bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochronology of orthogneiss adjacent to the Archean Lake of the Woods greenstone belt, northwestern Ontario: a possible basement complex
Authors: Clark G. S. , Bald R. , Ayres L. D.
Published: April 2011

Deformed and recrystallized, amphibolite facies, trondhjemitic to granodioritic orthogneiss along the north margin of the Archean Lake of the Woods greenstone belt has an Rb–Sr isochron age of 2950 ± 150 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0014. Preserved primary textures and complex internal intrusive relationships document the original plutonic nature of the orthogneiss. Based on isotopic age and degree of deformation and recrystallization, the orthogneiss is interpreted to be basement to the adjacent metavolcanic sequence of the greenstone belt. The contact between the orthogneiss and greenstone belt is the locus of deformation, but may be an unconformity. It is also the boundary between the English River subprovince on the north and the Wabigoon subprovince on the south.Similar orthogneiss ranging in age from 2800 to 3800 Ma is widespread in the Canadian Shield. It is basement to the 2650–2750 Ma Archean volcanism, at least in some areas, but is not necessarily basement to the older (2800–3000 Ma) volcanism. The orthogneisses are remnants of a once much more extensive sialic terrain, but the contemporaneity and extent of this sialic terrain are uncertain.
Characteristics of the western Quebec seismic zone
Authors: Forsyth D. A.
Published: April 2011

A comparison of geological data shows that most of the earthquakes of western Quebec lie within or near the eastern and western boundaries of a Grenville (ca. 1000 Ma) central metasedimentary belt and in the area of the younger fault zone along the Ottawa River. Although most of the earthquakes have occurred within terrain of Grenville age or older, the younger rift zone is characterized by the larger earthquakes (Temiskaming, M6.2, 1935; Cornwall–Massena, M5.7, 1944). The earthquakes also correlate with gradient zones around two prominent anomalies in the smoothed Bouguer gravity field.The pattern of aeromagnetic anomalies and drainage channels reflects Preeambrian structural trends and indicates the central metasedimentary belt continues beneath Paleozoic sediments to Lake Ontario. The strikes of magnetic, gravity, and drainage features north of Lake Ontario are parallel to features mapped to the south of the lake. Geological data and geophysical trends suggest that a cataclastic zone is continuous along most of the eastern border of the metasedimentary belt. A prominent, positive regional aeromagnetic trend and some cataclastic evidence characterize the western border.Although the seismicity may reflect the adjustment of existing structures to stresses from regional density variations, continental deglaciation, and interplate forces, the reason for the greater seismic activity in the Grenville age terrain than along the younger fault zones remains unclear.
Semicircular canal size in fossil fishes and amphibians
Authors: Bernacsek Garry M. , Carroll Robert L.
Published: April 2011

Mean semicircular canal radius of curvature as a function of body mass was estimated for 18 fossil fish and 2 fossil labyrinthodont amphibians. The statistically significant regression for fossil fish is closely comparable to that of Recent teleosts, but both differ substantially from that of Recent mammals. Fossil labyrinthodont amphibian data points fall fairly close to those of Recent mammals, suggesting that all tetrapods are characterized by smaller semicircular canal dimensions than those of fish. No simple explanation of this dichotomy can be offered because several other important parameters which may affect semicircular canal sensitivity are presently poorly known, or cannot be measured in fossils.
The use of alpha scintillation counting for measuring Th-230 and Pa-231 contents of ocean sediments
Authors: Huntley D. J. , Wintle A. G.
Published: April 2011

We describe here a simple method of determining Th-230 and Pa-231 contents of ocean sediments using alpha scintillation counting. The Pa-231 content is determined by counting pairs of alpha particles emitted within 4 ms of each other. The Th-232 content is determined by counting pairs of alpha particles emitted within 0.4 s of each other. The Th-230 content is found from the total alpha count rate after contributions from the Pa-231, Th-232, U-238, and U-235 decay chains are subtracted. The uranium content is obtained from independent measurements or from alpha counting measurements on samples deep enough that the Th-230 content is negligible.The method is checked by comparing measured and calculated count rates on six standards and then by comparing our results on a set of core samples with those obtained by alpha spectrometry. The agreement is generally satisfactory except for a possible discrepancy of ~20% in the pair count rates. Results are presented for two other cores; these did not show a simple decrease of Th-230 content with depth. One showed three oscillations superimposed on an overall decrease; the other showed fluctuations of at least 20%/cm along with an overall decrease. It is suggested that these fluctuations may be associated with variations in the manganese oxide content.
The age and origin of the garnet amphibolite underlying the Thetford Mines ophiolite, Quebec
Authors: Clague David , Rubin Jason , Brackett Russell
Published: April 2011

