A Revised Thermodynamic Melt Model for High-Titanium Magmatic Systems

Abstract

We present a thermodynamic model for silicate melt designed to calculate partial melting relations in high-Ti (>6 wt% TiO2), volatile-free mafic to ultramafic magmatic systems, such as those that generated lunar basalts. The melt model adopts the framework of that in Tomlinson & Holland (2021) [Journal of Petrology, 62, egab012], which represents melts in typical peridotitic systems. To adapt this melt model for high-Ti systems, we first incorporate an algebraic correction, and then re-calibrate the enthalpies of selected end-members. We demonstrate our melt model’s performance by comparing phase relations from four experimental datasets with calculations using our melt model, in conjunction with the models for solid phases from Tomlinson & Holland (2021). Calculations successfully reproduce the available experimental melt compositions, solidus, liquidus, and the loss of solid phases throughout the melting interval. In particular, the model accurately delineates the position of the ilmenite melt-out curve—an essential capability for effectively modelling high-Ti magma petrogenesis. We therefore recommend this model for applications to high-Ti systems involving Ti-rich phases at the solidus. This study enables thermodynamic modelling in high-Ti magmatic systems, expanding the scope of thermodynamic modelling for future petrological research.