台湾增生楔的构造单元划分及其变形特征

GEOLOGICAL CHARACTERISTICS AND TECTONIC MECHANISM OF TAIWAN ACCRETIONARY PRISM: EVIDENCES FROM A MULTI-CHANNEL SEISMIC PROFILE OF A "973" SURVEY

台湾增生楔位于欧亚板块、菲律宾海微板块和南海的结合部位,是现代弧陆碰撞研究的理想场所。通过对南海973航次在该区域的多道地震剖面的解释,对该增生楔进行了构造单元的划分,并分析了变形特征。认为台湾增生楔是由3个部分,即弧陆碰撞产生的增生部分、洋内俯冲产生的增生部分和增生楔后端在恒春海脊和北吕宋海槽之间的构造楔组成,研究区的高屏斜坡、恒春海脊和北吕宋海槽西端变形带分别是3个部分的反映。自中中新世以来,南海洋壳开始沿着马尼拉海沟向菲律宾海微板块俯冲,形成增生楔中洋内俯冲增生部分;与此同时菲律宾海微板块开始向NW方向移动,前缘的吕宋岛弧自6.5Ma B.P以来与亚洲陆缘斜向碰撞,形成增生楔中弧陆碰撞增生部分。碰撞首先发生在台湾岛的北部,由于弧陆强烈的挤压作用,增生楔后端部分向北吕宋海槽倒冲楔入,使得上部的北吕宋海槽的沉积发生隆升变形。滨海的各个地貌单元可以和台湾陆上的地貌单元相联系,它们具有相似的地质特征,但是由于陆上部分增生历史久,不仅抬升为陆,而且地层的年代也更老。

Taiwan accretionary prism lies in the conjunction area of the Eurasian Plate, the Philippine Sea Plate and the South China Sea, and is characterized by the young age of the arc-continent collision. The structural geometry, kinematics and density structure of the Taiwan accretionary prism were studied based on the interpretation of a multi-channel seismic profile obtained during a “973” survey. Geological evidence showed that the Taiwan accretionary prism consists of three distinct structural domains, the collision prism caused by the arc-continent collision, the subduction prism caused by the inner-ocean subduction, and the tectonic wedge between the Luzon arc and the prism. In the studied area, the three domains are the Gaoping Slope, the Hengchun Ridge and the west part of Luzon Through, respectively. Since the middle Miocene, the South China Sea had subducted beneath the Philippine Sea Plate along the Manila Trench, and the subduction prism came into being. The Philippine Sea Plate also moved northwestward and collided obliquely with the Asian continent since 6.5Ma B. P.. The arc-continent collision made the collision prism west of the subduction prism, together forming the Taiwan accretionary prism. With the continuous process of the arc-continent collision, a tectonic wedging took place along the rear of Taiwan accretionary prism and caused the uplift and deformation of the strata in the west part of the North Luzon Through. Compared with the onshore geology, the offshore Taiwan accectionary prism has the similar and relevant structure characteristics. They have the same tectonic mechanism but different deformation history, i.e. the collision began in the north of Taiwan, and then propagated southward. The onshore Taiwan has much longer deformation history.