High-precision Pb (double spike) and Sr-Nd-Hf-isotopoc record of upper oceanik crust at Leg 206 (Site 1256, Eastern Central Pacific)

206 段上洋地壳的高精度 Pb（双尖峰）和 Sr-Nd-Hf-同位素记录（1256 站点，太平洋东部）

• 批准号: 84662191
• 负责人: Professor Dr. Kaj Hoernle
• 金额: --
• 依托单位: Forschungseinheit Magmatische und Hydrothermale Systeme
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 财政年份: 2008
• 资助国家: 德国
• 起止时间: 2007-12-31 至 2010-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/84662191?language=en
• 关键词: precision; Pb; double; spike; Sr

About 50 % of the present-day ocean crust and thus -30 % of the Earth's surface was formed at mid-ocean ridges at fast to superfast spreading rates (> 80 mm/y full rate). IODP Site 1256 in the Cocos Plate (Eastern Central Pacific) represents the most complete in situ section of ocean crust formed at a superfast spreading center drilled thus far. Scientific participants of IODP Expeditions 309 and 312 are currently investigating the recovered material from the deeper, mainly intrusive, part of the hole (below 750 mbsf). Relatively few geochemical data, however, exist thus far for the upper part (drilled during OOP Leg 206) consisting of -250 m of marine sediments and -500 m of lava flows. The upper 750 m represent -50 % of the total depth drilled at Site 1256. In the course of an ongoing project, our group is investigating the Sr, Nd, Hf and Pb (with the double spike method, DS) isotopic variation in the Exp. 309/312 material, including the low- to high-temperature lava-dike alteration and the dike-gabbro transition zones. Here we propose to examine the down-hole geochemical variation of Leg 206 sediments and lavas, in order to generate a complete and detailed record of the Sr-Nd-Hf-Pb (DS) isotopic and relevant trace element variations of the entire oceanic crust drilled at Site 1256. These data will provide important new insights into 1) magma genesis at superfast spreading ridges (East Pacific Rise); 2) the effects and timing of subsequent alteration including element fluxes in oceanic crust formed at superfast spreading rates (compared to slower rates); 3) the chemical evolution of seawater; 4) element cycles in subduction zones, and 5) the contribution of ocean crust to mantle plume sources. The proposed project is an important extension of our current studies and complements well the research activities within the international Site 1256 IODP scientific community.

今天大约50%的海洋地壳和-30%的地球表面是以快速到超快的扩张速度(全速80毫米/年)在大洋中脊形成的。位于科科斯板块(中东部太平洋)的IODP站点1256代表了迄今为止在超快扩张中心形成的最完整的洋壳原位剖面。IODP第309次和第312次探险的科学参与者目前正在调查从较深的、主要是侵入的部分(低于750 Mbsf)找到的材料。然而，到目前为止，相对较少的地球化学数据存在于上部(在OOP第206段钻探)，包括-250米的海洋沉积物和-500米的熔岩流。上部750米占1256现场钻探总深度的-50%。在一个正在进行的项目中，我们小组正在研究Exp中的锶、钕、氢和铅(用双尖峰方法，DS)的同位素变化。309/312物质，包括低温-高温熔岩-岩脉蚀变和岩墙-辉长岩过渡带。在这里，我们建议研究206腿沉积物和熔岩的井下地球化学变化，以便生成完整而详细的1256站点整个洋壳的锶-钕-氢-铅(DS)同位素和相关微量元素变化的记录。这些数据将为以下方面提供重要的新见解：1)超快扩张海脊(东太平洋隆起)的岩浆成因；2)随后变化的影响和时间，包括以超快扩张速度形成的洋壳中的元素通量(与较慢的扩张速度相比)；3)海水的化学演化；4)俯冲带中的元素循环；以及5)洋壳对地幔热柱来源的贡献。拟议的项目是我们目前研究的一个重要扩展，很好地补充了1256 IODP国际站点科学界内的研究活动。