基于前人研究及已钻井、地震、重磁等资料,发现南沙地块与中沙-西沙地块在地壳结构、重力异常及基底岩性等方面具有对称相似性,认为二者以南海扩张脊为轴呈共轭关系.在三大区域构造事件的控制下,盆地发育三大不整合面:初始裂陷不整合面(RU面)、破裂不整合面(BU面)、碰撞不整合面(CU面).据此可将盆地划分为3套构造层,并建立起统一的构造格架.整体上,以CU面为界,裂离型盆地均呈"下断上坳"的结构特征:下构造层(RU—BU)主要为双断式的地堑结构,主要发育NE、NEE、NW向大型断裂;中构造层(BU—CU)主要为单断式的箕状—双断式的地堑结构,在继承早期大型断裂的基础上发育一系列近EW向次级断裂;上构造层(CU—海底)为稳定的坳陷结构,断裂不发育.

Based on drilling data, seismic data, gravity anomaly and magnetic anomaly, it is revealed that there is symmetrical similarity between Nansha massif and Zhongsha-Xisha massif in crustal structure, gravity anomaly and basement lithology, which are conjugated with the expansion ridge of South China Sea as axis. Under the control of three tectonic events, three unconformity surfaces developed including RU (Rift Unconformity), BU(Breakup Unconformity), and CU(Collision Unconformity), which can be identified on seismic profiles. Then a unified framework with three tectonic layers was setup in the basins of different massifs. According to seismic data, we study the tectonic characteristics of three basins such as Liyue Basin, Beikang Basin, and Nanweixi Basin in Nansha massif. Divided by the CU surface, the structure of these basins show the characteristics of "lower fault and upper depression" on the whole. In the lower tectonic layer (RU-BU), graben developed with faults of different strike such as NE, NEE and NW. In the middle tectonic layer (BU-CU), half-graben or graben developed with sub-faults of EW strike besides the former faults. In the upper tectonic layer (CU- seabed), stable depression developed.