Correlated isotopic and chemical evidence for condensation origins of olivine in comet 81P/Wild 2 and in AOAs from CV and CO chondrites
Correlated isotopic and chemical evidence for condensation origins of olivine in comet 81P/Wild 2 and in AOAs from CV and CO chondrites
复制标题
DOI：
10.1016/j.gca.2020.09.036
复制
发表时间：
2021-01-15
影响因子：
5
通讯作者：
Kita, Noriko T.
中科院分区：
文献类型：
--
作者：
Fukuda, Kohei;Brownlee, Donald E.;Kita, Noriko T.
用二次离子质谱法（西姆斯）测定了81 P/Wild 2彗星5个橄榄石颗粒的镁稳定同位素比值和微量元素丰度。Wild 2橄榄石颗粒的δ Mg-25值仅表现出-1.0（+0.4）/（-）（0.）（5）千分率至0.6（+0.5）/（-0.6）千分率（2 σ）。这种变化可以简单地解释从镁同位素组成的地球和散装陨石的质量依赖分馏，这表明野生2橄榄石颗粒形成在镁同位素组成的南极洲水库。我们还确定了微量元素丰度，和O和Mg同位素比值的变形橄榄石聚集体（AOAs）从卡巴（CV3.1）和DOM 08006（CO3.01）碳质方解石的橄榄石颗粒。我们新的西姆斯微量元素数据显示，来自DOM 08006的AOA橄榄石中FeO含量均匀，低至0.05wt%，这表明AOA在太阳星云中形成的还原环境比以前认为的要多。此外，SIMS衍生的FeO含量的AOA橄榄石始终低于通过电子探针分析（类似于1重量%的FeO），表明可能的荧光从周围的基质材料和/或铁，镍金属AOA在电子探针分析。对于Mg同位素，AOA橄榄石显示出更负的质量相关分馏（-3.8 +/-0.5 ‰
Magnesium stable isotope ratios and minor element abundances of five olivine particles from comet 81P/Wild 2 were examined by secondary ion mass spectrometry (SIMS). Wild 2 olivine particles exhibit only small variations in delta Mg-25 values from -1.0(+0.4)/(-)(0.)(5)parts per thousand to 0.6(+0.5)/(-0.6)parts per thousand (2 sigma). This variation can be simply explained by mass-dependent fractionation from Mg isotopic compositions of the Earth and bulk meteorites, suggesting that Wild 2 olivine particles formed in the chondritic reservoir with respect to Mg isotope compositions. We also determined minor element abundances, and O and Mg isotope ratios of olivine grains in amoeboid olivine aggregates (AOAs) from Kaba (CV3.1) and DOM 08006 (CO3.01) carbonaceous chondrites. Our new SIMS minor element data reveal uniform, low FeO contents of similar to 0.05 wt% among AOA olivines from DOM 08006, suggesting that AOAs formed at more reducing environments in the solar nebula than previously thought. Furthermore, the SIMS-derived FeO contents of the AOA olivines are consistently lower than those obtained by electron microprobe analyses (similar to 1 wt% FeO), indicating possible fluorescence from surrounding matrix materials and/or Fe,Ni-metals in AOAs during electron microprobe analyses. For Mg isotopes, AOA olivines show more negative mass-dependent fractionation (-3.8 +/- 0.5 parts per thousand