Tectonic evolution of the Northeastern South China Sea from seismic interpretation

We interpret a grid of 2-D seismic reflection profiles to resolve the tectonic evolution of the northeastern South China Sea (SCS), identifying two significant postbreakup events, T1 and T2, which occurred before the end of the SCS opening. In the absence of the drilling data in the deep basin, we date these two events using the identification of the magnetic anomalies, the age of major unconformities at Ocean Drilling Program Site 1148 drilled on the northeastern SCS margin, and the age of basalt samples in the deep SCS. The tectonic phase T1 is a slight tensional tectonic event which occurred in the deep SCS, south of the Luzon-Ryukyu Transform Plate Boundary (LRTPB). It is characterized by oceanic tilted blocks and fan-shaped deposits, which developed 8-10 Myr after the onset of SCS seafloor spreading (37.8 Ma). It corresponds to the first ENE-WSW to E-W change in spreading direction, which occurred around chron C10 (∼28.7 Ma). Event T2 is a magmatic phase observed in the deep SCS, south of the LRTPB. It is characterized by the uplift of former spreading features caused by an early Miocene (∼22 Ma) magmatic phase, which is also recorded in north and south-central Taiwan.