Zentraler Aare-Granit

Representation and status

Index

gamma-A, ZAG, ZAGR

Color CMYK

(0%,43%,52%,14%)

Color RGB

R: 220 G: 125 B: 105

Rank

lithostratigraphic Formation

Validity

Unit is in Use

Status

informal term

Nomenclature

Deutsch

Zentraler Aare-Granit

Français

Granite central de l'Aar

Italiano

Granito centrale dell'Aare

English

Central Aar Granite

Origin of the Name

Aar-Massiv

Historical Variants

Alpengranit auct., Protogingranit auct., Bankgranit (Baltzer 1888), nördlicher Aaregranit (Wyss 1932), Handeckgranit (Hügi 1934), Zentralaargranitische Zone (Huttenlocher 1947), Zentraler Aaregranit (Rutsch et al. 1966), Central Aar granite (Purdy & Stalder 1973), Zentraler Aaregranit (Schaltegger 1986), Aaregranit (Heitzmann & Auf der Maur 1989, Labhart 2007), Central Aar Granite (Berger et al. 2017), Granite de l'Aar, Zentraler Aare-Granit (Gisler 2018)

Description

Description

mylonite: Rosier 1929

Thickness

Ca. 6 km breite Zone bei der Grimselpass-Strasse.

Hierarchy and sequence

Superordinate unit

• Spät- bis postvariszische Intrusiva

Subordinate units

• Aplitische Randfazies des Zentralen Aare-Granits
• Varietät «Unter der Flue» des Zentralen Aare-Granits
• Varietät «Beesten» des Zentralen Aare-Granit

Upper boundary

Microgranitische Intrusion in die hangende Metasedimente des Frühkarbons. Die Sandalp-Rhyolit ist von triasische Sedimente überlagert.

Lower boundary

Im polymetamorphen Grundgebirge ("Altkristallin") intrudiert, Kontakt aber oft tektonisch überprägt.

Age

Age at top

• Asselian

Age at base

• Gzhelian

Dating Method

297 +/-15 Ma (Rb/Sr: Schaltegger 1986), 298 +/-2 Ma (Schaltegger & von Quadt 1990, Schaltegger & Corfu 1992)

Geography

Geographical extent

Grösste Intrusivkörper des Aar-Massivs mit über 100 km Länge und bis 10 km Breite (im Grimselgebiet).

Palaenography and tectonic

Tectonic unit (resp. main category)

• Aar

Kind of protolith

• plutonic

Metamorphism

monocyclic

References

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.51: The Central Aar Granite, with a currently exposed surface of more than 550 km2, is by far the largest Variscan granitoid body of all external massifs in the Alps (DEBON & LEMMET 1999). The NE–SW oriented intrusion, extending from the Bietschhorn in the west to the Oberalpstock in the east, forms the backbone of the Aar Massif. The whitish, medium grained, homogenous, leucocratic biotite granite shows locally different facies related to slight variations in composition and structure. The different facies were sometimes described as “Northern or Southern Rim Facies”, “aplitic rim facies” or “Bietschhorn Granite” (e.g., LABHART 1965, 1977, SCHALTEGGER 1990 a, SCHALTEGGER & VON QUADT 1990, LABHART & RENNER 2012, LABHART et al. 2015b). The Central Aar Granite is interpreted to be the result of a large degree of fractionation from mantle-derived calc-alkaline parental melts with minor crustal contribution (SCHALTEGGER 1990 a, SCHALTEGGER & VON QUADT 1990, SCHALTEGGER & CORFU 1992). SCHALTEGGER & VON QUADT (1990) suggested that even the neighbouring Grimsel Granodiorite and Mittagfluh Granite bodies belong to the same fractionation trend of the Central Aar Granite. A detailed description of their geochemical and isotope characteristics is given by SCHALTEGGER (1990 a). The geodynamic context of this intrusion is discussed in SCHALTEGGER & CORFU (1995) and DEBON & LEMMET (1999).
The Central Aar Granite was dated at different localities (SCHALTEGGER & VON QUADT 1990, SCHALTEGGER & CORFU 1992, SCHALTEGGER 1993, 1994). The resulting consensus intrusion age is 297±2 Ma. This intrusion age of the Central Aar Granite constrains one of the major tectonic activities in the area to the Carboniferous / Permian boundary. In fact, the Central Aar Granite intruded, at depths of at least 8–10 km, the deeply buried Late Carboniferous (Pennsylvanian) metasedimentary and volcaniclastic rocks of the Diechtergletscher-Tscharren Zone, deposited on the former land surface (SCHENKER 1986, SCHENKER & ABRECHT 1987, OBERHÄNSLI et al.1988, LABHART & RENNER 2012). Furthermore, the geochemical affinity of the Haslital Group and the late to post-Variscan metasedimentary and volcaniclastic rocks led to a discussion of the geodynamic link between tectonics and magmatism at the end of the Variscan cycle (SCHENKER 1986, MERCOLLI & OBERHÄNSLI 1988, SCHALTEGGER & CORFU 1995, SCHALTEGGER 1997).

Material and varia