Plate tectonics, driven primarily by subduction, requires the formation of plate boundaries. The initiation of subduction, the process of one plate sliding beneath another, remains poorly understood. This study uses a continuous, in situ record of subduction initiation from the Izu-Bonin-Mariana subduction system (recovered by IODP Expedition 352) and numerical models to demonstrate that this process is driven by internal, vertical forces rather than previously proposed horizontal external forcing. The models reproduce the observed temporal and spatial distribution of magmatic products, showcasing a rapid (~1 million years) transition from fore-arc basalt to boninite magmatism. This internally driven initiation is a whole-plate scale event, and the resulting rock sequence, also found along the Tethyan margin, serves as evidence for this type of subduction initiation.

B. Maunder, J. Prytulak, S. Goes, M. Reagan