The Thetford Mines ophiolite in southern Quebec is partially underlain by an 800 m thick amphibolite aureole. Rocks in the metamorphic unit grade inward towards the base of the ophiolite from chlorite–muscovite schist, epidote amphibolite, and garnet amphibolite to clinopyroxene-bearing garnet amphibolite closest to the fault contact with the basal tectonized peridotite unit of the ophiolite. The polydeformed metamorphic unit pinches out north and south of Belmina Ridge and is discordant with the overlying tectonized peridotite. Analyses of nine samples show a range of compositions, but the low K2O, P2O5, Rb, Zr, and Sr suggest that the amphibolite protolith was tholeiitic basalt, probably midocean ridge tholeiite.Microprobe mineral compositions determined for coexisting clinopyroxene–garnet–amphibole and garnet–amphibole suggest that amphibolites near the peridotite contact equilibrated at about 850 °C and that the temperatures decreased to about 380 °C 700 m from the contact. Geobarometers based on coexisting clinopyroxene and garnet, and Al and Na partitioning in amphibole yield variable results, but suggest that the pressure during formation of the amphibolite was probably greater than 5 kbar (5 × 105 kPa).Eight conventional K–Ar ages average 488 ± 11 Ma but show some scatter due to inaccuracy of K2O determinations at very low concentrations and, in some samples, possible inherited argon. A single 40Ar/39Ar incremental heating experiment gives concordant plateau and isochron ages of 491 ± 4 and 494 ± 4 Ma, respectively. The best weighted age of 491 ± 3 Ma probably dates the decoupling of the Thetford Mines ophiolite during the initial phase of closing of the Proto-Atlantic Ocean.
The Sept Iles anorthosite complex: field relationships, geochronology, and petrology
Authors: Higgins Michael D. , Doig Ronald
Published: April 2011

The Sept Iles anorthosite complex is located in the Grenville (structural) Province of the Canadian Shield. Geochronological studies of both the basic and acidic portions of the complex show that it was intruded approximately 540 Ma ago and thus post-dates the Grenville orogeny by at least 500 Ma. Field relationships confirm the contemporaneity of the basic (anorthosite and gabbro) and acidic (syenite and granite) rocks. Differentiation of the basic magma was controlled by preferential nucleation in the boundary layer. Crystal separation due to gravity and possibly liquid immiscibility caused differentiation once intermediate or acidic magma compositions were formed. There is no evidence that crustal contamination has played a role in the generation of the acidic rocks. The complex has been intruded along the St. Lawrence graben fault, known to have been active at this time from the profusion of igneous rocks elsewhere along this structure, which are contemporaneous with the Sept Iles complex. Activity on this fault has disrupted the complex so that rocks found on the mainland were originally formed at the base of the complex, whereas rocks exposed on the islands were formed at the top of the complex. This study of the Sept Iles complex shows that anorthosite is not restricted to Precambrian terranes, and may be associated with acidic alkaline rocks and large-scale ensialic rifting.
Chemical and X-ray diffraction analyses in tills of southern Ontario
Authors: Gwyn Q. H. J. , Fryer B. J. , Dreimanis A. , Reid A. M.
Published: April 2011

The ratio of red to purple garnets found in tills in the eastern Great Lakes area has been very useful in stratigraphic and provenance studies of the tills. In an attempt to determine the basis of the color difference, and to supplement the colour differences by more objective criteria in till studies, X-ray diffraction and fluorescence, atomic absorption, and microprobe analyses were made. X-ray diffraction analyses show a consistent difference in the cell parameter of 0.05 Å (0.005 nm) or more between the two groups. Microprobe analyses of major elements indicate that the calcium and calculated ferric iron contents are higher and magnesium is lower in dark red garnets than in purple garnets. Bulk analyses of minor and trace elements by X-ray fluorescence and atomic absorption of different colour groups show distinct differences in rare-earth element patterns and manganese, which is eight times more abundant in the dark red garnets.
Broad-scale magnetic anomalies over central and eastern Canada: a discussion
Authors: Coles R. L. , Haines G. V. , Hannaford W.
Published: April 2011

Profiles of anomalies in the vertical component of the Earth's magnetic field over central and eastern Canada, observed at an average altitude of 4 km above sea level, show broad regions with distinctive anomaly character. These subdivisions indicate major differences in the evolutions of regions within individual structural provinces. Particularly notable is a region of intense anomalies in the northern part of the Superior Province in Quebec, contrasting with much weaker anomaly relief to the south and east.
Mid-Tertiary volcanic rocks of the Cascade Mountains, southwestern British Columbia, ages and correlations
Authors: Mathews W. H. , Berman R. G. , Harakal J. E.
Published: April 2011

Potassium–argon dates and chemical data have been obtained from three mid-Tertiary volcanic centres in the Hope area of the Cascade Mountains, southwestern British Columbia. Two of these, the Coquihalla volcanic centre and the Podunk Creek body, prove to be of early Miocene age (ca. 22 Ma), whereas the Skagit Formation is mid- to late Miocene (ca. 12.5 Ma). All three bodies are calc-alkaline.
Earliest cavity-dwelling organisms (coelobionts), Lower Cambrian Poleta Formation, Nevada
Authors: Kobluk David R.
Published: April 2011

The record of cavity-dwelling organisms (coelobionts) is long ranging, and is known to extend as far back as the upper Lower Cambrian. Older coelobionts, from the middle Lower Cambrian Poleta Formation of western Nevada, have been found, however, in framework cavities in archaeocyathid patch reefs, thus extending the record of the coelobiontic community even further.The Poleta Formation coelobiontic community is less diverse than that found in the upper Lower Cambrian community (from cavities in archaeocyathid patch reefs of the Forteau Formation of Labrador); it is dominated by algae, in particular Epiphyton. Renalcis and encrusting mammillary algae play a secondary role. Juvenile archaeocyathids, soft sponges, Archaeotrypa, and microtubules make up the remainder of the skeletal cavity biota. Sediments that floor the cavities contain a low-diversity but abundant infauna represented by meandering burrows; horizontal feeding or locomotion traces were produced on the surface of the cavity sediments.
Geochronology of the Swift Current granite and host volcanic rocks of the Love Cove Group, southwestern Avalon zone, Newfoundland: evidence of a late Proterozoic volcanic–subvolcanic association
Authors: Dallmeyer R. D. , Odom A. L. , O'Driscoll C. F. , Hussey E. M.
Published: April 2011

