Abstract
On Earth, plate motion is accommodated by localized zones of weakness, comprised of brittle faults near the surface and ductile shear zones at depth. Interactions between microstructure and deformation mechanisms control bulk rock strength. The intermixing of mineral phases and a transition to grain size sensitive creep is thought to be an essential mechanism for creating long lasting weakness in the lithosphere. Chapter Two explores how microstructures evolve in experimentally deformed Maryland diabase. Microstructure evolves significantly with strain from an igneous texture characterized by large grains and large domains to a fine grained, narrowly banded microstructure. This reduction in grain size results in a partial transition to grain size sensitive creep. No microstructure measured reaches steady state by γ = 9.5. The results of this study indicate that steady state microstructure and viscosity may require millions of years to achieve. Chapter Three studies how interconnected mica layers disaggregate with strain. The interconnectivity of mica layers was measured with a new measure called spine length. With strain, interconnected layers disaggregate into a very fine grained well-mixed microstructure. Mica grain size is observed to reduce through brittle mechanisms, despite plastic deformation in fluorite or calcite. Similar microstructural evolution is inferred to have occurred in natural micaceous mylonites. Chapter Four uses synthetic orientation data to measure uncertainties in CPO measurements and seismic anisotropy. Thresholds for minimum sample size required for accurate data and the sample size required for precision are established. The results of this study are applied to natural and experimental results to constrain numerical CPO models. Chapter Five outlines planned work to characterize spatial heterogeneities and improve CPO measurements. It also details future directions for the study of microstructures in crustal shear zones. Taken as a whole, this dissertation details methods for detailed microstructural analysis and applies it to interpretations of lithosphere deformation.
Committee Chair
Philip Skemer
Committee Members
Bradley Jolliff; Joe Guinness; Michael Krawcynski; Paul Byrne
Degree
Doctor of Philosophy (PhD)
Author's Department
Earth & Planetary Sciences
Document Type
Dissertation
Date of Award
4-24-2026
Language
English (en)
DOI
https://doi.org/10.7936/q28k-hx06
Author's ORCID
https://orcid.org/0009-0009-2374-441X
Recommended Citation
Billings, Katherine Josephine, "Quantitative Microstructural Analysis with Applications to Planetary Lithosphere Deformation" (2026). Arts & Sciences Graduate Student Theses and Dissertations. 3747.
The definitive version is available at https://doi.org/10.7936/q28k-hx06