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Fluorapatites from the Skaergaard intrusion, East Greenland

Published online by Cambridge University Press:  05 July 2018

G. M. Brown  and
A. Peckett
G. M. Brown
Affiliation:
Department of Geological Sciences, Durham University
A. Peckett
Affiliation:
Department of Geological Sciences, Durham University
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Summary

The compositions of apatite crystals from seven Skaergaard rocks were obtained by electron-probe microanalysis. These span the range of occurrence from the base to the top of the exposed zones of the layered series. Apatite occurs as an intercumulus phase in the lower zones, but becomes a cumulus phase at a structural height of 1850 m (c. 98 % crystallized), defining the base of Upper Zone b. All apatite analyses show a high F:Cl ratio. There is a slight but significant increase in F and decrease in Cl when the apatite becomes a cumulus phase, the F/Cl values changing from < 10 to > 30. Variations in F:Cl:OH are attributed to differential volatile migration from trapped intercumulus liquid sites. The apatite data provide new support for ferrodiorite-granophyre liquid immiscibility.

Type
Research Article
Information
Mineralogical Magazine , Volume 41 , Issue 318 , June 1977 , pp. 227 - 232
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1977

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