Time after model start (in Myr): top, 15; middle, 24; bottom, 37. The upper plate has been made translucent to most clearly show the shape of the down-going plate and its relationship to the development of the orocline in the indenter. Reduced rollback rates in the convergence direction (Fig. 3) produce the folded slab geometry seen in the foreground. Two lines of markers have been traced along the strain-grid in the oceanic plate. They clearly show that the double-slab geometry is caused by foundering of the oceanic plate during lateral rollback. The trajectories of the individual points and the slab cross-section for the front of the pair of tracer-lines are shown in Extended Data Fig. 6.