bluuebunny/crossref_metadata_2025 huggingface dataset:
Age and correlation of the Honorat Group, southern Gaspé Peninsula
Authors: Riva John , Malo Michel
Published: April 2011

The Honorat Group of southern Gaspé consists of two formations: the Arsenault and the Garin. The Arsenault Formation, heretofore considered barren, has yielded a graptolite faunule indicative of a Llanvirn–Llandeilo age (early Middle Ordovician), suggesting a correlation with the lower Mictaw Group of Gaspé as revised by de Broucker. A hiatus of indeterminate magnitude, corresponding to the Taconic unconformity, probably separates the Arsenault Formation from the overlying Garin Formation. The Garin has yielded graptolites ranging from the upper Climacograptus spiniferus Zone to the Paraclimatograptus manitoulinensis Zone (late Middle to early Late Ordovician). The C. spiniferus Zone graptolites are identical to those of the upper γ sequence of the Cloridorme Formation of northern Gaspé and the Blind Brook Formation of the Munsungun Anticlinorium of Maine but differ somewhat from those from the upper Tetagouche Group of New Brunswick, which are closer to those from the Summerford and Exploits groups of north-central Newfoundland. The C. spiniferus zone has a wide distribution in eastern North America. It correlates with the Orthograptus amplexicaulis Zone of the southwestern United States and with the Climacograptus baragwathi Zone (Ea2) of the Pacific faunal province.The Matapédia Group, stratigraphically above the Honorat Group, has yielded both shelly fossils and a few graptolites. The ages of the graptolites now date it as Late Ordovician to late Early Silurian (Dicellograptus complanatus Zone – Monograptus sedgwickii Zone).
Contrasting assemblages and petrogenetic evolution of corona and noncorona gabbros in the Grenville Province of western Labrador
Authors: Rivers T. , Mengel F. C.
Published: April 2011

Contrasting coronas around olivines, pyroxenes, and ilmenites occur in metagabbros in two adjacent terranes in the Grenville Province of western Labrador. In the parautochthonous Gagnon terrane, coronas around olivines display evidence of evolution from double coronas of orthopyroxene- and fluorine-rich pargasitic amphibole, through triple coronas of orthopyroxene – garnet (clinopyroxene) – pargasitic amphibole, to double coronas of orthopyroxene – garnet (clinopyroxene) (parentheses enclose phase occurring as inclusions in previous phase). In the allochthonous Lac Joseph terrane, coronas around olivines consist of orthopyroxene – [clinopyroxene–spinel] or orthopyroxene–[pargasitic amphibole – spinel] (brackets enclose phases occurring in symplectic intergrowths). Possible reactions that explain the development of these assemblages are investigated, and it is concluded that the system was closed at the level of the corona. The silica required for the olivine–plagioclase reaction in Gagnon terrane was generated by the FMQ reaction during cooling and controlled the rate of reaction along olivine–plagioclase contacts. Alumina was relatively immobile, resulting in the formation of corundum and spinel inclusions in plagioclases in Gagnon and Lac Joseph terranes, respectively.Evolution of the corona gabbros in Gagnon terrane took place in two stages during isobaric cooling after emplacement, whereas formation of the symplectite coronas around olivines in Lac Joseph terrane is compatible with a single-stage reaction during isobaric cooling following emplacement. It is qualitatively estimated that the garnet-bearing coronas in Gagnon terrane formed at higher pressures than the spinel-bearing coronas in Lac Joseph terrane.Greenschist- and amphibolite-facies assemblages in noncorona gabbros in Gagnon terrane occur in locations corresponding to the regional greenschist- and amphibolite-facies metamorphic zones and are accordingly interpreted as being Grenvillian features. There is no apparent Grenvillian imprint in the gabbros in Lac Joseph terrane.
Isotopically depleted, alkalic lavas from Bowie Seamount, northeast Pacific Ocean
Authors: Cousens Brian L.
Published: April 2011

Bowie Seamount, located 200 km west of the Queen Charlotte Islands, British Columbia, is one of the southernmost of the Pratt–Welker Seamounts in the Gulf of Alaska. Eight dredge hauls recovered hawaiite and mugearite, with major-and trace-element compositions similar to those of Hawaiian alkali basalts. All samples are enriched in light incompatible elements but are isotopically MORB-like: 87Sr/86Sr = 0.70269–0.70285; 143Nd/144Nd = 0.51307–0.51315; and 206Pb/204Pb = 18.26–19.18. Sr- and Pb-isotope ratios correlate positively, whereas Sr and Nd correlate negatively, and lie on a mixing trend between DMM and HIMU mantle components. Juan de Fuca MORB have similar ratios and define similar mixing trends.The combined geochemical data require that the mantle source of Bowie (and Pratt–Welker) magmas has only recently been enriched in incompatible elements. The enrichment process could involve (i) metasomatism of the underlying lithosphere by CO2-rich fluids from a depleted source or (ii) mixing of silicate melts from a HIMU source with small-degree partial melts from depleted mantle. Alternatively, the magmas may be partial melts of subducted, 1.2 Ga oceanic crust that was variably enriched in U and Sr(?) during sea-floor alteration.
Geochronology of the Belmont Lake Metavolcanic Complex and implications for crustal development in the Central Metasedimentary Belt, Grenville Province, Ontario
Authors: Davis D. W. , Bartlett J. R.
Published: April 2011

