Physics and Chemistry of Minerals

, Volume 36, Issue 4, pp 183–191

Disproportionation of Fe2+ in Al-free silicate perovskite in the laser heated diamond anvil cell as recorded by electron probe microanalysis of oxygen

Original Paper

DOI: 10.1007/s00269-008-0268-9

Cite this article as:
Fialin, M., Catillon, G. & Andrault, D. Phys Chem Minerals (2009) 36: 183. doi:10.1007/s00269-008-0268-9

Abstract

Experimental evidence is reported for Fe2+ disproportionation in Al-free perovskite (Pv), when submitted to large temperature gradients (i.e., under off-equilibrium conditions) in a laser heated diamond anvil cell (LHDAC). To enable this effect, the experimental procedure was designed to produce large radial and axial temperature gradients. In the Pv and ferropericlase (Fp) assemblage synthesized after dissociation of natural olivine, the three chemical states of iron (i.e., Fe0, Fe2+ and Fe3+) could be evidenced by electron probe microanalysis (EPMA), through variations of oxygen contents attached to the Fe cations. Despite inherent difficulties for determination of O-contents and Fe3+/ΣFe ratios using EPMA, we recorded significant changes in iron oxidation state across the laser-heated strip. These changes are correlated with variations in composition for the major elements (Fe, Mg, and Si), which evidences that the Pv/Fp assemblage experienced large segregation under the strong temperature gradients. Grains of metallic iron were detected in parts of the laser-heated strip coexisting with a Pv phase with Fe/(Mg + Fe) = 6 at% and most of its iron as Fe3+. This Fe2+-disproportionation reaction involves insertion of Fe3+-defects in the Pv lattice. This Fe3+-bearing Pv phase is presumably unstable and decomposes into a mineral assemblage including magnesioferrite, which is detected at the border of the laser-heated strip.

Keywords

Ferrous iron disproportionation Electron probe microanalysis Determination Fe3+/ΣFe ratios 

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Michel Fialin
    • 1
  • Gilles Catillon
    • 2
  • Denis Andrault
    • 3
  1. 1.Centre de Microanalyse Camparis, UMR7097-CNRSParis Cedex 5France
  2. 2.Laboratoire Géomatériaux et Géologie de l’Ingénieur (G2I), Université Paris-EstMarne la Vallée Cedex 2France
  3. 3.Laboratoire Magmas et VolcansUniversité Blaise PascalClermont-FerrandFrance

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