bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal structure and kinematic framework of the northwestern Pontiac Subprovince, Quebec: an integrated structural and geophysical study
Authors: Benn Keith , Miles Warner , Ghassemi Mohammad R. , Gillett John
Published: April 2011

Structural mapping, gravity and magnetic modelling, and interpretation of a deep-seismic profile in the northwestern Pontiac Subprovince outline the crustal structure and early structural development of the region. Penetrative D1 fabrics in the Pontiac Group and in the underlying Opasatica Gneiss may record south-vergent thrusting of a high-grade nappe. D2 and D3 structures record southeast-vergent folding and thrusting within the Pontiac Group. Steeply dipping northeast-trending ductile shear zones may represent oblique ramps initiated during D1. Gravity and magnetic model profiles are consistent with north-dipping structures in the shallow crust, and indicate that the Pontiac Group is a wedge underlain by north-dipping slabs of different densities and magnetic susceptibilities. Interpretation of a seismic reflection profile shows mid-crustal duplex structures overlying a deeper thrust between 16 and 24 km. From the surface to the deep crust, the structure of the northwestern Pontiac Subprovince records south- to southeast-directed thrusting and important crustal thickening during a collisional event. In light of field observations, available isotopic ages suggest that D1 deformation began no earlier than 2694 Ma, and that deformation continued until at least 2668 Ma.
Age of low-grade regional metamorphism in the North Greenland fold belt: mineralogical and Rb–Sr-isotope evidence from pelitic metasediments
Authors: Springer N. , Friderichsen J. D.
Published: April 2011

Established isotopic sediment-dating techniques have been used to date the time of deformation and metamorphism of the lower Palaeozoic rocks within the North Greenland fold belt. Fine mineral fractions < 2 μm have been separated from pelitic sediments at widely distributed localities and analysed using X-ray diffraction, isotope, and geochemical techniques.The mineralogical study identified two slightly different mineral parageneses of low greenschist facies. One assemblage without the sodium mica paragonite is confined to calcareous lithologies of the Amundsen Land and Vølvedal groups. The second assemblage includes paragonite and is found in noncalcareous lithologies of the Polkorridoren Group.Rb–Sr isotope dating of the mineral fractions yielded isochron ages in the range 318–346 Ma, which shows that final uplift and cooling associated with Ellesmerian tectonism in North Greenland occurred in the Mississippian. The results suggest that, although the metamorphism was of regional scale, recrystallization and isotopic homogenization occurred in closed systems of local extent.
An integrated subsurface study of the Mannville–Colorado group boundary in the Cessford Field, Alberta
Authors: Banerjee Indranil , Ghosh Santosh K. , Abercrombie Hugh J. , Davies Edward H.
Published: April 2011

The stratigraphic boundary separating the Mannville and the Colorado groups in Alberta, occupying incised valleys cut within the Upper Mannville strata, has previously been interpreted as an unconformity recording post-Mannville erosion followed by a late Albian marine transgression initiated by the deposition of the Joli Fou Shale and locally by the Basal Colorado Sandstone (both of the Colorado Group). Sedimentology, paleontology, organic and inorganic geochemistry, mineralogy, and petrography of strata above and below the unconformity or the sequence boundary have been studied in 106 samples from 37 wells within the Cessford Field covering an area of 3600 km2. Cores through the boundary show a distinct physical break represented by a scoured surface overlain by basal conglomerates. Paleontological data, based on dinoflagellates and foraminifers, show establishment of restricted marine conditions in the Basal Colorado times (initial transgression) and onset of open marine condition (maximum flooding) during the Joli Fou times. Although paleosol horizons have not been found near the boundary, influence of meteoric water in the Upper Mannville sandstones is inferred from development of spherulitic siderite and extensive early kaolinization of the feldspar, mica, and lithic grains. The absence of paleosol or fluvial strata within the incised valley fills suggests that the subaerial unconformity was modified by tidal erosion during the Joli Fou transgression.
The petrogenesis and tectonic setting of lavas from the Baft Ophiolitic Mélange, southwest of Kerman, Iran
Authors: Arvin Mohsen , Robinson Paul T.
Published: April 2011

A Late Cretaceous ophiolite complex in the Baft area, southwest of Kerman, Iran, is characteristic of the Central Iranian Ophiolitic Mélange Belt, which wraps around the Lut Block. Despite the extensive tectonic disruption of the Baft complex, most ophiolitic lithologies are present and many original igneous contacts are preserved. A lack of cumulate gabbros within the sequence suggests that a large and continuous magma chamber did not exist beneath the Baft spreading axis. Geochemical data confirm the presence of two distinct compositional groups in the mafic lavas: (1) tholeiitic basalt and (2) transitional tholeiitic basalt. The tholeiitic lavas are similar to typical mid-ocean-ridge basalt compositions, whereas the transitional tholeiites are similar to intraplate basalts. The available data suggest that the Baft ophiolite complex formed in a small ocean basin, possibly at or near a ridge–transform intersection. Emplacement may have occurred as a result of conversion of the transform fault to a subduction zone during a change in relative plate motion. A ridge–transform setting is compatible with the intraplate character of some of the transitional basalts, which probably represent off-axis (seamount) magmatism, marked by the absence of cumulate gabbros and the presence of a serpentinite mélange cut by basaltic dykes. The ridge–transform model suggests formation of the ophiolite in a narrow ocean basin separating the Sanandaj-Sirjan microcontinent from the Central Iran Block in Late Cretaceous time.
Interpretation of gravity and magnetic data from southwestern Newfoundland and their correlation with Lithoprobe East seismic lines 89-11 and 89-12
Authors: Wiseman R. , Miller Hugh G.
Published: April 2011

