bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleomagnetism of the Harp Lake Complex and associated rocks
Authors: Irving E. , Emslie R. F. , Park J. K.
Published: April 2011

The remanent magnetism of anorthositic rocks from the Harp Lake Complex consists of two antiparallel components, M and H, defined on the basis of their coercivities. M has remanent coercivities generally in the range 100–1000 Oe (7.96 × 103–7.96 × 103 A/m) but sometimes exceeding 2000 Oe (159 × 103 A/m), and is carried by magnetite and hematite, the former being the predominant contributor. H has remanent coercivities in excess of 2000 Oe (159 × 103 A/m), and is carried by hematite probably containing some ilmenite in solid-solution. The mean direction, irrespective of sign, based on 110 samples from 24 collecting sites is 270°, + 01° (α95 = 6°) with a pole 02°N, 154°W (A95 = 4°). This is considered to be the average direction of the geomagnetic field during initial cooling following intrusion of the complex at about 1450 Ma. At this time the complex was at great depth. The Harp dikes, which intrude the complex, have steeper inclinations, (263°, + 44°, α95 = 7°, pole 19°N, 132°W). The country rocks in the thermal aureole have directions roughly similar to those of the complex, but deflected towards the directions in the dikes (272°, + 29°,α95 = 10°, pole 14°N, 144°W). It is suggested that the country rocks were magnetized during final uplift of the area but prior to the intrusion of the Harp dikes. These and other paleomagnetic poles for the interval 1300–1500 Ma fall in the central Pacific indicating that Laurentia was in low latitudes. Previous reviewers have connected these poles by a simple polar loop, but these new observations indicate that the polar path may be more complicated, and a doubly looped path is suggested as a means of reconciling the results. There are about 20 accurately determined pole positions for the interval 1500–1200 Ma from North America, but only 4 from the rest of the world, and it is not yet possible to determine from such an unbalanced body of data the positions of other Precambrian shields relative to North America during this time interval.
Tills deposited in arid polar environments
Authors: Shaw John
Published: April 2011

Tills deposited in arid polar environments retain more attributes of the transportation phase than do tills deposited in the humid polar environment. The difference results from high depositional activity under conditions of abundant meltwater in the humid environment, and only passive deposition during removal of ice by sublimation in the cold arid environment. Structural properties of tills such as fissility and foliation, and clast orientation and dip have a much higher preservation potential in the arid environment than in the humid one. A model of deposition under arid polar conditions is presented. Existing classifications based only on depositional processes do not use the range of information available from tills deposited in arid polar environments. An expanded classification of tills is proposed which utilizes the position of transport, the position of deposition, the process of deposition, and structural properties acquired during transportation.
Cornwallis Lead–Zinc District; Mississippi Valley-type deposits controlled by stratigraphy and tectonics
Authors: Kerr J. Wm.
Published: April 2011

Cornwallis Lead-Zinc District in the central Canadian Arctic includes occurrences of galena and sphalerite with similar geological settings and controls on mineralization. It includes the Polaris deposit, with 25 million tons of about 19% grade ore, representing 4.7 million tons of metal.The district occurs in and was controlled by the Cornwallis Fold Belt, a steep-sided anticlinorium of Proterozoic to Devonian formations, that overlies a basement horst.Four controls on mineralization are: (A) deposits are stratabound within the Ordovician Thumb Mountain Formation; (B) ore occurs in breciated dolomite, in contrast to usual limestone of the host formation; (C) deposits are located close to shale of the Cape Phillips Formation; and (D) the host formation was subject to erosion and karstification in Early Devonian time during Pulse 3 of the Cornwallis Disturbance.Mineralization is of Mississippi Valley-type, having formed in carbonate rock by epigenetic processes. The sequence of stratigraphic and tectonic events leading to mineral formation was as follows:(1) An Ordovician to Lower Devonian geosynclinal sequence was deposited, containing formations that could be a source of Zn, Pb, Fe, and S, as well as a potential host formation.(2) The sequence was folded by three pulses of the Cornwallis Disturbance.(3) Uplift in Early Devonian time allowed deep erosion that exposed the host Thumb Mountain Formation in anticlinal culminations.(4) Caverns and pores developed in the upper part of that formation, by karst-type solution.(5) During subsidence an unconformable sedimentary cover buried the host formation and its caverns to a considerable depth.(6) Two formation fluids developed, with metal ions in one and sulphur ions in the other.(7) These two brines migrated laterally and upward, and met in cavities in the Thumb Mountain Formation.(8) In these cavities temperatures and other conditions were suitable and the brines precipitated the sulphides, galena, sphalerite, and pyrite.Deposition probably occurred between temperatures of 52 °C and 102 °C, suggesting that the caverns were at depths of at least 1280 m (4200 ft). This probably occurred in Late Devonian time, prior to Pulse 4 of the Cornwallis Disturbance. Major structural events following mineral emplacement raised the occurrences to higher topographic levels where they became exposed.Metal deposition in this model resembles the accumulation of petroleum in that the components were carried upward and laterally from source formations to structural culminations, and deposited there in open spaces that served as traps.
Trace element geochemistry of the Sokoman Iron Formation
Authors: Fryer B. J.
Published: April 2011

