Cenozoic basement-involved rifting of the northern South China Sea margin

The northern South China Sea (SCS) margin developed on a thinning crust comprising basement-involved structures inherited from the post-orogenic extension of the Cathaysia Block. While, the pre-rift struc-tural configuration and its influence on the geometry and development of the Cenozoic rift basins are ambiguous. Based on 3D high-resolution seismic reflection data in the western Pearl River Mouth Basin (PRMB) and onshore fieldwork, we delineated the intrabasement boudinage structure which is con-stituted by the low-angle E-W-striking Indosinian fold-thrust belts and the steeply dipping NE-striking Yanshanian thrusts. It is concluded that the pre-rift structure played a key role in controlling the archi-tecture and two-phase early rifting of the northern SCS margin. (1) During the Early Eocene syn-rift phase, the Indosinian thrusts were rejuvenated first and controlled the formation of a series of ENE-striking gra-bens. (2) During the Late Eocene syn-rift phase, both the Indosinian and Yanshanian thrusts were reacti-vated. The Indosinian thrusts continued to maintain normal faulting and even evolved into the detachment faults. The Yanshanian thrusts were inverted into the NE-striking dextral strike-slip faults, which controlled the formation of the pull-apart basin group en echelon and even the SCS opening. The lithospheric thinning mechanism of the SCS continental margin experienced a major change from the Early Eocene pure shear to the Late Eocene simple shear. & COPY; 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

This study reveals the significant role of pre-rift structures in controlling the geometry and development of Cenozoic rift basins in the northern South China Sea margin. Based on seismic reflection data and fieldwork, it is found that the Indosinian thrusts controlled the formation of ENE-striking grabens during the Early Eocene syn-rift phase, and both the Indosinian and Yanshanian thrusts were reactivated during the Late Eocene syn-rift phase, leading to the formation of NE-striking right-lateral strike-slip faults and the opening of the South China Sea. This research is important for understanding the lithospheric thinning mechanism of the South China Sea continental margin.