In-situ Pb isotopic analysis of sulfides in abyssal peridotites: new insights into heterogeneity and evolution of the oceanic upper mantle


DOEI Funded Research: 2008


This proposal to DOEI requests support for an ion probe Pb isotope study of mantle sulfides in abyssal peridotites from ultraslow-spreading ridges.  Systematics of mantle Pb isotopes are more complicated than that for Sr and Nd isotopes because geochemical behavior of the lithophile parents (U and Th) is different from that of the chalcophilic daughter (Pb), and mantle sulfides are thought to play crucial roles in creating Pb isotopic variations observed in mid-ocean ridge basalts.  Despite the potential importance, systematic studies of Pb isotopes in mantle sulfides have never been made.  We propose here to make a significant step forward on this issue.  Abyssal peridotites from ultraslowspreading ridges provide unique opportunities for directly approaching geochemical characteristics of the original asthenospheric composition.  The proposed study attempts to characterize in detail sulfides from the Southwest Indian Ridge and the Gakkel Ridge.  This work attempts to produce in-situ Pb isotope data, using the WHOI IMS 1280, in sulfides characterized in detail for their petrographic contexts and major element compositions.  The proposed work is coordinated with a concurrent study of Os isotopes in sulfides from the same suites of sulfide samples and with a study of radiogenic isotopes in silicates from the same suites of peridotites, so that a comprehensive radiogenic isotope data will be gathered for both silicates and sulfides, and geochemical evolution of the asthenospheric mantle can be quantitatively examined. 

J. Blusztajn is the lead PI of the proposal and N.  Shimizu’s role will provide technical support with respect to the 1280 operation.  Both will work together on interpretation of the results.  The proposed research is concerned with the genetic relationship between the mantle and MORB, and is relevant to the DOEI themes.