Lithological characteristics of the Mafic Rocks of Tadpatri Formation of Pulivendla Taluk, Kadapa District, Andhra -Pradesh, India

Abstract

The mafic sills occur at various stratigraphic levels within the shale dominated Tadipatri Formation of the Chitravathi Group, Kadapa Super group of rocks. The Vempalli Formation of the Kadapa Super group of rocks underline the Tadipatri Formation with pulivendula Quartzite Formation lying in between two. Within the Tadipatri formation, the differentiated sills in the lower part, doleritic sills at different stratigraphic horizons and basaltic sills are emplaced in the upper part. The differentiated thick mafic sills of the tadipatri Formation are characterized by a lower thin chilled margin followed upwards by olivine gabbro and leucogabbro. The Tadipatri Formation conformably overlies the Pulivendula Formation with a gradational zone .This unit is characterized by more than 4 km thick sequence of shale with minor intercalated siltstone ,sandstone and stromatolytic dolomite .In addition ,there are different varieties of mafic sills and acid tuffs . They are very well exposed around Pulivendla, north east of Velpula, in between Chinna Ramgapuram and Pedda Rangapuram, north east of Ternampalle and in hill sections to the north and south of Eramareddipalle. The sills are characterized by chilled, fine grained margin followed by coarse grained olivine gabbro in the lower part and leucogabbro in the upper part. The olivine gabbro is melanocratic and highly pock marked on weathered surface due to differential weathering of olivine (The contact between the melanocratic olivine gabbro in lower and the leucogabbro forming the upper parts of the sills is sharp. The upper leucogabbro parts of these sills are columnar jointed and are quarried at places for construction materials.