Thermochronology of the Angara–Vitim Granitoid Batholith, Transbaikalia, Russia

Abstract

We reconstructed the history of the Angara–Vitim batholith (AVB), characterized by the formation of huge volumes of granitic magma using thermochronological analysis (40Ar/39Ar, U/Pb) and math testing selected age milestones on the basis of the model crystallization differentiation and dynamics of heat and mass transfer in a magmatic chamber. The consolidation time of the granite melt is estimated to be in the range of 320–290 Ma. Events with age are distinguished based on the presence of isotope dating clusters T1 = 245 ± 1 Ma; T2 = 212 ± 1 Ma; T3 = 156 ± 1 Ma; T4 = 125 ± 2 Ma. The thermal history of samples corresponding to the modern erosion level immediately imposes strict restrictions on the history of consolidation and cooling for rocks corresponding to the deep (>20 km) levels of the magmatic chamber. Calculations show that the lifetime of the residual melt at the deep levels of the magmatic chamber of the AVB can reach 100 Ma. Events with age 245 ± 1, 212 ± 1, 156 ± 1, 125 ± 2 Ma reflect the gradual transformation of the “semi-frozen granite layer” and the discrete nature of its tectonic exposure to the upper level of the Earth’s crust under the influence of tangential elastic deformations caused by the pulsating manifestation of intraplate mantle magmatism within the Siberian platform and its folded frame. The final stage of AVB tectonic exposure to the Earth’s surface (as a solid body) occurred from 60 Ma to the present time, reflecting the process of origin and development of the Baikal rift system.