Enthalpy Effects of Wet Albite Melting (2011)

Undergraduates: Will Frazier, none none none

Faculty Advisor: Allen Glazner
Department: Geology

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Temperature-composition (T-X) diagrams are widely employed in igneous petrology as a means to model magma crystallization for simple systems containing up to 4 components. The applications of such diagrams are limited in comparison with enthalpy-composition (H-X) diagrams, which allow for prediction of stable phase assemblages for mixing specified bulk compositions at given temperatures, and determination of the relative proportions of liquid and crystals at eutectic and peritectic points. A simple thermodynamic model for calculating the enthalpy of simple anhydrous magmatic systems at 1 bar pressure is presented and used to transform published T-X diagrams into H-X diagrams. As many natural magmatic systems are not anhydrous, it is important to understand how water affects the energetics of such systems. To investigate these enthalpy effects of water, the model is modified to account for increased pressures and the presence of water a one of the end member components. The binary system NaAlSi3O8-H2O is the studied to determine the differences between “dry” and “wet” melting of albite. Under water saturated conditions, as pressure increases, the wet melting temperature of albite is depressed relative to the dry melting temperature to a greater degree than the enthalpy required for wet melting relative to dry melting.