Prota-Avalonia: A 1.2-1.0 Ga tectonothermal event and constraints for the evolution of Rodinia

The Neoproterozoic evolution of Avalonia is thought to have been geodynamic ally linked to the amalgamation and dispersal of Rodinia. Similar Sm-Nd iso topic signatures for different periods of are activity suggest that Avaloni an basement, or proto-Avalonia, was generated in a series of primitive ocea nic island arcs between 1.2 and 1.0 Ga. Because this interval coincides wit h the amalgamation of Rodinia, proto-Avalonia is inferred to have been loca ted in a Panthalassa-like peri-Rodinian ocean. An early (760-660 Ma) phase of Avalonian are activity is attributed to renewed subduction in the peri-R odinian ocean following the breakup of Rodinia, which caused the accretion of Avalonian terranes to the Gondwanan margin by ca. 650 Ma. Further subduc tion along the margin occurred outboard of these terranes and resulted in t he onset of main-phase Avalonian volcanism at 630 Ma. The diachronous cessa tion of are magmatism is attributed to ridge-trench collision and the gener ation of a continental transform. The geodynamic link between Avalonia and Rodinia is analogous to that between the Mesozoic dispersal of Pangea and t he tectonothermal evolution of western North America. This event also resul ted in the accretion of outboard terranes and in arc-related magmatism that is currently being terminated in a diachronous manner by ridge collision a nd the generation of the San Andreas transform. The model implies that the Neoproterozoic evolution of Avalonia and other peri-Gondwanan terranes prov ide important constraints on the tectonic history of a large portion of the Rodinian continental margin.