TY - JOUR

T1 - Effects of melt composition on Fe3+/Fe2+ in silicate melts

T2 - a step to model ferric/ferrous ratio in multicomponent systems

AU - Borisov, Alexander

AU - Behrens, Harald

AU - Holtz, Francois

N1 - Funding information: The stay of AB in Hannover was funded by the German Science Foundation (DFG project Ho 1337/30-1). We thank Tim Müller and Eric Wolff for the electron microprobe assistance and Florian Pohl for the help in the determination of ferric/ferrous ratios in glasses. We are grateful to Alexey Ariskin and to an anonymous reviewer for their comments and suggestions which allowed us to improve the paper.

PY - 2015/2/15

Y1 - 2015/2/15

N2 - The effect of Al2O3, MgO and total iron on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts in the temperature range 1400–1550 °C at 1 atm total pressure. The experiments were done mostly in air and partially in pure CO2. It is demonstrated that an increase in Al2O3 concentration in a basaltic melt results in a moderate decrease of Fe3+/Fe2+ ratio. In contrast, the increase in Al2O3 in more silicic melts results in a much more pronounced decrease of Fe3+/Fe2+ ratio. The increase of MgO concentration in a basaltic melt results in a moderate increase of Fe3+/Fe2+ ratio but has a negligible effects in more silicic melts. The different behavior of Al2O3 and MgO in basaltic and more silicic melts indicates that at constant T–fO2 conditions, the effects of melt composition on ferric/ferrous ratio cannot be predicted accurately as a function of ΣdiXi where di are fixed empirical coefficients and Xi are mole fractions of the main oxide component in silicate melts. We suggest an alternative approach which accounts for the interaction of cations in complex silicate melts. Based on the data obtained in this study, an equation predicting the ferric/ferrous ratio of ultramafic to silicic melts at air conditions with changing SiO2, TiO2, Al2O3, total iron, MgO and P2O5 is proposed.

AB - The effect of Al2O3, MgO and total iron on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts in the temperature range 1400–1550 °C at 1 atm total pressure. The experiments were done mostly in air and partially in pure CO2. It is demonstrated that an increase in Al2O3 concentration in a basaltic melt results in a moderate decrease of Fe3+/Fe2+ ratio. In contrast, the increase in Al2O3 in more silicic melts results in a much more pronounced decrease of Fe3+/Fe2+ ratio. The increase of MgO concentration in a basaltic melt results in a moderate increase of Fe3+/Fe2+ ratio but has a negligible effects in more silicic melts. The different behavior of Al2O3 and MgO in basaltic and more silicic melts indicates that at constant T–fO2 conditions, the effects of melt composition on ferric/ferrous ratio cannot be predicted accurately as a function of ΣdiXi where di are fixed empirical coefficients and Xi are mole fractions of the main oxide component in silicate melts. We suggest an alternative approach which accounts for the interaction of cations in complex silicate melts. Based on the data obtained in this study, an equation predicting the ferric/ferrous ratio of ultramafic to silicic melts at air conditions with changing SiO2, TiO2, Al2O3, total iron, MgO and P2O5 is proposed.

KW - AlO

KW - Experiment

KW - Ferric/ferrous ratio

KW - MgO

KW - Silicate melt

UR - http://www.scopus.com/inward/record.url?scp=84924786941&partnerID=8YFLogxK

U2 - 10.1007/s00410-015-1119-6

DO - 10.1007/s00410-015-1119-6

M3 - Article

AN - SCOPUS:84924786941

VL - 169

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 2

ER -