The Effect of Water on Fe-Mg Interdiffusion Rates in Ringwoodite and Implications for the Electrical Conductivity in the Mantle Transition Zone

Baohua Zhang, Takashi Yoshino, Chengcheng Zhao

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

We determined the kinetics of Fe-Mg interdiffusion in ringwoodite aggregates as a function of water content (up to ~6,000 wt. ppm H2O) at 20 GPa and 1,373–1,673 K by the diffusion couple method. The dependence of Fe-Mg interdiffusivity (DFe-Mg) on Fe concentration was determined using the Boltzmann-Matano method. The experimentally reported DFe-Mg in ringwoodite within 0 ≤ XFe ≤ 0.1 could be fitted by the relation (Formula presented.), where E* = (1 − XFe)EMg + XFeEFe (EMg = 140 ± 5 kJ/mol, EFe = 4 ± 2 kJ/mol), D0 = 5:59+2:90−1:91× 10−10 m2/s, n = −0.21 ± 0.10, r = 0.25 ± 0.03, and α = −24 ± 4. The water content exponent r of 0.25 suggests a nonnegligible role of water in enhancing Fe-Mg interdiffusion in ringwoodite. The length scale over which the chemical heterogeneities are homogenized by Fe-Mg interdiffusion in the mantle transition zone is estimated to be only a few hundred meters even assuming the whole Earth age. Comparison between the conductivities predicted from Fe-Mg interdiffusion and those obtained from magnetotelluric surveys suggests that around 0.1 wt.% water can account for the high conductivity anomalies (~10−0.6–10−1 S/m) observed in the lower part of the mantle transition zone.

Original languageEnglish
Pages (from-to)2510-2524
Number of pages15
JournalJournal of Geophysical Research: Solid Earth
Volume124
Issue number3
DOIs
Publication statusPublished - Mar 2019

Keywords

  • Fe-Mg interdiffusion
  • electrical conductivity
  • mantle transition zone
  • ringwoodite
  • water

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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