Self-Consistent Thermodynamic Parameters of Diopside at High Temperatures and High Pressures: Implications for the Adiabatic Geotherm of an Eclogitic Upper Mantle

Abstract

Using an iterative numerical approach, we have obtained the self-consistent thermal expansion, heat capacity, and Grüneisen parameters of diopside (MgCaSi2O6) over wide pressure and temperature ranges based on experimental data from the literature. Our results agree well with the published experimental and theoretical data. The determined thermodynamic parameters exhibit nonlinear dependences with increasing pressure. Compared with other minerals in the upper mantle, we found that the adiabatic temperature gradient obtained using the thermodynamic data of diopside is larger than that of garnet while lower than that of olivine, when ignoring the Fe incorporation. Combining our results with thermodynamic parameters of garnet obtained in previous studies, we have estimated the adiabatic temperature gradient and geotherm of an eclogitic upper mantle in a depth range of 200–450 km. The results show that the estimated adiabatic temperature gradient of the eclogite model is ~16% and ~3% lower than that of the pyrolite model at a depth of 200 km and 410 km, respectively. However, the high mantle potential temperature of the eclogite model leads to a similar temperature as the pyrolite model in a depth range of 200–410 km.

Thermodynamic Properties of MgAl2O4 Spinel at High Temperatures and High Pressures

“…The method used in this study is summarized in our recent studies [39][40][41], and the fundamental procedure is described below. The uncertainties of the derived parameters at different temperature (T) and pressure (P) conditions are estimated using the Taylor series expansion based on the experimental measuring error, as well as the uncertainties of the fitting coefficients.…”

“…The advantage of this method is that all the obtained values are determined completely based on the experimental data, without using any empirical parameters. The feasibility of this method later has been proved on melts [37,38] and minerals [39][40][41]. Thus, the thermodynamic properties at HT-HPs can be determined totally based on the experimental data of minerals conveniently.…”