bluuebunny/crossref_metadata_2025 huggingface dataset:
Potassium–Argon Age Determinations of Metamorphic and Plutonic Rocks in the Yukon Crystalline Terrane
Authors: Tempelman-Kluit D. J. , Wanless R. K.
Published: April 2011

Forty-four new potassium–argon age determinations on minerals of metamorphic and igneous rocks from the Yukon Crystalline Terrane define the timing of the three most recent thermal events affecting this region. The oldest, 160 to 170 Ma ago, involved weak retrograde metamorphism of igneous and metamorphic rocks and coincides with the intrusion of batholiths of pink quartz monzonite. The next event, 90 to 100 Ma ago, reflects the emplacement of batholiths of the Coffee Creek quartz monzonite suite. The youngest thermal episode, 50 to 60 Ma ago, marks the time when the Nisling Range alaskite, with its porphyry dyke swarms and explosive acid volcanic rocks, was emplaced and when the K–Ar system of the Ruby Range Batholith was thermally reset. The data provide a younger limit to the age of the oldest Mesozoic plutonic rocks, the Klotassin suite, but they do not define its time of emplacement.
The Quebec–Maine Border Earthquake, 15 June 1973
Authors: Wetmiller R. J.
Published: April 2011

On 15 June 1973, a shallow-focus earthquake with magnitude mb 4.8 occurred in southern Quebec, in an area that has a record of only a few minor earthquakes during the previous 200 years. This event was felt throughout southern Quebec, eastern Ontario, and the New England States, to a distance of 300 km from the epicenter. A small amount of minor damage to plaster and chimneys occurred in the immediate epicentral area, indicating a maximum intensity of VI. The focal mechanism solution suggests that the earthquake was the result of primarily strike-slip movement along a plane trending northeast or a plane trending northwest. Arguments are presented that this event is part of the seismicity associated with the northern Appalachian Mountains.
The Blind Creek Limestone, Keremeos, British Columbia: Structure and Regional Tectonic Significance
Authors: Barnes W. C. , Ross J. V.
Published: April 2011

A large block of Upper Paleozoic limestone at Blind Creek near Keremeos, B.C. was emplaced by dry gravity sliding, probably associated with uplift related to nearby Eocene volcanism. The block is a nearly flat tabular unit, exposed over an area of 650 m by 1300 m, and is separated from underlying chaotic breccias derived from adjacent Paleozoic rocks and from Eocene volcanic flow rocks by a sole fault. The block comprises two lithologically and tectonically distinct units, a lower imbricated unit consisting of several slices repeating the same sequence of strata, separated from an upper unit of massive limestone by a low-angle fault. Within the imbricated unit, early faults emanate from lenticular masses of breccia along the sole, become increasingly steeper upward, and are truncated above by the upper low angle fault. Associated minor folds and fractures have a clockwise sense of rotation. Later fractures and associated minor folds have the opposite dip and sense of rotation. These two subsets comprise a conjugate set whose inferred compressive stress direction coincides with the present overall dip direction of the entire mass.The northwesterly adjacent autochthonous Olalla limestone, or a similar body now buried by younger units, is a likely source for the Blind Creek allochthon.Absence of any structures within the limestone indicative of ductile deformation contrasts markedly with those of the highly deformed rocks of the Old Tom and Shoemaker Formations, the Kobau Group, and the nearby gneisses of the western Shuswap Complex.
The Sedimentary Structures and Depositional Mechanics of Certain Ordovician Turbidites, Cloridorme Formation, Gaspé Peninsula, Quebec
Authors: Skipper Keith , Middleton Gerard V.
Published: April 2011

Turbidites, belonging to the β1, member, Cloridorme Formation, are exposed on the north shore of the Gaspé Peninsula, Quebec. Their structural attitude is such that vertical sections through turbidite beds are exposed on the wave-cut platform and their strike is approximately parallel to the paleocurrent direction, as shown by sole marks on the bases of beds.Certain thick turbidite beds, in a distal position, display a sequence of sedimentary structures which differs from the sequence defined by Bouma. Three broad divisions are recognized: a basal division consists of either limestone or quartz granule to pebble conglomerate (0–4 cm thick) or coarse sand graywacke or calcareous wacke (0–15 cm thick). Basal divisions of calcareous wacke frequently display ripple-lamination, parallel lamination, or upstream-inclined laminae. Where the upstream inclined laminae form a single set, they occur below a sinuous profile (wavelength 40–80 cm, and amplitude 2–5 cm).A second division (0–330 cm thick) consists in most places of spindle- or globular-shaped calcareous nodules scattered in an argillaceous host. In some beds, streaking and lobing of light colored, carbonate bearing material is associated with these nodules. Internal hemi-ellipsoid structures, arranged en echelon and convex towards the base of the bed, are displayed from the second division. The upper division consists of fine grained siltstone and shale.The upstream-inclined laminae in the basal division of calcareous wacke beds are interpreted as being the result of the upstream migration of antidunes. The nodules within the second division developed as 'pseudo-nodules'. The hemi-ellipsoid structures resemble damped, large scale (macroturbulent) eddies associated with the flow of dense grain dispersions.Correlation of these beds has been achieved over a distance of 12 km. Basal divisions of granule and pebble conglomerate persist over this distance and show that coarse particles may be transported by turbidity currents over long distances. The sedimentary structures of the basal divisions of several calcareous wacke beds might be interpreted as the result of either an increase in flow regime downcurrent, or of nonpreservation of structures at up-current localities.The beds were probably deposited from turbidity currents composed largely of mud and fine sand, but containing a zone of coarse grains concentrated near the bed. The basal division was deposited from this lower zone and a period of traction formed rippled, flat, or antidune bed forms. Stratification in the basal division was preserved by the rapid deposition on top of sediment that settled en masse from the subsequent high concentration body of the current. The formation of a succession of 'quick' beds led to the sedimentation of the second division. The flows responsible for the sequence of structures observed and the downcurrent persistence of the beds probably approached closely a state of 'autosuspension'.
The Age of the Sudbury Nickel Irruptive and the Murray Granite
Authors: Gibbins Walter A. , McNutt R. H.
Published: April 2011

