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The effect of water content on the strength of quartzite

Abstract Details

2017, Master of Science, University of Akron, 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 and 1300°C, Pc = 1.5 GPa, and strain rate = 1.6*10-5/s. Then examining the the difference related to water concentration. The COH exponents are 1.21 ± 0.1 and 0.50 ± 0.1. These variables resulted in a modified flow equation: ε = A σ^n d^(-m) f(H2O)^r COH^z exp^(-Q/RT) When extrapolated to natural conditions these flow laws predict higher strengths than previous flow laws (Gleason and Tullis, 1995; Hirth et al., 2001; Fukuda et al., in prep) and with increasing water content quartzite weakens. In conclusion quartzite strength is dependent on water content for both dislocation and grain size sensitive creep.
Caleb Holyoke, III (Advisor)
LaVerne Friberg (Committee Member)
John Senko (Committee Member)
95 p.

Recommended Citations

Citations

  • Barbery, A. M. (2017). The effect of water content on the strength of quartzite [Master's thesis, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493211543960308

    APA Style (7th edition)

  • Barbery, Albert. The effect of water content on the strength of quartzite. 2017. University of Akron, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1493211543960308.

    MLA Style (8th edition)

  • Barbery, Albert. "The effect of water content on the strength of quartzite." Master's thesis, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493211543960308

    Chicago Manual of Style (17th edition)