bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Quaternary sedimentation in St. George's Bay, southwest Newfoundland: acoustic stratigraphy and seabed deposits
Authors: Shaw J. , Forbes D. L.
Published: April 2011

Shallow seismic reflection data collected in St. George's Bay, southwest Newfoundland, reveal a complex pattern of subsurface topography and acoustic facies. Two basins in the inner bay are underlain by glacially overdeepened valleys that extend to depths in excess of 180 m. Within the thick Quaternary sequence in the inner bay we recognize eight acoustic units. Units 1 (ice contact), 2 (subaqueous outwash), and 3 (draped glaciomarine) record the presence and retreat of a major Late Wisconsinan ice margin. Unit 4 (postglacial mud) has resulted from reworking of glaciogenic sediments in response to changes in relative sea level. Unit 5 (postglacial sand) is a shoreface deposit on the seaward front of the former moraine. Unit 6 (postglacial delta) was formed by fluvial reworking of glaciogenic sediments during the postglacial lowstand of relative sea level. Unit 7 (postglacial barrier–platform) comprises seaward-fining clinoform prisms that have prograded into the basins, and underlie gravel beach-ridge plains at Stephenville and Flat Island. Unit 8 (postglacial spillover) results from entrainment of coarse sediment on the shallow sill and subsequent progradation into the basins of the inner bay.Seabed sediment in the basins is mud where sampled. The submarine platforms associated with the barriers at Stephenville and Flat Island are largely sandy. The sill is covered by a gravel veneer, with irregular patches of sand that coalesce and thicken seawards. Extensive areas of gravel ripples testify to the continued mobility of much of the coarse sediment on the sill.A major ice front in the inner bay was present prior to 13.7 ka BP. The draped glaciomarine sediments, dated at 13.7–11.2 ka BP in nearby Port au Port Bay, were deposited after withdrawal of the ice front to the vicinity of the present coast, during a readvance, and subsequently. During the postglacial lowstand of relative sea level much of the present sill area was emergent.
The Devonian ammonoid Agoniatites from Hungry Hollow, southwestern Ontario
Authors: Prosh Eric C.
Published: April 2011

A new specimen of the locally rare ammonoid Agoniatites has been recovered from the Middle Devonian Hamilton Group at Hungry Hollow, southwestern Ontario. Although immature, the specimen displays close affinity to Agoniatites vanuxemi Hall, with which it may be conspecific. An earlier and long-since discredited record of Agoniatites from Ontario is therefore reconfirmed. Despite continued uncertainty as to its precise stratigraphic provenance, the Ontario Agoniatites may prove important for regional correlation.
Crustal structure of the Valhalla complex, British Columbia, from Lithoprobe seismic-reflection and potential-field data
Authors: Eaton David W. S. , Cook Frederick A.
Published: April 2011

The Valhalla complex, situated in the Omineca crystalline belt in southeastern British Columbia, is a Cordilleran metamorphic core complex bordering the suture zone between Quesnellia and North American rocks. The region is tectonically interposed between a convergent plate margin along Canada's west coast and the stable North American craton, and is characterized by a crustal thickness of ~ 35 km, high surface heat flux, and elevated lower crustal electrical conductivity. In this study, Lithoprobe deep-crustal seismic-reflection data, potential-field data, and geological constraints have been used to gain a better understanding of crustal structure in the vicinity of the Valhalla complex. Analysis of Bouguer gravity and total-field aeromagnetic data indicates that mafic oceanic rocks and various syn- and post-accretionary granitoid plutonic rocks are not major constituents of the upper crust underlying the complex. The seismic data reveal a moderately reflective upper crust and image several fault zones, including a very high amplitude, west-dipping reflection that is interpreted as a significant Late Cretaceous or Paleocene thrust fault. The fault-zone reflectivity may be related to compositional heterogeneity and (or) seismic anisotropy associated with mylonites. The lower crust appears to be nonreflective, in contrast with other areas of high surface heat flux and elevated lower crustal conductivity. Taken together, the various data show that the Valhalla complex is likely cored by North American metasedimentary rocks and reveal features related to the Jurassic to Paleocene compressional fabric, which has been largely overprinted at the surface by subsequent Eocene extension.
Geochemical constraints on the tectonic setting of the mafic rocks of the Bathurst Camp, Appalachian Orogen
Authors: Paktunc A. Dogan
Published: April 2011

Abundant mafic rocks comprising basalts and gabbros occur in the Bathurst Camp, a complexly deformed Ordovician terrane in northeastern New Brunswick. The mafic rocks form a consanguineous suite of aphyric lavas, subvolcanic sills, and (or) dikes. Gabbros and basalts have somewhat similar major-element compositions but differ in terms of their trace-element contents. Medium-grained gabbros display tholeiitic compositions, whereas basalts and fine-grained gabbros have alkalic affinities. In general, trace-element abundances indicate an enriched source region for the Bathurst mafic rocks. Trace-element characteristics of the tholeiitic group point to a transitional setting going from back-arc to ocean basin, whereas the alkalic group has geochemical characteristics in common with within-plate basalts. Mixing between magmas of these contrasting settings could explain some of the trace-element characteristics of both groups. The back-arc-basin setting appears to be ensialic and is characterized by the absence of an underlying subducted slab during the formation of the basin. The tectonic reason for rifting in such a case could be the strike separation along a series of en echelon faults similar to those of the Gulf of California. Calc-alkaline characteristics of the upper mantle underlying the basin seem to have been inherited from southeasterly subduction of the proto-Atlantic Ocean in Early to Middle Ordovician times.
Cretaceous marine turtles from the Western Interior Seaway of Canada
Authors: Nicholls Elizabeth L. , Tokaryk Tim T. , Hills Len V.
Published: April 2011

