Source rock deformation and hydrocarbon accumulation controlled by a metamorphic core complex in the northern South China Sea rifted margin

The recent discovery of hundred-million-ton-class oil fields in the Kaiping sag, on the northern South China Sea rifted margin, is considered the first global breakthrough in hydrocarbon exploration within supra-detachment basins controlled by mature metamorphic core complexes (MCCs) at passive margins. We use three-dimensional seismic, petrological, and geochemical data to reconstruct source rock deformation and hydrocarbon accumulation in the context of detachment tectonism associated with uplift of the Kaiping MCC. In the pre-MCC stage, high-quality deep-water lacustrine source rocks of the lower Wenchang Formation were deposited during intense rifting. During the late Wenchang stage, the Kaiping MCC uplifted via a rolling-hinge process, which transformed the original attitude and position of the source rock layers in the lower Wenchang Formation. The distribution of the source rocks can be characterized by three distinct patterns: disconnected with antithetic dip direction (model I), moderate continuous and V-shaped (model II), and continuous with primitive original dip direction (model III). These models control the dominant migration direction of hydrocarbons. Furthermore, extensive development of fault systems and block rotations associated with the Kaiping MCC linked source rocks to traps and influenced local oil migration pathways. The breakthrough of hydrocarbon exploration in the Kaiping sag verifies that supra-detachment basins associated with MCCs also have the potential to develop high-quality source rocks, particularly during the rifting phase preceding uplift of the MCC. The source rock distribution models, antithetic faults, and rotating fault blocks resulting from the Kaiping MCC can serve as a reference model for evaluating source rocks and analyzing hydrocarbon accumulation patterns in similar-type basins.