Nitrogen solubility in upper mantle minerals
Nitrogen solubility in upper mantle minerals
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DOI：
10.1016/j.epsl.2013.07.013
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发表时间：
2013-09-01
影响因子：
5.3
通讯作者：
Keppler, Hans
中科院分区：
文献类型：
--
作者：
Li, Yuan;Wiedenbeck, Michael;Keppler, Hans
氮的溶解度在上地幔矿物镁橄榄石，透辉石，顽火辉石和镁铝榴石已被量化的西姆斯测量氮饱和，合成样品。晶体在由Ni-NiO、Co-CoO和Fe-FeO缓冲的N-15-H-O流体中在1000-1300 ℃和15-35 kbar下在活塞缸装置中生长。氮在矿物中的溶解度受温度、压力、矿物组成，特别是氧逸度的影响很大。在所有由Ni-NiO或Co-CoO缓冲的晶体中，氮在非常高的压力下低于检测限或至多几μ g/g。在1100摄氏度/15千巴的温度下，用Fe-FeO缓冲的透辉石、顽火辉石和镁铝榴石中的氮浓度已被定量为5-24微克/克。在高温顽火辉石或含铝顽火辉石和透辉石中的Fe-FeO缓冲层中观察到高达100 μ g/g的非常高的氮溶解度。氮在镁橄榄石中的溶解度在Fe-FeO缓冲中也明显地随温度和压力而增加;在1300 ℃/35 kbar下获得10 ppm的最大溶解度。在还原条件下氮溶解度的强烈增强可能与氮溶解为NH 4+或N3-直接取代O2-有关。这两种机制都需要一些电荷补偿，与顽火辉石中Al含量对氮溶解度的增强一致。我们的研究结果表明，上地幔的还原下部具有很大的氮储存能力，可能储存的氮比现在的大气多20-50倍。因此，一些“失踪”的氮可能仍然保留在地球的深处，减少地幔。上地幔矿物和硅酸盐熔体之间的氮分配系数的计算结果表明，氧化的地幔源将失去几乎所有的氮在部分熔融，而在还原条件下，相当一部分的氮可以保留在残留的固体。在还原条件下，上地幔矿物中氮的高溶解度也表明，早期地球上岩浆海洋的凝固应该保留了大量的氮，与年轻的大气相比，年轻的上地幔中产生了更高的N/Ar和N/C比值。(C)2013 Elsevier B. V.保留所有权利。
Nitrogen solubility in the upper mantle minerals forsterite, diopside, enstatite and pyrope has been quantified by SIMS measurements of nitrogen-saturated, synthetic samples. The crystals were grown in a N-15-H-O fluid buffered by Ni-NiO, Co-CoO, and Fe-FeO, at 1000-1300 degrees C and 15-35 kbar in a piston cylinder apparatus. Nitrogen solubility in minerals is significantly affected by temperature, pressure, mineral composition and, in particular, by oxygen fugacity. Nitrogen in all crystals buffered by Ni-NiO or Co-CoO is below detection limit or at most a few mu g/g at very high pressures. Concentrations of 5-24 mu g/g nitrogen have been quantified in diopside, enstatite and pyrope buffered by Fe-FeO at 1100 degrees C/15 kbar. Very high nitrogen solubility up to 100 mu g/g is observed at the Fe-FeO buffer in enstatite at high-temperature or in Al-bearing enstatite and diopside. The nitrogen solubility in forsterite at the Fe-FeO buffer also clearly increases with temperature and pressure; a maximum solubility of 10 ppm is obtained at 1300 degrees C/35 kbar. The strong enhancement of nitrogen solubility under reducing conditions may be related to nitrogen dissolution as either NH4+ or as N3- directly replacing O2-. Both mechanisms require some charge compensation, consistent with the enhancement of nitrogen solubility with Al content in enstatite. Our results demonstrate that the reduced lower part of the upper mantle has a large nitrogen storage capacity, and may store similar to 20-50 times more nitrogen than the present atmosphere. Therefore, some 'missing' nitrogen may still be retained in the Earth's deep, reduced mantle. The calculated nitrogen partition coefficients between upper mantle minerals and silicate melt reveal that an oxidized mantle source would lose almost its entire nitrogen during partial melting, whereas under reducing conditions a considerable fraction of nitrogen could be retained in the residual solids. The high nitrogen solubility in upper mantle minerals at reducing conditions also suggests that solidification of the magma ocean on the early Earth should have retained significant nitrogen, yielding higher N/Ar and N/C ratios in the young upper mantle as compared to the young atmosphere. (C) 2013 Elsevier B.V. All rights reserved.