【作者】 张亮；

【导师】 栾锡武；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋地质， 2012， 博士

【摘要】 边缘海处于大陆与深海洋盆的过渡地带，不仅是研究大陆边缘演化和地球动力学的主要地区，也是油气资源及天然气水合物等能源的重要富集区。南海是西太平洋最大的边缘海，地处欧亚板块、太平洋板块和印度-澳大利亚板块的交汇处，构造活动十分复杂。尽管国内外学者从不同角度提出了众多的南海演化模式，但至今未能形成一种被大家普遍接受的观点。因此，南海构造演化模式的研究仍是南海地质研究的热点和难点。本文根据南海地区典型的地震剖面和重磁资料，研究了南海及邻区主要断裂的展布特征和空间组合关系，从断裂规模、时间等不同角度进行了分类研究。根据不同的断裂组合关系，将新生代以来南海及邻区主要断裂划分为四个期次，即张裂Ⅰ期、张裂Ⅱ期、海底扩张期和扩张期后，并分析了不同断裂期次对应的区域应力场特征。结果表明，南海构造演化受到太平洋构造域和特提斯构造域的双重作用制约，可划分为四个不同的演化阶段。在此基础上，结合南海现有的演化模式，建立不同的数值模型，运用有限元方法分析了南海最合理的打开方式。平面模拟结果表明，印度-欧亚板块碰撞及楔入，可以造成南海地区产生明显的南东向地幔流作用，从而产生广泛的NW-SE向伸展。但随着哀牢山-红河剪切带及越东断裂带快速左旋运动的开始，以及东部太平洋板块俯冲速率加快，印度板块与欧亚板块的挤压碰撞对南海地区产生的影响变小。本论文认为，印欧碰撞主要影响南海大陆张裂阶段，引起南海南东向伸展，但不是促使南海海底扩张的主要因素。古南海俯冲拖曳产生的NS向拉张力，可在南海地区形成有效的南北向拉张作用，从而促使南海发生南北向海底扩张。此外，古南海俯冲南向俯冲速率的加快，与太平洋NWW向俯冲，共同造成了南海应力场由SE向转为近SN向。剖面模拟实验表明，南海东部受中生代古俯冲带的影响更为明显，在伸展应力场作用下发育为贯穿上地壳的拆离断层，最终在此发生破裂，因而南海东部大陆张裂更符合简单剪切模式。南海中部地区下地壳存在异常地壳，在区域拉张力作用下，异常地壳发生弱化、塌陷，促使了南海的破裂，因而更符合纯剪切模式。综上所述，从南海陆缘的地壳结构、盆地及断裂发育特征看，南海经历了拉张、张裂到海底扩张的演化过程，拉张动力来源主要是古南海向南俯冲的拖曳力，早期辅助于印度-欧亚板块碰撞引起的南东向的地幔流作用。中生代古俯冲带及下地壳存在的异常地壳与大陆破裂位置密切相关，表明张裂前存构造或继承性构造对南海演化模式具有重要作用。更多还原

【Abstract】 The margin sea, located at the transition zone between continent and oceanbasin, is a key area for studying geodynamics and evolution of continental margin, butalso an accumulation area of hydrocarbon and gas hydrate. The South China Sea isthe largest margin sea of the West Pacific, and surrounded by three plates of Eurasian,Pacific and Indo-Australia. Under the interaction of three plates, the geologicalprocesses of SCS are very complicated and have so far failed to established auniversally applicable model of tectonic evolution and thus become urgent issue ofthe SCS research to be resolved.In this paper, based on the typical seismic profiles and gravity and magnetic data,the distributing feature and combination relation of main fractures in SCS andadjacent region were studied. The main fractures were classified according the scaleand epoch. Based on the combination relation of main fractures in SCS, four periodscan be divided: rift Ⅰperiod, rift Ⅰperiod, seafloor spreading period and post ofseafloor spreading period. Further, regional stress fields were described in each periodrespectively. Results show that, tectonic evolution of SCS in Cenozoic is under thecontrol of the Pacific tectonic domain and the tethyan tectonic domain, and fourdifferent evolution stages can be divided.Considering the existing evolution models in SCS, different numerical modelswere established for analyzing the most appropriate model for the open of SCS. Theresults of plan-view models show that because of the obstruction from subduction ofPacific plate, the mantle flow generated by the collision of India-Eurasia movedtowards south and southeast, resulting in NW-SE trending extension in the SCSregions. However, associated rapid sinistral movement along the Ailao shan-RedRiver shear zone and the East Vietnam Boundary Fault, the collision of India-Eurasiawas mainly accommodated by SE trending Indochinese escape, the effect on SCSdecreased. We suggested that the India-Eurasia collision mainly result in NW-SEtrending extension during an initial stage of rifting, and do not the leading element forthe opening of SCS. The Neogene opening of SCS is suggested as a consequence of a slab-pullinduced by subduction of the Proto-SCS underneath Borneo, the latter can generateeffective N-S trending extension for the opening of SCS.The results of cross-section models show that the location of the position ofcontinental break-up is predetermined by a large lithosphere fracture, which is theMesozoic subduction zone in eastern of SCS. In center of SCS, the position ofcontinental break-up is predetermined by the abnormal lower crust, which could act asa weak zone. Under extensional stress field, strain concentrate on abnormal lowercrust zone and break-up in the end.In a word, according the characteristic of crust structure, basin and fractures,SCS has experienced the evolution from onset of rifting, break to seafloor spreading.The driving forces mainly came from the slab pull of the proto SCS, assistant with thesouthward and southeastward mantle flow in rift stage. Location of continentalbreak-up is determined by the proto-subduction and abnormal lower crust. Theseshow the importance of inherited structures and the pre-rift evolution of a margin.更多还原