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New bedrock mapping completed as part of the Nechako NATMAP Project indicates that the area between Babine and Takla lakes in central British Columbia is underlain by rocks of the Early Permian Asitka, Late Triassic Takla, and Early to Middle Jurassic Hazelton volcanic-arc assemblages of the Stikine Terrane. These are cut by large composite stocks of quartz diorite, granodiorite, and quartz monzonite previously mapped as the Late Triassic to Early Jurassic Topley intrusions. New U/Pb (n = 6) and laser [sup 40] Ar/[sup 39] Ar (n = 10) isotopic age dates reported in this paper suggest there are two distinct ages of plutons: the Topley intrusive suite with isotopic ages between 218 and 193 Ma; and, east of Babine Lake, the new Spike Peak intrusive suite with isotopic ages ranging from 179 to 166 Ma. West of the main plutonic belt is a thick volcanic succession of subaerial, porphyritic andesite flows, volcanic breccias, and rhyolitic ash-flow tuffs that have isotopic ages between 185 and 174 Ma. These rocks are assigned to the Saddle Hill Formation of the Hazelton Group. The plutonic roots of this proximal arc assemblage are most likely the coeval and compositionally similar plutons of the Spike Peak intrusive suite that have been unroofed in the area east of the Takla Fault. Major oxide and trace element data support the interpretation that the Topley and Spike Peak granitic rocks formed in a juvenile volcanic-arc environment and that magmatism is related to melts generated above a long-lived subduction zone of unknown orientation.Une nouvelle cartographie effectuée dans le cadre du projet NATMAP Nechako indique que la région entre les lacs Babine et Takla au centre de la Colombie-Britannique est recouverte de roches des assemblages d'arcs volcaniques du terrane de Stikine, soit Asitka du Permien précoce, Takla du Trias tardif et Hazelton du Jurassique précoce à moyen. Ces assemblages sont recoupés par des petits massifs intrusifs composites de diorite quartzique, de granodiorite et de monzonite quartzique qui avaient auparavant été cartographiés en tant que les intrusions Topley, du Trias tardif au Jurassique précoce. De nouvelles datations U-Pb (n = 6) et isotopes laser [sup 40] Ar/[sup 39] Ar (n = 10) présentées dans cet article suggèrent deux âges distincts de plutons, soit la suite intrusive de Topley avec des âges isotopiques entre 218 et 193 Ma et, à l'est du lac Babine, la nouvelle suite intrusive de Spike Peak dont les âges isotopiques varient de 179 à 166 Ma. À l'ouest de la ceinture plutonique principale se trouve une séquence volcanique épaisse d'écoulements subaériens d'andésite porphyrique, des brèches volcanique et des tufs d'écoulement de cendre rhyolitique dont les âges isotopiques varient entre 185 et 174 Ma. Ces roches sont assignées à la Formation de Saddle Hill du Groupe Hazelton. Les racines plutoniques de cet assemblage d'arc proximal sont fort probablement les plutons contemporains et à composition similaire de la suite intrusive de Spike Peak qui ont été décapés dans la région à l'est de la faille de Takla. Les données sur les principaux oxydes et les éléments traces corroborent l'interprétation que les roches granitiques de Topley et de Spike Peak se sont formées dans un environnement d'arc volcanique juvénile et que le magmatisme est relié aux fusions qui se sont produites au-dessus d'une ligne de subduction de longue durée mais dont l'orientation est inconnue.[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.)

