Mantle convection pattern and subcrustal stress field under Asia

Abstract

Gravitational field models derived from satellite tracking and surface gravity data have been used to derive the forces in the earth's mantle under Asia. Based on studies of tectonic forces from these models, a subcrustal stress field under China has been obtained. The stresses are due to mantle convection. According to the stress patterns, the east and west China blocks and five seismic zones are identified. The tensional stresses exerted by the upwelling mantle convection flows under the crust of Tibet seem to be related to the Tibetan uplift. The compressional orogenic region from the southern tip of Lake Baikal, through Tien Shan, Hindu Kush and the Himalayas to northern Burma appears to be connected with the downwelling mantle convection flows. It is found that the directions of the subcrustal stresses under China are disposed perpendicularly to the major fault systems and seismic belts. The results of stress calculations show that the crust of north China should be in compression and that stresses within it should be sufficient to form the Shansi Graben and Linfen Basin Systems and fracture the lithosphere. This gives a possible explanation of why strong earthquakes occurred in north China which is an isolated narrow region of highest seismicity far from plate boundaries. The tensional stress fields, caused by the upwelling mantle convection flows, are found to be regions of structural kinship characterized by major concentrations of mineral and metal deposits in China.