Porous fluid flow enables oceanic subduction initiation on Earth

Although most of the presently active intra‐oceanic subduction zones are relatively young and initiated during the Cenozoic, subduction initiation process remains poorly understood. Previous models of subduction initiation assumed excessive weakening of tectonic plate boundaries that does not reconcile with laboratory rock strength measurements. The weakening was assumed to be caused by fluids present along tectonic fractures; however no self‐consistent solid‐fluid model of subduction initiation has been developed so far. Here we present new numerical hydro‐thermo‐mechanical model of spontaneous intra‐oceanic subduction initiation where solid rock deformation and fluid percolation are fully coupled. Based on 2‐D numerical experiments, we demonstrate that although subduction fails to initiate under fluid‐absent conditions, it can naturally start when porous fluid is present inside oceanic crust and along the plate boundaries. Fluid percolation is localized along spontaneously forming faults where high fluid pressure compensates lithostatic pressure, thus dramatically decreasing friction along the incipient subduction zone. Through the parametric study, we conclude that the most important parameter for subduction initiation is the solid matrix permeability. Paradoxical at first, lowering the permeability indeed favors subduction initiation by maintaining high fluid pressure and thus decreasing friction along active faults.