Thermodynamic Modeling of Silicate Systems

Abstract

Thermodynamic modeling of silicate systems is aimed at predicting the behavior of rock-forming systems by using the principles of chemical equilibrium in combination with databases of mineral, melt, and fluid properties. These predictions are most useful for interpreting natural phenomena that occur at high temperatures, such as those found in magmas and high-grade metamorphic rocks, and also in fluid-saturated systems near Earth's surface. This article defines the uses and limits of thermodynamic models in geological sciences, defines the Gibbs free energy, and applies the first and second laws of thermodynamics to explain the significance of finding the minimum in Gibbs free energy. Then it introduces the types of empirical data that are needed to calculate the relative stability of various mineral, melt, and fluid phases in real chemical systems. Because many geological materials are solutions, an introduction is provided to solution models, which account for the mixing of multiple chemical components in a single phase. Finally, the two most popular software packages for thermodynamic calculations—rhyoliteMELTS and Perple_X—are introduced and example calculations are shown.

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