The ca. 1380 Ma Mashak igneous event of the Southern Urals

Abstract

A review of the geochronology, geochemistry and distribution of the 1380Ma Mashak Large Igneous Province (LIP) of the eastern margin of the East European craton indicates a potential link to a major breakup stage of the Mesoproterozoic supercontinent Columbia (Nuna), link to a major stratigraphic boundary (Lower–Middle Riphean), and economic significance for hydrocarbons and metallogeny. Specifically, the Mashak event likely has much greater extent than previously realized. Two U–Pb baddeleyite (ID TIMS) age determinations on dolerite sills obtained from borehole (Menzelinsk–Aktanysh-183) confirm the western extent of the Mashak event into the crystalline basement of the East European Craton (1382±2Ma) and into the overlying Lower Riphean sediments (1391±2Ma), and the imprecise ages reported elsewhere indicate the possible extension into the Timan region, with an overall areal extent of more than 500,000km2 (LIP scale). It has tholeiitic compositions and is associated with breakup on the eastern margin of the craton – in addition, precise SHRIMP zircon ages of 1386±5Ma and 1386±6Ma (this paper) provide confirmation of previous approximate 1380–1383Ma zircon age determination of the same formation, and suggest an age of ca. 1.4Ga for the Lower/Middle Riphean boundary which was formerly considered to be 1350±10Ma. Contemporaneous magmatic rocks in the northeastern Greenland part of Laurentia (Zig‐Zag Dal and Midsommerso formations) and Siberia (Chieress dykes and other dolerites) together with the Mashak event are suggested to be fragments of a single huge LIP and to correspond to breakup stage of the Columbia (Nuna) supercontinent. The Mashak LIP also has some significance, at least in Volgo-Uralia, for hydrocarbons and metallogeny.