bluuebunny/crossref_metadata_2025 huggingface dataset:
The Long Rapids Formation: an Upper Devonian black shale in the Moose River Basin, northern Ontario
Authors: Bezys Ruth K. , Risk Michael J.
Published: July 2009

The Long Rapids Formation, a sequence of interbedded black shales, green–grey mudstones, and carbonates in the Moose River Basin of northern Ontario, is Late Devonian in age and has counterpart equivalents in the Michigan, Appalachian, and Illinois basins. The Long Rapids Formation has a maximum known thickness of 85 m and can be divided into three informal members. Based on conodont studies, the formation spans the Frasnian–Famennian age boundary.The Long Rapids Formation is an organic-rich, laminated, marine black-shale sequence interbedded with green–grey mudstones and concretionary carbonate interbeds and nodules. The environment of deposition was principally reducing, allowing for preservation of large amounts of organic matter both originating in the overlying water column and derived from terrestrial sources. The depositional basin was stratified, and anoxic bottom waters and oxic surface waters were separated by a pycnocline. The position of the pycnocline (or the absence of it) dictated the type of sediment facies deposited.The Moose River Basin in the Late Devonian was located on the Laurasian Continent, proximal to the equator, in an area where tropical weather conditions prevailed. Conditions were warm and wet along the Appalachian highlands, and farther inland they were warm and dry as a result of the rain-shadow effect. The black shales in the Long Rapids Formation represent a period of transgression of the large epicontinental Catskill Sea, and the green–grey mudstones and carbonates represent periods of minor eustatic or tectonic perturbations.Dark-coloured, organic-rich shale facies (sometimes with abundant bioturbation) are succeeded by lighter coloured shale or mudstone facies and carbonate facies in a repetitive fashion. The facies sequences appear to represent a three-part sedimentary package, or "rhythm", that is very common in the lower two members of the Long Rapids Formation. Bioturbation and total organic carbon content are less in the green–grey shales or mudstones, as well as in the carbonate facies, than in the darker shale facies.
Recognition of a Cretaceous outlier in northwestern Ontario
Authors: Zippi Pierre A. , Bajc Andrew F.
Published: July 2009

Borehole F-88-33, located near Rainy River, Ontario, intersected Cretaceous nonmarine clastic sediments. This is the first documented occurrence in Ontario of Cretaceous sediments associated with the western interior. Lithologie and heavy-mineral analyses were used to differentiate this unit from the overlying Quaternary sediments. Seventy-five species of fossil angiosperm pollen, gymnosperm pollen, spores, megaspores, and algal cysts were recovered from borehole F-88-33 and used to date the pre-Quaternary sediments as late Albian to early Cenomanian. The occurrence of these nonmarine sediments in northwestern Ontario helps to better define the limits of Cretaceous sedimentation in the western interior.
Structural and lithological controls of gold-bearing quartz-breccia zones in Archean metaturbidites, Gordon Lake, Northwest Territories, Canada
Authors: Stokes T. R. , Zentilli M. , Culshaw N.
Published: July 2009

Gold lode deposits, hosted within shear zones of Archean metavolcanic belts, have produced some of the world's largest gold mines. Consequently, exploration has focussed on regional lineaments within these belts. However, commonly associated metaturbidite terrains may also become good exploration targets once previously unrecognized structural and lithological ore controls are determined and their genesis better understood. Mapping of lower-greenschist-grade metaturbidites of the Burwash Formation at Gordon Lake (62°54′N, 113°15′W) has identified gold-bearing, quartz-breccia zones that are confined to the central area of a south-closing regional refold of earlier, vertically plunging isoclinal (F1) folds. The refold is partly transected by a "regional" cleavage (S3) and has a crenulation cleavage (S4) restricted to its hinge region. Of five breccia types recognized, the strata-bound, gold-bearing, and sulphide-rich breccias found at Knight Bay are economically the most important. These breccias are restricted to the crenulated domains within the central part of the refold and are hosted preferentially in the black, carbon-rich siltstones. Our data are compatible with a model whereby metamorphic fluids, carrying gold extracted from the metaturbidite pile, were focussed into fractures within the central domain of the refold during (anticlockwise) rotation of the refold's east limb. The limb rotation induced dextral bedding-parallel slip in the central domain of the refold and resulted in the formation of a crenulation cleavage and hydraulic fracturing within overpressured siltstone beds. Decompression during the episodic hydraulic fracturing led to precipitation of grey quartz, gold, sulphides, and minor carbonates. The organic matter within the black siltstone host may have physically enhanced bedding-parallel slip and, if the mineralizing solutions were oxidizing, led to chemical reduction at the site of ore concentration.
Regional setting of vein-style gold mineralization around the Goldlund mine, Sandybeach Lake area, northwestern Ontario
Authors: Chorlton Lesley
Published: July 2009

