Fig. 5.

Conceptual model showing how ripplocations lead to kink bands or conjugate expansion structure arrays. A pristine undeformed biotite lattice (a) experiences differential stress with some component of compression parallel to the basal planes. As the lattice is confined this induces numerous small bulk ripplocations, which store the resulting c-axis parallel strain energy (b). Continued basal plane parallel compression imparts enough energy for ripplocations on different layers to migrate and merge to form a kink band between two kink band boundaries of opposite sign (c). The elastic c-axis strain energy becomes permanent strain on the formation of mature through-going kink bands. This may produce the kinked microstructures common in micas from viscously deformed rocks. Parts of a biotite lattice that have experienced a stress field similar to b but in which kinking has not been induced still contain stored elastic c-axis strain energy in the form of ripplocations. This energy is released on thinning for TEM analysis in the form of conjugate arrays of expansion structures and delaminations, which facilitate a grain-scale c-axis parallel expansion (d). This is represented by the structures shown in Fig. 2 of this study