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.

中文翻译：

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南海北部裂谷边缘既有基底断裂对新生界结构和近邻区域演化的影响

在本文中，我们研究了南海北部边缘（SCS）近端区域的新生代裂谷盆地的结构，重点研究了既存的基底断层对裂谷发育的影响。我们的研究结果表明，南海北部边缘近端裂谷的整体构造与伸展断裂相关，布置在两个主要的构造趋势上，即WNW-EW向和ENE-趋势。本文提供的结构证据表明，这两个主要结构趋势的伸展断裂主要是重新激活了先前工作中映射的两个既有的地下断裂系统，即一个从WNW到EW的逆冲冲断层系统（PFS1）和一个ENE冲动冲断层。系统（PFS2）。在第一个裂谷阶段，两个先前存在的断层系统都被重新激活。然而，应变和震源主要集中在重新启动PFS2的ENE打击正常断层系统上。相反，在第二裂谷阶段，扩展主要是由重新激活PFS1的WNW向EW冲击正常断层提供的，而大多数早期的ENE冲击正常断层则变得不活跃或不活跃。在两个裂谷阶段，两个既有断层系统的不同激活程度表明，区域扩展方向从顺裂阶段1的NNW-SSE到顺裂阶段2的N-S顺时针旋转。这项研究表明，除了新生代构造过程外，先前存在的结构在跨越南海边缘的裂谷演化中也起着关键作用。相反，在第二裂谷阶段，扩展主要是由重新激活PFS1的WNW向EW冲击正常断层提供的，而大多数早期的ENE冲击正常断层则变得不活跃或不活跃。在两个裂谷阶段，两个既有断层系统的不同激活程度表明，区域扩展方向从顺裂阶段1的NNW-SSE到顺裂阶段2的N-S顺时针旋转。这项研究表明，除了新生代构造过程外，先前存在的结构在跨越南海边缘的裂谷演化中也起着关键作用。相反，在第二裂谷阶段，扩展主要是由重新激活PFS1的WNW向EW冲击正常断层提供的，而大多数早期的ENE冲击正常断层则变得不活跃或不活跃。在两个裂谷阶段，两个既有断层系统的不同激活程度表明，区域扩展方向从顺裂阶段1的NNW-SSE到顺裂阶段2的N-S顺时针旋转。这项研究表明，除了新生代构造过程外，先前存在的结构在跨越南海边缘的裂谷演化中也起着关键作用。