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