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Sample records for flood basalt volcanism

  1. Flood basalt volcanism during the past 250 million years.

    PubMed

    Rampino, M R; Stothers, R B

    1988-08-05

    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 initation dates of the volcanic episodes determined from the distributions of the radiometric ages are, approximately, plus or minus 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 +/- 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.

  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 Basalt Chemistry, Age and Volcanic Volumes

    NASA Astrophysics Data System (ADS)

    Humler, E.; Doubre, C.; Doubre, C.

    2001-12-01

    We have compiled a large collection of published chemical analyses of the 11 known continental flood basalts of the last 250 millions years. Only basaltic lavas and some related basic intrusive rocks are considered to be representative of the major episodes. Differentiation trends exhibit varying amounts of scatter, the trends for SiO2, FeO, and TiO2 are quite well defined, have slopes of the same sign, and can be represented adaquately by straigth lines. In contrast, the trends of CaO, Al2O3 and Na2O are often poorly defined. There are clear differences in major element abundances between volcanic suites, particularly for elements with well defined slopes. The results of our regressions are generally consistent with those of Turner and Hawkesworth (1995), Peng et al (1994) and Lassister and DePaolo (1997), although some differences exist. Examination of the global data base shows that there are systematic global variations in continental flood basalt chemistry that correlate with age. Old CFB, such as the Central Atlantic and Karoo-Ferrar, show the following characteristics: low Na2O, TiO2 and FeO, high SiO2. In contrast, basalts associated with recent breakups such as Afar-Yemen and Ethiopia, show the opposite chemical trends. Between these old and young continental breakup, a continuum of compositions is observed. The observed chemical systematics suggest that basalts associated with old breakups are derived by larger extent of melting at shallower mean pressures of melt segregation. Estimating the original volumes of lava in flood basalt provinces is rendered difficult due to subsequent erosion, partial destruction during continental collisions or burial beneath passive margin sedimentation wedges. Many CFBs were erupted in geologically brief intervals (0.5 to 2 Ma) although some, notably the Siberian Traps and Brito-Arctic Province, were emplaced in two or more distinct phases separeted by quiescent intervals. Our calculated emplacement rate show correlation

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

    NASA Astrophysics Data System (ADS)

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

    1996-09-01

    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 (2σ) 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 (2σ)], and confirms Siberian basaltic volcanism as a possible contributor to the mass extinction.

  6. 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

  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. 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

  9. Pollution and paradigms: lessons from Icelandic volcanism for continental flood basalt studies

    NASA Astrophysics Data System (ADS)

    Grattan, John

    2005-02-01

    This paper is based on the premise that research into the environmental impact of continental flood basalt (CFB) volcanism has paid insufficient attention to the potential ecosystem damage that would result from the direct deposition of hundreds of megatons (Tg) of sulphur and other volatiles. The environmental impacts of the 1783 Laki Fissure eruption are reviewed in outline. It is shown that in a relatively brief period of volcanic activity, volatiles emitted by the eruption damaged and destroyed vegetation from the Arctic Ocean to the Mediterranean. Air pollution was so intense that human health was affected and the national death rate increased dramatically in both England and France. It is proposed that the events of 1783 may be used as a paradigm for the environmental impacts of a CFB lava flow, and the emissions of 1783 are scaled up to illustrate this point. Thus, if a Laki style event were to erupt for a year it would approach the physical scale of a single episode of the Roza flow in the Columbia River CFB and potentially yield 576 Tg of sulphur gases which could have been oxidised into approximately 945 Tg of aerosol. This could generate a tropospheric aerosol mass of approximately 708 Tg H 2SO 4. The ecosystem impact of the deposition of acids on this scale would be profound and, as with the actual Laki event, be continental in scale. All parts of the plant life cycle would be disrupted, including photosynthesis and fruiting. Inevitably, with the disruption of food webs animals would also be affected. Poorly buffered inland waters would be acidified, as would Boreal soils, reducing their biodiversity. In our already polluted and interdependent world, any future event on this scale would have serious consequences for human health and trade.

  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. Understanding cratonic flood basalts

    NASA Astrophysics Data System (ADS)

    Silver, Paul G.; Behn, Mark D.; Kelley, Katherine; Schmitz, Mark; Savage, Brian

    2006-05-01

    The origin of continental flood basalts has been debated for decades. These eruptions often produce millions of cubic kilometers of basalt on timescales of only a million years. Although flood basalts are found in a variety of settings, no locale is more puzzling than cratonic areas such as southern Africa or the Siberian craton, where strong, thick lithosphere is breached by these large basaltic outpourings. Conventionally, flood basalts have been interpreted as melting events produced by one of two processes: 1) elevated temperatures associated with mantle plumes and/or 2) adiabatic-decompression melting associated with lithospheric thinning. In southern Africa, however, there are severe problems with both of these mechanisms. First, the rifting circumstances of several well-known basaltic outpourings clearly reflect lithospheric control rather than the influence of a deep-seated plume. Specifically, rift timing and magmatism are correlated with stress perturbations to the lithosphere associated with the formation of collisional rifts. Second, the substantial lithospheric thinning required for adiabatic decompression melting is inconsistent with xenolith evidence for the continued survival of thick lithosphere beneath flood basalt domains. As an alternative to these models, we propose a new two-stage model that interprets cratonic flood basalts not as melting events, but as short-duration drainage events that tap previously created sublithospheric reservoirs of molten basalt formed over a longer time scale. Reservoir creation/existence (Stage I) requires long-term (e.g. ≫ 1 Ma) supersolidus conditions in the sublithospheric mantle that could be maintained by an elevated equilibrium geotherm (appropriate for the Archean), a slow thermal perturbation (e.g. thermal blanketing or large-scale mantle upwelling), or a subduction-related increase in volatile content. The drainage event (Stage II) occurs in response to an abrupt stress change in the lithosphere, which

  12. Flood basalt volcanism, end-Triassic deforestation, and intense weathering of soils and bedrock

    NASA Astrophysics Data System (ADS)

    van de Schootbrugge, Bas; Lindström, Sofie; Pross, Jörg; Dybkjaer, Karen; Heunisch, Carmen; Petschick, Rainer; Lyachenko, Lara; Püttmann, Willhelm; Oschmann, Wolfgang

    2010-05-01

    The end-Triassic mass-extinction on land was characterized by the widespread dieback of gymnospermous forests across the northern hemisphere and their transient replacement by ferns and fern allies. These floral changes are thought to have been triggered by the eruption of 2 million kubic kilometers of basalt belonging to the Central Atlantic Magmatic Province, releasing noxious and greenhouse gases into the atmosphere. Here, we provide evidence for the dramatic consequences of deforestation during the latest Triassic in the form of intense erosion of soils and the weathering of bedrock across northwest Europe. Together with abundant fern spores, representing a pioneer vegetation, we find enhanced levels of kaolinite in the boundary beds, indicating chemical weathering. In palynological samples from cores that span the Triassic-Jurassic boundary in Sweden, Denmark and Germany we notice abundant reworked Carboniferous spores, reworked Silurian and Devonian acritarchs, and mycorrhizal fungal remains. The latter suggest soils were being eroded across the Germanic Basin. In Northern Germany, Denmark, and Sweden, Paleozoic palynomorphs were reworked from the Fennoscandian Shield, while in Southern Germany such palynomorphs may have originated from the Bohemian Massive. The contemporaneous, intense weathering of bed rocks and soil erosion on landmasses during the latest Triassic was likely a direct result of deforestation, but was probably exacerbated by acid rain and greenhouse warming due to the emission of sulfur and carbon dioxide from volcanic activity.

  13. 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.

  14. A Plagioclase Ultraphyric Basalt group in the Neogene flood basalt piles of eastern Iceland: Volcanic architecture and mode of emplacement

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    3D photogrammetry in conjunction with ground mapping was applied in order to assess the architecture of a Plagioclase Ultraphyric Basalt (PUB) group in eastern Iceland, namely the Grænavatn group. The ~10 Myr old group is exposed in steep glacially carved fjords and can be traced over 60 km along strike. Two feeder dikes have been found and show that the group erupted along the trend of the dike swarm associated with the Breiddalur central volcano. The group has 9--14 flows where thickest, and thins to about 3--4 flows up-dip to the east within the distance of 15-20 km from the source. We have estimated the volume of the group to exceed 40 km3. The flows have mixed architecture of simple and compound morphology. The flow lobes have thicknesses from 1--24 m and many reach lengths over 1000 m. The surface morphology varies from rubbly to scoriaceous, but is dominantly of pahoehoe style. The internal structure of the lava flows is well preserved and the flows display abundant vesicle cylinders. The modal percentage of An-rich plagioclase macrocrysts varies from 25--50 % and they are in the range of 5--30 mm. The aspect ratio of the group and the nature of the flows indicate fissure-fed eruptions. A thick flow found at the base of the group in various locations seems to record the largest eruption episode in the formation of the group. This phase is also the most abundant in macrocryst. An asymmetric buildup is seen in one location and may have characterized the general buildup of the group. The general morphology of the lava flows suggests low viscous behavior, at odds with the high crystal content. Petrographic observations and mineral chemistry shows that the plagioclase macrocrysts are very calcic (An80-85) and in disequilibrium with the groundmass and plagioclases therein (An50-70). Thus the apparent lava rheology and emplacement of the PUBs was likely achieved due to fast ascent of the magma through the crust and transfer of heat from the primitive macrocrysts

  15. Are flood basalt eruptions monogenetic or polygenetic?

    NASA Astrophysics Data System (ADS)

    Sheth, Hetu C.; Cañón-Tapia, Edgardo

    2015-11-01

    A fundamental classification of volcanoes divides them into "monogenetic" and "polygenetic." We discuss whether flood basalt fields, the largest volcanic provinces, are monogenetic or polygenetic. A polygenetic volcano, whether a shield volcano or a stratovolcano, erupts from the same dominant conduit for millions of years (excepting volumetrically small flank eruptions). A flood basalt province, built from different eruptive fissures dispersed over wide areas, can be considered a polygenetic volcano without any dominant vent. However, in the same characteristic, a flood basalt province resembles a monogenetic volcanic field, with only the difference that individual eruptions in the latter are much smaller. This leads to the question how a flood basalt province can be two very different phenomena at the same time. Individual flood basalt eruptions have previously been considered monogenetic, contrasted by only their high magma output (and lava fluidity) with typical "small-volume monogenetic" volcanoes. Field data from Hawaiian shield volcanoes, Iceland, and the Deccan Traps show that whereas many feeder dykes were single magma injections, and the eruptions can be considered "large monogenetic" eruptions, multiple dykes are equally abundant. They indicate that the same dyke fissure repeatedly transported separate magma batches, feeding an eruption which was thus polygenetic by even the restricted definition (the same magma conduit). This recognition helps in understanding the volcanological, stratigraphic, and geochemical complexity of flood basalts. The need for clear concepts and terminology is, however, strong. We give reasons for replacing "monogenetic volcanic fields" with "diffuse volcanic fields" and for dropping the term "polygenetic" and describing such volcanoes simply and specifically as "shield volcanoes," "stratovolcanoes," and "flood basalt fields."

  16. 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.

  17. The onset of flood basalt volcanism, Northern Paraná Basin, Brazil: A precise U-Pb baddeleyite/zircon age for a Chapecó-type dacite

    NASA Astrophysics Data System (ADS)

    Janasi, Valdecir de Assis; de Freitas, Vivian Azor; Heaman, Larry H.

    2011-02-01

    We report the first U-Pb baddeleyite/zircon date for a felsic volcanic rock from the Paraná Large Igneous Province in south Brazil. The new date of 134.3 ± 0.8 Ma for a hypocrystalline Chapecó-type dacite from Ourinhos (northern Paraná basin) is an important regional time marker for the onset of flood basalt volcanism in the northern and western portion of the province. The dated dacite was erupted onto basement rocks and is overlain by a high-Ti basalt sequence, interpreted to be correlative with Pitanga basalts elsewhere. This new U-Pb date for the Ourinhos dacite is consistent with the local stratigraphy being slightly older than the few reliable step-heating 40Ar/39Ar dates currently available for overlying high-Ti basalts (133.6-131.5 Ma). This indicates an ~ 3 Ma time span for the building of the voluminous high-Ti lava sequence of the Paraná basin. On the other hand, it overlaps the 40Ar/39Ar dates (134.8-134.1 Ma) available for the stratigraphically older low-Ti basalt (Gramado + Esmeralda types) and dacite-rhyolite (Palmas type) sequences from South Brazil, which is consistent with the short-lived character of this volcanism and its rapid succession by the high-Ti sequence.

  18. 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

  19. 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.

  20. 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.

  1. Flood basalts and hot-spot tracks: plume heads and tails.

    PubMed

    Richards, M A; Duncan, R A; Courtillot, V E

    1989-10-06

    Continental flood basalt eruptions have resulted in sudden and massive accumulations of basaltic lavas in excess of any contemporary volcanic processes. The largest flood basalt events mark the earliest volcanic activity of many major hot spots, which are thought to result from deep mantle plumes. The relative volumes of melt and eruption rates of flood basalts and hot spots as well as their temporal and spatial relations can be explained by a model of mantle plume initiation: Flood basalts represent plume "heads" and hot spots represent continuing magmatism associated with the remaining plume conduit or "tail." Continental rifting is not required, although it commonly follows flood basalt volcanism, and flood basalt provinces may occur as a natural consequence of the initiation of hot-spot activity in ocean basins as well as on continents.

  2. 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.

  3. An ancient recipe for flood-basalt genesis.

    PubMed

    Jackson, Matthew G; Carlson, Richard W

    2011-07-27

    Large outpourings of basaltic lava have punctuated geological time, but the mechanisms responsible for the generation of such extraordinary volumes of melt are not well known. Recent geochemical evidence suggests that an early-formed reservoir may have survived in the Earth's mantle for about 4.5 billion years (ref. 2), and melts of this reservoir contributed to the flood basalt emplaced on Baffin Island about 60 million years ago. However, the volume of this ancient mantle domain and whether it has contributed to other flood basalts is not known. Here we show that basalts from the largest volcanic event in geologic history--the Ontong Java plateau--also exhibit the isotopic and trace element signatures proposed for the early-Earth reservoir. Together with the Ontong Java plateau, we suggest that six of the largest volcanic events that erupted in the past 250 million years derive from the oldest terrestrial mantle reservoir. The association of these large volcanic events with an ancient primitive mantle source suggests that its unique geochemical characteristics--it is both hotter (it has greater abundances of the radioactive heat-producing elements) and more fertile than depleted mantle reservoirs-may strongly affect the generation of flood basalts.

  4. 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.

  5. 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

  6. Using 40Ar/39Ar ages of intercalated silicic tuffs to date flood basalts: Precise ages for Steens Basalt Member of the Columbia River Basalt Group

    NASA Astrophysics Data System (ADS)

    Mahood, Gail A.; Benson, Thomas R.

    2017-02-01

    To establish causality between flood basalt eruptions and extinction events and global environmental effects recorded by isotopic excursions in marine sediments, highly accurate and precise ages for the flood basalts are required. But flood basalts are intrinsically difficult to date. We illustrate how 40Ar/39Ar feldspar ages for silicic tuffs intercalated with and overlying sections of Steens Basalt, the earliest lavas of the Middle Miocene Columbia River Basalt Group in the northwestern United States, provide high-precision ages that, for the first time, make it possible to resolve age differences with stratigraphic position within a section of these flood lavas. The stratigraphically lowest rhyolitic tuff, a fall deposit, yielded an age of 16.592 ± ± 0.028 Ma (FCs = 28.02 Ma), and the uppermost, the alkali rhyolite ignimbrite Tuff of Oregon Canyon, is 16.468 ± ± 0.014 Ma. The argon and stratigraphic data indicate that Steens Basalt eruptions occurred from ∼16.64 to 16.43 Ma in the southern end of its distribution. We estimate that the Steens Mountain geomagnetic reversal occurred at 16.496 ± ± 0.028 Ma (±0.18 Ma total error). Our estimates of the timing for initiation of volcanism and volumetric eruptive rates do not seem to support volcanic forcing by the initial stages of Columbia River Basalt Group eruptions as an explanation for the abrupt warming and carbonate dissolution at the beginning of the Miocene Climatic Optimum.

  7. Stratigraphic correlation of the Awahab and Tafelberg Formations, Etendeka Group, Namibia, and location of an eruptive site for flood basalt volcanism

    NASA Astrophysics Data System (ADS)

    Marsh, J. S.; Milner, S. C.

    2007-08-01

    Detailed field and geochemical investigations in the vicinity of the type section of the Tafelberg Formation of the early Cretaceous Etendeka Group, NW Namibia, have revealed the existence of a large eruptive vent in the lower part of the regional volcanic sequence produced by Strombolian and Vulcanian eruptions. The vent is filled with the thick, differentiated, ponded Kudu-Run olivine-rich basaltic flow, which has a distinctive low Zr/Y geochemical signature as well as a Tafelberg-type tabular basalt and the Nil Desperandum latite. Field evidence indicates that the Kudu-Run basalt and the latite were erupted from fissures located within the vent. Associated with the vent is an extensive pyroclastic apron extending from the vent edge and which is interbedded with the regional stratigraphy. Blocks of Precambrain basement lithologies occur within this deposit and indicate that the vent was excavated to a depth of at least 350 m below the palaeosurface at that time. The original Tafelberg Formation type section described by Erlank et al. [Erlank, A.J., Marsh, J.S., Duncan, A.R., Miller, R.McG., Hawkesworth, C.H., Betton, P.J., Rex, D.C. 1984. Geochemistry and petrogenesis of the Etendeka volcanic rocks from SWA/Namibia, 195-247. In: Erlank, A.J. (Ed.), Petrogenesis of Volcanic Rocks of the Karoo province. Special Publication of the Geological Society of South Africa, vol. 13, 395 p.] the Tafelberg Gully section, crosses from the lower part of the regional sequence into the intra-vent sequence and returns to the regional sequence higher up. In doing so it includes some of the localized intra-vent flows and excludes a number of flows which are part of the regional sequence in its lower part, thus rendering it inappropriate as a type section. A revised type section for the Tafelberg Formation is described by combining the upper part of the Tafelberg Gully section with a new section of 14 flows at the base of the regional sequence in the Tafelberg North (TBN) section

  8. 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

  9. 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

  10. 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

  11. 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

  12. Mars Crustal Magnetism: Plate Tectonics and Flood Basalts

    NASA Astrophysics Data System (ADS)

    Connerney, J.; Acuna, M.; Ness, N.

    2006-12-01

    The crustal magnetic field of Mars, mapped in unprecedented detail by the Mars Global Surveyor spacecraft, bears a record of crustal formation and subsequent evolution. The magnetic field in Meridiani has characteristics (transform faulting, symmetry) associated with crustal spreading in the presence of a reversing dynamo. The detailed erasure of crustal fields in and around filled basins (Utopia, Isidis) and massive volcanic constructs (Tharsis Montes, Oylmpus Mons, Alba Patera, Elysium Mons) suggests that the northern plains were largely demagnetized by emplacement of ~km thick flood basalts in single cooling events. Thermal demagnetization under a few km of flood basalts would require that the pre-existing magnetic imprint be borne in a layer only a few km thick. This in turn implies very intense magnetization (order 100 A/m) if the same layer thickness is applied to the intensely magnetized southern highlands. Icelandic basalts are rarely as intensely magnetized, but some samples - characterized by single domain magnetite formed from high temperature oxidation of olivine - approach this number.

  13. Controls on volcanism at intraplate basaltic volcanic fields

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

    A broad range of controlling mechanisms is described for intraplate basaltic volcanic fields (IBVFs) in the literature. These correspond with those relating to shallow tectonic processes and to deep mantle plumes. Accurate measurement of the physical parameters of intraplate volcanism is fundamental to gain an understanding of the controlling factors that influence the scale and location of a specific IBVF. Detailed volume and geochronology data are required for this; however, these are not available for many IBVFs. In this study the primary controls on magma genesis and transportation are established for the Pliocene-Recent Newer Volcanics Province (NVP) of south-eastern Australia as a case-study for one of such IBVF. The NVP is a large and spatio-temporally complex IBVF that has been described as either being related to a deep mantle plume, or upper mantle and crustal processes. We use innovative high resolution aeromagnetic and 3D modelling analysis, constrained by well-log data, to calculate its dimensions, volume and long-term eruptive flux. Our estimates suggest volcanic deposits cover an area of 23,100 ± 530 km2 and have a preserved dense rock equivalent of erupted volcanics of least 680 km3, and may have been as large as 900 km3. The long-term mean eruptive flux of the NVP is estimated between 0.15 and 0.20 km3/ka, which is relatively high compared with other IBVFs. Our comparison with other IBVFs shows eruptive fluxes vary up to two orders of magnitude within individual fields. Most examples where a range of eruptive flux is available for an IBVF show a correlation between eruptive flux and the rate of local tectonic processes, suggesting tectonic control. Limited age dating of the NVP has been used to suggest there were pulses in its eruptive flux, which are not resolvable using current data. These changes in eruptive flux are not directly relatable to the rate of any interpreted tectonic driver such as edge-driven convection. However, the NVP and other

  14. 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.

  15. Products of a Subglacial Flood Basalt Eruption

    NASA Astrophysics Data System (ADS)

    Gorny, C. F.; White, J. D. L.; Gudmundsson, M. T.

    2015-12-01

    The Snæbýlisheiði unit, SE Iceland, is a ca. 26 km³ elongate, flat-topped ridge of volcaniclastic debris coupled with and intruded by coherent basalt stretching over 34 km from the eruption site perpendicular to the rift fissure source. It formed from a single subglacial flood basalt eruption during a recent glaciation, and its elongation reflects glacial control on dispersal via the hydraulic potential gradient at the glacier's base, which drove towards the glacier terminus the meltwater+debris formed during the eruption by quenching and fragmentation. High magma discharge and outgassing drove segregation of magma into down-flow propagating intrusions. Edifice growth was mediated by the extent of ice melting, extent and efficiency of meltwater+debris drainage, and hydraulic gradients locally favoring meltwater accumulation. Eruption style reflected magma flux, edifice stability, and accessibility of water to the vent area via flooding or infiltration. Deposits reflect these competing factors in their chaotic internal organization and stratigraphy, limited lithofacies continuity, and diverse particle populations from multiple source vents. Linear growth of the ridge down-gradient from the eruption site was driven primarily by propagation and continuous fragmentation of shoaling intrusions that formed an interconnected intrusive complex with extensive peperites. Advance was along gently meandering and locally bifurcating sub-ice conduits within hyaloclastite with sheet-lobe levees and lobate fingered intrusions. Irregular dikes, apophyses, horns, and tendrils extended from the main body and generated voluminous lapilli tuff and contorticlasts while providing additional heat to the system. Prolonged transport and deposition of debris produced complexly bedded volcaniclastic deposits derived from and intruded by the basalt sheet. The bedding and depositional features of volcaniclastic debris and relationship to their adjacent intrusions suggest transport and

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. Nd-Sr isotopes, petrochemistry, and origin of the Siberian flood basalts, USSR

    SciTech Connect

    Sharma, M.; Basu, A.R. ); Nesterenko, G.V. )

    1991-04-01

    The Siberian Flood Basalt Province (SFBP) of Permo-Triassic age is one of the largest flood basalt provinces with an estimated area of exposure of 337 000 km{sup 2}, average thickness of 1 km, and a magma volume of 337 000 km{sup 3}. Forty-seven basaltic rocks from two main subprovinces, Norilsk (5-10{percent} of area, thickness up to 3 km) and Putorana (90-95{percent} of area, thickness of more than 2 km), were selected, on the basis of petrography and volcano-stratigraphic relation, for major-element analysis. Twenty-six of these basalts, twelve from Norilsk and fourteen from Putorana, were analyzed for Nd- and Sr-isotopic compositions. The Norilsk and Putorana basalts show some contrasting behavior in terms of the ratios of the highly incompatible elements of Ti, P, and K as a function of their Mg. The Norilsk basalts are more variable, suggesting the role of fractional crystallization-assimilation in their evolution. In contrast, the Putorana basalts show remarkable uniformity in their bulk chemical compositions. In Nd- and Sr-isotopic space, most of the Siberian basalts also fall within the field defined by the ocean island basalts data, implying common mantle sources. It is concluded that the SFBP originated by hotspot volcanism due to the rise of a large and relatively primitive lower mantle-derived plume beneath the Siberian continent.

  2. A mantle plume initiation model for the wrangellia flood basalt and other oceanic plateaus.

    PubMed

    Richards, M A; Jones, D L; Duncan, R A; Depaolo, D J

    1991-10-11

    The vast Wrangellia terrane of Alaska and British Columbia is an accreted oceanic plateau with Triassic strata that contain a 3- to 6-kilometers thick flood basalt, bounded above and below by marine sedimentary rocks. This enormous outpouring of basalt was preceded by rapid uplift and was followed by gradual subsidence of the plateau. The uplift and basalt eruptions occurred in less than approximately 5 million years, and were not accompanied by significant extension or rifting of the lithosphere. This sequence of events is predicted by a mantle plume initiation, or plume head, model that has recently been developed to explain continental flood volcanism. Evidence suggests that other large oceanic basalt plateaus, such as the Ontong-Java, Kerguelen, and Caribbean, were formed as the initial outbursts of the Louisville Ridge, Kerguelen, and Galapagos hot spots, respectively. Such events may play an important role in the creation and development of both oceanic and continental crust.

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

    PubMed

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

    2015-11-19

    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.

  4. 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

  5. Was Global Warming at the Paleocene-Eocene Boundary Terminated by Flood Volcanism?

    NASA Astrophysics Data System (ADS)

    Tegner, C.; Larsen, R. B.

    2008-12-01

    The Paleocene-Eocene thermal maximum (PETM) has recently been attributed to greenhouse gases released from sedimentary basins in the Northeast Atlantic due to interaction with continental flood basalt magmatism. In the marine section in Denmark the alkaline Ash-17 has been dated at 55.1 plus minus 0.1 Ma and the PETM at 55.6-55.4 Ma. A similar alkaline tephra deposit in the uppermost part of the East Greenland flood basalt succession has also been dated at 55.1 plus minus 0.1 Ma and provides a linkage to Ash-17. Our recent results on the pressure of the coeval Skaergaard intrusion indicate that the majority of flood basalts erupted in less than 300,000 years. It is therefore possible to correlate the main flood basalt event with the interval immediately postdating PETM (55.4-55.1 Ma). This is consistent with a report of a small dinoflagellate cyst assemblage with a high proportion of Apectodinium homomorphum in one productive sample from sediments within the lower volcanics underlying the main flood basalt succession. The Apectodinium genus is usually abundant in the PETM interval. A scarcity of ash layers within the PETM interval also supports a correlation of the main flood basalt event with the overlying marine section including more abundant ash layers. The high eruption rate of the main flood basalts is likely to have resulted in atmospheric cooling caused by sulfuric acid aerosols produced from volcanic sulfur dioxide. Available estimates for volume and composition of the Northeast Atlantic flood basalts indicate that at least 36 teratonnes of sulfur dioxide was pumped into the atmosphere. This average 120 megatonnes per year over 300,000 years. For comparison, the historic Laki eruption in Iceland is estimated to have released 120 megatonnes sulfur dioxide over 5 months. We suggest that flood volcanism of the Northeast Atlantic terminated the global warming event at the Paleocene-Eocene boundary.

  6. 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.

  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. Pliocene and Pleistocene alkalic flood basalts on the seafloor north of the Hawaiian islands

    USGS Publications Warehouse

    Clague, D.A.; Holcomb, R.T.; Sinton, J.M.; Detrick, R. S.; Torresan, M.E.

    1990-01-01

    The North Arch volcanic field is located north of Oahu on the Hawaiian Arch, a 200-m high flexural arch formed by loading of the Hawaiian Islands. These flood basalt flows cover an area of about 25,000 km2; the nearly flat-lying sheet-like flows extend about 100 km both north and south from the axis of the flexural arch. Samples from 26 locations in the volcanic field range in composition from nephelinite to alkalic basalt. Ages estimated from stratigraphy, thickness of sediment on top of the flows, and thickness of palagonite alteration rinds on the recovered lavas, range from about 0.75-0.9 Ma for the youngest lavas to somewhat older than 2.7 Ma for the oldest lavas. Most of the flow field consists of extensive sheetflows of dense basanite and alkalic basalt. Small hills consisting of pillow basalt and hyaloclastite of mainly nephelinite and alkalic basalt occur within the flow field but were not the source vents for the extensive flows. Many of the vent lavas are highly vesicular, apparently because of degassing of CO2. The lavas are geochemically similar to the rejuvenated-stage lavas of the Koloa and Honolulu Volcanics and were generated by partial melting of sources similar to those of the Koloa Volcanics. Prior to eruption, these magmas may have accumulated at or near the base of the lithosphere in a structural trap created by upbowing of the lithosphere. ?? 1990.

  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. Volatiles and the tempo of flood basalt magmatism

    NASA Astrophysics Data System (ADS)

    Black, Benjamin A.; Manga, Michael

    2017-01-01

    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 implies 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. The overpressure associated with a new injection of magma is inversely proportional to the total reservoir volume, and as a large magma body heats the surrounding rocks thermally activated creep will relax isotropic overpressure more rapidly. Here, we examine the viability of buoyancy overpressure as a trigger for continental flood basalt eruptions. We employ a new one-dimensional model that combines volatile exsolution, bubble growth and rise, assimilation, and permeable fluid escape from Moho-depth and crustal chambers. We investigate the temporal evolution of degassing and the eruptibility of magmas using the Siberian Traps flood basalts as a test case. We suggest that the volatile inventory set during mantle melting and redistributed via bubble motion controls ascent of magma into and through the crust, thereby regulating the tempo of flood basalt magmatism. Volatile-rich melts from low degrees of partial melting of the mantle are buoyant and erupt to the surface with little staging or crustal interaction. Melts with moderate volatile budgets accumulate in large, mostly molten magma chambers at the Moho or in the lower crust. These large magma bodies may remain buoyant and poised to erupt-triggered by volatile-rich recharge or external stresses-for ∼106 yr. If and when such chambers fail, enormous volumes of magma can ascend into the upper crust, staging at shallow levels and initiating substantial assimilation that contributes to pulses of large-volume flood basalt eruption. Our model further predicts that the Siberian Traps may have released 1019-1020 g of CO2

  12. 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

  13. 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.

