bluuebunny/crossref_metadata_2025 huggingface dataset:
P–T–t path for the lower plate of the Eocene Tatla Lake metamorphic core complex, southwestern Intermontane Belt, British Columbia
Authors: Friedman R. M.
Published: April 2011

The Tatla Lake metamorphic complex (TLMC) is a metamorphic core complex located along the western edge of the Intermontane Belt in southwestern interior British Columbia. Low- to moderate-angle normal faults separate lower plate greenschist- and amphibolite-grade, highly strained, commonly mylonitic rocks from unstrained to weakly deformed strata of the upper plate. The lower plate is divided into a core of granoblastic gneiss and migmatitic tonalite and an overlying, 1–2.5+ km thick mylonitic package called the ductilely sheared assemblage (DSA). Amphibolite-grade metamorphism of the gneissic core (Mc) largely accompanied the development and folding of gneissic layering (ca. 107–79 Ma). Eocene (ca. 55–47 Ma) fabric and mineral assemblages in the DSA (Ms) obscure any earlier history. Three metamorphic zones are observed within southern DSA metapelites with increasing structural depth: chlorite–biotite, garnet–staurolite, and garnet–staurolite–kyanite–sillimanite. The middle zone is about 300 m thick; the latter zone is now about 4 km below low-grade upper plate rocks, indicating late- or post-Ds metamorphic omission. DSA P–T conditions are calculated with the garnet–biotite thermometer and garnet–Al2SiO5–quartz–plagioclase (GASP) and total Al in hornblende barometers. Southern DSA metapelites record Eocene Ms conditions of 480–619 °C (± 50 °C), generally increasing with depth. One sample gave a calculated P–T of 0.72 ± 0.15 GPa and 500 ± 50 °C. P–T data from this area suggest that up to 10 km of structural section may be missing. Zoned garnet (pre-Ds) core to rim GASP pressures of 0.70–0.36 ± 0.15 GPa, for an outcrop-sized pelitic xenolith within a Late Cretaceous tonalitic body (U–Pb: 71 Ma) in the northwestern DSA, record its ascent during pluton emplacement and subsequent Eocene tectonic uplift. A total Al in hornblende crystallization pressure of 0.54 ± 0.1 GPa was calculated for the surrounding body. Biotite and hornblende K–Ar dates of 53.4–45.6 Ma for DSA and gneissic core rocks record cooling of the lower plate through the 530–280 °C (± 40 °C) interval. Mc metamorphism in the gneissic core is thought to have developed in response to crustal thickening and compression, beneath a regional mid-Cretaceous thrust belt. Characteristics of Eocene Ms metamorphism in the DSA, such as truncated and thinned metamorphic zones, are consistent with development during extensional tectonic exhumation of the lower plate.
Evidence of late and postglacial seismic activity in the Témiscouata–Madawaska Valley, Quebec – New Brunswick, Canada
Authors: Shilts W. W. , Rappol M. , Blais A.
Published: April 2011

Three types of geological phenomena independently suggest that the Témiscouata–Madawaska Valley was affected by one or more seismic events following its deglaciation:(1) Subbottom acoustic profiling of Lac Témiscouata and Grand lac Squatec revealed disturbance of bottom sediments by mass transport processes in both lakes. Erosional truncation of preexisting, acoustically laminated sediments and accumulation of hummocky, chaotic deposits over older hummocky surfaces or laminated sequences both result from mass transport processes. Unidirectional mass flows from several points in these symmetrical basins, in situ disruption of laminated sediment beneath flat bottoms, and the large area of the lake floors affected suggest strong similarities in sedimentation style with lakes that have been disturbed during strong earthquakes.(2) Southeast of Lac Témiscouata, in Saint-Jacques, New Brunswick, two separate mass flow deposits, made up largely of coarse (> 0.5 m), angular boulders of local bedrock, occur on opposite sides of the Madawaska River valley. These deposits have different source areas and transport directions, but occupy more or less the same stratigraphic position within sediments deposited in glacial Lake Madawaska.(3) At one site in Saint-Jacques, a near-vertical fault displaces a glacially striated bedrock surface at least 7 cm, suggesting a response to postglacial compressive stress similar to that observed on outcrops in the nearby epicentral region of the 1982 Miramichi earthquake.Although the Témiscouata–Madawaska Valley lacks historical evidence of seismic activity, and many of the phenomena observed could, individually, have been generated by aseismic processes, we conclude that the close proximity of diverse features related to mass transport and faulting suggest that the valley has been the locus of seismic activity from the time of its deglaciation to the recent, but prehistorical, past.
Advances in the U–Pb zircon geochronology of the Michipicoten greenstone belt, Superior Province, Ontario
Authors: Turek A. , Sage R. P. , Schmus W. R. Van
Published: April 2011

