DOCSLIB.ORG

Multi-Phase Late-Neogene Exhumation History of the Aar Massif, Swiss Central Alps

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Multi-Phase Late-Neogene Exhumation History of the Aar Massif, Swiss Central Alps doi: 10.1111/ter.12231 Multi-phase late-Neogene exhumation history of the Aar massif, Swiss central Alps Pierre G. Valla,1,2 Meinert Rahn,3,4 David L. Shuster5,6 and Peter A. van der Beek7 1Institute of Earth Surface Dynamics, University of Lausanne, Lausanne CH-1015, Switzerland; 2Department of Earth Sciences, ETH Zurich,€ Zurich€ CH-8092, Switzerland; 3Swiss Federal Nuclear Safety Inspectorate, Brugg CH-5200, Switzerland; 4Department of Mineral- ogy and Geochemistry, University of Freiburg, Freiburg D-79104, Germany; 5Department of Earth & Planetary Science, University of Cal- ifornia, Berkeley, CA 94720, USA; 6Berkeley Geochronology Center, Berkeley, CA 94707, USA; 7Institute of Earth Sciences (ISTerre), Universite Grenoble Alpes, Grenoble F-38400, France ABSTRACT The late-Neogene evolution of the European Alps was influ- exhumation phases in the Late Miocene–Pliocene and better enced by both tectonic and climatically driven erosion pro- constrain the onset of glacial valley carving. The hydrother- cesses, which are difficult to disentangle. We use low- mal activity and geothermal anomalies currently observed in temperature thermochronometry data from surface and bore- the borehole have been local and short-lived, with only a hole samples in the Aar massif–Rhone^ valley (Swiss central minor influence on thermochronometric observations. We thus Alps) to constrain the exhumation history of the region. Mul- suggest that late-stage glacial valley carving may have trig- tiple exhumation events are distinguished and linked to regio- gered topography-driven fluid flow and transient hydrother- nal-scale tectonic deformation (before 5 Ma), short-lived mal circulation. climatically driven orogen contraction (between 4 and 3 Ma), and glacial valley carving since c. 1 Ma. Compared with previ- Terra Nova, 00: 1–12, 2016 ous studies, we clearly show the existence of two separate deformation from the frontal Jura processes were the primary drivers Introduction (Becker, 2000) to the internal parts of the late-stage Alpine evolution. Quantifying mountain evolution, as of the belt (Willett et al., 2006). In this study, we apply multiple well as sediment transfer to sur- However, exhumation histories low-temperature thermochronometric rounding basins, is important for across the European Alps have led systems to bedrock samples along understanding potential feedbacks to contrasting conclusions concern- both a 2 km surface elevation profile between climate, erosion and tecton- ing the existence and precise timing and a 500 m deep borehole in the ics (e.g. Molnar and England, 1990; of this increase, as well as the nat- Swiss central Alps. Our objective is Raymo and Ruddiman, 1992). How- ure of the forcing processes. Ongo- to quantitatively constrain the late- ever, those couplings are difficult to ing tectonic deformation and crustal Neogene exhumation history of the decipher because the involved pro- accretion (Persaud and Pfiffner, region and assess the potential cli- cesses are often interrelated (Roe 2004; Schlunegger and Mosar, matic or tectonic controls on it. et al., 2008; Whipple, 2009), pro- 2011), orogen-perpendicular exten- moting transient erosion or topo- sion (e.g. Reinecker et al., 2008; Setting and methods graphic response (Willett and Cardello et al., 2015) and regional- Brandon, 2002; Whipple and Meade, scale slab unloading (Baran et al., The Visp-Brigerbad area lies in the 2006). The late-Neogene evolution 2014; Fox et al., 2015) have been upper Rhone^ valley between the crys- of the European Alps is a classic proposed as potential tectonic trig- talline Aar massif and the sedimen- illustration of such a debate (see gers. Drainage rearrangement lead- tary Helvetic and Penninic nappes review in Willett, 2010). Sediment ing to river capture and transient (Fig. 1). It encompasses two major budgets from basins surrounding the incision has also been proposed tectonic boundaries: the Penninic Alps suggest a significant increase in (Ziegler and Fraefel, 2009; Schluneg- frontal thrust (PFT) and the Rhone-^ accumulation rates since c. 5 Ma ger and Mosar, 2011; Yanites et al., Simplon fault (RSF) (Mancktelow, (Kuhlemann et al., 2002), roughly 2013). Alternatively, climatic pro- 1985, 1992; Seward and