Linking collisional and accretionary orogens during Rodinia assembly and breakup: Implications for models of supercontinent cycles

Periodic assembly and dispersal of continental fragments has been a characteristic of the solid Earth for much of its history. Geodynamic drivers of this cyclic activity are inferred to be either top-down processes related to near surface lithospheric stresses at plate boundaries or bottom-up processes related to mantle convection and, in particular, mantle plumes, or some combination of the two. Analysis of the geological history of Rodinian crustal blocks suggests that internal rifting and breakup of the supercontinent were linked to the initiation of subduction and development of accretionary orogens around its periphery. Thus, breakup was a top-down instigated process. The locus of convergence was initially around north-eastern and northern Laurentia in the early Neoproterozoic before extending to outboard of Amazonia and Africa, including Avalonia–Cadomia, and arcs outboard of Siberia and eastern to northern Baltica in the mid-Neoproterozoic (~760 Ma). The duration of subduction around the periphery of Rodinia coincides with the interval of lithospheric extension within the supercontinent, including the opening of the proto-Pacific at ca. 760 Ma and the commencement of rifting in east Laurentia. Final development of passive margin successions around Laurentia, Baltica and Siberia was not completed until the late Neoproterozoic to early Paleozoic (ca. 570–530 Ma), which corresponds with the termination of convergent plate interactions that gave rise to Gondwana and the consequent relocation of subduction zones to the periphery of this supercontinent. The temporal link between external subduction and internal extension suggests that breakup was initiated by a top-down process driven by accretionary tectonics along the periphery of the supercontinent. Plume-related magmatism may be present at specific times and in specific places during breakup but is not the prime driving force. Comparison of the Rodinia record of continental assembly and dispersal with that for Nuna, Gondwana and Pangea suggests grouping into two supercycles in which Nuna and Gondwana underwent only partial or no break-up phase prior to their incorporation into Rodinia and Pangea respectively. It was only after this final phase of assembly that the supercontinents then underwent full dispersal

Laurentia-Baltica-Amazonia relations during Rodinia assembly

Laurentia, Baltica and Amazonia are key building blocks of the end Mesoproterozoic to early Neoproterozoic supercontinent Rodinia. Integration of available data sets enables development of a dynamic model for the Proterozoic interaction of these continental fragments in which Amazonian collision with Laurentia is linked to rifting and rotation of Baltica from Laurentia to collide with Amazonia's northern margin. The geological record of the three blocks indicates a long history extending through the Paleoproterozoic and Mesoproterozoic involving continental growth onto Archean cratonic cores through convergent plate interaction and accretionary orogenesis. This history requires the existence of a long lived and probably large oceanic tract outboard of these continental fragments; the Mirovoi Ocean. Prior to 1265 Ma, Laurentia and Baltica formed a single tectonic plate. Sometime after this, but prior to 990 Ma, these blocks broke into two plates through opening of the triangular shaped Asgard Sea between northeast Laurentia and northern Baltica. After opening of the Asgard Sea the southern margin of Baltica lay at right-angles to east Laurentia. Thus, during final closure of the Mirovoi Ocean and collisional orogenesis, the western margin of Amazonia collided with the east Laurentian margin while the southern margin of Baltica collided with the northern margin of Amazonia. Laurentia, Baltica and Amazonia maintained this configuration until the final breakup of Rodinia with the opening of the Iapetus Ocean at the end of the Neoproterozoic