Preferred slip band orientations and bending observed in the Dome Concordia ice core
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چکیده
Fabric analysis of the upper 1300m of the Dome C ice core reveals a slight clustering tendency of c axes towards vertical, which gradually enhances with 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 of individual crystallites (slip bands), the evidence is quite contrasting. Direct observation of slip bands in samples from Dome C ice core taken from different 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 detected slip 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 of slip bands discerned at 20◦ (say) is usually not comparable with the number of slip bands found at 160◦. Such features are not consistent with the predicted slip activity induced by compression and/or extension. In this work, we present evidence for this unexpected orientational distribution of slip bands and discuss some of their possible causes. Natural and artificial agents are investigated, together with 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 the strong inhomogeneity of deformation on the crystal level. Moreover, it indicates that polygonization might be mathematically interpreted as a continuous process of rotation, characterized by the divergence of c-axes from a common direction.
منابع مشابه
Automatic reconstruction of polycrystalline ice microstructure from image analysis : application to the EPICA ice core at Dome Concordia, Antarctica
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تاریخ انتشار 2003