"Clifford's Rule" and the geodynamics of kimberlite magmatism

Abstract

The Clifford rule emphasizes the association of kimberlite magmatism with the crust areas of Archean and Early Proterozoic age. Though there are diamantiferous and highly productive primary diamond deposits outside Archean cratons, the Clifford rule is valid for most cases. However, from the geodynamics viewpoint the rule is not consistent because the kimberlites have a deep origin, and crustal structures can not affect the formation of protokimberlite melts. The extended Clifford rule associates the primary diamonds deposits not with the Archean crust but with the thick depleted lithosphere. It is geodynamically justified and has almost no exceptions. Besides, with such an interpretation of the Clifford rule the association of the kimberlite magmatizm with the ancient structures becomes self-evident because a lithosphere characteristic of Archean cratons could not be formed later due to a decrease of the potential temperature of the convecting mantle since Archean. Therefore the cooling of the convecting mantle is in fact the primary physical reason underlying the validity of the Clifford rule.