Collaborative Research: Tracking nitrogen in mélange matrix from fore-arc to sub-arc depths with implications for deep nitrogen cycling: A combined field and experimental approach

合作研究：追踪从弧前到弧下深度的混合基质中的氮，对深层氮循环的影响：现场和实验相结合的方法

• 批准号: 2350014
• 负责人: Emily Cooperdock
• 金额: $ 19.6万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-10-01 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2350014&HistoricalAwards=false
• 关键词: Collaborative; Research; Tracking; nitrogen; lange

The nitrogen (N)-cycle as it relates to the bio-, atmo-, and hydro-spheres have been well studied due to N’s abundance in Earth’s atmosphere and importance for life. In the less understood solid Earth N cycle, plate tectonics has regulated N fluxes between surface and deep Earth reservoirs over much of Earth’s history, affecting the bulk Earth N distribution over millennial timescales. Thus, the mass balance of nitrogen (N) delivered to the deep Earth during subduction and then returned to the surface during volcanism and degassing is critically important, yet efficiency estimates are highly variable. Current estimates suggest that 45-74% of subducted N does not return to the surface through arc volcanism. This implies that N is being sequestered in the deep Earth in variable amounts, which could reflect factors such as subducting plate composition or subduction conditions. Candidates for deep, poorly characterized N reservoirs include mid-lower continental crust, subcontinental mantle, fore-arc to sub-arc mantle, or deeper mantle (i.e., deeper upper mantle, transition zone or lower mantle). This highlights a need for N measurements on appropriate samples as well as thorough constraints on N behavior in these reservoirs. New key constraints on nitrogen (N) distribution and processing within the fore-arc to sub-arc regions of subduction zones will be provided. First, some of the first N composition measurements of sediment-rich and serpentinite-rich mélange matrix rocks and minerals to characterize the distribution of N during fore-arc processing will be made. Second, phase equilibria experiments to assess the stability of key N hosting minerals and measure N melt/fluid-mineral partition coefficients on mélange-matrix materials as a function of several factors (pressure, temperature, oxygen fugacity, chlorine content, and partial melt composition) to track N behavior during dehydration and partial melting in the slab at sub-arc depths will be performed. Data from the proposed study along with those from previous studies will be used to quantify the amount of N that is delivered from the fore-arc to the sub-arc processing zone, in which minerals it is hosted, and how it varies by dominant lithology (sediment or serpentinite). How much N is released from the slab during sub-arc processing versus how much is sequestered in the sub-arc mantle in subduction zones of different thermal states will then be quantified. These will constitute novel constraints on N behavior that can be applied to subduction regimes throughout Earth’s history. Hence, it will also be used to address the feedback and evolution of N across the coupled solid Earth-atmosphere systems. This proposal supports two early career female PIs, two graduate students, and two+ undergraduates from University of Arizona (UA) and University of Southern California (USC). To enhance collaboration and broaden participation, the PIs will offer a joint virtual graduate seminar on deep volatile cycling including students at UA and USC. The team at UA will develop a museum display at UA’s Alfie Norville Gem & Mineral Museum on high pressure-high temperature geoscience research (including laboratory equipment and research applications).As the most abundant constituent of the Earth’s atmosphere and as an essential ingredient of life, the behavior of nitrogen (N) in the present-day atmosphere, oceans, crust and biosphere (collectively known as the surficial reservoirs) have been relatively well-studied. However, the N composition of the Earth’s surficial reservoirs may not have remained the same throughout Earth’s history and this may have implications for early Earth climate and evolution of life. Nitrogen is exchanged between the Earth’s surficial reservoirs and the deep interior via plate tectonics, especially subduction zones. In subduction zones, N in the Earth’s crust (along with components from the atmosphere, ocean and biosphere) is pulled into the mantle or the interior of the Earth. Some proportion of the N from the mantle escapes back into the atmosphere and ocean by volcanic degassing. This N exchange between the surface and interior is not well-constrained and this proposed study aims to fulfill a key component of this knowledge gap. The N composition of typical subduction zone rocks will be measured to determine where N is hosted as pressure and temperature increase. Laboratory experiments at conditions in the Earth’s mantle will be performed to understand the behavior of N once the crust enters the mantle and melts. The objective is to eventually use these results to estimate how the N composition of the Earth’s mantle and atmosphere have changed through Earth’s history. This proposal supports two early career female PIs, two graduate students, and two+ undergraduates from University of Arizona (UA) and University of Southern California (USC). To enhance collaboration and broaden participation, the PIs will offer a joint virtual graduate seminar on the proposed theme including students from both institutions. The team at UA will develop a museum display at UA’s Alfie Norville Gem & Mineral Museum on plate tectonics connecting the surface and interior of the Earth, which would be an excellent medium to educate the public on state-of-the-art research.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.

