Carbonate-chloride enrichment in fresh kimberlites of the Udachnaya-East pipe, Siberia: A clue to physical properties of kimberlite magmas?

Kimberlites, the deepest terrestrial magmas and the principal source of diamonds, must have low viscosity and high buoyancy, which govern their exceptionally fast transport from mantle depths to the surface. Appreciation of the rheological properties of kimberlite magmas relies on research into their temperatures and compositions. Understanding of the alkali and volatile element budget is central to these studies, but is hampered by contaminated and altered compositions of kimberlites worldwide. Kimberlites of the diamondiferous Udachnaya-East pipe (Siberia) are exceptionally fresh, with low H₂O (<0.5 Wt%), but high CO₂ (up to 14 wt%), C1 (up to 6 wt%), and alkalies (up to 6 wt% Na₂O and 2.0 wt% K₂O). After crystallization of olivine the kimberlite melt evolved towards essentially carbonate-chloride compositions. The groundmass assemblage and compositions of the Udachnaya-East kimberlite resemble modern halogen-rich natrocarbonatite lavas from the Oldoinyo Lengai volcano. Rheological measurements on the Oldoinyo Lengai lavas can be used to constrain properties of the kimberlite magma.