Rare earth and other trace element data are presented for samples of the Sokoman Iron Formation, Labrador, and its associated sediments. The results show that the slates associated with the iron formation are typical in trace element contents compared to other argillaceous sediments except for the large Eu depletion characteristic of slates of their age. The iron formation, however, is fundamentally different in its trace element concentrations and patterns from those of the associated rocks. It is relatively enriched in the heavy REE and Eu and both the REE and Co, Cr, Sc, and Th concentrations bear no relationship to those of the slates and the dolomite.Trace element analyses of the various textural and mineralogic rock types in all cases substantiate the genetic conclusions of earlier workers based on field and petrographic observations. Silicate–carbonate facies samples show constant REE, Co, Sc, and Th distributions which are compatible with an origin as crystalline precipitates in equilibrium with sea water. Riebeckite-bearing iron formation is distinctive in that it reflects contamination by ordinary clastic material and (or) metamorphic solutions. Oxide facies rocks exhibit widely variable trace element abundances as is to be expected for rocks whose original trace element contents were controlled by adsorption processes. A group of iron-enriched oxide facies rocks show evidence of important heavy REE complexing associated with the migration of iron during diagenesis. Minor Ce anomalies in all facies of Sokoman Iron Formation indicate that oxidation of Ce to the +4 state was taking place at the time of iron deposition but probably not in close proximity to it.
Evolution of the Pacific Margin, Vancouver Island, and adjacent regions
Authors: Muller J. E.
Published: April 2011

The tectonic–stratigraphic evolution of Vancouver Island, a part of the Insular Belt, is reviewed as it relates to the other major tectonic belts recognized in the western Cordillera of Canada and the adjacent United States. The Pacific Belt, recognized south of the international border, is also identified in the west and south of the island. Oldest rocks of the Insular Belt are a late Paleozoic volcanic arc terrane and a crystalline 'basement' that is probably pre-Devonian. A thick Upper Triassic succession of tholeiitic pillow lavas and flows, overlain by carbonate–clastic sediments, rests in part on the Paleozoic. Elsewhere the tholeiite may represent oceanic floor, perhaps formed when the Insular Belt was fragmented and rifted off the continental margin far to the south. Above it the Early Jurassic volcanic arc with related batholiths may have been aligned with a similar terrane in the Intermontane Belt before the two belts assumed parallel positions in late Mesozoic time. An Upper Jurassic – Lower Cretaceous westward thickening clastic wedge indicates uplift and erosion of the volcanic arc in late Mesozoic time. Further west the 'inner Pacific Belt' of Jura-Cretaceous elastics and chert represent slope and trench deposits that have been deformed to mélange or converted to schist. They are coeval and homologous to Franciscan and Chugach Terranes and probably mark the late Mesozoic trench and subduction zone along the continental margin. The Coast Plutonic Belt represents the related volcanic arc, and pre-Cretaceous Insular Belt rocks, unconformably overlain by Cretaceous clastic sediments, represent the arc–trench gap and fore-arc basin. Until Late Cretaceous time convergence of the Insular and Pacific Belts occurred along San Juan Fault. In early Tertiary time Eocene oceanic basalt (Outer Pacific Belt) and Jura-Cretaceous metasediments (Inner Pacific Belt) converged by under-thrusting and (or) strike–slip faulting along Leech River Fault. In Late Eocene time the trench and subduction zone shifted westward to the present core zone of the Olympic Mountains and shifted again in Miocene time to its present position.
A down-draft fume hood for the control of toxic vapours of heavy liquids used for mineral separations
Authors: Johnson Wesley M. , Sheppard Lindsay E. , Beaton Donald N.
Published: April 2011

An inexpensive, down-draft, canopy-type fume hood incorporating activated charcoal filters has been designed and built for the control and disposal of the fumes of heavy liquids such as diiodomethane used during the separation of specific minerals from their host rock matrices.
Ice thickness measurements and their implications with respect to past and present ice volumes in the Canadian High Arctic ice caps
Authors: Koerner R. M.
Published: April 2011

The main ice caps on Devon Island, central and northeast Ellesmere Island, and Axel Heiberg Island were sounded using a 620 MHz radar. Ice depths were found to be generally between 300 and 800 m. The bedrock topography is everywhere very irregular. There is a pronounced difference between the thickness, and hence volume, of ice on the east and west sides of the Central Ellesmere and Devon ice caps. The greater thickness on the east sides is attributed to much higher snow accumulation rates there and it is calculated that the asymmetry between the east and west sides began to develop some 8000 years ago. The greater thickness of ice on the ice caps facing Baffin Bay must be considered in any derivation of the dimensions of the Wisconsin ice sheet from maps of isostatic rebound in the Queen Elizabeth Islands. Some of the northwest–southeast tilt of strandlines on Devon and Southern Ellesmere islands can be attributed to the suppression of rebound by these thick ice masses. It is inferred, from the greater symmetry of ice caps in Northern Ellesmere and to a lesser extent Axel Heiberg Island, that the Arctic Ocean is a much less effective moisture source than Baffin Bay.
Archean basin–craton complexes and the growth of Precambrian shields
Authors: Goodwin Alan M.
Published: April 2011

