bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochemistry of Neohelikian Nauyat plateau basalts, Borden rift basin, northwestern Baffin Island, Canada
Authors: Dostal J. , Jackson G. D. , Galley A.
Published: April 2011

Subaerial basalt flows of the Neohelikian Nauyat Formation from northwestern Baffin Island, Northwest Territories, constitute an approximately 360 m thick unit that overlies an Archean–Aphebian metamorphic basement. The lavas have undergone a low-grade regional metamorphism that affected the abundances of Na, K, and related trace elements. The basalts are continental tholeiites possessing some characteristics of mid-ocean-ridge basalts. They underwent fractional crystallization of clinopyroxene, plagioclase, and olivine. Mantle-normalized patterns show an enrichment of the lithophile elements, including Th and light rare-earth elements, relative to the high-field-strength elements and a distinct depletion of Nb and Sr. The parental magma of the basalts was derived either from oceanic-type mantle and subsequently affected by lower crustal contamination or from the subcontinental lithospheric mantle. The Nauyat basalts are probably related to the initial stage of the opening of the Poseidon (Proto-Arctic) Ocean.
Yvonaspis, nouveau genre d'Osteostraci (Vertebrata, Agnatha) du Dévonien (Emsien–Eifélien) des Grès de Gaspé (Québec, Canada)
Authors: Belles-Isles Michel
Published: April 2011

All Osteostracan species of the Gaspé Sandstones (Devonian of Canada), formerly attributed to the genus Cephalaspis, are referred here to the new genus Yvonaspis. The latter is characterized by the very elongated shape of the naso-hypophysal opening. This monophyletic genus may be the sister group of Parameteoraspis among cephalaspidians.
Primates of the Lac Pelletier Lower Fauna (Eocene: Duchesnean), Saskatchewan
Authors: Storer John E.
Published: April 2011

Four genera of primates are present in the early to mid-Duchesnean Lac Pelletier Lower Fauna. Phenacolemur leonardi sp.nov., Trogolemur sp., Omomys sp., and Macrotarsius cf. M. montanus make up the latest diverse primate assemblage known from North America and from the Great Plains. This primate assemblage is similar to the earliest Duchesnean assemblage from the Wood locality, Badwater Creek area of central Wyoming, and primate genera appear to have been widely distributed through the Great Plains and Rocky Mountains in the Uintan–Duchesnean.
Subprovince accretion tectonics in the south-central Superior Province
Authors: Williams Howard R.
Published: April 2011

Development of tectonic subprovinces as shear-bounded granite–greenstone and sediment-dominated terranes during the late Archaean is reviewed and interpreted from relationships between portions of the Wabigoon, Wawa, and Quetico subprovinces.Greenstone-dominated subprovinces (Wabigoon and Wawa) are complex successions of tholeiites, 2.76–2.70 Ga calc-alkaline volcanic centres, and derived sediments. Supracrustal rocks aggregated on a scale of tens of kilometres, forming homoclines, locally upright folded, intruded by granitoids, exhibiting variable fabric trends and strains, and cut by transcurrent shear zones. Small-scale (10–100 km) accretion juxtaposed these varied supracrustal sequences, which were engulfed granitoid magmas, to form greenstone belts.Sediment-dominated subprovinces (Quetico) are metamorphosed wacke sequences deposited during and after the volcanic climax in the period 2.70–2.69 Ga. Overthrust imbrication at both the Wabigoon–Quetico and the Quetico–Wawa contacts occurred along north-dipping shears, now vertical. Continued right-lateral convergence at subprovince margins induced progressive shortening within the Quetico Subprovince, producing a regional planar fabric. Abukuma–style metamorphism, migmatite formation, and S-type granite intrusions occurred during the period 2.67–2.65 Ga.Greenstone-belt developments, terminated during large-scale (100–1000 km) late neo-Archæan accretion, are preserved within elongate, batholith-dominated terranes separated by metasedimentary migmatite belts. Geochronological, lithotectonic, and metamorphic patterns on a scale of hundreds of kilometres are permissive of an accretionary model of greenstone terrane coalescence in which formation of long-lived, complex volcanic arcs and a complementary fore-arc accretionary prism culminated in large-scale accretion and the formation of stable continental crust.
Electrical resistivity structure of the Flathead Basin in southeastern British Columbia, Canada
Authors: Gupta Jagdish C. , Jones Alan G.
Published: April 2011

In June 1985, wide-band magnetotelluric data were acquired at 12 equally spaced sites along a 30 km profile crossing the Flathead (Kishenehn) Basin in southeastern British Columbia, Canada. These data have been modelled by both one-dimensional inverse techniques and two-dimensional forward trial-and-error fitting. The results indicate the presence in the area of the following three major zones of low electrical resistivity (10–500 Ω∙m):1. Sediments of the 10 km wide Flathead sedimentary basin, extending to a depth of about 2 km, dominate the responses in the middle of the profile.2. In the eastern part of the profile, in the area of the Lewis Range, a thin [Formula: see text] zone of low resistivity (35 Ω∙m) is imaged at a depth of some 3 km extending eastward from the edge of the basin. We associate this zone with the less dense thrusted Mesozoic clastic rocks lying directly below the Proterozoic rocks of the Lewis thrust sheet.3. Beneath the Flathead Basin is a third zone, of higher resistivity (500 Ω∙m), which extends to deep within the crust. This zone may originate from mantle upflow, as recently proposed to explain the existence of Cordilleran conductors in other localities. Additionally, to model the long-period geomagnetic transfer function responses, we are required to postulate the existence of a zone of low resistivity in the middle to lower crust, 50 km west of the survey line, corresponding to the location of the Rocky Mountain Trench.
Foliate: a useful term to complement the textural classification of foliated metamorphic rocks
Authors: Ashton Kenneth E. , Leclair Alain D.
Published: April 2011

