bluuebunny/crossref_metadata_2025 huggingface dataset:
A Transmembrane Domain-Containing Surface Protein fromToxoplasma gondiiAugments Replication in Activated Immune Cells and Establishment of a Chronic Infection
Authors: Pollard Angela M. , Skariah Sini , Mordue Dana G. , Knoll Laura J.
Published: July 2009

Toxoplasma gondiimutants identified as defective in the establishment of chronic infection were screened to isolate those specifically impaired in their ability to replicate within activated macrophages. One of the identified mutants contains an insertion in the hypothetical gene TGME49_111670. Genetic complementation restores the ability of the mutant to replicate in immune cells and produce cysts in the brains of mice. While the mutant is more sensitive to nitric oxide than is its parental strain, it is not defective in its ability to suppress nitric oxide. The disrupted protein has no significant homology to proteins with known functions, but is predicted to have one transmembrane domain. Immunofluorescence shows the protein on the parasite surface, even in activated macrophages, colocalizing with a tachyzoite surface antigen, SAG1, and oriented with its C-terminal end external. Western analysis reveals that the protein is downregulated in bradyzoites. Despite the tachyzoite specificity of this protein, mice infected with the mutant succumb to acute infection similarly to those infected with the parent strain. Serum samples from mice with chronicT. gondiiinfection react to a polypeptide from TGME49_11670, indicating that the protein is seen by the immune system during infection. This study is the first to characterize aT. gondiisurface protein that contains a transmembrane domain and show that the protein contributes to parasite replication in activated immune cells and the establishment of chronic infection.
Toward the Rational Design of a Malaria Vaccine Construct Using the MSP3 Family as an Example: Contribution of Immunogenicity Studies in Models
Authors: Daher Lena-Juliette , Demanga Corine G. , Prieur Eric , Pérignon Jean-Louis , Bouharoun-Tayoun Hasnaa , Druilhe Pierre
Published: July 2009

Plasmodium falciparum
merozoite surface protein 3 (MSP3), the target of antibodies that mediate parasite killing in cooperation with blood monocytes and are associated with protection in exposed populations, is a vaccine candidate under development. It belongs to a family of six structurally related genes. To optimize immunogenicity, we attempted to improve its design based on knowledge of antigenicity of various regions from the conserved C terminus of the six proteins and an analysis of the immunogenicity of “tailored” constructs. The immunogenicity studies were conducted in BALB/c and C57BL/6J mice, using MSP3 (referred to here as MSP3-1) as a model. Four constructs were designed in order to assess the effect of sequences flanking the 69-amino-acid region of MSP3-1 previously shown to be the target of biologically active antibodies. The results indicate major beneficial effects of removing (i) the subregion downstream from the 69-amino-acid sequence, since antibody titers increased by 2 orders of magnitude, and (ii) the upstream subregion which, although it defines a T-helper cell epitope, is not the target of antibodies. The construct, excluding both flanking sequences, was able to induce Th1-like responses, with a dominance of cytophilic antibodies. This led to design a multigenic construct based on these results, combining the six members of the MSP3 family. This new construction was immunogenic in mice, induced antibodies that recognized the parasite native proteins, and inhibited parasite growth in the functional antibody-dependent cellular inhibition assay, thus satisfying the preclinical criteria for a valuable vaccine candidate.
Structure of Compositionally Simple Lipopolysaccharide from Marine
Synechococcus
Authors: Snyder D. Scott , Brahamsha Bianca , Azadi Parastoo , Palenik Brian
Published: July 2009

Lipopolysaccharide (LPS) is the first defense against changing environmental factors for many bacteria. Here, we report the first structure of the LPS from cyanobacteria based on two strains of marine
Synechococcus
, WH8102 and CC9311. While enteric LPS contains some of the most complex carbohydrate residues in nature, the full-length versions of these cyanobacterial LPSs have neither heptose nor 3-deoxy-
d
-
manno
-octulosonic acid (Kdo) but instead 4-linked glucose as their main saccharide component, with low levels of glucosamine and galacturonic acid also present. Matrix-assisted laser desorption ionization mass spectrometry of the intact minimal core LPS reveals triacylated and tetraacylated structures having a heterogeneous mix of both hydroxylated and nonhydroxylated fatty acids connected to the diglucosamine backbone and a predominantly glucose outer core-like region for both strains. WH8102 incorporated rhamnose in this region as well, contributing to differences in sugar composition and possibly nutritional differences between the strains. In contrast to enteric lipid A, which can be liberated from LPS by mild acid hydrolysis, lipid A from these organisms could be produced by only two novel procedures: triethylamine-assisted periodate oxidation and acetolysis. The lipid A contains odd-chain hydroxylated fatty acids, lacks phosphate, and contains a single galacturonic acid. The LPS lacks any limulus amoebocyte lysate gelation activity. The highly simplified nature of LPSs from these organisms leads us to believe that they may represent either a primordial structure or an adaptation to the relatively higher salt and potentially growth-limiting phosphate levels in marine environments.
The Autolysin LytA Contributes to Efficient Bacteriophage Progeny Release in
Streptococcus pneumoniae
Authors: Frias Maria João , Melo-Cristino José , Ramirez Mário
Published: July 2009

