Superior craton

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The Superior craton (or Superior Province) forms the core of both the North American continent and the Canadian Shield. 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 the 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 and record 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, 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).

Contents 1 Archean Superior proto-craton 2 Northern Superior province 3 Northern Superior province, Oxford-Stull Lake domain 4 Northern Superior province, Minto Block 5 Western Superior province, Inukjuak domain 6 Tikkerutuk domain 7 Goudalie and Qualluviartuuq domains 8 Utsailk domain 9 Northeast Superior province, Douglas Harbour domain 10 Eastern Superior province, Abitibi subprovince 11 Western Superior province, North Caribou terrane 12 Northwestern Superior Province, English River subprovince 13 Northwestern Superior Province, Winnepeg River terrane 14 Northwestern Superior province, Wabigoon-Winnipeg River superterrane 15 Southwestern Superior province, Wabigoon subprovince 16 Southwestern Superior province, Quetico subprovince 17 Southwestern Superior province, Wawa subprovince 18 Southwestern Superior province, Quetico Subprovince 19 Southeastern Superior province 20 Southern Superior province 21 Southern Superior province, Schreiber-Hemlo greenstone belt 22 Economic Geology 23 See also 24 References

[edit] Archean Superior proto-craton

The oldest continental crust (up to 3.7 Ga) occurs in the Northern Superior superterrane and Inukjuak domain of the northeastern Superior province. A large region of the ca. 3.0 Ga North Caribou terrane, extending into northern Quebec, has been interpreted as a continental nucleus, or proto-craton, during assembly of the Superior Province. Farther south, the Winnipeg River and Marmion terranes are relatively small continental fragments dating back to 3.4 and 3.0 Ga, respectively. In the far south, the Minnesota River Valley terrane contains remnants of crust as old as ca. 3.6 Ga (Percival, 2006). Crustal evolution in the western Superior province occurred at 3.4, 3.0, and 2.7 Ga. The 2.7 Ga crustal additions were contaminated by crustal material subducted into the region or by intrusions into the sanukitoids.

U-Pb geochronology mapping with SHRIMP results support a ca. 3.0 Ga Superior proto-craton extending across Hudson Bay into the North Caribou Terrane of northwestern Ontario. Remnants of a 3.0-2.8 Ga proto-craton extend from Manitoba to Ungava with mainly TTG and volcanic septa overlain locally by remnants of a komatiite-quartzite-carbonate rift sequence. Juvenile volcanic rocks >2.8 Ga may have been incorporated into the proto-craton prior to establishment of Andean arcs on its margins (2.75-2.70 Ga), docking (2.71-2.69 Ga) of blocks of 2.75-2.70 Ga juvenile crust and subsequent seaward arc migration through the accreted terranes (2.69-2.68 Ga). (Percival, 2006a).

Plate tectonic activity in Superior province is rooted in the granite-greenstone and metasedimentary belts of the southern part of the craton. The northeastern domain of the Minto block evolved 3.1-2.8, 2.725, and 2.69 Ga events. Western and eastern protocratons (3.1-2.8 Ga) rifted ~2.79 Ga to produce an ocean basin that was consumed by subduction at 2.725 Ga. The Leaf River plutonic suite of calc-alkalic hornblende, biotite, orthopyroxene, and clinopyroxene granodiorite represent magmatic arcs built on the protocratons. The intervening Goudalie domain contains fault-bounded fragments of rifted continental crust, rift volcanics, primitive oceanic crust, 2.724 Ga island arc rocks, and a ca. 2.7 Ga back-arc assemblage that marks a suture. Terminal collision at 2.7 Ga led to thickening and crustally derived granitoid magmatism. A northern proto-Superior craton had continental magmatic arcs built on its eastern and southern flanks in response to west-northwest-directed subduction. Orthogonal convergence in the east produced wide plutonic arcs, in contrast to terrane-accretion tectonics along the southern margin. (Begin et al., 1994)

The microcontinental fragments and juvenile oceanic terranes were amalgamated into a composite Superior superterrane in a series of orogenic events between 2.72 and 2.68 Ga and are remnants of the ancient Kenorland supercontinent orogeny (~2.7-2.5 Ga). Ca. 2.5 Ga K-Ar ages from the Superior, Slave, Churchill and Nain Provinces, represent coincidental cooling within individual cratons carrying separate and distinct accretion histories that were not amalgamated until the Paleoproterozoic.

Major metasedimentary belts represent collisional flysch basins fed by detritus eroded from rising arc and cratonic highlands which were rapidly deformed and metamorphosed. By 2.670 Ga major tectonic activity including strike-slip faulting had waned. However, renewed high temperatures are indicated by Superior-wide leucogranite plutonism and metamorphism (2.66-2.64 Ga), as well as regional deep crustal metamorphism and ductile, orogen-parallel flow, correlated with ubiquitous subhorizontal reflectivity. The late activity marks thermal flux possibly related to asthenospheric replacement of gravitationally unstable lithosphere. Seismic profiles show a mosaic of accretionary, magmatic and late collapse-related structures. Although similar growth stages are recognized in Proterozoic and Phanerozoic orogens, remnants of the riftogenic phases of the Wilson cycle are very poorly preserved in Archean cratons. (Percival, 2006)

[edit] Northern Superior province

The 3.9-2.8 Ga Northern Superior superterrane (NSS) is at the northern fringe of the Superior Province and is dominated by granitic and gneissic rocks. It consists of an arcuate belt extending from Assean Lake in Manitoba to Porpoise Cove in northern Quebecb (Percival, 2003). Supracrustal units in the Assean Lake complex of Manitoba include greywacke with detrital zircon ages up to 3.9 Ga, iron formation and mafic to intermediate volcanic rocks. The ancient rocks have been strongly reworked by granitoid magmatism at 3.2-3.1, 2.85-2.81 and 2.74-2.71 Ga, representing evolution in a continental magmatic arc setting, followed by amphibolite-facies metamorphism at 2.68 and 2.61 Ga that may have resulted from collisions during tectonic assembly. The NSS merged with the North Caribou terrane (3.0-2.8 Ga) at 2.72 Ga. The NSS is bounded to the south by the North Kenyon fault, which juxtaposes it with the Oxford-Stull terrane. Correlation is uncertain between the NSS and units of similar antiquity in the Inukjuak domain of northern Quebec. (Percival, 2006).

