bluuebunny/crossref_metadata_2025 huggingface dataset:
Zircon U–Pb ages from the Kakagi Lake area, Wabigoon Subprovince, northwest Ontario
Authors: Davis Donald W. , Edwards Garth R.
Published: April 2011

Five rocks have been dated from the Kakagi Lake area of the Wabigoon Subprovince by means of U–Pb analysis of zircons. Using the techniques of air abrasion and high gradient magnetic separation, zircon fractions from four of the samples have been made concordant.Stratigraphy in the Kakagi Lake area consists of tholeiitic basalts of the Snake Bay and Katimiagamak Lake Formations overlain by mainly calc-alkalic pyroclastic rocks of the Kakagi Lake Group. A felsic tuff collected from the top of the Kakagi Lake Group is dated at [Formula: see text]. This group is intruded by differentiated ultramafic to mafic sills. The age for a gabbro pegmatite from the lowermost sill near the base of the group is [Formula: see text]. The Katimiagamak Lake Formation is intruded by tonalite of the Sabaskong batholith, which gives an age of [Formula: see text]. The tonalite is flanked by the Phinney–Dash Lakes Complex of subvolcanic stocks and dacite to rhyolite volcanic rocks that intrude and overlie the Katimiagamak Lake Formation. A dacite from the complex gives an age of 2727.7 ± 1.1 Ma. A porphyry complex to the north, the Berry Creek Complex, is separated from the other rocks by the Pipestone – Cameron Lakes Fault and gives an age of [Formula: see text] on a quartz porphyry.The predominantly mafic to intermediate pyroclastic rocks of the Kakagi Lake Group are interpreted to be approximately contemporaneous with the Kakagi sills and to have evolved from the basalt magmatism. Tonalitic rocks of the Sabaskong batholith and the Phinney–Dash Lakes Complex were derived from partial melting of the hydrous lower basalts during the early stage of regional granitoid diapirism. Because of the large age difference between the lowermost sill and the felsic tuff from the top of the Kakagi Lake Group, it is suggested that this formation is not part of the group. It and the Berry Creek Complex were formed from felsic melts separating from rising granitoid gneiss domes during a slightly later stage of regional granitoid diapirism that may have resulted from the reactivation of a predominantly sialic basement by the accumulation of heat over and adjacent to the mantle sources of the basalt.
Geology and age of the Precambrian basement in the Windsor, Chatham, and Sarnia area, southwestern Ontario
Authors: Turek A. , Robinson R. N.
Published: April 2011

Precambrian basement in the Windsor–Chatham–Sarnia area is covered by Paleozoic rocks that are up to 1300 m thick. The basement surface is characterized by a northeast–southwest arch system with a relief of about 350 m. Extensive oil and gas drilling has penetrated and sampled this basement, and an examination of core and chip samples from 133 holes and an assessment of the magnetic anomaly map of the area have been used to produce a lithologic map of the Precambrian basement. The predominant rocks are granite gneisses and syenite gneisses but also significant are gabbros, granodiorite gneisses, and metasedimentary rocks. The average foliation dips 50° and is inferred to have a northeasterly trend. The Precambrian basement has been regarded as part of the Grenville Province. An apparent Rb–Sr whole rock isochron, for predominantly meta-igneous rocks, yields an age of 1560 ± 140 Ma. This we interpret as pre-Grenvillian, surviving the later imprint of the Grenvillian Orogeny. Points excluded from the isochron register ages of 1830, 915, and 670 Ma, and can be interpreted as geologically meaningful.
Grenville iron-formations and associated stratiform zinc mineralization, Roddick Lake area, Mount Laurier Basin, Quebec
Authors: Brown Alex C.
Published: April 2011

Small iron-formations in Grenville metasediments have been examined as possible lateral stratigraphic equivalents of stratiform zinc deposits located along the western margin of the Mount Laurier Basin in the Maniwaki–Gracefleld area, Quebec. Similarities in carbonate and amphibolite units hosting the iron and zinc deposits tend to confirm this concept. Sphalerite sparsely disseminated along a dolomitic bed adjacent to the iron-formations, and the iron-formations themselves, are interpreted as the distal extremities of the massive sphalerite lenses found in the proximity of thick amphibolitic strata close to the (fault-bounded?) basin margin. A submarine exhalative model generating proximal zinc and distal iron deposits is proposed to explain this metal zoning. Originally the iron-formations probably consisted of sedimentary siderite that has been transformed under intense metamorphism to the present magnetite–graphite assemblage.
Conductive structures in southwestern Canada: a regional magnetometer array study
Authors: Gough D. I. , Bingham D. K. , Ingham M. R. , Alabi A. O.
Published: April 2011

