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

Abstract

Abstract —The tectonothermal evolution of Transbaikalia is reconstructed using U/Pb, 40Ar/39Ar, 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 ~3 km of rocks. Denudation was slow in the Paleogene–Miocene (60–5 Ma) but accelerated over the past 5 million years (a ~3–2 km thick layer) during rapid cooling of rocks and activity under a far-field effect of the India–Eurasia collision.