of the direct evidence for processes involved in Earth's formation and its initial chemical differentiation. Xenon isotopic ratios [1] and 3He/22Ne ratios [2] suggest that heterogeneities formed during Earth's accretion have been preserved to the present time. New opportunities to learn about early Earth history have opened up with the development of analytical techniques that allow high precision analysis of short-lived isotopic systems. The Hf-W system (t½ = 8.9 Ma) is particularly valuable for studying events that occurred during the first ~50 Ma of Solar System history. Here we report new data for ~ 60 Ma Baffin Bay and ~ 120 Ma Ontong Java Plateau lava samples. Both are large igneous provinces that may have sampled a primitive, less degassed deep mantle reservoir that has remained isolated since shortly after Earth formation [3,4]. Three samples analyzed have 182W/184W ratios that are 10 to 48 ppm higher than our terrestrial standard. These excesses in 182W are the highest ever measured in terrestrial rocks, and may reflect 182W ingrowth in an early-formed high Hf/W mantle domain that was produced by magma ocean differentiation [5]. Long and short-lived Sm-Nd systematics in these samples, however, are inconsistent with this hypothesis. The 182W excessses could rather reflect the derivation of these lavas from a mantle reservoir that was isolated from late accretionary additions [6]. The chondritic initial Os isotopic compositions and highly siderophile element abundances of these samples, however, are inconsistent with this interpretation. Tungsten concentrations for the Baffin Bay and Ontong Java Plateau samples range from 23 ppb to 62 ppb, and are negatively correlated with their 182W/184W ratios. We propose that the source reservoirs for these flood basalts likely formed through Hf/W fractionation caused by core-forming events occuring over a protacted time interval during Earth

  9. Contrasting magma types and steady-state, volume-predictable, basaltic volcanism along the Great Rift, Idaho.

    USGS Publications Warehouse

    Kuntz, M.A.; Champion, D.E.; Spiker, E. C.; Lefebvre, R.H.

    1986-01-01

    The Great Rift is an 85 km-long, 2-8 km-wide volcanic rift zone in the Snake River Plain, Idaho. Three basaltic lava fields, latest Pleistocene to Holocene, are located along the Great Rift: Craters of the Moon, Kings Bowl and Wapi. Craters of the Moon is the largest, covering 1600 km2 and containing approx 30 km3 of lava flows and pyroclastics. Field, radiocarbon and palaeomagnetic data show that this lava field formed in eight eruptive periods, each lasted several hundred years with a recurrence interval of several hundred to approx 3000 yr. The first eruption began approx 15 000 yr B.P. and the last ended at approx 2100 yr B.P. The other two lava fields formed approx 2250 yr B.P. Three magma types fed flows along the Great Rift. A contaminated and a fractionated type were erupted at the Craters of the Moon lava field. The third, little-fractionated Snake River Plain magma-type was erupted at the other two lava fields. The Craters of the Moon segment of the Great Rift has experienced quasi-steady state, volume-predictable volcanism for the last 15 000 yr. Based on this, about 5-6 km3 of lava will be erupted within the next 1000 yr.-L.C.H.

  10. Eruptive History and Chemical Evolution of the Precaldera and Postcaldera Basalt-Dacite Sequences, Long Valley, California: Implications for Magma Sources, Current Seismic Unrest, and Future Volcanism

    USGS Publications Warehouse

    Bailey, Roy A.

    2004-01-01

    The Long Valley Volcanic Field in east-central California straddles the East Sierran frontal fault zone, overlapping the Sierra Nevada and western Basin and Range Provinces. The volcanic field overlies a mature mid-Tertiary erosional surface that truncates a basement composed mainly of Mesozoic plutons and associated roof pendants of Mesozoic metavolcanic and Paleozoic metasedimentary rocks. Long Valley volcanism began about 4 Ma during Pliocene time and has continued intermittently through the Holocene. The volcanism is separable into two basalt-rhyolite episodes: (1) an earlier, precaldera episode related to Long Valley Caldera that climaxed with eruption of the Bishop Tuff and collapse of the caldera; and (2) a later, postcaldera episode structurally related to the north-south-trending Mono-Inyo Craters fissure system, which extends from the vicinity of Mammoth Mountain northward through the west moat of the caldera to Mono Lake. Eruption of the basalt-dacite sequence of the precaldera basalt-rhyolite episode peaked volumetrically between 3.8 and 2.5 Ma; few basalts were erupted during the following 1.8 m.y. (2.5?0.7 Ma). Volcanism during this interval was dominated by eruption of the voluminous rhyolites of Glass Mountain (2.2?0.8 Ma) and formation of the Bishop Tuff magma chamber. Catastrophic rupture of the roof of this magma chamber caused eruption of the Bishop Tuff and collapse of Long Valley Caldera (760 ka), after which rhyolite eruptions resumed on the subsided caldera floor. The earliest postcaldera rhyolite flows (700?500 ka) contain quenched globular basalt enclaves (mafic magmatic inclusions), indicating that basaltic magma had reentered shallow parts of the magmatic system after a 1.8-m.y. hiatus. Later, at about 400 ka, copious basalts, as well as dacites, began erupting from vents mainly in the west moat of the caldera. These later eruptions initiated the postcaldera basalt-rhyolite episode related to the Mono-Inyo Craters fissure system, which

  11. Temporal compositional trends over short and long time-scales in basalts of the Big Pine Volcanic Field, California

    NASA Astrophysics Data System (ADS)

    Blondes, Madalyn S.; Reiners, Peter W.; Ducea, Mihai N.; Singer, Brad S.; Chesley, John

    2008-05-01

    Primitive basaltic single eruptions in the Big Pine Volcanic Field (BPVF) of Owens Valley, California show systematic temporal-compositional variation that cannot be described by simple models of fractional crystallization, partial melting of a single source, or crustal contamination. We targeted five monogenetic eruption sequences in the BPVF for detailed chemical and isotopic measurements and 40Ar/ 39Ar dating, focusing primarily on the Papoose Canyon sequence. The vent of the primitive (Mg# = 69) Papoose Canyon sequence (760.8 ± 22.8 ka) produced magmas with systematically decreasing (up to a factor of two) incompatible element concentrations, at roughly constant MgO (9.8 ± 0.3 (1σ) wt.%) and Na 2O. SiO 2 and compatible elements (Cr and Ni) show systematic increases, while 87Sr/ 86Sr systematically decreases (0.7063-0.7055) and ɛ Nd increases (- 3.4 to - 1.1). 187Os/ 188Os is highly radiogenic (0.20-0.31), but variations among four samples do not correlate with other chemical or isotopic indices, are not systematic with respect to eruption order, and thus the Os system appears to be decoupled from the dominant trends. The single eruption trends likely result from coupled melting and mixing of two isotopically distinct sources, either through melt-rock interaction or melting of a lithologically heterogeneous source. The other four sequences, Jalopy Cone (469.4 ± 9.2 ka), Quarry Cone (90.5 ±17.6 ka), Volcanic Bomb Cone (61.6 ± 23.4 ka), and Goodale Bee Cone (31.8 ± 12.1 ka) show similar systematic temporal decreases in incompatible elements. Monogenetic volcanic fields are often used to decipher tectonic changes on the order of 10 5-10 6 yr through long-term changes in lava chemistry. However, the systematic variation found in Papoose Canyon (10 0-10 2 yr) nearly spans that of the entire volcanic field, and straddles cutoffs for models of changing tectonic regime over much longer time-scales. Moreover, ten new 40Ar/ 39Ar ages combined with chemistry from

  12. Southern Cordilleran basaltic andesite suite, southern Chihuahua, Mexico: A link between Tertiary continental arc and flood basalt magmatism in North America

    NASA Astrophysics Data System (ADS)

    Cameron, K. L.; Nimz, G. J.; Kuentz, D.; Niemeyer, S.; Gunn, S.

    1989-06-01

    the east from Phanerozoic basement to the west at the latitude of the transect. Most chemical changes near the inferred position of the megashear are subtle, and they may be gradational rather than abrupt. The uniformity of Sr and Nd isotopic compositions across the inferred position of the megashear indicates that one or more of the following statements is true: (1) Phanerozoic and Proterozoic subcontinental lithospheres are essentially indistinguishable in Sr and Nd compositions in southern Chihuahua, (2) the megashear is not a lithospheric boundary separating Phanerozoic and Proterozoic crust in the vicinity of the transect, or (3) the isotopic signatures were acquired in the asthenosphere rather than in subcontinental lithosphere. The principal difference between the SCORBA suite and the earlier mid-Cenozoic andesite to rhyolite orogenic suite is average SiO2 content. This difference reflects regional stress regimes at the time of eruption and magmatic plumbing. SCORBA was erupted in a more extensional tectonic environment than the orogenic suite. SCORBA magmas reached the surface more quickly and directly than most PRE-SCORBA basaltic magmas, and the suite experienced less differentiation. Although the tectonic setting of SCORBA was more extensional than the orogenic suite, it was less extensional than that of true flood basalts because SCORBA was erupted from central vents rather than major fissures. The SCORBA suite closely resembles the Grande Ronde Basalt in average SiO2 content, large ion lithophile/Nb ratios, voluminous nature, and Sr and Nd isotopic compositions. Furthermore, SCORBA west of the megashear and the Grande Ronde have similar Pb isotopic ratios. Voluminous continental basalts include a spectrum of compositions from intraplate tholeiites to rocks with more orogenic affinities. The common feature that they share is eruption in an extensional tectonic environment, be it intraplate, back arc, or perhaps intra-arc. The Grande Ronde is intermediate

  13. Lead and strontium isotopes and related trace elements as genetic tracers in the Upper Cenozoic rhyolite-basalt association of the Yellowstone Plateau volcanic field.

    USGS Publications Warehouse

    Doe, B.R.; Leeman, W.P.; Christiansen, R.L.; Hedge, C.E.

    1982-01-01

    Pb, U, Th, Rb and Sr contents and Pb- and Sr-isotopic compositions, together with field and petrological data, are consistent with the hypothesis of derivation of the basaltic and rhyolitic magmas of this volcanic field from source regions in the upper mantle and lower crust, respectively. It is suggested that the isotopic signatures of the basalts were inherited from a 2600 m.y.-old mantle 'keel' attached to the continental crust and were essentially unaffected by passage of the magma through the latter.R.J.P.

  14. Spectroscopy of olivine basalts using FieldSpec and ASTER data: A case study from Wadi Natash volcanic field, south Eastern Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Madani, Ahmed

    2015-10-01

    This paper aims at revealing the spectral characteristics of the olivine basalts exposed at Wadi Natash area, Egypt, using FieldSpec spectroradiometer. It also evaluates band ratios and fusion techniques for mapping purposes using ASTER data. Several volcanic episodes occurred during Early- to Late-Cretaceous are recorded in the study area. Early-Cretaceous olivine basalts are highly carbonated. Late-Cretaceous eruptions took place throughout several volcanic cones aligned in NW direction. Based on FieldSpec measurements and petrographic data, two groups of olivine basalt namely `A' and `B' are recognized. Fresh olivine basalt (group A) is characterized by low flat spectral profile with overall low reflectance values (˜20%). Spectral profile of altered olivine basalt (group B) shows moderate reflectance values (˜37%) with four little absorption features around the 1.10, 1.40, 2.00 and 2.35 μm wavelength regions. These absorption features are attributed mainly to the presence of chlorite and carbonate alteration products as indicated by petrographic examination. ASTER false colour composite band ratio image (3/2:R, 8/1:G and 8/5:B) discriminates easily the fresh and altered basalts by deep blue and reddish blue colours respectively. Image fusion between previously mentioned FCC ratios image and high spatial resolution ASTER panchromatic image are carried out using brovey and HSV transformation methods. Visual and statistical assessment methods proved that HSV fusion image yields better image interpretability results compared to brovey image. It improves the spatial resolution of original FCC ratios image with acceptable spectral preservation. The present study proved the usefulness of FieldSpec spectral profiles and the processed ASTER data for discriminating different olivine basalt groups exposed at the study area.

  15. Tomographic imaging of sub-basalt Mesozoic sediments and shallow basement geometry for hydrocarbon potential below the Deccan Volcanic Province (DVP) of India

    NASA Astrophysics Data System (ADS)

    Behera, Laxmidhar; Sen, Mrinal K.

    2014-10-01

    We have derived a shallow subsurface 2-D tomographic P-wave velocity image of the Deccan Volcanic Province (DVP) of India using first-arrival traveltime data along a 90-km-long N-S trending seismic profile in the Deccan Syneclise region. The tomographic image depicts smooth velocity variations of Quaternary and Tertiary (2.0-3.0 km s-1) sediments, basalts/traps (5.0-5.5 km s-1), sub-trappean Mesozoic sediments (4.3-4.5 km s-1) as well as the basement (5.9-6.1 km s-1) geometry down to a maximum depth of 5.0 km. Due to Late Cretaceous volcanism and outpouring of basaltic lava flows, this region is affected by numerous dyke intrusions and thick basaltic trap (2-3 km) exposed on the surface and surrounded by graben structures due to deep basinal faults forming a large igneous province. Although sub-basalt imaging is a major challenge for the oil industry, with the help of tomographic imaging technique of first-arrival seismic refraction data, we were able to image sub-trappean Mesozoic sediments (<0.75 km) deposited below the two sequences of thick basaltic flows above the basement. The imaged Mesozoic sediments are expected to contain hydrocarbon because of their wide extension in this sedimentary basin with suitable trapping mechanism due to basalts. The robustness of the velocity image is assessed through numerous tests like velocity perturbations, χ2 estimates, rms residuals of traveltime fit, uncertainty estimates through computation of ray-density or hits and series of checkerboard resolution tests with velocity anomalies having different cell size. The thickness of the basalt and the sub-trappean Mesozoic sediments along with the basement geometry obtained from tomography are constrained through ray-trace modelling and pre-stack depth migration (PSDM) of the wide-angle reflection phases for different shot gathers along the profile.

  16. Geology of the saucer-shaped sill near Mahad, western Deccan Traps, India, and its significance to the Flood Basalt Model

    NASA Astrophysics Data System (ADS)

    Duraiswami, Raymond A.; Shaikh, Tahira N.

    2013-07-01

    An ˜22-m-thick saucer-shaped sill occurs near Mahad and is exposed as a curvilinear, miniature ridge within the Deccan Traps. The sill has variable dips (42-55°). It has a 7.1-km long axis and 5.3 km short axis (aspect ratio of 1.4) and is larger than the MV sill of the Golden Valley sill complex, South Africa and the Panton sill, Australia. The sill has distinct glassy upper and lower chilled margins with a coarse-grained highly jointed core. The samples from the margin are invariably fractured and iron stained because of deuteric alteration. The rock from the sill is plagioclase-phyric basalt. At least three thick sill-like apophyses emanate from the base of the main sill. The apophyses change direction because of bending and thinning from a horizontal concordant sheet at the top to a discordant inclined form that bends again to pass into a lower horizontal concordant sheet. We interpret such features as `nascent saucer-shaped sills' that did not inflate to form nested sills. Geochemically, the sill consists of poorly differentiated tholeiitic basalt that has a restricted geochemical range. Critical trace element ratios and primitive mantle normalised trace and REE patterns indicate that the sills have geochemical affinities to the Poladpur chemical type and that the pahoehoe flow they intrude belongs to the Bushe Formation. Calculated magmatic overpressures during sill emplacement range from 8.4 to 11.3 MPa (for Young's modulus E = 5 GPa) and 16.7 to 22.5 MPa (for E=10 GPa) and depth to magma chamber ranges from 8.5 to 11.5 km ( E = 5 GPa) and 17.1 to 22.9 km ( E = 10 GPa), consistent with petrological and gravity modelling. The volume of the Mahad sill is approximately 276 km3 and is constant irrespective of the variations in the values of host-rock Young's modulus. In 1980, Cox (J Petrol 21:629-650, 1980) proposed a conceptual model of the crust-mantle section beneath the Karoo CFB which is considered as the fundamental model for flood basalt volcanism. Our

  17. Helium Isotopic Compositions of Antarctic High-Mg Rocks Related to the Karoo Continental Flood Basalts: Evidence for a Depleted Upper Mantle Source?

    NASA Astrophysics Data System (ADS)

    Heinonen, J. S.; Kurz, M. D.

    2014-12-01

    The isotopic composition of helium is often considered to be one of the key elements in resolving deep mantle plume vs. upper mantle origin of hotspot-related volcanic rocks. High 3He/4He values, greater than 10 times atmospheric (Ra), are generally thought to indicate plume-related sources in the lower mantle. The use of helium isotopes in continental flood basalt (CFB) provinces has been limited by the lack of fresh rock material, poor exposures, time-integrated ingrowth of radiogenic 4He, and strong lithospheric overprinting. Vestfjella mountain range at western Dronning Maud Land, Antarctica, is comprised of lava flows and intrusive rocks that belong to the Jurassic (~180 Ma) Karoo continental flood basalt province, the bulk of which is exposed in southern Africa. The Karoo CFBs and related rocks show strong lithospheric influence in their geochemistry in general, but some high-Mg dikes from Vestfjella show geochemical evidence of derivation from sublithospheric sources. In an attempt to determine the first estimate for the helium isotopic composition of the Karoo mantle sources, we performed He isotopic measurements on six primitive Vestfjella dike samples collected from variably exposed nunataks. Helium was extracted by in-vacuo stepwise crushing and melting of separated and carefully hand-picked olivine phenocrysts (Ø = 0.25-1 mm; ~10 000 grains in total; abraded and unabraded fractions). The results of coupled crushing and melting measurements show evidence of both cosmogenic and radiogenic helium contributions within the olivines (i.e. by having high He contents and anomalously low or high 3He/4He released by melting), which complicates interpretation of the data. As a best estimate for the mantle isotopic composition, we use the sample with the highest amount of He released (> 50%) during the first crushing step of an abraded coarse fraction, which gave 3He/4He of 7.03 ± 0.23 (2σ) Ra. This value is indistinguishable from those measured from Southwest

  18. Basalt-Limestone and Andesite-Limestone Interaction in the Arc Crust - Implications for Volcanic Degassing of CO2

    NASA Astrophysics Data System (ADS)

    Carter, L. B.; Dasgupta, R.

    2014-12-01

    Volcanically emitted CO2 is generally mantle-derived, but high degassing rates at some arcs (e.g. Merapi [1] and Colli Albani Volcanic District [2]) are thought to be affected by magma-carbonate interaction in the upper plate. However, the effects of depth, temperature, and composition on this process are poorly known. We experimentally simulated magma (50%)-limestone (50%) wallrock interactions at 0.5-1.0 GPa, 1100-1200 °C using pure calcite and a hydrous (~3-5 wt.% H2O) melt (basalt, andesite, or dacite). At 1.0 GPa, 1200 °C starting melts are superliquidus, whereas in the presence of calcite, Ca-rich cpx ± Ca-scapolite are produced. With increasing T, basalt-calcite interaction causes the melt, on a volatile-free basis, to become silica-poor and Ca-rich with alumina decreasing as cpx becomes more CaTs-rich. The same trend is seen with all starting melt compositions as P decreases at a constant T (1200 °C), producing melts similar to ultracalcic (CaO/Al2O3>>1) melt inclusions found in arc settings. Shifting from basalt to andesite has little effect on SiO2 and CaO of the reacted melt (e.g. 37 wt.% SiO2, 42 wt.% CaO at 0.5 GPa, 1200 °C), whereas Al2O3 of andesite-derived reacted melt is lower, likely a result of lower alumina in the starting andesite. Wall-rock calcite consumption is observed to increase with increasing T, decreasing P, and increasing melt XSiO2. At 0.5 GPa between 1100 and 1200 °C, our basalt experiments yield carbonate assimilation from 22 to 48 wt.%. This decreases to 20 wt.% at 1.0 GPa, 1200 °C, whereas an andesitic composition assimilates 59 to 52 wt.% from 0.5 to 1.0 GPa at 1200 °C. The higher assimilation in andesite-added runs at high-T is because of lower silicate liquidus as evidenced by lower modal proportion or absence of cpx ± scapolite. Using a magma flux rate estimated for Mt. Vesuvius [3], we obtain a CO2 outflux for a single such volcano experiencing arc magma-calcite reaction [4] of at least 2-4% of the present

  19. Basaltic maar-diatreme volcanism in the Lower Carboniferous of the Limerick Basin (SW Ireland)

    NASA Astrophysics Data System (ADS)

    Elliott, H. A. L.; Gernon, T. M.; Roberts, S.; Hewson, C.

    2015-05-01

    Lead-zinc exploration drilling within the Limerick Basin (SW Ireland) has revealed the deep internal architecture and extra-crater deposits of five alkali-basaltic maar-diatremes. These were emplaced as part of a regional north-east south-west tectonomagmatic trend during the Lower Carboniferous Period. Field relationships and textural observations suggest that the diatremes erupted into a shallow submarine environment. Limerick trace element data indicates a genetic relationship between the diatremes and extra-crater successions of the Knockroe Formation, which records multiple diatreme filling and emptying cycles. Deposition was controlled largely by bathymetry defined by the surrounding Waulsortian carbonate mounds. An initial non-diatreme forming eruption stage occurred at the water-sediment interface, with magma-water interaction prevented by high magma ascent rates. This was followed by seawater incursion and the onset of phreatomagmatic activity. Magma-water interaction generated poorly vesicular blocky clasts, although the co-occurrence of plastically deformed and highly vesicular clasts indicate that phreatomagmatic and magmatic processes were not mutually exclusive. At a later stage, the diatreme filled with a slurry of juvenile lapilli and country rock lithic clasts, homogenised by the action of debris jets. The resulting extra-crater deposits eventually emerged above sea level, so that water ingress significantly declined, and late-stage magmatic processes became dominant. These deposits, largely confined to the deep vents, incorporate high concentrations of partially sintered globular and large `raggy' lapilli showing evidence for heat retention. Our study provides new insights into the dynamics and evolution of basaltic diatremes erupting into a shallow water (20-120 m) submarine environment.

  20. Lunar Mare Basalts as Analogues for Martian Volcanic Compositions: Evidence from Visible, Near-IR, and Thermal Emission Spectroscopy

    NASA Technical Reports Server (NTRS)

    Graff, T. G.; Morris, R. V.; Christensen, P. R.

    2003-01-01

    The lunar mare basalts potentially provide a unique sample suite for understanding the nature of basalts on the martian surface. Our current knowledge of the mineralogical and chemical composition of the basaltic material on Mars comes from studies of the basaltic martian meteorites and from orbital and surface remote sensing observations. Petrographic observations of basaltic martian meteorites (e.g., Shergotty, Zagami, and EETA79001) show that the dominant phases are pyroxene (primarily pigeonite and augite), maskelynite (a diaplectic glass formed from plagioclase by shock), and olivine [1,2]. Pigeonite, a low calcium pyroxene, is generally not found in abundance in terrestrial basalts, but does often occur on the Moon [3]. Lunar samples thus provide a means to examine a variety of pigeonite-rich basalts that also have bulk elemental compositions (particularly low-Ti Apollo 15 mare basalts) that are comparable to basaltic SNC meteorites [4,5]. Furthermore, lunar basalts may be mineralogically better suited as analogues of the martian surface basalts than the basaltic martian meteorites because the plagioclase feldspar in the basaltic Martian meteorites, but not in the lunar surface basalts, is largely present as maskelynite [1,2]. Analysis of lunar mare basalts my also lead to additional endmember spectra for spectral libraries. This is particularly important analysis of martian thermal emission spectra, because the spectral library apparently contains a single pigeonite spectrum derived from a synthetic sample [6].

  1. Partial melting and fractionation in the Mesa Chivato alkali basalt-trachyte series, Mount Taylor Volcanic Field, New Mexico

    NASA Astrophysics Data System (ADS)

    Schrader, C. M.; Schmidt, M. E.; Crumpler, L. S.; Wolff, J. A.

    2012-12-01

    Mesa Chivato comprises a series of alkaline cones, flows, and domes within the Mount Taylor Volcanic Field (MTVF) in northwest New Mexico. Compositions range from alkali basalt to trachyte. Intermediate magmas are less well represented than mafic and felsic rocks, but benmoreites and transitional benmoreite-trachytes provide a window into the differentiation processes. Major element, trace element, and isotopic data suggest that petrogenesis of benmoreite proceeded by fractional crystallization of mafic liquids and magma mixing with partially melted mafic rocks. Major element mass balance models permit the derivation of transitional benmoreite/trachyte from the benmoreite by 20-25% crystallization of microphenocryst phases (olivine, plagioclase, Ti-magnetite, and apatite) and further fractionation to trachyte by 10-15% crystallization of olivine, plagioclase and alkali feldspar, Fe-Ti oxide, and apatite. These models are supported by SiO2-Sr and -Ba systematics. However, the hawaiite to benmoreite gap cannot be crossed by fractional crystallization alone. While major element models permit the mafic lavas to yield the benmoreite, they require extensive fractionation of clinopyroxene and plagioclase - this is unsupported by petrography (clinopyroxene phenocrysts are rare in the mafic rocks and lacking in the intermediate rocks) and cannot explain the benmoreite's very high Sr contents (>1800 ppm), which would have been depleted by plagioclase fractionation. From LA-ICPMS analysis of plagioclase: 87Sr/86Sr of early alkali basalt (0.70285-0.70300) and late hawaiite (0.70406-0.70421) bracket the 87Sr/86Sr of the benmoreite (0.70361-0.70406). Thus, either could represent the fractionated liquid parental to the benmoreite and the other the partially melted source.

  2. Ultraviolet digital imaging of volcanic plumes: Implementation and application to magmatic processes at basaltic volcanoes

    NASA Astrophysics Data System (ADS)

    Nadeau, Patricia Amanda

    Magmatic volatiles play a crucial role in volcanism, from magma production at depth to generation of seismic phenomena to control of eruption style. Accordingly, many models of volcano dynamics rely heavily on behavior of such volatiles. Yet measurements of emission rates of volcanic gases have historically been limited, which has restricted model verification to processes on the order of days or longer. UV cameras are a recent advancement in the field of remote sensing of volcanic SO2 emissions. They offer enhanced temporal and spatial resolution over previous measurement techniques, but need development before they can be widely adopted and achieve the promise of integration with other geophysical datasets. Large datasets require a means by which to quickly and efficiently use imagery to calculate emission rates. We present a suite of programs designed to semi-automatically determine emission rates of SO 2 from series of UV images. Extraction of high temporal resolution SO 2 emission rates via this software facilitates comparison of gas data to geophysical data for the purposes of evaluating models of volcanic activity and has already proven useful at several volcanoes. Integrated UV camera and seismic measurements recorded in January 2009 at Fuego volcano, Guatemala, provide new insight into the system's shallow conduit processes. High temporal resolution SO2 data reveal patterns of SO2 emission rate relative to explosions and seismic tremor that indicate tremor and degassing share a common source process. Progressive decreases in emission rate appear to represent inhibition of gas loss from magma as a result of rheological stiffening in the upper conduit. Measurements of emission rate from two closely-spaced vents, made possible by the high spatial resolution of the camera, help constrain this model. UV camera measurements at Kilauea volcano, Hawaii, in May of 2010 captured two occurrences of lava filling and draining within the summit vent. Accompanying high

  3. Tracing the sublithospheric sources of continental flood basalts: multi-elemental isotopic studies on the recently found ferropicrites and meimechites from the Karoo large igneous province

    NASA Astrophysics Data System (ADS)

    Heinonen, J. S.; Carlson, R. W.; Luttinen, A. V.

    2011-12-01

    There is a substantial debate on the mantle sources and ultimate origins of continental flood basalts (CFBs), e.g., whether they are related to deep-seated thermal upwellings (i.e. mantle plumes) or not. The Karoo CFB province that was emplaced on the juxtaposed land masses of Africa and Antarctica during the early stages of the breakup of the Gondwana supercontinent ~180 Ma ago has played a central role in this debate. Although most of the structural analyses, geochemical affinities, and temporal relationships of Karoo-related rocks point to a strong control of lithosphere on the magmatism, paleostress estimates for some of the Karoo dikes and high mantle potential temperatures estimated for the sources of recently found highly magnesian rocks from Antarctica are compatible with the plume theory. Volcanic rocks that do not show evidence of lithospheric influence in their geochemistry are extremely rare in the African part of the Karoo province. Here we present high-precision isotopic (Sr, Nd, Pb, and Os) whole-rock data on some primitive dike rocks (ferropicrites and meimechites) associated with its Antarctic extension. The isotopic data together with trace element data show that the parental melts of the studied rocks sampled two distinctive geochemical reservoirs in the deep sub-Gondwanan mantle. The isotopic signatures of the relatively depleted types show evidence of extensive melt extraction in the past and are indistinguishable from those of mid-ocean ridge basalts (MORBs) of the SW Indian Ridge, the modern successor of the Jurassic Africa-Antarctica rift. On the other hand, the relatively enriched type isotopically resembles modern oceanic island basalts (OIBs) and may sample pyroxenitic sources either formed by melt infiltration in the upper mantle or by reaction of peridotite with recycled oceanic crustal components. Recent Ar-Ar datings of the depleted types indicate that they are related to the main phase of Karoo magmatism ~180 Ma ago. Moreover

  4. Basaltic Diatreme To Root Zone Volcanic Processes In Tuzo Kimberlite Pipe (Gahcho Kué Kimberlite Field, NWT, Canada)

    NASA Astrophysics Data System (ADS)

    Seghedi, I.; Kurszlaukis, S.; Maicher, D.

    2009-05-01

    an external factor to control the explosive behaviour of the magma. The overall constant volatile content of the kimberlite does not explain the observed extreme change in emplacement behaviour. The facies architecture of fragmental facies dominated by vertical elements is similar to that in non- kimberlitic diatremes and indicates deposition from debris jets marking separate and repeated explosive volcanic events. In basaltic pipes, such jets are generated by phreatomagmatic explosions in the explosion chamber(s) of the root zone, causing abundant country rock fragmentation and further efficient mixture of the various particles. Phases of high explosivity formed the finely fragmented kimberlites containing a high percentage of wall-rock xenoliths, while the fluidal-shaped and partly welded texturally variable and wall-rock- poor transitional coherent facies suggest phases of repetitive, hot, and low-energy fragmentation forming kimberlite spatter. Peperite hosted in kimberlite tephra is also typically found in basaltic root zones. Time gaps in between volcanic eruptive periods are indicated by cognate pyroclasts and reworked wall-rock deposits emplaced by sporadic sedimentation events in subterranean cavities under the widening roof of the pipe. The presence of temporary caves in the root zone is proposed also by the occurrence of spherical CKC in deep- seated fragmental kimberlite and by spatter found in transitional coherent rocks. Evidence for caves was mostly preserved at deeper pipe levels advocating continuously recurring processes during the life span of Tuzo.

  5. Global Climate Change Resulting From Voluminous Intrusive Basaltic Volcanism in Sedimentary Basins: the Methane Production Potential

    NASA Astrophysics Data System (ADS)

    Planke, S.; Svensen, H.; Malthe-Srenssen, A.; Rasmussen, T.; Jamtveit, B.

    2003-12-01

    Large igneous provinces are often temporarily associated with global warming and mass extinction events, for instance (1) the Siberian Traps and the Permian-Triassic boundary, (2) the Karoo igneous event and the Early Toacian anoxic event, (3) the Deccan Traps and the Cretaceous-Tertiary boundary, and (4) the North Atlantic Volcanic Province (NAVP) and the initial Eocene thermal maximum (IETM). We propose a new theory for linking the volcanic and global warming events where the magma emplacement environment is a crucial parameter. Our theory is that massive production and release of isotopically light carbon gasses in metamorphic aureoles surrounding magmatic sill intrusions in organic-rich sedimentary basins may trigger global climate change. The greenhouse gasses have to be produced and released in a short time (about 104 years) to be able to explain large global warming events. The intrusion of magma into an organic-rich sedimentary basin may increase the carbon flux into the atmosphere by at least 5 to 30 times compared with degassing of the same volume of extruded magma. Field and seismic data, combined with temperature modelling, show that very voluminous sill complexes are intruded and solidified in a short time span (<1000 years) during the initial phase of volcanic activity. We have recently completed an extensive mapping of Paleocene/Eocene sill complexes in the Cretaceous Vøring and Møre basins off mid-Norway. The extent of the sill complex is >80,000 km2, whereas the estimated total volume of the sill complex is 0.9 to 2.5 x 104 km3. The methane production potential in metamorphic aureoles in these two basins is in the rage 0.3 to 3.3 x1018 g CH4 assuming that 0.5 to 2.0 wt. {%} organic carbon is converted to methane. The methane production potential in the entire NAVP is estimated to be about five times greater. The total volume of methane produced in metamorphic aureoles in NAVP is larger than the volumes required to explain the IETM and the

  6. Oligocene basaltic volcanism of the northern Rio Grande Rift: San Luis Hills, Colorado

    USGS Publications Warehouse

    Thompson, R.A.; Johnson, C.M.; Mehnert, H.H.

    1991-01-01

    The inception of the Rio Grande Rift in northern New Mexico and southern Colorado was accompanied by voluminous mafic volcanism preserved in part as erosional remnants on an intrarift horst within the current axial rift graben of the San Luis Valley. Major and trace element constraints support a petrogenetic model of fractionation plus lower crustal assimilation for petrologic suites within the San Luis Hills rocks, although the model cannot relate lavas for the entire series to a common parent. Most mafic lavas of the San Luis Hills were evolved (Mg # <60) and contaminated by LREE-enriched silicic partial melts of granulitic lower crust depleted in Rb, Th, and U. However, relatively noncontaminated lavas can be identified and indicate at least two mantle source regions were involved. -from Authors

  7. Geochemical and Sr-Nd isotope variations within Cretaceous continental flood-basalt suites of the Canadian High Arctic, with a focus on the Hassel Formation basalts of northeast Ellesmere Island

    NASA Astrophysics Data System (ADS)

    Estrada, Solveig

    2015-11-01

    Early- to mid-Cretaceous flood-basalt suites of the northeast Canadian High Arctic assigned to a High Arctic Large Igneous Province (HALIP) were studied for their whole-rock geochemistry and Sr-Nd isotopes. Data from basalt flows within the upper Albian to lower Cenomanian Hassel Formation of northeast Ellesmere Island are compared with former published data and new inductively coupled plasma mass spectrometry data of the stratigraphic equivalent Strand Fiord basalts and the older, late Hauterivian to Aptian Isachsen basalts from Axel Heiberg Island. The transitional to mildly alkaline aphyric Hassel basalts, with ocean island basalt (OIB)-like geochemical signatures in parts, have an Ar-Ar whole-rock age of on average 96.4 ± 1.6 Ma. They represent two geochemically different flow units without a fractional crystallization relationship: the high-phosphorous (HP) and low-phosphorous (LP) basalts. The Hassel HP basalts differ from the LP basalts by additionally higher Ba, K, Rb, Th and LREE contents, a pronounced positive Eu anomaly (Eu/Eu* = 1.74-1.76), as well as lower Ta, Nb, Zr and Hf concentrations. The Nd and Sr isotope ratios of the Hassel HP basalts [ ɛ Nd( t) of -1.3 to -1.4, 87Sr/86Sr( t) of 0.70706-0.70707] and the LP basalts [ ɛ Nd( t) of 4.5-4.9, 87Sr/86Sr( t) of 0.7038-0.7040] indicate an origin from different mantle sources. The geochemically similar tholeiitic Isachsen (ca. 130-113 Ma) and Strand Fiord basalts (ca. 105-95 Ma) are also incompatible element enriched relative to the primitive mantle, however, with negative Sr-P anomalies as well as partially negative K, Ta and Nb anomalies. In terms of incompatible element ratios (Zr/Nb, Nb/Th), several mantle components are involved in the formation of the flood-basalt suites: a component with primitive mantle composition, an OIB-like component (probably subducted and recycled oceanic crust) and an enriched lithospheric component. The latter component, probably metasomatized subcontinental

  8. Volatile Transport by Volcanic Plumes on Earth, Venus and Mars

    NASA Technical Reports Server (NTRS)

    Glaze, Lori S.; Self, Stephen; Baloga, Steve; Stofan, Ellen R.

    2012-01-01

    Explosive volcanic eruptions can produce sustained, buoyant columns of ash and gas in the atmosphere (Fig. 1). Large flood basalt eruptions may also include significant explosive phases that generate eruption columns. Such eruptions can transport volcanic volatiles to great heights in the atmosphere. Volcanic eruption columns can also redistribute chemical species within the atmosphere by entraining ambient atmosphere at low altitudes and releasing those species at much higher altitudes.

  9. Enriched Mantle Component(s) in Paleoproterozoic Continental Flood Basalts of the Cape Smith Foldbelt, Northern Quebec

    NASA Astrophysics Data System (ADS)

    Modeland, S.; Francis, D.; Hynes, A.

    2001-05-01

    The Cape Smith foldbelt is one of Earth's best exposed Proterozoic mobile belts and provides a natural laboratory for the study of Proterozoic mafic magmatism. Magmatism associated with circa 2.04 Ga rifting of the Superior Province resulted in the formation of tholeiitic and alkaline basalts as well as minor rhyolites, collectively known as the Povungnituk Group. Despite their continental setting, the tholeiites are not typical continental flood basalts in that they lack significant negative Nb and Ta anomalies relative to light rare earth elements and primitive mantle, indicating that crustal contamination did not play a major role in their evolution. Although crystal fractionation along a gabbroic cotectic can account for some of the variation in trace element concentrations, it cannot explain the wide range of observed incompatible-trace element ratios within the Povungnituk Group. Variations of La/Sm and Nb/Zr reveal the presence of a highly enriched component in many of the lavas. Mixing between this enriched component and a low Nb/Zr end-member can account for the range of trace element ratios observed in the Povungnituk Group, and may also account for enriched tholeiites found in other parts of the eastern Trans-Hudson orogen (Flaherty Formation). The most enriched tholeiites are spatially associated with an alkaline suite, but moderately enriched tholeiites are widespread in the Povungnituk Group. It appears that the Paleoproterozoic mantle source for the Povungnituk Group lavas contained a dispersed enriched component that was responsible for the generation of incompatible-trace element enriched tholeiites. Despite their continental setting, the Povungnituk Group lavas exhibit incompatible-trace element enrichment similar to that of tholeiitic to highly alkaline lavas from modern ocean island basalt suites, such as Hawaii.

  10. Repeated kimberlite magmatism beneath Yakutia and its relationship to Siberian flood volcanism: Insights from in situ U-Pb and Sr-Nd perovskite isotope analysis

    NASA Astrophysics Data System (ADS)

    Sun, Jing; Liu, Chuan-Zhou; Tappe, Sebastian; Kostrovitsky, Sergey I.; Wu, Fu-Yuan; Yakovlev, Dmitry; Yang, Yue-Heng; Yang, Jin-Hui

    2014-10-01

    We report combined U-Pb ages and Sr-Nd isotope compositions of perovskites from 50 kimberlite occurrences, sampled from 9 fields across the Yakutian kimberlite province on the Siberian craton. The new U-Pb ages, together with previously reported geochronological constraints, suggest that kimberlite magmas formed repeatedly during at least 4 episodes: Late Silurian-Early Devonian (419-410 Ma), Late Devonian-Early Carboniferous (376-347 Ma), Late Triassic (231-215 Ma), and Middle/Late Jurassic (171-156 Ma). Recurrent kimberlite melt production beneath the Siberian craton - before and after flood basalt volcanism at 250 Ma - provides a unique opportunity to test existing models for the origin of global kimberlite magmatism. The internally consistent Sr and Nd isotope dataset for perovskites reveals that the Paleozoic and Mesozoic kimberlites of Yakutia have distinctly different initial radiogenic isotope compositions. There exists a notable increase in the initial 143Nd/144Nd ratios through time, with an apparent isotopic evolution that is intermediate between that of Bulk Earth and Depleted MORB Mantle. While the Paleozoic samples range between initial 87Sr/86Sr of 0.7028-0.7034 and 143Nd/144Nd of 0.51229-0.51241, the Mesozoic samples show values between 0.7032-0.7038 and 0.51245-0.51271, respectively. Importantly, perovskites from all studied Yakutian kimberlite fields and age groups have moderately depleted initial εNd values that fall within a relatively narrow range between +1.8 and +5.5. The perovskite isotope systematics of the Yakutian kimberlites are interpreted to reflect magma derivation from the convecting upper mantle, which appears to have a record of continuous melt depletion and crustal recycling throughout the Phanerozoic. The analyzed perovskites neither record highly depleted nor highly enriched isotopic components, which had been previously identified in likely plume-related Siberian Trap basalts. The Siberian craton has frequently been suggested

  11. Origin and geodynamic relationships of the Late Miocene to Quaternary alkaline basalt volcanism in the Pannonian basin, eastern-central Europe

    NASA Astrophysics Data System (ADS)

    Harangi, Szabolcs; Jankovics, M. Éva; Sági, Tamás; Kiss, Balázs; Lukács, Réka; Soós, Ildikó

    2015-11-01

    Alkaline basaltic volcanism has been taking place in the Carpathian-Pannonian region since 11 Ma and the last eruptions occurred only at 100-500 ka. It resulted in scattered low-magma volume volcanic fields located mostly at the margins of the Pannonian basin. Many of the basalts have compositions close to those of the primitive magmas and therefore can be used to constrain the conditions of the magma generation. Low-degree (2-3 %) melting could occur in the convective asthenosphere within the garnet-spinel transition zone. Melting started at about 100 km depth and continued usually up to the base of the lithosphere. Thus, the final melting pressure could indicate the ambient lithosphere-asthenosphere boundary. The asthenospheric mantle source regions of the basalts were heterogeneous, presumably in small scale, and included either some water or pyroxenite/eclogite lithology in addition to the fertile to slightly depleted peridotite. Based on the prevailing estimated mantle potential temperature (1,300-1,400 °C) along with the number of further observations, we exclude the existence of mantle plume or plume fingers beneath this region. Instead, we propose that plate tectonic processes controlled the magma generation. The Pannonian basin acted as a thin spot after the 20-12 Ma syn-rift phase and provided suction in the sublithospheric mantle, generating asthenospheric flow from below the adjoining thick lithospheric domains. A near-vertical upwelling along the steep lithosphere-asthenosphere boundary beneath the western and northern margins of the Pannonian basin could result in decompressional melting producing low-volume melts. The youngest basalt volcanic field (Perşani) in the region is inferred to have been formed due to the dragging effect of the descending lithospheric slab beneath the Vrancea zone that could result in narrow rupture at the base of the lithosphere. Continuation of the basaltic volcanism cannot be excluded as inferred from the still fusible

  12. Distinguishing between basalts produced by endogenic volcanism and impact processes: A non-destrwuctive method using quantitative petrography of lunar basaltic samples

    NASA Astrophysics Data System (ADS)

    Neal, Clive R.; Donohue, Patrick; Fagan, Amy L.; O'Sullivan, Katie; Oshrin, Jocelyn; Roberts, Sarah

    2015-01-01

    Impact processes play an important role in shaping and reshaping the surfaces of airless planetary bodies. Such processes produce regoliths and generate melts that crystallize and record the homogenization of the geology at the impact site. If the volume of melt is substantial, the resultant crystallized product has an igneous texture and may be free of xenolithic clasts making it difficult to distinguish from melts produced by endogenic magmatic processes. This has been clearly demonstrated during the return of the Apollo samples from the Moon, where Apollo 14 basalt 14310 was initially described as a mare basalt and was only subsequently reclassified as an impact melt following detailed and time consuming crystallization experiments. Another way of distinguishing lunar impact melts from endogenically-derived mare basalts is through the quantification of the highly siderophile elements (HSE: Pd, Rh, Ru, Ir, Pt, Os), which have relatively low abundances in pristine lunar samples but are high in meteorites and, therefore, may be enriched in impact melts. However, these analyses consume relatively large quantities of valuable sample and because of mass constraints cannot be performed on many lunar samples. In this paper we present a quantitative petrographic method that has the potential to distinguish lunar impact melts from endogenically-derived mare basalts using plagioclase and olivine crystal size distributions (CSDs). The slopes and intercepts of these CSDs are used to show that olivine from impact melts displays a steeper CSD relative to olivine from mare basalts. For plagioclase, generally impacts melts display CSDs with shallower gradients than those from endogenous mare basalts and, as for olivines, plot in a distinct field on a CSD slope vs. CSD intercept plot. Using just a thin section to distinguish impact melts from mare basalts enables the goals of future robotic sample return missions to determine the age of the South Pole-Aitken basin in the Moon

  13. The significance of PGE variations with Sr-Nd isotopes and lithophile elements in the Emeishan flood basalt province from SW China to northern Vietnam

    NASA Astrophysics Data System (ADS)

    Li, Chusi; Ripley, Edward M.; Tao, Yan; Hu, Ruizhong

    2016-04-01

    New analyses of siderophile-lithophile elements and Sr-Nd isotopes in the Permian basalts and picrites from northern Vietnam, the southernmost occurrence of the Emeishan flood basalt province, together with previously published data, are used to address the question of whether any meaningful correlation between these elements and isotopes exists at a province scale. The available data show that negative correlations between εNd, (87Sr/86Sr)i and mantle-normalized (Nb/Th)n are present in the basalts but not in the associated picrites. This indicates that crustal contamination is negligible in the picrites but significant in some of the basalts. The picrites and basalts from the entire province show negative correlations between (Rh/Ru)n, (Pt/Ru)n, (Pd/Ru)n and Mg-number. This indicates that Ru behaves compatibly whereas Rh, Pt and Pd behave incompatibly during magma differentiation. The incompatible behavior of Rh in natural basaltic systems is also supported by the fact that (Pt/Rh)n remains constant with decreasing Mg-number in the lavas. Depletions of Pd and Pt, and to a lesser degree Cu, in some basaltic samples characterized by relatively low εNd and (Nb/Th)n support the notion that sulfide saturation in the magmas was triggered by a combination of siliceous crustal contamination and addition of external sulfur. Within the entire flood basalt province only the picrites from Song Da, northern Vietnam show clear depletion in Ir relative to Ru. These picrites are also characterized higher Al2O3/TiO2 and lower mantle-normalized La/Yb (0.2-2.4) than those from elsewhere in the province, possibly due to the involvement of an Ir-depleted, fertile mantle component in magma generation at this location.

