ALONG-STRIKE VARIATIONS IN AVALONIA AND OTHER PERI-GONDWANAN ARCS IN THE NEOPROTEROZOIC-CAMBRIAN: ANALOGOUS WITH THE MESOZOIC-CENOZOIC EVOLUTION OF THE CORDILLERA? (Invited Presentation)

The northern margin of Gondwana was dominated by arc activity throughout much of the Neoproterozoic and Early Cambrian. However, the composition and duration of arc activity varied considerably along and across strike. Sm-Nd isotopic systematics suggest arc magmas were derived from both juvenile (outboard) and ancient (inboard) sources, analogous with the spatial distribution of arc magmas in the Cordillera. The development of juvenile oceanic arcs at ca. 760 Ma (early Avalonian magmatism), their accretion to Gondwana at ca. 650 Ma, followed by 635-570 Ma continental arc magmatism (main phase of magmatism) accompanied the breakup of Rodinia may be analogous with the accretion of Cordilleran arcs to western North America was succeeded by the development of the main phase of Cordilleran arc magmatism following the Early Mesozoic breakup of Pangea. In the absence of evidence for continental collision, the diachronous termination of subduction is widely attributed to the development of an intracontinental transform regime at 590–500 Ma and to record ridge–trench collision in a manner analogous to the Cenozoic development of the San Andreas Fault. In this scenario, these peri-Gondwanan terranes would have continued to face an open ocean in the early Paleozoic, thereby providing important constraints for paleocontinental reconstructions.