Sound Velocities of Superhydrous Phase B up to 21 GPa and 900 K

Abstract

AbstractSound velocities and density of Mg10Si3H4O18 superhydrous phase B (SuB) were investigated by synchrotron X‐rays combined with ultrasonic interferometry techniques in a multi‐anvil apparatus, up to 21 GPa and 900 K. Our data show that SuB has compressional (VP) and shear velocities (VS) lower than major anhydrous minerals but higher than majorite garnet. Our data combined with those of other mantle minerals allowed estimation of VP and VS of hydrated mantle regions at depths of the mantle transition zone and upper lower mantle. The local hydration of pyrolitic mantle with SuB as the main water host could explain low VP and low VS anomalies near cold subduction zones while it would be associated with low VP and high VS anomalies in hot mantle regions. The anomalies may be particularly strong in the ∼30 km beneath the 660 km discontinuity, due to the discrepancy of post‐spinel transition between hydrous and dry pyrolite lithologies.