Comparison of representations of mineral properties at high pressures and temperatures: Application to MgO

Commonly used formulations for mineral properties as a function of pressure and temperature are compared with a suite of inversions applied to experimental data for MgO. A direct search approach in model space is used with the Neighbourhood Algorithm so that the same procedure is used for each formulation. The inversions for 9-dimensional parameter space, spanning effective isotropic elastic moduli and their derivatives as well as thermal properties, are applied for various data sets for each of the formulations with comparisons of level of fit to data. Equations of state are supplemented with a shear extension from Kennett (2020). For Periclase (MgO), the third-order Birch-Murnaghan constitutive equation and the Modified Tait EOS (Holland and Powell, 2011) that form the basis of current compilations of mineral properties perform well at moderate pressure, but become less effective for the higher pressures encountered in the lower mantle. For the mantle domain, the Vinet-Rydberg-Morse form Vinetet al. (1987) supplemented with shear gives a good rendering of the experimental properties of MgO. At core pressures formulations including infinite pressure constraints perform well, with a mild preference for the Keane (1954) approach with an explicit introduction of the pressure derivative of bulk modulus at infinite pressure.