Several Newfoundland Appalachian terranes converge in the southwest corner of the island. The recent Lithoprobe East deep seismic reflection profiles imaged the crust along a transect across this area. In this paper, we present the gravity and magnetic data for the area and process them using shaded relief, horizontal and vertical gradient, upward continuation, and layer stripping techniques to interpret the more subtle features of the fields.Traditional two and one-half dimensional gravity and magnetic modelling is undertaken using constraints from the reflection data to develop a model of the crust in this region. The results from the processing are then used to interpret the crustal structure away from the seismic line.In general, we find that the major features on the gravity and magnetic anomaly maps can be explained by sources in the upper crust. The major faults in the area bound terranes that differ in potential field character. A minor change to the location of one terrane boundary is suggested. The rest correlate well with the geophysical data.
An ammonite zonation for the Toarcian (Lower Jurassic) of the North American Cordillera
Authors: Jakobs Giselle K. , Smith Paul L. , Tipper Howard W.
Published: April 2011

This is the second in a series of papers intended to establish a Lower Jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the North American succession. In North America the lower boundary of the Toarcian is drawn at the first appearance of Dactylioceras above the last occurrence of Amaltheus and Fanninoceras. The lower Toarcian is represented by the Kanense Zone; the middle Toarcian by the Planulata and Crassicosta zones; and the upper Toarcian by the Hillebrandti and Yakounensis zones. Section 5 on the Yakoun River in the Queen Charlotte Islands is designated the stratotype for the Planulata, Crassicosta, and Hillebrandti zones; section 3 on the Yakoun River is designated the stratotype for the Yakounensis Zone; an ideal stratotype for the Kanense Zone is not presently known. Reference sections further illustrating the faunal associations that characterize the zones are designated in eastern Oregon (Snowshoe Formation) and northern British Columbia (Spatsizi Group). The Dactylioceratidae, Harpoceratinae, and Hildoceratinae provide the most important zonal indicators for the lower Toarcian; Dactylioceratidae, Phymatoceratinae, and Bouleiceratinae for the middle Toarcian; and Phymatoceratinae, Grammoceratinae, and Hammatoceratinae for the upper Toarcian. Phymatoceras hillebrandti is described as a new species.
The graptolites "Pristiograptus" praedeubeli (Jaeger) and "Pristiograptus" ludensis (Murchison) (uppermost Wenlock, Silurian) from Arctic Canada: taxonomy and evolution
Authors: Lenz Alfred C.
Published: April 2011

Isolated, uncompressed specimens of Pristiograptus dubius, "Pristiograptus" praedeubeli, and "Pristiograptus" ludensis are described from Arctic Canada. Pristiograptus dubius and early forms of "P." praedeubeli are very similar, suggesting a respective, ancestor-descendant relationship. The study shows that "P." praedeubeli and "P." ludensis are generally readily distinguishable, but that the sicular region of the latter shows a much greater variation than previously recognized. End member morphs of "P." ludensis are remarkably similar to "P." deubeli, further confirming a close evolutionary link between them. To facilitate refined biostratigraphic division of the uppermost Wenlock, therefore, large collections of specimens are required to separate those two species when co-occurring.
Granulite-facies metamorphism in the Quetico Subprovince, north of Manitouwadge, Ontario
Authors: Pan Yuanming , Fleet Michael E. , Williams Howard R.
Published: April 2011

A zone of granulites, defined by an orthopyroxene-in isograd and extending more than 100 km in length and about 10 km in width, occurs near the southern margin of the Quetico Subprovince, north of Manitouwadge, Ontario. Mineral assemblages in metasedimentary rocks and associated migmatites consist of quartz, plagioclase, garnet, orthopyroxene, biotite, cordierite, sillimanite, K-feldspar, hercynite, magnetite, ilmenite, and other accessory phases. Minor mafic gneisses and calc-silicate pods or lenses are also present. From equilibrium phase relations and thermobarometry, the granulites experienced a thermal-peak event (4–6 kbar (1 bar = 100 kPa), 680–770 °C, a(H2O) of 0.15–0.25 and fO2 of 1–2 log units above the FMQ buffer) in association with D2 deformation, followed by a retrogression (550–660 °C and 3–4 kbar) and a later hydrothermal alteration (1–2 kbar and 200–400 °C). The distribution and calculated peak metamorphic conditions of the granulite zone in the Quetico Subprovince are similar to those of granulites in the English River Subprovince and other proposed accretionary terranes. The low-pressure, high-temperature metamorphism in the Quetico Subprovince is interpreted to be related to both crustal thickening and addition of heat from subduction-related magmatism.
A magnetotectonic study correlating late Archean deformation in northwestern Ontario
Authors: Borradaile G. J. , Kehlenbeck M. M. , Werner T. W.
Published: April 2011

