Preferred slip band orientations and bending observed in the Dome Concordia ice core

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Fabric analysis of the upper 1300m of the Dome C ice core reveals a slight clustering tendency of c axes towards vertical, which gradually enhanceswith depth from an initially isotropic orientational distribution of c axes at the free surface. Such a strain induced anisotropy is compatible with the expected macroscale stress state in a dome, viz. dominated by vertical compression. Yet, when one analyses the orientational distribution of the visible gliding layers ofindividual crystallites (slip bands), the evidences are quite contrasting. Direct observation of slip bands in samples from Dome C ice core taken from dierent depths (ranging from 204m to 1291m depth) indicates a higher slip activity in nearly horizontal planes, in such a manner that more than 60% of the detectedslip bands have an inclination of less than 30 with respect to the horizontal.Furthermore, the observed slip activity is not symmetric, i.e., the amount ofslip bands discerned at 20 (say) is usually not comparable with the number ofslip bands found at 160. Such features are not consonant with the predictedslip activity induced by compression and/or extension. In this work, we presentevidences for this unexpected orientational distribution of slip bands and discusstheir possible causes. Natural and artificial agents are investigated, togetherwith their respective consequences for ice sheet modeling and ice core processing.Additionally, we show the occurrence of bent slip bands in certain crystallites.Such a bending represents an early stage of polygonization and it highlights thestrong inhomogeneity of deformation on the crystal level. Moreover, it indicatesthat polygonization might be mathematically interpreted as a continuous processof rotation, characterized by the divergence of c-axes from a common direction.This result is of great value for the modeling of polycrystalline ice within theframes of a continuum theory.

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Faria, S. and Kipfstuhl, S. (2003): Preferred slip band orientations and bending observed in the Dome Concordia ice core , . .

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