Master of Science, University of Akron, 2022, Geology

Stresses in the upper crust are redistributed to the lower crust after earthquakes. Stresses released by seismic slip induce crystal-plastic deformation in the mid to lower crust, which is composed of foliated, heterogeneous feldspathic rocks that deform and transfer stress back to the upper crust. Current models for the strength of the crust are primarily based on flow laws determined from experimentally deformed homogeneous quartzites or other monophase rocks. However, heterogeneities such as foliation orientations and foliation intensities, which are known to cause anisotropy of rock strength under brittle conditions, may cause viscous anisotropy at high temperatures and pressures where crystal-plastic mechanisms are dominant. To investigate if heterogeneities like foliation orientation and foliation intensity cause viscous anisotropy, I deformed weakly foliated Westerly Granite and strongly foliated Gneiss Minuti in different orientations that maximize (foliation at 45 degrees to the compression direction) and minimize (foliation parallel and foliation perpendicular to the compression direction) the shear stresses on the dispersed, elongate biotite grains in the quartz-feldspar framework, which should be the weakest and strongest orientations, respectively. These rocks were chosen because they both have similar low biotite contents (7%) and compositions: Westerly Granite is composed of 22 vol% quartz, 26 vol% K-feldspar, 45 vol% albite, and 7 vol% biotite and Gneiss Minuti is composed of 29 vol% quartz, 10 vol% K-feldspar, 53 vol% plagioclase and 7 vol% biotite. Experiments were performed using a Griggs apparatus at a temperature (T) of 800°C, confining pressure (Pc) of 1.5 GPa, and strain rate of 1.6 x 10-6/s. Westerly Granite and Gneiss Minuti reached peak stresses of 920 (+/- 50 MPa) and 670 (+/- 75 MPa), respectively, and viscous anisotropy was minor with anisotropy coefficients of 1.1x and 1.2x, respectively. Westerly Granite contained microstructures like (open full item for complete abstract)

Committee: Caleb Holyoke (Advisor); Molly Witter-Shelleman (Committee Member); John Peck (Committee Member) Subjects: Geology

Master of Science, University of Akron, 2024, Geology

Partial melting of hydrous phases such as amphibole, biotite, and muscovite occurs in orogens where distributed ductile thinning is causing exhumation of mid- to lower-crustal rocks. The partial melting of these hydrous phases contributes significantly to the physical and chemical evolution of the crust, as well as affecting the crust's strength. The Si-rich melts generated from partial melting reactions of mid- to lower-crustal assemblages migrate toward the upper crust leaving a more mafic restite. Previous laboratory experiments conducted on amphibole-, biotite-, or muscovite-bearing rocks performed at rapid strain rates (10-4/s to 10-5/s) result in brittle deformation due to high local pore pressures. These rapid experiments suggest this brittle behavior is the likely mechanism causing melt segregation in the crust. However, field evidence and slower strain rate experiments (10-6/s to 10-7/s) suggest that crystal plastic processes may be dominant during syndeformational partial melting. To investigate grain-scale melt segregation mechanisms in a common lower crustal protolith, I performed a suite of axial compression and general shear experiments on an amphibole-bearing source rock during syndeformational partial melting at T = 800-975°C, Pc = 1.5 GPa, at a strain rate (ε) of 1.6 x 10-6/s. I also performed axial compression experiments on a biotite-bearing gneiss and a muscovite-bearing quartzite at T = 950°C, Pc = 1.5 GPa, at a strain rate (ε) of 1.6 x 10-6/s to compare the differences in melt development depending on which hydrous phase is partially melting. The Nemo Amphibolite (d = 140 ± 85 μm) is composed of 62 vol% amphibole (Fe-hornblende), 27 vol% plagioclase (andesine; An30Ab69Or1), 8 vol% quartz, and 3 vol% titanite. The biotite-bearing gneiss (d = 80 +/- 40 microns) consists of quartz (43 vol%), plagioclase (andesine (An22Ab77Or1); 40 vol%), biotite (16 vol%), and ~1 vol% muscovite/Fe-Ti oxides. The muscovite-bearing quartzite is composed of 90 vol% q (open full item for complete abstract)

Committee: Caleb Holyoke (Advisor); Molly Witter-Shelleman (Committee Member); David Steer (Committee Member) Subjects: Earth; Experiments; Geochemistry; Geological; Geology; Mineralogy; Petrology; Plate Tectonics

