Lithium isotope compositions of chondrules, CAI and a dark inclusion from Allende and ordinary chondrites

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• 作者：Hans-Michael Seitz^a ; ^{h.m.seitz@em.uni-frankfurt.de} ; Jutta Zipfel^b ; Gerhard P. Brey^a ; Ulrich Ott^c ; ^d
• 关键词：lithium isotopes ; ordinary chondrites ; carbonaceous chondrites ; chondrules ; Ca&ndash ; Al-rich inclusions ; dark inclusions
• 刊名：Earth and Planetary Science Letters
• 出版年：2012
• 期刊代码：18_0012821x
• 类别：ph
• 出版时间：1 May, 2012
• 卷：329-330
• 期：Complete
• 页码：51-59
• 文件大小：773 K

摘要

Bulk carbonaceous and ordinary chondrites have distinct Li isotope compositions, indicating the existence of local reservoirs and distinct formation conditions in the early solar system. These differences may be also recorded in the components that compose chondrites. Here, Li concentrations and Li isotope compositions of 89 chondrules, 10 CAI and 1 dark inclusion (DI) from the Allende (CV3) meteorite and from 5 ordinary chondrites of low petrologic types Semarkona, Bishunpur, Saratov, Bjurb枚le and Bremerv枚rde are presented.

In general, chondrules have highly variable Li isotope compositions, ranging from 未⁷Li of 鈭?#xA0;8.5 to + 10鈥? whereby the mean isotope composition of chondrules separated from a single chondrite is slightly lighter than its bulk. Remarkable, however, are the differences in Li concentrations between bulk chondrite and chondrules. Of the entire set studied here, 98%of the chondrules have significantly lower Li abundances (in the range of 0.2 to 0.75 渭g/g) than their hosts (typically around 1.5 渭g/g). Our results indicate that Li elemental and isotopic fractionation has not occurred extensively during chondrule formation. Low, but highly variable Li abundances as well as the relatively large range in Li isotopes point to small-scale heterogeneities in the chondrule-forming reservoir. With respect to Li, such a non-chondritic reservoir is unique to all chondrules. The compositional differences in Li isotopes between bulk carbonaceous and ordinary chondrites (Seitz et al., 2007) are likely to be the result of mixing chondrules, CAI and matrix in different proportions.