DOCSLIB.ORG

Crustal Structure and Reflectivity of the Swiss Alps from Threeв

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Crustal Structure and Reflectivity of the Swiss Alps from Threeв View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Bern Open Repository and Information System (BORIS) TECTONICS, VOL. 12, NO. 4, PAGES 911-924, AUGUST 1993 CRUSTAL STRUCTURE AND INTRODUCTION REFLECTIVITY OF THE SWISS ALPS FROM THREE-DI•NS IONAL In 1 98 6, the Swiss Nat ional SEISMIC MODELING Research Program 20 (NFP 20) i . HELVETIC NAPPES recorded approximately 120 km of multifold seismic data across the eastern Swiss Alps (Figure 1) with M. Stfiuble 1 and O. A. Pfiffner the aim of imaging structures ob- Geological Institute University of served at the surface which are Bern, Bern, Switzerland, likely to have a subsurface continu- ation and dip toward the seismic lines [Pfiffner et al. 1988, 1990a, S. B. Smithson b] . Because the plunging structures Department of Geology and have been mapped in detail, these Geophysics, University of Wyoming, data can serve as calibration for Laramie crustal reflection surveys in a relatively young orogenic belt. One additional line, crossing the main Abstract. Forward modeling based NFP 20 profile at its northern end on combined geologic surface data, (Figure 2) was recorded in the mid- borehole and laboratory data on ve- seventies by the Schweizerische locities, and seismic reflection Erd61 AG for exploration purposes data aid in understanding the seis- and was reprocessed for this study mic response in a transect through by Stfiuble. complex Alpine nappe structures. The Interpretation of the seismic synthetic seismic response from the data recorded in the Swiss Alps model compares well with the ob- represents a three-dimensional served data. The results suggest, problem because of the complex shape however, that strong three-dimen- and plunge of the various tectonic sional effects result in out-of- units thrust northward over the plane reflections and diffractions, Northalpine foreland. The tectonic as well as defocussing and scatter- style is characterized by fold-and- ing of seismic rays, thus rendering thrust structures, multifold imbri- the use of two-dimensional migration cations, and considerable axial techniques questionable. The model plunges attaining up to 30 ø (see shows an unexpected rapid change in also companion paper by Litak et al. internal structure of the Helvetic [this issue]) . nappes between the seismic line and The purpose of this paper is to outcrops located 6-8 km farther give a three-dimensional interpreta- west. Moreover, the basement-cover tion of the reflection profiles interface on the northern flank of which cross the Helvetic nappes and the Aar Massif, a basement uplift its underlying units, using results with a heave of 8 km, does not rise from three-dimensional ray tracing regularly in the hanging wall of a and modeling software of SIERRA single major thrust fault, but rises Geophysical Inc. in a series of steps due to several thrusts and folds. The northernmost structures appear to be fault-relat- GEOLOGIC FRAMEWORK ed open folds, whereas tight fold structures appear to dominate in the south. The Helvetic Alps of eastern Switzerland have long been the aim of detailed studies. Here only a 1Also at Institute of Geophysics, general outline of the geology is ETH ZUrich, Switzerland. given; for detailed information, the reader is referred to Oberholzer [1933] , Tr•mpy [1969] , Schmid Copyright 1 9 93 by the [1975], Pfiffner [1978, 1981, 1986], American Geophysical Funk et al. [1983], and Pfiffner et Union. al. [1990a, b] . The study area Paper number 93TC00378. (Figure 1) lies within the Helvetic 0278-7407/93/93TC00378510.00 zone and is south of the Molasse 912 St•uble et al.' Three-Dimensional Seismic Modeling, Helvetic Alps ......... ........ ß + +++++ + +++ 0 NAPPES NAPPES NAPPES MASSIFS 1- -',- INTRUSIONS MOLASSE BASIN ALPS Fig. 1. Tectonic map of Switzerland showing the position of the seismic lines and the study area. Basin. The major geological units Alpine nappes [ see Stauble and covered are the Infrahelvetic com- Pfiffner, 1991, and references plex, the Subalpine Molasse, and the therein] . These clastics were Helvetic Nappes (Figure 2). deposited in a peripheral foreland The Infrahelvetic complex [Milnes basin, the Molasse Basin, at the and Pfiffner, 1977] is the lowermost close of the Alpine collision. The unit and consists essentially of study area covers the buried tran- crystalline basement rocks sition between the Flysch and (including the Aar Massif basement Molasse sediments. uplift ) and its Mesozoic to The Helvetic Nappes overly the Oligocene cover sediments. The cover Infrahelvetic complex to the south contains thick carbonate sequences and the Subalpine Molasse to the (notably Triassic dolomites and Late north. In the cross section pre- Jurassic-Cretaceous limestones) in- sented here, the Santis thrust sepa- terlayered with shaly and sandy rates the Helvetic Nappes into two clastics. The youngest sediments nappe complexes [Pfiffner, 1981]: belong to an Eocene-Oligocene the Lower Glarus nappe complex and Flysch. The general structure of the the Upper Glarus nappe complex, Infrahelvetic complex comprises a which is also called Santis Nappe. combination of folding and thrusting The Lower Glarus nappe complex con- at the interface between basement sists of a series of imbricate and cover rocks [Pfiffner et al. thrust sheets in the northern part 1990a, b, and references therein]; of the study area (Figure 3a) . thrust faults with considerable dis- Toward the south this structural placements and ductile folding at style gives way to folds (Figure smaller scale are particularly con- 3b). The sedimentary rocks involved spicuous within the sedimentary are of Triassic and Jurassic age cover [Pfiffner, 1978, 1985]. with approximately 600 m of thick To the north the Subalpine competent Upper Jurassic limestones Molasse consists of Oligocene to forming the mechanically stiff Miocene clastics which were layer. Secondary decoupling between imbricated and overridden by the these limestones and Triassic St•uble et al.' Three-Dimensional Seismic Modeling, Helvetic Alps 9]3 MODELING BASE S'•ntis"•' i For the case studied here we have the rare possibility to observe structures at outcrop adjacent to the profile (Figure 3) which are very likely to continue into the ß.,Santis nappe seismic line and thus can be sampled ß ß .o by the seismic experiment. The starting model is derived from previously published cross sections and maps, two of which are Walensee given in Figure 4 . These cross sections are based on downdip projections and surface structural LowerGlarus data and were completed by structure nappe complex contour maps. The determination of the velocity structure presented a serious prob- lem because no borehole data are available in the Alps. Several dif- ferent approaches were used to nar- row down the possible range of velo- cities; they will now be discussed 13 in more detail. 1. Borehole data from exploration wells drilled into the Molasse Basin Infrahelvetic complex northeast of the study area were used to determine the velocity of 200 the Jurassic and the Tertiary sedi- ments. Lithologies can be traced confidently over large distances, and studies by Lohr [1967, 1978] indicate a clear regional trend of velocities increasing from the Fig. 2. Detailed geologic map and the location of the seismic lines. Molasse Basin toward the Alps due to diagenetic lithification and in- Key' G1, Glarus; S•, S•ntis thrust; creased overburden. For these rea- and AA and BB, traces of cross sec- tions given in Figure 4ß Arrowsare sons,1 are theconsidered velocities to givenrepresent in Tablea major fold axes (with plunges) lower limit of a possible range of seismic velocities. 2. Seismic velocities were mea- sured in the laboratory from repre- dolomites occurs in the mechanically sentative rock samples from the weak shales and sandstones of the study area [Sellami et al., 1990] . Early and Middle Jurassic. The over- Despite the influence of porosity, lying S•ntis Nappe consists of a fluid content, pressure, tempera- folded, 1500-m-thick sequence of ture, and the high frequencies used, Cretaceous limestones (Figure 3a) . these velocities are considered to They were detached from the underly- be more reliable than the values ob- ing Jurassic limestones along the tained from the other methods. lowermost Cretaceous Palfris shales. 3. Interval velocities can be This detachment, the S•ntis thrust derived from stacking velocities, (Figure 3), produced a structural but care has to be applied in com- discontinuity between these two p!ex structures. Stacking velocities units. Particularly important for seem to increase toward the south. the seismic modeling is the 10ø-30 ø This trend, plus the average of the east-northeasterly plunge of the stacking velocities over the whole fold axes in the Helvetic Nappes area, was used as an additional (Figure 2) . constraint. .....