The amaltheids are restricted temporally to the late Pliensbachian and geographically to the northern part of the northern hemisphere. Amaltheus stokesi is the only species that occurs in all areas of North America where amaltheids are found. The craton north of the Canada–U.S.A. border yields the most diverse amaltheid fauna, including six of the seven taxa known in North America. On Quesnellia and Stikinia, there are no endemic amaltheids, and diversity is low; A. stokesi increases in abundance northwards where, in Stikinia, A. margaritatus makes rare appearances. Wrangellia, with its rich Pliensbachian Tethyan and east Pacific faunas, is almost devoid of amaltheids, but its amaltheid fauna does include two specimens of A. viligaensis, an eastern Russian species that is unknown elsewhere in North America. Cratonal amaltheid faunas have more in common with those of northwest Europe than eastern Eurasia, suggesting that the Arctic and northern North Atlantic constituted the main dispersal route. Paleobiogeographic patterns on the major allochthonous terranes argue against terrane rotation and in support of post-Pliensbachian northward displacement relative to the North American craton. In addition, the presence of western Pacific faunal elements on Wrangellia suggests a more significant longitudinal displacement relative to the craton for this terrane compared to that for Quesnellia and Stikinia. The Chilliwack terrane of southwestern British Columbia is a Pliensbachian paleobiogeographic anomaly.Les Amaltheidés sont restreints dans le temps au Pliensbachien et géographiquement à la partie septentrionale de l'hémisphère Nord. Amaltheus stokesi est la seule espèce qui se trouve dans toutes les régions de l'Amérique du Nord où on retrouve des Amaltheidés. Le craton au nord de la frontière entre le Canada et les États-Unis fournit la faune Amaltheidé la plus diversifiée, incluant six des sept taxons connus en Amérique du Nord. À Quesnellia et Stikinia, il n'y a pas d'Amaltheidés endémiques et la diversité est faible; A. stokesi est de plus en plus abondant vers le nord où, à Stikinia, A. margaritatus apparaît rarement. Wrangellia, avec ses riches faunes tethysiennes et du Pacifique oriental (Pliensbachcien), ne contient presque pas d'Amaltheidés mais sa faune Amaltheidé comprend en effet deux spécimens de A. viligaensis, une espèce russe orientale inconnue ailleurs en Amérique du Nord. Les faunes cratonales Amaltheidés ont plus en commun avec celles de l'Europe du Nord-ouest que celles de l'Eurasie de l'Est, suggérant que l'Arctique et l'Atlantique du Nord septentrional étaient les principales voies de dispersion. Les patrons paléobiogéographiques sur les grands terranes allochtones plaident contre une rotation du terrane et en faveur d'un déplacement relatif vers le nord par rapport au craton, après le Pliensbachien. De plus, la présence d'éléments fauniques du Pacifique ouest sur Wrangellia suggère, pour ce terrane, un déplacement longitudinal plus important par rapport au craton que celui pour Quesnellia et Stikinia. Le terrane de Chilliwack du sud-ouest de la Colombie-Britannique est une anomalie paléobiogéographique du Pliensbachien.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Early Cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of Nova Scotia are preserved in narrow half-grabens obscured by glacial drift. The Chaswood Formation sediments can be subdivided into three members; upper and lower members dominated by cyclical sand–mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin. Ferruginous oxisols are common in the fine-grained facies of the upper and lower members. Seismic data indicate that Chaswood Formation strata in the Elmsvale Basin are deformed into steeply dipping faults and fault-related folds (Rutherford Road fault zone). An Aptian–Albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the Late Cretaceous and Tertiary that truncates the Chaswood Formation. Exhumation of a thick cover of Mesozoic sediment (1–2 km) is needed to account for the preservation of Chaswood Formation outliers after ~80 Ma of erosion. The half-grabens that host the Chaswood Formation were formed in the Mesozoic and were antecedent to the present-day structurally controlled lowlands.Des dépôts non consolidés de sable quartzeux et d'argile à kaolin (Crétacé précoce) dans les basses-terres de la Nouvelle-Écosse sont préservés dans d'étroits demi-grabens sous des dépôts glaciaires. Les sédiments de la Formation de Chaswood peuvent être subdivisés en trois membres : des faciès cycliques sable-boue d'origine fluviale dominent les membres inférieur et supérieur et de l'argile ligneuse d'origine lacustre domine le membre intermédiaire. Les faciès à grain fin des membres inférieur et supérieur comprennent fréquemment des oxisols ferrugineux. Des données sismiques indiquent que les strates de la Formation de Chaswook dans le bassin d'Elmsvale ont été déformées en failles à pendage abrupte et en plis reliés aux failles (zone de failles Rutherford Road). L'âge de cet événement tectonique (Aptien-Albien) est déduit de la déformation synsédimentaire et de la discordance angulaire couvrant le Crétacé tardif et le Tertiaire qui recoupe la Formation de Chaswood. Pour tenir compte de la préservation des lambeaux externes après ~80 Ma d'érosion, il faut l'enlèvement d'une épaisse couverture (1 à 2 km) de sédiments mésozoïques. Les demi-grabens hôtes de la Formation de Chaswood ont été formés au cours du Mésozoïque et ils précèdent les basses-terres actuelles qui sont contrôlées par la structure.[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.)

