Dynamic recovery and recrystallization enable crystalline materials—including rocks, minerals, and ice—to accommodate large plastic strains by counteracting work hardening that arises from the accumulation of crystal lattice defects (e.g., dislocations). Broadly speaking, dynamic recrystallization involves the nucleation and/or growth of new, strain-free recrystallized grains at the expense of old, highly-strained relict grains, often resulting in grain size reduction. In laboratory experiments, dynamic recrystallization and grain size reduction frequently coincide with strain weakening during high-temperature creep. Meanwhile, recrystallized material is widely found within the high-strain interiors of lithospheric shear zones and cryospheric shear margins, suggesting an intimate relationship between dynamic recrystallization and strain localization. Recrystallized grain sizes can also be used to directly estimate paleostresses in exhumed rocks via paleopiezometry/paleowattmetry. Thus, by tracking the progression of dynamic recrystallization in Earth materials, we gain valuable insight into the (evolving) strength of Earth’s crust, mantle, and cryosphere.
This contribution will outline microstructural tools for identifying recrystallized grains formed across a broad range of stresses and temperatures in experimentally-deformed quartz and ice samples. At relatively low homologous temperatures typical of the crustal lithosphere, recrystallized grains can be identified on the basis of internal grain misorientations (i.e., lattice bending). At relatively high homologous temperatures such as those found within terrestrial ice masses, on the other hand, recrystallized grains can instead be identified by quantifying the tortuosity (i.e., irregularity) of grain boundaries. Using these microstructural tools, we will also briefly examine the timescales required for dynamic recrystallization across a broad range of homologous temperatures.