Crustal Decoupling in Collisional Orogenesis: Examples from the East Greenland Caledonides and Himalaya

Mature orogenic systems built by continent-continent collision feature orogenic plateaus flanked by accretionary wedges. Thermal-mechanical models of these systems predict the development of a thermally weakened orogenic infrastructure that is capable of lateral flow toward the orogenic foreland. Such flow, if it occurs, strongly influences the evolutionary pathway of a wedge. Although the architecture of a wedge features numerous large-displacement faults, three are preeminent in mature orogens: one that marks the base of the wedge and two others that mark the base and top, respectively, of the weakened infrastructure. These structures represent major decoupling horizons separating domains with distinctive deformational and thermal histories. Reviews of the geology of orogenic wedges in two mature orogenic systems-the Cenozoic Himalaya and the Paleozoic East Greenland Caledonides-show how this simple conceptual model provides a valuable context for studies of how collisional orogenic systems develop and how they interact with the surrounding lithosphere.