The Kunavaram series-a group of alkaline rocks, Khammam Distric, Andhra Pradesh, India

Abstract

The Kunavaram series, a group of alkaline rocks from Khammam District, Andhra Pradesh, India, may be classified into syenites and nepheline syenites. The rocks have been emplaced into highly-folded metamorphosed igneous and sedimentary rocks of the Eastern Ghats of South India. They have differences in mineral and chemical compositions and it is concluded that they originated as two independent magmas, each of which had its own series of fractional crystallization. In the nepheline syenites, both subsolvus and hypersolvus assemblages are recognized. The composition of nepheline is mostly restricted to the Morozewicz-Buerger convergence field in the system Ne-Ks-Qz, which is characteristic of subsolvus nepheline syenites. The recrystallization process at lower temperatures might have given rise to subsolvus types from a single high-temperature feldspar hypersolvus assemblage. The composition of the Kunavaram nepheline syenites, lying close to the nepheline-feldspar field boundary in the system Ne-Ks-Qz-H₂O at P_H2O=1000 kg/cm², suggests an igneous origin. The migration of tie-lines may indicate that these rocks have been subsequently metamorphosed. Metasomatic action accompanied by intrusion of the alkaline magma is also revealed by various textural features.