bluuebunny/crossref_metadata_2025 huggingface dataset:
Some inferences on the upper mantle structure and deep processes occurring in the northwest Pacific
Authors: Sychev P. M. , Tarakanov R. Z.
Published: April 2011

Results of analysis of gravimetric and seismological data for the island arc-trench systems and adjacent regions of the Northwest Pacific are briefly summarized. Gravimetric data indicate anomalously dense zones beneath the trenches, where densities 0.1 to 0.15 g/cm3 greater than normal occur to depths of the order of 100 km, while beneath the island arcs the Upper Mantle appears to be less dense than normal by −0.05 to −0.1 g/cm3. In general the gravimetric data agree well with seismic data, which suggest that the dipping high-velocity layer is not a continuation of the oceanic lithospheric plate, from which it differs in physical properties. Earthquake foci distribution also does not support the concept of a subsiding lithospheric plate. The main earthquake focal plane transects the surface not in the deep trenches, but on their steep slopes, and a second earthquake focal plane dips towards the ocean. Available data agree better with theories of differentiation of the mantle at large depths and with discontinuous movement of lighter components due to difference in lithostatic pressure.
Depth of burial from remanent magnetization: the Sudbury irruptive at the time of diabase intrusion (1250 Ma)
Authors: Schwarz E. J.
Published: April 2011

Forty-four oriented drill cores were collected from a 65 m thick northwest-trending olivine diabase dyke (1250 Ma) and the norite (1900 Ma) with which the dyke is in contact. Thermal and alternating field treatments show that the magnetic direction of the dyke and that of the norite up to 45 m from the contact are parallel and conform to directions reported by others for the diabase dyke swarm near Sudbury. Between 45 m and 70 m (end of outcrop) hybrid directions are observed intermediate between that of the dyke and that reported by others for the norite. The NRM unblocking temperature spectrum and the inferred acquisition of VRM at higher temperatures in the norite suggest that a maximum temperature of 450 °C was attained in the hybrid zone at about 50 m from the dyke. Calculation of the thermal effect of the diabase intrusion on the norite in the hybrid zone indicates a temperature increase of 270 °C. Consequently, the ambient temperature of the norite at the time of intrusion was 450 – 270 = 180 °C (± 30). Taking the contemporary geothermal gradient at 20 to 25 °C/km the present erosion level of the norite is estimated to have been at a depth of 7 km (± 25%) about 1250 Ma ago. This suggests that a 7 km thick layer of the pre-Grenvillian part of the Canadian Shield has been removed by erosion during the past 1250 Ma if the Shield can be regarded as a single block that has not been tilted. Similar work elsewhere in the Shield may show the extent of these vertical movements.
Structural evidence of the evolution of fore-arc basins off South America
Authors: Coulbourn W. T. , Moberly R.
Published: April 2011

The continental margin of southern Peru and northern Chile was surveyed during the 1973 and 1974 expeditions of the research vessel Kana Keoki. Seismic reflection profiles reveal three large basins at about 1000 m depth between Mollendo, Peru (17°00′ S) and Iquique, Chile (20°00′ S). Only small basins and discontinuous terraces are seen on profiles crossing the Iquique-to-Antofagasta, Chile (23°30′ S) segment of the continental margin.The structural cross-sections of the basins resemble those of arc-trench gaps. The undeformed uppermost reflectors probably represent turbidites, as evidenced by displaced shallow-water benthic foraminifera and coarse sands in cores. Deeper reflectors are generally inclined land-ward, with dips and deformation increasing in the lower reflectors down to about 1.5 seconds penetration. Seaward convergence of these reflectors indicates a progressive shoreward migration of the axis of maximum sedimentation. If the deeper beds are also turbidites, this axis marks the axis of the sediment trap on the continental slope.The structure is consistent with subduction of an oceanic plate and obduction of a portion of its sediment cover. The imbricate stacking of obducted material is lifting an anticlinal ridge visible in most traverses across the trench side of the basin. The growing ridge is deforming the older sediment trapped in the upperslope basin and shifting the locus of deposition shoreward. The irregular distribution of the basins apparently is a product of culminations and depressions of the surfaces of imbricate fault planes. These undulations may result from the transference of the irregular structure of the oceanic plate to the face of the continental block.
The structure of the crust and upper mantle under the highest ranges of the Canadian Rockies from a seismic refraction survey
Authors: Mereu R. F. , Majumdar S. C. , White R. E.
Published: April 2011

In the Project Edzoe seismic experiment, the seismic waves from a series of shots fired in Greenbush Lake near Revelstoke B.C. were recorded by the University of Western Ontario at approximately 100 stations along two seismic lines. The first began in the Rocky Mountain Trench, crossed the mountains near Jasper, Alberta and then extended NE across the Plains to Fort McMurray, Alberta, the maximum distance from the shotpoint being 800 km. The second line was roughly in line with the shotpoint and extended from Stanley Falls to Whitecourt, Alberta.An interpretation of the results revealed that the topography of the Moho under the highest ranges of the Rocky Mountains is relatively flat when compared with results from similar experiments on the Canadian Shield. In addition to the typical Pn layer, a very high velocity upper mantle layer (8.5 to 8.8 km/s) also exists at a depth of 60 km or approximately 10 km below the Moho. An interesting feature observed on the record sections was the echelon pattern formed by the crustal P wave trains. From a study of theoretical amplitudes it was found that this pattern could be explained by the presence of large positive gradients within the lower crust coupled with a relatively low value of Q near the Moho.
Pulsating pingos, Tuktoyaktuk Peninsula, N.W.T.
Authors: Mackay J. Ross
Published: April 2011

