Using equilibrium thermodynamics in the study of metasomatic alteration, illustrated by an application to serpentinites

Abstract

Metasomatic rocks, in which mineralogical change is driven by infiltration of an externally-derived fluid, are challenging for the application of equilibrium thermodynamics because fluid-driven changes in rock bulk composition can be faster than diffusive within-grain re-equilibration. Nevertheless, careful definition of systems in terms of appropriate length scales, an informed choice regarding the controlling variables, and detailed petrological analysis can provide useful results. Thermodynamic calculations using methods that solve for equilibrium between a set of independent end-member reactions produce valid results regardless of the identity of the controlling variables but determinati..