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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.

Mineral and petroleum exploration in the Cariboo-Chilcotin region of British Columbia is hampered by widespread and extensive cover of Pleistocene glacial deposits and Tertiary volcanic successions. Seeing through this geological cover is critical to reducing exploration risk and enhancing exploration activity. Also critical to exploration is effective community engagement, hopefully resulting in endorsement and support for exploration initiatives. The forests in the Cariboo-Chilcotin region have been extensively destroyed by an infestation of the mountain pine beetle, Dendroctonus ponderosae , disrupting established communities and greatly affecting economic activity in the region. Governments of all levels recognized that geological exploration activity could provide a ready and appreciable stimulus to economic activity, but only if local communities endorsed such programs. Relatively little oil and gas exploration and research has taken place in the region, and its effects have been poorly understood locally. Consequently, an extended effort was undertaken to establish an integrated geoscience program for the Cariboo-Chilcotin region, focused on mineral and petroleum exploration-related research and coupled with engagement with local communities to inform them of exploration benefits and risks. This Introduction to the “Mountain Pine Beetle” Special Issue of Canadian Journal of Earth Sciences provides a brief overview of the scientific papers included in the issue and also a review of the community engagement process that was undertaken to establish working relationships with First Nations and other communities in the region.

The south-central Intermontane belt of British Columbia has a complex architecture comprising late Paleozoic to Mesozoic volcanic and plutonic arc magmatic suites, marine and nonmarine clastic basins, high-grade metamorphic complexes, and accretionary rocks. Jurassic and Cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential. The geology is complicated by Cretaceous to Eocene deformation, dismemberment, and dislocation. The Eocene to Neogene history of the southern Intermontane belt is dominated by non-arc volcanism, followed by Pleistocene to Recent glaciation. The volcanic and glacial cover makes this a difficult region to explore for resources. Much recent work has involved re-evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis. This paper summarizes the lithological and stratigraphic framework of the region, with emphasis on description of the sedimentary units that have been the targets of hydrocarbon exploration.

In the Archean Blake River Group, mafic to intermediate fragmental units have controversially been proposed to have formed during the collapse of a giant submarine caldera. This paper describes and interprets these rocks, summarizing their physical characteristics, inferred origins, age relationships, and geochemical signatures. The widespread Stadacona member, south of Rouyn-Noranda, consists of several hundred metres of bedded volcaniclastic rocks interpreted to have been mostly deposited from aqueous density currents fed directly by explosive eruptions. The magmas involved in these eruptions were plagioclase-phyric, tholeiitic to transitional basalts. The similarly widespread D’Alembert tuff, in the northern part of the Blake River Group, shares many physical characteristics with the Stadacona member and is thought to have a similar origin. However, the D’Alembert tuff is approximately six million years younger than the Stadacona member. It is composed mostly of transitional to calc-alkaline andesites and basaltic andesites with very distinct trace element profiles. Volcaniclastic rocks from other areas, such as Tannahill Township in Ontario and the Monsabrais area in Quebec, are interpreted to represent mostly in situ to remobilized hyaloclastite, with no explosive eruptions involved in their genesis. Our observations and interpretations are not compatible with models in which the volcaniclastic units are emplaced during a catastrophic event in relation with the collapse of a giant caldera. Instead, the fragmental rocks were produced by various mechanisms at many distinct times during the evolution of the Blake River Group.

The Archean Blake River Group (BRG) of Ontario and Quebec is dominated by submarine mafic to intermediate lavas, with more restricted felsic volcanic rocks. Given the good quality of outcrop, and high level of preservation of some BRG rocks, the mafic to intermediate lavas were used in the 1970s and 1980s to better understand the evolution of massive and pillowed submarine flows, and their associated fragmental facies (pillow breccias, hyaloclastite). Potentially, the BRG could also represent a useful volcanic succession for the study of explosive submarine eruption products in the ancient record. Before this is possible, however, a regional inventory of the mafic to intermediate volcaniclastic units is needed in order to clarify their characteristics and origins. In this paper, we compare and contrast volcaniclastic rocks from three areas within the same formation of the northern BRG in Quebec: the Monsabrais area, the lac Duparquet area, and the D’Alembert tuff area. Close examination reveals pronounced differences in terms of lateral continuity, thickness, grading, bedding, clast shapes, textures, etc. in the volcaniclastic rocks. These differences are interpreted to reflect vastly different emplacement processes ranging from hyaloclastite generation as a result of self-fragmentation and lava contact with water (dominant in the Monsabrais and lac Duparquet areas) to aqueous density currents likely fed directly by explosive submarine eruptions (dominant in the D’Alembert tuff).

The Thompson Nickel Belt marks the boundary between the Archean Superior Province and the Trans-Hudson Orogen in Canada. It comprises Archean gneisses, and Paleoproterozoic rocks with metasediments and metavolcanites (Ospwagan Group) and intrusions. The gneisses are frequently migmatitic and host numerous pegmatites. The western belt boundary is a fault contact with the Kisseynew Domain of the Reindeer Zone. In the south, the transition zone between the belt and the Kisseynew Domain comprises granitoids and a detrital sequence (Grass River Group), part of which grades into turbidites in the Kisseynew Domain. The eastern belt boundary is a diffuse zone where the Archean east–west (E–W) structural trend changes into the north-northeast (NNE) trend of the belt. This paper presents U–Pb ages for granitoids and 207Pb/206Pb detrital zircon ages from the Ospwagan and Grass River groups. Ages and a comparison of events in the belt and in the eastern Reindeer Zone have major implications. The change from stable platform deposits to syn-tectonic filling and emplacement of mafic intrusions in the Ospwagan Group are attributed to the convergence between the Reindeer Zone and the Superior Province at 1891–1885 Ma. At ca. 1850 Ma, continuing convergence led to drowning of marginal basins of the Superior craton and to the development of a transpressive regime in the belt, the onset of which could be as old as ca. 1885 Ma. Metamorphic ages of 1818–1785 record closure of the Kisseynew basin and crustal thickening. Collision of the new continental block with the Superior Province was accommodated by transpression until 1750–1720 Ma.

The ∼51 Ma Montagnais impact crater on the outer Scotian Shelf is well known, but the potential effects from the impact event on the slope and rise seaward of the crater have, until now, remained poorly understood. Through detailed seismic stratigraphic correlation and ties to available wells, we define a threefold seismic stratigraphic subdivision for Upper Cretaceous to Eocene strata on the shelf and slope, calibrated to the most recent biostratigraphic results. Using this framework, we identify a number of depositional and erosional products that are temporally consistent with a late Ypresian impact event (within the limits of seismic and biostratigraphic resolution). We link a series of prominent failure scarps on the outer shelf and upper slope to a single widespread mass-transport deposit (MTD) on the lower continental slope, rise, and abyssal plain. Failed material amassed in a large debris field referred to here as the “Montagnais MTD”. It covers an area of ∼93 000 km2 and travelled up to 580 km from the impact site where its distal termination onlaps the New England Seamounts, making it one of the largest known debris avalanches on Earth. We interpret these deposits, and the associated pattern of erosion landward of them, as products of widespread margin collapse caused by a combination of ground shaking and ensuing tsunamis triggered by the Montagnais impact event. This study provides insight into the potential effects of outer-shelf marine impact events immediately downslope from impact sites, and their diminished effects with increasing distance along the margin.

