bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice-thrust features and the Maymont landslide in the North Saskatchewan River valley
Authors: Stauffer Mel R. , Gendzwill Don J. , Sauer E. Karl
Published: July 2009

The Battleford glacier created shearing and softening of bedrock clays, contributing to widespread slope instability along the valley of the North Saskatchewan River. The Battleford glacier flowed southeastward down the valley of the North Saskatchewan River during its final stage in west-central Saskatchewan. It created flutings, crevasse fillings, folding and faulting in ice-thrust ridges, and extensive horizontal gouge zones filled with soft, malleable clay. Extensive drilling and testing for the foundations of the Maymont bridge provided definitive data outlining at least three gouge zones. The shallowest gouge zone at an elevation of 465 m defines the base of the most severe glacial folding and deformation of the bedrock in at least one of the ice-thrust ridges. The deeper gouge zones are at about 433 and 438 m elevation. Postglacial landslides (slumps) along the southern side of the North Saskatchewan River are controlled by the gouge zones, which are low-friction slide surfaces along which large horizontal movements took place. Multiple normal faults and graben structures in the landslide mass could have been the mechanism for horizontal movement and extension with little or no rotation. Two main slide masses have been identified: the lower one moved on the middle gouge zone (438 m), and the upper one moved on the upper gouge zone (465 m).
Rock-slope deformation at Affliction Creek, southern Coast Mountains, British Columbia
Authors: Bovis Michael J.
Published: July 2009

A 7 year record of rock-slope deformation is reported from Affliction Creek, in the southern Coast Mountains of British Columbia. An estimated 3 × 107 m3 of monzonite basement and overlying Garibaldi-aged volcanic material is involved in a slow gravitational movement. Ground-motion vectors suggest that movement has occurred along a deep-seated shear zone and was accompanied by a downslope extension of the moving mass. Near-surface flexural toppling, producing antislope scarps, has taken place where tension cracks crop out on steep slopes or wherever rock faces with strong planar jointing are glacially undercut. Structural data indicate the feasibility of both sliding and toppling at this site.The stratigraphic evidence indicates that most of the tension cracks, grabens, and antislope scarps constituting the slope-movement complex are less than 4300 years old and that many of these landforms may have developed quite recently, as a result of rock-slope debuttressing during the retreat of Affliction Glacier from its late- Neoglacial maximum. Significant variations in the rate of instrumented movements over the 7 year period are not readily accounted for by variations in the level of seismic activity and may be driven by groundwater fluctuations.
Neoglacial history of the Coast Mountains near Bella Coola, British Columbia
Authors: Desloges J. R. , Ryder J. M.
Published: July 2009

The maximum Holocene extent of glaciers in the study area is marked by late Neoglacial (Little Ice Age) terminal moraines. Moraine stratigraphy and 14C dates from a small number of sites suggest that glacier advance, almost as extensive as that of the late Neoglacial, occurred about 2500 14C years BP, and that late Neoglacial advance began well before 770 14C years BP (or the thirteenth century A.D.); glacier termini then stood close to the position of the climax moraines for several centuries. Dates of stabilization of end moraines at 16 glaciers were determined by dendrochronology, with tree-ring counts corrected for sampling errors and ecesis. Most terminal moraines date from 1860 to 1900. Many recessional moraines were formed between 1900 and 1940, coincident with a regionally documented phase of cooler and wetter climate. The proposed chronology is similar to results from elsewhere in the Canadian Cordillera.
Relative timing of emplacement of an Archean lode-gold deposit in an amphibolite terrane: the Eastmain River deposit, northern Quebec
Authors: Couture J. F. , Guha J.
Published: July 2009

The Eastmain River deposit is located within the Archean Upper Eastmain River greenstone belt, approximately 320 km north of Chibougamau. The regional stratigraphy is dominated by ultramafic to felsic volcano-sedimentary units and aluminous sedimentary strata that have undergone amphibolite-grade regional metamorphism.The deposit is hosted by a narrow brittle–ductile shear zone striking northwest and dipping 45 °to the northeast. This shear zone affects a lithologically varied unit composed of MgO-rich rocks and mafic and felsic volcanics. Kinematic indicators within this deformation zone indicate thrust-sense displacement.Within this shear zone, surface drilling has outlined three ore zones characterized by deformed quartz–sulphide veins that form elongated lenses whose long axes parallel the steeply pitching stretching lineation, which plunges to the northeast.Hydrothermal alteration is restricted to within a few metres of the ore veins. It consists of two different mineral assemblages that are both associated with ore veins: a prograde garnet-bearing assemblage, and an epidote-bearing assemblage that locally retrogrades the garnet-bearing assemblage. The main pulse of Au mineralization appears to be relatively late, as suggested by grains of native gold occurring in fractures within quartz and sulphide.The general absence of carbonate alteration around the lodes in rocks generally susceptible to such a process contrasts strongly with Archean lode-gold deposits developed in greenschist-facies metamorphic terranes. Furthermore, the presence of garnet within ore veins raises a number of questions regarding the timing of mineralization of this deposit. On the other hand, the main pulse of Au mineralization appears relatively late, as is the case for the majority of Archean lode-gold deposits.Structural relations and alteration assemblages suggest a deeper structural level of emplacement, at least for the quartz-sulphide veins and the hydrothermal alteration. It is suggested that the Eastmain River deposit formed from a syntectonic hydrothermal system during peak metamorphic conditions.
Caractéristiques pétrographiques et géochimiques de la minéralisation aurifère à la mine Elder, Abitibi, Québec
Authors: Gaulin R. , Trudel P.
Published: July 2009

