南沙海域构造沉降特征

Characteristics of Tectonic Subsidence of Nansha Area

南海在新生代期间发生多次裂解和离散,在南海南部陆缘地层中留下了多次构造运动的痕迹.选取南沙海域内覆盖曾母、北康、南薇西、万安盆地的24个模拟井位,分别进行构造沉降速率的计算,并分析了自中生代末期以来的4次重要构造运动对南沙海域盆地的形成和构造演化的控制作用.结果显示,南沙海域构造沉降分为3幕:第一幕为40.5～30.0Ma,在西卫运动的影响下,南沙海域盆地进入断陷阶段,发生大规模的沉降作用,构造沉降速率最大达到了160m/Ma;第二幕为30.0～10.2Ma,随着南海的张开,区内盆地相继发生热沉降作用,进入拗陷期,由于古南海与婆罗洲的碰撞,区内盆地地层发生整体抬升,构造沉降速率达到最小值20～50m/Ma;第三幕为10.2～0Ma,晚中新世由于南沙运动影响,研究区内盆地发生了一次大规模的快速沉降作用,随着南沙地区一起进入区域沉降阶段.

Tectonic subsidence histories of Zengmu basin,Beikang basin,Nanweixi basin and Wan＇an basin in Nansha area are analyzed with back-stripping technique.1D tectonic subsidence histories of 24 presumed wells are calculated.The results show that Nansha area experienced 3 main subsiding stages in Cenozoic：（1） Nansha area experienced rifting stage in 40.5-30.0 Ma with a wide range of subsidence.In the first subsiding stage,the max tectonic subsidence rate is 160 m/Ma,which was supposed to be controlled by Xiwei movement.（2） In the second stage（30.0-10.2 Ma）,Nansha area ended rifting stage and shifted to depression stage in connection with collision between ancient South China Sea and Borneo.The max tectonic subsidence rate decreased to 20-50 m/Ma.（3） For the third stage（10.2-0 Ma）,the regional basins experienced a stage of accelerated subsidence in connection with Nasha movement since Late Miocene.Nansha area experienced regional subsiding stage.