Whole-rock samples of norite from the North and South Ranges of the Sudbury Irruptive yield a rubidium strontium isochron of 1956 ± 98 Ma age and (87Sr/86Sr)o = 0.7063 (λ87Rb = 1.39 × 10−11 a−1). Five samples of ore bearing 'sub-layer' from the South Range are compatible with this age. Four new determinations of South Range and six published analyses of North Range micropegmatite define an isochron of age = 1680 ± 30 Ma with (87Sr/86Sr)o = 0.708.The norite age is believed to represent the 'Sudbury event', a local event marked by the development of shock metamorphism and intrusion of the nickel irruptive. The 1680 Ma micropegmatite age is believed to be secondary and related to greenschist-facies metamorphism in the center of the Sudbury Basin during the Penokean Orogeny. Evidence supporting a later separate intrusion of granophyre-rich micropegmatite suggests that the time of this intrusion was relatively soon after the norite rather than 1680 Ma ago.Analyses of Murray granite samples indicate a pre-norite age of 2260 Ma. Most of the Murray granite shows evidence of later metamorphic events including the Sudbury event. Late (post-norite and post-Murray granite) granitic dikes (i.e., the Murray offshoots) intrude the norite near the Murray granite. These and other smaller granitic dikes appear to have formed 1700 to 1800 Ma ago. The origin of these dikes remains problematical.
The Application of Seismic Reflection Techniques for Subsurface Mapping in the Precambrian Shield near Flin Flon, Manitoba
Authors: Hajnal Z. , Stauffer Mel R.
Published: April 2011

Some of the conditions necessary for the use of seismic reflection techniques for subsurface mapping in Precambrian Shield terranes have been determined from field studies carried out near Flin Flon, Manitoba.In areas of unconsolidated overburden, geoflex-type surface energy sources provide sufficient energy. However, in outcrop regions, boreholes have to be drilled to a minimum depth of 1.5 m, preferably in patterns of 2–6 holes. Explosives with a higher detonation velocity than those presently available would be useful.A near-surface, low velocity layer was discovered on top of all examined rock types, and appears to be the result of open fractures in the rock. The thickness of this layer varies from 20–44 m in the rocks studied.A velocity contrast of 783.3 m/s exists between the Amisk volcanic rocks and Missi sedimentary rocks, making reflection mapping possible. Seismic events which were interpreted as reflections were identified, near contacts between these formations in the subsurface. A fault contact between Amisk and Missi rocks has been mapped to a depth of about 1.6 km, and a normal stratigraphic contact between the Amisk and Missi Groups has been mapped to a depth of about 0.25 km.Because of the complex structure in most Precambrian Shield terranes, it is necessary to locate seismic lines carefully with respect to the geological features being studied. In particular, it is best to keep the line within a rock unit that has constant velocity throughout, and to use short lines, so that a limited number of structures are intersected.
The Paleomagnetism of Kaminak Dikes—No Evidence of Significant Hudsonian Plate Motion
Authors: Christie K. W. , Davidson A. , Fahrig W. F.
Published: April 2011

A paleomagnetic study was done on 28 diabase and 6 lamprophyre dikes from the vicinity of Kaminak Lake in the District of Keewatin. These dikes are Proterozoic and cut across an area of Archean rocks. Their metamorphic grade within this region varies from nil to amphibolite facies. Two stable magnetization directions were obtained from the diabase on AF demagnetization; one from 3 unmetamorphosed diabase dikes of D = 205°, I = 3°, α95 = 24°, with a corresponding pole position at 23.8 °S, 122.3 °W, α95 = 16.5°; the other from the metamorphosed diabase of D = 176°,I = 65°, α95 = 4°, with pole position at 20.4 °N, 92.1 °W, = 6.1°. The first is believed to be thermoremanent and approximately 2300 Ma old, while the second is a metamorphic direction of approximately 1800 Ma. The six lamprophyres give a stable remanence of D = 174°, I = 78°, α9S = 10°, with a pole position at 40.9 °N, 92.8 °W, α95 = 17°, essentially the same as the metamorphosed diabase.A number of samples were also thermally demagnetized. Most of the results obtained were the same as those obtained from the AF treatment. However, one diabase site gave a direction similar to that obtained from the 3 unaltered dikes, and one of the lamprophyres showed a reversal.The pole position of the altered Kaminak diabase relative to that for the unconformably overlying Dubawnt Group suggests that the polar wandering curve for this part of the Aphebian may be more complex than previously thought. It is quite probable that the earlier Aphebian pole positions (Matachewan, Nipissing), as usually plotted, are actually antipodal points in terms of the polar wandering curve.
The Influence of a Causeway on Oceanography and Foraminifera in the Strait of Canso, Nova Scotia
Authors: Vilks G. , Schafer C. T. , Walker D. A.
Published: April 2011

