Extensional Structures of the Nanan Basin in the Rifting Tip of the Southwest South China Sea: Implications for Tectonic Evolution of the Western Continental Margin
Based on newly acquired seismic data from the southwestern margin of the South China Sea, this study analysed the structural units, evolution of the main tectonics and geodynamics of the southwest South China Sea margin. The new data suggests that the structural features of Nanan Basin could be a rift basin oriented in the NE-SW direction, rather than a pull-apart basin induced by strike-slip faults along the western margin. Nanan Basin is a continuation of the rifts in the southwest South China Sea since the Late Cretaceous. The basin continued rifting to the middle Miocene, even though oceanic crust occurred in the southwest subbasin. However, it had no transfer surface at the end of spreading, where it was characterized by a late middle Miocene unconformity (reflector T3). The Nanan Basin can be divided into eight structural units with NE-striking faults. This may provide evidence to confirm the relative importance and interplay between regional strike-slips and orthogonal displacement during basin development and deformation. The NE-SW-striking dominant rift basin indicates that the tectonic evolution of the western margin of the South China Sea did not have a large strike-slip mechanism. Therefore, we conclude that a large strike-slip fault system did not exist and or control the evolution of the western margin of the South China Sea.