Ca Isotope Variations in Oceanic Basalts

大洋基底中的钙同位素变化--智力价值初步工作表明，夏威夷玄武岩的可测量质量依赖于44Ca/40Ca同位素变化，这可以归因于下地幔中存在循环的古代碳酸盐。有人建议将这项工作扩展到其他海洋岛屿和其他构造背景，以确定夏威夷是一个独特的案例，还是古代碳酸盐的再循环是形成地幔不均质性的一个更普遍的过程？据预测，这一过程将显著影响S地幔的钙、锶和碳的收支。放射成因同位素地球化学(Rb-Sr、Sm-ND、U-Th-Pb、Lu-Hf和惰性气体系统)提供了令人信服的证据，表明存在广泛的地幔不均质性，并可用表观同位素端元组成(如EM1、EM2、HIMU和DMM)来描述。建议测定具有代表性的大洋玄武岩的钙同位素组成，以了解这一参数如何随其他同位素确定的端元变体的变化而变化，并进一步限制碳酸盐循环的重要性。具体地说，新的测量将被用来[1]检验当前的假设，即与质量相关的44Ca/40Ca变化是由于碳酸盐循环引起的，[2]研究由于40K衰变而导致的非质量相关的44Ca/40Ca变化是否存在于具有非常高的87Sr/86Sr比值的样品中，以及[3]量化可能导致变化的回收材料的通量。可以解释与质量有关的44Ca/40Ca变化的过程包括：[1]碳酸盐循环，[2]蚀变洋壳俯冲，[3]富斜长辉长质结壳的循环，[4]火成岩分馏(扩散、部分熔化和分离结晶)。设计了一项研究计划来帮助解决以下问题：[1]碳酸盐循环是87Sr/86Sr高的大洋玄武岩的共同特征，还是仅限于夏威夷等稀有和独特的地点？[2]钙同位素数据是否与上地壳循环一致，以解释萨摩亚熔岩中非常高的87Sr/86Sr比率？本研究旨在建立玄武岩地幔源区上地壳循环的钙同位素约束条件，并检验石榴石和斜长石分馏对大洋玄武岩的同位素变化的影响。更广泛的影响。这项拟议的研究首次促进了钙同位素在地幔地球化学领域的广泛应用。这项建议涉及哈佛大学的一位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。拟议研究的一部分将演变为本科生的高级论文。这项拟议的研究将通过使用从以前的NSF资助的项目中回收的样本来利用以前的NSF投资，例如ODP。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，将编制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项目网页和展览设置提供给外展教育。

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.