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 formed during the Archean period. A craton is a large part of the Earth's crust that stays stable and changes very little over time. The Superior Craton is about 1,572,000 km² in size.

The craton experienced many events from 4.3 to 2.57 Ga. These events included the movement and shaping of both oceanic and continental crusts.

Researchers split the Superior Craton into different areas based on rock types and how the rocks were shaped. These areas are grouped into western and eastern superior provinces. They include the North Superior Superterrane and Wawa Terrane, among others.

Studies of how the Superior Craton formed differ between the western and eastern parts. In the west, five major orogenies played a role. In the east, two models are suggested. One model focuses on the collision between terranes. The other model looks at the effect of active anorogenic magmatic activity.

Location

The Superior Craton is in central Canada. It includes parts of Quebec, Ontario, and Manitoba. It even reaches close to the border 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 is the core of the Canadian Shield and is surrounded by early Proterozoic mountains. On its western to northeastern side, it meets the Trans-Hudson orogens. The Grenville orogens are to the east and southeast. The southern edge touches the Keweenawan rift. The southernmost part in Minnesota reaches the Central Plain orogen.

The craton has three main sets of faults in different directions. In the northwest, the faults run west to northwest. In the northeast, they go northwest. In the south, they run east to west, splitting the craton into long, narrow parts.

Growth history of the terranes

The craton-forming terranes come from many different places, like oceanic arc, ancient forearc, and fold-thrust belt areas. These places were mostly made when things were being pushed together.

Some terranes, like the Western Wabigoon Terrane, come from an oceanic arc. An oceanic arc is a line of volcanoes that formed above subduction zones. The Superior Province has three parts. The first part is the northwestern area, made of high-grade gneiss, such as Minto and Pikwitonei. The second part is the northeastern area, filled with metamorphic rocks of granulite-facies. The last part is the southern area, like the Minnesota River Valley, which has metavolcanic or metasedimentary rocks that run east to west.

Development

Research on the Superior Craton has mostly looked at how its western part formed. We still don't know much 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, called orogenies, which are mountain-building events. These stages happened from oldest to 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.