[edit] Northern Superior province, Oxford-Stull Lake domain

The Oxford-Stull Lake domain in the northwest contains some of the largest greenstone belts in the province, including the Knee Lake-Gods Lake and Stull Lake belts of Manitoba. Mainly basaltic rocks of the Hayes River assemblage have been dated locally in the 2.83 Ga range, and volcanic rocks of the Oxford Lake assemblage fall between 2.729 and 2.719 Ga. The occurrence of coarse clastic sediments and alkaline volcanic rocks along some faults suggests that they were active during deposition of the Oxford Lake assemblage. Mafic intrusions are common in some belts such as at Big Trout Lake, and have some Ni-PGE potential. Plutons of tonalite, granodiorite and granite underlie large parts of the terrane and yield ages between 2.83 and 2.69 Ga. Isotopic data suggest that the Oxford-Stull terrane evolved in an oceanic setting, possibly on the edge of thinned North Caribou crust until ca. 2.71 Ga, when it was juxtaposed with the NSS along the North Kenyon fault. It is bounded by the Gods Lake Narrows shear zone in the south, bordering the North Carribou terrane. (Percival, 2006).

[edit] Northern Superior province, Minto Block

The early Archaean Minto Block of northern Quebec includes the following domains from west to east: the Inukjuak, Tikkerutuk, Lac Minto, Goudalie Utsalik and the Douglas Harbour Domains. The Inukjuak Domain is distinguished from the domains to the east by significantly older Nd isotopic ages that range from 4.0-3.0 Ga. The change in isotopic compositions from the Tikkerutuk and Inukjuak Domains is abrupt and not entirely coincident with the suggested aeromagnetic boundary between the two domains. There also appears to be very little addition of juvenile Kenoran crust (ca. 2.7 Ga) in this domain. This places the Inukjuak domain on par with such old domains such as Assean Lake in northern Manitoba and the Northern Superior Super Terrane (NSS) in northwestern Ontario.

The Inukjuak domain in the west hosts the ancient (ca. 3.825 Ga) Nuvvuagittuq supracrustal belt and ca. 3.65 Ga tonalitic gneisses but is dominated by younger plutonic rocks (2.84-2.69 Ga). To the east, the Tikkerutuk domain consists of pyroxene-bearing plutonic rocks, 3.02-2.71 Ga, that merge into the Bienville domain to the south, which is characterized by 2.71-2.69 Ga granite and granodiorite. Farther east, Lac Minto domain contains metasedimentary and derived migmatitic rocks, in addition to 2.76-2.70 Ga pyroxene-bearing plutonic rocks. The Goudalie domain forms a central spine consisting of relatively large volcano-sedimentary belts (2.88-2.71 Ga) with sparse 3.0 Ga tonalite and abundant pyroxene-bearing plutons (2.73-2.68 Ga). In the east-central Minto, the Utsalik domain consists of highly magnetic, 2.74-2.69 Ga pyroxene-bearing plutonic rocks with model ages in the 3.0 Ga range. To the northeast, Douglas Harbour domain consists of two large charnockitic massifs (2.74-2.73 Ga) within an older (2.88-2.75 Ga) tonalitic complex. Deformation and high-grade metamorphism in the western Minto block is attributed to collisional processes. (Percival, 2006).

The Minto block is dominated by mantle-derived, crustally contaminated granitoid-charnockitic massifs separated by sinuous greenstone belts that preserve a record of oceanic (2.84-2.77 Ga) and continental (2.76-2.70 Ga) volcanism, sedimentation and plutonism. In the northeastern Superior portion of the Minto Block this is interpreted as Andean marginal roots and oceanic arcs with terrane assembly between ~2.73 and 2.69 GA. The tonalite-trondjhemites are aged at 3 GA. (Bedard, 2001). Granitoid rocks are emplaced in continental arc settings and juxtaposed during a ca. 2.7 Ga arc - continent collision. Regional metamorphism related to emplacement of a hot arc terrane had minor effect on the anhydrous (charnockitic) plutons. Archaean tonalite-trondjhemites, enderbites, granodiorite granites, and clinopyroxene or orthopyroxene-bearing [[hornblende]-tonalite (most retain igneous microtextures). Outcrop-scale structures such as melt-filled shear zones and deformed intraplutonic dikes imply that deformation was synmagmatic. The multiple embayments are interpreted as magmatic resorption structures. Since epidote and muscovite stabilities are pressure dependent, these resorption structures suggest that magmas ascended as crystal-charged mushes. Amphibolite-grade supercrustal rocks are associated with tonalite-trondhjemite or granite-granodiorite plutons, while granulite-grade belts are associated with enderbite and clinopyroxene or orthopyroxene-bearing tonalite. This dichotomy suggests that metamorphism of supercrustal rocks reflects localized equilibration with adjacent plutons rather than orogenesis. (Bedard, 2003).

According to a study by Percival and Skulski (2006): Rare older plutonic bodies (3.12-2.87 Ga), coupled with inherited zircon and low epsilon Nd values in younger plutons, attest to the presence of sialic crust inferred to have been juxtaposed with oceanic assemblages ca. 2.77 Ga. Continental calc-alkaline magmatism produced granodiorite batholiths ca. 2.72 Ga, followed by widespread deformation, metamorphism and crustal magmatism at 2.70-2.69 Ga. Early (ca. 2.81 Ga) deformation is recorded locally in oceanic assemblages, but the main polyphase regional events postdate deposition of unconformable conglomerate-greywacke+/- iron formation sequences loosely constrained at <2.77, <2.75 and <2.72 Ga. Both basement and cover sequences were deformed into steeply-dipping, NW-trending belts, metamorphosed to low-P amphibolite facies, and variably affected by open E-W cross-folds. Monazite U-Pb ages of upper amphibolite to granulite facies gneisses record metamorphism at 2.70-2.67 Ga, indicating protracted metamorphism accompanying plutonism, whereas those in lower-grade schists range from 2.69 to 2.62 Ga, possibly reflecting continued monazite growth during late structural events. Late, possibly hydrothermal, disturbances are also indicated in lower-T isotopic systems, including [radiometric dating|U-Pb]] titanite (2.68-2.56 Ga), Ar/Ar hornblende (2.64 Ga) and rutile (2.50 Ga)

The main collisional-metamorphic event (ca. 2.70 Ga) in the Minto block coincides with the initiation of 2.70-2.69 Ga accretionary events recognized in the southwestern Superior province. Similarly, post-amalgamation events observed in the western Superior (2.68-2.63 Ga deep-crustal metamorphism and leucogranite plutonism) are evident in the Minto block as protracted metamorphism and deformation, isotopic resetting and renewed mantle-derived (alkalic) magmatism, suggesting a pan-Superior extent, possibly driven by foundering of mantle lithosphere on the 1000 km scale." (Percival and Skulski, 2006)

