bluuebunny/crossref_metadata_2025 huggingface dataset:
Geodynamic evolution of the Canadian Cordillera — progress and problems
Authors: Monger J. W. H. , Price R. A.
Published: June 2009

The present geodynamic pattern of the Canadian Cordillera, the main features of which were probably established in Miocene time, involves a combination of right-hand strike-slip movements on transform faults along the continental margin, and, in the south and extreme north, convergence in subduction zones in which oceanic lithosphere moves beneath the continent, with consequent magmatism along the continental margin. In the southern Canadian Cordillera, geophysical surveys have outlined the subducting slab and the asthenospheric bulge that occurs beneath and behind the magmatic arc. They also show that there is now no root of thickened Precambrian continental crust beneath the tectonically shortened supracrustal strata in the southern parts of the Omineca Crystalline Belt and Rocky Mountain Belt.The Rocky Mountain, Omineca Crystalline, Intermontane, Coast Plutonic, and Insular Belts, the structural and physiographic provinces that dominate the present configuration of the Canadian Cordillera, were established with the initial uplift and the intrusion of granitic rocks in the Omineca Crystalline Belt in Middle and Late Jurassic time and in the Coast Plutonic Complex in Early Cretaceous time, and they dominated patterns of uplift, erosion and deposition through Cretaceous and Paleogene time. Their development may be due to compression with thrust faulting in the eastern Cordillera, and to magmatism that accompanied subduction and to accretion of an exotic terrane, Wrangellia, in the western Cordillera. Major right-lateral strike-slip faulting, which occurred well east of but sub-parallel with the continental margin during Late Cretaceous and Paleogene time, accompanied major tectonic shortening due to thrusting and folding in the Rocky Mountain Belt as well as the main subduction-related (?) magmatism in the Coast Plutonic Complex.The configuration of the western Cordillera prior to late Middle Jurassic time is enigmatic. Late Paleozoic and early Mesozoic volcanogenic strata form a complex collage of volcanic arcs and subduction complexes that was assembled mainly in the Mesozoic. The change in locus of deposition between Upper Triassic and Lower to Middle Jurassic volcanogenic assemblages, and the thrust faulting in the northern Cordillera may record emplacement of another exotic terrane, the Stikine block, in latest Triassic to Middle Jurassic time.The earliest stage in the evolution of the Cordilleran fold belt involved the protracted (1500 to 380 Ma) development of a northeasterly tapering sedimentary wedge that discordantly overlaps Precambrian structures of the cratonic basement. This miogeoclinal wedge may be a continental margin terrace wedge that was prograded into an ocean basin, but it has features that may be more indicative of progradation into a marginal basin in which there was intermittent volcanic activity, than into a stable expanding ocean basin of the Atlantic type.
Appalachian Orogen in Canada
Authors: Williams Harold
Published: June 2009

The Appalachian Orogen is divided into five broad zones based on stratigraphic and structural contrasts between Cambrian–Ordovician and older rocks. From west to east, these are the Humber, Dunnage, Gander, Avalon, and Meguma Zones.The westerly three zones fit present models for the development of the orogen through the generation and destruction of a late Precambrian – Early Paleozoic Iapetus Ocean. Thus, the Humber Zone records the development and destruction on an Atlantic-type continental margin, i.e., the ancient continental margin of Eastern North America that lay to the west of Iapetus; the Dunnage Zone represents vestiges of Iapetus with island arc sequences and mélanges built upon oceanic crust; and the Gander Zone records the development and destruction of a continental margin, at least in places of Andean type, that lay to the east of Iapetus.The Precambrian development of the Avalon Zone relates either to rifting and the initiation of Iapetus or to subduction and a cycle that preceded the opening of Iapetus. During the Cambrian Period, the Avalon Zone was a stable platform or marine shelf.Cambrian–Ordovician rocks of the Meguma Zone represent either a remnant of the continental embankment of ancient Northwest Africa or the marine fill of a graben developed within the Avalon Zone.Silurian and younger rocks of the Appalachian Orogen are mixed marine and terrestrial deposits that are unrelated to the earlier Paleozoic zonation of the system. Silurian and later development of the orogen is viewed as the history of deposition and deformation in successor basins that formed across the already destroyed margins and oceanic tract of Iapetus.
A tectonic model for the evolution of the Finnmarkian Caledonides of North Norway
Authors: Rice A. H. N.
Published: June 2009

A revision of previous plate models for the evolution of the Finnmarkian orogen in North Norway, based on new structural, palaeogeographical, palaeontological, and geochemical evidence is proposed. In this model, two zones of crustal extension occurred within the Laurentia–Baltica craton, as preserved in North Norway. The eastern zone (Gaissa Basin) was an aulacogen that was filled by shallow-marine to fluviatile sediments, including dolomitic and sabkha facies, overlain by glacial and further shallow-marine deposits of Vendian age. The western zone developed into the Iapetus Ocean in which a transgressive sequence of shallow-marine sandstones and mudstones was followed by sporadic carbonate facies and, finally, distal turbidites. Development of the Gaissa Basin during the late Riphean was followed by the rifting of the Iapetus Ocean somewhat later, in the early Sinian. The two basins were separated by a topographic high, the Finnmark Ridge, which became submerged during the earliest Vendian. These ages have been inferred from the proposed stratigraphic correlations and by the qualitative application of modem concepts of continental-margin development. Metabasic dykes within the 3.3 km thick Iapetus Ocean sediments have been related to an unspecified period of tension, post-Iapetus rifting, and not to Iapetus rifting as previously inferred. Comparison of this model with those from central Scandinavia shows marked discrepancies; it is postulated (but not demonstrated) that the age of rifting in central Scandinavia may have been considerably older than previously interpreted from the emplacement ages of the Ottfjället metadolerite dykes.
A displaced and metamorphosed peralkaline granite related to the late Proterozoic Labrador and Gardar suites: the Doolough Granite of County Mayo, northwest Ireland
Authors: Winchester J. A. , Max M. D.
Published: June 2009