New models of magnetic data are presented that provide insight into the early stages of rifting and breakup between Morocco and Nova Scotia. The margins, which began forming during the Late Triassic rifting and Middle Jurassic separation of the North American and African plates, display considerable variability in deeper crustal structure, faulting style, and basin geometry along their length. The central and northeastern portions of the Nova Scotia margin show characteristics of a magma-poor margin, with a high degree of crustal thinning and a complex ocean-continent transition zone with little direct evidence of volcanism. In contrast, the margin to the southwest of Nova Scotia has clearly recognized characteristics of a volcanic-style rifted margin, including seaward-dipping reflector (SDR) sequences that are interpreted as rift-related volcanic flows overlying basement. These SDRs are coincident with a strong linear magnetic anomaly, the East Coast Magnetic Anomaly (ECMA), which shares many characteristics with the West African Coast Magnetic Anomaly (WACMA). Both magnetic anomalies change character and diminish in amplitude northward along the margins. The new models show the expected decrease in magnetic source material towards the northeastern end of the margin and suggest that modest amounts of igneous material, emplaced at or near the edge of the thinned continental crust, will satisfy the observed anomalies in this magma-poor section of the margin. These new interpretations and supporting evidence indicate volcanism was a factor along much of the margin during early rifting between Nova Scotia and Morocco.

Geochronology of detrital muscovite from the Lower Cretaceous of the central Scotian Basin has shown predominant supply of Meguma terrane detritus, including muscovite with Alleghanian (mid-Carboniferous to Permian) ages from the inner Scotian Shelf. In this study, 87 detrital muscovite grains from five wells in the eastern Scotian Basin, representing depositional ages from Tithonian to Early Albian, were dated by single-grain 40Ar/39Ar techniques. Previous work shows that the provenance of this sediment was different from wells in the central Scotian Basin. Compared with the central Scotian Basin, the muscovite age populations from the eastern Scotian Basin have more (20% versus 7%) pre-Devonian ages, derived from inboard terranes of the Appalachians. In both the central and eastern Scotian Basin, most old grains are found in the Tithonian and the Aptian–Albian, with fewer in the Valanginian and almost none in the Kimmeridgian and the Hauterivian–Barremian. These data suggest rapid unroofing of the Meguma terrane in the Kimmeridgian and Hauterivian–Barremian and greater supply of sediment from Newfoundland to the eastern Scotian Basin in the Tithonian and Aptian–Albian. Compared with the central Scotian Basin, which has most ages in the range 340–300 Ma, the muscovite age populations from the eastern Scotian Basin have a higher proportion of 420–340 Ma and in particular 300–260 Ma ages. Such late Alleghanian overprinting of argon ages is very rare on land in Nova Scotia, but in the Maritimes Basin, this was the time of uplift and erosion of strata.

There are two allochthonous salt canopies within the central Scotian margin, one on the shelf and another in deeper waters on the Scotian slope. The Sable Shelf Canopy trends southwest–northeast and covers an area approximately 650 km2. Salt thickness within this canopy is generally 2, and the allochthonous salt is as thick as 3500 m. Although the two canopies are separated by a significant distance, a common detachment surface connects them in multiple locations. Extensional systems detach in the Sable Shelf Canopy, displace strata downdip, and expel salt into the Sable Slope Canopy. The outer shelf and slope region separating these two canopies is dominated by detachment systems. One term, the Sable Canopy Complex, was developed to describe both salt canopies and the zone of detachment that separates them. Interpretation of two-dimensional and three-dimensional seismic data throughout the Sable Canopy Complex has resulted in a detailed allochthonous salt map and all related components including welded systems, salt stocks, faults, sutures, and minibasins. Four distinct expulsion styles are observed to contribute volumes of salt to the canopies: salt-based detachments, counterregional systems, hybrids, and salt stocks. Potential explanations for the variations in expulsion style range from varying volumes of sediment input to paleogeographic positions on the margin to salt sheet length.

Early Cretaceous volcanism is widespread in the eastern Scotian Basin. The stratigraphic position of volcanic rocks within wells was re-evaluated and the volcanological character of the rocks was refined by study of cuttings and well logs. Hauterivian–Barremian volcanic rocks on the SW Grand Banks and Aptian–Albian volcanic rocks in the Orpheus Graben and SE Scotian Shelf resulted from Strombolian type eruptions. More extensive Hawaiian type flows were mapped from seismic profiles near the Mallard and Brant wells on the SW Grand Banks and they appear to have been derived from local basement highs with a positive magnetic anomaly interpreted as volcanic centres. Igneous rocks in the Hesper well on the SE Scotian Shelf are the erosional remnant of basaltic flows that terminated at the paleoshoreline. They correlate with basalt flows both in extensive outcrop on Scatarie Ridge and in several Orpheus Graben wells. The interpretation of the Hesper basalts as an erosional remnant of more extensive basalt flows is consistent with detrital petrographic evidence for substantial uplift of the inboard part of the Scotian Basin in the Hauterivian–Aptian. Widespread volcanic activity indicates a regional and long-lived magma source, which resulted in elevated regional heat flow. Effects of this heat flow are seen in sedimentary rocks of the Sable Subbasin and it had a discernable impact on hydrocarbon maturation.

We have established a new plate kinematic model of the central and North Atlantic oceans between North America, Africa, Meseta, Iberia, Flemish Cap, and Galicia Bank from Late Triassic to Late Cretaceous to better understand the nature and timing of rifting of Nova Scotia and Morocco conjugate continental margins since Late Triassic. The maps of salt distributions at the Sinemurian–Pliensbachian limit (190 Ma; after salt deposition) and in middle Bajocian (170 Ma) show that an area of the Nova Scotia margin is devoid of allochthonous salt and that an area of similar size located oceanward of the West African Coast Magnetic Anomaly shows salt deposits, suggesting that a portion of the Nova Scotia margin with its overlying salt deposits could have been transferred onto the Moroccan side right after the formation of the conjugate East Coast Magnetic Anomaly and West African Coast Magnetic Anomaly. Seven paleogeographic maps, from Late Triassic to Late Cretaceous, are presented with structural elements and magnetic lineations. They show that the connection between the Central Atlantic and the Tethys, with an aborted rift between Iberia and North America ending in the north against the Flemish Cap – Galicia Bank dam, started to deepen at the end of the first rifting phase (190 Ma ago) after the rupture of the thinned continental crust. It is only during the Early Cretaceous, after the rupture of the Flemish Cap – Galicia Bank dam, that the deep connection around Iberia was finally established between the Central and North Atlantic, the Tethys, and the Bay of Biscay.