Southern Superior Province of the Canadian Shield contains cratonic and basinal elements arranged in high- to low-grade metamorphic terranes such that higher grade gneissic cratons are interpreted to represent primary infrastructure to lower grade volcanic-rich (greenstone) basins. Ensimatic accumulation of volcanic components is favoured with derivation of gneissic (granitic) components by ensuing metamorphic differentiation and granitization processes. Such vertically reconstructed basin–craton complexes which are tentatively ascribed to initial Archean mantle convection, are viewed as building units of growing Precambrian shields.Globally, twenty-seven identified Archean cratons belong to three main age groups based on maximum recorded ages as follows: 3.5–3.8 Ga, 2.9–3.1 Ga, and 2.6–2.7 Ga. The three age groups that correspond to major periods of Archean orogeny may represent accretion superevents (after Moorbath).Most cratons as presently exposed display lithologic characteristics of lower superstructure–upper infrastructure of typical basin–craton complexes thereby suggesting a common degree of crustal buoyancy, hence level of erosion. Archean belts of southern Superior Province provide unique opportunity for reconstruction of the typical basin–craton complex.
A note on post-Mississippian thrust faulting in northwestern Cape Breton Island
Authors: Currie K. L.
Published: April 2011

Thrust faulting, apparently of major proportions, has been observed at five localities in northwestern Cape Breton Island and inferred at several more. The thrust blocks of Precambrian crystalline rocks and Horton Group clastic sedimentary rocks have over-ridden Windsor Group (Viséan–Namurian) rocks but not Riversdale Group rocks (Westphalian). Thrusting can be explained by sliding of material from an elongate horst extending from northern Cape Breton Island to southwestern Newfoundland which rose throughout Tournaisian and Viséan time.
Alteration and ore-forming processes at Mattagami Lake Mine, Quebec
Authors: Roberts R. Gwilym , Reardon Eric J.
Published: April 2011

The altered rocks of the Mattagami Lake Mine, a stratabound, volcanogenic, massive sulphide deposit, were examined using whole rock analyses and electron microprobe studies of the constituent minerals. The significant chemical and mineralogical transformations involved in the progressive alteration of the footwall, vitroclastic tuff of rhyodacitic composition, are: (1) the removal of alkalies (sodium followed by potassium), and the addition of magnesium and iron during initial chloritization; (2) substantial removal of silica by the solution of quartz, to produce a chlorite-rich rock, and (3) gradual removal of aluminum and the transformation of chlorite (Mg2.5 Fe2.5Al2Si3O10(OH)8) to talc (MG2.5FE0.5Si4O10(OH)2 to produce units of talc–actinolite schist. The reaction: 3 chlorite + 10H2S(g) + 2.5 O2 + 11,H4SiO4 + 5Mg2+ = 5talc + 5pyrite + [Formula: see text] + 19H2O + 16H+ (log K, 25 °C = +145; log K, 100 °C = +102; log K, 250 °C = +68.2) is favoured by high temperature and Mg2+ activity, and low activity of aluminum.The alteration pipe zone immediately beneath the orebody is assumed to have been the discharge site of a thermally induced, convective flow system. The upper part of the system would have been characterized by the movement of seawater, of comparatively short residence time in the rocks, to areas of discharge. Under conditions of high permeability and high water flux in these zones, bulk seawater composition of comparatively high magnesium and low aluminum concentrations would ultimately control the composition of the volcanic material by the formation of alteration products in equilibrium with it, rather than the volcanic material significantly affecting the seawater chemistry. This would ensure the early development of magnesian chlorite in the vitric tuff. The transformation chlorite to talc took place at discharge sites, the locations of highest surface temperatures, under hydrologic conditions such that the flux rate was sufficiently high to remove the comparatively immobile aluminum.The massive sulphide units were emplaced in association with the development of talc. Layered pyrite–sphalerite, overlying and extending beyond talc units are chemical sediments.
Metamorphism, structure and stratigraphy in the Southern Park Ranges, British Columbia
Authors: Craw D.
Published: April 2011

The Southern Park Ranges lie immediately east of the Rocky Mountain Trench, near the Big Bend of the Columbia River, B.C. They are composed of quartzites, pelites and carbonates in an uninterrupted sequence from the Proterozoic Windermere Supergroup, through the Lower Cambrian Gog Group, to the Middle Cambrian Chancellor Group.Two phases of folding and metamorphism are recognized. The first phase of folding (F1) occurred before and during the first phase of metamorphism (M1), whereas the second phase of folding (F2) was associated with a second (very minor) phase of metamorphism (M2). Both F1 and F2 structures are apparently associated with the rise of the Porcupine Creek Anticlinorium, a major fold complex trending northwest–southeast across the eastern part of the study area. Associated with F2 folds are several west-dipping thrust faults, some of which terminate upwards in the cores of F2 anticlines. All structures are cut by late-stage, west-dipping normal faults.The first phase of metamorphism (M1) resulted in a Barrovian sequence of isograds such that chlorite zone rocks occur in the east and sillimanite zone rocks occur in the west. Phase equilibria studies suggest that the metamorphic temperatures in the area ranged from less than 480 °C (east) to 570 °C (west) at a pressure of approximately 5 kbar (5 × 105 kPa).The M1 isograds in the Park Ranges outline a thermal antiform whose western limb is truncated by the Purcell Fault (a major Cordilleran structure) on the western slopes of the study area.A comparison of main metamorphic phases between the Park Ranges and the Selkirk and Monashee Mountains across the Purcell Fault, suggests that the western (Selkirk–Monashee) terrane underwent temperatures approximately 40 °C higher than the study area (for equivalent metamorphic zones) and a pressure between 2 and 3 kbar (2 × 105 and 3 × 105 kPa) higher than the study area. This pressure difference suggests that there has been a minimum of 7 km post-metamorphic vertical motion on the Purcell Fault. A difference in structural style across the Purcell Fault, due to a higher ductility in the western terrane, is interpreted as a result of the difference in depth during the deformation of the two terranes.
The identification and interpretation of upper mantle travel-time branches from measurements of dT/dΔ made on data recorded at the Yellowknife seismic array
Authors: Ram A. , Mereu R. F. , Weichert D. H.
Published: April 2011

