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Towards understanding fold nappe dynamics in the Western Swiss Alps

English title Towards understanding fold nappe dynamics in the Western Swiss Alps
Applicant Schmalholz Stefan Markus
Number 131897
Funding scheme Project funding (Div. I-III)
Research institution Institut de géologie et de paléontologie Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geology
Start/End 01.10.2010 - 31.10.2013
Approved amount 316'672.00
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Keywords (10)

Fold nappes; Numerical modeling; Western Swiss Alps; Nappe; fold nappe; folding; finite element method; Morcles nappe; structural geology; tectonics

Lay Summary (English)

Lead
Lay summary
Fold nappes are kilometer-scale geological structures in the Western Swiss Alps and known since more than 100 years, but the basic mechanisms by which these fold nappes form are still not understood. In this project, the basic deformation mechanisms which formed these fold nappes are investigated with computer simulations in combination with structural geological field work.Fold nappes are large recumbent folds of sometimes more than 10 kilometers in size. Without a thorough knowledge of the mechanisms which formed these fold nappes, the tectonic history of the Western Swiss Alps cannot be understood and reconstructed correctly. Fold nappes have been observed also in many other mountain ranges, such as for example the Himalaya, and, therefore, a better understanding of fold nappe formation is also important to better understand the formation of mountain ranges in general. A better understanding of fold nappe formation will allow (i) to better constrain the amount of shortening that was necessary to form mountains, (ii) to better understand the deformation behavior of crustal rocks during mountain building and (iii) to more accurately assess the deeper structure of mountain ranges which cannot be observed directly in the field. The general aims of this project are to improve our understanding of (i) the mechanisms of fold nappe formation in general and (ii) the tectonic evolution of the fold nappes in the Western Swiss Alps. In this project, the mechanical deformation processes generating fold nappes are investigated with computer simulations. The computer simulations are based on the physical laws that describe the deformation of solids and fluids and are also widely applied in engineering applications (e.g. fluid dynamics). The computer programs applied in this project can simulate rock deformation in two and three dimensions. The simulations also consider the temperature evolution. The results of the computer simulations will be compared with already available and with during this project newly collected field data. These data will be saved in a common data base to allow a direct and quantitative comparison. The results of this comparison are used to modify the computer simulations (e.g. geometry or material parameters) in order to provide computer simulations of fold nappe formation which agree as good as possible with the field data, for example the fold nappe geometry. In particular, this project focuses on two main topics: (1) the two-dimensional large strain formation of fold nappes with application to the Morcles nappe and (2) the formation of ductile fold nappes in three dimensions with application to the Morcles-Doldenhorn nappe.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
3-D numerical models of viscous flow applied to fold nappes and the Rawil depression in the Helvetic nappe system (western Switzerland)
Von Tscharner Marina, Schmalholz Stefan, Epard Jean-Luc (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.
A 3-D Lagrangian finite element algorithm with remeshing for simulating large-strain hydrodynamic instabilities in power law viscoelastic fluids
Von Tscharner Marina, Schmalholz Stefan (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, 215-245.
Transition from thin- to thick-skinned tectonics and consequences for nappe formation: numerical simulations and applications to the Helvetic nappe system, Switzerland
Bauville Arthur, Schmalholz Stefan (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.
Three-dimensional necking during viscous slab detachment
Von Tscharner Marina, Schmalholz Stefan, Duretz Thibault (2014), Three-dimensional necking during viscous slab detachment, in Geophysical Research Letters, 41, 4194-4200.
Thermo-mechanical model for the finite strain gradient in kilometer-scale shear zones
Bauville Arthur, Schmalholz Stefan (2013), Thermo-mechanical model for the finite strain gradient in kilometer-scale shear zones, in Geology, 41(March), 567-570.
A simple thermo-mechanical shear model applied to the Morcles fold nappe (Western Alps)
Bauville Arthur, Epard Jean-Luc, Schmalholz Stefan M., A simple thermo-mechanical shear model applied to the Morcles fold nappe (Western Alps), in Tectonophysics.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Swiss Geoscience Meeting 2013 Poster 3D FEM modelling of geological structures caused by geometrical instabilities and contrasts in rock strength 15.11.2013 Lausanne, Switzerland Schmalholz Stefan Markus; von Tscharner Marina;
Swiss Geoscience Meeting 2013 Poster Slab detachment – 3D versus 1D 15.11.2013 Lausanne, Switzerland Schmalholz Stefan Markus; von Tscharner Marina;
Kolloquium Bern Individual talk Thermo-mechanics of shear zonesandapplication to Alpine nappes 29.04.2013 Bern, Switzerland Schmalholz Stefan Markus;
European Union of Geosciences Conference 2013 Talk given at a conference Thermo-mechanical model for the finite strain gradient in kilometer-scale shear zones 07.04.2013 Wien, Austria Schmalholz Stefan Markus; Bauville Arthur;
European Union of Geosciences Conference 2013 Poster 3D FEM modelling of geological structures caused by geometrical instabilities and contrasts in rock strength 07.04.2013 Wien, Austria Bauville Arthur; Schmalholz Stefan Markus;
European Union of Geosciences Conference 2012 Talk given at a conference Thermo-mechanical model for the finite strain gradient in kilometer-scale shear zones 07.04.2013 Wien, Austria Schmalholz Stefan Markus; Bauville Arthur;
Swiss Geoscience meeting 2012 Poster 3D FEM modeling of fold nappe formation in the Western Swiss Alps 16.11.2012 Bern, Switzerland von Tscharner Marina; Schmalholz Stefan Markus;
GeoMod 2012 Poster Thermo-mechanical model for the strain distribution in kilometer-scale shear zones 16.07.2012 Lausanne, Switzerland Bauville Arthur; Schmalholz Stefan Markus;
European Union of Geosciences Conference 2012 Poster 3D FEM modeling of fold nappe formation in the Western Swiss Alps 23.04.2012 Wien, Austria von Tscharner Marina; Schmalholz Stefan Markus;
Swiss GeoScience Meeting 2011 Poster 3D FEM modeling of fold nappe formation in the Western Swiss Alps 12.11.2011 Zürich, Switzerland von Tscharner Marina; Schmalholz Stefan Markus;
Swiss Geoscience Meeting 2011 Talk given at a conference A simple thermo-mechanical shear model for the Morcles fold nappe 12.11.2011 Zuerich, Switzerland Bauville Arthur; Schmalholz Stefan Markus;
Deformation localization in rocks: new advances Talk given at a conference Strain localization during folding and necking in viscous layers 27.06.2011 Cadaqués, Spain, Spain Schmalholz Stefan Markus;