Mancktelow, concordant with (1) the onset of cesses have been suggested, includ- 1994; Campani et al., 2010). The denudation in the northern Alpine ing a transition to wetter conditions modern drainage pattern follows the foreland basin (Cederbom et al., (Cederbom et al., 2004, 2011; Willett tectonic structures (Kuhni€ and Pfiff- 2004, 2011), (2) increased Alpine et al., 2006) or the (more recent) ner, 2001), influenced by the exhuma- exhumation (Vernon et al., 2008) impact of Pliocene–Quaternary tion of the External Crystalline and (3) potential migration of glaciation (Haeuselmann et al., 2007; Massifs (ECMs) since Oligocene– Glotzbach et al., 2011; Valla et al., Early Miocene times (Schmid et al., 2011, 2012; Maheo et al., 2012; Fox 2004), while the overall high Alpine Correspondence: Pierre G. Valla, Institute et al., 2015). Better temporal con- of Earth Surface Dynamics, University of elevation has been acquired at least Lausanne, Lausanne CH-1015, Switzer- straints on bedrock exhumation since Miocene times (Campani et al., land. E-mail: [email protected] should help to elucidate which 2012). The current kinematics of the © 2016 John Wiley & Sons Ltd 1 Multi-phase Alpine exhumation history • P. G. Valla et al. Terra Nova, Vol 0, No. 0, 1–11 ............................................................................................................................................................. occur along the Rhone^ valley, appar- 7°40‘0.7 7°50‘ 8°00‘ 8°10‘ ently associated with major tectonic 1.1 1.2 structures (e.g. Sonney and Vuataz, 1.0 0.8 2008, 2009). The importance and 1.3 persistence of these hydrothermal 46°25‘ systems remain poorly constrained. 0.9 We use low-temperature apatite 1.4 (U–Th–Sm)/He (AHe) and fission- track (AFT) thermochronometry, Profile in Fig. 2 including fission-track length (TL) measurements, to quantify the late- 46°20‘ Neogene exhumation history of the area. The AHe and AFT systems are BR-02 Penninic frontal thrust characterised by closure temperatures of 50–90 °C (Shuster et al., 2006) Visp and 100–120 °C (Gallagher et al., R 1998), respectively, and are sensitive hô ne 1.2 -Simp 46°15‘ to topographic changes (e.g. Stuwe€ lo t n f aul I et al., 1994; Braun, 2002). Geother- 1.3 CH mal anomalies and topography-dri- ven hydrothermal circulation may 10 km also affect low-temperature ther- mochronometers (Ehlers, 2005; Aar massif, Infra-Penninic sedimentary crystalline basement units Dempster and Persano, 2006; Whipp Autochthonous cover of Post-Variscan sediments and Ehlers, 2007); this sensitivity can Aar massif (Helvetics) of middle-Penninic nappes help in assessing the persistence of Allochthonous Helvetic Pre-Variscan cryst. basem. near-surface geothermal systems (e.g. sedimentary nappes of middle-Penninic nappes Gotthard nappe, Pre-Variscan crystalline Gorynski et al., 2014). Here, we crystalline basement nappes of Lepontine combine six surface samples (VIS) Parautochthonous cover Sample location collected along an elevation profile of Gotthard nappe -1 (Valla et al., 2011) with three new Major tectonic structures 1.3 Geodetic uplift (mm yr ) 43˚ 45˚ 47˚ samples (MRP) obtained along a 6˚ 9˚ Boundary between Italy (I) Quaternary valley infill and Switzerland (CH) 500 m deep geothermal borehole, covering ~3 km elevation in total Fig. 1 Geological sketch map of the Swiss central Alps (after Schmid et al., 2004) with (Table 1). AHe ages for the VIS main litho-tectonic units and major tectonic structures (see legend). White circles rep- samples have been previously resent sampling locations (BR-02 is the geothermal borehole, see Fig. 7B), the thick reported (Valla et al., 2011). We black line indicates the cross-section shown in Fig. 2A, and thin black lines depict sur- report here new AFT data including face-uplift rates from geodetic measurements with respect to Laufenburg (Schlatter, TL distributions for all VIS and 2014). Inset shows the location of the study area within the European Alps. MRP samples (Table 2) and central Swiss Alps show no active convergence (Nocquet and Calais, 2004) but evidence for orogen-paral- Sample locations for the elevation profile from the Garsthorn to Visp-Bri- lel extension (Champagnac et al., Table 1 € 2004). The area shows a strong gla- gerbad (VIS), with additional samples from the Brigerbad geothermal borehole (MRP). Asterisks mark samples from Valla et al. (2011). All sampled rocks are cial imprint with high topographic relief and glacially shaped cross-pro- orthogneisses