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<p>There are several models to account for the compositional effect of mafic silicate melts on ferric/ferrous ratio. However, felsic melts have been poorly investigated. In this study, both synthetic and natural silicic melts with a large compositional range (eighteen experimental series) were equilibrated at oxidizing (atmospheric conditions) and more reducing conditions in the temperature range 1401–1533&#xa0;°C at 1&#xa0;bar total pressure. The bulk glass composition was determined with electron probe microanalysis (EPMA) and the ferric/ferrous ratio in experimental glasses was analyzed using a wet-chemical technique. The experimental data were combined with previous data in order to formulate an empirical equation describing ferric/ferrous ratio in silicic melts as a function of oxygen fugacity, temperature and melt composition. The proposed equation predicts the log(X<sub>FeO1.5</sub>/X<sub>FeO</sub>) ratio of melts with a standard error of 0.077. The mean and standard deviation of the residuals for back-calculations of logfO<sub>2</sub> are 0.00 and 0.36 and are − 1 and 39&#xa0;°C for the temperature.</p>

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Ferric/ferrous ratio in silicate melts: a model calibrated for felsic compositions

  • 期刊论文

  • 发表日期：

    2025年11月22日

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  • Alexander Borisov,
  • Stepan Krasheninnikov,
  • Renat Almeev,
  • Francois Holtz

摘要

There are several models to account for the compositional effect of mafic silicate melts on ferric/ferrous ratio. However, felsic melts have been poorly investigated. In this study, both synthetic and natural silicic melts with a large compositional range (eighteen experimental series) were equilibrated at oxidizing (atmospheric conditions) and more reducing conditions in the temperature range 1401–1533 °C at 1 bar total pressure. The bulk glass composition was determined with electron probe microanalysis (EPMA) and the ferric/ferrous ratio in experimental glasses was analyzed using a wet-chemical technique. The experimental data were combined with previous data in order to formulate an empirical equation describing ferric/ferrous ratio in silicic melts as a function of oxygen fugacity, temperature and melt composition. The proposed equation predicts the log(XFeO1.5/XFeO) ratio of melts with a standard error of 0.077. The mean and standard deviation of the residuals for back-calculations of logfO2 are 0.00 and 0.36 and are − 1 and 39 °C for the temperature.