Late Paleozoic-Cenozoic Tectonothermal Evolution of Transbaikalia: Thermochronology of the Angara-Vitim Granitoid Batholith

The tectonothermal evolution of Transbaikalia is reconstructed using U/Pb, Ar-40/Ar-39, and apatite fission track thermo-chronology of samples from the Late Paleozoic Angara-Vitim granitoid batholith (AVB). Successive closure of the zircon and amphibole isotope systems provides evidence that the AVB rocks cooled down rapidly soon after crystallization and 7-4 km of rocks were denuded subsequently during an extensive late Paleozoic orogeny in southern Siberia. The isotopic system of feldspar closed in the Middle Jurassic-Early Cretaceous (170-140 Ma) after a period of tectonic stability and slow closure of the biotite isotopic system in the early Permian-Middle Jurassic (295-170 Ma). The 170-140 Ma span was the time when the Mongol-Okhotsk orogen began its evolution, and the orogeny caused denudation of similar to 3 km of rocks. Denudation was slow in the Paleogene-Miocene (60-5 Ma) but accelerated over the past 5 million years (a similar to 3-2 km thick layer) during rapid cooling of rocks and activity under a far-field effect of the India-Eurasia collision.