Field studies have been carried out on two pingos on Tuktoyaktuk Peninsula, N.W.T. One pingo was studied from 1969–1976; the other was studied from 1974–1976. Precise levelling of bench marks in permafrost shows that the tops of these pingos alternately rise and subside in response to the rate of accumulation and loss of water beneath them. The water lenses may exceed 50 cm in depth. The high pore water pressure that causes pingo uplift is produced by pore water expulsion adjacent to the pingo, where the thickness of permafrost is 2 to 3 times the pingo height. The pore water pressure beneath the permafrost surrounding the pingo may approach 100% of the lithostatic pressure. When uplift from the water lens exceeds the strength of the pingo, peripheral failure occurs, water escapes as a spring, and the pingo subsides. Pulsating pingos seem characterized by long radial tension cracks which extend far onto the drained lake floor.The pulsation of pingos has also been experimentally achieved by drilling holes through two pingos to release spring flow from subpingo pore water. The field evidence, from precise before-and-after surveys, indicates that the two pingos and their adjacent drained lake floors are virtually 'afloat' on subpermafrost water.
Revised stratigraphy of the Takla Group, north-central British Columbia
Authors: Monger J. W. H. , Church B. N.
Published: April 2011

The Takla Group of north-central British Columbia as originally defined contained volcanic and sedimentary rocks of Late Triassic and Jurassic ages. As redefined herein, it consists of three formations in the McConnell Creek map-area. Lowest is the Dewar Formation, composed of argillite and volcanic sandstone that is largely the distal equivalent of basic flows and coarse volcaniclastic rocks of the Savage Mountain Formation. These formations are overlain by the volcaniclastic, basic to intermediate Moosevale Formation. These rocks are Upper Triassic (upper Karnian and lower Norian). They are unconformably overlain by Lower Jurassic rocks of the Hazelton Group.
On the pressure dependence of solidus temperatures and electrical conductivity during melting of JOIDES Leg 37 samples
Authors: Schloessin H. H.
Published: April 2011

Premonitory decreases (to ~10−4 S cm−1) in the electrical conductivity of oceanic basalts found at the onset of partial melting signify breaks in solid phase coherence by the formation of isolated melt pockets, latent heat effects, and gradual interchanges in the dominant conduction mechanisms from extrinsic electronic in the solid to ionic in the melt phase. The conductivity rises sharply (to ~90 × 10−1 S cm−1) on formation of a contiguous melt phase. The corresponding formation temperature, which measures also the permeability of a heterogeneous, polycrystalline aggregate by the melt phase forming first appears to be as significant as the solidus temperature in a homogeneous system. Temperatures correlated with incipient melting lie on or parallel to (~150 °C below) the slope of the established solidus for gabbro–eclogite or peridotite materials; early crystallization points cluster along the garnet line. The pressure coefficient, (ΔT/ΔP) value, for the formation temperature of a contiguous melt phase in all of the samples comes closest to the slope of the melting curve for diopside. However, taking into account sample origin, the corresponding (ΔT/ΔP) values are found to vary between 8.7 and 24.5 °C kbar−1 (87 and 245 °C GPa−1). There are some indications of effects on solidus temperatures and conductivity values which are related to variations in chemical composition, especially Si, Al, and Fe concentrations. The conductivity decreases with increasing si-excess, increasing Al-component, and decreasing Fe-fraction of the femic component.
A centrifuge furnace for separating phases at high temperature in experimental petrology
Authors: Roeder Peter L. , Dixon John M.
Published: April 2011

In order to accelerate the gravitational settling and floating of crystals in silicate liquids at high temperatures we have built a furnace which operates at 1200 °C while being rotated in a centrifuge at 2200 RPM. The heating element is constructed of Kanthal wire wound around a 14.5 mm ID mullite tube and the temperature is controlled and measured by two Pt–10 Rh thermocouples. The power and thermocouple circuits are connected, through a slip-ring assembly mounted on the centrifuge shaft, to a temperature controller and potentiometer.The rotation of the furnace and experimental charges produces a gravitational force 700 times that of earth gravity (g). This increases the settling and floating rates for crystals or immiscible liquids by a factor of 700 over the rates at 1 g. A 1-h run in the centrifuge is thus dynamically equivalent to a 1-mo run at 1 g. Preliminary experiments with basaltic liquids containing olivine, pyroxene, plagioclase, and magnetite crystals are described.
The upper mantle of southern British Columbia
Authors: Wickens A. J.
Published: April 2011

A concentration of temporary and permanent long-period stations has been used to record Rayleigh and Love waves over a region bounded by Vancouver Island in the west and a line approximately 400 km to the east. Phase-velocity information for both Rayleigh and Love waves has been calculated and inverted to provide estimates of models along the profiles. Generalized matrix inversion techniques have been employed to set confidence limits on the models. No significant upper-mantle low-velocity zone was detected under Vancouver Island or the adjacent coastal region. To the east a shallow upper-mantle low-velocity zone dipping to the northeast was required to fit the data. The transition from crust to mantle was sharper and more prominent to the northeast than to the southwest.
Paleomagnetism of the upper Keweenawan sediments: the Nonesuch Shale and Freda Sandstone
Authors: Henry Steven G. , Mauk Frederick J. , der Voo Rob Van
Published: April 2011

