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

2 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 H 2 O) at 20 GPa and 1,373–1,673 K by the diffusion couple method. The dependence of Fe-Mg interdiffusivity (D Fe-Mg ) on Fe concentration was determined using the Boltzmann-Matano method. The experimentally reported D Fe-Mg in ringwoodite within 0 ≤ X Fe  ≤ 0.1 could be fitted by the relation (Formula presented.), where E* = (1 − X Fe )E Mg  + X Fe E Fe  (E Mg  = 140 ± 5 kJ/mol, E Fe  = 4 ± 2 kJ/mol), D 0 = (Formula presented.) × 10 −10  m 2 /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
JournalJournal of Geophysical Research: Solid Earth
DOIs
Publication statusPublished - Jan 1 2019

Keywords

  • electrical conductivity
  • Fe-Mg interdiffusion
  • 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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