CORDILLERAN MODEL FOR THE EVOLUTION OF AVALONIA

Striking similarities between the late Mesoproterozoic-Early Paleozoic record of Avalonia and the Late Paleozoic-Cenozoic history of western North America suggest that the North American Cordillera provides a modern analogue for the evolution of Avalonia and other peri-Gondwanan terranes in the late Precambrian. (1) The evolution of primitive Avalonian arcs (proto-Avalonia) at 1.2-1.0 Ga coincides with the assembly of Rodinia, just as the evolution of primitive Cordilleran arcs in Panthalassa coincided with the Permian amalgamation of Pangea. (2) Development of mature oceanic arcs at 750-650 Ma (early Avalonian magmatism), their accretion to Gondwana at ca. 650 Ma, and the development of a continental margin arc at 635-570 Ma (main Avalonian magmatism), followed the breakup of Rodinia at ca. 755 Ma in the same way that accretion of mature Cordilleran arcs to western North America and the development of the main phase of Cordilleran arc magmatism followed the Early Mesozoic breakup of Pangea. (3) In the absence of evidence for continental collision, the diachronous termination of subduction and its transition to an intracontinental wrench regime at 590-540 Ma is interpreted to record ridge-trench collision in the same way that North America's collision with the East Pacific Rise in the Oligocene led to the diachronous initiation of a transform margin. (4) Separation of Avalonia from Gondwana in the Early Ordovician resembles that brought about in Baja California by the Pliocene propagation of the East Pacific Rise into the continental margin. (5) Late Ordovician-Early Silurian sinistral accretion of Avalonia to eastern Laurentia emulates the Cenozoic dispersal of Cordilleran terranes and may model the future paths of terranes transferred to the Pacific plate. This similarity suggests that a geodynamic coupling like that linking the Cordillera to the assembly and breakup of Pangea, may have existed between Avalonia and the late Precambrian supercontinent Rodinia. Hence, the North American Cordillera is considered to provide an actualistic model for the evolution of Avalonia and other peri-Gondwanan terranes, the histories of which afford a proxy record of supercontinent assembly and breakup in the late Precambrian.