The direct observation and analysis of dislocations in experimentally deformed plagioclase feldspars

Transmission electron microscopy has been used to observe and analyse the dislocations in a series of plagioclase feldspars which had been experimentally deformed in compression. The results indicate that a moving dislocation in these materials leaves behind a fault in the structure. Two types of fault are observed but both define the slip plane of the associated dislocation. From these observations, together with stuctural considerations, the visibility of the dislocations and the orientatation of the applied shear stress it has been possible to determine the slip system uniquely for a number of dislocations. The origin of the dislocations and the nature of the faults are also discussed.