The geochemistry and cryptic zonation of pyrochlore from San Vicente, Cape Verde Islands

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doi: 10.1180/minmag.1992.056.383.06
Authors:Hodgson, N. A.; Le Bas, M. J.
Author Affiliations:Primary:
Leicester University, Department of Geology, Leicester, United Kingdom
Volume Title:Mineralogical Magazine
Source:Mineralogical Magazine, 56(383), p.201-214. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:1992
Note:In English. 23 refs.; illus., incl. 1 table
Summary:Zr-rich pyrochlore crystals in carbonatite from San Vicente (Cape Verdes Islands) show cryptic, concentric and rhythmic chemical zonation with Ca increasing and Ti, U and Zr decreasing towards the rims. In one carbonatite, taken from the Camile dyke, previously undocumented cryptic sector zonation of Ti, U and Zr is also observed in these crystals. The chemical variation is investigated by wavelength-dispersive electron microprobe, with both single spot and crystal map analyses. The concentric and rhythmic zonation, marked by element substitution, was generated by magma heterogeneity and/or element diffusion kinetics, but it is suggested that the sector zonation, marked by differential site substitution, was governed by protosite variation between octahedral and cubic faces. [R.A.H.]
Subjects:Backscattering; Carbonatites; Chemical composition; Crystal chemistry; Crystal growth; Crystal structure; Crystal zoning; Diffusion; Dikes; Geochemistry; Igneous rocks; Intrusions; Lattice; Magmas; Metals; Niobates; Oxides; Pyrochlore; Substitution; X-ray data; Zirconium; Africa; Atlantic Ocean Islands; Cape Verde Islands; Camile Dike; San Vincente Cape Verde Islands
Abstract Numbers:92M/4645
Record ID:2011017732
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
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