bluuebunny/crossref_metadata_2025 huggingface dataset:
Végétation et fluctuations climatiques postglaciaires sur la côte septentrionale gaspésienne, Québec
Authors: Marcoux Nancy , Richard Pierre J. H.
Published: April 2011

The postglacial (ca. 13 000 BP) vegetational and climatic history is reconstructed from the pollen analytical study of the sediments of two lakes located in coastal northern Gaspé Peninsula. J'Arrive Lake (altitude: 56 m) was submerged by the Goldthwait Sea until about 11 400 BP. Euloge Lake, 83 m in altitude and less than 1 km from the shore, escaped the marine invasion. Before 10 400 BP, the vegetation, very scarce at first, evolved to a herb tundra that lasted for over a millenium. A cold climatic oscillation correlative with the Younger Dryas is identified at both sites between 10 700 and 10 400 BP, during this herb tundra phase. After 10 400 BP, dwarf birch and willows colonized the sites, leading to a shrub tundra. The afforestation of the area began only around 9300 BP, with the late arrival of spruce and aspen. This phase was interrupted at 8650 BP by the upsurge of green alder, in response to another cold oscillation. Since 7250 BP, the present forested landscape finally developed in three steps, characterized by (i) a high diversity of forest species until 2500 BP, (ii) a loss of diversity until 1000 BP that favoured spruce and balsam fir, and (iii) an increase of heliophilous trees, shrubs, and herbs. These reconstructions contribute to the late-glacial palaeogeography of Eastern North America through the unravelling of conditions close to the retreating ice.
An Archean fold-thrust belt in the northwestern Abitibi Greenstone Belt: structural and seismic evidence
Authors: Lacroix S. , Sawyer E. W.
Published: April 2011

An integration of structural field data and Lithoprobe seismic reflection line 28 in the northwestern Abitibi Greenstone Belt (AGB) reveals a crustal-scale, south-to southwest-vergent thrusting event that developed "in sequence" above a shallowly (15°) north-dipping sole thrust at a mid-crustal level. Seismic reflector geometry above this décollement suggests a mid crust (6–20 km depth) dominated by low-angle thrusts with smooth trajectory ramps and culmination folds or antiformal stacks, similar to the structural style of neighbouring high-grade plutonic–gneissic (Opatica) and sedimentary (Pontiac) subprovinces. In contrast, low-to high-angle east–west-trending thrusts at the upper-crust greenstone belt level (6–9 km depth) are interpreted to be listric. They occur in two fault systems, the Chicobi and Taibi, that resemble "imbricate fan" systems. The contrasting structural geometry of the upper and mid crust is interpreted as variations in level through the thrust stack, and resembles Paleozoic mountain belts where the upper AGB would represent a ductile–brittle fold–thrust belt. However, the structural evolution of the AGB has been complicated by earlier intrusive–metamorphic contacts or set of thrusts beneath it, and (or) younger out-of-sequence thrusts with north-vergent backthrusts. Also, south-to southwest-vergent thrusts were reactivated, folded, and steepened during a younger dextral strike-slip event.
A seismic-reflection-based regional cross section of the southern Abitibi greenstone belt
Authors: Jackson S. L. , Cruden A. R. , White D. , Milkereit B.
Published: April 2011

Seismic reflection profiles from the southern Abitibi greenstone belt reveal four first-order subdivisions: (1) Between 0 and ~4.5 s, the upper crust is weakly reflective, with prominent local to laterally extensive reflections. (2) Between ~4 and ~9 s, the crust is strongly and heterogeneously reflective with laterally continuous reflections. (3) From ~9 to ~13 s, the crust is more homogeneously reflective and displays downward decreasing reflectivity. (4) Below ~13 s (Moho?) the upper mantle is weakly reflective. The upper layer may correspond to subgreenschist–greenschist-facies supracrustal rocks cut by low-angle shear zones and intruded by regional tabular batholiths; the middle layer, to ductiley deformed amphibolite-facies gneisses, granitoids, and (or) metasediments; and the lower layer, to more homogeneously deformed granulite-facies rocks. North-dipping, low-angle reflections extending beneath both diverse supracrustal assemblages and regional batholiths may represent structural detachments upon which both the supracrustal assemblages and batholiths were imbricated and translated southward. However, the preservation of regional low-pressure metamorphic rocks and the common para-autochthonous relationships between assemblages suggest that thrust-related vertical separations and the magnitude of crustal thickening were not large. Steeply dipping regional shear zones within the greenstone belt appear to disrupt subhorizontal reflections down to ~15 km and may represent late-tectonic strains, which were progressively concentrated into linear zones during continued north–south shortening. The crustal-scale structure determined from the seismic reflection profiles, combined with surface geology, is compatible with post-2.70 Ga north–south shortening accommodated by south-directed(?) thrusting in a thermally softened mid crust and by upright folding in the upper crust. This scenario is comparable to recently proposed models for the Paleozoic, high-temperature, low-pressure Lachlan fold belt of Australia.
Early Paleozoic chronology: a review in light of new U – Pb zircon ages from Newfoundland and Britain
Authors: Tucker R. D. , McKerrow W.S.
Published: April 2011