The chemically and lithologically distinct Doolough Granite from the Annagh Division in northwest County Mayo, Ireland, includes part of the northwesternmost exposures of Precambrian basement in Europe. The Doolough Granite is similar to Precambrian granitic intrusions found in Labrador and southwest Greenland, although its age of emplacement at [Formula: see text] (U–Pb in zircon) is slightly younger than the Canadian intrusions. A reconstruction of the pre-Iapetus disposition of the eastern Laurentian margin suggests that the Doolough Granite was probably emplaced at a location sufficiently close to both southwest Greenland and Labrador for it to have formed part of the same magmatic province during a period of restricted crustal extension that preceded the Grenville event.
Middle and Late Ordovician conodont faunas and biostratigraphy of graptolitic strata of the Road River Group, northern Yukon Territory
Authors: McCracken Alexander D. , Lenz Alfred C.
Published: June 2009

Ordovician conodont faunas from the fine-grained clastic Road River Group in northern Yukon Territory contain a mixture of species from both warm- and cold-water regions. This group in southwestern Northwest Territories also has mixed faunas, whereas conodonts from the carbonate facies are more characteristic of the warm-water regions.Six conodont associations and biozones are identified from the Yukon. Some, such as the early Llanvirn "Cordylodus" horridus – Spinodus spinatus association, contain reworked elements. The Pygodus serra Zone (middle–late Llanvirn) is within the upper P. tentaculatus Zone and well below the G. euglyphus Zone. Genera include Ansella, Periodon, Protopanderodus, Pygodus, and Walliserodus.At Peel River, conodonts are within the P. pacificus Zone. The Blackstone River conodonts occur above the P. pacificus Zone and below the G. persculptus Zone (?) and include Oulodus rohneri, Plectodina florida, and Noixodontus. Amorphognathus ordovicicus, Gamachignathus ensifer, O. ulrichi, and Plectodina tenuis occur in both faunas. These represent Fauna 12, found in late Richmondian strata, rather than the Gamachian Fauna 13 and are assigned to the G. ensifer Zone; both occurrences of G. ensifer are biohorizons. The C.? extraordinarius and G. persculptus zones are not recognized at Peel and Rock rivers and Tetlit Creek.The Ozarkodina n. sp. A – Icriodella sp. B association occurs at Pat Lake between the G. persculptus Zone (?) and the underlying P. pacificus Zone. The Ozarkodina have a Silurian aspect but must be regarded as Ordovician.The Ordovician–Silurian boundary in the Road River Group of the Yukon is best defined using graptolites because of the rare occurrence of conodonts.
Heleosuchus: an enigmatic diapsid reptile from the Late Permian or Early Triassic of southern Africa
Authors: Carroll Robert L.
Published: June 2009

The primitive diapsid reptile Heleosuchus griesbachi, from the Late Permian or Early Triassic of southern Africa, is redescribed on the basis of a new cast made from the type specimen. Few diagnostic features of the skeleton are preserved, making it difficult to establish specific affinities. No characters are known that are uniquely shared with archosauromorphs. In common with lepidosauromorphs, but in contrast with stem diapsids, cervical vertebrae 3–5 are shorter than the anterior trunk vertebrae, and the transverse processes are relatively short. Heleosuchus may be a member of the Eosuchia or an otherwise unrecognized lineage of primitive lepidosauromorphs. The possibility that this specimen shows thyroid fenestration of the pelvis and a shortened and (or) hooked fifth metatarsal cannot be unequivocally established.
The fall (and rise) of central Vancouver Island: 1930–1985
Authors: Dragert H.
Published: June 2009

Levelled height differences obtained from first-order vertical control surveys between 1930 and 1984 indicate large apparent elevation changes along the east coast of central Vancouver Island, British Columbia. The levelling survey following the 1946 earthquake (M = 7.3) indicated relative subsidence, likely coseismic, of up to 80 mm for the northern third of the 130 km traverse between Comox and Campbell River. Subsequent surveys indicated relative uplifts within this region at rates averaging 1 mm/year (1946–1977) and 5 mm/year (1977–1984). Tilting along a 90 km traverse across central Vancouver Island between Gold River and Campbell River is not well defined because of uncalibrated magnetic errors present in the 1976–1978 baseline data. Minimal estimates indicate a possible average uplift rate of 1–2 mm/year for the east coast region with respect to the outer coast between 1976 and 1985.Taken at face value, these data are consistent with the crustal deformation sequence expected for an earthquake cycle. The coseismic subsidence has been followed by gradual postseismic recovery totalling 30 mm over 30 years. The apparent recent acceleration of this uplift rate to 5 mm/year could mark a stage of more rapid strain accumulation prior to a seismic event. The sense of tilting, principally upwards to the northwest, is difficult to reconcile with two-dimensional, northeast subduction. If this tilting is being generated at depths directly by the subduction process, it implies that the northern part of the survey area overlies a locked or currently more resistive subduction zone. Alternatively, elastic strain accumulation within the crust across the Beaufort Range (or a subparallel) fault preceding right-lateral strike-slip rupture could also lead to the observed tilt pattern.
A succession of quartz veins in Archean metaturbidites, Yellowknife Bay, Slave Province
Authors: Fyson W. K.
Published: June 2009