  14. Construction of an Oceanic Plateau: Stratigraphic and Geochemical Perspectives from the Accreted Triassic Wrangellia Flood Basalts

    NASA Astrophysics Data System (ADS)

    Scoates, J. S.; Greene, A. R.; Weis, D. A.

    2009-12-01

    The accreted Wrangellia flood basalts and associated pre- and post-volcanic sedimentary rocks provide an unparalleled view of the architecture and compositional evolution of an oceanic plateau. Wrangellia may ultimately hold keys to answering some of the major questions about the development of oceanic plateaus, including how these large oceanic features initiate, build-up, and terminate, the timescale of eruptions, and the impact of very large-scale melting events and associated volcanism on the environment. The Wrangellia plateau extends ~2300 km in the Pacific Northwest as a discontinuous belt from central Alaska and western Yukon (Nikolai Formation: <3.5 km) to Vancouver Island (Karmutsen Formation: ~6 km). Wrangellia flood basalts are bounded by Middle to Late Triassic marine sediments and unconformably overlie Paleozoic arc volcanic sequences of different age. Based on combined radiometric (U-Pb, 40Ar/39Ar, K-Ar), paleontological, and magnetostratigraphic age constraints, the Wrangellia basalts were emplaced during a single phase of tholeiitic volcanism at ca. 230-225 Ma, and possibly within as little as 2 Myr, onto pre-existing submerged arc crust. The vast majority of the flood basalts are LREE-enriched high-Ti basalt (1.6-2.4 wt% TiO2; 6-8 wt% MgO) with relatively uniform isotopic compositions at 230 Ma (ɛHf = +9.1 to +12.6; ɛNd = +6.0 to +8.7). The lowest part of the stratigraphy in areas of Alaska and Yukon is LREE-depleted low-Ti basalt (0.4-1.2 wt% TiO2) with pronounced negative-HFSE anomalies and Hf isotopic compositions (ɛHf = +13.7 to +18.4) that are decoupled from Nd (ɛNd = +4.6 to +5.4) and displaced well above the OIB mantle array (ΔɛHf = +4 to +8). Submarine stratigraphy on northern Vancouver Island contains picritic basalts (9-20 wt%) depleted in LREE (La/YbCN = 0.5 ± 0.2) with overlapping initial ɛHf (+10.3 ± 2.1) and ɛNd (+7.7 ± 1.3) to the high-Ti basalts. A mantle plume initiation model for the Wrangellia flood basalts is

  15. 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

  16. 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.

  17. 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.

  18. 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

  19. Modes of emplacement of basalt terrains and an analysis of mare volcanism in the Orientale Basin

    NASA Technical Reports Server (NTRS)

    Greeley, R.

    1976-01-01

    Three distinctive types of basalt terrains can be recognized on earth on the basis of surface morphology: flood basalts, shield basalts, and plains basalts, each of which reflects unique styles of eruption and modes of emplacement. Two of these, flood basalts and plains basalts, appear to be important in the emplacement of mare basalts on the moon. Using surface features as identifying criteria, mare units in the Orientale Basin were examined and the following emplacement sequence was derived: (1) initial emplacement of impact melt in the basin center, (2) eruption of flood-type basalts in the basin center and approximately concurrent emplacement of plains type basalts in Lacus Veris, and (3) emplacement of plains type basalts in Lacus Autumni

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

    PubMed

    Liu, Lijun; Stegman, Dave R

    2012-02-15

    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.

  1. The position of continental flood basalts in rift zones and its bearing on models of rifting

    NASA Astrophysics Data System (ADS)

    Kazmin, V. G.

    1991-12-01

    Two models of rifting—"pure shear" and "simple shear"—are at present being widely discussed. In this paper attention is drawn to the fact that continental flood basalts (CFB), associated with rifts, usually display a strong asymmetry relative to the rift axis. The Karroo, the Parana, and the Deccan basalts, as well as the Ethiopian flood basalts and the basalts of the Arabian Shield are concentrated mainly on one side of the respective rifts. Structural data indicate that the eruptions occurred on the "upper plates", if the low-angle, simple-shear model of Wernicke (1985) is accepted. It is suggested that the asymmetry of eruptions is caused by the asymmetric position of the asthenopheic rise predicted by this model. The low-angle detachment may serve as a conduit for magmatic fluid. This fits well with data on the existence of large magmatic reservoirs of CFB at subcrustal or crustal levels and explains why eruptions are concentrated in the rift and on one of its shoulders, while being restricted on the other. This asymmetry of volcanism supports models of continental rifting associated with low-angle simple-shear detachment.

  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.

  4. Columbia River flood basalts from a centralized crustal magmatic system

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ramos, F. C.; Hart, G. L.; Patterson, J. D.; Brandon, A. D.

    2008-03-01

    The Columbia River Basalt Group in the northwestern United States, comprising about 230,000 cubic kilometres of rock, exhibits unusual patterns in lava distribution, geochemistry and its apparent relationship to regional tectonics. Consequently, there is little consensus on the origin of its magmas. Here, we examine the isotopic ratios of Sr, Nd, Pb and Os and trace-element abundances in Columbia River basalts. The results suggest that most of the lava was produced when magma derived from a mantle plume assimilated continental crust in a central magma chamber system located at the boundary between the North American craton and the accreted terranes of Idaho and Oregon. Other, related basalts are the product of mixing between the mantle plume and different types of regional upper mantle. Magma was then transported over a wide region by an extensive network of dykes, a process that has been identified in other flood basalt provinces as well. Interactions of the plume with surrounding upper mantle, and of mantle-derived magmas with regional crust, provide a relatively simple model to explain the more unusual features of the main-phase Columbia River Basalts.

  5. Cracking the lid: Sill-fed dikes are the likely feeders of flood basalt eruptions

    NASA Astrophysics Data System (ADS)

    Muirhead, James D.; Airoldi, Giulia; White, James D. L.; Rowland, Julie V.

    2014-11-01

    Although subparallel swarms of dikes are thought to be the primary feeders to voluminous volcanic eruptions, increasing recognition of volumetrically significant sill complexes suggests that they too play an important role in magma ascent through the shallow crust. However, the extent to which sills and interconnected, sill-fed dikes actually transport magma to the earth's surface in many large igneous provinces (LIP) is presently unclear. By analyzing field relationships and dimensions of intrusions of the Ferrar LIP in South Victoria Land, Antarctica, we show that sill-fed dikes were the likely feeders for voluminous flood basalt eruptions. These intrusions are small but numerous, with cumulative dimensions equivalent to a feeder network 308,000 km long and 1.8 m wide. Due to the tremendous aerial extent of this intrusive network, each individual dike-feeder segment would only be required to actively feed magma for 2 to 3 days on average to erupt the 70,000 km3 of flood lavas represented by the Kirkpatrick basalts. The Ferrar intrusions form a broadly-distributed array of small, moderately dipping dikes (<2 km long, 1.8 m wide, 56° mean dip) exhibiting almost any orientation. This sill-fed dike network contrasts with dike swarms conventionally depicted to feed flood basalt provinces, and has the appearance of a variably "cracked lid" atop a sill complex. The cracked lid model may apply to a range of shallow feeder systems (<4 km depth) intruding sedimentary basins, where the effects of far-field tectonic stresses are negligible and sill intrusions exert the dominant control on dike orientations. We conclude that sill inflation, and resulting deformation of surrounding host rock, plays a critical role in the ascent of magma in shallow volcanic systems that span the full spectrum of eruptive volumes.

  6. 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.

  7. High-3He Plume Origin and Temporal-Spatial Evolution of the Siberian Flood Basalts.

    PubMed

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

    1995-08-11

    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 (40)Ar/(39)Ar 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 (3)He/(4)He 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-chondritic, primitive plume. Geochemical data from the 250-million-year-old volcanic rocks higher up in the sequence indicate interaction of this high-(3)He SFBP plume with a suboceanic-type upper mantle beneath Siberia.

  8. 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.

  9. 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

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

    PubMed

    Depaolo, D J; Wasserburg, G J

    1979-07-01

    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.

  11. Double flood basalts and plume head separation at the 660-kilometer discontinuity.

    PubMed

    Bercovici, D; Mahoney, J

    1994-11-25

    Several of the world's flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years. These double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle. This detached plume head eventually triggers the first flood basalt event. The remaining conduit forms a new plume head, which causes the second eruptive event. The second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head, in general agreement with observations regarding double flood basalts.

  12. Petrogenesis of the flood-basalt sequence at Noril'sk, North Central Siberia

    USGS Publications Warehouse

    Fedorenko, V.A.; Lightfoot, P.C.; Naldrett, A.J.; Czamanske, G.K.; Hawkesworth, C.J.; Wooden, J.L.; Ebel, D.S.

    1996-01-01

    The 3500-m-thick sequence of volcanic rocks at Noril'sk, formed during a brief interval (???1 m.y.) at the Permian/Triassic time boundary (???251 Ma), represents the earliest part of the ???6500-m-thick sequence presently ascribed to the Siberian flood-basalt province. It is composed of picritic and basaltic lavas of both low-Ti and high-Ti parentage. Extensive geological, geochemical, and isotopic study of the lava sequence and related intrusions allows detailed reconstruction of its petrogenesis. Various crustal-related processes - fractionation, crustal contamination, sulfide separation, and magma mixing - participated in the formation of the lavas. The geochemical and isotopic characteristics indicative of these processes, as well as mantle-related signatures of lava compositions, are discussed. Based on these characteristics, detailed interpretations of lava genesis and evolution throughout the Noril'sk sequence are presented. Eight varieties of lavas are recognized to be primitive, similar in composition to primary mantle melts; they varied from low-Mg basalts to olivine tholeiites or picrites, with normal tholeiites predominating. The primitive lavas are subdivided into four groups (magma types) on the basis of trace-element ratios (principally. Gd/Yb, Th/U, La/Yb, Ta/La, Ti/Sc, and V/Yb) and isotopic data. Three of the groups include both basaltic and picritic primitive lavas (with low-Mg basalts present in one of them), whereas the fourth group is represented exclusively by tholeiites. Distinctions among the groups cannot be related to degree of melting, and isotopic data indicate that none of the magma types could have formed by mixing or contamination of other types. Apparently, only differences in source composition and/or depth of melting can explain the magmatic diversity. This multitude of primitive magma types may be explained by melting in different layers of the upper mantle, which is complexly layered beneath Siberia to depths of 270 km. Moreover

  13. 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

  14. Assessing eruption column height in ancient flood basalt eruptions

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    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 ∼ 45 ° N. Assuming 5 km long active fissure segments and 9000 Mt of SO2 released during explosive phases over a 10-15 year duration, the ∼ 180km of known Roza fissure length could have supported ∼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 (∼ 66Ma) 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 flood basalt eruptions could have influenced

  15. 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

    1992-11-06

    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.

  16. High water content in primitive continental flood basalts.

    PubMed

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

    2016-05-04

    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.

  17. 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

  18. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. Wrangellia flood basalts in Alaska: A record of plume-lithosphere interaction in a Late Triassic accreted oceanic plateau

    NASA Astrophysics Data System (ADS)

    Greene, Andrew R.; Scoates, James S.; Weis, Dominique

    2008-12-01

    The Wrangellia flood basalts are part of one of the best exposed accreted oceanic plateaus on Earth. They provide important constraints on the construction of these vast submarine edifices and the source and temporal evolution of magmas for a plume head impinging beneath oceanic lithosphere. Wrangellia flood basalts (˜231-225 Ma) extend ˜450 km across southern Alaska (Wrangell Mountains and Alaska Range) where ˜3.5 km of mostly subaerial flows are bounded by late Paleozoic arc volcanics and Late Triassic limestone. The vast majority of the flood basalts are light rare earth element (LREE) -enriched high-Ti basalt (1.6-2.4 wt % TiO2) with uniform ocean island basalt (OIB) -type Pacific mantle isotopic compositions (ɛHf(t) = +9.7 to +10.7; ɛNd(t) = +6.0 to +8.1; t = 230 Ma). However, the lowest ˜400 m of stratigraphy in the Alaska Range is LREE-depleted low-Ti basalt (0.4-1.2 wt % TiO2) with pronounced negative high field strength element (HFSE) anomalies and Hf isotopic compositions (ɛHf(t) = +13.7 to +18.4) that are decoupled from Nd (ɛNd(t) = +4.6 to +5.4) and displaced well above the OIB mantle array (ΔɛHf = +4 to +8). The radiogenic Hf of the low-Ti basalts indicates involvement of a component that evolved with high Lu/Hf over time but not with a correspondingly high Sm/Nd. The radiogenic Hf and HFSE-depleted signature of the low-Ti basalts suggest pre-existing arc lithosphere was involved in the formation of flood basalts that erupted early in construction of part of the Wrangellia plateau in Alaska. Thermal and mechanical erosion of the base of the lithosphere by the impinging plume head may have led to melting of arc lithosphere or interaction of plume-derived melts and subduction-modified mantle. The high-Ti lavas dominate the main phase of construction of the plateau and were derived from a depleted mantle source distinct from the source of MORB and with compositional similarities to that of ocean islands (e.g., Hawaii) and plateaus (e.g., Ontong

  4. Flood basalts and ocean island basalts: A deep source or shallow entrainment?

    NASA Astrophysics Data System (ADS)

    Lohmann, F. C.; Hort, M.; Phipps Morgan, J.

    2009-07-01

    Basalts from continental flood basalts (CFBs) and intraplate or hotspot ocean islands are found to have distinct geochemical signatures. This diversity in composition is generally believed to result from the upwelling plume entraining overlying reservoirs of shallow and intermediate depth mantle material during its ascent from the deep mantle. Here we present laboratory experiments and numerical model calculations which clarify that — for a strongly temperature dependent viscosity like that of the mantle — a rising plume head should be expected to bring up a surrounding sheath of deep mantle from its source region. Mixing between the central core of the plume and this sheath produces the whorl-like structures noted in previous studies where they were typically attributed to thermal entrainment of surrounding ambient mantle, but this is mainly the product of intermixing between neighboring parts of the plume's deep source material. These results imply that the popular idea that mantle plumes should typically mix small fractions of deep 'primitive' mantle material with much larger fractions of shallower depleted mantle needs to be critically reexamined.

  5. Comparing the evidence relevant to impact and flood basalt at times of major mass extinctions.

    PubMed

    Alvarez, Walter

    2003-01-01

    The five major mass extinctions identified in 1982 by Raup and Sepkoski have expanded to six, with the suggestion that the Permian-Triassic extinction was a double event. Is there a general explanation for great mass extinctions, or can they result from different triggers, or even from internal system instabilities? The two most-discussed candidates for a general extinction mechanism are impacts and flood-basalt eruptions. A compilation of evidence for impact at the times of mass extinctions shows that this cause is abundantly confirmed in the case of the Cretaceous-Tertiary extinction and the late Eocene, which is a time of minor and gradual extinction, but little or no evidence connects other major extinctions to impact. On the other hand, there is a remarkable time correlation between flood basalts and four major extinctions, but no other evidence that flood basalts cause mass extinctions. The evidence for an impact-extinction linkage is strikingly different from that for a connection between flood basalts and extinctions. Flood basalts cover larger areas than craters and their associated thick ejecta blankets, which are thus less likely to be found. Impacts distribute proxies globally at instantaneous time horizons, whereas flood-basalt events are extended in time, and no remote proxies have been recognized. Many global killing mechanisms have been proposed in the case of impacts, but few have been suggested for flood basalts. It is possible that flood basalts are triggered by impact, but it is not obvious how impacts could result from anything other than chance. The hypothesis that impacts are the general cause of mass extinctions has not received supporting evidence, but has not been falsified. The hypothesis that flood basalts are the general cause of mass extinctions is supported by evidence from timing, but is not susceptible to falsification. Other candidates for general extinction causes, especially sea-level changes and system instabilities, would

  6. Mush Column to Flood Basalt Differentiation: A Systematic Transition from Deep Ferrar Dolerites to the Kirkpatrick Basalt

    NASA Astrophysics Data System (ADS)

    Marsh, B.

    2002-05-01

    A Magmatic Mush Column (MMC) is an extensive, vertically interconnected stack of sills and chambers which extends upward through the lithosphere and is capped by a volcanic center. At any instant within the MMC, both fractionated and primitive melts are present as pools of nearly crystal-free or crustal-rich magma, thick beds of cumulates, and open or congested (by cognate and wall debris) conduits. Solidification fronts sheath all boundaries of the system, and their local rate of advance measures the local level of through-flow magmatic activity. The chemical nature of the erupted product is dependent on the strength of the erupted flux; the stronger the flux, the more crystal-laden and primitive is the eruptive material. Tracing variations in magma composition upward through the MMC and into associated lavas is key to understanding this overall process. A mush column of this basic nature, which is inferred to exist beneath, for example, Kilauea, Jan Mayen, Reunion, and the ocean ridges, exists in the McMurdo Dry Valleys region of Antarctica. The Dry Valleys system is vertically abbreviated (~3.5 km), but contains all the essential features of a major MMC (i.e., an interconnected stack of sills). Moreover, the course of magma through this system can be chemically and spatially linked to the Kirkpatrick flood basalts. The lowermost sill, the Basement Sill, is choked with phenocryst-rich ultramafic orthopyroxenite containing 20 wt.% MgO with locally abundant lenses and layers of anorthosite. Upward in the system, the abundance of orthopyroxene phenocrysts decreases, and the maximum MgO content drops to less than 14 wt.% in the Peneplain and Labyrinth sills. Continuing upward to the Mt Freya and Mt. Fleming sills, orthopyroxene phenocrysts are essentially absent, and the most mafic compositions do not exceed 6 wt.% and 5 wt.% MgO, respectively. These uppermost compositions form a smooth chemical transition with the contemporaneous Kirkpatrick flood basalts (Fleming

  7. 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.

  8. New 40Ar-39Ar ages for Basalts From the West Siberian Basin and Links With the Siberian Flood Basalt Province

    NASA Astrophysics Data System (ADS)

    Reichow, M. K.; Saunders, A. D.; White, R. V.; Pringle, M. S.; Al'Mukhamedov, A. I.; Medvedev, A. Y.

    2001-12-01

    The Siberian Traps represent the world's largest subaerial flood basalt province, and may be responsible for the Permo-Triassic mass extinction at 250 Ma (e.g., Campbell et al. 1992 Science 258, 1760). The total extent of the Traps, and whether or not the volcanism is a contributor to the Permo-Triassic mass extinction, are both still matters of debate. Basaltic and gabbroic rocks occur throughout the West Siberian Basin (WSB), but are covered by a thick succession of Mesozoic and Cenozoic sediments, unlike the more accessible Traps on the Siberian craton to the east. We have obtained material from three deep industrial boreholes (Hohryakovskaya, Permyakovskaya, Van Eganskaya), and show that basalts and gabbros from the WSB have ages indistinguishable from the Traps to the east. 40Ar-39Ar dating of plagioclase (from basalts) and phlogopite (from a gabbro) separates from 6 samples from three boreholes give ages of 249.3 to 250.5 Ma (plagioclase) and 253.4 Ma (phlogopite) (relative to GA1550 biotite at 98.79 Ma). The results are obtained by step heating and the apparent plateau ages include more than 90 percent of the total argon released. Two sigma errors are better than 1.0 Ma for 5 of the samples. Normalised to the same standard, these ages are in good agreement with ages obtained for the Siberian Traps (250 Ma: Renne and Basu 1991 Science 253, 176). On the basis of major and trace element data, the basalts from the WSB show affinities with the Nadezhinsky suite (Noril'sk area), which is known to immediately precede the main pulse of volcanism that extruded over large areas of the craton. Limited recovery from the boreholes indicates that the basalts were erupted subaerially or possibly into shallow water (e.g. presence of abundant, large amygdales). Lava flows are at least 20 m thick, indicating voluminous eruptions. The results from the Ar-Ar dating and chemical analysis emphasise a clear correlation between basalts from the WSB and the Siberian Traps. This

  9. Detecting volcanic resurfacing of heavily cratered terrain: Flooding simulations on the Moon using Lunar Orbiter Laser Altimeter (LOLA) data

    NASA Astrophysics Data System (ADS)

    Whitten, Jennifer L.; Head, James W.

    2013-09-01

    Early extrusive volcanism from mantle melting marks the transition from primary to secondary crust formation. Detection of secondary crust is often obscured by the high impact flux early in solar system history. To recognize the relationship between heavily cratered terrain and volcanic resurfacing, this study documents how volcanic resurfacing alters the impact cratering record and models the thickness, area, and volume of volcanic flood deposits. Lunar Orbiter Laser Altimeter (LOLA) data are used to analyze three different regions of the lunar highlands: the Hertzsprung basin; a farside heavily cratered region; and the central highlands. Lunar mare emplacement style is assumed to be similar to that of terrestrial flood basalts, involving large volumes of material extruded from dike-fed fissures over relatively short periods of time. Thus, each region was flooded at 0.5 km elevation intervals to simulate such volcanic flooding and to assess areal patterns, thickness, volumes, and emplacement history. These simulations show three primary stages of volcanic flooding: (1) Initial flooding is largely confined to individual craters and deposits are thick and localized; (2) basalt flows breach crater rim crests and are emplaced laterally between larger craters as thin widespread deposits; and (3) lateral spreading decreases in response to regional topographic variations and the deposits thicken and bury intermediate-sized and larger craters. Application of these techniques to the South Pole-Aitken basin shows that emplacement of ∼1-2 km of cryptomaria can potentially explain the paucity of craters 20-64 km in diameter on the floor of the basin relative to the distribution in the surrounding highlands.

  10. Lunar mare versus terrestrial mid-ocean ridge basalts - Planetary constraints on basaltic volcanism

    NASA Technical Reports Server (NTRS)

    Papike, J. J.; Bence, A. E.

    1978-01-01

    Major differences which exist between terrestrial midocean ridge basalts (MORBs) and lunar mare basalts reflect the different planetary characteristics of earth and moon. MORBs are enriched in aluminum and have higher Mg/(Mg + Fe(2+)). These features reflect a more aluminum- and magnesium-rich mantle source for MORBs. Mare basalts are depleted in sodium and potassium relative to MORBs and, consequently, mare feldspars are depleted in the albite component relative to MORB feldspars; these features are a reflection of the alkali-depleted nature of the moon relative to earth. The oxygen fugacities that obtained during MORB petrogenesis follow the quartz-magnetite-fayalite buffer curve very closely, while those of mare basalts are several orders of magnitude lower. This results in reduced valence states for Fe, Cr, and Ti in mare basalts, which, in turn, has a significant effect on mineral-melt partitioning.

  11. 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.

  12. 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.

  13. 40Ar/39Ar dates from the West Siberian Basin: Siberian flood basalt province doubled.

    PubMed

    Reichow, Marc K; Saunders, Andrew D; White, Rosalind V; Pringle, Malcolm S; Al'Mukhamedov, Alexander I; Medvedev, Alexander I; Kirda, Nikolay P

    2002-06-07

    Widespread basaltic volcanism occurred in the region of the West Siberian Basin in central Russia during Permo-Triassic times. New 40Ar/39Ar age determinations on plagioclase grains from deep boreholes in the basin reveal that the basalts were erupted 249.4 +/- 0.5 million years ago. This is synchronous with the bulk of the Siberian Traps, erupted further east on the Siberian Platform. The age and geochemical data confirm that the West Siberian Basin basalts are part of the Siberian Traps and at least double the confirmed area of the volcanic province as a whole. The larger area of volcanism strengthens the link between the volcanism and the end-Permian mass extinction.

  14. 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.

  15. A Fossil Mantle Plume under the Emeishan Flood Basalts: Integration of Geology, Geophysics and Geochemistry

    NASA Astrophysics Data System (ADS)

    Xu, Y.; He, B.; Chung, S.

    2004-12-01

    The plume hypothesis is now challenged because some fundamental aspects predicted by the modeling of plumes are found to be lacking in classic regions like Iceland and Yellowstone. Instead of invoking a ¡°bottom-up¡± process, some researchers favor a ¡°top-down¡± hypothesis for the formation of large igneous provinces (LIPs), in which shallow lithospheric processes may fuel melt production. Seismic investigations and tomographic models help trace mantle plumes in modern, active hotspots, but are of limited benefit in identifying ancient plumes, mainly because geophysics provides us with a snapshot of the present-day Earth¡_s structure. Consequently the geological ¡°footprint¡± associated with thermal anomalies are the clues to tracing ancient plumes. According to some theoretical models, pre-volcanic lithospheric uplift is the most important criteria used to identify the presence of plumes. The lack of such evidence, on the other hand, is an argument against the involvement of plumes in the formation of LIPs. Recent examination of the middle-late Permian sedimentology in southwest China reveals kilometer-scale lithospheric doming prior to the Emeishan flood volcanism (He et al., 2003). This, and correlations between diverse, independent parameters involving crustal doming, paleo-geography, sea level change, mantle melting mechanism and crust-mantle structure, provide evidence for a fossil mantle plume under the Emeishan LIP. Specifically, the consequences of plume-lithosphere interaction include: (a) pre-volcanic uplift including thinning of marine carbonates, a marine to sub-aerial transition, local provenance of clastic sediments, and a marked erosional unconformity, evident as palaeokarstic surfaces on the marine carbonates; (b) a domal structure (700 km radius); (c) variations in the thickness of volcanic rocks across the domal structure; (d) variations in flood basalt geochemistry from the center to the edge of the domal structure that are

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. Late Permian basalts in the Yanghe area, eastern Sichuan Province, SW China: Implications for the geodynamics of the Emeishan flood basalt province and Permian global mass extinction

    NASA Astrophysics Data System (ADS)

    Li, Hongbo; Zhang, Zhaochong; Santosh, M.; Lü, Linsu; Han, Liu; Liu, Wei

    2017-02-01

    We report the finding of a ∼20 m thick sequence of massive pyroxene-plagioclase-phyric basalt lava flows in the Yanghe area of the northeastern Sichuan Basin, within the Yangtze craton of SW China, which were previously considered to be located outside the Emeishan flood basalt province. This basaltic sequence above the middle Permian Maokou Formation (Fm.) is overlain by the late Permian Longtan Fm. Thus, the Yanghe basalts should be stratigraphically correlated with the Emeishan flood basalts. The Yanghe basalts show typical oceanic island basalt (OIB) affinity, and geochemically resemble Emeishan basalts, especially in the case of high-Ti (HT) basalts from the eastern domain of the Emeishan flood basalt province. The rocks have low age-corrected (87Sr/86Sr)t (t = 260 Ma) ratios (0.704158-0.704929) and Pb isotopic ratios [206Pb/204Pb(t) (18.264-18.524), 207Pb/204Pb(t) (15.543-15.58), and 208Pb/204Pb(t) (38.147-38.519)], and positive εNd(t) values (+3.15 to +3.61), suggesting that the lavas have not undergone any significant crustal contamination. The crystallization temperature of clinopyroxene is estimated to be 1368-1420 °C, suggesting anomalously thermal inputs from a mantle source and a possible plume-head origin. The fractionation of middle rare earth elements (MREE) to heavy REE (HREE) suggests that these rocks were produced by small degrees of partial melting of mantle peridotite within the garnet-spinel transition region. The stratigraphic relationships and similar geochemical signatures with the Emeishan flood basalts suggest that the Yanghe basalts are part of the Emeishan flood basalt province and can be considered as the northeastern limit of the Emeishan flood basalt province. Our finding extends the diameter of the Emeishan flood basalt province to ∼1200-1400 km, covering an area of up to ∼7 × 105 km2, two times more than previously estimated. The larger areal extent and giant eruption volume, incorporating the Sichuan Basin, lend support

  3. 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.

  4. Recent Flood Volcanism on Mars: Implications for Climate Change, Layered Deposits, and Lava-Water Interactions

    NASA Astrophysics Data System (ADS)

    Keszthelyi, L.; McEwen, A.

    2001-05-01

    In many ways, the high-resolution imaging of volcanic features on Mars has been disappointing due to the significantly degraded state of the ancient surfaces. One major exception has been the recent volcanism in the Cerberus Plains and Amazonis Planitia (Keszthelyi et al., 2000). Crater counts suggest some lava surfaces are less than 10 Ma (Hartmann and Berman, 2000), though rapid burial and very recent exhumation would allow for somewhat older eruptions. Investigation of the platy-ridged portion of the 1783-1784 Laki flow field in Iceland revealed that these lava flows have a morphology unlike any in Hawaii. We have called this form of lava "rubbly pahoehoe" and find it in several terrestrial flood basalt settings (Keszthelyi and Thordarson, 2000). Rubbly pahoehoe on Iceland and Mars transitions into undisrupted inflated pahoehoe flows at their margins. These flows are hypothesized to form as surges in flow rate travel through large inflating sheet flows. This allows emplacement underneath a thick mobile insulating crust, permitting lava to travel great distances in a rapid but laminar manner. Thermal modeling suggests eruption rates on the order of 105 m3/s feeding these sheets of lava, a rate about an order of magnitude larger than typical for terrestrial flood basalt eruptions. These huge eruptions potentially have significant climatic implications. If the dissolved volatile content of the Martian flood lavas were similar to that of large terrestrial basaltic eruptions (Thordarson and Self, 1996; McSween et al., 2001) we would expect on the order of 300 Gt of highly acidic gas to be released. Simultaneously, several thousand cubic kilometers of highly vesicular basaltic ash should be produced. Further gas release and ash production would come from the rootless cone fields found on the lavas (Lanagan et al., submitted). The acid-laced ash may be deposited to form the Medussae Fossae Formation and perhaps other finely layered sedimentary deposits seen on Mars

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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.