Most bacteriophages (phages) release their progeny through the action of holins that form lesions in the cytoplasmic membrane and lysins that degrade the bacterial peptidoglycan. Although the function of each protein is well established in phages infecting
Streptococcus pneumoniae
, the role—if any—of the powerful bacterial autolysin LytA in virion release is currently unknown. In this study, deletions of the bacterial and phage lysins were done in lysogenic
S. pneumoniae
strains, allowing the evaluation of the contribution of each lytic enzyme to phage release through the monitoring of bacterial-culture lysis and phage plaque assays. In addition, we assessed membrane integrity during phage-mediated lysis using flow cytometry to evaluate the regulatory role of holins over the lytic activities. Our data show that LytA is activated at the end of the lytic cycle and that its triggering results from holin-induced membrane permeabilization. In the absence of phage lysin, LytA is able to mediate bacterial lysis and phage release, although exclusive dependence on the autolysin results in reduced virion egress and altered kinetics that may impair phage fitness. Under normal conditions, activation of bacterial LytA, together with the phage lysin, leads to greater phage progeny release. Our findings demonstrate that
S. pneumoniae
phages use the ubiquitous host autolysin to accomplish an optimal phage exiting strategy.
In Situ Characterization of Differences in the Viscoelastic Response of Individual Gram-Negative and Gram-Positive Bacterial Cells
Authors: Vadillo-Rodriguez Virginia , Schooling Sarah R. , Dutcher John R.
Published: July 2009

We used a novel atomic force microscopy (AFM)-based technique to compare the local viscoelastic properties of individual gram-negative (
Escherichia coli
) and gram-positive (
Bacillus subtilis
) bacterial cells. We found that the viscoelastic properties of the bacterial cells are well described by a three-component mechanical model that combines an instantaneous elastic response and a delayed elastic response. These experiments have allowed us to investigate the relationship between the viscoelastic properties and the structure and composition of the cell envelope. In addition, this is the first report in which the mechanical role of Lpp, the major peptidoglycan-associated lipoprotein and one of the most abundant outer membrane proteins in
E. coli
cells, has been quantified. We expect that our findings will be helpful in increasing the understanding of the structure-property relationships of bacterial cell envelopes.
Staphylococcus aureus
YoeB Homologues Inhibit Translation Initiation
Authors: Yoshizumi Satoshi , Zhang Yonglong , Yamaguchi Yoshihiro , Chen Liang , Kreiswirth Barry N. , Inouye Masayori
Published: July 2009

YoeB is a bacterial toxin encoded by the
yefM-yoeB
toxin-antitoxin system found in various bacterial genomes. Here, we show that
Staphylococcus aureus
contains two YoeB homologues, both of which function as ribosome-dependent mRNA interferases to inhibit translation initiation in a manner identical to that of YoeB-ec from
Escherichia coli
.
Characterization of the Dicarboxylate Transporter DctA in
Corynebacterium glutamicum
Authors: Youn Jung-Won , Jolkver Elena , Krämer Reinhard , Marin Kay , Wendisch Volker F.
Published: July 2009

Transporters of the dicarboxylate amino acid-cation symporter family often mediate uptake of C
4
-dicarboxylates, such as succinate or
l
-malate, in bacteria. A member of this family, dicarboxylate transporter A (DctA) from
Corynebacterium glutamicum
, was characterized to catalyze uptake of the C
4
-dicarboxylates succinate, fumarate, and
l
-malate, which was inhibited by oxaloacetate, 2-oxoglutarate, and glyoxylate. DctA activity was not affected by sodium availability but was dependent on the electrochemical proton potential. Efficient growth of
C. glutamicum
in minimal medium with succinate, fumarate, or
l
-malate as the sole carbon source required high
dctA
expression levels due either to a promoter-up mutation identified in a spontaneous mutant or to ectopic overexpression. Mutant analysis indicated that DctA and DccT, a C
4
-dicarboxylate divalent anion/sodium symporter-type transporter, are the only transporters for succinate, fumarate, and
l
-malate in
C. glutamicum
.
Pneumococcal LytR, a Protein from the LytR-CpsA-Psr Family, Is Essential for Normal Septum Formation in
Streptococcus pneumoniae
Authors: Johnsborg Ola , Håvarstein Leiv Sigve
Published: July 2009

Proliferation of the human-pathogenic bacterium
Streptococcus pneumoniae
is fundamentally linked to the bacterial proteins that function in cell division. Here, we show that LytR, a pneumococcal protein from the LytR-CpsA-Psr family, is essential to this process.
Miniature mud volcanoes and other injection features in tidal flats, James Bay, Québec
Authors: Dionne Jean-Claude
Published: July 2009

Miniature injection features, including mud volcanoes, dikes forming polygonal patterns, and isolated patches of clay, occur in tidal flats along the east coast of James Bay. They are formed by localized upward ejection of a mixture of fluidized marine clay, silt, and fine sand through a surficial recent mud deposit. Liquefaction is related to the melting of ice in the clayey deposit. Upward flowing of clay, silt, and fine sand seems to result from overloading by the overlying sediments having a higher degree of density, and possibly also by pressures of ice floes or/and icefoot.
Determination of ground constants of permafrost terrains by an electromagnetic method
Authors: Sinha Ajit K.
Published: July 2009

