FORE-ARC DEFORMATION IN RESPONSE TO SLAB-PULL AND UPPER PLATE CONVERGENCE: NUMERICAL MODELS

We present numerical thermo-dynamical models, 100 km deep by 1500 km wide, that simulate the response of a forearc submitted to oceanic plate slab-pull and upper plate convergence over one million years. Deformation is distributed along the plate interface and propagates into the upper plate to deform de the surface. Associated to that deformation, a regional stress field is obtained, that exhibits the flexural state of the oceanic lithosphere, and the layered elastic-brittle-ductile behaviour of the continental crust and mantle. Models predict that under conditions of strong plate interface and resistent continental crust, the slab-pull tends to drag the upper plate downwards and may deflect the suface forming vertical faults zones associated to relative normal faulting, about 200 km away from the trench. A lithospheric scale secondary shear zone develops into the continent. As either the thermal field is modified, the plate interface made weaker, the crust made more ductile, or strain-softening accounted for, crustal deformation and thus topography develop compressive structures decoupled from deeper processes: compression overcomes the subsiding influence of the slab-pull boundary condition. The resulting position of faults zones, stress orientation, Moho and topography, give information comparable to that available along the Chilean fore-arc, which gives insight on the possible mechanical processes that produces present day observations.