Dynamics of slab detachment

Abstract

We investigate the dynamics of slab detachment around the detachment zone and evaluate the amount of time necessary for slabs to detach. The study combines results of two-dimensional (2D) state-of-the-art thermomechanical numerical simulations and a 1D analytical solution for viscous necking under gravity. We show that the dominant deformation mechanism during slab detachment is viscous necking, independent of the depth of slab detachment. When the slab dip is moderate (35-70), slab detachment is partly affected by localized simple shearing in the colder parts of the slab. Brittle fracturing (breaking) plays a minor role during slab detachment. Our 2D thermomechanical models indicate that the duration of slab detachment, quantified from the onset of slab thinning until the actual detachment (i.e. vanishing of slab-pull force), is relatively short (<5 Ma) and can occur in less than 0.5 Ma. No clear correlation between the depth and the duration of slab detachment was observed. The simulations suggest that even deep slab detachment (>250 km) can occur within a short time interval (<1 Ma) which has implications for geodynamic interpretations using slab detachment as explanation for processes such as melting, exhumation or surface uplift. The thinning of the slab during detachment, observed in 2D simulations, agrees well with predictions from a 1D analytical solution indicating that the 1D solution captures the first-order features of the detachment process. We also evaluate the impact of shear heating on the duration of slab detachment. The predictions of a simple semi-analytical solution, based on dimensionless parameters, agree well with our and previously published results. Copyright 2012 by the American Geophysical Union.