An array of 33 three-component recording magnetometers was operated in June and July 1980 in Alberta and British Columbia south of the Edmonton – Prince Rupert highway. This very large array, with its stations dispersed through 550 000 km2 and on average 150 km apart, had limited resolution and was designed to confirm known conductive structures, discover new ones, and locate them sufficiently for suitable placement of further arrays with closer spaced stations and, therefore, higher resolution. Magnetograms and three sets of Fourier transform anomaly maps are presented. They show the general attenuation of the vertical component of variation fields west of the Rocky Mountain Belt known from previous work and generally attributed to a conductive layer in the lower crust or upper mantle. Two prominent local anomalies are shown by variation fields of periods 15–30 min. The first indicates induced currents near Tête Jaune Cache, west of Jasper. The highly conductive structure carrying the induced currents may include wet sediments in the Rocky Mountain Trench and possibly partial melt at depth associated with recent volcanics. The second local anomaly appears to be associated with a crustal conductive structure that strikes northeast–southwest across southern Alberta and crosses the southeast corner of British Columbia into eastern Washington State. This may be associated with a Precambrian rift in the lower crust discovered by Kanasewich and his colleagues using deep crustal seismic reflections some 15 years ago. Both of these anomalies are under further investigation by means of arrays operated in 1981 in locations indicated by the results of the array reported here. The regional westward attenuation of the vertical fields has been quantified by means of single-station transfer functions and artificial event analysis, as developed by Bailey and others, to show the Z response to unit southwest–northeast horizontal field at three periods, along a profile from Squamish, near Vancouver, to Edmonton. These response curves will be used in model studies of the regional conductive structure.
Rb–Sr geochronology of the Coldwell Complex, northwestern Ontario, Canada
Authors: Platt R. Garth , Mitchell Roger H.
Published: April 2011

The Coldwell Complex of Northwestern Ontario is North America's largest structurally and petrologically complex alkaline intrusion. Situated on the north shore of Lake Superior, it consists of at least three intrusive centres and is cross-cut by a diverse suite of coeval–cogenetic dikes. The main intrusive rocks range from gabbros to ferroaugite syenites, nepheline syenites, and quartz syenites. The dikes are predominantly lamprophyric. A seventeen point whole rock Rb–Sr isochron (MSWD 2.22) gives an age of 1044.5 ± 6.2 Ma (2σ) and an initial ratio of 0.70354 ± 0.00016 (2σ). The age is late Neohelikian and is younger than the bulk of igneous activity (Keweenawan activity) prevalent in the Lake Superior Basin during the Neohelikian. The low initial ratio indicates an upper mantle origin for the parental magma of the complex.
Investigation of the Archaean crust by single-grain dating of detrital zircon: a greywacke of the Slave Province, Canada
Authors: Schärer Urs , Allègre Claude J.
Published: April 2011

U-Pb dating of single zircon grains from a graywacke of the Point Lake area of the Archaean Slave Structural Province in Canada indicates that this sediment is derived from two sources: (1) the ancient shield (parts of which are at least 3100 Ma old), which is the basement of the Slave Province supracrustal rocks; and (2) younger rocks (about 2700 Ma old). This implies the creation of large amounts of acidic to intermediate rocks during the 2700 Ma event. It also indicates that magma generation and intracontinental sedimentary basin formation and deepening are strongly related.
Histoire holocène du climat et de la végétation à Lanoraie (Québec)
Authors: Comtois Paul
Published: April 2011

Four different cores were recovered from the same peat complex at Lanoraie (Québec), and have been used to evaluate, by pollen analysis, possible differences in the representation of the vegetation history. The isotopic ratio of oxygen has been used to indicate climatic variations involved in these processes.This method was first tested and calibrated with modern moss samples. A transect of 15 samples, from the temperate forest to the tundra, indicates that annual mean temperatures and evapotranspiration rates have a predominant influence on oxygen isotopic ratios. A sequence of fossil sediments, interpreted in terms of these results, shows a climatic maximum at 3500 BP and a reduction of temperature since 1500 BP in the Lanoraie region.The history of the regional vegetation shows the following succession of stages: (1) establishment of pioneer tree vegetation of pine, oak, elm, and walnut; (2) buildup of a sugar maple forest, contemporaneous with the migration of beech and correlated with a maximum pollen influx and a climatic optimum at about 3500 BP; (3) increase of the representation of spruce and fir after 1500 BP, related to a climatic cooling. Paleobotanical data–the recurrence of ruderal spectra and the presence of Iva xanthifolia– suggest the occurrence of two prehistoric anthropic periods, one before 3500 BP and the other at ca. 1500 BP.
Paleomagnetism of Late Archean metavolcanics and metasediments, Abitibi orogen, Canada: volcanics of the Blake River Group and sediments and volcanics of the Timiskaming Group
Authors: Tasillo-Hirt Ann M. , Geissman John W. , Strangway David W. , Jensn Larry S.
Published: April 2011

A paleomagnetic study (159 samples, 30 sites) was done on calc-alkaline volcanics of the Blake River Group, dated at 2703 ± 2 Ma and occupying the central portion of a major synclinorium in the Abitibi Greenstone Belt. Magnetically stable single- and multi-vectorial components of magnetization were resolved in demagnetization; however, there was poor consistency of directions linearly decaying to the origin in vector analysis on the site, sample, and subsample levels (e.g., D = 190.0°, I = −29.2°, k = 1.5, α95 = 25.0°, n = 21 specimens from N = 21 samples). Preliminary results from a conglomerate test performed on the Chaput–Hughes Member of the overlying Timiskaming Group suggest that a pre-depositional remanence was retained and that there was not a widespread regional metamorphic event after the sediments were deposited. Cobbles derived from alkali volcanics of the Timiskaming Group and Kinojevis (tholeiites) and Blake River volcanics display dispersed directions of magnetization between cobbles. Preliminary magnetization data from the matrix of the conglomerate are well grouped, and correction for regional structure results in a direction similar to the characteristic one of Matachewan dikes. Paleomagnetic data from a downfaulted block of Timiskaming volcanics cut by Matachewan diabase dike may be interpreted to suggest that the fault block has been rotated clockwise (80°+) and subsequently tilted to the west (80°).
Historic changes in an urban watershed determined by pollen and geochemical analyses of lake sediment
Authors: Mathewes Rolf W. , D'Auria John M.
Published: April 2011

