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Phenocrystic fluorite in peralkaline rhyolites, Olkaria, Kenya Rift Valley.

Marshall, A. S. and Hinton, R. W. and MacDonald, Raymond (1998) Phenocrystic fluorite in peralkaline rhyolites, Olkaria, Kenya Rift Valley. Mineralogical Magazine, 62 (4). pp. 477-486. ISSN 0026-461X

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Abstract

The first occurrence of phenocrystic fluorite in a peralkaline rhyolite is reported from Quaternary lavas (agpaitic index 1.11-1.37) erupted from the Greater Olkaria Volcanic Complex, Kenya. Fluorite compositions are almost stoichiometric, with 0.65-1.49 REE + Y oxides. Relative to coexisting glass (melt), the fluorites are enriched in REE, Y and Sr, are strongly depleted in all other trace elements and concentrate MREE relative to LREE and HREE. Y partitions into fluorite more strongly than the HREE. Fractionation of fluorite in its modal abundance would not significantly affect the REE abundances in the residual liquids, nor result in stronger Sr depletion. The P, T and composition conditions which stabilize fluorite in rhyolitic magmas are still obscure.

Item Type: Article
Journal or Publication Title: Mineralogical Magazine
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Departments: Faculty of Science and Technology > Lancaster Environment Centre
ID Code: 21851
Deposited By: ep_ss_importer
Deposited On: 10 Feb 2009 13:48
Refereed?: Yes
Published?: Published
Last Modified: 09 Apr 2014 20:25
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/21851

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