Métamonzonite de Pormenaz

Torna a Aiguilles Rouges

Rappresentazione e statuto

Colore CMYK
(0%,51%,49%,16%)
Colore RGB
R: 215 G: 105 B: 110
Rango
Formazione litostratigrafica
Uso
Unità in uso.
Status
termine informale

Nomenclatura

Deutsch
Pormenaz-Metamonzonit
Français
Métamonzonite de Pormenaz
Italiano
Metamonzonite di Pormenaz
English
Pormenaz Metamonzonite
Origine del nome

Hameau/alpage de Pormenaz (France)

Varianti storiche

granite de Pormenaz (Dhellemmes 1955), Granite diffus de Pormenaz (Pairis et al. 1992), Pormenaz monzonite = Pormenaz granite (Bussy et al. 1997, Capuzzo et al. 2003)

Descrizione

Descrizione

gneiss et des micaschistes biotitiques fortement mylonitisés et rétromorphosés

Gerarchia e successione

Unità di rango superiore

Età

Geomorfologia
  • Visean
Età alla base
  • Visean
Metodo di datazione

332 +/-2 Ma (U/Pb on zircon and monazite ; Bussy et al. 1997, Bussy et al. 2000)

Geografia

Estensione geografica
Bande N-S de 500 m de large entre le chalet du Fer (rive gauche de la Diosaz) et les chalets de Chavanne (flanc SW de la Pointe Noire de Pormenaz).
Regione-tipo
Montagne de Pormenaz (France)

Paleogeografia e tettonica

Termini generici
Tipo di origine
  • plutonica

Referenze

Revisione
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.66: The Pormenaz monzonite is a 1.4 by 2.5 km porphyritic funnelshaped mass in vertical cross section, which intruded amphibolite-facies metamorphic rocks and lower Carboniferous metagraywackes (Délitroz & Fellay 1997). The shape and internal structures of the intrusion suggest a syntectonic emplacement of the magma and post-crystallization mylonitic deformations along a long-lasting dextral transpressive fault. The main facies is a porphyritic to equigranular monzonite with large pink or white K-feldspar megacrysts (up to 4 cm) in a dark graygreen amphibole-rich matrix. Euhedral crystals of brown sphene are clearly visible on hand specimen. Plurimetric bodies of durbachites (Holub 1977; Rock 1991) are found as dark green, equigranular, magmatic enclaves. The Pormenaz monzonite is characterized by high to very high concentrations in LILE like K, Rb, Ba, Sr, in Mg and transition elements like Cr, Ni, and V, and in incompatible elements like LREE, Zr and Th. Conversely, Ca is relatively low in this range of SiO2 content. REE are strongly fractionated without substantial Eu anomaly. The durbachitic enclaves have the same chemical characteristics as the monzonites, reminiscent of lamprophyres.

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