The Elder deposit is located on the southeast border of the Flavrian Batholith, which intrudes the Blake River Group of archean volcanic rocks. The ore zone is composed of veins 1, 3, 5, and 4. The first three veins are a series of brecciated quartz veins having mean strike and dip of N72°E and 28°SE. Least important is vein 4, striking N20°W and dipping 28°NE. A reverse fault and a mafic dike are associated with the main vein 1, which occurs within trondhjemite in contact with hybrid rocks. The mafic dike represents an important metallotect. The ore zone is marked by abundant carbonates and pyrite, is slightly enriched in hematite and rutile, and is lightly depleted in sericite and chlorite. The mineralogical variation depends on CaO, MgO, CO2, S, TiO2, Fe2O3, MnO, and P2O5 enrichments and SiO2, Na2O, Al2O3, and H2Odepletions. A gold-bearing halo 8 m wide surrounds the ore zone. Seventy-nine per cent of the gold grains are associated with pyrite; otherwise gold occurs mostly as inclusions in the plagioclase matrix. Gold enrichment and rare-earth-element (REE) losses in the ore zone are similar to those observed in other Abitibi gold mines. In veins 1, 3, and 5, divergences in Ag and As enrichments, gold content, and REE concentrations suggest different ore-forming solutions.[Journal Translation]
Résultats préliminaires d'une étude sur la dispersion de l'or en milieu latéritique autour de l'indice aurifère de Misséni, au Mali
Authors: Séa Frédéric , Tanguay Marc G. , Trudel Pierre , Perrault Guy
Published: July 2009

A study of gold dispersion in laterite above a gold zone is based on 58 analyses of soil samples from two shafts and one trench located in the Misséni gold anomaly area, Mali. The bedrock in this area includes Birrimian volcano-sedimentary rocks (lower Proterozoic). At Misséni, primary gold is associated with disseminated copper and iron sulfides in a silicified shear zone within andesites. The area is dominated by a dry tropical climate, including two contrasting seasons (a short rainy season and a long dry season) and a mean annual rainfall of less than 1500 mm. Misséni area is characterized by low plateaus averaging 350 m in altitude and by a very thick weathered cover (> 35 m) of laterite topped by iron cuirasse. In general, the laterite profiles show, from bottom to top (i) saprolith ("pistache" laterite), variegated and mottled clays, (ii) iron hardpan, (iii) iron cuirasse, and (iv) eluvium. Mineralogical analyses reveal that the laterite is dominated by kaolinite, goethite, quartz, mica, and hematite. The mean chemical composition is 46% SiO2, 22% Al2O3, 20% Fe2O3, 1% TiO2, 1% K2O, 0.05% CaO2, and 0.03% Na2O. The laterite profile showed an iron enrichment and a silica depletion (upper part: 0–2 m) and a very weak variation in alumina. This iron enrichment is correlated with increasing goethite toward the surface, whereas silica decreases with lower mica content. The gold concentration increases in the iron hardpan immediately below the cuirasse. The upper saprolith provides low gold values but these increase with depth. Conversely, As and Co tend to increase towards the surface (0–2 m) in the hardpan, cuirasse, or eluvium. A deep core (> 35 m) assayed for gold reveals (i) anomalous gold in latérite (0.2–1.0 ppm) and (ii) higher gold values (5.5–8.8 ppm) occurring between 11.45 and 17.75 m depth) associated with oxide minerals in certain saprolith levels, reflecting probably an ancient groundwater table. These preliminary results would call for further studies to explain the concentration of oxide minerals and gold in some soprolith levels inasmuch as they may lead to potential gold deposits in laterite soils. [Journal Translation]
Intracratonic indentation of the Archean Slave Province into the Early Proterozoic Thelon Tectonic Zone of the Churchill Province, northwestern Canadian Shield
Authors: Henderson John B. , McGrath Peter H. , Theriault Reginald J. , Breemen Otto van
Published: July 2009

Some time between 1735 and 1840 Ma an intracratonic compression resulted in the indentation and consequent underthrusting of the eastern Thelon Tectonic Zone by the central Slave Province and part of the western Thelon Tectonic Zone. The wedge-shaped indentation involved major, transcurrent displacement on the McDonald and Bathurst fault systems. The affected region is characterized by (i) a prominent negative Bouguer gravity anomaly within the Slave Province between the faults and a smaller positive anomaly over the Thelon Tectonic Zone to the east, (ii) an easterly decreasing regional aeromagnetic field over the indenter, and (iii) an easterly increase in Proterozoic metamorphic grade. Rb–Sr dating of biotite shows a 1735 Ma "age plateau" in the eastern part of the wedge, whereas to the west the ages range between 2.0 and 2.5 Ga. Close coincidence between the margin of the 1735 Ma plateau, the metamorphic isograd pattern, and the negative gravity anomaly contours suggests a probable temporal and formative relationship between the metamorphic gradient, gravity anomaly, and the faults. Following indentation and resultant crustal thickening, isostatic rebound in the younger, weaker Thelon Tectonic Zone took place along older Thelon structures. In the older, stronger, structurally more homogeneous Slave Province, isostatic rebound was incomplete. A consequence of the indentation and rebound was crustal flexure to the east of the uplifted area, which resulted in the formation of the large structural basin, symmetrically disposed with respect to the indenting wedge, in which the originally more extensive Middle Proterozoic Thelon Formation is preserved.
Devonian (Givetian–Frasnian) stromatoporoids from the subsurface of Saskatchewan, Canada
Authors: Stearn Colin W. , Shah Dasharathlal H.
Published: July 2009

