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Date of Award

Spring 5-15-2017

Author's School

Graduate School of Arts and Sciences

Author's Department

Earth & Planetary Sciences

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Earth’s plate tectonics is the outermost manifestation of mantle convection. Understanding plate tectonics at the global scale requires understanding of regional processes near plate boundaries. Flow patterns in the upper mantle are generally inferred from observations of anisotropy of seismic wave speed. In plate interiors, where flow patterns are assumed to be simple, interpretation of seismic anisotropy is straightforward. However, near plate boundaries, where flow patterns are complex, different strategies for interpreting seismic anisotropy may be required. This dissertation examines, using experimental and numerical tools, the effects of complex flow patterns on the evolution of olivine crystallographic preferred orientation (CPO). Chapter 2 presents a set of experiments designed to simulate the effects of complex deformation histories on the evolution of olivine CPO. These experiments demonstrate that crystallographic re-alignment of olivine requires larger strains to reach steady state, compared to experiments with simpler deformation histories. In Chapter 3, we present numerical models that assess the effect of deformation history on olivine CPO evolution at high strains and with different deformation geometries. The models were benchmarked to the experiments described in Chapter 2, and from this analysis new model parameters are proposed that improve fit between experiments and numerical simulations. In Chapter 4, we assess the CPO predictions of numerical models under complex strain histories using data of CPO evolution from the literature as reference. The CPO is depicted and assessed using the textural strength, orientation, and symmetry. The CPO evolution from these texture elements indicates the similarities and differences between the two models and between the models and the reference CPOs. In Chapter 5, we examine whether a CPO of highly strained mantle is preserved during annealing. Through experiments under hydrostatic conditions we demonstrate a mechanism for which the CPO is modified with the microstructural recovery processes. It is concluded that seismic anisotropy in the upper mantle may be affected by the flow history, both under dynamic or static conditions.

Language

English (en)

Chair and Committee

Philip Skemer

Committee Members

Katharine M. Flores, William B. McKinnon, Viatcheslav S. Solomatov, Douglas A. Wiens,

Comments

Permanent URL: https://doi.org/10.7936/K70C4T65

Available for download on Friday, October 13, 2017

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