Hydrous mineralogy of CM and CI chondrites from infrared spectroscopy and their relationship with low albedo asteroids
Hydrous mineralogy of CM and CI chondrites from infrared spectroscopy and their relationship with low albedo asteroids
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DOI：
10.1016/j.gca.2010.05.020
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发表时间：
2010-08-15
影响因子：
5
通讯作者：
Guillot, S.
中科院分区：
文献类型：
--
作者：
Beck, P.;Quirico, E.;Guillot, S.
红外光谱是为数不多的可以直接探测岩石中水分子的技术之一。该方法已用于表征水合/含水碳质球粒陨石的矿物学特征，并将已知的陨石家族与低反照率小行星的光谱观测联系起来。本文给出了3 CI和9 CM球粒陨石中基体块的红外透射光谱的测量结果。在环境条件下测量光谱，然后在初级真空下沿着高t（类似300℃）的脱水路径在不同温度下测量光谱。在环境条件下，3 μ m光谱范围总是被吸附的大气水分子所主导。在低压（P < 10（-4）毫巴）下，中等（类似于100摄氏度）和高（类似于300摄氏度）加热时，吸附的水和层状硅酸盐层间水被去除，显示出约3 μ m的残余吸收带。这条带是层状硅酸盐相的典型红外特征，它在水合碳质球粒陨石的矿物组合中占主导地位。在CM球粒陨石中，高t光谱显示出很强的变异性，这似乎与Rubin et al.（2007）和Howard et al. （2009a）的蚀变分类方案相关。3 μ m波段不断演变，弱蚀变的CMs （murchison型）在3550-3600 cm（-1）处有一个宽特征峰，而更广泛蚀变的样品（Cold bokkeveld型）在3675 cm（-1）处有一个尖锐的不对称峰。我们将这种光谱演变归因于层状硅酸盐相从富铁到富镁的化学变化。另一方面，10 μ m光谱区显示单一的宽峰，与已知的陆地蛇形岩光谱不同，可能是由于球粒陨石层状硅酸盐相的高度结构紊乱所致。目前的工作清楚地表明，以前发表的球粒陨石的反射光谱由于吸附的陆地水分子的存在而有偏差。需要在干燥条件下收集的实验室数据，通过比较它们的3 μ m吸收特征来重新解释球粒陨石与小行星的联系。(C) 2010 Elsevier Ltd.版权所有。
IR spectroscopy is one of the few techniques that can directly probe water molecules in rocks. This method has been used to characterize the mineralogy of hydrated/hydrous carbonaceous chondrites, and to link known meteorite families with spectroscopic observations of low albedo asteroids. In this paper, we present measurements of the infrared transmission spectra of matrix chunks from 3 CI and 9 CM chondrites. Spectra were measured at ambient conditions and then at different temperatures along a dehydration path toward high-T (similar to 300 degrees C) under primary vacuum. At ambient conditions, the 3-mu m spectral range is always dominated by adsorbed atmospheric water molecules. Upon moderate (similar to 100 degrees C) and high (similar to 300 degrees C) heating under low pressure (P < 10(-4) mbar), adsorbed water and then phyllosilicates interlayer water are removed, revealing a residual absorption band around 3 mu m. This band is a characteristic IR feature of the phyllosilicate phases which dominate the mineralogical assemblage of hydrated carbonaceous chondrites. Among the CM chondrites, the high-T spectra reveal a strong variability that appears correlated with the alteration classification scheme of Rubin et al. (2007) and Howard et al. (2009a). The 3-mu m band continuously evolves from a broad feature peaking at 3550-3600 cm(-1) for the weakly altered CMs (Murchison-type) to a sharp asymmetric peak at similar to 3675 cm(-1) for the more extensively altered samples (Cold Bokkeveld-type). We attribute this spectral evolution to variations in the chemistry of the phyllosilicate phases from Fe-rich to Mg-rich. On the other hand, the 10-mu m spectral region shows a single broad peak which does not compare with known terrestrial serpentine spectra, probably due to high structural disorder of the chondrite phyllosilicate phases. The present work clearly shows that previously published reflectance spectra of chondrites are biased by the presence of adsorbed terrestrial water molecules. Laboratory data collected under dry conditions are needed to reinterpret the chondrite-asteroid connection from the comparison of their 3-mu m absorption features. (C) 2010 Elsevier Ltd. All rights reserved.