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

Abstract

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 a 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. There are no known hotspots in close proximity to the site. The E-type basalts are relatively young compared to the N-type samples and were erupted after the extinction of the APR. 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 cause the extent of partial melting in this region to decrease. We interpret that geochemically enriched mantle might exist as a form of highly localized spots or veins in ambient depleted mantle of this region, and were the first fraction to melt to form the E-type basalts.