Late Cretaceous marine turtles are rare in Canada, but specimens are known from three formations: Toxochelys latiremis Cope and Protostega sp. from the Pierre Shale, Pembina Member (lower Campanian); Lophochelys niobrarae Zangerl and Chelonioidea genus indet. from the Bearpaw Formation (upper Campanian); Protostegidae genus indet. and one other taxon from the Niobrara Formation (Coniacian).The Canadian records of the listed taxa constitute the northernmost limits of their known range and may represent their northern limits in the Cretaceous inland sea. Taxonomic diversity and relative abundance of turtles in the Canadian samples are significantly less than in comparable faunas to the south. Cool marine climates may have excluded local nesting and discouraged migrations into northern areas.
Volcanic stratigraphy and structure in the Hunter Creek Fault area, Rouyn–Noranda, Quebec
Authors: Camiré G. , Watkinson D. H.
Published: April 2011

The Hunter Creek Fault (HCF) has been considered in the past as a major synvolcanic fault marked by a change in volcanic facies and separating two geologically distinct blocks within the Noranda volcanic complex: the North Mine and the Central Mine sequences. Detailed mapping in the HCF area, in conjunction with petrographic and geochemical studies, has revealed that most of the volcanic units defined south of the fault zone also occur on its northern side. Field and drill-hole correlations indicate that the rocks are cut by a N240–N250 reverse-slip fault dipping approximately 70° toward the northwest. Major- and trace-element data suggest that least-altered volcanic rocks are of tholeiitic affinity and that there is no calc-alkaline unit in the HCF area.
La tectonique cassante à Madagascar: son incidence sur la géomorphologie et sur les écoulements
Authors: Arthaud François , Grillot Jean-Claude , Raunet Michel
Published: April 2011

In Madagascar, evidence of a rift neotectonics oriented north–south is shown and analyzed on microtectonic, kilometric, and regional scales. This phase, reported for the first time, influences significantly the water flow patterns and the following modern processes: directional control of the hydrographic system; local changes in base water levels; development of zones of active erosion and sedimentation; opening and (or) reopening of drainage fractures in karstic systems; typological diversification of some depressions (lowland floodings); hydraulic transfer between surface and subsurface controlled by preferential major axes of underground water drainage. [Journal Translation]
Geology and geochemistry of the late Precambrian Coldbrook Group near Saint John, New Brunswick
Authors: Currie K. L. , Eby G. N.
Published: April 2011

The late Precambrian Coldbrook Group comprises basal basaltic flows and pyroclastic rocks, fragmental andesitic to rhyolitic rocks, and minor capping sedimentary strata, all deformed and metamorphosed to prehnite–pumpellyite grade. Sr-isotope data indicate metasomatism, and probably deformation and metamorphism, took place long after deposition, possibly during major Carboniferous deformation of the Bay of Fundy region. Geochemical data suggest that the Coldbrook Group formed in a subduction-related ensialic volcanic-arc environment, although some specimens appear transitional to within-plate tholeiites. Magma evolution was dominated by fractionation of ilmenite, pyroxene, and plagioclase. Trace-element ratios suggest crustal contamination of virtually all Coldbrook Group rocks, with the amount of crustal component larger in the more salic portion. Comparison of data for the Coldbrook Group with data of other late Precambrian volcanic sequences in Atlantic Canada suggests that similar arc-related sequences underlie slightly younger, continental bimodal sequences in many Avalonian terranes.
Trondhjemitic, 1.35–1.31 Ga gneisses of the Mount Holly Complex of Vermont: evidence for an Elzevirian event in the Grenville Basement of the United States Appalachians
Authors: Ratcliffe Nicholas M. , Aleinikoff John N. , Burton William C. , Karabinos Paul
Published: April 2011

A newly recognized suite of trondhjemite–tonalite and dacitic gneiss forms a 10 km wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif of Vermont. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the Middle Proterozoic regional deformation that affected the Mount Holly Complex. U–Pb zircon dates indicate ages as great as 1.35 Ga for crystallization of the volcanic protoliths and for intrusion of crosscutting trondhjemite. Tonalitic plutonism continued until 1.31 Ga.Map-scale contacts between the trondhjemitic–tonalitic–dacitic gneisses and the paragneiss sequence of the Mount Holly Complex are sharp, suggesting that the volcanic rocks of the trondhjemite–tonalite suite underlie the paragneiss units and do not intrude them. These relationships suggest that the trondhjemite–tonalite suite is either considerably older than, and unconformable beneath, the paragneiss cover rocks or represents a volcanic edifice slightly older than the deposition of the sedimentary precursor to the paragneiss units. The paragneiss and tonalite–trondhjemite gneisses are both intruded by younger granitoids that were intruded at about 1.25 Ga during strong dynamothermal metamorphism.The trondhjemitic gneisses of the Mount Holly Complex of Vermont have high Al2O3 and low Yb contents and light rare-earth element enrichment patterns that are more characteristic of continental than oceanic volcanic arcs. The Mount Holly intrusives and volcanics may have formed during 1.35–1.31 Ga ensialic volcanic-arc activity, contemporaneous with ensimatic arc activity during the early part of the Elzevirian phase of the Grenville orogeny. In Vermont, later deformation and granite intrusion at about 1.25 Ga coincide with the major pulse of the Elzevirian orogeny and associated trondhjemitic plutonism in the Central Metasedimentary Belt of eastern Canada.
The geochemistry and fluid history of the Proterozoic Laurel Lake Au–Ag deposit, Flin Flon greenstone belt
Authors: Ansdell Kevin M. , Kyser T. Kurtis
Published: April 2011

