Collaborative Research: Isotopic Constraints on the Mineralogy of the MORB Source

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Under this award, the PIs propose to analyze approximately 50 abyssal peridotites for Nd-isotopes to determine whether variations in Nd-isotopic composition in ridge basalts are also observed in the associated peridotites. Abyssal peridotites are thought to be the residues of melting that lead to mid-ocean ridge basalts, however in a study on two segments of the South West Indian Ridge (SWIR) the PIs showed that the 143Nd/144Nd of abyssal peridotites are more radiogenic than MORB and do not span the range as the basalts. This surprising result may indicate that the peridotite is not the sole source of the basalts, and most likely, a lithology with a lower melting temperature than peridotite (like pyroxenite) is present in the MORB source. The purpose of this study is to confirm and extend these observations. Samples of Normal MORB will come from the Kane and Gibbs fracture zone, Garrett FZ, Hess Deep and the orthogonal spreading segment between 17 degrees and 30 degrees E along the SWIR. In addition samples will be studied from areas that are clearly influenced by hot spots: the Oceanographer fracture zone (Azores plume) the area of the Indian Ocean between 33 degrees -45 degrees E (Marion hot spot).