The existing terminology for the textural classification of metamorphic rocks does not adequately take into account rocks that lack compositional layering or an abundance of platy or prismatic minerals. Whereas many workers consider compositional layering an essential characteristic of gneisses, others apply the name gneiss indiscriminately to almost any foliated metamorphic rock. The term schist is commonly misused for rocks containing less than the required 50% platy or prismatic grains displaying a preferred parallel orientation. To clarify this confusion and better constrain the existing terminology, it is suggested that the term foliate, introduced in the early 1900's, be reinstated to describe all foliated metamorphic rocks and be used specifically as a name for rocks that lack compositional layering or at least 50% platy or prismatic grains exhibiting a parallel orientation. Mineralogical, compositional, and (or) genetic modifiers may be applied to the term foliate, as they are to other textural rock names.
The mid-Paleozoic deformation in the Hazen fold belt, Ellesmere Island, Arctic Canada
Authors: Klaper Eva M.
Published: April 2011

The mid-Paleozoic deformation of lower Paleozoic subgreenschist-facies sediments of the Hazen fold belt in northern Ellesmere Island is represented predominantly by chevron-style folding. Folded multilayers display cleavage fans suggesting synchronous fold and cleavage formation. Bedding-parallel slip indicates a flexural slip mechanism of folding. The geometry of several large-scale anticlinoria has been interpreted as being due to formation of these structures over detachments and thrust ramps.The constant fold geometry, the parallel orientation of faults and large- and small-scale folds, and the axial-plane foliation are related to a single phase of folding with a migrating deformation front in the Hazen fold belt during the mid-Paleozoic orogeny. The minimum amount of shortening in the Hazen and Central Ellesmere fold belts has been estimated from surface geology to increase from 40–50% of the original bed length in the external southeastern part to 50–60% in the more internal northwestern part of the belts.The convergent, thin-skinned nature of the Hazen and Central Ellesmere fold belts indicates that the postulated transpressive plate motions during the accretion of Pearya did not affect the study area.
Where are the Eburnian–Transamazonian collisional belts?
Authors: Bertrand Jean Michel , Jardim de Sá Emmanuel Ferraz
Published: April 2011

The reconstruction of Early Proterozoic crustal evolution and geodynamic environments, in Africa and South America, is incomplete if cratonic areas alone are studied. If the presence of high-grade gneisses is considered as a first clue to past collisional behaviour, 2 Ga high-grade gneisses are more abundant within the Pan-African–Brasiliano mobile belts than in the intervening pre-Late Proterozoic cratons. The West African craton and the Guiana–Amazonia craton consist of relatively small Archaean nuclei and widespread low- to medium-grade volcanic and volcanoclastic formations intruded by Early Proterozoic granites. By contrast, 2 Ga granulitic assemblages and (or) nappes and syntectonic granites are known in several areas within the Pan-African–Brasiliano belts of Hoggar–Iforas–Air, Nigeria, Cameroon, and northeast Brazil. Nappe tectonics have been also described in the Congo–Chaillu craton, and Early Proterozoic reworking of older granulites may have occurred in the São Francisco craton. The location of the Pan-African–Brasiliano orogenic belts is probably controlled by preexisting major structures inherited from the Early Proterozoic. High-grade, lower crustal assemblages 2 Ga old have been uplifted or overthrust and now form polycyclic domains in these younger orogenic belts, though rarely in the cratons themselves. The Congo–Chaillu and perhaps the São Francisco craton are exceptional in showing controversial evidence of collisional Eburnian–Transamazonian assemblages undisturbed during Late Proterozoic time.
U–Pb garnet and titanite age for the Bristol Township lamprophyre suite, western Abitibi Subprovince, Canada
Authors: Barrie C. Tucker
Published: April 2011

A U–Pb age of 2687 ± 3 Ma has been determined for a garnetite dike, using melanite garnet and titanite mineral separates. This is the first primary igneous U–Pb age reported using garnet. The garnetite dike is part of the Bristol Township lamprophyre suite, which is extremely enriched in large-ion lithophile elements and light rare earth elements and which is located within the Destor Porcupine fault zone of the western Abitibi Subprovince. The age represents an upper limit for late-stage gold mineralization found along brittle fractures that cut the lamprophyre suite and it coincides with regional transpression documented in several locations in the southern Superior Province.
Computed tomography confirms that Eurhinosaurus (Reptilia: Ichthyosauria) does have a tailbend
Authors: McGowan Chris
Published: April 2011

Post-Triassic ichthyosaurus are characterized by a tailbend, a downward flexure of the vertebral column that forms the internal skeleton of the lower lobe of the caudal fin. The tailbend arises because several of the vertebrae at the apex of the bend have wedge-shaped centra. There has recently been some question whether the swordfish-like ichfhyosaur Eurhinosaurus, from the upper Liassic (Toarcian), had a tailbend. However, computed tomography of the tail region of an unprepared specimen from the Holzmaden area of Germany confirms a tailbend. This is angled at about 40° to the horizontal, which is less steeply downturned than early restorations depicted, but fairly steep compared with other upper Liassic species. Five markedly wedge-shaped centra, contribute to the tailbend, with lesser degrees of wedging in two others.
Sulphur-isotope and elemental geochemistry studies of the Hemlo gold mineralization, Ontario: sources of sulphur and implications for the mineralization process
Authors: Thode H. G. , Ding T. , Crocket J. H.
Published: April 2011