The Laurel Lake Au–Ag deposit is situated 25 km southwest of Flin Flon in the Proterozoic Flin Flon Domain and consists of branching quartz–muscovite–pyrite–tennantite–chalcopyrite–sphalerite–galena–electrum–carbonate veins (stage 1) surrounded by a widespread zone of sericitized and pyritized Amisk Group felsic volcanic rocks. The deposit has been deformed and metamorphosed during the Hudsonian orogeny and is crosscut by nonauriferous quartz–dolomite–tourmaline–pyrite veins (stage 2). The timing of mineralization, the lack of obvious relation to a major shear zone, and high base metal sulphide and Ag/Au ratio (5:1) distinguish this deposit from epigenetic mesothermal gold deposits in the Flin Flon Domain. Fluid inclusion and stable-isotope data indicate that the mineralizing fluids had a high temperature (>300 °C), were saline (>10.3 wt.% NaCl equivalent) and CO2 bearing and had an isotopic composition similar to modified seawater. This fluid leached sulphur, base metals, and precious metals as it interacted with Amisk Group volcanic rocks. The hydrogen isotopic compositions of fine-grained muscovites in the surrounding altered felsic volcanic rocks have been reset during later metamorphism, whereas the coarse stage 1 vein muscovites have partially preserved their primary hydrogen isotopic compositions and fluorine contents. Stage 2 veins were deposited from low-salinity (<6.4 wt.% NaCl equivalent), CO2-bearing fluids, which also have the hydrogen and oxygen isotopic compositions of modified seawater. The Laurel Lake deposit has fluid, vein, and alteration characteristics that distinguish it from both epithermal and mesothermal deposits, and they can be explained by the involvement of modified seawater.
Geochemical signature and seismic stratigraphic setting of Coppermine basalts drilled beneath the Anderson Plains in northwest Canada
Authors: Sevigny James H. , Cook Frederick A. , Clark Elizabeth A.
Published: April 2011

Basalts drilled in the Petro-Canada – Canterra Tweed Lake M-47 well in the Anderson Plains of northwestern Canada have geochemical characteristics, including of major, trace, and rare earth elements, that are similar to those of the most enriched Coppermine lavas but significantly different from those of the younger Proterozoic volcanics, such as the Natkusiak basalts. This result provides a geological tie and timing constraint for structures observed on seismic reflection data in this area. Correlation of stratigraphic data from the well to seismic data shows that the lavas are within a sequence of layered reflections that onlap, and are thus younger than, easterly verging structures, and that were themselves probably uplifted prior to deposition of the Mackenzie Mountains Supergroup. These relationships thus show that at least two stages of Proterozoic compressional deformation, one that predated and one that postdated the basalts, produced structures beneath the Anderson Plains.
The Savage Lode magnesian skarn in the Marvel Loch gold–silver mine, Southern Cross greenstone belt, Western Australia. Part 2: Pressure–temperature estimates and constraints on fluid sources
Authors: Mueller Andreas G. , Groves David I. , Delor Claude P.
Published: April 2011

The Savage Lode gold skarn orebody in the Marvel Loch mine, Southern Cross greenstone belt, Western Australia, replaces foliated metakomatiites in a subvertical ductile shear zone, and is located within the broad metamorphic aureole of the Ghooli Dome granodiorite–granite batholith. Pressure estimates based on metamorphic as well as alteration mineral parageneses indicate that skarn formation took place at P = 4 ± 1 kbar (1 kbar = 100 MPa), corresponding to a burial depth of about 13 km. Metamorphism reached temperatures of 550–630 °C in the mine area, and preceded skarn formation.Pressure–temperature calculations constrain the maximum temperature of the hydrothermal fluid in the Savage Lode to 640 ± 20 °C during the formation of early olivine–calcite and diopside–amphibole rocks, and to 500–600 °C during the formation of phlogopite–chlorite–calcite schists and quartz–diopside veins. Lower fluid temperatures (500 to ~ 400 °C) are recorded by retrograde serpentine (after olivine), talc (after tremolite), and petrographically late aggregates of muscovite + clinozoisite + prehnite. The oxygen fugacity of the fluid is estimated at 10−20–10−24 bar (1 bar = 100 kPa), based on the assemblage magnetite + ilmenite + olivine in calcite-rich prograde skarn. The sulphur fugacity of the fluid is estimated at 10−7–10−9 bar, based on the assemblages pyrrhotite + loellingite, pyrrhotite + arsenopyrite and pyrite + marcasite, which were deposited in a retrograde régime, when fluid temperatures fell from 550 to < 400 °C.The isotopic composition of the fluid (206Pb/204Pb = 13.77, 87Sr/86Sr = 0.7024, δ13C = −4.8‰), as inferred from hydrothermal galena, scheelite, and calcite, indicates equilibration at high temperatures with rocks of granodioritic or granitic composition. Late syn- to post-mineralization pegmatite dykes, exposed in the present mine workings, provide evidence for magmatic activity at depth. The Marvel Loch deposit represents the first well-described example of an Archean gold skarn system.
Orthopyroxene–poikilitic tonalites of the Desliens igneous suite, Ashuanipi granulite complex, Labrador–Quebec, Canada
Authors: Percival John A.
Published: April 2011

