Os, Nd and Sr isotope and trace element geochemistry of the Muli picrites: Insights into the mantle source of the Emeishan Large Igneous Province
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Large igneous province
Flood basalt
The Late Cretaceous-Early Tertiary Deccan Large Igneous Province (LIP) is one of the largest continental flood basalt provinces on Earth and extends from west coast of India to the area around Nagpur in central India. Here we present comprehensive whole-rock geochemical data (major and trace elements) for the six Deccan basalt lava flows exposed within Nagpur city. The horizontal basalt lava flows are in places separated by the partings of the Intertrappean Beds or red/green ‘bole’ horizons (inter-basaltic weathered material). Petrographically the basalts are either fine grained equigranular or exhibit a microporphyritic texture with plagioclase and olivine occasionally occurring as phenocrysts. Chemically, the basalts are low K, high Ti tholeiites that have a slightly oversaturated quartz normative character. It is concluded that there is definite evidence of the process of differentiation having operated in producing the basaltic lava flows at Nagpur.
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Deccan Traps
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Chromite
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The middle Miocene Columbia River Basalt Group (CRBG) is the youngest, smallest, and best-preserved continental flood-basalt province on Earth. The CRBG covers ~210,000 km2 of the Pacific Northwest, USA near the British Columbia border. CRBG consists of ~210,000 km3 of basalt that began erupting ~16.7 Ma in the southern part of the province with younger eruptions progressively migrating northward; the last eruption occurred at ~ 5 Ma. The CRBG consists of seven formations. The Steens Basalt is the oldest but the next oldest, the Imnaha Basalt, began erupting near the end of the Steens volcanic episode. After a short hiatus at the end of the Imnaha Basalt, the Grande Ronde Basalt began to erupt. Both the Picture Gorge Basalt and Prineville Basalt erupted simultaneously with the Grande Ronde Basalt. The Steens, Imnaha, and Grande Ronde Basalts are the main phase of the eruptions representing ~ 94% of the CRBG volume. The Wanapum Basalt followed the Grande Ronde Basalt, which in turn was followed by the Saddle Mountains Basalt, the final phase of the eruptions. The formations, members and many flows of the CRBG can be identified by using a combination of major, minor and trace element compositions, lithology, magnetic polarity, and stratigraphic position. This allows the aerial extent and volume of the individual flows and groups of flows to be calculated and correlated with their respective dykes and vents. The eruption and emplacement rate of the flows has been controversial, with various lines of evidence suggesting that some flows erupted very rapidly and others probably erupted over much longer periods of time. The CRBG was probably derived from a mantle plume, although this conclusion is controversial. Compositions indicate the CRBG magmas underwent varying degrees of recharge, contamination, and fractionation prior to each eruption. Although the peak eruptions occurred during the middle Miocene Climatic Optimum, at present no significant extinction or environmental consequence has been correlated with the CRBG.SOMMAIRELe Groupe de basaltes du fleuve Columbia (CRBG), du Miocène moyen, est la plus jeune, la plus petite et la mieux préservées des provinces de basaltes de plateau de la planète Terre. Le CRBG couvre une superficie d’environ 210 000 km2 dans la portion nord-ouest des États-Unis du Pacifique près de la frontière avec la Colombie-Britannique. Le CRBG, c’est environ 210 000 km3 de basaltes dont les premiers épanchements se sont produits il y a environ 16,7 Ma dans la portion sud de la province, les éruptions plus jeunes migrant progressivement vers le nord, la dernier s’étant produit il y a environ 5 Ma. Le CRBG est constitué de sept formations. La formation de basalte de Steens est le plus ancienne, mais la suivante, celle du basalte d’Imnaha est entrée en éruption près de la fin de l’épisode volcanique de Steens. Près une courte pause à la fin de l’épisode du basalte de la formation d'Imnaha, l’éruption du basalte de Grande Ronde a commencé. Et le basalte de Picture Gorge et le basalte de Prineville ont fait éruption en même temps que le basalte de Grande Ronde. Les basaltes de Steens, d’Imnaha, et de Grande Ronde forment la principale portion des éruptions avec environ 94% du volume du CRBG. Le basalte de Wanapum a succédé au basalte de la Grande Ronde, puis ce fut le basalte de Saddle Mountains, la phase finale des éruptions. Les formations, les membres et le nombre de coulées du CRBG peuvent être définis par analyse de leur composition en éléments majeurs, mineurs et traces, leur lithologie, leur polarité magnétique, et leur position stratigraphique. Ce qui permet d’estimer l’étendue et le volume de coulées individuelles, de groupes de coulées, et de les relier avec leur cheminée et dikes respectifs. Le taux des flux éruptifs ainsi que le leur mise en place ont été sujet à controverse étant donné que certaines indications suggèrent que certaines éruptions ont été très rapides alors que d'autres se seraient produites sur des périodes beaucoup plus longues. Le CRGB est probablement issus d’un panache mantellique, mais cela demeure controversé. Les compositions relevées indiquent que les magmas du CRBG ont subi à des degrés divers, des recharges, des contaminations et du fractionnement par cristallisation avant chaque éruption. Bien que les plus fortes éruptions se soient produites durant la période climatique optimum du Miocène moyen, jusqu’à présent, aucune extinction significative ou répercussion environnementale ont été mises en corrélation avec le CRBG.
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Large igneous province
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Flood basalt
Large igneous province
Petrogenesis
Mantle plume
Fractional crystallization (geology)
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Flood basalt
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The basalts of Patagonia, as determined from the literature and from the microscopical and chemical study of rocks from three widely separated localities, are found to belong to those slightly undersaturated types which appear to be characteristic of plateau-basalts in the restricted sense of Gregory and Reck. This type contrasts with that of flood-basalts which, in general, are oversaturated with silica.
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Deccan Traps
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More and more geochronological data show that large igneous province(LIP)coincide with the mass extinction event.At present,the late Permian Emeishan Flood Basalts province is commonly accepted as the large igneous province relative to mantle plume in China.In order to probe the environmental effect of the Emeishan LIP,the carbon isotopes of the marine carbonate rocks of the Lekang section in Wangmo County,Guizhou Province is performed.The results show that the evolution of δ 13C in this profile can be divided into three segments.The highly positive δ 13C(δ 13C=5.2‰ ～ 4.0‰)values during the Wuchiapingian suggest a mild climate and blooming of biomass.Before the eruption of the Emeishan flood basalts,the rapid crustal uplift was developed,which resulted in the regressing in the region.The extinction of biomass and the oxidation of the previously buried organism result in the drop of δ 13C values during regressing,and most of δ 13C values vary from 2‰ to 4‰.After that,the intensive volcanic activity in the southwest of China associated with the Emeishan LIP cause the further decrease of the δ 13C values.The δ 13C values fluctuate between 0‰ and 2‰.That is because the recovery was very slow in the severe environment during the volcanic activity,and the volcanic can release the CO2,which is isotopically light.The enrichment of the carbon isotope of the organisms after extinction cannot counteract the carbon isotope drops from volcanic eruption.Carbon isotope patterns indicate important information on the environmental effect during the Emeishan LIP activity.
Large igneous province
Flood basalt
Mantle plume
Permian–Triassic extinction event
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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.
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Deccan Traps
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Flood basalt
Large igneous province
Trace element
Mantle plume
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