The Sandybeach Lake area was deformed in four stages. Stage 1 produced gently south-southeast-dipping foliations at low angles to bedding. Stage 2 involved draping of these planes and formation of contact-strain aureoles related to the emplacement of granitoid stocks. Stage 3 produced doubly plunging folds, steep foliations, and shear zones, which resulted from regional transpression, with a sinistral lateral shear sense along this arm of the Wabigoon greenstone belt. Stage 4 produced minor folds and shear displacements in some places and final tightening of stage 3 folds in others, compatible with final regional convergence.Regional quartz veins, including those carrying gold, appear to have filled tensional fractures related to bulk belt-perpendicular shortening and belt-parallel extension, sinistral shear, and tightening of folds in sheetlike competent bodies. Veins and mineralization thus coincided with late stage 3 deformation, possibly overlapping stage 4.Auriferous vein occurrences at the Goldlund mine display geometries similar to those of veins in the surrounding region. The main body of auriferous vein mineralization is hosted by a thick, composite metatonalite–metadiorite sheet. The vein system of this zone likely originated during the steepening and axial-plane transposition of the southeast-dipping limb near the southwest-plunging end of a stage 3 fold.
Contexte structural et minéralisations aurifères des gîtes Casa-Berardi, Abitibi, Québec
Authors: Pilote P. , Guha J. , Daigneault R. , Robert F. , Golightly J. P.
Published: July 2009

The Casa-Berardi gold deposits are located 180 km north of Rouyn-Noranda within Archean rocks of the Abitibi Subprovince. The Casa-Berardi deformation zone (CBDZ), which contains these deposits, is an east–west trending structure that is recognized along a minimum distance of 80 km. Ductile deformation has affected the lithologies in the central portion of the CBDZ. The CBDZ juxtaposes distinct sedimentary and volcanic lithostratigraphic packages which locally display opposite facing directions. Within the CBDZ the Casa-Berardi fault has been recognized; it is a brittle structure with a reverse motion. This fault represents a distinct element associated with the progression of deformation in the CBDZ and appears late in the geodynamical evolution of this deformation zone. Two other deformation zones have been identified in this region: (i) the east–west-trending Boivin-Paradis deformation zone, which has limited lateral extent and is located at the periphery of a granitoid intrusion, and (ii) the Laberge deformation zone, which has a northwest to east–west trend and crosscuts the regional structural grain. Most of the economic gold mineralization in the Casa-Berardi deposits is found in the second set of four recognized vein and fracture sets. The mineralized veins are found within zones of intense deformation which are preferentially developed close to contacts between sedimentary and volcanic units. The geometry of the different sets of quartz veins, their relative chronology, and their respective hydrothermal alterations can be explained by the progression of deformation within the CBDZ and bracket the gold mineralization as syn- to late-tectonic. The CBDZ is distinguished from the other two deformation zones by its greater lateral extent, the juxtaposition of distinct lithological domains, the complexity of its internal fabrics, and the relative length of the deformation event. These features indicate that in contrast with the other two deformation zones, the CBDZ was the site of a major mineralizing event. The recognition of contrasting characteristics between the different deformation zones has repercussions on the understanding of the different criteria that control gold deposition and, ultimately, on gold exploration.
Tectonic evolution of the northeast portion of the Archean Abitibi greenstone belt, Chibougamau area, Quebec
Authors: Daigneault R. , St-Julien P. , Allard G. O.
Published: July 2009

The Chibougamau area, occupying the northeastern part of the Abitibi greenstone belt is a large synclinorium of volcanic and sedimentary rocks enclosed within tonalitic gneisses. Several east–west–trending regional folds within this synclinorium are responsible for the vertical attitude of the strata. Synclinal structures, with youngest sediments within the core, possess axial-plane schistosity. Anticlines, on the other hand, either form domes with a core occupied by earlier tonalitic to dioritic plutons or are transected by a series of east–west-trending ductile faults (the Waconichi tectonic zone).An early deformation phase of low intensity (D1) generated broad, north–south folds without schistosity. The subsequent regional deformation, event D2, produced the large east–west folds. These deformations, in combination, produced the regional interference pattern of domes and basins. North–south horizontal shortening generated an east–west-trending schistosity associated with a vertical stretching lineation. Regional deformation at its climax produced a tightening of folds and rotation of fold axes parallel to the stretching lineation.Plutons deflected the regional east–west schistosity and formed concentric trajectories associated with "contact-strain aureoles." This produced small interaction zones or triple points characterized by strong vertical extension. These relations suggest an interference between a regional stress field, which produced north–south horizontal shortening, and local stress fields, controlled or deflected by granitoid plutons acting as competent bodies.East–west-trending ductile shear zones represent the final stage of the regional deformation. The observed northward and southward reverse movement along these east–west faults, their parallelism to the axial trace of folds, and the regional schistosity are probable evidence of a regime dominated by a coaxial strain.
Origin of cross-stratal layering in fluvial conglomerates, Devonian Malbaie Formation, Gaspé, Quebec
Authors: Anketell J. M. , Rust B. R.
Published: July 2009

Planar cross-bedded conglomerates in proximal braid-plain deposits of the Devonian Malbaie Formation of eastern Gaspé, Quebec, display a distinctive cyclic layering of three facies: conglomerate with sand matrix (A); matrix-free conglomerate, in which the voids are filled by sparry white calcite cement (C); and coarse sandstone (B). The sequence was previously interpreted as ABC, but is here reinterpreted as ACB. B forms cross-strata parallel layers. Facies A and C together make up the gravel layers, with C passing down-foreset into A across a matrix–cement interface which dips at low angles in the same direction as the foreset. The sequence results from migration of gravel–sand bed forms across bar tops, with deposition of gravel at bar margins as foresets and infiltration of sand into the gravel fabric from blackflow currents induced by flow separation at the foreset crests. Infiltration proceeds until the framework voids are plugged by granules and coarser sand grains, after which sand and granules may continue to accumulate on the plugged surface to form a discrete layer. Occasional peaks on the matrix – open framework interface record sites of more effective infiltration. Elongate peaks, strike-parallel or downdip, possibly reflect organisation of the sand load into ripples across the foreset at the time of its infiltration, or they may reflect regular variation in grain size or packing, and hence ingress potential, of the framework. Partial sequences in which one or another of the layers is missing apparently result from variation in the efficiency of sand transport up the foreset coupled with variation in the efficacy and timing of framework plugging, or variable sorting in bar-top bed forms.
U–Pb geochronology of Late Proterozoic rocks of the eastern Cobequid Highlands, Avalon Composite Terrane, Nova Scotia
Authors: Doig Ronald , Murphy J. Brendan , Nance R. Damian
Published: July 2009