•.. :.-'• .:.;'' ':,..'.,. .•.,v ,,,,"•-::';..-"•:.:.¾' : :: :.:..•,::;:::'.' .-:--•,•,•.::...::.:.:. I ............•.;•::,:, .•'..."'"'""•'•½•-:'..:,':::::":::.?.-.:":"•'. ...:...:%..•?::;::;• ...%....-. :• %----,•'7::-..- ..... ,•. ::;::: • '"...',,:½-::•::----.•::,•¾:::;:::.•:....:.,,..:"-:":....'.:: ........ ....... ,3;{:-:.,'e •,.:,-,,,-•*- ,... :..•..,., / ß" ., ;•, ½ ½; . ,•. '•:• •:..,..; "::......... ....'•.:•... ....... :'•:=•' : ,..-:•½•;'",:•4'.:........... -.:'4: /" ¾'" ...,. .. •.•'".,"...::• - .,.•.. •-::•::4. ....... , . .......................:'"" ::::.:. St•uble et al.- Three-Dimensional Seismic Modeling, Helvetic Alps 9]5 The values ultimately chosen
Load more

Recommended publications
  • Fluid Flow and Rock Alteration Along the Glarus Thrust
    1661-8726/08/020251-18 Swiss J. Geosci. 101 (2008) 251–268 DOI 10.1007/s00015-008-1265-1 Birkhäuser Verlag, Basel, 2008 Fluid flow and rock alteration along the Glarus thrust JEAN-PIERRE HÜRZELER 1 & RAINER ABART 2 Key words: Glarus thrust, rock alteration, strain localization, Lochseiten calc tectonite ABSTRACT Chemical alteration of rocks along the Glarus overthrust reflects different the footwall units. In the northern sections of the thrust, the Lochseiten calc- stages of fluid rock interaction associated with thrusting. At the base of the tectonite has a distinct chemical and stable isotope signature, which suggests Verrucano in the hanging wall of the thrust, sodium was largely removed dur- that it is largely derived from Infrahelvetic slices, i.e. decapitated fragments of ing an early stage of fluid-rock interaction, which is ascribed to thrust-paral- the footwall limestone from the southern sections of the thrust, which were lel fluid flow in a damage zone immediately above the thrust. This alteration tectonically emplaced along the thrust further north. Only at the Lochseiten leads to the formation of white mica at the expense of albite-rich plagioclase type locality the original chemical and stable isotope signatures of the calc- and potassium feldspar. This probably enhanced mechanical weakening of the tectonite were completely obliterated during intense reworking by dissolution Verrucano base allowing for progressive strain localization. At a later stage and re-precipitation. of thrusting, fluid-mediated chemical exchange between the footwall and the hanging wall lithologies produced a second generation of alteration phenom- ena. Reduction of ferric iron oxides at the base of the Verrucano indicates DEDICATION fluid supply from the underlying flysch units in the northern section of the thrust.
    [Show full text]
  • Field Trip - Alps 2013
    Student paper Field trip - Alps 2013 Evolution of the Penninic nappes - geometry & P-T-t history Kevin Urhahn Abstract Continental collision during alpine orogeny entailed a thrust and fold belt system. The Penninic nappes are one of the major thrust sheet systems in the internal Alps. Extensive seismic researches (NFP20,...) and geological windows (Tauern-window, Engadin-window, Rechnitz-window), as well as a range of outcrops lead to an improved understanding about the nappe architecture of the Penninic system. This paper deals with the shape, structure and composition of the Penninic nappes. Furthermore, the P-T-t history1 of the Penninic nappes during the alpine orogeny, from the Cretaceous until the Oligocene, will be discussed. 1 The P-T-t history of the Penninic nappes is not completely covered in this paper. The second part, of the last evolution of the Alpine orogeny, from Oligocene until today is covered by Daniel Finken. 1. Introduction The Penninic can be subdivided into three partitions which are distinguishable by their depositional environment (PFIFFNER 2010). The depositional environments are situated between the continental margin of Europe and the Adriatic continent (MAXELON et al. 2005). The Sediments of the Valais-trough (mostly Bündnerschists) where deposited onto a thin continental crust and are summarized to the Lower Penninic nappes (PFIFFNER 2010). The Middle Penninic nappes are comprised of sediments of the Briançon-micro-continent. The rock compositions of the Lower- (Simano-, Adula- and Antigori-nappe) and Middle- Penninic nappes (Klippen-nappe) encompass Mesozoic to Cenozoic sediments, which are sheared off from their crystalline basement. Additionally crystalline basement form separate nappe stacks (PFIFFNER 2010).
