THE NEOPROTEROZOIC - EARLY PALEOZOIC GEOTECTONIC HISTORY OF CENTRAL EUROPE: DID CADOMIA EVER LEAVE GONDWANA IN PRE - VARISCAN TIMES ?

The Precambrian basement of Central Europe consists mainly of Late Neoproterozic volcaniclastic psammites deposited in marginal basins in a magmatic arc setting ("Avalonian-Cadomian Island Arc") at the Gondwana margin. The sedimentary units with arc-derived psammitic turbidites were intruded by postkinematic igneous rock units around 540 Ma. In Central Europe, Neoproterozoic to Early Paleozoic marginal basins, island arc remnants, and postkinematic plutons are referred to as the Cadomian basement or the Avalonian-Cadomian Orogen. Remnants of this orogen are involved in the peri-Gondwanan terranes Avalonia and Cadomia. Saxo-Thuringia is a crustal fragment of Cadomia. We use U/Pb - SHRIMP data of detrital zircons from volcaniclastic psammites intercalated within different Saxo-Thuringian Neoproterozoic sandstones and the Nd – Sr – Pb isotopic signature of the sediments to characterize the provenance of the detrital material. Currently, there is much debate about the paleogeography of the Avalonian-Cadomian Orogen, potential source areas being Amazonia, West Africa, and Baltica. Parts of these cratons became recycled during the Cadomian orogeny at the Gondwana margin. These three cratons differ in their mean age and the presence or absence of rocks from the Grenvillian orogeny (around 1.0 Ga). Rocks formed during the Grenville orogeny are prominent on Amazonia and Baltica, but are so far unknown from the West African Craton. The zircon age pattern strongly suggest a provenance of Saxo-Thuringia from West Africa. New Nd – Sr – Pb isotopic characterizations of Cambrian to Carboniferous sedimentary rocks consistently show the isotopic signature of Gondwana (there is no increase of a Baltica signature), suggesting that Cadomia never separated far from the West African Craton in pre-Variscan times. There is no evidence of an ocean between Cadomia and Africa as suggested by many authors.