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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.)

This paper presents evidence for an early Taconian, west-directed fault in northern Vermont, the Prospect Rock thrust, which represents the trace of the contact between the Taconian oceanic accretionary prism (Dunnage Zone) and less allochthonous, continental margin rocks (Humber Zone). Mapping at 1 : 24 000 over the last decade has led to reassessment of units within the Camels Hump Group, resulting in newly defined lithotectonic packages: the Green Mountain slice and the Prospect Rock slice. Rocks in these slices may be of similar age, but those in the Green Mountain slice were originally deposited as more proximal sediments and remained on the Humber side of the subduction zone, whereas those in the Prospect Rock slice were transferred by underplating to the accretionary prism. Both slices contain ultramafics. Motion on the Prospect Rock thrust (D[sub1]) preceded Taconian garnet-grade metamorphism and subsequent east-directed back-folding. However, D[sub1] structures were diachronous across the orogen. Late Taconian (D[sub2]) structures record a change from east-verging back-folds in northern Vermont and southern Quebec to west-verging folds farther south. The Prospect Rock thrust does not correspond exactly to Cameron's line nor to the Baie Verte Brompton line as originally defined. However, our understanding of the geometry of the Prospect Rock thrust demonstrates that the Dunnage Zone extends farther west than previously recognized and may also explain features farther to the east. [ABSTRACT FROM AUTHOR]

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]

For sheer complexity, braincases are generally considered anatomically conservative. However, recent research on the braincases of tyrannosaurids have revealed extensive morphological variations. This line of inquiry has its root in Dale Russell's review of tyrannosaurids in which he established Daspletosaurus torosus — a large tyrannosaurine from the Campanian of southern Alberta. In the wake of systematic revisions to tyrannosaurines previously assigned to Daspletosaurus, one potentially distinct species remains undescribed. This paper describes and compares a braincase referable to this species with that of the holotype for Daspletosaurustorosus using computerized-tomography-based reconstructions. The two braincases have numerous differences externally and internally. The specimen of Daspletosaurus sp. has a bottlenecked olfactory tract, short and vertical lagena, and a developed ascending column of the anterior tympanic recess. The holotype of Daspletosaurus torosus has many unusual traits, including an anteriorly positioned trochlear root, elongate common carotid canal, distinct chamber of the basisphenoid recess, asymmetry in the internal basipterygoid aperture, and laterally reduced but medially expanded subcondylar recess. This comparison also identified characters that potentially unite the two species of Daspletosaurus, including deep midbrain flexures in the endocasts. However, many character variations in the braincases are known in other tyrannosaurids to correlate with body size and maturity, or represent individual variations. Therefore, taxonomic and phylogenetic signals can be isolated from background variations in a more comprehensive approach by using additional specimens. New information on the two braincases of Daspletosaurus is consistent with the emerging view of tyrannosaurid braincases as highly variable, ontogenetically dynamic character complexes. [ABSTRACT FROM AUTHOR]

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.)

The structural geology of the northeastern Paleoproterozoic Amer belt, central Nunavut, has been evaluated in light of new field mapping combined with legacy data and independently acquired subsurface geophysics data. Proterozoic sequences Ps1–Ps4 of the Amer supergroup unconformably overlie Archean basement. Of these sequences, Ps1–Ps3 have been intensely deformed (D1) in association with the Snowbird Orogeny (2.05–1.865 Ga). Ps4 was deposited unconformably on the first three sequences and exhibits none of the D1 effects. Deformation within Ps4 is slight compared to the underlying sequences and is restricted to D2 folding that occurred in the 1.84–1.81 Ga Hudsonian Orogeny. Deformation of sequences Ps1–Ps3 forms the core of this study. D1 comprises imbricate thrusting, intersequence detachment, and three generations of isoclinal folding and transposition. The stratigraphic order is maintained in many areas by decoupling of sequence packages along incompetent units so as not to "mix" lithologies; there is a fundamental mechanical stratigraphy. Within sequences, transposition can be otherwise intense. The resultant architecture is a shallowly southwest-dipping sequence of tectonically rotated and transposed layering (primary and tectonic) similar in many ways in orientation regardless of whether preserved with original bedding features or completely transposed. D1 folding is characterized by recumbent folds, noncylindrical folds that are sometimes rooted in detachments, verging to the northeast. D2 folding is controlled by the pre-existing large-scale D1 fabric, resulting in the overturned synforms that parallel the belt. Post-D2 fault modification of northern side of the belt along northwest-trending faults is interpreted to relate to extension and exhumation. [ABSTRACT FROM AUTHOR]

