The extensional pattern and dynamics of Bohai Bay basin in Late Mesozoic-Cenozoic

Based on analyzing the model parameters of continental extension, the temporal-spatial evolution of igneous rock's geochemical characteristics, the geometry and kinematics of multi-level extension within lithosphere , the match and evolution between stress and deformation fields, this paper focuses on the Bohai Bay basin and its adjacent areas to discuss the dynamic mechanism of rifting in Late Mesozoic-Cenozoic. The continent extended by the way of core complex mode in the north and west of Bohai Bay basin, but by the way of wide rift mode in the south and east in Late Mesozoic. In the process of lithospheric extension, the crust was deformed by simple shear whereas the lithospheric mantle deformed by pure shear. In addition, the geochemical characteristics of igneous rock indicate that the basin was located in a back-arc tensional regime due to the subduction of ocean crust, the lithospheric mantle was of EM1 pattern under the basin and in its north and west, whereas the lithospheric mantle was of the EM2-like pattern in the south and the east of the basin because of the subduction of Yangtze plate. Combined with the stress and deformation fields of the basin, the stress source of rifting should be the tension mainly generated by the relative motion within the plate, and the basin was transformed by the strike slip of Tanlu fault. However, the continent extended by the way of narrow rift mode within Bohai Bay basin in Cenozoic. Additionally, the crust and the lithospheric mantle were deformed exclusively by pure shear, but the latter extended more intensively. On the other hand, the geochemical characteristics of igneous rocks indicate that the basin was involved in the continental rift, and the asthenosphere upwelled and transformed the lithospheric mantle. Apparently, the tension produced by the upwelling of asthenosphere played the crucial role in basin rifting.