Cheralite from Visakhapatnam Area in the Eastern Ghats Granulite Belt, India

Abstract

Cheralite is reported for the first time from a folded sillimanite schist layer in the garnetiferous quartzo-feldspathic gneisses from the Visakhapatnam area in the Eastern Ghats granulite belt. Cheralite of scarce occurrence was recorded from charnockites of Araku area in the catchment of Gosthani river basin, which was incidentally related to the concentration in the beach placers as cheralite component in Visakhapatnam - Bhimunipatnam Coastal region. The monazite data in the Eastern Ghats from quartzo-feldspathic gneiss, sapphirine/cordierite granulites generally shown ThO 2 range between 6-10% while hypersthene granulites have 9-19% with an exception of 2% in allanite bearing hypersthene granulites. Cheralite from spinel bearing sillimanite schist layer contains 14-22% ThO 2 and shows occasional enrichment towards the grain margins. Plagioclase rims noticed around ilmenite in the spinel bearing sillimanite schist are indicative of partial melt in the granulites. The pegmatite formation along the sheared contacts of garnetiferous quartzo-feldspathic gneisses and spinel bearing sillimanite schists/gneisses is related to metamorphic segregation phenomena in the quartzo-feldspathic gneisses. The enrichment of Th, U and Si is due to the element mobilities during high grade metamorphism. Based on the occurrence of cheralite in the major source rocks, garnetiferous quartzo-feldspathic gneisses, garnetiferous sillimanite gneisses and hypersthene granulites, it is believed that these rocks have substantially contributed to the placer concentrations in the coastal sediments.