Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Variscan very low-grade metamorphism of the basalt and rhyolite dykes in the Brno batholite
Abstract
Cadomian igneous and metamorphic rocks of the Brno batholite are crosscut by basalt and rhyolite dykes up to several meters thick. These dykes and surrounding granodiorites are affected by low-grade metamorphism. The primary igneous phases in the basalts (Pl + Amp ± Px ± Ol) and amphibole-biotite granodiorites (Pl + Qtz + Kfs + Amp ± Bt) are partially replaced (with the exception of amphibole) by chlorite, epidote (clinozoisite), prehnite and rarely pumpellyite. Secondary phases in the rhyolites and biotite granodiorites are mainly chlorite, sometime together with epidote and/or tourmaline. All mentioned mineral assemblages also included albite, sphene, white mica and usually quartz. The metamorphic conditions are estimated using secondary mineral assemblages. The calculated metamorphic conditions restricted to 200-300 °C and < 4 kbar are interpreted presumably as a result of the marked fluid influx into the rocks of the Brno batholite during Variscan orogenesis.