The time scale for the Cambrian through Early Devonian periods is revised using new U–Pb ages from volcanic and pyroclastic rocks in sequences that are stratigraphically well defined. A rhyolite flow from the latest Precambrian, dated at 551.4 ± 5.8 Ma, gives a maximum age for the base of the Cambrian (Phycodes pedum Zone) at Fortune Bay, Newfoundland. The age ranges of several Ordovician and Silurian series are now established to within 2–3 Ma based on stratigraphically controlled samples from Britain. A basal Llandeilo ash has an age of 460.4 ± 2.2 Ma; a basal Caradoc lava has an age of 456.1 ± 1.8 ± Ma; and K-bentonites from the latest Llandovery and latest Ludlow have ages of 430.1 ± 2.4 and 420.2 ± 3.9 Ma, respectively. Using other data from the literature, we interpolate the base of the Cambrian to be near 545 Ma, the base of the Ordovician as ca. 495 Ma, and the base of the Silurian as ca. 443 Ma. While we have a good estimate for the base of the Middle Devonian (at ca. 391 Ma), the base of the Devonian is less precise, probably around 417 Ma.
Nd–Sr isotope systematics of Nicola Group volcanic rocks, Quesnel terrane
Authors: Smith Alan D. , Brandon Alan D. , Lambert Richard StJ.
Published: April 2011

Volcanic rocks of the Nicola Group belong to an arc built on the western margin of the Quesnel terrane in the Late Triassic to Early Jurassic. Low-K – high-K compositional types define a Rb–Sr isochron of 222 ± 15 Ma with initial 87Sr/86Sr = 0.70367 ± 2. The corresponding Nd isotopic compositions of these samples (εNd(222 Ma) = +5.1 to +7.8) fall within the range for early Mesozoic island arcs. A comparable range of εNd(222 Ma) (+5.0 to +7.9) in picrite–shoshonite samples precludes generation of increasingly potassic magmas by progressive metasomatism of the mantle wedge alone. Source-region heterogeneity, possibly imparted by changes in the composition of subducted slab components or interaction with amphibole or phlogopite in the source remnant of an earlier (Permian) arc on the Quesnel terrane, is required to account for geochemical differences between these rock suites. Crustal contamination is severely limited from the high εNd values, such that continental basement now underlying the Quesnel terrane is likely an artifact of later terrane obduction.
Paleoproterozoic crustal history of the southwestern Grenville Province: evidence from Nd isotopic mapping
Authors: Holmden C. , Dickin A. P.
Published: April 2011

Nd isotopic mapping in the North Bay area of the Central Gneiss Belt, southwestern Grenville Province, has revealed the precise trend of a TDM model age line developed between the uplifted southern margin of the Archean Superior craton (TDM = 2.7 Ga) and a Paleoproterozoic allochthon (TDM = 1.9 Ga). Separating these two crustal blocks is a narrow zone of gneisses with intermediate TDM ages. These transitional gneisses are interpreted to reflect a remnant fault or ductile shear zone, of uncertain age, along which crustal material from both blocks mechanically mixed during their juxtaposition. Accordingly, the nature of the TDM line in the North Bay area is interpreted to be tectonic. In the Temiscaming area, widespread exposures of mature metasedimentary gneisses are shown by their TDM ages to be dominantly of Paleoproterozoic provenance. These results are consistent with the existing detrital zircon geochronology, inferring a maximum depositional age of ~1.7 Ga. The anorogenic chemistry of the North Bay orthogneiss and mixed calc-alkaline–alkaline chemistry of the Temiscaming gneisses suggest a connection between Paleoproterozoic anorogenic magmatism and synsedimentary quartzite deposition, which is a common association in 1.9–1.6 Ga accretionary orogens of southern Laurentia. The relatively close correspondence between widespread 1.9 Ga TDM ages and U–Pb crystallization ages as old as 1.74 Ga implies that rocks of the Central Gneiss Belt were originally the juvenile products of Paleoproterozoic orogenesis.
Paleomagnetism of the late Neoproterozoic Blueflower and Risky formations of the northern Cordillera, Canada
Authors: Park John K.
Published: April 2011

Paleomagnetic analysis of the Risky and underlying Blueflower formations at the top of the Neoproterozoic Windermere Supergroup in the northern Cordillera of Canada revealed several magnetic components of geological significance. Rock strata of the Blueflower locality in the Mackenzie Mountains yielded no primary remanence due to extensive "pyritization" and weathering. However, dolomitic rocks of the Risky locality in the eastern Wernecke Mountains, 250 km to the north, yielded a probable primary remanence. The remanence has a direction at D, I = 055°, −64° (N = 11 samples from 4 sites, k = 18, α95 = 11°) and pole at 007°E, 29°S (δp, δm = 14°, 18°), and indicates a paleolatitude of 46 ± 14°S. Comparison between poles from the Risky and the overlying Backbone Ranges and Ingta formations suggests a profound post-Risky unconformity. Three secondary components are also present. Component B in both the Blueflower and Risky units appears to be a thermal overprint, possibly related to Vendian rifting. Its respective direction in each unit is D, I = 062°, +77° (N = 4 sites, k = 143, α95 = 8°) and D, I = 064°, +56° (N = 6 sites, k = 21, α95 = 15°), yielding poles of 110°E, 64°S (δp, δm = 13°, 14°) and 142°E, 44°S (δp, δm = 15°, 21°). Component C, only found in the Risky, is attributed to Late Cambrian to Middle Ordovician extension and magmatism. Component D, which predominates in both formations, relates to late Mesozoic compression and to weathering.
Stratigraphy, diatom biofacies, and palaeogeomorphology of a mid Holocene distributary channel system, Fraser River delta, British Columbia, Canada
Authors: Hutchinson Ian , Roberts Michael C. , Williams Harry F. L.
Published: April 2011

