Extrusion, Extension and Exhumation in an Emerging Mountain Belt, Taiwan

这个项目的目标是测试一个新的假设，即台湾南部的伸展始于100万至200万年前，当时菲律宾海板块最初与一个过渡性大陆地壳带（5至20公里厚）碰撞，然后与更典型厚度的大陆地壳（约30公里）碰撞。碰撞方式的转变引发了沿走向流动或挤压和局部伸展，特别是在台湾中部山脉南部。现场构造地质学（脆性和韧性结构分析）、低温热年代学（裂变径迹和（U-Th)/He定年）、地震学（震源机制、簇几何）和GPS分析将进行，以确定：1）挖掘是否以及何时从相对缓慢的速度转变为快速的速度；2)掘尸率变化的区域范围；3)从缩短到延长的变化；4)确定哪些构造适合伸展和岩石隆起；5)记录特定构造、构造序列或挖掘的向南传播。总体目标将是记录该地区当前和过去的运动学，然后将解释的运动学演化与热年代学数据所揭示的隆升和挖掘历史联系起来。在了解影响地球表面的过程方面，最近最重要的突破之一是发现一些收缩造山带也经历了水平伸展。台湾造山带为更好地研究同造伸展的成因和意义提供了难得的机会。造山带横跨欧亚海板块和菲律宾海板块之间的边界，并在两个板块碰撞时积极传播。在造山带刚刚出现在海平面以上的地区，密集的GPS网络显示出一个相对较快的伸展应变的广阔区域。该地区的地形也上升到碰撞区的最高海拔（略低于4公里），现有的热年代学数据表明相对较高的隆升率。为什么这个有大量文献记载的伸展区同时也是一个岩石和地表隆起的地区？回答这个问题将大大提高对碰撞造山过程的理解。

This goal of this project is to test the new hypothesis that extension in southern Taiwan initiated 1 to 2 million years ago as the Philippine Sea plate initially collided with a zone of transitional continental crust (5 to 20 km thick) followed by collision with continental crust of more typical thickness (about 30 km). The transition in collision mode initiated along-strike flow or extrusion and local areas of extension, especially in the southern Central Range of Taiwan. Field-based structural geology (brittle and ductile structural analyses) and low-temperature thermochronology (fission track and (U-Th)/He dating) coupled with seismological (focal mechanisms, cluster geometries) and GPS analysis will be carried out to determine: 1) if and when exhumation changed from relatively slow to fast rates; 2) the regional extent of the any change in exhumation rates; 3) if there has been a change from shortening to extension; 4) determine which structures accommodate extension and rock uplift; and 5) document southward propagation of specific structures, structural sequences or exhumation. The overall goal will be to document the current and past kinematics in the area and then tie the interpreted kinematic evolution to the history of uplift and exhumation as revealed by the thermochronologic data.One of the most significant recent breakthroughs in understanding processes that affect the Earth's surface is the discovery that some contractional orogenic belts also experience horizontal extension. The orogenic belt in Taiwan provides an unusual opportunity to better constrain the origin and significance of synorogenic extension. The orogen straddles the boundary between the Eurasian and Philippine Sea plates and is actively propagating as the two plates collide. In the area where the orogen is just emerging above sea level, a dense GPS network shows a broad zone of relatively fast extensional strains. The topography in this area also climbs to the maximum elevation in the collision zone (just under 4 km) and available thermochronological data suggest relatively high uplift rates. Why is this area of well-documented extension also an area of substantial rock and surface uplift? Answering this question would greatly improve understanding of processes that operate during collisonal mountain building episodes.