Abstract

Subduction is fundamental for maintaining plate tectonics. Magmatic record of subduction initiation offers pivotal clues for understanding the nucleation and propagation of a new subduction zone. However, how subduction is elicited to induce the first-order magmatic observations is yet to be understood. Here, using numerical models, we demonstrate that magmatic ignitor of mantle melting triggered-upwelling along wide and weak fracture zones renders lithospheric mantle sinking and subduction initiation. Progressive decompression melting is sequentially followed by melting of oceanic crust, hydrated and depleted mantle, and sediment of the retreating slab, respectively. This scenario is compatible with the in-situ observations of petrogenesis in the western Pacific, which also explains the enigmatic deferred sediment involvement in the early magmatism. Our self-consistent model indicates that a continuous magmatic ignitor beneath a transform fault resulting in subduction initiation could be a prevalent process in Earth's evolution.