There is broad agreement among various seismological studies that the upper mantle has two regions where very high positive velocity gradients or transition zones exist. In most cases, the presence of these zones implies that two major triplications are likely to exist in the body-wave travel-time curve for distances less than 30°. Because of the difficulties in observing and identifying later arrivals belonging to the various travel-time branches, the inversion of the seismic data is often very difficult. In this paper an adaptive processing technique was employed to examine the variations in slowness that occur along the first 36 s of the short-period P-wave trains recorded at the Yellowknife medium aperture seismic array. Over 100 earthquakes from the Alaska Peninsula and California regions were selected. From the California results we were able to clearly observe the 12–13 s/deg slowness branch as a later arrival out to distances as great as 26°. Other later arrival branches as well as cusps associated with the 400 and 650 km discontinuities were not well defined even though the cross-over point as determined from slowness measurements on first arrivals were clearly located. An inversion of the data showed that the '650 km' transition zone occurred at a much shallower depth west of the array compared to the corresponding region to the south.
Early recumbent folds in the northeastern part of the northern Labrador Trough
Authors: Hynes Andrew
Published: April 2011

In the northeastern part of the Labrador Trough northwest of Fort Chimo, Quebec, a polydeformed metasedimentary sequence structurally overlies feldspathic gneisses. The gneisses are probably basement to the sediments. Rocks of the metasedimentary sequence were deformed into north-northwest vergent, isoclinal, recumbent folds and then refolded about subhorizontal northwest trending axes during the Hudsonian orogeny. The presence of early recumbent folds, apparently not involving basement, is compatible with the occurrence of gneiss domes and tight keels of metasediments in the eastern trough, as described by Dimroth, Gelinas and others. Recumbent folds like these could in part account for both the high metamorphic grades observed in the eastern trough and the commonly faulted contacts between metasediments and possible basement gneisses.
Frost mounds at Bear Rock, near Fort Norman, Northwest Territories, 1975–1976
Authors: Everdingen Robert O. van
Published: April 2011

A number of frost mounds of the frost blister type were observed at the site of a group of cold springs on the east side of Bear Rock, about 4 km west-northwest of Fort Norman, Northwest Territories, Canada. The mounds ranged in height from 2.0 to 3.0 m, with horizontal dimensions between 26 and 48 m. They contained a domed layer of ice, up to 85 cm thick, over an empty cavity up to 70 cm high, which was in turn underlain by frozen ground. Soil cover over the ice layer was 30–65 cm thick. The ice presumably formed from springwater injected under considerable hydraulic potential. New frost blisters are formed annually. Three recent frost blisters observed in June 1975 were partially destroyed by melting, slumping of the soil cover, and collapse of the ice dome by mid-September 1975. A portion of the ice lasted into summer 1976. Three new frost blisters, formed during the 1975–1976 winter, were observed in March 1976; two of these had completely collapsed by mid-June. An icing blister associated with one of them ruptured on March 21, 1976, producing a large flow of water, which lasted for several hours. A section of the icing blister subsequently subsided. Remnants of frost blisters have been observed in a spring area northeast of Turton Lake, Northwest Territories, and along the Dempster Highway in North Fork Pass and near the crossing of Blackstone River, Yukon Territory.
The late Precambrian mafic dikes of the southern Tobacco Root Mountains, Montana: geochemistry, Rb–Sr geochronology and relationship to belt tectonics
Authors: Wooden Joseph L. , Vitaliano Charles J. , Koehler Steven W. , Ragland Paul C.
Published: April 2011

During late Precambrian time three sets of mafic dikes were emplaced in southwestern Montana south of the east–west Helena embayment of the Belt Basin. The oldest dikes, intruded approximately 1455 Ma ago into both the southern Tobacco Root Mountains and the adjoining Ruby Range, are low K tholeiite in composition. The two other sets of dikes were intruded at approximately the same time, about 1120–1130 Ma ago. Both are high K quartz normative types: one is strongly enriched in Fe and is most similar to ferrobasalt or ferrogabbro in composition, the other is low in iron and differentiated along strong alkali and silica enrichment trends. The 1455 Ma old dikes and the iron-enriched 1120 Ma dikes have initial Sr ratios in the range 0.7020–0.7030 that indicate probable derivation from mantle material that has maintained a low Rb–Sr ratio (0.024) for much of the Earth's history. This mantle source is much lower in Rb–Sr ratio than that proposed for the source of dikes in the Beartooth–Bighorn Mountain area to the southeast. The iron-poor 1130 Ma old magma has an initial ratio of 0.709, which suggests contamination by crustal Sr.A strong correlation appears to exist between the timing of mafic intrusive events in the older Precambrian rocks to the south of the Belt Basin and tectonic-intrusive events within the basin. Intrusive events are recorded at 1455–1430 Ma ago both inside and outside the basin. A 1330 Ma old mafic intrusive event in the Beartooth Mountains is associated with a period of metamorphism and (or) a period of deposition in the basin. The 1120–1130 Ma old dikes are correlated with mafic flows and sills and another major period of deposition within the Belt Basin.
The geochemistry of altered volcanic rocks at Matagami, Quebec: a geothermal model for massive sulphide genesis
Authors: MacGeehan P. J.
Published: April 2011