The style of extensional quartz veins changed during deformation and metamorphism of greywacke–mudstones near Yellowknife, with successive types of veins accompanying a progression from steeply plunging, predominantly macroscopic F1, and F2 folds to mesoscopic F3 folds and subvertical S3 axial planar cleavages. (A) Early-stage multiple bedding-parallel veins are confined to pelitic units. Some form saddle reefs around hinges of F1 and a few later folds, whereas others are unrelated to fold hinges. Emplacement of most bedding veins during or before F1 folding is suggested. (B) Echelon veins pre-dominantly lie stratabound within pelites. Folding about S3 cleavage indicates a pre-F3 or early F3 origin. (C) Foliation veins more commonly cross sandstones than pelites and follow S3 or F3 axial surfaces. Boudinage of the veins indicates emplacement before S3 was fully developed. (D) Sporadic veins, discordant to bedding and cleavage, vary from undeformed to folded about S3. Evidently these veins were emplaced towards the end or after F3 folding.The change from pelite as the preferred host rock for bedding and echelon veins to sandstone for foliation veins could reflect migration of loci of hydraulic fracturing as fluid was produced and lost during metamorphism. Bedding and foliation veins apparently followed weakness planes (bedding fissility and cleavage), whereas the echelon vein arrangement suggests that during an intermediate stage of deformation pelites acted as shear zones. All veins could have formed during variably directed, subhorizontal, tectonic compression.
Late Quaternary geology and geomorphology of the Elk Valley, southeastern British Columbia
Authors: George H. , Gorman W. A. , VanDine D. F.
Published: June 2009

Glacial stratigraphy and geomorphology of the bottom areas of the Elk Valley support the existence of one major ice advance, presumably during the late Wisconsinan. Its retreat probably occurred in two stages by orderly frontal withdrawal. Glacial Lake Elk, formed within the Elk Valley from meltwaters released by this glacier, was dammed initially by an ice plug from the Rocky Mountain Trench glacier at a point near Morrissey and subsequently less than 3 km upvalley from Elko. The lake drained in at least three stages.
Évolution géochimique superficielle des pyroxénites ignées du Mont Saint-Bruno, Québec
Authors: Kimpe Christian de , Dejou Jean , Chevalier Yves
Published: June 2009

Samples were collected in a saprolite and soil profiles derived from the weathering of igneous pyroxenites at Mount Saint-Bruno, Quebec. Alternation of the disaggregated rock produces small amounts of < 2 μm material. The various minerals present in the pyroxenite–augite, plagioclases, olivine, and biotite–and their weathering products were separated and analyzed with a microprobe. All primary minerals are transformed into smectites identified as beidellites, montmorillonites, saponites, Fe–Mg smectites, and transition smectites. The microenvironment determines the nature of the secondary minerals.
Tourmalinites in the Aphebian Mistassini Group, Quebec
Authors: Chown E. H.
Published: June 2009

Tourmalinites, or fine-grained sedimentary rocks containing 15–20% or more tourmaline, occur within the Papaskwasati Formation of the Aphebian Mistassini Group in central Quebec. The formation, which is largely composed of fluvial sand-stones and conglomerates with minor argillite beds, was deposited in a restricted embayment close to the transition into marine carbonates. Concentrations of tourmaline are limited to fine-grained sediments and intraclasts, and fine sedimentary structures are preserved within the resulting tourmalinites. This suggests that the tourmalinites formed from preexisting boron-rich muds. It is unlikely that the muds were formed from sea-floor hydrothermal emanations, as no hydrothermal manifestations or spenecontemporaneous vulcanism is known to be associated with this formation. An evaporitic origin for the tourmalinites is consistent with both the sabkha conditions postulated for the origin of nearby carbonates and the limited areal extent of the sedimentary basin.
A Silurian sphinctozoan sponge from east-central Cornwallis Island, Canadian Arctic
Authors: Freitas T. de
Published: June 2009

The first Silurian sphinctozoan ever recorded is reported from the Canadian Arctic. The polysiphonate sphinctozoan, Rigbyspongia catenula n. gen., n. sp., is found associated with numerous anthaspidellid sponges. Diagnostic features of the new genus are its numerous axial siphons and vertical pillars within each chamber. Although it is structurally complex for a sphinctozoan of this age and is the only Silurian representative of the order, this new genus provides few clues to the still enigmatic problem of Paleozoic sphinctozoan phylogeny.
Middle to Late Ordovician rocky bottoms and rocky shores from the Manitoulin Island area, Ontario
Authors: Johnson Markes E. , Jia-yu Rong
Published: June 2009

The Precambrian Lorrain Quartzite is exposed on Manitoulin, Great Cloche, and Birch islands in Lake Huron off the mainland of Ontario. Metamorphism created a massive unit, which later formed a resistant angular unconformity overlain by a succession of strata deposited from Middle to Late Ordovician times. At the start of Ordovician sedimentation, topographic relief was at least 125 m when the quartzite hills formed an archipelago of small, rocky islands. The Ordovician–Precambrian unconformity provides insight on a changing series of depositional environments over rocky bottoms and rocky shores. Four Ordovician units are well represented. The Swift Current Formation includes some red beds, while the younger Cloche Island and Cobourg formations are carbonates. The Collingwood Formation is a black shale. The first three include eroded quartzite clasts typical of a rocky-shore setting. The unconformity marked by the Collingwood Formation indicates a rapid transgression with little time for the accumulation of eroded quartzite clasts. A rich trilobite and orthid brachiopod fauna was recovered from the Collingwood Formation immediately above the Lorrain Quartzite and it represents a rare association that lived in a rocky-bottom setting. This fauna includes the first-reported occurrence of the genus Triarthrus from Manitoulin Island. The Collingwood transgression is equated with a major rise in sea level widely recognized elsewhere in North America and Scandinavia.
Calcite rafts, peloids, and micrite in cave deposits from Cayman Brae, British West Indies
Authors: Jones Brian
Published: June 2009

