Development of detachment fault system associated with a mature metamorphic core complex: Insight from the Kaiping Sag, northern South China Sea rifted margin

Abstract

Detachment fault system associated with a mature metamorphic core complex (MCC) is still not well understood. Using high-resolution 3D seismic data, we analyse the geometries and kinematic development of detachment fault system associated with a mature and exhumated MCC in the northern South China Sea rifted margin, with an emphasis on the MCC-associated faults within the supra-detachment basin. Faults within the supra-detachment basin can be classified into three stages, the pre-MCC, syn-MCC and post-MCC faults, based on their formation time relative to the MCC. The NE to NEE-striking pre-MCC faults developed in the early syn-rift 1 stage, and the NW to WNW-striking post-MCC faults were both dominated by the regional tectonics and are perpendicular to the extension directions. While the syn-MCC faults, synchronous with the MCC development in the late syn-rift 1 stage, show overall EW-striking, consistent with the long axis of the KP MCC. These syn-MCC faults were well developed and are significant in shaping the basin architecture. Besides, the syn-MCC faults are regularly distributed in the four zones overlying the convex-upward master detachment fault surface, and are defined in this study as a synthetic fault zone, an upper collapse synformal-graben fault zone, a lower collapse antiformal-graben fault zone and an antithetic fault zone respectively. These four fault zones show distinct features and evolutionary patterns, and have a closed relationship with the rolling-hinge process of the KP MCC. An evolutionary model is established for the development of MCC-associated detachment fault system which should have global implications.