Petrogenesis and geodynamics of the Early Miocene Kashan granitoids in the central Urumieh-Dokhtar Magmatic Arc, Iran

The early Miocene granitoids from the Kashan area, located in the central Urumieh-Dokhtar Magmatic Arc of Iran, were investigated to provide essential insights into the sources of and geodynamic processes responsible for their formation. We present zircon U–Pb ages, zircon Hf isotopic data, and whole-rock geochemistry of rhyolites, dacites, granodiorites, and diorites. The diorites yielded a zircon U−Pb age of 22 Ma. Geochemically, the diorites are characterized by low Sr (258.0–289.5 ppm) contents, low Sr/Y (9.04–9.92) and (La/Yb) _N (4.42–6.05) ratios, and high Y (28.21–29.33 ppm) and Yb (2.94–3.09 ppm) contents, classifying them as non-adakitic rocks. They exhibit high-K calc-alkaline affinities, enrichment in light rare earth elements (LREEs) (La _N /Yb _N = 4.42–6.05), pronounced negative Nb-Ta anomalies, and negativeεNd(t) and εHf(t) values, ranging from − 3.6 to − 3.0 and − 3.5 to − 0.9, respectively. We therefore conclude that the diorites were derived from partial melting of an enriched subcontinental lithospheric mantle within the amphibole-bearing spinel stability field, which had been metasomatized by subduction-related fluids dehydrated from oceanic sediments. In contrast, the rhyolites, dacites, and granodiorites exhibit high Sr (377.2–595.4 ppm) contents, high Sr/Y (29.93–94.28) and (La/Yb) _N (13.48–51.21) ratios, and low Y (4.36–13.48 ppm) and Yb (0.35–1.42 ppm) contents, classifying them as adakitic rocks. They display high SiO ₂ (63.01–77.33 wt%) contents and low Mg ^# (29–47) values, along with highly fractionated rare earth element (REE) patterns with depletion in heavy rare earth elements (HREEs), consistent with generation by partial melting of the thickened lower crust. Based on the regional geology, together with the results of this study and previous works, we conclude that the diorites formed in a geodynamic processes associated with the initial collision between the Arabia and Eurasia plates related to the final breakoff of the subducted Neo-Tethys Ocean slab, whereas the adakitic rocks, rhyolites, dacites, and granodiorites, were generated in geodynamic processes related to the main collision between the Arabia and Eurasia plates.