  14. Igneous Rocks of the East Pacific Rise: The alkali volcanic suite appear to be differentiated from a tholeiitic basalt extruded from the mantle.

    PubMed

    Engel, A E; Engel, C G

    1964-10-23

    The apical parts of large volcanoes along the East Pacific Rise (islands and seamounts) are encrusted with rocks of the alkali volcanic suite (alkali basalt, andesine- and oligoclase-andesite, and trachyte). In contrast, the more submerged parts of the Rise are largely composed of a tholeiitic basalt which has low concentrations of K, P, U, Th, Pb, and Ti. This tholeiitic basalt is either the predominant or the only magma generated in the earth's mantle under oceanic ridges and rises. It is at least 1000-fold more abundant than the alkali suite, which is probably derived from tholeiitic basalt by magmatic differentiation in and immediately below the larger volcanoes. Distinction of oceanic tholeiites from almost all continental tholeiites is possible on the simple basis of total potassium content, with the discontinuity at 0.3 to 0.5 percent K(2)O by weight. Oceanic tholeiites also are readily distinguished from some 19 out of 20 basalts of oceanic islands and seamount cappings by having less than 0.3 percent K(2)O by weight and more than 48 percent SiO(2). Deep drilling into oceanic volcanoes should, however, core basalts transitional between the oceanic tholeiites and the presumed derivative alkali basalts. The composition of the oceanic tholeiites suggests that the mantle under the East Pacific Rise contains less than 0.10 percent potassium oxide by weight; 0.1 part per million of uranium and 0.4 part of thorium; a potassium:rubidium ratio of about 1200 and a potassium: uranium ratio of about 10(4). PMID:17806796

  15. High-resolution magnetics reveal the deep structure of a volcanic-arc-related basalt-hosted hydrothermal site (Palinuro, Tyrrhenian Sea)

    NASA Astrophysics Data System (ADS)

    Szitkar, Florent; Petersen, Sven; Caratori Tontini, Fabio; Cocchi, Luca

    2015-06-01

    High-resolution magnetic surveys have been acquired over the partially sedimented Palinuro massive sulfide deposits in the Aeolian volcanic arc, Tyrrhenian Sea. Surveys flown close to the seafloor using an autonomous underwater vehicle (AUV) show that the volcanic-arc-related basalt-hosted hydrothermal site is associated with zones of lower magnetization. This observation reflects the alteration of basalt affected by hydrothermal circulation and/or the progressive accumulation of a nonmagnetic deposit made of hydrothermal and volcaniclastic material and/or a thermal demagnetization of titanomagnetite due to the upwelling of hot fluids. To discriminate among these inferences, estimate the shape of the nonmagnetic deposit and the characteristics of the underlying altered area—the stockwork—we use high-resolution vector magnetic data acquired by the AUV Abyss (GEOMAR) above a crater-shaped depression hosting a weakly active hydrothermal site. Our study unveils a relatively small nonmagnetic deposit accumulated at the bottom of the depression and locked between the surrounding volcanic cones. Thermal demagnetization is unlikely but the stockwork extends beyond the limits of the nonmagnetic deposit, forming lobe-shaped zones believed to be a consequence of older volcanic episodes having contributed in generating the cones.

  16. Surface exposure dating of Holocene basalt flows and cinder cones in the Kula volcanic field (western Turkey) using cosmogenic 3He and 10Be

    NASA Astrophysics Data System (ADS)

    Heineke, Caroline; Niedermann, Samuel; Hetzel, Ralf; Akal, Cüneyt

    2015-04-01

    The Kula volcanic field is the youngest volcanic province in western Anatolia and covers an area of about 600 km2 around the town Kula (Richardson-Bunbury, 1996). Its alkali basalts formed by melting of an isotopically depleted mantle in a region of long-lived continental extension and asthenospheric upwelling (Prelevic et al., 2012). Based on morphological criteria and 40Ar/39Ar dating, four phases of Quaternary activity have been distinguished in the Kula volcanic field (Richardson-Bunbury, 1996; Westaway et al., 2006). The youngest lava flows are thought to be Holocene in age, but so far only one sample from this group was dated by 40Ar/39Ar at 7±2 ka (Westaway et al., 2006). In this study, we analysed cosmogenic 3He in olivine phenocrysts from three basalt flows and one cinder cone to resolve the Holocene history of volcanic eruptions in more detail. In addition, we applied 10Be exposure dating to two quartz-bearing xenoliths found at the surface of one flow and at the top of one cinder cone. The exposure ages fall in the range between ~500 and ~3000 years, demonstrating that the youngest volcanic activity is Late Holocene in age and therefore distinctly younger than previously envisaged. Our results show that the Late Holocene lava flows are not coeval but formed over a period of a few thousand years. We conclude that surface exposure dating of very young volcanic rocks provides a powerful alternative to 40Ar/39Ar dating. References Prelevic, D., Akal, C. Foley, S.F., Romer, R.L., Stracke, A. and van den Bogaard, P. (2012). Ultrapotassic mafic rocks as geochemical proxies for post-collisional dynamics of orogenic lithospheric mantle: the case of southwestern Anatolia, Turkey. Journal of Petrology, 53, 1019-1055. Richardson-Bunbury, J.M. (1996). The Kula Volcanic Field, western Turkey: the development of a Holocene alkali basalt province and the adjacent normal-faulting graben. Geological Magazine, 133, 275-283. Westaway, R., Guillou, H., Yurtmen, S., Beck, A

  17. From Dike to Bud to Neck: Critical Physical Transitions in the Evolution of Sustainable Basaltic Volcanic Eruptions

    NASA Astrophysics Data System (ADS)

    Townsend, M.; Pollard, D. D.

    2012-12-01

    Basaltic volcanic eruptions are commonly characterized by three stages. In the upper several kilometers of the crust, magma rises in dikes, resulting in fissure eruptions when they intersect the surface. In some cases, the fissures may not feed significant eruptions and may quickly (within hours) die out. In other fissures, magma continues to erupt and localizes into discrete vents, until the flow is sustained through a central vent area, where it is able to carry much greater volumes of magma to the surface. These types of eruptions have been well documented in places like Kilauea in Hawaii and are inferred to have operated in ancient systems like Ship Rock, New Mexico. However, the physical processes governing the evolution of basaltic conduit geometry from dike-like to plug-like and the associated eruptive dynamics are not well understood. Some current theories to explain flow localization and conduit widening include progressive melting of the host rock, pore-pressure and conduit-pressure buildup from water-magma interaction, variation in magmatic pressure inducing wall collapse, and erosion from particle collision and/or shear stress of flowing magma. Field evidence from Ship Rock provides insight we use to develop a conceptual framework for what processes may have caused the evolution of dikes into plugs. Ship Rock is a maar-type diatreme standing ~600 m above the surrounding land surface, with minette dikes and plugs extending radially away. Systematic joint sets (one parallel and the other perpendicular to the dike) are present in the host rock (Mancos shale) adjacent to dike contacts. The presence of breccia along the margins of dikes and around the plugs suggests that tensile fracturing and subsequent erosion of the host rock was responsible for changing conduit geometry. The breccias range in composition from mostly angular shale clasts in a "fluidized" shale matrix, to mostly shale clasts in a minette matrix, to both shale and minette clasts in a

  18. Tools and techniques for developing tephra stratigraphies in lake cores: A case study from the basaltic Auckland Volcanic Field, New Zealand

    NASA Astrophysics Data System (ADS)

    Hopkins, Jenni L.; Millet, Marc-Alban; Timm, Christian; Wilson, Colin J. N.; Leonard, Graham S.; Palin, J. Michael; Neil, Helen

    2015-09-01

    Probabilistic hazard forecasting for a volcanic region relies on understanding and reconstructing the eruptive record (derived potentially from proximal as well as distal volcanoes). Tephrostratigraphy is commonly used as a reconstructive tool by cross-correlating tephra deposits to create a stratigraphic framework that can be used to assess magnitude-frequency relationships for eruptive histories. When applied to widespread rhyolitic deposits, tephra identifications and correlations have been successful; however, the identification and correlation of basaltic tephras are more problematic. Here, using tephras in drill cores from six maars in the Auckland Volcanic Field (AVF), New Zealand, we show how X-ray density scanning coupled with magnetic susceptibility analysis can be used to accurately and reliably identify basaltic glass shard-bearing horizons in lacustrine sediments and which, when combined with the major and trace element signatures of the tephras, can be used to distinguish primary from reworked layers. After reliably identifying primary vs. reworked basaltic horizons within the cores, we detail an improved method for cross-core correlation based on stratigraphy and geochemical fingerprinting. We present major and trace element data for individual glass shards from 57 separate basaltic horizons identified within the cores. Our results suggest that in cases where major element compositions (SiO2, CaO, Al2O3, FeO, MgO) do not provide unambiguous correlations, trace elements (e.g. La, Gd, Yb, Zr, Nb, Nd) and trace element ratios (e.g. [La/Yb]N, [Gd/Yb]N, [Zr/Yb]N) are successful in improving the compositional distinction between the AVF basaltic tephra horizons, thereby allowing an improved eruptive history of the AVF to be reconstructed.

  19. Extensive 200-million-year-Old continental flood basalts of the central atlantic magmatic province

    PubMed

    Marzoli; Renne; Piccirillo; Ernesto; Bellieni; De Min A

    1999-04-23

    The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basalts that crop out in once-contiguous parts of North America, Europe, Africa, and South America and is associated with the breakup of Pangea. 40Ar/39Ar and paleomagnetic data indicate that CAMP magmatism extended over an area of 2.5 million square kilometers in north and central Brazil, and the total aerial extent of the magmatism exceeded 7 million square kilometers in a few million years, with peak activity at 200 million years ago. The magmatism coincided closely in time with a major mass extinction at the Triassic-Jurassic boundary. PMID:10213679

  20. Mantle Heterogeneities and Crustal Processes of the Cascade Arc Represented by Basalts of the Poison Lake Chain, Lassen Volcanic Center, California

    NASA Astrophysics Data System (ADS)

    Wenner, J. M.; Teasdale, R.; Hiebing, M. S.; Lenz, Q. A.; Kroeninger, K.

    2013-12-01

    Basalts in the Poison Lake chain (PLC) include eight chemically distinct groups of primitive calc-alkaline basalts (defined by major element geochemistry and mineralogy). Located east of the Lassen Volcanic Center, PLC primitive basalts span the range of basalt compositions exposed throughout the entire Cascade arc (e.g. Ba: 100-1000 ppm; (Sr/P)n: 1.3 - 3.8; La/Yb: 4-26). PLC groups have trace-element and isotope ratios that show little evidence of direct genetic relationships among groups or a common source. Major, trace element and isotope ratios show evidence of contributions from multiple mantle sources including MORB, fluid rich subduction component and subduction-related sediment. Some groups record compositional variations from multiple mantle sources with minimal crustal processing. Similarly, preliminary probe data for olivine-spinel pairs suggest that some PLC groups are derived from heterogeneous mantle sources. Geochemical evidence indicates that other groups have petrogenetic histories that include crustal processes such as fractional crystallization, mixing or crustal contamination. Isotope ratios, major and trace element compositions and crystal compositions provide insights into the extent of source heterogeneities versus the degree of crustal processing. The broad range of compositional variations in basalts of PLC provides the opportunity to examine the extent of mantle heterogeneities and crustal processing in a small geographic area (50km2) for rocks that are nearly the same age (100-110 ka). The diverse primitive compositions erupted in the constrained time and space of the Poison Lake chain and the lack of genetic relationship among groups make it the ideal place to investigate the small scale nature of mantle domains and the roles of subduction and modification processes in the generation of basaltic compositions in arcs such as the Cascades, Mexico, Japan.

  1. Balloon-borne measurement of the aerosol size distribution from an Icelandic flood basalt eruption

    NASA Astrophysics Data System (ADS)

    Vignelles, D.; Roberts, T. J.; Carboni, E.; Ilyinskaya, E.; Pfeffer, M.; Dagsson Waldhauserova, P.; Schmidt, A.; Berthet, G.; Jegou, F.; Renard, J.-B.; Ólafsson, H.; Bergsson, B.; Yeo, R.; Fannar Reynisson, N.; Grainger, R. G.; Galle, B.; Conde, V.; Arellano, S.; Lurton, T.; Coute, B.; Duverger, Vincent

    2016-11-01

    We present in situ balloon-borne measurements of aerosols in a volcanic plume made during the Holuhraun eruption (Iceland) in January 2015. The balloon flight intercepted a young plume at 8 km distance downwind from the crater, where the plume is ∼15 min of age. The balloon carried a novel miniature optical particle counter LOAC (Light Optical Aerosol Counter) which measures particle number concentration and size distribution in the plume, alongside a meteorological payload. We discuss the possibility of calculating particle flux by combining LOAC data with measurements of sulfur dioxide flux by ground-based UV spectrometer (DOAS). The balloon passed through the plume at altitude range of 2.0-3.1 km above sea level (a.s.l.). The plume top height was determined as 2.7-3.1 km a.s.l., which is in good agreement with data from Infrared Atmospheric Sounding Interferometer (IASI) satellite. Two distinct plume layers were detected, a non-condensed lower layer (300 m thickness) and a condensed upper layer (800 m thickness). The lower layer was characterized by a lognormal size distribution of fine particles (0.2 μm diameter) and a secondary, coarser mode (2.3 μm diameter), with a total particle number concentration of around 100 cm-3 in the 0.2-100 μm detection range. The upper layer was dominated by particle centered on 20 μm in diameter as well as containing a finer mode (2 μm diameter). The total particle number concentration in the upper plume layer was an order of magnitude higher than in the lower layer. We demonstrate that intercepting a volcanic plume with a meteorological balloon carrying LOAC is an efficient method to characterize volcanic aerosol properties. During future volcanic eruptions, balloon-borne measurements could be carried out easily and rapidly over a large spatial area in order to better characterize the evolution of the particle size distribution and particle number concentrations in a volcanic plume.

  2. Sulfur Release Associated with Eruption of the Washilla Ridge Member of the Columbia River Flood Basalts

    NASA Astrophysics Data System (ADS)

    Davis, K.; Wolff, J.; Rowe, M. C.

    2012-12-01

    Several estimates of S release associated with eruption of Columbia River Basalts (CRB) have been published. These estimates employ the 'petrologic method' which depends upon analysis of glassy melt inclusions within phenocrysts. Quantification of sulphur release from the most voluminous CRB formation, the Grande Ronde Basalt (~70% of total CRB volume), has proved to be an elusive target due to its perceived aphyric nature, leading to the development of predictive models based on global S abundance in basalts [1]. Here we present analyses of glassy melt inclusions within microphenocrysts of plagioclase and magnetite in glassy phreatomagmatic tephra produced during eruption of the Wapshilla Ridge Member of the Grande Ronde. Melt inclusion S concentrations are 1080 - 1880 ppm with an average of 1500 ppm. The variable S content suggests simultaneous microphenocryst growth and degassing. Sulfur contents in host glassy lapilli are 1290 - 240 ppm with an average of 410 ppm. Variable S in lapilli glasses indicates quenching before degassing was complete, consistent with a phreatomagmatic eruption style. Using the least degassed melt inclusions (representative of pre-eruptive magma) and the most degassed lapilli glasses (representative of degassed lava), we find the released sulfur yield to be 1640 ppm, somewhat in excess of 1190 ± 260 ppm given by the Blake et al. [1] predictive model. The volume of the Wapshilla Ridge Member is 40,000 km3 [2], and its chemical composition exhibits limited variability. Assuming that the tephra we have analyzed is representative, the total mass of S released during the eruption was 180 Gt. Injection would have peaked at 3.6 Mt of S per day during the peak stages of the Wapshilla Ridge eruption, estimated at 0.8 km3 magma/day [2]. This study demonstrates the significance of analysis of glassy tephra associated with the major CRB units toward yielding valuable petrologic information otherwise mostly inacessible from the lavas. References

  3. Extreme U-Th disequilibrium in rift-related basalts, rhyolites and granophyric granite and the timescale of rhyolite generation, intrusion and crystallization at Alid volcanic center, Eritrea

    USGS Publications Warehouse

    Lowenstern, J. B.; Charlier, B.L.A.; Clynne, M.A.; Wooden, J.L.

    2006-01-01

    Rhyolite pumices and co-erupted granophyric (granite) xenoliths yield evidence for rapid magma generation and crystallization prior to their eruption at 15.2 ?? 2.9 ka at the Alid volcanic center in the Danikil Depression, Eritrea. Whole-rock U and Th isotopic analyses show 230 Th excesses up to 50% in basalts <10 000 years old from the surrounding Oss lava fields. The 15 ka rhyolites also have 30-40% 230Th excesses. Similarity in U-Th disequilibrium, and in Sr, Nd, and Pb isotopic values, implies that the rhyolites are mostly differentiated from the local basaltic magma. Given the (230 Th/232Th) ratio of the young basalts, and presumably the underlying mantle, the (230Th/232Th) ratio of the rhyolites upon eruption could be generated by in situ decay in about 50 000 years. Limited (???5%) assimilation of old crust would hasten the lowering of (230Th/232Th) and allow the process to take place in as little as 30 000 years. Final crystallization of the Alid granophyre occurred rapidly and at shallow depths at ???20-25 ka, as confirmed by analyses of mineral separates and ion microprobe data on individual zircons. Evidently, 30 000-50 000 years were required for extraction of basalt from its mantle source region, subsequent crystallization and melt extraction to form silicic magmas, and final crystallization of the shallow intrusion. The granophyre was then ejected during eruption of the comagmatic rhyolites. ?? 2006 Oxford University Press.

  4. Lithospheric influences on magma compositions of late Mesozoic and Cenozoic intraplate basalts (the Older Volcanics) of Victoria, south-eastern Australia

    NASA Astrophysics Data System (ADS)

    Price, Richard C.; Nicholls, Ian A.; Day, Arthur

    2014-10-01

    Basaltic volcanism, ranging in age from Late Cretaceous to Holocene and extending across the southern part of the state of Victoria in south-eastern Australia was initiated during the earliest stages of rifting associated with opening of the Tasman Sea and Southern Ocean. Volcanism has continued sporadically since that time with major breaks in activity occurring between 77 and 62 Ma and 18 and 7 Ma. Basaltic rocks with ages in the range 95 to 18 Ma occur in small lava fields scattered across eastern and south-eastern Victoria and they have also been recovered from bore holes in the west of the state. They have been referred to as the “Older Volcanics” to differentiate them from more volumetrically extensive and younger (mainly < 4.6 Ma) lava fields comprising the “Newer Volcanics” of the Western District Province to the west. Older Volcanics vary in composition from SiO2-undersaturated nephelinites, basanites, basalts and hawaiites through transitional basalts to hypersthene and quartz normative tholeiites. Strontium, Nd and Pb isotopic compositions lie between depleted (DM) and enriched (EM1 and EM2) end member mantle components in Sr-Nd-Pb isotopic space. Trace element compositions are generally characterised by enrichment of Cs, Ba, Rb, Th, U, Nb, K and light REE over heavy REE, Ti, Zr and Y and the overall patterns of major and trace element behaviour can be explained in general terms by petrogenetic models involving partial melting of a complex spectrum of mantle compositions with subsequent but limited additional modification by fractional crystallisation with or without assimilation of crust. Among basalts with relatively high Mg# [100 ∗ Mol. MgO/(MgO + FeO) > 65], two distinct end member compositions can be differentiated using primitive mantle normalised extended element patterns. Group 1 basalts have convex upward patterns with enrichment of light over heavy REE and depletion of Rb, Ba, Th and U relative to Nb. Group 2 basalts also have

  5. Influence of seismic processes and volcanic activity on the formation of disastrous floods

    NASA Astrophysics Data System (ADS)

    Trifonov, Dmitriy

    2014-05-01

    models of hydraulic systems, but ultimately due to difference of pressures in their respective segments and areas of the transport network. At the exit of the groundwater on the surface such change in pressure is connected both with the state of the actual water flow in underground cavities, or violations of the structure (topology) of 3D-network. As one of the major and sudden reasons of change of pressure in the underground system can serve seismic processes, including volcanic eruptions (as magmatic and ash). During these processes enormous underground space can be freed from the dense rock. This leads to rapid changes in pressure and that, in principle, a new topology of 3D network and water flows in it. It is important that such dynamic processes occur over huge distances in underground basins of thousands of kilometers [3], of course, with a certain time delay. In the result of the analysis of large-scale flooding in Russia in 2001-2002, as well as the catastrophic floods in Western Europe, in the Amur region of Russia and in the state of Colorado USA in 2013, a correlation between seismic and volcanic activities and floods, expressed by specific numerical correlation coefficients, has been revealed. For example, knowing the date, location and magnitude of an earthquake, we can identify potentially dangerous territories in the aspect of the probability of occurrence of floods, because the stresses in the crust, spreading from the hypocenter of earthquakes, and their subsequent relaxation are one of the most important factors of floods. Mechanisms of distribution of these stresses are well-studied today [2] unlike their influence on the groundwater. The defined boundaries of potentially dangerous sites are broad enough; with regard to the direction of distribution of stress, it is about the sectors in 40 degrees (from the line of the movement of the crustal plate) in the direction from the boundaries of lithospheric plates. Distribution of this impact occurs, as a

  6. The Basalt of Summit Creek: Evidence for an Early Eocene Transition from Arc to Slab Window Volcanism in the Southern Washington Cascades

    NASA Astrophysics Data System (ADS)

    Tepper, J. H.; McKinley, E.

    2011-12-01

    Located south of Mt. Rainier, the Basalt of Summit Creek (BSC) is the largest of several small exposures of early- to mid-Eocene volcanic rocks that unconformably overlie highly deformed Mesozoic turbidites and represent the earliest record of Tertiary volcanism in the southern Washington Cascades. The steeply dipping BSC section consists of 2000m of subaerial basalt flows that preserve stratigraphic geochemical trends consistent with a transition from arc to slab window (or rift) magmatism between ~55 and ~44 Ma. Basalts low in the section are interbedded with hornblende andesites and display a variety of arc traits including spidergram HFSE depletions and elevated K2O (> 1.0 wt.%). Higher in the section the BSC is dominated by tholeiitic basalts that have OIB-like spidergrams, lower K2O (<0.4 wt.%) and a mix of MORB and arc affinities on trace element discrimination plots. Much of the compositional diversity among BSC lavas (45.9 - 54.2 wt.% SiO2; Mg# = 66 - 30) is consistent with low-pressure fractional crystallization (ol+plag+cpx+ilm), but incompatible element data indicate the existence of two distinct magma series that differ most notably in Sr, Zr, and K2O contents. Both series are represented throughout the BSC section but there is no evidence of mixing between them. The BSC is coeval with the youngest phase of activity in the Cretaceous-Tertiary North Cascades arc (Miller et al., 2009) and may represent a southern extension of that arc system. However, BSC lavas with OIB traits overlap in major and trace element composition with basalts of the ~55 - 50 Ma Crescent Formation, which crop out ~100 km to the west on the Olympic Peninsula. A marginal rift basin or slab window setting related to subduction of the Kula-Farallon Ridge has been proposed for the Crescent basalts (Babcock et al., 1992). We propose that the BSC may represent a farther-inboard manifestation of the Kula-Farallon slab window, recording its interaction with the southern continuation of

  7. Volcanic flood simulation of magma effusion using FLO-2D for drainage of a caldera lake at the Mt. Baekdusan

    NASA Astrophysics Data System (ADS)

    Lee, Khil-Ha; Kim, Sung-Wook; Kim, Sang-Hyun

    2014-05-01

    Many volcanic craters and calderas are filled with large amounts of water that can pose significant flood hazards to downstream communities due to their high elevation and the potential for catastrophic releases of water. Recent reports pointed out the Baekdusan volcano that is located between the border of China and North Korea as a potential active volcano. Since Millennium Eruption around 1000 AD, smaller eruptions have occurred at roughly 100-year intervals, with the last one in 1903. Sudden release of huge volume of water stored in temporarily elevated caldera lakes are a recurrent feature of volcanic environments, due to the case with which outlet channels are blocked by and re-cut through, unwelded pyroclastic deposits. The volcano is showing signs of waking from a century-long slumber recently. Volcanic floods, including breakouts from volcanic lakes, can affect communities beyond the areas immediately affected by a volcanic eruption and cause significant hydrological hazards because floods from lake-filled calderas may be particularly large and high. Although a number of case studies have been presented in the literature, investigation of the underlying physical processes is required as well as a method for interpreting the process of the rapid release of water stored in a caldera lake. The development of various forecasting techniques to prevent and minimize economic and social damage is in urgent need. This study focuses on constructing a flood hazard map triggered by the magma effusion in the Baekdusan volcano. A physically-based uplift model was developed to compute the amount of water and time to peak flow. The ordinary differential equation was numerically solved using the finite difference method and Newton-Raphson iteration method was used to solve nonlinear equation. The magma effusion rate into the caldera lake is followed by examples at other volcanic activities. As a result, the hydrograph serves as an upper boundary condition when hydrodynamic

  8. Relation of Volcanism to Crustal Deformation in Klamath Falls, Oregon: Transition from Calc-alkaline Basaltic Andesite to High Alumina Olivine Tholeiite

    NASA Astrophysics Data System (ADS)

    Priest, G. R.; Hladky, F. R.; Murray, R. B.

    2009-12-01

    This paper is based on geologic mapping by Priest et al. (2008) at Klamath Falls, Oregon on the southernmost end of the Klamath Graben. Northeast-southwest extension across this area caused northeast tilting of fault blocks on the east side and southwest tilting of blocks on the west side of the Graben. Dominant strike of these Basin and Range fault blocks is N. 30-40° W. At Klamath Falls the two opposing groups of tilted blocks are separated not by a keystone graben but by a complex of bounding faults striking ~N. 65° W. The bounding faults appear to have components of right-lateral or reverse motion, cut rocks dated at ~4 Ma, and terminate to the northwest against northeast-striking faults at the southern boundary of the Graben. Normal faults within the study area cut basalt dated at 1.8 Ma on the west side of the Graben. Holocene talus is cut on the east side of the Graben immediately north of the study area. The 1993 magnitude 5.9 and 6.0 earthquakes on the west margin of the Klamath Graben are evidence that extensional deformation is continuing there. The youngest proven deformation in the map area south of the Graben boundary is offset Pleistocene alluvial fans at the base of Hogback Mountain. These fans are now preserved as discontinuous hills but once filled the local Altamont basin by up to 150 m higher than its present surface. Much of this sand and gravel has been eroded, possibly coincident with breaching of the basin at ~1 Ma by headward erosion of the Klamath River. Magmatic composition changed as crustal extension in the area progressed and the width of the Cascade volcanic arc decreased. Between ~6 and 4 Ma, calc-alkaline basaltic andesite and andesite from local volcanic centers of the volcanic arc flowed unimpeded across the area, thus the current Basin and Range topography had not developed. Angular unconformities within sequences of volcanic and volcaniclastic rocks dated at 4-2.7 Ma indicate contemporaneous tilting of fault blocks, but much

  9. Isotopic analysis of basaltic fragments from lunar breccia 14321 - Chronology and petrogenesis of pre-Imbrium mare volcanism

    NASA Technical Reports Server (NTRS)

    Dasch, E. J.; Shih, C.-Y.; Bansal, B. M.; Wiesmann, H.; Nyquist, L. E.

    1987-01-01

    Internal (mineral) Rb-Sr isochrons were determined for six Apollo 14 mare basalts of lunar breccia 14321. The ages of these fragments, which represent the time of crystallization of the respective mafic lavas, range from about 4.05 to 4.24, and, possibly, to 4.33 Ga and are among the oldest dates reported for mare basalts. For three of the fragments, internal Sm-Nd isochron data were collected and initial Nd isotopic composition was determined. The results are discussed with reference to the original source of these different basaltic fragments.

  10. Trace Element Geochemistry of Basaltic Tephra in Maar Cores; Implications for Centre Correlation, Field Evolution, and Mantle Source Characteristics of the Auckland Volcanic Field, New Zealand

    NASA Astrophysics Data System (ADS)

    Hopkins, J. L.; Leonard, G.; Timm, C.; Wilson, C. J. N.; Neil, H.; Millet, M. A.

    2014-12-01

    Establishing volcanic hazard and risk management strategies hinges on a detailed understanding of the type, timing and tephra dispersal of past eruptions. In order to unravel the pyroclastic eruption history of a volcanic field, genetic links between the deposits and eruption source centre need to be established. The Auckland Volcanic Field (AVF; New Zealand) has been active for ca. 200 kyr and comprises ca. 53 individual centres covering an area of ca. 360km2. These centres show a range of sizes and eruptive styles from maar craters and tuff rings, to scoria cones and lava flows consistent with both phreatomagmatic and magmatic eruptions. Superimposition of the metropolitan area of Auckland (ca. 1.4 million inhabitants) on the volcanic field makes it critically important to assess the characteristics of the volcanic activity, on which to base assessment and management of the consequent hazards. Here we present a geochemical approach for correlating tephra deposits to their source centres. To acquire the most complete stratigraphic record of pyroclastic events, maar crater cores from different locations, covering various depths and thus ages across the field were selected. Magnetic susceptibility and x-ray density scanning of the cores was used to identify the basaltic tephra horizons, which were sampled and in-situ analysis of individual shards undertaken for major and trace elements using EPMA and LA-ICP-MS techniques, respectively. Our results show that tephra shard trace element ratios are comparable and complementary to the AVF whole rock database. The use of specific trace element ratios (e.g. Gd/Yb vs. Zr/Yb) allows us to fingerprint and cross correlate tephra horizons between cores and, when coupled with newly acquired 40Ar-39Ar age dating and eruption size estimates, correlate horizons to their source centres. This integrated style of study can provide valuable information to help volcanic hazard management and forecasting, and mitigation of related risks.

  11. Isotopic and trace-element constraints on mantle and crustal contributions to Siberian continental flood basalts, Noril'sk area, Siberia

    USGS Publications Warehouse

    Wooden, J.L.; Czamanske, G.K.; Fedorenko, V.A.; Arndt, N.T.; Chauvel, C.; Bouse, R.M.; King, B.-S.W.; Knight, R.J.; Siems, D.F.

    1993-01-01

    We present a tightly controlled and comprehensive set of analytical data for the 250-Ma Siberian flood-basalt province. Consideration of major- and trace-element compositions, along with strontium, lead and neodymium isotopic compositions, strongly supports earlier Russian subdivision of this magmatism into three magmatic cycles, giving rise to three assemblages of eleven basalt suites in the ascending order Ivakinsky-Gudchikhinsky, Khakanchansky-Nadezhdinsky and Morongovsky-Samoedsky. Geochemical and isotopic discontinuities of varying magnitude characterize most of the boundaries between the eleven recognized basalt suites in the Noril'sk area. Although we conclude that the dominant volume of erupted magma originated from an asthenospheric mantle plume, none of the lavas is interpreted to directly represent asthenospheric melts, which would have been far more magnesian. On the basis of thermal considerations, we consider it unlikely that vast volumes of basaltic melt were produced directly from the continental lithospheric mantle beneath the Siberian craton. Moreover, there is little evidence from mantle xenoliths that the geochemical signatures of such melts would correspond to those of the Siberian flood basalts. Studies of melt migration lead us to conclude that transport of asthenospheric melt through the lithospheric mantle would be rapid, by fracture propagation. Lavas from the Gudchikhinsky suite have negligible Ta-Nb anomalies and positive ??{lunate}Nd values and their parental magmas presumably interacted little with the continental lithospheric mantle or crust. All other lavas have negative Ta-Nb anomalies and lower ??{lunate}Nd values that we attribute to interaction with continental crust. The model that we have developed requires discrete contributions from the plume and complex processing of all erupted magmas in the continental crust. The earliest magmas represent small percentages of melt formed in equilibrium with garnet. Over time, the

  12. Nature of basalt-deep crust interaction in the petrogenesis of a potassium-rich, silicic-dominated eruptive system, Davis Mountain volcanic field, west Texas

    SciTech Connect

    Ward, R.L.; Walker, J.A. . Dept. of Geology)

    1993-04-01

    The Davis Mountain volcanic field (DMVF) is one of several silicic-dominated eruptive centers that constitute the bulk of the Trans Pecos volcanic province (TPVP). New major-, trace element, and Pb-O isotope data on local granulite-facies xenoliths and the DMVF are used in evaluating the extent of basalt-deep crust interaction to produce voluminous silicic lavas and -ignimbrites. The DMVF (39.3--35.4 Ma) is a high-K, alkali basalt-potassic trachybasalt-shoshonite-latite-trachyte-rhyolite volcanoplutonic series with the evolved members being silica-saturated. DMF silicic rocks are characterized by high concentrations of Rb, Th, U, and K, low-[sup 18]O and have a broad range in Pb isotopes. These characteristics are inconsistent with an origin by partial melting of a Rb-Th-U depleted, unradiogenic Pb granulitic deep crust. However, distinctly different Pb isotope compositions between mafic and silicic rocks preclude an origin by fractional crystallization alone. Multistage-AFC involving a mantle-source, various proportions of OL-CPX-PLAG-KSPAR-MAG-AP-BIO-QTZ-aenigmatite-ZR differentiation, limited (<10%) amounts of deep and upper crustal contamination, and mixing between mafic and silicic magmas can satisfactorily account for the observed chemical and isotopic variation in the DMVF.

  13. Seychelles alkaline suite records the culmination of Deccan Traps continental flood volcanism

    NASA Astrophysics Data System (ADS)

    Owen-Smith, T. M.; Ashwal, L. D.; Torsvik, T. H.; Ganerød, M.; Nebel, O.; Webb, S. J.; Werner, S. C.

    2013-12-01

    Silhouette and North Islands in the Seychelles represent an alkaline plutonic-volcanic complex, dated at 63 to 63.5 Ma by U-Pb zircon and 40Ar/39Ar methods. This magmatism coincides with the final stages of the cataclysmic Deccan Traps continental flood volcanism in India (67 to 63 Ma), and thus a causal link has been suggested. Recent reconstructions have placed the Seychelles islands adjacent to the Laxmi Ridge and at the western margin of the Réunion mantle plume at the time of formation of the complex. Here we present geochemical evidence in support of the notion that the Seychelles alkaline magmatism was initiated by the peripheral activity of the Réunion mantle plume and is thus part of the Deccan magmatic event. Positive εNd (0.59 to 3.76) and εHf (0.82 to 6.79) and initial Sr of 0.703507 to 0.705643 at 65 Ma indicate derivation of the Seychelles alkaline magmas from a Réunion-like mantle source with an additional minor enriched component, suggesting entrainment of sub-continental lithospheric mantle. The similarity in trace element composition between the Seychelles suite and Deccan alkaline felsic and mafic rocks provides additional evidence for a common mantle source for the Seychelles and Deccan magmatism. Furthermore, we demonstrate the role of fractional crystallisation in the evolution of the alkaline suite. Modelling using major elements suggests that fractional crystallisation and varying degrees of accumulation of olivine, plagioclase, ilmenite, clinopyroxene, alkali feldspar and apatite can describe the spectrum of rock types, from gabbro, through syenite, to granite.

  14. Flood, Seismic or Volcanic Deposits? New Insights from X-Ray Computed Tomography

    NASA Astrophysics Data System (ADS)

    Van Daele, M. E.; Moernaut, J.; Vermassen, F.; Llurba, M.; Praet, N.; Strupler, M. M.; Anselmetti, F.; Cnudde, V.; Haeussler, P. J.; Pino, M.; Urrutia, R.; De Batist, M. A. O.

    2014-12-01

    Event deposits, such as e.g. turbidites incorporated in marine or lacustrine sediment sequences, may be caused by a wide range of possible triggering processes: failure of underwater slopes - either spontaneous or in response to earthquake shaking, hyperpycnal flows and floods, volcanic processes, etc. Determining the exact triggering process remains, however, a major challenge. Especially when studying the event deposits on sediment cores, which typically have diameters of only a few cm, only a small spatial window is available to analyze diagnostic textural and facies characteristics. We have performed X-ray CT scans on sediment cores from Chilean, Alaskan and Swiss lakes. Even when using relatively low-resolution CT scans (0.6 mm voxel size), many sedimentary structures and fabrics that are not visible by eye, are revealed. For example, the CT scans allow to distinguish tephra layers that are deposited by fall-out, from those that reached the basin by river transport or mud flows and from tephra layers that have been reworked and re-deposited by turbidity currents. The 3D data generated by the CT scans also allow to examine relative orientations of sedimentary structures (e.g. convolute lamination) and fabrics (e.g. imbricated mud clasts), which can be used to reconstruct flow directions. Such relative flow directions allow to determine whether a deposit (e.g. a turbidite) had one or several source areas, the latter being typical for seismically triggered turbidites. When the sediment core can be oriented (e.g. using geomagnetic properties), absolute flow directions can be reconstructed. X-ray CT scanning, at different resolution, is thus becoming an increasingly important tool for discriminating the exact origin of EDs, as it can help determining whether e.g. an ash layer was deposited as fall out from an ash cloud or fluvially washed into the lake, or whether a turbidite was triggered by an earthquake or a flood.

  15. Southern Cordilleran Basaltic Andesite suite, southern Chihuahua, Mexico: A link between Tertiary continental arc and flood basalt magmatism in the North America

    SciTech Connect

    Cameron, K. L.; Nimz, G. J.; Kuentz, D.; Niemeyer, S.; Gunn, S.

    1989-06-10

    Mid-Cenozoic orogenic andesites and ignimbrites of western Mexico, southwestern New Mexico, and Arizona are commonly capped by basaltic andesites, most from 29--20 Ma. We refer to these mafic lavas as the Southern Cordilleran Basaltic Andesite (SCORBA) suite, and they may constitute the most extensive Cenozoic basaltic suite in North America. The SCORBA suite has trace element and isotopic characteristics of orogenic (arc) rocks (i.g., Ba/Nb/gt/40), and silica content (53--56% SiO/sub 2/) like the Grande Ronde Basalt, which represents about 80% of the volume of the Columbia River Group. Geochemical and isotopic data are presented on SCORBA lavas and rare mafic lavas (PRE-SCORBA) interlayered with older ignimbrites from a 700-km-long NE-SW transect of southern Chihuahua, Mexico. SCORBA and PRE-SCORBA lavas with relatively low K/P (/lt/7) and differing Ba/Nd (50 versus 18) have similar isotopic compositions, arguing against their isotopic signatures being controlled by crustal assimilation. Along the entire length of the transect, the basaltic rocks have /var epsilon//sub Nd/ and /sup 87/Sr//sup 86/Sr near bulk Earth and /sup 206/Pb//sup 204/Pb and /sup 207/Pb//sup 204/Pb ratios that lie along a 1.7 Ga pseudoisochron. The Pb isotopic variation is geographically controlled, becoming more radiogenic from east to west, reflecting mixing in mantle source regions. The eastern mantle source has low/sup 206/Pb//sup 204/Pb and is a mixture of an enriched, enriched-mantle-like (EMI) component with one or more depleted components, which could include an intraplate component with relatively high Nb/Y (/gt/0.8).

  16. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    NASA Astrophysics Data System (ADS)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    Mantle xenoliths in alkali basaltic rocks from the Catalan Volcanic Zone, associated with the Neogene-Quaternary rift system in NE Spain, are formed of anhydrous spinel lherzolites and harzburgites with minor olivine websterites. Both peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism, especially the harzburgites. These and the websterites display protogranular microstructures, whereas lherzolites show continuous variation between protogranular, porphyroclastic and equigranular forms. Thermometric data of new xenoliths indicate that protogranular harzburgites, lherzolites and websterites were equilibrated at higher temperatures than porphyroclastic and equigranular lherzolites. Mineral chemistry also indicates lower equilibrium pressure for porphyroclastic and equigranular lherzolites than for the protogranular ones. Crystal preferred orientations (CPOs) of olivine and pyroxenes from these new xenoliths were determined with the EBSD-SEM technique to identify the deformation stages affecting the lithospheric mantle in this zone and to assess the relationships between the deformation fabrics, processes and microstructures. Olivine CPOs in protogranular harzburgites, lherzolites and a pyroxenite display [010]-fiber patterns characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane. Olivine CPO symmetry in porphyroclastic and equigranular lherzolites varies continuously from [010]-fiber to orthorhombic and [100]-fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The rare [100]-fiber patterns display strong point concentration of [100] axis, with normal girdle distribution of the other two axes, which are aligned with each other. The patterns of pyroxene CPOs are more dispersed than those of olivine, especially for clinopyroxene, but

  17. Alkaline basaltic volcanism of the Sea of Japan and the Philippine Sea: Similar and distinct geochemical and genetic features

    NASA Astrophysics Data System (ADS)

    Lelikov, E. P.; Emelyanova, T. A.

    2016-05-01

    The results of study of the deep sources of volcanic rocks from the Sea of Japan and the Philippine Sea with continental and oceanic basements, respectively, are presented. This problem is considered with the example of alkaline volcanic rocks of the Middle Miocene to Pliocene complex of the Sea of Japan and the Eocene-Oligocene Urdaneta Plateau of the Philippine Sea. The rocks have a similar geochemistry typical of OIBs, which indicates their deep (plume) origin. The presence of the Oligocene calc-alkaline volcanic rocks, which were formed prior to the marginal sea volcanism in the Sea of Japan, however, is the main difference in volcanism of the Sea of Japan from that of the Urdaneta Plateau, and this is explained by the different basements of these seas.

  18. Volcanism in the Noachis-Hellas region of Mars, 2

    NASA Technical Reports Server (NTRS)

    Peterson, J. E.

    1978-01-01

    Mariner 9 and Viking Orbiter imagery has been examined to investigate volcanism in the Noachis-Hellas region of Mars. A wide variety of probable and possible volcanic features, including cinder cones, flood lavas, wrinkel ridges, cratered domes on the floors of impact craters, shield volcanoes, and possible stratovolcanoes has been observed. The flood lavas of ridged plains and broad, low shield volcanoes are indicative of very fluid lavas of ultrabasic or very basic basaltic composition. Evidence for relatively recent pyroclastic volcanism is present in numerous probable cinder cones and some isolated cratered mountains tentatively identified as stratovolcanoes. The volcanic complex and ridged plains at 68 deg S, 323 deg W appear to be relatively young. The occurrence of the five major volcanic centers of the Noachis-Hellas region at the intersections of ancient Hellas impact basin rings with a postulated northeast-trending fracture system suggests that large-scale volcanic activity may have begun soon after formation of the basin.

  19. 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.

