Active lithospheric thinning

This paper starts with a discussion of the physical mechanisms capable of inducing a rapid upward migration of the lithosphere-asthenosphere boundary. Two models based on a thermomechanical destabilization of the lower lithosphere are proposed. First, we consider the enhancement of small scale sublithospheric convection modes by a hot thermal plume. A perturbation of a few hundred degrees is found to thin the lithosphere and generate uplift within a few tens of million years. This efficient erosion from below only stops when it reaches a layer of low density such as the crust or some depleted mantle material. Second, we show that passive lithospheric stretching leads to an unstable lithospheric configuration on the sides of the rift. The denser unstretched lithosphere is subject to a lateral convective penetration by the hotter asthenospheric mantle material coming from the rift zone. This lateral destabilization generates uplift of the shoulders. Natural examples can be found along passive continental margins. A good example is given by the uplift of the Scandinavian Caledonides following the break-up in the North-Atlantic.