The Michipicoten greenstone belt in the Superior Province in Ontario developed over a period of approximately 240 Ma, between 2900 and 2660 Ma. The belt is made up of supracrustal rocks consisting of mafic to felsic metavolcanic and associated metasedimentary rocks intruded and embayed by granitoids of various ages. Generally, the external granitic terrane, a mosaic of plutons of various ages, is younger than the greenstone belt and equivalent in age to the plutons in the belt. Three major volcanic cycles have been recognized, and the older internal plutonism is coeval with the volcanism.This study reports 10 new U–Pb concordia ages that enhance the existing geochronological framework of the area. The 2889 Ma age determined for the Judith volcanic tuff documents the existence of the oldest volcanic cycle. This age is close to that of the Murray–Algoma porphyry, dated in this study at 2881 Ma, and similar to a previously published age of 2888 Ma for the Regnery granite within the same area. These three ages establish coeval felsic volcanism and plutonism within the oldest volcanic cycle 1.The new ages for the Jubilee volcanic centre are 2746 Ma (volcanic flow) and 2742 Ma (porphyry intrusion). These ages agree with previously published cycle 2 felsic volcanic ages of 2744 and 2749 Ma and hence establish coeval felsic volcanism and plutonism for this volcanic cycle. The Goudreau felsic volcanic terrane yields ages of 2729 Ma at Goudreau and 2741 Ma at Alden, which probably represent different stratigraphic positions within the same cycle.At McCormick Lake the felsic volcanic crystal tuff is 2701 Ma and belongs to cycle 3 volcanism. U–Pb ages have been determined for three plutons: 2677 Ma for the internal Dickenson Lake syenite, 2662 Ma for the internal Lund Lake granodiorite, and 2686 Ma for the external Dubreuilville granodiorite. These ages fit into an established period of granitoid plutonism in the area.
Episodic Early Proterozoic granitoid plutonism in the Makkovik Province, Labrador: U–Pb geochronological data and geological implications
Authors: Kerr A. , Krogh T. E. , Corfu F. , Schärer U. , Gandhi S. S. , Kwok Y. Y.
Published: April 2011

Episodic granitoid plutonism in the Early Proterozoic Makkovik Province of the easternmost Canadian Shield is revealed by high-precision U–Pb zircon studies of a range of intrusive rock types. The oldest granites yield ages of 1893 ± 2 and 1891 ± 5 Ma and document a previously unrecognized event that may correlate with an early migmatization of reworked Archean basement. These dates also constrain early structural reworking of the basement, the earliest deformational event grouped as part of the Makkovikian orogeny. Four samples have essentially identical zircon ages of 1801 ± 2, 1802 ± 2, [Formula: see text], and 1825–1799 Ma, and a fifth is slightly older, at [Formula: see text]. These ages suggest correlation with local volcanic sequences, dated in part at 1807 ± 4 Ma. The plutonic suites include both syn- and posttectonic granitoid assemblages and define the main magmatic pulse associated with the Makkovikian orogeny and constrain its final deformational episode. Distinctive, fluorine-enriched "A-type" granites yield an age of 1719 ± 3 Ma and represent a previously unrecognized late postorogenic to anorogenic magmatism of regional significance. Two layered, gabbro–diorite–monzonite–syenite suites yield identical zircon ages of 1649 ± 1 and 1649 ± 3 Ma. A regionally extensive granodioritic unit gives an age of 1647 ± 2 Ma, and a high-level alaskitic granite is dated imprecisely at 1640–1650 Ma. These plutonic suites correlate with volcanic rocks previously dated at 1649 ± 1 Ma.These data show that the plutonic evolution of the Makkovik Province is significantly more complex than previously supposed. The clustering of ages suggests episodic, rather than continuous, magmatism. The different age groupings can, to some extent, be correlated with compositional associations defined by major- and trace-element geochemistry. The new data also raise questions about the regional configuration of Early and Middle Proterozoic orogenic belts in Labrador. Previous correlations between the Makkovik Province, the Ketilidian Mobile Belt of Greenland, and the Svecofennian and Trans-Scandinavian belts of Sweden are supported and expanded by these new results.
Water sheet outburst floods from the Laurentide Ice Sheet
Authors: Shoemaker E. M.
Published: April 2011

Field evidence and a theoretical model support the concept that during Wisconsinan glaciation subglacial water sheet outburst floods issued from a large subglacial lake located in the Hudson Bay basin. The lake was fed by supraglacier meltwater that was trapped in a depressed ice lid over the lake. Water may have also fed the lake by reversed outburst floods from proglacial lakes, particularly after 9000 BP, when a very low ice elevation over Hudson Bay is calculated. Deglaciation was accelerated by surges associated with the lift-off of ice by the sheet floods; ice lobe extensions the order of 100 km are possible. The model supports the concept of a multidomed Laurentide Ice Sheet in the form of an annular dome around Hudson Bay.
Provenance of Albian–Cenomanian rocks of the Methow and Tyaughton basins, southern British Columbia: a mid-Cretaceous link between North America and the Insular terrane
Authors: Garver John Irwin
Published: April 2011

Basin analysis of Albian–Cenomanian rocks of the Tyaughton and Methow basins suggests that the two basins were filled by three principle petrofacies during a regionally significant contractional event. The Volcanic petrofacies, which occurs only in the Tyaughton basin, comprises west-derived volcaniclastic strata. This petrofacies is dominated by intermediate volcanic clasts and minor metavolcanic, sedimentary, and plutonic clasts. This petrofacies and correlatives to the west (Taylor Creek volcanics and the Gambier Group) are inferred to have been a volcanic cover and volcaniclastic apron to the Insular terrane.The Cherry petrofacies occurs in both the Tyaughton and the Methow basins. Paleocurrents suggest that these chert-rich sediments were shed both east and west off a topographic high that separated the two basins. The Cherry petrofacies is dominated by chert-lithic detritus with subordinate sedimentary and volcanic rock fragments. Locally, the petrofacies is characterized by clasts of chert, greenstone, serpentinite, and blueschist; all these lithologies are common in the unconformably underlying Bridge River terrane, which is inferred to have been the dominant source terrane.Rocks that contain the Arkosic petrofacies are 3–8 km thick in the Methow basin, but only a thin unit is present in the Tyaughton basin. This petrofacies is rich in quartz and feldspar, with lesser quantities of volcanic lithic and metamorphic lithic fragments. Detrital muscovite, which is the hallmark of this petrofacies, is interpreted to have been derived from granitic and metasedimentary rocks to the east. This petrofacies is interpreted to have been largely derived from the Omineca Crystalline Belt, which was rapidly uplifting during this time. The three petrofacies in the two basins provide the first provenance link between the Insular terrane to the west to what was then North America (Omineca Crystalline Belt and the Intermontane Belt) to the east; juxtaposition is inferred to have occurred in a contractional setting.
Ripple cross-stratification in swaley cross-stratified sandstones of the Chungo Member, Mount Yamnuska, Alberta
Authors: Arnott R. W. C.
Published: April 2011

