bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochronometry of the Bridge River Camp, southwestern British Columbia
Authors: Leitch C. H. B. , Heyden P. van der , Godwin C. I. , Armstrong R. L. , Harakal J. E.
Published: April 2011

Mineralization at the Bralorne mesothermal gold vein deposit is closely related to a suite of early Late Cretaceous to early Tertiary dykes. Premineral albitite dykes (91.4 ± 1.4 Ma by U–Pb on zircons) and postmineral lamprophyre dykes (43.5 ± 1.5 Ma by K–Ar on biotite) set definite age limits on the mineralizing event. A late intra- to post-mineral green hornblende dyke set (85.7 ± 3.0 Ma by K–Ar on hornblende) that forms a transitional series to the albitites may further restrict the age. Thus, mineralization occurred long after emplacement of the host Bralorne intrusions, dated as Early Permian (minimum age of approximately 270 ± 5 Ma by U–Pb on zircons, 284 ± 20 Ma by K–Ar on hornblende, and 40Ar/39Ar plateau at 276 ± 31 Ma). Lithologically similar intrusions 20 km to the north near Gold Bridge are also Early Permian (287 ± 20 Ma by K–Ar on hornblende and 320 ± 80 Ma by a Rb–Sr whole-rock isochron). Geochronology, radiogenic and stable isotopes, and fluid-inclusion studies suggest that there were several pulses of mineralizing activity adjacent to and east of the Coast Plutonic Complex (CPC). Decreasing temperatures and younger age of mineralization with increasing distance from the CPC imply that plutons of the CPC were the main heat source responsible for mineralization. The main pulses were about 90 Ma for mesothermal Au–Ag–As ± W,Mo mineralization at Bralorne near the CPC, ranging outwards to 65 Ma for Ag–Au–Sb–As ± Hg mineralization at the Minto and Congress deposits, to 45 Ma for Ag–Au epithermal mineralization at Blackdome, 100 km east of the CPC.The Bralorne intrusions may have been emplaced below the sea floor in a spreading-ridge oceanic environment, as suggested by the petrology of the intrusive suite, which includes serpentinized ultramafite, hornblende diorite, and soda granite (trondhjemite), typical of an ophiolite association. The chemistry of volcanic rocks mapped as Cadwallader Group, which host these intrusive bodies, is transitional from mid-ocean-ridge basalts to island-arc tholeiite, suggesting a back-arc-basin setting. Gradational contact relations between the hornblende diorite and the volcanic rocks suggest that the diorite intruded its own volcanic products. Intrusive contacts of the diorite with adjacent elongate ultramafic bodies imply that the ultramafic rocks are of Permian or older age and had been structurally emplaced into crustal levels by the time of diorite intrusion. In the Bralorne fault block the Bralorne intrusions appear to cut the adjacent Cadwallader and Bridge River groups, implying an Early Permian or older age for at least parts of these groups. Thus, rocks mapped as Cadwallader Group in the Bralorne area could be distinct from and older than lithologic equivalents exposed elsewhere, although they are similar in terms of their petrology and major- and trace-element chemistry.
A chronology of landslide activity in the valley of Rivière du Gouffre, Charlevoix, Quebec
Authors: Filion Louise , Quinty François , Bégin Christian
Published: April 2011

Data on earthquake-induced landslides in the valley of Rivière du Gouffre in the Charlevoix region of Quebec are presented. A set of 37 radiocarbon dates obtained from tree trunks buried in flow material and found at the bottom of a small lake was used to reconstruct landslide activity. In addition, large subfossil tree trunks were sampled for tree-ring analysis. The radiocarbon dates indicate that most landslide activity in the area is recent (<600 BP). Two tree-ring-dated landslides were triggered by a large earthquake in AD 1663.
Storm-deposited sandstones (tempestites) and related ichnofossils of the Late Ordovician Georgian Bay Formation, southern Ontario, Canada
Authors: Kerr Michael , Eyles Nicholas
Published: April 2011

The Late Ordovician Geogian Bay Formation of southern Ontario, Canada, comprises up to 250 m of grey to blue–grey shales interbedded with highly fossiliferous calcareous sandstones. These strata were deposited in equatorial paleolatitudes after 448 Ma in a shallow foreland basin created by overthrusting along the eastern margin of North America (the Taconic orogeny). The Georgian Bay Formation comprises the middle part of an upward-shallowing progradational sequence from deep-water transgressive shales of the underlying Whitby Formation to muddy tidal-flat sequences of the overlying Queenston Formation. Exposures in brickyard and river cuts near Toronto, and northwards along a narrow outcrop belt along the foot of the Niagara Escarpment, show laterally extensive (100 m+), sharp-based sheets of sandstone up to 1 m thick, with gutter casts and washed-out (hypichnial) trace fossils (dominantly Planolites and Paleophycus) on their lower bedding surfaces. Detailed examination of sandstone beds in outcrop and in three boreholes that penetrate the formation shows that the beds are composed internally of a basal fossil hash layer overlain by flat, hummocky, and wave-rippled divisions. Bed tops show a variety of wave-ripple forms and are heavily bioturbated (dominantly Bifungites, Conostichus, Diplocraterion, Didymaulichnus, Teichichnus). Sandstone sheets are interpreted as storm deposits (tempestites) resulting from tropical storms (hurricanes) transporting fine-grained suspended sediment from a delta plain onto a muddy shelf to the west.
Dissolved and particulate metal distributions in the St. Lawrence estuary
Authors: Yeats P. A. , Loring D. H.
Published: April 2011

