Complex Deformation of Central and North China Through Pn Velocity and Anisotropy Tomography

Abstract

AbstractUsing our recently developed Pn tomography method, we obtain high‐resolution Pn velocity and anisotropy structures of uppermost mantle beneath the Central and North China, which provide useful insight concerning the mechanism of intraplate mantle dynamics. The consistency between the new Pn model and seismic reflection/refraction profiles demonstrates the high quality of our model. Based on the Pn anisotropy structure surrounding the Alxa Block, we infer that material extrusion from northeastern Tibet was impeded and turned to the west and south edges of the Alxa Block. The Pn structures beneath the Sichuan Basin and Songpan‐Ganzi Orogen suggest that the stable Sichuan Basin impeded material extrusion from the Tibetan Plateau and caused material from Tibet to be extruded separately along the west and northwest edges of the Sichuan Basin. To the north of the Sichuan Basin, we infer that the extrusion has ceased within the Songpan‐Ganzi Orogen rather than to further east. The high Pn velocities beneath the Qinling Orogen do not support the proposal of large‐scale eastward material escaping flow in the shallow mantle beneath the western Qinling Orogen. The Pn velocity distribution beneath the North China Craton indicates that hot material from the mantle is more likely to upwell beneath deep faults or active orogenic areas. Our model indicates that the northern and central parts of the Ordos Block retain stable structures at the uppermost mantle, while its southeastern has been reworked by hot material.