Rötifirn-Gruppe (frühvariszische Intrusiva)

Representation and status

Color CMYK

(0%,59%,45%,14%)

Color RGB

R: 220 G: 90 B: 120

Rank

lithostratigraphic Group

Validity

Unit is in Use

Nomenclature

Deutsch

Rötifirn-Gruppe (frühvariszische Intrusiva)

Français

Groupe du Rötifirn

Italiano

Gruppo del Rötifirn

English

Rötifirn Group

Origin of the Name

Hinter Rötifirn (GL), am Tödi

Historical Variants

Early Variscan plutonic rocks = Rötifirn Group (Berger et al. 2017)

Hierarchy and sequence

Subordinate units

• Tödi-Granit
• Punteglias-Granit
• Pardatschas-Granit
• Alp-Crap-Ner-Granit
• Baltschieder-Granodiorit
• Russein-Diorit
• Giuv-Syenit
• Curtin-Monzodiorit

Age

Age at top

• Early Carboniferous (= Mississipian)

Age at base

• Early Carboniferous (= Mississipian)

Palaenography and tectonic

• Variscan plutonic rocks of the Helvetic

Paleogeography

European continental plate

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.35: A number of small intrusive bodies occurring in the Tödi and Val Punteglias areas, as well as the Giuv Syenite and the Baltschieder Granodiorite were grouped into the Rötifirn Group on the present map sheet. Already F. Weber (in ALB. HEIM 1921), HÜGI (1941) and FRANKS (1968 a, b) recognised that members of this magmatic suite intrude the metasedimentary and volcaniclastic rocks of the Bifertenfirn Formation and are unconformably overlain by the Late Pennsylvanian clastic and volcanic rocks of the Bifertengrätli Formation. SCHALTEGGER & CORFU (1992, 1995) dated some of these bodies as Visean (Fig. 4). Furthermore SCHALTEGGER et al.(1991) characterised the Rötifirn Group as a suite of shoshonitic to ultrapotassic rocks (“Group A” of SCHALTEGGER 1994).
The Strem Granite and the Baltschieder Granodiorite represent a special case within the Rötifirn Group. In fact, the only common characteristic of these two plutonic rocks with other members of the group is their Visean age. Zircon ages vary in the Strem Granite between 462–334 Ma (Fig.4, U/Pb zircon age, sample SU 89 -11 in SCHALTEGGER & CORFU 1992). The dominant age of ~340 Ma can be considered coeval with other ages of the Rötifirn Group and is older than that of the Central Aar Granite. A ~336 Ma U/Pb zircon age of the Baltschieder Granodiorite was calculated from the intercept of a multigrain fraction (HETTMANN et al. 2009), also pointing towards a similarity with the Rötifirn Group. On the other hand, the calc-alkaline petrographic affinity of the two granitic bodies seems to exclude a direct genetic link with the shoshonitic ultrapotassic suite that represents the major distinctive characteristic of the Rötifirn Group.