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.

Impact shock origin of diamonds in ureilite meteorites / Nestola, F. and Goodrich, C.A. and Morana, M. and Barbaro, A. and Jakubek, R.S. and Christ, O. and Brenker, F.E. and Domeneghetti, M.C. and Dalconi, M.C. and Alvaro, M. and Fioretti, A.M. and Litasov, K.D. and Fries, M.D. and Leoni, M. and Casati, N.P.M. and Jenniskens, P. and Shaddad, M.H.. - In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA. - ISSN 1091-6490. - ELETTRONICO. - 117:(2020), pp. 25310-25318. [10.1073/pnas.1919067117]

Impact shock origin of diamonds in ureilite meteorites

Morana, M.;
2020

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.
117
25310
25318
Nestola, F. and Goodrich, C.A. and Morana, M. and Barbaro, A. and Jakubek, R.S. and Christ, O. and Brenker, F.E. and Domeneghetti, M.C. and Dalconi, M.C. and Alvaro, M. and Fioretti, A.M. and Litasov, K.D. and Fries, M.D. and Leoni, M. and Casati, N.P.M. and Jenniskens, P. and Shaddad, M.H.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2158/1284666
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