Rapid subduction initiation and magmatism in the Western Pacific driven by internal vertical forces

Plate tectonics requires the formation of plate boundaries. Particularly important is the enigmatic initiation of subduction: the sliding of one plate below the other, and the primary driver of plate tectonics. A continuous, in situ record of subduction initiation was recovered by the International Ocean Discovery Program Expedition 352, which drilled a segment of the fore-arc of the Izu-Bonin-Mariana subduction system, revealing a distinct magmatic progression with a rapid timescale (approximately 1 million years). Here, using numerical models, we demonstrate that these observations cannot be produced by previously proposed horizontal external forcing. Instead a geodynamic evolution that is dominated by internal, vertical forces produces both the temporal and spatial distribution of magmatic products, and progresses to self-sustained subduction. Such a primarily internally driven initiation event is necessarily whole-plate scale and the rock sequence generated (also found along the Tethyan margin) may be considered as a smoking gun for this type of event. The magmatic progression produced during the initiation of the Izu-Bonin-Marianas subduction zone took place rapidly over 1 million years, but it has been unclear why. Here, using numerical models, the authors show that subduction initiation was dominated by vertical forces, internal to the system itself, progressing to self-sustained subduction.