A 60 cm long sediment core from Deer Lake, Burnaby, British Columbia was analyzed palynologically and geochemically in order to trace the effects of human disturbances since settlement. A settlement horizon was identified at 42.5 cm (ca. 1892) by pollen analysis. Declines in the percentages of coniferous tree species are mirrored by rapid increases in red alder and fern spores, and also by the presence of indicators of human influence, including introduced weeds, ornamental trees and herbs, and corn pollen.Geochemical analyses revealed marked increases in sedimentary aluminum, iron, potassium, titanium, and strontium soon after settlement, coinciding with declines in carbon, nitrogen, and sulfur. A corresponding shift from a highly organic gyttja to a silt- and clay-rich sediment also confirms the increased input up to the present day of inorganic sediment derived from soil erosion in the Deer Lake catchment.A peak in copper at 19 cm was attributed to the deliberate introduction of copper sulfate around 1957, and increasing lead concentrations are correlated with post-1947 traffic increases. Peak radioactivity of the fission product cesium-137 is recorded at 17 cm, probably corresponding to the maximum in above-ground bomb testing of 1963. Sediment accumulation rates were relatively constant from settlement until 1963 (0.3–0.4 cm year−1), increasing to 1.06 cm year−1 since then. An increased pollen influx since 1963 suggests a recent increase in runoff and soil erosion.
Eusthenopteron foordi, a predator on Homalacanthus concinnus from the Escuminac Formation, Miguasha, Quebec
Authors: Arsenault Marius
Published: April 2011

A specimen of Eusthenopteron foordi Whiteaves containing the acanthodian Homalacanthus concinnus (Whiteaves) was discovered in the Escuminac Formation (Frasnian). It represents the first specimen that demonstrates that E. foordi was carnivorous.
Paleomagnetism of the Deadman's Bay diabase dikes from northeastern central Newfoundland
Authors: Murthy G. S.
Published: April 2011

Twenty-six oriented samples were collected from six diabase dikes cutting the Deadman's Bay granite of northeastern central Newfoundland for the purpose of paleomagnetic investigations. The dikes probably form part of a general swarm of diabase dikes in this area of Devonian age (40Ar/39Ar age of 370 ± 10 Ma). Stepwise thermal demagnetization of individual specimens followed by vector subtraction based on Zijderveld plots revealed two characteristic magnetizations: one, a poorly grouped magnetization of [Formula: see text], Ī = 78.0°, α95 = 17.4°, κ = 16 carried by multidomain magnetite; and a better grouped magnetization of [Formula: see text], Ī = 4.0°, α95 = 10.0°, κ = 42 residing in hematite. A baked contact test of the host rock (Deadman's Bay granite) intruded by the diabase dikes revealed a steep well grouped magnetization, which is not dissimilar to that carried by magnetite in the dikes. The magnetization of the host rock seems to be well grouped irrespective of distance away from the dike, thus making the contact test inconclusive. It is not certain which, if any, of the two obtained poles corresponds to the (primary) age of intrusion of the dikes. The paleopole based on magnetite's magnetization, called the DB1 pole, is in the same general vicinity as some "anomalous" pole positions for intrusives from Newfoundland and New Brunswick. The paleopole based on hematite's magnetization, called the DB2 pole, happens to be the first one from eastern Newfoundland that agreed within error limits with the Acadian poles. The poles from diabase dikes of the Gander Zone are discussed in the context of other poles from the northern Appalachians. It is concluded that the Devonian poles from Acadia seem to be displaced relative to the cratonic North American poles for that age. However, critical testing for the confirmation of such a displacement during the Devonian had to wait a clearer definition of the positions of the poles and their ages. It was shown that such a displacement, if present during the Devonian, disappeared during the Mississippian times, suggesting that any relative motion between the two regions ceased by the Mississippian times.
Paleomagnetism of diabase dikes from the Bonavista Bay area of northeastern central Newfoundland
Authors: Murthy G. S.
Published: April 2011

Paleomagnetic results are reported for a swarm of diabase dikes from the northeastern Gander Zone of the Newfoundland Appalachians. Sixty-eight cores were collected from 19 dikes cutting the various granites and migmatites from the Bonavista Bay area of Newfoundland. From the earlier structural and Rb/Sr age data available, one can infer an age for the dike swarm of between 400 and 330 Ma. Paleomagnetic studies including alternating field and thermal demagnetizations reveal that the swarm can be divided into two groups: group 1 has a characteristic magnetization of D = 296.6°, I = 82.2° with α95 = 5.8° for N = 14 dikes with the corresponding pole position at 53.9°N, 77.4°W (δp, δm = 11.0°, 11.3°; group 2 has a characteristic magnetization of D = 157.6°, I = 53.9° with α95 = 9.0° for N = 5 dikes with the corresponding pole position at 3.9°S, 35.5°W (δp, δm = 8.8°, 12.6°). One dike's magnetization was found to be reversed relative to the other group 2 dikes. Various magnetic experiments (low- and high-field hysteresis, Curie temperatures, susceptibility variation with temperature, coercivity of remanence, Lowrie–Fuller test) conducted to study the bulk magnetic and remanent magnetic properties of the dike material suggest that their behavior is consistent with multidomain pure magnetite being the dominant magnetic mineral. The group 1 pole position lies close to Newfoundland and is similar to other poles of equivalent age for intrusives from New Brunswick and Newfoundland. Rock units from the southeastern margin of the Iapetus Ocean thus seem to be yielding consistent "high-latitude" poles, a factor that needs to be taken into account in any discussion of the tectonic evolution of the area.
River discharge, sedimentation, and benthic environmental variations in Miramichi Inner Bay, New Brunswick
Authors: Schafer C. T. , Smith J. N.
Published: April 2011

