Huang Weihua, Yang Yan, Li Yuan, Xu Zheng, Yang Shuiyuan, Guo Shengbin, Xia Qunke
Key Laboratory of Geoscience Big Data and Deep Resource of Zhejiang Province, School of Earth Sciences, Zhejiang University, Hangzhou, China.
State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China.
Nat Commun. 2024 Aug 14;15(1):6998. doi: 10.1038/s41467-024-51524-1.
The fate of sedimentary nitrogen during subduction is essential for understanding the origin of nitrogen in the deep Earth. Here we study the behavior of nitrogen in slab sediments during the phengite to K-hollandite transition at 10-12 GPa and 800-1100 °C. Phengite stability is extended by 1-3 GPa in the nitrogen (NH)-bearing system. The phengite-fluid partition coefficient of nitrogen is 0.031 at 10 GPa, and K-hollandite-fluid partition coefficients of nitrogen range from 0.008 to 0.064, showing a positive dependence on pressure but a negative dependence on temperature. The nitrogen partitioning data suggest that K-hollandite can only preserve ~43% and ~26% of the nitrogen from phengite during the phengite to K-hollandite transition along the cold and warm slab geotherms, respectively. Combined with the slab sedimentary nitrogen influx, we find that a maximum of ~1.5 × 10kg/y of nitrogen, representing ~20% of the initial sedimentary nitrogen influx, could be transported by K-hollandite to the lower mantle. We conclude that slab sediments may have contributed less than 15% of the lower mantle nitrogen, most of which is probably of primordial origin.
俯冲过程中沉积氮的命运对于理解深部地球中氮的起源至关重要。在此，我们研究了在10 - 12吉帕和800 - 1100℃条件下，板片沉积物中氮在多硅白云母向钾硬锰矿转变过程中的行为。在含氮（NH）体系中，多硅白云母的稳定性在压力上提高了1 - 3吉帕。10吉帕时，氮在多硅白云母 - 流体间的分配系数为0.031，而氮在钾硬锰矿 - 流体间的分配系数范围为0.008至0.064，显示出对压力呈正相关，对温度呈负相关。氮的分配数据表明，沿着冷和热的板片地热梯度，在多硅白云母向钾硬锰矿转变过程中，钾硬锰矿只能分别保留多硅白云母中约43%和约26%的氮。结合板片沉积氮的流入量，我们发现钾硬锰矿最多可将约1.5×10千克/年的氮输送到下地幔，这约占初始沉积氮流入量的20%。我们得出结论，板片沉积物对下地幔氮的贡献可能小于15%，其中大部分氮可能起源于原始物质。
