Deuterium-hydrogen exchange in olivine: Implications for point defects and electrical conductivity

Wyatt L. Du Frane, James Tyburczy

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

Knowledge about hydrogen self diffusion (D H) is critical for determining mantle hydrogen distribution and understanding point defects. Also, chemical diffusion of hydrogen in olivine, such as redox exchange with polarons (D Redox), depends on D H. In this study deuterium 2H was exchanged into hydrogen 1H saturated single crystals of San Carlos olivine between 750 and 900°C at 2 GPa. We measured and fit the resulting 2H profiles to obtain D H,[100] = 10 (-4.9±1.4)*e (-140±30kJ/mol)/(RT) m 2/s, which is ∼1 log unit lower than D Redox,[100], with similar activation enthalpy H a. By comparing these two diffusion coefficients, we estimate the small polaron diffusion coefficient. Additionally, we estimate D H in the [010] and [001] orientations, demonstrating that D H is highly anisotropic in olivine. These D H values were used with the Nernst-Einstein relation to estimate the electrical conductivity by hydrogen in olivine (σ H = 10 1.1*e (-130kJ/mol)/(RT) S/m for 10 -2 wt % H 2O) that is lower in magnitude than previous measurements. Our results suggest that hydrogen alone cannot account for high electrical conductivity anomalies observed at asthenospheric depths (∼10 -2 to ∼10 -1 S/m). The maximum anisotropic variation of D H and σ H in olivine is ∼2 log units between 750 and 900°C and increases when extrapolated to higher temperature (∼3.3 at 1400°C). Anisotropy observed in the mantle may indicate substantial amounts of hydrogen in olivine with lattice-preferred orientation.

Original languageEnglish (US)
Article number2
JournalGeochemistry, Geophysics, Geosystems
Volume13
Issue number3
DOIs
StatePublished - 2012

Fingerprint

Deuterium
deuterium
Point defects
olivine
point defects
electrical conductivity
defect
Hydrogen
hydrogen
conductivity
electrical resistivity
Earth mantle
estimates
diffusion coefficient
mantle
Gene Conversion
Polarons
preferred orientation
polarons
Electric Conductivity

Keywords

  • diffusion
  • electrical conductivity
  • hydrogen
  • olivine
  • point defects
  • SIMS

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Deuterium-hydrogen exchange in olivine : Implications for point defects and electrical conductivity. / Du Frane, Wyatt L.; Tyburczy, James.

In: Geochemistry, Geophysics, Geosystems, Vol. 13, No. 3, 2, 2012.

Research output: Contribution to journalArticle

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