A nebula setting as the origin for bulk chondrule Fe isotope variations in CV chondrites
A nebula setting as the origin for bulk chondrule Fe isotope variations in CV chondrites
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DOI：
10.1016/j.epsl.2010.05.029
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发表时间：
2010-08
影响因子：
5.3
通讯作者：
D. Hezel;A. Needham;R. Armytage;B. Georg;R. Abel;E. Kurahashi;B. Coles;M. Rehkämper;S. Russell
中科院分区：
文献类型：
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作者：
D. Hezel;A. Needham;R. Armytage;B. Georg;R. Abel;E. Kurahashi;B. Coles;M. Rehkämper;S. Russell
我们将Mokoia， Allende和Grosnaja球粒的Fe和Si同位素测量与显微计算机断层扫描相结合。十个莫科亚球粒含有0.9至11.8vol。%不透明相（金属+硫化物）和6阿连德球粒含有0.0至6.6vol。%不透明相。因此，许多球粒的铁同位素组成主要由其不透明相的铁同位素组成决定。我们研究了35个块状球粒的铁同位素。所研究的三颗陨石的δ56Fe范围各不相同，阿连德陨石的δ56Fe范围最大，为−0.82至+0.37‰。在Mokoia和Grosnaja的7个球粒中，有6个的Si同位素组成具有相似的δ29Si，约为- 0.12‰。Mokoia异常球粒的δ29Si值为+0.58‰。我们排除了同位素不均匀的球粒前体和不同同位素的球粒储层作为块状球粒中铁同位素变化的来源。我们得出结论，观测到的大块球粒铁同位素变化是在高尘埃密度的星云环境中蒸发和再冷凝过程的结果，这需要解释相对较低的同位素分馏。随后的母体蚀变略微叠加了这种增生前铁同位素的变化。
We combined micro computer tomography with Fe and Si isotope measurements of Mokoia, Allende and Grosnaja chondrules. Ten Mokoia chondrules contain 0.9 to 11.8vol.% opaque phases (metal+sulfide), and 6 Allende chondrules contain 0.0 to 6.6vol.% opaque phases. Hence, the Fe isotope composition of many chondrules is dominated by the Fe isotope composition of their opaque phases. We studied Fe isotopes of 35 bulk chondrules. The range is different for each of the three meteorites studied and largest for Allende with δ56Fe ranging from −0.82 to +0.37‰. Six out of seven chondrules analysed for their Si isotope composition in Mokoia and Grosnaja have similar δ29Si of around −0.12‰. One anomalous chondrule in Mokoia has a δ29Si of +0.58‰. We exclude isotopically heterogeneous chondrule precursors and different isotopic chondrule reservoirs as the source of the observed Fe isotope variation among bulk chondrules. We conclude that the observed bulk chondrule Fe isotope variation is the result of evaporation and re-condensation processes in a nebula setting with high dust densities, required to explain the comparatively low isotope fractionations. Subsequent parent body alteration slightly overprinted this pre-accretionary Fe isotope variation.