Isotopic compositions of volcanic glasses from the Lau Basin

Sr, Nd, and Pb isotopic compositions of fresh volcanic glasses from two regions in the Lau Basin give evidence of two different mantle sources for Lau Basin basalts. Samples from the northern part of the Lau Basin around 18°S show normal mid-ocean ridge basalt (N-MORB)-like major and trace-element compositions and isotopic characteristics, which are typical for Indian Ocean MORB rather than Pacific Ocean MORB. Samples from the Valu Fa Ridge between 21°S and 23°S in the Southern Lau Basin display an enrichment of Sr and Pb isotopes relative to Northern Lau Basin samples. These data are consistent with published major and trace-element data that indicate an influence of a slab-derived component on the composition of Valu Fa Ridge magmas and cannot be attributed to simply the mixing of a Northern Lau Basin type mantle source and Western Pacific sediments. They can, however, be explained by mixing between Pacific Ocean MORB and Western Pacific sediments. -from Authors