- © The Mineralogical Society Of America
Plastic deformation of rocks in the Earth is most strikingly illustrated in exposures of shear zones. Very large strains (shear strains of γ = 10 or more) may be developed in these zones. They appear to be ubiquitous within the continental and oceanic crust and may provide the dominant locus for deformation in these regions and, potentially, also in the lithospheric upper mantle. It is therefore of the greatest interest to obtain information about the deformation properties of rock at large strains
In the past, various approaches have been made to achieving in the laboratory the types of deformation seen in natural rocks. In some cases it has been possible to achieve plastic deformation in single crystals and fine-grained aggregates of minerals at atmospheric pressure at sufficiently high temperatures and a number of such experiments have been carried out (Mackwell et al. 1990, Dimanov et al. 1998). However, it is generally necessary to conduct experiments under conditions of high confining pressure as well as high temperature. The earliest experiments of this nature were those of Adams and Nicholson (1901) and von Kármán (1911), followed by the pioneering work of Bridgman (1949) and Griggs (1936, and many subsequent papers). These studies were carried out using fluid pressure media. Although Otto Mügge carried out some deformation experiments on single crystals of minerals in solid confining media already in the late 19th to early 20th century, the extensive use of solid media for high-pressure experiments was not introduced until the development of the Griggs solid medium apparatus in the 1960’s (e.g., Griggs et al. 1966, Griggs 1967).
Since the 1960s, extensive studies have been carried out in both gas-medium and solid-medium apparatus. The apparatus and techniques have been reviewed in several publications (Griggs et al. 1960, Paterson …