Grain boundary mobility of carbon in Earth's mantle: A possible carbon flux from the core
Grain boundary mobility of carbon in Earth's mantle: A possible carbon flux from the core
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DOI：
10.1073/pnas.0710806105
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发表时间：
2008-06
期刊：
影响因子：
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通讯作者：
Leslie A. Hayden;E. Watson
中科院分区：
文献类型：
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作者：
Leslie A. Hayden;E. Watson
碳在地球地幔中的重要性远远超过了其1000 - 4000 ppm的适度丰度。碳是关键的陆地挥发物（CO，CO2，CH 4）的组成部分，它形成钻石，它也可能有助于硅酸盐地球的整体电气特性。与地幔相比，地球金属核的碳含量可能相当高（约15%），这增加了地核在地质时期向地幔提供碳的可能性。这一过程的可解释性部分取决于固体地幔中碳原子的流动性。地幔矿物的晶界可能是碳迁移的快速通道，也可能是碳富集和储存的局部场所。在这里，我们报告的碳通过多晶方镁石（MgO）和橄榄石（[Mg，Fe] 2SiO 4）的晶界扩散的实验研究的结果，通过确定石墨源和金属汇（Ni或Fe）分离的多晶材料之间的固溶体形成的程度。实验材料在1，373 - 1，773 K和1.5-2.5 GPa压力下退火。计算出的扩散率范围高达10−11 m2·s−1，足以在地球年龄的地质学上显著的长度尺度（10 km）上进行传输。碳在晶界上的流动性和富集也可以解释上地幔岩石的高电导率，并可能导致C-H-O挥发物的形成，通过核源C与俯冲带中再循环的H2O的相互作用。
The importance of carbon in Earth's mantle greatly exceeds its modest abundance of ≈1,000–4,000 ppm. Carbon is a constituent of key terrestrial volatiles (CO, CO2, CH4), it forms diamonds, and it may also contribute to the bulk electrical properties of the silicate Earth. In contrast to that of the mantle, the carbon content of Earth's metallic core may be quite high (≈5 wt %), raising the possibility that the core has supplied carbon to the mantle over geologic time. The plausibility of this process depends in part upon the mobility of carbon atoms in the solid mantle. Grain boundaries of mantle minerals could represent fast pathways for transport as well as localized sites for enrichment and storage of carbon. Here, we report the results of an experimental study of grain-boundary diffusion of carbon through polycrystalline periclase (MgO) and olivine ([Mg,Fe]2SiO4) that were obtained by determining the extent of solid solution formation between a graphite source and a metal sink (Ni or Fe) separated by the polycrystalline materials. Experimental materials were annealed at 1,373–1,773 K and 1.5–2.5 GPa pressure. Calculated diffusivities, which range up to 10−11 m2·s−1, are fast enough to allow transport over geologically significant length scales (≈10 km) over the age of the Earth. Mobility and enrichment of carbon on grain boundaries may also explain the high electrical conductivity of upper mantle rocks, and could result in the formation of C-H-O volatiles through interactions of core-derived C with recycled H2O in subduction zones.