Lötschental–Maderanertal-Zone

Representation and status

Color CMYK

N/A

Color RGB

R: 241 G: 239 B: 237

Rank

tectonic zone

Validity

Unit is in Use

Nomenclature

Deutsch

Lötschental–Maderanertal-Zone

Français

zone du Lötschental–Maderanertal

Italiano

zona del Lötschental–Maderanertal

English

Lötschental–Maderanertal zone

Origin of the Name

Maderanertal (UR), Silenen

Historical Variants

Lötschental–Maderanertal Zone (Berger et al. 2017)

Hierarchy and sequence

Subordinate units

• Goltschenried-Formation
• Trift-Formation
• Intschi-Formation
• Windgällen-Formation
• Bifertengrätli-Formation

Age

Age at top

• Late Carboniferous (= Pennsylvanian)

Age at base

• Late Carboniferous (= Pennsylvanian)

Palaenography and tectonic

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.43: A suite of dark-coloured to black clastic, volcaniclastic and volcanic rocks forms discontinuous bands, ranging in thickness from a few metres to hundreds of metres, between the Lötschental and the Tödi area. The age of some of the clastic metasedimentary rocks (e.g., Bifertengrätli Formation) was determined on the basis of relictic flora by JONGMANS (1960) as Pennsylvanian (Westphalian–Stephanian) in agreement with the radiometric age of 300±2 Ma of an associated rhyolite at the Sandalp (SCHALTEGGER & CORFU 1995) and of 299±2 Ma (SCHALTEGGER 1993) of the rhyolitic “Windgällen-Porphyr” of the Windgällen Formation (see Fig.4). The principal lithological characteristics of the different local occurrences are identical, despite changes in thickness, stratigraphic completeness and facies within this unit (Fig.6, FRANKS 1968a, SCHENKER 1987, OBERHÄNSLI et al.1988). These rocks evidence an extended acid volcanic activity (the composition of the volcanic members is almost exclusively rhyolitic), alternating pyroclastic (ignimbrite s. l.) and volcaniclastic sequences. Small, rare subvolcanic intrusive bodies and many dykes testify to the completeness of the volcanic architecture. The volcanic activity was dominated by pyroclastic deposits and was consequently accompanied by coeval strong erosion as well as deposition of volcaniclastic sedimentary rocks. These genetic affinities together with a coherent regional distribution permitted us to group the different local formations into the same zone. Therefore the Goltschenried Formation, Trift Formation, Intschi Formation, Windgällen Formation and Bifertengrätli Formation were grouped into the Lötschental-Maderanertal Zone. Already OBERHÄNSLI et al.(1988), VON RAUMER et al. 1993) and ABRECHT (1994) proposed a similar type of association (Tab. 2) and OBERHÄNSLI et al.(1988) called this suite the “Maderaner Group”. In the present map sheet, the “Maderaner Group” of OBERHÄNSLI et al.(1988) was split into two zones to emphasise that even though the Lötschental-Maderanertal Zone was steeply wedged between blocks of polycyclic metamorphic basement, this zone was apparently not intruded by bodies of the Haslital Group. In contrast, this latter relationship is the case for the rocks of the Diechtergletscher-Tscharren Zone (p. 42 f.). The rocks of the Lötschental-Maderanertal Zone do not show any indications of a Late Carboniferous / Permian metamorphic overprint, whereas the Mesozoic and /or Alpine metamorphic overprint is present but variable.