International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

U-Pb ZIRCON AGES OF DIORITIC AND TRONDHJEMITIC ROCKS FROM A LAYERED AMPHIBOLITIC COMPLEX CROSSCUT BY GRANITE VEIN (VEPORIC BASEMENT, WESTERN CARPATHIANS)

Pages: 49 - 60

Authors: MARIAN PUTIS, ALEXANDER B. KOTOV, SERGEI P. KORIKOVSKY, EKATHERINA B. SALNIKOVA, SONYA Z. YAKOVLEVA, NATALYA G. BEREZHNAYA, VICTOR P. KOVACH, YULIA V. PLOTKINA

Abstract: The complex of Ky-Grt paragneisses, granitic to tonalitic orthogneisses, migmatitic gneisses and homogeneous to layered amphibolites was intruded by dioritic-gabbroic more or less concordant dykes and sills during the syn-metamorphic extension in the host regional metamorphic rocks. They now have the character of dioritic orthogneisses. The whole lithological sequence was then structurally unified during the late-metamorphic cooling and exhumation within the deep-crustal shear zone. The dioritic orthogneisses bear the features of pre-metamorphic compositional layering into cumulate-like hornblendite(±Px), gabbro-diorite, tonalite to trondhjemite. Magmatic layering has been transformed to subsolidus high-temperature layering along the extensional meso-shear bands filled with leucotonalitic melt seggregates crosscutting former magmatic structures at acute to medium angles. A new ductile strain relocalization enhanced mechanical differentiation of dark and felsic minerals into often isoclinally folded layers, with the crystallographic preferred orientation fabrics of amphibole, plagioclase and quartz indicating a layer parallel shear. The U-Pb zircon age of porphyric metadiorites 346±1 Ma (Early Carboniferous) is related to their magmatic emplacement, immediately followed by the high-temperature mylonitization. We also dated zircon of metatrondhjemitic orthogneiss from the layered amphibolite. An upper intercept age 514±24 Ma (Late Cambrian) is interpreted as dating the magmatic compositional differentiation of a gabbro-dioritic complex into cumulate-like hornblenditic, gabbrodioritic, tonalitic to trondhjemitic layers, which is an inherited feature in layered amphibolites (with blastic textures). The lower intercept age 348±31 Ma (Early Carboniferous) obviously reflects the time of regional-metamorphic event and formation of layered amphibolites. The whole composite (VZP-CB) structural complex is crosscut by plagiogranite-aplitic veins dated 233±4 Ma (Early Triassic).

Keywords: Western Carpathians, Veporic basement, layered metamagmatites and amphibolites, U-Pb zircon isotope dating

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