U–Pb analyses of zircon and titanite were carried out on eight rocks from the Belmont Lake Metavolcanic Complex, a volcano-sedimentary sequence in the Central Metasedimentary Belt of the Grenville Province of southeastern Ontario. The ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position.The youngest volcanic age is [Formula: see text] from a rhyolite near the base of the sequence. The oldest age, [Formula: see text], is from a dacite in the middle. This is overlain by a rhyolite [Formula: see text] in age. A rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 Ma old. The complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age. Tectonic emplacement of these segments was most likely along previously unrecognized thrust faults.The supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism. The earliest event was probably associated with thrusting. The age of the youngest volcanic unit, [Formula: see text], is an upper age estimate for this event. A lower estimate is probably given by the age of the Cordova Gabbro, 1242 ± 3 Ma. The later event, including peak regional metamorphism, should be younger than [Formula: see text], the age of a sheared, recrystallized felsic sill intruded into the supracrustal rocks, and older than [Formula: see text], the age of the undeformed and unmetamorphosed Belmont Granite.Titanite fractions in the Belmont Granite and a volcanic andesite both give an age of 1071 ± 5 Ma. The age from titanite in the Belmont Granite may be due to thermal resetting during slow cooling. Titanite in the andesite is secondary and may have grown as a result of late metamorphic reactions.The youngest age measured, 1039 ± 5 Ma, is from a concordant analysis of a single zircon grain found within the oldest rhyolite. This may be an example of zircon growth from low-temperature, late-metamorphic fluids.
The Queen Charlotte Islands refraction project. Part I. The Queen Charlotte Fault Zone
Authors: Dehler Sonya A. , Clowes Ron M.
Published: April 2011

The active margin between the continental North American plate and oceanic Pacific plate west of the Queen Charlotte Islands was the site of an extensive onshore–offshore seismic refraction project in 1983. An airgun line shot over two ocean-bottom seismographs (OBS's) and a 32-charge explosion line recorded on the two OBS's and eight land-based seismographs (LBS's) deployed across northern Moresby Island were selected to study the structure of the predominantly transform Queen Charlotte Fault Zone and the associated offshore terrace. Two-dimensional ray tracing and synthetic seismogram modelling produced a pronounced laterally varying velocity structural model showing three major crustal components (oceanic, terrace, and continental) separated by an outer, crustally pervasive fault and active Queen Charlotte Fault, respectively. The 3 km thick block-faulted upper terrace unit, overlain by deformed sediments, is indistinguishable from adjacent oceanic sediments and upper crustal basalts located to the west. The upper part of the 10–17 km thick lower terrace unit has anomalously low velocities relative to the adjacent oceanic and continental crustal units. A high gradient increases terrace velocity rapidly with depth until the contrast becomes negligible at approximately 17 km depth. Changes in depth to Moho beneath the terrace suggest an increase in eastward Moho dip from 2–5 °observed west of the terrace to 19 °below it. Tectonic mechanisms proposed to explain the anomalous terrace structure involve sediment accretion during subduction of oceanic lithosphere, alternating or combined with compressive upthrusting of material along near-vertical fault planes during periods of active transform motion.
Surficial sediments of the outer banks, Scotian Shelf, Canada
Authors: Amos Carl Leonetto , Nadeau Odette C.
Published: April 2011

The distribution, thickness, and mean grain size of surficial sediments on Sable Island Bank, Middle Bank, and Banquereau, Scotian Shelf, are used to re-evaluate interpretations made by others on mechanisms controlling long-term stability and net transport pathways of surface sand. A Holocene sand-ridge complex, the Sable Island Catena, extends 300 km across Sable Island Bank and Banquereau. This sand-ridge complex, which is up to 50 m thick, formed as a result of Holocene sediment transport on the outer banks and controls the modern-day distribution of bedforms and sediment size. A clockwise circulation of sand centred around Sable Island, which had been proposed as the mechanism maintaining the island, does not take place. Sand is transported from southwest to northeast across Sable Island Bank towards the Sable Island Catena; thereafter, sand is dispersed eastward. "Spillover" of sand from the banks to The Gully is not significant. Sand is trapped in depths less than 100 m. The processes proposed to have formed the Sable Island Catena are barotropic, storm-driven currents and associated sand transport and "fair-weather" dispersion of sand by strong, tidal flows or baroclinic currents, coupled with an abundant supply of sand-size sediment.
Seismic evidence for mantle flow beneath the Massif Central rift zone (France)
Authors: Ramananantoandro R.
Published: April 2011

The elastic-wave velocities in three spinel lherzolite xenoliths from the Massif Central rift zone (France) indicate that the high field seismic velocity (8.4 km/s) found parallel to the rift, at a depth of 40 km in the upper mantle beneath the Massif Central, can only be explained by a preferred orientation of the olivine a axis parallel to the rift. This is not predicted by two-dimensional models of mantle flow beneath a rift. Horizontal asthenospheric flow in lithospheric fractures associated with rifting would explain the olivine orientation and the high upper mantle velocity parallel to the rift axis.
New Bathonian (Middle Jurassic) ammonite faunas from the Fernie Formation, southern Alberta
Authors: Hall Russell L.
Published: April 2011