In 1955, a causeway was built across the Strait of Canso, Nova Scotia, Canada, preventing in the Strait a free interaction between the Gulf of St. Lawrence and Atlantic waters. In order to evaluate a possible impact of this barrier on the marine environment, the distribution of foraminifera in sediments was investigated.Data were collected from early May to late August, 1973. During this period, the water on the Gulf of St. Lawrence side of the causeway was colder in early spring, but warmer and less saline during the summer as compared to the Atlantic side.At the causeway, the surface 1–3 cm of the bottom sediment consists of very soft and black to dark brown mud on both sides. On the Atlantic side, these fine sediments cover bedrock; but on the Gulf of St. Lawrence side, they cover sands and gravels.The 76 foraminiferal species collected in surface samples were subjected to cluster analysis, which defined two distinct groups of stations separating the fauna on the two sides-of the causeway. The characteristic species of the Gulf of St. Lawrence side is Ammonia beccarii. In the subsurface layers the dominance of this species decreases within a zone extending 4 km to the north of the causeway. On this evidence it was concluded that prior to the causeway, the Atlantic waters extended at least 4 km further to the north.
Upper Mantle Structure in Southern Saskatchewan and Western Manitoba from Project Edzoe
Authors: Bates Allan , Hall D. H.
Published: April 2011

A line of eight recording sites in southern Saskatchewan and Manitoba, with ranges from 793 to 1284 km, recorded a series of chemical explosions in Greenbush Lake, British Columbia, as part of Project Edzoe in 1969.It is found that travel-times fall into two branches. The first branch is interpreted as representing the effect of a linear increase of P wave velocity, increasing from 8.10 km/s at the top of the mantle, with a gradient of 0.0017 s−1. The second branch indicates a rapid increase of gradient occurring somewhere between depths of 120 km and 150 km. Amplitude studies suggest, in the absence of complete triplication, a zone of low velocity gradient beneath the rapid increase. The presence or absence of a low velocity zone was not indicated in the data.Previous long-range refraction surveys indicate that a similar gradient in velocity also occurs beneath the Superior province of the Canadian shield, and that P-wave velocities are lowest at its center, reaching higher values at its edges.
Multivariate geochemical and mineral patterns in the Precambrian basement of western Canada
Authors: Burwash R. A. , Culbert R. R.
Published: April 2011

R-mode factor analysis, discrimant analysis, trend surface, and canonical trend surface analyses are applied to the 42 variables measured for 171 Precambrian igneous and high grade metamorphic rocks, sampled in deep drill holes in the western Canada sedimentary basin. Low-grade metasedimentary rocks and post-Hudsonian diabase intrusives are excluded. The four strongest R-mode factors are related to processes of regional metamorphism. These are: potassium metasomatism, shearing with the development of secondary foliation, chloritization, and mylonization. Potassium metasomatism appears mainly to be later than the three other processes.Regional lineaments in the western Shield, identified from tectonic, gravity, and magnetic maps, when combined with trend surface maps from drill hole data, suggest southwestward extensions of major lithologic tectonic units of the Churchill province. The fivefold division of the subsurface Precambrian includes, from north lo south: I—Liard block (Slave and Bear provinces, in part), II—Athabasca mobile belt (restricted). III—Cree Lake – Calgary belt, IV—Kisseynew–Sweetgrass belt, and V—Superior province (Assiniboia block, restricted).The two major Phanerozoic crustal flexures in the Western Canada basin, the Peace River arch and the Williston basin, correspond to canonical trend surface highs and lows, respectively. Their persistent isostatic tendencies are linked to differing Hudsonian metamorphic histories.A depletion of trace metal content, which accompanies shearing, can be traced diagonally across northern Alberta. The southwestward projection of this belt matches the portion of the Canadian Cordillera barren of major ore deposits.
The Vancouver Island earthquake of 5 July 1972
Authors: Rogers Garry C.
Published: April 2011

An earthquake occurred at 10 h 16 m 39 s GMT on 5 July 1972 in close proximity to the west coast of Vancouver Island, near 49.5 °N and 127.2 °W. Its magnitude (mb) was 5.7 and the hypocenter was near the middle of the crust. A well defined P nodal solution has a pressure axis with a north-south orientation and a tension axis with an east-west orientation. The preferred nodal plane suggests right lateral strike-slip faulting on a near vertical fault, striking in a north-northwest direction. The other nodal plane suggests that left lateral strike-slip faulting on a near vertical fault striking in an east-northeast direction is also a plausible solution. A field study with portable seismographs revealed that very few aftershocks were associated with this earthquake. The largest aftershock had a magnitude (ML) of 3.4. The distribution of intensity of the mainshock observed on Vancouver Island differs from that predicted by the intensity versus distance relation presently used for western Canada.
Geochemical evolution of copper-bearing granitic rocks of Guichon Creek Batholith, British Columbia, Canada
Authors: Olade M. A.
Published: April 2011

