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Quaternary sediment in the Labrador Sea was derived from many proglacial sources in Greenland and eastern Canada. Understanding the spatial and temporal changes in sediment provenance provides information on ice extent and sediment dispersal patterns. Variations in mineral composition of sediment from late Quaternary cores has been determined by a whole pattern of quantitative X-ray diffraction procedure. Mineral facies were extracted statistically by a supervised analysis of 90 samples from bedrock and ice-rafted clasts, which were then used to predict the most probable mineral facies in 1443 marine sediment samples. We used a non-parametric Classification Decision Tree (CDT) to validate that decision. Only 26% of the samples were misclassified in the CDT. The six facies identified consisted of four facies reflecting differences in the composition of Canadian and Greenland Precambrian igneous and metamorphic bedrock, a set of samples dominated by high weight percentages of calcite and dolomite (detrital carbonate (DC) and Hudson Strait Heinrich (HS-H) events), and a "shale" facies. We isolated 284 sediments from the HS-H DC facies and determined that they could be divided into four categories based on differences in their mineral proportions. These categories vary geographically, based on non-carbonate sediment supply during these events from Greenland, the Canadian Shield, the Appalachians, and the outer continental shelf. In the Holocene of the Labrador Sea, dolomite is derived from Baffin Bay and abundance of calcite is influenced by both biogenic productivity and dissolution. [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 area northeast of Sudbury, Ontario, is well known for hosting one of the largest unexplained geophysical anomalies in the Canadian Shield, the Temagami Anomaly. In search of a geological explanation for this anomaly, low-grade metamorphic ultrabasic dykes have been discovered in the overlying Huronian Supergroup sedimentary rocks, both in outcrop and in a deep drill core. Here, we report on the first geochemical and geochronological data obtained on these dykes and compare these data with known magmatic units in and around the 1850 Ma impact-generated Sudbury Igneous Complex (SIC). The NW-striking dykes, which cut across sedimentary rocks of the ca. 2.3 Ga Cobalt Group, and which are, in turn, crosscut by pseudotachylitic breccia, are characterized by distinctively high concentrations of Ti, P, Nb, and Zr, highly fractionated rare earth element patterns (La/YbN 7.6–15.5), and a lack of crustal contamination (Nb/Th > 10). Such features are typical of modern ocean island basalts but very different from Palaeoproterozoic rocks previously documented in the wider region. Multigrain U–Pb laser ablation inductively coupled plasma mass spectrometry analyses performed on magmatic titanite and apatite with high Th/U ratios yielded 1876.0 ± 8.7 and 1880.9 ± 8.3 Ma, respectively, which we interpret as the intrusion age of the dykes. This interpretation is supported by similar whole-rock Sm-Nd model ages of 1890–2000 Ma (initial εNd +2.5). This magmatic event in the footwall of the SIC shortly before the impact was coeval with, and likely genetically related to, the 1.88–1.87 Ga Circum-Superior Large Igneous Province. [ABSTRACT FROM AUTHOR]

John Tuzo Wilson coined the term 'plate' in plate tectonics. He is famous for inventing transform boundaries, hot spot tracks, and the Wilson cycle of ocean birth, growth, and decline. Less well remembered is his work in the 1950s on tectonic and radiometric age provinces of the Canadian Shield, as part of which he fathered U/Pb geochronology in Canada. This work gave strong support to the notion of continental growth through accretion of successively younger terranes onto an ancient cratonic core. The present paper reviews how paleomagnetism can trace the motions of continents to test Wilson's ideas. Continental accretion often involves deep burial of one of the colliding elements through subduction or crustal underplating; such was the case with the Grenville orogen and its subprovinces in their Proterozoic accretion onto the Laurentian craton. The resulting heating and metamorphism erases most pre-collisional magnetic information but adds something new: the possibility of following the post-metamorphic uplift and cooling history, in time and space. The time element is provided by a new form of isotopic geochronology, thermochronometry, which provides dates for specific minerals together with the temperatures at which they became closed to isotopic migration. U/Pb dating of sphene is one method used; another is the 40Ar/39Ar variant of K/Ar dating applied to hornblende, micas, and feldspars, which have a wide range of Ar closure temperatures. The two specific Grenville studies described deal with parallel uplift histories determined by 40Ar/39Ar dating and by magnetics for the accreted terranes of the Central Metasedimentary Belt in Ontario and with the paleomagnetic detection of the post-1240 Ma closing of a small ocean between the Elsevir terrane and Laurentia during the Grenvillian orogeny. [ABSTRACT FROM AUTHOR]

