DIFFUSION CREEP IN PEROVSKITE - IMPLICATIONS FOR THE RHEOLOGY OF THE LOWER MANTLE

High-temperature creep experiments on polycrystalline perovskite (CaTiO3), an analog of (Mg,Fe)SiO3 perovskite of the lower mantle, suggest that (grain size-sensitive) diffusion creep is important in the lower mantle and show that creep rate is enhanced by the transformation from the orthorhombic to the tetragonal structure. These observations suggest that grain-size reduction after a subducting slab passes through the 670-kilometer discontinuity or after a phase transformation from orthorhombic to tetragonal in perovskite will result in rheological softening in the top portions of the lower mantle.