The application of an automated fabric analyzer system to the textural evolution of folded ice layers in shear zones

Abstract

Layered ice has been used to investigate the initiation of fabrics in shear zones where there is preservation of a refolded layering. The fabrics were measured using an apparatus that acquires pixel-based images that illustrate the variation of c-axis orientation within and between grains. In the centre of the shear zones there is dynamic recrystallization with the production of an asymmetric two-maxima fabric. The way dynamic recrystallization modifies the inherited folds and microstructure suggests that there is little effect of inheritance from a precursor grain microstructure or fabric. No obvious evidence has been found for the occurrence of sub-grains, which implies that the role of sub-grain rotation is minimal or is obliterated by the recrystallization process. The final c-axis pattern is asymmetric with respect to the direction of shortening, with a strong maximum at ∼5° to the pole of the shear zone, and a sense of asymmetry in the direction of the shear, and a secondary maximum inclined at ∼45° to the plane of shearing. Distinct sets of nearest-neighbour c-axis distributions, namely, intermediate-angle (10-25°), high-angle (50-65°) and very high-angle (120-150° , suggest there may be special grain-boundary relationships. © International Glaciological Society.