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New K-Ar Age Data on the Alpine, Low-temperature Regional Metamorphism of Mt. Medvednica (Croatia) (CROSBI ID 509292)

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Judik, Katalin ; Balogh, Kadosa ; Tibljaš, Darko ; Balen, Dražen ; Tomljenović, Bruno ; Pamić, Jakob ; Árkai, Peter New K-Ar Age Data on the Alpine, Low-temperature Regional Metamorphism of Mt. Medvednica (Croatia) // Abstracts book / Tomljenović, Bruno ; Balen, Dražen ; Vlahović, Igor (ur.). Zagreb: Hrvatski geološki institut, 2005. str. 47-48

Podaci o odgovornosti

Judik, Katalin ; Balogh, Kadosa ; Tibljaš, Darko ; Balen, Dražen ; Tomljenović, Bruno ; Pamić, Jakob ; Árkai, Peter

engleski

New K-Ar Age Data on the Alpine, Low-temperature Regional Metamorphism of Mt. Medvednica (Croatia)

The systematic metamorphic petrogenetic investigation of three, major, pre-Neogene tectonostratigraphic units of Mt. Medvednica as one of the largest “ inselbergs” of the major tectonic zone between the Eastern and the Southern Alps and the Dinarides i.e. the Zagorje– Mid-Transdanubian Zone (ZMTZ ; PAMIÆ ; ; & TOMLJENOVIÆ ; ; , 1998) started in 2001. The results of the mineral paragenetic, microstruc-tural, X-ray powder diffractometric and mineral chemical studies were summarised by JUDIK et al. (2004). The .rstK– Ar isotopic age data (122– 110 Ma) obtained on the very low- to low-grade metamorphic complex of Mt. Medvednica were published by BELAK et al. (1995). These age values were mainly measured on whole rock samples from greenschists and syn-kinematic K-white mica separate from a quartz-rich vein. In spite of the several constraints in isotopic dating of very low-grade metamorphic rock sequences, e.g., the critical importance of the accurate mineral separation and characterisation, the preferential loss of radiogenic iso-topes due to the small grain size, the addition of radiogenic isotopes explained by the occurrence of detrital contami-nants increasing the obtained isotopic ages, the K– Ar iso-topic dating recently became a widely adopted method of age determination (e.g.: REUTER, 1987 ; ALTANER et al., 1987 ; CLAUER et al., 1995, ÁRKAI et al., 1995). The aim of the present study was to obtain K– Ar iso-topic age data on <2 ì ; ; m size K-white-mica rich separates of various lithotypes of the very low- to low grade meta-morphic complex, the diagenetic Jurassic Ophiolitic mé-lange and Cretaceous– Paleocene sequence of Mt. Medved-nica. The K– Ar age data measured on rock types from very low- to low-grade metamorphic complex varied between 64 and 124 Ma. For the metapelite samples the average value corresponded to ca. 110 Ma, while it was signi.cant-ly lower, ca. 80 Ma for the metavolcanic– volcanic– sedi-mentary rock types devoid of detrital K-white mica in the separates. Beside the Cretaceous, Alpine metamorphic age data, no isotopic evidence was found which would refer to an eventual Variscan metamorphic event. Similar conclu-sions were suggested by JUDIK et al. (2004) on the basis of mineral chemical investigation of selected slate samples from the very low- to low-grade metamorphic complex. The authors found mineral chemical homogeneity of K-white mica and chlorite grains situated parallel to S0– 1 and S2 foliation planes and the possible detrital ones. For this reason they suggested that the effect of a possible Variscan metamorphic event with temperature conditions not higher than the latest, Alpine one could not be directly proven. In the matrix of the Jurassic Ophiolithic mélange and the Cretaceous– Paleocene sequence the diagenetic (in some