Lateral impressions of ammonites are described from three levels in shales of the Ribbon Creek Member (Fernie Formation) at Adanac Pass, southern Alberta. The occurrence of Kepplerites cf. costidensus (Imlay) and Kepplerites subitus (Imlay) with East Pacific forms belonging to Xenocephalites and Lilloettia indicates correlation with the upper Bathonian of the Boreal sequence.
Regional clastic sediment yield in British Columbia
Authors: Church Michael , Kellerhals Rolf , Day Terry J.
Published: April 2011

The data archive of the Water Survey of Canada, supplemented by data of the British Columbia Hydro and Power Authority, is used to investigate the areal pattern of fluvial sediment yield in British Columbia. The data represent suspended-sediment loads at 63 stations derived from observations within the period 1966–1985. In most of the province there is a single annual peak in sediment transport in spring, corresponding to the dominant snowmelt freshet. However, on the coast winter rainfall induces the sediment peak, and in the Coast and Cascade mountains there is a transitional regime with two peaks. From 65 to 90% of annual sediment yield occurs in the spring three months. Sediment yield per unit area (specific sediment yield) increases with drainage area at all scales from 10 up to 30 000 km2. The pattern persists seasonally throughout the year. This contradicts the conventional model in which sediment yield declines downstream because of deposition along channels of a portion of the load derived from erosion of the land surface. In British Columbia much of the sediment derives from erosion of Quaternary materials along stream banks and valley sides. Rivers draining glaciers and lakes behave distinctively. The observed pattern of sediment yield complicates prediction of drainage-basin sediment yield.
Geologic sections across the onshore Senegal–Mauritania basin derived from geoelectric studies
Authors: Ritz M. , Bellion Y.
Published: April 2011

On the basis of magnetotelluric two-dimensional models along three traverses, the regional electrical structure within the Senegal–Mauritania basin sediments has been studied. Correlation of the computed models with the wells drilled in the region shows that the main gross lithologic units were detected. The models can be generalized into three resistivity layers: (i) post-Turonian; (ii) pre-Senonian; and (iii) basement. In the southern part of the basin, there are relatively conductive formations below the Mesozoic that are interpreted as sediments of the Paleozoic Bove basin sequence. By combining the information that has been provided by the geoelectric cross sections and the lithologic and electric log data, a schematic model for the generalized sedimentary structure of Senegal has been generated. The interpretation that emerges shows that the basin is a westward-sloping, open homocline in which the structure is controlled by north–south-trending basement faulting that portrays a staircase structural style.
Palynology of uppermost Proterozoic and lowermost Cambrian formations, central Mackenzie Mountains, northwestern Canada
Authors: Baudet D. , Aitken J. D. , Vanguestaine M.
Published: April 2011

The acritarch assemblages of strata from the base of the Upper Proterozoic Sheepbed Formation to the base of the Lower Cambrian (Atdabanian) Sekwi Formation are described. The sections sampled are in southwestern (internal) structural units where erosion beneath the "sub-Cambrian"(?) unconformity is least evident. Problems of lithostratigraphic correlation of post-Sheepbed, pre-Backbone Ranges formations remain. Acritarchs indicate the age of the Sheepbed Formation and the Blue-flower Formation above it is latest Proterozoic (Vendian), whereas that of the Vampire Formation is Early Cambrian (Atdabanian). The Backbone Ranges Formation has not yielded datable acritarchs, but it is for the most part Cambrian in age, based on other fossil evidence. Comparisons are made with the Russian Platform and southern Canadian Rocky Mountains successions. The total number of acritarch genera increases markedly across the Precambrian–Cambrian transition.
Paleoecological implications of Late Pleistocene and Holocene microtine rodents from the Bluefish Caves, northern Yukon Territory
Authors: Morlan Richard E.
Published: April 2011

Bluefish Caves 1, 2, and 3 have produced tens of thousands of vertebrate remains among which at least nine species of microtine rodents are represented: red-backed vole, Clethrionomys rutilus; collared lemming, Dicrostonyx torquatus; brown lemming, Lemmus sibiricus; singing vole, Microtus miurus; tundra vole, Microtus oeconomus; meadow vole, Microtus pennsylvanicus; yellow-cheeked or taiga vole, Microtus xanthognathus; muskrat, Ondatra zibethicus; and northern bog lemming, Synaptomys borealis. Late Pleistocene and Holocene components are clearly distinguishable from one another in each of the three caves, and each component can be subdivided within cave 1. This paper discusses (i) variations in taxonomic abundance through time and between site areas, (ii) contrasts in microhabitat between north-facing cave 1 and south-facing cave 2, and (iii) decreases in tooth size that may reflect a reduction in the length of the growing season. A general decrease in diversity is shown to involve increased dominance and decreased species richness and evenness. These changes are attributed to postglacial zonation of habitat.
Structural control of gold mineralization at the Bousquet mine, Abitibi, Quebec
Authors: Tourigny Ghislain , Hubert Claude , Brown Alex C. , Crépeau Robert
Published: April 2011

