The missing late Cretaceous magmatic arc in the Arabia-Eurasia collision zone (NW Iran): constraints from zircon geochronology, Hf isotopes, and geochemistry

The Late Cretaceous magmatic evolution of northwestern (NW) Iran reveals a previously unrecognized continental arc system, the Azerbaijan Continental Magmatic Arc, herein termed the Azerbaijan Continental Magmatic Arc, which is largely obscured by subsequent tectonic overprinting, erosion, and basin burial. Integration of new zircon U-Pb ages, Lu-Hf isotopic data, and whole-rock geochemical compositions from volcanic and plutonic rocks in the Misho, Sufian, Moro, Amand, Vanyar, and Iskandar regions identifies a subduction-related arc system distinct from the Sanandaj–Sirjan and Urumieh–Dokhtar magmatic belts. The ∼ 101–97 Ma gabbros and granodiorites record ε_Hf(t) values from + 9.8 to −7.2, reflecting variable mantle and crustal inputs. Arc-like trace-element patterns, including LREE enrichment and subduction-related anomalies, together with structural alignments along the Siah Cheshmeh–Khoy–Misho–Tabriz Fault (SKMT), indicate arc magmatism contemporaneous with transpressional deformation. The magmatic series evolved from juvenile tholeiitic to enriched shoshonitic compositions, tracking increasing crustal assimilation and slab rollback. This flare-up event represents a transient phase of Neo-Tethyan subduction, later overprinted by Eocene intrusions of the Urumieh–Dokhtar Magmatic Arc. Collectively, these results highlight the cryptic preservation of continental arcs and propose that the SKMT Fault marks a concealed suture accommodating Late Cretaceous arc migration and back-arc basin development in NW Iran.