Stability of naujakasite in hyperagpaitic melts, and the petrology of naujakasite lujavrite in the Ilímaussaq alkaline complex, South Greenland

Tom Andersen*, H. Sørensen

*Corresponding author for this work

    Research output: Contribution to journalArticle

    16 Citations (Scopus)

    Abstract

    Naujakasite (Na6(Fe,Mn)Al4Si8 O26) is a characteristic, rock-forming mineral of hyperagpaitic naujakasite lujavrite (arfvedsonite + naujakasite + steenstrupine + albite ± relict nepheline ± microcline ± ussingite) from the Ilímaussaq complex, South Greenland, and is only known from this complex. The qualitative stability relationships of naujakasite-bearing, low-variance liquidus mineral assemblages at near-solidus conditions in lujavritic magma can be modelled within the six-component system Si-Al-Fe-Na-O-H. The modelling suggests that an uncommon combination of elevated water activity and low oxygen fugacity is needed to stabilize arfvedsonite + naujakasite mineral assemblages in highly sodic liquids. These conditions are incompatible with the stable coexistence of aegirine and arfvedsonite. They are met in the arfvedsonite-bearing lujavrites of Ilímaussaq, but apparently not in rocks of similar composition in the Khibina and Lovozero complexes, Kola Peninsula, where aegirine-or aegirine-arfvedsonite-bearing mineral assemblages are characteristic. Liquid lines of descent leading to crystallization of naujakasite have to pass through the albite+nepheline+arfvedsonite liquidus field in the Si-Al-Fe-Na-O-H system, reaching this field at the high-Na side of the albite-nepheline-arfvedsonite plane.

    Original languageEnglish
    Pages (from-to)125-136
    Number of pages12
    JournalMineralogical Magazine
    Volume69
    Issue number2
    DOIs
    Publication statusPublished - Apr 2005

    Keywords

    • Agpaitic rocks
    • Greenland
    • Ilímaussaq complex
    • Naujakasite
    • Nepheline syenite
    • Oxygen fugacity
    • Water activity

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