Continent-scale linearity of kimberlite–carbonatite magmatism, mid-continent North America

• A N40°W kimberlite–carbonatite trend is identified from Louisiana to Alberta.
• Sr–Nd–Hf–Pb isotopes indicate changing mantle magma sources with time.
• Early lithospheric component evolved to increasing asthenospheric source.
• The trend has lowest Sr(i) and highest εNd(i)εNd(i) of K–T rocks in mid-continent.
• A slab edge in the transition zone focused melts upward to form linear trend.

Cretaceous–Tertiary kimberlite–carbonatite magmatism in mid-continent North America extends along a N40°W linear trend from Louisiana to Alberta, and occurs in at least four different pulses (∼109–85, 67–64, 55–52, and less than 50 Ma). The lack of spatial age progressions of magmatism consistent with motion of North America over a fixed hot spot, the presence of Sr–Nd–Hf–Pb isotopic and trace-element compositions that show a temporal evolution from lithospheric to asthenospheric melt-sources, and the orientation of the magmatic belt parallel to the western subduction margin of the North American plate, suggest that this linear zone is the surface expression of mantle melting related to the subduction system. We propose that fragmentation of Farallon and Kula plates opened slab windows perpendicular to their convergence direction. In this model, sheet-like mantle upwellings were induced along slab-window margins, and these upwellings underwent low-degree partial melting to produce highly alkalic magmas along the trend parallel to, but ∼2000km east of, the convergent margin. The N40°W trend may reflect melting associated with penetration of the mantle transition-zone by the downgoing oceanic plate(s).