Mantle heterogeneity beneath the Antarctic-Phoenix ridge off Antarctica peninsula

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 sub-ridge mantle source. There are no known hotspots in close proximity to the site. We observe that small scale isotopic heterogeneity does exist at shallow level in the sub-axial mantle of the APR. Enriched (E-type) mid-ocean ridge basalts (MORB) coexist with the normal (N-type) MORBs in this region. The E-type basalts are (1) relatively young compared to the N-type samples, (2) were erupted after the extinction of the APR, and (3) 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 the geochemically enriched materials dispersed in ambient depleted mantle might have been the first fraction to melt to form the E-type basalts.