Distinguishing relative aqueous alteration and heating among CM chondrites with IR spectroscopy
Distinguishing relative aqueous alteration and heating among CM chondrites with IR spectroscopy
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DOI：
10.1016/j.icarus.2020.113760
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发表时间：
2020-08-01
期刊：
影响因子：
3.2
通讯作者：
Friedrich, J. M.
中科院分区：
文献类型：
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作者：
Hanna, R. D.;Hamilton, V. E.;Friedrich, J. M.
使用薄片红外光谱，我们表征了一组CM球粒陨石的水蚀变和随后加热的相对程度，以记录这些过程的光谱指标，可以为碳质小行星的观测提供背景。我们发现，CMS的进行性水蚀变表现在两个光谱区。低波数区(1200-400 cm(-1)；8-25微米)记录了随着水蚀变的进行，镁铁层状硅酸盐相对于无水硅酸盐的比例增加，克里斯汀森特征(Cf)高度相关地向低波数移动，Si-O弯曲带最小向高波数移动，以及镁-OH带深度的增加(类似于625 cm(-1))。与岩石学亚型的相关性最强(R-2=0.90)的是Cf和Si-O伸展带之间的最小距离，预测样品的岩石学亚型在0.1以内。高波数区(4000-2500 cm(-1)，500℃)具有低波数区，以次生含铁橄榄石和低钙辉石的光谱特征为主，因此很容易与未加热和中等加热的CMS区分开来。所有加热的CMS的OH/H2O带宽而圆，发射峰位于比未加热的CMS更低的波数(=2.75微米)。然而，光谱和岩石学证据表明，我们加热的CMS已经受到陆地再水化的影响。我们的研究证实了热变质作用集中在基质中，并表明CM WIS 91600的基质在加热之前具有类似CI的矿物学。
Using infrared (IR) spectroscopy of thin sections, we characterize the relative degree of aqueous alteration and subsequent heating of a suite of CM chondrites to document spectral indicators of these processes that can contextualize observations of carbonaceous asteroids. We find that the progressive aqueous alteration of CMs manifests in two spectral regions. The low-wavenumber region (1200-400 cm(-1); 8-25 mu m) records the increasing proportion of Mg-Fe phyllosilicates relative to anhydrous silicates as aqueous alteration proceeds, with a highly correlated shift of the Christiansen feature (CF) to lower wavenumber and the Si-O bending band minimum to higher wavenumber, and an increase in depth of the Mg-OH band (similar to 625 cm(-1)). The strongest correlation (R-2 = 0.90) with petrologic subtype is the distance between the CF and Si-O stretching band minimum, which predicts the petrologic subtype of the sample to within 0.1. The high-wavenumber region (4000-2500 cm(-1), 500 degrees C) have a low-wavenumber region dominated by the spectral features of secondary, Fe-bearing olivine and low-Ca pymxene and thus are readily distinguished from unheated and mildly heated CMs. The OH/H2O band of all heated CMs is broad and rounded with an emission peak at lower wavenumbers (= 2.75 mu m) than in unheated CMs. However, spectral and petrographic evidence suggests that our heated CMs have been compromised by terrestrial rehydration. Our study confirms that thermal metamorphism effects are concentrated within the matrix and suggests that the matrix of the CM WIS 91600 had a CI-like mineralogy prior to heating.