CAREER: Experimental Investigation of Viscous Anisotropy of Foliated Rocks: Implications to the Strength of the Mid to Lower Continental Crust

浅层上地壳的地震余震被认为部分是由深层地壳或地幔的粘性控制的。下地壳的粘性如何影响地震周期的这一部分的模型是基于具有简单均质粘性的岩石。然而，大多数天然岩石由于被称为叶理的矿物排列而具有非均质性，这将影响这些岩石的力学行为。主要研究人员和学生正在确定普通面理岩石的粘度如何受到这些面理相对于加载方向的取向的影响。他们在模拟中下地壳变形的条件下，在两种不同面理的岩石上进行实验室实验，这些面理具有不同的方向。这些实验的结果将被合并到一个模型中，该模型将评估面理如何影响岩石相对于均质岩石的粘度，这将通过以下几个方面造福社会：1)提高我们对下地壳在地震周期中对载荷的响应的理解，2)支持几名研究生和几名本科生的研究经验，以及3)支持面向贫困学生的科学、技术、工程和数学(STEM)推广活动。了解面理取向、相互连通性和先前存在的晶格优先取向对粘性各向异性的影响对于准确模拟下地壳和地震周期的流变性至关重要。在这个项目中，主要的研究人员和学生将：1)确定云母面理取向是否导致下地壳岩石的粘性各向异性；2)确定云母面理的相互连通性如何影响下地壳岩石的粘性各向异性程度；3)确定先前存在的晶格择优取向(LPO)如何影响这些岩石的粘性各向异性。这些研究人员将对细粒黑云石石英斜长片麻岩或云母石英岩进行轴向压缩和剪切变形实验，这些片麻岩的面理和先前存在的晶格优先取向相对于压缩方向具有一定范围的取向。用岩相显微镜、扫描电子显微镜/电子背散射衍射仪(SEM/EBSD)表征颗粒尺度的微结构和晶格择优取向，用傅立叶变换红外光谱(FTIR)测定水分含量，用透射电子显微镜(TEM)确定变形机制，对实验样品进行分析。这项研究的一部分将在阿克伦大学的高级结构地质学课程中进行，实验样品的薄片将用于阿克伦大学结构地质学课程的实验室部分。预期的结果将提供大量的微观结构和力学数据，可用于模拟下地壳的粘性各向异性。首席研究员和学生还将为地壳岩石高压实验开发新的实验技术，并为STEM关于地震机制的外展活动开发一种新的廉价设备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Earthquake aftershocks in the shallow upper crust are thought to be controlled in part by the viscosity of the underlying deep crust or mantle. Models of how the viscosity of the lower crust affects this portion of the seismic cycle are based on rocks with simplistic homogeneous viscosities. However, most natural rocks have heterogeneities due to alignments of minerals called foliations, which will affect the mechanical behavior of these rocks. The principal investigator and students are determining how the viscosity of common foliated rocks is affected by the orientation of these foliations relative to the direction of loading. They are performing laboratory experiments at conditions that simulate deformation in the mid to lower crust on two different foliated rocks with the foliation in a variety of orientations. The results of these experiments will be incorporated into a model that evaluates how foliations affect the viscosity of rocks relative to homogeneous rocks, which will benefit society by: 1) improving our understanding of the response of the lower crust to loading during the seismic cycle, 2) supporting research experiences of several graduate students and several undergraduate students, and 3) supporting Science, Technology, Engineering and Mathematics (STEM) outreach activities to underprivileged students.Understanding the effects of foliation orientation, interconnectivity and preexisting lattice preferred orientations on viscous anisotropy is critical in order to accurately model the rheology of the lower crust and the earthquake cycle. In this project the principal investigator and students will: 1) determine if micaceous foliation orientation causes viscous anisotropy of lower crustal rocks, 2) determine how interconnectivity of the micaceous foliation affects the degree of viscous anisotropy of lower crustal rocks, and 3) determine how a preexisting lattice preferred orientation (LPO) affects viscous anisotropy of these rocks. These researchers will perform both axial compression and shear deformation experiments with a fine-grained biotite + quartz + plagioclase gneiss or a micaceous quartzite with the foliations and preexisting lattice preferred orientations in a range of orientations relative to the compression direction. The samples from these experiments will be analyzed using the petrographic microscope, Scanning Electron Microscopy/ Electron backscatter diffraction (SEM/EBSD) to characterize grain-scale microstructures and lattice preferred orientations, Fourier-transform infrared spectroscopy (FTIR) to determine water contents and Transmission Electron Microscopy (TEM) to determine deformation mechanisms. Portions of this study will be performed in the Advanced Structural Geology course at the University of Akron and thin sections from experimental samples will be used in the laboratory section of the Structural Geology course at the University of Akron. The expected results will provide significant sets of microstructural and mechanical data which can be applied to modeling the viscous anisotropy of the lower crust. The principal investigator and students will also develop new experimental techniques for high pressure experiments on crustal rocks and a new, inexpensive apparatus for STEM outreach activities about earthquake mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.