Mathematics – Logic
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.209c&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 209
Mathematics
Logic
1
Scientific paper
Yanzhuang (H6) and Jilin (H5) are two chondrites subjected to impact processes in space. The highest pressure and temperature of collision experienced by the Jilin was about 20 GPa and 500 degrees C (1), and that by the Yanzhuang was >100 GPa and 2000 degrees C (2). The shock effects of the orthopyroxenes (mostly bronzite) have been investigated by means of Raman microprobe spectra, using Jobin Yvon U-1000 system with an incident 488 nm green laser light. Raman spectra of orthopyroxenes collected from the two chondrites are shown in Fig. 1. For orthopyroxene of the Jilin, a very intense band near 1010 cm^-1, three intense bands in range of 660682 cm^-1 and 338 cm^-1 are shown. For orthopyroxene of the Yanzhuang bands in 1116 cm^-1, 1010 cm^-1, 800-850 cm^-1, 660-682 cm^-1 and 334 cm^-1 are revealed. The 1116 cm^-1 and 800-850 cm^-1 bands are two new-found Raman bands which did not appear in the orthopyroxenes of Jilin and other chondrites. The features of Raman spectra of orthopyroxenes in the Jilin are similar to those of unshocked orthopyroxene. The band near 1010 cm^-1 corresponds to symmetric stretching vibration of the Si-O Tetrahedron with two bridging oxygen. The bands in 660-682 cm^-1 are associated with the presence of inter-tetrahedral Si-O-Si linkages. These features show that, for moderately shocked Jilin chondrite (20 GPa and 500 degrees C), the crystal structure of orthopyroxene remains intact. The bands near 1050-1100 cm^-1 and 800-850 cm^-1 found in the Yanzhuang are attributed to symmetric stretching vibrations of Si-O Tetrahedron with respectively one and four non-bridging oxygen (3). Therefore, the presence of the two new bands indicates the crystal structure of orthopyroxene had been severely damaged due to very intense shock event (>100 GPa and 2000 degrees C). Here, we deduce that (a) The bridging oxygen in some Si-O Tetrahedron chains had been broken and some isolated Si-O Tetrahedron with four non-bridging oxygen was formed. In Raman spectra, the damaged structure is reflected by a broad band in 800-850 cm^-1. (b) Some SiO Tetrahedron are highly polymerized into network structure--a shock melt glass. In Raman spectra, the glass structure is reflected by the intense band at 1100 cm^-1. References: (1) XIE Xiande et al. (1991) Chinese Journal of Geochemistry Vol.10, 109-119. (2) CHEN Ming and XIE Xiande (1992), Acta Mineralogical Sinica, in press. (3) Paul McMillan (1984), America Mineralogist, Vol.69, 622-644. Figure 1, which in the hard copy appears here, shows Raman spectra of orthopyroxenes in the Jilin (A) and Yanzhuang (B) chondrite.
Chen Michelle
Xie x.
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