Non-chondritic iron isotope ratios in planetary mantles as a result of core formation
Non-chondritic iron isotope ratios in planetary mantles as a result of core formation
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DOI：
10.1038/ngeo2896
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发表时间：
2017-04-01
影响因子：
18.3
通讯作者：
Shahar, Anat
中科院分区：
文献类型：
--
作者：
Elardo, Stephen M.;Shahar, Anat
铁同位素比率记录了早期太阳系行星形成和分化所涉及的物质和条件的信息。来自地球、月球、火星和小行星灶神星的样本显示铁同位素比率存在显著差异，但这些差异的来源仍然不确定。在这里，我们提出的实验表明，在预期的月球，火星和灶神星的行星核心形成的条件下，由于镍的存在，铁同位素在金属和硅酸盐之间发生断裂，并在同位素轻铁中富集了天体的地幔。然而，镍的影响在较高的温度下减弱：在预期的地核形成条件下，我们推断铁同位素的分馏很小。从我们的实验结果和现有的概念模型的岩浆海洋结晶和地幔部分熔融，我们发现，镍引起的分馏可以解释铁同位素的变化，发现在行星样品中没有调用星云或吸积过程。我们认为，近南极铁同位素比值的玄武岩从火星和灶神星，以及最原始的月球玄武岩，是通过熔融同位素轻地幔，而重的铁同位素比值的陆地洋底玄武岩是近南极地球地幔熔融的结果。
Information about the materials and conditions involved in planetary formation and differentiation in the early Solar System is recorded in iron isotope ratios. Samples from Earth, the Moon, Mars and the asteroid Vesta reveal significant variations in iron isotope ratios, but the sources of these variations remain uncertain. Here we present experiments that demonstrate that under the conditions of planetary core formation expected for the Moon, Mars and Vesta, iron isotopes fractionate between metal and silicate due to the presence of nickel, and enrich the bodies' mantles in isotopically light iron. However, the effect of nickel diminishes at higher temperatures: under conditions expected for Earth's core formation, we infer little fractionation of iron isotopes. From our experimental results and existing conceptual models of magma ocean crystallization and mantle partial melting, we find that nickel-induced fractionation can explain iron isotope variability found in planetary samples without invoking nebular or accretionary processes. We suggest that near-chondritic iron isotope ratios of basalts from Mars and Vesta, as well as the most primitive lunar basalts, were achieved by melting of isotopically light mantles, whereas the heavy iron isotope ratios of terrestrial ocean floor basalts are the result of melting of near-chondritic Earth mantle.