The natural remanent magnetization of the upper Keweenawan Nonesuch Shale and Freda Sandstone has been analyzed with thermal, alternating field, and chemical demagnetization techniques. The results of this study are in good agreement with previously published works by DuBois and by Vincenz and Yaskawa, but place a tighter constraint on the North American apparent polar wander path. Fifty-eight samples, representing nearly 900 m of section, have been collected from the flanks of the Porcupine Mountain uplift. From principally thermal demagnetization analyses, a mean direction of primary magnetization has been calculated for the Nonesuch Shale, with declination 279.8°, inclination +9.8°, yielding a virtual geomagnetic pole position at 176.5° E, 10.3° N, and for the Freda Sandstone, with declination 271.3° inclination + 0.7°, yielding a virtual geomagnetic pole at 179.5° E, 1.2° N. A group of intermediate (secondary) components of magnetization is removed between temperatures of 350 °C and 550 °C, yielding well clustered directions. Its mean direction with declination 280.6°, inclination −9.5°, resulted in a virtual geomagnetic pole at 169.2° E, 3.7° N. This secondary magnetization is assumed to be of chemical origin and is most likely associated with the late Precambrian copper mineralization of the Nonesuch Shale. By thorough sampling of the stratigraphic column it is possible to infer the general direction of motion of a plate as the sediments were deposited. The motion of the North American plate as observed in the upper Keweenawan magnetizations is in agreement with the previously published polar wander paths for the late Precambrian.
The geochronology of the granitic rocks along the Bear–Slave Structural Province boundary, northwest Canadian Shield
Authors: Frith Rosaline , Frith R. A. , Doig R.
Published: April 2011

Archean granitic rocks along the southern Bear–Slave boundary fall into three age groups: the oldest are 3000 Ma old intrusive tonalites and granodiorites that form the basement to the Yellowknife Supergroup; the second are syn-volcanic granitic intrusions of ~ 2700 Ma; and the youngest are ~ 2560 Ma granitic and migmatitic diapirs formed in part from supracrustal and granitic rocks. Two Proterozoic thermal events are recognized within the Slave Province. A ~ 2300 Ma event may be related to early rift breakup of the Archean crust and is recorded in Rb–Sr whole-rock and K–Ar mineral systems. A ~ 1970 Ma event was less intense but may be related to further rifting of the Archean and to fault-block depression of the Indin Lake supracrustal basin, the intrusion of a group of granodioritic stocks, and the formation or granitic pegmatite.Within the Bear Province, evidence of a ~ 2700 Ma intrusive event and a ~ 2300 Ma thermal event are preserved in Rb–Sr whole rock systems. Practically all the granitic rocks of the Bear Province, including the Hepburn batholitic rocks, are thought to have been derived wholly or partly from Archean rocks. The main period of Hudsonian deformation and metamorphism was accompanied by a diapiric remobilization of the Archean basement about 1800 Ma ago. Twelve Rb–Sr isochrons, as well as other published geochronologic data from the region, support these conclusions.
A subdivision of the western English River subprovince
Authors: Beakhouse G. P.
Published: April 2011

In the western pan of the Superior province, gneisses and plutonic rocks of the English River subprovince form a 100 km wide, east trending unit bound on both north and south by metavolcanic-granitic subprovinces. Recent investigations have resulted in a major twofold subdivision of the western portion of the English River subprovince. The northern part of the subprovince, termed the Ear Falls – Manigotagan gneiss belt, is characterized by a preponderance of sedimentary gneiss that records the development of a major Early Precambrian sedimentary basin. The southern part, termed the Winnipeg River batholithic belt, is a dominantly plutonic terrain with subordinate felsic gneissic rocks and minor metavolcanic and metasedimentary rocks. This latter belt records the almost complete obliteration of a greenstone terrain of unknown age and extent by felsic plutonism. Regional seismic, gravity, and magnetic data reflect the differing physical characteristics of the two bells. The Ear Falls-Manigotagan gneiss belt has a thicker granitic crust, thinner lower crust, thinner total crust, higher Bouguer gravity values, and lower intensity and shorter wavelength magnetic anomalies than the Winnipeg River batholithic bell.
Macroinvertebrate teilzones and episodic faunal changes from an Upper Ordovician flysch in Quebec
Authors: Bretsky Peter W.
Published: April 2011

The present study reviews the chronological distribution of Upper Ordovician benthic marine macroinvertebrates from the most complete Upper Ordovician exposure in the St. Lawrence Lowlands. Pelecypods and brachiopods, associated with lesser numbers of bryozoans and gastropods, are preserved in fine-grained terrigenous clastics that comprise a thick (800 m) and almost continuously exposed section of Lorraine flysch in the Nicolet River Valley, Quebec. I was able to identify 122 species-level taxa within 407 discrete bedding plane samples, and here publish the teilzones for 70 of the most abundant species. These species are preserved within a flysch sequence of the tectonically parautochthonous domain.After the earliest colonization of the basin by a mud-bottom brachiopod and pelecypod fauna, episodic introductions are most often associated with the development of bryozoan thickets. Each of the major disappearances from this portion of the Nicolet Basin followed soon after a sudden introduction of new species into the area; determination of whether or not these introduction–disappearance couplets are cause and effect requires further, more detailed bed-by-bed studies of species replacements.
The Barnum Lake Pluton, Thunder Bay, Ontario
Authors: Kehlenbeck Manfred M.
Published: April 2011