Swaley cross-stratified sandstones are exposed in the Late Cretaceous Chungo Member of the Wapiabi Formation at Mount Yamnuska, Alberta. At this site, many of the individual flaggy-weathering, thin beds of sandstones that make up the swaley cross-stratified structure are internally ripple cross-stratified. The association of swaley and ripple cross-stratification has not previously been described and is interpreted to indicate compound cross-stratification generated under combined flow condi tions. Furthermore, this association brings into question the possible genetic relationship between swaley cross-stratification and hummocky cross stratification, a sedimentary structure generated under purely oscillatory conditions.
Tertiary extension and tilting in the Queen Charlotte Islands, evidence from dyke swarms and their paleomagnetism
Authors: Irving E. , Souther J. G. , Baker J.
Published: April 2011

The Queen Charlotte Islands form the western margin of the Tertiary Queen Charlotte Basin, which is situated on the western margin of the North American Plate. They contain seven major dyke swarms of Late Eocene to Miocene age, a period when the relative motions of the Pacific and the North American plates in this region were dominantly dextral strike slip (transform margin), with intervals of highly oblique divergence and convergence. Within each swarm, dykes have a systematic trend. However, trends vary from swarm to swarm, indicating that the stress field varied. A total of 678 cores (1352 specimens) were collected from 129 dykes in six swarms over a distance of about 200 km. Magnetic stability is variable. One hundred and one dykes yielded records of the paleofield. Data are also reported from an Oligocene pluton (5 sites, 27 cores, 52 specimens) and Miocene lavas (8 sites, 52 cores, 101 specimens). Both normal and reversed magnetizations occur, but irrespective of sign, the mean directions of remanent magnetization of each swarm and of the pluton and the lavas have systematically steeper inclinations than the value calculated from coeval rocks in North America. To explain this it is proposed that, after dyke emplacement, the sampling areas were tilted to the north or northwest by amounts that vary between 9 and 16°. Apparently, crustal tilting, similar in magnitude and direction, extended over distances of approximately 200 km. This cannot reflect tilting of a single block. Instead, it is argued that at least the southern Queen Charlotte Islands underwent considerable northerly or north-northwesterly directed extension and normal block faulting, which followed and in part was concurrent with the formation of widespread mid-Tertiary dyke swarms, plutons and lava flows. Making use of the fact that dykes propagate perpendicular to the direction of extension, and combining previously measured dyke orientations with paleomagnetic data, three stages of extension are proposed: east–west extension sometime during the Late Eocene to Early Oligocene; north–south extension sometime in the interval Late Oligocene to Early Miocene; and northwest–southeast extension sometime during Late Miocene or later time.
Proterozoic flood basalts from the Coppermine River area, Northwest Territories: isotope and trace element geochemistry
Authors: Dupuy C. , Michard A. , Dostal J. , Dautel D. , Baragar W. R. A.
Published: April 2011

The voluminous Proterozoic continental tholeiites of the Coppermine River province (Northwest Territories), which are coeval with the Mackenzie magmatic event (1.27 Ga old) and were emplaced over a short period of time (< 5 Ma), have trace element and Sr–Nd–Pb isotopic characteristics comparable to those of Phanerozoic flood basalts. The variations of the compositional parameters are inferred to be due to a mixing of at least two components: mantle and crust. In addition, the mantle component probably includes two end members. The first is a mantle plume, whereas the other represents the base of the continental lithosphere. The crustal component reflects contamination of the magma by Precambrian basement during its ascent to the surface.
The Labradorian orogeny in the Grenville Province, eastern Labrador, Canada
Authors: Gower Charles F. , Schärer Urs , Heaman Larry M.
Published: April 2011

