Date of Award

12-2023

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor

Christopher C. Gerbi

Second Committee Member

Scott E. Johnson

Third Committee Member

Alicia M. Cruz-Uribe

Additional Committee Members

Sandra Piazolo

Martin G. Yates

Abstract

Strain localization, a ubiquitous geological phenomenon, emerges when rock undergoes extensive weakening and accommodates disproportionate deformation. This phenomenon spans from brittle faulting to viscous flow, known as shear zones. Despite its prevalence, discussions on weakening primarily center on highly strained samples, rather than the initial deformation state. This research delves into the evolution of localization and rheology in intact rocks.

Heterogeneous mechanical properties within the lithosphere vary based on mineralogy, microstructure, and environmental conditions. Chapter 2 characterizes microscale structures termed "bridge zones." These zones, observed through optical and electron microscopy, exhibit distinctive morphologies. Comprising fine-grained aggregates, bridge zones link weak phases within shear zones and even less deformed rock margins. They result from grain size reduction, mass transfer, and reactions, ultimately weakening the rock and impacting its rheology.

Chapter 3 investigates stress field controls through finite element modeling. Spatial distribution profoundly influences stress magnitude and gradient. Stress behavior isn't linear with applied stress; weak material configuration and orientation significantly impacts stress concentration. Notably, stress concentration areas often connect weak domains, resembling bridge zones.

Chapter 4 focuses on shallow, low-temperature deformation in natural samples. These rocks, spanning a ductile shear zone gradient, exhibit extensive bridge zones formed associated with similar mechanical and chemical processes as in Chapter 2. Numerical modeling aligns high-stress amplification areas with bridge zones, corroborating their influence on rock strength reduction. We describe a conceptual model relating far-field loading through microscale change to bridge zone development.

Bridge zones present an avenue to comprehend the inception and progression of deformation localization, crucial for plate tectonics, metamorphism, landscape evolution, seismic activity, and other lithospheric processes. This research identifies microscale mechanisms driving weak domain development, advancing the understanding of rheological change. Ultimately, these findings lay the foundation for predictive algorithms pertaining to strength evolution across the lithosphere.

Download

Files over 10MB may be slow to open. For best results, right-click and select "save as..."

Share