EAR-PF: Advanced statistical analysis to relate microstructural fabrics and finite strain in ductilely deformed rocks

EAR-PF：高级统计分析，将延性变形岩石中的微观结构结构和有限应变联系起来

• 批准号: 2053072
• 负责人: Alexander Lusk
• 金额: $ 17.4万
• 依托单位: Lusk, Alexander Dmitri
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-12-01 至 2022-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2053072&HistoricalAwards=false
• 关键词: EAR; PF; Advanced; statistical; analysis

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Dr. Alexander Lusk has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education plans at the University of Wisconsin Madison. Geologists characterize how rocks deform by measuring a quantity called finite strain. Finite strain is conceptualized in three dimensions as an ellipsoid. When rocks are not deformed, the 3-D object is a sphere; with increasing deformation, it becomes more elliptical. However, most deformed rocks do not have any large-scale indicators that record finite strain. As a result, geologists make microscope slides of rocks to study microscopic features called microstructures. The goals of Dr. Lusk’s project are two-fold: (1) to provide methods of characterizing finite strain uncertainty (i.e. error bars) in three dimensions to better understand rock deformation, and (2) to provide geologists with methods to relate rock microstructures developed in quartz (a common crustal rock constituent) to the finite strain experienced during deformation. To characterize finite strain, Dr. Lusk will apply statistical methods to rocks that contain quartz pebbles, which preserve a direct record of finite strain. During his postdoctoral fellowship, Dr. Lusk will carry out an education plan involving the following: (1) development of an undergraduate level, exploration based virtual education module that will aim to make students comfortable with measuring and interpreting finite strain in the field; (2) development of software for the statistical analysis of finite strain, integrated in the StraboSpot field app; (3) mentoring of two UW-Madison students in undergraduate research projects. This project aims to evaluate the response of rock microstructure developed in ductile quartz-rich rocks to the finite strain magnitude, geometry, and strain path in which deformation occurred. The proposed approach differs from previous work in that it applies multivariate statistical methods to quantitatively characterize ellipsoidal finite strain data – with a measure of uncertainty – for the first time. The key to statistical analysis of ellipsoids is that orientations and magnitudes, while independent measurements, must be combined and transformed into an ellipsoid tensor; in tensor form, multivariate statistical analysis can be applied. The project will be carried out by analyzing finite strain and rock microstructure in the ductile Bygdin (Norway) and Funzie (Scotland) quartz-rich metaconglomerates. Finite strain will be determined at the outcrop scale by measuring clast orientation and all three ellipsoid axes to constrain clast shape. At the grain scale, two measures of finite strain will be determined: (1) the grain shape and shape preferred orientation of relict metamorphic grains, and (2) the spatial relationship of relict metamorphic grain center points. Electron backscatter diffraction will be used for microstructural characterization, including measurement of grain shape, crystallographic vorticity axis orientation, and crystallographic preferred orientation. By relating statistical measures of finite strain directly to rock microstructural fabrics, Dr. Lusk aims to improve our current understanding of how finite strain and strain history is preserved in the microstructural record and to provide structural geologists with methods to infer strain history without a direct measurement of finite strain.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.

该奖项全部或部分根据2021年美国救援计划法案（公法117-2）资助。亚历山大卢斯克博士已被授予NSF博士后奖学金，在威斯康星州麦迪逊大学开展研究和教育计划。地质学家通过测量一个叫做有限应变的量来描述岩石变形的特征。有限应变在三维中被概念化为椭球体。当岩石没有变形时，三维物体是一个球体;随着变形的增加，它变得更加椭圆。然而，大多数变形的岩石没有任何记录有限应变的大尺度指标。因此，地质学家制作岩石的显微镜载玻片来研究称为微观结构的微观特征。Lusk博士的项目有两个目标：（1）提供三维有限应变不确定性（即误差条）的表征方法，以更好地了解岩石变形，以及（2）为地质学家提供将石英（一种常见的地壳岩石成分）中形成的岩石微观结构与变形过程中经历的有限应变联系起来的方法。为了描述有限应变的特征，Lusk博士将对含有石英卵石的岩石应用统计方法，石英卵石保留了有限应变的直接记录。在博士后研究期间，Lusk博士将开展一项教育计划，涉及以下内容：（1）开发一个本科水平的基于探索的虚拟教育模块，旨在使学生能够在现场测量和解释有限应变;（2）开发有限应变统计分析软件，集成在StraboSpot现场应用程序中;（3）两个威斯康星大学麦迪逊分校的学生在本科研究项目的指导。该项目旨在评估富石英韧性岩石中发育的岩石微结构对有限应变大小、几何形状和变形发生的应变路径的响应。所提出的方法不同于以前的工作，它应用多元统计方法来定量表征椭球有限应变数据-与不确定性的措施-第一次。椭球体统计分析的关键是，方向和大小，而独立的测量，必须结合起来，并转化为椭球张量;在张量形式，多元统计分析可以应用。该项目将通过分析韧性Bygdin（挪威）和Funzie（苏格兰）富含石英的变砾岩中的有限应变和岩石微结构来进行。将通过测量碎屑方向和所有三个椭球轴来确定露头尺度的有限应变，以约束碎屑形状。在晶粒尺度上，确定了两种有限应变的度量：（1）残余变质晶粒的晶粒形状和形状择优取向;（2）残余变质晶粒中心点的空间关系。电子背散射衍射将用于微观结构表征，包括测量晶粒形状、晶体学涡旋轴取向和晶体学择优取向。通过将有限应变的统计测量直接与岩石微结构组构相关联，Lusk博士旨在提高我们目前对有限应变和应变历史如何保存在显微构造记录中的理解，并为结构地质学家提供无需直接测量有限应变即可推断应变历史的方法。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的学术价值和更广泛的影响审查标准。