ZIRCON DATING OF NORTH BOHEMIAN GRANULITES, CZECH-REPUBLIC - FURTHER EVIDENCE FOR THE LOWER CARBONIFEROUS HIGH-PRESSURE EVENT IN THE BOHEMIAN MASSIF

U-Pb zircon and rutile multigrain ages and Pb-207/Pb-206 zircon evapor ation ages are reported from high-pressure felsic and metapelitic gran ulites from northern Bohemia, Czech Republic. The granulites, in contr ast to those from other occurrences in the Bohemian Massif, do not sho w evidence of successive HT/MP-LP overprints. Multigrain size fraction s of nearly spherical, multifaceted, metamorphic zircons from three sa mples are slightly discordant and yield a U-Pb Concordia intercept age of 348 +/- 10 Ma, whereas single zircon evaporation of two samples re sulted in Pb-207/Pb-206 ages of 339 +/- 1.5 and 339 +/- 1.4 Ma, respec tively. A rutile fraction from one sample has a U-Pb Concordia interce pt age of 346 +/- 14 Ma. All ages are identical, within error, and a m ean age of 342 +/- 5 Ma was adopted to re fleet the peak of HP metamor phism. Because rutile has a lower closing temperature for the U-Pb iso topic system than zircon, the results and the P-T data imply rapid upl ift and cooling after peak metamorphism. The above age is identical to ages for high-grade metamorphism reported from the southern Bohemian Massif and the Granulite Massif in Saxony. It can be speculated that a ll these granulites were part of the same lower crustal unit in early Carboniferous, being separated later due to crustal stacking and subse quent late Variscan orogenic collapse.