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 an 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.

The structure of the Taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment. In recent years, however, a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust, suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment, imbricate thrust belt model. To address this issue, we present new geological mapping, together with earthquake focal mechanism and seismic energy release data from the central part of Taiwan. We concur with the interpretation that the foreland basin part of the Western Foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth. To the east of the foreland basin, however, in the Hsuehshan and Central Ranges, our data show the presence of two fault systems. An earlier, inactive thrust system with a well‐developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more. In the Hsuehshan Range, the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal‐scale positive flower structure. Eastward, in the Central Range, Mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first, now inactive, thrust system. The involvement of deep crustal levels and Mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin‐bounding faults that were located on the Eurasian continental margin.