Métamonzonite de Pormenaz
Retour à Aiguilles RougesReprésentation et statut
- Couleur CMYK
- (0%,51%,49%,16%)
- Couleur RGB
- R: 215 G: 105 B: 110
- Rang
- Formation lithostratigraphique
- Usage
- Ce terme est en usage.
- Status
- terme informel
Nomenclature
- Deutsch
- Pormenaz-Metamonzonit
- Français
- Métamonzonite de Pormenaz
- Italiano
- Metamonzonite di Pormenaz
- English
- Pormenaz Metamonzonite
- Origine du nom
-
Hameau/alpage de Pormenaz (France)
- Variantes historiques
-
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)
Description
- Description
-
gneiss et des micaschistes biotitiques fortement mylonitisés et rétromorphosés
Hiérarchie et succession
- Unité hiérarchiquement supérieure
Âge
- Âge au sommet
-
- Viséen
- Âge à la base
-
- Viséen
- Méthode de datation
-
332 +/-2 Ma (U/Pb on zircon and monazite ; Bussy et al. 1997, Bussy et al. 2000)
Géographie
- Extension géographique
- 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).
- Région-type
- Montagne de Pormenaz (France)
Paléogéographie et tectonique
- Termes génériques
-
-
Aiguilles Rouges
:
massif des Aiguilles Rouges
-
Aiguilles Rouges
:
- Type de protolithe
-
- plutonique
Références
- Révision
-
(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.