Presence of continental slivers in oceanic transform faults determined by rift inheritance

The theory of plate tectonics describes how continents are separated from each other by lateral movement that is accommodated by transform faults connecting mid-ocean ridge sections, which leaves inactive fracture zones on the ocean floor. The occurrence of continental crustal slivers in these fracture zones at distances of hundreds of kilometres to 1,000 kilometres from continents has been documented worldwide, yet their occurrence is not expected from classical plate tectonic theory. Here we use three-dimensional magmatic-thermomechanical numerical simulations to investigate the transition from continental rifting to the birth of oceanic transform fault zones and their relationship to mantle melting and crustal tectonics. These simulations show that continental slivers are entrapped within shear zones in the oceans inherited from preceding continental rifting stage. They also show three distinct stages of transform fault zone formation-continental rift linkage, proto-transform, oceanic transform-resulting from progressive strain localization into a narrowing extension-parallel strike-slip shear zone. Additionally, continental sliver emplacement into oceanic lithosphere is shown to be associated with specific stages of subsidence and uplift linked to the changing transtensional and transpressional stress field, thereby notably modifying the ocean floor morphology, mid-ocean ridge melting conditions and transform fault seismicity.