A buried distributary channel system that delivered sediment to the currently inactive southern front of the Fraser River delta during the mid Holocene is described from 32 vibracores and 403 core logs. Sedimentary properties in core and cone logs as well as fossil diatom assemblages were used to distinguish channel fill from associated deltaic facies (overbank deposits, tidal flats, and peat bogs). Active-channel fill fines upwards from a coarse base into medium-fine sand capped by thin silt beds. It contains a sparse diatom assemblage dominated by heavily silicified freshwater planktonics. The channel fill deposited during the period of diminishing flow consists of silt with thin sandy interbeds deposited during flood events. Diatoms are abundant in these deposits. The diatom biofacies is dominated by sessile freshwater species at upstream sites and by brackish-marine species at channel mouths. The transition to organic-rich silt and peat and an aerophile diatom assemblage marks channel abandonment. The palaeochannel was 500–800 m wide and 18 m deep, slightly smaller than the present main distributary channel of the Fraser River. Calibrated radiocarbon ages suggest that the palaeochannel was active from around 8000 to 6000 BP and was finally abandoned by 5000 BP.
40Ar/39Ar geochronological evidence for multiple postmetamorphic hydrothermal events focused along faults in the southern Abitibi greenstone belt
Authors: Powell W. G. , Hodgson C. J. , Hanes J. A. , Carmichael D. M. , Mcbride S. , Farrar E.
Published: April 2011

Thermal histories in the Abitibi and Pontiac subprovinces vary for three general domains: (1) zones of impermeable rock with cooling rates of >8 °C/Ma; (2) zones of impermeable rock that are spatially associated with monzogranite plutons, with apparent cooling rates of 1–2 °C/Ma; and (3) permeable high-strain zones with apparent cooling rates of <l °C/Ma. Evidence for multiple hydrothermal events in fault zones includes (1) most age spectra having a disturbed form; (2) concave-down spectra for samples from subgreenschist-facies faults, indicating multiple episodes of white mica growth; (3) Cr-muscovite from a greenschist-facies segment of the Larder Lake–Cadillac fault yielding a plateau age of 2543 ± 8 Ma, postdating regional metamorphism by 120 Ma; (4) two discrete ages for postmetamorphic amphibole from the Larder Lake–Cadillac fault (2578 ± 10, 2421 ± 15 Ma); and (5) two discrete dates for white mica (2414 ± 9, >2594 Ma) from the volcanogenic massive sulphide-related sericite alteration, with the coarser mica yielding the younger date. Based on radiometric dating, impermeable rocks were affected weakly by postmetamorphic hydrothermal events. Minerals in zones of higher permeability were reset during the intrusion of monzogranite plutons. Highly permeable zones, such as the Larder Lake–Cadillac and Porcupine–Destor faults, were overprinted repeatedly. This produces a drawn-out series of dates from minerals with varying closure temperatures. Radiometric ages from fault zones, or ore deposits, cannot be used to interpret the cooling history and evolution of the Abitibi belt as a whole.
Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec
Authors: Powell W. G. , Carmichael D. M. , Hodgson C. J.
Published: April 2011

Regional metamorphism, ranging in grade from the subgreenschist-facies to the greenschist–amphibolite-facies transition, affects all Archean supracrustal rocks (>2677 Ma) in the Rouyn–Noranda area. Contact metamorphic minerals associated with the posttectonic Preissac–Lacorne batholith (2643 Ma) show no evidence of a regional retrograde event. Accordingly, the age of regional metamorphism can be bracketed between 2677 and 2643 Ma. Three reaction isograds were mapped in subgreenschist-facies metabasites, dividing the low-grade rocks into three metamorphic zones: the pumpellyite–actinolite zone, the prehnite–pumpellyite zone, and the prehnite–epidote zone. In addition, the pumpellyite–actinolite–epidote–quartz bathograd, corresponding to a pressure of approximately 200 MPa, occurs on both sides of the Porcupine–Destor fault. Low-pressure regional metamorphism is also indicated both by the occurrence of an actinolite–oligoclase zone, and the persistence of pre-regional-metamorphic andalusite. The coincidence of andalusite and the actinolite-oligoclase zone indicates that pressure was <330 MPa at the greenschist-amphibolite transition. The geothermal gradient during metamorphism was approximately 30 °C/km. Regionally, isograds dip shallowly to the north and trend subparallel to lithological and structural trends. Metamorphic minerals in metabasites define tectonic fabrics only near major fault zones and in zones of CO2 metasomatism. In biotite zone metasedimentary rocks the schistosity is defined by mica and amphibole. These textures indicate that metamorphism and fabric development were coeval. However, the actinolite–epidote isograd cuts the Porcupine–Destor fault, indicating that regional metamorphism postdates movement along this fault. The strong fabrics associated with the Porcupine–Destor and Larder Lake–Cadillac faults must have developed through a process dominated by flattening strain.
Phylogenetic analysis of some Silurian rostroconchs (Mollusca) from northwestern Canada
Authors: Caldwell Michael W. , Chatterton Brian D. E.
Published: April 2011

The new genus Avalanchia and the new species Avalanchia pterocarina, Cassowarioides anisomorpha, Cassowarioides polgari, Nehedia bergeraci, Nehedia restricta, and Nehedia tricarina are proposed from exceptionally preserved silicified faunas. Two new but unnamed rostroconch species are also described. These conocardioid rostroconchs were collected from Silurian deposits (late Llandovery to early Ludlow) near Avalanche Lake in the Mackenzie Mountains, Northwest Territories, Canada, and, when added to global rostroconch faunal lists, indicate a previously unrecognized diversity of Silurian conocardioid rostroconchs. The morphology of conocardioid rostroconchs is discussed, and a glossary of terms presented. Sexual dimorphism is recognized in species of Cassowarioides. Phylogenetic analysis of hippocardiids and bransoniids supports the monophyly of several genera. The hippocardiid genus Bigalea Pojeta and Runnegar, 1976, is recognized as paraphyletic and three species are assigned to a new genus, Redstonia. Preliminary analysis of bransoniids and hippocardiids for familial relationships, using data sets from the within-family analyses, indicates that the Bransoniidae is polyphyletic. The generic complex Mulceodens, considered to be derived bransoniid, is consistently reconstructed within a clade of derived hippocardiids.
Synsedimentary collapse of portions of the lower Blomidon Formation (Late Triassic), Fundy rift basin, Nova Scotia
Authors: Ackermann Rolf V. , Schlische Roy W. , Olsen Paul E.
Published: April 2011

