A Two‐Step K‐Ar Experiment on Mars: Dating the Diagenetic Formation of Jarosite from Amazonian Groundwaters
A Two‐Step K‐Ar Experiment on Mars: Dating the Diagenetic Formation of Jarosite from Amazonian Groundwaters
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火星上的两步 K-Ar 实验：确定亚马逊地下水中黄钾铁矾的成岩形成年代
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
R. Navarro
中科院分区：
文献类型：
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作者：
Peter E. Martin;K. Farley;M. Baker;C. Malespin;S. Schwenzer;B. Cohen;P. Mahaffy;A. McAdam;D. W. Ming;P. Vasconcelos;R. Navarro
在对一个泥岩和一个砂岩进行K-Ar测年后，第三个样品已经被探索盖尔陨石坑的Currency漫游者测年。莫哈韦2号泥岩含有相对丰富的黄钾铁矾，其K-Ar体积年龄为2.57 ± 0.39 Ga（1σ精度）。两步加热实验的实施是为了解决样品中的主要和次要矿物成分的K-Ar年龄。该技术涉及测量低温（500°C）和高温（930°C）步骤中释放的40 Ar，以及样品矿物成分中钾分布的模型。使用这种方法，高温步骤产生了与碎屑斜长石有关的4.07 ± 0.63 Ga的K-Ar模型年龄，与Currencia在坎伯兰泥岩上获得的年龄一致。低温阶跃与黄钾铁矾和含钾镁矾和/或页硅酸盐的混合有关，给出了年轻的K-Ar模型年龄为2.12 ± 0.36 Ga。矿物形成后氩的潜在损失使这一结果的解释变得复杂。与坎伯兰的结果和先前发表的对可能存在的各个相的氩保持性的限制的比较表明，二次物质的形成年龄，校正氩损失的合理程度，仍然小于3 Ga，这表明在盖尔陨石坑的沉积物中发生了3 Ga后的水过程。这样的结果与盖尔湖的含钾矿物形成不一致，而是表明在火星表面河流活动被认为基本停止后的沉积后流体流动。
Following K‐Ar dating of a mudstone and a sandstone, a third sample has been dated by the Curiosity rover exploring Gale Crater. The Mojave 2 mudstone, which contains relatively abundant jarosite, yielded a young K‐Ar bulk age of 2.57 ± 0.39 Ga (1σ precision). A two‐step heating experiment was implemented in an effort to resolve the K‐Ar ages of primary and secondary mineralogical components within the sample. This technique involves measurement of 40Ar released in low‐temperature (500°C) and high‐temperature (930°C) steps, and a model of the potassium distribution within the mineralogical components of the sample. Using this method, the high‐temperature step yields a K‐Ar model age of 4.07 ± 0.63 Ga associated with detrital plagioclase, compatible with the age obtained on the Cumberland mudstone by Curiosity. The low‐temperature step, associated with jarosite mixed with K‐bearing evaporites and/or phyllosilicates, gave a youthful K‐Ar model age of 2.12 ± 0.36 Ga. The interpretation of this result is complicated by the potential for argon loss after mineral formation. Comparison with the results on Cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials, correcting for plausible extents of argon loss, is still less than 3 Ga, suggesting post‐3 Ga aqueous processes occurred in the sediments in Gale Crater. Such a result is inconsistent with K‐bearing mineral formation in Gale Lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on Mars is thought to have largely ceased.
影响因子：
18.3
作者：
Martin-Torres, F. Javier;Zorzano, Maria-Paz;Vaniman, David
通讯作者：
Vaniman, David
影响因子：
56.9
作者：
Blake, D. F.;Morris, R. V.;Sarrazin, P.
通讯作者：
Sarrazin, P.