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The Superior Craton is a stable crustal block located in Canada, covering Quebec, Ontario, SE Manitoba and northern Minnesota, the USA. 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 1572000 km2. The cratonhas undergone a series of events during 4.3-2.57 Ga. These events include the growth, drifting and deformation of both oceanic and continental crust s.

Researchers divided the Superior Craton into many different domains based on rock types and deformation styles. These domains can be grouped into the western and the eastern superior provinces, such as the North Superior Superterrane, Wawa Terrane and so on.

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. They include the Northern Superior Orogeny (2720 Ma), the Uchian Orogeny (2720–2700 Ma), Central Superior Orogeny (2700 Ma), Shebandowanian Orogeny (2690 Ma), and the Minnesotan Orogeny (2680 Ma). For the eastern part, two models are suggested. The first model by Percival and Skulski (2000) focuses on the collision between the terranes. The second model by Bédard (2003) and Bédard et al. (2003) focuses on the effect of an active anorogenic magmatic activity.

Location
The Superior Craton covers central Canada. It occupies the northern and central part of Quebec, extending across and the central and the southern part of Ontario. It also covers southeast Manitoba, with its tip reaching the boundary between South Dakota and Minnesota, the USA.

Tectonic setting
The Archean Superior Craton extends approximately over 1572000 km2 of the North America n Continent. Comprising the core of the Canadian Shield, the Archean Superior craton is encompassed by early Proterozoic orogens. The western to the northeastern part of the craton is bound by the Trans-Hudson orogens. The eastern and the southeastern side is neighbouring the Grenville orogens. The southern side meets the Keweenawan rift, while the southern-most tip of the craton in Minnesota reaches the Central Plain orogen.

Regarding the faults, there are three major trends of subparallel faults slicing the craton into linear subprovinces. In the northwestern part, faulting occurs in a west-northwest direction. The northeastern part has northwest-trending faults. The faults in the remaining southern part possess an east-west direction.

General composition
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 rock s 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.

Northern Superior Superterrane (NSS)
The Northern Superior Superterrane is located at the northwestern end of the craton, in the southeastern Manitoba. This subprovince is bounded to the north by the Trans-Hudson orogens, and to the south by a W-NW trending fault called North Kenyon Fault. This makes the subprovince strip-like lying at the north of another subprovince called Oxford-Skull Domain.

The Northern Superior Superterrane is covered by a great extent of granitic and gneissic rocks. There are also iron formation, mafic to intermediate volcanic rocks, and a minor amount of greywacke which contains 3.9-Ga-old detrital zircon.

These rocks have been reworked by three events of granitoid magmatism from 3.2 to 2.71 Ga. After the magmatism, metamorphism (forming amphibolite facies) took place during 2.68-2.61 Ga, which was caused by the tectonic accretion with other terranes.

Lode gold deposits can be found in the area, as well as Diamond-containing kimberlite pipes.

Oxford-Skull Domain (OSD)
The Oxford-Skull Domain is comprised of two major rock assemblages: the Hayers River assemblage and the Oxford Lake assemblage. The Hayers River assemblage is dominated by 2.83 Ga basaltic rocks, while the Oxford Lake assemblage is characterized by 2.729-2.719 Ga volcanic rock. Interestingly, those volcanic rocks include some coarse-grained clastic sediments along multiple faults, implying that the faulting was active when the assemblage underwent deposition.

Apart from the two assemblages, significantly large greenstone belts appear in the domain, such as the Stull Lake belts and the Knee Lake-Gods Lake belts in Manitoba.

The main part of the domain is also underlain by tonalitic, granodioritic and granitic plutons formed during 2.83-2.69 Ga, while mafic intrusion is as well common in belts like that at the Big Trout Lake.

Studies suggest that the Oxford-Skull Domain possesses an oceanic setting at the northern margin of the North Caribou terrane. At roughly 2.71 Ga, the assembly of the North Superior Superterrane from the north sealed the domain, trapping the sediments in the area.