The Bousquet gold deposits are structurally controlled, disseminated and vein type lodes located within a 500 m wide anastomosing deformation zone. Ore is located within narrow zones of high strain surrounded by lozenge-shaped panels of less-deformed rock. Strain characteristics are those of the bulk inhomogeneous flattening style. Ore lenses are spatially related to highly sheared, fractured, and altered mafic and felsic volcanic and volcaniclastic rocks of contrasting rheologic properties. Deformation features can be ascribed to multistage progressive ductile → brittle deformation. Strain markers and kinematic indicators show that the principal displacement within the deformation zone was reverse faulting with a minor sinistral throw. A structural analysis demonstrates that the deformation responsible for the development of a pervasive regional foliation, brittle fractures, and oblique reverse faults can be attributed to a north–south compression.Metamorphic minerals such as andalusite, kyanite, garnet, biotite, chlorite, chloritoid, and calcic plagioclases indicate that upper greenschist metamorphism was attained locally within the ductile deformation zones. Subsequent pervasive retrograde alteration, including carbonatization and hydration of silicates to white mica and chlorite, suggests an important period of hydrothermal activity after peak metamorphism. Native gold is typically closely associated with pyrite and with these hydrothermal assemblages and was probably channelled into ductile and brittle structural zones prior to and after peak metamorphism.Two principal types of steeply dipping auriferous sulphide veins are present in the mine: foliation-oblique veins and foliation-parallel veins. Foliation-oblique veins occur within steeply dipping conjugate shear fractures spatially related to competent protoliths. The main set was emplaced during late stages of the regional tectonic deformation, after the initial development of a pervasive regional foliation and before the end of the progressive deformation. Foliation-parallel veins are located within openings created by decoupling schistosity laminae or by overriding of irregular surfaces such as fault planes and shear zones. These veins are relatively younger and less deformed than the foliation-oblique veins.Pervasive pyritic disseminations along foliation surfaces are earliest and synchronous with the development of foliation and probably continued throughout the progressive deformation. Early disseminated sulphides may also have been remobilized by pressure solution into later vein systems.
Offshore continuation of Meguma Terrane, southwestern Nova Scotia
Authors: Pe-Piper Georgia , Loncarevic Bosko D.
Published: April 2011

Eight short drill cores have been examined from the continental shelf southwest of Nova Scotia. Four cores recovered granitoid rocks of two types. Ilmenite-bearing granitoid rocks petrographically and geochemically resemble granodiorites of the South Mountain Batholith and granites of the Seal Island Pluton. Magnetite-bearing granitoid rocks are also peraluminous but have no exact analogues onshore in Nova Scotia. Two cores recovered metamorphic rocks in a small area 50 km south of Seal Island. One consits of chlorite–muscovite–quartz schist, geochemically similar to rocks of the Halifax Formation. The second sampled epidote–chlorite–quartz schist similar to metavolcanic rocks of the White Rock Formation. One further core sampled quartzite, and another sampled a metavolcanic rock (possibly erratic).The regional extent of these lithotypes can be inferred from gravity and aeromagnetic data. Regional gravity data suggest the presence of a large granite body off southwestern Nova Scotia. In this area, magnetic anomalies are irregular, apparently reflecting the presence of magnetite-bearing granites. The layer-stripping method of analyzing the magnetic field shows that the area is underlain at depth by high magnetic anomalies. Large near-surface linear magnetic anomalies are used to map the extent of the volcanic rocks of the White Rock Formation. The area is cut by several northwest-trending faults that postdate Acadian folding but predate the earliest Jurassic magmatism of the Shelburne Dyke and North Mountain basalt. The unusual magnetic signature of the area off southwestern Nova Scotia may reflect a different basement; it is possible that Meguma rocks are thrust over the Avalon Terrane. Alternatively, it may be solely the result of magnetite-bearing granites. These granites may be related to a Permian thermal event in southwest Nova Scotia, and they have some petrographic similarity to young granites of the Piedmont Zone of South Carolina.
Anorogenic magmatism and the Grenvillian Orogeny
Authors: Windley Brian F.
Published: April 2011

The Grenvillian Orogeny was preceded by extensive anorogenic volcanism and plutonism in the period 1500–1300 Ma in the form of rhyolites, epizonal granites, anorthosites, gabbros, alkaline complexes, and basic dykes. An analogue for the mid-Proterozoic anorogenic complexes is provided by the 2000 km by 200 km belt of anorogenic complexes in the Hoggar, Niger, and Nigeria, which contain anorthosites, gabbros, and peralkaline granites and were generated in a Cambrian to Jurassic rift that farther south led to the formation of the South Atlantic. An analogue for the 1 × 106 km2 area of 1500–1350 Ma rhyolites (and associated epizonal granites) that underlie the mid-continental United States is provided by the 1.7 × 106 km2 area of Jurassic Tobifera rhyolites in Argentina, which were extruded on the stretched continental margin of South America immediately preceding the opening of the South Atlantic. The mid-Proterozoic complexes were intruded close to the continental margin of the Grenvillian ocean and were commonly superimposed by the craton-directed thrusts that characterized the final stages of the Grenvillian Orogeny. The bulk of the Keweenawan rift and associated anorogenic magmatism formed about 1100 Ma at the same time as the Ottawan Orogeny in Ontario, which probably resulted from the collision of the island arc of the Central Metasedimentary Belt attached to the continental block in the east with the continental block to the west. The most appropriate modern equivalent would be the Rhine Graben, which formed at the same time as the main Alpine compression.
Cyclical variation in composition in continental tholeiites of East Greenland
Authors: Hogg A. J. , Fawcett J. J. , Gittins J. , Gorton M. P.
Published: April 2011

