The Pangea conundrum

Geodynamic models for supercontinent assembly, whereby the dispersing continental fragments of a supercontinent break up and migrate from geoid highs to reassemble at geoid lows, fail to account for the amalgamation of Pangea. Such models would predict that the oceans created by continental breakup in the early Paleozoic (e.g., Iapetus, Rheic) would have continued to expand as the continents migrated toward sites of mantle downwelling ill the paleo-Pacific, reassembling an extroverted supercontinent as this ocean closed. Instead, Pangea assembled as a result of the closure of the younger Iapetus and Rheic Oceans. Geodynamic linkages between these three oceans preserved in the rock record suggest that the reversal in continental motion may have coincided with the Ordovician emergence of a super-plume that produced a geoid high in the paleo-Pacific. If so, the top-down geodynamics used to account for the breakup and dispersal of a supercontinent at ca. 600-540 Ma may have been overpowered by bottom-up geodynamics during the amalgamation of Pangea.