Superior Craton - Archean Superior Proto-craton

Archean Superior Proto-craton

The planet's oldest continental crust (up to 3.7 Ga) occurs in the Northern Superior superterrane and the 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 during 3.1-2.8, 2.725, and 2.69 Ga events. Western and eastern proto-cratons (3.1-2.8 Ga) rifted about 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 (also known as Algoman orogeny) 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)