from the Aar crystalline basement. files along the Rhone^ valley (Norton Elevation (m) et al., 2010). This valley has been Sample Longitude (°E) Latitude (°N) (depth below valley floor) glacially deepened during Quaternary times (Valla et al., 2011), with large VIS-01* 7.91667 46.34390 2925 glacial overdeepenings (Finckh and VIS-03* 7.92035 46.32918 2100 Frei, 1991; Rosselli and Olivier, VIS-04* 7.92432 46.31988 1600 2003) filled by post-glacial sediments VIS-05* 7.93780 46.31788 1400 VIS-06* 7.98339 46.32999 850 (Hinderer, 2001). Average Quater- VIS-07* 7.95333 46.30967 670 nary and Holocene erosion patterns MRP-424 7.93032 46.30220 487 ( 167) À (Champagnac et al., 2007, 2009) clo- MRP-425 7.93032 46.30220 321 ( 333) sely correlate with surface-uplift rates À 1 MRP-426 7.93032 46.30220 157 ( 497)
Load more

Recommended publications
  • Kinematics and Extent of the Piemont-Liguria Basin
    https://doi.org/10.5194/se-2020-161 Preprint. Discussion started: 8 October 2020 c Author(s) 2020. CC BY 4.0 License. Kinematics and extent of the Piemont-Liguria Basin – implications for subduction processes in the Alps Eline Le Breton1, Sascha Brune2,3, Kamil Ustaszewski4, Sabin Zahirovic5, Maria Seton5, R. Dietmar Müller5 5 1Department of Earth Sciences, Freie Universität Berlin, Germany 2Geodynamic Modelling Section, German Research Centre for Geosciences, GFZ Potsdam, Germany 3Institute of Geosciences, University of Potsdam, Potsdam, Germany 4Institute for Geological Sciences, Friedrich-Schiller-Universität Jena, Germany 10 5EarthByte Group, School of Geosciences, The University of Sydney, NSW 2006, Australia Correspondence to: Eline Le Breton ([email protected]) Abstract. Assessing the size of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont- Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of 15 the Western Mediterranean-Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modelling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e. ages of syn-rift sediments, rift-related fault activity and mafic rocks) and shows that the PL Basin opened in four stages: (1) Rifting of the proximal continental margin in Early Jurassic (200-180 Ma), (2) Hyper- extension of the distal margin in Early-Middle Jurassic (180-165 Ma), (3) Ocean-Continent Transition (OCT) formation with 20 mantle exhumation and MORB-type magmatism in Middle-Late Jurassic (165-154 Ma), (4) Break-up and “mature” oceanic spreading mostly in Late Jurassic (154-145 Ma).
    [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]
  • Tracing the Exhumation of the Eclogite Zone (Tauern Window, Eastern Alps) by 40Ar/39Ar Dating of White Mica in Eclogites
    1661-8726/08/01S191-16 Swiss J. Geosci. 101 (2008) Supplement 1, S191–S206 DOI 10.1007/s00015-008-1281-1 Birkhäuser Verlag, Basel, 2008 Tracing the exhumation of the Eclogite Zone (Tauern Window, Eastern Alps) by 40Ar/39Ar dating of white mica in eclogites WALTER KURZ 1, ROBERT HANDLER 2 & CHRISTIAN BERTOLDI 3 Key words: 40Ar/39Ar dating, white mica, eclogite exhumation, microstructures, Subpenninic nappes, Tauern Window ABSTRACT New radiometric ages from the Subpenninic nappes (Eclogite Zone and Rote maximum age due to the possible influence of homogenously distributed Wand – Modereck Nappe, Tauern Window) show that phengites formed under excess argon. During exhumation deformation was localised along distinct eclogite-facies metamorphic conditions retain their initial isotopic signature, mylonitic shear zones. This stage is mainly characterised by the formation of even when associated lithologies were overprinted by greenschist- to amphib- dynamically recrystallized omphacite2 and phengite. Deformation resulted in olite-facies metamorphism. Different stages of the eclogite-facies evolution the resetting of the Ar isotopic system within the recrystallized white mica. can be dated provided 40Ar/39Ar dating is combined with micro-structural Flat argon release spectra showing ages of 32 Ma within mylonites record the analyses. An age of 39 Ma from the Rote Wand – Modereck Nappe is inter- timing of cooling along the exhumation path, and the emplacement onto the preted to be close to the burial age of this unit. Eclogite deformation within Venediger Nappe. Ar-release patterns and 36Ar/40Ar vs. 39Ar/40Ar isotope cor- the Eclogite Zone started at the pressure peak along distinct shear zones, and relation analyses indicate no significant 40Ar-loss after initial closure, and only prevailed along the exhumation path.