A chaotic mudstone unit within the lower Blomidon Formation (Late Triassic) has been traced for 35 km in the Mesozoic Fundy rift basin of Nova Scotia. This unit is characterized by highly disrupted bedding that is commonly cut by small (<0.5 m) domino-style synsedimentary normal faults, downward movement of material, geopetal structures, variable thickness, and an irregular, partially faulted contact with the overlying unit. The chaotic unit is locally overlain by a fluvial sandstone, which is overlain conformably by mudstone. Although the thickness of the sandstone is highly variable, the overlying mudstone unit exhibits only gentle regional dip. The sandstone unit exhibits numerous soft-sediment deformation features, including dewatering structures, convoluted bedding, kink bands, and convergent fault fans. The frequency and intensity of these features increase dramatically above low points at the base of the sandstone unit. These stratigraphic relations suggest buried interstratal karst, the subsurface dissolution of evaporites bounded by insoluble sediments. We infer that the chaotic unit was formed by subsidence and collapse resulting from the dissolution of an evaporite bed or evaporite-rich unit by groundwater, producing dewatering and synsedimentary deformation structures in the overlying sandstone unit, which infilled surface depressions resulting from collapse. In coeval Moroccan rift basins, facies similar to the Blomidon Formation are associated with halite and gypsum beds. The regional extent of the chaotic unit indicates a marked period of desiccation of a playa lake of the appropriate water chemistry. The sedimentary features described here may be useful for inferring the former existence of evaporites or evaporite-rich units in predominantly clastic terrestrial environments.
A Grenville-age layered intrusion in the subsurface of west Texas: petrology, petrography, and possible tectonic setting
Authors: Kargi Hulusi , Barnes Calvin G.
Published: April 2011

The Nellie intrusion is a thick (more than 4420 m) mafic to ultramafic layered intrusion with a radiometric age of ~1163 Ma. Rock types change abruptly with stratigraphic height and include norite, pyroxenite, gabbronorite, hornblende gabbro, gabbro, anorthosite, harzburgite, and lherzolite. Norite is most abundant, but gabbro and hornblende gabbro are locally abundant. Rare olivine-rich layers are also present. The general order of crystallization was olivine, orthopyroxene, plagioclase + clinopyroxene, and hornblende. Mg#'s, expressed as 100 Mg/(Mg + Fe), range from 76.3 to 85.8 for olivine, 56.7 to 84.9 for orthopyroxene, 62.5 to 90.3 for clinopyroxene, and 52.4 to 82.8 for amphibole. Mg#'s vary with height and display abrupt reversals, which indicate open-system addition of new mafic magma. Eleven cyclic units were identified on the basis of evidence for injection of basaltic magma; these can be grouped into three megacyclic units. The abundance of orthopyroxene, and mineral compositional evidence for Fe enrichment within cyclic units, indicates that parental magmas were subalkaline and tholeiitic. Plagioclase in equilibrium with olivine ranges from An65 to An46, which precludes an arc-related magma source. Although the intrusion is approximately coeval with Keweenawan magmatism and with emplacement of diabasic dikes in western North America, it is dissimilar in detail to both suites of rocks. Nevertheless, its composition and geophysical setting are consistent with emplacement in an extensional tectonic environment.
Pliocene–Pleistocene genesis for the Murray Brook and Heath Steele Au–Ag gossan ore deposits, New Brunswick, from paleomagnetism
Authors: Symons D. T. A. , Lewchuk M. T. , Boyle D. R.
Published: April 2011

Several Au–Ag gossans occur over massive sulphide deposits in the Ordovician Tetagouche Group near Bathurst, New Brunswick. The Murray Brook and Heath Steele B zone goethite gossans were about 45 and 15 m thick, respectively, prior to mining. They contain no minerals suitable for radiometric age dating. Geologically they must be younger than the Devonian Acadian orogeny and older than the last glaciation. Paleomagnetic methods were used to analyse specimens from 29 sites, mostly from ore on the pit walls. Host rocks and sulphide mineralization retain characteristic remanent magnetization directions in magnetite and pyrrhotite with a variety of directions that include possible Devonian overprints. Fertile and barren gossan specimens at 21 sites retain antiparallel normal and reversed A characteristic remanence components in goethite and (or) hematite. The A direction is D = 357.7°, I = 61.7 °(α95 = 4.5°, k = 31). Its pole of 134.2°E, 85.2°N (dp = 5.4°, dm = 7.0°) falls on the North American apparent polar wander path and circumscribes the Earth's present rotational axis, indicating that the gossans formed during the Pliocene–Pleistocene. Examination of the site locations in the pits, along with the remanence polarity of their goethite and hematite A components, suggests the gossans formed during Chrons 1 and 2 only, or in the past 2.3 ± 0.3 Ma.
Geological development of eastern Humber and western Dunnage zones: Corner Brook–Glover Island region, Newfoundland
Authors: Cawood Peter A. , van Gool Jeroen A.M. , Dunning Greg R.
Published: April 2011