Speleothemic deposits from the Oligocene–Miocene Bluff Formation of Cayman Brae include calcite rafts that formed in cave pools. The rafts, which formed at the surface of the cave pools where rapid degassing of CO2 from the surface waters led to the precipitation of the calcite, can be divided into single- or double-sided spar calcite rafts and symmetrical, asymmetrical, or composite micrite – spar calcite rafts. Agitation of the water caused the rafts to sink and accumulate on the floor of the pool.Cavities formed by stacking of the calcite rafts are filled or partly filled with spar calcite, micrite, peloids, and terra rossa glaebules. The micrite laminae, like those in the micrite – spar calcite rafts, probably formed through the merger of peloids, which are formed of either subhedral to euhedral crystals or anhedral to subhedral grains. Available petrographic evidence suggests that the micrite and the peloids formed by precipitation from cave water. This example demonstrates that high-magnesium calcite peloids are not necessarily indicative of early marine diagenesis in reefs.
A regional perspective of the Quetico metasedimentary belt, Superior Province, Canada
Authors: Percival John A.
Published: June 2009

Alternating greenstone–granite and metasedimentary gneiss belts are a first-order tectonic feature of the southern Superior Province. The tectonic development of the Quetico metasedimentary belt is reviewed with regard to depositional, structural, and metamorphic–plutonic history. Over its 1200 km length, the belt consists of marginal metasedimentary schists of turbiditic origin and interior metasedimentary migmatite and peraluminous leucogranite. Polyphase deformation has resulted in a steep easterly-striking foliation and regional, gently east-plunging stretching lineation. Metamorphic grade varies in a low-P facies series from greenschist at the belt margins to upper amphibolite and local granulite in the central migmatite – intrusive granite zone. Mineral assemblages in the central zone yield estimates of metamorphic pressure that increase systematically eastward over 800 km from about 250 MPa (2.5 kbar) near the Canada – United States border to 600 MPa (6 kbar) in granulites adjacent to the Kapuskasing structural zone.Geochronology suggests that sediments were deposited at approximately the same time as active volcanism in adjacent volcanic belts, although evidence of volcanic–sedimentary stratigraphic contiguity is weak as a result of later transcurrent movement parallel to major lithological boundaries. Adjacent belts are inferred to have been contiguous since common D2 deformation, 2689–2684 Ma ago. Major plutonism and associated metamorphism occurred in the Quetico Belt approximately 2670–2650 Ma ago, significantly later than major plutonism in the adjacent volcanic belts.The linear disposition of greywacke-rich sediments over 1200 km invites an analogy with modern accretionary prisms. However, the high-temperature, low-pressure metamorphism of the Quetico Belt is inconsistent with such a low-heat-flow environment, and a change in tectonic regime would be required to account for the metamorphism and intracrustal plutonism. Simple cessation of subduction beneath the thick sedimentary prism could have led to restoration of isotherms, with possible attendant crustal melting and isostatic recovery.
The geology and geochemistry of an Early Proterozoic volcanic-arc association at Cartwright Lake: Lynn Lake greenstone belt, northwestern Manitoba
Authors: Peck D. C. , Smith T. E.
Published: June 2009

The geology of the Cartwright Lake area consists of a >2 km thick conformable sequence of Early Proterozoic supracrustal rocks intruded by calc-alkaline granitoid plutons. The supracrustal succession comprises a basal series of tholeiitic basalts, an overlying bimodal sequence, and an uppermost series of calc-alkaline andesites. The bimodal sequence incorporates abundant tholeiitic basalts and associated mafic tuffs, lesser felsic hyaloclastites and pyroclastics, and minor interflow greywacke–mudstone turbidites.Petrogenetic models involving trace-element concentrations indicate that most of the extrusive and intrusive rocks were derived from similar parent magmas that formed by extensive partial melting of a garnet lherzolite upper-mantle source. The parent liquids fractionated along an early tholeiitic trend and a later calc-alkaline trend, producing the observed geochemical variations in the mafic and intermediate volcanic assemblages. Ponding of mafic magma at the base of the crust may have promoted crustal fusion, thereby generating felsic liquids, which erupted and formed the dacite–rhyolite suite.The geology and geochemistry of the volcanic assemblages are consistent with a subduction-related origin in a volcanic-arc setting. The majority of geochemical evidence favours the interpretation that the Cartwright Lake segment of the arc developed on relatively thin sialic crust.
Turbidity-current channels in Queen Inlet, Glacier Bay, Alaska
Authors: Carlson Paul R. , Powell Ross D. , Rearic Douglas M.
Published: June 2009

