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REE partitioning between apatite and melt in a peralkaline volcanic suite, Kenya Rift Valley

Mineralogical Magazine

By:
, , , , and
DOI: 10.1180/minmag.2008.072.6.1147

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Abstract

Electron microprobe analyses are presented for fluorapatite phenocrysts from a benmoreite-peralkaline rhyolite volcanic suite from the Kenya Rift Valley. The rocks have previously been well characterized petrographically and their crystallization conditions are reasonably well known. The REE contents in the M site increase towards the rhyolites, with a maximum britholite component of ~35 mol.%. Chondrite-normalized REE patterns are rather flat between La and Sm and then decrease towards Yb. Sodium and Fe occupy up to 1% and 4%, respectively, of the M site. The major coupled substitution is REE3+ + Si4+ ??? Ca2+ + P5+. The substitution REE3+ + Na+ ??? 2Ca2+ has been of minor importance. The relatively large Fe contents were perhaps facilitated by the low fo2 conditions of crystallization. Zoning is ubiquitous and resulted from both fractional crystallization and magma mixing. Apatites in some rhyolites are relatively Y-depleted, perhaps reflecting crystallization from melts which had precipitated zircon. Mineral/glass (melt) ratios for two rhyolites are unusually high, with maxima at Sm (762, 1123). ?? 2008 The Mineralogical Society.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
REE partitioning between apatite and melt in a peralkaline volcanic suite, Kenya Rift Valley
Series title:
Mineralogical Magazine
DOI:
10.1180/minmag.2008.072.6.1147
Volume
72
Issue:
6
Year Published:
2009
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Mineralogical Magazine
First page:
1147
Last page:
1161