[S-CG44] Rheology, fracture and friction in Earth and planetary sciences

[SCG44-16] Evolution of crystallographic preferred orientations in ice and its causes: view from an experimentalist

★Invited Papers

*Chao Qi^1,2, Qinyu Wang^1,2, Sheng Fan³, David J. Prior³, David L. Goldsby⁴ (1.Institute of Geology and Geophysics, Chinese Academy of Sciences, 2.University of Chinese Academy of Sciences, 3.University of Otago, 4.University of Pennsylvania)

Keywords:Crystallographic preferred orientation, Dynamic recrystallization, ice, rheology

Plastic deformation of polycrystalline ice Ih induces crystallographic preferred orientations (CPOs), which give rise to anisotropies in the viscosity of ice, thereby exerting a strong influence on the flow of glaciers and ice sheets. The development of CPOs is governed by two pivotal mechanisms: recrystallization dominated by subgrain/lattice rotation and by strain-induced grain boundary migration (GBM). Using uniaxial compression experiments carried out at different constant strain rates/stresses and different temperatures, we found a transition with stress and temperature in the CPO patterns, and thus, the dominant CPO formation mechanisms. Using simple shear experiments to different strains, we also found this transition with strain. At lower stresses, warmer temperatures and/or smaller strains, the CPO in ice is characterized by a cone fabric of c axes under compression and a double-cluster fabric under shear, dominated by GBM mechanism. At higher stresses, colder temperatures and/or larger strains, the CPO is characterized by a single cluster of c axes under compression and shear, dominated by lattice rotation mechanism. A synthesis of various experimental data and comparisons with numerical models suggest that the evolution of CPO pattern results from a balance of the two competing mechanisms. These experimental studies improve our comprehensions of CPO development in ice.