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Three Orosirian basins and associated foreland thrust-fold belts are preserved on the margins of the Slave craton. All three are related to orogenic belts where oceans opened and later closed, uniting new crustal partners. The Great Slave basin differs from the Kilhigok and Coronation basins in ways that have defied explanation. It lacks a passive margin sequence and hosts two discrete igneous suites, separated by large-scale thrusting, that occurred well after the adjacent paleocean had closed. Here we report U–Pb zircon geochronology by chemical abrasion isotope dilution thermal ionization mass spectrometry for a member of each suite to constrain the age and origin of postcollisional thrusting. A widespread pulse of mainly phreatic alkaline volcanism, coeval with renewed foredeep flexure, occurred at 1889.0 ± 0.7 Ma (2σ internal error). A quartz-monzodiorite body, one of a belt-parallel chain of laccoliths that postdate thrusting, was emplaced at 1866.9 ± 0.9 Ma. These ages bracket renewed foredeep sedimentation and thrusting that telescoped major facies zones and was rooted within the basin. The older age is 70 and 30−60 Myr younger than collision in the Thelon and Taltson orogens, respectively. We attribute postcollisional thrusting and foredeep subsidence to "eduction"—the upward and outward ejection of partly subducted crust—and postulate that the top of the ejected wedge was a normal-sense detachment fault projecting beneath the Nonacho basin. We infer that eduction was triggered by slab failure, producing alkaline volcanism, and ended with delamination and laccolith emplacement. Eduction was facilitated by tradewind-driven erosion. Delamination was enabled by crustal transfer to the educted wedge, reducing footwall buoyancy. Slab failure and/or delamination removed the passive margin. [ABSTRACT FROM AUTHOR]

The Laird Lake property, southwest Red Lake greenstone belt, straddles the contact between the Balmer (2.99–2.96 Ga) and the Confederation (2.74–2.73 Ga) assemblages. The property is 10 km along strike from the Madsen and Starrat–Olsen Au mines that are hosted near the contact. The Balmer assemblage consists of fine-grained, aphyric, locally pillowed mafic volcanic rocks, ultramafic intrusive and volcanic rocks with flow breccia textures hosting local spinifex-bearing clasts, and banded-iron formations. In contrast, the Confederation assemblage comprises porphyritic mafic volcanic rocks intercalated with intermediate to felsic volcanic rocks that include crystal lapilli tuffs, crystal tuffs, and tuffs. The Balmer assemblage is composed of tholeiitic mafic volcanic rocks with minor Al-undepleted komatiites, whereas the Confederation assemblage is calc–alkalic. Neodymium isotopes, in conjunction with trace element geochemistry, suggests that parts of the Balmer assemblage were weakly contaminated by an older intermediate basement. Both arc and back-arc volcanism occurs in the Confederation assemblage, with the arc rocks showing a stronger crustal component than the back-arc rocks. A maximum U–Pb age of 2741 ± 19 Ma for a crystal tuff and an age of 2737.68 ± 0.79 Ma for a diorite are consistent with a Confederation assemblage affinity for the intermediate calc–alkaline rocks south of the Au-bearing horizon. The Balmer assemblage represents an oceanic plateau formed by plume magmatism on the margins of the North Caribou Terrane, whereas the Confederation assemblage at Laird Lake formed in an oceanic arc setting where both arc and back-arc volcanism occurred simultaneously. [ABSTRACT FROM AUTHOR]

New U/Pb and [sup 40] Ar/[sup 39] Ar isotopic dating in the Babine porphyry copper district of central British Columbia documents three distinct magmatic events at 107–104, 85–78, and 54–50 Ma. The earliest event involved emplacement of rhyolite domes into submarine volcanic rocks of the Rocky Ridge Formation. The rhyolite domes and related dacitic to basaltic volcanic rocks gave a U–Pb age of 107.9 ± 0.2 Ma and an [sup 40] Ar/[sup 39] Ar age of 104.8 ± 1.2 Ma. The rhyolites, which were previously mapped as Eocene, are reinterpreted to be part of a previously unrecognized mid-Cretaceous cauldron subsidence complex. The regionally extensive Late Cretaceous magmatic event is also recognized in the Babine district and is represented by [sup 40] Ar/[sup 39] Ar ages of 85.2 ± 2.8 and 78.3 ± 0.8 Ma on two Bulkley intrusions, one of which has associated