【摘要】 为了认识南沙海域新生代的整体沉降规律,对覆盖南沙海域的5条地震剖面进行了构造分析和沉降计算.结果表明,南沙海域大部分伸展断层活动到T40(16Ma)和T60(23.8Ma),而T60(23.8Ma)前的构造沉降表现为断陷盆地特征,T60后为坳陷特征,所以T60(23.8Ma)应为南沙海域大的构造转换面;南沙海域的沉降中心出现在NE向南沙海槽的延伸带上,它和前缘的逆冲推覆体一起成为南沙海域最显著的特征;由逆冲推覆体的构造和地层特征判断其形成于T40(16Ma)后,构造沉降速率拟合曲线也表明,南沙海域在T40(16Ma)-T32(10.2Ma)受到SE端的挤压和负载最强烈,产生宽约200km的相对隆升,并伴生有火山、张裂活动,因此,T40(16Ma)可能是南沙海域区域应力场由伸展向挤压转换的界面;上新世-第四纪(5.3～0Ma)是南沙海域的快速构造沉降期,可能与SE端的挤压强度减弱有关.更多还原

【Abstract】 Tectonic evolution in Nansha is analyzed by depicting the faults and calculating the tectonic subsidence along 5 profiles across Nansha.The study shows the following results:1.T60(23.8 Ma) is an important tectonic transformation boundary(except for the region around Youngshu basin) because most normal faults have been activated until sequence boundary T40(16 Ma) or T60(23.8 Ma) and subsidence curves across the region are characterized by syn-rift basin before T60(23.8 Ma) and post-rift basin after that.2.The Southeast of Nansha is the outstanding topography with a combination of a NE-SW belt of high subsidence along Nansha trough and its NE elongating zone with a NE-SW belt of thrust to the Southeast indicating there is a stress reverse in T40 boundary.3.There is high subsidence period since 5.3 Ma which may relate to the weakness of compression to the SE of Nansha.更多还原