东沙海区反射/折射联合成像与南海裂谷发生机制研究

裂谷发生机制和早期过程是南海构造演化中重要但认识模糊的问题。陆续发现的高磁异常带、下地壳高速体、火山富集的盆坡带及裂前褶皱构造，加之大量深地震探测资料的积累，使东沙海区成为研究南海裂谷-扩张发生机制的有利区域。项目拟跨东沙海区，沿已有长电缆地震剖面进行大容量气枪震源OBS探测，通过共线反射深度偏移及折射波走时反演联合成像，构建骨干剖面，揭示裂谷前后详细的构造形变与地壳-上地幔深度及速度结构；通过东沙及邻近区地球物理资料综合分析处理，追踪褶皱构造带、下地壳高速体、岩浆/火山活动以及断裂系的时空分布，探究下地壳高速体、高磁异常带的成因；通过分析褶皱构造带、下地壳高速体、岩浆/火山活动、断裂等构造间的相互关系，认识先存构造以及岩浆作用对裂谷发生的影响。长电缆与OBS技术的联合将改进深部构造探测及分析效果，可望在南海张开成因方面获得新认识，为其早期演化过程提供有力的依据。

The dynamic mechanisms and early stages of rifting are important but poorly understood topics in the evolution of the South China Sea. Neighboring the oceanic basin, Dongsha Waters area features a lower crustal high-velocity zone, a high magnetic anomaly zone, a volcano-festooned continent-ocean transition zone, and newly found pre-rift blind fold structures. High-quality seismic data have been acquired here so it is a very favorable area to study the dynamic mechanisms initiating the opening of the SCS. It is planned to carry out an OBS survey using a large-volume air-gun array along pre-existing, long-streamer, reflection profiles. These data will be used to jointly image the deep structure, incorporating depth migration of multi-channel seismic reflection data and travel-time tomography using OBS data. This work will establish key profiles with interpretation of detailed pre- and post-rift deformed structures, and crust-mantle structures. Seismic, gravity and magnetic profiles will be analyzed to trace the tempo-spatial distribution of the pre-rift folding belt, lower crust high-velocity zone, magmatism and fracturing, and to understand the origin of the lower crust high-velocity zone and the high magnetic anomaly zone. Then, the tectonic relationships among lower crust high-velocity zone, high magnetic anomaly zone, volcano-festooned continent-ocean transition zone, and pre-rift fold structures will be delineated in order to reveal the roles of pre-existing tectonics and magmatism in the rifting process. Incorporation of long-streamer and OBS deep-penetration techniques will improve the imaging of deep-crustal structures, and bring new insights with comprehensive analysis to the opening dynamics and more compelling evidence for the early evolution of the South China Sea.