GeoFocus volume 17 Cécile BONNET Interactions between tectonics and surface processes in the Alpine foreland: Insights from analogue model and analysis of recent faulting Dent de Bimis fault (Vanil Noir area) Crystalline Penninic Molasse Prealpes massifs nappes klippen Jura basin Département de Géosciences, Géologie et Paléontologie, Université de Fribourg (Suisse) DÉPARTEMENT DE GÉOSCIENCES – GÉOLOGIE ET PALÉONTOLOGIE UNIVERSITÉ DE FRIBOURG (SUISSE) Interactions between tectonics and surface processes in the Alpine foreland: Insights from analogue model and analysis of recent faulting THÈSE présentée à la Faculté des Sciences de l’Université de Fribourg (Suisse) pour l’obtention du grade de Doctor rerum naturalium Cécile BONNET de Villecerf, France Thèse N° 1551 Multiprint, Fribourg, 2007 Acceptée par la Faculté des Sciences de l’Université de Fribourg (Suisse) sur la proposition de: Dr. Jon MOSAR Université de Fribourg (Suisse) Directeur Dr. Jacques MALAVIEILLE Université de Montpellier (France) Co-directeur Prof. Maurice BRUNEL Université de Montpellier (France) Expert Prof. André STRASSER Université de Fribourg (Suisse) Président du Jury Fribourg, le 02 février 2007 A la mémoire de Martin Burkhard Contents - 1 CONTENTS ABSTRACT ____________________________________ 3 3 - SURFACE PROCESSES VERSUS KINEMATICS OF RÉSUMÉ _____________________________________ 5 THRUST BELTS: RATES OF EROSION, SEDIMENTA- ZUSAMMENFASSUNG _____________________________ 7 TION, AND EXHUMATION - INSIGHTS FROM ANA- REMERCIEMENTS _______________________________ 9 LOGUE MODELLING ABSTRACT _____________________________ 31 1 - INTRODUCTION 3.1 INTRODUCTION _________________________ 31 3.2 ANALOGUE MODELLING EXPERIMENTS _________ 32 1.1 INSIGHTS FROM ANALOGUE MODELLING ________ 11 3.2.1 Experimental set up, basic model and expe- 1.2 FRACTURE PATTERNS AND STRESS IN THE rimental procedure ____________________32 PREALPES _____________________________ 11 3.2.2 Main stages of the reference experiment ___35 3.3 RESULTS OF MODEL ANALYSIS AND TECTONIC IMPLICATIONS __________________________ 36 2 - INTERACTIONS BETWEEN TECTONICS, EROSION 3.3.1 Frontal accretion vs. underplating _________36 AND SEDIMENTATION DURING THE RECENT EVO- 3.3.2 Variations of erosion and sedimentation LUTION OF THE ALPINE OROGEN - ANALOGUE rates ________________________________39 MODELING INSIGHTS 3.3.2.1 Insights from different experiments ___39 3.3.2.2 Comparison with Alpine cross sec- ABSTRACT _____________________________ 13 tions ____________________________40 2.1 INTRODUCTION AND SCOPE OF THE STUDY ______ 13 3.3.3 Material paths ________________________42 2.2 THE NW OROGEN-FORELAND BASIN SYSTEM AND 3.3.3.1 Major experimental tectonic stages MODELING _____________________________ 14 through the trajectories of points 2.2.1 Geological framework of the NW Alps ____14 located in the subducted plate ________42 2.2.2 Experimental setup: geological constraints 3.3.3.2 Complex uplift paths of points located given on models by the restored cross sec- in the lid __________________________ 45 tion of the NW Alps ___________________15 3.4 CONCLUSIONS __________________________ 46 2.2.3 Apparatus and experimental procedure _____18 2.3 EXPERIMENTAL RESULTS ___________________ 21 2.4 DISCUSSION____________________________ 23 4 - SWISS MOLASSE BASIN DYNAMICS: INSIGHTS 2.4.1 Experimental results (tectonic and structural) AND LESSONS FROM ANALOGUE MODELING versus observed structures ______________23 2.4.2 Interactions between mechanics and surface ABSTRACT _____________________________ 49 processes ____________________________24 4.1 INTRODUCTION _________________________ 49 2.4.2.1 Propagation of the thrust fronts _______25 4.2 ANALOGUE TAPERED WEDGE MODEL __________ 50 2.4.2.2 Evolution of foreland basin width _____27 4.2.1 Model setup __________________________51 2.4.2.3 Sediment budget: a semi-quantitative 4.2.2 Results from modeling _________________52 study of the experimental results _____27 4.2.2.1 Inherited structures and initial 2.5 CONCLUSIONS __________________________ 29 basin geometry ___________________52 2 - Contents 4.2.2.2 Stages of structural development _____52 5.4 CHABLAIS PREALPES _____________________ 91 4.2.2.3 Basin evolution or erosion 5.4.1 Presentation of the study area ____________91 versus sedimentation _______________52 5.4.1.1 Structural and tectonic features _______91 4.3 SEDIMENTATION IN THE MOLASSE BASIN 5.4.1.2 Stratigraphy and sedimentology ______92 OF SWITZERLAND ________________________ 56 5.4.2 Results of the feature analyses ___________94 4.3.1 Sedimentation and sedimentary budgets ____56 5.4.2.1 Lineament and fracture analysis ______94 4.3.2 Basin evolution and tectonics ____________57 5.4.2.2 Stress analysis ____________________94 4.3.3 Flexural models