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

Wyatt L. Du Frane, James Tyburczy

Research output: Contribution to journalArticle

52 Scopus citations

Abstract

Knowledge about hydrogen self diffusion (DH) is critical for determining mantle hydrogen distribution and understanding point defects. Also, chemical diffusion of hydrogen in olivine, such as redox exchange with polarons (DRedox), depends on DH. 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 DH,[100] = 10(-4.9±1.4)*e(-140±30kJ/mol)/(RT) m2/s, which is ∼1 log unit lower than DRedox,[100], with similar activation enthalpy Ha. By comparing these two diffusion coefficients, we estimate the small polaron diffusion coefficient. Additionally, we estimate DH in the [010] and [001] orientations, demonstrating that DH 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 (σH = 10 1.1*e(-130kJ/mol)/(RT) S/m for 10-2 wt % H2O) 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 DH and σH 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 - Mar 1 2012

Keywords

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

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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