Science2014-06-11 6:53 PM

来自莫哈韦陨石坑的火星陨石 The Source Crater of Martian Shergottite Meteorites

论文摘要 

已知的火星陨石大约有150个;对于这些陨石具体来自于火星上的什么地方,研究人员现在颇有把握。Stephanie Werner及其同事对火星表面的辉熔长石无球粒陨石的源头进行了搜寻。先前对辉熔长石无球粒陨石的研究提示,它们可能相当年轻,在某些陨石中它们是在不到6亿年前形成结晶的。但是Werner及其同事认为,所有的辉熔长石无球粒陨石源自火星的莫哈韦陨石坑——其宽度大约有34英里(55公里),并在大约43亿年前被置于其壳层之中。研究人员对这些陨石的矿物组成与该陨石坑中的具有类似地带的矿物组成进行了比对并提出,这些陨石的年龄与该陨石坑形成的年龄一致。有可能辉熔长石无球粒陨石来自某些最古老的火星地带,但它们因为诸如撞击熔融或因水而改变等“重新设定”的过程而显得较为年轻。

Abstract 

Absolute ages for planetary surfaces are often inferred by crater densities and only indirectly constrained by the ages of meteorites. We show that the <5 million-year-old and 55-km-wide Mojave Crater on Mars is the ejection source for the meteorites classified as shergottites. Shergottites and this crater are linked by their coinciding meteorite ejection ages and the crater formation age and by mineralogical constraints. Because Mojave formed on 4.3 billion-year-old terrain, the original crystallization ages of shergottites are old, as inferred by Pb-Pb isotope ratios, and the much-quoted shergottite ages of <600 million years are due to resetting. Thus, the cratering-based age determination method for Mars is now calibrated in situ, and it shifts the absolute age of the oldest terrains on Mars backward by 200 million years.

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