PETROLOGICAL MODELING VS PETROLOGICAL MODELING: A COMPARATIVE STUDY OF TWO PHASE EQUILIBRIUM MODELING TOOLS
Here, we systematically compare the results of two such models that are routinely used for modeling phase equilibria in melt-bearing systems: rhyolite-MELTS and the metabasite set of Green et al. (2016) using the thermodynamic database ds62 (hereafter denoted as “MG16”). We selected a N-MORB composition and modeled closed system equilibrium phase relations as a function of temperature at 0.25 GPa and 1 GPa for N-MORB with 0.5 wt% and 4 wt% H2O. Our results show that phase relations exhibit some key differences that, in some instances, impact geological inferences. High-T liquids are generally similar in SiO2 contents but diverge at lower temperatures; in these cases, MG16 liquids are SiO2-depleted compared to those produced by rhyolite-MELTS. Liquids are also systematically and substantially more mafic in MG16, and alumina and the alkali concentrations are relatively different and show different trends as a function of temperature at constant pressure. Overall, liquid compositions show the greatest differences near the solidus. Differences in modal abundances of phases and liquid compositions influence liquid trace-element signatures, and these differences can affect geological interpretations. Finally, a comparison between melting experiments of basaltic bulk composition and both thermodynamic models show that rhyolite-MELTS better reproduces the higher temperature experiments, whereas MG16 better reproduces the lower temperature experiments.