Experimental Deformation and Recrystallization of Quartz

Abstract

Plastic deformation of quartz, as evidenced by undulatory extinction, deformation bands, and deformation lamellae, was obtained in sand, quartzite, and single crystals deformed experimentally in several types of apparatus. Extensive syntectonic recrystallization of flint and quartzite was also produced in experiments at high temperatures. Undulatory extinction commonly occurs in zones subparallel to the c-axis and, rarely, in zones with other orientations. Deformation bands vary considerably in orientation, but most of the bands are oriented subparallel to the c-axis. The lamellae form in three more or less distinct orientations: the most common lamellae are inclined at small angles to the base; a weaker concentration is inclined at 20°-60° to the base; and the weakest concentration is subparallel to the c-axis. Deformation lamellae subparallel to the base and zones of undulatory extinction and deformation bands subparallel to the c-axis originate by slip on (0001), accompanied by bending or kinking of the slip planes. Lamellae, bands, and undulatory extinction inclined at moderate angles (20°-60°) to the base are present only in grains in which the shear stress on (0001) is low. They must be produced by another slip mechanism (or mechanisms) not yet identified. Lamellae oriented subparallel to the c-axis and bands and undulatory extinction subparallel to the base are considered to have formed by slip parallel to the c-axis. The poles of lamellae in polycrystalline aggregates with nearly random orientation form small-circle girdle patterns about the axis of greatest compressive stress. The deformation lamellae and bands originate in planes of high shear stress, and it is shown that the orientation of lamellae in rocks may be used to determine the orientation of the stress when the lamellae were formed. In short-term tests flint recrystallizes at 900° C. and above and quartzite at 1,000° C. and above. The products are similar, texturally, to quartzites recrystallized in nature, and the recrystallized grains show strong preferred orientations. The amount of present in the sample does not apparently influence the temperature at which recrystallization begins, but the recrystallized grains appear to be larger when more is present.