Preface: Evolution of the deep South China Sea: Integrated IODP Expedition 349 results

Abstract

The offshore Chinese basins are located in the transition zone from the East Asia to the Western Pacific plate. The Cenozoic evolution of these basins reflects the geodynamic processes in East Asia. However, the coupling of the evolution of the offshore Chinese basins to the geodynamic processes occurring in the East Asian continental margin is still poorly understood. Here, the rifting processes of the offshore Chinese basins and the relationship between the basin evolution and the geodynamic processes of the East Asia Plate were analyzed using seismic data, fault activity, syn-sedimentary fault maps, and isopach maps. In the Offshore Bohai Bay Basin, the regional extension and local shearing occurred simultaneously. Accordingly, the regional NNW-SSE extension and local NNE-strike-slip shearing resulted in the NNE-striking graben-horst structure in the Liaodong Bay area while the NW-striking extensional faults and NNE-striking transtensional faults jointly control the structure of the Bozhong area. In addition, the NNE-striking branches of the Tan-lu Fault Zone led to the pull-apart structure in the Bonan area, and the NW-striking normal faults governed the half-graben structure in the Boxi area. Two stages of eastward movement of the rifting center in the East China Sea Basin were triggered by a change in the direction of subduction of the Pacific plate at ~43 Ma, and subduction of the Philippine Sea plate at ~20 Ma, respectively. In the South China Sea (SCS), Paleocene to E. Eocene initial extension occurred in the present northern and southern marginal basins of the SCS. Subsequently, the Ailao Shan Red River shear zone (ASRRSZ) traversed the eastern margin of the Indochina block, and pull-apart rifting dominated in the basins along this fault. Combined with the southward slab pull of proto-SCS and the strike-slip movement of ASRRSZ, sea floor spreading occurred, and the southern marginal basins drifted southerly and apart from the South China from 33 to 16 Ma.