Cenozoic continental deformation in northern China and its geodynamic mechanism

Abstract: Continental deformation is one of the basic contents of continental dynamics. Researches on the faults and basin?mountain evolution are the most direct and effective way to understand the continental deformation. During the late Mesozoic—Cenozoic, northern China was long influenced by northward subduction of Indian plate, westward movement of Pacific plate and blocking of Siberia plate. The crustal deformation was complex, which made northern China an ideal natural laboratory for the study of continental deformation. In this paper, based on the detailed analysis of field structures, combined with remote sensing and digital geomorphology, seismic reflection data interpretation, and low temperature thermochronology, the authors clarified the fault development sequence and tectonic stress field with the help of studying the Cenozoic faulting and the uplift history of mountain ranges in northern China. The causes of the present tectonic landform pattern difference between eastern and western China were found and the geodynamic mechanism of continental deformation was explored. NNE-striking faults were widely developed in northern China during Paleocene—Early Eocene, but they were not uniform, with larger scale and clear geomorphological features in the east. These NNE-trending faults were characterized by sinistral strike?slip, indicating NW—SE compressive stress field. The authors infer that the forming of NNE strike?slip faults was related to the NNW movement of Pacific plate in early Cenozoic. The NE dextral strike- slip and NW sinistral strike?slip faults, forming a conjugate fault system, developed in Bohai Bay region after the NNE strike?slip faults, and the direction of corresponding compressive stress field was nearly east—west. On the contrary, there were conjugate faults with NE sinistral strike?slip and NW dextral strike?slip in the west of Junggar Basin. The direction of compressive stress field was nearly north—south. These conjugate faults were superimposed on and cut the early NNE strike?slip faults. It is held that the formation of later faults in the east was related to the conversion of the movement direction of Pacific plate from north—northwest to west-northwest in 43~42 Ma. In the west, the later faults resulted from distant effect of the collision between India and Eurasia plates. With the continued northward movement of Indian plate together with the clockwise rotation, the western region maintains experienced north—northeast compressive stress field and developed a series of NW and NNW trending faults, whereas the eastern region still exhibited the EW compressive stress field. Affected by these Cenozoic faults, the mountains and basins in northern China showed a grid pattern assembled by lines and planes. Statistical analysis of apatite fission track ages shows that the eastern region experienced regional uplift?exhumation during Paleocene—Early Eocene (ca. 65~42 Ma). This tectonic event made a major contribution to the formation of present tectonic landform pattern in the east. Different from the east, the western region had undergone regional uplift?exhumation in about 8~6 Ma, hence forming the present tectonic landform pattern.