台湾晚中新世以来活跃弧陆碰撞过程的弧前盆地沉积响应

This proposal『Neogene Forearc sedimentation in response to active Taiwan arc-continent collision』 intents to study also to test a working hypothesis of『Backthrusting controls dynamic forearc sedimentation』. The Taiwan mountain belt represents one of the most typical examples of an active arc-continent collision on the world. The 『Backthrusting controls dynamic forearc sedimentation』working hypothesis is established from a regional study on the modern sedimentation in forearc basin off SE Taiwan. The working hypothesis demonstrates that modern transportation paths and the sedimentation in the North Luzon Trough forearc basin are fundamentally controlled by an arcward backthrusting deformation in forearc basin caused by the active oblique arc-continent collision. This forearc backthrusting deforms the forearc strata as the Huatung Ridge, which further changes the forearc morphology and thus controls the transportation paths of sediments and sedimentation in the forearc basin spatially. We intents to combine both geology of the forearc deformation-sedimentation from the modern active arc-continent collision region off SE Taiwan and also from exposed forearc sequences in the Coastal Range, eastern Taiwan, for a better understanding of the fundamental driven mechanisms that control the forearc sedimentation in the modern and ancient forearc basins.

项目『台湾晚中新世以来活跃弧陆碰撞过程的弧前盆地沉积响应』旨在利用台湾为最典型活跃斜向弧陆碰撞构造的优势,以海陆地质结合的方法,研究并检验『背逆冲构造控制弧前盆地沉积』工作假说, 以解决造成台湾东部海岸山脉弧前盆地在东西及南北方向空间上沈积层序差异之原因及机制。『背逆冲构造控制弧前盆地沉积』工作假说认为欧亚大陆-南海海洋岩石圈自17 Ma向东俯冲,并自6.5 Ma开始与吕宋火山岛弧发生斜向碰撞,北吕宋海槽弧前盆地发生向岛弧方向前进的背逆冲构造,导致整个弧前盆地变形为花东海脊,进而影响弧前盆地沉积物输送路径及残留弧前盆地的沉积;继之于1 Ma发生的向西仰冲构造,花东海脊再次剪裂并混入火山岛弧地壳及上地幔岩块形成弧前碰撞混杂岩。拟比较台湾东南海域现代活跃弧陆碰撞区弧前变形特征及海岸山脉关键剖面层序之沉积时间,以了解弧陆碰撞过程中弧前盆地的沈积响应,提供了解现代及古老碰撞造山带弧前盆.

计划执行完成台湾東南海域20oN以北板块聚合构造区内海上七条东-西向地震剖面解释,并和陆域海岸山脉出露层序进行详细弧前盆地地层学研究，概述了同沉积变形，动力层序地层学，弧前层序沉积的时空变化响应特征。将陆上和近海的弧前盆地地质结合在一起，使我们能够重建北吕宋盆地弧前盆地从俯冲到碰撞到仰冲的构造演化，并讨论活动台湾造山期间造成现代弧前碰撞混杂岩的发展机制和形成过程。. 海上地震勘探表明，在俯冲带内弧前盆地层序的变形主要是由于增生楔的后部斜率增加和弧前盆地层序沿增生楔斜坡发生向西逆冲奴重构造;在碰撞带内弧前沉积层序发生向东反逆冲,反逆冲构造向岛弧方向迁移前进。双向逆冲构造导致弧前届序推覆变形并抬升为花东海脊,再反过来控制后期的年轻弧前层序沉积。为了响应同沉积变形，弧前盆地的沉积中心逐渐东移。因此，在碰撞带内弧前层序可分成由两个不整合面分隔、并由西向东并置的三个巨型沉积层序。因此，在台湾东南部的斜向碰撞带内，显示出一种弧前变形和地层分布时空格局变化特征:地层最老、变形也最为强烈的层序,出露在弧前盆地的最西部，而轻度变形的弧前中部及上部层序分别出露在盆地中心和弧前盆地的东部。