Samples from the Duperow, Souris River, and Dawson Bay formations collected from a mine shaft near Esterhazy, Saskatchewan, contain the stromatoporoids that are described in this paper. The lower beds of the Duperow Formation, corresponding to members 1 and 2, contain a stromatoporoid fauna of 11 species, most of which occur in the Upper Cairn and Peechee formations of the Rocky Mountains. The underlying Souris River fauna consists of two species known from the correlative Beaverhill Lake, Mikkwa, Flume, and Cairn formations. Seven species were identified from the Dawson Bay Formation, of which the most diagnostic is Schistodictyon bailliei McCammon.Widening the species concept applied to stromatoporoids places several species described from these intervals in synonymy, decreases apparent endemism, and leads to the recognition of the wide distribution of the Flume–Cairn fauna from the Northwest Territories to Iowa.
Intra-Iapetus brachiopods from the Ordovician of eastern Ireland: implications for Caledonide correlation
Authors: Harper D. A. T. , Parkes M. A. , Höey A. N. , Murphy F. C.
Published: July 2009

A newly discovered brachiopod fauna from the Hilltown Formation (lower Llanvirn), Bellewstown Terrane, eastern Ireland, contains elements more typical of sites within the Iapetus Ocean than those associated with the bordering platform provinces. The association of Paralenorthis, "Ahtiella," and Jaanussonites suggests a comparison with the more diverse fauna of the Summerford Group on New World Island, central Newfoundland, and correlation of the Bellewstown Terrane of the Irish Caledonides with parts of the Dunnage and, possibly, Gander terranes of the northern Appalachians.
Massive sulfide deposits of the Noranda area, Quebec. I. The Horne mine
Authors: Barrett T. J. , Cattalani S. , MacLean W. H.
Published: July 2009

The Horne massive sulfide deposits occur within volcanic rocks of the Blake River Group of the Archean Abitibi greenstone belt. The orebodies dip subvertically within rhyolitic flows, breccias, and tuffs that are bounded by the Andesite and the Horne Creek faults. Least-altered rhyolites have low K2O contents and other geochemical features that place them within the FII tholeiitic series. Graded volcaniclastic beds, metal zoning in the orebodies, and locations of chloritized–mineralized rhyolites indicate that the volcanic sequence youngs to the north. The volcanics in the fault wedge are variably silicified and sericitized, and local zones in the orebody sidewalls and footwall are chloritized.The H orebodies formed podiform masses up to 120 m wide, 100 m thick, and 300 m in downplunge extent, consisting of chalcopyrite–pyrrhotite–pyrite Au ore. Between 1927 and 1976, 54 × 106 t of ore were recovered, grading 2.2% Cu, 6.1 g/t Au, and 13.0 g/t Ag (Zn and Pb are <0.1% and <0.01%, respectively). A semicontinuous Cu-rich base (up to ~15 m thick) exists above the footwall and adjacent to the sidewalls of the orebodies. The ore changes stratigraphically upwards from a chalcopyrite-rich base, through middle pyrrhotite–pyrite-rich zones, to upper pyrite-rich zones. Au enrichments occur in some of the Cu-rich ores but also in overlying pyritic ores and in adjacent host volcanics. Cu–Au-bearing chloritized rhyolites occur mainly in the western and eastern sidewalls and at downplunge terminations of the H orebodies.The No. 5 zone occurs at lower mine levels and consists of numerous, partly overlapping Zn-bearing pyritic lenses up to 30 m thick, within mineralized rhyolitic breccias and tuffs. The No. 5 zone extends up to 750 m along strike and at least 1500 m downdip, with high-pyrite reserves of ~22 × 106 t between the 21st and 39th levels, grading 1.2% Zn, 0.15% Cu, and 1.4 g/t Au. Massive pyritic lenses are richer in Zn (> 50 ×) and Pb, Ag, As, Cd, and Sb relative to the H orebodies but are low in Cu and Au.The restored stratigraphic level of the H orebodies and No. 5 zone was dominated from south to north by rhyolite flows and breccias, then rhyolite breccias and tuffs. The volcanic rocks are interpreted as proximal to distal facies on a volcanic edifice that was affected by widespread silicification and sericitization. A graben system on the flank of the edifice became the depositional site of the H orebodies. High-temperature fluid discharge occurred along the fault-bounded graben margins, producing zones of chloritization and stringer-type Cu mineralization ± Au in rhyolites, and infilling the grabens with Cu-bearing massive sulfides. Lower on the edifice, in the No. 5 zone, Zn-bearing pyritic sulfide lenses accumulated within broader, breccia-based depressions roughly on strike with the H orebodies. Mineralization in the No. 5 zone may reflect lower temperature, more diffuse fluid discharge through a permeable sequence of volcaniclastic rocks.
On folds and thrusts affecting the Coppermine River Group, northwestern Canadian Shield
Authors: Hildebrand R. S. , Baragar W. R. A.
Published: July 2009

Examination of existing geological and aeromagnetic maps of the Coppermine homocline reveals two periods of deformation which affect rocks of the Coppermine River Group but predate rocks of the Rae Group. The oldest event generated easterly-trending folds and southerly-vergent thrust faults and is probably related to events along the northern margin of Laurentia. The younger event caused northerly-trending folds, possibly correlates with an east–west compressional event seen in the subsurface of the Interior Plains, and was likely a result of plate interactions along the western margin of Laurentia. Both deformational events that affect the Coppermine homocline are younger than 1267 Ma and are not correlative with the pre-1268 Ma Racklan orogeny of the northern Cordillera.
Seismic evidence for the migration of fluids within the accretionary complex of western Canada
Authors: Calvert A. J. , Clowes R. M.
Published: July 2009