Dissolved and particulate metal concentrations in the St. Lawrence estuary were determined during the high spring runoff and at a period of lower runoff in the fall. The distributions in the estuary are influenced by seasonally variable freshwater discharges and a turbidity maximum zone (TMZ). Dissolved Al, Fe, Mn, Co, Cu, Ni, and Zn concentrations generally decrease significantly with increasing salinity, but Cd shows no significant covarience with salinity. Most metals show complex distribution patterns, and only the distributions of Cu and Ni can be described by linear regression equations. Maximum concentrations of dissolved Al, Fe, Mn, and Co occur in the turbidity maximum and decrease seaward with increasing salinity. During the spring runoff period, total particulate mass was almost twice that in the lower fall runoff period. Chemical partition of the suspended particulate matter (SPM) shows that detrital particulate Fe, Mn, and Zn concentrations vary directly with SPM load and inversely with salinity. Nondetrital metal concentrations vary inversely with SPM (Mg, Pb, Cd) and salinity (Al, Fe, Mn, Zn, Cu). Such changes are not evident in the particulate composition during the low-runoff sampling period. Factor analyses imply that fine-grained aluminosilicates are the main carriers of detrital Si, Al, Ca, Cu, Fe, Mn, and Zn. Nondetrital Al, Cu, Fe, Mn, Pb, and Zn appear to be held in ion-exchange positions, and Fe–Mn grain coatings during the period of high spring runoff and for the fall data set (Cd, Fe, Al, and Pb only). Nondetrital Ca appears to carried by carbonates in the spring data set and along with mixed Ca–Mg carbonates in the fall data set. During high and low river-flow periods, riverine particulate inputs predominate and control the overall abundance, dispersal, and composition of the particulates. Data analyses indicate that, within the TMZ, internal particle cycling and resuspension combined with adsorption–desorption processes override some of the riverine effects and control or modify the particulate composition. Model calculations suggest that dissolved – nondetrital particulate metal exchanges can account for some but not all of the observed changes in the distribution of the dissolved and nondetrital phases.
Structural analysis of Bic fault, a thrust-related strike-slip fault of the external domain of the Taconic Orogen, Appalachians, Quebec, and metallogenic implications
Authors: Rhéaume P. , Schrijver K.
Published: April 2011

The Bic fault is exposed along the shoreline of the St. Lawrence River, 21 km southwest of Rimouski, for 210 m at Cap à l'Orignal and for 100 m at Cap Enragé. The fault brings in contact two major thrust sheets, the Des Seigneuries and the Des Iles, Cambrian lithologies of the former overlying Ordovician rocks of the latter. In the Taconic Orogen, such contacts are normally thrust faults, but the Bic fault is a dextral strike-slip fault, striking east–west and dipping southward. A study of a narrow zone straddling the fault and an adjacent part of the Des Seigneuries thrust sheet has led to the recognition of four successive stages of deformation, all compatible with a northeast–southwest-trending strain ellipsoid. The two first stages are most important: stage 1 brought about regional folding and faulting, whereas stage 2 was characterized by the development of various structural elements (C–S fabrics, stretching lineation, Riedel shears, and kink bands) exclusive to the fault zone. We infer that (i) in the study area, the Bic fault constituted a lateral ramp along which the Des Seigneuries thrust sheet slid horizontally westward; and (ii) emplacement of Ba–Pb–Zn deposits took place slightly after this movement, probably during regional uplift of the orogen in Late Ordovician to Early Silurian time. The latter hypothesis tends to be corroborated by model lead ages of galena in two deposits.
Magma emplacement in a convergent tectonic orogen, southern Revillagigedo Island, southeastern Alaska
Authors: Crawford M. L. , Crawford W. A.
Published: April 2011

The western metamorphic belt of the British Columbia – Alaska coastal orogen consists of lithostratigraphic units assigned to the Taku terrane and the Gravina sequence. On Revillagigedo Island and Cleveland Peninsula in the Ketchikan quadrangle of southeastern Alaska, greenschist- and amphibolite-grade schists of the western metamorphic belt are intruded by mid-Cretaceous tonalite and leucotonalite plutons and sills. A number of these igneous bodies are spatially associated with northwest-trending shear zones developed along thrust faults that formed during the main phase of metamorphism of the schists. Observations of field relations and structural fabric in the igneous rocks and the country-rock schist show the following: (i) Along the southern shore of Revillagigedo Island, the Moth Bay pluton was emplaced along a shear zone. Magmatic and submagmatic flow foliation in the southern border zone of the pluton parallels foliations in the sheared country rock; rocks in the interior of the pluton are generally unfoliated. (ii) At Carroll Point a group of sills intrude along the same shear zone. In some of the sills, tabular plagioclase phenocrysts are oriented parallel to the shear fabric. (iii) Foliation-parallel sills lie within a shear zone that separates Gravina sequence and Taku terrane rocks at Point Francis on Cleveland Peninsula. Older sills within the shear zone are deformed, and younger intrusions are unfoliated and cut across the fabric. Based on these and similar observations elsewhere in the area, we suggest the mid-Cretaceous tonalite and leucotonalite magmas in the Ketchikan quadrangle intruded during the regional compressional deformation that formed the shear zones.
Geochronology at the Namew Lake Ni–Cu deposit, Flin Flon area, Manitoba, Canada: a Pb/Pb study of whole rocks and ore minerals
Authors: Cumming G. L. , Krstic D.
Published: April 2011

