Dynamic quartz recrystallization

Quartz is the most abundant single mineral in the earth's crust (behind the feldspar group), and as such is present in a very large proportion of rocks both as primary crystals and as detrital grains in sedimentary and metamorphic rocks. Dynamic recrystallization is a process of crystal regrowth under conditions of stress and elevated temperature, commonly applied in the fields of metallurgy and materials science. Dynamic quartz recrystallization happens in a relatively predictable way with relation to temperature, and given its abundance quartz recrystallization can be used to easily determine relative temperature profiles, for example in orogenic belts or near intrusions.

Previous research has outlined several dislocation creep regimes present in experimental conditions. Two main mechanisms for altering grain boundaries have been defined. The first is the process by which quartz softens as temperature increases, providing a means for internal stress reduction by migration of dislocations in the crystal lattice, known as dislocation creep. These dislocations concentrate into walls, forming new grain boundaries. The other process involves differences in stored strain energy between neighboring grains, resulting in migration of existing grain boundaries. The extent to which these occur is a function of strain rate and temperature, those being, respectively, the factors controlling introduction of new dislocations and the ability of dislocations to migrate and form subgrain boundaries which themselves migrate.

Observable microstructures in quartz can be classified into three semi-distinct groupings that form a continuum of dynamic recrystallization textures. These regimes will be discussed in terms of temperature changes, assuming a constant level of shear.

...
Wikipedia