南沙北部伸展构造的基本特征及其动力学意义

南沙地块辫啊以中南－美洲断裂为分界，其东、西两侧伸展构造的几何学与运动学表明，晚白垩世至早渐新世，其伸展作用以纯剪切为主；中渐新世至早中新世，伸展带东段转换为简单剪切，西段剪切渐停。伸展作用的主要动力来源于陆缘俯冲板片的拆沉、软流圈地幔热物质乘隙上拱和部分熔融作用及周边板块的相互作用。

BASIC CHARACTERISTICS OF EXTENSION STRUCTURE IN NORTHERN NANSHA ISLANDS, CHINA, AND ITS DYNAMICAL IMPLICATIONS

Based on a study of geometric and kinematic characteristics of the extensional structure in the east and west sections of northern Nansha block, the basic models and the dynamics of the Cenozoic extension in South China Sea (SCS)area are discussed in this paper. It is proposed that the evolution of extension includes a pure shear model in late Cretaceous early Oligocene and a simple shear model after mid Oligocene in the east section. The pure shear extension was initiated by the delamination of the subducted slabs of paleo Pacific plate. It yielded a number of half grabens which distributed symmetrically on both sides of the southwest basin (SWB) of SCS. And the upper crust and lithospheric mantle on both sides of SWB had undergone uniform extensional deformation. The simple shear extension, which was caused by further upwarping and partial melting of the hot asthenospheric mantle and by the collision of Indian plate with Eurasia plate in Tibet Plateau, resulted in asymmetrical extensional deformation on both northern and southern margin of central basin of SCS.In the northern margin, there are several different plane assemblage types of half grabens, including series type, parallel type, en echelon type,face to face type and back to back type. But there is only one kind of plane normal faults in the eastern section.This is different from the western section which separated from the eastern section by the Zhongnan fault. In the northern and southern margin of eastern SCS,the extensional deformations of the crusts were evidently nonuniform with that of the lithospheric mantle under them.