MagMin_PT: An Excel-based mineral classification and geothermobarometry program for magmatic rocks

Abstract

ABSTRACTIgneous rock forming minerals carry valuable information from the deep earth that is not directly accessible at the surface. Each mineral represents the physico-chemical conditions at which various magmatic processes have occured over a wide range of depths from upper mantle to shallow crustal levels. These processes are cryptically inscribed in the whole-rock and mineral compositions (e.g. major elements, trace elements and isotopic ratios) and textures (equilibrium vs. disequilibrium features), together with intensive variables (e.g. pressure, P; temperature, T). Therefore, particular attention should be given to igneous minerals to understand better the processes that took place during their journey from the source through magma chambers and conduit systems to the Earth's surface.MagMin_PT is an Excel© based user-friendly program, designed to calculate mineral formulae and end-members, and to estimate pressure and temperature (e.g. geothermobarometry) from electron microprobe analytical data. The program operates using the most common igneous rock-forming minerals (olivine, pyroxene, amphibole, biotite, feldspar, magnetite, ilmenite, apatite and zircon), resulting in various classification diagrams and P–T diagrams. The program allows for whole-rock or glass composition to be entered together with the EPMA data to evalaute the equilibration status for most P–T calculation models. Fe2+ and Fe3+ estimation is routinely performed in MagMin_PT based on stoichiometric constraints, and to some extent using machine learning methods for different iron-bearing minerals. MagMin_PT is also able to carry calculations of fugacity, magmatic water content and saturation temperature. Graphical and numerical outputs produced by the program can be easily copied to other media for further processing.