Structure and formation mechanism of the Pearl River Mouth Basin: Insights from multi-phase strike-slip motions in the Yangjiang Sag, SE China

• The Pearl River Mouth Basin experienced two stages of strike-slip motions along the ENE and WNW directions. • The partial reactivation of the intrabasement faults controlled the evolution of intrabasin faults. • The formation of the basin resulted from the joint effect of oblique Pacific-Eurasian subduction and the Indo-Eurasian collision. The Pearl River Mouth Basin (PRMB) experienced multi-phase rifting and complex tectono-sedimentary evolution during the Cenozoic, and is a topic of many studies regarding the basin-forming mechanism. In the present study, detailed seismic interpretation and tectonic analysis based on the 3D seismic reflection data of the Yangjiang Sag in the northwestern PRMB were carried out, to provide clues to its tectonic evolutionary history. The qualitative-quantitative analysis of fault strikes and migration of depocenter in the Yangjiang Sag indicated the dextral transtensional setting during the Paleocene to Miocene. Meanwhile, the horsetail and en echelon structures on plane view and negative flower structures in cross-section are exhibited, indicating the successive occurrence of strike-slip motions in ENE and WNW directions respectively after initial rifting combined with the structural analysis of Huizhou Sag and Baiyun Sag. In addition, thrust fault systems trending in WNW and ENE were identified in the basement. Their partial and selective reactivation in strike-slip character during the Cenozoic restricted the faults developed in the basin with differential properties. Geometrically, rhombic-shaped sags with cross-basin fault zones were formed, implying the formation of pull-apart structures along with multi-phase strike-slip motions. The pull-apart mechanism could be accounted due to the joint effect of the oblique Pacific-Eurasian subduction and the Indo-Eurasian collision during the Cenozoic.