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite-trondhjemite-granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550-600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh-Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province. Le batholite néoarchéen de Pukaskwa comprend des phases pré-, syn- et post-tectoniques mises en place durant une période de 50 Ma. Les phases pré-tectoniques sont largement synvolcaniques et elles ont une affinité Al et TTG (« tonalite-trondhjemite-granodiorite ») élevée qui est interprétée comme étant le reflet de la dérivation par fusion partielle d'une croûte basaltique à des profondeurs de croûte inférieure ou de manteau supérieur. Des phases syntectoniques mineures sont légèrement plus tardives que le volcanisme et elles ont des caractéristiques géochimiques qui suggèrent une certaine implication ou interaction avec une composante de source ultramafique (manteau). La mise en place magmatique des phases pré- et syntectoniques a eu lieu dans le milieu de la croûte à des paléopressions de 550-600 MPa et ces composantes du batholite seraient représentatives des ceintures de roches vertes sous-jacentes, au centre de la croûte durant leur développement. Après la mise en place des phases syntectoniques, et probablement vers 2680 Ma, le batholite de Pukaskwa a été soulevé en dôme structural par rapport aux ceintures de roches vertes de part et d'autre, et ce, de manière synchrone avec la déformation transpressive régionale senestre en cours. La force motrice derrière le tectonisme vertical serait une inversion de densité (instabilités de type Rayleigh-Taylor) impliquant les ceintures de roches vertes plus denses et la croûte felsique plutonique sous-jacente. Le déclencheur pour l'initiation de ce processus est interprété comme étant un changement abrupt dans la rhéologie de la croûte moyenne attribué à l'introduction de chaleur du manteau auxiliaire à la rupture de la dalle ou à la délamination lithosphérique suivant la cessation de la subduction. Ce processus a aussi mené à une fusion partielle de la croûte moyenne intermédiaire à felsique générant des phases granitiques post-tectoniques vers 2667 Ma. Nous proposons que la tectonique verticale poussée par l'inversion de densité tardive soit une conséquence inévitable des processus tectoniques horizontaux (plaques) associés au développement de ceintures vertes dans la Province du Supérieur. [ABSTRACT FROM AUTHOR]

Lithoprobe is Canada’s national, collaborative, multidisciplinary, Earth science research project established to develop a comprehensive understanding of the evolution of northern North America. It is regarded internationally as one of the most successful national geoscience projects ever undertaken. Part of Lithoprobe’s success derives from its history and organizational structure. A one-year Phase I program (1984–1985) was highly successful. Phases II to V carried the project forward until 2005, when funding terminated. Lithoprobe was organized as a decentralized research network of multidisciplinary scientific studies and collaborating scientists. About 1500 scientific publications were generated. Lithoprobe’s legacy also includes economic and social benefits. New and improved understanding of Earth history provides petroleum and mining companies with an enhanced knowledge base. Lithoprobe demonstrated the applicability of high-resolution seismic reflection studies to mineral exploration. Development of a portable seismic refraction recorder and a long-period magnetotelluric system led to technology transfer to Canadian companies. Very high-resolution seismic reflection studies, applied first by Lithoprobe, are proving effective for exploration for uranium deposits in Saskatchewan. In the cratonic areas of Canada, Lithoprobe seismic and magnetotelluric studies have provided significant new information relevant to exploration for diamonds. On the west coast of Canada, Lithoprobe studies provided data and a framework for better understanding the mega-thrust earthquake hazard in the region. Lithoprobe established a highly effective public outreach strategy that involved the print and electronic media as well as material for educational purposes. Unequivocally, Lithoprobe has enhanced the already strong reputation of the Earth sciences in Canada. Lithoprobe est le