Glacial sediment research using thin sections began post-1945. Microsedimentology examines sediments at the microscopic level deriving insights into the processes of glacial erosion, transport, and deposition. Two issues exist (1) the difficulty by some in recognizing microstructures in thin section and (2) the absence of quantitative data making data reproduction difficult. The latter is hard to resolve but more image capture and software methodologies are now becoming available at reasonable costs. Thin sections are two-dimensional sections of three-dimensional objects, and this must be considered when measurements, fabrics and other data are assessed. Research into the microaspects of glacial sediments followed a typical scientific trajectory: thin sections description with little uniformity or common "language" for observed microstructures: standardization allowed comparison between different sediments; with standardization, came an open-ended classification; and with cross-comparison with multiple thin sections—a quantitative means of study needs developed. It has become apparent that the basic principles of structural geology had to be applied. Thus, micromorphology has subsumed into a microsedimentological study of glacial sediments where stress parameters, structural fabrics and the mapping of deformation structures and contextual integration allows an understanding of how these sediments have been formed. Examples of the development stages of glacial micromorphology/sedimentology are presented here as well as discussion of future avenues of study. In addition, multiple thin sections are used to illustrate the many aspects of glacial micromorphology and the parameters necessary to understand glacial sedimentology and the processes of glacial sedimentation. [ABSTRACT FROM AUTHOR]

Published estimates on the paleoclimate of the Florissant fossil beds site of Colorado (34.1 Ma) have led to extremely different estimates of paleoelevation. The purpose of this paper is to review the paleoclimate methods used and to add the coexistence approach (CA) method to estimate paleotemperature for the Florissant site. The basis of the CA method is the dependence on overlapping climatic requirements for different taxa in the flora and their nearest living relatives. These relationships tie the fossil identities to the actual plant habitats and climatic requirements of close relatives. Based on the CA method, we conclude that the mean annual temperature ranged between 14.3 and 18.2 °C. These results support the conclusions offered by several other studies that the Florissant was a warm temperate to subtropical flora, and they are consistent with recent conclusions by structural geologists as well as other studies, indicating that the Florissant site was deposited at a relatively low elevation, probably between 1 and 1.5 km. [ABSTRACT FROM AUTHOR]

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.)

This paper provides a re-interpretation of the crustal architecture of the Ottawan hinterland of the Grenville Province in light of published empirical and numerical models of orogenic collapse. It is now seen as a series of high-grade, mid-crustal core complexes from tens to hundreds of kilometres across that are juxtaposed against segments of the lower grade upper and uppermost crust including the orogenic lid. Juxtaposition of such contrasting crustal levels, which exhibit decoupled tectonic styles corresponding to the orogenic infrastructure and suprastructure, respectively, is interpreted as a signature of the foundering of an orogenic plateau into a mid-crustal channel. Ottawan metamorphism progressed from granulite-facies in the mid crust at ∼1090-1050 Ma, through amphibolite-facies in the upper crust at ∼1050-1020 Ma, to heating to ≤500 °C in the uppermost crust at ∼1020-980 Ma. This temporal progression is interpreted to reflect conductive heat transfer during collapse, as hot mid-crustal core complexes were exhumed against successively higher crustal levels. Exhumation was facilitated by substantial thinning and lengthening of the mid crust by simple- and pure-shear mechanisms. This was accompanied by wholesale boudinage of the brittle uppermost crust. Moreover, it may have resulted in excision of part of the ductile upper crust, which appears under-represented. Collapse was accompanied by diverse magmatic and hydrothermal products, their range of structural states implying that high-strain Ottawan deformation in the mid crust took place beneath an orogenic lid that was not penetratively deformed. Preliminary analysis indicates the Grenvillian inliers exhibit a comparable range of crustal levels to the Grenville Province, suggesting the orogenic plateau may have extended ∼5000 km along strike from Labrador to Texas. [ABSTRACT FROM AUTHOR]

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.)

