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Jussi S Heinonen - One of the best experts on this subject based on the ideXlab platform.
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deep open storage and shallow closed transport system for a continental Flood Basalt sequence revealed with magma chamber simulator
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jussi S Heinonen, Wendy A Bohrson, Frank J Spera, Arto V. LuttinenAbstract:The Magma Chamber Simulator (MCS) quantitatively models the phase equilibria, mineral chemistry, major and trace elements, and radiogenic isotopes in a multicomponent–multiphase magma + wallrock + recharge system by minimization or maximization of the appropriate thermodynamic potential for the given process. In this study, we utilize MCS to decipher the differentiation history of a continental Flood Basalt sequence from the Antarctic portion of the ~ 180 Ma Karoo large igneous province. Typical of many Flood Basalts, this suite exhibits geochemical evidence (e.g., negative initial eNd) of interaction with crustal materials. We show that isobaric assimilation-fractional crystallization models fail to produce the observed lava compositions. Instead, we propose two main stages of differentiation: (1) the primitive magmas assimilated Archean crust at depths of ~ 10‒30 km (pressures of 300–700 MPa), while crystallizing olivine and orthopyroxene; (2) subsequent fractional crystallization of olivine, clinopyroxene, and plagioclase took place at lower pressures in upper crustal feeder systems without significant additional assimilation. Such a scenario is corroborated with additional thermophysical considerations of magma transport via a crack network. The proposed two-stage model may be widely applicable to Flood Basalt plumbing systems: assimilation is more probable in magmas pooled in hotter crust at depth where the formation of wallrock partial melts is more likely compared to rapid passage of magma through shallower fractures next to colder wallrock.
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Deep open storage and shallow closed transport system for a continental Flood Basalt sequence revealed with Magma Chamber Simulator
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jussi S Heinonen, Frank J Spera, Arto V. Luttinen, Wendy A BohrsonAbstract:The Magma Chamber Simulator (MCS) quantitatively models the phase equilibria, mineral chemistry, major and trace elements, and radiogenic isotopes in a multicomponent–multiphase magma + wallrock + recharge system by minimization or maximization of the appropriate thermodynamic potential for the given process. In this study, we utilize MCS to decipher the differentiation history of a continental Flood Basalt sequence from the Antarctic portion of the ~ 180 Ma Karoo large igneous province. Typical of many Flood Basalts, this suite exhibits geochemical evidence (e.g., negative initial ε _Nd) of interaction with crustal materials. We show that isobaric assimilation-fractional crystallization models fail to produce the observed lava compositions. Instead, we propose two main stages of differentiation: (1) the primitive magmas assimilated Archean crust at depths of ~ 10‒30 km (pressures of 300–700 MPa), while crystallizing olivine and orthopyroxene; (2) subsequent fractional crystallization of olivine, clinopyroxene, and plagioclase took place at lower pressures in upper crustal feeder systems without significant additional assimilation. Such a scenario is corroborated with additional thermophysical considerations of magma transport via a crack network. The proposed two-stage model may be widely applicable to Flood Basalt plumbing systems: assimilation is more probable in magmas pooled in hotter crust at depth where the formation of wallrock partial melts is more likely compared to rapid passage of magma through shallower fractures next to colder wallrock.
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deep mixing of mantle melts beneath continental Flood Basalt provinces constraints from olivine hosted melt inclusions in primitive magmas
Geochimica et Cosmochimica Acta, 2017Co-Authors: Eleanor S Jennings, S A Gibson, John Maclennan, Jussi S HeinonenAbstract: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 Parana–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 Parana–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 Parana–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, Galapagos, 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 Parana–Etendeka and Karoo CFB have the least variable compositions of all global melt inclusion suites, which may be a function of their unusually deep origin and low viscosity.
