A nebula setting as the origin for bulk chondrule Fe isotope variations in CV chondrites

作者：Hezel Dominik C^*; Needham Andrew W; Armytage Ros; Georg Bastian; Abel Richard L; Kurahashi Erika; Coles Barry J; Rehkaemper Mark; Russell Sara S

来源：Earth and Planetary Science Letters, 2010, 296(3-4): 423-433.

DOI：10.1016/j.epsl.2010.05.029

• Fe isotopes
• Si isotopes
• micro-CT
• chondrules
• Solar nebula

We combined micro computer tomography with Fe and Si isotope measurements of Mokoia, Allende and Grosnaja chondrules. Ten Mokoia chondrules contain 0.9 to 11.8 vol.% opaque phases (metal + sulfide), and 6 Allende chondrules contain 0.0 to 6.6 vol.% 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 delta(56)Fe ranging from -0.82 to + 0.37%.. Six out of seven chondrules analysed for their Si isotope composition in Mokoia and Grosnaja have similar delta(29)Si of around -0.12%.. One anomalous chondrule in Mokoia has a delta(29)Si 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.

• 出版日期2010-8-1