Ubiquitous isotopic anomalies in Ti from normal Allende inclusions
Ubiquitous isotopic anomalies in Ti from normal Allende inclusions
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DOI：
10.1016/0012-821x(81)90155-2
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发表时间：
1981-04
影响因子：
5.3
通讯作者：
S. Niemeyer;G. W. Lugmair
中科院分区：
文献类型：
--
作者：
S. Niemeyer;G. W. Lugmair
新开发的高精度钛同位素分析技术已应用于陆地岩石以及粗粒和细粒阿连德包裹体。对三种陆地岩石的重复分析与钛金属标准具有极好的一致性（通常小于 2 × 10−4 偏差）。这里研究的所有七个阿连德夹杂物先前均被确定含有同位素正常的 Nd 和/或 Sm，这表明没有一个属于一小群特殊的夹杂物，称为 FUN 夹杂物。然而，每个夹杂物在 50Ti 时都显示出明显可分辨的过量，其中 5 个夹杂物的 ε(50/46) [与 Ti 标准的偏差为 104 部分] 范围为 +7 至 +10，而两个粉红色细粒夹杂物则给出了 +15 和 +28 的较大过量。 6 个夹杂物在 47Ti/46Ti 处也表现出大于 2σ 的缺陷，平均值大于 -2 ε 单位。对辉石和黄长石分离物以及来自一个包裹体的大量样品的分析没有提供单一包裹体内钛同位素不平衡的证据。然而，辉石在所有样品中贡献了大部分钛的可能性使得这是一个相当不敏感的测试。这些正常阿连德夹杂物、两个先前分析的 FUN 夹杂物以及陆地样品的 Ti 同位素丰度图形表示表明，至少需要三种不同的成分。正常阿连德夹杂物中 Ti 中广泛同位素异常的发现使 Ti 成为自氧以来第一个显示出这种同位素异质性的非稀有气体元素。对已发表的 Ti 同位素核合成起源的调查表明，这些包裹体中主要的 50 Ti 过量是由于大质量恒星核心内或核心附近静水燃烧过程中合成的同位素相对富集所致。这样的来源似乎与先前分析的元素中不存在同位素异常一致，并且可以通过其对 Cr、Fe 和 Ni 的富中子同位素及其各自的放射性衰变产物的类似过量的预测来进行测试。
A newly developed technique for high-precision isotopic analyses of titanium was applied to terrestrial rocks and course- and fine-grained Allende inclusions. Repeated analyses of three terrestrial rocks gave excellent agreement (usually less than 2 × 10−4deviations) with a Ti metal standard. All seven Allende inclusions studied here were previously determined to contain isotopically normal Nd and/or Sm, indicating that none belongs to a small group of peculiar inclusions, dubbed as FUN inclusions. Yet, every inclusion showed a clearly resolvable excess at50Ti, with ε(50/46) [deviation from the Ti standard in parts in 104] ranging from +7 to +10 for five of the inclusions, while two pink fine-grained inclusions gave larger excesses of +15 and +28. Six inclusions also exhibited greater than 2σ deficits at47Ti/46Ti, with an average value greater than −2 ε-units. Analyses of pyroxene and melilite separates and bulk samples from one inclusion furnished no evidence for Ti isotopic disequilibrium within a single inclusion. However, the possibility that pyroxene contributed the bulk of the Ti in all samples renders this a rather insensitive test. A graphical presentation of Ti isotopic abundances for these normal Allende inclusions, two previously analyzed FUN inclusions, and terrestrial samples demonstrates that at least three distinct components are required.The discovery of widespread isotopic anomalies in Ti fromnormalAllende inclusions establishes Ti as the first non-noble-gas element studied since oxygen to show such isotopic heterogeneity. A survey of published nucleosynthetic origins of Ti isotopes suggests that the dominant50Ti excesses in these inclusions are due to the relative enrichment of isotopes synthesized during hydrostatic burning in or near the core of a massive star. Such a source is seemingly consistent with the absence of isotopic anomalies in previously analyzed elements, and can be tested via its prediction of similar excesses for the neutron-rich isotopes of Cr, Fe and Ni and their respective radioactive decay products.