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Gaps in hypocentral distributions and within tomographic images of subducted slabs provided the first observations of possible slab detachment (or break-off), the process by which a portion of a subducted slab breaks away from subducting lithosphere. The existence of detached slabs has been increasingly supported by more recent studies. For instance, slab break-off is suggested to have occurred beneath such regions as the Alps, the Mediterranean- Carpathian Region, and New Hebrides Islands and is surmised to be a cause for observations including surface uplift, magmatism, and cessation of subduction. Previous investigations of slab detachment have largely been limited to 2D static models and force balance calculations to determine the feasibility of detachment of a slab to occur, and to assessment of the maximum surface uplift and thermal effects of shallow detachment. Recently, 2D numerical models have indicated that following the cessation of subduction, necking of the slab and rapid detachment occurs over a few millions years due to weakening of the slab by shear heating. Although slab detachment has not yet been modeled in 3D, observations of lateral migration of subsidence along strike above the possibly detaching Carpathian slab suggest that the process of slab detachment is inherently 3D and may initiate at the edge of a slab and migrate laterally as a tear along the slab. We present fully dynamic numerical flow models exploring the process of slab detachment in 3D. Our study also investigates the effect of slab thickness or age and maximum yield stress of the cold slab interior on the process of slab detachment. The flow models employ an effective viscosity in which the total strain rate is accommodated by diffusion and dislocation creep. At the cold temperatures of the slab interior, a yield stress criteria is used to simulate the deformation by Peierls mechanism of low temperature plasticity. We report on the time scale and morphology of detachment, the resulting surface deformation, and the dynamics of the detached slab within the mantle. Comparison of model results to the observed time-scale and geometry of surface deformation provides initial constraints on the rheology of cold subducted lithosphere.
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