Using the isotope dating of endocontact hybrid rocks for the age determination of mafic rocks (southern Siberian craton)

Geological observations and petrological and geochemical criteria are used to detect hybrid rocks at the endocontact of a dolerite dike. The hybrid rocks were produced when the material of a mafic intrusion mixed with a felsic melt. The latter was produced by the melting of the metamorphic rocks making up the Goloustnaya basement inlier of the Siberian craton, under the thermal effect of the intruded dike. Two age groups of zircon have been identified in the hybrid rock by SHRIMP analysis. The Paleoproterozoic age of inherited zircon (1902, 1864, 1859, and 1855 Ma) reflects the contribution of ancient sources to the hybrid-rock composition. The young, primary-magmatic, zircon grains, produced by melting at the endocontact of the mafic intrusion (494 ± 5 Ma), are coeval with the hybrid rocks, and their age indicates when the mafic rocks intruded the metamorphic framework. Dikes of close age, with similar geochemical characteristics, are present on the vast southern margin of the Siberian craton—from Goloustnaya to Biryusa salients.