A study of the sulphur-isotope and minor-element composition of gold ores and country rock from the Hemlo deposit, Ontario, has been carried out on 10 drill cores from the mineralization zone and two occurrences of stratiform barite west of Hemlo. The work confirms that Mo, As, and Sb correlate strongly with Au, whereas Ba, and by inference barite, does not. A preferential association of heavy rare-earth elements with higher grades of Au was also established. The isotopic compositions of barite and pyrite reflect a deposit-wide thermal equilibration at 504 °C. Whole-rock sulphur isotopic compositions can be modelled as a mix of sulphate and sulphide end members, the former marked by a relatively constant isotopic composition of roughly 10‰ and the latter by variable and negative isotopic compositions in mineralized zones.These isotopic characteristics are interpreted as the result of (i) preliminary fluid–rock reactions in which some isotope exchange between sedimentary barite and hydrothermal sulphide has occurred and (ii) a later stage metamorphic event in which sulphur-isotope equilibrium is established between the precipitated, distinctly isotopically light pyrite and bedded barite. These two fractionation events, separated in space and time, are required to explain both the variable and distinctly negative δ34S values observed for the pyrite in the Hemlo ores (−15.9 to +1.0%o) and the uniform Δδ34S value of 12.7 ± 1‰ obtained for the coexisting barite and pyrite pairs, in widely different proportions on a deposit-wide scale. Both the production of light isotopic sulphide and the later precipitation of Au are thought to have been influenced by an increase in fluid[Formula: see text].
The geochemistry of the La Galissonnière Pluton: a Middle Proterozoic late-orogenic intrusion from the eastern Grenville Province, Quebec
Authors: Bourne James
Published: April 2011

The La Galissonnière Pluton is a late-orogenic pluton located in the eastern Grenville Province of Quebec. The pluton contains biotite > hornblende, zircon, titanite, allanite, and apatite, along with secondary sericite and epidote. The pluton features elevated values of Nb, Y, and F. The normalized rare-earth element patterns have light rare-earth element concentrations of 400–500× chondrite, moderate slopes (10–20), and noticeable Eu anomalies. Trace-element discriminant diagrams suggest that the pluton formed in a late-orogenic environment and indicate a possible period of late Precambrian crustal attenuation in the eastern Grenville Province.
The geometric and kinematic development of the Emma Lake thrust stack, Grenville Front, southwestern Labrador
Authors: Brown Dennis , Gool Jeroen van , Calon Tom , Rivers Toby
Published: April 2011

The Emma Lake thrust stack is a duplex structure consisting of basement-cored fold nappes with thrust-through overturned limbs developed in greenschist-facies metamorphic rocks. Geometric relationships between fold nappes and thrust surfaces indicate both regular-sequence and out-of-sequence thrusting occurred during development of the thrust stack. Microstructural analysis shows that regular-sequence thrusts developed under ductile conditions, whereas out-of-sequence thrusts developed in a brittle–ductile field.The structural geometry and metamorphic grade of the Emma Lake thrust stack indicate that it developed under ductile conditions at upper midcrustal levels. The geometry of the Emma Lake thrust stack suggests that structural styles common to higher level fold and thrust belts may be traced into deeper levels of the crust.
Geochronological evidence for multiple tectono-thermal overprinting events in the East Kemptville muscovite–topaz leucogranite, Yarmouth County, Nova Scotia, Canada
Authors: Kontak D. J. , Cormier R. F.
Published: April 2011

The East Kemptville muscovite–topaz leucogranite, located in Yarmouth County, Nova Scotia, Canada, is host rock to the only producing primary tin deposit in North America (56 Mt, 0.165% Sn). Previous geochronological studies include (i) Rb–Sr whole-rock analyses of the quartz–topaz greisens, which indicated a date of 337 ± 5 Ma, and (ii) 40Ar/39Ar analyses of greisen muscovite, which indicated apparent plateau dates of ca. 300 Ma. However, the pervasive development of deformational fabrics at East Kemptville suggests that both the Rb–Sr whole-rock and 40Ar/39Ar muscovite ages are at best minimum estimates for the inferred time of mineralization. In the present study, Rb–Sr whole-rock and mineral (muscovite, plagioclase, K-feldspar) analyses and 40Ar/39Ar incremental-step heating of a muscovite separate indicate the following: (i) diffusion of Sr on the whole-rock scale terminated at 344 ± 5 Ma (11 point isochron date), coincident with closure of muscovite to intracrystalline diffusion of Ar (apparent plateau date of 338 ± 2 Ma) and (ii) internal reequilibration of Sr among muscovite, feldspar, and whole rock varied considerably such that Rb–Sr whole rock – muscovite pairs give dates of 361–311 Ma (mean = 330 Ma, n = 7), whereas whole rock – plagioclase – K-feldspar give dates of 276–240 Ma (mean = 254 Ma, n = 7). This younger thermal event is reflected in apparent dates of 269–286 Ma for the low-temperature steps of the 40Ar/39Ar muscovite age spectrum.Collectively the data indicate that the East Kemptville area either cooled slowly over a protracted period of time (ca. 100 Ma) or experienced episodic tectono-thermal activity at ca. 344, 330, and 254 Ma. Examination of previously published geochronological data for the southern Meguma Terrane indicates that these aforementioned ages broadly coincide with earlier documented magmatic or tectono-thermal events (e.g., intrusion of Wedgeport Pluton at 315 Ma). Inferences by some workers of mid-Carboniferous magmatism in the Meguma Terrane are, however, not supported by the present study.
On the extent and thickness of the Innuitian Ice Sheet: a postglacial-adjustment approach
Authors: Tushingham A. M.
Published: April 2011

