Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Karel Breiter, Scharbert

Two-mica and biotite granites in the Weitra-Nové Hrady area, Austria - Czech Republic

Journal of the Czech Geological Society, volume 51 (2006), issue 3-4, 217 - 230

DOI: http://doi.org/10.3190/JCGS.995

The South Bohemian Pluton consists, in traditional view, of three major granite suites - the Weinsberg, Eisgarn, and Freistadt suites. In reality, the composition of the pluton is even more complicated than this subdivision would suggest. For instance, in the area among towns of Weitra, Freistadt and Nové Hrady, besides the clearly defined Weinsberg granite, four additional granite types have been distinguished on the basis of their field relations, petrology, whole-rock and isotope geochemistry: (1) medium-grained, locally porphyritic peraluminous two-mica Žofín granite, 324 ± 14 Ma old with initial Sr isotopic ratios (⁸⁷Sr/⁸⁶Sr_i) of 0.712; (2) peraluminous fractionated suite of coarse-grained two-mica Mandelstein granite, accompanied by muscovite Nakolice-Pyhrabruck and Šejby granites with ⁸⁷Sr/⁸⁶Sr_i ∼ 0.706; (3) chemically primitive Karlstift biotite granite with high magnetic susceptibility and ⁸⁷Sr/⁸⁶Sr_i = 0.706; (4) Weitra biotite granite with a magnetic and a non-magnetic varieties followed by dykes of muscovite granite (⁸⁷Sr/⁸⁶Sr_i ∼ 0.705). The evolution of the peraluminous granites towards lower Sr initial ratios may indicate change in the magma sources at the end of the Variscan magmatic cycle and a shift to deeper, more metaigneous material.