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Chemical composition of the Moss meteorite via FTIR and Raman spectroscopy

Mehmet Yesiltas
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Abstract Text: 

The Moss chondritic meteorite fell in 2006 in Ostfold, Norway after a bright fireball followed by a loud explosion [1]. Based on initial studies, it was classified as a type 3.6 CO chondrite [1]. According to previous studies, Moss contains small but abundant chondrules and a dark matrix [2] with olivine, troilite, and kamacite embedded in the matrix [1], with an unusually low matrix-to-chondrule ratio [2]. Organic matter in Moss amounts to a total of ~0.21-0.25 wt% [2], lower than other carbonaceous chondrites [3, 4]. Nevertheless, some organic molecules (e.g., naphthalene), and the mineral graphite are found in Moss [2, 4]. Lower organic content seen in the Moss meteorite suggests a higher degree of thermal metamorphism than that of other members of the CO group [4]; however, considering all CO3 chondrites are thought to originate from a single asteroid [2], organic matter seen in the Moss meteorite is not consistent with its thermal metamorphic grade [5].
The type, spatial distribution, and lateral relationships of molecular compounds present in the Moss meteorite can provide clues to its complex parent body histories. As a part of our ongoing study, we have collected micro-FTIR and micro-Raman chemical distribution maps as well as spectra in the mid-infrared region in order to understand and investigate the mineralogy and organic content of the Moss meteorite. Infrared maps were collected using a Nicolet iN10 MX FTIR microscope with a liquid nitrogen cooled MCT detector. Spectra were collected in the 4000–700 cm−1 region in reflection mode at 4 cm−1 resolution, and 32 scans were co-added for each spectrum. Micro-Raman measurements were performed using a WiTEC alpha300R confocal Raman imaging system coupled to a 512 nm NdYAG green laser (~2 mW/µm2). A 50X (NA 0.80) objective was used, which resulted a spatial resolution of ~0.8 µm. Furthermore, by collecting 2D intensity distribution images of a region of interest at different focal planes, 3D reconstructions of individual chemical components were generated using ImageJ and Chimera software packages.
Raman spectra indicate presence of Mg-rich olivine (evident from the doublet near 835 cm-1) and orthopyroxene (evident from the bands at 688 cm-1 and 1025 cm-1). The distribution of organic matter in the Moss meteorite is reported to be highly heterogeneous, and we see that different regions of the investigated sample indicate different degree of disordered carbon, which may suggest complex post-accretionary parent body alteration events. By studying the carbon peaks in the Raman spectra, we observed that (i) there seem to be regions in the meteorite that have undergone varying degrees of thermal alteration, (ii) carbon is more ordered than in other primitive carbonaceous chondrites, (iii) carbon spectra point to a higher degree of metamorphism than other members of the CO group.
[1] Connolly et al. (2007) MAPS, 42, 413–416. [2] Greenwood et al. (2007) LPSC XXXVIII, 2267. [3] Grady et al. (2002) MAPS, 37, 713–735. [4] Pearson et al. (2006) MAPS, 41 1891-1918. [5] Pearson et al. (2007) LPSC XXXVIII, 1846.

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