bluuebunny/crossref_metadata_2025 huggingface dataset:
Geophysical observations of the northern Juan de Fuca Ridge system: lessons in sea-floor spreading
Authors: Davis E. E. , Currie R. G.
Published: April 2011

By virtue of its proximity to the coastline of North America and to numerous oceanographic institutions, the Juan de Fuca Ridge has been the focus of a large number of marine geological, geochemical, and geophysical investigations. Systematic studies began in the early 1960's with the geophysical survey of A. D. Raff and R. G. Mason, which provided much of the foundation for the development of the extraordinarily successful paradigms of sea-floor spreading and plate tectonics. Subsequent systematic and detailed studies of the plates and plate boundaries of the area by investigators from many academic, industrial, and government agencies, including the Geological Survey of Canada, have provided the basis for much of the fundamental understanding we now have of global plate motions and the processes that are involved in the creation of new oceanic crust at sea-floor spreading centres. Much of the success of these studies can be attributed to the geological diversity found along the Juan de Fuca Ridge. Clear examples are present of "normal" volcanically robust ridge segments, deep extensional rift valleys, stable and evolving transform faults, nontransform ridge offsets, propagating rifts, and off-axis seamount chains. Much has been learned about the nature of hydrothermal circulation through intensive studies of the many active hydrothermal systems and mature hydrothermal deposits that occur in both unsedimented and sedimented environments along the ridge. Better understanding of the way that oceanic crust chemically and physically "ages" is emerging from studies on the ridge and ridge flank. A clear history of the evolution of the ridge and of plate motions is provided by the magnetic anomalies mapped over the ridge and adjacent plates. From this history, lessons have been learned about the causes and consequences of plate motions, fragmentation, and internal deformation. Some of the success of these studies can be attributed to the rapidly evolving geophysical tools which provide ever increasing efficiency of operation and resolution. A new phase of study most recently begun involves the deployment of sea-floor geophysical "observatories" that provide a means by which temporal variations and events can be monitored over extended periods of time. These new studies are expected to yield yet another level of understanding of the processes that have produced two thirds of the Earth's surface as well as many important geologic formations in terrestrial settings.
Glaciomarine environments in Canada: an overview
Authors: Syvitski James P. M.
Published: April 2011

The present understanding of Canada's glaciomarine environments owes much to the remarkable role played by the scientists of the Geological Survey of Canada. Their efforts have led to the review and partial revision of three scientific paradigms: (1) There is a mechanical rather than a climatic control of the collapse of a tidewater ice sheet; (2) ice sheets were mostly grounded on Canada's continental shelves (rather than with floating ice shelves); (3) ice-loaded glaciomarine sediments are sometimes indistinguishable from deposits of till. A proposed stratigraphic framework for Canadian glaciogenic sequences can be quantified, allowing insights into ice sheet dynamics. For instance, the arctic margin of the Wisconsinan ice complex appears to have generated comparatively little meltwater, ice margin retreat being principally by iceberg calving. Surprisingly, the Atlantic margin of the Wisconsinan ice complex appears to have transported larger quantities than its Pacific counterpart. This is contrary to the present postglacial sediment yields discharged onto each margin. Glaciogenic sedimentation rates are shown to vary with the distance from a sediment source and the delivery rate of sediment. Glaciogenic accumulation rates are dependent on basin history and basin shape. Numerical examples include (1) the determination of accumulation rates from carbon stratigraphy; (2) the evaluation of the flux of sediment from a fjord to the open shelf during the retreat phase of an ice sheet; and (3) the application of a basin fill model to predict the styles of sedimentation within a fjord.
Basin development and inversion at the Appalachian structural front, Port au Port Peninsula, western Newfoundland Appalachians
Authors: Waldron John W. F. , Stockmal Glen S. , Corney Randolph E. , Stenzel Sheila R.
Published: April 2011

In the Humber Zone of the Newfoundland Appalachians, Cambro-Ordovician shelf and foreland basin successions are affected by Middle Ordovician (Taconian orogeny) and Devonian (Acadian orogeny) deformation. On Port au Port Peninsula the presence of the Late Ordovician to Late Silurian Long Point – Clam Bank succession allows these episodes to be separated. The Taconian foreland basin stratigraphy on Port au Port Peninsula is highly variable. On the west coast, platform carbonates are overlain by megaconglomerates of the Cape Cormorant Formation, which record progressive exposure of 1 km of the platform succession. The conglomerates are restricted to a narrow zone, consistent with derivation from a fault scarp originally immediately west of the outcrops (in palinspastic restoration). Farther east, at Victors Brook, the Cape Cormorant Formation is absent, but the overlying, almost undeformed Goose Tickle Group contains conglomerate derived both from the upper part of the platform succession and from the Taconian Humber Arm Allochthon. Southeast of Victors Brook, the top of the platform is overlain directly by scaly shales and mélange of the Humber Arm Allochthon, which includes deformed equivalents of the foreland basin succession. The distribution of conglomeratic units, the presence and configuration of faults, and the preservation of the Goose Tickle Group in the Victors Brook area imply that a fault-bounded basin developed in advance of the Humber Arm Allochthon during the Taconian orogeny. This basin is interpreted to have resulted from flexural extension of North American lithosphere. The close spatial coincidence between later Acadian structures and the Taconian basin boundaries implies that the basin-bounding faults were reactivated as thrusts and reverse faults, and that the basin underwent inversion during Acadian thrusting. The western basin-bounding fault, modified by the development of a "short cut" thrust, developed into the present-day Round Head thrust.
Thermoluminescence dating tests for lacustrine, glaciomarine, and floodplain sediments from western Washington and British Columbia
Authors: Berger Glenn W. , Easterbrook Don J.
Published: April 2011

