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

The Enganepe ophiolite, Polar Urals was formed at ∼670 Ma and records a diverse geochemical association of tholeiite, arc-tholeiite, adakite, and OIB-like lithologies. This constrains the tectonic setting of the protolith of the ophiolite to an oceanic island-arc, with ridge-trench interaction most readily explaining the diverse compositions. The initiation of intra-ocean subduction and the development of the Enganepe island arc 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-arc magmatism is similar in age to that recorded off Avalon in the Cadomian arc. We propose that the active margin of Baltica in the Vendian is an extension of the Cadomian arc. This requires the northeast margin of Baltica (present-day coordinates) to have been in a southerly position in the Vendian, in agreement with proposed tectonic reconstructions. Consequently, the post-Rodinia continental amalgamation, Pannotia, had active ocean-continent convergence along its entire southerly (west Avalonia and Amazonian cratons) margin at the time of its break-up.