The formation and alteration of allanite in skarn from the Beinn an Dubhaich Granite aureole, Skye

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doi: 10.1127/0935-1221/2002/0014-0471
Authors:Smith, Martin P.; Henderson, Paul; Jeffries, Teresa
Author Affiliations:Primary:
Natural History Museum, Department of Mineralogy, London, United Kingdom
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 14(3), p.471-486. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:2002
Note:In English. 54 refs.; illus., incl. 5 tables, geol. sketch map
Summary:Allanite-(Ce) occurs as a metasomatic phase in diopside - hedenbergite - anorthite - hastingsite endoskarn from the Beinn an Dubhaich granite aureole, Skye. Fluid-inclusion studies indicate formation of pyroxene at temperatures in the range 600-700°C from Na-K-Fe-Ca bearing brines (45-60 wt. % NaCl eq.) assuming pressures of 280-640 bars. Allanite and amphibole formed from similar brines at 500-600°C (mean ∼550°C). Fluorite formed during cooling and dilution of these brines. Vesuvianite formed at much lower temperatures (230-250°C) from low- to moderate-salinity fluids (∼0-15 wt % NaCl eq.). High F contents in both amphibole and vesuvianite indicate that the fluids were F bearing at all stages in the paragenesis. Allanite has textures resulting from growth and alteration. Britholite-(Y) occurs as either a discrete phase, or as an alteration product of allanite. LA-ICP-MS analyses demonstrate that whilst Th remained relatively constant in individual allanite grains, U was leached during alteration. The Th content does vary with zonation, however, and may be altered by processes such as over-growth. The hydrothermal mobility of the REE and Th was almost certainly a result of high F contents in the hydrothermal fluids. The hydrothermal formation and alteration of allanite may have important consequences for geochronological studies of other allanite occurrences.
Sections:Mineral data
Subsections:Silicates
Subjects:Actinides; Allanite; Aureoles; Epidote group; Fluid inclusions; Granites; Hydrothermal alteration; Igneous rocks; Inclusions; Metals; Metamorphic rocks; Metasomatic rocks; Metasomatism; Orthosilicates; Plutonic rocks; Rare earths; Silicates; Skarn; Sorosilicates; Europe; Great Britain; Hebrides; Highland region Scotland; Inner Hebrides; Inverness-shire Scotland; Isle of Skye; Scotland; United Kingdom; Western Europe; Beinn an Dubhaich Granite
Coordinates:N570000 N574000 W0054000 W0064500
Abstract Numbers:02M/4414
Record ID:2002047649
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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