    [Show full text]
  • The Glarus Thrust: Excursion Guide and Report of a Field Trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.–16
    1661-8726/08/020323-18 Swiss J. Geosci. 101 (2008) 323–340 DOI 10.1007/s00015-008-1259-z Birkhäuser Verlag, Basel, 2008 The Glarus thrust: excursion guide and report of a field trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.–16. 09. 2006) MARCO HERWEGH 1, *, JEAN-PIERRE HÜRZELER 2, O. ADRIAN PFIFFNER 1, STEFAN M. SCHMID 2, RAINER ABART 3 & ANDREAS EBERT 1 Key words: Helvetics, Glarus thrust, deformation mechanism, mylonite, brittle deformation, geochemical alteration, fluid pathway PARTICIPANTS Ansorge Jörg (ETHZ) Nyffenegger Franziska (Fachhochschule Burgdorf, University of Bern) den Brok Bas (EAWAG-EMPA) Pfiffner Adrian (University of Bern) Dèzes Pierre (SANW) Schreurs Guido (University of Bern) Gonzalez Laura (University of Bern) Schmalholz Stefan (ETHZ) Herwegh Marco (University of Bern) Schmid Stefan (University of Basel) Hürzeler Jean-Pierre (University of Basel) Wiederkehr Michael (University of Basel) Imper David (GeoPark) Wilson Christopher (Melbourne University) Mancktelow Neil (ETHZ) Wilson Lilian (Melbourne University) Mullis Josef (University of Basel) ABSTRACT This excursion guide results form a field trip to the Glarus nappe complex or- and fluid flow, and (iii) the link between large-scale structures, microstruc- ganized by the Swiss Tectonic Studies Group in 2006. The aim of the excursion tures, and geochemical aspects. Despite 150 years of research in the Glarus was to discuss old and recent concepts related to the evolution of the Glarus nappe complex and the new results discussed during the excursion,
    [Show full text]
  • Alpine Thermal and Structural Evolution of the Highest External Crystalline Massif: the Mont Blanc
    TECTONICS, VOL. 24, TC4002, doi:10.1029/2004TC001676, 2005 Alpine thermal and structural evolution of the highest external crystalline massif: The Mont Blanc P. H. Leloup,1 N. Arnaud,2 E. R. Sobel,3 and R. Lacassin4 Received 5 May 2004; revised 14 October 2004; accepted 15 March 2005; published 1 July 2005. [1] The alpine structural evolution of the Mont Blanc, nappes and formed a backstop, inducing the formation highest point of the Alps (4810 m), and of the of the Jura arc. In that part of the external Alps, NW- surrounding area has been reexamined. The Mont SE shortening with minor dextral NE-SW motions Blanc and the Aiguilles Rouges external crystalline appears to have been continuous from 22 Ma until at massifs are windows of Variscan basement within the least 4 Ma but may be still active today. A sequential Penninic and Helvetic nappes. New structural, history of the alpine structural evolution of the units 40Ar/39Ar, and fission track data combined with a now outcropping NW of the Pennine thrust is compilation of earlier P-T estimates and geo- proposed. Citation: Leloup, P. H., N. Arnaud, E. R. Sobel, chronological data give constraints on the amount and R. Lacassin (2005), Alpine thermal and structural evolution of and timing of the Mont Blanc and Aiguilles Rouges the highest external crystalline massif: The Mont Blanc, massifs exhumation. Alpine exhumation of the Tectonics, 24, TC4002, doi:10.1029/2004TC001676. Aiguilles Rouges was limited to the thickness of the overlying nappes (10 km), while rocks now outcropping in the Mont Blanc have been exhumed 1.
