Thermodynamic Model for Energy-Constrained Open-System Evolution of Crustal Magma Bodies Undergoing Simultaneous Recharge, Assimilation and Crystallization: the Magma Chamber Simulator

Abstract

The Magma Chamber Simulator quantifies the impact of simultan-eous recharge, assimilation and crystallization through mass and enthalpy balance in a multicomponent^multiphase (meltþ solids fluid) composite system. As a rigorous thermodynamic model, the Magma Chamber Simulator computes phase equilibria and geochemical evolution self-consistently in resident magma, re-charge magma and wallrock, all of which are connected by specified thermodynamic boundaries, to model an evolving open-system magma body. In a simulation, magma cools from its liquidus tem-perature, and crystals fluid are incrementally fractionated to a sep-arate cumulate reservoir. Enthalpy from cooling, crystallization, and possible magma recharge heats wallrock from its initial subsolidus temperature. Assimilation begins when a critical wallrock melt volume fraction (0·04^0·12) in a range consistent with the rheology of partially molten rock systems is achieved.The mass of melt above