Kimberlite and related rocks from Garnet Lake, West Greenland, including their mantle constituents, diamond occurrence, age and provenance

Diamonds are typically colourless and occur as fragments or with a dominant octahedral morphology. Crysts exhibit very high quantities of nitrogen (up to 2133 ppm N) and yet are not strongly aggregated to IaB centres (typically about 33% aggregation). This suggests either a short residence time, low residence temperature or likely a combination of both. Employing the restricted range of equilibrium conditions exhibited by mantle xenoliths, calculated diamond formation ages peaking around 583-593 Ma are favoured. This is a short time before the 568 Ma Garnet Lake main sheet emplacement age which coincides with the age of the nearby Sarfartoq carbonatite complex. A model of mantle refertilisation and diamond formation culminating in conditions favourable for creating carbonate-rich melts acting as carriers of mantle constituents to the surface is presented. Data suggest close temporal, chemical and geographic associations between kimberlite, aillikite and carbonatite.