To help further develop reliable procedures for accurate thermoluminescence (TL) dating of Quaternary waterlaid sediments, we tested TL dating procedures on sediment types rarely examined: six glaciolacustrine samples, three samples of glaciomarine drift, and eight samples of floodplain deposits. We used the partial-bleach (R-beta/gamma) technique applied to fine-silt polymineral grains. Results from our younger known-age glaciolacustrine sediments confirm earlier observations that only the clayey laminae are generally suitable for TL dating. A clayey lamina older than ca. 140 – 150 ka produced no age underestimation, and this result (ca. 300 ka) suggests that such older lake sediments are probably suitable for TL dating. Two proximal samples of glaciomarine drift produced large TL age overestimates, whereas the single distal glaciomarine-drift sample yielded an expected age (177 ± 38 ka), suggesting that follow-up studies are warranted. Our results for eight flood-plain samples confirm that zeroing of light-sensitive TL is more likely to be effective for sediments deposited in quiet, ponded water on the floodplain than for proximal sediments deposited from turbid floodwater. TL age estimates for floodplain sediments of the regional Whidbey Formation are consistent with its expected last-interglacial age, and those for two samples from stratigraphically older beds are consistent with deposition near or beyond 200 ka. Two of our younger samples (one lacustrine and one floodplain) gave TL age underestimates, perhaps because of use of ultraviolet TL emissions for these samples.
The influence of dikes on auriferous shear zone development within granitoid intrusions: the Bourlamaque pluton, Val-d'Or district, Abitibi greenstone belt
Authors: Belkabir Abdelhay , Robert François , Vu L. , Hubert C.
Published: April 2011

Shear-zone-related gold–quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes, which may have a profound influence on the localization, orientation, and kinematics of auriferous shear zones. The Bourlamaque pluton of the Val-d'Or district contains several economic auriferous shear zones, most of which follow and overprint diorite dikes. Mineralization in all deposits consists of quartz–tourmaline–pyrite veins in reverse- oblique orientation with a significant range of strike, dip, and slip direction. The geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion. The stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly-directed compression recorded by similar shear zones outside the pluton. This indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes, which acted as weak layers that were activated during subsequent deformation, showing the importance of layer anisotropy in auriferous shear zone development.The plunges of orebodies bear simple geometric relationships to the slip direction along a host shear zone: these are generally perpendicular to, or in some cases parallel to, the slip direction. Knowledge of the slip directions along activated dikes would therefore allow prediction of the possible plunge(s) of orebodies at early stages of exploration programs. Slip direction along an activated layer is controlled by the orientation of the layer with respect to the stress field and by the relative magnitudes of the three principal stresses. Using techniques developed for analysis of fault slip data, both parameters can be determined, provided there is a sufficient database, and slip direction can be predicted for activated layers of any orientations.
Late Silurian – Early Devonian rifting during dextral transpression in the southern Gaspé Peninsula (Quebec): petrogenesis of volcanic rocks
Authors: Dostal J. , Laurent R. , Keppie J. D.
Published: April 2011

The Upper Silurian – Lower Devonian volcanic rocks in the southern Gaspé Peninsula of the Quebec Appalachians crop out at the northeast end of the Connecticut Valley – Gaspé Synclinorium. These shallow marine and subaerial sequences reach a thickness of up to at least 2000 m and comprise two groups: (1) the Late Silurian volcanic rocks, which are mainly transitional alkalic–tholeiitic basalts with steeply sloping REE patterns; (2) the Early Devonian volcanic rocks, which include a significant proportion of intermediate rocks in addition to tholeiitic basalts. Compared with the Silurian rocks, the Devonian basalts have lower abundances of strongly incompatible trace elements such as Ba, Th, Ta, Nb, and light REE and relatively flat heavy REE patterns. Basalts of both groups display negative Nb and Ta anomalies (relative to Th and La).Although the basalts of both sequences were derived from lithospheric mantle, the Silurian basalts were generated from garnet peridotite at ~ 80 km depth while the Devonian basalts appear to have resulted from a larger degree of melting of spinel peridotite at a shallower depth (~ 60 km). Devonian intermediate rocks are probably the result of mixing of the basaltic magma with upper crustal material through assimilation – fractional crystallization processes. The basalts are interpreted to have formed in a northwest-trending rift zone located in the Quebec Reentrant during dextral transpression along the Appalachian Orogen. Rotation during and after the volcanism reoriented the rift zone to a northeast trend. The high density layer at the base of the crust under the Magdalen Basin may be the former magma chamber for the Silurian–Devonian volcanism. The change from transitional to tholeiitic volcanism at the Silurian–Devonian boundary suggests that the stretching value (ratio of final to initial surface area) increased from < 2 to > 2 at that time. This boundary is also coincident with the Salinic disturbance that is inferred to have been produced by erosion of the thermally uplifted block associated with rifting.
Labradorian and Grenvillian crustal evolution of the Goose Bay region, Labrador: new U–Pb geochronological constraints
Authors: Philippe S. , Wardle R. J. , Schärer U.
Published: April 2011

