Plastic Deformation of Upper Mantle Silicate Minerals

Several minerals which from their occurrence in nodular inclusions in basalts and on theoretical grounds are believed to occur in the upper mantle have been deformed experimentally at high temperature and pressure. The glide mechanisms on which olivine crystals in naturally occurring aggregates are deformed operate in the experimentally deformed specimens in addition to other glide mechanisms which occur naturally only in meteorites. The glide mechanisms which predominate in olivine are shown to be a function of temperature and strain-rate. Diopside deforms chiefly by mechanical twinning in the experiments and enstatite by slip and shear-transformation to clinoenstatite.