Aqueous alteration on asteroids: Linking the mineralogy and spectroscopy of CM and CI chondrites

摘要: Abstract CM/CI meteorites range in degree of aqueous alteration suggesting differences initially accreted materials including water ice and possible spatial heterogeneities within their parent bodies. As progresses, the total abundance magnesium content phyllosilicates increases. In this paper we present results a coordinated spectral–mineralogical study well-characterized suite that from 60 to 90% alteration. By acquiring spectra same meteorite powders as Howard et al. (Howard, K.T., Benedix, G.K., Bland, P.A., Cressey, G. [2009]. Geochim. Cosmochim. Acta 73, 4576–4589; Howard, [2011]. 75, 2735–2751) Bland (Bland, G., Menzies, O.N. [2004]. Meteorit. Planet. Sci. 39(1), 3–16), are able for first time directly correlate mineralogy with features reflectance spectra. At visible/near-infrared wavelength, presence 0.7-μm charge transfer band is indicative However, not all altered exhibit feature; thus lack 0.7 μm absorption asteroids does necessarily signify Furthermore, position depth shows no correlation mineralogical changes associated Similarly, near-infrared slope, which related mineralogic progression increasing alteration, unambiguously studied. mid-infrared contain broad feature 10–13-μm region, convolution vibrational due Mg-rich unaltered olivine. The overall continuously phyllosilicate shorter wavenumber/longer wavelength peak (815 cm −1 , 12.3-μm) less longer wavenumber/shorter (875 cm 11.4-μm) highly meteorites, roughly equal spectral contributions producing doublet intermediately Using analyses spectra, it estimate on dark primitive asteroids. We find Asteroid (24) Themis have 1000–700 cm (10–13-μm) at wavelengths has complex surface approximately 70 vol.% 25 vol.% anhydrous silicates.