The Guichon Creek batholith, located in south-central British Columbia, is host to numerous porphyry copper deposits that are considered as being closely related to the pluton. Variations in major and trace element distribution are consistent with a model of crystallization-fractionation of a K-poor calc-alkaline magma of intermediate composition. Relatively low Rb and Rb/Sr values, and high K/Rb ratios are consistent with Sr isotopic ratios that suggest a subcrustal source region for the generation of the magma, probably by partial melting of subducted oceanic crust at relatively shallow depths.Cu, like other femic elements, (Zn, Mn, V, Ni, Co, Ti) generally decreases with increasing fractionation, which reflects normal differentiation trends. The apparent lack of positive correlation between Cu contents of rocks and ore potential of intrusive units may be explicable if mineralization is regarded as an independent by-product of magma generation, rather than the result of differentiation processes. Close relationships between trace metal values and degree of fractionation emphasize the need for assigning different background values to each intrusive unit, during geochemical exploration.
The Goulding–Keene nepheline pegmatite near Bancroft, Ontario
Authors: Reeve E. J. , Anderson G. M.
Published: April 2011

The Goulding–Keene pegmatite consists essentially of albite, nepheline, and biotite with minor amounts of microline and other minerals. It is enclosed by plagioclase–nepheline–biotite–hastingsite–calcite gneisses and is apparently intrusive into these gneisses since it cuts the foliation of the gneisses, has some sharp contacts, and is not itself foliated. The gneisses and the pegmatite were sampled by more than 240 m of diamond drill core. Rock and mineral analyses show that the present composition of the pegmatite is very unlikely to be an igneous composition, and therefore that metasomatism has changed the original composition after emplacement of the pegmatite as a melt. This is consistent with textures observed in the gneisses and pegmatite.
Uranium and thorium in the Precambrian basement of western Canada. I. Abundance and distribution
Authors: Burwash R. A. , Cumming G. L.
Published: April 2011

Delayed neutron activation analyses of 182 core samples from the basement of the western Canada sedimentary basin give mean values of 4.13 ppm U and 21.1 ppm Th. These values are almost twice the published values for the Shield as a whole. Replicate analyses of a composite sample of all cores indicates an analytical precision of ±1% for uranium and ±7% for thorium.Histograms of number of samples vs. U and Th values indicate a negatively skewed frequency distribution. Analysis of composite samples prepared from a large number of hand specimens may tend to conceal this skewed nature. Mean abundance values will also be influenced by the form of the U and Th frequency distributions.Trend surface analysis, with smoothing to reduce the effect of high or low single sample values, indicates two 'highs' common to both U and Th. The helium-producing area around Swift Current, Saskatchewan is associated with a high U–Th plutonic complex. A linear belt trending northeast from Edmonton appears to be a Hudsonian metamorphic belt in which U and Th have been concentrated. Several local concentrations of U or Th are found in the Peace River Arch of northern Alberta.
Paleomagnetic results from the Lower Paleozoic of Ireland
Authors: Morris W. A.
Published: April 2011

Paleomagnetic data are presented for a variety of Ordovician rocks from two regions in Ireland: the South Mayo Trough and some Ordovician inliers of east-central Ireland. Some of these data update previous preliminary results, while others provide new information. In some instances the original remanence direction has been obscured by subsequent remagnetization.Although magnetic inclinations of the Ordovician results are mostly shallower than contemporaneous British results, poor precision precludes any reliable estimate of closure across this sector of the Proto-Atlantic ocean. Declination differences between the South Mayo Trough and British data indicate a 30° clockwise rotation of this tectonic block during the Middle to Upper Devonian.
Plate tectonics and planetary convection
Authors: Kanasewich E. R.
Published: April 2011

A series of azimuthal–equidistant map projections, centered on each of the plates of lithosphere, is used to demonstrate the high degree of ordering and symmetry in the major plates. The Pacific and African plates are approximately circular with a radius of 60°. The entire pattern is dominated by these two major plates, exactly antipodal to one another in the form of a dipole. Between the two 'circular' plates is a ring of elliptical plates with irregular boundaries but a organized geometric interrelationship. The average major and minor axes of the 'elliptical' plates, measured at the center of the earth, are 62° ± 6 °and 30° ± 5°, and the major axes are oriented at angles of 56° ± 3 °to lines joining the center of the African plate. The centers of the 'elliptical' plates are arranged within 6° ± 3 °of a great circle path through the North pole. This organized distribution of the major plates is most likely the result of convection currents involving the entire mantle, from the lithosphere to the core. To a first approximation, the convective pattern may be modelled by a superposition of third order spherical harmonics, P03, P13, and P23 in a pattern that regressed from a first spherical harmonic, −P01.
Rb/Sr dating of rocks from the Wollaston Lake Belt, Saskatchewan
Authors: Cumming G. L. , Scott B. P.
Published: April 2011

Rb and Sr measurements on rocks of the Wollaston Lake fold belt in Saskatchewan indicate a major metamorphic resetting of most of the whole-rock Rb/Sr systems, particularly in the arkosic units, associated with the Hudsonian orogeny and dated at 1850 m.y. (λ = 1.39 × 10−11 y−1).Some of the so-called 'young' granites in the area appear to be primary intrusives of that age, but others contain clear evidence of containing older material. A tentative age of 2650 m.y. for the Archean granites is suggested on the basis of three samples that appear to have retained their original Rb/Sr ratios. Two quartzite samples suggest an Archean age of about 2360 m.y. for the sediments in the area although the data are inconclusive. A late metamorphism is well dated at 1730 m.y. by a mineral isochron and by ratios in remobilized material along the edge of the Johnson River batholith.
A model for the origin of the Lac St. Jean anorthosite massif
Authors: Frith R. A. , Currie K. L.
Published: April 2011

