Baikal rift zone: Structure and geodynamics

Abstract

The Cenozoic Baikal rift zone is superimposed on the Caledonian Baikal fold belt, representing the suture between the Precambrian Siberian craton and several microcontinents. The Baikal rift zone consists of a system of disconnected fault-bounded basins and extensional and wrench faults that straddles a major arch, having a topographic relief of 2–3 km. Rifting activity commenced during the Oligocène and is still active as evident from high seismicity of the Baikal rift zone. Across the Baikal rift zone, upper crustal extension is considerably smaller than would be expected from its crustal thickness which decreases by 8–11 km across the Baikal basins as compared to the adjacent unextended areas. The discrepancy between upper and lower crustal attenuation could be attributed to intrusion of a major diapir. Indeed, geophysical data indicate that the Sayan-Baikal dome coincides with such a diapir, the top of which is located at the crust/mantle boundary. This intrusion is held responsible for Oligocene and Quaternary doming of the rift zone. Development of the intra-continental Baikal rift system is thought to be related to asthenospheric diapirism (active rifting); however, intra-plate stresses in conjunction with the Himalayan collision may have played some role.