North of Thunder Bay. Ontario, rocks of the Shebandowan–Wawa and Quelico Bell form the site for a number of plutons. These intrusions are distributed in an east–northeast trending line over a distance of 45 km. The Barnum Lake Pluton occupies a central position in this zone and has been emplaced into pelitic to semipditic metasedimentary schists and gneisses.The major rock type is a quartz monzonite in which composite megacrysts of feldspar occur abundantly. Composition of the matrix varies from quartz dioritic to tonalitic. Mafic-rich inclusions confined to a narrow zone paralleling the contact are of dioritic to monzodioritic composition.Major element and mineralogical variations in the rocks are primarily caused by magmatic processes. No evidence of partial melting has been found in the enclosing rocks.The internal structure of the pluton is the result of primary flow. A high degree of conformity characterizes the foliated border phase, contact, and the attitude of the country rocks.Development of contact metamorphic textures in the regionally metamorphosed metasedimentary sequence suggests a late syntectonic emplacement for the pluton.
Iron-rich basaltic komatiites in the early Precambrian Vermilion District, Minnesota
Authors: Green John C. , Schulz Klaus J.
Published: April 2011

Pillowed basalts showing relict skeletal calcic augites, are present in several parts of the lower Precambrian Newton Lake Formation near Ely, Minnesota. Chemical analyses presented here show these rocks to be low in Al2O3 and SiO2, and high in FeO compared to tholeiites, and to be similar though not identical to many basaltic komatiites reported elsewhere.
The stability of ice-push features, Mackenzie River, Canada
Authors: Mackay J. Ross , MacKay D. K.
Published: April 2011

Ice-push features have been studied along the Mackenzie River through the 1966–1975 period in order to determine the long term stability of the features. The principal field method was to paint a series of parallel lines, across an ice-push feature, and then to measure changes in subsequent years. The ice-push features were: boulder pavements with tightly embedded boulders; loose boulder pavements with the rocks resting on a bouldery matrix; loose boulders; ice-push island buttresses; and rhythmically spaced boulder ridges. The stability of a feature is directly correlated with the embedment depth of the boulders, for the deeper the burial the more stable the boulder. Boulder pavements, the most stable feature, may persist for decades, if not centuries. The overriding action of rock shod river ice tends to align the boulders with their long axes parallel to the river bank, to size sort the pavement boulders so that the sizes decrease downstream, and to abrade and striate the pavement surface. Loose bouldery areas can change from breakup to breakup. The localization of bouldery ice-push features reflects, in general, a nearby source of stony till. Ice-push features may occur high above the flood limit in the form of driftwood, bulldozed heaps, and a trimline. The melting of stranded river ice produces a variety of melt features which help to modify the river banks.
Dynamic clustering and strong patterns recognition: new tools in automatic classification
Authors: Lefebvre Denis , David Michel
Published: April 2011

The dynamic clustering method (D.C.M.) developed by Diday is a nonhierarchical classification procedure which can help the geologist who is faced with the problem of forming groups among a multidimensional population of chemical analyses. Instead of computing the similarity between every possible pair of elements of a population, the D.C.M. suggests the use of a set of nuclei which will act as a template in the process of grouping elements together to form a partition of the population. By using the concept of similarity between an element and a group of elements, called a nucleus, the D.C.M. will assign a group number to every individual of the original population.When the first partition has been completed, the more representative elements of the groups are chosen and combined into an improved set of nuclei. This set will then be used to perform a second grouping and the whole process will be repeated over and over until no improvement can be achieved by an other iteration. The result is a local optimum, i.e. a stable partition into a given number of groups. The D.C.M. can be applied several times to the same set of data to generate different local optima (the starting set of nuclei being different). By grouping the elements which were classified together for every local optimum, a partition into an equal or greater number of groups can result. This is the concept of strong patterns.Three hundred and thirty-three rocks of the Monteregian Hills petrogenetic suite were classified on the basis of their content in ten major elements. Five major groups, corresponding to five different rock types could be easily recognized and discriminated without any a priori assumptions. It is suggested that the algorithms presented here could be used to achieve more subtle partitioning problems, efficiently and economically, on larger sets of data.
Some geomorphic effects of a catastrophic flood on the Grand River, Ontario
Authors: Gardner James S.
Published: April 2011

A flood of unprecedented magnitude was recorded on the Grand River in southwestern Ontario on May 16–17, 1974. Peak discharge recorded at Galt has a return period of about 1 in 500 or a probability of 0.20 in any given year. Rare, high magnitude floods are of interest to the geomorphologist for the work they do on the terrain. Channel, floodplain, and valley side features produced by the 1974 flood were mapped and described on a reach of the Grand and its tributary, the Conestoga River. Erosional and depositional effects were minor except in the vicinity of man-made obstructions such as bridge piers where scour was evident. The minor geomorphic impact of the 1974 flood suggests that the Grand River valley is geomorphologically well-adjusted to handling large discharges. The findings coincide with observed effects of other high magnitude floods described in the literature.
Coleoptera fossils: their potential value for dating and correlation of late Cenozoic sediments
Authors: Matthews Jr. John V.
Published: April 2011

