PETROCHEMICAL NATURE OF BARADANGUA ALKALINE IGNEOUS COMPLEX, ORISSA, INDIA

The Baradangua alkaline complex on the southern bank of the Brahmani r iver, Orissa, strikes E-W with steep southerly dips, in conformity wit h the regional trend of the lithe units of the Eastern Ghat Mobile Bel t 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 [(Na2O + K2O)/Al2O3 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 be ing reflected by the distribution of the trace elements. Copyright (C) 1996 Elsevier Science Ltd