Master of Science, University of Akron, 2023, Geology

Within the mid to lower continental crust distributed ductile thinning occurs, in orogens that form mountains like the Himalayas and Appalachia, due to a weak middle to lower crust that deforms laterally in response to loading of a thickened, cold upper crust. This thinning destabilizes large orogens and causes the exhumation of hot and weak rock from the mid to lower crust that begins to partially melt. This melting further weakens the rocks and may affect the deformation mechanisms operating in the crust. Melting has been seen to have impacts on the deformation mechanisms and resulting lattice preferred orientations (LPO) that form in olivine-basalt aggregates (Holtzman et al., 2003). To investigate the effects of partial melting on deformation mechanisms and LPO development in two common foliated felsic rocks, I performed general shear deformation experiments on a fine-grained quartzite and fine-grained gneiss at T = 800°C, 850°C, 900°C, 950°C, or 975°C, P = 1.5 GPa, and strain rate of 6*10-5/s. The quartzite (grain size ~30 microns) is composed of 90% quartz and 10% muscovite. The fine-grained gneiss (grain size ~50 microns) is composed of 43% quartz, 40% plagioclase, 16% biotite, and 1% accessory minerals. The foliation in the slices of each rock was oriented parallel to the shear plane between Al2O3 shear pistons with a cut made at 45° to the compression direction. Experiments were performed at a range of temperatures to change the melt fraction present in the rocks during deformation (Melt = ~0%, 0.25%, 0.5%, and 1%). The yield stress of Moine Thrust quartzite decreased as a function of increasing temperature from ~1000 to ~300 MPa. However, all the experiments with melt present (T equal to to greater than 850°C) significantly strain hardened after a shear strain (g) of 1. This hardening may be due to the presence of melt along grain boundaries which is absorbing water from the recrystallizing quartz grains which slows diffusive recovery in quartz. The Gne (open full item for complete abstract)

Committee: Caleb Holyoke (Advisor); John Peck (Committee Member); Molly Witter-Shelleman (Committee Member) Subjects: Earth; Environmental Geology; Experiments; Geochemistry; Geological; Geology; Geophysics; Geotechnology; High Temperature Physics; Mineralogy; Petrology

Master of Science, University of Akron, 2022, Geology

Current deformation models of shear zones in Earth's crust are generally based on the strength of monophase quartz or feldspar aggregates, but heterogeneities such as foliation and processes such as weak phase interconnection can cause a strong anisotropic response to stress. A fine-grained layer of Gneiss Minuti containing 56% biotite and muscovite, 27% quartz, 16% plagioclase, and 1% accessory minerals was deformed in axial compression to determine how the foliation and lineation orientation affect the viscous anisotropy of foliated rocks with interconnected micas deformed at conditions where all phases deform by crystal plastic mechanisms. The starting material was cored at six orientations relative to the foliation and lineation directions and deformed at T = 750°C, Pc = 1500 MPa, and strain rate = 1.6x10^-6 s^-1 using a Griggs-type piston-cylinder rock deformation apparatus. Cores collected within the plane that contains the lineation and is perpendicular to the foliation (XY plane) have similar peak strengths. However, cores from orientations outside of this plane are generally weaker than those from the XY plane, which was unexpected. In all cores, quartz and plagioclase display undulatory extinction and deformation lamellae, but their size and shape were not significantly changed. Cores with foliation parallel to the compression direction initially deformed by microkinking of the micas and crenulation folding at high strains. Cores with the foliation at 45° to the compression direction deformed by basal shear and kinking of micas within localized zones of interconnected micas. Kink formation in micas resulted in work hardening of the shear zones and redistribution of strain into new shear zones. Cores with the foliation perpendicular to the compression direction deformed by mica grain rotation forming shear zones of interconnected micas cross cutting the core at 45° to the foliation. Shear zones of interconnected micas that formed during deformation were on (open full item for complete abstract)

Committee: Caleb Holyoke III (Advisor); John Peck (Committee Member); David Steer (Committee Member) Subjects: Geology

