Rhyolites from Metadiorite Zone of the Brno Massif

The rhyolite dykes up to 4 m thick crosscuts basic and ultrabasic plutonic rocks in the Metadiorite Zone of the Brno Massif. Two distinct rhyolite types have been recognized. The first unaltered type occurs mainly in the southern part of the Metadiorite Zone. They are fine-grained porphyritic rhyolites, locally with spherules and skeletal crystals of K-feldspar. However majority of dykes are porphyritic to aphanitic fine-grained rocks, which are strongly affected by hydrothermal alteration (albitization, sericitization, turmalinization, chloritization). Unaltered rhyolites in the Metadiorite Zone have very similar geochemical signatures (e. g. content REE or HFSE) as volcanoclastic stratas in the Devonian sedimentary cover of the Brno Massif.The rhyolite dykes up to 4 m thick crosscuts basic and ultrabasic plutonic rocks in the Metadiorite Zone of the Brno Massif. Two distinct rhyolite types have been recognized. The first unaltered type occurs mainly in the southern part of the Metadiorite Zone. They are fine-grained porphyritic rhyolites, locally with spherules and skeletal crystals of K-feldspar. However majority of dykes are porphyritic to aphanitic fine-grained rocks, which are strongly affected by hydrothermal alteration (albitization, sericitization, turmalinization, chloritization). Unaltered rhyolites in the Metadiorite Zone have very similar geochemical signatures (e. g. content REE or HFSE) as volcanoclastic stratas in the Devonian sedimentary cover of the Brno Massif