Craton delamination induces circum-supercontinent subduction

Over the past billion years, Earth’s large-scale tectonics have been dominated by the assembly and breakup of supercontinents Rodinia and Pangea. It is widely accepted that circum-supercontinent subduction and associated sub-supercontinent upwelling trigger supercontinent breakup. Yet, previous geodynamic simulations predicted that whole mantle convection would stabilize in a fixed, long-wavelength mode, with a common degree-1 pattern resembling a stable supercontinent. In contrast, geological records show that continental arcs rapidly formed along circum-supercontinent passive margins shortly prior to the breakup of Rodinia and Pangea, indicating successful subduction initiation and an evolving supercontinent cycle. Thus, it requires an additional mechanism for subduction initiation along circum-supercontinent passive margins beyond self-organizing mantle flow. Here, we propose a new mechanism for subduction initiation at the passive margin before supercontinent breakup, based on geological records and the recent finding that the cratonic lithospheric mantle comprises a buoyant upper layer, a weak mid-lithospheric discontinuity, and a dense lower layer. We demonstrate that perturbations, such as plume underplating or melt infiltration, could initiate delamination of the dense lower cratonic mantle lithosphere, while the remaining buoyant continent uplifts, weakening the nearby passive margin and decoupling the continental and oceanic lithosphere. Eventually, the enhanced density contrast across the former passive margin leads to the formation of a new ocean-continent subduction zone. We suggest that this new subduction initiation mechanism is a key driver of the periodic operation of supercontinent cycles, modulating Earth’s long-term tectonic evolution.