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 granite-quartzmonzonite (chemical) and records a Rb-Sr whole rock isochron age of 2549 ± 39 Ma. Variation observed in the major and trace element concentrations (SiO₂ = 67.09-73.83%; Al₂O₃ = 12.76-14.51%; total iron = 2.31-4.97%; MgO = 1.03-3.66%; Cr = 7-102 ppm; Rb = 169-223 ppm and Sr = 128-423 ppm) and the low CaO (less than 2%) in the granite suggest that it is a crustal remelting (CR) type granite formed by the anatectic remelting of an intermediate source rock. The high total REB (201.38-245.63 ppm), their well fractionated nature (La_N/Yb_N= 17.83-22.32) and the negative Eu anomaly of the granite support that the source rock was intermediate in composition having hydroxyl-bearing minerals like biotite and hornblende.

The Rb-Sr whole rock age (2459 ± 39 Ma) of the granite is similar to that of Closepet, Lepakshi and Hyderabad granites suggesting that this granite has formed along with the other K-rich granites by extensive crustal remelting during the Archaean-Proterozoic Transition (APT).