Metamorfované horniny západní části brněnského batolituČlánek v PDF
Metamorphic rocks western part Brno batholith
Biotite and amphibole biotite granitoids of the northern part of Thaya terrane (western part of the Brno batholith) contains large enclaves of polyphase-metamorphosed sedimentary and igneous rocks. The enclaves, up to several km long, consist mainly of biotite to muscovite-biotite gneisses (Qtz + Pl + Bt ±Ms ± Sil ± Ky), biotite to cordierite-biotite migmatites (Qtz + Pl + Bt ± Kfs ± Ms ± Sil ± Crd), metagabbros (Amp + Pl ± Px), calc-silicate rocks (Amp + Pl + Px + Qtz ± Cal ± Grt ± Qtz and Cpx ± Grt ± Ves ± Wo ±Cal ± Qtz ± Pl ± Kfs ± Czo) and amphibolites (Amp + Pl ± Qtz). Three metamorphic events with different P-T conditions are distinguished in the studied rocks. The first stage M1 was marked by regional metamorphism under amphibolite facies conditions (700 °C and 6–7 kbar). Regional metamorphism was followed by a decompression stage and intrusion of Cadomian granitoids of the Thaya terrane (Tetčice suite). P-T estimates for low-pressure contact metamorphism M2 correspond to approximately 700–800 °C and 3–5 kbar. The metamorphic assemblage (Pl + Cpx ± Grt ± Ves ± Wo ± Cal ± Qtz ± Kfs ± Czo) of skarnoid layers from enclaves of calc-silicate rocks indicates high water activity (XCO2 < 0.03) during this metamorphic event. The subsequent Variscan metamorphic overprint (M3) was characterized by regional hydrothermal alteration under prehnite-pumpellyite facie (2–3 kbar and >300 °C).
David Buriánek, Czech Geological Survey, Leitnerova 22, 658 59, Brno; CzechRepublic; email@example.com