Sources of Tithonian–Albian sediment in the Scotian Basin are interpreted from detrital zircon geochronology to test previous hypotheses about the sources and pathways of sediment to thick deltaic successions that are important hydrocarbon reservoirs. Sediment provenance influences reservoir quality, but also provides information on tectonism during rifting of the North Atlantic Ocean. More than 760 zircons were dated by laser ablation U–Pb methods from nine offshore wells and one borehole on land and were characterized by external morphology, internal zoning, and Th/U ratio. A Meguma terrane source to the LaHave Platform was confirmed by peaks in detrital zircon abundance at 550–650 Ma, 1.0–1.2 Ga, and ∼2.1 Ga. Samples from the Sable Subbasin show a large peak in detrital zircon abundance at ∼1050 Ma, with lower peaks from 400–650, ∼1480, ∼1650, ∼1860 Ma and 2.7 Ga, characteristic of inboard Appalachian terranes of Laurentide affinity. Many late Paleozoic to Neoproterozoic zircons are euhedral or subhedral, and apparently first cycle, as are a few older zircons that indicate transport from the rising rift shoulder in southern Labrador as far north as the Makkovik Province (∼1860 Ma). About half the zircons are rounded and polycyclic. Samples from the Abenaki Subbasin are similar, but late Paleozoic to Neoproterozoic zircons are rare and ∼40% of the Mesoproterozoic zircons are subhedral, implying a different Laurentide source through the Humber valley. Euhedral–subhedral unzoned zircons yielded two groups of Cretaceous dates: ∼105 Ma from the Cree Member, and ∼120 Ma from the Missisauga Formation.

In this study, we build on a foundation of previous biostratigraphic studies for the Scotian Basin, offshore eastern Canada, by conducting new quantitative multidisciplinary biostratigraphic studies of the Mesozoic sections in eight wells: Bonnet P-23, Chebucto K-90, Cohasset L-97, Glenelg J-48, Glooscap C-63, Mohican I-100, South Desbarres O-76, and South Griffin J-13. These wells were chosen to provide good spatial coverage, stratigraphic penetration, and correlation with the seismic grid. We have also evaluated pre-existing biostratigraphic data and undertaken the well-log sequence-stratigraphic interpretation of Upper Triassic to Cenozoic sediments in 16 additional wells using a consistent multidisciplinary event scheme derived from the new wells. Key to the dating of some horizons has been integration of the palynology and micropaleontology (disciplines mostly used previously on the Scotian Margin) with new nannofossil data. Simultaneously we have closely integrated the biostratigraphic results with lithofacies, well-log, and seismic interpretations. Using this integrated approach, we have identified nine regionally mappable sequence-stratigraphic events (unconformities and maximum flooding surfaces, or MFSs): the Intra-Oligocene Unconformity; the Ypresian Unconformity; the Turonian/Cenomanian Unconformity; the Late Albian Unconformity; the Aptian/Barremian Unconformity; the Intra-Hauterivian MFS; the Near-Base Cretaceous Unconformity; the Tithonian MFS; and the Top-Callovian MFS. Additional events of local extent were also recognized in some wells. Our study has led to significant revision of some previous lithostratigraphic picks. The Early Jurassic on the Scotian Margin remains poorly resolved and may be represented by an unconformity on much of the basin periphery.

We describe and present preliminary results from an independent bending-angle algorithm implementation for the calculation of radiowave bending angles propagated from a Global Positioning System (GPS) to a Low Earth Orbiting (LEO) satellite. The algorithm utilizes raw atmospheric excess phases and satellite kinematics to determine Doppler frequency shifts of the GPS signals from which bending-angle profiles are derived. The intent is twofold: (a) perform a series of sensitivity studies to investigate the effect of Doppler frequency shift and satellite velocity variations on bending-angle profiles; and (b) examine and compare our results against the bending-angle profiles provided by the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) Data Analysis and Archive Centre (CDAAC). In this paper, we employ the same GPS observations as by CDAAC to analyze various occultation events in 2006, 2007, 2008, and 2009. Our principal finding is that radiowave bending angles exhibit an inversely proportional behaviour to orbital velocity variations while they change proportionally to the variations of Doppler frequency shift. Our studies also reveal that bending angles are more sensitive to orbital velocity than to Doppler frequency shift variations and show “wave-like” structures in the upper part of the atmosphere, unlike COSMIC-derived profiles. We discuss the differences between our derived bending-angle profiles and the COSMIC-derived profiles, emphasizing the advantages of our algorithm implementation.

In carrier-phase measurements, which are the most precise observations for Global Positioning System (GPS) relative positioning, multipath error is still a factor that interferes with achieving the desired accuracy. Various improvements in receiver and antenna technologies, as well as modeling strategies, have resulted in better ways of coping with this error source. However, errors caused by multipath can be as large as 5 cm, which is not an acceptable accuracy, especially in precise surveying applications like deformation monitoring. In this paper, a full assessment of different wavelets techniques that can be used in multipath mitigation is made to evaluate the optimum way of using wavelets to reduce or remove this type of error. Also, a new approach based on the wavelet detrending technique is introduced to remove carrier-phase multipath error in the measurement domain. To mitigate multipath, GPS double-difference observables are fed to an adaptive wavelet analysis procedure based on high- and low-pass filter decomposition with different levels of resolution. Consequently, the observable sequences are corrected; these corrected observables can then be used to reduce the ambiguity search volume during the initial float solution stage. Meanwhile, double-difference observations with multipath mitigation offer an efficient method for obtaining a better baseline solution.

This paper introduces a refined trend surface analysis (TSA) for detecting faults with small, metre-scale offsets (5–20 m). Conventional TSA uses a global polynomial method to model the trend; the power of the polynomial (e.g., first, second, or third order) is the only parameter for input. The refined approach is different in that it uses local-fit techniques to generate the trend. The refined approach provides greater flexibility for inputting geological knowledge in the trend surface modelling process. This results in a trend surface with the maximum amount of unwanted information, which is removed from the residual surface after removal of the trend from the data, leaving features of interest optimally highlighted in the residuals. Such a trend is referred to as a geologist-controlled trend to differentiate it from the trend surface modelled by conventional TSA, which is primarily a computer-controlled global polynomial surface. The refined approach goes one step beyond conventional TSA by incorporating advanced geostatistics for modelling the trend, interpolating the resultant residuals, and then extracting formation-top offset patterns from the residual surface using spatial analysis. Modelling the geologist-controlled trend in the refined approach results in higher resolution in detecting formation-top offsets and higher accuracy in digitizing fault locations, compared with various techniques that have been traditionally used in subsurface structure mapping of the West Canada Sedimentary Basin (WCSB) (e.g., structural and isopach contour mapping, cross-section construction, and seismic and aeromagnetic data interpretation). The refined approach is demonstrated using the Basal Fish Scale Zone in the Peace River Arch region as an example.

Air and near-surface ground temperatures, late-winter snow conditions, and characteristics of the vegetation cover and soil were measured across the forest–tundra transition in the uplands east of the Mackenzie Delta, Northwest Territories, in 2004–2010. Mean late-winter snow depth decreased northward from 73 cm in the subarctic boreal forest near Inuvik to 22 cm in low-shrub tundra. Annual near-surface ground temperatures decreased northward by 0.1–0.3 °C/km near the northern limit of trees, in association with an abrupt change in snow depth. The rate decreased to 0.01–0.06 °C/km in the tundra. The freezing season is twice as long as the thawing season in the region, so measured differences in the regional ground thermal regime were dominated by the contrast in winter surface conditions between forest and tundra.