of the Molasse Basin _____59 5.5 INTERPRETATION IN TERMS OF DEFORMATION 4.3.4 Insights and lessons from analogue modeling MODEL _______________________________ 97 on the Alps and Molasse Basin ___________60 5.5.1 Theoretical models ____________________97 4.4 CONCLUSIONS __________________________ 62 5.5.2 Local interpretation ___________________100 5.5.2.1 Prealpes Romandes _______________100 5.5.2.2 Chablais ________________________102 5 - TRANSCURRENT FAULTING IN THE PREALPES 5.6 CONCLUSIONS _________________________ 104 KLIPPEN BELT 5.6.1 Morphologic analysis _________________104 5.6.2 Fault and lineament analysis ____________104 5.1 INTRODUCTION _________________________ 65 5.6.3 Stress analysis _______________________105 5.1.1 Aims of the study _____________________65 5.6.4 Regional fracture model: transcurrent 5.1.2 Methodology _________________________68 faulting ____________________________105 5.1.2.1 Data ____________________________68 APPENDICES TRANSCURRENT FAULTING _______ 109 5.1.2.2 Structure analysis _________________68 5.1.2.3 Orientation analysis________________69 5.1.2.4 Stress analysis ____________________69 REFERENCES ________________________________ 117 5.2 PREALPES GEOLOGY ______________________ 70 APPENDICES _________________________________ 127 5.2.1 Tectonics ____________________________70 Appendix 1 Sandbox device and experimental 5.2.2 Stratigraphy and paleogeography _________71 procedure _____________________128 5.3 PREALPES ROMANDES ____________________ 73 Appendix 2 Description of the experiments ____130 5.3.1 Presentation of the study area ____________73 Appendix 3 List of the experimental movies ____152 5.3.1.1 Structural and tectonic features _______73 Appendix 4 Evolutionary plates of the experi- 5.3.1.2 Stratigraphy, sedimentology and rheo- ments 42 to 47 _________________153 logy ____________________________75 Appendix 5 Structural evolutionary plates of 5.3.2 Results of the feature analyses ___________78 the experiments 42 and 46 ________168 5.3.2.1 Morphologic features ______________78 Appendix 6 Properties of analogue materials ___170 5.3.2.2 Lineament and fracture analysis ______82 Appendix 7 Structural map of the western Alpine 5.3.2.3 Comparison of methods and analyses __83 orogen-foreland system __________184 5.3.2.4 Stress analysis ____________________85 CURRICULUM VITAE ___________________________ 187 ***** Abstract - 3 ABSTRACT To study the dynamics of an orogen-foreland The experiments show that two main mechanisms system and more particularly the impact of surface control the orogenic growth: frontal accretion and processes on its development, we base our work on underplating. In the foreland basin, frontal accretion two main axes. In a fi rst part, using analogue tapered leads to the development of a foreland thrust belt, wedge models, we investigate the interplay between while in the hinterland, simple underthrusting and tectonics, erosion and sedimentation during the oro- subsequent underplating lead to the formation of an genic growth. The basis model mimics the evolution antiformal nappe stack. The foreland basin evolution of a wedge section extending from the orogen to its is mainly towards the front of the orogenic wedge but foreland basin, with both the structural and the litho- it differs depending on the amounts of erosion/sedi- logical heritages simulated. In a second part, the focus mentation. Its evolution and internal structuring are is on the recent tectonic and geomorphologic pro- governed by the wedge mechanics, thought to be the cesses affecting the Swiss Prealpes klippen belt and main controlling mechanism in a feedback interaction surrounding structural units (Molasse Basin and Jura with surface processes. The basin grows to a threshold fold-and-thrust belt). Remote sensing analyses allow width and remains more or less constant during the to evaluate the impact of tectonics on the drainage pat- subsequent evolution. This is possible because some tern and landscape morphology. In addition, local fi eld older formed fold-and-thrust units are being eroded investigations in the Prealpes provide information on out of the record in the trailing part of the basin, while the nature and kinematic of brittle fractures and the new units grow in its frontal part. During the develop- paleostress fi elds. ment of the foreland fold-and-thrust belt, we observe the erosion of entire thrust units of freshly sedimented Insights from analogue modeling materials. As these types of events are untraceable in the tectonic and sedimentary record, this process leads The series of seventeen analogue model experi- to underestimating total shortening obtained from ments is based on a section across the north-wes tern balan cing remaining units only. Alpine wedge and foreland