The Ashuanipi complex of the Archean Superior Province consists of an older sequence of sedimentary rocks cut by sills and goblet-shaped intrusions of the Desliens igneous suite (DIS). The complex was regionally metamorphosed to granulite facies and subsequently intruded by peraluminous granodiorite batholiths. Tonalites of the DIS contain characteristic < 2 cm inclusion-filled orthopyroxene crystals of probable igneous origin, variably recrystallized and overgrown by garnet, biotite and blocky orthopyroxene that suggest metamorphic P–T conditions of 0.5–0.62 GPa and 750–850 °C. Andesine in tonalite contains abundant drop-like quartz inclusions. Inclusion-filled pyroxene and plagioclase are both inferred to have nucleated on partly resorbed quartz and plagioclase grains within a melt. Similar poikilitic textures characterize subordinate leucotonalite, diorite, gabbro, and pyroxenite, which together with tonalite make up the DIS. Some of the petrological characteristics of the suite are unusual, but known from other regions: (i) some felsic magmatic rocks in the southern Sierra Nevada and Barrington Tops (Australia) batholiths contain primary orthopyroxene; (ii) goblet-shaped plutons are common in orogenic belts, and tonalites with this geometry occur within a sedimentary succession in the Trinity Alps of California; (iii) orthopyroxene oikocrysts characterize parts of the Bjerkreim–Sokndal lopolith of southwestern Norway.
Chronology of Cadomian tectonothermal activity in the baie de Saint-Brieuc (north Brittany), France: evidence from 40Ar/39Ar mineral ages
Authors: Dallmeyer R. D. , Strachan R. A. , D'Lemos R. S.
Published: April 2011

The late Precambrian Cadomian Orogen exposed in the North Armorican Massif (northwest France) is a collage of displaced terranes that, in part, developed during amalgamation of continental-arc and marginal-basin complexes. 40Ar/39Ar mineral ages reported here place new constraints on the timing of Cadomian tectonothermal activity in the southern part of the St Brieuc terrane. In the baie de Saint-Brieuc area Brioverian supracrustal units were deformed, metamorphosed, and intruded by calc-alkaline plutonic complexes. Metamorphic hornblende from a metabasic amphibolite sheet within Brioverian rocks records an isotope correlation age of 568.4 ± 2.6 Ma (interpreted to date postmetamorphic cooling through appropriate argon closure temperatures). Similar isotope correlation cooling ages are recorded by metamorphic hornblende within both an amphibolite sheet intrusive into the Penthièvre complex (567.5 ± 1.2 Ma) and the La Croix Gibat amphibolite (574.8 ± 2.1 Ma). Igneous hornblende from the late tectonic to posttectonic St Quay quartz diorite and muscovite from Brioverian metasedimentary rocks in the contact aureole record isotope correlation ages of ca. 565–570 Ma. These and a ca. 568 Ma isotope correlation age determined for hornblende from the foliated Fort de la Latte quartz diorite are interpreted to date postmagmatic cooling.The 40Ar/39Ar ages indicate that Cadomian tectonothermal activity within southern parts of the St Brieuc terrane occurred prior to ca. 570 Ma. This is markedly older than the ca. 540 Ma date previously suggested for peak Cadomian metamorphism and granite emplacement in the adjacent St Malo terrane and is consistent with palinspastic separation of the contrasting Cadomian elements until at least the latest Precambrian. A pre-570 Ma age for Cadomian tectonothermal activity in the St Brieuc terrane suggests correlation with similar-aged orogenic activity in other circum-Atlantic, late Precambrian Gondwanan marginal terranes (including southern portions of the Iberian massif and various sectors of the West African orogens).
Structural relationships of the Skeena Fold Belt west of the Bowser Basin, northwest British Columbia
Authors: Evenchick Carol A.
Published: April 2011

The Skeena Fold Belt is a regional fold and thrust belt that extends across most of the width of the northern Intermontane Belt of the Canadian Cordillera. Structural and stratigraphic relationships at its northeast margin show that it developed between latest Jurassic(?) and early Tertiary time, that it involved strata at least as low as Lower and Middle Jurassic Hazelton Group, and that it is characterized by northeast-verging folds and thrust faults. The structures accommodated at least 44% shortening and appear to root to the west.Most of the fold belt is distinguished by folds in thinly layered Jurassic and Cretaceous clastic rocks of the Bowser and Sustut basins. Its boundary is difficult to establish west of the Bowser Basin in poorly layered Middle Jurassic and older strata. However, map relationships show that Hazelton Group strata are folded with Bowser Lake Group. It is suggested here that the fold belt continues westward to the east margin of the Coast Plutonic Complex, where the increase in metamorphic grade and dominance of plutonic rocks effectively mark the western boundary of the Skeena Fold Belt. The difference in structural style between the Bowser Lake Group and massive volcanic rocks of the Hazelton Group is attributed to their difference in competency. Shortening by thrust faults and large-scale folds in volcanic rocks west of the Bowser Basin may balance with shortening by folds and related detachments in Bowser Lake Group farther east.
Stratigraphy and petrology of the lower part of the Mulcahy Gabbro, northwestern Ontario: origin of reverse and normal fractionation trends and implications for tectonic setting of late Archean mafic magmatism
Authors: Sutcliffe Richard H. , Smith Alan R. , Edgar Alan D.
Published: April 2011