[edit] Western Superior province, Inukjuak domain

The Inukjuak domain is the western-most domain in the Superior province. It is distinguished from the domains to the east by its significantly older Nd isotopic compositions of 4.0-3.0 Ga. The change in isotopic compositions from the Tikkerutuk and Inukjuak Domains is abrupt and is not entirely coincident with the suggested aeromagnetic boundary between the two domains. There appears to be an addition of juvenile Kenoran crust (ca. 2.7 Ga) in this domain. This places the Inukjuak domain on par with the Assean Lake domain in northern Manitoba and the Northern Superior super terrane in northwestern Ontario (Stevenson, 2003). The orogenic framework for the western Superior Province appears to continue northeastward into the Minto block. In particular, the Uchian orogeny (2.70 Ga) of high-grade metamorphism in the western Minto block is comparable to that of Alpine-style mountain belts in the northeast.

[edit] Tikkerutuk domain

The Tikkerutuk domain represents a north-trending, 50-km wide calc-alkaline magmatic arc with ages between 2.71 and 2.70 Ga, that extends southward into the Bienville subprovince on the basis of aeromagnetic anomalies and geochronology. Zircon inheritance ages indicate that the Tikkerutuk area was built upon antecedent arcs of 2.84, 2.77 and 2.725 Ga. (Percival et al., 2001).

[edit] Goudalie and Qualluviartuuq domains

A tonalitic rock from the southern Goudalie domain with an age of 2.833 Ga supports a linkage to 2.84-2.83 Ga units of the Qalluviartuuq domain along the strike to the north. (Percival et al., 2001).

[edit] Utsailk domain

The Utsailk domain is made up of pyroxene and hornblende-bearing Leaf River plutons with consistent 2.725-2.723 Ga ages and local inheritance of 2.82 and 2.77 Ga. However, the southern extension of Utsalik domain contains pyroxene-bearing granodiorites both older (2.762 Ga) and younger (2.692 Ga) than the Leaf River suite. (Percival et al., 2001).

[edit] Northeast Superior province, Douglas Harbour domain

The Douglas Harbour domain is the eastern-most domain in the northeast Superior province (3.1 to 2.7 Ga) and lies east of Hudson and James Bays. It is dominated by 2.78-2.69 Ga plutonic rocks emplaced into older crust (3.8-2.83 Ga). U-Pb ages obtained through SHRIMP analyses of zircon samples reveal a history of successive magmatism between 3.07 and 2.70 Ga, followed by metamorphism, emplacement of crustally-derived granites (2.702-2.685 Ga), and late hydrothermal events (ca. 2.65 Ga). In the northeastern Minto block of the Douglas Harbour domain, dated localities to the northeast are 2.87 Ga. The Leaf River suite is dated at 3.01 Ga and the tonalitic crust contains 2.734-2.725 Ga granodioritic plutons. (Percival et al., 2001).

To the east of the Douglas Harbour domain are the Utsalik, Goudalie, Lac Minto and Tikkerutuk Domains that yield almost exclusively late Archean ages of 3.0 to 2.7 Ga. This range of ages is evidence for recycling of earlier crustal lithologies by younger orogenic events and reflects melting of mid-Archean lithologies during the emplacement of juvenile late Archean magmas.

The Douglas Harbour Domain includes two TTG suites: the Faribault-Thury West and the Faribault-Thury East. Both contain embedded KT greenstone belts. The tonalities display elevated La/Yb ratios and are enriched in LILE (Ba-Rb-K-Cs-U-Th-Pb) with Sr-Pb anomalies and B Nb-Ta-Ti anomalies. This implies melting rates of subducted oceanic crust, but could also be the result of melting at the base of a basaltic plateau in the presence of garnet and rutile. Trace element models collectively imply that the evolution of trondhjemitic tonalite resulted from hornblende-dominated crystallization and is probably not caused by variable rates of partial melting in the subducted oceanic crust. The repetitive process of catalytic delamination explains the synchronous genesis of Archean crust and mantle, explains progressive crustal maturation (tonalite to granite transition), and simplifies tectonic models because all Archean magmatic suites can be generated in a single environment. (Bedard, 2005).

[edit] Eastern Superior province, Abitibi subprovince

The Abitibi subprovince tectono-stratigraphic evolution is explained in terms of oceanic geodynamic settings from plateau, to arc and rift environments. The Abitibi subprovince has been subdivided into three domains with overlapping tectonostratigraphic histories. In the northern Abitibi, volcanic assemblages are mainly 2.735-2.72 Ga and associated with layered intrusions, whereas volcanic rocks of 2.71-2.695 Ga are restricted to the southern Abitibi. The southern Abitibi has relatively young sedimentary-volcanic deposits including ca. 2.69 Ga greywackes of the Porcupine Group and 2.677-2.673 Ga conglomeratic and alkaline volcanic rocks of the Timiskaming Group. The central zone is dominated by plutonic rocks.

The Opatica belt in the south divides the Abitibi belt to the north and consists of units ranging from 2.82 Ga tonalite, through 2.77-2.70 Ga. tonalite-granodiorite, to 2.68 Ga granite and pegmatite. Polyphase deformation includes early, west-verging shear zones (<2.72 Ga), overprinted by 2.69-2.68 Ga south-vergent structures.

The Opinaca belt is characterized by metagreywacke, derived migmatite and granite. Polydeformed schists occur at the belt margins, whereas the interior portions are metamorphosed to amphibolite and granulite facies. These rocks are cut by the 2.67 Ga Broadback River granite. (Percival, 2006).

[edit] Western Superior province, North Caribou terrane

The North Caribou terrane is the largest domain of the Superior Province. The North Caribou terrane sustained protracted reworking that culminated with 2.7 Ga Kenoran Orogeny. Prior to the 2.99 Ga Balmer volcanism, the North Caribou protocraton comprised a 3.02 Ga island arc mafic-felsic volcanic crust and a 3.01 to 3.0 Ga tonalitic crust. The Balmer volcanic-plutonic substrate is a voluminous mafic-ultramafic submarine sequence with intercalated komatiite and basalt that has been interpreted to be the product of a mantle plume in which the hot, deep, mantle-derived axis produced komatiite magma that mixed with asthenospheric mantle to produce tholeiitic basalt magma. The north trending calc-alkalic volcanic centers may reflect a contiguous continental arc built during eastward subduction below the western margin of the North Caribou terrane at ca. 2.94 to 2.92 Ga. At ca. 2.9 Ga volcanism was widespread across the North Caribou terrane. (Parker, 2001).