Sequential studies of benthonic foraminifera in the Miramichi estuary, New Brunswick over a 12 year period indicate that a "transitional" foraminiferal assemblage, which defines a zone of interaction of river and open bay environmental factors, has developed in Miramichi Inner Bay since 1964. Abundance variations of the transitional foraminiferal indicator species Ammotium cassis relative to Miliammina fusca (upper estuarine indicator) and Elphidium excavatum forma clavata (marginal marine indicator) in short cores suggest that the regional extent of this transitional thanatotope in the western part of Miramichi Inner Bay has varied considerably during the past 80–100 years. These changes appear to be related to total annual river discharge variations, competence of the Miramichi River system, and. possibly, changes in the tidal circulation pattern of bay water. Tidal circulation may have been altered by the location and cross-sectional area of several channels that occur between the barrier islands on the seaward side of the bay.
Geology and petrology of Proterozoic mafic dikes, north-central Minnesota and western Ontario
Authors: Southwick D. L. , Day W. C.
Published: April 2011

Proterozoic diabase and gabbro dikes (~2120 Ma old) form a major northwest-oriented swarm extending about 300 km from the Mesabi iron range in Minnesota to the vicinity of Kenora, Ontario. The dikes were emplaced into Archean crust at about the time that the Early Proterozoic basin of the Lake Superior region was opening by rifting, and the swarm and the basin may therefore be tectonically related. The dikes are overlain unconformably by the Animikie Group, the upper sedimentary sequence in the Proterozoic basin in Minnesota, but may be approximately coeval with mafic volcanic rocks in the pre-Animikie Mille Lacs Group. A two-stage tectonic model involving (1) regional right-lateral crustal shear in the late Archean and (2) hot-spot rifting in the Early Proterozoic is proposed to account for the swarm.The dikes are iron-rich quartz tholeiites that are differentiated toward dioritic compositions. Late alteration to hydrous phases, including blue–green amphibole, chlorite, and sericite, together with lesser amounts of prehnite and epidote, is ubiquitous but variable in intensity, and is regarded as a deuteric phenomenon. The interior portions of some large dikes are compositionally layered parallel to contacts; the layers differ from each other in the proportions of primary hornblende, clinopyroxene, and plagioclase and thus range in composition across the gabbro–diorite boundary.Chilled margins of the dikes contain flow-aligned phenocrysts of plagioclase, clinopyroxene, titanomagnetite, and ilmenite. The clinopyroxenes occur as three morphotypes that have distinct compositions, indicating a complex intratelluric history. The dike magma was emplaced into cool Archean crust at an inferred temperature of about 1085 °C and was quenched in a matter of minutes at the dike walls. Complete solidification at the centers of dikes wider than 100 m appears to have taken more than 40 years.
Timing of emplacement of the Muskox intrusion: constraints from Coppermine homocline cover strata
Authors: Kerans Charles
Published: April 2011

The Muskox intrusion is a Middle Proterozoic shallow-level mafic–ultramafic layered intrusion in the northwest corner of the Bear Province of the Canadian Shield. The intrusion was emplaced into the Lower Proterozoic Akaitcho Group and Hepburn metamorphic–plutonic complex of the Wopmay orogen and overlying Middle Proterozoic Coppermine homocline strata. To date, radiometric, paleomagnetic, and geochemical evidence has produced only equivocal results concerning the age of the Muskox intrusion relative to overlying Coppermine River Group basalts and Mackenzie diabase dykes. Stratigraphic redefinition of and structural relationships to the cover sequence of the intrusion provide the best available evidence for the age of the Muskox intrusion.Although previously inferred to be a pre-Dismal Lakes Group structure, the Canoe Lake Fault is here shown to cross-cut Dismal Lakes strata with west-side-down displacement equivalent to that documented to the south where it offsets the intrusion. This relationship, supported by detailed mapping that shows that the Muskox intrusion intrudes units 11 and 12 of the Dismal Lakes Group, demonstrates a post-Dismal Lakes age for the intrusion. This conclusion strongly supports the contention that the Muskox intrusion and Coppermine River Group are coeval and comagmatic.Syndepositional uplift and normal faulting within uppermost Dismal Lakes Group strata were most pronounced near the exposed roof of the intrusion, and are interpreted to have been related to emplacement of a small sill-like body that probably was the precursor to the main intrusive event. At least 70 m of sediments was deposited after this initial disturbance, but before extrusion of the Coppermine River Group basalts (which heralded the main emplacement event). This thickness of sedimentary strata implies a period of several hundred thousand years between the two igneous events.These results support earlier contentions that the Mackenzie igneous event, comprising emplacement of Mackenzie dykes, Coppermine River Group basalts, and the Muskox intrusion, was a coherent mafic igneous event that occurred approximately 1200 Ma ago, with the Muskox intrusion as a locus.
Plagioclase–clinopyroxene–garnet–quartz equilibria and the geobarometry and geothermometry of garnet amphibolites from Mica Creek, British Columbia
Authors: Ghent Edward D. , Stout Mavis Z. , Raeside Robert P.
Published: April 2011

