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Complex chromite textures reveal the history of an early Archaean layered ultramafic body in West Greenland

Published online by Cambridge University Press:  05 July 2018

C. C. Appel ,
P. W. U. Appel  and
H. R. Rollinson
C. C. Appel
Affiliation:
Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
P. W. U. Appel*
Affiliation:
Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350, Copenhagen, Denmark
H. R. Rollinson
Affiliation:
GEMRU, University of Gloucestershire, Cheltenham, Glos. GL50 4AZ, UK
*
*E-mail: pa@geus.dk
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Abstract

Massive chromitite, banded chromitite and disseminated chromite grains are found in a ˜3800 Ma layered ultrabasic body in West Greenland. The major part of the ultrabasite is dominated by dunite. In the upper exposed part, harzburgite and sheets of gabbro-anorthosite occur. Chromite grains in dunites, and in massive and banded chromitites are homogeneous, with increasing Fe contents upwards in the intrusion. In harzburgites chromites show unusual and very complex textural relationships, with two generations ofchromites one replacing the other, and both exhibiting exsolution textures. In harzburgites, an Fe-rich chromite crystallized first. This first chromite exsolved two spinel phases in a very fine-scale pattern and ilmenite lamellae in a trellis pattern. The Fe-rich chromite was later partly replaced by Al-rich chromite, which crystallized contemporaneously with formation of a late gabbro-anorthositic melt. Subsequently, the Al-rich chromite exsolved a very fine-scale magnetite-rich phase. The exsolutions in the first generation chromite were formed under magmatic conditions. Exsolution of ilmenite lamellae in Fe-rich spinel was caused by oxidation under magmatic conditions.

Keywords

chromitereplacementharzburgiteArchaeanGreenland
Type
Research Article
Information
Mineralogical Magazine , Volume 66 , Issue 6 , December 2002 , pp. 1029 - 1041
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2002

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Footnotes

†

Present address: Haldor Topsøe A/S, DK-2800 Lyngby, Denmark

‡

Present address: Sultan Qaboos University, Department of Earth Sciences, P.O. Box 36, Al Khadh, Postal Code 123, Oman

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