Re-Os geochronology and abundances of highly siderophile elements in ancient lunar impact rocks

高亲铁元素（HSE）在硅酸盐土中的过剩丰度最常见的原因是地球核形成后原始星子的晚期增积。然而，硅酸盐土的HSE组成与已知的原始陨石不同，似乎需要地幔中残余的分馏成分或与原始陨石组成不同的晚期物质增生。与地球不同的是，月球表面保留了45亿到38亿年前晚期吸积的成分和年代记录。最近对与大型盆地形成影响有关的月球撞击岩的研究为早期月球撞击事件的详细组成和时间提供了新的限制。这些仍然非常有限的数据表明，从古代撞击熔融岩中鉴定出的一些主要撞击物成分的混合物可以解释硅酸盐土的HSE成分。地球和月球的接近使这个假设很有吸引力，然而，它需要更多的数据来证实。这些撞击可能早于39 - 38亿年前假定的晚期重轰击时期。该项目将使用古代月球撞击岩石来验证一些假设，这些假设解决了早期地月系统中晚期吸积的组成和时间等主要问题。

The excess abundances of highly siderophile elements (HSE) in the silicate earth are most commonly attributed to a late veneer of primitive planetesimals that were accreted after formation of the earths core. The HSE composition of the silicate earth, however, is unlike known primitive meteorites, and seems to require either a residual fractionated component in the mantle or late accretion of material that differs from the composition of primitive meteorites. In contrast to earth, the lunar surface retains a compositional and chronological record of late accretion, 4.5 to 3.8 billion years ago. Recent work on lunar impact rocks that are related to the large basin forming impacts has provided new constraints on the detailed composition and timing of early lunar impact events. These, still very limited, data suggest that a mixture of some of the major impactor compositions identified from ancient impact melt rocks can explain the HSE composition of the silicate earth. The proximity of Earth and Moon make this hypothesis attractive, however, it needs to be substantiated with additional data. These impacts may predate the period of the presumed late heavy bombardment 3.9-3.8 billion years ago. This project will use ancient lunar impact rocks to test hypotheses that address the main questions of composition and timing of late accretion in the early Earth-Moon system.