Rapid eruption of Siberian flood-volcanic rocks and evidence for coincidence with the Permian-Triassic boundary and mass extinction at 251 Ma

摘要

The Siberian flood-volcanic event is the most voluminous and explosive, continental, volcanic event known in the Phanerozoic record. U-Pb perovskite and zircon ages were obtained for lavas of the lowermost unit (251.7±0.4 Ma) and near-uppermost unit (241.1±0.3 Ma), respectively, of the volcanic sequence in the Maymecha-Kotuy area, Russia. Along with stratigarphic correlations and paleomagnetic evidence,these ages suggest that rapid extrusion of the entire ～6500 m thick composite sequence occurred in less than 1 million years. the time of extrusion coincides precisely with an age of 251.4±0.3 Ma previously obtained for the Permian-Triassic mass-extinction event, the most devastating biotic crisis known. Emplacement of the Noril'sk-Talnakh ore-bearing intrusions, notable for their prodigious Cu-Ni-PGE deposits, was synchronous with these two major geologic events at 251.2±0.3 Ma. The Guli volcanic-intrusive complex in the Maymecha-Kotuy area appears to represent the final mafic amgmatism of the entire Siberian flood-volcanic event. Basseleyite from a carbonate that intrudes the complex gives an age of 250.2±0.3 Ma, and shows possible ~(231)Pa excess. The Bolgokhotkh granodiorite stock has a zircon age of 229.0±0.4 Ma, and represents the youngest known magmatism in the region.