North Caribou Superterrane (NCS)
As the biggest subprovince of the Superior Craton, the North Caribou Superterrane can be generally described by the two layers of assemblages. The base layer is mainly comprised of intrusive belts (aged 3.0 Ga) with the subordinate extent of volcanic belts. It is overlain by the arc sequences formed between 2.98 and 2.71 Ga. These two layers were heavily influenced by the later continental arc magmatism during 2.75-2.70 Ga.

The northern North Caribou Superterrane connects with Oxford-Stull, Island Lake and Munro Lake domains. Studies show that they were developed on the thinned North Caribou Superterrane crust. Also, gold mineralization aged about 2.685 Ga can be observed along the shear zones in the area, such as the Little Stull Lake area.

The Central North Caribou Superterrane is signified by pervasive plutonism emplaced 10-18km below the ground surface during 2.745-2.697 Ga. This plutonism produced a package of granite, granodiorite, diorite and tonalite, which also occasionally retained pieces of older tonalitic and supracrustal rocks. Apart from the plutonism, greenstone belts (North Caribou greenstone belt) can be found in the central area, which gives proof to the deformation happened earlier than 2.87 Ga. What is also worth mentioning is the lode gold mineralization (Musselwhite lode gold deposit) and Cu-Mo porphyry deposits found in the area, which were formed concurrently with the pervasive plutonism.

The southern North Caribou Superterrane known as the Uchi domain is characterized by substantial mineral deposits such as the Red Lake Gold Camp, coupled with massive sulphide deposits in the area. This domain was formed by rifting at about 2.99 Ga, after that were intermittent yet long-lasting continental arc magmatism (from 2.94 Ga to 2.72 Ga).

English River Domain
The English River Domain lies between the margins of the North Caribou Terrane and Winnipeg River Terrane. Its presence is related to the suture between the two terranes.

This domain is characterized by the sedimentary facies. deposited during 2.705-2.698 Ga. The sedimentary facies in the northern domain is formed from a submarine fan setting, with southward gradual changes to wackes formed from a deep sea.

Also, the domain possesses metamorphic rocks such as the amphibolite and low-pressure granulite. These metamorphic facies bumped into the formation of migmatite and diatexite at 2.691 Ga.

Between the English River domain and the Winnipeg River domain at the south, the margin is occupied with metasedimentary and metaplutonic rocks.

Winnipeg River Terrane
The Winnipeg River Terrane is located at the north and the east of the western Wabigoon terrane, and at the south of the North Caribou and English River Terrane. Formerly it was regarded as a part of the Wabigoon Terrane. Now it is distinguished by characteristic magmatic and structural events.

This terrane is comprised of two major parts: the first part is the basement of the metaplutonic rocks formed during the Mesoarchean period. The second part is another pervsasive pluton formed during the Neoarchean period, which intruded the Mesoarchean pluton.

The mesoarchean pluton remained a big mystery since the rocks are pervasively overlain by the neoarchean rocks. Still, gneiss and foliated tonalite is identified in the area, formed at 3.32-3.05 Ga. Mafic volcanic belt formed at >3.0 Ga are also identified, which was intruded by granites 0.3 Ga later.

The Marmion terrane is at the southeastern side of the Winnipeg River terrane. It is also recognized by tonalite formed at a similar period at those tonalites in WRT. Apart from this, mineral deposits are economical in the area, such as the iron deposits and native silver deposits (in a volcanic massive sulphide setting) in areas like Lumby Lake greenstone belt.

Wabigoon Terrane
The Wabigoon terrane is comprised of two separated zones. The Western and Eastern Wabigoon terrane. This terrane is characterized by dominating igneous rocks, both plutonic and volcanic.

The Western Wabigoon Terrane is made of mafic volcanic rocks aged 2.745-2.72 Ga and tonalitic plutons. The mafic volcanic rocks have tholeiitic to calc-alkaline compositions, implying that they were formed in an oceanic arc setting. For the plutonic rocks, some of them are batholiths of tonalite-diorite-gabbro formed concurrently with the volcanic rocks, while others are batholiths of granodiorite, monzogranite, and monzodiorite formed later (at about 2.710-2.66 Ga). Apart from the igneous rocks, there are narrow belts of clastic metasedimentary sequences found among the volcanic rocks, which are formed during 2.711 to <2.702 Ga, younger than the volcanic rocks.

