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New data on metamorphic event in the eastern part of Mt. Papuk, Slavonia, Croatia

K-Ar dating was performed on whole rock, <6&#956; m and <2&#956; m fractions of nine samples from Papuk Mountain located in Slavonia, the northeastern region of Croatia. This research is based on studies concerning the Radlovac metamorphic complex and the Kutjevo transect (including sedimentary rocks and Psunj metamorphic complex). The whole rock XRPD analyses yields quartz, illite-muscovite and plagioclase in all samples. Additionally, hematite, chloritoid, chlorite, K-feldspar and pyrophyllite were found in some samples. Kübler index values indicate thermal alterations at 300-350°C. Systematic difference observed between ages of whole rock and phyllosilicate fractions is due to prolonged formation of the clay minerals (EBERL et al., 1990). Similar age differences recorded on different size fraction have been reported from Carpathian basin by ÁRKAI et al. (1995). The prolonged clay mineral formation took place below the closure temperatures of most mineral constituents of the rock. Finer-grained fractions gave lower ages, because they contain newly formed minerals in greater proportion. The measured K-Ar age is the average value of mineral ages when whole rock samples are dated or average value of illitic minerals in a grain size range. This suggests that the oldest K-Ar ages constrain the lowest age for the metamorphic event which reset all mineral ages in the dated rock. The youngest ages (measured on <2&#956; m fractions) set the oldest limit for the termination of illite formation.

K-Ar dating; metamorphism; illite; Papuk; Slavonia; Croatia

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