porphyry copper mineralization. The final magmatic event is the most widespread and involved emplacement of the Babine intrusions and formation of numerous porphyry copper deposits including the Bell and Granisle past producers. Twenty-one new [sup 40] Ar/[sup 39] Ar isotopic ages for these intrusions and coeval andesites of the Newman Formation have a narrow range from 53.6 ± 0.9 to 49.9 ± 0.6 Ma, whereas previous K–Ar isotopic dating had a possible range of 15 Ma. The mid-Cretaceous, Late Cretaceous, and Eocene magmatic suites in the Babine district are interpreted to be part of a long-lived volcano-plutonic complex that was the site of periodic magmatism and porphyry copper mineralization over a 60 Ma time period. This complex may have evolved within a zone of extension (pull-apart basins) situated between dextral strike-slip faults that were active during periods of rapid oblique plate convergence.De nouvelles datations U–Pb et isotopiques [sup 40] Ar/[sup 39] Ar dans le district de cuivre porphyrique Babine, du centre de la Colombie-Britannique, documentent trois événements magmatiques distincts à 107–104 Ma, 85–78 Ma et 54–50 Ma. L'événement le plus précoce impliquait la mise en place de dômes de rhyolite dans les roches volcaniques sous-marines de la Formation de Rocky Ridge. Les dômes de rhyolite et les roches volcaniques apparentées dacitiques à basaltiques ont donné un âge U–Pb de 107,9 ± 0,2 Ma et un âge [sup 40] Ar/[sup 39] Ar de 104,8 ± 1,2 Ma. Les rhyolites, antérieurement cartographiées comme datant de l'Éocène, sont réinterprétées comme faisant partie d'un complexe de cuvettes d'effondrement auparavant non reconnues et qui dateraient du Crétacé moyen. Le magmatisme extensif régional du Crétacé tardif est aussi reconnu dans le district de Babine et il est représenté par des âges [sup 40] Ar/[sup 39] Ar de 85,2 ± 2,8 et 78,3 ± 0,8 Ma sur deux intrusions Bulkley, dont l'une présente une minéralisation associée de cuivre porphyrique. L'événement magmatique final est le plus répandu et il comprend la mise en place des intrusions Babine et la formation de nombreux gisements de cuivre porphyrique incluant les anciens gisements productifs de Bell et de Granisle. Vingt et un nouveaux âges [sup 40] Ar/[sup 39] Ar pour ces intrusions et des andésites contemporaines de la Formation Newman ont une plage étroite de 53,6 ± 0,9 à 49,9 ± 0,6 alors que des datations antérieures d'isotopes K–Ar avaient une plage de 15 Ma. Les suites magmatiques du Crétacé moyen, du Crétacé tardif et de l'Éocène dans le district de Babine sont interprétées comme faisant partie d'un complexe volcano-plutonique de longue durée où s'est produit du magmatisme périodique et de la minéralisation en cuivre porphyrique durant une période de 60 Ma. Ce complexe peut avoir évolué à l'intérieur d'une zone d'extension (basins d'extension) située entre des failles dextres à décrochement horizontal qui étaient actives durant les périodes de convergence rapide et oblique des plaques.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The Thompson Nickel Belt marks the boundary between the Archean Superior Province and the Trans-Hudson Orogen in Canada. It comprises Archean gneisses, and Paleoproterozoic rocks with metasediments and metavolcanites (Ospwagan Group) and intrusions. The gneisses are frequently migmatitic and host numerous pegmatites. The western belt boundary is a fault contact with the Kisseynew Domain of the Reindeer Zone. In the south, the transition zone between the belt and the Kisseynew Domain comprises granitoids and a detrital sequence (Grass River Group), part of which grades into turbidites in the Kisseynew Domain. The eastern belt boundary is a diffuse zone where the Archean east-west (E-W) structural trend changes into the north-northeast (NNE) trend of the belt. This paper presents U-Pb ages for granitoids and 207Pb/206Pb detrital zircon ages from the Ospwagan and Grass River groups. Ages and a comparison of events in the belt and in the eastern Reindeer Zone have major implications. The change from stable platform deposits to syn-tectonic filling and emplacement of mafic intrusions in the Ospwagan Group are attributed to the convergence between the Reindeer Zone and the Superior Province at 1891-1885 Ma. At ca. 1850 Ma, continuing convergence led to drowning of marginal basins of the Superior craton and to the development of a transpressive regime in the belt, the onset of which could be as old as ca. 1885 