The kimberlite clan: relationship with olivine and leucite lamproites, and inferences for upper-mantle metasomatism

B. Dawson S U M M A RY: Kimberlites are rare ultrabasic potassic low-volume melts that originate in the diamond stability field of the upper mantle. They are petrographically complex, and wide mineralogical nd chemical variations suggest that they should be regarded as a group or clan rather than a single narrowly-defined rock type. In S African kimberlites there is a major division between highly-micaceous (Group II) kimberlites that are mineralogically, chemically and isotopically distinct from poorly-micaceous (Group I) kimberlites. Nd and Sr isotope studies of diamondiferous olivine and leucite lamproites from NW Australia indicate that they are isotopically similar to Group II kimberlites but are distinct from Group I. New bulk rock analyses of Group II kimberlites indicate closer chemical similarities with olivine lamproites than previously supposed. Varieties of kimberlite Kimberlites are rare ultrabasic potassic igneous rocks occupying small vents, sills and dykes. They are petrographically complex because o