Multiphase faults activation in the southwest Huizhou Sag, Pearl River Mouth basin: Insights from 3D seismic data

The southwest Huizhou Sag is located in the Zhu I depression in the northern part of Pearl River Mouth Basin, which is influenced by the pre-existing basement fabrics and multiphase rifting, and has complex fault patterns in the Cenozoic. Using 3D seismic data of the southwest Huizhou Sag, we used seismic interpretation, fault pattern analysis from isochron maps, detailed fault throw analysis and structural evolution section analysis to constrain the initial formation timing, active periods and genesis of different striking normal faults, and the influence of basement faults on Cenozoic faults and the evolution progress of the sag was discussed, which significantly improve our understanding on the tectonic evolution of the northern Pearl River Mouth Basin. There are four groups of faults developed in the southwest Huizhou Sag, consisting of NE-SW, ENE-WSW, E-W and WNW-ESE striking, and the boundary faults of the subsag are mostly curved. Selective reactivation of ENE-WSW and WNW-ESW striking basement faults controlled the evolution of fault system during the Cenozoic. The southwest Huizhou Sag experienced multiple phases of extension, and the extension direction rotated clockwise from NW-SE to NNE-SSW. During the Early Eocene (Rift Ia), a large number of NE-SW striking faults were formed, accompanied by reactivation of ENE-WSW and WNW-ESW striking basement faults. These group of faults continued to be active during the Middle Eocene (Rift Ib) and some ENE-WSW striking faults were newly formed. The Late Eocene to Early Oligocene (Rift II) was dominated by E-W striking faults, and the depocenter shifted to the northwestern part of the study area. The Middle-Late Oligocene to Quaternary (Post-rift) was dominated by WNW-ESE striking faults, and the depocenter was not obvious.