The Corner Brook–Glover Island region records the development of the internal domain of the Humber Zone and its relationship to the adjoining external domain and Dunnage Zone. The region preserves both the Laurentian margin basement–cover contact and the siliciclastic–carbonate transition within the cover sequence. Precambrian Grenville basement of the Corner Brook Lake Complex is the oldest lithostratigraphic unit and yielded a U/Pb zircon age of 1510 ± 6 Ma. Three main lithostratigraphic assemblages overlie basement: silicic and mafic igneous rocks of the Lady Slipper Pluton which yielded a U/Pb zircon age of [Formula: see text] Ma; siliciclastic lithologies which include the South Brook and Summerside formations; and carbonate-dominated sequences with clastic incursions which include the Port au Port, St. George, and Table Head groups, and the Breeches Pond, Irishtown, and Pinchgut formations. Dunnage Zone units include plutonic ultramafic to mafic rocks of the Grand Lake Complex, dated by U/Pb zircon from trondhjemite at 490 ± 4 Ma, volcanic and epiclastic rocks of the Glover Island Formation, and the Matthews Brook Serpentinite, the latter restricted to fault slivers within the Humber Zone sequence. The deformed Glover Island Granodiorite intrudes the Dunnage Zone rocks on Glover Island and is dated by U/Pb zircon and titanite at 440 ± 2 Ma. Little deformed Carboniferous sedimentary rocks unconformably overlie both Humber Zone and Dunnage Zone rock units. Timing of regional deformation and peak amphibolite-facies metamorphism in the eastern Humber Zone is constrained by isotopic data to the Early Silurian. In the Dunnage Zone, shear zones and foliation development both pre- and postdate the age of the Glover Island Granodiorite, with the later possibly temporally equivalent to deformation in the Humber Zone. Final juxtaposition of the two zones occurred during Carboniferous movement of the Cabot Fault.
Quaternary geology of the Buchans area, Newfoundland: implications for mineral exploration
Authors: Klassen R. A. , Murton Julian B.
Published: April 2011

Mineral exploration for volcanogenic massive sulphide deposits in the Buchans area of central Newfoundland is hindered by thick and widespread Quaternary overburden comprising glacial, glaciolacustrine, glaciofluvial, and resedimented deposits. Mapping of striations and indicator erratics suggests that the area was affected by four ice-flow events: I, southward; II, northeastward and westward to southwestward; III, southward; and IV, northeastward and southwestward. Vertical and areal distributions of lead, copper, and zinc indicate that till and glaciolacustrine sediments overlying sulphide deposits can be enriched in mineralized debris. Near mines at Buchans surficial debris-flow deposits contain much material derived from the Topsails igneous terrane and are generally impoverished in mineralized debris. Southwest of Buchans, however, they can be enriched. Mineral exploration in the Buchans area must take into account that (i) sulphide-rich debris in till does not reflect only the youngest ice-flow event; (ii) glaciolacustrine sedimentation and resedimentation can result in burial of older sediments containing mineralized debris, in the redistribution of that debris, and in the geochemical masking of subcropping ore deposits; (iii) dispersal of sulphide debris during resedimentation is not necessarily related to ice-flow directions indicated by striations; (iv) a geochemical dispersal train originating at Buchans reflects both southwestward glacial transport and later redistribution of mineralized debris within debris-flow and glaciolacustrine deposits; and (v) marked geochemical variations with depth can occur with small variations in sampling depth, reflecting change in provenance and depositional process. The depositional and ice-flow model developed for the Buchans area likely has wider application in central Newfoundland.
Sunosuchus junggarensis sp.nov. (Archosauria: Crocodyliformes) from the Upper Jurassic of Xinjiang, People's Republic of China
Authors: Wu Xiao-Chun , Brinkman Donald B. , Russell Anthony P.
Published: April 2011

A new species of Crocodyliformes, Sunosuchus junggarensis, is established on the basis of six individuals from the Upper Jurassic of the Junggar Basin, Xinjiang, northwest China. It differs from other species of Sunosuchus primarily in having a dorsoventrally depressed supraoccipital that, in occipital view, lacks a median crest; a frontal that is ridged anteriorly; a distinct depression distal to the foramen aëreum on the dorsal surface of the quadrate; and an elongate, undivided maxillary depression. Cranial ontogenetic variation in S. junggarensis is discussed. Sunosuchus is probably a goniopholidid crocodyliform. It is distinguished from other genera of the Goniopholididae by a narrow and elongate snout, a small skull table, a partially ridged frontal, a pair of anteriorly located anterior palatal fenestrae, a lateroventrally–mediodorsally expanded retroarticular process, some enlarged pits on the frontal, and an elongate mandibular symphysis, with the splenial forming a small part of it. Sunosuchus, Eutretauranosuchus, and some species of Goniopholis may form a monophyletic group within the Mesoeucrocodylia.
U–Pb geochronology of the Raglan gabbro belt, Central Metasedimentary Belt, Ontario: implications for an ensialic marginal basin in the Grenville Orogen
Authors: Pehrsson Sally , Hanmer Simon , van Breemen Otto
Published: April 2011

