Fault interaction and evolution during two‐phase rifting in the Xijiang Sag , Pearl River Mouth Basin , northern South China Sea

Fault geometries, various fault interactions, and fault evolution during the Palaeogene two-phase rifting in the north-west Xijiang Sag, Pearl River Mouth Basin, are examined using 2D and 3D seismic data. The study area is characterised as a half-graben bounded by a NE-striking SE-dipping listric fault, and it has been proven to have undergone two phases of extension during the Palaeogene rifting stage. The study area comprises several fault sets with different strikes, mainly including NE-striking and E-W-striking faults. Various styles of fault interactions have been examined in this study, which vary in different regions. Based on observations made in this study, we suggest that (1) major E-W-striking faults may either abut against or cross-cut the boundary fault; (2) many thin-skinned E-W-striking faults mainly develop in groups in the unruptured sub-sag; and (3) most NE-striking faults are continuously active in Rift Phase 2 on the slope. The NE-striking faults initiated in Rift Phase 1, while most of the E-W-striking faults formed in Rift Phase 2. Our results demonstrate that the major E-W-striking faults are prone to cross-cutting the boundary fault surface during Rift Phase 2, which results in the transformation of two-phase basin architectures. Compared to previous physical model results, we suggest that our natural fault characteristics support the model's conclusions and that the angle between the first- and second-phase extension directions is an important factor that influences the styles of fault interaction and fault evolution during a two-phase extension.