  20. The basaltic volcanism of the Dumisseau Formation in the Sierra de Bahoruco, SW Dominican Republic: A record of the mantle plume-related magmatism of the Caribbean Large Igneous Province

    NASA Astrophysics Data System (ADS)

    Escuder-Viruete, Javier; Joubert, Marc; Abad, Manuel; Pérez-Valera, Fernando; Gabites, Janet

    2016-06-01

    The basaltic volcanism of the Dumisseau Fm in the Sierra de Bahoruco, SW Dominican Republic, offers the opportunity to study, on land, the volcanism of the Caribbean Large Igneous Province (CLIP). It consists of an at least 1.5 km-thick sequence of submarine basaltic flows and pyroclastic deposits, intruded by doleritic dykes and sills. Three geochemical groups have been identified: low-Ti tholeiites (group I); high-Ti transitional basalts (group II); and high-Ti and LREE-enriched alkaline basalts (group III). These geochemical signatures indicate a plume source for all groups of basalts, which are compositionally similar to the volcanic rocks that make up various CLIP fragments in the northern region of the Caribbean Plate. Trace element modelling indicates that group I magmas are products of 8-20% melting of spinel lherzolite, group II magmas result 4-10% melting of a mixture of spinel and garnet lherzolite, and group III basalts are derived by low degrees (0.05-4%) of melting of garnet lherzolite. Dynamic melting models suggest that basalts represent aggregate melts produced by progressive decompression melting in a mantle plume. There is no compositional evidence for the involvement of a Caribbean supra-subduction zone mantle or crust in the generation of the basalts. Two 40Ar/39Ar whole-rock ages reflect the crystallisation of group II magmas at least in the late Campanian (~ 74 Ma) and the lower Eocene (~ 53 Ma). All data suggest that the Dumisseau Fm is an emerged fragment of the CLIP, which continues southward through the Beata Ridge

  1. Geochemistry of the Quaternary alkali basalts of Garrotxa (NE Volcanic Province, Spain): a case of double enrichment of the mantle lithosphere

    NASA Astrophysics Data System (ADS)

    Cebriá, J. M.; López-Ruiz, J.; Doblas, M.; Oyarzun, R.; Hertogen, J.; Benito, R.

    2000-11-01

    The area of Garrotxa (also known as the Olot area) represents the most recent (700,000-11,500 y) and better preserved area of magmatic activity in the NE Volcanic Province of Spain (NEVP). This region comprises a suite of intracontinental leucite basanites, nepheline basanites and alkali olivine basalts, which in most cases represent primary or nearly primary liquids. The geochemical characteristics of these lavas are very similar to the analogous petrologic types of other Cenozoic volcanics of Europe, which are intermediate between HIMU, DM and EM1. Quantitative trace element modeling, suggests derivation from an enriched mantle source by degrees of melting that progressively increased from the leucite basanites (˜4%) to the olivine basalts (˜16%). However, the relatively more variable Sr-Nd-Pb isotope signature of the magmas suggests the participation of at least two distinct components in the mantle source: (1) a sublithospheric one with a geochemical signature similar to the magmas of Calatrava (Central Spain) and other basalts of Europe; and (2) an enriched lithospheric component with a K-bearing phase present. The geochemical model proposed here involves the generation of a hybrid mantle lithosphere source produced by the infiltration of the sublithospheric liquids into enriched domains of the mantle lithosphere, shortly before the melting event that generated the Garrotxa lavas. The available geological data suggest that the first enrichment event of the mantle lithosphere under the NEVP could be the result of Late Variscan mantle upwelling triggered by the extensional collapse of the Variscan orogen during the Permo-Carboniferous. By Jurassic/Cretaceous time, large-scale NNE-directed sublithospheric mantle channeling of thermally and chemically anomalous plume material was placed under the Iberian Peninsula and Central Europe. However, the geodynamic conditions in the NEVP did not favor magmatism, which could not take place until the Cenozoic after

  2. Petrologic insights into basaltic volcanism at historically active Hawaiian volcanoes: Chapter 6 in Characteristics of Hawaiian volcanoes

    USGS Publications Warehouse

    Helz, Rosalind L.; Clague, David A.; Sisson, Thomas W.; Thornber, Carl R.

    2014-01-01

    Contributions to our knowledge of the nature of the mantle source(s) of Hawaiian basalts are reviewed briefly, although this is a topic where debate is ongoing. Finally, our accumulated petrologic observations impose constraints on the nature of the summit reservoirs at Kīlauea and Mauna Loa, specifically whether the summit chamber has been continuous or segmented during past decades.

  3. Results of analyses performed on basalt adjacent to penetrators emplaced into volcanic rock at Amboy, California, April 1976

    NASA Technical Reports Server (NTRS)

    Blanchard, M.; Bunch, T.; Davis, A.; Shade, H.; Erlichman, J.; Polkowski, G.

    1977-01-01

    The physical and chemical modifications found in the basalt after impact of four penetrators were studied. Laboratory analyses show that mineralogical and elemental changes are produced in the powdered and crushed basalt immediately surrounding the penetrator. Optical microscopy studies of material next to the skin of the penetrator revealed a layer, 0-2 mm thick, of glass and abraded iron alloy mixed with fractured mineral grains of basalt. Elemental analysis of the 0-2 mm layer revealed increased concentrations of Fe, Cr, Ni, No, and Mn, and reduced concentrations of Mg, Al, Si, and Ca. The Fe, Cr, Ni, and Mo were in fragments abraded from the penetrator. Mineralogical changes occurring in the basalt sediment next to the penetrator include the introduction of micron-size grains of alpha-iron, magnetite, and hematite. The newly formed silicate minerals include metastable phases of silica (tridymite and cristobalite). An increased concentration of Fe, Cr, Ni, and Mo occurred in the 2-mm to 1-cm layer of penetrator no. 1, which impacted at the highest velocity. No elemental concentration increase was noted for penetrators nos. 2 and 3 in the 2-mm to 1-cm layer. Contaminants introduced by the penetrator occur up to 1 cm away from the penetrator's skin. Although volatile elements do migrate and new minerals are formed during the destruction of host minerals in the crushed rock, no changes were observed beyond the 1-cm distance.

  4. Volcanically-Induced Nile Flood Failure Promotes Internal Revolt and Suppresses Interstate Conflict in Hellenistic Egypt, 305-30 BCE

    NASA Astrophysics Data System (ADS)

    Ludlow, Francis; Manning, Joseph; Stine, Alexander; Boos, William; Storelvmo, Trude; Sigl, Michael; Marlon, Jennifer

    2016-04-01

    Explosive volcanic eruptions are a primary driver of abrupt short-term climatic changes. State-of-the-art revisions to polar ice-core chronologies now allow us to track the impacts of a sequence of major and closely-recurring volcanic eruptions on the great Ptolemaic kingdom centred in Egypt, between 305-30 BCE. This was a formidable Mediterranean cultural and economic power in the efflorescent Hellenistic era of the first four centuries BCE, a period bracketed by Alexander the Great on one end and Cleopatra on the other, and known for its considerable advancement in science and material culture. In this paper we show a link between major volcanic eruptions that register through elevated sulphate deposition in the polar ice, and a suppression of the agriculturally-critical Nile summer flood, identifiable in annual Nilometer measurements from Rhoda, Cairo, between 641 and 1469 CE. This likely relates to a volcanic perturbation of the East African monsoon, responsible for the rainfall in the Ethiopian highlands that drives the annual summer flood, and the effect can also be identified in ancient papyri that indicate the quality of the Nile flood in the first several centuries BCE. Volcanic eruptions in this period are also shown to correspond in timing with the initiation of a series of hitherto poorly understood internal revolts against Ptolemaic rule in Egypt, while also corresponding in timing to the cessation of major interstate conflicts (the nine "Syrian Wars", running 274-96 BCE) between the Ptolemaic kingdom and their powerful Near Eastern rival, the Seleukid empire. Subsistence crises driven by volcanically-induced suppression of the Nile flood are likely to have played a key causal role in these events, an understanding that helps to advance our knowledge of the major historical events of the formative Hellenistic era, which set the scene for the rise of the Roman Empire. Our findings also suggest the potential of integrating human and natural archives to

  5. Increased thyroid cancer incidence in a basaltic volcanic area is associated with non-anthropogenic pollution and biocontamination.

    PubMed

    Malandrino, Pasqualino; Russo, Marco; Ronchi, Anna; Minoia, Claudio; Cataldo, Daniela; Regalbuto, Concetto; Giordano, Carla; Attard, Marco; Squatrito, Sebastiano; Trimarchi, Francesco; Vigneri, Riccardo

    2016-08-01

    The increased thyroid cancer incidence in volcanic areas suggests an environmental effect of volcanic-originated carcinogens. To address this problem, we evaluated environmental pollution and biocontamination in a volcanic area of Sicily with increased thyroid cancer incidence. Thyroid cancer epidemiology was obtained from the Sicilian Regional Registry for Thyroid Cancer. Twenty-seven trace elements were measured by quadrupole mass spectrometry in the drinking water and lichens (to characterize environmental pollution) and in the urine of residents (to identify biocontamination) in the Mt. Etna volcanic area and in adjacent control areas. Thyroid cancer incidence was 18.5 and 9.6/10(5) inhabitants in the volcanic and the control areas, respectively. The increase was exclusively due to the papillary histotype. Compared with control areas, in the volcanic area many trace elements were increased in both drinking water and lichens, indicating both water and atmospheric pollution. Differences were greater for water. Additionally, in the urine of the residents of the volcanic area, the average levels of many trace elements were significantly increased, with values higher two-fold or more than in residents of the control area: cadmium (×2.1), mercury (×2.6), manganese (×3.0), palladium (×9.0), thallium (×2.0), uranium (×2.0), vanadium (×8.0), and tungsten (×2.4). Urine concentrations were significantly correlated with values in water but not in lichens. Our findings reveal a complex non-anthropogenic biocontamination with many trace elements in residents of an active volcanic area where thyroid cancer incidence is increased. The possible carcinogenic effect of these chemicals on the thyroid and other tissues cannot be excluded and should be investigated. PMID:26438396

  6. Crustal seismic structure beneath the source area of the Columbia River flood basalt: Bifurcation of the Moho driven by lithosphere delamination

    NASA Astrophysics Data System (ADS)

    Gao, Haiying

    2015-11-01

    The source area of the ~16 Ma Columbia River flood basalt eruptions originated beneath the Wallowa Mountains in northeast Oregon, with a distinct circular pattern of topographic uplift. Teleseismic receiver functions reveal two layers between latitude 45.5° and 46.5° beneath north of the Wallowas, one at 25 km depth and the other one at 45 km depth. A new full-wave ambient noise tomography model shows a circular anomaly, which is seismically fast in the upper crust and slow from lower crust to uppermost mantle in comparison with the surroundings, coincident with the circular pattern of the Wallowas. The seismic structures suggest that delamination of the Farallon lithosphere initiated the basalt eruptions and, consequently, modified the lowermost crust, forming a new shallow Moho. The Farallon slab is probably detached directly beneath the Wallowas while being maintained at the northern edge of the Wallowas, corresponding to the deeper interface.

  7. Causal Link Between Flood Basalts and Large Impacts: Were The K-t and P-tr Impactors `verneshots' Fired From Terrestrial Plume-fed Co2-guns?

    NASA Astrophysics Data System (ADS)

    Phipps Morgan, J.; Reston, T.; Ranero, C.

    Both bolide impacts (Alvarez et al., 1980) and Continental Flood Basalt (CFB) events (Courtillot, 1996; Courtillot et al., 1994; Morgan, 1986) have been proposed to be the cause of the three largest Phanerozoic mass-extinctions. The Cretaceous-Tertiary (K-T) boundary is the age of both one of the largest known terrestrial impact struc- tures (the Chixculub site on the Yucatan peninsula) and a very large continental flood basalt (the Deccan Traps event, the first well-documented trace of the Reunion plume- hotspot). In the past year, two papers (Becker et al., 2001; Kaiho et al., 2001) have suggested that the Permian-Triassic (P-Tr) boundary, the age of the largest well- documented CFB (the Siberian Traps), is also marked, in some marine sediments, by the geochemical signature of a large bolide impact. If correct, this would require that both a bolide impact and a CFB occurred at the P-Tr boundary. Finally, the Frasnian- Famennian (Late Devonian) event appears to be contemporaneous with an impact or impacts (e.g. Siljan Ring - Grieve and Robertson, 1987), the eruption of both a Siberian Kimberlite field (Agashev et al., 2001), and the Dniepr-Donets CFB (Wilson et al., 1996). Both large bolide impacts (flood basalts (once every 30-50 Ma) occur very infrequently. The odds of two such simultaneous events occurring by chance within the past 400 Ma are only 1 in 22,500, odds so unlikely that is seems prudent to consider a causal link. Most obvious is the intuition that somehow a bolide impact can trigger a flood basalt. However, in Deccan there appears to be good evidence that the `impact event' occurred during, not before, flood basalt activity, as the iridium-rich K-T anomaly appears to occur well within the flood-basalt stratigraphy (Bhandari et al., 1994). Therefore, here we examine whether terrestrial processes can produce the `signal' of an extraterrestrial impact event. We explore a physical model where sub-cratonic plume

  8. Variation in parental magmas of Mt Rouse, a complex polymagmatic monogenetic volcano in the basaltic intraplate Newer Volcanics Province, southeast Australia

    NASA Astrophysics Data System (ADS)

    Boyce, Julie A.; Nicholls, Ian A.; Keays, Reid R.; Hayman, Patrick C.

    2015-02-01

    Monogenetic volcanoes have long been regarded as simple in nature, involving single magma batches and uncomplicated evolutions; however, recent detailed research into individual centres is challenging that assumption. Mt Rouse (Kolor) is the volumetrically largest volcano in the monogenetic Newer Volcanics Province of southeast Australia. This study presents new major, trace and Sr-Nd-Pb isotope data for samples selected on the basis of a detailed stratigraphic framework analysis of the volcanic products from Mt Rouse. The volcano is the product of three magma batches geochemically similar to Ocean-Island basalts, featuring increasing LREE enrichment with each magma batch (batches A, B and C) but no evidence of crustal contamination; the Sr-Nd-Pb isotopes define two groupings. Modelling suggests that the magmas were sourced from a zone of partial melting crossing the lithosphere-asthenosphere boundary, with batch A forming a large-volume partial melt in the deep lithosphere (1.7 GPa/55.5 km); and batches B and C from similar areas within the shallow asthenosphere (1.88 GPa/61 km and 1.94 GPa/63 km, respectively). The formation and extraction of these magmas may have been due to high deformation rates in the mantle caused by edge-driven convection and asthenospheric upwelling. The lithosphere-asthenosphere boundary is important with respect to NVP volcanism. An eruption chronology involves sequential eruption of magma batches A, C and B, followed by simultaneous eruption of batches A and B. Mt Rouse is a complex polymagmatic monogenetic volcano that illustrates the complexity of monogenetic volcanism and demonstrates the importance of combining detailed stratigraphic analysis alongside systematic geochemical sampling.

  9. Quaternary adakite—Nb-enriched basalt association in the western Trans-Mexican Volcanic Belt: is there any slab melt evidence?

    NASA Astrophysics Data System (ADS)

    Petrone, Chiara M.; Ferrari, Luca

    2008-07-01

    A spatial and temporal association between adakitic rocks and Nb-enriched basalts (NEB) is recognised for the first time in the western sector of the Trans-Mexican Volcanic Belt in the San Pedro-Cerro Grande Volcanic Complex (SCVC). The SCVC is composed of subalkalic intermediate to felsic rocks, spanning in composition from high-silica andesites to rhyolites, and by the young transitional hawaiite and mugearite lavas of Amado Nervo shield volcano. Intermediate to felsic rocks of the SCVC show many geochemical characteristics of typical adakites, such as high Sr/Y ratios (up to 180) and low Y (<18 ppm) and Yb contents. Mafic Amado Nervo rocks have high TiO2 (1.5-2.3 wt%), Nb (14-27 ppm), Nb/La (0.5-0.9) and high absolute abundances of HFSE similar to those shown by NEB. However, the Sr and Nd isotopic signature of SCVC rocks is different from that shown by typical adakites and NEB. Although the adakites-NEB association has been traditionally considered as a strong evidence of slab-melting, we suggest that other processes can lead to its generation. Here, we show that parental magmas of adakitic rocks of the SCVC derive their adakitic characteristic from high-pressure crystal fractionation processes of garnet, amphibole and pyroxene of a normal arc basalt. On the other hand, Amado Nervo Na-alkaline parental magmas have been generated by sediment melting plus MORB-fluid flux melting of a heterogeneous mantle wedge, consisting of a mixture of depleted and an enriched mantle sources (90DM + 10EM). We cannot exclude a contribution to the subduction component of slab melts, because the component signature is dominated by sediment melt, but we argue that caution is needed in interpreting the adakites-NEB association in a genetic sense.

  10. Unrest at Bárdarbunga: Preparations for possible flooding due to subglacial volcanism

    NASA Astrophysics Data System (ADS)

    Hardardottir, Jorunn; Roberts, Matthew; Pagneux, Emmanuel; Einarsson, Bergur; Thorarinsdottir, Tinna; Johannesson, Tomas; Sigurdsson, Oddur; Egilson, David; Sigurdsson, Gunnar; Imo hydrological-monitoring-team

    2015-04-01

    Located partly beneath northwest Vatnajökull, Iceland, the Bárdarbunga volcanic system comprises an ice-capped central volcano and a fissure swarm extending beyond the ice margin. During the last 1100 years the volcano has erupted on at least 26 occasions. Outburst floods (jökulhlaups) on a scale of >100,000 m3 s-1 are known to have occurred during major explosive eruptions. Repeated jökulhlaups from Bárdarbunga have inundated the Jökulsá á Fjöllum River, which drains over 200 km northwards from the Dyngjujökull outlet glacier to the north coast of Iceland. Depending on the location of the eruption within the 80 km2 caldera, jökulhlaups could also flow northwards along Skjálfandafljót River and towards west and southwest into present-day tributaries of the extensively hydropower-harnessed Thjórsá River. On 16 August 2014, an intense earthquake swarm began within the Bárdarbunga caldera. Seismicity propagated from the caldera, extending ~10 km northwards of the ice margin where a fissure eruption developed in late August and remains ongoing in early January 2015. In connection with the lateral migration of magma from the caldera, the ice surface of Bárdarbunga has lowered by over 60 m; also associated with increased geothermal heat on the caldera rim, as manifested by the development of ice-surface depressions. In preparation for a subglacial eruption in the Bárdarbunga volcanic system, the Icelandic Meteorological Office (IMO) has made several assessments of likely hydrological hazards. Assessments were undertaken on Jökulsá á Fjöllum and Skjálfandafljót at key locations where preliminary evacuation plans for populated areas were made in cooperation with the local police. Floodwater extent was estimated for key infrastructures, such as bridges, telecommunication and power lines for maximum discharge levels ranging from 3,000 to 20,000 m3 s-1. The estimations were made using either simple Manning's calculations or HEC-RAS modelling

  11. Lead and strontium isotopic evidence for crustal interaction and compositional zonation in the source regions of Pleistocene basaltic and rhyolitic magmas of the Coso volcanic field, California

    USGS Publications Warehouse

    Bacon, C.R.; Kurasawa, H.; Delevaux, M.H.; Kistler, R.W.; Doe, B.R.

    1984-01-01

    The isotopic compositions of Pb and Sr in Pleistocene basalt, high-silica rhyolite, and andesitic inclusions in rhyolite of the Coso volcanic field indicate that these rocks were derived from different levels of compositionally zoned magmatic systems. The 2 earliest rhyolites probably were tapped from short-lived silicic reservoirs, in contrast to the other 36 rhyolite domes and lava flows which the isotopic data suggest may have been leaked from the top of a single, long-lived magmatic system. Most Coso basalts show isotopic, geochemical, and mineralogic evidence of interaction with crustal rocks, but one analyzed flow has isotopic ratios that may represent mantle values (87Sr/86Sr=0.7036,206Pb/204Pb=19.05,207Pb/204Pb=15.62,208Pb/204Pb= 38.63). The (initial) isotopic composition of typical rhyolite (87Sr/86Sr=0.7053,206Pb/204Pb=19.29,207Pb/204Pb= 15.68,208Pb/204Pb=39.00) is representative of the middle or upper crust. Andesitic inclusions in the rhyolites are evidently samples of hybrid magmas from the silicic/mafic interface in vertically zoned magma reservoirs. Silicic end-member compositions inferred for these mixed magmas, however, are not those of erupted rhyolite but reflect the zonation within the silicic part of the magma reservoir. The compositional contrast at the interface between mafic and silicic parts of these systems apparently was greater for the earlier, smaller reservoirs. ?? 1984 Springer-Verlag.

  12. Basaltic melt evolution of the Hengill volcanic system, SW Iceland, and evidence for clinopyroxene assimilation in primitive tholeiitic magmas

    SciTech Connect

    Troennes, R.G. )

    1990-09-10

    The thick oceanic crust of Iceland is formed by tholeiitic central volcanoes arranged in en echelon patterns along the 40-50 km wide rift zones. The Hengill central volcano in the southwestern rift zone has produced 25-30 km{sup 3} of hyaloclastites and lava during the last 0.11 m.y., with maximum productivity during the isostatic rebound following the degalciations 0.13 and 0.01 m.y. ago. The petrographic relations of pillow rim and hyaloclastite glass indicate that the basaltic melts were saturated with olivine and plagioclase, except for the most primitive ones that were undersaturated with plagioclase. Saturation with clinopyroxene was reached in some of the intermediate and evolved basaltic melts. Corroded and partly resorbed crystals of clinopyroxene and partly disintegrated gabbro nodules with resorbed clinopyroxene indicate that selective assimilation contributed to the evolution of the most primitive melts. The intermediate and evolved basaltic glass compositions fall along the low-pressure cotectic for mid-ocean ridge basalt (MORB) compositions saturated with olivine, plagioclase, and clinopyroxene, but the primitive glasses fall well inside the low-pressure olivine + plagioclase primary phase volume. The dense picritic magmas were driven to the surface by magmatic overpressure in the mantle at an early deglaciation stage characterized by the absence of large, trapping magma chambers in the lower crust. The assimilation of clinopyroxene in these melts could proceed by direct contact with the solidified cumulate sequences and gabbro intrusions. Clinopyroxene assimilation in combination with olivine fractionation may also contribute to the chemical evolution of some of the most primitive MORB magmas.

  13. Basaltic island sand provenance

    SciTech Connect

    Marsaglia, K.M. . Dept. of Geological Sciences)

    1992-01-01

    The Hawaiian Islands are an ideal location to study basaltic sand provenance in that they are a series of progressively older basaltic shield volcanoes with arid to humid microclimates. Sixty-two sand samples were collected from beaches on the islands of Hawaii, Maui, Oahu and Kauai and petrographically analyzed. The major sand components are calcareous bioclasts, volcanic lithic fragments, and monomineralic grains of dense minerals and plagioclase. Proportions of these components vary from island to island, with bioclastic end members being more prevalent on older islands exhibiting well-developed fringing reef systems and volcanic end members more prevalent on younger, volcanically active islands. Climatic variations across the island of Hawaii are reflected in the percentage of weathered detritus, which is greater on the wetter, northern side of the island. The groundmass of glassy, basaltic lithics is predominantly black tachylite, with lesser brown sideromelane; microlitic and lathwork textures are more common than holohyaline vitric textures. Other common basaltic volcanic lithic fragments are holocrystalline aggregates of silt-sized pyroxene or olivine, opaque minerals and plagioclase. Sands derived from alkalic lavas are texturally and compositionally indistinguishable from sands derived from tholeiitic lavas. Although Hawaiian basaltic sands overlap in composition with magmatic arc-derived sands in terms of their relative QFL, QmPK and LmLvLs percentages, they are dissimilar in that they lack felsic components and are more enriched in lathwork volcanic lithic fragments, holocrystalline volcanic lithic fragments, and dense minerals.

  14. Sensitivity of geochemical monitoring for CO2 sequestration in basalt

    NASA Astrophysics Data System (ADS)

    Zakharova, N. V.; Goldberg, D.; Herron, M.; Grau, J.

    2010-12-01

    Continental flood basalts is a promising target for carbon dioxide (CO2) storage due to high storage capacity, presence of seals, and potential for geochemical trapping which results in binding CO2 into stable carbonate minerals. The success of long-term CO2 storage in igneous rocks highly depends on our ability to monitor mineralization under in situ conditions. The direct chemistry measurements on cores are costly and typically do not provide continuous coverage. In this study we investigate the potential of borehole geochemical logging for monitoring of CO2 mineralization in basalt. Neutron-induced capture gamma ray spectroscopy tools allow obtaining in-situ concentration logs for up to 10 major elements which can be used to construct a quantitative mineralogical model. While this usually provides good bulk mineralogy estimates, detecting small-volume mineral alteration in volcanic rocks remains challenging, especially if borehole conditions are poor. We analyze Schlumberger Elemental Capture Spectroscopy logs and chemical core analysis from the pilot CO2 sequestration project in the Columbia River flood basalt. We use the geochemical spectroscopy logs and quantitative modeling to quantify their sensitivity to secondary mineralization in basalt. We apply statistical analysis to explain the variance in elemental concentrations (and other logs) and establish detection limits for various mineral alteration products in basalt. We use these results to evaluate monitoring capabilities and limitations of geochemical logging for CO2 mineralization after underground injection in basalt and suggest areas for future research.

  15. Hf isotope compositions and chronology of magmatic zircons from Tarim continental flood basalts: implications for magmatic evolution of the Early Permian Tarim Large Igneous Province in NW China

    NASA Astrophysics Data System (ADS)

    Li, Y.; Li, Z.; Yu, X.; Langmuir, C. H.; Yang, S.; Chen, H.

    2013-12-01

    The Early Permian Tarim Large Igneous Province (TLIP) in the Tarim cratonic block of northwestern China has been largely regarded to be genetically linked with a mantle plume. Recently, some euhedral zircon crystals with magmatic growth zoning have been obtained from the Tarim continental flood basalts (TCFB) for detailed U-Pb chronological and genetic study. The zircons have the concordant 206Pb/238U ages of 297~283 Ma, coinciding with the previously reported whole-rock 40K/39Ar and 40Ar/39Ar ages (292~283 Ma) of their host basalts. In-situ LA-MC-ICPMS Lu-Hf isotopic analyses of Early Permian zircons from the Keping area of the TCFB reveal that the zircons from two basalt sub-groups (Groups 1a, 1b) have a narrow range of 176Hf/177Hf ratios between 0.282422 and 0.282568. Their corresponding ɛHf(t) (t = 290 Ma) values (-6.8~-1.4) are generally lower than their host basalts (-2.3~2.1), and distinctively different from the intrusive rocks (3.0~7.1) and their zircons (4.9~8.8) from the TLIP and the Precambrian crustal rocks (<-18) in the Tarim block. Combined with their embayed margins produced by magmatic corrosion, these zircons may have crystallized in a concealed pluton shortly prior to the extrusion of basalts and been captured as xenocrysts by the rapidly erupted basaltic lavas. Almost the same ɛHf(t) values between the corroded and uncorroded zircons suggest that the zircons have preserved the initial Hf isotopic compositions from their original source region. Moreover, the very close but relatively higher ɛHf(t) values from the zircons than the inferred sub-continental lithospheric mantle (SCLM) beneath Tarim in the Early Permian [ɛHf(t) = -8.7~-5.2; t = 290 Ma] indicate that the zircons were probably originated from the SCLM with minor addition of depleted mantle magmas during the mantle source partial melting. Both the zircons and their host basalts have almost the same formation ages (~290 Ma) and Hf TDM model ages (ca. 1300~1000 Ma), suggesting that

  16. Basaltic Magmatism: The Dominant Factor in the Petrologic and Tectonic Evolution of the Earth

    NASA Technical Reports Server (NTRS)

    Lowman, Paul D., Jr.

    2003-01-01

    Silicate bodies such as the Moon, Mars, probably Mercury, and possibly Venus, appear to have evolved in three main stages: a first (felsic) differentiation, a late heavy bombardment, and a second (basaltic) differentiation. It has been proposed that the Earth underwent a similar sequence. This paper argues that the second differentiation, basaltic magmatism, has dominated the petrologic and tectonic evolution of the Earth for four billion years. A global andesitic crust, formed during and after accretion of the planet, was disrupted by major impacts that triggered mantle upwelling and sea-floor spreading about 4 billion years ago. The oceanic crust collectively has since been formed by basaltic volcanism, from spreading centers and mantle plumes. However, the continental crust has also been greatly affected. Basaltic underplating has promoted anatexis and diapiric intrusion of granitoids in granite-greenstone terrains, as well as providing heat for regional metamorphism. Basaltic intrusions, such as the Nipissing diabase of the Sudbury area, have added to the thickness of continental crust. Satellite magnetic surveys suggest that there are more such basaltic intrusions than previously realized; examples include the Bangui anomaly of central Africa and the Kentucky anomaly. Basaltic overplating from mafic dike swarms has repeatedly flooded continents; had it not been for erosion, they would be covered with basalt as Venus is today. The tectonic effects of basaltic volcanism on continents have only recently been realized. The World Stress Map project has discovered that continents are under horizontal compressive stress, caused by push from mid-ocean ridges, i.e., by basaltic volcanism. The stress fields are generally uniform over large intraplate areas, and could contribute to intraplate tectonism. Seafloor spreading has demonstrably been effective for at least 200 million years, and ridge push thus a contributor to tectonic activity for that long. Collectively, the

  17. 40Ar/39Ar ages of flood basalt provinces in Russia and China and their possible link to global faunal extinction events: A cautionary tale regarding alteration and loss of 40Ar∗

    NASA Astrophysics Data System (ADS)

    Baksi, Ajoy K.

    2014-04-01

    The hypothesis that the Permo-Triassic boundary (PTB) mass extinctions were caused by flood basalt volcanism in Russia (Siberian Traps) and/or China (the Emeishan Traps) is investigated from the point of view of time of occurrence (40Ar/39Ar ages). Numerous published ages in the literature are rejected as good estimates of the time of crystallization. The filters applied in this respect are (a) statistical reliability of plateau/isochron sections of stepheating data and (b) the alteration state of the material that was dated. Alteration appears to be ubiquitous, unsurprising since most of the material dated was used without acid leaching - a procedure that is effective in yielding fresh(er) samples. Of ˜70 ages in the literature for the main pulse of Siberian Trap volcanism, less than ten prove to be reliable ages. Similar techniques applied to 40Ar/39Ar for the Emeishan Traps, leaves only a single reliable age for the magmatic episode. These ages are compared to both published and new 40Ar/39Ar ages for the PTB as based on analysis of minerals from critical ash beds in China. There is good overlap in the ages (PTB - 250.0 ± 0.1 Ma, Siberian Trap lavas - 250.1 ± 0.4 Ma), lending credence to a genetic link between the formation of the Siberian Traps and the faunal extinction event at the PTB. A similar link for the formation of the Viluy Traps (Russia) and the Late Devonian extinction event is investigated; only a single reliable 40Ar/39Ar age is available for the Viluy Traps, and falls close to the interpolated age for the Frasnian-Fammenian boundary. The use of the unspiked K-Ar technique to yield accurate ages for such (altered) samples is questioned.

  18. Basaltic rocks from the Andean Southern Volcanic Zone: Insights from the comparison of along-strike and small-scale geochemical variations and their sources

    NASA Astrophysics Data System (ADS)

    Hickey-Vargas, Rosemary; Holbik, Sven; Tormey, Daniel; Frey, Frederick A.; Moreno Roa, Hugo

    2016-08-01

    The origin of spatial variations in the geochemical characteristics of volcanic rocks erupted in the Andean Southern Volcanic Zone (SVZ) has been studied by numerous researchers over the past 40 years. Diverse interpretations for along-strike, across-strike, and small-scale variations have been proposed. In this paper, we review geochemical data showing along-strike geochemical variations and address the processes causing such trends. We compare large- and small-scale changes of the same geochemical parameters in basaltic rocks in order to use spatial scale as a tool for isolating processes that may have the same result. Along-strike geochemical variations in the SVZ are expected, due to 1) greater thickness or age of the sub-arc continental crust and mantle lithosphere in the Northern SVZ (NSVZ; 33°S-34°30‧S) and Transitional SVZ (TSVZ; 34°30‧S-37°S) compared with the Central SVZ (CSVZ; 37°S-41.5°S) and Southern SVZ (SSVZ: 41.5°S-46°S); and 2) along-strike changes of the subducting Nazca plate and overlying asthenosphere. Basalts and basaltic andesites erupted at volcanic front stratovolcanoes define several along-strike geochemical trends: 1) higher 87Sr/86Sr and lower 143Nd/144Nd at volcanoes in the NSVZ compared with the TSVZ, CSVZ, and SSVZ; 2) higher and more variable La/Yb at volcanoes in the NSVZ and TSVZ compared with the CSVZ and SSVZ; 3) lower 87Sr/86Sr for a given 143Nd/144Nd at volcanoes in the TSVZ compared with the CSVZ and SSVZ; and 4) large values for time-sensitive subduction tracers such as 10Be/9Be and (238U/230Th) at some volcanoes in the CSVZ, but not in the NSVZ and TSVZ. Geochemical parameters that distinguish the TSVZ from the CSVZ and SSVZ are also found within the CSVZ at small basaltic eruptive centers (SEC) aligned with the Liquiñe-Ofqui Fault System (LOFS), which extends from 38°S to the southernmost SVZ. Our interpretation is that CSVZ magmas with strong time-sensitive subduction tracers represent the ambient subduction

  19. Elemental and Sr-Nd isotopic geochemistry of Permian Emeishan flood basalts in Zhaotong, Yunnan Province, SW China

    NASA Astrophysics Data System (ADS)

    Li, Juan; Zhong, Hong; Zhu, Wei-Guang; Bai, Zhong-Jie; Hu, Wen-Jun

    2016-05-01

    This study presents new whole-rock elemental and isotopic data for the basalts from the Zhaotong area, located in the intermediate zone of the ~260 Ma Emeishan large igneous province (ELIP). The Zhaotong basalts belong to high-Ti series with TiO2 from 2.93 to 5.26 % and Ti/Y from 519 to 974. The parental magma was subjected to minor crustal contamination as indicated by slight Nb-Ta depletion (Nb/La: 0.72-1.10). Meanwhile, the relatively invariable Sr-Nd isotopes (ɛNd(t): -0.74 to +2.86, mostly +1.10 to +2.86; (87Sr/86Sr)i: 0.7050-0.7072) and the light rare earth elements (LREE) enrichment (La/Yb: 10.3-19.1) of the basalts prefer a mantle plume origin. A garnet-dominated peridotite mantle source was further suggested on the basis of the REE distribution patterns and high Sm/Yb and high La/Yb ratios. This study further confirms the geochemical zoning of the high-Ti basalts in the ELIP, which is in accordance with both the spatial distribution and the thickness of the basalts. The high-Ti basalts in the intermediate and outer zones of ELIP (e.g., Zhaotong and Guizhou) share similar Sr-Nd isotopic and elemental compositions, suggesting that they originated directly from the Emeishan mantle plume. By contrast, the high-Ti basalts in the inner zone (e.g., Longzhoushan and Binchuan) have variable compositions, indicating a rather heterogeneous mantle source possibly involved with subcontinental lithospheric mantle (SCLM) components.

  20. Chemical weathering rate, denudation rate, and atmospheric and soil CO2 consumption of Paraná flood basalts in São Paulo State, Brazil

    NASA Astrophysics Data System (ADS)

    da Conceição, Fabiano Tomazini; dos Santos, Carolina Mathias; de Souza Sardinha, Diego; Navarro, Guillermo Rafael Beltran; Godoy, Letícia Hirata

    2015-03-01

    The chemical weathering rate and atmospheric/soil CO2 consumption of Paraná flood basalts in the Preto Stream basin, São Paulo State, Brazil, were evaluated using major elements as natural tracers. Surface and rain water samples were collected in 2006, and analyses were performed to assess pH, temperature, dissolved oxygen (DO), electrical conductivity (EC) and total dissolved solids (TDS), including SO42-, NO3-, PO43 -, HCO3-, Cl-, SiO2, Ca2 +, Mg2 +, Na+ and K+. Fresh rocks and C horizon samples were also collected, taking into account their geological context, abundance and spatial distribution, to analyze major elements and mineralogy. The Preto Stream, downstream from the city of Ribeirão Preto, receives several elements/compounds as a result of anthropogenic activities, with only sulfate yielding negative flux values. The negative flux of SO42 - can be attributed to atmospheric loading that is mainly related to anthropogenic inputs. After corrections were made for atmospheric inputs, the riverine transport of dissolved material was found to be 30 t km- 2 y- 1, with the majority of the dissolved material transported during the summer (wet) months. The chemical weathering rate and atmospheric/soil CO2 consumption were 6 m/Ma and 0.4 · 106 mol km- 2 y- 1, respectively. The chemical weathering rate falls within the lower range of Paraná flood basalt denudation rates between 135 and 35 Ma previously inferred from chronological studies. This comparison suggests that rates of basalt weathering in Brazil's present-day tropical climate differ by at most one order of magnitude from those prevalent at the time of hothouse Earth. The main weathering process is the monosiallitization of anorthoclase, augite, anorthite and microcline. Magnetite is not weathered and thus remains in the soil profile.

  1. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing

    USGS Publications Warehouse

    Chang, J.M.; Feeley, T.C.; Deraps, M.R.

    2009-01-01

    The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

  2. A conceptual model of geological risk in the Ischia Island (Italy): highlights on volcanic history, seismicity and flooding

    NASA Astrophysics Data System (ADS)

    Carlino, Stefano; Cubellis, Elena; Iannuzzi, Raffaello; Luongo, Giuseppe

    2010-05-01

    During the last eight centuries the island of Ischia was hit by earthquakes, volcanic eruptions and floods producing heavy damages and numerous fatalities. Since the last twenty century the Ischia population is grown very fast, nowadays more than 56.000 people live in the island and 4 million of people visit it during the year, thus this area is characterised as an high geological risk territory. The island is here presented as an interesting "laboratory" for volcanic, seismic and hydrogeological risks assessment, from which to draw lessons for planning in risk areas. Ischia is a volcanic field, formed by the succession of effusive and explosive eruptions which formed lavas, welded and loose pyroclastic rocks. The succession of rock layers, with different permeability, promotes, during heavy rainfall, the formation of flows with high kinetic energy, which can produce devastating landslides. In this context, the remarkable development of settlements in the island, occurred in recent times, and the lack of planning that bring attention to the vulnerability of the area, have produced an exponential risk increase. Eruptions, earthquakes, flooding occurred in the island of Ischia in the past, have produced a wealth literature about catastrophic natural events. In general, the accounts of the events were recorded by various means, such as: newspaper, property disputes, historical and sociological analysis, poetic or artistic works, scientific analysis. As regard volcanism, earthquakes, tsunamis, there are myths, legends, historical documents, archaeological findings and results of recent surveys. Documented descriptions of historical eruptive events are only available for the last eruption of 1301-1302, while there are records for eruptive events in the early centuries of the Christian Age. More comprehensive accounts are available about historical seismicity. Information and documentations are available since the 1228 earthquake. However, more detailed and useful

  3. Restoration of new volcanic gas analyses from basalts of the afar region: Further evidence of CO 2 -degassing trends

    NASA Astrophysics Data System (ADS)

    Gerlach, T. M.

    1981-05-01

    The restored compositions for approximately 70 new analyses reported recently for Erta'Alelava lake (LeGuern et al., 1979) are in good agreement with restored compositions (Gerlach, 1980a) based on previously published data. The results confirm earlier indications that gas collections taken at different times from the lava lake are related principally by variations in CO 2 content. Restored compositions for gas samples collected in the final stages of a November 1978 Ardoukoba eruption along the Asal Rift spreading axis resemble the Erta'Ale gases except for a much lower CO 2 content. The Ardoukoba gases fall close to a CO 2-decreasing control line for gases with initial compositions similar to the 1971-1973 Erta'Ale gases. These results suggest that gases released from basaltic lava along zones of crustal spreading follow compositional trends dominated by changes in CO 2 content.

  4. Silicic Volcanism at the Northern and Western Extent of the Columbia River Basalt Rhyolite Flare-up: Rhyolites of Dooley Mountain and Buchanan, Oregon

    NASA Astrophysics Data System (ADS)

    Large, A.; Streck, M. J.; Jenkins, E. N.; Ferns, M. L.

    2015-12-01

    Mid-Miocene (16.5-15 Ma) rhyolite volcanism associated with the eruption of lavas of the Columbia River Basalt Group (CRBG) stretches from NE Nevada to SW Idaho to NE Oregon over an area with about a 400 km diameter. Dooley Mountain and Buchanan rhyolite complexes are located along the northern termination near Baker City and along the western periphery near Burns of this rhyolite flare-up, respectively. Despite their importance for understanding co-genetic rhyolite volcanism to CRBG magmatism prior data on both complexes are sparse. Limited geochemical data exist only for Dooley Mountain and there is only one age date for either complex. Our ongoing study of both complexes is targeted to establish eruptive units and stratigraphy, to determine activity span, and to detail the petrology of rhyolite units by mapping or remapping key areas building on prior work (e.g., Evans, J. G., 1992, U.S.G.S. Map GQ-1694), by petrographic analysis and whole rock geochemistry, and by Ar-Ar geochronology. Both complexes are multi-phase, apparently long-lived centers that erupted mostly rhyolite lava flows and domes but locally derived pyroclastic units occur as well but are subordinate in volume. Rhyolite activity is currently pinned at 15.5-14.7 Ma at Dooley Mountain and at 16.1 Ma at Buchanan but is expected to be extending with more dating. Rhyolites range from aphyric to containing ~ 15% phenocrysts dominated by feldspar or quartz. Rhyolites range from low- to high-silica varieties and indicate variable degrees of differentiation as established by the following ranges for Ba, Sr, and Eu/Eu*, respectively: 1500-500, 200-75, 0.6-0.15 for Dooley Mountain and 1700-100, 250-8, 0.88-0.19 for Buchanan. In addition, preliminary data indicate rhyolites range in their affinity from calc-alkaline to more A-type rhyolites. We speculate that A-type varieties coincide in these peripheral rhyolite complexes with the peak of Grande Ronde Basalt activity that impacted the greater area.

  5. Petrology and Eruptive Styles of Central WA Teanaway Basalt: Uplift and Bimodal Volcanism in Subsiding Eocene Basin

    NASA Astrophysics Data System (ADS)

    Ivener, D.; Tepper, J. H.

    2013-12-01

    The 47 Ma Teanaway Basalt (TB) is a bimodal unit that erupted in Central Washington during the poorly-understood Challis Event. The TB consists of over 2500 meters of subaerial mafic flows, hyaloclastite, rhyolite domes, and tuff. In order to better understand the origin and tectonic setting of the TB, we have studied three localities that encompass the geographic extent of the unit: Easton Ridge (ER), Teanaway River Middle Fork (MF), and Liberty Ridge (LR). The TB lies stratigraphically between two thick arkosic sedimentary units (Swauk and Roslyn Formations) that are thought to have accumulated in a rapidly subsiding basin (Tabor et al., 1990). The gently-dipping, 380 meter thick, MF section is comprised of subaerial flows interbedded with hyaloclastite layers; no pillows were observed. These observations suggest that the TB erupted in shallow water and that the rate of subsidence was approximately equal to the rate of construction. In addition, the absence of arkosic interbeds within the MF section suggests that the sediment supply to the basin was interrupted during TB eruptions and/or that the basin was a highland during this period. Based on tectonic reconstructions (Heller et al., 1987), which place the Kula-Farallon Ridge in this area during the Eocene, we suggest that uplift during TB magmatism is a result of ridge subduction. Furthermore, the evidence of extensional dikes at a convergent margin can be accounted for by the subduction of a spreading ridge. Mafic TB lavas are moderately evolved (45.2 - 63.1 wt. % SiO2, Mg # = 0.13-0.48). These rocks are aphanitic to very fine-grained with sparse phenocrysts of plagioclase. These flows are commonly either massive or display spectacular columnar jointing and range in thickness from less than two feet to almost 150 feet (Clayton, 1973). They show extensive compositional overlap with dikes in the underlying Swauk Formation although the dikes tend to be slightly more primitive. These data support interpretation

  6. On the potential for CO2 mineral storage in continental flood basalts - PHREEQC batch- and 1D diffusion-reaction simulations.