The Raglan gabbro belt of the Ontario Grenville Orogen is coincident with the top of the Central Metasedimentary Belt boundary thrust zone, a major mid-crustal shear zone separating the Central Gneiss Belt in the footwall from the Central Metasedimentary Belt in the hanging wall. It has been suggested that the gabbros making up the belt are coeval, that they formed in a marginal basin within the Central Metasedimentary Belt, and that they formed a horizon of Theologically stiff material that controlled the localization of the top of the boundary thrust zone during its initiation as the marginal basin closed at ca. 1190 Ma. U–Pb zircon dating of plutons within the Raglan gabbro belt was undertaken to test the coeval nature of intrusions in the belt. Magmatic crystallization ages for three of the gabbros fall in the range 1246–1227 Ma, and a fourth yields a minimum age of ca. 1175 Ma. The results are permissive of a common origin for the gabbros and allow that the Raglan gabbro belt may have been related to the marginal basin, at least with respect to the later stages of its evolution. Inherited 1440–1301 Ma zircons in the gabbros suggest interaction with underlying Central Gneiss Belt crust during magmatism and support an ensialic marginal-basin model, as opposed to an island-arc model, for the evolution of the northwestern part of the Central Metasedimentary Belt.
The velocity structure of the Britt Domain, southwestern Grenville Province, from laboratory and refraction experiments
Authors: Long C. , Salisbury M. H.
Published: April 2011

The Britt Domain in the southwestern Grenville Province of the Canadian Shield is believed to be an exposure of high-grade (upper amphibolite facies) mid-crustal rocks of predominantly granitic and granodioritic composition. A 270 km refraction line was conducted by Lithoprobe across the Britt Domain and the Grenville Front Tectonic Zone to the north in order to determine the deep velocity structure under the region. This data set demonstrates a uniform velocity structure to a depth of 15 km in the central Britt Domain, with near-surface P- and S-wave velocities of 6.15 and 3.55 km/s, respectively, and linear vertical gradients at depth of 0.02 and 0.01 s−1, respectively. The data also show that the Grenville Front Tectonic Zone is strongly anisotropic at shallow depths. To determine the acoustic properties of rocks from the Britt Domain, 80 velocity samples representing different lithologies in this area were measured at confining pressure up to 600 MPa. These studies show that P-wave velocities at 600 MPa range from 6.29 km/s (granitic gneiss) through 6.51 km/s (intermediate gneiss) to 6.90 km/s (mafic rocks), and have an area-weighted mean of 6.36 ± 0.08 km/s. S-wave velocities for selected samples range from 3.54 km/s (paragneiss) through 3.62 km/s (granitic gneiss) to 4.04 km/s (amphibolite). P-wave velocity anisotropy is weak in the granitic rocks (1.1% on average), but stronger in paragneisses and amphibolites from the region (5.2–5.9%). Comparison of laboratory and refraction data suggests that the Britt Domain is granodioritic in composition to mid-crustal levels. The lower crust beneath the Grenville Front Tectonic Zone in the central Britt Domain appears to be composed of diorite at the top, but becomes increasingly mafic toward the Moho.
Fluid-rock reactions and resulting change in rheological behavior of a composite granitoid: the Archean Mooshla stock, Canada
Authors: Belkabir Abdelhay , Hubert Claude , Hoy Larry
Published: April 2011

The composite Mooshla stock displays clear evidence of variations in style and intensity of strain that are closely related to its internal lithological heterogeneity. Gabbro-diorite, quartz diorite, and tonalite rocks are weakly foliated and characterized by brittle and brittle-ductile small-scale shear zones, whereas leucotonalitic rocks are strongly foliated and transected by numerous wide and extensive ductile shear zones. Increasing degrees of penetrative deformation and marked changes of strain style in the pluton, from the more mafic rocks to the more felsic ones, are interpreted to reflect metamorphism-related rheological contrasts, rather than differences in the physical conditions of deformation. Metamorphism of the stock is characterized by an intensive hydration of the igneous rocks that has greatly enhanced their original heterogeneities. Petrographic, microstructural, and chemical studies show that the least deformed rocks are characterized by abundant albite-oligoclase (65-80%) with a matrix of minor quartz (5-10%) and actinolitic amphibole. The resistant plagioclase laths, although altered and replaced, form a stress-supporting framework that has protected the interstitial weak minerals, such as quartz, chlorite, and biotite, from deformation. However, the least deformed leucotonalites are characterized by low albite (35-45%) and high quartz contents (up to 65%). Extensive metamorphic hydration of these rocks produces quartz and phyllitic minerals that had enhanced significantly the ductility of the leucotonalites. Characterization of the chemical changes and the thermochemical conditions of the fluid, using microstructure and measurement of stable isotopes, indicates that fluid-rock interactions during metamorphism and syntectonic hydrothermal alteration have played an important role in creating the contrasting deformation of the composite granitoid.
Paleoproterozoic stromatolites, Hurwitz Group, Quartzite Lake area, Northwest Territories, Canada
Authors: Hofmann H J , Davidson A
Published: April 2011

Decimetric to metric domal stromatolites with constituent ministromatolites characterize reddish, 13C-enriched dolostones in the Watterson Formation of the Quartzite Lake area west of Hudson Bay. They provide paleontologic support for a correlation with the only other known early Paleoproterozoic stromatolite occurrences in North America: the Kona Formation of Michigan, and the Nash Formation in southern Wyoming. They also are similar to stromatolites in probable coeval Jatulian carbonates in Karelia on the Baltic Shield, and possibly to stromatolites in the Hutuo Group in China.
Geochemical evolution of Devonian-Carboniferous igneous rocks of the Magdalen basin, Eastern Canada: Pb- and Nd-isotope evidence for mantle and lower crustal sources
Authors: Pe-Piper Georgia , Piper David JW
Published: April 2011

