strati.ch - Lithostratigraphic Lexicon of Switzerland

Representation and status

Historical Variants: Préalpes romandes = zone du Chablais et du Stockhorn = zone du Stockhorn = Alpes calcaires du versant nord des Alpes = Préalpes du Chablais et du Stockhorn = nappe du Chablais et du Stockhorn = nappe de recouvrement du Chablais-Stockhorn = nappe du Chablais = nappe chablaisienne = nappe du Stockhorn (Schardt 1893), Chablais-Decken (Vonderschmitt 1935), Voralpen, Pre-Alps, Präalpen (Trümpy 1974), nappes préalpines (Plancherel 1998), Prealps (TK500 / Gouffon et al. 2024)

Description: Empilement allochtone comprenant: la nappe des Préalpes Médianes (briançonnais s.l.), la nappe de la Brèche (prépiémontais) et les «nappes supérieures» (piémontais-ligure), ainsi que des unités ultrahelvétiques à valaisannes (formant ensemble les «Préalpes Internes» et les «Préalpes Externes»).

Paleogeography

Prepiemont Domain , Valaisan Basin , Briançonnais Terrane :

microcontinent briançonnais

Tectonic unit (resp. main category)

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

p.55: A number of nappes consisting of sedimentary rocks, originating from regions located further south than the European continental margin, form klippen resting in front or on top of the Helvetic nappes (e. g., Schardt 1898, Jeannet 1922, Trümpy 1960). Several klippen can be recognized from the west (Annes and Sulens klippen) to the east (e. g., Mythen Klippe; see § 6.3). The largest lies south and west of Le Léman, known as the Prealps, and is distributed in two distinct regions: 1) the Chablais Prealps situated between the Arve Valley and the Rhône Valley, 2) the Romandes Prealps between the Rhône Valley and the Thunersee. The Prealps contain the most complete nappe stack; the other klippen contain only one or two of the units described in this chapter.
The Prealps were previously structurally subdivided into “Lower”, “Middle” and “Upper Prealps” (ref. in Mass on 1976 and Sartori 1990). The search for the root and origin of each nappe of the Prealps has led them to be considered as Penninic. However, the Prealps are a particular entity, having experienced a tectono-metamorphic history distinct from that of the Penninic units located further south in the internal part of the Alps.