Circum-Superior Belt northwestern Superior craton margin intrude an older, 2,090 to 2,070 million-year-old dike swarm. The Ospwagan Group is younger than and the 1,864 million-year-old Winnipegosis komatiite belt lies to the southwest. Numerous tectonic settings have been suggested for triggering magmatism in the Fox River Belt, including a marginal basin rifting event. At the southern portion of the Circum-Superior Belt, a group of fragmental sediments composed of iron formation was formed during a period of magmatic activity in the Marquette Range Supergroup. Included in the Marquette Range Supergroup is the Hemlock Formation, a bimodal volcanic group that is estimated to have an
Circum-Superior Belt features are present in the Circum-Superior Belt, including dikes, sills and volcanics that comprise geologic formations. This geologic belt is considered to be a large igneous province because its magmatic rocks were emplaced over an extremely short geological time span. Even though the Circum-Superior Belt was emplaced during an extremely short geological time span, the associated magmas were probably derived from a number of separate sources. Most of the Circum-Superior Belt lies along the margin of the Superior Craton, which is the most extensive fragment of Archean crust on Earth. However, a number of igneous rocks within the Superior craton