Deep and near-surface consequences of root removal by asymmetric continental delamination

Abstract

The occurrence of continental delamination has been proposed for a number of areas characterized by highly variable geodynamic settings. In this study we present results of numerical simulations considering different initial setups, representative for geodynamic scenarios where delamination could potentially develop. To mimic a post-collisional orogenic scenario we have designed an initial state characterized by the presence of an area of orogenic lithosphere, with both crustal and lithospheric roots. In a second setup, we have considered a lithospheric root representative of a remnant slab with a flat overlying crust. We focus on predicted evolution of surface and near-surface observables, namely the crustal structure, surface heat flow and isostatic and dynamic topography evolution. Our results show that a high density orogenic lower crust, likely related to the presence of eclogite, significantly accelerates the sinking of the lithospheric mantle. The pattern of local isostatic elevation is characterized by laterally migrating surface uplift/subsidence. This pattern is shown to be little sensitive to lower crust density variations. In contrast, predicted dynamic topography is more sensitive to these changes, and shows surface subsidence adjacent to the delaminating lithospheric mantle for the model with a high density lower crust, and surface uplift above the slab for a model with a less dense lower crust. The reason for uplift in this second model is that the effect of the positive buoyancy of the thickened crust overwhelms the effect of negative buoyancy of the slowly sinking lithospheric mantle. We infer from our modeling that there is not a specific characteristic pattern of topography changes associated with delamination, but it depends on the interplay between highly variable factors, as slab sinking velocity, asthenospheric upwelling and changes in crustal thickness.