Impact shock origin of diamonds in ureilite meteorites

Fabrizio Nestola; Cyrena A Goodrich; Marta Morana; Anna Barbaro; Ryan S Jakubek; Oliver Christ; Frank E Brenker; M Chiara Domeneghetti; M Chiara Dalconi; Matteo Alvaro; Anna M Fioretti; Konstantin D Litasov; Marc D Fries; Matteo Leoni; Nicola P M Casati; Peter Jenniskens; Muawia H Shaddad

doi:10.1073/pnas.1919067117

Impact shock origin of diamonds in ureilite meteorites

Proc Natl Acad Sci U S A. 2020 Oct 13;117(41):25310-25318. doi: 10.1073/pnas.1919067117. Epub 2020 Sep 28.

Authors

Fabrizio Nestola^{1

2}, Cyrena A Goodrich³, Marta Morana⁴, Anna Barbaro⁴, Ryan S Jakubek⁵, Oliver Christ⁶, Frank E Brenker², M Chiara Domeneghetti⁴, M Chiara Dalconi⁶, Matteo Alvaro⁴, Anna M Fioretti⁷, Konstantin D Litasov⁸, Marc D Fries⁹, Matteo Leoni^{10

11}, Nicola P M Casati¹², Peter Jenniskens¹³, Muawia H Shaddad¹⁴

Affiliations

¹ Department of Geosciences, University of Padova, I-35131 Padova, Italy; fabrizio.nestola@unipd.it goodrich@lpi.usra.edu.
² Geoscience Institute, Goethe University Frankfurt, 60323 Frankfurt, Germany.
³ Lunar and Planetary Institute, Universities Space Research Association, Houston, TX 77058; fabrizio.nestola@unipd.it goodrich@lpi.usra.edu.
⁴ Department of Earth and Environmental Sciences, University of Pavia, I-27100 Pavia, Italy.
⁵ Astromaterials Research and Exploration Science Division, Jacobs Johnson Space Center Engineering, Technology and Science, NASA, Houston, TX 77058.
⁶ Department of Geosciences, University of Padova, I-35131 Padova, Italy.
⁷ Institute of Geosciences and Earth Resources, National Research Council, I-35131 Padova, Italy.
⁸ Vereshchagin Institute for High Pressure Physics RAS, Troitsk, 108840 Moscow, Russia.
⁹ NASA Astromaterials Acquisition and Curation Office, Johnson Space Center, NASA, Houston, TX 77058.
¹⁰ Department of Civil, Environmental and Mechanical Engineering, University of Trento, I-38123 Trento, Italy.
¹¹ Saudi Aramco R&D Center, 31311 Dhahran, Saudi Arabia.
¹² Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland.
¹³ Carl Sagan Center, SETI Institute, Mountain View, CA 94043.
¹⁴ Department of Physics and Astronomy, University of Khartoum, 11111 Khartoum, Sudan.

Abstract

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.

Keywords: carbon phases; diamond; impact shock; ureilites; ureilitic diamonds.

Abstract

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