Queen Inlet is unique among Glacier Bay fjords because it alone has a branching channel system incised in the Holocene sediment fill of the fjord floor. Bathymetry and seismic-reflection profiles show that four channels begin on, or at the base of, the delta front of this marine-outwash fjord. By midpoint of the fjord, these channels have merged into one main channel that extends the length of the fjord. The main channel cuts deeply into the scarp that separates this hanging tributary from the West Arm of Glacier Bay. The Queen Inlet channel ends on the main fjord floor as several small distributaries that form part of a lobate-fan deposit. Sand from the channel and lobate fan, in contrast to fjord-floor mud, plus steep truncated channel walls indicate that turbidity currents created this apparently active channel system. Queen Inlet and other known channel-containing fjords are marine-outwash fjords; the tidewater glacial fjords do not have steep delta fronts on which slides are generated and may not have a sufficient reservoir of potentially unstable coarse sediment to generate channel-cutting turbidity currents. Presence or absence of channels, as revealed in the ancient rock record, may be one criterion for interpreting types of fjords.
Paleomagnetism of the Eocene Kamloops Group and the cratonization of Terrane I of the Canadian Cordillera
Authors: Symons D. T. A. , Wellings M. R.
Published: June 2009

The lower Middle Eocene (49.4 ± 2.4 Ma) Kamloops Group is exposed in the middle of the Quesnellia subterrane of Terrane I. The group consists of the siliciclastic Tranquille Beds and the overlying Dewdrop Flats plateau basalts and andesites. Detailed alternating field (AF) and thermal step demagnetization was carried out on 282 specimens from 26 flow sites and one conglomerate site, and saturation isothermal remanent magnetization (SIRM) tests were performed to examine the remanence carriers. The petrology of the gently dipping flows, the presence of antiparallel normal and reverse remanence, the conglomerate test, and the fold test all indicate that a primary remanence has been isolated. It resides in both magnetite and hematite over a broad range of AF coercivities, blocking temperatures, and domain sizes. Its mean direction of 355.0°, 73.4 °(α95 = 6.9°) gives a pole position of 138.4°W, 81.4°N (dp = 11.0°, dm = 12.3°) that is statistically indistinguishable from the 50 Ma reference pole for the North American craton. This indicates that the cratonization of Terrane I was complete by the Middle Eocene after it had undergone ~1300 km of northward translation and ~45 °of clockwise rotation since the mid-Cretaceous.
New heat flow density and radiogenic heat production data in the Canadian Shield and the Quebec Appalachians
Authors: Mareschal J. C. , Pinet C. , Gariépy C. , Jaupart C. , Bienfait G. , Coletta G. Dalla , Jolivet J. , Lapointe R.
Published: June 2009

New heat flow density (HFD) measurements were performed at 10 sites in Quebec. For five of the sites located in the Superior Province, the heat flow density varies between 24 and 35 mW/m2 (26 and 37 mW/m2 after adjustment for Pleistocene climatic variations). In the Grenville Province, the values obtained range between 25 and 28 mW/m2 (29 and 31 mW/m2 after adjustment). For two nearby sites in the Gaspé region (Appalachians), the heat flow density is 47 mW/m2 (48 mW/m2 after adjustment). Radiogenic heat production was also measured. At the sites located in the meta-volcano-sedimentary sequences of the Superior Province, the heat production is low (0.1–0.6 μW/m3) and it does not always correlate with the surface heat flow. In the Grenville Province, the HFD is close to (slightly higher than) the reduced heat flow of the Superior. The higher HFD in the Appalachians is partly explained by the higher crustal heat production, and partly by higher deep heat flow.
Wenlock (Silurian) graptolite biostratigraphy of the Cape Phillips Formation, Canadian Arctic Islands
Authors: Lenz A. C. , Melchin M. J.
Published: June 2009

The Canadian Arctic Islands Wenlock is represented by a diverse assemblage of graptolites from the Cape Phillips Formation. Cyrtograptids are continuously present throughout all but the uppermost Wenlock. Species of Cyrtograptus constitute the main basis for biostratigraphic zonation, supported to a much lesser degree by Monograptus, Monoclimacis, and Pristiograptus through most of the series. The uppermost Wenlock is dominated by Pristiograptus in association with rare Gothograptus.The following biostratigraphic zones and their correlations are proposed: (1) Cyrtograptus centrifugus – Cyrtograptus insectus Zone (earliest Wenlock); (2) Cyrtograptus aff. rigidus – Monograptus aff. riccartonensis Zone (late early Wenlock); (3) Cyrtograptus perneri – Monograptus cf. munchi Zone, in which Cyrtograptus multiramis is a particularly common element (mid-Wenlock age); (4) Cyrtograptus lundgreni – Monograptus testis Zone, divisible into a lower Monograptus testis n.ssp. and an upper Monograptus testis testis Subzone (late Wenlock); and (5) Pristiograptus ludensis Zone (latest Wenlock). The second and third zones are also possibly divisible into lower and upper subzones, but with less certainty.The degree of zonal subdivision in the Cape Phillips is lower than in Europe. It was observed locally that a number of the key species showed a high degree of overlap and some inconsistencies in their ranges from section to section.Paleoecologically, a few species, particularly Cyrtograptus preclarus, Cyrtograptus cf. malgusaricus, and Pristiograptus meneghini, appear to have preferred basin-margin regions.
Carbonate platform to foreland basin: revised stratigraphy of the Table Head Group (Middle Ordovician), western Newfoundland
Authors: Stenzel Sheila R. , Knight Ian , James Noel P.
Published: June 2009

