Silvretta-Decke

Representation and status

Color CMYK

N/A

Color RGB

R: 241 G: 239 B: 237

Rank

nappe

Validity

Unit is in Use

Status

valid

Status discussion

Nomenclature

Deutsch

Silvretta-Decke

Français

Nappe de la Silvretta

Italiano

Falda della Silvretta

English

Silvretta Nappe

Origin of the Name

Silvretta-Gebirgsgruppe (GR)

Historical Variants

Silvretta-Masse (Stotter 1858), Silvrettamasse (Koch 1875, Koch 1876a, Koch 1877a/b), Silvrettadecke (Staub & Cadisch 1921, Ott 1922), oberostalpine Decke = Silvretta-Decke (Alb. Heim 1922), Silvrettiden (Medwenitsch 1962), Silvretta-Scholle = Silvretta-Schubmasse (Trümpy 1972), Silvretta-Masse = Silvrettadecke (Kräyenbühl 1984), Silvretta-Einheit (Dössegger 1987), Silvretta nappe (Maggetti & Flisch 1993), Silvretta thrust sheet (Biino 1996), Silvretta-Decke (Gruber et al. 2010, Furrer et al. 2015), Silvretta Nappe (TK500 / Gouffon et al. 2024)

Nomenclatorial Remarks

die Silvretta

Description

Description

Oberostalpine Decke mit polymetamorphes Altkristallin (inkl. variszisch steilgestellten Schlingen), postvariszische Diabasgänge, sowie permo-mesozoische Sedimentbedeckung im SE (Ducan- und Landwassergebiet).

Furrer et al. 1985: "This is another large thrust mass of basement rocks, similar in many respects to the Oetztal nappe. Triassic sediments are preserved only near its western margin, where they occur in SW-NE trending synclines; the NW ("normal") flank of these is often cut by lags. These (early?) Alpine folds as well as the Variscan and pre-Variscan basement structures are truncated by the basal thrust, implying important E-W movements. The base of the nappe is further deformed by E-W trending synforms and antiforms."

Thickness

Maximal 5 km dicke Platte.

Hierarchy and sequence

Subordinate units

• Ducan-Synklinal
• Landwasser-Synklinal
• «Phyllitgneiszone»
• Kristallines Grundgebirge der Silvretta-Decke

Upper boundary

Ötztal-Decke, Nördliche Kalkalpen (mit Landecker Phyllitgneiszone am Übergang)

Lower boundary

Arosa-Decke bzw. Flysch der Tasna-Decke (Bollin 1989), Subsilvrettide Schollen, Err-Bernina-Deckenkomplexe, Ela-Decke, Engadiner Störung

Geography

Geographical extent

Verwall- und Samnaungruppe.

Palaenography and tectonic

Paleogeography

Adriatic continental margin :

southern, passive continental margin / platform

Tectonic unit (resp. main category)

• Silvretta

Kind of protolith

• tectonic

Metamorphism

polycyclic (Alpine, Variscan and older)

Metamorphic facies

• greenschist facies (epizone)
• amphibolite facies

Note on facies

prävariszische Metamorphose (Maggetti & Galetti 1988, Frank et al. 1978), variszische (360-350 Ma) Amphibolit-fazielle Metamophose, gefolgt von einer späteren (310-300 Ma) Grünschiefer-faziellen Metamorphose (Flisch 1987)

References

Definition

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

p.92: The Silvretta Nappe is the northernmost Upper Austroalpine basement-cover nappe extending over a large area located between the southern rim of the Northern Calcareous Alps in the north and the Engadine Fault in the south. Most of its area is occupied by high-grade metamorphic basement that was multiply deformed since the Precambrian, ending with an amphibolite-facies Variscan tectono-metamorphic event in the Carboniferous (Magetti & Flisch 1993). A top-N Alpine thrust of secondary importance separates this high-grade basement from a narrow belt of low-grade basement referred to as the “Phyllitgneiszone” (including the Landeck Quartzphyllites) that is nowadays also considered to be a part of the Silvretta Nappe (Gruber et al. 2010). It has a lower grade of pre-Alpine metamorphism and has been intensely sheared during the Alpine orogeny (Rockenschaub 1990).
The Triassic cover of the Silvretta Nappe is preserved in two SW– NE striking synclines located at the western edge of the Silvretta Nappe, known as the Landwasser and Ducan synclines (Froitzheim et al. 1994). They formed during top-NW thrusting in the Cretaceous, and then were overprinted by normal faulting still in the latest Cretaceous. This was followed by top-N thrusting of the entire Silvretta Nappe over the Penninic units during Cenozoic times. Only very small lenses of Permo-Carboniferous and Early Triassic slivers (“Puschlin Zone”) are preserved within the Landeck Quarzphyllites (Gruber et al. 2010).