Geochemistry of Garnets from the Precambrian of South Karnataka

Field features and the mineralogical relations of rocks in the Precambrian of South Karnataka indicate progressive increase in intensity of metamorphism from greenschist facies in the north-west through amphibolite facies in the middle to granulite facies in the southern and south-western parts of the State. Chemical analyses of fifty garnets developed in the amphibolite and granulite facies rocks of Karnataka are furnished. The cell edges of these garnets have been determined accurately by X-ray powder diffraction, using the extrapolation technique of Nelson and Riley. The changing pattern of chemical composition and cell edges of garnets enable recognition of successive zones of progressive metamorphism in the amphibolite facies terrain in the Precambrian of South Karnataka.