This video shows the entire evolution of model M1 (reference model). A ca. 400 km wide basin floored by exhumed mantle forms during the extensional period. This embryonic ocean is bounded by two magma-poor hyper-extended passive margins. During the cooling period, small-scale convection cells develop in the upper mantle. Horizontally forced subduction is initiated without prescription of a major weak-zone at one of the passive margins during convergence and single-slab subduction is stabilised.