In the Cobequid Highlands of Nova Scotia, low-grade late Precambrian arc-related volcano-sedimentry rocks typical of the Avalon Composite Terrane overlie platformal metasedimentry rocks and are spatially associated with gneisses previously considered to be basement to both these units. U–Pb zircon dates of 580–587 Ma from an orthogneiss and an amphibolite are similar to the U–Pb zircon dates of 580–610 Ma from both syntectonic granites in ductile shear zones and high-level posttectonic plutons that intruded the Avalonian successions. Hence, the gneisses do not represent basement but are an integral part of the Avalonian orogenic cycle. The geochronological data indicate that penetrative fabrics in the gneisses, syntectonic granites, and volcano-sedimentary successions are penecontemporaneous (ca. 580–620 Ma) and not sequential, as previously interpreted. The gneisses have a metamorphic fabric (S1a), crystallized under amphibolite-facies conditions, and may represent the deeper roots of a late Precambrian magmatic arc. Fabrics within the deformed granite gneisses (S1b) are interpreted as reflecting crystallization within active ductile shear zones associated with intra-arc transtension and basin development. Fabrics in the volcano-sedimentary successions (S1c) are associated with deformation of the basin.
Geophysics and geochronology of the crystalline basement of the Alberta Basin, western Canada
Authors: Ross G. M. , Parrish R. R. , Villeneuve M. E. , Bowring S. A.
Published: July 2009

Although progressively muted by the increasing thickness of Phanerozoic sediments in the Alberta Basin, the geophysical signature of tectonic domains in the Canadian Shield can be traced nearly to the Foothills of the Canadian Cordillera. A combination of potential field data for Alberta and U–Pb zircon and monazite age determinations on drill core samples of crystalline basement recovered during hydrocarbon exploration was used to subdivide the basement of the Alberta Basin into 22 distinct domains. The Canadian Shield was used to ground truth the interpretation of the geophysical signatures and infer possible kinematic relationships between basement domains. Ages of crystalline basement range from 1.7 to 3.2 Ga and demonstrate that a large expanse of 2.1–2.4 Ga crust is present in northern Alberta. This suggests a continuum of tectonic activity and crust formation(?) in Alberta rather than the 2.6 Ga and 2.0–1.8 Ga episodicity apparent in the exposed Canadian Shield.
Stratigraphy and graptolites of the Upper Ordovician Point Leamington Formation, central Newfoundland
Authors: Williams S. Henry
Published: July 2009

The Point Leamington Formation, as redefined herein, comprises a thick sequence of siliciclastic turbidites containing occasional Upper Ordovician graptolites and lies with the Exploits Subzone of the Dunnage Zone in central Newfoundland. The base of the unit is marked by the first coarse- to medium-grained sandstone, at a level that varies from the Dicranograptus clingani Zone to the Pleurograptus linearis Zone. Several intervals of interbedded black shales and siltstones higher in the formation yield assemblages characteristic of the P. linearis, Dicellograptus complanatus and Dicellograptus anceps zones. Debris-flow breccias occur at several levels within the Point Leamington Formation—some contain graptolitic, black shale clasts derived from the underlying Lawrence Harbour Formation—and range in age from Nemagraptus gracilis Zone to D. clingani Zone. Both the graptolite assemblages and lithostratigraphic succession of the Point Leamington Formation are similar to those of coeval rocks in southern Scotland, confirming a strong relationship between the two areas during the Late Ordovician.
Erosion of bedrock by subglacial meltwater, Georgian Bay, Ontario: a regional view
Authors: Kor P. S. G. , Shaw J. , Sharpe D. R.
Published: July 2009

A spectacular series of sculpted erosional forms (s-forms) is mapped and described from a 70 km wide area along the shore of Georgian Bay, Ontario, which, except for a scattered boulder lag, has been swept clean of sediment. A great variety of sculpted forms is described and illustrated and grouped into three classes: transverse, longitudinal, and nondirectional forms. Transverse forms comprise transverse troughs, muschelbrüche, sichelwannen, and comma forms; longitudinal forms comprise spindle flutes, cavettos, and furrows; and nondirectional forms consist of undulating surfaces and potholes. Transverse forms are preferentially located on stoss slopes, and longitudinal forms on lee slopes of rock rises. Undulating, nondirectional forms are found on distal slopes, and potholes at major breaks in slope. This correlation of form and bed topography suggests that relief exerts considerable control on both form and location. Form geometry is also inferred to be related to coherent flow structures and their interaction with the bed. Flow scale, vorticity, separation, bifurcation, strength, and direction are inferred from erosional-mark properties. In some cases, erosional forms appear to have caused the flow structure by which they were perpetuated. Sculpted forms occur at different scales, and the inferred flow structures are thought to have operated over the same scale range.Attributes of the forms, boulder lags, and inferred flow structures clearly reflect erosion by powerful, turbulent, subglacial meltwater flows. The erosional forms are observed over an area 70 km wide, which, taken together with a strongly uniform paleoflow direction, indicates regional-scale flow. The Georgian Bay floods were comparable in discharge (~107 m3/s) with floods from glacial Lake Missoula, Livingstone Lake drumlins, and Sable Island tunnel valleys. The most likely site for the storage of meltwater that drained catastrophically to form the erosional-mark field was the lowland stretching north from the Abitibi Highlands to Hudson Bay.
Représentation pollinique actuelle à la limite des arbres au Nouveau-Québec
Authors: Gajewski K.
Published: July 2009