Magmatism associated with the extensional Magdalen basin includes voluminous tholeiitic gabbro and basalt and local granite and rhyolite. Pb- and (or) Nd-isotope determinations have been made on 70 igneous rocks from throughout the basin, and a further 15 samples of Avalonian basement from the southern margin of the basin, to characterize the contribution of lower crustal blocks and mantle sources to the magmatism and to constrain tectonic models for the basin. Five phases of magmatic evolution are distinguished in the Magdalen basin. (1) Middle to Late Devonian partial melting of lithospheric mantle, producing principally tholeiites and minor alkalic basalt. Tholeiites have Pb isotopic compositions similar to that of younger Triassic tholeiites generated from the same mantle, but experienced less crustal contamination. Regional variations in trace element composition of the mantle can be recognized. (2) The mafic magma triggered anhydrous base-of-crust melting, principally along the transpressive Cobequid and Rockland Brook faults, producing A-type granites in which radiogenic Pb increases northeastward. (3) In the latest Devonian, a large base-of-crust fractionating magma chamber evolved. It contained immiscible mafic and minor felsic magma, with uniform Nd isotopes, and high Ti in the mafic magma. (4) Although late Tournaisian dykes are not strongly fractionated, their evolution involved more crustal assimilation than earlier mafic rocks. (5) Local Viséan-Westphalian alkalic magmas, which ascended along crustal-scale faults, have Pb and Nd isotopic compositions resembling mantle plumes or their mixtures with lithospheric mantle sources. Only these youngest rocks show any isotopic evidence for input from an asthenospheric plume source, suggesting that regional extension was responsible for most of the magmatism.
Stromatolites of the late Archean Back River stratovolcano, Slave structural province, Northwest Territories, Canada
Authors: Lambert M B
Published: April 2011

Nine stromatolite localities in the Back River volcanic complex occur at the boundary between 2692 Ma felsic dome-flow complexes, marking the latest eruptions of this stratovolcano, and overlying turbiditic sedimentary rocks of the Beechy Lake Group, Yellowknife Supergroup. Stromatolites form lenses isolated within coarse volcanic breccia at margins of felsic dome-flow complexes, and 2 m thick bioherms that extend laterally for hundreds of metres. Thin units contain wavy laminae and open-spaced, linked mounds, which form thin encrustations on breccia blocks, or clusters of mounds with low synoptic relief. Thick successions comprise undulatory, flat laminated dolomite that contains wrinkled wavy laminae, pseudocolumnar forms, and locally elongate, low-relief mounds. These units typically contain millimetre-scale layers of fine volcanic ash at regular intervals, testifying periodic explosive eruptions during deposition of microbial mats. The stromatolites, which are identified by gross morphology and distinctive laminae, are all stratiform types. Carbonate units all occur on the seaward side of the volcanic dome-flow complexes that straddled the shoreline around the volcano. The stromatolites probably represent isolated microbial communities that may have developed around areas of fumarolic (or hydrothermal) activity associated with these domes. Stratigraphy seaward from the domes comprises carbonate-cemented dome-flanking breccia, stromatolitic and oolitic carbonate, pebbly rhyolite volcarenite, carbonaceous mudstones, banded iron formation, and turbidites. Thus the stromatolites mark a local environment where life flourished in an Archean sea that lapped onto active volcanic domes along the shallow flanks of an emergent stratovolcano.
Preliminary Proterozoic apparent polar wander paths for the South China Block and their tectonic implications
Authors: Zhang Huimin
Published: April 2011

Results of a regional paleomagnetic study of Precambrian rocks in central-east China are summarized and interpreted. The study is a partial outcome of a geoscience transect incorporating three terranes, namely the Yangzi, Jiangnan, and Huaxia blocks. Paleomagnetic poles derived from a range of metamorphic, igneous, and sedimentary rocks define a northeast to southwest swath crossing the present Pacific Ocean and interpreted to embrace Early to Late Proterozoic times. All three terranes define segments of the same swath and correlate with a similar apparent polar wander path previously defined from the North China Block. The results imply that the constituent blocks of eastern China formed a united block during Early to Middle Proterozoic times. Later relatively large fragmentation is confirmed by Late Proterozoic apparent polar wander path records of the North China and South China Blocks.
Quaternary history of Axel Heiberg Island bordering Nansen Sound, Northwest Territories, emphasizing the last glacial maximum
Authors: Bednarski Jan M
Published: April 2011

The landscape of northeastern Axel Heiberg Island records an erosional history since the Neogene, whereas the glacial and sea-level history relate to Late Wisconsinan glaciation. During the last glacial maximum northeastern Axel Heiberg Island was covered by glaciers emanating from local and regional sources. Local ice caps expanded from highlands on Axel Heiberg Island across the coastal slope. A trunk glacier flowed northward out of Eureka and Flat sounds into Nansen Sound and reached northernmost Axel Heiberg Island. Radiocarbon ages on marine shells suggest that the last glacial maximum was attained along the coast after 29 ka BP and extensive deglaciation was taking place by 10.3 ka BP. The postglacial marine limit rises continuously from 78 m above sea level near the entrance to Nansen Sound to 158 m above sea level at the mouth of Eureka Sound, showing greatest glacioisostatic loading to the south.
Changes in the extent of North American ice sheets during the late Cenozoic
Authors: Barendregt René W , Irving Edward
Published: April 2011

Magnetostratigraphy indicates that Early Pleistocene glaciations in North America, instead of forming one continuous ice mass from Atlantic to Pacific as they did in the Late Pleistocene, were characterized by eastern and western ice masses separated by a 2000 km wide north-south ice-free corridor down the centre of the continent. We argue, therefore, that the area covered by ice during periods of glaciation, and hence probably ice volume, in North America was considerably less in the first 2 Ma of the late Cenozoic than it was in the last 0.7 Ma. This is consistent with delta 18O records of ocean cores indicating the ice volumes were much less in the earlier than in the later part of the Cenozoic Ice Age.
Intercontinental, trilobite-based correlation of the Moroccan early Middle Cambrian
Authors: Geyer Gerd
Published: April 2011

