Abstract Crustal thinning and hyperextension have been clearly imaged and well‐documented in the Qiongdongnan Basin (QDNB), located in the NW South China Sea. Integrated analysis of newly acquired 3D seismic data, covering the majority of the QDNB, reveals the presence of two distinct fault systems: a NE‐trending set and an E‐W‐trending set, both of which played significant roles in controlling sedimentation patterns and crustal deformation during Cenozoic rifting. The NE‐trending faults were primarily active during a first stage (∼42.5–33.9 Ma) and led to crustal stretching. In contrast, the E‐W‐trending faults developed during a second stage (∼33.9–25.5 Ma) and induced crustal necking and hyperextension, resulting in the formation of metamorphic core complexes and associated detachment faults. Kinematic restoration of seismic profiles indicates that detachment fault activity and crustal thinning progressed through a gradual westward migration during the second stage. This evolution followed a core complex necking model, wherein ductile lower crustal material flowed into the footwall region beneath the detachment fault, thereby expanding the exhumation domain until the lower crust in the hanging wall was fully attenuated. Subsequently, fault deformation transitioned from decoupled to coupled behavior, with strain progressively localizing within the brittle upper crust of the hanging wall, ultimately resulting in the formation of a hyperextended crustal architecture.
Xu et al. (Sun,) studied this question.