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In the Archean Blake River Group, mafic to intermediate fragmentai units have controversially been proposed to have formed during the collapse of a giant submarine caldera. This paper describes and interprets these rocks, summarizing their physical characteristics, inferred origins, age relationships, and geochemical signatures. The widespread Stadacona member, south of Rouyn-Noranda, consists of several hundred metres of bedded volcaniclastic rocks interpreted to have been mostly deposited from aqueous density currents fed directly by explosive eruptions. The magmas involved in these eruptions were plagioclase-phyric, tholeiitic to transitional basalts. The similarly widespread D'Alembert tuff, in the northern part of the Blake River Group, shares many physical characteristics with the Stadacona member and is thought to have a similar origin. However, the D'Alembert tuff is approximately six million years younger than the Stadacona member. It is composed mostly of transitional to calc-alkaline andesites and basaltic andesites with very distinct trace element profiles. Volcaniclastic rocks from other areas, such as Tannahill Township in Ontario and the Monsabrais area in Quebec, are interpreted to represent mostly in situ to remobilized hyaloclastite, with no explosive eruptions involved in their genesis. Our observations and interpretations are not compatible with models in which the volcaniclastic units are emplaced during a catastrophic event in relation with the collapse of a giant caldera. Instead, the fragmental rocks were produced by various mechanisms at many distinct times during the evolution of the Blake River Group. Resume : Dans le Groupe archeen de Blake River, il a ete propose que des unites volcanoclastiques mafiques a intermediaires aient ete formees durant l'effondrement d'une caldeira sous-marine geante, mais cette proposition est controversee. Le present article decrit et interprete ces roches, resume leurs caracteristiques physiques, leurs origines inferees, les relations d'ages et les signatures geochimiques. Au sud de Rouyn-Noranda, le membre de Stadacona, d'etendu importante, comprend plusieurs centaines de metres de roches volcanoclastiques litees qui sont interpretees comme ayant ete deposees a partir de courants de densite aqueux alimentes directement par des eruptions explosives. Les magmas impliques dans ces eruptions etaient des basaltes d' affinite tholeiitique a transitionnelle contentant des phenocristaux de plagioclase. Dans la partie nord du Groupe de Blake River, le tuf de D'Alembert, egalement tres etendu, partage de nombreuses caracteristiques avec le membre de Stadacona et son origine serait similaire. Toutefois, le tuf de D'Alembert est approximativement six millions d'annees plus jeune que le membre Stadacona. Il est surtout compose d'andesites et d'andesites basaltiques transitionnelles a calco-alcalines avec des profils d'elements traces tres distincts. Les roches volcanoclastiques d'autres secteurs, tels que le comte de Tannahill en Ontario et le secteur de Monsabrais au Quebec, sont interpretees comme representant surtout des hyaloclastites in situ a remobilisees, sans eruption explosive impliquee dans leur genese. Nos observations et interpretations ne sont pas compatibles avec un modele selon lequel les unites volcanoclastiques aient ete mises en place durant un evenement catastrophique en relation avec l'effondrement d'une caldeira geante. Les roches fragmentaires ont plutot ete produites par divers mecanismes a plusieurs epoques distinctes durant l' evolution du Groupe de Blake River. [Traduit par la Redaction], Introduction The Archean Blake River Group (BRG) in the southern part of the Abitibi Greenstone Belt (Fig. 1) hosts numerous volcanogenic massive sulphide (VMS) deposits, several of which--most notably the [...]

Abstract: 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 [...]

Abstract: 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 [...]

Abstract: In western Superior province, the North Caribou terrane (NCT) constitutes a Mesoarchean proto-continent heavily overprinted by Neoarchean magmatism and deformation resulting from the western Superior Province accretion. Locally, along [...]

The Annieopsquotch accretionary tract in Newfoundland is composed of a series of west-dipping structural panels, each containing remnants of ophiolitic and arc-backarc complexes of Laurentian affinity formed during the Ordovician closure of Iapetus. Panels were transferred from an upper-plate to a lower-plate setting during their Middle to Late Ordovician accretion to the Laurentian margin and become progressively younger eastward. Geochronological data indicate a complex and rapid history of generation and accretion of peri-Laurentian suprasubduction zone rocks. The rapid changes in tectonic environments and the complexity of the relationships are analogous to the complex arc-backarc relationships observed in the western Pacific today. The recognition of the peri-Laurentian provenance of these units based on stratigraphy, geochronology, isotopes, and geochemistry defines the position of the Red Indian Line, the fundamental suture zone in the northern Appalachians, but more importantly enables the development of a realistic tectonic model for the Annieopsquotch accretionary tract involving both thrust and sinistral transcurrent displacements. The oldest and most inboard unit in the Annieopsquotch accretionary tract is the Annieopsquotch ophiolite belt (ca. 480 Ma), which marks the initiation of subduction outboard of the Laurentian margin. The Lloyds River ophiolite complex (ca. 473 Ma) preserves a fragment of younger, more mid-ocean-ridge-like backarc-oceanic crust than the adjacent, structurally overlying Annieopsquotch ophiolite belt. The Lloyds River ophiolite complex originated as a backarc to the Buchans Group (ca. 473 Ma) ensialic bimodal calc-alkaline arc. The panels containing the Annieopsquotch ophiolite belt and Lloyds River ophiolite complex were stitched and overlain by ensialic arc rocks of the Otter Pond Complex (ca. 468 Ma) immediately alter their accretion to composite Laurentia together with the structurally underlying Buchans Group. The youngest, structurally lowest two panels comprise the elements of the Red Indian Lake group (465-460 Ma), which record the opening of a backarc basin and the subsequent establishment of a bimodal ensialic calc-alkaline arc sequence. The observed relationships indicate that the Annieopsquotch accretionary tract was generated above a single west-dipping subduction zone outboard of the Laurentian margin over ~20 m.y. Accretion mainly took place in two stages at ca. 468 and 450 Ma, which correspond with the collision between Laurentia and the Dashwoods ribbon continent and the collision with the peri-Gondwanan Victoria Arc along the Red Indian Line, respectively. Both collisions form part of the Taconic orogeny. The latter, Late Ordovician collision terminated the relatively rapid closure of the main Iapetan tract. The proposed model is similar to the correlative tracts in the British and Irish Caledonides, and may encourage a new look at the New England Appalachians. Keywords: Notre Dame subzone, accretion, trace elements, whole-rock geochemistry, Sm-Nd isotopes, U-Pb geochronology.