DECIPHERING TEXTURAL RELATIONSHIPS AMONG LITHIUM ALUMINOSILICATES IN DIBS PEGMATITE, WINNIPEG RIVER DISTRICT, SUPERIOR PROVINCE, SE MANITOBA, CANADA

The English River subprovince is one of two metasediment-dominated terranes in the western Superior Province. It has been interpreted as an accretionary complex, a foreland, or a fore-arc basin that developed and was subsequently deformed between the metavolcanic-rich Uchi subprovince and the orthogneiss- and metaplutonic-dominated Winnipeg River subprovince during a prolonged transpressive orogeny. To test these hypotheses, we combined a satellite image, aeromagnetic image, and Lithoprobe reflection seismic profile interpretation with detailed structural mapping to better characterize the internal geometry and significance of structural features in the western part of the subprovince in Ontario. Northward-directed subduction and collision of the Winnipeg River subprovince with the Uchi subprovince at ca. >2713–2698 Ma can account for the deposition of the sedimentary rocks, initial metamorphism, and the main phase of deformation in the subprovince, whereas the subduction of Wabigoon crust generated extensive tonalite magmatism in the Winnipeg River and English River subprovinces during the same period. A period of extension, after the docking of the Winnipeg River and Wabigoon subprovinces at ca. 2698 Ma, punctuated the compressive phases of the orogeny and was responsible for high-grade metamorphism, upward bending of the Moho, and localized deposition of late, coarse, alluvial–fluvial metasedimentary rocks. Renewed compression caused by the docking of the Wawa subprovince at ca. 2689–2684 Ma is likely responsible for a largely unrecognized regional upright folding and faulting event that controls the dominant structural geometry of the subprovince. Late in its tectonic evolution, strain was partitioned into dextral deformation that was strongly domainal and limited to the subprovince margins.

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Age and isotopic composition of late Archean leucogranites: implications for continental collision in the western Superior Province

Canadian Journal of Earth Sciences ◽

10.1139/e98-113 ◽

1999 ◽

Vol 36 (4) ◽

pp. 495-510 ◽

Cited By ~ 11

Author(s):

Y Larbi ◽

R Stevenson ◽

F Breaks ◽

N Machado ◽

C Gariépy

Keyword(s):

Rare Metal ◽

Superior Province ◽

Similar Data ◽

Metasedimentary Rocks ◽

Northwestern Ontario ◽

Metavolcanic Rocks ◽

Abitibi Subprovince ◽

Winnipeg River ◽

Rare Metal Mineralization ◽

Mantle Component

U-Pb and Sm-Nd isotopic data are presented for leucogranites and pegmatites from the boundary zones of the English River, Winnipeg River, and Wabigoon subprovinces in the late Archean Superior Province of northwestern Ontario. The Ghost Lake batholith and the Separation Rapids pluton are posttectonic, rare-metal-bearing, S-type leucogranites that were generated during the final stages of the amalgamation of the Superior Province. U-Pb dating of monazites yields ages of 2650 ± 3 Ma for a pegmatite from the Dryden area and 2646 ± 2 Ma for the Separation Rapids pluton. Sm-Nd data from these granitoids are compared with similar data from late Archean intrusions and adjacent rocks from the same regions. Values of εNd range from 0 to +2 for pretectonic tonalites, from -2 to +2 for both the Ghost Lake batholith and the Separation Rapids pluton, from +1 to +3.5 for metavolcanic rocks, and from -0.5 to -1.5 for metasedimentary rocks. There is an overall trend of decreasing εNd values from pretectonic tonalites to the latest leucocratic pegmatites. This reflects the origin of more and more granitoids as a result of anatexis as the crust grew and thickened through accretion. The ranges of εNd values found among leucogranites from the two regions overlap with the isotopic values of the basalts and sediments. This suggests that the leucogranites were generated by similar processes involving both a crustal and a juvenile mantle component. Furthermore, the ages from this study and from pegmatites (2652-2643 Ma) in the Bird River greenstone belt provide the best estimate of the age of rare metal mineralization in the western Superior Province. Similar ages (2651-2639 Ma) for rare-metal-bearing leucogranites in southern Abitibi subprovince suggest a specific period of emplacement over a wide area.

