Tectono-metamorphic evolution of an evaporitic décollement as recorded by mineral and fluid geochemistry: The 'Nappe des Gypses' (Western Alps) case study

Autor: Guillaume Barré, Laurent Truche, Raymond Michels, Pierre Cartigny, Stéphane Guillot, Pierre Strzerzynski, Emilie Thomassot, Catherine Lorgeoux, Nelly Assayag
Přispěvatelé: GeoRessources, Centre National de la Recherche Scientifique (CNRS)-Université de Lorraine (UL)-Centre de recherches sur la géologie des matières premières minérales et énergétiques (CREGU)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA), Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Université de Lorraine (UL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre de recherches sur la géologie des matières premières minérales et énergétiques (CREGU)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), ANR-10-LABX-0021,RESSOURCES21,Strategic metal resources of the 21st century(2010), ANR-10-LABX-0056,OSUG@2020,Innovative strategies for observing and modelling natural systems(2010)
Jazyk: angličtina
Rok vydání: 2020
Předmět:
Zdroj: Lithos
Lithos, Elsevier, 2020, 358-359, pp.105419. ⟨10.1016/j.lithos.2020.105419⟩
Lithos, 2020, 358-359, pp.105419. ⟨10.1016/j.lithos.2020.105419⟩
ISSN: 0024-4937
DOI: 10.1016/j.lithos.2020.105419⟩
Popis: International audience; 16 Evaporites play a major role on the structuration of collisional orogens especially when they 17 act as décollement units. However, their exact pressure-temperature-deformation (P-T-d) paths 18 are poorly documented. In this study, the first direct P-T-d constraints of the "Nappe des 19 Gypses" formation (western French Alps) have been established. An innovative association of 20 structural geology, petrography, crystallochemistry, and detailed study of both fluid inclusions 21 and stable isotopes (C, O) analysis has been applied to this evaporitic facies. Geochemical 22 analysis shows that the "Nappe des Gypses" formation has recorded the three typical 23 metamorphic and deformational events of the Alps (namely D1, D2 and D3). These different 24 constraints allow the determination of the first determination of the P-T path for this unit. 25 Metamorphic peak conditions of the "Nappe des Gypses" are at 16.6 ± 2.3 kbars and 431°C ± 26 28°C. This formation was buried at similar conditions than the oceanic units. During the 27 exhumation path, the D1-D2 transition is reached at 350°C ± 20°C and 6.5 ± 1.8 kbars and the 28 D2-D3 transition is assumed to be at 259°C ± 24°C and 2.0 ± 1.0 kbars (Strzerzynski et al., 29 2012). Peak P-T conditions overlap those of the median Liguro-Piemontese units but are 30 different from those of the Briançonnais units. It implies 1) an active and crucial role of the 31 "Nappe des Gypses" during the exhumation of the Alpine oceanic complex. And 2) confirms the 32 allochthonous and more distal origin of the European Thetysian passive margin of the "Nappe 33 des Gypses" formation. Consideration of sulfates dehydration probably between 15.0 and 16.6 34 kbars and 200 and 300°C, allows to discuss pore pressure excess and its mechanical 35 consequences on the exhumation process. This process is very likely to amplify the 36 "décollement" effect of the evaporites and allow the nappe stack formation. 37 This illustrates the role of this formation as a décollement surface. This difference of 38 evolution highlights the major role of the evaporitic formations on the exhumation and 39 structuration of a collisional chain. Such methodology could contribute to decipher the role of 40 evaporites in the structural context of other collisional chains such as Himalaya, Pyrenees or 41 Zagros. 42
Databáze: OpenAIRE
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