Multichannel deep seismic reflection data from the subduction zone of western Canada delineate the wedge of accereted sediments and the principal terranes (Crescent, Pacific Rim, and Wrangellia) that form the convergent margin. The top of the igneous oceanic crust is defined by subhorizontal reflections extending at least 100 km landward of the deformation front. Upon incorporation into the accretionary wedge, the clearly defined stratigraphy of the incoming oceanic sedimentary section is destroyed over a distance of about 10 km. Initially, an unreflective zone, which correlates well with maximum fluid expulsion, is formed. Farther landward, a predominantly landward-dipping reflectivity exists. A number of reflections are thrust faults, which appear to merge at depth with the subhorizontal reflections, but most have another origin. These reflections may be related to the movement of fluids generated by the compaction of sediments or possibly by the dehydration of the subducting plate. They are strongest in a region of depressed seismic velocities beneath the continental slope, where an analysis of reflection amplitude with offset implies that a high Poisson's ratio exists; this is consistent with the presence of elevated pore pressures. Thus, pore pressure variations associated with the migration of fluids may be the cause of much of the reflectivity within the accreted wedge, although the precipitation of minerals from rising fluids could also be important. Evidence from the seismic data also indicates that fluids from the accretionary prism are being expelled into the sediments of the overlying Tofino basin. A number of anomalously strong reflections and disruption of the horizontally stratified sediments within the lower levels of the basin probably represent fluids that migrated upward from the accreted wedge and were trapped against impermeable barriers created through the deposition of sediments on the continental slope and in the basin.
Foraminifera of the middle to upper Albian transition (Lower Cretaceous), northeastern British Columbia
Authors: Stelck C. R.
Published: July 2009

Throughout Alberta and Saskatchewan, the upper Albian Substage lies unconformably on subjacent beds. However, on the Peace River in northeastern British Columbia, 32 km below Hudson Hope, a silty shale outcrop shows uninterrupted marine deposition across the Middle–Upper Albian substage boundary. An arenaceous foraminiferal fauna of 21 genera and 57 sub-generic taxa is illustrated from this outcrop of the Hasler Shale. The collections come from above the previously illustrated microfauna of the Stelckiceras liardense Zone and below the occurrence of Haplophragmoides gigas gigas and provide a spectrum of transitional faunules spanning the middle–upper Albian boundary. The corresponding boundary of the Ammobaculites wenonahae Subzone of the Gaudryina nanushukensis Zone with the overlying Haplophragmoides uniorbis Subzone (new) at the base of the Haplophragmoides gigas Zone is defined at 73 m above the top of the Cadotte Sandstone by the disappearance of A. wenonahae. Genera within the upper part of the A. wenonahae Subzone and the H. uniorbis Subzone include Bathysiphon, Saccammina, Pelosina, Hippocrepina, Psammosphaera, Thuramminoides, Ammodiscus, Miliammina, Psamminopelta, Reophax, Scherochorella, Haplophragmoides, Ammobaculites, Bulbophragmium, Ammobaculoides, Textulariopsis, Pseudobolivina, Trochammina, Gravellina, Eggerella, and Verneuilinoides. Two new species and two new subspecies are established, viz. Ammobaculites kokei, Trochammina bredini, Haplophragmoides gigas Cushman pregigas, and Reophax deckeri Tappan sliteri. Species originally described from the upper Albian of Wyoming, such as Haplophragmoides uniorbis Eicher, originated out of boreal stock, as they are recognized within the middle Albian upper A. wenonahae Subzone north of the Peace River Arch. On the Peace River, the passage from middle Albian to upper Albian is marked by water depth at or below wave base, but regression is reflected at the substage boundary by the sharp reduction in variety of taxa.
Cyanobacterial–archaeocyathan–radiocyathan bioherms in the Wirrealpa Limestone of South Australia
Authors: Kruse Peter D.
Published: July 2009

The 140 m thick Wirrealpa Limestone of South Australia is an open-shelf marine deposit of Early–Middle Cambrian (Botomian or Toyonian) age. Bioherms preserved within this unit have a distinctive Epiphyton thrombolitic stromatolite framestone core colonized by a low-diversity archaeocyathan–radiocyathan biota of Ajacicyathus sp., Archaeocyathus abacus n.sp., and Girphanovella gondwana n.sp., together with other skeletal invertebrates and macroborers. The largest bioherm, some 3 m in thickness and 36 m in length, is enclosed within an interval of thin-bedded to nodular silty bioclast limestone, but rests directly on a substrate of bioclast, intraclast, and onkoid packstone–floatstone–rudstone. The archaeocyathan–radiocyathan biota represents the youngest known Australian occurrence of these groups.
The peculiar Ordovician trilobite Hypodicranotus from the Whittaker Formation, District of Mackenzie
Authors: Ludvigsen Rolf , Chatterton Brian D. E.
Published: July 2009

The complete exoskeleton of the widely dispersed remopleuridid trilobite Hypodicranotus is reconstructed for the first time based on well-preserved silicified material of Hypodicranotus striatulus (Walcott 1875) from the lower Whittaker Formation (Upper Ordovician, Edenian) of the southern Mackenzie Mountains. The minute oval pygidium consists of a single segment and, as such, it is the most reduced trilobite pygidium known. The subfamily Hypodicranotinae Přibyl and Vaněk is a junior synonym of the Remopleuridinae Hawle and Corda.
The Ordovician volcanics of the Elmtree–Belledune inlier and their relationship to volcanics of the northern Miramichi Highlands, New Brunswick
Authors: Winchester J. A. , Staal C. R. van , Langton J. P.
Published: July 2009