Modern pollen spectra from a series of lakes in northwestern Quebec reflect the major vegetation zones of the forest–tundra transition from latitude 55°N to 59°N. Shrub tundra samples are dominated by Betula and herb pollen, whereas Picea percentages are between 10 and 20%. Lichen woodland samples can contain over 60% Picea, with Betula and Alnus crispa each less than 20%. Pollen assemblages from the shrub subzone of the forest–tundra resemble those of the shrub tundra, while those from the forest subzone resemble lichen woodland samples. Maximum percentages of Alnus crispa are found in the forest–tundra. Classification of the samples using cluster analysis and an ordination by principal coordinates analysis suggest that densely and sparsely forested regions can be discriminated.
Glacigenic rafting of weathered granite: Charlie Lake, New Brunswick
Authors: Broster Bruce E. , Seaman Allen A.
Published: July 2009

Glaciation in the area of Charlie Lake, New Brunswick, has produced a granitic till very similar in appearance to weathered bedrock. Portions of weathered granite were moved intact and redeposited as imbricated rafts under basal till. The rafts vary from 0.3 to 2 m in thickness over a 10 m wide exposure and show deep weathering zones and brittle deformation, despite the fact that they are highly friable. The rafts are separated by glacigenic fault planes defined by lenses of diamict and rare clasts of distant origin. They are recognizable only in excavations where fault planes can be seen to delineate slabs of rock imbricated mainly upglacier. Surface weathering features, including core-stones, were preserved during movement over short distances.
The age of the Lac-Saint-Jean Anorthosite Complex and associated mafic rocks, Grenville Province, Canada
Authors: Higgins Michael D. , van Breemen Otto
Published: July 2009

U–Pb analyses of zircon and baddeleyite from the south-central and southeastern parts of the Lac-Saint-Jean Anorthosite Complex (LSJA) give an igneous crystallization age of 1157 ± 3 Ma. Parts of the anorthosite were deformed in the solid state and subsequently intruded by a diorite megadyke, which also gives a crystallization age of 1157 ± 3 Ma, indicating that crystallization and deformation of the anorthosite were essentially synchronous. The diorite megadyke was intruded into a north-northeast-trending shear zone and deformed by sinistral strike-slip movements. Emplacement was followed by intrusion of a subparallel leucotroctolite megadyke that again gives the same crystallization age and hence dates movement of the shear zone at 1157 ± 3 Ma. This short history of crystallization and synchronous deformation rules out slow diapiric rise as the emplacement mechanism for the anorthosite. Instead, anorthosite parental magmas probably rose up offsets in subvertical strike-slip shear zones to their present level.In the southwestern part of the LSJA an age of 1142 ± 3 Ma is interpreted to represent igneous crystallization. Contemporary thermal metamorphic effects recorded in the southeastern sector by growth of new zircon in granophyric segregations and zircon coronas on baddeleyite suggest this event was more widespread at slightly deeper levels. Evidence has not been found for a separate Grenville regional metamorphism.The emplacement into the LSJA at 1076 ± 3 Ma of two small leucogabbro intrusions was part of a widespread magmatic event similar to the main event at 1157–1142 Ma.
U–Pb baddeleyite ages of the Kerns and Triangle Mountain intrusions, Nipissing Diabase, Ontario
Authors: Noble Stephen R. , Lightfoot Peter C.
Published: July 2009

U–Pb ages have been determined for two diabase intrusions from Kerns and Hudson townships that are part of the Nipissing diabase suite from the Proterozoic Southern Province, Canada. The ages of the Kerns and Triangle Mountain intrusions are 2217.2 ± 4 and 2209.6 ± 3.5 Ma, respectively, based on analysis of primary baddeleyite from both intrusions. Together with a published U–Pb age for the Castle Mine intrusion, these data indicate that the Nipissing sills were emplaced separately over a time span of 2.8–1.6 Ma, given by the maximum and minimum overlap of errors on the U–Pb ages.
Integrated geophysical modelling of terranes and other structural features along the western Canadian margin
Authors: Dehler S. A. , Clowes R. M.
Published: July 2009