    [Show full text]
  • Paleotectonic Evolution of the Central and Western Alps
    BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 71, PP. 843-908, 14 FIGS.. 2 PLS. JUNE 1960 PALEOTECTONIC EVOLUTION OF THE CENTRAL AND WESTERN ALPS BY RUDOLF TRUMPY ABSTRACT This paper deals with the general features of Mesozoic and Tertiary rock sequences and paleogeography in the Alps. It seeks to outline the paleotectonic significance of the rocks and to discuss the structural evolution of the Alpine geosyncline up to the main deformation, with special reference to the sector between the rivers Rhine and Durance. Accent is placed on the relative independence of Alpine structures involving the pre-Triassic basement rocks and of cover nappes consisting only of Mesozoic and Tertiary formations. Normal shallow-water deposits of platform or miogeosynclinal type were laid down over the whole area before eugeosynclinal conditions set in. The typical eugeosynclinal sediments in the central, Penninic belt of the Alps are the Schistes lustres and Bundner- schiefer, with sills and submarine lava flows of basic volcanic rocks (ophiolites). Before metamorphism they consisted mainly of shales and of impure arenaceous and argillaceous limestones. The bathymetric environment of radiolarian cherts and associated rocks is examined, and their deep-water origin is upheld for the Alpine occurrences. Marine polygenic breccias are characteristic of geosynclinal slopes (commonly fault scarps) and not of a particular depth zone. The Alpine Flysch is a particularly significant sediment. Flysch is a thick marine deposit of predominantly detrital rocks, in part turbidites, generally without volcanic rocks, and laid down during compressional deformation of the geosyncline. Of the many different kinds of Flysch some represent transitions to either Bundnerschiefer or Molasse.
    [Show full text]
  • New Aspects on the Timing of Deformation Along the South
    Originally published as: Bachmann, R., Glodny, J., Oncken, O., Seifert, W. (2009): Abandonment of the South Penninic-Austroalpine palaeosubduction zone, Central Alps, and shift from subduction erosion to accretion: constraints from Rb/Sr geochronology. - Journal of the Geological Society London, 166, 2, 217-231 DOI: 10.1144/0016-76492008-024. Abandonment of the South Penninic-Austroalpine palaeo-subduction zone, Central Alps, and shift from subduction erosion to accretion: constraints from Rb/Sr geochronology Raik Bachmann Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, 14473 Potsdam, Germany. [email protected] Present address: Horizon Energy Partners, Prinses Margrietplantsoen 81, 2595 BR The Hague, The Netherlands [email protected] Johannes Glodny Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, 14473 Potsdam, Germany, [email protected] Onno Oncken Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, 14473 Potsdam, Germany, [email protected] Wolfgang Seifert Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, 14473 Potsdam, Germany, [email protected] Corresponding author: Raik Bachmann 1 Abstract We present new age data for the evolution of the suture zone between lower-plate South Penninic and upper-plate Austroalpine units in the Central European Alps. Rb/Sr deformation ages for mylonitized rocks of the South Penninic palaeo-subduction mélange and for deformed Austroalpine basement (Eastern Switzerland) shed light on the pre-Alpine and Alpine deformation history along the suture, as well as on syn-subduction interplate mass transfer. Rb/Sr age data define two age groups. The first group reflects pre-Alpine events within the upper plate basement, with varying degree of resetting by subsequent Alpine overprints. The second group marks the waning of subduction-related deformation along the South Penninic-Austroalpine suture zone, at around 50 Ma, and termination at ~47 Ma.