Pb-isotope ratios of whole-rock specimens and mineral separates from the gneisses surrounding the Namew Lake Ni–Cu deposit, south of Flin Flon, Manitoba, are compared with the Pb-isotope ratios in the ore minerals and with recently reported zircon U/Pb analyses of samples from the gneisses and the ultramafic host of the ore. The Pb/Pb age from the gneisses is 1864 ± 8 Ma, and there is no evidence for any differences in slopes or initial ratios between individual samples. Thus, there is good agreement between the youngest zircon ages for the gneisses (1862 ± 3 Ma) and Pb/Pb ages for the same rocks. A suite of analyses from a late pegmatite, which cuts the gneisses and the ultramafic rock, yields a well-defined age of 1824 ± 5 Ma, consistent with the geologic requirement that it be younger than the ultramafic host to the orebody (zircon age of 1847 ± 6 Ma) and similar in age to late intrusive bodies in the Flin Flon area to the north.All these data are in marked contrast to apparent Pb/Pb ages for the sulfphides of the ore deposit. Pb/Pb isochron ages on the ore minerals themselves are significantly older than the ages obtained for the gneisses and the ultramafic host. The Pb/Pb data show evidence for multi-stage evolution, with most leach-residue sets yielding en echelon lines with an apparent age of 1948 ± 13 Ma, whereas the residues indicate an older age of 1996 ± 19 Ma. The apparent ages can be explained as being the result of a three-stage process whereby U/Pb ratios were reduced by a factor of 1.6–2.0 at the time of supergene enrichment of the upper part of the ore deposit. This presumably occurred during the formation of the late Precambrian peneplane in the area. One sulphide sample from near the Precambrian–Paleozoic unconformity indicates resetting of the U/Pb system at about 1121 Ma, consistent with what would be expected from the supergene enrichment process.There is some indication of retrograde metamorphic formation of epidote in the gneisses at 1728 ± Ma but no direct evidence for late Hudsonian (1700–1750 Ma) effects on the ore.
Precambrian U–Pb ages of igneous rocks, Wrangel Complex, Wrangel Island, USSR
Authors: Cecile M. P. , Harrison J. C. , Kos'ko M. K. , Parrish R. R.
Published: April 2011

Proterozoic rocks exposed in an anticlinorium at the centre of Wrangel Island are among some of the few exposures of Precambrian strata around Canada Basin. U–Pb zircon dating of samples collected during joint Canadian–Soviet fieldwork on the island has provided crystallization ages of [Formula: see text] on a volcanic rock, 699 ± 2 Ma on a porphyritic granite sill, and a very imprecise age of ca. 0.7 Ga on a small leucogranite. Broadly similar 600–750 Ma, mostly metamorphic, ages are known from both the Arctic Alaska and northern Chukotkan parts of what is called the Arctic Alaska – Chukotka Ancestral Plate, supporting the hypothesis that they were once a single entity. By contrast, potential Late Proterozoic equivalents in the Canadian Arctic Islands include a deeply buried and relatively undeformed seismically defined succession of hypothesized Late Proterozoic age, now at greenschist-facies metamorphic grade, and the unmetamorphosed 725 Ma Franklin mafic sills, dykes, and volcanic rocks. The differences in metamorphic and igneous ages between the Arctic Alaska–Chukotka Ancestral Plate and the Canadian Arctic Islands suggest that these two areas have fundamentally different Precambrian rocks. If so, this challenges the fundamental assumption of most paleogeographic models of the pre-Canada Basin Arctic that the two areas once formed a single continuous plate. Earlier K–Ar dates together with major unconformities in Phanerozoic successions on Wrangel Island suggest early Paleozoic orogenic events.
Stratigraphy and paleomagnetism of the Jaw Face section, Wellsch Valley site, Saskatchewan
Authors: Barendregt R. W. , Thomas F. F. , Irving E. , Baker J. , Stalker A. Macs. , Churcher C. S.
Published: April 2011

The basal part of Jaw Face section at the Wellsch Valley site, some 50 km north-northwest of Swift Current, Saskatchewan, contains mammalian fossils that are considered to be late Blancan to early Irvingtonian in age. It has been sampled for paleomagnetic studies through a thickness of 11 m. The section above 8.8 m has normal polarity; that below has reversed polarity. A tephra, which has yielded a minimum fission-track age of 0.69 ± 0.11 Ma, lies within the reversely magnetized part, near the top of the fossiliferous zone and just below the reversal at the 8.8 m level. Therefore, the change from normal to reversed polarity at the 8.8 m level is probably the Brunhes–Matuyama reversal at 0.73 Ma. Earlier studies have indicated that the Jaramillo (0.9–0.97 Ma) and Olduvai (1.67–1.87 Ma) Normal Polarity subzones occur within the lower predominantly reversed part of the Jaw Face section. In this more detailed study, we find no evidence of these normal subzones. We suggest that earlier results could have been artifacts of the procedures used. Several stratigraphic interpretations are possible. Our preferred interpretation is that the Jaw Face section extends from the upper part of the Matuyama Zone into the lower Brunhes Zone, that is, the mammalian faunas are entirely Irvingtonian in age. Alternatively, the section could contain a substantial hiatus, so the lower part would be early Matuyama in age and its faunas late Blancan – early Irvingtonisn, and the upper part could span the latest Matuyama and lower Brunhes zones. Other possibilities are discussed in the text.
Debris avalanche impoundments of Squamish River, Mount Cayley area, southwestern British Columbia
Authors: Brooks Gregory R. , Hickin Edward J.
Published: April 2011

