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Characterizing Mineral Crystallographic Preferred Orientations (cpos) Along The Eastern North American Margin In The Southern Appalachians: Implications For Middle And Lower Crustal Seismic Anisotropy
Date of Award
Sarah J. Brownlee
The Southern Appalachians Mountains have a complex and distinctive tectonic history, characterized by structural deformation extending from late Precambrian throughout the Paleozoic. The Southern Appalachians, known as the Blue Ridge of western North Carolina and eastern Tennessee, is mainly composed of schists and gneisses, granitic and ultramafic intrusives, as well as a sedimentary portion. The main tool for understanding the composition and structure of the deeper parts of the crust that cannot be directly sampled by seismology. Seismic anisotropy is the directional dependence of seismic velocity, and it is an invaluable tool for interpreting the development of sub-surficial dynamics. Seismic anisotropy can have a number of controlling parameters including shear strain, mineral grain aspect ratios, and aligned cracks, and crystallographic preferred orientations. If these parameters are known, we can use anisotropy to constrain lower and middle crustal composition. In an effort to characterize the southern Appalachian region’s compositional and structural variability, we will present results from calculations of elastic tensors derived from electron backscatter diffraction (EBSD) data from a variety of metamorphic rocks with different mineral compositions. Here we will report analyses from 14 samples that are distributed into two transects across the Blue Ridge. Our goal is to address how deformational fabric controls the strength of mineral CPOs and thus seismic anisotropy.
Robles, Laura, "Characterizing Mineral Crystallographic Preferred Orientations (cpos) Along The Eastern North American Margin In The Southern Appalachians: Implications For Middle And Lower Crustal Seismic Anisotropy" (2017). Wayne State University Theses. 584.