The Mulcahy Gabbro (2.73 Ga) is an exceptionally well-preserved tholeiitic layered intrusion located in the Wabigoon Subprovince of the Superior Province. The intrusion has a 900 m thick marginal zone of weakly layered gabbronoritic cumulate rocks characterized by a trend of upward Mg-enrichment. The overlying 1100 m thick lower zone consists of well-layered cumulate rocks that display a prominent trend of upward Fe-enrichment. The order of appearance of cumulus minerals in the lower zone is orthopyroxene + plagioclase, augite, apatite, pigeonite, Fe-rich olivine, magnetite.The upward increase in the XMg in marginal-zone cumulus low-Ca pyroxene and augite from 0.44 to 0.72 and 0.57 to 0.79, respectively, is primarily attributed to the injection of successively less fractionated batches of magma into the chamber, rather than to the effect of trapped liquid on cumulus mineral compositions. In the lower zone, crystal fractionation control results in an upward decrease in XMg in low-Ca pyroxene and augite from 0.72 to 0.32 and 0.79 to 0.45, respectively. The change from weakly developed layering in the marginal zone to the well-layered lower zone may represent the transition from a regime of cooling through the chamber floor to one of cooling predominantly through the chamber roof and walls. Rhythmic layering on a scale of centimetres to metres in the lower zone is largely attributed to magmatic density currents. Sulphur saturation occurs near the marginal zone – lower zone transition from reverse to normal fractionation and is attributed to mixing of the older fractionated magma with an injection of buoyant younger primitive magma.Based on cumulus mineral compositions, the most primitive parental magma for the lower zone is determined to have had an Mg# equal to or less than 0.46 and weak enrichment of light rare-earth elements ((Ce/Yb)N = 1.4). The cumulates are derived from a hydrous, high-Al2O3 basaltic magma with a moderately high silica activity. These constraints and the close temporal and spatial association with calc-alkaline granitoid rocks suggest that the Mulcahy Gabbro is a cumulate assemblage from a high-Al tholeiite magma and is part of a late Archean calc-alkaline, arc-related plutonic complex.
Temperature changes and thaw of permafrost adjacent to Richards Island, Mackenzie Delta, N.W.T.
Authors: Dyke Larry D.
Published: April 2011

Thawing of ice-bonded sediment below the sea floor accompanies sea-level rise and shoreline retreat along the Beaufort Sea coast. The rate of thaw is primarily controlled by the warm spring and summer discharge of the Mackenzie River, which affects sea-bottom temperatures to water depths of 10–20 m. The intensity of the warming at any one location decreases with depth until continuous sub-0 °C temperatures are encountered. Sea-level rise eventually brings the sea floor into the cold sea-water zone and thawing stops. Therefore thawing is also controlled by the residence time in the warm zone. Sedimentation or scouring can, respectively, slow or accelerate the increase in water depth and thereby modify the rate of thaw progression. This, combined with changes in the rate of coastal retreat, can produce a subbottom frost table with considerable relief. In the extreme, ice bonding within a few metres of the sea floor can be explained by accelerated submergence.
An Ordovician rift environment for the Memphremagog polymetallic massive sulphide deposit, Appalachian Ophiolite Belt, Quebec
Authors: Trottier Jacques , Brown Alex C. , Gauthier Michel
Published: April 2011

The Memphremagog polymetallic massive sulphide deposit occurs at the contact between a pillowed volcanic sequence and a detrital sedimentary sequence consisting principally of shale and greywacke. The deposit, situated about 100 km east of Montréal in the Appalachians of southeastern Quebec, is composed of massive sulphide breccia. Major minerals include pyrrhotite, pyrite, sphalerite, galena, chalcopyrite, and calcite, with minor amounts of arsenopyrite, freibergite ((Cu,Ag,Fe)12Sb4S13), meneghinite (CuPb13Sb7S24), gudmundite (FeSbS), and kersteritic stannite (Cu2(Fe,Zn)SnS4). The mineral assemblage, metal content, and primary textures are comparable to modern sea-floor sulphide mounds enclosed by thick sedimentary sequences deposited in basins such as the Guaymas Basin in the Gulf of California.Although the footwall basalt unit is interstratified with the St-Daniel Formation of the Ophiolite Belt, it possesses a transitional geochemical signature of alkaline affinity that is uncharacteristic of ophiolitic basalts. We propose that this volcanic unit was emplaced within a transtensional basin of a rifted fore-arc system that formed during the Taconic orogeny as a result of diachronous oblique collision of an island- arc system (Ascot–Weedon?) with the North American continent. During magmatic activity, a hydrothermal system was imprinted on the volcanics and underlying sediments. Subsequent hydrothermal fluid emanations led to the formation of the Memphremagog sulphide deposit, which is quite distinct from sulphide deposits generally found within ophiolite belts.
U–Pb geochronology of the Hope Bay – Elu Inlet area, Bathurst Block, northeastern Slave Structural Province, Northwest Territories
Authors: Bevier Mary Lou , Gebert James S.
Published: April 2011

U–Pb ages for six felsic samples from the dominantly mafic Hope Bay and Elu Inlet metavolcanic belts of the Bathurst Block provide the first constraints on the timing of felsic volcanism (2685–2677 Ma) and plutonism (2672–2608 Ma) in the northeastern corner of the Slave Structural Province. Gold veins that cut a pluton in the eastern Hope Bay belt are younger than 2672 Ma. Early Proterozoic magmatic activity is recorded in a pegmatite dyke that crosscuts metavolcanic rocks of the northern Hope Bay belt. Initial Nd and Sr isotopic ratios from the Hope Bay and Elu Inlet belts indicate a juvenile source for the magmas.
Mid-Paleozoic thrusting at the Appalachian deformation front: Port au Port Peninsula, western Newfoundland
Authors: Waldron John W. F. , Stockmal Glen S.
Published: April 2011

