抄録
We synthesized vapor-growth diamonds and shock-produced diamonds, and examined elemental abundances and isotopic compositions of noble gases in them. The trapping mechanism of noble gases in these synthetic diamonds has been verified from this study. We have examined various features of diamonds in ureilites and compared with those in synthetic diamonds, and concluded that the vapor-growth hypothesis is better than the impact-shock hypothesis for the origin of diamonds in ureilites. The diamond (and graphite, amorphous carbon, too) have been deposited on early condensate such as Re, Ir, W etc. in the primitive solar nebula, which explains the chemical features of vein material in ureilites. The vapor-growth model shows that nebular processes are primarily responsible for the chemical composition of ureilites.
