Low-grade schists from the Slavonian Mountains (Tisia Mega-Unit, Mt Papuk, Croatia), previously assigned to Precambrian to Lower Palaeozoic metamorphism, have been subjected to geochemical investigations, P-T modelling, and in situ age dating of monazite. The studied fine-grained metasediments consist of chlorite (5–15 vol.%), K white-mica (40–55 vol.%), quartz (20–35 vol.%), feldspar (albite 15–20 vol.%), opaques (<2 vol.%), and accessory minerals. According to their whole-rock geochemistry, the detritus of the former sediments came from upper crustal felsic rocks as they occur, for instance, at Mt Papuk. The schists show a complex microtectonic fabric, including well-developed schistosity systems. P-T pseudosections in the system MnNCKFMASHTO, constructed for typical schists of the study area, resulted in peak P-T conditions of 445–465 °C and 4.6–6.0 kbar for a sample from Kutjevo (eastern part of the study area) and 450–460 °C and 5.2–6.0 for a Vranovo sample (western part). Electron microprobe (EMP) dating of monazite in the schists gave a weighted average age of 109.0 ± 13.1 Ma (2σ) eventually with three subgroups of ages at 225 ± 63 (two analyses), 114 ± 24 and 83 ± 22 Ma. We conclude that the metamorphism of the studied schists at depths of c. 20 km is due to an Alpine collisional event.

The Slavonian Mts. (including Mt. Papuk), located in the southwestern part of the Pannonian Basin in Croatia, consist mostly of a pre-Alpine crystalline basement made of igneous and metamorphic rocks (Tisia Mega-Unit). However, at the Trešnjevica geosite from Mt. Papuk (Papuk UNESCO Global Geopark), dike swarms of igneous rocks cut through migmatitic gneiss and granitoid from the Variscan basement. These younger rocks are classified as basalt, andesite and rhyolite. Their mineral assemblage and chemical composition reflect the high-temperature, dry and oxidised nature of magmas typical of a divergent tectonic setting (A-type for the acidic varieties). Accessory zircon from four rhyolite and one andesite sample was used to unveil the timing of the magmatic event and constrain the origin of the parental magma. Zircon dating (LA-ICP-MS) reveals a Late Cretaceous (between 81.1±1.1 and 81.5±1.1 Ma) and brief (< 3 Ma) magmatic pulse. The geochemical record of zircon (trace elements and Hf isotopes) indicates a magmatic origin as an early crystallised phase in a deep magma chamber at relatively high (~850 °C) and constant temperature. The parental magma was derived either directly from melting of a metasomatized mantle or from re-melting of mafic lower crust extracted from mantle earlier. The new zircon data support previously proposed geodynamic models, which suggest the formation of deep rifts and melting in a late-orogenic setting during the Late Cretaceous closure of the Neotethys Ocean. The ultimately mantle-derived melt underwent extensive fractional crystallisation and evolved towards a rhyolitic composition during its ascent through the slightly thickened crust (up to 42 km).