    [Show full text]
  • Strain Localization in the Morcles Nappe (Helvetic Alps, Switzerland)
    1661-8726/08/020341-20 Swiss J. Geosci. 101 (2008) 341–360 DOI 10.1007/s00015-008-1264-2 Birkhäuser Verlag, Basel, 2008 Strain localization in the Morcles nappe (Helvetic Alps, Switzerland) NICHOLAS AUSTIN 1, *, BRIAN EVANS 1, MARCO HERWEGH 2 & ANDREAS EBERT 2 Key words: rheology, calcite, localization, recrystallization, microstructure, crystallographic preferred orientation ABSTRACT Deformation in orogenic belts is frequently accommodated in calcite-rich structure at a range of locations, with varying peak metamorphic tempera- lithologies, owing to their relatively low strength, particularly compared to tures, along the Morcles nappe. The strain-rates predicted by extrapolation quartz-rich rocks. Here, we investigate the coupling between calcite grain size, of these laboratory relationships agree well with the geologic constraints. We the presence and mineralogy of second phases, and crystallographic preferred then applied the same approach to the samples from the present study. The orientation (CPO) in a transect through deformed limestones, perpendicu- results indicate that strain became progressively localized towards the thrust lar to the dominant foliation in the inverted limb of the Morcles nappe of contact of the Morcles nappe, leading to an increase in strain rate of >1 order the Swiss Helvetic Alps. Calcite grain size becomes progressively finer as the of magnitude in a zone <0.50 m thick. For localization to occur system and/or thrust contact is approached, and there is a concomitant increase in CPO in- material softening is necessary. If dislocation activity is positively correlated tensity, with the strongest CPO’s in the finest-grained, quartz-rich limestones, with CPO, then softening cannot have occurred by a complete transition to nearest the thrust contact.
    [Show full text]
  • Dating the Tethyan Ocean in the Western Alps with Radiolarite
    Dating the Tethyan Ocean in the Western Alps with radiolarite pebbles from synorogenic Oligocene molasse basins (southeast France) Fabrice Cordey, Pierre Tricart, Stéphane Guillot, Stéphane Schwartz To cite this version: Fabrice Cordey, Pierre Tricart, Stéphane Guillot, Stéphane Schwartz. Dating the Tethyan Ocean in the Western Alps with radiolarite pebbles from synorogenic Oligocene molasse basins (southeast France). Swiss Journal of Geosciences, Springer, 2012, 105 (1), pp.39-48. 10.1007/s00015-012-0090-8. hal-02178343 HAL Id: hal-02178343 https://hal.archives-ouvertes.fr/hal-02178343 Submitted on 30 Jun 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. 1 Dating the Tethyan ocean in the Western Alps with radiolarite pebbles from 2 synorogenic Oligocene molasse basins (southeast France) 3 4 5 Running title: Radiolarite pebbles from Alpine Oligocene molasses 6 7 8 Fabrice Cordey1*, Pierre Tricart2, Stéphane Guillot2, Stéphane Schwartz2 9 10 11 12 1Département des Sciences de la Terre, CNRS UMR 5276 Laboratoire de Géologie de Lyon, 13 Université Lyon 1, 69622 Villeurbanne, France 14 2IsTerre, CNRS, Université de Grenoble I, 38041 Grenoble, cedex 9, France 15 16 *corresponding author: [email protected] 17 18 19 20 21 22 23 Keywords: Western Alps, radiolarite, Jurassic, molasse, Oligocene, subduction wedge.
