P-T Conditions of Granulite-Upper Amphibolite Facies Metamorphism in the Precambrian Granitic Rocks of the Chipurupalle-Razam Area of the Eastern Ghats

In the Chipurupalle-Razam area, garnetiferous and orthopyroxene-bearing granitic rocks and their associated Khondalite Group constitute the Precambrians of the Eastern Ghats. The mineral assemblages and textural features of the different rock types indicate that the rock types in the area were subjected to at least two periods of metamorphism.

The first period of metamorphism under conditions of granulite facies was around a minimum temperature of the order of 600° to 700°C, but below 800°C, with P_load of about 6 to 7 kb. The second period of metamorphism under the upper almandine-amphibolite facies conditions took place above 550° and below 700°C at about 1.5 kb P_H2O. The bulk composition of the rock is the primary controlling factor for the presence or absence of garnet, orthopyroxene, and sillimanite, as well as the composition of individual minerals like biotite, garnet, and orthopyroxene.