Influence of the subducting plate velocity on the geometry of the slab and migration of the subduction hinge

Geological observations indicate that along two active continental margins (East Asia and Mediterranean) major phases of overriding plate extension, resulting from subduction hinge-retreat, occurred synchronously with a reduction in subducting plate velocity. In this paper, results of fluid dynamical experiments are presented to test the influence of the velocity of the subducting plate on the hinge-migration velocity and on the geometry of the slab. Results show that hinge-retreat decreases with increasing subducting plate velocity. In addition, phases of hinge-retreat alternate with phases of hinge-advance for relatively high subducting plate velocities due to interaction of the slab with the bottom of the box, simulating the upper-lower mantle discontinuity. Such slab kinematics could explain the episodic behaviour of back-arc opening observed in convergent settings. The geometry of the slab and the kinematics of subduction are significantly affected by the velocity of the subducting plate. Three subduction modes with accompanying slab geometry can be recognized. A relatively low subducting plate velocity is accompanied by relatively fast hinge-retreat with backward sinking of the slab and a backward draping slab geometry. With increasing subducting plate velocity hinge-migration is relatively small, resulting in subvertical sinking of the slab and a folded slab piling geometry. For a very high velocity the hinge migrates forward, resulting in forward oriented subduction vectors and a forward draping slab geometry.