Rubidium-Strontium Age of Rapakivi Granites From the Primorskii Complex in Western Prebaikalia

A new thorough investigation of Primorskii rapakivi granites has been carried out in four sections of a band extended to 200 km along the Lake Baikal shore. According to the petrochemical data obtained by factor and cluster analyses, granites of the Bugulda-Khargino (BKh) and Sarma-Zunduk (SZ) massifs appeared to be close to each other, while the similar granites in the EIokhin cape are shown to be of low affinity. Isotopic Rb–Sr data for 16 samples of the BKh Massif are described by two isochrons, one of which corresponds to the I phase of intrusion, and the other is related with the II phase of the Primorskii complex granites. Isotopic data for 30 samples of the SZ massif need 3 isochrons for their description. Thus, intense magmatic activity in the western Prebaikalian region did not stop during Middle and Upper Proterozoic. This confirms ideas on polycyclic development of volcano-plutonic formations of the Baikal-Vitim greenstone belt in the Precambrian.