strati.ch - Lexique lithostratigraphique de la Suisse

Représentation et statut

Variantes historiques: Austroalpin valaisan, Salassic p.p. (TK500 / Gouffon et al. 2024)

Paléogéographie

terrane Cervinia :

terrane or continental fragment

Termes génériques

Type de protolithe

Définition: Gouffon Yves (Editor) (2024) : Tectonic Map of Switzerland 1:500000, Explanatory notes. Federal Office of Topography swisstopo, Wabern

p.81: The Dent Blanche, Mont Mary and Sesia nappes are structurally similar, with an upper continental crust unit at the base (Arolla Unit, Lower Unit and Gneiss Minuti Unit) and a lower crustal unit at the top (Valpelline Unit, Upper Unit and 2 DK Zone). In the Sesia Nappe, the intermediate Eclogitic Micaschist Unit appears to be derived from a relatively deep part of the upper crust. The high-pressure metamorphism lasted from the Late Cretaceous to the Early Paleogene (Vho et al. 2020 and ref. therein), mainly in the lower and intermediate units; later only, the lower units were significantly re-equilibrated under greenschist-facies conditions. This peculiar situation may be explained by the following succession of events (Manzotti et al. 2014 b): 1) Jurassic opening of the Piemonte-Liguria Ocean and detachment of exotic blocks of Adriatic upper crust as well as lower crust further back, 2) Late Cretaceous to Early Paleogene closure of the ocean and subduction of the exotic blocks below the Adriatic margin, with the most distal blocks (upper crust) moving under the most proximal blocks (lower crust), then of the oceanic crust and sediments under this preformed assemblage, and 3) Paleogene continental collision with folding to create the present-day structure of the nappes.