The Xisha area, a representative passive margin of the South China Sea, is a region where the extensional style and deep dynamic processes of the lithosphere during continental rifting remain highly debated. The Zhongsha Trough and Xisha Trough, located in the eastern and northeastern Xisha Block respectively, have tectonic evolutions closely linked to the regional structural framework. Sparse, uneven seafloor heat flow data preclude systematic understanding of the area's tectonic evolution and its control on current heat flow. In this study, seafloor heat flow measurements were acquired in the Zhongsha Trough, Zhongshannan Basin, and Xisha Trough using the R/V Tan Kah Kee (equipped with a Lister-type heat flow probe) and the R/V Shiyan 3 (equipped with an Ewing-type heat flow probe). A total of 29 high-quality heat flow sites were obtained (22 in the Xisha Trough, 5 in the Zhongsha Trough, and 2 in the Zhongshanan Basin), systematically revealing the present‑day heat flow distribution in the study area. These data were further integrated into a coupled tectonic–sedimentary–thermal numerical model for analysis.
The heat flow survey results show that heat flow in the Xisha Trough ranges from 55 to 111 mW/m² (avg. ~83 mW/m²), increasing from flanks to a central peak of >110 mW/m², indicating intense crustal stretching and thinning. Locally anomalous heat flow suggests fluid circulation along fault systems. Heat flow averages 84 ± 2.6 mW/m² in the southeastern Zhongsha Trough and 86.2 ± 2.5 mW/m² in the eastern Zhongshanan Basin.The elevated heat flow at the Zhongsha Trough sites may be partly influenced by heat flow refraction caused by basement highs at the measurement sites. The heat flow values of the Zhongshanan Basin are close to the average of the Southwest Sub-basin (91.3 ± 18.7 mW/m²; Xu et al., 2018), indicating that this area may have undergone partial oceanization. Numerical simulations demonstrate that the lithospheric thickness decreases from ~90 km beneath the Xisha Block to 50–70 km beneath the Xisha Trough, and the crustal thickness is significantly reduced to 4–6 km in the Xisha Trough. The regional heat flow pattern is highly consistent with deep structural features, suggesting that lithospheric extension in this region is controlled by a depth-dependent differential extension mechanism. This study offers key data and theoretical constraints for understanding thermal evolution and deep processes of the SCS passive margin.
This research was supported by the National Natural Science Foundation of China (Grants. 42276074, 42076075, 41776078). Data and samples were collected onboard R/V Tan Kah Kee implementing the open research cruises NORC2022-06 and NORC2023-06, and onboard R/V Shiyan 3 implementing NORC2022-07 and NORC2023-07, supported by the NSFC Shiptime Sharing Project (project numbers: 42149906, 42249906, 42149907, 42249907).