Epard Jean-Luc

The Adula Nappe: Stratigraphy, structure and kinematics of an exhumed high-pressure nappe

Project Number: CH-5705
Project Type: Dissertation
Project Duration: 01/01/2010 - 05/31/2013 project completed
Funding Source: SNSF ,
Leading Institution: Université de Lausanne
Project Leader: Prof. Jean-Luc Epard
géologie structurale et alpine
Institut des Sciences de la Terre (ISTE)
Université de Lausanne
Mouline - Géopolis
1015 Lausanne
Phone: +41 (0) 21 692 43 66 ; +41 (0) 21 692 43 06
FAX: +41 (0) 21 692 43 05
e-Mail: jean-luc.epard(at)unil.ch
http://www.unil.ch/iste

related to this project.
for which the project has a relevance.


Research Areas:
Landscape

Disciplines:
environmental sciences

Keywords:
geology, lithostratigraphy, paleozoic basement, paleogeographic domains, nappe structure, tectonics, metamorphism


Abstract:
This study analyses the stratigraphy, structure and kinematics of the northern part of the Adula nappe of the Central Alps. The Adula nappe is one of the highest basement nappes in the Lower Penninic nappe stack of the Lepontine Dome. This structural position makes possible the investigation of the transition between the Helvetic and North Penninic paleogeographic domains.
The Adula nappe is principally composed of crystalline basement rocks. The investigation of the pre-Triassic basement shows that it contains several Palaeozoic detrital metasedimentary formations dated from the Cambrian to the Ordovician. These formations contain also some volcanic or intrusive magmatic rocks. Ordovician metagranites dated at ~450 Ma are also a common rock-type of the Adula basement. These formations underwent Alpine and Variscan deformation and metamorphism. Permian granites (Zervreila orthogneiss, dated at ~290 Ma) have intruded this pre-structured basement in a post-orogenic geodynamic context. Due to their age, the Zervreila orthogneiss are good markers for lpine deformation.
The stratigraphy of the Mesozoic and Paleogene sedimentary cover of the Adula nappe is essential to unraveling its pre- orogenic history. The autochthonous cover is assigned to a North Penninic Triassic series that testifies for a transition between the Helvetic and Briançonnais Triassic domains. The Adula domain goes through an emersion during the Middle Jurassic, and is part of a topographic high during the first phase of the Alpine rift. The sediments of the late Middle Jurassic show a drowning phase associated with a tectonic activity and a breccia formation. In the neighbouring domains, coeval with the drowning phase in the Adula domain, a strong extensional crustal delamination and a scattered magmatic activity is associated with the main opening of the North Penninic domain. The Upper Jurassic of the Adula nappe is characterized by a carbonate formation comparable with those in the Helvetic or Subbriaçonnais domains. Flysch s.l. deposition starts probably at the end of the Cretaceous. These sediments are deposited on a large unconformity testifying for a Cretaceous sedimentary gap.
The Adula nappe exhibits a very complex structure. This structure is formed by several deformation phases. Two ductile deformations are responsible for the nappe emplacement. The first deformation phase is associated with a folding compatible with a top-to-south movement at the top of the nappe. The second phase is dominant and pervasive throughout the whole nappe. It goes with a strong north vergent folding and the main nappe emplacement. These two phases cause the exhumation and emplacement of a coherent, although pre-structured, piece of continental crust. Two further deformation phases postdate the nappe emplacement.


Leading questions:
  • geometry and kinematics of the Adula nappe emplacement

  • exhumation of high-pressure metamorphic rocks

  • paleogeographic affiliation of highly deformed Alpine domain


    PDF: https://serval.unil.ch/resource/serval:BIB_5FF5D2D01CE0.P001/REF

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