Ma. Metamorphic ages of 1818-1785 record closure of the Kisseynew basin and crustal thickening. Collision of the new continental block with the Superior Province was accommodated by transpression until 1750-1720 Ma. La ceinture de Thompson est située entre le Craton archéen du Supérieur et l'orogène paléoprotérozoïque du Trans-Hudson, au Canada. Elle comprend des gneiss archéens souvent migmatitiques, et des roches paléoprotéroïques, métasédiments et métavolcanites (Groupe Ospwagan), et intrusions. A l'ouest, une zone de faille marque le contact entre la ceinture et le domaine Kisseynew de la Zone de Reindeer. Vers le sud, cette zone de transition entre la ceinture et le domaine Kisseynew comprends des granitoïdes et une séquence détritique (Groupe Grass River), qui passe graduellement aux turbidites du domaine Kisseynew. Sur la bordure orientale de la ceinture, le grain structural E-W du Craton archéen se réoriente dans le grain NNE de la ceinture. Cet article présente des âges U-Pb pour différents granitoïdes et des âges 207Pb/206Pb pour les zircons détritiques des groupes Ospwagan et Grass River. Les âges et une comparaison des événements affectant la ceinture et l'est de la zone Reindeer ont des implications importantes. Dans le groupe Ospwagan, le passage de dépôts de type plate-forme à des dépôts syn-tectoniques, et l'intrusion de roches basiques, sont attribuées à la convergence entre la zone Reindeer et le Craton du Supérieur vers 1891-1885 Ma. Vers 1850 Ma, la convergence conduit à l'enfouissement des bassins de la marge du Craton et à un régime transpressif pouvant avoir débuté dès ca. 1885 Ma. La fermeture du bassin de Kisseynew et l'épaississement crustal sont enregistrés par des âges de métamorphisme entre 1818 et 1785 Ma. Le régime transpressif se poursuit jusqu'à ca. 1750-1720 Ma. [ABSTRACT FROM AUTHOR]

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This article presents a history of the development of U–Pb geochronology with emphasis on the role of Canadian researchers and some of its applications to Canadian geology. Modern U–Pb dating is the result of work by many individuals over the past 60 years, but the most important was Tom Krogh, who established methods that allowed determination of precise ages (<0.1% errors) on zircon using isotope dilution thermal ionization mass spectrometry. This was followed by the introduction of new analytical approaches by others, notably secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry that allow intracrystal domains to be dated. U–Pb geochronology is now an indispensable tool for understanding the Earth. In collaboration with field mapping, it has vastly improved our understanding of the geological history of Canada as well as important geological events such as mass extinctions, secular changes in geological processes, and the birth of the solar system. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The calc-alkaline Great Bear continental arc in the Wopmay Orogen developed after a collision ca. 1890 Ma of the Archean Slave craton with the Paleoproterozoic Hottah terrane to the west. U–Pb zircon dating of three volcanic and six intrusive rocks from the southern part of the arc shows four stages of development: (i) intrusion of a few small sodic leucogranite plutons at 1873 ± 2 Ma into a previously folded metasedimentary sequence; (ii) abundant calc-alkaline felsic volcanism and subvolcanic intrusions during the period 1870–1866 Ma, bracketed by five ages; (iii) intrusion of large calc-alkaline granitic plutons, including the Marian River batholith, dated by zircon and titanite from two samples at 1866 [sup +2] [sub –3] Ma; and (iv) emplacement of the potassic Faber Lake rapakivi granite at 1856 [sup +2] [sub –3] Ma. The arc was developed on the Hottah terrane due to easterly subduction of an oceanic plate under the amalgamated Slave craton – Hottah terrane. The oldest exposed rocks in the southern part of the arc are remnants of a Paleoproterozoic platformal sequence. They were regarded previously as equivalents of the initial passive margin sequence on the Slave craton, but are interpreted here as part of the Hottah terrane. The ages reported here are comparable with earlier data from the northern part of the arc, which show an age range from 1875 to 1840 Ma and also identify two suites of compositionally and temporally distinct granites. The age constraints show that the Great Bear arc evolved rapidly in time from sodic through