LATE CADOMIAN CRUSTAL TILTING AND CAMBRIAN TRANSTENSION IN THE TEPLA-BARRANDIAN UNIT (BOHEMIAN MASSIF, CENTRAL-EUROPEAN VARISCIDES)

The Cadomian basement of the Tepla-Barrandian unit is characterized by a classic Barrovian-type metamorphism, the degree of which increases considerably towards the west reaching amphibolite facies conditions i n the Domazlice crystalline complex (DCC). The number and volume of pl utons also increases towards the west. The emplacement ages of the Tes ovice granite and the Mracnice trondhjemite have been determined at 52 1.7 +/- 2 Ma and 523 +4/-5 Ma, respectively, applying conventional U-P b analyses of zircons. Pervasive high-temperature prolate fabrics and north-/northwest-dipping, dextral oblique-slip shear zones within the Mracnice trondhjemite suggest a synkinematic melt emplacement within a Lower Cambrian transtensional setting. Transtension is probably relat ed to early-stage rifting that introduced the separation of the Tepla- Barrandian unit (as part of Armorica) from Gondwana. Structural and pe trological data of the country rocks show that the Barrovian-type meta morphism and two deformation stages (D-1 with unknown kinematics and D , top-to-the-north shearing) are older than the melt emplacement, and thus can be attributed to the Cadomian orogeny. The intrusion depth of both plutons is nearly the same (ca. 7km), although the degree of Bar rovian-type metamorphism differs significantly within the country rock s. This suggests late Cadomian eastward tilting of the metamorphic iso grad planes. The weak post-plutonic, lower-greenschist to subgreenschi st facies folding and thrusting result from Variscan northwest/southea st compression.