Zoned hibonites from Punalur, South India
Zoned hibonites from Punalur, South India
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来自印度南部普纳鲁尔的分区黑铝石
DOI：
10.1180/minmag.1991.055.379.02
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发表时间：
1991
影响因子：
2.7
通讯作者：
S. Reed
中科院分区：
文献类型：
--
作者：
M. Santosh;M. Sandiford;S. Reed
摘要印度南部喀拉拉邦普纳卢尔附近麻粒岩区的六方钾霞石、白榴石、尖晶石、尖晶石、钙钛矿片麻岩中的带状黑云母，有史以来钛含量最高的轮圈（0.83-0.87 Ti原子/19 O），基本上不含REE元素而岩芯是迄今为止记录的最富REE的组成（REE = 0.55-0.65原子/19 O）。在分析不确定度范围内，当稀土元素R2 + Al 11 O 19端元含量超过50%时，稀土元素R2 + Al CaAl和R2 + R4 + Al CaAl 2可与钙铝榴石的理论端元CaAl 12 O 19相对应。轻微的取代钠钙发生在轮辋，而非化学计量的核心和轮辋表示部分12倍的网站占有率。离子探针分析表明，稀土元素富集，LREE含量高，La/Lu c。250 000。
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 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.