Metabasites form a small but significant volume of the Upper Precambrian Horsethief Creek Group near Mica Creek, British Columbia. Sillimanite zone assemblages in metabasites are: hornblende–plagioclase–ilmenite ± quartz ± garnet ± clinopyroxene ± sphene ± calcite. The incoming of garnet–clinopyroxene in metabasites very nearly coincides with the kyanite–sillimanite isograd. Fe–Mg distributions between coexisting garnet and clinopyroxene suggest a temperature range of 650–705 °C (Ellis and Green calibration). The higher temperature estimates disagree with the upper thermal stability limits of muscovite–plagioclase–quartz–sillimanite from adjacent pelitic rocks. Pressure estimates based upon clinopyroxene–garnet–plagioclase–quartz equilibria are 5.6 ± 0.3 and 7.2 ± 0.3 kbar (560 ± 30 and 720 ± 30 MPa), respectively, using two different calibrations of this geobarometer. These estimates bracket the pressure estimated from garnet–plagioclase–Al2SiO5 equilibria in pelitic rocks.
The structure of sheeted dikes and associated rocks in North Arm massif, Bay of Islands ophiolite complex, and the intrusive process at oceanic spreading centers
Authors: Rosencrantz Eric
Published: April 2011

The structures of North Arm Mountain ophiolitic basalt and diabase indicate that these formed as a frozen lid to an underlying magma chamber in a system analogous to present-day mid-ocean spreading systems. Volcanics consist of pillow lavas, flows, and breccias. Volcanics grade downward into sheeted dikes by increase in dike frequency across a transition commonly less than 50 m thick. Sheeted dikes, subparallel throughout, dip away from the paleospreading axis, located to the west of present ophiolite position as indicated by chilled margin bias, implying rotation of the lid down and away from the axis. One-way chilling statistics, dike thickness, and dike intrusion sequence analyses all point toward a relatively narrow but complex zone of dike intrusion. The mean measured dike thickness is 0.90 m. Diabase contains zones of fracturing subparallel to dike trends, interpreted to reflect oceanic fissuring and faulting. These commonly terminate downward in foliated gabbro and (or) lineated amphibolite. Diabase grades into gabbros across a complex transition wherein (1) dikes grade into gabbro by gradual decrease in dike frequency, (2) dikes grade abruptly into gabbro, and (3) gabbro intrusions truncate and stope overlying diabase.
Further thermochronometric unravelling of the age and palaeomagnetic record of the southwest Grenville Province
Authors: Lopez-Martinez Margarita , York Derek
Published: April 2011

The Cordova gabbro in the Hastings Basin of the southwestern Grenville Province has been studied thermochronometrically to see if the anomalous C magnetic pole was actually acquired prior to 1200 Ma ago. Resetting of the plagioclase argon clock very strongly indicates that, in fact, the C pole was acquired during a mild Siluro-Ordovician event and does not record the existence of a pre-Grenville small ocean between a Grenville plate and Interior Laurentia. Such a hypothesized mild event is consistent with the magnetic, isotopic, and fluid inclusion record. Finally, it is noted that the age and blocking temperature points for the two hornblendes analyzed are consistent with the cooling curve derived for the Thanet gabbro, another Hastings Basin intrusive.
Marathon dikes: Rb–Sr and K–Ar geochronology of ultrabasic lamprophyres from the vicinity of McKellar Harbour, northwestern Ontario, Canada
Authors: Platt R. Garth , Mitchell Roger H. , Holm Paul M.
Published: April 2011

The ultrabasic lamprophyre dikes from the vicinity of McKellar Harbour, northwestern Ontario, are composed essentially of a mixture of phlogopite, olivine, primary carbonate, spinel, and apatite with associated perovskite and (?) melilite. Petrologically and chemically they have strong affinities with alnöites and magmas derived from upper mantle sources in stable continental regimes.Rb–Sr isotopic studies give an isochron age of 1.65 ± 0.12 Ga (2σ) with an initial 87Sr/86Sr ratio of 0.70167 ± 0.00036 (2σ). This age is considerably older than the Neohelikian Keweenawan magmatic event associated with the development of the Lake Superior Basin (e. g., 950–1170 Ma). K–Ar data indicate a mean whole-rock age for the dikes of 1144 Ma and a pseudoisochron age of 1120 ± 34 Ma (2σ). These ages are thought to reflect partial degassing of phlogopite and incomplete updating of the rocks under thermal influences induced by the intrusion of the Coldwell alkaline complex at 1044 Ma.Ages of carbonatitic and alkaline rock intrusions in the general vicinity of the McKellar Harbour – Marathon region closely approximate those associated with the intrusion of similar magmas in the Kapuskasing structural zone, i.e., 1650–1700 and 1020–1050 Ma. By analogy with the Kapuskasing zone, it is suggested that periodic activation of a deep-seated, long-lived structural zone in the Marathon region has lead to the tapping of upper mantle magmas. The McKellar Harbour ultrabasic lamprophyres are the product of one such event.
An introductory overview to the concept of displaced terranes
Authors: Ben-Avraham Zvi , Nur Amos
Published: April 2011

