TY - JOUR

T1 - The effect of titanium and phosphorus on ferric/ferrous ratio in silicate melts

T2 - An experimental study

AU - Borisov, Alexander

AU - Behrens, Harald

AU - Holtz, Francois

N1 - Funding Information: Acknowledgments The stay of AB in Hannover was funded by the German Science Foundation (DFG, projects Ho 1337/24-1, Ho 1337/27-1 and Ho 1337/30-1). We thank Eric Wolff for the electron microprobe assistance and Anika Husen and Franziska Adams for the help in the determination of ferric/ferrous ratios in glasses. We are grateful to editor Jochen Hoefs and to the anonymous reviewers for Copyright: Copyright 2013 Elsevier B.V., All rights reserved.

PY - 2013/10/6

Y1 - 2013/10/6

N2 - The effect of TiO2 and P2O5 on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts at air conditions in the temperature range 1,400-1,550 °C at 1-atm total pressure. The base composition of the anorthite-diopside eutectic composition was modified with 10 wt % Fe2O3 and variable amounts of TiO2 (up to 30 wt %) or P2O5 (up to 20 wt %). Some compositions also contained higher SiO2 concentrations to compare the role of SiO2, TiO2, and P2O5 on the Fe3+/Fe2+ ratio. The ferric/ferrous ratio in experimental glasses was analyzed using a wet chemical technique with colorimetric detection of ferrous iron. It is shown that at constant temperature, an increase in SiO2, TiO2, and P2O5 content results in a decrease in the ferric/ferrous ratio. The effects of TiO2 and SiO2 on the Fe3+/Fe2+ ratio was found to be almost identical. In contrast, adding P2O5 was found to decrease ferric/ferrous ratio much more effectively than adding silica. The results were compared with the predictions from the published empirical equations forecasting Fe3+/Fe2+ ratio. It was demonstrated that the effects of TiO2 are minor but that the effects of P2O5 should be included in models to better describe ferric/ferrous ratio in phosphorus-bearing silicate melts. Based on our observations, the determination of the prevailing fO2 in magmas from the Fe3+/Fe2+ ratio in natural glasses using empirical equations published so far is discussed critically.

AB - The effect of TiO2 and P2O5 on the ferric/ferrous ratio in silicate melts was investigated in model silicate melts at air conditions in the temperature range 1,400-1,550 °C at 1-atm total pressure. The base composition of the anorthite-diopside eutectic composition was modified with 10 wt % Fe2O3 and variable amounts of TiO2 (up to 30 wt %) or P2O5 (up to 20 wt %). Some compositions also contained higher SiO2 concentrations to compare the role of SiO2, TiO2, and P2O5 on the Fe3+/Fe2+ ratio. The ferric/ferrous ratio in experimental glasses was analyzed using a wet chemical technique with colorimetric detection of ferrous iron. It is shown that at constant temperature, an increase in SiO2, TiO2, and P2O5 content results in a decrease in the ferric/ferrous ratio. The effects of TiO2 and SiO2 on the Fe3+/Fe2+ ratio was found to be almost identical. In contrast, adding P2O5 was found to decrease ferric/ferrous ratio much more effectively than adding silica. The results were compared with the predictions from the published empirical equations forecasting Fe3+/Fe2+ ratio. It was demonstrated that the effects of TiO2 are minor but that the effects of P2O5 should be included in models to better describe ferric/ferrous ratio in phosphorus-bearing silicate melts. Based on our observations, the determination of the prevailing fO2 in magmas from the Fe3+/Fe2+ ratio in natural glasses using empirical equations published so far is discussed critically.

KW - Experiment

KW - Ferric/ferrous ratio

KW - PO

KW - Silicate melt

KW - TiO

UR - http://www.scopus.com/inward/record.url?scp=84887575972&partnerID=8YFLogxK

U2 - 10.1007/s00410-013-0943-9

DO - 10.1007/s00410-013-0943-9

M3 - Article

AN - SCOPUS:84887575972

VL - 166

SP - 1577

EP - 1591

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 6

ER -