Metallogeny and tectonic evolution of the Cenozoic Ahar–Arasbaran volcanic belt, northern Iran

Abstract

The Cenozoic Ahar–Arasbaran volcanic belt (AHAVB) in northern Iran is part of the Alborz–Azerbaijan magmatic zone, which developed along the southern margin of Eurasia. Upper Jurassic–Cretaceous flysch deposits and platform carbonates were deposited adjacent to this margin, are overlain by Eocene volcanic rocks, and are intruded by Oligo-Miocene, shallow-crustal to hypabyssal plutons that collectively make up the AHAVB. The volcanic and plutonic rocks have medium- to high-K, calc-alkaline to alkaline compositions and show similar geochemical features, indicating a common subduction-metasomatized continental lithospheric mantle source. Granodioritic, tonalitic, and quartz monzonitic plutons provided the heat flux and magmatic fluids that played a major role in the precipitation of porphyry, skarn, and epithermal copper, molybdenum, and gold deposits. The distribution of mineralization shows three major zones parallel to the general NW–SE trend of the AHAVB. Most of the major Cu ± Mo porphyry and skarn deposits occur in Zone A in the north, whereas porphyry and epithermal Cu, Au, and As deposits are present in Zone C in the south. Epithermal Au mineralization occupies a narrow, intermediate Zone B. NW-trending transtensional fault systems locally control the distribution of both late-stage volcanism and mineralization. Cenozoic magmatism and attendant mineralization in the AHAVB were a result of post-collisional, slab breakoff-induced heat and fluid flow from upwelling asthenosphere beneath the young orogenic belt. Magmatically induced transient increase in the geothermal gradient and associated extensional deformation weakened the orogenic crust and produced enhanced permeability, facilitating the emplacement of granodioritic to monzonitic plutons at shallow crustal depths as well as the associated mineralization.