Continental Delamination Initiates Subduction and Supercontinent Breakup

Abstract Subduction is a fundamental process that drives plate tectonics1, 2 and supercontinent cycles3-5. The separation of a supercontinent requires the initiation of new subduction zones along its passive margins, evidenced in the appearance and increase in global continental arc volcanism6, 7 during the breakup of Pangea and Rodinia. However, the mechanism of subduction initiation (SI) at the passive margin remains elusive. Previous studies show that the mechanical resistance for SI at a mature passive margin cannot be overcome by the gravitational force of old oceanic lithosphere, even with the addition of ridge push and sediment loading8-10. Here we propose a new mechanism for passive margin SI due to delamination of the nearby cratonic lithospheric mantle (CLM), following recent findings that the CLM consists of a buoyant upper layer and a dense lower layer11-14, with the net CLM buoyancy significantly greater than that of the ambient mantle13, 14. We demonstrate that dynamic perturbations, such as plume underplating, could trigger lower CLM delamination along preexisting weak zones, while the buoyant upper CLM uplifts to damage the passive margin, ultimately leading to the formation of a new subduction zone. We further show that the developing oceanic subduction generates large extensional stress in the overriding plate, facilitating supercontinent breakup. We suggest that this new SI mechanism represents a key driving force for the periodic operation of supercontinent cycles.