Structures exposed on Port au Port Peninsula in western Newfoundland record the nature of the Appalachian deformation front, which forms the western boundary of the Humber tectono-stratigraphic zone. The major structures affect the Late Ordovician to Late Silurian Long Point – Clam Bank succession, but not the unconformably overlying Carboniferous rocks; they are probably of Devonian age.At the west coast of the peninsula, Long Point and Clam Bank strata are affected by both east-vergent and west-vergent structures. The basal surface of the succession is interpreted as an east-vergent thrust, forming the upper detachment of a "triangle zone," and correlates with a similarly located contact seen in offshore multichannel seismic profiles. Within the succession, east-vergent deformation zones locally duplicate the stratigraphy. West-vergent structures, including a map-scale overturned fold north of Round Head mountain, are probably younger.Farther south, Middle Ordovician foreland basin sediments are also affected by east-vergent thrusts, which have been variably rotated by west-vergent folds. In the underlying Cambrian–Ordovician platform carbonate succession, east-vergent thrusts duplicate the stratigraphy.These structures are related to telescoping of the carbonate platform and the overlying Humber Arm Allochthon during Devonian westward wedging of the structural triangle zone beneath the Long Point – Clam Bank succession. The platform succession must therefore be allochthonous, and the Humber Arm Allochthon has been transported to the west of its Late Ordovician position.
Three crustal zones in the Thor–Odin – Pinnacles area, southern Omineca Belt, British Columbia
Authors: Carr Sharon D.
Published: April 2011

The present crustal architecture of the southern Omineca Belt in the Canadian Cordillera is a product of Eocene extension and crustal thinning superimposed on a crust that was thickened and deformed during Paleozoic and Jurassic to Late Paleocene compression. Amphibolite-facies rocks exposed as gneiss complexes within the Shuswap Metamorphic Complex, in the southern Omineca Belt, were buried during compression and were exhumed in the lower plates of low- to moderate-angle plastic–brittle Eocene extensional faults.In the Thor–Odin – Pinnacles area three crustal zones, which have experienced different deformation and thermal histories, and intervening shear zones can be correlated with Lithoprobe seismic reflection data. The Basement Zone, which comprises crystalline basement and overlying supracrustal gneisses, is bounded above by the Monashee décollement, a deep-seated northeasterly directed Mesozoic–Paleocene thrust fault. In the hanging wall of the décollement, polydeformed gneisses and schists of the Middle Crustal Zone are characterized by Late Cretaceous–early Tertiary ductile strain, plutonism, and thermal quenching. They are bounded at the top by crustal-scale Eocene normal faults that juxtapose Upper Crustal Zone rocks characterized by Jurassic and older structures and a Jura-Cretaceous cooling history.Middle Crustal Zone rocks of the Thor–Odin – Pinnacles area are correlative with part of the Late Proterozoic Horsethief Creek Group and Cambrian to Jurassic strata and host extensive plutons, stocks, and sheets of the syntectonic and posttectonic Late Paleocene – Early Eocene Ladybird granite suite. Field mapping and geochronology indicate that (i) a substantial part of the penetrative compressional polydeformation history and the thermal peak of metamorphism within the Middle Crustal Zone occurred in the Late Cretaceous–Paleocene; (ii) thrusting on the Monashee décollement had ended by 58 Ma; (iii) the onset of extensional deformation either overlapped or closely followed the compressional regime; (iv) Middle Crustal Zone metamorphic and igneous rocks were hot in the Paleocene and cooled rapidly in the early Tertiary because of extensional denudation.
Petrogenesis of amphibole – biotite – calcite – plagioclase alteration and laminated gold – silver quartz veins in four Archean shear zones of the Norseman district, Western Australia
Authors: Mueller Andreas G.
Published: April 2011

The Norseman mining district in the Archean Yilgarn Block, Western Australia, has produced 140 t of gold and about 90 t of silver from 11.24 × 106 t of ore. The district is located within a metamorphic terrane of mafic and minor ultramafic greenstones, intruded by granite cupolas and swarms of porphyry dykes. The orebodies consist of laminated quartz veins, controlled by narrow (0.5–5 m) reverse shear zones that, in general, follow the contacts of metapyroxenite or porphyry dykes. Petrological studies of four shear zones, exposed on the Regent shaft 14 level, Ajax shaft 10 level, and in the stope above the North Royal shaft 5 level, show that the host rocks were metamorphosed to hornblende–plagioclase amphibolites and actinolite–chlorite rocks at temperatures of 500–550 °C prior to mineralization.At the localities studied, intense wall-rock replacement and low-grade (0.5 g/t) gold mineralization are confined to ductile or brittle–ductile shear structures. Alteration is similar in both ultramafic and mafic greenstones, and consists of an inner zone of biotite–quartz–calcite–plagioclase rock with minor actinolitic hornblende and quartz–calcite–actinolite veinlets, and an outer zone, locally developed, of chlorite–calcite–quartz rock. At an estimated pressure of 3 kbar (300 MPa), fluid temperatures during wall-rock alteration are constrained by the hydrothermal mineral assemblages to 480 ± 30 °C in two shear zones on the Regent shaft 14 level, and to 450 ± 20 °C in one shear zone in the North Royal shaft 5 level stope. The mole fraction of CO2 of the fluids is estimated at [Formula: see text], and the sulphur fugacity at 10−6 bar (10−1 kPa) (at 450 °C), based on the assemblage pyrrhotite + pyrite ± arsenopyrite. The development of an outer chloritic alteration zone at North Royal is related to the lower fluid temperature at this locality.High-grade (up to 75 g/t Au, 283 g/t Ag) veins formed within three of the shear zones studied at fluid temperatures of 400 °C and less, by the successive accretion of quartz laminae, separated by films of retrograde chlorite and sericite. The assemblage of ore minerals in the veins differs from that in the altered wall rocks, and includes disseminated galena, Pb–Bi–Ag tellurides, and native gold, which coprecipitated with the quartz. The orebodies at Norseman show affinities to Phanerozoic and Archean gold skarn deposits.
Tectonic implications of syn- and post-emplacement deformation of the Mount Stuart batholith for mid-Cretaceous orogenesis in the North Cascades
Authors: Miller Robert B. , Paterson Scott R.
Published: April 2011

