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Title: Local structural variation with oxygen fugacity in Fe 2SiO 4+x fayalitic iron silicate melts

Here, the structure of molten Fe 2SiO 4+x has been studied using both high-energy X-ray diffraction and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe 3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature ( T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and –5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K and –2.1(3) < ΔFMQ < +4.4(3) log units. Fe 3+ contents, x = Fe 3+/ΣFe, estimated directly from the pre-edge peaks of the XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the redox kinetics and the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe–O coordination numbers, n FeO, close to 5 for all Fe 3+/ΣFe. Diffraction measurements yielded values of 4.4(2) < n FeO < 4.7(1). There is limitedmore » evidence for a linear trend n FeO(x) = 4.46(3) + 0.4(1)x. Asymmetric Fe–O bond length distributions peak at around 1.96 Å and have a shoulder arising from longer interatomic distances. Mean r FeO lie close to 2.06 Å, consistent with n FeO close to 5. These observations suggest that Fe 2+ is less efficient at stabilizing tetrahedral Fe 3+ compared to large monovalent alkali cations. Comparison of in-situ XANES estimates of Fe 3+/ΣFe in the melts to those of the quenched solids obtained from XANES as well as Mössbauer spectroscopy indicate rapid oxidation during cooling, enabled by stirring of the melt by the levitation gas flow. As such, the oxidation state of hot komatiitic and other highly fluid melts may not be retained, even during rapid cooling, as it is for cooler basaltic and more silicic magmas.« less
Authors:
; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Grant/Contract Number:
AC02-06CH11357; SBIR DE-SC0007564
Type:
Accepted Manuscript
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 203; Journal Issue: C; Journal ID: ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1374595
Alternate Identifier(s):
OSTI ID: 1397831

Alderman, O. L.G., Lazareva, L., Wilding, M. C., Benmore, C. J., Heald, S., Johnson, C. E., Johnson, J. A., Hah, H. -Y., Sendelbach, S., Tamalonis, A., Skinner, L. B., Parise, J. B., and Weber, J. K.R.. Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts. United States: N. p., Web. doi:10.1016/j.gca.2016.12.038.
Alderman, O. L.G., Lazareva, L., Wilding, M. C., Benmore, C. J., Heald, S., Johnson, C. E., Johnson, J. A., Hah, H. -Y., Sendelbach, S., Tamalonis, A., Skinner, L. B., Parise, J. B., & Weber, J. K.R.. Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts. United States. doi:10.1016/j.gca.2016.12.038.
Alderman, O. L.G., Lazareva, L., Wilding, M. C., Benmore, C. J., Heald, S., Johnson, C. E., Johnson, J. A., Hah, H. -Y., Sendelbach, S., Tamalonis, A., Skinner, L. B., Parise, J. B., and Weber, J. K.R.. 2017. "Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts". United States. doi:10.1016/j.gca.2016.12.038. https://www.osti.gov/servlets/purl/1374595.
@article{osti_1374595,
title = {Local structural variation with oxygen fugacity in Fe2SiO4+x fayalitic iron silicate melts},
author = {Alderman, O. L.G. and Lazareva, L. and Wilding, M. C. and Benmore, C. J. and Heald, S. and Johnson, C. E. and Johnson, J. A. and Hah, H. -Y. and Sendelbach, S. and Tamalonis, A. and Skinner, L. B. and Parise, J. B. and Weber, J. K.R.},
abstractNote = {Here, the structure of molten Fe2SiO4+x has been studied using both high-energy X-ray diffraction and Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature (T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and –5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K and –2.1(3) < ΔFMQ < +4.4(3) log units. Fe3+ contents, x = Fe3+/ΣFe, estimated directly from the pre-edge peaks of the XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the redox kinetics and the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe–O coordination numbers, nFeO, close to 5 for all Fe3+/ΣFe. Diffraction measurements yielded values of 4.4(2) < nFeO < 4.7(1). There is limited evidence for a linear trend nFeO(x) = 4.46(3) + 0.4(1)x. Asymmetric Fe–O bond length distributions peak at around 1.96 Å and have a shoulder arising from longer interatomic distances. Mean rFeO lie close to 2.06 Å, consistent with nFeO close to 5. These observations suggest that Fe2+ is less efficient at stabilizing tetrahedral Fe3+ compared to large monovalent alkali cations. Comparison of in-situ XANES estimates of Fe3+/ΣFe in the melts to those of the quenched solids obtained from XANES as well as Mössbauer spectroscopy indicate rapid oxidation during cooling, enabled by stirring of the melt by the levitation gas flow. As such, the oxidation state of hot komatiitic and other highly fluid melts may not be retained, even during rapid cooling, as it is for cooler basaltic and more silicic magmas.},
doi = {10.1016/j.gca.2016.12.038},
journal = {Geochimica et Cosmochimica Acta},
number = C,
volume = 203,
place = {United States},
year = {2017},
month = {1}
}