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Access Type

WSU Access

Date of Award

January 2017

Degree Type

Thesis

Degree Name

M.S.

Department

Geology

First Advisor

Sarah Brownlee

Abstract

Our knowledge of composition and structure in middle and lower crustal rocks is limited due to restricted accessibility, and thus comes mainly from studies of seismic velocities. But isotropic seismic velocities are not sufficient to distinguish between the many possible rock types in the middle and lower crust. Seismic anisotropy is the directional dependence of seismic velocity, and may provide further constraints on mineralogy and rock type. This study is focused on characterizing the seismic anisotropy of rocks from the Chester dome in southeast Vermont. We have simplified the Chester dome rock types into four groups based on rock type and composition: gneisses (felsic (7) and mafic (4)), and schists (felsic (5) and mafic (5)). We calculated elastic tensors from electron backscatter diffraction (EBSD) measurements of mineral crystallographic preferred orientations. Results show that gneiss Vp anisotropy (AVp) ranges 4.0-14.8% and schist AVp ranges from 9.2-25.1%. On average, the mafic gneiss samples are slightly more anisotropic than the felsic gneiss but the felsic schist samples are more anisotropic than the mafic schist. Both mineralogy and rock type are important for controlling elastic properties, and thus seismic anisotropy has the potential for distinguishing between different rock types, and similar rock types with different mineralogy.

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