13:45 〜 15:15
[SMP27-P06] 高温高圧下におけるナトリウムアルミノケイ酸塩ガラス・メルトの弾性波速度測定
キーワード：弾性波速度、ケイ酸塩メルト、超音波法、重合度
The elastic wave velocity of magma provides us with fundamental information to constrain the internal structure of the Earth. Silicate glass has been studied as an analogue of magma, and its degree of polymerization (the ratio of non-bridging oxygen to tetrahedral cation, NBO/T) at ambient pressure has been revealed to affect the pressure dependence of the elastic wave velocity. The elastic wave velocity of depolymerized glasses (NBO/T > 1) tends to increase monotonically with pressure (e.g., refs. 1). Whereas the elastic wave velocity of polymerized glasses (NBO/T < 1) shows a minimum at around 3–6 GPa (e.g., refs. 1, 2).
At ambient pressure, the elastic wave velocity of silicate melts has been studied (e.g., refs. 3). However, there are few reports on high-pressure elastic wave velocity of silicate melts due to the experimental difficulty, and there is no velocity data of highly polymerized melts (NBO/T < 1). In this study, we have conducted elastic wave velocity measurements of the sodium aluminosilicate glass and melt with composition Na3AlSi3O9 (NAS, NBO/T = 0.5) up to 7.3 GPa at ambient temperature (for glass), and up to 4.3 GPa and 2100 K (for melt). These measurements were performed using the ultrasonic technique combined with synchrotron X-ray radiography and diffraction experiments in a multi-anvil apparatus for high-pressure generation at BL04B1, SPring-8. The compressional wave velocity (VP) of the NAS glass was almost constant up to 3–4 GPa and then increased with pressure, while the shear wave velocity (VS) exhibited a negative pressure dependence up to 4 GPa. In the case of the NAS melt, the VP showed a weak negative pressure dependence up to about 3 GPa. We will compare our results with the velocity of depolymerized melts (refs. 4, 5) and discuss the effect of the composition (especially the degree of polymerization) on the elastic properties of silicate melts at high pressure.
References:
[1] Sakamaki et al. Earth Planet. Sci. Lett., 391, 288–295 (2014).
[2] Zha et al. Phys.Rev. B, 50, 13105–13112 (1994).
[3] Rivers & Carmichael. J. Geophys. Res., Solid Earth 92, 9247–9270 (1987).
[4] Xu et al. J. Geophys. Res., 123, 8676–8690 (2018).
[5] Xu et al. Earth Planet. Sci. Lett., 577, 117250 (2022).
At ambient pressure, the elastic wave velocity of silicate melts has been studied (e.g., refs. 3). However, there are few reports on high-pressure elastic wave velocity of silicate melts due to the experimental difficulty, and there is no velocity data of highly polymerized melts (NBO/T < 1). In this study, we have conducted elastic wave velocity measurements of the sodium aluminosilicate glass and melt with composition Na3AlSi3O9 (NAS, NBO/T = 0.5) up to 7.3 GPa at ambient temperature (for glass), and up to 4.3 GPa and 2100 K (for melt). These measurements were performed using the ultrasonic technique combined with synchrotron X-ray radiography and diffraction experiments in a multi-anvil apparatus for high-pressure generation at BL04B1, SPring-8. The compressional wave velocity (VP) of the NAS glass was almost constant up to 3–4 GPa and then increased with pressure, while the shear wave velocity (VS) exhibited a negative pressure dependence up to 4 GPa. In the case of the NAS melt, the VP showed a weak negative pressure dependence up to about 3 GPa. We will compare our results with the velocity of depolymerized melts (refs. 4, 5) and discuss the effect of the composition (especially the degree of polymerization) on the elastic properties of silicate melts at high pressure.
References:
[1] Sakamaki et al. Earth Planet. Sci. Lett., 391, 288–295 (2014).
[2] Zha et al. Phys.Rev. B, 50, 13105–13112 (1994).
[3] Rivers & Carmichael. J. Geophys. Res., Solid Earth 92, 9247–9270 (1987).
[4] Xu et al. J. Geophys. Res., 123, 8676–8690 (2018).
[5] Xu et al. Earth Planet. Sci. Lett., 577, 117250 (2022).