Geochemical evidence for plume—mantle interactions beneath Kerguelen and Heard Islands, Indian Ocean

Abstract

Within-plate ocean island basalts probably originate by the partial melting of upwelling plumes coming from deep within the Earth's mantle1. Part of the observed heterogeneity in Sr, Nd and Pb isotopic ratios in oceanic basalts may result from the interaction of plumes with the lithosphere 2–4. and asthenosphere2, 5. Kerguelen and Heard Islands, in the southern Indian Ocean, are the latest products of a large and long-lived plume system6, comparable to the Hawaiian–Emperor chain in the Pacific. Kerguelen Island began forming ∼40 Myr ago on the Antarctic plate, near to the embryonic Southeast Indian Ridge (SEIR), and represents the continuation of the hotspot activity preserved on the Indian plate as the Ninety east Ridge7 (Fig. 1). With continuing sea-floor spreading, younger volcanism on Kerguelen has occurred further away from the influence of the SEIR. Here we show that the isotopic compositions of Kerguelen basalts vary in sympathy with this changing tectonic environment, and suggest not only that depleted asthenosphere, but also that Cretaceous oceanic plateau litho-sphere, may have contributed significantly to the earlier magmatic history of the island.