An integrated geophysical data set has been used to develop structural models across the continental margin west of Vancouver Island, Canada. A modern accretionary complex underlies the continental slope and shelf and rests against and below the allochthonous Crescent and Pacific Rim terranes. These terranes in turn abut against the pre-Tertiary Wrangellia terrane that constitutes most of the island. Gravity and magnetic anomaly data, constrained by seismic reflection, seismic refraction, and other data, were interpreted to determine the offshore positions of these terranes and related features. Iterative 2.5-dimensional forward models of anomaly profiles were stepped laterally along the margin to extend areal coverage over a 70 km wide swath oriented normal to the tectonic features. An average model was then developed to represent this part of the margin. The Pacific Rim terrane appears to be continuous and close to the coastline along the length of Vancouver Island, consistent with emplacement by strike-slip motion along the margin. The Westcoast fault, the boundary between the Pacific Rim and Wrangellia terranes, is interpreted to be 15 km farther seaward than in previous interpretations in the region of Barkley Sound. The Crescent terrane forms a thin landward-dipping slab along the southern half of the Vancouver Island margin, and cannot be confirmed along the northern part. Model results suggest the slab has buckled into an anticline beneath southern Vancouver Island and Juan de Fuca Strait, uplifting high-density lower crustal or upper mantle material close to the surface to produce the observed intense positive gravity anomaly. This geometry is consistent with emplacement of the Crescent terrane by oblique subduction.
Structure beneath Queen Charlotte Sound from seismic-refraction and gravity interpretations
Authors: Yuan Tianson , Spence G. D. , Hyndman R. D.
Published: July 2009

A combined multichannel seismic reflection and refraction survey was carried out in July 1988 to study the Tertiary sedimentary basin architecture and formation and to define the crustal structure and associated plate interactions in the Queen Charlotte Islands region. Simultaneously with the collection of the multichannel reflection data, refractions and wide-angle reflections from the airgun array shots were recorded on single-channel seismographs distributed on land around Hecate Strait and Queen Charlotte Sound. For this paper a subset of the resulting data set was chosen to study the crustal structure in Queen Charlotte Sound and the nearby subduction zone.Two-dimensional ray tracing and synthetic seismogram modelling produced a velocity structure model in Queen Charlotte Sound. On a margin-parallel line, Moho depth was modelled at 27 km off southern Moresby Island but only 23 km north of Vancouver Island. Excluding the approximately 5 km of the Tertiary sediments, the crust in the latter area is only about 18 km thick, suggesting substantial crustal thinning in Queen Charlotte Sound. Such thinning of the crust supports an extensional mechanism for the origin of the sedimentary basin. Deep crustal layers with velocities of more than 7 km/s were interpreted in the southern portion of Queen Charlotte Sound and beneath the continental margin. They could represent high-velocity material emplaced in the crust from earlier subduction episodes or mafic intrusion associated with the Tertiary volcanics.Seismic velocities of both sediment and upper crust layers are lower in the southern part of Queen Charlotte Sound than in the region near Moresby Island. Well velocity logs indicate a similar velocity variation. Gravity modelling along the survey line parallel to the margin provides additional constraints on the structure. The data require lower densities in the sediment and upper crust of southern Queen Charlotte Sound. The low-velocity, low-density sediments in the south correspond to high-porosity marine sediments found in wells in that region and contrast with lower porosity nonmarine sediments in wells farther north.
Crust and upper mantle velocity structure of the Intermontane belt, southern Canadian Cordillera
Authors: Zelt B. C. , Ellis R. M. , Clowes R. M. , Kanasewich E. R. , Asudeh I. , Luetgert J. H. , Hajnal Z. , Ikami A. , Spence G. D. , Hyndman R. D.
Published: July 2009

As part of the Lithoprobe Southern Cordillera transect, seismic refraction data were recorded along a 330 km long strike profile in the Intermontane belt. An iterative combination of two-dimensional traveltime inversion and amplitude forward modelling was used to interpret crust and upper mantle P-wave velocity structure. This region is characterized by (i) a thin near-surface layer with large variations in velocity between 2.8 and 5.4 km/s, and low-velocity regions that correlate well with surface expressions of Tertiary sedimentary and volcanic rocks; (ii) an upper and middle crust with low average velocity gradient, possibly a weak low-velocity zone, and lateral velocity variations between 6.0 and 6.4 km/s; (iii) a distinctive lower crust characterized by significantly higher average velocities relative to midcrustal values beginning at 23 km depth, approximately 8 km thick with average velocities of 6.5 and 6.7 km/s at top and base; (iv) a depth to Moho, as defined by wide-angle reflections, that averages 33 km with variations up to 2 km; and (v) a Moho transition zone of depth extent 1–3 km, below which lies the upper mantle with velocities decreasing from 7.9 km/s in the south to 7.7 km/s in the north. Where the refraction line obliquely crosses a Lithoprobe deep seismic-reflection profile, good agreement is obtained between the interpreted reflection section and the derived velocity structure model. In particular, depths to wide-angle reflectors in the upper crust agree with depths to prominent reflection events, and Moho depths agree within 1 km. From this comparison, the upper and middle crust probably comprise the upper part of the Quesnellia terrane. The lower crust from the refraction interpretation does not show the division into two components, parautochthonous and cratonic North America, that is inferred from the reflection data, indicating that their physical properties are not significantly different within the resolution of the refraction data. Based on these interpretations, the lower lithosphere of Quesnellia is absent and presumably was recycled in the mantle. At a depth of ~ 16 km below the Moho, an upper mantle reflector may represent the base of the present lithosphere.
The early diagenesis of submerged sulphide-rich mine tailings in Anderson Lake, Manitoba
Authors: Pedersen T. F. , Mueller B. , McNee J. J. , Pelletier C. A.
Published: July 2009

