TEM INVESTIGATION OF DISLOCATION MICROSTRUCTURE OF EXPERIMENTALLY DEFORMED SILICATE GARNET

Deformation experiments have been carried out on single crystals of ga rnet (Py25 Al67 Sp2 Gr6) under high confining pressure (P = 6.5 GPa) a nd temperature (T = 1440 degrees C) in a multi-anvil apparatus. The hi gh pressure sample assembly was designed so as to generate high differ ential stress. In one experiment, the differential stress was limited by a single crystal of San Carlos olivine (oriented along [010]) added on top of the specimen. Garnet crystals have been plastically deforme d which shows that under our experimental conditions, garnet is ductil e. The dislocation microstructure, analysed by transmission electron m icroscopy (TEM), suggests that both 1/2[111]{110} and [100]{110} glide systems have been activated. Some dislocations appear to be dissociat ed. The observations of dislocation junctions and subgrain structures indicate that dislocation climb is enhanced under our experimental con ditions.