    [Show full text]
  • The Glarus Thrust: Excursion Guide and Report of a Field Trip of the Swiss
    1661-8726/08/020323-18 Swiss J. Geosci. 101 (2008) 323–340 DOI 10.1007/s00015-008-1259-z Birkhäuser Verlag, Basel, 2008 The Glarus thrust: excursion guide and report of a field trip of the Swiss Tectonic Studies Group (Swiss Geological Society, 14.–16. 09. 2006) MARCO HERWEGH 1, *, JEAN-PIERRE HÜRZELER 2, O. ADRIAN PFIFFNER 1, STEFAN M. SCHMID 2, RAINER ABART 3 & ANDREAS EBERT 1 Key words: Helvetics, Glarus thrust, deformation mechanism, mylonite, brittle deformation, geochemical alteration, fluid pathway PARTICIPANTS Ansorge Jörg (ETHZ) Nyffenegger Franziska (Fachhochschule Burgdorf, University of Bern) den Brok Bas (EAWAG-EMPA) Pfiffner Adrian (University of Bern) Dèzes Pierre (SANW) Schreurs Guido (University of Bern) Gonzalez Laura (University of Bern) Schmalholz Stefan (ETHZ) Herwegh Marco (University of Bern) Schmid Stefan (University of Basel) Hürzeler Jean-Pierre (University of Basel) Wiederkehr Michael (University of Basel) Imper David (GeoPark) Wilson Christopher (Melbourne University) Mancktelow Neil (ETHZ) Wilson Lilian (Melbourne University) Mullis Josef (University of Basel) ABSTRACT This excursion guide results form a field trip to the Glarus nappe complex or- and fluid flow, and (iii) the link between large-scale structures, microstruc- ganized by the Swiss Tectonic Studies Group in 2006. The aim of the excursion tures, and geochemical aspects. Despite 150 years of research in the Glarus was to discuss old and recent concepts related to the evolution of the Glarus nappe complex and the new results discussed during the
    [Show full text]
  • Towards a Nappe Theory
    https://doi.org/10.5194/se-2019-130 Preprint. Discussion started: 26 August 2019 c Author(s) 2019. CC BY 4.0 License. Towards a nappe theory: Thermo-mechanical simulations of nappe detachment, transport and stacking in the Helvetic Nappe System, Switzerland Dániel Kiss1, Thibault Duretz2,1, and Stefan M. Schmalholz1 1Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland 2Univ. Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France Correspondence: Dániel Kiss ([email protected]) Abstract. Tectonic nappes are observed for more than a hundred years. Although geological studies often refer to a “nappe theory”, the physical mechanisms of nappe formation are still incompletely understood. We apply two-dimensional numerical simulations of shortening of a passive margin, to investigate the thermo-mechanical processes of detachment, transport and stacking of 5 nappes. We use a visco-elasto-plastic model with standard creep flow laws and Drucker-Prager yield criterion. We consider tectonic inheritance with two initial mechanical heterogeneities: (1) lateral heterogeneity of the basement-cover interface due to half-grabens and horsts and (2) vertical heterogeneities due to layering of mechanically strong and weak sedimentary units. The model shows detachment and horizontal transport of a thrust nappe and stacking of this thrust nappe above a fold nappe. The detachment of the thrust sheet is triggered by stress concentrations around the sediment-basement contact and the resulting 10 brittle-plastic shear band formation. The horizontal transport is facilitated by a basal shear zone just above the basement-cover contact, composed of thin, weak sediments. Fold nappe formation occurs by a dominantly ductile closure of a half-graben and the associated extrusion of the half-graben fill.
    [Show full text]
  • Interactions Between Tectonics Erosion and Sedimentation During The
    Interactions between tectonics erosion and sedimentation during the recent evolution of the Alpine orogen : analogue modeling insights Cécile Bonnet, Jacques Malavieille, J. Mosar To cite this version: Cécile Bonnet, Jacques Malavieille, J. Mosar. Interactions between tectonics erosion and sedimentation during the recent evolution of the Alpine orogen : analogue modeling insights. Tectonics, American Geophysical Union (AGU), 2007, 26 (6), pp.TC6016. 10.1029/2006TC002048. hal-00404424 HAL Id: hal-00404424 https://hal.archives-ouvertes.fr/hal-00404424 Submitted on 22 Mar 2021 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. TECTONICS, VOL. 26, TC6016, doi:10.1029/2006TC002048, 2007 Interactions between tectonics, erosion, and sedimentation during the recent evolution of the Alpine orogen: Analogue modeling insights Ce´cile Bonnet,1 Jacques Malavieille,2 and Jon Mosar3 Received 8 September 2006; revised 24 July 2007; accepted 4 October 2007; published 29 December 2007. [1] On the basis of a section across the northwestern Molasse Basin is largely driven by the subduction mecha- Alpine wedge and foreland basin, analogue modeling is nism of the European plate under the Adriatic promontory. used to investigate the impact of surface processes on the However, it appears that erosion of the overlying Penninic orogenic evolution.