Relations between snow cover, active-layer thickness, and near-surface ground temperatures were determined in 2005–2009 for a diverse range of alluvial and upland settings in the outer Mackenzie Delta. Here, the snow cover developed primarily by wind redistribution, with its spatial variation controlled by topography in uplands and vegetation height in alluvial lowlands. Snow cover was the primary influence on freeze-back duration and the mean annual temperature at the top of permafrost (TTOP), with the difference in median TTOP between alluvial (–3.7 °C) and upland (–6.1 °C) settings related to the greater snow depth and soil moisture in the alluvial plain. The active layer was generally deeper in the wet alluvial lowlands, where the average duration of active-layer freeze back (101 days) was nearly double the time taken in the well-drained uplands (55 days). The surface offset (ΔTS; up to 11 °C) dominated the difference between annual mean air temperature (AMAT) and TTOP (ΔT). In alluvial terrain, ΔTS varied with snow depth, but in the uplands, ΔTS was more consistent from site to site. The small thermal offset (

A thermo-erosion gully has been monitored in the valley of glacier C-79 on Bylot Island since 1999. The main channel of the gully reached 390 m in length a few months after its initiation and grew between 38 and 50 m/year over the following decade, for an overall approximated average of 75 m/year. In 2009, the total gully length and area, including the main and relict channels, were 2500 m and 25 000 m2, respectively. Gullies affect snow accumulation, and therefore ground temperature, local water flow, and drainage. Sinkholes, gully heads, pools, baydzherakhi, tunnels, and collapses were grouped as a function of time since gully formation in that area. Sinkholes and tunnels were formed every year after gully inception, and baydzherakhi were found in 3–10 year old sections of the gully. Stabilization of the gully floor and sides took about a decade.

Climate – ground temperature relations are examined under a range of conditions for 10 sites across northern Canada. The sites are located between 60°N and 83°N and at elevations of 40 to 1840 m above sea level. They encompass various environmental and climatic conditions, with permafrost temperatures that range from just below 0 to –15 °C. The substrates range from bedrock to fine-grained sediment with high ice content, and vegetation types include coniferous forests in the Mackenzie Valley, shrub tundra at high elevation in the southern Yukon Territory, and polar desert in the High Arctic. Permafrost conditions at all of these sites are determined primarily by air temperature, followed by snow and substrate conditions. The apparent thermal diffusivity is relatively high at colder sites and in bedrock and is lower at sites in sediment with high ice content. Snow has a greater influence on air–ground temperature relations at sites where mean annual air temperatures and active-layer moisture contents are relatively high, leading to physically significant latent heat effects and a slower freeze-back of the active layer.

We present a detailed cryostratigraphic reconstruction of the degradation and recovery of near-surface permafrost in the southern Klondike goldfields, central Yukon Territory. Two ice-rich layers are recognized in near-surface permafrost and attributed to thermal impacts following vegetation disturbance. At an undisturbed forest site, the base of the modern active layer is stable. At an adjacent site, where a late twentieth century disturbance of surface vegetation and permafrost degradation occurred, there is evidence of recovery in the form of aggradation (upward shift) of the permafrost table following limited vegetation succession. Underlying both the undisturbed forest and the late twentieth century disturbance is an older thaw unconformity corresponding to a thaw depth of ∼2 m, likely associated with early twentieth century (gold rush era) impacts. Field and air photo surveys allow identification of the nature of the disturbances, while a chronology of the surface disturbance has been established using age estimates from tree rings, and the presence of tritium and post-bomb 14C from organic samples within aggradational ice. Collectively, these data underscore the importance of vegetation cover in maintaining ground temperatures in the discontinuous permafrost zone and suggest that, at least at the study site in recent decades, permafrost shows the potential to recover from disturbance in the modern climatic regime of the region.

Temperature loggers were placed in 17 lakes and 13 channels throughout the Mackenzie Delta to determine the annual mean bottom temperature ([Formula: see text]) and its spatial and temporal variation for June 2009 – June 2010. The lakes were classified as perched or connected, depending on the duration of their connection to the channel hydrologic system. Average [Formula: see text] values for nine perched lakes, five channels, and eight connected lakes distributed throughout the Mackenzie Delta were 5.5, 4.6, and 3.4 °C, respectively. The range of [Formula: see text] among all instrumented water bodies in the Delta was 4.0 °C. Over the year, bottom temperatures ranged from >20 °C in midsummer to –5 °C in midwinter, with relative stability between freeze-up in mid-October and breakup at the beginning of June. Channel, perched, and connected lake [Formula: see text], and mean annual near-surface ground temperatures of –4 °C in alluvial sedge wetlands and –2.25 °C in forest, were used to estimate that about 60% of Delta lakes and nearly the entire channel network maintain through-taliks.

Most spatial modelling of permafrost distribution and dynamics has been conducted at half-degree latitude/longitude or coarser resolution. Such coarse results are difficult to use for land managers and ecologists. Here we mapped permafrost distribution at 30 m × 30 m resolution for a region in the northwest Hudson Bay Lowlands using a process-based model. Land-cover types and leaf area indices were derived from Landsat imagery; peat thickness was estimated from elevation based on field measurements; and climate data were interpolated from station observations. The modelled active-layer thickness and permafrost extent compared well with field observations, demonstrating that modelling and mapping permafrost at a high spatial resolution is practical for terrains such as these lowlands. The map portrayed large variations in active-layer thickness, with land-cover type and peat thickness being the most important controlling variables. The modelled active-layer thickness on average increased by 37% during the twentieth century due to increases in air temperature and precipitation, and permafrost disappeared in some southern areas. The spatial scale of the permafrost maps developed in this study is close to that of the ecosystem and landscape features; therefore, the results are useful for land management and ecosystem assessment.

Climate and ground temperature records up to 30 years in length from permafrost monitoring sites in a polar desert at Alert, Nunavut, and a boreal forest at Table Mountain, Northwest Territories, were analyzed by season and year to assess the ground thermal response to recent climate warming. Methods were developed to standardize incomplete ground temperature data sets and to hindcast air temperatures for comparative analysis. The timing and magnitude of climate warming varied, beginning in the 1960s in the Mackenzie Valley and the 1970s in the High Arctic. Ground temperature increases occurred in both regions but varied in magnitude and timing in relation to the external forcing and permafrost conditions. Significant increases in winter air temperatures in both regions appear to be largely responsible for recent increases in ground temperature, particularly at the polar desert sites where snow cover is minimal.

For the past few decades, northwestern North America has been affected by climate warming, leading to permafrost degradation and instability of the ground. This is problematic for all infrastructure built on permafrost, especially roads and runways. Thaw settlement and soil consolidation promote embankment subsidence and the development of cracks, potholes, and depressions in road pavement. In this study, we investigate highway stability in permafrost terrain at an experimentally built road embankment near Beaver Creek, Yukon. A network of 25 groundwater monitoring wells was installed along the sides of the road to estimate groundwater flow and its thermal impact on the permafrost beneath the road. Data on topography, water-table elevation, ground temperature, and stratigraphy of the soil were collected at the site. The geotechnical properties of each soil layer were determined by laboratory analysis and used to calibrate a two-dimensional groundwater flow model. Field observations showed that water was progressively losing heat as it flowed under the road embankment. Our results suggest that advective heat transfer related to groundwater flow accelerated permafrost degradation under the road embankment.

