Numerical simulations of the mantle lithosphere delamination

Abstract

[1] Sudden uplift, extension, and increased igneous activity are often explained by rapid mechanical thinning of the lithospheric mantle. Two main thinning mechanisms have been proposed, convective removal of a thickened lithospheric root and delamination of the mantle lithosphere along the Moho. In the latter case, the whole mantle lithosphere peels away from the crust by the propagation of a localized shear zone and sinks into the mantle. To study this mechanism, we perform two-dimensional (2-D) numerical simulations of convection using a viscoplastic rheology with an effective viscosity depending strongly on temperature, depth, composition (crust/mantle), and stress. The simulations develop in four steps. (1) We first obtain ''classical'' sublithospheric convection for a long time period ($300 Myr), yielding a slightly heterogeneous lithospheric temperature structure.(2) At some time, in some simulations, a strong thinning of the mantle occurs progressively in a small area ($100 km wide). This process puts the asthenosphere in direct contact with the lower crust. (3) Large pieces of mantle lithosphere then quickly sink into the mantle by the horizontal propagation of a detachment level away from the ''asthenospheric conduit'' or by progressive erosion on the flanks of the delaminated area. (4) Delamination pauses or stops when the lithospheric mantle part detaches or when small-scale convection on the flanks of the delaminated area is counterbalanced by heat diffusion. We determine the parameters (crustal thicknesses, activation energies, and friction coefficients) leading to delamination initiation (step 2). We find that delamination initiates where the Moho temperature is the highest, as soon as the crust and mantle viscosities are sufficiently low. Delamination should occur on Earth when the Moho temperature exceeds $800°C. This condition can be reached by thermal relaxation in a thickened crust in orogenic setting or by corner flow lithospheric erosion in the overriding lithosphere of subduction zones.

Delamination vs. break-off: the fate of continental collision

“…The major control of the lower crustal strength on the evolution of delamination that we observe is consistent with previous models [Schott and Schmeling, 1998;Morency and Doin, 2004]. Values of lower crust viscosity necessary to obtain the delamination of the lithospheric mantle of 2 x 10 20 Pa s [Gemmer and Houseman, 2007] and Schmeling, 1998] are in agreement with our results.…”

“…[16] Previous numerical and analogue studies on continental collision showed that both delamination [Schott and Schmeling, 1998;Morency and Doin, 2004;Göğüş and Pysklywec, 2008;Valera et al, 2008;Göğüş et al, 2011;Bajolet et al, 2012;Ueda et al, 2012] and slab detachment [Davies and Von Blanckenburg, 1995;Wong A Ton and Wortel, 1997;Gerya et al, 2004;Toussaint et al, 2004;Andrews and Billen, 2009;Burkett and Billen, 2009;Duretz et al, 2011;van Hunen and Allen, 2011] are likely to occur. The major control of the lower crustal strength on the evolution of delamination that we observe is consistent with previous models [Schott and Schmeling, 1998;Morency and Doin, 2004].…”

Asymmetric Delamination and Convective Removal Numerical Modeling: Comparison with Evolutionary Models for the Alboran Sea Region

“…We considered an adiabatic temperature profile for the asthenosphere. This initial state differs from that considered by MORENCY and DOIN (2004), who introduced a crustal structure superimposed and forced on the computed thermal initial state. The values assumed in each run for density and viscosity can be found in Table 2.…”

Physics and Chemistry of Deep Continental Crust Recycling

“…Below, a simplified view of delamination is provided. More detailed presentations can be found elsewhere (Bird, 1979;Jull and Kelemen, 2001;Le Pourhiet et al, 2006;Morency and Doin, 2004;Schott and Schmeling, 1998).…”