Acta Musei Moraviae

Highly mafie amphibolites in the Moldanaubian Zone of the Bohemian-Moravian Heights (Českomoravská vrchovina)

In the Chýnov zone which encompasses the area E of the town of Tábor and belongs to the Moldanubian Varied series, highly mafie amphibolites occur that are almost monomineral. They are associated with marginal-sea-type metasediments, forming there very long and narrow layers. Their chemistry points to an igneous rock which evidently was originally part of a volcanosedimentary complex. Their chemical composition recalls basaltic komatiites. However, other members of the komatiite series, particularly the peridotite metakomatiites, which are the parent rock of the komatiite series, are completely lacking in the Chýnov zone, the highly mafic amphibolites being in contrast associated there with metatholeiites. The content of femic minerals in the original igneous rock must have been higher than in primitive MORBs. Thus, they probably were olivine- and clinopyroxene-enriched accumulative magmas. This opinion is supported by the fact that several amphibolites of the Chýnov zone contain intercalations of olivine-chlorite-tremolite-aetinolite schists which are assumed by MACHART (1984) to have been originally cogenetic olivine-pyroxene-plagioclase cumulates.