Plutone della Bregaglia

Rappresentazione e statuto

Index

Ber

Colore RGB

R: 241 G: 237 B: 239

Rango

Gruppo litostratigrafico

Uso

Unità in uso.

Status

termine informale

Discussione del statuto

Nomenclatura

Deutsch

Bregaglia-Pluton

Français

Pluton de la Bregaglia

Italiano

Plutone della Bregaglia

English

Bregaglia Pluton

Origine del nome

SO Val Bregaglia (Italia)

Varianti storiche

Granite der Valle della Mera = Granite der Bassa Valle della Mera (Wenk 1956), batolite bregagliotta = Massiccio Bregagliotto (Godenzi 1963), Bergeller Intrusion = tertiäre synorogene granitoide Intrusiva des Bergell (Bucher-Nurminen 1970), Zone Giubasco-Jorio-Sorico-Monte Bassetta-Val Masino-Monte Sissone = Zone Jorio-Sissone = Serizzo-Zug (Wenk 1982), Bregaglia-Iorio Intrusive (Trommsdorf & Nivergelt 1986), plutone di Val Màsino-Bregaglia-Iorio (Sciesa 1991), plutoniti di Bregaglia (Dal Piaz et al. 1992a), intrusion de la Bregaglia (Mayerat Demarne 1994), Masino-Bregaglia igneous body (Hansmann 1996), Plutone Val Masino-Bregaglia (Spalla et al. 1998), Complesso di Bregaglia (Wenk 2012), Bregaglia intrusion = Bregaglia-Intrusionskörper = intrusion de la Bregaglia (TK500)

Gerarchia e successione

Unità di rango inferiore

• Aplite di Zocca
• Microgranito del Monte Rosso
• Granodiorite dell'Alpe Cameraccio
• Minestronite
• Granodiorite della Bregaglia (ghiandone)
• Tonalite della Bregaglia (serizzo)

Età

Geomorfologia

• Oligocene

Età alla base

• Oligocene

Metodo di datazione

32-30 Ma

Geografia

Estensione geografica

Massiccio intrusivo compresso fra le Valli Bregaglia, Masino e Malenco.

Regione-tipo

Val Bregaglia (GR)

Paleogeografia e tettonica

Termini generici

• Bregaglia

Tipo di origine

• plutonica

Condizioni di formazione

Hansmann 1996 S.422: Field evidence defines the following magmatic sequence in the MB area:

(i) Andesitic-basaltic dikes that crosscut the Alpine fohation in the neighbouring units (Nievergelt and Dietrich, 1977) show a contact metamorphic overprint in the MB aureole (Gautschi and Montrasio, 1978).These were interpreted as precursors of the main intrusions on geochemical grounds (Diethelm, 1989; von Blanckenburg et al., 1992).

(ii) Gabbros and hornblendites occur as variously-sized inclusions only in the tonahte and are interpreted as early magmatic differentiates (Diethelm, 1985,1989).

(iii) The two main intrusions, the tonalite ("Serizzo") and the granodiorite ("Serizzo Ghiandone" in the older Italian hteräture). These are in-contact along a complex transition zone (Moticska, 1970; Reusser. 1987) but age relationships of the two are ambiguous in the western part of the main igneous body. The tonalite is considered to be older (e.g. Cornelius, 1928; Bucher-Nurminen, 1977; Berger and Giere, 1995). Field evidence in support of this hypothesis is given by a small granodioritic stock intruding the tonahte in the Val Sissone (Montrasio and Trommsdorff, 1983; Berger and Giere, 1995).

(iv) Lamprophyric dikes of calc-alkaline and shoshonitic compositions are present in the granodiorite with variable degrees of disintegration from undisturbed dikes through disrupted dikes and swarms of inclusions to isolated inclusions. These dikes intruded the granodioritic magma prior to its complete sohdification (Diethelm, 1989).

(v) The youngest major intrusion in the area is represented by a garnet-bearing two-mica-leucogranite, the Novate Granite. Pegmatites, leucocratic inicro-granjtes and aplites are widespread in the whole MB region. Some of these dikes radiate from the Novate intrusion. Among the several generations of leucocratic dikes (e.g. Moticska, 1970), Reusser (1987) distinguished pre- and post granodioritic types, therefore only some of the dikes can actually be associated with the Novate intrusion.