Volcanogenic exhalative massive sulphide deposits at Matagami are associated with a bimodal suite of tholeiitic basalt and rhyolite. However, these rocks now exhibit pseudo calc-alkaline alteration trends resulting from a hydrothermal alteration process in which footwall basalt was spilitized, and the host rhyolite was chloritized. These two alteration processes were contemporaneous events, which shared a common aqueous fluid, developed within cooling submarine volcanic rocks shortly after the extrusion of rhyolite, and terminated prior to extrusion of succeeding units.The geochemistry of the Garon Lake rhyolite and underlying basalt are examined in detail. Massive quantities of Fe, Mg and Ti, and over 10 ppm Zn and 5 ppm Cu were leached from basalt during spilitization, providing 30 000 t Zn and 15 000 t Cu, or approximately 1 Mt of ore grade material per km3 of basalt. Chlorite alteration zones and massive sulphide deposits in the overlying rhyolite were enriched in all those elements depleted from basalt. This evidence suggests a geothermal model for massive sulphide genesis, where Fe, Mg, Ti, Cu and Zn were leached from footwall rocks, flushed through a geothermal system, and then precipitated at the discharge point to form chlorite alteration zones in the overlying rhyolite and exhalite deposits at the sediment–seawater interface.
New stromatolites from the Aphebian Mistassini Group, Quebec
Authors: Hofmann H. J.
Published: April 2011

New taxa are described from dolostones of the Lower Albanel Formation. The branching columnar Mistassinia wabassinon n.g. n.f. is characterized by concentric, bipartite organization and strong bimodal development of lamina shape. Straticonophyton icon n.g. n.f. occurs with Stratifera icon n. comb. in partially silicified, metre-sized colleniellid mounds characterized by extremely fine, uniform laminae with high inheritance.The application of the two independent and fundamentally different concepts of stromatolite (macromorphology) and spongiostrome (microstructure) to a more orderly taxonomy is discussed.
Triassic reptile tracks in the Lepreau Formation, southern New Brunswick, Canada
Authors: Sarjeant William A. S. , Stringer Peter
Published: April 2011

The discovery of reptilian footprints in the Lepreau Formation of southern New Brunswick affords the first direct evidence for the Triassic age of this sequence of red clastic sediments. The footprints are assigned to the ichnogenus Isocampe, but do not correspond exactly with any type described hitherto: Isocampe lepreauense ichnosp. nov. comprises quadrupedal, tetradactyl tracks with manus larger than pes, relatively broad trackway and short stride. The tracks are considered to be those of a lepidosaur, most probably lacertoid or rhynchosauroid. They indicate a late Middle to Upper Triassic age for these beds. Folds and cleavage of compressional origin, not previously recognized in the Lepreau Formation, are dated as later than Middle or Upper Triassic on the basis of the paleontological evidence.
Grenville paleomagnetism and tectonics
Authors: McWilliams M. O. , Dunlop D. J.
Published: April 2011

The determination of magnetization age is fundamental to the understanding and interpretation of paleomagnetic data from metamorphic terranes such as the Grenville Province. Assignment of absolute magnetization ages in slowly cooled rocks, although indeed possible, is difficult in practice due to variability in blocking temperatures of both magnetic and isotopic systems, and in local uplift and cooling rates. Characteristic Grenville paleomagnetic poles of likely post-metamorphic age can be grouped in a relative chronology on the basis of equal age 'thermochron' contours. These pole groups define a post-Keeweenawan loop that can explain the apparently discordant poles without invoking plate collision. As poles postdate the Grenville event, it is unlikely that paleomagnetic data from within the Grenville itself will be useful in testing collisional models for the ca. −1000 Ma orogeny.
Displacement history of the Denali fault system, Alaska and Canada
Authors: Lanphere Marvin A.
Published: April 2011

The Denali Fault system, a major crustal break in Alaska and northwestern Canada, is characterized by horizontal movement although vertical separation has been suggested for parts of the system. Essentially all of the dextral displacement on this structure apparently has occurred during the Tertiary and Quaternary. About 350 km of dextral displacement occurred between 55 and 38 Ma ago on the McKinley. Shakwak and Dalton segments and displacement there since 38 Ma ago cannot be more than about 40 km. Holocene displacement has taken place on the McKinley and Totschunda segments and the western part of the Shakwak segment; high microearthquake activity on the eastern part of the Shakwak and Dalton segments has been cited as evidence that this part of the Denali system currently also may be active.
The Hinterland Belt of the Canadian Cordillera: new data from northern and central British Columbia
Authors: Monger J. W. H. , Richards T. A. , Paterson I. A.
Published: April 2011