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

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

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

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

Geothermal studies were conducted within the framework of Lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the Canadian Shield. One of the main conclusions is that in the Shield the variations in surface heat flow are dominated by the crustal heat generation. Horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements. Different methods constrain the mantle heat flow to be in the range of 12–18 mW·m–2. Most of the heat flow anomalies (high and low) are due to variations in crustal composition and structure. The vertical distribution of radioelements is characterized by a differentiation index (DI) that measures the ratio of the surface to the average crustal heat generation in a province. Determination of mantle temperatures requires the knowledge of both the surface heat flow and DI. Mantle temperatures increase with an increase in surface heat flow but decrease with an increase in DI. Stabilization of the crust is achieved by crustal differentiation that results in decreasing temperatures in the lower crust. Present mantle temperatures inferred from xenolith studies and variations in mantle seismic P-wave velocity (Pn) from seismic refraction surveys are consistent with geotherms calculated from heat flow. These results emphasize that deep lithospheric temperatures do not always increase with an increase in the surface heat flow. The dense data coverage that has been achieved in the Canadian Shield allows some discrimination between temperature and composition effects on seismic velocities in the lithospheric mantle. Des études géothermiques ont été effectuées dans le cadre du projet Lithoprobe afin de systématiquement documenter les variations du flux thermique et de la production de chaleur à la surface dans les grandes provinces géologiques du Bouclier canadien. L’une des principales constatations a été que, dans le Bouclier, les variations de flux thermique à la surface sont dominées par la génération de chaleur par la croûte. Les variations horizontales dans le flux thermique du manteau sont trop petites pour être résolues par des mesures du flux thermique. Différentes méthodes limitent le flux thermique à la plage de 12–18 unités de flux calorique. La plupart des anomalies de flux thermique (hautes et basses) sont dues à des variations dans la composition et la structure de la croûte. La distribution verticale des radioéléments est caractérisée par un indice de différenciation DI qui mesure le rapport entre la surface et la génération moyenne de chaleur par la croûte dans une province. La détermination de la température du manteau exige la connaissance à la fois du flux thermique à la surface et du DI. Les températures du manteau augmentent avec le flux thermique en surface mais diminuent avec un indice DI croissant. La stabilisation de la croûte est obtenue par différenciation crustale ce qui engendre des températures décroissantes dans la croûte inférieure. Les températures actuelles du manteau, déduites d’études sur les xénolites et des variations dans la vélocité des ondes sismiques primaires (Pn) du manteau obtenues des levés de sismique réfraction, concordent avec les géothermes calculés à partir du flux thermique. Ces résultats soulignent le fait que les températures lithosphériques profondes n’augmentent pas toujours avec le flux thermique à la surface. La couverture dense de données qui a été atteinte dans le Bouclier canadien permet une certaine discrimination entre les effets de la température et de la composition sur la vitesse des ondes sismiques dans le manteau lithosphérique. [ABSTRACT FROM AUTHOR]

