Ultrasonic interferometry study of the effect of Al, Ti and Fe on the density, elasticity and the post-stishovite transition of eclogitic H2

Al-bearing stishovite and, later, post-stishovite becomes one of the chief hydrogen-bearing phases in subducted oceanic crust (eclogite) at lower mantle conditions. This study aims to establish the effect of the incorporation of defects typical of eclogitic systems (Al, Ti, Fe) on the high-P-T phase diagram, density, structure and elasticity of hydrated stishovite. In particular, we intend to determine, for the first time, the compressional (VP) and shear wave velocities (VS) that precisely locate the stishovite to post-stishovite phase transition in P and T space using model eclogitic Al-, Ti-, Fe- and H2O-bearing SiO2 compositions. This will be completed by application of state-of-the-art in situ x-ray diffraction combined with simultaneous ultrasonic interferometry and imaging at ID06-LVP. It will provide information essential to the interpretation of the seismic observables and contribute to more complete modelling of eclogitic bodies inside the deep Earth.