Résumé
Understanding subduction rheology in both space and time has been a challenge since the advent of plate tectonics.We herein focus on "subduction infancy", which corresponds to the first 0-2 My immediately following subductionnucleation, when a newly born slab penetrates into the overriding plate mantle and heats up.The only remnants of this critical, yet elusive, geodynamic step are thin metamorphic soles, commonly found beneathpristine, 100-1000 km long portions of oceanic lithosphere emplaced on top of continents (i.e. ophiolites).In this study, we show how, during subduction infancy, transient mechanical properties of both the mantle and crustacross the subduction plate interface (during 100s ky) control and hinder the penetration of tectonic plates intothe mantle, and how this results in strong peaks of resistance and even slicing of their surface — leaving behindthin, chopped-off metamorphic slivers (i.e. metamorphic soles).These findings constrain the mechanical behaviour of the subduction plate interface (with implications for couplingprocesses and earthquake generation) as well as the properties of the crust and mantle. They also highlight the roleof fluids in enabling subduction to overcome this early resistance.