    [Show full text]
  • Engadin Window) Near Ischgl/Tyrol
    MITT. ÖSTERR. MINER. GES. 163 (2017) WALKING ON JURASSIC OCEAN FLOOR AT THE IDALPE (ENGADIN WINDOW) NEAR ISCHGL/TYROL Karl Krainer1 & Peter Tropper2 1Institute of Geology, University of Innsbruck, Innrain 52f, A-6020 Innsbruck 2Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52f, A-6020 Innsbruck Introduction In the Lower Engadine Window rocks of the Penninic Unit are exposed which originally were formed in the Piemont-Ligurian Ocean, the Iberian-Brianconnais microcontinent and the Valais Ocean. The Penninic rocks of the Lower Engadi- ne Window are overlain by Austrolpine nappes: the Silvretta Metamorphic Com- plex (Silvretta-Seckau Nappe System sensu SCHmiD et al. 2004) in the north, the Stubai-Ötztal Metamorphic Complex (Ötztal-Bundschuh Nappe System sensu SCHmiD et al. 2004) in the southeast and east, and the Engadine Dolomites. The Penninic rocks of the Lower Engadine Window are characterized by a com- plex tectonic structure and can be divided into three nappe systems (SCHmiD et al., 2004; GRubeR et al., 2010; see also Tollmann, 1977; ObeRHauseR, 1980): a.) Lower Penninic Nappes including rocks of the former Valais Ocean (Cre- taceous – Paleogene) b.) Middle Penninic Nappes composed of rocks of the Iberia-Brianconnais microcontinent, and c.) Upper Penninic Nappe, composed of rocks oft he former Piemont-Ligu- rian Ocean. Lower Penninic Nappes include the Zone of Pfunds and Zone of Roz – Cham- patsch – Pezid. The dominant rocks are different types of calcareous mica schists and „Bündnerschiefer“. Locally fragments of the oceanic crust and upper mantle (ophiolites) are intecalated. The Middle Penninic Nappes include the Fimber-Zone and Zone of Prutz – Ramosch.
    [Show full text]
  • Abstract the Helvetic Nappe System in Western Switzerland Is a Stack of Fold Nappes and Thrust Sheets Em
    ABSTRACT The Helvetic nappe system in Western Switzerland is a stack of fold nappes and thrust sheets em- placed at low grade metamorphism. Fold nappes and thrust sheets are also some of the most common features in orogens. Fold nappes are kilometer scaled recumbent folds which feature a weakly de- formed normal limb and an intensely deformed overturned limb. Thrust sheets on the other hand are characterized by the absence of overturned limb and can be defined as almost rigid blocks of crust that are displaced sub-horizontally over up to several tens of kilometers. The Morcles and Doldenhorn nappe are classic examples of fold nappes and constitute the so-called infra-Helvetic complex in Western and Central Switzerland, respectively. This complex is overridden by thrust sheets such as the Diablerets and Wildhörn nappes in Western Switzerland. One of the most famous example of thrust sheets worldwide is the Glarüs thrust sheet in Central Switzerland which features over 35 kilometers of thrusting which are accommodated by a ~1 m thick shear zone. Since the works of the early Alpine geologist such as Heim and Lugeon, the knowledge of these nappes has been steadily refined and today the geometry and kinematics of the Helvetic nappe system is generally agreed upon. However, despite the extensive knowledge we have today of the kinematics of fold nappes and thrust sheets, the mechanical process leading to the emplacement of these nappe is still poorly understood. For a long time geologist were facing the so-called ‘mechanical paradox’ which arises from the fact that a block of rock several kilometers high and tens of kilometers long (i.e.
    [Show full text]
  • Kinematics and Extent of the Piemont–Liguria Basin – Implications for Subduction Processes in the Alps
    Solid Earth, 12, 885–913, 2021 https://doi.org/10.5194/se-12-885-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Kinematics and extent of the Piemont–Liguria Basin – implications for subduction processes in the Alps Eline Le Breton1, Sascha Brune2,3, Kamil Ustaszewski4, Sabin Zahirovic5, Maria Seton5, and R. Dietmar Müller5 1Department of Earth Sciences, Freie Universität Berlin, Berlin, Germany 2Geodynamic Modelling Section, German Research Centre for Geosciences, GFZ Potsdam, Potsdam, Germany 3Institute of Geosciences, University of Potsdam, Potsdam, Germany 4Institute for Geological Sciences, Friedrich-Schiller-Universität Jena, Jena, Germany 5EarthByte Group, School of Geosciences, The University of Sydney, Sydney, NSW 2006, Australia Correspondence: Eline Le Breton ([email protected]) Received: 18 September 2020 – Discussion started: 8 October 2020 Revised: 3 March 2021 – Accepted: 5 March 2021 – Published: 21 April 2021 Abstract. Assessing the size of a former ocean of which only 84–35 Ma, 260 km between 35–0 Ma), which greatly exceeds remnants are found in mountain belts is challenging but cru- the width of the ocean. We suggest that at least 63 % of the cial to understanding subduction and exhumation processes. subducted and accreted material was highly thinned conti- Here we present new constraints on the opening and width nental lithosphere and most of the Alpine Tethys units ex- of the Piemont–Liguria (PL) Ocean, known as the Alpine humed today derived from OCT zones. Our work highlights Tethys together with the Valais Basin. We use a regional tec- the significant proportion of distal rifted continental margins tonic reconstruction of the Western Mediterranean–Alpine involved in subduction and exhumation processes and pro- area, implemented into a global plate motion model with vides quantitative estimates for future geodynamic modeling lithospheric deformation, and 2D thermo-mechanical mod- and a better understanding of the Alpine Orogeny.
