Date of Award

May 2020

Degree Type

Thesis

Degree Name

Master of Science

Department

Geosciences

First Advisor

Dyanna M Czeck

Committee Members

Barry I Cameron, Lindsay J McHenry

Keywords

FTIR, Hydrolytic, Quartz, Weakening, Willard

Abstract

Evidence of water infiltration was examined in naturally deformed quartzite clasts from diamictite of the Mineral Fork Formation sampled from Antelope Island in the Great Salt Lake, Utah. The diamictite deformed via subsimple shear in the footwall of the Willard thrust fault and displays spatial variations in strain intensity. Evidence of water infiltration was investigated utilizing three complimentary techniques: standard petrographic microscopy to identify microstructures and interpret deformation mechanisms; scanning electron microscopy cathodoluminescence (SEM-CL) to create maps of healed microfractures and subgrain boundaries related to pathways of fluid infiltration; and synchrotron-source Fourier-transform infrared spectroscopy (FTIR) to create micron-scale water absorbance maps in quartz grains. Integrated data from these techniques allowed for a comprehensive analysis of water pathways within quartz grains. At low strain, quartz grains exhibited healed microfractures, linear fluid inclusion traces, and microfractures, evidencing mostly brittle deformation. At moderate strain, quartz grains had more extensive healed microfracture networks, as well as undulose extinction and subgrains showing increased water infiltration and crystal plastic deformation. At high strain, quartz grains exhibited extensive recrystallization, documenting intensified plastic deformation and resetting of microstructure with fewer microfractures present. FTIR data indicated two wavelength peaks related to infiltration of water within grains: liquid water at ~3400 cm-1 and OH groups contained within hydrous minerals such as mica at ~3600 cm-1. Water identified at the ~3400 cm-1 peak is preferentially located along healed microfractures, whereas OH associated with the ~3600 cm-1 peak is primarily found along grain boundaries. These data indicate that water infiltrated grains through microfractures during progressive deformation. Water then entered the main crystal lattice, presumably through diffusion or movement along dislocations that intersected the microfractures, leading to increased crystal plasticity through hydrolytic weakening and strain softening. Through these progressive deformation processes, the deformation style evolved from primarily brittle to primarily ductile within the footwall of the thrust fault. This finding has important implications in relation to the understanding of crustal rheology. This study was one of the first of its kind to document the distribution of water in naturally deformed quartz grains. The innovative sample preparation technique and analysis should prove helpful to future investigators.

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