The following study is mostly from Percival (2006): The basement consists of ca. 3.0 Ga tonalitic and juvenile plutonic and minor volcanic belts, upon which were deposited early rift-related (2.98-2.85 Ga) and younger (2.85-2.71 Ga) arc sequences. It was severely reworked by continental arc magmatism at 2.75-2.70 Ga. The terrane has wide transitional margins in both the north and south and an uncomformable platform/rift succession of quartzite, carbonate, banded iron formation and komatiite. The unconformity is exposed between the tonalitic basement and the overlying Lewis-Storey rift assemblage, where tectonically juxtaposed mafic volcanic rocks are a common feature.

The core of the North Caribou terrane lies to the north and consists of a 2.745-2.69 Ga Neoarchaean pluton called the Berens River Plutonic Complex. It is intruded by widespread tonalitic, dioritic, granodioritic and granitic plutons at depths ranging from 18 to 10 km. Remnants of ca. 3.0 Ga tonalite and supracrustal rocks are sporadically preserved through the younger magmatism. Within the greenstone belts, thin packages of quartz arenite-carbonate-komatiite have variably been interpreted as platformal cover strata and plume-related rift deposits. Evidence of early (>2.87 Ga) deformation is recorded in the North Caribou greenstone belt.

In the north, the Munro Lake and Island Lake terranes are inferred to have been formed on thinned crust of the North Caribou terrane. These regions are dominated by plutonic rocks with several small supracrustal belts. In the Ponask Lake area near the Ontario-Manitoba border, detrital zircons from a quartzite-komatiite sequence indicate a depositional age of <2.865 Ga that infer a breakup at the northern North Caribou margin. The main phase of plutonism was followed by localized strain and shear-zone-hosted gold mineralization, particularly in the Little Stull Lake area near the Ontario-Manitoba border.

The North Caribou terrane collided with the Northern Superior superterrane (NSS) between 2.72 and 2.71 Ga on the north, and the Winnipeg River terrane to the south, trapping the English River flysch belt in between at 2.70 and 2.69 Ga. Docking of the juvenile western Wabigoon subprovince occurred at a similar time, followed by collision of the Abitibi-Wawa subprovince and syntectonic Quetico sedimentation (2.698-2690 Ga).

The western margin of the North Caribou terrane and the Superior province is the ~3.0 Ga Lewis-Storey rift assemblage, a sedimentary-volcanic sequence in eastern Lake Winnipeg. The East Shore Plutonic Complex, adjacent and east of the Lewis-Storey rift, contain two enclaves of fine-grained schistose sandstone and quartz diorite porphyroclastic gneiss within hornblende tonalite that may represent remnants of an ancient supracrustal sequence. These rocks are similar to the 3.0-2.92 Ga quartzite, iron-formations, and komatiite at Wallace Lake and predate the emplacement of the East Shore Plutonic Complex. (Percival, 2006).

The southern margin of the North Caribou terrane is the Uchi subprovince. Aeromagnetic trends show the complex structural configuration of supracrustal rocks in a chain of greenstone belts separated by large lobes of plutonic material. The stratigraphic record preserved in the Rice Lake, Wallace Lake, Red Lake, Confederation Lake, Meen-Dempster, Pickle Lake and Fort Hope greenstone belts reflects a history of rifting beginning ca. 2.99 Ga, followed by a protracted history of continental arc magmatism at 2.94-2.91, 2.90-2.89, 2.85 and 2.75-2.72 Ga. Several deformation episodes are recognized within the greenstone belts, including pre-2.74, 2.73, 2.72 and 2.70 Ga events that have produced composite, steep, east-trending fabrics. Coarse clastic sedimentary rocks generally represent the youngest strata along the southern margin of the North Caribou terrane. These sequences contain detrital zircons as young as 2.703 Ga, and may be facies equivalents of the marine greywacke turbidites of the English River subprovince to the south. (Percival, 2006).

The Gray Point sequence at the south margin, along Wanipigow Lake, is a basalt ~1000 meter thick unit of aphyric, nonvesicular pillow basalt and basaltic andesite flows with some hyaloclastite, overlain by 700-1200 meters of massive porphyritic basalt (pyroxene-plagioclase-phyric) and basaltic andesite flows. Using N-MORB compositional data and Th/Nb ratios, the Gray Point sequence represents an oceanic plateau setting. (Balles, 2001)

The Trout bay assemblage of the Red Lake greenstone belt at the south margin of the North Caribou terrane may represent a back arc or oceanic plateau crust, tectonically juxtaposed with the North caribou terrane between 2.853 and 2.735 Ga. A final phase of ca. 2.73 Ga Andean-style arc magmatism is recorded at Red Lake by the Grave sequence and throughout the Berens arc. At ca. 2.718, continued subduction in the Red Lake and Birch-Uchi belts culminated in collision of the Winnepeg River terrane during the Uchian phase of the Kenoran Orogeny. This was a protracted event involving brittle-ductile reworking during extensive hydrothermal alteration and metamorphism that ultimately led to syn- to late-tectonic precipitation of gold to form one of Canada's foremost gold mining camps. (Parker, 2001).

[edit] Northwestern Superior Province, English River subprovince

The English River subprovince (ERS) is thought to mark the suture between the North Caribou and Winnipeg River terranes. The English River-Winnipeg River boundary separates dominantly metasedimentary rocks of the English River subprovince from mainly metaplutonic rocks of the Winnipeg River subprovince to the south. The east-trending Sydney Lake-Lake St. Joseph fault (450 km strike length) separates rocks of the North Caribou margin to the north from metasedimentary schists and migmatitic rocks of the English River subprovince to the south. The ERS also displays high metamorphic grade, and a prominent east-west structural grain.

Between the two subprovinces lies the metavolcanic Bird River subprovince in eastern Manitoba, with mafic intrusion-hosted Cr deposits, and its narrow eastward extension, the Separation Lake belt. These belts consist dominantly of largely juvenile mafic rocks with ages of ca. 2.78 to 2.73 Ga. Depositional contacts have been inferred between English River clastic rocks and both volcanic strata of the Separation Lake belt and gneissic tonalitic basement to the east. The Separation Lake belt appears to be in tectonic and intrusive contact with granitic rocks of the Winnipeg River subprovince to the south. The boundary zone is a focus for emplacement of ca. 2.646 Ga rare metal pegmatites, including the Tanco and Separation Rapids fields. (Percival, 2006).

