Preliminary Investigation of Ba-rich Sanidine in Phonolites of Badmer, Rajasthan

Abstract: In melaphonolite of the Sarnu-Dandali, Badmer alkaline complex, high Ba- K-feldspar (sanidine) occurs as phenocrysts. Ba concentration ranges between 2% and 10% by weigth from core to rim. Many BSE images of this Ba-rich sanidine were examined. Large numbers of zoned Ba-rich sanidine phenocrysts were analysed using electron microprobe. BaO shows positive correlation with Al2O3 while there is negative correlation between BaO and K2O suggesting substitution of K by Ba. Petrographic evidence is clear that K-feldspar phenocrysts reacted with the melt which was getting richer in Ba during fractionation of melanephelinite to melaphonolite and subsequently this Ba deposited on the rims of K-feldspar. This short note reports results of preliminary investigation of number of Ba-rich sanidine grains from melaphonolite of Badmer and suggests incompatible behaviour Ba and that it was getting enriched in the melt during crystallization of magma.