中国南海构造演化历史的古地磁约束－IODP349航次航后研究

The primary aim of this proposal is to improve understanding of one of the most important geological processes operating on Earth, namely the generation of ocean lithosphere by seafloor spreading. The International Ocean Discovery Program (IODP) Expedition 349 was designed to understand the tectonic processes that operated at the South China Sea (SCS), including the mechanisms, timing, and sequences of Cenozoic seafloor spreading and paleoceanographic and sedimentary responses to the tectonic evolution of the SCS. Drilling and logging were conducted at five sites in the deep basin of the South China Sea, with a total recovery of 1524 m of sediment/sedimentary rock and 78 m of oceanic basalt. These core materials provide exciting opportunities to use paleomagnetic analyses to: (i) answer first-order questions concerning the processes responsible for generating the oceanic crust at spreading ridges; and (ii) further constrain the sedimentation process of the SCS basins. The time of constraints on the ship and distribution of shipboard paleomagnetic samples did not allow the establishment of a definite magnetostratigraphy of the drill sites. More complete and detailed paleomagnetic and rock magnetic data are needed for Expeditions 349 cores. Here we present an integrate investigation of detailed magnetostratigraphy, paleolatitude determination, and rock magnetic characterization with depths on cores recovered from Sites U1431, U1433, and U1434. Together with the constraints from biostratigraphy and basin analyses, the paleomagnetic work will establish high-resolution timescales for these sites and provide age constraints for examining the tectonic evolution of the SCS. The new data will have important bearing on the key questions of the South China Sea Deep Project, such as ‘The timing and process of seafloor spreading’. The results of this project will be also useful for the new IODP drilling expeditions in the South China Sea.

从海底扩张到洋壳和海盆的形成是地球系统演变中最重要的地质过程之一。为加深对南海构造演化和沉积过程的理解，国际大洋发现项目349航次在南海5个站位实施了钻探和测井。从南海深海盆中直接获得了1524 m沉积物岩芯和 78 m玄武岩。这些岩芯可以用于古地磁学研究来：（一）回答有关洋壳扩张过程的一阶问题；（二）进一步约束南海深海盆的沉积过程。由于受到船上古地磁样品分布和测量时间等限制，这些岩芯高分辨率年代标尺的建立还有待于更详尽的航次后古地磁研究。本项目拟对该航次的U1431, U1433, 和U1434站位岩芯样品开展更深入细致的磁性地层学、基岩古纬度确定、岩石磁学特征随深度变化等综合研究。综合生物地层学和盆地分析结果，建立南海地区高精度的年代标尺和格架，为研究南海构造演化提供可靠的年代学基础。本项目的实施有助于“南海深海过程演变”重大研究计划最核心的科学问题“南海海底扩张的年代与过程”的解答，

南海是西太平洋边缘海的典型代表，其地层层序保留了东南亚新生代构造事件的地质记录。本项目对国际海洋发现计划（IODP）349航次的U1431、U1433站位）岩芯样品开展了的古地磁学和岩石磁学特征研究。进一步细化了这两个站位地层的年代标尺，补充和验证磁性地层的完整性和准确性，建立南海形成以来高分辨率磁性地层学年代框架，进而确定出沉积速率的变化特征，为更好地理解南海海底扩张过程提供关键性年代证据。鉴定了主要磁性矿物并确定其对剩磁特征的影响，确定出岩石磁学特征，建立了南海高分辨率环境磁学参数剖面，有助于探讨南海形成以来环境磁学特征对南海演化的响应与指示意义。