9 - Mineralogical applications of TEM – II. Dislocations and microstructures associated with deformation

Summary

Although the role of dislocations in the plastic deformation of crystalline materials was appreciated by physical metallurgists by 1950, structural geologists concerned with the deformation of rocks were relatively slow to respond to the new concepts. For example, dislocations are mentioned only briefly by Turner and Weiss (1963) in their classic book Structural Analysis of Metamorphic Tectonites. John Christie and David Griggs of the University of California at Los Angeles were probably the first geologists to use dislocation concepts to interpret the deformation characteristics of an important rock-forming mineral (Wenk 1979). In 1964, Christie, Griggs, and Carter (1964) succeeded, after many earlier failures, in plastically deforming high-quality single crystals of natural quartz and attempted to explain the deformation lamellae observed in the optical microscope in terms of en echelon arrays of edge dislocations lying in the slip planes. TEM observations of replicas of etched surfaces of the deformed crystals provided some supporting evidence for the proposed model. However, the first direct observations of the dislocations and other defects in thin foils of these deformed specimens were made by McLaren et al. (1967), following an earlier TEM investigation of dislocations in thin foils of milky vein quartz by McLaren and Phakey (1965b).

Since then, TEM has been used to study dislocation microstructures in a wide range of naturally and experimentally deformed minerals and rocks.