Superior Craton

The Superior Craton is a stable crustal block covering Quebec, Ontario, and southeast Manitoba in Canada, and northern Minnesota in the United States. It is the biggest craton among those formed during the Archean period. A craton is a large part of the Earth's crust that has been stable and subjected to very little geological changes over a long time. The size of Superior Craton is about 1,572,000 km².

The craton underwent a series of events from 4.3 to 2.57 Ga. These events included the growth, drifting and deformation of both oceanic and continental crusts.

Researchers have divided the Superior Craton into many different domains based on rock types and deformation styles. These domains, grouped into western and eastern superior provinces, include the North Superior Superterrane and Wawa Terrane, among others.

Studies on the formation of the Superior Craton varied in progress between the western and the eastern part. For the western part, five major orogenies were involved. For the eastern part, two models are suggested, one focusing on the collision between terranes, and the other on the effect of an active anorogenic magmatic activity.

Location

The Superior Craton covers central Canada, including the northern and central part of Quebec, the central and southern part of Ontario, and southeast Manitoba. It even reaches a point near the boundary between the U.S. states of South Dakota and Minnesota.

Tectonic setting

The Superior Craton covers more than 1,572,000 km² of North America. It forms the core of the Canadian Shield and is surrounded by early Proterozoic mountain ranges. On its western to northeastern side, it is bounded by the Trans-Hudson orogens, while the Grenville orogens lie to the east and southeast. The southern edge meets the Keweenawan rift, and the southernmost part in Minnesota reaches the Central Plain orogen.

The craton is cut by three main sets of faults running in different directions. In the northwest, the faults run west to northwest. In the northeast, they trend northwest, and in the south, they run east to west, dividing the craton into long, narrow sections.

Growth history of the terranes

The craton-forming terranes are created from very diverse settings, such as oceanic arc, ancient forearc, oceanic tectonic melange, uplift within the craton, fold-thrust belt and extra. Common among them is that these features were mostly formed in a compression setting.

Some terranes, such as the Western Wabigoon Terrane, are formed from the setting of an oceanic arc. An oceanic arc is a chain of volcanoes which formed above and parallel to the subduction zones. The Superior Province can be divided into three parts. The first part is the northwestern region characterized by high-grade gneiss, such as Minto and Pikwitonei. The second part is the northeastern region, which is characterized by pervasive metamorphic rocks of granulite-facies. The last part is the southern region like the Minnesota River Valley, which are metavolcanic or metasedimentary subprovinces with an east–west orientation.

Development

Research on the Superior Craton has mostly focused on how its western part formed, leaving some uncertainties about how it connects to the eastern part.

The western Superior Craton grew as different land pieces, called terranes, joined together over time during the Neoarchean period. This joining happened in five main stages, known as orogenies, which are mountain-building events. These stages happened from the oldest to the youngest: the Northern Superior Orogeny, the Uchian Orogeny, the Central Superior Orogeny, the Shebandowanian Orogeny, and the Minnesotan Orogeny. These events show that the land pieces joined starting from the north and moving southward.

The North Caribou Terrane was the central piece around which other terranes joined, attaching to its north and south sides.