Permian Felsic Volcanism in the Tisza Mega-Unit (East-Central Europe): A Guadalupian Chronostratigraphic Marker Horizon

During the Late Paleozoic, several intramontane basins developed across the European Variscan Orogenic Belt in response to post-collisional to extensional geodynamic processes. These basins were filled with thick molasse-type successions dominated by siliciclastic deposits (mudstones to conglomerates) and continental red beds, constituting the Permo-Carboniferous lithostratigraphy of the Tisza Mega-unit (Carpathian–Pannonian region). However, these sedimentary formations almost entirely lack numerical age constraints, limiting stratigraphic subdivision and regional correlation; intercalated volcanic and volcaniclastic rocks, in contrast, provide datable horizons that we investigated to establish a robust temporal framework. Over the past decade, comprehensive petrographic, bulk-rock geochemical, and zircon U–Pb geochronological investigations have been carried out on Late Paleozoic mafic to felsic volcanic and volcaniclastic rocks from the Mecsek Mts (southern Transdanubia, Hungary), the western–central Apuseni Mts (Romania), and drill cores from southern Transdanubia and the eastern Pannonian Basin (Hungary). Petrographic observations indicate that the felsic rocks are predominantly crystal-rich dacitic to rhyolitic lapilli tuffs derived from large-volume explosive eruptions, while mafic to intermediate rocks represent lava flows and subvolcanic bodies. Although many samples were affected by post-magmatic alteration (e.g., hydrothermal metasomatism, low-grade metamorphism and deformation, mainly during the Cretaceous), petrogenetic interpretations based on immobile elements (e.g., high field strength elements) indicate an extensional, continental rift-related tectonic setting and suggest a broadly similar crustal source for all studied volcanic and volcaniclastic rocks. Zircon U–Pb dating of 19 distinct felsic samples from the three study areas yielded overlapping Guadalupian ages (~270–259 Ma). The consistency of ages, mineralogical features, and bulk-rock geochemical signatures supports the interpretation that these felsic pyroclastic rocks represent a regionally correlatable Middle Permian chronostratigraphic marker horizon. Importantly, these data provide the first robust numerical age constraints within the thick Permo–Carboniferous intramontane molasse successions of the Tisza Mega-unit. Comparable felsic volcanic and volcaniclastic rocks with similar geochemical characteristics and zircon ages have been reported from the Western Carpathians (ALCAPA Mega-unit, e.g., Gemeric and Silicic Units, Slovakia), indicating that this Guadalupian marker horizon is regionally significant within the Tisza Mega-unit and adjacent Western Carpathians, whereas Permian magmatism in more westerly parts of the stable European plate is generally older (~300–290 Ma). This study was funded by NRDIF projects K 131690 and K 108375, as well as by the New National Excellence Program (ÚNKP-18-3-I-SZTE-90) and the University Research Scholarship Programme (EKÖP-577-SZTE).