TY - JOUR
T1 - Unique large diamonds in a ureilite from Almahata Sitta 2008 TC3 asteroid
AU - Miyahara, Masaaki
AU - Ohtani, Eiji
AU - El Goresy, Ahmed
AU - Lin, Yangting
AU - Feng, Lu
AU - Zhang, Jian Chao
AU - Gillet, Philippe
AU - Nagase, Toshiro
AU - Muto, Jun
AU - Nishijima, Masahiko
N1 - Funding Information:
We appreciate the help of Y. Ito in the EMPA analysis and the assistance by Y. Xu and J. Hao in the nanoSIMS analysis. We are grateful to T. Irifune of GRC, Ehime Univ., Japan for providing a sintered diamond. We express our thanks to Sokol A.G. of Sobolev Institute of Geology and Mineralogy for discussion on diamond formation mechanism. Part of this work was supported by the “Nanotechnology Support Project” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This study was supported by a grant-in-aid for Scientific Research (No. 22000002 ) by MEXT , Japan and partly by the Ministry of Education and Science of Russian Federation , project 14.B25.31.0032 to E.O. M.M. and Y.L. were financially supported by a grant-in-aid for Scientific Research (No. 26800277 ) by MEXT, Japan and Natural Science Foundation of China (No. 41173075 , 41273077 ), respectively. This work was conducted as a part of Tohoku University’s Global COE program entitled “Global Education and Research Center for Earth and Planetary Dynamics”. Two anonymous reviewers and Associate Editor Christian Koeberl are acknowledged to have improved an early version of this manuscript.
Publisher Copyright:
© 2015 Elsevier Ltd.
PY - 2015/8/5
Y1 - 2015/8/5
N2 - The Almahata Sitta MS-170 ureilite (a piece of a breccia originating from the asteroid, 2008 TC3) consists mainly of olivine, with many diamond and graphite grains existing between the olivine grains. The occurrences of the diamonds are unique; i.e., (i) some diamonds exhibit sub-euhedral habits and (ii) some diamonds have large grain-size (up to about 40μm). Several diamonds are segmented into many fragments by fractures. Individual fragments have similar crystallographic orientation, which implies that the adjacent diamond segments were originally a single crystal. Large diamond assemblages occur besides such individual diamond grains. In one of the largest assemblages (almost about 100μm in size) has also the same crystallographic orientation. They can be regarded as the pieces of a previously unique single diamond, which provides evidence for large single-crystals diamond in meteorites. Almahata Sitta MS-170 is a meteorite fragment from the 2008 TC3 asteroid that underwent less shock than other ureilitic meteorites. It is unlikely that such large diamonds were formed from graphite through a shock-induced phase transformation during planetesimal collision, despite this idea being now widely accepted as the diamond formation mechanism of ureilites. Fine-scale heterogeneous distribution of impurities (hydrogen, nitrogen, and oxygen) exists in single crystal diamonds, indicative of sluggish growth. This distribution is reminiscent of sector zoning growth. Its grain size, the shock features of MS-170, and the C- and N-isotopic composition signatures allow us to revive classical and but not widely accepted models for diamond formation in ureilites; i.e., a diamond formed from partially melted magma or a C-O-H fluid in the deep interior of the ureilite parent-body or, alternatively, through a chemical vapor deposition (CVD) process in the solar nebula. Considering present mineralogical and isotopic features, the former scenario is more favorable.
AB - The Almahata Sitta MS-170 ureilite (a piece of a breccia originating from the asteroid, 2008 TC3) consists mainly of olivine, with many diamond and graphite grains existing between the olivine grains. The occurrences of the diamonds are unique; i.e., (i) some diamonds exhibit sub-euhedral habits and (ii) some diamonds have large grain-size (up to about 40μm). Several diamonds are segmented into many fragments by fractures. Individual fragments have similar crystallographic orientation, which implies that the adjacent diamond segments were originally a single crystal. Large diamond assemblages occur besides such individual diamond grains. In one of the largest assemblages (almost about 100μm in size) has also the same crystallographic orientation. They can be regarded as the pieces of a previously unique single diamond, which provides evidence for large single-crystals diamond in meteorites. Almahata Sitta MS-170 is a meteorite fragment from the 2008 TC3 asteroid that underwent less shock than other ureilitic meteorites. It is unlikely that such large diamonds were formed from graphite through a shock-induced phase transformation during planetesimal collision, despite this idea being now widely accepted as the diamond formation mechanism of ureilites. Fine-scale heterogeneous distribution of impurities (hydrogen, nitrogen, and oxygen) exists in single crystal diamonds, indicative of sluggish growth. This distribution is reminiscent of sector zoning growth. Its grain size, the shock features of MS-170, and the C- and N-isotopic composition signatures allow us to revive classical and but not widely accepted models for diamond formation in ureilites; i.e., a diamond formed from partially melted magma or a C-O-H fluid in the deep interior of the ureilite parent-body or, alternatively, through a chemical vapor deposition (CVD) process in the solar nebula. Considering present mineralogical and isotopic features, the former scenario is more favorable.
UR - http://www.scopus.com/inward/record.url?scp=84929329485&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84929329485&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2015.04.035
DO - 10.1016/j.gca.2015.04.035
M3 - Article
AN - SCOPUS:84929329485
VL - 163
SP - 14
EP - 26
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
ER -