Diffusion in minerals of the Earth's lower mantle: constraining rheology from first principles.
Doctoral thesis, UCL (University College London).
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.
|Title:||Diffusion in minerals of the Earth's lower mantle: constraining rheology from first principles|
|Open access status:||An open access version is available from UCL Discovery|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences|
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