Acoustic velocites of (MgxFe1-x)2SiO4 wadsleyite

By comparing laboratory elasticity data with the seismic observations, constraints on the mineralogy, chemistry, and temperature of the mantle and core can
be obtained. Wadsleyite (beta-(Mg,Fe)2SiO4), the high-pressure polymorph of olivine (alpha-(Mg,Fe)2SiO4), is the dominant mineral from 410 km to 520 km depth in the Earth’s mantle transition zone. However, all existing measurements of its elastic properties are restricted to pressure and temperature conditions significantly below those of the mantle geotherm, with many made outside wadsleyite’s stability field. We propose to experimentally measure the acoustic velocities of wadsleyite with compositions between Mg2SiO4 and (Mg0.7Fe0.3)2SiO4 at relevant mantle PT conditions using ultrasonic interferometry in the multi-anvil press. When combined with synchrotron X-ray source, it’s possible to accurately determine the pressure, density and length of the sample, therefore allow precise sound wave velocities to be obtained.