SPINMELT-2.0: Simulation of Spinel–Melt Equilibrium in Basaltic Systems under Pressures up to 15 Kbar: II. Description of the Program Package, the Topology of the Cr-spinel–Melt Model System, and Petrological Implications

Abstract

The paper represents an algorithmic implementation of the SPINMELT-2.0 model designed to simulate Cr-spinel–melt equilibrium, and provides a description of its petrologic options. The properties of the SPINMELT-2.0 model were studied by modeling the topology of the liquidus surface of spinel and its dependence on pressure, redox potential, and concentrations of major components (including Cr₂O₃ and H₂O) in the melt. Reference simulations were carried out for primitive MORB tholeiite. The spinel composition is demonstrated to depend on variously (and often oppositely) acting factors. Providing an accurate estimate of a parental magma composition, the SPINMELT-2.0 program allows one to evaluate a range of P–T–fO₂–H₂ O parameters responsible for the composition of an original magmatic spinel. The SPINMELT program makes it possible not only to effectively correlate available independent petrological estimates but also to consciously correct them, which is particularly important when the composition of the model melts should be estimated. This is illustrated by the application of the model to data on the composition of rocks and minerals of two young volcanoes in Kamchatka: Tolbachik and Gorely.