New data on the composition of tagamites of the Popigai astrobleme

Resumo

New data on the composition of tagamites (impact melt rocks) of the Popigai atsrobleme (Siberia) are presented. The preliminary results support the following major conclusions: (1) the matrix of the studied tagamites is crystallized and is composed of identified minerals; (2) the degree of the matrix crystallization and the amount of inclusions in tagamites can vary significantly; (3) tagamites are identical to the intracrater gneisses of the Popigai astrobleme by the REE contents and are distinct from them by significantly lower SiO₂ and higher Al₂O₃, FeO, MgO, and CaO contents; (4) the Popigai tagamites and intracrater gneisses are enriched in Ni (on average) in comparison with gneisses of the Khapchan Group; and (5) the various (often sufficient) degrees of crystallization of tagamites indicate the duration of the cooling of the melt, when diamonds could possibly have been dissolved.