Isotopic Composition of Deccan and Ocean Ridge Basalts: Implications for their Mantle Sources

Isotopic data suggest that the mantle sources for ocean ridge basalts and some continental flood basalts, particularly the Deccan, may be in the same global depleted convecting mantle. If this is the case, the upwelling Deccan mantle source must have mixed with small amounts of an ancient enriched mantle component, similar to that detected in some kimberlites, prior to interaction with the crust. Such a scenario appears to be required by the facts that the isotopic composition of the depleted end members is approximately constant throughout the Deccan but different from ocean ridge basalts, and the oxygen isotopic composition of the most depleted Deccan sample is characteristic of mantle values. The wide variability in isotopic composition of Deccan and some other continental flood basalts is then the result of crustal processes, as has been suggested by many authors.