Based on the turbiditic nature of its chemically immature greywackes, the setting of the English River has traditionally been considered a fore-arc basin or accretionary prism. Detrital zircon studies indicate that the sediments were deposited after arc activity in adjacent volcanic belts and close to the time of collisional orogeny, thereby implying an origin as a syn-orogenic flysch basin. The small Melchett Lake greenstone belt in the central English River subprovince comprises a juvenile, ca. 2.723 Ga calc-alkaline volcanic sequence, possibly correlative with the Lake St. Joseph assemblage to the north. Metamorphic conditions in the English River range from middle amphibolite facies near the margins, to low-pressure granulite facies, coinciding with widespread generation of migmatite and diatexite at 2.691 Ga. The main tectonothermal event was followed by a second thermal pulse at 2.669 Ga, intrusion of ca. 2.65 Ga pegmatites, and growth of hydrothermal minerals. (Percival, 2006).

[edit] Northwestern Superior Province, Winnepeg River terrane

The following study is from Percival (2006): The Winnipeg River terrane is a collective term used to describe the plutonic domain exposed north and east of the western Wabigoon subprovince. It consists of two main elements: 1) the Winnipeg River subprovince proper, a >500 km long terrane composed of Mesoarchean metaplutonic rocks variably intruded by Neoarchean plutons; and 2) a largely Neoarchean plutonic domain, formerly referred to as the central Wabigoon granitoid complex and Wabigoon diapiric axis, that contains scattered remnants of Mesoarchean crust. The 3.4 Ga Winnipeg River terrane stands apart from the Northern Superior and North Caribou terranes to the north and the Marmion domain to the south. It also carries a distinct record of magmatic and structural events, typically characterized by amphibolite to granulite facies metamorphism.

The Mesoarchean tonalitic rocks are the oldest units recognized, and include both 3.32-3.05 Ga gneissic and 3.04 Ga foliated varieties. Similar isotopic signatures characterize younger (2.88, 2.84 and 2.83 Ga) tonalitic rocks, reflecting the antiquity of the basement. Mafic volcanic belts older than ca. 3.0 Ga and ca. 2.93-2.88 Ga volcanic rocks in the eastern Savant-Sturgeon greenstone belt are also considered part of the Winnipeg River terrane. Significant pulses of Neoarchean tonalite-granodiorite magmatism occurred at 2.715-2.705 Ga followed by emplacement of granites at ca. 2.70-2.69 Ga. A complex Neoarchean structural-metamorphic history began with deposition of metasedimentary rocks after 2.72 Ga. The supracrustal rocks and older gneisses were folded between 2.717 and 2.713 Ga, prior to syntectonic injection of 2.713-2.707 Ga tonalite and granodiorite sheets accompanying horizontal extensional deformation. Upright folding during deformation took place after 2.705 Ga, and younger upright folds indicate a period of north-south compression associated with emplacement of 2.695-2.685 Ga granite and granodiorite. Late pegmatites and granites intruded during a dextral transpressive regime.

The eastern Winnipeg River terrane hosts east-trending greenstone belts including the Caribou Lake, Obonga, Garden Lake and Heaven Lake belts that have ages >3.075 to 2.703 Ga . Dated granitoid units have ages in the range 3.075-2.680 ga and some of the oldest rocks have eNd values of -1 to + 1, suggesting derivation from even older crustal sources. At least five generations of Neoarchean structures have been recognized in complex tonalitic gneisses. The Marmion domain, formerly included as part of the south-central Wabigoon subprovince, is now recognized to consist of 3.01-2.999 Ga tonalite, upon which the Steep Rock, Finlayson Lake and Lumby Lake greenstone belts formed between 2.99 and 2.78 Ga.

A period of continental arc magmatism in the Winnipeg River subprovince (2.72-2.70 Ga) is attributed to north- and eastward subduction of oceanic rocks followed by 2.708-2.701 Ga deformation. Post-2.704 Ga regional deformation across the Wabigoon outlasted deposition of syncollisional coarse clastic sedimentary overlap sequences. Late faults with both strike-slip and dip-slip motion define the present subprovince boundary.

[edit] Northwestern Superior province, Wabigoon-Winnipeg River superterrane

Amalgamation of the Wabigoon subprovince (2.77-2.72 Ga) with Winnipeg River (3.5-2.8 Ga) subprovince in the western Superior province occurred ca. 2.715 Ga. During the Uchian orogeny (ca. 2.70 Ga) the Wabigoon-Winnipeg River superterrane collided with and was subducted beneath the active southern margin of the composite Superior superterrane (CSS), resulting in deposition and burial of the English River turbidite wedge. Collision between the largely juvenile Abitibi-Wawa subprovince and its subduction beneath the CSS resulted in the 2.69 Ga Shebandowanian orogeny, including deposition and burial of the Quetico turbiditic prism. The final, ca. 2.68 Ga Minnesotan orogeny is responsible for collision and underthrusting of the Minnesota River Valley terrane (3.6-2.7 Ga) beneath the CSS. This orogeny was accompanied by the intrusion of alkalic suites that range in composition from syenite to nepheline syenite and rare carbonitic compositions, and their parental magmas formed by smaller degrees of partial melting of a large-ion lithophile elements (LILE)-enriched upper mantle. The involvement of a deeper asthenospheric source in the petrogenesis of these late mantle-derived magmas has been inferred by many workers. The involvement of a sublithospheric source is indicated by the Beaverhouse Lake intrusion, which is distinct in its lack of negative Nb-Ta anomalies in primitive-mantle-normalized diagrams. Instead, its chemical characteristics resemble those of present-day ocean-island basalts and imply that it is related to hot spots. The upwelling of asthenospheric mantle could have provided heat for extensive magmatism in southwestern Superior province by melting of metasomatized lithospheric mantle." (Hattori, 2001).

