Ca Isotope Variations in Oceanic Basalts

大洋玄武岩中的 Ca 同位素变化

• 批准号: 1144727
• 负责人: Stein Jacobsen
• 金额: $ 35.21万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-02-01 至 2016-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1144727&HistoricalAwards=false
• 关键词: Ca; Isotope; Variations; Oceanic; Basalts

Ca Isotope Variations in Oceanic BasaltsIntellectual Merit. Preliminary work demonstrates that measurable mass dependent 44Ca/40Ca isotopic variations Hawaiian basaltic lavas can be attributed to the presence of recycled ancient carbonates in the underlying mantle. It is proposed to extend this work to other oceanic islands and other tectonic settings to determine if Hawaii is a unique case or if recycling of ancient carbonates is a more general process in generating mantle heterogeneity? It is predicted that such a process would significantly affect the Ca and Sr, as well as C, budgets of the Earth?s mantle. Radiogenic isotope geochemistry (Rb­Sr, Sm-Nd, U-Th­Pb, Lu­Hf, and noble gas systems) provides compelling evidence that widespread mantle heterogeneity exists, and can be described in terms of apparent isotopic end­member compositions (e.g., EM1, EM2, HIMU and DMM). It is proposed to determine Ca isotope compositions of representative oceanic basalts to see how this parameter varies with the other isotopically determined end­member variants, and to further constrain the importance of carbonate recycling. Specifically, the new measurements will be used to [1] test current hypothesis that mass dependent 44Ca/40Ca variations are due to carbonate recycling, [2] investigate if non-mass dependent 44Ca/40Ca variations, due to 40K decay, are present in samples with very high 87Sr/86Sr ratios and [3] quantify fluxes of recycled materials that may have caused the variations. Processes that could account for mass dependent 44Ca/40Ca variations incluse: [1] carbonate recycling, [2] altered oceanic crust subduction, [3] recycling of plagioclase­rich gabbroic crust, and [4] igneous fractionation (diffusion, partial meting and fractional crystallization). A research plan is designed to help resolve the following questions: [1] Is carbonate recycling a common feature in oceanic basalts with high 87Sr/86Sr or is it limited to rare and unique sites like Hawaii? [2] Are Ca isotope data consistent with upper crustal recycling proposed to explain very high 87Sr/86Sr ratios in Samoan lavas? This research aims to establish a Ca isotope constraint on the magnitude of upper crustal recycling in mantle sources of basalts and also to test the influence of garnet and plagioclase fractionation on isotopic variations in oceanic basalts. Broader Impacts. T the proposed research facilitates for the first time extensive application of Ca isotopes to the field of mantle geochemistry. This proposal involves an early career research scientist (Huang) at Harvard University, and will educate and train graduate and undergraduate students in application of state­of­the-art analytical techniques to geosciences. Part of the proposed study will evolve into the senior thesis of an undergraduate student. The proposed research will leverage previous NSF investments by using samples recovered from previous NSF funded programs, such as ODP. The scientific results from this research will be presented in an educational website, which will be used in undergraduate and graduate education. As part of the proposed study, a new silicate standard will be prepared for intercalibration of future Ca isotopic work. Finally, results of the proposed study will be made available for outreach education via a project web page and an exhibition setup.

大洋玄武岩Ca同位素变化的智力价值初步工作表明，夏威夷玄武岩熔岩的44 Ca/40 Ca同位素变化可归因于下伏地幔中存在循环的古碳酸盐。建议将这项工作扩展到其他海洋岛屿和其他构造环境，以确定是否夏威夷是一个独特的情况下，或者如果回收的古碳酸盐是一个更普遍的过程中产生地幔的异质性？据预测，这样的过程将显着影响钙和锶，以及C，地球的预算？的斗篷。放射性同位素地球化学（Rb → Sr、Sm-Nd、U-Th → Pb、Lu → Hf和稀有气体系统）提供了令人信服的证据，表明存在广泛的地幔不均匀性，并可以用表观同位素末端成员组成（例如，EM 1、EM 2、HIMU和DMM）。建议确定Ca同位素组成的代表性的大洋玄武岩，看看这个参数如何变化与其他同位素确定的终端的成员变量，并进一步限制碳酸盐循环的重要性。具体而言，新的测量将用于[1]测试当前假设，即质量相关的44 Ca/40 Ca变化是由于碳酸盐再循环，[2]调查由于40 K衰变导致的非质量相关的44 Ca/40 Ca变化是否存在于具有非常高的87 Sr/86 Sr比率的样品中，[3]量化可能导致变化的再循环材料的通量。可以解释44 Ca/40 Ca质量变化的过程包括：[1]碳酸盐再循环，[2]蚀变洋壳俯冲，[3]富含斜长石的辉长岩地壳再循环，[4]火成岩分馏（扩散，部分熔融和分离结晶）。一项研究计划旨在帮助解决以下问题：[1]碳酸盐再循环是具有高87 Sr/86 Sr的海洋玄武岩的共同特征，还是仅限于像夏威夷这样罕见和独特的地点？ [2]钙同位素数据一致的上地壳再循环建议解释非常高的87 Sr/86 Sr比值在萨摩亚熔岩？本研究的目的是建立一个Ca同位素的地幔源区玄武岩的上地壳再循环的大小的限制，并测试石榴石和斜长石分馏的同位素变化在大洋玄武岩的影响。更广泛的影响。该研究首次将Ca同位素广泛应用于地幔地球化学领域。这项建议涉及哈佛大学的一名早期职业研究科学家（黄），并将教育和培训研究生和本科生将最先进的分析技术应用于地球科学。部分拟议的研究将演变成一个本科生的毕业论文。拟议的研究将利用以前的NSF投资，使用从以前的NSF资助计划（如ODP）中回收的样本。这项研究的科学成果将在一个教育网站上展示，该网站将用于本科生和研究生教育。作为拟议研究的一部分，将准备一个新的硅酸盐标准，用于未来钙同位素工作的相互校准。最后，拟议研究的结果将通过一个项目网页和一个展览装置提供给外联教育。