Huang, D; Brodholt, J; Sossi, P; Li, Y; Murakami, M; (2022) Nitrogen Speciation in Silicate Melts at Mantle Conditions From Ab Initio Simulations. Geophysical Research Letters , 49 (7) , Article e2021GL095546. 10.1029/2021gl095546.

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Abstract

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.

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