The origin and evolution of North American kimberlites

Recent discoveries of kimberlites in North America have revealed that different processes are involved in the generation of kimberlite magma. A multi-disciplinary approach combining mineralogical, petrological, geochemical, and geochronological methods is used to classify the kimberlites, investigate possible sources of magma and evaluate current tectonic models proposed for the generation of kimberlite magma. The two main study areas are (1) the diamond-poor Churchill kimberlite field (Nunavut); and (2) the highly diamondiferous Lac de Gras kimberlite field (NWT). The Attawapiskat kimberlite field, the Kirkland Lake kimberlite field and the Timiskaming kimberlite field (Ontario) are also included in this study.;The Churchill kimberlites are classified as sparsely macrocrystic, oxide-rich calcite evolved hypabyssal kimberlite and macrocrystic oxide-rich monticellite phlogopite hypabyssal kimberlite. Electron microprobe analyses of olivine, phlogopite, spinel and perovskite support this petrographical classification. Twenty-seven precise U-Pb perovskite and Rb-Sr phlogopite emplacement ages indicate that magmatism spans ∼45 million years (225-170 Ma).;The crystallization ages and the Sr and Nd isotopic compositions of groundmass perovskite from a well-established, SE-trending Triassic-Jurassic corridor of kimberlite magmatism in Eastern North America (ENA) were determined to investigate the origin of this magmatism. The Sr isotopic results indicate that the Churchill (0.7032-0.7036) and Attawapiskat kimberlites (0.7049-0.7042) have unique isotopic compositions, while Kirkland Lake/Timiskaming perovskite have a larger range of 87Sr/86Sr ratios. This implies the derivation of kimberlite magma from two distinct sources in the mantle, a depleted MORB mantle source and a kimberlite magma with a Bulk Silicate Earth signature. The pattern of increasing 87Sr/86Sr initial with younging of kimberlite magmatism along the ∼2000 km corridor of continuous Triassic/Jurassic magmatism could be explained from either a single or multiple hotspot track(s), responsible for the addition of heat required to generate small volume mantle melting of a kimberlite source.;The 55-56 Ma Diavik kimberlite cluster (NWT) have been classified as resedimented volcaniclastic > olivine-bearing volcaniclastic > mud-bearing volcaniclastic > macrocrystic oxide-bearing hypabyssal kimberlite > calcite oxide hypabyssal kimberlite > tuffisitic kimberlite breccia. Geochemical features of Diavik kimberlites include: (1) LREE enrichment, (2) large intra-field range in REE content, and (3) highly diamondiferous kimberlites at Diavik with primitive geochemical signatures.