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

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doi: 10.1180/0026461056920240
Authors:Andersen, Tom; Sorensen, H.
Author Affiliations:Primary:
University of Oslo, Department of Geosciences, Oslo, Norway
Other:
Copenhagen University, Denmark
Volume Title:Mineralogical Magazine
Source:Mineralogical Magazine, 69(2), p.125-136. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:2005
Note:In English. 18 refs.; illus., incl. 1 table
Summary:Naujakasite (Na6(Fe,Mn)Al4Si8O26) is a characteristic, rock-forming mineral of hyperagpaitic naujakasite lujavrite (arfvedsonite+naujakasite+steenstrupine+albite ± relict nepheline ± microcline ± ussingite) from the Ilimaussaq 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 Ilimaussaq, 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.
Sections:Experimental mineralogy; Mineral data
Mineral Groups:Framework silicates
Subjects:Aegirine; Agpaite; Alkalic composition; Amphibole group; Arfvedsonite; Chain silicates; Clinoamphibole; Clinopyroxene; Fugacity; Igneous rocks; Lujavrite; Magmas; Melts; Mineral assemblages; Nepheline syenite; Peralkalic composition; Plutonic rocks; Pyroxene group; Silicate melts; Silicates; Syenites; Volatiles; Water vapor; Arctic region; Commonwealth of Independent States; Europe; Greenland; Ilimaussaq; Khibiny Mountains; Lovozero Massif; Murmansk Russian Federation; Russian Federation; South Greenland; Naujakasite
Abstract Numbers:05M/2000
Record ID:2005044699
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland, Reference includes data from GeoScienceWorld, Alexandria, VA, United States
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