Gli gneiss-pseudoporfido; particolare tipo litologico dell'Argentera meridionale; gli affioramenti del bacino della Beonia (Bieugne) (Alpes-Maritimes, Francia)  [Pseudoporphyric gneisses; a lithological type in the southern Argentera Massif, Beonia Basin (Alpes-Maritimes, France)]

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Alternate Title:Pseudoporphyric gneisses; a lithological type in the southern Argentera Massif, Beonia Basin (Alpes-Maritimes, France)
Authors:Malaroda, R.
Author Affiliations:Primary:
University of Turin, Turin, Italy
Volume Title:Memorie Lincee Scienze Fisiche e Naturali
Source:Memorie Lincee Scienze Fisiche e Naturali, 1(5), p.129-152. Publisher: Associazione Amici dell'Accademia dei Lincei, Rome, Italy
Publication Date:1991
Note:In Italian with English summary
Summary:This unusual rock-type is composed essentially of 30-55 vol.% plagioclase (andesine, Ab66-71Or0-5An24-34, or albite, Ab97-99An1-3, spor- adically antiperthitic), 7.5-30 vol.% K-feldspar (perthite, with the host having the optical characters of anorthoclase or iso-orthoclase [2Vgamma < 2-3 degrees) with composition Or92Ab7Cs1, and the albite exsolutions having composition Ab97Or1An2), 15-30 vol.% quartz and 5-20 vol.% biotite (two generations: large and small flakes), plus accidental garnet, sillimanite and many accessory phases (apatite, hematite, rutile, zircon, titanite, etc.) It is associated with and fades into biotite anatexites, itself being mildly affected by migmatitic phenomena with new formation of albite. It is distinguished by the marked pseudoporphyritic texture, mainly of large euhedral crystals of embayed quartz similar to that of rhyolites, and the persistence of typical detrital features that suggest derivation by the migmatization of Carboniferous or Permian sediments, also outcropping in the area. The presence of sillimanite needles in andesine and of chlorite rims around biotite bracket their two- phase metamorphic evolution. Six bulk rock chemical analyses of the main and melanocratic facies, and one of a dark inclusion are also given. [A.M.]
Subjects:Accessory minerals; Alkali feldspar; Andesine; Biotite; Chemical composition; Feldspar group; Framework silicates; Garnet group; Genesis; Gneisses; K-feldspar; Metamorphic rocks; Metamorphism; Mica group; Migmatization; Mineral composition; Nesosilicates; Orthosilicates; Petrography; Plagioclase; Quartz; Sheet silicates; Silica minerals; Silicates; Sillimanite; Textures; Alpes-Maritimes France; Alps; Argentera Massif; Europe; France; Maritime Alps; Western Alps; Western Europe
Coordinates:N433000 N442000 E0074500 E0064000
Abstract Numbers:92M/2285
Record ID:2014026526
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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