Towards Characterizing the Nitrogen Isotope Systematics of the Oceanic Mantle

描述大洋地幔氮同位素系统学特征

• 批准号: 2015789
• 负责人: Peter Barry
• 金额: $ 47.87万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-06-01 至 2023-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2015789&HistoricalAwards=false
• 关键词: Towards; Characterizing; Nitrogen; Isotope; Systematics

Nitrogen is far more abundant in the Earth’s atmosphere than in the mantle. Therefore, nitrogen can reflect interactions between Earth’s interior and exterior. However, few studies have investigated the nature of nitrogen in basalts that form as the mantle melts. The difficulty in measuring nitrogen in basalts is because of analytical challenges and the difficulty in obtaining representative samples. This is an important gap in knowledge because basalts make up the ocean crust that underlies two-thirds of the Earth's surface. This project will measure nitrogen isotopes from key mantle-derived samples. The samples were obtained from the main environments of basaltic magmatism in the world's oceans. The project thus aims to produce the best measure, to date, of the global nitrogen cycle over Earth history. The study will establish Woods Hole Oceanographic Institution as a key USA-based laboratory. The unique capability of the laboratory is the measure of high-precision nitrogen isotopes on extremely low concentration samples. Findings from the study will address many broader questions pertaining to the origin of the most abundant gas in our atmosphere. The recycling of this gas is tied to the evolution of the Earth and the solar system.Measurements of oceanic basalts from the Lau Basin, Manus Basin, Alarcon Basin, Galapagos and Mid-Atlantic Ridge Popping Rocks will allow us, for the first time, to define the scale of delta-N-15 variability in the oceanic mantle by targeting samples with high 3He/4He values (plume-influenced mantle) as well as other glasses with 3He/4He values within the nominal range of depleted MORB mantle (DMM). Given the well characterized geochemistry of these samples – including radiogenic isotopes (Sr-Nd-Pb), noble gases and major volatiles (He-Ne-Ar-CO2-H2O) –the relationship between delta-N-15 and petrogenetic tracers will be assessed to distinguish between mantle source features and secondary controls (e.g., degassing fractionation and/or surficial contamination). All samples will allow scrutiny of δ15N-3He/4He relationships and further characterization of the variability of delta-N-15 in the oceanic mantle from the perspective of different sampling media and regional controls. As a proof of concept, mafic crystals and xenoliths from the Canary Islands hotspot will also be measured, however this task is significantly more challenging due to extremely low N abundances in mafic crystals. Studies on mafic crystals will define limits for sample N-contents required for analysis, potentially leading to a significant increase in the sample base amenable to delta-N-15 studies. All results will provide important constraints on modeling the evolution of the DMM vs. plume-influenced mantle, and the advent of plate tectonics over Earth history. Specifically, N isotope data generated in the proposed study will be incorporated into a newly developed forward model that couples observations from N and other volatiles species (i.e., heavy noble gases) to understand the relative recycling efficiency of different volatile species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球大气中的氮比地幔中的要丰富得多。因此，氮可以反映地球内部和外部的相互作用。然而，很少有研究调查了地幔融化时形成的玄武岩中氮的性质。测定玄武岩中氮的困难是由于分析方面的挑战和获得代表性样品的困难。这是一个重要的知识缺口，因为玄武岩构成了占地球表面三分之二的海洋地壳。该项目将测量关键地幔源样品的氮同位素。这些样品是从世界海洋玄武岩岩浆活动的主要环境中获得的。因此，该项目旨在对地球历史上的全球氮循环进行迄今为止最好的测量。这项研究将使伍兹霍尔海洋研究所成为美国的重点实验室。该实验室的独特能力是对极低浓度样品进行高精度氮同位素测量。这项研究的发现将解决许多更广泛的问题，这些问题与我们大气中最丰富的气体的起源有关。这种气体的循环利用与地球和太阳系的演化密切相关。对劳盆地、马努斯盆地、Alarcon盆地、加拉帕戈斯群岛和中大西洋脊爆岩的海洋玄武岩的测量将使我们第一次能够通过针对具有高3He/4He值（羽状地幔）的样品以及在贫MORB地幔（DMM）标称范围内具有3He/4He值的其他玻璃样品来定义海洋地幔中三角洲- n -15变化的尺度。考虑到这些样品的地球化学特征-包括放射性同位素（Sr-Nd-Pb），稀有气体和主要挥发物(He-Ne-Ar-CO2-H2O) -将评估δ - n -15和岩石成因示踪剂之间的关系，以区分地幔源特征和次要控制因素（例如脱气分馏和/或表面污染）。所有样品将允许从不同采样介质和区域控制的角度审视δ15N-3He/4He关系，并进一步表征海洋地幔中δ - n -15的变异性。作为概念验证，来自加那利群岛热点的基性晶体和捕虏体也将被测量，但由于基性晶体中极低的N丰度，这项任务更具挑战性。对基性晶体的研究将确定分析所需样品n含量的限制，这可能导致可用于δ n -15研究的样品碱的显着增加。所有的结果将为模拟DMM与羽流影响的地幔的演化以及地球历史上板块构造的出现提供重要的约束。具体来说，在提出的研究中产生的N同位素数据将被纳入一个新开发的正演模型，该模型将N和其他挥发物（即重惰性气体）的观测结果结合起来，以了解不同挥发物的相对回收效率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Recycling of nitrogen and light noble gases in the Central American subduction zone: Constraints from 15N15N

中美洲俯冲带氮气和轻惰性气体的回收：来自15N15N的限制

• DOI: 10.1016/j.epsl.2021.117112
• 发表时间: 2021
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Labidi, J.;Young, E.D.;Fischer, T.P.;Barry, P.H.;Ballentine, C.J.;de Moor, J.M.
• 通讯作者: de Moor, J.M.

Nitrogen and noble gases reveal a complex history of metasomatism in the Siberian lithospheric mantle

氮气和稀有气体揭示了西伯利亚岩石圈地幔复杂的交代作用历史

• DOI: 10.1016/j.epsl.2020.116707
• 发表时间: 2021
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Barry, Peter H.;Broadley, Michael W.
• 通讯作者: Broadley, Michael W.

Hydrothermal 15N15N abundances constrain the origins of mantle nitrogen

• DOI: 10.1038/s41586-020-2173-4
• 发表时间: 2020-04-16
• 期刊: NATURE
• 影响因子: 64.8
• 作者: Labidi, J.;Barry, P. H.;Young, E. D.
• 通讯作者: Young, E. D.