The 93–96 Ma Mount Stuart batholith intruded across the boundary between the Northwest Cascades thrust system and the crystalline core of the North Cascades. Although previously considered posttectonic, the northeast margin of the Mount Stuart batholith and its wall rocks have been involved in syn- to post-emplacement, southwest-directed thrusting and folding, and west-northwest stretching. Contraction ended shortly after emplacement, as indicated by high-temperature recrystallization in thrust-related mylonites of the pluton and by geochronological data, whereas west-northwest stretching continued for an unknown period of time. This is the best documented mid-Cretaceous contractional belt in the main part of the crystalline core. The shortening direction and timing are identical to that of southwest-vergent thrusts in the offset continuation of the core in British Columbia. The contractional belt provides a link between thrusting in the Northwest Cascades thrust system and deformation in the crystalline core.
Les contraintes phanérozoïques dans la plate-forme du Saint-Laurent, région de Montréal, Québec
Authors: Gélard Jean-Pierre , Jébrak Michel , Prichonnet Gilbert
Published: April 2011

The tectonic evolution of the Appalachian platform is still not well understood. The Montréal area, however, shows evidence of major fracturing events, some of which cut the Cretaceous intrusions. The history of the different stress events recorded in the platform was studied by the analysis of brittle faults and dykes, followed by the calculation, by way inversion of tensors, of the corresponding stresses. The tectonics represented is polyphased and its analysis allows a historical reconstitution of the carbonate and flyschoid platform since the Lower Paleozoic. Five tectonic stages are recognized, corresponding to the major geodynamic events characteristics of northeast North America: (i) early north–south distensional events; (ii) Appalachian compression in a west-northwest–east-southeast direction; (iii) terminal Appalachian compression oriented north-northeast–south-southwest; (iv) Cretaceous north–south distension; (v) a Cenozoic to Recent compression in a northwest–southeast direction. [Journal Translation]
Mise en évidence de cordiérite héritée des terrains traversés dans le pluton granitique des Oulad Ouaslam (Jebilet, Maroc)
Authors: Bouloton Jacky
Published: April 2011

Cordierite, a quite common mineral in granitic rocks, originates from various processes; many types of crystals can be found in a given massif. The high-level Oulad Ouaslam pluton, in Morocco, displays cordierites of three different origins. Primary magmatic crystals, as well as later ones, grown in equilibrium with a water-rich fluid phase, are readily distinguishable from inherited metamorphic cordierites. The latter, which are characterized by numerous spinel (Zn-poor hercynite) inclusions, are the most interesting. They originated from the disaggregation of peraluminous enclaves, which either represent refractory assemblages or solid products of incongruent melting reactions. Thermobarometric data indicate that these rocks equilibrated at about 750 °C and 3,5 kbar (350 MPa). These values are believed to represent the conditions under which the rocks were enclaved, and of the resulting partial melting event. Peraluminous enclaves, and thus inherited cordierite, are not derived from the source region of the granite. They are partly digested pelitic xenoliths, picked up by the ascending magma. Therefore, they represent true relicts of assimilated rocks. Among the possible mechanisms of cordierite formation, contamination of the magma by aluminous rocks is a classical one. However, no clear textural evidence of the process has ever been presented in the literature. The Oulad Ouaslam pluton provides such evidence and thus confirms, at least locally, the validity of this hypothesis.
Glacial Lake Invermere, upper Columbia River valley, British Columbia: a paleogeographic reconstruction
Authors: Sawicki Oswald , Smith Derald G.
Published: April 2011

Terraces of thick lacustrine silt and deltaic gravel flank parts of the valley floor of the Rocky Mountain Trench between Skookumchuck and Donald, British Columbia. These indicate the presence of former Late Wisconsinan glacial Lake Invermere, which at its maximum extent occupied the Rocky Mountain Trench from Bluewater Creek, 6 km north of Donald, to 7 km north of Skookumchuck. The lake was 210 km long, an average of 2.5 km wide by 100 m deep, and had an area of 530 km2. Retreating glacier ice is interpreted to have formed a dam at the northern end of the lake, and blockage to the south resulted from a sediment valley fill.Glacial Lake Invermere formed as two water bodies, at elevations 885 and 900 m asl, separated by glacier ice. These two water bodies later joined to form a continuous lake at 835 m asl. Evidence of isostatic tilting is absent, suggesting uniform ice thickness and thinning, a pattern contrary to that inferred for other areas of southern British Columbia. After breaching of the valley fill at its south end, the lake terminated with final melting of Rocky Mountain Trench ice. At that time the southerly flow of water reversed to a northerly direction. A radiocarbon date from an adjacent valley indicates the lake drained prior to 10 000 BP.
Exhumation of high-grade terranes—a review
Authors: Martignole Jacques
Published: April 2011

