Studies on Some Granitic Rocks of Palni-Dindigul Area, Tamil Nadu

The temperatures of formation of some granitic and charnockitic rocks from parts of Palni-Dindigul area have been determined by the felspar geologic thermometer. Two distinct ranges of temperatures are indicated among the rocks on the basis of which they are classified. Their petrogenesis is discussed on the evidences furnished by the temperatures, field relationships, twin laws of plagioclases and some significant petrographic characters. The older grey granitic rocks are of metasomatic origin and were probably products of synkinematic granitization while the pink perthite-quartz granites represent later magmatic intrusions. Among the charnockites also, two different types are recognized. One is formed by the charnockitization of the gneisses, while the other represents a magmatic type of charnockite.