The slab detachment benchmark

The slab detachment benchmark#

This section was contributed by Cedric Thieulot and Anne Glerum.

Slab detachment (slab break-off) may occur in the final stages of subduction as a consequence of the combination of a buoyant crust and strong slab pull. It is often invoked to explain geophysical and geological observations such as tomographic images of slab remnants and exhumed ultra-high-pressure rocks [Garzanti et al., 2018, Wortel and Spakman, 2000, van Hunen and Allen, 2011].

This benchmark is based on the setup by S. Schmalholtz [Schmalholz, 2011], which was subsequently run with by A. Glerum [Glerum et al., 2018]. The computational domain is a \(1000 \text{ km}\times 660 \text{ km}\) box. No-slip boundary conditions are imposed on the sides of the system, while free-slip boundary conditions are imposed at the top and bottom.

Initial geometry

Fig. 186 Slab detachment benchmark: Initial geometry#

Two materials are present in the domain: the lithosphere and the mantle as shown in Fig. 186. The gravity acceleration is Earth-like with \(g=9.81 \text{ m}\text{ s}^2\). The overriding plate is \(80\text{ km}\) thick and is placed at the top of the domain. The already subducted lithosphere extends vertically into the mantle for \(250 \text{ km}\). This slab has a density \(\rho_s=3300\text{ kg/m}^3\) and is characterized by a power-law flow law so that its effective viscosity depends on the square root of the second invariant of the strainrate \(\dot\varepsilon\):

\[\eta_{eff} = \eta_0 \, \dot\varepsilon^{1/n-1}\]

with \(n=4\) and \(\eta_0=4.75\times 10^{11}\text{ Pa . s}\). The mantle occupies the rest of the domain and has a constant viscosity \(\eta_m=1\times 10^{21}\text{ Pa . s}\) and a density \(\rho_m=3150\text{ kg/m}^3\). Viscosity is capped between \(1\times10^{21}\text{ Pa . s}\) and \(1\times 10^{25} \text{ Pa . s}\). Fig. 187 shows the various fields and their evolution through time. As shown in Glerum et al. [2018], Schmalholz [2011] the hanging slab necks, helped by the localizing effect of the nonlinear rheology. Model results were shown to compare favorably to the results of Schmalholz [2011] in Glerum et al. [2018], Hillebrand et al. [2014] and the effect of viscosity and material averaging was explored in [Glerum et al., 2018].


Fig. 187 Slab detachment benchmark: a,b) velocity and strain rate fields at \(t=0\). c,d,e) and f,g,h) time evolution of the viscosity and slab composition fields at \(t=0, 6, 12\text{ Myr}\).#