The role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates

Abstract

Experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction, the lattice preferred orientation (LPO) of the recrystallized grains depends on the recrystallization mechanism. At low temperatures and fast strain rates, strain-induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes, resulting in an LPO of c-axes parallel to the θ 1 direction. At higher temperatures or slower strain rates, progressive subgrain rotation produces recrystallized grains which inherit the small-circle girdle LPO of their deformed host grains and which continue to re-orient by slip. At even higher temperatures and slower strain rates, progressive subgrain rotation is accompanied by rapid grain boundary migration, which does not favor grains of any particular orientation; thus the LPO is again similar to that of non-recrystallized grains. In contrast, when dynamic recrystallization involves grain growth driven by surface energy reduction, a strong LPO of c-axes parallel to θ 1 develops during grain growth but then evolves with increasing strain toward a small-circle girdle. The correlation of LPOs with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of LPOs and for interpreting natural LPOs in recrystallized rocks.