Recycling of orogenic arc crust triggers porphyry Cu mineralization in Kerman Cenozoic arc rocks, southeastern Iran

Pre-collisional Eocene-Oligocene arc diorites, quartzdiorites, granodiorites, and volcanic equivalents in the Kerman arc segment in central Iran lack porphyry Cu mineralization and ore deposits, whereas collisional middle-late Miocene adakite-like porphyritic granodiorites without volcanic equivalents host some of the world's largest Cu ore deposits. Petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment. Ore-hosting Kuh Panj porphyry intrusions exhibit high Sr (>400 ppm), low Y (<12 ppm) contents, significant REE fractionation (La/Yb>20), no negative Eu anomalies (Eu/ Eu*≥1), and relatively non-radiogenic Sr isotope signatures (87Sr/86Sr=0.7042-0.7047), relative to Eocene-Oligocene granitoids (mainly Sr<400 ppm; Y>12; La/Yb<15; Eu/Eu*<1; 87Sr/86Sr=0.7053-0.7068). Trace element modeling indicates peridotite melting for the barren Eocene-Oligocene intrusions and a hydrous garnet-bearing amphibolite source for middle-late Miocene ore-hosting intrusions. The presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30-35 to 40-45 km or 12 kbar. The changes in residual mineralogy in the source of Eocene to Miocene rocks in the Kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel. Underplating of Cu and sulfur-rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust-mantle boundary, and dehydration melting under oxidizing conditions produced syn- and post-collisional ore-hosting intrusions, while the lack of post-collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur-rich and oxidized adakitic magmas. © Springer-Verlag 2008.