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

由于氮在地球大气中的丰度和对生命的重要性，人们对与生物圈、大气层和水圈有关的氮循环进行了很好的研究。在鲜为人知的固体地球N循环中，板块构造在地球历史的大部分时间里调节了地表和深层水库之间的N通量，影响了地球N在千年时间尺度上的整体分布。因此，在俯冲过程中输送到地球深处，然后在火山活动和排气过程中返回地表的氮(N)的质量平衡至关重要，但效率估计是高度可变的。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N正以不同的数量被隔离在地球深处，这可能反映了诸如俯冲板块组成或俯冲条件等因素。深部、特征较差的N气藏的候选者包括中下陆壳、陆下地幔、弧前至弧下地幔或更深的地幔(即更深的上地幔、过渡带或下地幔)。这突显了对适当样品进行氮测量的必要性，以及对这些储集层中氮行为的彻底限制。将提供在俯冲带弧前到弧下区域内氮(N)分布和处理的新的关键约束。首先，将对富含沉积物和蛇纹岩的混杂岩和矿物进行一些首次的氮成分测量，以表征在弧前处理过程中氮的分布。其次，将进行相平衡实验，以评估主要含N矿物的稳定性，并测量混合基质材料上N熔体/流体-矿物分配系数作为几个因素(压力、温度、氧逸度、氯含量和部分熔体组成)的函数，以跟踪在弧下深度板坯脱水和部分熔化期间的N行为。拟议研究的数据以及以前研究的数据将用于量化从弧前输送到弧下加工带的N的数量，这些N赋存于哪些矿物中，以及它如何因主要岩性(沉积物或蛇纹岩)而变化。然后将量化在弧下处理过程中从板材释放多少N，以及在不同热状态的俯冲带中隔离在弧下地幔中有多少N。这些将构成对N行为的新限制，可以应用于地球历史上的俯冲制度。因此，它还将用于解决氮在耦合的固体地球-大气系统中的反馈和演化问题。这项提案支持亚利桑那大学(UA)和南加州大学(USC)的两名早期职业女性PI、两名研究生和两名+本科生。为了加强合作和扩大参与，PIS将为加州大学和南加州大学的学生提供一个关于深度波动自行车的联合虚拟研究生研讨会。UA的团队将在UA的Alfie Norville宝石和矿物博物馆开发一个关于高压-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。作为地球大气中最丰富的组成部分和生命的基本成分，氮(N)在当今大气、海洋、地壳和生物圈(统称为地表水库)中的行为得到了相对较好的研究。然而，地球表面水库的氮组成在整个地球历史上可能并不是一成不变的，这可能对地球早期的气候和生命的进化产生影响。氮通过板块构造，特别是俯冲带，在地球表面的储集层和深层之间进行交换。在俯冲带，地壳中的氮(以及来自大气、海洋和生物圈的成分)被拉入地幔或地球内部。地幔中的一部分氮通过火山脱气逃逸回大气和海洋。地表和内部之间的这种氮交换没有受到很好的限制，这项拟议的研究旨在填补这一知识鸿沟的一个关键组成部分。随着压力和温度的升高，将测量典型俯冲带岩石的N组分，以确定N的赋存位置。将在地幔条件下进行实验室实验，以了解一旦地壳进入地幔并融化时N的行为。我们的目标是最终利用我们的结果来估计地球地幔和大气的氮组成在地球历史上是如何变化的。这项提案支持亚利桑那大学(UA)和南加州大学(USC)的两名早期职业女性PI、两名研究生和两名+本科生。为了加强协作和扩大参与，私人投资促进机构将就拟议的主题举办一个联合虚拟毕业生研讨会，与会人员包括两所院校的学生。UA的团队将在UA的Alfie Norville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，这将是教育公众进行最先进研究的绝佳媒介。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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 fulfil 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 our 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.