Rubidium-strontium age of rapakivi-like granites and metasomatities of Katugino-Ayansk zone (North-East Transbaikal region)

New data on age and genetic relations of protoplatform rapakivi-like granites of the Kodarsk complex of the Early Proterozoic and feldspar metasomatities of the Katuginsk field obtained by the isochonous Rb-Sr method are considered. Data on strontium isotopic composition are presented along with Rb and Sr concentrations in granites and metasomatities obtained by the method of isotopic dilution. The absolute metasomatite age constituted 2014+-20 million years. The granite-gneiss age is close to 2280 million years. The above magnitudes confirm the Early Proterozoic age of these formations. The process of formation of feldspar metasomatites and rapakivi-like granites is close to the age boundary of 2 billion years, characterizing the first large-scale epoch of granite formation in the Earth history