    PubMed

    Van Pham, Thi Hai; Aagaard, Per; Hellevang, Helge

    2012-01-01

    Continental flood basalts (CFB) are considered as potential CO2 storage sites because of their high reactivity and abundant divalent metal ions that can potentially trap carbon for geological timescales. Moreover, laterally extensive CFB are found in many place in the world within reasonable distances from major CO2 point emission sources.Based on the mineral and glass composition of the Columbia River Basalt (CRB) we estimated the potential of CFB to store CO2 in secondary carbonates. We simulated the system using kinetic dependent dissolution of primary basalt-minerals (pyroxene, feldspar and glass) and the local equilibrium assumption for secondary phases (weathering products). The simulations were divided into closed-system batch simulations at a constant CO2 pressure of 100 bar with sensitivity studies of temperature and reactive surface area, an evaluation of the reactivity of H2O in scCO2, and finally 1D reactive diffusion simulations giving reactivity at CO2 pressures varying from 0 to 100 bar.Although the uncertainty in reactive surface area and corresponding reaction rates are large, we have estimated the potential for CO2 mineral storage and identified factors that control the maximum extent of carbonation. The simulations showed that formation of carbonates from basalt at 40 C may be limited to the formation of siderite and possibly FeMg carbonates. Calcium was largely consumed by zeolite and oxide instead of forming carbonates. At higher temperatures (60 - 100 C), magnesite is suggested to form together with siderite and ankerite. The maximum potential of CO2 stored as solid carbonates, if CO2 is supplied to the reactions unlimited, is shown to depend on the availability of pore space as the hydration and carbonation reactions increase the solid volume and clog the pore space. For systems such as in the scCO2 phase with limited amount of water, the total carbonation potential is limited by the amount of water present for hydration of basalt

  7. On the potential for CO2 mineral storage in continental flood basalts – PHREEQC batch- and 1D diffusion–reaction simulations

    PubMed Central

    2012-01-01

    Continental flood basalts (CFB) are considered as potential CO2 storage sites because of their high reactivity and abundant divalent metal ions that can potentially trap carbon for geological timescales. Moreover, laterally extensive CFB are found in many place in the world within reasonable distances from major CO2 point emission sources. Based on the mineral and glass composition of the Columbia River Basalt (CRB) we estimated the potential of CFB to store CO2 in secondary carbonates. We simulated the system using kinetic dependent dissolution of primary basalt-minerals (pyroxene, feldspar and glass) and the local equilibrium assumption for secondary phases (weathering products). The simulations were divided into closed-system batch simulations at a constant CO2 pressure of 100 bar with sensitivity studies of temperature and reactive surface area, an evaluation of the reactivity of H2O in scCO2, and finally 1D reactive diffusion simulations giving reactivity at CO2 pressures varying from 0 to 100 bar. Although the uncertainty in reactive surface area and corresponding reaction rates are large, we have estimated the potential for CO2 mineral storage and identified factors that control the maximum extent of carbonation. The simulations showed that formation of carbonates from basalt at 40 C may be limited to the formation of siderite and possibly FeMg carbonates. Calcium was largely consumed by zeolite and oxide instead of forming carbonates. At higher temperatures (60 – 100 C), magnesite is suggested to form together with siderite and ankerite. The maximum potential of CO2 stored as solid carbonates, if CO2 is supplied to the reactions unlimited, is shown to depend on the availability of pore space as the hydration and carbonation reactions increase the solid volume and clog the pore space. For systems such as in the scCO2 phase with limited amount of water, the total carbonation potential is limited by the amount of water present for hydration of basalt

  8. Emplacement history and inflation evidence of a long basaltic lava flow located in Southern Payenia Volcanic Province, Argentina

    NASA Astrophysics Data System (ADS)

    Bernardi, Mauro I.; Bertotto, Gustavo W.; Jalowitzki, Tiago L. R.; Orihashi, Yuji; Ponce, Alexis D.

    2015-02-01

    The El Corcovo lava flow, from the Huanul shield volcano in the southern Mendoza province (central-western Argentina) traveled a distance of 70 km and covered a minimum area of ~ 415 km2. The flow emplacement was controlled both by extrinsic (e.g., topography) and intrinsic (e.g., lava supply rate, lava physicochemical characteristics) factors. The distal portion of the lava flow reached the Colorado River Valley, in La Pampa Province, where it spread and then was confined by earlier river channels. Cross-sections through the flow surveyed at several localities show two vesicular layers surrounding a dense central section, where vesicles are absent or clustered in sheet-shaped and cylindrical-shaped structures. Lavas of the El Corcovo flow are alkaline basalts with low values of viscosity. The morphological and structural characteristics of the flow and the presence of landforms associated with lava accumulation are the evidence of inflation. This process involved the formation of a tabular sheet flow up to 4 m of thick with a large areal extent in the proximal sectors, while at terminal sectors frontal lobes reached inflation values up to 10 m. The numerous swelling structures present at these portions of the flow suggest the movement of lava in lava tubes. We propose that this aspect and the low viscosity of the lava allowed the flow travel to a great distance on a gentle slope relief.

  9. Using AVIRIS Data to Map and Characterize Subaerially and Subaqueously Erupted BasalticVolcanic Tephras: The Challenge of Mapping Low-Albedo Materials

    NASA Technical Reports Server (NTRS)

    Farrand, William H.

    2004-01-01

    Increases in the signal-to-noise ratio (SNR) in AVIRIS has enabled the mapping and characterization of low albedo materials. Low albedo materials of interest include certain soils, man-made materials (asphalt, certain building materials, tires, etc.), and basaltic lava flows and ashes. Early in its history, the response of the AVIRIS sensor was not sensitive enough so that these low albedo materials could be reliably mapped. However, as indicated by Green and Pavri (2002) the noise equivalent delta radiance (NEdL) of AVIRIS in the 2001 flight season was below 0.010 in all but the shortest wavelength channels. This is approximately a ten-fold improvement from the 1989 flight season when NEdL was closer to 0.1 (Green et al., 1990). In the current investigation, AVIRIS data from the 2002 flight season collected over the Pavant Butte tuff cone, Tabernacle Hill tuff ring, and an associated lava flow in the Black Rock Desert of west central Utah were examined to determine how well these generally low albedo volcanic lavas and tephras could be discriminated from background materials. The Pavant Butte tuff cone was examined by the author in an earlier study with a 1989 AVIRIS dataset (Farrand and Singer,

  10. Subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling, Lake Purrumbete Maar, Newer Volcanics Province, southeastern Australia

    NASA Astrophysics Data System (ADS)

    van den Hove, Jackson C.; Ailleres, Laurent; Betts, Peter G.; Cas, Ray A. F.

    2015-10-01

    Lake Purrumbete Maar (LPM) is situated in the Late Cenozoic intraplate, basaltic Newer Volcanics Province, southeastern Australia. It is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake. Gellibrand Marl accidental lithics, which occurs to a maximum depth of 250 m below LPM, represent the deepest excavated host rock unit present in the volcanic succession. Irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption. High-resolution lake- and land-based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar. This is done to test the assumption, based on lithics, that the diatreme is limited to 250 m depth and identify the reasons behind LPM's large size. The collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces (< 1 mGal) associated with the maar, on an inherently unstable water body. The magnetic anomaly over LPM shows several irregularly shaped high magnetic anomalies. Four 2.5-D forward models transecting LPM were constructed based on the observed potential field data. Five coalesced vents forming an undulating shallow bowl-shaped diatreme contained within the Gellibrand Marl (240 m depth) were modelled to satisfy the observed magnetic response, while a large sill body at 350 m depth is modelled to satisfy the observed gravity response. A second forward model, completed to satisfy the observed magnetic response, also includes coalesced shallow bowl-shaped diatremes within the Gellibrand Maar, which then taper down to become thin and steep sided and extend down to the basement (1,050 m depth). Three-dimensional property and geometry inversions suggest the diatreme most likely extends to a greater depth than the initial maximum depth of 240 m. This suggests the

  11. Longevity of Yellowstone hotspot volcanism: Isotopic evidence linking the Siletzia LIP (56 Ma) and early Columbia River Basalt Group (17 Ma) mantle sources

    NASA Astrophysics Data System (ADS)

    Pyle, D. G.; Duncan, R. A.; Wells, R. E.; Graham, D. W.; Hanan, B. B.; Harrison, B. K.; Haileab, B.

    2015-12-01

    Siletzia is a Paleocene-Eocene accreted terrane of submarine and subaerially erupted mafic lavas exposed in the Cascadia forearc. This large igneous province [LIP] is exposed in multiple volcanic sections from Vancouver Island, B.C., to southern Oregon [~700 km]. We estimate Siletzia magmatism at ~2.3 x 106 km3 west of the Cascades and may reach 4.6 x 106 km3 if correlative with Alaskan Yakutat terrane and significant portions of the LIP filled the Oregon Embayment. 40Ar-39Ar ages show the bulk of Siletzia erupted over a 6-7 Myr interval beginning at 56 Ma, implying eruption rates of 0.3-0.7 km3/yr. In Oregon, Siletz River volcanism began in the south [56-53 Ma] and migrated northward [54-50 Ma]. Concurrent eruptions of Metchosin and Crescent basalts do not show a southerly age progression. Therefore, Siletzia likely erupted south of the Kula-Farallon spreading center with ridge collision at or north of the Metchosin igneous complex. Isotopic data for 29 Siletzia lavas have initial 7/6Sr 0.7030-0.7037, ΕNd +4.9 - +7.7, 6/4Pb 18.70-19.94, 7/4Pb 15.49-15.63 and 8/4Pb 38.27-39.53. Olivine yield 3He/4He from 9.4 to 13.7 (R/Ra) and high MgO lavas display a narrow 187Os/188Os range (0.131-0.134) when age corrected. Both He and Os tracers are elevated above typical depleted MORB mantle and indicate plume involvement. Pb-Pb and Pb-Nd arrays suggest 3 mantle components for Siletzia volcanism: a depleted source with isotopic and trace element characteristics expected for spreading center lavas (i.e., Ku-Fa) influenced by a plume, a HIMU contaminant (i.e., high 6/4Pb; low 7/6Sr) confined to southern Siletzia, and a plume source (6/4Pb 19.00; 7/4Pb 15.55; 8/4Pb 38.60; 7/6Sr; 0.7033; ΕNd +6.4; γOs +5.0). Siletzia plume mantle is a close match to recent Yellowstone plume estimates based on early CRBG lavas. Mounting geophysical and geochemical evidence supports the contention that Siletzia is an early product of the Yellowstone hot spot in a sub-oceanic setting.

  12. Geochemistry of the Palitana flood basalt sequence and the Eastern Saurashtra dykes, Deccan Traps: clues to petrogenesis, dyke-flow relationships, and regional lava stratigraphy

    NASA Astrophysics Data System (ADS)

    Sheth, Hetu C.; Zellmer, Georg F.; Kshirsagar, Pooja V.; Cucciniello, Ciro

    2013-04-01

    Recent studies of large mafic dyke swarms in the Deccan Traps flood basalt province, India, indicate that some of the correlative lava flows reached several hundred kilometers in length. Here we present field, petrographic, mineral chemical, and whole-rock geochemical (including Sr-Nd isotopic) data on the Palitana lava sequence and nearby dykes in the Saurashtra region of the northwestern Deccan Traps. These rocks are moderately evolved, many with low-Ti-Nb characteristics. We infer that most dykes are notably (and systematically) less contaminated by ancient continental crust than the Palitana flows, but four dykes are equally or significantly more contaminated, with some of the most extreme Sr-Nd isotopic compositions seen in the entire Deccan Traps (initial ɛNd is as low as -18.0). A Bhimashankar-type and a Poladpur-type dyke are present several hundred kilometers from the type section of these magma types in the Western Ghats escarpment. We find no geochemical correlations between the Palitana sequence and three subsurface sequences in NE Saurashtra containing abundant picritic rocks, surface lavas previously studied from Saurashtra, or the Western Ghats sequence. Intriguingly, the Eastern Saurashtra dykes cannot have been feeders to any of these lava sequences. Feeder dykes of these sequences may be located in southwestern or central Saurashtra, or in the Dhule-Nandurbar-Dediapada areas across the Gulf of Cambay, 200-300 km east of Palitana. Our results indicate polycentric flood basalt eruptions not only on the scale of the Deccan Traps province, but also within the Saurashtra region itself.

  13. Geochronology and geochemistry of late Cenozoic basalts from the Leiqiong area, southern China

    NASA Astrophysics Data System (ADS)

    Ho, Kung-suan; Chen, Ju-chin; Juang, Wen-shing

    2000-06-01

    The Leiqiong area, which includes the Leizhou Peninsula and the northern part of the Hainan Island, is the largest province of exposed basalts in southern China. Ar-Ar and K-Ar dating indicates that incipient volcanism in the Leiqiong area may have taken place in late Oligocene time and gradually increased in tempo toward the Miocene and Pliocene Epoch. Volcanic activities were most extensive during Pleistocene, and declined and ended in Holocene. Based on radiometric age dating and geographic distribution, Pliocene and Quaternary volcanism in Hainan Island can be grouped into two stages and six eruptive regions. The early volcanism is dominated by flood type fissure eruption of quartz tholeiites and olivine tholeiites whereas the later phase is dominated by central type eruption of alkali olivine basalts and olivine tholeiites. The systematic decrease of MgO, ΣFeO and TiO 2 with increasing SiO 2 content for basalts from Hainan Island indicates that fractional crystallization of olivine, clinopyroxene and Ti-bearing opaques may have occurred during magmatic evolution. From coexisting Fe-Ti oxide minerals, it is estimated that the equilibrium temperatures range from 895-986°C and oxygen fugacities range from 10 -13.4 to 10 -10.7 atmospheres in the basaltic magmas. The incompatible element ratios and the chondrite-normalized REE patterns of basalts from the Leiqiong area are generally similar to OIB. The Nb/U ratios (less than 37) in most of the tholeiitic rocks and the negative Nb anomaly observed in the spidergram of some basalts indicated that the influence of a paleo-subduction zone derived component can not be excluded in considering the genesis of the basalts from the Leiqiong area. The tholeiites in the Leiqiong area may have mixed with a more enriched lithospheric mantle component as well as undergone relatively larger percentages of partial melting than the alkali basalts.

  14. InSAR observations of aseismic slip associated with an earthquake swarm in the Columbia River flood basalts

    USGS Publications Warehouse

    Wicks, C.; Thelen, W.; Weaver, C.; Gomberg, J.; Rohay, A.; Bodin, P.

    2011-01-01

    In 2009 a swarm of small shallow earthquakes occurred within the basalt flows of the Columbia River Basalt Group (CRBG). The swarm occurred within a dense seismic network in the U.S. Department of Energys Hanford Site. Data from the seismic network along with interferometric synthetic aperture radar (InSAR) data from the European Space Agencys (ESA) ENVISAT satellite provide insight into the nature of the swarm. By modeling the InSAR deformation data we constructed a model that consists of a shallow thrust fault and a near horizontal fault. We suggest that the near horizontal lying fault is a bedding-plane fault located between basalt flows. The geodetic moment of the modeled fault system is about eight times the cumulative seismic moment of the swarm. Precise location estimates of the swarm earthquakes indicate that the area of highest slip on the thrust fault, ???70mm of slip less than ???0.5km depth, was not located within the swarm cluster. Most of the slip on the faults appears to have progressed aseismically and we suggest that interbed sediments play a central role in the slip process. Copyright 2011 by the American Geophysical Union.

  15. The role of basalt weathering on climate: the Siberian traps

    NASA Astrophysics Data System (ADS)

    Grard, A.; François, L.; Dessert, C.; Dupré, B.; Goddéris, Y.

    2003-04-01

    The Siberian traps represent one of the most important flood basalt provinces on Earth. Their onset coincides with a profound faunal mass extinction at the Permo-Trias boundary (250 my ago). The volcanic eruption has also environmental and climatic effects through aerosols and gases injection into the atmosphere. Chemical weathering processes play a major role in biogeochemical cycles and climate evolution. In particular, the weathering of silicate rocks represents an important sink of atmospheric CO_2. At the million-year timescale, the volcanic release of CO_2 into the atmosphere-ocean system is balanced by its consumption during silicate weathering followed by carbonate deposition on the seafloor. Recent data have shown that chemical weathering of basalt is five to ten times more efficient than weathering of acidic silicate rocks such as granite or gneiss (Dessert et al., EPSL, 188 : 459-474, 2001). Thus the weathering of basaltic rocks consumes more atmospheric CO_2 than other silicate rocks. In the case of subaerial basaltic volcanism, an eruption not only releases CO_2 to the atmosphere, but also produces basaltic rocks which weather rapidly, enhancing CO_2 consumption rates. Currently, the Siberian basaltic traps are located in a cold and dry region. The weathering rates of this province are low, and the climatic impact is thus currently low. But in the past, the latitudinal temperature gradient was smaller. During the Permian, the climate was significantly warmer than today. Thus the chemical weathering of the Siberian traps was enhanced at that time, and this process led to a long-term impact on the Triassic climate and on the carbon cycle. The used model calculates the traps impact on the long-term carbon cycle and climate evolution. This model has been refined and adapted to high latitudes environments. We quantify the cooling caused by traps weathering.

  16. Plumbing of continental basaltic volcanoes from the mantle to the surface, 1: Insights from field relationships at the Lunar Crater Volcanic Field (Nevada, USA)

    NASA Astrophysics Data System (ADS)

    Valentine, G. A.; Cortes, J. A.; Widom, E.; Smith, E. I.

    2011-12-01

    Monogenetic intraplate volcanoes offer unique insights into the linkages between magma sources, crustal ascent, and eruption processes. We focus here on the northernmost part of the Lunar Crater Volcanic Field (LCVF), Nevada, with ~45 monogenetic volcanoes in a 10 km long, 5 km wide band. Within that band, many volcanoes occur in localized clusters with up to 5 volcanoes (of different ages) per square kilometer. Most of the clusters are elongated in a direction that parallels the trend of the LCVF as a whole. Currently it is uncertain whether such clusters are related to faults in the underlying rocks because of the thick, young cover of basaltic volcanic products. However, in other areas, especially along the periphery of the volcanic field, vents often correspond with pre-existing normal faults, and it seems likely that elongated clusters represent areas of repeated (over time scales of ~1-2 Ma) injection of feeder dikes into faults in the shallow crust. The edges of the volcanic field in the northernmost part are defined by sharp boundaries, where there is a sharp transition from high volcano concentration on one side, to no volcanoes on the other. A fundamental question is whether this transition reflects a similar spatial distribution in the mantle source area, or whether it is due entirely to shallow structural controls on magma ascent. The northernmost part of the LCVF provides an ideal case study for testing relationships between physical parameters (volume, fissure length, eruptive style) and geochemistry. We focus on three volcanoes, two of which are closely spaced (~500 m) but occurred at times separated by 100s ka (based upon surface morphology). The older of these two, informally called the OPB volcano (older, phenocryst bearing) is likely mid-Pleistocene in age; the younger is referred to as YMB (younger, megacrysts bearing). The third volcano, previously named Marcath/Black Rock, is the youngest in the volcanic field, located ~4 km southwest of OPB

  17. Black swans, power laws, and dragon-kings: Earthquakes, volcanic eruptions, landslides, wildfires, floods, and SOC models

    NASA Astrophysics Data System (ADS)

    Sachs, M. K.; Yoder, M. R.; Turcotte, D. L.; Rundle, J. B.; Malamud, B. D.

    2012-05-01

    Extreme events that change global society have been characterized as black swans. The frequency-size distributions of many natural phenomena are often well approximated by power-law (fractal) distributions. An important question is whether the probability of extreme events can be estimated by extrapolating the power-law distributions. Events that exceed these extrapolations have been characterized as dragon-kings. In this paper we consider extreme events for earthquakes, volcanic eruptions, wildfires, landslides and floods. We also consider the extreme event behavior of three models that exhibit self-organized criticality (SOC): the slider-block, forest-fire, and sand-pile models. Since extrapolations using power-laws are widely used in probabilistic hazard assessment, the occurrence of dragon-king events have important practical implications.

  18. Floods

    MedlinePlus

    Floods are common in the United States. Weather such as heavy rain, thunderstorms, hurricanes, or tsunamis can ... is breached, or when a dam breaks. Flash floods, which can develop quickly, often have a dangerous ...

  19. Pre-eruptive volatile and erupted gas phase characterization of the 2014 basalt of Bárðarbunga volcanic system, Iceland.

    NASA Astrophysics Data System (ADS)

    Haddadi, Baptiste; Moune, Séverine; Sigmarsson, Olgeir; Gauthier, Pierre-Jean; Gouhier, Mathieu

    2015-04-01

    The 2014 Holuhraun eruption on the Bárðarbunga Volcanic System is the largest fissure eruption in Iceland since the 1783 Laki eruption. The eruption started end of August 2014 and has been characterized by large emission of SO2 into the atmosphere. It provides a rare opportunity to study in details magmatic and degassing processes during a large-volume fissure eruption. In order to characterize the pre-eruptive magmatic composition and to assess the plume chemistry at the eruption site, lava and tephra were sampled together with the eruption plume. The basalt composition is olivine tholeiite with MgO close to 7 wt%. It is phenocryst-poor with plagioclase as the dominant mineral phase but olivine and clinopyroxene are also present together with sulphide globules composed principally of pyrite and chalcopyrite. The volatile (S, Cl and F) and major element concentrations were measured by the electron microprobe in melt inclusions (MIs) trapped in plagioclase and clinopyroxene and groundmass glass. The MIs composition ranges from fairly primitive basaltic compositions (MgO: 9.03 wt%) down to evolved qz-tholeiites (MgO: 5.57 wt%), with estimated pre-eruptive S concentrations of 1500 ppm. Tephra groundmass glass contains 400 ppm S, whereas Cl and F concentrations are respectively slightly lower and indistinguishable from those in the MIs. This implies limited exsolution of halogens but 75% of the initial sulphur content. Relatively to their total iron content, MIs are sulphur saturated, and their oxygen fugacity close to the FMQ buffer. The difference between the estimated initial volatile concentrations measured in the MIs and in the tephra groundmass (i.e. the so-called petrological method) yields 7.2 Mt SO2, limited HCl and no HF atmospheric mass loading from the Holuhraun 2014 eruption. The SO2/HCl molar ratio of the gas phase, calculated from the MIs, is 13 and 14, respectively, using average and estimated pre-eruptive S and Cl concentrations in the MIs. Filter

  20. Hydrous basalt-limestone interaction at crustal conditions: Implications for generation of ultracalcic melts and outflux of CO2 at volcanic arcs

    NASA Astrophysics Data System (ADS)

    Carter, Laura B.; Dasgupta, Rajdeep

    2015-10-01

    High degassing rates for some volcanoes, typically in continental arcs, (e.g., Colli Albani Volcanic District, Etna, Vesuvius, Italy; Merapi, Indonesia; Popocatepetl, Mexico) are thought to be influenced by magma-carbonate interaction in the crust. In order to constrain the nature of reaction and extent of carbonate breakdown, we simulated basalt-limestone wall-rock interactions at 0.5-1.0 GPa, 1100-1200 °C using a piston cylinder and equal mass fractions of calcite (CaCO3) and a hydrous (∼4 wt.% H2O) basalt in a layered geometry contained in AuPd capsules. All experiments produce melt + fluid + calcite ± clinopyroxene ± plagioclase ± calcic-scapolite ± spinel. With increasing T, plagioclase is progressively replaced by scapolite, clinopyroxene becomes CaTs-rich, and fluid proportion, as inferred from vesicle population, increases. At 1.0 GPa, 1200 °C our hydrous basalt is superliquidus, whereas in the presence of calcite, the experiment produces calcite + clinopyroxene + scapolite + melt. With the consumption of calcite with increasing T and decreasing P, melt, on a volatile-free basis, becomes silica-poor (58.1 wt.% at 1.0 GPa, 1100 °C to 34.9 wt.% at 0.5 GPa, 1200 °C) and CaO-rich (6.7 wt.% at 1.0 GPa, 1100 °C to 43.7 wt.% at 0.5 GPa, 1200 °C), whereas Al2O3 drops (e.g., 19.7 at 1100 °C to 12.8 wt.% at 1200 °C at 1.0 GPa) as clinopyroxene becomes more CaTs-rich. High T or low P melt compositions are 'ultracalcic,' potentially presenting a new hypothesis for the origin of ultracalcic melt inclusions in arc lava olivines. Wall-rock calcite consumption is observed to increase with increasing T and decreasing P. At 0.5 GPa, our experiments yield carbonate assimilation from 21.6 to 47.6% between 1100 and 1200 °C. Using measured CO2 outflux rates for Mts. Vesuvius, Merapi, Etna and Popocatepetl over a T variation of 1100 to 1200 °C at 0.5 GPa, we calculate 6-92% of magmatic input estimates undergo this extent of assimilation, suggesting that up to ∼3

  1. 40Ar/39Ar incremental heating experiments on celadonite from the Skessa Tuff, eastern Iceland: Thermochronology of low-temperature alteration of a flood basalt pile during burial metamorphism

    NASA Astrophysics Data System (ADS)

    Riishuus, M. S.; Miggins, D. P.; Koppers, A. A. P.; Duncan, R. A.

    2014-12-01

    burial rate is 2x that of estimates from contemporaneous sections located away from central volcanoes. Considering the proximity of the sampling site to Thingmuli, it seems reasonable to expect a greater burial rate. Thermochronology and celadonite 40Ar/39Ar dating can unravel tectono-magmatic processes associated with the burial of flood basalt piles.

  2. Gas slug rise in open versus plugged basaltic conduits: the transition from Strombolian to sustained volcanic eruptions

    NASA Astrophysics Data System (ADS)

    Llewellin, Ed; Mathias, Simon; Del Bello, Elisabetta; Lane, Steve; Taddeucci, Jacopo

    2010-05-01

    Strombolian eruptions are characterized by low-energy explosive activity, which may repeat, at fairly regular intervals, for long periods of time. Explosions at the vent are thought to result from the arrival of discrete slugs of magmatic gas that have risen through the magmatic plumbing system. We develop a one dimensional, analytical model of gas slug rise in a volcanic conduit which we use to investigate the controls on the dynamics of Strombolian eruptions. We consider a partially-filled, cylindrical conduit containing degassed magma, that is initially in magma-static equilibrium with a constant pressure magma reservoir at depth. We introduce a slug of gas at the base of the conduit and consider the temporal evolution of the pressure distribution in the conduit, and the motion of the magma above and below the slug, as the slug rises, decompresses, and expands isothermally. We validate our model against published data for gas slugs rising and decompressing in a vertical pipe [James et al., 2008, Geological Society of London, Special Publications 307, 147-167] by imposing the condition of zero magma-flux at the base of the conduit, and constant pressure at the top; we find excellent agreement. If we impose the more geologically-sound condition of constant pressure at the base of the conduit, we can consider two scenarios of volcanological relevance: 1) Vent plugged with cooler, more-viscous magma. In this case, as the slug rises and expands beneath the plug, it pushes the degassed magma below it down the conduit, consequently, magma re-enters the chamber from the base of the conduit. The slug reaches the viscous plug at the top of the conduit with a significant over-pressure; this may be sufficient to disrupt the plug, causing a Strombolian explosion, or the gas may percolate away. Fresh magma then moves up from the chamber, into the conduit to restore magma-static equilibrium. 2) Open vent. As the slug rises and expands, the volume of magma held in the falling

  3. Characterization of the sub-continental lithospheric mantle beneath the Cameroon volcanic line inferred from alkaline basalt hosted peridotite xenoliths from Barombi Mbo and Nyos Lakes

    NASA Astrophysics Data System (ADS)

    Pintér, Zsanett; Patkó, Levente; Tene Djoukam, Joëlle Flore; Kovács, István; Tchouankoue, Jean Pierre; Falus, György; Konc, Zoltán; Tommasi, Andréa; Barou, Fabrice; Mihály, Judith; Németh, Csaba; Jeffries, Teresa

    2015-11-01

    We carried out detailed petrographic, major and trace element geochemical, microstructural and FTIR analyses on eight characteristic ultramafic xenoliths from Nyos and Barombi Mbo Lakes in the continental sector of the Cameroon Volcanic Line (CVL). The studied xenoliths are spinel lherzolites showing lithologies similar to the other xenoliths reported previously along the CVL. They have protogranular and porphyroclastic textures. One of the Barombi xenolith contains amphibole, which had not been previously reported in this locality. Amphibole is common in the Nyos xenoliths suite. Peridotite xenoliths from both localities show some chemical heterogeneity, but Barombi xenoliths generally are less depleted in basaltic elements with respect to Nyos xenoliths. Trace element compositions of Nyos spinel lherzolites show a moderately depleted initial (premetasomatic) composition and variable enrichment in REE. Evidence for both modal and cryptic metasomatism is present in Nyos xenoliths. Rare earth element patterns of clinopyroxene suggest that interaction between mafic melts and the upper mantle occurred beneath the Nyos locality. Barombi Mbo xenoliths, on the other hand, record a small degree of partial melting. The Barombi Mbo xenoliths have weak, dominantly orthorhombic olivine crystal preferred orientations, whereas Nyos ones have strong axial-[010] patterns, which may have formed in response to transpression. Nominally anhydrous mantle minerals (NAMs) of the Barombi Mbo xenoliths show generally higher bulk concentrations of 'water' (70-127 ppm) than Nyos xenoliths (32-81 ppm). The Barombi Mbo xenoliths could originate from a juvenile segment of the lithospheric mantle, which had been originally part of the asthenosphere. It became a part of the lithosphere in response to thermal relaxation following the extension, forming a weakly deformed lower lithospheric mantle region along the CVL. The Nyos xenoliths, however, represent a shallow lithospheric mantle bearing

  4. Basaltic Ring Structures as an Analog for Ring Features in Athabasca Valles, Mars

    NASA Technical Reports Server (NTRS)

    Jaeger, W. L.; Keszthelyi, L. P.; Burr, D. M.; Emery, J. P.; Baker, V. R.; McEwen, A. S.; Miyamoto, H.

    2005-01-01

    Basaltic ring structures (BRSs) are enigmatic, quasi-circular landforms in eastern Washington State that were first recognized in 1965. They remained a subject of geologic scrutiny through the 1970 s and subsequently faded from the spotlight, but recent Mars Orbiter Camera (MOC) images showing morphologically similar structures in Athabasca Valles, Mars, have sparked renewed interest in BRSs. The only known BRSs occur in the Channeled Scabland, a region where catastrophic Pleistocene floods from glacial Lake Missoula eroded into the Miocene flood basalts of the Columbia Plateau. The geologic setting of the martian ring structures (MRSs) is similar; Athabasca Valles is a young channel system that formed when catastrophic aqueous floods carved into a volcanic substrate. This study investigates the formation of terrestrial BRSs and examines the extent to which they are appropriate analogs for the MRSs in Athabasca Valles.

  5. Highly siderophile element behaviour during flood basalt genesis and evidence for melts from intrusive chromitite formation in the Mackenzie large igneous province

    NASA Astrophysics Data System (ADS)

    Day, James M. D.; Pearson, D. Graham; Hulbert, Larry J.

    2013-12-01

    The 1.27 Ga Coppermine continental flood basalt (CFB) province in northern Canada represents the extrusive manifestation of the 2.7 Mkm2 Mackenzie large igneous province (LIP) that includes the Mackenzie dyke swarm and the Muskox layered intrusion. New Re-Os isotope and highly siderophile element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundance data are reported together with whole-rock major- and trace-element abundances and Nd isotopes to examine the behaviour of the HSE during magmatic differentiation and to place constraints on the extent of crustal interaction with mantle-derived melts. Mineral chemistry and petrography are also reported for an unusual andesite glass flow (CM19; 4.9 wt.% MgO) found in close proximity to newly recognised picrites (> 20 wt.% MgO) in the lowermost stratigraphy of the Coppermine CFB. Compositions of mineral phases in CM19 are similar to the same phases found in Muskox Intrusion chromitites and the melt composition is equivalent to inclusions trapped within Muskox chromites. The apparently conflicting elevated HSE contents (e.g., 3.8 ppb Os) and mantle-like initial 187Os/188Os (γOs = + 2.2), versus stable isotope (δ18O = + 12‰) and lithophile element evidence (εNdi = - 12.8) for extensive crustal contamination, implicate an origin for CM19 as a magma mingling product formed within the Muskox Intrusion during chromitite genesis. Combined with Nd isotope data that places the feeder for lower Coppermine CFB picrites and basalts within the Muskox Intrusion, this result provides compelling evidence for direct processing of some CFB within upper-crustal magma chambers. The Coppermine CFB defines a 187Re-187Os isochron with an age of 1263 + 16/- 20 Ma and initial γOs = + 2.2 ± 0.8. The initial Os isotope composition for the Coppermine CFB is slightly higher than the near-primitive-mantle initial 187Os/188Os for the Muskox Intrusion (γOs = + 1.2 ± 0.3). This result is interpreted to reflect greater crustal contamination in extrusive CFB

  6. Paleomagnetic Correlation of Late Miocene-Pliocene Basalt Flows in the Northwestern Basin and Range: Documenting Timing of Faulting, Volcanism and Vertical-axis Rotation in Surprise Valley, Northeastern California

    NASA Astrophysics Data System (ADS)

    Ritzinger, B. T.; Glen, J. M. G.; Egger, A. E.

    2014-12-01

    Examining the temporal and spatial relationship between basaltic volcanism and extensional faulting can help delineate the influence of faulting on the location of source vents and distribution of subsequent lava flows. Young extensional environments offer a unique opportunity to resolve the interdependence of faulting and volcanism as faults have not yet been buried and precise ages can be acquired on volcanic rocks. The Larkspur Hills, located along the northwestern margin of the Basin and Range in northeastern California preserve flow-on-flow basalt sequences exposed in the footwalls of numerous normal faults. The eruption of these 3 to 8 Ma flows was coeval with the development and progression of extensional faulting, but the detailed relationship was not clear. Although several flows have previously been dated using 40Ar/39Ar geochronology, individual flows cannot easily be identified in outcrop or geochemically. Paleomagnetic analyses have allowed us to differentiate individual flows possessing unique remanence directions, and to correlate flow sequences. Nearly 1,300 paleomagnetic core samples from 167 flows were collected within the Larkspur Hills. Generalized magnetostratigraphy and detailed remanent magnetic directions were analyzed in conjunction with the existing geochronology to correlate flows and constrain the relative timing of faulting and volcanism. Results indicate that volcanic activity occurred during four distinct episodes between 3 to 8 Ma, and suggest that contemporaneous faulting likely influenced the distribution of subsequent flows by producing topographic barriers or pathways to the flows. In addition, when compared to the expected reference direction for stable North America, the paleomagnetic data indicate that the region has undergone 11.9 ± 4.5˚ of clockwise rotation. This result agrees favorably with studies that have inferred appreciable rotation of our study area associated with clockwise rotation of the Oregon coastal block.

  7. Paleomagnetism and multi-model stereo photogrammetry of the West Greenland flood volcanic province

    NASA Astrophysics Data System (ADS)

    Riisager, J.; Riisager, P.; Pedersen, A. K.

    2002-12-01

    We present new paleomagnetic and multi-model photogrammetry data from the West Greenland part of the North Atlantic igneous province (NAIP). During fieldwork the paleomagnetic sampling sites were photographed from helicopter with stereoscopic overlap and in colour. The photographs have been set up for multi-model photogrammetry allowing three-dimensional lithological mapping, giving us important information for interpreting the paleomagnetic data in their stratigraphic context. Another advantage of the multi-model photogrammetry coverage is that individual lavas can be traced in three-dimensional space allowing very precise measurements of the attitude of strata (+/-0.5°) to be made for tectonic correction of the paleomagnetic data. The paleomagnetic study is based on a large collection of 586 oriented paleomagnetic drill cores collected from 81 lava flows. All sampled flows carry stable thermoremanent magnetization of reversed polarity. The earliest part of the volcanic sequence (i.e. Vaigat Fm.) is characterized by several consecutive flows recording statistically indistinguishable paleomagnetic field directions. The thickest Vaigat Fm. directional group consists of 37 lava flows (combined thickness 104 meter), which based on photogrammetry and XRF observations we interpret to represent a single flow field (i.e. one eruption consisting of several lavas erupted in a short period of time). If Paleocene paleosecular variation was similar to Holocene variations, the thick directional groups would form within 100 years implying an extreme volcanic activity at the onset of NAIP volcanism on West Greenland. Based on directional groups we obtain a new well-defined paleomagnetic pole for Greenland, which is statistically similar to a recently published NAIP pole from Faroe Islands (Riisager et al., 2002) rotated to Greenland. The corresponding paleolatitude of the central NAIP in Paleocene is ~20° south of the present latitude of the Iceland hotspot, indicating that the

  8. D/H on Mars - Effects of floods, volcanism, impacts, and polar processes

    SciTech Connect

    Carr, M.H. )

    1990-09-01

    An effort is made to ascertain whether the recently measured Martian atmospheric water's D/H ratio, which is greater than the terrestrial atmospheric water value by a factor of 5.1, entails a revision of the Martian geological evolution model that has been developed over the last 20 years. It is suggested that the D/H enrichment of the atmosphere is compatible with previous geologic conceptualizations involving (1) the outgassing of large quantities of water from the planet, (2) the periodic introduction of juvenile water onto the planet's surface by volcanic action, and (3) the extensive sculpting of the Martian surface by running water. 63 refs.

  9. Planetary Volcanism

    NASA Technical Reports Server (NTRS)

    Antonenko, I.; Head, J. W.; Pieters, C. W.

    1998-01-01

    The final report consists of 10 journal articles concerning Planetary Volcanism. The articles discuss the following topics: (1) lunar stratigraphy; (2) cryptomare thickness measurements; (3) spherical harmonic spectra; (4) late stage activity of volcanoes on Venus; (5) stresses and calderas on Mars; (6) magma reservoir failure; (7) lunar mare basalt volcanism; (8) impact and volcanic glasses in the 79001/2 Core; (9) geology of the lunar regional dark mantle deposits; and (10) factors controlling the depths and sizes of magma reservoirs in Martian volcanoes.

  10. Geochemical variations in Andean basaltic and silicic lavas from the Villarrica-Lanin volcanic chain (39.5° S): an evaluation of source heterogeneity, fractional crystallization and crustal assimilation

    NASA Astrophysics Data System (ADS)

    Hickey-Vargas, Rosemary; Roa, Hugo Moreno; Escobar, Leopolde Lopez; Frey, Frederick A.

    1989-11-01

    At 39.5° S in the southern volcanic zone of the Andes three Pleistocene-recent stratovolcanoes, Villarrica, Quetrupillan and Lanin, form a trend perpendicular to the strike of the Andes, 275 to 325 km from the Peru-Chile trench. Basalts from Villarrica and Lanin are geochemically distinct; the latter have higher incompatible element abundances and La/Sm but lower Ba/La and alkali metal/La ratios. These differences are consistent with our previously proposed models involving: a) a west to east decrease in an alkali metal-rich, high Ba/La slab-derived component which causes an across strike decrease in degree of melting; or b) a west to east increase in the contamination of subduction-related magma by enriched subcontinental lithospheric mantle. Silicic and mafic lavas from the stratovolcanoes have overlapping Sr, Nd and O isotopic ratios. Silicic lavas also have geochemical differences that parallel those of their associated basalts, e.g., rhyolite from Villarrica has lower La/Sm and incompatible element contents than high-SiO2 andesite from Lanin. At each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing. Apparently crustal contamination was not an important process in deriving the evolved lavas. Basaltic flows from small scoria cones, 20 35 km from Villarrica volcano have high incompatible element contents and low Ba/La, like Lanin basalts, but trend to higher K/Rb (356 855) and lower 87Sr/ 86Sr (0.70361 0.70400) than basalts from either stratovolcano. However all basalts have similar Nd, Pb and O isotope ratios. The best explanation for the unique features of the cones is that the sources of SVZ magmas, e.g., slab-derived fluids or melts of the subcontinental lithospheric mantle, have varying alkali metal and radiogenic Sr contents. These heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing. This model is

  11. Nature of mantle source contributions and the role of contamination and in situ crystallisation in the petrogenesis of Proterozoic mafic dykes and flood basalts Labrador

    NASA Astrophysics Data System (ADS)

    Cadman, A. C.; Tarney, J.; Baragar, W. R. A.

    1995-12-01

    Proterozoic tholeiitic dyke swarms share many compositional features with, and pose similar petrogenetic problems to, Phanerozoic continental flood basalts, but there are few extrusive equivalents of such swarms. The Mesoproterozoic (1.27 Ga) Harp dyke swarm in Labrador is one where possible extrusive equivalents exist in the Seal Lake group, but are slightly displaced in space and time, and can probably be related by models of progressive crustal extension. Here we try to evaluate the roles of crystal differentiation, in situ crystallisation, crustal assimilation and the relative contributions of asthenosphere- and lithosphere-derived melts in the petrogenesis of the mafic magmas. Modelling of the major and trace element variations both within individual dykes and between dykes, and within the lava sequence, does not suggest an important role for continental crust involvement. While in situ crystallisation processes could account for some of the compositional variations, the most successful models invoke mixing or contamination of asthenospheric magmas with/by veined material in the lower lithosphere / upper asthenosphere which carries the ‘continental’ characteristics. The results imply an important role for hydrous phases such as phlogopite and hornblende in the sub-lithosphere mantle. Much of the low-MgO character of mafic dykes may result from significant removal of mafic phases during in situ crystallisation within the lithosphere.

  12. The quality of our Nation's waters: groundwater quality in the Columbia Plateau and Snake River Plain basin-fill and basaltic-rock aquifers and the Hawaiian volcanic-rock aquifers, Washington, Idaho, and Hawaii, 1993-2005

    USGS Publications Warehouse

    Rupert, Michael G.; Hunt, Charles D., Jr.; Skinner, Kenneth D.; Frans, Lonna M.; Mahler, Barbara J.

    2015-01-01

    The Columbia Plateau, Snake River Plain, and Hawaii are large volcanic areas in the western United States and mid-Pacific ocean that contain extensive regional aquifers of a hard, gray, volcanic rock called basalt. Residents of the Columbia Plateau, the Snake River Plain, and the island of Oahu depend on groundwater as their primary source of drinking water. Although the depth to the water table can be several hundred feet, the groundwater is highly vulnerable to contamination because the permeable sediments and rocks allow contaminants to move readily down to the water table. Intense agricultural and urban activities occur above the drinking-water supply and are increasing in some areas. Contaminants, such as nitrate, pesticides, and volatile organic compounds, associated with agricultural and urban activities, have adversely affected groundwater quality.

  13. Land use and Hydrological Characteristics of Volcanic Urban Soils for Flood Susceptibility Modeling, Ciudad de Colima (Mexico)

    NASA Astrophysics Data System (ADS)

    Perez Gonzalez, M. L.; Capra, L.; Borselli, L.; Ortiz, A.

    2015-12-01

    The fast population rate growth and the unplanned urban development has created an increase of urban floods in the City of Colima. Land use change has transformed the hydrological behavior of the watersheds that participates on the runoff-infiltration processes that governs the pluvial concentrations. After the urban areas enlargement, 13% from 2010 to 2015, rainfall has caused significant damages to the downtown community. Therefore it is important to define the main hydraulic properties of the soils surrounding the city. The soil of the region is derived from the debris avalanche deposits of the Volcano of Colima. The volcanic soil cover is only 10 to 15 cm depth. To test the soils of the region, sampling locations were chosen after making a land use map from a Landsat image. The map was done by selecting and dividing similar surface images patterns into three main classifications: Natural (N1), Agricultural (N5) and Urban (N4) surfaces. Thirty-Three soil samples were collected and grouped in nine out of ten land use subdivisions. The 10thsubdivision, represents the completed urbanized area. The land use model is made using spot 4 1A images from the year 2010 up to year 2015. This land use evolutionary analysis will be a base to evaluate the change of the runoff-infiltration rate, direction, and concentration areas for the future flood susceptibility model. To get the parameters above, several soil analysis were performed. The results were that all the soil samples tested were classified as sandy soils. The water content values were from 7% (N4) to 45% (N1) while bulk density values for the same sample were form 0.65 (N1) to 1.50 (N4) g/cm3. The particle density and the porosity values were from 1.65 g/cm3 /5.5% (N4) - 2.65 g/cm3/ 75.40% (N1). The organic matter content was around 0.1% for urban soils and up to 6% on natural and agricultural soils. Some other test like electric conductivity and pH were performed. The obtained parameters were used to get other

  14. Peeking below Columbia River flood basalts with high-resolution aeromagnetic data: implications for central Washington earthquake hazards

    NASA Astrophysics Data System (ADS)

    Blakely, R. J.; Sherrod, B. L.; Wells, R. E.; Weaver, C. S.

