Self-consistent thermodynamic parameters of pyrope and almandine at high-temperature and high-pressure conditions: Implication on the adiabatic temperature gradient

Thermodynamic parameters of minerals are valuable quantities in geophysics and petrology, and have been investigated extensively. However, the self-consistent thermodynamic parameters of minerals are limited. Also, of the thermodynamic parameters, the investigations on the variations of thermal expansions, heat capacities, and Gruneisen parameters with pressure are lacking. The goals of this work are to gain the self-consistent thermodynamic parameters and study the behavior of the thermal expansions, heat capacities, and Gruneisen parameters of two important pyralspite garnets, pyrope and almandine, depending on temperature and pressure simultaneously, which are obtained based on a series of classical thermodynamic equations and published experimental data. The results show that the pressure effects on the thermal expansions, heat capacities, and Gruneisen parameters increase along with the temperature for both pyrope and almandine. And the pressure effects on Gruneisen parameters decrease to a minimum at certain temperatures, then increase with temperature slightly. Also, the content of Fe may increase the pressure effects on those thermodynamic parameters of garnets. Moreover, the adiabatic temperature gradients and simplified models of geotherms obtained using the calculated thermodynamic parameters are presented, which indicate that the adiabatic temperature gradient would be moderately enlarged by Fe incorporation. Therefore, ignoring the influence of Fe will underestimate the temperature in the Earth's interior.

Automated summary

The study aimed to obtain and analyze the self-consistent thermodynamic parameters of two important pyrope and almandine garnets, and to examine their thermal properties with variations in temperature and pressure. The results showed that pressure effects on thermal expansions, heat capacities, and Gruneisen parameters increase with temperature and iron content may enhance the pressure effects on the thermodynamic parameters of garnets.