Abstract
When mountain ranges upper parts express crustal extension direction collinear to the convergence direction, it is traditionally accepted that the extensive motor is gravitational collapse. However, recent studies challenge this paradigm by showing that erosion induces uplift and extension in the central part of the low convergent mountain ranges. Our goal is to investigate the impact of the denudation on the seismotectonic regime of mountain ranges.In order to identify a relationship between seismotectonic regime and erosion, the first part of this work presents a compilation of data in the mountain ranges. Based on these observations, a simple kinematic model is proposed to predict the seismotectonic regime of the chain. Thus, for low convergence rate chains with a moderate mean elevation, this model predicts an extension regime when the denudation rate is 15% higher than the convergence rate.The second part is devoted to the development of thermomechanical 2D finite element model to study the impact of surface processes on the deformation of the Pyrenees. The results show that the isostatic response to erosion reactivates pre-existing structures. The kinematics of an inherited fault plane can be predicted due to the gradient of the horizontal surface velocities profile. Thus, a plane located in the eroded zone is reactivated in normal fault when in a border area of this same plane is reactivated in reverse fault. These results suggest that the current deformation in the North Pyrenean Zone could be the result of surface processes.Given the small number of studies quantifying erosion rates in the Pyrenees, the models developed in the second part suffer from high uncertainty. To remedy this, we sought to quantify it in the central Pyrenees through a study that combines two types of data: watershed denudation rates from cosmogenic isotopes concentration, and incision rates from sediments buried in the karst. These results are presented in chapter 3. Denudation profiles obtained are consistent with a replay of a normal fault plane located in the North Zone of the Central Pyrenees.In the Alps, a good correlation appears between the value of the rate of erosion and geodetic vertical velocities, which raises the question of the impact of the late-würmian deglaciation in the Alps on the present deformation. A numerical model detailing this relationship is presented in the fourth chapter. The results show that deglaciation of the western Alps is controlled by the rheological heterogeneity of the crust. Some of our models predict uplift rates consistent with those highlighted by geodesy.