Petrochronological study of chloritoid schist from the Medvednica Mts. (Croatia, Zagorje Mid-Transdanubian zone)

Abstract

A chloritoid schist from the Medvednica Mts. (Croatia, Zagorje-Mid-Transdanubian zone) is part of the metasedimentary succession of a Palaeozoic-Mesozoic Metamorphic Complex. The studied samples show the mineral association of chloritoid, chlorite, quartz and white mica. A P-T pseudosection, combined with modal and chemical isopleths, and classical thermobarometric calculations yield peak metamorphic conditions of 0.8 – 1.0 GPa at around 500 °C. Monazite in-situ dating with the electron microprobe results in an age of 156 ± 3 (2σ) Ma interpreted as dating monazite growth during prograde metamorphism. Laser ablation multicollector ICP mass spectrometry of U-Th-Pb isotope systematics in detrital zircon grains indicate a maximal deposition time of the sedimentary protolith in the Permian in accordance with published palaeontological records. The presented results are synchronous with the Late Jurassic obduction of a Neotethys-derived ophiolitic mélange onto a Permotriassic sedimentary sequence originated from the continental margin of Adria. This obduction caused regional collision metamorphism by thrusting Ophiolitic units (i.e. Neotethys) upon tectonic units of continental margin of Adria. Studied chloritoid schist is a part of the continental margin of Adria and is metamorphosed during collisional metamorphic event at upper greenschist-facies.