Reconstructing tectonic histories involving continental collision, subduction, and exhumation at plate-tectonic rates of ~1 cm/year, requires precise U-Pb zircon geochronology. The Western Gneiss Region has exceptional exposures of high-pressure (HP) and ultra-high-pressure (UHP) rocks. The strategy adopted here involved sampling eclogite and associated late unstrained pegmatites to acquire the time of eclogite crystallization and subsequent exhumation, respectively. The oldest eclogite sampled is 415 ±1 Ma from layered, probably UHP eclogite at Tevik, Averøya, also with a garnet-hornblende assemblage at 410 ±1 Ma. The Flem Gabbro eclogite margin, with implied UHP conditions, is 410 ±2 Ma. Hornblende eclogite at Seth, Lepsøya, never at UHP, is 412 ±2 Ma. These compare to Devonian ages of 401 ±1 Ma for overgrowths on Proterozoic baddeleyite in Selnes Gabbro, 402 ±2 Ma for coesite eclogite at Hareidlandet, 405-400 Ma for coesite eclogite at Flatraket, and 405 ±2 Ma for near-UHP eclogite at Hjelmelandsdalen. The 415 Ma eclogite at Tevik compares to granitic pegmatite in the same outcrop at 395.2 ±1.3 Ma and to pegmatite in eclogite at Aspøya at 395.3 ±2 Ma. The 410 Ma age at Flem compares to nearby pegmatite in eclogite at 396 ±4 Ma. Collectively, these results imply 14-20 million years between deep eclogite crystallization at ~130 km and return to amphibolite-facies conditions at ~30 km, with crystallization of locally derived granitoid melts. Nearby garnet-pyroxenite records older ages (~430) and greater depths (~200 km), but on similar exhumation paths at ~0.4-0.7 cm/year. La reconstruction d'historiques tectoniques impliquant des collisions continentales, de la subduction et de l'exhumation à des taux tectoniques d'environ 1 cm/année demande une géochronologie U-Pb sur zircon précise. La région du gneiss occidental de la Norvège présente des affleurements exceptionnels de roches ayant subi des pressions hautes (HP) et ultra-hautes (UHP). La stratégie adoptée ici était d'échantillonner l'éclogite et des pegmatites associées tardives n'ayant pas subi de contraintes afin d'obtenir respectivement le moment de cristallisation de l'éclogite et son exhumation subséquente. L'éclogite échantillonnée la plus ancienne a 415 ±1 Ma et provient d'une éclogite, probablement formée à ultra-haute pression, située à Tevik, Averøya, avec un assemblage grenat-hornblende datant de 410 ±1 Ma. La bordure éclogite du gabbro Flem, possédant des conditions UHP, est âgée de 410 ±2 Ma. L'éclogite à hornblende à Seth, Lepsøya, n'ayant jamais subi de UHP, date de 412 ±2 Ma. Elles se comparent avec des âges dévoniens de 401 ±1 Ma pour des accroissements sur une baddeleyite datant du Protérozoïque dans le gabbro Selnes, de 402 ±2 Ma pour l'éclogite coésite à Hareidlandet, de 405-400 Ma pour l'éclogite coésite à Flatraket et de 405 ±2 Ma pour l'éclogite presque UHP à Hjelmelandsdalen. À Tevik, l'éclogite datant de 415 Ma peut être comparée à une pegmatite granitique dans le même affleurement et datant de 395,2 ±1,3 Ma et à une pegmatite dans l'éclogite à Aspøya datant de 395,3 ±2 Ma. L'âge de 410 Ma à Flem se compare bien à celui de la pegmatite dans une éclogite avoisinante datant de 396 ±4 Ma. Ensemble, ces résultats signifient une période de 14 à 20 Ma entre la cristallisation en profondeur de l'éclogite, à ~130 km, et le retour aux conditions du faciès des amphibolites à ~30 km, avec la cristallisation de granitoïdes en fusion de provenance locale. La pyroxénite à grenat avoisinante enregistre des âges plus anciens (~430 Ma) et une plus grande profondeur (~200 km) mais avec des cheminements d'exhumation similaires d'environ 0,4-0,7 cm/année. [ABSTRACT FROM AUTHOR]