Two minor intrusions within the Hawke River terrane in the Grenville Province, eastern Labrador, have upper intercept U–Pb ages as follows: (i) [Formula: see text] for a megacrystic intermediate dyke and (ii) 1622 ± 3 Ma for a pegmatite dyke. The upper intercepts date time of emplacement and the lower intercepts (508 and 320 Ma, respectively) record the timing of early Paleozoic events in the region. A third sample, a sillimanite-bearing pelitic gneiss from the Paradise metasedimentary gneiss belt in the Hawke River terrane, yielded a range of ages between 1647 and 1627 Ma from seven single zircon analyses. The zircons in the metasedimentary gneiss are interpreted as detrital because of their variation in morphology, the range of ages obtained, and their extreme variation in U content. A detrital origin implies that the sedimentary protolith must have been deposited after 1627 Ma, and is therefore not the same age as morphologically similar metasedimentary gneiss that occurs as enclaves within pre-1670 Ma migmatized quartz diorite. The timing of the post-1627 Ma high-grade metamorphic event that subsequently affected the gneiss is not known. It is unlikely to have been Grenvillian, as other evidence denies the likelihood that the Hawke River terrane was affected by more than moderate Grenvillian metamorphism. Using the emplacement ages of the minor intrusions, coupled with previous U–Pb dating and unequivocal field relationships, the following history is proposed. An early (northward subduction?) event, which possibly should be defined as being pre-Labradorian, occurred at ca. 1710 Ma and included distal magmatism in the Makkovik Province. There were two short-lived, closely related calc-alkaline plutonic events at 1677 and 1670 Ma, then mafic dyke injection and migmatization. These events are interpreted to reflect the times of rapid island-arc formation (over a southward-dipping subduction zone) from a mantle reservoir having a chondritic isotopic signature. After local granitoid emplacement at 1663 Ma (succeeded by further mafic dyke injection and then megacrystic dyke injection at 1660 Ma?), there was a widespread, major felsic magmatic event at ca. 1650 Ma. This was followed by another phase of mafic dyke injection and amphibolite facies metamorphism, which ended by ca. 1646 Ma. These events are interpreted to record the time of accretion of the island arcs to proto-Laurentia. A final Labradorian felsic magmatic event occurred between 1632 and 1622 Ma and is considered to be related to postcollisional anatectic plutonism and crustal thickening. This crustal thickening resulted in erosion that led to the deposition and burial of sediments in the Paradise metasedimentary belt.
Geological Survey of Canada's contributions to understanding the composition of glacial sediments
Authors: Shilts W. W.
Published: April 2011

Drift compositional studies were initiated at the Geological Survey of Canada (GSC) in the mid-1960's in projects that drew heavily on the technology and approaches developed in Fennoscandia over the previous century. As this research progressed and expanded in the 1970's, its Fennoscandian character diminished and, like the geochemical exploration research program that it closely paralleled, drift prospecting began to acquire a distinctly Canadian character, imposed by the geographical and logistical constraints of climate and asymmetric population distribution. GSC research has increasingly focused on understanding and explaining the geochemical expression of the mineralogical composition of glacial sediments that are unaltered or only slightly altered by postdepositional weathering. Because glacial sediments are generated largely by crushing and abrasion, their various mineral and lithological components attain characteristic size modes based on physical properties such as cleavage and hardness. This size sorting by physical properties is expressed geochemically by chemical partitioning in various size ranges. Also, the crushing process disaggregates fresh bedrock and incorporates all of its mineral components, labile as well as stable, into glacial sediment. GSC research has concentrated on the best ways to sample and analyze drift to avoid the compositional size bias and potential weathering alterations of labile minerals, so that geochemical analyses truly representative of provenance may be attained. As it has become possible to filter provenance signals from noise generated by weathering, partitioning, sediment facies misidentification, and stratigraphic variations, the principles of glacial dispersal of components of economic and environmental significance have been clarified and dispersal patterns mapped.
Stratigraphy and floristics of Eocene swamp forests from Axel Heiberg Island, Canadian Arctic Archipelago
Authors: Greenwood David R. , Basinger James F.
Published: April 2011

A record of polar Eocene forests is preserved as in situ tree-stump fields and leaf-litter mats in Buchanan Lake Formation sediments on Axel Heiberg Island, in the Canadian Arctic Archipelago. Stratigraphic examination at the centimetre to metre scale of peat–coal lithology and macrofossil floristics in two levels of these fossil forests reflects small-scale changes in forest composition and swamp hydrology horizontally and temporal variation vertically. Root system structure and tree base stratigraphy suggest that exposed tree stumps may not include only coeval individuals of a single forest stand, but rather also individuals representing different phases of the forest through one cycle of the hydrological development of this Eocene polar forest community. Earlier calculations of stand density and biomass, based upon the assumption that all stumps represent coeval trees, may therefore be greatly overestimated. A mosaic of Alnus – fern bog, mixed coniferous community, and taxodiaceous (Metasequoia–Glyptostrobus) swamp appears to have produced both the leaf mats and the in situ stumps, with the taxodiaceous swamp the dominant peat-accumulating phase.
Source and timing of gold and other mineralization in the Red Lake area, northwestern Ontario, based on lead-isotope investigations
Authors: Gulson Brian L. , Mizon Karen J. , Atkinson Brian T.
Published: April 2011

The problems of the timing and source of gold mineralization and the sulfidation mechanism in the Red Lake area, north-western Ontario, have been addressed using more than 300 Pb-isotope analyses of more than 250 samples of sulfides, oxides, gold, and potential source rocks. Base metals and some gold from the Campbell and Dickenson mines are interpreted to have been mainly derived from the mafic–intermediate and felsic volcanic rocks of the lower sequence at ca. 2865 Ma, the model age calculated for samples of gold, chalcopyrite, pyrite, and galena. Other samples of gold are considered to have formed at younger ages, perhaps at ca. 2700 Ma. Differences in isotopic patterns for deposits in possibly different deformation zones but hosted by rocks of the same age and composition, e.g., Campbell–Dickenson, McFinley, Cochenour Willans, are interpreted to mean that some of the deposits formed at different times or from different sources or both (i.e., by multistage processes). The older period of gold mineralization is supported by a 2865 ± 10 Ma Pb–Pb isochron age (mean square of weighted deviates (MSWD) 2.9) for Cu–Ni and Fe sulfides and a similar model age for pyrite from the Bridget Lake prospect in the western sector. Younger mineralization at ca. 2700 Ma is represented by, for example, disseminated sulfides in the Dome stock, Balmer Lake arsenopyrite, the Red Summit mine in the Red Crest stock, sulfides and gold from the McFinley mine, and the model age for the Abino galena. A well-constrained Pb–Pb line for magnetites, mainly from 2700–2730 Ma felsic intrusions, gives an apparent age of 2660 ± 10 Ma (MSWD 3.7). This event may represent late-stage hydrothermal activity. Analyses of gold grains yield very complex isotopic patterns possibly because of remobilization and the very low contents of Pb in the gold grains. In environments such as Red Lake, Pb-isotope analyses of gold appear to give unreliable estimates of genesis and timing.
Conodont biofacies and taphonomy along a carbonate ramp to black shale basin (latest Devonian and earliest Carboniferous), southernmost Canadian Cordillera and adjacent Montana
Authors: Savoy Lauret E. , Harris Anita G.
Published: April 2011

