Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes

Micaela Longo*, Catherine A. McCammon, Steven D. Jacobsen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)1249-1257
Number of pages9
JournalContributions to Mineralogy and Petrology
Volume162
Issue number6
DOIs
StatePublished - Dec 1 2011

Keywords

  • Electron microprobe
  • Ferropericlase
  • Flank method
  • Iron oxidation state

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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