Structural segmentation in the Qiongdongnan Basin, South China Sea: Insights from analogue models and implications for hydrocarbon exploration

The Qiongdongnan Basin at the northern margin of the SouthChina Sea shows distinct lateral variations in trends, deforma-tional styles, and structural complexities from the western to theeastern zones. It is widely accepted that the western zone under-goes orthogonal stretching, whereas the eastern zone undergoesoblique stretching under the control of preexisting structureswith changed orientation. In addition, the weak lower crust mayaffect the structural segmentation of the Qiongdongnan Basin.This study considers factors related to crustal strength, such asbrittle-to-viscous thickness ratios and extensional velocities toexplore the structural segmentation between the western andeastern zones using physical analogue modeling. The resultsshow that the control of preexisting velocity discontinuity (VD)in the segmentation of the overlying structure is strongly associ-ated with these two factors. In the case of a thinner lower crustor fast extension, deformation was concentrated along the VD,showing an apparent segmentation between the orthogonal andoblique zones. Conversely, when there was a thicker weak lowercrust or slow velocity, the rift basin discrete development due tothe control of preexisting VD weakened, and the segmentationwas indistinct. A model with a thinner lower crust and fasterstretching velocity successfully accounted for the observed segmentation characteristics of the Qiongdongnan Basin. Basedon the experimental results, we explain the differential tectonicevolution between the eastern and western zones and theirimpact on the structurally formed reservoirs in the Qiongdong-nan Basin.