GEOCHEMICAL DIVERSITY OF THE LARGE LAVA-FIELD ON THE FLANK OF THE EAST PACIFIC RISE AT 8-DEGREES-17'S

We recovered samples by dredge and glass corer from ten sites on the l arge lava flow field near 8 degrees 17'S on the East Pacific Rise and the nearby ridge crest. The lava field comprises at least four distinc t normal MORE compositions, different from the lavas collected from th e ridge axis. All of the samples appear relatively young, and are indi stinguishable in apparent age from the axis samples. Incompatible elem ent variations suggest that the flow field had at least two distinct p arental magmas, one of which had greater and one smaller trace element concentrations at the same MgO than the parent of the axis samples. T he 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 homogeneo us mantle source, but that they are consistent with melting of a gener ally depleted mantle containing variable volumes of embedded enriched heterogeneities. The presence of seamounts on the flanks of the axis i n this area and the fact that the samples from one dredge appear to ha ve come from an off-axis vent, along with the compositional bracketing of the axis parental magma by the lava field parents, suggests that t his lava field may be an off-axis flow field similar to seamount field s and other smaller lava fields common along the East Pacific Rise.