菲律宾海九州-帕劳海脊南段的深部结构、岩浆作用和形成过程——对板块俯冲起始机制的启示

Kyushu-Palau Ridge (KPR) is a textbook place for the studies on the subduction initiation, providing a unique natural laboratory for developing plate tectonic theory. In this study, significantly improved high-resolution models of lithospheric solid and liquid structure of the Southern KPR and adjacent region will be constructed based on geophysical observations from OBS and OBEM deployment along a regional transection crossing the West Philippine Basin, the KPR, and the Perce-Vela basin. Combined with geochemical analysis and computational geodynamic simulations, the characteristics of the deep subducted slabs, the different oceanic lithosphere, the corresponding magmatic activities and mechanism will be investigated and revealed, as well as the flux and cycling of the subducted materials. A complete evolution model including a subduction initiation, a followed island arc splitting, and the back-arc seafloor spreading will be constructed. The major scientific goal is to reveal the mechanism of the subduction initiation, dynamic process and controlling factors.

九州-帕劳海脊是研究俯冲带起始机制的典型地区，而板块俯冲起始机制是板块构造理论发展的关键和新方向。课题通过在九州-帕劳海脊南段及邻区开展海底地震仪和海底电磁结合的综合地球物理剖面观测，获得研究区高分辨率的岩石圈固体-流体结构。同时在岩石地球化学分析和地球动力学模拟的基础上，揭示古太平洋板块向西菲律宾海盆俯冲不同阶段的板块深部行为、岩浆响应和物质循环的特点，并在数值模拟实验及与实际对比的基础上，建立九州-帕劳海脊及邻区从俯冲起始-岛弧裂离-弧后伸展的完整演化历史，揭示板块俯冲起始机制、动力学过程及其控制因素。

九州-帕劳海脊是研究俯冲带从初始俯冲-岛弧裂离-弧后扩张过程的理想场所，本课题基于2019年执行的九州-帕劳洋脊的综合地球物理探测航次所获得的重、磁、多波束、多道地震和深反射地震数据，对九州-帕劳海脊深部地壳结构特征和代表岩浆喷发活动的海山时空分布特征及形成机制进行研究，并通过动力学数值模拟对俯冲的起始过程进行模拟。对九州-帕劳海脊南段高分辨率的沿洋脊和垂直洋脊的地壳结构研究，发现洋脊代表了洋壳向岛弧型地壳发展的过渡阶段，是多期次、多来源的岩浆作用共同塑造的结果；对沿脊海山时空分布特征表明岩浆加载区域受到先存薄弱带，弧后盆地渐进式扩张以及上地幔的不均一性等影响；初始俯冲的地球动力学模拟研究表明，古太平洋板块向西菲律宾海之下的俯冲在起始阶段为受重力诱发的自发俯冲，在自发俯冲约5 Myrs后，开始进入成熟的俯冲阶段，在16 Myrs后发生不对称的弧后扩张。

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