An ancient tonalitic complex becomes migmatitic around the Lac St. Jean massif, ultimately losing its identity in the high grade metamorphic rocks surrounding the anorthosite. Field relations suggest extreme metamorphism and anatexis of tonalitic rocks. Experimental data show that extensive partial melting of the tonalite leaves an anorthositic residue. The same process operating on more potassic rocks would leave monzonitic or quartz syenitic residues. Synthesis of experimental data suggests that the process could operate at pressures of 5–8 kbar and temperatures of 800–1000 °C, which are compatible with mineral assemblages around the anorthosite massif. Slightly higher temperatures at the end of the process could generate magmatic anorthosite.Application of the model to the Grenville province as a whole predicts generation of anorthosite during a long-lived thermal event of unusual intensity. Residual anorthosite would occur as a substratum in the crust, overlain by high-grade metamorphic rocks intruded by anorthosite and syenitic rocks, while higher levels in the crust would display abundant calc-alkaline plutons and extrusives.
An Albian microflora from the Mattagami Formation, James Bay Lowlands, Ontario
Authors: Norris G. , Telford P. G. , Vos M. A.
Published: April 2011

The Mattagami Formation is of variable thickness, consisting of several hundred feet of interbedded sands, clays and lignites. Spores and pollen from near the top of the formation indicate a late Middle or Late Albian age. Other palynologic studies suggest that deposition of the lower part of the formation commenced in Aptian or Early Albian times.
Codiacées (Algues) ordoviciennes des Basses-Terres du Saint-Laurent
Authors: Guilbault J. P. , Mamet B. L.
Published: April 2011

Description and illustration of 15 Ordovician Codiaceae from the St Lawrence Lowlands (Quebec and Ontario). Two genera (Lowvillia and Dimorphosiphonoides) and five species (Dimorphosiphonoides lesperancei, D. hofmanni, Lowvillia grandis, L. raripora, and L. multipora) are new.
Climacograptus typicalis typicalis and associated shelly fossils from Lake Waswanipi, Québec
Authors: Walters M. , Sheehan P. M. , Lespérance P. J.
Published: April 2011

Graptolites have been recovered from limestones at Lake Waswanipi, Québec, in an Ordovician outlier on the Precambrian Shield. These limestones were previously interpreted as Wilderness, Trenton, or Richmond in age. They are now assigned a middle Climacograptus spiniferus to C. pygmaeus Zone age, dating the transgression over this part of the shield. Associated megafossils, though poorly preserved, are described. Correlations are made with other graptolite-bearing carbonates in eastern and central North America.
Length distribution of strike-slip faults and the process of breakage in continental crust
Authors: Ranalli G.
Published: April 2011

The distribution of lengths of regional strike-slip faults in continental crust is adequately described by the lognormal probability distribution. It is therefore suggested that the faulting process can be modelled as a random process obeying the law of proportionate effect (Kolmogorov type).
Late Precambrian structural evolution of Pigeon Point, Minnesota and relations to the Lake Superior syncline
Authors: Mudrey Jr. M. G.
Published: April 2011

A sequence of semi-brittle deformational tectonic events in gently dipping middle Precambrian argillite and graywacke, and late Precambrian sandstone and volcanic rocks on the northwest coast of Lake Superior is interpreted from detailed geologic mapping in the Pigeon Point, Cook County, Minnesota area. The earliest tectonic event was broad, open folding in the middle Precambrian Rove Formation along N 35 °E axes and the development of two sets of joints (North and N 70° E). The second event was eastward trending, high-angle faulting in the Rove Formation and the disconformably overlying late Precambrian Puckwunge sandstone and North Shore Volcanic Group; the south sides moved upward relative to the north sides. These faults and associated joints were the loci of emplacement of 'early mafic' dikes of ilmenite-bearing diabase, which probably correlate with the 'Logan intrusions'. Subsequently, east-northeastward trending olivine diabase sills and dikes were emplaced in the Rove Formation and the North Shore Volcanic Group, and they cross-cut the early mafic dikes and sills. The third event occurred after cessation of igneous activity; two sets of regional joints (N 14 °W and N 53 °E) were formed, apparently as a result of fracturing accompanying initial subsidence of the so-called 'Lake Superior syncline' to the southeast. The fourth event was the development of a zone of cataclastic rock trending N 65 °E from the Pigeon Point area northeastward at least 60 km. To the north of this fracture zone, bedding in the Rove Formation dips 15–25 °SE. Copper and silver mineralization was subsequently emplaced within this fracture zone.The first three tectonic events appear to represent reactivation of structures of early Precambrian age, and appear to control the general outcrop pattern. The fourth event is an entirely Keweenawan feature, and marks the beginning of subsidence of the 'Lake Superior syncline'. It may correlate in time with the deposition of the Copper Harbor Conglomerate, and other late middle Keweenawan events.
Oceanic heat flow measurements over the continental margins of eastern Canada
Authors: Lewis J. F. , Hyndman R. D.
Published: April 2011

