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2341488 
Journal Article 
Metamorphism of Proterozoic agpaitic nepheline syenite gneiss from North Singhbhum Mobile Belt, eastern India 
Goswami, B; Basu, SK 
2013 
1 
Mineralogy and Petrology
ISSN: 0930-0708 
Springer-Verlag (Heidelberg) 
WIEN 
107 
4 (Aug 2013) 
517-538 
English 
WOS:000321919000004 
Sushina nepheline syenite gneisses of Early Proterozoic North Singhbhum Mobile Belt (NSMB), eastern India suffered regional metamorphism under greenschist-amphibolite transitional facies condition. The Agpaitic Sushina nepheline syenite gneisses consist of albite, K-feldspar, nepheline (close to Morozewicz-Buerger composition), aegirine, biotite, epidote, piemontite, sodalite, cancrinite, natrolite and local alkali amphibole. Accessory phases include zircon, hematite, magnetite, rare pyrochlore and occasional eudialyte and manganoan calcic zirconosilicates. Mineral chemistry of albite, K-feldspar, nepheline, aegirine, alkali amphibole, natrolite and zirconium silicate minerals are described. The detailed textural features together with chemical data of some minerals indicate metamorphic overprint of these rocks. A new reaction is given for the genesis of metamorphic epidote. Metamorphic piemontite suggests greenschist facies metamorphism under high fO sub(2) (Hematite-Magnetite buffer). Up to 15.34 mol% of jadeite component in aegirine suggests that the metamorphic grade of the nepheline syenite gneiss reached at least to greenschist-amphibolite transitional facies or higher. Nepheline geothermometry suggests temperature of metamorphism 
Physical Sciences - Other Topics; crystal-chemistry, shear zone, eudialyte, evolution, nomenclature,; constraints, stability, minerals, complex, rocks