Squamish River has been impounded temporarily by debris avalanches from Mount Cayley on numerous occasions. Evidence of these impoundments comes from backwater deposits and also from a cluster of in situ stumps protruding from a bar along Squamish River. Backwater deposits consist of both lacustrine and fluvial deposits that have formed within the low-energy depositional environment created by a river impoundment. Three main backwater deposits occur in the study area. The fan toe deposit is ~14 m thick and represents a single impoundment of Squamish River that likely formed behind a large ~4800 BP debris avalanche. In situ ~3200 BP stumps along Squamish River probably were killed by a river impoundment due to a debris avalanche. The upper terrace backwater deposit is ~6 m thick and forms an aggradational terrace along Squamish River which probably accumulated behind an ~1100 BP debris avalanche. The lower terrace deposit also forms an aggradational terrace along Squamish River but represents four or possibly five separate impoundments. These occurred between ~1100 BP and 1955 AD, and it seems likely that one of the deposits relates to an ~500 BP debris avalanche. Seven or eight Holocene impoundments of Squamish River have been identified in the study area.
The Duparquet Formation: sedimentation in a late Archean successor basin, Abitibi greenstone belt, Quebec, Canada
Authors: Mueller W. , Donaldson J. A. , Dufresne D. , Rocheleau M.
Published: April 2011

In the south-central part of the Abitibi greenstone belt, a succession of Archean epiclastic sediments at least 2 km thick was deposited in the Duparquet Basin. The Destor–Porcupine fault and a secondary fault that splays off the major fault define the margins of this basin, which is at least 15 km long and up to 2.5 km wide. Sedimentary evidence of tectonic influence includes (i) rapid vertical and lateral facies changes over tens of metres; (ii) cyclic repetition of facies associations; (iii) mixed fining-upward – coarsening-upward – fining-upward sequences in conglomerate units; (iv) local derivation of most clasts; and (v) asymmetric distribution of fan deltas and braid deltas along the strike of the fault-bounded basin. Three basic facies associations are recognized: (i) conglomerate–sandstone facies association (CSFA); (ii) sandstone–argillite facies association (SAFA); and (iii) argillite–sandstone facies association (ASFA). The CSFA, which predominates at the faulted basin margins, constitutes 60–70% of the basin sediments. It exhibits salient features of streamflow-dominated fans or fan deltas, proximal braid deltas, and (or) coarse clastic braidplains. Large angular clasts of local derivation near the basin margins reflect limited distances of transport, supporting the alluvial fan – fan delta interpretation. The SAFA is assigned to a subaerial to subaqueous fan delta – braid delta setting, in part deposited during episodic storms and floods. The ASFA for the most part records sedimentation in a calm aqueous environment in which suspension deposition prevailed; a lacustrine setting is inferred, but incised conglomerates and channel-fill sandstones attest to sporadic floods and (or) storms. The CSFA in places occupies channels in the ASFA, suggesting progradation of alluvial fans into shallow water in response to source-area uplift. Modern analogues of the Duparquet Basin occur at convergent plate margins. Because it developed during a late orogenic stage, the Duparquet Basin may be classified as a successor basin. Sedimentary facies organization and basin configuration are similar to successor basins of the Cordillera of western Canada, as well as pull-apart basins adjacent to the San Andreas fault in California and the East Anatolian fault in Turkey.
Two komatiitic pyroclastic units, Superior Province, northwestern Ontario: their geology, petrography, and correlation
Authors: Schaefer Stephen J. , Morton Penelope
Published: April 2011

Two Archean komatiitic pyroclastic rock units occur on opposite sides of the Quetico Fault in northwestern Ontario. The eastern unit, the Dismal Ashrock, is located 3 km north of Atikokan, Ontario, on the north side of the Quetico Fault within the Wabigoon Subprovince of the Superior Province. It is part of a suprascrustal sequence, the Steep Rock Group. The Grassy Portage Bay ultramafic pyroclastic rock unit (GUP) is located 100 km to the west, on the south side of the Quetico Fault, and is part of an overturned succession comprising mafic metavolcanic rocks, GUP, and metasedimentary rocks. The Dismal Ashrock dips steeply, is little deformed, has undergone greenschist metamorphism, and is divided into komatiitic lapilli tuff, komatiitic volcanic breccia, komatiitic volcaniclastic rocks, and a mafic pillowed flow. GUP outcrops form an arcuate fold interference pattern, are strongly deformed, and have undergone amphibolite metamorphism. GUP is divided into komatiitic lapilli tuff and komatiitic volcanic breccia. Both pyroclastic units contain cored and composite lapilli, evidence for explosive volcanism. Locally, some of the lapilli fragments are highly vesicular (up to 30% by volume), greater than reported for any other komatiites. Other fragments show no vesicularity. The low vesicularity of some of the pyroclasts and, in the case of the Dismal Ashrock, their association with pinowed lava flows may indicate explosive hydrovolcanic activity. The Dismal Ashrock and GUP are high in MgO, Cr, and Ni and are unusually enriched in Fe, Ti, Zr, Mn, P, Ba, Nb, Rb, and Sr compared with other komatiites. These unique geochemical compositions are not understood at this time.
Pétrologie et gîtologie d'un filon-couche différencié et minéralisé archéen : le gisement aurifère Sigma-2, canton de Louvicourt, Québec
Authors: Hébert Réjean , Rocheleau Michel , Giguère Christine , Perrier Benoît , Gaudreau Roch
Published: April 2011

