Nucleosynthetic sources and the age of the solar system: U isotope variations in meteorite components

核合成来源和太阳系的年龄：陨石成分中的 U 同位素变化

• 批准号: 145777827
• 负责人: Professor Dr. Stefan Weyer, Ph.D.
• 金额: --
• 依托单位: Institut für Mineralogie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2012-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/145777827?language=en
• 关键词: Nucleosynthetic; sources; age; solar; system

We propose to investigate the U isotope composition (235U/238U) of meteorites and their components, particularly that of CAIs. Uranium has two long-lived isotopes, 238U and 235U, which were produced by r-process nucleosynthesis. Its isotope composition in meteoritc materials is generally considered to be constant, which is an essential prerequisite for U-Pb and Pb-Pb dating. However, recent studies revealed significant (‰-range) U isotope variations on low-T terrestrial materials and preliminary investigations on meteoritic material have revealed that some CAIs display even more heterogeneous U isotope compositions. Such U isotope variations produce an offset on Pb-Pb ages of CAIs on the order of several Ma, if for these samples the commonly accepted U isotope composition (238U/235U = 137.88) is used for age calculations.In this study, (1) we plan to systematically investigate the U isotope composition of various groups of CAIs, mineral separates of such CAIs, and other meteoritic materials, such as leachates of bulk chondrites. (2) We plan to combine the U isotope compositions with Pb-Pb dating on the same CAIs, applying the individually analyzed U isotope composition (instead of a constant ratio of 137.88) for age calculations. (3) The measured U isotope ratios will be used to develop constraints on the possible source(s) of U isotope heterogeneities that may result from a) inherited nucleosynthetic anomalies, b) initial 247Cm excess or depletion, or c) chemical reactions that caused U isotope fractionation (similar to those observed for oceanic sediments on Earth).

我们建议研究陨石及其组分，特别是CAIs的U同位素组成（235 U/238 U）。铀有两种长寿命的同位素，238 U和235 U，它们是由r-过程核合成产生的。陨石中的铀同位素组成一般认为是恒定的，这是进行U-Pb和Pb-Pb定年的必要条件。然而，最近的研究表明，显着的（‰范围内）U同位素变化的低T陆地材料和陨石材料的初步调查表明，一些CAIs显示更异质U同位素组成。如果这些样品的普遍接受的U同位素组成（238 U/235 U = 137.88）进行年龄计算，本研究计划（1）系统地研究各类CAIs、CAIs矿物分离物和其他陨石物质的U同位素组成，例如散装垃圾的沥滤物。(2)我们计划将联合收割机的U同位素组成与Pb-Pb定年在同一个CAIs，应用单独分析的U同位素组成（而不是一个恒定的比率137.88）的年龄计算。(3)测量的铀同位素比将用于对铀同位素不均匀性的可能来源进行限制，这些不均匀性可能来自a）遗传性核合成异常，B）初始247 Cm过量或耗尽，或c）导致铀同位素分馏的化学反应（类似于在地球上的海洋沉积物中观察到的那些）。