    [Show full text]
  • Structure and Tectonic Evolution Penninic Cover
    001,2-94021 0I I020231 -16 $ 1.50 + 0.2010 Eclogaegeol. Helv.94 (2001)237-252 EirkhäuserVerlag, Basel, 2001 Penniniccover nappesin the Prättigauhalf-window (EasternSwitzerland):Structure and tectonicevolution Manrus Wenl'2 & Nrr<olaus FRorrzi{ErM1'3 Key words: Alps, Penninic, Bündnerschiefer,Falknis nappe,Prättigau half-window, structural geology,Alpine tectonics ZUSAMMENFASSUNG ABSTRACT Die Sedimentabfolgeder zum Valaisan gehörenden Grava-Decke im Prätti- The sedimentary sequence of the Grava nappe (Valaisan) in the Prättigau gau-Halbfensterder Ostschweizbesteht aus kretazischenSchiefern (Bündner- half-window of easternSwitzerland consistsof Cretaceouscalcschists (,,8ünd- schiefer) und spätkretazisch/alttertiärem Flysch. Diese Gesteine wurden durch nerschiefer") and Late CretaceouslEarly Tertiary flysch. It records the follow- die folgenden alpinen Deformationsvorgänge überprägt: (D1a) Abscherung ing stagesof Alpine deformation: (D1a) d6collement of the sediment cover of der Sedimentbedeckungeiner südwärts abtauchendenLithosphärenplatte und a southward-subductedlithospheric slab and accretion of this cover as a hin- Akkretion der abgeschertenSerien als Duplex an der Basis des Orogenkeils, terland-dippingduplex at the baseof the orogenic wedge,beginning around 50 etrva 50 Ma; (D1b) lokale Verfaltung der D1a-Strukturen; (D2) top-SE- Ma; (D1b) local refolding of D1a structures; (D2) rop-SE shearing and Scherung und "Rückfaltung" in einem extensionalenRegime, zwischen35 und "backfolding" in an exlensionalregime, between 35 and 30 Ma; (D3)
    [Show full text]
  • Italian Alps S
    TECTONICS, VOL. 15, NO. 5, PAGES 1036-1064, OCTOBER 1996 Geophysical-geological transect and tectonic evolution of the Swiss-Italian Alps S. M. Schmid,10. A. Pfiffner,2 N. Froitzheim,1 G. Sch6nborn,3 and E. Kissling4 Abstract. A complete Alpine cross section inte- relatively strong lower crust and detachmentbetween grates numerous seismicreflection and refraction pro- upper and lower crust. files, across and along strike, with published and new field data. The deepest parts of the profile are con- strained by geophysicaldata only, while structural fea- Introduction tures at intermediate levelsare largely depicted accord- ing to the resultsof three-dimensionalmodels making Plate 1 integrates geophysicaland geologicaldata useof seismicand field geologicaldata. The geometryof into one singlecross section acrossthe easternCentral the highest structural levels is constrainedby classical Alps from the Molasse foredeep to the South Alpine along-strikeprojections of field data parallel to the pro- thrust belt. The N-S section follows grid line 755 of nounced easterly axial dip of all tectonic units. Because the Swisstopographic map (exceptfor a southernmost the transect is placed closeto the westernerosional mar- part near Milano, see Figure i and inset of Plate 1). gin of the Austroalpinenappes of the Eastern Alps, it As drawn, there is a marked difference between the tec- contains all the major tectonic units of the Alps. A tonic style of the shallower levels and that of the lower model for the tectonic evolution along the transect is crustal levels. This difference in style is only partly real. proposedin the form of scaledand area-balancedprofile The wedgingof the lower crust stronglycontrasts with sketches.Shortening within the Austroalpinenappes is the piling up and refolding of thin flakesof mostly up- testimonyof a separateCretaceous-age orogenic event.
