Tavetsch-Decke

Representation and status

Index

TZM

Color CMYK

N/A

Color RGB

R: 241 G: 239 B: 237

Rank

nappe

Validity

Unit is in Use

Status

valid

Nomenclature

Deutsch

Tavetsch-Decke

Français

Nappe du Tavetsch

Italiano

Falda del Tavetsch

English

Tavetsch Nappe

Origin of the Name

Tavetsch = Tujetsch (GR), Surselva

Historical Variants

Somvixer Zwischenmassiv (Niggli & Staub 1914), Tavetscher Zwischenmassiv (Niggli 1944), Tavetsch-Zwischenmassiv, Tavetsch massive [sic] (Purdy & Stalder 1973), Tavetschermassiv (Büchi & Trümpy 1976), Tavetsch massif (Biino 1994), Tavetsch Nappe (Berger et al. 2017)

Description

Description

Biotitgneis, Zweiglimmergneis, Serizit-Chlorit-Schiefer bis -Phyllit, sowie Amphibolit- und Serpentinitlinsen.

Thickness

Ca. 30 km lang und bis max. 5 km breit.

Age

Age at top

• Paleozoic

Age at base

• Precambrian

Geography

Geographical extent

Surselva (Vorderrheintal), zwischen Oberalppass und Trun/Schlans.

Type area

Tujetsch (GR)

References

Definition

Niggli E. (1944) : Das westliche Tavetscher Zwischenmassiv und der angrenzende Nordrand des Gotthardmassivs. Schweiz. mineral. petrogr. Mitt. 14 /1– 2, 58 –301

Definition

Berger Alfons, Mercolli Ivan, Herwegh Marco, Gnos Edwin (2017) : Geological Map of the Aar Massif, Tavetsch and Gotthard Nappes. Geological Special Map 1:100'000, Explanatory Notes 129

p.60: Between the Oberalppass and Trun, a thick suite of gneisses occurs between the mylonitic Clavaniev Zone (Aar Massif) to the north and the Urseren-Garvera Zone (Gotthard Nappe) to the south. NIGGLI (1944) mapped this region in detail and interpreted it as an independent tectonic unit called “Tavetscher Zwischenmassiv”, earlier also known as “ Somvixer Zwischenmassiv ” (NIGGLI & STAUB 1914). In order to better describe its allochthonous nature, illustrated by the intense Alpine deformation and diaphoretic overprint at its borders (NIGGLI 1944), the denomination “Tavetscher Zwischenmassiv” (e. g., SCHMID et al. 2004, PFIFFNER 2014) was abandoned in favour of the term Tavetsch Nappe. The Tavetsch Nappe is not the eastern equivalent of the Goms Zone (previously named “Gomser Zwischenmassiv”, see p. 67 f.), but lies north of the Urseren -Garvera Zone. Its Alpine structural position is therefore intermediate between the southern margin of the Aar Massif and the Gotthard Nappe.

The lithological associations of the Tavetsch and Gotthard Nappes show the same pre -Alpine history (MERCOLLI et al. 1994, BIINO 1994). A short summary of this history will be provided in the description of the lithostratigraphic units of the Gotthard Nappe (see p. 64 ff.). The characteristic Alpine overprint including the occurrence of “ Paraschiefer ” along the borders of the nappe and in discrete mylonitic shear zones in its interior was accurately described by NIGGLI (1944).

The metasedimentary rocks of the Urseren-Garvera Zone south of the Tavetsch Nappe are interpreted as the northern autochthonous cover of the polycyclic metamorphic basement of the Gotthard Nappe, while the Mesozoic relics at the northern border of the Tavetsch Nappe (“ Disentiser Mulde” of NIGGLI 1944) represent parts of the ancient, now strongly tectonised and mylonitised autochthonous cover of the Aar Massif (grouped into the Clavaniev Zone). Thus, the Tavetsch Nappe consists only of pre -Variscan polycyclic metamorphic basement with rare occurrence of Permian metasedimentary rocks and lacks a Mesozoic sedimentary cover.