东海陆架盆地南部生长断层活动特征

生长断层是在伸展和走滑盆地中一种重要且广泛存在的构造样式。通过地震资料定性识别出东海陆架盆地南部地区18条生长断层; 根据断裂对研究区各级构造单元控制作用和纵向切穿地层情况, 将其划分为一级控盆断裂、二级控凹断裂、三级控带断裂和盖层断裂; 通过断裂平面分布特征研究认为研究区的断裂以NE、NNE延伸为主, 少数为NEE方向; 利用地震剖面在研究区识别出阶梯状组合断层带、“Y”字型组合断层、多米诺式断层带、地堑、地垒等多种断裂组合样式; 又结合生长指数和断层落差两种方法对研究区生长断层的运动学特征进行了定量统计分析, 发现研究区生长断层在古近纪时期活动强度具有自西向东逐渐递减趋势, 区内断层活动期次自西向东逐渐变新, 整个研究区内生长断层在古近纪盆地裂陷—断陷期活动强度最大, 中新世后断裂活动趋于稳定。认为晚中生代以来太平洋板块西缘俯冲后撤和印度板块向亚欧板块俯冲碰撞在东海陆架盆地形成的远程蠕散效应, 使东海陆架盆地形成了拉张伸展应力场环境, 是研究区发育大量生长断层的首要原因。同时, 加强对研究区生长断层伴生构造如滚动背斜和缓坡带阶梯状断裂组合封堵形成的岩性圈闭研究, 有利于推动东海陆架中新生代盆地资源勘探可持续发展。

Research on characteristics of growth faults in the southern East China Sea Shelf Basin

The growth fault is an important and widely distributed structure in extensional and strike-slip basins. 18 growth faults have been identified by the authors with seismic data in the south East China Sea Shelf Basin (ECSSB). According to their roles in controlling tectonic units development and the vertical sequence they cut through, the faults may be divided into several orders, i.e. the 1st order basin-controlling faults, the 2nd order concave controlling faults, the 3rd order band controlling faults and cap faults. As to the distribution pattern, the majority of the growth faults of the study area are distributed in NE and NNE directions with a few in NEE direction. Various types of faults combinations are identified in seismic profiles, such as the steplike faults, the "Y" type faults, the domino-type faults, and the combination of graben and horst faults. According to the kinematics characteristics of faults such as growth index and fault throw, it is found that the growth faulting movement of Paleogene was in a decreasing trend from west to east, and thus the faults became younger to the east. The intensity of growth faulting in the whole study area reached a peak in Paleocene and became stable after Miocene, resulted from the joint effects of the extension dynamics background, that is the retrogradation of the subduction slab of the west Pacific margin and the eastern vermiculation of the ECSSB due to the subduction and collision between the India plate and Eurasian plate. Further study on growth fault and associated structures as well as the steplike fault zone in gentle slope belts is suggested to push forward the explorationin ECSSB basins.