    [Show full text]
  • Control of 3D Tectonic Inheritance on Fold-And-Thrust Belts
    https://doi.org/10.5194/se-2019-173 Preprint. Discussion started: 2 December 2019 c Author(s) 2019. CC BY 4.0 License. Control of 3D tectonic inheritance on fold-and-thrust belts: insights from 3D numerical models and application to the Helvetic nappe system Richard Spitz1, Arthur Bauville2, Jean-Luc Epard1, Boris J.P. Kaus3, Anton A. Popov3, and Stefan M. Schmalholz1 1Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland 2Department of Mathematical Science and Advanced Technology, Japan Agency for Marin-Earth Science and Technology, 3173-25, Showa-machi, Kanazawa-ku Yokohama, Japan 3Institute of Geosciences, Johannes Gutenberg University Mainz, Mainz 55128, Germany Correspondence: Richard Spitz ([email protected]) Abstract Fold-and-thrust belts and associated tectonic nappes are common in orogenic regions. They exhibit a wide variety of geometries and often a considerable along-strike variation. However, the mechanics of fold-and-thrust belt formation and the control of the initial geological configuration on this formation are still incompletely understood. Here, we apply three-dimensional (3D) 5 thermo-mechanical numerical simulations of the shortening of the upper crustal region of a passive margin to investigate the control of 3D laterally variable inherited structures on the fold-and-thrust belt evolution and associated nappe formation. We consider tectonic inheritance by applying an initial model configuration with horst and graben structures having laterally variable geometry and with sedimentary layers having different mechanical strength. We use a visco-plastic rheology with temperature dependent flow laws and a Drucker-Prager yield criterion. The models show the folding, detachment and horizontal 10 displacement of sedimentary units, which resemble structures of fold and thrust nappes.
    [Show full text]
  • Thermochronometry Across the Austroalpine
    PUBLICATIONS Tectonics RESEARCH ARTICLE Thermochronometry Across the Austroalpine- 10.1002/2017TC004619 Pennine Boundary, Central Alps, Switzerland: Special Section: Orogen-Perpendicular Normal Fault Slip on a Major Orogenic cycles: from field observations to global “Overthrust” and Its Implications for Orogenesis geodynamics Jason B. Price1 , Brian P. Wernicke1 , Michael A. Cosca2, and Kenneth A. Farley1 Key Points: 1 2 • Thermal histories of the Austroalpine Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA, Geology, hanging wall and Pennine footwall, Geophysics, and Geochemistry Science Center, U.S. Geological Survey Denver, CO, USA constrained by nine thermochronometric systems, show that they did not thermally equilibrate Abstract Fifty-one new and 309 published thermochronometric ages (nine systems with closure until after 29 Ma, and possibly not until 18 Ma temperatures ranging from ~450 to 70°C) from the Graubünden region of the Central Alps demonstrate • The thermal data indicate that the that a pronounced thermal mismatch between the Austroalpine allochthon (Alpine “orogenic lid”) and the Austroalpine-Pennine contact zone is Pennine zone persisted until at least 29 Ma and, allowably, until circa 18 Ma. The observed mismatch supports a top-south to top-southeast normal “ ” fault with at least 60 km of previous suggestions that the famous overthrust between the Austroalpine allochthon and the Pennine zone, displacement, active during the main historically regarded as primarily an Eocene top-north thrust fault, is in fact primarily an Oligocene-Miocene phase of Alpine mountain building normal fault that has a minimum of 60 km of displacement with top-south or top-southeast sense of shear.
    [Show full text]
  • The Helvetic Nappe System and Landscape Evolution of the Kander Valley
    The helvetic nappe system and landscape evolution of the Kander valley Autor(en): Pfiffner, Adrian O. Objekttyp: Article Zeitschrift: Swiss bulletin für angewandte Geologie = Swiss bulletin pour la géologie appliquée = Swiss bulletin per la geologia applicata = Swiss bulletin for applied geology Band (Jahr): 15 (2010) Heft 1 PDF erstellt am: 09.10.2021 Persistenter Link: http://doi.org/10.5169/seals-227477 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. Das Veröffentlichen von Bildern in Print- und Online-Publikationen ist nur mit vorheriger Genehmigung der Rechteinhaber erlaubt. Die systematische Speicherung von Teilen des elektronischen Angebots auf anderen Servern bedarf ebenfalls des schriftlichen Einverständnisses der Rechteinhaber. Haftungsausschluss Alle Angaben erfolgen ohne Gewähr für Vollständigkeit oder Richtigkeit. Es wird keine Haftung übernommen für Schäden durch die Verwendung von Informationen aus diesem Online-Angebot oder durch das Fehlen von Informationen. Dies gilt auch für Inhalte Dritter, die über dieses Angebot zugänglich sind. Ein Dienst der ETH-Bibliothek ETH Zürich, Rämistrasse 101, 8092 Zürich, Schweiz, www.library.ethz.ch http://www.e-periodica.ch Swiss Bull. angew. Geol. Vol. 15/1, 2010 S. 53-61 The Helvetic nappe system and landscape evolution of the Kander valley O. Adrian Pfiffner1 Summary of presentation and excursion guide given at the VSP/ASP annual convention, Interlaken, Switzerland, June 2009 1.
    [Show full text]