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Geochemistry and petrology of high-pressure kyanite-garnet-albite-K-feldspar felsic gneisses and granulites from the Kutná Hora Complex, Bohemian Massif

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Author(s): Vrána S | Štědrá V | Nahodilová R

Journal: Journal of Geosciences
ISSN 1802-6222

Volume: 54;
Issue: 2;
Start page: 159;
Date: 2009;
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ABSTRACT
Three types of kyanite-garnet-albite-K-feldspar rocks studied include: (1) an early Variscan felsic granulite from the Běstvina Unit equilibrated under eclogite-facies conditions (P = 1.8-2.1 GPa, metamorphic event M1), (2) a garnet-kyanite leucosome from a polymetamorphic migmatite (P ˜ 1.6 GPa, metamorphic event M2), and (3) a felsic kyanite-garnet-muscovite gneiss derived from garnetiferous leucogranite, equilibrated under amphibolite-facies conditions (P = 0.9-1.1 GPa, metamorphic event M3). All the three rock types exhibit geochemical characteristics of highly evolved leucogranitic rocks with low Zr/Hf ratios (14 to 19), relatively low FeOt/MnO (10 to 33), and contain < 30 ppm Zr, < 15 ppm Y, and low ΣREE (< 28 ppm) abundances. The kyanite-garnet-muscovite felsic gneiss contains locally garnet porphyroclasts up to 3 cm in diameter, with up to 28 mol. % spessartine and 0.55 wt. % P2O5, which represent relics from the magmatic stage of the garnetiferous leucogranite precursor. Accessory tourmaline (dravite-schorl) and dumortierite occur in migmatitic gneisses of the Malín Unit, while dumortierite is common in the felsic gneiss (M3). Textural relationships indicate a late, post-kinematic growth of tourmaline and dumortierite in relation to D3/M3.The repetitive high-pressure record manifested during three metamorphic events in the Kutná Hora Complex represents a unique example in the Bohemian Massif. These relations indicate a separate evolution of the Kutná Hora Complex and the Moldanubian Zone during much of their Variscan tectonometamorphic history. Several aspects of possible correlation among the Kutná Hora Complex (plus the Svratka Unit) and the Orlice-Sněžník Unit at the Czech-Polish border, which all have a record of Palaeo-Variscan (U)HP evolution, are discussed. ]]>
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