Coleoptera (beetle) fossils play an important role in paleoecological research, but as yet have contributed little information bearing on dating and correlation. The reason for this is that most Quaternary fossils represent extant species, precluding the evolutionary approach to dating, while the rarity and poor preservation of Tertiary beetle fossils, many of which are from extinct species, seriously limit their application to stratigraphic studies.Tertiary beetle fossils recently discovered in Arctic Canada and Alaska are both well preserved and abundant. Most of them represent extinct species that are closely related to living forms, hence they have potential stratigraphic value. In one case treated herein comparison of fossils of an Alaskan Tertiary species with those of a related species from the Beaufort Formation on Meighen Island (Canadian Arctic Archipelago) implies that the latter sediments were deposited less than 5.7 Ma ago. However, this conclusion requires testing because it is at odds with the date on Meighen Island exposures reached by study of fossil plants. I submit that further study of the insect fossils from the Beaufort Formation and other late Tertiary sites will help resolve such problems of dating and correlation.Quaternary beetle fossils have stratigraphic value even though fragments of that age represent for the most part only existing species. For example, it has been shown that late Pleistocene fossils of stenothermal Coleoptera species can provide a sensitive record of climatic change, and thus such fossils may be used for site to site correlation in areas where climatic history is well documented. In exceptional cases beetle fossils appear to provide a more accurate basis for correlation than even fossil pollen.
The Harp dikes and their relationship to the Helikian geological record in central Labrador
Authors: Meyers R. E. , Emslie R. F.
Published: April 2011

The Harp olivine diabase dikes, of Neohelikian age, form an east-northeast trending swarm that cuts rocks of the Harp Lake Complex in central Labrador. The petrography, and rock and mineral chemistry of the dikes indicate that they are transitional in character between tholeiitic and alkalic compositions. The major element chemistry of the dikes is similar to basaltic magmas from other comparable continental settings and in particular closely resembles basalts and diabase sills of the Neohelikian Seal Lake Group.Correlation of the Seal Lake – Harp dikes magmatism is suggested with two other groups of hypabyssal intrusions of olivine gabbro east and southeast of the Seal Lake synclinorium (Michael gabbros and diabase dikes in the Mealy Mountains complex). All of this basic magmatism may have been related to a Neohelikian zone of continental rifting or incipient rifting. Intrusion and extrusion of basic magma under conditions indicative of crustal extension closely follows, or is associated with, uplift and erosion of anorogenic anorthosite–'granite' complexes in other places in the world and is inferred to be a consequence of a continuing evolving process of mantle–crust interactions; in Labrador, the process began in the Paleohelikian with intrusion of major anorthosite–adamellite complexes.
Second microearthquake survey of the St. Lawrence Valley near La Malbaie, Quebec
Authors: Leblanc G. , Buchbinder G.
Published: April 2011

A second microseismicity survey was conducted in the La Malbaie region during 2 summer months of 1974. Up to 19 stations were occupied simultaneously for most of the period. Thirty-four microearhquakes were located using at least four stations; the epicenters cover a region of about 70 × 40 km, centred in the St. Lawrence River. Thirty-three of the events are within the station configuration. All hypocenters are in the Precambrian rocks of the Grenville Province at an average focal depth of 11 km; none was located in the Ordovician sediments. Six fault-plane solutions were obtained, all having one nodal plane striking from north to northeast; thrust motion is predominant. On the basis of the confined and clearly delineated distribution of the hypocenters the influence of the Charlevoix impact structure on the length of the active zone is again proposed; this idea had already been advanced after the first microearthquake survey in 1970. The conjunction of this structure with Logan's line could also have some influence on the seismicity. Strikingly, both the focal parameters, and rate of occurrence of 1 event per 2 days observed in the two surveys are in agreement. Finally it is suggested, in view of the confined zone of microactivity, that the epicentral distribution of historical events could be regarded as less extensive than it appears.
The stratigraphy and depositional environment of the Aphebian Snyder Group, Labrador
Authors: Speer J. Alexander
Published: April 2011

The Snyder Group is an Aphebian sedimentary sequence unconformably overlying Archean rocks that has undergone deformation and a medium to high grade contact metamorphism as the result of the emplacement of the Elsonian Kiglapait intrusion. Five lithostratigraphic units totaling 239 m in thickness have been recognized; in ascending order they are: (1) a lower quartz arenite with local arkosic arenites, pelites, conglomerates and a discontinuous basal conglomerate; (2) a manganiferous silicate iron formation; (3) a marble with associated calc-silicates and quartzites; (4) a sphalerite- and pyrrhotite-bearing quartz-rich, graphitic siltstone; and (5) an upper quartzite. The several intrusive rocks are largely basic and intermediate in composition and are grouped as being emplaced either before or after the contact metamorphism by the Kiglapait intrusion. Collectively, their sills and dikes have expanded the section to 355 m.The lower and upper quartzites with their high maturity; poly modal festoon, trough crossbedding; reactivation surfaces; flaser and lenticular bedding; ripple marks; graded bedding; and conglomerates were probably deposited on a shallow, subtidal, tide- and current-dominated sand flat dissected by tidal channels. The few metapelites record deposition during an occasional less turbulent environment. The fine grain size, intraformational conglomerates, cross-laminations, and thin laminations of the intermediate formations indicate that they were deposited in a quiet, probably shallow water environment disturbed only by occasional storms. The sedimentary structures, lithologies and thin, sheet geometries of the beds suggest that the Snyder Group represents a siliciclastic sea shelf sedimentation, which, if reconstructions of the North Atlantic craton are correct, was epicontinental.
Overturned Nicola and Ashcroft strata and their relation to the Cache Creek Group, Southwestern Intermontane Belt, British Columbia
Authors: Travers William B.
Published: April 2011

