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Abstract

I have studied the Raman spectroscopic signatures of nanodiamonds from the Allende meteorite, in which some portions must be of presolar origin as indicated by the isotopic compositions of various trace elements. The spectra of the meteoritic nanodiamonds show a narrow peak at 1326 cm−1 and a broad band at 1590 cm−1. Compared to the intensities of these peaks, the background fluorescence is relatively high. A significant frequency shift from 1332 to 1326 cm−1, peak broadening, and appearance of a new peak at 1590 cm−1 might be due to shock effects during formation of the diamond grains. Such changes may have several origins: an increase in bond length, a change in the electron density function or charge transfer, or a combination of these factors. However, Raman spectroscopy alone does not allow distinguishing between a shock origin of the nanodiamonds and formation by a CVD process, as is favored by most workers.

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Abstract

We investigated three types of shocked feldspar in the Asuka-881757,531-2 sample with midinfrared spectroscopy (reflectance mode). Under the petrographic microscope three types of site were characterized by (1) undulatory extinction, (2) undulatory extinction with isotropic patches and decreased interference color, and (3) isotropic, lath-shaped feldspars, which is indicative of maskelynite. The IR emissivity maximum (Christiansen feature=CF) changes with the chemical composition of feldspar. One of the Christiansen composition features exhibits a wave length peak of 1234 cm−1 for anorthite; another feature appears at 1245 cm−1 for maskelynite (Palomba et al. 2006).

With the help of IR spectroscopy we observed three vibrational types in our spectra: (1) peaks of depolimerization of SiO4 tetrahedra (500–650 cm−1, 950–1150 cm−1), (2) peaks of stretching and bending vibrational modes of SiO6 octahedra (750–850 cm−1), and (3) Si-O stretching vibration of SiO4 units (Johnson and Hörz 2003; Johnson et al. 2003, 2007). All these vibration types were observed at the less shocked sites. In the spectrum of highly shocked maskelynite only a broader band close to 1000 cm−1 was observed, which is the main vibrational band of maskelynite (Palomba et al. 2006). The calculated FWHM showed the disordering rate of shocked feldspars. On the basis of the measurements it could be concluded that the estimated shock pressure range gradually increases from 17–35 GPa for different degrees of undulatory sites, to 35–45 GPa for maskelynite sites.

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Central European Geology
Authors:
Arnold Gucsik
,
Tasuku Okumura
,
Hirotsugu Nishido
,
Ildikó Gyollai
,
Kiyotaka Ninagawa
,
Natalie Deseta
, and
Péter Rózsa

Quartz grains from the Ries impact structure containing shock-induced microstructures were investigated using Scanning Electron Microscopy in cathodoluminescence (SEM-CL), secondary electron (SEM-SE) and back-scattered electron (SEM-BSE) modes as well as Mott–Seitz analysis. The purpose of this study is to evaluate the mechanism by which CL detects Planar Deformation Features (PDFs) in quartz, which is one of the most important indicators of shock metamorphism in rock-forming minerals. PDFs are micron-scale features not easily identified using optical microscopy or scanning electron microscopy. The CL spectrum of PDFs in quartz that has suffered relatively high shock pressure shows no or a relatively weak emission band at around 385 nm, whereas an emission band with a maximum near 650 nm is observed independent of shock pressure. Thus, the ~385 nm intensity in shocked quartz demonstrates a tendency to decrease with increasing shock metamorphic stage, whereas the 650 nm band remains fairly constant. The result indicates that the emission band at 385 nm is related to the deformed structure of quartz as PDFs.

Open access
Central European Geology
Authors:
Ildikó Gyollai
,
Ildikó Gyollai
,
Szaniszló Bérczi
,
Krisztián Fintor
,
Szabolcs Nagy
, and
Arnold Gucsik

The Mócs chondrite was studied by optical microscopy, element mapping, as well as scanning electron microscope backscattered electron (SEM—BSE) imaging, in order to gain a better understanding of the thermal metamorphic as well as post-shock annealing evolution and the mineralogical signatures in this meteorite. The studied thin section of Mócs meteorite contains 26 chondrules with a variety of chondrule textures, which are characterized by a blurry rim. The chondrules mostly consist of pyroxene and olivine, whereas feldspars occur only in the recrystallized groundmass, chondrule mesostasis, and mineral melt inside and beyond the shock veins. It was found that the matrix was completely recrystallized. According to the scanning electron microscope and optical microscope observations mentioned above, it can be concluded that the Mócs chondrite is a 6.5 petrographic type.

Open access
Central European Geology
Authors:
Szabolcs Nagy
,
Sándor Józsa
,
Arnold Gucsik
,
Szaniszló Bérczi
,
Kiyotaka Ninagawa
,
Hirotsugu Nishido
,
Miklós Veres
,
Ákos Kereszturi
, and
Henrik Hargitai

Abstract

We studied optical microscopic and micro-Raman spectroscopic signatures of shocked olivine from the ALH 77005 Martian meteorite sample. The purpose of this study is to document pressure and temperature-related effects in olivine over the entire sample, which can aid in understanding structural changes due to shock metamorphism and the post-shock thermal annealing processes of lherzolitic Martian meteorites. According to the optical microscope observations, three areas may be discernible in olivine of the ALH 77005 in the vicinity of the melt pocket. The first area is the thermally undisturbed part of a grain, which contains a high density of shock-induced planar microdeformations such as Planar Deformation Features (PDFs) and Planar Fractures (PFs). Compared to the first area, the second area shows less shock-induced microstructures, while the third area is a strongly recrystallized region, but not formed from a melt.

A common Raman spectral feature of these olivines is a regular doublet peak centered at 823 and 852 cm−1; additionally, two new peaks at 535 and 755 cm−1 appear in the weakly annealed transition zones.

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