The Archean Sigma-2 orebody is hosted in the felsic granophyric zone of the differentiated Vicour sill. The sill contains anomalous gold valves and is intrusive into the uppermost part of the Val-d'Or Formation. A geochemical study shows that the Vicour sill has evolved from a ferriferous tholeiitic melt and is comagmatic with the Héva Formation to the south. The competent granophyric zone has been affected by several ductile–brittle deformation events. Three systems of faults and fractures are recognized. Each of these systems is composed of two to three subsystems. The main fault system is oriented east–west with subvertical dip and has a dextral component of movement. Two east–west oriented fault subsystems, moderately dipping (45°) towards north and south, are associated with this feature. The second major structural feature consists of northeast and north-northwest conjugate fractures superimposed on structures of the first tectonic event. The shear movement is sinistral for the northeast fractures and dextral for the north-northwest fractures. The third structural feature is the most interesting with respect to gold mineralization. It consists of east–west-trending, moderately dipping fractures that could be genetically linked with the first structural feature and resulted from a northwest–southeast compression. These fractures increased the tectonic permeability of the granophyre, which allowed Cl- and Na-rich and Ca- and CO2-poor hydrothermal fluids to circulate through the rock and produced subhorizontal mineralized quartz lenses. The lenses are composed of quartz–tourmaline ± carbonate and of pyrite–pyrrhotite ± chalcopyrite. Arsenopyrite is observed in the bleached wall rock surrounding the lenses as well as in east–west faults and northeast and north-northwest conjugate fractures. Bleaching is the result of metasomatic sericitization, albitization, silicification, and low carbonatization of the wall rock and decreases away from the mineralized lenses. Gold is associated with pyrite and arsenopyrite and occurs as inclusions and veinlets crosscutting sulfide grains. It was deposited at a late stage along with quartz and, locally, chalcopyrite. Metasomatism was responsible for the formation of arsenopyrite, coarse-grained pyrite, pyrrhotite, and chalcopyrite while ilmenite recrystallized in the veins. Fractures within arsenopyrite and pyrite are filled with late deposits of pyrrhotite and chalcopyrite. The tholeiitic composition and anomalous gold values of the mafic section of the sill could be additional valuable guidelines in the exploration for similar orebodies.
Neodymium–strontium–lead isotopic study of Vancouver Island igneous rocks
Authors: Andrew A. , Armstrong R. L. , Runkle D.
Published: April 2011

Combined neodymium, strontium, and lead isotope measurements show that Vancouver Island is made up of Phanerozoic crustal material accreted to North America in the Mesozoic and early Cenozoic, but that there are differences in the relative proportions of depleted mantle and aged, enriched crustal components in the Phanerozoic magmatic episodes that contribute to this new crust.The Devonian Sicker Group volcanic arc has an isotopic signature that can be explained by mixing mantle material with subducted continentally derived sediments. The Early to Middle Jurassic Bonanza Volcanics and Island Intrusions magmatic arc isotopic signature indicates mixing of magma from a depleted mantle source with crustal material of Sicker arc-type, rather than of continental origin. This is consistent with large-scale assimilation of Sicker Group and Karmutsen rocks by Jurassic mantle-derived magmas, or introduction of arc-derived sediments into the Jurassic mantle by subduction. Eocene calc-alkaline Flores Volcanics – Catface Intrusions may be derived from reworked Vancouver Island crust with little addition of mantle material.Late Triassic Karmutsen Formation flood basalts are similar to the lower parts of the Columbia River Basalt in all three isotope systems and in petrochemistry. Radiogenic isotopic data are consistent with the interpretation that the Karmutsen basalts were extruded in a post-arc or back-arc setting, with mantle lithosphere and depleted mantle components, and perhaps some plume source input and crustal contamination, but the latter are not provable from the radiogenic isotopic data alone.Early Eocene Metchosin basalts show a depleted mantle source, consistent with their origin as ocean islands, before Middle to Late Eocene accretion to the rest of Vancouver Island.
The Spi Group: a post-Archean, pre-2.1 Ga rift succession, Trans-Hudson hinterland
Authors: Patterson Judith G.
Published: April 2011

A succession of mafic flows intercalated with sandstone and overlain by conglomerate, herein named the Spi Group, lies unconformably on Archean basement and is preserved in a syncline near Spi Lake, N.W.T. An alluvial fan setting near active rift fault escarpments is the interpreted environment of deposition. The nearby Montgomery Lake Group, Mackenzie Lake metasediments, and Padlei Formation at the base of the Hurwitz Group are possible correlatives of the Spi Group; diabase dykes of the Kaminak swarm, common in the Archean basement, are possibly related to the mafic flows. Correlation with the upper, coarse clastic part of the Hurwitz Group (Tavani Formation) is discounted because the Spi conglomerate does not contain clasts of Hurwitz lithology. The Montgomery Lake, Padlei and Spi successions are interpreted as being rift-related, and are older than the 2.1 Ga gabbro that intrudes the Hurwitz Group. Recognition of widespread rifting in this part of the Hearne Province constrains tectonic modelling of the preorogenic history of the Trans-Hudson hinterland.
Paleomagnetism of the Proterozoic Wathaman batholith and the suturing of the Trans-Hudson orogen in Saskatchewan
Authors: Symons D. T. A.
Published: April 2011

