Diffusive fractionation of carbon isotopes in 纬-Fe: Experiment, models and implications for early solar system processes

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• 作者：Thomas Mueller ; E. Bruce Watson ; Dustin Trail ; Michael Wiedenbeck ; James Van Orman ; Erik H. Hauri
• 刊名：Geochimica et Cosmochimica Acta
• 出版年：15 February, 2014
• 年：2014
• 卷：127
• 期：Complete
• 页码：57-66
• 全文大小：1092 K

文摘

Carbon is an abundant element of planets and meteorites whose isotopes provide unique insights into both organic and inorganic geochemical processes. The identities of carbonaceous phases and their textural and isotopic characters shed light on dynamical processes in modern Earth systems and the evolution of the early solar system. In meteorites and their parent bodies, reduced carbon is often associated with Fe-Ni alloys, so knowledge of the mechanisms that fractionate C isotopes in such phases is crucial for deciphering the isotopic record of planetary materials. Here we present the results of a diffusion-couple experiment in which cylinders of polycrystalline Fe containing 11,500 and 150 渭g/g of C were juxtaposed at 1273 K and 1.5 GPa for a duration of 36 min. Diffusion profiles of total C concentration and ¹³C/¹²C were measured by secondary ion mass spectrometry (SIMS). The elemental diffusivity extracted from the data is 鈭?.0 脳 10^鈭?1 m² s^鈭?, where ¹³C/¹²C was observed to change significantly along the diffusion profile, reflecting a higher diffusivity of ¹²C relative to ¹³C. The maximum isotopic fractionation along the diffusion profile is 鈭?0-40鈥? The relative diffusivities (D) of the carbon isotopes can be related to their masses (M) by ; the exponent 尾 calculated from our data has a value of 0.225 卤 0.025. Similarly high 尾 values for diffusion of other elements in metals have been taken as an indication of interstitial diffusion, so our results are consistent with C diffusion in Fe by an interstitial mechanism. The high 尾-value reported here means that significant fractionation of carbon isotopes in nature may arise via diffusion in Fe(-Ni) metal, which is an abundant component of planetary interiors and meteorites.