The Omineca Crystalline Belt of the Canadian Cordillera is flanked on the west by the Hinterland Belt, characterized by folds and faults that show predominant westward directed tectonic transport. Rocks involved in northern and central British Columbia comprise the Cache Creek Group and, to the west, various Permian, Triassic and Jurassic units. The structures in this belt record three major episodes of deformation. Earliest folds in the Cache Creek Group probably reflect latest Triassic deformation and cannot be related to the Hinterland Belt for they trend obliquely to it. In northern and central British Columbia the Hinterland Belt as a structural entity was produced by probable latest Jurassic or earliest Cretaceous deformation. Major east-dipping thrust and reverse faults, associated locally with folds and schist terranes, bring Cache Creek strata over and against coeval and younger rocks to the west. This belt was later disrupted by strike-slip faults in Late Cretaceous – Early Tertiary time.
A side-scan sonar mosaic of pockmarks on the Scotian Shelf
Authors: Josenhans Heiner W. , King Lewis H. , Fader Gordon B.
Published: April 2011

Pockmarks, cone-shaped depressions that occur in unconsolidated fine sediments at the seabed, are generally thought to be formed by gas ascending from underlying sediments. A mosaic of pockmarks in Emerald Basin on the Scotian Shelf was constructed and the problems of mosaic construction are discussed. Within the study area pockmarks have an average depth of 6 m, an average diameter of 85 m and cover up to 18% of the seabed. Pockmarks that occur in thin clay (LaHave clay) are generally < 5 m deep and those in thick clay are up to 15 m deep. Many pockmarks are elongate in shape and show a preferred orientation, both of which may be due to the influence of bottom currents. Within the study area, the process of pockmark formation has displaced 2.5 × 105 m3 km−2 of sediment. Pockmarks on the Scotian Shelf appear to be inactive (relict) and in cases where they are buried they are referred to as ancient.
The anatomy and interpretation of an Archean volcaniclastic sequence, Noranda region, Quebec
Authors: Tassé Normand , Lajoie Jean , Dimroth Erich
Published: April 2011

Archean pyroclastic rocks at Reneault and D'Alembert in the Noranda region are composed of crystals and lithic, vitric and pumiceous fragments. The pyroclastic rocks contain two types of beds, whose primary structure sequences and other characteristics show that the deposits accumulated from different types of density flows. The first bed-type (A) is characterized by greater bed-thickness, reverse grading and the coarsest fragments in the deposit. Closest to source, the primary structure sequence in Type A beds is indicative of deposition from debris flows, but in more distal sections it suggests deposition from turbulent suspensions. The second bed-type (B) is characterized by a smaller fragment size, thinner beds, normal grading and the presence of parallel and (or) oblique stratifications. The primary structure sequence in Type B beds is similar to that observed in turbidites, which suggests deposition from turbulent suspensions of low density.Lateral and vertical variations of grain size, bed thickness and structure sequences indicate that the vent was south of Reneault and that the volcanic activity increased with time. Pillowed flows both underlie and overlie the pyroclastic units which suggests accumulation under water, but there is evidence that some eruptions were subaerial.
Structure and organization of Archean subaqueous basalt flows, Rouyn–Noranda area, Quebec, Canada
Authors: Dimroth Erich , Cousineau Pierre , Leduc Maxime , Sanschagrin Yves
Published: April 2011

Archean subaqueous basalt flows in Rouyn–Noranda area consist of several structural divisions in vertical sequence. The complete, ideal sequence of structural divisions within a typical flow is, from base to top: massive lava, pillow lava, isolated- and broken-pillow breccia (pillow breccia), and stratified hyalotuff. Any variant of this standard sequence, formed by omission of one or several of the structural divisions, has been observed. Most commonly encountered are the following four sequences: (1) massive lava – pillow breccia, associated in the field with the sequence pillow lava – ± pillow breccia, and (2) massive lava – pillow breccia – hyalotuff, associated with the sequence pillow lava – pillow breccia – hyalotuff.Lateral transitions from massive lava into pillow lava have been mapped and suggest that pillow lava is distal relative to massive lava. Large flow lobes or tubes (megapillows) are present in the transition zone. Mapping of the relations of megapillows and normal-size pillows suggests that pillows form by a budding and branching process, rather like present-day pillows observed to form during the flow of lava into the sea. Relations between massive lava, pillow lava, and pillow breccia suggest that massive lava formed by the surging advance of large volumes of hot lava of low viscosity; pillows formed at the distal flow front due to a decrease of temperature and an increase of viscosity, resulting in a decrease of the flow velocity; pillow breccias apparently formed at the waning stage of the eruption, when the supply of fresh lava was reduced. Hyalotuff apparently formed by lava-fountaining at the fissure, in shallow water.
Geochemistry of suspended particulate matter in the Saguenay Fjord
Authors: Sundby Bjørn , Loring Douglas H.
Published: April 2011

Analysis of major elements in suspended particulate matter from the Saguenay Fjord in May and September 1974 shows that the content of Si, Al, Ca, Mg, and K remain relatively constant in time and space, reflecting the constancy of the silicate mineralogy of the particulate matter. Large variations in time and space occur, however, in the content of Fe and Mn. High levels of Fe occur in particulate matter from near-bottom waters of the fjord during both time periods. Variations in the Fe/Al ratios indicate that Fe is enriched in the non-silicate fraction of the particulate matter (oxides, hydroxides, etc.) in the near-bottom waters, but not elsewhere. In contrast, Mn is enriched relative to both Al and Fe in particulate matter from intermediate depths, and varies in time and space. This is attributed to the in situ uptake of Mn from seawater and (or) the input of particles, already containing high levels of Mn, from the St. Lawrence Estuary.
Age of Aiyansh Volcano, British Columbia
Authors: Wuorinen Vilho
Published: April 2011

