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Zoned hibonites from Punalur, South India

Published online by Cambridge University Press:  05 July 2018

M. Santosh ,
M. Sandiford  and
S. J. B. Reed
M. Santosh
Affiliation:
Department of Geosciences, Faculty of Science, Osaka City University, Osaka 558, Japan Centre for Earth Science Studies, Akkulam, Trivandrum 695 031, India
M. Sandiford
Affiliation:
Department of Geology and Geophysics, University of Adelaide, Adelaide, G.P.O. Box 498, South Australia, Australia
S. J. B. Reed
Affiliation:
Department of Earth Sciences, Bullard Laboratories, Cambridge CB3 0EZ, U.K.
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Abstract

Zoned hibonites from a kalsilite, leucite, spinel, corundum, perovskite gneiss from the southern Indian granulite terrain near Punalur, Kerala, have rims that are the most Ti-rich yet recorded (0.83–0.87 Ti atoms per 19 O) and are essentially free of REE elements (ΣREE < 0.01 atoms per 19 O) while the cores are the most REE-rich compositions yet recorded (ΣREE = 0.55–0.65 atoms per 19 O). Within the limits of analytical uncertainty, the compositions of the hibonite can be related to the theoretical end-member CaAl12O19 by the substitutions REE R2+ ⇌ CaAl and R2+R4+ ⇌ Al2 with the REE-rich cores containing in excess of 50% of the REE R2+ Al11O19 end member. Minor substitution of Na for Ca occurs in the rims, while non-stoichiometry in both the cores and rims is indicated by partial 12-fold site occupancy. Ion-microprobe analysis of the REE-rich hibonites reveals strong enrichment in LREE with La/Lu c. 250 000.

Keywords

hiboniterare earth elementstitaniumzoningion-microprobe analysisIndia
Type
Mineralogy and Geochemistry
Information
Mineralogical Magazine , Volume 55 , Issue 379 , June 1991 , pp. 159 - 162
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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