The generalized solution of the scattering of electromagnetic fields by an n-layer earth in the presence of oscillating magnetic dipoles carrying harmonic currents has been obtained. The solutions are valid for all frequency ranges and for arbitrary parameters of the n-layer earth. The results have been expressed in terms of six infinite integrals, four of which depend on the transverse electric modes and the rest on the transverse magnetic modes. These solutions have been used to obtain the generalized expressions for the mutual coupling ratios for five coil systems, most often used in the geophysical industry.Using the solutions, a study has been made on the relative performance of the five coil systems for mapping permafrost terrains by multifrequency techniques, assuming the earth to be a homogeneous lossy dielectric, which may be a valid model in winter. It has been observed that the responses in all five coil systems are quite similar, but the magnitude of the response is largest in the horizontal coplanar system. A graphical technique of obtaining the resistivity and dielectric constant of the ground from the mutual coupling ratios has also been described. The results would be useful for designing portable multifrequency e.m. dipole systems for the detection and delineation of permafrost at high latitudes. The inclined, parallel, null-coupled system comes next in order of preference for the mapping of permafrost terrain, followed by the vertical coplanar and the perpendicular systems.
The Kulyk Lake monazite deposit, northern Saskatchewan
Authors: Watkinson David H. , Mainwaring Paul R.
Published: July 2009

Massive monazite occurs in a zoned deposit in the Wollaston Lake fold belt, Kulyk Lake area, northern Saskatchewan. The deposit is enclosed by pegmatitic, graphic, and aplitic granite, which are slightly bleached adjacent to the contact. Ilmeno-hematite and hematite (in part after magnetite), located adjacent to the silicate rocks, are followed inward by massive monazite and then minor concentrations of apatite. Monazite has a constant chemical composition: the average microprobe analysis is CaO—0.5, La2O3—15.1, Ce2O3—36.1, Pr2O3—4.9, Nd2O3—10.1, ThO2—4.3, P2O5—27.8; total, 98.8%. Monazite grains in a small segregation in granitic gneisses have variable thoria contents. Apatite in the deposit contains about 0.2% total rare earths. The oxide–monazite–apatite deposit probably precipitated from an aqueous phase generated during crystallization of a water-rich granitic liquid. The monazite deposit and enclosing granitic rocks may have been generated during anatexis of a metasedimentary unit containing abundant monazite and Fe–Ti oxides.
Some characteristics of a pingo in the Simpson Peninsula, N.W.T.
Authors: Tarnocai C. , Netterville J. A.
Published: July 2009

The 7 m high pingo is situated on a poorly drained, marine silt deposit in the Simpson Peninsula, and has a relatively shallow active layer (31 cm) underlain by frozen silt material with alternating layers of pure ice, 5–15 cm thick. The relative flatness of the surrounding terrain suggests that this pingo is of the closed-system type.
Phosphate – clay mineral relations in soils and sediments
Authors: Nriagu Jerome O.
Published: July 2009

The geochemical constraints that determine the environments of formation of calcium and aluminum phosphates are assessed in relation to the stabilities of these compounds. In neutral to acidic environments, the weathering of calcareous phosphorites may result in the formation of crandallite and wavellite (low phosphate concentration) or montgomeryite (high phosphate concentration). Phosphatization of argillaceous sediments will invariably lead to the formation of millisite and taranakite, and may involve palmerite as an intermediate phase. Variscite is unstable relative to the other aluminum hydroxyphosphates and is unlikely to be a major constituent in phosphorite beds. The phase relations show the characteristic association of quartz – apatite – clay minerals to be thermodynamically stable in near neutral environments. The predicted reaction paths during progressive desilication of phosphatized clays and decalcification of apatite are clays→ (palmerites)→ millisite→ wavellite and apatite→ crandallite→ wavellite→ augelite; these match the paragenetic sequence observed in many localities. Within the framework of phosphate – clay mineral reaction, calcitization and silicification of apatite may be effected even in acidific environments.The effect of Eh on the formation of phosphatic beds is indirect and mediated by the iron cycle. The association of iron minerals with phosphorites is considered and the suggestion made that iron oxide accumulates may be the source material for some phosphorite formations.
Nature of the Quetico–Wabigoon boundary in the de Courcey – Smiley Lakes area, northwestern Ontario
Authors: Kehlenbeck Manfred M.
Published: July 2009

In the de Courcey – Smiley Lakes Area, the boundary between the Quetico and Wabigoon Belts is expressed by a sequence of pelitic to semi-pelitic schists and gneisses. At the present level of erosion, these metasedimentary rocks are in contact with granodioritic gneisses, granites, and pegmatites, which are exposed to the south.To the north of this area, regional metamorphism of volcanic and sedimentary rocks has resulted in greenschist facies assemblages, which characterize the Wabigoon Belt in general. In the boundary zone, the metamorphic grade increases southward toward de Courcey and Smiley Lakes.Formation of three distinct foliation surfaces was accompanied by syn-tectonic as well as post-tectonic recrystallization, producing polymetamorphic schists.In the boundary zone, mineral assemblages comprising andalusile, sillimanite, cordierite, garnet. biotite, and muscovite form a facies series of the Abukuma type.The boundary between the Quetico and Wabigoon Belts in this area is a complex zone in which rocks of both belts have been reconstituted by multiple-phase metamorphism and partial melting.
The petrology, geochemistry, and remanent magnetization of metabasalts and metagabbros in the Lac Patu – Fort McKenzie region, New Quebec Territory
Authors: K.-Seguin Maurice
Published: July 2009