Master of Science, University of Akron, 2017, Geology

The response of the Earth's continental crust to the release of stress following earthquakes in the seismic cycle is an essential process to understand. However, quartz and quartzite must still be studied to determine additional flow equation variables that describe the deformation of the crust. Previous studies have determined the temperature, strain rate, pressure, and grain size dependences on the strength of quartz. This study attempts to determine the water content dependence of the strength of quartzite. Water weakening of quartz has previously been attributed to water fugacity. However, when experiments are performed on relatively dry quartzite (COH ~100 – 1500 H/106 Si) the material is significantly stronger than predicted by dislocation creep or grain size sensitive flow laws (experiments with COH ~2500 – 4000 H/106 Si). This increased strength in dry synthetic quartzite is evidence for water concentration dependence. To determine the flow equation variables, including COH, experiments were performed at the conditions: T = 1200 – 1370°C, Pc = 1230 – 1500, and strain rate = 1.6*10-6 to 1.6*10-4/s. Low-temperature (T = 1200 – 1250°C) experiments display microstructures consistent with dislocation creep but occasionally samples will have microstructures related to grain size sensitive creep. High-temperature (1300 – 1370°C) experiments display grain size sensitive microstructures including recrystallization. The stress exponents observed from my data are 3.5 ± 0.40 for low-temperature experiments and 1.8 ± 0.25 for high-temperature experiments. Using the mechanical data from the pressure-stepping experiment we observed the water fugacity exponent for high-temperature experiments to be 1.4 ± 0.24. Temperature dependence data was used to determine the activation energy for both the low-temperature and high-temperature experiments (Q = 378 ± 60 kJ/mol and 267 ± 30 kJ/mol). The COH dependence and exponent was determined by normalizing data to constant T = 1200 an (open full item for complete abstract)

Committee: Caleb Holyoke III (Advisor); LaVerne Friberg (Committee Member); John Senko (Committee Member) Subjects: Experiments; Geology

Master of Science, University of Akron, 2017, Geology

A Griggs rig apparatus was used to perform a number of strain rate stepping and pressure stepping experiments of O+ oriented synthetic quartz crystals. These samples were annealed at 1 atm and 900°C for 24 hours to convert the gel type water inclusions to free water inclusions similar to those that are found in natural milky quartz. Strain rate stepping experiments were performed at temperatures from 1000°C to 750°C, and strain rates from 1.6 X 10-4 s-1 to 1.6 X 10-6s-1, while confining pressure was held constant at 1.5 GPa. These samples were observed to yield over a range of <10 to ~300 MPa in many cases, though under some of the conditions tested samples did not yield. Two pressure stepping experiments were performed, one at 800°C and one at 750°C, with a strain rate of 1.6 X 10-6s-1 and confining pressures between 0.6 GPa and 1.5 GPa. The sample strengths measured in the pressure stepping experiments were between ~30 MPa and ~60 MPa. Microstructures observed within deformed samples include undulatory extinction and deformation lamellae. The mechanical data from those experiments that were consistent with dislocation creep fit the flow law: ε′=0.00177*CH2O1.9*fH2O* ςdiff3.29* e(-268.6/(R*T)) Under natural conditions, this suggests plastic yielding of quartz occurs at ~9 km (~225°C) deep in the crust.

Committee: Caleb Holyoke III (Advisor); LaVerne Friberg (Committee Member); John Peck (Committee Member) Subjects: Geology; Geophysical; Geophysics

Master of Science (MS), Bowling Green State University, 2012, Geology

Characterization of texture using population statistics neglects spatial and temporal relations of the grains within the sample which provide valuable information about process and history. Despite the importance of space and time in textural analysis, little has been done to analyze the spatial variability of textures. In order to investigate the question of textural heterogeneity at a thin section scale in detail, the Standard Deviational Ellipse (ME) function from ArcGIS was used to create an extensive database from two different samples: an Elle simulation of crystal-plastic deformation and a weakly deformed quartz arenite photomicrograph. Both samples were deformed by the same increments of simple shear (γ = 0.00 - 0.87); the Elle sample by the deformation simulation and the quartz arenite by passively displacing grain boundaries according to the geometry of simple shear. Each sample was divided into nine cells and the textures in each was analyzed in the GIS using the Standard Deviational Ellipse as well as other parameters such as grain perimeter, area, ellipticity, and long axis orientation. In addition to using the Standard Deviational Ellipse to characterize textural variations, this tool was also evaluated for use as a finite strain marker. The study revealed non-systematic spatial and temporal variation in the change of the ME long axis orientations and ellipticity for the Elle simulation and systematic variation for the quartz arenite. The spatial variation in the texture categorized by the ME is partly due to the variations of grain distribution, shape, and grain position in the undeformed state and partly due to the nature of the deformation. The systematic variations in the quartz arenite are to be expected because of the way in which the sample was passively deformed. While analyzing the ME as a strain marker, it was found to correlate with the grain strain for quartz arenite, but varies significantly from the strains in the Elle simulation. Furthe (open full item for complete abstract)

Committee: Charles Onasch PhD (Advisor); John Farver PhD (Committee Member); Peter Gorsevski PhD (Committee Member) Subjects: Geographic Information Science; Geological; Geology