Late Archean lamprophyre dikes crop out on both sides of the Quetico–Shebandowan subprovince boundary. They post date F1 folds in late Archean rocks (2690 Ma) but their intrusion overlapped with the waning phase of S1 development. S1 developed to varying degrees or is absent in some dikes. Nevertheless, the dikes show a cryptic tectonic fabric in the ferromagnetic minerals revealed by anisotropy of magnetic susceptibility (AMS). This is parallel to S1 in the host metamorphic rocks. Thus, the S1 fabric-forming episode may be correlated from one subprovince to the other using the dike swarm as a chronological marker.
Ordovician emplacement of the Mount Dingley Diatreme, Western Ranges of the Rocky Mountains, southeastern British Columbia
Authors: Norford B. S. , Cecile M. P.
Published: April 2011

External and internal morphologies are well shown by a newly discovered diatreme that is exceptionally well exposed in a cirque within the north face of Mount Dingley. The diatreme contains abundant brecciated host rocks mixed with highly altered, fine-grained, light-green igneous fragments (minerals include muscovite, chlorite, quartz, carbonate, and some remnant K-feldspar). The diatreme cuts Lower Ordovician rocks of the McKay Group. Olistostromes and other volcaniclastic rocks that are directly associated with the diatreme are bevelled beneath a regional unconformity below the Upper Ordovician Beaverfoot Formation. Lower Ordovician gastropods are present just below the volcaniclastic rocks and within what appears to be a lens of sediment within one of the olistostrome beds. These occurrences indicate a mid-Early Ordovician time of intrusion, but there is the possibility that the pipe was emplaced later within the interval mid-Early to early Late Ordovician. In the Western Ranges, three other episodes of emplacement of diatremes have been documented previously as within the intervals early Middle to early Late Ordovician, latest Early Silurian to early Middle Devonian, and Late Permian. Many of the diatremes are broadly contemporaneous with widespread, but volumetrically small, Ordovician and Lower Paleozoic volcanic and intrusive rocks found throughout the Canadian Cordillera. These volcanic and intrusive rocks have been interpreted as evidence of continued Lower Paleozoic extensional tectonism and some are associated with large base-metal deposits.
Postglacial alluvial terraces and an incorporated bison skeleton, Ghostpine Creek, southern Alberta
Authors: Rains R. Bruce , Burns James A. , Young Robert R.
Published: April 2011

Ghostpine Creek near Three Hills, southern Alberta, is a tributary of the Red Deer River. It has three sets of paired alluvial terraces (T-1 to T-3) in a downstream part of the valley. The rare discovery of a largely intact skeleton of plains bison (Bison bison bison) in a T-2 point bar prompted terrace mapping, 14C dating, and interpretation of the postglacial evolution of the valley. Downvalley portions of the creek began incision into the newly drained bed of glacial Lake Drumheller probably about 13 000 BP. Localized valley deepening up to 20 m, the production of erosional benches and residual spurs, and the development of partly convex-up creek paleothalwegs occurred between about 13 000 and 7600 BP, by which time basal T-1 alluvium was beginning to accumulate. Subsequent aggradation of T-1 sediment and then degradation of about 3–4 m were followed by aggradation of T-2 alluvium. These trends had taken place by 2600 BP, when the bison died and its skeletal remains were buried in uppermost sediment of a T-2 point bar. Between 2600 BP and now, the creek incised about 5 m below the former T-2 channel position and aggraded, partly synchronously, up to 3 m of T-3–floodplain alluvium. Radiocarbon-dated alluvial terrace sequences in Alberta show generally comparable trends of rapid early creek incision followed by partially overlapping episodes of net aggradation and degradation from basin to basin. However, such episodes were not closely synchronized between basins.
Depositional history of the southeastern outcrop belt of the Chuckanut Formation: implications for the Darrington – Devil's Mountain and Straight Creek fault zones, Washington (U.S.A.)
Authors: Evans James E. , Ristow Jr. R. John
Published: April 2011

The southeastern outcrop belt of the Eocene Chuckanut Formation contains the erosional remnants of a larger depositional system. In the study area, the Chuckanut Formation can be split into four units based upon differences in age, lithology, sedimentology, paleocurrents, and provenance relationships. The Coal Mountain unit (Early Eocene) represents a southwest-flowing fluvial system that shows no evidence for fault control of drainage. The overlying Higgins Mountain unit (early Middle Eocene) represents a northeast-flowing fluvial system east of the Devil's Mountain fault zone (DMFZ), with lithologies derived from western source areas. The Sperry Peak unit (early Middle Eocene) represents a fluvial system with a wide dispersion of paleocurrent azimuths and a possible mixture of sediment source areas. We believe the Sperry Peak unit was deposited in a fault-wedge graben at the junction of the DMFZ and Straight Creek fault zone (SCFZ), with sediment sources from both east and west. The Grade Creek unit (age unknown) is a fluvial unit found along the trace of the SCFZ with paleo-flow subparallel to the fault zone. The sedimentary evidence suggests that onset of Paleogene faulting on the DMFZ and SCFZ was at about 50–48 Ma, while movement on the Darrington fault zone may have been later (post-42 Ma).
New upper Homerian (uppermost Wenlock, Silurian) monograptids from Arctic Canada
Authors: Lenz Alfred C.
Published: April 2011

