Journal article

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

Tim JB Holland, Neil FC Hudson, Roger Powell, Ben Harte



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..

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Awarded by Australian Research Council

Funding Acknowledgements

The authors wish to thank Paul Asimov for his perceptive and constructive comments, which greatly improved the paper. Responsibility for any remaining errors rests entirely with us. B.H., T.J.B.H. and R.P. wish to to pay tribute to Neil Hudson, who died in November 2012, shortly after the initial submission of this paper. Neil was responsible for much of the initial groundwork that led to the development of the present paper. R.P. acknowledges support of Australian Research Council DP0987731.