Sound Velocities of Basaltic Glass at Earth's Deep‐Mantle Pressures

Abstract The elasticity of compressed silicate melts is essential to decipher seismic properties and dynamic evolution of deep mantle magmas. Here, we report the compressional ( V P ) and shear ( V S ) wave velocities of a basaltic glass (Na 0.036 Ca 0.220 Mg 0.493 Fe 0.115 Al 0.307 Ti 0.012 K 0.002 Si 0.834 O 3 ) up to 63 GPa at 300 K using Brillouin and impulsive stimulated light scattering spectroscopies coupled with diamond anvil cells. The V P and V S data from 2.4 to 62.8 GPa exhibit convex upward trend, but the pressure‐dependent velocity slopes become flatter at around 38 ± 3 GPa. The V P and V S values increase from 6.86 ± 0.03 to 11.62 ± 0.20 km/s and from 3.70 ± 0.03 to 5.28 ± 0.07 km/s, respectively. These velocity behaviors are likely associated with the 4‐ to 6‐fold silicon coordination number increase. Comparison with literature data on MgSiO 3 glass, silicate, and pyrolitic glasses at high pressure suggests that the addition of Al 2 O 3 can enhance the V S and V P of the basaltic glass, whereas FeO and CaO substitutions decrease its velocities. Using our results as an analog for basaltic melts, which can incorporate significant amounts of Al 2 O 3 and FeO, the countercationic effects of Al 2 O 3 and FeO on velocities and density of the basaltic melt could make it less visible seismically at the mid‐lower mantle depths of ∼1,500 km.