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

挤压造山带稳定生长的概念是近二十年来大陆构造学中最被接受的概念之一，但令人惊讶的是，几乎没有直接数据来检验已经提出的模型。测试和完善稳态造山的概念需要查明挤压造山带中的瞬时响应和动态反馈情况，并记录地壳变形对侵蚀作出反应的空间和时间尺度。该项目利用台湾中西部活动褶皱冲断带独特的自然实验，那里有足够的现代地震学、大地测量学、构造和地质年代学资料，以评估造山带对数十公里尺度上楔形体积的快速和突变的响应。台湾中西部的埔里海湾比褶皱冲断带的邻近部分低约1.5公里。地质和大地测量证据表明，逆冲作用发生在地形海湾的宽度上，而不是集中在冲断带的前部，就像冲断带南面邻近部分的情况一样，那里的地形保持着典型的楔形。检验应变和地形梯度之间的假设联系的方法是：(A)综合运用构造、地质年代学和地貌学方法建立晚第四纪滑动速率和变形模式数据库；(B)利用三维有限元模型确定产生观测地形和变形模式所需的充要条件。断层滑动速率是由变形的河流阶地和盆地充填沉积测年得到的。年龄测定还可以测试和校准长期的溪流切割规律。校准后的定律为从地形上估计该带难以到达或限制较差的地区(如阿里山山脉)的应变模式提供了量化基础。

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.