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Abstract
This project builds on previous studies of olivine deformation and fabric formation through two avenues: analysis of natural peridotite samples from the Talkeetna Arc, Alaska, and experimental deformation of olivine samples on a Griggs-type rig. The overarching goal was to study olivine crystallographic preferred orientation (CPO) formation in rocks of differing bulk lithologies - both natural peridotites and experimental olivine-serpentine aggregates - paying particular attention to the pressure/temperature transitions between fabric types. We analyzed six natural samples from Mehl et al., 2003: one each of dunite, harzburgite, and websterite from two field sites, Bernard Mountain and Sheep Mountain. In each sample, we identified the CPO of naturally deformed olivine grains using an Electron Backscatter Diffraction (EBSD) detector as well as the chemical makeup and mineralogy using an energy-dispersive detector (EDS). This work was conducted under the supervision of Jessica Warren at the University of Delaware. We aimed to discern differences in deformation fabric formation between rock types with widely varying ultramafic lithologies, as well as corroborate data and claims made by manual analysis in Mehl et al., 2003. The experimental portion of the project was carried out on a mechanically confined Griggs-type rig at Brown University. We ran one hydrostatic and one deformation experiment with the goal of refining the conditions necessary for E-type olivine fabric formation, which typically occurs in hydrated portions of the mantle, such as island arcs. Analysis of natural samples yielded insights into the relative insignificance of phases other than olivine on bulk anisotropy, as well as the role of modal percentage on increased misalignment with one CPO type. Results from our deformation experiment added to a growing body of evidence using CPO of hydrated olivine grains to address longstanding anomalies in seismic anisotropy and core principles of plate tectonic theory.