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Zoned hibonites from Punalur, South India

  • M. Santosh (a1), M. Sandiford (a2) and S. J. B. Reed (a3)


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 R 2+ ⇌ CaAl and R 2+ R 4+ ⇌ Al2 with the REE-rich cores containing in excess of 50% of the REE R 2+ 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.



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Zoned hibonites from Punalur, South India

  • M. Santosh (a1), M. Sandiford (a2) and S. J. B. Reed (a3)


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