Relics of an early-Panafrican metabasite-metarhyolite formation in the Brno Massif, Moravia, Czech Republic

The Brno Massif in Moravia, Czech Republic, is an important exposure of Pre cambrian basement in central Europe. It includes large volumes of Cadomian granitoids and a narrow fault-bounded zone with metagabbros, metadiorites, and metabasalts. This so-called Central Basic Belt also contains some metar hyolites; one of these was dated by means of the zircon evaporation method at 725+/-15 Ma. Chemical and isotope data show that the dated rock represen ts a mantle-derived magma which is cosanguinous with surrounding MORB-type metabasites. The data suggest that the Brno Massif hosts the oldest metabas ite complex currently known in central Europe. Its formation apparently coi ncides with the main period of ocean-floor spreading and island-are formati on in the Panafrican orogens. This lends further support to the theory that the Bmo Massif is a Gondwana-derived element.