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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 °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 dating of monazite in the schists gave a weighted average age of 109.0±13.1 Ma (2 σ) eventually with three subgroups of ages at 225±63 (2 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.

Cretaceous, low-grade metamorphism, monazite, Slavonian Mountains, Tisia Mega-Unit

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