One hundred and five specimens were collected from 40 different sites in northwest-striking metabasalts and metagabbros of Lower Proterozoic (Aphebian) age in the northeastern part of the Labrador Trough (longitude: 69 °W, latitude: 57 °N). The radiogenic age determinations of surrounding rocks of the same age yielded 1860 m.y. A petrological and chemical description of the rocks is included. The chemical results for total Fe, MgO, and Na2O + K2O combined, drawn on a ternary diagram show that the metabasalts and metagabbros fall in the tholeiite field. Magnetite (with some occasional 5% ulvospinel) is the most frequent magnetic memory carrier; pyrrhotite is less commonly found. In order to obtain some pertinent information relative to the stability of the NRM component, step-wise alternating field demagnetization was conducted on 40% of the specimens and the others were demagnetized at a specific AF intensity. In 35% of the specimens, the AF demagnetization process induced an anhysteretic magnetization component above 250 Oe. A secondary isothermal remanent magnetization of lesser stability was often detected in the 50–150 Oe range. Tilting of the formations sometimes increased and sometimes decreased the dispersion of the NRM vectors. After tilting the lithological units that were AF demagnetized, the mean paleomagnetic pole position is 152 °E, 20° S (dm = 14°,dp = 07°, K = 34), with at least one reversal.
Paleomagnetism of the Tulemalu dykes, Northwest Territories, Canada
Authors: Fahrig W. F. , Christie K. W. , Eade K. E. , Tella S.
Published: July 2009

Easterly trending Tulemalu diabase dykes that cut an area of predominantly Archean rock in southern Keewatin were magnetized more than 2200 Ma ago. Thirteen of the sampled sites (dykes) exhibit a southeast-down remanent magnetization and five sites give a more poorly grouped direction that is reversed to this. Their combined pole is at 122.4°E, 0.5°S, δm = 10.4°, δp = 6.0°. Six northeasterly trending Kazan dykes, which are probably correlatives of the Kaminak dykes, give a metamorphic pole at 94.2°W, 30.7°N, δm = 35°, δp = 31°. The age of their magnetization is thought to be between 1900 and 2000 Ma.The pole for the Tulemalu dykes lies within a group of poles of similar age derived from basic rocks of the Slave Province. It is about 30° away from the pole for the MacKay dykes, which occur north of Great Slave Lake and which have an easterly trend similar to that of the Tulemalu.Poles whose ages range between 1900 and 2200 Ma and that are derived from the Slave, western Churchill, and Superior provinces all suggest that during this period these three continental plates occupied approximately the same relative positions as they do today.
Late Cretaceous age of the Hutshi, Mount Nansen, and Carmacks groups, southwestern Yukon Territory and northwestern British Columbia
Authors: Grond H. C. , Churchill S. J. , Armstrong R. L. , Harakal J. E. , Nixon G. T.
Published: July 2009

Volcanic rocks of the Hutshi, Mount Nansen, and Carmacks groups occur in the southwestern Yukon where they unconformably overlie the Yukon Crystalline Terrane and deformed strata of the Whitehorse Trough. The volcanic rocks are faulted and tilted, locally altered, and largely postorogenic. The more basic Carmacks volcanics locally overlie intermediate to acid rocks of the Mount Nansen Group, but are mostly in isolated exposures northwest of the Hutshi and Mount Nansen volcanics.Hutshi – Mount Nansen volcanics of the Miners Range are porphyritic, partly vesicular calc-alkaline andesite flows and flow breccias intruded by calc-alkaline alkali-rich rhyolite and two-feldspar andesite dikes. A low-greenschist metamorphic overprint affects most rocks.Carmacks volcanics, near Carmacks, are flows, epiclastic breccias, and sintered tuffs interbedded with immature volcanic sandstone. One analysed breccia clast is calc-alkaline andesite, but the flows are potassic basalt, trachybasalt, and tristanite.Recent assignments of the Hutshi – Mount Nansen and Carmacks volcanic suites to early and mid-Tertiary ages, respectively, are incorrect as all are late Cretaceous. K–Ar dates for a Hutshi – Mount Nansen whole rock and plagioclase of 72.4 ± 2.5 and 69.1 ± 2.6 Ma and Carmacks whole rocks and biotite of 73.1 ± 2.5, 67.9 ± 2.3, and 68.0 ± 2.2 Ma are concordant among themselves and agree with a Rb–Sr whole-rock date of 72.4 ± 2.1 Ma for rhyolite from the Hutshi Group in northern British Columbia.This widespread late Cretaceous volcanic episode has typical subduction-related volcanic arc chemical polarity: calc-alkaline to alkaline from active trench towards stable craton. There is a dearth of documented early to mid-Cenozoic rocks in the Yukon.
Uranium series disequilibrium in young surficial uranium deposits in southern British Columbia
Authors: Levinson A. A. , Bland C. J. , Dean J. R.
Published: July 2009

Disequilibrium studies involving the determination of total U and the activity ratios of 234U/238U and 234U/230Th or activities of 230Th, 226Ra, and 210Pb were carried out on samples from three surficial (generally within 5 m of the surface) uranium deposits in south-central British Columbia that give apparent 234U/230Th ages of 1000–20 000 years. As a result of the young ages, the deposits have not yet reached radioactive secular equilibrium and, therefore, yield very little gamma activity.The deposits formed from groundwaters that leached labile uranium from intermediate to felsic igneous rocks. Two accumulation mechanisms concentrate the uranium: evaporation, and adsorption onto organic matter.The uranium content and the activities of the various daughter nuclides are highly variable within and between the various deposits studied. Some of the variations can be explained in terms of the accumulation processes. In the evaporative process the highest value of uranium and daughter nuclides will be found at the surface, whereas in those deposits in which adsorption is the dominant mechanism these nuclides are found in association with buried organic matter. Under these circumstances, accumulations will be influenced by the flow of groundwater from different sources and also depend on whether daughter nuclides remain immobile or are leached after formation.
Geochronology and tectonic implications of magmatism and metamorphism, southern Kootenay Arc and neighbouring regions, southeastern British Columbia. Part II: Mid-Cretaceous to Eocene
Authors: Archibald D. A. , Krogh T. E. , Armstrong R. L. , Farrar E.
Published: July 2009

