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 ∼90° 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.