Fukuyama Ko, Kagi Hiroyuki, Inoue Toru, Kakizawa Sho, Shinmei Toru, Hishita Shunichi, Takahata Naoto, Sano Yuji
Geochemical Research Center, Graduate School of Science, The University of Tokyo, Hongo, Tokyo, 113-0033, Japan.
Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8526, Japan.
Sci Rep. 2020 Jul 2;10(1):10897. doi: 10.1038/s41598-020-67621-2.
Nitrogen is a crucial volatile element in the early Earth's evolution and the origin of life. Despite its importance, nitrogen's behavior in the Earth's interior remains poorly understood. Compared to other volatile elements, nitrogen is depleted in the Earth's atmosphere (the so-called "missing nitrogen"), calling for a hidden deep reservoir. To investigate nitrogen's behavior in the deep Earth including how the reservoir formed, high-pressure and high-temperature experiments were conducted at 28 GPa and 1,400-1,700 °C. To reproduce the conditions in the lower mantle, the redox was controlled using a Fe-FeO buffer. We observed that depending on the temperature conditions, stishovite can incorporate up to 90-404 ppm nitrogen, experimentally demonstrating that stishovite has the highest nitrogen solubility among the deep mantle minerals. Stishovite is the main mineral component of subducted nitrogen-rich sedimentary rocks and eroded continental crust that are eventually transported down to the lower mantle. Our results suggest that nitrogen could have been continuously transported into the lower mantle via subduction, ever since plate tectonics began.
氮是地球早期演化和生命起源中一种至关重要的挥发性元素。尽管其很重要，但氮在地球内部的行为仍知之甚少。与其他挥发性元素相比，氮在地球大气中含量较低（即所谓的“缺失的氮”），这表明存在一个隐藏的深部储库。为了研究氮在地球深部的行为，包括储库如何形成，我们在28吉帕斯卡和1400 - 1700摄氏度的条件下进行了高温高压实验。为了重现下地幔的条件，使用铁 - 氧化亚铁缓冲剂来控制氧化还原状态。我们观察到，根据温度条件，斯石英可容纳高达90 - 404 ppm的氮，实验证明斯石英在深部地幔矿物中具有最高的氮溶解度。斯石英是俯冲的富氮沉积岩和被侵蚀的大陆地壳的主要矿物成分，这些物质最终会被输送到下地幔。我们的结果表明，自板块构造开始以来，氮可能一直通过俯冲作用持续被输送到下地幔。