A north–south-trending belt of amphibolite facies regional metamorphism parallels the Purcell Trench, transects the Kootenay Arc, and is, in part, fault bounded. Towards the axis of this belt progressively higher pressure metamorphic mineral assemblages are exposed in the contact aureoles of post-kinematic, mid-Cretaceous (~100 Ma) plutons and in metapelites. Contours of K–Ar biotite dates for plutonic rocks (55–95 Ma) are regular, are broadly conformable with metamorphic isograds, appear to cross internal intrusive contacts of post-kinematic plutons, and young towards the highest pressure and temperature regional metamorphic zones. Within the sillimanite zone most micas yield K–Ar dates between 40 and 55 Ma; Rb–Sr muscovite dates for deformed and undeformed pegmatites and for muscovite-bearing monzogranite and granodiorite fall between 53 and 84 Ma. U–Pb zircon dates for the Kaniksu batholith and nearby gneiss of uncertain origin yield a lower concordia intercept of 94 Ma. Micas from mid-Jurassic and mid-Cretaceous plutons yielding conventional K–Ar dates between 55 and 100 Ma also yield plateau-shaped 40Ar/39Ar age spectra that are indicative of normal closure to Ar diffusion due to cooling during this time interval.Contrasting isotopic cooling curves for plutonic rocks in the Purcell Anticlinorium and in the metamorphic infrastructure imply that these regions had different thermal histories. Combined with metamorphic mineral assemblage data and interpreted in terms of uplift and erosion, these curves support a tectonothermal model for the development of the Kootenay Arc and Purcell Anticlinorium that involves (1) mid-Cretaceous emplacement of post-kinematic plutons into a tectonically dormant supra-structure accompanying renewed heating, deformation, and metamorphism in the deepest levels of an evolving infrastructure; (2) slow cooling from mid- to Late Cretaceous time; (3) uplift and erosion of the continental terrace wedge and post-kinematic plutons and parts of the mid-Cretaceous infrastructure in latest Cretaceous–earliest Tertiary time as these rocks were thrust eastward over a steplike feature in the basement leading to the formation of the Purcell Anticlinorium; and (4) rapid uplift and cooling of the metamorphic infrastructure in Eocene time.
Probable Archean nepheline syenite plutons in the Superior Province adjacent to the Labrador Trough
Authors: Fumerton S. L. , Barry A. P.
Published: July 2009

Three nepheline-bearing plutons have recently been discovered in the Superior Province northwest of Schefferville. They are apparently related miaskitic nepheline syenites, varying to leucocratic nepheline syenite, juvite, and rarely ijolite. All three plutons are crudely zoned with an increasing nepheline content towards the centres. The foliation and lineation in these rocks are the same as those in the surrounding country rocks. Together with folding, microscopic comminution, and metamorphic recrystallization, this structure suggests that these plutons were intruded prior to or during the Kenoran Orogeny. This conclusion is consistent with a K/Ar biotite minimum age of 2398 ± 72 Ma (3%) obtained for one sample.
Paleomagnetism, structure, and longitudinal correlation of Middle Precambrian dykes from northwestern Ontario and Minnesota
Authors: Halls H. C.
Published: July 2009

A primary magnetization about 2.1 Ga old is well preserved in the Kenora–Kabetogama dyke swarm in Minnesota and Ontario. Its direction, the mean for 12 dykes, incorporating results from 30 paleomagnetic sites, is 115.9°, −55.6°, yielding a paleomagnetic pole position of latitude 42.7°S, longitude 4.2°E (dm = 7.3°, dp = 5.2°).The primary nature of the magnetization can be demonstrated using geochemistry to correlate individual dykes over distances that can exceed 300 km. Whereas the remanence direction varies between dykes, it remains constant along a dyke, sufficient proof that it was formed during initial cooling of the intrusion.A weak, longitudinal increase in hydrous alteration, MgO content, and degree of magnetic overprinting is observed as the swarm is followed to the south and may reflect increasing proximity to a Precambrian continental margin that underwent rifting, sedimentation, and deformation during the time interval 2.2–1.6 Ga BP. Although the cause of the longitudinal changes in terms of margin evolution can only be surmised, the results illustrate the potential of dyke swarms as sensitive indicators of how shield terrains may respond to events occurring around their margins.
Crustal evolution of Archean rocks in the Kakagi Lake area, Wabigoon Subprovince, Ontario, as interpreted from high-precision U–Pb geochronology
Authors: Davis D. W. , Edwards G. R.
Published: July 2009

