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

上地壳浅层的地震余震被认为部分是由下地壳或地幔的粘性控制的。关于下地壳粘度如何影响这部分地震周期的模型是基于具有简单均匀粘度的岩石。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。首席研究员和学生们正在确定，相对于加载方向，这些片理的方向如何影响普通片理岩石的粘度。他们在实验室的条件下进行了实验，模拟了两种不同面理岩石在不同方向上的中下地壳变形。这些实验的结果将被纳入一个模型，该模型将评估叶理如何影响岩石相对于均匀岩石的粘度，这将通过以下方面造福社会：1)提高我们对地震周期下地壳对载荷响应的理解；2)支持几名研究生和几名本科生的研究经验；3)支持面向贫困学生的科学、技术、工程和数学（STEM）外展活动。为了准确地模拟下地壳流变学和地震周期，了解片理方向、连通性和预先存在的晶格优选方向对粘性各向异性的影响至关重要。在这个项目中，首席研究员和学生将：1)确定云母片理取向是否导致下地壳岩石的粘性各向异性，2)确定云母片理的相互连接如何影响下地壳岩石的粘性各向异性程度，以及3)确定预先存在的晶格优先取向（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母+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，并在相对于压缩方向的一系列方向上选择片理和预先存在的晶格。这些实验样品将使用岩石显微镜、扫描电子显微镜/电子背散射衍射（SEM/EBSD）来表征晶粒级微观结构和晶格优选取向，傅里叶变换红外光谱（FTIR）来确定水分含量，透射电子显微镜（TEM）来确定变形机制。本研究的部分内容将在阿克伦大学的高级构造地质学课程中进行，实验样品的薄片将用于阿克伦大学构造地质学课程的实验室部分。预期结果将提供重要的微观结构和力学数据集，可用于模拟下地壳的粘性各向异性。首席研究员和学生们还将开发新的实验技术，用于地壳岩石的高压实验和一种新的、廉价的设备，用于有关地震机制的STEM推广活动。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.