    2012-12-01

    The largest crustal earthquake in Washington's recorded history (M 6.8) occurred in 1872 in the vicinity of Lake Chelan. Numerous smaller earthquakes (>1000 earthquakes since 1971 with 1.0 ≤ MW ≤ 4.3) continue to occur 20 km south of Lake Chelan near the town of Entiat, yet little is known about active structures responsible for this ongoing deformation. A 2011 aeromagnetic survey may provide insights. The survey was flown with a fixed-wing aircraft along flight lines spaced 400 m apart and at an altitude 250 m above terrain or as low as safely possible. The survey illuminates two distinct magnetic patterns. Northwest of Entiat, broad, subdued magnetic anomalies are caused by weakly magnetic, pre-Tertiary basement rocks striking generally NW. Magnetic lineaments are associated, for example, with the NW-striking Entiat fault, the structural margin of the Chiwaukum graben, which is well represented by gravity anomalies. Southeast of Entiat, high-amplitude, short-wavelength magnetic anomalies are caused by strongly magnetic rocks of the Miocene Columbia River Basalt Group (CRBG) exposed throughout this region. Northwest-striking basement anomalies, so clear NW of Entiat, are not obvious SE of Entiat, yet there is no reason to believe basement structures do not extend beneath CRBG. We used matched filtering methods to illuminate the crustal framework of the Entiat earthquakes beneath CRBG. We selected two sub regions, one over pre-Tertiary basement NW of Entiat (sub region 1), the other over CRBG SE of Entiat (sub region 2). We modeled each sub region by fitting layer parameters to power spectra determined from magnetic anomalies (Phillips, 2007). A strongly magnetic layer was determined 470 m below the aircraft in sub region 2, which we interpret as the average top of CRBG. This interpretation is supported by the absence of a similar magnetic layer in sub region 1, where CRBG is in fact absent. Using this determination, we designed a matched filter to subdue

  15. Quantifying the Chemical Weathering Efficiency of Basaltic Catchments

    NASA Astrophysics Data System (ADS)

    Ibarra, D. E.; Caves, J. K.; Thomas, D.; Chamberlain, C. P.; Maher, K.

    2014-12-01

    The geographic distribution and areal extent of rock type, along with the hydrologic cycle, influence the efficiency of global silicate weathering. Here we define weathering efficiency as the production of HCO3- for a given land surface area. Modern basaltic catchments located on volcanic arcs and continental flood basalts are particularly efficient, as they account for <5% of sub-aerial bedrock but produce ~30% of the modern global weathering flux. Indeed, changes in this weathering efficiency are thought to play an important role in modulating Earth's past climate via changes in the areal extent and paleo-latitude of basaltic catchments (e.g., Deccan and Ethiopian Traps, southeast Asia basaltic terranes). We analyze paired river discharge and solute concentration data for basaltic catchments from both literature studies and the USGS NWIS database to mechanistically understand geographic and climatic influences on weathering efficiency. To quantify the chemical weathering efficiency of modern basalt catchments we use solute production equations and compare the results to global river datasets. The weathering efficiency, quantified via the Damköhler coefficient (Dw [m/yr]), is calculated from fitting concentration-discharge relationships for catchments with paired solute and discharge measurements. Most basalt catchments do not demonstrate 'chemostatic' behavior. The distribution of basalt catchment Dw values (0.194 ± 0.176 (1σ)), derived using SiO2(aq) concentrations, is significantly higher than global river Dw values (mean Dw of 0.036), indicating a greater chemical weathering efficiency. Despite high Dw values and total weathering fluxes per unit area, many basaltic catchments are producing near their predicted weathering flux limit. Thus, weathering fluxes from basaltic catchments are proportionally less responsive to increases in runoff than other lithologies. The results of other solute species (Mg2+ and Ca2+) are comparable, but are influenced both by

  16. Volcanic Flooding Experiments in Impact Basins and Heavily Cratered Terrain Using LOLA Data: Patterns of Resurfacing and Crater Loss

    NASA Technical Reports Server (NTRS)

    Whitten, Jennifer L.; Head, James W.; Neumann, Gregory A.; Zuber, Maria T.; Smith, David E.

    2012-01-01

    Terrestrial planetary bodies are characterized by extensive, largely volcanic deposits covering their surfaces. On Earth large igneous provinces (LIPs) abound, maria cover the nearside of the Moon, and volcanic plains cover large portions of Venus, Mars and Mercury.

  17. The architecture of tholeiitic lava flows in the Neogene flood basalt piles of eastern Iceland: constraints on the mode of emplacemement

    NASA Astrophysics Data System (ADS)

    Oskarsson, B. V.; Riishuus, M. S.

    2012-12-01

    Tholeiites comprise 50-70% of the Neogene lava piles of eastern Iceland and have been described largely as flood basalts erupted from fissures (Walker, 1958). This study incorporates lava piles found in the Greater Reydarfjördur area and emprises the large-scale architecture of selected flows and flow groups, their internal structure and textures with the intention of assessing their mode of emplacement. A range of lava morphologies have been described and include: simple (tabular) flows with a'a and rubbly flow tops, simple flows with pahoehoe crust and compound pahoehoe flows, with simple flows being most common. Special attention is given here to the still poorly understood simple flows, which are characterized by extensive sheet lobes with individual sheet lengths frequently exceeding 2 km and reaching thicknesses of ~40 m (common aspect ratios <0.01). The sheets in individual flow fields are emplaced side by side with an overlapping contact and are free of tubes. Their internal structure generally constitutes an upper vesicular crust with no or minor occurrences of horizontal vesicle zones, a poorly vesicular core and a thin basal vesicular zone. The normalized core/crust thickness ratios resemble modern compound pahoehoe flows in many instances (0.4-0.7), but with the thicker flows reaching ratios of 0.9. Flow crusts are either pahoehoe, rubbly or scoriaceous with torn and partially welded scoria and clinker. Frequently, any given flow morphology is repeated in sequences of three to four flows with direct contacts. Preliminary assessments suggest that simple flows are the product of high and sustained effusion rates from seemingly short-lived fissures. Simple flows with a'a flow tops may comprise the annealed emplacement mode of sheet flows and channeled a'a, in which the flow propagated as a single unit, whereas the brecciated flow top formed by continuous tearing and brecciation as occurs in channeled lava flowing at high velocity. The absence of a

  18. Magma flow-direction indicators in the diabase feeder dike to the first flood basalt in the Mesozoic Hartford basin, Connecticut

    SciTech Connect

    Philpotts, A.R.; Asher, P.M. . Dept. of Geology and Geophysics)

    1993-03-01

    Recent kinematic analysis has indicated that magma may have been emplaced horizontally rather than vertically in some large regional diabase dikes. Such analysis, however, has commonly relied on a single flow indicator, such as anisotropy of magnetic susceptibility, which may reflect only late stage adjustments in a body of crystallizing magma. This study of kinematic indicators in a Mesozoic diabase dike in southern New England indicates that the direction of flow in large dikes may change during emplacement, and that a single flow indicator cannot give a complete picture of the flow history. The 250-km-long Higganum dike fed the first flood basalt in the Hartford basin of Connecticut. The margins of this dike contain 8 independent magma flow indicators, which involve the imbrication and deformation of phenocrysts, the shearing of felsic wisps, and the segregation of residual liquids. The felsic wisps, which were derived by partial melting of the wallrock, preserve the most complete record of flow in the dike. Early felsic liquids exchanged alkalis with the still largely molten diabase magma and consequently are K-poor; ones that entered after the diabase was largely solid are relatively K-rich. Most K-poor felsic wisps were deformed into recumbent folds by back-flowing magma. Later K-rich felsic streaks parallel the axial planes of these folds. The shear of magma past phenocrysts near the dike margins also caused K-rich felsic liquids to segregate in low-pressure zones on the opposing ends of these crystals. All of these flow indicators record a complex history of dike emplacement, with periods of upward intrusion always being followed by periods of back-flow.

  19. How Volcanism Controls Climate Change

    NASA Astrophysics Data System (ADS)

    Ward, P. L.

    2013-12-01

    km decrease in tropopause height. Changes in the rates and types of volcanism have been the primary cause of climate change throughout geologic time. Large explosive volcanoes erupting as frequently as once per decade increment the world into ice ages. Extensive, effusive basaltic volcanism warms the world out of ice ages. Twelve of the 13 dated basaltic table mountains in Iceland experienced their final eruptive phase during the last deglaciation when deposits of sulfate and volcanic ash fell over Greenland at their highest rates. Massive flood basalts are typically accompanied by extreme warming, ozone depletion, and major mass extinctions. The Paleocene-Eocene Thermal Maximum occurred when subaerial extrusion of basalts related to the opening of the Greenland-Norwegian Sea suddenly increased to rates greater than 3000 cubic km per km of rift per million years. Dansgaard-Oeschger sudden warming events are contemporaneous with increased volcanism especially in Iceland and last longer when that volcanism lasts longer. Sudden influxes of fresh water often observed in the North Atlantic during these events are most likely caused by extensive sub-glacial volcanism. The Medieval Warm Period, Little Ice Age, major droughts, and many sudden changes in human civilization began with substantial increases in volcanism. Extensive submarine volcanism does not affect climate directly but is linked with increases in ocean acidity and anoxic events.

  20. Subglacial to emergent basaltic volcanism at Hlöðufell, south-west Iceland: A history of ice-confinement

    NASA Astrophysics Data System (ADS)

    Skilling, I. P.

    2009-09-01

    Hlöðufell is a familiar 1186 m high landmark, located about 80 km northeast of Reykjavík, and 9 km south of the Langkjökull ice-cap in south-west Iceland. This is the first detailed study of this well-exposed and easily accessible subglacial to emergent basaltic volcano. Eight coherent and eleven volcaniclastic lithofacies are described and interpreted, and its evolution subdivided into four growth stages (I-IV) on the basis of facies architecture. Vents for stages I, II, and IV lie along the same fissure zone, which trends parallel to the dominant NNE-SSW volcano-tectonic axis of the Western Volcanic Zone in this part of Iceland, but the stage III vent lies to the north, and is probably responsible for the present N-S elongation of the volcano. The basal stage (I) is dominated by subglacially erupted lava mounds and ridges, which are of 240 m maximum thickness, were fed from short fissures and locally display lava tubes. Some of the stage I lavas preserve laterally extensive flat to bulbous, steep, glassy surfaces that are interpreted to have formed by direct contact with surrounding ice, and are termed ice-contact lava confinement surfaces. These surfaces preserve several distinctive structures, such as lava shelves, pillows that have one flat surface and mini-pillow (< 10 cm across) breakouts, which are interpreted to have formed by the interplay of lava chilling and confinement against ice, ice melting and ice fracture. The ice-contact lava confinement surfaces are also associated with zones of distinctive open cavities in the lavas that range from about 1 m to several metres across. The cavities are interpreted as having arisen by lava engulfing blocks of ice, that had become trapped in a narrow zone of meltwater between the lava and the surrounding ice, and are termed ice- block meltout cavities. The same areas of the lavas also display included and sometimes clearly rotated blocks of massive to planar to cross-stratified hyaloclastite lapilli tuffs and

  1. Sulfide Stability of Planetary Basalts

    NASA Technical Reports Server (NTRS)

    Caiazza, C. M.; Righter, K.; Gibson, E. K., Jr.; Chesley, J. T.; Ruiz, J.

    2004-01-01

    The isotopic system, 187Re 187Os, can be used to determine the role of crust and mantle in magma genesis. In order to apply the system to natural samples, we must understand variations in Re/Os concentrations. It is thought that low [Os] and [Re] in basalts can be attributed to sulfide (FeS) saturation, as Re behaves incompatibly to high degrees of evolution until sulfide saturation occurs [1]. Previous work has shown that lunar basalts are sulfide under-saturated, and mid-ocean ridge, ocean-island and Martian (shergottites) basalts are saturated [2,3]. However, little is known about arc basalts. In this study, basaltic rocks were analyzed across the Trans-Mexican Volcanic Belt.

  2. Geochemical discrimination of five pleistocene Lava-Dam outburst-flood deposits, western Grand Canyon, Arizona

    USGS Publications Warehouse

    Fenton, C.R.; Poreda, R.J.; Nash, B.P.; Webb, R.H.; Cerling, T.E.

    2004-01-01

    Pleistocene basaltic lava dams and outburst-flood deposits in the western Grand Canyon, Arizona, have been correlated by means of cosmogenic 3He (3Hec) ages and concentrations of SiO2, Na2O, K2O, and rare earth elements. These data indicate that basalt clasts and vitroclasts in a given outburst-flood deposit came from a common source, a lava dam. With these data, it is possible to distinguish individual dam-flood events and improve our understanding of the interrelations of volcanism and river processes. At least five lava dams on the Colorado River failed catastrophically between 100 and 525 ka; subsequent outburst floods emplaced basalt-rich deposits preserved on benches as high as 200 m above the current river and up to 53 km downstream of dam sites. Chemical data also distinguishes individual lava flows that were collectively mapped in the past as large long-lasting dam complexes. These chemical data, in combination with age constraints, increase our ability to correlate lava dams and outburst-flood deposits and increase our understanding of the longevity of lava dams. Bases of correlated lava dams and flood deposits approximate the elevation of the ancestral river during each flood event. Water surface profiles are reconstructed and can be used in future hydraulic models to estimate the magnitude of these large-scale floods.

  3. Thermal and mass implications of magmatic evolution in the Lassen volcanic region, California, and minimum constraints on basalt influx to the lower crust

    SciTech Connect

    Guffanti, M.; Clynne, M.A.; Muffler, L.J.P.

    1996-02-10

    This report investigates the heat and mass demands of the petrologic model of Clynne, and Bullen and Clynne for the Lassen region of Cascade Range. Basalt-driven magmatic evolution is dominated by mixing of fractionated mafic magmas with silicic partial melts of the lower crust.

  4. Potassium-argon geochronology of a basalt-andesite-dacite arc system: the Mount Adams volcanic field, Cascade Range of southern Washington

    USGS Publications Warehouse

    Hildreth, W.; Lanphere, M.A.

    1994-01-01

    High-precision K-Ar dating and detailed mapping have established an eruptive chronology for a Cascade stratovolcano and its surrounding array of coeval basaltic centers. The time-volume-composition data bear upon several fundamental questions concerning the long-term behavior of arc volcanoes. -from Authors

  5. Gish Bar Patera, Io: Geology and Volcanic Activity, 1996-2001

    NASA Technical Reports Server (NTRS)

    Perry, Jason; Radebaugh, Jani; Lopes, Rosaly; McEwen, Alfred; Keszthelyi, Laszlo

    2003-01-01

    Since the two Voyagers passed by Jupiter in 1979, it has been known that volcanic activity is ubiquitous on the surface of Io. With over 400 volcanic centers, Io is even more volcanically active than the earth with massive flood basalt-style eruptions and komatitite lavas a common occurrence. Additionally, some volcanoes appear to be giant lava lakes, with violent activity churning the crust of the lake for periods of 20 years or more. Finally, sulfur is believed to play a large role in Io's volcanism, be it as a primary lava or as a secondary product of large, high-temperature eruptions. By studying one volcano in particular, Gish Bar Patera, one can observe many of these characteristics in one volcanic center.

  6. Subduction-modified oceanic crust mixed with a depleted mantle reservoir in the sources of the Karoo continental flood basalt province

    NASA Astrophysics Data System (ADS)

    Heinonen, Jussi S.; Carlson, Richard W.; Riley, Teal R.; Luttinen, Arto V.; Horan, Mary F.

    2014-05-01

    The great majority of continental flood basalts (CFBs) have a marked lithospheric geochemical signature, suggesting derivation from the continental lithosphere, or contamination by it. Here we present new Pb and Os isotopic data and review previously published major element, trace element, mineral chemical, and Sr and Nd isotopic data for geochemically unusual mafic and ultramafic dikes located in the Antarctic segment (Ahlmannryggen, western Dronning Maud Land) of the Karoo CFB province. Some of the dikes show evidence of minor contamination with continental crust, but the least contaminated dikes exhibit depleted mantle - like initial ɛNd (+9) and 187Os/188Os (0.1244-0.1251) at 180 Ma. In contrast, their initial Sr and Pb isotopic compositions (87Sr/86Sr = 0.7035-0.7062, 206Pb/204Pb = 18.2-18.4, 207Pb/204Pb = 15.49-15.52, 208Pb/204Pb = 37.7-37.9 at 180 Ma) are more enriched than expected for depleted mantle, and the major element and mineral chemical evidence indicate contribution from (recycled) pyroxenite sources. Our Sr, Nd, Pb, and Os isotopic and trace element modeling indicate mixed peridotite-pyroxenite sources that contain ˜10-30% of seawater-altered and subduction-modified MORB with a recycling age of less than 1.0 Ga entrained in a depleted Os-rich peridotite matrix. Such a source would explain the unusual combination of elevated initial 87Sr/86Sr and Pb isotopic ratios and relative depletion in LILE, U, Th, Pb and LREE, high initial ɛNd, and low initial 187Os/188Os. Although the sources of the dikes probably did not play a major part in the generation of the Karoo CFBs in general, different kind of recycled source components (e.g., sediment-influenced) would be more difficult to distinguish from lithospheric CFB geochemical signatures. In addition to underlying continental lithosphere, the involvement of recycled sources in causing the apparent lithospheric geochemical affinity of CFBs should thus be carefully assessed in every case.

  7. Chemical and Isotopic Constraints on the Origin of Cenozoic Pacific Northwest Volcanism

    NASA Astrophysics Data System (ADS)

    Carlson, R. W.; Hart, W. K.; Grove, T. L.; Donnelly-Nolan, J. M.; Barr, J. A.; Till, C. B.

    2009-12-01

    Though there is little debate about the connection of Cascade volcanism to subduction of the Juan de Fuca plate, the cause of extensive Neogene volcanism east of the Cascades is not as well understood. Volumetrically, the most significant component of this volcanism, the flood basalts of the Columbia Plateau and Steens Mountain, are dominated by lavas that have suffered extensive crystal fractionation in crustal magma chambers. The evolved, crustally contaminated, nature of most of these basalts makes identification of the primary magma difficult, confounding interpretation of the background cause of the volcanism. Some Steens lavas are relatively undifferentiated (Johnson et al., USGS Open File report 98-0482). These Steens basalts have compositions that are distinguished from younger primitive basalts on the High Lava Plains (HLP) by distinctly lower Al and higher FeO, Ti, Zr and Nb concentrations, but also Mg#s that are too low to be in equilibrium with mantle that has Fo90 olivine. If these are primary magmatic characteristics, they suggest either a more fertile, FeO-rich source, or lower, not higher, degrees of melting at greater depth during the flood basalt era as opposed to the much smaller-volume younger HLP volcanism. Experimental results on primitive Quaternary HLP and Newberry Volcano lavas suggest last equilibration at pressures corresponding to just below the Moho (30-40 km) with water contents that range from substantial (up to 4 wt %) at Newberry to low (<0.3 wt %) at the eastern-most HLP activity at the Jordan Valley volcanic center. The high water contents, high Ba/Nb and other features of Newberry lavas suggest that this volcano is a Cascades volcano, not the western terminus of an HLP hot-spot. All the young HLP lavas, however, have at least somewhat elevated Ba/Nb and Pb isotopic compositions approaching those of Pacific Northwest oceanic sediments suggesting a subduction overprint on most of the young HLP magmatism. In contrast to the small

  8. Chaitén town (Chile) inundated by a complex multi-peaked volcanic flood in May 2008 (Invited)

    NASA Astrophysics Data System (ADS)

    Pierson, T. C.; Major, J. J.; Amigo, A.; Moreno, H.

    2010-12-01

    alternating pulses of hyperconcentrated flow and highly concentrated normal streamflow produced the next 1.5 to 2 m of aggradation and initial levee breaching, followed by 1.5 to 3 m of deposition by normal streamflow on the floodplain and in the town. Thus, a complex and prolonged multi-peaked volcanic flood of varying sediment concentration, combined with rapid channel aggradation, was the physical process responsible for damage to most of the town. A mixture of white tubular pumice and foliated glassy to microcrystalline rhyolite sand grains in the upper channel-fill sediments suggests that both the tephra blanket and the lithic pyroclastic flow deposit contributed sediment during the later phases of flooding. The question of whether a highly concentrated lahar dominated the early phase of channel aggradation awaits exposure of the lower channel-fill deposits.

  9. Petrogenetic modeling of 74220 high-Ti orange volcanic glasses and the Apollo 11 and 17 high-Ti mare basalts

    NASA Technical Reports Server (NTRS)

    Hughes, S. S.; Schmitt, R. A.; Delano, J. W.

    1989-01-01

    An INAA analysis of 16 individual spherules of orange volcanic glass extracted from the 74220,680 soil was performed in order to determine trace element signatures in a primary high-Ti mare magma. The composition of these glasses is shown to be nearly identical to that of 74220 bulk soil, indicating a general absence of constituents other than volcanic glass in the soil. The results suggest that the evolving lunar mantle included processes of cumulate-mass transport and/or segregation of the primordial lunar magma ocean into separate differentiating zones, allowing commingling of early and late components.

  10. Isotope geochemistry of caliche developed on basalt

    NASA Astrophysics Data System (ADS)

    Knauth, L. Paul; Brilli, Mauro; Klonowski, Stan

    2003-01-01

    Enormous variations in oxygen and carbon isotopes occur in caliche developed on < 3 Ma basalts in 3 volcanic fields in Arizona, significantly extending the range of δ 18O and δ 13C observed in terrestrial caliche. Within each volcanic field, δ 18O is broadly co-variant with δ 13C and increases as δ 13C increases. The most 18O and 13C enriched samples are for subaerial calcite developed on pinnacles, knobs, and flow lobes that protrude above tephra and soil. The most 18O and 13C depleted samples are for pedogenic carbonate developed in soil atmospheres. The pedogenic caliche has δ 18O fixed by normal precipitation in local meteoric waters at ambient temperatures and has low δ 13C characteristic of microbial soil CO 2. Subaerial caliche has formed from 18O-rich evapoconcentrated meteoric waters that dried out on surfaces after local rains. The associated 13C enrichment is due either to removal of 12C by photosynthesizers in the evaporating drops or to kinetic isotope effects associated with evaporation. Caliche on basalt lava flows thus initially forms with the isotopic signature of evaporation and is subsequently over-layered during burial by calcite carrying the isotopic signature of the soil environment. The large change in carbon isotope composition in subsequent soil calcite defines an isotopic biosignature that should have developed in martian examples if Mars had a "warm, wet" early period and photosynthesizing microbes were present in the early soils. The approach can be similarly applied to terrestrial Precambrian paleocaliche in the search for the earliest record of life on land. Large variations reported for δ 18O of carbonate in Martian meteorite ALH84001 do not necessarily require high temperatures, playa lakes, or flood runoff if the carbonate is an example of altered martian caliche.

  11. Possible Juventae Chasma subice volcanic eruptions and Maja Valles ice outburst floods on Mars: Implications of Mars Global surveyor crater densities, geomorphology, and topography

    USGS Publications Warehouse

    Chapman, M.G.; Gudmundsson, M.T.; Russell, A.J.; Hare, T.M.

    2003-01-01

    This article discusses image, topographic, and spectral data from the Mars Global Surveyor (MGS) mission that provide new information concerning the surface age, geomorphology, and topography of the Juventae Chasma/Maja Valles system. Our study utilizes data from two instruments on board MGS: images from the Mars Orbiter Camera (MOC) and topography from the Mars Orbiter Laser Altimeter (MOLA). Within Maja Valles we can now observe depositional bars with megaripples that unequivocally show catastrophic floods occurred in the channel. Viking impact crater densities indicated the chasma and channel floor areas were all one age (late Hesperian to Amazonian); however, MOC data indicate a marked difference in densities of small craters between Juventae Chasma, Maja Valles, and the channel debouchment area in Chryse Planitia basin. Although other processes may contribute to crater variability, young resurfacing events in the chasma and episodes of recent erosion at Maja Valles channel head may possibly account for the disparate crater densities along the chasma/channel system. Relatively young volcanic eruptions may have contributed to resurfacing; as in Juventae Chasma, a small possible volcanic cone of young dark material is observed. MOC data also indicate previously unknown interior layered deposit mounds in the chasma that indicate at least two periods of mound formation. Finally, MOLA topography shows that the entire floor of the chasma lies at the same elevation as the channel debouchment area in Chryse basin, resulting in a 3-km-high barrier to water flow out of the chasma. Blocked ponded water would rapidly freeze in the current (and likely past) climate of Mars. For catastrophic flow to occur in Maja Valles, some process is required to melt ice and induce floods out of the chasma. We suggest subice volcanic eruption and calculate estimates of water discharges and volumes that these eruptions might have produced.

  12. Ion microprobe studies of trace elements in Apollo 14 volcanic glass beads - Comparisons to Apollo 14 mare basalts and petrogenesis of picritic magmas

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Papike, J. J.; Simon, S. B.; Shimizu, N.; Yurimoto, H.

    1990-01-01

    Results are presented from trace element analysis, by ion microprobe techniques, of individual glass beads representing seven compositionally distinct types of picritic glass beads from the Apollo 14 landing site. The picritic glass beads at the A-14 exhibited a wide range of primary magma compositions and a lack of petrogenetic linkage (via crystal fractionation) to crystalline basalts. The wide range of major and trace element characteristics of the picritic glass beads is consistent with derivation from mineralogically distinct sources which consist of varying proportions of olivine + orthopyroxene +/- clonopyroxene +/- ilmenite +/- plagioclase +/- KREEP component.

  13. F, Cl, and S contents of olivine-hosted melt inclusions in mafic dikes and the environmental impact of flood volcanism in the Paraná-Etendeka LIP

    NASA Astrophysics Data System (ADS)

    Marks, Linda; Trumbull, Robert; Keiding, Jakob; Veksler, Ilya; Wenzel, Thomas; Markl, Gregor; Wiedenbeck, Michael

    2014-05-01

    Large Igneous Provinces (LIPs) have been proposed to trigger mass-extinction events by the release of large quantities of volcanic gases which results in major climatic perturbations causing worldwide ecological stress and collapse. A prerequisite for understanding the proposed link between LIP volcanism and biological crisis is reliable information about the total gas emissions during these events. We present the first estimations of total F, Cl and S emissions from the Paraná-Etendeka LIP in the South Atlantic. Data from this province are of special interest because it is among the world's largest LIPs but is not associated to a mass extinction event. We have determined pre-eruption concentrations of F, Cl and S by in-situ analysis of melt inclusions preserved in olivine phenocrysts from basaltic dikes in the Etendeka province of NW Namibia. The melt inclusions have Mg-rich basaltic bulk compositions with about 8 to 18 wt.% MgO, overlapping the compositional range of the host rocks. A major feature of the melt inclusions is their wide variation in major and minor element concentrations, including F, Cl and S. This is attributed to trapping of variably-mixed melt fractions during crystallization of olivine in the roots of the dike system. Fluorine concentrations vary from about 190 to 450 ppm, Cl from <10 to 125 ppm and S from <30 to 1100 ppm. All inclusions were rehomogenized in heating experiments and the lowest concentrations may be due to partial leakage of S and halogens. Therefore, the maximum values are considered best estimates of the true melt concentrations. These melt inclusion data are combined with the volume of extruded magma in the province (2.2 to 2.35 million cubic km) and with published degassing efficiencies to calculate total emissions from the Paraná-Etendeka LIP of 600-1200 Gt fluorine, 200-500 Gt chlorine and 3100-5400 Gt sulfur. The estimated sulfur emissions are similar to those from the similar-sized Deccan and Siberian LIPs, both of

  14. Pleistocene cataclysmic flooding along the Big Lost River, east central Idaho

    NASA Astrophysics Data System (ADS)

    Rathburn, Sara L.

    1993-12-01

    Relationships between cataclysmic flood-generated landforms and flood hydraulics were investigated along Box Canyon, an 11 km long bedrock gorge of the lower Big Lost River. Geomorphic mapping along Box Canyon indicates that a cataclysmic flood completely inundated the gorge, resulting in large-scale erosional and depositional features on the adjacent basalt upland. Step-backwater hydraulic modeling indicates that a discharge of 60,000 m 3 s -1 was required to produce the geologic paleostage evidence. Maximum stream power per unit area of bed locally attained values of 26,000 W m -2 during the peak, ranking the Big Lost River flood third, in terms of power, behind the famous Missoula and Bonneville floods. The spatial distribution of unit stream power indicates that bedrock erosion and boulder deposition on the basalt upland adjacent to Box Canyon were governed primarily by decreasing unit stream power and/or fluctuating unit stream power gradients. A preliminary depositional threshold for the largest flood boulders defines a lower limit of flood power required to sustain boulder transport along this bedrock fluvial system. Ultimately, hydrodynamic controls on Box Canyon flood erosion and deposition derive from the irregular volcanic rift topography of the eastern Snake River Plain. Outburst floods from a glacial lake in headwater regions during the late Pleistocene may have induced the torrential discharges within Box Canyon.

  15. Apollo 17 KREEPy basalt - A rock type intermediate between mare and KREEP basalts

    NASA Technical Reports Server (NTRS)

    Ryder, G.; Stoeser, D. B.; Wood, J. A.

    1977-01-01

    The Apollo 17 KREEPy basalt is a unique lunar volcanic rock, observed only as clasts in the light friable breccia matrix (72275) of Boulder 1, Station 2 at Taurus-Littrow. Its status as a volcanic rock is confirmed by the absence of any meteoritic contamination, a lack of cognate inclusions or xenocrystal material, and low Ni contents in metal grains. The basalt was extruded 4.01 + or - 0.04 b.y. ago, approximately contemporaneously with the high-alumina mare basalts at Fra Mauro; shortly afterwards it was disrupted, probably by the Serenitatis impact, and its fragments emplaced in the South Massif. The basalt, which is quartz-normative and aluminous, is chemically and mineralogically intermediate between the Apollo 15 KREEP basalts and the high-alumina mare basalts in most respects. It consists mainly of plagioclase and pigeonitic pyroxene in approximately equal amounts, and 10-30% of mesostatis.

  16. Volatile emissions from Central Atlantic Magmatic Province Basalts: Mass assumptions and environmental consequences

    NASA Astrophysics Data System (ADS)

    McHone, J. Gregory

    Mesozoic basins that contain extrusive basalts of the 200 Ma Central Atlantic Magmatic Province (CAMP) presently total about 320,000 km2. However, CAMP dikes and sills similar to those that fed the basin basalts are also spread widely across an area greater than 10 million km2 within four continents. In addition, basalts of the east coast margin igneous province (ECMIP) of North America, which cause the east coast magnetic anomaly, covered about 110,000 km2 with 1.3 million km3 of extrusive lavas. If only half of the continental CAMP area was originally covered by 200 m of surface flows, the total volume of CAMP and ECMIP lavas exceeded 2.3 million km3. Weighted averages for the volatile contents of 686 CAMP tholeiitic dikes and sills, in weight %, are: CO2 = 0.117; S = 0.052; F = 0.035; and Cl = 0.050. Atmospheric emissions of volatiles from flood basalts are conservatively estimated as 50% to 70% of the volatile content of the sub-volcanic magmas, mainly exsolved into gaseous plumes from lava curtains at the erupting fissures. Total volcanic emissions of these gases therefore ranged between 1.11×1012 and 5.19×1012 metric tons, enough for major worldwide environmental problems. Radiometric and stratigraphic dates indicate that most CAMP volcanic activity was brief, widespread, and close to the Tr-J boundary, which is marked by a profound mass extinction. More precise information about the timing, duration, and chemical emissions of volcanic episodes is needed to support a model for CAMP in the extinction event.

  17. The Karoo igneous province — A problem area for inferring tectonic setting from basalt geochemistry

    NASA Astrophysics Data System (ADS)

    Duncan, Andrew R.

    1987-06-01

    Tholeiitic basalts and associated intrusives are the major component of the Karoo igneous province. They are of Mesozoic age and constitute one of the world's classic continental flood basalt (CFB) provinces. It has been argued that most Karoo basalts have not undergone significant contamination with continental crust and that their lithospheric mantle source areas were enriched in incompatible minor and trace elements during the Proterozoic. The only exceptions to this are late-stage MORB-like dolerites near the present-day continental margins which are considered to be of asthenospheric origin. When data for the "southern" Karoo basalts are plotted on many of the geochemical discriminant diagrams which have been used to infer tectonic setting, essentially all of them would be classified as calc-alkali basalts (CAB's) or low-K tholeiites. Virtually none of them plot in the compositional fields designated as characteristic of "within-plate" basalts. There is little likelihood that the compositions of the Karoo basalts can be controlled by active subduction at the time of their eruption and no convincing evidence that a "subduction component" has been added to the subcontinental lithospheric mantle under the entire area in which the basalts crop out. It must be concluded that the mantle source areas for CAB's and the southern Karoo basalts have marked similarities. In contrast, the data for "northern" Karoo basalts largely plot in the "within-plate" field on geochemical discriminant diagrams. Available data suggest that the source composition and/or the restite mineralogy and degree of partial melting are different for southern and northern Karoo basalts. There is no evidence for any difference in tectonic setting between the southern and northern Karoo basalts at the time they were erupted. This appears to be clear evidence that specific mantle source characteristics and/or magmatic processes can vary within a single CFB province to an extent that renders at least

  18. The roles of fractional crystallization, magma mixing, crystal mush remobilization and volatile-melt interactions in the genesis of a young basalt-peralkaline rhyolite suite, the greater Olkaria volcanic complex, Kenya Rift valley

    USGS Publications Warehouse

    Macdonald, R.; Belkin, H.E.; Fitton, J.G.; Rogers, N.W.; Nejbert, K.; Tindle, A.G.; Marshall, A.S.

    2008-01-01

    The Greater Olkaria Volcanic Complex is a young (???20 ka) multi-centred lava and dome field dominated by the eruption of peralkaline rhyolites. Basaltic and trachytic magmas have been erupted peripherally to the complex and also form, with mugearites and benmoreites, an extensive suite of magmatic inclusions in the rhyolites. The eruptive rocks commonly represent mixed magmas and the magmatic inclusions are themselves two-, three- or four-component mixes. All rock types may carry xenocrysts of alkali feldspar, and less commonly plagioclase, derived from magma mixing and by remobilization of crystal mushes and/or plutonic rocks. Xenoliths in the range gabbro-syenite are common in the lavas and magmatic inclusions, the more salic varieties sometimes containing silicic glass representing partial melts and ranging in composition from anorthite ?? corundum- to acmite-normative. The peralkaline varieties are broadly similar, in major element terms, to the eruptive peralkaline rhyolites. The basalt-trachyte suite formed by a combination of fractional crystallization, magma mixing and resorption of earlier-formed crystals. Matrix glass in metaluminous trachytes has a peralkaline rhyolitic composition, indicating that the eruptive rhyolites may have formed by fractional crystallization of trachyte. Anomalous trace element enrichments (e.g. ??? 2000 ppm Y in a benmoreite) and negative Ce anomalies may have resulted from various Na- and K-enriched fluids evolving from melts of intermediate composition and either being lost from the system or enriched in other parts of the reservoirs. A small group of nepheline-normative, usually peralkaline, magmatic inclusions was formed by fluid transfer between peralkaline rhyolitic and benmoreitic magmas. The plumbing system of the complex consists of several independent reservoirs and conduits, repeatedly recharged by batches of mafic magma, with ubiquitous magma mixing. ?? The Author 2008. Published by Oxford University Press. All

  19. Differentiation and volcanism in the lunar highlands: photogeologic evidence and Apollo 16 implications

    USGS Publications Warehouse

    Trask, N.J.; McCauley, J.F.

    1972-01-01

    Materials of possible volcanic origin in the lunar highlands include (1) highland plains materials, (2) materials forming closely spaced hills in which summit furrows and chains of craters are common and (3) materials forming closely spaced hills (some of which parallel the lunar grid) on which summit furrows and chain craters are rare. The highland plains materials probably are basaltic lavas with less Fe and Ti than the mare plains materials. The two hilly units appear to consist of materials that, if volcanic, were more viscous in the molten state than any of the lunar plains units; thus these materials may be significantly enriched in felsic components. Most of the highland materials of possible volcanic origin formed after the Imbrium multi-ring basin but before mare material completed flooding parts of the moon; they therefore postdate accretion of the moon and may represent several episodes of premare volcanism. ?? 1972.

  20. The relation of catastrophic flooding of Mangala Valles, Mars, to faulting of memnonia fossae and Tharsis volcanism

    USGS Publications Warehouse

    Tanaka, K.L.; Chapman, M.G.

    1990-01-01

    Detailed stratigraphic relations indicate two coeval periods of catastrophic flooding and Tharsis-centered faulting (producing Memnonia Fossae) in the Mangala Valles region of Mars. Major sequences of lava flows of the Tharsis Montes Formation and local, lobate plains flows were erupted during and between these channeling and faulting episodes. First, Late Hesperian channel development overlapped in time the Tharsis-centered faulting that trends north 75?? to 90??E. Next, Late Hesperian/Early Amazonian flooding was coeval with faulting that trends north 55?? to 70??E. In some reaches, resistant lava flows filled the early channels, resulting in inverted channel topography after the later flooding swept through. Both floods likely originated from the same graben, which probably was activated during each episode of faulting. Faulting broke through groundwater barriers and tapped confined aquifers in higher regions west and east of the point of discharge. The minimum volume of water required to erode Mangala Valles (about 5 ?? 1012 m3) may have been released through two floods that drained a few percent pore volume from a relatively permeable aquifer. The peak discharges may have been produced by hydrothermal groundwater circulation induced by Tharsis magmatism, tectonic uplift centered at Tharsis Montes, and compaction of saturated crater ejecta due to loading by lava flows. -Authors

  1. The largest volcanic eruptions on Earth

    NASA Astrophysics Data System (ADS)

    Bryan, Scott E.; Peate, Ingrid Ukstins; Peate, David W.; Self, Stephen; Jerram, Dougal A.; Mawby, Michael R.; Marsh, J. S. (Goonie); Miller, Jodie A.

    2010-10-01

    silicic eruptions, however, are moderately to highly explosive, producing co-current pyroclastic fountains (rarely Plinian) with discharge rates of 10 9-10 11 kg s -1 that emplace welded to rheomorphic ignimbrites. At present, durations for the large-magnitude silicic eruptions are unconstrained; at discharge rates of 10 9 kg s -1, equivalent to the peak of the 1991 Mt Pinatubo eruption, the largest silicic eruptions would take many months to evacuate > 5000 km 3 of magma. The generally simple deposit structure is more suggestive of short-duration (hours to days) and high intensity (~ 10 11 kg s -1) eruptions, perhaps with hiatuses in some cases. These extreme discharge rates would be facilitated by multiple point, fissure and/or ring fracture venting of magma. Eruption frequencies are much elevated for large-magnitude eruptions of both magma types during LIP-forming episodes. However, in basalt-dominated provinces (continental and ocean basin flood basalt provinces, oceanic plateaus, volcanic rifted margins), large magnitude (> M8) basaltic eruptions have much shorter recurrence intervals of 10 3-10 4 years, whereas similar magnitude silicic eruptions may have recurrence intervals of up to 10 5 years. The Paraná-Etendeka province was the site of at least nine > M8 silicic eruptions over an ~ 1 Myr period at ~ 132 Ma; a similar eruption frequency, although with a fewer number of silicic eruptions is also observed for the Afro-Arabian Province. The huge volumes of basaltic and silicic magma erupted in quick succession during LIP events raises several unresolved issues in terms of locus of magma generation and storage (if any) in the crust prior to eruption, and paths and rates of ascent from magma reservoirs to the surface. Available data indicate four end-member magma petrogenetic pathways in LIPs: 1) flood basalt magmas with primitive, mantle-dominated geochemical signatures (often high-Ti basalt magma types) that were either transferred directly from melting regions in

  2. Evidence for Noachian flood volcanism in Noachis Terra, Mars, and the possible role of Hellas impact basin tectonics

    NASA Astrophysics Data System (ADS)

    Rogers, A. D.; Nazarian, A. H.

    2013-05-01

    Spectral and imaging data sets from Mars Reconnaissance Orbiter and Mars Odyssey, as well as spectral and topographic data from Mars Global Surveyor, are used to understand the origin of in-place rock units found in the intercrater plains and Hellas circumferential graben floors of Noachis Terra, Mars. The rocky units are interpreted as effusive volcanic plains on the basis of broad areal extent, structural competence, association with topographic lows, distinct mineralogy from regolith, and lack of sedimentary textures or minerals associated with aqueous processes. Some rocky expanses contain at least two compositionally distinct units. The relatively light-toned unit exhibits a higher plagioclase/pyroxene ratio than the lower, dark-toned unit. Both units exhibit ~10% olivine enrichment compared to surrounding regolith. These units are heavily degraded and exhibit crater model ages between ~3.80 and 4.0 Ga, making these some of the oldest preserved volcanic plains accessible by remote sensing. They are found in association with Hellas ring structures, where the westward extent of these rocky units is limited to the outermost ring structure. Fracturing associated with the Hellas impact may have enabled magmas to ascend from the base of the crust in the circum-Hellas region. Identification of these units as volcanic materials extends previous estimates for volume of outgassed volatiles. Though the estimated volcanic volume increase is minor, the local effects could have been significant. The role of multi-ring impact basins in providing a spatial control on Martian highlands volcanism and subsurface mineralization may have been underestimated in the past.

  3. A 13 ± 3 ka age determination of a tholeiite, Pinacate volcanic field, Mexico, and improved methods for 40Ar/ 39Ar dating of young basaltic rocks

    NASA Astrophysics Data System (ADS)

    Turrin, Brent D.; Gutmann, James T.; Swisher, Carl C., III

    2008-11-01

    Among the youngest lava flows of the Pinacate volcanic field, Sonora, Mexico, is a large outpouring of tholeiite, the Ives flow. This tube-fed pahoehoe flow contrasts sharply with other Pinacate lavas in its great volume, alkali-poor composition and morphologic features, which include novel small structures named "spatter tubes." Despite its K-poor character, young age, and the presence of excess 40Ar, we determined a 40Ar/ 39Ar age on samples of this flow at 13 ± 3 ka. Such an age determination is made possible via careful monitoring of the mass discrimination of the mass spectrometer and by stacking results from multiple incremental-heating experiments into a single, composite isochron. This age is among the youngest ever to be determined with such precision by the 40Ar/ 39Ar method on a K-poor tholeiite.

  4. A catastrophic flood caused by drainage of a caldera lake at Aniakchak Volcano, Alaska, and implications for volcanic hazards assessment

    USGS Publications Warehouse

    Waythomas, C.F.; Walder, J.S.; McGimsey, R.G.; Neal, C.A.

    1996-01-01

    Aniakchak caldera, located on the Alaska Peninsula of southwest Alaska, formerly contained a large lake (estimated volume 3.7 ?? 109 m3) that rapidly drained as a result of failure of the caldera rim sometime after ca. 3400 yr B.P. The peak discharge of the resulting flood was estimated using three methods: (1) flow-competence equations, (2) step-backwater modeling, and (3) a dam-break model. The results of the dam-break model indicate that the peak discharge at the breach in the caldera rim was at least 7.7 ?? 104 m3 s-1, and the maximum possible discharge was ???1.1 ?? 106 m3 s-1. Flow-competence estimates of discharge, based on the largest boulders transported by the flood, indicate that the peak discharge values, which were a few kilometers downstream of the breach, ranged from 6.4 ?? 105 to 4.8 ?? 106 m3 s-1. Similar but less variable results were obtained by step-backwater modeling. Finally, discharge estimates based on regression equations relating peak discharge to the volume and depth of the impounded water, although limited by constraining assumptions, provide results within the range of values determined by the other methods. The discovery and documentation of a flood, caused by the failure of the caldera rim at Aniakchak caldera, underscore the significance and associated hydrologic hazards of potential large floods at other lake-filled calderas.

  5. Snowball Earth and basaltic traps

    NASA Astrophysics Data System (ADS)

    Dupre, B.; Godderis, Y.; Nedelec, A.; Donnadieu, Y.; Dessert, C.; Francois, L. M.; Grard, A.