Zircon fractions from the variably deformed and metamorphosed Swift Current granite and host volcanic rocks of the Love Cove Group record individually discordant U–Pb ages with well-defined upper concordia intercept ages of 580 ± 20 and 590 ± 30 Ma, respectively. These are interpreted to be crystallization dates and indicate a late Proterozoic cogmagmatic relationship. Primary hornblende from the pluton record disturbed 40Ar/39Ar age spectra that suggest postcrystallization argon loss, probably during Acadian (Devonian) regional metamorphism. 40Ar/39Ar plateau ages of 560–566 Ma are well defined for the hornblende and are interpreted to date times of postmagmatic cooling. The similarity between zircon and hornblende dates suggests relatively rapid postmagmatic cooling. A six-point, Rb–Sr whole-rock isochron age of 548 ± 11 Ma is defined for the pluton. The slight discordancy of this date in comparison with the zircon and hornblende ages may reflect a minor disturbance of whole-rock isotopic systems during Acadian regional metamorphism.
The vertebrae of Youngina (Reptilia: Eosuchia)
Authors: Currie Philip J.
Published: April 2011

Since 1914, Youngina has formed the basis of our concept of the Eosuchia, the basal stalk from which all later diapsid reptiles probably evolved. Recent examination of the type specimen has revealed the presence of accessory intervertebral articulations. This derived character suggests close relationship between Youngina and the Tangasauridae, but also suggests that Youngina is too specialized to be an ancestral morphotype for other eosuchians, eolacertilians, or archosaurs.
Paleomagnetism of the Fond du Lac Formation and the Eileen and Middle River sections with implications for Keweenawan tectonics and the Grenville problem
Authors: Watts Doyle R.
Published: April 2011

Overlying the Keweenawan lavas of northern Wisconsin and Michigan is a thick sequence of terrestrial sandstone, shale, and siltstone that has undergone some tectonic deformation associated with movement along thrust faults and the development of the Lake Superior syncline. Thermal and alternating field demagnetization, chemical leaching, and multivector analysis using orthogonal projections reveal a trivector structure of the natural remanent magnetization (NRM) of the Fond du Lac Formation and Middle River section (Amnicon and Orienta Formations), and a bivector structure of the NRM of the Eileen section (Eileen Formation). The components may be classified by their physical properties as revealed by demagnetization. A population of high blocking temperature components, K1, is found in all three sections and gives poles as follows: Fond du Lac, 16°N, 160°E; Middle River, 25°N, 148°E; Eileen, 20°N, 156°E after structural correction is applied. A population of intermediate blocking temperature components, K2, is post-tectonic and found only in the Fond du Lac Formation and Middle River section. Poles calculated from K2 fall among the Grenville type poles (Fond du Lac, 9°S, 145°E; Middle River, 24°S, 162°E). A third population of components, K3, has low blocking temperature and coercivity and is isolated only by chemical leaching. K3 has steep positive inclination, northern declination, and is post-tectonic. It is interpreted as a recent magnetization.Any interpretation of the path of apparent polar wander for North America must accommodate the sequence of magnetization K1 to K2. The timing of tectonism in the Keweenawan basin is bracketed by the times of acquisition of K1 and K2. These results reconfirm some recent interpretations that include Grenville poles on the polar wander track of interior Laurentia.
Geology of the Nemo Lakes belt, northern Valhalla Range, southeast British Columbia
Authors: Parrish Randall R.
Published: April 2011

High-grade metasedimentary rocks, probably of both early Paleozoic and late Paleozoic – Triassic ages, underlie an area termed the Nemo Lakes belt between Slocan and Arrow Lakes in the northern Valhalla Range, southeastern British Columbia. The rocks have experienced two possibly related periods of major folding. Phase 1, accompanied and outlasted by metamorphism at P–T conditions of 5.0–6.8 kbar (500–680 MPa) and 630–680 °C, involved emplacement of ultramafic rocks, major faulting, and folding. Phase 2 involved large-scale inclined to upright folds which were dominantly south-verging, deforming the phase 1 fabric. Both phases probably occurred in the Middle to Late Jurassic, as part of the Columbian Orogeny.Rocks lithologically and structurally similar to those of the Nemo Lakes belt are found across the Rodd Creek fault near the Columbia River and extend the general continuity of the belt into the Shuswap metamorphic complex.Plutonic rocks, some of which bracket the movement on the Rodd Creek fault, the southern extension of the Columbia River fault zone, range in age from Middle Jurassic to EoceneIn the valley of Slocan Lake, a major normal fault is postulated on structural and metamorphic grounds and may be related to the north–south arching of the Valhalla gneiss complex. It is suggested that this arching and uplift, which followed phase 2 deformation, produced both the fault and a zone of cataclasis on the eastern side of the complex, and gave rise to its domal shape.
Upper Middle Ordovician submarine fans and associated facies, northeast of Quebec City
Authors: Belt Edward S. , Bussières Louise
Published: April 2011

