From Orogeny to Rifting: The Role of Inherited Structures During the Formation of the South China Sea

Many of the world's rifts and rifted margins have developed within former orogens. The South China Sea (SCS) formed during Cenozoic rifting by utilizing pre-existing orogenic structures, like thrust faults, thickened crust, and corresponding thermal weaknesses. The mechanisms explaining how inherited structures influence the spatiotemporal evolution of a rift remain a topic of on-going research. Here, we explore the impact of orogenic inheritance on rift evolution through a numerical forward model that reproduces geodynamic and landscape evolution processes. By imposing time-dependent phases of shortening and extension, we model rifted margin formation that is consistent with the available geological and geophysical observations of the SCS. Our numerical models allow us to identify thrust faults that are reactivated as normal faults during extensional phases. Not all pre-existing thrust faults, however, undergo full reactivation, as their behavior is influenced by variations in lithospheric strength and the pre-existing structural discontinuities. We further show that inherited orogenic structures compete with each other during extensional reactivation and ultimately govern the location of continental breakup. Our results provide valuable insights into the broader implications of inherited orogenic structures and how they affect subsequent rift system evolution.