    2003-04-01

    The causes of the Neo-Proterozoic glaciations is still a matter of debate. One potential trigger for those glaciations is a major perturbation of the global carbon cycle, leading to the consumption of atmospheric CO_2, and finally to the cooling of the global climate. The first glacial episode is characterized by intense rift formations. The Proto-Pacific ocean starts to open within the Sturtian stage (800-750 Ma). The onset of rifts cutting through continental surfaces might have been coeval with the spreading of continental flood basalts. As demonstrated by Dessert et al (2001) for the K-T boundary, such events might severely impacts the long term evolution of the global climate, through intense consumption of atmospheric CO_2 by fresh basaltic surfaces, leading to non negligible global cooling at the million year timescale. Based on weathering laws for basaltic and granitic surfaces, we estimate that the onset of continental flood basalts over 6 million km^2 along the equator (crossed by the Proto-Pacific rift) will drive the Earth into global glaciation 1.5 My after the event, assuming a pre-perturbation level of 280 ppmv of CO_2 and a solar luminosity reduced by 6%. The δ13C of carbonates accumulating between the start of the continental plume and the onset of the global glaciation is expected to fall by about 3 ppm in response to the degassing of large amount of mantle carbon into the atmosphere, in agreement with data. This hypothesis raises the question of the cyclicity of the glaciations. Once the glaciation ends, the basaltic surface starts again to weather, and plunge the Earth into a new deep glaciation. Within 30 My, the basaltic trap, originally located at the equator, might have migrated 3500 km southward, within the dryer tropical area. Such migration reduces the consumption of CO_2 by the basaltic surface, preventing the Earth from a new global glaciation.

  6. Thickness of western mare basalts

    NASA Technical Reports Server (NTRS)

    Dehon, R. A.

    1979-01-01

    An isopach map of the basalt thickness in the western mare basins is constructed from measurements of the exposed external rim height of partially buried craters. The data, although numerically sparse, is sufficiently distributed to yield gross thickness variations. The average basalt thickness in Oceanus Procellarum and adjacent regions is 400 m with local lenses in excess of 1500 m in the circular maria. The total volume of basalt in the western maria is estimated to be in the range of 1.5 x 10 to the 6th power cu km. The chief distinction between the eastern and western maria appears to be one of basalt volumes erupted to the surface. Maximum volumes of basalt are deposited west of the central highlands and flood subjacent terrain to a greater extent than on the east. The surface structures of the western maria reflect the probability of a greater degree of isostatic response to a larger surface loading by the greater accumulation of mare basalt.

  7. The Quaternary volcanic rocks of the northern Afar Depression (northern Ethiopia): Perspectives on petrology, geochemistry, and tectonics

    NASA Astrophysics Data System (ADS)

    Hagos, Miruts; Koeberl, Christian; van Wyk de Vries, Benjamin

    2016-05-01

    The northern Afar Depression is one of the most volcano-tectonically active parts of the East African Rift system, a place where oceanic rifting may be beginning to form an incipient oceanic crust. In its center, over an area that is ∼80 km long and ∼50 km wide, there are seven major NNW-SSE-aligned shield volcanoes/volcanic edifices surrounded by compositionally distinct fissure-fed basalts. The Quaternary lavas in this area range from transitional to tholeiitic basalts, with significant across-axis variation both in mineralogy and chemistry. The variation in the contents of the major elements (TiO2, Al2O3, and Fe2O3), incompatible trace elements (Nd, Hf, Th, Ta), and the contents and ratios of the rare earth elements (REE) (e.g., (La/Yb)n = 5.3-8.9) indicate some variation in the petrogenetic processes responsible for the formation of these basalts. However, the variation in isotopic compositions of the mafic lavas is minimal (87Sr/86Sr = 0.7036-0.7041, 143Nd/144Nd = 0.51286-0.51289), which suggests only one source for all the Danakil Depression basalts. These basalts have isotope and incompatible trace element ratios that overlap with those of the Oligocene High-Ti2 flood basalts from the Ethiopian Plateau, interpreted as being derived from the last phase/tail of the Afar mantle plume source. Moreover, the Ce/Pb, Ba/U ratios indicate that the involvement of continental crust in the petrogenesis of the basaltic rocks is minimal; instead, both depth and degree of melting of the source reservoir underneath the northern Afar Depression played a major role for the production of incompatible element-enriched basalts (e.g., AleBagu Shield basalts) and the incompatible element-depleted tholeiitic basalts (e.g., Erta'Ale and Alu Shield basalts).

  8. The basalts of Mare Frigoris

    NASA Astrophysics Data System (ADS)

    Kramer, G. Y.; Jaiswal, B.; Hawke, B. R.; Öhman, T.; Giguere, T. A.; Johnson, K.

    2015-10-01

    This paper discusses the methodology and results of a detailed investigation of Mare Frigoris using remote sensing data from Clementine, Lunar Prospector, and Lunar Reconnaissance Orbiter, with the objective of mapping and characterizing the compositions and eruptive history of its volcanic units. With the exception of two units in the west, Mare Frigoris and Lacus Mortis are filled with basalts having low-TiO2 to very low TiO2, low-FeO, and high-Al2O3 abundances. These compositions indicate that most of the basalts in Frigoris are high-Al basalts—a potentially undersampled, yet important group in the lunar sample collection for its clues about the heterogeneity of the lunar mantle. Thorium abundances of most of the mare basalts in Frigoris are also low, although much of the mare surface appears elevated due to contamination from impact gardening with the surrounding high-Th Imbrium ejecta. There are, however, a few regional thorium anomalies that are coincident with cryptomare units in the east, the two youngest mare basalt units, and some of the scattered pyroclastic deposits and volcanic constructs. In addition, Mare Frigoris lies directly over the northern extent of the major conduit for a magma plumbing system that fed many of the basalts that filled Oceanus Procellarum, as interpreted by Andrews-Hanna et al. (2014) using data from the Gravity Recovery and Interior Laboratory mission. The relationship between this deep-reaching magma conduit and the largest extent of high-Al basalts on the Moon makes Mare Frigoris an intriguing location for further investigation of the lunar mantle.

  9. Temperature dependence of basalt weathering

    NASA Astrophysics Data System (ADS)

    Li, Gaojun; Hartmann, Jens; Derry, Louis A.; West, A. Joshua; You, Chen-Feng; Long, Xiaoyong; Zhan, Tao; Li, Laifeng; Li, Gen; Qiu, Wenhong; Li, Tao; Liu, Lianwen; Chen, Yang; Ji, Junfeng; Zhao, Liang; Chen, Jun

    2016-06-01

    The homeostatic balance of Earth's long-term carbon cycle and the equable state of Earth's climate are maintained by negative feedbacks between the levels of atmospheric CO2 and the chemical weathering rate of silicate rocks. Though clearly demonstrated by well-controlled laboratory dissolution experiments, the temperature dependence of silicate weathering rates, hypothesized to play a central role in these weathering feedbacks, has been difficult to quantify clearly in natural settings at landscape scale. By compiling data from basaltic catchments worldwide and considering only inactive volcanic fields (IVFs), here we show that the rate of CO2 consumption associated with the weathering of basaltic rocks is strongly correlated with mean annual temperature (MAT) as predicted by chemical kinetics. Relations between temperature and CO2 consumption rate for active volcanic fields (AVFs) are complicated by other factors such as eruption age, hydrothermal activity, and hydrological complexities. On the basis of this updated data compilation we are not able to distinguish whether or not there is a significant runoff control on basalt weathering rates. Nonetheless, the simple temperature control as observed in this global dataset implies that basalt weathering could be an effective mechanism for Earth to modulate long-term carbon cycle perturbations.

  10. The Cenozoic volcanic province of Tibesti (Sahara of Chad): major units, chronology, and structural features

    NASA Astrophysics Data System (ADS)

    Deniel, C.; Vincent, P. M.; Beauvilain, A.; Gourgaud, A.

    2015-09-01

    Using both field relationships and some absolute ages, the sequence of volcanic units in the Cenozoic Tibesti Volcanic Province (TVP) (Chad) is established as follows: (1) plateau volcanism, between at least 17 and 8 Ma, consisting of flood basalts and silicic lava plugs, with intercalated ignimbritic sheets in the upper basalt succession increasing in amount upwards. Ages decrease from NE to SW, following the migration of the small NW-SE flexures concentrating the feeding dike swarms; (2) Late Miocene large central composite volcanoes exhibiting diverse and original structures. Some of them (Tarso Toon, Ehi Oyé, and Tarso Yéga) are located along a major NNE fault, representing the main tectonic direction in Tibesti since Precambrian times; (3) construction of three large ignimbritic volcanoes, associated with significant updoming of the basement, ending with the collapse of large calderas: Voon (about 5-7 Ma), Emi Koussi (2.4-1.33 Ma), and Yirrigué (0.43 Ma); (4) basaltic activity, starting at about 5-7 Ma, and essentially consisting of cinder cones and associated lava flows (Tarso Tôh, Tarso Ahon, and Tarso Emi Chi); and (5) final volcanic activity represented by post-Yirrigué caldera activity in the Tarso Toussidé Volcanic Complex, and especially Ehi Toussidé (the only active volcano in Tibesti), plus Ehi Timi and Ehi Mousgou volcanoes, similar to Ehi Toussidé. The two tectonic directions controlling some volcanic features of the province correspond to the major old lithospheric structures delimiting the volcanic province, namely, the great NW-SE Tassilian flexure to the SW and a major NE-NNE fault zone to the E. Unusual conditions of uplift and erosion in the TVP enable exceptional exposure of the internal structure of its volcanoes.

  11. Pahoehoe-a‧a transitions in the lava flow fields of the western Deccan Traps, India-implications for emplacement dynamics, flood basalt architecture and volcanic stratigraphy

    NASA Astrophysics Data System (ADS)

    Duraiswami, Raymond A.; Gadpallu, Purva; Shaikh, Tahira N.; Cardin, Neha

    2014-04-01

    Unlike pahoehoe, documentation of true a‧a lavas from a modern volcanological perspective is a relatively recent phenomenon in the Deccan Trap (e.g. Brown et al., 2011, Bull. Volcanol. 73(6): 737-752) as most lava flows previously considered to be a‧a (e.g. GSI, 1998) have been shown to be transitional (e.g. Rajarao et al., 1978, Geol. Soc. India Mem. 43: 401-414; Duraiswami et al., 2008 J. Volcanol. Geothermal. Res. 177: 822-836). In this paper we demonstrate the co-existence of autobrecciation products such as slabby pahoehoe, rubbly pahoehoe and a‧a in scattered outcrops within the dominantly pahoehoe flow fields. Although volumetrically low in number, the pattern of occurrence of the brecciating lobes alongside intact ones suggests that these might have formed in individual lobes along marginal branches and terminal parts of compound flow fields. Complete transitions from typical pahoehoe to 'a‧a lava flow morphologies are seen on length scales of 100-1000 m within road and sea-cliff sections near Uruli and Rajpuri. We consider the complex interplay between local increase in the lava supply rates due to storage or temporary stoppage, local increase in paleo-slope, rapid cooling and localized increase in the strain rates especially in the middle and terminal parts of the compound flow field responsible for the transitional morphologies. Such transitions are seen in the Thakurwadi-, Bushe- and Poladpur Formation in the western Deccan Traps. These are similar to pahoehoe-a‧a transitions seen in Cenozoic long lava flows (Undara ˜160 km, Toomba ˜120 km, Kinrara ˜55 km) from north Queensland, Australia and Recent (1859) eruption of Mauna Loa, Hawaii (a‧a lava flow ˜51 km) suggesting that flow fields with transitional tendencies cannot travel great lengths despite strong channelisation. If these observations are true, then it arguably limits long distance flow of Deccan Traps lavas to Rajahmundry suggesting polycentric eruptions at ˜65 Ma in Peninsular India.

  12. Deccan volcanism and K-T boundary signatures

    NASA Technical Reports Server (NTRS)

    Murali, A. V.; Schuraytz, B. C.; Parekh, P. P.

    1988-01-01

    The Deccan Traps in the Indian subcontinent represent one of the most extensive flood basalt provinces in the world. These basalts occur mainly as flat-lying, subaerially erupted tholeiitic lava flows, some of which are traceable for distances of more than 100 km. Offshore drilling and geophysical surveys indicate that a part of the Deccan subsided or was downfaulted to the west beneath the Arabian Sea. The presence of 1 to 5 m thick intertrappean sediments deposited by lakes and rivers indicates periods of quiescence between eruptions. The occurrence of numerous red bole beds among the flows suggests intense weathering of flow tops between eruptive intervals. Although the causative relationship of the Cretaceous-Tertiary (K-T) biotic extinctions to Deccan volcanism is debatable, the fact that the main Deccan eruptions straddle the K-T event appears beyond doubt from the recent Ar-40/Ar-39 ages of various Deccan flows. This temporal relationship of the K-T event with Deccan volcanism makes the petrochemical signatures of the entire Deccan sequence (basalt flows, intercalated intertrappean sediments, infratrappean Lameta beds (with dinosaur fossils), and the bole beds) pertinent to studies of the K-T event. The results of ongoing study is presented.

  13. Morphology and development of pahoehoe flow-lobe tumuli and associated features from a monogenetic basaltic volcanic field, Bahariya Depression, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Khalaf, Ezz El Din Abdel Hakim; Hammed, Mohamed Saleh

    2016-01-01

    The dimensions, landforms, and structural characteristics of pahoehoe flow-lobe tumuli from Bahariya Depression are collectively reported here for the first time. The flow-lobe tumuli documented here characterize hummocky flow surfaces. These tumuli are characterized by low, dome-like mounds, lava-inflation clefts, and squeeze ups. Flow-lobe tumuli are of various shapes and sizes, which are affected by the mechanism of inflation because they formed in response to the increase of pressure within the flow when the flow's crust becomes thicker. The tumuli often appear isolated or in small groups in the middle sectors of the lava flows, whereas in the distal sectors they form large concentration, suggesting the presence of complex lava tubes inside of the flow. Tumuli exhibited by El Bahariya lava flows are between 3.0 and 50 m in length and up to 5.0 m in height with lenticular geometry in aerial view. The flow emplacement of flow-lobe tumuli is controlled by variations in local characteristics such as nature of the substrate, flow orientation, slope, interferrence with other lobes, and rate of lava supply. Their presence generally towards the terminal ends of flow fields suggests that they seldom form over the clogged portions of distributary tubes or pathways. Thus, localized inflations that formed over blockages in major lava tubes result in formation of flow-lobe tumuli. The three-tiered (crust-core-basal zone) internal structure of the flow-lobe tumuli, resembling the typical distribution of vesicles in P-type lobes, confirms emplacement by the mechanism of inflation. All the available data show that the morphology and emplacement mechanism of the studied flow-lobe tumuli may be analogous to similar features preserved within topographically confined areas of the Hawaiian and Deccan hummocky lava flows. Considering the age of the studied volcanic fields (˜22 Ma) it is most probable that the structures described here may be amongst the oldest recognized examples

  14. Composition of basalts from the Mid-Atlantic Ridge

    USGS Publications Warehouse

    Engel, A.E.J.; Engel, C.G.

    1964-01-01

    Studies of volcanic rocks in dredge hauls from the submerged parts of the Mid-Atlantic Ridge suggest that it consists largely of tholeiitic basalt with low values of K, Ti, and P. In contrast, the volcanic islands which form the elevated caps on the Ridge are built of alkali basalt with high values of Ti, Fe3+, P, Na, and K. This distinct correlation between the form of the volcanic structures, elevation above the sea floor, and composition suggests that the islands of alkali basalt are derived from a parent tholeiitic magma by differentiation in shallow reservoirs. The volume of low-potassium tholeiites along the Mid-Atlantic Ridge and elsewhere in the oceans appears to be many times that of the alkali basalts exposed on oceanic islands. Tholeiitic basalts with about 0.2 K2O appear to be the primary and predominant magma erupted on the oceanic floor.

  15. The largest volcanic eruptions on Earth

    NASA Astrophysics Data System (ADS)

    Bryan, Scott E.; Peate, Ingrid Ukstins; Peate, David W.; Self, Stephen; Jerram, Dougal A.; Mawby, Michael R.; Marsh, J. S. (Goonie); Miller, Jodie A.

    2010-10-01

    silicic eruptions, however, are moderately to highly explosive, producing co-current pyroclastic fountains (rarely Plinian) with discharge rates of 10 9-10 11 kg s -1 that emplace welded to rheomorphic ignimbrites. At present, durations for the large-magnitude silicic eruptions are unconstrained; at discharge rates of 10 9 kg s -1, equivalent to the peak of the 1991 Mt Pinatubo eruption, the largest silicic eruptions would take many months to evacuate > 5000 km 3 of magma. The generally simple deposit structure is more suggestive of short-duration (hours to days) and high intensity (~ 10 11 kg s -1) eruptions, perhaps with hiatuses in some cases. These extreme discharge rates would be facilitated by multiple point, fissure and/or ring fracture venting of magma. Eruption frequencies are much elevated for large-magnitude eruptions of both magma types during LIP-forming episodes. However, in basalt-dominated provinces (continental and ocean basin flood basalt provinces, oceanic plateaus, volcanic rifted margins), large magnitude (> M8) basaltic eruptions have much shorter recurrence intervals of 10 3-10 4 years, whereas similar magnitude silicic eruptions may have recurrence intervals of up to 10 5 years. The Paraná-Etendeka province was the site of at least nine > M8 silicic eruptions over an ~ 1 Myr period at ~ 132 Ma; a similar eruption frequency, although with a fewer number of silicic eruptions is also observed for the Afro-Arabian Province. The huge volumes of basaltic and silicic magma erupted in quick succession during LIP events raises several unresolved issues in terms of locus of magma generation and storage (if any) in the crust prior to eruption, and paths and rates of ascent from magma reservoirs to the surface. Available data indicate four end-member magma petrogenetic pathways in LIPs: 1) flood basalt magmas with primitive, mantle-dominated geochemical signatures (often high-Ti basalt magma types) that were either transferred directly from melting regions in

  16. The Spokane flood controversy

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1978-01-01

    An enormous plexus of proglacial channels that eroded into the loess and basalt of the Columbia Plateau, eastern Washington is studied. This channeled scabland contained erosional and depositional features that were unique among fluvial phenomena. Documentation of the field relationships of the region explains the landforms as the product of a relatively brief, but enormous flood, then so-called the Spokane flood.

  17. Volcano-sedimentary characteristics in the Abu Treifiya Basin, Cairo-Suez District, Egypt: Example of dynamics and fluidization over sedimentary and volcaniclastic beds by emplacement of syn-volcanic basaltic rocks

    NASA Astrophysics Data System (ADS)

    Khalaf, E. A.; Abdel Motelib, A.; Hammed, M. S.; El Manawi, A. H.

    2015-12-01

    This paper describes the Neogene lava-sediment mingling from the Abu Treifiya Basin, Cairo-Suez district, Egypt. The lava-sediment interactions as peperites have been identified for the first time at the study area and can be used as paleoenvironmental indicators. The identification of peperite reflects contemporaneous time relationship between volcanism and sedimentation and this finding is of primary importance to address the evolutional reconstruction of the Abu Treifiya Basin. Characterization of the facies architecture and textural framework of peperites was carried out through detailed description and interpretation of their outcrops. The peperites and sedimentary rocks are up to 350 m thick and form a distinct stratigraphic framework of diverse lithology that is widespread over several kilometers at the study area. Lateral and vertical facies of the peperites vary from sediment intercalated with the extrusive/intrusive basaltic rocks forming peperitic breccias to lava-sediment contacts at a large to small scales, respectively. Peperites encompass five main facies types ascribed to: (i) carbonate sediments-hosted fluidal and blocky peperites, (ii) lava flow-hosted blocky peperites, (iii) volcaniclastics-hosted fluidal and blocky peperites, (iv) sandstone/siltstone rocks-hosted blocky peperites, and (iv) debris-flows-hosted blocky peperites. Soft sediment deformation structures, vesiculated sediments, sediments filled-vesicles, and fractures in lava flows indicate that lava flows mingled with unconsolidated wet sediments. All the peperites in this study could be described as blocky or fluidal, but mixtures of different clast shapes occur regardless of the host sediment. The presence of fluidal and blocky juvenile clasts elucidates different eruptive styles, reflecting a ductile and brittle fragmentation. The gradual variation from fluidal to blocky peperite texture, producing the vertical grading is affected by influencing factors, e.g., the viscosity, magma

  18. Rise of volcanic plumes to the stratosphere aided by penetrative convection above large lava flows

    NASA Astrophysics Data System (ADS)

    Kaminski, E.; Chenet, A.-L.; Jaupart, C.; Courtillot, V.

    2011-01-01

    Turbulent volcanic plumes disperse fine ash particles and toxic gases in the atmosphere and can lead to significant temperature drops in the atmosphere. In the geological past, the emplacement of large continental flood basalts (CFB) has been associated with large changes in the global environment and extinctions of biological species. The variable intensity of environmental changes induced by otherwise similar CFB events, however, begs for a reevaluation of physical controls on the environmental impact of volcanic eruptions. The climatic impact of an eruption depends on its ability to inject gases in the stratosphere and on the eruption rate. Using integral models of turbulent plumes above line and point sources, we find that mass rate estimates for CFBs are in general not large enough for volcanic plumes to reach the stratosphere on their own. Basaltic eruptions, however, are also associated with widespread lava flows which lose large amounts of heat and generate convection in the atmosphere. This form of convection, known as penetrative convection, acts to erode the stably stratified lower atmosphere and generates a thick well-mixed heated atmospheric layer in a few hours. The added buoyancy provided by such a layer almost always ensures that volcanic gases get transported to the stratosphere. The environmental consequences of CFBs are therefore controlled not by the inputs to the atmosphere from individual volcanic plumes, but by the dynamic response of the climate system to a succession of short eruptive pulses within a longer-lasting eruption sequence.

  19. Rise of Volcanic Plumes to the Stratosphere Aided by Penetrative Convection above Large Lava Flows

    NASA Astrophysics Data System (ADS)

    Kaminski, E.; Chenet, A.; Jaupart, C. P.; Courtillot, V.

    2011-12-01

    Turbulent volcanic plumes disperse fine ash particles and toxic gases in the atmosphere and can lead to significant temperature drops in the atmosphere. In the geological past, the emplacement of large continental flood basalts (CFB) has been associated with large changes in the global environment and extinctions of biological species. The variable intensity of environmental changes induced by otherwise similar CFB events, however, begs for a reevaluation of physical controls on the environmental impact of volcanic eruptions. The climatic impact of an eruption depends on its ability to inject gases in the stratosphere and on the eruption rate. Using integral models of turbulent plumes above line and point sources, we find that mass rate estimates for CFBs are in general not large enough for volcanic plumes to reach the stratosphere on their own. Basaltic eruptions, however, are also associated with widespread lava flows which lose large amounts of heat and generate convection in the atmosphere. This form of convection, known as penetrative convection, acts to erode the stably stratified lower atmosphere and generates a thick well-mixed heated atmospheric layer in a few hours. The added buoyancy provided by such a layer almost always ensures that volcanic gases get transported to the stratosphere. The environmental consequences of CFBs are therefore controlled not by the inputs to the atmosphere from individual volcanic plumes, but by the dynamic response of the climate system to a succession of short eruptive pulses within a longer-lasting eruption sequence.

  20. Volcanically Active Regions on Io

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Shown here is a portion of one of the highest-resolution images of Io (Latitude: +10 to +60 degrees, Longitude: 180 to 225 degrees) acquired by the Galileo spacecraft, revealing immense lava flows and other volcanic landforms. Several high-temperature volcanic hot spots have been detected in this region by both the Near Infrared Mapping Spectrometer and the imaging system of Galileo. The temperatures are consistent with active silicate volcanism in lava flows or lava lakes (which reside inside irregular depressions called calderas). The large dark lava flow in the upper left region of the image is more than 400 km long, similar to ancient flood basalts on Earth and mare lavas on the Moon.

    North is to the top of the picture and the sun illuminates the surface from the left. The image covers an area 1230 kilometers wide and the smallest features that can be discerned are 2.5 kilometers in size. This image was taken on November 6th, 1996, at a range of 245,719 kilometers by the Solid State Imaging (CCD) system on the Galileo Spacecraft.

    Launched in October 1989, Galileo entered orbit around Jupiter on December 7, 1995. The spacecraft's mission is to conduct detailed studies of the giant planet, its largest moons and the Jovian magnetic environment. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC.

    This image and other images and data received from Galileo are posted on the Galileo mission home page on the World Wide Web at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  1. Flood Lavas of the r2 Magnetostratigraphic Interval of the Grande Ronde Basalt: New Investigations Into Stratigraphy, Eruption Mechanisms and Volatile Release

    NASA Astrophysics Data System (ADS)

    Davis, K.; Wolff, J. A.; Rowe, M. C.; Boroughs, S.; Self, S.

    2013-12-01

    The Grande Ronde Basalt makes up 71% of the ~210,000 km3 Columbia River Basalt Group. The largest identified unit within the Columbia River lavas is the Wapshilla Ridge Member of the R2 magnetostratigraphic interval of the GRB, with a volume of 40,350 km3 [1]. In the vent area in NE Oregon, it is under- and overlain by the Mt. Horrible and Grouse Creek Members of the GRB. Field relations and chemical correlation indicate that the 8,150 km3 Mt. Horrible lava was extruded during the same eruptive episode as the Wapshilla. The Grouse Creek Member may also be part of the same eruptive sequence ; if so the total volume of this event is in excess of 50,000 km3. Here we present field observations and petrologic data, including analyses of glassy melt inclusions in microphenocrysts, from several locations within the source region for the Wapshilla Ridge Member. Coarse phreatomagmatic tephra of the Wapshilla Ridge Member is found over a 500 km2 area of NE Oregon which we identify as a vent field. Both glassy lapilli and melt inclusions exhibit a broader range in compositions than do tightly-clustered whole-rock compositions of dense lava collected from throughout the Columbia plateau, indicating that the perceived homogeneity of Columbia River lavas is due in part to syn-eruptive, within-flow homogenization. Glassy lapilli have highly variable S contents between 100 and 1260 ppm with an average of 540 ppm. This is consistent with quenching before degassing was complete, a common feature of phreatomagmatic eruptions. S concentrations in melt inclusions in plagioclase, pyroxene, and magnetite microphenocrysts are 1100 - 2900 ppm. Scaling these results to the total volume, atmospheric S release from this giant event is estimated at 161 × 37 Gt, approximately 3,000 times that from the Tambora 1815 event. Preliminary SIMS analysis indicates water concentrations as high as 2.6 wt% in glassy melt inclusions. References: [1] Reidel and Tolan (2013) GSA Special Paper 497.

  2. Late stage Imbrium volcanism on the Moon: Evidence for two source regions and implications for the thermal history of Mare Imbrium

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Zhu, M.-H.; Zou, Y. L.

    2016-07-01

    Large open fissures or volcanic rifts can form in volcanic terrain and they are also conduits for magma ascending through the lunar crust. On the Moon, we investigated two volcanic source regions within Mare Imbrium by tracking surface morphologic features and compositional information. The Euler source region is situated at the southwest edge of the basin, while the Lambert source region lies off the south margin of the Imbrium mascon. Survey of dike surface manifestations in Euler source site suggest that dikes are the possible source of the local upper basaltic flows and the last lava phases with well developed scarps near the Euler crater, which extend northeast to the basin center. The Euler dike swarm are radial to the basin and reveal possible dike-to-conduit transition mechanism. They reveal radial subsurface fractures which may be tensional cracks preceding to the emplacement of the last stage of the mare fill. Of these, the largest dike has a more than 100 km length. The spatial arrangement of tectonic and volcanic features in Lambert source site is directly or indirectly controlled by the regional compression and extension stresses associated with flexure in response to mascon and basalt loading. In addition, compositional variation trends show a general southwest-to-northeast flooding direction of the exposed high-Ti basalts. This will have important implications for both the Imbrium basin's mare volcanism and for the thermal evolution of Mare Imbrium and the Moon.

  3. What lies below the Columbia River Basalt?

    NASA Astrophysics Data System (ADS)

    Reidel, S.; Kauffman, J.; Garwood, D.; Bush, J.

    2006-12-01

    , suggesting a major fault separating two fundamental basement structural zones. Overall, basement structures have had a significant influence on the tectonic development of the flood-basalt province and may help explain why 75 percent of the basalt occurs in the northern part of the province.

  4. Palynological constraints on timing and duration of Siberian Traps volcanic events

    NASA Astrophysics Data System (ADS)

    Visscher, Henk; Svensen, Henrik; Looy, Cindy; Fristad, Kirsten; Polozov, Alexander; Planke, Sverre

    2010-05-01

    Lacustrine sediments intercalated locally in the voluminous flood basalts and pyroclastic rocks of the Siberian Traps igneous province are characterized by the presence of surprisingly diverse assemblages of macroscopic and microscopic plant fossils. In addition, these intertrappean sediments contain a wide variety of faunal remains, such as conchostracans, ostracodes, gastropods and insects. Outside the area of presently exposed flood basalt, plant fossils may also occur abundantly in the sedimentary infill of crater lakes above vent structures in the southern part of the Tunguska Basin on the Siberian Platform. Because of a possible cause-effect relationship between Siberian Traps magmatism and end-Permian mass-extinctions, vegetation that must have grown in the immediate vicinity of the eruptive centres is one of the most obvious biota to be investigated for evidence of terrestrial biosphere crisis. On the basis of literature information and new palynological data from cored crater-lake sediments, in this presentation we briefly address the basic question to what extent the Siberian plant fossil record confirms age-equivalence between biotic and volcanic events. At present, most published biostratigraphic interpretations of the floral and faunal records refute any correspondence of end-Permian biotic turnover with the Siberian Traps. In effect, the records are long since being used to advocate an exclusively Triassic age for the Siberian volcanism, the main phase of flood basalt eruption taking place during late Early Triassic (Olenekian) and early Middle Triassic (Anisian) times. However, re-evaluation of the chronostratigraphic significance of plant megafossils and faunal remains has resulted in alternative views, which suggest a Late Permian age for part or the whole of the volcanic sequence exposed on the Siberian Platform. Compositional characters of palynomorph assemblages indicate age-equivalence of the flood basalts in the northern part of the Tunguska

  5. Geochemistry and geochronology of Hangay Dome volcanic rocks: exploring the source of high topography and volcanism in an intracontinental setting

    NASA Astrophysics Data System (ADS)

    Ancuta, L. D.; Carlson, R. W.; Idleman, B. D.; Zeitler, P. K.

    2013-12-01

    . Flow stratigraphy clearly shows the presence of substantial paleotopography that has been completely blanketed by flows, and a complex history of incision spanning the duration of volcanism. A plume source for the volcanism unlikely, given the basalt geochemistry, the lack of a large flood basalt province, and the lack of a discernable hot spot track. Large-scale slab-like delamination of the lower lithosphere also seems unlikely given the significant duration and diffuse nature of the magmatic activity. Geodynamic processes consistent with the high topography in the Hangay, the long duration of volcanism, and the sub-lithosphereic EM-1 isotopic signature include shear driven asthenospheric upwelling, thermal blanketing of the asthenosphere by thick crust, several small scale lithospheric drips or a small-scale edge-driven convection cell in the upper mantle.

  6. Degassing of carbon dioxide from basaltic magma at spreading centers: I. Afar transitional basalts

    NASA Astrophysics Data System (ADS)

    Gerlach, Terrence M.

    1989-11-01

    This study investigates the hypothesis that a significant fraction of the CO 2 in basalt supplied to axial volcanic ranges of spreading centers in the Afar depression, escapes by degassing during residence in crustal magma reservoirs. The investigation employs volcanic gas data to test the degassing hypothesis. Volcanic gases emitted from source vents at Erta'Ale lava lake are used to represent volatiles present in the basalt supplied to magma reservoirs underlying Afar spreading centers. For comparison, volcanic gases from a large fissure eruption at Ardoukoba are used to represent volatiles in basalt after a period of storage in the Afar magma reservoirs. The results confirm the hypothesis. Gases from the lava lake and fissure eruption are the same except for CO 2. They lie along a common CO 2 control line. The fissure eruption gases are six-fold depleted in CO 2 compared to gases from the continuously supplied lava lake. This difference corresponds to a loss of approximately 85% of the initial CO 2. Moreover, gases from the fissure eruption are nearly identical to those emitted by Kilauea basalts that have lost CO 2 by magma reservoir degassing. Mass balance modeling indicates an initial CO 2 content for Afar basalt of 0.12 wt.% compared to CO 2 concentrations as low as 0.02 wt.% after degassing at depth.

  7. Volcanic studies: Part E: Eratosthenian volcanism in Mare Imbrium: source of youngest lava flows

    USGS Publications Warehouse

    Schaber, Gerald G.

    1973-01-01

    Orbital photographs taken at low-Sun illumination during both the Apollo 15 (ref. 30-14) and Apollo 17 missions have provided excellent data on the lava flows in the southwestern Mare Imbrium. These photographs have been used recently to present a detailed photogeologic evaluation of these flows and their role in mare volcanism of Eratosthenian age in the basin (ref. 30-15). Eruption of these flood basalts apparently took place in at least three major episodes with suggested dates of 3.0 ± 0.4 billion years (phase I), 2.7 ± 0.3 billion years (phase II), and 2.5 ± 0.3 billion years (phase III) using the mare age-dating method described by Soderblom and Lebofsky (ref. 30-16) and recent data by Soderblom and Boyce (ref. 30-17).

  8. Shock Deformation and Volcanism across the Cretaceous - Transition.

    NASA Astrophysics Data System (ADS)

    Huffman, Alan Royce

    1990-01-01

    The cause of the Cretaceous-Tertiary (K/T) transition remains one of the most controversial scientific topics in the geosciences. Geological and geophysical evidence associated with the K/T boundary have been used to argue that the extinctions were caused by meteor impact or volcanism. The goal of this study was to assess the viability of a volcanic model for the K/T transition. Comparison of natural and experimentally-shocked quartz and feldspar using optical and transmission electron microscopy (TEM) revealed that the optical and statistical character of shock-induced microstructures in volcanic rocks are different from both classic impact microstructures, and from the Raton K/T samples. A series of 31 high-explosive (HE) shock-recovery experiments at pressures to 25 GPa and temperatures to 750^circC were completed on samples of granite and quartzite. TEM and optical microscopy reveal that pre-shock temperature and pulse duration have a first-order effect on the development of shock-induced microstructures in quartz and feldspar. Application of the experimental results to natural shock-induced microstructures indicates that the volcanic microstructures are probably produced at elevated temperatures and shock pressures that do not exceed 15 GPa. The results also suggest that the Raton K/T deposits were produced at pressures below about 25 GPa. Analysis of samples from the K/T transition at DSDP Site 527 and correlations between biostratigraphy, isotopes, and the data from this study suggest that the decline in marine productivity over an extended period of time may be due to climate changes induced by basaltic volcanism. The eruption of the Deccan Traps is a viable mechanism for the K/T extinctions, and the correlation of flood basalts with every major biotic crisis in the last 250 Ma supports the link between these two phenomena. Eruption of flood basalts enriched in F, Cl, CO_2 , and SO_2, could disrupt the terrestrial ecosystem, and could produce effects

  9. The Environmental Impact of Siberian Traps Volcanism

    NASA Astrophysics Data System (ADS)

    Saunders, A. D.; Reichow, M. K.

    2008-12-01

    volcanism began. Arguably, the earth system was much more vulnerable to the additional carbon loading from volcanism. The environmental impact of flood basalt eruptions may thus be strongly influenced by the prevailing global climate conditions and atmosphere-ocean composition.

  10. Basalts Dredged from the Northeastern Pacific Ocean.

    PubMed

    Engel, C G; Engel, A E

    1963-06-21

    Volcanic rocks dredged from seamounts, fault ridges, and other major geological features of the northeast Pacific Ocean include a wide variety of basalts. Most of these are vesicular, porphyritic types with near analogues in the Hawaiian and other oceanic islands. In addition, aluminous basalts and diabasic theoleiites impoverished in potassium also occur. There is no simple correlation of composition, degree of oxidation, vesiculation, or hydration of these basalts with texture, or depth of dredge site. Most samples appear to have been extruded at much shallower depths than those now pertaining at the dredge site. The distribution of these basalts suggests that the andesite line coincides with or lies on the continent side of the foot of the continental slope. PMID:17802173

  11. Basalts dredged from the northeastern Pacific Ocean

    USGS Publications Warehouse

    Engel, C.G.; Engel, A.E.J.

    1963-01-01

    Volcanic rocks dredged from seamounts, fault ridges, and other major geological features of the northeast Pacific Ocean include a wide variety of basalts. Most of these are vesicular, porphyritic types with near analogues in the Hawaiian and other oceanic islands. in addition, aluminous basalts and diabasic tholeiites impoverished in potassium also occur. There is no simple correlation of composition, degree of oxidation, vesiculation, or hydration of these basalts with texture, or depth of dredge site. Most samples appear to have been extruded at much shallower depths than those now pertaining at the dredge site. the distribution of these basalts suggests that the andesite line coincides with or lies on the continent side of the foot of the continental slope.

  12. Climate Throughout Geologic Time Was Cooled by Sequences of Explosive Volcanic Eruptions Forming Aerosols That Reflect and Scatter Ultraviolet Solar Radiation and Warmed by Relatively Continuous Extrusion of Basaltic Lava that Depletes Ozone, Allowing More Solar Ultraviolet Radiation to Reach Earth

    NASA Astrophysics Data System (ADS)

    Ward, P. L.

    2015-12-01

    Active volcanoes of all sizes and eruptive styles, emit chlorine and bromine gases observed to deplete ozone. Effusive, basaltic volcanic eruptions, typical in Hawaii and Iceland, extrude large lava flows, depleting ozone and causing global warming. Major explosive volcanoes also deplete ozone with the same emissions, causing winter warming, but in addition eject megatons of water and sulfur dioxide into the lower stratosphere where they form sulfuric-acid aerosols whose particles grow large enough to reflect and scatter ultraviolet sunlight, causing net global cooling for a few years. The relative amounts of explosive and effusive volcanism are determined by the configuration of tectonic plates moving around Earth's surface. Detailed studies of climate change throughout geologic history, and since 1965, are not well explained by greenhouse-gas theory, but are explained quite clearly at OzoneDepletionTheory.info. Ozone concentrations vary substantially by the minute and show close relationships to weather system highs and lows (as pointed out by Dobson in the 1920s), to the height of the tropopause, and to the strength and location of polar vortices and jet streams. Integrating the effects of volcanism on ozone concentrations and the effects of ozone concentrations on synoptic weather patterns should improve weather forecasting. For example, the volcano Bárðarbunga, in central Iceland, extruded 85 km2 of basaltic lava between August 29, 2014, and February 28, 2015, having a profound effect on weather. Most surprising, more than a week before the March 4 eruption of Eyjafjallajökull in 2010, substantial amounts of ozone were released in the vicinity of the volcano precisely when surface deformation showed that magma first began moving up from sills below 4 km depth. Ozone similarly appears to have been emitted 3.5 months before the Pinatubo eruption in 1991. Readily available daily maps of ozone concentrations may allow early warning of an imminent volcanic

  13. Can Volcanic Eruptions Produce Ice Ages or Mass Extinctions?

    NASA Astrophysics Data System (ADS)

    Robock, A.; Ammann, C.; Oman, L.; Shindell, D.; Stenchikov, G.

    2006-12-01

    Volcanic eruptions are well known to be important causes of interannual and even interdecadal climate change. But can very large eruptions initiate ice ages, as has been suggested for the Toba eruption ~74,000 years ago? Could flood basalt eruptions, such as the Deccan Traps 65,000,000 years ago or the Siberian Traps 250,000,000 years ago, have produced climate change large enough and long-lasting enough, along with other atmospheric pollution, to have caused mass extinctions? Here we conduct climate model simulations of the effects of a volcanic eruption 100 times larger than the 1991 Pinatubo eruption as a test of the climatic effects of Toba. We use two different state-of-the-art climate models, CCSM 3.0 from the National Center for Atmospheric Research and ModelE from the NASA Goddard Institute for Space Studies, to investigate the dependence of the results on the climate model used. We find that although the "Toba" eruption produces very large global cooling for a couple years, of up to 10°C, the volcanic aerosols leave the atmosphere quickly and the climate largely recovers in a decade. We investigated the mechanism of vegetation response to the cold and dark, but this mechanism was not strong enough to prolong the response enough to allow ice sheets to grow. On the other hand, continuous emissions from massive flood basalt eruptions lasting several decades could make it so cold and dark at the Earth's surface that many species would find it hard to survive. On longer time scales, however, continued large greenhouse gas emissions would have a significant warming effect. With good estimates of the amount and timing of gas and particle emissions into the atmosphere, we have the climate modeling tools to calculate their impact on climate.

  14. The Rhyolite Flare-up of the Columbia River Basalt Province and its Bearing on Plume vs. Non-plume Models

    NASA Astrophysics Data System (ADS)

    Streck, M. J.; Ferns, M. L.

    2012-12-01

    The decades-long controversy as to whether the Columbia River Basalt province results from arrival of a deep mantle plume is far from over, as new non-plume models are proposed. Age-progressive rhyolites of the Snake River Plain are a centerpiece to a migrating plume model that ties mid-Miocene flood basalt magmatism to the present location of the Yellowstone hotspot. However voluminous mid-Miocene rhyolites coeval with the flood basalts of the Columbia River Basalt province have received little attention. These long-known but relatively underappreciated rhyolite occurrences in eastern Oregon and neighboring areas erupted across the province over a narrow time window making the Columbia River province a strongly bimodal (basalt-rhyolite) Large Igneous Province. The entire rhyolite distribution area has roughly a circular area of about a diameter of 300 km and stretches from rhyolite centers near the towns of Baker City and John Day, Oregon in the north to rhyolite centers of the High Rock Desert, Nevada in the SW and the Jarbidge Rhyolite, Idaho in the SE. Oldest rhyolites are ~16.5 Ma in age and occur both along the southern E-W tangent (including McDermitt) and, in lesser volumes, in the central to northern sector. The considerable data that have been generated over the last few years on rhyolites of the southern sector is now being supplemented by new data that we have begun collecting on rhyolites further north. Province-wide rhyolite volcanism was strongest between ~16.4 and 15.4 Ma coincident with eruptions of the most voluminous member of the CRBG - the Grande Ronde Basalt. This widespread rhyolite volcanism indicates that CRBG crustal inputs were focused during this narrow time window over a large area. Magmas in the upper Grande Ronde Basalt that compositionally correlate with glassy mafic inclusions in the rhyolitic Dinner Creek Tuff effectively place one CRBG crustal storage site below a major silicic center. Youngest rhyolites range from ~14.5 to 12

  15. Turbulent atmospheric plumes above line sources with an application to volcanic fissure eruptions on the terrestrial planets

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1989-01-01

    The theory of turbulent plumes maintained above steady line sources of buoyancy is worked out in detail within the limitations of Taylor's entrainment assumption. It is applied to the structure of a pure plume injected into a stably stratified atmosphere. Volcanic basalt eruptions that develop from long, narrow vents create line source plumes, which rise well above the magmatic fire fountains playing near the ground level. The eruption of Laki in 1783 may provide an example of this style of eruption. Flood basalts are more ancient examples. Evidence of enormous fissure eruptions that occurred in the past on Mars and Venus also exists. Owing to the different properties of the atmospheres on these two planets from those on the earth, heights of line source plumes are expected to vary in the ratios 1:6:0.6 (earth:Mars:Venus). It is very unlikely that the observed increase of sulfur dioxide above the Venusian cloud deck in 1978 could have been due to a line source volcanic eruption, even if it had been a flood basalt eruption.

  16. Characteristics of terrestrial basaltic rock populations: Implications for Mars lander and rover science and safety

    NASA Astrophysics Data System (ADS)

    Craddock, Robert A.; Golombek, Matthew P.