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Nd and Pb isotopes from the Lake of the Woods greenstone belt, northwestern Ontario: implications for mantle evolution and the formation of crust in the southern Superior Province

Canadian Journal of Earth Sciences ◽

10.1139/e00-067 ◽

2000 ◽

Vol 37 (12) ◽

pp. 1677-1689 ◽

Cited By ~ 26

Author(s):

John A Ayer ◽

Jaroslav Dostal

Keyword(s):

Greenstone Belt ◽

Crustal Contamination ◽

Pb Isotopes ◽

Superior Province ◽

Elevated Concentration ◽

Lake Of The Woods ◽

Metavolcanic Rocks ◽

Depleted Mantle ◽

Winnipeg River ◽

Mantle Reservoir

Nd and Pb isotopes from the Lake of the Woods greenstone belt indicate the presence of three distinct reservoir sources: old enriched crust (>3.0 Ga); pre-2.7 Ga, homogeneous depleted mantle; and post-2.70 Ga heterogeneous mantle. EpsilonNd values of +1.1 to +2.3 for ultramafic to felsic metavolcanic rocks (2.742.72 Ga) indicate derivation from depleted mantle. The εNd value of 0.9 for younger turbidite (2.71 Ga), in conjunction with detrital zircon ages ranging from 2.72 to 3.0 Ga, indicates detritus from local greenstone belt sources (depleted mantle) mixed with an older crustal source. Post-2.70 Ga heterogeneity is demonstrated by εNd values ranging from 0.4 to +0.4 in shoshonitic to calc-alkaline metavolcanic rocks and +2.1 in a coeval ultrapotassic pluton. Pb isotopes from the pluton indicate derivation from a depleted mantle reservoir with an initial 207Pb/204Pb of 14.52, an initial 206Pb/204Pb of 13.29, and µ1 of 7.86. Isotopic comparison with post-2.70 Ga potassic suites from across the Superior Province indicates widespread mixing between depleted mantle and enriched end members. The enriched end member has isotopic characteristics of rocks derived from old crustal terrains, such as the Winnipeg River and Opatica subprovinces. This type of isotopic heterogeneity could be the result of crustal contamination or derivation from metasomatized mantle. Contamination of the mantle wedge by influx of fluids derived from partial melting of isotopically evolved, subducted sediments is favoured for the Superior Province potassic suite, because elevated concentration of Sr, Nd, and Pb in conjunction with primitive Mg#s suggest only limited crustal contamination has occurred.

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Sedimentary and structural evidence for 2.7 Ga continental arc–oceanic-arc collision in the Savant–Sturgeon greenstone belt, western Superior Province, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e06-060 ◽

2006 ◽

Vol 43 (7) ◽

pp. 995-1030 ◽

Cited By ~ 7

Author(s):

M Sanborn-Barrie ◽

T Skulski

Keyword(s):

Continental Margin ◽

Volcanic Rocks ◽

Shear Zones ◽

Iron Formation ◽

Superior Province ◽

Geophysical Surveys ◽

Winnipeg River ◽

Minimum Age ◽

The Rich ◽

Oceanic Rocks

The western Superior Province sustained rapid crustal growth in the interval 2.72–2.68 Ga through amalgamation of microcontinental crustal blocks and juvenile oceanic terranes. Recent field, isotopic, and geophysical surveys provide insight on the nature, timing, and scale of this accretionary growth. However, few places offer the rich tectono-stratigraphic and structural detail with which to establish accretion of oceanic and continental blocks as does the Savant–Sturgeon area. Here, 3.4–2.8 Ga continental crust of the Winnipeg River terrane is juxtaposed with 2.775–2.718 Ga juvenile oceanic rocks of the western Wabigoon terrane across a 2.85–2.75 Ga, southwest-facing, continental margin sequence. The continental margin was reactivated at ~2.715 Ga with the establishment of an arc, recorded by 2.715–2.70 Ga tonalite and associated intermediate volcanic rocks. This magmatic activity is interpreted to reflect north- and east-dipping subduction that led to consumption of a small tract of oceanic crust between the Winnipeg River and western Wabigoon terranes, ultimately leading to their amalgamation after 2.703 Ga. The telescoped fore arc also includes continental-derived turbiditic wacke, siltstone, and iron formation (Warclub assemblage) that are in tectonic contact with diverse oceanic rocks of the western Wabigoon terrane. Collision is bracketed between 2.703 Ga (the maximum age of marine fore arc deposits) and ~2.696 Ga (the minimum age of a late-tectonic pluton). Effects include thrust stacking and the development of shallow-plunging folds and bedding-parallel fabrics (D1), overprinted by steeply plunging inclined folds, steep foliations, and shear zones (D2). Collectively, these structures have penetratively reworked the suture between the ancient fore-arc and oceanic rocks in the Savant–Sturgeon area.