The oxidation of sulphide-rich mine tailings stored on land by acidophilic bacteria is frequently associated with severe environmental degradation, as metal-rich acid drainage from the tailings contaminates groundwater and surface runoff. Permanent storage of tailings underwater may prove to be more chemically benign if oxidation is inhibited sufficiently. To assess this possibility, the chemistry of interstitial waters and the associated solid phases in tailings and organic-rich (20–30 wt.% C) natural sediments in Anderson Lake, Manitoba, is examined. The lake has been used as a receiving basin for sulphide-rich tailings since 1979, and is contaminated with metals as a result of the input of acid mine drainage along the north shore and the discharge of mill process water with the tailings. Three cores were collected and processed under nitrogen to extract interstitial waters. At all sites, the occurrence of high concentrations of dissolved iron in shallow pore waters indicates that the deposits are anoxic within several millimetres of the sediment–water interface. Despite high dissolved metal inventories in the lake, the concentrations of Zn, Cu, Pb, and Cd decrease abruptly with depth in the pore waters. This cannot be due to non-steady-state effects and indicates unequivocally that both the tailings and natural sediments are acting as sinks for metals, rather than as sources. Dissolved sulphate data and the widespread occurrence of framboidal pyrite in surface sediments suggest that the metals are being precipitated as sulphide phases at shallow depths.
Differentiation and source of the Nipissing Diabase intrusions, Ontario, Canada
Authors: Lightfoot P. C. , Souza H. de , Doherty W.
Published: July 2009

Major and trace element data are presented for 2.2 Ga Proterozoic diabase sills from across the Nipissing magmatic province of Ontario. In situ differentiation of the magma coupled with assimilation of Huronian Supergroup roof sediments is responsible for the variation in composition between quartz diabase and granophyric diabase seen within many of the differentiated intrusions. Uniform trace element and isotope ratio signatures, such as La/Sm (2.8 – 3.7) and εNdCHUR (−2.7 to −5.9) characterize chilled margins and undifferentiated quartz diabases. These chemical signatures suggest the existence of a single magma source that was parental to intrusions throughout the magmatic province; this magma has higher La/Sm and lower Ti/Y than primitive mantle and is displaced towards the composition of shales. Most chilled diabases and quartz diabases have a similar Mg# (0.64 and 0.60) and Ni content (98 and 127 ppm), and it is argued that the magma differentiated at depth and was emplaced as a uniform low-Mg magma. The Wanapitei intrusion and Kukagami Lake sill are an exception in that although the quartz diabase has La/Sm similar to the Nipissing magma type, which suggests that they came from the same source, the Mg# (0.68–0.71) and Ni content (130–141 ppm) are higher, which may suggest that they are either slightly more primitive examples of the normal Nipissing magma or that cumulus hypersthene has been resorbed. The light rare earth element enriched signature of the Nipissing magmas was perhaps introduced from the continental crust as the magma migrated from the mantle to the surface, but a remarkably constant and large amount (>20%) of crustal contamination would be required. An addition of 1 –3% shale to the source of a transitional mid-ocean ridge basalt type magma can broadly reproduce the compositional features of the Nipissing magma type. The source characteristics were perhaps imparted during subduction accompanying the terminal Kenoran orogeny.
Isotopic study of basaltic dikes in the Nain Plutonic Suite: evidence for enriched mantle sources
Authors: Carlson R. W. , Wiebe R. A. , Kalamarides R. I.
Published: July 2009

Basaltic dikes cutting the Nain Plutonic Suite (NPS) of Labrador include two chemically distinct groups. One is a high-Fe tholeiitic to transitional alkalic composition similar to some of the magmas involved in the formation of the NPS. The other, distinguished by high phosphorus and incompatible element contents, is similar in major element composition to intraplate oceanic alkalic basalts. A Rb–Sr mineral isochron for one high-P2O5 sample defines an age of 1276 ± 23 Ma indicating that it is similar in age to, or only slightly younger than, the circa 1305 Ma anorthosites.Compositional and isotopic characteristics of the high- and low-P2O5 dikes show that the gross features of their initial isotopic characteristics (i.e., low 87Sr/86Sr, negative εNd, nonradiogenic Pb) probably derive from a distinct lithospheric mantle source with similar characteristics. To have developed these isotopic characteristics by the time of dike emplacement, their mantle source must have formed and separated from oceanic-type upper mantle well prior to Nain anorthosite genesis, possibly between 2.0 and 2.6 Ga.
Geochemistry and tectonic setting of late Precambrian volcanic and plutonic rocks in southeastern Cape Breton Island, Nova Scotia
Authors: Barr Sandra M.
Published: July 2009