calc-alkaline, and then, with a pause, to potassic composition.L'arc continental calco-alcalin de Great Bear dans l'orogène Wopmay s'est développé après une collision entre le craton de Slave, de l'Archéen et, à l'ouest, le terrane de Hottah, du Paléoprotérozoïque, il y a environ 1980 Ma. Des datations U–Pb sur des zircons de trois roches volcaniques et de six roches intrusives provenant de la partie sud de l'arc montrent quatre stages de développement : (i) l'intrusion de quelques petits plutons leucogranitiques sodiques (1873 ± 2 Ma) dans une séquence métasédimentaire plissée antérieurement; (ii) beaucoup de volcanisme calco-alcalin felsique et des intrusions subvolcaniques au cours de la période 1870-1866 Ma, encadré par cinq âges; (iii) intrusion de grands plutons calco-alcalins granitiques, incluant le batholite de Marian River, daté par du zircon et de la titanite provenant de deux échantillons à 1866 [sup +2] [sub –3] Ma, et (iv) la mise en place du granite rapakivi potassique de Faber Lake à 1856 [sup +2] [sub –3] Ma. L'arc s'est développé sur le terrane de Hottah en raison de la subduction vers l'est d'une plaque océanique sous l'amalgamation du craton de Slave et du terrane de Hottah. Les roches les plus anciennes qui affleurent dans la partie sud de l'arc sont des lambeaux d'une séquence de plate-forme datant du Paléoprotérozoïque. Auparavant, elles étaient considérées comme les équivalents de la séquence initiale de marge passive du craton de Slave, mais on les interprète ici comme faisant partie du terrane de Hottah. Les âges rapportés ici sont comparables aux données antérieures de la partie nord de l'arc, qui montent une plage d'âges de 1875 à 1840 Ma et identifient aussi deux suites de granites distincts en composition et dans le temps. Les limites d'âge montrent une évolution temporelle rapide de l'arc de Great Bear de sodique à calco-alcalin et, après une pause, à potassique. [Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

U–Pb geochronology, palynology, and lithostratigraphy were employed on the Late Cretaceous rocks in southern Alberta and Montana to solve litho- and chronostratigraphic correlation problems. In the outcrop area around Writing-On-Stone Provincial Park, southern Alberta, the Milk River Formation has a Santonian to possibly very earliest Campanian age and was deposited between ~84.5 Ma and 83.5 Ma. In southern Montana, the Eagle Formation was deposited from ~83.5 Ma to 81.2 Ma, and contains different lithologies and depositional environments as opposed to southern Alberta. In north-central Montana, the Telegraph Creek Formation and Virgelle and Deadhorse Coulee members are equivalent in depositional environments and time to those of the Milk River Formation in southern Alberta. The upper Eagle member, however, has no time- or facies-equivalent rocks around Writing-On-Stone Provincial Park, but is time equivalent to the Alderson Member of the Lea Park Formation in southeastern Alberta. A hiatus of ~2.5 Ma is present between the top of the Milk River Formation in the outcrop area and the basal beds of the Pakowki Formation. The Pakowki transgression occurred at around 81.0 Ma based on a U–Pb zircon age of 80.7 ± 0.2 Ma from bentonite beds just above the bottom of the Pakowki Formation in southern Alberta. This age agrees with previous ages of 80.7 ± 0.6 Ma for the Ardmore Bentonite Beds and ~81.0 Ma for the Claggett transgression in southern Montana.Afin de résoudre des problèmes de corrélations lithostratigraphiques et chronostratigraphiques, on s'est servi de géochronologie U–Pb, de palynologie et de lithostratigraphie sur des roches du Crétacé tardif du sud de l'Alberta et du Montana. Dans la région des affleurements autour du parc provincial de Writing-On-Stone, au sud de l'Alberta, la Formation de Milk River date possiblement du Santonien au Campanien très précoce et aurait été déposée il y a environ 84,5 à 83,5 Ma. Dans le sud du Montana, la Formation Eagle a été déposée il y a environ 83,5 à 81,2 Ma; elle présente des lithologies et des milieux de déposition différents de ceux du sud de l'Alberta. Dans le centre-nord du Montana, la Formation de Telegraph Creek et les membres Virgelle et Deadhorse Coulee ont des milieux et des temps de déposition équivalents à ceux de la Formation de Milk River du sud de l'Alberta. Toutefois, le membre supérieur de Eagle n'a d'équivalent ni dans le temps ni dans les faciès dans les roches autour du parc provincial de