There is at present a controversy concerning the extent and thickness of the Innuitian Ice Sheet during the last glacial maximum (ca. 18 000 BP). Here, both a thick, extensive Innuitian Ice Sheet and a thin, limited ice sheet are isostatically modelled by employing disc-shaped elements and a radially symmetric Maxwellian Earth. The predicted relative sea-level curves for both models are compared with new data from Thores River, northernmost Ellesmere Island, and data from 29 other sites located in and around the Queen Elizabeth Islands. The data from Thores River are presented as an illustrative case study that particularly emphasizes the difficulty of relating sample elevations to ancient sea levels in this region. At all 30 sites, the relative sea-level data overwhelmingly favour the thick, extensive ice model. The hypothesis of tectonic uplift to explain the high raised beaches (> 100 m) found on Ellesmere Island and elsewhere in the region is rejected. The residual uplift of the thin, limited model is not spatially coherent, nor is it likely that tectonic uplift would exactly mimic the distinctive postglacial uplift. To reconcile geomorphological evidence (in the form of the preservation of preglacial maximum sediments and the general lack of glacial deposits) and the presence of high raised beaches, it is proposed that the Innuitian Ice Sheet was for part, possibly most, of its history a cold-based ice sheet (i.e., frozen to its bed).
A test of airborne, side-looking synthetic-aperture radar in central Newfoundland for geological reconnaissance
Authors: Graham D. F. , Grant D. R.
Published: April 2011

Side-looking, C-band synthetic-aperture radar (SAR) penetrates cloud and fog, and operates day or night, to produce pseudo-three-dimensional terrain images with enhanced topography and surface roughness. The images, which have a 20 m resolution and cover large areas, have been used to map the regional trends, patterns of lineaments, and terrain types over a 6200 km2 area of complex lithology, structure, and drift cover. Four lineament classes are differentiated. Glacial trends are clear, and bedrock structures (faults, fractures, joints, foliation, and folded bedding) with relief expression at the surface show through the drift as lineaments. They accurately reproduce most known features when compared with bedrock and Quatenary geology maps. Hitherto unrecognized structural elements are revealed. Tones and textures reflect minute surface roughness variations useful in terrain classification. SAR wide-swath-mode imagery is thus a valuable complement to aerial photography, and is superior in revealing hummocky moraine, ribbed moraine, boulder fields and stony till. Wider use of this imagery is encouraged.
Sedimentary record of Harrison Lake: implications for deglaciation in southwestern British Columbia
Authors: Desloges Joseph R. , Gilbert Robert
Published: April 2011

A sedimentary record from 60 km long Harrison Lake was constructed by using 3.5 kHz subbottom acoustic profiles and gravity cores of surface sediments. In places, the glaciolacustrine sediments exceed 70 m in thickness and represent the entire deglacial and postglacial accumulation record. An upper, acoustically transparent layer decreases in thickness from 12 to 4 m. southward from the upper lake. Cores from the upper metre of this layer demonstrate that deposition is dominated by settling of suspended sediment transported in a laterally mixed, wind-driven surface plume from the north. Depositional rates, inferred from 14C dating of organic macrofossils and counting of probable annual laminated couplets in the cores, are almost 2 mm/a in the north and decline to less than 0.1 mm/a in the south. Hence, the upper acoustic layer accounts for all postglacial (last 10 500 years BP) lacustrine deposition, with most of the sediment derived from Lillooet River. A lower, thicker (12–22 m), acoustically stratified layer is interpreted as high-energy glaciolacustrine deposits. This large volume of deglaciation sediment is derived from two sources: (i) ice retreating rapidly northwest up the Lillooet valley, which may have existed for no more than 400 years in the lower valley prior to opening of Lillooet Lake (which now traps most sediment derived from the upper basin); and (ii) inflow from the south as the late-glacial Fraser River rapidly built a delta north from the sill at Harrison Hot Springs. Despite known higher sea levels during deglaciation of the eastern Fraser Lowland, we have no evidence for a marine incursion.
A new species of graptoloid, Dicellograptus uncatus n.sp., from the Blue Mountain Formation of southern Ontario, Canada
Authors: Senior Sherrill J. H.
Published: April 2011

A recently discovered graptoloid, Dicellograptus uncatus n.sp., is described from the Blue Mountain Formation of southern Ontario, Canada. This species is characterized by an axial angle of 120–180° and a prominent, hook-shaped virgella. Dicellograptus uncatus n.sp. is Late Ordovician in age and occurs in the Paraclimacograptus manitoulinensis Zone.
Thermobarometric constraints on the structural evolution of the Coast Mountains batholith, central southeastern Alaska
Authors: McClelland William C. , Anovitz Lawrence M. , Gehrels George E.
Published: April 2011

