Evaluating ice fabrics using fabric analyser techniques in Sørsdal Glacier, East Antarctica

Abstract

Ice cores (∼4 m long) obtained from areas of different surface velocities near the terminus of Sørsdal Glacier, East Antarctica, have been investigated using two versions of a fabric analyser (G50). In sections parallel to the flow plane, the microstructure is typically interlocking with elongate grains that parallel air-bubble elongation, X, reflecting their development in an earlier ductile regime. The c-axis fabric patterns vary with respect to X and vary from single-double maxima to asymmetric smallcircle girdles oblique to the planar foliation, which can be attributed to a simple shear regime. The siteto-site variations in the c-axis patterns can be related to areas of different surface velocities, the asymmetry of fabrics correlating with localized strain variations and differences in the deformation path, but not to the current strain pattern recorded by the near-surface deformation conditions. Overprinting fractures have little effect on microstructure except for local dissolution and precipitation along stylolitic surfaces. Comparison of results from the two different fabric analysers reveals that with a higher pixel resolution the incorporation of additional monochromatic light-emitting diodes and repositioning of a retarder plate produce more reliable c-axis measurements.