The Wathaman (Wathaman–Chipewyan) batholith is an 1854 ± 11 Ma, northeast-trending, homogenous, felsic pluton that is over 900 km long. It is thought to be a magmatic arc, with the Archean Hearne craton on its northwestern side as the hinterland and the remains of the Early Proterozoic Manikewan oceanic crust of the Trans-Hudson orogen on its southeastern side. Alternating-field and thermal step demagnetization methods isolate an A remanence component with a mean direction of D = 134.6°, I = 54.1° (α95 = 3.5°, k = 94, N = 19). Isothermal remanent magnetization tests confirm that this A magnetization component is preserved in pseudosingle to multidomain magnetite and in hematite. Contact tests with intruded older rocks of the Peter Lake domain, with younger crosscutting mafic dikes and with younger crosscutting shear zones, indicate that A is a primary remanence. Its pole position of 67°W, 9°N (dp = 3°, dm = 5°) confirms that it was formed along the margin of the Slave–Rae–Hearne craton, supporting tectonic models that it records a suture zone. It also indicates that the LaRonge – Lynn Lake domain, Flin Flon domain, and Superior Province were translated relatively northwestward into the suture by at least 11 ± 11°, 27 ± 12°, and 49° ± 16°, respectively, as the Manikewan Ocean closed.
Tectonic setting, age, and regional correlation of ultrabasic–ultrapotassic dykes in the northern Purcell Mountains, southeast British Columbia
Authors: Pope Alasdaire J. , Thirlwall Matthew F.
Published: April 2011

Ultrabasic–ultrapotassic dykes have been identified in the Toby–Horsethief Creek area of the Purcell Mountains, in southeast British Columbia. The dykes intrude Helikian and Hadrynian strata of the Purcell Anticlinorium, a parautochthonous terrane of folded and faulted sub-lower greenschist-facies metasediments of the ancestral Cordilleran Miogeocline. Structural–stratigraphic relationships indicate that the loci of the dykes are controlled by Helikian to Upper Paleozoic extensional fault systems associated with rifting of the ancestral passive margin.Two dyke types have been distinguished. Group A dykes are typically light green and xenolithic. They may be phlogopitephyric, and consist dominantly of carbonate (commonly pseudomorphing olivine). These dykes are transitional between group II and group III ultrapotassic rocks (rift to active orogen). Group B dykes are dark green, phlogopite- and apatitephyric, with a carbonate, apatite, chlorite, and phlogopite matrix. They are classified as group II (continental rift) ultrapotassic rocks, with kimberlitic affinities.One of the group B dykes yielded a 245 ± 2.4 Ma Rb–Sr phlogopite–apatite mineral-pair age of emplacement, which is contemporaneous with the petrogenetically and tectonically similar Cross kimberlite, in Paleozoic miogeoclinal sediments of the adjacent Rocky Mountain terrane. The presence of these group II ultrapotassic intrusives in the Purcell Mountains suggests that Helikian through Paleozoic rifting of the passive margin continued into the Permo-Triassic. Palinspastic separation of the Cross kimberlite and the Toby–Horsethief Creek dykes indicates a belt of continental rifting at least 150 km wide. An initial 87Sr/86Sr ratio of 0.70707 for the dated group B dyke suggests a (palinspatically restored) stabilized continental lithosphere source approximately 50 km to the west, and supports geophysical evidence that the Hudsonian basement extends west, below the Kootenay Arc.
Geomorphic implications of glacier outburst flooding: Noeick River valley, British Columbia
Authors: Desloges Joseph R. , Church Michael
Published: April 2011

An outburst flood from Ape Lake in October 1984 severely affected channel and floodplain morphology of Noeick River. This event, estimated to have exceeded 103 m3∙s−1, was as much as 2.4 times greater than the probable maximum meteorological flood. Storage of water in ponds, lakes, and floodplain margins resulted in attenuation of the flood peak as it progressed downstream. As a result, flood effects were most evident in the alluvial reaches of upper Noeick River, below Ape Lake between km 10 and km 23. Here, the channel zone widened from a preflood average of 75 m to almost 200 m, the area of eroded valley bottom increased by about 2.5 times, and a cumulative length of 2.5 km of valley-side colluvial fans was eroded. Transported sediment stored in the floodplain and along valley margins resulted in aggradation of up to 0.75 m, except in restricted reaches where limited sediment supply and increased stream power caused degradation of up to 3 m. A second, and fractionally larger, outburst flood in August 1986 caused mobilization of sediment and some channel infilling but, overall, further morphological changes were minimal. The first flood in this sequence can be characterized as "catastrophic" because it destroyed the normal (climatic) regime of the river. The event effected an abrupt change in the regime of the river, resetting it to be in equilibrium with channel-forming events of order 103 m3∙s−1, such as the second outburst event. There have been no further outburst floods, resulting in a return to disequilibrium conditions. Ultimate recovery, measured in morphological terms as adjustment to accommodate normal meteorological floods or, in sediment transport terms as a balance between boundary shear stress and available sediment sue, will take on the order of decades to a century. Establishment of riparian vegetation will be an important determinant of the extent and timing of channel and floodplain recovery.
Magnetotelluric soundings, structure, and fluids in the southern Canadian Cordillera
Authors: Gough D. Ian , Majorowicz Jacek A.
Published: April 2011