Major initial crust formation in the northeastern Grenville Province of Labrador occurred during the Labradorian orogeny (1710–1620 Ma) prior to re-deformation in the Grenvillian orogeny between 1050 and 950 Ma. The Goose Bay region includes several types of juvenile Labradorian crust, including calc-alkaline (arc-related?) terranes and the granite–anorthosite massif of the Mealy Mountains Terrane. New U–Pb dates corroborate previous evidence that calc-alkaline plutonism occurred ca. 1672 Ma and was followed closely by Labradorian metamorphism ca. 1659 Ma. Dates from strongly deformed rocks at the base of the Mealy Mountains Terrane have yielded ca. 1712, 1754, and 1775 Ma maximum upper intercept ages of plutonic and (or) metamorphic origin. These apparent ages represent the oldest component of the Labradorian crust that has been recognized to date and appear to be a distinctive feature of Mealy Mountains Terrane. The initial Pb isotope signature of these rocks, however, precludes the presence of significantly earlier (pre-1.8 Ga) crust.New U–Pb ages also support previous models for episodic Grenvillian metamorphism and indicate metamorphic pulses ca. 1035, 1010, 990, and 970 Ma, which probably represent the metamorphic response to progressive overthrusting by Mealy Mountains Terrane. Overthrusting of this terrane occurred along the Grand Lake thrust system, which is highlighted as a fundamental structure of the eastern Grenville Province and one that may have developed by reactivation of a Labradorian terrane boundary.
Metallogenic significance of trace element and U–Pb isotope data for uraninite-rich mineral separates from the Labrador Central Mineral Belt
Authors: Wilton Derek H. C. , Longerich Henry P.
Published: April 2011

Thirteen concentrates of uraniferous material were prepared from uranium occurrences in the Central Mineral Belt of Labrador. Host rocks to these occurrences include granitoid rocks of the Archean basement, ca. 2000 Ma metasedimentary rocks of the Lower Aillik Group, and 1860 Ma felsic volcanic rocks of the Upper Aillik Group. Common lead corrected Pb isotope data from inductively coupled plasma mass spectrometry analyses define 207Pb/206Pb ages ranging from 1805 to 1697 Ma for all but one sample, with a mean age of 1752 ± 27 Ma (1 σ). Ages calculated for individual samples are similar to those derived by previous workers using standard analytical techniques. Eleven of these samples define linear trends that intersect the U–Pb concordia at 1741 ± 23 Ma and a Tera-Wasserburg curve at 1740 ± 21 Ma, respectively. These data suggest that the occurrences are epigenetic with respect to host rocks and possibly related to a common metallogenic event, therefore resolving a long-standing controversy about the timing and mode of occurrence of the widespread uranium mineralization in this part of the belt. These ages broadly correlate with a period of migmatization, metamorphism, and granitoid plutonism, as defined by U–Pb zircon geochronological data for regional units. Rare earth element data for uraninite from all concentrates resemble those of uraninite in granite-related deposits. One sample has a distinctly different calculated 207Pb/206Pb age of 495 Ma, indicative of a later remobilization of the ca. 1741 Ma mineralization. The geochemical and geochronological data collectively suggest that the Central Mineral Belt uranium occurrences were related to posttectonic granite magmatism and have no direct genetic relationships with nongranitoid host rocks.
Crustal velocity structure in the southern Coast Belt, British Columbia
Authors: O'Leary D. M. , Clowes R. M. , Ellis R. M.
Published: April 2011

We applied an iterative combination of two-dimensional traveltime inversion and amplitude forward modelling to seismic refraction data along a 350 km along-strike profile in the Coast Belt of the southern Canadian Cordillera to determine crust and upper mantle P-wave velocity structure. The crustal model features a thin (0.5–3.0 km) near-surface layer with an average velocity of 4.4 km/s, and upper-, middle-, and lower-crustal strata which are each approximately 10 km thick and have velocities ranging from 6.2 to 6.7 km/s. The Moho appears as a 2 km thick transitional layer with an average depth of 35 km and overlies an upper mantle with a poorly constrained velocity of over 8 km/s. Other interpretations indicate that this profile lies within a collision zone between the Insular superterrane and the ancient North American margin and propose two collision-zone models: (i) crustal delamination, whereby the Insular superterrane was displaced along east-vergent faults over the terranes below; and (ii) crustal wedging, in which interfingering of Insular rocks occurs throughout the crust. The latter model involves thick layers of Insular material beneath the Coast Belt profile, but crustal velocities indicate predominantly non-Insular material, thereby favoring the crustal delamination model. Comparisons of the velocity model with data from the proximate reflection lines show that the top of the Moho transition zone corresponds with the reflection Moho. Comparisons with other studies suggest that likely sources for intracrustal wide-angle reflections observed in the refraction data are structural features, lithological contrasts, and transition zones surrounding a region of layered porosity in the crust.
Glacial Lake Arkona – Whittlesey transition near Leamington, Ontario: geology, plant, and muskox fossils
Authors: Morris T. F. , McAndrews J. H. , Seymour K. L.
Published: April 2011

