On the deformation of quartzite

In view of the apparent difficulty of satisfying the von Mises criterion for general plasticity by dislocation glide alone, the climb mechanism proposed by Nabarro (1967) has been considered as an important contributor to the steady state deformation of quartzites in the earth's crust. The proposed deformation mechanism can provide the necessary strain rates; it is consistent with the observed dislocation structures and leads to a simple explanation of the water weakening phenomenon in terms of the increase in diffusivity of the atom species. In addition, the experimentally observed effects of strain rate and temperature on the opening angle of the characteristic ‘girdle’ fabrics of quartzite are a natural consequence of the model and this relationship could provide analytical procedures for the establishment of crustal deformation conditions.