Role of the Kerguelen Plume in generating the eastern Indian Ocean seafloor

Mid‐ocean ridge basalts (MORB) in the Indian Ocean have Sr‐Nd‐Pb isotopic characteristics that distinguish them from seafloor basalts in the Atlantic and Pacific Oceans. These differences have important implications for mantle dynamics. We discuss the isotopic variation with eruption age of seafloor basalts recovered by deep sea drilling at 10 sites in the eastern Indian Ocean ranging in age from Eocene to Late Jurassic. Except for alkalic basalts recovered from near Christmas Island in the northeast Indian Ocean, the basement lavas are tholeiitic basalts that are characterized by a wide range in incompatible element abundance ratios, such as La/Yb and Zr/Nb. Most of the tholeiitic basalts from seven sites are geochemically similar to recent Indian Ocean MORB, but the alkalic basalts and tholeiitic lavas from two other sites have isotopic and incompatible element abundance ratios similar to lavas associated with the Kerguelen Plume. Two of these three sites, however, are not close to the track of this plume. The Dupal isotopic signature (relatively high 87 Sr/ 86 Sr and high 208 Pb/ 204 Pb at a given 206 Pb/ 204 Pb) is characteristic of lavas that have been attributed to the Kerguelen Plume, i.e., the Kerguelen Archipelago, Ninetyeast Ridge, and Kerguelen Plateau. Among eastern Indian Ocean seafloor basalts, a Dupal component is apparent in basement lavas from six of the seven drill sites in the eastern Indian Ocean that range in inferred age from ∼57 to 125 Ma. The oldest (∼155 Ma) seafloor lavas recovered from the Indian Ocean, derived from a spreading center in the Argo Abyssal Plain near northwest Australia, have high 143 Nd/ 144 Nd and low 87 / 86 Sr similar to the most depleted recent Indian MORB. Because the oldest volcanism on the Kerguelen Plateau (∼118 Ma) is the first evidence of the activity of the Kerguelen Plume, this plume is inferred to be the source of Dupal isotopic characteristics in Indian Ocean MORBs. Some recent Indian Ocean MORB are also distinctive because many have relatively low 206 Pb/ 204 Pb (<17.4). Some of the oldest (110 to 155 Ma) seafloor lavas in the eastern Indian Ocean also have relatively low 206 Pb/ 204 Pb ratios. This low 206 Pb/ 204 Pb signature predates volcanism associated with the Kerguelen Plume and may reflect a significant role for continental lithosphere as a long‐term source component for Indian Ocean MORB.