Abstract
We report application of the flank method using the electron microprobe to a suite of twelve (Mg,Fe)O samples with composition 2–47 wt% Fe and Fe3+/ΣFe = 1 to 11%, where Fe3+/ΣFe was determined independently using Mössbauer spectroscopy on the same grains used for the flank method measurements. A calibration curve of the form Fe2+ = A + B × (ΣFe)2 + C × (Lβ/Lα) was fit to the data and gave excellent agreement between Fe3+/ΣFe calculated from the flank method and Fe3+/ΣFe determined using Mössbauer spectroscopy. We found the method to be sufficiently sensitive to determine meaningful variations in Fe3+/ΣFe for geophysically relevant compositions of (Mg,Fe)O (<25 wt% Fe), and calibration parameters remained constant within experimental uncertainty over the course of the entire study (20 months). Flank method measurements on an inhomogeneous sample of synthetic (Mg,Fe)O showed evidence of diffusion processes resulting from rupture of the capsule during the high-pressure experiment and the possibility to measure Lβ/Lα variations with a spatial resolution of a few microns. We detected the presence of exsolved magnesioferrite in a suite of (Mg,Fe)O single crystals using transmission electron microscopy and Mössbauer spectroscopy. Flank method measurements on the same suite of single crystals showed enhanced Fe3+/ΣFe values, consistent with the presence of magnesioferrite even though the grains were too small to be resolved by conventional electron microprobe measurements.
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References
Berry AJ, Danyushevsky LV, HStC O’Neill, Newville M, Sutton SR (2008) The oxidation state of iron in komatiitic melt inclusions indicates hot Archean mantle. Nature 455:961–963
De Grave E, Govaert A, Chambaere D, Robbrecht G (1979) Mössbauer effect study of MgFe2O4. Physica 96B:103–110
Dobson DP, Richmond NC, Brodholt JP (1997) A high-temperature electrical conduction mechanism in the lower mantle phase (Mg, Fe)1-xO. Science 275:1779–1781
Eeckhout SG, Bolfan-Casanova N, McCammon C, Klemme S, Amiguet E (2007) XANES study of the oxidation state of Cr in lower mantle phases: periclase and magnesium silicate perovskite. Am Mineral 92:966–972
Hazen RM, Jeanloz R (1984) Wüstite (Fe1-xO): a review of its defect structure and physical properties. Rev Geophys Space Phys 22:37–46
Höfer HE, Brey GP (2007) The iron oxidation state of garnet by electron microprobe: its determination with the flank method combined with major-elements analysis. Am Mineral 92:873–885
Höfer HE, Weinbruch S, McCammon CA, Brey GP (2000) Comparison of two electron probe microanalysis techniques to determine ferric iron in synthetic wüstite samples. Eur J Mineral 12:63–71
Jacobsen SD, Reichmann HJ, Spetzler HA, Mackwell SJ, Smyth JR, Angel RJ, McCammon CA (2002) Structure and elasticity of single-crystal (Mg,Fe)O and a new method of generating shear waves for gigahertz ultrasonic interferometry. J Geophys Res 107(B2):2037. doi:10.1029/2001JB000490
Longo M (2009) Iron oxidation state of (Mg,Fe)O: calibration of the flank method (EMPA) on synthetic samples and applications on natural samples from lower mantle diamonds. Dissertation. University of Bayreuth, Germany
McCammon CA (1994) A Mössbauer milliprobe: practical considerations. Hyperfine Interact 92:1235–1239
McCammon C (2001) Deep diamond mysteries. Science 293:813–814
McCammon CA (2004) Mössbauer spectroscopy: Applications. In: Beran A, Libowitsky E (eds) Spectroscopic Methods in Mineralogy, vol 6. Eötvös University Press, Budapest, pp 369–398
McCammon CA, Hutchison M, Harris J (1997) Ferric iron content of mineral inclusions in diamonds from São Luiz: a view into the lower mantle. Science 278:434–436
McCammon CA, Peyronneau JP, Poirier J-P (1998) Low ferric iron content of (Mg, Fe)O at high pressures and high temperatures. Geophys Res Lett 25:1589–1592
McCammon CA, Stachel T, Harris JW (2004) Iron oxidation state in lower mantle mineral assemblages II. Inclusions in diamonds from Kankan, Guinea. Earth Planet Sci Lett 222:423–434
Reichmann HJ, Jacobsen SD, Mackwell SJ, McCammon CA (2000) Sound wave velocities and elastic constants for magnesiowüstite using gigahertz interferometry. Geophys Res Lett 27:799–802
Speidel DH (1967) Phase equilibria in the system MgO-FeO-Fe2O3: the 1300°C isothermal section and extrapolations to other temperatures. J Amer Ceram Soc 50:243–248
van Aken PA, Liebscher B, Styrsa VJ (1998) Quantitative determination of iron oxidation state in minerals using FeL23-edge electron energy-loss near-edge structure spectroscopy. Phys Chem Mineral 25:323–327
van Orman JA, Fei Y, Hauri EH, Wang J (2003) Diffusion in MgO at high pressures: constraints on deformation mechanisms and chemical transport at the core-mantle boundary. Geophys Res Lett 30: doi:10.1029/2002GL016343, 2003
Waychunas GA, Dollase WA, Ross C II (1994) Short-range order measurements in MgO-FeO and MgO-LiFeO, solid solutions by DLS simulation-assisted EXAFS analysis. Am Miner 79:274–288
Wuensch BJ, Vasilos T (1962) Diffusion of transition metal ions in single-crystal MgO. J Chem Phys 36:2917–2922
Yamazaki D, Karato S (2001) Some mineral physics constraints on the rheology and geothermal structure of Earth’s lower mantle. Am Miner 86:385–391
Acknowledgments
We are grateful to Stephen Mackwell for supplying some of the samples examined in this study, to Hugh O’Neill for valuable advice concerning (Mg,Fe)O synthesis, to Heidi Höfer for her support on the flank method calibration, to Detlef Krauße for his technical support at the electron microprobe, to Nobuyoshi Miyajima for TEM investigations and to Florian Heidelbach for SEM analyses. The manuscript was significantly improved by the comments of Andrew Berry and an anonymous reviewer. ML received financial support from the European Commission under the Marie Curie Action for Early Stage Training of Researchers within the 6th Framework Programme (contract number MEST-CT-2005-019700). SDJ is supported in part by the US NSF (EAR-0748707) and by the David and Lucile Packard Foundation.
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Communicated by M. W. Schmidt.
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Longo, M., McCammon, C.A. & Jacobsen, S.D. Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes. Contrib Mineral Petrol 162, 1249–1257 (2011). https://doi.org/10.1007/s00410-011-0649-9
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DOI: https://doi.org/10.1007/s00410-011-0649-9