A short (∼5 m.y.) episode of deformation accompanied the onset of the present phase of subduction beneath northern and eastern New Zealand in the earliest Miocene. At many places along the continental margin, the structures produced were dominated by subhorizontal thrust sheets with tens of kilometres of displacement. Thrusting was directed both landward (with or without involvement of the upper part of the downgoing plate) and seaward. The structures are different in style from those typical of active trench slopes, which are predominantly seaward-directed imbricate thrusts and associated folds. The structures show that delamination of the downgoing plate occurred at some places and suggest that a high degree of coupling between upper and lower plates occurred at others.