The origin of Earth’s mantle nitrogen: primordial or early biogeochemical cycling?
The origin of Earth’s mantle nitrogen: primordial or early biogeochemical cycling?
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地幔氮的起源：原始或早期生物地球化学循环？
DOI：
10.1029/2021gc010295
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
H. J. Cleaves II
中科院分区：
文献类型：
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作者：
H. Kurokawa;M. Laneuville;Y. Li;N. Zhang;Y. Fujii;H. Sakuraba;C. Houser;H. J. Cleaves II
地球地幔中的氮（N）含量与其富氮大气中的含量相当。地幔N被认为是原始的或起源于后来的俯冲，但其起源尚未阐明。在这里，我们模型N分配在岩浆海洋阶段行星形成和随后的地球历史上的表面和地幔之间的循环使用氩（Ar）和N同位素作为示踪剂。Ar约束的分配模型表明，只有约10%的总N含量可以被困在固化地幔中，由于N的低溶解度的岩浆和低分配系数的矿物在氧化条件下的地球物理和地球化学研究的支持。对于原始起源的一个可能的解决方案是，地球在岩浆海洋凝固时的N大约是地球的10倍。我们表明，多余的N可以通过后期吸积过程中的冲击侵蚀去除。由N同位素约束的循环模型表明，地幔N可以来自有效的N俯冲，如果沉积N埋藏速率在早期地球上是现代地球的可比。如此高的氮埋藏率需要生物处理。最后，我们的模型提供了一种方法来区分这两种可能的起源与未来的分析的表面和地幔N同位素记录。
Earth's mantle nitrogen (N) content is comparable to that found in its N‐rich atmosphere. Mantle N has been proposed to be primordial or sourced by later subduction, yet its origin has not been elucidated. Here we model N partitioning during the magma ocean stage following planet formation and the subsequent cycling between the surface and mantle over Earth history using argon (Ar) and N isotopes as tracers. The partitioning model, constrained by Ar, shows that only about 10% of the total N content can be trapped in the solidified mantle due to N's low solubility in magma and low partitioning coefficients in minerals in oxidized conditions supported from geophysical and geochemical studies. A possible solution for the primordial origin is that Earth had about 10 times more N at the time of magma ocean solidification. We show that the excess N could be removed by impact erosion during late accretion. The cycling model, constrained by N isotopes, shows that mantle N can originate from efficient N subduction, if the sedimentary N burial rate on early Earth is comparable to that of modern Earth. Such a high N burial rate requires biotic processing. Finally, our model provides a methodology to distinguish the two possible origins with future analysis of the surface and mantle N isotope record.