南海中央海盆重力流沉积物来源及沉积过程研究:碎屑锆石U-Pb测年物源示踪分析

The first expedition (Exp.349:South China Sea Tectonics) of International Ocean Discovery Program (IODP),formerly known as the Integrated Ocean Drilling Program,is being executed in South China Sea from January to March,2014.Its aim is to determine the age of SCS and to resolve ongoing controversy over how it formed with several boreholes in 3 sites in the central SCS.The preliminary results of the expedition show that the gravity flow deposits are common over the central SCS and throughout most lithological units overlying the basement. It is necessary to investigate their provenances and sedimentary processes since the generation of these gravity flow deposits should be responded to the opening of South China Sea as well as the uplifts of Taiwan Island,Tibet Plateau and the subduction of SCS under the Luzon Arc.Therefore, this study will focus on the recovered cores during the expedition in central South China Sea. The core description will be done based on the visual assessment of sediment composition, consolidation, sedimentary structers,bottom contacts and the petrographic analysis of smear slides and thin section. Furthermore, the components of heavy minerals in the core samples will be analyzed and the detrital zircon U-Pb dating will be detected. Compared with their chracteristics in several potential provenances around South China Sea, the provenance evolution of these gravity flow deposits could be illustrated.Consequently,their sedimentary processes will be hydrodynamically simulated via FLUENT and their triggering mechanisms (i.e. earthquake and volconic eruption) will be discussed, which would provide the constraints on the the opening of South China Sea as well as on the tectonic activities around South China Sea.

继"综合大洋钻探计划（IODP）"之后的新十年"国际大洋发现计划（IODP）"首个钻探航次（349航次），于2014年1-3月在南海实施.该航次在南海中央海盆钻探了5个站位（其中3个站位钻探至基底），旨在揭示南海的形成年龄及其张裂过程.初步钻探结果表明,在南海中央海盆发现了大量重力流沉积物.通过深入研究这些重力流沉积物的来源及其沉积过程,将有助于阐明南海张裂及其周缘物源区的构造活动过程（如台湾造山运动、青藏高原隆升以及南海向其东部的吕宋岛弧俯冲等构造事件）.本研究将以大洋钻探所获取的宝贵深海岩芯为研究对象，在对其进行沉积学观察描述基础上，通过分析其重矿物组合特征并进行碎屑锆石U-Pb测年物源示踪分析，试图阐明南海中央海盆内不同地质历史时期的重力流沉积特征及其物源演化，进而借助沉积水动力学模拟技术再现其沉积过程，并进一步分析其可能的触发机制及其对南海张裂过程和周缘物源区构造活动的响应.

该项目以IODP349航次在南海中央海盆所钻遇的大量深水重力流沉积物为研究对象，通过对其进行沉积学观察描述，明确其重力流沉积类型及其沉积特征基础上，通过常微量元素分析、重矿物组合分析以及锆石U-Pb测年研究等，并与南海周缘潜在物源区对比基础上，阐明了南海中央海盆和西北次海盆中中新世以来沉积演化过程，准确厘定了南海扩张停止之后发育了2期岩浆活动的时间、特征、空间分布及其成因机制，并借助水动力学模拟揭示了南海北部珠江口盆地陆架边缘三角洲和多分支水道化扇等两类沉积体系的沉积过程，建立了南海中央海盆更新世以来高精度年代格架，研究结果不但为南海周缘构造演化研究提供了制约，而且也丰富了深水沉积动力学理论，为南海古环境古气候研究提供了坚实的年代学约束，有关深海环境所发育的大型沉积体的沉积过程的研究对指导深水油气勘探也具有重要的现实意义。