A paleomagnetic study of subaerial volcanic rocks and associated siltstones of the Ediacaran Bull Arm Formation in the Avalon Zone of Newfoundland revealed a stable bipolar, hematite-borne primary remanence supported by positive conglomerate, contact, and fold tests. Mean remanence directions in two distal areas (Bonavista and Argentia) are similar, indicating a low paleolatitude position of Avalonia at ∼570 Ma. Redbeds of the overlying ∼550 Ma Crown Hill Formation also carry a primary bipolar hematite-borne remanence with moderate inclination, indicating that Avalonia remained at low to medium paleolatitudes through the end of the Ediacaran. Combining our results with previously published paleomagnetic data of Avalonia suggests moderate-scale drift of Avalonia through low southern paleolatitudes through the latter half of the Ediacaran, providing a paleogeographic context for the development of the first complex metazoan life.

Fluids responsible for regional 18O-depletion of Neoproterozoic igneous rocks in Avalonia are investigated here through a petrographic, microthermometric, and stable isotopic examination of fluid inclusions and minerals from the abundant vein networks of the Mira terrane, Cape Breton Island. Six categories of vein assemblages — from oldest to youngest — are present: (i) quartz–albite, (ii) quartz–epidote, (iii) quartz, (iv) quartz–chlorite–calcite, (v) quartz–calcite, and (vi) calcite. Vein system temperatures were initially as high as ∼300 °C and gradually decreased to ∼200 °C. Moderate salinities (18O values (–1.9‰ to +1.4‰) calculated for most of the vein assemblages is suggestive of a seawater-dominated system, as are the δDH2O values (–12‰ to –3‰) obtained for epidote. Decreasing fluid salinities, however, suggest that meteoric water became dominant during later stages of vein formation. The carbon isotopic compositions of trace CO2 and CH4 from the fluid inclusions (δ13CCO2 = –22‰ to –4‰; δ13CCH4 = –52‰ to –37‰) are indicative of externally derived (i.e., non-magmatic) fluids of organic origin.

The Dog Bay Line, a Silurian suture key to deciphering Appalachian accretionary history, was first recognized in Newfoundland. It marks where the Ordovician Tetagouch–Exploits ensimatic back-arc basin (TEB), which had opened within the leading peri-Gondwanan Gander terrane, finally closed. Here, we extrapolate this suture into New England, placing it between the Liberty–Orrington–Miramichi inliers (LOM) and the Merrimack–Fredericton trough (MFT). Southeastward, marine strata of the MFT overlie the TEB passive margin, exposed in the Ganderian St. Croix block, and display southeast-vergent structures transected by Acadian cleavage. They structurally underlie southeast-vergent thrusts at the base of the LOM. Northwestward, the LOM, Central Maine – Matapedia trough (CMMT), and Lower Silurian igneous rocks record elements of the upper plate trench–arc system, respectively, a subduction complex, forearc basin, and arc. The CMMT forearc received detritus both from the northwesterly arc region, and also from the Early Silurian-exhumed subduction complex. Minimal contrast in Silurian turbidites near the line may be due to sediment bypassing the subduction complex, and (or) a common provenance when the complex emerged above sea level. Salinic unconformities in the upper plate (arc–trench) reflect episodes of shortening, within an overall extensional setting that resulted in thinned, weakened lithosphere, and also final uplift accompanying latest Silurian slab breakoff. Silurian strata of the Coastal Volcanic Belt document a separate arc system built on Ganderia’s trailing edge, where northwest-directed subduction of a narrow seaway led to latest Silurian collision with buoyant, strong lithosphere of Avalonia’s passive margin, and the onset of Acadian typically dextral-oblique, northwest-vergent deformation.

The Red Indian Line is the fundamental Iapetus suture zone in the Newfoundland Appalchians along which the main tract of the Iapetus Ocean was consumed. Despite being the site of the closure of a wide ocean, few vestiges of the Iapetus plate have been accreted along Red Indian Line. Ordovician rocks in the Notre Dame Bay area preserve the only evidence for accretion of a seamount in Newfoundland. The seamount is characterized by alkali basalt and hypabyssal rocks that are juxtaposed with Darriwilian peri-Laurentian volcanic arc rocks (466 ± 4 and 467 ± 4 Ma) along a major mylonite zone. The mylonite zone lacks sedimentary rocks suggesting that the seamount was accreted to the arc along a sediment-starved interface and that significant subduction erosion took place along the Laurentian margin. Identification of subduction erosion indicates that an accretionary prism did not exist outboard of Laurentia in Newfoundland, in contrast to the well developed accretionary prisms of the Caledonides.

Avalonia was a microcontinent during most of the Ordovician, separating the Iapetus Ocean to the north from the Rheic Ocean to the south. In the northern Antigonish Highlands, Nova Scotia, volcanic rocks (Dunn Point and McGillivray Brook formations) underlie Early Silurian – Early Devonian strata (Arisaig Group) and were thought to represent extension that heralded the development of the basin into which Arisaig Group strata were deposited. However, recent U–Pb (zircon, thermal ionization mass spectrometry) data from rhyolite in the Dunn Point Formation (DPF) yielded an age of 460.0 ± 3.4 Ma, and, here, we report a concordant age of 454.5 ± 0.7 Ma for an ignimbrite in the overlying McGillivray Brook Formation (MBF). These data confirm a ca. 10 million year gap between volcanism and onset of Arisaig Group deposition, which occurred after accretion of Avalonia to Baltica. The DPF and MBF both resemble A-type SiO2-rich magmas. The MBF has very high concentrations of Zr (745–1965 ppm), Y (65–213 ppm), Nb (57 to 185 ppm), and high Ga/Al. Several MBF samples exhibit strong LREE depletion, consistent with fractionation of LREE-bearing accessory phases. εNdt values for MBF (t = 455 Ma) range from +1.5 to +3.9, and overlap with DPF rhyolites that range from +2.9 to +3.7. Depleted mantle model ages for MBF and DPF samples unaffected by accessory phase fractionation are between 0.9 and 1.2 Ga and are similar to TDM values in older (Neoproterozoic, Cambrian) crustally derived felsic rocks, suggesting derivation from the lower crustal basement beneath the Antigonish Highlands. DPF and MBF rocks were probably erupted in a local extensional environment within an ensialic arc, perhaps analogous to the modern Taupo Volcanic Zone in northern New Zealand.

Metamorphosed mafic rocks from west-central Vermont crop out in tectonic slices of the Stowe Formation within the Rowe–Hawley Belt of New England. The rocks include greenstone and amphibolite, which are interpreted to have been basaltic flows and gabbroic intrusions, respectively. Even though the rocks have been metamorphosed to greenschist or amphibolite facies, their igneous origins can be deciphered through careful use of geochemistry. Three geochemical types have been identified. Type 1 and 2 samples have geochemical characteristics similar to those found in mid-ocean ridge basalts (MORB), except that they have slightly elevated light rare-earth element (LREE) concentrations and are higher in Nb/Y ratios. Their Nb/Y ratios are similar to basalts found in Iceland and parts of the Afar region of the East African Rift. Types 1 and 2 are similar to metabasalts of the Caldwell and Maquereau formations in southern Quebec. The less-common type 3 samples have highly enriched LREE and are high in Nb/Y and Zr/Y ratios, similar to some alkali basalts from Afar and Iceland. Detailed analysis of the geochemistry suggests that greenstones and amphibolite from the Stowe Formation formed as basaltic eruptions during very late stages in rifting of the Rodinian continent that eventually led to formation of the Iapetus Ocean. This interpretation is consistent with tectonic models of the Vermont and Quebec Appalachians.

