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

Turkic-type orogeny is a class of collisional mountain building, in which the precollision history of one, or both, of the colliding continents involves the growth of very large, subcontinent-size subduction-accretion complexes, into which magmatic arc axes commonly migrate and thus 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 that this type of orogeny may have been the principal builder of the continental crust through recorded Earth history. The total juvenile material added to Turkic-type orogens at any one time in the Phanerozoic seems close to 1 km³/year, which about equals the amount of material annually fed into the mantle at subduction zones. As some 0.02 to 0.03% of that material is generally agreed to return to the crust by arc magmatism, these figures provide a minimum net growth rate for the continental crust during the Phanerozoic.