Details
| Original language | English |
|---|---|
| Pages (from-to) | 55-67 |
| Number of pages | 13 |
| Journal | Chemical geology |
| Volume | 189 |
| Issue number | 1-2 |
| Early online date | 24 May 2002 |
| Publication status | Published - 16 Sept 2002 |
Abstract
The dependence of the ferric-ferrous ratio in silicate melts on oxygen fugacity was studied in the system spectroscopy. Experiments were performed under water-saturated conditions at 500 MPa, and at temperatures of 850 and 950 °C, covering a range typical for magmatic processes. The oxygen fugacity was varied in the fO2 range from Cu-Cu2O buffer to slightly more reducing conditions than the wüstite-magnetite buffer. The iron redox ratio was determined by analyzing the Mössbauer parameter distribution that was modeled based on experimental spectra collected at room temperature on the quenched samples. The obtained iron redox ratios show a linear dependence on oxygen fugacity on a logarithmic scale for both temperatures. The iron redox ratio (Fe3+/Fe2+) decreases with temperature for a given oxygen fugacity. The spectroscopic data at 850 °C are in good agreement with Fe3+/Fe2+ ratios derived from element partitioning but show considerable deviations from iron redox ratios predicted by the empirical equation given by Kress and Carmichael [Contrib. Mineral. Petrol. 108 (1991) 82]. This indicates that an extrapolation of this equation to such low temperatures may have large errors. A sample quenched slowly through the temperature range near and below Tg shows considerable differences in the obtained Mössbauer spectra compared to more rapidly cooled samples, indicating ordering of the iron environment at least in the mesoscopic range. The oxidation state, however, does not differ when compared to the more rapidly quenched melts.
Keywords
- Iron oxidation state, Mössbauer spectroscopy, Oxygen fugacity, Silicate melt
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
Cite this
- Standard
- Harvard
- Apa
- Vancouver
- BibTeX
- RIS
In: Chemical geology, Vol. 189, No. 1-2, 16.09.2002, p. 55-67.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The oxidation state of iron in silicic melt at 500 MPa water pressure
AU - Wilke, Max
AU - Behrens, Harald
AU - Burkhard, Dorothee J.M.
AU - Rossano, Stéphanie
N1 - Funding Information: Technical assistance during the sample synthesis by W. Hurkuck and B. Aichinger and sample preparation by O. Diedrich are highly appreciated. We thank J. Klein, formerly at the Universität Marburg, for help in spectrum acquisition. We would like to thank F. Farges for enthusiastic and fruitful discussions. Helpful comments by M.D. Dyar and H.S.C O'Neill are gratefully acknowledged. This study was funded by the Deutsche Forschungsgemeinschaft, Schwerpunktprogramm Elementverteilung (Project Be/1720/4). [RR]
PY - 2002/9/16
Y1 - 2002/9/16
N2 - The dependence of the ferric-ferrous ratio in silicate melts on oxygen fugacity was studied in the system spectroscopy. Experiments were performed under water-saturated conditions at 500 MPa, and at temperatures of 850 and 950 °C, covering a range typical for magmatic processes. The oxygen fugacity was varied in the fO2 range from Cu-Cu2O buffer to slightly more reducing conditions than the wüstite-magnetite buffer. The iron redox ratio was determined by analyzing the Mössbauer parameter distribution that was modeled based on experimental spectra collected at room temperature on the quenched samples. The obtained iron redox ratios show a linear dependence on oxygen fugacity on a logarithmic scale for both temperatures. The iron redox ratio (Fe3+/Fe2+) decreases with temperature for a given oxygen fugacity. The spectroscopic data at 850 °C are in good agreement with Fe3+/Fe2+ ratios derived from element partitioning but show considerable deviations from iron redox ratios predicted by the empirical equation given by Kress and Carmichael [Contrib. Mineral. Petrol. 108 (1991) 82]. This indicates that an extrapolation of this equation to such low temperatures may have large errors. A sample quenched slowly through the temperature range near and below Tg shows considerable differences in the obtained Mössbauer spectra compared to more rapidly cooled samples, indicating ordering of the iron environment at least in the mesoscopic range. The oxidation state, however, does not differ when compared to the more rapidly quenched melts.
AB - The dependence of the ferric-ferrous ratio in silicate melts on oxygen fugacity was studied in the system spectroscopy. Experiments were performed under water-saturated conditions at 500 MPa, and at temperatures of 850 and 950 °C, covering a range typical for magmatic processes. The oxygen fugacity was varied in the fO2 range from Cu-Cu2O buffer to slightly more reducing conditions than the wüstite-magnetite buffer. The iron redox ratio was determined by analyzing the Mössbauer parameter distribution that was modeled based on experimental spectra collected at room temperature on the quenched samples. The obtained iron redox ratios show a linear dependence on oxygen fugacity on a logarithmic scale for both temperatures. The iron redox ratio (Fe3+/Fe2+) decreases with temperature for a given oxygen fugacity. The spectroscopic data at 850 °C are in good agreement with Fe3+/Fe2+ ratios derived from element partitioning but show considerable deviations from iron redox ratios predicted by the empirical equation given by Kress and Carmichael [Contrib. Mineral. Petrol. 108 (1991) 82]. This indicates that an extrapolation of this equation to such low temperatures may have large errors. A sample quenched slowly through the temperature range near and below Tg shows considerable differences in the obtained Mössbauer spectra compared to more rapidly cooled samples, indicating ordering of the iron environment at least in the mesoscopic range. The oxidation state, however, does not differ when compared to the more rapidly quenched melts.
KW - Iron oxidation state
KW - Mössbauer spectroscopy
KW - Oxygen fugacity
KW - Silicate melt
UR - http://www.scopus.com/inward/record.url?scp=0037120065&partnerID=8YFLogxK
U2 - 10.1016/S0009-2541(02)00042-6
DO - 10.1016/S0009-2541(02)00042-6
M3 - Article
AN - SCOPUS:0037120065
VL - 189
SP - 55
EP - 67
JO - Chemical geology
JF - Chemical geology
SN - 0009-2541
IS - 1-2
ER -