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This paper provides a comprehensive synthesis of virtually all units and events of Early and Middle Proterozoic age in the Yukon, spanning ~1 Ga. Early and Middle Proterozoic time was dominated by a series of extensional-basin-forming events punctuated by orogenesis, magmatism, and hydrothermal activity. Basinal deposits include the Wernecke Supergroup (>1.71 Ga), Pinguicula Group (~1.38 Ga), and Mackenzie Mountains Supergroup (1.00–0.78 Ga). Igneous rocks include the Bonnet Plume River Intrusions (1.71 Ga), Slab volcanics (≥1.6 Ga), Hart River sills and volcanics (1.38 Ga), and Bear River (Mackenzie) dykes (1.27 Ga). A voluminous hydrothermal event generated the widespread Wernecke breccias at 1.60 Ga. The Racklan orogeny deformed the Wernecke Supergroup prior to emplacement of the Wernecke Breccia. The Corn Creek orogeny deformed Mackenzie Mountains Supergroup and older rocks prior to deposition of the Windermere Supergroup (<0.78 Ga). Long intervals with scanty rock records extended for as much as 300 Ma and appear to represent periods of crustal stability and subaerial conditions. By the time of Windermere rifting (<0.78 Ga), the supracrust of northwestern Laurentia was a mature, largely denuded orogenic belt with a composite sedimentary–metamorphic–igneous character. New isotopic data include Nd depleted mantle model ages for the Wernecke Supergroup (2.28–2.69 Ga) and Wernecke Breccia (2.36–2.96 Ga), a U–Pb zircon age for a Hart River sill 1381.9+5.3-3.7 (Ma), detrital U–Pb zircon ages from the basal Pinguicula Group (1841–3078 Ma), detrital muscovite ages from the Mackenzie Mountains Supergroup (1037–2473 Ma), and muscovite 40Ar/39Ar cooling ages from the Wernecke Supergroup (788 ± 8 and 980 ± 4 Ma). [ABSTRACT FROM AUTHOR]

New U-Pb igneous and detrital zircon ages reveal that despite being separated by younger orogens, three of Alaska's terranes that contain Precambrian rocks-Farewell, Kilbuck, and Arctic Alaska-are related. The Farewell and Kilbuck terranes can be linked by felsic magmatism at ca. 850 Ma and by abundant detrital zircons in the Farewell that overlap the ca. 2010-2085 Ma age range of granitoids in the Kilbuck. The Farewell and Arctic Alaska terranes have already been linked via correlative Neoproterozoic to Devonian carbonate platformdeposits that share nearly identical faunas of mixed Siberian and Laurentian affinity. New igneous ages strengthen these ties. Specifically, 988, 979, and 979 Ma metafelsites in the Farewell terrane are close in age to a 971 Ma granitic orthogneiss in the Arctic Alaska terrane. Likewise, 852, 850, 845, and 837 Ma granitic orthogneisses, metafelsite, and rhyolite in the Farewell terrane are similar to the reported 874 to 848 Ma age range of metarhyolites in the Arctic Alaska terrane. The Kilbuck and Arctic Alaska terranes have been previously linked on the basis of provenance: detrital zircons from the Carboniferous Nuka Formation in the Arctic Alaska terrane range from 2013 to 2078 Ma, overlapping the age of Kilbuck granitoids. A new 849 Ma age of a Kilbuck granitoid strengthens the proposed connection. Among the other new results from Kilbuck terrane is a 2085 Ma zircon from a granitoid that now stands as the oldest tightly dated rock in Alaska. We conclude that the Kilbuck, Farewell, and Arctic Alaska terranes were not independent entities with unique geologic histories but instead are related pieces of the circum-Arctic tectonic puzzle. [ABSTRACT FROM AUTHOR]

The 1.27 Ga Mackenzie dyke swarm, the largest on Earth, radiates from a point in the western Canadian Arctic and extends across much of the Canadian Shield. Possible western extensions of the swarm are largely obscured by younger sedimentary cover. Paleoproterozoic inliers in northern Yukon host the Bear River dykes (BRD), herein dated by U–Pb baddeleyite and zircon methods at 1268.5 ± 1.5 Ma and 1264.6 ± 1.2 Ma. The BRD share similar geochemical and Nd-isotopic characteristics with the Mackenzie dykes and the coeval Coppermine River basalts, and are regarded as products of the same plume. Hydrothermal activity at ∼1270 Ma in breccia of the Nor mineral occurrence, northwest of the BRD, was probably generated by BRD at depth. The BRD generally strike northwest, approximately 90° to the orientation predicted by the radiating dyke model. This difference may be explained by an anomalous local stress field at the time of BRD emplacement, or reorientation of BRD during subsequent events of Cordilleran deformation. Using the Nor mineral occurrence as the westernmost locale of Mackenzie dyking, and assuming a model of uniform dyke radiation, the arc of the Mackenzie swarm is at least 50° greater than previously recognized, bringing the total arc of dyke radiation to >150°. [Copyright &y& Elsevier]