The eastern edge of the Appalachian orogen is composed of a collection of Neoproterozoic – early Paleozoic domains, Avalonia, Carolinia, Ganderia, Meguma, and Suwannee, which are exotic to North America. Differences in the geological histories of these peri-Gondwanan domains indicate that each separated independently from Gondwana, opening the Rheic Ocean in their wake. Cambrian departure of Ganderia and Carolina was followed by the Ordovician separation of Avalonia and Silurian separation of Meguma. After separation in the early Paleozoic, these domains constituted the borderline between the expanding Rheic Ocean and contracting Iapetus Ocean. They were transferred to Laurentia by early Silurian closure of Iapetus and Devonian–Carboniferous closure of the Rheic Ocean during the assembly of Gondwana and Laurentia into Pangaea. The first domain to arrive at Laurentia was Carolinia, which accreted in the Middle Ordovician during the Cherokee orogeny. Salinic accretion of Ganderia occurred shortly thereafter and was followed by the Acadian accretion of Avalonia. The Acadian orogeny was immediately followed by Middle Devonian – Early Carboniferous accretion of Meguma and possibly Suwannee which led to the Fammenian orogeny. The episodicity of orogeny suggests that the present location of these domains parallels their order of accretion. However, each of these crustal blocks was translated along strike by large-scale Late Devonian – Carboniferous dextral strike–slip motion. The breakup of Pangaea occurred outboard of the Paleozoic collision zones that accreted Carolinia, Ganderia, Avalonia, Meguma, and Suwannee to Laurentia, leaving these terranes appended to North America during the Mesozoic opening of the Atlantic.

The Dunnage zone of central Newfoundland records the closing of an oceanic tract — the Iapetus Ocean. Within this tract, the Red Indian line separates arc terranes developed close to Laurentia (Notre Dame subzone) from those associated with the peri-Gondwanan terrane Ganderia (Exploits subzone). Sandstones and conglomerates of the Badger Group were deposited on the Exploits subzone, southeast of the Red Indian line, from Late Ordovician (Katian) to early Silurian (Llandovery) time. Two samples were collected from the base and top of the Badger Group for detrital zircon U/Pb dating. The lower sample yielded detrital zircon populations with a large statistical peak at ca. 1.0 Ga, and other features characteristic of derivation from Laurentian sources. Paleozoic zircons with ages from Late Cambrian to Late Ordovician were probably derived from the Notre Dame arc on the margin of Laurentia. The upper sample yielded a comparable age distribution, but with a much smaller proportion of Mesoproterozoic relative to Paleozoic detrital zircon. These results date the earliest arrival of Laurentia-derived detritus on the peri-Gondwanan Exploits subzone crust in the early Katian (ca. 455 Ma). However, the absence, in both samples, of Neoproterozoic grains suggests that there was still a seaway separating the Gander margin from arc terranes accreted to Laurentia until at least the middle Llandovery (ca. 436 Ma).

Detailed field work conducted in the Dunnage zone of the Quebec Appalachians, is herein combined with 40Ar/39Ar dating on a series of ophiolitic massifs, crosscutting granites, and associated metamorphic rocks occurring along the Baie Verte–Brompton line, the Taconian suture between Laurentia and Lower Paleozoic peri-Laurentian oceanic terranes. Studied massifs are the Lac-Brompton ophiolite and the Rivière-des-Plante Ultramafic Complex in southern Quebec, and the Nadeau Ophiolitic Mélange in the Gaspé Peninsula. Our work suggests that these massifs form remnants of eroded ophiolitic nappes, which are unconformably overlain by the Saint-Daniel and Rivière-Port-Daniel mélanges, and correlate with the Thetford-Mines and Mont-Albert ophiolitic complexes. Our 40Ar/39Ar data and compiled regional age constraints indicate that ophiolite obduction was diachronous along the strike of the orogen. The timing of obduction and mélange formation varies according to the irregular geometry of the Early Paleozoic Laurentian margin, with earlier collision occurring along, or at the margins of promontories. Obduction was initiated with the formation of infraophiolitic metamorphic soles between ca. 479 and 472 Ma in southern Quebec and the Nadeau Ophiolitic Mélange, and possibly as late as ca. 470–466 Ma for the Mont-Albert Complex. These sole rocks were later exhumed and translated onto the Laurentian margin with the overlying ophiolites between 475 and 460–457 Ma. The uplifting and erosion of the orogenic wedge during the waning stages of obduction, has resulted in the sedimentation of olistostromal mélanges and onlapping flysch units above the ophiolitic nappes, as well as foredeep flysch successions during the latest Arenig(?) to earliest Caradoc.

The Newfoundland Appalachians are a classic area for studying the record of arc development and terrane accretion processes with excellent exposure to different crustal levels that are minimally deformed and metamorphosed. This area also provides a link between the once continuous Appalachian and Caledonian orogens. The Annieopsquotch Accretionary Tract lies along the Red Indian Line, within the peri-Laurentian realm of the central Newfoundland Appalachians. The Darriwilian (468–461 Ma) tectonostratigraphic units of the Annieopsquotch Accretionary Tract are commonly characterized by polymictic volcanogenic conglomerate horizons. A conglomerate horizon at the interface between a suprasubduction zone ophiolite and its calc-alkaline volcanic arc cover sequence is herein investigated for zircon and geochemical provenance. Geochronology revealed a maximum age of deposition of 467 ± 4 Ma with zircon inheritance ranging from ca. 500 to 2800 Ma, consistent with a peri-Laurentian continental basement source. Four types of volcanogenic conglomerate clasts are noted on the basis of lithogeochemistry: arc andesite; calc-alkaline basalt; tholeiitic basalt; and non-arc rhyodacite. Tholeiitic basalt clasts are likely locally derived, perhaps from the underlying Skidder Formation. Other volcanic clasts do not have any known geochemical equivalents in the Annieopsquotch Accretionary Tract and hence appear to be exotic. The dominant zircon population suggests that the exotic clasts were derived from a ca. 467 Ma peri-Laurentian andesitic volcanic arc that once formed part of the Annieopsquotch Accretionary Tract.