Proglacial subaquatic fans between Leamington and Colchester, Essex County, Ontario, were deposited in glacial Lake Maumee at the end of the Port Bruce Stade by ice retreating northward. Some fans were buried by till and glaciolacustrine materials. One fan surface, northwest of Leamington, was only modified by lake current that transgressed and regressed over it. An aggregate excavation (Bondi site) exists within the surface of this fan. We describe the sedimentology of the site that provides evidence for fan and overlying bar deposits.Lake levels fell to the levels of lakes Arkona (216 m) and Ypsilanti (122 m) following the deposition of the fans. Large terrestrial areas supported plants and animals. Their presence is recorded at the Bondi site by a single bone and several organic mats recovered from the fan and bar sediment contact at two separate exposures. Radiocarbon dates on the bone of 13 410 ± 100 BP (TO-1803), organic material dates of 13 225 ± 200 BP (BGS-1404) and 13 150 ± 100 BP (WE-01-89), the altitude. (209 m), and the sedimentological setting indicate deposition during the Lake Arkona (216 m) – Lake Whittlesey (226 m) transition period.The pollen and plant macrofossil assemblages recovered from the organic material indicate a forest–tundra environment, with a mean July temperature of 14 °C. This interpretation fits well with the bone identified as cf. Euceratherium sp., a shrubox. The discovery of cf. Euceratherium sp. is surprising, as its previous range was south and west of this site. The organic material was subsequently buried by the formation of a bar as water levels rose within the Lake Erie basin and transgressed the site.
Seismic structure of the Central Metasedimentary Belt, southern Grenville Province
Authors: Zelt C. A. , Forsyth D. A. , Milkereit B. , White D. J. , Asudeh I. , Easton R. M.
Published: April 2011

Crust and upper-mantle structure interpreted from wide-angle seismic data along a 260 km profile across the Central Metasedimentary Belt of the southern Grenville Province in Ontario and New York State shows (i) relatively high average crustal and uppermost mantle velocities of 6.8 and 8.3 km/s, respectively; (ii) east-dipping reflectors extending to 24 km depth in the Central Metasedimentary Belt; (iii) weak lateral velocity variations beneath 5 km; (iv) a mid-crustal boundary at 27 km depth; and (v) a depth to Moho of 43–46 km. The wide-angle model is generally consistent with the vertical-incidence reflectivity of an intersecting Lithoprobe reflection line. The mid-crustal boundary correlates with a crustal detachment zone in the Lithoprobe data and the depth extent of east-dipping wide-angle reflectors. Regional structure and aeromagnetic anomaly trends support the southwest continuity of Grenville terranes and their boundaries from the wide-angle profile to two reflection lines in Lake Ontario. A zone of wide-angle reflectors with an average apparent eastward dip of 13° has a surface projection that correlates spatially with the boundary between the Elzevir and Frontenac terranes of the Central Metasedimentary Belt and resembles reflection images of a crustal-scale shear zone beneath Lake Ontario. A high-velocity upper-crustal anomaly beneath the Elzevir–Frontenac boundary zone is positioned in the hanging wall associated with the concentrated zone of wide-angle reflectors. The high-velocity anomaly is coincident with a gravity high and increased metamorphic grade, suggesting northwest transport of mid-crustal rocks by thrust faulting consistent with the mapped geology. The seismic data suggest (i) a reflective, crustal-scale structure has accommodated northwest-directed tectonic transport within the Central Metasedimentary Belt; (ii) this structure continues southwest from the exposed Central Metasedimentary Belt to at least southern Lake Ontario; and (iii) crustal reflectivity and complexity within the eastern Central Metasedimentary Belt is similar to that observed at the Grenville Front and the western Central Metasedimentary Belt boundary.
Aluminosilicate mineral assemblages in the Cargo Muchacho Mountains, southern California: metasomatism and gold concentration associated with magmatism and deformation in mesozonal environments
Authors: Owens E. O. , Hodder R. W.
Published: April 2011

Aluminous, kyanite-bearing mineral assemblages with more than 30% Al2O3 and less than 2% CaO + Na2O + K2O, like aluminous occurrences elsewhere, are spatially associated with gold deposits in the Cargo Muchacho Mountains, southeastern California. They are part of a zoned sequence of mineral assemblages that grade from regional amphibolite-facies quartzofeldspathic gneiss into locally occurring quartz–oligoclase–biotite–epidote–magnetite (feldspar zone), quartz–muscovite–biotite–magnetite–apatite–tourmaline (muscovite zone), and quartz–kyanite–magnetite–rutile–apatite–tourmaline–lazulite (kyanite zone). Field relations show that the mineral assemblages developed during emplacement of a Jurassic metaluminous–peraluminous plutonic suite, and that magmatism and aluminosilicate formation were partly contemporaneous with crosscutting low-angle shear zones.Mineral assemblage variation and bulk rock compositions point to aluminosilicate formation by pervasive H -ion metasomatism. Replacement of biotite by magnetite and variation in biotite Fe/(Fe+Mg) from 0.51 in the feldspar zone to 0.38 in the kyanite zone indicate oxidation was important during metasomatism. Calculated pH is 6.5 or less, and oxygen fugacity is 10−27 to 10−18 bars (1 kbar = 100 MPa) for fluids in equilibrium with the kyanite zone. Staurolite-bearing kyanite zone limits pressures to more than 400 MPa, and garnet–biotite geothermometry gives temperatures of 500–550 °C for metasomatism. The data are consistent with an origin by oxidizing, near-neutral magmatic fluids arising from crystallization of Jurassic mesozonal metaluminous–peraluminous magma. The high oxidation state suggests gold would have been transported to more reduced chlorite- and pyrite-bearing assemblages distal to the aluminosilicates.
U–Pb geochronometry in the Horseranch Range, northern Omineca Belt, British Columbia, Canada
Authors: Plint Heather E. , Parrish Randall R.
Published: April 2011