    2016-08-01

    We analyzed the morphometry of basaltic rock populations that have been emplaced or affected by a variety of geologic processes, including explosive volcanic eruptions (as a proxy for impact cratering), catastrophic flooding, frost shattering, salt weathering, alluvial deposition, and chemical weathering. Morphometric indices for these rock populations were compared to an unmodified population of rocks that had broken off a solidified lava flow to understand how different geologic processes change rock shape. We found that a majority of rocks have an sphericity described as either a disc or sphere in the Zingg classification system and posit that this is a function of cooling fractures in the basalt (Zingg [1935] Schweiz. Miner. Petrogr. Mitt., 15, 39-140). Angularity (roundness) is the most diagnostic morphometric index, but the Corey Shape Factor (CSF), Oblate-Prolate Index (OPI) and deviation from compactness (D) also sometimes distinguished weathering processes. Comparison of our results to prior analyses of rock populations found at the Mars Pathfinder, Spirit, and Curiosity landing sites support previous conclusions. The observation that the size-frequency distribution of terrestrial rock populations follow exponential functions similar to lander and orbital measurements of rocks on Mars, which is expected from fracture and fragmentation theory, indicates that these distributions are being dominantly controlled by the initial fracture and fragmentation of the basalt.

  17. Correlation of Triassic advanced rifting-related Neotethyan submarine basaltic volcanism of the Darnó Unit (NE-Hungary) with some Dinaridic and Hellenidic occurrences on the basis of volcanological, fluid-rock interaction, and geochemical characteristics

    NASA Astrophysics Data System (ADS)

    Kiss, Gabriella; Molnár, Ferenc; Palinkaš, Ladislav A.; Kovács, Sándor; Horvatović, Hazim

    2012-09-01

    Comparative volcanological, mineralogical, petrological, and geochemical studies of blocks of Triassic submarine basalt occurrences hosted by the Jurassic mélange have been carried out. The studied localities are located in displaced parts of the Dinarides in NE-Hungary (Darnó Unit), in the Dinarides (Kalnik Mts., Croatia and Vareš-Smreka, Bosnia and Herzegovina), and in the Hellenides (Stragopetra, Greece). The common characteristic of the studied occurrences is the well observable result of the lava-water-saturated sediment mingling, i.e., the presence of the so-called carbonate peperitic facies. Mixing of the basaltic lava with pelagic lime mud (representing the unconsolidated stage of the red, micritic limestone), as well as fluid inclusion and chlorite thermometry data support that the carbonate peperite was formed above CCD and at the Bosnian locality, a shallower water, about 1.4 km depth is proven. The igneous rocks show mainly within-plate basalt geochemical characteristics; MORB signatures are not common. Low temperature (<200°C) hydrothermal alteration is characteristic to the pillow basalt blocks with peperitic facies. The similarities in the volcanological, geochemical, and textural characteristics observed at the different localities support a strong genetic connection among them. The results of this study suggest to the advanced rifting stage origin of the Triassic basaltic suits and their distinction from the true oceanic basalt pillow units of the Dinarides can be based on the occurrences of the peperite facies.

  18. An estimate of the juvenile sulfur content of basalt

    USGS Publications Warehouse

    Moore, J.G.; Fabbi, Brent P.

    1971-01-01

    Sulfur analyses by X-ray fluorescence give an average content of 107 ppm for 9 samples of fresh subaerially-erupted oceanic basalt and 680 ppm for 38 samples of submarine erupted basalt. This difference is the result of retention of sulfur in basalt quenched on the sea floor and loss of sulfur in basalt by degassing at the surface. The outer glassy part of submarine erupted basalt contains 800??150 ppm sulfur, and this amount is regarded as an estimate of the juvenile sulfur content of the basalt melt from the mantle. The slower cooled interiors of basalt pillows are depleted relative to the rims owing to degassing and escape through surface fractures. Available samples of deep-sea basalts do not indicate a difference in original sulfur content between low-K tholeiite, Hawaiian tholeiite, and alkali basalt. The H2O/S ratio of analyzed volcanic gases is generally lower than the H2O/S ratio of gases presumed lost from surface lavas as determined by chemical differences between pillow rims and surface lavas. This enrichment of volcanic gases in sulfur relative to water may result from a greater degassing of sulfur relative to water from shallow intrusive bodies beneath the volcano. ?? 1971 Springer-Verlag.

  19. Volcanic eruptions, global change and evolution of species

    NASA Astrophysics Data System (ADS)

    Courtillot, V.

    2007-12-01

    Our group proposed in 1986 that the Deccan traps of India had been co-eval with the Cretaceous-Tertiary mass extinction, had lasted less than 800 kyears, straddling the KT. In 1995, Bhandari and colleagues showed that the iridium level marking the Chicxulub impact could be found in the Deccan and was sandwiched between flows, demonstrating that they were co-eval events but that volcanism had started first and could not be a consequence of impact. Since then, many groups have contributed to dating more precisely continental flood basalts around the world and found that there was almost a one to one correspondance between flood basalts and mass extinctions (but not impacts, except for the KT) : for a recent review see Courtillot and Renne (2003). In recent years, a number of significant advances have been made. It has been shown in the case of the historically large but geologically very small Icelandic Laki eruption of 1783 that such eruptions could inject large amounts of sulfate aerosols all the way to the stratosphere and have a global impact on climate : therefore, effusive basaltic volcanism on a large scale could alter climate (our group with Frédéric Fluteau and Anne-Lise Chenet and Steve Self with Thor Thordarson). Petrologic, volcanological, paleomagnetic, paleontological and geochronologic studies of the entire 3000m thick Deccan pile have been resumed (mainly our group, that of Self with Mike Widdowson and Anne Jay, and that of Gerta Keller). The result is that the thick lava pile actually erupted in a relatively small number of gigantic pulses (with mega-flows up to 10000 km3 in volume having erupted in decades !). Field evidence has been given that flows could extend over almost 1000km, and paleontological and K-Ar dating now reveals a history of mainly two mega-pulses having occurred, one just prior to the KT the second somewhat afterwards explaining the long delay of recovery of species from the catastrophe. There is little doubt now that the KT

  20. Floods and Flash Flooding

    MedlinePlus

    Floods and flash flooding Now is the time to determine your area’s flood risk. If you are not sure whether you ... If you are in a floodplain, consider buying flood insurance. Do not drive around barricades. If your ...

  1. The oxygen-hafnium isotope paradox in the early post Columbia River Basalt silicic volcanism: Evidence for complex batch assembly of upper crustal, lower crustal and low-δ18O silicic magmas

    NASA Astrophysics Data System (ADS)

    Colon, D.; Bindeman, I. N.; Ellis, B. S.; Schmitt, A. K.; Fisher, C. M.; Vervoort, J. D.

    2013-12-01

    Eruptions of the Columbia River flood basalts were immediately followed by large eruptions of silicic magmas; some may have been coeval, others genetically-linked to the CRB. Among the most voluminous of these eruptions was the Jarbidge Rhyolite, which comprises ~500 km3 of lava erupted from 16.1-15.0 Ma in northern Nevada. Activity at Jarbidge was followed at 15.0 Ma by a series of rhyolitic ignimbrites and lavas in the J-P Desert of Idaho ~50 km NW of the Jarbidge Rhyolite center. To constrain magmatic origins and upper crustal magma storage conditions of these two silicic magmatic systems, we conducted bulk and high spatial resolution analysis of whole rocks and minerals (quartz, feldspar, and zircon). Bulk quartz and plagioclase δ18O values of the J-P Desert units are only moderately lower than mantle values, with δ18O-quartz of 5.0-5.5‰ and plagioclase δ18O of ~3.9-5.8‰, along with slightly unradiogenic Nd and Hf whole rock values (average ɛHf and ɛNd of -13.1 and -10.0, respectively), while quartz from the Jarbidge Rhyolite has normal δ18O (+8.4‰), but very unradiogenic ɛHf-ɛNd (ɛHf = -34.7, ɛNd = -24.0), fingerprinting Archean upper crust. SIMS analysis of J-P Desert zircons reveals considerably diverse δ18O values, ranging from -0.6‰ to +6.5‰ in a single unit. The same zircon spots yielded U-Pb SIMS ages which generally agree with the 40Ar/39Ar eruption ages, with no evidence of inheritance of pre-Miocene zircons. Combined with LA-MC-ICP-MS analysis of Hf isotopes overlapping the earlier SIMS spots, these zircons show a clear near-linear correlation between ɛHf and δ18O values observed in individual zircons. This relationship suggests variable mixing of two distinct silicic magmas prior to eruption of the J-P Desert rhyolites. One of these, characterized by extremely low ɛHf values and normal δ18O values, is likely a mantle magma strongly contaminated with shallow Archean crust, represented by the Jarbidge Rhyolite. The other is

  2. Polyphase rifting within Rodinia as seen through multiple episodes of mafic volcanism within the Canadian Cordillera

    NASA Astrophysics Data System (ADS)

    Cox, G. M.; Halverson, G. P.; Roots, C. F.; MacDonald, F. A.; Plavsa, D.

    2010-12-01

    Neoproterozoic continental flood basalts (CFB) are known from the North American Cordillera and are thought to be associated with the breakup of Rodinia. However, unlike the short eruptive timeframe of Phanerozoic flood basalt provinces, instances of Neoproterozoic CFB within the North American Cordillera are separated by the unusually long time interval of ca 56 My (ca 780 Ma Gunbarrel Event and the ca 717 Ma Franklin Igneous Event), suggestive of poly-phase rifting and a long lived thermal anomaly and/or fertile mantle situated under ancient Laurentia. The Neoproterozoic Tatonduk Inlier, spanning the Alaskan-Yukon border, preserves both mafic volcanics (Pleasant Creek Volcanics) and a large arcuate dyke swarm (Tindir Dyke Swarm). Previous K/Ar dates on the dikes ranging from 532 ± 11 Ma to 644 ± 18 Ma appear to be inconsistent with geological constraints and correlations between the Tatonduk strata and the Neoproterozoic sequence of the well-dated Coal Creek Inlier to the east. We present geochemical data and discuss age and correlative constraints on these mafic rocks and relate these results in terms of the breakup history of Rodinia, timing of mafic magmatism within the possible conjugate margins to Neoproterozoic Laurentia (e.g. Australia and South China) and the role of a mantle plume in the rifting of Rodinia.

  3. Zeolite parageneses in the North Atlantic igneous province: Implications for geotectonics and groundwater quality of basaltic crust

    SciTech Connect

    Neuhoff, P.S.; Fridriksson, T.; Bird, D.K.

    2000-01-01

    Zeolites are among the most common products of chemical interaction between groundwaters and the Earth's crust during diagenesis and low-grade metamorphism. The unique crystal structures of zeolites result in large molar volumes, high cation-exchange capacities, and reversible dehydration. These properties influence both the stability and chemistry of zeolites in geologic systems, leading to complex parageneses and compositional relationships that provide sensitive indicators of physicochemical conditions in the crust. Observations of zeolite occurrence in Tertiary basaltic lavas in the North Atlantic region indicate that individual zeolite minerals are distributed in distinct, depth-controlled zones that parallel the paleosurface of the plateau basalts and transgress the lava stratigraphy. The zeolite zones are interpreted to have formed at the end of burial metamorphism of the lavas. Relative timing relations between various mineral parageneses and crustal-scale deformal features indicate that the minerals indicative of the zeolite zones formed within 1 million years after cessation of volcanism. Empirical correlation between the depth distribution of zeolite zones and the temperatures of formation of zeolites in geothermal systems provides estimates of regional thermal gradients and heat flow in flood-basalt provinces. Similarly, the orientations of zeolite zones can be used to distinguish synvolcanic and post-volcanic crustal deformation. Because zeolites that characterize the individual zones display different ion-exchange selectivities for various cations, reactions between groundwaters and zeolites in basaltic aquifers can result in depth-controlled zones where individual elements are concentrated in the crust. This is established for Sr, which is concentrated by at least an order of magnitude in heulandite, resulting in an overall SR enrichment of lavas in the heulandite-stilbite zeolite zone.

  4. Volcanic Stratigraphy of the Quaternary Rhyolite Plateau in Yellowstone National Park

    USGS Publications Warehouse

    Christiansen, Robert L.; Blank, H. Richard, Jr.

    1972-01-01

    The volcanic sequence of the Quaternary Yellowstone plateau consists of rhyolites and basalts representing three volcanic cycles. The major events of each cycle were eruption of a voluminous ash-flow sheet and formation of a large collapse caldera. Lesser events of each cycle were eruption of precaldera and postcaldera rhyolitic lava flows and marginal basaltic lavas. The three major ash-flow sheets are named and designated in this report as formations within the Yellowstone Group. The lavas are assigned to newly named formations organized around the three ash-flow sheets of the Yellowstone Group to represent the volcanic cycles. Rocks of the first volcanic cycle comprise the precaldera Junction Butte Basalt and rhyolite of Broad Creek; the Huckleberry Ridge Tuff of the Yellowstone Group; and the postcaldera Lewis Canyon Rhyolite and basalt of The Narrows. Rocks of the second volcanic cycle do not crop out within Yellowstone National Park, and only the major unit, the Mesa Falls Tuff of the Yellowstone Group, is named here. The third volcanic cycle is represented by the precaldera Mount Jackson Rhyolite and Undine Falls Basalt; the Lava Creek Tuff of the Yellowstone Group; and the postcaldera Plateau Rhyolite and five post-Lava Creek basaltic sequences. Collapse to form the compound and resurgent Yellowstone caldera was related to eruption of the Lava Creek Tuff. The Plateau Rhyolite is divided into six members - the Mallard Lake, Upper Basin, Obsidian Creek, Central Plateau, Shoshone Lake Tuff, and Roaring Mountain Members; all but the Mallard Lake postdate resurgent doming of the caldera. The basalts are divided into the Swan Lake Flat Basalt, Falls River Basalt, basalt of Mariposa Lake, Madison River Basalt, and Osprey Basalt. Sediments are intercalated in the volcanic section below the Huckleberry Ridge and Mesa Falls Tuffs and within the Junction Butte Basalt, sediments and basalts of The Narrows, Undine Falls Basalt, Plateau Rhyolite, and Osprey Basalt.

  5. Plagioclase mineralogy of olivine alkaline basalt

    NASA Technical Reports Server (NTRS)

    Hoffer, J. M.

    1973-01-01

    A geological and mineralogical study of the Potrillo volcanics is reported. The investigation consisted first of field mapping to establish and identify the different rock types and volcanic features in order to determine the geological history. Next, samples were collected and analyzed petrographically to determine suitable rocks from the various stratigraphic units for study of plagioclase. Samples selected for further study were crushed and the plagioclase extracted for the determination of composition and structural state. These results were then related to the petrology and crystallization of the basalt.

  6. Geochemistry of 24 Ma Basalts from Northeast Egypt: Implications for Small-Scale Convection Beneath the East African Rift System

    NASA Astrophysics Data System (ADS)

    Endress, C. A.; Furman, T.; Ali Abu El-Rus, M.

    2009-12-01

    . However, measured 207Pb/204Pb and 87Sr/86Sr values are higher than those observed in the Ethiopian flood basalts (Pik et al., 1999) and suites from the Red Sea and Gulf of Aden (Schilling et al., 1992; Volker and McCulloch, 1993; Volker et al., 1997), consistent with trace element evidence of crustal contamination. We aim to develop a broad framework for understanding tectono-magmatic activity throughout northern Africa since the Miocene. The NE Egyptian basalts show evidence of both lithospheric and sublithospheric contributions and represent a time period that is critical to ongoing debate surrounding the relationship between shallow magmatism, crustal extension, and deep mantle processes exemplified by the features within and beneath the African Plate. A plausible model for the widespread volcanism during the early Miocene is that each local magmatic event was related to small scale convection rising above a plume or plumes.

  7. Closer look at lunar volcanism

    SciTech Connect

    Vaniman, D.T.; Heiken, G.; Taylor, G.J.

    1984-01-01

    Although the American Apollo and Soviet Luna missions concentrated on mare basalt samples, major questions remain about lunar volcanism. Lunar field work will be indispensable for resolving the scientific questions about ages, compositions, and eruption processes of lunar volcanism. From a utilitarian standpoint, a better knowledge of lunar volcanism will also yield profitable returns in lunar base construction (e.g., exploitation of rille or lava-tube structures) and in access to materials such as volatile elements, pure glass, or ilmenite for lunar industry.

  8. A Plume Head and Tail in the Bengal Basin and Bay of Bengal: Rajmahal and Sylhet Traps with Surrounding Alkalic Volcanism and the Ninetyeast Ridge

    NASA Astrophysics Data System (ADS)

    Basu, A. R.; Weaver, K. L.; Sengupta, S.

    2001-12-01

    Although the 116-113 Ma-old Rajmahal-Sylhet Traps of the Bengal basin, potentially covering an area > 2x105 km2, can be directly linked via Ninetyeast Ridge to the Kerguelen Plume, more than 5,000 kms away, it is generally believed that this flood basalt volcanism originated from a normal MORB-type mantle at the boundary of a mantle plume. This model, primarily based on geochemical analysis of a limited number of Rajmahal basalts, requires initiation of rifting of the eastern Indian margin by a smaller thermal flux than necessary for creating a large igneous province. Here we show that the extent of volcanism associated with the Rajmahal-Sylhet Traps is far greater than usually assumed, thus requiring a direct involvement of the Kerguelen Plume. In addition to the surface exposures of the flood basalts in Rajmahal-Sylhet, the basaltic rocks have been encountered in many parts of the Bengal Basin in bore holes reaching a maximum thickness of 600 m in the western margin of the Basin (Sengupta, Bull. AAPG, 1966) Most importantly, several suites of ultrapotassic and alkalic intrusive complexes, similar to those associated with the Deccan and Siberia Traps, occur over wide areas within and outside the Basin: i) southwest of the surface exposures of Rajmahal basalts, distance 200km, intrusive in Lower Gondwana coalbeds, Ar-Ar age 114 Ma (P.R. Renne, personal communication), ii) 400 km north of Rajmahal, exposed in Sikkim, intrusive into metamorphic crystalline nappes of the Himalayas; distance here is not real and must be a minimum as the nappes have been transported from the north, iii) northeast of Rajmahal in Meghalaya State, distance 550 km, intrusive into metamorphic Precambrian basement rocks. Nd-Sr isotopic ratios and trace element characteristics of these above ultrapotassic and alkaline rocks are consistent with their origin associated with the Kerguelen Plume. The wide range in Nd-Sr array for these rocks, including the Sylhet and Rajmahal basalts, shows

  9. Investigating the Processes of Crust Formation and Intraplate Continental Volcanism in the High Lava Plains, Oregon

    NASA Astrophysics Data System (ADS)

    Carlson, R. W.; James, D. E.; Fouch, M. J.; Grove, T. L.; Hart, W. K.; Grunder, A. L.; Duncan, R. A.; Keller, G. R.; Harder, S. H.; Kincaid, C. R.

    2006-12-01

    East of the southern Cascades is an area of voluminous Late-Cenozoic volcanism built on an immature crustal section accreted to North America in the Mesozoic. With the exception of the Snake River Plain, the High Lava Plains (HLP) of eastern Oregon has been the most volcanically active area in the western United States in the late Cenozoic. Through much of this area, the oldest exposed basement is early Miocene intermediate composition volcanic rocks. Beginning at approximately 16.5 Ma, the HLP was blanketed with flood basalts from both the Steens and Columbia River eruptive centers. The flood basalt era was followed by a time- progressive migration of large silicic centers beginning near the Oregon-Nevada-Idaho borders and extending to the present day activity at Newberry volcano. Quaternary basaltic volcanism is scattered along this whole trend, making the HLP more of a hot-line than a hot-spot. A variety of mechanisms have been proposed to explain this activity including: outflow of the Yellowstone plume-head, back-arc spreading, lithosphere delamination, Basin and Range extension, and asthenospheric inflow around the northward migrating edge of the subducting Juan de Fuca plate. These models make distinct predictions about the flow patterns and temperature structure of the shallow mantle underlying this area, but geophysical information capable of discriminating these models is sparse to absent. To remedy this situation and better define the causes of the voluminous volcanism in this area, the HLP project, funded by the NSF Continental Dynamics program, has initiated a multi-level broadband and active-source seismic study combined with field geology, geochemistry, petrology, geochronology and 3D geodynamic modeling of an area reaching from the southern Cascades across eastern Oregon into Idaho and northernmost Nevada. The seismic part of the project employs very dense station spacing that will provide high-resolution images of the crust and upper 100 km of the

  10. The Mineralogy of the Youngest Lunar Basalts

    NASA Astrophysics Data System (ADS)

    Staid, M. I.; Pieters, C. M.

    1999-01-01

    The last stage of lunar volcanism produced spectrally distinct basalts on the western nearside of the Moon, which remain unsampled by landing missions. The spectral properties of these late-stage basalts are examined using high-spatial-resolution Clementine images to constrain their mineralogic composition. The young high-Ti basalts in the western Procellarum and Imbrium Basins display a significantly stronger ferrous absorption than earlier mare basalts, suggesting that they may be the most Fe-rich deposits on the Moon. The distinct long-wavelength shape of this ferrous absorption is found to be similar for surface soils and materials excavated from depth. The pervasive character of this absorption feature supports the interpretation of abundant olivine within these late-stage lunar deposits. Important distinctions exist between the early-stage eastern maria and the late-stage western basalts, even though both appear to be Ti-rich. For example, the western maria are more radiogenic than eastern deposits. Telescopic spectra of the high-Ti western maria also exhibit a unique combination of a strong 1 micron feature and a relatively weak or attenuated 2-micron absorption. Pieters et al. concluded that the unusual strength and shape of the 1-micron absorption in western basalts results from an additional absorption from abundant olivine and/or Fe-bearing glass. Either mineralogy could produce the strong long wavelength 1-micron band, but a glassy Fe-rich surface could only form by rapid cooling along the exterior surfaces of flows. Clementine UV-VIS data of late-stage basalts are examined for regions in Oceanus Procellarum and Mare Imbrium. The spectral properties of western regions are compared to the sampled Apollo 11 basalts in Mare Tranquillitatis, which contain similar albedos and UV-VIS spectral properties. For reference, the western basalts are also compared to the low-Ti and Fe-rich basalts in Mare Serenitatis (mISP). Serenitatis basalts have the strongest

  11. Petrogenesis of the Eocene and Mio Pliocene alkaline basaltic magmatism in Meseta Chile Chico, southern Patagonia, Chile: Evidence for the participation of two slab windows

    NASA Astrophysics Data System (ADS)

    Espinoza, Felipe; Morata, Diego; Pelleter, Ewan; Maury, René C.; Suárez, Manuel; Lagabrielle, Yves; Polvé, Mireille; Bellon, Hervé; Cotten, Joseph; De la Cruz, Rita; Guivel, Christelle

    2005-06-01

    The Meseta Chile Chico (MCC, 46.4°S) is the westernmost exposure of Eocene (lower basaltic sequence, LBS; 55-40 Ma, K-Ar ages) and Mio-Pliocene (upper basaltic sequence, UBS; 16-4 Ma, K-Ar ages) flood basalt volcanism in Patagonia. The MCC is located south of the Lago General Carrera-Buenos Aires (LGCBA), southeast from the present day Chile Triple Junction (CTJ), east of the actual volcanic gap between Southern South Volcanic Zone and Austral Volcanic Zone (SSVZ and AVZ, respectively) and just above the inferred location of the South Chile Ridge segment subducted at ˜6 Ma (SCR-1). Erupted products consist of mainly ne-normative olivine basalt with minor hy-normative tholeiites basalt, trachybasalt and basanite. MCC lavas are alkaline (42.7-53.1 wt.% SiO 2, 3-8 wt.% Na 2O+K 2O) and relatively primitive (Ni: 133-360 ppm, Cr: 161-193 ppm, Co: 35-72 ppm, 4-16.5 MgO wt.%). They have a marked OIB-like signature, as shown by their isotopic compositions ( 87Sr/ 86Sr o=0.70311-0.70414 and ɛNd=+4.7-+5.1) and their incompatible trace elements ratios (Ba/La=10-20, La/Nb=0.46-1.09, Ce/Pb=15.52-27.5, Sr/La<25), reflecting deep mantle origin. UBS-primitive lavas have characteristics similar to those of the Eocene LBS basalts, while UBS-intermediate lavas show geochemical imprints (La/Nb>1, Sr/La>25, low Ce/Pb, Nb/U) compatible with contamination by arc/slab-derived and/or crustal components. We propose that the genesis and extrusion of magmas is related to the opening of two slab windows due to the subduction of two active ridge segments beneath Patagonia during Eocene and Mio-Pliocene.

  12. 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].

  13. Flooding and Flood Management

    USGS Publications Warehouse

    Brooks, K.N.; Fallon, J.D.; Lorenz, D.L.; Stark, J.R.; Menard, Jason

    2011-01-01

    Floods result in great human disasters globally and nationally, causing an average of $4 billion of damages each year in the United States. Minnesota has its share of floods and flood damages, and the state has awarded nearly $278 million to local units of government for flood mitigation projects through its Flood Hazard Mitigation Grant Program. Since 1995, flood mitigation in the Red River Valley has exceeded $146 million. Considerable local and state funding has been provided to manage and mitigate problems of excess stormwater in urban areas, flooding of farmlands, and flood damages at road crossings. The cumulative costs involved with floods and flood mitigation in Minnesota are not known precisely, but it is safe to conclude that flood mitigation is a costly business. This chapter begins with a description of floods in Minneosta to provide examples and contrasts across the state. Background material is presented to provide a basic understanding of floods and flood processes, predication, and management and mitigation. Methods of analyzing and characterizing floods are presented because they affect how we respond to flooding and can influence relevant practices. The understanding and perceptions of floods and flooding commonly differ among those who work in flood forecasting, flood protection, or water resource mamnagement and citizens and businesses affected by floods. These differences can become magnified following a major flood, pointing to the need for better understanding of flooding as well as common language to describe flood risks and the uncertainty associated with determining such risks. Expectations of accurate and timely flood forecasts and our ability to control floods do not always match reality. Striving for clarity is important in formulating policies that can help avoid recurring flood damages and costs.

  14. Basaltic cannibalism at Thrihnukagigur volcano, Iceland

    NASA Astrophysics Data System (ADS)

    Hudak, M. R.; Feineman, M. D.; La Femina, P. C.; Geirsson, H.

    2014-12-01

    cannibalism, we suggest that it is not limited to this volcanic system. Rather it is a process that likely occurs throughout Iceland and may contribute to the evolution of the crust in other predominately basaltic settings.

  15. Volcanic Gas

    MedlinePlus

    ... Hazards Tephra/Ash Lava Flows Lahars Volcanic Gas Climate Change Pyroclastic Flows Volcanic Landslides Preparedness Volcano Hazard Zones ... Please see our discussion of volcanic gases and climate change for additional information. Hydrogen sulfide (H 2 S) is ...

  16. Age estimates of the seaward-dipping volcanic wedge, earliest oceanic crust, and earliest drift-stage sediments along the North American Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Benson, Richard N.

    Owing to their depths of burial along and adjacent to the North American continental margin, there is no direct evidence obtained from boreholes for the ages of the seaward-dipping volcanic wedge, earliest drift-stage sediments overlying the wedge, and the earliest Atlantic oceanic crust between the East Coast (ECMA) and Blake Spur (BSMA) magnetic anomalies. Maximum ages of late Sinemurian for drift-stage sediments have been determined from exploration wells in the Scotian Basin. A similar age is postulated for those sediments in the Georges Bank Basin, but palynomorphs from exploration wells may indicate that earliest drift-stage sediments, in places associated with volcanic rocks, are of Bajocian age and occur higher in the section above the postrift unconformity as recognized on seismic lines. In the Southeast Georgia Embayment of the Blake Plateau Basin, the oldest drift-stage sediments overlying the postrift unconformity that were drilled are of Kimmeridgian-Tithonian age. In the Baltimore Canyon Trough, the volcanic wedge overlies the postrift unconformity which truncates buried synrift rocks that may be as young as Sinemurian. In the Carolina Trough and Blake Plateau Basin, a possible offshore flood basalt marking the postrift unconformity and traced as a reflector to the volcanic wedge may correspond to a subsurface flood basalt onshore that may be part of CAMP (Hettangian). Alternatively, its magmatic source may have been that of the possibly younger volcanic wedge. Sea-floor-spreading-rate lines based on the latest Jurassic time scales and extended to the BSMA and ECMA indicate ages of 166 and 171 Ma for the BSMA and 172 and 179 Ma for the ECMA. An alternative model suggests a middle Pliensbachian/early Toarcian age (188-190 Ma) for the igneous activity that produced the volcanic wedge and earliest oceanic crust.

  17. Thicknesses of Mare Basalts from Gravity and Topograhy

    NASA Astrophysics Data System (ADS)

    GONG, S.; Wieczorek, M.; Nimmo, F.; Kiefer, W.; Head, J.; Smith, D.; Zuber, M.

    2015-10-01

    Mare basalts are derived from partial melting of the lunar interior and are mostly located on the near side of the Moon [1, 2]. Their iron-rich composition gives rise to their dark color, but also causes their density to be substantially higher than normal crustal rocks. The total volume of mare basalts can provide crucial information about the Moon's thermal evolution and volcanic activity. Unfortunately, the thicknesses of the mare are only poorly constrained. Here we use gravity data from NASA's GRAIL mission to investigate the thickness of mare basalts.

  18. Origin of high-alumina basalt, andesite, and dacite magmas

    USGS Publications Warehouse

    Hamilton, W.

    1964-01-01

    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it.

  19. Origin of High-Alumina Basalt, Andesite, and Dacite Magmas.

    PubMed

    Hamilton, W

    1964-10-30

    The typical volcanic rocks of most island arcs and eugeosynclines, and of some continental environments, are basalt, andesite, and dacite, of high alumina content. The high-alumina basalt differs from tholeiitic basalt primarily in having a greater content of the components of calcic plagioclase. Laboratory data indicate that in the upper mantle, below the level at which the basaltic component of mantle rock is transformed by pressure to eclogite or pyroxenite, the entire basaltic portion probably is melted within a narrow temperature range, but that above the level of that transformation plagioclase is melted selectively before pyroxene over a wide temperature range. The broad spectrum of high-alumina magmas may represent widely varying degrees of partial melting above the transformation level, whereas narrow-spectrum tholeiite magma may represent more complete melting beneath it. PMID:17794034

  20. Geophysical expression of caldera related volcanism, structures and mineralization in the McDermitt volcanic field

    NASA Astrophysics Data System (ADS)

    Rytuba, J. J.; Blakely, R. J.; Moring, B.; Miller, R.

    2013-12-01

    The High Rock, Lake Owyhee, and McDermitt volcanic fields, consisting of regionally extensive ash flow tuffs and associated calderas, developed in NW Nevada and SE Oregon following eruption of the ca. 16.7 Ma Steens flood basalt. The first ash flow, the Tuff of Oregon Canyon, erupted from the McDermitt volcanic field at 16.5Ma. It is chemically zoned from peralkaline rhyolite to dacite with trace element ratios that distinguish it from other ash flow tuffs. The source caldera, based on tuff distribution, thickness, and size of lithic fragments, is in the area in which the McDermitt caldera (16.3 Ma) subsequently formed. Gravity and magnetic anomalies are associated with some but not all of the calderas. The White Horse caldera (15.6 Ma), the youngest caldera in the McDermitt volcanic field has the best geophysical expression, with both aeromagnetic and gravity lows coinciding with the caldera. Detailed aeromagnetic and gravity surveys of the McDermitt caldera, combined with geology and radiometric surveys, provides insight into the complexities of caldera collapse, resurgence, post collapse volcanism, and hydrothermal mineralization. The McDermitt caldera is among the most mineralized calderas in the world, whereas other calderas in these three Mid Miocene volcanic fields do not contain important hydrothermal ore deposits, despite having similar age and chemistry. The McDermitt caldera is host to Hg, U, and Li deposits and potentially significant resources of Ga, Sb, and REE. The geophysical data indicate that post-caldera collapse intrusions were important in formation of the hydrothermal systems. An aeromagnetic low along the E caldera margin reflects an intrusion at a depth of 2 km associated with the near-surface McDermitt-hot-spring-type Hg-Sb deposit, and the deeper level, high-sulfidation Ga-REE occurrence. The Li deposits on the W side of the caldera are associated with a series of low amplitude, small diameter aeromagnetic anomalies that form a continuous

  1. Can we identify source lithology of basalt?

    PubMed

    Yang, Zong-Feng; Zhou, Jun-Hong

    2013-01-01

    The nature of source rocks of basaltic magmas plays a fundamental role in understanding the composition, structure and evolution of the solid earth. However, identification of source lithology of basalts remains uncertainty. Using a parameterization of multi-decadal melting experiments on a variety of peridotite and pyroxenite, we show here that a parameter called FC3MS value (FeO/CaO-3*MgO/SiO2, all in wt%) can identify most pyroxenite-derived basalts. The continental oceanic island basalt-like volcanic rocks (MgO>7.5%) (C-OIB) in eastern China and Mongolia are too high in the FC3MS value to be derived from peridotite source. The majority of the C-OIB in phase diagrams are equilibrium with garnet and clinopyroxene, indicating that garnet pyroxenite is the dominant source lithology. Our results demonstrate that many reputed evolved low magnesian C-OIBs in fact represent primary pyroxenite melts, suggesting that many previous geological and petrological interpretations of basalts based on the single peridotite model need to be reconsidered. PMID:23676779

  2. Tsunami flooding

    USGS Publications Warehouse

    Geist, Eric; Jones, Henry; McBride, Mark; Fedors, Randy

    2013-01-01

    Panel 5 focused on tsunami flooding with an emphasis on Probabilistic Tsunami Hazard Analysis (PTHA) as derived from its counterpart, Probabilistic Seismic Hazard Analysis (PSHA) that determines seismic ground-motion hazards. The Panel reviewed current practices in PTHA and determined the viability of extending the analysis to extreme design probabilities (i.e., 10-4 to 10-6). In addition to earthquake sources for tsunamis, PTHA for extreme events necessitates the inclusion of tsunamis generated by submarine landslides, and treatment of the large attendant uncertainty in source characterization and recurrence rates. Tsunamis can be caused by local and distant earthquakes, landslides, volcanism, and asteroid/meteorite impacts. Coastal flooding caused by storm surges and seiches is covered in Panel 7. Tsunamis directly tied to earthquakes, the similarities with (and path forward offered by) the PSHA approach for PTHA, and especially submarine landslide tsunamis were a particular focus of Panel 5.

  3. The Quaternary volcanic rocks of the northern Afar Depression (northern Ethiopia): Perspectives on petrology, geochemistry, and tectonics

    NASA Astrophysics Data System (ADS)

    Hagos, Miruts; Koeberl, Christian; van Wyk de Vries, Benjamin

    2016-05-01

    The northern Afar Depression is one of the most volcano-tectonically active parts of the East African Rift system, a place where oceanic rifting may be beginning to form an incipient oceanic crust. In its center, over an area that is ∼80 km long and ∼50 km wide, there are seven major NNW-SSE-aligned shield volcanoes/volcanic edifices surrounded by compositionally distinct fissure-fed basalts. The Quaternary lavas in this area range from transitional to tholeiitic basalts, with significant across-axis variation both in mineralogy and chemistry. The variation in the contents of the major elements (TiO2, Al2O3, and Fe2O3), incompatible trace elements (Nd, Hf, Th, Ta), and the contents and ratios of the rare earth elements (REE) (e.g., (La/Yb)n = 5.3-8.9) indicate some variation in the petrogenetic processes responsible for the formation of these basalts. However, the variation in isotopic compositions of the mafic lavas is minimal (87Sr/86Sr = 0.7036-0.7041, 143Nd/144Nd = 0.51286-0.51289), which suggests only one source for all the Danakil Depression basalts. These basalts have isotope and incompatible trace element ratios that overlap with those of the Oligocene High-Ti2 flood basalts from the Ethiopian Plateau, interpreted as being derived from the last phase/tail of the Afar mantle plume source. Moreover, the Ce/Pb, Ba/U ratios indicate that the involvement of continental crust in the petrogenesis of the basaltic rocks is minimal; instead, both depth and degree of melting of the source reservoir underneath the northern Afar Depression played a major role for the production of incompatible element-enriched basalts (e.g., AleBagu Shield basalts) and the incompatible element-depleted tholeiitic basalts (e.g., Erta'Ale and Alu Shield basalts).

  4. The June 27, 2001 landslide on volcanic cones in Limbe, Mount Cameroon, West Africa

    NASA Astrophysics Data System (ADS)

    Ayonghe, S. N.; Ntasin, E. B.; Samalang, P.; Suh, C. E.

    2004-06-01

    On 27 June 2001, between 12:00 and 14:00 hours GMT, the worst ever recorded landslides and floods in the history of Cameroon occurred on volcanic cones in Limbe, killing 24 people. This brisk event, which from eyewitness reports, lasted for about 30 min, produced more than 43 landslide scars, several tension cracks, destroyed 120 houses and rendered over 2800 people homeless. Field studies indicated the alignment of the landslide scars along a northwest-southeast zone antithetic to the Mabeta fault previously identified by a linear pattern of earthquake epicentres along its length, although volcanic rocks cover this fault. The landslides occurred on slopes with dips ranging from 35° to 80°. The regolith from the slide surfaces destroyed trees and houses, and blocked gutters producing floods along the low-lying coastal parts of Limbe. The mechanism of sliding ranged from planar sliding or mud flows on impermeable surfaces of basaltic flows and/or compacted clayey volcanic tuff, to rotational sliding, or toppling failure on the steeper slopes. Intensive rainfall which preceded the event for two days as well as human intervention on slopes in the form of farming and terracing to build houses, were important contributory factors. On the basis of these findings, measures aimed at reducing the impact of future landslides on the population in the area are proposed.

  5. Recurrence models of volcanic events: Applications to volcanic risk assessment

    SciTech Connect

    Crowe, B.M.; Picard, R.; Valentine, G.; Perry, F.V.

    1992-03-01

    An assessment of the risk of future volcanism has been conducted for isolation of high-level radioactive waste at the potential Yucca Mountain site in southern Nevada. Risk used in this context refers to a combined assessment of the probability and consequences of future volcanic activity. Past studies established bounds on the probability of magmatic disruption of a repository. These bounds were revised as additional data were gathered from site characterization studies. The probability of direct intersection of a potential repository located in an eight km{sup 2} area of Yucca Mountain by ascending basalt magma was bounded by the range of 10{sup {minus}8} to 10{sup {minus}10} yr{sup {minus}1 2}. The consequences of magmatic disruption of a repository were estimated in previous studies to be limited. The exact releases from such an event are dependent on the strike of an intruding basalt dike relative to the repository geometry, the timing of the basaltic event relative to the age of the radioactive waste and the mechanisms of release and dispersal of the waste radionuclides in the accessible environment. The combined low probability of repository disruption and the limited releases associated with this event established the basis for the judgement that the risk of future volcanism was relatively low. It was reasoned that that risk of future volcanism was not likely to result in disqualification of the potential Yucca Mountain site.

  6. Use and Features of Basalt Formations for Geologic Sequestration

    SciTech Connect

    McGrail, B. Peter; Ho, Anita M.; Reidel, Steve P.; Schaef, Herbert T.

    2003-01-01

    Extrusive lava flows of basalt are a potential host medium for geologic sequestration of anthropogenic CO2. Flood basalts and other large igneous provinces occur worldwide near population and power-producing centers and could securely sequester a significant fraction of global CO2 emissions. We describe the location, extent, and general physical and chemical characteristics of large igneous provinces that satisfy requirements as a good host medium for CO2 sequestration. Most lava flows have vesicular flow tops and bottoms as well as interflow zones that are porous and permeable and serve as regional aquifers. Additionally, basalt is iron-rich, and, under the proper conditions of groundwater pH, temperature, and pressure, injected CO2 will react with iron released from dissolution of primary minerals in the basalt to form stable ferrous carbonate minerals. Conversion of CO2 gas into a solid form was confirmed in laboratory experiments with supercritical CO2 in contact with basalt samples from Washington state.

  7. Modelling massive sulphate aerosol pollution, following the large 1783 Laki basaltic eruption

    NASA Astrophysics Data System (ADS)

    Chenet, Anne-Lise; Fluteau, Frédéric; Courtillot, Vincent

    2005-08-01

    The climatic impact of volcanic eruptions depends mainly on the amount of sulphur-rich gases released into the stratosphere. These are rapidly converted to sulphate aerosols, which result in cooling of the lower troposphere and warming of the lower stratosphere. These gases are retained in the stratosphere and then concentrated by atmospheric processes, forming acid fog near the Earth's surface, with potentially dramatic environmental consequences on plants, animals and humans. We have modelled such emissions in the case of the unusually large 1783-1784 basaltic fissure eruption of Laki (Iceland), using an Atmospheric General Circulation Model. Results show good agreement with historical observations, such as typical time taken by individual pulses to reach continental Europe or geographical extent of the deadly haze that covered much of the northern hemisphere. The model could be adjusted to predict the climatic consequences of very large eruptions, up to the scale of massive flood basalts, and test the proposal that these are the main agent in most mass extinctions of life on Earth.

  8. H 2O in basalt and basaltic andesite glass inclusions from four subduction-related volcanoes

    NASA Astrophysics Data System (ADS)

    Sisson, T. W.; Layne, G. D.

    1993-06-01

    Total dissolved H 2O and major element abundances were measured in basalt and basaltic andesite glass inclusions in olivine phenocrysts from Quaternary eruptions of four subduction-related volcanoes to test the hypothesis that low-MgO high-alumina basalts contain high H 2O at depth [1] and to reveal any petrogenetically significant correlations between arc basalt compositions and H 2O contents. Total dissolved H 2O (combined molecular H 2O and OH groups) measured by ion microprobe in mafic glass inclusions from the 1974 eruption of Fuego, Guatemala, reaches 6.2 wt.%. Dissolved H 2O contents decrease in more evolved Fuego glasses. Correlations of H 2O with MgO, Na 2O, K 2O, S and Cl indicate that aqueous fluid exsolution during magma ascent forced crystallization and differentiation of residual liquids. Low-K 2O magnesian high-alumina basalt glass inclusions from the 3 ka eruption of Black Crater (Medicine Lake volcano, California) have low H 2O contents, near 0.2 wt.%, which are consistent with the MORB-like character of these and other primitive lavas of the Medicine Lake region. Basalt and basaltic andesite glass inclusions from Copco Cone and Goosenest volcano on the Cascade volcanic front north of Mt. Shasta have H 2O contents of up to 3.3 wt.%. The range of H 2O contents in Cascade mafic magmas is too large to have resulted solely from enrichment by crystallization and indicates the participation of an H 2O-rich component in magma generation or crustal-level modification. Whereas fluid-absent melting of amphibole-bearing peridotite can account for the H 2O in most mafic arc liquids, the very high H 2O/alkali ratios of the 1974 Fuego eruptives suggest that an aqueous fluid was involved in the generation of Fuego basalts.

  9. Distribution and stratigraphy of basaltic units in Maria Tranquillitatis and Fecunditatis: A Clementine perspective

    NASA Technical Reports Server (NTRS)

    Rajmon, D.; Spudis, P.

    2004-01-01

    Maria Tranquillitatis and Fecunditatis have been mapped based on Clementine image mosaics and derived iron and titanium maps. Impact craters served as stratigraphic probes enabling better delineation of compositionally different basaltic units, determining the distribution of subsurface basalts, and providing estimates of total basalt thickness and the thickness of the surface units. Collected data indicate that volcanism in these maria started with the eruption of low-Ti basalts and evolved toward medium- and high-Ti basalts. Some of the high-Ti basalts in Mare Tranquillitatis began erupting early and were contemporaneous with the low- and medium-Ti basalts; these units form the oldest units exposed on the mare surface. Mare Tranquillitatis is mostly covered with high- Ti basalts. In Mare Fecunditatis, the volume of erupting basalts clearly decreased as the Ti content increased, and the high-Ti basalts occur as a few patches on the mare surface. The basalt in both maria is on the order of several hundred meters thick and locally may be as thick as 1600 m. The new basalt thickness estimates generally fall within the range set by earlier studies, although locally differ. The medium- to high-Ti basalts exposed at the surfaces of both maria are meters to tens of meters thick.

  10. Paraná-Etendeka basalts in Misiones, Argentina; characterization and petrogenetic inferences

    NASA Astrophysics Data System (ADS)

    Rämö, O. T.; Heikkilä, P. A.

