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Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006ALTERATION PROCESSES IN THE MESOZOIC ISLAND ARC VOLCANICS FROM THETRASCĂU MOUNTAINS (ROMANIA)GROVU, P.Department of Mineralogy, Babeş-Bolyai University, 1 Kogălniceanu Str., RO-400084 Cluj-Napoca, RomaniaE-mail: pgrovu@bioge.ubbcluj.roIn the eastern part of the Apuseni Mountains (Romania),Mesozoic island arc volcanics occur. Tectonically, they arepart of the Bedeleu Nappe (BALINTONI & IANCU, 1986)and have on the top Oxfordian–Tithonian radiolarites andlimestones and, in places, post-tectonic Miocene sediments.The volcanic sequence is Middle to Late Jurassic in age andis not genetically related with ophiolites from the southernparts of the Apuseni Mts. (SACCANI et al., 2001). In theBuru–Borzeşti–Corneşti area (Trascău Mountains, north ofArieş Valley), the island arc volcanics show a wide range ofrocks such as basalts, basaltic andesites, andesites, dacitesand rhyolites. They form massive or pillowed lava flows,dykes or pyroclastic deposits, e.g. agglomerates, breccias andtuffs.Basalts and basaltic andesites have a dark green, almostblack colour and form massive or pillowed lavas. The porphyriticfabric is expressed by olivine, augite and plagioclase(An 50–90 and An 45–80 , respectively) phenocrysts, in intergranularor pilotaxitic groundmass, sometimes containing smallvacuoles filled in with calcite, quartz and/or chlorite. Andesiteshave greyish-greenish colour and form massive lavaflows. The structure is glomeroporphyritic, with clusters ofplagioclase (An 40–60 ) and isolated phenocrysts of augite, ferrohornblendeand quartz. The groundmass has microcrystallineto pilotaxitic fabric. Dacites and rhyolites are rare andform small, isolated dykes with porphyritic or aphyric fabric.The pyroclastites, represented by layers of andesitic agglomeratesand breccias, andesitic lapilli tuffs and vitroclasticrhyolitic tuffs, interbedded with massive lava flows or pillowlavas levels, are the prevalent rocks in the studied area.The above-described volcanic rocks exhibit different degreesof hydrothermal alteration, which affected mainly clinopyroxeneand plagioclase phenocrysts and the glassygroundmass. Clinopyroxenes (augite) are partly or completelyaltered and transformed into clinochlore. Plagioclaseoccurs either in fresh crystals or is partly replaced by a mixtureof albite, calcite and illite. The groundmass exhibitsmuch more intense alteration processes, expressed by thepresence of clinochlore, smectite, calcite, fibrous microquartz(chalcedony) and pyrite.The andesitic agglomerates, breccias and lapilli tuffs exhibitadvanced hydrothermal alteration, which affected lessthe clasts and mainly the matrix, in general almost completelytransformed into clinochlore, smectites and calcite.The rhyolitic vitroclastic tuffs are completely replaced bysmectites and form deposits of bentonites.The hydrothermal alteration of the Mesozoic volcanicsfrom the Trascău Mountains can be assigned to the activity ofthe postmagmatic fluids.ReferencesBALINTONI, I. & IANCU, V. (1986): Dări de Seamă ale ŞedinţelorInstitutul de Geologie şi Geofizică, 5. Tectonică şigeologie regională, 70–71: 45–56.SACCANI, E., NICOLAE, I. & TASSINARI, R. (2001):Ofioliti, 26: 9–22.34www.sci.u-szeged.hu/asvanytan/acta.htm
Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006INFRARED SPECTROSCOPY OF THE MUSCOVITE (SOPRON)–ILLITE (FÜZÉRRADVÁNY)SYSTEMGUCSIK, A. 1 , GASHAROVA, B. 2 , BIDLÓ, A. 1 , KOVÁCS, G. 1 , HEIL, B. 1 & PATOCSKAI, Z. 11 Dept. of Soil Sciences, University of West Hungary, Bajcsy Zs. E. u. 4., H-9400 Sopron, HungaryE-mail: ciklamensopron@yahoo.com2 Institute for Synchrotron Radiation, P.O. Box 36040, D-76021 Karlsruhe, GermanyMid-infrared (MIR) spectral regions of muscovite (Sopron,Hungary) and illite (Füzérradvány, Hungary) sampleswere measured as KBr pellets with a Globar source and aMCT detector at ANKA, Institute for Synchrotron Radiation(ISS), Forschungszentrum Karlsruhe, Germany. The cut-offof this detector is about 530 cm –1 . Muscovite/illite exhibitsMIR spectral features at 552/538 (bending vibration ofSiO 4 4– ), 1030/1038 (stretching vibrations of SiO 4 4– ),1661/1664 (bending vibrations of H 2 O), 3475/3481 and3634/3641 (stretching vibrations of OH group) (Figs. 1A,B).These spectral features mainly show similarities indicatingthat there is a very strong structural relationship betweenmuscovite and illite. But, in the lower frequencies some differencesoccur, which might be due to more stretching Simodes involving weakly bonded cations in illite. FIR spectrumof Sopron muscovite as reference material for the muscovite-illitesystem contains ten peaks at 110, 137, 166, 189,262, 351, 382, 407, 478, and 532 cm –1 . Füzérradvány illiteshows eleven peaks at 94, 118, 193, 260, 334, 384, 419, 473,505, 528, and 544 cm –1 . There are five peaks, which aredominant in both spectra at around 189, 262, 382, and478 cm –1 (Figs. 1C,D). These peaks also belong to the bendingand stretching vibrations (NAVROTSKY, 1994).ReferenceNAVROTSKY, A. (1994): Physics and chemistry of earthmaterials. Cambridge: Cambridge University Press, 116p.Absorbance1,81,61,41,210,80,60,455275610303634AAbsorbance0,40,350,30,250,20,150,1110137166189262351407382478 532C0,234750,05016610400 800 1200 1600 2000 2400 2800 3200 3600 40000 100 200 300 400 500 600Wavenumber (cm -1 )Wavenumber (cm -1 )Absorbance0,50,450,40,350,30,250,20,1553810383641BAbsorbance0,30,250,20,150,194118193260D334 38 419 473528505 5440,10,05166434810,050400 800 1200 1600 2000 2400 2800 3200 3600 400000 100 200 300 400 500 600Wavenumber (cm-1)Wavenumber (cm -1 )Fig. 1: Mid-infrared (MIR) and far-infrared (FIR) spectroscopic features of muscovite (Sopron: A, C) andillite (Füzérradvány: B, D).www.sci.u-szeged.hu/asvanytan/acta.htm 35
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