BACKTRACKING THE KIMBERLITES EMPLACED OVER THE NORTH AMERICAN CONTINENT

Kimberlites are fairly rare ultramafic igneous rocks that are most generally emplaced on Archean cratons. Their distribution over central North America is surprising because here they occur on younger Proterozoic terranes far from such ancient cratonic crust. Several hypotheses have been proposed to account for the kimberlites emplacement: e.g., fluids derived from subducting slabs, edge-driven convection, entrainment by mantle plumes, or upwellings initiating along the edges of large low shear velocity provinces (LLSVPs). In this study, we backtrack the locations of North American kimberlites using the GPlates software and new rotation poles, in order to bring new insights into their emplacement. We also consider constraints from models that provide the depth to the lithosphere-asthenosphere boundary and the LLSVPs locations provided by tomography models. We find that the emplacement processes vary through time. The oldest kimberlites (350-660 Ma old) were emplaced over the Pacific LLSVP, while the kimberlites with ages between 110 and 350 Ma were emplaced over the Atlantic LLSVP. Kimberlites with ages less than 110 Ma are not associated with upwellings originating from LLSVPs, but were more likely emplaced though edge-driven convection.