Deep Structure of Lithospheric Fault Zones

本项目将调查形成板块边界的断层带的类型和规模如何随发震上地壳以下岩石圈的深度而改变特征。该项目旨在重建一个经过充分研究的主要断层带在运动时的特征，目的是确定控制断层带行为的重要因素之间是否存在比例关系：剪切带宽度，流变学，应力，应变率和温度。该项目将侧重于瑞士阿尔卑斯山的Simplon断层，这是一个位移速率受到很好限制的断层，因此可以计算不同结构水平的应变速率，并确定剪切带流变学。这项研究的结果将是有价值的地球动力学模拟的岩石圈响应板块运动，地球物理数据的解释跨板块边界剪切带，解释地震后变形的大地测量，并了解如何孕震断层加载。拟议的活动将通过妇女充分参与STEM，公众通过虚拟实地考察参与STEM，以及通过本科生和研究生培训以及本科生实地课程发展多样化的具有全球竞争力的STEM劳动力来促进预期的社会成果。适应相对板块运动的断层必须横切岩石圈的大部分，但它们的宽度，内部结构，和作为时间和深度的函数的机械性能知之甚少。该建议旨在重建一个经过充分研究的主要断层带运动时的特征，目的是确定剪切带宽度、流变学、应力、应变率和温度之间是否存在比例关系。将使用现场和实验室技术对瑞士阿尔卑斯山的辛普伦断层进行调查，以确定其原始宽度、流动应力、应变率和流变性随温度和深度的变化。断层是一个正向剪切带，在25至3 Ma之间以3-5 mm/年的速率活动，在运动过程中其下盘被挖出，暴露出深度达30 km的高度变形岩石。分析方法将包括：（a）使用光学和SEM方法进行微观结构分析;（B）测量石英的动态再结晶粒度，以确定变形期间的应力;（c）使用电子背散射衍射方法测量石英的晶体学优选取向，以确定活动滑移系;（d）利用石英的Ti含量、含碳材料的激光拉曼光谱法和共存矿物的多平衡温压测定法确定变形期间的温度和压力;（e）角闪石、白云母和黑云母的~（39）Ar/~（40）Ar热年代学分析以及锆石和磷灰石的U-Th/He热年代学分析;（f）折返剪切带热演化的数值分析。变形过程中的应变速率将根据宽度和位移速率计算;与应力一起，这可用于校准剪切区流变学。

This project will investigate how fault zones, of the type and scale that form plate boundaries, change character with depth in the lithosphere below the seismogenic upper crust. This project aims to reconstruct the characteristics of a well-studied example of a major fault zone at the time of motion, with the aim of determining if there is a scaling relationship between important factors that control fault zone behavior: shear zone width, rheology, stress, strain-rate and temperature. The project will focus on the Simplon fault in the Swiss Alps, a fault with a well-constrained rate of displacement, so that strain-rate at different structural levels can be calculated and the shear zone rheology determined. The results of this research will be of value for geodynamic modeling of the lithospheric response to plate motions, the interpretation of geophysical data across plate boundary shear zones, the interpretation of geodetic measurements of post-seismic deformation, and for understanding how seismogenic faults are loaded. The proposed activity will advance desired societal outcomes by full participation of women in STEM, public engagement with STEM through virtual field trips, and development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training plus an undergraduate field course.Faults that accommodate relative plate motion must transect much of the lithosphere, yet their width, internal structure, and mechanical properties as a function of time and depth are poorly understood. This proposal aims to reconstruct the characteristics of a well-studied example of a major fault zone at the time of motion, with the aim of determining if there is a scaling relationship between shear zone width, rheology, stress, strain-rate and temperature. The Simplon fault in the Swiss Alps, will be investigated using field and laboratory techniques to determine its original width, flow stress, strain-rate, and rheology as a function of temperature and depth. The fault is a normal sense shear zone, active between 25 and 3 Ma at a rate of 3-5 mm/year, which exhumed its footwall during motion, exposing highly deformed rocks from depths of up to 30 km. Analytical methods will include: (a) microstructural analysis using optical and SEM methods; (b) measurement of the dynamically recrystallized grain size of quartz for determination of stress during deformation; (c) measurement of the crystallographic preferred orientation of quartz, using electron backscatter diffraction methods, to determine the active slip systems; (d) determination of temperature and pressure during deformation using the Ti content of quartz, laser Raman spectrometry of carbonaceous material, and multi-equilibrium thermobarometry of coexisting minerals; (e) thermochronology using 39Ar/40Ar analysis on hornblende, muscovite and biotite plus U-Th/He analysis on zircon and apatite; and (f) numerical analysis of the thermal evolution of the exhumed shear zone. Strain-rate during deformation will be calculated from the width and displacement rate; together with the stress, this can be used to calibrate the shear zone rheology.