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mixed pyroxenite peridotite sources for mafic and ultramafic dikes from the antarctic segment of the karoo continental Flood Basalt province
Lithos, 2013Co-Authors: Jussi S Heinonen, Arto V. Luttinen, Teal R Riley, Radoslaw M MichallikAbstract:Abstract Primitive rocks that are related to continental Flood Basalts are rare, but often reveal crucial information on the ultimate sources of these huge outpourings of mantle-derived magma. Here we present mineral chemical data for mafic and ultramafic dikes from the Antarctic extension of the Jurassic (~ 180 Ma) Karoo continental Flood Basalt province that was emplaced during the initial stages of the breakup of the Gondwana supercontinent. We concentrate on two previously recognized high-Ti dike rock suites (Group 3 and Group 4) that exhibit high MgO contents (up to 22 wt.%). Both groups are characterized by Mg-rich olivine phenocrysts (up to Fo90) that are not mantle xenocrysts and indicate derivation from relatively Mg-rich parental magmas. Orthopyroxene is a common phenocryst and groundmass phase indicating emplacement at mid-crustal pressures (2–5 kbar; depth of ~ 10–20 km). The parental magmas of Group 3 and Group 4 dikes can be associated with pyroxenite sources on the basis of high olivine NiO, high whole-rock Zn/Fe, and low whole-rock CaO. In the case of Group 3 dikes, however, the samples that contain the most Mg-rich olivine also exhibit the mildest pyroxenite fingerprint and indications of an additional olivine-bearing (peridotitic) source component. We propose that the pyroxenite fingerprint of Group 3 and Group 4 dikes reflects relatively low-degree melting of fertile mantle at high pressures beneath the thick and cold Gondwanan lithosphere. Such conditions limited high-degree melting of peridotite sources which may have been more predominant in the generation of the Karoo low-Ti Basalts within lithospheric thinning zones.
Wendy A Bohrson - One of the best experts on this subject based on the ideXlab platform.
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deep open storage and shallow closed transport system for a continental Flood Basalt sequence revealed with magma chamber simulator
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jussi S Heinonen, Wendy A Bohrson, Frank J Spera, Arto V. LuttinenAbstract:The Magma Chamber Simulator (MCS) quantitatively models the phase equilibria, mineral chemistry, major and trace elements, and radiogenic isotopes in a multicomponent–multiphase magma + wallrock + recharge system by minimization or maximization of the appropriate thermodynamic potential for the given process. In this study, we utilize MCS to decipher the differentiation history of a continental Flood Basalt sequence from the Antarctic portion of the ~ 180 Ma Karoo large igneous province. Typical of many Flood Basalts, this suite exhibits geochemical evidence (e.g., negative initial eNd) of interaction with crustal materials. We show that isobaric assimilation-fractional crystallization models fail to produce the observed lava compositions. Instead, we propose two main stages of differentiation: (1) the primitive magmas assimilated Archean crust at depths of ~ 10‒30 km (pressures of 300–700 MPa), while crystallizing olivine and orthopyroxene; (2) subsequent fractional crystallization of olivine, clinopyroxene, and plagioclase took place at lower pressures in upper crustal feeder systems without significant additional assimilation. Such a scenario is corroborated with additional thermophysical considerations of magma transport via a crack network. The proposed two-stage model may be widely applicable to Flood Basalt plumbing systems: assimilation is more probable in magmas pooled in hotter crust at depth where the formation of wallrock partial melts is more likely compared to rapid passage of magma through shallower fractures next to colder wallrock.
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Deep open storage and shallow closed transport system for a continental Flood Basalt sequence revealed with Magma Chamber Simulator
Contributions to Mineralogy and Petrology, 2019Co-Authors: Jussi S Heinonen, Frank J Spera, Arto V. Luttinen, Wendy A BohrsonAbstract:The Magma Chamber Simulator (MCS) quantitatively models the phase equilibria, mineral chemistry, major and trace elements, and radiogenic isotopes in a multicomponent–multiphase magma + wallrock + recharge system by minimization or maximization of the appropriate thermodynamic potential for the given process. In this study, we utilize MCS to decipher the differentiation history of a continental Flood Basalt sequence from the Antarctic portion of the ~ 180 Ma Karoo large igneous province. Typical of many Flood Basalts, this suite exhibits geochemical evidence (e.g., negative initial ε _Nd) of interaction with crustal materials. We show that isobaric assimilation-fractional crystallization models fail to produce the observed lava compositions. Instead, we propose two main stages of differentiation: (1) the primitive magmas assimilated Archean crust at depths of ~ 10‒30 km (pressures of 300–700 MPa), while crystallizing olivine and orthopyroxene; (2) subsequent fractional crystallization of olivine, clinopyroxene, and plagioclase took place at lower pressures in upper crustal feeder systems without significant additional assimilation. Such a scenario is corroborated with additional thermophysical considerations of magma transport via a crack network. The proposed two-stage model may be widely applicable to Flood Basalt plumbing systems: assimilation is more probable in magmas pooled in hotter crust at depth where the formation of wallrock partial melts is more likely compared to rapid passage of magma through shallower fractures next to colder wallrock.
