Winnipegosis komatiite belt

Geological setting

The Winnipegosis Komatiite Belt is in the Superior Boundary Zone, in Manitoba, Canada, adjacent to the Thompson Nickel Belt. The Superior Boundary Zone lies along the northwestern margin of the Archaean Superior Craton, and forms the eastern foreland of the ~1.8-billion-year-old Trans-Hudson Orogen. The Trans-Hudson Orogen was a continental collision that formed following the closure of the ancient Manikewan Ocean. It resulted in the juxtaposition of the Superior Craton with the amalgamated Rae and Hearne Cratons, and a number of continental fragments, including the Sask Craton. Closure of the Manikewan Ocean is believed to have begun by 1915 million years ago, though the first evidence of this ocean closure along the western Superior margin is the initiation of magmatism in the 1890-million-year-old Snow Lake Arc, interpreted as a subduction zone that formed outboard (towards the ocean) from the Superior Boundary Zone. Mafic to ultramafic magmatism in the Winnipegosis Komatiite Belt is contemporaneous with ongoing magmatism in the Snow Lake Arc, which implies the Winnipegosis Komatiite Belt formed along a convergent plate boundary. The Winnipegosis Komatiite Belt forms part of the ~3000 km Circum-Superior Belt, considered a mantle-plume-derived large igneous province.

The Winnipegosis Komatiite Belt itself predominantly consists of tholeiitic basalt and komatiite, intercalated with lesser amounts of shale and dolomitic sediments, and intruded by mafic and ultramafic cumulates. These overlie a thin interval of conglomerate and sandstone, which lies unconformably on Superior Craton tonalites dated to 2792 million years old. The entire belt underwent sub–greenschist to greenschist facies metamorphism, during the Trans-Hudson Orogeny.