P‐V‐T equation of state of stishovite up to mid‐lower mantle conditions

Abstract

In situ P‐V‐T measurements of stishovite have been performed throughout its stability field from 17 to 54 GPa and from 300 to 1700 K, by using a sintered‐diamond multianvil apparatus and synchrotron radiations. The P‐V‐T equation of state of stishovite was precisely determined on the basis of the Mie‐Grüneisen‐Debye model using both Morse‐Rydberg (Vinet) and third‐order Burch‐Murnaghan equations for reference isotherms. The new equation of state of stishovite gives the thermoelastic properties such as density, adiabatic bulk modulus, thermal expansivity, and isobaric heat capacity without extrapolation to mid‐lower mantle conditions, and these properties at zero pressures are consistent with those of previous measurements. The present equation of state yields a lower density and larger adiabatic modulus at lower mantle conditions compared to those obtained by extrapolate on using a previous equation of state determined at upper mantle conditions. Our new equation of state and thermoelastic properties for stishovite at lower mantle conditions is important for quantitatively modeling the fate of subducted silica‐rich rocks such as MORB and pelagic sediments, and for interpreting seismological observations.