The Prinsen of Wales Bjerge (PWB), part of the Tertiary volcanic province of East Greenland, consists of tholeiitic basalts overlain by alkalic basalts that were erupted 100–150 km west of the original axis of continental rifting and active ocean-floor development during the creation of the North Atlantic Ocean. They have many features of continental flood basalts but are somewhat enriched in Fe and in Ti relative to Fe and have slightly lower Al2O3. They have slight enrichments in the light rare-earth elements (La/Yb = 3–4). A nunatak within the PWB displays four cycles of tholeiitic basalt, each about 50 m thick, which are defined by trace-element variations (Ni, Cr, Sr, Zr, and Zr/Y). In three of the four cycles the lowermost flows are the most highly differentiated, and successive flows are increasingly primitive. These changes are thought to be the result of frequent injection of primitive, mantle-derived tholeiitic magma into small crustal magma chambers that contain evolved tholeiitic magma. The resultant mixing and expulsion of hybrid magma produce flows of small volume (0.01–0.03 km3) that display increasingly primitive character upward within each cycle (increasing Mg# and decreasing content of incompatible elements). This process is expected to be more efficient in small reservoirs than in the very large magma chambers that have been invoked by previous exponents of the differentiation–replenishment hypothesis. We suggest that cyclical volcanism in areas well back from the line of active rifting may be more common than is realized and is controlled by the fractionation–magma-replenishment process operating in numerous small reservoirs in an extensively fractured continental crust.
Late Quaternary events in the Lethbridge area, Alberta
Authors: Vreeken Willem J.
Published: April 2011

New observations in the Lethbridge area permit a more complete reconstruction of the landscape history in Late Wisconsinan and Holocene time. The plain of glacial Lake Macleod, the Lethbridge moraine, and the plain of glacial Lake Lethbridge became exposed in that order and in quick succession. Almost immediately thereafter, a discontinuous mantle of loess began to accumulate on those surfaces. The presence of Glacier Peak layer G or Manyberries tephra near the base of the loess indicates these events occurred just before 11 200 BP. The similarity of this chronology to that established for the older Green Lake end moraine in the Cypress Hills region and the fact that the younger Buffalo Lake moraine was formed before 11 000 BP indicate that deglaciation of southern Alberta proceeded very rapidly.The oldest buried paleosol observed near Lethbridge began to form shortly after 11 200 BP. Subsequently, and throughout the Holocene, intervals of loess deposition alternated with soil-forming intervals. At least six soil–landscape cycles occurred between 11 200 and 6800 BP (before the Mazama tephra was deposited), and at least five cycles occurred subsequently. Occurrences of postglacial loess more than 3 m thick are common. A column of 6.7 m of loess, including 12 paleosols, was observed at one site.
Quantitative trace-element modelling of the crystallization history of the Kinojévis and Blake River groups, Abitibi Greenstone Belt, Ontario
Authors: Fowler A. D. , Jensen L. S.
Published: April 2011

The Archean tholeiitic Kinojévis suite is characterized by an iron-enrichment trend and abundant Fe–Ti oxides in its evolved basalts, andesites, and rhyolites. The rare-earth-element (REE) patterns of the suite remain flat from the basalts through to the rhyolites, with the development of small, negative Eu anomalies. Quantitative modelling of the trace elements from little-altered samples is consistent with the mineralogy, suggesting that the suite was produced through fractional crystallization of olivine, pyroxene, plagioclase, and Fe–Ti oxides. The evolved rhyolites are interpreted as having developed by greater than 90% fractional crystallization in a high-level magma chamber.The calc-alkaline Blake River Group conformably overlies the Kinojévis rocks and is characterized by enrichment in alkalis and silica. The REE patterns are light rare-earth-element (LREE) enriched, and the felsic rocks have prominent negative Eu anomalies. Geochemical modelling shows that the suite could have developed either through fractional crystallization dominated by plagioclase and clinopyroxene or by assimilation of tonalite, coupled with fractional crystallization.
A note on the Quesnel Lake Gneiss, Caribou Mountains, British Columbia
Authors: Montgomery John R. , Ross John V.
Published: April 2011

The Quesnel Lake Gneiss is one of several large bodies of gneiss emplaced into the westernmost exposure of the Hadrynian to Paleozoic(?) metasedimentary rocks of the Snowshoe Group in the Omineca Belt, central British Columbia. The gneiss has a deformational history comparable to that of its enveloping rocks, and isotope studies indicate that its age of emplacement is Late Devonian to Early Mississippian and that its age of synkinematic metamorphism is mid-Jurassic. From petrochemical analyses and structural studies, we interpret the gneiss as being a late Paleozoic igneous intrusion into the probable western margin of the North American craton.
The Lower Jurassic phosphorites of southeastern British Columbia and terrane accretion to western North America
Authors: Poulton T. P. , Aitken J. D.
Published: April 2011

Sinemurian phosphorites in southeastern British Columbia and southwestern Alberta conform with the "West Coast type" phosphorite depositional model. The model indicates that they were deposited on or near the Early Jurassic western cratonic margin, next to a sea or trough from which cold water upwelled. This suggests that the allochthonous terrane Quesnellia lay well offshore in Sinemurian time. The sea separating Quesnellia from North America was partly floored by oceanic crust ("Eastern Terrane") and partly by a thick sequence of rifted, continental terrace wedge rocks comprising the Purcell Supergroup and overlying Paleozoic sequence. This sequence must have been depressed sufficiently that access of upwelling deep currents to the phosphorite depositional area was not impeded.
Pleistocene geology and geomorphology of the Smoking Hills Upland and lower Horton River Arctic coast of mainland Canada
Authors: Mathews William H. , Mackay J. Ross , Rouse Glenn E.
Published: April 2011

