蒙古-贝加尔地区上地幔小尺度对流及地球动力学意义

Small-scale upper mantle convection is one of the main mechanisms to control regional geodynamic processes. Some regional geodynamic processes in the Mongolia-Baikal Rift Zone (MBRZ) are suggested to be related to the small-scale upper mantle convection beneath the area. The aim of the present work is to study the small-scale upper mantle convection beneath the MBRZ by gravity data, and to investigate its contribution to the regional dynamics. Based on the equations relating regional isostatic gravity anomalies and small-scale upper mantle convection, the convection flow field beneath the MBRZ and convection-generated stress field were investigated by using the regional isostatic gravity anomalies data. The numerical results exhibit a very complicated pattern of the mantle convection and the generated stress field, which correlates well with the regional tectonics. The mantle flow and the stress beneath the Siberia Platform and Mongolian fold belt are weak, being consistent with the current inactive tectonics in these regions. A mantle upwelling and extension stress regime is found beneath the Baikal Rift Zone. The magnitude of the extension stress is low Q-8 MPa) , suggesting that the mantle convection is not the cause responsible for the rifting of the Baikal rift. Mantle upwellings are also found beneath the Hangay Plateau, Altai and Gobi-Altai, leading to extension stress in these regions. The mantle upwellings may be the mechanism responsible for the uplift of the Hangay Plateau, and the dynamic background for defining the western boundary of the Amurian Plate.