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)

我们建议系统地测定IODP Exp期间钻探的整个洋壳(喷出熔岩、席状岩脉、辉长岩)的高分辨率铅同位素数据和U、Th、Pb浓度以及ND和Hf同位素组成。309和312(1256D站点)。新形成的洋壳在热液循环过程中与海水进行了广泛的化学交换，并在随后的低温改造过程中。这种相互作用影响了海洋、洋壳的化学成分，并通过俯冲作用影响了上地幔的组成，并最终通过地壳再循环促进了地幔羽流的特征特征。对这些化学相互作用的全面了解取决于了解海洋和整个洋壳部分之间的元素通量。然而，目前关于不同地壳深度的热液蚀变不均质性的信息很少。该项目的结果将使我们能够评估高、低温变化对洋壳铅同位素收支的影响。

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.