【作者】 赵淑娟；

【导师】 吴时国；

【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， 硕士

【摘要】 南海北部陆缘在南海扩张结束后发生了一次重要的构造运动—东沙运动。由于前人对其研究较少，目前对其发生时间、影响范围、构造属性和形成机制等都存在较大的争议。该论文通过对东沙海区及其邻区新近纪地层二维、三维地震资料的详细解释，分析了东沙运动的构造变形特征，圈定了其分布范围，厘定了其发生时间。东沙隆起构造上主要表现为断块升降，其中隆起区沉积物遭受剥蚀，造成中新世及部分上新世地层的缺失，并在地震剖面上形成了明显的角度不整合面。这次运动还形成了大量北西-北西西向的张性、张扭性断裂，且断裂规模都较小，平面上多为几百米到几千米。研究区内与东沙运动相伴的岩浆活动较少，除了在洋—陆过渡带处有部分岩浆侵入上地壳甚至喷出地表，研究区内未见其它新近纪岩浆活动。东沙运动整体上还具有东强西弱的特点。东沙运动主要波及东沙隆起和潮汕坳陷地区，此外，番禺低隆起东部、珠Ⅰ坳陷南部及东北部等区域也受到影响。东沙运动发生在晚中新世晚期，并在晚中新世末/早上新世初（5.5Ma）停止活动，是一次伸展环境下形成的断块升降运动。东沙运动可能与新近纪以来菲律宾海板块持续向北西西方向运动导致的吕宋岛弧与欧亚大陆在9-6Ma期间开始发生的弧陆碰撞有关。同时，由于南海向马尼拉海沟下的俯冲及洋壳的冷却沉降作用，使得南海北部陆缘处于拉张环境，岩浆底侵到下地壳底部形成高速层，破坏了该区域的地壳均衡，从而造成上部地壳的隆升。东沙运动的发生说明被动大陆边缘在演化成熟后并不一定处于稳定状态，同时也进一步证明了南海北部陆缘应属于非火山型被动大陆边缘。更多还原

【Abstract】 After the end of the spreading of the South China Sea (SCS), an importantstructural movement-the Dongsha Movement took place at the Northern Margin ofthe SCS. However, timing, range, tectonic attribution and dynamic mechanism of theDongsha Movement are still unclear. Based on the well explained2D/3D seismic datain the Dongsha area and its neighboring, we analysis the structures of the deformation,and define the range and the timing of the movement. The main deformation of themovement is characterized by faulting with the coeval sedimentation in the area ofuplift eroded which causes the hiatus of part of Miocene and Pliocene stratums. It alsocaused clear angular unconformity which marked the time of the Dongsha Movementon the seismic sections. The movement causes abundant secondary NW-NWWtensional and transtensional faults, the length of which is mainly several hundredmeters to several kilometers. Magmatism related to the Dongsha Movement is scarcein the study area, and little igneous activity could be found in the Neogene stratum.However, magma intruded or erupted around the ocean and continent boundary,southeast of Dongsha Rise, probably due to the weakness of the crust. Besides, thedeformation of the movement is more intensive in the eastern area than in the westernarea. The Dongsha Movement mainly affects the Dongsha Rise and the ChaoshanDepression. Besides, the eastern part of the Panyu Low-High and the southern andnortheastern part of the ZhuⅠDepression are also deformed. The movement mainlyoccurred in the late period of late Miocene and ended at the Mio/Pliocene boundary(5.5Ma) in this paper, and it occurred in the extensional environment. The DongshaMovement might be related to a collision between9-6Ma of the Luzon Arc to theEurasian Plate which was caused by the NWW movement of the Philippine Sea Platein Neogene. At the mean time, the northern margin of SCS is in a setting of extensionfor a subduction of SCS towards the Manila Trench and a cooling of oceanic crust,which caused magma underplating at the bottom of lower crust in the study area. Thismechanism resulted in the unbalanced isostasy of the area and the uplifting of the upper crust. The Dongsha Movement suggests that the passive continental marginsmay not keep stable all the time after they evolve to the mature stage. At the sametime, the movement gives more evidence to prove that the northern margin of the SCSis a non-volcanic continental margin.更多还原