陆缘扩张型地洼盆地系构造-岩浆作用的独特性──以南海北部陆缘盆地系为例

PECULIARITIES OF TECTONO-MAGMATISM IN A CONTINENTAL-MARGIN-SPREADING-TYPE DIWA BASIN SYSTEM──With special reference to the continental margin basin system of the northern South China Sea

南海北部陆缘扩张型地洼盆地系既显示了裂谷构造的某些一般性特征，又以其位于大陆壳体与大洋壳体相互作用的东亚陆缘地带；具有复杂的动力场和应力场环境；张裂发生于华夏型地洼余动期；发育由陆变海、陆海相交替的沉积建造；出现由钙碱性岩系、双峰式岩系到拉斑玄武岩和碱性玄武岩系的岩浆演化序列；形成宽阔而弥散的拉伸变形带，具条块状分割的构造格局，总体表现为由大陆盆岭型构造带（地壳张裂）发展到陆缘海盆地系（岩石圈张裂）的演变过程；强烈而持久的地壳运动，发生多幕式拉伸-造盆作用，晚期并在局部出现挤压（反转）构造；以及含丰富油气等矿产资源而展示特色。比较学研究进一步表明，地洼区的裂谷构造可以分出两种基本类型：①华夏型，其中包括东亚陆缘式和里奥格兰德陆内式两种亚型，它们是在地洼型挤压造山阶段之后发生拉伸裂陷；②东非型，它们是在古老克拉通（地台）基础上发生张裂，形成裂谷型地洼区。

The continental-margin-spreading-type diwa basins in the northern South China Sea are not only of some general characteristics of rift systems, but also of obviously distinguishing features, that is, lying on the East Asia continental margin which is the interaction zone between a continental and an oceanic crustobody, and of complicated geodynamic and stress fields: forming on the basis of the Cathaysian diwa-type compressive orogens; occurring of extension mainly in the residual-mobility period of diwa stage; bearing a sedimentary formation from terrestrial to marine facies;being of a sequence of volcanism from eruption of calcalkali and bimodal rocks to eruption of tholeiitic and alkali-basaltic rocks; forming a wide and diffuse extensional belt, with the structural framework of block-zone intersection; having a process changing from the continental basin-and-range type structural zones (extension of the crust) to the continental marginal sea basins (extension of the lithosphere);being of intense and lasting crust movements, manifesting multi-episodic extension and basin-making, locally showing compressive inversion tectonics in the late stage; being rich in oil-gas and other mineral resources, and so on. It has been further found out through a comparative study that rifts in diwa regions can be divided into two basic types: ①the Cathaysian type,in which two subtypes are included, the East Asia continental margin style and the Rio Grande style, their main characteristics are that extension takes place in the late orogenic period or in the residual-mobility period of diwa stage;②the East African type, its main characteristics are that rifting occurs on the basis of ancient cratons (platforms) and rift-type diwa regions come into existense.