Alkali loss and retention in an iron-rich peralkaline phonolite dyke from the Gardar province, south Greenland

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    Abstract

    An unusually iron-rich, strongly peralkaline dyke occurring near the Ilimaussaq intrusion, south Greenland, is described. The dyke has developed two facies characterised respectively by the mafic assemblages pyroxene+amphibole+aemigmatite, and pyroxene+magnetite. The differences can be explained as an effect of loss of up to 4% Na1O from the magnetite-bearing facies (relative to the magnetite-free facies). The effect is in accordance with the phase relations at 1 atm in the synthetic system Na2OAl2O2Fe2O2SiO2. Continued alkali loss and magnetic precipitation will change the differentiation trend from agpaitic with iron enrichment towards miaskitic with iron depletion. It is suggested that the extreme degree of iron enrichment in the dyke resulted from the coincidence of low oxygen fugacity and strong peralkalinity tending to stabilise both ferrous and ferric iron in the liquid.

    Original languageEnglish
    Pages (from-to)81-90
    Number of pages10
    JournalLithos
    Volume7
    Issue number2
    DOIs
    Publication statusPublished - 1974

    Programme Area

    • Programme Area 4: Mineral Resources

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