Petrochemical nature of baradangua alkaline igneous complex, Orissa, India

Abstract

The Baradangua alkaline complex on the southern bank of the Brahmani river, Orissa, strikes E-W with steep southerly dips, in conformity with the regional trend of the litho units of the Eastern Ghat Mobile Belt of this sector. The nepheline syenite, a hypersolvus rock, comprises potash feldspar, nepheline, plagioclase and calcite, with biotite as the dominant mafic mineral. The agpaitic index [$\text{(}\text{Na}{}_2\text{O}\text{+}\text{K}{}_2\text{O}\text{)}\text{Al}{}_2\text{O}{}_3$ mol prop] ranges from 0.43 to 0.74 in the nepheline syenites, indicating their miaskitic nature. Field, petrography and geochemistry suggest a magmatic origin for nepheline syenites, the differentiation pattern being reflected by the distribution of the trace elements.