An application of two-dimensional finite-element modelling for studying the deformation of the Variscan fold-and-thrust belt (Belgium)

摘要

This paper presents 2D finite-element simulations of fold-and-thrust belts with a focus on the Variscan foreland thrust belt in Belgium. The numerical models are limited to the deformation of a 5 km thick sedimentary layer separated from a backstop by a deformable zone. The sedimentary layer obeys an elastic-plastic law and can include one detachment horizon with some ramps. Our study deals with the effects of rheological and geometrical parameters on the structural characteristics of the belt. For regular basin geometries (rectangular and wedge shapes), results of numerical simulations show that deformation continuously propagates and decreases towards the foreland. In agreement with sandbox experiments, the basal friction appears to be a major parameter controlling the tectonic style of a fold-and-thrust belt. Our analysis has also shown that the strain propagation in time and space is strongly controlled by the presence of a weak intra-detachment and of ramps which initiate shear bands. For the Rhenohercynian fold-and-thrust belt, a major decollement is usually considered within the Palaeozoic sediments and the existence of steps in the basin geometry is proven by numerous geological data showing the activity of pre-orogenic normal faulting. During the Variscan orogeny, this irregular detachment horizon influenced the regional tectonics. Simulation results show that ramps create strongly deformed anticlinioria separated by weakly deformed synclinoria which is the basic structure observed in the western and northern Rhenohercynian belt.