The Eastern Wabigoon Terrane is made of greenstone belts intruded by granitoid pluton during the Mesoarchean period. The northwestern part of this area is characterized by the Toronto and Tashota assemblages (mainly intermediate to felsic volcanic rocks) which indicate a continental margin setting. The central and southern part of the area is composed of tholeiitic pillowed basalt overlain by younger calc-alkaline rocks.

Quetico Terrane
The Quetico Terrane is an ancient forearc , sealed by the Wabigoon Terrane in the north, and the Wawa Terrane in the south. It is mainly composed of greywacke, migmatite, granite and metasedimentary successions. The successions show a north-to-south younging direction, which is possibly compatible with the geometry of an accretionary prism.

Apart from this, the metasedimentary successions were intruded by a couple of plutonic suites, such as tonalite at 2.696 Ga ; nepheline, syenite and carbonatite during 2.69-2.68 Ga; and granitic pluton at about 2.65 Ga.

Wawa Terrane
The Wawa terrane is located at the south of the Marmion terrane and east of the Lake Superior. It is associated with the Abitibi terrane at the east side of the terrane, which is cut across by North-South trending the Kapuskasing Uplift.

Studies interpret that this terrane is an area of tectonic melange with an oceanic setting. What is significant is the consecutive magmatic activities. during 2.89-2.68 Ga. These activities produce calc-alkalic to alkalic rocks, as well as sanukitoids.

The mineral deposits in the area are abundant in the Michipicoten-Mishubishu belt and the Shebandowan-Schreiber belt. The former one possesses Fe, Au, Cu and minor Ni deposits. while the latter one possesses Fe, Au, volcanic-hosted massive sulphide (VMS) , and Ni deposits.

Kapuskasing Uplift
The Kapuskasing Uplift is an North-South trending fault zone, separating the Superior Craton into the Eastern and Western parts. It is interpreted as an intracratonic uplift (an uplift within the craton). The thrusting in the uplifted area exposed the middle and lower parts of the Wawa-Abitibi and Quetico terranes, such as tonalite, paragneiss and anorthosite.

Abitibi Terrane
The Abitibi Terrane can be described as three major regions: the northern, central and southern regions. The northern region is dominated by volcanic rocks related to the emplacement of a layered intrusion formed during 2.735-2.72 Ga. Massive sulphide deposits and the vein deposits containing Cu and Zn, as well as minor lode gold deposits.

The central region is composed of mainly plutonic rocks and minor volcanic rocks, which Massive sulphide deposits and vein gold deposits can be found (Normetal belt).

The southern Abitibi belt is composed of younger clastic deposits from both the sedimentary and volcanic origin. These include greywackes, conglomerate and alkaline volcanic rocks formed during about 2.69-2.673 Ga. Gold deposits, Cu-Zn massive sulphide deposits, intrusive Ni deposits, and minor porphyry deposits.

Pontiac Terrane
The Pontiac Terrane is a fold-thrust belt dipping towards the south, overlapped by the Abitibi Terrane from the north. It can be described as the northern and southern regions. The northern region is mainly composed of metamorphic rocks like schists and paragneiss, whose protoliths are greywacke and conglomerate. Tonalitic, granodioritic and granitic plutons were also emplaced in the northern area. The southern region is composed of volcanic rocks formed during 2.682 Ga.

Quartz-vein-hosted gold deposits and Gabbroic-sill-hosted Ni-Cu sulphide deposits can be found in the terrane.

Opatica Subprovince
The Opatica Subprovince is located at the north of the Abitibi Terrane. The region is dominated by plutonic rocks, such as tonalite, granodiorite, granite and pegmatite. Several deformation events occurred including a west-verging shearing movement during <2.72 Ga, as well as, a south-vergent movement during 2.69-2.68 Ga.

