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Ferromagnesian silicates in a differentiated alkaline complex: Kûngnât Fjeld, South Greenland

Published online by Cambridge University Press:  05 July 2018

D. Stephenson  and
B. G. J. Upton
D. Stephenson
Affiliation:
Institute of Geological Sciences, Murchison House, Edinburgh EH9 3LA
B. G. J. Upton
Affiliation:
Institute of Geological Sciences, Murchison House, Edinburgh EH9 3LA
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Abstract

Kûngnât Fjeld is an intrusive complex resulting from three intrusive events involving trachyte, mafic trachyte and hawaiite magmas tapped successively from a single magmatic source. In situ differentiation produced gabbroic, syeno-gabbroic, syenitic, and quartz syenitic cumulates showing strong cryptic variation. Layered sequences of syenitic rocks total c. 3500 m. The compositional range is extended by late-stage minor intrusions of microsyenite and peralkaline granite. The principal cumulus minerals are feldspar (Ab40An60 to Or45Ab51An4); olivine (Fo56 to Fo1) and clinopyroxene (Di70Hd27Ac3 to Di6Hd90Ac4 followed by an abrupt change of trend towards Di3Hd78Ac19 in the layered series and nearly pure aegirine in some peralkaline residues). Intercumulus phases are amphibole (hastingsite to ferro-edenite to ferro-actinolite in the layered series with riebeckite to arfvedsonite in some associated granites) and biotite (annite31 to annite98.5).

Type
Research Article
Information
Mineralogical Magazine , Volume 46 , Issue 340 , September 1982 , pp. 283 - 300
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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