3D slab breakoff in laboratory experiments

International audienceWe study slab breakoff of subducting plates with variable orientations of passive margins (ocean-continent transition: OCT) using three-dimensional laboratory experiments. Our results show that the initial obliquity of the OCT with the trench determines the depth and timing of slab breakoff. The reference model involves a straight OCT parallel to the trench. Slab breakoff first starts in the central section of the subduction zone at a depth equivalent to ∼250 km and then propagates rapidly towards the edges of the subduction zone where it develops at slightly higher depths (∼280 km). In the models where passive margin arrives first at the edges of the subduction zone, slab breakoff starts at that location and propagates laterally towards 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, slab-breakoff starts at that location and propagates towards the edges of the subduction zone over a period that can be as large as 31 Ma and with a large range of depths (maximum difference of 170 km). The rate of lateral propagation of slab breakoff decreases with the increasing initial obliquity of the OCT with the trench. The model with the maximum obliquity shows a correlation between the surface topography and the slab breakoff at depth. The plate surface is uplifted after the oceanic and continental slab segments are mechanically decoupled, and in the final stage of the experiment, when the slab is educted, subsidence develops as the isostatic and dynamic support diminish