Shear zones are microscopic to regional scale domains across which displacement has occurred. Brittle, brittle-ductile, or ductile deformation processes occur in shear zones at shallow, intermediate, or deep levels in the crust, respectively.

In brittle shear zones (equivalent to fault zones), displacement occurs on discrete fracture surfaces. In brittle-ductile shear zones, all or portions of the zone may undergo both ductile and brittle deformation. Displacement across brittle-ductile shear zones can be accommodated by oblique, en échelon stepping extensional veins (tension fractures) and/or shear fractures in addition to through-going shears parallel to zone boundaries. Extensional veins may be subsequently deformed into sigmoidal shapes (S shapes) and cut by younger veins. The sense of stepping of veins and their sigmoidal shape is used to determine the sense of displacement. Folds within transcurrent brittle-ductile shear zones (i.e., where displacement across steeply dipping shear zones is sub-horizontal) are...