Structural and kinematic analysis of Cenozoic rift basins in South China Sea: A synthesis

Abstract The East Asian continental margin straddles the boundary between the Pacific Plate subduction Domain to the east and the Indo-Eurasian collision Domain to the west. The spatial and temporal interaction between these two dynamic domains induced dextral trans-tensional stress field, which resulted in generating nearly 75% of the globe's marginal seas and continental margin rifts during the Cenozoic. Among these, the South China Sea (SCS) and its northern margin are located in the core of the Pacific Tectonic Domain and the Tethyan Tectonic Domain. The evolution of the SCS and its northern margin are of prime interest because of the spectacular magnetic lineation and strong rifting. In spite of the several investigations on the Cenozoic marginal seas and rift basins occurred, their mechanisms of formation remain equivocal. Here we perform a comprehensive analysis of seismic profiles and fault architecture data with a view to understanding the Cenozoic tectonic evolution of the northern margin of the SCS. Based on detailed structural analysis of the geometry and kinematics, we demonstrate that the NE- and ENE-striking faults assembled to horsetail- or feather-shaped structures in plan view, with flower-like structures on seismic profiles. Two stages of faulting with NE-trending are identified along the northern margin of the SCS. The earlier oblique extension developed during the Paleocene to the early Middle Eocene (~44–42 Ma), accompanied by strong rifting and some left-stepping en echelon-like faults. The later trans-tensional faulting developed during the late Middle Eocene to the Early Miocene (~21 Ma), resulting in the formation of the dextral right-stepping trans-tensional fault system. Two stages of faulting were linked to the joint effect among the collision domain of Indian-Eurasian plates to the west, the subduction domain of the Pacific Plate to the east and the slab-pull system of the proto-SCS to the south. Our study provides important insights into the dynamics and tectonics that controlled the opening of the South China Sea. During the Late Eocene to the Oligocene, the later trans-extensional faulting and right-stepping strike-slip fault system caused the opening of the Northwest Sub-basin, East Sub-basin and Northeast Sub-basin. However, during the Early Miocene, the left-lateral strike-slip of the Ailao Shan-Red River (ASRR) shear zone and the slab-pull force of the Proto-SCS resulted in the opening of the Southwest Sub-basin and the change in the spreading direction of the East Sub-basin.