11:45 〜 12:00
[PPS06-11] Goalpara隕石中の炭素質物質
キーワード：ユレイライト、ダイヤモンド、ラマン、炭化ケイ素
Ureilites comprise a major group of primitive achondrites. They show highly fractionated igneous features, and at the same time they also show primitive characteristics, such as planetary-type noble gases and O-isotopic compositions [1-3]. Ureilites contain a huge amount of noble gases whose characteristics are similar to those of the Q-gases in primitive chondrites. The carrier of these noble gases is known to be diamond [4] and the origin of the diamond has been debated for years. There are two hypotheses. One is that diamond was transformed from graphite by shock-induced high pressure. The other one is that they formed by chemical vapor deposition (CVD).
All mineralogical observations [5-8] support that ureilite diamonds formed via transformation from graphite by shock. There is no mineralogical observation to support the presence of CVD diamonds. A strong support for CVD diamonds comes from simulation experiments of trapping noble gases in CVD diamonds and shock-produced diamonds [9, 10]. To better understand the origin of the diamond and ureilites, we have launched the project to examine carbonaceous matter in ureilites.
2.85 g of Goalpara, provided by The Smithsonian National Museum of Natural History, was treated alternately with HF-HCl and HCl to remove silicates followed by H3BO3 treatment to completely dissolve fluorides. The residue was treated with HClO4 at 205°C for 2 hours four times to ensure that reactive carbonaceous materials would be destroyed. We examined the oxidized residue with a field-emission scanning electron microscope JEOL JSM-7000F at The University of Tokyo. Of the 67 grains examined, 54 grains were carbonaceous, 12 grains were Si-rich grains, and one grain was Al-Mg-Fe-Si-rich oxide.
We examined Raman spectra of the grains in the residue. Silicon-rich grains showed peaks at 787-788 cm–1 and 967-968 cm–1. These peaks are consistent with those of 6H-SiC [4].
Many carbonaceous grains in our Goalpara sample show peaks at 1320 – 1332 cm–1. Since the peak of diamond is expected to be at 1332 cm–1, thus the peaks of the grains were shifted toward the lower wave number. Such a shift was also observed in diamond from the ureilite Almahata Sitta, where a peak center ranged between 1318.5 cm–1 and 1330.2 cm–1 [11]. The shift has been attributed to the presence of lonsdaleite, or shock-produced diamond. Alternatively, it has been caused by laser-induced heat [12].
References
[1] Clayton R. N. and Mayeda T. K. (1988) Geochim. Cosmochim. Acta, 52, 1313-1318.
[2] Clayton R. N. and Mayeda T. K. (1996) Geochim. Cosmochim. Acta, 60, 1919-2018.
[3] Kita N. T. et al. (2004) Geochem. Cosmochim. Acta, 68, 4213-4235.
[4] Okumura H. et al. (1987) Journal of Applied Physics, 61, 1134-1136.
[5] Nakamuta Y. and Aoki Y. (2000) Meteorit. Planet. Sci., 35, 487-493.
[6] Nakamuta Y. and Toh S. (2013) Amer. Mineralogist, 98, 574-581.
[7] Nakamuta Y. et al. (2016) Journal of Mineralogical and Petrological Sciences, 252-269.
[8] Le Guillou C. et al. (2010) Geochim. Cosmochim. Acta, 74, 4167-4185.
[9] Matsuda J. et al. (1991) Geochem. Cosmochim. Acta, 55, 2011-2023.
[10] Matsuda J. et al. (1995) Geochem. Cosmochim. Acta, 59, 4939-4949.
[11] Ross A. J. et al. (2011) Meteorit. Planet. Sci., 46, 364-378.
[12] Kagi H. et al. (1994) Geochim. Cosmochim. Acta, 58, 3527-3530.
All mineralogical observations [5-8] support that ureilite diamonds formed via transformation from graphite by shock. There is no mineralogical observation to support the presence of CVD diamonds. A strong support for CVD diamonds comes from simulation experiments of trapping noble gases in CVD diamonds and shock-produced diamonds [9, 10]. To better understand the origin of the diamond and ureilites, we have launched the project to examine carbonaceous matter in ureilites.
2.85 g of Goalpara, provided by The Smithsonian National Museum of Natural History, was treated alternately with HF-HCl and HCl to remove silicates followed by H3BO3 treatment to completely dissolve fluorides. The residue was treated with HClO4 at 205°C for 2 hours four times to ensure that reactive carbonaceous materials would be destroyed. We examined the oxidized residue with a field-emission scanning electron microscope JEOL JSM-7000F at The University of Tokyo. Of the 67 grains examined, 54 grains were carbonaceous, 12 grains were Si-rich grains, and one grain was Al-Mg-Fe-Si-rich oxide.
We examined Raman spectra of the grains in the residue. Silicon-rich grains showed peaks at 787-788 cm–1 and 967-968 cm–1. These peaks are consistent with those of 6H-SiC [4].
Many carbonaceous grains in our Goalpara sample show peaks at 1320 – 1332 cm–1. Since the peak of diamond is expected to be at 1332 cm–1, thus the peaks of the grains were shifted toward the lower wave number. Such a shift was also observed in diamond from the ureilite Almahata Sitta, where a peak center ranged between 1318.5 cm–1 and 1330.2 cm–1 [11]. The shift has been attributed to the presence of lonsdaleite, or shock-produced diamond. Alternatively, it has been caused by laser-induced heat [12].
References
[1] Clayton R. N. and Mayeda T. K. (1988) Geochim. Cosmochim. Acta, 52, 1313-1318.
[2] Clayton R. N. and Mayeda T. K. (1996) Geochim. Cosmochim. Acta, 60, 1919-2018.
[3] Kita N. T. et al. (2004) Geochem. Cosmochim. Acta, 68, 4213-4235.
[4] Okumura H. et al. (1987) Journal of Applied Physics, 61, 1134-1136.
[5] Nakamuta Y. and Aoki Y. (2000) Meteorit. Planet. Sci., 35, 487-493.
[6] Nakamuta Y. and Toh S. (2013) Amer. Mineralogist, 98, 574-581.
[7] Nakamuta Y. et al. (2016) Journal of Mineralogical and Petrological Sciences, 252-269.
[8] Le Guillou C. et al. (2010) Geochim. Cosmochim. Acta, 74, 4167-4185.
[9] Matsuda J. et al. (1991) Geochem. Cosmochim. Acta, 55, 2011-2023.
[10] Matsuda J. et al. (1995) Geochem. Cosmochim. Acta, 59, 4939-4949.
[11] Ross A. J. et al. (2011) Meteorit. Planet. Sci., 46, 364-378.
[12] Kagi H. et al. (1994) Geochim. Cosmochim. Acta, 58, 3527-3530.