Thermobarometric data from amphibolite-facies metamorphic rocks west of the Coast Mountains batholith provide important constraints on the structural evolution of the mid-Cretaceous Sumdum–Fanshaw fault system and Late Cretaceous – Paleocene Le Conte Bay shear zone in central southeastern Alaska. Ductile structures that make up the Sumdum–Fanshaw fault system record the east-directed underthrusting of the Alexander terrane and Gravina belt beneath the Ruth assemblage (Yukon–Tanana terrane) and Taku terrane. These structures are truncated to the east by the Le Conte Bay shear zone. Temperature and pressure estimates calculated from the garnet–biotite geothermometer and garnet–rutile–ilmenite–plagioclase–quartz geobarometer suggest juxtaposition of the Gravina belt and Yukon–Tanana terrane at relatively deep levels (>7 kbar) during mid-Cretaceous time. Rocks west of the Le Conte Bay shear zone yield thermobarometric estimates of 465–890 ± 50 °C and 7.1–11.8 ± 1 kbar (1 kbar = 100 MPa). Late Cretaceous and Paleocene metamorphism associated with the Le Conte Bay shear zone reflects synkinematic emplacement of tonalitic intrusions along the western margin of the Coast Mountains batholith. Thermobarometric results from samples adjacent to the tonalite bodies record uplift and retrogression and suggest tonalite emplacement at 7.5–7.7 ± 1 kbar. An eastward increase in thermobarometric estimates observed in Thomas and Le Conte bays is inferred to record uplift and east-side-up tilting of rocks west of and within the Le Conte Bay shear zone during Late Cretaceous and Paleocene time. Rocks within the Le Conte Bay shear zone were apparently rapidly (1.5–2 mm/a) uplifted to shallow crustal levels prior to mid-Eocene time. Thermobarometric results for the Petersburg region are similar to those previously reported along the western flank of the northern Coast Mountains batholith.
Massive sulfide deposits of the Noranda area, Quebec. II. The Aldermac mine
Authors: Barrett T. J. , Cattalani S. , Chartrand F. , Jones P.
Published: April 2011

The original Aldermac mine near Noranda contained several Cu–Zn massive sulfide lenses hosted by felsic to mafic volcanic rocks of the late Archean Blake River Group. The original Nos. 3–6 orebodies, which consisted of massive pyrite, with lesser magnetite, pyrrhotite, chalcopyrite, and sphalerite, contained 1.87 Mt of Cu–Zn ore that averaged 1.47% Cu (Zn was not recovered). The orebodies occurred within felsic breccias and tuffs up to 100 m thick that are stratigraphically overlain by an extensive dome of mainly massive rhyolite and rhyodacite (up to 250 m thick and at least 550 m across). Most of the volcanic rocks that laterally flank and overlie the felsic dome are dacitic to andesitic flows, breccia, and tuff, with minor rhyolites, and associated subvolcanic sills of quartz-feldspar porphyry and gabbro.The new massive sulfide deposit, discovered in 1988, lies 150–200 m east of the mined-out orebodies, at a similar stratigraphic level within altered felsic breccia and tuff. The sulfides are mainly in the No. 8 lens, which contains 1.0 Mt at an average grade of 1.54% Cu, 4.12% Zn, 31.2 g/t Ag, and 0.48 g/t Au. Pyrite forms porphyroblastic megacrysts in a groundmass of pyrrhotite, sphalerite, magnetite, and chalcopyrite. A funnel-shaped, chloritized stockwork zone underlies the No. 8 lens and contains Cu-stringer mineralization. The No. 8 lens appears to be zoned, with overall decreasing Cu:Zn ratios from the core to the fringes of the lens. Massive sulfides in this lens have high Ag, Cd, and Hg contents relative to other massive sulfide deposits near Noranda.Ti versus Zr trends for least-altered Aldermac volcanic rocks indicate a more or less continuous magmatic fractionation trend ranging from high-Ti andesite to andesite, dacite, rhyodacite, and two distinct rhyolites (A and B). Most volcanic rocks were derived from a common parental magma that was transitional between tholeiitic and calc-alkaline compositions, as indicated by Ti–Y–Zr–Nb data and rare-earth-element distributions.Ti versus Zr trends in altered volcanic rocks indicate that silicification (mass gain) has affected some of the andesitic to rhyodacitic rocks, whereas chloritization (mass loss) has affected many of the rhyolitic rocks. Intermediate to mafic volcanic rocks above and lateral to the felsic dome are commonly silicified, possibly the result of hydrothermally remobilized silica derived from underlying felsic volcanic rocks.The orebodies appear to have formed at an eruptive hiatus between mafic → felsic and felsic → mafic cycles, during explosive activity and accumulation of felsic breccia and tuff. Ore was deposited mainly within a felsic fragmental sequence (rhyolite A), but before emplacement of the dome of rhyolite B. In compositionally diverse volcanic terrains, the contact between successive mafic–felsic and felsic–mafic cycles may be a good exploration target, in particular specific geochemical contacts within the felsic stratigraphy.
Postglacial deltaic sediments, southern Fraser River delta, British Columbia
Authors: Clague John J. , Luternauer J. L. , Pullan S. E. , Hunter J. A.
Published: April 2011

The Fraser River delta, the largest delta on the west coast of Canada, has been built into the Strait of Georgia during the Holocene. Drill-hole and seismic reflection records reveal a succession of sedimentary units deposited during early Holocene progradation of the delta. These overlie an irregular surface developed on Pleistocene drift. Mud and silt, similar to sediments presently accumulating off the mouth of Fraser River in the southern Strait of Georgia, are conformably overlain by a thick unit of sandy foreset beds, dipping gently to the south-southwest into Boundary Bay and deposited in a foreslope environment. The foreset unit is sharply overlain by a much thinner topset sequence comprising silt and sand deposited in intertidal, fluvial-channel, and overbank environments, and peat deposited in swamps and bogs. Fifteen accelerator mass spectrometry radiocarbon dates on shell and wood indicate that most of the deltaic sediments south of the Main Channel of Fraser River were deposited between ca. 7500 and 5000 BP. By 5000 BP the locus of sedimentation had shifted from the south, into Boundary Bay, to the west and southwest, into the Strait of Georgia proper.
Lower Paleozoic tholeiitic dykes from central New Brunswick: possible evidence for the early opening of an ensialic Taconian back-arc basin
Authors: David Jean , Gariépy Clément , Philippe Sylvie
Published: April 2011

