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Journal of Petrology Advance Access originally published online on October 25, 2007
Journal of Petrology 2007 48(12):2359-2377; doi:10.1093/petrology/egm064
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© The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

A Textural Record of Solidification and Cooling in the Skaergaard Intrusion, East Greenland

Marian B. Holness1,*, Christian Tegner2, Troels F. D. Nielsen3, Gemma Stripp1 and Stearns A. Morse4

1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
2Department of Earth Sciences, University of Aarhus, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark
3Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
4Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst, MA 01003-9297, USA

RECEIVED MAY 29, 2007; ACCEPTED OCTOBER 1, 2007


  Abstract

The clinopyroxene–plagioclase–plagioclase dihedral angle, {Theta}cpp, in gabbroic cumulates records the time-integrated thermal history in the sub-solidus and provides a measure of textural maturity. Variations in {Theta}cpp through the Layered Series of the Skaergaard intrusion, East Greenland, demonstrate that the onset of crystallization of clinopyroxene (within LZa), Fe–Ti oxides (at the base of LZc) and apatite (at the base of UZb) as liquidus phases in the bulk magma is recorded by a stepwise increase in textural maturity, related to an increase in the contribution of latent heat to the total heat loss to the surroundings and a reduction in the specific cooling rate at the crystallization front of the intrusion. The onset of both liquidus Fe–Ti oxide and apatite crystallization is marked by a transient increase in textural maturity, probably linked to overstepping before nucleation. Textural maturation at pyroxene–plagioclase–plagioclase triple junctions effectively ceases in the uppermost parts of the Layered Series as a result of the entire pluton cooling below the closure temperature for dihedral angle change, which is ≤1075°C. Solidification of the Layered Series of the Skaergaard intrusion occurred via the upwards propagation of a mush zone only a few metres thick.

KEY WORDS: magma; partial melting; asthenosphere; olivine; mantle

*Corresponding author. Telephone: 01223 333434. Fax: 01223 333450. E-mail: marian{at}esc.cam.ac.uk


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