Ice deformed in compression and simple shear: control of temperature and initial fabric

Layered and polycrystalline ice was experimentally deformed in general shear involving axial compression (strain magnitude 0.5-17%) and simple shear (strain magnitude gamma=0.1-1.4). As the temperature is increased from -20 degrees C to -2 degrees C, there is at least a twofold enhancement in octahedral shear strain rate, which coincides with the onset of extensive dynamic recrystallization and a change in grain-size distribution at -15 degrees C. Between -15 degrees C and -10 degrees C the c-axis preferred orientation rapidly evolves with the initiation of two-maxima fabrics in shear zones. From -10 degrees C to -2 degrees C there is progressive evolution of a final c-axis pattern that is asymmetric with respect to the direction of shortening, with a strong maximum at similar to 5 degrees to the pole of the shear zone, a sense of asymmetry in the direction of the shear, and a secondary maximum inclined at similar to 45 degrees to the plane of shearing. An initial c-axis preferred orientation plays a critical role in the initial mechanical evolution. In contrast to established ideas, a strong alignment of basal planes parallel to the plane of easy glide inhibited deformation and there was an increased component of strain hardening until recrystallization processes become dominant.