A step towards unraveling the paleogeographic attribution of pre-Mesozoic basement complexes in the Western Alps based on U–Pb geochronology of Permian magmatism - Archive ouverte HAL Access content directly
Journal Articles Swiss Journal of Geosciences Year : 2020

A step towards unraveling the paleogeographic attribution of pre-Mesozoic basement complexes in the Western Alps based on U–Pb geochronology of Permian magmatism

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Michel Ballèvre
  • Function : Correspondent author
Marc Poujol

Abstract

The Briançonnais Domain (Western Alps) represented the thinned continental margin facing the Piemonte-LiguriaOcean, later shortened during the Alpine orogeny. In the external part of the External Briançonnais Domain (ZoneHouillère), the Palaeozoic basement displays microdioritic intrusions into Carboniferous sediments and andesiticvolcanics resting on top of the Carboniferous sediments. These magmatic rocks are analysed at two well-knownlocalities (Guil volcanics and Combarine sill). Geochemical data show that the two occurrences belong to the samecalc-alkaline association. LA-ICP-MS U–Pb ages have been obtained for the Guil volcanics (zircon: 291.3 ± 2.0 Ma andapatite: 287.5 ± 2.6 Ma), and the Combarine sill (zircon: 295.9 ± 2.6 Ma and apatite: 288.0 ± 4.5 Ma). These ages showthat the calc-alkaline magmatism is of Early Permian age. During Alpine orogeny, a low-grade metamorphism, bestrecorded by lawsonite-bearing veins in the Guil andesites, took place at about 0.4 GPa, 350 °C in the External Briançonnaisand Alpine metamorphism was not able to reset the U–Pb system in apatite. The Late Palaeozoic history ofthe Zone Houillère is identical to the one recorded in the Pinerolo Unit, located further East in the Dora-Maira Massif,and having experienced a garnet-blueschist metamorphism during the Alpine orogeny. The comparison of these twounits allows for a better understanding of the link between the Palaeozoic basements, mostly subducted during theAlpine convergence, and their Mesozoic covers, generally detached at an early stage of the convergence history
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insu-02957285 , version 1 (14-10-2020)

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Michel Ballèvre, Audrey Camonin, Paola Manzotti, Marc Poujol. A step towards unraveling the paleogeographic attribution of pre-Mesozoic basement complexes in the Western Alps based on U–Pb geochronology of Permian magmatism. Swiss Journal of Geosciences, 2020, 113 (1), pp.12. ⟨10.1186/s00015-020-00367-1⟩. ⟨insu-02957285⟩
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