A U–Pb geochronometric study of granitic rocks in the Horseranch Range in the northern Omineca Belt, north-central British Columbia, was carried out to determine the age of deformation, metamorphism, and magmatism and to determine if Precambrian basement is exposed in the range.Our results document Eocene (48–54 Ma) and late Early Cretaceous (113 Ma) granitic magmatism, limit the regional schistosity development to 113 Ma and older, and constrain the peak of syn- to posttectonic regional metamorphism to about 113 Ma. There is no direct evidence for Jurassic metamorphism, although our data do not preclude it. Dextral, oblique-slip mylonitization along the western side of the range is, in part, of Eocene age and related to transtensional tectonics synchronous with movement along regional, dextral strike-slip faults. No Precambrian basement was identified. However, U–Pb data indicate Early Proterozoic inheritance in some of the granitic rocks, a common observation in magmatic rocks of the Omineca Belt.
Pleistocene mammals of the Edmonton area, Alberta. Part I. The carnivores
Authors: Burns James A. , Young Robert R.
Published: April 2011

Late Pleistocene fossils have been recovered sporadically in the Edmonton area, in central Alberta, for many years but there has been little work in determining their age. Fossils from quarries in North Saskatchewan River terraces and buried valley gravels are recognized as Late Pleistocene (mid-Wisconsinan) and early Holocene taxa, and numerous 14C dates on mammalian remains now support the assessment. The mammalian fauna consists of at least 16 taxa, including mostly grazing herbivores, but also three carnivores: Canis cf. Canis lupus (gray wolf), Arctodus simus (giant short-faced bear), and Panthera leo atrox (Pleistocene lion). The carnivores are first records for the region, and Arctodus is a first record for Alberta.
Proposed Younger Dryas glaciation of the eastern Scotian Shelf
Authors: King Lewis H.
Published: April 2011

A refined synthesis of the stratigraphy of the Scotian Shelf is presented, based on recently published borehole and seismic-reflection data and detailed correlation along high-resolution seismic profiles between the outer banks and the central basins.One of the new stratigraphic units of the outer bank region is of glacigenic origin and represents the last glacial event near the margin of the shelf. These deposits appear to be part of a morainal bank complex formed at a tidewater front. A Younger Dryas age is proposed for the glacial deposits, and the ice may have been widely distributed across the eastern Scotian Shelf. Evidence for the late glaciation is expressed in the central shelf area by an unconformity, which on the bank areas is associated with subglacial meltwater channels. 14C dates for the basin sediments of this region provide the most reliable chronology for the shelf stratigraphy.The origin of Sable Island is closely related to the depositional history of the moraine, and its surface has been modified by a Holocene transgressive event. A similar moraine formed on Banquereau but at greater depths.
Stratigraphie et paléogéographie d'un bassin d'avant-arc ordovicien, Estrie-Beauce, Appalaches du Québec
Authors: Cousineau Pierre A. , St-Julien Pierre
Published: April 2011

Two new formations, the Frontière and Etchemin formations, have been found to lie below the Beauceville and Saint-Victor formations, the two known formations of the Magog Group. The Frontière Formation, at the base of the group, is made up of centimeter-thick beds of medium- to coarse-grained litharenite and of greyish green mudstone; the sandstone, greyish green, contains abundant felsic volcanic rock fragments and chromite grains. The Etchemin Formation is composed mostly of centimeter-thick dusky yellow green siliceous mudstone; at the base, there is also a purple mudstone, and meter-thick beds of dusky green volcaniclastic rocks rich in intermediate to felsic volcanic rock fragments and crystals of feldspar and quartz occur near its top. The Beauceville Formation consists of interbedded centimeter-thick beds of black clayslate and centimeter- to meter-thick beds of black volcaniclastic rocks. The Saint-Victor Formation consists of classic turbidite beds with few meter-thick yellowish volcaniclastic rock beds similar to those of the Beauceville Formation; the sandstone is a litharenite rich in quartz grains and sedimentary rock fragments. Most rocks of the Frontière and Etchemin formations as well as the volcaniclastic rocks of the Beauceville and Saint-Victor formations were derived from a magmatic arc located to the southeast. However, the shale of the Beauceville Formation and the turbidites of the Saint-Victor Formation were derived from an orogenic source located to the northwest. The Magog Group is located between the Saint-Daniel Mélange and the Ascot Complex interpreted as remnants of an accretionary prism and a magmatic arc, respectively. The sediments of this group were thus deposited in a fore-arc basin active during the Taconian orogeny of the Middle to Late Ordovician.
A Holocene soil-geomorphic record from the Ham site near Frontier, southwestern Saskatchewan
Authors: Vreeken Willem J.
Published: April 2011