Late Precambrian volcanic–sedimentary belts in the Mira (Avalon) terrane of southeastern Cape Breton Island display differences in rock types, petrochemistry, and age, showing that they did not form contemporaneously above a single northwest-dipping subduction zone, as proposed in earlier models. The oldest rocks are 680 Ma mafic and felsic flows and tuffs, and abundant, mainly tuffaceous, sedimentary rocks in the Stirling belt. They are interpreted to have formed in a trough within or peripheral to a volcanic-arc complex. Northwest of the Stirling belt, the East Bay Hills, Coxheath Hills, and Sporting Mountain belts consist of ca. 620 Ma mafic to felsic subaerial pyroclastic rocks and flows and contemporaneous dioritic to granitic plutons. Both volcanic and plutonic rocks are calc-alkalic to high-K calc-alkalic suites, formed in a continental margin volcanic arc. A correlative 620 Ma plutonic suite intruded the western margin of the Stirling belt, suggesting that subduction may have been toward the present southeast. The ca. 575 Ma Coastal belt, located southeast of the Stirling belt, is significantly younger than the other belts and appears to represent a less evolved calc-alkalic to low-K continental margin volcanic-arc and intra-arc basin formed above a northwest-dipping subduction zone. These various volcanic–sedimentary belts were juxtaposed by lateral movements along major faults in the late Precambrian to form this part of the Avalon composite terrane. Subduction-related, calc-alkalic magmatism at ca. 620 Ma was apparently widespread throughout the Avalon terrane of the northern Appalachian Orogen. However, ca. 680 Ma magmatism like that in the Stirling belt has been documented elsewhere only in the Connaigre Bay Group of Newfoundland. Circa 575 Ma and younger subduction-generated igneous activity like that in the Coastal belt has been recognized in southern New Brunswick, but alkaline magmas were forming in extensional regimes in other areas of the Avalon terrane at that time.
40Ar/39Ar chronology of the Nain anorthosites, Canada
Authors: Yu Yang , Morse S. A.
Published: July 2009

A hornblende 40Ar/39Ar age of 1328 ± 8 Ma has been obtained from the contact aureole of the Bird Lake Massif, confirming it as one of the oldest members of the Nain plutonic suite. This age constrains the timing of the early stage magma activity of the Nain plutonic suite.Plagioclase samples from the intrusions yield either U-shaped, or staircase-shaped 40Ar/39Ar age spectra, and most of them have two isochrons of similar age but greatly different initial argon composition. Most plagioclase closure ages are >95% of either the hornblende age from a contact aureole or coexisting biotite ages, and appear to reflect single cooling events for each intrusion. Two major stages of emplacement for the Nain anorthosites are identified: an older anorthosite event and a main anorthosite event, in agreement with results from earlier field studies. The Port Manvers Run, Paul Island, and Nukasorsuktokh Island intrusions yield much younger plagioclase ages than any previously established intrusion ages, probably reflecting previously unknown later, local heating events.The total duration of the major anorthositic magma activity in the Nain region is about 23 Ma, estimated from the Bird Lake massif margin at 1328 ± 8 Ma and the Kiglapait intrusion at 1305 ± 2 Ma (Sm/Nd, U/Pb), implying an emplacement rate of about 0.0022 km3/year. This rate is far less than the effusion rate of magma on some of the Phanerozoic rifted margins and supports the "aborted rifting" model for the generation of massif anorthosite.
U–Pb geochronology of the central Uchi Subprovince, Superior Province
Authors: Corfu F. , Stott G. M.
Published: July 2009

U–Pb zircon and titanite ages for rocks of the central Uchi Subprovince in northwestern Ontario indicate a late Archean magmatic and tectonic development spanning over 200 Ma. An early period at 2900–2800 Ma formed volcano-plutonic complexes, presumably linked to 3.1–2.8 Ga terrains of the northwestern Superior Province. A later period of southward growth by magmatic and tectonic accretion occurred at 2750–2710 Ma and was concluded by large scale compression and plutonism at 2700 Ma.The oldest 2890–2860 and 2840–2820 Ma components occur in the Pickle Lake and Meen–Dempster greenstone belts and as gneisses in the Seach–Achapi and the Lake St. Joseph batholiths in northern and central sectors of the region. Together with distinct 2750–2740 Ma volcano-plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion. Plutons of 2730–2710 Ma age are intrusive into these older, northern domains, whereas their volcanic counterparts compose the Lake St. Joseph and Miminiska – Fort Hope greenstone belts to the south. Late-tectonic to posttectonic granitoid rocks intruded a region extending from the northern Berens River Subprovince to the southern English River Subprovince at 2700 Ma. These plutons were cut by regional scale faults formed by residual north-northwest directed shortening. The timing of this movement seems to be recorded by titanite ages of 2690–2670 Ma. Reactivation of the same faults may account for Proterozoic Pb loss observed in some of the zircon populations. The age patterns are consistent with crustal growth along a continental margin in a north-dipping subduction environment.
A new species of large, long-snouted ichthyosaur from the English lower Lias
Authors: McGowan C.
Published: July 2009

A large ichthyosaur, with a total length in excess of 7 m, is described from the Lower Jurassic (Sinemurian) of Dorset, England. Like Leptopterygius tenuirostris the new species, named Leptopterygius solei, has a long slender snout armed with slender teeth that are remarkably small for the large size of the skull. There are also similarities in the forefin: the humerus is widely expanded distally, and the phalanges are rounded rather than polygonal and are probably well spaced distally. However, in contrast to L. tenuirostris, there is no notch on the leading edge of the radius. The snout is also relatively shorter and the orbit smaller. Thus in the holotype the estimated values for the snout and orbital ratios are 0.68 and 0.15 respectively, compared with observed ranges for L. tenuirostris of 0.71–0.76 (n = 7) and 0.18–0.24 (n = 7). Leptopterygius solei also has a somewhat higher prepelvic vertebral count, being at least 50 in the holotype compared with an observed range of 44–48 (n = 9) for L. tenuirostris. Furthermore, the ischium is considerably wider than the pubis, whereas these elements have approximately similar widths in L. tenuirostris. The possibility that the new material might merely represent the upper end of a growth series of L. tenuirostris is dismissed. Based on skull length, the holotype of L. solei is 66% larger than the largest specimen of L. tenuirostris.
Eocene bird tracks from the Chuckanut Formation, northwest Washington
Authors: Mustoe George E.
Published: July 2009

