基于深部结构探测的南海北部陆缘岩石圈张裂-破裂机制的模拟研究

The structure and rifting-breakup mechanism of the continental margin is one of the frontier scientific problems of the Earth System evolution, and also the hotspot of global research. The quick development of this basic problem is greatly attributed to the application of deep seismic exploration techniques with OBS, the verification through ocean drilling and the comprehensive use of modeling experiments. South China Sea continental margin is a passive continental margin of a marginal sea. Beneath the northern continental margin, a maximum of 12km lower crustal high velocity body was found, also deep lithospheric layer was found to expose at the continent-ocean boundary. In order to discriminate the rifting-breakup style and the driving mechanism, this application plan to carry out deep structure exploration with OBS as well as the boat-borne gravity and magnetic measurement along the multi-channel seismic line L1555. The clear reflection of the layer boundaries and the detachment fault structures could provide more informative constraints on later structure interpretation. Based on which, the Vp velocity structure and the poisson’s ratio profile could be obtained. Joint inversion with gravity and magnetics confined with seismic profiles could provide a lithological profile. With the Vp, poisson’s ratio map and the lithological information, the deep lithospheric structure and breakup style could be discriminated. Analogue modeling and mathematical modeling will be carried out to explore the rifting-breakup process and mechanism, based upon them a dynamic evolving model will be set up. This research will contribute not only to the research on the rifting-breakup process of the intermediate spreading margin, but also help resolve the basic scientific problems met in the exploration of deep water oil and gas, such as the unresolved deep structure and evolving mechanism.

大陆边缘岩石圈结构及其张裂-破裂机制是地球系统演化的前沿基础问题，也是全球研究的热点。这一问题的快速推进与岩石圈深部结构探测技术的应用、大洋钻探的证实、及综合模拟技术的交叉运用分不开。南海陆缘是边缘海型被动陆缘，其北部陆缘之下，发现了最厚达12公里的下地壳高速体，深部圈层在洋陆边界剥露。为了揭示南海陆缘的张裂-破裂方式和驱动机制，本申请计划沿着界面反射清楚、构造清晰、有圈层剥露至海底的1555多道反射剖面开展自陆架到洋盆边缘的深部结构探测及船载重磁测量，开展多道反射地震约束基础上的深部速度结构和泊松比计算，开展重震联合反演，分析深部岩体组成及横向展布规律，鉴定陆缘张裂-破裂方式，开展物理模拟和数值模拟实验，正演模拟岩石圈伸展-破裂过程，形成一个有实验依据的张裂-破裂机制模型。该研究将推动对中速扩张的边缘海型被动陆缘张裂-破裂过程的认识，还可以解决深水盆地油气勘探中遇到的深部结构和演化机制。

大陆边缘岩石圈结构及其张裂-破裂机制是地球系统演化的前沿基础问题，也是全球研究的热点。这一问题的快速推进与岩石圈深部结构探测技术的应用、大洋钻探的证实、及综合模拟技术的交叉运用分不开。南海陆缘是边缘海型被动陆缘，其北部陆缘之下，发现了最厚达12公里的下地壳高速体，深部圈层在洋陆边界剥露。为了揭示南海陆缘的张裂-破裂方式和驱动机制，中国科学家主导的国际大洋发现计划（IODP）367,368和368X航次在南海北部洋陆过渡带开展了7个站位的钻探，发现在过渡带上钻遇的都是玄武岩，未发现地幔剥露特征。为何南海陆缘破裂过程有如此多的岩浆参与，是从何时开始参与张破裂过程？.为了结合钻探揭示这一动力学机制，本项目沿着界面反射清楚、构造清晰、有圈层剥露至海底的1555多道反射剖面开展自陆架到洋盆边缘的深部结构探测及船载重磁测量，测线总长度360公里，共投放30台主动源OBS，回收29台，数据质量较好。之后开展了多道反射地震约束基础上的深部速度结构和泊松比计算，以及重震联合反演，分析深部岩体组成及横向展布规律，鉴定陆缘张裂-破裂方式，开展物理模拟和数值模拟实验，正演模拟岩石圈伸展-破裂过程，形成了一个有实验依据的张裂-破裂机制模型。.研究发现，南海陆缘结构特征与伊伯利亚-纽芬兰等存在地幔剥露的非火山型大陆边缘完全不同，这里下地壳较厚，地壳底部岩浆底侵和侵入量较大，在云荔凸起之下最厚底侵岩浆达到10公里以上，大量岩浆底侵和侵入导致下地壳增生和向洋的流动，从而阻止了应力沿大型断层集中导致破裂，使陆缘宽度变大；地壳以韧性变形为主，破裂方式表现为点状破裂逐渐连接为区域破裂。该研究为提升人们对被动陆缘张破裂过程和机制的认识，提供了新的观测数据。推动了中速扩张边缘海型被动陆缘张裂-破裂过程的认识。这些认识为正确解读深水盆地的成盆机制和解答深水盆地油气勘探中遇到的基础地质问题提供了新的思路。