VolFe: an open-source Python package for calculating melt-vapor equilibria including silicate melt, carbon, hydrogen, sulfur, and noble gases

Ery Catherine Hughes, Philippa Liggins, Penny Wieser, Edward M. Stolper

VolFe is an open-source flexible and adaptable thermodynamic framework in Python for calculating the equilibrium composition of melt and vapor. VolFe considers basaltic through rhyolitic melts including the volatiles carbon, hydrogen, sulfur, and the noble gases. VolFe models both reduced and oxidised systems due to the range of melt and vapor species included. Hence, VolFe is applicable to terrestrial (e.g., mid-ocean ridges to arcs) and extra-terrestrial (e.g., the Moon and Mars) systems. New parameterisations of “model-dependent variables” (e.g., volatile solubility functions, sulfide-saturation conditions, fugacity coefficients, etc.) can be added as new experimental studies come out, enhancing VolFe’s future applicability. The main calculations currently included in VolFe are the pressure of vapor-saturation based on the dissolved volatile content of melts; H₂O-CO₂ isobars, open- and closed-system degassing and regassing; an oxybarometer based on the melt sulfur content; and uncertainty propagation of the input melt compositions on calculation outputs. As an example, we apply VolFe to melt inclusion and submarine pillow glass data from the Marianas arc.