PLASTICITY AND DISSOCIATION OF DISLOCATIONS IN WATER-POOR QUARTZ

Water-poor quartz (i.e. containing 100ppm H/Si in the form of hydrogarnet defects) was deformed by compression under confining pressure (approximate to IGPa) in the temperature range 500-900 degrees C under high differential stresses (2-3GPa). Transmission electron microscope observations have shown that limited or no precipitation occurred during the deformation experiments and that plastic deformation is achieved by dislocation glide only; dislocation climb is inhibited. The activated (i.e. water weakened) glide systems are a basal and c + a prismatic in {10 ($) over bar 10}. Both glide systems show perfect dislocations and dislocations widely dissociated into partials with identical Burgers vectors. The present study suggests that glide motion of basal a and prismatic c +/- a dislocations is rendered easier when (i) dislocations are dissociated and (ii) (4H)(si) point defects are available in the crystal.