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.

由于地球大气中氮的丰富性以及对生命的重要性，与生物圈、大气圈和水圈相关的氮 (N) 循环已得到充分研究。在地球历史的大部分时间里，调节了地球表面和深层储层之间的氮通量，影响了千年时间尺度上地球氮的整体分布，因此，氮（N）的质量平衡在俯冲过程中输送到地球深处，然后在俯冲过程中返回到地表。火山作用和脱气至关重要，但目前的估计表明，45-74% 的俯冲氮不会通过弧火山作用返回地表，这意味着氮被以不同的量封存在地球深处。其可以反映诸如俯冲板块组成或俯冲条件等因素。深部、特征较差的氮储层的候选者包括中下大陆地壳、次大陆地幔、弧前至地幔。弧下地幔，或更深的地幔（即更深的上地幔、过渡带或下地幔），这突出表明需要对适当的样本进行氮测量，并对这些储层中的氮行为进行彻底的限制。 N) 将提供俯冲带弧前至弧下区域内的分布和处理，首先，对富含沉积物和富含蛇纹岩的混杂岩和矿物进行一些首次 N 测量，以表征俯冲带的特征。其次，将进行相平衡实验，以评估关键含氮矿物的稳定性，并测量混杂基体材料上的氮熔体/流体矿物分配系数作为多个因素（压力、将使用拟议研究和先前研究的数据来跟踪板坯脱水和部分熔化过程中的氮行为。用于量化从弧前输送到弧下加工区的氮量、其所含矿物以及它如何随主要岩性（沉积物或蛇纹岩）而变化。然后，将量化弧下加工过程中的板片与不同热状态的俯冲带中弧下地幔中被隔离的量，这些将构成对可应用于俯冲区域的氮行为的新约束。因此，它也将用于解决耦合固体地球大气系统中的 N 的反馈和演化。该提案支持亚利桑那大学 (UA) 的两名早期职业女性 PI、两名研究生和两名以上本科生。 ）和南加州大学 (USC) 旨在加强合作并扩大参与范围，PI 将举办一场有关深度波动自行车的联合虚拟研究生研讨会，UA 团队将在 UA 的学生中举办博物馆展览。阿尔菲·诺维尔宝石和矿物博物馆致力于高压高温地球科学研究（包括实验室设备和研究应用）。作为地球大气中最丰富的成分和生命的重要成分，氮 (N) 在当前的行为大气、海洋、地壳和生物圈（统称为地表水库）已得到相对充分的研究，然而，地球地表水库的氮成分在整个地球历史中可能并不保持不变。可能对早期地球气候和生命进化产生影响。氮通过板块构造在地球表面储层和深层内部进行交换，特别是在俯冲带中，地壳中的氮（以及来自大气、海洋的成分）。地幔和生物圈中的一部分氮通过火山脱气被吸入地幔或内部。没有很好的约束，这项拟议的研究旨在填补这一知识空白的一个关键组成部分，将测量典型俯冲带岩石的氮成分，以确定随着地幔条件下的压力和温度增加而存在的氮的位置。将进行以了解地壳进入地幔并融化后氮的行为，目的是最终利用这些结果来估计地球历史上地幔和大气的氮成分如何变化。女性 PI，亚利桑那大学 (UA) 和南加州大学 (USC) 的两名研究生和两名以上本科生为了加强合作并扩大参与范围，PI 将围绕拟议主题举办联合虚拟研究生研讨会，其中包括来自两所院校的学生。 UA 将在 UA 的阿尔菲·诺维尔宝石和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示，这将是教育公众了解最先进研究的绝佳媒介。该奖项反映了通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。