Thermodynamic model for the calculation of multi pressure melting phase relation of anhydrous spinel lherzolite

Abstract:

Partial melting of mantle peridotite is an essential process for both material fractionation and cooling of the Earth.
Melt generation process in the natural system is an open system process in terms of both energy and mass, and evolves with time. Thermodynamic modeling is a powerful approach to describe such phase relation, mass balance and energy balance during melting.
This study presents a new thermodynamic model for the calculation of phase relations during the melting of anhydrous spinel lherzolite at pressures between 1–2.5 GPa. The model is based on the total energy minimization algorithm for calculating phase equilibria within multicomponent systems and the thermodynamic configuration of Ueki and Iwamori [2013]. The model is based on a SiO₂−Al₂O₃−FeO−Fe₃O₄−MgO−CaO system that includes silicate melt, olivine, clinopyroxene, orthopyroxene, and spinel as possible phases. The thermodynamic parameters for silicate melt end-member components are newly calibrated with a expanded-pressure calibration database. The temperatures and pressures used in this newly compiled calibration dataset are 1230−1600^◦C and 0.9–3 GPa, corresponding to the stability range of spinel lherzolite.
The modeling undertaken during this study reproduces the general features of experimentally determined spinel lherzolite melting phase relations at 1–2.5 GPa, including the solidus temperature, the melt composition, melting reaction, the degree of melting and the dF/dT curve.
This new thermodynamic modeling also reproduces phase relations of various bulk compositions from relatively fertile to deplete spinel lherzolite and can be used in the modeling of multi-pressure mantle melting within various natural settings.