北康盆地基底构造特征及其对南海南部构造演化的启示  

Features of the basement-involved structure in the Beikang Basin and their implication for the tectonic evolution of the southern South China Sea

作　　者：徐俊杰 佟殿君[2] 高圆圆 XU Junjie;TONG Dianjun;GAO Yuanyuan(Wuhan Center,China Geological Survey(Central South China Innovation Center for Geosciences),Wuhan 430205,Hubei,China;China University of Geosciences(Wuhan),Wuhan 430074,Hubei,China)

机构地区：[1]中国地质调查局武汉地质调查中心(中南地质科技创新中心),湖北武汉430205 [2]中国地质大学(武汉),湖北武汉430074

出　　处：《地质通报》2024年第9期1607-1619,共13页Geological Bulletin of China

基　　金：国家自然科学基金面上项目《南海南部陆缘中中新世不整合地质属性研究——对南海扩张停止机制的约束》(批准号:42172125)。

摘　　要：南海南部是研究东南亚地区构造演化的关键场所,以构造相对简单的北康盆地为基础探讨其构造演化过程。为了确定研究区的构造特征,进行了地震综合解释、主控断层的定性、定量分析和盆地之下的岩石圈伸展因子分析。通过构造分析,发现北康盆地15.5 Ma界面(MMU)之下发育了多条大规模、低角度的拆离断层,界面之下的原型盆地为裂陷盆地,并且局部可表现为拆离盆地,符合被动大陆边缘细颈化带内的构造特征。对北康盆地构造演化过程进行分析并将其与曾母盆地进行对比,发现2个盆地的构造演化特征迥然不同,据此重新将南海南部挤出-逃逸构造区和古南海俯冲-拖曳构造区之间的分界线确定为西巴拉姆线。结合南海南、北部的陆缘盆地基底卷入构造的发育特征发现,南海陆缘岩石圈在发生破裂后,应变的集中主要体现在靠近洋壳的细颈化带和远端带部位,远离洋壳地区的应变受海底扩张的影响较小,这一特征可能与被动陆缘岩石圈的近端和远端在拉伸过程中的解耦相关。Southern South China Sea,where abundant geological information and hydrocarbon preserved,is the key to figure out the tectonic evolution of Southeast Asia.The southern South China Sea has been attracting attentions because of that.However,tectonic framework of southern South China Sea is complex,which hinders the researches on it.The Beikang Basin locates in the southern South China Sea.The basement-involved structures in the Beikang Basin are relatively simple,which can be a key to the evolution of the southern South China Sea.Seismic interpretation,qualitative and quantitative analysis of faults and the extensional factor analysis of lithosphere are used to analyze the structural characteristics of the basin.Analysis suggests that the prototype of the lower Beikang Basin is rift basin,locally detachment basin,bounded by the Saba Orogeny unconformity.The prototype basin of this section is rifted basin.The basin locates in the thinning zone of the passive continental margin.The formation of the rift basin is mainly related to the pull of the subducted proto-South China Sea.The entirely different evolutional histories of the Zengmu Basin and Beikang Basin testify the existent of the West Baram Line and suggest new division of geodynamic provinces for the South China Sea.The area was divided by the West Baram Line into collision-extrusion basin group and proto-South China Sea slab pull basin group.The strike-slip of the line began at Late Eocene and ended at latest Early Miocene.Comparisons between basement-involved structures in the southern and northern South China Sea reveal that deformation concentration towards the oceanic crust can only be found in necking zone and distal zone of the South China Sea margin,while deformations away from the ocean are rarely affected by seafloor spreading.The variety of extensional tectonics perpendicular to the passive margin may be associated with the decoupling between the proximal and distal margin before seafloor spreading.

关 键 词：北康盆地 构造特征 南海南部 构造演化 拉伸应变 动力变形分区 

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