Understanding the Paleoproterozoic Circum-Superior Large Igneous Province constrains the thermal properties of Earth’s mantle through time

•Basalts and komatiites from the CSLIP melted from a thermally homogeneous mantle source.•There is no Phanerozoic mantle plume analog for the CSLIP.•Melting occurred in ambient mantle at a convergent margin plate tectonic setting.•CSLIP results critically constrain ambient mantle temperatures through time.•Mantle plumes were ∼100–250 °C hotter than ambient mantle through time. Basalts and komatiites in the ∼1880 Ma Paleoproterozoic Circum-Superior Large Igneous Province are associated in space and time with the closure/subduction of the Manikewan ocean and formation of the Trans-Hudson Orogen during the construction of Laurentia and the supercontinent of Nuna/Columbia. In one model, the igneous rocks formed by the melting of ambient mantle during contemporaneous closure of the Manikewan ocean and rifting of the margins of the Superior craton. In another model melting took place in a mantle plume. Resolution to this problem can help in the understanding of the role of LIPS in supercontinent assembly or breakup over the last 2 billion years of Earth history. It can also constrain the thermal properties of ambient mantle and mantle plumes over the last 3.5 billion years. The contrasting hypotheses were tested by petrological modeling of a large database of basalts and komatiites from the Circum-Superior Large Igneous Province. Results reveal limited variability in mantle potential temperature, from 1540 to 1570 °C, over ∼12 to 15 million years in time and over 1500 km in space from the Cape Smith Belt in the north to the Winnipegosis Belt in the southwest. The essential problem with the mantle plume model for the Circum-Superior LIP is that it predicts thermal heterogeneity, in contrast with the evidence presented here; there is no Phanerozoic mantle plume analog. The limited long wavelength variation in TP is characteristic of ambient mantle magmatism, evidence supporting the plate tectonic model for the Circum-Superior LIP. Results are consistent with ambient mantle thermal models characterized by sluggish mantle convection in the past and with a present-day Urey ratio of about 0.38 (Korenaga, J. 2008. Urey ratio and the structure and evolution of Earth's mantle. Rev. Geophys. 46, RG2007). In contrast, most high MgO komatiites in Paleoproterozoic and Archean greenstone belts melted from sources that were ∼100–200 °C higher. This temperature excess is similar to 100–250 °C for most Phanerozoic mantle plumes, demonstrating approximate constancy of thermal pro