Nature and degree of aqueous alteration in CM and CI carbonaceous chondrites
Nature and degree of aqueous alteration in CM and CI carbonaceous chondrites
复制标题
DOI：
10.1111/maps.12171
复制
发表时间：
2013-09
影响因子：
2.2
通讯作者：
D. Takir;J. Emery;H. McSween;C. Hibbitts;R. Clark;N. Pearson;Alian Wang
中科院分区：
文献类型：
--
作者：
D. Takir;J. Emery;H. McSween;C. Hibbitts;R. Clark;N. Pearson;Alian Wang
我们研究了9个CM球粒陨石和1个CI(依凡纳)碳质球粒陨石中与水蚀变类型和程度有关的岩石学、地球化学和光谱参数。我们的基本假设是，3μm带的位置和形状是层状硅酸盐矿物学的诊断。我们测量了球粒陨石在干燥条件(高温)和真空(10−8至10−7 Torr)下的反射光谱，以最大限度地减少吸附水并模拟空间环境，以便随后与小行星的反射光谱进行比较。除了依夫纳，我们还鉴定了三个光谱CM基团。根据各种蚀变指标确定的变化最小的群--群1，具有较长波长的3个μm带中心的特征，与方铅矿(铁蛇纹石)一致。“组3”是变化最大的组，其特征是波长较短的3个μm带中心，并与反蛇纹岩(蛇纹岩)一致。“群2”是介于群1和群3之间的中间群。伊夫纳具有独特的光谱，不同于CM陨石，与蜥蜴石和温石棉(蛇纹石)一致。用电子探针分析和显微观察确定的岩石学和地球化学参数与三个谱群一致。这些结果表明，利用反射光谱可以区分这些碳质球粒陨石所经历的不同的母体水蚀变环境。对主带小行星进行高质量的地面望远镜观测，预计不仅能揭示小行星是否水合，还能揭示小行星蚀变状态的细节。
We investigated the petrologic, geochemical, and spectral parameters that relate to the type and degree of aqueous alteration in nine CM chondrites and one CI (Ivuna) carbonaceous chondrite. Our underlying hypothesis is that the position and shape of the 3 μm band is diagnostic of phyllosilicate mineralogy. We measured reflectance spectra of the chondrites under dry conditions (elevated temperatures) and vacuum (10−8 to 10−7 torr) to minimize adsorbed water and mimic the space environment, for subsequent comparison with reflectance spectra of asteroids. We have identified three spectral CM groups in addition to Ivuna. “Group 1,” the least altered group as determined from various alteration indices, is characterized by 3 μm band centers at longer wavelengths, and is consistent with cronstedtite (Fe‐serpentine). “Group 3,” the most altered group, is characterized by 3 μm band centers at shorter wavelengths and is consistent with antigorite (serpentine). “Group 2” is an intermediate group between group 1 and 3. Ivuna exhibits a unique spectrum that is distinct from the CM meteorites and is consistent with lizardite and chrysotile (serpentine). The petrologic and geochemical parameters, which were determined using electron microprobe analyses and microscopic observations, are found to be consistent with the three spectral groups. These results indicate that the distinct parent body aqueous alteration environments experienced by these carbonaceous chondrites can be distinguished using reflectance spectroscopy. High‐quality ground‐based telescopic observations of Main Belt asteroids can be expected to reveal not just whether an asteroid is hydrated, but also details of the alteration state.