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  • Author or Editor: Darko Tibljaš x
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K-Ar age data of illite-K-white mica-rich, <2 µm grain size fraction samples were determined on various lithotypes of the Paleozoic-Mesozoic, very low- to low-grade metamorphic complex, the Jurassic ophiolitic mélange and the Cretaceous-Paleocene sedimentary sequence of Mt. Medvednica, Croatia. K-Ar ages of the high-temperature anchizonal-epizonal Paleozoic-Mesozoic complex scatter around ca. 110 Ma for slates, phyllites and marbles with phyllite intercalations, while they are significantly younger (ca. 80 Ma) for metavolcanoclastic rocks that are devoid of detrital K-white mica. Beside the Cretaceous (Alpine) K-Ar radiometric age data, no evidence of a possibly older, Variscan metamorphic event was detected. In the Jurassic ophiolitic mélange and the Cretaceous-Paleocene sequence the obtained mixed isotopic age data do not provide reliable estimates for the age of the diagenetic alterations. In the Paleozoic and Mesozoic formations from the Bükk, Szendrõ and Uppony Mts. (NE Hungary) and in the Paleozoic rocks series from the Internal Dinarides, similar Alpine (Cretaceous) K-Ar ages were determined. These data may suggest metamorphic processes related to the subduction of the Dinaridic oceanic crust beneath Eurasia accompanied by compressional crustal thickening.

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