南沙群岛海域构造地层及构造运动

根据对“实验2”号调查船1987—1991年测得的反射地震剖面的解释,论述了南沙群岛海域的构造层划分、时代属性与分布发育特征。提出本区自白垩纪中期以来发生过两次重大的构造运动,形成两个裂谷作用构造旋回。

TECTONOSTRATIGRAPHY AND TECTONIC MOVEMENT IN THE REGION OF NANSHA ISLANDS

The Nansha Islands are located in the southern part of South China Sea. Based on the multichannel seismic data (6 883km in total length) which was collected by Research Vessel "Shi Yan 2" from 1987 to 1991.three tectonic sequences exist in the studied area, their ages are Early Cretaceous or Earlier, Late Cretaceous to Eocene, and Late Eocene to Recent, respectively. They are divided by regional tectonic unconformities Th and T8, which corresponded to two major significant tectonic movements occurring in Middle Cretaceous and Late Eocene and formed a series of extensional tectonics. Thus, it can be seen that two rifting evolutionary cycles occurred in the continental margin of South China since Middle Cretaceous. Each cycle underwent uplifting - onset of rifting ?seafloor spreading- -regional subsiding. Two times of rifting caused two times spreading of the seafloor. forming the old South China Sea (in the south to Nansha Microconti-nental block) and the new South China Sea Basin (in the north to Nansha Microcontinental block) subsequently.