3D Slab-breakoff in laboratory experiments
Résumé
We study slab-breakoff of subducting plates with variable orientations of passive margins (continental-ocean transition (COT)) by using three-dimensional laboratory experiments. Our results show that the initial obliquity of the continental-oceanic transition with the trench determines the depth and timing at which slab-breakoff occurs. Models with straight COT show that slab-breakoff takes place first in the central section of the subduction zone at a depth equivalent to ~250 km and then propagates rapidly toward the edges of the subduction zone where it develops at slightly larger depths (~280 km). In models in which the passive margin arrives first on the edges of the subduction zone, slab-breakoff starts at that location and propagates laterally toward the center of the subduction zone. It results in higher slab-breakoff depths at the edges of the subduction zone than at the center (maximum difference of 170 km). In models where the passive margin arrives first in the center of the subduction zone the opposite is observed. Slab-breakoff starts first at the center of the subduction zone and propagates toward the edges over a period that can be as large as 31 Ma and with variable depths (maximum difference of 165 km). The rate of lateral propagation of slab-breakoff lowers with increasing initial obliquity of the OCT with the trench. A set of experiments exploring slab-breakoff propagation along oceanic corridors with variable geometries has been performed. Preliminary results show that the buoyant material surrounding the oceanic corridor driven into subduction along with the 3D geometry effect, could explain the drastically diminish on the subduction velocity. We also tested models in which we implemented STEP faults that show the opposite behavior: high subduction velocities and fast slab-breakoff along the COT in the oceanic corridor.