Nitrogen isotope fractionation during terrestrial core-mantle separation
Nitrogen isotope fractionation during terrestrial core-mantle separation
复制标题
陆地核幔分离过程中的氮同位素分馏
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
H. Keppler
中科院分区：
文献类型：
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作者：
Yanfen Li;B. Marty;S. Shcheka;L. Zimmermann;H. Keppler
陆地氮的起源和演化在很大程度上仍未解决。为了了解核-幔分离对陆地氮演化的潜在影响，在1.5~7.0 Gpa和1600~1800℃条件下，研究了富铁液态金属与硅酸盐熔体共存时的氮同位素分馏。结果表明，N、D、N、金属/硅酸盐的金属/硅酸盐分配系数在1~15 0之间，15N金属硅酸盐的氮同位素分馏δ为−3 5±1 7‰。计算表明，块体地球的δ^15N比现代地幔亏损得更多，而现今的δ^15N的−5‰可能是由一种顽辉岩的球粒陨石组成通过陆源核幔分离而来的，无论有没有碳质球粒陨石的加入。这些结果有力地支持了顽火辉石球粒陨石可能是地球形成的主要成分和陆地氮的主要来源的观点。此外，在深部还原地幔中，富铁金属相可能储存了大部分氮，共存硅酸盐的部分熔融可能产生δ^15N略为正的洋岛玄武岩(OIB)。
The origin and evolution of the terrestrial nitrogen remains largely unresolved. In order to understand the potential influence of core-mantle separation on terrestrial nitrogen evolution , experiments were performed at 1.5 to 7.0 GPa and 1600 to 1800 °C to study nitrogen isotope fractionation between coexisting liquid Fe-rich metal and silicate melt. The results show that the metal/silicate partition coefficient of nitrogen D N metal/silicate ranges from 1 to 150 and the nitrogen isotope fractionation δ^15N metal–silicate is −3.5 ± 1.7 ‰. Calculations show that the bulk Earth is more depleted in δ^15N than the present-day mantle, and that the present-day mantle δ^15N of −5 ‰ could be derived from an enstatite chondrite composition via terrestrial core-mantle separation, with or without the addition of carbonaceous chondrites. These results strongly support the notion that enstatite chondrites may be a main component from which the Earth formed and a main source of the terrestrial nitrogen. Moreover, in the deep reduced mantle, the Fe-rich metal phase may store most of the nitrogen, and partial melting of the coexisting silicates may generate oceanic island basalts (OIBs) with slightly positive δ^15N values.