Constraining the isotopic endmembers contributing to 1.1 Ga Keweenawan large igneous province magmatism

Continental flood basalt lavas often contain deeply-sourced, thermo-chemically anomalous material that can provide a potential probe of inaccessible reservoirs. However, continental flood basalts interact with geochemically diverse domains within the continental lithosphere, which may complicate interpretations of deep mantle signatures. We examine the role of continental lithospheric mantle in continental flood basalts erupted as part of the 1.1 Ga Keweenawan large igneous province, centered on the Lake Superior region of North America. We show that flood basalts at Mamainse Point exhibit a range of ε Hf 1100 from −14.1 to +6, plotting along the global ε Hf— ε Nd mantle array. Lithospheric mantle melts represented by alkaline rocks from the Coldwell and Seabrook Lake Complexes yield positive ε Nd 1100 (+0.7 to +4.3) and ε Hf 1100 from −6.9 to +2.4, placing them below the mantle array. Mamainse Point lavas are interpreted to be variably crustally contaminated melts of the Keweenawan plume and ambient upper mantle; there is no clear evidence for contributions from an enriched lithospheric mantle.