EAGER: Collaborative Research: Testing the marine carbonate recycling hypothesis

EAGER：合作研究：测试海洋碳酸盐回收假说

• 批准号: 1747600
• 负责人: Paterno Castillo
• 金额: $ 5.6万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1747600&HistoricalAwards=false
• 关键词: EAGER; Collaborative; Research; Testing; marine

This EArly-concept Grant for Exploratory Research (EAGER) project will test if it is possible to trace geochemically the inclusion of ancient marine carbonates, a common type of sedimentary rock formed in the ocean floor, in volcanic rocks currently erupting in oceanic islands such as Hawaii, Saint Helena and the Cook-Australs. The confirmation of such a crustal recycling process would have a number of significant implications that would advance the field of Earth Sciences. Marine carbonates have a distinctively high content of the radioactive parent U (Uranium), which decays to radiogenic daughter Pb (Lead) isotopes. This project will test this hypothesis using a new combination of geochemical proxies. Recycling of surface sediments via subduction zones into the source of oceanic volcanic rocks has been documented before. The project, however, will try to explore if variations of the stable isotopes of Ca (Calcium) and Mg (Magnesium) could be a good way of tracking this process for subducted carbonates. Finally, it would also help us better constrain the various chemical components in the Earth's mantle and further elucidate the evolution of our planet over time. These results will be accessible and disseminated through presentations in scientific meetings and publications in scientific journals. The unusually radiogenic Pb isotopic ratios of many, if not all, oceanic basalts have generated three major problems, or so-called Pb paradoxes, regarding their mantle sources. These sources must be characterized by 1) long time-integrated high U/Pb, 2) long time-integrated low Th/U and 3) constant Ce/Pb and Nb/U. Although some of the currently proposed solutions to individual Pb paradoxes are highly satisfactory, they are generally independent and at odds with each other. The Pb paradoxes, however, are inter-related and constitute a system of equations that should be solved all together, as the solution to each paradox must also be able explain the other paradoxes. This study hopes to test a hypothesis that recycled marine carbonates, with their high U/Pb and U/Th ratios, can flux-melt the subducted oceanic slab to produce some oceanic basalts. Melts containing mixtures of enriched and depleted mantle components (i.e., between recycled crust and the proposed FOZO and/or DMM mantle components) can generate the radiogenic Pb isotopic ratios and concomitant Pb paradoxes in oceanic basalts. This pilot project will verify the proposed marine carbonate recycling hypothesis through the analysis of a select set of extreme oceanic basalts using coupled Ca and Mg isotopic analysis combined with conventional geochemical methods. The results will have the potential to transform our understanding of mantle geodynamics including the formation of ocean island basalts, recycling of crustal materials, mantle convection, and history and evolution of the composition of the mantle.

这项对探索性研究的早期概念赠款（急切）项目将测试是否可以在地球化学上追踪古代海洋碳酸盐，这是一种在海底形成的一种常见的沉积岩石，目前在海洋岩石中，目前在海洋岛屿上爆发，如夏威夷，夏威夷，圣海伦娜，圣海伦娜和库克斯特拉尔。确认这种地壳回收过程将具有许多重要的含义，可以推进地球科学领域。海洋碳酸盐的放射性母体U（铀）的含量明显高，它会衰减放射性子PB（铅）同位素。该项目将使用新的地球化学代理来检验该假设。以前已经记录了通过俯冲带回收表面沉积物到海洋火山岩来源的。但是，该项目将尝试探索CA（钙）和MG（镁）稳定同位素的变化是否可能是跟踪俯冲碳酸盐过程的好方法。最后，这也将帮助我们更好地限制地球地幔中的各种化学成分，并进一步阐明我们星球随着时间的推移的演变。这些结果将可以通过科学期刊的科学会议和出版物中的演讲来访问和传播。许多（如果不是全部）海洋玄武岩的异常放射性PB同位素比，就其地幔来源产生了三个主要问题，或所谓的PB悖论。这些来源必须以1）长时间整合高U/PB的特征，2）长时间集成的低Th/U和3）恒定CE/PB和NB/U。尽管目前针对单个PB悖论的一些目前提出的解决方案非常令人满意，但它们通常是独立的，并且相互矛盾。但是，PB悖论是相互关联的，并且构成了一个方程系统，应将所有方程式求解，因为对每个悖论的解决方案也必须能够解释其他悖论。这项研究希望测试一个假设，即回收具有高U/PB和U/TH比的海洋碳酸盐可以融合俯冲的海洋板以产生一些海洋玄武岩。含有富含和耗尽的地幔成分混合物的熔体（即，在回收的地壳和拟议的Fozo和/或DMM地幔组件之间）可以产生放射性PB同位素比率和一致的PB PB PARADOXES中的PB Paradoxes。该试点项目将通过使用耦合的CA和MG同位素分析与常规地球化学方法结合使用一组精选的极端海洋玄武岩来验证拟议的海洋碳酸盐回收假设。结果将有可能改变我们对地幔地球动力学的理解，包括形成海洋岛玄武岩，地壳材料的回收，地幔对流以及地幔组成的历史和演变。