Superior Craton

The Superior Craton (or Superior Province) forms the core of the Canadian Shield at the heart of the North American continent. It extends from Quebec in the east to eastern Manitoba in the west. The western margin extends from northern Minnesota through eastern Manitoba to northwestern Ontario.

The formation of the Superior Craton is best explained within the context of 2.72-2.68 Ga accretion of small continental plates and trapped oceanic terranes in a tectonic regime resembling that of today's rapidly changing southwestern Pacific Ocean. The craton is made up of a collage of small continental fragments of Mesoarchean age and Neoarchean oceanic plates and tracts of oceanic crust that consists of the following domains: Northern Superior, North Caribou, Winnipeg River, Marmion, Minnesota River Valley, Opatica, and Goudalie. These domains are generally separated by greenstone-granite terranes with long strike lengths that record various geodynamic environments, including oceanic floor, plateau, island arc and back-arc settings. Examples include the Oxford-Stull terrane in the north, the western Wabigoon in the west, and the Wawa-Abitibi subprovince in the southeastern Superior Province. A suite of Neoarchean monzodiorite intrusions from greenstone belts of the western Superior province have been termed "sanukitoid" because of their similarity in bulk chemical composition to high-magnesium andesite from Japan known as "sanukite."

Neoarchean volcano-plutonic rocks of arc affinity dominate the oceanic margins of the Superior Craton and indicate that there was widespread subduction prior to the 2.72-2.68 Ga collisional events that amalgamated the present-day Superior Craton. However, during the amalgamation-collisions, five discrete orogenies are recognized. In the western and southern Superior province, the orogenies resulting from these collisional events all have the following common elements: 1) widespread calc-alkaline arc magmatism on the upper plate preceding collision; 2) deposition, rapid burial and deformation of syn-orogenic sediments (conglomerate, greywacke) in suture zones over strike lengths of >1000 km; 3) high-temperature, low-pressure regional metamorphism over broad regions; 4) steep foliation and orogen-parallel strike-slip faults attributed to transpressive deformation; 5) emplacement of mantle-derived, post-orogenic plutons of the sanukitoid suite; 6) widespread emplacement of late granitic plutons of crustal derivation; and 7) rapid post-orogenic uplift and cooling. (Percival, 2003).

Sedimentary rocks as old as 2.48 Ga unconformably overlie Superior Province granites indicating that most erosion had occurred prior to ca. 2.5 Ga. Younger metasedimentary belts separate some of the continental and oceanic domains and extend across the entire province. These 50–100 km wide belts of metagreywacke, migmatite and derived granite appear to represent thick syn-orogenic sequences that were deposited, deformed and metamorphosed during collisional orogeny. Faults developed in association with several distinct tectonic events host a variety of orogenic gold deposits across the province. (Percival, 2006).

The Superior Craton has a lithosphere thickness of at least 250 km beneath the craton, and possibly as much as 350 km. The Kapuskasing uplift represents a 500-km long fault-bounded structure that divides the Superior Province into eastern and western halves. 2.765-2.66 Ga mid to lower crustal levels of the Abitibi-Wawa and Quetico belts contain amphibolite- to granulite-facies tonalite gneiss, paragneiss, mafic gneiss and anorthosite exposed through east-directed thrusting and sinistral transcurrent motion during the Paleoproterozoic. Recent work suggests that the Kapuskasing structure accommodated a 20-degree counterclockwise rotation of the western Superior with respect to the east. (Percival, 2006).