Volcanogenic massive sulphide (VMS) deposits, Cu-Au vein deposits, Intrusion-hosted Ni-Cu deposits and iron formation can be found in the area.

Opinaca Subprovince
The Opinaca Subprovince is located at the north of the Opatica subprovince. Its margins at the north, west and southeast are bounded by La Grande subprovince.

The 90000-km2 region is characterized by a lower metasedimentary layer (>85% metagreywacke ) containing granulite facies, which was intruded by massive leucogranite dykes and veins.

It is noted that schists are found at the margins of the subprovince comprising of amphibolitic and granulitic core. Rare metals can be found in peraluminous granites and pegmatites.

Ashuanipi Complex
The Ashuanipi Complex is located at the eastern margin of the Superior Craton. Its margins connect with Minto Block at the north and northeast, La Grande Subprovince at the west, and the Opinaca Subprovince at the south.

The region is dominated by high-grade metamorphic and plutonic rocks. At about 2.725 Ga, a tonalite-diorite suite intruded in the sedimentary and volcanic rocks in the region. The intruded rocks then transformed into granulite facies by deformation and metamorphism. After that, Intrusions of several rock types, including diatexite, syenite, granodiorite, granite, occurred during 2.65-2.62 Ga, followed by the intrusion of A-type granite.

La Grande Subprovince
The La Grande Subprovince is bounded by the Opinaca Subprovince at the south and the Bienville Subprovince at the north.

The northern region is characterized by a gneissic basement (Langelier, formed at about 2.8-2.9 Ga).

The western part of the region is composed of a Mesoarchean base overprinted the volcaniclastic Apple formation formed during 2.75-2.73 Ga.

The Guyer lake area is composed of strata formed earlier than the rest of the region. These strata include komatiites which are associated with sills. Porphyry and igneous mineralization can be found in the Eastmain sector.

Bienville Subprovince
The Bienville Subprovince is bounded by the La Grande Subprovince at the south and the east, as well as the Hudson Bay at the West and the Minto Block at the north.

The geology of the Bienville Subprovince can be described as the northern and the southern parts. The northern part is composed of granitic and granodioritic intrusions (Desbergères Suite), penetrating the pyroxene-containing felsic plutonic rocks (Loups Marins Suite formed at 2.73-2.70 Ga) during 2.72-2.71 Ga.

At the south of the region, a massive granodioritc complex with a volcanic-sedimentary klippe cuts through the rocks in La Grande Subprovince at 2.71 Ga.

Northeastern Superior Province (Minto Block)
The Minto Block is divided into several regions based on their rock composition, rock structure and their general magnetic properties (such as the orientation and the magnitude). These domains produce an NW-SW trending, strip-like pattern, with a west-to-east order in naming.

The first region is called the Inukjuak domain (Domain I). It is located the western margin of the Minto Block, bounded by the Hudson Bay at the west, and the Tikkerutuk at the east. The Inukjuak domain is composed of mainly plutonic rocks like tonalite. These tonalites host the tonalitic gneisses formed during 3.65Ga, as well as an old rock formation called Nuvvuagttuq supracrustal belt (formed during 3.825 Ga).

At the east of the Inukjuak domain, the Tikkerutuk domain (II) is bounded by the Bienville Subprovince at the south. The domain is characterized by the pyroxene-bearing plutonic rocks formed during 3.02-2.71 Ga.

The Lake Minto domain (IV) is mainly composed of metasedimentary and derived migmatic rocks, with minor pyroxene-bearing plutonic rocks formed during 2.76-2.70 Ga.

To the east, the Goudalie domain (V) is a large central belt at the middle of the Minto Block, which is composed of volcanic and sedimentary rocks. Also, pyroxene-bearing pluton is pervasive in the area, with minor tonalite.

The Utsalik domain (VI) lies at the east-central part of the Minto Block, which is dominated by pyroxene-bearing plutonic rocks, which are with strong magnetism.

Meeting the northeastern boundary of the Goudalie domain, the Douglas Harbour domain (VII) is composed of a tonalitic complex formed during 2.88-2.75 Ga, surrounding two major massifs, which are mainly charnockite.