The soil-geomorphic evolution of a hillslope in hummocky moraine terrain in one of the most arid parts of the Palliser Triangle is reconstructed from ca. 12 600 BP to the present. A transect from a moraine plateau into an internally drained basin provided evidence for seven postglacial landscape cycles. Each cycle includes a phase of land-surface instability, marked by erosional and depositional imprints, and a phase of stability, marked by pedologic imprints. Five cycles of slope-wash-dominated erosion left behind four superposed downslope-thickening and downslope-fining sediment mantles and were followed by two eolian cycles, each of which left behind a loess mantle that accumulated from a local loess-dispersal system. Accumulation of long-range calcareous dust coincided with each of these loess cycles. The five complete buried soil catenas and the surficial catena have systematic textural differentiation, reflecting the preceding geomorphic regimen, and color differentiation, reflecting the soil-drainage continua. Changes in hillslope hydrology occurred repeatedly throughout the postglacial. The evidence indicates that each element from the 14 successive local soil landscapes reacted to environmental change as a component from a functionally integrated process–response system.
Pre-Grenvillian evolution and Grenvillian overprinting of the Parautochthonous Belt in Key Harbour, Ontario: U–Pb and field constraints
Authors: Corrigan David , Culshaw Nicholas G. , Mortensen Jim K.
Published: April 2011

The Parautochthonous Belt in the region of Key Harbour, Ontario, is composed of Early Proterozoic migmatitic para- and orthogneiss and Mid-Proterozoic granitoids, which were reworked during the Grenville orogeny. Grenvillian deformation is localized into anastomosing arrays of high-strain shear zones enclosing elongate bands and lozenges of rock subjected to lower and near-coaxial strain. Crosscutting relationships preserved in the low-strain domains document two pre-Grenvillian plutonic and tectonometamorphic events, which are bracketed in age by U–Pb zircon geochronology. A 1694 Ma leucogranite intrudes, and provides a minimum age for, high metamorphic grade gneisses formed during an earlier tectonometamorphic event (D1–M1). The leucogranite was intruded by mafic dykes, deformed, and metamorphosed at uppermost amphibolite facies during D2–M2, before the emplacement of Mid-Proterozoic granitoids at ca. 1450 Ma. Following the emplacement of gabbro dykes and pods at ca. 1238 Ma, the area was overprinted by granulite to uppermost amphibolite facies metamorphism (Grenvillian), for which monazites provide a minimum age of ca. 1035 Ma. Titanite U–Pb ages of 1003 – 1004 Ma record cooling through 600 °C. A regionally important swarm of east–west-trending posttectonic pegmatite dykes dated by U–Pb zircon at 990 Ma provides a minimum age for Grenvillian ductile deformation. The present data support the contention that the Parautochthonous Belt in the Key Harbour area consists in part of reworked midcontinental crust of Early to Mid-Proterozoic age.
Rare earth element contents and multiple mantle sources of the transform-related Mount Edgecumbe basalts, southeastern Alaska
Authors: Riehle J. R. , Budahn J. R. , Lanphere M. A. , Brew D. A.
Published: April 2011

Pleistocene basalt of the Mount Edgecumbe volcanic field (MEF) is subdivided into a plagioclase type and an olivine type. Olivine basalt crops out farther inboard from the nearby Fairweather transform than plagioclase basalt. Th/La ratios of plagioclase basalt are similar to those of mid-ocean-ridge basalt (MORB), whereas those of olivine basalt are of continental affinity. The olivine basalt has higher 87Sr/86Sr ratios than the plagioclase basalt.We model rare earth element (REE) contents of the olivine basalt, which resemble those of transitional MORB, by 10–15% partial melting of fertile spinel–plagioclase lherzolite followed by removal of 8–13% olivine. Normative mineralogy indicates melting in the spinel stability field. REE contents of an undersaturated basalt (sample 5L005) resemble those of Mauna Loa tholeiite and are modelled by 5–10% partial melting of fertile garnet lherzolite followed by 10% olivine removal. Plagioclase basalt resembles sample 5L005 in REE contents but is lower in other incompatible-element contents and 87Sr/86Sr ratios. Plagioclase basalt either originated in depleted garnet lherzolite or is a mixture of sample 5L005 and normal MORB; complex zoning of plagioclase and colinear Sc and Th contents are consistent with magma mixing.We conclude that olivine basalt originated in subcontinental spinel lherzolite and that plagioclase basalt may have originated in suboceanic lithosphere of the Pacific plate. Lithospheric melting seemingly requires vertical flow of mantle material, although there is no direct evidence at the MEF for crustal extension that might provide a mechanism for mantle advection. In any case, most MEF magmas are subalkaline because of moderately high degrees of partial melting at shallow depth.
Crustal thickness variations between the Greenland and Ellesmere Island margins determined from seismic refraction
Authors: Jackson H. Ruth , Reid I.
Published: April 2011

Two densely sampled marine refraction lines were shot in northern Baffin Bay on the shelves of Devon and Ellesmere islands (North American plate) and Greenland (Greenland plate). A total of 11 ocean-bottom seismometers recorded the airgun signals. The processed data were analyzed by the use of ray tracing and amplitude modelling. Two-dimensional models were derived that reproduce the characteristics of the observed data. A 5 km deep sedimentary basin was identified on the south end of line 3. On both lines the crustal velocity has a range of 5.7–6.6 km/s. Midway along the line on the shelf of Devon and Ellesmere islands, the Moho shallows abruptly northward from 27 to 20 km. The thinned crust is not overlain by a sedimentary basin to compensate for the elevated Moho, suggesting this is not an extensional feature. The thickness of the crust adjacent to northwest Greenland increases from south (22 km) to north (37 km). The thickening occurs in two stages: a sharp increase in the depth to Moho northwest of the sedimentary basin followed by a gradual deepening to the end of the line. The thin crust on the shelf of Ellesmere Island is located adjacent to the thick crust of Greenland. Plate reconstructions based on regional magnetic anomalies and transform faults indicate that Greenland is a separate plate. The crustal structure revealed by seismic refraction and reflection profiles and the variations in the depth to Moho are consistent with the plate boundary occurring between the refraction lines.
Sedimentary processes and the evolution of the distal bayside of Long Point, Lake Erie
Authors: Davidson-Arnott Robin G. D. , Reid Heather E. Conliffe
Published: April 2011