    2013-12-01

    The Early Cretaceous (ca. 130 Ma) Paraná-Etendeka flood basalts constitute one of the major Phanerozoic LIP sequences with an original volume probably in excess of 2.3 Mkm3.The bulk of this volcanic system is preserved in South America (Brazil, Uruguay, Paraguay, Argentina), where it manifests the onset of South Atlantic opening at present 25 degrees Southern Latitude. The sequence is overwhelmingly basaltic (ca. 90%), but also includes contemporaneous silicic volcanic rocks. Known as the Serra Geral Suite (e.g., Bellieni et al., 1984), it fills the Paraná Basin with a northward deepening strata of lavas with a maximum thickness of ca. 1500 m. We have collected and examined basalt samples from the west-central part (western flank) of the Paraná Basin in Misiones State, northeastern Argentina (54-55 degrees Western Longitude), where the estimated thickness of the basalt succession decreases from ca. 700 m in the east to ca. 300 m in the west. The examined samples are massive, aphyric (or microphyric with plagioclase and altered olivine microphenocrysts), and geochemically relatively evolved (Mg number 50-35) basalts and basaltic andesites. Their MgO values are between 6 and 3.7 wt.% and Ni content is relatively low (65-20 ppm). Incompatible trace element values increase with increasing fractionation (decreasing Mg number), e.g., Zr from 135 to 290 ppm, Ce from 45 to 105 ppm, Nd from 20 to 50 ppm, Sm from 5 to 11 ppm, Ba from 280 to 600 ppm, and Y from 25 to 50 ppm. In terms of Ti, the samples fall into two groups (1.9-2.3 and ca. 3.8 wt.% TiO2). These values conform, respectively, to the high-Ti, high-Ti/Y Paranapanema and Pitanga magma types of Peate et al. (1992) that govern the northern half of the Paraná basalt succession. Initial Nd and Sr isotope compositions of the two groups are remarkably uniform. Our analyzed ten samples have an average initial (at 134.6 Ma) epsilon-Nd value of -4.2 × 0.3 (1 SD) and an average initial 87Sr/86Sr of 0.70570 × 0

  11. New Field, Geochronological, and Geochemical Data on the Miocene Lovejoy Basalt and its Source, Northern California

    NASA Astrophysics Data System (ADS)

    Garrison, N. J.; Busby, C. B.; Gans, P. B.; Wagner, D. L.

    2003-12-01

    The Lovejoy Basalt is a distinctive, aphanitic olivine basalt that flowed through a paleovalley across the northern end of the Sierra Nevada from the Diamond Mountains near Honey Lake to the Sacramento Valley in northern California. Approximately 150 km3 of basalt was erupted in a tectonic setting transitional between subduction, Basin and Range extension, and hot spot volcanism, but the eruptive source and timing of the Lovejoy Basalt have remained controversial. Recent field mapping and geochemical analyses suggest that Thompson Peak, located south of Susanville, California, is the source vent for the Lovejoy Basalt. At Thompson Peak, Lovejoy Basalt forms an elongate, NNW-SSE trending ridge that is capped in its central section by the Basalt of Thompson Peak. Scoria deposits, volcanic bombs, agglutinate and other near vent deposits indicate Thompson Peak as the source for the Lovejoy Basalt. Previous and new mapping indicate that the basalt was channelized within granitic basement, and flowed south from the vent 30 km to Red Clover Creek before bending to the southwest and flowing 65 km to the Sacramento Valley. The Lovejoy Basalt consists of up to 13 flows, all aphyric except for an uppermost plagioclase-phyric flow present between Thompson Peak and Red Clover Creek that locally contains xenocrysts of olivine and garnet. At Table Mountain, the basalt appears to have ponded or inflated, forming very thick flows with prominent N-S trending pressure ridges. The Lovejoy Basalt is a quartz-normative tholeiite that is geochemically similar to the Columbia River Basalt. While a conclusive statement cannot yet be made about the source magma for the Lovejoy Basalt, initial analyses show that it does not appear to be related to the main phase of Cascade arc volcanism, which is predominantly calc-alkaline. Recently published age data for the Lovejoy Basalt suggests that it is coeval with the main phase of the Columbia River Basalt Group; however, our further attempts to

  12. Thermoluminescence dating of Hawaiian basalt

    USGS Publications Warehouse

    May, Rodd James

    1979-01-01

    The thermoluminescence (TL) properties of plagioclase separates from 11 independently dated alkalic basalts 4,500 years to 3.3 million years old and 17 tholeiitic basalts 16 years to 450,000 years old from the Hawaiian Islands were investigated for the purpose of developing a TL dating method for young volcanic rocks. Ratios of natural to artificial TL intensity, when normalized for natural radiation dose rates, were used to quantify the thermoluminescence response of individual samples for age-determination purposes. The TL ratios for the alkalic basalt plagioclase were found to increase with age at a predictable exponential rate that permits the use of the equation for the best-fit line through a plot of the TL ratios relative to known age as a TL age equation. The equation is applicable to rocks ranging in composition from basaltic andesite to trachyte over the age range from about 2,000 to at least 250,000 years before present (B.P.). The TL ages for samples older than 50,000 years have a calculated precision of less than :t 10 percent and a potential estimated accuracy relative to potassium-argon ages of approximately :t 10 percent. An attempt to develop a similar dating curve for the tholeiitic basalts was not as successful, primarily because the dose rates are on the average lower than those for the alkalic basalts by a factor of 6, resulting in lower TL intensities in the tholeiitic basalts for samples of equivalent age, and also because the age distribution of dated material is inadequate. The basic TL properties of the plagioclase from the two rock types are similar, however, and TL dating of tholeiitic basalts should eventually be feasible over the age range 10,000 to at least 200,000 years B.P. The average composition of the plagioclase separates from the alkalic basalts ranges from oligoclase to andesine; compositional variations within this range have no apparent effect on the TL ratios. The average composition of the plagioclase from the tholeiitic

  13. Geochemical characterization of a Quaternary monogenetic volcano in Erciyes Volcanic Complex: Cora Maar (Central Anatolian Volcanic Province, Turkey)

    NASA Astrophysics Data System (ADS)

    Gencalioglu-Kuscu, Gonca

    2011-11-01

    Central Anatolian Volcanic Province (CAVP) is a fine example of Neogene-Quaternary post-collisional volcanism in the Alpine-Mediterranean region. Volcanism in the Alpine-Mediterranean region comprises tholeiitic, transitional, calc-alkaline, and shoshonitic types with an "orogenic" fingerprint. Following the orogenic volcanism, subordinate, within-plate alkali basalts ( sl) showing little or no orogenic signature are generally reported in the region. CAVP is mainly characterized by widespread calc-alkaline andesitic-dacitic volcanism with orogenic trace element signature, reflecting enrichment of their source regions by subduction-related fluids. Cora Maar (CM) located within the Erciyes pull-apart basin, is an example to numerous Quaternary monogenetic volcanoes of the CAVP, generally considered to be alkaline. Major and trace element geochemical and geochronological data for the CM are presented in comparison with other CAVP monogenetic volcanoes. CM scoria is basaltic andesitic, transitional-calc-alkaline in nature, and characterized by negative Nb-Ta, Ba, P and Ti anomalies in mantle-normalized patterns. Unlike the "alkaline" basalts of the Mediterranean region, other late-stage basalts from the CAVP monogenetic volcanoes are classified as tholeiitic, transitional and mildly alkaline. They display the same negative anomalies and incompatible element ratios as CM samples. In this respect, CM is comparable to other CAVP monogenetic basalts ( sl), but different from the Meditterranean intraplate alkali basalts. Several lines of evidence suggest derivation of CM and other CAVP monogenetic basalts from shallow depths within the lithospheric mantle, that is from a garnet-free source. In a wider regional context, CAVP basalts ( sl) are comparable to Apuseni (Romania) and Big Pine (Western Great Basin, USA) volcanics, except the former have depleted Ba contents. This is a common feature for the CAVP volcanics and might be related to crustal contamination or source

  14. Volcanism Studies: Final Report for the Yucca Mountain Project

    SciTech Connect

    Bruce M. Crowe; Frank V. Perry; Greg A. Valentine; Lynn M. Bowker

    1998-12-01

    This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. An assessment of the risk of future volcanic activity is one of many site characterization studies that must be completed to evaluate the Yucca Mountain site for potential long-term storage of high-level radioactive waste. The presence of several basaltic volcanic centers in the Yucca Mountain region of Pliocene and Quaternary age indicates that there is a finite risk of a future volcanic event occurring during the 10,000-year isolation period of a potential repository. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The risk of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The Crater Flat volcanic zone is

  15. Geology, geochronology, and potential volcanic hazards in the Lava Ridge-Hells Half Acre area, eastern Snake River Plain, Idaho

    USGS Publications Warehouse

    Kuntz, Mel A.; Dalrymple, G. Brent

    1979-01-01

    The evaluation of volcanic hazards for the proposed Safety Test Reactor Facility (STF) at the Argonne National Laboratory-West (ANLW) site, Idaho National Engineering Laboratory (INEL), Idaho, involves an analysis of the geology of the Lava Ridge-Hells Half Acre area and of K-At age determinations on lava flows in cored drill holes. The ANLW site at INEL lies in a shallow topographic depression bounded on the east and south by volcanic rift zones that are the locus of past shield-type basalt volcanism and by rhyolite domes erupted along the ring fracture of an inferred rhyolite caldera. The K-At age data indicate that the ANLW site has been flooded by basalt lava flows at irregular intervals from perhaps a few thousand years to as much as 300,000-400,000 years, with an average recurrence interval between flows of approximately 80,000-100,000 years. At least five major lava flows have covered the ANLW site within the past 500,000 years.

  16. The Nature of Mare Basalts in the Procellarum KREEP Terrane

    NASA Technical Reports Server (NTRS)

    Haskin, Larry A.; Gillis, Jeffrey J.; Korotev, Randy L.; Jolliff, Bradley L.

    2000-01-01

    Unlike Apollo 12 and 15 basalts, many mare lavas of the Procellarum KREEP Terrane (PKT) have Th concentrations of 2.5-6 ppm and perhaps greater, as well as high TiO2. Lunar "picritic" volcanic glasses from the PKT have a similar range.

  17. Signal from noise: Insights into volcanic system processes from ambient noise correlations

    NASA Astrophysics Data System (ADS)

    Hanson-Hedgecock, Sara

    This first section of dissertation concerns the imaging of the crust and upper most mantle structure of the mid-Miocene volcanic provinces of the Northwestern United States using ambient noise tomography. Chapter 1 introduces the complex tectonic history of the northwestern United States and describes the development of volcanism from the ignimbrite sweep that occurred with the extension of the Basin and Range province, initiation and evolution of the mid-Miocene volcanism of the Steens/Columbia River flood basalts, and mirror-image volcanic tracks of the High Lava Plains, Oregon and Yellowstone-Snake River Plains. Chapter 2 describes in detail the concepts and methods for determining the 3D shear velocity structure in the crust and uppermost mantle from ambient noise correlations. Chapter 3 contains the text and supplementary materials of Hanson-Hedgecock et al. [2012] published in the Geophysical Research Letters that describes the application of the ambient noise methods to the imaging of the Western United States. The second section of this work discusses the results of measuring velocity changes associated with three episodes of increased eruptive activity at Tungurahua in 2010 using ambient noise correlations. The third section of this work discusses the results of using the H/V ratio to measure the level of equipartition of the ambient noise wavefield at Tungurahua in 2010.

  18. Origin of the Early Permian zircons in Keping basalts and magma evolution of the Tarim Large Igneous Province (northwestern China)

    NASA Astrophysics Data System (ADS)

    Li, Yin-Qi; Li, Zi-Long; Yu, Xing; Langmuir, Charles H.; Santosh, M.; Yang, Shu-Feng; Chen, Han-Lin; Tang, Zhong-Li; Song, Biao; Zou, Si-Yuan

    2014-09-01

    The Tarim continental flood basalts (CFBs) provide important clues about the genesis and magmatic evolution of the Early Permian Tarim Large Igneous Province (Tarim LIP) in northwestern China. Here we present results of LA-MC-ICPMS Lu-Hf isotope analysis on Early Permian (ca. 290 Ma) zircons extracted from the Tarim CFBs in the Keping area, northwest of the Tarim Basin. Zircons from two sub-groups of Keping basalts (Groups 1a and 1b) have similar Lu-Hf isotopic compositions and exhibit a relatively large range of 176Hf/177Hf ratios between 0.282422 and 0.282568. Their negative εHf(t) values (- 6.8-- 1.4) are generally lower than the whole-rock εHf(t) values of their host basalts (- 2.8-2.1), and are distinct from other known intrusive rocks (- 0.3-7.1) in the Tarim LIP and their hosted zircons (4.9-8.8). Systematic studies of Hf isotopic data from Tarim and its adjacent regions reveal that these zircons are probably xenocrysts, sourced from coeval igneous rocks in the South Tianshan Orogen (e.g., the Lower Permian Xiaotikanlike Formation volcanic and pyroclastic rock suite). This, together with the presence of Precambrian zircons in Keping basalts, clearly indicates crustal contamination during their eruptions and provides hints about the potential contaminant sources. Geochemical modeling further suggests that the earlier erupted Group 1b basalts experienced more contamination, predominantly by some high Th-U-Pb rock components, most likely from the South Tianshan Orogen. The later erupted Group 1a basalts in the Keping area have been less contaminated with mainly the Tarim Precambrian rocks. Another group of the Tarim CFBs in the Northern Tarim Uplift (Group 2) appears to have undergone negligible crustal contamination but possesses evidence for variable source compositions. The modeling also indicates that the uncontaminated parental magmas of various Tarim LIP rocks (from the picrites and basalts to ultramafic-mafic and syenitic intrusive rocks) exhibit a

  19. The mantle sources beneath the Afar volcanic province and their interplay with extension

    NASA Astrophysics Data System (ADS)

    Pik, Raphael; Stab, Martin; Ancellin, Marie-Anne; Medynski, Sarah; Cloquet, Christophe; Ayalew, Dereje; Yirgu, Gezahegn; Chazot, Gilles; Vye-Brown, Charlotte; Bellahsen, Nicolas; Leroy, Sylvie

    2015-04-01

    The evolution of mantle sources beneath the Ethiopian volcanic province has long been discussed and debated with a long-lived controversy in identifying mantle reservoirs and locating them in the mantle. One interpretation of the isotopic composition of erupted lavas considers that the Afar mantle plume composition is best expressed by recent lavas from Afar and Gulf of Aden (e.g. Erta Ale, Manda Inakir and the 45°E torus anomaly on the Gulf of Aden) implying that all other volcanics (including other active segments and the initial flood basalt province) result from mixing of this plume component with additional lithospheric and asthenospheric components. A completely opposite view considers that the initial Oligocene continental flood basalts best represent the isotopic composition of the Afar mantle plume, which is subsequently mixed in various proportions with continental lithospheric mantle for generating some of the specific signature of Miocene and Quaternary volcanics. The precise and correct identification of mantle components involved in the generation of magmas is of particular importance because this is the only way to document the participation of mantle during extension and its potential role in break-up processes. In this contribution we provide new isotopic data for central Afar and we revisit the whole data set of the Ethiopian volcanic province and African/Arabian intraplate volcanics in order to: (i) precisely identify the distinct mantle components implicated, (ii) discuss their location and evolution in space and time, and (3) link the evolution of mantle with extensional processes beneath the Afar province. This new interpretation of geochemical data allows reconsidering the evolution of mantle in the course of rift evolution. In terms of mantle sources, two populations of active segments are frontally opposed in the volcanic province: those that share exactly the same composition with plume related CFBs (e.g. the Manda Hararo and the Main

  20. Petrogenesis and geodynamic significance of silicic volcanism in the western Trans-Mexican Volcanic Belt: role of gabbroic cumulates

    NASA Astrophysics Data System (ADS)

    Petrone, Chiara Maria; Orozco-Esquivel, Teresa; Ferrari, Luca

    2014-05-01

    In the western Trans-Mexican Volcanic Belt voluminous silicic volcanism has been associated with the rifting of the Jalisco block from mainland Mexico. Rhyolitic volcanism started at 7.5 Ma after a major pulse of basaltic volcanism aged 11-8.5 Ma associated with slab detachment. This was followed by a second period, between 4.9 and 2.9 Ma, associated with rhyolitic domes and ignimbrite coexisting with basaltic volcanism. The similarity in rare earth element contents between basalts and rhyolites excludes a simple liquid line of descent. The low Ba and Sr contents and the ferroan character of the rhyolites suggest extensive fractional crystallization. Late Miocene-early Pliocene rhyolite Sr isotope values are only slightly more radiogenic than the basalts, whereas Nd isotope ratios are indistinguishable. We successfully modelled the 7.5-3 Ma silicic magmatism as a result of partial melting of crustal gabbroic complexes that we infer to have formed in the mid-lower crust due to the high-density Fe-enriched composition of the late Miocene basaltic volcanism. Slab rollback since ~7.5 Ma favoured decompression melting and arrival of additional mafic magmas that intruded in the lower crust. These basalts heated and melted the gabbroic complexes forming the silicic magmas, which subsequently underwent assimilation and fractional crystallization processes. The first silicic pulse was emplaced during a period of low tectonic activity. Extensional faulting since the Pliocene favours the eruption of both silicic magma and lesser amount of mafic lavas.

  1. Pb, Sr, Nd and Hf isotopic evidence of multiple sources for Oahu, Hawaii basalts

    NASA Technical Reports Server (NTRS)

    Stille, P.; Unruh, D. M.; Tatsumoto, M.

    1983-01-01

    Pb, Sr, Nd and Hf isotopic compositions of Oahu volcanics indicate that the three principal volcanic series on Oahu Koolau, Honolulu and Waianae - were derived from isotopically distinct sources. Honolulu and Waianae basalts plot on the Nd-Pb-Sr 'mantle plane' whereas Koolau data plot distinctly below the plane.

  2. The history of mare volcanism in the Orientale Basin: Mare deposit ages, compositions and morphologies

    NASA Technical Reports Server (NTRS)

    Kadel, S. D.; Greeley, R.; Neukum, G.; Wagner, R.

    1993-01-01

    The eruptive history of mare basalts in the Orientale Basin has been studied, using Lunar Orbiter 4 high-resolution photographs, Zond 8 photographs, and recently acquired Galileo EM-1 multispectral images. This work represents a refined set of compositional data incorporating the use of a linear mixing model for mare compositions, crater count data, and a comprehensive morphologic analysis of Orientale Basin mare deposits. Evidence for multiple eruptive episodes has been found, with compositions ranging from medium- to high-Ti basalt (less than 4 to greater than 6 wt. percent TiO2). Eruptive styles included flood, rille-forming, and shield-forming eruptions. Impact crater densities of mare units in the Orientale Basin enable determination of the ages of these deposits, using the method of Neukum et al. Earliest eruptions of mare basalt in the basin occurred at greater than or equal to 3.80 Ga and the latest eruptions occurred at about 2.3-2.5 Ga. Hence, mare volcanism occurred over a period of nearly 1.5 Ga.

  3. Continental basaltic volcanoes — Processes and problems

    NASA Astrophysics Data System (ADS)

    Valentine, G. A.; Gregg, T. K. P.

    2008-11-01

    Monogenetic basaltic volcanoes are the most common volcanic landforms on the continents. They encompass a range of morphologies from small pyroclastic constructs to larger shields and reflect a wide range of eruptive processes. This paper reviews physical volcanological aspects of continental basaltic eruptions that are driven primarily by magmatic volatiles. Explosive eruption styles include Hawaiian and Strombolian ( sensu stricto) and violent Strombolian end members, and a full spectrum of styles that are transitional between these end members. The end-member explosive styles generate characteristic facies within the resulting pyroclastic constructs (proximal) and beyond in tephra fall deposits (medial to distal). Explosive and effusive behavior can be simultaneous from the same conduit system and is a complex function of composition, ascent rate, degassing, and multiphase processes. Lavas are produced by direct effusion from central vents and fissures or from breakouts (boccas, located along cone slopes or at the base of a cone or rampart) that are controlled by varying combinations of cone structure, feeder dike processes, local effusion rate and topography. Clastogenic lavas are also produced by rapid accumulation of hot material from a pyroclastic column, or by more gradual welding and collapse of a pyroclastic edifice shortly after eruptions. Lava flows interact with — and counteract — cone building through the process of rafting. Eruption processes are closely coupled to shallow magma ascent dynamics, which in turn are variably controlled by pre-existing structures and interaction of the rising magmatic mixture with wall rocks. Locations and length scales of shallow intrusive features can be related to deeper length scales within the magma source zone in the mantle. Coupling between tectonic forces, magma mass flux, and heat flow range from weak (low magma flux basaltic fields) to sufficiently strong that some basaltic fields produce polygenetic

  4. Volcanism in Kamchatka, Russia

    NASA Astrophysics Data System (ADS)

    Eichelberger, J. C.; Eichelberger, L. G.

    2008-12-01

    -Russians than they should be. Among the best natural laboratories for understanding subduction volcanism are: (1) The spectacular edifice collapse/explosive eruption/continuing dome-effusion sequences of Bezymianny (1956) and Shiveluch (1964), which together with Mount St Helens (1980) provide a valuable time series in system evolution; (2) The two-magma, multiple vent eruptions of Tolbachik (1975), Karymsky (1996), and Gorely (1737) interpretable as large dikes interacting with shallow magma pods; (3) Ksudach with 3 caldera-forming eruptions within just the Holocene; (4) Hydrothermally diverse Mutnovsky with strong passive SO2 degassing, fumaroles to 600°C, and flanking 50 MWe geothermal production; and (5) The ever-active Kliuchevskoi Volcano, which may demonstrate the requirement of gas-lift to push basalt to the top of its towering, hastily built cone without rupturing it.

  5. Geology and geochronology of the Tana Basin, Ethiopia: LIP volcanism, super eruptions and Eocene-Oligocene environmental change

    NASA Astrophysics Data System (ADS)

    Prave, A. R.; Bates, C. R.; Donaldson, C. H.; Toland, H.; Condon, D. J.; Mark, D.; Raub, T. D.

    2016-06-01

    New geological and geochronological data define four episodes of volcanism for the Lake Tana region in the northern Ethiopian portion of the Afro-Arabian Large Igneous Province (LIP): pre-31 Ma flood basalt that yielded a single 40Ar/39Ar age of 34.05 ± 0.54 / 0.56 Ma; thick and extensive felsic ignimbrites and rhyolites (minimum volume of 2- 3 ×103 km3) erupted between 31.108 ± 0.020 / 0.041 Ma and 30.844 ± 0.027 / 0.046 Ma (U-Pb CA-ID-TIMS zircon ages); mafic volcanism bracketed by 40Ar/39Ar ages of 28.90 ± 0.12 / 0.14 Ma and 23.75 ± 0.02 / 0.04 Ma; and localised scoraceous basalt with an 40Ar/39Ar age of 0.033 ± 0.005 / 0.005 Ma. The felsic volcanism was the product of super eruptions that created a 60-80 km diameter caldera marked by km-scale caldera-collapse fault blocks and a steep-sided basin filled with a minimum of 180 m of sediment and the present-day Lake Tana. These new data enable mapping, with a finer resolution than previously possible, Afro-Arabian LIP volcanism onto the timeline of the Eocene-Oligocene transition and show that neither the mafic nor silicic volcanism coincides directly with perturbations in the geochemical records that span that transition. Our results reinforce the view that it is not the development of a LIP alone but its rate of effusion that contributes to inducing global-scale environmental change.

  6. Sulfur, Chlorine and Fluorine Degassing and Atmospheric Loading by the Roza eruption, Columbia River Basalt Group, Washington

    NASA Technical Reports Server (NTRS)

    Thordarson, Th.; Self, S

    1996-01-01

    In this study we attempt to quantify the amount of S, Cl and F released by the 1300 cu km Roza member (approximately 14.7 Ma) of the Columbia River Basalt Group, which was produced by a moderate-size flood basalt eruption in the mid-Miocene. Our results are the first indication of the potential atmospheric SO2 yield from a flood basalt eruption, and indicate the mechanism by which flood basalt eruptions may have seriously affected the environment. Glass inclusions in phenocrysts and quenched glass in products from various stages of the eruption were analyzed for concentrations of S, Cl and F and major elements. Glass inclusions contain 1965 +/- 110 ppm S, 295 +/- 65 ppm Cl and 1310 +/- 110 ppm F. Groundmass glass of Roza dike selvages contains considerably lower concentrations: 1110 +/- 90 ppm S, 245 +/- 30 ppm Cl and 1020 +/- 25 ppm F. Scoria clasts from near vent deposits contain 665 +/- 75 ppm S, 175 +/- 5 ppm Cl and 950 +/- 20 ppm F, and the groundmass glass of lava selvages contains 520 +/- 30 ppm S, 190 +/- 30 ppm Cl and 890 +/- 55 ppm F. In crystalline lava, the concentrations are 195 ppm S, 100 ppm Cl and 830 ppm F. Volatile element concentrations in these samples represent the progress of degassing through the eruption and can be used to estimate the potential amount of the volatiles S, Cl and F released by the magma into the atmosphere, as well as to evaluate the amount liberated by various phases of the eruption. The total amount of volatiles released by the Roza eruption is estimated to have been approximately 12,420 MtSO2, approximately 710 MtHCI and approximately 1780 MtHF. The Roza magma liberated approximately 9620 MtSO, (77% of the total volatile mass released), approximately 400 MtHCI (56%) and approximately 1450 MtHF (81%) at the vents and lofted by the eruption columns to altitudes of 7-13 km. Degassing of the lava is estimated to have released an additional approximately 2810 MtSO2, approximately 310 MtHCI and approximately 330 MtHF. The Roza

  7. A Strongly Calc-alkaline Suite in the Midst of the Tholeiitic Columbia River Basalt Province: Implications for Generating the Calc-alkaline Trend Without Subduction Processes

    NASA Astrophysics Data System (ADS)

    Steiner, A. R.; Streck, M. J.

    2012-12-01

    The mid-Miocene lavas of the Strawberry Volcanics (SV), distributed over 3,400 km2 in NE Oregon, comprise a diverse volcanic suite, which span the range of compositions from basalt to rhyolite. The volcanic suite is mainly composed of calc-alkaline (CA) basaltic andesite and andesite, yet tholeiitic (TH) lavas of basalt to andesite occur as well. The SV lies in the heart of nearly coeval flood basalts of the Columbia River province of the Pacific Northwest. The unique combination of strongly CA rocks of the SV in a non-subduction setting provide an excellent opportunity to study controls on inducing CA evolution in the midst of a TH province and independent of processes taking places at an active subduction zone. New 40Ar/39Ar ages indicate CA basaltic andesites to andesites of the SV erupted at least from 14.78±0.13 Ma to 12.44±0.12 Ma demonstrating that CA magmatism of the SV was ongoing during the eruptions of the tholeiitic Wanapum Basalt member of the Columbia River Basalt Group (CRBG). This range will likely be extended to even older ages in the future because existent age dates did not include samples from near the base of the SV. Thickness of intermediate lavas flows of the SV range from 15 m to as thin as 2 m and lavas are characterized by mostly phenocryst poor lithologies. When phenocrysts are abundant they are very small suggesting growth late during eruption. Single lava flow sections can include on the order of 30 conformable flows, testifying to a vigorous eruption history. The thickest andesitic sections are located in the glacially carved mountains of the Strawberry Mountain Wilderness (i.e. Strawberry Mountain, High Lake, and Slide Lake) where several vent complexes are exposed, which are delineated by dikes and plugs with finely interlocking plutonic textures, cross-cutting SV lava flows. Dikes generally strike NW-SE. Subtle variations in major and trace element compositions exist between TH and CA lavas of the SV. The CA lavas of the SV are

  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. Modeling Central American basalts using the Arc Basalt Simulator

    NASA Astrophysics Data System (ADS)

    Feigenson, M.; Carr, M. J.

    2011-12-01

    We have used the Arc Basalt Simulator (ABS), developed by JI Kimura, to explore the conditions and components of melting beneath the Central American volcanic front. ABS is a comprehensive forward model that incorporates slab dehydration and melting and mantle wedge fluxing and melting using realistic P-T conditions and experimentally determined phase relations. We have applied ABS versions 3 and 4 to model representative magma types in Nicaragua, which span a broad geochemical range including proximal high- and low-Ti lavas in Nicaragua. Sr-Nd-Pb data require appropriate selection of previously identified sources, including: separate carbonate and hemipelagic sediments, DMM, an enriched mantle isotopically similar to the alkaline basalts of Yojoa, a Himu-influenced mantle derived from Galapagos material and altered oceanic crust (AOC) derived from both MORB and Galapagos seamounts. Following the dry solidus, the dominant arc basalts, exemplified by Cerro Negro lavas, can be generated at about 80-90 km where lawsonite and zoisite break down, releasing LILEs into a hydrous fluid that travels into the wedge. The fluid-triggered melting occurs just above the garnet stability field in the wedge to fit the HREEs. Below 90 Km, slab melting begins and the AOC component dominates, generating a fluid with little or no HFSE depletions, consistent with the unusual high-Ti lavas found in Nicaragua. However, the isotopic data require a much lower sediment input for the high-Ti lavas (consistent with 10Be results on the high-Ti lavas) and an enriched component for the AOC and/or mantle wedge. Following the wet solidus, fits to the Cerro Negro magma only occur in the absence of phengite in the AOC and with the presence of HFSE attracting minerals, rutile, zircon and allanite. The depth of the best fit is 135 km, consistent with current best estimates of the depth to the seismic zone beneath Cerro Negro. Below 150 km, the high-Ti lavas can be generated if the HFSE retaining

  10. Evolution of bimodal volcanism in Gona, Ethiopia: geochemical associations and geodynamic implications for the East African Rift System

    NASA Astrophysics Data System (ADS)

    Ghosh, N.; Basu, A. R.; Gregory, R. T.; Richards, I.; Quade, J.; Ebinger, C. J.

    2013-12-01

    The East African rift system in Ethiopia formed in the Earth's youngest flood basalt province, and provides a natural laboratory to study the geochemistry of bimodal volcanism and its implications for plume-derived magmatism, mantle-lithosphere interactions and evolution of continental rifts from plate extension to rupture. Our geochemical studies of the ~6 Ma to recent eruptive products from Gona within the Afar Rift Zone are understood in context of crustal and upper mantle seismic imaging studies that provide constraints on spatial variations. Geochemical (major element, trace element and isotope) analyses of basalts and rhyolitic tuff from Gona indicate a common magma source for these bimodal volcanics. Light rare earth elements (LREEs) are enriched with a strong negative Eu anomaly and a positive Ce anomaly in some of the silicic volcanic rocks. We observe strong depletions in Sr and higher concentrations of Zr, Hf, Th, Nb and Ta. We hypothesize that the silicic rocks may be residues from a plume-derived enriched magma source, following partial melting with fractional crystallization of plagioclase at shallow magma chambers. The absence of Nb-Ta anomaly shows no crustal assimilation by magmas. Sr isotopes, in conjunction with Nd and Pb isotopes and a strong Ce anomaly could reflect interaction of the parent magma with a deep saline aquifer or brine. Nd isotopic ratios (ɛNd = 1.9 to 4.6) show similarity of the silicic tuffs and basalts in their isotopic compositions except for some ~6 Ma lavas showing MORB-like values (ɛNd = 5 to 8.7) that suggest involvement of the asthenosphere with the plume source. Except for one basaltic tuff, the whole rock oxygen isotopic ratios of the Gona basalts range from +5.8‰ to +7.9‰, higher than the δ values for typical MORB, +5.7. The oxygen isotopes in whole rocks from the rhyolite tuffs vary from 14.6‰ to 20.9‰ while their Sr isotope ratios <0.706, indicative of post-depositional low T alteration of these silicic

  11. Additive Construction using Basalt Regolith Fines

    NASA Technical Reports Server (NTRS)

    Mueller, Robert P.; Sibille, Laurent; Hintze, Paul E.; Lippitt, Thomas C.; Mantovani, James G.; Nugent, Matthew W.; Townsend, Ivan I.

    2014-01-01

    Planetary surfaces are often covered in regolith (crushed rock), whose geologic origin is largely basalt. The lunar surface is made of small-particulate regolith and areas of boulders located in the vicinity of craters. Regolith composition also varies with location, reflecting the local bedrock geology and the nature and efficiency of the micrometeorite-impact processes. In the lowland mare areas (suitable for habitation), the regolith is composed of small granules (20 - 100 microns average size) of mare basalt and volcanic glass. Impacting micrometeorites may cause local melting, and the formation of larger glassy particles, and this regolith may contain 10-80% glass. Studies of lunar regolith are traditionally conducted with lunar regolith simulant (reconstructed soil with compositions patterned after the lunar samples returned by Apollo). The NASA Kennedy Space Center (KSC) Granular Mechanics & Regolith Operations (GMRO) lab has identified a low fidelity but economical geo-technical simulant designated as Black Point-1 (BP-1). It was found at the site of the Arizona Desert Research and Technology Studies (RATS) analog field test site at the Black Point lava flow in adjacent basalt quarry spoil mounds. This paper summarizes activities at KSC regarding the utilization of BP-1 basalt regolith and comparative work with lunar basalt simulant JSC-1A as a building material for robotic additive construction of large structures. In an effort to reduce the import or in-situ fabrication of binder additives, we focused this work on in-situ processing of regolith for construction in a single-step process after its excavation. High-temperature melting of regolith involves techniques used in glassmaking and casting (with melts of lower density and higher viscosity than those of metals), producing basaltic glass with high durability and low abrasive wear. Most Lunar simulants melt at temperatures above 1100 C, although melt processing of terrestrial regolith at 1500 C is not

  12. Tectonic implications of space-time patterns of Cenozoic volcanism in the Palo Verde Mountain volcanic field, southeastern California

    SciTech Connect

    Murray, K.S.

    1981-01-01

    Variations in Cenozoic volcanism in the western United States are believed to correlate closely with changes in tectonic setting. A transition in volcanic association from calc-alkaline to fundamentally basaltic volcanism and subsequent crustal extension, appears to have coincided temporally with the initial collision of the East Pacific Rise with the continental margin trench off western North America, between 28 and 25 Ma. The volcanic stratigraphy of the Palo Verde Mountain volcanic field is broadly similar to other volcanic centers in southeastern California and can be divided into tripartite regional stratigraphy. A basal sequence of andesitic to rhyolitic lava flows, plugs, domes, and extensive pyroclastic deposits rests unconformably on pre-Cenozoic basement rocks. The basal sequence is intruded by cogenetic Cenozoic plutonic rocks and overlain by basaltic to rhyolitic lava flows, dikes, and a second widespread assemblage of pyroclastic deposits, cumulatively referred to as the silicic sequence. The youngest volcanic rocks of the field include olivine basalt flows and breccia which occur at scattered localities in the Palo Verde Mountains. The age, stratigraphy, and chemistry of the intermediate and basaltic composition volcanic rocks broadly supports previously cited volcanic-tectonic models, if modified to incorporate modern plate reconstruction theory. This modification results in a southeast migration of the transition to basaltic volcanism to southeastern California occurring significantly later in time than the previously cited ages of transition. Moreover, this southeast migration of the volcanic transition is coincident with the inception of Basin and Range faulting and the initiation of movement on the San Andreas fault south of the Transverse Ranges, corresponding to the southward migration of the Pacific-Cocos Ridge.

  13. A possible K-T boundary bolide impact site offshore near Bombay and triggering of rapid Deccan volcanism

    NASA Astrophysics Data System (ADS)

    Negi, J. G.; Agrawal, P. K.; Pandey, O. P.; Singh, A. P.

    1993-03-01

    The temporal coincidence of a major biological mass extinction (including dinosaurs), the well-known iridium excess anomaly at the Cretaceous-Tertiary (K-T) boundary and the eruption of Deccan flood basalts at about 65 Ma has aroused global interest among geologists and biologists. It is widely debated whether the mass extinction and iridium anomaly are due to an asteroid impact or the massive outpouring of extensive Deccan volcanism. An oval shaped unusual positive gravity anomaly (10 000 km 2 in area) near Bombay has attracted our attention during a search for an impact site near Deccan basalts. A detailed gravity interpretation indicates the presence of a fossil conduit structure of 12 km height extending from a shallow crust-mantle boundary (at 18 km) to an approximate depth of 6 km from the surface. The conduit structure, with a maximum diameter of about 35 km at its base, may originate from cracking of a weak pre-Deccan trap shallow upwarped mantle. The structure may have been caused by a bolide impact which triggered the eruption of massive flood basalts (Deccan traps) on the western margin of the fast-moving Indian plate. An impact in this locality can explain the sudden detachment of the arcuate Seychelles block from India as well as the large-scale reorganisation of plate boundaries in the Indian Ocean. Our hypothesis of impact-triggered volcanism at 65 Ma advocates a bimodal cause for the mass extinction at the K-T boundary. Extraordinary geothermal and structural conditions of the nearby region are also discussed as circumstantial evidence to support the twin-cause mechanism by weakened features and the presence of partial melt at subcrustal depth.

  14. Migration of volcanism in the San Francisco volcanic field, Arizona.

    USGS Publications Warehouse

    Tanaka, K.L.; Shoemaker, E.M.; Ulrich, G.E.; Wolfe, E.W.

    1986-01-01

    The remanent magnetization of volcanic rocks has been determined at 650 sites in this volcanic field in the S part of the Colorado plateau. The polarity of remanent magnetization, combined with K/Ar age determinations, spatial and petrographic association, stratigraphic relations and state of preservation of the cinder cones, provides a basis of assignment to a known magnetic polarity epoch of 610 mafic vents and >100 intermediate to silicic flows, flow sequences and vents. Basaltic volcanism migrated NE before Matoyama time (2.48-5.0 m.y.) at a rate of approx 1.2 cm/yr and eastward over the past 2.5 m.y. at a rate of 2.9 cm/yr. Total magma production and frequency of basaltic eruption accelerated between 5 and 0.25 m.y. and have decreased thereafter; this evolutionary sequence, coupled with the Sr-isotopic composition of the rocks, can be explained by magmatism caused by shear heating at the base of the lithosphere. The eastward drift of volcanism represents the absolute westward motion of the North America plate.-L.C.H.

  15. Monogenetic volcanic hazards and assessment

    NASA Astrophysics Data System (ADS)

    Connor, C.; Connor, L. J.; Richardson, J. A.

    2012-12-01

    Many of the Earth's major cities are build on the products of monogenetic volcanic eruptions and within geologically active basaltic volcanic fields. These cities include Mexico City (Mexico), Auckland (New Zealand), Melbourne (Australia), and Portland (USA) to name a few. Volcanic hazards in these areas are complex, and involve the potential formation of new volcanic vents and associated hazards, such as lava flows, tephra fallout, and ballistic hazards. Hazard assessment is complicated by the low recurrence rate of volcanism in most volcanic fields. We have developed a two-stage process for probabilistic modeling monogenetic volcanic hazards. The first step is an estimation of the possible locations of future eruptive vents based on kernel density estimation and recurrence rate of volcanism using Monte Carlo simulation and accounting for uncertainties in age determinations. The second step is convolution of this spatial density / recurrence rate model with hazard codes for modeling lava inundation, tephra fallout, and ballistic impacts. A methodology is presented using this two-stage approach to estimate lava flow hazard in several monogenetic volcanic fields, including at a nuclear power plant site near the Shamiram Plateau, a Quaternary volcanic field in Armenia. The location of possible future vents is determined by estimating spatial density from a distribution of 18 mapped vents using a 2-D elliptical Gaussian kernel function. The SAMSE method, a modified asymptotic mean squared error approach, uses the distribution of known eruptive vents to optimally determine a smoothing bandwidth for the Gaussian kernel function. The result is a probability map of vent density. A large random sample (N=10000) of vent locations is drawn from this probability map. For each randomly sampled vent location, a lava flow inundation model is executed. Lava flow input parameters (volume and average thickness) are determined from distributions fit to field observations of the low

  16. Naming Lunar Mare Basalts: Quo Vadimus Redux

    NASA Astrophysics Data System (ADS)

    Ryder, G.

    1999-01-01

    and ordering. Classification functions as a primary tool of perception, opening up ways of seeing things and sealing off others. Lacking a classification, mare-basalt petrology appears immature with little consensual perception of the qualities and signifigances of the basalts. The appearance may or may not be the reality, but it demonstrates a need for a functioning, communicatory classification, in particular for the dissemination of ideas and the furtherance of studies. Names are inconsistent both among lunar rocks and between lunar and terrestrial rocks. Samples are labeled by elements, chemistry with tags, chemistry cast into mineralogy, or a mineralogical attribute (respective examples A 14 VHK A 17 high-Ti Group B 1, A 15 quartz-normative, A-12 pigeonite). Such inconsistency is bound to lead to confusion. Chemical descriptions mean different things in mildly different contexts: A low-K Fra Mauro basalt (not a basalt!) contains slightly more K than an Apollo 11 high-K basalt. High-alumina means more than about 11% Al2O3 for mare basalts, but 21% for highlands "basalts." Volcanic KREEP basalts, about 18% Al2O3, are not (usually) qualified with "high-alumina." Yet for terrestrial basalts, high-alumina means more than about 17% Al2O3, Further, even very-low-Ti mare basalts have Ti abundances (about 0.5-1.5% Ti02) as great as typical terrestrial basalts. Thus, parallels between lunar and terrestrial nomenclatures are nonexistent (reinforced by the fact that a mare-basalt composition found on Earth would be too ultramafic to name basalt at all). A separate type of name exists for mare-basalt glasses, which are identified by site, color, and a letter for any subsequent distinctions, e.g., A15 Green Glass C. While the inconsistencies cited above by themselves make nomenclature arcane, a greater source of difficulty is the common use of acronyms such as VHK and VLT. Most of these are partly chemical acronyms, but degrading the symbol Ti to T (for instance) makes them

  17. Mare basalts on the Apennine Front and the mare stratigraphy of the Apollo 15 landing site

    NASA Technical Reports Server (NTRS)

    Ryder, Graham

    1989-01-01

    Olivine-normative mare basalts are present on the Apennine Front as crystalline particles and shocked or shock-melted fragments. Picritic basalts, which may be related to the olivine-normative basalts by olivine accumulation, not only occur on the Front but such samples so far recognized are confined to it. Mare volcanic and impact glasses also occur on the Front; all are olivine-normative, though none are quite the equivalent of the typical olivine-normative mare group. The quartz-normative mare basalts are not present (or are extremely rare) on the Front either as crystalline basalts or shocked or glass equivalents. These observations are consistent with the olivine-normative mare basalts being both local and the youngest flows at the site, and the fragments being emplaced on the Front by impacts. The picritic basalts raise the distinct possibility that the olivine-normative basalts also ponded on the Front. An influx of olivine-normative basalts from exotic sources (e.g., a ray from Aristillus) is inconsistent with their abundance, their dominance in the mare soil chemistry, and their age, isotopic, and trace element similarities with the quartz-normative basalts. However, the thermal histories of the olivine-normative basalts require elucidation.

  18. Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations

    SciTech Connect

    Crowe, B.M.; Vaniman, D.T.; Carr, W.J.

    1983-03-01

    Volcanism studies of the Nevada Test Site (NTS) region are concerned with hazards of future volcanism with respect to underground disposal of high-level radioactive waste. The hazards of silicic volcanism are judged to be negligible; hazards of basaltic volcanism are judged through research approaches combining hazard appraisal and risk assessment. The NTS region is cut obliquely by a N-NE trending belt of volcanism. This belt developed about 8 Myr ago following cessation of silicic volcanism and contemporaneous with migration of basaltic activity toward the southwest margin of the Great Basin. Two types of fields are present in the belt: (1) large-volume, long-lived basalt and local rhyolite fields with numerous eruptive centers and (2) small-volume fields formed by scattered basaltic scoria cones. Late Cenozoic basalts of the NTS region belong to the second field type. Monogenetic basalt centers of this region were formed mostly by Strombolian eruptions; Surtseyean activity has been recognized at three centers. Geochemically, the basalts of the NTS region are classified as straddle A-type basalts of the alkalic suite. Petrological studies indicate a volumetric dominance of evolved hawaiite magmas. Trace- and rare-earth-element abundances of younger basalt (<4 Myr) of the NTS region and southern Death Valley area, California, indicate an enrichment in incompatible elements, with the exception of rubidium. The conditional probability of recurring basaltic volcanism and disruption of a repository by that event is bounded by the range of 10{sup -8} to 10{sup -10} as calculated for a 1-yr period. Potential disruptive and dispersal effects of magmatic penetration of a repository are controlled primarily by the geometry of basalt feeder systems, the