Northwestern Laurentia, after cratonization at about 1.85 Ga, underwent a series of tectonic and magmatic events during the Proterozoic that were followed by separation of Laurentia from another landmass, probably Australia. The oldest magmatic event produced the Bonnet Plume River Intrusions (BPRI), which intruded the Wernecke Supergroup as short dikes and small stocks. The BPRI are hydrothermally altered tholeiitic diorites, gabbros, and subordinate anorthositic and syenitic rocks, with trace element signatures consistent with a rift origin. Depleted mantle model ages range from 2.29 to 2.57 Ga and ℇ[sub Nd] values range from +0.7 to –1.7. An increasing crustal component is apparent in rocks with more evolved compositions. Four U–Pb zircon ages (1705.9 ± 0.7, 1709.4 ± 1.4, 1711.1 ± 5.1, and 1713.6 ± 12.7 Ma) indicate a Paleoproterozoic age for the BPRI. These dates constrain the age of the Wernecke Supergroup to ca. 1710 Ma, making it the oldest supracrustal succession in western Laurentia, e.g., >240 Ma older than the Belt Supergroup of southeastern British Columbia and the northwestern United States. The Wernecke Supergroup was deposited in the first rift basin to open along the western margin of Laurentia, but was later inverted by the pre-1.6 Ga Racklan Orogeny, an event possibly influenced by transmission of compression from the Yavapai and Mazatzal orogenies in southern Laurentia. The Neoproterozoic southwestern United States – east Antarctica (SWEAT) reconstruction, which places Australia next to northwestern Laurentia, is supported by linkages between Paleoproterozoic and Mesoproterozoic geological features in northwestern Canada and Australia.Après une cratonisation vers 1,85 Ga, le nord-ouest du continent laurentien (Laurentia) a subi une série d'événements tectoniques et magmatiques au cours du Protérozoïque; ces événements ont été suivis par la séparation de Laurentia d'une autre masse continentale, probablement l'Australie. L'événement magmatique le plus ancien a produit les intrusions de la rivière Bonnet Plume (BPRI) qui ont pénétré le Supergroupe de Wernacke en tant que de courts dykes et de petits massifs intrusifs. Les BPRI consistent en des diorites tholéiitiques, des gabbros et des roches subordonnées anorthositiques et syénitiques qui ont subi une altération hydrothermale, avec des signatures d'éléments traces qui concordent avec une origine de fosse. La plage pour les modèles de manteau appauvri varie de 2,29 à 2,57 Ga et les valeurs ℇ[sub Nd] varient de +0,7 à –1,7. Une plus grande composante crustale est apparente dans les roches avec des compositions plus évoluées. Quatre déterminations d'âge U–Pb sur des zircons donnent un âge paléoprotérozoïque pour les BPRI : 1705,9 ± 0,7 Ma, 1709,4 ± 1,4 Ma , 1711,1 ± 5,1 Ma et 1713,6 ± 12,7 Ma. Ces dates limitent l'âge du Supergroupe de Wernecke à environ 1710 Ma, faisant de la séquence supracrustale la plus ancienne du Laurentia occidental, par ex., > 240 Ma plus ancien que le Supergroupe de Belt du sud-est de la Colombie-Britannique et du nord-ouest des États-Unis. Le Supergroupe de Wernecke a été déposé dans le premier bassin de distension qui s'est ouvert le long de la limite ouest de Laurentia mais il a été par la suite inversé par l'orogène de Racklan pré-1,6 Ga, un événement possiblement influencé par la transmission de la compression des orogènes Yavapai et Mazatzal dans le sud du Laurentia. La reconstruction du transect sud-ouest américain – est de l'Antarctique (SWEAT), au Néoprotérozoïque, qui place l'Australie à côté du nord-ouest de Laurentia, est appuyé par des liens entre les caractéristiques géologiques Paléo- et Méso- protérozoïques au nord-ouest du Canada et en Australie.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]