THE CADOMIAN OROGENY IN THE SUPERCONTINENT CYCLE AND ITS IMPORTANCE FOR ALLEGHANIAN-VARISCAN OROGENIC PROCESSES

During Ediacaran to earliest Cambrian times, the Cadomian Orogen formed on the periphery of the Gondwana supercontinent. The orogenic belt was structured in the geotectonic style of the recent western Pacific. Aside the relatively small cratonic relicts of the Dobra Gneiss (c. 1.38 Ga) and the Svetlik Gneiss (c. 2.05-2.1 Ga) the Cadomian basement represents the oldest rock unit in the of the Bohemian Massif. The Cadomian basements was formed in Upper Ediacaran to Lower Cambrian times (c. 580-530 Ma) in an active plate tectonic setting. The volcano-sedimentary complexes of the Cadomian basement were formed in marginal basins linked to a dominant magmatic arc activity and an intense recycling (remelting) of a cratonic hinterland. The latter was provided by the West African and the Sub-Sahara cratons. Further, the recycling of a major portion of Pan-African orogenic events most probably was involved. Palaeographically, the Cadomian orogen of the Bohemian Massif was located at the northern periphery of the West African and the Sub-Sahara cratons. The existence of an Upper Ediacaran glacial period at c. 566-560 Ma places the origin of the Cadomian orogen in high latitudes of the southern hemisphere. The Cadomian orogen shared a part of its geotectonic history with East Avalonia. Detrital zircon zircon populations from Cambrian strata witness a strong relation of both geotectonic domains. As a consequence of the split-off of Avalonia from Gondwana mainland the Rheic ocean became opened.