Petrogenesis of a newly discovered ∼1.1 Ga aillikite, carbonate-rich kimberlite, and carbonatite association on the northern margin of the Mid-continental Rift System, Ontario, Canada

In this study, we present new field, petrographic, and whole-rock major and trace element, and Nd–Pb–Sr radiogenic isotope data for a newly discovered aillikite, carbonate-rich kimberlite, and carbonatite association on the northern shore of Lake Superior, Canada. The aillikite, carbonate-rich kimberlite, and carbonatite association is exposed as sills and dykes in the Neoarchean Schreiber-Hemlo greenstone belt in the Ripple Bay area, Ontario. The carbonatite and carbonate-rich kimberlite occur in the same dykes and sills, whereas the aillikite occurs in separate dykes and sills. Boundaries between the carbonatite and carbonate-rich kimberlite are mostly sharp, with some gradational outcrops. Field relationships, near 1.1 Ga Pb–Pb and Rb–Sr errorchron ages, and Nd depleted mantle model ages (T_DM = 1.14–1.46 Ga) reported in this study, collectively suggest that the Ripple Bay aillikite, carbonate-rich kimberlite, and carbonatite association formed as part of the late Mesoproterozoic Mid-continental Rift System in North America. New geochemical data are used to constrain the petrogenesis of the Ripple Bay aillikite, carbonate-rich kimberlite, and carbonatite association and address the long-standing debate on the co-genetic relationship of aillikite, kimberlite, and carbonatite occurrences worldwide. Each rock type displays distinct major and trace element characteristics. On the chondrite-normalized REE diagram, all three rock types exhibit subparallel trends characterized by large enrichments of LREEs over HREEs (La/Yb_cn = 33–62), with the carbonatite displaying the most enriched patterns and carbonate-rich kimberlites showing the least enrichment, and aillikites plot between the carbonatites and carbonate-rich kimberlites. Aphanitic texture and flow patterns in the carbonatite indicate that it solidified from a carbonatite melt. All three rock types resulted from small degrees of partial melting in different parts of the same mantle source region, which had different proportions of metasomatic minerals, and represent near-primary melt compositions. The carbonate-rich kimberlite and carbonatite melts were transported simultaneously to the surface through the same magma conduits, with minimal mixing, indicating that their sources were spatially associated. Initial Nd (εNd=+0.6 to + 7.0) and Sr (Sr_i = 0.700309–0.704111) compositions and ²⁰⁶Pb/²⁰⁴Pb (17.83–40.23) and ²⁰⁸Pb/²⁰⁴Pb (37.66–62.88) isotope ratios reflect heterogeneous asthenospheric mantle sources containing strongly depleted to enriched components.