Detachment and Transfer Fault Systems in the Northern South China Sea, Insights Into 3D Tectonic Segmentation of Rifted Margins

The 2D rifting modes interpreted in traditional “magma‐poor” and “magma‐rich” margins cannot explain the crustal structure and inferred rifting processes in the northern South China Sea (SCS) rifted margin. The “intermediate‐type” terminology has been therefore applied to the mid‐northern SCS, where a “wide‐rift” model has been widely accepted. However, the tectono‐magmatic processes of the SCS are still debated and at least five contrasting models exist. We present a compilation of 3‐D seismic volumes and regional 2‐D seismic surveys covering the entire Baiyun and Liwan Sub‐basins to investigate their tectonic structure and faulting style in this “wide‐rift” region. We interpret two segments with contrasting tectonic styles separated by a volcanic lineament and steep transfer faults. The Baiyun Sub‐basin was controlled by a landward‐dipping detachment system. The Liwan Sub‐basin, however, was formed by a ∼100 km‐long oceanward‐dipping, concave‐up detachment fault working at a low angle of 190 km‐long N‐S‐trending left‐lateral strike‐slip fault to the east. The planar low‐angle detachment does not resemble classical metamorphic core complex domes interpreted previously. Our results indicate a 60‐80 km‐wavelength segmentation within a single “wide‐rift” system, indicating complex 3D rifting during crustal extension. This study supports that the intermediate SCS margin had a kinematically complex deformation style locally dominated by the interaction between detachment and transfer fault systems that might be yet unrecognized in other margins. Key Points The landward‐dipping Baiyun detachment and seaward‐dipping Liwan detachment were decoupled by a volcanic lineament possibly related to a transfer fault zone The Liwan Sub‐basin with a rough rectangular geometry possibly resembles a non‐typical rhomboidal pull‐apart basin rather than a Metamorphic Core Complex structure A previously undetected short‐wavelength segmentation within a “wide‐rift” system suggests a complex 3D rifting mode not well understood