Influence of hydrogen on Fe-Mg interdiffusion in (Mg,Fe)O and implications for Earth's lower mantle

Sylvie Demouchy, Stephen J. Mackwell, David L. Kohlstedt

Research output: Contribution to journalArticlepeer-review

34 Scopus citations

Abstract

Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg0.73Fe0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni-NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann-Matano analysis. For a water fugacity of ∼300 MPa, the Fe-Mg interdiffusion coefficient in FexMg1-xO with 0.01 ≤ x ≤ 0.25 can be described by D̃ = D̃0xB exp-(Q+Cx)/RT with D̃0 = (5 ± 1) × 10-4 m2 s-1, Q = 270 ± 20 kJ mol-1, B = 0.8 ± 0.1, and C = -80 ± 10 kJ mol-1. For x = 0.1 and at 1,000°C, Fe-Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.

Original languageEnglish (US)
Pages (from-to)279-289
Number of pages11
JournalContributions to Mineralogy and Petrology
Volume154
Issue number3
DOIs
StatePublished - Sep 1 2007

Keywords

  • Earth's mantle
  • Fe-Mg interdiffusion
  • Hydrogen
  • Periclase

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