Detachment fault

A detachment fault is a gently dipping normal fault associated with large-scale extensional tectonics. Detachment faults often have very large displacements (tens of km) and juxtapose unmetamorphosed hanging walls against medium to high-grade metamorphic footwalls that are called metamorphic core complexes. They are thought to have formed as either initially low-angle structures or by the rotation of initially high-angle normal faults modified also by the isostatic effects of tectonic denudation. They may also be called denudation faults. Examples of detachment faulting include:

• The Snake Range detachment system of the Basin and Range Province of western North America which was active during the Miocene
• The Nordfjord-Sogn detachment of western Norway active during the Devonian Period
• The Whipple detachment in southeastern California

Detachment faults have been found on the sea floor close to divergent plate boundaries characterised by a limited supply of upwelling magma, such as the Southwest Indian Ridge. These detachment faults are associated with the development of oceanic core complex structures.