Deformation microfabric development in chalcopyrite in fault zones, Mt. Lyell, Tasmania

Deformation of chalcopyrite (CuFeS₂) under low-grade metamorphic conditions within fault zones in the Mt. Lyell area of western Tasmania (Australia) has occurred dominantly by dislocation flow processes. Elongate grain fabrics and well-developed crystallographic preferred orientations have developed by {112} 〈110〉/〈201〉 dislocation glide. However, the presence of recovered dislocation substructures indicate that dislocation climb has also been important. At strains greater than about 30% shortening, strain induced grain boundary migration and deformation band boundary migration are associated with the initial development of a dynamically recrystallized microstructure. However, subgrain rotation and subgrain coalescence mechanisms of recrystallization appear to have been important following the initial dynamic recrystallization of the original grain boundary regions of host grains. In some cases significant grain growth by twin coalescence has followed new grain nucleation. Deformation by {112} twin glide, and to a lesser extent brittle failure mechanisms, has been significant in some fault zones. The twin glide deformation mechanism is interpreted to have operated in a higher deviatoric stress environment and possibly lower temperature regime than that in which dislocation glide and climb have been the dominant mechanisms. Brittle failure may have occurred in a still higher deviatoric stress regime, a lower temperature regime, or perhaps by hydraulic fracture during periods of local high fluid pressure in the fault zones.