Offshore observations at modern ocean-margin subduction zones (OMSZs) reveal that bodies of accreted material are commonly volumetrically small or missing, that crustal thinning and subsidence (3–5 km) has occurred, and that most trench axes lie close (5–30 km) to the seaward tapering edge of coastal basement rock. Onshore mapping commonly documents missing or only narrow terranes of former forearc rock and the inboard migration of the arc magmatic front. These observations are evidence that subduction is accompanied by the removal of sediment and crustal material from the submerged forearc by the kindred tectonic processes, respectively, of sediment subduction and subduction erosion. Subduction erosion truncates the margin (migrates the trench inboard) at ~2.5 km/Ma. Onshore observations at ancient crust-suturing subduction zones (CSSZs) imply that collisional suturing is accompanied by sediment subduction and truncation of both upper and lower plates. During a protracted period of suturing (20–50 million years), a 100–200 km wide (or wider) band of the seaward edge of each plate can be removed subductively. Truncation of the upper plate is effected by subduction erosion, and that of the lower plate by the necking and break-off of its subducted edge. The average linear rate of crustal loss for each plate is estimated at ~1.5 km/Ma, or ~3 km/Ma combined. Because significant crustal loss occurs before and during tectonic fusing of colliding crustal blocks, structures and rock bodies that might be expected to record a former OMSZ and the formation of a CSSZ may be absent, unimpressively small, or preserved only as exhumed masses of once deeply subducted material. Des observations au large à des zones modernes de subduction de marge océanique révèlent que des amas de matériel accrété ont fréquemment une petite taille volumétrique ou sont manquants, qu’il s’est produit un amincissement de la croûte et de la subsidence (3–5 km) et que la plupart des axes des tranchées reposent à proximité (5–30 km) de la bordure, à épaisseur décroissante, du socle rocheux de la côte. La cartographie du continent signale souvent des terranes manquants ou seulement étroits, d’anciennes roches d’avant-arc et la migration vers le continent du front magmatique de l’arc. Ces observations constituent des preuves que la subduction est accompagnée du retrait de matériel sédimentaire et de la croûte de l’avant-arc submergé par des processus tectoniques apparentés, respectivement de subduction de sédiments et d’érosion de la subduction. L’érosion de la subduction tronque la bordure (fait migrer la tranchée vers le continent) à un taux d’environ 2,5 km/Ma. Les observations sur le continent à des anciennes zones de subduction de suture de la croûte impliquent que les sutures de collisions sont accompagnées de subduction de sédiments et d’une troncation des plaques inférieures et supérieures. Au cours d’une période prolongée de suture (20–50 Ma), une bande de 100 à 200 km (ou plus large) de la bordure océanique de chaque plaque peut être retirée par subduction. La troncation de la plaque supérieure est causée par une érosion de subduction, c’est-à-dire de la plaque inférieure par étranglement et par rupture de la bordure subductée. Le taux moyen de perte linéaire de la croûte pour chaque plaque est estimé à ~1,5 km/Ma ou ~3 km/Ma pour les deux ensemble. Puisqu’une importante perte de la croûte a lieu avant et durant la fusion tectonique de blocs de croûte en collision, les structures et les amas rocheux qui pourraient enregistrer une ancienne zone de subduction de marge océanique et la formation de zones de subduction de suture de la croûte peuvent être manquants, très petits ou préservés uniquement en tant que masses exhumées de matériel jadis subduit à de grandes profondeurs. [ABSTRACT FROM AUTHOR]

