U-PB ZIRCON AGES AND STRUCTURAL DEVELOPMENT OF METAGRANITOIDS OF THE TEPLA CRYSTALLINE COMPLEX - EVIDENCE FOR PERVASIVE CAMBRIAN PLUTONISM WITHIN THE BOHEMIAN MASSIF (CZECH-REPUBLIC)

U-Pb zircon dating of three metagranitoids, si tuated within a tilted crustal section at the northwestern border of the Tepla Barrandian uni t (Tepla crystalline complex, TCC), yields similar Cambrian ages. The U-Pb data of zircons of the Tepla orthogneiss define an upper intercep t age of 513 +7/-6 Ma. The (207)pb/(206)pb ages of 516+/-10 and 511+/- 10 Ma of nearly concordant zircons of the Hanov orthogneiss and the Le stkov granite are interpreted to be close to the formation age of the granitoid protolith. Similar to the Cambrian granitoids of the southwe stern part of the Tepla Barrandian unit (Domazlice crystalline complex , DCC) the Middle Cambrian emplacement of the TCC granitoids postdates Cadomian deformation and metamorphism of the Upper Proterozoic countr y rocks, but predates Variscan tectonometamorphic imprints. Structural data as well as sedimentological criteria suggest a dextral transtens ional setting during the Cambrian plutonism, related to the Early Pale ozoic break-up of northern Gondwana. Due to strong Variscan crustal ti lting, the degree of Variscan tectonometamorphic overprint is striking ly different in the dated granitoids. it is lowest in the weakly or un deformed Lestkov granite, located in the greenschist-facies domain. Th e Tepla orthogneiss in the north underwent pervasive top-to-NW mylonit ic shearing under amphibolite-facies conditions. There is no indicatio n for a resetting of the U-Pb isotopic system of the Tepla orthogneiss zircons that could be attributed to this imprint. Radiation damages a ccumulated until recent have probably caused lead loss.