Falda di Antigorio

Representation and status

Historical Variants: Untere Gneissmasse = Antigori-Gneiss (Gerlach 1869), nappe I = nappe d'Antigorio (Argand 1911b), Antigoriodecke (Bosshard 1925), Antigoriodecke bzw. Antigorioteildecke (Grütter 1929), Antigorio-Monte Leone-Decke (Günthert 1958), Falda Antigorio (Godenzi 1963), Antigorio-Gneismasse = Antigorio-Zone = Antigorio-Gneisszone (Wieland 1966), nappe n°1 = Antigorio nappe (Carrupt 2003), Antigorio recumbent fold (Steck 2008), Antigorio fold nappe (Steck et al. 2013), Falde di Antigorio (Della Torre & Maggini 2015)

Description: Steck et al. 2013, p.430: The Antigorio fold nappe in the Antigorio (Toce) and Devero valleys is composed of three granitoid intrusions: (a) the 296 ± 2 Ma old Antigorio tonalite, (b) the dominant middle to coarse grained 290 ± 4 Ma old Antigorio granodiorite and (c) the 289 ± 4 Ma old Antigorio granite (Bergomi et al. 2007). The Antigorio granitoids are farther east intrusive in an older polycyclic and migmatitic basement. The granodiorite is also intrusive in the Paleozoic Baceno schist of the Devero valley and the Verampio window. The Pioda di Crana gneiss is dominated by a strongly foliated middle to fine grained 301 ± 4 Ma old granite gneiss (Bergomi et al. 2007). Locally and especially near the contact with the higher Mergoscia zone, polycyclic micaschists and amphibolites are common. The granodioritic and tonalitic Alpigia hornblende-biotite gneiss, here attributed to the Antigorio nappe, exhibits a regular contact with the staurolite–kyanite–garnet–micaschist of the Campo Tencia unit of the Simano nappe (Keller et al. 1980; Steck 1998; Berger et al. 2005). This contact may be tectonic or intrusive.

Subordinate units

Age at top

Note about top

unsicher

Age at base

Geographical extent: Alpi Lepontine: Val Divedro (Gondoschlucht), Valle Antigorio, Val Formazza, Val Bavona, Valle di Campo, Val di Vergeletto e Valle Onsernone.
Type area: Valle Antigorio (Italia)

Tectonic unit (resp. main category)

Kind of protolith

Definition: Gerlach Heinrich (1869) : Die penninischen Alpen, Beiträge zur Geologie der Schweiz. Neue Denkschriften allg. Ges. ges. Natf. 23

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

The Antigorio Nappe consists mainly of Variscan granitoids (ca. 290–300 Ma, Bergomi et al. 2007). In its northwestern part, this basement is surrounded by an autochthonous Mesozoic–Paleogene sedimentary cover, which could be connected to the cover of the Verampio Nappe via an early thrust syncline (§ 5.1). Late folding is responsible for two multi-kilometer-scale isoclinal structures: the Alpe Bosa-Wandfluhhorn fold and the Ziccher fold (e.g., Milnes 1974a, Steck et al. 2013).