On land much of the Pacific margin is composed of allochthonous terranes, which are of continental and noncontinental origins. In the oceans numerous oceanic rises, some of which are submerged continental fragments, are presently embedded in the oceanic plates. These oceanic rises are probably future accreted terranes. They thus represent one stage in the development of allochthonous terranes found in orogenic zones. Minerals found in these terranes were formed at locations that in the past could have been thousands of kilometres away. This is because some oceanic terranes were split into several parts that moved with their respective plates in different directions. Also, faulting at the continental margins caused large-scale concurrent and post-accretionary horizontal translations of hundreds of kilometres of the allochthonous terranes.Studying the allochthonous terranes may provide important information about the Paleozoic and early Mesozoic history of the Pacific Ocean, because most of the oceanic crust of this age has disappeared leaving only those allochthonous terranes that were once oceanic plateaus within this crust. Understanding the history of the Pacific basin plates and of the allochthonous terranes may lead to the discovery of minerals within the submerged oceanic plateaus.
Tectono-stratigraphic terranes and mineral resource distributions in Mexico
Authors: Campa Maria Fernanda , Coney Peter J.
Published: April 2011

About 80% of the southern part of the North American Cordillera within the Republic of Mexico is made up of suspect terranes. These terranes are suspect because their paleogeographic setting with respect to cratonic North America at various times through much of Phanerozoic time is uncertain. Much of northeastern and southeastern Mexico is underlain by basement accreted during late Paleozoic time, an extension of the Appalachian–Ouachita orogeny. This orogen has been considerably modified by Jurassic strike-slip translations related to the opening of the Gulf of Mexico. Western and southwestern Mexico is largely made up of several distinct but coeval latest Jurassic to Late Cretaceous submarine magmatic arc terranes with unknown basement that appear to have accreted against the disrupted North American margin by early Tertiary time. Only northeastern Sonora and the State of Chihuahua appear to be floored by unmoved North American cratonic basement. The combined effect of Mesozoic accretions and translations essentially eliminates the overlap of South America upon Mexico that is drived from late Paleozoic – early Mesozoic reconstructions of the closed Atlantic Ocean. This new vision of accretionary and translational tectonics in Mexico has profound implications for the study of tectogenesis in the southern Cordillera as well as for the interpretation of Mexico's vast natural resources. Preliminary analysis indicates that Mexico's gold–silver and lead–zinc deposits are directly or indirectly related to the terrane distributions discussed.
The geology and structural history of the Cape Ray Fault Zone in southwestern Newfoundland
Authors: Wilton Derek H. C.
Published: April 2011

Structural studies within the Cape Ray Fault Zone, southwestern Newfoundland indicate that three tectonic events (D1 to D3) have deformed all regional lithologic units. These lithologies are distributed as a tonalitic terrain (intrusive into ophiolitic remnants) to the northwest, a central volcanic–sedimentary terrain, and a staurolite–kyanite gneiss terrain to the southeast. D1 produced the dominant northeasterly striking planar fabrics in the host rocks that are axial planar to isoclinal folds. The fold axes parallel a synkinematic mineral elongation lineation. D2 formed open asymmetrical folds with curvilinear fold axes and local crenulation cleavage. The D3 event produced local conjugate kink folds. Radiometric dates on deformed plutons indicate these deformational events were post-369 ± 12 Ma (post-Middle Devonian) and pre-352 ± 6 Ma (pre-Late Carboniferous).The fault was previously interpreted as a "cryptic suture" along which opposed margins of the Iapetus Ocean were juxtaposed. Supposedly this suture was subsequently partially covered by volcanic and sedimentary rocks. The present work indicates that the deformational events that produced the fault zone overprinted all regional lithologies in a similar manner and that the delineating mylonites were the products of ductile simple shear due to intense localized deformation. The fault itself is a large-scale shear zone and is not the end result of intercontinental collision.
Bimodal volcanism in Archean greenstone belts exemplified by greywacke composition, Lake Superior Park, Ontario
Authors: Ayres L. D.
Published: April 2011

In the Archean Gamitagama Lake greenstone belt, a metagreywacke–metasiltstone formation at least 3.6 km thick largely had an easily eroded, unconsolidated, subaerial, pyroclastic felsic volcanic provenance. The remains of this provenance are now represented by a 0–600 m thick felsic formation sandwiched between mafic flow formations in an adjacent and laterally equivalent 4.5 km thick metavolcanic sequence. The felsic formation includes flows plus various pyroclastic units including crystal-rich ash-flow tuff. Volcanism, erosion, transportation, and sedimentation appear to have been essentially contemporaneous with subaerially erupted ash that was being transported rapidly by rivers to the sedimentary basin where it was deposited in a submarine fan.Angular to rounded framework sand grains form 39% of the greywacke in the proportion 49% plagioclase, 36% quartz, and 15% lithic clasts (dominantly felsic volcanic). Despite the moderately high quartz content, a felsic pyroclastic volcanic provenance can be shown by the absence of plutonic and metamorphic clasts, the felsic nature of the volcanic clasts, the volcanic characteristics such as subhedral shape, oscillatory zoning, and high-temperature structure of some of the plagioclase, and facies relationships. The quartz/plagioclase ratio of the greywacke, when compared with that of the preserved volcanic units, is most consistent with a volcanic source that was silicic rhyodacite to rhyolite in composition and Plinian in nature. A western plutonic–metamorphic cratonic provenance is postulated for some detritus to the upper part of the metasedimentary formation.The volume of felsic volcanic material preserved in the volcanic sequence is small, and was apparently small at any given time during the development of the volcano. However, because of concomitant eruption and erosion the total volume of felsic magma erupted and dispersed to the sedimentary basin during the felsic volcanic event was several times larger than the volume of greywacke and equal to or larger than the volume of preserved mafic metavolcanics. The volcanism was thus bimodal, producing basalt and rhyodacite + rhyolite. The high silicic component implies a thick crust that presumably developed by extensive mafic volcanism loading the Archean crust.
Evidence for an unconformity at the Scollard–Battle contact, Upper Cretaceous strata, Alberta
Authors: Russell Loris S.
Published: April 2011