projet national multidisciplinaire canadien de recherche en sciences de la Terre; il est effectué en collaboration et il a établi afin de développer une compréhension approfondie de l’évolution de l’Amérique du Nord. D’un point de vue international, il est considéré être l’un des projets nationaux géoscientifiques les plus réussis jamais entrepris. Une partie du succès de Lithoprobe découle de son histoire et de sa structure organisationnelle. Un programme de Phase I, d’une durée d’un an (1984–1985), a été très réussi. Les Phases II à V ont fait progresser le projet jusqu’en 2005 alors que le financement a été terminé. Lithoprobe était organisé en tant qu’un réseau décentralisé d’études scientifiques multidisciplinaires et de scientifiques qui collaborent ensemble. Environ 1500 publications scientifiques ont été générées. Le legs de Lithoprobe comprend aussi des bénéfices économiques et sociaux. Une meilleure, et souvent nouvelle, compréhension de l’historique de la Terre fournit aux compagnies minières et pétrolières une base de connaissances élargie. Lithoprobe a démontré l’applicabilité d’études sismiques réflexion haute résolution à l’exploration minérale. Le développement d’un enregistreur sismique réfraction portable et d’un système magnétotellurique longue période a mené à un transfert de technologie vers les compagnies canadiennes. Des études de sismique réflexion à très haute résolution, tout d’abord effectuées par Lithoprobe, s’avèrent effectives dans la recherche de gisements d’uranium en Saskatchewan. Dans les régions cratoniques du Canada, les études sismiques et magnétotelluriques Lithoprobe ont fournit de nouvelles données pertinentes à l’exploration pour les diamants. Sur la côte Ouest du Canada, les études Lithoprobe ont fournit des données et un cadre de référence pour une meilleure compréhension des risques de tremblement de terre à grand chevauchement dans la région. Lithoprobe a établi une stratégie d’ouverture au public hautement effective qui impliquait la presse écrite et les médias électroniques ainsi que du matériel pour fins éducatives. Sans aucun doute, Lithoprobe a rehaussé la réputation déjà forte du Canada en sciences de la Terre. [ABSTRACT FROM AUTHOR]

Application of regional geophysical and geological methods throughout two decades of Canada’s Lithoprobe project provides new opportunities to analyze the Mohorovičić discontinuity (Moho) and crust–mantle transition. The transect format employed during Lithoprobe, in which 10 specified regions of Canada were targeted for approximately a decade each, between 1984 and 2003, permitted teams of scientists to focus on geological, geophysical, and tectonic issues for each transect. As a primary objective was to enhance knowledge of the structure of the crust and lithosphere, an obvious target in each transect was the nature and origin of the Moho and crust–mantle transition. Accordingly, the combined results provide new perspectives on the Moho and the relationship of the Moho to the crust–mantle transition. Perhaps the most important result is that the continental geophysical Moho is a deceptively simple feature; it has a variety of signatures at different scales that preclude a single, universally applicable interpretation. In methods that provide large-scale information, such as regional seismic studies, it is a relatively abrupt refraction velocity contrast that often displays a dramatic downward decrease in seismic reflectivity. However, its origin in a geological or tectonic sense is perhaps best determined by careful analyses of structural details near the geophysical Moho, which are complex and varied. In some areas within Canada, it appears that the geophysical Moho may be old and perhaps remains from the time the crust formed; in other areas, it appears to be a relatively young feature that was superimposed onto older crustal fabrics. L’application de méthodes géophysiques et géologiques régionales durant les deux décennies du projet canadien Lithoprobe a fourni de nouvelles possibilités d’analyser la discontinuité de Mohorovičić (Moho) et la transition croûte–manteau. Le format de transects utilisés durant Lithoprobe, selon lequel 10 régions spécifiques du Canada ont été ciblées pour environ une décennie chacune entre 1984 et 2003, a permis à des équipes de scientistes de se pencher sur les