Acta Musei Moraviae

Geological position, petrology and geochemistry of durbachite bodies in the vicinity of Nové Město na Moravě

Three bodies of ultrapotassic rocks (durbachites) crop out in the vicinity of Nové Město na Moravě. The western most body dips to the NW, while the orientation of other bodies is not clear. Geologic position is comparable with Třebíč pluton. The chemistry of these rocks can be explained by simple magma mixing proposed by HOLUB (1997). One of the bodies is unlike the others peraluminious, which is caused by assimilation of surrounding metamorphic rocks. Fractional crystallization of mafic minerals (hornblende) is also probable. Crystallization conditions were estimated on the basis of hornblend – plagioklase thermometer, zircon saturation temperature and equilibrium pairs of amphibol and biotite. The inferred temperatures ranged between 700–830 °C. Water contents in the magma could reache up to 8 wt. %. All of the bodies underwent subsolidus deformation in the temperature range 300–400 °C resulting in the occurrence of slip cleavage dipping to the NW at. ca. 30° (sinistral strike slip in a NW–SE direction) which could be attributed to the gravitational collapse of Variscan orogeny in the Lower Carboniferous.