Effects of melt composition on Fe3+/Fe2+ in silicate melts: a step to model ferric/ferrous ratio in multicomponent systems

  • Alexander Borisov
  • Harald Behrens
  • Francois Holtz
Original Paper
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Accepted:

Abstract

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 Σd i X i where d i are fixed empirical coefficients and X i 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.

Keywords

Ferric/ferrous ratio Silicate melt Experiment Al2O3 MgO 
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Notes

Acknowledgments

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.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Alexander Borisov
    • 1
    • 2
  • Harald Behrens
    • 2
  • Francois Holtz
    • 2
  1. 1.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and GeochemistryRussian Academy of SciencesMoscowRussia
  2. 2.Institut für MineralogieLeibniz Universität HannoverHannoverGermany

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