Stephen Self - One of the best experts on this subject based on the ideXlab platform.
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assessing eruption column height in ancient Flood Basalt eruptions
Earth and Planetary Science Letters, 2017Co-Authors: L S Glaze, Stephen Self, Anja Schmidt, S J HunterAbstract: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 climate on time scales of decades to centuries but the location (i.e., latitude) of the province and relevant paleoclimate is important and must be considered.
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selective environmental stress from sulphur emitted by continental Flood Basalt eruptions
Nature Geoscience, 2016Co-Authors: Anja Schmidt, Stephen Self, Thorvaldur Thordarson, R A Skeffington, Piers M Forster, A Rap, Andy RidgwellAbstract: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.
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chapter 24 large igneous provinces and Flood Basalt volcanism
The Encyclopedia of Volcanoes (Second Edition), 2015Co-Authors: Stephen Self, Millard F Coffin, Michael R Rampino, John A WolffAbstract:Abstract Large igneous provinces (LIPs) represent huge volumes of erupted and intruded magma and are exceptional volcanic events in Earth history. They were erupted over a brief period of geologic time. The volume of magma emitted during each individual eruption that makes up an LIP (frequently 103 to perhaps 104 km3) is also exceptional, and these form Earth's largest eruptions. LIPs occur on continental crust (Flood Basalt provinces) and in ocean basins (oceanic plateaus), and at the transition between continents and oceans (“volcanic-”divergent margins). Basaltic LIPs usually form within a geologically brief period of time, especially the climax, or peak, of volcanic output, which may be less than 1 million years in duration. The eruptions that form Flood Basalt provinces have been proposed as a cause of major environmental perturbations throughout much of Earth history, including mass extinctions. Pāhoehoe-type lavas dominate in Flood Basalt provinces, and eruptions are thought to have durations of decades to perhaps centuries. The huge flow fields of pāhoehoe lavas are dominated by sheet lobes in many provinces, as well as alternations with flow fields dominated by smaller inflated lava lobes. Vents are poorly known, but some, at least, were long fissure-type systems.
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pyroclastic edifices record vigorous lava fountains during the emplacement of a Flood Basalt flow field roza member columbia river Basalt province usa
Geological Society of America Bulletin, 2014Co-Authors: Richard J Brown, Stephen Blake, Thorvaldur Thordarson, Stephen SelfAbstract:The 1300 km 3 tholeiitic lava flow field of the 14.98 Ma Roza Member of the Columbia River Basalt Province has the best-preserved vent system of any known continental Flood Basalt. Detailed geological mapping and logging of the exposed pyroclastic rocks along the >180-km-long vent system enable the reconstruction of pyroclastic edifices (partial cones) built around vents. The pyroclastic cones differ from those constructed during typical Basaltic effusive eruptions and are characterized by low to moderate slope angles ( 1 km) fountains enhanced by fallout from the lower parts of convective plumes that rose above the fountains.
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emplacement of continental Flood Basalt lava flows
Geophysical monograph, 2013Co-Authors: Stephen Self, Thorvaldur Thordarson, Laszlo P KeszthelyiAbstract:We propose that continental Flood Basalt (CFB) lavas were predominantly emplaced as inflated compound pahoehoe flow fields via prolonged, episodic eruptions. Our most detailed observations come from the ∼14,7 Ma Roza flow field of the Columbia River Basalt (CRB) Group. The Roza flow field seems to be typical of many Flood Basalt lavas. Individual flows show a wide range of pahoehoe surface features and a three-part internal structure in vesicularity and other textural parameters. This three-fold division into an upper crust, core, and basal crust appears to be diagnostic of the inflation process and is ubiquitous in Basaltic lava flows over a remarkable range of sizes. The pahoehoe surface features and indications of inflation are inconsistent with rapid emplacement of these lava flows. Instead, we interpret the observations to imply that the Roza, and other CFB flows, were emplaced over an extended period of time. From the thickness of the upper crust, which we suggest formed while the flow was actively inflating, and an empirical expression for the rate of crust growth of Hawaiian inflated sheet flows, we estimate that individual Roza flows were emplaced over 5 to 50 months and that the Roza flow field was constructed over a period of 6 to 14 years. However, even with this longer eruption duration, the average lava effusion rate of ∼4000 m 3 /s is similar to that of the highest-effusion-rate eruption in recorded history (the 1783-4 Laki eruption in Iceland). Our observations of lava characteristics in other CRB flows and in the Deccan Traps suggest that this emplacement style is typical of many, if not most, CFB flows. Initial estimates of the volatile release from the Roza eruption indicate that prodigious amounts of S, Cl, and F were injected into the upper troposphere and lowermost stratosphere; thus this single Flood Basalt eruption could have had a significant effect on the global atmosphere If other Flood Basalt eruptions produced similar amounts of volatiles, volatile release might provide a link between Flood Basalt eruptions and mass extinctions.
