Collaborative Research: Erosional Forcing of Late Quaternary Compressive Strain, West Central Taiwan

压缩造山带的稳定状态增长的概念是近二十年来大陆构造学中最被接受的观点之一，然而令人惊讶的是，很少有直接的数据来检验已经提出的模型。测试和完善稳态造山概念需要确定压缩造山带的瞬态响应和动态反馈情况，并记录地壳变形响应侵蚀的空间和时间尺度。本项目利用台湾中西部活动褶皱冲断带的独特自然实验，在那里有足够的现代地震学、大地测量学、构造和地质年代学数据，可以评估造山带如何在数十公里尺度上对楔形体积的快速突变做出反应。台湾中西部的蒲里凹陷比邻近的褶皱冲断带低约1.5 km。地质和大地测量证据表明，逆冲作用发生在地形坝的宽度上，而不是集中在冲断带的前部，就像冲断带南部的邻近部分一样，那里的地形保持着典型的楔形。应变和地形梯度之间的假设联系通过(a)结合构造、地质年代学和地形学方法开发了一个晚第四纪滑动速率和变形模式数据库，以及(b)使用三维有限元模型来确定产生观测到的地形和变形模式所需的必要和充分条件来验证。断层滑动速率是通过对变形的河流阶地和盆地填充物进行定年得到的。年龄测年还可以测试和校准长期流切割规律。校正后的规律为从地形出发的应变模式估计提供了定量基础，这些应变模式估计是在该带难以进入或约束较差的地区，如阿里山山脉。

The concept of steady-state growth of compressive orogens is one of the most accepted ideas in continental tectonics developed in the last two decades, yet surprisingly few direct data exist to test the models that have been advanced. Testing and refining the concept of steady-state mountain building requires identification of cases of transient response and dynamic feedback in compressive orogens, and documentation of the spatial and temporal scales at which crustal deformation responds to erosion. This project takes advantage of a unique natural experiment in the active fold-thrust belt of west-central Taiwan where enough modern seismologic, geodetic, structural and geochronologic data exist to assess how an orogen responds to rapid and abrupt changes in wedge volume at scales of tens of kilometers. The Puli embayment in the west-central Taiwan lies approximately 1.5 km lower than neighboring parts of the fold-thrust belt. Geologic and geodetic evidence suggests that thrusting occurs over the width of the topographic embayment, rather than being concentrated at the front of the thrust belt, as is the case in the adjacent part of the thrust belt to the south where the topography maintains a classic wedge shape. The hypothesized connection between strain and topographic gradients is tested by (a) development of a database of late Quaternary slip rates and deformation patterns using a combination of structural, geochronologic and geomorphic methods, and (b) use of a 3D finite element model to determine the necessary and sufficient conditions required to produce the observed topography and deformation patterns. Fault-slip rates are obtained via dating of deformed stream terrace and basin fill deposits. Age dating also enables testing and calibration of long-term stream incision laws. The calibrated laws provide a quantitative basis for topographically derived estimates of strain patterns in inaccessible or poorly constrained areas of the belt such as the Alishan Range.