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

The Siberian Traps large igneous province is of enormous size (similar to 7 x 10(6) km(2)) and volume (similar to 4 x 10(6) km(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 Ar-46/39Ar ages for two lava units of the geographic center of the Siberian Traps, the Central Putorana region (240.9 +/- 13/2.6/5.5 and 246.6 +/- 1.4/2.7/5.6 Ma, 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 +/- 1.3/2.6/5.0 Ma, 239.1 +/- 1.1/2.5/4.9 Ma and 255.8 +/- 4.7/53/6.9 Ma) and a lamproite dyke from the Noril'sk region (2383 +/- 13/2.6/53 Ma). 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 (similar to 249 Ma or 252 Ma using the Ar-46/39Ar and U-Pb timescales, respectively) and about 10 Ma later in the Middle Triassic. Granitic magmatism overlapped in time with the two flood basalt pulses, but continued into the Late Triassic (similar to 229 Ma 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. (C) 2013 Elsevier B.V. All rights reserved.