[PPS10-12] Origin and evolution of distinct isotopic variabilities for Sr, Mo, and Nd within inner and outer solar system
Keywords:CCs vs NCs, nucleosynthetic isotope anomalies, early solar system
We have investigated the variabilities of the isotopic compositions for Sr, Nd, and Mo in CC and NC meteorites [3-4]. The CCs are characterized to form an s-process mixing line in the µ95Mo–µ94Mo space. As opposed to this observation, the data of CCs deviate from the s-process mixing line in the µ84Sr–µ150Nd space. The inconsistency could be caused by the difference in the chemical characteristics of Mo (siderophile elements) and Sr-Nd (lithophile elements), specifically for the non-uniform distribution in some CCs (e.g., CV chondrites) of isotopically anomalous calcium-aluminum-rich inclusions (CAIs) in which large proportions of Sr and Nd are hosted. In fact, the data for CAI-subtracted CCs are plotted on the s-process mixing line in the µ84Sr-µ150Nd space. Therefore, the isotope variabilities for Sr, Nd, and Mo within the CCs indicate that s-process matter distributed heterogeneously throughout various chondritic components in the different outer solar system materials.
In contrast, the data for NCs are relatively homogeneous and plotted on the s-process mixing line in the µ84Sr-µ150Nd space. Unlike this observation, the NCs show Mo isotope variability in the µ95Mo-µ94Mo space. The Mo isotope variability for NCs suggests the presence of two end-member components in the NC reservoir (i.e., NC-A and NC-B), where the involvement of an additional nucleosynthetic component other than the s-process is required. Two models are proposed to account for the Mo isotopic variation within the NCs; (i) Mo isotopic composition of the NC region changed gradually from NC-A- to NC-B-like components as a function of the heliocentric distance, or (ii) a fractionation process involving chondritic matrix and metal, which most likely occurred locally in time and/or space, has generated the Mo isotope variability in the NC region.
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