Carbonates of the Table Head Group and associated strata were deposited along the western margin of a foreland basin during initial stages of the Taconian Orogeny and record collapse and cannibalization of a long-lived carbonate platform. The stratigraphy of Klappa, Opalinski, and James is here revised to reflect better understanding of lithologic units within this complex tectono-stratigraphic assemblage. The Table Head Group now contains only three formations: the Table Point and Table Cove formations, as originally defined, and the Cape Cormorant Formation, redefined and restricted to western Port au Port Peninsula. Black Cove Formation shales are removed from the Table Head. Distinctive conglomerates once placed in the Cape Cormorant are now recognized as separate units within the overlying flysch and called the Daniel's Harbour Member.The foreland basin developed in three stages: (1) fragmentation, uplift, and erosion of the platform and subsequent deposition of shallow-water limestones (Table Point) on a tectonically unstable shelf; (2) foundering of platform blocks and deposition of deep-water-slope carbonates (Table Cove), basinal black shales (Black Cove), or conglomerates of older shelf carbonates shed from submarine cliffs (Cape Cormorant); and (3) siliciclastic sedimentation interrupted by sediment gravity flows of Table Head clasts shed from submarine escarpments (Daniel's Harbour).
Chalcopyrite–bornite and chalcopyrite–bornite–barite in the Acton Vale Limestone, southeastern Quebec: mineralized shelf-margin slivers in a Taconian nappe
Authors: Kumarapeli P. Stephen , Kheang Lao , Hoy Larry , Pintson H.
Published: June 2009

The Acton Vale limestone units of probable Early Ordovician age in the external nappe zone of the Appalachian foldbelt in southeastern Quebec host numerous occurrences of vein- and breccia-type copper deposits. Associated with these are two significant occurrences of barite: one at Upton consisting of a stratiform mass of probable economic potential; and the other at Lord Aylmer consisting of thin, tabular, karstic infillings of barite. Studies of the mineral occurrences at Acton Vale, Upton, and Lord Aylmer show that the mineralization is epigenetic and formed largely by open-space filling at shallow depths in parts of the limestones that had undergone ground preparation by brecciation and (or) karsting. Fluid-inclusion, sulphur-isotope, and strontium-isotope analyses show that mineral deposition occurred at temperatures ranging from 110° to 135 °C, that sea water formed the bulk of the mineralizing fluids, and that altered basaltic volcanic rocks associated with the Acton Vale limestones are. the most important source of metals and Ba.The mineral deposits seem to have formed during the evolution of the passive margin of Laurentia. The preferred model for their genesis is one involving deep circulation of water, which, on coming into contact with the volcanic rocks, leached metals and Ba and subsequently deposited them in favourable parts of Acton Vale limestones. Recurrent movements of faults of the Ottawa Graben, which is the failed arm of the Sutton Mountains triple junction, may have been a factor that facilitated deep circulation of fluids. In their present setting, the Acton Vale limestones and the associated volcanic rocks and shales probably represent slivers of the passive margin incorporated into the Cambrian shale – feldspathic sandstone assemblages of the Granby Nappe.
Geochemistry and origin of Archean granites from the Black Hills, South Dakota
Authors: Gosselin D. C. , Papike J. J. , Shearer C. K. , Peterman Z. E. , Laul J. C.
Published: June 2009

The Little Elk Granite (2549 Ma) and granite at Bear Mountain (BMG) (~2.5 Ga) of the Black Hills formed as a result of a collisional event along the eastern margin of the Wyoming Province during the late Archean. Geochemical modelling and Nd isotopic data indicate that the Little Elk Granite was generated by the partial melting of a slightly enriched (εNd = −1.07 to −3.69) granodioritic source that had a crustal residence time of at least 190 Ma. The medium-grained to pegmatitic, peraluminous, leucocratic BMG was produced by melting a long-lived (>600 Ma), compositionally variable, enriched (εNd = −7.6 to −12.3) crustal source. This produced a volatile-rich, rare-earth-element-poor magma that experienced crystal–melt–volatile fractionation, which resulted in a lithologically complex granite.The production of volatile-rich granites, such as the BMG and the younger Harney Peak Granite (1715 Ma), is a function of the depositional and post-depositional tectonic environment of the sedimentary source rock. These environments control protolith composition and the occurrence of dehydration and melting reactions that are necessary for the generation of these volatile-rich leucocratic granites. These types of granites are commonly related to former continental–continental accretionary boundaries, and therefore their occurrence may be used as signatures of ancient continental suture zones.
The tectonic relationship of two Early Proterozoic dyke swarms to the Kapuskasing Structural Zone: a paleomagnetic and petrographic study
Authors: Halls H. C. , Palmer H. C.
Published: June 2009

A tea-coloured cloudiness in groundmass feldspars characterizes dykes of two Early Proterozoic swarms (2.45 Ga Matachewan; 2.04 Ga Kapuskasing) that intrude amphibolite to granulite host rocks within the Kapuskasing Structural Zone (KSZ) of northern Ontario. Outside the KSZ the dykes occur in lower-grade terranes and contain unclouded feldspars. Matachewan dykes within the KSZ are also fresh, contain an aluminous, blue–green amphibole, have fewer plagioclase phenocrysts, and on average are thinner compared with their counterparts outside, which are more hydrously altered, contain a green, fibrous amphibole, and are locally abundant in felspar phenocrysts.Within the Matachewan swarm, magnetic polarity domains — areas of dominantly normal or reversed magnetization — have been identified; the boundaries of these domains correspond closely to major faults. Two of these faults form the boundaries of the KSZ and separate normal dykes within from dominantly reversed ones outside.The foregoing petrological and paleomagnetic observations are related to differential vertical crustal movements that have raised younger, normal-polarity Matachewan dykes (as exemplified by those within the KSZ) from a deeper crustal level and juxtaposed them against older, reversely magnetized dykes that were intruded at shallower crustal levels.Paleomagnetic baked-contact tests on Kapuskasing dykes suggest that they were intruded both before and after the main period of crustal uplift and tilting along the KSZ and that dykes within 4 km of the southeastern boundary fault were raised from depths where temperatures exceeded 580 °C, the Curie-point isotherm for magnetite.
Seismic tomography to obtain velocity gradients and three-dimensional structure and its application to reflection data on Vancouver Island
Authors: Phadke Suhas , Kanasewich Ernest R.
Published: June 2009