Five species of new or little-known upper Homerian (uppermost Wenlock) graptolites are described from the Arctic Islands. These are Lobograptus? sherrardae (Sherwin), Lobograptus? aff. sherrardae, Lobograptus? claudiae Koren, Lobograptus? cf. cornuatus Lenz, and "Pristiograptus" schedidoneus n.sp. The first- and last-named species range through the "Pristiograptus" praedeubeli and "Pristiograptus" ludensis biozones, that is, through the entire upper Homerian, whereas, the remaining three species appear to be confined to the (older) "P." praedeubeli Biozone. These species further document the rapid global evolution of the late Homerian graptolites, and this study records Lobograptus? claudiae Koren from outside central Asia for the first time.
Striding-Athabasca mylonite zone: implications for the Archean and Early Proterozoic tectonics of the western Canadian Shield
Authors: Hanmer Simon , Williams Michael , Kopf Chris
Published: April 2011

Study of the northern Saskatchewan–District of Mackenzie segment of the Snowbird tectonic zone suggests that fragments of relatively stiff mid-Archean crust, possibly arc related, have controlled the localization, shape, and complex kinematics of the multistage Striding–Athabasca mylonite zone during the Archean, as well as the geometry of the Early Proterozoic rifted margin of the western Churchill continent. By the late Archean, the Striding–Athabasca mylonite zone was located in the interior of the western Churchill continent, well removed from the contemporaneous plate margins. Except for the Alberta segment, the Snowbird tectonic zone was not the site of an Early Proterozoic plate margin. We suggest that the geometry of the Archean–Early Proterozoic boundary in the western Canadian Shield represents a jagged continental margin, composed of a pair of reentrants defined by rifted and transform segments. These segments were inherited from Early Proterozoic breakup and controlled by the Archean structure of the interior of the western Churchill continent. The geometry of this margin appears to have strongly influenced the Early Proterozoic tectono-magmatic evolution of the western Canadian Shield.
Magnetic spherules from Recent fluvial sediments in Alberta, Canada: characteristics and possible origins
Authors: Bi Dong , Morton Roger D.
Published: April 2011

Magnetic spherules were recently recovered in recent fluvial sediments in Alberta, Canada, and have been studied using X-ray diffraction, electron microprobe, scanning electron microscope, and neutron activation analysis. Results show that these spherules are composed of magnetite, wüstite, and hematite; some of them contain α-iron metal cores. The similarities in morphology, mineralogy, and internal structure of these spherules to spherules of extraterrestrial origin found in other environments suggest that some of these spherules from Alberta might also be of extraterrestrial origin, in spite of their unusual compositions.
Neodymium isotopic constraints for the origin of Mesoproterozoic felsic magmatism, Gawler Craton, South Australia
Authors: Creaser Robert A.
Published: April 2011

Mesoproterozoic felsic magmatism of the Gawler Range Volcanics and Hiltaba Suite granites occurred at 1585–1595 Ma across much of the Gawler Craton, South Australia. Nd isotopic analysis of this felsic magmatism, combined with petrological and geochemical arguments, suggest derivation by partial melting of both Paleoproterozoic and Archean crust. The majority of samples analyzed have Nd isotopic and geochemical characteristics compatible with the involvement of Paleoproterozoic crust stabilized during the 1.85–1.71 Ga Kimban orogeny as sources for the Mesoproterozoic magmatism; others require derivation from sources dominated by Archean rocks. This cycle of Paleoproterozoic crustal stabilization followed by involvement of this crust Mesoproterozoic felsic magmatism is one previously documented from many parts of Mesoproterozoic Laurentia. On the basis of models proposing East Australia–Antarctica to be the conjugate landmass at the rifted margin of western North America, it appears that the voluminous magmatism of South Australia is another example of a typically Mesoproterozoic style of magmatism linked to Laurentia. This Mesoproterozoic magmatism appears temporally linked to regional high-temperature, low-pressure metamorphism of the region, and together with the presence of mantle-derived magmas, implicates the operation of large-scale tectono-thermal processes in the origin of felsic magmatism at 1590 Ma.
Geochemical polarity of the Early Cretaceous Gambier Group, southern Coast Belt, British Columbia
Authors: Lynch Gregory
Published: April 2011

The Gambier Group of the southern Coast Belt was developed on the eastern edge of the Wrangellia terrane in Early Cretaceous time. A U–Pb zircon age determination from rhyolite produced a date of 112.0 ± 0.3 Ma, consistent with Albian fauna in sedimentary units. Major element geochemistry of volcanic rocks from separate east-northeast and southwest volcanic centres displays both tholeiitic and calc-alkalic affinities across the axis of the Coast Belt. However, assemblages in the east-northeast have higher FeOT/MgO ratios, highlighting a more pronounced tholeiitic trend, and are characterized by high-Al basalts. Volcanic rocks in the southwest are enriched in K. Trace element variations feature a southwesterly increase in Ba, Rb, and Zr/Ti towards more alkalic values, and a decrease in Sr. When compared with across-arc geochemical trends from numerous other arcs, the data may be interpreted to suggest that the Gambier arc was east facing above a west- to southwest-dipping subduction zone. Such an interpretation is consistent with the occurrence of a subduction-melange complex along the southeastern Coast Belt and with a structural style dominated by southwest-verging thrusts in mid-Cretaceous time.
Geologic history of the Archean Buhwa Greenstone Belt and surrounding granite–gneiss terrane, Zimbabwe, with implications for the evolution of the Limpopo Belt
Authors: Fedo Christopher M. , Eriksson Kenneth A. , Blenkinsop Tom G.
Published: April 2011