  12. Rise and Collapse of Volcanic Plumes Produced By Explosive Basaltic Fissure Eruptions

    NASA Astrophysics Data System (ADS)

    Paillat, S.; Kaminski, E. C.

    2014-12-01

    Explosive basaltic fissure eruptions, which release large amounts of sulfur gases in the atmosphere, can have a big impact on climate. The effect on climate depends on the rate of gas injection above the tropopause. The key parameter is the height reached by the eruptive plume as a function of mass flux and entrainment rate. We propose a model of entrainment in 2D volcanic plumes based on lab scale experiments on turbulent jets and plumes. In this model, entrainment varies with the Richardson number and we predict that the height of the column critically depends on the source buoyancy flux determined by the eruptive temperature and the amount of gas in the volcanic mixture at the vent. We obtain that "hot" basaltic planar plumes form stable eruptive columns, even for large eruption rates. Only if fragmentation is not efficient enough, the column collapse will prevent the injection of gas in the stratosphere.

  13. 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

  14. Origin of pegmatitic segregation veins within flood basalts

    SciTech Connect

    Puffer, J.H.; Horter, D.L. )

    1993-06-01

    Subhorizontal veins and lenses of coarse-grained rock composed of plagioclase, augite, and Fe-Ti oxides in a glassy and vesicular mesostasis occur within several thick subaerial basalt flows in the Columbia River Basalt province of Washington and in the eastern North American Mesozoic basalt province. The veins and lenses, referred to as pegmatitic segregation veins, are typically 1-10 cm thick and are enriched in Fe, Ti, K, P, Cu, Zr, Ba, and REE by a factor of about 1.1 to 3 over the host basalt; Al, Ca, Sr, Mg, Ni, and Cr are lower, and Si and Na are typically unchanged. We interpret the pegmatitic segregation veins as the product of residual melt carried in vapor bubbles from the lower crystallization front of partially crystallized flows to the crystal mush within the upper crystallization front. Movement through the elevated temperatures of flow interiors fused any crystal nuclei in the segregation melt. Diminished nucleation density during crystallization may partially account for coarse grain sizes. In addition, diffusion of ions to large, rapidly growing skeletal crystals was probably enhanced by the viscosity-reduction effect of water enrichment. The water content of accumulated segregation melt may have increased whenever the escape of volatiles from partially crystallized flows was temporarily sealed off under a rigid barrier of solidified basalt. Rupture of the barrier by downward propagation of columnar joints would allow the resumption of effervescence and any remaining partially crystallized segregation melt-phase would be degassed and quenched into a glassy and vesicular mesostasis. 59 refs., 8 figs., 2 tabs.

  15. 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

  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. 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.

  18. 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.

  19. Vestiges of the Kerguelen Plume in alkalic mafic-ultramafic, carbonatitic complexes and flood basalts in NE India

    NASA Astrophysics Data System (ADS)

    Basu, A. R.; Ghatak, A.

    2011-12-01

    The Archean East Indian craton was affected by the Kerguelen plume at ~117 Ma causing flood-basalt eruptions at the cratonic margin giving rise to the Rajmahal-Bengal-Sylhet Traps. Rajmahal-age volcanics are wide-spread in and around the Bengal Basin, from the intrusive lamproites and lamprophyres in the west and Sikkim in the north, to the Sylhet basalts and alkalic-carbonatitic-ultramafic intrusives of the Shillong plateau and the Mikir hills in northeastern India. These volcano-plutonic complexes are exposed over an approximate area of 0.8 million km2 in and around the Bengal Basin. This study demonstrates that all these diverse volcanic rocks are caused by the Kerguelen plume activity. We provide isotopic and geochemical data of the Rajmahal Traps, and associated alkalic-carbonatitic-mafic-ultramafic complexes, and relate them to the Sylhet Traps in northeastern India, some contemporaneous Kerguelen Plateau basalts, and associated volcanics in the Southern Indian Ocean. Specifically, we report here Nd-Sr-Pb-isotopic and multiple trace element data of discrete lava flows from the Rajmahal Traps; mafic, alkalic, ultrabasic, and carbonatitic rocks from four alkalic complexes, and three ultramafic dikes from the Bokaro coal fields southwest of the Rajmahal Traps. In Nd-Sr-Pb isotopes, the Rajmahal Traps lavas of this study show remarkable similarity with previously reported Rajmahal Groups I and II basalts, Sylhet Traps, Bunbury basalts and lavas from the southern Kerguelen Plateau. The combined geochemical data and their correlation with the Rajmahal, Bunbury basalts, and some Kerguelen Plateau lavas in the Indian Ocean imply a relatively primitive Kerguelen plume source for the Rajmahal lavas similar to the Rajmahal Group I basalts. We estimate the average composition of this plume source to be: ɛNd(I)=+2, 87Sr/86Sr(I)=0.7045, with relatively flat rare earth element (REE) patterns. Rajmahal lavas similar to the Group II Rajmahal basalts have slightly enriched

  20. 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

  1. A Helium Isotope Perspective on Mantle Sources for Basaltic Volcanism in the Northwestern US

    NASA Astrophysics Data System (ADS)

    Graham, D. W.; Reid, M. R.; Jordan, B. T.; Grunder, A. L.; Leeman, W. P.; Lupton, J. E.

    2006-12-01

    Helium isotope variations in continental basalts provide valuable constraints on mantle source relationships. 3He/4He ratios between 7 and 9 RA (where RA is the isotopic ratio in air) are typical of mid-ocean ridge basalts and are indicative of a convecting upper mantle source. Lower (more radiogenic) 3He/4He reflects additional contributions from either the lithospheric mantle or continental crust. Elevated 3He/4He, above 10 RA, indicates derivation from a region with lower time-integrated (U+Th)/3He, usually taken to be a deep mantle (thermochemical plume) source. The Oregon High Lava Plains is a bimodal (basalt-rhyolite) volcanic province distinguished by its pattern of westward-migrating silicic volcanism that mirrors the pattern along the Snake River Plain. This mirror pattern is sometimes taken as evidence against the SRP as a hotspot track produced by a mantle plume currently located beneath Yellowstone. New helium isotope results for young basalts from the eastern Snake River Plain, the Owyhee Plateau and the Oregon High Lava Plains, along with published data for Yellowstone and the Cascades volcanic arc, provide insight to the relationship between the enigmatic High Lava Plains and Yellowstone-Snake River Plain system. Basalts from the eastern SRP display a gradient in 3He/4He over a lateral distance of ~400 km, from >13 RA in the west to >19 RA adjacent to Yellowstone. Such high ratios are absent elsewhere in the western US. These high 3He/4He ratios suggest the presence of plume-derived material, either in the shallow asthenosphere or emplaced within the continental lithosphere downstream from Yellowstone. The gradient indicates that the contribution from this plume source decreases westward along the SRP. In contrast, 3He/4He in basalts from the Oregon High Lava Plains and the Owyhee Plateau show a narrow 3He/4He range of 8.8-9.3 RA, while basalts from Newberry Volcano have 3He/4He = 7.6-8.3 RA and overlap the range for the Cascades arc (7.0-8.4 RA

  2. New data on the Late Cenozoic basaltic volcanism in Syria, applied to its origin

    NASA Astrophysics Data System (ADS)

    Trifonov, V. G.; Dodonov, A. E.; Sharkov, E. V.; Golovin, D. I.; Chernyshev, I. V.; Lebedev, V. A.; Ivanova, T. P.; Bachmanov, D. M.; Rukieh, M.; Ammar, O.; Minini, H.; Al Kafri, A.-M.; Ali, O.

    2011-01-01

    New data on geology and 21 K-Ar dates of the Late Oligocene-Quaternary basalts in Syria, combined with analysis of the new and previous data are used to reconstruct the volcanic history and relations between it and tectonic events. Volcanism began at the end of Oligocene (26-24 Ma) and was concentrated in the Late Oligocene-Early Miocene along a N-trending band, which stretches from the Jebel Arab (Harrat Ash Shaam) up to Kurd Dagh and southern Turkey. Activity waned in the Middle Miocene (17-12 Ma), but was resumed in the same band in the Tortonian and increased in the Messinian and Early Pliocene (6.3-4 Ma), when volcanism spread to the Shin Plateau and its coastal extension. After a brief hiatus ˜ 4-3.5 Ma, volcanism became still more intensive and spread from the N-trending band to the east into the northern margin of the Mesopotamian Foredeep and to the west into the Dead Sea Transform zone. Additional eruptions continued into the Holocene. Volcanism lasted > 25 million years in the Jebel Arab Highland and > 15 million years in the Aleppo Plateau. The long duration of volcanism in the same parts of the moving Arabian plate and absence of records of one-way migration of the activity mean that the magmatic sources moved together with the plate, i.e., they were situated within the lithosphere mantle. Coincidence of the tectonic and volcanic stages of the Arabian plate development proves that volcanic activity depended on the geodynamic situation, caused by the plate motion. Situated within the lithosphere, magmatic sources within this transverse band were possibly caused by thermal and deforming influences of the asthenospheric lateral flow, moved laterally from the Ethiopia-Afar deep superplume.

  3. 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

    2005-12-08

    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.

  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.

  6. 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

  7. Geochemistry of Triassic flood basalts from the Yukon (Canada) segment of the accreted Wrangellia oceanic plateau

    NASA Astrophysics Data System (ADS)

    Greene, Andrew R.; Scoates, James S.; Weis, Dominique; Israel, Steve

    2009-06-01

    A large part of the accreted Middle to Late Triassic Wrangellia oceanic plateau is exposed as a linear belt (< 30 km × 300 km) in southwest Yukon. The first major- and trace-element, and isotopic compositions of the Nikolai Formation in Yukon are presented here, along with compositions for underlying Paleozoic arc rocks. The Nikolai Formation in Yukon is predominantly massive tholeiitic subaerial flows (~ 1000 m) with no intervening sediments and a thin zone of pillow breccia along the base (< 100 m). The Nikolai basalts unconformably overlie Late Paleozoic volcanic arc and marine sedimentary sequences and are overlain by Late Triassic limestone, which grades upwards into pelagic sediments. The Nikolai Formation is comprised of two distinct lava types: low-titanium basalts form most of the lower stratigraphy and high-titanium basalts form the upper parts of the volcanic stratigraphy. All of the low-titanium basalts (0.5-1.0 wt.% TiO 2; 5.6-11.3 wt.% MgO) have prominent negative HFSE anomalies, whereas the high-titanium basalts (1.4-2.3 wt.% TiO 2; 5.8-8.7 wt.% MgO) do not have HFSE anomalies and are more LREE-enriched. The low-titanium basalts are characterized by mostly higher initial ɛHf (+ 11.1 to + 15.8) and lower initial ɛNd (+ 2.3 to + 6.8) than the high-titanium basalts (initial ɛHf = + 10.4 to + 12.0; initial ɛNd = + 6.6 to + 9.0), and their Pb isotopic compositions overlap. Incongruent dynamic melting modeling of trace element compositions indicate the low-titanium basalts could have been derived from small degrees of melting (< 5%) of Paleozoic sub-arc lithospheric mantle that was HFSE-depleted and evolved with high 176Hf/ 177Hf. The high-titanium basalts formed from melting of Pacific plume-type mantle, similar to the source of the Caribbean Plateau. Plume-derived melts dominated the upper stratigraphy of the oceanic plateau as a result of increased decompression melting of the underlying mantle plume in response to thinning of the lithosphere.

  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. 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

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

    USGS Publications Warehouse

    Pieters, C.M.; Head, J. W.; 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.

  11. Petrogenesis of a basalt-comendite-pantellerite rock suite: the Boseti Volcanic Complex (Main Ethiopian Rift)

    NASA Astrophysics Data System (ADS)

    Ronga, Fiorenzo; Lustrino, Michele; Marzoli, Andrea; Melluso, Leone

    2010-03-01

    Petrological and geochemical data for basic (alkali basalts and hawaiites) and silicic peralkaline rocks, plus rare intermediate products (mugearites and benmoreites) from the Pleistocene Boseti volcanic complex (Main Ethiopian Rift, East Africa) are reported in this work. The basalts are slightly alkaline or transitional, have peaks at Ba and Nb in the mantle-normalized diagrams and relatively low 87Sr/86Sr (0.7039-0.7044). The silicic rocks (pantellerites and comendites) are rich in sanidine and anorthoclase, with mafic phases being represented by fayalite-rich olivine, opaque oxides, aenigmatite and slightly Na-rich ferroaugite (ferrohedenbergite). These rocks were generated after prolonged fractional crystallization process (up to 90-95 %) starting from basaltic parent magmas at shallow depths and fO2 conditions near the QFM buffer. The apparent Daly Gap between mafic and evolved Boseti rocks is explained with a model involving the silicic products filling upper crustal magma chambers and erupted preferentially with respect to basic and intermediate products. Evolved liquids could have been the only magmas which filled the uppermost magma reservoirs in the crust, thus giving time to evolve towards Rb-, Zr- and Nb-rich peralkaline rhyolites in broadly closed systems.

  12. Rangitoto Volcano Drilling Project: Life of a Small 'Monogenetic' Basaltic Shield in the Auckland Volcanic Field

    NASA Astrophysics Data System (ADS)

    Shane, P. A. R.; Linnell, T.; Lindsay, J. M.; Smith, I. E.; Augustinus, P. M.; Cronin, S. J.

    2014-12-01

    Rangitoto is a small basaltic shield volcano representing the most recent and most voluminous episode of volcanism in the Auckland Volcanic Field, New Zealand. Auckland City is built on the field, and hence, Rangitoto's importance in hazard-risk modelling. The symmetrical edifice, ~6 km wide and 260 m high, has volume of 1.78 km3. It comprises summit scoria cones and a lava field. However, the lack of deep erosion dissection has prevented the development of an eruptive stratigraphy. Previous studies suggested construction in a relatively short interval at 550-500 yrs BP. However, microscopic tephra have been interpreted as evidence of intermittent activity from 1498 +/- 140 to 504 +/- 6 yrs BP, a longevity of 1000 years. A 150-m-deep hole was drilled through the edifice in February 2014 to obtain a continuous core record. The result is an unparalleled stratigraphy of the evolution of a small shield volcano. The upper 128 m of core comprises at least 27 lava flows with thicknesses in the range 0.3-15 m, representing the main shield-building phase. Underlying marine sediments are interbedded with 8 m of pyroclastic lapilli, and a thin lava flow, representing the explosive phreatomagmatic birth of the volcano. Preliminary geochemical analyses reveal suite of relatively uniform transitional basalts (MgO = 8.1 to 9.7 wt %). However, 4 compositional groups are distinguished that were erupted in sequential order. High-MgO magmas were erupted first, followed by a two more heterogeneous groups displaying differentiation trends with time. Finally, distinct low-MgO basalts were erupted. Each magma type appears to represent a new magma batch. The core places the magma types in a time series, which can be correlated to the surface lava field. Hence, allowing a geometrical reconstruction of the shield growth. Additional petrologic investigations are providing insight to magmatic ascent processes, while radiocarbon and paleomagnetic secular variation studies will reveal the

  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. Recent volcanism in the Siqueiros transform fault: Picritic basalts and implications for MORB magma genesis

    USGS Publications Warehouse

    Perfit, M.R.; Fornari, D.J.; Ridley, W.I.; Kirk, P.D.; Casey, J.; Kastens, K.A.; Reynolds, J.R.; Edwards, M.; Desonie, D.; Shuster, R.; Paradis, S.

    1996-01-01

    Small constructional volcanic landforms and very fresh-looking lava flows are present along one of the inferred active strike-slip faults that connect two small spreading centers (A and B) in the western portion of the Siqueiros transform domain. The most primitive lavas (picritic and olivine-phyric basalts), exclusively recovered from the young-looking flows within the A-B strike-slip fault, contain millimeter-sized olivine phenocrysts (up to 20 modal%) that have a limited compositional range (Fo91.5-Fo89.5) and complexly zoned Cr-Al spinels. High-MgO (9.5-10.6 wt%) glasses sampled from the young lava flows contain 1-7% olivine phenocrysts (Fo90.5-Fo89) that could have formed by equilibrium crystallization from basaltic melts with Mg# values between 71 and 74. These high MgO (and high Al2O3) glasses may be near-primary melts from incompatible-element depleted oceanic mantle and little modified by crustal mixing and/or fractionation processes. Phase chemistry and major element systematics indicate that the picritic basalts are not primary liquids and formed by the accumulation of olivine and minor spinel from high-MgO melts (10% < MgO < 14%). Compared to typical N-MORB from the East Pacific Rise, the Siqueiros lavas are more primitive and depleted in incompatible elements. Phase equilibria calculations and comparisons with experimental data and trace element modeling support this hypothesis. They indicate such primary mid-ocean ridge basalt magmas formed by 10-18% accumulative decompression melting in the spinel peridotite field (but small amounts of melting in the garnet peridotite field are not precluded). The compositional variations of the primitive magmas may result from the accumulation of different small batch melt fractions from a polybaric melting column.

  15. Diverse Primitive Basalts from an Extensional Back-arc Setting, Fort Rock Volcanic Field, Oregon.

    NASA Astrophysics Data System (ADS)

    Popoli, F. M., Jr.; Schmidt, M. E.

    2014-12-01

    The Pleistocene to Pliocene Fort Rock Volcanic Field (FRVF), situated in a back-arc extensional setting ~65 km east of the Central Oregon High Cascades has erupted a diverse array of basaltic magmas, including some primitive compositions with an Mg#>60. Major and trace element concentrations have been determined for 80 mafic bulk lava samples by X-ray Fluorescence (XRF) and selected minerals by electron microprobe. Petrological and geochemical data suggest three primitive basalt end-members similar to basalts in the nearby Oregon Cascade arc and High Lava Plains: high-alumina olivine tholeiite or low-K tholeiites (LKT), calc-alkaline basalts (CAB), ocean island basalts (OIB). Primitive Mg# (61-68) HAOTs are aphyric to phenocryst-poor (~2-5 %) olivine and plagioclase bearing and diktytaxitic. HAOTs are distinguished by low K2O (0.22-0.44 wt%), high Al2O3 (17.19-18.67 wt%) and CaO contents. CABs are the most dominant basalt type in the area with higher large ion lithophile element (LILE) concentrations (e.g., 170-426 ppm Ba) relative to high field strength elements (HFSE; 4.6-10.4 ppm Nb) and lower Mg#s (60-64) than HAOTs. CABs have more abundant (~5-15 %) and larger phenocrysts (~2-4 mm) of olivine and plagioclase than in HAOTs. OIBs contain higher Nb contents ranging from 11.7-18.6 ppm (vs. 3.0-7.2 ppm in HAOTs). OIBs are similar to both HAOTs and CABs, ranging from aphyric to porphyritic and diktytaxitic and may include amphibole phenocrysts. Tectonic extension associated with the Basin and Range in this area likely facilitated eruptions of primitive magmas. A comparison of the most primitive magmas (HAOTs with Mg#>65) found in eastern and western FRVF indicates that the western HAOTs contain higher incompatible element concentrations relative to eastern HAOT (Ba, Sc, Sr, Zr, Nb), which may reflect lower degrees of melting of a more enriched mantle source to the west.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. Modeling Central American Volcanic Front Primitive Lavas with the Arc Basalt Simulator (abs 4.0)

    NASA Astrophysics Data System (ADS)

    Feigenson, M.; Carr, M. J.; Gazel, E.

    2012-12-01

    We have used the Arc Basalt Simulator (ABS), developed by J-I 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 and partition coefficients. We have applied ABS version 4.00, which includes melting/dehydration relations in eight distinct subducting layers, to model representative magma types along the Central American volcanic front. These magmas are first projected to primary melt compositions by the addition of olivine until they reach Fo90. Then, using a wide range of input parameters including variations in slab components, extent of peridotite depletion, depth of slab dehydration and wedge fluxing and degree of peridotite melting, successful model fits are generated (based on trace element and isotope matching). The solution space is probed using a Monte Carlo technique to cover the enormous range of parameter values. Nicaragua and Costa Rica represent geochemical and geophysical end members of the volcanic front, differing greatly in volcano volume, slab dip beneath the volcano, isotopic composition and incompatible element enrichment. Using appropriate input compositions for ABS 4.0, we find through millions of simulations that the Cerro Negro primary magma (Nicaragua) requires high degrees of source melting (22-27%) and large amounts of slab-derived water (3-5%). In contrast, the Irazu primary magma (central Costa Rica) is generated from more enriched sources with only a small amount of water (less than 0.5%) and at low degrees of partial melting (less than 5%). Other Central American lavas with intermediate geochemical characteristics are produced from conditions within the Nicaragua-Costa Rica range. By reproducing the lava geochemistry with ABS 4.0, it becomes possible to extract constraints on source input

  1. 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.

  2. Geochemistry of Kauai volcanics and a mixing model for the origin of Hawaiian alkali basalts

    NASA Astrophysics Data System (ADS)

    Feigenson, Mark D.

    1984-09-01

    A comprehensive model is developed to explain the major, trace element and strontium and neodymium isotopic characteristics of alkali basalts from Hawaii. The model is similar to that of Chen and Frey (1983) in that it requires mixing of a small melt fraction of MORB-source material with another component to generate the alkalic suite of a particular Hawaiian volcano. It differs from the Chen and Frey model in that the other end-member must be different from primitive mantle if it is to be consistent with both trace element and isotopic data. Alkali basalts and tholeiites from Kauai analyzed in this study show a nearly complete transition in Sr and Nd isotopes. There is a relatively well-constrained array on a Nd-Sr isotope correlation plot that can be explained by two-component mixing of Kauai tholeiite magma and a small amount of melt of East Pacific Rise source rock. After corrections are made for fractional crystallization (involving primarily clinopyroxene and olivine), the Sr and Ba concentrations of Kauai lavas plot along mixing curves defined by the above sources, providing positive tests of the mixing hypothesis. Implications of this model are: (1) the main source of Hawaiian shield-building tholeiites is a mixture of subducted crust, primitive mantle and depleted asthenosphere that has been homogenized prior to melting, (2) early alkalic volcanism (as at Loihi seamount) will be characterized by greater isotopic heterogeneity than will late-stage alkali basalt production, and (3) there are two fundamentally distinct types of alkalic lavas erupted towards the end of magmatism at a given Hawaiian volcano. One represents smaller degrees of melting of the same source that generated shield-building tholeiites (Kohala-type); the other derives from the mixed source discussed in this paper (Haleakala-, Kauai-type).

  3. The Siberian Flood Basalts: Connecting the Mantle, the Continental Crust, and the Atmosphere

    NASA Astrophysics Data System (ADS)

    Elkins-Tanton, L. T.; Arndt, N.; Black, B. A.; Fristad, K. E.; Kiehl, J. T.; Lamarque, J.; Meyer, K. M.; Payne, J.; Planke, S.; Shields, C. A.; Svensen, H.

    2012-12-01

    Around 252 million years ago the Siberian flood basalts intruded into and erupted onto the Siberian craton. At that time the craton was at about its present latitude, and was a part of Pangaea, with inward-dipping subduction on several sides. The flood basalt event is among several possible causes for the end-Permian extinction, the largest extinction in Earth history. Our team hypothesizes that the magmas caused the injection of sufficient volatiles into the atmosphere to produce global climate change. These volatiles were in part sweated out of the crustal rocks by the chambered magmas, and in part assimilated from the crust by the magmas and released upon eruption. The magmas intruded a 12-km-deep evaporate basin containing hydrocarbon reservoirs. The complex interactions of heat and rock with silicate, hydrous, and hydrocarbon fluids produced rich ore bodies, a variety of magmatic rocks including carbonatites, and significant volumes of carbon, sulfur, chlorine, and fluorine-bearing volatiles. We will present an overview of our results to date, including paleomagnetic data on rates of eruption, dynamic models of plume-lithosphere interaction, isotopic evidence of the changes in ocean chemistry, field and laboratory data on volatile release in intrusive aureoles, melt inclusion measurements of magmatic volatile loads, and early climate model results. Because of its volume and the specific crustal region it passed through, the magmatic event produced significant chemical and heat transfer between Earth's interior and its surface. Though other continental flood basalts are similarly sized, the Siberian event interacted with particularly toxic crustal rocks and is a likely candidate for triggering the end-Permian global climate change and mass extinction.

  4. The "Large" in Large Igneous Provinces: Using Digital Geological Maps to Determine the Area, Magma Flux, and Potential Environmental Impact of the Wrangellia Flood Basalts

    NASA Astrophysics Data System (ADS)

    Scoates, J. S.; Greene, A. R.; Weis, D. A.

    2010-12-01

    Large igneous provinces (LIPs), such as continental flood basalts and oceanic plateaus, are formed by relatively short duration, massive outpourings of basalt in intraplate settings. Their emplacement has been associated with global climatic and biotic change (e.g., end-Permian Siberian LIP). The magmatic products of a LIP typically cover an area >1 Mkm2, however erosion and exhumation may substantially reduce the original area and volume of a LIP, especially oceanic plateaus that have been tectonically dispersed during accretion (e.g., Caribbean, Wrangellia). The availability of digital geologic maps from government geologic surveys now allows for measuring the precise areal distribution of remnant LIP-products, which is essential information for estimating total volumes and ultimately potential environmental effects. The Wrangellia flood basalts represent one of the best-exposed accreted oceanic plateaus on Earth. This Triassic LIP is exposed in numerous fault-bound blocks in a belt extending discontinuously for 2300 km in the Pacific Northwest of North America. It contains exposures of submarine and subaerial volcanic rocks representing composite stratigraphic thicknesses of 3.5-6 km. From recently compiled digital geologic maps (British Columbia, Yukon, Alaska), the mapped exposures of the Wrangellia flood basalts are relatively small (25,256 km2 with 75% from Vancouver Island), which leads to minimum calculated erupted volumes of up to 1.4 x 105 km3 and an estimated magma flux of 0.03 km3/yr. The original areal distribution was substantially greater, perhaps by an order of magnitude or more, as the outcrop extent does not include regions covered by younger strata and surficial deposits nor does it account for the volcanic component of the terrane that may have been subducted. However, even this minimum volumetric output rate is comparable to recent estimates of long-term volumetric eruption rates for ocean islands such as Iceland (0.02-0.04 km3/yr) and Hawaii

  5. 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.

  6. 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.

  7. 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.

  8. Crystal fractionation of the basalt comendite series of the mount Edziza volcanic complex, British Columbia: Major and trace elements

    NASA Astrophysics Data System (ADS)

    Souther, J. G.; Hickson, C. J.

    1984-06-01

    The Mount Edziza Volcanic Complex in north-central British Columbia includes a group of overlapping basaltic shields, salic composite volcanoes, domes and small calderas that range in age from 7.5 Ma to less than 2000 years B.P. The volcanic assemblage is chemically bimodal, comprising voluminous alkali olivine basalt and hawaiite, a salic suite of mainly peralkaline trachyte and comendite, plus a relatively small volume of intermediate rocks (trachybasalt, tristanite, mugearite, benmoreite). The complex is the product of five cycles of magmatic activity, each of which began with alkali olivine basalt and culminated with the eruption of salic magma. The regular chemical variation shown by almost 100 major- and trace-element analyses suggests a genetic lineage between the basic and salic members of each cycle. Least-squares mathematical modelling, indicates that the salic rocks (trachyte and comendite) have formed by fractionation of observed phenocryst and cumulate nodule mineral phases from a common alkali olivine basalt parent magma. Hawaiite is thought to be a cumulate rock, formed by partial fractionation and feldspar accumulation within rising columns of primary alkali olivine basalt. Fractionation leading from alkali olivine basalt through trachybasalt and trachyte to comendite is believed to have taken place where primary basalt became trapped in large crustal reservoirs. The early removal of olivine, clinopyroxene and plagioclase, leading to a trachytic residuum, and subsequent fractionation of mainly alkali feldspar, leading to the peralkaline end members, is consistent with major- and trace-element variation and with isotopic and REE data. The chemical diversity of the complex is attributed to its location over a zone of crustal extension where mantle-derived basalt, trapped in large high-level reservoirs, underwent prolonged fractionation.

  9. Volatiles in a Subduction-Related Primitive Basaltic Cinder Cone: Investigating Volcan Jorullo, Mexico

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.; Wallace, P.; Granados, H. D.

    2004-12-01

    To investigate volatiles in primitive subduction-related basaltic magmas, we have analyzed volatile (H2O, CO2, Cl, S) concentrations in olivine-hosted melt inclusions from the 1759-1774 eruption of Jorullo volcano in the central Trans-Mexican Volcanic Belt (TMVB). Jorullo's earliest lavas are primitive (9.3 wt% MgO, Fo86-90 olivine), and lava compositions evolved over time as a result of crystal fractionation (Luhr and Carmichael, 1985, CMP). Tephra samples were collected from a 5-meter-thick proximal ash fall sequence. Olivine crystals from the base of the section are fractured and contain clusters and chains of Cr-spinel inclusions in addition to melt inclusions. Samples from the top of the section have more euhedral crystals with solitary Cr-spinel inclusions and fewer melt inclusions. Melt inclusions from the basal tephra have variable H2O (<1-4.8 wt%) and CO2 (34-770 ppm), corresponding to crystallization pressures of <100 bars to 3.7 kbars. This indicates that olivine crystallized over a wide range of depths, trapping variably degassed melts during magma ascent. Melt inclusions from the upper sample have lower H2O (0.2-1.4 wt%) and no detectable CO2, suggesting shallow crystallization of degassed magma toward the end of the violent-Strombolian-style eruptions. For Jorullo melt inclusions, the maximum H2O contents (4-5 wt%), which should most closely represent primary values, compare with values of ˜4 wt% H2O at nearby Paricutin (Luhr, 2001, CMP) and 1.3-5.2 wt% in cinder cones in the Chichinautzin volcanic field to the east (Cervantes and Wallace, 2003, Geology). Relatively high Ba/Nb in Jorullo lavas shows that the underlying mantle wedge in this region of the TMVB has been enriched by a subduction-derived component. Ratios of H2O to incompatible trace elements follow similar patterns to those observed for Chichinautzin cinder cones, and thus further demonstrate a link between H2O and trace element enrichment in the mantle wedge. The high H2O in Jorullo

  10. 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

  11. Constraints on the Cretaceous thermal event in the Transantarctic Mountains from alteration processes in Ferrar flood basalts

    NASA Astrophysics Data System (ADS)

    Molzahn, M.; Wörner, G.; Henjes-Kunst, F.; Rocholl, A.