Refined correlations of Lower-Middle Cambrian boundary strata and Middle Cambrian strata between Cambrian paleocontinents require an improved understanding of local stratigraphic ranges of well-defined trilobite genera and species. The conventional definition of the base of the Middle Cambrian in Spain (base of Acadoparadoxides mureroensis Zone) has led to problems even when correlations into other West Gondwanan regions (i.e., Moroccan) are attempted because Paradoxides (Acadoparadoxides) mureroensis and protolenid species from immediately underlying strata have been regularly misidentified. The A. mureroensis Zone is shown to correlate into strata above the base of the Moroccan Middle Cambrian, and paradoxidid trilobites, a guide to the Middle Cambrian, have a lower occurrence in Morocco. These correlations are strengthened by a reevaluation of higher Middle Cambrian trilobite genera and species in Morocco and their use in correlation into Spain and Baltica. Two new genera and eight new species of Middle Cambrian trilobites from the Moroccan High Atlas and Anti-Atlas are proposed. They areCondylopyge eli n.sp., Schistocephalus?ornatus n.sp., Paradoxides (Acadoparadoxides) nobilis n.sp., Parasolenopleura lemdadensis n.sp., Bailiella inconspicua n.sp., Bailiella dilatata n.sp., Atopiaspis tikasraynensis n.gen. and n.sp., and Cambrophatictor cataractis n.gen. and n.sp. Gigoutella atlasensis Hupé 1953 is described in detail for the first time. Gonzaloia n.gen. (type species Calymene holometopa Angelin 1851) is based on a well-known species from the Middle Cambrian of Baltica. The occurrences of the majority of the new Moroccan taxa clearly corroborate earlier interregional and intercontinental correlations by the author and refine and modify proposals by K. Sdzuy, which were largely based on generalized taxonomic assignments of G. atlasensis and the new species S.? ornatus and P. (A.) nobilis.
Solute chemistry of inclusion fluids from sparry dolomites and magnesites in Middle Cambrian carbonate rocks of the southern Canadian Rocky Mountains
Authors: Nesbitt Bruce E , Prochaska Walter
Published: April 2011

Middle Cambrian carbonate rocks of the southern Canadian Rocky Mountains are host to widespread units of white, sparry, hydrothermal, replacement, and open-space filling dolomite. Contained within the dolomites are occurrences of talc and Mississippi Valley type Pb-Zn (the former Kicking Horse and Monarch mines) mineralization and economic concentrations of magnesite (Mount Brussilof mine). Results of studies of solute chemistry of saline (18-25 equivalent wt.% NaCl) inclusion fluids reveal distinctly low Na/Br (55-220) and Cl/Br (95-340) values. These values indicate that the brines which formed the dolomite originated from seawater that had deposited large amounts of halite in an evaporitic environment. Low I/Br ratios for the dolomite-magnesite inclusion fluids are consistent with their derivation from seawater and contrast sharply with the high I/Br ratios of Laramide-age fluids, which formed veins throughout the Rocky Mountains. Variations in F/Br ratios between texturally early and late magnesites indicate the involvement of a second fluid in the formation of the late magnesites. Results of the study of solute chemistry of inclusion fluids from hydrothermal dolomites, magnesites, and associated mineralization are consistent with a model of the pre-Laramide formation of these materials from seawater that had undergone extensive evaporation and halite deposition. Distinct differences in I/Br, total salinity, and delta D values between the dolomite-magnesite depositing fluids and Laramide-age vein-forming fluids clearly indicate the lack of the involvement of Laramide-age fluids in the genesis of the dolomites, magnesites, and associated mineralization.
Alteration and ore mineral characteristics of the Archean Coniagas massive sulfide deposit, Abitibi belt, Quebec
Authors: Doucet Pierre , Mueller Wulf , Chartrand Francis
Published: April 2011

The Coniagas Mine in the northeastern Abitibi greenstone belt is a small, isolated Archean, volcanic-hosted, massive sulfide deposit rich in Zn-Pb-Ag. The Main lens, which is part of four massive sulfide lenses, is restricted to a 40 m thick massive felsic lapilli tuff unit of the 280 m thick sequence. The massive sulfides, a product of subsurface replacement, have features common to both Mattabi- and Noranda-type deposits. The Coniagas Mine sequence represents part of a small subaqueous volcanic edifice that probably evolved close to an arc or back-arc spreading ridge. A distinct alteration halo of chlorite + sericite ± epidote ± spessartine garnet in the immediate footwall and a hanging wall alteration assemblage of quartz + sericite ± epidote ± chlorite characterize the deposit. The sphalerite + pyrite + galena ± chalcopyrite sulfide mineral assemblage in the Main lens differs significantly from the pyrite + chalcopyrite + sphalerite + pyrrhotite ± galena assemblage in the stringer zone. Chlorite compositions are Fe rich close to the mineralized zone, with an Fe/(Fe + Mg) ratio of 0.38-0.48 in the hanging wall and 0.65-0.70 below the ore. Delicate sulfide textures including colloform pyrite and concentric sphalerite are consistent with a low temperature of formation, whereas higher temperatures are inferred for the stockwork zone. Electron probe microanalysis of sphalerite supports inferred hydrothermal fluid temperatures. The low Fe contents (6.7-10.8 mol% FeS) in sphalerite associated with colloform pyrite of the Main lens contrast with the elevated Fe content (12.7-14.1 mol% FeS) in sphalerite from the stockwork.