The mineral deposits in Minto Block can be classified into two types: Syngenetic type means the mineral deposits were formed at the same time when the host rock is formed. This type of deposits can be found on the surface or subsurface of the Minto Block, such as Algoma-type iron formation, volcanogenic massive sulphide, Ni-Cu deposits, Fe-Ti-V deposits (hosted by mafic intrusions), and U-Th-Mo bearing porphyry deposits.

In contrast, Another type is called epigenetic deposits, meaning that the mineral deposits were formed later than the rocks enclosing them. This kind of deposits can be found in the mineral veins penetrating the rocks in Minto Block, which contain Cu, Ni, Ag, Au, rare earth elements (REE) and limited U.

Development
To explain the formation of the Superior Craton, we have to separate the explanations between the western and eastern parts. This is because the research in the past had been focused on how the western part formed. This leaves uncertainties in the linkage between the west and the east.

Western Superior Craton
The western Superior Craton is formed by different terranes stitching with each other continuously during the Neoarchean period. Such a progressive assembly can be explained by five discrete orogenies (mountain-building processes). They are, from the oldest event to the youngest event, the Northern Superior Orogeny, the Uchian Orogeny, the Central Superior Orogeny, the Shebandowanian Orogeny and the Minnesotan Orogeny. These events show that the timeline of accretions starts from the north with a southward assembling direction.

For these accretions, the North Caribou Terrane acted as the accretion nuclei onto which other terranes dock on its northern and southern side.

Northern Superior Orogeny (2720 Ma)
Before 2720 Ma, there were many pieces of microcontinent fragments which E-W trending conduit-like ocean crusts (with unknown extent) separates them. During 2720 Ma, active subduction along the Northern Superior Superterrane and the North Caribou Terrane caused the southward drifting of the Northern Superior Superterrane. Over time, it united the North Caribou Superterrane and confined the Oxford-Stull domain, which contains rock assemblages related to the continental margin and oceanic crust. The combination of the Northern Superior Superterrane and the North Caribou Superterrane by subduction marked the initiation of the Superior Craton formation. The southward movement of the Northern Superior Superterrane to the North Caribou Superterrane driven by subduction activity is evident by a) arc-related magmatism in Oxford-Stull domain during 2775-2733 Ma ; b) the south-over-north shearing zone at the contact between the two terranes. The suture zone of the subduction is inferred to be the margin of the North Kenyon Fault. The docking of the Northern Superior Superterrane is evident by the >3.5 Ga detrital zircons found in synorogenic (meaning that it forms during an orogenic event) sedimentary rocks aged <2.711 Ga. The docking also initiated the eruption of shoshonitic volcanic rocks during 2710 Ma and the regional shortening. The regional shortening had undergone folding and foliation to form right-lateral, NW-trending shear zones.

Uchian Orogeny (2720–2700 Ma)
During this period, the Winnipeg River Terrane at the south docked northward onto the North Caribou Terrane. The two terranes then sutured to form the English River belt, which was no earlier than <2705 Ma.

During the orogeny, at the south-central North Caribou Superterrane, rocks were deformed thoroughly (from 2718 to 2712 Ma). After the deformation, plutons were emplaced in the area after the tectonic movements and cooled by about 2700 Ma. Following the cooling of the pluton was the swift burial and melting of the rocks in the English River belt and Winnipeg River Terrane, as well as the overthrusting of the North Caribou Superterrane onto the English River Basin in a southward direction. Arc-related magmatic activities sustained in other areas of the southern North Caribou Superterrane margin at <2710 Ma. What was following is the deformation penetrative in both eastern (occurred at 2714-2702 Ma) and western (occurred at <2704 Ma) margins, followed by ductile-brittle faults.

Central Superior Orogeny (2700 Ma)
The Central Orogeny is significant as it involves the accretion of the younger Western Wabigoon terrane to the southwestern margin of the Winnipeg River Terrane.

