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On the non-existence of a Cadomian basement in southern France (Pyrenees, Montagne Noire): implications for the significance of the pre-Variscan (pre-Upper Ordovician) series ; Conséquences de l'absence de socle cadomien sur l'âge et la signification des séries pré-varisques (anté-Ordovicien supérieur) du sud de la France (Pyrénées, Montagne Noire)

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  • معلومة اضافية
    • Contributors:
      Laboratoire Environnement Géomécanique et Ouvrages (LAEGO); Institut National Polytechnique de Lorraine (INPL); Chercheur indépendant; Centre de Recherches Pétrographiques et Géochimiques (CRPG); Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS); Bureau de Recherches Géologiques et Minières (BRGM)
    • بيانات النشر:
      HAL CCSD
      Société géologique de France - EDP Sciences
    • الموضوع:
      2004
    • Collection:
      BRGM: HAL (Bureau de Recherches Géologiques et Minières)
    • نبذة مختصرة :
      International audience ; The deepest Hercynian metamorphic terrains in the Pyrenees and in the nearby Montagne Noire are made up of medium-grade orthogneisses and micaschists, and of high-grade, often granulitic, paragneisses. The existence of a granitic-metamorphic Cadomian basement and of its sedimentary Lower Paleozoic cover was advocated from the following main arguments: (i) a supposed unconformity of the Lower Cambrian Canaveilles Group (the lower part of the Paleozoic series) upon both granitic and metamorphic complexes; (ii) a ca. 580 Ma U-Pb age for the metagranitic Canigou gneisses. A SE to NW transgression of the Cambrian cover and huge Variscan recumbent (“penninic”) folds completed this classical model. However, recent U-Pb dating provided a ca. 474 Ma, early Ordovician (Arenigian) age for the me-tagranites, whereas the Vendian age (581 ± 10 Ma) of the base of the Canaveilles Group was confirmed [Cocherie et al., 2005]. In fact, these granites are laccoliths intruded at different levels of the Vendian-Lower Cambrian series. So the Cadomian granitic basement model must be discarded. In a new model, developed in the Pyrenees and which applies to the Montagne Noire where the orthogneisses appear to be Lower Ordovician intrusives too, there are neither transgression of the Paleozoic nor very large Hercynian recumbent folds. The pre-Variscan (pre-Upper Ordovician) series must be divided in two groups: (i) at the top, the Jujols Group, mainly early to late Cambrian, that belongs to a Cambrian-Ordovician sedimentary and magmatic cycle ; the early Ordovician granites pertain to this cycle; (ii) at the base, the Canaveilles Group of the Pyrenees and the la Salvetat-St-Pons series of the Montagne Noire, Vendian (to earliest Cambrian?), are similar to the Upper Alcudian series of Central Iberia. The Canaveilles Group is a shale-greywacke series with rhyodacitic volcanics, thick carbonates, black shales, etc. The newly defined olistostromic and carbonated, up to 150 m thick Tregurà Formation forms the base of ...
    • Relation:
      hal-03783854; https://brgm.hal.science/hal-03783854; https://brgm.hal.science/hal-03783854/document; https://brgm.hal.science/hal-03783854/file/643.pdf
    • الرقم المعرف:
      10.2113/175.6.643
    • الدخول الالكتروني :
      https://brgm.hal.science/hal-03783854
      https://brgm.hal.science/hal-03783854/document
      https://brgm.hal.science/hal-03783854/file/643.pdf
      https://doi.org/10.2113/175.6.643
    • Rights:
      info:eu-repo/semantics/OpenAccess
    • الرقم المعرف:
      edsbas.9254292C