    1999-12-01

    K-Ar and 40Ar/ 39Ar incremental-heating analyses on apophyllite formed during hydrothermal alteration of volcanic rocks from the Ferrar Supergroup in North Victoria Land, Antarctica, provide strong evidence for hydrothermal events during mid-Cretaceous time. A last event has been dated at 96.7±0.6 Ma. Variable older ages between 112 and 125 Ma are interpreted as mixed ages of hydrothermal events or may be caused by disturbances of the Ar-Ar system. The Rb-Sr isotope system of the apophyllites is not applicable to dating because a large portion of the Sr is radiogenic and because of Rb-mobility in the crystal structure. Secondary mineralogy suggests a temperature for alteration between 300° and 400°C. Assuming a normal thermal gradient, this temperature implies a burial depth of about 10 km. However, there is no evidence for such a burial of the Ferrar flood basalts. Therefore, an elevated thermal gradient in mid-Cretaceous time in combination with circulating fluids is proposed for the origin of the alteration phenomena.

  12. Changes in Pacific Absolute Plate Motion and Formation of Oceanic Flood Basalt Plateaus

    NASA Astrophysics Data System (ADS)

    Kroenke, L. W.; Wessel, P.

    2006-12-01

    The origin of the large oceanic flood basalt plateaus that are prominent features of the central western Pacific Basin remains unclear. Major changes in Pacific Absolute Plate Motion (APM) have been identified as occurring at 145, 125, 96, and 47 Ma. Formation of the Shatsky Rise (~145 Ma), the Ontong Java Plateau (122+ Ma), the Southern Hess Rise (95±5 Ma), and the Louisiade Plateau (~48 Ma) appear to coincide with these changes. A smaller, but still prominent change in Pacific APM also occurred at 110 Ma when the Northern Hess Rise formed. Although these concurrent events may simply be chance occurrences, initiation of plate tectonic reorganizations upon arrival of mantle plume heads also was proposed by Ratcliff et al. (1998), who suggested that the mantle plume head delivery of hot material to produce flood basalts also had the potential to trigger reorganizations of plate motions. It should be noted, however, that Pacific Rim subduction zone development also coincides with these APM changes, and that the actual cause and effect of each change in APM has yet to be clearly established. Here we present a modified Pacific APM model that uses several older seamount chains (Musicians, Ratak-Gilbert-Ellice, the Wake trails, and the Liliuokalani trails) to constrain the oldest Pacific plate motion using the hybrid technique of Wessel et al (2006).

  13. Rock magnetic evidence of inflation of a flood basalt lava flow

    NASA Astrophysics Data System (ADS)

    Cañón-Tapia, Edgardo; Coe, Robert

    2002-07-01

    The anisotropy of magnetic susceptibility (AMS) of lava flows is an innovative method which has been proved to be directly related to the shear history of lava. One of the advantages of this method is that it can be used in the absence of other morphological features commonly employed to study the mechanism of emplacement of lava flows. This feature of the AMS method makes it very attractive to gain insight into the mechanism of emplacement of massive, relatively featureless, long lava flows such as those forming flood basalt provinces. In this work, we report the results of the measurement of AMS as a function of vertical position within the Birkett lava flow, one of the Columbia River Basalt Group flows. The observed variation of AMS allows us to identify at least 16 discrete events of lava injection and to estimate the thickness of individual injection events. The AMS-estimated thickness of each injection event (in the range of 0.5-4.0 m) coincides with the range inferred for injected lava pulses in modern Hawaiian lava flows. Thus, the evidence provided by the AMS method supports the notion that at least some flood basalt lava flows were emplaced by the same mechanism as many present-day inflated pahoehoe flows. Regarding the orientation of the principal susceptibilities, in the central part of the flow they define a preferred orientation along an E-W trend, whereas in the outer parts of the flow they have a NNE-SSW trend. This difference in the orientation of the principal susceptibilities is interpreted as the result of a change of flow direction of the lava as emplacement progressed. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00445-002-0203-8.

  14. 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.

  15. Selected hydrologic and geochemical issues in site characterization for nuclear waste disposal: flood basalts at the Hanford Reservation. [Pasco Basin basalt

    SciTech Connect

    Carnahan, C.L.; Delany, J.M.; Long, J.C.S.; Silva, R.J.; Watkins, D.J.; White, A.F.; Wilson, C.R.

    1982-09-01

    Four issues are considered that must be addressed by a site characterization program designed to evaluate the suitability of the flood basalts of the Pasco Basin in central Washington as a site for the construction of a repository for the disposal of high-level nuclear waste. The four issues are (1) identification of hydrostratigraphic units within a sequence of flood basalts, (2) mechanisms and points of groundwater recharge and discharge, (3) solubility of radionuclides, and (4) phase transformation of fracture filling materials. Each issue is discussed in terms of its significance to waste isolation. Available approaches for resolving the issues are presented and their limitations identified. Where appropriate, research programs for overcoming these limitations are indicated.

  16. 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

  17. 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.

  18. 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

  19. 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

  20. The discovery of late Quaternary basalt on Mount Bambouto: Implications for recent widespread volcanic activity in the southern Cameroon Line

    NASA Astrophysics Data System (ADS)

    Kagou Dongmo, Armand; Nkouathio, David; Pouclet, André; Bardintzeff, Jacques-Marie; Wandji, Pierre; Nono, Alexandre; Guillou, Hervé

    2010-04-01

    At the north-eastern flank of Mount Bambouto, a lateral cone, the Totap volcano, is dated at 0.480 ± 0.014 Ma, which corresponds to the most recent activity of this area. The lava is a basanite similar to the older basanites of Mount Bambouto. Two new datations of the lavas of the substratum are 11.75 ± 0.25 Ma, and 21.12 ± 0.45 Ma. A synthetic revision of the volcanic story of Mount Bambouto is proposed as follows. The first stage, ca. 21 Ma, corresponds to the building of the initial basaltic shield volcano. The second stage, from 18.5 to 15.3 Ma, is marked by the collapse of the caldera linked to the pouring out of ignimbritic rhyolites and trachytes. The third stage, from 15 to 4.5 Ma, renews with basaltic effusive activity, together with post-caldera extrusions of trachytes and phonolites. The 0.5 Ma Totap activity could be a fourth stage. In the recent Quaternary, a number of basaltic activities, similar to that of the Totap volcano, are encountered elsewhere in the Cameroon Line, from Mount Oku to Mount Cameroon. The very long-live activity at Mount Bambouto and the volcanic time-space distribution in the southern Cameroon Line are linked to the working of a hotline.

  1. 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

  2. Future Volcanism at Yucca Mountain - Statistical Insights from the Non-Detection of Basalt Intrusions in the Potential Repository

    NASA Astrophysics Data System (ADS)

    Coleman, N.; Abramson, L.

    2004-05-01

    Yucca Mt. (YM) is a potential repository site for high-level radioactive waste and spent fuel. One issue is the potential for future igneous activity to intersect the repository. If the event probability is <1E-8/yr, it need not be considered in licensing. Plio-Quaternary volcanos and older basalts occur near YM. Connor et al (JGR, 2000) estimate a probability of 1E-8/yr to 1E-7/yr for a basaltic dike to intersect the potential repository. Based on aeromagnetic data, Hill and Stamatakos (CNWRA, 2002) propose that additional volcanos may lie buried in nearby basins. They suggest if these volcanos are part of temporal-clustered volcanic activity, the probability of an intrusion may be as high as 1E-6/yr. We examine whether recurrence probabilities >2E-7/yr are realistic given that no dikes have been found in or above the 1.3E7 yr-old potential repository block. For 2E-7/yr (or 1E-6/yr), the expected number of penetrating dikes is 2.6 (respectively, 13), and the probability of at least one penetration is 0.93 (0.999). These results are not consistent with the exploration evidence. YM is one of the most intensively studied places on Earth. Over 20 yrs of studies have included surface and subsurface mapping, geophysical surveys, construction of 10+ km of tunnels in the mountain, drilling of many boreholes, and construction of many pits (DOE, Site Recommendation, 2002). It seems unlikely that multiple dikes could exist within the proposed repository footprint and escape detection. A dike complex dated 11.7 Ma (Smith et al, UNLV, 1997) or 10 Ma (Carr and Parrish, 1985) does exist NW of YM and west of the main Solitario Canyon Fault. These basalts intruded the Tiva Canyon Tuff (12.7 Ma) in an epoch of caldera-forming pyroclastic eruptions that ended millions of yrs ago. We would conclude that basaltic volcanism related to Miocene silicic volcanism may also have ended. Given the nondetection of dikes in the potential repository, we can use a Poisson model to estimate an

  3. 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

  4. Short Timescales for Crustal Residence, Transport and Contamination of Flood Basalt Magma: Crystal Isotope Stratigraphy of the Columbia River Basalt Group.

    NASA Astrophysics Data System (ADS)

    Tollstrup, D. L.; Ramos, F. C.; Wolff, J. A.

    2002-12-01

    Geochemical studies of continental flood basalt magmas provide evidence for contributions from one or more enriched reservoirs. There is, however, no consensus on the role of continental crust as a major source of enriched signatures. With its stratigraphy defined and mapped at the scale of individual flows, the Columbia River Basalt Group (CRBG) is the most thoroughly studied continental flood basalt province in the world. Its tectonic position (overlying both thin accreted Mesozoic crust and thick ancient cratonic crust) makes the CRBG ideal for isolating the contribution of crust in the petrogenesis of continental flood basalts. Many flows are plagioclase-phyric. Because plagioclase in basaltic magmas can be assumed to have grown at crustal pressures, growth layers in plagioclase phenocrysts record changes in the chemical and isotopic composition of the magma occurring at crustal depths. We have initiated a micro-sampling study utilizing laser ablation multicollector ICP-MS (ThermoFinnigan Neptuner) to analyze 87Sr/86Sr variability in plagioclase and clinopyroxene phenocrysts (where present) and associated groundmass. Initial results are: 1) plagioclase and clinopyroxene phenocrysts within CRBG lavas are overall less radiogenic than host groundmass and 2) plagioclase phenocrysts are commonly zoned from less radiogenic cores to more radiogenic rims. The rims may have similar compositions to, or be less radiogenic than, host groundmass. One-dimensional diffusion modeling applied to observed 87Sr/86Sr zoning and crystal/groundmass gradients constrains phenocryst residence times, and the timescale of crustal-level petrogenetic events that modified CRBG magmas. Residence times for phenocrysts in their final host liquid may be as little as 10 years prior to quenching. These results require that the 87Sr/86Sr composition of the CRBG magmas increased rapidly with time at crustal pressures during and after phenocryst growth. This could result from mixing between magmas

  5. 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.

  6. 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

  7. Zeolites in Eocene basaltic pillow lavas of the Siletz River Volcanics, Central Coast Range, Oregon.

    USGS Publications Warehouse

    Keith, T.E.C.; Staples, L.W.

    1985-01-01

    Zeolites and associated minerals occur in a tholeiitic basaltic pillow lava sequence. Although the zeolite assemblages are similar to those found in other major zeolite occurrences in basaltic pillow lavas, regional zoning of the zeolite assemblages is not apparent. The formation of the different assemblages is discussed.-D.F.B.

  8. Intraplate Basaltic Volcanism in the Basin and Range, USA: Relationship to Low-Velocity S- wave Anomalies and Asthenospheric Dynamics

    NASA Astrophysics Data System (ADS)

    Tibbetts, A. K.; Smith, E. I.; Conrad, C.; Lee, C.; Plank, T.; Yang, Y.

    2009-05-01

    Pliocene to Recent intraplate mafic volcanic rocks of the Basin and Range Province mostly formed by asthenospheric melting, as can be seen by melting temperatures. Here asthenosphere is defined by mantle rheology and temperature and not by geochemistry. The duration of melting in a volcanic field may be related to the size and shape of pockets of low velocity asthenosphere moving under the areas of volcanism. Seismic S- wave velocity profiles constrained by ambient noise and earthquake tomography of the mantle (Yang et al., 2008) show low velocity pockets, which may correspond to higher temperatures and/or higher water contents. By applying an asthenospheric flow velocity of 5 cm/yr east (Silver and Holt 2002, Conrad et al., 2007), the distance the mantle has moved since the time of volcanism can be calculated for basalts of known age. Past positions of low-velocity anomalies in the asthenosphere combined with depths and temperatures of melting calculated using the silica-liquid geobarometer (Lee et al., 2009) were used to determine if a low velocity anomaly existed under an area of volcanism at the depth of melting and time of eruption. The data constraints used for calculating depths and temperatures of melting are dry, MgO > 7.5 wt. %, SiO2 > 44 wt.%, and Fe as 90% Fe2+. Depths and temperatures of melting were calculated for several basalt fields of known age. Ages, temperatures, and depths are as follows: Death Valley 4 Ma, 1295-1350°C, and 42-63 km; Crater Flat 80 ka, 1 Ma, 3.8 Ma, 1388-1415°C, and 80-90 km; Lunar Crater 2.9-5.7 Ma, 1414-1480°C, and 80-121 km; Reveille 3.8-4.6 Ma, 1458-1516°C, and 110-140 km; Coso 0.23-5.3 Ma, 1244-1399°C, and 39.6-72 km; Big Pine 0.9-1.8 Ma, 1276-1356°C, and 42-72 km; Long Valley 0.4-3.2 Ma, 1289- 1323°C, and 44-50 km; Cima 0.3-8.3 Ma, 1330-1376°C, and 53-82 km; Snow Canyon <10,000 years, 1470-1485°C, and 75-85 km. Ages were converted to km of mantle motion and to degrees of longitude and plotted on seismic profiles

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

    USGS Publications Warehouse

    Gerlach, T.M.

    1993-01-01

    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 CO2-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 H2 and CO escape during crustal storage, CO2-rich Type I gases and CO2-poor Type II gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories. Volcanic gas data give a tightly co

  10. Alkali basalts and leucitites in an extensional intracontinental plate setting: The late Cenozoic Calatrava Volcanic Province (central Spain)

    NASA Astrophysics Data System (ADS)

    Cebriá, J.-M.; López-Ruiz, J.

    1995-04-01

    The Calatrava Volcanic Province (CVP) of central Spain is characterised by a intracontinental plate magmatic association of leucitites, melilitites, nephelinites and olivine basalts extruded during the late Miocene to Quaternary. Most of the rocks represent relatively primitive magmas and less than 45% have experienced small degrees ( < 25%) of crystal fractionation. Melilitites, nephelinites and olivine basalts form a suite generated by variable degrees of partial melting ( F = 5-17%) of a nearly homogeneous enriched (up to x18 chondritic values for the highly incompatible elements and × 3 for the moderately incompatible) mantle source, composed of Ol+Opx+Cpx+Gt+Phl. The leucitites appear to be derived by low degrees of partial melting ( ~ 4%) from a different mantle source, characterized by higher Rb, Ba, K and 87Sr enrichment and the presence of residual apatite. Phlogopite contributed to the leucititic liquids in a higher proportion than in the basaltic suite whereas clinopyroxene participated in lower amounts. The geochemical characteristics of the primary liquids suggest a contribution from two source components: (1) a subcontinental lithospheric component which appears to be a strongly enriched garnet-lherzolite with phlogopite ± apatite and (2) an asthenospheric diapir component with characteristics similar to the HIMU reservoir. These conclusions combined with geophysical observations indicate that the CVP magmatism could develop in two stages. In a first stage, a HIMU-like mantle diapir would trigger magma generation in the overlying subcontinental lithosphere by melting of pervasive enriched streaks or veins with phlogopite + apatite, giving rise to small amounts of leucititic liquids and to initial extension of the upper crust. In subsequent steps the extension developed, the lithosphere becomes stripped of its enriched components and the asthenospheric diapir starts to melt giving rise to the basaltic liquids which are virtually OIB-like magmas. This

  11. The Etendeka Igneous Province: magma types and their stratigraphic distribution with implications for the evolution of the Paraná-Etendeka flood basalt province

    NASA Astrophysics Data System (ADS)

    Marsh, J. S.; Ewart, A.; Milner, S. C.; Duncan, A. R.; Miller, R. McG.

    2001-02-01

    Detailed geochemical and field data for the volcanic sequence and intrusions of the Etendeka Igneous Province are used to construct a stratigraphic framework for petrogenetic interpretation of the evolution of the Etendeka-Paraná continental flood volcanic event. Geochemical and petrographic characterization of over 1,000 analyzed samples allows 8 mafic and 17 silicic magma types to be recognized. Both silicic and mafic types can be grouped into high-Ti and low-Ti suites on the basis of elevated Ti relative to other elements. The mafic magmas are: Khumib (high-Ti), Tafelberg, Kuidas, Horingbaai, Huab, Tafelkop, Albin, and Esmeralda (all low-Ti). Amongst the silicic types, the Goboboseb, Springbok, Wereldsend, Grootberg, and Beacon low-Ti quartz latites, and the Nil Desperandum high-Ti latite have been described previously. In addition, the Hoas (low-Ti), Nadas, Sechomib, and Hoarusib, (all high-Ti) latites and the Fria (low-Ti), Sarusas, Ventura, Khoraseb, Naudé, and Elliott (all high-Ti) quartz latites are described for the first time here. There is a marked provinciality in the distribution of the high- and low-Ti suites, with the former concentrated in the Northern Etendeka region and the latter dominant in the Southern Etendeka. Stratigraphic distribution of magma types allows two new formations to be defined in the Northern Etendeka - the Khumib Formation of basaltic flows and the Skeleton Coast Formation dominated by silicic sheets. The geochemical provinciality hampers precise correlations between Northern and Southern Etendeka. Available evidence suggests that the lower part of the Awahab Formation in the Southern Etendeka is coeval with the lower part of the Khumib Formation and that the silicic units in the upper part of the Tafelberg Formation probably correlate with the Skeleton Coast Formation. The paucity of Khumib dykes in relation to Tafelberg dykes and their field relationships with regard to the volcanic sequence in the Northern Etendeka

  12. Geology and petrology of the basalts of Crater Flat: applications to volcanic risk assessment for the Nevada Nuclear Waste Storage investigations

    SciTech Connect

    Vaniman, D.; Crowe, B.

    1981-06-01

    Volcanic hazard studies of the south-central Great Basin, Nevada, are being conducted for the Nevada Nuclear Waste Storage Investigations. This report presents the results of field and petrologic studies of the basalts of Crater Flat, a sequence of Pliocene to Quaternary-age volcanic centers located near the southwestern part of the Nevada Test Site. Crater Flat is one of several basaltic fields constituting a north-northeast-trending volcanic belt of Late Cenozoic age extending from southern Death Valley, California, through the Nevada Test Site region to central Nevada. The basalts of Crater Flat are divided into three distinct volcanic cycles. The cycles are characterized by eruption of basalt magma of hawaiite composition that formed cinder cone clusters and associated lava flows. Total volume of erupted magma for respective cycles is given. The basalts of Crater Flat are sparsely to moderately porphyritic; the major phenocryst phase is olivine, with lesser amounts of plagioclase, clinopyroxene, and rare amphibole. The consistent recurrence of evolved hawaiite magmas in all three cycles points to crystal fractionation from more primitive magmas at depth. A possible major transition in mantle source regions through time may be indicated by a transition from normal to Rb-depleted, Sr-enriched hawaiites in the younger basaltic cycles. The recurrence of small volumes of hawaiite magma at Crater Flat supports assumptions required for probability modeling of future volcanic activity and provides a basis for estimating the effects of volcanic disruption of a repository site in the southwestern Nevada Test Site region. Preliminary data suggest that successive basalt cycles at Crater Flat may be of decreasing volume but recurring more frequently.

  13. 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.

  14. 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.

  15. 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.

  16. 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).

  17. The Role of Volcanic Sour Gas on the Alteration of Martian Basalt: Insights from Geochemical Modeling

    NASA Astrophysics Data System (ADS)

    Berger, G.; Treguier, E.; D'Uston, C.; Pinet, P.; Toplis, M. J.

    2008-03-01

    We assess the chemical constraints of the alteration of basaltic material by a cold aqueous phase under atmospheric sour gas containing SO3. Secondary chemistry and mineralogy are calculated by a geochemical simulator and compared to MER data.

  18. 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.

  19. 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.

  20. 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.

  1. Origin of basaltic magmas of Perşani volcanic field, Romania: A combined whole rock and mineral scale investigation

    NASA Astrophysics Data System (ADS)

    Harangi, Szabolcs; Sági, Tamás; Seghedi, Ioan; Ntaflos, Theodoros

    2013-11-01

    The Perşani volcanic field is a low-volume flux monogenetic volcanic field in the Carpathian-Pannonian region, eastern-central Europe. Volcanic activity occurred intermittently from 1200 ka to 600 ka, forming lava flow fields, scoria cones and maars. Selected basalts from the initial and younger active phases were investigated for major and trace element contents and mineral compositions. Bulk compositions are close to those of the primitive magmas; only 5-12% olivine and minor spinel fractionation occurred at 1300-1350 °C, followed by clinopyroxenes at about 1250 °C and 0.8-1.2 GPa. Melt generation occurred in the depth range from 85-90 km to 60 km. The estimated mantle potential temperature, 1350-1420 °C, is the lowest in the Pannonian Basin. It suggests that no thermal anomaly exists in the upper mantle beneath the Perşani area and that the mafic magmas were formed by decompression melting under relatively thin continental lithosphere. The mantle source of the magmas could be slightly heterogeneous, but is dominantly variously depleted MORB-source peridotite, as suggested by the olivine and spinel composition. Based on the Cr-numbers of the spinels, two coherent compositional groups (0.38-0.45 and 0.23-0.32, respectively) can be distinguished that correspond to the older and younger volcanic products. This indicates a change in the mantle source region during the volcanic activity as also inferred from the bulk rock major and trace element data. The younger basaltic magmas were generated by lower degree of melting, from a deeper and compositionally slightly different mantle source compared to the older ones. The mantle source character of the Perşani magmas is akin to that of many other alkaline basalt volcanic fields in the Mediterranean close to orogenic areas. The magma ascent rate is estimated based on compositional traverses across olivine xenocrysts using variations of Ca content. Two heating events are recognized; the first one lasted about 1

  2. 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

  3. 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

  4. 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.

  5. Unconventional sub-basalt imaging and geological interpretation in terms of porosity/permeability in buried volcanic reservoirs.

    NASA Astrophysics Data System (ADS)

    De Siena, Luca; Healy, David; Emanuele Rizzo, Roberto; Schofield, Nicholas

    2016-04-01

    Seismic absorption-scattering mapping is becoming the new standard in volcano imaging, as it allows a description of the Earth in terms of parameters tangibly related to porosity and permeability. This technique has an unexplored interpretational potential for the oil & gas industry in terms of how we relate rock-matrix permeability with unconventional seismic parameters, more sensitive to the presence of fluids and to the location of interfaces than seismic velocity. We propose a joint sub-basalt imaging and geological interpretational project inspired by the experience acquired in volcanic environments and focused on the application of volcanological mapping techniques to industrial data. The project will involve processing raw seismic data to understand the effect of different volcanic facies on absorption and scattering of seismic energy. These two parameters will then be linked to the porosity and permeability of the host rock by means of petrophysical and seismic experiments on core samples and field analogues, using state of the art facilities at the University of Aberdeen funded by the Oil & Gas Innovation Centre (OGIC). After careful petrophysical mapping of dry and fluid-saturated samples, P- and S- waves will be propagated at a range of frequencies into them to understand the potential subsurface seismic response. The final up-scaling will tackle the problem of exposing the physical properties of the basin trying to set new benchmarks in seismic interpretation of volcanic oil & gas fields.

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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.

  11. Modern analogues for Miocene to Pleistocene alkali basaltic phreatomagmatic fields in the Pannonian Basin: "soft-substrate" to "combined" aquifer controlled phreatomagmatism in intraplate volcanic fields Research Article

    NASA Astrophysics Data System (ADS)

    Németh, Károly; Cronin, Shane; Haller, Miguel; Brenna, Marco; Csillag, Gabor

    2010-09-01

    The Pannonian Basin (Central Europe) hosts numerous alkali basaltic volcanic fields in an area similar to 200 000 km2. These volcanic fields were formed in an approximate time span of 8 million years producing smallvolume volcanoes typically considered to be monogenetic. Polycyclic monogenetic volcanic complexes are also common in each field however. The original morphology of volcanic landforms, especially phreatomagmatic volcanoes, is commonly modified. by erosion, commonly aided by tectonic uplift. The phreatomagmatic volcanoes eroded to the level of their sub-surface architecture expose crater to conduit filling as well as diatreme facies of pyroclastic rock assemblages. Uncertainties due to the strong erosion influenced by tectonic uplifts, fast and broad climatic changes, vegetation cover variations, and rapidly changing fluvio-lacustrine events in the past 8 million years in the Pannonian Basin have created a need to reconstruct and visualise the paleoenvironment into which the monogenetic volcanoes erupted. Here phreatomagmatic volcanic fields of the Miocene to Pleistocene western Hungarian alkali basaltic province have been selected and compared with modern phreatomagmatic fields. It has been concluded that the Auckland Volcanic Field (AVF) in New Zealand could be viewed as a prime modern analogue for the western Hungarian phreatomagmatic fields by sharing similarities in their pyroclastic successions textures such as pyroclast morphology, type, juvenile particle ratio to accidental lithics. Beside the AVF two other, morphologically more modified volcanic fields (Pali Aike, Argentina and Jeju, Korea) show similar features to the western Hungarian examples, highlighting issues such as preservation potential of pyroclastic successions of phreatomagmatic volcanoes.

  12. 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

  13. Assessing Magmatic Processes and Hazards at two Basaltic Monogenetic Centers: Volcan Jorullo, Mexico, and Blue Lake Maar, Oregon

    NASA Astrophysics Data System (ADS)

    Johnson, E. R.; Cashman, K.; Wallace, P.; Delgado Granados, H.

    2007-05-01

    Although monogenetic basaltic volcanoes exhibit a wide variety of eruption styles, the origin of this diversity is poorly understood and often ignored when assessing volcanic hazards. To better understand magmatic processes and hazards associated with these eruptions, we have studied two monogenetic centers with differing behavior: Volcan Jorullo, a cinder cone in Mexico, and Blue Lake, a maar in the Oregon High Cascades. Although compositionally similar (medium-K basalt to basaltic andesite), their eruptive styles and products are quite different. Jorullo had violent strombolian eruptions that deposited alternating beds of ash and tephra, as well as lava flows. In contrast, Blue Lake exhibited initial phreatomagmatism that formed a 100m deep crater and produced surge deposits. This activity was followed by magmatic eruptions that produced deposits of tephra and bombs, but no lava flows. The diversity in eruptive style at these two centers reflects different magma ascent and crystallization processes, deduced using olivine-hosted melt inclusions. Jorullo melt inclusions trap variably degassed melts (0.5-5 wt% H2O; 0-1000 ppm CO2), with associated crystallization pressures that decrease from early (<4 kbars) to late (<100 bars) in the eruption. These data support the formation of a shallow storage region beneath the volcano that facilitated both crystallization and magma degassing, which is consistent with effusion of degassed lavas from the base of the cone throughout the eruption. In contrast, Blue Lake inclusions trap melts with a restricted range of volatiles (2.6-4 wt% H2O; 677-870 ppm CO2) corresponding to crystallization pressures of 2.2-3.2 kbars. This suggests that the magma feeding Blue Lake stalled in the upper crust and crystallized before ascending rapidly to the surface, without further crystallization of olivine or shallow storage. This is consistent with both the observed unstratified tephra deposits (indicating single rather than pulsatory eruptions

  14. The Hawaiian Volcano Observatory: a natural laboratory for studying basaltic volcanism: Chapter 1 in Characteristics of Hawaiian volcanoes

    USGS Publications Warehouse

    Tilling, Robert I.; Kauahikaua, James P.; Brantley, Steven R.; Neal, Christina A.; Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M.

    2014-01-01

    This chapter summarizes HVO’s history and some of the scientific achievements made possible by this permanent observatory over the past century as it grew from a small wooden structure with only a small staff and few instruments to a modern, well-staffed, world-class facility with state-of-the-art monitoring networks that constantly track volcanic and earthquake activity. The many successes of HVO, from improving basic knowledge about basaltic volcanism to providing hands-on experience and training for hundreds of scientists and students and serving as the testing ground for new instruments and technologies, stem directly from the acquisition, integration, and analysis of multiple datasets that span many decades of observations of frequent eruptive activity. HVO’s history of the compilation, interpretation, and communication of long-term volcano monitoring and eruption data (for instance, seismic, geodetic, and petrologic-geochemical data and detailed eruption chronologies) is perhaps unparalleled in the world community of volcano observatories. The discussion and conclusions drawn in this chapter, which emphasize developments since the 75th anniversary of HVO in 1987, are general and retrospective and are intended to provide context for the more detailed, topically focused chapters of this volume.

  15. 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

  16. Hf Isotope Evidence for Subducted Basalt and Sediment Contributions to the Eastern Trans-Mexican Volcanic Belt

    NASA Astrophysics Data System (ADS)

    Cai, Y.; Tuena, A. G.; Capra, L.; Straub, S. M.; Goldstein, S. L.; Langmuir, C. H.

