TURKIC-TYPE OROGENY AND ITS ROLE IN THE MAKING OF THE CONTINENTAL-CRUST

Turkic-type orogeny is a class of collisional mountain building, in wh ich the precollision history of one, or both, of the colliding contine nts involves the growth of very large, subcontinent-size subduction-ac cretion complexes, into which magmatic are axes commonly migrate and t hus enlarge the continent to which they are attached. A review of the evolution of two Phanerozoic (Altaids, Nipponides), one Neoproterozoic (East African), and one Archean (Yilgarn) Turkic-type orogens shows t hat this type of orogeny may have been the principal builder of the co ntinental crust through recorded Earth history. The total juvenile mat erial added to Turkic-type orogens at any one time in the Phanerozoic seems close to 1 km(3)/year, which about equals the amount of material annually fed into the mantle at subduction zones. As some 0.02 to 0.0 3% of that material is generally agreed to return to the crust by are magmatism, these figures provide a minimum net growth rate for the con tinental crust during the Phanerozoic.