[edit] Southwestern Superior province, Wabigoon subprovince

The following study is from Percival (2006): The Wabigoon subprovince has long been recognized as a composite terrane comprising volcanic-dominated domains and consists of distinct western and eastern segments. The Western Wabigoon subprovince is dominated by mafic volcanic rocks with large tonalitic plutons. Volcanic rocks range in composition from tholeiitic to calc-alkaline, and are interpreted to represent ocean floor or plateau and arc environments, respectively. Most of the preserved volcanic rocks were deposited between ca. 2.745 and 2.72 Ga, with rare older rocks, such as the 2.775 Ga Fourbay assemblage of oceanic plateau affinity and minor younger (2.713-2.70 Ga) volcanic-sedimentary sequences. Plutonic rocks range from broadly synvolcanic batholiths composed of tonalite-diorite-gabbro (ca. 2.735-2.72 Ga) to younger granodiorite batholiths and plutons (ca. 2.710 Ga), monzodiorite plutons of sanukitoid affinity (ca. 2.698-2.690 Ga), and plutons and batholiths of monzogranite (2.69-2.66 Ga). Immature clastic metasedimentary sequences are preserved in narrow belts within volcanic sequences. They are commonly younger than the volcanic rocks with local unconformable relationships and geochronological constraints indicating deposition between ca. 2.711 and <2.702 Ga. Detrital zircons >3 Ga indicate old components in source regions. At least two phases of deformation affected supracrustal rocks of the western Wabigoon subprovince, with apparent diachroneity in the onset of deformation from ca. 2.709 Ga in the Lake of the Woods area, to ca. 2.700 Ga in the Sioux Lookout-Savant area in the east. These events involved at least local tectonic inversion, through thrust imbrication and possible formation of nappe-like structures.

The Sturgeon-Savant greenstone belt consists of several tectonostratigraphic packages, including the previously described Jutten assemblage, the ca. 2.775 Ga Fourbay assemblage, and 2.745-2.735 Ga sequence, the Handy Lake and South Sturgeon assemblages. The 2.735 Ga Lewis Lake batholith may have provided the heat source for seawater convection and massive sulphide mineralization. Younger (ca. 2.718 Ga), high Fe, Ti basalt and minor dacite of the central Sturgeon assemblage represent a rifted arc sequence. Associated sedimentary rocks contain both arc (2.745-2.730 Ga) and continental (3.1-2.8 Ga) detritus. Two younger sedimentary sequences complete the stratigraphic record: 1) greywacke-iron formation (ca. 2.705 Ga) of the Warclub assemblage; and 2) sandstone and arkose (<2.698 Ga) of the syn-orogenic Ament Bay assemblage. Two sets of ductile structures postdate <2.704 Ga rocks: 1) north-trending upright folds; and 2) east-trending upright folds and penetrative foliation. Pre-D1 folds have been inferred locally.

The Eastern Wabigoon subprovince is a composite terrane with greenstone belts and intervening granitoid plutons that show variable Mesoarchean (Winnipeg River and Marmion) and oceanic affinity. In the northwest part of the belt the 3.0-2.92 Ga Toronto and Tashota assemblages may represent a continental margin sequence built on the Winnipeg River terrane. Calc-alkaline rocks of the 2.74 Ga Marshall assemblage have small massive sulphide deposits. The central part of the belt is dominated by rocks of oceanic affinity including tholeiitic juvenile pillowed basalt of the 2.78-2.738 Ga Onaman and Willet assemblages and the overlying calc-alkaline 2.725-2.715 Ga Metcalfe-Venus assemblage. Parts of these assemblages contain widespread hydrothermal alteration and host small massive sulphide deposits. Across the southern part of the eastern Wabigoon domain, the 2.78-2.74 Ga calc-alkaline Elmhirst-Rickaby assemblage is possibly built on Marmion-age substrate. Unconformably overlying clastic rocks (Albert-Gledhill and Conglomerate assemblages) were deposited after ca. 2.71 Ga. At least two deformation events affected the eastern Wabigoon domain: east-striking structures (<2.706 Ga) and east-striking, dextral transpressive shear zones. The 2.694 Ga Deeds Lake pluton provides a lower limit on the age of D2 deformation.

[edit] Southwestern Superior province, Quetico subprovince

The Quetico-western Wabigoon boundary is well defined as the Seine River-Rainy Lake fault. The Wabigoon-Quetico interface is also marked sporadically by <2.692 Ga coarse clastic rocks of the Seine assemblage that were deposited in transtensional basins or delta fan environments.

The following study is from Percival (2006): The Quetico subprovince consists dominantly of greywacke, derived migmatite and granite. No stratigraphic sequence has been established within the steeply dipping, polydeformed and variably metamorphosed sedimentary succession; however, younging directions are dominantly to the north. Depositional age constraints indicate slightly older ages for the northern Quetico (<2.698>2.696 Ga) than for the south (<2.692 Ga).

Several plutonic suites cut metasedimentary units, including early (2.696 Ga) tonalite. An early deformation event predated emplacement of a chain of Alaskan type mafic-ultramafic intrusions in the northern Quetico. They are associated with alkaline plutons including nepheline syenite and carbonatite with ages in the range 2.69-2.68 Ga and geochemical affinities with the Archean sanukitoid suite. Two subsequent deformation events were followed by low-pressure, high-temperature metamorphism that reached upper amphibolite and local granulite facies at ca. 2.67-2.65 Ga in the central region and greenschist facies at the margins Coeval, crust-derived granitic plutons and pegmatites, including ca. 2.67 Ga peraluminous granite and ca. 2.65 Ga biotite granite have sporadic rare-element mineralization.

Tectonic models for the Quetico subprovince have favoured forearc settings. Depositional ages of ca. 2.698 to 2.690 Ga overlap those of late arc magmatism in the Wabigoon. The dominantly sanukitoid plutons of this age may have been triggered by slab breakoff.

The southern Quetico boundary separates metasedimentary rocks from the dominantly volcano-plutonic Wawa-Abitibi subprovince to the south. Stratigraphic linkages between subprovinces are evident in some areas, although at ca. 2.685 Ga dextral transpressive shear zones are common.

[edit] Southwestern Superior province, Wawa subprovince

The Wawa and Abitibi subprovinces correlate across the transverse Kapuskasing uplift. Within the Wawa subprovince, volcanism appears to have begun with the 2.89-2.88 Ga Hawk assemblage. The 2.775 Ga Hemlo-Black River, 2.745 Ga Wawa and 2.72 Ga Greenwater and Manitouwadge assemblages indicate an oceanic setting, the latter contains significant massive sulphide mineralization. There is a variety of oceanic magma types from the Schreiber belt, and interpreted the belt as a tectonic mélange. Late-stage volcanism occurred at ca. 2.695 Ga. Subsequent calc-alkalic to alkalic magmatism (ca. 2.689 Ga) and associated coarse clastic sedimentation was followed by emplacement of sanukitoid plutons (2.65-2.68 Ga) and dextral transpressive deformation.