The evolution of the Archean volcanic–plutonic complex in the Kakagi Lake area occurred during a time interval of ca. 32 Ma. The earliest age is [Formula: see text] from analysis of zircon and baddeleyite in a gabbro intruding the lowermost Katimiagamak Volcanic Group. An age of 2723.2 ± 1.8 Ma on a tonalite gneiss from the interior of the underlying Sabaskong Batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component. An early tonalite phase from the adjacent Aulneau Batholith is dated at [Formula: see text], and the latest granodiorite phase is dated at [Formula: see text]. This defines a time span of about 7 Ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence, above the Kakagi Lake Volcanic Group, is coeval with late plutonic activity in the Aulneau Batholith. The end of regional deformation in the area is given by the ages of two late-tectonic intrusions, the Heronry Lake pluton and the Stephen Lake pluton, dated at 2701.0 ± 1.2 and 2699.2 ± 1.9 Ma, respectively.U–Pb analyses of sphene were carried out on four of the samples in an effort to establish details of the post-folding thermal history of the area. Sphene is least reset in the Heronry Lake pluton (2699.2 ± 1.6 Ma), which is spatially most closely associated with the volcanic rocks and most reset in the Sabaskong gneiss (2673.7 ± 6.6 Ma), the sample most strongly affected by diapirism. The data indicate that regional deformation was a relatively late event, possibly caused by diapirism in the centres of the large batholiths and driven by a long-lived heat source in the mantle or lower crust.
The geochemistry and petrogenesis of ophiolitic volcanic rocks from Lac de l'Est, Thetford Mines Complex, Quebec, Canada
Authors: Oshin I. O. , Crocket J. H.
Published: July 2009

The Cambro-Ordovician age Thetford Mines Complex from the Quebec Appalachians, Canada, preserves a remarkably complete section of ophiolites at Lac de l'Est, where mafic volcanics overlie a plutonic mafic–ultramafic plate. The basaltic volcanics consist of a lower unit, representing the extrusive component of the ophiolite assemblage, and an upper unit, whose petrogenetic and tectonic relationships with the ophiolitic volcanics are problematic.The lower unit ophiolitic volcanics include high- and low-TiO2 basalts. The upper unit volcanics, of which the basal 80 m was sampled, are low-TiO2 basalts. Fractional crystallization was important in the evolution of high-TiO2 lower unit magmas but played only a minor role in the formation of other magmas. Partial melting processes were dominant, or much more important than fractional crystallization, in controlling the composition of other magmas. The parental magmas of the high-TiO2 lower unit basalts were partial melts of undepleted mantle, whereas the low-TiO2 volcanics were partial melts of residual, depleted mantle. Despite different mantle sources, the high- and low-TiO2 basalts of the lower unit are interbedded in the field.The close spatial association of chemically diverse magma types is best accounted for by generation in a back-arc or marginal basin environment. This interpretation is supported by the geochemistry of argillaceous sediments in the Lac de l'Est pile and the absence of a sheeted dike facies in the Thetford Mines ophiolites.
Anisotropic fragments in strongly folded and faulted coals from the Rocky Mountain area of southeast British Columbia
Authors: Goodarzi Fariborz
Published: July 2009

The "Mammoth" coal seam in southeastern British Columbia, Canada, was structurally thickened to 100 m as a result of Laramide folding and faulting. Samples from the coal seam, examined using reflected-light microscopy, include thermally altered coal macerals, their by-products (e.g., pyrolytic carbon), and, in addition, heat-affected preoxidized coke.The heat-affected residues are composed of material formed by friction produced from faulting of the coal-bearing strata. The pyrolytic carbon was formed from the distillation of coal and from coal tar pitch.The occurrence of preoxidized, heat-affected vitrinite suggests that the Mammoth coal seam was oxidized before faulting.
Oxygen, hydrogen, and carbon isotopic studies of the Great Bear Lake silver deposits, Northwest Territories
Authors: Changkakoti A. , Morton R. D. , Gray J. , Yonge C. J.
Published: July 2009

The native-silver-bearing deposits of the Great Bear Lake region occur within two separate domains, namely the Echo Bay sector and the Camsell River sector. In all these deposits, native silver occurs in veins, associated with a wide range of Ni-, Co-, and Fe- arsenides, Cu-, Fe-, Ni-, and Co-sulfides, and pitchblende in gangues of quartz, calcite, dolomite, siderite, rhodochrosite, and fluorite. The host rocks of the veins are for the most part Aphebian volcano-sedimentary roof pendants within the Great Bear batholithic complex. The carbonates (calcite, dolomite, siderite, and rhodochrosite) show a wide range of δ18O (6.8 to 22.5‰, SMOW) and δ13C (−2.7 to −13.3‰, PDB) values. A single analysis of quartz gave a δ18O value of 16.54‰ (SMOW). The δD of water in fluid inclusions in quartz, dolomite, and calcite shows a range from −62.2 to −98.5‰ (SMOW). The δD of present-day meteoric waters from the region shows a range of −146.5 to −165.2‰ (SMOW). The δ18O of the hydrothermal fluids (0.47 to 9.12‰, SMOW) was calculated from the δ18O values of the quartz, calcite, and dolomite belonging to different paragenetic sequences. The δ13C of carbon (−2.8 to −8.6‰, PDB) in the hydrothermal fluid was calculated from the δ13C values of the calcites. The oxygen, carbon, and hydrogen isotopic values indicate that in the early stages of mineralization, magmatic water and carbon from a magmatic source were predominant. During the late stages of mineralization, the influence of meteoric water became more pronounced.
Electron microprobe analyses of native silver and associated arsenides from the Great Bear Lake silver deposits, Northwest Territories, Canada
Authors: Changkakoti A. , Morton R. D.
Published: July 2009

