ROLE OF DISCRETE HETEROGENEITIES AND LINEAR FABRICS IN THE FORMATION OF CRENULATIONS

The fabric elements in pelitic rocks of Brioverian age in South Finistere (France) consist of three main components; planar, linear and discrete, corresponding to schistosity, elongate mineral alignment and porphyroblast distribution respectively. Each component plays a role in the initiation, propagation and evolution of crenulations which deform the planar anisotropy. Strain associated with the initiation of crenulation is heterogeneous on the thin section scale, producing spatially associated, contemporaneous microshears and kink-structures. The influence of porphyroblasts becomes increasingly evident as crenulation develops and microshearing becomes the dominant mode of deformation. Linear fabric appears to influence the orientation of crenulation structures and slip directions on microshear planes. © 1979.