Investigation of Al-rich clays on Mars: Evidence for kaolinite-smectite mixed-layer versus mixture of end-member phases
Investigation of Al-rich clays on Mars: Evidence for kaolinite-smectite mixed-layer versus mixture of end-member phases
复制标题
火星上富铝粘土的调查： 高岭石-直闪石混合层与端粒相混合物的证据
DOI：
10.1016/j.icarus.2012.11.006
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发表时间：
2013-01-01
期刊：
影响因子：
3.2
通讯作者：
Michalski, Joseph R.
中科院分区：
文献类型：
--
作者：
Cuadros, Javier;Michalski, Joseph R.
从遥感红外光谱特征中可以识别出火星上的铝土矿矿床，这些矿床类似于蒙脱石、贝得石和/或高岭石。火星上的铝粘土矿床的性质令人感兴趣，因为它们可能表明与铁镁粘土不同的形成机制，后者在火星上广泛分布，可能是富铁镁玄武岩地壳的蚀变产物。含铝火星粘土矿床的近红外反射光谱经常显示蒙脱石和高岭石的典型特征。问题是，这种混合特征是由于端员相的存在还是由于高岭石-蒙皂石混合层（K-S）。这个问题是相关的，因为K-S意味着存在一个蒙皂石前体，改变成高岭石，从而限制了时间和强度的蚀变过程，产生it.A混合物的高岭石和蒙皂石端员可能表明局部异质蚀变过程，或者，可能是由于物理混合的蚀变材料的不同来源。一组天然K-S样品和已知比例的合成高岭石/蒙皂石混合物，所有这些都已在以前的工作中使用几种分析技术进行了彻底的表征，在这里使用近红外（NIR）光谱进行了研究。近红外光谱特征与高岭石-蒙皂石的相对比例有很好的相关性。K-S中Al-OH的光谱特征的形状与高岭石和蒙皂石的物理混合物中的光谱特征的形状有细微的不同。根据定性比较，火星上的一些地区似乎有类似于K-S的光谱特征。我们还应用了定量技术，使用光谱的二阶导数。在这种技术中，图的高度的功能（λ =）2.21 μ m（带存在于高岭石和蒙脱石）和2.17 μ m（仅高岭石）能够区分K-S和高岭石-蒙脱石物理混合物，因为它们产生的相关性与不同的斜率。将这种鉴别方法应用于火星光谱，得到了尼利槽沟和莫斯谷中存在K-S以及莫斯谷和莱顿陨石坑中存在端元混合物的合理证据。这是第一次在火星上收集混合层粘土矿物的证据，特别是K-S。探测混合层粘土的能力是进一步发展我们对火星上产生粘土的过程的理解的重要一步。(C)2012 Elsevier Inc. All rights reserved.
Aluminous clay deposits on Mars are recognized from remotely sensed infrared spectral features similar to those of montmorillonite, beidellite, and/or kaolinite. The nature of aluminous clay deposits on Mars is of interest because they likely indicate a different formation mechanism than that of Fe-Mg clays, which are widespread on Mars and likely alteration products of the Fe-Mg-rich basaltic crust. The near-infrared reflectance spectra of aluminous martian clay deposits frequently display characteristics typical of both montmorillonite and kaolinite. The question arises whether such mixed character is due to the existence of end-member phases or to kaolinite-smectite mixed-layer (K-S). The issue is relevant because K-S implies the existence of a smectite precursor that alters into kaolinite, and thus constrains the timing and intensity of the alteration processes that generates it. A mixture of kaolinite and smectite end-members may indicate locally heterogeneous alteration processes, or alternatively, could result from the physical mixing of altered materials of different provenance. A group of natural K-S samples and synthetic kaolinite/smectite mixtures of known proportion, all of which had been thoroughly characterized in previous work using several analytical techniques, were investigated here using near-infrared (NIR) spectroscopy. The NIR spectral features correlate well with their kaolinite-smectite relative proportions. The shape of spectral features attributed to Al-OH in K-S is subtly different from those in physical mixtures of kaolinite and smectite. Based on qualitative comparison, some regions on Mars appear to have spectral signatures similar to K-S. We also applied a quantitative technique using the second derivative of spectra. In this technique, plots of the height of the features at (lambda=) 2.21 mu m (band present in kaolinite and montmorillonite) and 2.17 mu m (kaolinite only) were able to discriminate between K-S and kaolinite-smectite physical mixtures, as they generated correlations with different slopes. The method of discrimination was applied to Mars spectra, which resulted in reasonable evidence for the existence of K-S in Nili Fossae and Mawrth Vallis, and mixtures of end-members in Mawrth Vallis and Leighton Crater. This is one of the first times that evidence for mixed-layer clay minerals, and particularly K-S, on Mars has been gathered. The ability to detect mixed-layer clays is an important step forward for further development of our understanding of the processes that generated clay on Mars. (C) 2012 Elsevier Inc. All rights reserved.