Autochthonous upper Middle Ordovician strata northwest of Logan's Line and northeast of Quebec City have been subdivided into six facies types. One or more facies type characterizes the revised formations of our previous report (Belt et al.). These facies were deposited in the following depositional environments: moderately shallow carbonate bank; deeper carbonate slope and foot of slope; submarine fan; and basin plain. The submarine fan facies (Beaupré and Saint-Irénée Formations) contain the only facies with appreciable sandstone. The source region of the sandstones (determined by petrography and paleocurrents) lay to the southeast of Logan's Line. This source was uplifted and eroded during the early phases of the Taconic Orogeny. Turbidity currents and debris flows brought sand into a foredeep trough that lay between the mobile Taconic Orogen and the more stable Canadian Shield. During Trenton time, a carbonate bank developed on the margin of the shield, northwest of the trough axis. Olistostromes, produced by bank-edge collapse, slid southeast into the trough and intercalated with the Saint-Irénée sandy fan lobes derived from the other side of the foredeep basin. Bottom currents, reworking the sand, flowed southwest along the axis of the trough. Later, after regional foundering of the carbonate bank, a larger (Beaupré Formation) submarine fan developed in the foredeep basin. Bottom currents continued reworking the sands down the trough to the southwest.The submarine fans found in this region never developed some of the facies associations commonly expected of suprafan lobes. The initial fan facies consists of lenticular coarse and pebbly sandstone and shale that are only rarely organized into coarsening-up successions. No definite feeder channel deposits are found in the Saint-Irénée Formation although three are recognized in the middle Beaupré Formation at the type section. The presence of these channels plus the geometry of all Beaupré facies and the paleocurrent divergence show that these facies are not disorganized base-of-slope or basin-plain deposits, but best fit a submarine fan model.
Petrochemistry of late Aphebian (~ 1.8 Ga) calc-alkaline diorites from the East Arm of Great Slave Lake, N.W.T., Canada
Authors: Badham J. P. N.
Published: April 2011

The East Arm of Great Slave Lake is a 2.5–1.7 Ga graben connected to the contemporaneous Wopmay Orogen on the margins of the Archean (2.5 Ga) Slave craton. It contains three major groups of sedimentary and volcanic rocks. The two earlier ones are cut by ~ 1.79 Ga diorites, which outcrop over 220 km along the graben.The diorites were preferentially emplaced as laccoliths into a horizon of megabreccia thought to be the product of evaporite solution and collapse. The diorites are similar down the entire length of the East Arm. Main phases are usually plagioclase–hornblende poryphyritic, but younger and possibly high level phases contain biotite and quartz. The diorites are calc-alkaline but show no obvious chemical trends along the graben. They cannot be related directly to the proposed easterly dipping, late Aphebian subduction zone that generated the Wopmay Orogen.
Temporal and spatial variations of mercury, lead, zinc, and copper in sediments of the Saguenay fjord
Authors: Barbeau C. , Bougie R. , Côté J.-E.
Published: April 2011

Sediment profiles of 19 cores from the Saguenay fjord, Québec, Canada, have been analyzed for mercury, lead, zinc, and copper. Core dating of post-1940 sediments is possible with above background concentrations of mercury. The results agree well with those obtained previously with 137Cs. The northern basin of the fjord is the site of a major accumulation of trace elements. The chronological distribution of mercury follows the events related to the operation of a chlor-alkali plant: construction, increased production, control of losses, and closing. The effect of a major landslide in 1971 is clearly shown in many sediment profiles. The western basin of the fjord contains sediments enriched in mercury, lead, and zinc. Mercury input in the fjord has diminished since 1970 but other trace element influxes keep increasing. Trace elements in the north basin correlate well with carbon. Atmospheric lead appears to be a major anthropogenic source in sediments of the western basin.
Uplift estimated from remanent magnetization: Munro area of Superior Province since 2150 Ma ago
Authors: Buchan Kenneth L. , Schwarz Erik J.
Published: April 2011

A method for determining depth of burial from remanent magnetization was applied to three igneous contacts of two different ages in Munro Township of the Superior Province of the Canadian Shield. Sampling profiles perpendicular to the contact of a 2150 Ma diabase dike, one collected in an older (2690 Ma) diabase dike and a second in gabbro country rock, yielded ambient temperatures for the present erosion surface at the time of dike emplacement of 219 ± 23 and 181 ± 7 °C, respectively. A third sampling profile perpendicular to a 2690 Ma dike failed to provide a usable magnetic contact zone.A secondary magnetic component with shallow inclination and easterly declination was detected in individual samples collected from both dikes as well as from the surrounding country rock. Converging remagnetization circles indicate that this component, acquired some time after emplacement of the younger (2150 Ma) dike, has the direction D = 70°, I = −39° and corresponding paleopole 39°E, 4°S.
Paleomagnetism of Lower Cambrian volcanics and a cross-cutting Cambro-Ordovician diabase dyke from Buckingham (Quebec)
Authors: Danker Peter , Lapointe Pierre
Published: April 2011