Previous work on Aiyansh Volcano has suggested one period of volcanic activity, about 250 ± 130 years BP. A new radiocarbon dating of 625 ± 70 years BP suggests that two eruptions have occurred.
The Rubble Creek landslide, southwestern British Columbia
Authors: Moore D. P. , Mathews W. H.
Published: April 2011

A 19th century slide, involving an estimated 25 × 106 m3 of rock, devastated Rubble Creek Valley, 80 km north of Vancouver, B.C. Breaking away from a headwall composed of late glacial dacitic lava, the slide travelled as much as 4.6 km with a maximum drop of 1060 m, thus moving on an average slope of 8.5°. Velocities, estimated from the superelevation of the slide as it moved around curves in the valley, exceed 20 m/s (72 km/h) and sliding was probably completed within 10 min. Tree-ring data indicate that the slide occurred in the fall or winter of 1855–1856. The trigger mechanism has not been identified, but the presence of an exceedingly steep original slope of the lava front, attributed to ponding against latest Pleistocene ice occupying the valley below, was clearly a contributing factor. Both the precipitous headwall and a second ice-dammed lava front are considered to be potential sources for new slides. Some evidence suggests that previous slides have occurred here since the last glaciation, about 11 000 years ago. A court ruling barring residential development in the area devastated in 1855–1856 on the grounds of future hazard to life seems justified.
A 1950 ± 60 Ma Rb–Sr whole-rock isochron age from two Kangâmiut dykes and the timing of the Nagssugtoqidian (Hudsonian) orogeny in West Greenland
Authors: Kalsbeek F. , Bridgwater D. , Zeck H. P.
Published: April 2011

Thirteen samples from two Kangâmiut dykes give a Rb–Sr whole-rock isochron age of 1950 ± 60 Ma. This age is interpreted as the age of intrusion of the dykes. The post-dyke Nagssugtoqidian orogeny took place between ca. 2000 and ca. 1800 Ma and can be correlated with the Hudsonian in Canada and the Laxfordian in Scotland.
Lower Devonian Gastropoda from the Canadian Arctic Islands
Authors: Rohr David M. , Smith R. E.
Published: April 2011

Gastropods from Lochkovian (Lower Devonian) beds on Prince of Wales and Baillie-Hamilton Island, Canadian Arctic, compose a small but relatively diverse part of a brachiopod-dominated fauna. The fossils probably represent subtidal photic, and shallow subphotic zone environments. Seventeen species are described including six new species: Odontomaria linsleyi (an openly coiled septate species), Phanerotrema perryi, Gyronema thorsteinssoni, Cyclonema (Cyclonema) supralirata, Platyceras (Platyceras) daschi, and Subulites sinistralis. Based on the limited amount of previous work on Lower Devonian gastropods, the gastropod fauna appears to have Old World affinities, with genera such as Lytospira and Codonocheilus representing holdovers from the Silurian.
Upper Silurian trilete spores and other microfossils from the Read Bay Formation, Cornwallis Island, Canadian Arctic
Authors: McGregor D. C. , Narbonne G. M.
Published: April 2011

A diverse palynomorph assemblage of trilete spores, tetrads, acritarchs, chitinozoans, scolecodonts, and fragments of arthropods, ?hydrozoans, ?graptolites, and possibly nematophytalean and vascular plants occurs 20 m above the base of member B of the Read Bay Formation at the type section on eastern Cornwallis Island, District of Franklin. This assemblage, here described briefly, is late Ludlow according to faunas above and below. The palynomorphs, other fossils, and stratigraphic framework indicate that the shales of member B were deposited in a sheltered near-shore marine environment. One new species of trilete spores, Retusotriletes chartulatus McGregor, is erected.
Patterns of total strain in the crestal region of immature diapirs
Authors: Schwerdtner W. M. , Sutcliffe R. H. , Tröeng Björn
Published: April 2011

Conformable domes can result from diapirism as well as cross buckling and other types of cross folding. The total-strain pattern of natural structures offers a means of discriminating between diapiric domes and nondiapiric domes. Similarly, one may distinguish between diapiric ridges and other types of antiforms.Immature diapirs in metamorphic terrains and appropriate quantitative models are characterized by crestal zones of horizontal extension. Similar zones occur in the convex-hinge regions of very competent buckles and the adjacent incompetent matrix of fold models. But these model experiments are rarely applicable to natural buckle folds in metamorphic terrains, which typically involve low competency contrasts. Where upright buckle folds can be identified by means of independent evidence, their hinge zones are generally devoid of stratiform foliation and other features due to horizontal extension. An Archean gneiss dome of the northwestern Ontario is subjected to structural analysis, and interpreted as an immature diapir on the basis of widespread subhorizontal foliation about the dome's centre. The strain pattern of the gneiss dome corresponds to that of salt diapirs in New Brunswick.
Frequency spectrum of the electrical properties of seawater-saturated ocean crust and oceanic island basalts
Authors: Drury M. J.
Published: April 2011

