Effect of pressure on the deformation of quartz aggregates in the presence of H2O

Quartzite samples of high purity with a grain size ~200 ?m have been experimentally deformed by coaxial shortening in solid medium apparatus at 900 °C and confining pressures ranging from 0.6 to 2 GPa. Most shortened ~30% 0.1 wt% added H2O. The dominantly crystal plasticity (dislocation creep), there is systematic decrease flow stress increasing pressure. Strain rate stepping tests yield exponents n ? 1.4. strain determined individual shapes matches that bulk shortening. In addition plastic strain, mode I cracks developed all samples, principally the boundary regions. Recrystallized material, visible through cathodoluminescence colours, forms two mechanisms: (1) progressive subgrain rotation (2) cracking, nucleating small new grains. After high-angle boundaries established, migration takes place, distinction grains nucleation origin (subgrain or cracking) impossible. At higher pressure, more recrystallized material forming it inferred inverse pressure dependence caused enhanced consistent previous studies.