The Buhwa Greenstone Belt (BGB) of southern Zimbabwe is the only major greenstone belt in the Archean Zimbabwe Craton directly adjacent to the granulite-facies rocks that constitute the Northern Marginal Zone of the Limpopo Belt. The deformational history and assembly of the BGB shed light on the evolution of the Northern Marginal Zone – Zimbabwe Craton transition. Assembly of the region began with deposition of the dominantly sedimentary cover succession at ~3.0 Ga on banded gneisses of the ~3.5 Ga Tokwe segment. At ~2.9 Ga the northern margin of the greenstone belt experienced kilometres of ductile, oblique-slip, dextral shearing. This shear zone was later intruded by the granitic to tonalitic ~2.9 Ga Chipinda batholith. The remaining events recognized in the region occurred during the time span 2.9–2.5 Ga. Northwest-directed thrusting of the Northern Marginal Zone over the Zimbabwe Craton took place along a collection of discrete, typically metre-wide shear zones, which collectively form the tectonic break between the Zimbabwe Craton and the Northern Marginal Zone. In response to thrusting, the cover succession and surrounding granitoids were folded and underwent regional greenschist-facies metamorphism. Two suites of potassic granites were emplaced north and south of the greenstone belt towards the end of thrusting. Plutonism was followed by conjugate faulting and later filling of the fractures by the Great Dyke of Zimbabwe. The youngest events may have occurred between ~2.5 and ~2.0 Ga, and include sinistral shearing along the southern margin of the belt, transecting cleavage formation, and open folding as a result of northeast-directed crustal shortening.
Grain-size trends and provenance of southwestern Gulf of Mexico beach sands
Authors: Carranza-Edwards Arturo , Rosales-Hoz Leticia
Published: April 2011

Sand samples from 30 beach locations of the southwestern Gulf of Mexico littoral zone were texturally and mineralogically investigated. Based on their source lithology and fluvial network, they were subdivided into two groups: (1) sands with volcanic rocks in the source region and (2) sands with a nonvolcanic source. Sands from foreshore and backshore areas exhibit similar textural characteristics, with less rock fragments than those from the inshore zone, where the high energy of breaking waves and littoral currents is present. A quartz–feldspar–rock fragment triangular diagram indicates that the proximity of volcanic sources is responsible for the enrichment of rock fragment content in the beach sands. Beach sands associated with Tampico and Veracruz embayments have greater quartz content, caused by a greater transport distance. Mineralogical maturity and provenance indexes used in a binary diagram are helpful in discriminating sand samples from volcanic and nonvolcanic domains.
Invertebrate trace fossils and agglutinated foraminifera as indicators of marine influence within the classic Carboniferous section at Joggins, Nova Scotia, Canada
Authors: Archer Allen W. , Calder John H. , Gibling Martin R. , Naylor Robert D. , Reid Donald R. , Wightman Winton G.
Published: April 2011

The sea cliffs at Joggins, Nova Scotia, are the most extensive and continuous Carboniferous section in eastern North America. Although the section has been considered to have formed within a nonmarine depositional basin, paleobiological information indicates that parts of the section were deposited in brackish water. The occurrence of a trace-fossil assemblage, which includes Cochlichnus, Kouphichnium, and Treptichnus, is part of an assemblage of biogenic structures that apparently reflects paleodeposition within fluvial systems that may have experienced distal marine influences. Presence of agglutinated foraminifera characteristic of brackish-water environments supports this interpretation. This information provides new evidence of brackish-water conditions at Joggins such as those now being widely recognized in other Carboniferous coal-bearing sections.
A record of Early Pleistocene glaciation on the Mount Edziza Plateau, northwestern British Columbia
Authors: Spooner I. S. , Osborn G. D. , Barendregt R. W. , Irving E.
Published: April 2011

Mount Edziza is a Plio-Pleistocene volcanic complex that is located in the Stikine Terrane in northwestern British Columbia. A sequence of diamictites preserved between Ice Peak Formation basalts on the northwestern blank of Mount Edziza records an Early Pleistocene regional glaciation. The lowest Ice Peak Formation basalt flow (IP1; about 1 Ma) was probably extruded onto glacial ice because it is deformed and brecciated, it is pillowed at the base, it lies directly on hyaloclastite deposits, and there is a lack of fluvial and lacustrine sediments at the base. Fabric measurements from the underlying diamictites are consistent with lodgement processes and indicate northwest and southwest transport directions. These data, and an abundance of striated exotic cobbles, indicate that the sediment was deposited by Coast Mountain ice. Radiometric, paleomagnetic, and stratigraphic data all support the interpretation that diamictites at the section are the sedimentary record of an Early Pleistocene (about 1.1 Ma, isotope stage 32–34) regional glaciation(s). The normal paleomagnetic polarity of one of the Ice Peak Formation basalts (IP2) records extrusion during the Jaramillo normal polarity subchron (1.07–0.99 Ma) and further constrains the age of the underlying diamictites.
Ice-flow patterns and glacial transport in the eastern Hudson Bay region: implications for the late Quaternary dynamics of the Laurentide Ice Sheet
Authors: Parent Michel , Paradis Serge J. , Boisvert Éric
Published: April 2011

