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

这项计画的目的是验证一种新的假设，即台湾南部的伸展始于100-200万年前，当时菲律宾海板块最初与一过渡性陆壳带(厚度5-20公里)相撞，然后与更典型厚度的陆壳相撞(约30公里)。碰撞模式的转换开始于沿走向流动或挤压和局部伸展区域，特别是在台湾中南部山脉。将利用实地构造地质学(脆性和韧性构造分析)和低温热年代学(裂变径迹和(U-Th)/He测年)结合地震学(震源机制、簇几何)和GPS分析来确定：1)折返是否以及何时从相对较慢的速率变为较快的速率；2)折返速率的区域范围是否发生变化；3)是否有从缩短到伸展的变化；4)确定哪些构造适合伸展和岩石抬升；5)记录特定构造、构造序列或折返的向南传播。总的目标将是记录该地区现在和过去的运动学，然后将解释的运动学演化与热年代学数据揭示的隆升和折返历史联系起来。最近在理解影响地球表面的过程方面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。台湾造山带提供了一个难得的机会，可以更好地约束同造山伸展的起源和意义。造山带横跨欧亚板块和菲律宾海板块之间的边界，并随着两个板块的碰撞而活跃地传播。在造山带刚刚浮出海平面的地区，一个密集的GPS网络显示了一个相对快速的伸展应变的宽阔地带。该地区的地形也攀升到碰撞带的最高海拔(略低于4公里)，现有的热年代学数据表明，相对较高的隆升速率。为什么这个有充分记录的延伸区也是一个岩石和地表隆起很大的地区？回答这个问题将极大地提高对大学造山过程的理解。

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.