Intracontinental magmatism as an indicator of formation of the Baikal RiftZone

The evolution of the territory of Prebaikalia and Transbaikalla during the last 300 Ma was governed by intraplate sources of tectonomagmatic activity. Geological, geochronological, and isotope-geochemical studies showed the f ollowing epochs of this activity: Late Carboniferous, Late Permian-Triassic , Early Jurassic, Late Jurassic, Early Cretaceous, Late Cretaceous-Early Ce nozoic, and Late Cenozoic. Each epoch is characterized by large-scale occur rences of magmatism of alkaline-basic, alkaline-salic, and alkaline-granite compositions typical of intraplate associations. At the same time, the int raplate geodynamic conditions within this territory established only at the boundary of 170 Ma, and prior to this the intraplate magmatism occurred on the background of geodynamic conditions of continental margin. Isotope-geo chemical characteristics of basic rocks evidence that moderately depleted P REMA-type and Sr-enriched EM-II-type mantle was the source of intraplate pr ocesses and magmatic melts up to the Late Cenozoic. From the second half of the Cenozoic, a source of EM-I-type was also involved in the formation of volcanites. During the intraplate activity, a linear structural plan of dis tribution of taphrogenic zones formed, which was persistent at all stages o f intraplate processes. Formation of the Baikal system of troughs also fitt ed this plan.