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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.Back to Table of Contents [ABSTRACT FROM AUTHOR]

Five discrete accretionary events assembled fragments of continental and oceanic crust into a coherent Superior craton by 2.60 Ga. They exhibit similar sequences of events at ~10 million year intervals: cessation of arc magmatism, early deformation, synorogenic sedimentation, sanukitoid magmatism, bulk shortening, regional metamorphism, late transpression, orogenic gold localization, emplacement of crust-derived granites, and postorogenic cooling. The Northern Superior superterrane recorded 3.7–2.75 Ga events prior to 2.72 Ga collision with the 3.0 Ga North Caribou superterrane. Following 2.98 Ga rifting, the Uchi margin of the North Caribou superterrane evolved in an upper plate setting before 2.72–2.70 Ga collision of the <3.4 Ga Winnipeg River terrane, which trapped synorogenic English River turbidites in the collision zone. The Winnipeg River terrane was reworked in 2.75–2.68 Ga magmatic and tectonic events, including the central Superior orogeny (2.71–2.70 Ga) that marks accretion of the juvenile western Wabigoon terrane. In the south, the Wawa–Abitibi terrane evolved in a mainly oceanic setting until Shebandowanian collision with the composite Superior superterrane at 2.695 Ga. Synorogenic Quetico turbidites were trapped in the collision zone. The final accretionary event involved addition of the Minnesota River Valley terrane (MRVT) from the south, and deposition and metamorphism of synorogenic turbidites of the Pontiac terrane during the ~2.68 Ga Minnesotan orogeny. Seismic reflection and refraction images indicate north-dipping structures, interpreted as a stack of discrete 10–15 km thick terranes. A slab of high-velocity material, possibly representing subcreted oceanic lithosphere, as well as Moho offsets, support a model of progressive accretion through plate-tectonic-like processes. [ABSTRACT FROM AUTHOR]

Integrated mapping, structural analysis, and U-Pb geochronology of the Committee Bay area, Nunavut, establish a record of Neoarchean crustal growth followed by penetrative Paleoproterozoic deformation. Supracrustal rocks include a lower ca. 2.73 Ga mafic-ultramafic volcanic-dominated sequence, a middle, economically significant 2.71 Ga intermediate volcanic-bearing sequence with intercalated sulphidized, gold-bearing iron formation, and an upper <2.69 Ga clastic ± komatiite-quartzite sequence. Following an 80 million year hiatus, this succession was intruded by voluminous ca. 2.61-2.57 Ga granodiorite-tonalite-granite ± diorite, which do not appear to have thermally or tectonically affected the supracrustal belt. Instead, three generations of structures record polyphase Paleoproterozoic deformation of the region. D1 structures are consistent with a doubly vergent structural fan developed at ca. 2.35 Ga in response to the Arrowsmith orogeny that affected the western Rae margin. Penetrative D2 structures dominate the map pattern and include northeast-trending, southeast-dipping folds and fabrics within which gold is localized. The general southeast dips of S2 and inclined, northwest-vergent attitude of F2 reflect northwest-directed shortening at 1.84-1.82 Ga. The absence of syn-D2 plutonic rocks in the west and central Committee Bay belt support amphibolite-facies metamorphism as a response to crustal thickening, which, in turn, led to syn-D2 crustal melting in the east. Regionally extensive upright to northwest-vergent D2 structures and associated ca. 1.85-1.82 Ga tectonometamorphism across the Rae craton are attributed to an early stage of the Hudsonian orogeny involving microcontinent collision(s) with its southeastern margin. D3 folds and dextral shearing at ca. 1780 Ma accommodated localized, late-stage compressional strain during final amalgamation of Laurentia. [ABSTRACT FROM AUTHOR]

Abstract: The basal Paleoproterozoic supracrustal succession of the Churchill Province in northern Canada comprises sedimentary basins overlying the Archean Rae and Hearne domains. The Rae domain supracrustal succession (e.g. Amer, Ketyet River, Chantrey and Montresor groups) comprises four lithotectonic assemblages which include, in ascending stratigraphic position: (1) shallow marine-fluvial quartzarenite with mainly Neoarchean detrital zircons of local provenance; (2) shallow marine quartzarenite with mainly local provenance that locally includes carbonates±mafic volcanic flows; (3) abrupt but conformable transition to basinal dark shales and overlying platformal carbonates that pass upward into siltstones and sandstones that record gradual emergence of the platform. Sandstones within this assemblage display a substantially different detrital zircon provenance signature dominated by early Paleoproterozoic zircons, with grains as young as 1.95Ga; (4) unconformably to conformably overlying immature marine sandstones, including turbidites, with a significant component of 2.0–1.9Ga detritus probably derived from a combination of local and distal sources. The thickness and relative compositional maturity of the basal lithotectonic assemblage 1 records a protracted period of enhanced weathering on a slowly subsiding but stable supercontinent (e.g. Kenorland). This was followed by mafic volcanism and marine transgression, consistent with partial rifting of the Rae domain and crustal extension attending supercontinent break-up (lithotectonic assemblage 2). Strata of lithotectonic assemblage 3 record basin flooding and deepening followed by platformal sedimentation along the margins of extended continental blocks. Assemblage 4 is interpreted to represent deposition in foreland basins during early amalgamation of Laurentia (part of Nuna) at ca. 1.9Ga. The stratigraphy and detrital zircon geochronology of the Hurwitz Group, which overlies the Hearne domain, is broadly similar to the supracrustal sequence of the Rae domain, but differs through the presence of basal diamictites and lack of 2.5Ga detritus, a major local source in the Rae. Our data suggest that the Rae and Hearne domains were assembled together by max. 1.91Ga (i.e. max. age of deposition of the uppermost Hurwitz and Amer groups). The Paleoproterozoic stratigraphic assemblage framework for the Churchill Province compares well with that of other cratons derived from break-up of Kenorland and ultimately amalgamated in Nuna. Examples from Laurentia include supracrustal rocks that overlie the southern margin of the Superior Province (Southern Province, e.g. Huron Supergroup, Animikie Group, Marquette Range Supergroup, Whitewater Group and Mistassini-Otish Group). The Paleoproterozoic assemblages of the Southern and Churchill provinces exhibit first-order stratigraphic similarities that indicate a shared history of stable continental sedimentation followed by rifting, basin opening and basin closure. [Copyright &y& Elsevier]

