Another Look at Actinide Chemistry in Ca-Al-Rich Inclusions

摘要

Th/U values for Allende inclusions are often high relative to the accepted solar systemudaverage (3.8). In order to understand this fractionation, we are using fission track radiographyudto measure Th and U distributions in a group of Allende inclusions. We previously reportedud(Murrell and Burnett, 1984) on TS-23, a type Bl inclusion. Th and U were found to be enriched greater than 100 x’s Cl with Th/U = 3. 8 ± 0.l in the spinel + perovskite portionudof the rim on this inclusion. The Ti-Al-rich clinopyroxene band in this rim is also enrichedudin Th and U but with Th/U = 1. In the interior of TS-23, fassaite and melilite were foundudto contain 40 ppb and 90 ppb U, respectively, with little Th-U fractionation. Also, enrichmentsudof Th and U to about 80 x's Cl were observed along grain boundaries which containedudalteration products.