We describe a classification scheme for orogens using Temperature–Magnitude (T–M) diagrams and use this framework for modelling large, hot orogens that evolve in continents comprising cratonic nuclei bordered by a series of juvenile accreted, reworked, and metamorphosed terranes. Modelling the complete evolution of an orogen is difficult, particularly large orogens with multiple orogenic phases. Early phases during which a continent is assembled produce a tectonic and metamorphic fabric that needs to be taken into account when modelling the main collisional orogeny. This inherited fabric is represented in a simple way in models described here by a series of lower crustal blocks that are arranged to be systematically stronger toward the cratonic continental interiors. We investigate how this fabric influences the development of the model orogen during the main collisional phase using upper-mantle-scale (UMS) and crustal-scale (CS) finite element models. The models exhibit a diachronous three-phase evolution: crustal thickening, thermal incubation, and lower crustal indentation. The UMS and CS models are shown to give comparable results in regard to crustal deformation. The UMS models exhibit additional features including single- and double-slab breakoffs and corresponding episodes of uplift and gravitational spreading within the orogenic crust. Protracted postconvergent gravitational spreading of the hot, decoupled crust is also demonstrated. Lastly, we demonstrate the application of this type of model to natural orogens, the Grenville orogen in western Ontario and the southern Canadian Cordillera, and in terms of the T–M diagram. Le présent article décrit un système de classification des orogènes basé sur des diagrammes température–magnitude et nous utilisons ce cadre pour modéliser de gros orogènes chauds qui ont évolué dans les continents qui comportaient des noyaux de cratons délimités par une série de terranes juvéniles, accrétés, retravaillés et métamorphosés. Il est difficile de modéliser l’évolution complète d’un orogène, surtout les gros orogènes comportant de multiples phases orogéniques. Les premières phases durant lesquelles un continent est assemblé produisent une fabrique tectonique et métamorphique dont il faut tenir compte lors de la modélisation de l’orogène principale de collision. Cette fabrique héritée est représentée d’une manière simple dans les modèles décrits ici par une série de blocs dans la croûte inférieure qui sont arrangés pour être systématiquement plus forts vers l’intérieur des cratons continentaux. Nous étudions comment cette fabrique influence le développement de l’orogène modèle au cours de la principale phase de collision en utilisant des modèles aux éléments finis à l’échelle du manteau supérieur et à l’échelle de la croûte. Les modèles présentent une évolution en trois phases diachroniques, un épaississement de la croûte, une incubation thermique et une indentation de la croûte inférieure. Les modèles à l’échelle du manteau supérieur et à l’échelle de la croûte donnent des résultats comparables en ce qui concerne la déformation de la croûte. Les modèles à l’échelle du manteau supérieur montrent des caractéristiques additionnelles incluant le détachement de dalles simples et doubles et des épisodes correspondants de soulèvement et d’étalement gravimétrique à l’intérieur de la croûte orogénique. L’étalement gravitationnel prolongé qui a eu lieu après la convergence de la croûte chaude découplée est aussi démontré. Finalement, nous démontrons l’application de ce type de modèle aux orogènes naturels, l’orogène de Grenville dans l’Ouest de l’Ontario, la Cordillère canadienne méridionale et selon le diagramme température–magnitude. [ABSTRACT FROM AUTHOR]

The eastern margin of the Kechika Graben in the vicinity of Muncho and Moose lakes, northeastern British Columbia, contains Middle Cambrian rift-related strata herein named the Mount Roosevelt Formation. The formation conformably overlies a quartzite package equivalent to the uppermost clastic unit of the informal late Early Cambrian Gataga group (Bonnia–Olenellus zone) and is conformably overlain by a thick, unnamed carbonate sequence of Middle Cambrian age (Plagiura–Poliella zone). The Mount Roosevelt Formation is subdivided into three members. The lowermost member is characterized by oöid-bearing siltstone and sandstone, interbedded with dolostone, limestone, and hematitic conglomerate. Conformably above this, the middle member is a thick sequence of polymict cobbly pebble conglomerate. The upper member includes karstified dolostone, calcareous-cemented conglomerate and sandstone, and limestone. Collectively the Mount Roosevelt Formation reflects alluvial fan delta progradation into a transgressive marine environment. Deposition occurred in an active fault-controlled basin, located on the eastern margin of the Kechika Graben adjacent to the Muskwa High. Basin initiation in the late Early Cambrian coincided with the reactivation of pre-existing regional faults. High rates of subsidence during the initial phase of extension were accommodated on these faults, which provided a locus for fan delta deposition. Continuing high rates of subsidence limited basinward fan delta development. Deposition of the formation ended with base-level transgression in the early Middle Cambrian that drowned the fan deltas and the adjacent Muskwa High and allowed development of the Kechika Trough above the older graben system. Située à proximité des lacs Muncho et Moose dans le nord-est de la Colombie-Britannique, la bordure est du graben de Kechika contient des strates, ici nommées la Formation de Mount Roosevelt (Cambrien moyen), qui sont reliées à la distension. La formation repose en concordance sur un ensemble de quartzite équivalent à l’unité supérieure, clastique, du groupe de Gataga, informel, datant du Cambrien précoce (zone à Bonnia–Olenellus); elle est recouverte en concordance par une épaisse séquence de carbonate, sans nom, datant du Cambrien moyen (zone à Plagiura–Poliella). La Formation de Mount Roosevelt est subdivisée en trois membres. Le membre inférieur est caractérisé par des siltstones et des grès à oolites, interstratifiés avec des dolomies, des calcaires, et des conglomérats hématitiques. Par-dessus, en concordance, le membre du centre est composé d’une épaisse séquence de conglomérat grenu, hétérogène et caillouteux. Le membre supérieur comprend de la dolomie karstifiée, du conglomérat et du grès à ciment calcaire, et du calcaire. Dans son ensemble, la Formation de Mount Roosevelt est le reflet de la progradation d’un delta alluvionnaire en un environnement marin de transgression. La déposition a eu lieu dans un bassin contrôlé par des failles actives situé sur la bordure est du graben de Kechika, voisin de la zone surélevée de Muskwa. L’amorce du bassin à la fin du Cambrien précoce coïncide avec la réactivation de failles régionales préexistantes. Au cours de la phase initiale d’extension, des taux élevés de subsidence ont été facilités sur ces failles, ce qui a fourni un endroit pour la déposition du delta alluvionnaire. Des taux de subsidence continuellement élevés ont limité le développement du delta alluvionnaire du côté du bassin. La déposition de la formation s’est terminée avec une transgression au niveau de la base au Cambrien moyen précoce, ce qui a ennoyé les deltas alluvionnaires et la zone avoisinante surélevée de Muskwa et a permis le développement de la fosse Kechika par-dessus l’ancien système de graben. [ABSTRACT FROM AUTHOR]