enjeux géologiques, géophysiques et tectoniques de chaque transect. Puisqu’un des principaux objectifs était de rehausser la connaissance de la structure de la croûte et de la lithosphère, une cible évidente dans chaque transect était la nature et l’origine de la transition entre le Moho et la croûte–manteau. Les résultats combinés fournissent donc de nouvelles perspectives du Moho et de la relation du Moho à la transition croûte–manteau. Le résultat peut-être le plus significatif est que le Moho géophysique continental est une caractéristique dont la simplicité est trompeuse; il possède plusieurs signatures à différentes échelles qui empêchent une interprétation unique et universellement applicable. Lorsque les méthodes donnaient de l’information à grande échelle, par exemple les études sismiques régionales, il se présente comme un contraste de vitesse de réfraction relativement abrupt, souvent avec une diminution de réflectivité sismique vers le bas. Toutefois, son origine dans un sens géologique ou tectonique est peut-être le mieux déterminé par une analyse soignée des détails structuraux à proximité du Moho géophysique, et ces détails sont complexes et variés. Dans certains secteurs du Canada, il semble que le Moho géophysique puisse être vieux et constituer un vestige du temps de formation de la croûte; dans d’autres secteurs, il semble constituer une caractéristique jeune qui a été superposée sur des fabriques plus anciennes de la croûte. [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.)

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.)

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.)

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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An improved paleogeography of the Quebec reentrant has been achieved by examining the nature and distribution of major sediment buildups within this reentrant. The Quebec reentrant has one side produced by rift faults and one side by a major transform fault. The Oak Hill Group was deposited near a triple-rift zone. Clastic sediments of this group formed a large delta that was fed by a major river flowing in the rift valley of the Ottawa graben. The delta must have prograded on a gentle slope platform. No other thick deltaic deposits ark known towards the northeast. Instead, facies analyses favor the existence of a promontory near Québec. Still farther to the northeast, the Saguenay graben was not the product of a triple-rift junction. However, it served to funnel sediments to a deep-sea fan, and the adjacent platform was narrow with a steep slope. The lateral distribution of sediments from the Ordovician Taconic orogeny can be explained by this improved paleogeographic reconstruction. The configuration of the Quebec reentrant required the arc to move into the reentrant. The Taconian tectonic wedge progressively accreted the thick sediment buildups that were the Oak Hill delta and the Bas-du-Fleuve deep-sea fan. This allowed them to act as new barriers to orogenic sediment dispersal as the orogeny proceeded. [ABSTRACT FROM AUTHOR]

The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the rift drift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in early-middle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (Tremadocian-Arenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession. [ABSTRACT FROM AUTHOR]

The Charlevoix area, which is host to an impact structure of Devonian age, straddles the boundaries among crystalline rocks of the Grenville Province, the Cambrian-Ordovician sedimentary succession of the St. Lawrence Platform, and accreted units of the Appalachian orogen. The area features well-developed supracrustal fault systems attributed to impact cratering. A major fault system oriented from northeast to northwest consists of normal faults marked by cataclastic and gouge breccias and, less frequently, by pseudotachylyte. Detailed mapping of faults both within and outside the Charlevoix impact crater suggests that brittle faulting occurred both before and after impact cratering. Polymictic fault breccias occurring along some supracrustal faults are the clearest evidence of impact-related fault rocks in the Charlevoix area. The St-Laurent fault, trending to the northeast, represents a major structure interpreted as being related to Late Proterozoic - early Paleozoic rifting of the lapetus Ocean. However, the St-Laurent fault crosses the Charlevoix impact crater without major deflection, suggesting post-impact reactivation. The fault systems in the Charlevoix area are interpreted to be pre-impact structures related to the opening of the Iapetus Ocean, most of which have also been reactivated during the Devonian cratering event and in post-impact time, the latter most likely coeval with the Atlantic Ocean rifting in Mesozoic time. [ABSTRACT FROM AUTHOR]