An investigation of the geology and chemistry of the basic igneous rocks in the Elmtree and Belledune inliers in northern New Brunswick shows that the bulk of the Middle Ordovician rocks of the ophiolitic Fournier Group are best interpreted as the products of volcanism and sedimentation in an extensive ensimatic back-arc basin southeast of a volcanic arc. The oceanic back-arc-basin igneous rocks form the basement to renewed arc-related basaltic volcanism in late Middle to Late Ordovician time. The Fournier Group is separated from the structurally-underlying, shale-dominated Elmtree Formation of the Tetagouche Group by an extensive tectonic melange, which incorporates lenses of serpentinite, mafic volcanic rocks, and sedimentary rocks of both the Tetagouche and Fournier groups. The mafic volcanic rocks in the Elmtree Formation correlate best with those intercalated with the lithologically similar sediments of the Llandeilian–Caradocian Boucher Brook Formation in the northern Miramichi Highlands. The melange and the present structural amalgamation of the Tetagouche and Fournier groups result from closure of the marginal basin by northward-directed subduction at the end of the Ordovician. Most mafic suites in the Elmtree and Belledune inliers can be chemically correlated with similar suites in the northern Miramichi Highlands, showing that the two areas are not separated by a terrane boundary.
Tholeiitic volcanic rocks of the late Archean Blake River Group, southern Abitibi greenstone belt: origin and geodynamic implications
Authors: Laflèche M. R. , Dupuy C. , Dostal J.
Published: July 2009

The late Archean Blake River Group volcanic sequence forms the uppermost part of the southern Abitibi greenstone belt in Quebec. The group is mainly composed of mid-ocean-ridge basalt (MORB)-like tholeiites that show a progressive change of several incompatible trace element ratios (e.g., Nb/Th, Nb/Ta, La/Yb, and Zr/Y) during differentiation. The compositional variations are inferred to be the result of fractional crystallization coupled with mixing–contamination of tholeiites by calc-alkaline magma which produced the mafic–intermediate lavas intercalated with the tholeiites in the uppermost part of the sequence. The MORB-like tholeiites were probably emplaced in a back-arc setting.
Multistage dolomitization in the Society Cliffs Formation, northern Baffin Island, Northwest Territories, Canada
Authors: Ghazban Fereydoun , Schwarcz Henry P. , Ford Derek C.
Published: July 2009

Dolostones of the Upper Proterozoic Society Cliffs Formation on northern Baffin Island are host to the Nanisivik lead–zinc sulfide deposits. Two distinct stages of dolomitization have occurred, distinguished by their petrographic, cathodoluminescence, and isotopic characteristics: (1) massive dolomitization of precursor carbonates, and (2) late-stage cementation. Sabkha facies of the lower member of the formation and laminated algal stromatolitic to massive dolostones of the upper member are isotopically similar: δ18O ranges from −1.5 to −6.5‰; δ13C from +1.7 to +3.1‰ PDB; and 87Sr/86Sr averages 0.70761. Petrographic and geochemical evidence indicates that these dolostones formed chiefly by seawater thermal convection beneath shale of the overlying Victor Bay Formation, although mixing of meteoric and marine water also could have occurred. Later fracture-filling dolomitic cements have consistently lower δ18O, but δ13C is similar to that in the host dolostones. Microtraverses of single fractures filled with dolomitic cements show progressive δ18O depletion through time; the last (innermost) generation is correlated with sparry gangue in the ore deposits and also has lower δ13C with respect to the Society Cliffs dolostones, due to mixing of bicarbonate produced from sulfate reduction. The cement was precipitated from warmer fluids, with partial replacement of earlier dolomite. Dolomitizing fluids responsible for later fracture and vug-filling cements may have been released by compaction of the underlying Arctic Bay shales, which also appears to have been the source of the base metals.
Paleomagnetism and the evolution of fluids in the Proterozoic Athabasca Basin, northern Saskatchewan, Canada
Authors: Kotzer T. G. , Kyser T. K. , Irving E.
Published: July 2009

In the Athabasca Basin, diagenetic hematite of variable paragenesis occurs throughout the sandstones and underlying paleoregolith. This hematite carries three distinct, single-component magnetizations: A (D = 158°, I = 62°, α95 = 5°, n = 21); B (D = 11°, I = −36°, α95 = 7°, n = 6); and C (D = 18°, I = 79°, α95 = 3°, n = 27). In some areas of the sandstones, such as near reactivated fault zones, the diagenetic hematite has been altered to goethite which yields a very low-intensity, incoherent D magnetization. Ages for the A, B, and C magnetizations, inferred from comparisons with paleomagnetic directions in Precambrian rocks whose ages are known approximately, are 1750–1600, 1600–1450, and about 900 Ma, respectively. The A magnetization is carried by the earliest formed hematite, and its estimated age compares well with U–Pb ages of 1650–1700 Ma for early diagenetic apatite. U–Pb and Rb–Sr ages of approximately 1500 and 900 Ma for uraninite and illite coeval with hematite that carries the B and C magnetizations compare well with their ages estimated from paleomagnetism. The development of B magnetization appears to be coeval with high-grade, unconformity-type uranium mineralization.Petrographic and field relationships indicate that the A magnetization is carried by hematite formed during initial diagenesis of the Athabasca sandstones, the B magnetization is carried by hematite formed during peak diagenesis, and the C magnetization is carried by hematite formed during subsequent high-temperature hydrothermal alteration. The incoherent D magnetizations have resulted from degradation of hematite to goethite as a result of incursion of low-temperature meteoric waters along fault zones that have been continuously reactivated since the late Precambrian. δ18O values of clay minerals and of the coeval hematite which carries the B and C magnetization indicate that they were formed from a fluid having temperatures of 150–200 °C and δ18O values near 1.0‰. Fluids that deposited the early formed hematite carrying the A magnetism are relatively 18O depleted, with values of approximately 0.8‰ and somewhat lower temperatures of 120–160 °C. Intermingling of A, B, and C magnetizations indicates either that hematite may be deposited by one fluid and reprecipitated by a subsequent fluid, or that fluid flow was controlled by local variations in permeability. Evidently, fluid flow has been episodic and basin wide and has occurred over a time span on the order of 108 years. It is suggested that the stratigraphy of the sandstones controlled the basin-wide lateral migration of the basinal fluids and that faults facilitated interformational fluid flow.
Shallow and deep crustal conductivity studies in the Miramichi earthquake zone, New Brunswick
Authors: Kurtz R. D. , Gupta J. C.
Published: July 2009