Long Point spit, on the north shore of Lake Erie, is >40 km long and presently building into water that is >40 m deep. Annual sediment supply to the spit is estimated to be 1.0 × 106 m3∙a−1 and is derived from the erosion of cohesive bluffs along more than 90 km of shoreline to the west. The shoreline of the distal bayside consists of narrow barriers that connect the ends of dune ridges and enclose interdune ponds and swales. Unlike most barrier spits, the distal end shows little evidence of the formation of dune recurves, and the shoreline of the bayside, rather than fronting a protected bay, is exposed to waves generated by northeast winds blowing over a fetch >100 km. Results of wave refraction analysis indicate that because of the great depth of water at the tip, there is almost no refraction of the dominant westerly and southwesterly waves around the distal end, thus inhibiting the formation of recurves. Net sediment transport on the distal bayside is towards the distal end of the spit. The result is the development of a narrow spit platform extending the spit directly into the deepest part of Lake Erie. All sediment reaching the distal end along the exposed south shore is transported onto this platform and none reaches the distal bayside.The negative sediment budget on the distal bayside results in transgression of the shoreline through truncation of the dune ridges, and overwash and breaching of the small barriers. Historical aerial photographs show that most of the overwash and breaching occurs during periods of long-term high lake levels, with the barriers being rebuilt landward of their former position during the following periods of lower lake levels. Progradation of the south shore at the distal end is thus partly counterbalanced by the transgression of the bayside.
Palynologie et paléoenvironnements des épisodes du Sable de Lotbinière et des Varves de Deschaillons (Pléistocène supérieur) de la vallée du Saint-Laurent
Authors: Clet Martine , Occhietti Serge
Published: April 2011

Lotbinière Sand and Deschaillons Varves are indicators of the drainage pattern of the St. Lawrence watershed, which presumably occurred during the Late Sangamonian (5c and 5c–5b transition?). The pollen content of the Lotbinière Sand suggests there was a Picea mariana – Betula – Pinus boreal forest in the valley. In the lowermost zone of the Deschaillons Varves, the pollen is very abundant: the boreal forest was progressively flooded by Lake Deschaillons. Above this zone, the vegetation seems to evolve toward a Picea and Betula open forest. The pollen of the upper contorted varves was presumably reworked from older material or transported from remote sources. The following paleoenvironmental sequence is reconstructed in the St. Lawrence Valley: (i) lowering of the relative drainage level, as indicated by the erosional disconformity in lower rythmites; this phase, of unknown duration, is ascribed to an eustatic lowering related to a global climatic cooling; (ii) an aggradation phase, as indicated by the Lotbinière Sand, before and at the beginning of a glacial damming in the middle estuary; (iii) progressive flooding of the valley and its boreal forest as ice caps are present on adjacent Laurentian and Appalachian highlands; (iv) expansion of Lake Deschaillons, limited by the Glens Falls sill, New York. The relative elevation of the lake was at least 56 m. Great Lakes and upper St. Lawrence River drainage system was probably deflected to the Hudson River. According to the number of varves, the regional ice caps preceded the general invasion by Laurentide Ice Sheet of approximatively 3800 years.
Crustal velocity models for the Archean Abitibi greenstone belt from seismic refraction data
Authors: Grandjean Gilles , Wu Hua , White Donald , Mareschal Marianne , Hubert Claude
Published: April 2011

We present velocity models for two seismic wide–angle-refraction profiles across the Archean Abitibi greenstone belt and the Pontiac Subprovince. The seismic profiles are 210 and 220 km long. Traveltime inversion and amplitude forward modelling were used to obtain two-dimensional velocity structure and interface geometry. The main features of the velocity models include (1) three crustal layers; (2) variable velocities (5.6–6.4 km/s) in the upper crust (~0–12 km), with the higher velocities generally associated with mafic metavolcanics and the lower velocities with metasediments and granitic plutons; (3) a relatively uniform middle crust (~12–30 km) with velocities ranging from 6.4 to 6.6 km/s; (4) a velocity increase of 0.3 km/s across the middle crust–lower crust boundary; (5) a lower crust (~30–40 km) with velocities increasing from 6.9 km/s at the top to 7.3 km/s at the base; (6) an average upper mantle velocity of 8.15 km/s; (7) depth to Moho of about 40 km in the north-central Abitibi belt, decreasing southward to 37 km beneath the Pontiac Subprovince; and (8) observed attenuation of seismic energy propagating through the Casa–Berardi deformation zone, suggesting a complex structure in this fault zone. The velocity model is generally consistent with seismic reflection interpretations that suggest that the shallow supracrustal assemblages form an allochthonous veneer, overlying a mid-crustal imbricate sequence of metaplutonic and metasedimentary rocks. The uniform-velocity structure below 12 km depth indicates that the tectonic zones juxtaposing disparate crustal blocks may have limited depth extent. The 40 km thick crust and 10 km thick high-velocity lower crustal layer exceed the thicknesses observed in other studies of Archean crust.
The Eckler Mountain basalts and associated flows, Columbia River Basalt Group
Authors: Hooper P. R. , Gillespie B. A. , Ross M. E.
Published: April 2011

