3D structure and genesis of synrift uplift within the Baiyun Sag, northern South China Sea

The South China Sea (SCS) is located in the region of convergence between the Eurasian, Indo-Australian and Pacific plates. In previous studies, the diachronic movement of these plates led to a complex picture of tectonic evolution of the rifting stage before opening of the SCS. The Yundong Low Uplift (YLU) is a synrift uplift with an asymmetric structure located in the Baiyun Sag in the northern SCS. In this study, the formation process of the YLU is studied on the basis of 3D seismic reflection data. Based on multiple profiles comparing the 3D structures, we determined that the detachment faults controlling the formation of the YLU are composed of several secondary faults. There is significant cross-cutting and uplift on these secondary faults, accompanied by rotation of the fault blocks, denudation of the strata and some synrift magmatism. Therefore, the cross-cutting and merging relationships of multiple faults revealed in the seismic profiles indicate that the formation of the YLU in the northern SCS is consistent with the classical listric normal fault-controlled model proposed for North American metamorphic core complexes. Finally, we determined that the YLU formed during the synrift stage and underwent three uplift processes, and the formation of the YLU corresponded to the Huizhou movement ( c. 43 Ma) defined by previous studies in the Zhu 1 Depression. This study enriches the model for genesis of synrift uplift in the northern SCS margin, and also contributes to our understanding of the regional tectonic evolution.