The late Neoproterozoic Enganepe ophiolite, Polar Urals, Russia: An extension of the Cadomian arc?

The Enganepe ophiolite, Polar Urals was formed at similar to 670 Ma and rec ords a diverse geochemical association of tholeiite, arc-tholeiite, adakite , and GIB-like lithologies. This constrains the tectonic setting of the pro tolith of the ophiolite to an oceanic island-are, with ridge-trench interac tion most readily explaining the diverse compositions. The initiation of in tra-ocean subduction and the development of the Enganepe island are off the eastern margin of Baltica probably pre-dated the formation of the Enganepe ophiolite, i.e. prior to 670 Ma. The timing of island-are magmatism is sim ilar in age to that recorded off Avalon in the Cadomian are. We propose tha t the active margin of Baltica in the Vendian is an extension of the Cadomi an are. This requires the northeast margin of Baltica (present-day coordina tes) to have been in a southerly position in the Vendian, in agreement with proposed tectonic reconstructions. Consequently, the post-Rodinia continen tal amalgamation, Pannotia, had active ocean-continent convergence along it s entire southerly (west Avalonia and Amazonian cratons) margin at the time of its break-up. (C) 2001 Elsevier Science B.V. All rights reserved.