Hydrolytic weakening of quartz aggregates: The effects of water and pressure on recovery

In order to test the effect of ‘water‧ at high pressure on the rate of dislocation climb in quartz, we have performed annealing experiments on portions of a quartzite sample previously deformed at 700°C, 10 −5 sec −1 , and 1500 MPa which had a high dislocation density but few subgrain boundaries. Portions of the deformed sample were annealed at 1500 MPa and 800°C for 1 and 4 days; samples with 0.17 wt % water added have a lower average dislocation density and a greater number of subgrain boundaries than those without water added. Annealing at 800°C for 4 days at 1500 MPa after vacuum drying at 800°C, or at 550 MPa with 0.17 wt % water added, produces no significant change in the dislocation microstructure. These results indicate that: (1) the presence of a water‐related defect in quartz accomplishes hydrolytic weakening by making the climb of dislocations easier, thus increasing the rate of recovery at a given imposed strain rate, and (2) for laboratory times this weakening requires a pressure >550 MPa.