Earth and Planetary Sciences ETDs

Publication Date

Summer 7-6-2022

Abstract

Aggregates with varying volume proportions of antigorite and olivine were deformed at mantle wedge conditions of high-pressure (P) (2.5-7.6 GPa), -temperature (T) (675 K), and strain rates from ~1.0*10-5 to ~1.0*10-4 s-1 using the deformation-DIA (D-DIA) to investigate deformation mechanisms and stress/strain partitioning. Macroscopic strain, lattice strain, and texture were measured in situ using synchrotron x-ray diffraction and radiography and were modeled for olivine using Elasto-Viscoplastic Self-Consistent (EVPSC) simulations. These modeled results are coupled with microstructure images and electron backscatter diffraction (EBSD) measurements results to determine stress and deformation mechanisms. Previous to this study, investigations have been limited to static microscopy studies of exhumed serpentinized peridotites or single-phase deformation experiments. Our results demonstrate the importance and feasibility of evaluating complicated geologic settings like the mantle wedge with more accurate multiphase systems for in situ observations. Antigorite, the softer mineral, is the strain-accommodating phase, and deforms like a single phase when mixed with olivine, the harder mineral. When the vol.% of olivine increases, most of the stress seems to be accepted into the strong framework, increasing aggregate stress. This observation could have implications for determining the maximum depth of decoupling, which is dependent on the strength contrast between the serpentinized interface layer above a subducting slab and the mantle wedge. Olivine’s deformation is primarily through activity of unidirectional kink systems with influence from pencil glide ang B-type slip. We see a change in dominant slip systems when the starting sample was polished so the initial aggregate texture was rotated, implying the orientation of antigorite and/or olivine effects transient deformation of these aggregates. We conclude the distribution of stress, strain, and anisotropy in the forearc mantle wedge will vary with the degree of serpentinization, which in turn varies with depth and other local subduction zone attributes such as temperature and rate of subduction.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Jin Zhang

Second Committee Member

Lowell Miyagi

Third Committee Member

Brandon Schmandt

Language

English

Keywords

mineral physics, high pressure, high temperature, stress, antigorite, olivine

Document Type

Thesis

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