Comparative Study of Lamprophyres from the Cuddapah Intrusive Province (CIP) of Andhra Pradesh, India

The mid-Proterozoic lamprophyric rocks broadly represented by kimberlites, lamproites and lamprophyres (sensu stricto) are emplaced in and adjacent to the intracratonic Cuddapah basin in the eastern Dharwar craton of India which was recently recognized as the Cuddapah (intrusive) province (CIP). While the kimberlite pipes and lamprophyre dykes are located outside but close to the western and eastern margins of the Cuddapah basin respectively, the lamproites are hosted within the basin. Lamprophyres occur in seven locations of the Prakasam district of Andhra Pradesh. EIchuru, where more than one hundred lamprophyre dykes are found, represents a prominent centre of lamprophyre magmatism. Purimetla comes next to Elchuru with a tally of twenty lamprophyre dykes. At other places lamprophyres are numerically insignificant. The CIP lamprophyres encompass different varieties and they cut across an equally wide-ranging variety of host rocks; these lamprophyres come under 1) feldspathoidal or non- feldspathoidal and 2) plagioclase- or orthoclase-bearing categories. With a single exception, all the lamprophyres are micaceous and distinctly alkaline. The genesis of CIP lamprophyres as a manifestation of alkaline magmatism is discussed.