PETROLOGY AND GEOCHEMISTRY OF KIMBERLITE PIPE 11 OF CHIGICHERLA AREA,ANANTAPUR DISTRICT, ANDHRA-PRADESH, SOUTH-INDIA

Newly discovered kimberlite pipe 11 of Chigicherla area of Andhra Prad esh consists of two generations of olivine with phlogopite, spinel, pe rovskite, melilite etc., A comparative study of chemical characterstic s of pipe 11 with those of pipe 1,2,3,4 and 5 of Wajrakarur- Lattavara m area and pipe 10 of Chighicherla indicate that Zr-Hf, Nb-Ta Th-U hav e a high degree of correlation. The ratio of Ba/Nb(<10), Z/Hf(similar to 50) and Nb/Zr (>0.5) are similar to the Group-I kimberlites. The ch ondrite normalised REE pattern of pipe 11 is similar to the other kimb erlites and shows enrichment in LREE. Spider diagram of incompatible e lements indicate similarity with those of many oceanic island alkalic basalts or other types of alkalic intraplate volcanics. They are highl y enriched in incompatible elements. Major elements, Ce/Yb and La/Yb r atios suggest that the formation of kimberlite is due to low degree of partial melting of ultrabasic source along with an earlier subducted oceanic lithosphere.