BEYOND EM-1 - LAVAS FROM AFANASY-NIKITIN RISE AND THE CROZET ARCHIPELAGO, INDIAN-OCEAN

Lavas from Afanasy-Nikitin Rise, possibly the Late Cretaceous product of the Crozet hotspot, cover a wide range of isotopic compositions tha t includes the lowest (Pb-206/Pb-204), (to 16.77) and epsilon(Nd)(t) ( to -8) values yet found among oceanic islands or spreading centers wor ldwide, as well as high (Sr-87/Sr-86)(t) (to 0.7066). In contrast, you ng basalts from the Crozet Archipelago exhibit a narrow range of varia tion around epsilon(Nd) similar to +4, Sr-87/Sr-86 similar to 0.7040, and Pb-206/Pb-204, 19.0, closely resembling that of shield lavas of th e Reunion hotspot. The Afanasy-Nikitin rocks also have much higher Ba/ Nb, Ba/Th, and Pb/Ce than modern oceanic island or ridge lavas, as wel l as high La/Nb, The data do not obviously support the Crozet plume mo del but, assuming the model to be plate tectonically correct, would in dicate that the plume-source composition either changed dramatically o r that Afanasy-Nikitin magmatism involved significant amounts of nonpl ume mantle, The low Pb-206/Pb-204, low epsilon(Nd) lavas provide the b est evidence to date of the sort of material that, by variably contami nating much of the Indian mid-ocean-ridge basalt (MORE) source astheno sphere, may be responsible for the isotopic difference between most In dian MORE and Pacific or North Atlantic MORB, The combined isotopic an d trace element results suggest an ultimate origin in the continental crust or mantle lithosphere for this material, although whether it was cycled through the deep mantle or resided at shallow levels in the co nvecting mantle cannot currently be determined.