The frequency spectrum of electrical properties of seawater-saturated oceanic crust and oceanic island basalts has been studied. All samples showed at least two of three possible polarization mechanisms: dielectric, membrane, and electrode. The membrane polarization appears to result from the presence of clay minerals, which frequently line or block pores and cracks in the samples. The dominant conduction mechanism in the samples is pore fluid (seawater) conduction, but the electrical properties of samples containing clay are modified by the clay. The results support the suggestion by Drury that a model of three conduction mechanisms acting approximately in parallel—pore fluid, clay mineral, and metallic mineral conduction—describes the electrical properties of seawater-saturated basalts.
Rock glacier types and their drainage systems, Grizzly Creek, Yukon Territory
Authors: Johnson P. G.
Published: April 2011

Moraine rock glaciers, talus-derived rock glaciers, and avalanche rock glaciers are described from Grizzly Creek. The main moraine rock glacier has a number of flow lobes of different ages as indicated by lichen and vegetation development. On many of these surfaces there is evidence for recent movement in the form of overridden vegetation surfaces and unstable frontal slopes. Meltwater drainage through the landform is slow, allowing precipitation of the suspended sediment load, and as resurgences do not occur for all of the inflow the possibilities of addition to the ice core or drainage below Grizzly Creek gravels are discussed. The talus-derived rock glaciers differ morphologically from the moraine forms with far greater complexity of the flow ridges but with fewer flow episodes indicated. Drainage through these forms is slow and variable and indicates percolation of meltwater over an impermeable surface within the form. Avalanche rock glaciers by contrast are relatively simple morphologically and the extension from the base of the talus is attributed to ice content derived from the avalanches.
Permafrost mapping by audiofrequency magnetotellurics
Authors: Koziar A. , Strangway D. W.
Published: April 2011

The audiofrequency magnetotelluric (AMT) method has been used to study permafrost thickness near Tuktoyaktuk, N.W.T. in the Mackenzie Delta. In the frequency range of 10 Hz–10 kHz the permafrost behaves as a simple resistive layer over a conductive layer. This simple two-layer model can be inverted by asymptotic models to give a unique value for the thickness of the highly resistive frozen layer. In areas of simple layering, these results correlate well with drilling. In areas of sharp lateral variations in resistivity, depths tend to be underestimated. Unlike other electrical methods, AMT is not hampered by the presence of a surface melt layer in the summer if the conductivity–thickness product of this 'active layer' is less than about 0.03 mho (0.03 S).
Paleomagnetism and age of the Aston dykes and Savage Point sills of the Boothia Uplift, Canada
Authors: Jones D. L. , Fahrig W. F.
Published: April 2011

Oriented samples (107) have been drilled for paleomagnetic studies from diabase sills and dykes on either side of the Boothia Uplift, Canada. Six sites at Savage Point are in sills which intrude the Aston Formation; three, at Whitehead Point, north of Savage Point on the east coast of Prince of Wales Island, are in sills which also intrude these strata. Six sites in the Aston Bay area of Somerset Island are in dykes and a sill which cut the Aston Formation; the former also intrude the Hunting Formation. No meaningful results were obtained from the Whitehead Point samples. Paleomagnetic measurements on the Savage Point samples, together with new K–Ar data, strongly suggest these sills belong to the Mackenzie igneous episode (ca. 1240 Ma). The sill in the Aston Bay area apparently belongs to this episode too, whereas most of the dykes are Franklin dykes (ca. 675 Ma). One large dyke was possibly emplaced in Tertiary times. Thus the Aston Formation is older than 1240 Ma and the Hunting Formation is bracketed between 1240 and 675 Ma.
Shackanite and related analcite-bearing lavas in British Columbia
Authors: Church B.N.
Published: April 2011

New localities of shackanite and related analcite-bearing lavas have been discovered in a broad field of early Tertiary phonolite and mafic phonolite in south-central British Columbia. The development of primary and secondary analcite in these rocks is probably the result of cooling lava during and shortly after extrusion.The possibility of leucite to analcite transformation in Daly's shackanite is unlikely because of lack of petrographic evidence and a preponderance of Na2O over K2O in bulk rock composition. It is also unlikely that analcite, and particularly groundmass analcite, crystallized at great depth and was transported to surface during eruption.
Rodents of the Swift Current Creek local fauna (Eocene: Uintan) of Saskatchewan
Authors: Storer John E.
Published: April 2011

The ischyromyid rodents Reithroparamys sp., Ischyrotomus cf. I. compressidens, and Is-chyrotomus cf. I. eugenei are present in the Swift Current Creek local fauna (Eocene: Uintan), Cypress Hills Formation of Saskatchewan. Co-occurrence of these taxa strengthens correlation with the fauna of the Myton Member, Uinta Formation of Utah.
A new fossil occurrence from the Vendom Fiord Formation (type area), Ellesmere Island
Authors: Perry D. G.
Published: April 2011

Probable reworked Lochkovian (early Early Devonian) brachiopods and conodonts were recovered from the basal clastic beds of the Vendom Fiord Formation in the type area on central Ellesmere Island. Although most of the fossils are reworked from underlying strata, none appear to be younger than Lochkovian. Data obtained by other workers from more northerly exposures of the Vendom Fiord Formation show that the lower part of the formation is no older than late Pragian (middle Early Devonian). Elsewhere, the North American Early Devonian eustatic sea-level minimum occurs in the Pragian and is followed by transgressive deposits of late Early Devonian age of which the Vendom Fiord Formation possibly represents the basal transgressive unit in the Arctic Archipelago.