A seismic-reflection survey was carried out on Vancouver Island as part of Lithoprobe – Phase I to study the crustal structure and tectonics of this convergent margin. Four seismic profiles, which provided structural and velocity information using standard common-depth-point stacking, were shot. The lines were crooked; hence, this approach does not give one full confidence in the results obtained. However, because of the crookedness of the lines, the reflection points were located in three-dimensional space; therefore, it was possible to obtain the three-dimensional structure of the subsurface.Since the traveltime is a nonlinear function of model parameters, an iterative, damped least-squares technique is used to obtain three-dimensional structure and velocity with gradients. The ray tracing is performed for each shot–receiver pair by solving a system of nonlinear equations. In constant-velocity media the raypath is a straight line, whereas in media with velocity varying linearly with depth the raypath follows the arc of a circle. The interfaces are defined by polynomial surfaces where the raypaths satisfy Snell's law.The method was tested for a synthetic model: it was fast and effective. Then the method was applied to a small portion of line 1 to obtain velocity gradients and three-dimensional structures of the décollement and subduction zones. For reflector C on line 1 at an approximate depth of 15 km the velocity at the top of the horizon is found to be 6.8 km/s, with a gradient of 0.034 km/s per km. The dip and strike are 3 °and N18°E, respectively. For reflector E on line 1 at an approximate depth of 28 km the velocity at the top of the horizon is found to be 7.8 km/s. The dip and strike are 8.9 °and N65°E, respectively. To obtain more precise results, efforts should be made to record at wider angles of incidence.
U–Pb and K–Ar dates related to the timing of magmatism and deformation in the Cache Creek terrane and Quesnellia, southern British Columbia
Authors: Mortimer N. , Heyden P. van der , Armstrong R. L. , Harakal J.
Published: June 2009

U–Pb dating of zircon from the Guichon Creek batholith indicates an emplacement age of 210 ± 3 Ma. Comparison with previously published K–Ar (211–188 Ma) and Rb–Sr (205 and 196 Ma) dates reveals that intrusion, mineralization, cooling, and uplift of the batholith took some 20 Ma, spanning the Triassic–Jurassic boundary on the Decade of North American Geology (DNAG) time scale.The Mount Martley pluton and Tiffin Creek stock yield Late Jurassic dates of 155 ± 2 Ma (U–Pb, zircon) and 152 ± 5 Ma (K–Ar, hornblende), respectively, and provide a reliable minimum age (Kimmeridgian) for penetrative deformation in the Cache Creek terrane. K–Ar whole-rock dates from Cache Creek terrane and Ashcroft Formation argillites range from Early Permian (266 ± 8 Ma) and Early Jurassic (194 ± 6 Ma) to Late Jurassic, Kimmeridgian (154 ± 5 Ma). We interpret the younger dates as recording Middle–Late Jurassic tectonism and the older ones as possible relics from earlier deformation episodes.An Early Cretaceous K–Ar date (129 ± 5 Ma) for a lamprophyre dike that cuts the Nicola Group suggests that the Early Cretaceous magmatic arc of the Coast Plutonic Complex had an eastern alkalic fringe in the Intermontane Belt.
Late Cenozoic paleomagnetic record of Duck Hawk Bluffs, Banks Island, Canadian Arctic Archipelago
Authors: Barendregt R. W. , Vincent Jean-Serge
Published: June 2009

Detailed paleomagnetic investigations have been completed on unconsolidated sediments from Duck Hawk Bluffs on Banks Island, in the Canadian Arctic Archipelago, that record some of the oldest late Cenozoic glacial and nonglacial events in Canada. The preglacial Worth Point Formation, the overlying Duck Hawk Bluffs Formation, including marine and glacial deposits laid down during the Banks Glaciation, and the lower part of the interglacial Morgan Bluffs Formation have magnetically reversed directions and therefore are of Matuyama age (>790 ka). Upper Morgan Bluffs Formation organic beds and deposits of the younger Thomsen Glaciation, Cape Collinson Interglaciation, and Amundsen Glaciation are normally magnetized and therefore of Brunhes age (<790 ka). The Brunhes–Matuyama boundary is recorded in the upper portion of the Morgan Bluffs Formation. Its precise position within the interglacial sequence can be identified, since the sediments document the gradual change from reversely inclined directions to normally inclined ones. These results confirm that the preglacial Worth Point Formation is at least Early Pleistocene in age and that the Banks Glaciation (the oldest and strongest continental glaciation recorded in the western Arctic) and a good part of the Morgan Bluffs Formation are of Early Pleistocene age. The study also documents a rare site in Canada where terrestrial sediments record the Brunhes–Matuyama transition and in doing so permits a precise correlation of part of the Banks Island stratigraphy with other key late Tertiary and Early to Middle Pleistocene arctic terrestrial and marine sequences.
The end of the ice age
Authors: Nisbet E. G.
Published: June 2009