The Buckingham area (Quebec) is characterized by Cambrian volcanic flows (573 ± 32 Ma) cut by a Cambro-Ordovician diabase dyke, which is dated at 497 ± 14 Ma by K–Ar method. The volcanics yield multicomponent magnetizations: a hard characteristic magnetization and a relatively soft one. These components could be separated easily and the intensity decay curves of the different components could also be obtained separately using Zijderveld's method. Three different groups of site-mean characteristic magnetizations can be distinguished, each representing a different stratigraphic level. The paleopoles derived from these magnetizations are, from oldest to youngest, 186°E, 10°S; 173°E, 01°N; and 154°E, 06°N. This is interpreted as a rapid motion of the paleopole for the North American craton during the Early Cambrian. The paleopole derived from the hard characteristic dyke direction is 123°E, 03°S. This magnetization direction was also found at one of the sites in the volcanics. This means that the contact test is positive and that the hard characteristic magnetization of the dyke is acquired at the time of intrusion.
Paleomagnetic investigations in igneous–metamorphic rock units in eastern New England
Authors: Hurley P. M. , Shearer C. K.
Published: April 2011

A clustering of paleomagnetic poles for rock units of mid-Paleozoic (ca. 400 Ma) age in eastern New England indicates that a variety of lithologic types may be used to obtain virtual geomagnetic poles (VGP's) in an igneous–metamorphic terrain. These rock types include chilled margins of basaltic dikes or narrow dikes, hydrothermal alterations such as epidote veinlets, mafic rocks reset by low-grade metamorphism, and hypabyssal igneous bodies, particularly where there is evidence of hydrothermal activity.The results suggest the approach to be followed to obtain valid VGP's in similar geological belts in the Precambrian. The remanence directions in Devonian and Mississippian rock units in eastern Massachusetts and southern and northern Maine are close to other determinations of similar age within the Maritime block, demonstrating the potential usefulness of the procedures.
Thermodynamic regime of greenstone metamorphism of basic volcanic rocks after experimental data
Authors: Pluysnina L. P. , Ivanov I. P.
Published: April 2011

The stability fields of laumontite, prehnite, pumpellyite, zoisite, and tremolite-bearing assemblages were experimentally examined in the CaO–MgO–Al2O3–SiO2–H2O–CO2 system. The influence of the Fe content on the shift of the upper stability boundary towards both lower temperature and [Formula: see text] equilibrium values is shown for pumpellyite. The runs for some dehydration–carbonatization reactions in the complex H2O–CO2–NaCl fluid have revealed a decrease in the [Formula: see text] equilibrium values for even low salt content. The zeolite, prehnite–pumpellyite, and greenschist facies limits are plotted in the schematic [Formula: see text] diagram, and their possible Pfl limits are discussed. For examined P–T conditions of greenschist to amphibolite facies transition the absence of the compositional gap between tremolite and Ca-hornblende is found.
Pleistocene fishes (Coregonus, Osmerus, Microgadus, Gasterosteus) from Green Creek, Ontario, Canada
Authors: McAllister Don E. , Cumbaa Stephen L. , Harington C. R.
Published: April 2011

Specimens of Coregonus cf. artedii and Microgadus tomcod are reported for the first time from calcareous nodules at Green Creek. The occurrence of Osmerus mordax and fully plated Gasterosteus aculeatus in these nodules is confirmed. Analysis of the 10 species of fishes now known of late Wisconsin or early postglacial age from this region suggests the following not necessarily contemporaneous paleoenvironments: oligotrophic lakes, a cool deep marine bay with gravel beaches, and a brackish estuary fed by creeks.
The structure of a talus-derived rock glacier deduced from its hydrology
Authors: Johnson P. G.
Published: April 2011

The paper presents the results of an experiment in the use of hydrological parameters to study the internal structure of a rock glacier. The rock glacier selected for the study lies at the head of Grizzly Creek in the southwest Yukon Territory. The hydrological network suggests two independent drainage systems, which demonstrate the occurrence of a planar impervious structure at depth and independent lines of drainage controlled by the flow structures in the near-surface deposits. Chemical changes in the water are inconclusive with respect to the evaluation of ice contents of the landform although the physical evidence strongly suggests no massive ice component. Chemical characteristics of each drainage system are sufficiently different that chemical tests can be used to differentiate sources of the drainage.
Thawing of seasonally frozen ground in organic terrain in central Saskatchewan
Authors: FitzGibbon J. E.
Published: April 2011

Surveys of ground frost in three peatland types, sedge fen, transitional (tamarack) fen, and black spruce – Sphagnum bog, in central Saskatchewan showed differences in depth of freezing and rates of thawing. The maximum depth of freezing and most rapid removal of ground frost occurred in the fen and transitional fen. Seasonal frost was found in the bog until late August. Thawing occurs primarily from the surface downward. However, some thawing from below may occur in the fen. Thawing from the surface is strongly related to the number of thawing degree–days.
Natural temporal variations in the chemistry of shallow groundwater, Athabasca Oil Sands area, Alberta
Authors: Hackbarth Douglas A.
Published: April 2011