    2005-12-01

    Magmas generated at thick crust continental arcs often have enriched continental crust-like trace element patterns and Pb-Sr-Nd isotope ratios that are intermediate to both upper mantle and crustal compositions. Thus it is difficult to distinguish between contributions from (a) the subducted basalt and the upper mantle wedge, and (b) subducted sediment and the continental crust. These issues have been the focus of major controversy. Here we show evidence for subduction contributions to lavas in a classic thick crust environment. In Eastern Trans-Mexican Volcanic Belt, the upper continental crust is 30 km to 45 km thick. However, primitive mafic lavas erupt on many sites across the arc. We have analyzed the subducting sediments as represented by DSDP 487, located seaward of the trench, where the lower third of the sediment column has strongly hydrothermal pelagic features and the upper two-thirds is composed of terrigenous sediments. The pelagic sediments have distinctive features that could be used to identify a subduction component in the volcanics, including high REE/Hf, negative Ce anomalies, and Nd-Hf isotopes that lie on the "seawater array" and offset from the "mantle-crust" array. We have focused on a unique series of lavas from volcano Nevado de Toluca, located southwest of Mexico City. These lavas show negative Ce anomalies coupled with low REE/Hf and Zr/Nd ratios. Hf-Nd isotope ratios show a shallow trend compared to the mantle-crust array, consistent with a pelagic component. In addition, Hf isotopes show a striking positive correlation with Ce anomalies that trend toward the pelagic sediment compositions. These and other observations provide clear evidence for a component from subducted sediment in the lavas. In addition, there is a negative correlation of Lu/Hf and Hf isotopes that requires a mixing endmember with MORB-like Hf isotope ratios but with lower than MORB Lu/Hf. This indicates a melt from eclogitic subducted basalt. Compared to other

  17. Spatial analysis of an intra-plate basaltic volcanic field in a compressional tectonic setting: South-eastern Australia

    NASA Astrophysics Data System (ADS)

    van den Hove, Jackson; Grose, Lachlan; Betts, Peter G.; Ailleres, Laurent; Van Otterloo, Jozua; Cas, Ray A. F.

    2017-04-01

    The Newer Volcanics Province (NVP) is a Pliocene to Recent intra-plate basaltic volcanic field (BVF) that has formed in a compressive tectonic setting (σv < σhmin < σHmax) and is not readily attributed to a single geodynamic process. A comprehensive spatial analysis of both monogenetic eruption centres and coeval vents of the NVP constrain factors that control the distribution and emplacement of volcanoes. A point-set of 434 eruption centres totalling 726 vents are divided into three geographical sub-provinces for analysis. Kernel density estimation and Poisson nearest neighbour analysis are used to scrutinize the distribution of eruption centres. A simple and novel fitted regression line method is used to determine the orientation of coeval vents, and Hough transform and two-point azimuth methods are used to identify alignments and alignment trends between eruption centres. The distribution of eruption centres and their relative spatial density corresponds with the extent of thinner lithosphere. Eruption centres of the NVP have a clustered distribution whilst smaller sub-sets of eruption centres are distributed more uniformly. The main alignment trends between coeval vents related to individual dikes and between eruption centres related to successive temporally discrete dikes are primarily oriented nearly parallel with pre-existing crustal fault trends. The frequency of volcanic alignments shows faults oriented nearly parallel to the orientation of the regional maximum horizontal compressive stress (σ1) are favourably utilised by intrusions over other fault trends. The depth from which pre-existing faults facilitate dike propagation is not constrained. We interpret they are likely important in preventing dikes from stalling and forming sills under a compressive stress field in the case of the NVP. It is also observed that coeval vent alignments are more strongly aligned in areas overlying consolidated basement relative to areas of poorly consolidated basin

  18. Crustal contamination and mantle source characteristics in continental intra-plate volcanic rocks: Pb, Hf and Os isotopes from central European volcanic province basalts

    NASA Astrophysics Data System (ADS)

    Jung, S.; Pfänder, J. A.; Brauns, M.; Maas, R.

    2011-05-01

    We report new Os-Pb-Hf isotope data for a suite of alkaline to basaltic (nephelinites, basanites, olivine tholeiites to quartz-tholeiites) lavas from the Miocene Vogelsberg (Germany), the largest of the rift-related continental volcanic complexes of the Central European Volcanic Province (CEVP). 187Os/ 188Os in primitive (high-MgO) alkaline lavas show a much wider range than has been observed in alkaline basalts and peridotite xenoliths from elsewhere in the CEVP, from ratios similar to those in modern MORB and OIB (0.1260-0.1451; 58.9-168 ppt Os) to more radiogenic ratios (0.1908 and 0.2197; 27.6-15.1 ppt Os). Radiogenic Os is associated with high ɛ Hf and ɛ Nd, low 87Sr/ 86Sr and does not correlate with Mg ∗ or incompatible trace elements (e.g. Ce/Pb), suggesting the presence of a radiogenic endmember in the mantle rather than crustal contamination as the source of radiogenic Os. This contrasts with another high-Mg alkaline lava characterized by highly radiogenic 187Os/ 188Os (0.4344, 10.3 ppt Os), lower ɛ Hf and ɛ Nd, higher 87Sr/ 86Sr, and Pb isotope signatures than the other alkaline lavas with similar trace element composition suggestive of contamination with crustal material. Hafnium (ɛ Hf: +8.9 to +5.0) and Pb isotope compositions ( 206Pb/ 204Pb: 19.10-19.61; 207Pb/ 204Pb: 15.56-15.60) of the alkaline rocks fall within the range of enriched MORB and some OIB. The Vogelsberg tholeiites show even more diverse 187Os/ 188Os, ranging from 0.1487 in Os-rich olivine tholeiite (31.7 ppt) to ratios as high as 0.7526 in other olivine-tholeiites and in quartz-tholeiites with lower Os concentrations (10.3-2.0 ppt). Low- 187Os/ 188Os tholeiites show Pb-Hf isotope ratios ( 206Pb/ 204Pb:18.81; 207Pb/ 204Pb: 15.61; ɛ Hf: +2.7) that are distinct from those in alkaline lavas with similar 187Os/ 188Os and originate from a different mantle source. By contrast, the combination of radiogenic Os and low 206Pb/ 204Pb and ɛ Hf in the other tholeiites probably reflects

  19. Relationships between internal structures and petrographic textures of basalt flows: example from a continental flood tholeiite province

    SciTech Connect

    Long, P.E.; Snow, M.G.; Davidson, N.J.

    1980-12-01

    Excellent exposures of numerous, well-preserved flows of continental flood tholeiite in south-central Washington provide opportunity to study primary internal structures of subaerial basalt flows. Typical intraflow structures (top to bottom) of a flow include: ropy to brecciated, vesicular flow top; coarsely columnar basalt (upper colonnade); hackly to columnar basalt with relatively small columns (entablature); relatively large, regular columns (lower colonnade); and a glassy basal zone that may be pillowed, vesicular, or highly fractured. One or more of these intraflow structures may be absent or present in multiples in any given flow. Predominance of certain combinations of intraflow structures define three basic types of flows. Type I flows consist principally of relatively large (> 0.9 m), irregular columns with little or no entablature and a poorly developed flow top. Type II flows exhibit alternating tiers of entablature and colonnade 1 to 5 m thick, which give way upward to a more uniform entablature that commonly contains vesicular layers. Type III flows have sharp entablature-colonnade contacts and typically exhibit an upper colonnade. Petrography of samples from different intraflow structures and flow types shows that entablature invariably has abundant black, tachylitic glass; whereas, colonnade typically has much less abundant, brown, transparent glass. Simple conductive cooling models do not explain sharp contacts between the distinctive textures of entablature and colonnade or textural differences between flow types. These textural differences require either different cooling rates or perhaps different oxygen fugacities across a relatively sharp contact within a flow.

  20. The petrology, phase relations and tectonic setting of basalts from the taupo volcanic zone, New Zealand and the Kermadec Island arc - havre trough, SW Pacific

    NASA Astrophysics Data System (ADS)

    Gamble, John A.; Smith, Ian E. M.; Graham, Ian J.; Peter Kokelaar, B.; Cole, James W.; Houghton, Bruce F.; Wilson, Colin J. N.

    1990-10-01

    Volcanism in the Taupo Volcanic Zone (TVZ) and the Kermadec arc-Havre Trough (KAHT) is related to westward subduction of the Pacific Plate beneath the Indo-Australian Plate. The tectonic setting of the TVZ is continental whereas in KAHT it is oceanic and in these two settings the relative volumes of basalt differ markedly. In TVZ, basalts form a minor proportion (< 1%) of a dominant rhyolite (97%)-andesite association while in KAHT, basalts and basaltic andesites are the major rock types. Neither the convergence rate between the Pacific and Indo-Australian Plates nor the extension rates in the back-arc region or the dip of the Pacific Plate Wadati-Benioff zone differ appreciably between the oceanic and continental segments. The distance between the volcanic front and the axis of the back-arc basin decreases from the Kermadec arc to TVZ and the distance between trench and volcanic front increases from around 200 km in the Kermadec arc to 280 km in TVZ. These factors may prove significant in determining the extent to which arc and backarc volcanism in subduction settings are coupled. All basalts from the Kermadec arc are porphyritic (up to 60% phenocrysts) with assemblages generally dominated by plagioclase but with olivine, clinopyroxene and orthopyroxene. A single dredge sample from the Havre Trough back arc contains olivine and plagioclase microphenocrysts in glassy pillow rind and is mildly alkaline (< 1% normative nepheline) contrasting with the tholeiitic nature of the other basalts. Basalts from the TVZ contain phenocryst assemblages of olivine + plagioclase ± clinopyroxene; orthopyroxene phenocrysts occur only in the most evolved basalts and basaltic andesites from both TVZ and the Kermadec Arc. Sparsely porphyritic primitive compositions (Mg/(Mg+Fe 2) > 70) are high in Al 2O 3 (>16.5%), and project in the olivine volume of the basalt tetrahedron. They contain olivine (Fo 87) phenocrysts and plagioclase (> An 60) microphenocrysts. These magmas have ratios of

  1. Paleoproterozoic arc basalt-boninite-high magnesian andesite-Nb enriched basalt association from the Malangtoli volcanic suite, Singhbhum Craton, eastern India: Geochemical record for subduction initiation to arc maturation continuum

    NASA Astrophysics Data System (ADS)

    Rajanikanta Singh, M.; Manikyamba, C.; Ganguly, Sohini; Ray, Jyotisankar; Santosh, M.; Dhanakumar Singh, Th.; Chandan Kumar, B.

    2017-02-01

    The Singhbhum Craton of eastern India preserves distinct signatures of ultramafic-mafic-intermediate-felsic magmatism of diverse geodynamic affiliations spanning from Paleo-Mesoarchean to Proterozoic. Here we investigate the 2.25 Ga Malangtoli volcanic rocks that are predominantly clinopyroxene- and plagioclase-phyric, calc-alkaline in nature, display basalt-basaltic andesite compositions, and preserve geochemical signatures of subduction zone magmatism. Major, trace and rare earth element characteristics classify the Malangtoli volcanic rocks as arc basalts, boninites, high magnesian andesites (HMA) and Nb enriched basalts (NEB). The typical LILE enriched-HFSE depleted geochemical attributes of the arc basalts corroborate a subduction-related origin. The boninitic rocks have high Mg# (0.8), MgO (>25 wt.%), Ni and Cr contents, high Al2O3/TiO2 (>20), Zr/Hf and (La/Sm)N (>1) ratios with low (Gd/Yb)N (<1) ratio, TiO2, and Zr concentrations. The HMA samples are marked by moderate SiO2 (>54 wt.%), MgO (>6 wt.%), Mg# (0.47) with elevated Cr, Co, Ni and Th contents, depleted (Nb/Th)N, (Nb/La)N, high (Th/La)N and La/Yb (<9) ratio, moderate depletion in HREE and Y with low Sr/Y. The NEBs have higher Nb contents (6.3-24 ppm), lower magnitude of negative Nb anomalies with high (Nb/Th)pm = 0.28-0.59 and (Nb/La)pm = 0.40-0.69 and Nb/U = 2.8-34.4 compared to normal arc basalts [Nb = <2 ppm; (Nb/Th)pm = 0.10-1.19; (Nb/La)pm 0.17-0.99 and Nb/U = 2.2-44 respectively] and HMA. Arc basalts and boninites are interpreted to be the products of juvenile subduction processes involving shallow level partial melting of mantle wedge under hydrous conditions triggered by slab-dehydrated fluid flux. The HMA resulted through partial melting of mantle wedge metasomatized by slab-dehydrated fluids and sediments during the intermediate stage of subduction. Slab-melting and mantle wedge hybridization processes at matured stages of subduction account for the generation of NEB. Thus, the arc basalt

  2. 3-D high-speed imaging of volcanic bomb trajectory in basaltic explosive eruptions

    NASA Astrophysics Data System (ADS)

    Gaudin, D.; Taddeucci, J.; Houghton, B. F.; Orr, T. R.; Andronico, D.; Del Bello, E.; Kueppers, U.; Ricci, T.; Scarlato, P.

    2016-10-01

    Imaging, in general, and high speed imaging in particular are important emerging tools for the study of explosive volcanic eruptions. However, traditional 2-D video observations cannot measure volcanic ejecta motion toward and away from the camera, strongly hindering our capability to fully determine crucial hazard-related parameters such as explosion directionality and pyroclasts' absolute velocity. In this paper, we use up to three synchronized high-speed cameras to reconstruct pyroclasts trajectories in three dimensions. Classical stereographic techniques are adapted to overcome the difficult observation conditions of active volcanic vents, including the large number of overlapping pyroclasts which may change shape in flight, variable lighting and clouding conditions, and lack of direct access to the target. In particular, we use a laser rangefinder to measure the geometry of the filming setup and manually track pyroclasts on the videos. This method reduces uncertainties to 10° in azimuth and dip angle of the pyroclasts, and down to 20% in the absolute velocity estimation. We demonstrate the potential of this approach by three examples: the development of an explosion at Stromboli, a bubble burst at Halema'uma'u lava lake, and an in-flight collision between two bombs at Stromboli.

  3. 3-D high-speed imaging of volcanic bomb trajectory in basaltic explosive eruptions

    USGS Publications Warehouse

    Gaudin, D.; Taddeucci, J; Houghton, B. F.; Orr, Tim R.; Andronico, D.; Del Bello, E.; Kueppers, U.; Ricci, T.; Scarlato, P.

    2016-01-01

    Imaging, in general, and high speed imaging in particular are important emerging tools for the study of explosive volcanic eruptions. However, traditional 2-D video observations cannot measure volcanic ejecta motion toward and away from the camera, strongly hindering our capability to fully determine crucial hazard-related parameters such as explosion directionality and pyroclasts' absolute velocity. In this paper, we use up to three synchronized high-speed cameras to reconstruct pyroclasts trajectories in three dimensions. Classical stereographic techniques are adapted to overcome the difficult observation conditions of active volcanic vents, including the large number of overlapping pyroclasts which may change shape in flight, variable lighting and clouding conditions, and lack of direct access to the target. In particular, we use a laser rangefinder to measure the geometry of the filming setup and manually track pyroclasts on the videos. This method reduces uncertainties to 10° in azimuth and dip angle of the pyroclasts, and down to 20% in the absolute velocity estimation. We demonstrate the potential of this approach by three examples: the development of an explosion at Stromboli, a bubble burst at Halema'uma'u lava lake, and an in-flight collision between two bombs at Stromboli.

  4. 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

  5. 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

  6. 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.

  7. 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.

  8. Assimilation in lunar basalts and volcanic glasses: Implications for a heterogenous mantle source region

    NASA Technical Reports Server (NTRS)

    Finnila, A. B.; Hess, P. C.; Rutherford, M. J.

    1993-01-01

    Several scientists have called on assimilation of anorthositic crustal material or KREEP compositions to explain various lunar lithologies. In order to address the practicality of such processes, some techniques for calculating how much assimilation is possible in magma chambers and dikes based on thermal energy balances and simple fluid mechanical constraints are outlined. In a previous effort, it was demonstrated that dissolution of plagioclase in an iron-free basalt was too slow to contaminate magmas, and that the energy cost of melting plagioclase-rich crustal material was prohibitive both in magma chambers and in dike conduits. This analysis was extended to include dissolution rates in an orange glass composition and to quantitatively predict the maximum contamination possible due to assimilation of both lunar crustal material and KREEP.

  9. 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

  10. 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.

  11. Covariance of initial sup 87 Sr/ sup 86 Sr ratios,. delta. sup 18 O, and SiO sub 2 in continental flood basalt suites: The role of contamination and alteration

    SciTech Connect

    Harris, C. )

    1989-07-01

    When mutual positive correlations occur between {delta}{sup 18}O, {sup 87}Sr/{sup 86}Sr initial ratio (R{sub o}), and SiO{sub 2} in continental flood basalt suites, they are generally accepted as being due to crustal contamination. In continental flood basalt suites that have undergone coupled assimilation-fractional crystallization in which the contaminant is granitic continental crust, R{sub o} reflects the degree of contamination and will correlate positively with SiO{sub 2} which reflects the degree of differentiation. Posteruptive alteration of a suite having a range of SiO{sub 2} values should result in a positive correlation between SiO{sub 2} and {delta}{sup 18}O because the ability of a volcanic rock to concentrate {sup 18}O depends, in part, on silica content. Suites that have undergone assimilation-fractional crystallization followed by alteration after eruption may there for exhibit a positive correlation between {delta}{sup 18}O, SiO{sub 2}, and R{sub o}. The {delta}{sup 18}O data in such suites may consequently suggest erroneously high degrees of contamination.

  12. 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].

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

    SciTech Connect

    Gerlach, T.M. )

    1993-02-01

    Volcanic gases collected during episode 1 of the Puu Oo eruption along the east rift zone of Kilauea Volcano, Hawaii, have uniform C-O-H-S-Cl-F compositions that are sharply depleted in CO[sub 2]. The CO[sub 2]-poor gases are typical of Type II volcanic gases (GERLACH and GRAEBER, 1985) and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing CO[sub 2]-rich gases during an earlier period of temporary residence in the summit magma chamber. The samples are remarkably free of contamination by atmospheric gases and meteoric water. Thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032[degrees]C. Open- and closed-system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling. These models indicate that the F[sub o[sub 2

  14. Deep mixing of mantle melts beneath continental flood basalt provinces: Constraints from olivine-hosted melt inclusions in primitive magmas

    NASA Astrophysics Data System (ADS)

    Jennings, Eleanor S.; Gibson, Sally A.; Maclennan, John; Heinonen, Jussi S.

    2017-01-01

    We present major and trace element compositions of 154 re-homogenised olivine-hosted melt inclusions found in primitive rocks (picrites and ferropicrites) from the Mesozoic Paraná-Etendeka and Karoo Continental Flood Basalt (CFB) provinces. The major element compositions of the melt inclusions, especially their Fe/Mg ratios, are variable and erratic, and attributed to the re-homogenisation process during sample preparation. In contrast, the trace element compositions of both the picrite and ferropicrite olivine-hosted melt inclusions are remarkably uniform and closely reflect those of the host whole-rocks, except in a small subset affected by hydrothermal alteration. The Paraná-Etendeka picrites and ferropicrites are petrogenetically related to the more evolved and voluminous flood basalts, and so we propose that compositional homogeneity at the melt inclusion scale implies that the CFB parental mantle melts were well mixed prior to extensive crystallisation. The incompatible trace element homogeneity of olivine-hosted melt inclusions in Paraná-Etendeka and Karoo primitive magmatic rocks has also been identified in other CFB provinces and contrasts with findings from studies of basalts from mid-ocean ridges (e.g. Iceland and FAMOUS on the Mid Atlantic Ridge), where heterogeneity of incompatible trace elements in olivine-hosted melt inclusions is more pronounced. We suggest that the low variability in incompatible trace element contents of olivine-hosted melt inclusions in near-primitive CFB rocks, and also ocean island basalts associated with moderately thick lithosphere (e.g. Hawaii, Galápagos, Samoa), may reflect mixing along their longer transport pathways during ascent and/or a temperature contrast between the liquidus and the liquid when it arrives in the crust. These thermal paths promote mixing of mantle melts prior to their entrapment by growing olivine crystals in crustal magma chambers. Olivine-hosted melt inclusions of ferropicrites from the Paran

  15. 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.

  16. D/H on Mars: Effects of floods, volcanism, impacts, and polar processes

    USGS Publications Warehouse

    Carr, M.H.

    1990-01-01

    Water in the Martian atmosphere is 5.1 times more enriched in deuterium than terrestial water. The enrichment has been previously attributed to either a massive loss of water early in the planet's history or the presence of only a very small reservoir of water that has exchanged with the atmosphere over geologic time. Both these interpretations appear inconsistent with geologic evidence of large floods and sustained volcanism. Large floods are believed to have episodically introduced large amounts of water onto the surface. During a large flood roughly 1017 g of water would almost immediately sublime into the atmospher and be frozen out on polar terrain, to form a new layer several centimeters thick. The long-term effect of a flood would depend on where the water pooled after the flood. If the water pooled at low latitudes, all the water would slowly sublime into the atmosphers and ultimately be frozen out at the poles, thereby adding several meters to the polar deposits for each flood. If the water pooled at high latitude, it would form a permanent ice deposit, largely isolated from further interchange with the atmosphere. Volcanism has also episodically introduced water into the atmosphere. Most of this water has become incorporated into the polar deposits. That released over the last 3.5 Ga could have added a few kilometers to the polar deposits, depending on the amount of dust incorporated along with the ice. Large cometary impacts would have introduced additional large amounts of water into the atmosphere. The long-term evolution of D/H in the atmosphere depends on the rate of exchange of water between the atmosphere and the polar deposits. If exchange is active, then loss rates of hydrogen from the upper atmosphere are substantially higher than those estimated by Y. L. Yung, J. Wen, J. P. Pinto, M. Allen, K. K. Pierce, and S. Paulsen [Icarus 76, 146-159 (1988)]. More plausibly, exchange of water between the atmosphere and the polar deposits is limited, so

  17. 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

  18. 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

  19. 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.

  20. Constraining the Origin of Basaltic Volcanic Rocks Observed by Opportunity Along the Rim of Endeavour Crater

    NASA Technical Reports Server (NTRS)

    Bouchard, M. C.; Jolliff, B. L.; Farrand, W. H.; Mittlefehldt, D. W.

    2017-01-01

    The Mars Exploration Rover (MER) Opportunity continues its exploration along the rim of Endeavour Crater. While the primary focus for investigation has been to seek evidence of aqueous alteration, Opportunity has observed a variety of rock types, including some that are hard and relatively unaltered. These rocks tend to occur most commonly as "float rocks" or "erratics" where the geologic setting does not clearly reveal their origin. Along the rim of Endeavour crater (Fig. 1), such rocks, commonly noted in Panoramic Camera (Pancam) left eye composites as "blue rocks", are abundant components of some of the Endeavour crater rim deposits, scree slopes, and colluvium deposits. In this abstract, we examine the similarity of several of these rocks analyzed using Opportunity's Alpha Particle X-Ray Spectrometer (APXS), images and color from the Pancam, and textures observed with the Microscopic Imager (MI. At issue is the blue rocks origin; are they impact melt or volcanic, what is their age relative to Endeavour crater, and how they are related to each other?

  1. 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.

  2. 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).

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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.

  8. Analysing diagenetic effects of flood basalts on sedimentary basins during Gondwanan break-up: case studies from NW Namibia.

    NASA Astrophysics Data System (ADS)

    Thompson, G. A.; Jerram, D. A.; Harris, C.; Pearson, D. G.

    2003-04-01

    ABSTRACT The eruption of large volumes of lava associated with the break-up and dispersal of the Gondwana Supercontinent is a phenomenon that has been well documented in literature. The Etendeka Flood Basalt Province of NW Namibia is correlated with the Paraná Flood Basalt Province of South America and was extruded between 139Ma for the earliest flows and 130Ma for the most recent. The passive, inflated pahoehoe lava flows have preserved bedforms within sand dunes found in the Huab Basin without significant deformation. This allows the internal structures of the palaeo-dunes to be analysed with great accuracy; a phenomenon rarely seen within the geological record. The sediments directly beneath, and interbedded with, the Etendeka Flood Basalt are lithostratigraphically similar to those in the Kudu Gas Province, offshore Namibia, where gas-bearing aeolian sands are interspersed with lava flows. Research by the authors is focussed on the diagenetic effects, both direct and indirect, of the emplacement of the lava, and the associated sills and dykes, on the aeolian sands. Specific interests include: the compartmentalisation of the basin by sills/dykes/lava: how does this affect fluid flow paths? Diagenesis along hot contacts: is the dramatic reduction in porosity/permeability along such contacts the result of the igneous bodies alone or do they need ground water present? Can large igneous events trigger the movement of hot fluids through the basin and to what extent does this cause alteration to sediments? To address these issues we have identified a number of outcrop case studies within the Huab Basin in NW Namibia. Here, excellent 3 dimensional outcrop coupled with almost 100 percent exposure allows detailed sampling strategies to be employed on locations of interest. In some cases igneous dykes have acted as flow barriers to pore fluids and have therefore altered the type and degree of cementation either side of the dyke. Geochemical analysis of the cement can

  9. 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 230Th 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 (230Th/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.

  10. 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

  11. 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

  12. 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

  13. Relationship Between Low-Velocity S-wave Anomalies, Asthenospheric Dynamics and Basaltic Volcanism in the Intraplate Setting of the Basin and Range, USA

    NASA Astrophysics Data System (ADS)

    Tibbetts, A. K.; Smith, E. I.; Conrad, C. P.; Lee, C.; Plank, T.; Yang, Y.

    2009-12-01

    Pliocene to Recent intraplate mafic volcanic rocks of the Basin and Range Province mostly formed by asthenospheric melting, as determined from calculated melting temperatures ranging from 1249-1521 degrees C. Here asthenosphere is defined by mantle rheology and temperature and not by geochemistry. The duration of melting in a volcanic field may be related to the size and shape of pockets of low velocity asthenosphere moving under the areas of volcanism. Seismic S-wave velocity profiles constrained by ambient noise and earthquake tomography of the mantle (Yang et al., 2008) show low velocity pockets, which may correspond to higher temperatures and/or higher water contents. The lack of wider scale volcanism in the Basin and Range despite large scale anomalies indicates that the anomalies are not the only cause of melting. The observed smaller scale magmatism can be explained by circulatory flow driven by the small scale structure of the anomalies causing localized melting within the anomalies. By applying an asthenospheric shear flow velocity of 0 cm/yr at the base of the lithosphere and 5 cm/yr east at depth (Silver & Holt 2002, Conrad et al., 2007), the distance the mantle has moved since the time of volcanism can be calculated for basalts of known age. Past positions of low-velocity anomalies in the asthenosphere combined with depths and temperatures of melting calculated using the silica-liquid geobarometer (Lee et al., 2009) were used to determine if a low velocity anomaly existed under an area of volcanism at the depth of melting and time of eruption. The data constraints used for calculating depths and temperatures of melting are dry, MgO > 7.5 wt.%, SiO2 > 44 wt.%, and Fe as 90% Fe2+. Depths and temperatures of melting were calculated for San Francisco in AZ; Amboy, Pisgah, Death Valley, Coso, Big Pine, Cima, Long Valley, in CA; Crater Flat, Lunar Crater, Reveille in NV; and Black Rock, Hurricane, Snow Canyon, UT; and others all of which have known ages. Ages

  14. Origin of Late Paleogene to Neogene basalts and associated coeval felsic volcanic rocks in Southwest Hokkaido, northern NE Japan arc: Constraints from Sr and Nd isotopes and major- and trace-element chemistry

    NASA Astrophysics Data System (ADS)

    Takanashi, Koshiro; Shuto, Kenji; Sato, Makoto

    2011-07-01

    Basalts and felsic volcanic rocks (mainly dacite and rhyolite) found in southwest Hokkaido, northern part of the NE Japan arc, result from protracted volcanism during the Oligocene (34-30 Ma), Early Miocene (25-17 Ma), Middle Miocene (16-12 Ma), Late Miocene (10-5 Ma), Pliocene (4 Ma) and Quaternary (2 Ma), thus spanning the pre-Japan Sea opening to post-opening stages. The majority of basaltic rocks after about 16 Ma show depleted Sr (SrI) and Nd (NdI) isotopic signatures compared with some Middle to Early Miocene basalts, which strongly resemble, in terms of both timing and extent, the change in SrI and NdI values for back-arc basaltic rocks of the central NE Japan arc. However, significant differences exist for younger basaltic rocks, in that basaltic rocks with depleted SrI and NdI signatures are found from the Middle Miocene onwards throughout the eastern-, transitional- and western-volcanic zones in SW Hokkaido, whereas in the central NE Japan arc, basaltic rocks with similar isotopic signatures are confined to the back-arc side. Felsic volcanic rocks in southwest Hokkaido have SrI and NdI values, which overlap with coeval southwest Hokkaido basaltic rocks. Although the relationship between mafic and felsic rocks could be attributed to fractional crystallization, this process is inconsistent with REE chemistry, as total REE do not increase systematically from basaltic rocks to felsic volcanic rocks. Alternatively, lower crustal mafic rocks, represented by gabbroic and amphibolitic xenoliths found in basaltic rocks at Itinome-gata (Oga Peninsula), are a possible source for Late Paleogene to Quaternary felsic magmas, as both felsic volcanic rocks and xenoliths have similar SrI and NdI. A possible tectono-magmatic model for the production of post-Late Paleogene volcanic rocks from SW Hokkaido commences in the Oligocene (34 Ma) with asthenospheric mantle upwelling followed by partial melting to generate basalt magma (Matsue basalt) with depleted SrI and Nd

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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).

  20. 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

  1. 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.

  2. Climate-Floods relationship in the mountainous volcanic region of Morelia, Michoacan, Mexico.

    NASA Astrophysics Data System (ADS)

    Vinson, D.; Gratiot, N.; Saenz-Romero, C.; Prat, C.; Esteves, M.

