Mantle heterogeneity beneath the Antarctic-Phoenix Ridge in the Drake Passage,

Summary We determined Sr, Nd and Pb isotopic compositions for basalts recovered from the fossilized Antarctic-Phoenix Ridge (APR) in the Drake Passage, Antarctica, in order to understand the nature of sub-ridge mantle source. Enriched (E-type) mid-ocean ridge basalts (MORB) coexist with the normal (N-type) MORBs in the axial region of the APR, being far from any known hotspots. The E-type basalts are relatively young in comparison with the N-type samples, and erupted after the extinction of the APR. Extent of enrichment in incompatible elements in the basalts correlates positively with isotopic ratios of Sr and Pb, and negatively with Nd. The E-type melts have been generated by low-degree of partial melting of an enriched mantle source. Extinction of the APR is likely to lead the extent of partial melting in this region to decrease. We interpret that the geochemically enriched materials might exist as a form of highly localized spots or veins in ambient depleted mantle of this region, and have been the first fraction to melt for generating the E-type basalts studied