Recent mapping of flows of the Columbia River Basalt Group between Lewiston and Pomeroy, southeast Washington, places the chemically distinctive Shumaker Creek flow as a new member between the Frenchman Springs and Roza members of the Wanapum Basalt. This leaves the Eckler Mountain Formation composed of only the Robinette Mountain and Dodge chemical types, with the Lookingglass flow forming the base of the overlying Wanapum Basalt. One Robinette Mountain flow and five separate flows of Dodge composition are recognized and traced across the Blue Mountains Anticline of southeast Washington and northeast Oregon. The aerial distribution of the flows is used to constrain the onset of deformation in the Blue Mountains area between the Hite and Limekiln faults. A series of open east–west folds formed during late Wanapum and Saddle Mountains time, cut by northeast-trending faults with left-lateral strain. Chemical variations between Eckler Mountain, Grande Ronde, and Wanapum Basalt flows require different source components. But between the Eckler Mountain flows the variation of most chemical parameters is consistent with fractional crystallization in the crust and can be modeled for major and trace elements. An exception is the behaviour of Cr and Zr/Y between the Robinette Mountain and Dodge flows, which suggests variable partial melting or possibly olivine accumulation.
Mineralogy of the Lake zone, Thor Lake rare-metals deposit, N.W.T., Canada
Authors: Pinckston D. Robert , Smith Dorian G. W.
Published: April 2011

The Proterozoic (ca. 2.1 Ga) Blatchford Lake suite hosts significant concentrations of rare metals at the core of a peralkaline granite–syenite pluton. After emplacement of the Grace Lake Granite and the Thor Lake Syenite within it, bodies of nepheline syenite, ijolite, and urtite were intruded beneath the present-day Lake zone. This is the largest of five zones of mineralization and lies close to the apex of the Thor Lake Syenite, a region which was then subjected to albitization, microclinization, and, finally, rare-metal mineralization. The underlying silica-undersaturated rocks contain clots of rare-metal-bearing minerals, including cerianite-(Ce), britholite-(Ce), thorite, and calcium catapleiite, interstitial to nepheline and aegirine. The Lake zone itself contains major quantities of Zr (in zircon), Nb (in ferrocolumbite, pyrochlore group minerals, aeschynite group minerals, and fergusonite-(Y)), and Ce (in allanite-(Ce), monazite-(Ce), and bastnäsite group minerals). Lesser amounts of Ta, Y, heavy rare earth elements, U, Th, and Ga are also present, mainly as minor components of rare-metal-bearing minerals. Electron microprobe analyses of the major rare-metal-bearing minerals are presented.
The significance of various garnet types in surficial materials in southeastern Gaspé Peninsula, Quebec
Authors: Maurice Yvon T.
Published: April 2011

The distribution patterns of four types of garnet in surficial materials of southeastern Gaspé Peninsula are interpreted in terms of the glacial history of the area, the lithostratigraphy of the bedrock, and mineral occurrences. Each type is derived from a distinct source, and all have undergone at least some southeastward glacial dispersion. Type 1 garnets, anhedral Ca-garnet fragments, are from the McGerrigle granite metamorphic aureole and were brought into the region by the same ice flow that caused the well-documented southward dispersal of granite debris. Their distribution within the study area depicts the southern part of this important dispersal train with an improved degree of precision. Type 2 garnets, Ca-garnet crystals, seem to be related to skarns within the boundaries of the study area; some patterns cannot be linked to any known source, thus providing challenging exploration opportunities. Type 3 garnets, colored pyralspite garnet crystals, are related to a tectonic breccia within the Maquereau–Mictaw contact zone. Type 4 garnets, Grenville-type anhedral garnets, were not brought into the region by Laurentide ice, as one might suspect, but rather seem to be related to specific horizons within the Silurian Lower Chaleurs Group. On the basis of a palinspastic reconstruction of southern Gaspé Peninsula and a plate tectonic model for the Paleozoic of eastern North America, we propose that these garnets were derived from the erosion of a metamorphic Grenvillian terrane, which presently forms the Northwestern Highlands Zone of Cape Breton Island. The distribution data for this garnet type also lends support to the concept put forth in a previous study whereby a local Late Wisconsinan ice mass penetrated some 5–6 km into the region from the southeast near Saint-Godefroi.
Late Devonian conodonts define the precise horizon of the Frasnian–Famennian boundary at Cinquefoil Mountain, Jasper, Alberta
Authors: Wang K. , Geidsetzer H. H. J.
Published: April 2011

Conodonts from carbonate slope sediments of the Ronde Member at Cinquefoil Mountain near Jasper, Alberta, have constrained the Frasnian–Famennian boundary in the Upper Devonian for the first time in Canada. Based on conodont Palmatolepis species, the Frasnian–Famennian boundary has been precisely identified in this section at the base of a tempestite bed (20 cm thick), 14 m above the base of the Ronde Member and directly below a prominent oncolite bed (65 cm thick). Recognized standard conodont zones are the Upper rhenana–linguiformis (or Montagne Noire Zone 13), the Lower triangularis, and the Middle triangularis zones. Conodonts exhibit a mixed Palmatolepis–Polygnathus–Icriodus biofacies, supporting the paleogeographic interpretation of this site as an upperslope depositional setting along the southeastern margin of the paleo-Jasper Basin.