Experimental folding in ice and the resultant c-axis fabrics

Abstract

FOLDS are commonly observed features of naturally deformed rocks1 and glaciers2,3. Many different materials4 have been used to model naturally occurring fold patterns. The deformation experiment described here used ice as an analogue for quartz in quartz-rich rocks by deforming a sample with an initially planar layering or anisotropy. This deformation is compared with samples of unlayered isotropic polycrystalline ice (Fig. 1a). Ice is convenient to use in the laboratory because of its relative ease of deformation at readily controlled temperatures. When used to model the behaviour of quartz-rich rocks, ice is a realistic analogue because both ice and quartz have: (1) hexagonal crystal structures; (2) exhibit similar optical properties; (3) form polycrystalline aggregates; and (4) deform using common crystallographic slip planes, particularly the (0001) basal planes5,6. In our experiments, a sample of multilayered ice consisting of plates of fine-grained ice sandwiched between layers of coarser ice (Fig. 1c) was deformed in a plane strain apparatus. The c-axis orientations of the grains were initially random and therefore the composite sample resembled the structure of many naturally occurring quartzites7. The experimental technique described here makes it possible to explore the relationship between initial anisotropy on folding and fabric development.