Eo-Alpine metamorphism in the Western Carpathians: evidence for a collisional metamorphic gradient coeval with along-strike subduction metamorphic gradient in the Eastern Alps

In this work, we report the Lu–Hf garnet age and associated pressure-temperature (PT) estimates, related to the Eo-Alpine event in the Western Carpathians. Dated garnet comes from Permian quartzite of the Foederata cover overlying the Variscan basement complexes in the southern part of the Vepor Unit. The quartzite contains quartz, garnet, paragonite intergrowths with muscovite, chlorite, sporadic albite, and ilmenite overgrown by rutile. Garnet shows a honeycomb microstructure with numerous quartz inclusions and slightly curved inclusion trails, suggesting its synkinematic growth. Garnet is dominated by almandine and grossular components with a slight rimward decrease in spessartine and increase in pyrope, indicating a prograde metamorphic evolution. Thermodynamic modelling performed in MAGEMin suggests an increase in PT conditions from ~7.5 kbar and ~545°C to ~12.5 kbar and ~590°C, based on the mineral assemblage and core to rim compositional zoning of garnet. The resulting Lu–Hf garnet age obtained by MC–ICP–MS indicates 101.9 ± 2.7 Ma. This age shows an excellent match with recent Lu–Hf garnet ages obtained for eclogites in the along-strike Eastern Alps and interpreted to date the Eo-Alpine intracontinental subduction. The PT conditions of the Eo-Alpine metamorphism in the Vepor Unit, however, point to the intermediate metamorphic gradient typical for continental collision. Our results thus imply coeval collisional thickening in the Western Carpathians and continental subduction in the Eastern Alps.