U-Pb zircon ages of dioritic and trondhjemitic rocks from a layered amphibolitic complex crosscut by granite vein (Veporic basement, Western Carpathians)

The complex of Ky-Grt paragneisses, granitic to tonalitic orthogneisses, mi gmatitic gneisses and homogeneous to layered amphibolites was intruded by d ioritic-gabbroic more or less concordant dykes and sills during the synmeta morphic extension in the host regional metamorphic rocks. They now have the character of dioritic orthogneisses. Tile whole lithological sequence was then structurally unified during the late-metamorphic cooling and exhumatio n within the deep-crustal shear zone. The dioritic orthogneisses bear the f eatures of pre-metamorphic compositional layering into cumulate-like hornbl endite(+/- Px), gabbro-diorite, tonalite to trondhjemite. Magmatic layering has been transformed to subsolidus high-temperature layering along the ext ensional meso-shear bands filled with leucotonalitic melt seggregates cross cutting former magmatic structures at acute to medium angles. A new ductile strain relocalization enhanced mechanical differentiation of dark and fels ic minerals into often isoclinally folded layers, with the crystallographic preferred orientation fabrics of amphibole, plagioclase and quartz indicat ing a layer parallel shear. The U-Pb zircon age of porphyric metadiorites 3 46 +/- 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 u pper intercept age 514 +/- 24 Ma (Late Cambrian) is interpreted as dating t he magmatic compositional differentiation of a gabbro-dioritic complex into cumulate-like hornblenditic, gabbrodioritic, tonalitic to trondhjemitic la yers, which is an inherited feature in layered amphibolites (with blastic t extures). The lower intercept age 348 +/- 31 Ma (Early Carboniferous) obvio usly reflects the time of regional-metamorphic event and formation of layer ed amphibolites. The whole composite (VZP-CB) structural complex is crosscu t by plagiogranite-aplitic veins dated 233 +/- 4 Ma (Early Triassic).