Argon-39-argon-40 "ages" and trapped argon in Martian shergottites, Chassigny, and Allan Hills 84001
Argon-39-argon-40 "ages" and trapped argon in Martian shergottites, Chassigny, and Allan Hills 84001
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DOI：
10.1111/j.1945-5100.1999.tb01353.x
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发表时间：
1999-05-01
影响因子：
2.2
通讯作者：
Garrison, DLH
中科院分区：
文献类型：
--
作者：
Bogard, DD;Garrison, DLH
测量了经中子辐照的火星陨石夏斯蒂、艾伦山(Allan Hills)84001、Allan Hills 77005、大象Moraine(Eet)79001、Yamato(Y)793605、Shergoty、Zagami和Queen Alexandra Range(QUE)94201的Ar同位素丰度，以及ALH 77005的未辐照样品。Chassigny给出的Ar-39-Ar-40年龄为1.32+/-0.07Ga，与纳赫利特岩的放射性年龄相似。ALH 84001的Ar-39-Ar-40数据显示年龄在3.9Ga到4.3Ga之间。对这一年龄的更准确的定义需要详细地描述在ALH 84001中捕获的多个Ar组分和Ar-39反冲分布。所有六个硅铝榴石样品都显示出明显的Ar-39-Ar-40年龄，大大超过了其他同位素测年技术给出的类似于165-200 Ma的年龄范围。雪榴石似乎含有无处不在的Ar组分，这些成分来自火星大气、火星地幔，以及通常是陆地大气污染。Zagami长石也表明遗传的辐射成因Ar-40。这些数据分析表明，最近困在雪榴石中的火星大气成分的Ar-40/Ar-36比率可能低至1750，但不高于1900。这些比率低于维京报告的3000+/-500。火星地幔成分的Ar-40/Ar-36比值可能是
Argon-isotopic abundances were measured in neutron-irradiated samples of Martian meteorites Chassigny, Allan Hills (ALH) 84001, ALH 77005, Elephant Moraine (EET) 79001, Yamato (Y) 793605, Shergotty, Zagami, and Queen Alexandra Range (QUE) 94201, and in unirradiated samples of ALH 77005. Chassigny gives a Ar-39-Ar-40 age of 1.32 +/- 0.07 Ga, which is similar to radiometric ages of the nakhlites. Argon-39-Argon-40 data for ALH 84001 indicate ages between 3.9 and 4.3 Ga. A more precise definition of this age requires detailed characterization of the multiple trapped Ar components in ALH 84001 and of Ar-39 recoil distribution. All six shergottite samples show apparent Ar-39-Ar-40 ages substantially older than the similar to 165-200 Ma range in ages given by other isotope dating techniques. Shergottites appear to contain ubiquitous Ar components acquired from the Martian atmosphere, the Martian mantle, and commonly terrestrial atmospheric contamination. Zagami feldspar also suggests inherited radiogenic Ar-40. These data analyses indicate that the recent Martian atmospheric component trapped in shergottites has a Ar-40/Ar-36 ratio, possibly as low as similar to 1750 and no greater than similar to 1900. These ratios are less than the value of 3000 +/- 500 reported by Viking. The Ar-40/Ar-36 ratio for the Martian mantle component is probably