Eocene non-mineralization to Miocene porphyry copper mineralization-related magmatism in the Urumieh–Dokhtar magmatic arc, Iran

Abstract

The Saveh-Yazd porphyry copper (the middle segment) and the Kerman porphyry copper (the Southeastern segment) belts of the Urumieh–Dokhtar Magmatic Arc (UDMA) in Iran consist of two Eocene and Miocene magmatic flare-ups and coincide with barren and ore-bearing intrusions, respectively. The Eocene barren intrusions show characteristics of high-K calk-alkaline to shoshonitic, normal arc and composed of amphibole and plagioclase fractionation during the Eocene magmatism. Base on trace element–REE contents and ratios, the Eocene magmas were mainly derived from lithospheric mantle and enriched by the melt-component of subducted slab. Also, the geochemical data (e.g., Eu/Eu*, La/Yb, Y contents and Sr-isotope compositions) indicate that Eocene magmas formed during crustal thinning and had low water contents content and oxidized. Subsequent the Miocene ore-bearing intrusions exhibited features of calc-alkaline to high-K calc-alkaline, adakite-like and amphibole with minor amount of garnet fractionation in the absence of plagioclase during Miocene magmatism. These ore-bearing intrusions derived from partial melting of a thickened and delaminated juvenile lower crust intruded by mantle material of the underlying metasomatized lithospheric mantle during the Miocene in a post-collision tectonic setting. Progressive trends of crustal thickening were recognized in the middle (Saveh-Yazd porphyry copper belt) to southeastern segment (Kerman porphyry copper belt belt) in the UDMA from the early to middle Miocene. Also, magmas tend to be more hydrous and oxidized associated with increasing crustal thickness. These trends probably explain cause of occurrence of major porphyry copper deposits mostly along the Kerman porphyry copper belt and in the middle Miocene epoch.