cases low-temperature anchimetamorphic) condi-tions were probably not suf.cienttoresettheK– Arsystemof the samples giving mixed isotopic ages. The chronological correlation of the K– Ar age data measured on various rock types of the high-temperature anchizonal metamorphic complex of Mt. Medvednica with anchi-epizonal sequences of the Bükkia Composite Terrane, the Uppony and Szendrõ ; ; Units (KOVÁCS et al., 2000) indicates that similarly to the orogenic metamorphism of the Bükk, Szendrõ ; ; and Uppony Mts., the eo-Hellenic (160– 120 Ma) and the Austrian (100– 95 Ma) phases connected to the subduction– obduction of the Dinaridic Tethys and the further compressional thickening (ÁRKAI et al., 1995) could be responsible for tectono– metamorphic evolution of these units. PAMIÆ ; ; et al. (2004) also obtained Cretaceous K– Ar whole rock age data on metarhyolite samples from the Mid-Bosnian Schist Mts. of the Internal Dinarides, explained by the Late Jurassic– Cretaceous subduction – obduction of the Dinaridic oceanic crust. References ALTANER, S.P., WHITNEY, G. & ARONSON J.L. (1984): Mod-el for K-bentonite formation: evidence from zoned K-white mica bentonites in the disturbed belt, Montana.– Geology, 12, 412– 415. ÁRKAI, P., BALOGH, K. & DUNKL, I. (1995): Timing of low-temperature metamorphism and cooling of the Paleozoic and Mesozoic formations of the Bükkium, innermost Western Carpathians, Hungary.– Geol. Rundschau, 84, 334– 344. BELAK, M., PAMIÆ ; ; , J., KOLAR-JURKOVŠEK, T., PÉCSKAY, Z. & KARAN, D. (1995): Alpinski regionalno metamorfni kompleks Medvednice (sjeverozapadna Hrvatska).– In: VLA-HOVIÆ ; ; , I., VELIÆ ; ; , I. & ŠPARICA, M. (eds.): 1st Croatian Geological Congress, Proceedings, 1, Inst. geol. istr., Zagreb, 67– 70. CLAUER, N., RAIS, N., SCHALTEGGER, U. & PIQUÉ, A. (1995): K– Ar systematics of clay-to-mica minerals in a multi-stage low-grade metamorphic evolution.– Chem. Geol., Iso-tope Geoscience Section, 124, 305– 316. JUDIK, K., ÁRKAI, P., HORVÁTH, P., DOBOSI, G., TIBLJAŠ, D., BALEN, D., TOMLJENOVIÆ ; ; , B. & PAMIÆ ; ; , J. (2004): Diagenesis and low-temperature metamorphism of Mt. Med-vednica, Croatia: mineral assemblages and phyllosilicate characteristics.– Acta Geol. Hung., 47, 151– 176. KOVÁCS, S., SZEDERKÉNYI, T., HAAS, J., BUDA, Gy., CSÁ-SZÁR, G. & NAGYMAROSY, A. (2000): Tectonostratigra-phic terranes in the pre-Neogene basement of the Pannonian area.– Acta Geol. Hung., 43, 225– 329. PAMIÆ ; ; , J. & TOMLJENOVIÆ ; ; , B. (1998): Basic geologic data from the Croatian part of the Zagorje Mid-Transdanubian Zone.– Acta Geol. Hung., 41, 389– 400. PAMIÆ ; ; , J., BALOGH, K., HRVATOVIÆ ; ; , H., BALEN, D., JURKOVIÆ ; ; , I. & PALINKAŠ, L. (2004): K– Ar and Ar– Ar dating of the Palaeozoic metamorphic complex from the Mid-Bosnian Schist Mts., Central Dinarides, Bosnia and Herce-govina.– Mineral. and Petrol., 82, 65– 79. REUTER, A. (1987): Implications of K– Ar ages of whole rock and grain-size fractions of metapelites and intercalated meta-tuffs within an anchizonal terrane.– Contrib. Mineral. Petrol., 97, 105– 115.

Alpine ; Low-T metamorphism ; K– Ar dating ; K-white mica ; Mt. Medvednica ; Croatia ; Bükk ; Szendrõ ; and Uppony Mts. ; NE-Hungary

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Podaci o prilogu

47-48.

2005.

objavljeno

Podaci o matičnoj publikaciji

Abstracts book

Tomljenović, Bruno ; Balen, Dražen ; Vlahović, Igor

Zagreb: Hrvatski geološki institut

Podaci o skupu

7th Workshop on Alpine Geological Studies

poster

29.09.2005-01.10.2005

Opatija, Hrvatska

Povezanost rada

Geologija, Rudarstvo, nafta i geološko inženjerstvo