The Thermodynamics of Diffusion Controlled Metamorphic Processes
Many metamorphic processes involve diffusive exchange of material between interacting mineral assemblages, and in most such processes, diffusion appears to be the rate-determining step. The overall stoichiometry of diffusion-controlled processes involving p phases containing c components depends upon c — 1 ratios of diffusive fluxes. In the steady state, the flux ratios are constrained by p — 1 restrictions on the potential gradients driving the diffusion, and by c — p restrictions on the fluxes, which can be derived either from the fact that steady-state diffusion corresponds to a minimum rate of irreversible entropy production, or from the stoichiometry of the participating phases. The c — 1 flux ratios are therefore entirely determined, and can be calculated if the composition of the minerals and the ratios of phenomenological coefficients are known. Determination of the applicable diffusion coefficients is a vitally important problem.
KeywordsMineral Assemblage Potential Gradient Flux Ratio Invariant Point Boundary Network
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