GEOCHEMISTRY, AGE AND ORIGIN OF PERUR GRANITE, CHITTOOR DISTRICT, ANDHRA-PRADESH

The homophanous coarse-grained granite near Perur, Chittoor district, Andhra Pradesh ranges in composition from granite (normative) to grani te-quartzmonzonite (chemical) and records a Rb-Sr whole rock isochron age of 2549 +/- 39 Ma. Variation observed in the major and trace eleme nt concentrations (SiO2 = 67.09- 73.83%; Al2O3 = 12.76-14.51%; total i ron = 2.31-4.97%; MgO = 1.03-3.66%; Cr = 7-102 ppm; Rb = 169-223 ppm a nd Sr = 128-423 ppm) and the low CaO (less than 2%) in the granite sug gest that it is a crustal remelting (CR) type granite formed by the an atectic remelting of an intermediate source rock. The high total REE ( 201.38-245.63 ppm), their well fractionated nature (La(N)/Yb(N) = 17.8 3-22.32) and the negative Eu anomaly of the granite support that the s ource rock was intermediate in composition having hydroxyl-bearing min erals like biotite and hornblende. The Rb-Sr whole rock age (2459 +/- 39 Ma) of the granite is similar to that of Closepet, Lepakshi and Hyd erabad granites suggesting that this granite has formed along with the other K-rich granites by extensive crustal remelting during the Archa ean-Proterozoic Transition (APT).