The Smoking Hills Upland and lower Horton River valley, on the Arctic coast of Canada 300 km east of the Mackenzie Delta, retain an extended record of subaerial erosion of nearly flat-lying Cretaceous shales. This erosion led to the development of (i) a very gently sloping low-relief upland surface (Early Pleistocene(?)), (ii) a slightly steeper intermediate surface, and (iii) younger steep valley walls, terraces, and broad valley bottoms. No direct glacial contribution to any of these landforms can be recognized. An early interglacial(?) fluvial episode is recorded in plateau-cap sediments. Suggestions of an early (mid-Pleistocene or earlier) glaciation overwhelming the Smoking Hills Upland are found in (i) anomalies in drainage patterns, (ii) disturbances in bedding, believed to have been caused by ice thrusting, and (iii) local occurrences of diamictons. Later, probably Early Wisconsinan, glaciation left meltwater channels in peripheral areas. The Late Wisconsinan ice sheet did not reach the Smoking Hills Upland but may have had an indirect influence by modyfying discharge and sediment transport of Horton River.
Paleomagnetism of the 1.1 Ga Lackner Lake Complex and tectonics of the Kapuskasing Structural Zone
Authors: Symons D. T. A.
Published: April 2011

The Middle Proterozoic Lackner Lake Complex is a circular alkalic syenite–carbonatite stock with a diameter of about 5.5 km. It intrudes granulite-rank Archean gneisses in the Kapuskasing Structural Zone of the Wawa Subprovince in the Superior Province of the Canadian Shield. It adjoins the Ivanhoe Lake fault zone, which forms the boundary with the Abitibi Subprovince and is the probable locus of maximum motion between the subprovinces. Specimens from 18 sites in the complex were analyzed paleomagnetically by alternating-field and thermal demagnetization and by saturation isothermal remanence tests. Large, recent viscous remanence components required removal before a stable remanence with a mean direction of 305.4°, 64.1 °(α95 = 5.2°) was isolated. Its pole of 53.7°N, 156.5°W (dp = 6.7°, dm = 8.3°) indicates emplacement at 1108 ± 10 Ma during a brief normal interval in a predominantly reversed-polarity time. This study indicates that there has been no postintrusion tilting of the Kapuskasing Structural Zone and that postintrusion uplift by unroofing did not exceed about 8 km.
U–Pb, Rb–Sr, and K–Ar isotopic constraints for ductile deformation and related metamorphism in the Teslin suture zone, Yukon–Tanana terrane, south-central Yukon
Authors: Hansen Vicki L. , Mortensen James K. , Armstrong Richard L.
Published: April 2011

The Teslin suture zone (TSZ) comprises a portion of the Yukon–Tanana terrane (YT), in the Yukon, formed by steeply dipping layering and L–S tectonite foliation. The TSZ forms the fundamental tectonic boundary between rocks deposited along the ancient margin of North America and allochthonous terranes to the west. TSZ tectonites evolved during initial penetrative dip-slip deformation (Dds) and later dextral strike-slip shear (Dss) along steep, 1–3 km wide shear zones. Several workers have speculated that the TSZ and related YT heterogeneous ductile deformation and associated metamorphism are Devonian to Mississippian in age and related to the intrusion of a similar-age orthogneiss throughout the Yukon and Alaska. However, recent structural and metamorphic studies of the TSZ provide evidence contradicting this view. New isotopic evidence, presented herein, indicates that TSZ dynamothermal metamorphism was cooled by Early Jurassic time, that it cannot be related to Devonian–Mississippian and Permian granitic intrusion, and that it predates Cretaceous plutonism.U–Pb zircon dating of peraluminous orthogneiss constrains primary peraluminous granite crystallization at 355 ± 25 Ma. Three Rb–Sr whole rock + muscovite and three K–Ar muscovite cooling dates of rocks containing Dds and Dss fabrics place a younger age limit of 182–213 Ma (latest Triassic to Early Jurassic) on Dds/Dss deformation. In addition, three Rb–Sr whole-rock + muscovite isochrons and one K–Ar date on biotite indicate peraluminous orthogneisses in the eastern portion of the study area were affected by a mid-Cretaceous thermal event. These data, togemer with structural and metamorphic relationships reported elsewhere, are summarized in pressure–temperature–time–displacement diagrams illustrating the evolution of TSZ and adjacent rocks from Devonian to Late Cretaceous time. Tectonites within the TSZ can be differentiated from peraluminous orthogneiss east of the d'Abbadie fault on the basis of their respective cooling histories.
Failles de chevauchement acadiennes dans la région de Weedon, Estrie, Québec
Authors: Labbé Jean-Yves , St-Julien Pierre
Published: April 2011

