How far did the Cadomian ?terranes travel from Gondwana during early Palaeozoic? A critical reappraisal based on detrital zircon geochronology
Abstract
In this paper, laser ablation ICP-MS U-Pb detrital zircon ages are used to discuss provenance and early Palaeozoic palaeogeography of continental fragments that originated in the Cadomian-Avalonian active margin of Gondwana at the end of Precambrian, were subsequently extended during late Cambrian to Early Ordovician opening of the Rheic Ocean, and finally were incorporated into and reworked within the European Variscan belt. The U-Pb detrital zircon age spectra in the analysed samples, taken across a late Neproterozoic (Ediacaran) to Early/Middle Devonian metasedimentary succession of the southeastern Tepla-Barrandian unit, Bohemian Massif, are almost identical andexhibit a bimodal age distribution with significant peaks at about 2.1-1.9Ga and 650-550Ma.
We interpret the source area as an active margin comprising a cratonic (Eburnean) hinterland rimmed by Cadomian volcanic arcs and we suggest that this source was available at all times during deposition. The new detrital zircon ages also corroborate the West African provenance of the Tepla-Barrandian and correlative Saxothuringian and Moldanubian units, questioned in some palaeogeographic reconstructions.
Finally, at variance with the still popular concept of the Cadomian basement units as far-travelled terranes, we propose that early Palaeozoic basins, developed upon the Cadomian active margin, were always part of a wide Gondwana shelf and drifted northwards together before involvement in the Variscan collisional belt.