Abstract: Petrology and in situ SHRIMP monazite geochronology provide new constraints on the polymetamorphic and polydeformational history of the Committee Bay belt, Rae Province, Nunavut, Canada. Rare ca. 2.58Ga monazite inclusions in garnet porphyroblasts in the eastern part of the belt are interpreted to reflect regional contact metamorphism (M1) associated with voluminous 2.61–2.58Ga plutonism. Monazite also occurs as ca. 2.35Ga inclusions in andalusite in the central supracrustal belt, but is absent from the east. These data complement previous studies to the west, and suggest that the Committee Bay belt represents a ca. 2.35Ga tilted crustal section that was tectonically thickened±imbricated during the Arrowsmith orogeny (D1–M2). Penetrative reworking of the belt occurred during a diachronous D2–M3 tectonometamorphic event which involved northwest-vergent thickening to depths of ∼5kbar across most of the belt. Although D2 folds and fabrics across the belt are geometrically correlative, monazite is ∼20Myr older in the western migmatite domain (ca. 1.86Ga) than in the western supracrustal belt (ca. 1.84Ga). This temporal difference is attributed to burial of more radiogenic lithologies in the migmatite domain. Tectonic thickening is attributed to ca. 1.87Ga collision of Meta Incognita microcontinent with the southeastern flank of the Rae Province. The eastern supracrustal belt exposes similar amphibolite-facies (M3) northeast-striking, northwest-vergent D2 structures that are dated at 1.815Ga. This younger reworking may reflect the influence of a major northward projecting promontory of the Superior Province which continued to affect the softened hinterland of the Rae Province during terminal collision at ca. 1.82Ga. The central Committee Bay belt records a younger, ca. 1.79Ga structural overprinting (D3–M4) which involved dextral shearing and differential burial to temperatures above monazite growth in a gentle synformal structure formed during the final stages of amalgamation of Laurentia. [Copyright &y& Elsevier]

Ophiolitic rocks emplaced following closure of the Ordovician Iapetus Ocean outcrop around the western margins of Notre Dame Bay in western Newfoundland. Previous geological and geophysical models have interpreted the Betts Cove Ophiolite Complex (BCO) as a series of imbricate thrust slices. A new three-dimensional (3-D) model indicates that locally the BCO has the form of a northeast-trending doubly plunging syncline that was later segmented by a series of normal and high-angle reverse faults. This segmentation is interpreted in terms of a Carboniferous graben structure that is responsible for the current morphology of the Notre Dame Bay. The 3-D model incorporates new high-resolution aeromagnetic, marine magnetic, and topographic imagery. In addition, newly available structural information is used to both constrain the geometry of the geological contacts in the near surface and to map contacts in the subsurface. Calibration of the computed geophysical models was achieved using newly acquired magnetic susceptibility data. The resulting 3-D model, which is compatible with all aspects of the geological and geophysical data, provides an explanation for the distribution of Ordovician ophiolites around Notre Dame Bay. [ABSTRACT FROM AUTHOR]

Recent advances in the use of Geographic Information Systems (GIS) software and analysis can be used in conjunction with traditional geoscience data sets to determine effective predictors for gold mineralization, from which mineral prospectivity maps can be generated that highlight potential exploration targets on a regional scale. In this paper, key components of the Archean lode gold deposit model for the Red Lake belt are selected and modeled using weights of evidence (WofE) analysis and logistic regression, leading to the creation of gold prospectivity maps. The best predictors for past and present gold producers in the Red Lake camp, according to WofE analysis include (1) elevated trace elements, Au, As, and Sb; (2) a number of alteration indices calculated from oxide geochemical data; (3) alteration characterized by pervasive and vein-style ferroan carbonate and elevated Au, As, Sb, and S anomalies; (4) proximity to the Mackenzie Island stock and diorite phases of the Dome stock; and, (5) tholeiitic basaltic flows and associated gabbroic rocks of the Balmer assemblage. Gold prospectivity maps produced by logistic regression using binary evidence maps highlight anomalous localities within known and highly prospective areas in the district (Madsen – Red Lake corridor, Balmertown – Cochenour – East Bay). In addition, a number of localities not known to contain significant deposits were also identified as prospective. [ABSTRACT FROM AUTHOR]

