Impact shock origin of diamonds in ureilite meteorites.

Autor:	Nestola F; Department of Geosciences, University of Padova, I-35131 Padova, Italy; fabrizio.nestola@unipd.it goodrich@lpi.usra.edu.; Geoscience Institute, Goethe University Frankfurt, 60323 Frankfurt, Germany., Goodrich CA; Lunar and Planetary Institute, Universities Space Research Association, Houston, TX 77058; fabrizio.nestola@unipd.it goodrich@lpi.usra.edu., Morana M; Department of Earth and Environmental Sciences, University of Pavia, I-27100 Pavia, Italy., Barbaro A; Department of Earth and Environmental Sciences, University of Pavia, I-27100 Pavia, Italy., Jakubek RS; Astromaterials Research and Exploration Science Division, Jacobs Johnson Space Center Engineering, Technology and Science, NASA, Houston, TX 77058., Christ O; Department of Geosciences, University of Padova, I-35131 Padova, Italy., Brenker FE; Geoscience Institute, Goethe University Frankfurt, 60323 Frankfurt, Germany., Domeneghetti MC; Department of Earth and Environmental Sciences, University of Pavia, I-27100 Pavia, Italy., Dalconi MC; Department of Geosciences, University of Padova, I-35131 Padova, Italy., Alvaro M; Department of Earth and Environmental Sciences, University of Pavia, I-27100 Pavia, Italy., Fioretti AM; Institute of Geosciences and Earth Resources, National Research Council, I-35131 Padova, Italy., Litasov KD; Vereshchagin Institute for High Pressure Physics RAS, Troitsk, 108840 Moscow, Russia., Fries MD; NASA Astromaterials Acquisition and Curation Office, Johnson Space Center, NASA, Houston, TX 77058., Leoni M; Department of Civil, Environmental and Mechanical Engineering, University of Trento, I-38123 Trento, Italy.; Saudi Aramco R&D Center, 31311 Dhahran, Saudi Arabia., Casati NPM; Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland., Jenniskens P; Carl Sagan Center, SETI Institute, Mountain View, CA 94043., Shaddad MH; Department of Physics and Astronomy, University of Khartoum, 11111 Khartoum, Sudan.
Jazyk:	angličtina
Zdroj:	Proceedings of the National Academy of Sciences of the United States of America [Proc Natl Acad Sci U S A] 2020 Oct 13; Vol. 117 (41), pp. 25310-25318. Date of Electronic Publication: 2020 Sep 28.
DOI:	10.1073/pnas.1919067117
Abstrakt:	The origin of diamonds in ureilite meteorites is a timely topic in planetary geology as recent studies have proposed their formation at static pressures >20 GPa in a large planetary body, like diamonds formed deep within Earth's mantle. We investigated fragments of three diamond-bearing ureilites (two from the Almahata Sitta polymict ureilite and one from the NWA 7983 main group ureilite). In NWA 7983 we found an intimate association of large monocrystalline diamonds (up to at least 100 µm), nanodiamonds, nanographite, and nanometric grains of metallic iron, cohenite, troilite, and likely schreibersite. The diamonds show a striking texture pseudomorphing inferred original graphite laths. The silicates in NWA 7983 record a high degree of shock metamorphism. The coexistence of large monocrystalline diamonds and nanodiamonds in a highly shocked ureilite can be explained by catalyzed transformation from graphite during an impact shock event characterized by peak pressures possibly as low as 15 GPa for relatively long duration (on the order of 4 to 5 s). The formation of "large" (as opposed to nano) diamond crystals could have been enhanced by the catalytic effect of metallic Fe-Ni-C liquid coexisting with graphite during this shock event. We found no evidence that formation of micrometer(s)-sized diamonds or associated Fe-S-P phases in ureilites require high static pressures and long growth times, which makes it unlikely that any of the diamonds in ureilites formed in bodies as large as Mars or Mercury. Competing Interests: The authors declare no competing interest. (Copyright © 2020 the Author(s). Published by PNAS.)
Databáze:	MEDLINE
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