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Alpine (Cretaceous) very low- to low-grade metamorphism recorded on illite fraction from South Tisia (eastern Mt. Papuk, Croatia

Alpine very low- to low-grade metamorphism related to Cretaceous orogenesis has been investigated in the Slavonian Mts., Croatia. Samples belonging to the Psunj metamorphic complex (PMC), Radlovac metamorphic complex (RMC) and clastic-carbonate succession of the Late Permian to Early Triassic age i.e. Permian-Triassic sedimentary sequences (PTSS) were studied. Kübler and Árkai indices of all analysed samples indicate high temperature anchizonal to epizonal conditions of thermal alteration (~300°C). The degree of thermal alteration tends to be constant in all measured samples implying that different complexes passed through and recorded the same event. Measurements of b0-parametar of samples belonging to the RMC imply transitional low-medium pressure metamorphism. K-Ar ages measured on <2 μm fraction indicate Late Cretaceous very low-grade metamorphism of PTSS as well as Late Cretaceous overprint of older Paleozoic metamorphic rocks (PMC and RMC). No considerable systematic or gradual variation between the K-Ar age of <2 μm fraction and metamorphic indicators of analysed samples, regardless to the stratigraphy, was observed. All these data together with K-Ar ages measured on <2 μm fraction point to Late Cretaceous very low- to low-grade regional metamorphism related to the Austrian and/or Subhercynian phase of Alpine orogeny that were responsible for the main nappe-forming compressional events in the Pannonian Basin area and the Carpathians. Metamorphic and geochronological evolution of the studied area is in good agreement with similar scenario for the surrounding area of Tisia, but also from ALCAPA.

Alpine; Cretaceous; very low-grade; low-grade; metamorphism; illite fraction; Tisia; Papuk; Croatia

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