台湾海岸山脉弧前盆地的构造反转机制

Fore-arc basins, whose birth, growth and demise closely relate to the subduction and collision of oceanic plates, contain precious information on seismogenesis, deformation, erosion, and magmatism during plate convergence. Since the late Cenozoic arc-continent collision, the northern segment of the Luzon Volcanic Arc has been exhuming as the Coastal Range, eastern Taiwan. This proposal will research into deformation structures in residual fore-arc basins and their basements in the range. Structural analysis will be integrated with magnetic fabric analysis, vitrinite reflectance measurement, and numerical simulation so as to establish the deformation sequence of the study area, to restore the tectonic stress for each stage, to determine the dominant mechanism of regional folds as well as its manifestation in the basins and basements, and to infer the denuded strata thicknesses of the basins. Based upon these results, the inversion of fore-arc basins in the area will be numerically simulated to uncover the deep dynamics beneath the volcanic arc during oblique arc-continent collision. This study will enhance our understanding the process of arc-continent collision.

弧前盆地的形成、演化乃至消亡与板块俯冲和碰撞密切相关，记录到板块汇聚过程的地震、构造、侵蚀和岩浆等宝贵信息。由于晚新生代以来的斜向弧–陆碰撞，吕宋火山岛弧的北段露出海平面，形成台湾东部的海岸山脉。本项目将以海岸山脉残留弧前盆地及其基底的变形构造为研究对象，通过构造分析、磁组构分析、镜质体发射率测量和数值模拟，建立研究区的构造变形序列，反演各阶段的古构造应力场，阐明区域性褶皱的主导机制及其在弧前盆地和基底的表现形式，恢复残留弧前盆地的地层剥蚀厚度，最后实时再现脉弧前盆地的反转过程，揭示出在斜向弧–陆碰撞下火山岛弧变形的深部动力学特征，由此深化我们对斜向弧–陆碰撞作用的理解。

晚新生代以来吕宋火山岛弧与中国大陆发生斜向碰撞形成台湾造山带，并导致吕宋弧北段露出海平面成为台湾东部的海岸山脉。本项目的研究对象是海岸山脉残留弧前盆地（早上新–早更新世）及其基底的变形机制。通过对南部泰源向斜泥岩镜质体反射率的热演化模拟，获得盆地的剥蚀地层厚度下限为3.2–4.8 km，同沉积的热流值为36.84–41.87 mW/m2，意味着所谓的弧前盆地其实是“冷”的。成功、乐和和八里湾向斜四条剖面泥岩磁组构的应变分析揭示出多期的构造变形过程，即前褶皱的NW–WNW向顺层挤压、同褶皱的地层倾斜和后褶皱的NNW向挤压，表明火山弧的整体变形主要取决于坚硬的基底岩石。石梯坪火山碎屑岩中变形带的古应力分析给出两期构造作用，即前褶皱的NW–WNW向顺层挤压和同褶皱的E–W向挤压，很可能与斜向弧–陆碰撞有关。这些成果从不同方面刻画了弧前盆地的反转过程，有助于深化理解斜向弧–陆碰撞作用。