Late metamorphic veins with dominant PS-15 polygonal serpentine in the Monte Avic ultramafite
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Published:2023-05-31
Issue:3
Volume:35
Page:347-360
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ISSN:1617-4011
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Container-title:European Journal of Mineralogy
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language:en
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Short-container-title:Eur. J. Mineral.
Author:
Barale LucaORCID, Capitani Giancarlo, Castello Paolo, Compagnoni Roberto, Cossio RobertoORCID, Fiore Gianluca, Pastero LindaORCID, Mellini Marcello
Abstract
Abstract. The ultramafic body of Monte Avic (Aosta Valley, Western Alps,
Italy) consists of antigorite serpentinite and Ti-clinohumite metadunite.
They host late metamorphic veins, up to a couple of centimeters thick,
compact, and homogeneous, with a “porcelain” appearance. Vein colors range
from yellowish to light greenish, light yellowish fading to white, or rare
orange. The veins consist of 15-sector PS-15 polygonal serpentine,
with chemical composition Mg2.85 Fe0.08 Si2.05 O7.05
[OH]3.95. Recognition of this unusual phase is supported by diagnostic
satellite reflections in the X-ray powder diffraction pattern (e.g., at
dobs of 2.502, 2.336, 2.151, and 1.966 Å) TEM images (showing
15-sector polygonal fibers, mostly 200 nm in diameter and a few µm in
length, forming a randomly oriented felt) and a µ-Raman wavenumber,
matching previous data. This different evidence affords the successful
distinction of PS-15 and PS-30, alternatively using TEM images, X-ray powder
diffraction, or the low- and high-wavenumber µ-Raman spectra. At Monte
Avic, the vein emplacement was accompanied by significant fluid pressure, as
suggested by deformation and dismembering of the host rock, with PS-15 grown
within isotropic stress microenvironments characterized by fluid-filled
voids. Random growth of the mass-fiber polygonal serpentine was favored by
low-strain conditions. PS-15 veins formed at the end of the long polyphase
Alpine orogenic evolution, with hydrous fluids possibly deriving from
serpentinite dehydration in the depth.
Funder
Istituto Nazionale per l'Assicurazione Contro Gli Infortuni sul Lavoro
Publisher
Copernicus GmbH
Subject
Pulmonary and Respiratory Medicine,Pediatrics, Perinatology and Child Health
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