Significant natural variation of the chemistry of shallow groundwater was observed from 1977 through 1979 in three wells located in the Athabasca Oil Sands area, Alberta. The wells are between 5 and 8 m deep and are located in boreal forest far from any direct influence by man.The coefficient of variation of total dissolved solids for the well sampled monthly for 35 months was 34%, while those for the two wells sampled bi-monthly were 21 and 11%. The coefficient of variation for individual constituents was generally higher than the above values.An annual pattern of variation in shallow groundwater chemistry is recognized. Calcium, magnesium, and bicarbonate reach lowest annual concentration in the spring and rise rapidly by early summer. Concentration of these ions gradually decreases through fall and winter. This cycle is related to the abundance of dissolved carbon dioxide in recharge water and is controlled to a great extent by the abundant muskeg.Spring and fall are typically times of highest sulfate concentrations. This is coincident with recharge events and is related to leaching of sulfur compounds. High chloride during winter is related to slower rates of groundwater flow and the consequent increased opportunity for release of ions from chloride-bearing minerals.Information from other wells in the Athabasca Oil Sands area indicates that the coefficient of variation of total dissolved solids with respect to time generally decreases with depth. Coefficients of variation might be expected to be as high as 35% at depths of 10 m; the range declines to a relatively constant 4% at depths greater than 150 m.
A re-examination of the type area of the Devono-Mississippian Cariboo Orogeny, central British Columbia
Authors: Struik L. C.
Published: April 2011

Three tectonostratigraphic successions are established from remapping of the area near Barkerville and Cariboo River. The first, of Late Proterozoic to Cambrian sediments, was deposited on the shallow to moderately deep platformal shelf west of and derived from the exposed North American craton. The second is an unconformably overlying Ordovician to Permian sequence of sedimentary and volcanic rocks representing a basinal environment with periodic highs. These packages of sediments were deposited on the North American craton and its western transitional extensions. The third succession, composed of oceanic chert and basalt of the Permo-Pennsylvanian Antler Formation, was thrust eastward over the other two during the early Mesozoic. The three successions were folded, faulted, and metamorphosed during the mid-Mesozoic Columbian Orogeny. The Devono-Mississippian Cariboo Orogeny, which was thought to have affected all of the first sequence and part of the second, could not be documented in its type locality. The geology of the Barkerville – Cariboo River area has many similarities with that of Selwyn Basin and Cassiar platform of northern British Columbia and Yukon.
Paleomagnetism of parts of the Late Triassic diabase dike system associated with the trans-New Brunswick aeromagnetic lineament
Authors: Seguin M. K. , Rao K. V. , Venugopal D. V. , Gahe E.
Published: April 2011

A paleomagnetic study was conducted on dike samples taken from three widely separated localities along the northeasterly trending Caraquet dike system (New Brunswick) in order to define their age relationship. This dike system is recognized on the basis of a well defined aeromagnetic lineament. Stable magnetization directions were isolated after alternating field (15–40 mT) and thermal (300–550 °C) treatments of the samples taken from the three localities: C (353°, +56°), N (353°, +50°), and T (14°, +37°). The virtual pole derived from dike T (82°E, 62°N) agrees well with previously determined Late Triassic – Early Jurassic (200–190 Ma) poles for the Appalachians. On the other hand, the other two virtual pole positions from dikes C (143°E, 78°N) and N (133°E, 74°N) fall in the general area of average paleopoles for the Middle–Late Jurassic (180–170 Ma) age. The possibility that the dike at T differs in age from that of the dikes at localities C and N by at least 20 Ma is suggested. In the absence of reliable radiometric data, it is premature at the present stage to predict a likely occurrence of "younger" magnetization in these dikes related in origin to viscous partial thermoremanence possibly associated with the rifting and opening of the Atlantic in Middle Jurassic. Further investigations on newly found diabase outcrops along the magnetic lineament are in progress.
Étude paléomagnétique des roches protérozoïques de la formation de Sakami, région de la Grande Rivière, Territoire du Nouveau-Québec, Canada
Authors: Seguin Maurice K. , Sharma Kamal N. M. , Woussen Gérard
Published: April 2011

We describe a paleomagnetic study of Mid-Proterozoic sandstone of the Sakami Formation. The thermal demagnetization is more effective than by alternating field; this indicates that part of the magnetic memory is located in hematite. The mean direction of magnetization after thermal and alternating field treatments is 031, −25 α95 = 7.1°, K = 73 and the corresponding paleopole position is 103°W, 18°S (dm = 11°, dp = 8°). These results are important because a part of this geological formation will be covered with water after completion of the development works of La Grande Rivière. [Journal Translation]
New evidence for the age of the Skonun Formation, Queen Charlotte Islands, British Columbia
Authors: Champigny N. , Henderson C. M. , Rouse G. E.
Published: April 2011

Recent palynological, megafaunal, and intrusive evidence from a section low in the Skonun Formation in the Cinola deposit on Graham Island indicates that it was deposited in the late Early Miocene, and that the age of the Skonun ranges up to the early Middle Miocene in outcrop sections on northeastern Graham Island. Correlations are made with several Miocene series of the Pacific Northwest and Alaska.
Volcanism of shoshonite to high-K andesite affinity in an Archean are environment, Oxford Lake, Manitoba
Authors: Brooks C. , Ludden J. , Pigeon Y. , Hubregtse J. J. M. W.
Published: April 2011

