Lateral variations of crustal structure in the northeastern of the South China Sea

The northeastern margin of the South China Sea (SCS) has experienced a transition from a convergent continental margin in the Late Mesozoic to a divergent continental margin in the Cenozoic. This evolution has strongly influenced the heterogeneity of crustal structure in the northeastern SCS. In order to investigate the lateral variations of crustal structure, we use newly acquired wide-angle seismic data to model 2-D crustal structures along 10 profiles. Then we apply the Kriging interpolation to obtain the pseudo 3-D crustal structure in the northeastern margin of the SCS, combined with previous published crustal profiles. The 3-D crustal structure delineates the Moho morphology, the Cenozoic sediment layer ( 1.7 km/s-3.5 km/s), the Mesozoic strata ( 3.5 km/s-5.5 km/s) and magmatic intrusion bodies in the lowermost crust ( 7.0 km/s-7.5 km/s). The Cenozoic sediment layer in the continental slope is generally thicker than that in the continental shelf. The Mesozoic strata has a limited distribution around the Dongsha Islands. The magmatic intrusion bodies are thicker beneath the continental shelf than that beneath the slope. Overall, the crust thins from 25 km in the continental shelf to 15 km in the continental slope along the direction of SE. This direction is not parallel to the direction of initial seafloor extension (SSE) but perpendicular to the boundary of the Mesozoic strata and the trend of the inferred pre-Cenozoic residual structure. We speculate that these pre-existing and relative rigid structures are not easy to be stretched during the continental rifting. They therefore controled the direction of crustal thinning and subsequently influenced the crustal lateral heterogeneity.