Diffusion in MgO at high pressures: Constraints on deformation mechanisms and chemical transport at the core-mantle boundary

Details Diffusion in MgO at high pressures: Constraints on deformation mechanisms and chemical transport at the core-mantle boundary Diffusion in MgO at high pressures: Constraints on deformation mechanisms and chemical transport at the core-mantle boundary

Jan 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003georl..30b..28v&link_type=abstract

Geophysical Research Letters, Volume 30, Issue 2, pp. 28-1, CiteID 1056, DOI 10.1029/2002GL016343

Physics

19

Mineral Physics: Creep And Deformation, Mineral Physics: Defects, Mineral Physics: High-Pressure Behavior, Physical Properties Of Rocks: Plasticity, Diffusion, And Creep, Tectonophysics: Rheology-Mantle

Scientific paper

High-pressure experiments on diffusion in MgO were performed to model the rheological and chemical transport properties of the lower mantle. Lattice and grain boundary diffusion coefficients for Mg, O and Al were determined at 2273 K and pressures up to 25 GPa. The results for pure MgO are in excellent agreement with first-principles calculations. In samples doped with Al2O3, cation vacancies were found to attach to Al impurities with a binding energy of ~0.7 eV. Our results predict that a transition from diffusion creep to dislocation creep will occur in the deep lower mantle if the shear stress exceeds ~1-10 MPa, for a grain size of ~0.1-1 mm. Diffusion through periclase is fast enough to allow substantial chemical exchange across the core-mantle boundary since core formation, with length scales of ~1-10 km for lattice diffusion and 100 km for grain boundary diffusion.

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