由于氮在地球大气中的丰度和对生命的重要性，氮循环与生物、大气和水圈的关系已经得到了很好的研究。在了解较少的固体地球N循环，板块构造调节地表和地球深部水库之间的N通量在地球的历史上，影响了散装地球N分布在千年的时间尺度。因此，在俯冲过程中输送到地球深部，然后在火山作用和脱气过程中返回到地表的氮（N）的质量平衡至关重要，但效率估计值差异很大。目前的估计表明，45-74%的俯冲N不会通过弧火山作用返回地表。这意味着氮以不同的数量被封存在地球深处，这可能反映了俯冲板块组成或俯冲条件等因素。深的、特征不佳的氮储层的候选者包括中-下大陆地壳、次大陆地幔、弧前-弧下地幔或更深的地幔（即，更深的上地幔、过渡带或下地幔）。这突出了对适当样品的N测量的需要以及对这些储层中的N行为的彻底约束。将提供俯冲带弧前至弧下区域内氮（N）分布和加工的新的关键制约因素。首先，将对富含沉积物和富含蛇纹岩的混杂岩基质岩石和矿物进行首次N成分测量，以表征弧前加工过程中N的分布。第二，相平衡实验，以评估关键的N托管矿物的稳定性和测量N熔体/流体矿物分配系数的混杂基质材料作为几个因素的函数（压力，温度，氧逸度，氯含量，和部分熔体组合物），以跟踪N的行为在脱水和部分熔化的板坯在亚弧深度将进行。从拟议的研究数据沿着从以前的研究将被用来量化的数量的N是从弧前交付到弧下加工区，在其中的矿物托管，以及它如何变化的主要岩性（沉积物或蛇纹岩）。有多少N是从板在弧下加工过程中释放多少是隔离在不同的热状态的俯冲带的弧下地幔，然后将被量化。这些将构成新的约束N的行为，可以适用于整个地球的历史俯冲制度。因此，它也将被用来解决整个耦合固体地球-大气系统的N的反馈和演变。该提案支持来自亚利桑那大学（UA）和南加州大学（USC）的两名职业女性PI，两名研究生和两名本科生。为了加强合作和扩大参与，PI将提供一个关于深度波动循环的联合虚拟研究生研讨会，包括UA和南加州大学的学生。该团队将在阿尔菲·诺维尔宝石矿物博物馆（Alfie Norville Gem Mineral Museum）开展一项关于高压高温地球科学研究（包括实验室设备和研究应用）的博物馆展示。氮（N）是地球大气中含量最丰富的成分，也是生命的重要组成部分，其在当今大气、海洋、地壳和生物圈（统称为表层储层）中的行为已经得到了比较充分的研究。然而，地球表面碳库的氮成分在整个地球历史中可能并不相同，这可能对早期地球气候和生命进化产生影响。氮通过板块构造，特别是俯冲带，在地球表层储层和深部内部之间进行交换。在俯冲带中，地壳中的氮（沿着来自大气、海洋和生物圈的成分）被拉入地幔或地球内部。来自地幔的部分N通过火山脱气作用逃逸回大气和海洋。这种表面和内部之间的N交换没有很好的约束，这项研究的目的是实现这一知识差距的一个关键组成部分。将测量典型俯冲带岩石的氮成分，以确定随着压力和温度的增加，氮在哪里被托管。将在地幔条件下进行实验室实验，以了解地壳进入地幔并熔化后N的行为。我们的目标是最终使用这些结果来估计地球的地幔和大气的N成分如何通过地球的历史发生变化。该提案支持来自亚利桑那大学（UA）和南加州大学（USC）的两名职业女性PI，两名研究生和两名本科生。为加强合作及扩阔参与范围，两所研究院将就建议的主题举办一个虚拟研讨会，邀请两所院校的学生参加。UA的团队将在UA的Alfie Norville宝石矿物博物馆开发一个关于连接地球表面和内部的板块构造的博物馆展览，这将是一个很好的媒介，教育公众最先进的研究。这个奖项反映了NSF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。