(Internal) Middle Penninic of Western Switzerland

Representation and status

Color RGB

R: 239 G: 237 B: 235

Rank

tectonic subdomain

Validity

Unit is not in Use

Status

local name (informal)

Nomenclature

Deutsch

(Internes) Mittelpenninikum der Westschweiz

Français

Pennique Moyen (interne) de Suisse occidentale

Italiano

Pennidico Medio (interno) della Svizzera occidentale

English

(Internal) Middle Penninic of Western Switzerland

Historical Variants

Middle Penninic in Western Switzerland (TK500 / Gouffon et al. 2024)

Palaenography and tectonic

Tectonic unit (resp. main category)

• Middle Penninic

Kind of protolith

• tectonic

Metamorphism

non metamorphic

References

Definition

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

p.62: The Middle Penninic subdomain of the Western Alps comprises units between the Lower Penninic subduction surface and the major thrust of the Upper Penninic. In the area described here, they were first grouped together within the “Grand St-Bernard Nappe” (Argand 1911), which was then subdivided into several nappes (e. g., Escher 1988) described below.
In the Valle d’Aosta, the Middle Penninic units are crosscut by the Col de Bard Fault (Gouffon 1993, Gouffon & Burri 1997), which separates two structurally very different sectors. In the hangingwall, north of the fault, the nappes overlie each other regularly towards the west and their structures dip E – SE. In the footwall, south of the fault, only the Zone Houillère and the Ruitor Nappe are present; their structures are backfolded and dip W– NW, while a large isoclinal synform (Avise) with a core attributed to the Tsaté Nappe splits the Ruitor Nappe. The Col de Bard Fault is related either to the Aosta-Ranzola Fault (Gouffon & Burri 1997) or to the Cogne Fault Zone (Malusà et al. 2009) (see § 10.4).
The Middle Penninic units are thought to be derived from the Briançonnais Terrane, which consisted of a polycyclic crystalline basement cut by Late Cambrian (ca. 500 Ma) and Permian (ca. 270 Ma) granitic intrusions, Permo-Carboniferous sediments that filled narrow basins and a characteristic Mesozoic – Paleogene sedimentary cover. Much of this Briançonnais cover was detached at the level of the Triassic evaporites to form some of the nappes in the Prealps (§ 6.1). This detachment probably occurred during an early phase of the Alpine orogeny, following the closure of the Piemonte-Liguria Ocean, when the Briançonnais Terrane was subducted below the Adriatic margin. The Middle Penninic subdomain in turn formed the hangingwall during the closure and subduction of the oceanic Valaisan Basin.