SPINMELT-2.0: Simulation of Spinel-Melt Equilibrium in Basaltic Systems under Pressures up to 15 Kbar: I. Model Formulation, Calibration, and Tests

The paper presents results of testing currently used models proposed to describe Cr-spinel-melt equilibrium: models of the MELTS family by M.S. Ghiorso with colleagues, the SPINMELT program by A.A. Ariskin and G.S. Nikolaev, and the "MELT-CHROMITE spinel calculator" by A.A. Pustovetov and R.L. Roeder. The new calibration of the SPINMELT model presented in this publication enables calculating a six-component (Mg, Fe2+, Cr, Al, Fe3+, and Ti) composition of Cr-spinel and the T-fo(2) parameters of its stability on the liquidus of basaltic melts under pressures up to 15 kbar. The model is based on results of 392 runs from 43 experimental studies, including systems of normal alkalinity fo(2) <= QFM + 2. The experimental dataset (which was extended compared to that used for the previous calibration) allowed us not only to estimate the pressure effect, but also apply the model to aluminous and hydrous systems. Tests of the SPINMELT-2.0 model show that the errors of the calculated temperature of the spinel-melt equilibrium increase with pressure from 16 degrees C at 1 atm to 50 degrees C at 15 kbar. Experimental spinel compositions are reproduced by the model accurate to < 3 at % Al and Cr, and no worse 1 at % for the other cations.