New Identity of the Kimberlite Melt

This study presents detailed petrographic, mineralogical, chemical, and isotope data on exceptionally fresh kimberlite samples from the diamondiferous Udachnaya-East pipe (Daldyn-Alakit region, Siberia). I demonstrate that the Udachnaya-East rocks have radiogenic isotopic compositions, petrographic features and major and trace element geochemistry typical of group-I kimberlites. However, unlike common kimberlites, the studied samples show no primary or secondary serpentine, and thus are essentially anhydrous (< 0.5 wt% H2O), but CO2-rich (10-11 wt%). In contrast with other kimberlites worldwide, the Udachnaya-East samples are uniquely enriched in chlorine and alkalies (2.3-3.2 wt% Cl, 2.6-3.7 wt% Na, and 1.6-2.0 wt% K). I propose that significant amounts of alkali chlorides and carbonates in the Udachnaya-East kimberlite are pristine magmatic components inherited from the kimberlite parental/primary magma. This enrichment may be responsible for the kimberlite low liquidus temperatures, low viscosities, and rapid ascent.