Magmatic evolution and mineralization of the Eocene back-arc magmatic rocks from NE Iran

• Eocene back-arc magmatism in NE Iran shows distinct magma evolution paths. • Torud magmas are juvenile, hydrous, and linked to Cu-Au porphyry mineralization. • Nokeh rocks formed from oxidized, evolved magmas associated with Fe-rich skarns. • Zircon trace elements and Hf isotopes distinguish crust-mantle melt contributions. • Magmatic differences reflect temporal shifts in slab rollback and mantle input. The Eocene magmatism in NE Iran represents a significant component of the broader Cenozoic magmatic activity associated with the subduction of the Neotethys Ocean beneath the Iranian plateau. This study focuses on the petrogenesis, geochronology, and mineralization of magmatic rocks from the Nokeh area, which hosts Fe-skarn mineralization, in comparison with the Torud intrusions, associated with Cu-Au mineralization. Both sites are located in the northeastern sector of the Iranian back-arc belt, behind the Urumieh-Dokhtar magmatic front. Our comprehensive dataset includes bulk rock geochemistry, zircon U-Pb ages, zircon trace element compositions, and Lu-Hf isotopes. Geochemical and isotopic signatures indicate that Torud rocks are predominantly intermediate to felsic, derived from a metasomatized mantle source with limited crustal interaction, whereas Nokeh rocks display broader compositional diversity (e.g., zircon Hf isotope) and higher degrees of crustal assimilation. Zircon U-Pb dating constrains magmatic activity in Nokeh between 53 and 52 Ma, coeval with Eocene arc-backarc magmatism across Iran. Zircon trace element compositions and Hf isotope data further reveal distinct melt evolution pathways at each site. These differences in magmatic evolution correlate with contrasting mineralization styles: iron-rich skarn formation in Nokeh versus Cu-Au porphyry-style mineralization in Torud. The results provide new insights into the spatial and temporal variation of Eocene back-arc magmatism and its control on the metallogenic fertility in NE Iran.