Nature and Age of Metamorphic Rocks from the Basement of the West Siberian Megabasin(according to U-Pb Isotopic Dates)

摘要

The SHRIMP-Ⅱ zircon U-Pb dates for metamorphic rocks from the West Siberian basement are determined for the first time. It is established that the major protolith of the metamorphic strata from the Shaimsk-Kuznetsovsk meganticlinorium is composed of sedimentary Late- and Middle-Devonian rocks (395-398 Ma). It is likely that the greywackes, whose strata were mainly formed under erosion of ophiolitic rocks, served as a substrate for the metamorphic rocks. The metamorphic transformations of the rocks occurred under conditions of greenschist and occasionally lower amphibolite facies of metamorphism during the Late Carboniferous-Early Permian period.