Previously unrecognized A-type granitoid and gabbroic rocks cover an area of ∼100 km 2 in the central Antigon- ish Highlands in Avalonian northern mainland Nova Scotia. The granitoid rocks in this suite occur, together with minor gab- bro, in separate mappable bodies named the Brora Lake, Haggarts Lake, West Barneys River, McGraths Mountain, and Leadbetter Road plutons and are the focus of this study. They are mainly alkali feldspar granite and quartz syenite with var- ied texture and modal mineralogy. Close spatial association, gradational contact relations, and magma-mingling relationships suggest that all of these rocks, including the gabbro, are coeval. Hence a U-Pb (zircon) age of 469.4 +/- 0.5 Ma obtained for a quartz syenite sample from the Brora Lake pluton is interpreted to indicate a Middle Ordovician age for all of these granitoid and gabbroic rocks. Most granitic and quartz syenitic samples have hypersolvus texture, characterized by strongly perthitic alkali feldspar, and some also contain interstitial granophyre, both features indicative of shallow emplacement. Mafic minerals include iron-rich calcic and calcic-sodic amphibole, hedenbergite, and in some samples fayalite. Most of the rocks have high concentrations of K, Na, P, Ti, and Fe and are alkalic, with agpaitic indices as high as 0.98. Discrimination diagrams indicate that they are A-type granitoid rocks formed in a within-plate extensional setting. Age correlatives of these A-type granitoid and gabbroic rocks are not yet known elsewhere in Avalonia. The available data suggest that this ca. 470 Ma magmatism occurred while Avalonia was a separate microcontinent in the Rheic Ocean. Resume : Des roches gabbroiques et granitoides de type A, auparavant non reconnues, recouvrent un secteur d'environ 100 km 2 dans les hautes terres centrales d'Antigonish dans la partie continentale septentrionale de l'Avalonie en Nouvelle

We present the first description of organic-walled microfossils from Cambrian strata of the Bourinot belt, central Cape Breton Island. Age-diagnostic acritarchs have been recovered from the Dugald and MacMullin formations and from probable levels within the upper part of the Eskasoni Formation, which permit detailed correlations with acritarch-based zones in Newfoundland and Spain. The assemblage of acritarchs from the Dugald Formation confirms earlier assignments to the early middle Cambrian eteminicus Zone, but it also indicates that the upper part of the formation belongs to the hicksi Zone of the Drumian Stage. Acritarchs from the MacMullin Formation provide the first biostratigraphic evidence that this unit extends into the forchhammeri Zone of the Guzhangian Stage. These acritarchs are present in the lower part of the MacMullin Formation, putting into question earlier identification of hicksi Zone trilobites in this unit and raising the possibility of an unconformity. The data from the Bourinot belt provide additional evidence for the biostratigraphic utility of acritarchs in the Cambrian Acado-Baltic province.

The Moreton’s Harbour Group lies along the Red Indian Line, the fundamental Iapetus suture that separates rocks of peri-Laurentian affinity with rocks of peri-Gondwanan affinity in the Newfoundland Appalachians. Characterization of age and environment of formation of the Moreton’s Harbour Group is an important constraint on evolution of the Laurentian margin during Ordovician closure of Iapetus Ocean and associated marginal basins. The Moreton’s Harbour Group comprises a fault-bounded ophiolitic sequence of layered gabbro, sheeted diabase, pillow basalt, and felsic intrusive rocks. It is offset by high-angle shear zones that were contemporaneous with a 477.4 ± 0.4 Ma syn-tectonic and syn-magmatic suite of trondhjemite and tonalite. Trace element data from the felsic suite indicate formation in a supra-subduction zone setting, although isotopic data from the felsic intrusive rocks (εNd (–5.02) to (–10.53), Tdm 1200–1800 Ma) indicate a significant amount of contamination from Mesoproterozoic or older continental crust. The age and tectonic setting of the Moreton’s Harbour Group suggest that it is the northernmost extent of the ca. 480 Ma Annieopsquotch Ophiolite Belt. We present a model in which the Moreton’s Harbour Group formed in response to propagation of the Annieopsquotch Ophiolite Belt spreading centre into the Dashwoods microcontinent. This ridge propagation model supports the formation of the Annieopsquotch Ophiolite Belt immediately outboard of Dashwoods and explains its rapid accretion to the composite Laurentian margin.

The Salinic Orogeny is defined to encompass tectonic interactions that affect all elements of Ganderia involved in the closure of the Tetagouche–Exploits back-arc basin between the Late Ordovician and Early Devonian. Hence, the D1 and D2 deformations in the Miramichi Highlands and Elmtree Inlier of northern New Brunswick are Salinic events, and onlap of Lower Silurian rocks onto exhumed parts of the Brunswick Subduction Complex represents the earliest (Salinic A) of three Silurian unconformities in the region. Upper Ordovician to Lower Silurian rocks of the Matapédia successor basin contain widespread evidence of Middle Silurian tectonism (e.g., disconformities, angular unconformities, and fold interference patterns) created by Devonian overprinting of Silurian folds lacking axial planar cleavage (Salinic B). Recent U–Pb radioisotopic dating of chemically abraded zircon from rhyolite just above the Salinic B unconformity has yielded an age of 422.3 ± 0.3 Ma; combined with late Early Silurian fossil ages just below the unconformity, this indicates a ca. 5 million year Middle Silurian hiatus. Finally, Upper Silurian (Ludfordian) rocks are locally disconformably overlain by polymictic conglomerates that form the base of the Devonian section (Salinic C). All Silurian rocks in northeastern New Brunswick have historically been included in the Chaleurs Group; however, unconformities and local stratigraphic variations (especially compared with the type locality) support the introduction of new higher rank names in New Brunswick. Hence, the Quinn Point Group is introduced to incorporate Lower Silurian rocks, the Petit Rocher Group to include Upper Silurian sedimentary rocks in the Nigadoo River Syncline, and the Dickie Cove Group for Upper Silurian volcanic rocks in the Charlo – Jacquet River area. Upper Silurian rocks west of Campbellton that are contiguous with the Chaleurs Group in Quebec, will remain part of the Chaleurs Group.

The Penobscot arc system of the northeastern Appalachians is an Early Cambrian to early Tremadocian (ca. 514- 485 Ma) ensialic to ensimatic arc-back-arc complex that developed along the margin of the peri-Gondwanan microcontinent Ganderia. Remnants of this Paleozoic arc system are best preserved in the Exploits Subzone of central Newfoundland. Cor- relative rocks in southern New Brunswick are thought to occur in the ca. 514 Ma Mosquito Lake Road Formation of the Ellsworth Group and ca. 497-493 Ma Annidale Group; however in the past, the work that has been conducted on the latter has been of a preliminary nature. New data bearing on the age and tectonic setting of the Annidale Group provides more conclusive evidence for this correlation. The Annidale Group contains subalkaline, tholeiitic to transitional, basalts to basal- tic andesites, picritic tuffs and calc-alkaline to tholeiitic felsic dome complexes that have geochemical signatures consistent with suprasubduction zone magmatism that was likely generated in a back-arc basin. New U-Pb ages establish that the Late Cambrian to Early Tremadocian Annidale Group and adjacent ca. 541 Ma volcanic rocks of the Belleisle Bay Group in the New River belt were affected by a period of younger magmatism ranging in age from ca. 479-467 Ma. This provides im- portant constraints on the timing of tectonism in the area. A ca. 479 Ma age for the Stewarton Gabbro that stitches the faulted contact between the Annidale and Belleisle Bay groups, demonstrates that structural interleaving and juxtaposition occurred during early Tremadocian time, which closely coincides with the timing of obduction of Penobscottian back-arc ophiolites onto the Ganderian margin in Newfoundland. Resume : Le systeme d'arc Penobscot du nord-est des Appalaches est un complexe d'arc-d'arriere-arc ensialique a ensima- tique datant du Cambrien precoce au Tremadocien precoce (~514-485 Ma) qui s'est developpe le long de la bordure peri- gondwannienne du microcontinent Ganderia. Des lambeaux de ce systeme d'arc paleozoique sont le mieux conserves dans la sous-zone Exploits du centre de Terre-Neuve. Des roches correlatives dans le sud du Nouveau-Brunswick seraient presen- tes dans la Formation de Mosquito Lake Road (~514 Ma) du Groupe d'Ellsworth et dans le Groupe d'Annidale (~497-493 Ma); toutefois, par le passe, le travail effectue sur ce dernier groupe n'a ete que preliminaire. De nouvelles donnees sur l'âge et l'environnement tectonique du Groupe d'Annidale fournissent des evidences plus concluantes de cette correlation. Le Groupe d'Annidale contient des basaltes a des andesites basaltiques, subalcalins, tholeiitiques a intermediaires, des tufs picritiques et des complexes de domes felsiques, calco-alcalins a tholeiitiques, possedant des signatures geochimiques qui concordent avec un magmatisme de zone de suprasubduction probablement generee dans un bassin d'arriere-arc. De nou- veaux âges U-Pb ont etabli que le Groupe d'Annidale, Cambrien tardif a Tremadocien precoce, et les roches volcaniques ad- jacentes du Groupe de Belleisle Bay (~541 Ma) dans la ceinture de New River ont ete affectes par une periode de magmatisme plus jeune, datant d'environ 479 a 467 Ma. Ces donnees fournissent des contraintes importantes sur le moment du tectonisme dans la region. Un âge d'environ 479 Ma pour le gabbro de Stewarton, qui reunit le contact de faille entre les groupes d'Annidale et de Belleisle Bay, demontre que l'imbrication et la juxtaposition structurales ont eu lieu au debut du Tremadocien, ce qui coincide de pres avec le moment de l'obduction des ophiolites d'arriere-arc de Penobscot par-dessus la bordure de Ganderia a Terre-Neuve. (Traduit par la Redaction)