The Scollard Formation is the uppermost division of the Edmonton Group in the Red Deer River valley of central Alberta. It dates from the close of Cretaceous and the beginning of Tertiary time. It rests on a very distinctive clay sequence consisting in descending order of the Battle and Whitemud formations, which overlie in turn the Horseshoe Canyon Formation, the lowest division of the Edmonton Group. Near the top of the Battle Formation is a distinctive and widespread bed of volcanic origin (Kneehills Tuff). The contact of the Battle clay above this bed with the Scollard Formation varies in level within single exposures. A widespread coal seam (Ardley or No. 14) divides the Scollard Formation into lower and upper members. The thickness of the lower member decreases markedly from south to north, as does the level of the highest recognized dinosaur remains. There is a marked contrast between the dinosaur fauna of the lower Scollard Member and that of the Horseshoe Canyon Formation. A similar break has been observed in the floral succession. These physical and biological discordances at the Scollard–Battle contact are taken to indicate an interval of non-deposition, with or without erosion. Evidence for an analogous break occurs in southwestern and southeastern Alberta and in southern Saskatchewan.
A geophysical interpretation of the geology of Conception Bay, Newfoundland
Authors: Miller H. G.
Published: April 2011

Geophysical data from Conception Bay and the adjacent peninsulas of the Avalon Peninsula, Newfoundland are presented and quantitatively interpreted using two-dimensional models to interpret the geology beneath the bay. The portion of the bay underlain by mafic volcanic rocks is determined and the maximum extent of the Cambro-Ordovician rocks containing the Wabana hematite deposit is delineated. All gravity and magnetic anomalies in the area are explained in terms of density and magnetic susceptibility variations confined to the upper 12 km of the crust. The geophysical models indicate that mafic volcanics underlie a significant portion of the study area and are more extensive than indicated by the surface outcrop on land. The models also indicate significant vertical movement on the Topsail Fault and on the extension of a fault passing out into the bay near Holyrood. The Cambro-Ordovician sediments are confined to the southern portion of the block bounded by these faults. The geophysical data are unable to detect the presence of the mafic volcanics east of the Topsail Fault in the study area.
Protogrammoceras paltum (Buckman), a late Pliensbachian (Jurassic) ammonite from Axel Heiberg Island, Canadian Arctic Archipelago
Authors: Hall Russell L. , Howarth M. K.
Published: April 2011

Ammonites collected from red-weathering sandstones lying between the Heiberg and Savik formations north of Wolf Fiord on southeastern Axel Heiberg Island are identified as Protogrammoceras paltum (Buckman). These strata are probably latest Pliensbachian in age (Spinatum Standard Zone; Early Jurassic) and are tentatively correlated with the Jaeger Formation.
The stratigraphy and biofacies trends of the Lower Mesozoic Gabbs and Sunrise formations, west-central Nevada
Authors: Taylor David G. , Smith Paul L. , Laws Richard A. , Guex Jean
Published: April 2011

The boundary between the Gabbs and Sunrise formations of west-central Nevada is redefined and the two units are combined to form the new Volcano Peak Group. The Nun Mine, Mount Hyatt, and Muller Canyon members are named and assigned to the Gabbs Formation, and six new lithostratigraphic units for the Sunrise Formation are the Ferguson Hill, Five Card Draw, New York Canyon, Joker Peak, and Mina Peak members. The boundary for the Triassic and Jurassic systems is placed above the last Choristoceras and below the first certain Psiloceras. The section at Ferguson Hill is proposed as the system boundary stratotype. The transgressive–regressive curve for the formations points to a strong tectonic influence, but the late Norian and late Hettangian regressions and early Sinemurian, early Pliensbachian, and early late Pliensbachian transgressions are consistent with inferred eustatic events. The facies and faunal data are consistent with an early Mesozoic record in the western Cordillera suggesting widespread anoxia. The high within-habitat diversity in Neogene offshore benthic communities compared with those in the Mesozoic may correspond to the breakdown of widespread marine anoxic conditions as polar regions cooled and worldwide climatic zonation intensified.
A gravity study of the Coldwell Complex, northwestern Ontario and its petrological significance
Authors: Mitchell Roger H. , Platt R. Garth , Cheadle Scott P.
Published: April 2011

Gravity studies of the Coldwell alkaline complex show that the complex is associated with a positive gravity anomaly. The anomaly indicates that a significant volume of dense material occurs below the current levels of exposure of principally felsic rocks. A new high-resolution gravity profile used to model the infrastructure of the complex shows that the felsic rocks form a 3–5 km thick layer over a differentiated basic intrusion. This intrusion is interpreted to consist of a layer of gabbro 3–5 km in thickness underlain by 3 km of peridotite and (or) pyroxenite. Intrusion of the basic magma was associated with Keeweenawan continental rifting. The presence of large volumes of basic magma supports the hypothesis that some of the Coldwell felsic rocks were derived by differentiation of a basic parent.
Shallow crustal structure of the continental margin off Nova Scotia
Authors: Brocher Thomas M.
Published: April 2011