The Great Bear Lake silver deposits in the Northwest Territories of Canada occur within two separate domains, namely the Echo Bay sector and the Camsell River sector. In these deposits, native silver occurs in veins, associated with a wide range of Ni-, Co-, and Fe-arsenides, sulphides, and pitchblende in gangues of quartz, calcite, dolomite, rhodochrosite, and fluorite. The host rocks of the veins are for the most part Aphebian volcano-sedimentary roof pendants within the Great Bear batholithic complex. Native silver, nickeline (niccolite), maucherite, safflorite, rammelsbergite, pararammelsbergite, loellingite, skutterudite, cobaltite, gersdorffite, and arsenopyrite were analyzed on the electron microprobe to determine any local or regional chemical variations. Mercury and antimony were found to occur in significant quantities in the majority of the native-silver samples. The silver samples from the Camsell River sector were found to be generally more enriched in mercury than those of the Echo Bay sector. Nickeline, cobaltite, and gersdorffite were found to be enriched in arsenic in the ores of the Camsell River sector, versus those of the Echo Bay sector. Such variations are probably related to differing magmatic sources for the hydrothermal fluids or even to precursor metallo-organic associations and are not due to different rocks hosting the silver-bearing veins.
Lead-isotope study of mineralization in the Cobalt district, Ontario
Authors: Thorpe R. I. , Goodz M. D. , Jonasson I. R. , Blenkinsop J.
Published: July 2009

Twenty-seven lead-isotope analyses for galena specimens from 14 localities in the Cobalt district represent sulphide-rich interflow sedimentary units in the Archean volcanic sequence, mineralized zones, fracture fillings, and local sulphide concentrations in the Cobalt Group (Proterozoic) sedimentary rocks, and vein-filling and breccia-cementing sulphides from within and near silver–arsenide veins. The analyses define a very homogeneous composition, averaging 206Pb/204Pb = 14.732, 2O7Pb/204Pb = 15.114, and 208Pb/204Pb = 34.301, for lead from these different geological settings. This result is in agreement with textural observations indicating a late paragenetic position for galena in the different settings mentioned. The model age for this lead is in general accord with the U–Pb age obtained in a study by Andrews et al. for a Nipissing diabase sheet at Gowganda.About one third of the galena specimens are interpreted by a two-stage evolution model to have formed or been remobilized during an event in the time range 1650–1945 Ma. The timing and character of this event are not clearly defined. The radiogenic composition of a specimen from the Pan Silver property is comparable to radiogenic values reported by Thorpe and suggests a young galena-forming event in the area.The lead-isotope data are permissive evidence for a genetic link between the Nipissing diabase sheets and mineralization of a variety of types in the Cobalt district. The metal source is not clearly indicated, but one analysis for Archean interflow sulphides suggests than an Archean source is unlikely for the lead in the silver–arsenide veins and other mineralized zones.
The Scott Lake deposit: a contact-metamorphosed volcanogenic massive sulfide deposit, Chibougamau area, Quebec
Authors: Saunders James A. , Allard Gilles O.
Published: July 2009

The Scott Lake volcanogenic massive sulfide deposit lies near the margin of a large, early kinematic granitoid intrusion in the vicinity of Chibougamau, Quebec. The deposit was contact metamorphosed by the intrusion, and subsequently it was metamorphosed to the greenschist facies during the Kenoran Orogeny. Pyrite, magnetite, and sphalerite are the most abundant metallic minerals, and minor amounts of chalcopyrite, pyrrhotite, and loellingite are also present. Both pyrite and magnetite locally occur as porphyroblasts up to several centimetres in diameter. Metamorphic textures developed in the massive sulfide ore appear to have formed during contact metamorphism, and they remained intact through the subsequent regional event. However, silicate minerals (biotite and possibly amphibole) that grew during contact metamorphism were largely retrograded during regional metamorphism. The presence of biotite indicates that contact metamorphism took place at 400°–500 °C. Application of the sphalerite geobarometer gives a pressure of approximately 4.5 kbar (450 MPa), which probably reflects the later regional event.
Structural cross sections based on a gravity survey of parts of the Quetico and Wawa subprovinces near Thunder Bay, Ontario
Authors: Kehlenbeck M. M. , Cheadle S. P.
Published: July 2009

In this study, gravity data from 350 new gravity stations are combined with those from 50 previously surveyed stations in a detailed Bouguer anomaly map of a portion of the Quetico and Wawa subprovinces north and west of Thunder Bay, Ontario.In general, high gravity values characterize the southern and southwestern part of the area where metavolcanic rocks of the Wawa subprovince dominate. Much of the Quetico subprovince forms a broad gravitational low, reflecting extensive exposures of gneisses, schists, and migmatites. Well-defined gravity lows are associated with several granitic intrusive bodies.Three- and [Formula: see text]-dimensional gravity models of subsurface configuration of the density contrasts, representative of major rock units, indicate a trough-like structure for the metavolcanic rocks of the Wawa subprovince. This trough-like structure is flanked by a domical feature in the granitoid rocks to the south. North of the metavolcanic rocks, a succession of low-grade greywackes and slates occupies a basinal structure. These structures form the principal subsurface elements of the Wawa subprovince in this area.The gneisses, schists, and migmatites of the Quetico subprovince form a thick, southward-dipping, wedge-shaped structure that may extend under the structures of the Wawa subprovince. This wedge-shaped structure is underlain by a model unit of greater density representative of mafic gneisses and amphibolites. The denser substratum is modelled with local abrupt changes in dip corresponding in position with the Quetico and Hawkeye Lake faults.
Upper limit of docking time for Stikinia and Terrane I: paleomagnetic evidence from the Eocene Ootsa Lake Group, British Columbia
Authors: Vandall T. A. , Palmer H. C.
Published: July 2009

