Using Micromechanical Experiments to Investigate the Rheology of Geologic Materials

地质物质的物理和化学性质控制着地球表面和内部的发展。流变学是材料性质研究的一个特殊分支，它表征了材料流动或粘性变形的能力。地质物质的流变学主要控制着地幔对流、板块构造和山脉的形成。因此，流变学与地震、火山、海啸等众多自然灾害以及自然资源的生产直接相关。在这个项目中，研究人员正在使用材料科学的工具来了解构成地壳和上地幔大部分的矿物的流变学。从这项研究中得到的数据将使地球科学家更好地了解板块构造是如何在地球和其他行星上运作的。该研究项目通过女性充分参与STEM，提高公众科学素养和公众对STEM的参与，通过本科生和研究生培训培养有竞争力的STEM劳动力，以及改进实验室以增强研究基础设施，来推进预期的社会成果。该项目的目的是利用微力学方法，包括纳米压痕和微柱压缩测试，研究地质材料的粘塑性流变学。在纳米压痕测试中，用精确控制的力将锋利的压痕器推入感兴趣的样品，通常深度为数十到数百纳米。同时记录的力和位移被用来评估试样的弹性和塑性响应。在微柱压缩测试中，使用聚焦离子束制造直径小至几百纳米的材料柱。使用配备圆柱形探头的纳米压痕仪，进行单轴压缩测试，以确定微柱在一系列变形条件下的机械响应。在本项目中，将对石英、斜长石、正辉石和橄榄石的定向单晶在低至中温（T = -10至600℃）下进行微力学变形实验。这些实验数据将用于约束岩石圈强大条件下矿物的流变学，并且预测低温塑性是主要的变形机制。流变各向异性的影响将使用相同的微力学方法进行评估。实验结果将辅以高分辨率的像差校正扫描透射电子显微镜成像和电子能量损失光谱，以深入了解由变形引起的晶体缺陷的原子尺度结构和化学性质。

The physical and chemical properties of geologic materials control the development of Earth's surface and interior. Rheology is one particular branch of the study of material properties, which characterizes materials' ability to flow or deform viscously. The rheology of geologic materials is mainly responsible for controlling mantle convection, plate tectonics, and the formation of mountains. As such, rheology is directly related to numerous natural hazards such as earthquakes, volcanoes, and tsunami, as well as the production of natural resources. In this project, the investigators are using tools from materials science to understand the rheology of minerals that make up the bulk of Earth's crust and upper mantle. The data that result from this study will allow geoscientists to better understand how plate tectonics works, both on Earth and on other planetary bodies. The research project advances desired societal outcomes by full participation of women in STEM, public outreach to increase public scientific literacy and public engagement with STEM, development of a competitive STEM workforce through undergraduate and graduate student training, and laboratory improvement that enhances infrastructure for research.The objective of this project is to investigate the viscoplastic rheology of geological materials using micromechanical methods, including nanoindentation and micropillar compression testing. In a nanoindentation test, a sharp indenter is pushed into a specimen of interest with a precisely controlled amount of force, typically to depths of tens to hundreds of nanometers. A simultaneous record of the force and the displacement is used to assess the elastic and plastic response of the test specimen. In a micropillar compression test, a column of material with a diameter as small as a few hundred nanometers is fabricated using a focused ion beam. Using a nanoindentation instrument equipped with a cylindrical probe, uniaxial compression tests are performed to determine the mechanical response of the micropillar over a range of deformation conditions. In this project, micromechanical deformation experiments will be performed at low to moderate temperatures (T = -10 to 600 degrees C) on oriented single crystals of quartz, plagioclase feldspar, orthopyroxene, and olivine. Data from these experiments will be used to constrain the rheology of minerals under conditions where the lithosphere is strong and low-temperature plasticity is predicted to be the dominant deformation mechanism. The effects of rheological anisotropy will be assessed using the same micromechanical methods. Experimental results will be complemented by high resolution aberration-corrected scanning transmission electron microscope imaging and electron energy loss spectroscopy to provide insight into the atomic-scale structure and chemistry of crystalline defects introduced by deformation.