Characterization and mapping of continental breakup and seafloor spreading initiation: The example of the northern rifted margin of the South China Sea

Mapping ocean-continent transitions (OCTs) separating equivocal continental and oceanic crusts is fundamental to investigate breakup processes and define the age and location of initial seafloor spreading. However, proposed limits of OCTs are rarely consistent, do not use uniform criteria, and result in conflicting interpretations as shown for the case of the northern South China Sea (SCS). We review original datasets including reflection and refraction seismic sections, drilling and potential field data with the aim to develop a ‘drilling-constrained integrated geological-geophysical’ approach to define the OCT along the northern SCS, understand the breakup process, and to compare the OCT in the SCS with those at Atlantic type rifted margins. The result shows a narrow, 5–15 km wide OCT. It separates a segmented margin that rifted a former arc in the west and a forearc in the east, both facing a Penrose oceanic crust that thins from the west towards the east. Seafloor spreading may have first nucleated at two centres during magnetic anomaly C11 in the NE and central subbasins, which then locally propagated both W and E to break through salients and produce full breakup at 29 Ma (anomaly C10r). Breakup at the SCS shows many differences to Atlantic type margins, in part due to inheritance but also due to rift/spreading-related parameters such as strain/spreading rates.