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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]

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Lithoprobe's sponsorship has led to the acquisition of paleomagnetic data from ~20 units throughout the Paleoproterozoic Trans-Hudson Orogen (THO) of Saskatchewan and Manitoba, essentially the first such data for the region. Discussed summarily in this paper, they provide an initial framework for the THO's tectonic evolution. They show that the Archean Hearne and Superior cratons were at subtropical and subpolar paleolatitudes, respectively, at ~1875 Ma, with the Lynn Lake – LaRonge arc midway between them in the Manikewan Ocean. By ~1855 Ma, this ocean was still ~5500 ± 700 km wide, and its seafloor was subducting northwestward under the Hearne craton and pericratonic Peter Lake domain margin with the coeval development of an Andean-type continental magmatic arc, the Wathaman–Chipewyan batholith. Between ~1855 and ~1810 Ma, coalescing apparent polar wander path (APWP) segments record closing of the ocean at a rate of ~12 cm/a, trapping and accreting the several separate intervening terranes (Flin Flon, Hanson Lake, Lynn Lake – LaRonge, Rottenstone, and presumably also other THO terranes). From ~1815 to ~1775 Ma, the assembled terranes drifted as a coherent craton, yielding a stillstand and hairpin in the APWP. [ABSTRACT FROM AUTHOR]

