Plutone della Bregaglia

Representation and status

Index

Ber

Color RGB

R: 241 G: 237 B: 239

Rank

lithostratigraphic Group

Validity

Unit is in Use

Status

informal term

Status discussion

Nomenclature

Deutsch

Bregaglia-Pluton

Français

Pluton de la Bregaglia

Italiano

Plutone della Bregaglia

English

Bregaglia Pluton

Origin of the Name

SO Val Bregaglia (Italia)

Historical Variants

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)

Hierarchy and sequence

Subordinate units

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

Age

Age at top

• Oligocene

Age at base

• Oligocene

Dating Method

32-30 Ma

Geography

Geographical extent

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

Type area

Val Bregaglia (GR)

Palaenography and tectonic

Tectonic unit (resp. main category)

• Bregaglia

Kind of protolith

• plutonic

Conditions of formation

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.