Date of Award

Summer 8-2025

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

First Committee Advisor

Scott Johnson

Second Committee Member

Christopher Gerbi

Third Committee Member

Senthil Vel

Abstract

This thesis investigates microstructural controls on thermal conductivity anisotropy in geological materials, with a focus on quartz-muscovite composites representative of common crustal rocks. While thermal conductivity is often simplified as a scalar value in geoscience applications, it constitutes a second-rank tensor with directional variation that significantly influences heat flow patterns in structurally complex geological environments. Traditional volumetric averaging approaches frequently fail to capture the full complexity of thermal anisotropy in rocks with strong structural fabrics or mineral alignment.

Using the Thermal Elastic Seismic Analysis (TESA) toolbox implementing Asymptotic Expansion Homogenization (AEH), this research systematically examines how variations in muscovite content and crystallographic orientation quantitatively affect bulk thermal anisotropy. Model microstructures with controlled mineralogy, grain geometry, and orientation distributions were generated to isolate the effects of specific microstructural attributes on directional heat flow.

Results demonstrate that thermal anisotropy in quartz-muscovite composites is governed by both mineral content and grain alignment, interacting in mathematically predictable ways best described by a third-order polynomial function (R² = 0.995). Thermal anisotropy reaches values approaching but remaining just below 140% in highly aligned, muscovite-rich compositions, while diminishing below 20% in poorly aligned, quartz-dominated assemblages. The AEH method consistently provides more physically realistic predictions of thermal anisotropy than traditional averaging schemes by explicitly incorporating microstructural geometry and interactions of the thermally anisotropic minerals rather than relying solely on volumetric proportions.

These findings establish quantitative relationships between microstructure and thermal anisotropy that can enhance modeling capabilities across multiple geoscience applications, including basin thermal modeling, geothermal energy systems, continental heat flow studies, and subduction zone thermal structure. By providing a robust framework for predicting directional heat transport from microstructural data, this research advances our ability to interpret and model thermal processes in complex geological settings.

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