Superior Craton - Western Superior Province - North Caribou Terrane

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 unconformable 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 Neoarchean 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 Winnipeg 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).