SHOCK TEMPERATURE RECORDED BY GRAPHITE IN UREILITES FROM ALMAHATA SITTA

Ureilites are a major group of achondrites that have very high (up to ~8.5 wt.%) carbon contents [1,2]. The origin and history of their carbon phases (mainly graphite and minor diamond) are important for understanding their petrogenesis, and the distribution of carbon in the early solar system. We have been studying the origin of diamonds in ureilites from Almahata Sitta [3,4]. The Almahata Sitta meteorite fell in 2008 from the impact of asteroid 2008 TC3, and is a polymict breccia with approximately 70% ureilitic clasts [5,6]. These ureilite samples have the lowest degree of terrestrial weathering of any ureilites, which makes them ideal for studying the origin of the carbon phases in ureilites. In Almahata Sitta (AhS) ureilites 72 and 209b [4], diamonds with crystallite sizes at the nanometric scale (diamond particles < 100 nm) were found associated with nanographite. This same association was found in main group ureilite NWA 7983, and also included micrometric sized diamonds [3,4]. The diamonds in these samples were interpreted to be a product of impact shock from original graphite.