[S-IT17] Property and role of liquids inside terrestrial planets

[SIT17-P02] Elastic wave velocity of silicate glasses at high pressure

*Tatsuya Sakamaki¹ (1.Department of Earth Science, Tohoku University)

Keywords:Elastic wave velocity, Silicate glass, High pressure

I would like to review the elastic wave velocity measurements of silicate glasses under high pressures. Knowledge of the elastic properties of silicate melts/glasses enables us to infer the magma behavior at high pressure. Elastic wave velocities have been reported for several silicate glasses. Sakamaki et al. (2014) have investigated sound velocities of polymerized (jadeite and albite composition: NBO/T=0 at 1 atm) and depolymerized (diopside composition: NBO/T=2 at 1 atm) glasses at pressures up to 10 GPa using an ultrasonic technique and synchrotron radiation in a Paris-Edinburgh press, and demonstrated the dichotomous trend of elastic wave velocity of silicate glasses. The pressure dependence of velocities also clearly falls into two groups, one for polymerized (jadeite, albite, and silica) glasses, and the other for depolymerized (diopside and enstatite) glasses. These results indicate that the degree of polymerization fundamentally affects the behavior of silicate glasses under compression. For fully polymerized glasses, sound velocities first decrease with pressure before increasing above a certain pressure, similarly to silica glass. The velocity softening is much more pronounced for V_S than V_P. In contrast, for partially depolymerized glasses such as diopside and enstatite glasses, both V_P and V_S change only slightly with increasing pressure, a behavior different from that of polymerized glasses. The cation substitution of Fe and Al into the enstatite composition glass reduces the velocities at ambient pressure. Glasses with higher SiO₂ content have lower sound velocities, while the higher MgO content promotes increases in velocities. Basaltic glasses, which have the most complex composition among all glasses and an NBO/T around 0.7, have an intermediate pressure dependence: V_P and V_S decrease slightly with increasing pressure.