Petrography and Petrochemistry of the Cordierite Bearing Metapelites of Nartamalai Area, Pudukkottai District, Tamil Nadu

Abstract Occurrence of cordierite bearing metapelites of Khondalitic suite of rocks is reported from Nartamalai area, Pudukkottai district for the first time. The cordierite bearing gneiss occurs in close association with chamockite and pyroxene granulite in the vicinity of the Nartamalai granites. The mineral assemblages seen in the metapelites are cordierite-almandine-sillimanite-plagioclase-K-feldspar- biotite and quartz. Zircon, magnetite and spinel are the accessory minerals. The texture of the metapelites is generally gneissose except in the eastern part of the area where it simulates a hornfels. The Nartarnalai cordierite contains 59% Mg-cordierite and 41 % Fe-cordierite. The Fe+2/Fe+2+Mg ratio of the Nartamalai cordierite is 0.414 which is strikingly higher than that of the cordierites of regional metamorphism and it is comparable with the Fe2/Fe+2+Mg ratios of the cordieritcs described from hornfels assemblage. The coexisting garnet is an almandine-pyrope with very minor andradite and spessartitc, which is comparable with the garnets of regional metamorphic assemblage. The tie-line joining the composition of the coexisting cordierite and garnet indicates a regional metamorphic environment. An overprint of thermal metamorphism, attributable to the intrusion of Nartamalai granites, on the pre-existing regional metamorphic fabric is suggested.