Origin of Diamonds in Ureilites

The origin of diamonds in the 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 with size similar to Mars or Mercury, like typical lithospheric diamonds formed in the 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). We argue that diamonds within these ureilite were formed during an impact shock event characterized by peak pressures of ~13-15 GPa. There is no evidence that formation of micrometer(s) sized diamonds or associated Fe-S-P phases in ureilites require high static pressures and long times for formation1,2. It is highly unlikely that any of the diamonds in ureilites formed in bodies as large as Mars or Mercury, as recently suggested.