Uppermost Devonian – lowermost Carboniferous strata in the southernmost Canadian Cordillera and adjacent Montana record the onset and termination of low-oxygen conditions in carbonate-dominated epicontinental and shelf seas. Several distinct conodont biofacies representative of shallow-ramp to deep-basin settings are recognized on the basis of conodont distribution and preservation patterns.During early and middle Famennian time, the region was the site of a westward-deepening carbonate ramp (Palliser Formation) that was bordered to the west by a deep, shale basin (Lussier syncline strata). Palliser carbonates contain low-diversity conodont faunas of indigenous to transported Palmatolepis-, Polygnathus-, and Apatognathus-dominated assemblages. Basinal deposits yield a pelagic palmatolepid biofacies. Middle to late Famennian time was marked by termination of carbonateramp sedimentation and flooding of the margin with oxygen-depleted water. Deposition of organic-rich facies began in the expansa Zone in shelf to basin environments (Exshaw Formation and correlative units). These deposits contain indigenous pelagic Palmatolepis- and (or) Bispathodus-dominated assemblages; reworked or transported fragments are primarily polygnathids and icriodontids.Sedimentation of anaerobic to aerobic, deep-water, lower Banff facies occurred intermittently until middle Tournaisian and, locally, late Tournaisian time prior to westward progradation of younger carbonate deposits. Middle Tournaisian biofacies include transported and indigenous assemblages of siphonodellids (deep–middle ramp). Late Tournaisian biofacies parallel lithofacies changes associated with shallowing of the Banff sequence and are characterized by scaliognathid–doliognathid (basin to deep ramp), polygnathid and polygnathid–bactrognathid (deep to middle ramp), and bactrognathid–hindeodid (middle to shallow ramp) indigenous and displaced biofacies. The spatial relations of these Famennian and Tournaisian biofacies are generally consistent with models developed for correlative strata elsewhere.
The reappearance of the Huronian in Wyoming: rifting and drifting of ancient continents
Authors: Roscoe S. M. , Card K. D.
Published: April 2011

Striking stratigraphic and sedimentological similarities between the Early Proterozoic Huronian Supergroup of the Canadian Shield and the Snowy Pass Supergroup of Wyoming suggest that they were deposited in a single, broad, epicratonic basin developed atop a large Archean continent that included the Superior and Wyoming geological provinces. Breakup of the continent after the 2.2 Ga intrusion of widespread gabbro sheets and dykes resulted in the separation of the Archean Superior and Wyoming cratons and their Early Proterozoic covers. These crustal fragments were subsequently reassembled during Early Proterozoic (~1.85 Ga) orogenesis, the end result being the present 2000 km separation of the Huronian and Snowy Pass supergroups and their Archean basements.
The deep structure of the Grenville Front: a new perspective from western Quebec
Authors: Kellett R. L. , Barnes A. E. , Rive M.
Published: April 2011

The Grenville Front is a major tectonic boundary exposed on the Canadian Shield. The front is defined as the northwestern limit of Grenvillian deformation, on the basis of geochronological and metamorphic data. This boundary is also evident in some geophysical data sets. The Lithoprobe Abitibi–Grenville transect crosses the Grenville Front near Lac Témiscamingue in western Quebec. A new 114 km long deep seismic reflection line shows a crustal structure quite different from that seen on previous surveys across the Grenville Front. The Archean foreland (Pontiac Subprovince) has a pattern of reflectivity similar to that seen in most of the Superior Province. This pattern continues for some 30 km south of the surface exposure of the Grenville Front. There is no evidence for a band of dipping reflectors truncating the horizontal Pontiac reflectors; in fact, the leading edge of the Grenville Province is difficult to identify on the seismic section. The Moho is well defined and reveals that the crust thins under the Grenville Front. The magnetotelluric survey shows that the upper crust is resistive across the entire profile, but the resistivity is higher within a Grenvillian allochthonous terrane at the southern end of the profile. The mid-crustal low-resistivity layer and the upper mantle electrical anisotropy are also continuous across the Grenville Front. The Grenville Front is highly variable in its character along the Grenville Orogen, and this character may be strongly controlled by the nature of the foreland to the northwest.
Geochemical and isotopic (Nd, O, and Pb) constraints on granite sources in the Humber and Dunnage zones, Gaspésie, Quebec, and New Brunswick: implications for tectonics and crustal structure
Authors: Whalen Joseph B. , Jenner George A. , Hegner Ernst , Gariépy Clément , Longstaffe Frederick J.
Published: April 2011

