The assembly of Pangea; geodynamic conundrums revisited

Geodynamic models for Pangea assembly require knowledge of Paleozoic mantle convection patterns. Application of basic geodynamic principles to Neoproterozoic-Paleozoic plate reconstructions yields Pangea in the incorrect configuration (predicting that Pangea should have formed by consumption of the exterior paleo-Pacific Ocean instead of Iapetus, Rheic, and Proto-Tethys oceans). We contend that the mantle legacy of Late Neoproterozoic-Cambrian amalgamation of Gondwana must be factored into models for Pangea amalgamation. Proxy data suggest that the mantle downwelling driving Pan-African collisions and Gondwana assembly evolved into a mantle upwelling as evidenced by the interplay between subduction-related and plume-related tectonics around the periphery of Gondwana. Orthoversion theory, whereby a supercontinent assembles approximately 90 degrees away from the centre of the previous supercontinent, suggests that Gondwana amalgamated above an intense downwelling along a meridional subduction girdle that bisected two antipodal sub-equatorial upwellings. Several processes beneath and around Gondwana reduced the intensity of the original downwelling, as evidenced by plume-related activity along its margins, initiation of subduction zone roll-back, and the export of terranes from Gondwana that collided with the margin of Laurentia-Baltica. As upwelling beneath it intensified, Gondwana migrated along the girdle until it collided with Laurentia-Baltica, resulting in the final assembly of Pangea.