Fast exhumation rate during late orogenic extension: The new timing of the Pilat detachment fault (French Massif Central, Variscan belt) - Université Clermont Auvergne Accéder directement au contenu
Article Dans Une Revue Gondwana Research Année : 2022

Fast exhumation rate during late orogenic extension: The new timing of the Pilat detachment fault (French Massif Central, Variscan belt)

Véronique Gardien
  • Fonction : Auteur
Jean-Emmanuel Martelat
Philippe-Hervé Leloup
Gweltaz Mahéo
  • Fonction : Auteur
Benoit Bevillard
  • Fonction : Auteur
Pascal Allemand
Patrick Monié
  • Fonction : Auteur
Jean-Louis Paquette
Anne-Sabine Grosjean
  • Fonction : Auteur
  • PersonId : 778093
  • IdRef : 181697920
Michel Faure
  • Fonction : Auteur
Cyril Chelle-Michou
Clémentine Fellah
  • Fonction : Auteur

Résumé

A leucogranite sill in the footwall of the extensional Pilat shear zone (PSZ) Eastern French Massif Central was emplaced and sheared in a short time interval, between 301.8–3.1 and 303.0–1.6 Ma (zircon U–Pb and mica 40 Ar/ 39 Ar ages, respectively). Extension ended at 298.5–1.5 Ma ( 40 Ar/ 39 Ar on mica) as shown by a non deformed dike cross cutting the sheared zone. On the hanging wall of the fault, the opening of the St. Etienne Basin filled by coarse clastic sedimentation confirms the existence of a relief south of the PSZ. U-Pb dating of a lithic-rich ignimbrite at the bottom of the basin and of a volcanic layer at the top delivred ages of 310.5–3.4 Ma and 299.3–1.3 Ma, respectively. Close U-Pb and 40 Ar/ 39 Ar ages from syn- to post-tectonic granites indicate very fast cooling (150°C/Myr) and exhumation rate (6 mm/yr) corresponding to the emplacement of granites in the middle crust immediately followed by their fast tectonic exhumation and cooling into the upper crust. The development of the Pilat fault in the thermally softened crust is responsible for the rapid exhumation of the Velay dome, a Metamorphic Core Complex localized in the footwall of the sheared zone. Here we propose that its rapid exhumation was due to localized sub crustal lithospheric mantle dripping. These new data show that there was only one extensional phase in the PSZ coeval with the opening of the St. Etienne coal Basin. Finally, the new chronology obtained in this study is challenging previous ages suggesting 20 Ma activity for the Pilat shear zone.

Domaines

Géochimie
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hal-03615479 , version 1 (28-11-2022)

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Paternité - Pas d'utilisation commerciale

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Citer

Véronique Gardien, Jean-Emmanuel Martelat, Philippe-Hervé Leloup, Gweltaz Mahéo, Benoit Bevillard, et al.. Fast exhumation rate during late orogenic extension: The new timing of the Pilat detachment fault (French Massif Central, Variscan belt). Gondwana Research, 2022, 103, pp.260-275. ⟨10.1016/j.gr.2021.10.007⟩. ⟨hal-03615479⟩
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