Ofenhorn–Stampfhorn-Gneiskomplex

Representation and status

Index

G-OF

Color CMYK

(0%,24%,30%,2%)

Color RGB

R: 250 G: 190 B: 175

Rank

lithostratigraphic Formation

Validity

Unit is in Use

Status

informal term

Nomenclature

Deutsch

Ofenhorn–Stampfhorn-Gneiskomplex

Français

Complexe gneissique de l'Ofenhorn–Stampfhorn

Italiano

Complesso gneissico dell'Ofenhorn–Stampfhorn

English

Ofenhorn–Stampfhorn Gneiss Complex

Historical Variants

Nördliche Mischgesteinsserie (Eugster 1951), Ofenhorn-Stampfhorn Einheit, Ofenhorn-Stampfhorn Zone, Ofenhorn-Stampfhorn Gneiss Complex (Berger et al. 2017), Ofenhorn-Stampfhorn-Gneiskomplex (Gisler 2018)

Age

Age at top

• Paleozoic

Age at base

• Precambrian

Palaenography and tectonic

• Pre-Variscan polycyclic basement of the Helvetic

Paleogeography

European Continent

Tectonic unit (resp. main category)

• Aar

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.27: In the Haslital, SCHENKER & ABRECHT (1987) defined the “Ofenhorn-Stampfhorn Unit” as a high-grade metamorphic series consisting of banded biotite-plagioclase gneiss, migmatitic leucocratic gneiss, biotite gneiss, amphibolite, and minor amounts of ultramafic rocks. ABRECHT (1980) described in great detail the anatectic structures and their relationship to the formation of “Schollenamphibolite” (massive and banded amphibolites, agmatitic amphibolite and garnet amphibolite), a typical rock type in this unit, but also widespread in other parts of the Aar Massif. Elongated granitic bodies up to 150m in length or metre-sized dykes discordantly intrude the migmatitic banding (SCHENKER & ABRECHT 1987). These are most probably related to a late stage of anataxis, in spite of Rb/Sr data indicating a Triassic age (ABRECHT & SCHALTEGGER 1988). The same authors interpret these ages as re-equilibration of isotopic ratios caused by hydrothermal alteration of rocks possibly related to the late Variscan (Asselian) intrusion of members of the Haslital Group.
To distinguish the tectonic character of the Sustenhorn Zone from its lithological content, the Ofenhorn-Stampfhorn Gneiss Complex was defined as a banded migmatitic rock sequence that, in association with larger amphibolite bodies, forms the Sustenhorn Zone. The name was chosen to link it directly to the existing “Ofenhorn-Stampfhorn Unit” of SCHENKER & ABRECHT (1987). EUGSTER (1951) described a high-grade migmatitic metasedimentary gneiss (“Nördliche Mischgesteinsserie”) in the northern Val Russein. Due to the presence of large amphibolite bodies, these rocks were also assigned to the Ofenhorn-Stampfhorn Gneiss Complex.