James D. L. White - One of the best experts on this subject based on the ideXlab platform.
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cracking the lid sill fed dikes are the likely feeders of Flood Basalt eruptions
Earth and Planetary Science Letters, 2014Co-Authors: James D Muirhead, James D. L. White, Giulia Airoldi, J V RowlandAbstract: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.
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Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of Flood Basalt volcanism in the Ferrar-Karoo LIP
Bulletin of Volcanology, 2006Co-Authors: Murray Mcclintock, James D. L. WhiteAbstract:The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related to the onset of Ferrar-Karoo Flood Basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km^2). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within vent-fill, and pyroclastic density current deposits point to explosive interaction of Basalt with groundwater in porous country rock and wet vent filling debris. Metre-scale dikes and pods of coherent Basalt in places merge imperceptibly into peperite and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris + steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however, probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents. The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water, as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture, lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the complex evolved.
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mafic volcaniclastic deposits in Flood Basalt provinces a review
Journal of Volcanology and Geothermal Research, 2005Co-Authors: Pierresimon Ross, Murray Mcclintock, James D. L. White, I P Skilling, Ukstins I Peate, B F HoughtonAbstract:Flood volcanic provinces are assumed generally to consist exclusively of thick lavas and shallow intrusive rocks (mostly sills), with any pyroclastic rocks limited to silicic compositions. However, mafic volcaniclastic deposits (MVDs) exist in many provinces, and the eruptions that formed such deposits are potentially meaningful in terms of potential atmospheric impacts and links with mass extinctions. The province where MVDs are the most voluminous—the Siberian Traps—is also the one temporally associated with the greatest Phanerozoic mass extinction. A lot remains to be learned about these deposits and eruptions before a convincing genetic link can be established, but as a first step, this contribution reviews in some detail the current knowledge on MVDs for the provinces in which they are better known, i.e. the North Atlantic Igneous Province (including Greenland, the Faeroe Islands, the British Isles, and tephra layers in the North Sea basin and vicinity), the Ontong Java plateau, the Ferrar, and the Karoo. We also provide a brief overview of what is known about MVDs in other provinces such as the Columbia River Basalts, the Afro-Arabian province, the Deccan Traps, the Siberian Traps, the Emeishan, and an Archean example from Australia. The thickest accumulations of MVDs occur in Flood Basalt provinces where they underlie the lava pile (Faeroes: N1 km, Ferrar province: z400 m, Siberian Traps: 700 m). In the Faeroes case, the great thickness of MVDs can be attributed to accumulation in a local sedimentary basin, but in the Ferrar and Siberian provinces the deposits are widespread (N310 5 km 2 for the latter). On the Ontong Java plateau over 300 m of MVDs occur in one drill hole without any overlying lavas. Where the volcaniclastic deposits are sandwiched between lavas, their thickness is much less. In most of the cases reviewed, primary MVDs are predominantly of phreatomagmatic origin, as indicated by the clast assemblage generally consisting of Basaltic clasts of variable vesicularity (dominantly non- to poorly-vesicular) mixed with abundant country rock debris. The accidental lithic components often include loose quartz particles derived from poorly consolidated sandstones in underlying sedimentary basins (East Greenland, Ferrar, Karoo). These underlying sediments or sedimentary rocks were not only a source for debris but also aquifers that supplied water to fuel phreatomagmatic activity. In the
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immense vent complex marks Flood Basalt eruption in a wet failed rift coombs hills antarctica
Geology, 2001Co-Authors: James D. L. White, M K McclintockAbstract:Large lava effusions can have impressive explosive antecedents. Although our picture of Flood Basalt is overwhelmingly effusive, phreatomagmatic eruptions have preceded quiet effusion of some Flood Basalts and reflect the same influence of vent architecture and hydrology on eruptive style as seen for small-volume eruptions. The scale of phreatomagmatic deposits associated with Flood Basalts can be huge. At Coombs Hills a vast, but otherwise typical, phreatomagmatic vent complex is exposed over more than 25 km 2 , and its features are interpreted to reflect processes of tephra-jet eruptions with diatreme development. Similar vent complexes are probably the source of laharic deposits reported elsewhere in the Transantarctic Mountains and in the Karoo province of South Africa.