Cambrian and Early Ordovician sedimentary rocks of the Lower Tetagouche Group from the southern Miramichi Terrane in New Brunswick were intruded by a series of mafic dykes. The age of dykes is unknown, but their stratigraphic context and state of deformation indicate that they were intruded during the Taconian orogeny. The geochemistry of the dykes shows that they are a cogenetic magmatic suite of basaltic composition (48–55 wt.% SiO2) and tholeiitic affinity. The dykes are low in silica and high in TiO2 (1.5–3.5 wt.%) and FeO* (8–16 wt.%). Magmatic evolution of the suite resulted from processes involving both crystal fractionation and crustal contamination, as indicated by depletion of compatible elements, important enrichment in high-field-strength elements, and the presence of inherited zircons of Precambrian age. The most primitive samples resemble mid-ocean-ridge basalts, except for higher alkali contents, or continental tholeiites depleted of light rare-earth elements. In comparison, the most evolved dykes have a transitional character similar to within-plate basalts.The general evolution of the Lower Tetagouche Group dykes is similar to that of nascent basins formed within volcanic-arc complexes. Dyke intrusion resulted from the early development of an ensialic back-arc basin during the Taconian orogeny. The paroxysmal stage of this tectonic event is represented by the ocean-floor fragment of the Elmtree Terrane, north of the Miramichi Terrane.
Reinterpretation of a larval dissorophoid amphibian from the Lower Permian of Texas
Authors: Dilkes David W.
Published: April 2011

Restudy of the only indisputable larval temnospondyl from the Lower Permian (Arroyo Formation: Clear Fork Group) of North America has revealed the presence of a narial flange, which supports its assignment to the superfamily Dissorophoidea. Two families of dissorophoids, the Trematopsidae and Dissorophidae, are recognized in the Pennsylvanian and Permian of North America. Contrary to the initial description, the elongated external naris of the larva differs significantly from that of trematopsids, and it is reinterpreted as a homoplastic character. No definitive characters of trematopsids can be found in the larva, and it is, therefore, excluded from this family. In the absence of a diagnosis of the Dissorophidae, it is not possible to assign this extremely immature specimen to that family. The unique configuration of the external naris excludes the larva from any known genus of dissorophid, but only on the assumption that an adult would have a similarly shaped external naris. Future studies of the Dissorophidae using modern systematic techniques could resolve the taxonomic position of the larva. At present, the only supportable conclusion is that the larva is a dissorophoid.
Broad-scale Proterozoic deformation of the central Superior Province revealed by paleomagnetism of the 2.45 Ga Matachewan dyke swarm
Authors: Bates M. P. , Halls H. C.
Published: April 2011

An extensive paleomagnetic study of the 2.45 Ga Matachewan dyke swarm of the North American Superior Province suggests that the interior of an Archean shield can undergo broad-scale distortion as a result of later (Proterozoic) orogenic activity around the craton margins. Data collected from over 300 sites, of which 137 are reported here for the first time, reveal that the dykes contain a dual-polarity primary remanence that varies across the swarm in both inclination and declination. These regional variations are statistically significant at the 95% confidence level, and cannot be attributed to remagnetization or to magnetic anisotropy. Inclination variation is probably due to real or apparent polar wander during the emplacement of the swarm, and may in part explain the declination variation as well. However, for dykes within and northwest of the Kapuskasing Structural Zone (KSZ) a positive correlation is found between regionally averaged values of declination and dyke trend. Here the dykes appear to have suffered differential rotations about vertical axes of up to 40° since emplacement. The Matachewan swarm radiates northwards from a broad focus situated approximately in northern Lake Huron but the trend of the western half of the swarm follows a broad Z-shaped pattern where it crosses the KSZ. Our data suggest that this changing trend is a secondary feature and that the western dykes, like their eastern counterparts, originally had a more uniform trend. This large-scale distortion of the western Matachewan swarm and Archean host rocks within and north of the KSZ is probably the result of broad-scale deformation during the Trans-Hudson Orogeny at about 1.95 Ga, coeval with uplift along the KSZ.
Petrology, palynology, and depositional environments of coals of the Upper Carboniferous Barachois Group (Westphalian A and C), southwestern Newfoundland
Authors: Hyde Richard S. , Kalkreuth Wolfgang D. , Utting John
Published: April 2011

