Alpine metamorphism of low-grade schists from the Slavonian Mountains (Croatia): new P-T and geochronological constraints

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 degrees C and 4.6-6.0 kbar for a sample from Kutjevo (eastern part of the study area) and 450-460 degrees 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 +/- 13.1Ma (2 sigma) eventually with three subgroups of ages at 225 +/- 63 (two analyses), 114 +/- 24 and 83 +/- 22Ma. We conclude that the metamorphism of the studied schists at depths of c. 20km is due to an Alpine collisional event.