11:00 AM - 1:00 PM
[SCG49-P03] Shear Deformation and decomposition reactions of Lawsonite and Glaucophane at high pressures
Keywords:Intermediate-depth earthquakes, Shear Instability, Dehydration reaction
In this study, we conducted shear deformation experiments on lawsonite and glaucophane polycrystals at various pressure and temperature conditions of 1-6 GPa and 400-800℃ using a D-DIA apparatus at the BL04B1 beamline of SPring-8. Monochromatic X-ray (60keV) from synchrotron radiation was used for in-situ observation of stress-strain curves and reaction kinetics. MA6-6 type AE measurement system (Iwasato et al., 2020) were used to monitor AEs. Once the sample reached the target pressure and temperature, it was deformed isothermally for 30 minutes and then further deformed with increasing temperature (0.05℃/s) to cause decomposition reactions. The final shear strains reached to 52-140% with shear strain rates of 1.8-67 x10-5 s-1. After the reaction completed, the sample was quenched and slowly decompressed.
In the lawsonite runs, dehydration reaction occurred near the equilibrium boundary at 1.5 GPa and 470℃, and 2.5 GPa and 620℃. However, at the higher pressure of ~5.5 GPa, the dehydration reaction started at lower temperatures than the equilibrium boundary. In contrast to Okazaki and Hirth (2016), AE activities were not observed at around 1.5 GPa even when dehydration reaction occurred. Instead, we observed AE activities at 5-6 GPa before starting the reaction, and the activities became greater after the dehydration reaction completed at ~800℃. In this sample, slip displacements were observed both in radiography and SEM images, which may indicate shear instability although more detailed analysis is needed. Stress drop occurred especially during the isothermal deformation stage as observed in Shiraishi et al. (2022), but the related AE activities were not detected. Thus, we have not obtained a clear relationship between AE activities and the dehydration reaction and the stress drop in the lawsonite sample so far. We also conducted three runs using glaucophane polycrystal along the similar P-T-t paths as the lawsonite runs. Large shear strains were achieved during the decomposition reaction of glaucophane, however clear AE activities were not detected and the deformation seems to be homogeneous even in large shear strains.