The occurrence in early 1982 of four earthquakes in north-central New Brunswick with magnitudes ranging from 5.0 to 5.7 mb prompted detailed electromagnetic surveys of the epicentral region. Scalar audiomagnetotelluric (AMT) measurements, spaced at 100 m intervals or less, along a 7.5 km east–west profile located two conductors but did not find anomalies that could be associated with the proposed fault plane defined by the earthquake hypocentres.The 150 AMT measurements, combined with broad-band tensor soundings at 11 sites in a confined region (6 km × 7.5 km), provided an opportunity to study the distorting effects of near-surface anomalies and also to determine the regional conductivity structure. The apparent resistivity and phase curves from all tensor stations, calculated in a common coordinate system, were remarkably similar (except for static shift of the apparent resistivity curves) to those derived from the rotationally invariant Berdichevsky determinant averages. These averages appear to be very effective for deriving a first-order estimate of the conductivity structure in areas for which near-surface anomalies are a problem.A geometric mean of the AMT measurements was used to estimate the correct level for the high-frequency asymptotes of the tensor apparent resistivity curves. A one-dimensional inversion of the tensor magnetotelluric (MT) data, with the apparent resistivity shifted to the AMT average, yields a four-layer electrical conductivity model for the crust, with depths from the surface of 2.4, 19, and 32 km and with resistivities of 10 000, >100 000, 10 000, and 300 Ω∙m. The crustal resistivities in the Miramichi region are considerably larger than those in other regions in eastern North America but are typical for the Precambrian Shield. As well, there is an indication of lower crustal and (or) upper mantle electrical anisotropy. The geomagnetic transfer function data suggest the presence of a north-northwest-trending structure 7–12 km east of the Miramichi survey area. At present there is little other geophysical or geological evidence for this conductive anomaly.
Deformation of the Gowganda Formation, Matachewan area, Ontario, by post-Early Proterozoic reactivation of the Archean Larder Lake – Cadillac break, with implications for gold exploration
Authors: Powell W. G. , Hodgson C. J.
Published: July 2009

Segments of the Larder Lake – Cadillac break (LLCB), an east–west-trending Archean shear zone in the southern Abitibi greenstone belt, are covered by Early Proterozoic sedimentary rocks of the Gowganda Formation. These rocks severely hamper exploration for Archean gold deposits associated with the LLCB. Along the parts of the LLCB covered by Gowganda Formation in the Matachewan area, Ontario, synsedimentary structures localized along the paleotopographic lineament of the LLCB and deformation structures due to post-Gowganda reactivation of the LLCB and related splay faults can be used to locate underlying Archean faults. Deformation structures in the Gowganda Formation are localized where the northeast–southwest-trending LLCB and associated splay faults are intersected by north–south-trending Archean faults. These Proterozoic structures comprise an array of right-stepping, en echelon folds with variably developed axial-planar cleavage, aligned along the trend of the northeast–southwest-trending basement faults, and linear zones of folds with associated axial-planar cleavage aligned along the trend of north–south-trending basement faults. Kinematic analysis of the structures in the Gowganda Formation indicates dominantly dextral strike-slip reactivation of northeast–southwest-trending faults, and dominantly reverse reactivation of north–south-trending faults. Reactivation of Archean faults may have occurred during the tectonic event that produced the Kapuskasing structure, and (or) during the Grenville orogeny. Past geochemical surveys conducted in one of these deformation zones within the Gowganda Formation in western Quebec indicate that Au can be remobilized from the Archean basement into the deformed Proterozoic rocks. Thus it is possible to delineate the Archean shear zones and test for the presence of associated gold mineralization in areas where the Archean faults are overlain by the Gowganda Formation.
Geologic framework and geochronology of ultramafic complexes of southern Mexico
Authors: Delgado-Argote L. A. , López-Martínez M. , York D. , Hall C. M.
Published: July 2009