Siluro–Devonian granitoids span a wide compositional range (~50–76% SiO2) and can be subdivided into two groups: (i) monzonitic or incompatible element enriched with affinities to within-plate magmatism (WPG); and (ii) calc-alkalic or incompatible element depleted with supra-subduction zone affinities (VAG). Granitoid εNd(T = 0.4 Ga) values range from −1 to +5.5; most lie between +3 and +5.5. 207Pb/204Pb isotopic compositions range from 15.52 to 15.61; most fall between ~15.55 and 15.59. Most δ18O values lie between +5.5 and +8‰. No well-established trends exist between SiO2 and isotopic composition, and isotopic compositions do not differ between the two trace element defined granitoid groups.Though Pb isotopic data are consistent with a major contribution to the granitoids from Proterozoic-aged Laurentian plate rocks (i.e., Grenville basement), Nd and O isotopic data are not. These isotopic data are consistent with major source components derived from early Paleozoic depleted or supra-subduction zone affected mantle and (or) crustal rocks derived from the early Paleozoic mantle(s). These protoliths would not have seen significant interaction with time-integrated old crustal material or surficial processes. Granitoid Pb isotopic data can be reconciled with an early Paleozoic mantle–crust origin, but it may also be that the Pb isotopes are decoupled from other isotopic systems. In either case, Nd and O isotopic data clearly prohibit the involvement of significant amounts of Grenville crust and suggest that seismic-reflection data do not define crustal blocks, or at least not blocks having a tectonic and geologic history easily related to the surface geology.
Le bivalve Montanaria Spriestersbach, 1909: habitat et morphologie d'une nouvelle espèce emsienne de la Formation de York River de Gaspé, Québec
Authors: Desbiens Sylvain
Published: April 2011

A new Emsian species of the Rhenish bivalve Montanaria Spriestersbach, 1909 is described from specimens that were collected in the York River Formation, Gaspé area. It is reported for the first time in America. This endobenthic species, M.honquedoensis n.sp., developed communities in areas of fine sand embayments or in brackish lagoons related to a sedimentation in a deltaic environment. The acidic benthos in which it lived corroded deeply the beak in the mature population. The diffusion of Montanaria towards Gaspé is explained by the restricted dimension of the Emsian Iapetus Ocean, and it coincides with the bivalve migration, from the western Europe to the northeast of North America, from Early to Middle Devonian. The monogenic family of Montanariidae is revised and its taxonomic affiliation is discussed. The dental and ligamental features of Montanaria indicate an intermediate level of organization between primitive actinodontoids and heterodonts. [Journal Translation]
Postglacial vegetation history of the Mariana Lake region, Alberta
Authors: Hutton M. J. , MacDonald G. M. , Mott R. J.
Published: April 2011

A fossil pollen record extending from 11 300 BP to the present was recovered from Mariana Lake, Alberta (55°57′N, 112°01′W). Initially, the region had a sparse vegetation dominated by forbs and graminoids, which at approximately 10 500 BP succeeded to Picea glauca forest. Picea mariana – Sphagnum peatlands began to develop between 10 000 and 9500 BP. After 9000 BP Sphagnum-dominated sites decreased; P. glauca declined while Betula increased. From 7500 to 5500 BP Populus reached its maximum Holocene representation in the vegetation. Sphagnum-dominated peatlands almost disappeared. The changes following 9000 BP were likely caused by increased aridity. However, the presence of P. mariana, Abies, and Larix in the pollen record suggests that mesic sites remained. Beginning at 6500–6000 BP the extent of Sphagnum peatlands began to increase. Abies declined in importance following 5000 BP, possibly due to paludification of mesic sites. The expansion of parkland into central Alberta during the mid-Holocene did not extend to Mariana Lake. However, Mariana Lake records changes in vegetation resulting from increased aridity in the early to mid-Holocene which are not apparent at more northerly sites in Alberta.
Inversion of the Proterozoic Wernecke basin during tectonic development of the Racklan Orogen, northwest Canada
Authors: Mitchelmore Marlene Dredge , Cook Frederick A.
Published: April 2011

New deep seismic reflection data coupled with regional stratigraphic correlations, drill-hole information, and potential field data are interpreted to provide images of Middle Proterozoic Wernecke Supergroup (meta-)sedimentary layers that were uplifted during tectonic development of the ca. 0.9–1.3 Ga Racklan Orogen in Canada's western Northwest Territories. The reflection data are located at the eastern front of the Mackenzie Mountains portion of the Canadian Cordillera and on the western flank of the Fort Simpson structural trend that is a prominent Proterozoic structure in the subsurface throughout the region. Along three parallel profiles, layers that are correlated with thick Wernecke Supergroup sedimentary rocks produce prominent reflections between about 3.0 and 9.0 s (about 7.5 and 23 km) that were arched prior to deposition of younger Proterozoic (probably Mackenzie Mountains Supergroup) and Phanerozoic sedimentary rocks. The strata are considered to be Wernecke basin sedimentary rocks that were uplifted during deformation associated with the development of the Racklan Orogen.
Luminescence dating of sediments from Buctouche Spit, New Brunswick
Authors: Ollerhead Jeff , Huntley D. J. , Berger Glenn W.
Published: April 2011

In this paper we describe our efforts to determine the formation chronology of a sequence of dunes on Buctouche Spit, a Holocene deposit on the northeast coast of New Brunswick. Optical dating, using infrared stimulation of K-feldspar grains, yielded ages ranging from 5 ± 30 a for an embryo dune to 765 ± 45 a for the oldest dune. Thermoluminescence ages, although less precise, support the recent formation of the dunes. The ages exhibit the expected sedation from youngest to oldest and are consistent with historical evidence coupled with an assumed constant sediment aggradation rate. The age resolution obtained was very good and we conclude that the optical dating method used here shows great promise.
Evidence for the Two Creeks interstade in the Lake Huron basin
Authors: Larson Grahame J. , Lowell Thomas V. , Ostrom Nathaniel E.
Published: April 2011

