Abstract
We present new high-precision 40Ar/ 39Ar ages on feldspar and biotite separates to establish the age, duration and extent of the larger Siberian Traps volcanic province. Samples include basalts and gabbros from Noril'sk, the Lower Tunguska area on the Siberian craton, the Taimyr Peninsula, the Kuznetsk Basin, Vorkuta in the Polar Urals, and from Chelyabinsk in the southern Urals. Most of the ages, except for those from Chelyabinsk, are indistinguishable from those found at Noril'sk. Cessation of activity at Noril'sk is constrained by a 40Ar/ 39Ar age of 250.3 ± 1.1 Ma for the uppermost Kumginsky Suite. The new 40Ar/ 39Ar data confirm that the bulk of Siberian volcanism occurred at 250 Ma during a period of less than 2 Ma, extending over an area of up to 5 million km 2. The resolution of the data allows us to confidently conclude that the main stage of volcanism either immediately predates, or is synchronous with, the end-Permian mass extinction, further strengthening an association between volcanism and the end-Permian crisis. A sanidine age of 249.25 ± 0.14 Ma from Bed 28 tuff at the global section and stratotype at Meishan, China, allows us to bracket the P–Tr boundary to 0.58 ± 0.21 myr, and enables a direct comparison between the 40Ar/ 39Ar age of the Traps and the Permo–Triassic boundary section. Younger ages (243 Ma) obtained for basalts from Chelyabinsk indicate that volcanism in at least the southern part of the province continued into the Triassic.
Highlights
The outpouring of enormous volumes of magma during short periods of time produces socalled large igneous provinces (LIPs) on the Earth’s seafloor and continents
Russian geologists have placed the Permo-Triassic boundary at the transition, but biostratigraphic ages on the sedimentary rocks immediately overlying the unconformity are lacking
The Global Stratotype Section and Point (GSSP) of the Permo-Triassic (P-Tr) boundary is located within Section D, at Meishan, South China (Yin et al, 2001)
Summary
The outpouring of enormous volumes of magma during short periods of time produces socalled large igneous provinces (LIPs) on the Earth’s seafloor and continents. The Siberian Traps represent the largest continental flood basalt province, and they have been linked to the end-Permian crisis, the largest known mass extinction (Erwin, 1994; Wignall, 2001). Ar/39Ar dates on basalt plagioclase refine the timing of the emplacement of the province, and to assess its geographical extent To this end we have analysed a series of samples from Noril’sk and Tunguska on the main outcrop of the Traps exposed on the Siberian craton and from a series of geographically dispersed outliers of basalt This will aid in refining the timing of deposition between Meishan Beds 25 and 28 bracketing the P-Tr boundary
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