Late Cenozoic Volcanism in the Baikal Rift System: Evidence for Formation of the Baikal and Khubsugul Basins due to Thermal Impacts on the Lithosphere and Collision-Derived Tectonic Stress

Abstract

To constrain the timing of uplift and basin subsidence related to the formation of the South Baikal and Khubsugul lake basins, we present new 40 Ar/ 39 Ar and K-Ar geochronology on basalts interbedded occasionally with rift-related sedimentary rocks. Based on the new results and previous data, the late Cenozoic magmatism in the Baikal Rift System is considered to be an expression of four important thermal events in the lithosphere at 22-17 Ma, 16-12 Ma, 12-8 Ma, and 4-0 Ma. It is inferred that tectonic instability was first imparted at 22-17 Ma by a deep thermal event beneath the South Baikal basin, followed at 10-8 Ma by a similar event beneath the Khubsugul basin. These events resulted from tectonic stress associated with the Indian-Asian collision, 3000 km to the south, which was focused along a lithospheric-scale boundary, and in turn triggered upwelling of hot mantle material. Episodes of continued extension at 16-12 Ma and 4-0.6 Ma contributed to the development of the deep lake basins and also led to extensional faulting along the whole length of the rift system.