How Pre‐Existing Strength Heterogeneities and Differential Extension Shaped Rift Initiation and Propagation in the South China Sea: An Analog Perspective

Abstract

Continental rifting rarely occurs synchronously along strike and with uniform width. Instead, it commonly involves diachronous, progressive opening and rift propagation resulting in V‐shaped rifts. Rotational, scissor‐like opening is a common model explaining V‐shaped rifts near plate tectonic rotational poles with steep extension gradients along‐strike. However, the mechanisms driving V‐shaped rifts located far from such poles, such as the South‐China Sea (SCS), remain less well understood. Here, we use crustal‐scale analog modeling to investigate the processes and mechanisms of V‐shaped rift formation in regions distant from rotational poles, taking the SCS as a prototype. Our results demonstrate that the V‐shaped opening of basins can be governed by the combined effects of differential extension and inherited strength heterogeneities in the lithosphere. Applied to the SCS, our models indicate that along‐strike variations in Proto‐SCS subduction drove spatially variable extension, producing east‐to‐west diachronous rift initiation and contrasting crustal‐thinning patterns between the eastern and western segments. In addition, weak remnants of Mesozoic magmatic arcs in the eastern segment and strong, pre‐existing continental basement blocks in the western segment acted as key structural‐rheologic controls on strain localization, shaping the geometry of the basin and regulating the degree of necking along the continent–ocean boundary. Collectively, these processes produced the east‐ward younging and narrowing V‐shaped rift represented by the SCS today. These findings provide new insights into the debated origin of the SCS in particular and broadens our understanding of rift propagation in settings distant from rotational poles in general.