Recent field surveys in the eastern Hudson Bay region have led to the discovery of regional ice-flow sequences that require a significant reassessment of the late Quaternary dynamics of the Laurentide Ice Sheet. Two regional ice-flow phases can be recognized from till compositional data and from crosscutting relationships observed on striated bedrock surfaces: the oldest is directed toward the northwest and north-northwest, while the youngest is directed toward the west and includes a late-glacial deflection toward the southwest. The wide regional distribution of striae formed during the early northwestward glacial movement together with the recognition of palimpsest glacial dispersal trains associated with this phase suggest that it was a long-lived, time-transgressive regional event. The ensuing glacial movement is a regionally dominant westward ice-flow phase during which several large glacial dispersal trains were formed downglacier from distinctive bedrock sources. The largest of these trains extends westward over a distance of 120 km from Lac à l'Eau Claire to Hudson Bay. Regional glacial transport data as well as glacial and deglacial landforms indicate that this was a long-lived glacial phase, likely lasting throughout the Late Wisconsinan glacial maximum and until déglaciation about 8000 BP. The erosional and depositional record of the northwestward ice-flow event is quite comparable to that of the ensuing glacial phase, and it is thus thought to represent the Early Wisconsinan glacial maximum. In view of the large regional extent of the northwestward ice-flow phase, it must postdate the early buildup of the ice sheet. Along the southeastern Hudson Bay coast, the Late Wisconsinan westward glacial movement was followed by a southwestward deflection that was likely caused by glacial streaming prior to 8000 BP in James Bay, in response to calving and surging into Glacial Lake Ojibway.
A new sea-level curve from Nova Scotia: evidence for a rapid acceleration of sea-level rise in the late mid-Holocene
Authors: Scott D. B. , Brown K. , Collins E. S. , Medioli F. S.
Published: April 2011

A new late Holocene sea-level curve is presented from the Atlantic coast of Nova Scotia. Contrary to earlier data from the same area, this curve starts at 4400 sidereal years before present (BP) and shows a rapid acceleration between 4400 and 3800 BP, which coincides with a similar acceleration already reported from the Northumberland Strait (Nova Scotia) and an oscillation observed in South Carolina. Comparing the two Nova Scotia curves suggests that the acceleration lasts just over 1000 years and has a vertical extent of 10 m. One puzzling fact is that the 10 m vertical extent in Nova Scotia is 8 m more than the same event measured in South Carolina and it cannot be accounted for simply by postglacial isostatic depression, since that occurs on a much longer time scale. A closer examination of most of the sea-level curves from northeastern North America reveals that either the record is missing from this interval or it is inconsistent. We suggest that this acceleration is part of a global response that coincides with the end of the mid-Holocene warming period, possibly indicating a lag response between warming and ice melt.
Stitching together the Ungava Orogen, northern Quebec: geochronological (TIMS and ICP–MS) and geochemical constraints on late magmatic events
Authors: Dunphy J. M. , Ludden J. N. , Parrish R. R.
Published: April 2011

Late magmatic activity in the Ungava Orogen of northern Quebec is manifest as granitic dykes and small, rare plutons that crosscut all tectono-stratigraphic elements of the orogen. Conventional U–Pb geochronology (thermal ionization mass spectrometry (TIMS)) on one particularly important pluton that cuts all these domains (the Lac Duquet monzogranite) indicates its age of emplacement at 1742.2 ± 1.3 Ma. This undeformed and nonmetamorphosed pluton postdates the youngest structures in the orogen (D4 folds), thereby constraining the timing of the latest deformation to >1742 Ma. Laser ablation inductively coupled plasma–mass spectrometry (ICP–MS) on zircons from the same sample identified a large range in 207Pb/206Pb ages of inherited grains from 1.7 to 3.2 Ga, corresponding to the ages of the host rocks for the pluton. This high-K peraluminous monzogranite pluton contains moderate to high concentrations of large ion lithophile elements and fractionated and enriched light rare earth elements, similar in composition to the surrounding continental crust and to other crustally derived granites. Initial 87Sr/86Sr values of 0.7040–0.7051 and εNd ranging from −4.4 to −9.7 indicate incorporation of a significant amount of older material in the petrogenesis of the pluton. It is proposed that anatexis of the surrounding continental crust due to structural thickening during the waning stages of the Ungava orogeny resulted in the generation of the Lac Duquet pluton and was the source for its inherited zircons.
An assessment of long-wavelength magnetic anomalies over Canada
Authors: Pilkington Mark , Roest Walter R.
Published: April 2011

The reliability of the long-wavelength portion (> 300 km) of the magnetic field over Canada, as represented by the national aeromagnetic anomaly database compiled by the Geological Survey of Canada (GSC), is assessed by comparison with two independent data sets: a high-altitude country-wide survey carried out by the former Earth Physics Branch (EPB) and data from the MAGSAT and POGO satellite missions. The different altitudes at which each data set was measured (300 m, ~4 km, and ~400 km), and their different resolution and time span of observations allow a determination of the integrity of selected wavelength bands in each data set. The (upward-continued) EPB and MAGSAT–POGO fields compare well for wavelengths of 300–2500 km. The GSC data show significant differences to the former, indicating that the levelling and merging of several hundred individual surveys has degraded the longer wavelength components of the magnetic field. Replacing the GSC wavelength components >300 km with those from the EPB field produces a magnetic data set containing more dependable information within the largest possible waveband.
Analyses minéralogiques multivariées de sédiments du Wisconsinien supérieur au sud-ouest du Yukon
Authors: Dewez Véronique , Geurts Marie-Anne
Published: April 2011

