The Cenozoic Alpine, and Paleozoic Variscan and eo-Variscan collisional belts are compared in the framework of the Wilson cycle considering differences between cold and hot orogens. The W. Alps result of the opening and closure of the Liguro-Piemonte ocean, whereas the Paleozoic Eovariscan and Variscan orogenies document multiple ocean openings and collisions in space and a polyorogenic history in time. Jurassic or Early Ordovician break-up of Pangea or Pannotia megacontinents led to the formation of passive continental margins, and the opening of Liguro-Piemonte, or Rheic, Tepla-Le Conquet, and Medio-European oceans, respectively. In Paleozoic or Mesozoic, microcontinents such as Apulia and Sesia or Armorica and Saxo-Thuringia were individualized. The oceanic convergence stage was associated with the development of arcs and back-arc basins in the Variscan belt but magmatic arcs are missing in the W. Alps, and inferred in the Eo-variscan one. Though the nappe stack is mainly developed in the subducted European or Gondwana crust in the western Alps and Eo-variscan cases, the Moldanubian nappes formed in the upper plate in the Variscan case. The Alpine and Variscan metamorphic evolutions occurred under ca. 8 °C/km and 30 °C/km gradients, respectively. During the late-to post-orogenic stages, all belts experienced "unthickening" accommodated by extensional tectonics, metamorphic retrogression, and intramontane basin opening. The importance of crustal melting, represented by migmatites, granites, and hydrothermal circulations in the Variscan and Eo-Variscan belts is the major difference with the W. Alpine one. The presence, or absence, of a previous Variscan or Cadomian continental basement might have also influenced the rheological behavior of the crust.
Authors
- Bibliographic Reference
- Michel Faure. Alpine, Variscan, eo-Variscan belts: comparison between hot and cold orogens from the examples of French segments. Comptes Rendus. Géoscience, 2024, pp.1-19. ⟨10.5802/crgeos.215⟩. ⟨insu-04106009⟩
- DOI
- https://doi.org/10.5802/crgeos.215
- HAL Collection
- ['Observatoire de Paris', "INSU - Institut National des Sciences de l'Univers", 'Bureau de Recherches Géologiques et Minières', 'CNRS - Centre national de la recherche scientifique', "Université d'Orléans", "institut des sciences de la terre d'orléans", "Observatoire des Sciences de l'Univers en région Centre", 'Université Paris sciences et lettres', 'Observatoire de Paris - PSL']
- HAL Identifier
- 4106009
- Institution
- ['Bureau de Recherches Géologiques et Minières (BRGM)', "Institut national des sciences de l'Univers", 'Observatoire de Paris', "Université d'Orléans"]
- Laboratory
- Institut des Sciences de la Terre d'Orléans - UMR7327
- Published in
- France
Table of Contents
- 1. Introduction 3
- 2. Tectonic zonation 4
- 3. The pre-orogenic stage 5
- 3.1. Liguro-Piemonte ocean: Pangea breakup 5
- 3.2. Variscan rifting: Pannotia break-up 6
- 4. The oceanic convergence stage 8
- 4.1. Western Alps: Liguro-Piemonte Ocean closure 8
- 4.2. The Eo-Variscan belt: Medio-European ocean closure 8
- 4.3. The Variscan belt: Rheic and Tepla oceans closure 10
- 5. The collisional stage 11
- 5.1. Western Alps: suturing of the Liguro-Piemonte ocean 11
- 5.2. The Eo-Variscan Gondwana–Armorica: suturing of the Medio-European ocean 12
- 5.3. The Variscan collisions: suturing of the Rheic and Tepla-Le Conquet ocean 13
- 6. The intracontinental syn- to late convergence 13
- 6.1. Western Alps 13
- 6.2. Variscan belt 14
- 7. Conclusive remarks 14
- 7.1. Passive continental margins 14
- 7.2. Crustal melting 15
- 7.3. Fluid circulation and ore deposits 16
- 7.4. The basement question 16
- 7.5. Orogenic time scale 16
- Conflicts of interest 17
- Acknowledgements 17
- References 17
