| Abstract: | Isotopic data for Sr and Nd from fresh glassy East Pacific Rise basalts suggest that this part of the suboceanic mantle is characterized by subtle but distinct large-scale regional isotopic variability which may reflect differences between cells of the convecting mantle. In spite of a systematic N—S change in spreading rate of a factor of three along the sampled portion of the EPR, no correlation is observed between spreading rate and range of isotopic composition, indicating that the regional variations override homogenization effects which may be correlated with rate of magma generation and hence spreading rate. There is no clear signature in our data of effects from the postulated global “Dupal Anomaly” 30,31]. However, for a restricted ridge segment at the latitude of Easter Island, anomalously high87Sr/86Sr and low143Nd/144Nd occur, coupled with high incompatible element concentrations. These features are most easily understood as being the result of inclusion of a “plume” component in these ridge basalts. |
