Orogen‐scale decollements

The continental lithosphere responds to stress by deforming as a generally layered medium. Deep seismic reflection data, coupled with a variety of ancillary geological and geophysical data, are interpreted to provide images of fault zones that tend to form moderately dipping ramp structures in mechanically rigid layers, and flat detachments in mechanically weak layers. This geometry is similar to ramp and flat structures observed at smaller scales in thrust and fold belts and leads to the interpretation that most orogens are underlain by orogen‐scale décollements in a manner that is analogous to so‐called “thin skin” deformation in sedimentary rocks. Décollements may occur within the crust (for example, near the base of a sedimentary section or in the middle crust), near the Moho, in the subcrustal lithosphere, or in the asthenosphere. Even intracratonic basement‐cored (“thick skin”) uplifts that occasionally occur in foreland regions such as the Wyoming province are probably large (crustal) scale versions of ramp/flat features observed in supracrustal rocks and are thus likely caused by the same fundamental tectonic processes.