New radiocarbon age dates for the Cheboygan bryophyte bed in northern lower Michigan indicate that the bed was not deposited during the Mackinaw interstade, as was previously proposed, but is correlative to the Two Creeks forest bed deposited during the Two Creeks interstade approximately 11 850 BP. Furthermore, the till overlying the bryophyte bed does not represent continuous deposition by ice throughout the Two Creeks interstade, as proposed by others, but represents deposition during the Greatlakean stade. A major implication resulting from the reassignment of the age of the Cheboygan bryophyte bed is that the Straits of Mackinac could have been ice free during the Two Creeks interstade and that during that time the Kirkfield phase of glacial Lake Algonquin may have extended into the Lake Michigan basin.
Modelling of permafrost thickness during the late glacial stage in France: preliminary results
Authors: Lebret P. , Dupas A. , Clet M. , Coutard J.-P. , Lautridou J.-P. , Courbouleix S. , Garcin M. , Levy M. , Vliet-Lanoë B. Van
Published: April 2011

Research on permafrost in France has concentrated on field evidence of fossil permafrost and the mapping of its possible distribution. Few attempts have been made to estimate permafrost thickness. Studies devoted to this subject in North America and Siberia have shown that permafrost may be very thick (several hundred metres), may be rapidly laid down (in < 2000 years in northwest Canada) and causes complex water flow patterns between the base of the permafrost and the soil surface. Using the "Gelsol" code developed by the Laboratoire central des ponts et chaussées (Central Laboratory of the French Department of Public Works) for geotechnical purposes, this paper presents the first results of modeling permafrost development at depth. These preliminary tests show the influence of parameters such as mean annual ground temperature, heat flow, thermal conductivity related to lithology, and water content of the rocks involved on permafrost depth during the last glacial cycle (Weichselian). The results from simple cases indicate that the permafrost was from ten of metres to over 300 m thick. Although these are only calculated values, they are much higher than the few figures found in the literature, and must betaken into consideration when searching for fossilized traces of deep permafrost.
Gravity, flexure, and the deep structure of the Grenville Front, eastern Quebec and Labrador
Authors: Hynes Andrew
Published: April 2011

The Grenville Front in eastern Quebec and southern Labrador is characterized by a large negative Bouguer gravity anomaly with flanking highs. Forward flexural modelling of this anomaly provides constraints on the deep structure of the eastern Grenville. The Grenville Front is assumed to mark the surface trace of a boundary between less dense crust to the northwest and more dense crust to the southeast, with constant dip all the way to the Moho. An end load is applied to the northwestern plate to simulate the effect of orogenic and (or) subsurface loads, but is then removed underneath a continuous plate to simulate the transient nature of the load. This simple model yields good fits to the gravity anomaly, provided the effective elastic thickness of the lower plate is less than about 30 km and the crustal boundary dips at about 20°. The deep structure of the eastern Grenville Front may therefore be dominated by a major shallow-dipping straight thrust. The applied end loads for the best-fitting models are only a few tens of kilometres southeast of the Grenville Front. This may reflect the former presence of allochthonous crust at and near the present Grenville Front in the eastern Grenville, or delamination of the lithospheric mantle of the northern plate from its overlying mantle, which could also be responsible for the low modelled elastic thicknesses. The absence of a similarly pronounced gravity anomaly in the western Grenville may reflect a lower orogenic load, as evidenced by the absence of a fold-and-thrust belt there, and a steeper dip for the crustal boundary.
Archean, deep-marine, volcanic eruptive products associated with the Coniagas massive sulfide deposit, Quebec, Canada
Authors: Doucet P. , Mueller W. , Chartrand F.
Published: April 2011

The mafic-dominated volcanic and related volcaniclastic sedimentary rocks, which host the Archean Coniagas Zn–Pb–Ag massive sulfide deposit, are inferred to be the result of submarine explosive and effusive eruptions at depths of approximately 1000 m, as suggested by the presence of volcaniclastic turbidites, the absence of wave-induced sedimentary structures, pillowed lava flows, the sulfide deposit itself, and the incipient arc setting. The rock assemblage includes massive, pillowed and brecciated, basaltic to andesitic flows, massive, andesitic to rhyodacitic lapilli tuffs, andesitic stratified lapilli tuffs, and bedded tuffs. Preserved fragments and delicate volcanic textures, such as angularity of clasts, chilled clast margins, and clast vesicularity, and sedimentary structures are consistent with a subaqueous hydroclastic origin for the volcaniclastic sedimentary rocks. Explosive degasification of magma and (or) lava, in conjunction with fragmentation due to the interaction of magma–water, or nonexplosive hydroclastic fragmentation can account for the observed characteristics in the volcaniclastic deposits.The 280 m thick Coniagas volcano-sedimentary succession, used to reconstruct the volcanic history of the deposit, records two explosive–effusive volcanic cycles. The initial stage of each cycle is envisaged to have commenced with a small fire fountain or boiling-over eruption. Transport and deposition of the fragmented debris along the flanks of the volcanic edifice is attributed to high-concentration particulate gravity flows. The massive lapilli tuffs are interpreted as laminar debris flows, whereas the stratified lapilli tuffs may reflect turbulent flow deposits. The bedded tuffs were produced during the waning eruptive stages or elutriated from high-concentration syneruption flows. Ingestion of water, causing hydroclastic fragmentation, occurred during the eruptive and (or) the transport process. Calm, effusive mafic volcanism, characterized by massive, pillowed and brecciated flows and reworked counterparts, terminates each volcanic cycle. The massive, felsic lapilli tuffs, which host the mineralization, are inferred to represent locally reworked hydroclastic products of explosive or nonexplosive origin. The Coniagas mine deposit may serve as a guide for future exploration of small Archean volcanic-hosted massive sulfide deposits with a restricted alteration halo.
Occurrences of pseudotachylyte at the East Bull Lake and Shakespeare–Dunlop intrusions, Ontario, Canada
Authors: Chubb P. T. , Vogel D. C. , Peck D. C. , James R. S. , Keays R. R.
Published: April 2011

