Continental slivers in oceanic transform faults controlled by rift inheritance

The theory of plate tectonics describes how continents are separated from each other by continental rifting and breakup followed by the birth of new oceans and divergent plate boundaries ^1,2 . The lateral movement of plates is accommodated by transform faults connecting mid-ocean ridge sections and leaving scars of inactive fracture zones on the ocean floor ^3,4 . The occurrence of continental crustal slivers at distances of hundreds to thousand kilometres from the ocean-continent boundary has been documented worldwide ^5,6,7,8 , which does not fit into the classical plate tectonic models and a physical mechanism for their origin and emplacement into oceanic plates has remained elusive. Here, we use 3D magmatic-thermomechanical numerical models to investigate the transition from continental rifting to the birth of oceanic transform fault zones and their relationship to mantle melting and crustal tectonics. Our numerical models are the first to show the formation and evolution of continental slivers entrapped within shear zones in the oceans inherited from the preceding continental rifting stage. We show three distinct stages of transform fault zone formation — continental rift linkage, proto-transform, oceanic transform — controlled by the progressive strain localization into a narrowing extension-parallel strike-slip shear zone. The continental sliver emplacement into the oceanic lithosphere is associated with specific pulses of subsidence and uplift linked to the changing stress field, thereby notably modifying the ocean floor morphology, mid-ocean ridge melting conditions and transform seismicity. The modelled emplacement of continental slivers into emerging and mature oceanic transform faults explains well the observed global distribution of oceanic and continental lithosphere.