Siberian Traps large igneous province: Evidence for two flood basalt pulses around the Permo-Triassic boundary and in the Middle Triassic, and contemporaneous granitic magmatism

摘要

The Siberian Traps large igneous province is of enormous size (~7×10~6km~2) and volume (~4×10~6km~3). It contains effusive, intrusive and volcanoclastic rocks varying in compositions from ultramafic to felsic, though low-Ti basalts and their intrusive analogs are the predominant rock types. In this paper, we provide new ~(40)Ar/~(39)Ar ages for two lava units of the geographic center of the Siberian Traps, the Central Putorana region (240.9±1.3/2.6/5.5 and 246.6±1.4/2.7/5.6Ma, where ages are calculated relative to Bern4M with an assigned age of 18.7 (±0.096) Ma and errors are stated in the form ±x/y/z, where x and y and z are analytical, internal and external errors, respectively), three dolerite sills from the Angara-Taseevskaya syncline of the southeastern Siberian Traps (242.8±1.3/2.6/5.0Ma, 239.1±1.1/2.5/4.9Ma and 255.8±4.7/5.3/6.9Ma) and a lamproite dyke from the Noril'sk region (238.3±1.3/2.6/5.3Ma). In combination with available geochronologic data our results suggest that voluminous low-Ti basaltic magmatism appeared during different pulses. At least two volcanic pulses are recognized: at the Permo-Triassic boundary (~249Ma or 252Ma using the ~(40)Ar/~(39)Ar and U-Pb timescales, respectively) and about 10Ma later in the Middle Triassic. Granitic magmatism overlapped in time with the two flood basalt pulses, but continued into the Late Triassic (~229Ma using the U-Pb timescale). Prolonged magmatism of the Siberian Traps province is also supported by geologic observations and paleomagnetic data. New geochronologic findings are discussed in light of the different models for the origin of the Siberian Traps and applied to a Middle Triassic mass extinction event.