«Quarzite del tetto»
Back to Leventina-LucomagnoRepresentation and status
- Index
- Gq
- Color CMYK
- (0%,46%,71%,6%)
- Color RGB
- R: 240 G: 130 B: 70
- Rank
- lithostratigraphic unit
- Validity
- Unit is in Use
- Status
- incorrect name (though informally used)
Nomenclature
- Deutsch
- «Dachquarzit»
- Français
- «Quartzite du toit»
- Italiano
- «Quarzite del tetto»
- English
- «Dachquarzit»
- Origin of the Name
-
Cave di Morasco (TI) risp. Dazio Grande
- Historical Variants
-
Quarziti a sericite (Casasopra 1939b), quarzite del margine superiore = Quarzite di Morasco-Bedrina = quarzite del tetto (Bianconi 1971), Quarzitischer Gneis bis Quarzit = Dachquarzit (Bianconi & Strasky 2015), Quarzite (Bl. Biasca)
Description
- Description
-
Gneiss quarzitico fino quarzite. Quarzitischer Gneiss bzw. Serizitquarzit, plattig bis stark verschiefert im Dach des Leventina-Gneises (Teil des Chironico-Faido-Piottino-Komplexes).
Bianconi & Strasky 2015 p.37: Il tetto dello Gneiss Leventina è separato dalle rocce soprastanti della Falda di ricoprimento Lucomagno rispettivamente della Falda di ricoprimento Simano da un banco discontinuo di gneiss quarzitico chiaro fino quarzite, dello spessore di 6 a 8 m, localmente fino a 10 m. Il contatto del tetto è netto, mentre quello del letto è graduale. La roccia ha un colore bianco-latteo e affiora in forma di letti sottili. I piani della scistosità sono ricoperti da lamine di muscovite o, localmente, da arricchimenti di muscovite e biotite. La proporzione del feldspato diminuisce verso l’alto e questo viene successivamente sostituito da quarzo, per cui la parte superiore del banco spesso consiste di una quarzite pressoché pura e in banchi compatti quasi massicci. Quest’ultimi nel passato furono sfruttati.
- Geomorphology
- Potenza fino a ca. 10 m (Bianconi 1971)
Age
- Age at top
-
- Triassic
- Age at base
-
- Triassic
Palaenography and tectonic
- Kind of protolith
-
- sedimentary
References
- Definition
-
(2024) :
Tectonic Map of Switzerland 1:500000, Explanatory notes. Federal Office of Topography swisstopo, Wabern
p.50: The Leventina-Lucomagno Nappe is the lowest unit of the Ticino Culmination. The lower part of the nappe (“Leventina Unit”) is made up of several orthogneisses forming a deformed Late Variscan magmatic edifice composed of several magmatic pulses. Along the northeastern flank of the Valle Leventina, the Leventina orthogneisses are covered by a thick stack of paragneisses and micaschists (“Lucomagno Unit”). Along this boundary, sparse quartzitic gneisses (“roof quartzites”) were interpreted as being Mesozoic in age by several authors and hence used to discriminate between a “Leventina Nappe” and a “Lucomagno Nappe”. However, these quartz-rich horizons above the orthogneisses form metasomatically altered zones – in places sheared – and cannot be considered as Mesozoic metasediments (Rütti et al. 2005; see Fig. 7). The “Lucomagno Unit” can therefore be regarded as a pre-Alpine sedimentary shell of the Leventina magmatic edifice deformed during the Alpine orogeny. Quartzitic horizons, similar to those mentioned above, also occur where the Simano Nappe directly overlies the Leventina orthogneisses. The northern part of this nappe contact is often characterized by a mylonitic band (Rütti et al. 2005 and ref. therein). To the south, this mylonitic shear zone dissipates within the Leventina orthogneisses in an anastomosing network of shear bands (Fig. 7). There, the upper limit of the Leventina-Lucomagno Nappe is difficult to trace since paragneiss and calcsilicate lenses – traditionally used to trace the tectonic contact – are in fact deformed xenoliths within the Leventina orthogneisses.
Remnants of Triassic rocks crop out around the frontal part of the Leventina-Lucomagno Nappe, although for some of them it is not clear whether they belong to the Leventina-Lucomagno Nappe or to the adjacent units. Permo-Triassic metasediments crop out also within the Leventina-Lucomagno Nappe, likely as pinched synclines (e.g., Molare Syncline; see Fig. 7) or as intranappe slices.