Deep crustal structure and rifting-spreading evolution of the southwest subbasin, South China Sea

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ID: 322493
2026
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Abstract
Summary The Southwest Subbasin (SWSB) of the South China Sea represents a young oceanic basin formed by continental rifting and subsequent seafloor spreading between ∼23.6 and 16 Ma. Yet the deep crustal structures of its continental margins and the oceanic crustal accretion processes remain poorly understood. This study presents integrated two-dimensional seismic and density models along the OBS2020-3 profile, which traverses the continental margins and oceanic basin, using seismic refraction, multichannel seismic reflection, and free-air gravity data. Our results reveal prominent intra-crustal reflectors at ∼11.5 km depth beneath the northwestern continental margin, which we interpret as the brittle-ductile transition marking depth-dependent extension during rifting, without any evidence of high-velocity lower crust layers. Within the oceanic basin, the thin magmatic crust overlying serpentinized mantle suggests reduced magmatic supply during its opening. Combined with published seismic profiles crossing the ridge axis to the northeast and southwest, our results reveal a systematic southwestward decrease in crustal thickness in the ridge-parallel direction, suggesting a progressive reduction in melt supply toward the southwestern termination of the SWSB. The ridge axis (Longmen Seamount) is characterized by pronounced crustal low-velocity anomalies accompanied by apparent crustal thickening. We interpret that these features resulted from enhanced porosity and mantle serpentinization, both facilitated by extensive faulting during the final, tectonically dominated spreading stage. Together, these findings provide new constraints on continental extension along the northwestern margin of the SWSB and oceanic crustal accretion within the basin, and highlight comparable fault-controlled processes in other marginal seas.
Reference Key
openalex_W7170201985 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Li Zhang, Chen Cai, Hongjian Fang, Lun Li, Rui Gao
Journal geophysical journal international
Year 2026
DOI
10.1093/gji/ggag286
URL
https://doi.org/10.1093/gji/ggag286
Keywords Keywords not found

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