3:45 PM - 4:00 PM
[SCG57-02] High-pressure ultrasonic measurement of annealed antigorite samples
High-pressure and high-temperature annealing experiments were conducted at 500, 600, and 650 °C under 3 GPa pressure condition. We found breakdown of antigorite and formation of olivine at 650 °C, while there are no visible change in the samples annealed at 500 and 600 °C. On the other hand, SEM-EDS analysis of antigorite in the 500 °C and 600 °C samples show smaller value of the total deficiency compared to the original natural sample. In addition, Raman spectroscopy analyses of these samples show new peaks around 1350 cm-1 and 1600 cm-1. The peak around 1600 cm-1 may be interpreted as due to H-O-H bending mode in water, which imply partial release of water from antigorite. High-pressure ultrasonic measurement of the antigorite samples annealed at 500 °C and 600 °C show ~4% lower Vp and Vs compared to those of natural antigorite sample, which may be due to partial release of water from antigorite. On the other hand, the Vp and Vs reported in Wang et al. (2019) is >10 % lower than those of this study and Bezacier et al. (2013), and therefore, the high-pressure and high-temperature annealing cannot explain the marked difference of Vp and Vs reported in previous studies. Although the cause of the discrepancy is still not clear, our observations show Vp and Vs of antigorite similar to those reported in Bezacier et al. (2013).