Premium
Diffusion in MgO at high pressures: Constraints on deformation mechanisms and chemical transport at the core‐mantle boundary
Author(s) -
Van Orman James A.,
Fei Yingwei,
Hauri Erik H.,
Wang Jianhua
Publication year - 2003
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2002gl016343
Subject(s) - grain boundary diffusion coefficient , lattice diffusion coefficient , diffusion creep , mantle (geology) , periclase , materials science , core–mantle boundary , grain boundary , effective diffusion coefficient , creep , thermodynamics , dislocation creep , diffusion , impurity , mineralogy , geology , metallurgy , chemistry , geophysics , physics , microstructure , medicine , magnesium , organic chemistry , magnetic resonance imaging , radiology
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 Al 2 O 3 , 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.