Impact shock origin of diamonds in ureilite meteorites
Open Access
- 28 September 2020
- journal article
- research article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences of the United States of America
- Vol. 117 (41), 25310-25318
- https://doi.org/10.1073/pnas.1919067117
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.Funding Information
- NASA (NASA grants 80NSSC17K0165, NNX17AH09GS03, and 80NSSC19K0507)
- Ministero dell'Istruzione, dell'Università e della Ricerca (R164WEJAHH)
- PNRA (PNRA 2016)
- PNRA (PNRA18 00247-A)
This publication has 70 references indexed in Scilit:
- Spectral reflectance properties of ureilitesMeteoritics & Planetary Science, 2010
- The recovery of asteroid 2008 TC3Meteoritics & Planetary Science, 2010
- The impact and recovery of asteroid 2008 TC3Nature, 2009
- Sulfur and phosphorus in the Earth's core: The Fe‐P‐S system at 23 GPaGeophysical Research Letters, 2007
- Ultrahard polycrystalline diamond from graphiteNature, 2003
- Noble gas studies in diamonds synthesized by shock loading in the laboratory and their implications on the origin of diamonds in ureilitesGeochimica et Cosmochimica Acta, 1995
- Shock-induced martensitic phase transformation of oriented graphite to diamondNature, 1991
- Noble-gas enrichment in vapour-growth diamonds and the origin of diamonds in ureilitesNature, 1987
- Raman Spectrum of DiamondPhysical Review B, 1970
- Hexagonal Diamond—A New Form of CarbonThe Journal of Chemical Physics, 1967