SECULAR VARIATION IN KIMBERLITE FORMATION: THE VARIABLE CONNECTION WITH LLSVPS FOR KIMBERLITES FROM NORTH AMERICAN AND AFRICA

Kimberlites are fairly rare ultramafic igneous rocks and most emplaced on or very near to Archean cratons. Within this study, we bring new insights into the emplacement of kimberlites within the North American and African continents by studying their connections with Large Low Shear Velocity Provinces ( LLSVPs). We backtrack kimberlite emplacement position, i.e., compute the position of the lithospheric plate at the time when the kimberlites were emplaced. We use the GPlates software and new rotation poles that allow us to go back 1,000 Myr in time. We have also designed a method to quantitatively estimate the correlation between backtracked position and LLSVP locations, which has previously only been assessed “by eye”. We find that periods of enhanced kimberlitic magmatism correspond to periods when the continental lithosphere was drifting over LLSVPs, whereas quiet periods, i.e., periods during which few kimberlites were emplaced, correspond to times when lithospheric plates are not over LLSVPs. These results provide new constraints for the phenomena at the origin of kimberlites emplacement. In particular, our study shows that the mantle plays an active role in kimberlite emplacement. This contrasts with previous studies in which the emplacement of kimberlites is considered a (passive) “successful drainage event”, facilitated by tectonic triggers (e.g., breakup of a supercontinent). It also implies that LLSVPs have been stable for at least 1 billion years and, therefore, play an essential role in creating and stabilizing global mantle flow.