Shear Zones

Abstract

AbstractShear zones are tabular bodies of rock that accommodate the bulk or whole deformation so that there is practically no or less deformation outside this zone. As such, they constitute anisotropy in a rock mass. An ideal shear zone is bounded by two parallel surfaces. Shear zones can occur in any rock type and can develop in various geologic settings, commonly in contractional, extensional and strike-slip settings. Most shallow-level faults continue at deeper levels where they form ductile shear zones containing rocks deformed under high temperature-pressure conditions and over a wide zone ranging up to tens of kilometres. Shear zones are characterized by the occurrence of some typical rocks because deformation pattern within a shear zone is different from that of the outside rocks. Common brittle shear zone rocks include breccia, cataclasite and gouge while those of ductile shear zones include mylonite. Large-scale ductile shear zones are characterized by progressive development of crystallographic preferred orientation (CPO) of their minerals, mainly quartz. Formation of shear zones depends upon the mechanisms that are able to localize strains in a narrow zone. Most shear zones grow in length and thickness over time. We take you through this chapter to explore the concept of shear zones, their geometry, rock types, classification, formation and significance.KeywordsShear zoneBrittle shear zoneDuctile shear zoneBrecciaCataclasiteMyloniteMylonitic foliationShear heatingGeometrical softening