The ∼470 Ma Ammonoosuc Volcanics of the Bronson Hill terrane of New Hampshire have back-arc basin basalt compositions. Major and trace element compositions compare favorably to coeval volcanic rocks in the Miramichi Highlands of New Brunswick and the Munsangan and Casco Bay volcanics of Maine, back-arc basin basalts of known peri-Gond- wanan origins. Additionally, the Ammonoosuc Volcanics have Nd and Pb isotopic compositions indicative of peri-Gond- wanan provenance. Thus, the Ammonoosuc Volcanics correlate with Middle Ordovician, peri-Gondwanan, Tetagouche- Exploits back-arc rocks of eastern New England and Maritime Canada. This correlation indicates that the Red Indian Line, the principle Iapetus suture, lies along the western margin of the Bronson Hill terrane. However, the younger (∼450 Ma) Oliverian Plutonic Suite rocks that intruded the Ammonoosuc Volcanics, forming domes along the core of the Bronson Hill anticlinorium, have Laurentian isotopic signatures. This suggests that the Ammonoosuc Volcanics were thrust westwardly over the Laurentian margin, and that Laurentian basement rocks are present under the Bronson Hill terrane. A plausible ex- planation for these relationships is that an easterly dipping subduction zone formed the Ammonoosuc Volcanics in the Tetagoughe-Exploits oceanic tract, just east of the coeval Popelogan arc. With the closure of the Iapetus Ocean, this terrane was thrust over the Laurentian margin. Subsequent to obduction of the Ammonoosuc Volcanics, subduction polarity flipped to the west, with the Oliverian arc resulting from a westerly dipping subduction zone that formed under the Taconic Orog- eny-modified Laurentian margin. Resume : Les roches volcaniques Ammonoosuc, ∼470 Ma, du terrane de Bronson Hill au New Hampshire ont des compo- sitions de bassins basaltiques d'arriere-arc. Les compositions en elements majeurs et traces se comparent favorablement aux roches volcaniques contemporaines des terres hautes de Miramichi au Nouveau-Brunswick et les roches volcaniques de Munsangan et de Casco Bay au Maine, des bassins basaltiques d'arriere-arc d'origine peri-gondwanienne connue. De plus, les roches volcaniques Ammonoosuc ont des compositions d'isotopes de Nd et de Pb qui indiquent leur provenance peri- gondwanienne. Ainsi, les roches volcaniques Ammonoosuc sont correlees avec les roches d'arriere-arc Tetagouche-Exploits, Ordovicien moyen peri-Gondwana, de l'est de la Nouvelle-Angleterre et des provinces maritimes canadiennes. Cette correla- tion signifie que la ligne Red Indian, la principale suture Iapetus, se situe le long de la bordure ouest du terrane de Bronson Hill. Toutefois, les roches de la suite plutonique Olivierian, plus jeune (∼450 Ma), formant des domes le long du cœur de l'anticlinorium Bronson Hill, ont des signatures isotopiques laurentiennes. Cela suggere que les roches volcaniques Ammo- noosuc aient ete chevauchees vers l'ouest par-dessus la bordure laurentienne et que les roches du socle laurentien se retrou- vent sous le terrane de Bronson Hill. Une explication plausible pour ces relations est qu'une zone de subduction a pendage vers l'est a forme les roches volcaniques Ammonoosuc dans l'etendue oceanique Tetagouche-Exploits, tout juste a l'est de l'arc Popelogan contemporain. Avec la fermeture de l'Ocean Iapetus, ce terrane a ete chevauche par-dessus la bordure lau- rentienne. Apres l'obduction des roches volcaniques Ammonoosuc, la polarite de la subduction a bascule vers l'ouest; l'arc Oliverian proviendrait d'une zone de subduction a faible pendage vers l'ouest qui s'est formee sous la bordure laurentienne modifiee par l'orogenese taconienne. (Traduit par la Redaction)

This special issue reports on some of the results of a multi-disciplinary research program conducted in the Boreal Plains of northwest Alberta and northeast British Columbia. Several innovative approaches to conducting geoscientific research in this remote drift-covered region are presented, including geochemical analysis of bentonites for evaluating kimberlite potential, the use of electromagnetic surveys for mapping buried aggregate deposits, and paleo-topographic mapping techniques to define buried channels. Results of the program include the discovery of several large aggregate deposits, the first kimberlite indicator minerals in northeast British Columbia, a significant sphalerite dispersal train in northwest Alberta, the first documented report of kimberlite-sourced bentonites, and numerous previously unknown interglacial sites. Together these papers provide a greatly enhanced understanding of the glacial history, Quaternary stratigraphy, and kimberlite geology of northwest Alberta and northeast British Columbia and provide an improved framework for resource exploration in the region.

This study demonstrates how ice-flow history, geochronology, geology, and geophysics may be integrated to enhance the effectiveness of boulder tracing in glaciated regions affected by multiple ice-flow events. Mineralized felsic granitoid boulders (erratics) were discovered 18 years ago on a claim block located 10 km northwest of Little Fort, in the Bonaparte Lake map area (NTS 092P), in south-central British Columbia. Although the boulders have yielded significant gold concentrations (up to 4.15 g/t), their bedrock source is not known. The till near the boulders contains up to 1382 gold grains per 15 kg of bulk material with 75% of the grains having pristine morphology, suggesting a short distance of glacial transport. A U–Pb zircon crystallization age of 198.1 ± 0.5 Ma on one mineralized boulder indicates derivation from an Early Jurassic intrusion. Using a vector addition model based on regional ice-flow patterns, the most recent and detailed bedrock geology map, and recently acquired airborne radiometrics and magnetic data, the northeast sector of the Thuya Batholith (195–205 Ma) is interpreted as the most likely bedrock source of the mineralized boulders.