Nitrogen Speciation in Silicate Melts at Mantle Conditions From Ab Initio Simulations
Nitrogen Speciation in Silicate Melts at Mantle Conditions From Ab Initio Simulations
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DOI：
10.1029/2021gl095546
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发表时间：
2022-03
影响因子：
5.2
通讯作者：
D. Huang;J. Brodholt;P. Sossi;Y. Li;M.Murakami
中科院分区：
文献类型：
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作者：
D. Huang;J. Brodholt;P. Sossi;Y. Li;M.Murakami
氮 (N) 是大气的主要成分，但也是硅酸盐地球中的微量成分。在地球早期分化过程中，这些储层中的初始库存需要了解岩浆中的氮形态，例如，它是否以 N2 的形式脱气，或者以 N3− 的形式封存在硅酸盐熔体中，而 N3− 在整个地幔体系中基本上不受约束。在这里，我们通过从头计算检查不同 P-T 氧化还原条件下无水和含水热解熔体中的 N 物种，并发现从常压到较低地幔压力的氧化条件下的 N-N 键合。在还原条件下，N 与硅酸盐网络相互作用或形成 N-H 键，具体取决于氢的可用性。氮形态形成的氧化还原控制在包含可能的岩浆海洋深度的 P-T 空间中被证明是有效的。最后，如果地球在其吸积结束时由日益氧化的物质吸积，则可能会产生富含氮的次生大气并持续存在，直到后来的撞击。
Nitrogen (N) is a major ingredient of the atmosphere, but a trace component in the silicate Earth. Its initial inventory in these reservoirs during Earth's early differentiation requires knowledge of N speciation in magmas, for example, whether it outgasses as N2 or is sequestered in silicate melts as N3−, which remains largely unconstrained over the entire mantle regime. Here we examine N species in anhydrous and hydrous pyrolitic melts at varying P‐T‐redox conditions by ab‐initio calculations, and find N‐N bonding under oxidizing conditions from ambient to lower mantle pressures. Under reducing conditions, N interacts with the silicate network or forms N‐H bonds, depending on the availability of hydrogen. Redox control of N speciation is demonstrated valid over a P‐T space encompassing probable magma ocean depths. Finally, if the Earth accreted from increasingly oxidized materials toward the end of its accretion, an N‐enriched secondary atmosphere might be produced and persist until later impacts.