Lattice preferred orientation in deformed-then-annealed material: Observations from experimental and natural polycrystalline aggregates

In order to investigate the evolution of latice preferred orientation (LPO) obtained during deformation, we carried out post-deformational annealing experiments for rock analog materials, octachloropropane (C₃Cl₈) and norcamphor (C₇H₁₀O). Polycrystalline aggregates deformed at low-temperature/high-strain-rate conditions show complete obliteration of grain-boundary microstructures (e.g., grain-shape foliation) during annealing, but maintain the LPO by rapidly growing small grains which have inherited crystallographic orientations from the adjacent old grains. On the other hand, polycrystalline aggregates deformed at high-temperature/low-strain-rate conditions tend to maintain deformation microstructures during annealing, due mainly to the presence of subgrain boundaries which pin the motion of grain boundaries. The limited mobility of grain boundaries also allows preservation of the LPO obtained during deformation. During grain growth at the stage when textural equilibrium is reached, polycrystalline aggregates show no preferential removal of grains of certain crystallographic orientations. Therefore, our experimental results suggest that LPO obtained during deformation is insensitive to post-deformational annealing process. A microstructural analysis of naturally deformed-then-annealed quartzite indicates that the similar processes may operate in natural rocks.