Ammann, M.W.; (2011) Diffusion in minerals of the Earth's lower mantle: constraining rheology from first principles. Doctoral thesis , UCL (University College London).

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Abstract

Absolute di�ffusion rates in minerals of the Earth's lower mantle are calculated from �first principles using density functional theory. The agreement with the available experimental data is excellent and provides con�fidence in predicting di�ffusivities in regions of the lower mantle inaccessible to current experimental techniques. I have calculated the di�ffusivity of all constituting species in ferro-periclase ((Fe,Mg)O), (Fe,Mg)SiO3 perovskite and MgSiO3 post-perovskite. This enables me to put tight constraints on the viscosity of the Earth's lower mantle, and, in particular, on the viscosity of post-perovskite for which no experimental data are available. I �find that perovskite deforming in diff�usion creep can readily reproduce the Earth's lower mantle viscosity profi�le that has been inferred from inversion modelling. I also show that postperovskite is either much stiff�er (if also deforming in di�ffusion creep) or up to four orders of magnitude weaker than perovskite (if deforming in dislocation creep). This leads to a new interpretation of the sharp seismic reflector in the lowermost lower mantle, known as D00, as the onset of a sudden rheological transition and the generation of a mineral texture therewith. Finally, I also �find that the pressure induced high-to-low-spin transition of iron in ferro-periclase and perovskite has a negligible e�ffect on the rheology of the lower mantle.

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