Ice Fabrics and Petrography, Meserve Glacier, Antarctica

Abstract

Results of petrographic and fabric analysis of fine-grained cold ice from the tongue of Meserve Glacier, Antarctica, are described. Most of the basal ice is remarkably uniform in texture and shows an optic-axis fabric with a single strong maximum, which is consistent with the steady-state conditions of flow. Within 0.5 m of the ice–rock interface, irregularities in the bed cause flow perturbations which are correlated with recrystallization and changes in fabric of the ice. Optic-axis fabrics in the basal ice show close symmetry relationships with dimensional fabric and deformation symmetry. Grain-size of the ice increases towards the surface of the glacier and the single maximum of the optic-axis fabric undergoes a rotation about the flow vector. In the near surface, where strain-rates are relatively much lower, the optic-axis fabric symmetry is not closely related to either deformation symmetry or the dimensional fabric. Syntectonic recrystallization of ice throughout the glacier tongue characteristically produces a strong single-maximum fabric, the orientation of which in relation to the stress field is apparently determined by stress level. Under steady-state conditions of flow, the strength of the maximum also appears to be a function of stress level.