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Publication Detail
Ferrous iron diffusion in ferro-periclase across the spin transition
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Article
  • Authors:
    Ammann MW, Brodholt JP, Dobson DP
  • Publisher:
    ELSEVIER SCIENCE BV
  • Publication date:
    01/02/2011
  • Pagination:
    393, 402
  • Journal:
    EARTH PLANET SC LETT
  • Volume:
    302
  • Issue:
    3-4
  • Print ISSN:
    0012-821X
  • Language:
    EN
  • Keywords:
    DFT, diffusion, ferro-periclase, iron spin transition, lower mantle, EARTHS LOWER MANTLE, FE-MG INTERDIFFUSION, SINGLE-CRYSTAL MGO, SELF-DIFFUSION, IMPURITY DIFFUSION, SEISMIC ANISOTROPY, LOWERMOST MANTLE, LATTICE-DYNAMICS, POST-PEROVSKITE, FERROPERICLASE
  • Addresses:
    Ammann, MW
    UCL
    London
    WC1E 6BT
    England
Abstract
We present first-principle calculations on absolute diffusion rates of high- and low-spin ferrous iron in ferro-periclase. The diffusivity of high- and low-spin iron depends on the physical conditions (pressure and temperature), iron concentration and the value of the chosen Hubbard U. We also find that low-spin iron swaps back to high-spin during migration. Our results show that throughout the Earth's lower mantle, iron diffuses at a faster rate than magnesium (up to an order of magnitude). Thus, the effect of the spin transition only has a small impact on the rheology of periclase in the Earth's mantle. Using reasonable vacancy concentrations, we find that ferro-periclase is much weaker than MgSiO3-perovskite throughout the mantle. We conclude, therefore, that ferro-periclase controls the viscosity of the mantle in regions where it becomes interconnected, such as regions of high strain around slabs or near plumes. At very high pressures, such as in Super-Earths, low-spin iron diffusion is expected to become much slower than magnesium, eventually making ferro-periclase more viscous than pure periclase. (c) 2010 Elsevier B.V. All rights reserved.
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