    2009-04-01

    The present study provides an analysis of the water flows in the mountainous volcanic watershed of Cointzio, Michoacan (Mexico). Daily precipitations and river flows data, gathered over the period 1940-2007, were analysed to estimate the dynamic of superficial waters and its change over years. Precipitation data pointed out the intensity of rains in this tropical region with 5% of the yearly precipitation occurring during a single day. It also reveals an unexpected feature with some extreme events occurring during the dry season. This obviously as some major consequences for the floods and sediment transport within the watershed. For the studied period, the precipitation (mean annual and extreme values) did not reveal any major change while the water flows increased significantly. This specific behaviour is examined in terms of land use change through the evolution of an aridity index over years and literature data. Predictions from a global climate change model for the decades centred in the years 2030, 2060 and 2090 indicate (in comparison to a normalized period of years 1961 to 1990) an increment in mean annual temperature of 1.6, 2.5 and 4.4 °C and a decrease in precipitation of 15.4, 19.1 and 27.7 %, respectively. The consequent increment of aridity leads to expect a reduction of the vegetation coverage and an increment of the runoff with erosive effects.

  3. 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

  4. Rheological evolution of planetary basalts during cooling and crystallization

    NASA Astrophysics Data System (ADS)

    Sehlke, Alexander

    Basaltic lavas cover large portions of the surface of the Earth and other planets and moons. Planetary basalts are compositionally different from terrestrial basalts, and show a variety of unique large-scale lava flow morphologies unobserved on Earth. They are usually assumed to be much more fluid than basalts on Earth, such as Hawaiian basalt, but their rheology is largely unknown. I synthesized several synthetic silicate melts representing igneous rock compositions of Mars, Mercury, the Moon, Io and Vesta. I measured their viscosity, as well as several terrestrial lavas including Hawaiian basalt, by concentric cylinder and parallel plate viscometry. Planetary melts cover a wide range of viscosity at their liquidus, overlapping with terrestrial basaltic melts. I derived a new viscosity model that is based on the Adam-Gibbs theory of structural relaxation, predicting these viscosities much more accurately than previously published viscosity models. During crystallization, the rheological behavior changes from Newtonian to pseudoplastic. Combining rheology experiments with field observations, the rheological conditions of the pahoehoe to `a`a morphological transition for Hawaiian basalt were determined in strain rate-viscosity space. This transition occurs at temperatures around 1185+/-15°C. For Mercurian lavas, this transition is predicted to occur at higher temperatures around 1250+/-30°C. We find that the rheology of these lavas is broadly similar to terrestrial ones, suggesting that the large smooth volcanic plains observed on Mercury's northern hemisphere are due to flood basalt volcanism rather than unusually fluid lavas. We also show that KREEP lavas, a type of basalt associated with sinuous rilles on the lunar surface, is more likely to form rilles through levee construction, as the high and rapidly increasing viscosity prohibits sufficient thermo-mechanical erosion.

  5. 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

  6. Combined U/Pb and (U-Th)/He geochronometry of basalt maars in Western Carpathians: implications for age of intraplate volcanism and origin of zircon metasomatism

    NASA Astrophysics Data System (ADS)

    Hurai, Vratislav; Danišík, Martin; Huraiová, Monika; Paquette, Jean-Louis; Ádám, Alexander

    2013-10-01

    The age of intraplate volcanism in northern Pannonian Basin of Carpathians is revisited using a combination of zircon U/Pb, zircon (U-Th)/He and apatite (U-Th)/He dating techniques, complemented by electron microprobe (EMP) characterisation of dated minerals. A total of six maar structures and diatremes in the South-Slovakian Volcanic Field (SSVF) were dated and the obtained new ages yielded the following key findings: Two isolated maars in SE part indirectly dated by geomorphologic constraints to Late Pleistocene are actually of Pliocene (2.8 ± 0.2 Ma) and Late Miocene (5.5 ± 0.6 Ma) ages. In contrast, two maars in NW part of the study area are of Late Pliocene age (4.1 ± 0.4 and 5.2-5.4 Ma), younger than the Late Miocene age (~6.5 Ma) inferred previously from K/Ar data on the proximal basaltic lava flows. These maars therefore belong to the second volcanic phase that was previously identified only in SE part of the SSVF. In the light of the new geochronologic data, it seems likely that the Pliocene phreatomagmatic eruptions may have occurred along extension-related, NW- and NE-trending orthogonal faults. EMP analyses and imaging revealed an extensive syn- and post-growth metasomatic replacement by dissolution-reprecipitation in the majority of zircons. Abundant silicate melt inclusions in porous metasomatised parts of the zircons are diagnostic of magmatic rather than hydrothermal metasomatism. Consistent ages of the metasomatised and non-metasomatised zones do not indicate disturbance of the U-Pb system during the metasomatism. Enrichment in U and Th loss in the metasomatised zircons are diagnostic of an increasing oxygen fugacity triggered by degassing of the volatile residual melt during the final stages of alkali basalt fractionation. Rare zircon-to-baddeleyite transformation was probably connected with lowered silica activity in carbonated basaltic magmas in south-eastern part of the study area.

  7. 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

  8. 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.; Poland, Michael P.; Takahashi, T. Jane; Landowski, Claire M.

    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.

  9. 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.

  10. 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.

  11. Flooding

    MedlinePlus

    ... flooding Prepare for flooding For communities, companies, or water and wastewater facilities: Suggested activities to help facilities ... con monóxido de carbono. Limit contact with flood water. Flood water may have high levels of raw ...

  12. 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

  13. 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.

  14. Across-arc variations of isotope and trace element compositions from Quaternary basaltic volcanic rocks in northeastern Japan: Implications for interaction between subducted oceanic slab and mantle wedge

    NASA Astrophysics Data System (ADS)

    Shibata, Tomoyuki; Nakamura, Eizo

    1997-04-01

    Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for Quaternary island arc basaltic rocks from northeastern Japan. Sr and Pb isotopic ratios decrease, and Nd isotopic ratios increase from the volcanic front toward the back arc. The isotopic compositions nearest the back arc side are nearly identical to those of mid-ocean ridge basalt (MORB). The high field strength elements and heavy rare earth elements show homogeneous and MORB-like characteristics. These observations indicate that the mantle wedge beneath northeastern Japan originally had a MORB-type mantle composition that was homogeneous across the arc. Pb isotope compositions show a mixing relationship between mantle wedge and oceanic sediments reflecting the introduction of subduction component into the mantle wedge, Across-arc isotopic variations were caused by interaction between MORB-type mantle wedge and the subducting slab, and the amount of subduction component correlates with the depth to the slab. The isotopic compositions of subduction component are expressed by bulk mixing of 15 wt % of oceanic sediment and 85 wt % of altered MORB. Inversion analyses of isotopic compositions using two-component mixing relationships show that the Sr/Nd and Pb/Nd ratios in subduction component decrease with increasing depth to the slab, while the Sr/Pb ratio is nearly constant. These changes can be explained only by a preferential discharge of the elements into the wedge mantle associated with continuous dehydration of the subducting slab. The present study further demonstrates that a very wide range of isotopic and elemental compositions in island arc magmas is a consequence of the interaction between subducting slab and mantle wedge without the involvement of an oceanic island basalts component, and the slab can carry water and supply a subduction component as a fluid to the overlying mantle wedge to depths exceeding 150 km.

  15. 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.

  16. 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.

  17. 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

  18. Application of two-phase flow models along vertical pipes for the description of basaltic explosive volcanic activity

    NASA Astrophysics Data System (ADS)

    Pioli, L.; Cashman, K. V.

    2006-12-01

    Gas segregation and two-phase flow processes play a fundamental role in the explosive dynamics of basaltic magma. For example, Strombolian activity, consisting of intermittent explosions occurring at a few seconds to several minutes time intervals, has segregation and formation of large, conduit-size bubbles rising through the magma column and bursting at the surface (Blackburn et al., 1976). The ability of gas bubbles to rise separately from the magma is attributed to coalescence phenomena within the conduit at low magma rise speed, or partial to total collapse of a magma foam layer at the top of the magma chamber (Parfitt, 2004). However, basaltic explosive activity includes a wider spectrum of phenomena ranging from rather continuous lava fountaining with fallout of molten lava clots around the vent (Hawaiian activity), to higher explosivity events, forming plumes up to several km high (Violent Strombolian to Subplinian and Plinian activities) and characterized by more efficient magma fragmentation. Transitional activity, characterized by intermittent to contemporaneous effusive and explosive activity, several seconds to hours-scale fluctuations of the explosion intensity, with formation of both lava fountains and weak, ash-laden plumes, is also common in hydrous basalts. We suggest that not only Hawaiian and Strombolian end members, but also the whole spectrum of basaltic explosive activity could be explained by distinct two phase flow patterns within the conduit; but several unsolved questions point out our limited comprehension of the explosive dynamics affecting low viscosity basaltic magma: What is the role of conduit processes in eruptive dynamics? How are the vertical and lateral variations of flow properties within the conduit recorded in pyroclast textures? What is the role of degassing induced crystallization on the explosive dynamics? We address these topics using both field and textural evidence, and explore the different explosive categories and

  19. Tectonic significance of basalts of the Middle Run Formation (Upper Proterozoic) of the East Continent Rift Basin, Indiana and Kentucky

    SciTech Connect

    Walker, D. . Kentucky Geological Survey); Misra, K.C. . Dept. of Geological Sciences)

    1992-01-01

    Thirty-five samples of mafic rock recovered from three basement wells in Lawrence Co., Ind., Campbell Co., Ky., and Jessamine Co., Ky, were analyzed for major, minor, and trace-element composition by XRF and single-acid extraction ICP in a commercial laboratory. Petrographic examination indicates that these mafic rocks are, in part, amygdaloidal basalts, and therefore represent some portion of a Late Proterozoic mafic volcanic center that existed in the East Continent Rift Basin (ECRB). These samples possess systematic trends in the distribution of many trace elements, indicating the original compositions have been preserved. This suggests that these basalts possess their original concentrations of the majority of the large ion lithophile (LIL) elements. The concentrations of the LIL elements in the Middle Run basalts indicate that the Middle run basalts can best be characterized as being continental flood basalts. Comparison with published data from the Keweenanwan basalts of the North Shore Volcanic Group, exposed along the Lake Superior portion of the Midcontinent Rift, indicates that the Middle Run basalts are similar to the more evolved basalts of that suite. However, primitive MORB-like compositions that are present in the North Shore Group are apparently absent in the basalts of the ECRB. This may suggest that the Lake Superior segment of the Midcontinent Rift underwent a greater degree of crustal extension than the Middle Run basin. Alternatively, the basalts associated with the Middle Run Formation may represent magmatic activity early in the rift evolution.

  20. 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

  1. 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

  2. Subduction zone mantle enrichment by fluids and Zr-Hf-depleted crustal melts as indicated by backarc basalts of the Southern Volcanic Zone, Argentina

    NASA Astrophysics Data System (ADS)

    Holm, Paul M.; Søager, Nina; Alfastsen, Mads; Bertotto, Gustavo W.

    2016-10-01

    We aim to identify the components metasomatizing the mantle above the subducting Nazca plate under part of the Andean Southern Volcanic Zone (SVZ). We present new major and ICP-MS trace element and Sr, Nd and high-precision Pb isotope analyses of primitive olivine-phyric alkali basalts from the Northern Segment Volcanic Field, part of the Payenia province in the backarc of the Transitional SVZ. One new 40Ar-39Ar age determination confirms the Late Pleistocene age of this most northerly part of the province. All analysed rocks have typical subduction zone type incompatible element enrichment, and the rocks of the Northern Segment, together with the neighbouring Nevado Volcanic Field, have isotopic compositions intermediate between adjacent Transitional SVZ arc rocks and southern Payenia OIB-type basaltic rocks. Modelling the Ba-Th-Sm variation we demonstrate that fluids as well as 1-2% melts of upper continental crust (UCC) enriched their mantle sources, and La-Nb-Sm variations additionally indicate that the pre-metasomatic sources ranged from strongly depleted to undepleted mantle. Low Eu/Eu* and Sr/Nd also show evidence for a UCC component in the source. The contribution of Chile Trench sediments to the magmas seems insignificant. The Zr/Sm and Hf/Sm ratios are relatively low in many of the Northern Segment rocks, ranging down to 17 and 0.45, respectively, which, together with relatively high Th/U, is argued to indicate that the metasomatizing crustal melts were derived by partial melting of subducted UCC that had residual zircon, in contrast to the UCC melts added to Transitional SVZ arc magmas. Mixing between depleted and undepleted mantle, enriched by UCC and fluids, is suggested by Sr, Nd and Pb isotopes of the Northern Segment and Nevado magmas. The metasomatized undepleted mantle south of the Northern Segment is suggested to be part of upwelling OIB-type mantle, whereas the pre-metasomatically depleted mantle also can be found as a component in some arc

  3. 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.

  4. 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

    2017-03-01

    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.

  5. 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.

  6. The mode of emplacement of Neogene flood basalts in Eastern Iceland: The plagioclase ultraphyric basalts in the Grænavatn group

    NASA Astrophysics Data System (ADS)

    V. Óskarsson, Birgir; B. Andersen, Christina; S. Riishuus, Morten; Sørensen, Erik Vest; Tegner, Christian

    2017-02-01

    Plagioclase ultraphyric basalt lava with high fraction of solids have a mode of emplacement that is poorly understood. In this study we conduct detailed mapping of a PUB group in eastern Iceland, namely the Grænavatn group, and assess the group architecture, flow morphology and internal structure with additional constraints from petrography, petrology and crystal size distribution, to derive information on emplacement dynamics of plagioclase ultraphyric basalts. We also derive information on the plumbing system of the group with reference to the source of the macrocysts. The group is exposed in steep glacially carved fjords and can be traced for more than 70 km along strike. The flows have mixed architecture of simple and compound flows. Individual flow lobes have thicknesses in the range of 1-24 m and many reach widths and lengths exceeding 1000 m. The flows vary from rubbly to slabby pahoehoe, but are predominantly of pahoehoe type. The aspect ratio of the group and the nature of the flows indicate fissure-fed eruptions. The plagioclase macrocrysts (5-30 mm) are An-rich, exhibit bimodal size distribution and the modal proportions within the group varies from 15-40%. Clinopyroxene macrocrysts are also present ranging from 1-6%. The lowermost flow is thickest and carries the greatest crystal cargo load. The morphology of the lava flows suggests low viscous behavior, at odds with the high crystal content. The very calcic plagioclase macrocrysts (An80-85) are in disequilibrium with the groundmass and plagioclase microlaths therein (An50-70), meaning that the crystal-laden magmas quickly ascended from deeper crustal levels to the surface. The flows with highest crystal content may have maintained high temperatures by heat exchange with the primitive macrocrysts in the flows and developed non-Newtonian behavior such as shear thinning. Such conditions would have enabled the flows to advance rapidly during episodes with high effusion rates forming the simple flows, and

  7. 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

  8. 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

  9. Initiation and Impact of Siberian Traps Volcanism

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    tuffs are virtually absent along a 125 km long transect along the Dyupkun lake, even though tuff is shown on available geological maps. The cross section represents about 1000 meters of lava stratigraphy measured from the base of the flood basalts. 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). The new results questions the notion of province-scale explosive volcanism in Siberia during the onset of flood volcanism, its continuation up into the stratigraphy as many maps suggest, and stress that local eruptive centers dominated, likely triggered by the presence of surface water.

  10. 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

    2012-06-14

    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.

  11. 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

  12. Chemostratigraphic evidence of Deccan volcanism from the marine osmium isotope record.

    PubMed

    Ravizza, G; Peucker-Ehrenbrink, B

    2003-11-21

    Continental flood basalt (CFB) volcanism is hypothesized to have played a causative role in global climate change and mass extinctions. Uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of CFB volcanism. Our results document a 25% decline in the marine 187Os/188Os record that predates the Cretaceous-Tertiary boundary (KTB) and coincides with late Maastrichtian warming. We argue that this decline provides a chemostratigraphic marker of Deccan volcanism and thus constitutes compelling evidence that the main environmental consequence of Deccan volcanism was a transient global warming event of 3 degrees to 5 degrees C that is fully resolved from the KTB mass extinction.

  13. 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.

  14. From olivine nephelinite, basanite and basalt to peralkaline trachyphonolite and comendite in the Ankaratra volcanic complex, Madagascar: 40Ar/39Ar ages, phase compositions and bulk-rock geochemical and isotopic evolution

    NASA Astrophysics Data System (ADS)

    Cucciniello, Ciro; Melluso, Leone; le Roex, Anton P.; Jourdan, Fred; Morra, Vincenzo; de'Gennaro, Roberto; Grifa, Celestino

    2017-03-01

    The Ankaratra volcanic field covers an area of 3800 km2 in central Madagascar and comprises of lava flows, lava domes, scoria cones, tuff rings and maars emplaced at different ages (Miocene to Recent). The volcanic products include ultramafic-mafic (olivine-leucite nephelinite, basanite, alkali basalt, hawaiite and tholeiitic basalt), intermediate (mugearite and benmoreite) and felsic rocks (trachyphonolite, quartz trachyte and rhyolite), the latter often peralkaline. The 40Ar/39Ar determinations for mafic lavas yield ages of 17.45 ± 0.12 Ma, 16.63 ± 0.08 Ma and 8.62 ± 0.09 Ma, indicating a prolonged magmatic activity. The mineralogical and geochemical variations suggest that the magmatic evolution of the alkali basalt-hawaiite-mugearite-benmoreite-trachyte series can be accounted for by removal of olivine, feldspars, clinopyroxene, Fe-Ti oxides and accessory phases, producing residual trachytic and trachyphonolitic compositions mineralogically very similar to those of other volcanic areas and tectonic settings. The Ankaratra olivine leucite nephelinites, basanites and tholeiitic basalts do not seem to be associated with significant amounts of evolved comagmatic rocks. The 87Sr/86Sr (0.70504-0.71012), 143Nd/144Nd (0.51259-0.51244) and 206Pb/204Pb (17.705-18.563) isotopic ratios of trachytes and comendite are consistent with open-system processes. However, other trachyphonolites have 143Nd/144Nd (0.51280), 206Pb/204Pb (18.648), 207Pb/204Pb (15.582) and 208Pb/204Pb (38.795) similar to those of mafic rocks, suggesting differentiation processes without appreciable interaction with crustal materials. The Ankaratra volcanism is to be directly linked to a broadly E-W-trending intracontinental extension. A large-scale thermal anomaly, associated with an anomalously hot source region, is not required to explain the Cenozoic magmatism of Madagascar.

  15. 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,

  16. 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.

  17. 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.

  18. 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

  19. The effects of scale and spatial heterogeneities on diffusion in volcanic breccias and basalts: Amchitka Island, Alaska.

    PubMed

    Benning, Jennifer L; Barnes, David L

    2009-05-12

    Knowledge of the factors that influence the diffusion of contaminants, such as the diffusivity and the connected porosity, is crucial to modeling the long-term fate and transport of contaminants in subsurface systems with small or negligible advective flow, such as in fractured crystalline rock. Fractured rock is naturally heterogeneous, and hence, understanding the diffusivity of a molecule through this material (or the formation factor of the medium) becomes a complex problem, with critical concerns about the scale of laboratory measurements and about the spatial variability of these measurements relative to the scale needed for fate and transport modeling. This study employed both electrical and tracer-based laboratory methods to investigate the effects of scale and pore system connectivity on the diffusivity for volcanic matrix rock derived from the study site, a former underground nuclear test site at Amchitka Island, Alaska. The results of these investigations indicate a relatively well-connected pore system with scale effects generally limited to approximately 6 cm lengths and well-correlated to observed heterogeneous features. An important conclusion resulting from this study, however, is that there is a potential for the estimated diffusivity to be misrepresented by an order of magnitude if multiple samples or longer sample lengths are not used. Given the relatively large number of measurements resulting from these investigations, an analysis of the probability density function (PDF) of the diffusivity was possible. The PDF of the diffusivity was shown to generally follow a normal distribution for individual geologic layers. However, when all of the geologic layers are considered together, the distribution of the subsurface as a whole was shown to follow a lognormal distribution due to the order of magnitude differences amongst the layers. An understanding of these distributions is essential for future stochastic modeling efforts.

  20. Constraining the Early Isotopic and Trace Element Signature of the Yellowstone Mantle Plume: Evidence from Imnaha Basalts

    NASA Astrophysics Data System (ADS)

    Patterson, J. D.; Ramos, F. C.; Wolff, J. A.

    2007-12-01

    Characterizing the geochemical signatures of plumes is critical for evaluating the petrogenetic evolution of plume- related volcanic rocks. The main phase of Columbia River flood basalt activity (16.6 - 15.5 Ma), considered to represent the first clear manifestation of the Yellowstone hotspot on the North American continent, includes the Steens Mountain, Imnaha, Grande Ronde and Picture Gorge basalts. Isotopic and trace element covariations defined by Grande Ronde, Steens Mountains, and Picture Gorge basalts diverge radially from the field of Imnaha basalts, which retain signatures that most closely reflect the 'undiluted' geochemical characteristics of the Yellowstone mantle plume. Sr, Nd, Pb isotope ratios and incompatible trace element abundances and ratios of Imnaha basalts closely resemble those of some Pacific EM II OIB groups. Nonetheless, the compositions of some Imnaha lavas reflect mixing of the plume with different mantle types. Others have clearly been affected by interaction of plume-derived basalt with continental crust, although the latter process is much more significant in the genesis of the succeeding Grande Ronde basalts. We will review the geochemical characteristics of the Yellowstone plume as recorded in the Imnaha basalt in the context of later-erupted volcanic products of the Columbia - Snake - Yellowstone system, and Pacific mantle plumes more generally.

  1. Paleomagnetic directional groups and paleointensity from the flood basalt in the Tarim large igneous province: implications for eruption frequency

    NASA Astrophysics Data System (ADS)

    Usui, Yoichi; Tian, Wei

    2017-01-01

    We present paleomagnetic secular variation and paleointensity from the Early Permian Tarim large igneous province, NW China. The studied sections comprise a total of 400 m of basaltic flows. Paleomagnetic directions were determined for 11 flows. Four successive flows with a cumulative thickness of 150 m showed a statistically identical paleomagnetic direction. Assuming a paleosecular variation speed similar to that of the present day, the 150-m-thick basalt was estimated to have erupted within the past few centuries. Paleointensity experiments were performed on both whole-rock and single plagioclase samples. Although alterations during the experiment and/or weak remanence degraded the data quality, the flows with the same paleomagnetic direction revealed similar paleointensity estimates, supporting the hypothesis that the eruption of these flows was rapid. More generally, flows from the Lower Kupukuziman Formation seem to record lower paleointensity compared to flows from the overlying Kaipaizileike Formation. [Figure not available: see fulltext. Caption: Left the extent of the Tarim large igneous province. Center in-situ paleomagnetic directions obtained from the Tarim large igneous province. Subashi and Yingan represents directions reported in a previous research. Right tilt-corrected paleomagnetic directions. Tight clustering of the direction indicate fast eruption relative to the paleomagnetic secular variation (PSV) speed.

  2. 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

  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. Io volcanism

    SciTech Connect

    Carr, M.H.

    1985-01-01

    Io is the most volcanically active body in the Solar System. The Voyage spacecraft observed nine active eruption plumes in 1979, and detected numerous thermal anomalies. Loki the most active volcanic region has been emitting 1.5 x 10/sup 13/ W over the last few years. Many of the volcanic features have been interpreted as the result of sulfur volcanism because 1) the spectral reflectance of the surface resembles sulfur, 2) SO/sub 2/ has been positively identified, 3) the satellite leaves a trail of sulfur atoms in its wake; and 4) many of the hot spots have surfaces temperatures less than 400/sup 0/K, compatible with low-temperature melts. The evidence for sulfur has led to suggestions of sulfur lava flows hundreds of kilometers long, and sulfur lava lakes as large as Lake Erie. The observations are, however, equally compatible with basaltic volcanism. Modeling of the cooling of basaltic lava flows indicates that regions of basaltic volcanism on Io should have temperatures similar to those detected by the Voyager spacecraft. High eruption rates are required. High rates of fumarolic activity accompanying the eruptions and expulsion of volatiles by the plumes give the surface its sulfur-like spectral reflectance.

  6. Volcanism, impact and mass extinctions: incredible or credible coincidences?

    NASA Astrophysics Data System (ADS)

    White, Rosalind V.; Saunders, Andrew D.

    2005-02-01

    Massive continental volcanism and/or bolide impacts are considered by many authors to have caused three major mass extinction events during the last 300 million years: the end-Permian, end-Cretaceous and end-Triassic extinctions. However, re-evaluation of the frequency of bolide impacts and plume-related flood basalt provinces indicates that both types of event occur much more frequently than mass extinctions, and so, in isolation, may not be responsible for the largest extinctions. Furthermore, the kill mechanisms associated with either flood basalts or impacts do not appear to be sufficiently powerful to cause worldwide collapse of ecosystems leading to the largest mass extinctions. Contemporaneous flood basalts and bolide impact may be prerequisites for the largest mass extinctions. We present a statistical analysis of the probability of coincidence between volcanism and impact, and show that three random coincidences of these events in the last 300 m.y. are likely. No causal relationship between impact and volcanism is necessary. The lesser mass extinctions, on the other hand, may not require juxtaposition of two such catastrophic events; such coincidences occurring on more than three occasions during the last 300 m.y. become increasingly unlikely.

  7. Pressure conditions for the solidification of the Skaergaard intrusion: Eruption of East Greenland flood basalts in less than 300,000 years

    NASA Astrophysics Data System (ADS)

    Larsen, Rune B.; Tegner, Christian

    2006-11-01

    Primary granophyres are differentiated from olivine tholeiitic magma and occur interstitially throughout the cumulus stratigraphy of the Skaergaard intrusion, East Greenland. Samples from the Lower Zones a-c (LZa-c), the Middle Zone (MZ) and the Sandwich Horizon (SH) are included in the present study together with granophyric accumulations in gabbroic pegmatite from LZa-c. Fluid inclusions in quartz and the mineral assemblage in the granophyres record the pressure under which the Skaergaard intrusion crystallised. Pegmatitic granophyre from LZa-c consists mainly of quartz, plagioclase (An 4-7) and alkali feldspar (Or 40-80) enclosing an earlier formed assemblage of ferrohastingsitic and ferroedenitic hornblende, fayalite (Fo 4-5), titanite, biotite and fluor-apatite. Granophyric quartz, albite and alkali feldspar crystallised from water-saturated granitic melts near eutectic minimum conditions between 680 and 660 °C. The pressure of granophyre crystallisation was modelled by the intercept between fluid inclusion isochores and the minimum melt solidus for granitic compositions. Pressures, recalculated to the roof pendant of the intrusion, are 0.7 ± 0.5 for LZa, 2.0 ± 0.2 for LZb-c, 2.3 ± 0.8 for MZ (the Triple Group level) and 3.3 ± 1.3 kb for SH. Amphibole geobarometry, independently, confirm the pressure estimates for pegmatitic granophyres in LZa-c. The granophyres formed as the intrusion cooled through the minimum melt solidus in LZa, LZb, LZc, MZ and SH, respectively. The pressure increase from LZa to SH granophyres is explained by progressive burial during cooling of the intrusion and contemporaneous outpouring of 5.3-6.3 ± 2.7 km of flood basalts during the initial opening of the Northeast Atlantic Ocean. Accordingly, the Skaergaard intrusion evolved from a subvolcanic magma chamber at emplacement to a more deep-seated igneous system during terminal crystallization when the majority of the intercumulus phases formed. The present cooling history suggests

  8. 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

  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. 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

  11. 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.; 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.

  12. 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

  13. 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

  14. 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.

  15. 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.

  16. Floods

    MedlinePlus

    ... quickly, often have a dangerous wall of roaring water. The wall carries rocks, mud, and rubble and can sweep away most things in its path. Be aware of flood hazards no matter where you live, but especially if you live in a low-lying area, near water or downstream from a dam. Although there are ...

  17. Diverse mid-Miocene silicic volcanism associated with the Yellowstone Newberry thermal anomaly

    NASA Astrophysics Data System (ADS)

    Brueseke, Matthew E.; Hart, William K.; Heizler, Matthew T.

