Tectono-stratigraphic evolution of a supra-detachment basin controlled by an exhumed metamorphic core complex: Insights from the northern South China Sea

Supra-detachment basins associated with exhumed metamorphic core complexes (MCCs) are significantly influenced by uplift, flexural deformation, and erosion. However, the tectono-stratigraphic evolution of such basins has not been fully reported. This study investigates a supra-detachment basin (the Kaiping [KP] Sag) above an exhumed MCC (KP MCC) in the northern South China Sea. Due to varied uplift amplitude of the KP MCC along its axis, the rift architecture displays varying degrees of transformation from west to east. Typically, in the KP9 High, the western part of the basin, where the uplift amplitude is the greatest, ∼0.5 km of ductile crust and 1.5 km of sedimentary strata have been eroded. The tectono-stratigraphic evolution of the KP Sag has three main stages: (1) the Early Wenchang stage (pre-MCC), during which the KP Sag initiated as a NE-striking half graben, bounded by a moderate-angle normal fault, controlled by the stretching of the upper brittle crust with regional NW-SE extension; (2) the Late Wenchang stage (syn-MCC), during which the development of the KP MCC induced intense rotation and deformation of the sedimentary strata, resulting in the numerous synthetic and antithetic faults, which transformed the architecture and distribution of the pre-MCC formation and controlled the depocenter of the syn-MCC formation; and (3) the Enping stage (post-MCC), during which the KP Sag experienced widespread exposure and erosion, with the widespread development of the T80 angular unconformity. The Enping Formation thins and overlaps toward the core of the KP MCC, resembling more of a post-rift sag basin.