Volcanic rocks of the Archean Oxford Lake Group are characterized by a stratigraphic progression from mafic to felsic compositions, accompanied by a systematic decrease in incompatible element abundances. This, coupled with high abundances of Sr, Rb, K2O, and La, high (La/Yb)n, and unfractionated (flat to concave) heavy-REE (rare earth element) profiles, distinguishes these rocks as an Archean shoshonite to high-K andesite – dacite–rhyolite series, directly comparable to modern analogues formed in convergent tectonic settings. The trace-element data support a model of petrogenesis in which an Archean mantle source region was modified by volatiles rich in large-ion-lithophile elements, the modified mantle was subjected to partial melting forming a parental liquid of shoshonitic character, and this liquid principally underwent amphibole fractionation to form the evolved rock compositions. This process is envisaged as terminal magmatism during the final (senile) stage of activity in an arc setting. The Rb–Sr age (2650 ± 80 Ma) and initial-Sr ratio (0.70145 ± 38) of the Oxford Lake Group are in accord with this model; when coupled with the 2.7 Ga age for the underlying Hayes River Group volcanics, these data indicate a short interval (<50 Ma?) for Archean crustal development in the area.
A reconsideration of the relationships of the fossil amphibian Albanerpeton
Authors: Fox Richard C. , Naylor Bruce G.
Published: April 2011

Previously thought to be a salamander (Prosirenidae), Albanerpeton Estes and Hoffstetter (Jurassic to Miocene) possesses no known features otherwise restricted to salamanders. Its salamander-like features are only those held in common with small, limbed, non-saltatorial amphibians in general. In still other aspects (including feeding apparatus, dermal bones of the skull, and anterior cervical vertebrae), Albanerpeton appears unique. Already well isolated from salamanders, Albanerpeton seems no nearer phyletically to any other known amphibians, from Devonian to Recent. The relationships of Albanerpeton are most consistently indicated by classification in its own family (Albanerpetontidae, new) and order (Allocaudata, new), perhaps referrable to the Lissamphibia.
Magnetic hysteresis as a function of low temperature for deep-sea basalts containing large titanomagnetite grains—inference of domain state and controls on coercivity
Authors: Hodych J. P.
Published: April 2011

Hysteresis loops to 1200 Oe (95 kA∙m−1) are measured between 295 and 105 K for two deep-sea basalts (DSDP, legs 34 and 37) containing large (~200 μm) unexsolved titanomagnetite grains. The Curie points, electron microprobe analyses, and saturation magnetizations of the magnetic grains are the same as for synthetic titanomagnetite (xFe2TiO4∙(1 −x)Fe3O4) with x = 0.6.As temperature is lowered from 295 to 190 K, coercive force Hc slowly rises from ~40 to ~95 Oe (3.2 to 7.6 kA∙m−1) approximately in proportion to the rise in the magnetostriction constant λ. Presumably, Hc is controlled by λ through internal stresses impeding domain wall motion. As expected of multidomain grains, the ratio of saturation remanence to saturation magnetization (in 1200 Oe (95 kA∙m−1) cycles) jR/jS rises approximately in proportion to Hc with a constant of proportionality consistent with titanomagnetite (x = 0.6).As temperature is lowered from 190 to 120 K, Hc rises rapidly to ~400 Oe (32 kA∙m−1) as a roughly linear function of the magnetocrystalline anisotropy constant K1. Perhaps Hc is now controlled by K1 through non-magnetic inclusions impeding domain wall motion.As temperature is lowered from 120 to 105 K, Hc rises even more rapidly to ~600 Oe (48 kA∙m−1). The control over Hc seems to have changed again, though most of the titanomagnetite is in grains large enough to still likely contain a few domains. The ratio jR/jS reaches 0.7 by 105 K and appears to be saturating towards the theoretical limit of 0.83.
Sr, Y, Zr, Nb, Ti, and REE in Grenville amphibolites at Montauban-les-Mines, Quebec
Authors: MacLean W. H. , St. Seymour K. , Prabhu M. K.
Published: April 2011

Distribution of Ti, Sr, Y, Zr, Nb, and REE in Proterozoic amphibolites and a rarely preserved pillowed metabasalt in the vicinity of Pb–Zn mineralization at Montauban-les-Mines in the Grenville Province of Quebec are used to assess the tectonic setting of the volcanism and, hence, the environment of ore deposition. Absolute abundances of Ti, Sr, Y, Zr, and Nb are close to those reported for modem island-arc and back-arc basalts. The flat patterns of the chondrite-normalized REE distribution and the discrimination plots of the other elements indicate a tholeiitic affinity for the volcanism. Specifically, plots of Ti against Zr and Ti–Zr–Y are mostly in the fields reported for ocean-floor (MOR and back-arc) basalts, but overlap with arc tholeiites. Cr and Ni are, however, higher than for most arc tholeiites. Overall, the data are most compatible with tholeiitic volcanism in an island-arc (including back-arc) environment.
Identifying tephras by alpha counting
Authors: Cormie A. B. , Huntley D. J. , Nelson D. E.
Published: April 2011

Alpha counting, as used for determination of uranium and thorium concentrations, was found useful for identifying some tephras found in northwest North America. The method has the advantage of requiring only minimal sample preparation and the potential of providing a field technique for identifying tephras.
Tectonic structures related to thrusting of ophiolitic complexes: the White Hills Peridotite, Newfoundland
Authors: Girardeau J.
Published: April 2011

