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Abstract
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Over 90% of the porphyry deposits are found at convergent margins, especially above active subduction zones, with much fewer occurrences at post-collisional or other tectonic settings. Porphyry Cu deposits are essentially magmatic–hydrothermal systems, which are generally initiated by injection of oxidized magmas saturated with metal-rich aqueous fluids, i.e., the parental magmas need to be water rich and oxidized with most of the sulfur appearing as sulfate in the magma. The Cenozoic magmatic arcs of Iran, built on mature continental crust, are an excellent candidate for studying the geochemical-isotopic feedback of magmatic pulses to understand the triggers for a flare-up. Our new data constrain the timing of the flare-up in NE Iran to the Early to Middle Eocene (51–43 Ma). This flare-up is characterized by the outpouring of high-K calc-alkalic to shoshonitic magmas at 110 ± 8 km3/myr - km. Crustal thickness influences the longevity of lower crustal magma reservoirs and the sulfide saturation history. For example, in thick crust, prolonged magma activity with hydrous and oxidized evolving magmas increases ore potential, whereas thin crust favors high chalcophile element fertility, owing to late sulfide saturation. A shallow depth (<7 km) of fluid exsolution might play a role in increasing Au precipitation efficiency, as immiscible sulfide melts act as a transient storage of chalcophile metals and liberate them to ore fluids. Future studies should aim to identify the predominant sulfide phases in felsic systems to determine their influence on the behavior of chalcophile elements during magma differentiation. Exhaustion of mantle sulfides during partial melting in the mantle wedge, metasomatized by slab-derived oxidizing fluids and/or melts, can increase the ore potential by increasing initial Cu and Au contents of hydrous basaltic magmas. The mantle-derived magmas then undergo differentiation in multi-depth reservoirs in the mid to lower crust (∼30–70 km), where th
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