Sixteen heat flow measurements have been obtained on the continental rise and slope off Nova Scotia and off the southern Grand Banks of Newfoundland. The mean of the 14 most reliable values is 48 ± 4 mW m−2 (1.15 ± 0.09 μcal cm−2 s−1), which is in agreement with the mean for previous measurements on ocean floor of age greater than 100 m.y. However, the heat flux from the crust indicated by the new values is significantly lower because of the heat produced in the some 5 km of terrigenous sediments underlying the stations. The low values could represent an edge effect between continent and ocean. Two lines of stations across the Nova Scotia rise show large heat flow variations. Numerical models indicate that the variations could arise from thermal refraction by high thermal conductivity salt, which probably constitutes the 'sedimentary ridge complex' outlined by deep seismic reflection profiles. The salt or evaporites formed in the restricted basin that was parallel to this rifted margin during the first phase of opening of the Atlantic Ocean. The heat flow variations measured on a profile perpendicular to the southern edge of the Grand Banks are smaller. This margin was a transform fault between Newfoundland and northwest Africa during the early ocean opening, so that the seafloor in the region of the profile was produced after the restricted basin phase of evaporite formation.
Calc-silicate isograds in the Riondel area, southeastern British Columbia
Authors: Höy Trygve
Published: April 2011

Five metamorphic isograds have been mapped in the calc-schists of the Riondel area, British Columbia. These isograds are based on the following model reactions:[Formula: see text]The first four of these isograds represent discontinuities in the observed mineral assemblages and are located by plotting all occurrences of the complete reactant and product assemblages. The fifth isograd occurs over a wide zone in which the anorthite component of the plagioclase in the assemblage Ep–Ac–Q–Di–Pl increases with increasing metamorphic grade, from approximately An30 in the lower grade eastern part of the area to approximately An60 in the western part.The distribution of isograds and the systematic variation in plagioclase compositions in the Ep–Ac–Q–Di–Pl assemblage is modelled using [Formula: see text]diagrams that have been calculated at 5000 bars pressure under the simplifying constraint that[Formula: see text]. These diagrams provide a basis for estimating the physical conditions of regional metamorphism in the Riondel area. Maximum temperatures exceeded 600 °C in the highest grade part of the area and the composition of the hypothetical binary fluid phase varied from approximately [Formula: see text]in the lower grade to 0.5 or 0.6 in the higher grade areas.
Sedimentary basins developed during evolution of Mesozoic–Cenozoic arc–trench system in western North America
Authors: Dickinson William R.
Published: April 2011

Development of Mesozoic and Cenozoic sedimentary basins in western North America was linked to the overall geodynamics of an active continental margin. The Cordilleran margin, now largely of Californian-type with a bounding transform, was Atlantic-type from late Precambrian to early Paleozoic, Japanese-type from late Paleozoic to early Mesozoic, and Andean-type from late Mesozoic to early Tertiary, when a continental-margin arc–trench system included the following tectonic elements from west to east: (a) the subduction complex at the main subduction zone; (b) forearc basins within the arc–trench gap; (c) the magmatic arc of generally andesitic volcanics and subjacent granitic plutons; (d) a backarc fold-thrust belt, commonly with an associated metamorphic infrastructure; and (e) the retroarc foreland basin adjacent to the craton. Progressive broadening of this tectonic system was achieved by tectonic accretion of oceanic elements to the edge of the continental block and by peeling of cover off rigid basement underthrust behind the arc along the edge of a zone of ductile lithosphere formed thermally beneath the arc. An initial Jurassic island arc evolved through the Cretaceous into a terrestrial Tertiary arc as subsiding forearc and retroarc basins were filled with sediment.
The Slate Islands: a probable complex meteorite impact structure in Lake Superior
Authors: Halls H. C. , Grieve R. A. F.
Published: April 2011

Shock metamorphic effects in samples from the Slate Islands, Lake Superior (48°40' N, 87°00' W) suggest that the islands are part of a meteorite impact structure. The islands form the central uplift of a complex crater and are ringed by a submerged trough and annular ridge with a diameter of 30 km. Precambrian bedrock units are locally brecciated and cut by allochthonous breccia dikes. These dikes contain clasts of identifiable country rock and also fragments of a sedimentary unit, possibly Upper Keweenawan in age, which is no longer present in outcrop. The orienta tions of shatter-cones present in the breccia host-rocks indicate the interior of the islands as the approximate shock centre. Microscopic planar features, equivalent to those described from other impact sites, occur in quartz and plagioclase and the level of shock deformation increases towards the interior of the islands. The shock event postdates Keweenawan igneous activity (about 1.1 b.y. old) and, on the basis of the erosion level, may be early Paleozoic in age.
Significance of a new fossil locality containing a Salopina community in the Waweig Formation (Silurian–uppermost Ludlow/Pridoli) of southwest New Brunswick
Authors: Pickerill R. K.
Published: April 2011

A new fossil locality in the Waweig Formation of southwest New Brunswick is described. The assemblage contains elements typical of the Salopina community, and consequently, the new locality indicates that the formation developed in a generally quiet, shallow, nearshore shelf or low intertidal environment that was subject to periodic storm influxes. The age of the Waweig Formation is suggested to be uppermost Ludlow – Pridoli (?Pridoli).
Geochemistry and environmental implications of the surficial sediments in northern Placentia Bay, Newfoundland
Authors: Willey Joan D.
Published: April 2011

