Diamonds and cratons: does the relationship hold for the Canadian deposits?

The exclusive association of primary (kimberlite- or lamproite-hosted) diamond deposits with longterm stable continental cores, termed cratons, was established empirically in the 1960s and became known as Clifford’s Rule. In its original version (Clifford, 1966), Clifford’s Rule defined cratons as those cores that have remained stable for at least 1.5 billion years; later revisions pushed this age standard back to the end of the Archean eon, 2.5 billion years ago. Through a combination of geophysical data and geochemical studies—employing mantle xenoliths (mantle-derived rock fragments) and inclusions in diamonds— it was recognized in the 1980s that the ultimate cause for this link between diamonds and cratons lies in unusually deep-reaching lithospheric keels beneath cratons, extending about 200 km into the convecting mantle.