In southern Mexico, discrete ultramafic intrusive bodies larger than 4 km2 are genetically related to their enclosing volcano-sedimentary terranes. These terranes are the Cuicateco and Guerrero, which include the Cuicateco and Tierra Caliente metamorphic complexes, respectively. Their basement is largely unknown, and the ultramafic masses previously have been interpreted as allochthonous dismembered ophiolites. To constrain the age of these accreted terranes, the geologic setting and 40Ar/39Ar ages are presented from the localities of Loma Baya – El Tamarindo, Guerrero, and San Pedro Limón, State of México, in the Tierra Caliente Complex, and Teotitlán – Conceptión Pápalo, Oaxaca, in the Cuicateco Complex. The Teotitlán – Conceptión Pápalo area is characterized by a sequence of metamorphosed intermediate granitoid rocks, andesitic lavas, tuffs, and psammites. The intrusive rocks and lavas are pervasively mylonitized and show abundant ultramafic segregations. The largest ultramafic bodies were emplaced into metatuffs, following the regional east-verging structural trend. Three hornblende separates from a hornblende diorite and one from a hornblende-rich clinopyroxenite yielded plateau ages of ca. 130 Ma. The ultramafic rocks in the Tierra Caliente Complex lack orthopyroxene and transitionally grade outward into hornblende diorites. The El Tamarindo ultramafic body (4.6 km2) rose as a diapir into an Albian volcano-sedimentary sequence. The best estimate for the age of this body is ca. 112 Ma from a hornblende separated from a pegmatite dike sample. This age is similar to the Albian fauna reported at Zihuatanejo and other K–Ar ages from ultramafic rocks at Camalotitos. The rigid and poorly serpentinized San Pedro Limon Stock (15 km2) was vertically emplaced into the Xochipala Formation (Cenomanian) during a regional Neogene transpressive disturbance. Four hornblende samples from hornblende clinopyroxenites and hornblendites yielded remarkably flat age spectra, indicating an age of ca. 105 Ma for the San Pedro Limon Stock. Based on the good correlation between the 40Ar/39Ar ages reported here and earlier faunistic data, it is concluded that the ultramafic rocks cooled penecontemporaneously with the deposition of the enclosing volcano-sedimentary sequences.
Mafic and ultramafic amphibolites from the northwestern Pontiac Subprovince: chemical characterization and implications for tectonic setting
Authors: Camiré G. E. , Ludden J. N. , Flèche M. R. La , Burg J. -P.
Published: July 2009

In the northwestern Pontiac Subprovince, metavolcanic rocks are exposed within a metagraywacke sequence that is intruded by metamorphosed mafic dykes. The metavolcanics are Al-undepleted komatiites ([La/Sm]N = 0.3, [Tb/Yb]N = 0.9) and tholeiitic Fe-basalts ([La/Sm]N = 0.8 and [Tb/Yb]N = 0.8). The nearly flat chondrite-normalized distributions of high field strength elements (HFSE), Ti and P, the constant Zr/Y, Nb/Th, Ti/Zr, and Ti/P ratios, and the lack of depletion of HFSE relative to rare-earth elements (REE) in both ultramafic and mafic metavolcanics, imply that crustal assimilation and magma mixing with crustal melts were not significant during differentiation and argue against the presence of subduction-related magmatic components. Contemporaneous volcanism and sedimentation in the northwestern Pontiac Subprovince are unlikely. The metavolcanics do not show any evidence of crustal contamination and likely represent a structurally emplaced, disrupted assemblage, chemically similar to early volcanics of the adjacent southern Abitibi Subprovince.Metamorphosed mafic dykes intruding the metagraywackes are not genetically related to the metavolcanics. The dykes have high CaO, P2O5, K2O, Ba, Rb, and Sr, intermediate Cr and Ni contents, and strongly fractionated REE patterns ([La/Yb]N = 10.8). Normalized to the primitive mantle, they display pronounced negative Nb, Ta, Ti, Zr, and Hf anomalies. These amphibolites are metamorphosed equivalents of Mg-rich calc-alkaline lamprophyre dykes, most likely derived from a hybridized mantle source. Mantle metasomatism was probably related to a subduction event prior to the peak of compressional Kenoran deformation in the Pontiac Subprovince.
Age of deformation within the Central Metasedimentary Belt boundary thrust zone, southwest Grenville Orogen: constraints on the collision of the Mid-Proterozoic Elzevir terrane
Authors: McEachern Sally J. , Breemen Otto van
Published: July 2009

U–Pb zircon and titanite geochronology on syntectonic intrusions from the Ontario Central Metasedimentary Belt boundary thrust zone has constrained the timing of two major periods of northwest-directed ductile thrusting on this crustal-scale shear zone. Initiation of deep-seated uppermost amphibolite facies deformation is constrained to a period before 1190 Ma, over 100 Ma earlier than previous estimates. Major reimbrication of the shear zone took place ca. 1080 – 1060 Ma and was more pronounced in the southwestern segment. The initiation of deformation within the boundary thrust zone coincides with the emplacement of the hanging wall Elzevir terrane of the Central Metasedimentary Belt onto the Mid-Proterozoic Laurentian margin. The structural nature and temporal and kinematic consistency of the reimbrication phase along the 200 km exposed length of the shear zone is thought to be due to within-plate reactivation of the existing, rheologically weak structure, a result of continent–continent collision ca. 1080–1060 Ma during the later stage of the Grenville orogenic cycle.Collision of the Elzevir terrane, interpreted to be an ensialic marginal basin, with the Laurentian margin along the Central Metasedimentary Belt boundary thrust zone is thought to potentially record closure of the marginal basin ca. 1190 Ma. A distinctive tonalitic suite of rocks preserved in the boundary thrust zone may be composed of fragments of the remnant arc to the marginal basin.
Red Deer Hill: a drumlinized, glaciotectonic feature near Prince Albert, Saskatchewan, Canada
Authors: Christiansen E. A. , Sauer E. Karl
Published: July 2009