The Ascot–Weedon Formation and Magog Group are part of the Cambro-Ordovician oceanic domain of the Quebec Appalachians. The purpose of this work is to define the stratigraphic and structural relationships that exist between these units and the Siluro-Devonian sedimentary rocks: the Lac Aylmer Formation, to the northwest, and the St-Francis Group, to the southeast. Two structural domains are defined in the area. The first one, the northwestern zone, is essentially autochthonous. The Magog Group units are overlain by the Siluro-Devonian sediments of the Lac Aylmer Formation. Both units make up the northwest flank of the St-Victor Synclinorium, plunging slightly to the southwest. The second domain, to the southeast is made up of allochthons (Ascot–Weedon Formation and St-Francis Group) thrust on a large part of the southeast flank of the St-Victor Synclinorium. Structural analysis at mesoscopic, microscopic, and macroscopic scales indicates that the Ascot–Weedon Formation and the St-Francis Group are thrust northwesterly on southeast-dipping imbricate faults. Rocks of both units underlie the major La Guadeloupe Fault, bringing the Connecticut Valley – Gaspé Synclinorium over the St-Victor Synclinorium.
Paleomagnetism of Archean granites and Matachewan dikes in the Wawa Subprovince, Ontario: reevaluation of the Archean apparent polar wander path
Authors: Vandall T. A. , Symons D. T. A.
Published: April 2011

Paleomagnetic measurements have been completed on 400 specimens from dated Archean granites and Matachewan dikes in the Michipicoten and Gamitagama greenstone belts in the western Wawa Subprovince of the Superior Province, Ontario. Detailed alternating-field and thermal step demagnetization analyses were used to isolate stable remanence directions. A single-component remanence was isolated within three adjacent dated granitic plutons on the eastern margin of the Michipicoten belt, including the Hawk Lake trondhjemite, the Southern external granite, and the Eastern external granite (HSE). The maximum possible age for this remanence is constrained by the intrusion of the last pluton at 2694 Ma. The corresponding HSE paleopole is located at 10°W, 41°S (dp = 8°, dm = 13°). A second paleopole, NB, is derived from the Northern external granite and the Baldhead River quartz monzonite, which give U–Pb zircon ages of 2662 and 2668 Ma, respectively. Their single-component remanence defines a paleopole on the Archean apparent polar wander path (APWP) at 15°E, 27°S (dp = 8°, dm = 13°), with a maximum possible age of 2.66 Ga. A third paleopole, GD, is derived from the north-northwest-trending Gamitagama diabase dikes and yields a position of 57°E, 41°N (dp = 7°, dm = 14°), which agrees with poles determined by other workers from the 2454 Ma Matachewan dike swarm. The GD pole, along with previously determined Matachewan dike poles, demonstrates that a tectonically stable craton has existed since intrusion of this extensive dike swarm, and it improves the precision of the 2454 Ma Matachewan pole on the APWP. These poles, when compared with coeval poles from the eastern side of the Kapuskasing Structural Zone in the Superior Province, imply no tectonic rotation or translation between the Wawa and Abitibi subprovinces along this Early Proterozoic structure.
Crust and upper mantle Q from seismic refraction data: Peace River region
Authors: Zelt C. A. , Ellis R. M.
Published: April 2011

Crustal refraction data from the Peace River region of Alberta, Canada, have been analyzed using the spectral ratio method to obtain Q. A total of 1205 first and later arrivals corresponding to turning and reflected P-waves within the crust and upper mantle were studied. Source spectra were estimated from near-offset traces assuming typical sedimentary Q values. The large scatter of measured spectral ratios restricted the resolution to a three-layer model of the crust and upper mantle with Q constant in each layer. This model was obtained using a linear inverse method since the measured spectral ratios and known traveltimes in each layer are linearly related through the attentuation (Q−1) in each layer. A weighted L1 norm was minimized using linear programming, the weights being a measure of the certainty of each spectral ratio. The inversion was performed using the 25% most certain spectral ratios, regardless of magnitude or sign. Model bounds taking account of the scattered data were estimated. The results suggest that Q is between 200 and 500 in the upper crust and greater than 600 in the lower crust and upper mantle. This model is generally consistent with Q obtained from studies on nearby crust.
Clastic dykes of the Chibougamau Formation: distribution and origin
Authors: Chown E. H. , Gobeil André
Published: April 2011

Undeformed clastic dykes cut Archean crystalline rocks in two northeast-trending zones west of Chibougamau, Quebec. The dykes contain varying amounts of granule- to pebble-sized lithic fragments in a fine-grained matrix of angular mineral clasts, identical to material composing the nearby Lower Proterozoic Chibougamau Formation. This extends the area known to have been covered by the Chibougamau Formation more than 80 km to the west. Dyke structures suggest forceful downward intrusion of water-laden sediment, related to either syn- or postsedimentary fault movements.
Geochemistry of the Mamainse Point volcanics, Ontario, and implications for the Keweenawan paleomagnetic record
Authors: Klewin Kenneth W. , Berg Jonathan H.
Published: April 2011

The Keweenawan (1100 Ma) Mamainse Point volcanics, located along the eastern shore of Lake Superior in Ontario, formed in the Midcontinent Rift of North America. They are a 5250 m thick sequence of over 350 predominantly basaltic lava flows. The Mamainse Point section is the most continuous Keweenawan volcanic sequence and spans nearly the entire igneous history of the rift. The lower part of the section consists of high-MgO picrites and basalts, but the upper part of the section is composed of olivine tholeiites intercalated with numerous conglomerate layers. Major- and trace-element data reveal that the section consists of numerous stratigraphically constrained, geochemically distinct groups of lava flows. The comprehensive geochemical data on the entire sequence indicate that the section has no repetition due to faulting, as has been suggested by other workers on the basis of paleomagnetic studies. Evidently, the three paleomagnetic reversals previously found in the Mamainse Point section are real, and therefore there were multiple paleomagnetic reversals during Keweenawan time.
40Ar/39Ar ages of detrital muscovite within early Paleozoic overstep sequences, Avalon composite terrane, southern New Brunswick: implications for extent of late Paleozoic tectonothermal overprint
Authors: Dallmeyer R. D. , Nance R. D.
Published: April 2011

