Zona di Mergoscia
Representation and status
- Color CMYK
- N/A
- Color RGB
- R: 241 G: 239 B: 237
- Rank
- tectonic zone
- Validity
- Unit is in Use
- Status
- informal term
- Status discussion
Nomenclature
- Deutsch
- Mergoscia-Zone
- Français
- Zone de Mergoscia
- Italiano
- Zona di Mergoscia
- English
- Mergoscia Zone
- Origin of the Name
- Historical Variants
-
Arbedozone (Mittelholzer 1936), Zone von Mergoscia (Kobe 1954 und 1956), zona di Mergoscia, Mergoscia-Zone, Someo zone (Brouwer et al. 2005), Mergoscia zone, Mergoscia nappe, Mergoscia mélange, Mergoscia unit (Steck et al. 2013), --- (Bächlin et al. 1974, Spicher & Wenk 1981, Steck et al. 2013), Zona di Mergoscia (Della Torre & Maggini 2015)
Description
- Description
-
eclogites-bearing mélange unit ; Le litologie più comuni sono costituite da micascisti con frequenti granati rossi e gneiss chiari a granulometria da media a fine, entrambi di origine sedimentaria.
Steck et al. 2013, p.433: The eclogitic Mergoscia and Cima Lunga units and the amphibolite facies Bosco–Bombogno–Isorno–Orselina zone have a very similar lithology and occur in the same tectonic position on top of the Antigorio and below the Maggia nappes to the east and below the Osbarino unit and the Monte Leone nappe to the west, in the Wandfluhhorn–Alpe Bosa fold structure. The delimitation of the eclogitic Mergoscia unit from the Antigorio nappe is arbitrary and only based on the presence or absence of rare eclogite relicts. The very heterogeneous Mergoscia and Bosco–Bombogno–Isorno–Orselina units are composed of polycyclic basement rocks, granite gneiss, ophiolites and calcschists, the latter of a probable Mesozoic age. The heterogeneity of these units indicates a strong deformation by folding and boudinage of more competent layers. Only a detailed mapping can show if the term ‘‘tectonic mélange’’ used by Trommsdorff (1990) and Engi et al. (2001a, b) is justified. Berger et al. (2005) attribute these units to a Paleogene tectonic accretion channel. Contrary to them, we distinguish in this zone, (1) the Mergoscia and Cima Lunga units characterised by Paleogene eclogites and their relicts, later overprinted by the Oligocene amphibolite facies regional metamorphism, from (2) the Bosco–Bombogno–Isorno–Orselina zone of the southern steep belt (...)
Age
- Age at top
-
- Mesozoic
- Note about top
-
unsicher
- Age at base
-
- Paleozoic
- Note about base
-
unsicher
Geography
- Geographical extent
- Lepontin [kommt auf den GA25-Blättern 145_Bosco/Gurin und 159_Locarno vor]
Palaenography and tectonic
- Tectonic unit (resp. main category)
- Kind of protolith
-
- tectonic
- Metamorphism
- metamorphic
- Metamorphic facies
-
- amphibolite facies
- eclogite facies
References
- Definition
-
(2024) :
Tectonic Map of Switzerland 1:500000, Explanatory notes. Federal Office of Topography swisstopo, Wabern
The Mergoscia Zone is heterogeneous as it is composed of ortho- and paragneisses, metapelites, calcschists, metabasites and meta-ultrabasites. Both metabasites and meta-ultrabasites contain rare relics of high-pressure metamorphism (retrogressed eclogites and garnet-metaperidotites). This zone, displaying a high degree of deformation, is also interpreted as a mélange rather than as an originally stratified framework. According to Berger et al. (2005a), the metabasites and meta-ultrabasites imbricated within a tectonic accretion channel during the Alpine subduction.