    2008-01-01

    The Santa Rosa Calico volcanic field (SC) of northern Nevada is a complex, multi-vent mid-Miocene eruptive complex that formed in response to regional lithospheric extension and flood basalt volcanism. Santa Rosa Calico volcanism initiated at ˜16.7 Ma, concurrent with regional Steens Columbia River flood basalt activity and is characterized by a complete compositional spectrum of basalt through high-silica rhyolite. To better understand the relationships between upwelling mafic magmatism, coeval extension, and magmatic system development on the Oregon Plateau we have conducted the first comprehensive study of Santa Rosa Calico silicic volcanism. Detailed stratigraphic-based field sampling and mapping illustrate that silicic activity in this volcanic field was primarily focused along its eastern and western margins. At least five texturally distinct silicic units are found in the western Santa Rosa Calico volcanic field, including abundant lava flows, near vent deposits, and shallow intrusive bodies. Similar physical features are found in the eastern portion of the volcanic field where four physically distinct units are present. The western and eastern Santa Rosa Calico units are characterized by abundant macro- and microscopic disequilibrium textures, reflecting a complex petrogenetic history. Additionally, unlike other mid-Miocene Oregon Plateau volcanic fields (e.g. McDermitt), the Santa Rosa Calico volcanic field is characterized by a paucity of caldera-forming volcanism. Only the Cold Springs tuff, which crops out across the central portion of the volcanic field, was caldera-derived. Major and trace element geochemical variations are present within and between eastern and western Santa Rosa Calico silicic units and these chemical differences, coupled with the observed disequilibrium textures, illustrate the action of open-system petrogenetic processes and melt derivation from heterogeneous source materials. The processes and styles of Santa Rosa Calico silicic

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. Nature and composition of interbedded marine basaltic pumice in the ˜52-50 Ma Vastan lignite sequence, western India: Implication for Early Eocene MORB volcanism offshore Arabian Sea

    NASA Astrophysics Data System (ADS)

    Sensarma, Sarajit; Singh, Hukam; Rana, R. S.; Paul, Debajyoti; Sahni, Ashok

    2017-03-01

    The recognition of pyroclasts preserved in sedimentary environments far from its source is uncommon. We here describe occurrences of several centimetres-thick discontinuous basaltic pumice lenses occurring within the Early Eocene Vastan lignite mine sedimentary sequence, western India at two different levels - one at ˜5 m and the other at 10 m above a biostratigraphically constrained 52 Ma old marker level postdating the Deccan Volcanism. These sections have received global attention as they record mammalian and plant radiations. We infer the repetitive occurrence of pumice have been sourced from a ˜52-50 Ma MORB related to sea-floor spreading in the western Arabian Sea, most plausibly along the Carlsberg Ridge. Pyroclasts have skeletal plagioclase with horsetail morphologies ± pyroxene ± Fe-Ti oxide euhedral crystals, and typically comprise of circular polymodal (radii ≤10 to ≥30 μm), non-coalescing microvesicles (>40-60%). The pumice have undergone considerable syngenetic alteration during oceanic transport and post-burial digenesis, and are a composite mixture of Fe-Mn-rich clay and hydrated altered basaltic glass (palagonite). The Fe-Mn-rich clay is extremely low in SiO 2, Al 2 O 3, TiO 2, MgO, alkalies and REE, but very high in Fe 2 O 3, MnO, P, Ba, Sr contents, and palagonitization involved significant loss of SiO 2, Al 2 O 3, MgO and variable gain in Fe 2 O 3, TiO 2, Ni, V, Zr, Zn and REE. Bubble initiation to growth in the ascending basaltic magma (liquidus ˜1200-1250 ∘C) may have occured in ˜3 hr. Short-distance transport, non-connected vesicles, deposition in inner shelf to more confined lagoonal condition in the Early Eocene and quick burial helped preservation of the pumice in Vastan. Early Eocene Arabian Sea volcanism thus might have been an additional source to marginal sediments along the passive margin of western India.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Glassy orthopyroxene granodiorites of the Pannonian Basin: tracers of ultra-high-temperature deep-crustal anatexis triggered by Tertiary basaltic volcanism

    NASA Astrophysics Data System (ADS)

    Huraiová, Monika; Dubessy, Jean; Konečný, Patrik; Simon, Klaus; Král', Ján; Zielinski, Grzegorz; Lipka, Jozef; Hurai, Vratislav

    2005-01-01

    Glassy orthopyroxene granodiorite-tonalite (named pincinite after type locality) was described from basaltic lapilli tuffs of the Pliocene maar near Pinciná village in the Slovakian part of the Pannonian Basin. Two pincinite types exhibit a qualitatively similar mineral composition (quartz, An20 55 plagioclase, intergranular silicic glass with orthopyroxene and ilmenite, ±K-feldspar), but strongly different redox potential and formation PT conditions. Peraluminous pincinite is reduced (6 7% of total iron as Fe3+ in corundum-normative intergranular dacitic glass) and contains ilmenite with 8 10 mol% Fe2O3 and orthopyroxene dominated by ferrosilite. High-density (up to 0.85 g/cm3) primary CO2 inclusions with minor H2, CH4, H2S, CO and N2 (<2 mol% total) are present in Qtz and Plg. Equilibrium PT conditions inferred from the intergranular Opx Ilm Glass assemblage and fluid density correspond to 1,170±50°C, 5.6±0.4 kbar, respectively. Metaluminous pincinite is more oxidised (25 27% of total iron as Fe3+ in diopside-normative intergranular glass of rhyolite trachyte dacite composition) and contains Fe2O3-rich ilmenite (17 29 mol%) associated with enstatite. Fluid inclusions are composed of CO2 H2O mixtures with up to 38 mol% H2O. Raman spectroscopy revealed H2S along with dominant CO2 in the carbonic phase. Equilibrium PT parameters for the intergranular Opx Ilm Glass assemblage correspond to 740±15°C, 2.8±0.1 kbar, respectively. Reducing gas species (<2 mol% total) in the CO2-inclusions of the peraluminous pincinite resulted from hydrogen diffusion due to fH2 gradient imposed during decrease of redox potential from the log fO2 values near QFM during Qtz

  11. 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

  12. 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

  13. Icelandic Analogs for Volcanic and Fluvial Processes on Mars

    NASA Astrophysics Data System (ADS)

    McEwen, A.; Burr, D.; Hardardottir, J.; Hoskuldsson, A.; Keszthelyi, L.; Lanagan, P.; Snorrason, A.; Thordarson, T.

    2001-12-01

    Iceland has proven to be an excellent location to study a wide range of Martian geologic analogs. Among these are basaltic volcanism and aqueous flooding--key geologic processes that have shaped the Martian surface and that remain active in Iceland. On both Mars and Iceland, volcanic units are interfingered in space and time with fluvial units. Well-preserved flood lavas in SE Elysium Planitia, Amazonis Planitia, and portions of the Tharsis rise are dominated by a distinctive morphology of plates and ridges, very similar to the "apalhraun" or "rubbly pahoehoe" of Iceland (Keszthelyi and Thordarson, 2000, GSA Abstract 52593). On both Iceland and Mars there are marginal regions of undisrupted inflated pahoehoe, small rootless cones, and long parallel structures in the wake of topographic obstacles. The Icelandic paleoflood channels of Jokulsa a Fjollum, extending from the Vatnajokull ice cap to the north coast, have eroded basaltic plains and provide many insights into morphologies seen on Mars. The manner in which different types of lava erode in a catastrophic flood is well illustrated and sometimes surprising. For example, there are channel floors where the crusts of inflated lavas have been completely stripped off by the floodwater, but then suddenly transitions upstream into a stretch with almost no erosion--even the cm-scale pahoehoe ropes are intact. This implies that significant aqueous floods could have occurred over some well-preserved lava flows on Mars. A streamlined "island" or mesa extending downstream from the volcanic crater Hrossaborg in Iceland appears to be mixture of remobilized older glacial deposits and a debris flow deposit. The debris flow apparently formed by collapse of the western outer crater slopes into the active floodwaters, diverting the flow northward; this process may have occurred on Mars at some of the impact craters eroded by outflow channels.

  14. 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.

  15. Basaltic fissure eruptions, plume heights, and atmospheric aerosols

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.; Wolff, J. A.; Self, S.; Rampino, M. R.

    1986-01-01

    Convective plumes that rise above Hawaiian-style fire fountains consist of volcanic gases, aerosols, fine ash, and entrained heated air. Plume theory has been applied to observational estimates of the rate of thermal energy release from large fire fountains. The theoretically predicted heights of maintained plumes agree very well with the heights found from actual observations. Predicted plume heights for both central-vent (point-source) and fissure (line-source) eruptions indicate a stratospheric penetration by plumes that form over vents with very high magma-production rates. Flood basalt fissure eruptions that produce individual lava flows with volumes greater than 100 cu km at very high mass eruption rates are capable of injecting large quantities of sulfate aerosols into the lower stratosphere, with potentially drastic short-term atmospheric consequences, like acid precipitation, darkening of the sky, and climatic cooling.

  16. 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.

  17. 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).

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. The 2007 and 2014 eruptions of Stromboli at match: monitoring the potential occurrence of effusion-driven basaltic paroxysmal explosions from a volcanic CO2 flux perspective

    NASA Astrophysics Data System (ADS)

    Liuzzo, Marco; Aiuppa, Alessandro; Salerno, Giuseppe; Burton, Mike; Federico, Cinzia; Caltabiano, Tommaso; Giudice, Gaetano; Giuffrida, Giovanni

    2015-04-01

    The recent effusive unrests of Stromboli occurred in 2002 and 2007 were both punctuated by short-lived, violent paroxysmal explosions generated from the volcano's summit craters. When effusive activity recently resumed on Stromboli, on 6 August 2014, much concern was raised therefore on whether or not a paroxysm would have occurred again. The occurrence of these potentially hazardous events has stimulated research toward understanding the mechanisms through which effusive eruptions can perturb the volcano's plumbing system, to eventually trigger a paroxysm. The anomalously large CO2 gas emissions measured prior to the 15 March 2007 paroxysmal explosion of Stromboli [1] have first demonstrated the chance to predict days in advance the effusive-to-explosive transition. Here 2007 and 2014 volcanic CO2 flux records have been compared for exploring causes/conditions that had not triggered any paroxysm event in the 2014 case. We show that the 2007 and 2014 datasets shared both similarities and remarkable differences. The pre-eruptive trends of CO2 and SO2 flux emissions were strikingly similar in both 2007 and 2014, indicating similar conditions within the plumbing system prior to onset of both effusive crises. In both events, the CO2 flux substantially accelerated (relative to the pre-eruptive mean flux) after onset of the effusion. However, this CO2 flux acceleration was a factor 3 lower in 2014 than in 2007, and the excess CO2 flux (the fraction of CO2 not associated with the shallowly emplaced/erupted magma, and therefore contributed by the deep magmatic system) never returned to the very high levels observed prior to the 15 March 2007 paroxysm. We conclude therefore that, although similar quantities of magma were effusively erupted in 2007 and 2014, the deep magmatic system was far less perturbed in the most recent case. We speculate that the rate at which the deep magmatic system is decompressed, rather than the level of de-compression itself, determine if the deep

  4. 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

  5. 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.

  6. 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

  7. Spectroscopic Analysis of Flooded Craters from Oceanus Procellarum

    NASA Astrophysics Data System (ADS)

    Besse, Sebastien; Staid, Matthew; Hiesinger, Harald

    2013-04-01

    The last major phases of lunar volcanism produced compositionally unique, high-titanium basalts that are not observed elsewhere on the Moon's surface or earlier in its history. These volcanic deposits include some of the Moon's most extensive flows and age estimates suggest that these basalts are among the youngest. These flows are concentrated in Oceanus Procellarum, a very large volcanic province on the lunar near side. Investigations using the Moon Mineralogy Mapper (M3) data have shown that these basalts exhibit strong mineralogical variations, with compositions strongly dominated by either high -Ca pyroxene, or low-Ca pyroxene, or olivine, and even a combination of these minerals. Following the surprising high olivine content of the crater Marius, we examine other flooded craters of the large Oceanus Procellarum (O.P.) province to characterize the uniquess, or not, of Marius. If a large number of flooded craters within O.P. exhibits similar high-olivine content, this will help us to constrain the magmatic history of the last major phases of lunar volcanism. The Moon Mineralogy Mapper (M3) onboard the Indian Space Research Organization's (ISRO) Chandrayaan-1 Spacecraft is an imaging spectrometer that imaged the Moon in 85 spectral channels with a combination of high spectral and spatial mapping, enabling spectra to be placed in a geological context. M3 data have a spectral range from 460 to 3000 nm, and a spectral resolution of 20 to 40 nm. This range allows detailed investigations of the 1 and 2 μm absorption bands characteristic of mafic minerals on the lunar surface. A selection of flooded craters has been performed to investigate their spectral properties. Craters with unbreached walls have been selected as much as possible in order to better constrain the origin of the volcanic flows. Preliminary results show that few craters share the high-olivine content properties of Marius. Compositionally, crater Billy seems to be the closest one, and to a certain

  8. Isotopic heterogeneity in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Wolff, J. A.; Ramos, F. C.; Tollstrup, D. L.

    2003-04-01

    The growing microsample database on volcanic rocks is showing that isotopic disequilibrium between and among phenocryst phases, their melt inclusions, and groundmass is the rule rather than the exception. This applies even in cases of little or no petrographic evidence for disequilibrium. Erupted magmas must therefore be regarded, to some extent, as mechanical mixtures of isotopically distinct components assembled from different sources. The preservation of isotopic disequilibrium requires that the assembly takes place before diffusion can eradicate evidence of disequilibrium. For a wide range of magmas (mafic, intermediate and felsic, silica under- and oversaturated) from different volcano types (flood basalts, monogenetic cones, stratocones, silicic calderas) this timescale ranges from thousands of years down to one year or less, with no consistent pattern of mixing-to-eruption time vs. volcano or magma type. Among many issues arising from these findings, we note that estimation of magmatic temperatures from application of equilibrium thermodynamics to phenocryst assemblages in volcanic rocks should be approached with extreme caution. The isotope ratio variations observed among the components of a single volcanic rock sample, in most cases, indicate interaction between magma and the local wall-rock. This is consistent with the view that the vast majority of magmas undergo modification during transport through and residence within the crust. Three physical origins of heterogeneity have been proposed: melting of wallrock, magmatic recharge, and mixing of components within a magma chamber initially segregated into melt-rich and crystal-rich portions. Time constraints on preservation of disequilibrium imply either a causal link with eruption, or that these processes occur through the lifetime of a chamber.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. On the Causes of Continental Intraplate Volcanism: An Example From the High Lava Plains of Eastern Oregon

    NASA Astrophysics Data System (ADS)

    Carlson, R. W.

    2008-12-01

    Fluid-fluxing at convergent margins, adiabatic ascent beneath extending crust, and thermo-chemically driven mantle upwelling are obvious causes of the mantle melting that leads to volcanism along convergent margins, ocean ridges, and intraplate hotspots, respectively. Each of these mechanisms has at one time or another been used to explain the cause of the widely dispersed late-Cenozoic volcanism of the High Lava Plains (HLP) of eastern Oregon. Covering an area of nearly 105 km3 east of the Cascade arc, the exposed HLP upper-crustal stratigraphy is dominated by volcanic rocks: evolved mafic calc-alkaline rocks older than 20 Ma, high-Fe differentiated flood basalts between 12-17 Ma, and scattered bimodal large volume siliceous and small-volume primitive basalt eruptions for the last 10 Ma. Post-17 Ma HLP volcanism shows only hints of the compositional signatures expected for convergent margin volcanism. Both the composition and the orthogonal to plate-motion propagation of HLP volcanism argue against the type of hotspot that may be responsible for Snake River Plain volcanism to the east. The HLP form the northern limit of the Basin and Range province, but most workers consider that extension in the HLP has been relatively limited, and hence unlikely to be driving the volcanism through lithospheric thinning. What process then explains the fact that the HLP is among the most volcanically active areas in western North America in the late-Cenozoic? This is the question at the heart of the on-going HLP project where a multitude of collaborators are combining volcanology, geochronology, geochemistry, experimental petrology, seismology, and geodynamic modeling investigations to better define the history and character of volcanism in the HLP, whether or not the volcanism can be connected to structures imaged in the upper mantle, and whether a common dynamic cause to the volcanism can be deciphered. Preliminary results highlight the complexities of mantle flow in a

  14. The Physical and Petrologic Evolution of a Multi-vent Volcanic Field Associated With Yellowstone-Newberry Volcanism

    NASA Astrophysics Data System (ADS)

    Brueseke, M. E.; Hart, W. K.

    2004-12-01

    The Santa Rosa-Calico volcanic field (SC) of northern Nevada is perhaps the most chemically and physically diverse of all volcanic fields associated with mid-Miocene northwestern USA volcanism. SC volcanism occurred from 16.5 to 14 Ma and was characterized by the eruption of a complete compositional spectrum from basalt through high-Si rhyolite. Locally derived tholeiitic lava flows and shallow intrusive bodies are chemically and isotopically identical to the Steens Basalt (87/86Sri=<0.7040), the Oregon Plateau-wide mid-Miocene flood basalt. Andesite-dacite lava flows are exposed as at least four geographically and chemically distinct packages representing products of multiple, discrete magmatic systems. The most voluminous of these is calc-alkaline and characterized by abundant granitoid and mafic xenoliths/xenocrysts and radiogenic Sr isotopic ratios. Subalkaline silicic lava flows, domes, and shallow intrusive bodies define three diffuse north-south trending zones. Textural, chemical, and isotopic variability within the silicic units is linked to their spatial and temporal distribution, again necessitating the existence of multiple magmatic systems. The youngest locally derived silicic units are ash flows exposed in the central portion of the SC that erupted in actively forming sedimentary basins at ˜15.4 Ma. Underlying the 400-1500m thick package of SC volcanic rocks are temporally ( ˜103 and ˜85 Ma), chemically, and isotopically (87/86Sr at 16 Ma= 0.7045 to 0.7058 and 0.7061 to >0.7070) heterogeneous granitoid plutons and a package of ˜20-23 Ma calc-alkaline, arc-related intermediate lava flows. The observed disequilibrium textures, xenoliths, and chemical/isotopic diversity suggests that upwelling Steens magma interacted with local crust, siliceous crustal melts, and the mafic plutonic roots of early Miocene arc volcanism in multiple magmatic systems characterized by heterogeneous open system processes. The formation of these systems is tectonically

  15. 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.

  16. 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.

  17. 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.

  18. Intermediate composition magma production in an intracontinental setting: Unusual andesites and dacites of the mid-Miocene Santa Rosa-Calico volcanic field, Northern Nevada

    NASA Astrophysics Data System (ADS)

    Brueseke, Matthew E.; Hart, William K.

    2009-11-01

    The mid-Miocene Santa Rosa-Calico volcanic field (SC) of northern Nevada provides an outstanding example of the role open-system magmatic processes play in producing calc-alkaline and tholeiitic andesite-dacite magmas in an intracontinental setting. SC volcanism commenced at ˜ 16.7 Ma and is associated with the initial manifestations of the Yellowstone hotspot, the Columbia River-Steens flood basalt event(s), and the formation of the Northern Nevada rift. Locally a diverse package of magmatic products ranging from tholeiitic basalt to high-Si rhyolite was produced during an ˜ 2 myr duration. Within this package are the products of at least four distinct intermediate composition magmatic systems that may represent as much as 40% of the SC volcanic pile. These help differentiate the SC from contemporaneous Oregon Plateau volcanic fields (e.g. McDermitt, Lake Owyhee, Northwest Nevada) that are dominated by bimodal basalt-rhyolite assemblages. All SC intermediate units are characterized by textural and mineralogic complexities including xenoliths and xenocrysts of local crust and crystal clots of plagioclase ± clinopyroxene ± orthopyroxene ± oxide. SC intermediate units are dominantly tholeiitic, but include lava flows with transitional to calc-alkaline affinities. Relative to locally erupted Steens Basalt, SC intermediate lava flows have similar elemental enrichments and depletions, but dissimilar Sr and Nd isotopic compositions. These isotopic differences, coupled with the abundant disequilibrium features and variable incompatible element ratios, indicate that open system magmatic processes played a major role in the genesis of the intermediate units. SC silicic magmas were produced primarily via upper crustal melting of chemically and isotopically heterogeneous Cretaceous granitoid. Interaction between fractionating mafic Steens flood basalt magmas and the more evolved crustal melts ± assimilation of local upper crust provides a general template for the

  19. 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

  20. Atmospheric outgassing and native-iron formation during carbonaceous sediment-basalt melt interactions

    NASA Astrophysics Data System (ADS)

    Pernet-Fisher, John F.; Day, James M. D.; Howarth, Geoffrey H.; Ryabov, Victor V.; Taylor, Lawrence A.

    2017-02-01

    Organic carbon-rich sediment assimilation by basaltic magmas leads to enhanced emission of greenhouse gases during continental flood basalt eruptions. A collateral effect of these interactions is the generation of low oxygen fugacities (fO2) (below the iron-wüstite [IW] buffer curve) during magmatic crystallization, resulting in the precipitation of native-iron. The occurrence of native-iron bearing terrestrial basaltic rocks are rare, having been identified at three locations: Siberia, West Greenland, and Central Germany. We report the first combined study of Re-Os isotopes, highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), and trace-element abundances for these three occurrences, in addition to host sediments at West Greenland. To quantify the amount of crustal assimilation experienced by the magmas, we present combined crystallization and assimilation models, together with fractional crystallization models, to assess how relative abundances of the HSE have been modified during crystallization. The radiogenic osmium isotopic compositions (γOsinitial +15 to +193) of mafic igneous samples are consistent with assimilation of old high Re/Os crustal contaminants with radiogenic 187Os/188Os, whereas the HSE inter-element fractionations (Pd/Os 2 to >10,000) suggest that some Siberian samples underwent an early stage of sulfide removal. Metalliferous samples from the Siberian intrusions of Khungtukun and Dzhaltul (associated with the Siberian flood basalts) yield internal 187Re-187Os ages of 266 ± 83Ma and 249 ± 50Ma, respectively, reflecting late-Permian emplacement ages. These results imply that crustal assimilation took place prior to crystallization of native-Fe. In contrast, metalliferous samples from Disko Island and Bühl (associated with the West Greenland flood basalts, and the Central European Volcanic Province, respectively) have trends in 187Re/188Os-187Os/188Os space corresponding to apparent ages older than their reported crystallization ages

  1. Mechanisms of Basalt-plains Ridge Formation

    NASA Technical Reports Server (NTRS)

    Watters, T. R.; Maxwell, T. A.

    1985-01-01

    The morphologic similarities between the Columbia Plateau ridges and ridges on the Moon, Mercury and Mars form a strong basis for the interpretation of basalt-plains ridges as compressional folds. The basalt-plains ridges appear to have formed on competent flood basalt units deformed at the surface with essentially no confining pressure. Estimates of compressive strain for planetary ridges range from a few tenths of a percent on the Moon to up to 0.4% on Mars, to as high as 35% for Columbia Plateau folds with associated thrust faults. Such values have strong implications for both deformational mechanisms as well as for the source of stress. Deformational mechanisms that will attempt to account for the morphology, fold geometry, possible associated thrust faulting and regular spacing of the basalt-plains ridges on the terrestrial planets are under investigation.

  2. 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.

  3. 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.

  4. Columbia River Basalt Chemistry, Degassing, and Eruption Dynamics: Insights From Quenched Glassy Lapilli and Tuffs

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Primary eruptive vent areas for several lavas in the Imnaha and Grande Ronde Formations of the Columbia River Basalt exhibit phreatomagmatic character, due to the interaction of rising flood basalt magma with groundwater and/or surface water. Vent constructional forms range from extensive (>1 km) maar complexes with abundant basement lithics to small (<<1 km), lithic-poor low-angle cones. Phreatomagmatic tephra is lithified and variably palagonitized, but glassy basaltic lapilli can be recovered from many locations. Many lapilli have experienced variable degrees of Na leaching but preserve magmatic abundances of most other elements; nonetheless in many cases pristine, unmodified glass is amenable to analysis. In addition, phenocrysts in lapilli have fully glassy melt inclusions. Glassy lapilli have highly variable S contents between ~100 and ~1300 ppm. This is consistent with quenching before degassing was complete, a common feature of phreatomagmatic eruptions. Melt inclusions have ≤2900 ppm S, ≤3400 ppm CO2 and ≤2.6 wt% H2O, allowing estimates of atmospheric input from the main phase of Columbia River volcanism. In addition, the lithophile trace element contents, and petrogenetically significant ratios such as Ba/Nb, of glassy lapilli exhibit differ from those in the equivalent 'stony' lava flows by up to a factor of 2. This suggests that processes in the flow and crystallization of lava serve to modify trace element abundances, and may place limits on the petrogenetic significance of trace element data from crystalline lava samples.

  5. 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.

  6. 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.

  7. Great Holocene floods along Jokulsa a Fjollum, north Iceland

    USGS Publications Warehouse

    Waitt, R.B.

    2002-01-01

    Jokulsa a Fjollum, Iceland's largest glacial river, drains from Vatnajokull icecap northward to the sea along a broad low that includes an active volcanic belt. Geomorphic features along this path reveal an ancient discharge of water large enough to fill the river valley and spill among a plexus of lows in the volcanic landscape. Stratigraphy in most places reveals just one late Holocene great flood down Jokulsa a Fjollum, between 2500 and 2000 yr ago. Step-back water computation suggests its peak flow was 0.7 million m3/s or more. An early scabland-carving great flood had swept down the Asbyrgi area of lowermost Jokulsa just after deglaciation, 9000-8000 yr ago. Stratigraphy near Vesturdalur reveals at least 16 additional floods, perhaps of moderate discharge, between about 8000 and 4000 yr ago. Dispersed field evidence of the late Holocene great flood-anastomosing channels whose basalt surfaces are water fluted and half-potholed, in places plucked down to small-scale scabland replete with dry cataracts, huge boulders, long gravel bars, giant current dunes-is traced the length of Jokulsa valley. From Vatnajokull's north margin at Kverkfjoll, water anastomosed through diverse lows of a high-relief landscape. Thus swift release of meltwater from subglacial Kverkfjoll caldera must have been a source of flood. But even this catastrophic outflow was insufficient to constitute the huge discharges evident farther down-valley. Field evidence reveals a yet greater discharge directly from the large outlet glacier Dyngjujokull. There is no evidence that subglacial Baraoarbunga caldera was involved, but subglacial melting during eruption of a more eastern fissure system could be a source of flood.

  8. 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 ...

  9. Rare earth element contents and multiple mantle sources of the transform-related Mount Edgecumbe basalts, southeastern Alaska

    USGS Publications Warehouse

    Riehle, J.R.; Budahn, J.R.; Lanphere, M.A.; Brew, D.A.

    1994-01-01

    Pleistocene basalt of the Mount Edgecumbe volcanic field (MEF) is subdivided into a plagioclase type and an olivine type. Th/La ratios of plagioclase basalt are similar to those of mid-ocean-ridge basalt (MORB), whereas those of olivine basalt are of continental affinity. Rare earth element (REE) contents of the olivine basalt, which resemble those of transitional MORB, are modelled by 10-15% partial melting of fertile spinel-plagioclase lherzolite followed by removal of 8-13% olivine. It is concluded that olivine basalt originated in subcontinental spinel lherzolite and that plagioclase basalt may have originated in suboceanic lithosphere of the Pacific plate. -from Authors

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. Volcanic Stratigraphy of the Quaternary Rhyolite Plateau in Yellowstone National Park

    USGS Publications Warehouse

    Christiansen, Robert L.; Blank, H. Richard

    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.

  15. 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.

  16. Flooding and Flood Management

    USGS Publications Warehouse

    Brooks, K.N.; Fallon, J.D.; Lorenz, D.L.; Stark, J.R.; Menard, Jason; Easter, K.W.; Perry, Jim

    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.

  17. 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].

  18. 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.

  19. 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.

  20. 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 ...

  1. 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.

  2. Can we identify source lithology of basalt?

    PubMed Central

    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

  3. 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.

  4. 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

  5. Ages, Thicknesses and Mineralogy of Lunar Mare Basalts

    NASA Astrophysics Data System (ADS)

    Hiesinger, H.; Head, J. W.; Wolf, U.; Jaumann, R.; Neukum, G.

    2002-01-01

    About 17% of the lunar surface are covered with lunar mare basalts. Mare basalts occur preferentially on the lunar nearside and their presence on planetary surfaces is indicative of the thermal activity and volcanic evolution of the body. In order to place constraints on the thermal/volcanic evolution and petrogenetic models for the formation of lunar mare basalts, we dated basalts exposed on the lunar nearside. Over the last 6 years we performed crater counts for Oceanus Procellarum, Mare Nubium, Cognitum, Insularum, Humorum, Imbrium, Serenitatis, Tranquillitatis, Humboldtianum, and Australe. Currently we are extending our crater counts to basalt areas in Mare Frigoris, Nectaris, Vaporum, Smythii, and Marginis. We are also in the progress of dating some lava-filled impact craters such as Schickard, Cr?ger, and Grimaldi. Crater counts not only allow one to determine the age of a basalt unit but also provide important information about the thickness, the volume, and the temporal separation of individual basalt flow units. In addition, age data in combination with Clementine and Lunar Prospector data allow one to investigate changes in mineralogy with time.

  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. The largest volcanic eruptions on Earth

    NASA Astrophysics Data System (ADS)

    Bryan, Scott; Peate, David; Ukstins Peate, Ingrid; Self, Stephen; Mawby, Michael; Jerram, Dougal; Marsh, Goonie

    2010-05-01

    Large igneous provinces (LIPs) are sites of the most frequently recurring, largest volume basaltic and silicic eruptions in Earth history. The magma volumes, eruptive mechanisms, frequency and associated aerosol emissions of these eruptions are critical for understanding any interpreted climate forcing and environmental change by LIPs. The largest volume (>1000 km3 dense rock equivalent) and magnitude (>M8) eruptions produce areally extensive (104-105 km2) basaltic lava flow fields and silicic ignimbrites and are the main building blocks of LIPs. Available information on the largest eruptive units are primarily from the Columbia River and Deccan provinces for the dimensions of flood basalt eruptions, and the Paraná-Etendeka and Afro-Arabian provinces for the silicic ignimbrite eruptions. In addition, three large-volume (675- 2,000 km3) silicic lava flows have also been mapped out in the Mesoproterozoic Gawler Range province (Australia), an interpreted LIP remnant. Magma volumes of >1000 km3 have also been emplaced as high-level basaltic and rhyolitic sills in LIPs, and may contribute substantial aerosol emissions through shallow degassing and crystallisation. The data sets indicate comparable eruption magnitudes between the basaltic and silicic eruptions, but due to considerable volumes residing as co-ignimbrite ash deposits, the current volume constraints for the silicic ignimbrite eruptions may be considerably underestimated. Magma composition thus appears to be no barrier to the volume of magma emitted during an individual eruption. Despite this general similarity in magnitude, flood basaltic and silicic eruptions are very different in terms of eruption style, duration, intensity, vent configuration, and emplacement style. Flood basaltic eruptions are dominantly effusive and Hawaiian-Strombolian in style, with magma discharge rates of ~107-108 kg s-1 producing dominantly compound pahoehoe lava flow fields. The major flood basalt eruption durations are most

  8. 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.

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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

  14. Field and petrographic characteristics of Cenozoic basaltic rocks, Northwestern Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Saif, S. I.; Shah, S. M. A.

