漳浦外海新生代沉积基底的地震重力综合研究  

Cenozoic sedimentary basement off the coast of Zhangpu: a joint interpretation of seismic and gravity data

作　　者：王笋[1,2,3] 姚道平 方伟华[1] 闫培 WANG Sun;YAO Dao-ping;FANG Wei-hua;YAN Pei(Xiamen Centre for Seismic Survey, Earthquake Administration of Fujian Province, Xiamen 361021, China;CAS Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Guangzhou 510301, China;University of Chinese Academy of Sciences, Beijing 100049, China)

机构地区：[1]福建省地震局厦门地震勘测研究中心,厦门361021 [2]中国科学院边缘海与大洋地质重点实验室(南海海洋研究所),广州510301 [3]中国科学院大学,北京100049

出　　处：《地球物理学进展》2017年第5期2241-2245,共5页Progress in Geophysics

基　　金：福建省地震局青年科技基金(Y201407)资助

摘　　要：台湾海峡位于东海陆架盆地和南海东北部的边界,其西南端构造上属于隆起区,分隔厦澎断陷和珠江口盆地,勘探程度较低,以往对该区地质结构的认识仅来源于邻区零星钻井和早期的地震、重磁资料.本文对福建省地震局2015年在漳浦外海部署的一条长约69.7 km的浅层反射地震测线进行了处理,得到了反射波组特征明显、构造现象易于识别的偏移叠加时间剖面.剖面上有一强反射界面可从西端的约300 ms连续追踪到东侧的约600 ms,推测为新生代沉积的底界.偏移速度分析得到的上覆地层P波速度约为2200 m/s,而从海底地震仪记录的折射波中提取的下伏地层P波速度约为5100 m/s.为研究新生代沉积基底的岩性,我们通过融合研究区多种来源的重力数据得到较为准确的剖面重力异常,依据反射地震剖面给出的界面模型进行了重力模拟,结果显示该强反射界面两侧密度差高达0.75 g/cm^3,根据这些特征结合邻区地质露头和钻井资料推测该测线海底至300~700 m深度可能为新生代低固结度的砂岩或泥岩,而其下的沉积基底极有可能为玄武岩等基性火成岩.该结果为研究台湾海峡西南部的地质构造和新生代演化提供了新的地球物理学证据.The southwestern Taiwan Strait（ TWS） is the border between the East China Sea shelf basin and the Pearl River Mouth Basin in the north South China Sea. The degree of exploration in this area is still low due to lack of hydrocarbon potential,and the research on the Cenozoic sedimentary basement is insufficient. A shallow reflection seismic profile（ HX7,in length of 69. 7 km） was carried out in 2015 off the coast of Zhangpu under the direction of Earthquake Administration of Fujian Province,CEA. This paper introduces the seismic data processing and presents the migratedstacked section with high signal to noise ratio and resolution. On the section there is a strong continuous reflection event,in the two-way travel time for the 300 ms at the north western extremity,slow dip to the south east end to about 600 ms,which probably means an unconformable contact between Cenozoic sediment and the basement. The P-wave velocity of overlying strata derived from reflection seismic data is about 2200 m/s,while the P-wave velocity of underlying strata is about 5100 m/s according to refraction data in the OBS（ Ocean Bottom Seismometer） records. By combining heterogeneous gravity data we obtained the gravity anomalies along this profile,which were inverted for the density contrast of the main boundary. The result show that the density of Cenozoic sedimentary basement is about 2. 87 g/cm^3,which higher than the density of overlying strata with amount of 0. 75 g/cm3. Uniting these geophysical characteristics,adding up to outcrops and drilling data in adjacent area,we speculated that below the seabed there is sandstone or mudstone of low consolidation degree with thickness300-700 m,and its underlying strata might be basic rocks such as basalt. This result provides new geophysical evidences for the further research on the shallow geological structure and Cenozoic tectonic evolution of the southwestern Taiwan Strait.

关 键 词：台湾海峡西南部 澎湖—北港隆起 新生代沉积基底 地震剖面 重力拟合 

分 类 号：P312[天文地球—固体地球物理学] P738[天文地球—地球物理学]