Granite du Mont Blanc

Representation and status

Index

gammaMB

Color CMYK

(0%,41%,59%,10%)

Color RGB

R: 230 G: 135 B: 95

Rank

lithostratigraphic Formation

Validity

Unit is in Use

Status

informal term

Status discussion

Nomenclature

Deutsch

Mont-Blanc-Granit

Français

Granite du Mont Blanc

Italiano

Granito del Monte Bianco

English

Mont-Blanc Granite

Origin of the Name

Mont Blanc (France/Italia)

Historical Variants

protogine (Jurine 1806), granits du Mont-Blanc (Guyot 1844), eigentlicher granitischer Centralkörper = Mont Blanc-Granit = Protogin (Gerlach 1871), Protogine à grands cristaux du Mont Blanc (Behmer 1912), Protogine de Monthey à quartz violet (Behmer 1912), Protogine du Mont-Blanc (Corbin & Oulianoff 1928, 1931, 1932), granit du Mont-Blanc, granite central du Mont Blanc, Granite du Mont Blanc (Marro 1986, Morard 1998), granito del Monte Bianco (Dal Piaz et al. 1992a), granite du mont Blanc (Drouet & Leloup 2015)

Description

Description

faciès +/- porphyrique

Components

• biotite
• potassic feldspar
• quartz

Quartz gris vitreux, feldspath blanc et mica noir ou vert (biotite chloritisée).

Hierarchy and sequence

Superordinate unit

• Mittelvariszische Intrusiva

Subordinate units

• Faciès (central) porphyrique du Granite du Mont-Blanc
• Faciès (de bordure) équigranulaire du Granite du Mont-Blanc

Lower boundary

Limite orientale primaire avec passage vers le haut à un leucogranite porphyre, puis à une rhyolite. Recouvert en discordance par la couverture sédimentaire mésozoïque. Limite occidentale tectonique (mylonitique).

Age

Age at top

• Late Pennsylvanian

Age at base

• Late Pennsylvanian

Dating Method

303 +/-3 Ma (U/Pb sur zircon ; Bussy et al. 1989), 304 +/-3 Ma (Bussy & von Raumer 1994), 303 +/-2 Ma (Bussy et al. 2000)

Geography

Type area

Massif du Mont Blanc.

Type locality

• éperon au sud de la cabane du Trient (VS)
  Site particularities
  • typische Fazies
  Site accessibility
  • Grat
  Coordinates
  • (2569460 / 1094065)
  Note
  • Marro 1986 p.18, Burri & Marro 1993 p.7

Reference profiles

• Plan de l'Aiguille (Chamonix, France)
  Site particularities
  • Untergrenze
  Coordinates
  • (2557150 / 1083230)
  Note
  • Contact magmatique avec l'encaissant (Corbin et Oulianoff 1926b)

Palaenography and tectonic

• Variscan plutonic rocks of the Helvetic

Paleogeography

European continental plate

Tectonic unit (resp. main category)

• Mont Blanc :
  massif du Mont Blanc

Kind of protolith

• plutonic

Metamorphism

monocyclic

References

Definition

Bussy François, von Raumer Jürgen, Capuzzo Nicola (2001) : Mont-Blanc, Aiguilles-Rouges massifs (External Massifs) - an example of polyorogenic evolution. Fieldtrip Guide 1, 53-84, Univ. Lausanne

p.68: The 303 Ma magmatic pulse It is represented by the voluminous 303 ± 2 Ma Mont-Blanc granite, located in the Mont-Blanc massif. It is a foliated, porphyritic monzo- to syenogranite with K-feldspar megacrysts and Ferich biotite as the only mafic mineral (Marro 1988; Bussy 1990). It hosts numerous mafic microgranular enclaves, calc-alkaline micromonzodioritic stocks and synplutonic dykes of mantellic origin, which record magma mingling processes (Bussy 1990). The Mont-Blanc granite is a metaluminous, ferro-potassic, alkali-calcic intrusion characterized by high K, Y, Zr contents and Fe/Mg ratios, and a low 87Sr/86Sr initial isotopic ratio of 0.705 (Bussy et al. 1989). Zircon morphology shows an extreme typology with very high A and T indices, typical of alkaline granites. The Mont Blanc granite is the last magmatic event recorded in the area, apart from ash-fall deposits embedded at different levels of the Salvan Dorénaz basin, which testify a 295 +3/-4 Ma old episode of high-explosive volcanism from distant volcanic centers, possibly located in the Aar-Gotthard massifs (Central Alps).

Important Publications

Marro Christian (1986) : Les granitoïdes du Mont Blanc en Suisse. Thèse de doctorat, Université de Fribourg, 145 pages

Material and varia