Magmatic ignitor kick-starts subduction initiation

Abstract

The mechanisms and tectonic context of subduction initiation remain enigmatic. Magmatic records of subduction initiation offer pivotal clues for understanding the nucleation and propagation of new subduction zones. However, the expression of initial subduction-related magmatism is poorly constrained. Using numerical modeling, we demonstrate that a “magmatic ignitor” of mantle melting triggered by upwelling along releasing bends in transform faults that leads to decompression mantle melting and subduction initiation. Initial mantle melting is followed by melting of oceanic crust, hydrated and depleted mantle, and lastly melting of subducted sediment as subduction continues and the slab retreats. This scenario is compatible with the in-situ observations of petrogenesis in the western Pacific. Our self-consistent model suggests that a continuous magmatic ignitor beneath a transform fault resulting in subduction initiation could be a prevalent process in Earth’s plate tectonic evolution.