Mike Widdowson - One of the best experts on this subject based on the ideXlab platform.
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new 40ar 39ar dating of the antrim plateau volcanics australia clarifying an age for the eruptive phase of the kalkarindji continental Flood Basalt province
Journal of the Geological Society, 2018Co-Authors: Peter E Marshall, Mike Widdowson, S P Kelley, Alison M Halton, Sarah C SherlockAbstract:The Kalkarindji Flood Basalt province of northern Australia erupted in the mid-Cambrian. Today, the province consists of scattered volcanic and intrusive suites, the largest being the Antrim Plateau Volcanics (APV) in Northern Territory. Accurate dating of the Kalkarindji Flood Basalt province has proved challenging, with previous studies focused on minor volcanic rocks and intrusive dykes in Northern Territory and Western Australia. These previously published data, corrected to the same decay constants, range from 512.8 to 509.6 ± 2.5 Ma [2σ], placing the Kalkarindji Flood Basalt province in apparent synchronicity with the Cambrian Stage 4–5 biotic crisis at 510 ± 1 Ma. This study utilizes 40Ar/39Ar dating of Basalts from the APV to accurately date the major volcanic eruptions in this province. The results yield an age of 508.0–498.3 ± 5.5 Ma [2σ], indicating that the APV is younger than the intrusive rocks. These dates allude to a relative timing discrepancy, where intrusive activity in the North Australian Craton preceded the eruption of the APV as the last magmatic activity in the region. The determination of these largest eruptions to be later than 510 Ma effectively disassociates the Kalkarindji lavas from being a major cause of the 510 Ma biotic crisis, but cannot definitively discount any deleterious effects on the fragile Cambrian ecosystem. Supplementary material: 40Ar/39Ar analysis data tables, XRF geochemical data, alteration study and photomicrographs of all five samples are available at: https://doi.org/10.6084/m9.figshare.c.4176674
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tectonic setting and timing of the final deccan Flood Basalt eruptions
Geology, 2010Co-Authors: Peter Hooper, Mike Widdowson, S P KelleyAbstract:The role of extensional tectonics in the generation of Basaltic melt and eruption of continental Flood Basalts is controversial, and yet it remains crucial to understanding the origin and cause of these large-volume eruptions. Establishing the timing of lithospheric extension, continental rifting, and the onset of continental Flood Basalt volcanism is therefore of importance to petrogenetic models. Detailed mapping along the Mumbai coast, India, reveals three chemically distinct sets of dikes, which, together with high-precision 40 Ar/ 39 Ar dating, demonstrate the temporal relationship between lithospheric extension and Deccan volcanism. The east-west extension evident along the west coast of India, which led to the separation of the Seychelles from the Indian plate, only began during the final phases of the Basalt eruptions, and cannot have initiated the large-volume eruptions of the Deccan Flood Basalt province.
