New Thermodynamic Models and Calculated Phase Equilibria in NCFMAS for Basic and Ultrabasic Compositions through the Transition Zone into the Uppermost Lower Mantle

Abstract

Phase equilibria calculated with THERMOCALC for simplified mantle ultrabasic and basic bulk compositions in Na2O-CaO-FeO- MgO-Al2O3-SiO2 (NCFMAS) at depths down to the Transition Zone and uppermost lower mantle are presented here for the first time. This capitalizes on a new equation of state for solid phases and ties in deep mantle phases (wadsleyite, ringwoodite, akimotoite, garnet, MgSi-perovskite, CaSi-perovskite, cf phase, ferropericlase, nal, corundum and stishovite) to the thermodynamic dataset used at lower pressures in THERMOCALC. Activity-composition relationships for these complex phases are formulated that combine the end-member properties, allowing such phase equilibria to be ca..