Constraints on the P-V-T equation of state of MsSiO3 perovskite

Equation of state fits to experimental P,V,T data were examined by the inve rsion of synthetic data sets using the thermoelastic parameters of MgSiO3 p erovskite. Our results show that by extending the pressure and temperature range to 130 GPa and 2500 K, the Volume dependence of the Gruneisen paramet er, q (=partial derivative ln gamma/partial derivative lnV), could be resol ved to similar to 10% under the best circumstances. However, simulations al so showed strong correlation between the bulk modulus, K-T0, and its pressu re derivative, K'(T0), and q within the currently accepted uncertainty of e lastic parameters for MgSiO3 perovskite. n/e considered the effect of rando m error based on the reported uncertainty for different measurement techniq ues. Even though the laser heated diamond-anvil cell (LHDAC) technique has significantly larger temperature uncertainty, the ability to extend the pre ssure and temperature ranges allows for improved resolution of higher order thermodynamic parameters. However, systematic error from temperature inhom ogeneity in the LHDAC sample could result in overestimation of q. We also p erformed Birch-Murhanghan-Debye (BMD) equation of state (EOS) fits for curr ently available data sets. Consistent with the simulation results, combinin g recent LHDAC (Fiquet et al. 1998) and resistance heated diamond-anvil cel l (RHDAC) (Saxena et al. 1999) with lower P-T measurements (Ross and Hazen 1989; Wang et al. 1994; Utsumi et al. 1995; Funamori et al. 1996) we obtain ed q = 2.0(3) and gamma(0) = 1.42(4). The difference between q = 2.0(3) and the normally assumed value of q = 1 strongly affects calculated values for higher order thermoelastic parameters [e.g., alpha, (partial derivative K- T/partial derivative T)(P)] as well as first order parameters, such as dens ity and bulk modulus at lower mantle conditions. However, possible systemat ic error sources need to be further investigated and measurements at higher P-T conditions promise to yield better constraints on the thermoelastic pa rameters of MgSiO3 perovskite.