The nature of the upper sediments of the shelf and slope on a passive margin was investigated by using high-quality refraction profiles recorded by ocean-bottom seismometers off Nova Scotia. In agreement with previously published reflection profiles, well data, and lithospheric models for the evolution of passive margins, we found little thickening of the post-Early Cretaceous section, implying an even sedimentation rate over the outer shelf for this time period. The velocity model determined from slant stacks agreed reasonably well with well-log data, but had velocities slightly lower than those found from a nearby refraction line using first-arrival travel-time methods. Starting at the sea floor the compressional velocity–depth model consists of a gradient of roughly 0.4 s−1 to a depth of about 1.25 km, followed by another gradient of roughly 1 s−1 to a depth of about 3.5 km. Beneath this depth the velocity gradient approaches zero and can be modelled as a constant velocity layer. Stoneley waves were used to investigate the velocity structure of the upper 260 m of the sediment column. These velocities cannot be measured in the oil wells located on the shelf by conventional 3.5 kHz echo sounders or by measuring the sonic velocities of sediments collected in piston cores. A thinning of the Pleistocene–Holocene Sable Island Sand and Gravel layer was documented by pronounced differences in the propagation of Stoneley waves across the shelf. Although the origin of the thinning is uncertain, the shear-wave velocity determined for this unit, 260 m/s, is appropriate for an unconsolidated sand.
Paleomagnetism and time-stratigraphic correlation of Proterozoic redbeds of the Labrador Trough and outliers of northern Quebec
Authors: Schwarz E. J. , Freda G. N.
Published: April 2011

One hundred and forty-two oriented cores were collected from redbeds of the Sakami Formation near LG-4 (85), Dieter (19), Cambrian (18), and Snow-ball (4) lakes, all in Quebec, and from two outliers in Labrador: Evening Lake (6) and Sims Lake (10). A further 73 oriented drill cores were collected from the strongly folded Chakonipau Formation redbeds (44) in the Labrador Trough and undeformed redbeds near Lac Imbault (29) on the western edge of the trough. Thermal demagnetization of the trough redbeds yielded 52 core directions, each of which showed good specimen end points and sufficient homogeneity of magnetization, and 101 such core directions were obtained for the outlier redbeds. In most of these samples, there are no indications that the stable remanence is multi-component, and the fold test yields (for LG-4 Sakami Formation and the Chakonipau Formation) a significant (95% probability) improvement of the dispersion parameter K. Thus, the Chakonipau Formation remanence is probably pre-Hudsonian and the Sakami Formation remanence is probably pre-faulting (not dated). Furthermore, a near reversal (165°) in the Chakonipau Formation suggests that the stable remanence was acquired during or soon after deposition. The pole positions for Circum-Superior orogen rocks, the Proterozoic outliers, and the Sutton Lake inlier suggest: (1) a time-stratigraphic correlation between the LG-4 Sakami, Dieter Lake, Sutton Lake, and the upper part of the Belcher Island sequences; and (2) a time-stratigraphic correlation between the lower part of the Belcher Islands sequence and the Richmond Gulf sequence, which must be substantially older than group 1. The Circum-Superior apparent polar wander path (APWP) is drawn through magnetic North poles from the group 1 poles to the group 2 poles, yielding a slightly lower age for the trough sediments represented by the Chakonipau Formation (two opposing polarities) and the Lac Imbault redbeds. The general North American APWP is simplified by the deletion of the Richmond Gulf South poles, and seems to be positioned as much as about 30° north of the Circum-Superior APWP down to about 1800 Ma ago. This may indicate (pre-) Hudsonian movement between the northeastern part of the Canadian Shield and paleomagnetically better investigated parts to the (south-) west.
Sedimentary fades, depositional environments, and faunal associations of the lower Llandovery (Silurian) Beechill Cove Formation, Arisaig, Nova Scotia
Authors: Pickerill R. K. , Hurst J. M.
Published: April 2011

Six facies are recognised in the Beechill Cove Formation. These are: (1) conglomerate facies deposited as a transgressive beach lag; (2) red shale facies deposited in shoreface environments; (3) mottled mudstone facies; extensively bioturbated sediments indicative of shallow subtidal areas influenced by low sedimentation rates; (4) regular layered facies; shelf turbidites generated by storm activity and superimposed on quiescent subtidal environments; (5) lenticular facies, including a thinner bedded more persistent and a thicker bedded lenticular subfacies, induced by storm activity and deposited in shallow subtidal environments; and (6) laminated shale facies produced by sediment fallout from suspension in a low-energy environment where the oxygen, minimum layer intersected the sediment–water interface. Three faunal associations occur, which have distinct distributional patterns. The Lingula clintoni association, which is characterized by L. clintoni in life position and a moderately diverse but abundant trace-fossil assemblage, is restricted to the mottled mudstone facies. The Leptostrophia beechillensis association, a transported residue, is dominated by brachiopods and restricted to the regular layered facies. The low-diversity Dalmanella primitiva association is transported and restricted to the lenticular facies. No faunas are known from the conglomerate or laminated shale facies, and only rare trace fossils occur in the red shale facies.