THE ROLE OF DYNAMIC RECRYSTALLIZATION IN THE DEVELOPMENT OF LATTICE PREFERRED ORIENTATIONS IN EXPERIMENTALLY DEFORMED QUARTZ AGGREGATES

Experiments on coaxially deformed quartz aggregates show that when dyn amic recrystallization involves grain size reduction, the lattice pref erred orientation (LPO) of the recrystallized grains depends on the re crystallization mechanism. At low temperatures and fast strain rates, strain-induced grain boundary migration recrystallization favors growt h of grains oriented poorly for slip on the basal and prism planes, re sulting in an LPO of c-axes parallel to the sigma1 direction. At highe r temperatures or slower strain rates, progressive subgrain rotation p roduces recrystallized grains which inherit the small-circle girdle LP O of their deformed host grains and which continue to re-orient by sli p. At even higher temperatures and slower strain rates, progressive su bgrain rotation is accompanied by rapid grain boundary migration, whic h 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 ene rgy reduction, a strong LPO of c-axes parallel to sigma1 develops duri ng grain growth but then evolves with increasing strain toward a small -circle girdle. The correlation of LPOs with recrystallization mechani sms has important implications for the assumption of homogeneous strai n in theoretical models of LPOs and for interpreting natural LPOs in r ecrystallized rocks.