The Great Lakes tectonic zone is the unexposed boundary between the Minnesota River Valley terrane and Wawa subprovince and is identified from aeromagnetic images. It is inferred to dip northward based on the presence of isotopic inheritance in plutons of the Vermilion district of the southern Wawa-Abitibi subprovince. (Percival, 2006).

[edit] Southwestern Superior province, Quetico Subprovince

The Quetico Subprovince of the western Superior province has several alkalic intrusions emplaced 2.696 Ga into turbiditic metasedimentary rocks and are cut by granite dykes ranging from 2.67-2.66 Ga. The intrusions consist of four main rock types: undersaturated mafic rocks, hornblendite and hornblende-pyroxenite, alkali syenite, and silicocarbonatite and carbonatite. These rocks share much of the same characteristics as the Neoarchean shonitic rocks from other western Superior province greenstone belts, such as high Al2O3, high total alkalis, high large-ion lithophile elements (LILE), and low high-field strength elements (HFSE). The Gheen intrusion near Linden, Minnesota ranges in composition from pyroxenite to monzosyenite and are rich in hornblende. the common occurrence of hornblende suggests that the magma was hydrous and crystallized at low temperatures, although water might have been introduced at shallow levels. (Hattori, 2001).

[edit] Southeastern Superior province

The southeast part of the Superior province is divided into the following subdivisions: to the north is the E-W oriented Opinaca subprovince located between the La Grande and Ashuanipi, and to the south is the Opatica Subprovince.

Detrital zircons from the Opinaca metasediments give ages between 3.3 and 2.7 Ga indicating that they were deposited prior to 2.7 Ga. To the east is the Hublet Group composed of detritic metasediments and some metavolcanic rocks. The Hublet Group is a lateral equivalent of the Rossignol-Laguiche Group to the west. The Joubert Suite to the east is dated at 2.7 Ga. The Gamart suite, composed of monzogranite, is dated at 2.647 Ga. The Lataignant Suite is composed of megaporphyric granite and dated at 2.645-2.638 Ga. The Opinaca/Ashuanipi contact is constrained by the Nichicun Fault, presenting a mylonite zone that reveals a southward vergence of Ashuanipi. The LaGrande/Opinaca contact is marked by the Dalmas Fault. The Duhesme Group is located near this contact and consists of tholeiitic and calc-alkaline volcanic rocks and polygenic conglomerates deposited during a period of extension on the sides of a volcanic arc that was formed around 2.735 Ga. They are thought to represent the base of the Opinaca now interpreted like a large sedimentary basin deposited in a rift environment. (Caderon, 2000).

[edit] Southern Superior province

The Southern Superior province is of Late Archaen origin: 2.75-2.65 Ga. There were two primary volcanic associations: the tholeiitic basalt-komatiite and the tholeiitic to calc-alkaline bimodal basalt-rhyolite. The tholeiitic basalt-komatiite association is "characterized by near-flat REE patterns and complex Th-U-Nb-LREE systematics; rare transitional to alkaline basalts and Al-depleted komatiites have fractional crystallization REE patterns and OIB-like trace element signatures. This is interpreted as representing an oceanic plateau derived from a heterogeneous mantle plume. The latter bimodal association has fractionated REE patterns and negative Nb, Ta, P, and Ti anomalies typical of arc magmas. Turbidites plot on mixing hyperbolae between mafic and felsic end members. This association is interpreted as an arc-trench system. Tonalite plutons derived from partial melting of subducted oceanic slabs intrude the subduction-accretion complex as the magmatic arc axis migrated towards the trench....The variability of the mantle mineral ratios in these oceanic plateau basalts is interpreted in terms of recycling variable quantities of oceanic crust processed through a subduction zone (high Nb/U, Nb/Th), and complementary arc crust (low Nb/U, Nb/Th) into the source of the plumes. Collectively, these events are interpreted as a part of a late Archean supercontinent cycle, involving accretion of oceanic plateaus, island arcs, continental fragments, closure of ocean basins, rifting of magmatic arcs, and plume arc interactions." (Polat et al., 2001).

The Southern province consists of the following early Paleoproterozoic thick cover sequence: from west to east there is the Animikie Group, Marquette Range Supergroup, Huronian Supergroup-Whitewater Group and Mistassini-Otish Mountains Group. Glacial diamictites characterize the Southern province sequence All of the successions are characterized by deep-water marine deposits, Fe-formation and mafic volcanic rocks above the quartzarenites. Above the deep-water deposits is a ca. 1.95-1.85 Ga upward-coarsening succession thought to have been formed during collisional orogeny during the formation of Laurentia. (Rainbird, 2004).

The 1.85 Ga Sudbury Intrusive Complex is situated on the southern edge of the Superior Province and represents one of the most richly mineralized bodies of the Canadian Shield. Current thinking regards the gabbro-noritic intrusion to have been generated in response to meteorite impact. (Percival, 2006).

[edit] Southern Superior province, Schreiber-Hemlo greenstone belt

The Late Archaean (2.7 Ga) Schreiber-Hemlo greenstone belt in the Wawa Subprovince is located just north of Lake Superior and is characterized by lithologically and geochemically diverse convergent margin igneous rocks. Supracrustal assemblages of the Schreiber-Hemlo greenstone belt (ca. 2.75-2.69 Ga) are composed of tectonically juxtaposed fragments of oceanic plateaus, oceanic island arcs, and siliciclastic arc-derived trench turbidites. Bedrock exposure of the Schreiber-Hemlo greenstone belt is of intermediate and mafic metavolcanic rocks. These rocks are generally pillowed or massive to foliated flows, and or fragmental tuffs and breccias. This is the classic locality of the Gunflint Chert where ~1.88 Ga cyanobacteria and other microfossils were first discovered in the 1950's. Paleoproterozoic Gunflint Chert rests unconformably on the 2.7 Ga pillow basalts (see photos:[1])

According to a study by Kerrich and Polat (1999): The late Archean (ca. 2.75-267 Ga) Schreiber-Hemlo greenstone belt, is composed of tectonically juxtaposed fragments of oceanic plateaus, oceanic island arcs, and siliciclastic trench turbidites. Following this juxtaposition, these diverse lithologies were collectively intruded by synkinematic, ultramafic to felsic dykes, and Tonalite-Trondhjemite-Granodiorite TTG plutons (ca. 2.72-2.69 Ga) and ultramafic to felsic dikes and sills (ca. 2.69-2.68 Ga) with subduction zones. Overprinting relations between different sequences of structures suggest that this greenstone belt underwent at least three phases of deformation:

During the first phase (2.695-2.685 Ga) oceanic plateau basalts and associated komatiites, arc-derived trench turbidites, and oceanic island arc sequences were all tectonically juxtaposed as they were incorporated into the accretionary complex. Fragmentation of these sequences resulted in broken formations and a tectonic mélange assemblage.

