Elasticity of (Mg0.87Fe0.13)2SiO4 wadsleyite to 12 GPa and 1073 K

Elasticity of (Mg0.87Fe0.13)2SiO4 wadsleyite has been measured at simultaneous high pressure and high temperature to 12 GPa and 1073 K using ultrasonic interferometry in conjunction with synchrotron X-radiation. The elastic moduli and their pressure and temperature derivatives are precisely determined using pressure-standard-free third-order and fourth-order finite strain equations. Combined with previous thermoelastic data on olivine, the density, velocity and acoustic impedance contrasts between α- and β-(Mg0.9Fe0.1)2SiO4 at 410-km depth are calculated along a 1673 K adiabatic geotherm. Both the third- and fourth-order finite strain equation fitting results give estimation of ∼33–58% olivine content in the upper mantle to account for a seismic discontinuity of ∼5% velocity jumps, and 8.5% (P wave) and 11.1% (S wave) impedance jumps at 410 km depth.