⁴⁰ Ar/ ³⁹ Ar Dates from the West Siberian Basin: Siberian Flood Basalt Province Doubled

Abstract

Widespread basaltic volcanism occurred in the region of the West Siberian Basin in central Russia during Permo-Triassic times. New 40 Ar/ 39 Ar age determinations on plagioclase grains from deep boreholes in the basin reveal that the basalts were erupted 249.4 ± 0.5 million years ago. This is synchronous with the bulk of the Siberian Traps, erupted further east on the Siberian Platform. The age and geochemical data confirm that the West Siberian Basin 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.

Crustal redistribution, crust–mantle recycling and Phanerozoic evolution of the continental crust

“…North Atlantic province comprises East and West Greenland, the Faeroes, together with the British Isles, including the Faeroe-Shetland Basin and the Rockall Trough. (Fedorenko et al, 1996;Wignall, 2001;Reichow et al, 2002) (Brown, 1963;Boldreel and Andersen, 1998;Escher and Watts, 1976;Larsen et al, 1992;Emeleus and Bell, 2005;Waagstein, 1988;White et al, 2003) White et al (2008), who examined a range of igneous provinces estimating the ratios of extrusive versus intrusive products. Although ratios ranged wildly in some of the small examples, many of the extrusive: intrusive ratios lie in the range 1:2 to 1:5.…”

“…Because this was emplaced at the PermianTriassic boundary (ca. 250 Ma) (Reichow et al, 2002) we average the net contribution to the crust by dividing the total by 250 Ma. This results in a long-term addition rate of 0.12 km 3 /a for all flood basalt provinces.…”

The Siberian Traps and the End-Permian mass extinction: a critical review

“…We have not included U/Pb ages in this diagram because the techniques used in the preparation of the dated zircons from Meishan [34] and from Siberia [26] are different; we cannot be sure that annealing and leaching will not affect the ages of Siberian zircons (i.e., give them a slightly greater age); this is a discrepancy that needs addressing. From the 40 Ar/ 39 Ar data alone, it is apparent from Figure 3 that there is strong evidence of synchrony between the ages of the extinction event and of the Siberian Traps, as reported by several workers [1,[14][15][16]25,26] .…”

“…Published 40 Ar/ 39 Ar determinations (whole-rock and plagioclase separates) exist for basalts from Noril'sk [14,22,23] , Putorana [14] , Maymecha-Kotuy [24] and the West Siberian Basin [25] (Figure 3 [16] at Meishan, China (see below). Zircons and baddeleyites from intrusions at Noril'sk, together with perovskite, zircon and baddeleyite from Maymecha-Kotuy, give U/Pb concordia ages that are slightly but significantly older than the 40 Ar/ 39 Ar ages.…”

“…Error propagation was established by including the uncertainty of each age as the square root of the sum of the squares of the errors. Sources of data: green symbols: Reichow et al [1] ; red symbols: Noril'sk [14,22,23] , Putorana [14] , Maymecha-Kotuy [24] , and West Siberian Basin [25] . Data for Meishan Bed 28 are from Reichow et al [1] .…”