Three chemically distinct sediment types, as defined by factor analysis, occur in northern Placentia Bay; these correspond to the muds, the sands, and the amodal sediments (tills) in this area. Factors that control the sediment geochemistry in Placentia Bay are: the organic-rich fraction, the clay-size fraction, the calcium carbonate fraction, the iron-containing fraction, the non-clay-size aluminous minerals, and the silica-rich fraction. The relative importance of these factors in controlling sediment chemistry is different in each sediment type. The trace metal concentrations and associations are also different in the three sediment types.The weak acid leachable fractions of the metals investigated are derived primarily from the organic material, the clay-size fraction, and the calcium carbonate, even in the sands where these three fractions are only a small part of the sediment. The non-leachable fractions of the metals are controlled by the organic material and by minerals such as feldspars and micas.The average concentrations of the major components and of the trace metals, and the factors that control these concentrations, are not significantly different in Long Harbour sediments (after five years of operation of the phosphorous plant there) compared with similar sediments in Placentia Bay. The association of Pb in Long Harbour sediments may be different than in other areas.
Barite nodules of possibly late diagenetic origin from Twitya River area, Mackenzie Mountains, Northwest Territories
Authors: Laznicka Peter
Published: April 2011

Conspicuous spherical and subspherical barite nodules occur in Devonian(?)/Mississippian carbonaceous shales and argillaceous dolomitic limestones in Twitya river area (western foothills of the Backbone Ranges, Mackenzie Mountains, N.W.T.).The majority of barite nodules are spherulitic, composed of grey radiating barite crystals. The microscopic study of barite and of sedimentary fabrics in its host rocks has demonstrated that the crystallization of nodules was a late diagenetic event postdating the formation of carbonate concretions in shales, dolomitization, and the early phase of fracturing, but predating the late phase of fracturing and tectonic deformation. The nodules have clearly developed by replacement of their carbonate host.The middle to late Paleozoic, black shale sequence that occurs on both sides of the Yukon – Northwest Territories boundary at the latitude of Macmillan Pass (Canol road) appears to be in a distinct barite province with numerous occurrences of mostly bedded barite recorded. The presently available evidence indicates that the introduction of barium into the sedimentary basin had probably been syndepositional, followed by diagenetic concentration and barite emplacement well before the 'Laramide Orogeny' and the emplacement of Cretaceous quartz monzonite stocks.
Comparative petrology and source of sediments in Newfoundland fiords
Authors: Slatt Roger M. , Gardiner William W.
Published: April 2011

Comparative petrology of the gravel- and sand-sized fractions of sediments from Conception Bay, Placentia Bay, and Halls Bay, Newfoundland, has shown gravel clasts to be of the same composition as local bedrock, and sands to range in composition from litharenite to lithic arkose depending upon the proportion of fine and coarse grained local bedrock. Sand-sized lithic fragments comprise the same lithologies as local bedrock. The petrology provides conclusive evidence that almost all of the sediments in each fiord are glacially eroded from local bedrock; they are deposited in the fiords and subsequently reworked. However, the occurrence and distribution of garnet and other less frequently occurring mineral and lithic species indicates that a minor proportion of the sediments has been transported into the fiords from offshore by ice-rafting and/or from the adjacent continental shelf by bottom currents.
Phacops and other trilobites from Emsian age beds of the Delorme Formation, Mackenzie Mountains, Northwest Territories
Authors: Perry D. G. , Chatterton B. D. E.
Published: April 2011

The trilobite genus Phacops is documented for the first time in northwestern or Arctic Canada from Emsian age beds of the Delorme Formation, western Mackenzie Mountains. Phacops natlenis n. sp. is described; it shows closest morphologic affinity to P. spedeni Chatterton from late Emsian age beds of southeastern Australia. Other Emsian trilobite genera from the Delorme Formation in the Sekwi Mountain map-area, Mackenzie Mountains include: Lacunoporaspis, Ceratarges?, Acanthopyge (Mephiarges), Leonaspis, and Koneprusia?.
Upper mantle P-wave model catalogue
Authors: McMechan George A. , Sinclair Judith J.
Published: April 2011

This note is a description of a catalogue that contains tables of parameters and synthetic seismograms for 50 upper-mantle P-wave velocity–depth profiles. The table for each model contains values of ray parameter, epicentral distance, travel time, velocity, and bottoming depth for a number of representative rays. Short-period synthetic seismograms are computed at 1 °intervals from 10° to 30° by the quantized ray theory algorithm and are vertical component traces for a surface focus point source. The catalogue is designed as a comprehensive reference and so includes a wide variety of mantle models.
An Arctic foraminiferal fauna from Champlain Sea deposits in Ontario
Authors: Cronin Thomas M.
Published: April 2011