    [Show full text]
  • Late Jurassic to Eocene Palaeogeography and Geodynamic Evolution of the Eastern Alps
    © Österreichische Geologische Gesellschaft/Austria; download unter www.geol-ges.at/ und www.biologiezentrum.at Mi-: ür-ile-r. Gfi'.ü. Os. ISSN 02hl 7-li\s 92i;!jW; /:) 04 W^r J'i 2000 Late Jurassic to Eocene Palaeogeography and Geodynamic Evolution of the Eastern Alps PETER FAUPL1 & MICHAEL WAGREICH1 4 Figures and 1 Table Abstract The Mesozoic orogeny of the Eastern Alps is controlled by subduction, collision and closure of two oceanic domains of the Western Tethyan realm: The Late Jurassic to Early Cretaceous closure of a Triassic Tethys Ocean, probably connected to the Vardar Ocean in the Hellenides, and the Mid-Cretaceous to Early Tertiary closure of the Penninic Ocean to the north of the Austroalpine unit. Based on facies analysis and provenance studies, the evolution of the major palaeogeographic domains is discussed. Ophiolitic detritus gives insights into the history of active margins and collisional events. Synorogenic sediments within the Northern Calcaerous Alps from the Late Jurassic and Early Cretaceous onwards record shortening within the Austroalpine domain, due to suturing in the south and the onset of subduction of the Penninic Ocean in the north. Transtension following Mid-Cretaceous compression led to the subsidence of Late Cretaceous Gosau Basins. Tectonic erosion of the accretionary structure at the leading margin of the Austroalpine plate resulted in deformation and deepening within the Northern Calcareous Alps. Cretaceous to Early Tertiary deep-water deposition ended in a final stage of compression, a consequence of the closure of the Penninic Ocean. Introduction troalpine zone is subdivided into a Lower, Middle and Upper Austroalpine nappe complex.
    [Show full text]
  • Opening and Closure of the Penninic Ocean Basin at the Alpine-Carpathian Transition: New Structural Data and U-Pb Zircon Ages
    Geophysical Research Abstracts Vol. 21, EGU2019-3175, 2019 EGU General Assembly 2019 © Author(s) 2019. CC Attribution 4.0 license. Opening and closure of the Penninic ocean basin at the Alpine-Carpathian transition: new structural data and U-Pb zircon ages Franz Neubauer (1), Xiaoming Liu (2), Shuyun Cao (1,3), Yunpemg Dong (2), and Isabella Merschdorf (1) (1) University of Salzburg, Dept. Geography and Geology, Salzburg, Austria ([email protected]), (2) State Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, China, (3) State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan, China In Alps, ophiolite formation has been poorly correlated with formation of adjacent passive margins, and uncertain- ties in mode of symmetric vs. asymmetric rifting and timing of passive margin formation and oceanic spreading exist. The Rechnitz window group of the Eastern Alps exposes Penninic Mesozoic oceanic and metasedimentary syn- and postrift continental margin successions along the South Burgenland basement High/Bohemian Spur, an inherited crustal-scale structure at the Alpine-Carpathian-Pannonian transition. In the Rechnitz window group, two tectonic units are distinguished, the Schlaining unit with ophiolites, which show a Paleogene history of subduction, and the structurally underlying Kösczeg unit with distal passive continen- tal margin successions indicated by their richness of continent-derived siliciclastic material. A blueschist with a plagiogranite protolith of the Schlaining yields a weighted mean zircon 206Pb/238U age of 142.5±2.8 Ma (earliest Cretaceous) interpreted to represent the age of oceanic spreading . The age is younger than the 166 to 148 Ma-ages of the ophiolites in the main Piemontais-Ligurian oceanic basin and older than the ca.
    [Show full text]