Red Deer Hill is 5 km long, 3 km wide, and 70 m high. The hill is a glaciotectonic structure formed by a single 106 m thick thrust block, presumably derived from the 80 m deep, upglacier Holmes depression. The thrust block became dislodged by displacement along a presheared horizontal gouge zone where the shearing resistance of the clay was reduced to a residual state by the first (Mennon) glaciation. The hill–depression structure was formed by the Battleford glacier, which drumlinized Red Deer Hill before depositing a veneer of till over the structure. The Holmes depression was filled with glacial Lake Saskatchewan lacustrine and deltaic sediments. Horizontal displacement along a décollement in the direction of the activating force resulted in a stress environment changing from extension to compression. In the zone of extension (Holmes depression), an active Rankine state developed and beds stretched and thinned. In the zone of compression (Red Deer Hill), conversely, a passive Rankine state developed and the beds resisted compression and thickened. Drumlinization of the thrust block occurred as lateral pressures in the block mass changed from passive (stoss slope) to active (lee slope) downglacier.
Intersecting intracontinental Tertiary transform fault systems in the North American Cordillera
Authors: Struik Lambertus C.
Published: July 2009

In central British Columbia, north-trending dextral strike-slip faults that cut Late Eocene granite also truncate northwest-trending dextral strike-slip faults. The northwest-trending strike-slip faults bound the Wolverine Metamorphic Complex (Wolverine Complex), which has been uplifted primarily by northwest–southeast Eocene crustal extension and somewhat by Late Eocene northerly extension. The crustal extension is indicated by shallow-dipping extensions faults, dyke complexes, and stretching lineations. The Wolverine Complex and its bounding faults define a crustal pull-apart in an en echelon dextral transform. The northwest- and north-trending dextral strike-slip faults in central British Columbia are the continuations of faults that transect the interior of the North American Cordillera, and they represent at least two distinct plate boundaries intermittently active during the Early to Middle Eocene, and the Late Eocene to Early Oligocene. Each of these systems consists of en echelon strike-slip faults linked by extensional pull-aparts, locally represented by metamorphic core complexes. These two plate-boundary systems represent two distinct plate-motion configurations between the North American and Kula–Pacific plates. The older plate boundary is truncated and disrupted by the younger one. These two systems may in turn be disrupted by a younger and different plate-motion configuration represented by the transverse Basin and Range extension complex and its northern and southern transform boundary faults.
Archean and Proterozoic tectono-magmatic activity along the southern margin of the Superior Province in northwestern Iowa, United States
Authors: Windom Kenneth E. , Schmus W. Randall Van , Seifert Karl E. , Wallin E. Timothy , Anderson Raymond R.
Published: July 2009

A Precambrian igneous body of ultramafic and mafic rocks, named the Otter Creek layered igneous complex, occurs within the basement of northwestern Iowa, United States. It is marked by a circular magnetic anomaly, one of several that lie north and west of an inferred suture between the Archean Superior Province and Early Proterozoic juvenile crust. Sm–Nd whole-rock analyses for several rock types from the Otter Creek complex yield an isochron age of 2890 ± 90 Ma, with an εNd(t) of −0.9 ± 2.4. A block of older banded iron formation, itself intruded by lamprophyre dikes, is contained within the layered sequence. The iron formation – lamprophyre block has undergone high-temperature metamorphism followed by a retrograde event. A quartz monzodiorite gneiss, with a U–Pb age of 2523 ± 5 Ma, occurs near the layered complex, but the contact relations are not known. The layered series is overlain by Proterozoic keratophyre with a U–Pb age of 1782 ± 10 Ma. These felsic pyroclastic rocks are extremely depleted in K, Rb, Ba, and Cs. Our data are consistent with Archean greenstone-belt formation, including chemical sedimentation followed by mafic–ultramafic magmatism at approximately 2.9 Ga, followed by two later episodes of magmatism, one at approximately 2.5 Ga and the other at approximately 1.78 Ga. The Otter Creek complex is the first Archean greenstone reported south of the Great Lakes Tectonic Zone (GLTZ); its 2.9 Ga age is older than those reported for the granite–greenstone rocks north of the GLTZ. The southern portion of the Superior Province thus appears to have formed later, and in a different tectonic environment, than the high-grade gneisses of the Minnesota River Valley, but before the bulk of the granite–greenstone rocks exposed in northern Minnesota, Ontario, and eastern Manitoba.
SURFACE POLARON SELF-ENERGY AND EFFECTIVE MASS IN A WURTZITE GaN NANOWIRE
Authors: ZHANG LI
Published: July 2009

The ground-state self-trapping energy and effective mass of surface polarons in a freestanding wurtzite GaN nanowire (NW) are studied using the second-order perturbation approach. Based on the dielectric continuum and Loudon's uniaxial crystal models, the polar optical phonon modes in the one-dimensional (1D) systems are analyzed, and the vibrating spectra of surface optical (SO) modes and electron–SO phonon coupling functions are discussed and analyzed. The calculations of the ground-state polaron self-trapping energy and the correction of effective mass due to the SO phonon modes in the 1D GaN NWs reveal that the polaron self-trapping energy and the correction of effective mass is far larger than those in 1D GaAs NW systems. The reasons for this obvious difference in the two 1D structures can be attributed to the different electron–phonon coupling constants and electron effective masses of bulk material constituting the two types of 1D confined systems. Finally, the polaronic properties of the wurtzite 1D GaN NWs are compared with those of wurtzite GaN -based two-dimensional quantum wells. The physical origins leading to these characteristics and their distinction in the different-dimensionality systems is carefully analyzed.