Polyphase Faulting Controlling the Tectono‐Sedimentary and Volcanic History of the SE ‐Bohai Bay Basin, NE China

ABSTRACT The Bohai Bay basin, located at the eastern margin of the North China Carton, underwent a complex tectonic evolution since the Mesozoic. Here, we present high‐resolution seismic profiles across the whole southern Bohai Bay basin, enabling the identification of two types of Mesozoic normal fault systems: an E‐W trending fault set and a NNE trending fault set. Based on drilling data and seismic interpretation, it is inferred that the two sets of normal faults intersected at a high angle (~60°–90°) and developed under NW–SE‐directed extension during the Early Cretaceous rifting episode. However, their orientations are oblique to the regional extension direction, which contrasts with typical rift basins, where fault strikes are nearly perpendicular to the extension direction. Therefore, these fault systems are interpreted as reactivated, preexisting structures. Considering the tectonic events that occurred in the region prior to the Early Cretaceous rifting phase and the cross‐cutting relationships between the two fault sets, the E–W‐striking faults are likely inherited from the N–S‐directed Triassic orogeny, whereas the NNE‐striking faults may have originated from the WNW‐directed Jurassic orogeny. During the Early Cretaceous rifting (~135–102 Ma), both fault systems were reactivated along their original trends. The widespread Early Cretaceous extension promoted volcanic activity, allowing significant volumes of deep‐seated magmatic material to rise along these two sets of faults and to erupt at the surface. The spatial distribution of the volcanic products was structurally controlled by fault boundaries, leading to the formation of a large‐scale, quadrangular Cretaceous volcanic basin.