Métamonzonite de Pormenaz
Back to Aig. Rouges MassifRepresentation and status
- Color CMYK
- (0%,51%,49%,16%)
- Color RGB
- R: 215 G: 105 B: 110
- Rank
- lithostratigraphic Formation
- Validity
- Unit is in Use
- Status
- informal term
Nomenclature
- Deutsch
- Pormenaz-Metamonzonit
- Français
- Métamonzonite de Pormenaz
- Italiano
- Metamonzonite di Pormenaz
- English
- Pormenaz Metamonzonite
- Origin of the Name
-
Hameau/alpage de Pormenaz (France)
- Historical Variants
-
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
Hierarchy and sequence
- Superordinate unit
Age
- Age at top
-
- Visean
- Age at base
-
- Visean
- Dating Method
-
332 +/-2 Ma (U/Pb on zircon and monazite ; Bussy et al. 1997, Bussy et al. 2000)
Geography
- Geographical extent
- 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).
- Type area
- Montagne de Pormenaz (France)
Palaenography and tectonic
- Tectonic unit (resp. main category)
-
-
Aiguilles Rouges
:
massif des Aiguilles Rouges
-
Aiguilles Rouges
:
- Kind of protolith
-
- plutonic
References
- Definition
-
(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.