During the second phase (ca. 2.685-2.680 Ga), oceanic island arc sequences, with right-lateral transpressional deformation; further fragmentation and mixing of ocean plateau fragments; synkinematic dikes and sills; arc-derived trench turbidites; and arc-derived mafic to felsic igneous rocks with associated komatiites, and further development of the broken formations, suggest that the tectonic mélange formation continued. The oceanic island arc sequences were all tectonically juxtaposed and incorporated into the accretionary complex. The phase one to phase two transition is interpreted in terms of a trenchward migration of the magmatic arc axis due to continued accretion and underplating.

During this second sequence the strike-slip faults in the fore-arc region of the Schreiber-magmatic arc may have provided conduits for uprising melts from the descending slab, and induced decompressional partial melting in the sub-arc mantle wedge. This yielded the syn-kinematic ultramafic to felsic and gabbroic intrusions. A similar close relationship between orogen-parallel strike-slip faulting and magmatism has been recognized in several Phanerozoic transpressional orogenic belt counterparts, including the North American Cordillera, Japanese island arcs, and British Caledonides, suggesting that the orogen-parallel strike-slip faulting in the Schreiber-Hemlo greenstone belt played an important role in magma emplacement and lateral crustal accretion. It is suggested that subduction-accretion, with associated mélange formation and magmatism, was an important mechanism of continental growth in the late Archean southern Superior Province. (Kerrich and Polat, 1999)

In a further analyses of the belt by Polat (1999), the Schreiber-Hemlo greenstone belt includes mafic to intermediate tholeiitic flows, mafic to intermediate calc-alkaline flows, felsic calc-alkaline flows, syn-kinematic ultramafic (picritic) to felsic dykes, and high-Al TTG plutons. All these suites share positively fractionated REE patterns, and negative anomalies of Nb and Ti....Fractionated REE patterns, negative Nb and Ti anomalies, and transition metal contents are all consistent with a metasomatized mantle wedge source for the tholeiitic and calc-alkaline volcanic suites, and ultramafic to intermediate dykes. The geochemical characteristics of mafic to intermediate tholeiitic and calc-alkaline flows suggest a deeper and more primitive mantle source compositions for the calc-alkaline suite than the tholeiitic counterpart. Felsic flows and dykes, and TTG plutons are all defined by the enrichment of LREE, Th, and Zr, and by the depletion of Nb, Ti, Cr, Sc abundances. High Al₂O₃/TiO₂, Zr/Y, Sr/Y, La/Yb, and Gd/Yb ratios for felsic rocks are consistent with slab melting and garnet-amphibole-clinopyroxene residue in the source. The existence of overlapping fields between mafic, intermediate, and felsic suites on trace element ratios suggest that processes controlling the production of these arc rocks were more complex than simple slab and/or wedge melting. This complexity may have resulted from a mixture of slab and wedge melts, second stage melting, magma mixing, fractional crystallization, partial equilibration with sub-arc wedge peridotite, crustal contamination, or some combination.

[edit] Economic Geology

The Superior Province is the mining heartland of Canada with major mining camps in the Abitibi district of Ontario-Quebec and Red Lake region of western Ontario. The Sudbury structure located on the southeastern edge of the Superior Province is one of the world's largest nickel producing regions. The Big Trout Lake belt and others have nickel and platinum group elements (PGE) potentials. (Percival, 2006).

The Northern Superior Superterrane (NSS) hosts diamondiferous kimberlite at the Victor pipe in the Attawapiskat area. Additional exploration targets have been identified through kimberlite indicator minerals in the Ontario-Manitoba border region, the Wemindgi and Otish Mountains in Central Quebec, the Wawa region in south Ontario, and the Timiskaming/Temagami areas in southeastern Ontario near the border of Quebec. Production at Victor project is planned for 2008.

Twenty-five percent of Canadian gold production has come from the Schreiber-Hemlo Greenstone Belt in the Wawa subprovince in the south Ontario. The Shebandowan-Schreiber mineral belt hosts important gold, iron, volcanic-hosted massive sulphide and intrusion-hosted Ni deposits (Percival, 2006). The most significant is the Hemlo gold camp. At present, three mines exploit the Hemlo gold deposit (Williams, Golden Giant, and David Bell mines). The world-class Hemlo deposit was a major gold discovery in Canada during the 1980's and contains ~22 million ounces (680 t) of gold. Average gold grade for the main deposit (84 Mt of ore, 21 Moz Au) is 7.7 g/t. (Bodycomb, 2000). The Uchi subprovince of the North Carribou terrane hosts some of the largest mineral deposits of the western Superior region, including the Red Lake gold camp. These rocks host both world-class gold deposits and massive sulphide mineralization. Iron formations in the central North Caribou terrane host the Musselwhite lode gold deposit. The Quetico-western Wabigoon Seine River-Rainy Lake fault is an area known for numerous gold showings. Small deposits East of Lake Nipigon hosts the Long Lac vein gold deposits. (Percival, 2006).

The Abitibi subprovince in the east hosts some of the richest mineral deposits of the Superior Province, including the giant Kidd Creek massive sulphide deposit and the large gold camps of Ontario and Quebec. The northern Abitibi belt is best known for the Matagami-Chibougamau mineral belt, characterized mainly by Cu-Zn massive sulphide deposits, Cu-Zn vein deposits and some lode gold deposits. The central zone has massive sulphides as well as vein gold deposits. The southern Abitibi belt hosts the Timmins-Val d'Or mineral belt, known for its numerous gold deposits, major Cu-Zn massive sulphide deposits, komatiite and intrusion-related Ni deposits, some pegmatite-hosted deposits and minor porphyry type mineralization. The richly gold-mineralized Cadillac-Larder Lake break forms the southern boundary of the belt. The Abitibi belt also has some of the largest massive sulphide deposits in the province. (Percival, 2006).

[edit] See also

• Canadian Shield
• North American craton

[edit] References