Age and origin of monzogranites from the Kosmaj Mts. (central Serbia): new constraints on post-collisional magmatism in the Internal Dinarides

We present new constraints on post-collisional magmatism in the Internal Dinarides based on a study of the monzogranite intrusion exposed along the southwestern flank of the Kosmaj Mts. in central Serbia. The studied rocks are calc-alkaline granitoids composed predominantly of K-feldspar, plagioclase, quartz, biotite, and amphibole. Amphibole–plagioclase thermobarometry yields crystallization temperatures of 774–831 °C and pressures of ~1.6–2.6 kbar, indicating emplacement at shallow upper-crustal levels. Zircon U–Pb analyses define a concordant age of 24.92 ± 0.31 Ma, constraining emplacement to the latest Oligocene. Zircon Lu–Hf isotopic compositions (εHf(t) = −1.2 to +7.0) indicate a dominantly juvenile magma source with limited crustal contribution. The Kosmaj monzogranite is assigned to the Oligocene I-type granitoid suite, interpreted as the product of Neotethyan slab break-off beneath the Dinarides, which triggered asthenospheric upwelling, enhanced heat flux, and generation of mantle-derived melts variably modified by crustal assimilation.