Fractionation of highly siderophile elements in the lower oceanic crust

导致地壳中高度亲铁元素（HSE、铂族元素、稀土元素和金）强烈分馏的过程尚未得到很好的理解。洋脊玄武岩中某些HSE的丰度比地幔低1000倍或更多，Re、Au和Pd比其他HSE更丰富。由于大多数喷发玄武岩的硫化物饱和，它已被建议，高度可变的丰度的HSE玄武岩可能反映在更深的海洋地壳的晶体分馏过程。地壳与地幔中岩浆HSE分馏的相关性仍然是一个未解决的主要问题，特别是因为HSE数据和下地壳岩石系统工作的可用性有限。我们建议研究大洋中低地壳岩石从ODP站点735B西南印度洋海岭。主要目标将是限制HSE，硒和碲的丰度在典型的岩性，以确定HSE载体阶段和它们的组成，并评估其对海洋地壳的HSE预算的影响。这将限制HSE在下地壳中可能的岩浆富集，并将提高我们对HSE在壳幔系统中分馏的认识。

The processes that lead to the strong fractionation of highly siderophile elements (HSE, the platinum group elements, rhenium and gold) in the crust are not well understood. Compared to the mantle, abundances of some HSE in ocean ridge basalts are lower by a factor of 1000 or more, with Re, Au and Pd being more abundant than other HSE. Because most erupting basalts are sulphide saturated it has been suggested that the highly variable abundances of the HSE in basalts may reflect crystal fractionation processes in the deeper oceanic crust. The relevance of magmatic HSE fractionation in the crust vs. the mantle is still an unresolved major question, particularly because of the limited availability of HSE data and systematic work on lower crustal rocks. We propose to study oceanic middle to lower crustal rocks from ODP site 735B on the SW Indian ridge. The main goals will be to constrain HSE, Se and Te abundances in typical lithologies, to identify HSE carrier phases and their composition, and to assess their impact on the HSE budget of oceanic crust. This will produce constraints on possible magmatic enrichment of HSE in the lower crust and will improve our knowledge of the fractionation of the HSE in the crust-mantle system.