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Two Cordilleran and three Laurentide glacial advances are recorded in Quaternary sediments and landforms in the Peace River valley, northeast British Columbia. The advances are inferred from fluvial gravels, glaciolacustrine sediments, and tills within nested paleovalleys excavated during three interglaciations and from the distribution of granitoid clasts derived from the Canadian Shield. Till of the last (Late Wisconsinan) Laurentide glaciation occurs at the surface, except where it is overlain by postglacial sediments. The advance that deposited this till was the most extensive in the study area, and the only advance definitively recognized in western Alberta south of the study area. Late Wisconsinan Cordilleran till has not been found in the study area, but Cordilleran and Laurentide ice may have coalesced briefly during the last glaciation. Support for this supposition is provided by the inferred deflection of Laurentide flutings to the southeast by Cordilleran ice. The earliest Laurentide advance may have been the least extensive of the three Laurentide events recognized in the study area. Erratics attributed to this advance occur only east of the Halfway River – Beatton River drainage divide. Deux avancées glaciaires de la Cordillère et trois de l’Inlandsis laurentidien sont évidentes dans les sédiments et la topographie du Quaternaire de la vallée de la rivière de la Paix, dans le nord-est de la Colombie-Britannique. Les avancées sont déduites à partir des graviers fluviatiles, des sédiments glacio-lacustres et des tills dans des paléovallées emboîtées excavées durant trois périodes interglaciaires et à partir de la distribution des clastes granitoïdes provenant du Bouclier canadien. Un till de la dernière glaciation laurentidienne (Wisconsinien tardif) se retrouve à la surface, sauf là où il est recouvert de sédiments post-glaciaires. L’avancée qui a déposé ce till a été la plus extensive dans le secteur à l’étude et c’est la seule avancée définitivement reconnue dans l’ouest de l’Alberta, au sud du secteur à l’étude. Aucun till de la Cordillère datant du Wisconsinien n’a été trouvé dans le secteur à l’étude. Cependant, la glace de la Cordillère et celle de l’Inlandsis laurentidien pourraient s’être unis durant une brève période au cours de la dernière glaciation. Cette hypothèse est soutenue par la déflexion inférée de rainures glaciaires laurentidiennes vers le sud-est par la glace de la Cordillère. L’avancée glaciaire laurentidienne la plus précoce pourrait être la moins étendue des trois événements laurentidiens reconnus dans le secteur à l’étude. Les blocs erratiques attribués à cette avancée ne se retrouvent qu’à l’est de la ligne de partage des eaux entre les rivières Halfway et Beatton. [ABSTRACT FROM AUTHOR]

Exposures in the Prophet River valley in northeast British Columbia provide a unique glimpse into the Quaternary history of the northwest Canadian Boreal Plains. The region shows evidence of Late Wisconsinan Laurentide glaciation in the form of widespread till, containing abundant erratic clasts derived from the Canadian Shield. Vertical sections along the Prophet River expose non-glacial and advance glacial sediments below this till. Pre-Late Wisconsinan non-glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites. Macrofossils within horizontally laminated organic-rich black clay and silt indicate deposition on the floodplain of the paleo-Prophet River within an oxbow lake. The climate during deposition is interpreted to be similar to present, supporting a dominantly spruce forest. Wood obtained from eight sites provided non-finite radiocarbon ages, and one sample provided an age of 49 300 ±2000 BP, which is also considered non-finite. Glaciolacustrine clays and silts, deposited during impoundment of eastward-flowing drainage by the advance of the Laurentide Ice Sheet (LIS) in the Late Wisconsinan, overlie the non-glacial sediments throughout the valley. A blanket of clast-poor, clay-rich till up to 20 m thick, and deposited by the LIS, drapes the glaciolacustrine sediments. Since deglaciation, the Prophet River has incised the valley and formed fluvial terraces at different levels above the modern river. Des affleurements dans la vallée de la rivière Prophet dans le nord-est de la Colombie-Britannique offrent un coup d’œil unique sur l’historique du Quaternaire dans les plaines boréales du Nord-Ouest canadien. La région porte des preuves de la glaciation laurentidienne au Wisconsin tardif sous forme de till répandu contenant de nombreux clastes erratiques provenant du Bouclier canadien. Des coupes verticales le long de la rivière Prophet exposent des sédiments non glaciaires et des sédiments d’avancée glaciaire sous ce till. À de nombreux sites, des sédiments non glaciaires ou des sédiments de plaine d’inondation interglaciaire datant du pré-Wisconsin tardif sont interstratifiés avec les graviers fluviatiles. Des macrofossiles dans des laminations horizontales de silt et d’argile noire, riches en matière organique, indiquent une déposition sur la plaine d’inondation de la paléorivière Prophet dans un méandre mort. Lors de la déposition, le climat aurait été semblable au climat actuel, supportant une forêt où dominaient les épinettes. Du bois obtenu de huit sites fournissent des âges radiocarbone non finis et un échantillon a donné un âge de 49 300 ±2000 ans avant le présent, ce qui est aussi considéré non fini. Des argiles et des silts glacio-lacustres, déposés durant une retenue du drainage qui s’écoulait vers l’est par l’avancée de l’Inlandsis laurentidien au Wisconsinien tardif, reposent sur des sédiments non glaciaires à travers toute la vallée. Une couverture de till, pauvre en clastes et riche en argile, atteignant une épaisseur de 20 mètres et déposée par l’Inlandsis laurentidien, recouvre les sédiments glacio-lacustres. Depuis la déglaciation, la rivière Prophet a découpé la vallée et formé des terrasses fluviatiles à différents niveaux au-dessus de la rivière actuelle. [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.)