Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Stanislav Vrána, Kröner

Pb-Pb zircon ages for tourmaline alkali-feldspar orthogneiss from Hluboka nad Vltavou in southern Bohemia

Journal of the Czech Geological Society, volume 40 (1995), issue 1-2, 127 - 131

The pre-Variscan tourmaline-bearing orthogneiss occurring near Hluboká nad Vltavou is tectonically intercalated in sillimanite-biotite paragneisses of the Monotonous Unit of the Moldanubian Zone and is a metamorphosed biotite-muscovite alkali-feldspar granite with a composition comparable to pegmatite. Zircons from a sample of this orthogneiss were dated by single grain evaporation and yielded a mean ²⁰⁷Pb/ ²⁰⁶Pb age of 508 ± 7 Ma, interpreted to approximate the time of granite emplacement. One xenocrystic zircon grain with a ²⁰⁷Pb/ ²⁰⁶Pb age of 606 ± 8 Ma either suggests derivation of the granite by anatexis from a late Precambrian crustal source or digestion of such material during ascent and/or emplacement of the granite. The emplacement age is similar to zircon ages for granitoid gneisses exposed in the Orlické hory Mts. and Sněžník Dome and may suggest that Ordovician granitoid activity was widespread in southern a eastern Bohemian Massif.