The influence of pre-existing basement faults on the Cenozoic structure and evolution of the proximal domain, northern South China Sea rifted margin

In this paper, we investigate the structure of the Cenozoic rift basin in the proximal domain of the northern South China Sea (SCS) margin, with an emphasis on the influence exerted by pre-existing basement faults on rift development. Results of our work indicate that the overall rift architecture of the proximal domain of the northern SCS margin is associated with extensional faults arranged in two main structural trends, WNW- to EW- trending and ENE- trending. Structural evidence presented in this paper suggests that extensional faults of the two main structural trends mainly reactivated two pre-existing basement fault systems mapped in previous works, a WNW- to EW- striking thrust fault system (PFS1) and a ENE-striking thrust fault system (PFS2). During the first rifting phase, both pre-existing fault systems were reactivated; however, strains and depocenters were mainly localized on the ENE-striking normal fault system that reactivated the PFS2. On the contrary, in the second rifting phase, extension was mainly accommodated by WNW- to EW- striking normal faults that reactivated the PFS1, while most of the earlier ENE-striking normal faults became inactive or less active. These different degrees of reactivation of the two pre-existing fault systems during the two rifting phases suggest a clockwise rotation of the regional extension direction from NNW-SSE in the syn-rift stage 1 to N-S in the syn-rift stage 2. This study implies that apart from Cenozoic tectonic processes pre-existing structures have also played a key role during rifting evolution across the SCS margin.