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首页> 美国卫生研究院文献>Proceedings of the National Academy of Sciences of the United States of America >Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System
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Uranium isotope compositions of the basaltic angrite meteorites and the chronological implications for the early Solar System

机译：玄武质天使陨石的铀同位素组成及其对早期太阳系的年代学意义

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Events occurring within the first 10 million years of the Solar System’s approximately 4.5 billion-year history, such as formation of the first solids, accretion, and differentiation of protoplanetary bodies, have determined the evolutionary course of our Solar System and the planetary bodies within it. The application of high-resolution chronometers based on short-lived radionuclides is critical to our understanding of the temporal sequence of these critical events. However, to map the relative ages from such chronometers onto the absolute time scale, they must be “anchored” to absolute ages of appropriate meteoritic materials using the high-precision lead–lead (Pb–Pb) chronometer. Previously reported Pb–Pb dates of the basaltic angrite meteorites, some of which have been used extensively as time anchors, assumed a constant 238U/235U ratio (= 137.88). In this work, we report measurements of 238U/235U ratios in several angrites that are distinct from the previously assumed value, resulting in corrections to the Pb–Pb ages of ≥1 million years. There is no resolvable variation in the 238U/235U ratio among the angrite bulk samples or mineral separates, suggesting homogeneity in the U isotopic composition of the angrite parent body. Based on these measurements, we recalculated the Pb–Pb age for the commonly used anchor, the D’Orbigny angrite, to be 4563.37 ± 0.25 Ma. An adjustment to the Pb–Pb age of a time anchor (such as D’Orbigny) requires a corresponding correction to the “model ages” of all materials dated using that anchor and a short-lived chronometer. This, in turn, has consequences for accurately defining the absolute timeline of early Solar System events.
机译：在太阳系大约45亿年历史的前一千万年中发生的事件，例如初固体的形成，增生和原行星体的分化，决定了太阳系及其内部行星体的演化过程。 。基于寿命短的放射性核素的高分辨率天文钟的应用对于我们理解这些关键事件的时间顺序至关重要。但是，要将此类天文钟的相对年龄映射到绝对时间刻度上，必须使用高精度铅-铅（Pb-Pb）天文钟将它们“锚定”到适当的气象材料的绝对年龄。先前报道的玄武质天使陨石的Pb–Pb日期，其中一些已被广泛用作时间锚点，假定 238 U / 235 U比率恒定（= 137.88） 。在这项工作中，我们报告了在与先前假定值不同的几个角度中测量 238 U / 235 U比的结果，从而校正了Pb-Pb年龄≥一百万年。角铁块大块样品或矿物分离物中的 238 U / 235 U比值没有可分辨的变化，表明角铁母体的U同位素组成均匀。根据这些测量，我们重新计算了常用锚点D'Orbigny天使的Pb-Pb年龄为4563.37±0.25 Ma。要调整时间锚点（例如D’Orbigny）的Pb-Pb年龄，需要对使用该锚点和短时计的所有材料的“模型年龄”进行相应的校正。反过来，这对准确定义早期太阳系事件的绝对时间表具有影响。

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