The Cordillera of western Canada lies in a region of oceanic and island-arc lithosphere accreted to North America during subductions of the last 200 Ma. Magnetometer arrays have shown the crust of the region to be highly conductive. Magnetotelluric (MT) soundings across the Intermontane and Omineca tectonic belts between 50°N and 54°N reveal structure in terms of electrical resistivity. Pseudosections of phase and apparent resistivity and preliminary resistivity–depth sections are shown for three transects. The resistivity range is from less than one ohm metre to several thousands of ohm metres. In old continental shields, crustal resistivities cover a similar four-decade range transposed up two decades, i.e., 102–106 Ω∙m. We show that the observed resistivities can be produced by water with NaCl and (or) CO2 in solution, at the high temperatures of the Cordilleran crust, in fractured rock of effective porosity 4–5%. The resistivity variations may represent varying fracture densities. By following structures from outcrops we infer that the more resistive rocks are probably granitoid plutons, with low fracture densities. The highly conductive basalts probably have higher fracture densities. Sections and phase maps indicate that granitoid plutons continue from the Coast Plutonic Complex, under a thin layer of basalt, across the southwestern half of the Intermontane Belt. Near the centre of the Intermontane Belt, in line with the Fraser fault system, highly conductive rock continues from the surface at least to midcrustal depths. Resistivities as low as 1 Ω∙m in the uppermost crust under the Cariboo Mountains, in the Omineca Belt, are ascribed to intense fracturing or mineralization. For the southernmost transect, between 50°N and 51°N, a phase pseudosection shows informative resemblances to the sections farther north. Resistivity–depth inversions at seven sites from six-decade MT data give penetration into the upper mantle, but some of these sites may be affected by static shift. All results fit the mantle upflow hypothesis advanced earlier by Gough.
Origins of stratiform and stratabound Fe–Cu–Zn horizons in the Lower Proterozoic Moran Lake Group, Labrador Central Mineral Belt
Authors: North Jon , Wilton D. H. C.
Published: April 2011

Zn, Cu, and Fe are concentrated as stratiform and stratabound sulphide-rich beds in the Lower Proterozoic Warren Creek Formation, Moran Lake Group, central Labrador. Upper Member sedimentary rocks have a hydrothermal-like Fe enrichment but a dominantly hydrogenous signature as indicated by high Al2O3 relative to SiO2, and high Al and Fe relative to Mn. The Upper Member shales and sulphide-rich beds were deposited as Fe-rich pelagic sediments. The paucity of Mn and abundance of Fe in typical shale samples and lack of Cu, Pb, and Zn fractionation in stratiform massive sulphide beds that contain up to 4702 ppm Zn, 533 ppm Cu, and 15 ppm Pb suggest that deposition occurred in restricted brine pools (i.e., Cu and Zn were precipitated rapidly and were not fractionated). Stratabound sphalerite mineralization containing > 3.7% Zn and 121 ppm Cu (but no Pb) was deposited in a porous lithology at the top of the Warren Creek Formation and represents a unique style of metal concentration.The stratiform deposits probably formed by advection of low-temperature connate waters in a situation typical of sediment-hosted exhalative mineralization (SEDEX). The potential for ore-grade metal concentration is apparently low because metal associations (Fe,Cu,Pb,Zn,Ba) are unlike those of sediment-hosted massive sulphide deposits, the sediments have a dominantly hydrogenous rather than hydrothermal signature, and the absolute grades of known occurrences are very low. The stratabound Zn deposit was probably formed by converting Zn-rich brines (≤ 200 °C) trapped during development of a hydrothermal convection system during a period of increased geothermal gradient. The potential for this type of occurrence in the Warren Creek area to reach economic grade is limited because the convection cells were shallow, ephemeral, and without the metal associations of sediment-hosted massive sulphide deposits.
Structural evolution of the Alaska Juneau lode gold deposit, southeastern Alaska
Authors: Miller Lance D. , Barton Christopher C. , Fredericksen Rick S. , Bressler Jason R.
Published: April 2011

The Alaska Juneau lode gold deposit is hosted by a series of polydeformed Permian to Late Triassic volcanic, pelitic, volcaniclastic, and mafic intrusive rocks. Rocks in the mine area have been sheared and metamorphosed to greenschist grade. Interpretation of rock fabrics indicates several generations of ductile and brittle deformation. Prior to mineralization, reverse shear occurred along northwest-striking and northeast-dipping ductile shear zones. Mineralization consists of Eocene auriferous quartz–carbonate veins, which cut the regional metamorphic fabrics. Mineralization was followed by reverse right-lateral shear along northwest-trending ductile–brittle shear zones. Two northwest-striking and steeply dipping vein sets host the bulk of the ore. Orientation of carbonate fibers within the quartz veins were used to determine the deformation regime that existed during mineralization. Plunge of the fibers indicate that down-to-the-northeast extension occurred synchronous with mineralization. Structural data support a model whereby the Alaska Juneau deposit formed after the peak of ductile deformation during a period of local extension. Localization of veins to areas of infolded phyllite and gabbro suggests that competency contrasts within host rocks enhanced vein emplacement. Veining may have been facilitated by a change from a contractional to a transpressive deformational regime which may have led to local extension and fluid migration to favorable deposition sites.
Structural geology of the Lardeau Group near Trout Lake, British Columbia: implications for the structural evolution of the Kootenay Arc
Authors: Smith Moira T. , Gehrels George E.
Published: April 2011

