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Abstract: Lithospheric domains in the Slave Province, inferred from regional variations in chemistry of mantle-derived garnets, are parallel with northeasterly structural trends in Neoarchean surface rocks and were used previously to infer Late Neoarchean crust–mantle coupling and argue against the presence of diamondiferous Mesoarchean lithosphere under the western Slave craton prior to its late Neoarchean orogenic climax. A review of more recent evidence does not support this view but concludes that a Mesoarchean lithospheric root was coupled to Mesoarchean crust of the Central Slave superterrane (CSST) prior to accretion of adjacent juvenile Neoarchean terranes. A significant part of this root survived the Neoarchean break-up of the CSST, Neoarchean terrane accretion and a complex sequence of post-accretion deformation, granitoid plutonism and metamorphism. It was least modified in the ultra-depleted harzburgitic layer (UDL) under the central part of the Contwoyto terrane, where it is trapped above the deepest part of an underplated Paleoproterozoic slab which stabilized the remnants of the Archean root and caused downward younging of the lithosphere. Upper mantle domains recognized on the basis of the distribution of peridotitic garnets are not primary Neoarchean features but were either inherited from the original Mesoarchean root or resulted from Neoarchean and Paleoproterozoic tectonic erosion and/or metasomatism of this root. The Slave Province resembles other diamondiferous cratons in that its diamond endowment consists of both Mesoarchean and Paleoproterozoic stones. [Copyright &y& Elsevier]

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 [ABSTRACT FROM AUTHOR]

The Archean (2.8 Ga) Banded Iron Formation (BIF) of the Bell Lake region of Yellowknife greenstone belt, Canada is recrystallized to metamorphic assemblages of the amphibolite facies. This BIF is characterized by centimetre-scale Fe-rich and Si-rich mesobands. In the Si-rich mesobands, thin layers of magnetite microbands are developed in a quartz matrix. The Fe-rich mesobands are composed mainly of Ca-amphibole (hornblende), Fe-Mg amphibole (grunerite), and magnetite. The metamorphic foliation locally cuts across the mesoband boundaries, indicating the mesobanding was formed prior to peak metamorphism. Variations in mineral modal proportions between Fe-rich mesobands and microbands are diagnostic of depositional compositional differences between beds. Micro-X-ray fluorescence imaging reveals metamorphic differentiation within Fe-rich mesobands, with segregation of Fe-Mg amphibole, and the incompatible element Mn is concentrated at the margins of the Fe-rich mesobands during the amphibole-forming reactions. Ti was relatively immobile during metamorphic segregation and its distribution provides a record of the original structures in the Fe-rich mesobands. [ABSTRACT FROM AUTHOR]

Abstract: The longevity of the continental lithosphere mantle is explained by its unusual composition. This part of the mantle is made up mainly of forsterite-rich olivine (Fo92–94), with or without orthopyroxene, and it is essentially anhydrous. The former characteristic makes it buoyant, the latter makes it viscous, and the combination of these features that allow it to remain isolated from the convecting mantle. Highly forsteritic olivine is not normally produced during mantle melting. Possible explanations for its abundance in old Archean subcontinental lithospheric mantle include: (a) high-degree mantle melting in a plume or at an Archean ocean ridge; (b) accretion of this material to older lithosphere and its reworking in a subduction zone; (c) redistribution of material to eliminate high-density, low-viscosity lithologies. Following an evaluation of these models based on petrological and numerical modeling, we conclude that the most likely explanation is the accumulation of the residues of melting of one or more mantle plumes following by gravity-driven ejection of denser, Fe-rich components. [Copyright &y& Elsevier]

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]

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]