Timing and geochemistry of 1.88Â Ga Molson Igneous Events, Manitoba: Insights into the formation of a craton-scale magmatic and metallogenic province

The tectonic setting of Molson Igneous Events is intriguing as it occurs at a convergent margin during initiation of oceanic arc formation and closure of the Manikewan Ocean. This magmatism is relatively short-lived (<20 m.y.), has a dominantly MORB-like chemical and neodymium isotopic composition, and can be traced into the highly deformed Thompson Nickel Belt where it forms sediment-sill complexes associated with Ni-Cu mineralization. The majority of the northern Superior craton margin, including the Thompson Nickel Belt, Fox River Belt, Cape Smith Belt and the New Québec Orogen, share a strikingly similar Paleoproterozoic evolution with two periods of mafic/ultramafic magmatism at ∼2.2-2.1 and 1.90-1.87 Ga, similarity in basalt geochemistry, and the development of ∼1.88 Ga fine-grained sediment-sill complexes that are host to significant nickel mineralization. The similarity in the timing and geochemistry of the 1.88 Ga mafic/ultramafic magmatism and its location along the western, northern and eastern Superior Province margin, extending for more than 3000 km, is interpreted to indicate Molson Igneous Events are linked to a unique and widespread Paleoproterozoic depleted mantle melting phenomena. Possible tectonic settings include development of a series of contemporaneous continental back-arcs during convergence and subduction of Manikewan oceanic crust or more likely passive upwelling of asthenosphere focused along the thinned margin of the Superior craton.