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Four U–Pb dating sites straddling the Grenville front on the Labrador coast were investigated. Sites 1 and 2 exhibit complex intrusive, deformational, and metamorphic histories and were studied in detail, whereas two simpler outcrops (sites 3 and 4) were examined only at a reconnaissance level. At site 1, south of the Grenville front, a 1799[sup +3] [sub –2] Ma granodioritic gneiss is intruded by two phases of mafic dykes, then by a 1647[sup +7] [sub –5] Ma aplite and a ca. 1647–1500 Ma pegmatite, and lastly by the Michael gabbro. The pegmatite was metamorphosed at 1030 ± 10 Ma. Site 2 is on the Cut Throat Island thrust, which defines the Grenville front in the area. Early mylonitization occurred at 1790 ± 2 Ma, followed by 1730 ± 2 Ma pegmatite emplacement and then cooling at 1703 ± 15 Ma. A post-deformational melt pod gave a titanite age of 1662 ± 10 Ma. In the mylonitic host, based on positive correlation between Pb loss and degree of granularization in monazite, Grenvillian deformation was very short-lived. Sites 3 and 4 (north of the Cut Throat Island thrust), yielded 1709 ± 10 and 1726 ± 34 Ma ages, respectively. Lack of marked younger Pb loss demonstrates that these sites escaped both Labradorian and Grenvillian metamorphism. Emplacement, deformation, and (or) metamorphism occurred at 1800–1790 Ma, 1730–1700 Ma, 1660–1650 Ma, possibly at 1500 Ma, and at 1040–1030 Ma. The Cut Throat Island thrust was active during all events, but none was confined to it. The thrust marks the northern limit of Labradorian and Grenvillian orogenesis, but because similar pre-Labradorian history is preserved on both sides of the thrust, it is not a fundamental tectonic boundary after 1800 Ma. Nevertheless, because reactivation occurred during every geological orogenic event known in the region, it clearly represents a zone of persistent crustal weakness.Quatre sites de datations U-Pb chevauchant le front du Grenville sur la côte du Labrador ont été étudiés. Les sites 1 et 2 montrent des historiques complexes d'intrusion, de déformation et de métamorphisme et ils ont été étudiés en détail, alors que deux affleurements plus simples (sites 3 et 4) n'ont fait l'objet que d'une reconnaissance. Au site 1, au sud du front du Grenville, un gneiss à granodiorite, 1799[sup +3] [sub –2] Ma, est pénétré par deux phases de dykes mafiques, puis par une aplite, 1647[sup +7] [sub –5] , par une pegmatite vers 1647–1500 Ma et finalement par le gabbro Michael. La pegmatite a été métamorphosée vers 1030 ± 10 Ma. Le site 2 est situé sur le chevauchement Cut Throat Island, qui définit le front du Grenville dans la région. Une mylonitisation a eu lieu vers 1790 ± 2 Ma, suivie de la mise en place d'une pegmatite vers 1730 ± 2 Ma, puis il y a eu un refroidissement vers 1703 ± 15 Ma. Une lentille de fusion post-déformation a donné à de la titanite un âge de 1662 ± 10 Ma. Selon des corrélations positives entre la perte de Pb et le degré de granularité dans la monazite, la déformation du Grenville dans la roche mylonitique hôte a été de très courte durée. Les sites 3 et 4 (au nord du chevauchement de Cut Throat Island) ont donné des âges respectifs de 1709 ± 10 Ma et 1726 ± 34 Ma. Le fait qu'il n'y ait pas de perte de Pb nettement plus jeune démontre que ces sites ont échappé aux métamorphismes du Labrador et du Grenville. La mise en place et la déformation et/ou le métamorphisme ont eu lieu à 1800–1790 Ma, 1730–1700 Ma, 1660–1650 Ma, possiblement à 1500 Ma et à 1040–1030 Ma. Le chevauchement de Cut Throat Island était actif durant tous ces événements mais aucun ne lui était confiné. Le chevauchement marque la limite nord de l'orogène du Labrador et du Grenville mais, puisqu'un historique similaire pré-Labrador est préservé des deux côtés du chevauchement, il ne constitue pas une frontière tectonique fondamentale après 1800 Ma. Néanmoins, étant donné que de la réactivation a eu lieu durant chaque événement orogénique géologique connu dans la région, ce chevauchement représente clairement une zone de faiblesse crustale persistante.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

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]

In the article, the authors present a comparison of the terrane wreck (TW) model and the in-order terrane (IOT) model that were used in the analysis of rocks and other geological formations in the New Brunswick and Newfoundland areas in Canada. Other topics include the correlative histories of sequential and pseudosynchronous accretionary orogenesis in the IOT model, and the analysis of primary oceans and secondary faulting.

In the article, the authors discuss the distribution of Cambrian to Ordovician volcanic rocks in the Northern Appalachian region in North America using the Devonian to Carboniferous oroclinal bending hypothesis and dextral strike-slip translation of a single arc terrane. Topics include the relationship between the Middle Ordovician arc and backarc basin and the Matapedia belt and the Fredericton Trough.

The article presents a study related to the localization of the brittle Bathurst fault on pre-existing fabrics. It mentions that the Bathurst fault is a component of the Bathurst–MacDonald conjugate fault system and displaces the thelon tectonic zone (TTZ) and paleoproterozoic Kilohigok basin and is overlain by the Thelon basin.

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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.)