Complesso gneissico della Tremola

Representation and status

Index

P-Tr

Color CMYK

(12%,0%,15%,35%)

Color RGB

R: 145 G: 165 B: 140

Rank

lithostratigraphic Formation

Validity

Unit is in Use

Status

informal term

Nomenclature

Deutsch

Tremola-Gneiskomplex

Français

Complexe gneissique de la Tremola

Italiano

Complesso gneissico della Tremola

English

Tremola Gneiss Complex

Origin of the Name

mittlere Val Tremola (TI), NW Airolo

Historical Variants

Zone VII = Schiefer der Tremolaserie (Alb. Heim), Tremola-Schiefer (Waindziok 1906), Tremolaserie (Hezner 1909), Karbonserie der Tremola (Bosshard 1925), Tremola-Serie (Hafner 1958, Steiger 1962, Rutsch et al. 1966), Tremola-Serie = Tremolagesteine (Gansser & Dal Vesco 1964), Tremolaserie (Ambühl 1929), scisti cristallini della Val Tremola (Godenzi 1963), Tremola series (Steck 1976, Wenk & Wenk 1977, Beffa 1993), Tremola Serie (Mercolli et al. 1994), Serie della Tremola, Tremola Gneiss Complex (Berger et al. 2017)

Description

Description

Wechsellagerung von dunklen Hornblendegneissen und -schiefern, Glimmergneissen, -schiefern und -phylliten, Quarziten und Silikat-karbonatgesteinen; Hornblende-(oft garbenförmig) und Granat-Porphyroblasten häufig.

Bianconi & Strasky 2015, p.25: La «Serie della Tremola» è caratterizzata da litologie scistose molto variate e finemente interstratificate, fra le quali spiccano i famosi scisti a granato e orneblenda a covoni.

Hierarchy and sequence

Superordinate unit

• Streifengneis-Komplex

Subordinate units

• Scisti di Pontino
• Scisti di Nelva
• Gneiss del Sasso Rosso

Upper boundary

Trias der Piora-Mulde

Lower boundary

Hafner (1958) described discordant contacts between Prato [= Nalps-Gneiskomplex] and Tremola series ; Sorescia-Gneis

Age

Age at top

• Paleozoic

Age at base

• Paleozoic

Geography

Geographical extent

Südliche Einheit des zentralen Teil der Gotthardt-Decke zwischen Val Bedretto (Sorescia-Gneis) und Val Piora (Trias).

Palaenography and tectonic

Tectonic unit (resp. main category)

• Gotthard

Kind of protolith

• sedimentary

Metamorphism

polycyclic (Alpine and Variscan)

Metamorphic facies

• greenschist facies (epizone)
• amphibolite facies

Note on facies

The first (Late Variscan?) prograde event is charaterized by a metamorphic grade increasing towards the north. The later metamorphic phase is responsible for the formation of the garben texture, and the metamorphic grade increases towards the south (Steiger 1962).

References

Definition

Heer Oswald (1846) : Bergbau. In: Heer O. & Blumer-Heer J.J.: Der Kanton Glarus. Gemälde der Schweiz, 7: 441. St. Gallen & Bern (Huber)

S.157: Der als Tremolaserie zusammengefasste Gesteinskomplex lehnt sich im Norden dem die zentralen Gotthardgneise begrenzenden Soresciagneis konkordant an; südlich ist er durch den Dolomitzug abgeschlossen, der dicht bei Airolo Ost – West streichend herüberzieht

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.69: An up to 2 km-thick series of metasedimentary rocks extends from the Val Bedretto to the Val Piora, forming the southern element of the central part of the Gotthard Nappe. This unit has been traditionally called the “Tremola-Serie”. HEZNER (1909) described this spectacular rock association outcropping south of the Gotthardpass. HAFNER (1958) mapped the portion west of Airolo, while STEIGER (1962) mapped and described in detail the “Tremola-Serie” east of Airolo and subdivided it into three subunits: the Pontino Zone, the Sasso Rosso Zone and the Nelva Zone from north to south, respectively. The Pontino Zone of STEIGER (1962) is equivalent to the northern portion of the “Motto di Dentro Zone” of HAFNER (1958), whereas the Sasso Rosso Zone is the equivalent of the southern portion of the “Motto di Dentro Zone”. On the present map sheet, the “Tremola-Serie” was renamed as the Tremola Gneiss Complex (including its undifferentiated subunits Pontino Zone, Nelva Zone and Sasso Rosso Zone, Tab.1).
The dominant rock types are garnet and hornblende-bearing mica schist and gneiss followed by hornblende schist and gneiss. Minor quartzite, carbonate-bearing mica schist, calcsilicate rocks and amphibolite are intercalated with mica schist and gneiss (BIANCONI & STRASKY 2015, Tab.1, p. 28). Garnet-bearing “Hornblendegarbenschiefer” is the most spectacular and famous lithological member of the Tremola Gneiss Complex. This rock type is particularly widespread in the Pontino Zone and Sasso Rosso Zone. Differences between the subunits manifest essentially in the relative abundance of the rock types and the variation in thickness of the alternating layers (STEIGER 1962, BIANCONI & STRASKY 2015). In the eastern part of the Tremola Gneiss Complex, the subunits thin out eastwards at high angles to the boundary with Triassic rocks. This is interpreted as primary sedimentary unconformity (BIANCONI & STRASKY 2015).