ABSTRACT
In this paper the authors summarize the results of their trace element study of lavas from 50 near-ridge seamounts on the flanks of the East Pacific Rise (EPR) between 5°N and 15°N. These seamount lavas are dominated by depleted N–type mid-ocean ridge basalts (MORB) with variably enriched E–type MORB and some extremely enriched ones resembling average compositions of ocean island basalts (OIB). This large compositional variation reflects with great fidelity the mantle source heterogeneity that is masked in lavas erupted at the EPR axis. In terms of incompatible trace element abundances, this source heterogeneity can be readily envisioned as being due to the presence of enriched domains of variable size and unevenly distributed within the ambient depleted mantle. The geochemical consequence of melting such a heterogeneous source is to produce apparent mixing relationships in the lavas. The enriched domains may be dikes or veins resulting from low-degree melt metasomatism. The low degree melts may be genetically related to eastward asthenospheric flow of Hawaii plume materials towards the EPR, as suggested by mantle tomographic studies. Trace element data suggest that the enriched materials (hence Hawaii plume materials) are ultimately derived from recycled oceanic crust.