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new 40ar 39ar dating of the grande ronde lavas columbia river Basalts usa implications for duration of Flood Basalt eruption episodes
Lithos, 2010Co-Authors: T. L. Barry, Stephen Self, S P Kelley, Stephen P Reidel, P Hooper, Mike WiddowsonAbstract:Abstract Grande Ronde Basalt (GRB) lavas represent the most voluminous eruptive pulse of the Columbia River–Snake River–Yellowstone hotspot volcanism. With an estimated eruptive volume of 150,000 km 3 , GRB lavas form at least 66% of the total volume of the Columbia River Basalt Group. New 40 Ar/ 39 Ar dates for GRB lavas reveal they were emplaced within a maximum period of 0.42 ± 0.18 My. A well-documented stratigraphy indicates at least 110 GRB flow fields (or individual eruptions), and on this basis suggests an average inter-eruption hiatus of less than 4000 years. Isotopic age-dating cannot resolve time gaps between GRB eruptions, and it is difficult to otherwise form a picture of the durations of eruptions because of non-uniform weathering in the top of flow fields and a general paucity of sediments between GR lavas. Where sediment has formed on top of GRB lavas, it varies in thickness from zero to 20–30 cm of silty to fine-sandy material, with occasional diatomaceous sediment. Individual GRB eruptions varied considerably in volume but many were greater than 1000 km 3 in size. Most probably eruptive events were not equally spaced in time; some eruptions may have followed short periods of volcanic repose (perhaps 10 2 to 10 3 of years), whilst others could have been considerably longer (many 1000 s to > 10 4 years). Recent improvements in age-dating for other continental Flood Basalt (CFB) lava sequences have yielded estimates of total eruptive durations of less than 1 My for high-volume pulses of lava production. The GRB appears to be a similar example, where the main pulse occupied a brief period. Even allowing for moderate to long-duration pahoehoe flow field production, the amount of time the system spends in active lava-producing mode is small — less than c . 2.6% (based on eruption durations of approximately 10,000 years, compared to the duration of the entire eruptive pulse of c. 420,000 years). A review of available 40 Ar/ 39 Ar data for the major voluminous phases of the Columbia River Basalt Group suggests that activity of the Steens Basalt–Imnaha Basalt–GRB may have, at times, been simultaneous, with obvious implications for climatic effects. Resolving intervals between successive eruptions during CFB province construction, and durations of main eruptive pulses, remains vital to determining the environmental impact of these huge eruptions.
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new palaeomagnetic data from the mahabaleshwar plateau deccan Flood Basalt province india implications for the volcanostratigraphic architecture of continental Flood Basalt provinces
Journal of the Geological Society, 2009Co-Authors: Anne E Jay, Mike Widdowson, Stephen Self, Conall Mac Niocaill, William L TurnerAbstract:Abstract: New magnetostratigraphic data from seven Western Ghats sections in the Deccan Volcanic Province are presented. These are combined with an established geochemically defined stratigraphy, and volcanological logs, to provide a correlated, chronological eruptive framework. We identify two magnetic polarities in five of the sections, and these are assigned to chrons 29r and 29n. Importantly, the reversal boundary represents an identifiable isochronous surface within the volcanic pile. This surface occurs at different elevations, as does the altitude of the geochemically defined formation boundary (i.e. Ambenali–Mahabaleshwar Fms), which defines a second isochronous surface. Inspection reveals significant differences in the number and thickness of lava units preserved between these two surfaces. This indicates that there was significant local topography ( c . 80 m) across Deccan Volcanic Province lava fields during their development; an interpretation consistent with topographies observed across modern and historical examples (e.g. Hawaii, Iceland). These data also indicate that the geochemical stratigraphies of continental Flood Basalt provinces can mask local and sub-regional detail in lava stacking patterns when applied at smaller spatial scales ( 2 –10 4 m). Finally, transitional (R–N) directions preserved in some eruptive units place constraints upon the rates of eruption, and indicate c . 2 ka periods of volcanic repose.
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stratigraphy structure and volcanology of the se deccan continental Flood Basalt province implications for eruptive extent and volumes
Journal of the Geological Society, 2008Co-Authors: Anne E Jay, Mike WiddowsonAbstract:The Deccan Volcanic Province is one of the world9s largest continental Flood Basalt provinces, and derives additional importance because its eruptions (64–67 Ma) straddle the Cretaceous–Tertiary boundary. To better assess the environmental impact of Deccan volcanism, and its possible effect upon Cretaceous–Tertiary boundary biota, it is necessary to document the stratigraphy, chronology and volume of the eruptions. New chemostratigraphical data permit mapping of the SE Deccan. These data strengthen the likelihood that the Rajahmundry Traps of eastern India were originally fed by long-distance flows, and are an extension of the Main Deccan Volcanic Province. An east–west cross-section reveals a depression or ‘moat’ around the SE periphery of the Deccan Volcanic Province. This provided a site in which shallow lakes initially formed, and along which later lava eruptions became channelled and confined. Published palaeomagnetic data indicate that the lavas of the SE Deccan were erupted during Chron 29R, coeval with the Cretaceous–Tertiary boundary, and the chemostratigraphic data place the associated lake sediments (i.e. Lameta Group) beneath and within lavas of the Wai Subgroup. Finally, these new map data are combined with previous work to provide a quantitative estimate for the original Deccan Volcanic Province eruptive volume of c . 1.3 × 10 6 km 3 .