中文摘要：

为了确定中南—司令断裂带在南海海盆及其在南部陆缘的延伸位置,并探讨其与南海扩张的关系,本文利用重磁异常、地震、莫霍面深度、P波速度特征、钻井拖网资料,对中南—司令断裂带的延伸位置进行了综合地质和地球物理研究,厘定了中南—司令断裂带在东部次海盆与西南、西北次海盆之间呈NS向延伸,并南延至南海南部陆缘之上,深度上切割至莫霍面。根据南海海盆中磁异常条带走向的变化,及磁异常条带、走滑/转换断裂、扩张方向的印证关系,结合前人对古南海＂剪刀状＂碰撞闭合、南海扩张演化、构造应力场的研究,提出在32～25 Ma,伴随着南海东部次海盆的NNW向扩张,南海海盆及南沙地块整体发生顺时针旋转,使中南—司令断裂走向由形成初期的NNW向转变为N—S向;23.5 Ma之后,顺时针旋转停止,南海东部次海盆继续NNW向扩张,西南次海盆呈NW—SE向渐进式扩张。作为一条切穿地壳的深大断裂,中南—司令断裂与红河-越东断裂、马尼拉海沟断裂三条深大断裂一起组成区域＂滑线场＂,制约南海海盆的扩张与南沙地块的南移。

英文摘要：

In order to detect the extension pattern of the Zhongnan-Siling fault zone in the oceanic basin,to define the southern margin of South China Sea,and to explore its relationship with the evolutionary history of seafloor spreading of the South China Sea,comprehensive geological and geophysical studies are made by the authors based on the data of gravity and magnetic anomalies,seismic profiles,depth of Moho,seismic P-wave velocity,drilling and dredging samples.The Zhongnan-Siling fault zone,which cuts down to the Moho-boundary,extends in N-S trend between the Eastern Sub-basin and Northwest Sub-basin along the southern margin of the South China Sea,and can be traced to the southern continental margin of the South China Sea.According to the variation in the trend of the magnetic anomaly belt in the oceanic basin of the South China Sea and the mutual relationship of the magnetic anomaly belt with the strike-slip or transform fault and the seafloor spreading direction,combined with previous research results on the＂scissors-like＂collision,seafloor spreading evolution and the tectonic stress of the South China Sea,the authors proposed in this paper that in the period of 32 Ma to 25 Ma,the South China Sea basin and the Nansha block had experienced a clockwise rotation along with the spreading of the Eastern Sub-basin in NNW trend,which caused the change in the direction of the Zhongnan-Siling fault from NNW in the early stage to N-S later on.After 23.5Ma,the clockwise rotation was stopped,while the Eastern Sub-basin continued to spread in NNW trend,the southwestern Sub-basin began spreading in a NW-SE trend with SW-ward propagation.The three crust-cutting deep faults,the Zhongnan-Siling fault,together with the other two regional crust-cutting deep faults,the Red River-East Vietnam fault and the Manila trench fault,formed a regional＂slip line field＂,which constrained the seafloor spreading of the South China Sea and the southward drifting of the Nansha block.