Overthrusting; Western Swiss Alps; Nappe stacking; Numerical modeling
Spitz Richard, Schmalholz Stefan M., Kaus Boris J.P., Popov Anton A. (2019), Quantification and visualization of finite strain in 3D viscous numerical models of folding and overthrusting, in Journal of Structural Geology
Kiss Dániel, Podladchikov Yuri, Duretz Thibault, Schmalholz Stefan M. (2019), Spontaneous generation of ductile shear zones by thermal softening: Localization criterion, 1D to 3D modelling and application to the lithosphere, in Earth and Planetary Science Letters
, 519, 284-296.
Bauville Arthur, Schmalholz Stefan M. (2017), Tectonic inheritance and kinematic strain localization as trigger for the formation of the Helvetic nappes, Switzerland, in Swiss Journal of Geosciences
, 110(2), 523-534.
von Tscharner M., Schmalholz S.M., Epard J.-L. (2016), 3-D numerical models of viscous flow applied to fold nappes and the Rawil depression in the Helvetic nappe system (western Switzerland), in Journal of Structural Geology
, 86, 32-46.
Bauville Arthur, Schmalholz Stefan M. (2015), Transition from thin- to thick-skinned tectonics and consequences for nappe formation: Numerical simulations and applications to the Helvetic nappe system, Switzerland, in Tectonophysics
, 665, 101-117.
von Tscharner M., Schmalholz S. M. (2015), A 3-D Lagrangian finite element algorithm with remeshing for simulating large-strain hydrodynamic instabilities in power law viscoelastic fluids, in Geochemistry, Geophysics, Geosystems
, 16(1), 215-245.
von Tscharner M., Schmalholz S. M., Duretz T. (2014), Three-dimensional necking during viscous slab detachment, in Geophysical Research Letters
, 41(12), 4194-4200.
Bauville Arthur, Schmalholz Stefan M. (2013), Thermo-mechanical model for the finite strain gradient in kilometer-scale shear zones, in Geology
, 41(5), 567-570.
Bauville Arthur, Epard Jean-Luc, Schmalholz Stefan M. (2013), A simple thermo-mechanical shear model applied to the Morcles fold nappe (Western Alps), in Tectonophysics
, 583, 76-87.
A 3-D Lagrangian finite element algorithm with remeshing for simulating large-strain hydrodynamic instabilities in power law viscoelastic fluids
The 3D numerical algorithm is available as supplementary material associated to the publication of von Tscharner and Schmalholz (2015)
The Alps are a mountain range made of tectonic nappes and have long been a testing ground for revolutionary ideas in tectonics, such as the nappe theory. However, despite more than 100 years of research and an enormous amount of geological data the mechanisms by which nappes form are still one of the major unsolved problems in tectonics. To understand the mechanism of nappe formation, it is not enough to perform field work and data analysis, it is equally necessary to apply numerical models which relate the thermo-mechanical processes acting during nappe formation to the acquired data. This project studies the dynamics of nappe formation with numerical modeling and compares numerical results with available data from the Helvetic nappe system. In this project two ongoing PhD studies focusing on the formation of fold nappes in two (2D) and three (3D) dimensions will be finished and two new PhD studies will be started. The first new study applies a 2D thermo-mechanical numerical algorithm to investigate large-displacement overthrusting and nappe stacking. The stacking, or emplacement, of nappes in the Alps happened in an ordered succession such that the stacking order from top to bottom reflects the palaeogeographic position from south to north, respectively. However, the thermo-mechanical conditions (i.e. flow laws, geotherm, layer thickness etc.) necessary to generate such ordered nappe stacking have not been studied until now. The applied 2D algorithm is based on the finite element method, uses a viscoelastoplastic rheology, considers thermo-mechanical coupling, gravity and a free surface. The remeshing is done by a contour-line method that guarantees high numerical accuracy for the large strain deformation of layers with strongly varying strength representing the competent limestone units and the weak shale units in the Helvetic nappe system. The first sub-study will investigate systematically the necessary thermo-mechanical conditions for large-displacement overthrusting applying an initial weak zone in the strong layer from where overthrusting can initiate. The second sub-study will investigate the necessary conditions for the ordered stacking of several nappes. The third sub-study will provide a model configuration that can simulate the formation of the Morcles fold nappe together with the overthrusting Diablerets nappe and the deformation of the underlying basement. The second study will investigate the lateral transition from folding to overthrusting in 3D which is also characteristic for the Helvetic nappe system. The 3D algorithm is also based on the finite element method, considers viscoelastocplastic rheologies and gravity, and uses a remeshing strategy based on contour lines. The first sub-study will investigate the control of lateral variations in the thickness of a weak detachment horizon on the transition from folding (larger thickness of the detachment horizon) to overthrusting. The geometry, finite strain, strain rate and stress fields will be quantified and compared with available data from the Helvetic nappe system. The second sub-study investigates the impact of laterally varying strength in the strong layer on the transition between folding and overthrusting. The critical strength variation causing a transition from folding to overthrusting will be quantified. The results will be applied to available data for the Morcles nappe west of the Rhone valley because there different tectonic interpretations exist and the numerical results can be used to test these interpretations. The results of this project will improve our understanding of the dynamics of tectonic napes and of the tectonic evolution of the Alps. The project involves collaboration with other scientists of the Faculty of Geosciences and Environment at the University of Lausanne.