In the southern Quebec Appalachians, the early tectonic history of the Laurentian margin (Humber zone) comprises foreland-propagating, northwest-directed thrust faulting, nappe emplacement, and regional prograde metamorphism in response to the obduction of large ophiolitic nappes during the Taconian orogeny. In the internal Humber zone, this event is dated at 462 ± 3 Ma (late Middle Ordovician), which is interpreted to represent the timing of near-peak Taconian metamorphism. Superimposed hinterland-directed structures are accompanied by retrograde metamorphism and consist of back thrusts and normal faults, which respectively delimit the northwestern and southeastern limbs of the Sutton and Notre-Dame mountains anticlinoria, both salient structures of the internal Humber zone of southern Quebec. Geochronologic data on the timing of hinterland-directed deformation vary from 431 to 411 Ma. Two tectonic models are presented and discussed, which may account for the Silurian Early Devonian evolution of the Laurentian margin: (1) back thrusting and syn- to post-compressional crystal extension in response to the tectonic wedging of basement-cored duplexes inducing delamination of supracrustal rocks; (2) tectonic exhumation of the internal Humber zone by extensional collapse. Evidence for Silurian - Early Devonian extensional tectonism in the Humber zone provides the basement infrastructures necessary for the creation and the onset of sedimentation in the Gaspé Belt basins (e.g., Connecticut Valley - Gaspé synclinorium). Several structural, metamorphic features in the internal Humber zone of the northwestern New England Appalachians yield analogous characteristics with those of southern Quebec and may have shared a similar Silurian Early... [ABSTRACT FROM AUTHOR]

Distribution of facies in the lower half of the Bylot Supergroup suggests overall westward deepening of the Mesoproterozoic Borden Basin. In marked contrast, the upper half of the succession records a reversal in the overall bathymetric trend, such that the eastern portion underwent relative deepening as the west experienced relative shallowing. Strata deposited during this reversal belong to the Victor Bay Formation, a ramp composed predominantly of limestone. Karsting of carbonate strata and development of an angular unconformity in the west contrast with back-stepping and drowning of the ramp in the east, followed by mantling by deep-water limestone, carbonaceous carbonate, and turbidites. Increased accommodation space during this time, via both tectonic subsidence and eustatic sea-level rise, led to a profusion of stromatolite pinnacle reefs and large biostromes. The reversal of basin polarity is best reconciled with development of a distal foreland basin superimposed on the Borden aulacogen. Crustal rethickening and uplift occurred along reactivated basement faults during an eastward-directed compressional event and could be related to thrusting of similar age and vergence in the Coppermine River Group of northwestern Canada.La distribution des faciès dans la moitié inférieure du Supergroupe de Bylot suggère un approfondissement général vers l'ouest du bassin de Borden (Mésoprotérozoïque). Par contre, la moitié supérieure de la séquence montre un renversement de la tendance bathymétrique, de telle façon que la partie orientale subissait un approfondissement relatif alors que la partie occidentale subissait un rehaussement relatif. Les strates déposées au cours de ce renversement appartiennent à la Formation de Victor Bay, une rampe composée surtout de calcaire. Le développement de karsts dans les strates calcareuses et le développement d'une discordance angulaire à l'ouest contrastent avec la rétrogradation et l'ennoiement de la rampe à l'est, suivi d'un recouvrement par des calcaires d'eau profonde, des