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic eugeoclinal strata present in the Kootenay Arc in southeastern British Columbia. It is in fault contact with lower Paleozoic miogeoclinal strata for all or some of its length along a structure termed the Lardeau shear zone. The Lardeau Group was deformed prior to mid-Mississippian time, as manifested by layer-parallel faults, folds, and evidence for early greenschist-facies metamorphism. Regional constraints indicate probable Devono-Mississippian timing of orogeny, and possible juxtaposition of the Lardeau Group over miogeoclinal strata along the Lardeau shear zone at this time. Further ductile deformation during the Middle Jurassic Columbian orogeny produced large folds with subhorizontal axes, northwest-striking foliation and faults, and orogen-parallel stretching lineations. This deformation was apparently not everywhere synchronous, and may have continued through Late Jurassic time northeast of Trout Lake. This was followed by Cretaceous(?) dextral strike-slip and normal movement on the Lardeau shear zone and other parallel faults. While apparently the locus of several episodes of faulting, the Lardeau shear zone does not record the accretion of far-travelled tectonic fragments, as sedimentological evidence ties the Lardeau Group and other outboard units to the craton.
Geology and geochemistry of granitoid rocks in the Archean Northern complex, Michigan, U.S.A.
Authors: Wilkin Richard T. , Bornhorst Theodore J.
Published: April 2011

The Northern complex, located in the Upper Peninsula of Michigan, is an Archean greenstone–granite terrane that lies at the southern margin of the Superior Province. The origin of the plutonic suites in the Northern complex can be interpreted within a plate tectonic model proposed for the Superior Province and related to northward-directed subduction and subsequent collision along the Great Lakes tectonic zone. The following plutonic suites are recognized based on intrusive relationships, as well as textural and compositional differences: (i) gneissic tonalite suite; (ii) foliated tonalite suite; (iii) trondhjemite–granite suite; (iv) hornblendite–syenite suite; and (v) late granite dike suite. Rocks in the gneissic and foliated tonalite suites have lithologic and geochemical characteristics typical of Archean trondhjemite–tonalite–granodiorite assemblages exposed elsewhere in the Superior Province. They were emplaced during a primary deformation event and are interpreted to represent partial melts that formed during north-directed subduction of oceanic crust just prior to collision along the Great Lakes tectonic zone. During a second deformation event, stocks and plugs of the trondhjemite–granite suite, derived by intracrustal melting of amphibolite associated with collision and tectonic thickening, intruded both interior and exterior to a preexisting volcanic portion of the Northern complex. The hornblendite–syenite suite, composed of hornblende-rich syenites to monzodiorites with geochemical features that include high Mg numbers, and elevated Cr and Ni content, was derived from partial melting of the mantle during collision along the Great Lakes tectonic zone. The late granite dike suite, comprising late-stage, muscovite- and biotite-bearing quartz – alkali feldspar pegmatite and finer grained granitic lithologies, represents the last magmatic event in the Northern complex emplaced after collision.
Late Wisconsinan glaciation of the Glenlyon Range, Pelly Mountains, Yukon Territory, Canada
Authors: Ward Brent C. , Jackson Jr. Lionel E.
Published: April 2011

Airphoto analysis, identification of erratics, and stratigraphic and geomorphic investigations were used to determine the nature of McConnell (Late Wisconsinan) age glaciation in the Glenlyon Range, Yukon Territory. Most of the peaks of the Glenlyon Range were nunataks within the Selwyn Lobe of the Cordilleran Ice Sheet. The configuration of local and Selwyn Lobe moraines indicates that local glaciers did not extend beyond the cirques and made no contribution to the Selwyn Lobe. These conclusions are confirmed by the character of sediments examined in sections along Little Sheep Creek and by the distribution of erratics in one of the cirque valleys. Aridity limited local ice growth; large glaciers did not grow because of insufficient precipitation.
Reading the stripes: offshore discoveries in plate tectonics with examples from eastern Canada
Authors: Verhoef Jacob , Roest Walter R.
Published: April 2011

The emergence and wide acceptance of plate tectonics has had a profound influence on the way we look at the Earth. Starting as a theory to explain similarities in coast lines across the Atlantic, plate tectonics has become a unifying theory in the earth sciences. In this paper, we describe the role of staff of the Geological Survey of Canada in the developing and refining of this theory. At the same time, we illustrate the effect plate tectonics has had on our understanding of the evolution of offshore eastern Canada. Of critical importance in this development was the unique data set collected by systematic surveying of this region, largely by the Geological Survey of Canada, making the Grand Banks of Newfoundland one of the best-studied offshore areas in the world. Plate tectonic theory not only offers a framework for the evolution of ocean basins, continental margins, and their sedimentary basins, but also for the assemblage of continents.