Raman spectroscopy of shocked enstatite‐rich meteorites

Abstract

We present Raman patterns of enstatite in different classes of enstatite‐rich chondrites and achondrites of various shock levels as previously reported from petrographic observations and X‐ray diffraction analyses. Thin sections or mineral separates of four enstatite chondrites (LaPaz Icefield [LAP] 02225, MacAlpine Hills [MAC] 02837, Pecora Escarpment [PCA] 91020, and Itqiy), three aubrites (Larkman Nunatak [LAR] 04316, Khor Temiki, and Allan Hills [ALH] 84008), and a ureilite (Sayh al Uhaymir [SaU] 559) were examined by laser Raman spectroscopy. We find that the frequencies of fundamental Raman peaks of enstatites from the chondrites and aubrites deviate by ≤2 cm−1 from the values for unshocked enstatite. This small difference implies a negligible effect of shock metamorphism on peak positions. Significant differences (<6 cm−1) for peak positions are found for the pyroxenes of SaU 559 and may be attributed to minor substitution of Fe and Ca for Mg. Linear regressions of peak widths of enstatite chondrites against their established shock stages show a strong positive correlation for each mode (r2 > 0.94). From this linear relationship, the 343 and 1014 cm−1 peaks of the aubrites coincide with S4 determined from petrography. For Itqiy, we find S4–5, while the shock levels of SaU 559 exceed the petrologic scheme (S1–6), suggesting that the ureilite might have sustained multiple shock events or have been deformed in a high‐pressure environment. Alternatively, for Itqiy (peak 343 cm−1) and SaU 559 (all peaks) enstatites, minor substitutions of Fe and Ca for Mg may have further broadened their peak widths.

Raman and Infrared Microspectroscopy of Experimentally Shocked Basalts

“…Wang et al, , , ). These were not tracked as a function of pressure owing to their greater resistance to shock at the pressures examined here (e.g., Farrell‐Turner et al, ; Harriss & Burchell, ; Johnson et al, ; Zhang et al, ). The broad humps near 1,000 cm −1 may also vary with composition (Al–O to Si–O ratios) in plagioclase glass or maskelynite (e.g., Fritz et al, ).…”

Raman spectroscopy investigations of the Martian regolith breccia Northwest Africa 7533: A support to in situ Raman spectroscopy on Mars

“…In our data, peak position shifts of the most intense peaks can be observed down to a few cm −1 , explained by the variation of the structural cations, as described in depth by Huang et al 39 Finally, Raman investigation of various pyroxenes in the breccia confirmed the absence of any shock‐induced transformation of pyroxene, in agreement with the literature. Modification by high‐pressure processes should be visible in Raman spectra through significant peak broadening or the occurrence of amorphous glass 44,45 which is not observed in our spectra. However, Leroux et al 46 observed some local shock microstructures inside pyroxenes at the nanoscale with TEM microscopy, which may be too small and/or scarce to be detected at the Raman scale of observation.…”

Vibrational spectroscopic, crystallographic, and microscopic investigation on the Aioun El Atrouss diogenite

“…Existence of enstatite in AAT-1 was also determined by its characteristic peaks (Figure 6) observed for Si-O-Si stretching at 665 cm À1 , Si-O-Si stretching at 687 cm À1 , Si-O stretching at 1014 cm À1 , and 1034 cm À1 . 34 The peaks at $106-300 cm À1 regions obtained in the sample mapping analysis and most of the single spectra (Figure 7) are most closely matched with titanium oxide minerals. It is known that titanium oxide minerals, which are found in three types of crystalline 35 Anatase converts into rutile at high temperatures and pressures.…”

“…S, represented by yellow color in the image, displays a collective structure in coarse‐grained pyroxene. This structure can be associated with a troilite‐orthopyroxene ingrowth in diogenites 34 . However, an increase in Ti is observed towards the sample edge (Figure 9C area).…”

“…Existence of enstatite in AAT‐1 was also determined by its characteristic peaks (Figure 6) observed for Si‐O‐Si stretching at 665 cm −1 , Si‐O‐Si stretching at 687 cm −1 , Si‐O stretching at 1014 cm −1 , and 1034 cm −1 34 …”