10:45 AM - 11:00 AM
[SCG50-07] Steady-state recrystallization microstructures of wet quartz at 1.5 GPa confining pressure
Keywords:quartz, high-PT deformation experiment, dynamic recrystallization, dislocation creep
Quartz has been considered to control the rheology of the middle to upper crust. Field observations show that plastically deformed quartz rocks have distinctive dynamic recrystallization microstructures. High pressure (P) and temperature (T) experiments of quartz have been conducted to investigate the relationships between temperature, strain rate, and deformation and recrystallization microstructures of quartz. Extrapolation of the experimental results to natural deformation conditions have also been discussed.
To attain steady-state microstructures of quartz in the laboratory, Masuda and Fujimura (1981) conducted deformation experiments of fine-grained wet quartz aggregates (agate) at a confining pressure of 0.4 GPa, temperatures of 700-1000oC and strain rates of 10-4-10-6 sec-1 They reported that a quartz microstructure characterized by highly oblate grains with serrated grain boundaries, named Type S, was developed at low temperatures and high strain rates, while those characterized by equant and polygonal grains with straight grain boundaries, named Type P, was observed at high temperatures and low strain rates. However, further investigations on the pressure dependence of steady-state microstructures are needed to establish a theoretical basis for the microstructural changes and extrapolate the S-P boundary to natural deformation conditions. In this study, we conducted high-PT deformation experiments on agate at 1.5 GPa solid confining pressure, 800-900oC and strain rates of 10-4-10-5 sec-1.
The cylindrical specimens of agate with 8.0 mm in diameter and 8.0 mm in height were cored parallel to the original fibrous structure. Talc was used as the pressure medium. Pyrophyllite (with dehydration temperature of ca. 500oC) and talc (ca. 800oC) sleeves were set around the agate specimens at 800oC and 900oC runs, respectively, to maintain wet environments. The experiments were conducted with a Kumazawa-type solid-medium deformation apparatus at Kyoto University, which could measure the differential stress during experiments with a pair of load cells attached to the upper and lower piston (Shimizu and Michibayashi, 2022). The temperature at the center of the specimen was measured with a thermocouple. After the experiments, thin sections of deformed specimens were observed under an optical microscope with a polarized light.
The mechanical data obtained in the current experiments were consistent with the dislocation creep flow laws of quartz that calibrated semi-empirically by Fukuda and Shimizu (2017) using experimental data of diffusion coefficients. Type S microstructure was observed at 900oC and 10-5 sec-1, although this deformation condition was previously assigned as Type P at 0.4 GPa confining pressure by Masuda and Fujimura (1981). These results suggest that the S-P boundary shift to the higher temperature and lower strain rate side with increasing confining pressure.
Reference
Fukuda, J., and Shimizu, I. (2017) J. Geophys. Res. Solid Earth, 122, 5956-5971
Masuda, T. and Fujimura, A. (1981) Tectonophysics, 72, 105-128
Shimizu I. and Michibayashi, K. (2022) Minerals, 12, 329.
To attain steady-state microstructures of quartz in the laboratory, Masuda and Fujimura (1981) conducted deformation experiments of fine-grained wet quartz aggregates (agate) at a confining pressure of 0.4 GPa, temperatures of 700-1000oC and strain rates of 10-4-10-6 sec-1 They reported that a quartz microstructure characterized by highly oblate grains with serrated grain boundaries, named Type S, was developed at low temperatures and high strain rates, while those characterized by equant and polygonal grains with straight grain boundaries, named Type P, was observed at high temperatures and low strain rates. However, further investigations on the pressure dependence of steady-state microstructures are needed to establish a theoretical basis for the microstructural changes and extrapolate the S-P boundary to natural deformation conditions. In this study, we conducted high-PT deformation experiments on agate at 1.5 GPa solid confining pressure, 800-900oC and strain rates of 10-4-10-5 sec-1.
The cylindrical specimens of agate with 8.0 mm in diameter and 8.0 mm in height were cored parallel to the original fibrous structure. Talc was used as the pressure medium. Pyrophyllite (with dehydration temperature of ca. 500oC) and talc (ca. 800oC) sleeves were set around the agate specimens at 800oC and 900oC runs, respectively, to maintain wet environments. The experiments were conducted with a Kumazawa-type solid-medium deformation apparatus at Kyoto University, which could measure the differential stress during experiments with a pair of load cells attached to the upper and lower piston (Shimizu and Michibayashi, 2022). The temperature at the center of the specimen was measured with a thermocouple. After the experiments, thin sections of deformed specimens were observed under an optical microscope with a polarized light.
The mechanical data obtained in the current experiments were consistent with the dislocation creep flow laws of quartz that calibrated semi-empirically by Fukuda and Shimizu (2017) using experimental data of diffusion coefficients. Type S microstructure was observed at 900oC and 10-5 sec-1, although this deformation condition was previously assigned as Type P at 0.4 GPa confining pressure by Masuda and Fujimura (1981). These results suggest that the S-P boundary shift to the higher temperature and lower strain rate side with increasing confining pressure.
Reference
Fukuda, J., and Shimizu, I. (2017) J. Geophys. Res. Solid Earth, 122, 5956-5971
Masuda, T. and Fujimura, A. (1981) Tectonophysics, 72, 105-128
Shimizu I. and Michibayashi, K. (2022) Minerals, 12, 329.