Author name: Larry M. Heaman

Key to deciphering the origin and tectonic setting of kimberlite magmatism is an accurate understanding of when they formed. Although determining absolute emplacement ages for kimberlites is challenging, recent methodological advances have contributed to a current database of >1,000 precisely dated kimberlite occurrences. Several profound findings emerge from kimberlite geochronology: kimberlites were absent in the first half of Earth history; most kimberlites were emplaced during the Mesozoic; kimberlite magma formation may be triggered by a variety of Earth processes (deep mantle plumes, subduction of oceanic lithosphere, continental rifting); and enhanced periods of kimberlite magmatism coincide with supercontinent breakup.

Kimberlites are ultrabasic, Si-undersaturated, low Al, low Na rocks rich in CO2 and H2O. The distinctive geochemical character of kimberlite is strongly influenced by the nature of the local underlying lithospheric mantle. Despite this, incompatible trace element ratios and radiogenic isotope characteristics of kimberlites, filtered for the effects of crustal contamination and alteration, closely resemble rocks derived from the deeper, more primitive, convecting mantle. This suggests that the ultimate magma source is sub-lithospheric. Although the composition of primitive kimberlite melt remains unresolved, kimberlites are likely derived from the convecting mantle, with possible source regions ranging from just below the lithosphere, through the transition zone, to the core–mantle boundary.

Kimberlites are rare, enigmatic, low-volume igneous rocks. They are highly enriched in magnesium, volatiles (CO2 and H2O) and incompatible trace elements and are thought to be the most deeply derived (>150 km) magmatic rocks on Earth. Kimberlites occur in ancient and thick continental lithosphere, forming intrusive sheets and composite pipes, commonly in clusters. Despite their rarity, kimberlites have attracted considerable attention because they entrain not only abundant mantle fragments but also diamonds, which can provide a uniquely rich picture of the deep Earth. This issue summarises current thinking on kimberlite petrology, geochemistry, and volcanology and outlines the outstanding questions on the genesis of kimberlites and associated diamond mines.