| Summary: | Widespread basaltic volcanism occurred in the region of the West Siberian Basin (WSB) and the Taimyr Peninsula in central Russia, and voluminous A-type magmatism within the Mongolian-Transbaikalian belt in southeast Siberia, during Permo-Triassic times. New 40Ar/39Ar age determinations on plagioclase grains from deep boreholes in the WSB reveal that the basalts were erupted at ~250 million years ago. This is synchronous with the main period of the Siberian Traps volcanism, which was located farther east. The age and geochemical data presented confirm that the WSB 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. Furthermore, it is argued that the WSB and Taimyr basalts are genetically related to the Siberian Traps basalts, especially the Nadezhdinsky Suite found at Noril’sk. This suite immediately preceded the main pulse of volcanism that extruded lava over large areas of the Siberian Craton. Magma volume and timing constraints strongly suggest that a mantle plume was involved in the formation of the Earth’s largest continental flood basalt province. The Mongolian-Transbaikalian granitoid belt covers over 600,000 km2 with over 350 single A-type plutons. New U-Pb geochronological data presented here demonstrate that no plutonic complex dated is 250 Ma old. Although mantle-derived material played a prominent role in the granitoid generation, these melts may have been generated by processes other than decompressional melting within the head of a mantle plume. The new U-Pb ages and other observations contradict the idea of a relation between the Siberian plume and magmatic activity in the territory of Transbaikalia. An alternative preferred model inducing up rise of asthenospheric material includes slab break-off after a long period of subduction.
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