Pseudotachylyte bodies were recently identified within and adjacent to the Early Proterozoic East Bull Lake and Shakespeare–Dunlop intrusions, located approximately 25–40 km west-southwest of the western margin of the Sudbury Igneous Complex. These breccia-like bodies locally form extensive vein networks and are preferentially developed along the contact between the intrusions and older Archean granitoid rocks. The pseudotachylyte veins comprise variable proportions of locally derived rock fragments and an aphanitic to fine-grained crystalline matrix that commonly displays flow textures. The veins appear to have formed by intense cataclasis and (or) frictional melting. These occurrences are very similar in appearance to Sudbury Breccia dykes that are observed at a radial distance of up to 80 km from the Sudbury Igneous Complex. Sudbury Breccia is widely believed to have formed as a result of the Sudbury event—a cataclysmic explosion that occurred at 1.85 Ga. The location of the pseudotachylyte veins described herein may coincide with one of the concentric bands of relatively intense Sudbury Breccia development observed to the north of the Sudbury Igneous Complex.
Provenance of igneous clasts in conglomerates of the Archaean Timiskaming Group, Kirkland Lake area, Abitibi greenstone belt, Canada
Authors: Legault Marc I. , Hattori Keiko
Published: April 2011

Four types of igneous clasts from Timiskaming conglomerates of the Kirkland Lake area are identified: calc-alkaline porphyry, trachyte (K2O + N2O > 7.25 wt.%), trondhjemite, and tholeiitic basalt. Clasts derived from quartz–carbonate veins and carbonatized porphyries and komatiites indicate CO2-rich hydrothermal activity along the Larder Lake – Cadillac Fault before sedimentation. Calc-alkaline porphyry, the predominant clast, is similar in appearance to feldspar porphyry intrusions widely exposed in the area, but the two are not related. The porphyry clasts are cogenetic with diorite–granodiorite intrusions and volcanic rocks of the greenstone belt. Andesite clasts are only observed near the base of the assemblage, and the ratio of basalt to andesite increases up stratigraphic sections. The change suggests progressive erosion of arc-related volcanic rocks during sedimentation. Composition, texture, and mineralogy of the trondhjemite clasts are consistent with their derivation from the marginal phases of the Round Lake batholith. Intrusive rocks of the Timiskaming Group (coarse-grained holocrystalline syenitic–monzonitic rocks, biotite-bearing feldspar porphyries, and mica-rich lamprophyres) were not observed in the clasts, which suggests sedimentation prior to unroofing of these rocks. Sedimentation of the conglomerates postdated unroofing of underlying plagioclase porphyry (~2685 Ma), but predated unroofing of Timiskaming intrusions. The distribution of alkaline clasts only in proximity to the fault implies that alkaline magmatism was confined along the fault. Derivation of clasts from both sides of the fault and proximity of inferred sources support a pull-apart basin for sedimentation with minor strike-slip movement during and after the sedimentation.
U–Pb geochronology of late Neoarchean tonalites in the Flin Flon Belt, Trans-Hudson Orogen: surprise at surface
Authors: David J. , Syme E. C.
Published: April 2011

The Flin Flon volcanic belt of the Trans-Hudson Orogen in northern Manitoba comprises magmatic rocks (1.88 – 1.90 Ga) generated in an intra-oceanic arc and identified as one of the best examples of juvenile Paleoproterozoic crust. In the Flin Flon – Athapapuskow Lake area, the belt consists of a series of fault-bounded blocks, each having distinct stratigraphic and magmatic affinities, juxtaposed to form an accretionary collage. Two tonalitic bodies within the Northeast Arm shear zone, a major deformation corridor separating two of the most important blocks in the area, have been dated by the U–Pb zircon method at [Formula: see text] and [Formula: see text]. These results indicate the presence of fragments of late Neoarchean crust within the Flin Flon belt, possibly related to ca. 2.5 Ga granitic bodies found in terranes beyond the western limit of the belt. The presence of ca. 2.5 Ga tonalites within the Flin Flon Belt, herein reported for the first time, has major implications for basement involvement in the early tectonic evolution of the Flin Flon Belt.
A new heteromyid rodent (Mammalia) from the Barstovian (Miocene) of Saskatchewan
Authors: Korth William W.
Published: April 2011

A new species, Harrymys canadensis, referable to the Harrymyinae (Heteromyidae), is described from the Barstovian Wood Mountain Formation of Saskatchewan. The genus Stratimus Korth et al. is included in the heteromyid subfamily Harrymyinae. Harrymys canadensis is the youngest species of the subfamily and is more derived than Stratimus or the Hemingfordian species of Harrymys. The Harrymyinae may be derived from the latest Arikareean Proheteromys matthewi Wood.