Gerontology of the Allende meteorite
Gerontology of the Allende meteorite
复制标题
阿连德陨石的老年学
作者：
E. Jessberger;B. Dominik
在阿连德陨石中发现了几种元素的同位素组成，这些元素不可能是由于放射性、碎裂或分选过程造成的。这些同位素异常大多局限于富含难熔元素2的白色包裹体（富钙铝包裹体），并被认为是由预凝聚颗粒引入太阳系的。我们以前曾报道过来自Allende陨石的五个白色包裹体的复合样品的异常高K-Ar年龄4；由于在40ar - 39ar实验中，除了一小块用于薄片的夹杂物外，材料都是熔融的，所以无法直接验证这个单独的4800 Myr的结果。因此，我们开始在其他富钙铝包裹体中寻找古老的物质。从一种新型包裹体中提取的三个不同样本被证明并不比阿连德的大多数成分早，4510迈瑞（参考文献5）。一个小的白色夹杂物在几乎整个39Ar释放上形成了一个发育良好的40ar /39Ar平台，年龄为4500±20 Myr（参考文献6）。我们在这里报告了另外两个粗粒Allende包裹体的40ar - 39ar分析，显示年龄超过4,550 Myr。
IN the Allende meteorite several elements are found to have an isotopic composition that cannot be due to radioactive or spallation or fractionation processes1. These isotope anomalies are mostly confined to white inclusions enriched in refractory elements2(Ca–Al-rich inclusions) and are thought to be introduced into the Solar System by precondensed grains3. We have previously reported an anomalously high K–Ar age of a composite sample of five white inclusions from the Allende meteorite4; no direct verification of this lone-standing result of 4,800 Myr was possible because, with the exception of a small chip of one of the inclusions used for a thin section, the material was fused in the40Ar–39Ar experiment. We therefore began a search for old material in other Ca–Al-rich inclusions. Three different samples from a new type of inclusion proved to be no older than most of Allende's constituents, 4,510 Myr (ref. 5). A small white inclusion gave a well developed40Ar/39Ar plateau over almost the entire39Ar release, with an age of 4,500±20 Myr (ref. 6). We report here on the40Ar–39Ar analysis of two further coarsegrained Allende inclusions that showed ages in excess of 4,550 Myr.