南沙海域盆地的地层系统与深部结构研究：从南部陆缘解读南海的演化历史

The northern and southern South China Sea (SCS) continental margin crustal structure and tectonic features contains important information of the evolution process of the formation of the SCS. The formation of the SCS is an important basis for research the evolution framework and dynamics. At present, there is two main points: North-South conjugate (Taylor et al) and NW-SE conjugate (Briai et al), they due to the differences on the stripe contrast results, through the multi stage evolution, basin, expansion to different time. In addition, used for the identification of the transform fault are sediments buried not directly tracking. In order to accurately understand the relationship between the northern and southern SCS continental margin of SCS, to further confirm the expansion of evolution and history, need to accurately establish the southern continental margin stratigraphy system, confirm the unconformity surface properties and age, to conduct a comprehensive analysis of deep structure from the southern SCS area and its comparison with the northern margin of the SCS, write up the other half of history the SCS from the southern SCS continental margin data. Therefore, we can constrain new drilling and trawl data, high quality seismic reflection profile on the new acquisition and processing (especially across the north south margin of Nansha block and runs through the east-west), to carry out comprehensive stratigraphic, geological interpretation system contrast, southern SCS continental margin layer framework. Based on the analysis of structural characteristics of continental margin basin, south of the major stages of evolution and unconformity structure attribute, the re development of magnetic basement of the basin lithosphere structure seismic inversion, establish the deep structure of the plane and profile distribution characteristics, through North South contrast edge of continental margin and continental analysis of things, the southern SCS and the northern continental marginal differences and changes along the direction of the SCS, understanding the tensile rupture drift process. Through evolution and North and South conjugate rule.

南海南北陆缘地层及构造蕴含南海形成演化过程重要信息，是研究南海形成演化骨架及动力学基础。目前存在南北共轭和北西南东向共轭两种观点，分歧源于磁条带对比其经历多期演化，海盆走向扩张时间不同，此外用于鉴别的转换断层也被沉积物掩埋无法直接追踪。为了准确认识南北陆缘关系，进一步确认扩张演化方式和历史，需要精准建立南部陆缘地层系统，确认不整合面性质年龄，从南部全区域分析深部结构及与北部陆缘对比，从南部陆缘数据中补写南海另一半历史。因此，在钻井拖网资料约束下，对新采集重处理地震骨干剖面综合地层地质解释对比，系统建立南部陆缘地层格架。在此基础上分析主要演化阶段盆地结构和不整合面属性，盆地基底岩石圈结构重磁震反演，建立深部结构平面剖面分布特征，通过南北陆缘和东西陆缘对比分析南北部陆缘差异及沿东西方向变化，认识南海张裂-破裂-漂移-停止过程东西穿时演化特点及南北共轭规律

为了准确认识南海南北陆缘关系，进一步确认扩张演化方式和历史，补写南海构造演化的完整历史，本项目围绕精准建立南部陆缘地层系统和照明深部结构展开研究工作。项目通过高质量的地震剖面、重磁与OBS资料，结合钻井-拖网岩石地层与古生物地层资料约束，运用地震地层学、层序地层学和构造分析以及多参数约束迭代地球物理反演方法，从浅部-深部多层次、地层-构造-岩相-地壳结构多领域，详细分析研究区主要盆地的地层发育特征、深部结构及沿陆缘东西方向变化。厘定与裂陷结束不整合面相关的T7、T6和T5三个界面的性质、时代以及时空迁移规律，T7与南海岩石圈初始破裂相关不整合面，时代32-29Ma；T6与南海洋脊跃迁和西南次海盆海底扩张相关不整合面，时代26-23Ma；T5主要与南海俯冲结束相关的不整合面，时代20-16Ma，在平面上呈现东北早西南晚，南侧靠陆早、北侧近洋晚的穿时特征。在此基础上，分析主要盆地结构和不整合面属性，建立中新生代地层系统，提出研究区东、西部盆地新生界发育具有“早期差异、晚期趋同”的特征，并刻画了始新世以来碳酸盐岩时空规律，提出了渐新世-早中新世Nido灰岩不同演化模式以及控制因素。初步明确了南海东南部中生界空间分布特征和构造归属，提出了中生界主要形成活动大陆边弧前盆地的构造模式。通过重磁震联合反演以及上下和全地壳厚度和拉张因子的计算和比较，揭示了南海南部大陆边缘地壳结构存在东西差异，与岩石圈流变作用有关，反映在礼乐盆地西部，下地壳拉伸程度更大，而礼乐盆地东部，上下地壳拉伸程度相当。探讨了中南-礼乐断裂深部结构特征，认为该断裂可能是控制了礼乐陆块和郑和陆块在南海扩张时期的相对运动。这些成果可为认识南海张裂-破裂-漂移-停止过程东西穿时演化特点及南北共轭规律、南海成因机制研究以及油气与天然气水合物资源勘探开发、我国海域划界提供盆地地层系统、深部结构和构造演化的依据。

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