Lithospheric Thermal Structure and Dynamic Processes of the South China Sea and Adjacent Regions

The South China Sea (SCS) and its adjacent regions lie at the junction of the Eurasian, Pacific, and Indian plates, characterized by complex tectonic evolution and diverse lithospheric features. This study integrates magnetic anomaly, gravity, and heat flow data to investigate the lithospheric thermal structure, effective elastic thickness (Te) distribution, and dynamic processes in the region. Curie depth was constrained using EMAG2 magnetic anomaly data with traditional and improved centroid methods, and the lithospheric thermal structure was calculated using the steady-state heat conduction equation. Te was derived from the fan wavelet coherence method based on WGM2012 gravity data, topographic data, and Moho depth models, providing a comprehensive understanding of the thermal and mechanical properties of different tectonic units.

The results reveal that the lithosphere in the SCS basin is thin (40–50 km) with high geothermal gradients and heat flow, resulting in low thermal and mechanical strength and Te values of 10–15 km, indicative of young oceanic lithosphere. In contrast, the northern continental margins exhibit thicker lithosphere (>80 km) with lower heat flow and higher rigidity, reflected in Te values of 25–35 km, which align with craton stability and compressional forces from the Eurasian plate. Transitional crustal regions, such as the Xisha and Nansha Islands, exhibit intermediate lithospheric thickness (50–70 km), geothermal gradients, and Te values (10–20 km), representing a transition between oceanic and continental lithosphere. The subduction zones, such as the Manila Trench, display combined characteristics of lithospheric bending and mantle wedge thermal anomalies, with outer trench regions showing Te values of 15–25 km, while forearc regions exhibit significant weakening with reduced Te.

Dynamic analysis suggests that the diverse lithospheric thermal structure and Te distribution in the SCS reflect the combined effects of seafloor spreading, subduction, and extensional deformation. High temperatures and thin lithosphere in the basin support its extensional setting; low-temperature, high-Te features of continental margins indicate compressional deformation; transitional crust reflects dual controls from continental extension and oceanic spreading; and subduction zones demonstrate complex mechanical interactions, including lithospheric bending, compressional stresses, and mantle upwelling, which significantly impact lithospheric dynamics.

This study provides new insights into the thermomechanical and dynamic evolution of the lithosphere in the SCS and adjacent regions, offering a robust framework for regional tectonic and geophysical research.