Rocks can deform in two main ways: brittlely or ductilely. Brittle deformation occurs when rocks break or fracture under stress. Ductile deformation occurs when rocks bend or flow under stress. The type of deformation that occurs depends on a number of factors, including the type of rock, the temperature and pressure conditions, and the rate at which the stress is applied.
Brittle deformation is most common in the upper crust of the Earth, where the temperature and pressure conditions are relatively low. Brittle deformation can produce a variety of features, including:
- Faults: Faults are fractures in rocks along which there has been displacement. Faults can be caused by a variety of stresses, including compression, tension, and shear.
- Joints: Joints are fractures in rocks that do not show any displacement. Joints are often caused by cooling or drying of rocks.
- Breccia: Breccia is a type of rock that is made up of angular fragments of other rocks. Breccia is often formed by brittle deformation of rocks.
Ductile deformation is most common in the lower crust and mantle of the Earth, where the temperature and pressure conditions are relatively high. Ductile deformation can produce a variety of features, including:
- Folds: Folds are bends in rocks. Folds can be caused by a variety of stresses, including compression and tension.
- Foliation: Foliation is a layering that can be seen in some metamorphic rocks. Foliation is caused by the alignment of minerals in the rock during ductile deformation.
- Lineation: Lineation is a linear feature that can be seen in some metamorphic rocks. Lineation is caused by the alignment of minerals or elongated grains in the rock during ductile deformation.