Oxygen isotope values in granulite facies rocks from the eastern ghats granulite belt, India

Oxygen isotope values in metapelites including garnet-sillimanite gneisses (khondalites) quartzo-feldspathic gneisses (leptynites), cordierite-sapphirine gneisses and the associated marbles, calc-silicates, quartzites, basic granulites and charnockites from the eastern ghats granulite belt are presented and their significance discussed. Metapelites show a wide variation in δ18O values (4.50 to 13.90%) that is controlled largely by the mineralogy of the rock. Coarse grained porphyritic charnockites have higher δ18O values (8.60-11.20%) than that of medium grained ones (5.90-6.60%). Basic granulites have the minimum δ18O values (∼ 5.0%). Oxygen isotope values of different rock units in the granulite belt are constrained mostly by the composition of the source rocks of the sediments and of the protoliths in the case of charnockites. Post-depositional metamorphic and metasomatic fluids had little contribution to the δ18O variations in these rocks. (author)