For this study, 84 samples of glacial and juxtaglacial sediments were collected in valleys of the Ruby Range and Aishihik Basin (southwestern Yukon). Analyses were conducted to quantify the heavy minerals in the sand fraction and to assess the petrography of the gravel fraction. A cluster analysis performed on the heavy mineral results showed five groups of deposits, three of which are related to local glaciers inside the Ruby Range, the other two being related to regional ice lobes of Kluane and Aishihik, respectively. The three groups of local sediments correspond to the three lithologies of the Ruby Range, i.e., the granitic batholith, the schists, and the alaskite. The sediments from the regional ice lobes are characterized by highly diversified mineralogy and petrography and the relative abundance of minerals from the Saint Elias Mountains, the main source of the ice lobes. A correspondance factor analysis performed on the heavy mineral results organizes samples and minerals into a triangular cloud, the three vertices corresponding to biotite, carbonate, and titanite–garnet. These are the key elements of local glaciers, Kluane ice lobe, and Aishihik ice lobe, respectively. Finally, the study shows the extension of Kluane lobe in one valley of the Ruby Range, the ice flow pattern in another valley, as well as a transfluence from Kluane lobe inside the Range.
Late Quaternary history of the Mackenzie–Beaufort region, Arctic Canada, from modelling of permafrost temperatures. 2. The Mackenzie Delta–Tuktoyaktuk Coastlands
Authors: Taylor Alan E. , Dallimore Scott R. , Judge Alan S.
Published: April 2011

In the Mackenzie–Beaufort region, maximum permafrost thickness is 750 m in the Pleistocene Tuktoyaktuk Coastlands, less than 100 m in the Holocene Mackenzie Delta, and 500 m and anomalously warm in the Big Lake Delta Plain between the two areas. Numerical modelling has been used to derive surface temperature histories that fit ground temperatures and permafrost conditions at 12 wells in the Unipkat, Kumak, and Taglu hydrocarbon fields. The models indicate that the present Holocene Mackenzie Delta was built by fluvial processes into a submarine trough. The delta front passed a site presently some 20 km from the coast about 4.5 ka, and subsequently 58 m of ice-bonded permafrost has aggraded. In contrast, the Big Lake Delta Plain was a subaerial platform for much of the Wisconsinan. It experienced several thousand years of inundation in the Holocene, probably due to widespread development of thermokarst lakes. At sites 8–12 km from the coast, the present subaerial conditions were established 0.5–1.5 ka through lake drainage and fluvial–deltaic deposition.
Genesis of cockade breccias in the tectonic evolution of the Cirotan epithermal gold system, West Java
Authors: Genna A. , Jébrak M. , Marcoux E. , Milési J. P.
Published: April 2011

The Pliocene Cirotan gold deposit provides an exceptional example of mineralized breccias, and in particular cockade breccias. Analysis of these breccias, approached through both field observation and image analysis on photographs, made it possible to determine their method of graded formation. The mineralized structure, as much a 25 m thick in places, is a right-lateral strike-slip fault that evolved to a normal fault at the end of the system's development. It consists of juxtaposed breccia bodies separated by major slip, or "septa," which formed at a major inflection of the host fault. The breccia bodies all show a similar internal organization. From footwall to hanging wall, one passes from a siliceous breccia with angular clasts to a thick infill of cockade breccia showing a reverse grading with small centimetre-size cockades (aspect ratios of 1:10) passing to larger (up to 1 m) more equant cockades (aspect ratios 1:3) in contact with the hanging wall. The different stages of cockade formation demonstrate genesis in an open milieu through rolling-accretion and collapse of the clasts, which show signs of mechanical attrition. The large cockades are formed of an agglomeration of several small cockades. Ore deposition occurred during a pulsating process that was active throughout the complex evolution of the structure. The final ore stage, filling the intercockade spaces, marked the end of the structure's evolution. High fluid pressures and the local structural context combined to maintain open the hydrothermal channelways, enabling cockade growth and collapse. The process of breccia formation at Cirotan was therefore exclusively of hydrothermal origin in an active tectonic context. It represents a self-organizing system within a fault zone.
Tectonic setting of Avalonian volcanic and Plutonic rocks in the Caledonian Highlands, southern New Brunswick, Canada
Authors: Barr S. M. , White C. E.
Published: April 2011

The Caledonian Highlands of southern New Brunswick consist of Late Proterozoic to Cambrian rocks generally considered typical of the Avalon terrane of the northern Appalachian Orogen. Mainly tuffaceous volcanic and sedimentary rocks of the Broad River Group and cogenetic dioritic to granitic plutons with ages ca. 620 Ma form most of the eastern Caledonian Highlands. They have petrological features indicative of origin in a continental margin subduction zone. Significantly younger ca. 560–550 Ma dacitic to rhyolitic lapilli tuffs and flows, laminated tuffaceous siltstone, basaltic and rhyolitic flows, and clastic sedimentary rocks of the Coldbrook Group form most of the western highlands, and occur locally throughout the highlands. The mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group. This voluminous subaerial magmatism may have formed during postorogenic extension in the earlier ca. 620 Ma subduction zone complex represented by the Broad River Group and associated plutons. This tectono-magmatic model differs from other interpretations that related most of the igneous units to ca. 630–600 Ma subduction, and did not recognize the importance of ca. 560–550 Ma magmatism. The ca 620 Ma subduction-related volcanic and plutonic rocks of the Caledonian Highlands are comparable to units in other parts of the Avalon terrane, but voluminous ca. 560–550 Ma igneous activity like that represented by the Coldbrook Group and related plutons has not been documented yet in other Avalonian areas.
Intense silicification of footwall sedimentary rocks in the stockwork alteration zone beneath the Brunswick No. 12 massive sulphide deposit, Bathurst, New Brunswick
Authors: Lentz David R. , Goodfellow Wayne D.
Published: April 2011

