3D structure and development of a metamorphic core complex in the northern South China Sea rifted margin

The 3D structure of continental metamorphic core complexes (MCCs) and their co-evolution along with the associated extensional detachments are still not well understood. In this study, analysis of a newly acquired high-resolution 3D seismic reflection volume reveals for the first time a well-imaged MCC in the proximal northern South China Sea (SCS) rifted margin, the Kaiping MCC (KP MCC). These data provide a 3D view of the KP MCC and the associated KP detachment fault. The KP MCC is characterized by ascend of ductile mid-crustal materials, and it is partially exhumated in the KP9 High. The KP detachment fault displays a domed low-angle geometry, and is characterized by pronounced NS-plunging corrugations, among which two mega-corrugations of tens of kilometers are revealed. Evidence show that the KP MCC developed according to the classical rolling-hinge model. A group of secondary normal faults and fractures, which are parallel to the axis of the KP MCC and offset the KP detachment surface at the crest of the MCC, developed in response to inelastic bending during progressive warping of the footwall. The migration of the domal seismic reflection layers provides a visual evidence for the kinematic process of the rolling-hinge activity, during which the brittle-ductile transition (BDT) and the rolling hinge gradually migrate as the detachment fault slips. The origin of the KP MCC in the northern SCS margin is suggested to have been favored by the existence of a pre-existing mid-crustal ductile layer and basement structures within the upper brittle crust.