Stable chromium isotopic composition of meteorites and metal-silicate experiments: Implications for fractionation during core formation
Stable chromium isotopic composition of meteorites and metal-silicate experiments: Implications for fractionation during core formation
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DOI：
10.1016/j.epsl.2015.11.026
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发表时间：
2016-02-01
影响因子：
5.3
通讯作者：
Halliday, A. N.
中科院分区：
文献类型：
--
作者：
Bonnand, P.;Williams, H. M.;Halliday, A. N.
我们提出了新的质量无关和质量依赖的陨石铬同位素组成测量双峰热电离质谱。据报道，与质量无关的Cr-53和Cr-54相对于体积硅酸盐土的差异很小，与先前发表的值非常相似。与普通和顽辉石球粒陨石相比，碳质球粒陨石的特征是Cr-54含量过量，这使得与质量无关的Cr同位素成为区分陨石群的有用工具。同样的样品也报道了质量依赖的稳定Cr同位素组成。碳质球粒陨石和普通球粒陨石在不确定度范围内相同，平均δ Cr-53值分别为-0.118 +/- 0.040和-0.143 +/- 0.074。最重的同位素组成记录为顽辉石球粒陨石和CO碳质球粒陨石，两者的化学成分都相对减少，这意味着一些稳定的Cr同位素分异与星周盘的氧化还原过程有关。球粒陨石的平均δ Cr-53值与同样由双尖峰测定的块状硅酸盐土（BSE）的估计误差范围内。球粒物质与BSE之间缺乏同位素差异，证明地球岩心形成过程中Cr同位素没有分选。我们还进行了一系列高压实验来研究金属和硅酸盐之间的稳定Cr同位素分馏，没有观察到明显的分馏，这与我们的陨石数据一致。无球粒陨石的质量相关Cr同位素数据表明，Cr同位素在岩浆分异过程中发生分异，因此需要进一步的工作来约束灶神星和火星地幔的Cr同位素组成。(C) 2015年作者。Elsevier B.V.出版
We present new mass independent and mass dependent Cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry. Small differences in both mass independent Cr-53 and Cr-54 relative to the Bulk Silicate Earth are reported and are very similar to previously published values. Carbonaceous chondrites are characterised by an excess in Cr-54 compared to ordinary and enstatite chondrites which make mass independent Cr isotopes a useful tool for distinguishing between meteoritic groups. Mass dependent stable Cr isotope compositions for the same samples are also reported. Carbonaceous and ordinary chondrites are identical within uncertainty with average delta Cr-53 values of -0.118 +/- 0.040 parts per thousand and -0.143 +/- 0.074 parts per thousand respectively. The heaviest isotope compositions are recorded by an enstatite chondrite and a CO carbonaceous chondrite, both of which have relatively reduced chemical compositions implying some stable Cr isotope fractionation related to redox processes in the circumstellar disk. The average delta Cr-53 values for chondrites are within error of the estimate for the Bulk Silicate Earth (BSE) also determined by double spiking. The lack of isotopic difference between chondritic material and the BSE provides evidence that Cr isotopes were not fractionated during core formation on Earth. A series of high-pressure experiments was also carried out to investigate stable Cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed, consistent with our meteorites data. Mass dependent Cr isotope data for achondrites suggest that Cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the Cr isotopic compositions of the mantles of Vesta and Mars. (C) 2015 The Authors. Published by Elsevier B.V.