Numerical analysis of lithosphere deformation

This thesis comprises several studies in the modelling of lithosphere deformation, using an improved thin viscous sheet model. The lithosphere is represented by a thin viscous sheet with power-law viscosity, which is deformed by external forces as surf ace forces and also by buoyancy forces arising through density heterogeneities. The lithosphere is in isostatic equilibrium and the effects of a lithospheric root or anti-root are incorporated. The thickness of the lithosphere, when perturbed by deformation, tends to be restored to the initial value by thermal processes which can be approximated mathematically. The model is then used to test some hypotheses relating to the tectonics of the Tibetan Plateau. The results show that the late E-W extension of the Tibetan Plateau is probably associated with recent uplift of the plateau due to the detachment of the lower part of the thickened lithosphere, which is denser than the asthenosphere. Three instances of continental extension leading in some circumstances to rifting have also been studied, with the mantle playing a different role in each of them: a) Airy type of compensation is assumed during extension, so that the subsidence of the top surface is totally balanced by the ascent of the Moho (or crustal anti-root); b) the subsidence of the top surface is partly compensated by the lithospheric anti-root, as well as the crustal anti-root; c) mantle upwelling elevates the lithosphere and causes initial doming. The results suggest, among other things, that currently active continental rifts, where the rifting had not been predated by initial doming, have developed along preexisting weak belts