U-Th-Pb, Nd and Hf isotopic investigation of a complete in situ section of upper oceanic crust formed at a superfast spreading ridge (IODP Site 1256D)

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We propose the systematic determination of high-resolution Pb isotopic data and U, Th and Pb concentrations, as well as Nd and Hf isotopic compositions of a complete in situ section of oceanic crust (extrusive lavas, sheeted dikes, gabbros) drilled during IODP Exp. 309 and 312 (Site 1256D). Newly formed oceanic crust undergoes extensive chemical exchange with seawater during hydrothermal circulation processes and subsequent low-temperature alteration. This interaction influences the chemistry of the oceans, the oceanic crust and, through subduction, the composition of the upper mantle and eventually contributes to the characteristic signatures in mantle plumes by crustal recycling. A complete understanding of these chemical interactions depends on knowing the elemental fluxes between the oceans and the entire ocean crust section. Little information, however, presently exists on the heterogeneity of hydrothermal alteration at different crustal depths. The results of this project will allow us to assess the impact of high- and low-temperature alteration on the Pb isotopic budget of the oceanic crust.