Multi-Stage Magmatic Evolution in the Central Urumieh–Dokhtar Magmatic Arc (NE Saveh, Iran): Evidence from Zircon U-Pb Dating, Lu-Hf Isotopes, and Whole-Rock Geochemistry

The Cenozoic plutonic assemblages exposed in northeast Saveh, located within the central segment of the Urumieh–Dokhtar Magmatic Arc (UDMA) in Iran, include monzonite, monzodiorite, gabbro, and gabbrodiorite lithologies. Integrated zircon U-Pb geochronology, Lu-Hf isotopic analysis, and whole-rock geochemistry reveal that these rocks belong to a medium-K calc-alkaline, metaluminous suite with typical arc-related geochemical signatures. Zircon U-Pb ages ranging from ~60 to 3 Ma point to a long-lasting and multi-phase magmatic evolution from the Middle Paleocene to the Middle Pliocene. Contrary to earlier studies suggesting a prolonged magmatic lull between 72–57 Ma, our results indicate a shorter dormancy period (~10–12 Ma). Three major magmatic pulses are identified: in the Late Eocene (~47–40 Ma), Early Miocene (~23–18 Ma), and Late Miocene to Pliocene (~11–5.2 Ma), all reflecting a subduction-related tectonomagmatic setting. The youngest zircon ages (~11–2.5 Ma) from gabbroic units suggest that magmatism continued up to the Pliocene–Pleistocene boundary, likely linked to ongoing subduction processes shaping the Zagros orogen. Zircon εHf(t) values (−11.43 to +12.5) along with geochemical trends indicate magma generation involving fractional crystallization, assimilation of crustal material, and mantle-derived inputs. Crystallization temperatures of clinopyroxene (1150–1200 °C), coupled with trace element data, support a melt source in a metasomatized spinel-bearing lherzolitic mantle at depths shallower than 80 km. This magmatism was likely driven by asthenospheric upwelling and slab rollback, which induced partial melting of the lithospheric mantle and sustained the region’s long-lived magmatic activity.