Early Tertiary nonmarine sediments occur as a discontinuous series of outcrops that extends throughout large areas of northwest Washington and southwestern British Columbia. These fluvial and deltaic deposits contain abundant plant fossils, but faunal remains are rare. The recent discovery of an outcrop of Chuckanut Formation arkose containing nine fossil bird tracks provides the first clear evidence of terrestrial vertebrate life in the extensive coastal wetland zone that existed prior to the uplift of the Cascade Range.
Petrology, mineralogy, and geochemistry of sandstones of the lower Huronian Matinenda Formation: resemblance to underlying basement rocks
Authors: Sutton S. J. , Maynard J. B.
Published: July 2009

Bulk chemistry, mineralogy, mineral chemistry, cathodoluminescence characteristics, and textural data are used to constrain provenance and the role of postdepositional alteration processes in sandstones of the lower Huronian Matinenda Formation. Samples studied are from the Elliot Lake – Blind River and Agnew Lake areas, which experienced subgreenschist and biotite-grade greenschist metamorphism, respectively. Both areas, but particularly the lower grade area, contain some K-rich samples, with much of the K in detrital-appearing K-feldspar. In places K-feldspar is partially replaced by potassic mica. Plagioclase (mostly albite) is rare in the Elliot Lake – Blind River samples, and only common along a few horizons in the Agnew Lake section. It is suggested that the predominance of K-feldspar over plagioclase and the high K/Na ratios indicate a K-rich source area and in particular a weathered granite source. Framework mineralogy is found to be similar to material reported from sub-Matinenda weathered granite. The abundance of fine-grained micaceous matrix within the Matinenda varies considerably among samples, and the composition of the mica varies, correlating strongly with bulk chemistry. Some matrix has clearly been generated by alteration of framework K-feldspar. Feldspar alteration may have liberated K that was carried to the underlying regolith where it was fixed by weathering-product clay minerals. Fluids involved in alteration do not appear to have pervasively affected the Matinenda in either the Elliot Lake – Blind River or the Agnew Lake area.
EFFECT OF DOPING ON SUPERCONDUCTIVITY AND CHEMICAL POTENTIAL IN La2-xSrxCuO4
Authors: SAHOO B. K. , PANDA B. N. , ROUT G. C.
Published: July 2009

We examine the doping dependence of SC gap (Δ) and chemical potential (μ) of the hole-doped cuprates by using the Fulde model. It is assumed that SC arises due to BCS pairing mechanism in lattices of Cu–O planes. The expression for SC, AFM, and doping concentration are calculated analytically by using the Green function technique of D. N. Zubarev. The value of SC gap (Δ) and chemical potential (μ) are solved self-consistently for different model parameters. The variation of critical temperature and chemical potential with doping are also studied.
QUANTUM PHASE ANALYSIS OF AN ANISOTROPIC (XYZ) HEISENBERG SPIN-1/2 CHAIN UNDER A UNIFORM AND STAGGERED MAGNETIC FIELD
Authors: SARKAR SUJIT
Published: July 2009

We study quantum phases of an anisotropic (XYZ) Heisenberg spin-1/2 chain under a mixed magnetic field (uniform and staggered), along with its variant. Our model consists of two competing relevant operators, anisotropy a, and staggered magnetic field hs. Depending on the sign of a this model describes either the physics of solitonic confinement, or the Ising transition between gapped phases. In our case excitations are the integer spin particle in contrast to the half-integer spin particle of frustrated dimerized spin chain. We do all analysis in weak coupling limit.
SPIN DEGREES AND POLARIZATION OBSERVABLES IN ELECTROMAGNETIC REACTIONS
Authors: ARENHÖVEL HARTMUTH
Published: July 2009

After a brief introduction into the general importance of polarization observables for the analysis of a reaction, the basic density matrix formalism for the description of polarization phenomena is outlined and illustrated by explicit examples for spin one-half and one. Then various electromagnetic processes like photoreactions and electron scattering are discussed in some detail. Finally, the question of how to determine a complete set of polarization observables providing the maximum information on a reaction is considered.
SEARCH OF η-NUCLEUS BOUND STATE FORMATION IN RECOIL FREE TRANSFER REACTIONS
Authors: JHA V. , Budzanowski A. , Chatterjee A. , Hawranek P. , Jahn R. , Jain B. K. , Kailas S. , Kilian K. , Kliczewski S. , Kirillov Da. , Kirillov Di. , Kolev D. , Kravcikova M. , Lesiak M. , Lieb J. , Liu L. C. , Machner H. , Magiera A. , Maier R. , Martinska G. , Nedev S. , Piskunov N. , Protić D. , Ritman J. , von Rossen P. , Roy B. J. , Shukla P. , Sitnik I. , Siudak R. , Tsenov R. , Urban J. , Vankova G.
Published: July 2009

We have performed an experiment to search for the bound state of η meson in nuclei. We have measured the reaction p + 27Al → 3He + p + π- + X at recoil-free kinematics. An η meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if bound nuclear η states exist. The decay of such a state through the N*(1535) resonance would lead to a proton-π- pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of ≈ 0.5 nb for the formation cross section is found.