Oxygen isotope evidence for crustal contamination in Deccan Basalts

A set of whole rock lava flows and dykes from the western part of Deccan Traps, Western India, was analyzed for oxygen isotope ratios. δ18O stratigraphy of the upper formations in the Mahabaleshwar section of the Western Ghats area can be correlated with the Sr- and Nd-isotopic stratigraphy, in that increasing δ18O is associated with increasing initial 87Sr/86Sr and decreasing initial ɛNd. The increases of δ18O (up to +11.8‰) exceed the range of primitive mantle-derived materials, strongly suggesting that isotopic variations of these Deccan basalts are due to crustal contamination rather than input of continental lithospheric mantle as previously considered. The variations of δ18O–87Sr/86Sr and δ18O–ɛNd indicate that there are at least two contaminating domains, most likely (1) Archean granitic upper crust and (2) Archean carbonates + granulitic lower crust.