Coal samples from the Barachois Group of western Newfoudland vary in rank from high-volatile C to high-volatile A. The coals are vitrinite rich (> 70%), except some from Coal Brook that contain substantial quantities of inertinite (up to 52%). Liptinite ranges up to 18% but is a relatively minor component. The most abundant constituents amongst the three maceral groups are vitrinite – vitrinite A, inertinite–semifusinite, and liptinite–sporinite. Compositional profiles in three of the seams show no clear correlation between maceral group content and stratigraphic position. The Barachois Group coals are relatively high in ash (mean = 12.8%) and sulphur (mean = 6.9%). Spore assemblages from coal samples of the Barachois Group indicate a Westphalian A age in the Barachois Brook and Coal Brook areas and a Westphalian C age along Blanche Brook.Barachaois coals are part of a mudstone-dominated facies association that developed in an assemblage of floodplain environments. Plots of tissue preservation – gelification indices (TPI/GI) and the assemblages of spores derived from vascular plants suggest that most peats were generated in wet, forested tracts that, from the high ash content, occupied low-lying interfluves. Less wooded fen environments are also indicated, particularly in the Blanche Brook seams, by TPI/GI plots and a spore assemblage suggesting incursion of flood waters and dominance of herbaceous vegetation. Inertinite-rich samples from Coal Brook show extreme variation in paleoenvironmental conditions, which include dry forested regions.
Origin of a postglacial kettle-fill sequence near Georgetown, Ontario
Authors: Warner Barry G. , Kubiw Helen J. , Karrow Paul F.
Published: April 2011

Stratigraphic relationships, radiocarbon dating, and pollen and plant macrofossil analyses establish the origin and developmental history of a kettle near Georgetown, Ontario. The early inorganic sediments contain redeposited fossils, particularly from local vegetation. Fossils in peat younger than 10 000 BP largely represent past wetland plant communities in the basin. Although the fossil record probably began about 1300 years after deglaciation of the site, an additional 1700 years passed before the dead ice block melted; only then did sedimentation and biological activity stabilize in the basin and produce an accurate fossil record of past vegetation. Truncated fossil records, illustrated further here by a pollen diagram from nearby Heart Lake, should be expected from kettle-hole deposits, and the radiocarbon ages and fossils from the earliest parts of such sequences should be interpreted with caution.
On the formation of large subglacial lakes
Authors: Shoemaker E. M.
Published: April 2011

The role of subglacial water storage beneath continental ice sheets is investigated, primarily for a deformable bed. Subglacial ponding is shown to occur under most regions of warm-based ice sheets, and large subglacial lakes can become established, for example in the Hudson Bay basin. The formation of large lakes depends upon the fact that the ice-surface gradient is reduced once subglacial ponding occurs and upon the feedback between the reduced ice-surface gradient and increased subglacial ponding. Subglacial ponding likely played a large role in determining the ice-sheet topography during late deglaciation and in speeding up the deglaciation process.
Hornblende geobarometry of the Nelson Batholith, southeastern British Columbia: tectonic implications
Authors: Ghent E. D. , Nicholls J. , Simony P. S. , Sevigny J. H. , Stout M. Z.
Published: April 2011

Hornblende geobarometry has been applied to granitic rocks of the Middle Jurassic Nelson Batholith, British Columbia, locally containing magmatic epidote. Geobarometry suggests equilibration pressures of less than 4.5 kbar (1 kbar = 0.1 GPa) in the northern part of the batholith, which lacks magmatic epidote. This part of the pluton shows clear magmatic intrusive relations, and the contact metamorphic rocks contain andalusite, which suggests that the equilibration and emplacement pressures are compatible.In the southern part of the batholith, granitic rocks containing magmatic epidote have equilibration pressures of 4.8–6.4 kbar. South and west of Nelson, there is a distinct contrast in pressure between the pluton and the country rock. Both the contact metamorphic rocks and the low-grade regional metamorphic rocks suggest pressures in the 2–3 kbar range.The pressure difference of about 2 kbar across the southwestern contact and the variation in pressure within the batholith can be explained by a model combining a late postequilibration upsurge (diapiric) of a deeper part of the pluton in the south, with a much later rotation and tilting of the batholith, associated with Eocene motion on the upper listric portion of the Slocan Lake Fault. The late diapiric (?) upsurge may account for the pressure contrast across the southwestern contact.
Les bassins d'avant-pays de la chaîne hercynienne au Carbonifère inférieur
Authors: Beauchamp Jacques , Izart Alain , Piqué Alain
Published: April 2011

The evolution of marine sedimentary basins deformed by the Hercynian Orogeny was studied in Germany, France, Iberia, Northwest Africa, and North America in the Lower Carboniferous. These basins opened along strike–slip faults and were filled with turbidites and shelf deposits until the main compressive phase at the end of Visean and the Namurian. The infilling was interrupted with frequent volcanic episodes and gravity-induced movements. According to sedimentary vergence, these basins were set into two festoons on both sides of an elongated and emergent swell structured during the Devonian and corresponding to the internal zones of the orogen. These basins were filled during a general tectonic compression phase; they correspond to the foreland basins of the Hercynian belt.
Ludlow (Silurian) lithistid and hexactinellid sponges, Cape Phillips Formation, Canadian Arctic
Authors: Freitas Tim A. de
Published: April 2011