The Lower Jurassic, Ashcroft Formation contains a thick section of carbonaceous marine shale and a few graded sandstones. Along the south and east margins of the Ashcroft Basin, Ashcroft strata rest unconformably on calc-alkaline and alkaline volcanic flows and sediments of the Upper Triassic, Nicola Group. On the west margin Nicola and Ashcroft strata lie against mélange of the Cache Creek Group. This contact is faulted in some places, but it may be a depositional unconformity elsewhere.South of Cache Creek village, overturned allochthons of Nicola strata were placed on top of Ashcroft beds in Early Jurassic time before Ashcroft sediments were lithified. Turbidity currents flowed southeast contemporaneous with sliding or thrusting of allochthons.Near the Guichon Creek Batholith, the Ashcroft Formation contains a disconformity that separates Sinemurian–Pliensbachian from Callovian strata. However, in the western part of the Ashcroft basin strata appear continuous from Sinemurian–Pliensbachian to Callovian. The Guichon Creek Batholith was emplaced into Nicola strata along the eastern edge of the Ashcroft Basin about 200 Ma ago (late Sinemurian*) and was quickly unroofed to provide granitic debris to the basin.The Ashcroft Basin appears to have been an early Mesozoic outer arc basin. It formed seaward of calc-alkaline magmatism and landward of and possibly on top of a mélange. Middle or Late Triassic radiolaria found in the Cache Creek show that deformation of the mélange took place as late as Late Triassic time. Arc-directed thrusting and sliding may be gravity processes due to elevation of the outer arc ridge during subduction.
Magma mixing in the Flavrian pluton, Noranda area, Quebec
Authors: Goldie Raymond
Published: April 2011

The Archean Flavrian pluton is composed of quartz gabbroic, trondhjemitic, tonalitic and hybrid rocks. Field relationsips indicate that, when trondhjemitic magma was emplaced, some quartz gabbro was solid and some was still mobile.The tonalites are homogenous rocks which were formed when quartz gabbroic and trondhjemitic magmas mixed, largely by a process of diffusion down chemical potential gradients. The most characteristic feature of the tonalites is the presence of large, elongated, branching and curved pyroxene crystals. These crystals owe their unusual size and habits to high levels of pre-nucleation supersaturation, a condition which in turn resulted from the mixing of magmas.The hybrid rocks are heterogeneous mixtures of quartz gabbro, tonalite and trondhjemite. They were produced when quartz gabbroic and trondhjemitic magmas mixed turbulently.Because they are thought to indicate the paleotectonic environment, field relationships indicative of coexisting acid and basic magmas should be routinely recorded during mapping.
Geochemistry of Paleozoic granitoid plutons from contrasting tectonic zones of northeast Newfoundland
Authors: Strong D. F , Dickson W. L.
Published: April 2011

Granitoid plutons of similar (Silurian–Devonian) age intrude four of the tectono-stratigraphic zones of northeastern Newfoundland, and show systematic petrographic and chemical differences corresponding to the tectonic zone in which they occur. Those intruding the dominantly mafic volcanic and sedimentary rocks of the Botwood and Exploits Zones are dominated by calc-alkaline hornblende–biotite bearing granodiorite, quartz diorite and granite. Those intruding the metamorphic rocks of the Gander Zone are two-mica garnet-bearing 'leucogranites' mainly in metasedimentary rocks, and microcline – megacrystic biotite granites and quartz monzonites, mainly in gneissic terrains. The Gander Zone plutons are more silicic and have lower Na/(Na + K) and K/Rb ratios than those of the Botwood and Exploits Zones, although the Rocky Bay pluton, close to the boundary between them, shows some transitional features. This close correspondence between granitoid plutons and crustal rocks of different tectonic settings is taken as evidence for their formation by partial melting of the crustal rocks.
A sub-critical seismic crustal reflection survey over the Aulneau batholith, Kenora region, Ontario
Authors: Green A. G. , Hall D. H. , Stephenson O. G.
Published: April 2011