carbonates carbonés et des turbidites. Durant ce temps, une augmentation de l'espace disponible, grâce à la subsidence tectonique et à l'élévation eustatique du niveau de la mer, a conduit à une profusion de récif-pinacles à stromatolites et à de vastes biostromes. L'inversion de la polarité du bassin concorde très bien avec le développement d'un bassin d'avant-pays distal surimposé à l'aulacogène de Borden. Un nouvel épaississement et un rehaussement de la croûte se sont produits le long de failles du socle réactivées lors d'un événement de compression dirigé vers l'est et qui pourrait être relié à un chevauchement d'âge et de vergence similaires dans le Groupe de Coppermine River du nord-ouest du Canada.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The Lac Nominingue – Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation – transposed compositional layering (S[sub 1] ; host to peak-pressure parageneses) has been folded by isoclinal folds (F[sub 2] and F[sub 3] ) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F[sub 3] folds, indicating that 1.20–1.18 Ga granulite-facies metamorphism post-dated D[sub 3] . D[sub 3] structures are cut by ductile shear zones and boudinaged in D[sub 4] and are folded by regional-scale, open, upright north–south folds (F[sub 5] ). Folds with shallowly dipping axial surfaces (F[sub 6] ) are subsequently developed in the Sourd group. F[sub 5] (and probably F[sub 6] ) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the Nominingue–Chénéville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F[sub 8] ) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F[sub 2] to F[sub 5] folds may have formed during either subhorizontal, east–west contraction or east–west extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESE–WNW contraction and NNE–SSW (orogen-parallel) extension in D[sub 7] syn- to post-intrusion of the Chevreuil suite. F[sub 8] folds imply a late, Grenvillian SSE–NNW contraction.La région de Lac Nominingue – Mont-Laurier de la Ceinture métasédimentaire centrale, dans la Province de Grenville, au Québec, comprend le complexe gneissique de Bondy au faciès des granulites (coeur du dôme gneissique de Bondy) et les roches métasédimentaires sus-jacentes du Groupe du Sourd. Un litage de composition transposé et la foliation métamorphique (S[sub 1] ; hôte des paragenèses de pression maximale) ont été plissés isoclinalement (F[sub 2] et F[sub 3] ) et entrecoupés par des leucosomes qui comprennent les assemblages métamorphiques de température maximale. L'isograde de l'orthopyroxène coupe obliquement à travers les plis F[sub 3] , indiquant que le métamorphisme au faciès des granulites à 1,20 à 1,18 Ga, s'est produit après D[sub 3] . Les structures D[sub 3] sont recoupées par des zones de cisaillement ductiles et boudinées en D[sub 4] puis plissées par des plis nord-sud, droits, ouverts et d'échelle régionale (F[sub 5] ). Des plis de surface axiale à faible pendage (F[sub 6] ) se sont développés subséquemment dans le Groupe du Sourd. Les plis F[sub 5] (et probablement F[sub 6] ) précèdent la mise en place de la suite intrusive de Chevreuil, il y a environ 1165 Ma. Dans la zone de déformation de Nominingue–Chénéville (ZDNC), à l'est du dôme gneissique de Bondy, les intrusions de cette suite présentent des foliations magmatiques et tectoniques orientées nord-sud. Ces foliations et les roches hôtes gneissiques et métasédimentaires sont reprises par des zones conjuguées de cisaillement ductile (dextre NE et senestre SSE) et par du chevauchement à direction NNE. Des plis ouverts tardifs (F[sub 8] ) de surfaces axiales orientées ENE produisent des patrons d'interférence de type domes et bassins. Les plis F[sub 2] à F[sub 5] peuvent avoir été formés lors d'une contraction ou d'une extension est-ouest sub-horizontale résultant d'un effondrement orogénique ou encore lors d'un amincissement lithosphérique convectif après un épaississement de la croûte lors de l'assemblage de terranes durant l'orogène elzevirien. Les structures dans la ZDNC impliquent une contraction ESE–WNW et une extension NNE–SSW (parallèle à l'orogène) durant D[sub 7] qui a eu cours pendant et après la mise en place de la suite Chevreuil. Les plis F[sub 8] impliquent une contraction grenvillienne tardive SSE–NNW.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]