Collaborative Research: Geological Investigations of Non-Andersonian Conjugate Strike-slip Faults in Central Tibet

地球科学的一个基础是能够将构造板块边界、与地震有关的断裂、山脉隆起和断层模式等地质特征的空间布置与它们的成因联系起来。在这方面，地球科学家长期以来一直使用实验建立的库仑断裂准则来解释断层形成的动力学原因。库仑断裂准则预测了断层之间的某些角度关系。随着更多和系统的观察表明，许多天然断层与这些角度关系背道而驰，这种方法面临着越来越多的困难。这项研究将涉及使用一种新的实验设备来模拟天然断层作用，以及检查西藏中部大型断层系统的几何演化，以确定是否需要不同于库仑准则的力学原理来解释天然断层的几何形状。我们解释岩石圈变形的能力，也许更重要的是解释流动的中地壳和破裂的上地壳之间的耦合，关键取决于将观察到的断层几何形状与成因动力学条件联系起来的知识。在这方面最常用的关系是库仑断裂准则，它预测X形共轭断层从最大压应力方向定向到~30°。在自然界中，走滑系统中的X形共轭断层几何形状很少被观察到，尽管断层几何形状可能由于断层后变形而复杂且难以解释，但从Sigma One开始，断层方向为60-75°的V形几何形状基本上被忽略了。这些V型断裂系统在自然界中是常见的，在阿尔卑斯-喜马拉雅碰撞带中有突出的大型例子。这些调查者将通过构造填图和古地磁分析来检验西藏中部的V形共轭断层是由垂直轴旋转还是成对的普通剪切流形成的。这些结果和相关模型应该对大陆的大规模变形在地质时间范围内基本上是板状还是流体状具有重要意义。该奖项是根据2009年美国复苏和再投资法案(公共法律111-5)资助的。

A foundation of Earth Sciences is the ability to relate spatial arrangements of geologic features such as tectonic plate boundaries, earthquake-related ruptures, mountain uplifts and fault patterns in general to their causative forces. In this regard, geoscientists have long used the experimentally established Coulomb fracture criterion, which predicts certain angular relationships between faults, to explain the dynamic causes of fault formation. This approach has faced increasing difficulties as more and systematic observations show that many natural faults defy these angular relationships. This research will involve the use of a new experimental apparatus to simulate natural faulting, as well as an examination of the geometric evolution of large fault systems in central Tibet, to determine if a mechanical principle different to the Coulomb criterion is needed to explain the geometry of natural faults. Our ability to interpret lithospheric deformation, and perhaps more importantly the coupling between the flowing middle and fracturing upper crust, depends critically on the knowledge that relates observed fault geometries to causative dynamic conditions. The most commonly used relationship in this regard is the Coulomb fracture criterion that predicts X-shaped conjugate faults oriented at ~30° from the maximum compressive-stress direction. In nature, X-shaped conjugate fault geometries in strike-slip systems are rarely observed, and while fault geometries can be complex and difficult to interpret due to post-faulting deformation, V-shaped geometries with faults orientated at 60-75º from sigma one have been essentially overlooked. These V-shaped fault systems are common in nature with prominent large-scale examples in the Alpine-Himalayan collision zone. These investigators will test whether V-shaped conjugate faults in central Tibet were created by vertical-axis rotation or paired-general-shear flow by performing structural mapping and paleomagnetic analysis. The results and associated models should have important implications for whether the large-scale deformation of continents is fundamentally plate-like or fluid-like over geologic timescales.This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).