Can primitive kimberlite melts be alkali‐carbonate liquids: Composition of the melt snapshots preserved in deepest mantle xenoliths

The study of kimberlite rocks is important as they provide critical information regarding the composition and dynamics of the continental mantle and are the principal source of diamonds. Despite many decades of research, the original compositions of kimberlite melts, which are thought to be derived from depths > 150 km, remain highly debatable due to processes that can significantly modify their composition during ascent and emplacement. Snapshots of the kimberlite‐related melts were entrapped as secondary melt inclusions hosted in olivine from sheared peridotite xenoliths from the Udachnaya‐East pipe (Siberian craton). These xenoliths originated from 180‐ to 220‐km depth and are among the deepest derived samples of mantle rocks exposed at the surface. The crystallised melt inclusions contain diverse daughter mineral assemblages (>30 mineral species), which are dominated by alkali‐rich carbonates, sulfates, and chlorides. The presence of aragonite as a daughter mineral suggests a high‐pressure origin for these inclusions. Raman‐mapping studies of unexposed inclusions show that they are dominated by carbonates (>65 vol.%), whereas silicates are subordinate (65 vol.%, especially alkali‐rich varieties), whereas silicates are subordinate (