    Cenozoic volcanism has produced 13, vast, basaltic fields in western saudi Arabia, covering a total area of about 100,000 sq.km. The volcanism started in the late Cretaceous time and continued periodically into the Holocene. The basaltic field presently investigated is known as Harrat Al-Hamad (or Harrat As-Shamah) which lies in northwestern Saudi Arabia, and continues northwards into Jordan. On the basis of field exposures, five distinct volcanic episodes have been recognized, three of which are represented by basaltic layers interstratified with underformed flat-lying post-Cretaceous sedimentary rocks. The fourth phase is represented by vast veneers of volcanic rubbles that intermittently cover Paleogene and Neogene sedimentary rocks. Numerous fresh cinder-cones, tuff rings, etc. represent the fifth and last volcanic episode. The outcropping volcanic rocks in this area clearly indicate that such activity began around the Middle Miocene, and continued intermittently until about few hundred years ago, but drilled subsurface sections present older basaltic layers as well. Tectonic features such as grabens, fault scarps, fissures and fractures are common in the area, and the linear trend of both the volcanic dykes and the cinder cones suggests that the eruptions did take place along such lines. The petrographic investigation revealed the alkali oiivine basaltic nature of the rocks.

  15. Sources of oceanic basalts: radiogenic isotopic evidence

    SciTech Connect

    White, W.M.

    1985-02-01

    Oceanic basalts can be subdivided into five distinct groupings on the basis of their Sr, Nd, and Pb isotope composition. These classes, represented by mid-ocean ridge basalts (MORB) and St. Helena, Kerguelen, the Society Islands, and the Hawaiian Islands, may represent different but internally heterogeneous mantle reservoirs or merely distinct groups within which chemical evolution has proceeded in a similar manner. Little systematic geographic distribution of volcanism tapping these sources is apparent. Depletion has been most important in the evolution of the MORB-type reservoirs, whereas crustal recycling has dominated the evolution of sources of the Kerguelen and Society types. Primitive mantle is identifiable in the Sr, Nd, Hf, and Pb isotope characteristics of the Hawaiian source only. The evolution of St. Helena-type sources remains enigmatic. 33 references, 2 figures.

  16. Determination of trace elements in volcanic rock samples collected from cenozoic lava eruption sites using LIBS.

    PubMed

    Gondal, Mohammed A; Nasr, Mohamed M; Ahmed, Zulfiqar; Yamani, Zain H

    2009-04-01

    Trace elements of environmental significance present in the volcanic rock samples collected from sites of the Cenozoic era flood basalt flows and eruptions were detected using locally developed laser-induced breakdown spectrometer. For spectro-chemical analysis of these samples, the plasma was generated by focusing a pulsed Nd: YAG laser radiation at 1064 nm wavelength on the target rock samples. These samples were collected from four widely separated locations surrounding the volcanic eruption sites belonging to the Harrat Hutaymah volcanic field in the vicinity of Taba town, situated to the east of Hail city of northern Saudi Arabia. These samples represent the scoria basalt lava flows as well as a large tuff-ring crater and it contains xenoliths. These flows occur widespread over the Earth's surface in this region, and their contained xenoliths are brought up from depths of a few tens of kilometers. This volcanic field has received much less attention in the previous geological studies; and consequently, its effects on the environment are not well defined. The concentration of different elements of environmental significance like Cr, Pb, Mn, Cd, Sr and other trace metals like Cu, Al, Ca, Mg, Zn, Ti and Fe in these rock samples were determined by spectral analysis. Parametric dependence for improvement of LIBS sensitivity for detection of these elements was also carried out. The highest concentration detected of environmentally significant elements like Cr, Mn, Pb, Sr and Ni are 1910, 1399, 90.5, 12412 and 461.5 ppm, respectively in four different lava samples which are considered to be much higher than the safe permissible limits. The LIBS results were compared with the results obtained using other analytical techniques such as the inductively coupled plasma atomic emission spectroscopy (ICP-AES).

  17. The volcanic and tectonic history of Enceladus

    USGS Publications Warehouse

    Kargel, J.S.; Pozio, S.

    1996-01-01

    reaccretion of Enceladus. Another area of cratered plains has modified craters (e.g., Ali Baba and Aladdin), which some workers have explained by anomalous heat flow and viscous relaxation; lateral shear and shield-building volcanism also may have been important. A young rift-like structure (northern Samarkand Sulci) has few craters and a concentration of cracks or grabens and flattened, flooded, and rifted craters. Pit chains and cratered domes suggest explosive volcanism. Smooth plains may have formed by cryovolcanic equivalents of flood-basalt volcanism. Pure H2O would be difficult to extrude through an icy crust and is cosmochemically improbable as a cryovolcanic agent. Density relations rule out eutectic brine lavas on Enceladus, but NH3-H2O volcanism is possible. Current steady-state tidal dissipation may cause melting of ammonia hydrate at a depth of ???25 km if the crust is made of ammonia hydrate or ???100 km if it is made of water ice. ?? 1996 Academic Press, Inc.

  18. 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.

  19. 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.

  20. Experimental and theoretical study of entrainment in volcanic line plumes produced by fissure eruptions

    NASA Astrophysics Data System (ADS)

    Paillat, S.; Kaminski, E. C.

    2013-12-01

    Basaltic fissure eruptions can produce turbulent line plumes injecting gas and particles in the atmosphere. The dynamic of these line plumes is controlled by the efficiency of entrainment as quantified by the so-called entrainment coefficient α. There are only scarce experimental constraints on α in planar jets and plumes. Whereas a constant value of the entrainment coefficient is used in models, data from the literature show a variation of α in pure planar jets. Only a few data are available for plumes. In order to better constrain the entrainment coefficient, we propose a theoretical expression of the entrainment coefficient α, as a function of buoyancy and turbulent structure. The model is validated first, using data from the literature and new experiments in pure jets and plumes. We show that the entrainment coefficient reaches a constant value at large distances from the source and high Reynolds number in pure jets. Positive buoyancy enhances the entrainment in pure plumes where α is about two times larger. The theoretical expression of the entrainment coefficient is then used to study the effect of variable entrainment on the dynamics of volcanic line plumes produced above an eruptive fissure at different scales, ranging from small Hawaiian fountains to basaltic Plinian eruptions (e.g. 1783 Laki eruption) and flood basalts. Both the stability of the eruptive column and the maximum height it reaches in the atmosphere are affected by variable entrainment.

  1. Degassing-driven crystallisation in basalts

    NASA Astrophysics Data System (ADS)

    Applegarth, L. J.; Tuffen, H.; James, M. R.; Pinkerton, H.

    2013-01-01

    Syn-eruptive crystallisation can drastically increase magma viscosity, with profound implications for conduit dynamics, lava emplacement and volcanic hazards. There is growing evidence that crystallisation is not only cooling-driven, but can also occur almost isothermally during decompression-induced degassing on ascent from depth. Here we review field and experimental evidence for degassing-driven crystallisation in a range of magma compositions. We then present new results showing, for the first time, experimental evidence for this process in basaltic magma. Our experiments use simultaneous thermogravimetric analysis and differential scanning calorimetry coupled with mass spectrometry (TGA-DSC-MS) to monitor degassing patterns and thermal events during heating and cooling of porphyritic basaltic samples from Mt. Etna, Italy. The partly degassed samples, which contained 0.39-0.81 wt.% total volatiles in the glass fraction, were subjected to two cycles of heating from ambient to 1250 °C. On the first heating, TGA data show that 30-60% of the total volatiles degassed slowly at < 1050 °C, and that the degassing rate increased rapidly above this temperature. DSC data indicate that this rapid increase in the degassing rate was closely followed (≤ 3.4 min) by a strongly exothermic event, which is interpreted as crystallisation. Enthalpies measured for this event suggest that up to 35% of the sample crystallises, a value supported by petrographic observations of samples quenched after the event. As neither degassing nor crystallisation was observed at high temperature during the second heating cycle we infer that the events on first heating constitute degassing-driven crystallisation. The rapidity and magnitude of the crystallisation response to degassing indicates that this process may strongly affect the rheology of basaltic magma in shallow conduits and lava flows, and thus influence the hazards posed by basaltic volcanism.

  2. 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

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. Basaltic fragments in lunar feldspathic meteorites: Connecting sample analyses to orbital remote sensing

    NASA Astrophysics Data System (ADS)

    Robinson, Katharine L.; Treiman, Allan H.; Joy, Katherine H.

    2012-03-01

    The feldspathic lunar meteorites contain rare fragments of crystalline basalts. We analyzed 16 basalt fragments from four feldspathic lunar meteorites (Allan Hills [ALHA] 81005, MacAlpine Hills [MAC] 88104/88105, Queen Alexandra Range [QUE] 93069, Miller Range [MIL] 07006) and utilized literature data for another (Dhofar [Dho] 1180). We compositionally classify basalt fragments according to their magma's estimated TiO2 contents, which we derive for crystalline basalts from pyroxene TiO2 and the mineral-melt Ti distribution coefficient. Overall, most of the basalt fragments are low-Ti basalts (1-6% TiO2), with a significant proportion of very-low-Ti basalts (<1% TiO2). Only a few basalt clasts were high-Ti or intermediate Ti types (>10% TiO2 and 6-10% TiO2, respectively). This distribution of basalt TiO2 abundances is nearly identical to that obtained from orbital remote sensing of the moon (both UV-Vis from Clementine, and gamma ray from Lunar Prospector). However, the distribution of TiO2 abundances is unlike those of the Apollo and Luna returned samples: we observe a paucity of high-Ti basalts. The compositional types of basalt differs from meteorite to meteorite, which implies that all basalt subtypes are not randomly distributed on the Moon, i.e., the basalt fragments in each meteorite probably represent basalts in the neighborhood of the meteorite launch site. These differences in basalt chemistry and classifications may be useful in identifying the source regions of some feldspathic meteorites. Some of the basalt fragments probably originate from ancient cryptomaria, and so may hold clues to the petrogenesis of the Moon's oldest volcanism.

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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

  13. Petrographic analysis and correlation of volcanic rocks in Bostic 1-A well near Mountain Home, Idaho

    SciTech Connect

    Arney, B.H.; Gardner, J.N.; Belluomini, S.G.

    1984-01-01

    Detailed examination of volcanic rock cuttings from the Bostic 1-A well near Mountain Home, Idaho, provides data that correlate the stratigraphy of the well with the regional stratigraphy of the western Snake River Plain. The Bostic 1-A well penetrates basalt of the Middle Pleistocene Bruneau Formation and underlying sedimentary rocks of the Upper Pliocene Glenns Ferry Formation. Basalt underlying the Glenns Ferry Formation is most likely Banbury Basalt of Middle Pliocene age or Banbury equivalent. A 350-ft interval of felsic volcanics is then intersected above another 600 ft of basalt. The well bottoms in altered felsic volcanics. The lowest 600 ft of basalt flows has not been correlated with any basalt observed on the surface. From the established stratigraphy of the region, and from petrographic evidence, the silicic volcanic rocks occurring both above and below the lowermost basalts in the well are probably lower Pliocene Idavada Volcanics. North of the well, in the Mt. Bennett Hills, Idavada Volcanics overlie crystalline rocks of the Idaho batholith. No estimate of depth to plutonic bedrock can be made from the well data alone. Stratigraphic comparisons suggest as little as 0.2 to 0.3 km more of Idavada lie beneath the Bostic 1-A well. Results of geophysical studies suggest additional basalt lies beneath the Bostic 1-A rather than granitic rocks of the batholith.

  14. Endeavour basalt geology and petrology

    NASA Astrophysics Data System (ADS)

    Gill, J. B.; Stakes, J.; Ramos, F.; Michael, P.; Stakes, D.

    2005-12-01

    We report major and trace element and isotope data from 250 basalt samples recently collected by submersible from the axial valley and flanks of the Endeavour segment of the Juan de Fuca Ridge. Off-axis volcanism is abundant on both flanks which are mirror images of one another geologically. Axial valley walls up to 1 km off axis appear to be steps of in tact but variably fractured sheet, lobate, and hackly lava flows similar to the youngest lavas seen in collapse features in the axis. Coverage by pillow terrane increases with distance off axis and coverage becomes complete after 1 km. The similarity of the two flanks suggests that the currently asymmetric axial magma chamber (van Ark et al., 2004) may be shorter-lived than the off-axis volcanism. MgO contents range from 6.0-8.5% and generally are lower on the flanks consistent with consistently cooler chamber edges there. La/Yb ratios vary 3-fold within 100 m in the axial valley, with normalized La/Sm = 0.8-2.5 in contrast to constant Sr and Nd isotopes. However, Th/U and 230Th/232Th ratios vary only slightly in the axial valley, which may enable dating of off-axis samples. H2O/Ce is less than 170, typical of values throughout much of the Pacific. Variations in depth and degree of melting, and in source composition, are implied. At times, these heterogeneities escaped homogenization in axial magma chambers. Cl concentrations and Cl/K ratios are surprisingly low considering the active hydrothermal systems in close proximity and the potential for brine incorporation into the magma chamber.

  15. Rapid formation of ontong java plateau by aptian mantle plume volcanism.

    PubMed

    Tarduno, J A; Sliter, W V; Kroenke, L; Leckie, M; Mayer, H; Mahoney, J J; Musgrave, R; Storey, M; Winterer, E L

    1991-10-18

    The timing of flood basalt volcanism associated with formation of the Ontong Java Plateau (OJP) is estimated from paleomagnetic and paleontologic data. Much of OJP formed rapidly in less than 3 million years during the early Aptian, at the beginning of the Cretaceous Normal Polarity Superchron. Crustal emplacement rates are inferred to have been several times those of the Deccan Traps. These estimates are consistent with an origin of the OJP by impingement at the base of the oceanic lithosphere by the head of a large mantle plume. Formation of the OJP may have led to a rise in sea level that induced global oceanic anoxia. Carbon dioxide emissions likely contributed to the mid-Cretaceous greenhouse climate but did not provoke major biologic extinctions.

  16. Rapid formation of Ontong Java Plateau by Aptian mantle plume volcanism

    USGS Publications Warehouse

    Tarduno, J.A.; Sliter, W.V.; Kroenke, L.; Leckie, M.; Mayer, H.; Mahoney, J.J.; Musgrave, R.; Storey, M.; Winterer, E.L.

    1991-01-01

    The timing of flood basalt volcanism associated with formation of the Ontong Java Plateau (OJP) is estimated from paleomagnetic and paleontologic data. Much of OJP formed rapidly in less than 3 million years during the early Aptian, at the beginning of the Cretaceous Normal Polarity Superchron. Crustal emplacement rates are inferred to have been several times those of the Deccan Traps. These estimates are consistent with an origin of the OJP by impingement at the base of the oceanic lithosphere by the head of a large mantle plume. Formation of the OJP may have led to a rise in sea level that induced global oceanic anoxia. Carbon dioxide emissions likely contributed to the mid-Cretaceous greenhouse climate but did not provoke major biologic extinctions.

  17. Mare volcanism in the Taurus-Littrow region

    NASA Technical Reports Server (NTRS)

    Delano, J. W.

    1992-01-01

    The products of mare volcanism at Taurus-Littrow occur in the form of crystalline basalts and volcanic glass beads. Both categories of samples define a compositionally diverse, but petrogenetically unrelated, suite of magmas derived by partial melting of a heterogenous, differentiated mantle beneath the region of the Apollo 17 landing site. This is a brief review of what is known and what is not known about mare volcanism at this location on the Moon.

  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 mechanism of waste incorporation in magma, and Strombolian eruption processes.

  19. The chemistry and element fluxes of the July 2011 Múlakvísl and Kaldakvísl glacial floods, Iceland

    NASA Astrophysics Data System (ADS)

    Galeczka, Iwona; Oelkers, Eric H.; Gislason, Sigurdur R.

    2014-05-01

    during the floods and dominated chemical transport during these events. The toxic metal concentrations were below WHO (World Health Organisation) drinking water limits. The most soluble elements were Na, Ca, K, Sr, Mn, and Mg, whereas the least soluble were Ti, Al, and REE. This is consistent with the compositions of typical surface waters in basaltic terrains and the compositions of global rivers in general. Increased concentrations of DOC, formate, and acetate in the flood waters suggests subglacial microbiological activity in the melt water prior to the floods. According to PHREEQC modelling, flood waters were supersaturated with respect to a number of clays, zeolites, carbonates, and Fe hydroxides. Reaction path modelling of the flood water chemical evolution suggests that it experienced subglacial water-rock interaction for at least a year in the presence of limited amounts of acid gases (e.g. SO2, HCl and HF). This indicates that the heat source for glacier melting was geothermal rather than volcanic.

  20. Timeline of Martian Volcanism

    NASA Astrophysics Data System (ADS)

    Martel, L. M. V.

    2011-05-01

    A recent study of Martian volcanism presents a timeline of the last major eruptions from 20 large volcanoes, based on the relative ages of caldera surfaces determined by crater counting. Stuart Robbins, Gaetano Di Achille, and Brian Hynek (University of Colorado) counted craters on high-resolution images from the the Context Camera (CTX) on Mars Reconnaissance Orbiter to date individual calderas, or terraces within calderas, on the 20 major Martian volcanoes. Based on their timeline and mapping, rates and durations of eruptions and transitions from explosive to effusive activity varied from volcano to volcano. The work confirms previous findings by others that volcanism was continuous throughout Martian geologic history until about one to two hundred million years ago, the final volcanic events were not synchronous across the planet, and the latest large-scale caldera activity ended about 150 million years ago in the Tharsis province. This timing correlates well with the crystallization ages (~165-170 million years) determined for the youngest basaltic Martian meteorites.

  1. A re-evaluation of the volcanism of the Palaeoproterozoic Pretoria Group (Kaapvaal craton) and a hypothesis on basin development

    NASA Astrophysics Data System (ADS)

    Reczko, B. F. F.; Oberholzer, J. D.; Res, M.; Eriksson, P. G.; Schreiber, U. M.

    1995-11-01

    The Palaeoproterozoic (approximately 2.3-2.1 Ga) Pretoria Group, Transvaal Supergroup, contains three main volcanic units, i.e the basal Bushy Bend Lava Member, the medial Hekpoort Formation and the Machadodorp Volcanic Member. Field relationships and geochemistry of the latter two volcanic successions have similarities with continental flood basalts (CFB), such as comparable trace element patterns and a distinct niobium anomaly. The genesis of the Pretoria Group volcanic rocks is inferred to be related to processes in a replenished, fractionated, tapped, assimilated (RFTA) magma chamber, involving an asthenospheric source, replenishing and tapping of the magma chamber and contamination of the primary partial melts by crustal material accompanied by fractional crystallization. The proposed basin development of the Pretoria Group, thought to have been related to asymmetric stretching of crust and lithosphere, may have been complicated further by decoupling of the extension in the sedimentary cover from the basement below, due to the presence of over-pressured basal shales. The tectonic setting of the Pretoria Group is inferred to lie in the rift-to-intracratonic-sag-type continuum.

  2. Volcanic rocks

    USGS Publications Warehouse

    1986-01-01

    Volcanoes have contributed significantly to the formation of the surface of our planet. Volcanism produced the crust we live on and most of the air we breathe. Often the remnants of an eruption are as revealing as the eruption itself, for they tell us many things about the eruption. Included here are examples of several volcanic products and other magmatic features, with descriptions of how they were formed and what they tell us about volcanism.

  3. Evidence for widespread effusive volcanism near the Noachian-Hesperian transition in circum-Hellas cratered uplands of Mars

    NASA Astrophysics Data System (ADS)

    Fergason, R. L.; Rogers, D.

    2011-12-01

    Constraining the volume, style and timing of volcanism on Mars is important for understanding its climatic and magmatic history. Early geomorphic mapping efforts using Mariner and Viking data identified numerous isolated occurrences of late Noachian/early Hesperian "ridged plains" or "smooth plateau material" (e.g. Hr, Hpl3) in the cratered uplands. The origin of these units was interpreted to be a combination of volcanic, sedimentary or impact materials with unknown proportions. We present new evidence for the volcanic origin of some of these materials, and constrain their areal extent, volume and general style (e.g., flood basalt as opposed to pyroclastic). Using THEMIS, TES and CRISM data over a region of cratered uplands located between Syrtis Major and Hellas Basin, over one hundred isolated exposures of rocky materials with distinctively higher olivine abundance than surrounding intercrater plains materials were identified. The units are found in intercrater plains and in shallow, relatively flat crater floors, and comprise a total area of ~165,000 sq km. The thickness of individual exposures is estimated to be between 100-500 m, resulting in a total volume of 16,500-82,500 km3, far below that of major flood basalt provinces on Earth. The isolated exposures are dispersed throughout the entire study area (~2.4 million sq km), which is comparable in size to the Siberian flood basalts. The age estimate arises from the observation that many exposures coincide with areas previously mapped as Hpl3 or Hr. The units are interpreted to be primarily volcanically emplaced based on embayment relationships, textural appearance consistent with a relatively resistant morphology, and higher thermal inertia than surrounding materials. The lack of a clear sedimentary source region for the olivine-enriched material also precludes a dominantly sedimentary origin, though it may explain some occurrences of this unit. The lack of obvious lava flow fronts or source vents suggest

  4. Volcanic hazard studies for the Yucca Mountain project

    SciTech Connect

    Crowe, B.; Turrin, B.; Wells, S.; Perry, F.; McFadden, L.; Renault, C.E.; Champion, D.; Harrington, C.

    1989-05-01

    Volcanic hazard studies are ongoing to evaluate the risk of future volcanism with respect to siting of a repository for disposal of high-level radioactive waste at the Yucca Mountain site. Seven Quaternary basaltic volcanic centers are located a minimum distance of 12 km and a maximum distance of 47 km from the outer boundary of the exploration block. The conditional probability of disruption of a repository by future basaltic volcanism is bounded by the range of 10{sup {minus}8} to 10{sup {minus}10} yr{sup {minus}1}. These values are currently being reexamined based on new developments in the understanding of the evaluation of small volume, basaltic volcanic centers including: (1) Many, perhaps most, of the volcanic centers exhibit brief periods of eruptive activity separated by longer periods of inactivity. (2) The centers may be active for time spans exceeding 10{sup 5} yrs, (3) There is a decline in the volume of eruptions of the centers through time, and (4) Small volume eruptions occurred at two of the Quaternary centers during latest Pleistocene or Holocene time. We classify the basalt centers as polycyclic, and distinguish them from polygenetic volcanoes. Polycyclic volcanism is characterized by small volume, episodic eruptions of magma of uniform composition over time spans of 10{sup 3} to 10{sup 5} yrs. Magma eruption rates are low and the time between eruptions exceeds the cooling time of the magma volumes. 25 refs., 2 figs.

  5. Mantle dynamics beneath the Pacific Northwest and the generation of post-20 Ma volcanism

    NASA Astrophysics Data System (ADS)

    Long, M. D.; Till, C. B.; Druken, K. A.; Fouch, M. J.; James, D. E.; Grove, T. L.; Wagner, L. S.; Kincaid, C. R.; Carlson, R. W.

    2011-12-01

    The Pacific Northwest (PNW) has a complex recent tectonic history and over the past ~17 Ma has played host to several major episodes of intraplate volcanism. These include the Steens/Columbia River flood basalts (CRB) and the striking spatiotemporal trends of the Yellowstone/Snake River Plain (Y/SRP) and High Lava Plains (HLP) regions. Several different models have been proposed to explain these features, which variously invoke the putative Yellowstone plume, the rollback and steepening of the Cascadia slab, extensional processes in the lithosphere, or a combination of these. Here we integrate seismological, geodynamical, petrological, and geochemical results from the multidisciplinary HLP project and associated efforts related to EarthScope data to propose a conceptual model for mantle dynamics beneath the PNW and the relationships between mantle flow and surface tectonomagmatic activity. The model invokes rollback subduction as the main driver for mantle flow beneath the PNW; a major pulse of upwelling due to the initiation of rollback drove melting associated with the Steens/CRB volcanism and continuing trench migration enabled hot, shallow melting beneath the HLP. A buoyant mantle upwelling is required to explain the Y/SRP volcanism, but subduction-related processes likely played a role in controlling its timing and location. This conceptual model makes predictions that are broadly consistent with seismic anisotropy measurements, tomographic velocity models, geodynamical modeling experiments, petrological constraints, and geochemical observations.

  6. Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations. Volume II

    SciTech Connect

    Crowe, B.M.; Wohletz, K.H.; Vaniman, D.T.; Gladney, E.; Bower, N.

    1986-01-01

    Volcanic hazard investigations during FY 1984 focused on five topics: the emplacement mechanism of shallow basalt intrusions, geochemical trends through time for volcanic fields of the Death Valley-Pancake Range volcanic zone, the possibility of bimodal basalt-rhyolite volcanism, the age and process of enrichment for incompatible elements in young basalts of the Nevada Test Site (NTS) region, and the possibility of hydrovolcanic activity. The stress regime of Yucca Mountain may favor formation of shallow basalt intrusions. However, combined field and drill-hole studies suggest shallow basalt intrusions are rare in the geologic record of the southern Great Basin. The geochemical patterns of basaltic volcanism through time in the NTS region provide no evidence for evolution toward a large-volume volcanic field or increases in future rates of volcanism. Existing data are consistent with a declining volcanic system comparable to the late stages of the southern Death Valley volcanic field. The hazards of bimodal volcanism in this area are judged to be low. The source of a 6-Myr pumice discovered in alluvial deposits of Crater Flat has not been found. Geochemical studies show that the enrichment of trace elements in the younger rift basalts must be related to an enrichment of their mantle source rocks. This geochemical enrichment event, which may have been metasomatic alteration, predates the basalts of the silicic episode and is, therefore, not a young event. Studies of crater dimensions of hydrovolcanic landforms indicate that the worst case scenario (exhumation of a repository at Yucca Mountain by hydrovolcanic explosions) is unlikely. Theoretical models of melt-water vapor explosions, particularly the thermal detonation model, suggest hydrovolcanic explosion are possible at Yucca Mountain. 80 refs., 21 figs., 5 tabs.

  7. Geochemical characterization of oceanic basalts using Artificial Neural Network.

    PubMed

    Das, Pranab; Iyer, Sridhar D

    2009-12-23

    The geochemical discriminate diagrams help to distinguish the volcanics recovered from different tectonic settings but these diagrams tend to group the ocean floor basalts (OFB) under one class i.e., as mid-oceanic ridge basalts (MORB). Hence, a method is specifically needed to identify the OFB as normal (N-MORB), enriched (E-MORB) and ocean island basalts (OIB). We have applied Artificial Neural Network (ANN) technique as a supervised Learning Vector Quantisation (LVQ) to identify the inherent geochemical signatures present in the Central Indian Ocean Basin (CIOB) basalts. A range of N-MORB, E-MORB and OIB dataset was used for training and testing of the network. Although the identification of the characters as N-MORB, E-MORB and OIB is completely dependent upon the training data set for the LVQ, but to a significant extent this method is found to be successful in identifying the characters within the CIOB basalts. The study helped to geochemically delineate the CIOB basalts as N-MORB with perceptible imprints of E-MORB and OIB characteristics in the form of moderately enriched rare earth and incompatible elements. Apart from the fact that the magmatic processes are difficult to be deciphered, the architecture performs satisfactorily.

  8. Status of volcanism studies for the Yucca Mountain Site Characterization Project

    SciTech Connect

    Crowe, B.; Perry, F.; Murrell, M.; Poths, J.; Valentine, G.A.; Wells, S.; Bowker, L.; Finnegan, K.; Geissman, J.; McFadden, L.

    1995-02-01

    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. 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 Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. Geophysical data are described for the YMR and are used as an aid to understand the distribution of basaltic volcanic centers. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the Basin and Range province. The long time of activity and characteristic small volume of the Postcaldera basalt of the YMR result in one of the lowest eruptive rates in a volcanic field in the southwest United States. Chapter 5 summarizes current concepts of the segregation, ascent, and eruption of basalt magma. Chapter 6 summarizes the history of volcanism studies (1979 through early 1994), including work for the Yucca Mountain Site Characterization Project and overview studies by the state of Nevada and the Nuclear Regulatory Commission. Chapter 7 summarizes probabilistic volcanic hazard assessment using a three-part conditional probability model. Chapter 8 describes remaining volcanism work judged to be needed to complete characterization studies for the YMR. Chapter 9 summarizes the conclusions of this volcanism status report.

  9. Volcanism at rifts

    SciTech Connect

    White, R.S.; McKenzie, D.P.

    1989-07-01

    The earth's outer shell rifts continuously, stretching and splitting both on the ocean's floor and on continents. Every 30 million years or so the rifting becomes cataclysmic, releasing continent-size floods of magma. This paper explains that the same mechanism is at work in both cases, the difference being in the slightly hotter temperature of the parent mantle for spectacular volcanic outbursts. Two kinds of evidence are described: quantitative descriptions of rock melting and a wide range of observations made on the rifted edges of continents and in the oceans that have opened between them.

  10. The Spokane flood controversy and the Martian outflow channels

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1978-01-01

    The controversy over Bretz's hypothesis concerning the cataclysmic Spokane flood is discussed. Attention is directed to similarities between the Channeled Scabland of Washington and some Martian land features considered to be catastrophic flood channels. Characteristics of the enormous plexus of proglacial stream channels eroded into the loess and basalt of the Columbia Plateau in eastern Washington are described. The controversiality of the suggestion that a catastrophic flood is responsible for the Martian features is considered with respect to the Spokane flood controversy.

  11. Young flood lavas in the Elysium Region, Mars

    NASA Technical Reports Server (NTRS)

    Plescia, J. B.

    1990-01-01

    The nature and origin of a smooth plains unit (the Cerberus Plains) in southeastern Elysium and western Amazonis are reported. The interpretation that the Cerberus Plains resulted from flood plains style volcanism late in martian history is presented which carries implications for martian thermal history and volcanic evolution of a global scale. Although central construct volcanism (e.g., Olympus Mons) has long been recognized as occurring late in time, flood volcanism has not. Flood volcanism has been suggested as the origin of the ridged plains units (e.g., Lunae Planum, Solis, and Sinai Planum). This type of volcanic activity generally occurred early, and in Tharsis, the style of volcanism evolved from flood eruptions into centralized eruptions which built the large Tharsis Montes and Olympus Mons shields. Volcanism in the Elys