Intensely silicified volcaniclastic mudstones that underlie the Brunswick No. 12 massive sulphide deposit in northern New Brunswick resemble silicified rocks described in the immediate footwall of many ancient and modern massive sulphide deposits. The white to grey, cryptocrystalline silica in the silicified rocks becomes more common with proximity to the vent, and is most abundant immediately below the massive sulphide zone. Mass-balance analysis of altered footwall sedimentary rocks on the 850 m level of the mine shows that SiO2 increases up to 300%. The high silica enrichment in the feeder zone is consistent with the presence of cherty silica in the massive sulphides and in associated exhalative iron formation. Coincident with silicification are enrichments in S, FeOt, MgO, MnO, CaO, P2O5, F, Cl, Y, Cu, Co, Cr, and Ni, as well as light rare earth elements and Eu. Oxygen isotope analyses of chloritized and silicified footwall sedimentary rocks suggest that the hydrothermal fluid had a δ18O composition of approximately 4[Formula: see text] and probably was dominated by chemically modified sea water. Rapid oversaturation of the silica-bearing fluid likely explains the intensity and fine-grained nature of this silicification, although the actual mechanism for this oversaturation is uncertain.
Pre-ore burial dolomitization adjacent to the carbonate-hosted Gays River Zn–Pb deposit, Nova Scotia
Authors: Savard M. M.
Published: April 2011

The Gays River Formation of the Lower Windsor Group in the vicinity of the Gays River Zn–Pb deposit was completely dolomitized via a volume for volume transformation prior to mineralization. Premineralization porosity was the precursor limestone porosity, comprising fenestrae, dissolution molds, and intercrystalline, intraskeletal, and growth pores, which remained essentially unchanged through dolomitization. Regionally, the dolomites (one replacement and one cement) overlapped with sediment compaction and dissolution of aragonite. The dolomites are characterized by low δ18OPDB values (−14 to −4[Formula: see text]; average −8[Formula: see text]), slightly radiogenic 87Sr/86Sr ratios (0.70778–0.70900), and locally high percentages of FeCO3 and MnCO3 (up to 13.5 and 9.5 mol%, respectively). The presented petrographic and geochemical data compiled with existing fluid-inclusion microthermometry data suggest dolomitization by hot brines, in a burial setting. High Fe and Mn concentrations south of the studied area, with progressive depletion towards the northeast and northwest, suggest either a northward flow of an Fe- and Mn-rich fluid or interaction with local sources of Fe and Mn, during single or multiple flows. By preserving the host-rock permeability, dolomitization played a role in ground preparation but was not genetically associated with the Zn– and Pb–rich fluid that mineralized the Gays River deposit.
Characteristics of gold mineralization in volcanogenic massive sulphide deposits of the Notre Dame Bay area, central Newfoundland
Authors: Santagulda F. , Hannington M. D.
Published: April 2011

A reconnaissance study of 19 volcanogenic massive sulphide deposits in the Notre Dame Bay area indicates Au concentrations of up to 30 ppm (Betts Cove), and elevated gold contents (>1 ppm Au) have been found in samples from 10 additional past producers and developed prospects. Systematic trends in the occurrence of gold are observed in two principal sulphide assemblages: polymetallic, pyrite–sphalerite–chalcopyrite–galena ± arsenopyrite assemblages (type I) and pyrite–chalcopyrite ± sphalerite ± pyrrhotite assemblages (type II). Type I assemblages occur in deposits with dominantly felsic host rocks, whereas type II assemblages are restricted to deposits in mafic-dominated ophiolite sequences. Free gold grains were observed in samples from eight different deposits in both type I and type II assemblages. X-ray emission spectra and electron microprobe analyses of the gold indicate that most grains are electrum, although a Au-bearing telluride occurs at Point Leamington. Ion microprobe analyses indicate that as much as 50% of bulk gold may be present as "invisible gold" locked in pyrite or arsenopyrite (up to 140 ppm Au at Point Leamington). Well-preserved primary depositional features in gold-bearing sulphides from several deposits suggest that the gold in type I assemblages is syngenetic. A strong correlation between gold and a polymetallic suite of Zn, Ag, Pb, As, and Sb, similar to that observed in Kuroko-type massive sulphides and in modern seafloor sulphides, supports a primary origin for gold in type I assemblages. In type II assemblages primary depositional features have been largely destroyed by deformation and annealing of sulphide grains. Gold is locally enriched in Zn-rich sulphides, and sulphides containing abundant pyrrhotite have the lowest gold contents. However, consistent geochemical associations with other elements are not observed, and this may reflect the strong remobilization of gold during structural deformation. The abundant free gold in some type II assemblages is a product of recrystallization during deformation and was derived locally from primary gold originally present in the host sulphides.