Falda del Tonale

Représentation et statut

Couleur CMYK

N/A

Couleur RGB

R: 241 G: 239 B: 237

Rang

unité lithostratigraphique délimitée tectoniquement

Usage

Ce terme est en usage.

Status

valide

Nomenclature

Deutsch

Tonale-Decke

Français

Nappe du Tonale

Italiano

Falda del Tonale

English

Tonale Nappe

Origine du nom

Monte Tonale (Italia)

Variantes historiques

Serie del Tonale = Tonale-Serie (Knoblauch & Reinhard 1939), Tonale-Serie (Weber 1957), Tonaleserie (Koenig 1967, Heitzmann 1974), Tonale Series (Vogel & Voll 1976), Berger & Mercolli 2007), Tonale-Zone, Tonale Nappe (TK500 / Gouffon et al. 2024)

Description

Description

Blastomylonitische Zone bestehend aus Metasedimente (u.a. "alte Marmore" und Graphitschiefer), Metamafite und Metagranite.

prealpine gneisses with marbles, quartzites and amphibolites, transformed in garnet-staurolite-kyanite schists + subvolcanic dykes (Vogel & Voll 1976)

Hiérarchie et succession

Unités hiérarchiquement subordonnées

• Ulten-Einheit

Paléogéographie et tectonique

Paléogéographie

marge continentale adriatique :

southern continental margin / platform

Termes génériques

• Tonale

Type de protolithe

• tectonique

Faciès métamorphique

• faciès à amphibolites

Remarque sur le métamorphisme

Amphibolit-Fazies > Sillimanit-Subfazies (Bockemühl & Pfister 1985)

Références

Révision

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

p.99: The largest part of the Tonale Nappe is characterized by a very distinct and lithologically variable association of predominantly sillimanite-bearing paragneisses, marbles, quartzites and amphibolites metamorphosed during the Variscan cycle, referred to as the Tonale Gneiss Complex (formerly “series”). The Tonale Gneiss Complex systematically follows the E–W striking part of the Tonale Fault (Insubric Fault) all the way from Giubiasco (Ticino) beyond the eastern margin of the map area over a distance of 150 km (Cornelius & Furlani-Cornelius 1930). In the west, the Tonale Nappe forms a steeply N-dipping narrow strip of mylonitic series that are part of the Southern Steep Belt (or “root zone” north of the Tonale Fault), bounded by the tonalites of the Bregaglia Intrusion to the north and Alpine mylonites and cataclasites of the Tonale Fault in the south (Lardell i 1981). The mylonitic series of the Tonale Nappe was strongly affected by dextral shearing under ductile and later brittle conditions along the Tonale Fault (Fumasoli 1974). Between Sondrio and Tirano, the Tonale Nappe represents the hangingwall of the Late Cretaceous Mortirolo Normal Fault (Meier 2003). Further east, a second Late Cretaceous normal fault, the SE-dipping Pejo Normal Fault, accommodates top-E extension combined with a sinistral strike-slip component in the present-day map view (Werling 1992, Viola et al. 2003). The amount of displacement across the Pejo Normal Fault seems to be substantial since this fault juxtaposes the Tonale Nappe that lacks Alpine metamorphic overprint with the southernmost Campo Nappe Complex that was at least locally metamorphosed under upper greenschist-facies conditions during the Alpine cycle (Werling 1992).
Near the eastern margin of the map area, the Tonale Nappe additionally comprises a rock association that is lithologically distinct from the Tonale Gneiss Complex; it is referred to as the Ulten (or Ultimo) Unit in the literature (Martin et al. 2009). It overlies the Tonale Gneiss Complex along a pre-Alpine tectonic contact. The Ulten Unit is characterized by kyanite-bearing paragneisses and migmatites, containing boudins of amphibolitized eclogites, metagabbros and peridotites. After a high-pressure event of unknown age, the Ulten Unit was exhumed to a lower crustal depth of around 30 km between Devonian and Carboniferous times, associated with trondhjemitic intrusions and related migmatization; it then slowly cooled during Permian to Jurassic times (Del Moro et al. 1999). Its thermal history, as well as its original location in the lower crust within the Variscan orogen, are reminiscent of the Ivrea Zone of the South Alpine domain. A direct correlation of the Ivrea Zone located south of the Tonale Fault with the Ulten Unit north of this fault suggests a dextral offset across the Tonale Fault by some 150 km (Laubscher 1991) that largely occurred during the Oligocene (Stipp et al. 2004). This dextral offset is compatible with the kinematic analysis of mylonites accompanying the Tonale Fault east of the Bregaglia Intrusion, characterized by a subhorizontal stretching lineation and indicating dextral shear (Schmid et al. 1989, Werling 1992, Stipp et al. 2004).