High-grade (granulite-facies) terranes are brought to the surface by a combination of uplift and erosion (exhumation). The reported mechanisms and durations of exhumation are variable and depend partly on the mode of formation of a given high-grade terrane. In this paper, we consider the case of granulite-facies conditions that are attained (i) in juvenile crust, in the roots of magmatic arcs (e.g., Kohistan, Fiordland), (ii) around deep-seated high-temperature plutonic complexes, and (iii) in the lower parts of thickened continental crust. In the case of the roots of magmatic arcs, Phanerozoic examples suggest that they are exhumed along shallow-dipping contraction faults or shear zones that developed during continental obduction in a convergent tectonic regime. This process is not fundamentally different from processes leading to the exhumation of high-pressure (blueschist, eclogite) terranes. In contrast, deep-seated high-temperature plutonic complexes are thermostructural domes, analogous to the lower levels of core complexes, which may also have contributed to the uprise of high-grade terranes. Such domes should be sought for around anorthositic or mafic plutons, where their ascent may also have been favoured by continental extension. These modes of exhumation are compatible with a monocyclic evolution. However, many high-grade terranes show evidence of a polycyclic evolution and, in such cases, the nature of the thermal perturbation responsible for granulite-facies metamorphism is still debated. Thermal modelling based on heat conduction in collision orogens shows that granulites cannot form at mid-cristal levels, namely those exposed after isostatically driven denudation. Thus, magmatic underplating and crustal extension have been suggested as causes of steepened geotherms. Underplating (or intraplating) supplies the heat and thickens the crust from below. Postcollisional extension has also been considered as a mechanism providing a heat pulse emanating from the asthenosphere, probably after the "detachment" of a relatively cold thermal boundary layer. Finally, isolated crustal-scale intracratonic thrusting may favour the rise of intermediate to lower crustal wedges (e.g., the Kapuskasing wedge, uplifted prior to the trans-Hudson collision).
Terrane accretion in the internal zone of the Ungava orogen, northern Quebec. Part 1: Tectonostratigraphic assemblages and their tectonic implications
Authors: St-Onge M. R. , Lucas S. B. , Parrish R. R.
Published: April 2011

The tectonostratigraphic record of the Ungava orogen contains evidence for the interaction of divergent, transform, and convergent plate boundaries over a > 0.2 Ga period in the Early Proterozoic. Three principal tectonic domains are recognized: (1) autochthonous basement plutonic and supracrustal rocks of Archean age; (2) autochthonous and allochthonous sedimentary and volcanic units associated with a ca. 1.99–1.92 Ga rift-to-drift margin; and (3) "suspect' ' crustal components of a ca. 2.00 Ga ophiolite and ca. 1.90–1.83 Ga island-arc terrane. Domain 1 is the stratigraphic or structural basement to domains 2 and 3. Field relationships indicate that domain 2 units were accumulated on or near domain 1, whereas no tectonostratigraphic linkages are known between domain 3 and the others. Accumulation of continent-derived sedimentary rocks, continental tholeiites, komatiitic basalts, and mafic lavas equivalent to modern normal mid-oceanic ridge basalts (n-MORB's) in domain 2 is interpreted as recording continental rifting leading to the possible formation of oceanic crust. Pillowed basalts, sheeted dykes, and cumulate rocks suggest that the crustal portion of an ophiolite is preserved within domain 3. The ophiolite is interpreted as a "suspect" fragment of oceanic crust, which may represent an earlier rifted portion of domain 2, possibly juxtaposed by transform plate boundary motions. Within domain 3, calc-alkaline volcanic and plutonic units and sequences of volcanogenic and siliciclastic sedimentary rocks are thought to indicate the development of a magmatic arc and fore-arc basin and thus the establishment of a convergent plate boundary. The most internal lithotectonic packages in domain 3 are predominantly crystalline thrust sheets containing (i) an older intrusive suite, interpreted as the plutonic foundation of the magmatic arc, and (ii) younger plutons, interpreted as the result of a reversal in subduction polarity. The reversal may have followed attempted subduction of domains 1 and 2 beneath the upper-plate arc assemblage of domain 3.
Archean magmatism in the Kaminak Lake area, District of Keewatin, Northwest Territories: ages of the carbonatite-bearing alkaline complex and some host granitoid rocks
Authors: Cavell P. A. , Wijbrans J. R. , Baadsgaard H.
Published: April 2011

U–Pb zircon data, obtained on the ion microprobe (SHRIMP), have yielded an age of 2700 ± 11 Ma for tonalite of the Kaminak batholith where it is intruded by a carbonatite-bearing alkaline complex at Kaminak Lake, Northwest Territories, Canada, and a crystallization age of 2659 ± 5 Ma for the alkaline intrusion. Relatively undisturbed age spectra determined by laser probe 40Ar/39Ar analysis of hornblende from a gabbro and from a second tonalite of the batholith yielded cooling or minimum ages of 2727 ± 14 and 2599 ± 9 Ma, respectively. Spectra for hornblendes from two other gabbros suggest overprinting more recent than 2.04 Ga, with a minimum cooling age of 2.69 ± 0.09 Ga in one case, and, with incorporation of excess argon, a maximum cooling age of 2.80 ± 0.03 Ga in the other. Correlation of these data with those recently reported by other workers indicates that the volcanic sequence and the plutonic granitoid units of the Kaminak Lake granitoid–greenstone belt are approximately coeval. Plutonic units both older and younger than the volcanic pile are now recognized. The carbonatite-bearing alkaline complex is confirmed as one of the oldest of this type worldwide. Overlap of the age of alkaline intrusion with those of other plutonic units in the Kaminak Lake and adjacent Tavani areas suggests that rifting of stable continental crust (a typical anorogenic tectonic setting) may be an inappropriate interpretation for this late Archean carbonatitic activity.