Classic models of orogens involve a Wilson cycle of ocean opening and closing with orogenesis related to continent-continent collision. Such models fail to explain the geological history of a significant number of orogenic belts throughout the world in which deformation, metamorphism and crustal growth took place in an environment of ongoing plate convergence. These belts are termed accretionary orogens but have also been refereed to as non-collisional or exterior orogens, Cordilleran-, Pacific-, Miyashiro-, and Turkey-type orogens.
Accretionary orogens form at sites of subduction of oceanic lithosphere and consist of magmatic arcs systems along with material accreted from the downgoing plate and eroded from the upper plate. Accretionary orogens have been active throughout Earth history. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products and include Archean greenstone belts, the Paleoproterozoic Birimian orogen (W. Africa), the Arabian-Nubian shield (Pan African) and Paleozoic orogens in Asia. They are also major sites of consumption and reworking of continental crust through time (e.g. Andean margin) and understanding the balance between crustal generation and consumption in accretionary orogens is fundamental to resolving models of continental growth throughout Earth history. Orogenesis takes place through coupling across the plate boundary with strain concentrated in zones of mechanical and thermal weakening such as the magmatic arc and back arc region. Potential driving mechanisms for coupling include accretion of buoyant lithosphere (terrane accretion), flat slab subduction, and rapid absolute upper plate motion over-riding the downgoing plate.
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