New field work, U–Pb ages, geochemical data, and Sm–Nd isotopic analyses have established the timing and determined the nature of volcanism, deformation, and tectonic assembly of the Pickle Lake greenstone belt in the Uchi subprovince of the western Superior Province of the Canadian Shield. The >2860 Ma Pickle Crow assemblage has been redefined to include the former Northern Pickle assemblage on the basis of stratigraphic continuity and similar volcanic geochemistry between the two units across a previously inferred fault contact. The Pickle Crow assemblage consists of tholeiitic basalt with thin, but laterally extensive, oxide-facies iron formation overlain by alkalic basalts and minor calc-alkaline andesites to dacites with primitive Nd isotopic compositions (εNd2.89 Ga = +2.1 to +2.4) suggestive of deposition in a sediment-starved oceanic basin. The ~2 km thick ~2836 Ma Kaminiskag assemblage (former Woman assemblage) consists of tholeiitic basalt interbedded with intermediate and rare felsic pyroclastic flows with primitive Nd isotopic compositions (εNd2.836 Ga = +2.4). Two samples of intermediate volcanic rocks interbedded with southeast-younging pillowed basalt, previously inferred to be part of the Pickle Crow assemblage, yielded U–Pb zircon ages of 2744 Ma and 2729 ± 3 Ma. These rocks are thus part of the younger Confederation assemblage, which consists of intercalated basalt and dacite (εNd2.74 Ga = +0.1 to +0.8) exhibiting diverse compositions probably reflecting eruption in a continental margin arc to back-arc setting. The contact between the Confederation and Kaminiskag assemblages is assumed to be a fault. The greenstone belt is intruded by late syn- to posttectonic plutons including the composite quartz dioritic to gabbroic July Falls stock with a new U–Pb zircon age of 2749 Ma, and the ~2741 to 2740 Ma trondhjemitic to granodioritic Ochig Lake pluton and Pickle Lake stock, as well as the ~2697 to 2716 Ma Hooker–Burkoski stock. The earliest recognized deformation (D1) is recorded by a local bedding-parallel foliation in the Pickle Crow assemblage. This foliation is truncated by the ~2735 Ma Albany quartz–feldspar porphyry dyke and is not recognized in the volcanic rocks of the Confederation assemblage. The early deformation event is attributed to overturning of the Pickle Crow assemblage prior to deposition of the ~2744 to 2729 Ma Confederation assemblage. Subsequent deformation and development of a regionally penetrative planar fabric (S2) postdates ~2729 Ma volcanism, pre-dates the intrusion of the ca. <2716 Ma Hooker–Burkoski stock and is host to gold mineralization. [ABSTRACT FROM AUTHOR]

Here we present Re-Os geochronological data from two carbonaceous shale units from the Hornby Bay and Amundsen basins that provide important chronological markers for Mesoproterozoic stratigraphic successions within northern Canada. Shale from the basal Escape Rapids Formation yields a robust depositional age of 1067.3 ± 13.5 Ma for the lowermost Shaler Supergroup of Amundsen basin with a remarkably unradiogenic initial 187Os/188Os value (0.15), implying that it derived from weathering of juvenile source material, such as basalt. Sedimentological features, indicative of large basin conditions, suggest deposition within an extensive epeiric sea that was intermittently mixed with waters from an exterior ocean. This age, and the 720 Ma age of the uppermost Shaler Supergroup, constrain deposition of the ∼4 km-thick succession to a period of approximately 350 myr, recording sedimentation through a complete supercontinent cycle - amalgamation through to break-up of Rodinia. Further, it indicates that the Amundsen basin formed at the same time as the Borden, and Fury and Hecla basins on northern Baffin Island, and the Thule basin in northwestern Greenland, and that these basins were perhaps connected as part of a much larger basin situated in the interior of Rodinia. Diagenetic pyrite from sandstone dykelets in carbonaceous shales of the Fort Confidence Formation yielded a Re-Os model age of 1438 ± 8 Ma, providing a minimum age for deposition of the lower Dismal Lakes Group of the Hornby Bay basin. This age strengthens proposed regional correlation of the Hornby Bay basin with the large intracontinental Athabasca and Thelon basins, located on the Rae craton to the southeast, and is evidence for a Laurentia-wide marine flooding episode ca. 1500 Ma. Both new ages place important constraints on newly discovered eukaryotic microfossils from the Shaler Supergroup and Dismal Lakes Group and calibration points for critical chemostratigraphic data. • New Re-Os isotope ages from Mesoproterozoic successions in northern Canada. • Allow calibration of Rodinia supercontinent cycle. • Improve correlation with Mesoproterozoic sedimentary basins across northern Canada. • Ages constrain newly discovered eukaryotic microfossils from these strata. [ABSTRACT FROM AUTHOR]