EAR-PF: Strength, deformation, and recovery of phyllosilicates: How do phyllosilicates accommodate large amounts of shear strain?

Caroline Seyler博士被授予NSF EAR博士后奖学金，在明尼苏达大学进行研究，研究有助于适应构造板块之间滑动的层状硅酸盐的变形和恢复机制。层状硅酸盐是一组在成熟断层和剪切带中极其常见的矿物，这些成熟断层和剪切带定义了从主要走滑断层到俯冲带的板块边界。它们还在广泛的深度范围内保持稳定，以粘土的形式存在于地表附近，以云母的形式存在于地壳中，以滑石和蛇纹石的形式存在于地幔中。它们的晶体结构由原子片组成，通过弱的层间键合在一起，使这些原子片上的滑移成为一种容易变形的机制。这种变形方式随着应变的增加而增强颗粒，然而，在自然界中观察到的层状硅酸盐即使在高应变后也被推断为弱的。这个项目将通过创新的变形实验来确定层状硅酸盐如何在高应变下保持疲软。这些结果将把原子和颗粒尺度上的变形机制与断层和剪切带的动力学行为联系起来。除了研究，Seyler博士还将通过UMN的岩石变形研究机会(RORD)REU和机械工程系的Capstone课程指导学生。塞勒博士还将通过该大学开展持续的外展工作，并在明尼苏达州的部落学院组织外展活动。岩石圈的强度分布依赖于实验室得出的本构定律，但对于常见断层和剪切带材料的变形机制，如果没有严格约束的流变学模型，这些模型仍然不完善。将对黑云母进行高应变和高压变形实验，以确定层状硅酸盐的变形和恢复机制，并解释为什么层状硅酸盐变形可能比位错理论预测的更有效地适应大量应变。高应变实验将在明尼苏达大学(UMN)的气体介质帕特森装置中进行，高压形变-DIA实验将在阿贡国家实验室的高级光子源(APS)进行。变形样品的微观结构分析将利用光学和电子显微镜作为诊断工具，以确定活跃的变形和恢复机制。这些结果还将与富含层状硅酸盐的板片边界剪切带中记录的微观结构进行比较，以确保在实验室中再现自然变形的微观结构。提高我们对层状硅酸盐力学行为的理解将导致更好的强度估计和流变参数。这些参数是地球动力学模型以及地震周期破裂模型的基本输入，为地震危险性评估提供信息。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。

Dr. Caroline Seyler has been awarded an NSF EAR Postdoctoral Fellowship to conduct research at the University of Minnesota investigating the deformation and recovery mechanisms in phyllosilicates that help accommodate slip between tectonic plates. Phyllosilicates are a group of minerals that are incredibly common in the mature faults and shear zones that define plate boundaries from major strike-slip faults to subduction zones. They are also stable across a wide range of depths, persisting as clays near the surface, micas in the crust, and talc and serpentine in the mantle. Their crystal structure consists of sheets of atoms held together by weak interlayer bonding, making slip on these sheets an easy deformation mechanism. This style of deformation strengthens grains with increasing strain, however, phyllosilicates observed in nature are inferred to be weak, even after high strain. This project will determine how phyllosilicates remain weak at high strains through innovative deformation experiments. These results will connect the deformation mechanisms operating at the atomic- and grain-scale to the dynamic behavior of faults and shear zones. Beyond research, Dr. Seyler will mentor students through the Research Opportunities in Rock Deformation (RORD) REU at UMN and the Department of Mechanical Engineering’s capstone course. Dr. Seyler will also engage in ongoing outreach efforts through the university and organize outreach to students at the tribal colleges in Minnesota.Lithospheric strength profiles rely on lab-derived constitutive laws, but without well-constrained rheological models for the deformation mechanisms in common fault and shear zone materials, these models remain incomplete. High-strain and high-pressure deformation experiments will be performed on biotite to determine the deformation and recovery mechanisms operating in phyllosilicates and explain why phyllosilicate deformation may be more effective at accommodating large amounts of strain than predicted by dislocation theory. High-strain experiments will be conducted in torsion in the gas-medium Paterson apparatus at the University of Minnesota (UMN), and high-pressure Deformation-DIA experiments will be conducted at the Advanced Photon Source (APS) at Argonne National Laboratories. Microstructural analysis of deformed samples will utilize optical and electron microscopy as a diagnostic tool to identify active deformation and recovery mechanisms. These results will also be compared with the microstructures documented in phyllosilicate-rich plate boundary shear zones to ensure the reproduction of natural deformation microstructures in the lab. Improving our understanding of phyllosilicate mechanical behavior will result in better strength estimates and rheological parameters. These parameters are essential inputs for geodynamic models as well as for rupture modeling of the earthquake cycle that informs seismic hazard assessment.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.