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Strike-slip juxtaposition of ca. 2.72 Ga juvenile arc and >2.98 Ga continent margin sequences and its implications for Archean terrane accretion, western Superior Province, Canada

Canadian Journal of Earth Sciences ◽

10.1139/e06-039 ◽

2006 ◽

Vol 43 (7) ◽

pp. 895-927 ◽

Cited By ~ 16

Author(s):

J A Percival ◽

V McNicoll ◽

A H Bailes

Keyword(s):

Strike Slip ◽

Iron Formation ◽

Superior Province ◽

Arc Magmatism ◽

Calc Alkaline ◽

Lake Winnipeg ◽

Red Lake ◽

The North ◽

Winnipeg River ◽

Terrane Accretion

The North Caribou terrane of the western Superior Province attained continental thickness (~35 km) by 2997 Ma. It records a subsequent 300 million years history of continental fragmentation, arc magmatism, and terrane accretion. At Lake Winnipeg the ~2978 Ma Lewis–Storey quartzite–komatiite–iron formation assemblage marks Mesoarchean breakup. Unlike the relatively continuous 2980–2735 Ma stratigraphic record of the Red Lake and Birch–Uchi greenstone belts to the east, little of this interval is recorded at Lake Winnipeg. Rather, two belts of younger, juvenile rocks are tectonically juxtaposed: the Black Island assemblage of isotopically depleted, 2723 Ma basalt, and calc-alkaline andesite; and Rice Lake greenstone belt of basalt, calc-alkaline andesite, and dacite (2731–2729 Ma). Collectively these terranes represent a short-lived island-arc–back-arc system that docked with the southwestern North Caribou margin along a northwest-trending, dextral, transpressive, D1 suture. This zone is marked by the highly deformed coarse clastic Guano Island sequence (<2728 Ma) that contains detritus of North Caribou affinity and is interpreted as a strike-slip basin deposit. Younger clastic sequences, including the Hole River (<2708 Ma), San Antonio (<2705 Ma), and English River (<2704 Ma) assemblages, occur in east–west belts that may have been deposited during the terminal collision (D2, D3) between the North Caribou terrane and continental crust of the Winnipeg River terrane to the south. Several terrane docking events within a framework of north-dipping subduction and continental arc magmatism appear necessary to explain structural and stratigraphic relationships in the 2735–2700 Ma interval.

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GIS compilation of geology and tectonostratigraphic assemblages, Wabigoon-Winnipeg River-Marmion transect, western Superior Province, Ontario

10.4095/221526 ◽

2005 ◽

Author(s):

D R Lemkow ◽

M Sanborn-Barrie ◽

G M Stott ◽

J A Percival ◽

D Stone ◽

...

Keyword(s):

Superior Province ◽

Winnipeg River

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Structural analysis of the Miniss River and related faults, western Superior Province: post-collisional displacement initiated at terrane boundaries

Canadian Journal of Earth Sciences ◽

10.1139/e06-017 ◽

2006 ◽

Vol 43 (7) ◽

pp. 1031-1054

Author(s):

K M Bethune ◽

H H Helmstaedt ◽

V J McNicoll

Keyword(s):

Accretionary Prism ◽

Vertical Displacement ◽

Strike Slip ◽

Superior Province ◽

The North ◽

Winnipeg River ◽

Granitoid Rocks ◽

Restraining Bend ◽

Dextral Strike Slip ◽

Fundamental Boundary

Mountain building in the western part of the Archean Superior Province culminated with the formation of regional strike-slip faults. This paper reports on the kinematics and timing of several major faults at the juncture between the Uchi, English River, Winnipeg River, and western Wabigoon subprovinces. Sinistral-oblique mylonitization along the northeast-striking Miniss River fault occurred at 2681 [Formula: see text] Ma. This involved ~40 km of sinistral offset and a scissor-like motion whereby vertical displacement increased southwestward toward a restraining bend near Sioux Lookout. To the north, the Miniss River fault is intersected by the east-striking, dextral strike-slip Sydney Lake – Lake St. Joseph fault; the latter merges along strike with the Pashkokogan fault. Restoration of respective displacements indicates that the faults formed sequentially, not simultaneously in response to tectonic indentation. Dextral strike-slip motion along the Sydney Lake – Lake St. Joseph (– Pashkokogan) fault was instigated at ≤2670 Ma and drove greenschist-grade, dextral reactivation of the southwest segment of the Miniss River fault. U–Pb geochronology suggests that the latter coincides with an older terrane-boundary fault that juxtaposed ca. 2735 Ma juvenile, western Wabigoon arc complexes against ca. 3.05 Ga granitoid rocks of the Winnipeg River terrane. The Sydney Lake – Lake St. Joseph (– Pashkokogan) fault similarly demarcates a fundamental boundary between Uchian volcanoplutonic rocks and the English River accretionary prism. Strike-slip faults in this region therefore initiated at terrane boundaries and in some cases evolved so as to transect and displace these boundaries to accommodate further shortening during final stages of Archean orogenesis.

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