Two types of models were proposed to illustrate the process accretion with distinctive subduction polarity: Sanborn-Barrie and Skulski (2006) suggested that the accretion was achieved by the northeastward subduction of the Western Wabigoon Terrane underneath the Winnipeg River Terrane. This model is supported by evidence like the formation of the tonalitic and pyroclastic rocks in 2715-2700Ma and the deformation style of the Warclub turbidite assemblage which infers the over-riding of Winnipeg River Terrane on Western Wabigoon Terrane.

Another type of Models was suggested by Davis and Smith (1991), Percival et al. (2004a) and Melnyk et al. (2006) , which suggested an opposite direction of subduction (Southwestward). These models are supported by the ductile rock textures in the lower plate of the Winnipeg River Terrane and the open folds in the Western Wabigoon Terrane, implying the overriding role of Western Wabigoon Terrane instead of Winnipeg River Terrane shown in the previous model.

Shebandowanian Orogeny (2690 Ma)
Shebandowanian orogeny marks the accretion of the Wawa-Abitibi terrane to the composite Superior superterrane at the southern margin of the Wabigoon terranes.

The northward direction of the subduction is evident due to the ceased arc magmatism in Winnipeg River superterrane at about 2695 Ma. Apart from the ceased magmatism, the sanukitoid plutons formed in the area during 2695-2685 Ma (which inferred the breakoff of a subduction slab) also indicated the subduction towards the north. After the subduction, the two terranes were sutured under the Quetico belt. This also trapped the clastic sediments fluxing into the belt, marking its transition from an accretionary wedge to a foreland basin. At the northern Wawa-Abitibi terrane, researchers identified two events of deformation occurred during the orogeny. The first one (D1 deformation event) is the intra-arc deformation accompanied by calc-alkaline magmatism during 2695 Ma. The second one (D2 deformation event) is the transpressive deformation at the margin between the Wawa-Abitibi Terrane and the Wabigoon terranes during 2685-2680 Ma.

Minnesotan Orogeny (2680 Ma)
As the last significant accretion event, The Minnesotan Orogeny is associated with the accretion of the oceanic Minnesota River Valley Terrane and the composite Superior Craton. Subduction between the to terranes drove the Minnesota River Valley Terrane northward to meet the gigantic craton, which the two terranes sutured along the Great Lake tectonic zone.

The northward direction of the subduction is proven by the peraluminous granitoid magmatism in the southern margin of the Abitibi terrane, as well as the isotopic signature of the ancient crust underneath it.

The Minnesotan orogeny accounts for most of the deformation events in the Wawa-Abitibi Terrane and Minnesota River Valley Terrane. Research in the past regarded the Minnesota River Valley Terrane as a stiff crust with higher resistance relative to the weaker zones between the Minnesota River Valley Terrane and the Wawa-Abitibi Terrane, like a rigid "jaw" juxtaposing a weak zone in the "vice" models suggested by Ellis et al. (1998). However, the study of seismic reflection images by Percival et al. reveals that Minnesota River Valley Terrane positions at the bottom of a thrust sequence, providing evidence that it is an oceanic slab.

Orogenesis in the northeastern Superior Craton
The correlations of different building processes of the NE Superior Craton remains sophisticated. Still, there are two general understandings to unveil the relationships among the overlapping magmatic and metamorphic events.

The first one is suggested by Percival and Skulski (2000). It is a collisional model which at 2700 Ma, the Rivière terrane from the east collided with the Hudson Bay terrane located at the west side. This collision leads to the high-grade metamorphism followed by a regional folding event. Apart from this, the model relates the collision with the Uchian orogeny concurrently happening at the south and the west.

The second one is suggested by Bédard (2003) and Bédard et al. (2003). This model puts emphasis on the role of magmatic diapirism in the linear structure and metamorphism of the NE superior craton, implying an active anorogenic magmatism during the accretion of the southern Superior Craton.

Categories
Category:Archean Category:Cratons Category:Geology of Manitoba Category:Geology of Minnesota Category:Geology of North Dakota Category:Geology of Ontario Category:Geology of South Dakota Category:Geology of Quebec Category:Lake Superior Category:Palaeogeography stubs Category:Historical geology Category:Historical tectonic plates Category:Historical continents