Nitrogen solubilities in bridgmanite (MgSiO₃) and periclase (MgO) determined from high-pressure and high-temperature experiments and SIMS analysis: formation of the deep nitrogen reservoir through solidification of magma ocean

Abstract

Nitrogen, the main component of the Earth's atmosphere, is a geochemically important volatile element, but its behavior in the Earth's interior remains still unclear. Although previous studies suggested that mantle minerals can store nitrogen in the Earth's deep interior from high-pressure and high-temperature experiments (Li et al., 2013; Yoshioka et al., 2018), there are few experimental reports about nitrogen solubilities in the lower-mantle minerals.In this study, we investigated the nitrogen incorporation to bridgmanite (MgSiO3) and periclase (MgO), the major minerals in the lower mantle. High-pressure and high-temperature experiments were conducted using multi-anvil apparatus installed at Geodynamics Research Center. For analysis of nitrogen in recovered samples, we used high-resolution SIMS installed at Centre de Recherches Pétrographiques et Géochimiques and NanoSIMS installed at Atmosphere and Ocean Research Institute. 14N+-implanted standards for NanoSIMS were prepared at National Institute for Materials Science.We found that the maximum nitrogen solubility in bridgmanite was 5.7 ppm and almost no nitrogen dissolves into periclase. In the solidification of magma ocean, the first crystallized bridgmanite can store nitrogen in the lower mantle, while the second crystallized periclase might trap nitrogen in the lower mantle.