Communication with the public

Communication Title Media Place Year
Media relations: print media, online media The evolution of the Alps International Innovation International 2012

Associated projects

Number Title Start Funding scheme
149380 Towards understanding the dynamics of tectonic nappe stacking and overthrusting in the Helvetic nappe system 01.11.2013 Project funding (Div. I-III)
144250 Towards understanding the tectonic evolution from magma-poor rifted margins to the Alpine orogen: Insights from 2D and 3D numerical modeling 01.11.2012 Project funding (Div. I-III)

Abstract

Fold nappes are large recumbent folds with amplitudes of sometimes more than 10 kilometers. The aims of this project are to improve our understanding of (1) the dynamics of fold nappe formation in general and (2) the tectonic evolution of the fold nappes in the Western Swiss Alps. Although fold nappes are prominent geological structures in the Western Swiss Alps and in other mountain ranges and field work and data analysis has been performed since more than 100 years, the basic mechanisms by which fold nappes form are still not understood. In this project the mathematical equations of continuum mechanics are solved with numerical algorithms to study the dynamics of fold nappe formation. The different numerical algorithms applied in this project are based on the finite element method and can simulate (1) ductile (i.e. Newtonian viscous or power-law rheology) rock deformation in 2D and 3D, and (2) the thermo-mechanical processes acting during continental lithosphere deformation in 2D. The numerical results will be compared with already available and with during this project newly collected field data. Data, such as nappe geometry, shear sense orientation or finite strain ellipsoid, are available from both the numerical simulations and field work and will be saved in a common data base to allow a direct and quantitative comparison. The results of this comparison are used to adjust the numerical models (e.g. boundary conditions, initial geometry or material parameters) in order to provide numerical simulations of fold nappe formation which agree as good as possible with the basic field data (e.g. nappe geometry, finite strain pattern or distribution of metamorphic grade). To improve the understanding of fold nappe dynamics this project focuses on three main topics: (1) the 2D large strain formation of recumbent folds, including parasitic folds, in ductile multilayers under a combination of simple and pure shear with application to the Morcles nappe, (2) the 2D formation of basement fold nappes and the thermo-mechanical conditions controlling folding versus faulting (i.e. thrusting) of basement-cover sequences with application to the Antigorio nappe and (3) the formation of ductile fold nappes in 3D focusing on fold-axis parallel strain and fold-axis deformation with application to the Morcles-Doldenhorn nappe. Three different and well-established leading-edge numerical algorithms are available for this project and will be applied, elaborated and adjusted to perform the simulations. The numerical simulations will be performed on a high-end computational cluster which is also available for this project. The theoretical modeling work is accompanied by field work and structural analysis which will focus on field areas where (1) existing data is controversial, sparse or unclear and (2) numerical results differ significantly from existing data. We request three PhD students to perform this study, integrating computational tectonics with geological field work and structural analysis. The results of this project will improve our understanding of mountain building processes and the deformation of the Earth’s crustal rocks. The project involves collaboration with other scientists of the Faculty of Geosciences and Environment at the University of Lausanne and will strengthen the already established collaboration with the Department of Earth Sciences at the ETH Zurich.
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