Nitrogen partitioning between silicate phases and aqueous fluid depends on concentration
Nitrogen partitioning between silicate phases and aqueous fluid depends on concentration
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氮在硅酸盐相和水性流体之间的分配取决于浓度
DOI：
10.1016/j.gca.2023.05.017
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发表时间：
2023
影响因子：
5
通讯作者：
Cottrell, Elizabeth
中科院分区：
文献类型：
--
作者：
Jackson, Colin R.M.;Cottrell, Elizabeth
氮在地质系统中的分布受其在硅酸盐(矿物和熔体)和流体之间的分配的调节。在地质适用的氧逸度、压力和温度下，氮可以是多种形态的，氮与还原的氮化物(N−3)共存。非极性、中性的物种，包括氮，倾向于在流体中浓缩，而带电的氮化物物种更倾向于在硅酸盐相中浓缩。N2转化为单N原子氮化物物种的化学计量学表明，氮的形态可能取决于它的浓度，这导致了氮在硅酸盐和液体相之间的分配也取决于浓度的假设，这可能会偏向先前在掺杂体系中的实验工作，并影响氮在地质体系中的行为。为了验证这一假设，我们完成了一系列高压(∼1.75 GPA，800°C)实验，使矿物、熔体和流体与不同的氮浓度(3.1-17.1wt%N)反应。我们的结果表明，随着氮浓度在自然范围内的降低，矿物/熔体和熔体/流体分配的数量级增加。例如，在恒定的PT条件下，将N浓度从2500降低到2ppm，预测的D熔体/f L u i d N值将增加一个数量级以上。这意味着脱气岩浆或脱水板材中氮的损失是一个自我限制的过程，随着氮浓度的下降，这种过程的效率变得越来越低。尽管如此，氮在大气中仍然高度集中，大气从板岩和岩浆中排出的流体中接收氮。因此，为了保持富含氮的大气，我们认为温暖和氧化条件优于俯冲带，因为温暖的板岩在较低的压力下脱水，那里的氮更容易分配到流体中，而氧化条件也促进了氮分配到流体中。氮的浓度依赖性分配也有助于缓和板状物质脱水后N/K的初始变化，这可能有助于解释MORB地幔中相对均匀的N/K比。我们在氮浓度实验中补充了一系列温度(1.5-2 GPa750-950°C)。我们的温度系列数据显示，在高温下，氮有利于熔体而不是流体，而温度没有黑云母-流体分配的可分辨效应。
The distribution of nitrogen in geologic systems is modulated by its partitioning between silicate (mineral and melt) and fluid phases. Under geologically applicable oxygen fugacity, pressure, and temperatures, nitrogen can be multiply-speciated, with N 2 coexisting with reduced nitride (N− 3) species. Non-polar, neutral species, including N 2, tend to concentrate in fluids, while charged nitride species have a greater propensity to concentrate in silicate phases. The stoichiometry of converting N 2 to single N atom nitride species implies that nitrogen speciation may depend on its concentration, and this leads to the hypothesis that the partitioning of nitrogen between silicate and fluid phases also depends on concentration, potentially biasing prior experimental work in doped systems and influencing the behavior of nitrogen in geologic systems. To test this hypothesis, we have completed a series high pressure (∼ 1.75 GPa, 800° C) experiments that react minerals, melts, and fluids with variable nitrogen concentrations (3.1–17.1 wt% N). Our results imply order-of-magnitude-scale increases in mineral/melt and melt/fluid partitioning as nitrogen concentrations decrease within natural ranges. For example, decreasing the N concentration from 2500 to 2 ppm increases predicted D melt/f l u i d N values by over an order of magnitude at constant PT conditions. This means that loss of nitrogen from a degassing magma or dehydrating slab is a self-limiting process that becomes increasingly inefficient as nitrogen concentration falls. Despite this, nitrogen remains highly concentrated in the atmosphere, which receives N from fluids exsolved from slabs and magmas. To maintain a nitrogen-rich atmosphere we therefore suggest that warm and oxidizing conditions have prevailed over subduction zones because warm slabs dehydrate under lower pressures where nitrogen is more easily partitioned into fluids, and oxidizing conditions also promote nitrogen partitioning into fluids. Concentration-dependent partitioning of nitrogen will also serve to moderate any initial variations of N/K in slab materials upon dehydration, and this may help to explain the relatively uniform N/K ratio of MORB mantle. We supplement our nitrogen concentration experiments with a temperature series (1.5–2 GPa, 750–950° C). Our temperature series data reveal that at high temperature nitrogen favors melts over fluids, while temperature has no resolvable effect of biotite-fluid partitioning.
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影响因子：
5.3
作者：
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影响因子：
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作者：
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通讯作者：
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水性流体和硅酸盐熔体之间的氮分布
DOI：
--
发表时间：
2015
期刊：
影响因子：
--
作者：
Yuan Li;Ruifang Huang;M. Wiedenbeck;H. Keppler
通讯作者：
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