Geochemical diversity of the large lava field on the flank of the East Pacific Rise at 8°17′S

We recovered samples by dredge and glass corer from ten sites on the large lava flow field near 8°17′S on the East Pacific Rise and the nearby ridge crest. The lava field comprises at least four distinct normal MORB compositions, different from the lavas collected from the ridge axis. All of the samples appear relatively young, and are indistinguishable in apparent age from the axis samples. Incompatible element variations suggest that the flow field had at least two distinct parental magmas, one of which had greater and one smaller trace element concentrations at the same MgO than the parent of the axis samples. The three parental magmas can be related by a magma mixing model. Major and trace element modeling shows that the three parental magmas could not have been produced by different degrees of melting of a homogeneous mantle source, but that they are consistent with melting of a generally depleted mantle containing variable volumes of embedded enriched heterogeneities. The presence of seamounts on the flanks of the axis in this area and the fact that the samples from one dredge appear to have come from an off-axis vent, along with the compositional bracketing of the axis parental magma by the lava field parents, suggests that this lava field may be an off-axis flow field similar to seamount fields and other smaller lava fields common along the East Pacific Rise.