A sub-critical seismic reflection survey has been conducted across the Aulneau granite batholith in northwest Ontario. Shot to receiver distances ranged from 2.23 to 71.9 km and the total amount of explosives used for each shot–receiver configuration ranged from 54 to 327 kg. Multiple shots with vertical stacking, frequency filtering and time varying velocity filtering were used to increase the signal to noise ratio for each trace. Reflections from shallow vertical faults and deep horizontal crustal discontinuities were observed on the processed records. From these data a model of the crustal structure in the region of the Aulneau batholith has been derived. The model has a number of near vertical faults and an essentially three layered crust in which the upper layer is 16 km thick with P-wave and S-wave velocities of 6.1 and 3.6 km/s, respectively, in the top part of the layer. The average P-wave velocity throughout the layer is 6.2 km/s. This layer probably represents the relatively homogeneous part of the batholith. The middle layer is 5 km thick beneath the shot point and thins to the southeast. It has a P-wave velocity of 6.9 km/s. The lower layer extends to the Mohorovicic discontinuity at 38 km depth and has an interval velocity of 7.2 km/s. The proposed crustal model is generally supported by other geophysical data collected in northwest Ontario.
Sulfide fabrics in some nickel sulfide ores from Kambalda, Western Australia
Authors: Ostwald J. , Lusk J.
Published: April 2011

Pyrrhotite and pentlandite fabric studies were carried out on oriented cubes of nickel sulfide ore from the tabular Durkin and Lunnon shoots associated with the Archaean Kambalda dome. Grain sizes, grain shapes, triple junction angles and preferred dimensional and lattice orientations were determined for the monoclinic pyrrhotite. Spatial orientations were determined also for pentlandite foliation and lineation in the same samples.Two distinct pyrrhotite grain morphologies were identified. The foliated pyrrhotite comprises a flattened variety, and an equant variety occurs as microvolumes within the former. Pyrrhotite foliations are separated from pentlandite foliations by consistently small angles.The pyrrhotite and pentlandite foliations are acquired features that developed at about the same time, probably following the peak of the principal dynamo-thermal event. Subsequent deformation(s)and recrystallization produced rotations within the ores and the equant pyrrhotite that crystallized from the flattened variety.
Late Quaternary geological history of Mahone Bay, Nova Scotia
Authors: Barnes Neal E. , Piper David J. W.
Published: April 2011

Mahone Bay is located on the Atlantic coast of Nova Scotia. It is an exhumed Carboniferous basin, overdeepened by glacial erosion, with widespread late Wisconsinan sheet and drumlin tills. Subglacial channels that cut both till and bedrock were formed when the ice sheet stagnated after marine incursion into the Bay of Fundy. Seismic reflection profiling and piston cores show up to 75 m of proglacial lake silts ponded behind a bedrock sill at the entrance to the bay. These are overlain by a thin lagoonal sequence, and then by marine sediments accumulated over the last 6000 years, reflecting the gradual Holocene transgression.
The thermal regime of the descending lithosphere: the effect of varying angle and rate of subduction
Authors: Sydora L. J. , Jones F. W. , Lambert R. St. J.
Published: April 2011

The local temperature and gravity fields associated with a subducting plate are investigated using a finite-difference numerical approach. A model that simulates the downgoing slab is used to study various dip angles, different rates of subduction, heat sources and the effect of rising material from the upper surface of the slab. The model assumes a simple descent mechanism that is discussed in terms of the associated earthquake field. The amount of shear-strain heating along the upper surface of the slab is a crucial factor in determining the thermal regime. When melting occurs, rising material from the top of the slab produces high heat flow values at the surface of the Earth on the continental side of the oceanic trench. Also, the results indicate that rising melt will mask the gravity effect of the cold sinking slab at low subduction velocities, and it is the presence of rising melt that is the dominant factor that influences the surface heat flux and gravity field.
Late Quaternary offsets along the Fairweather fault and crustal plate interactions in southern Alaska
Authors: Plafker George , Hudson Travis , Bruns Terry , Rubin Meyer
Published: April 2011

The northwest-trending Fairweather fault has undergone Cenozoic strike-slip displacement, with the most recent pulse of movement occurring in late Quaternary time. During the Lituya Bay earthquake (Ms = 7.9) of July 10, 1958, movement occurred probably along the entire 280 km onshore length of the Fairweather fault, with maximum measured displacements of 6.5 m dextral slip and 1 m dip slip near Crillon Lake. Three streams at Crillon Lake that flow on glacial till and bedrock have dextral displacements with maximum offset of roughly 55 m, and a lateral moraine of Finger Glacier southeast of Crillon Lake appears to have been offset at least 50 m in the same sense. Radiometric dating of wood from moraines near Crillon Lake and at Finger Glacier indicates that the offset stream drainages are probably not older than 940 ± 200 years BP and that the offset lateral moraine is about 1300 ± 200 years old. Data from the offset streams indicate that the minimum average displacement rate along this part of the Fairweather fault for the last millennium was at least 4.8 cm year−1 and was probably closer to 5.8 cm year−1.The deduced average offset rate is approximately equal to the full relative displacement of about 5.4 cm year−1 between the Pacific and North American plates in the Gulf of Alaska region that has been deduced from deep sea paleomagnetic data. These data indicate that the Fairweather fault is presently a transform boundary along which most, if not all, of the relative motion between the Pacific and North American plates is currently being taken up. Major valleys crossing the Fairweather fault that are probably older than Sangamon are systematically offset in a dextral sense an average of 5.5 km. These data suggest that the present high displacement rate on the Fairweather fault could not have begun more than 100 000 years ago and, together with data from other onshore faults, imply that before that time the relative motion between the plates was mainly on one or more submarine faults.
Paleomagnetism of the 1180 Ma Grenvillian Umfraville gabbro, Ontario
Authors: Symons D. T. A.
Published: April 2011

