晚中生代-新生代西太平洋的古纬度：利用国际大洋钻探项目岩芯和陆地样品的古地磁对比性研究

The primary aim of this proposal is to improve understanding of one of the most important geological processes operating on the Western Pacific regions, namely the seafloor spreading and subduction. The international ocean drilling programs (DSDP, ODP. IODP) have designed and drilled hundred holes to understand the tectonic processes that operated at the Western Pacific. These core materials provide exciting opportunities to use paleomagnetic analyses to answer first-order questions concerning the geodynamic parameters (paleolatitude and rotations) and the sedimentation process of the Western Pacific basins and plateaus. We propose to conduct a paleomagnetic and rock magnetic study to analyze and characterize new minicore samples from DSDP Legs 6, 17, 30, 31, 32, 55, 58, 59, 60, 61, 89, and ODP Legs 124, 125, 126, 129, 130,143,145 and 192. Many of these cores, especially those from DSDP sites, have not been well-studied paleomagnetically. By carefully resampling and thoroughly studying these drill cores with highly sophisticated paleomagnetic and rock magnetic techniques, we will seek firm answers to a set of fundamental questions such as: (1) What was the original plate-tectonic setting (paleolatitude) of various plateaus and basins of the Western Pacifc during late Mesozoic-Cenozoic? (2) What is the extent of almost simultaneous mid-Cretaceous volcanism in Pacific? (3) what are environmental and rock magnetic characterizations with depths on cores recovered from these sites? Our proposed research makes full use of existing ODP and DSDP core materials and may provide useful information for the new IODP Legs in the Western Pacific. Successful completion of the paleomagnetic program proposed here will produce reliable paleolatitudes that constrain paleogeographic reconstruction of the Western Pacific. Accurate paleogeographic reconstructions serve as a framework for Earth surface processes and provide boundary conditions for mantle dynamics models.

本项目旨在加深对西太平洋区域海底扩张和板块俯冲过程的理解。国际大洋钻探计划（DSDP/ODP/IODP）在西太平洋设计和钻取了数百个站位。我们拟充分利用这些现有的岩芯材料，对DSDP航次6, 17, 30, 31, 32, 55, 58, 59, 60, 61, 89 和ODP 航次 124, 125, 126, 129, 130, 143, 145，192的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。通过重新采样和用现代先进的古地磁学和岩石磁学仪器和技术深入研究，我们将寻求对一系列基本科学问题的答案，包括确定西太平洋盆地和高原在晚中生代-新生代的原始板块构造背景（古纬度）。本项目的实施有助于西太平洋古地理重建和地幔动力学边界条件的模拟，也将为西太平洋开展新的一轮IODP大洋钻探提供有用信息。

西太平洋地区处于欧亚板块、太平洋板块、菲律宾海板块和印度-澳大利亚板块的交汇处，是研究海底扩张和板块俯冲过程的天然实验室和研究海陆相互作用演化的枢纽地带。重构该区的构造演化历史极具挑战．研究该区详尽的构造演化历史，不但是全球板块重建的重要前沿科学课题，更是深入理解该区矿产资源分布、边缘海演化机制、气候演化模型等重大地学问题的基础。项目开展了对西太平洋海底高原和盆地的DSDP和ODP岩芯更深入细致的古地磁退磁实验、基岩古纬度确定、岩石磁学特征等综合研究。由于受到当时船上古地磁样品分布、测量时间、以及缺乏现代先进的古地磁学和岩石磁学仪器和技术等限制，许多熔岩流层都未能开展更详尽的航次后古地磁研究。因此，若要可靠地确定西太平洋盆地白垩世以来古纬度复合记录和区划白垩纪火山活动的范围，需要通过重新采样和用现代先进的古地磁学和岩石磁学仪器和技术深入研究，我们对西太平洋海底高原和盆地的DSDP和ODP岩芯更深入细致的古地磁退磁实验、基岩古纬度确定、岩石磁学特征等综合研究。从Ontong Java高原（OJP）ODP Leg 192四个站位玄武岩获得可靠古地磁数据，分别获得了四个站位特征剩磁独立倾角平均值为-41.4 º，对应的古纬度为南纬23.8 º。这个新数据表明之前的太平洋板块的APWP在中白垩纪部分可能有错，需要给与修正。菲律宾海板块四国盆地内部最老的大洋钻探岩心 ＯＤＰ１１７７孔的古地磁研究新证据与其他现有观测结果相结合，强烈表明四国盆地可能在中新世早期与南海动态耦合。南海与菲律宾海板块四国盆地在早中新世时为同一构造动力学演化系统。