The White Hills Peridotite and its underlying metamorphic rocks represent the basal portion of a partly eroded ophiolitic complex. At the contact with the metamorphic rocks, the peridotites display low-temperature–high-stress mylonitic textures, which grade upwards to fine-grained porphyroclastic textures indicative of higher temperatures and lower stresses. Petrological and structural evidence indicates that the mylonitic peridotites and underlying metamorphic rocks have been deformed during the oceanic thrusting of the lithosphere. The analysis of the main tectonic structures observed in the peridotites shows that the complex has been thrust northwestward along a southeast-dipping thrust plane. The data are compared with those obtained from the Bay of Islands ophiolite complex.
Complex evolution of folds and cleavages in Archean rocks, Yellowknife, N.W.T.
Authors: Fyson W. K.
Published: April 2011

Overturned folds and later cleavages in a metasedimentary terrain with marginal volcanics near Yellowknife form a complex succession in which structures repeatedly trend eastward and northward. Early major east–west folds are overturned away from a southern granodioritic complex and terminate westward against a major syncline, with limbs overturned inward, trending north–south along the western granitoid boundary of the terrain. Later smaller folds (limbs ~1 km), which die out away from granitoid plutons, include a progression from northerly to easterly trending structures. Several sets of cleavage foliations, mostly steeply inclined, transgress the folds: an east–west set, succeeded by a regionally dominant set striking northwest to north, and a later north–south set confined to near the western margin of the terrain.The easterly and northerly, near-orthogonal trends followed by successive structures could reflect the influence of fault-bounded crustal blocks. During emplacement of fault-controlled granitoid bodies, the blocks may have tilted successively about easterly or northerly axes with gravitational collapse, folding, and overturning of the supracrustal rocks. Further tilting could in part have led to the compressions that formed the cleavages.
Construction of type curves of geomagnetic secular variation for dating lake sediments from east central North America
Authors: Creer K. M. , Tucholka P.
Published: April 2011

Type curves of palaeomagnetic secular variations of declination and inclination through the last 12 000 radiocarbon years have been constructed by combining data from the Minnesota Lakes with parallel data from the Great Lakes. The former records were well dated by reliable radiocarbon age determinations at frequent depth increments but the curves are not so well formed as the corresponding Great Lakes curves, which, however, cannot be so accurately dated. The same characteristic features can be identified in the records from both areas, particularly in inclination. Thus the Great Lakes records have been redated by correlation of the inclination features with the Minnesota records. Inclination and declination records from both areas were then stacked and the resulting curves serve as type curves for east-central North America. Standard error bars are shown at each time increment of 40 years. Significant swings on declination and inclination curves were used for reinterpretation of Lake Erie and Lake Michigan records.
Regional patterns in magnetic anomalies over Hudson Bay
Authors: Coles R. L. , Haines G. V.
Published: April 2011

A new shipborne magnetic survey data set provides an overview of magnetic trends and patterns over Hudson Bay. Northeasterly trends characterize the northern part of the bay, with indications of several major faults. Northerly trends predominate in the central and eastern parts of the bay. Several distinct magnetic signatures are associated with an interpreted suture between the Churchill and Superior structural provinces.
Archean volcanoes in southwestern Abitibi Belt, Ontario and Quebec: form, composition, and development
Authors: Goodwin A. M.
Published: April 2011

Southwestern Abitibi Volcanic Belt is composed of numerous deformed volcanoes that were originally circular to subcircular in outline, 100–200 km in diameter, and 10–16 km in stratigraphic thickness. Tholeiitic (TH) lava flows with local komatiitic (KM) flows and intrusions predominate in the lower parts of each volcano and calc-alkalic (CA) lava flows or pyroclastic rocks in the upper parts. Subsidence of the volcanoes more or less kept pace with magma extrusion such that volcano slopes remained mainly horizontal to subhorizontal. The lower TH parts accumulated rapidly at substantial water depths. The upper CA parts also accumulated rapidly but at decreasing water depths with possible local, brief, island emergence.The lower TH division is dominated by thick, uniform TH basalt lava flows. This changes abruptly at about volcano mid-thickness to the conformably overlying CA andesite-rich division characterized by irregularly recurring basalt–andesite– dacite–rhyolite flow or pyroclastic alternations that become increasingly felsic upwards. Multicyclic volcanoes include second-order internal TH–CA subdivisions. The generalized Abitibi succession is represented by a simplified, composite Abitibi volcano.The salient control in volcano development is attributed to diapiric ascent within a heterogeneously layered Archean mantle. TH and CA components are attributed to direct mantle sources. The major TH–CA volcano pattern represents a full Archean thermal cycle. The TH–CA discontinuity reflects the switch from an earlier, mainly depleted mantle source to a later, mainly undepleted mantle source. Second-order volcano subdivisions (subgroups) represent thermal pulses in diapiric ascent. Such a system of recurring, migrating mantle plumes gave rise, in due course, to the volcano-dominated greenstone belt.
Bayloria morei Olson 1941 identified as an immature specimen of the Permian reptile Captorhinus aguti (Cope, 1882)
Authors: Reisz R. R. , Heaton M. J.
Published: April 2011

Bayloria morei from the Lower Permian (Arroyo Formation, Clear Fork Group: Leonardian) of Baylor County, Texas, formerly thought to be the smallest known pelycosaur, is an immature specimen of the captorhinid reptile Captorhinus aguti. As the latter name has priority, Bayloria Olson 1941 is the junior synonym of Captorhinus Case 1911 and B. morei Olson 1941 of C. aguti (Cope, 1882). Removal of Bayloria morei from the pelycosaurian family Eothyrididae reduces the latter to two monospecific genera, Eothyris parkeyi and Oedaleops campi.