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

Seyler, Caroline Elizabeth, Austin TX

Investigators

Abstract

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.