Writing-On-Stone, mais il est équivalent dans le temps au membre Alderson de la Formation de Lea Park dans le sud-est de l'Alberta. Il existe un hiatus d'environ 2,5 Ma entre le sommet de la Formation de Milk River dans la région des affleurements et les lits à la base de la Formation de Pakowki. La transgression de Pakowki a eu lieu vers 81,0 Ma selon une détermination d'âge U–Pb de 80,7 ± 0,2 Ma sur un échantillon de zircon provenant de lits de bentonite juste au-dessus de la base de la Formation de Pakowki dans le sud de l'Alberta. Cet âge concorde avec des âges obtenus antérieurement de 80,7 ± 0,6 Ma pour les lits de bentonite Ardmore et d'environ 81,0 Ma pour la transgression de Claggett dans le sud du Montana.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Anyox Pendant contains complexly deformed greenschist-facies volcanic strata overlain by a thick succession of turbidite sedimentary rocks. At the contact between the two are well-studied copper-rich volcanogenic massive sulphide deposits; however the age and correlation of the volcanic strata, including the ore horizon, are poorly known. New stratigraphic, structural, and geochronology studies elucidate the regional stratigraphic, tectonic, and metallogenic settings and significance of these strata. The thick turbidite succession is correlated with Bowser Lake Group and conformably overlies the volcanic succession. Volcanogenic units include pillowed basalt, volcaniclastic rocks, chlorite phyllite, tuffaceous siltstone, and abundant gabbroic sills and dykes. Strained leucocratic intrusions yielded U–Pb zircon crystallization ages of 176.9 ± 0.2 Ma and 185.6 ± 0.3 Ma. Volcaniclastic rocks yielded detrital zircons that constrain the maximum ages of the volcanic succession. The youngest zircon grains from four samples in different structural segments limit strata to younger than ca. 186 Ma, ca. 178 Ma, ca. 183 Ma, and ca. 186 Ma. The results, combined with the regional oldest age limit of Bowser Lake Group, constrain the volcanic succession to late Early Jurassic(?) and early Middle Jurassic age, and support correlation with Hazelton Group of Stikinia. Furthermore, they enable comparisons with the coeval Au-Ag-rich stratiform Eskay Creek deposit, expanding southward the zone of extension in western Stikinia, which tapped primitive mafic magmas and accompanied the last vestiges of Stikinian volcanism in the early Middle Jurassic.Le pendant Anyox contient des strates volcaniques au faciès des schistes verts, déformées de façon complexe et recouvertes d'une épaisse succession de roches turbidites sédimentaires. Au contact entre les deux, on retrouve des gisements d'origine volcanique de sulfures massifs, riches en cuivre, qui ont été étudiés en détail; toutefois, l'âge et la corrélation des strates volcaniques, incluant l'horizon contenant le minerai, sont mal connus. De nouvelles études stratigraphiques, structurales et géochronologiques définissent les contextes régionaux stratigraphiques, tectoniques et métallogéniques ainsi que l'importance de ces strates. L'épaisse succession de turbidites est corrélée au Groupe de Bowser Lake et repose en concordance sur la succession volcanique. Les unités d'origine volcanique comprennent des basaltes en coussins, des roches volcanoclastiques, de la phyllite chloriteuse, une siltite tufacée et un grand nombre de filons-couches et de dykes gabbroïques. Des intrusions leucocratiques sous contraintes ont donné des âges de cristallisation U–Pb sur zircon de 176,9 ± 0,2 Ma et 185,6 ± 0,3 Ma. Des roches volcanoclastiques ont fourni des zircons détritiques qui restreignent les âges maximums de la succession volcanique. Les grains de zircon les plus jeunes provenant de quatre échantillons dans des segments structuraux différents limitent les strates à plus jeunes que ~186 Ma, ~178 Ma, ~183 Ma et ~186 Ma. Les résultats, combinés à la limite d'âge régionale la plus vieille du Groupe de Bowser Lake, restreignent la succession volcanique au Jurassique précoce (?) et au Jurassique moyen précoce et appuient la corrélation avec le Groupe de Hazelton de Stikinia. De plus, ils permettent des comparaisons avec le gisement contemporain de Eskay Creek, riche en Au-Ag, qui étend vers le sud la zone d'extension dans le Stikinia occidental, laquelle a pénétré les magmas mafiques primitifs et a accompagné les derniers vestiges du volcanisme stikinien au Jurassique moyen précoce.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]