The dynamics of extrusion tectonics: insights from numerical modeling

To elucidate the dynamics of extrusion tectonics, I investigate the relation between subduction processes and intraplate deformation. Three-dimensional numerical models of subducting upper plate systems show that subduction of a heterogeneous buoyancy slab, that is, hosting continental and oceanic lithosphere, causes the retreat of the oceanic trench and the localization of deformation in the back arc. Similar trench evolution is found when the subducting slab partially detaches from the impinging continent; however, deformation in the upper plate interiors widens, with indentation, plastic yielding and rotation of a large block extruding laterally toward the retreating margin. Indentation stresses are consequence of the partial slab breakoff at depth and vanish when the detached slablet reaches the mantle transition zone, resulting in transient extrusion tectonics. The distance to which indentation deformation propagates depends on the ability of subducting lithosphere to propagate stress laterally and is linear with the lithospheric strength. While in the stretching back arc the plate deformation and the underlying mantle flow are coupled, they are uncoupled in the extrusion tectonics, where mostly stresses propagated through the margin drive rotations. The potential role of these diverse subduction processes in the eastern Mediterranean is discussed, suggesting that different mechanisms likely drive the tectonics of this area.