Different styles of continental delamination: the influence of the viscosity structure and radiogenic heat production.

Abstract

Thermo-mechanical algorithms are applied in this study to model the asymmetric evolution of a thickened orogenic lithosphere with an adjacent ‘low viscosity conduit’ across the lithosphere. We investigate the influence of viscosity stratification, crustal radiogenic heat production, and nature of the material filling the ‘low viscosity conduit’ on the evolution of delamination. This evolution is shown here to be very sensitive to the lithospheric mantle viscosity and, to a lesser degree, to asthenosphere and lower crust viscosities. An increase of only one order of magnitude in the maximum viscosity of the lithospheric mantle (from 1022 to 1023 Pa s) causes a change from a well-developed delamination with large displacement of delamination point to a complete inhibition of this process. Radiogenic heat production is shown to have a strong influence on the resulting geometry of the sinking lithospheric mantle. Models with high radiogenic heat production in lower crust reproduce asthenospheric upwelling but without creating a slab-like structure in the upper mantle. We obtain that the nature of the material filling the low viscosity conduit, either asthenospheric material or low viscosity lithospheric mantle, does not significantly affect the development of delamination. We suggest that both lithospheric weakening by dehydration processes and thermal thinning processes are plausible mechanisms for the formation of ‘low viscosity conduits’ able to sustain delamination.