In geology, shearing often occurs where tectonic plates slide past one another (plate tectonic movement). This is known as plate tectonic deformation or faulting.
During shearing, rocks are subject to both tensile and compressive forces. This results in a shear zone which is an area of more highly strained rock. Shear zones can be small or large, and may be isolated or extend over a wide area. Typically they form along the boundaries of tectonic blocks and are a key part of the deformation of orogenic belts. Shear zones host en echelon veins and are the source of ore deposits in many areas.
In most shear zones a dextral shear foliation forms and is defined by the shear sense. This shear foliation is accompanied by a C-plane or cisaillement plane which is parallel to the shear zone and defines the flattened long axis of the strain ellipse. These shear fabrics are observed in a wide variety of rocks and are diagnostic for the direction of shear sense.
A shear zone can be described as a tabular to sheetlike zone that is more highly strained than rocks adjacent to it. Shear zones are sometimes difficult to map as they can develop into a series of en echelon veins and folds, or even disappear altogether.
A common problem with metal shearing is 'twist' which is the tendency of the sheared material to curl into a corkscrew shape. This is usually caused by excessive rake angle on the shear and is easy to prevent by ensuring that the blade gap is set correctly for the type of material and thickness being sheared.