The Middle Eocene Ootsa Lake Group is exposed in the central portion of the Stikine Terrane, where it was sampled along the shoreline of Tahtsa Reach and Whitesail Reach. The group consists of dominantly subaerial flows, which range in composition from basalt to rhyolite, that unconformably overly the Jurassic Hazelton Group. Detailed alternating-field and thermal stepwise demagnetizations were done on all specimens from the 21 sites collected. The presence of a normal- and reversed-polarity remanence, a positive fold test, and high coercivities and unblocking temperatures indicate that a prefolding primary remanence has been isolated. The mean tilt-corrected direction of D = 002.2°, I = 69.2 °(α95 = 7.4°) from 13 sites for which paleohorizontal is well known yields a pole position at 354.6°E, 88.0°N (A95 = 11.5°), which is statistically indistinguishable from published 50 Ma reference poles for cratonic North America. This evidence demonstrates that the proposed large-scale northward displacement of Stikinia since mid-Cretaceous was completed by at least Middle Eocene time. This result is consistent with other paleomagnetic results from Stikinia, Quesnellia, and the Coast Plutonic Complex indicating that much of the allochthonous Cordillera had assembled and docked with cratonic North America by the Middle Eocene.
The late Quaternary history of Greely Fiord and its tributaries, west-central Ellesmere Island
Authors: England John
Published: July 2009

Moraines and meltwater channels mark the limit of the last glaciation that interfingered with the sea around the perimeter of Greely Fiord and its tributaries. The extent of this ice advance was dictated predominantly by its proximity to the sea. Consequently, the large tidewater glaciers at the fiord heads today were so constrained by calving that they advanced only 5–10 km. Similarly, grounding-line deposits from widespread plateau ice caps also terminate just below marine limit. The most extensive outlet glaciers, which advanced 20–35 km beyond present margins, are simply those that had access to the most extensive terrain above marine limit, i.e., the northwest margin of the Agassiz Ice Cap.Forty-one new 14C dates are presented. The onset of the last ice advance must predate marine shells collected from sediments overlying a former grounding line when sea level was 122 m higher than present. At this site, the lowermost shells collected from glaciomarine silts dated 38 070 ± 410 BP, whereas a surface sample 13 m above them dated 22 900 ± 190 BP. Although both dates may be minimum estimates, they are nonetheless associated with an ice margin that retreated only a few kilometres by 7850 BP, suggesting the maintenance of the glacioisostatic loading (and relative sea level) during the interim. Nearby, shells in growth position overlying bedrock confirm that relative sea level was > 83 m asl by 38 010 ± 410 BP (minimum age). These marine deposits lie outside the last ice limit and are not overlain by glacigenic sediments.Distal to the last ice limit, Greely Fiord was occupied by the full glacial sea, whose limit is marked by discontinuous beaches and wave-cut benches. The full glacial sea rises from 116 m north of Greely Fiord to a maximum elevation of 148 m bordering its south shore from which it descends to 112 m asl near the head of Cañon Fiord. Numerous 14C dates on shells collected within 8 m of marine limit show that the full glacial sea remained stable from at least 8400 to 7400 BP. Several other shell samples collected ~20 m below marine limit are much older (> 22 000 BP). The position of relative sea level between ca. 8000 and > 22 000 BP is uncertain; however, stratigraphic evidence for an intervening regression has not been found.The modest extent of the last ice limit encircling Greely Fiord, together with its occupancy by the full glacial sea, is fully compatible with the paleogeography previously reported from northeast Ellesmere Island and northwest Greenland. Furthermore, this data base provides a reinterpretation of a 500 km transect previously reported along west-central Ellesmere Island to the south and affirms that the Innuitian Ice Sheet, defined sensu stricto for the last glaciation, is supplanted by the full glacial Innuitian Sea, which penetrated the Queen Elizabeth Islands, constraining the last ice limit.
Holocene sedimentary environment of Cambridge Fiord, Baffin Island, Northwest Territories
Authors: Gilbert Robert , Naldrett Dana L. , Horvath Valeria V.
Published: July 2009

The Holocene sedimentary environment of Cambridge Fiord in northeastern Baffin Island is interpreted from six piston cores. Distinct sediment types represent three sedimentary processes. (1) Muds deposited from suspension from fluvial sources at the fiord head and glacial sources near the mouth are the dominant components of the sediments. The rate of accumulation in mid-fiord based on a radiocarbon date on dispersed organic material indicates an average rate of sedimentation of 1.24 mm/a since about 5800 BP. Upper portions of the cores are bioturbated, although bands of well-preserved fine rhythmites indicate the sudden loss of the benthos, perhaps caused by oxygen depletion associated with reduced circulation. Rhythmites near the sediment surface have a mean thickness similar to the calculated annual accumulation, indicating that they probably are varves; those at depth average 8.1 mm thick. Fine sediment at depth in several cores was not bioturbated for long periods, indicating reduced effectiveness of the benthos during periods of higher rates of sedimentation. Graded muds and sandy muds are interpreted as deposits from weak underflows generated in the sediments on the fiord walls. (2) Massive sands deposited near the head of the fiord are the result of cohesionless debris flows from sources of fluvial and littoral sand widely distributed along the fiord floor. (3) Single sand- and pebble-sized particles found everywhere in the muds are interpreted as ice-rafted debris.