The 1180 ± 20 Ma Umfraville gabbro is a slightly metamorphosed stock in the Grenville Province. It was sampled at 17 sites (183 specimens). After alternating field and thermal demagnetization the gabbro retains the same very stable remanent magnetization of primary origin both before and after screening. The screened AF direction from 10 sites (96 specimens) gives a pole position of 166°E, 11°S (δp = 7°, δm = 10°). This position is ≈ 13° southeast of that originally reported for the gabbro by Hood. This pole position either does not fit or necessitates modifications to the four hypotheses that have been invoked to explain Grenville paleomagnetic data.
Late Pleistocene stratigraphy of south-central British Columbia
Authors: Fulton Robert J. , Smith Geoffrey W.
Published: April 2011

The late Pleistocene deposits of south-central British Columbia record two major glacial and two major nonglacial periods of deposition. The oldest recognized Pleistocene deposits, called Westwold Sediments, were deposited during a nonglacial interval more than 60 000 years ago. Little information is available on the climate of this period, but permafrost may have been present at one time during final stages of deposition of Westwold Sediments. The latter part of this nonglacial period is probably correlative with the early Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. However, deposition of the Westwold Sediments may have begun during the Sangamon Interglacial.Okanagan Centre Drift is the name applied to sediments deposited during the glaciation that followed deposition of Westwold Sediments. Okanagan Centre Drift is known to be older than 43 800 years BP and probably is older than 51 000. It is considered to correlate with an early Wisconsin glacial period.Bessette Sediments were deposited during the last major nonglacial period, which in south-central British Columbia persisted from at least 43 800 years BP (possibly more than 51 000) to about 19 000 years BP. This episode corresponds to Olympia Interglaciation of the Pacific Coast region and the mid-Wisconsin Substage of the Great Lakes – St. Lawrence Valley area. During parts of Olympia Interglaciation the climate was probably as warm as the present-day climate in the interior of British Columbia. Information from coastal regions indicates that there may have been periods of cooler and moister climate.Kamloops Lake Drift was deposited during the last major glaciation of south-central British Columbia. Ice occupied lowland areas from approximately 19 000 to 10 000 years BP. This period corresponds approximately to the Fraser Glaciation of the Pacific Coast region and the late Wisconsin Substage of central and eastern parts of North America.
An analytical representation of the geomagnetic field in Canada for 1975. Part III: the north magnetic pole
Authors: Dawson E. , Newitt L. R.
Published: April 2011

Three methods are used to determine a 1975 position for the north magnetic dip pole. A cubic polynomial in the horizontal components X (north) and Y (east) is fitted by least squares to 3050 component observations in an area of 2.65 × 106 km2 around the pole. A second analysis, in grid components U (north) and V (east), is carried out on 1394 component observations in a smaller area of 106 km2. In the third analysis, a linear fit is made to data obtained from four stations operating during a special survey of the dip pole region in 1973. The mean position adopted for 1975.0 is 76.2°N, 100.6°W.The present secular motion of the dip pole is 11 km/year north and 3 km/year west. Its secular motion has been mainly northward for the past 75 years. Plots of the diurnal motion of the dip pole show that on an average disturbed day, the pole may be as much as 65 km from its mean position.
Eolian sediment transport during dust storms: Slims River Valley, Yukon Territory
Authors: Nickling W. G.
Published: April 2011

The amount of sediment transported by wind in surface creep, saltation, and suspension was measured during 15 dust storms in the Slims River Valley, Yukon Territory. Results of the investigation showed that the quantity of sediment transported in creep and saltation varied approximately with the cube of shear velocity, which supports theoretical and empirical models presented by other investigators. The suspended sediment flow rate, however, seemed to be more directly controlled by the degree of air turbulence than by shear velocity. The total sediment transport rate was also shown to be directly affected by the surface moisture content and the presence of soluble salts at or near the surface. Both these factors tend to stabilize the surface by holding individual grains in place. Although eolian sediment transport is common in the Slims River Valley, high saltation–creep flow rates and major dust storms appear to be associated with a distinct set of atmospheric conditions, which are best developed on warm clear days following periods of heavy or extended rainfall.
Isotopic studies of ore-leads of the circum-Kisseynew volcanic belt of Manitoba and Saskatchewan
Authors: Sangster D. F.
Published: April 2011

Volcanic rocks, distributed to the north, west, and south of the Kisseynew gneissic belt in Manitoba and Saskatchewan, define a crescent-shaped belt herein informally referred to as the 'circum-Kisseynew volcanic belt'. Field relationships lead to the conclusion that the flanking volcanics are correlative with, and grade basinward to, greywackes and shales.Nearly 30 volcanogenic massive sulfide deposits, interpreted as coeval with their host rocks, are distributed throughout the circum-Kisseynew volcanic belt. Lead isotopic abundances in a representative number of these deposits are, apart from 204-error, relatively homogeneous in composition and model lead ages determined from these isotopic ratios fall, for the most part, between 1700 and 1900 Ma. This is regarded as good evidence that the circum-Kisseynew volcanic belt, as well as its greywacke equivalent, is largely Aphebian in age.Model lead ages for sulfide deposits from the entire circum-Kisseynew volcanic belt, with one exception, agree well with recent Rb–Sr and U–Pb age determinations from the southern portion of the belt. Reasons for the exception, in the Hanson Lake area, are discussed in some detail.