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

Caroline Seyler博士获得了美国国家科学基金会EAR博士后奖学金，在明尼苏达大学进行研究，研究层状硅酸盐的变形和恢复机制，帮助适应构造板块之间的滑动。层状硅酸盐是一组在成熟断层和剪切带中非常常见的矿物，这些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。它们在很大的深度范围内都是稳定的，在地表附近以粘土的形式存在，在地壳中以云母的形式存在，在地幔中以滑石和蛇纹石的形式存在。它们的晶体结构是由层间弱键连接在一起的原子片组成的，这使得这些片上的滑动成为一种容易变形的机制。随着应变的增加，这种变形方式使晶粒增强，然而，在自然界中观察到的层状硅酸盐被推断为弱的，即使在高应变之后。该项目将通过创新的变形实验确定层状硅酸盐如何在高应变下保持弱。这些结果将把在原子和颗粒尺度上运行的变形机制与断层和剪切带的动态行为联系起来。除了研究之外，塞勒博士还将指导学生通过UMN的岩石变形研究机会（RORD） REU和机械工程系的顶点课程。塞勒博士还将通过大学参与正在进行的外展工作，并组织向明尼苏达州部落学院的学生进行外展。岩石圈强度剖面依赖于实验室推导的本构定律，但如果没有共同断层和剪切带材料变形机制的良好约束流变模型，这些模型仍然是不完整的。将对黑云母进行高应变和高压变形实验，以确定层状硅酸盐中的变形和恢复机制，并解释为什么层状硅酸盐的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）的气体介质帕特森设备上进行扭转，高压变形- dia实验将在阿贡国家实验室的先进光子源（APS）上进行。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来识别主动变形和恢复机制。这些结果还将与在富含层状硅酸盐的板块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和地震周期破裂模型的重要输入，从而为地震危险性评估提供信息。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。

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.