Experimental quantification of the fractionation of Fe isotopes during metal segregation from a silicate melt
Experimental quantification of the fractionation of Fe isotopes during metal segregation from a silicate melt
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DOI：
10.1016/j.epsl.2006.06.037
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发表时间：
2006-08
影响因子：
5.3
通讯作者：
M. Roskosz;B. Luais;H. Watson;M. Toplis;C. Alexander;B. Mysen
中科院分区：
文献类型：
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作者：
M. Roskosz;B. Luais;H. Watson;M. Toplis;C. Alexander;B. Mysen
在1500 °C下，硅酸盐熔体和金属合金之间的Fe同位素分馏已经通过实验进行了量化。氧逸度和运行时间的影响进行了研究，以区分动力学和平衡分馏。提出了一种新的实验装置，在该装置中，由于氧化还原条件的改变，金属铁由硅酸盐熔体中的氧化铁还原而产生。该金属Fe从硅酸盐中物理去除并作为（Pt，Fe）合金螯合。使用多收集器ICP-MS方法的硅酸盐和金属馏分的散装分析与使用离子微探针的原位分析相结合。实验结果表明，在金属偏析过程中，Fe发生了显著的同位素分馏。在早期阶段的实验中，我们发现的动力学分馏的证据所造成的更快的扩散of 54 Fe沿着浓度梯度的合金。这一过程导致金属相的形成，与残余硅酸盐相比，金属相的同位素较轻（金属硅酸盐分馏高达−2.35‰/a.m.u.）。这些数据被用来量化的铁的每种同位素的扩散系数的差异，提供了一种手段来预测Fe在金属合金中的扩散过程中的Fe同位素分馏。另一方面，这种状态本质上是短暂的，在超液相线温度下，系统迅速达到同位素平衡状态，其中金属比硅酸盐熔体的同位素重约+0.2 ~0.15 ‰/a.m.u.这些结果与在天然样品中观察到的变化范围一致。这些动力学和平衡数据提供了一个实验框架，以了解在高温下形成的火成岩和陨石材料，特别是铁和帕拉斯陨石之间观察到的变化。
Fractionation of Fe isotopes between a silicate melt and metallic alloys has been quantified experimentally at 1500 °C. The effects of oxygen fugacity and run duration have been investigated to distinguish between kinetic and equilibrium fractionations. A new experimental setup is presented, in which metallic Fe is produced by reduction of oxidized iron from a silicate melt due to a change of redox conditions. This metallic Fe is physically removed from the silicate and sequestered as a (Pt,Fe) alloy. Bulk analyses of the silicate and metallic fractions using multi-collector ICP-MS methods are coupled with in situ analyses using an ion microprobe. Experimental results indicate that significant isotopic fractionation of Fe occurs during metal segregation. During the early stages of the experiments, we find evidence for kinetic fractionation caused by faster diffusion of54Fe along concentration gradients in the alloy. This process leads to the formation of a metallic phase which is isotopically light compared to the residual silicate (metal–silicate fractionation up to −2.35‰/a.m.u.). The data are used to quantify the difference in diffusion coefficient of each isotope of iron, providing a means to predict Fe isotope fractionation during Fe diffusion in metallic alloys. On the other hand, this state of affairs is transient in nature, and at superliquidus temperature, the systems rapidly reach a state of isotopic equilibrium in which the metal is isotopically heavier than the silicate melt by about +0.2±0.15‰/a.m.u. These results are consistent with the range of variation observed in natural samples. These kinetic and equilibrium data provide an experimental framework to understand the observed variability among igneous and meteoritic materials formed at high temperature, particularly for iron and pallasite meteorites.