Gravity-Driven Collapse of Continental Crust in the Northern South China Sea Margin

Gravity-driven tectonics is a fundamental process in Earth's geological evolution; however, its role and governing mechanisms during syn-extensional deformation at the crustal scale along passive continental margins remain poorly constrained. In this study, we use high-resolution seismic reflection data to investigate coupled brittle and ductile deformation in the Xingning sub-basin of the northern South China Sea. Our analysis documents deformation of the supradetachment basin, the Xingning detachment fault, and associated ductile deformations in the footwall. Key observations include: (1) the supradetachment basin comprises late Eocene syn-rift strata that wedge toward the bounding detachment fault; (2) the NW-striking Xingning detachment fault extends for ~90 km along strike and shows marked along-strike variations in geometry, characterized by a ramp-flat-ramp segment in the southern and northern domains and a listric geometry in the central domain; (3) three footwall domes developed from 40 to 23 Ma; and (4) recumbent folds within the ductile crust beneath the Xingning detachment fault show two distinct hinge orientations, including NW-trending hinges parallel to regional extension and NE-trending hinges aligned with the slip direction of the Xingning detachment fault. The syn-kinematic coupling between detachment faulting and ductile flow is interpreted to reflect gravity-driven collapse along the flank of an elevated ductile dome, thermally weakened by magmatic underplating in the deep crust. These results provide clear evidence for gravity-driven, syn-extensional crustal-scale deformation along a rifted continental margin in the northern South China Sea, highlighting the fundamental role of gravitational processes during continental rifting.