Abundant hexactinellid and lithistid sponges occur in Ludlow (Silurian) platform slope strata of the Cape Phillips Formation, Canadian Arctic Islands. The following are new: in the Anthaspidellidae Miller, 1889, rhodesispongia simplex n.gen and sp., Climacospongia snowblindella n.sp., and Climacospongia undulata n.sp.; in the Sphaerocladina Schrammen, 1910, Caryospongia tuberosa n.sp.; in the Hexactinellida Schmidt, 1870 Malumispongium? cornwallisi n.sp., of the monospecific superfamily Malumispongium Rigby, 1967. Other previously described sponges recognized in the study assemblage include Hindia sphaeroidalis Duncan, 1879 and Caryospongia juglans Rauff, 1894. These occur in association with abundant Archaeoscyphia sp. in thin, laterally extensive lithistid sponge biostromes which throve on platform slope sediments during the Late Silurian. Based on the dominant dendroclone forms in the skeletons of these and other genera, Anthaspidellidae can be divided informally into two groups: (i) the polyclonids, possessing complex skeletons built of variable dendroclones types, including I-, X-, and Y-shape dendroclones, and accessory spicules, including rhizoclones, chiastoclones, and monactines; and (ii) the monoclonids, possessing simpler parenchymal canal systems and skeletons constructed mainly of I-shaped (amphiarborescent) dendroclones and lacking accessory spicules. The classification, based chiefly on skeletal architecture, suggests two main evolutionary trends in the family. The monoclonids generally maintained structural simplicity, inherited from the probable ancestral monactinellid, whereas the polyclonids evolved a varied and complex skeletal architecture that was more successful.
The use of magnetotellurics for mineral exploration: an experiment in the Chibougamau region of Quebec
Authors: Zhang Ping , Chouteau Michel
Published: April 2011

Ten magnetotelluric (MT) soundings were recorded in the range 300 Hz to 200 s along an 11 km profile across a long, well-defined, east–west sub vertical conductor in the vicinity of Chibougamau. This conductor had been recognized by the airborne transient electromagnetic technique and confirmed by other ground electromagnetic methods. The primary purpose of the MT survey was to further understand and constrain the structure of the conductor, especially its extent at depth. This study is the first to demonstrate the utility of the MT method for mineral exploration in Abitibi subprovince.The subsurface of the survey area can be roughly divided into a resistive northern section, a conductive central section (containing the conductive sheet), and a resistive southern boundary. Although some data are distorted by static shifts or three-dimensional effects, there is evidence that the data from the central conductive section are relatively free of static distortions. Therefore, taking into account existing geological and geophysical information and with extensive two-dimensional modelling, it is concluded that a conductive sheet with conductivity of 2 S∙m−1 and a width of 25 m should extend to a depth of no more than 750 m; an additional conductive block is required below this sheet. Cores from boreholes have shown that the conductivity of the near-surface sheet is mainly caused by sulfide minerals and graphite. It is also believed that graphite in the metasedimentary rocks under the central section may be responsible for the conductivity at depth.There is a clear boundary in terms of geoelectric characteristics between the northern part of the MT profile which is located in the Optica subprovince and the southern MT profile located in the Abitibi subprovince. Under the Optica subprovince, there are no structures other than a very resistive block with a thickness of at least 20 km. In contrast, conductive layers are found in the upper crust in the western and central parts of the Abitibi subprovince.
Suspension freezing of bottom sediment and biota in the Northwest Passage and implications for Arctic Ocean sedimentation
Authors: Reimnitz Erk , Marincovich Jr. Louie , McCormick Michael , Briggs W. M.
Published: April 2011

Ice observations and sediment collected in a summer transit through the Northwest Passage provide insights on suspension freezing, the most important sediment entrainment mechanism for the Arctic Ocean. No evidence was seen for entrainment by bottom adfreezing, bluff slumping, river flooding, dragging ice keels, or significant eolian transport from land to sea. Lack of eolian sediment loading in the Northwest Passage, together with that already reported for northern Alaska, eliminates wind as an important source for fine sediment in the pack of the Beaufort Gyre and related parts of the Transpolar Drift. Muddy sediment with pebbles and cobbles, algae with holdfasts, ostracodes with appendages, and well-preserved mollusks and sea urchins were collected from two sites in a 50 km long stretch of turbid ice. These materials indicate that suspension freezing reaching to a water depth of 25–30 m during the previous fall was responsible for entrainment. This mechanism requires rapid ice formation in open, shallow water during a freezing storm, when the ocean becomes supercooled, and frazil and anchor ice attach to and ultimately lift sediment and living organisms to the sea surface. The mechanism, already known to be important in the Beaufort Sea, probably also affects wide, shallow Siberian shelves and leads to cross-shelf transport of shallow-water organisms and dropstones with "glacial striations" toward deep basins. This makes distinguishing glacial–interglacial cycles more difficult.
Déformation coaxiale en bordure de la discontinuité structurale de Lyndhurst, sous-province de l'Abitibi
Authors: Labbé Jean-Yves , Daigneault Real , Cousineau Pierre A.
Published: April 2011

The Lyndhurst discontinuity is a major east–west structure located some 40 km north of Rouyn–Noranda. It separates the rhyolitic and sedimentary units of the Hunter Mine Group to the north from the basalts of the Kinojévis Group to the south. Evidence of deformation is observed only in the rhyolites and sediments along the south edge of the Hunter Mine Group. The deformation zone is approximately 1 km wide and is continuous for about 30 km. The Kinojévis Group rocks are not deformed. Deformed rhyolites show a strong sericite and chlorite alteration of hydrothermal origin. The competency of the rhyolites is significantly reduced by the presence of these phyllosilicates, which results in the deformation being preferentially localized in the more altered rocks. Competency contrasts observed on a mesoscopic scale are also valid on the microscopic and megascopic scales. The structural analysis of the deformation zone reveals different arrays that characterize three distinct sectors. These arrays reflect competency contrasts of the lithology and a crenulation cleavage. The stretching lineation is generally steeply plunging. Although the deformation seems significant in a zone contiguous to the Lyndhurst discontinuity, the poor development of the stretching lineation, the preservation of the original crystalline shapes of phenocrysts in the rhyolites, and the constant symmetry of the pressure shadows suggest a global coaxial deformation. This deformation regime is difficult to reconcile with a compressive fault such as a thrust fault.