Methane-gas hydrates may have contributed to the rapid rise in atmospheric CH4, CO2, and global temperatures at the end of the last major glaciation about 13 500 years ago. Given suitable orbital conditions and insolation at high latitude, a small triggering event, such as the release of one or more Arctic gas pools, may have initiated massive release of methane from hydrate under ice and in permafrost. The consequent greenhouse warming would have provided strong positive feedback, amplifying emission. This warming, driven by CH4, may have induced the release of CO2 from the oceans to the biosphere, stabilizing the interglacial carbon cycle.
U–Pb geochronology of the eastern Abitibi Subprovince. Part 2: Noranda – Kirkland Lake area
Authors: Mortensen J. K.
Published: June 2009

U–Pb zircon ages for 15 volcanic and plutonic units in the Noranda and Kirkland Lake areas help constrain the history of volcanism, plutonism, sedimentation, and deformation in the south-central part of the Abitibi belt. Volcanism occurred over an interval of at least 50 Ma, beginning with the deposition of the volcanic and volcaniclastic units within the Pacaud Structural Complex at 2747 Ma. Following a period of apparent quiescence, magmatism resumed at 2730–2725 Ma with the eruption of volcanic rocks in the Normétal and Lac Abitibi area. From 2715 until about 2698 Ma, volcanism occurred sporadically throughout much of the area, culminating in the eruption of the Blake River Group from 2703 to 2698 Ma. Several large intrusive bodies yield ages that indicate that they are plutonic equivalents of the Blake River Group. Plutons that are considered to have been emplaced during the Kenoran orogeny give ages that are only slightly younger than the youngest volcanic units of the Blake River Group, emphasizing the very rapid onset of Kenoran deformation following the cessation of volcanic activity.The Cléricy syenite, dated at 2682 ± 3 Ma, postdates the main period of Kenoran deformation in this area and intrudes sedimentary rocks of the Kewagama Group which contain detrital zircons as young as 2687 Ma. These data suggest that the Kewagama Group is the same age as late sedimentary sequences such as the Timiskaming Group and may have been deposited in a similar tectonic setting.
U–Pb geochronology of the Lapparent Massif, northeastern Abitibi belt: basement or synvolcanic pluton?
Authors: Mortensen J. K.
Published: June 2009

U–Pb ages of 2713–2711 Ma for zircon and titanite from tonalitic gneiss of the Lapparent Massif in the northeastern Abitibi belt are younger than those obtained for surrounding supracrustal rocks. These data indicate that the Lapparent gneisses are not old basement on which the supracrustal rocks were deposited, as has been postulated by some workers, but rather represent a late synvolcanic intrusion that was emplaced at a relatively deep crustal level. The earliest phase of penetrative deformation recognized in the gneiss must have occurred during or immediately after emplacement of the body and represents a deformation event that is not presently recognized in the higher level rocks in this area. The Lapparent gneisses were apparently juxtaposed against adjacent supracrustal rocks along outward-dipping mylonite zones.
Geochemistry and tectonic setting of volcanics from the Anyox mining camp, British Columbia
Authors: Smith Alan D.
Published: June 2009

Volcanogenic massive sulphide deposits at Anyox in the Tracy Arm terrane of the Canadian Cordillera are associated with a sequence of tholeiitic basalts with minor intercalated basaltic andesite tuffs and siliceous sediments. Sm–Nd and Pb–Pb systematics indicate an Early to Middle Jurassic age. The tholeiites are characterized by normal mid-ocean-ridge basalt to weak island-arc tholeiite trace element signatures with slight enrichment in large-ion lithophile elements and depletion in high-field-strength elements, high 207Pb/204Pb, and εNd(170 Ma) values of +8.2 to +8.4. The mineralized sequence is conformably overlain by argillaceous sediments and minor limestones. These features, combined with the location of the strata and similarities with the Spider Peak Formation of the Methow terrane, indicate an origin in a narrowing marginal basin that once separated superterranes I and II.
Density, temperature, and rheological models for the southeastern Canadian Cordillera: implications for its geodynamic evolution
Authors: Lowe C. , Ranalli G.
Published: June 2009

Two-dimensional density, temperature, and rheological models are constructed for a 350 km northeast-trending transect of the southeastern Canadian Cordillera. All models highlight several major physical differences between foreland and hinterland lithosphere. Significant features of the density model are the presence of an anomalously low-density (3.10 × 103 kg∙m−3) layer, with a maximum thickness of 12 km, beneath the Moho in the hinterland; the similar densities of the Monashee Terrane and the cratonic crust of the foreland; and an increase in crustal thickness beneath the Southern Rocky Mountain Trench. The temperature model shows steeper gradients and higher Moho temperatures beneath the hinterland than beneath the foreland. In the rheological model the hinterland is characterized by a thin, brittle, upper crust beneath which the entire lithosphere is hot, weak, and ductile. In contrast, the foreland is composed of a thick, brittle, upper crust, with an additional brittle zone in the upper mantle. The Moho is a large strength discontinuity beneath the foreland, and the total lithospheric strength there is an order of magnitude larger than in the hinterland. The models are constrained and supported by geological mapping and a number of independent geophysical data sets. Palinspastic cross sections, together with paleotemperature and paleopressure information, are used to generate a time series of one-dimensional paleorheological profiles at a number of times during deformation. This sequence of profiles indicates that the foreland and hinterland have been rheologically distinct since pre-Late Cretaceous times. The profiles are used to clarify the geodynamic evolution of the area and to explain why deformation remained thin skinned in the foreland whereas in the hinterland the entire lithosphere was deformed.