Accretionary orogens form at intraoceanic and continental margin convergent plate boundaries. They include the supra-subduction zone forearc, magmatic arc and back-arc components. Accretionary orogens can be grouped into retreating and advancing types, based on their kinematic framework and resulting geological character. Retreating orogens (e.g. modern western Pacific) are undergoing long-term extension in response to the site of subduction of the lower plate retreating with respect to the overriding plate and are characterized by back-arc basins. Advancing orogens (e.g. Andes) develop in an environment in which the overriding plate is advancing towards the downgoing plate, resulting in the development of foreland fold and thrust belts and crustal thickening. Cratonization of accretionary orogens occurs during continuing plate convergence and requires transient 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 overriding the downgoing plate. Accretionary orogens have been active throughout Earth history, extending back until at least 3.2 Ga, and potentially earlier, and provide an important constraint on the initiation of horizontal motion of lithospheric plates on Earth. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products but are also major sites of consumption and reworking of continental crust through time, through sediment subduction and subduction erosion. It is probable that the rates of crustal growth and destruction are roughly equal, implying that net growth since the Archaean is effectively zero.Classic models of orogens involve a Wilson cycle of ocean opening and closing with orogenesis related to continent-continent collision. These imply that mountain building occurs at the end of a cycle of ocean opening and closing, and marks the termination of subduction, and that the mountain belt should occupy an internal location within an assembled continent (supercontinent). The modern Alpine -Himalayan chain exemplifies the features of this model, lying between the Eurasian and colliding African and Indian plates (Fig.

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GraphicalabstractCondensed timetable of major geologic events in the East African Orogen. Opening of the Mozambique Ocean and formation of rift basins in Zambia, Malawi, Mozambique and SW Madagascar was accompanied by emplacement of anorthosite melt in extending crust. A first phase of ocean closure and accretion of terranes defines the East African Orogeny. The second orogen phase, Kuungan Orogeny, mainly affected the southern parts of east Africa and Madagascar. Both shortening events were followed by extension phases that were accompanied by emplacement of late- to post-tectonic granitoids. EGCD: Eastern Granulite–Cabo Delgado Nappe Complex; Madag: Madagascar; Ub–Us: Usagaran/Ubendian Belts; WG: Western Granulite Belt; IB (Z–M): Irumide Belt of Zambia and Malawi; IB (M): Irumide Belt of Mozambique.

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We report a thick, laterally extensive 2505 +/- 2.2-million-year-old (uranium-lead ratio in zircon) Archean ophiolite complex in the North China craton. Basal harzburgite tectonite is overlain by cumulate ultramafic rocks, a mafic-ultramafic transition zone of interlayered gabbro and ultramafic cumulates, compositionally layered olivine-gabbro and pyroxenite, and isotropic gabbro. A sheeted dike complex is rooted in the gabbro and overlain by a mixed dike-pillow lava section, chert, and banded iron formation. The documentation of a complete Archean ophiolite implies that mechanisms of oceanic crustal accretion similar to those of today were in operation by 2.5 billion years ago at divergent plate margins and that the temperature of the early mantle was not extremely elevated, as compared to the present-day temperature. Plate tectonic processes similar to those of the present must also have emplaced the ophiolite in a convergent margin setting.