Crustal Segmentation Between Failed Rift and Successful Rifted Margin Along the NW South China Sea

Abstract

Most works propose a genetic “wide-rift” model for the northern South China Sea (SCS) rifted margin, where low-angle detachment faults accommodate significant deformation during crustal extension. However, a new seismic grid along the northern SCS shows along-strike changes in tectonics. At least two distinct tectonic domains, i.e., “wide-rift” Eastern Domain and “narrow-rift” Western Domain, have been revealed, which indicates that the current conceptual SCS rift models are likely too simplistic. Whereas, the Western Domain remains little explored because of the lack of available 3D seismic data and boreholes here. The 3D rift architecture in this tectonic domain is therefore inadequately constrained, which leads to insufficient knowledge of the syn-tectonic rift evolution in this region. Based on an unpublished 2D deep-penetration grid of seismic reflection sections, we have investigated the faulting style, sedimentary structure, and crustal architecture in the Western Domain of the mid-northern SCS. Our data display that the Western Domain contains the Changchang and Heshan Segments separated by a transfer fault zone. The aborted Changchang Segment is characterised by landward-dipping faults and younger T60 breakup unconformity. The neighbouring Heshan Segment, reaching the final continental breakup, is characterised by oceanward-dipping faults and older T70 breakup unconformity. The observations imply abrupt along-strike rifting changes not contemplated by current models, requiring unexplained crustal or mantle heterogeneity during extension.