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arXiv 2009.08684astro-ph.EP
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从单个球粒中的Cr-Ti-O同位素推断太阳吸积盘的早期演化

Early evolution of the solar accretion disk inferred from Cr-Ti-O isotopes in individual chondrules

Jonas M. Schneider, Christoph Burkhardt, Yves Marrocchi, Gregory A. Brennecka, Thorsten Kleine

摘要:

陨石球粒中的同位素异常是太阳吸积盘中混合和传输过程动力学的重要线索。这些异常已被解释为表明无论是盘范围内的球粒运输或球粒前体的局部异质性。然而,所有以前的研究都依赖于单一元素(Cr,Ti或O)的同位素数据,这无法区分陨石球粒同位素异常的来源和前体特征。在这里,我们获得了第一个合并的O,Ti和Cr同位素数据的顽火辉石,普通和碳质陨石的个别球粒。非碳质(NC)辉长岩球粒具有相对均匀的Δ 17 O、ε 50 Ti和ε 54 Cr,与其寄主辉长岩的成分相似。相比之下,来自碳质陨石(CC)的球粒具有更多变的成分。虽然分析的CC和NC球粒的成分可能重叠的ε 50 Ti,ε 54 Cr,或Δ 17 O,在多同位素空间中没有CC球粒图在NC陨石的成分领域,没有NC球粒图在CC陨石领域。因此,我们的数据揭示了一个基本的同位素之间的差异NC和CC球粒,这是不一致的整个磁盘之间的NC和CC水库球粒运输。相反,CC球粒之间的同位素变化反映了当地的前体不均匀性,这最有可能是由于NC样尘埃和化学上不同的尘埃成分之间的混合,这些成分与CAIs和AOA的同位素相似。相同的混合过程,但在更大的盘宽范围内,可能负责建立NC和CC水库的不同同位素组成,这代表了内外盘,分别

英文摘要:

Isotopic anomalies in chondrules hold important clues about the dynamics of mixing and transport processes in the solar accretion disk. These anomalies have been interpreted to indicate either disk-wide transport of chondrules or local heterogeneities of chondrule precursors. However, all previous studies relied on isotopic data for a single element (either Cr, Ti, or O), which does not allow distinguishing between source and precursor signatures as the cause of the chondrules isotope anomalies. Here we obtained the first combined O, Ti, and Cr isotope data for individual chondrules from enstatite, ordinary, and carbonaceous chondrites. We find that chondrules from non-carbonaceous (NC) chondrites have relatively homogeneous Δ17O, ε50Ti, and ε54Cr, which are similar to the compositions of their host chondrites. By contrast, chondrules from carbonaceous chondrites (CC) have more variable compositions. Although the compositions of the analyzed CC and NC chondrules may overlap for either ε50Ti, ε54Cr, or Δ17O, in multi-isotope space none of the CC chondrules plot in the compositional field of NC chondrites, and no NC chondrule plots within the field of CC chondrites. As such, our data reveal a fundamental isotopic difference between NC and CC chondrules, which is inconsistent with a disk-wide transport of chondrules across and between the NC and CC reservoirs. Instead, the isotopic variations among CC chondrules reflect local precursor heterogeneities, which most likely result from mixing between NC-like dust and a chemically diverse dust component that was isotopically similar to CAIs and AOAs.The same mixing processes, but on a larger, disk-wide scale, were likely responsible for establishing the distinct isotopic compositions of the NC and CC reservoirs, which represent in inner and outer disk, respectively.

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