A new Champlain Sea fossil locality near Kars, Ontario has yielded at least 41 species of benthonic Foraminifera, 18 of which are recorded from this sea for the first time. Taxonomically the assemblage is almost identical to living faunas from Arctic seas. Paleosalinities of about 30 to 35 ppt and a range of annual paleotemperatures from 0 °C to 12 °C are indicated by the Foraminifera. A 14C radiocarbon date of 10 900 ± 100 a BP (GSC 2312) was obtained from shells of Hiatella arctica, suggesting deposition relatively late in the marine episode. The existence of arctic-subarctic environmental conditions at this time in Ontario can be directly attributed to the proximity of the post-Valders Laurentide ice sheet.
Permafrost thermal amelioration tests near Schefferville, Quebec
Authors: Nicholson Frank H.
Published: April 2011

Permafrost thermal amelioration techniques have been tested for 4 years near Schefferville (mean annual temperature −6 °C). The most important amelioration measure tested was the use of snow fences to increase snow depth and hence reduce winter heat losses, which affect the permafrost much more than changing the summer heat input conditions. However, when different summer treatments were tested, stripping the vegetation, darkening the ground and using thin transparent covers proved beneficial. Monitoring included deep ground temperature measurements (to 25 m), radiation instruments, lysimeters, and measurement of ground thermal properties. At 5 m depth, between 20 and 40 × 106 Jm−2 are gained and lost each year under natural conditions, whereas the amelioration gave a continuous gain of 20 × 106 Jm−2 per annum (nearly 2% of net radiation), increasing mean temperature by 2.5 °over 4 years. At the 10 m depth corresponding gains were 10 × 106 Jm−2 and 1.5°. The rocks (iron-rich) have high thermal conductivities, and slower amelioration results are likely in other areas. Limited plot size (7500 m2) has resulted in significant lateral heat loss. The overall test result is that the active layer has been greatly deepened but no thaw has yet been held through a full winter. The method would be useful in several mining applications, including the prevention of new permafrost.
A gravity survey of the central Labrador Trough, northern Quebec
Authors: Kearey P.
Published: April 2011

The Labrador Trough is the best preserved and exposed of several Aphebian (lower Proterozoic) fold belts which surround the Archaean Ungava Craton of northern Quebec and is characterised by three longitudinal facies zones: predominantly meta-sedimentary rocks in the west and east and predominantly basic meta-igneous rocks in the centre. The results of a detailed gravity survey of the central part of the Labrador Trough between latitudes 55° 45′ and 57° 30′ and longitudes 66° 30′ and 70° are presented. Over 1500 rock samples provide density control for the interpretation of four residual gravity anomaly profiles in terms of the surface geology.In the eastern part of the Labrador Trough positive gravity anomalies correlate with outcrops of basic meta-igneous rocks. Their causative bodies extend subsurface to the east and reach depths of up to 9 km in the central part of the area, but are considerably thinner to the north and south. This interpreted depth is considerably less than the 15–20 km that has been inferred by other workers from surface geological investigations. Small positive gravity anomalies are associated with iron formation. A persistent depression in the observed gravity field over the centre of the trough in the south coincides with deposits of the basal sedimentary unit. Uncertainty in the location of the regional level prohibits accurate thickness determinations of the causative bodies of negative anomalies in this area, but the approximate values of 2–3 km obtained for the basal unit are of the same order as estimates based on geological investigations. In the northern part of the area the causative bodies of the negative anomalies are probably elevated areas of granitic basement. These elevated basement features may be related to a ridge that controlled sedimentation during much of the trough's history.
Lead isotopes in the Grenville and adjacent Palaeozoic formations
Authors: Fletcher Ian R. , Farquhar R. M.
Published: April 2011

Lead-isotope ratios have been determined for a preliminary set of 16 galenas from the Grenville and some adjacent Palaeozoic formations in southern Ontario and Quebec. The 206Pb/204Pb ratios of the Grenville-hosted deposits range from 16.24 to 20.20. Six of the Grenville-hosted samples have a post-Ordovician age of mineralization, but may represent re-mineralized Grenville lead. With the five 'true' Grenville samples they can be used to define a Grenville 'secondary isochron' on a 207Pb/204Pb–206Pb/204Pb plot. The trend of this isochron appears to be consistent with published feldspar- and marble-lead data for nearby sections of the Grenville. Its slope (.120 ±.015) is compatible with a time of ~1300 Ma ago for inclusion of uranium in the sediments of the Grenville supergroup, followed by lead mineralization at ~1000 Ma. Calculations based on a simple lead-isotope evolution model give a similar age (1280 ± 15 Ma) for the stratabound Tétrault Pb–Zn deposit.The geologically similar New Calumet deposit has a quite different model age of 1115 ± 20 Ma. This is similar to the model age of the Balmat, New York ore deposits and it appears that New Calumet and Balmat may be members of a contemporaneous mantle (volcanic)–continental sequence.An apparent correspondence of the isotopic ratios of the Palaeozoic samples with the Grenville secondary isochron raises some critical questions regarding the development and migration of the Pb in these deposits.
A gravity study of the Saguenay area, Quebec
Authors: Duncan P. M. , Garland G. D.
Published: April 2011

Results are presented of a detailed gravity survey over the Saguenay valley and adjacent areas. Gravity anomalies have been separated into features of long and short wavelength by the method of upward projection, and interpreted in terms of crustal models. A negative anomaly over the lowlands can be explained by downfaulting of denser units within the crust, giving support to the hypothesis of a graben structure. Downward displacement of the Mohorovicic discontinuity would be compatible with the observations, but cannot be verified by the gravity field alone.