Concentrates of coarse-grained detrital muscovite from the Ratcliffe Brook Formation (lowermost Cambrian) display internally discordant 40Ar/39Ar age spectra. Gas fractions evolved at intermediate and high experimental temperatures record apparent ages of ca. 610–620 Ma. These are interpreted as dating initial cooling through temperatures appropriate for intracrystalline retention of 40Ar and may indicate derivation from mylonite zones developed within proximal late Precambrian granitic rocks. Gas fractions evolved at lower experimental temperatures record patterns of spectra discordance that suggest the constituent grains experienced partial, intracrystalline diffusive loss of 40Ar during a late Paleozoic, low-grade thermal overprint. A muscovite concentrate from pelitic schist beneath the allochthonous, latest Precambrian Cranberry Head granite records a 40Ar/39Ar plateau age of 318 ± 1 Ma. This is interpreted as closely dating Late Carboniferous thrust emplacement of the allochthon.
Terrestrial fossils in the marine Presumpscot Formation: implications for Late Wisconsinan paleoenvironments and isostatic rebound along the coast of Maine
Authors: Anderson R. Scott , Miller Norton G. , Davis Ronald B. , Nelson Robert E.
Published: April 2011

Investigation of terrestrially derived organic remains within the late-glacial-marine Presumpscot Formation near Portland, Maine, adds one new shrub species, six moss species, and representatives of six families of insects to the fossil biota of the deposit. White spruce (Picea glauca) dominates the plant macrofossil assemblage; the dominant pollen type is also spruce. The total biotic assemblage probably represents remnants of a forest-floor litter layer, eroded along a stream and subsequently deposited offshore. Three accelerator mass spectrometer (AMS) dates on spruce needles and cones suggest rapid burial, with marine regression from the area by ca. 11 500 BP.
Palynostratigraphic zonation of Paleocene strata in the central and south-central Alberta Plains
Authors: Demchuk Thomas D.
Published: April 2011

Paleocene strata of the Scollard and Paskapoo formations in the central and south-central Alberta Plains can be subdivided into five formal biostratigraphic zones, based in part on a Momipites–Caryapollenites palynofloral lineage. A similar zonation previously identified from strata of the Wind River basin in Wyoming displays similar palynomorph occurrences. However, differences that are present are likely a result of latitudinal climatic zonation between Alberta and Wyoming during Paleocene time.Lowermost Paleocene strata of Alberta (Wodehouseia fimbriata Zone) are barren of Momipites species, which subsequently first appear in the Momipites wyomingensis Zone. These two zones include strata from the Cretaceous–Tertiary boundary (Nevis coal seam) to the top of the Scollard Formation. A diverse assemblage of Momipites spp. plus Aquilapollenites spinulosus, Caryapollenites prodromus, and Tiliaepollenites danei are present in the Aquilapollenites spinulosus Zone within the lowermost Paskapoo Formation. Two more species of Caryapollenites appear in the Caryapollenites wodehousei Zone. The Pistillipollenites mcgregorii Zone is characterized by the presence of Pistillipollenites mcgregorii, Insulapollenites rugulatus, and Caryapollenites inelegans. Momipites leffingwellii is absent from the lower portion of this zone, with Momipites waltmanensis, Momipites actinus, and Momipites triorbicularis absent from the upper portion. Lower P. mcgregorii Zone strata are the youngest strata encountered in the vicinity of the Red Deer River valley. Upper P. mcgregorii Zone strata include strata of the Obed–Marsh coal zone within the uppermost part of the Paskapoo Formation adjacent to the Alberta Foothills.
Geochemistry and age of Timiskaming alkali volcanics and the Otto syenite stock, Abitibi, Ontario
Authors: Othman D. Ben , Arndt N. T. , White W. M. , Jochum K. P.
Published: April 2011

Tephrites and trachytes of the Timiskaming volcanics from the Kirkland Lake area (Ontario) and syenites and a granite from the nearby Otto Stock are characterized by extreme enrichment of incompatible elements coupled with relative depletion of Nb, Ti, and to a lesser extent Zr and Y.The volcanic rocks have a whole-rock Sm–Nd isochron age of 2740 ± 117 Ma (2σ error), and minerals separated from the Otto Stock, a Sm–Nd age of 2544 ± 50 Ma. Conventional and ion probe U–Pb analyses of zircons from the Otto Stock yielded an upper intercept age of 2700 ± 19 Ma, whereas the more concordant ion probe analyses had a mean 207Pb/206Pb age of 2671 ± 8 Ma (2σ). The latter is interpreted as the age of emplacement of both the volcanics and the pluton, and the Sm–Nd mineral isochron age is thought to reflect a period of later disturbance, probably during regional metamorphism.A high initial εNd of 2.5 ± 1.5 for Kirkland Lake volcanics indicates long-term isotopic depletion of their source. This value is the same as that for volcanic rocks throughout the Abitibi belt and indicates that any chemically enriched material in the source cannot have been much older than the volcanics themselves. An environment remote from older continents is inferred.