Cenozoic porphyry and other hydrothermal ore deposits along the South Caucasus-West Iranian tectono-magmatic belt: A critical reappraisal of the controlling factors

In this contribution, we investigate the space and time distribution of the Cenozoic magmatism and the asso-ciated porphyry Cu-Mo +/- Au and other hydrothermal (mostly epithermal) ore deposits along the south Caucasus -west Iranian tectono-magmatic belt. We use a comprehensive georeferenced database containing whole-rock and geochronological analyses of 3150 samples from the igneous rocks distributed in the study area. Overall, the timing of the ore deposits overlaps with the timing of the Eocene to Miocene diachronous collision between the Arabia and Eurasia plates. This is associated with a change in the geochemical fingerprints of the magmas during and after collisional thickening, with a marked increase in Sr/Y values associated with a general transition to-wards adakitic signatures. This is interpreted with a change towards an amphibole-(+/- garnet) rich residue at the arc roots. Clusters of ore mineralization are observed within areas of long-lived magmatism (lasting >10 Myr), usually located at the intersections of basement fault zones, parallel and orthogonal to the collisional boundaries and likely formed along inherited zones of crustal/lithospheric weakness. The isotopic data of the ore-forming magmas show a pronounced correlation with young (<0.7 Ga) Nd depleted mantle model ages (TDMNd) and (87Sr/86Sr)i isotopic ratios ranging from-0.704 to-0.706. This evidence attests to post-Cadomian metal-and volatile-rich sources at crust roots, during incremental magmatic underplating. We suggest that optimum con-ditions to form clusters of ore deposits along the collisional zone are achieved when passive asthenosphere upwelling along slab windows (or induced by lithosphere delamination and/or slab break-off) causes the partial melting of the fertile arc roots in the amphibole +/- garnet stability field. The end of mineralization along the west Iran magmatic belt is associated with crust overthickening (as evidenced by the inferred presence of a garnet -dominated residue), either as a consequence of consumption of the fertile metal-enriched sources or after the total removal/foundering of the arc roots.