Contamination of Indian Ocean asthenosphere by the Kerguelen-Heard mantle plume

THE mid-ocean-ridge basalts (MORBs) from the Indian Ocean are isotopically distinctive. They have higher ⁸⁷Sr/⁸⁶Sr, ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁷Pb/²⁰⁶Pb ratios than Pacific andAtlantic counterparts^1,2 (see Fig. 1), suggesting that the upper mantle beneath the Indian Ocean has remained a partially isolated system². The Australian-Antarctic discordance, a bathymetrically depressed segment of the South-East Indian Ridge, may represent a fundamental boundary between the Indian and Pacific mantle domains³. What processes are responsible for such domains? We argue here that the Kerguelen-Heard plume, which is producing Dupal-type basalts on Kerguelen and Heard Islands in the southern Indian Ocean, has contaminated large volumes of the Indian Ocean asthenosphere. This has produced the distinctive composition of Indian Ocean MORBs.