The Eocene to Miocene Urumieh-Dokhtar Magmatic Arc (UDMA), Iran, hosts numerous porphyry Cu deposits including the large Sarcheshmeh and Miduk deposits. The formation of porphyry intrusions with economic ore deposits is restricted to the Miocene arc magmatism in the southeast. In this study, a compiled arc-wide geochemical dataset of Eocene-Miocene magmatic rocks was combined with new whole-rock geochemical and isotopic data from Sarcheshmeh and Miduk drill cores to decipher the magmatic evolution of the UDMA. Two magma series with typical subduction zone-related geochemical signatures exist in the UDMA, which both range from ~50 to 75 wt.% SiO2 implying magma formation in the mantle followed by crystal fractionation. The Eocene-Oligocene magmatic rocks along the entire arc and Miocene rocks in the central UDMA are calc-alkaline and characterized by Dy/Yb systematics indicating amphibole fractionation. By contrast, Miocene magmatic rocks in the southeastern UDMA have high La/Yb and Sr/Y resembling adakitic compositions. These were previously attributed to garnet fractionation due to extensive crustal thickening during continent collision in this region. However, we do not find evidence for garnet fractionation in the Sarcheshmeh and Miduk samples, nor did residual garnet affect partial melting in the mantle, which is consistent with pressure conditions corresponding to a crustal thickness of ~45km in this region. The compositions of the UDMA magmatic rocks suggest a sediment component derived from the subducted slab, with the high La/Yb and Sr/Y of the Miocene porphyry rocks possibly reflecting either slab melts of sediments with residual garnet or variable degrees of melting.